Patent Grant
7312041
The present invention relates to detection of biological markers from pathogenic organisms, such as observed in certain human Papillomavirus (HPV) infections, and methods for using such diagnostics to identify samples that are infected and may lead to cancerous growth or other disorders. The present invention also discloses composition, methods and kits for the detection of oncogenic HPV E6 proteins in clinical samples as a cancer diagnostic.
Cervical cancer is the second most common cancer diagnosis in women and is linked to high-risk human papillomavirus infection 99.7% of the time. Currently, 12,000 new cases of invasive cervical cancer are diagnosed in US women annually, resulting in 5,000 deaths each year. Furthermore, there are approximately 400,000 cases of cervical cancer and close to 200,000 deaths annually worldwide. Human papillomaviruses (HPVs) are one of the most common causes of sexually transmitted disease in the world. Overall, 50-75% of sexually active men and women acquire genital HPV infections at some point in their lives. An estimated 5.5 million people become infected with HPV each year in the US alone, and at least 20 million are currently infected. The more than 100 different isolates of HPV have been broadly subdivided into high-risk and low-risk subtypes based on their association with cervical carcinomas or with benign cervical lesions or dysplasias.
A number of lines of evidence point to HPV infections as the etiological agents of cervical cancers. Multiple studies in the 1980's reported the presence of HPV variants in cervical dysplasias, cancer, and in cell lines derived from cervical cancer. Further research demonstrated that the E6-E7 region of the genome from oncogenic HPV 18 is selectively retained in cervical cancer cells, suggesting that HPV infection could be causative and that continued expression of the E6-E7 region is required for maintenance of the immortalized or cancerous state. The following year, Sedman et al demonstrated that the E6-E7 genes from HPV 16 were sufficient to immortalize human keratinocytes in culture. Barbosa et al demonstrated that although E6-E7 genes from high risk HPVs could transform cell lines, the E6-E7 regions from low risk, or non-oncogenic variants such as HPV 6 and HPV 11 were unable to transform human keratinocytes. More recently, Pillai et al examined HPV 16 and 18 infection by in situ hybridization and E6 protein expression by immunocytochemistry in 623 cervical tissue samples at various stages of tumor progression and found a significant correlation between histological abnormality and HPV infection.
Current treatment paradigms are focused on the actual cervical dysplasia rather than the underlying infection with HPV. Women are screened by physicians annually for cervical dysplasia and are treated with superficial ablative techniques, including cryosurgery, laser ablation and excision. As the disease progresses, treatment options become more aggressive, including partial or radical hysterectomy, radiation or chemotherapy. A significant unmet need exists for early and accurate diagnosis of oncogenic HPV infection as well as for treatments directed at the causative HPV infection, preventing the development of cervical cancer by intervening earlier in disease progression. Human papillomaviruses characterized to date are associated with lesions confined to the epithelial layers of skin, or oral, pharyngeal, respiratory, and, most importantly, anogenital mucosae. Specific human papillomavirus types, including HPV 6 and 11, frequently cause benign mucosal lesions, whereas other types such as HPV 16, 18, and a host of other strains, are predominantly found in high-grade lesions and cancer. Individual types of human papillomaviruses (HPV) which infect mucosal surfaces have been implicated as the causative agents for carcinomas of the cervix, anus, penis, larynx and the buccal cavity, occasional periungal carcinomas, as well as benign anogenital warts. The identification of particular HPV types is used for identifying patients with premalignant lesions who are at risk of progression to malignancy. Although visible anogenital lesions are present in some persons infected with human papillomavirus, the majority of individuals with HPV genital tract infection do not have clinically apparent disease, but analysis of cytomorphological traits present in cervical smears can be used to detect HPV infection. Papanicolaou tests are a valuable screening tool, but they miss a large proportion of HPV-infected persons due to the unfortunate false positive and false negative test results. In addition, they are not amenable to worldwide testing because interpretation of results requires trained pathologists.
Conventional viral detection assays, including serologic assays, sandwich ELISA assays and growth in cell culture, are not commercially available and/or are not suitable for the diagnosis and tracking of HPV infection. Recently, several PCR (polymerase chain reaction)-based tests for HPV infections have become available. Though the tests provide the benefit of differentiating oncogenic from non-oncogenic infections, they are fairly expensive to administer and require highly trained technicians to perform PCR and/or luminometer assays. In addition, PCR has a natural false positive rate that may invoke further testing or procedures that are not required. Since the oncogenicity of HPV has been shown to be protein based, early detection of HPV DNA or RNA may lead to unnecessary medical procedures that the body's immune system may solve naturally.
The detection and diagnosis of disease is a prerequisite for the treatment of disease. Numerous markers and characteristics of diseases have been identified and many are used for the diagnosis of disease. Many diseases are preceded by, and are characterized by, changes in the state of the affected cells. Changes can include the expression of pathogen genes or proteins in infected cells, changes in the expression patterns of genes or proteins in affected cells, and changes in cell morphology. The detection, diagnosis, and monitoring of diseases can be aided by the accurate assessment of these changes. Inexpensive, rapid, early and accurate detection of pathogens can allow treatment and prevention of diseases that range in effect from discomfort to death.
The following publications are of interest: Munger (2002) Front. Biosci. 7:d641-9; Glaunsinger (2000) Oncogene 19:5270-80; Gardiol (1999) Oncogene 18:5487-96; Pim (1999) Oncogene 18:7403-8; Meschede (1998) J. Clin. Microbiol. 36:475-80; Kiyono (1997) Proc. Natl. Acad. Sci. 94:11612-6; and Lee (1997) Proc. Natl. Acad. Sci. 94:6670-5. In addition, the following patents and patent applications are of interest: Bleul, 6,322,794; Cole, 6,344,314; Schoolnik, 5,415,995; Bleul, 5753233; Cole, 5,876,723; Cole, 5,648,459; Orth, 6,391,539; Orth, 5,665,535; Schoolnik, 4,777,239.
Methods and compositions for detection of proteins from pathogens that may result in oncogenic cellular transformation or biological abnormalities in a variety of cell types (e.g., cervical, anal, penile, throat) are provided herein. These methods and compositions can be utilized to detect the presence of pathogens including, but not limited to, those that result in diseases such as cervical cancer, penile cancer, anal cancer and throat cancer, for example. More specifically, methods, compositions and kits are described for the detection of oncogenic HPV E6 proteins in clinical samples
I. Definitions
A “marker” or “biological marker” as used herein refers to a measurable or detectable entity in a biological sample. Examples or markers include nucleic acids, proteins, or chemicals that are present in biological samples. One example of a marker is the presence of viral or pathogen proteins or nucleic acids in a biological sample from a human source.
As used herein the term “isolated” refers to a polynucleotide, a polypeptide, an antibody, or a host cell that is in an environment different from that in which the polynucleotide, the polypeptide, the antibody, or the host cell naturally occurs. A polynucleotide, a polypeptide, an antibody, or a host cell which is isolated is generally substantially purified. As used herein, the term “substantially purified” refers to a compound (e.g., either a polynucleotide or a polypeptide or an antibody) that is removed from its natural environment and is at least 60% free, preferably 75% free, and most preferably 90% free from other components with which it is naturally associated. Thus, for example, a composition containing A is “substantially free of” B when at least 85% by weight of the total A+B in the composition is A. Preferably, A comprises at least about 90% by weight of the total of A+B in the composition, more preferably at least about 95% or even 99% by weight.
The term “biological sample” encompasses a variety of sample types obtained from an organism and can be used in a diagnostic or monitoring assay. The term encompasses blood and other liquid samples of biological origin, solid tissue samples, such as a biopsy specimen or tissue cultures or cells derived therefrom and the progeny thereof. The term encompasses samples that have been manipulated in any way after their procurement, such as by treatment with reagents, solubilization, or enrichment for certain components. The term encompasses a clinical sample, and also includes cells in cell culture, cell supernatants, cell lysates, serum, plasma, biological fluids, and tissue samples. The term “biological sample” is meant to distinguish between a sample in a clinical setting from a sample that may be a recombinant sample or derived from a recombinant sample.
A “fusion protein” or “fusion polypeptide” as used herein refers to a composite protein, i.e., a single contiguous amino acid sequence, made up of two (or more) distinct, heterologous polypeptides that are not normally fused together in a single amino acid sequence. Thus, a fusion protein can include a single amino acid sequence that contains two entirely distinct amino acid sequences or two similar or identical polypeptide sequences, provided that these sequences are not normally found together in the same configuration in a single amino acid sequence found in nature. Fusion proteins can generally be prepared using either recombinant nucleic acid methods, i.e., as a result of transcription and translation of a recombinant gene fusion product, which fusion comprises a segment encoding a polypeptide of the invention and a segment encoding a heterologous protein, or by chemical synthesis methods well known in the art.
A “fusion protein construct” as used herein is a polynucleotide encoding a fusion protein.
An “oncogenic HPV strain” is an HPV strain that is known to cause cervical cancer as determined by the National Cancer Institute (NCI, 2001). “Oncogenic E6 proteins” are E6 proteins encoded by the above oncogenic HPV strains. Exemplary oncogenic strains are shown in Table 3.
An “oncogenic E6 protein binding partner” can be any molecule that specifically binds to an oncogenic E6 protein. Suitable oncogenic E6 protein binding partners include a PDZ domain (as described below), an antibody against an oncogenic E6 protein; other proteins that recognize oncogenic E6 protein (e.g., p53, E6-AP or E6-BP); DNA (i.e., cruciform DNA); and other partners such as aptamers or single chain antibodies from phage display). In some embodiments, detection of more than 1 oncogenic E6 protein (e.g., all oncogenic E6 proteins, E6 proteins from HPV strains 16, 18 and 33 or E6 proteins from HPV strains 16, 18 and 45) is desirable, and, as such, an oncogenic E6 protein binding partner may be antibody that binds to these proteins, a mixture of antibodies that each bind to a different proteins. As is known in the art, such binding partners may be labeled to facilitate their detection. In general, binding partner bind E6 with an binding affinity of 10−5 M or more, e.g., 10−6 or more, 10−7 or more, 10−8 M or more (e.g., 10−9 M, 10−10, 10−11, etc.).
As used herein, the term “PDZ domain” refers to protein sequence (i.e., modular protein domain) of less than approximately 90 amino acids, (i.e., about 80-90, about 70-80, about 60-70 or about 50-60 amino acids), characterized by homology to the brain synaptic protein PSD-95, the Drosophila septate junction protein Discs-Large (DLG), and the epithelial tight junction protein ZO1 (ZO1). PDZ domains are also known as Discs-Large homology repeats (“DHRs”) and GLGF repeats. PDZ domains generally appear to maintain a core consensus sequence (Doyle, D. A., 1996, Cell 85: 1067-76).
PDZ domains are found in diverse membrane-associated proteins including members of the MAGUK family of guanylate kinase homologs, several protein phosphatases and kinases, neuronal nitric oxide synthase, tumor suppressor proteins, and several dystrophin-associated proteins, collectively known as syntrophins.
Exemplary PDZ domain-containing proteins and PDZ domain sequences are shown in TABLE 2 and EXAMPLE 4. The term “PDZ domain” also encompasses variants (e.g., naturally occurring variants) of the sequences (e.g., polymorphic variants, variants with conservative substitutions, and the like) and domains from alternative species (e.g. mouse, rat). Typically, PDZ domains are substantially identical to those shown in U.S. patent application Ser. No. 09/724553, e.g., at least about 70%, at least about 80%, or at least about 90% amino acid residue identity when compared and aligned for maximum correspondence. It is appreciated in the art that PDZ domains can be mutated to give amino acid changes that can strengthen or weaken binding and to alter specificity, yet they remain PDZ domains (Schneider et al., 1998, Nat. Biotech. 17:170-5). Unless otherwise indicated, a reference to a particular PDZ domain (e.g. a MAGI-1 domain 2) is intended to encompass the particular PDZ domain and HPV E6-binding variants thereof. In other words, if a reference is made to a particular PDZ domain, a reference is also made to variants of that PDZ domain that bind oncogenic E6 protein of HPV, as described below. In this respect it is noted that the numbering of PDZ domains in a protein may change. For example, the MAGI-1 domain 2, as referenced herein, may be referenced as MAGI-1 domain 1 in other literature. As such, when a particular PDZ domain of a protein is referenced in this application, this reference should be understood in view of the sequence of that domain, as described herein, particularly in the sequence listing. Table 9, inserted before the claims, shows the relationship between the sequences of the sequence listing and the names and Genbank accession numbers for various domains, where appropriate.
As used herein, the term “PDZ protein” refers to a naturally occurring protein containing a PDZ domain. Exemplary PDZ proteins include CASK, MPP1, DLG1, DLG2, PSD95, NeDLG, TIP-33, SYN1a, TIP-43, LDP, LIM, LIMK1, LIMK2, MPP2, NOS1, AF6, PTN-4, prIL16, 41.8kD, KIAA0559, RGS12, KIAA0316, DVL1, TIP-40, TIAM1, MINT1, MAGI-1, MAGI-2, MAGI-3, KIAA0303, CBP, MINT3, TIP-2, KIAA0561, and TIP-1.
As used herein, the term “PDZ-domain polypeptide” refers to a polypeptide containing a PDZ domain, such as a fusion protein including a PDZ domain sequence, a naturally occurring PDZ protein, or an isolated PDZ domain peptide. A PDZ-domain polypeptide may therefore be about 60 amino acids or more in length, about 70 amino acids or more in length, about 80 amino acids or more in length, about 90 amino acids or more in length, about 100 amino acids or more in length, about 200 amino acids or more in length, about 300 amino acids or more in length, about 500 amino acids or more in length, about 800 amino acids or more in length, about 1000 amino acids or more in length, usually up to about 2000 amino acids or more in length. PDZ domain peptides are usually no more than about 100 amino acids (e.g. 50-60 amino acids, 60-70 amino acids, 80-90 amino acids, or 90-100 amino acids), and encode a PDZ domain.
As used herein, the term “PL protein” or “PDZ Ligand protein” refers to a naturally occurring protein that forms a molecular complex with a PDZ-domain, or to a protein whose carboxy-terminus, when expressed separately from the full length protein (e.g., as a peptide fragment of 4-25 residues, e.g., 8, 10, 12, 14 or 16 residues), forms such a molecular complex. The molecular complex can be observed in vitro using the “A assay” or “G assay” described infra, or in vivo. Exemplary PL proteins listed in TABLES 3 and 4 are demonstrated to bind specific PDZ proteins. This definition is not intended to include anti-PDZ antibodies and the like.
As used herein, a “PL sequence” refers to the amino acid sequence of the C-terminus of a PL protein (e.g., the C-terminal 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 20 or 25 residues) (“C-terminal PL sequence”) or to an internal sequence known to bind a PDZ domain (“internal PL sequence”).
As used herein, a “PL peptide” is a peptide of having a sequence from, or based on, the sequence of the C-terminus of a PL protein. Exemplary PL peptides (biotinylated) are listed in TABLE 3.
As used herein, a “PL detector” is a protein that can specifically recognize and bind to a PL sequence.
As used herein, a “PL fusion protein” is a fusion protein that has a PL sequence as one domain, typically as the C-terminal domain of the fusion protein. An exemplary PL fusion protein is a tat-PL sequence fusion.
As used herein, the term “PL inhibitor peptide sequence” refers to PL peptide amino acid sequence that (in the form of a peptide or PL fusion protein) inhibits the interaction between a PDZ domain polypeptide and a PL peptide (e.g., in an A assay or a G assay).
As used herein, a “PDZ-domain encoding sequence” means a segment of a polynucleotide encoding a PDZ domain. In various embodiments, the polynucleotide is DNA, RNA, single stranded or double stranded.
As used herein, the terms “antagonist” and “inhibitor,” when used in the context of modulating a binding interaction (such as the binding of a PDZ domain sequence to a PL sequence), are used interchangeably and refer to an agent that reduces the binding of the, e.g., PL sequence (e.g., PL peptide) and the, e.g., PDZ domain sequence (e.g., PDZ protein, PDZ domain peptide).
As used herein, the terms “agonist” and “enhancer,” when used in the context of modulating a binding interaction (such as the binding of a PDZ domain sequence to a PL sequence), are used interchangeably and refer to an agent that increases the binding of the, e.g., PL sequence (e.g., PL peptide) and the, e.g., PDZ domain sequence (e.g., PDZ protein, PDZ domain peptide).
As used herein, the terms “peptide mimetic,” “peptidomimetic,” and “peptide analog” are used interchangeably and refer to a synthetic chemical compound that has substantially the same structural and/or functional characteristics of a PL inhibitory or PL binding peptide of the invention. The mimetic can be either entirely composed of synthetic, non-natural analogues of amino acids, or, is a chimeric molecule of partly natural peptide amino acids and partly non-natural analogs of amino acids. The mimetic can also incorporate any amount of natural amino acid conservative substitutions as long as such substitutions also do not substantially alter the mimetic's structure and/or inhibitory or binding activity. As with polypeptides of the invention which are conservative variants, routine experimentation will determine whether a mimetic is within the scope of the invention, i.e., that its structure and/or function is not substantially altered. Thus, a mimetic composition is within the scope of the invention if it is capable of binding to a PDZ domain and/or inhibiting a PL-PDZ interaction.
Polypeptide mimetic compositions can contain any combination of nonnatural structural components, which are typically from three structural groups: a) residue linkage groups other than the natural amide bond (“peptide bond”) linkages; b) non-natural residues in place of naturally occurring amino acid residues; or c) residues which induce secondary structural mimicry, i.e., to induce or stabilize a secondary structure, e.g., a beta turn, gamma turn, beta sheet, alpha helix conformation, and the like.
A polypeptide can be characterized as a mimetic when all or some of its residues are joined by chemical means other than natural peptide bonds. Individual peptidomimetic residues can be joined by peptide bonds, other chemical bonds or coupling means, such as, e.g., glutaraldehyde, N-hydroxysuccinimide esters, bifunctional maleimides, N,N═-dicyclohexylcarbodiimide (DCC) or N,N═-diisopropylcarbodiimide (DIC). Linking groups that can be an alternative to the traditional amide bond (“peptide bond”) linkages include, e.g., ketomethylene (e.g., —C(═O)—CH2— for —C(═O)—NH—), aminomethylene (CH2—NH), ethylene, olefin (CH═CH), ether (CH2—O), thioether (CH2—S), tetrazole (CN4—), thiazole, retroamide, thioamide, or ester (see, e.g., Spatola (1983) in Chemistry and Biochemistry of Amino Acids, Peptides and Proteins, Vol. 7, pp 267-357, A Peptide Backbone Modifications, Marcell Dekker, N.Y.).
A polypeptide can also be characterized as a mimetic by containing all or some non-natural residues in place of naturally occurring amino acid residues. Nonnatural residues are well described in the scientific and patent literature; a few exemplary nonnatural compositions useful as mimetics of natural amino acid residues and guidelines are described below.
Mimetics of aromatic amino acids can be generated by replacing by, e.g., D- or L-naphylalanine; D- or L-phenylglycine; D- or L-2 thieneylalanine; D- or L-1, -2, 3-, or 4-pyreneylalanine; D- or L-3 thieneylalanine; D- or L-(2-pyridinyl)-alanine; D- or L-(3-pyridinyl)-alanine; D- or L-(2-pyrazinyl)-alanine; D- or L-(4-isopropyl)-phenylglycine; D-(trifluoromethyl)-phenylglycine; D-(trifluoromethyl)-phenylalanine; D-p-fluorophenylalanine; D- or L-p-biphenylphenylalanine; K- or L-p-methoxybiphenylphenylalanine; D- or L-2-indole(alkyl)alanines; and, D- or L-alkylainines, where alkyl can be substituted or unsubstituted methyl, ethyl, propyl, hexyl, butyl, pentyl, isopropyl, iso-butyl, sec-isotyl, iso-pentyl, or a non-acidic amino acids. Aromatic rings of a nonnatural amino acid include, e.g., thiazolyl, thiophenyl, pyrazolyl, benzimidazolyl, naphthyl, furanyl, pyrrolyl, and pyridyl aromatic rings.
Mimetics of acidic amino acids can be generated by substitution by, e.g., non-carboxylate amino acids while maintaining a negative charge; (phosphono)alanine; sulfated threonine. Carboxyl side groups (e.g., aspartyl or glutamyl) can also be selectively modified by reaction with carbodiimides (R═—N—C—N—R═) such as, e.g., 1-cyclohexyl-3(2-morpholinyl-(4-ethyl)carbodiimide or 1-ethyl-3(4-azonia-4,4-dimetholpentyl)carbodiimide. Aspartyl or glutamyl can also be converted to asparaginyl and glutaminyl residues by reaction with ammonium ions.
Mimetics of basic amino acids can be generated by substitution with, e.g., (in addition to lysine and arginine) the amino acids omithine, citrulline, or (guanidino)-acetic acid, or (guanidino)alkyl-acetic acid, where alkyl is defined above. Nitrile derivative (e.g., containing the CN-moiety in place of COOH) can be substituted for asparagine or glutamine. Asparaginyl and glutaminyl residues can be deaminated to the corresponding aspartyl or glutamyl residues.
Arginine residue mimetics can be generated by reacting arginyl with, e.g., one or more conventional reagents, including, e.g., phenylglyoxal, 2,3-butanedione, 1,2-cyclohexanedione, or ninhydrin, preferably under alkaline conditions.
Tyrosine residue mimetics can be generated by reacting tyrosyl with, e.g., aromatic diazonium compounds or tetranitromethane. N-acetylimidizol and tetranitromethane can be used to form O-acetyl tyrosyl species and 3-nitro derivatives, respectively.
Cysteine residue mimetics can be generated by reacting cysteinyl residues with, e.g., alpha-haloacetates such as 2-chloroacetic acid or chloroacetamide and corresponding amines, to give carboxymethyl or carboxyamidomethyl derivatives. Cysteine residue mimetics can also be generated by reacting cysteinyl residues with, e.g., bromo-trifluoroacetone, alpha-bromo-beta-(5-imidozoyl) propionic acid; chloroacetyl phosphate, N-alkylmaleimides, 3-nitro-2-pyridyl disulfide; methyl 2-pyridyl disulfide; p-chloromercuribenzoate; 2-chloromercuri-4 nitrophenol; or, chloro-7-nitrobenzo-oxy-1,3-diazole.
Lysine mimetics can be generated (and amino terminal residues can be altered) by reacting lysinyl with, e.g., succinic or other carboxylic acid anhydrides. Lysine and other alpha-amino-containing residue mimetics can also be generated by reaction with imidoesters, such as methyl picolinimidate, pyridoxal phosphate, pyridoxal, chloroborohydride, trinitrobenzenesulfonic acid, O-methylisourea, 2,4, pentanedione, and transamidase-catalyzed reactions with glyoxylate.
Mimetics of methionine can be generated by reaction with, e.g., methionine sulfoxide. Mimetics of proline include, e.g., pipecolic acid, thiazolidine carboxylic acid, 3- or 4-hydroxy proline, dehydroproline, 3- or 4-methylproline, or 3,3,-dimethylproline. Histidine residue mimetics can be generated by reacting histidyl with, e.g., diethylprocarbonate or para-bromophenacyl bromide.
Other mimetics include, e.g., those generated by hydroxylation of proline and lysine; phosphorylation of the hydroxyl groups of seryl or threonyl residues; methylation of the alpha-amino groups of lysine, arginine and histidine; acetylation of the N-terminal amine; methylation of main chain amide residues or substitution with N-methyl amino acids; or amidation of C-terminal carboxyl groups.
A component of a natural polypeptide (e.g., a PL polypeptide or PDZ polypeptide) can also be replaced by an amino acid (or peptidomimetic residue) of the opposite chirality. Thus, any amino acid naturally occurring in the L-configuration (which can also be referred to as the R or S, depending upon the structure of the chemical entity) can be replaced with the amino acid of the same chemical structural type or a peptidomimetic, but of the opposite chirality, generally referred to as the D-amino acid, but which can additionally be referred to as the R— or S— form.
The mimetics of the invention can also include compositions that contain a structural mimetic residue, particularly a residue that induces or mimics secondary structures, such as a beta turn, beta sheet, alpha helix structures, gamma turns, and the like. For example, substitution of natural amino acid residues with D-amino acids; N-alpha-methyl amino acids; C-alpha-methyl amino acids; or dehydroamino acids within a peptide can induce or stabilize beta turns, gamma turns, beta sheets or alpha helix conformations. Beta turn mimetic structures have been described, e.g., by Nagai (1985) Tet. Lett. 26:647-650; Feigl (1986) J. Amer. Chem. Soc. 108:181-182; Kahn (1988) J. Amer. Chem. Soc. 110:1638-1639; Kemp (1988) Tet. Lett. 29:5057-5060; Kahn (1988) J. Molec. Recognition 1:75-79. Beta sheet mimetic structures have been described, e.g., by Smith (1992) J. Amer. Chem. Soc. 114:10672-10674. For example, a type VI beta turn induced by a cis amide surrogate, 1,5-disubstituted tetrazol, is described by Beusen (1995) Biopolymers 36:181-200. Incorporation of achiral omega-amino acid residues to generate polymethylene units as a substitution for amide bonds is described by Banerjee (1996) Biopolymers 39:769-777. Secondary structures of polypeptides can be analyzed by, e.g., high-field 1H NMR or 2D NMR spectroscopy, see, e.g., Higgins (1997) J. Pept. Res. 50:421-435. See also, Hruby (1997) Biopolymers 43:219-266, Balaji, et al., U.S. Pat. No. 5,612,895.
As used herein, “peptide variants” and “conservative amino acid substitutions” refer to peptides that differ from a reference peptide (e.g., a peptide having the sequence of the carboxy-terminus of a specified PL protein) by substitution of an amino acid residue having similar properties (based on size, polarity, hydrophobicity, and the like). Thus, insofar as the compounds that are encompassed within the scope of the invention are partially defined in terms of amino acid residues of designated classes, the amino acids may be generally categorized into three main classes: hydrophilic amino acids, hydrophobic amino acids and cysteine-like amino acids, depending primarily on the characteristics of the amino acid side chain. These main classes may be further divided into subclasses. Hydrophilic amino acids include amino acids having acidic, basic or polar side chains and hydrophobic amino acids include amino acids having aromatic or apolar side chains. Apolar amino acids may be further subdivided to include, among others, aliphatic amino acids. The definitions of the classes of amino acids as used herein are as follows:
“Hydrophobic Amino Acid” refers to an amino acid having a side chain that is uncharged at physiological pH and that is repelled by aqueous solution. Examples of genetically encoded hydrophobic amino acids include Ile, Leu and Val. Examples of non-genetically encoded hydrophobic amino acids include t-BuA.
“Aromatic Amino Acid” refers to a hydrophobic amino acid having a side chain containing at least one ring having a conjugated π-electron system (aromatic group). The aromatic group may be further substituted with groups such as alkyl, alkenyl, alkynyl, hydroxyl, sulfanyl, nitro and amino groups, as well as others. Examples of genetically encoded aromatic amino acids include Phe, Tyr and Trp. Commonly encountered non-genetically encoded aromatic amino acids include phenylglycine, 2-naphthylalanine, β-2-thienylalanine, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, 4-chloro-phenylalanine, 2-fluorophenyl-alanine, 3-fluorophenylalanine and 4-fluorophenylalanine.
“Apolar Amino Acid” refers to a hydrophobic amino acid having a side chain that is generally uncharged at physiological pH and that is not polar. Examples of genetically encoded apolar amino acids include Gly, Pro and Met. Examples of non-encoded apolar amino acids include Cha.
“Aliphatic Amino Acid” refers to an apolar amino acid having a saturated or unsaturated straight chain, branched or cyclic hydrocarbon side chain. Examples of genetically encoded aliphatic amino acids include Ala, Leu, Val and Ile. Examples of non-encoded aliphatic amino acids include Nle.
“Hydrophilic Amino Acid” refers to an amino acid having a side chain that is attracted by aqueous solution. Examples of genetically encoded hydrophilic amino acids include Ser and Lys. Examples of non-encoded hydrophilic amino acids include Cit and hCys.
“Acidic Amino Acid” refers to a hydrophilic amino acid having a side chain pK value of less than 7. Acidic amino acids typically have negatively charged side chains at physiological pH due to loss of a hydrogen ion. Examples of genetically encoded acidic amino acids include Asp and Glu.
“Basic Amino Acid” refers to a hydrophilic amino acid having a side chain pK value of greater than 7. Basic amino acids typically have positively charged side chains at physiological pH due to association with hydronium ion. Examples of genetically encoded basic amino acids include Arg, Lys and His. Examples of non-genetically encoded basic amino acids include the non-cyclic amino acids ornithine, 2,3-diaminopropionic acid, 2,4-diaminobutyric acid and homoarginine.
“Polar Amino Acid” refers to a hydrophilic amino acid having a side chain that is uncharged at physiological pH, but which has a bond in which the pair of electrons shared in common by two atoms is held more closely by one of the atoms. Examples of genetically encoded polar amino acids include Asx and Glx. Examples of non-genetically encoded polar amino acids include citrulline, N-acetyl lysine and methionine sulfoxide.
“Cysteine-Like Amino Acid” refers to an amino acid having a side chain capable of forming a covalent linkage with a side chain of another amino acid residue, such as a disulfide linkage. Typically, cysteine-like amino acids generally have a side chain containing at least one thiol (SH) group. Examples of genetically encoded cysteine-like amino acids include Cys. Examples of non-genetically encoded cysteine-like amino acids include homocysteine and penicillamine.
As will be appreciated by those having skill in the art, the above classification are not absolute—several amino acids exhibit more than one characteristic property, and can therefore be included in more than one category. For example, tyrosine has both an aromatic ring and a polar hydroxyl group. Thus, tyrosine has dual properties and can be included in both the aromatic and polar categories. Similarly, in addition to being able to form disulfide linkages, cysteine also has apolar character. Thus, while not strictly classified as a hydrophobic or apolar amino acid, in many instances cysteine can be used to confer hydrophobicity to a peptide.
Certain commonly encountered amino acids which are not genetically encoded of which the peptides and peptide analogues of the invention may be composed include, but are not limited to, β-alanine (b-Ala) and other omega-amino acids such as 3-aminopropionic acid (Dap), 2,3-diaminopropionic acid (Dpr), 4-aminobutyric acid and so forth; α-aminoisobutyric acid (Aib); ε-aminohexanoic acid (Aha); δ-aminovaleric acid (Ava); N-methylglycine or sarcosine (MeGly); omithine (Orn); citrulline (Cit); t-butylalanine (t-BuA); t-butylglycine (t-BuG); N-methylisoleucine (MeIle); phenylglycine (Phg); cyclohexylalanine (Cha); norleucine (Nle); 2-naphthylalanine (2-Nal); 4-chlorophenylalanine (Phe(4-Cl)); 2-fluorophenylalanine (Phe(2-F)); 3-fluorophenylalanine (Phe(3-F)); 4-fluorophenylalanine (Phe(4-F)); penicillamine (Pen); 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic); β-2-thienylalanine (Thi); methionine sulfoxide (MSO); homoarginine (hArg); N-acetyl lysine (AcLys); 2,3-diaminobutyric acid (Dab); 2,3-diaminobutyric acid (Dbu); p-aminophenylalanine (Phe(pNH2)); N-methyl valine (MeVal); homocysteine (hCys) and homoserine (hSer). These amino acids also fall conveniently into the categories defined above.
The classifications of the above-described genetically encoded and non-encoded amino acids are summarized in TABLE 1, below. It is to be understood that TABLE 1 is for illustrative purposes only and does not purport to be an exhaustive list of amino acid residues which may comprise the peptides and peptide analogues described herein. Other amino acid residues which are useful for making the peptides and peptide analogues described herein can be found, e.g., in Fasman, 1989, CRC Practical Handbook of Biochemistry and Molecular Biology, CRC Press, Inc., and the references cited therein. Amino acids not specifically mentioned herein can be conveniently classified into the above-described categories on the basis of known behavior and/or their characteristic chemical and/or physical properties as compared with amino acids specifically identified.
In the case of the PDZ domains described herein, a “HPV E6-binding variant” of a particular PDZ domain is a PDZ domain variant that retains HPV E6 PDZ ligand binding activity. Assays for determining whether a PDZ domain variant binds HPV E6 are described in great detail below, and guidance for identifying which amino acids to change in a specific PDZ domain to make it into a variant may be found in a variety of sources. In one example, a PDZ domain may be compared to other PDZ domains described herein and amino acids at corresponding positions may be substituted, for example. In another example, the sequence a PDZ domain of a particular PDZ protein may be compared to the sequence of an equivalent PDZ domain in an equivalent PDZ protein from another species. For example, the sequence a PDZ domain from a human PDZ protein may be compared to the sequence of other known and equivalent PDZ domains from other species (e.g., mouse, rat, etc.) and any amino acids that are variant between the two sequences may be substituted into the human PDZ domain to make a variant of the PDZ domain. For example, the sequence of the human MAGI-1 PDZ domain 2 may be compared to equivalent MAGI-1 PDZ domains from other species (e.g. mouse Genbank gi numbers 7513782 and 28526157 or other homologous sequences) to identify amino acids that may be substituted into the human MAGI-1-PDZ domain to make a variant thereof. Such method may be applied to any of the MAGI-1 PDZ domains described herein. Minimal MAGI-PDZ domain 2 sequence is provided as SEQ ID NOS: 293-301. Particular variants may have 1, up to 5, up to about 10, up to about 15, up to about 20 or up to about 30 or more, usually up to about 50 amino acid changes as compared to a sequence set forth in the sequence listing. Exemplary MAGI-1 PDZ variants include the sequences set forth in SEQ ID NOS: 302-330. In making a variant, if a GFG motif is present in a PDZ domain, in general, it should not be altered in sequence.
In general, variant PDZ domain polypeptides have a PDZ domain that has at least about 70 or 80%, usually at least about 90%, and more usually at least about 98% sequence identity with a variant PDZ domain polypeptide described herein, as measured by BLAST 2.0 using default parameters, over a region extending over the entire PDZ domain.
As used herein, a “detectable label” has the ordinary meaning in the art and refers to an atom (e.g., radionuclide), molecule (e.g., fluorescein), or complex, that is or can be used to detect (e.g., due to a physical or chemical property), indicate the presence of a molecule or to enable binding of another molecule to which it is covalently bound or otherwise associated. The term “label” also refers to covalently bound or otherwise associated molecules (e.g., a biomolecule such as an enzyme) that act on a substrate to produce a detectable atom, molecule or complex. Detectable labels suitable for use in the present invention include any composition detectable by spectroscopic, photochemical, biochemical, immunochemical, electrical, optical or chemical means. Labels useful in the present invention include biotin for staining with labeled streptavidin conjugate, magnetic beads (e.g., Dynabeads™), fluorescent dyes (e.g., fluorescein, Texas red, rhodamine, green fluorescent protein, enhanced green fluorescent protein, and the like), radiolabels (e.g., 3H, 125I, 35S, 14C, or 32P), enzymes (e.g., hydrolases, particularly phosphatases such as alkaline phosphatase, esterases and glycosidases, or oxidoreductases, particularly peroxidases such as horse radish peroxidase, and others commonly used in ELISAs), substrates, cofactors, inhibitors, chemiluminescent groups, chromogenic agents, and colorimetric labels such as colloidal gold or colored glass or plastic (e.g., polystyrene, polypropylene, latex, etc.) beads. Patents teaching the use of such labels include U.S. Pat. Nos. 3,817,837; 3,850,752; 3,939,350; 3,996,345; 4,277,437; 4,275,149; and 4,366,241. Means of detecting such labels are well known to those of skill in the art. Thus, for example, radiolabels and chemiluminescent labels may be detected using photographic film or scintillation counters, fluorescent markers may be detected using a photodetector to detect emitted light (e.g., as in fluorescence-activated cell sorting). Enzymatic labels are typically detected by providing the enzyme with a substrate and detecting the reaction product produced by the action of the enzyme on the substrate, and colorimetric labels are detected by simply visualizing the colored label. Thus, a label is any composition detectable by spectroscopic, photochemical, biochemical, immunochemical, electrical, optical or chemical means. The label may be coupled directly or indirectly to the desired component of the assay according to methods well known in the art. Non-radioactive labels are often attached by indirect means. Generally, a ligand molecule (e.g., biotin) is covalently bound to the molecule. The ligand then binds to an anti-ligand (e.g., streptavidin) molecule which is either inherently detectable or covalently bound to a signal generating system, such as a detectable enzyme, a fluorescent compound, or a chemiluminescent compound. A number of ligands and anti-ligands can be used. Where a ligand has a natural anti-ligand, for example, biotin, thyroxine, and cortisol, it can be used in conjunction with the labeled, naturally occurring anti-ligands. Alternatively, any haptenic or antigenic compound can be used in combination with an antibody. The molecules can also be conjugated directly to signal generating compounds, e.g., by conjugation with an enzyme or fluorophore. Means of detecting labels are well known to those of skill in the art. Thus, for example, where the label is a radioactive label, means for detection include a scintillation counter, photographic film as in autoradiography, or storage phosphor imaging. Where the label is a fluorescent label, it may be detected by exciting the fluorochrome with the appropriate wavelength of light and detecting the resulting fluorescence. The fluorescence may be detected visually, by means of photographic film, by the use of electronic detectors such as charge coupled devices (CCDs) or photomultipliers and the like. Similarly, enzymatic labels may be detected by providing the appropriate substrates for the enzyme and detecting the resulting reaction product. Also, simple colorimetric labels may be detected by observing the color associated with the label. It will be appreciated that when pairs of fluorophores are used in an assay, it is often preferred that they have distinct emission patterns (wavelengths) so that they can be easily distinguished.
As used herein, the term “substantially identical” in the context of comparing amino acid sequences, means that the sequences have at least about 70%, at least about 80%, or at least about 90% amino acid residue identity when compared and aligned for maximum correspondence. An algorithm that is suitable for determining percent sequence identity and sequence similarity is the FASTA algorithm, which is described in Pearson, W. R. & Lipman, D. J., 1988, Proc. Natl. Acad. Sci. U.S.A. 85: 2444. See also W. R. Pearson, 1996, Methods Enzymol. 266: 227-258. Preferred parameters used in a FASTA alignment of DNA sequences to calculate percent identity are optimized, BL50 Matrix 15: −5, k-tuple=2; joining penalty=40, optimization=28; gap penalty -12, gap length penalty=−2; and width=16.
As used herein, the terms “sandwich”, “sandwich ELISA”, “Sandwich diagnostic” and “capture ELISA” all refer to the concept of detecting a biological polypeptide with two different test agents. For example, a PDZ protein could be directly or indirectly attached to a solid support. Test sample could be passed over the surface and the PDZ protein could bind it's cognate PL protein(s). A labeled antibody or alternative detection reagent could then be used to determine whether a specific PL protein had bound the PDZ protein.
By “solid phase support” or “carrier” is intended any support capable of binding polypeptide, antigen or antibody. Well-known supports or carriers, include glass, polystyrene, polypropylene, polyethylene, dextran, nylon, amylases, natural and modified celluloses, polyacrylamides, agaroses, and magnetite. The nature of the carrier can be either soluble to some extent or insoluble for the purposes of the present invention. The support material can have virtually any possible structural configuration so long as the coupled molecule is capable of binding to a PDZ domain polypeptide or an E6 antibody. Thus, the support configuration can be spherical, as in a bead, or cylindrical, as in the inside surface of a test tube, or the external surface of a rod. Alternatively, the surface can be flat, such as a sheet, culture dish, test strip, etc. Those skilled in the art will know many other suitable carriers for binding antibody, peptide or antigen, or can ascertain the same by routine experimentation.
As used herein, the terms “test compound” or “test agent” are used interchangeably and refer to a candidate agent that may have enhancer/agonist, or inhibitor/antagonist activity, e.g., inhibiting or enhancing an interaction such as PDZ-PL binding. The candidate agents or test compounds may be any of a large variety of compounds, both naturally occurring and synthetic, organic and inorganic, and including polymers (e.g., oligopeptides, polypeptides, oligonucleotides, and polynucleotides), small molecules, antibodies (as broadly defined herein), sugars, fatty acids, nucleotides and nucleotide analogs, analogs of naturally occurring structures (e.g., peptide mimetics, nucleic acid analogs, and the like), and numerous other compounds. In certain embodiment, test agents are prepared from diversity libraries, such as random or combinatorial peptide or non-peptide libraries. Many libraries are known in the art that can be used, e.g., chemically synthesized libraries, recombinant (e.g., phage display libraries), and in vitro translation-based libraries. Examples of chemically synthesized libraries are described in Fodor et al., 1991, Science 251:767-773; Houghten et al., 1991, Nature 354:84-86; Lam et al., 1991, Nature 354:82-84; Medynski, 1994, Bio/Technology 12:709-710; Gallop et al., 1994, J. Medicinal Chemistry 37(9):1233-1251; Ohlmeyer et al., 1993, Proc. Natl. Acad. Sci. USA 90:10922-10926; Erb et al., 1994, Proc. Natl. Acad. Sci. USA 91:11422-11426; Houghten et al., 1992, Biotechniques 13:412; Jayawickreme et al., 1994, Proc. Natl. Acad. Sci. USA 91:1614-1618; Salmon et al., 1993, Proc. Natl. Acad. Sci. USA 90:11708-11712; PCT Publication No. WO 93/20242; and Brenner and Lemer, 1992, Proc. Natl. Acad. Sci. USA 89:5381-5383. Examples of phage display libraries are described in Scott and Smith, 1990, Science 249:386-390; Devlin et al., 1990, Science, 249:404-406; Christian, R. B., et al., 1992, J. Mol. Biol. 227:711-718); Lenstra, 1992, J. Immunol. Meth. 152:149-157; Kay et al., 1993, Gene 128:59-65; and PCT Publication No. WO 94/18318 dated Aug. 18, 1994. In vitro translation-based libraries include but are not limited to those described in PCT Publication No. WO 91/05058 dated Apr. 18, 1991; and Mattheakis et al., 1994, Proc. Natl. Acad. Sci. USA 91:9022-9026. By way of examples of nonpeptide libraries, a benzodiazepine library (see e.g., Bunin et al., 1994, Proc. Natl. Acad. Sci. USA 91:4708-4712) can be adapted for use. Peptoid libraries (Simon et al., 1992, Proc. Natl. Acad. Sci. USA 89:9367-9371) can also be used. Another example of a library that can be used, in which the amide functionalities in peptides have been permethylated to generate a chemically transformed combinatorial library, is described by Ostresh et al. (1994, Proc. Natl. Acad. Sci. USA 91:11138-11142).
The term “specific binding” refers to binding between two molecules, for example, a ligand and a receptor, characterized by the ability of a molecule (ligand) to associate with another specific molecule (receptor) even in the presence of many other diverse molecules, i.e., to show preferential binding of one molecule for another in a heterogeneous mixture of molecules. Specific binding of a ligand to a receptor is also evidenced by reduced binding of a detectably labeled ligand to the receptor in the presence of excess unlabeled ligand (i.e., a binding competition assay).
In some embodiments “proteasome inhibitors”, i.e., inhibitors of the proteasome, may be used. These inhibitors, including carbobenzoxyl-leucinyl-leuciny-1 norvalinal II (MG 115) or CBZ-LLL can be purchased from chemical supply companies (e.g., Sigma). As a skilled person would understand, proteasonie inhibitors are not protease inhibitors.
As used herein, a “plurality” of PDZ proteins (or corresponding PDZ domains or PDZ fusion polypeptides) has its usual meaning. In some embodiments, the plurality is at least 5, and often at least 25, at least 40, or at least 60 different PDZ proteins. In some embodiments, the plurality is selected from the list of PDZ polypeptides listed in TABLE 2. In some embodiments, the plurality of different PDZ proteins are from (i.e., expressed in) a particular specified tissue or a particular class or type of cell. In some embodiments, the plurality of different PDZ proteins represents a substantial fraction (e.g., typically at least 50%, more often at least 80%) of all of the PDZ proteins known to be, or suspected of being, expressed in the tissue or cell(s), e.g., all of the PDZ proteins known to be present in lymphocytes or hematopoetic cells. In some embodiments, the plurality is at least 50%, usually at least 80%, at least 90% or all of the PDZ proteins disclosed herein as being expressed in a particular cell.
When referring to PL peptides (or the corresponding proteins, e.g., corresponding to those listed in TABLE 3, or elsewhere herein) a “plurality” may refer to at least 5, at least 10, and often at least 16 PLs such as those specifically listed herein, or to the classes and percentages set forth supra for PDZ domains.
II. Overview
The present inventors have identified a large number of interactions between PDZ proteins and PL proteins that can play a significant role in the biological function of a variety of physiological systems. As used herein, the term “biological function” in the context of a cell, refers to a detectable biological activity normally carried out by the cell, e.g., a phenotypic change such as cell proliferation (e.g., cancer), cell activation, cytokine release, degranulation, tyrosine phosphorylation, ion (e.g., calcium) flux, metabolic activity, apoptosis, changes in gene expression, maintenance of cell structure, cell migration, adherence to a substrate, signal transduction, cell-cell interactions, and others described herein or known in the art.
Because the interactions involve proteins that are involved in diverse physiological systems (see Background section supra), the methods provided herein can be utilized to broadly or selectively diagnose inappropriate cellular phenotypes or pathogenic infections. Methods are also disclosed herein for determining whether vertebrate biological samples contain pathogenic organisms using PDZ:PL protein interactions.
As will be discussed in great detail below, the use of PDZ-PL interactions for diagnostic purposes is amenable to a number of different test formats and is not intended to be limited by the discussion herein. Diagnostic tests could be formatted for ELISA assays, as a dipstick test such as is used for pregnancy tests, as a film test that can be incubated with test sample, as a slide test that sample could be placed upon, or other such mediums. Such formats are well known in the art, and are described in U.S. Pat. Nos. 6,180,417, 4,703,017 5,591,645
III. PDZ Protein and PL Protein Interactions
TABLE 4 lists PDZ proteins and PL proteins which the current inventors have identified as binding to one another. Each page of TABLE 4 includes four columns. The columns in each section are number from left to right such that the left-most column in each section is column 1 and the right-most column in each section is column 4. Thus, the first column in each section is labeled “HPV Strain” and lists the various E6 proteins that contain the PDZ-Ligand sequences (PLs) that were examined (shown in parenthesis). This column lists C-terminal four amino acids that correspond to the carboxyl-terminal end of a 20 amino acid peptide used in this binding study. All ligands are biotinylated at the amino-terminus and partial sequences are presented in TABLE 3.
The PDZ protein (or proteins) that interact(s) with HPV E6—PL peptides are listed in the second column labeled “PDZ binding partner”. This column provides the gene name for the PDZ portion of the GST-PDZ fusion that interacts with the PDZ-ligand to the left. For PDZ domain-containing proteins with multiple domains the domain number is listed to the right of the PDZ (i.e., in column 4 labeled “PDZ Domain”), and indicates the PDZ domain number when numbered from the amino-terminus to the carboxy-terminus. This table only lists interactions of a stronger nature, e.g., those that give a ‘4’ or ‘5’ classification in the ‘G assay’. “Classification” is a measure of the level of binding. In particular, it provides an absorbance value at 450 nm which indicates the amount of PL peptide bound to the PDZ protein. The following numerical values have the following meanings: ‘1’—A450 nm 0-1; ‘2’—A450nm 1-2; ‘3’—A450nm 2-3; ‘4’—A450 nm 3-4; ‘5’—A450 nm of 4 more than 2× repeated; ‘0’—A450 nm 0, i.e., not found to interact.
The third and fourth columns of TABLE 4 are merely a repetition of the columns 1 and 2 with different E6 PLs tested and the PDZs bound by them at higher affinity.
Further information regarding these PL proteins and PDZ proteins is provided in TABLES 2 and 3 and EXAMPLEs 4 and 5. In particular, TABLE 3 provides a listing of the partial amino acid sequences of peptides used in the assays. When numbered from left to right, the first column labeled “HPV strain” provides the HPV strain number used to refer to the E6 protein from that strain. The column labeled “E6 C-terminal sequence” provides the predicted sequence of the carboxy-terminal 10 amino acids of the E6 protein. The third column labeled “PL yes/no” designates whether the E6-PL sequence contains sequence elements predicted to bind to PDZ domains. The final column labeled “oncogenic” indicates that this HPV strain is known to cause cervical cancer as determined by the National Cancer Institute (NCI, 2001).
EXAMPLE 5 lists representative sequences of PDZ domains cloned into a vector (PGEX-3× vector) for production of GST-PDZ fusion proteins (Pharmacia). An extended list of PDZ domains cloned into pGEX vectors for production of GST-PDZ fusion proteins is listed in U.S. Pat. No. 09/724553.
As discussed in detail herein, the PDZ proteins listed in TABLE 2 are naturally occurring proteins containing a PDZ domain. Only significant interactions are presented in this table. Thus, the present invention is particularly directed to the detection and modulation of interactions between a PDZ protein and PL protein. In a similar manner, PDZ domains that bind other pathogens can be used to diagnose infection. Additional examples of PL proteins from pathogens suitable for diagnostic applications are included in TABLE 8, but are not intended to limit the scope of the invention.
In another embodiment of the invention, cellular abnormalities or diseases can be diagnosed through the detection of imbalances in the expression levels of cellular PDZ proteins or PL proteins. Using either the PL protein or the PDZ protein in an assay derived from the ‘A assay’ or ‘G assay’ one can determine the protein expression levels of binding partners in a normal or abnormal cell. Differences in protein expression levels have been correlated with a number of diseases.
In certain embodiments of the invention, a PDZ protein is used to diagnose the presence of a PL protein from a pathogenic organism. Examples of pathogenic organisms with PL sequences include, but are not limited to, viruses such as Human Papillomaviruses, Hepatitus B virus, Adenovirus, Human T Cell Leukemia Virus, bacteria and fungi.
IV. Assays for Detection of PDZ Proteins or PDZ-Ligand Proteins (PL Proteins)
Two complementary assays, termed “A” and “G”, were developed to detect binding between a PDZ-domain polypeptide and candidate PDZ ligand. In each of the two different assays, binding is detected between a peptide having a sequence corresponding to the C-terminus of a protein anticipated to bind to one or more PDZ domains (i.e. a candidate PL peptide) and a PDZ-domain polypeptide (typically a fusion protein containing a PDZ domain). In the “A” assay, the candidate PL peptide is immobilized and binding of a soluble PDZ-domain polypeptide to the immobilized peptide is detected (the “A′” assay is named for the fact that in one embodiment an avidin surface is used to immobilize the peptide). In the “G” assay, the PDZ-domain polypeptide is immobilized and binding of a soluble PL peptide is detected (The “G” assay is named for the fact that in one embodiment a GST-binding surface is used to immobilize the PDZ-domain polypeptide). Preferred embodiments of these assays are described in detail infra. However, it will be appreciated by ordinarily skilled practitioners that these assays can be modified in numerous ways while remaining useful for the purposes of the present invention.
A. Production of Fusion Proteins Containing PDZ-Domains
GST-PDZ domain fusion proteins were prepared for use in the assays of the invention. PCR products containing PDZ encoding domains (as described supra) were subcloned into an expression vector to permit expression of fusion proteins containing a PDZ domain and a heterologous domain (i.e., a glutathione-S transferase sequence, “GST”). PCR products (i.e., DNA fragments) representing PDZ domain encoding DNA were extracted from agarose gels using the “Sephaglas” gel extraction system (Pharmacia) according to the manufacturer's recommendations.
As noted supra, PCR primers were designed to include endonuclease restriction sites to facilitate ligation of PCR fragments into a GST gene fusion vector (pGEX-3×; Pharmacia, GenBank accession no. XXU13852) in-frame with the glutathione-S transferase coding sequence. This vector contains an IPTG inducible lacZ promoter. The pGEX-3× vector was linearized using Bam HI and Eco RI or, in some cases, Eco RI or Sma I, and dephosphorylated. For most cloning approaches, double digestion with Bam HI and Eco RI was performed, so that the ends of the PCR fragments to clone were Bam HI and Eco RI. In some cases, restriction endonuclease combinations used were Bgl II and Eco RI, Bam HI and Mfe I, or Eco RI only, Sma I only, or BamHI only. When more than one PDZ domain was cloned, the DNA portion cloned represents the PDZ domains and the cDNA portion located between individual domains. Precise locations of cloned fragments used in the assays are indicated in U.S. patent application Ser. No. (60/360061). DNA linker sequences between the GST portion and the PDZ domain containing DNA portion vary slightly, dependent on which of the above described cloning sites and approaches were used. As a consequence, the amino acid sequence of the GST-PDZ fusion protein varies in the linker region between GST and PDZ domain. Protein linker sequences corresponding to different cloning sites/approaches are shown below. Linker sequences (vector DNA encoded) are bold, PDZ domain containing gene derived sequences are in italics.
The PDZ-encoding PCR fragment and linearized pGEX-3× vector were ethanol precipitated and resuspended in 10 ul standard ligation buffer. Ligation was performed for 4-10 hours at 7° C. using T4 DNA ligase. It will be understood that some of the resulting constructs include very short linker sequences and that, when multiple PDZ domains were cloned, the constructs included some DNA located between individual PDZ domains.
The ligation products were transformed in DH5alpha or BL-21 E. coli bacteria strains. Colonies were screened for presence and identity of the cloned PDZ domain containing DNA as well as for correct fusion with the glutathione S-transferase encoding DNA portion by PCR and by sequence analysis. Positive clones were tested in a small-scale assay for expression of the GST/PDZ domain fusion protein and, if expressing, these clones were subsequently grown up for large scale preparations of GST/PDZ fusion protein.
GST-PDZ domain fusion protein was overexpressed following addition of IPTG to the culture medium and purified. Detailed procedure of small scale and large-scale fusion protein expression and purification are described in “GST Gene Fusion System” (second edition, revision 2; published by Pharmacia). In brief, a small culture (50 mls) containing a bacterial strain (DH5α, BL21 or JM109) with the fusion protein construct was grown overnight in 2×YT media at 37° C. with the appropriate antibiotic selection (100 ug/ml ampicillin; a.k.a. 2×YT-amp). The overnight culture was poured into a fresh preparation of 2×YT-amp (typically 1 liter) and grown until the optical density (OD) of the culture was between 0.5 and 0.9 (approximately 2.5 hours). IPTG (isopropyl β-D-thiogalactopyranoside) was added to a final concentration of 1.0 mM to induce production of GST fusion protein, and culture was grown an additional 1 hour. All following steps, including centrifugation, were performed on ice or at 4° C. Bacteria were collected by centrifugation (4500×g) and resuspended in Buffer A− (50 mM Tris, pH 8.0, 50 mM dextrose, 1 mM EDTA, 200 uM phenylmethylsulfonylfluoride). An equal volume of Buffer A+ (Buffer A−, 4 mg/ml lysozyme) was added and incubated on ice for 3 min to lyse bacteria, or until lysis had begun. An equal volume of Buffer B (10 mM Tris, pH 8.0, 50 mM KCl, 1 mM EDTA. 0.5% Tween-20, 0.5% NP40 (a.k.a. IGEPAL CA-630), 200 uM phenylmethylsulfonylfluoride) was added and incubated for an additional 20 min on ice. The bacterial cell lysate was centrifuged (×20,000 g), and supernatant was run over a column containing 20 ml Sepharose CL-4B (Pharmacia) “precolumn beads,” i.e., sepharose beads without conjugated glutathione that had been previously washed with 3 bed volumes PBS. The flow-through was added to glutathione Sepharose 4B (Pharmacia, cat no. 17-0765-01) previously swelled (rehydrated) in 1× phosphate-buffered saline (PBS) and incubated while rotating for 30 min-1 hr. The supematant-Sepharose slurry was poured into a column and washed with at least 20 bed volumes of 1×PBS. GST fusion protein was eluted off the glutathione sepharose by applying 0.5-1.0 ml aliquots of 5 mM glutathione and collected as separate fractions. Concentrations of fractions were determined by reading absorbance at 280 nm and calculating concentration using the absorbance and extinction coefficient. Those fractions containing the highest concentration of fusion protein were pooled and an equal volume of 70% glycerol was added to a final concentration of 35% glycerol. Fusion proteins were assayed for size and quality by SDS gel electrophoresis (PAGE) as described in “Sambrook.” Fusion protein aliquots were stored at minus 80° C. and at minus 20° C.
The amino acid sequences provided in Table 2 above may contain amino acids derived from a fusion protein, e.g., GST. PDZ domain sequence of particular interest may be up to 20 amino acids shorter (e.g., 5, 8, 10, 12 or 15 amino acids shorter) than the sequence provided in Table 2. For example, a sequence may be shortened by up to 3, 6, 9, or 12 amino acids from the C-terminus, the N-terminus, or both termini.
B. Identification of Candidate PL Proteins and Synthesis of Peptides
Certain PDZ domains are bound by the C-terminal residues of PDZ-binding proteins. To identify PL proteins the C-terminal residues of sequences were visually inspected for sequences that one might predict would bind to PDZ-domain containing proteins (see, e.g., Doyle et al., 1996, Cell 85, 1067; Songyang et al., 1997, Science 275, 73), including the additional consensus for PLs identified at Arbor Vita Corporation (U.S. patent application Ser. No. 60/360061). TABLE 3 lists some of these proteins, and provides corresponding C-terminal sequences.
Synthetic peptides of defined sequence (e.g., corresponding to the carboxyl-termini of the indicated proteins) can be synthesized by any standard resin-based method (see, e.g., U.S. Pat. No. 4,108,846; see also, Caruthers et al., 1980, Nucleic Acids Res. Symp. Ser., 215-223; Horn et al., 1980, Nucleic Acids Res. Symp. Ser., 225-232; Roberge, et al., 1995, Science 269:202). The peptides used in the assays described herein were prepared by the FMOC (see, e.g., Guy and Fields, 1997, Meth. Enz. 289:67-83; Wellings and Atherton, 1997, Meth. Enz. 289:44-67). In some cases (e.g., for use in the A and G assays of the invention), peptides were labeled with biotin at the amino-terminus by reaction with a four-fold excess of biotin methyl ester in dimethylsulfoxide with a catalytic amount of base. The peptides were cleaved from the resin using a halide containing acid (e.g. trifluoroacetic acid) in the presence of appropriate antioxidants (e.g. ethanedithiol) and excess solvent lyophilized.
Following lyophilization, peptides can be redissolved and purified by reverse phase high performance liquid chromatography (HPLC). One appropriate HPLC solvent system involves a Vydac C-18 semi-preparative column running at 5 mL per minute with increasing quantities of acetonitrile plus 0.1% trifluoroacetic acid in a base solvent of water plus 0.1% trifluoroacetic acid. After HPLC purification, the identities of the peptides are confirmed by MALDI cation-mode mass spectrometry.
C. Detecting PDZ-PL Interactions
The present inventors were able in part to identify the interactions summarized in TABLE 4 by developing new high throughput screening assays which are described in greater detail infra. Various other assay formats known in the art can be used to select ligands that are specifically reactive with a particular protein. For example, solid-phase ELISA immunoassays, immunoprecipitation, Biacore, and Western blot assays can be used to identify peptides that specifically bind PDZ-domain polypeptides. As discussed supra, two different, complementary assays were developed to detect PDZ-PL interactions. In each, one binding partner of a PDZ-PL pair is immobilized, and the ability of the second binding partner to bind is determined. These assays, which are described infra, can be readily used to screen for hundreds to thousands of potential PDZ-ligand interactions in a few hours. Thus these assays can be used to identify yet more novel PDZ-PL interactions in cells. In addition, they can be used to identify antagonists of PDZ-PL interactions (see infra).
In various embodiments, fusion proteins are used in the assays and devices of the invention. Methods for constructing and expressing fusion proteins are well known. Fusion proteins generally are described in Ausubel et al., supra, Kroll et al., 1993, DNA Cell. Biol. 12:441, and Imai et al., 1997, Cell 91:521-30. Usually, the fusion protein includes a domain to facilitate immobilization of the protein to a solid substrate (“an immobilization domain”). Often, the immobilization domain includes an epitope tag (i.e., a sequence recognized by an antibody, typically a monoclonal antibody) such as polyhistidine (Bush et al, 1991, J. Biol Chem 266:13811-14), SEAP (Berger et al, 1988, Gene 66: 1-10), or M1 and M2 flag (see, e.g, U.S. Pat. Nos. 5,011,912; 4,851,341; 4,703,004; 4,782,137). In an embodiment, the immobilization domain is a GST coding region. It will be recognized that, in addition to the PDZ-domain and the particular residues bound by an immobilized antibody, protein A, or otherwise contacted with the surface, the protein (e.g., fusion protein), will contain additional residues. In some embodiments these are residues naturally associated with the PDZ-domain (i.e., in a particular PDZ-protein) but they may include residues of synthetic (e.g., poly(alanine)) or heterologous origin (e.g., spacers of, e.g., between 10 and 300 residues).
PDZ domain-containing polypeptide used in the methods of the invention (e.g., PDZ fusion proteins) of the invention are typically made by (1) constructing a vector (e.g., plasmid, phage or phagemid) comprising a polynucleotide sequence encoding the desired polypeptide, (2) introducing the vector into an suitable expression system (e.g., a prokaryotic, insect, mammalian, or cell free expression system), (3) expressing the fusion protein and (4) optionally purifying the fusion protein.
(1) In one embodiment, expression of the protein comprises inserting the coding sequence into an appropriate expression vector (i.e., a vector that contains the necessary elements for the transcription and translation of the inserted coding sequence required for the expression system employed, e.g., control elements including enhancers, promoters, transcription terminators, origins of replication, a suitable initiation codon (e.g., methionine), open reading frame, and translational regulatory signals (e.g., a ribosome binding site, a termination codon and a polyadenylation sequence. Depending on the vector system and host utilized, any number of suitable transcription and translation elements, including constitutive and inducible promoters, can be used.
The coding sequence of the fusion protein includes a PDZ domain and an immobilization domain as described elsewhere herein. Polynucleotides encoding the amino acid sequence for each domain can be obtained in a variety of ways known in the art; typically the polynucleotides are obtained by PCR amplification of cloned plasmids, cDNA libraries, and cDNA generated by reverse transcription of RNA, using primers designed based on sequences determined by the practitioner or, more often, publicly available (e.g., through GenBank). The primers include linker regions (e.g., sequences including restriction sites) to facilitate cloning and manipulation in production of the fusion construct. The polynucleotides corresponding to the PDZ and immobilization regions are joined in-frame to produce the fusion protein-encoding sequence.
The fusion proteins of the invention may be expressed as secreted proteins (e.g., by including the signal sequence encoding DNA in the fusion gene; see, e.g., Lui et al, 1993, PNAS USA, 90:8957-61) or as nonsecreted proteins.
In some embodiments, the PDZ-containing proteins or PL polypeptides are immobilized on a solid surface. The substrate to which the polypeptide is bound may in any of a variety of forms, e.g., a microtiter dish, a test tube, a dipstick, a microcentrifuge tube, a bead, a spinnable disk, a permeable or semi-permeable membrane, and the like. Suitable materials include glass, plastic (e.g., polyethylene, PVC, polypropylene, polystyrene, and the like), protein, paper, carbohydrate, lipid monolayer or supported lipid bilayer, films and other solid supports. Other materials that may be employed include ceramics, metals, metalloids, semiconductive materials, cements and the like.
In some embodiments, the PDZ and/or PL fusion proteins are organized as an array. The term “array,” as used herein, refers to an ordered arrangement of immobilized fusion proteins, in which particular different fusion proteins (i.e., having different PDZ domains) are located at different predetermined sites on the substrate. Because the location of particular fusion proteins on the array is known, binding at that location can be correlated with binding to the PDZ domain situated at that location. Immobilization of fusion proteins on beads (individually or in groups) is another particularly useful approach. In one embodiment, individual fusion proteins are immobilized on beads. In one embodiment, mixtures of distinguishable beads are used. Distinguishable beads are beads that can be separated from each other on the basis of a property such as size, magnetic property, color (e.g., using FACS) or affinity tag (e.g., a bead coated with protein A can be separated from a bead not coated with protein A by using IgG affinity methods). Binding to particular PDZ domain may be determined.
Methods for immobilizing proteins are known, and include covalent and non-covalent methods. One suitable immobilization method is antibody-mediated immobilization. According to this method, an antibody specific for the sequence of an “immobilization domain” of the PDZ-domain containing protein is itself immobilized on the substrate (e.g., by adsorption). One advantage of this approach is that a single antibody may be adhered to the substrate and used for immobilization of a number of polypeptides (sharing the same immobilization domain). For example, an immobilization domain consisting of poly-histidine (Bush et al, 1991, J. Biol Chem 266:13811-14) can be bound by an anti-histidine monoclonal antibody (R&D Systems, Minneapolis, Minn.); an immobilization domain consisting of secreted alkaline phosphatase (“SEAP”) (Berger et al, 1988, Gene 66:1-10) can be bound by anti-SEAP (Sigma Chemical Company, St. Louis, Mo.); an immobilization domain consisting of a FLAG epitope can be bound by anti-FLAG. Other ligand-antiligand immobilization methods are also suitable (e.g., an immobilization domain consisting of protein A sequences (Harlow and Lane, 1988, Antibodies A Laboratory Manual, Cold Spring Harbor Laboratory; Sigma Chemical Co., St. Louis, Mo.) can be bound by IgG; and an immobilization domain consisting of streptavidin can be bound by biotin (Harlow & Lane, supra; Sigma Chemical Co., St. Louis, Mo.). In a preferred embodiment, the immobilization domain is a GST moiety, as described herein.
When antibody-mediated immobilization methods are used, glass and plastic are especially useful substrates. The substrates may be printed with a hydrophobic (e.g., Teflon) mask to form wells. Preprinted glass slides with 3, 10 and 21 wells per 14.5 cm2 slide “working area” are available from, e.g., SPI Supplies, West Chester, Pa.; also see U.S. Pat. No. 4,011,350). In certain applications, a large format (12.4 cm×8.3 cm) glass slide is printed in a 96 well format is used; this format facilitates the use of automated liquid handling equipment and utilization of 96 well format plate readers of various types (fluorescent, colorimetric, scintillation). However, higher densities may be used (e.g., more than 10 or 100 polypeptides per cm2). See, e.g., MacBeath et al, 2000, Science 289:1760-63.
Typically, antibodies are bound to substrates (e.g., glass substrates) by adsorption. Suitable adsorption conditions are well known in the art and include incubation of 0.5-50 ug/ml (e.g., 10 ug/ml) mAb in buffer (e.g., PBS, or 50 to 300 mM Tris, MOPS, HEPES, PIPES, acetate buffers, pHs 6.5 to 8, at 4° C.) to 37° C. and from lhr to more than 24 hours.
Proteins may be covalently bound or noncovalently attached through nonspecific bonding. If covalent bonding between the fusion protein and the surface is desired, the surface will usually be polyfunctional or be capable of being polyfunctionalized. Functional groups which may be present on the surface and used for linking can include carboxylic acids, aldehydes, amino groups, cyano groups, ethylenic groups, hydroxyl groups, mercapto groups and the like. The manner of linking a wide variety of compounds to various surfaces is well known and is amply illustrated in the literature.
Exemplary assays are provided below.
“A Assay” Detection of PDZ-Ligand Binding Using Immobilized PL Peptide.
In one aspect, the invention provides an assay in which biotinylated candidate PL peptides are immobilized on an avidin-coated surface. The binding of PDZ-domain fusion protein to this surface is then measured. In a preferred embodiment, the PDZ-domain fusion protein is a GST/PDZ fusion protein and the assay is carried out as follows:
(1) Avidin is bound to a surface, e.g. a protein binding surface. In one embodiment, avidin is bound to a polystyrene 96 well plate (e.g., Nunc Polysorb (cat #475094) by addition of 100 uL per well of 20 ug/mL of avidin (Pierce) in phosphate buffered saline without calcium and magnesium, pH 7.4 (“PBS”, GibcoBRL) at 4° C. for 12 hours. The plate is then treated to block nonspecific interactions by addition of 200 uL per well of PBS containing 2 g per 100 mL protease-free bovine serum albumin (“PBS/BSA”) for 2 hours at 4° C. The plate is then washed 3 times with PBS by repeatedly adding 200 uL per well of PBS to each well of the, plate and then dumping the contents of the plate into a waste container and tapping the plate gently on a dry surface.
(2) Biotinylated PL peptides (or candidate PL peptides, e.g. see TABLE 3) are immobilized on the surface of wells of the plate by addition of 50 uL per well of 0.4 uM peptide in PBS/BSA for 30 minutes at 4° C. Usually, each different peptide is added to at least eight different wells so that multiple measurements (e.g. duplicates and also measurements using different (GST/PDZ-domain fusion proteins and a GST alone negative control) can be made, and also additional negative control wells are prepared in which no peptide is immobilized. Following immobilization of the PL peptide on the surface, the plate is washed 3 times with PBS.
(3) GST/PDZ-domain fusion protein (prepared as described stpra) is allowed to react with the surface by addition of 50 uL per well of a solution containing 5 ug/mL GST/PDZ-domain fusion protein in PBS/BSA for 2 hours at 4° C. As a negative control, GST alone (i.e. not a fusion protein) is added to specified wells, generally at least 2 wells (i.e. duplicate measurements) for each immobilized peptide. After the 2 hour reaction, the plate is washed 3 times with PBS to remove unbound fusion protein.
(4) The binding of the GST/PDZ-domain fusion protein to the avidin-biotinylated peptide surface can be detected using a variety of methods, and detectors known in the art. In one embodiment, 50 uL per well of an anti-GST antibody in PBS/BSA (e.g. 2.5 ug/mL of polyclonal goat-anti-GST antibody, Pierce) is added to the plate and allowed to react for 20 minutes at 4° C. The plate is washed 3 times with PBS and a second, detectably labeled antibody is added. In one embodiment, 50 uL per well of 2.5 ug/mL of horseradish peroxidase (HRP)-conjugated polyclonal rabbit anti-goat immunoglobulin antibody is added to the plate and allowed to react for 20 minutes at 4° C. The plate is washed 5 times with 50 mM Tris pH 8.0 containing 0.2% Tween 20, and developed by addition of 100 uL per well of HRP-substrate solution (TMB, Dako) for 20 minutes at room temperature (RT). The reaction of the HRP and its substrate is terminated by the addition of 100 uL per well of IM sulfuric acid and the absorbance (A) of each well of the plate is read at 450 nm.
(5) Specific binding of a PL peptide and a PDZ-domain polypeptide is detected by comparing the signal from the well(s) in which the PL peptide and PDZ domain polypeptide are combined with the background signal(s). The background signal is the signal found in the negative controls. Typically a specific or selective reaction will be at least twice background signal, more typically more than 5 times background, and most typically 10 or more times the background signal. In addition, a statistically significant reaction will involve multiple measurements of the reaction with the signal and the background differing by at least two standard errors, more typically four standard errors, and most typically six or more standard errors. Correspondingly, a statistical test (e.g. a T-test) comparing repeated measurements of the signal with repeated measurements of the background will result in a p-value <0.05, more typically a p-value <0.01, and most typically a p-value <0.001 or less.
As noted, in an embodiment of the “A” assay, the signal from binding of a GST/PDZ-domain fusion protein to an avidin surface not exposed to (i.e. not covered with) the PL peptide is one suitable negative control (sometimes referred to as “B”). The signal from binding of GST polypeptide alone (i.e. not a fusion protein) to an avidin-coated surface that has been exposed to (i.e. covered with) the PL peptide is a second suitable negative control (sometimes referred to as “B2”). Because all measurements are done in multiples (i.e. at least duplicate) the arithmetic mean (or, equivalently, average) of several measurements is used in determining the binding, and the standard error of the mean is used in determining the probable error in the measurement of the binding. The standard error of the mean of N measurements equals the square root of the following: the sum of the squares of the difference between each measurement and the mean, divided by the product of (N) and (N−1). Thus, in one embodiment, specific binding of the PDZ protein to the plate-bound PL peptide is determined by comparing the mean signal (“mean S”) and standard error of the signal (“SE”) for a particular PL-PDZ combination with the mean B1 and/or mean B2.
“G Assay”—Detection of PDZ-Ligand Binding Using Immobilized PDZ-Domain Fusion Polypeptide
In one aspect, the invention provides an assay in which a GST/PDZ fusion protein is immobilized on a surface (“G” assay). The binding of labeled PL peptide (e.g., as listed in TABLE 3) to this surface is then measured. In a preferred embodiment, the assay is carried out as follows:
(1) A PDZ-domain polypeptide is bound to a surface, e.g. a protein binding surface. In a preferred embodiment, a GST/PDZ fusion protein containing one or more PDZ domains is bound to a polystyrene 96-well plate. The GST/PDZ fusion protein can be bound to the plate by any of a variety of standard methods known to one of skill in the art, although some care must be taken that the process of binding the fusion protein to the plate does not alter the ligand-binding properties of the PDZ domain. In one embodiment, the GST/PDZ fusion protein is bound via an anti-GST antibody that is coated onto the 96-well plate. Adequate binding to the plate can be achieved when:
a. 100 uL per well of 5 ug/mL goat anti-GST polyclonal antibody (Pierce) in PBS is added to a polystyrene 96-well plate (e.g., Nunc Polysorb) at 4° C. for 12 hours.
b. The plate is blocked by addition of 200 uL per well of PBS/BSA for 2 hours at 4° C.
c. The plate is washed 3 times with PBS.
d. 50 uL per well of 5 ug/mL GST/PDZ fusion protein) or, as a negative control, GST polypeptide alone (i.e. not a fusion protein) in PBS/BSA is added to the plate for 2 hours at 4° C.
e. The plate is again washed 3 times with PBS.
(2) Biotinylated PL peptides are allowed to react with the surface by addition of 50 uL per well of 20 uM solution of the biotinylated peptide in PBS/BSA for 10 minutes at 4° C., followed by an additional 20 minute incubation at 25° C. The plate is washed 3 times with ice cold PBS.
(3) The binding of the biotinylated peptide to the GST/PDZ fusion protein surface can be detected using a variety of methods and detectors known to one of skill in the art. In one embodiment, 100 uL per well of 0.5 ug/mL streptavidin-horse radish peroxidase (HRP) conjugate dissolved in BSA/PBS is added and allowed to react for 20 minutes at 4° C. The plate is then washed 5 times with 50 mM Tris pH 8.0 containing 0.2% Tween 20, and developed by addition of 100 uL per well of HRP-substrate solution (TMB, Dako) for 20 minutes at room temperature (RT). The reaction of the HRP and its substrate is terminated by addition of 100 uL per well of 1M sulfuric acid, and the absorbance of each well of the plate is read at 450 nm.
(4) Specific binding of a PL peptide and a PDZ domain polypeptide is determined by comparing the signal from the well(s) in which the PL peptide and PDZ domain polypeptide are combined, with the background signal(s). The background signal is the signal found in the negative control(s). Typically a specific or selective reaction will be at least twice background signal, more typically more than 5 times background, and most typically 10 or more times the background signal. In addition, a statistically significant reaction will involve multiple measurements of the reaction with the signal and the background differing by at least two standard errors, more typically four standard errors, and most typically six or more standard errors. Correspondingly, a statistical test (e.g. a T-test) comparing repeated measurements of the signal with —repeated measurements of the background will result in a p-value <0.05, more typically a p-value <0.01, and most typically a p-value <0.001 or less. As noted, in an embodiment of the “G” assay, the signal from binding of a given PL peptide to immobilized (surface bound) GST polypeptide alone is one suitable negative control (sometimes referred to as “B 1”). Because all measurement are done in multiples (i.e. at least duplicate) the arithmetic mean (or, equivalently, average.) of several measurements is used in determining the binding, and the standard error of the mean is used in determining the probable error in the measurement of the binding. The standard error of the mean of N measurements equals the square root of the following: the sum of the squares of the difference between each measurement and the mean, divided by the product of (N) and (N−1). Thus, in one embodiment, specific binding of the PDZ protein to the platebound peptide is determined by comparing the mean signal (“mean S”) and standard error of the signal (“SE”) for a particular PL-PDZ combination with the mean B1.
“G′ assay” and “G″ assay”
Two specific modifications of the specific conditions described supra for the “G assay” are particularly useful. The modified assays use lesser quantities of labeled PL peptide and have slightly different biochemical requirements for detection of PDZ-ligand binding compared to the specific assay conditions described supra.
For convenience, the assay conditions described in this section are referred to as the “G′ assay” and the “G″ assay,” with the specific conditions described in the preceding section on G assays being referred to as the “G0 assay.” The “G′ assay” is identical to the “G0 assay” except at step (2) the peptide concentration is 10 uM instead of 20 uM. This results in slightly lower sensitivity for detection of interactions with low affinity and/or rapid dissociation rate. Correspondingly, it slightly increases the certainty that detected interactions are of sufficient affinity and half-life to be of biological importance and useful therapeutic targets.
The “G” assay” is identical to the “G0 assay” except that at step (2) the peptide concentration is 1 uM instead of 20 uM and the incubation is performed for 60 minutes at 25° C. (rather than, e.g., 10 minutes at 4° C. followed by 20 minutes at 25° C.). This results in lower sensitivity for interactions of low affinity, rapid dissociation rate, and/or affinity that is less at 25° C. than at 4° C. Interactions will have lower affinity at 25° C. than at 4° C. if (as we have found to be generally true for PDZ-ligand binding) the reaction entropy is negative (i.e. the entropy of the products is less than the entropy of the reactants). In contrast, the PDZ-PL binding signal may be similar in the “G″ assay” and the “G0 assay” for interactions of slow association and dissociation rate, as the PDZ-PL complex will accumulate during the longer incubation of the “G″ assay.” Thus comparison of results of the “G″ assay” and the “G0 assay” can be used to estimate the relative entropies, enthalpies, and kinetics of different PDZ-PL interactions. (Entropies and enthalpies are related to binding affinity by the equations delta G=RT 1 n (Kd)=delta H—T delta S where delta G, H, and S are the reaction free energy, enthalpy, and entropy respectively, T is the temperature in degrees Kelvin, R is the gas constant, and Kd is the equilibrium dissociation constant). In particular, interactions that are detected only or much more strongly in the “G0 assay” generally have a rapid dissociation rate at 25° C. (t½<10 minutes) and a negative reaction entropy, while interactions that are detected similarly strongly in the “G″ assay” generally have a slower dissociation rate at 25° C. (t½>10 minutes). Rough estimation of the thermodynamics and kinetics of PDZ-PL interactions (as can be achieved via comparison of results of the “G0 assay” versus the “G″ assay” as outlined supra) can be used in the design of efficient inhibitors of the interactions. For example, a small molecule inhibitor based on the chemical structure of a PL that dissociates slowly from a given PDZ domain (as evidenced by similar binding in the “G″ assay” as in the “G0 assay”) may itself dissociate slowly and thus be of high affinity.
In this manner, variation of the temperature and duration of step (2) of the “G assay” can be used to provide insight into the kinetics and thermodynamics of the PDZ-ligand binding reaction and into design of inhibitors of the reaction.
Assay Variations
As discussed supra, it will be appreciated that many of the steps in the above-described assays can be varied, for example, various substrates can be used for binding the PL and PDZ-containing proteins; different types of PDZ containing fusion proteins can be used; different labels for detecting PDZ/PL interactions can be employed; and different ways of detection can be used.
The PDZ-PL detection assays can employ a variety of surfaces to bind the PL and/or PDZ-contaning proteins. For example, a surface can be an “assay plate” which is formed from a material (e.g. polystyrene) which optimizes adherence of either the PL protein or PDZ-containing protein thereto. Generally, the individual wells of the assay plate will have a high surface area to volume ratio and therefore a suitable shape is a flat bottom well (where the proteins of the assays are adherent). Other surfaces include, but are not limited to, polystyrene or glass beads, polystyrene or glass slides, papers, dipsticks, plastics, films and the like.
For example, the assay plate can be a “microtiter” plate. The term “microtiter” plate when used herein refers to a multiwell assay plate, e.g., having between about 30 to 200 individual wells, usually 96 wells. Alternatively, high-density arrays can be used. Often, the individual wells of the microtiter plate will hold a maximum volume of about 250 ul. Conveniently, the assay plate is a 96 well polystyrene plate (such as that sold by Becton Dickinson Labware, Lincoln Park, N.J.), which allows for automation and high throughput screening. Other surfaces include polystyrene microtiter ELISA plates such as that sold by Nunc Maxisorp, Inter Med, Denmark. Often, about 50 ul to 300 ul, more preferably 100 ul to 200 ul, of an aqueous sample comprising buffers suspended therein will be added to each well of the assay plate.
The detectable labels of the invention can be any detectable compound or composition which is conjugated directly or indirectly with a molecule (such as described above). The label can be detectable by itself (e.g., radioisotope labels or fluorescent labels) or, in the case of an enzymatic label, can catalyze a chemical alteration of a substrate compound or composition which is detectable. The preferred label is an enzymatic one which catalyzes a color change of a non-radioactive color reagent.
Sometimes, the label is indirectly conjugated with the antibody. One of skill is aware of various techniques for direct and indirect conjugation. For example, the antibody can be conjugated with biotin and any of the categories of labels mentioned above can be conjugated with avidin, or vice versa (see also “A” and “G” assay above). Biotin binds selectively to avidin and thus, the label can be conjugated with the antibody in this indirect manner. See, Au subel, supra, for a review of techniques involving biotin-avidin conjugation and similar assays. Alternatively, to achieve indirect conjugation of the label with the antibody, the antibody is conjugated with a small hapten (e.g. digoxin) and one of the different types of labels mentioned above is conjugated with an anti-hapten antibody (e.g. anti-digoxin antibody). Thus, indirect conjugation of the label with the antibody can be achieved.
Assay variations can include different washing steps. By “washing” is meant exposing the solid phase to an aqueous solution (usually a buffer or cell culture media) in such a way that unbound material (e.g., non-adhering cells, non-adhering capture agent, unbound ligand, receptor, receptor construct, cell lysate, or HRP antibody) is removed therefrom. To reduce background noise, it is convenient to include a detergent (e.g., Triton X) in the washing solution. Usually, the aqueous washing solution is decanted from the wells of the assay plate following washing. Conveniently, washing can be achieved using an automated washing device. Sometimes, several washing steps (e.g., between about 1 to 10 washing steps) can be required.
Various buffers can also be used in PDZ-PL detection assays. For example, various blocking buffers can be used to reduce assay background. The term “blocking buffer” refers to an aqueous, pH buffered solution containing at least one blocking compound which is able to bind to exposed surfaces of the substrate which are not coated with a PL or PDZ-containing protein. The blocking compound is normally a protein such as bovine serum albumin (BSA), gelatin, casein or milk powder and does not cross-react with any of the reagents in the assay. The block buffer is generally provided at a pH between about 7 to 7.5 and suitable buffering agents include phosphate and TRIS.
Various enzyme-substrate combinations can also be utilized in detecting PDZ-PL interactions. Examples of enzyme-substrate combinations include, for example:
(i) Horseradish peroxidase (HRP or HRPO) with hydrogen peroxidase as a substrate, wherein the hydrogen peroxidase oxidizes a dye precursor (e.g. orthophenylene diamine [OPD] or 3,3′,5,5′-tetramethyl benzidine hydrochloride [TMB]) (as described above).
(ii) alkaline phosphatase (AP) with para-Nitrophenyl phosphate as chromogenic substrate.
(iii) Beta-D-galactosidase (Beta D-Gal) with a chromogenic substrate (e.g. p-nitrophenyl-Beta-D-galactosidase) or fluorogenic substrate 4-methylumbelliferyl-Beta-D-galactosidase.
Numerous other enzyme-substrate combinations are available to those skilled in the art. For a general review of these, see U.S. Pat. Nos. 4,275,149 and 4,318,980, both of which are herein incorporated by reference.
Further, it will be appreciated that, although, for convenience, the present discussion primarily refers to detection of PDZ-PL interactions, agonists or antagonists of PDZ-PL interactions can be used to diagnose cellular abnormalities.
V. Collection of Tissue Samples Such as Cervical Tissues
Diagnosing the presence of pathogens requires collection of samples appropriate to the organism. For detection of oncogenic HPV E6 proteins, one would collect tissue for testing from the cervix, penis, anus, or throat using a scrape, swab or biopsy technique. For diagnosis of bloodborne pathogens such as HIV, collection of blood through standard means would be most appropriate. Diagnosis of fungal or viral infections that may have caused skin lesions would require the collection of a sample from the affected area.
This invention is not intended to cover sampling devices. However, it should be noted that since the invention is predicated on the detection of PDZ or PL proteins, appropriate care must be taken to collect a sufficient amount of sample to detect pathogen proteins and to maintain the integrity of proteins in the sample. The amount of sample to collect should be determined empirically for each diagnostic test. Factors in the decision may include, but not be limited to, the stage at which detection is desired, the amount of pathogen per unit sample, the amount of diagnostic protein per unit per unit sample, availability of diagnostic epitopes and the stability of diagnostic epitopes.
Exemplary collection devices for cervical tissue include, but are not limited to, those described in U.S. Pat. Nos. 6,241,687, 6,352,513, 6,336,905, 6,115,990 and 6,346,086. These collection devices would facilitate the collection of cervical tissue for the diagnosis of oncogenic human papillomavirus infection. These devices are predominantly collection of cervical cells or tissues through scraping; alternatively, one could use standard biopsy methods to collect samples from any tissues to be examined.
Although the diagnostic method disclosed in this application is directed at the detection of PL proteins, sample collection need not be limited to collection of proteins. One could alternatively collect RNA from tissue samples, use an in vitro translation kit to produce protein from collected templates, and then assay using methods disclosed herein. In a similar manner, DNA could be collected from test samples, specific primers for oncogenic E6 proteins could be used to either amplify the DNA content (using a DNA polymerase) or transcribe and translate the sample into proteins that could be tested with methods disclosed herein.
VI. Assays for Detecting Oncogenic E6 Proteins
Oncogenic E6 proteins can be detected by their ability to bind to PDZ domains. This could be a developed into a single detection stage approach or more favorably as a two-stage or ‘sandwich’ approach for increased sensitivity and specificity.
For single stage approaches, a ‘tagged’ version of a PDZ domain that specifically recognizes oncogenic E6 proteins, such as those disclosed in TABLES 3 and 4, can be used to directly probe for the presence of oncogenic E6 protein in a sample. As noted supra, an example of this would be to attach the test sample to a solid support (for example, cervical cells or tissue could be coated on a slide and ‘fixed’ to permeablize the cell membranes), incubate the sample with a tagged ‘PL detector’ protein (a PDZ domain fusion) under appropriate conditions, wash away unbound PL detector, and assay for the presence of the ‘tag’ in the sample. In addition, even without a tag, one could measure the physical properties of the PDZ protein and the PDZ protein bound to and E6 protein. Techniques such as surface plasmon resonance, circular dichoism, and other techniques that directly assess binding could be used to detect the presence of oncogenic E6 proteins. One should note, however, that PDZ domains may also bind endogenous cellular proteins. Thus, frequency of binding must be compared to control cells that do not contain E6 oncoproteins or the ‘PL detector’ should be modified such that it is significantly more specific for the oncogenic E6 proteins (see section X).
For two-stage or sandwich approaches, use of the PL detector is coupled with a second method of either capturing or detecting captured proteins. The second method could be using an antibody that binds to the E6 oncoprotein or a second compound or protein that can bind to E6 oncorproteins at a location on the E6 protein that does not reduce the availability of the E6 PL. Such proteins may include, but not be limited to, p53, E6-AP, E6-BP or engineered compounds that bind E6 oncoproteins. Alternatively, one could also use DNA binding or Zn2+ binding to assay for the presence of captured E6 protein, since oncogenic E6 proteins are known to bind certain DNA structures through the use of divalent cations. Additionally, one could use the PDZ-captured E6 protein in an activity assay, since E6 is known to degrade DNA and certain proteins including p53 in the presence of a reticulocyte lysate.
Antibodies
Many biological assays are designed as a ‘sandwich’, where an antibody constitutes one side of the sandwich. This method can improve the signal to noise ratio for a diagnostic by reducing background signal and amplifying appropriate signals. Antibodies can be generated that specifically recognize the diagnostic protein. Since this invention discloses the method of using PDZ or PL proteins to diagnose pathogen infections, antibodies should be generated that do not conflict with the PDZ:PL interaction.
For the production of antibodies, various host animals, including but not limited to rabbits, mice, rats, etc., may be immunized by injection with a peptide. The peptide may be attached to a suitable carrier, such as BSA or KLH, by means of a side chain functional group or linkers attached to a side chain functional group. Various adjuvants may be used to increase the immunological response, depending on the host species, including but not limited to Freund's (complete and incomplete), mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin, dinitrophenol, and potentially useful human adjuvants such as BCG (bacilli Calmette-Guerin) and Corynebacterium parvum.
Monoclonal antibodies to a peptide may be prepared using any technique which provides for the production of antibody molecules by continuous cell lines in culture. These include but are not limited to the hybridoma technique originally described by Koehler and Milstein, 1975, Nature 256:495-497, the human B-cell hybridoma technique, Kosbor et al., 1983, Immunology Today 4:72; Cote et al., 1983, Proc. Natl. Acad. Sci. U.S.A. 80:2026-2030 and the EBV-hybridoma technique (Cole et al., 1985, Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96 (1985)). In addition, techniques developed for the production of “chimeric antibodies” (Morrison et al., 1984, Proc. Natl. Acad. Sci. U.S.A. 81:6851-6855; Neuberger et al., 1984, Nature 312:604-608; Takeda et al., 1985, Nature 314:452-454) by splicing the genes from a mouse antibody molecule of appropriate antigen specificity together with genes from a human antibody molecule of appropriate biological activity can be used. Alternatively, techniques described for the production of single chain antibodies (U.S. Pat. No. 4,946,778) can be adapted to produce peptide-specific single chain antibodies.
Antibody fragments which contain deletions of specific binding sites may be generated by known techniques. For example, such fragments include but are not limited to F(ab′)2 fragments, which can be produced by pepsin digestion of the antibody molecule and Fab fragments, which can be generated by reducing the disulfide bridges of the F(ab′)2 fragments. Alternatively, Fab expression libraries may be constructed (Huse et al., 1989, Science 246:1275-1281) to allow rapid and easy identification of monoclonal Fab fragments with the desired specificity for the peptide of interest.
The antibody or antibody fragment specific for the desired peptide can be attached, for example, to agarose, and the antibody-agarose complex is used in immunochromatography to purify peptides of the invention. See, Scopes, 1984, Protein Purification: Principles and Practice, Springer-Verlag New York, Inc., N.Y., Livingstone, 1974, Methods Enzymology: Immunoaffmity Chromatography of Proteins 34:723-731. Antibodies can also be linked to other solid supports for diagnostic applications, or alternatively labeled with a means of detection such an enzyme that can cleave a colorimetric substrate, a fluorophore, a magnetic particle, or other measurable compositions of matter.
Specific antibodies against E6 proteins have historically been difficult to produce. In conjunction with the methods describe supra, one could employ a number of techniques to increase the likelihood of producing or selecting high affinity antibodies. An example is to prepare the E6 antigen (to raise antibodies against) in the same manner that one would prepare tissue or cell samples for testing. Alternatively, one could immunize with E6 fusion protein prepared in one manner, and screen for specific E6 antibodies using a second E6 protein prepared in a different manner. This should select for antibodies that recognize E6 epitopes that are conserved under different sample collection and preparation procedures. In another example, one could immunize animals with E6 antigen that has been rapidly denatured and renatured, such that epitopes that are insensitive to preparation conditions are selected for. Another method that could be employed is to use peptides corresponding to antigenic regions of the E6 proteins as predicted by Major Histocompatibility Complex (MHC) and T Cell Receptor (TCR) consensus binding.
2. Alternative Detection Methods for Captured E6 Protein
E6 proteins that have been captured by PDZ domains could be detected by several alternative methods. Several proteins are known to associate with E6 proteins. Any of them that had a reasonable affinity for E6 could be used to detect the presence of captured and concentrated E6 protein in a sample by one skilled in the art. In addition, new binding proteins or aptamers could be identified that bound to E6 proteins. Third, activity assays specific for E6 could be employed.
The detection assay itself could also be carried out using a variety of methods. A standard ELISA using a PDZ to capture could be set up as a competition, where the PDZ domain is pre-loaded with a labeled PL that has lower affinity than the E6 proteins. Thus, in the presence of E6, the label is displaced and one sees a reduction of signal that corresponds to E6 presence. Other variants that use aspects of competition and inhibition of binding are intended to be included as well. One variant could even have the PL covalently attached to the PDZ domain through a linker such that the PL could bind it's own PDZ domain. Using donor quenching dyes, one would only see an increase in signal when the PL of an oncogenic E6 protein was able to displace the labeled PL. All such competition methods must be measured against controls that assess the amount of endogenous PL proteins that can bind the PDZ domain used to assess the presence of oncogenic E6 proteins.
VIII. Measurements of Assay Sensitivity
The “A” and “G” assays of the invention can be used to determine the “apparent affinity” of binding of a PDZ ligand peptide to a PDZ-domain polypeptide. Apparent affinity is determined based on the concentration of one molecule required to saturate the binding of a second molecule (e.g., the binding of a ligand to a receptor). Two particularly useful approaches for quantitation of apparent affinity of PDZ-ligand binding are provided infra. These methods can be used to compare the sensitivity and affinity of differing PL detector constructs. Understanding the sensitivity of the PDZ for pathogen PLs is essential because it helps to define the amount of tissue or cell sample that must be tested to obtain a definitive result.
(1) A GST/PDZ fusion protein, as well as GST alone as a negative control, are bound to a surface (e.g., a 96-well plate) and the surface blocked and washed as described supra for the “G” assay.
(2) 50 uL per well of a solution of biotinylated PL peptide (e.g. as shown in TABLE 3) is added to the surface in increasing concentrations in PBS/BSA (e.g. at 0.1 uM, 0.33 uM, 1 uM, 3.3 uM, 10 uM, 33 uM, and 100 uM). In one embodiment, the PL peptide is allowed to react with the bound GST/PDZ fusion protein (as well as the GST alone negative control) for 10 minutes at 4° C. followed by 20 minutes at 25° C. The plate is washed 3 times with ice cold PBS to remove unbound labeled peptide.
(3) The binding of the PL peptide to the immobilized PDZ-domain polypeptide is detected as described supra for the “G” assay.
(4) For each concentration of peptide, the net binding signal is determined by subtracting the binding of the peptide to GST alone from the binding of the peptide to the GST/PDZ fusion protein. The net binding signal is then plotted as a function of ligand concentration and the plot is fit (e.g. by using the Kaleidagraph software package curve fitting algorithm; Synergy Software) to the following equation, where “Signal[ligand]” is the net binding signal at PL peptide concentration “[ligand],” “Kd” is the apparent affinity of the binding event, and “Saturation Binding” is a constant determined by the curve fitting algorithm to optimize the fit to the experimental data:
Signal[ligand]=Saturation Binding×([ligand]/([ligand]+Kd))
For reliable application of the above equation it is necessary that the highest peptide ligand concentration successfully tested experimentally be greater than, or at least similar to, the calculated Kd (equivalently, the maximum observed binding should be similar to the calculated saturation binding). In cases where satisfying the above criteria proves difficult, an alternative approach (infra) can be used.
Approach 2:
event, and “Saturation Binding” is a constant determined by the curve fitting algorithm to optimize the fit to the experimental data:
Signal[Ligand]=Saturation Binding×([ligand]/([ligand+Kd])
Measurement of the affinity of a labeled peptide ligand binding to a PDZ-domain polypeptide is useful because knowledge of the affinity (or apparent affinity) of this interaction allows rational design of inhibitors of the interaction with known potency. The potency of inhibitors in inhibition would be similar to (i.e. within one-order of magnitude of) the apparent affinity of the labeled peptide ligand binding to the PDZ-domain.
Thus, in one aspect, the invention provides a method of determining the apparent affinity of binding between a PDZ domain and a ligand by immobilizing a polypeptide comprising the PDZ domain and a non-PDZ domain on a surface, contacting the immobilized polypeptide with a plurality of different concentrations of the ligand, determining the amount of binding of the ligand to the immobilized polypeptide at each of the concentrations of ligand, and calculating the apparent affinity of the binding based on that data. Typically, the polypeptide comprising the PDZ domain and a non-PDZ domain is a fusion protein. In one embodiment, the e.g., fusion protein is GST-PDZ fusion protein, but other polypeptides can also be used (e.g., a fusion protein including a PDZ domain and any of a variety of epitope tags, biotinylation signals and the like) so long as the polypeptide can be immobilized In an orientation that does not abolish the ligand binding properties of the PDZ domain, e.g, by tethering the polypeptide to the surface via the non-PDZ domain via an anti-domain antibody and leaving the PDZ domain as the free end. It was discovered, for example, reacting a PDZ-GST fusion polypeptide directly to a plastic plate provided suboptimal results. The calculation of binding affinity itself can be determined using any suitable equation (e.g., as shown supra; also see Cantor and Schimmel (1980) B
Thus, in a preferred embodiment, the polypeptide is immobilized by binding the polypeptide to an immobilized immunoglobulin that binds the non-PDZ domain (e.g., an anti-GST antibody when a GST-PDZ fusion polypeptide is used). In a preferred embodiment, the step of contacting the ligand and PDZ-domain polypeptide is carried out under the conditions provided supra in the description of the “G” assay. It will be appreciated that binding assays are conveniently carried out in multiwell plates (e.g., 24-well, 96-well plates, or 384 well plates).
The present method has considerable advantages over other methods for measuring binding affinities PDZ-PL affinities, which typically involve contacting varying concentrations of a GST-PDZ fusion protein to a ligand-coated surface. For example, some previously described methods for determining affinity (e.g., using immobilized ligand and GST-PDZ protein in solution) did not account for oligomerization state of the fusion proteins used, resulting in potential errors of more than an order of magnitude.
Although not sufficient for quantitative measurement of PDZ-PL binding affinity, an estimate of the relative strength of binding of different PDZ-PL pairs can be made based on the absolute magnitude of the signals observed in the “G assay.” This estimate will reflect several factors, including biologically relevant aspects of the interaction, including the affinity and the dissociation rate. For comparisons of different ligands binding to a given PDZ domain-containing protein, differences in absolute binding signal likely relate primarily to the affinity and/or dissociation rate of the interactions of interest.
IX. Measurements of Assay Specificity
As described supra, the present invention provides powerful methods for analysis of PDZ-ligand interactions, including high-throughput methods such as the “G” assay and affinity assays described supra. In one embodiment of the invention, the affinity is determined for a particular ligand and a plurality of PDZ proteins. Typically the plurality is at least 5, and often at least 25, or at least 40 different PDZ proteins. In a preferred embodiment, the plurality of different PDZ proteins are from a particular tissue (e.g., central nervous system, spleen, cardiac muscle, kidney) or a particular class or type of cell, (e.g., a hematopoietic cell, a lymphocyte, a neuron) and the like. In a most preferred embodiment, the plurality of different PDZ proteins represents a substantial fraction (e.g., typically a majority, more often at least 80%) of all of the PDZ proteins known to be, or suspected of being, expressed in the tissue or cell(s), e.g., all of the PDZ proteins known to be present in lymphocytes. In an embodiment, the plurality is at least 50%, usually at least 80%, at least 90% or all of the PDZ proteins disclosed herein as being expressed in hematopoietic cells.
In one embodiment of the invention, the binding of a ligand to the plurality of PDZ proteins is determined. Using this method, it is possible to identify a particular PDZ domain bound with particular specificity by the ligand. The binding may be designated as “specific” if the affinity of the ligand to the particular PDZ domain is at least 2-fold that of the binding to other PDZ domains in the plurality (e.g., present in that cell type). The binding is deemed “very specific” if the affinity is at least 10-fold higher than to any other PDZ in the plurality or, alternatively, at least 10-fold higher than to at least 90%, more often 95% of the other PDZs in a defined plurality. Similarly, the binding is deemed “exceedingly specific” if it is at least 100-fold higher. For example, a ligand could bind to 2 different PDZs with an affinity of 1 uM and to no other PDZs out of a set 40 with an affinity of less than 100 uM. This would constitute specific binding to those 2 PDZs. Similar measures of specificity are used to describe binding of a PDZ to a plurality of PLs.
It will be recognized that high specificity PDZ-PL interactions represent potentially more valuable targets for achieving a desired biological effect. The ability of an inhibitor or enhancer to act with high specificity is often desirable. In particular, the most specific PDZ-ligand interactions are also the diagnostic targets, allowing specific detection of the interaction or disruption of an interaction.
Thus, in one embodiment, the invention provides a method of identifying a high specificity interaction between a particular PDZ domain and a ligand known or suspected of binding at least one PDZ domain, by providing a plurality of different immobilized polypeptides, each of said polypeptides comprising a PDZ domain and a non-PDZ domain; determining the affinity of the ligand for each of said polypeptides, and comparing the affinity of binding of the ligand to each of said polypeptides, wherein an interaction between the ligand and a particular PDZ domain is deemed to have high specificity when the ligand binds an immobilized polypeptide comprising the particular PDZ domain with at least 2-fold higher affinity than to immobilized polypeptides not comprising the particular PDZ domain.
In a related aspect, the affinity of binding of a specific PDZ domain to a plurality of ligands (or suspected ligands) is determined. For example, in one embodiment, the invention provides a method of identifying a high specificity interaction between a PDZ domain and a particular ligand known or suspected of binding at least one PDZ domain, by providing an immobilized polypeptide comprising the PDZ domain and a non-PDZ domain; determining the affinity of each of a plurality of ligands for the polypeptide, and comparing the affinity of binding of each of the ligands to the polypeptide, wherein an interaction between a particular ligand and the PDZ domain is deemed to have high specificity when the ligand binds an immobilized polypeptide comprising the PDZ domain with at least 2-fold higher affinity than other ligands tested. Thus, the binding may be designated as “specific” if the affinity of the PDZ to the particular PL is at least 2-fold that of the binding to other PLs in the plurality (e.g., present in that cell type). The binding is deemed “very specific” if the affinity is at least 10-fold higher than to any other PL in the plurality or, alternatively, at least 10-fold higher than to at least 90%, more often 95% of the other PLs in a defined plurality. Similarly, the binding is deemed “exceedingly specific” if it is at least 100-fold higher. Typically the plurality is at least 5 different ligands, more often at least 10.
A. Use of Array for Global Predictions
One discovery of the present inventors relates to the important and extensive roles played by interactions between PDZ proteins and PL proteins, particularly in the biological function of hematopoietic cells and other cells involved in the immune response. Further, it has been discovered that valuable information can be ascertained by analysis (e.g., simultaneous analysis) of a large number of PDZ-PL interactions. In a preferred embodiment, the analysis encompasses all of the PDZ proteins expressed in a particular tissue (e.g., spleen) or type or class of cell (e.g., hematopoietic cell, neuron, lymphocyte, B cell, T cell and the like). Alternatively, the analysis encompasses at least about 5, or at least about 10, or at least about 12, or at least about 15 and often at least 50 different polypeptides, up to about 60, about 80, about 100, about 150, about 200, or even more different polypeptides; or a substantial fraction (e.g., typically a majority, more often at least 80%) of all of the PDZ proteins known to be, or suspected of being, expressed in the tissue or cell(s), e.g., all of the PDZ proteins known to be present in lymphocytes.
It will be recognized that the arrays and methods of the invention are directed to the analysis of PDZ and PL interactions, and involve selection of such proteins for analysis. While the devices and methods of the invention may include or involve a small number of control polypeptides, they typically do not include significant numbers of proteins or fusion proteins that do not include either PDZ or PL domains (e.g., typically, at least about 90% of the arrayed or immobilized polypeptides in a method or device of the invention is a PDZ or PL sequence protein, more often at least about 95%, or at least about 99%).
It will be apparent from this disclosure that analysis of the relatively large number of different interactions preferably takes place simultaneously. In this context, “simultaneously” means that the analysis of several different PDZ-PL interactions (or the effect of a test agent on such interactions) is assessed at the same time. Typically the analysis is carried out in a high throughput (e.g., robotic) fashion. One advantage of this method of simultaneous analysis is that it permits rigorous comparison of multiple different PDZ-PL interactions. For example, as explained in detail elsewhere herein, simultaneous analysis (and use of the arrays described infra) facilitates, for example, the direct comparison of the effect of an agent (e.g., an potential interaction inhibitor) on the interactions between a substantial portion of PDZs and/or PLs in a tissue or cell.
Accordingly, in one aspect, the invention provides an array of immobilized polypeptide comprising the PDZ domain and a non-PDZ domain on a surface. Typically, the array comprises at least about 5, or at least about 10, or at least about 12, or at least about 15 and often at least 50 different polypeptides. In one preferred embodiment, the different PDZ proteins are from a particular tissue (e.g., central nervous system, spleen, cardiac muscle, kidney) or a particular class or type of cell, (e.g., a hematopoietic cell, a lymphocyte, a neuron) and the like. In a most preferred embodiment, the plurality of different PDZ proteins represents a substantial fraction (e.g., typically a majority, more often at least 60%, 70% or 80%) of all of the PDZ proteins known to be, or suspected of being, expressed in the tissue or cell(s), e.g., all of the PDZ proteins known to be present in lymphocytes.
Certain embodiments are arrays which include a plurality, usually at least 5, 10, 25, 50 PDZ proteins present in a particular cell of interest. In this context, “array” refers to an ordered series of immobilized polypeptides in which the identity of each polypeptide is associated with its location. In some embodiments the plurality of polypeptides are arrayed in a “common” area such that they can be simultaneously exposed to a solution (e.g., containing a ligand or test agent). For example, the plurality of polypeptides can be on a slide, plate or similar surface, which may be plastic, glass, metal, silica, beads or other surface to which proteins can be immobilized. In a different embodiment, the different immobilized polypeptides are situated in separate areas, such as different wells of multi-well plate (e.g., a 24-well plate, a 96-well plate, a 384 well plate, and the like). It will be recognized that a similar advantage can be obtained by using multiple arrays in tandem.
B. Analysis of PDZ-PL Inhibition Profile
In one aspect, the invention provides a method for determining if a test compound inhibits any PDZ-ligand interaction in large set of PDZ-ligand interactions (e.g., a plurality of the PDZ-ligands interactions described in U.S. patent application Ser. No. 09/724553; a majority of the PDZ-ligands identified in a particular cell or tissue as described supra (e.g., cervical tissue) and the like. In one embodiment, the PDZ domains of interest are expressed as GST-PDZ fusion proteins and immobilized as described herein. For each PDZ domain, a labeled ligand that binds to the domain with a known affinity is identified as described herein.
For any known or suspected modulator (e.g., inhibitor) of a PDZ-PL interaction(s), it is useful to know which interactions are inhibited (or augmented). This information could be used as a diagnostic marker for the presence of a pathogen (e.g., oncogenic HPV strains). The profile of PDZ interactions inhibited by a particular agent is referred to as the “inhibition profile” for the agent, and is described in detail below. The profile of PDZ interactions enhanced by a particular agent is referred to as the “enhancement profile” for the agent. It will be readily apparent to one of skill guided by the description of the inhibition profile how to determine the enhancement profile for an agent. The present invention provides methods for determining the PDZ interaction (inhibition/enhancement) profile of an agent in a single assay.
In one aspect, the invention provides a method for determining the PDZ-PL inhibition profile of a compound by providing (i) a plurality of different immobilized polypeptides, each of said polypeptides comprising a PDZ domain and a non-PDZ domain and (ii) a plurality of corresponding ligands, wherein each ligand binds at least one PDZ domain in (i), then contacting each of said immobilized polypeptides in (i) with a corresponding ligand in (ii) in the presence and absence of a test compound, and determining for each polypeptide-ligand pair whether the test compound inhibits binding between the immobilized polypeptide and the corresponding ligand.
Typically the plurality is at least 5, and often at least 25, or at least 40 different PDZ proteins. In a preferred embodiment, the plurality of different ligands and the plurality of different PDZ proteins are from the same tissue or a particular class or type of cell, e.g., a cervical cell, a penile cell, an anal cell and the like. In a most preferred embodiment, the plurality of different PDZs represents a substantial fraction (e.g., at least 80%) of all of the PDZs known to be, or suspected of being, expressed in the tissue or cell(s), e.g., all of the PDZs known to be present in lymphocytes (for example, at least 80%, at least 90% or all of the PDZs disclosed herein as being expressed in hematopoietic cells).
In one embodiment, the inhibition profile is determined as follows: A plurality (e.g., all known) PDZ domains expressed in a cell (e.g., cervical cells) are expressed as GST-fusion proteins and immobilized without altering their ligand binding properties as described supra. For each PDZ domain, a labeled ligand that binds to this domain with a known affinity is identified. If the set of PDZ domains expressed in lymphocytes is denoted by {P1 . . . Pn}, any given PDZ domain Pi binds a (labeled) ligand Li with affinity Kdi. To determine the inhibition profile for a test agent “compound X” the “G” assay (supra) can be performed as follows in 96-well plates with rows A-H and columns 1-12. Column 1 is coated with P1 and washed. The corresponding ligand L1 is added to each washed coated well of column 1 at a concentration 0.5 Kd1 with (rows B, D, F, H) or without (rows A, C, E, F) between about 1 and about 1000 uM) of test compound X. Column 2 is coated with P2, and L2 (at a concentration 0.5 Kd2) is added with or without inhibitor X. Additional PDZ domains and ligands are similarly tested.
Compound X is considered to inhibit the binding of Li to Pi if the average signal in the wells of column i containing X is less than half the signal in the equivalent wells of the column lacking X. Thus, in this single assay one determines the full set of lymphocyte PDZs that are inhibited by compound X.
In some embodiments, the test compound X is a mixture of compounds, such as the product of a combinatorial chemistry synthesis as described supra. In some embodiments, the test compound is known to have a desired biological effect, and the assay is used to determine the mechanism of action (i.e., if the biological effect is due to modulating a PDZ-PL interaction).
It will be apparent that an agent that modulates only one, or a few PDZ-PL interactions, in a panel (e.g., a panel of all known PDZs lymphocytes, a panel of at least 10, at least 20 or at least 50 PDZ domains) is a more specific modulator than an agent that modulate many or most interactions. Typically, an agent that modulates less than 20% of PDZ domains in a panel (e.g., Table 2) is deemed a “specific” inhibitor, less than 6% a “very specific” inhibitor, and a single PDZ domain a “maximally specific” inhibitor.
It will also be appreciated that “compound X” may be a composition containing mixture of compounds (e.g., generated using combinatorial chemistry methods) rather than a single compound.
Several variations of this assay are contemplated:
In some alternative embodiments, the assay above is performed using varying concentrations of the test compound X, rather than fixed concentration. This allows determination of the Ki of the X for each PDZ as described above.
In an alternative embodiment, instead of pairing each PDZ-PL with a specific labeled ligand Li, a mixture of different labeled ligands is created that such that for every PDZ at least one of the ligands in the mixture binds to this PDZ sufficiently to detect the binding in the “G” assay. This mixture is then used for every PDZ domain.
In one embodiment, compound X is known to have a desired biological effect, but the chemical mechanism by which it has that effect is unknown. The assays of the invention can then be used to determine if compound X has its effect by binding to a PDZ domain.
In one embodiment, PDZ-domain containing proteins are classified in to groups based on their biological function, e.g. into those that regulate chemotaxis versus those that regulate transcription. An optimal inhibitor of a particular function (e.g., including but not limited to an anti-chemotactic agent, an anti-T cell activation agent, cell-cycle control, vesicle transport, apoptosis, etc.) will inhibit multiple PDZ-ligand interactions involved in the function (e.g., chemotaxis, activation) but few other interactions. Thus, the assay is used in one embodiment in screening and design of a drug that specifically blocks a particular function. For example, an agent designed to block chemotaxis might be identified because, at a given concentration, the agent inhibits 2 or more PDZs involved in chemotaxis but fewer than 3 other PDZs, or that inhibits PDZs involved in chemotaxis with a Ki>10-fold better than for other PDZs. Thus, the invention provides a method for identifying an agent that inhibits a first selected PDZ-PL interaction or plurality of interactions but does not inhibit a second selected PDZ-PL interaction or plurality of interactions. The two (or more) sets of interactions can be selected on the basis of the known biological function of the PDZ proteins, the tissue specificity of the PDZ proteins, or any other criteria. Moreover, the assay can be used to determine effective doses (i.e., drug concentrations) that result in desired biological effects while avoiding undesirable effects.
C. Agonists and Antagonists of PDZ-PL Interactions
As described herein, interactions between PDZ proteins and PL proteins in cells (e.g., cervical cells) may be disrupted or inhibited by the presence of pathogens. Pathogens can be identified using screening assays described herein. Agonists and antagonists of PDZ-Pathogen PL interactions or PDZ-Cellular PL interactions can be useful in discerning or confirming specific interactions. In some embodiments, an agonist will increase the sensitivity of a PDZ-pathogen PL interaction. In other embodiments, an antagonist of a PDZ-pathogen PL interaction can be used to verify the specificity of an interaction. In one embodiment, the motifs disclosed herein are used to design inhibitors. In some embodiments, the antagonists of the invention have a structure (e.g., peptide sequence) based on the C-terminal residues of PL-domain proteins listed in TABLE 3. In some embodiments, the antagonists of the invention have a structure (e.g., peptide sequence) based on a PL motif disclosed herein or in U.S. patent application Ser. No. 09/724553.
The PDZ/PL antagonists and antagonists of the invention may be any of a large variety of compounds, both naturally occurring and synthetic, organic and inorganic, and including polymers (e.g., oligopeptides, polypeptides, oligonucleotides, and polynucleotides), small molecules, antibodies, sugars, fatty acids, nucleotides and nucleotide analogs, analogs of naturally occurring structures (e.g., peptide mimetics, nucleic acid analogs, and the like), and numerous other compounds. Although, for convenience, the present discussion primarily refers antagonists of PDZ-PL interactions, it will be recognized that PDZ-PL interaction agonists can also be use in the methods disclosed herein.
In one aspect, the peptides and peptide mimetics or analogues of the invention contain an amino acid sequence that binds a PDZ domain in a cell of interest. In one embodiment, the antagonists comprise a peptide that has a sequence corresponding to the carboxy-terminal sequence of a PL protein listed in TABLE 3 or in U.S. patent application Ser. No. 09/724553, e.g., a peptide listed TABLE 3. Typically, the peptide comprises at least the C-terminal two (3), three (3) or four (4) residues of the PL protein, and often the inhibitory peptide comprises more than four residues (e.g., at least five, six, seven, eight, nine, ten, twelve or fifteen residues) from the PL protein C-terminus.
In some embodiments, the inhibitor is a peptide, e.g., having a sequence of a PL C-terminal protein sequence.
In some embodiments, the antagonist is a fusion protein comprising such a sequence. Fusion proteins containing a transmembrane transporter amino acid sequence are particularly useful.
In some embodiments, the inhibitor is conserved variant of the PL C-terminal protein sequence having inhibitory activity.
In some embodiments, the antagonist is a peptide mimetic of a PL C-terminal sequence.
In some embodiments, the inhibitor is a small molecule (i.e., having a molecular weight less than 1 kD).
D. Peptide Antagonists
In one embodiment, the antagonists comprise a peptide that has a sequence of a PL protein carboxy-terminus listed in TABLE 3. The peptide comprises at least the C-terminal two (2) residues of the PL protein, and typically, the inhibitory peptide comprises more than two residues (e.g, at least three, four, five, six, seven, eight, nine, ten, twelve or fifteen residues) from the PL protein C-terminus. The peptide may be any of a variety of lengths (e.g., at least 2, at least 3, at least 4, at least 5, at least 6, at least 8, at least 10, or at least 20 residues) and may contain additional residues not from the PL protein. It will be recognized that short PL peptides are sometime used in the rational design of other small molecules with similar properties.
Although most often, the residues shared by the inhibitory peptide with the PL protein are found at the C-terminus of the peptide. However, in some embodiments, the sequence is internal. Similarly, in some cases, the inhibitory peptide comprises residues from a PL sequence that is near, but not at the c-terminus of a PL protein (see, Gee et al., 1998, J Biological Chem. 273:21980-87).
Sometime the PL protein carboxy-terminus sequence is referred to as the “core PDZ motif sequence” referring to the ability of the short sequence to interact with the PDZ domain. For example, in an embodiment, the “core PDZ motif sequence” contains the last four C-terminus amino acids. As described above, the four amino acid core of a PDZ motif sequence may contain additional amino acids at its amino terminus to further increase its binding affinity and/or stability. Thus, in one embodiment, the PDZ motif sequence peptide can be from four amino acids up to 15 amino acids. It is preferred that the length of the sequence to be 6-10 amino acids. More preferably, the PDZ motif sequence contains 8 amino acids. Additional amino acids at the amino terminal end of the core sequence may be derived from the natural sequence in each hematopoietic cell surface receptor or a synthetic linker. The additional amino acids may also be conservatively substituted. When the third residue from the C-terminus is S, T or Y, this residue may be phosphorylated prior to the use of the peptide.
In some embodiments, the peptide and nonpeptide inhibitors of the are small, e.g., fewer than ten amino acid residues in length if a peptide. Further, it is reported that a limited number of ligand amino acids directly contact the PDZ domain (generally less than eight) (Kozlov et al., 2000, Biochemistry 39, 2572; Doyle et al., 1996, Cell 85, 1067) and that peptides as short as the C-terminal three amino acids often retain similar binding properties to longer (>15) amino acids peptides (Yanagisawa et al., 1997, J. Biol. Chem. 272, 8539).
E. Peptide Variants
Having identified PDZ binding peptides and PDZ-PL interaction inhibitory sequences, variations of these sequences can be made and the resulting peptide variants can be tested for PDZ domain binding or PDZ-PL inhibitory activity. In embodiments, the variants have the same or a different ability to bind a PDZ domain as the parent peptide. Typically, such amino acid substitutions are conservative, i.e., the amino acid residues are replaced with other amino acid residues having physical and/or chemical properties similar to the residues they are replacing. Preferably, conservative amino acid substitutions are those wherein an amino acid is replaced with another amino acid encompassed within the same designated class.
F. Peptide Mimetics
Having identified PDZ binding peptides and PDZ-PL interaction inhibitory sequences, peptide mimetics can be prepared using routine methods, and the inhibitory activity of the mimetics can be confirmed using the assays of the invention. Thus, in some embodiments, the agonist or antagonist is a peptide mimetic of a PL C-terminal sequence. The skilled artisan will recognize that individual synthetic residues and polypeptides incorporating mimetics can be synthesized using a variety of procedures and methodologies, which are well described in the scientific and patent literature, e.g., Organic Syntheses Collective Volumes, Gilman et al. (Eds) John Wiley & Sons, Inc., NY. Polypeptides incorporating mimetics can also be made using solid phase synthetic procedures, as described, e.g., by Di Marchi, et al., U.S. Pat. No. 5,422,426. Mimetics of the invention can also be synthesized using combinatorial methodologies. Various techniques for generation of peptide and peptidomimetic libraries are well known, and include, e.g., multipin, tea bag, and split-couple-mix techniques; see, e.g., al-Obeidi (1998) Mol. Biotechnol. 9:205-223; Hruby (1997) Curr. Opin. Chem. Biol. 1:114-119; Ostergaard (1997) Mol. Divers. 3:17-27; Ostresh (1996) Methods Enzymol. 267:220-234.
G. Small Molecules
In some embodiments, the agonist or antagonist is a small molecule (i.e., having a molecular weight less than 1 kD). Methods for screening small molecules are well known in the art and include those described supra.
X. Methods of Optimizing a PL Detector
Although described supra primarily in terms of identifying interactions between PDZ-domain polypeptides and PL proteins, the assays described supra and other assays can also be used to identify the binding of other molecules (e.g., peptide mimetics, small molecules, and the like) to PDZ domain sequences. For example, using the assays disclosed herein, combinatorial and other libraries of compounds can be screened, e.g., for molecules that specifically bind to PDZ domains. Screening of libraries can be accomplished by any of a variety of commonly known methods. See, e.g., the following references, which disclose screening of peptide libraries: Parmley and Smith, 1989, Adv. Exp. Med. Biol. 251:215-218; Scott and Smith, 1990, Science 249:386-390; Fowlkes et al., 1992; BioTechniques 13:422-427; Oldenburg et al., 1992, Proc. Natl. Acad. Sci. USA 89:5393-5397; Yu et al., 1994, Cell 76:933-945; Staudt et al., 1988, Science 241:577-580; Bock et al., 1992, Nature 355:564-566; Tuerk et al., 1992, Proc. Natl. Acad. Sci. USA 89:6988-6992; Ellington et al., 1992, Nature 355:850-852; U.S. Pat. No. 5,096,815, U.S. Pat. No. 5,223,409, and U.S. Pat. No. 5,198,346, all to Ladner et al.; Rebar and Pabo, 1993, Science 263:671-673; and PCT Publication No. WO 94/18318.
In a specific embodiment, screening can be carried out by contacting the library members with a PDZ-domain polypeptide immobilized on a solid support (e.g. as described supra in the “G” assay) and harvesting those library members that bind to the protein. Examples of such screening methods, termed “panning” techniques are described by way of example in Parmley and Smith, 1988, Gene 73:305-318; Fowlkes et al., 1992, BioTechniques 13:422-427; PCT Publication No. WO 94/18318; and in references cited hereinabove.
In another embodiment, the two-hybrid system for selecting interacting proteins in yeast (Fields and Song, 1989, Nature 340:245-246; Chien et al., 1991, Proc. Natl. Acad. Sci. USA 88:9578-9582) can be used to identify molecules that specifically bind to a PDZ domain-containing protein. Furthermore, the identified molecules are further tested for their ability to inhibit transmembrane receptor interactions with a PDZ domain.
In one aspect of the invention, antagonists of an interaction between a PDZ protein and a PL protein are identified. In one embodiment, a modification of the “A” assay described supra is used to identify antagonists. In one embodiment, a modification of the “G” assay described supra is used to identify antagonists.
In one embodiment, screening assays are used to detect molecules that specifically bind to PDZ domains. Such molecules are useful as agonists or antagonists of PDZ-protein-mediated cell function (e.g., cell activation, e.g., T cell activation, vesicle transport, cytokine release, growth factors, transcriptional changes, cytoskeleton rearrangement, cell movement, chemotaxis, and the like). In one embodiment, such assays are performed to screen for leukocyte activation inhibitors for drug development. The invention thus provides assays to detect molecules that specifically bind to PDZ domain-containing proteins. For example, recombinant cells expressing PDZ domain-encoding nucleic acids can be used to produce PDZ domains in these assays and to screen for molecules that bind to the domains. Molecules are contacted with the PDZ domain (or fragment thereof) under conditions conducive to binding, and then molecules that specifically bind to such domains are identified. Methods that can be used to carry out the foregoing are commonly known in the art.
It will be appreciated by the ordinarily skilled practitioner that, in one embodiment, antagonists are identified by conducting the A or G assays in the presence and absence of a known or candidate antagonist. When decreased binding is observed in the presence of a compound, that compound is identified as an antagonist. Increased binding in the presence of a compound signifies that the compound is an agonist.
For example, in one assay, a test compound can be identified as an inhibitor (antagonist) of binding between a PDZ protein and a PL protein by contacting a PDZ domain polypeptide and a PL peptide in the presence and absence of the test compound, under conditions in which they would (but for the presence of the test compound) form a complex, and detecting the formation of the complex in the presence and absence of the test compound. It will be appreciated that less complex formation in the presence of the test compound than in the absence of the compound indicates that the test compound is an inhibitor of a PDZ protein -PL protein binding.
In one embodiment, the “G” assay is used in the presence or absence of a candidate inhibitor. In one embodiment, the “A” assay is used in the presence or absence of a candidate inhibitor.
In one embodiment (in which a G assay is used), one or more PDZ domain-containing GST-fusion proteins are bound to the surface of wells of a 96-well plate as described supra (with appropriate controls including nonfusion GST protein). All fusion proteins are bound in multiple wells so that appropriate controls and statistical analysis can be done. A test compound in BSA/PBS (typically at multiple different concentrations) is added to wells. Immediately thereafter, 30 uL of a detectably labeled (e.g., biotinylated) peptide known to bind to the relevant PDZ domain (see, e.g., TABLE 4) is added in each of the wells at a final concentration of, e.g., between about 2 uM and about 40 uM, typically 5 uM, 15 uM, or 25 uM. This mixture is then allowed to react with the PDZ fusion protein bound to the surface for 10 minutes at 4° C. followed by 20 minutes at 25° C. The surface is washed free of unbound peptide three times with ice cold PBS and the amount of binding of the peptide in the presence and absence of the test compound is determined. Usually, the level of binding is measured for each set of replica wells (e.g. duplicates) by subtracting the mean GST alone background from the mean of the raw measurement of peptide binding in these wells.
In an alternative embodiment, the A assay is carried out in the presence or absence of a test candidate to identify inhibitors of PL-PDZ interactions.
In one embodiment, a test compound is determined to be a specific inhibitor of the binding of the PDZ domain (P) and a PL (L) sequence when, at a test compound concentration of less than or equal to 1 mM (e.g., less than or equal to: 500 uM, 100 uM, 10 uM, 1 uM, 100 nM or 1 nM) the binding of P to L in the presence of the test compound less than about 50% of the binding in the absence of the test compound. (in various embodiments, less than about 25%, less than about 10%, or less than about 1%). Preferably, the net signal of binding of P to L in the presence of the test compound plus six (6) times the standard error of the signal in the presence of the test compound is less than the binding signal in the absence of the test compound.
In one embodiment, assays for an inhibitor are carried out using a single PDZ protein-PL protein pair (e.g., a PDZ domain fusion protein and a PL peptide). In a related embodiment, the assays are carried out using a plurality of pairs, such as a plurality of different pairs listed in TABLE 4.
In some embodiments, it is desirable to identify compounds that, at a given concentration, inhibit the binding of one PL-PDZ pair, but do not inhibit (or inhibit to a lesser degree) the binding of a specified second PL-PDZ pair. These antagonists can be identified by carrying out a series of assays using a candidate inhibitor and different PL-PDZ pairs (e.g., as shown in the matrix of TABLE 4) and comparing the results of the assays. All such pairwise combinations are contemplated by the invention (e.g., test compound inhibits binding of PL1 to PDZ1 to a greater degree than it inhibits binding of PL1 to PDZ2 or PL2 to PDZ2). Importantly, it will be appreciated that, based on the data provided in TABLE 4 and disclosed herein (and additional data that can be generated using the methods described herein) inhibitors with different specificities can readily be designed.
For example, according to the invention, the Ki (“potency”) of an inhibitor of a PDZ-PL interaction can be determined. Ki is a measure of the concentration of an inhibitor required to have a biological effect. For example, administration of an inhibitor of a PDZ-PL interaction in an amount sufficient to result in an intracellular inhibitor concentration of at least between about 1 and about 100 Ki is expected to inhibit the biological response mediated by the target PDZ-PL interaction. In one aspect of the invention, the Kd measurement of PDZ-PL binding as determined using the methods supra is used in determining Ki.
Thus, in one aspect, the invention provides a method of determining the potency (Ki) of an inhibitor or suspected inhibitor of binding between a PDZ domain and a ligand by immobilizing a polypeptide comprising the PDZ domain and a non-PDZ domain on a surface, contacting the immobilized polypeptide with a plurality of different mixtures of the ligand and inhibitor, wherein the different mixtures comprise a fixed amount of ligand and different concentrations of the inhibitor, determining the amount of ligand bound at the different concentrations of inhibitor, and calculating the Ki of the binding based on the amount of ligand bound in the presence of different concentrations of the inhibitor. In an embodiment, the polypeptide is immobilized by binding the polypeptide to an immobilized immunoglobulin that binds the non-PDZ domain. This method, which is based on the “G” assay described supra, is particularly suited for high-throughput analysis of the Ki for inhibitors of PDZ-ligand interactions. Further, using this method, the inhibition of the PDZ-ligand interaction itself is measured, without distortion of measurements by avidity effects.
Typically, at least a portion of the ligand is detectably labeled to permit easy quantitation of ligand binding.
It will be appreciated that the concentration of ligand and concentrations of inhibitor are selected to allow meaningful detection of inhibition. Thus, the concentration of the ligand whose binding is to be blocked is close to or less than its binding affinity (e.g., preferably less than the 5× Kd of the interaction, more preferably less than 2× Kd, most preferably less than 1× Kd). Thus, the ligand is typically present at a concentration of less than 2 Kd (e.g., between about 0.01 Kd and about 2 Kd) and the concentrations of the test inhibitor typically range from 1 nM to 100 uM (e.g. a 4-fold dilution series with highest concentration 10 uM or 1 mM). In a preferred embodiment, the Kd is determined using the assay disclosed supra.
The Ki of the binding can be calculated by any of a variety of methods routinely used in the art, based on the amount of ligand bound in the presence of different concentrations of the inhibitor. In an illustrative embodiment, for example, a plot of labeled ligand binding versus inhibitor concentration is fit to the equation:
Sinhibitor=S0*Ki/([I]+Ki)
where Sinhibitor is the signal of labeled ligand binding to immobilized PDZ domain in the presence of inhibitor at concentration [I] and S0 is the signal in the absence of inhibitor (i.e., [I]=0). Typically [I] is expressed as a molar concentration.
In another aspect of the invention, an enhancer (sometimes referred to as, augmentor or agonist) of binding between a PDZ domain and a ligand is identified by immobilizing a polypeptide comprising the PDZ domain and a non-PDZ domain on a surface, contacting the immobilized polypeptide with the ligand in the presence of a test agent and determining the amount of ligand bound, and comparing the amount of ligand bound in the presence of the test agent with the amount of ligand bound by the polypeptide in the absence of the test agent. At least two-fold (often at least 5-fold) greater binding in the presence of the test agent compared to the absence of the test agent indicates that the test agent is an agent that enhances the binding of the PDZ domain to the ligand. As noted supra, agents that enhance PDZ-ligand interactions are useful for disruption (dysregulation) of biological events requiring normal PDZ-ligand function (e.g., cancer cell division and metastasis, and activation and migration of immune cells).
The invention also provides methods for determining the “potency” or “Kenhancer” of an enhancer of a PDZ-ligand interaction. For example, according to the invention, the Kenhancer of an enhancer of a PDZ-PL interaction can be determined, e.g., using the Kd of PDZ-PL binding as determined using the methods described supra. Kenhancer is a measure of the concentration of an enhancer expected to have a biological effect. For example, administration of an enhancer of a PDZ-PL interaction in an amount sufficient to result in an intracellular inhibitor concentration of at least between about 0.1 and about 100 Kenhancer (e.g., between about 0.5 and about 50 Kenhancer) is expected to disrupt the biological response mediated by the target PDZ-PL interaction.
Thus, in one aspect the invention provides a method of determining the potency (Kenhancer) of an enhancer or suspected enhancer of binding between a PDZ domain and a ligand by immobilizing a polypeptide comprising the PDZ domain and a non-PDZ domain on a surface, contacting the immobilized polypeptide with a plurality of different mixtures of the ligand and enhancer, wherein the different mixtures comprise a fixed amount of ligand, at least a portion of which is detectably labeled, and different concentrations of the enhancer, determining the amount of ligand bound at the different concentrations of enhancer, and calculating the potency (Kenhancer) of the enhancer from the binding based on the amount of ligand bound in the presence of different concentrations of the enhancer. Typically, at least a portion of the ligand is detectably labeled to permit easy quantitation of ligand binding. This method, which is based on the “G” assay described supra, is particularly suited for high-throughput analysis of the Kenhancer for enhancers of PDZ-ligand interactions.
It will be appreciated that the concentration of ligand and concentrations of enhancer are selected to allow meaningful detection of enhanced binding. Thus, the ligand is typically present at a concentration of between about 0.01 Kd and about 0.5 Kd and the concentrations of the test agent/enhancer typically range from 1 nM to 1 mM (e.g. a 4-fold dilution series with highest concentration 10 uM or 1 mM). In a preferred embodiment, the Kd is determined using the assay disclosed supra.
The potency of the binding can be determined by a variety of standard methods based on the amount of ligand bound in the presence of different concentrations of the enhancer or augmentor. For example, a plot of labeled ligand binding versus enhancer concentration can be fit to the equation:
S([E])=S(0)+(S(0)*(Denhancer−1)*[E]/([E]+Kenhancer)
where “Kenhancer” is the potency of the augmenting compound, and “Denhancer” is the fold-increase in binding of the labeled ligand obtained with addition of saturating amounts of the enhancing compound, [E] is the concentration of the enhancer. It will be understood that saturating amounts are the amount of enhancer such that further addition does not significantly increase the binding signal. Knowledge of “Kenhancer” is useful because it describes a concentration of the augmenting compound in a target cell that will result in a biological effect due to dysregulation of the PDZ-PL interaction. Typical therapeutic concentrations are between about 0.1 and about 100 Kenhancer.
For certain of the PDZ proteins and PL proteins shown to bind together and for which Kd values had been obtained, additional testing was conducted to determine whether certain pharmaceutical compounds would act to antagonize or agonize the interactions. Assays were conducted as for the G′ assay described supra both in the presence and absence of test compound, except that 50 ul of a 10 uM solution of the biotinylated PL peptide is allowed to react with the surface bearing the PDZ-domain polypeptide instead of a 20 uM solution as specified in step (2) of the assay.
Another method of increasing the specificity or sensitivity of a PDZ-PL interaction is through mutagenesis and selection of high affinity or high specificity variants. Methods such as V, chemical (e.g., EMS) or biological mutagenesis (e.g. Molecular shuffling or DNA polymerase mutagenesis) can be applied to create mutations in DNA encoding PDZ domains or PL domains. Proteins can then be made from variants and tested using a number of methods described herein (e.g., ‘A’ assay, ‘G’ assay or yeast two hybrid). In general, one would assay mutants for high affinity binding between the mutated PDZ domain and a test sample (such as an oncogenic E6 PL) that have reduced afinity for other cellular PLs (as described in section IX). These methods are known to those skilled in the art and examples herein are not intended to be limiting.
XI. Recombinant Detector Synthesis
As indicated in the Background section, PDZ domain-containing proteins are involved in a number of biological functions, including, but not limited to, vesicular trafficking, tumor suppression, protein sorting, establishment of membrane polarity, apoptosis, regulation of immune response and organization of synapse formation. In general, this family of proteins has a common function of facilitating the assembly of multi-protein complexes, often serving as a bridge between several proteins, or regulating the function of other proteins. Additionally, as also noted supra, these proteins are found in essentially all cell types. Consequently, detection of inappropriate PDZ:PL interactions or abnormal interactions can be utilized to diagnose a wide variety of biological and physiological conditions. In particular, detection of PL proteins from pathogenic organisms can be diagnosed using PDZ domains. Most, but not all, embodiments of this invention, require the addition of a detectable marker to the PDZ or PL protein used for detection. Examples are given below.
A. Chemical Synthesis
The peptides of the invention or analogues thereof, may be prepared using virtually any art-known technique for the preparation of peptides and peptide analogues. For example, the peptides may be prepared in linear form using conventional solution or solid phase peptide syntheses and cleaved from the resin followed by purification procedures (Creighton, 1983, Protein Structures And Molecular Principles, W. H. Freeman and Co., N.Y.). Suitable procedures for synthesizing the peptides described herein are well known in the art. The composition of the synthetic peptides may be confirmed by amino acid analysis or sequencing (e.g., the Edman degradation procedure and mass spectroscopy).
In addition, analogues and derivatives of the peptides can be chemically synthesized. The linkage between each amino acid of the peptides of the invention may be an amide, a substituted amide or an isostere of amide. Nonclassical amino acids or chemical amino acid analogues can be introduced as a substitution or addition into the sequence. Non-classical amino acids include, but are not limited to, the D-isomers of the common amino acids, α-amino isobutyric acid, 4-aminobutyric acid, Abu, 2-amino butyric acid, γ-Abu, ε-Ahx, 6-amino hexanoic acid, Aib, 2-amino isobutyric acid, 3-amino propionic acid, ornithine, norleucine, norvaline, hydroxyproline, sarcosine, citrulline, cysteic acid, t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, β-alanine, fluoro-amino acids, designer amino acids such as β-methyl amino acids, Cα-methyl amino acids, Nα-methyl amino acids, and amino acid analogues in general. Furthermore, the amino acid can be D (dextrorotary) or L (levorotary).
B. Recombinant Synthesis
If the peptide is composed entirely of gene-encoded amino acids, or a portion of it is so composed, the peptide or the relevant portion may also be synthesized using conventional recombinant genetic engineering techniques. For recombinant production, a polynucleotide sequence encoding a linear form of the peptide is inserted into an appropriate expression vehicle, i.e., a vector which contains the necessary elements for the transcription and translation of the inserted coding sequence, or in the case of an RNA viral vector, the necessary elements for replication and translation. The expression vehicle is then transfected into a suitable target cell which will express the peptide. Depending on the expression system used, the expressed peptide is then isolated by procedures well-established in the art. Methods for recombinant protein and peptide production are well known in the art (see, e.g., Maniatis et al., 1989, Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y.; and Ausubel et al., 1989, Current Protocols in Molecular Biology, Greene Publishing Associates and Wiley Interscience, N.Y.).
A variety of host-expression vector systems may be utilized to express the peptides described herein. These include, but are not limited to, microorganisms such as bacteria transformed with recombinant bacteriophage DNA or plasmid DNA expression vectors containing an appropriate coding sequence; yeast or filamentous fungi transformed with recombinant yeast or fungi expression vectors containing an appropriate coding sequence; insect cell systems infected with recombinant virus expression vectors (e.g., baculovirus) containing an appropriate coding sequence; plant cell systems infected with recombinant virus expression vectors (e.g., cauliflower mosaic virus or tobacco mosaic virus) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing an appropriate coding sequence; or animal cell systems.
In some embodiments, increasing the number of copies of a PL detector may be used to increase the specificity or sensitivity of detection. An example of this is presented in EXAMPLE 4. The TIP-TIP-IgG vector produces a fusion protein that has duplicated copies of the PDZ domain from TIP-1 and the protein itself should dimerize on the basis of the IgG constant region backbone. Hence, a single protein contains 2-4 copies of the TIP-1 PDZ domain. In a similar manner, addition tandem repeats of PL detectors could be fashioned. In some embodiments, different PDZ domains from different proteins could be engineered to express as a single protein (e.g., the PDZ domains of TIP-1 and MAGI-1 could be engineered to detect oncogenic HPV E6 proteins). In a similar manner, a different Ig backbone could be used to increase the avidity of a construct. For example, the IgG constant regions will dimerize with itself, but the IgM constant regions will form a complex of ten monomers.
The expression elements of the expression systems vary in their strength and specificities. Depending on the host/vector system utilized, any of a number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used in the expression vector. For example, when cloning in bacterial systems, inducible promoters such as pL of bacteriophage λ, plac, ptrp, ptac (ptrp-lac hybrid promoter) and the like may be used; when cloning in insect cell systems, promoters such as the baculovirus polyhedron promoter may be used; when cloning in plant cell systems, promoters derived from the genome of plant cells (e.g., heat shock promoters; the promoter for the small subunit of RUBISCO; the promoter for the chlorophyll a/b binding protein) or from plant viruses (e.g., the 35S RNA promoter of CaMV; the coat protein promoter of TMV) may be used; when cloning in mammalian cell systems, promoters derived from the genome of mammalian cells (e.g., metallothionein promoter) or from mammalian viruses (e.g., the adenovirus late promoter; the vaccinia virus 7.5 K promoter) may be used; when generating cell lines that contain multiple copies of expression product, SV40-, BPV- and EBV-based vectors may be used with an appropriate selectable marker.
In cases where plant expression vectors are used, the expression of sequences encoding the peptides of the invention may be driven by any of a number of promoters. For example, viral promoters such as the 35S RNA and 19S RNA promoters of CaMV (Brisson et al., 1984, Nature 310:511-514), or the coat protein promoter of TMV (Takamatsu et al., 1987, EMBO J. 6:307-311) may be used; alternatively, plant promoters such as the small subunit of RUBISCO (Coruzzi et al., 1984, EMBO J. 3:1671-1680; Broglie et al., 1984, Science 224:838-843) or heat shock promoters, e.g., soybean hsp17.5-E or hsp17.3-B (Gurley et al., 1986, Mol. Cell. Biol. 6:559-565) may be used. These constructs can be introduced into planleukocytes using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transformation, microinjection, electroporation, etc. For reviews of such techniques see, e.g., Weissbach & Weissbach, 1988, Methods for Plant Molecular Biology, Academic Press, NY, Section VIII, pp. 421-463; and Grierson & Corey, 1988, Plant Molecular Biology, 2d Ed., Blackie, London, Ch. 7-9.
In one insect expression system that may be used to produce the peptides of the invention, Autographa californica nuclear polyhidrosis virus (AcNPV) is used as a vector to express the foreign genes. The virus grows in Spodoptera frugiperda cells. A coding sequence may be cloned into non-essential regions (for example the polyhedron gene) of the virus and placed under control of an AcNPV promoter (for example, the polyhedron promoter). Successful insertion of a coding sequence will result in inactivation of the polyhedron gene and production of non-occluded recombinant virus (i.e., virus lacking the proteinaceous coat coded for by the polyhedron gene). These recombinant viruses are then used to infect Spodoptera frugiperda cells in which the inserted gene is expressed. (e.g., see Smith et al., 1983, J. Virol. 46:584; Smith, U.S. Pat. No. 4,215,051). Further examples of this expression system may be found in Current Protocols in Molecular Biology, Vol. 2, Ausubel et al., eds., Greene Publish. Assoc. & Wiley Interscience.
In mammalian host cells, a number of viral based expression systems may be utilized. In cases where an adenovirus is used as an expression vector, a coding sequence may be ligated to an adenovirus transcription/translation control complex, e.g., the late promoter and tripartite leader sequence. This chimeric gene may then be inserted in the adenovirus genome by in vitro or in vivo recombination. Insertion in a non-essential region of the viral genome (e.g., region E1 or E3) will result in a recombinant virus that is viable and capable of expressing peptide in infected hosts. (e.g., See Logan & Shenk, 1984, Proc. Natl. Acad. Sci. USA 81:3655-3659). Alternatively, the vaccinia 7.5 K promoter may be used, (see, e.g., Mackett et al., 1982, Proc. Natl. Acad. Sci. USA 79:7415-7419; Mackett et al., 1984, J. Virol. 49:857-864; Panicali et al., 1982, Proc. Natl. Acad. Sci. USA 79:4927-4931).
Other expression systems for producing linear peptides of the invention will be apparent to those having skill in the art.
C. Tags or Markers
Tags and markers are frequently used to aid in purification of components or detection of biological molecules. Examples of biological tags include, but are not limited to, glutathione-S-transferase, maltose binding protein, Immunoglobulin domains, Intein, Hemagglutinin epitopes, myc epitopes, etc. Examples of chemical tags include, but are not limited to, biotin, gold, paramagnetic particles or fluorophores. These examples can be used to identify the presence of proteins or compounds they are attached to or can be used by those skilled in the art to purify proteins or compounds from complex mixtures.
D. Purification of the Peptides and Peptide Analogues
The peptides and peptide analogues of the invention can be purified by art-known techniques such as high performance liquid chromatography, ion exchange chromatography, gel electrophoresis, affinity chromatography and the like. The actual conditions used to purify a particular peptide or analogue will depend, in part, on factors such as net charge, hydrophobicity, hydrophilicity, etc., and will be apparent to those having skill in the art. The purified peptides can be identified by assays based on their physical or functional properties, including radioactive labeling followed by gel electrophoresis, radioimmuno-assays, ELISA, bioassays, and the like.
XII. Kits
The present invention also includes kits for carrying out the methods of the invention. A subject kit usually contains a first and a second oncogenic HPV E6 binding partner. In most embodiments, the first binding partner is a PDZ domain polypeptide, and, the second binding partner is at least one antibody for E6. In some embodiments, the second binding partner is labeled with a detectable label. In other embodiments, a secondary labeling component, such as a detectably labeled secondary antibody, is included. In some embodiments, a subject kit further comprises a means, such as a device or a system, for isolating oncogenic HPV E6 from the sample. The kit may optionally contain proteasome inhibitor.
A subject kit can further include, if desired, one or more of various conventional components, such as, for example, containers with one or more buffers, detection reagents or antibodies. Printed instructions, either as inserts or as labels, indicating quantities of the components to be used and guidelines for their use, can also be included in the kit. In the present disclosure it should be understood that the specified materials and conditions are important in practicing the invention but that unspecified materials and conditions are not excluded so long as they do not prevent the benefits of the invention from being realized. Exemplary embodiments of the diagnostic methods of the invention are described above in detail.
In a subject kit, the oncogenic E6 detection reaction may be performed using an aqueous or solid substrate, where the kit may comprise reagents for use with several separation and detection platforms such as test strips, sandwich assays, etc. In many embodiments of the test strip kit, the test strip has bound thereto a PDZ domain polypeptide that specifically binds the PL domain of an oncogenic E6 protein and captures oncogenic E6 protein on the solid support. In some embodiments, the kit further comprises a detection antibody or antibodies, which is either directly or indirectly detectable, and which binds to the oncogenic E6 protein to allow its detection. Kits may also include components for conducting western blots (e.g., pre-made gels, membranes, transfer systems, etc.); components for carrying out ELISAs (e.g., 96-well plates); components for carrying out immunoprecipitation (e.g. protein A); columns, especially spin columns, for affinity or size separation of oncogenic E6 protein from a sample (e.g. gel filtration columns, PDZ domain polypeptide columns, size exclusion columns, membrane cut-off spin columns etc.).
Subject kits may also contain control samples containing oncogenic or non-oncogenic E6, and/or a dilution series of oncogenic E6, where the dilution series represents a range of appropriate standards with which a user of the kit can compare their results and estimate the level of oncogenic E6 in their sample. Such a dilution series may provide an estimation of the progression of any cancer in a patient. Fluorescence, color, or autoradiological film development results may also be compared to a standard curves of fluorescence, color or film density provided by the kit.
In addition to above-mentioned components, the subject kits typically further include instructions for using the components of the kit to practice the subject methods. The instructions for practicing the subject methods are generally recorded on a suitable recording medium. For example, the instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e., associated with the packaging or subpackaging) etc. In other embodiments, the instructions are present as an electronic storage data file present on a suitable computer readable storage medium, e.g. CD-ROM, diskette, etc. In yet other embodiments, the actual instructions are not present in the kit, but means for obtaining the instructions from a remote source, e.g. via the internet, are provided. An example of this embodiment is a kit that includes a web address where the instructions can be viewed and/or from which the instructions can be downloaded. As with the instructions, this means for obtaining the instructions is recorded on a suitable substrate.
Also provided by the subject invention is are kits including at least a computer readable medium including programming as discussed above and instructions. The instructions may include installation or setup directions. The instructions may include directions for use of the invention with options or combinations of options as described above. In certain embodiments, the instructions include both types of information.
Providing the software and instructions as a kit may serve a number of purposes. The combination may be packaged and purchased as a means for producing rabbit antibodies that are less immunogenic in a non-rabbit host than a parent antibody, or nucleotide sequences them.
The instructions are generally recorded on a suitable recording medium. For example, the instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e., associated with the packaging or subpackaging), etc. In other embodiments, the instructions are present as an electronic storage data file present on a suitable computer readable storage medium, e.g., CD-ROM, diskette, etc, including the same medium on which the program is presented.
Methods of Determining if a Subject is Infected with an Oncogenic Strain of HPV
The present invention provides methods of detecting oncogenic HPV E6 protein in a sample and finds utility in diagnosing HPV infection in a subject. In many embodiment, a biological sample is obtained from a subject, and, the presence of oncogenic HPV E6 protein in the sample is determined. The presence of a detectable amount of oncogenic HPV E6 protein in a sample indicates indicates that the individual is infected with a oncogenic strain of HPV. In other embodiments, the level of oncogenic HPV E6 protein in a biological sample is determined, and compared to the amount of a control in the sample. The relative amount of oncogenic HPV E6 protein in a sample indicates the severity of the infection by HPV.
The methods generally involve two binding partners of oncogenic HPV E6 protein, one of which is a PDZ domain polypeptide, as described above. In general, the methods involve a) isolating the oncogenic HPV E6 protein from a sample using one of the binding partners, and b) detecting the oncogenic HPV E6 protein with the other binding partner.
Isolating Oncogenic HPV E6 Protein
In general, methods of the invention involve at least partially separating (i.e., isolating) native oncogenic HPV E6 protein from other proteins in a sample. This separation is usually achieved using a first binding partner for the oncogenic HPV E6. In many embodiments, the first binding partner is a PDZ domain polypeptide, or, in other embodiments an anti-HPV E6 antibody or mixture of antibodies.
In certain embodiments, one of the oncogenic HPV E6 binding partners is bound, directly or via a linker, to an insoluble support. Insoluble supports are known in the art and include, but are not limited to, a bead (e.g, magnetic beads, polystyrene beads, and the like); a membrane; and the like. In one non-limiting example, a PDZ domain polypeptide is bound to a magnetic bead. The PDZ domain polypeptide bound to the magnetic bead is contacted with the sample, and, after a complex is formed between the antibody and any E6 protein in the sample, a magnetic field is applied, such that the complex is removed from the sample. Where the PDZ domain polypeptide is bound to an insoluble support, such as a membrane, E6 protein bound to the PDZ domain polypeptide is removed from the sample by removing the membrane, or by transferring the sample to a separate container. Where the PDZ domain polypeptide is bound to a bead, the E6 protein bound to the bead is removed from the sample by centrifugation or filtration. Such embodiments are envisioned using a different E6 binding partner, e.g., an anti-E6 antibody.
In general, a suitable separation means is used with a suitable platform for performing the separation. For example, where oncogenic HPV E6 is separated by binding to PDZ domain polypeptides, the separation is performed using any of a variety of platforms, including, but not limited to, affinity column chromatography, capillary action or lateral flow test strips, immunoprecipitation, etc.
In many embodiments, oncogenic HPV E6 is separated from other proteins in the sample by applying the sample to one end of a test strip, and allowing the proteins to migrate by capillary action or lateral flow. Methods and devices for lateral flow separation, detection, and quantitation are known in the art. See, e.g., U.S. Pat. Nos. 5,569,608; 6,297,020; and 6,403,383. In these embodiments, a test strip comprises, in order from proximal end to distal end, a region for loading the sample (the sample-loading region) and a test region containing an oncogenic E6 protein binding partner, e.g., a region containing an PDZ domain polypeptide or, in other embodiments, a region containing an anti-E6 antibody. The sample is loaded on to the sample-loading region, and the proximal end of the test strip is placed in a buffer. oncogenic E6 protein is captured by the bound antibody in the first test region. Detection of the captured oncogenic E6 protein is carried out as described below. For example, detection of captured E6 proteins is carried out using detectably labeled antibody specific for an epitope of E6 proteins that is common to all oncogenic E6 proteins, or a mixture of antibodies that can, together, bind to all oncogenic E6 proteins. In alternative embodiments, an E6 antibody may be present in the test region and detection of oncogenic E6 bound to the E6 antibody uses a labeled PDZ domain polypeptide.
Detecting and Quantitating Oncogenic E6 Protein
Once oncogenic E6 protein is separated from other proteins in the sample, oncogenic E6 protein is detected and/or the level or amount of oncogenic E6 protein is determined (e.g., measured). As discussed above, oncogenic E6 protein is generally detected using a binding partner, e.g. an antibody or antibodies specific to E6, or a PDZ domain polypeptide.
Detection with a specific antibody is carried out using well-known methods. In general, the binding partner is detectably labeled, either directly or indirectly. Direct labels include radioisotopes (e.g., 125I; 35S, and the like); enzymes whose products are detectable (e.g., luciferase, β-galactosidase, horse radish peroxidase, and the like); fluorescent labels (e.g., fluorescein isothiocyanate, rhodamine, phycoerythrin, and the like); fluorescence emitting metals, e.g., 152Eu, or others of the lanthanide series, attached to the antibody through metal chelating groups such as EDTA; chemiluminescent compounds, e.g., luminol, isoluminol, acridinium salts, and the like; bioluminescent compounds, e.g., luciferin; fluorescent proteins; and the like. Fluorescent proteins include, but are not limited to, a green fluorescent protein (GFP), including, but not limited to, a “humanized” version of a GFP, e.g., wherein codons of the naturally-occurring nucleotide sequence are changed to more closely match human codon bias; a GFP derived from Aequoria victoria or a derivative thereof, e.g., a “humanized” derivative such as Enhanced GFP, which are available commercially, e.g., from Clontech, Inc.; a GFP from another species such as Renilla reniformis, Renilla mulleri, or Ptilosarcus guernyi, as described in, e.g., WO 99/49019 and Peelle et al. (2001) J. Protein Chem. 20:507-519; “humanized” recombinant GFP (hrGFP) (Stratagene); any of a variety of fluorescent and colored proteins from Anthozoan species, as described in, e.g., Matz et al. (1999) Nature Biotechnol. 17:969-973; and the like.
Indirect labels include second antibodies specific for E6-specific antibodies, wherein the second antibody is labeled as described above; and members of specific binding pairs, e.g., biotin-avidin, and the like.
In some embodiments, a level of oncogenic E6 is quantitated. Quantitation can be carried out using any known method, including, but not limited to, enzyme-linked immunosorbent assay (ELISA); radioimmunoassay (RIA); and the like. In general, quantitation is accomplished by comparing the level of expression product detected in the sample with a standard curve.
In some embodiments, oncogenic HPV E6 is separated on a test strip, as described above. In these embodiments, oncogenic HPV E6 is detected using a detectably labeled binding partner that binds oncogenic HPV E6. Oncogenic HPV E6 may be quantitated using a reflectance spectrophotometer, or by eye, for example.
Biological Samples
Biological samples to be analyzed using the methods of the invention are obtained from any mammal, e.g., a human or a non-human animal model of HPV. In many embodiments, the biological sample is obtained from a living subject.
In some embodiments, the subject from whom the sample is obtained is apparently healthy, where the analysis is performed as a part of routine screening. In other embodiments, the subject is one who is susceptible to HPV, (e.g., as determined by family history; exposure to certain environmental factors; etc.). In other embodiments, the subject has symptoms of HPV (e.g., cervical warts, or the like). In other embodiments, the subject has been provisionally diagnosed as having HPV (e.g. as determined by other tests based on e.g., PCR).
The biological sample may be derived from any tissue, organ or group of cells of the subject. In some embodiments a cervical scrape, biopsy, or lavage is obtained from a subject.
In some embodiments, the biological sample is processed, e.g., to remove certain components that may interfere with an assay method of the invention, using methods that are standard in the art. In some embodiments, the biological sample is processed to enrich for proteins, e.g., by salt precipitation, and the like. In certain embodiments, the sample is processed in the presence proteasome inhibitor to inhibit degradation of the E6 protein.
In the assay methods of the invention, in some embodiments, the level of E6 protein in a sample may be quantified and/or compared to controls. Suitable control samples are from individuals known to be healthy, e.g., individuals known not to have HPV. Control samples can be from individuals genetically related to the subject being tested, but can also be from genetically unrelated individuals. A suitable control sample also includes a sample from an individual taken at a time point earlier than the time point at which the test sample is taken, e.g., a biological sample taken from the individual prior to exhibiting possible symptoms of HPV.
Utility
The methods of the instant invention are useful for a variety of diagnostic analyses. The instant methods are useful for diagnosing infection by an oncogenic strain of HPV in an individual; for determining the likelihood of having cancer; for determining a patient's response to treatment for HPV; for determining the severity of HPV infection in an individual; and for monitoring the progression of HPV in an individual.
The subject methods may generally be performed on biological samples from living subjects. A particularly advantageous feature of the invention is that the methods can simultaneously detect, in one reaction, all known oncogenic strains of HPV.
PDZ proteins are known to bind certain carboxyl-terminal sequences of proteins (PLs). PL sequences that bind PDZ domains are predictable, and have been described in greater detail in U.S. patent applications Ser. Nos. 09/710059, 09/724553 and 09/688017. One of the major classes of PL motifs is the set of proteins terminating in the sequences —X—(S/T)-X—(V/I/L). We have examined the C-terminal sequences of E6 proteins from a number of HPV strains. All of the strains determined to be oncogenic by the National Cancer Institute exhibit a consensus PDZ binding sequence. Those E6 proteins from papillomavirus strains that are not cancerous lack a sequence that would be predicted to bind to PDZ domains, thus suggesting that interaction with PDZ proteins is a prerequisite for causing cancer in humans. This correlation between presence of a PL and ability to cause cancer is 100% in the sequences examined (Table 3A). In theory, with the disclosed PL consensus sequences from the patents listed supra, new variants of HPVs can be assessed for their ability to bind PDZ proteins and oncogenicity can be predicted on the basis of whether a PL is present. Earlier this year, five new oncogenic strains of Human papillomavirus were identified and their E6 proteins sequenced. As predicted, these proteins all contain a PL consensus sequence (Table 3B).
These tables provide a classification of the HPV strains based on the sequence of the C-terminal four amino acids of the E6 protein encoded by the HPV genome. The 21 oncogenic strains of HPV fall into one of 10 classes, and HPV strains not specifically listed above may also fall into these classes. As such, it is desirable to detect HPV strains from all 10 classes: the instant methods provide such detection.
In order to determine the PDZ domains that can be used to detect oncogenic E6 proteins in a diagnostic assay, the ‘G assay’ (described supra) was used to identify interactions between E6 PLs and PDZ domains. Peptides were synthesized corresponding to the C-terminal amino acid sequences of E6 proteins from oncogenic strains of human papillomavirus. These peptides were assessed for the ability to bind PDZ domains using the G-assay described above and PDZ proteins synthesized from the expression constructs described in greater detail in U.S. patent applications Ser. Nos. 09/710059, 09/724553 and 09/688017. Results of these assays that show a high binding affinity are listed in Table 4 below.
As we can see below, there a large number of PDZ domains that bind some of the oncogenic E6 proteins. However, only the second PDZ domain from MAGI-1 seems to bind all of the oncogenic E6 PLs tested. The PDZ domain of TIP-1 binds all but one of the oncogenic E6 PLs tested, and may be useful in conjunction with MAGI-1 domain 2 for detecting the presence of oncogenic E6 proteins.
In a similar manner, peptides corresponding to the C-terminal ends of several non-oncogenic E6 proteins were tested with the G-assay. None of the peptides showed any affinity for binding PDZ domains.
This example describes the cloning of HPV E6 genes or portions of HPV E6 genes into eukaryotic expression vectors in fusion with a number of protein tags, including but not limited to Glutathione S-Transferase (GST), Enhanced Green Fluorescent Protein (EGFP), or Hemagglutinin (HA).
A. Strategy
cDNA fragments were generated by RT-PCR from HPV cell line (cervical epidermoid carcinoma, ATCC# CRL-1550 and CRL-1595 for HPV E6 16 and 18, respectively) derived RNA, using random (oligo-nucleotide) primers (Invitrogen Cat.#48190011). DNA fragments corresponding to HPV E6 were generated by standard PCR, using above purified cDNA fragments and specific primers (see Table 5). Primers used were designed to create restriction nuclease recognition sites at the PCR fragment's ends, to allow cloning of those fragments into appropriate expression vectors. Subsequent to PCR, DNA samples were submitted to agarose gel electrophoresis. Bands corresponding to the expected size were excised. DNA was extracted by Sephaglas Band Prep Kit (Amersham Pharmacia Cat#27-9285-01) and digested with appropriate restriction endonuclease. Digested DNA samples were purified once more by gel electrophoresis, according to the same protocol used above. Purified DNA fragments were coprecipitated and ligated with the appropriate linearized vector. After transformation into E. coli, bacterial colonies were screened by colony PCR and restriction digest for the presence and correct orientation of insert. Positive clones were innoculated in liquid culture for large scale DNA purification. The insert and flanking vector sites from the purified plasmid DNA were sequenced to ensure correct sequence of fragments and junctions between the vectors and fusion proteins.
B. Vectors:
Cloning vectors were pGEX-3X (Amersham Pharmacia #27-4803-01), MIE (a derivative of MSCV, containing IRES and EGFP, generated by recombinant DNA technology), pmKit, pcDNA3.1 (Invitrogen, modified to include a HA tag upstream of the cloning site) and pMAL (New England Biolabs Cat#N8076S, polylinker modified in house to include BamH1 and EcoR1 sites).
DNA fragments containing the ATG-start codon and the TAG-stop codon of HPV E6 were cloned into pGEX3×. HPV E6 genes, and 3′ truncated (ΔPL) versions, were subsequently cloned into MIE (MSCV-IRES-EGFP) vector, pcDNA-HA vector, and pmKit vector, using the purified HPV E6-pGEX3× fusion plasmid as the PCR template, and using the same purification protocols as listed above. Truncated versions of HPV E6 have a stop codon inserted after the −3 position amino acid, so as to delete the last three amino acids from the coding region of the gene.
C. Constructs:
Primers used to generate DNA fragments by PCR are listed in Table 5. PCR primer combinations and restriction sites for insert and vector are listed below.
1. Human Papillomavirus (HPV) E6 16
Primers: 2542 & 2543
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): BamH1/EcoR1
pGEX-3X contains GST to the 5′ end (upstream) of the cloning site
Primers: 2560 & 2561
Vector Cloning Sites(5′/3′): EcoR1/BamH1
Insert Cloning Sites(5′/3′): EcoR1/BamH1
MIE contains IRES and EGFP to the 3′ end (downstream) of the cloning site
Primers: 2560 & 2562
Vector Cloning Sites(5′/3′): EcoR1/BamH1
Insert Cloning Sites(5′/3′): EcoR1/BamH1
MIE contains IRES and EGFP to the 3′ end (downstream) of the cloning site
Primers: 2603 & 2604
Vector Cloning Sites(5′/3′): Hind III/Hind III
Insert Cloning Sites(5′/3′): Hind III/Hind III
pcDNA3.1 (modified) contains HA to the 5′ end (upstream) of the cloning site
Primers: 2603 & 2605
Vector Cloning Sites(5′/3′): Hind III/Hind III
Insert Cloning Sites(5′/3′): Hind III/Hind III
pcDNA3.1 (modified) contains HA to the 5′ end (upstream) of the cloning site
Primers: 2606 & 2607
Vector Cloning Sites(5′/3′): Sal I/Xho I
Insert Cloning Sites(5′/3′): Sal I/Xho I
Primers: 2606 & 2608
Vector Cloning Sites(5′/3′): Sal I/Xho I
Insert Cloning Sites(5′/3′): Sal I/Xho I
2. Human Papillomavirus (HPV) E6 18
Primers: 2548 & 2549
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): Bgl II/EcoR1
pGEX-3X contains GST to the 5′ end (upstream) of the cloning site
Primers: 2563 & 2564
Vector Cloning Sites(5′/3′): EcoR1/BamH1
Insert Cloning Sites(5′/3′): EcoR1/Bgl II
MIE contains IRES and EGFP to the 3′ end (downstream) of the cloning site
Primers: 2563 & 2565
Vector Cloning Sites(5′/3′): EcoR1/BamH1
Insert Cloning Sites(5′/3′): EcoR1/Bgl II
MIE contains IRES and EGFP to the 3′ end (downstream) of the cloning site
Primers: 2615 & 2616
Vector Cloning Sites(5′/3′): Hind III/Hind III
Insert Cloning Sites(5′/3′): Hind III/Hind III
pcDNA3.1 (modified) contains HA to the 5′ end (upstream) of the cloning site
Primers: 2615 & 2617
Vector Cloning Sites(5′/3′): Hind III/Hind III
Insert Cloning Sites(5′/3′): Hind III/Hind III
pcDNA3.1 (modified) contains HA to the 5′ end (upstream) of the cloning site
Primers: 2612 & 2613
Vector Cloning Sites(5′/3′): Sal I/Xho I
Insert Cloning Sites(5′/3′): Sal I/Xho I
Primers: 2612 & 2614
Vector Cloning Sites(5′/3′): Sal I/Xho I
Insert Cloning Sites(5′/3′): Sal I/Xho I
D. GST Fusion Protein Production and Purification
The constructs using pGEX-3X expression vector were used to make fusion proteins according to the protocol outlined in the GST Fusion System, Second Edition, Revision 2, Pharmacia Biotech. Method II and was optimized for a 1L LgPP.
Purified DNA was transformed into E. coli and allowed to grow to an OD600 of 0.4-0.8 (600λ). Protein expression was induced for 1-2 hours by addition of IPTG to cell culture. Cells were harvested and lysed. Lysate was collected and GS4B beads (Pharmacia Cat#17-0756-01) were added to bind GST fusion proteins. Beads were isolated and GST fusion proteins were eluted with GEB II. Purified proteins were stored in GEB II at −80° C.
Purified proteins were used for ELISA-based assays and antibody production.
This example describes the cloning of PDZ domain containing genes or portions of PDZ domain containing genes were into eukaryotic expression vectors in fusion with a number of protein tags, including but not limited to Glutathione S-Transferase (GST), Enhanced Green Fluorescent Protein (EGFP), or Hemagglutinin (HA).
A. Strategy
DNA fragments corresponding to PDZ domain containing genes were generated by RT-PCR from RNA from a library of individual cell lines (CLONTECH Cat#K4000-1) derived RNA, using random (oligo-nucleotide) primers (Invitrogen Cat.#48190011). DNA fragments corresponding to PDZ domain containing genes or portions of PDZ domain containing genes were generated by standard PCR, using above purified cDNA fragments and specific primers (see Table 6). Primers used were designed to create restriction nuclease recognition sites at the PCR fragment's ends, to allow cloning of those fragments into appropriate expression vectors. Subsequent to PCR, DNA samples were submitted to agarose gel electrophoresis. Bands corresponding to the expected size were excised. DNA was extracted by Sephaglas Band Prep Kit (Amersham Pharmacia Cat#27-9285-01) and digested with appropriate restriction endonuclease. Digested DNA samples were purified once more by gel electrophoresis, according to the same protocol used above. Purified DNA fragments were coprecipitated and ligated with the appropriate linearized vector. After transformation into E. coli, bacterial colonies were screened by colony PCR and restriction digest for the presence and correct orientation of insert. Positive clones were innoculated in liquid culture for large scale DNA purification. The insert and flanking vector sites from the purified plasmid DNA were sequenced to ensure correct sequence of fragments and junctions between the vectors and fusion proteins.
B. Vectors:
All PDZ domain-containing genes were cloned into the vector pGEX-3X (Amersham Pharmacia #27-4803-01, Genemed Acc#U13852, GI#595717), containing a tac promoter, GST, Factor Xa, β-lactamase, and lac repressor.
The amino acid sequence of the pGEX-3X coding region including GST, Factor Xa, and the multiple cloning site is listed below. Note that linker sequences between the cloned inserts and GST-Factor Xa vary depending on the restriction endonuclease used for cloning. Amino acids in the translated region below that may change depending on the insertion used are indicated in small caps, and are included as changed in the construct sequence listed in (C).
In addition, TAX Interacting Protein 1 (TIP1), in whole or part, was cloned into many other expression vectors, including but not limited to CD5γ, PEAK10 (both provided by the laboratory of Dr. Brian Seed at Harvard University and generated by recombinant DNA technology, containing an IgG region), and MIN (a derivative of MSCV, containing IRES and NGFR, generated by recombinant DNA technology).
C. Constructs:
Primers used to generate DNA fragments by PCR are listed in Table 6. PCR primer combinations and restriction sites for insert and vector are listed below, along with amino acid translation for insert and restriction sites. Non-native amino acid sequences are shown in lower case.
1. DLG 1, PDZ domain 2 of 3:
Primers: 1928 & 1929
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): BamH1/EcoR1
2. MAGI 1. PDZ domain 2 of 6:
Primers: 1453 & 1454
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): BamH1/EcoR1
3. TAX Interacting Protein 1 (TIP1):
Primers: 399& 400
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): BamH1/EcoR1
Primers: 1319& 1320
Vector Cloning Sites(5′/3′): Bam H1/EcoR1
Insert Cloning Sites(5′/3′): BamH1/EcoR1
Primers: 2753& 2762
Vector Cloning Sites(5′/3′): EcoR1/EcoR1
Insert Cloning Sites(5′/3′): EcoR1/EcoR1
Primers: 2584& 2585
Vector Cloning Sites(5′/3′): Bam H1/Bam H1
Insert Cloning Sites(5′/3′): BamH1/Bam H1
D. GST Fusion Protein Production and Purification
The constructs using pGEX-3X expression vector were used to make fusion proteins according to the protocol outlined in the GST Fusion System, Second Edition, Revision 2, Pharmacia Biotech. Method II and was optimized for a 1L LgPP.
Purified DNA was transformed into E. coli and allowed to grow to an OD600 of 0.4-0.8 (600λ). Protein expression was induced for 1-2 hours by addition of IPTG to cell culture. Cells were harvested and lysed. Lysate was collected and GS4B beads (Pharmacia Cat#17-0756-01) were added to bind GST fusion proteins. Beads were isolated and GST fusion proteins were eluted with GEB II. Purified proteins were stored in GEB II at −80° C.
Purified proteins were used for ELISA-based assays and antibody production.
E. IgG Fusion Protein Production and Purification
The constructs using the CD5 gamma or Peak10IgG expression vectors were used to make fusion protein. Purified DNA vectors were transfected into 293 EBNA T cells under standard growth conditions (DMEM +10% FCS) using standard calcium phosphate precipitation methods (Sambrook, Fritsch and Maniatis, Cold Spring Harbor Press) at a ratio of ˜1 ug vector DNA for 1 million cells. This vector results in a fusion protein that is secreted into the growth medium. Transiently transfected cells are tested for peak expression, and growth media containing fusion protein is collected at that maxima (usually 1-2 days). Fusion proteins are either purified using Protein A chromatography or frozen directly in the growth media without addition.
A. Abstract
An experiment was conducted to demonstrate and confirm that PDZ domains would only recognize the C-termini of full-length oncogenic HPV E6 proteins and not non-oncogenic E6 variants. This validates the method of using peptides representing the PL sequences of E6 proteins by asking if the PDZ binding can be reproduced using full length E6 fusion proteins.
Briefly, GST-E6 fusion proteins were constructed as described in Example 3 corresponding to the full length protein sequence of E6 from HPV18 (oncogeneic) and HPV11 (non-oncogenic). Using a modified ELISA assay, binding of a TIP-TIP-IgG fusion protein (two copies of the TIP-1 PDZ domain fused to the hIgG constant region, purification of fusion protein partially described in Example 4) to these two E6 variants was assessed.
A subsequent experiment is also shown to demonstrate that the assay for binding to E6 using GST-Tip or GST-Magi fusion proteins is not significantly affected by incubation at 4° C. or room temperature (RT).
B. Modified ELISA Method
Reagents and Materials
TIP-1, a representative PDZ domain that binds most oncogenic E6 PLs (EXAMPLE 2), is able to specifically recognize PLs from full length oncogenic E6 variants (HPV18-E6) without binding to non-oncogenic variants (HPV 11-E6;
Furthermore, this assay is robust and the off rates are stable enough that the incubation steps of this assay can be performed at 4° C. or RT. Little difference in signal is seen between the two temperatures for either GST-Magi1 of GST-TIP1 binding to E6 (
E6 activity may be further determined by its ability to bind DNA, or to allow degradation of p53 in the presence of a lysate, Zn2+ binding, etc.
Using the G-assay described above, several GST-PDZ domain fusion proteins were tested to determine their relative binding strength to the PL of the HPV16 E6 protein. Peptide corresponding to the PL of HPV16 E6 was titrated against a constant amount of GST-PDZ domain fusion and the results are shown below. These results demonstrate that although a number of PDZ domains can bind the E6 protein from HPV16, the first functional domain of MAGI1 (domain 2 in this specification) binds the most tightly, making it the most suitable for diagnostic purposes. This is unexpected, especially in conjunction with MAGI1 being the only PDZ domain containing protein demonstrated to bind to all classes of oncogenic E6 proteins identified. Together, these suggest that MAGI1 is a useful capture/detection agent for oncogenic HPV infections.
In order to achieve the added benefits of a sandwich ELISA-based diagnostic for oncogenic HPV infection, high-affinity antibodies specific to E6 proteins should be generated. Ideally, monoclonal antibodies could be generated from these animals to have a continually renewable resource for the diagnostic.
Balb/c mice were injected with 25 ug of bacterially purified GST-HPV18E6 protein at 5 day intervals (Josman Labs). Sera from these mice were collected 3 days after each injection of antigen and tested for reactivity with GST-14PV 18E6 (the immunogen) or GST alone following anti GST-depletion (Pharmacia protocol). The results using sera collected at day 28 are shown in
Many other proteins from pathogens can be detected using proteins or compounds directed at detection of a PDZ:PL interaction. Table 8 contains some exemplary proteins that could be detected using technology disclosed herein, but is not meant to be limiting in any manner.
A) Abstract:
Experiments were designed and performed to determine quantities of endogenous E6 protein in HPV16 infected cervical cancer cell lines. Results demonstrate that HPV16 infected cervical cancer cell lines contain in the order of 10,000 to 100,000 molecules E6. From this finding is concluded, that E6 protein can be used as a diagnostic or prognostic marker for cellular HPV infection. Use of protein degradation pathway inhibitors may facilitate such an assay.
B) Methods:
Immunoprecipitation of E6 protein:
HPV16-infected cervical cancer cell lines SiHa and CasKi are washed with cold PBS and resuspended in HEPES lysis buffer (50 mM HEPES pH 7.4, 150 mM NaCl, 10% glycerol, 0.5% triton X-100, 1 mg/ml BSA, one pellet protease inhibitor cocktail (Roche), and 1 mM PMSF) at 2×107 cells/ml. Lysis proceeds on ice for 30 min. and lysates are cleared by centrifugation at 14,000× g for 5 minutes at 4° C. E6 proteins are immunoprecipitated with a mouse anti-E6 antibody (clone 6F4) and protein G beads (Pharmacia, Piscataway, N.J.). After 2 hours incubation at 4° C. with rotation, beads are washed 3 times with washing Buffer [50 mM HEPES pH 7.4, 150 mM NaCl, 10% glycerol, 0.1% Triton X-100, protease inhibitor cocktail (CALBIOCHEM), 1 mM PMSF]. Pellets are resuspended in SDS-PAGE sample buffer and analyzed by immuno blotting using 6F4 anti-E6 antibody and anti-mouse-IgG-HRP conjugated (Jackson Immuno Research).
Detection of E6 Protein from Cervical Cancer Cell Lysates by Western Technology:
SiHa and CasKi cervical cancer cell lines were lysed at 2×107 cells/ml in lysis buffer 30 min. on ice. Lysates corresponding to approx. 106 cells are immediately resolved on a 12% SDS-PAGE gel followed by transfer to a PVDF membrane. E6 proteins were detected with 6F4 anti-E6 HPV16 antibody and anti-mouse-IgG-HRP conjugated (Jackson Immuno Research).
C) Results:
To determine the apparent molecular weight of endogenous E6 protein as present in cervical cancer cells upon infection with HPV16 and to ensure that a anti E6 monoclonal antibody-specific band seen in PAGE represents viral E6 protein, 293 EBNA-T cells were transfected with a construct expressing untagged E6 protein of HPV type 16. Cell lysates were prepared of those cells, and HPV infected SiHa cervical cancer cells. E6 protein from both lysates (transfected and HPV infected) was immunoprecipitated by use of an anti E6-specific monoclonal antibody. Both lysates were analyzed side by side using PAGE technology (
In a different experimental procedure, endogenous viral E6 protein of HPV 16 infected cervical cancer cell line SiHa and CasKi was directly detected from their cell lysates (
To test, whether E6 in vivo stability can be enhanced by selectively blocking proteasome involved in protein degradation, cell lysates of some samples were treated with proteasome inhibitor MG132. In those samples, the E6 specific band is about 2-3 times more intense. This demonstrates, that addition of an appropriate mixture of protein degradation pathway inhibiting agents can be used to increase the signal specific to E6 protein by augmenting its accumulation temporarily in cells.
Quantities of E6 protein in lysates were measured by comparing E6-Specific signal in PAGE with signals obtained by MBP-E6 (HPV16) fusion protein loaded onto the same gel. In some cases, MBP-E6 fusion protein was digested with factor X to release the E6 portion only. Signal intensity comparison studies demonstrated, that cervical cancer derived cell lines injected with HPV16 (SiHa, CasKi) contain E6 at a concentration of 0.3 to 3 ng per 1×106 cells. It is concluded, that quantities and stability of E6 are such that detection by an E6-specific (ELISA-) assay will be feasible.
A) Abstract
Experiments were undertaken to test, whether oncogenic E6-PL-detector will selectively bind endogenous E6 of cells transfected with E6 encoding vector. Moreover, it was tested whether the oncogenic E6-PL-detector can be used to separate E6 from other molecules in the cell lysate subsequent to binding. Findings demonstrate that oncogenic E6-PL-detector, is selective and can be applied to separate E6 protein from the complex mixture of cell lysate molecules.
B) Methods
Pull Down of E6 Protein with Recombinant PDZ Proteins:
GST-PDZ fusion proteins (i.e. Magil PDZ domain #2, Syn2bp, Magi3 PDZ domain #1, Tip 1, PSD-95 PDZ domain #2, and SAST1 were tested in pull down experiments. Briefly, 10 ug recombinant GST-PDZ proteins were incubated with 30 ul of glutathione-sepharose beads in 1 ml of buffer [50 mM HEPES pH 7.4, 150 mM NaCl, 10% glycerol, 0.1% Triton X-100, protease inhibitor cocktail, 1 mM PMSF] for 1 h at 4° C. with rotation. Subsequently, cell lysates of 107 293 cells transiently transfected with either pMKit-HA-HPV16-E6 or pMKit-HA vector alone were incubated with the beads bound to PDZ proteins for 3 h at 4° C. with rotation. Beads were washed and analyzed in 12% SDS-PAGE gel electrophoresis followed by Western blotting. Membranes were probed with biotin conjugated anti-HA antibodies (clones 3F10, or 12CA5, Boebringer Mannheim) and HRP-Streptavidin (Zymed).
Alternatively, cell lysates from 293 cells transiently transfected with pmKit-HA, pmkit-HPV16-HA-E6 or pmKit-HA-HPV16 E6-ΔPL, were incubated with recombinant GST-Magil-PDZ domain 2 protein and immobilized on glutathione-sepharose beads and bound fractions were immunoblotted with anti HA antibodies. In parallel, lysates were immunoprecipitated and detected with anti-HA antibodies.
C) Results
G-assay PDZ-E6-PL binding studies and the determination of experimental binding affinities of the E6-PDZ interactions suggested candidate PDZ domains to be tested for the engineering of an oncogenic E6-PL-detector. In a “pull down” experiment, five different PDZ domains (Tip1; Magi1 domain 2; Sast2; Psd95 domain 2; Synaptojanin-2 binding protein) were tested for pull down of endogenous over expressed E6 from cell lysate. Lysates of cells transfected with HA-tagged E6 HPV-16 were incubated with GST-PDZ fusion protein representing the above PDZ domains bound to Sepharose beads (
A) Abstract:
Experiments are described, in which the oncogenic E6-PL detector is used to selectively detect presence of E6 protein in HPV infected cells via a sandwich ELISA. The specific capturing of oncogenic E6 but not non-oncogenic E6 demonstrates that the PDZ based oncogenic E6-PL detector can be applied for a E6 detection based diagnostic test for HPV infection and/or cervical cancer test.
B) Methods:
Sandwich type 1 ELISA: Anti-E6 antibody is coated onto a 96-well Polysorp or Maxysorp ELISA plate at 5 ug/ml in PBS (100 ul/well) overnight at 4° C. Plates were washed with PBS and blocked with 200 ul PBS/2% BSA for 2 hours at 4° C. Cell lysates diluted in PBS/2% BSA are added and incubated at room temperature for 1 hour. After 3 washes with PBS, 100 ul of oncogenic E6 detector (for example MAGI1-MAGI1-IgG or GST-MAGI1-PDZ1) at 5 ug/ml was added in PBS/2% BSA, and plates are incubated at room temperature for 45 min. Plates are then washed 3 times with PBS and incubated with anti-hIgG-HRP (Jackson Immuno Research) or anti-GST-HRP (Pharmacia) at the appropriate concentration in PBS/2% BSA at room temperature for 45 minutes. After 5 washes with 50 mM Tris/0.2% Tween-20, plates were incubated with 100 ul /well TMB substrate (Dako Industries). The colorimetric reaction is stopped at appropriate times (usually after 20 minutes) by addition of 100 ul of 0.1 M H2SO4 and plates read at A450 nm in an ELISA plate reader.
In a variant of sandwich 1 ELISA, cell lysates were preincubated with oncogenic E6 detector at 2.5-5 ug/ml final concentration, for 1-2 hours at 4° C., prior to adding to the anti-E6 antibody coated plate.
Sandwich type 2 ELISA: In sandwich 2, reagents and procedures mostly correspond to those used in sandwich 1. In contrast to sandwich 1, 100 ul of oncogenic E6 detector is coated onto the ELISA plate and the anti-E6 antibody is used for detection of oncogenic detector-bound E6, followed by anti-mouse IgG-HRP (Jackson Immuno Research). In a modified version of sandwich 2, biotinylated reagents (anti-E6 antibody or oncogenic detector) will be used followed by streptavidin-HRP to further diminish background and to increase sensitivity.
C) Results:
A sandwich ELISA was conceived in two different variations. In Type 1 sandwich ELISA, E6 protein present in cell lysates in captured by E6-specific monoclonal antibody, and detection of specifically oncogenic variants occurs via the oncogenic E6-PL detector. In the type 2 ELISA set up, oncogenic E6 protein is captured via the oncogenic E6-PL detector to the solid phase and E6 detection occurs via a specific E6 antibody or another E6 binding specific agent like nucleic acid based binding compounds, chemicals binding E6, E6 binding proteins or a combination of those compounds. Cells were lysed directly on a tissue culture plate and lysates were precleared by centrifugation from insoluble components. Lysates were preincubated at 4° C. with oncogenic E6-PL detector, a fusion protein of GST and Magi1 PDZ domain 2. Subsequently, lysates were loaded onto E6-specific antibody coated ELISA plates. Detection occurred via addition of HRP conjugated GST-specific antibody and addition of the HRP substrate TMB after appropriate washes between different incubation steps. Detection signal is constituted by a colorimetric change that is quantified using absorbance measurements at 450 nm.
Results obtained from a type 1 ELISA assay are shown. HPV 16-E6 of over expressing E6 transfected 293 EBNA-T cells and of HPV16 infected cervical cancer derived cell lines was detected. For HPV infected cells, the detection limit is at approximately 250,000 cells (
A) Abstract:
Experiments were conducted to demonstrate that the cervical cancer ELISA test types 1 and 2 can be performed using a membrane based format. In the membrane-based form of the cervical cancer diagnostic kit, the principles of the traditional ELISA based sandwich 1 and 2 are maintained, especially with regard to the capturing or detection of exclusively the oncogenic forms of E6. Sensitivity is found to be largely increased in the membrane based assay versus the traditional ELISA.
B) Methods:
Preblock 12 well coming plates (tissue culture treated with lid, polystyrene, 22 mm well diameter) with 2 ml PBS/2% BSA and then rinse 3× with 2 ml PBS Spot nitrocellulose membrane with 2 ul GST-Magi1 domain 2 solution (88.6, 0.17 mg/ml) using 2 ul pipetman (duplicate spots in 1×1.5 cm membrane, transblot, transfer medium, supported nitrocellulose membrane, catalog no. 162-0097 (0.2 uM), Lot No. 8934). Allow to air dry for ˜5-10 minutes.
Hydrate membrane with 1 ml PBS for a couple of minutes in plate.
Block membrane in each well with 1 ml PBS/2% BSA for 30 minutes at room temperature while rocking
Wash 3× with PBS ˜5-10 minutes/wash, 1 ml/wash, aspirate directly first wash. OK to wash at room temperature.
Incubate membrane with cell lysate, ˜300 ul, 3 million cells total, for 30 minutes at room temperature (rock solutions). Also perform 1:10 dilutions (3 million, 300K, 30K, 3K) in PBS/2% BSA (33.33 ul sample, 300 ul PBS/2% BSA)
Wash 3× with PBS, 3-5′/wash, all at 4° C., 1 ml/wash.
Incubate membrane with anti-E6 (6F4) for 30 minutes at 4° C. (1:5000 dilution, or 1:50 of 1:100 6F4 in PBS/2% BSA). (Need 0.4 ml/well, and for 36 wells need 16 ml a) 1) 320 ul of 1:100 6F4, 15.68 ml PBS/2% BSA.
Wash 3× with PBS, 4° C., ˜5-10 minutes/wash.
Incubate with HRP-anti-mouse (1:1000) for 30′ at 4° C. while rocking(HRP-anti-Mouse Ig Horseradish peroxidase linked whole antibody from Sheep, Amersham, NA931V, lot 213295. Use 400 ul per well. For 36 wells would need a) 16 ul HRP-anti-mouse, 16 ml PBS/2% BSA
Wash 5× with PBS at 4° C., ˜5-10 minutes rocking/wash, last wash 10 minutes. Then aspirate last wash, and add 1 ml fresh PBS to each well.
Develop with ECL+ system in Petri dish and expose in Kodak film.
C) Results:
In a sandwich type 2 setup, GST-MAGI1 domain 2 oncogenic E6-PL detector was spotted on a membrane and decreasing quantities of HPV11 and HPV16 MBP-E6 fusion proteins were added for binding. Detection with E6 specific antibodies clearly demonstrated specificity of signal for oncogenic (HPV16), but not non-oncogenic E6 (HPV11). Upon longer exposure (5 minutes), HPV16 MBP-E6 quantities of 0.1 nanogram total were readily detectable (
In the same experiment, lysates of HPV16-E6 transfected cells and mock transfected cells were applied to a membrane based S2 test. E6-specific signal was obtained only for the E6 expressing cells, not for mock transfected cells (
In a subsequent experiment, lysates of HPV infected cells were tested (
The present invention is not to be limited in scope by the exemplified embodiments which are intended as illustrations of single aspects of the invention and any sequences which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.
All publications cited herein and priority documents cited in the Applicant Data Sheet are incorporated by reference in their entirety and for all purposes.
This application: a) claims the benefit of U.S. Provisional Application No. 60/409,298, filed Sep. 9, 2002, and U.S. Provisional Application No. 60/450,464, filed Feb. 27, 2003 b) is a CIP of of PCT Application No. US02/24655, filed Aug. 2, 2002, which application clalms the benefit of U.S. Provisional Application No. 60/309841, filed Aug. 3, 2001, and U.S. Provisional Application No. 60/360061, filed Feb. 25, 2002, and c) is a CIP of U.S. Non-Provisional Application No. 10/080,273, filed Feb. 19, 2002, now abandoned, which application clalms the benefit of U.S. Provisional Application No. 60/269,523, filed Feb. 16, 2001 all of which applications are incorporated herein by reference in their entirety.
This invention was made with Government support under Small Business Innovation Research Grant No. IR43CA103383-01, awarded by the National Cancer Institute. The Government may have certain rights in this invention.
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| Number | Date | Country |
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| 0523391 | Jan 1993 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20040018487 A1 | Jan 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60450464 | Feb 2003 | US | |
| 60409298 | Sep 2002 | US | |
| 60360061 | Feb 2002 | US | |
| 60309841 | Aug 2001 | US | |
| 60269523 | Feb 2001 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US02/24655 | Aug 2002 | US |
| Child | 10630590 | US | |
| Parent | 10080273 | Feb 2002 | US |
| Child | PCT/US02/24655 | US |
