Patent Application
20060068441
The present invention relates to the fields of gene regulation, autoimmunity, cancer, and apoptosis.
Goodpasture antigen binding protein (GPBP), is a non-conventional protein kinase that binds to and phosphorylates the human α3(IV)NC1 in vitro. [1,2,3] Its expression is associated with cells and tissue structures that are target of common autoimmune responses, including the alveolar and glomerular basement membranes [3]. GPBP Δ26 is an alternatively spliced GPBP variant, which is less active than GPBP, but more widely expressed [3]. A balanced expression of the two isoforms appears to be critical for homeostasis, whereas an augmented expression of GPBP relative to GPBPΔ26 has been associated with several autoimmune conditions, including Goodpasture disease and cutaneous lupus[3].
GPBP is expressed at very low levels in cancer cells and highly expressed in apoptotic blebs of differenced keratinocytes at the periphery of normal epidermis [3]. Keratinocytes from patients suffering skin autoimmune processes show an increased sensitivity to UV-induced apoptosis, and a premature apoptosis at the basal keratinocytes has been reported to occur in these patients [38-41]. GPBP is expressed in apoptotic bodies expanding from basal to peripheral strata in epidermis undergoing autoimmune attack [3]. Altered autoantigens, including phosphorylated versions thereof, have been reported to be produced and released from these apoptotic bodies [40]. All these data suggest that GPBP is part of an apoptotic-mediated strategy for desired cell removal that generates aberrant counterparts of critical cell components which operates illegitimately during autoimmune pathogenesis [3].
Pol κ is a member of the UmuC/DinB superfamily of DNA polymerases that can extend aberrant replication forks. Pol κ displays low fidelity, moderate processivity, and extends mispaired DNA by misaligning primer-template to generate −1 frameshift products [4-9]. Pol κ can bypass DNA lesions in both an error-prone [10,11] and an error-free [10] manner. These data indicate that pol κ is a DNA polymerase with a role in the cellular response to DNA-damage, and also in spontaneous mutagenesis, by facilitating base pairing at aberrant replication forks.
In the present study, we have determined that the structural genes encoding polK and GPBP are present in a head-to-head arrangement in the human genome at chromosome position 5q12-13, and that the genes share a common promoter from which the corresponding transcripts are expressed in a divergent mode. Our results demonstrate that TNF (α/β) induces divergent transcription directed by this promoter, suggesting that bi-directional promoters link the expression of proteins that are partners in biological programs which are orchestrated by TNF and are relevant in autoimmune pathogenesis. Furthermore we report the molecular cloning of pol κ76 an alternatively spliced variant preferentially expressed in skin and keratinocytes which like GPBP shows a relative augmented expression in cutaneous lupus, suggesting that pol κ76 and GPBP are partners in apoptotic programs which are relevant in autoimmune pathogenesis.
The present invention provides an isolated nucleic acid encoding pol κ76 consisting of the nucleic acid sequence of SEQ ID NO:30, or the complement thereof. In another embodiment of this aspect, the present invention provides an isolated and purified pol κ76 protein consisting of the amino acid sequence of SEQ ID NO:31.
In a further embodiment of this aspect, the present invention provides a method for detecting an autoimmune condition in a patient, comprising providing a tissue or body fluid sample from the patient; providing a control tissue or body fluid sample in which no autoimmune condition is present; and detecting altered pol κ76 RNA or protein expression in the tissue or body fluid sample compared to the control sample, wherein an alteration in pol κ76 RNA or protein expression relative to the control indicates the presence of an autoimmune condition.
In a further embodiment, the present invention provides a method for treating a patient with an autoimmune disorder or cancer, comprising modifying the expression or activity of pol κ76 RNA or protein in the patient with the autoimmune disorder.
Within this application, unless otherwise stated, the techniques utilized may be found in any of several well-known references such as: Molecular Cloning: A Laboratory Manual (Sambrook, et al., 1989, Cold Spring Harbor Laboratory Press), Gene Expression Technology (Methods in Enzymology, Vol. 185, edited by D. Goeddel, 1991. Academic Press, San Diego, Calif.), “Guide to Protein Purification” in Methods in Enzymology (M. P. Deutshcer, ed., (1990) Academic Press, Inc.); PCR Protocols: A Guide to Methods and Applications (Innis, et al. 1990. Academic Press, San Diego, Calif.), Culture of Animal Cells: A Manual of Basic Technique, 2nd Ed. (R. I. Freshney. 1987. Liss, Inc. New York, N.Y.), Gene Transfer and Expression Protocols, pp. 109-128, ed. E. J. Murray, The Humana Press Inc., Clifton, N.J.), and the Ambion 1998 Catalog (Ambion, Austin, Tex.).
As used herein, the term “COL4A3BP” means the genomic sequence encoding GPBP, as well as controlling sequences for GPBP mRNA expression.
As used herein, the term “POLK” means the genomic sequence encoding pol κ, as well as controlling sequences for pol κ mRNA expression.
As used herein, the term “GPBP” refers to Goodpasture antigen binding protein, and includes both monomers and oligomers thereof, as disclosed in WO 00/50607.
As used herein, the term “GPBPΔ26” refers to the Goodpasture antigen binding protein alternatively spliced product deleted for 26 amino acid residues as disclosed in WO 00/50607, and includes both monomers and oligomers thereof.
As used herein pol κ means the primary protein product of the POLK.
As used herein, pol κ76 means the 76 kDa alternatively spliced isoform product of the POLK.
In one aspect, the present invention provides an isolated nucleic acid encoding a pol κ76 polypeptide consisting of an amino acid sequence of SEQ ID NO:31. In a preferred embodiment, the isolated nucleic acid consists of the sequence of SEQ ID NO:30, the complement thereof, or the RNA expression product thereof.
An used herein, an “isolated nucleic acid sequence” refers to a nucleic acid sequence that is free of gene sequences which naturally flank the nucleic acid in the genomic DNA of the organism from which the nucleic acid is derived (i.e., genetic sequences that are located adjacent to the gene for the isolated nucleic molecule in the genomic DNA of the organism from which the nucleic acid is derived). An “isolated” pol κ76 nucleic acid sequence according to the present invention may, however, be linked to other nucleotide sequences that do not normally flank the recited sequence, such as a heterologous promoter sequence, or other vector sequences. It is not necessary for the isolated nucleic acid sequence to be free of other cellular material to be considered “isolated”, as a nucleic acid sequence according to the invention may be part of an expression vector that is used to transfect host cells (see below).
In another embodiment, the present invention provides an expression vector comprising an isolated nucleic acid encoding pol κ76 operatively linked to a promoter, wherein the isolated nucleic acid consists of the sequence of SEQ ID NO:30. In a preferred embodiment, the promoter is heterologous (i.e.: is not the naturally occurring POLK promoter).
A promoter and a pol κ76 nucleic acid sequence are “operatively linked” when the promoter is capable of driving expression of the pol κ76 DNA into RNA.
As used herein, the term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a “plasmid”, which refers to a circular double stranded DNA into which additional DNA segments may be cloned. Another type of vector is a viral vector, wherein additional DNA segments may be cloned into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors), are integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as “recombinant expression vectors” or simply “expression vectors”. In the present invention, the expression of any genes is directed by the promoter sequences of the invention, by operatively linking the promoter sequences of the invention to the gene to be expressed. In general, expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. In the present specification, “plasmid” and “vector” may be used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors, such as viral vectors (e.g., replication defective retroviruses, adenoviruses and adeno-associated viruses), which serve equivalent functions.
The vector may also contain additional sequences, such as a polylinker for subcloning of additional nucleic acid sequences, a polyadenylation signal to effect proper polyadenylation of the transcript. The nature of the polyadenylation signal is not believed to be crucial to the successful practice of the invention, and any such sequence may be employed, including but not limited to the SV40 and bovine growth hormone poly-A sites. Also contemplated as an element of the vector is a termination sequence, which can serve to enhance message levels and to minimize read through from the construct into other sequences. Finally, expression vectors typically have selectable markers, often in the form of antibiotic resistance genes, that permit selection of cells that carry these vectors.
In a further embodiment, the present invention provides recombinant host cells transfected with the expression vectors disclosed herein. As used herein, the term “host cell” is intended to refer to a cell into which a nucleic acid of the invention, such as a recombinant expression vector of the invention, has been introduced. Such cells may be prokaryotic, which can be used, for example, to rapidly produce a large amount of the expression vectors of the invention, or may be eukaryotic, for functional studies.
The terms “host cell” and “recombinant host cell” are used interchangeably herein. It should be understood that such terms refer not only to the particular subject cell but to the progeny or potential progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within the scope of the term as used herein.
The host cells can be transiently or stably transfected with one or more of the expression vectors of the invention. Such transfection of expression vectors into prokaryotic and eukaryotic cells can be accomplished via any technique known in the art, including but not limited to standard bacterial transformations, calcium phosphate co-precipitation, electroporation, or liposome mediated-, DEAE dextran mediated-, polycationic mediated-, or viral mediated transfection. (See, for example, Molecular Cloning: A Laboratory Manual (Sambrook, et al., 1989, Cold Spring Harbor Laboratory Press; Culture of Animal Cells: A Manual of Basic Technique, 2nd Ed. (R. I. Freshney. 1987. Liss, Inc. New York, N.Y.).
In another embodiment, the present invention provides an isolated and purified pol κ76 polypeptide consisting of the amino acid sequence of SEQ ID NO:31.
As used herein, an “isolated polypeptide” refers to a polypeptide that is substantially free of other proteins, cellular material and culture medium when isolated from cells or produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Thus, the protein can either be purified from natural sources, or recombinant protein can be purified from the transfected host cells disclosed above. In a preferred embodiment, the proteins are produced by the transfected cells disclosed above, and purified using standard techniques. (See for example, Molecular Cloning: A Laboratory Manual (Sambrook, et al., 1989, Cold Spring Harbor Laboratory Press.)) The protein can thus be purified from prokaryotic or eukaryotic sources. In various further preferred embodiments, the protein is purified from bacterial, yeast, or mammalian cells.
The protein may comprise additional sequences useful for promoting purification of the protein, such as epitope tags and transport signals. Examples of such epitope tags include, but are not limited to FLAG (Sigma Chemical, St. Louis, Mo.), myc (9E10) (Invitrogen, Carlsbad, Calif.), 6-His (Invitrogen; Novagen, Madison, Wis.), and HA (Boehringer Manheim Biochemicals). Examples of such transport signals include, but are not limited to, export signals, secretory signals, nuclear localization signals, and plasma membrane localization signals.
In a further aspect, the invention provides methods for detecting the presence of the pol κ76 in a protein sample, comprising providing a protein sample to be screened, contacting the protein sample to be screened with an antibody against pol κ76, or another compound that specifically interacts with pol κ76, and detecting the formation of antibody-antigen or pol κ76-compound complexes. Where the detection is done via antibody detection, the antibody can be either polyclonal or monoclonal, although monoclonal antibodies are preferred. As used herein, the term “protein sample” refers to any sample that may contain pol κ76, including but not limited to tissues and portions thereof, tissue sections, intact cells, cell extracts, purified or partially purified protein samples, bodily fluids, nucleic acid expression libraries. Accordingly, this aspect of the present invention may be used to test for the presence of pol κ76 antigen in these various protein samples by standard techniques including, but not limited to, immunolocalization, immunofluorescence analysis, Western blot analysis, ELISAs, aid nucleic acid expression library screening, (See for example, Sambrook et al, 1989.) In one embodiment, the techniques may determine only the presence or absence of pol κ76. Alternatively, the techniques may be quantitative, and provide information about the relative amount of pol κ76 in the sample. For quantitative purposes, ELISAs are preferred.
Detection of immunocomplex formation between pol κ76 and antibodies or fragments thereof, directed against pol κ76, can be accomplished by standard detection techniques. For example, detection of immunocomplexes can be accomplished by using labeled antibodies or secondary antibodies. Such methods, including the choice of label are known to those ordinarily skilled in the art. (Harlow and Lane, Supra). Alternatively, the polyclonal or monoclonal antibodies can be coupled to a detectable substance. The term “coupled” is used to mean that the detectable substance is physically linked to the antibody. Suitable detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials and radioactive materials. Examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, β-galactosidase, or acetylcholinesterase. Examples of suitable prosthetic-group complexes include streptavidin/biotin and avidin/biotin. Examples of suitable fluorescent materials include umbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerytirin. An example of a luminescent material includes luminol. Examples of suitable radioactive material include 125I, 131I, 35S or 3H.
Such methods of detection are useful for a variety of purposes, including but not limited to detecting an autoimmune condition, identifying cells targeted for or undergoing apoptosis, immunolocalization of pol κ76 in a tissue sample, Western blot analysis, and screening of expression libraries to find related proteins.
Antibodies can be made by well-known methods, such as described in Harlow and Lane, Antibodies; A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., (1988). In one example, preimmune serum is collected prior to the first immunization. A peptide portion of the amino acid sequence of pol κ76 that is not co-linear in pol κ, due to the alternative splicing of the pre-mRNA, together with an appropriate adjuvant, is injected into an animal in an amount and at intervals sufficient to elicit an immune response. Animals are bled at regular intervals, preferably weekly, to determine antibody titer. The animals may or may not receive booster injections following the initial immunization. At about 7 days after each booster immunization, or about weekly after a single immunization, the animals are bled, the serum collected, and aliquots are stored at about −20° C. Polyclonal antibodies against pol κ76 can then be purified directly by passing serum collected from the animal through a column to which non-antigen-related proteins prepared from the same expression system without pol κ76 bound.
Monoclonal antibodies can be produced by obtaining spleen cells from the animal. (See Kohler and Milstein, Nature 256, 495-497 (1975)). In one example, monoclonal antibodies (mAb) of interest are prepared by immunizing inbred mice with peptide portion of the amino acid sequence of pol κ76 that is not co-linear in pol κ, due to the alternative splicing of the pre-mRNA. The mice are immunized by the IP or SC route in an amount and at intervals sufficient to elicit an immune response. The mice receive an initial immunization on day 0 and are rested for about 3 to about 30 weeks. Immunized mice are given one or more booster immunizations of by the intravenous (IV) route. Lymphocytes, from antibody positive mice are obtained by removing spleens from immunized mice by standard procedures known in the art. Hybridoma cells are produced by mixing the splenic lymphocytes with an appropriate fusion partner under conditions which will allow the formation of stable hybridomas. The antibody producing cells and fusion partner cells are fused in polyethylene glycol at concentrations from about 30% to about 50%. Fused hybridoma cells are selected by growth in hypoxanthine, thymidine and aminopterin supplemented Dulbecco's Modified Eagles Medium (DMEM) by procedures known in the art. Supernatant fluids are collected from growth positive wells and are screened for antibody production by an immunoassay such as solid phase immunoradioassay. Hybridoma cells from antibody positive wells are cloned by a technique such as the soft agar technique of MacPherson, Soft Agar Techniques, in Tissue Culture Methods and Applications, Kruse and Paterson, Eds., Academic Press, 1973.
To generate such an antibody response, the peptide portion of the amino acid sequence of pol κ76 that is not co-linear in pol κ, is typically formulated with a pharmaceutically acceptable carrier for parenteral administration. Such acceptable adjuvants include, but are not limited to, Freund's complete, Freund's incomplete, alum-precipitate, water in oil emulsion containing Corynebacterium parvum and tRNA. The formulation of such compositions, including the concentration of the polypeptide and the selection of the vehicle and other components, is within the skill of the art.
The term antibody as used herein is intended to include antibody fragments thereof which are selectively reactive with pol κ76. Antibodies can be fragmented using conventional techniques, and the fragments screened for utility in the same manner as described above for whole antibodies. For example, F(ab′)2 fragments can be generated by treating antibody with pepsin. The resulting F(ab′)2 fragment can be treated to reduce disulfide bridges to produce Fab′ fragments.
In yet another aspect, the invention provides methods for detecting the presence in a sample of nucleic acid sequences encoding pol κ76 comprising providing a nucleic acid sample to be screened, contacting the sample with a nucleic acid probe derived from the isolated nucleic acid sequences of the invention, or fragments thereof, and detecting complex formation.
As used herein, the term “sample” refers to any sample that may contain pol κ76 -encoding nucleic acid, including but not limited to tissues and portions thereof, tissue sections, intact cells, cell extracts, purified or partially purified nucleic acid samples, DNA libraries, and bodily fluids. Accordingly, this aspect of the present invention may be used to test for the presence of pol κ76 mRNA or DNA in these various samples by standard techniques including, but not limited to, in situ hybridization, Northern blotting, Southern blotting, DNA library screening, polymerase chain reaction (PCR) or reverse transcription-PCR (RT-PCR). (See for example, Sambrook et al, 1989.) In one embodiment, the techniques may determine only the presence or absence of the nucleic acid of interest. Alternatively, the techniques may be quantitative, and provide information about the relative amount of the nucleic acid of interest in the sample. For quantitative purposes, quantitative PCR and RT-PCR are preferred. Thus, in one example, RNA is isolated from a sample, and contacted with an oligonucleotide derived from the pol κ76 nucleic acid sequence, together with reverse transcriptase under suitable buffer and temperature conditions to produce cDNAs from the pol κ76 RNA. The cDNA is then subjected to PCR using primer pairs derived from the nucleic acid sequence of interest. In a preferred embodiment, the primers are designed to detect the presence of the RNA expression product of SEQ ID NO:30, and the amount of pol κ76 gene expression in the sample is compared to the level in a control sample.
For detecting pol κ76 nucleic acid sequences, standard labeling techniques can be used to label the probe, the nucleic acid of interest, or the complex between the probe and the nucleic acid of interest, including, but not limited to radio-, enzyme-, chemiluminescent-, or avidin or biotin-labeling techniques, all of which are well known in the art. (See, for example, Molecular Cloning: A Laboratory Manual (Sambrook, et al., 1989, Cold Spring Harbor Laboratory Press), Gene Expression Technology (Methods in Enzymology, Vol. 185, edited by D. Goeddel, 1991. Academic Press, San Diego, Calif.); PCR Protocols: A Guide to Methods and Applications (Innis, et al. 1990. Academic Press, San Diego, Calif.)).
Such methods of nucleic acid detection are useful for a variety of purposes, including but not limited to diagnosing an autoimmune condition, identifying cells targeted for or undergoing apoptosis, in situ hybridization, Northern and Southern blot analysis, and DNA library screening.
As demonstrated in the following examples, pol κ76 shows preferential expression in skin and keratinocytes that are commonly targeted in naturally-occurring automimmune responses, and is expressed at an elevated level in systemic lupus erythematosus (SLE) patients. Furthermore, pol κ76 is shown herein to be associated through another protein with GPBP, which is known to be associated with autoimmune conditions.
Thus, in a preferred embodiment, detection of pol κ76 expression is used to detect an autoimmune condition. A sample that is being tested is compared to a control sample for the expression of pol κ76 RNA, wherein an increased level of pol κ76 RNA expression indicates the presence of an autoimmune condition. In this embodiment, it is preferable to use quantitative RT-PCR and to employ oligonucleotides that generate a product from pol κ76 RNA but not polK RNA, or that produce distinguishable products from pol κ76 RNA and pol κ RNA.
Furthermore, pol κ76/pol K are likely to be involved in cell signaling pathways that induce apoptosis, which may be up-regulated during autoimmune pathogenesis and down-regulated during cell transformation to prevent autoimmune attack to transformed cells during tumor growth. Thus, the detection methods disclosed herein can be used to detect cells that are targeted for, or are undergoing apoptosis.
In another aspect, the present invention provides a method for treating an autoimmune disorder or cancer comprising modification of the expression or activity of pol κ76 RNA or pol κ76 polypeptide, such as by increasing or decreasing their expression or activity. Modifying the expression of or activity of pol κ76 RNA or pol κ76 polypeptide can be accomplished by using specific inducers or inhibitors of pol κ76 expression or activity, pol κ76 antibodies, antisense therapy, or other techniques known in the art. As used herein, “modification of expression or activity” refers to modifying expression or activity of either the RNA or protein product.
The present invention may be better understood with reference to the accompanying examples that are intended for purposes of illustration only and should not be construed to limit the scope of the invention, as defined by the claims appended hereto.
Materials and Methods.
Synthetic oligonucleotides. The following oligonucleotides and other used for DNA sequencing were synthesized by Genosys, Life Technology Inc., Roche or Pharmacia:
Isolation of the 5′ genomic region of COL4A3BP. The 5′-end region of COL4A3BP was isolated by PCR using ON-GPBP-6c, Adapter primer 2 (AP2)(Clontech) and DNA from human genomic libraries (PromoterFinder DNA Walking Kit (Clontech)). We obtained a single DNA fragment in four of the five of the libraries screened (1.6, 1.3, 0.8, and 0.4 kb, respectively). By sequencing the 0.4-kb DNA fragment we characterized the COL4A3BP region immediately upstream of the cDNA clone (n4′) (SEQ ID 1) previously reported (Disclosed in WO 00/50607; GenBank accession no AF136450) [2]. Based on the sequence of the 0.4 kb fragment, we designed and synthesized ON-GPBP-14c, and used it in combination with AP2 to perform PCR on the 1.6 kb genomic library fragment. From this PCR, we obtained a PCR DNA fragment of ˜1.5 kb containing the 5′ genomic region of COL4A3BP without any exon sequences present in n4′. This DNA fragment was then used to screen a HeLa-derived cDNA library, from which we isolated HeLa 4.1, a clone containing 1.3 kb of cDNA (SEQ ID NO:2 (GenBank accession no AF315601). Finally, we used ON-GPBP-18m (an oligonucleotide derived from HeLa 4.1) and ON-GPBP-6c (an oligonucleotide derived from n4′) to conduct PCR on human genomic DNA, from which we generated a 955-bp PCR product (SEQ ID NO:3)(GenBank accession no AF315603) that contained HeLa 4.1 sequence, the 5′ region of the first exon of COL4A3BP, and the intervening DNA region (
Plasmid construction. A 772-bp DNA fragment was generated by digesting the 955-bp PCR product (SEQ. ID NO:3) with XbaI and Ec1XI, the ends were filled-in, and the orientation expressing COL4A3BP (SEQ ID NO:4) or POLK (SEQ ID NO:5) cloned into the HincII site of pΦGH (Nichols Institute) immediately upstream of human growth hormone reporter gene to generate LpromGPBP and LpromPolK. Alternatively, ON-XbaG/Bpro1m and ON-XbaG/Bprolc were used to obtain a 140-bp PCR product which contained the intergene region, the major transcription start sites for each gene and a few nucleotides of the corresponding exon 1 from either COL4A3BP or POLK (shaded sequence in
To generate pΦGH-based constructs containing 140-bp homologous regions of COL4A3/COL4A4, LMP2/TAP1 and HSP10/HSP60, human DNA was prepared from blood cells using a DNA purification kit (Epicenter), and the regions of interest amplified by PCR using the following pair of synthetic oligonucleotides ON-S2A3A4m/ON-S2A3A4c, ON-SA3A4m/ON-SA3A4c, ON-INGA3A4m/ON-INGA3A4c to obtain the DNA regions corresponding to 182-318 (SEQ ID NO: 8; SEQ ID NO:9), 849-990 (SEQ ID NO: 10; SEQ ID NO:11), 675-1045 nucleotides (SEQ ID NO: 12; SEQ ID NO:13) of AF218541; ON-LMPTAP1m/ON-LMPTAP1c to obtain the DNA fragment containing the 24579-24718 nucleotides (SEQ ID NO: 14; SEQ ID NO:15) of X66401; and ON-HSP1m/ONHSP1c to obtain the 3451-3590 nucleotides (SEQ ID NO: 26; SEQ ID NO:27) of AJ250915. The DNA fragments were individually digested with XbaI and cloned in the corresponding site of the polylinker region of pΦDGH in each of the two orientations.
To generate pGBT9 and pGAD424 plasmids for pol κ and pol κ76 the corresponding cDNA fragments obtained by RT-PCR (see below) were digested with BamHI and SalI and cloned in the corresponding sites of a FLAG modified version of the corresponding expression vectors (Clontech) engineered essentially as previously described [2] but containing a BamHI site immediately downstream of the FLAG peptide sequence.
All the plasmid-based constructs were characterized by nucleotide sequencing.
Plasmid expressing human glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was provided by Erwin Knecht.
Ribonuclease protection assays. By digesting LpromGPBP with ApaI and EclXI we obtained a DNA fragment of 503-bp containing the two 5′ end regions of POLK and COL4A3BP genes and the intergene region. The DNA fragment was blunt-end with T4 DNA polymerase and cloned into the HincII site of Bluescribe M13+ (Stratagene). Ribonucleotide probes from T3 and T7 promoters representing the antisense of the GPBP or pol κ mRNAS respectively were obtained using MAXIscript™ T7/T3 in vitro transcription kit (Ambion). Individual ribonucleotide probes were subject to ribonuclease protection assays using RPAIII™ (Ambion) and total RNA from human cultured hTERT-RPE1 (Clontech) or 293 cells (ATCC # CRL-1573). The digestion mixtures were analyzed by gel electrophoresis (8M urea 8% acrylamide gel) and autoradiography.
RNA purification. Total RNA was prepared from human tissues or cultured cells using TRI-REAGENT (Sigma) and following the manufacturer's recommendations.
Reverse transcription (RT) and polymerase chain reactions studies(PCR).
To obtain a continuous cDNA fragment containing HeLa 4.1 and pol κ coding sequences (GenBank accession no AF318313 (SEQ ID NO: 32) we carried out a PCR on human striated muscle cDNA library (MATCHMAKER™ from Clontech) with ON-GPBP-39c and ON-DINB1-R2 primers using the Expand™ Long Template PCR System (Roche). To obtain the cDNA for pol κ or pol κ76, 5 μg of total RNA extracted from human foreskin was reverse-transcribed with ON-DIN2c using the Ready-To-Go system (Pharmacia). An aliquot (0.5 μl) of the resulting cDNA-RNA hybrid was similarly subjected to PCR using ON-DIN5'm and ON-DIN-THc.
Real Time PCR studies were performed using a SDS 7700 Applied Biosystems apparatus and aliquots of either human cDNA libraries for striated muscle, HeLa cells, keratinocytes, pancreas, brain and kidney (MATCHMAKER from Clontech) or random hexamer reverse-transcriptase reactions performed as above using total RNA extracted from human hTERT-RPE1 cells, foreskin, lung, spleen, adrenal gland and kidney or from mouse kidney.
The mRNA determinations in hTERT-RPE were done on 5 μl of a 1:10 (for the different genes of interest) or 1:1000 (for GAPDH) dilution of a single reverse transcriptase reaction using the Relative Quantitation Method analysis (ΔΔCt) following manufacturer's recommendations. GAPDH was used as endogenous control to normalize quantification. The pair of oligonucleotides were, ON-IDH-F1 and ON-IDH-R1 for IDHG; ON-TRAPD-F1 and ON-TRAPD-R1 for TRAPD; ON-LMP2-F2 and ON-LMP2-R2 for LMP2; ON-TAP1-F2 and ON-TAP1-R2 for TAPI; ON-DHFR-F1 and ON-DHFR-R1 for DHFR; ON-MSH3-F1 and ON-MSH3-R1 for MRP1; ON-HO3-F2 and ON-HO3-R2 for HO3; ON-HARS-F2 and ON-HARS-R2 for HRS; ON-Hsp10-F1 and ON-Hsp10-R1 for HSP10; ON-Hsp60-F1 and ON-Hsp60-R1 for HSP60; ON-COL4A1-F1 and ON-COL4A1-R1 for COL4A1; ON-COL4A2-F1 and ON-COL4A2-R1 for COL4A2; ON-GP-F1 and ON-GP-R1 for COL4A3; ON-COL4A4-F1 and ON-COL4A4-R1 for COL4A4; ON-COL4A5-F1 and ON-COL4A5-R1 for COL4A5; ON-COL4A6-F1 and ON-COL4A6-R1 for COL4A6; ON-GPBP-F1 and ON-GPBP-R1 for COL4A3BP; ON-DinB1-F3 and ON-DinB1-R3 for POLK; ON-hGAPDH-F1 and ON-hGAPDH-R1 for GAPDH.
To determine mRNA levels for human pol κ or pol κ76 PCR reactions were performed using ON-DINB1-F3 and ON-DINB1-R3 or ON-huDINB-76-F1 and ON-huDINB-76-R1 respectively, and either 6 and 60 ng of the different cDNA libraries, or 5 μl of a 1:10 dilution of the individual reverse transcriptase reactions. Standard curves for each PCR were done using the same oligonucleotides and different amounts of individual plasmids containing the corresponding cDNAs.
To determine GPBP and GPBPΔ26 mRNA levels in mouse kidney PCR reactions were done using ON-GPBP-26-1F and ON-GPBPe26-1R or ON-mGPBP-26-1R, respectively and 5 μl of a 1:10 and 1:100 dilution of the individual reverse transcriptase reactions.
To determine GPBP and GPBPΔ26 mRNA levels in human skin samples PCR reactions were done using ON-GPBP-26-1F and ON-GPBPe26-1R or ON-hGPBP-26-1R, respectively and 5 μl of a 1:10 dilution of the individual reverse transcriptase reactions.
Northern analysis. Pre-made Northern blots (Clontech) were probed with 32P-labeled cDNAs representing GPBP (n4′) or pol κ (see above) according to manufacturer's instructions.
Cell culture and transient gene expression assays. Cells were grown in DMEM (NIH 3T3 and 293) or DMEM F-12 HAM (hTERT-RPE1) with 100 units/ml of penicillin and 100 μg/ml streptomycin, and supplemented with 10% calf serun (NIH 3T3 cells) or fetal calf serum (hTERT-RPE1 and 293). For transient gene expression assays, NIH 3T3 cells (1.4×105) were seeded in 9.5 cm2 plates, cultured for 14-16 hours, and then transfected for 16-18 hours with 2.5 μg of each individual pΦGH-derived plasmid and 2.5 μg of β-galactosidase expression vector (Promega) using the calcium phosphate precipitation method of the Profection Mammalian Transfection System (Promega). After transfection, the cells were rinsed with phosphate-buffered saline, fresh medium was added, and the levels of human growth hormone in the media were determined after 48 hours using a solid phase radioimmunoassay system (Nichols Institute). β-galactosidase activity determination was performed following manufacturer's recommendations. For some purposes, after transfection the cells were cultured in low serum (0.5%) media for 24 hours, media was discarded, and fresh low serum media containing TNFα (10 ng/ml) or TNFβ(50 ng/ml) was added, and levels of human growth hormone similarly determined.
For other purposes hTERT-RPE1 cells were grown up to 60-70% confluence, media removed and fresh serum-free media added and culture continued. After 24 hours the media was removed, fresh serum-free media containing TNFβ (50 ng/ml) added, and, after one hour, the media was discarded and cells were used for RNA preparation.
Isolation of genomic DNA encoding GPBP. We have used human GPBP cDNA fragments obtained from specific PCR amplification of n4′ to screen a human genomic library, λfix-w138 (Stratagene). Two independent and overlapping genomic clones λfixGPBP1 and λfixGPBP3, of ˜14 kb and ˜13 kb respectively, were characterized by restriction mapping and partial nucleotide sequencing. The nucleotide sequence of ˜12 Kb of the λfixGPBP1 has been recently reported (GenBank accession no AF232935) [3].
Chromosome localization of COL4A3BP, the structural gene for GPBP. To map COL4A3BP, a fluorescence in situ hybridization (FISH) analysis was performed essentially as described in Ref. 13 on metaphase chromosomes obtained from control peripheral blood using λfixGPBP1 and λfixGPBP3, labeled by standard nick-translation with digoxigenin-11-dUTP and biotin-16-dUTP respectively. The hybridized material was detected using either sheep anti-digoxigenin-FITC (fluoresceine isothiocyanate (Roche) or avidine-rhodamine (Vector Laboratories).
Computer analysis. Alignments were generated with the program GAP of the GCG-package (Genetics Computer Group). GAP uses the algorithm of Needleman and Wunsch [14] As originally introduced the algorithm sought to maximize a similarity, or quality (Q), between two sequences. From any pair of bases, an alignment can be extended in three ways: adding a base in each sequence, with a specified addition to the distance if the bases do not match, or adding a base in one sequence but a gap in the other, or vice versa. Introduction of a gap also contributes a specific amount to the distance. Formally, the best alignment will be the one that keeps up the relationship Q=max(x−Σzkwk), where x is the number of matched pairs, zk the number of gaps with length k, and wk the penalty for a gap of length k. Many systems of gap penalty have been used; the liner system being the most commonly used because it saves computer time. In this system wk=α+βk, where a (the gap-opening penalty) and β (the gap-extension penalty) are non-negative parameters. Which alignment is preferable depends upon the penalty weights used. For example, a small a along with a big β will favor an alignment with many short gaps, whereas a large a with a small β will favor an alignment with few long gaps. The gap parameters employed in the analysis were α=50 and β=3. The statistical distribution of Q is not well characterized. Therefore, to assess the statistical significance of an alignment it is necessary to use a bootstrapping technique. In brief, the sequence being aligned is shuffled 100 times, maintaining its length and composition, and then realigned to the target POLK/COL4A3BP sequence. The average alignment quality, E(Q), plus or minus the standard deviation, of all randomized alignments can be used to evaluate the significance of the alignment. If the observed Q is significantly larger than that expected by chance, E(Q), then a P<0.05 would be obtained.
Animal studies. The implication of TNF and GPBP in the development of murine systemic lupus erythematosus (SLE) was analyzed in F1 hybrids between NZW females and C57BL/6 (B6) males that over-express a human Bcl-2 transgene in the B cell compartment under the regulation of the SV40 promotor and IgM enhancer. These Bcl-2-transgenic F1 mice develop an aggressive SLE characterized by the production of a large spectrum of pathogenic autoantibodies resulting in the development of an immunocomplex-mediated gomerulonephritis and early death (50% of mortality is observed at 9-10 months of age) [15]. In contrast, non-transgenic (NZW×B6)F1 mice are immunologically normal and are used as controls. The development of the disease in the Bcl-2-transgenic F1 mice is believed to be a consequence of an over-expression of human Bcl-2 in B cells that prolongs the survival of potentially autoreactive B cells generated either in the bone marrow or in the germinal centers of secondary lymphoid organs in the course of T cell-dependent antibody responses, and also because of the genetic predisposition to SLE provided by the NZW genetic background. In this respect, several genetic loci associated with the production of autoantibodies and/or glomerulonephritis (GN) have been mapped in the NZW mouse strain. However, the nature of these genetic defects associated with the different autoimmune traits remains at the present largely unknown. The production of autoantibodies in Bcl-2-transgenic F1 mice is first observed at 2 months, and glomerular lesions are already evident at 3-5 months of age. As observed in other murine models of spontaneous SLE, both autoantibody production and GN are inhibited after the treatment from birth of (NZW×B6)F1-Bcl-2 mice with an anti-CD4 monoclonal antibody, indicating that the disease is a CD4-dependent phenomenon.
For some purposes, (NZW×B6)F1 mice were treated from birth with anti-CD4 antibodies as previously reported [16], and the presence of the transgene (Tg) in each animal determined as described [17]. The anti-CD4 treatment was continued for the F1Tg(+) up to three month and then half of mice were maintained without additional treatment whereas the other half were enrolled in a program with anti-TNF antibodies (V1q) essentially as described [18] but using 30 μl of V1q ascites three times per week. After two and a half months both anti-TNF treated and non-treated animals were sacrificed and one of the kidneys used for histology and immohistochemistry, and the other for mRNA studies. For similar purposes we also obtained the kidneys of animals representing the parental strands, female NZW and male C57BL/6-Bcl-2 and three month old (NZW×B6)F1Tg(−) and (NZW×B6)F1Tg(+) maintained without anti-CD4 treatment.
For other purposes, B6 mice were intraperitoneally injected with 50 μg of lipopolysaccharides (LPS) obtained from Salmonella minnesota (Sigma), which induces a dramatic increase in the serum levels of TNFα, resulting in the development of endotoxic shock [19]. Either three or six hours after LPS injection, mice were sacrificed and their kidneys immediately extracted, frozen in dry ice, and used for RNA isolation. Non injected C57BL/6 mice were similarly sacrificed and their kidneys obtained for use as controls.
Immunochemical techniques. Immunihistochemical studies were performed on formalin-fixed, paraffin-embedded mouse kidneys essentially as described [2,3], using GPBP polyclonal antibodies [2] at 1:50 dilutions. Prior to antibody detection, antigen retrieval was achieved heating with autoclave (1.5 atmospheres for 3 minutes in 10 mM sodium citrate buffer pH 6.0).
For some purposes the presence of anti-ssDNA autoantibodies was determined in the sera of the mice using an ELISA approach [17].
Results
Structural characterization of the 5′ region of COL4A3BP. To characterize the promoter region of COL4A3BP we first attempted to determine the transcriptional start site by primer extension analysis. However, and likely due to the high G+C content at the 5′-end untranslatable region (UTR)[2], we obtained premature stops during reverse transcription at positions 56, 61 or 68 of the cDNA in n4′ (GenBank accession no AF136450) (not shown). A similar negative results were obtained when a 5′-RACE approach was used to identify mRNA species extending beyond the 5′ end of n4′ (not shown). To overcome this inconvenient, we isolated and characterized by partial nucleotide sequencing ˜1.5 kb of genomic DNA located upstream of the 5′-UTR of n4′, and screened a cDNA human library to identify clones containing additional 5′-UTR of GPBP not present in n4′. We isolated and sequenced 1.3-kb HeLa 4.1 ((SEQ ID NO:2) GenBank accession no AF315601), which did not overlap with n4′ although contained sequence present in the 1.5-kb DNA. Because HeLa 4.1 did not contain open readings of consideration in the six frames (not shown), its cDNA likely represents either 5′-UTR of GPBP not present in n4′ or sequence corresponding to an UTR of other gene mapping 5′ of COL4A3BP. The first possibility was abandoned since we failed to amplify by RT-PCR a continuous cDNA fragment containing both HeLa 4.1 and n4′ sequences (not shown). As expected, however, we succeeded obtaining a DNA fragment of 955-bp ((SEQ ID NO:3) GenBank accession no AF315603) when subjecting human DNA to PCR using ON-GPBP-18m, a forward primer derived from HeLa 4.1, and ON-GPBP-6c, a reverse primer derived from n4′ (
Chromosomal mapping of the human COL4A3BP gene. By FISH analysis others have shown a single locus for POLK at band 5q13 [5]. In similar studies and consistent with the proposed head-to-head arrangement of COL4A3BP and POLK, two independent overlapping DNA fragments of COL4A3BP hybridized with a single locus mapping at 5q12-13. According to the last publicly available data on the human genome sequence, both COL4A3BP and POLK map to 5q13.3. In the last freeze of the sequence (http://genome.ucsc.edu/goldenPath/apr2001Tracks.html) there still remains a gap between both genes that is bridged with the sequence reported here (SEQ ID NO:3) GenBank accession no AF315603) (
Characterization of the bidirectional transcription unit for POLK and COL4A3BP. To investigate the presence of a bidirectional promoter in the intergene region we cloned in pΦGH each of the two orientations of a 772-bp DNA fragment (SEQ ID NO: 4 and SEQ ID NO:5) encompassing the region of interest (LpromPolκ and LpromGPBP) and we assessed their ability to drive heterologous gene expression in NIH 3T3 cells (
The contribution that the individual DNA elements identified in the 140-bp DNA region had on the transcriptional activity was assessed using promoter constructs in which the Sp1 site or/and the TATA box were deleted (
The expression of the bidirectional unit in human tissues The transcriptional activity of the bidirectional promoter in human tissues was investigated by Northern blot analysis. With the exception of brain and pancreas that showed a relatively reduced expression of pol κ, comparison of mRNA levels among tissues revealed that the two genes are expressed in a coordinated manner in normal human tissues, whereas coordination appears to be disrupted during cell transformation as comparison of mRNA levels in human cancer cell lines showed that cells with a relative higher expression of GPBP expressed relatively less pol κ and vice versa (not shown). In either case this suggests that pol κ and GPBP are likely partners in specific biological functions and that the head-to-head arrangement of the corresponding genes is the strategy to co-regulate their expression.
Sequence homology between POLK/COL4A3BP and COL4A3/COL4A4 promoters. Several housekeeping genes, including those encoding α chains of collagen type IV, are transcribed from short, bi-directional, G+C rich promoters containing Sp1 sites [22]. Six related genes organized in three transcriptional units encode the human α(IV)chains (α1/α2, α3/α4 and α5/α6) [23-25] which likely have evolved from a primitive genetic unit the proto-α1/proto-α2 resulting from duplication and inversion of a unique primitive gene with an unidirectional promoter [26-29]. Consistent with this evolutionary model the structural genes for α1,α3 and α5 on one site and α2,α4 and α6 on the other, are more closely related [26-29].
Because GPBP has been shown to bind and phosphorylate the α3(IV)NC1 domain and a similar binding to the homologous α1 and α5 NC1 domains has been found to exist [3] we searched for sequence homology between the 140-bp of POLK/COL4A3BP containing the intergene region and genomic regions expected to contain the core of each transcriptional collagen IV unit (
Sequence homology between COL4A3BP/POLK and other bidirectional human promoters. The genomic regions representing the intergene and flanking structural genes of a number of bidirectional transcriptional units others than collagen α(IV) (GenBank accession no X66401, K01612, U00239, M96646, AJ250915 and Z68129) [30-37] were similarly analyzed for sequence homologies with the 140-bp of POLK/COL4A3BP (
These data demonstrate that the COL4A3BP/POLK base pair promoter sequence, which was shown to comprise a bi-directional promoter, contain sequences that are significantly homologous to a number of other known bi-directional promoters, and thus probably constitute regulatory elements shared in common by a family of bi-directional promoters.
TNF induce the POLK/COL4A3BP and COL4A3/COL4A4 promoters in transient gene expression assays. GPBP is highly expressed in apoptotic blebs in tissues undergoing autoimmune attack and is virtually not expressed in transformed cell lines [3]. Consequently to identify modulators of the transcriptional activity of POLK/COL4A3BP, a number of cytokines (TNFα, TNFβ and γIFN) with ability to cause cell death, with an anti-tumoral potential and with a role in the immune defense but also in autoimmune pathogenesis were used as inducers on cultured NIH3T3 or HeLa cells transfected with the 140-bp promoter constructs (SpromPolκ and SpromGPBP). Whereas we found no effect on the transcriptional activity of the constructs when inducing the cells with IFNγ (20 ng/ml) or when inducing HeLa cells with any of the three cytokines, we found that either TNFα (10 ng/ml) or TNFβ (50 ng/ml) induced the two promoter constructs in NIH 3T3 cells (
To date no functional characterization of the transcriptional unit for COL4A3/COL4A4 has been reported. To explore the biological significance of sequence homology between this bidirectional promoter and the promoter of POLK/COL4A3BP (SEQ ID NOS: 6-7), we cloned each of the two orientations of the COL4A3/COL4A4 homologous regions (
TNF induce dual homologous bidirectional promoters other than COL4A3/COL4A4. The coordinated regulation above could be understood as a part of a regulatory mechanism which depend of TNF in the context of the previously identified biological partnership of GPBP and the α chains of collagen IV [2,3], however, no immediate biological relation exists between pol κ and GPBP, and between GPBP and the products of the other bidirectional units which have been identified by sequence homology. To explore the scope of our findings we cloned and similarly assayed the 140-bp homologous DNA fragment mapping at the intergene region of LMP2/TAP1 (SEQ ID NO: 14 (LMP2 orientation) and SEQ ID NO:15 (TAP1 orientation) and HSP10/HSP60 (SEQ ID NO: 26 (HSP10 orientation) and SEQ ID NO:27 (HSP60 orientation), which represented the statistically more significant homologies (
Finally the transcriptional induction of the different dual units in response to TNF was investigated in cultured human hTERT-RPE1 cells by determining mRNA levels using a Real Time PCR approach (
All these data indicate that at least for the number of genes we have reported the head-to-head arrangement is a convergent evolution phenomenon to coordinate their expression in response to TNF and that the 140-bp homologous modules contain responsive elements for the coordinated expression. Finally, our findings indicate that TNF not only induces the expression of COL4A3BP by increasing the copy number of the corresponding mRNA molecular species but also increases the relative expression of GPBP versus GPBPΔ26, a phenomenon which we have previously shown to be related with autoimmune pathogenesis [3].
Evidences for TNF increasing the relative expression of GPBP in vivo, a phenomenon critical for SLE development in a lupus prone mouse model. The role of TNF regulating GPBP/GPBPΔ26 ratio in the kidney was explored in B6 mice by inducing endogenous TNF production in response to LPS (
To explore the role of TNF inducing the expression of GPBP in an autoimmune response we first determined the expression of GPBP and GPBPΔ26 in a recently reported lupus prone model [15] which we have described here under Material and Methods (
Treatment with anti-CD4 immediately after birth (see Material and Methods) had important consequences in both mRNA expression and immunohistochemical pattern of the (NZW×B6)F1Tg(+) (
To investigate the consequences that the immunological treatment had on the autoimmune response the levels of anti-ssDNA autoantibodies in the sera (a standard and very sensitive marker for autoimmunity) of six month old (NZW×B6)F1Tg(−) or (NZW×B6)F1Tg(+) maintained untreated, were compared with the levels of these autoantibodies in (NZW×B6)F1Tg(+) treated with anti-CD4 for three months and either untreated or treated with anti-TNF for three additional months (
From all these data we conclude that the autoimmune response in the lupus prone model studied is mediated by TNF and operates through an elevated ratio of GPBP/GPBPΔ26.
Molecular cloning of a 76-kDa alternatively spliced variant of DNA polymerase κ. Alternatively spliced variants of pol κ have been reported to exist in human and mouse testis [5]. The presence in HeLa and in human striated muscle of molecular species with different 5′-UTR (see above) also indicated the presence of molecular species representing alternatively spliced variants previously unrecognized. We have use RT-PCR on total human RNA from foreskin and we have cloned a previously unidentified mRNA species for pol κ. This novel mRNA species contain a 672-residue open reading frame predicting pol κ76, a 76-kDa pol κ isoform (GenBank accession no AF315602) (SEQ ID NO:31), which represents an alternatively exon splicing variant that diverged with respect to the alternatively spliced isoforms previously identified in that exon skipping does not cause a reading frame shift but eliminates the bulk of the sequence predicting two in tandem helix-hairpin-helix domains and a coiled-coil motif characteristic of the primary product (
To estimate the relative expression of this novel molecular species in human tissues we performed specific Real Time PCR on several cDNA libraries or reverse transcriptase reactions from human tissues (
Discussion
In normal human tissues GPBP is expressed at a lower level than GPBPΔ26, an alternatively spliced variant devoid of 26-residues serine-rich motif which represents a less active isoform of the protein kinase [3]. Although GPBP and GPBPΔ26 are widely expressed in human tissues they show a preferential expression in cells and tissue structures which are the target of common autoimmune responses. [2,3]. These isoforms represent two different strategies to regulate the activity of a common catalytic domain, and several lines of evidence indicate that homeostasis is achieved by a balanced expression of each isoform, whereas a breakage of the homeostasis caused by a relative increase in GPBP expression results in autoimmune pathogenesis [3].
GPBP is expressed at very low levels in cancer cells and is highly expressed in apoptotic blebs of differenced keratinocytes at the periphery of normal epidermis [3]. Keratinocytes from patients suffering from skin autoimmune processes show an increased sensitivity to UV-induced apoptosis, and a premature apoptosis at the basal keratinocytes has been reported to occur in these patients [38-41]. Consistently, we have found GPBP to be expressed in apoptotic bodies expanding from basal to peripheral strata in epidermis undergoing an autoimmune attack [3]. Altered autoantigens including phosphorylated versions thereof have been reported to be produced and released from these apoptotic bodies [40]. All these suggest that GPBP is part of an apoptotic-mediated strategy for desired cell removal that generates aberrant counterparts of critical cell components and operates illegitimately during autoimmune pathogenesis [3].
It has been shown that dinB1 (pol IV) and the eukaryotic counterpart pol κ induces spontaneous mutation on undamaged DNA [4,6,7], likely as a result of a high error nucleotide incorporation rates and an efficient mismatch extension [7). The latter feature largely depends on the formation of a primer-template misalignment that generates −1 frameshift products [4,6].
The coordinated expression of COL4A3BP and POLK demonstrated herein suggest that the products encoded by these genes are partners in specific cell program(s), and that pol κ may represent a somatic mutation-based strategy to generate structural diversity which in some instances, such as in keratincocytes could be used to generate aberrant counterparts of critical cellular components as part of an apoptotic strategy. The disruption of the coordinated expression of the two genes during cell transformation (see Northern blot results) and its maintenance at higher levels in autoimmune affected tissues further supports the implication pol κ/κ76 in apoptotic strategies relevant in autoimmune pathogenesis. Finally, disruption of transcriptional coordination of POLK and COL4A3BP may be required in cancer to prevent cell death but also autoimmune attack during tumor growth.
Alternative exon splicing of the pre-mRNA of pol κ serves to generate three different types of mRNA products. Transcripts encoding truncated forms of the polymerase contain divergent, shortened C-termini that are devoid of the Zn clusters and bipartite nuclear localization signals [5], and therefore are expected to play a regulatory role in the expression or activity of the primary pol κ product rather than to represent an alternative replicating enzyme. Transcripts with alternative 5′-UTR, essentially differing from each other in the nucleotide sequence at the vicinity of the translation start site, may represent mRNAs translated with different efficiency or molecules with different stability.
Pol κ76 is the first member of the UmuC/DinB superfamily that contains the N-terminal nucleotidyl transferase domain, but lacks the helix-hairpin-helix motifs and the predictable coiled-coil structure at the C-terminal conserved domain. This isoform retains the Zn clusters for DNA binding also existing in other family members devoid of nucleotidyl transferase domain, but with demonstrated DNA repair activity (Rab18 and Snm1) [5]. The helix-hairpin-helix has been implicated in non-specific binding to DNA and the coiled-coil structure could mediate protein-protein interactions. The fact that pol κ76 still harbors the critical structural requirements for DNA polymerase, and also maintain those characteristic of the DNA repair related enzymes, suggest that pol κ76 may represent the version of pol κ to generate aberrant counterparts of critical cell components in the context of a common apoptotic-mediated strategy for a desired cell removal, similarly to the proposed role for GPBP versus GPBPΔ26 in keratinocyte apoptosis. [3]
Multiple sclerosis is an autoimmune disorder with a complex mode of inheritance. A genome search has suggested co-segregation of a locus for this disease with the marker D5S815 [42]. Whereas this marker maps at positions 79000 Kbp and 81556 Kbp from the telomere according to GeneMap (http://www.ncbi.nlm.nih.gov/genome/guide), POLK, and consequently COL4A3BP, maps to position 80300 Kbp. This, in addition to the other data presented above and in WO 00/50607, suggests that the expression products of the POLK and GPBP genes play a role in human autoimmunity.
We show here that each orientation of a 140 base pair fragment of the bi-directional promoter for POLK/COL4A3BP is highly homologous to DNA regions at the gene junctions of a variety of bi-directional promoters. The sequence homology found among different intergene regions transcribing structurally unrelated genes, as well as the TNF-induced coordinated expression of these genes, likely reflect a strategy to link the expression of proteins that are partners in complex biological programs. Furthermore, we have shown that this 140 base pair fragment and homologous regions in other bi-directional units contain the structural requirements to initiate transcription and to respond to TNF.
Anti-TNF based therapeutic approaches have been shown to be effective in several autoimmune conditions including rheumatoid arthritis and Crohn's disease and is presently at the stage of critical clinical trials [12,43]. Anti-TNF based therapy has been shown also to have important therapeutic effects on experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis, however similar therapeutic approach in human clinical trials resulted in clinical worsening [12]. In our case, although the animals treated maintained the autoantibody levels one developed a GN more aggressive than untreated animals and mice in which anti-TNF treatment was extended for one additional month showed more abundant histological damage and very high GPBP/GPBPΔ26 ratios (not shown).
All the evidences above suggest that, in our model, the anti-TNF treatment is likely operating over the autoimmune response, and is very effective at inhibiting autoantibody production. However, likely because the cytokine is expected to be high in the pathogenic cascade and is known to be involved in various biological functions [12], anti-TNF treatment appears to have limitations. The coordinated expression of the multiple bi-directional promoters in response to TNF and the coordinated elevation of the CPBP/GPBPΔ26 and pol κ76/pol κ ratios in human cutaneous lupus suggest that bi-directional promoters are partners in apoptotic programs which become upregulated during autoimmune pathogenesis. Consequently, an intervention at the transcriptional level over common transacting factor(s) likely represent a way to achieve therapeutic effects on the autoimmune response with less site effects than anti-TNF based therapy.
The rationale for the current boom in anti-TNF□treatment. Is there an effective means to define therapeutic targets for drugs that provide all the benefits of anti-TNFα and minimise hazards? Ann. Rheum. Dis. 58 Suppl1, I27-31.
This application claims priority to U.S. provisional application Ser. No. 60/254,649, filed Dec. 8, 2001.
| Number | Date | Country | |
|---|---|---|---|
| 60254649 | Dec 2000 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10010920 | Dec 2001 | US |
| Child | 11274658 | Nov 2005 | US |
