Patent Application
20090081195
The present invention relates to kinase inhibitors. More specifically, the present invention relates to inhibitors of Ste20-like kinase (SLK) and methods of modulating cell cycle progression and motility of cells using such inhibitors.
Cell cycle progression is monitored through kinase mediated signal transduction and the binding of various cyclin proteins to their respective cyclin-dependent kinases (Cdks; (2,3)). The activity of a cyclin/Cdk complex is regulated by cycles of expression and destruction of the cyclin subunit (reviewed in (4)).
G1 progression is regulated, in part, by cyclins D and E and their respective cyclin dependent kinases in a complex pathway that results in the retinoblastoma (Rb) protein phosphorylation and consequently the production of cyclin A leading to S phase entry (Reviewed in (5)). Cyclin B synthesis initiates at the end of S phase (6,7) and forms a complex with p34cdc2/cdk1. This complex has been termed MPF (maturation promoting factor or mitosis promoting factor) and is required for mitotic entry (reviewed in (8)). During interphase, cytosolic MPF is kept inactive by inhibitory phosphorylation of cdc2 on threonine 14 (Thr14) and tyrosine 15 (Tyr15) by Myt1 and Wee1, respectively (9-11). Activation of this complex is triggered by the Cdc25C phosphatase through cdc2 dephosphorylation of Thr14 and Tyr 15 (12-14). Following dephosphorylation of these residues, MPF is believed to phosphorylate and further activate Cdc25C resulting in full activation of MPF through an autocatalytic feedback loop (15,16). This results in the translocation of MPF from the cytoplasm to the nucleus at the beginning of mitosis (17) where it phosphorylates histone H1 (18) and induces changes in the microtubule network (19) and actin filaments (20).
In Xenopus, polo like kinase (Plx1) has been shown to phosphorylate and activate Cdc25 (21) and polo like kinase (xPlkk1) has been shown to be a direct activator of Plx1 (22). However, this may be an organism specific phenomenon since depletion of mammalian polo like kinase (Plk1) results in elevated activity of Cdc2 (23) suggesting a role for Plk in mitotic progression rather than mitotic entry. To date, a bona fide upstream activator of mammalian Cdc25C has not been identified.
Chromosome condensation is accompanied by the hyperphosphorylation of histone H1 (24) and phosphorylation of H3 on serine 10 (Ser10) (25,26). Microtubules then organize into a bipolar spindle and attach to the kinetochores of each sister chromosome. Chromosome attachment prior to segregation is monitored by the spindle check point protein MAD2 (mitotic arrest deficient) which binds kinetochores lacking microtubule attachment generating a “wait-anaphase” signal (Reviewed in (27)). Following the attachment of the last unattached kinetochore, the “wait anaphase” signal is silenced and the anaphase-promoting complex (APC), in association with Cdc20 initiates chromosome segregation (Reviewed in (28)) and culminates into cytokinesis (Reviewed in (29)).
The murine Ste20-like kinase (SLK) is a 220 kDa serine/threonine kinase that was first demonstrated to induce actin remodeling and apoptosis in a wide range of cell lines (30,31). The amino terminal kinase domain of SLK is closely related to that of lymphocyte oriented kinase (LOK) and xPlkk1. In addition, SLK bears a central microtubule and nuclear associated protein (M-NAP) domain, and a carboxyl AT1-46 homology (termed ATH) domain that is also found in LOK and xPlkk1 (30,31). The function of both the M-NAP and AT1-46 domains has yet to be elucidated. SLK is expressed early in development, preferentially in neuronal and myogenic lineages, and ubiquitously in adult tissue (32). It has been shown to co-localize with adhesion markers during cell spreading, is intimately linked to the microtubule network (1), has been shown to phosphorylate and activate Plk (33), and is required for fusion of C2C12 myoblasts (43). SLK has also been shown to regulate cell cycle progression (44).
Several LIM domain-containing proteins have roles in cell migration. LIM kinases are required for actin dynamics during directional migration (45) and paxillin modulates focal adhesion turnover, a process required for cell migration (46). Ldb1 (CLIM2, NL1) and the highly related paralog Ldb2 (CLIM1) (hereafter referred to Ldb2 and Ldb1) are LIM domain binding transcription co-factors required for the function of LIM homeodomain transactivators (47-49). Appropriate interactions of these factors are important for normal neuronal sub-type identity and development (50,51).
Here we show that SLK is implicated in cell proliferation, motility and migration and further, that the Ldb1/2 co-activators interact with SLK in vitro and in vivo. We also show that Ldb1 and 2 function to inhibit SLK activity in vitro. Furthermore we establish that Ldb2 but not Ldb1 can bind directly to α-tubulin, providing a link between SLK and the microtubule network. Finally, Cre-mediated excision of Ldb1 or treatment of fibroblasts with siRNA for Ldb1 and 2 results in a 4-fold increase in migration rate in a Boyden chamber haptotaxis assay thus ascribing a novel extranuclear function to Ldb1 and 2 as regulators of SLK and cell migration.
WO 00/49139 discloses a caspase activated protein kinase called SMAK which is identical in amino acid sequence to murine Ste20-like kinase. The reference discloses that SMAK activates two distinct signalling pathways that are involved in mediating apoptosis. Further, the reference notes that it may not be desirable to inhibit the expression of the SMAK protein as the protein appears to be associated with apoptosis and may play a role in preventing neoplasia development.
There is a need in the art to identify compounds that inhibit the proliferation of cells. Further, there is a need in the art for compounds that inhibit the proliferation of cancers or tumor cells. There is also a need in the art to identify compounds that inhibit the motility or migration of cells. There is a further need in the art for compounds that inhibit cancer or tumor cells from metastasizing.
The present invention relates to kinase inhibitors. More specifically, the present invention relates to inhibitors of Ste20-like kinase (SLK) and methods of modulating cell cycle progression and motility of cells using such inhibitors.
According to the present invention there is provided a method of inhibiting proliferation, motility or both proliferation and motility of a cell, for example, but not limited to a cancer or tumor cell in a subject, the method comprising administering an SLK inhibitor to said subject. The subject may be an animal subject, preferably a mammalian subject, more preferably a human subject.
The present invention also provides a method as defined above, wherein the SLK inhibitor is an antisense nucleic acid, a short interfering RNA (siRNA), a catalytically inactive SLK or a nucleic acid encoding a catalytically inactive or kinase-dead SLK. The SLK inhibitor may also comprise a fragment of SLK that is catalytically inactive or kinase-dead.
The present invention also provides a method as defined above wherein the SLK inhibitor is an antibody or fragment thereof which is capable of binding SLK.
The present invention also provides a method as defined above, wherein the SLK inhibitor is a binding partner of SLK, a variant thereof, or a fragment of a binding partner of SLK that is capable of binding to SLK and inhibiting the activity of SLK. In a preferred embodiment, the SLK inhibitor is a heterologous SLK inhibitor meaning an inhibitor that does not exist naturally in a cell.
The present invention also provides for the use of an SLK inhibitor to treat a cancer or tumour in a subject. Further the SLK inhibitor may be employed for the production of a medicament to treat a cancer or tumour in a subject.
The present invention also provides a cell comprising an SLK inhibitor. In a preferred embodiment the cell is a non-cultured cell, preferably a non-cultured cancer or a tumour cell. In still a further embodiment, the cell is a HER2+ carcinoma or sarcinoma.
The present invention also contemplates SLK inhibitors that can be used in the methods as described above.
Also contemplated by the present invention is an in vitro method of inhibiting the proliferation, motility or both the proliferation and motility of a cell comprising administering an SLK inhibitor to said cell. In a preferred embodiment, which is not meant to be limiting in any manner, the cell is a cancer or tumor cell. In a more preferred embodiment the cell is a human cell.
Also contemplated is an in vitro method as defined above, wherein the SLK inhibitor is encoded by a virus, for example, but not limited to a lentivirus, adenovirus or a retrovirus.
The present invention also contemplates an in vitro method as defined above wherein the SLK inhibitor comprises a catalytically inactive SLK or a nucleic acid encoding a catalytically inactive SLK kinase.
Further, the present invention contemplates an in-vitro method as defined above wherein the SLK inhibitor comprises a fragment of SLK. Also provided are in vitro methods wherein the SLK inhibitor is an antisense nucleic acid or a short interfering RNA (siRNA), an antibody or fragment thereof which is capable of binding SLK, a binding partner of SLK, a variant of a naturally occurring binding partner, or a fragment of a binding partner of SLK.
The present invention also provides a method of screening a compound to determine if said compound is effective as an anticancer agent, the method comprising,
It is generally preferred that the second group of cells is treated with an appropriate control under conditions substantially similar to the first group of cells. Further, in an alternate embodiment, which is not meant to be limiting in any manner, the first group of cells are cancer or tumor cells and the second group of cells are non-cancerous normal cells of the same cell type. In a further embodiment, the non-cancerous normal cells and the cancer or tumor cells are from the same initial cell line. In such cases, the first group of cells may be made cancerous by any means known in the art. In still a further embodiment, the non-cancerous normal cells and the cancer or tumor cells may be obtained from a subject, for example, a human subject.
This summary of the invention does not necessarily describe all necessary features of the invention.
The present invention relates to kinase inhibitors. More specifically, the present invention relates to inhibitors of Step 20-like kinase (SLK) and methods of modulating cell cycle progression or cell motility using such inhibitors.
The following description is of a preferred embodiment by way of example only.
According to an embodiment of the present invention, there is provided an inhibitor of Ste20-like kinase (SLK).
By “inhibitor of Ste20-like kinase (SLK)” or “SLK inhibitor” it is meant a product, compound or composition that is capable of interfering with the normal kinase activity of SLK. Various inhibitors of SLK are contemplated by the present invention, for example, but not limited to antibodies or fragments thereof that bind to and inhibit the activity of SLK, antisense or siRNA nucleic acids that for example, but not limited to downregulate SLK production thereby inhibiting SLK activity, catalytically inactive SLK proteins, variants or fragments of SLK that act for example, but not limited to, act as dominant negatives or molecular decoys for protein binding partners of SLK, or small molecules that interfere with the biological activity of SLK.
Without wishing to be considered limiting in any manner, and as will be appreciated by a person of skill in the art, an SLK inhibitor that reduces the production of SLK protein, sequesters, binds or stabilizes SLK in an in-active conformation, promotes increased degradation of SLK protein or that inhibits interaction of SLK with normal binding partners necessary for signal transduction may be considered an inhibitor of Ste20-like kinase (SLK) provided it interferes with the normal kinase activity of SLK. It is to be understood that the SLK inhibitors as described herein may or may not affect the specific activity of an endogenous SLK enzyme present in a cell. The present invention is meant to include all such inhibitors.
Preferably, the SLK inhibitor reduces endogenous SLK kinase activity by at least about 20%, more preferably at least about 30%, still more preferably at least about 40%, 50%, 60%, 70%, 80%, 90% or 100% compared to wild-type SLK. Further, the SLK inhibitors of the present invention may exhibit a range of activity inhibition as defined by any two of the values listed above. In an alternate embodiment, the SLK inhibitor reduces the specific activity of SLK by about 20%, more preferably about 30%, still more preferably about 40%, 50%, 60%, 70%, 80%, 90%, or about 100% compared to wild-type SLK. Further, the SLK inhibitors of the present invention may exhibit a range of specific activity inhibition defined by any two of the values listed above.
SLK kinase activity may be determined using any suitable assay known in the art, for example, but not limited to, as described in Example 1 under the section “Western Blotting, Immunoprecipitations and in vitro Kinase Assays” or the kinase assay as provided herein (30; which is incorporated by reference). Alternatively, SLK kinase activity may be assayed by flow cytometric analysis as described herein, wherein an inhibitor of SLK reduces or inhibits cell cycle progression as compared to a control. For example, but not wishing to be limiting, expression of a kinase inactive SLK results in a G2/M block in cells, whereas control cells continue to cycle. For comparative purposes, a wild-type SLK comprises the SLK protein sequence defined by SEQ ID NO:1.
The SLK inhibitor may comprise a catalytically inactive SLK protein, fragment or variant of a wild-type protein. For example, but not to be considered limiting in any manner, the catalytically inactive SLK may be prepared by mutating one or more amino acids required for kinase activity. Also, catalytically inactive variants of SLK may be prepared by deleting one or more polypeptide segments required for kinase activity, for example, entire protein regions or domains responsible for kinase activity may be deleted or mutated. Examples of catalytically inactive SLK proteins are known in the art and are described herein. It is preferred that SLK inhibitors exhibit no kinase activity. However, it is contemplated that the inhibitor may exhibit reduced kinase activity, that is, less than that of wild-type SLK. In such embodiments, preferably the SLK kinase exhibits less than about 50% of wild-type SLK activity, more preferably less than about 40%, 30%, 20% and still more preferably less than about 10% of wild-type SLK kinase activity.
The SLK inhibitor also may comprise one or more fragments of a wild-type SLK that interfere with the normal kinase activity of the protein. For example, but not to be considered limiting, or bound by theory, a fragment of SLK may bind to one or more protein binding partners of SLK required for normal signal transduction activity. Accordingly, an SLK inhibitor may comprise a fragment of SLK, for example, a polypeptide comprising 5, 7, 9, 10, 12, 15, 17, 20, 21, 25, 30, 35, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200 or more amino acids of SLK. Further, SLK inhibitors that are fragments of SLK may be characterized as comprising a length defined by a range of any two of the values listed.
An SLK inhibitor may also comprise one or more compounds that interact with a wild-type SLK and inhibit kinase activity. In an embodiment, which is not meant to be limiting, the SLK inhibitor binds to wild-type SLK. For example, but not to be considered limiting in any manner, the SLK inhibitor may comprise myosin binding protein (mybp-c), CLIM1/lbd2, CLIM2/Ldb1, nm23 or a fragment thereof. In an alternate embodiment, the inhibitor of SLK may comprise an antibody, or a fragment thereof that is capable of binding to SLK and inhibiting cell cycle proliferation.
Without wishing to be limiting in any manner, a representative wild-type SLK kinase is described under genbank accession number AAD28717 (SEQ ID NO:1). Other variants of wild-type SLK kinase sequences from different species are also known in the art and/or can be readily identified, for example, by performing a blast search using SEQ ID NO:1 or a fragment thereof. In a preferred embodiment, the SLK inhibitor is a human SLK protein that is kinase dead. Thus, the present invention contemplates mutants of the above known SLK kinases which are substantially identical to SEQ ID NO:1 but that are kinase deficient, more preferably kinase dead. For example, but not wishing to be considered limiting, the present invention contemplates inhibitors of SLK kinase that comprise one or more mutations that abolish ATP binding, for example, but not to be considered limiting, the K63R mutation (relative to the amino acid sequence defined by SEQ ID NO:1). Such a sequence is shown in SEQ ID NO:2. Other SLK inhibitors having the corresponding lysine (K) mutated to any other amino acid are also contemplated, as are fragments and variants thereof which inhibit endogenous SLK activity in a cell. By way of example, the present invention contemplates SLK inhibitors that are kinase dead and that exhibit between about 70% and 100% identity with SEQ ID NO:1, for example, but not limited to 70%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or about 100% sequence identity with SEQ ID NO:1.
An SLK inhibitor also may comprise a fusion polypeptide comprising an SLK inhibitor and a heterologous polypeptide sequence. In a preferred embodiment, which is not meant to be limiting, there is provided a fusion protein or fusion polypeptide comprising an SLK inhibitor and a protein transduction domain. By “protein transduction domain” it is meant a sequence of nucleic acids that encode a polypeptide, or a sequence of amino acids comprising the polypeptide, wherein the polypeptide facilitates localization to a particular site, for example a cell or the like, or it may facilitate transport across a membrane or lipid bilayer. The polypeptides and nucleic acids of the present invention may be fused to a protein transduction domain to facilitate transit across lipid bilayers or membranes.
Many polypeptides and nucleic acids do not efficiently cross the lipid bilayer of the plasma membrane, and therefore enter into cells at a low rate. However, there are certain naturally occurring polypeptides that can transit across membranes independent of any specific transporter. Antennapedia (Drosophila), TAT (HIV) and VP22 (Herpes) are examples of such polypeptides. Fragments of these and other polypeptides have been shown to retain the capacity to transit across lipid membranes in a receptor-independent fashion. These fragments, termed protein transduction domains, are generally 10 to 27 amino acids in length, possess multiple positive charges, and in several cases have been predicted to be ampipathic. Polypeptides and nucleic acids that are normally inefficient or incapable of crossing a lipid bilayer, can be made to transit the bilayer by being fused to a protein transduction domain.
U.S. Publication 2002/0142299 (which is incorporated herein by reference) describes a fusion of TAT with human beta-glucuronidase. This fusion protein readily transits into various cell types both in vitro and in vivo. Furthermore, TAT fusion proteins have been observed to cross the blood-brain-barrier. Frankel et al. (U.S. Pat. No. 5,804,604, U.S. Pat. No. 5,747,641, U.S. Pat. No. 5,674,980, U.S. Pat. No. 5,670,617, and U.S. Pat. No. 5,652,122; which are incorporated herein by reference) have also demonstrated transport of a protein (beta-galactosidase or horseradish peroxidase) into a cell by fusing the protein with amino acids 49-57 of TAT.
PCT publication WO01/15511 (which is incorporated herein by reference) discloses a method for developing protein transduction domains using a phage display library. The method comprises incubating a target cell with a peptide display library and isolating internalized peptides from the cytoplasm and nuclei of the cells and identifying the peptides. The method further comprised linking the identified peptides to a protein and incubating the peptide-protein complex with a target cell to determine whether uptake is facilitated. Using this method a protein transduction domain for any cell or tissue type may be developed. US Publication 2004/0209797 (which is incorporated herein by reference) shows that reverse isomers of several of the peptides identified by the above can also function as protein transduction domains.
PCT Publication W099/07728 (which is incorporated herein by reference) describes linearization of protegrin and tachyplesin, naturally occurring as a hairpin type structure held by disulphide bridges. Irreversible reduction of disulphide bridges generated peptides that could readily transit cell membranes, alone or fused to other biological molecules. US Publication 2003/0186890 (which is incorporated herein by reference) describes derivatives of protegrin and tachyplesin that were termed SynB1, SynB2, SynB3, etc. These SynB peptides were further optimized for mean hydrophobicity per residue, helical hydrophobic moment (amphipathicity), or beta hydrophobic moment. Various optimized amphipathic SynB analog peptides were shown to facilitate transfer of doxorubicin across cell membranes. Further, doxorubicin linked to a SynB analog was observed to penetrate the blood-brain-barrier at 20 times the rate of doxorubicin alone.
The protein transduction domains described in the preceeding paragraphs are only a few examples of the protein transduction domains available for facilitating membrane transit of small molecules, polypeptides or nucleic acids. Other examples are transportan, W/R, AlkCWK18, DipaLytic, MGP, or RWR. Still many other examples will be recognized by persons skilled in the art. The SLK inhibitors of the present invention may employ any of such sequences.
An SLK inhibitor may comprise a nucleic acid encoding one or more of the SLK inhibitors described above. In an embodiment the SLK inhibitor is a nucleic acid encoding a catalytically inactive SLK, a variant or fragment thereof that interferes with SLK kinase activity. Also contemplated, the SLK inhibitor may comprise an SLK antisense nucleic acid or fragment thereof, for example, but not limited to antisense DNA, antisense RNA, a short interfering nucleic acid, for example, but not limited to siRNA. In a preferred embodiment, the SLK antisense nucleic acid comprises a short interfering RNA (siRNA), RNAi or duplex thereof.
In an embodiment that is not meant to be limiting in any manner, the nucleic acid encodes the SLK inhibitor defined by SEQ ID NO:2.
To determine whether a protein or nucleic acid exhibits identity with the sequences presented herein, oligonucleotide or protein alignment algorithms may be used, for example, but not limited to a BLAST (GenBank URL: www.ncbi.nlm.nih.gov/cgi-bin/BLAST/, using default parameters: Program: blastn; Database: nr; Expect 10; filter: default; Alignment: pairwise; Query genetic Codes: Standard(1)), BLAST2 (EMBL URL: http://www.embl-heidelberg.de/Services/index.html using default parameters: Matrix BLOSUM62; Filter: default, echofilter: on, Expect: 10, cutoff: default; Strand: both; Descriptions: 50, Alignments: 50), or FASTA, search, using default parameters. Polypeptide alignment algorithms are also available, for example, without limitation, BLAST 2 Sequences (www.ncbi.nlm.nih.gov/blast/bl2seq/bl2.html, using default parameters Program: blastp; Matrix: BLOSUM62; Open gap (11) and extension gap (1) penalties; gap x_dropoff: 50; Expect 10; Word size: 3; filter: default).
An alternative indication that two nucleic acid sequences are substantially identical is that the two sequences hybridize to each other under moderately stringent, or preferably stringent, conditions. Hybridization to filter-bound sequences under moderately stringent conditions may, for example, be performed in 0.5 M NaHPO4, 7% sodium dodecyl sulfate (SDS), 1 mM EDTA at 65° C., and washing in 0.2×SSC/0.1% SDS at 42° C. for at least 1 hour (see Ausubel, et al. (eds), 1989, Current Protocols in Molecular Biology, Vol. 1, Green Publishing Associates, Inc., and John Wiley & Sons, Inc., New York, at p. 2.10.3). Alternatively, hybridization to filter-bound sequences under stringent conditions may, for example, be performed in 0.5 M NaHPO4, 7% SDS, 1 mM EDTA at 65° C., and washing in 0.1×SSC/0.1% SDS at 68° C. for at least 1 hour (see Ausubel, et al. (eds), 1989, supra). Hybridization conditions may be modified in accordance with known methods depending on the sequence of interest (see Tijssen, 1993, Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes, Part I, Chapter 2 “Overview of principles of hybridization and the strategy of nucleic acid probe assays”, Elsevier, N.Y.). Generally, but not wishing to be limiting, stringent conditions are selected to be about 5° C. lower than the thermal melting point for the specific sequence at a defined ionic strength and pH.
The present invention also contemplates nucleic acids which hybridize under high stringency conditions to a nucleic acid molecule which encodes an SLK kinase, preferably the human SLK. Appropriate stringency conditions which promote DNA hybridization are known to those skilled in the art, or can be found in several reference documents, for example, but not limited to Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), which is herein incorporated by reference.
SLK inhibitors that are nucleic acids may comprise part of a larger nucleic acid or genetic construct, for example, but not limited to a vector or the like. In an embodiment, which is not meant to be limiting, an SLK inhibitor is produced in a cell by infecting the cell with a virus genetically engineered to produce the SLK inhibitor. In a preferred embodiment, but without wishing to be limiting, the SLK inhibitor may be encoded by a virus, for example, but not limited to an adenovirus, lentivirus, retrovirus or the like. In a preferred embodiment, the virus is an adenovirus or retrovirus.
The nucleotide sequence may be operably linked to regulatory elements in order to achieve preferential expression at desired times or in desired cell or tissue types. Furthermore, as will be known to one of skill in the art, other nucleotide sequences including, without limitation, 5′ untranslated region, 3′ untranslated regions, cap structure, poly A tail, translational initiators, sequences encoding signalling or targeting peptides, translational enhancers, transcriptional enhancers, translational terminators, transcriptional terminators, transcriptional promoters, may be operably linked with the nucleotide sequence encoding a polypeptide (see as a representative examples “Genes VII”, Lewin, B. Oxford University Press (2000) or “Molecular Cloning: A Laboratory Manual”, Sambrook et al., Cold Spring Harbor Laboratory, 3rd edition (2001)). A nucleotide sequence encoding a SLK inhibitor or a fusion polypeptide comprising a SLK inhibitor and a protein transduction domain may be incorporated into a suitable vector. Vectors may be commercially obtained from companies such as Stratagene or InVitrogen. Vectors can also be individually constructed or modified using standard molecular biology techniques, as outlined, for example, in Sambrook et al. (Cold Spring Harbor Laboratory, 3rd edition (2001)). A vector may contain any number of nucleotide sequences encoding desired elements that may be operably linked to a nucleotide sequence encoding a polypeptide or fusion polypeptide comprising a protein transduction domain. Such nucleotide sequences encoding desired elements, include, but are not limited to, transcriptional promoters, transcriptional enhancers, transcriptional terminators, translational initiators, translational, terminators, ribosome binding sites, 5′ untranslated region, 3′ untranslated regions, cap structure, poly A tail, origin of replication, detectable markers, affinity tags, signal or target peptides and the like. Persons skilled in the art will recognize that the selection and/or construction of a suitable vector may depend upon several factors, including, without limitation, the size of the nucleic acid to be incorporated into the vector, the type of transcriptional and translational control elements desired, the level of expression desired, copy number desired, whether chromosomal integration is desired, the type of selection process that is desired, or the host cell or the host range that is intended to be transformed.
The SLK inhibitors described herein, as well as SLK inhibitors known in the art may be employed in a method to reduce or inhibit cell proliferation. For example, the present invention provides a method for inhibiting the proliferation of a cell by inhibiting endogenous SLK activity in the cell. In an alternate embodiment, there is provided a method of inhibiting the proliferation of a cancer or tumor cell by inhibiting endogenous SLK activity in the cell. Methods to reduce or inhibit cell proliferation may be practised in vitro or in vivo. In a preferred embodiment, the method is practised in a subject, preferably a human subject.
The present invention also contemplates a method of inhibiting the movement or migration of a cell by inhibiting endogenous SLK activity in the cell. In a further embodiment, there is provided a method of preventing a cancer cell or tumor cell from metastasizing by inhibiting endogenous SLK activity in the cancer or tumor cell. In a preferred embodiment, the method is practised in a subject, preferably a human subject.
The present invention also contemplates a method of inhibiting the proliferation of a cancer or tumor cells in a subject by administering an SLK inhibitor. The subject may be an animal subject, preferably a mammalian subject. In a preferred embodiment, the subject is a human subject.
Various types of cancers and tumors may be treated using the SLK inhibitors and methods as described herein, including those types of cancers with a high propensity to metastasize. Without wishing to be limiting, the present invention contemplates treating cancers including, but not limited to breast, bone, brain, blood including any blood cell type cancer, prostate, liver, kidney, skin, stomach, spleen, colon, rectal, testicular, ovarian, uteral, thyroid, and the like. Accordingly, the present invention contemplates a method for treating a cancer or tumour in a subject comprising the step of administering an SLK inhibitor to the subject in need thereof. Further, the present invention contemplates a method of preventing metastasis of a cancer comprising the step of administering an SLK inhibitor to subject in need thereof. The invention also contemplates a method of preventing proliferation of a cancer or tumour in a subject, comprising the step of administering an SLK inhibitor to a subject in need thereof.
The present invention also contemplates a cell, group of cells, tissue or the like that comprises the SLK inhibitors as described herein. In an embodiment, which is not meant to be limiting, the cell is a non-cultured cell, preferably an in-vivo cell. In a further embodiment, the cell is a cancer cell or a tumour cell, more preferably an in vivo cancer cell or tumour cell. The present invention also contemplates cancers that are carcinomas and sarcomas. In still a further embodiment, the cell is a HER2+ carcinoma. In all of such cases, it is preferred the SLK inhibitor is a heterologous SLK inhibitor that does not exist naturally in the cell. However, the present invention also contemplates artificially increasing the presence of a naturally occurring SLK inhibitor in a cell, for example, but not limited to by overexpressing the a naturally occurring SLK inhibitor in the cell.
All citations are hereby incorporated by reference.
Cell Lines, Culture, and Adenovirus Infection—The mouse fibroblast lines MEF-3T3 (MEF Tet-Off, C3018, Clontech) and C3H10T½ (ATCC number CCL-226) were employed in experiments. Similar results were obtained for both cell lines. The GFP-tubulin expressing cells (LLCKP-1) were a kind gift from Patricia Wadsworth (34). Cell lines were maintained at 37° C. with 5% CO2 in Dulbecco's modified Eagle's medium (DMEM, Bio-Whitaker) supplemented with 10% fetal bovine serum (FBS), 2 mM L-glutamine, 50 μg/mL penicillin, and 50 μg/mL streptomycin. For cell cycle experiments, fibroblasts were arrested by 48 hour incubations in 0.25% FBS-DMEM and released from quiescence by the addition of 20% FBS-DMEM. The epitope-tagged kinase dead or activated versions of SLK used in these studies (HA-KΔC or HA-YΔC) have been previously described (1) and consist of a C-terminal truncation (aa 1-373) with or without an ATP-binding site (Lys 63->Arg) mutation. To monitor the effect of kinase deficient SLK on cell cycle kinetics, adenoviral vectors expressing HA-KΔC or a β-galactosidase (LacZ) control were used to infect quiescent cultures. Cells were infected at a MOI of 100 by the addition of the adenovirus directly to cells in 0.25% FBS-DMEM 16 hours before the addition of 20% FBS-DMEM and analysis. To isolate fibroblast populations synchronized at M phase, the cultures were treated overnight with nocodazole (40 ng/mL, Sigma-Aldrich) and shaken off into PBS by aggressive tapping against a solid surface. Detached cells floating in PBS were then collected by centrifugation.
For mitotic spindle induction experiments, LLCKP-1 cells expressing GFP-tubulin were microinjected with HA-YΔC expression plasmid as described previously (1). Xenopus oocytes were prepared and injected with cRNA as described (35). Germinal vesicle breakdown (GVBD) was determined from at least 20 oocytes pooled from two animals 15 hours following SLK injection or progesterone treatment. Western blot analysis for Myc-SLK was performed 15 hours post-injection.
Western Blotting, Immunoprecipitations, and in vitro Kinase Assays—For protein analysis, the cells were lysed in modified RIPA buffer as previously described (1). Equal amounts of extracts were resolved by SDS-PAGE and transferred to polyvinylidene difluoride (PVDF) membranes (Perkin Elmer Life Sciences Inc.) which were then probed with the following antibodies. Anti-Cdc2, cyclins D, E, A, and B (Upstate Biotechnology). The SLK antibody was as previously described (30). Primary antibodies were detected using either a goat anti-rabbit IgG or goat anti-mouse IgG horseradish peroxidase-labeled secondary antibody (BioRad) and visualized using Western Lightning chemiluminescence reagent (Perkin Elmer Life Sciences Inc.) and exposure to X-ray film. SLK immunoprecipitations and kinase assays were carried out essentially as previously described (31). Briefly, equal amounts of lysate were immunoprecipitated for 2 hours at 4° C. using 1 μg of SLK antibody and 20 μL of protein A sepharose (4 fast flow, Amersham Biosciences). Immunoprecipitates were then washed three times with NETN (50 mM Tris-HCl [pH 7.5], 150 mM NaCl, 1 mM EDTA, 0.1% Nonidet P-40) and once with kinase buffer (20 mM Tris-HCl [pH 7.5], 15 mM MgCl2, 10 mM NaF, 10 mM β-glycerophosphate, 1 mM orthovanadate). Kinase reactions (20 μL) were then initiated by the addition of 5 μCi of [32P]ATP and incubated at 30° C. for 30 minutes. These reactions were terminated by the addition of 4×SDS loading buffer and then resolved by SDS-PAGE, transferred to PVDF membranes, and exposed to X-ray film. Membranes were then probed for SLK to assess immunoprecipitation efficiency. SLK autophosphorylation was used as an indicator of kinase activity.
Immunofluorescence and Flow Cytometry—Immunofluorescence studies were carried out by fixation of cells growing on glass cover slips in 4% paraformaldehyde for 10 minutes. The cells were then washed twice with PBS and incubated with primary antibodies for 1 hour. The primary antibodies used in immunofluorescence studies were as follows: anti-α-tubulin(clone DM1, Sigma), anti-phospho-H3 (Ser10) (Cell Signaling Technology), anti-beta-galactosidase (Promega), anti-HA (12CA5 or sc-805, Santa Cruz Biotechnology Inc.) and anti-SLK (30). Antibodies were detected with either anti-mouse or anti-rabbit antibodies conjugated to either fluorescein isothiocyanate (FITC) or tetramethyl rhodamine isothiocyanate (TRITC) (Sigma). DAPI (4′, 6-diamidino-2-phenylindole, 0.25 μg/mL) was used to stain DNA and the samples were visualized with a Zeiss Axioscope100 epifluorescence microscope equipped with the appropriate filters and photographed with a digital camera (Sony Corporation HB050) using the Northern Eclipse software package. Quantitative analysis for phospho-H3 (pH3) immunostaining was performed by visually scoring stained cells for both HA (or LacZ) and pH3. The data were graphed as double positive (HA or LacZ+pH3) cells for each time point analysed. At least 200 HA or LacZ-positive cells were scored for each time point. Cells analysed by flow cytometry were trypsinized and washed once in 10% FBS-DMEM. Cells were then washed twice in PBS supplemented with 1 mM EDTA (PBSE) and then fixed in 1 mL of PBSE by the drop wise addition of 2 mL of 80% ethanol pre-chilled to −20° C. The samples were then stored at −20° C. for a minimum of 2 hours, washed once in PBSE, resuspended in DNA content staining buffer (1.1% citrate buffer, 10 μg/mL propidium iodide, 1 mg/ml RNase) and incubated for 30 minutes at 37° C. before being analyzed on a Beckman-Coulter flow cytometer using the Expo 32 software package. BrdU pulse labeling was performed using a BrdU Flow Kit (BD Biosciences) according to the manufacturers instructions. Briefly, 16 hours before labeling, cultures were infected with either HA-KΔC or LacZ adenovirus at a MOI of 100 for 90 minutes in unsupplemented DMEM and then grown in 10% FBS-DMEM. The cultures were then labeled with BrdU for 1 hour and collected at various times. The DNA content of BrdU positive cells was then analyzed flow cytometrically.
Cell Counts, Cloning, and Transfections—To monitor cell proliferation, the cells were counted after infection on day 0 at a MOI of 100 as described above. Cell populations were trypsinized and scored by trypan blue exclusion over time. Cell counts were performed in triplicates in three independent experiments. For anti-sense SLK expression, a 5-prime 300 base pair SLK fragment was cloned into the pEMSV-puro expression vector in the reverse orientation. The antisense SLK plasmid and the puromycin control were then transfected into MEF-3T3 cells using LipofectAMINETM 2000 (Invitrogen) according to the manufacturers protocol and selected in puromycin (100 μg/mL) over a two-week period. Following selection, stable transfectants were visualized using CYTO-QUIK staining (Fisher Health Care) followed by several PBS washes. SLK Smart Pools siRNAs were obtained from Dharmacon against the following murine SLK target sequences: 5′-GGTTGAGATTGACATATTA-3′(SEQ ID NO:3). In addition to a scrambled siRNA (5′-GATAATTTATGGATGTGAC-3′) (SEQ ID NO:4), control siRNA comprised in the siCONTROL (Dharmacon; 5′-UAGCGACUAAACACAUCAAUU-3′) (SEQ ID NO:5), having no perfect match to known human or mouse sequences. All siRNAs were transfected using the Transit-TKO reagent (Mirrus Corp.) according to the manufacturer's instructions.
SLK Colocalizes with the Mitotic Spindle and is Regulated During the Cell Cycle
We have previously shown that a proportion of SLK is associated with the microtubule network of exponentially growing fibroblasts (1). During immunofluorescence studies involving the colocalization of SLK to the microtubule network in asynchronous cultures, we observed rare patterns of SLK and α-tubulin colocalization that resembled the mitotic spindle. To further investigate the possibility that SLK might co-localize with the mitotic spindle, we performed confocal microscopy. Although some SLK was found outside of the mitotic spindle, confocal analysis of DAPIstained cells, in combination with anti-SLK and anti-α-tubulin, shows that most of the SLK staining co-localized with tubulin during metaphase (
To further investigate the potential role of SLK in cell cycle progression, its activity was monitored throughout the different phases of the cell cycle using synchronized cell populations. Serum-starved cultures were released from G0 by the addition of serum, collected at various times, and monitored for SLK activity and DNA content by kinase assays and FACS analysis, respectively.
To investigate the potential role of SLK in proliferation, an expression vector bearing an antisense SLK fragment was transfected into MEF-3T3 fibroblasts and subjected to puromycin selection. Stable clones were visualized after 14 days using Cyto-Quick stain (Fisher). As shown in
As for antisense SLK expression, infection of MEF-3T3 cells with an adenoviral vector carrying a kinase dead truncation of SLK (SLK1-373K63R, termed HA-KΔC) suppressed cell proliferation as determined by dye exclusion cell counts (
To further investigate the mechanism by which KΔC inhibits proliferation, quiescent MEF-3T3 cultures were infected with a KΔC-expressing adenovirus, or control LacZ virus, serum-stimulated and subjected to DNA content analysis over time. As shown in
Supporting these data, flow tracking of BrdU-pulsed exponentially growing KΔC-infected cultures shows that they proceed through the G2/M compartment with delayed kinetics when compared to LacZ-infected cells. Taken together, these results suggest that SLK is required for normal progression through the G2 or M phase.
The levels of the various cyclins have been demonstrated to fluctuate during the cell cycle (reviewed in (5)). Cyclin D has been observed to be induced prior to S phase and to remain elevated in proliferating cells. Cyclin E is transiently upregulated at the G1/S boundary whereas cyclins A and B are induced at the S/G2 boundary and downregulated at the onset and the end of M phase, respectively. Therefore, to better define the cell cycle block induced by kinase deficient SLK, control and KΔC-infected cultures were surveyed for cyclin expression over time following release from Go. The infection efficiency was found to be typically between 70-80% for both viruses and the HA-KΔC protein was observed to be expressed at levels that were similar to endogenous SLK (data not shown). Our results show that, relative to actin, cyclin D was slightly upregulated following serum stimulation in both the control and KΔC-infected cultures, suggesting that they re-entered the cell cycle (
During interphase, cytosolic MPF is kept inactive by inhibitory phosphorylation of cdc2 on threonine 14 (Thr14) and tyrosine 15 (Tyr15) by Myt1 and Weel, respectively (9-11). Activation of this complex is triggered by the Cdc25C phosphatase through cdc2 dephosphorylation of Thr14 and Tyr 15 (12-14). In agreement with elevated cyclin A levels, KΔC-infected cultures did not significantly upregulate Cdc2 activity as evidenced by the high levels of Cdc2 tyrosine 15 phosphorylation (
Chromosome condensation initiated in early G2 (38) is accompanied by the hyperphosphorylation of histone H1 (24) and phosphorylation of H3 (25) on serine 10 (Ser10) (26). To further refine the cell cycle block induced by KΔC expression, adenovirus-infected cultures were stained for both KΔC expression and phospho-H3. Double immunostaining of serum stimulated fibroblast cultures at 24 hours (FIG. 5AF) shows that H3 phosphorylation was markedly reduced in KΔC-expressing cells in comparison to control infected cultures. Although the proportion of HA- and phospho-H3-positive cells slightly increased at 28 and 32 hours post stimulation, their number was significantly lower than control cells, suggesting that KΔC-expressing cells are delayed in early G2.
Our results show that expression of a kinase inactive SLK is sufficient to induce an early G2 cell cycle block in cycling fibroblasts, suggesting that an SLK-dependent pathway is required during G2 for progression into mitosis. To determine whether SLK plays a central role in G2 and to rule out potential non-specific effects by KΔC overexpression, exponentially growing fibroblasts were transfected with an SLK siRNA pool and subjected to DNA content analysis. Transfection of SLK siRNAs downregulated SLK protein levels by 80-90% within 48 hours (
Cell cycle progression is regulated by complex signaling networks involving posttranslational modification, gene expression and cytoskeletal reorganization. Progress through the various phases involves the activation of key factors and is monitored by various “checkpoint” proteins. We have previously isolated a Ste20-like kinase termed SLK that is involved in cytoskeletal reorganization (1,30,31). Interestingly, a fraction of SLK protein is also observed to associate with the microtubule (MT) network in spreading and exponentially growing cells (1). Here it is shown that SLK also associates with the MT network at mitosis, suggesting that it plays a role in cell cycle progression. To investigate this, the activity and expression of SLK was evaluated throughout the cell cycle and the effect of a kinase-defective SLK on cell cycle progression was assessed.
The results show that SLK co-localizes with the mitotic spindle during M phase and that its kinase activity is upregulated as synchronized fibroblast cultures enter the G2/M compartment. Expression of an antisense SLK construct or a kinase-deficient mutant inhibited cell proliferation. Flow cytometric analysis of these populations showed that SLK is required for progression through the G2/M compartment and that cells expressing a kinase inactive SLK fail to downregulate cyclin A. Furthermore, we have observed that cultures expressing an inactive SLK show reduced histone H3 phosphorylation and p34Cdc2 activation. Supporting this, overexpression of activated SLK induced spindle formation and cell cycle re-entry in Xenopus oocytes. Overall our data suggests that SLK is required upstream of Cdc2 and that interfering with SLKdependent pathways leads to cell cycle arrest early in the G2 phase of the cell cycle.
Without wishing to be bound by theory or limiting in any manner, an interpretation of the data presented here indicates that SLK is required during G2, at a point after cyclin A expression and before Cdc2 activation, for progression into mitosis. A Xenopus Lok/Si tx10 homolog, xPolo-like kinase (xPlkk1), has been demonstrated to activate Plx1 (22). Interestingly, SLK has been demonstrated to phosphorylate and activate Plk in a mammalian system (33).
An evolutionary conserved relationship appears to exist between mammalian and amphibian Ste20 like kinases, the polo like kinase family, and the Cdc25C phosphatase. The human homolog of the Ste20 like kinase Lok, Stx10, has been shown to associate with and phosphorylate Plk1 (40) and Plk3 has been shown to initiate the nuclear translocation of Cdc25C by phosphorylating Cdc25C on serine 191(41). In Xenopus, the polo like kinase, Plx1, has been shown to activate Cdc25C (21), an event that has not been unarguably proven in a mammalian system and may be species specific. If Plk requires a signal from SLK to activate Cdc25C in a mammalian system, one would predict a G2/M arrest, similar to the findings presented here. This would result in a Cdc25C protein that is deficient in all of the post-translational modifications required to initiate mitosis. However, the questionable validity and specificity of phospho-specific Cdc25C antibodies has made the identification of the various forms of the phospho-Cdc25C difficult and inconclusive (not shown). We have previously shown that SLK can induce actin depolymerization and cell death in various cell lines (1,31). Without wishing to be bound by theory or limiting in any manner, one possibility is that SLK overexpression in cycling cells induces a deregulated mitotic entry, bypassing cell cycle controls, resulting in actin breakdown and death. Alternatively, SLK-mediated cytoskeletal reorganization may be required for, or trigger, checkpoint activation, G2 progression and mitotic entry.
Without wishing to be limiting or bound by theory,
We have identified several SLK binding proteins, including the CLIM2 adapter protein (
In addition to the regulation of nm23 expression, one study has shown that HRG stimulation of MCF-7 results in the serine phosphorylation of the signaling adapter paxillin. Serine phosphorylation of paxillin is associated with increased adhesion turnover and motility. We have recently found that SLK can phosphorylate paxillin in vitro in its LD domains (
Ldb1-floxed primary MEFs were generated from homozygous Ldb1 floxed 13.5 dpc embryos. Briefly, the internal organs were removed and the embryos were minced 3 ml of trypsin-EDTA solution (0.05%, Gibco). Dissociated embryos were incubated for 3 minutes at 37° C. followed by the addition of complete growth medium. The tissue was then triturated several times and incubated at 37° C. with 5% CO2 for 1-3 days. After 3-4 days in culture the cells were split 1:4, grown for 48 h and frozen as live stocks. All experiments were performed on cultures passaged 2-6 times. MEF 3T3, NIH3T3 and primary MEFs were all maintained in Dulbecco's modified MEM (DMEM, Gibco) supplemented with 10% fetal bovine serum (FBS, Gibco), 2 mM L-glutamine (Gibco) and penicillin G (200 U/ml, Gibco) and streptomycin sulfate (200 μg/ml, Gibco) in a humidified 37° C. incubator at 5% CO2. DNA transfections into cultured cells were performed using lipofectamine and plus reagent (Invitrogen) according to manufacturers recommendations using a total of 2 μg of plasmid DNA. Rat primary cortical neurons were generated essentially as described (60). Embryos were obtained from pregnant Sprague-Dawley rats at embryonic day 15 and the cortical tissue removed to 1× Hank's balanced salt solution (HBSS). Tissue was triturated several times, incubated with trypsin and DNase for 30 minutes at 37° C. with shaking. Cells were recovered and plated on poly-L-lysine coated dishes in neurobasal medium supplemented with B2 and N27.
MEF 3T3 or NIH 3T3 cells were either co-transfected as described with GFP and deletions of Ldb1 and 2, treated with siRNA to either SLK, Ldb1, 2 or both Ldb1 and 2 and serum starved overnight. Cells were trypsinized the following day and trypsinization halted with the addition of soybean trypsin inhibitor (1×, Sigma). Cells (1−3×104) were resuspended in DMEM containing 0.5% BSA and added to the top of a Boyden transwell migration chamber pre-coated with fibronectin (10 μg/ml). The cells were then allowed to migrate for 3 hours. Residual cells were removed from the top of the chamber and the filter was rinsed in PBS, fixed in 4% PFA for 10 minutes and stained with DAPI (0.5 mg/ml, Sigma). The cells that migrated to the underside of the filter were enumerated using DAPI fluorescence. 5 to 10 random fields were counted. Cell counts were performed in triplicate for three independent experiments. Representative experiments are shown. Scratch wound induced migration was performed as described (52). Briefly, MEFs were plated on fibronectin (10 μg/ml) and confluent monolayers were then scratched with pipette tips such that 50% of the monolayer was removed. Cells were then washed with PBS, refed and collected at various time points.
NIH 3T3 cells plated at a density of 3×105 in 60 mm plates were transfected with 50 or 100 nM siRNA (Dharmacon) duplex for SLK (5′-GGUUGAGAUUGACAUAUUA) (SEQ ID NO:6), Ldb2 (5′-ACAAGCAGCACGUCCAAUAUU) (SEQ ID NO:7) or Ldb1 (5′-GAACUUAUGUCCCGCCACAUU) (SEQ ID NO:8) using the Trans-IT TKO transfection reagent (Mirus Corp.) according to manufacturers recommendations. Cells were collected at 24 or 48 hours post-transfection and assayed for cell migration by Boyden chamber and protein expression by western blot analysis. Control siRNAs consisted of Dharmacon's non-targeting duplex. Similar results were obtained with scrambled siRNAs.
DNA plasmids were constructed using standard molecular cloning techniques. Myc-tagged SLK plasmids were constructed as described (31). The GST-SLK plasmids were generated by subcloning the corresponding fragments from the Myc-tagged versions (Sabourin et al., 2000) to pGEX-5× or 4T1 (Amersham). The yeast two hybrid SLK-ATH bait plasmid was constructed by inserting the ATH (XhoI digested, blunted with Klenow) domain of SLK in frame with the Gal4 DNA binding domain in pAS2 (BD Clontech). Ldb1 and 2 were excised from pACT2 (XhoI/EcoRI) and subcloned in frame into Myc and HA epitope-tagged vectors (pCAN-HA or pCAN-Myc). The following Ldb2 constructs were generated by excising fragments of Ldb2 from HA-Ldb2 and recloning into pCAN-HA. HA-Ldb2 DLBD (aa 1-296), HA-Ldb2 DD (aa 1-186), HA-Ldb2 NLS (aa 188-288), and HA-Ldb2 DDDC (aa 1-124). HA-Ldb2 LBD (aa 298-373) was generated by PCR (5′-ggggggatccagctgcaaacctgagtctgtcc-3′ (SEQ ID NO:9) and 5′-gggggaattcacgggcctattgacagtggattct-3′) (SEQ ID NO:10) using VENT polymerase (NEB). All clones were verified by DNA sequencing.
The primary antibodies used in these studies were as follows: SLK polyclonal antibodies were as described previously (31), Ldb1 (Santa Cruz), Paxillin (BD Transduction labs), PKR (Santa Cruz), α-tubulin (Sigma) and Ldb2 (Abcam) was used at 1:100.
For immunofluorescence studies, mouse embryo fibroblasts were plated on coverslips coated with or fibronectin (10 μg/ml) and incubated overnight. The following day cells were rinsed with PBS, fixed in 4% PFA and blocked in PBS containing 5% goat or donkey serum and 0.3% triton-X100 for 20 minutes. Fresh blocking solution containing primary antibody was added and incubated for 1 h at room temperature. Antibodies were detected with either anti-mouse, anti-goat or anti-rabbit secondaries conjugated to either fluorescein isothiocyanate (FITC) or tetramethyl rhodamine isothiocyanate (TRITC) (Sigma). The samples were visualized with a Zeiss Axioscope100 epifluorescence microscope equipped with the appropriate filters and photographed with a digital camera (Sony Corporation HB050) using the Northern Eclipse software package.
Cells were lysed in RIPA buffer as previously described (44) and lysates were cleared by centrifugation at 10000 g for 2 minutes. Protein concentrations were determined using protein assay dye reagent (Biorad). Equal amounts of protein (20-40 μg) were electrophoresed on 8-15% polyacrylamide gels and transferred to PVDF membrane. Membranes were probed with the indicated antibodies overnight at 4° C. in 5% skim milk powder in 1×TBST (50 mM Tris pH 7.4, 150 mM NaCl, 0.05 Tween 20). Membranes were washed in TBST and incubated with horseradish peroxidase coupled secondary antibodies and the reactive proteins were detected using chemiluminescence (Perkin Elmer) and exposure to X-ray film.
For immunoprecipitations, 300 μg of protein lysate was immunoprecipitated with 2-3 μg of antibody and 20 μl of protein A sepharose (Pharmacia) for 2-12 hours. Immunecomplexes were recovered by centrifugation and washed with NETN buffer (20 mM Tris-HCl pH 8.0, 1 mM EDTA, 150 mM NaCl, 0.5% Nonidet P-40) and subjected to SDS-polyacrylamide gel electrophoresis (PAGE) or kinase assay.
In vitro SLK kinase assays were performed following SLK immunoprecipitation as described previously (44). Kinase reactions were stopped by adding 7 ml of 4× sodium dodecyl sulfate (SDS) sample buffer and electrophoresed on 8% SDS-PAGE. The gels were transferred to PVDF membranes and subjected to autoradiography followed by western blotting with SLK antibody.
GST fusion proteins were generated by induction of bacterial cultures with 1 mM isopropyl-beta-D-thiogalactopyranoside (IPTG, Sigma) for 2 hours. Bacteria were pelleted, resuspended in 1 ml bacterial lysis buffer (20% sucrose, 10% glycerol, 50 mM Tris-HCl pH 8.0, 2 mM MgCl2, 2 mM DTT, 10 μg/ml leupeptin, 10 μg/ml pepstatin, 10 μg/ml aprotinin, 1 mM phenylmethylsulphonylfluoride [PMSF] and 100 μM benzamidine) and sonicated on ice.
Glutathione sepharose beads (Amersham Pharmacia) were added to the cleared supernatants and bound GST fusions were collected by centrifugation, washed three times with NETN and subjected to binding assays. In vitro translated proteins were generated using the TNT quick coupled in vitro transcription translation kit (Promega) according to the manufacturer's instructions. Translated proteins were incubated with either GST or GST fusions in NETN buffer, washed with NETN and eluted from the beads by boiling in sample buffer. Proteins were fractionated by SDS-PAGE, the gels were stained with Coomassie brilliant blue (Sigma) to visualize the proteins, destained (30% methanol, 10% acetic acid), dried and subjected to autoradiography.
Recombinant SLK was prepared by inducing an overnight culture of GST-SLK with IPTG and preparing GST SLK as described above. Recombinant His-tagged Ldb2 and 2 were prepared by inducing overnight cultures with IPTG and purifying recombinant protein through a Ni-NTA columns (Qiagen) according to manufacturer's instructions. Kinase assays were performed as described above.
Yeast two-hybrid screens were performed as suggested by the manufacturer (BD Clontech). Briefly, the ATH domain of SLK was subcloned into pAS2, in frame with the GAL4-DBD as described above. Yeast strain AH109 (BD Clontech) was transformed and tested for self activation using the endogenous LacZ reporter and His auxotrophy. The resulting AH109 clones were mated with library (mouse E10.5 cDNA) pre-transformed Y187 and His/Trp/Leu auxotrophs were screened for positive interaction. Of the resulting 29 clones, 5 contained the Ldb1 cDNA and three the Ldb2 cDNA. cDNAs were subcloned into HA or Myc-tagged vectors and further tested for ATH binding.
We have previously shown that SLK can be co-precipitated with α-tubulin and that it localizes to membrane ruffles at the periphery of spreading fibroblasts (1). In addition, SLK induces cytoskeletal rearrangements through a Rac1-mediated pathway (1). Therefore, we hypothesized that SLK plays a role in cell migration and investigated its activity at various time points following scratch wound induced migration of fibroblast monolayers (52). In vitro kinase assays show that SLK activity markedly increased following scratch wounding of confluent fibroblasts, reaching a maximum at about 60 minutes, suggesting a role for this kinase in cell migration (
Ldb1 and 2 Interact with SLK ATH Domain
Our previous studies have shown that deletion of the SLK ATH domain increases its kinase activity, suggesting that it plays a role in SLK regulation (31). To gain further insight into the autoinhibitory role of the ATH domain, we performed a yeast two-hybrid screen using a GAL4-DBD-ATH domain fusion as bait. Surprisingly, we identified the transcription co-factors Ldb1 and Ldb2 as ATH-interacting proteins (
Interactions of Ldbs and SLK were confirmed by direct binding assays. In vitro translated Ldbs labeled with [35S]-methionine was incubated with various GST-SLK fusion protein deletions (
To refine the binding region of SLK to Ldb2. GST fusions of the of the SLK MNAP carboxy-terminus and the ATH amino and carboxy-termini were assayed for binding to [35S]-labeled Ldb2 (
To map the Ldb1/2 domains of interaction, [35S]-labeled deletions of Ldb1 were assayed for binding to a GST-tagged SLK ATH domain (
Association of Ldb2 and 2 with SLK In Vivo
We next tested whether Ldb1 and 2 were able to bind the SLK ATH domain in cultured cells. To address this, HA-tagged Ldb2 and Myc-tagged SLK deletion constructs (
Ldb Proteins Co-Localize with SLK at Cytoskeletal Structures
We have established that Ldb factors associate with the ATH domain of SLK in vitro and in living cells. We then sought to investigate whether the SLK/Ldb complex also co-localized in migrating cells. We first performed immunostaining of endogenous Ldb1 and SLK in C2C12 myoblasts (not shown) and mouse embryo fibroblasts (MEFs) plated on collagen and fibronectin respectively (
We have previously shown that SLK is indirectly associated with microtubules in spreading and migrating cells (1). High magnification of leading edge immunostains shows that SLK, Ldb2 and Ldb1 (not shown) co-localize with α-tubulin in membrane ruffles. Since SLK does not bind tubulin directly, we tested the possibility that it may be tethered to the microtubule through Ldb2 or Ldb1. Supporting our immunofluorescence results, Ldb2, but not Ldb1, was found to bind α-tubulin in vitro, indicating that Ldb2 may act as a link between SLK and the microtubule network. Taken together, these data indicate that SLK/Ldb complexes exist on microtubules and at the leading edge of migrating cells, further supporting a role for this complex in cell motility.
To assess the role of Ldb1 in SLK function, we used MEFs derived from mice homozygous for a ‘floxed’ Ldb1 locus (
The observation that Ldb factors regulate SLK activity led to the hypothesis that downregulation of Ldb1 or 2 may result in an SLK “open” conformation and increased motility. We therefore transfected Ldb1/2 siRNAs in NIH 3T3 cells and assayed migration rates using Boyden chambers. Following siRNA treatment, the levels of Ldb2 and 2 protein were reduced by at least 50% compared to siRNA control (
SLK and cell Migration
We have previously observed that SLK can indirectly associate with the microtubule network and mediate actin stress fibre dissolution in a Rac1-dependent manner 3.
Here, we have shown that interfering with SLK levels or activity negatively affects cell migration and microtubule-dependent focal adhesion turnover, suggesting that SLK is required for cell motility. Without wishing to be limiting or bound by theory, one possibility is that SLK is an actin disassembling-factor required for the destabilization of focal adhesions/contacts during migration. It has been reported that microtubules target focal contacts to modify their characteristics, including their disassembly (55, 56). Therefore, SLK may represent a microtubule-associated signal required to induce actin and adhesion remodeling during migration.
Ldb1 and 2 Association with SLK
Our results show that Ldb1 and 2 associate with the ATH domain of SLK in vitro and in vivo. Both the dimerization and NLS domains of Ldb1 and 2 independently bind the SLK ATH domain in vitro, suggesting a strong multi-contact association between these proteins. Since Cre-mediated depletion of Ldb1 did not affect the intracellular distribution of SLK (not shown) we propose that the association of Ldb1 and 2 with SLK likely controls its activity as the kinase activity of recombinant SLK is drastically reduced when incubated with either Ldb1 or 2 (see
ErbB-2/HER2 is a member of the epidermal growth factor (EGF) receptor tyrosine kinase (RTK) family. It has been shown that about 25-30% of human breast cancers overexpress ErbB2 and present with poor prognosis due to more invasive tumors. Despite the importance of HER2/ErbB2 in the etiology of breast carcinomas, the molecular mechanisms by which activated ErbB2 confers an invasive phenotype is still unclear.
As discussed herein, cell migration involves a multitude of signals converging on cytoskeletal reorganization, essential for development, immune responses and tissue repair. More importantly, increasing evidence show that the cell migration machinery is required for invasion and metastasis of tumor cells. Here we show that the microtubule-associated Ste20 kinase SLK is required for cell migration and is activated by scratch wounding of cell monolayers. SLK activation requires the src-family kinases and Focal adhesion kinase. Knockdown of SLK in fibroblasts and breast carcinoma inhibits cell motility. Interestingly, we find that SLK is activated in HER2/ErbB2 overexpressing cells and Heregulin treatment in breast carcinoma. Significantly, interfering with SLK levels or activity in breast carcinoma results in a block of Heregulin-induced chemotaxis in vitro. We have also shown that SLK is regulated by the metastasis suppressor nm23, a gene frequently downregulated in invasive tumors and HER2-positive carcinomas. We show that nm23 inhibits SLK activity and that this direct binding is lost upon activation by Heregulin treatment. The SLK inhibitors as described herein may be used as anti-metastasis inhibitors for the prevention of cancer spread. Alone or in combination with chemotherapy, radiation therapy or both, these inhibitors may improve patient survival by limiting further dissemination of disease.
Collectively, the findings presented herein suggest that inhibitors of SLK, for example, but not limited to by nm23 or CLIM1/2 peptide mimics or small molecules that have affinity for SLK may be beneficial in treatment of cancer including invasive cancers. Further, inhibitors of SLK may be beneficial in preventing cancer and tumor cells from metastasizing. Accordingly, the present invention contemplates protein variants of naturally occurring nm23, CLIM1/2, or fragments thereof that interfere with SLK activity. Furthermore, the present invention contemplates nucleic acids that encode said variants of nm23, CLIM1/2 or fragments thereof.
All citations are herein incorporated by reference.
The present invention has been described with regard to preferred embodiments. However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA2006/001613 | 9/29/2006 | WO | 00 | 7/31/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60722080 | Sep 2005 | US |
