This invention relates to nucleic acids and encoded polypeptides which interact with the PTPL1 phosphatase and which are GTPase activating proteins. The invention also relates to agents which bind the nucleic acids or polypeptides. The invention further relates to methods of using such nucleic acids and polypeptides in the treatment and/or diagnosis of disease.
The Rho family of Ras-like GTPases, which includes Rho, Rac and Cdc42, control actin-based cytoskeletal rearrangements (reviewed in Hall, Annu. Rev. Cell Biol. 10:31-54, 1994; Zigmond, Curr. Opin. Cell Biol. 8:66-73, 1996). Rho regulates receptor-mediated assembly of focal adhesions and stress fibers (Ridley and Hall, Cell 70:389-399, 1992), while Rac regulates the formation of membrane ruffles (Ridley et al., Cell 70:401-410, 1992) and Cdc42 controls the formation of filopodia (Nobes and Hall, Cell 81:53-62, 1995). Rho proteins have also been shown to be important in the regulation of cell proliferation (reviewed in Symons, Trends Biochem. Sci. 21:178-181, 1996). As members of the Ras superfamily, Rho proteins function as molecular switches, having an active, GTP-bound form, and an inactive, GDP-bound form. The active, GTP-bound form, is negatively regulated by GTPase activating proteins (GAPs) which enhance the intrinsic GTPase activity of Rho proteins. A number of GAPs that are active on proteins of the Rho family have been identified (reviewed in Lamarche and Hall, TIG 10:436-440, 1994). These include p50RhoGAP (Lancaster et al., J. Biol. Chem. 269:1137-1142, 1994), Myr5 (Reinhard et al., EMBO J. 14:697-704, 1995), and p190 (Settleman et al., Nature 359:153-154, 1992) which are also active on Rac and Cdc42. Another GAP, p122-RhoGAP (Homma and Emori, EMBO J. 14:286-291, 1995) appears to be specific for Rho.
Intracellular protein tyrosine phosphatases (PTPs) are a diverse group of proteins involved in signal transduction (reviewed in Streuli, Curr. Opin. Cell Biol. 8:182-188, 1996). They contain a conserved PTP domain which specifically dephosphorylates tyrosine residues and, in addition, domains that regulate their subcellular localization and activity (reviewed in Mauro and Dixon, Trends Biochem. Sci. 19:151-155, 1994). For example, the SH2 domains of SHP-1 and SHP-2 enables these PTPs to localize to and interact with activated growth factor receptors (Mauro and Dixon, 1994). Correct localization of PTPs is of importance, since the PTP domains usually have broad substrate specificity.
PTPL1 (Saras et al., J. Biol. Chem. 269:24082-24089, 1994) also called PTP-BAS (Maekawa et al., FEBS Lett. 337:200-206, 1994), hPTP1E (Banville et al., J. Biol. Chem. 269:22320-22327, 1994) and FAP-1 (Sato et al., Science 268:411-415, 1995), is a 250 kDa protein expressed in many tissues and cell lines. PTPL1 is fully described in PCT published application WO95/06735. It contains an N-terminal leucine zipper motif followed by a domain with homology to the Band 4.1 superfamily. Band 4.1-like domains are found in proteins involved in the linkage of actin filaments to the plasma membrane (Arpin et al., Curr. Opin. Cell Biol. 6:136-141, 1994). Five PDZ domains [PDZ is derived from PSD-95 (Cho et al., Neuron 9:929-942, 1992), Dlg-A (Woods and Bryant, Cell 66:451-464, 1991) and ZO-1 (Itoh et al., J. Cell. Biol. 121:491-502, 1993), each of which contains three such domains] are present between the Band 4.1-like domain and the C-terminal PTP domain. These domain structures of about 90 amino acid residues have also been called GLGF repeats or DHRs and are identified in a variety of proteins (Ponting and Phillips, Trends Biochem. Sci. 20:102-103, 1995). A PDZ domain of PTPL1 has been shown to interact with the C-terminal tail of the membrane receptor Fas (Sato et al., 1995) and PDZ domains of PSD-95 bind to the C-terminals of the NMDA-receptor and Shaker-type K+ channels (Kim et al., Nature 378:85-88, 1995; Kornau et al., Science 269:1737-1740, 1995). The crystal structures of two PDZ domains have recently been published (Doyle et al., Cell 85:1067-1076, 1996; Morais Cabral et al., Nature 382:649-652, 1996).
There exists a need to influence the receptor-mediated intracellular signal transduction pathways to treat disease. There also exists a need to identify the gene(s) responsible for increased or decreased signal transduction and to provide a genetic therapy for treating diseases resulting from aberrant signal transduction.
An object of the invention is to provide compounds that desirably influence the signal transduction by the Rho family of Ras-like GTPases.
Another object of the invention is to provide therapeutics for treating diseases resulting from aberrant signal transduction by the Rho family of Ras-like GTPases.
Still another object of the invention is to provide diagnostics and research tools relating to PARG, PTPL1 and the Rho family of Ras-like GTPases. These and other objects will be described in greater detail below.
The invention provides isolated nucleic acid molecules, unique fragments of those molecules, expression vectors containing the foregoing, and host cells transfected with those molecules. The invention also provides isolated polypeptides and agents which bind such polypeptides, including antibodies. The foregoing can be used in the diagnosis or treatment of conditions characterized by the expression of a PARG nucleic acid or polypeptide. The invention also provides methods for identifying pharmacological agents useful in the diagnosis or treatment of such conditions. Here, we present the cDNA cloning of a PTPL1-associated RhoGAP, PARG, a 150 kDa protein that contains a GAP domain that displays strong activity towards Rho. Furthermore, the C-terminal tail of PARG specifically interacts with the fourth PDZ domain (PDZ4) of PTPL1.
According to one aspect of the invention, an isolated nucleic acid molecule is provided. The molecule hybridizes under stringent conditions to a molecule consisting of the nucleic acid sequence of SEQ ID NO:1. The isolated nucleic acid molecule codes for a GTPase activating polypeptide. The invention further embraces nucleic acid molecules that differ from the foregoing isolated nucleic acid molecules in codon sequence due to the degeneracy of the genetic code. The invention also embraces complements of the foregoing nucleic acids.
In preferred embodiments, the isolated nucleic acid molecule comprises a molecule consisting of the nucleic acid sequence of SEQ ID NO:1. More preferably, the isolated nucleic acid molecule comprises a molecule consisting of nucleotides 184-3966 of SEQ ID NO:1. Preferably the isolated nucleic acid comprises a molecule having a sequence which encodes amino acids 666-853 of SEQ ID NO:2, amino acids 613-652 of SEQ ID NO:2, and/or amino acids 193-509 of SEQ ID NO:2.
According to another aspect of the invention, an isolated nucleic acid molecule is provided. The isolated nucleic acid molecule comprises a molecule consisting of a unique fragment of nucleotides 184-3966 of SEQ ID NO:1 between 12 and 3781 nucleotides in length and complements thereof, provided that the isolated nucleic acid molecule excludes molecules consisting solely of nucleotide sequences selected from the group consisting of accession numbers T32345 (SEQ ID NO:3), Z28937 (SEQ ID NO:4), Z28520 (SEQ ID NO:5), AA431926 (SEQ ID NO:14), AA326126 (SEQ ID NO:15), AA342471 (SEQ ID NO:16), AA716829 (SEQ ID NO:17), L49573, Z43348 (SEQ ID NO:18), AA303722 (SEQ ID NO:19), T32495 (SEQ ID NO:20), AA330162 (SEQ ID NO:21), Z25350 (SEQ ID NO:22), AA794256 (SEQ ID NO:23), T32506 (SEQ ID NO:24), T32263 (SEQ ID NO:25), F06673 (SEQ ID NO:26), AA462548 (SEQ ID NO:27), X85558 (SEQ ID NO:28), R14952 (SEQ ID NO:29), AA870705 (SEQ ID NO:30), AA120493 (SEQ ID NO:3 1), AA415591 (SEQ ID NO:32), AA1 31400 (SEQ ID NO:33), C76597 (SEQ ID NO:34), C76601 (SEQ ID NO:35), AA870475 (SEQ ID NO:36), AA234871 (SEQ ID NO:37), C77518 (SEQ ID NO:38), and AA672012 (SEQ ID NO:39). In one embodiment, the isolated nucleic acid molecule consists of between 12 and 32 contiguous nucleotides of SEQ ID NO:1, or complements of such, nucleic acid molecules. In preferred embodiments, the unique fragment is at least 14, 15, 16, 17, 18, 20 or 22 contiguous nucleotides of the nucleic acid sequence of SEQ ID NO:1, or complements thereof.
According to another aspect of the invention, an isolated nucleic acid molecule which encodes a PDZ domain binding site is provided, comprising a sequence selected from the group consisting of SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10, or nucleic acid molecules that differ from the nucleic acid molecules of the group consisting of SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10 in codon sequence due to the degeneracy of the genetic code. Preferably the isolated nucleic acid consists of a molecule having a sequence selected from the group consisting of SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10.
According to another aspect of the invention, the invention involves expression vectors, and host cells transformed or transfected with such expression vectors, comprising the nucleic acid molecules described above.
According to another aspect of the invention, an isolated polypeptide is provided. The isolated polypeptide is encoded by the isolated nucleic acid molecule, and the polypeptide has GTPase activating activity. In preferred embodiments, the isolated polypeptide comprises a polypeptide having the sequence of amino acids 658-898 of SEQ ID NO:2.
According to a further aspect of the invention, an isolated polypeptide is provided. The isolated polypeptide comprises a polypeptide encoded by a nucleic acid which hybridizes under stringent conditions to nucleotides 2020-2139 of SEQ ID NO:1. In preferred embodiments, the isolated polypeptide comprises a polypeptide having the sequence of amino acids 613-652 of SEQ ID NO:2 is provided. The isolated polypeptide has a Cys-rich domain.
According to another aspect of the invention, an isolated polypeptide is provided. The isolated polypeptide comprises a polypeptide encoded by a nucleic acid which hybridizes under stringent conditions to nucleotides 760-1710 of SEQ ID NO:1. In preferred embodiments, the isolated polypeptide comprises a polypeptide having the sequence of amino acid 193-509 of SEQ ID NO:2 is provided. The isolated polypeptide is a ZPH domain polypeptide.
In other embodiments, the isolated polypeptide consists of a fragment or variant of the foregoing which retains the activity of the foregoing.
According to still another aspect of the invention, an isolated polypeptide is provided. The isolated polypeptide is encoded by a nucleic acid molecule having a sequence selected from the group consisting of SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10. The isolated polypeptide comprises a polypeptide selected from the group consisting of a polypeptide having the sequence of SEQ ID NO:7, a polypeptide having the sequence of SEQ ID NO:9, and a polypeptide having the sequence of SEQ ID NO:11.
According to another aspect of the invention, there are provided isolated polypeptides which selectively bind a PARG protein or fragment thereof. The isolated polypeptide in certain embodiments binds to a polypeptide comprising the sequence of amino acids 658-898 of SEQ ID NO:2, amino acids 613-652 of SEQ ID NO:2, SEQ ID NO:7, SEQ ID NO:9, SEQ ID NO:11 or amino acids 193-509 of SEQ ID NO:2. The isolated polypeptide preferably binds to a polypeptide consisting essentially of the sequence of amino acids 658-898 of SEQ ID NO:2, amino acids 613-652 of SEQ ID NO:2, SEQ ID NO:7, SEQ ID NO:9, SEQ ID NO:11 or amino acids 193-509 of SEQ ID NO:2. In preferred embodiments, isolated binding-polypeptides include antibodies and fragments of antibodies (e.g., Fab, F(ab)2, Fd and antibody fragments which include a CDR3 region which binds selectively to the PARG polypeptides of the invention).
The invention provides in another aspect an isolated complex of polypeptides. The isolated complex includes a PTPL1 polypeptide, such a polypeptide including the amino acid sequence of SEQ ID NO:12 bound to a polypeptide as claimed in claim 1. The isolated complex has both PTPL1 phosphatase activity and PARG GAP activity. Preferably the isolated complex consists essentially of the polypeptide of SEQ ID NO:12 and the polypeptide of SEQ ID NO:2.
According to still another aspect of the invention, methods for reducing Rho family GTPase signal transduction in a mammalian cell are provided. The methods involve administering to a mammalian cell an amount of an inhibitor of Rho family GTPase activity effective to reduce Rho family GTPase signal transduction in the mammalian cell. In certain embodiments, the inhibitor is an isolated PARG polypeptide, having Rho GAP activity, encoded by SEQ ID NO:1. In other embodiments, the inhibitor is an isolated complex of polypeptides comprising a polypeptide comprising the amino acid sequence of SEQ ID NO:12 and a polypeptide comprising the amino acid sequence of SEQ ID NO:2.
According to still another aspect of the invention, methods for reducing proliferation of a cancer cell are provided. The methods involve administering to a cancer cell an amount of a PARG polypeptide, comprising a polypeptide encoded by the nucleic acid of claim 1, effective to reduce proliferation of the cancer cell.
The invention in a further aspect provides methods for increasing Rho family GTPase signal transduction in a mammalian cell. A dominant negative variant of the polypeptide of SEQ ID NO:2 is administered to the mammalian cell in an amount effective to increase Rho family GTPase signal transduction. Preferably the dominant negative polypeptide includes an inactivated GTPase activating domain which contains a deletion or at least one inactivating point mutation.
According to a further aspect of the invention, methods for reducing binding of a protein which includes a PDZ4 domain to a protein which includes a PDZ4 domain binding site are provided. The methods involve contacting the protein which includes PDZ4 domain with an agent which binds to the PDZ4 domain for a time effective to reduce the binding of the protein which includes PDZ4 domain to the protein which includes PDZ4 domain binding site. In certain embodiments the agent is an isolated peptide and includes at its carboxyl terminus the amino acid sequence of SEQ ID NO:7. The isolated peptide can include conservative substitutions of the amino acid sequence of SEQ ID NO:7, excepting the terminal valine. In preferred embodiments the amino acid sequence of the peptide is selected from the group consisting of SEQ ID NO:7, SEQ ID NO:9 and SEQ ID NO:11. In other embodiments the agent is an antibody which binds to the PDZ4 domain, preferably a monoclonal antibody. In some embodiments, methods provide inhibiting binding of a protein which includes a PDZ4domain and a protein which includes a PDZ4domain binding site in a mammalian cell. Such methods involve contacting the mammalian cell with an agent which binds to the PDZ4 domain for a time effective to reduce the binding of the protein which includes PDZ4 domain to the protein which includes PDZ4 domain binding site.
The invention in another aspect provides methods of modulating mast cell secretion in a subject. The methods include administering to the subject in need of such treatment an amount of a modulator of PARG GTPase activating activity effective to modulate mast cell secretion in the subject.
The invention in still another aspect provides compositions comprising a PARG polypeptide which has GTPase activating activity, a complex of such a PARG polypeptide and PTPL1 phosphatase, or a peptide agent which binds to a PDZ4 domain and which includes the sequence of SEQ ID NO:7, and a pharmaceutically acceptable carrier.
The invention in a further aspect involves a method for decreasing PARG GTPase activating activity in a subject. An agent that selectively binds to an isolated nucleic acid molecule of the invention or an expression product thereof is administered to a subject in need of such treatment, in an amount effective to decrease PARG GTPase activating activity in the subject. Preferred agents are antisense nucleic acids, including modified nucleic acids, and polypeptides.
According to another aspect of the invention, methods are provided for identifying lead compounds for a pharmacological agent useful in the diagnosis or treatment of disease associated with PARG GTPase activating activity or with PARG binding to a protein containing a PDZ4 domain. The methods involve forming a mixture of a PARG polypeptide or fragment thereof containing a GTPase activating domain or a PDZ4 domain binding site, a protein which interacts with the foregoing GTPase activating domain or PDZ4 domain binding site, and a candidate pharmacological agent. The mixture is incubated under conditions which, in the absence of the candidate pharmacological agent, permit a first amount of specific activation of the GTPase by the PARG GTPase activating domain or permit a first amount of selective binding of the protein containing a PDZ4 domain by the PDZ4 domain binding site. A test amount of the specific activation of the GTPase by the PARG GTPase activating domain or the selective binding of the protein containing a PDZ4 domain by the PDZ4 domain binding site then is detected. Detection of an increase in the foregoing activities in the presence of the candidate pharmacological agent indicates that the candidate pharmacological agent is a lead compound, for a pharmacological agent which increases specific activation of the GTPase by the PARG GTPase activating domain or selective binding of the protein containing a PDZ4 domain by the PDZ4 domain binding site. Detection of a decrease in the foregoing activities in the presence of the candidate pharmacological agent indicates that the candidate pharmacological agent is a lead compound for a pharmacological agent which decreases specific activation of the GTPase by the PARG GTPase activating domain or selective binding of the protein containing a PDZ4 domain by the PDZ4 domain binding site. Where the activity tested is specific activation of the GTPase, the protein which interacts with the GTPase activating domain preferably is Rho. Where the activity tested is selective binding of a PDZ4 domain, the protein which interacts with the PDZ4 domain binding site preferably is PTPL1.
These and other objects of the invention will be described in further detail in connection with the detailed description of the invention.