Source: {"pile_set_name": "USPTO Backgrounds"}

Protein phosphorylation is now well recognized as an important mechanism utilized by cells to transduce and regulate signals during different stages of cellular function (Hunter, Phil. Trans. R. Soc. Lond. B 353: 583–605 (1998); Chan et al., Annu. Rev. Immunol. 12: 555–592 (1994); Zhang, Curr. Top. Cell. Reg. 35: 21–68 (1997); Matozaki and Kasuga, Cell. Signal. 8: 113–19 (1996); Fischer et al, Science 253:401–6 (1991); Flint et al., EMBO J. 12:1937–46 (1993)). The level of tyrosine phosphorylation is balanced by the opposing action of protein tyrosine kinases and protein tyrosine phosphatases. There are at least two major classes of phosphatases: (1) those that dephosphorylate proteins (or peptides) that contain a phosphate group(s) on a serine or threonine moiety (termed Ser/Thr phosphatases) and (2) those that remove a phosphate group(s) from the amino acid tyrosine (termed protein tyrosine phosphatases or PTPases or PTPs).
The PTPases are a family of enzymes that can be classified into two groups: a) intracellular or nontransmembrane PTPases and b) receptor-type or transmembrane PTPases. In addition, dual-specificity phosphatases and low molecular weight phosphatases are able to dephosphorylate phospho tyrosyl proteins. See, e.g., WO 97/39746; WO 97/40017; WO 99/15529; WO 97/08934; WO 98/27065; WO 99/46236; WO 99/46244; WO 99/46267; WO 99/46268 and WO 99/46237.
Intracellular PTPases: Most known intracellular type PTPases contain a single conserved catalytic phosphatase domain consisting of 220–240 amino acid residues. The regions outside the PTPase domains are believed to play important roles in localizing the intracellular PTPases subcellularly (Mauro, L. J. and Dixon, J. E. TIBS 19: 151–155 (1994)). The first intracellular PTPase to be purified and characterized was PTP1B, which was isolated from human placenta (Tonks et al., J. Biol. Chem. 263: 6722–6730 (1988)). Shortly after, PTP1B was expressed recombinantly (Charbonneau et al., Proc. Natl. Acad. Sci. USA 86: 5252–5256 (1989); Chernoff et al., Proc. Natl. Acad. Sci. USA 87: 2735–2789 (1989)). Other examples of intracellular PTPases include (1) T-cell PTPase/TC-PTP (Cool et al. Proc. Natl. Acad. Sci. USA 86: 5257–5261 (1989)), (2) rat brain PTPase (Guan et al., Proc. Natl. Acad. Sci. USA 87:1501–1502 (1990)), (3) neuronal phosphatase STEP (Lombroso et al., Proc. Natl. Acad. Sci. USA 88: 7242–7246 (1991)), (4) ezrin-domain containing PTPases: PTPMEG1 (Guet al., Proc. Natl. Acad. Sci. USA 88: 5867–57871 (1991)). PTPH1 (Yang and Tonks, Proc. Natl. Acad. Sci. USA 88: 5949–5953 (1991)), PTPD1 and PTPD2 (Møller et al., Proc. Natl. Acad. Sci. USA 91: 7477–7481 (1994)); FAP-1/BAS (Sato et al., Science 268: 411–415 (1995); Banville et al., J. Biol. Chem. 269, 22320–22327 (1994); Maekawa et al., FEBS Letters 337: 200–206 (1994)), and SH2 domain containing PTPases: PTP1C/SH-PTP1/SHP-1 (Plutzky et al., Proc. Natl. Acad. Sci. USA 89: 1123–1127 (1992); Shen et al., Nature Lond. 352: 736–739 (1991)) and PTP1D/Syp/SH-PTP2/SHP-2 (Vogel et al., Science 259: 1611–1614 (1993); Feng et al., Science 259: 1607–1611 (1993); Bastein et al., Biochem. Biophys. Res. Comm. 196: 124–133 (1993)).
Receptor-type PTPases consist of a) a putative ligand-binding extracellular domain, b) a transmembrane segment, and c) an intracellular catalytic region. The structures and sizes of the putative ligand-binding extracellular domains of receptor-type PTPases are quite divergent. In contrast, the intracellular catalytic regions of receptor-type PTPases are very homologous to each other and to the intracellular PTPases. Most receptor-type PTPases have two tandemly duplicated catalytic PTPase domains.
The first receptor-type PTPases to be identified were (1) CD45/LCA (Ralph, S. J., EMBO J. 6: 1251–1257 (1987)) and (2) LAR (Streuli et al., J. Exp. Med. 168: 1523–1530 (1988)) that were recognized to belong to this class of enzymes based on homology to PTP1B (Charbonneau et al., Proc. Natl. Aced. Sci. USA 86: 5252–256 (1989)). CD45 is a family of high molecular weight glycoproteins and is one of the most abundant leukocyte cell surface glycoproteins and appears to be exclusively expressed upon cells of the hematopoietic system (Trowbridge and Thomas, Ann. Rev. Immunol. 12: 85–116 (1994)).
The identification of CD45 and LAR as members of the PTPase family was quickly followed by identification and cloning of several different members of the receptor-type PTPase group. Thus, 5 different PTPases, (3) PTPα, (4) PTPβ, (5) PTPδ, (6) PTPε, and (7) PTPζ, were identified in one early study (Krueger et al., EMBO J. 9: 3241–3252 (1990)). Other examples of receptor-type PTPases include (8) PTPγ(Barnea et al., Mol. Cell. Biol. 13: 1497–1506 (1995)) which, like PTPζ (Krueger and Saito, Proc. Natl. Acad. Sci. USA 89: 7417–7421 (1992)) contains a carbonic anhydrase-like domain in the extracellular region, (9) PTPμ (Gebbink et al., FEBS Letters 290: 123–130 (1991)), (10) PTPκ (Jiang et al., Mol. Cell. Biol. 13: 2942–2951 (1993)). Based on structural differences the receptor-type PTPases may be classified into subtypes (Fischer et al., Science 253: 401–406 (19991)): (I) CD45; (II) LAR, PTPd, (11) PTPσ; (III) PTPβ, (12) SAP-1 (Matozaki et al., J. Biol. Chem. 269: 2075–2081 (1994)), (13) PTP-U2/GLEPP1 (Seimiya et al., Oncogene 10: 1731–1738 (1995); Thomas et al., J. Biol. Chem. 269: 19953–19962 (1994)), and (14) DEP-1; (IV) PTPα,_PTPε. All receptor-type PTPases except Type III contain two PTPase domains. Novel PTPases are frequently identified, and it is anticipated that between 100 and more than 500 different species will be found in the human genome.
PTPases are the biological counterparts to protein tyrosine kinases (PTKs). Therefore, one important function of PTPases is to control, and especially down-regulate, the activity of PTKs. However, a more complex picture of the function of PTPases has emerged. Thus, several studies indicate that some PTPases act as positive mediators of cellular signaling. As an example, the SH2 domain-containing SHP-2 acts as a positive mediator in insulin-stimulated Ras activation (Noguchi et al., Mol. Cell. Biol. 14: 6674–6682 (1994)) and of growth factor-induced mitogenic signal transduction (Xiao et al., J. Biol. Chem. 269: 21244–21248 (1994)), whereas the homologous SHP-1 acts as a negative regulator of growth factor-stimulated proliferation (Bignon and Siminovitch, Clin. Immunol. Immunopathol. 73: 168–179 (1994)). Another example of PTPases as positive regulators has been provided by studies designed to define the activation of the Src-family of tyrosine kinases. In particular, several lines of evidence indicate that CD45 is positively regulating the activation of hematopoietic cells, and that the mechanism of such positive regulation may involve dephosphorylation of the C-terminal tyrosine of Fyn and Lck (Chan et al., Annu. Rev. Immunol. 12: 555–592 (1994)).
The association of many PTPases with cell proliferation, tranformation and differentiation has now been established. PT