In contrast to the kinase receptors, RPTPs dephosphorylate downstream proteins. Most RPTPs contain two intracellular catalytic domains that are arranged in tandem. Receptor homodimerization inhibits the constitutive activity of RPTPalpha(53, 54). The majority of RPTPs are orphan receptors and only midkine and pleiotrophin have been suggested as ligands for RPTP-zeta (55). Pleiotrophin appears to suppress the receptor's constitutive activity, thus increasing the levels of tyrosine phosphorylation of various intracellular proteins (56).
One known function of RPTPs is the regulation of neuronal migration (57). Some RPTPs have extracellular domains similar to cell adhesion molecules, suggesting potential roles in cellular adhesion. Because of their presence in sponges, RPTPs likely originated before the parazoan-eumetazoan split (58).
Relevant reviews and publications:
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53. A. Petrone, J. Sap, Emerging issues in receptor protein tyrosine phosphatase function: lifting fog or simply shifting? J Cell Sci 113, 2345-2354 (2000).
54. G. Jiang, J. den Hertog, J. Su, J. Noel, J. Sap, T. Hunter, Dimerization inhibits the activity of receptor-like protein-tyrosine phosphatase-alpha. Nature 401, 606-610 (1999).
55. N. Maeda, K. Ichihara-Tanaka, T. Kimura, K. Kadomatsu, T. Muramatsu, M. Noda, A receptor-like protein-tyrosine phosphatase PTPzeta/RPTPbeta binds a heparin-binding growth factor midkine. Involvement of arginine 78 of midkine in the high affinity binding to PTPzeta. J Biol Chem 274, 12474-12479 (1999).
56. K. Meng, A. Rodriguez-Pena, T. Dimitrov, W. Chen, M. Yamin, M. Noda, T. F. Deuel, Pleiotrophin signals increased tyrosine phosphorylation of beta beta- catenin through inactivation of the intrinsic catalytic activity of the receptor-type protein tyrosine phosphatase beta/zeta. Proc Natl Acad Sci U S A 97, 2603-2608 (2000).
57. K. G. Johnson, D. Van Vactor, Receptor protein tyrosine phosphatases in nervous system development. Physiol Rev 83, 1-24 (2003).
58. K. Ono, H. Suga, N. Iwabe, K. Kuma, T. Miyata, Multiple protein tyrosine phosphatases in sponges and explosive gene duplication in the early evolution of animals before the parazoan- eumetazoan split. J Mol Evol 48, 654-662 (1999).