Abstract
RPTP mu is a transmembrane protein tyrosine phosphatase with an adhesion molecule-like ectodomain. It has recently been shown that RPTP mu mediates homophilic interactions when expressed in insect cells. In this study, we have examined how RPTP mu may function as a cell contact receptor in mink lung epithelial cells, which express RPTPmu endogenously, as well as in transfected 3T3 cells. We find that RPTP mu has a relatively short half-life (3-4 hours) and undergoes posttranslational cleavage into two noncovalently associated subunits, with both cleaved and uncleaved molecules being present on the cell surface (roughly at a 1:1 ratio); shedding of the ectodomain subunit is observed in exponentially growing cells. Immunofluorescence analysis reveals that surface expression of RPTPmu is restricted to regions of tight cell-cell contact. RPTPmu surface expression increases significantly with increasing cell density. This density-induced upregulation of RPTP mu is independent of its catalytic activity and is also observed when transcription is driven by a constitutive promoter, indicating that modulation of RPTPmu surface expression occurs posttranscriptionally. Based on our results, we propose the following model of RPTP mu function: In the absence of cell-cell contact, newly synthesized RPTP mu molecules are rapidly cleared from the cell surface. Cell-cell contact causes RPTPmu to be trapped at the surface through homophilic binding, resulting in accumulation of RPTP mu at intercellular contact regions. This contact-induced clustering of RPTPmu may then lead to tyrosine dephosphorylation of intracellular substrates at cell-cell contacts.
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- Beckmann G., Bork P. An adhesive domain detected in functionally diverse receptors. Trends Biochem Sci. 1993 Feb;18(2):40–41. doi: 10.1016/0968-0004(93)90049-s. [DOI] [PubMed] [Google Scholar]
- Brady-Kalnay S. M., Flint A. J., Tonks N. K. Homophilic binding of PTP mu, a receptor-type protein tyrosine phosphatase, can mediate cell-cell aggregation. J Cell Biol. 1993 Aug;122(4):961–972. doi: 10.1083/jcb.122.4.961. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Brady-Kalnay S. M., Tonks N. K. Identification of the homophilic binding site of the receptor protein tyrosine phosphatase PTP mu. J Biol Chem. 1994 Nov 11;269(45):28472–28477. [PubMed] [Google Scholar]
- Burgoon M. P., Grumet M., Mauro V., Edelman G. M., Cunningham B. A. Structure of the chicken neuron-glia cell adhesion molecule, Ng-CAM: origin of the polypeptides and relation to the Ig superfamily. J Cell Biol. 1991 Mar;112(5):1017–1029. doi: 10.1083/jcb.112.5.1017. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gebbink M. F., Verheijen M. H., Zondag G. C., van Etten I., Moolenaar W. H. Purification and characterization of the cytoplasmic domain of human receptor-like protein tyrosine phosphatase RPTP mu. Biochemistry. 1993 Dec 14;32(49):13516–13522. doi: 10.1021/bi00212a017. [DOI] [PubMed] [Google Scholar]
- Gebbink M. F., Zondag G. C., Wubbolts R. W., Beijersbergen R. L., van Etten I., Moolenaar W. H. Cell-cell adhesion mediated by a receptor-like protein tyrosine phosphatase. J Biol Chem. 1993 Aug 5;268(22):16101–16104. [PubMed] [Google Scholar]
- Gebbink M. F., van Etten I., Hateboer G., Suijkerbuijk R., Beijersbergen R. L., Geurts van Kessel A., Moolenaar W. H. Cloning, expression and chromosomal localization of a new putative receptor-like protein tyrosine phosphatase. FEBS Lett. 1991 Sep 23;290(1-2):123–130. doi: 10.1016/0014-5793(91)81241-y. [DOI] [PubMed] [Google Scholar]
- Jiang Y. P., Wang H., D'Eustachio P., Musacchio J. M., Schlessinger J., Sap J. Cloning and characterization of R-PTP-kappa, a new member of the receptor protein tyrosine phosphatase family with a proteolytically cleaved cellular adhesion molecule-like extracellular region. Mol Cell Biol. 1993 May;13(5):2942–2951. doi: 10.1128/mcb.13.5.2942. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Margolis B., Rhee S. G., Felder S., Mervic M., Lyall R., Levitzki A., Ullrich A., Zilberstein A., Schlessinger J. EGF induces tyrosine phosphorylation of phospholipase C-II: a potential mechanism for EGF receptor signaling. Cell. 1989 Jun 30;57(7):1101–1107. doi: 10.1016/0092-8674(89)90047-0. [DOI] [PubMed] [Google Scholar]
- Miyazono K., Hellman U., Wernstedt C., Heldin C. H. Latent high molecular weight complex of transforming growth factor beta 1. Purification from human platelets and structural characterization. J Biol Chem. 1988 May 5;263(13):6407–6415. [PubMed] [Google Scholar]
- Ostman A., Yang Q., Tonks N. K. Expression of DEP-1, a receptor-like protein-tyrosine-phosphatase, is enhanced with increasing cell density. Proc Natl Acad Sci U S A. 1994 Oct 11;91(21):9680–9684. doi: 10.1073/pnas.91.21.9680. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schaap D., van der Wal J., van Blitterswijk W. J., van der Bend R. L., Ploegh H. L. Diacylglycerol kinase is phosphorylated in vivo upon stimulation of the epidermal growth factor receptor and serine/threonine kinases, including protein kinase C-epsilon. Biochem J. 1993 Feb 1;289(Pt 3):875–881. doi: 10.1042/bj2890875. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Serra-Pages C., Saito H., Streuli M. Mutational analysis of proprotein processing, subunit association, and shedding of the LAR transmembrane protein tyrosine phosphatase. J Biol Chem. 1994 Sep 23;269(38):23632–23641. [PubMed] [Google Scholar]
- Smith D. B., Johnson K. S. Single-step purification of polypeptides expressed in Escherichia coli as fusions with glutathione S-transferase. Gene. 1988 Jul 15;67(1):31–40. doi: 10.1016/0378-1119(88)90005-4. [DOI] [PubMed] [Google Scholar]
- Spivak G., Ganesan A. K., Hanawalt P. C. Enhanced transformation of human cells by UV-irradiated pSV2 plasmids. Mol Cell Biol. 1984 Jun;4(6):1169–1171. doi: 10.1128/mcb.4.6.1169. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Streuli M., Krueger N. X., Ariniello P. D., Tang M., Munro J. M., Blattler W. A., Adler D. A., Disteche C. M., Saito H. Expression of the receptor-linked protein tyrosine phosphatase LAR: proteolytic cleavage and shedding of the CAM-like extracellular region. EMBO J. 1992 Mar;11(3):897–907. doi: 10.1002/j.1460-2075.1992.tb05128.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Walton K. M., Dixon J. E. Protein tyrosine phosphatases. Annu Rev Biochem. 1993;62:101–120. doi: 10.1146/annurev.bi.62.070193.000533. [DOI] [PubMed] [Google Scholar]
- Yu Q., Lenardo T., Weinberg R. A. The N-terminal and C-terminal domains of a receptor tyrosine phosphatase are associated by non-covalent linkage. Oncogene. 1992 Jun;7(6):1051–1057. [PubMed] [Google Scholar]
- Zondag G. C., Koningstein G. M., Jiang Y. P., Sap J., Moolenaar W. H., Gebbink M. F. Homophilic interactions mediated by receptor tyrosine phosphatases mu and kappa. A critical role for the novel extracellular MAM domain. J Biol Chem. 1995 Jun 16;270(24):14247–14250. doi: 10.1074/jbc.270.24.14247. [DOI] [PubMed] [Google Scholar]