DYNAMIC INTERACTION OF PTP-MU WITH MULTIPLE CADHERINS IN-VIVO

There is a growing body of evidence to implicate reversible tyrosine p hosphorylation as an important mechanism in the control of the adhesiv e function of cadherins. We previously demonstrated that the receptor protein tyrosine phosphatase PTP mu associates with the cadherin-caten in complex in various tissues and cells and, therefore, may be a compo nent of such a regulatory mechanism (Brady-Kalnay, S.M., D.L. Rimm, an d N.K. Tonks. 1995. J. Cell Biol. 130:977-986). In this study, we pres ent further characterization of this interaction using a variety of sy stems. We observed that PTP mu interacted with N-cadherin, E-cadherin, and cadherin-4 (also called R-cadherin) in extracts of rat lung. We o bserved a direct interaction between PTP mu, and E-cadherin after coex pression in Sf9 cells. In WC5 cells, which express a temperature-sensi tive mutant form of v-Src, the complex between PTP mu and E-cadherin w as dynamic, and conditions that resulted in tyrosine phosphorylation o f E-cadherin were associated with dissociation of PTP mu from the comp lex. Furthermore, we have demonstrated that the COOH-terminal 38 resid ues of the cytoplasmic segment of E-cadherin was required for associat ion with PTP mu in WC5 cells. Zondag et al. (Zondag, G., W. Moolenaar, and M. Gebbink. 1996. J. Cell Biol. 134: 1513-1517) have asserted tha t the association we observed between PTP mu and the cadherin-catenin complex in immunoprecipitates of the phosphatase arises from nonspecif ic cross-reactivity between BK2, our antibody to PTP mu, and cadherins . In this study we have confirmed our initial observation and demonstr ated the presence of cadherin in immunoprecipitates of PTP mu. obtaine d with three antibodies that recognize distinct epitopes in the phosph atase. In addition, we have demonstrated directly that the anti-PTP mu antibody BK2 that we used initially did not cross-react with cadherin . Our data reinforce the observation of an interaction between PTP mu, and E-cadherin in vitro and in vivo, further emphasizing the potentia l importance of reversible tyrosine phosphorylation in regulating cadh erin function.