INHIBITION OF P130CAS TYROSINE PHOSPHORYLATION BY CALYCULIN-A

P130cas is a dominant tyrosine phosphorylated protein in v-src-and v-c rk-transformed cells. Tyrosine phosphorylation also occurs in response to integrin-mediated cell adhesion. P130cas has a unique structure,vi th multiple SH2 and SH3 binding sites, which makes it a candidate, doc king protein that might be involved in several signal transduction pat hways. Little is known about how p130cas itself is regulated. In this report we present evidence that tyrosine phosphorylated p130cas was ra pidly dephosphorylated in several lymphatic cell lines after treatment with calyculin A, a serine/threonine phosphatase inhibitor. A similar result was obtained with okadaic acid, but higher concentrations and longer incubation times were required, Constitutive phosphorylation as well as receptor-cross linking-induced p130cas phosphorylation was in hibited. Furthermore, the p130cas-Crk association was disrupted by tre atment of cells with calyculin A. However, the p130cas-Lyn association was not affected. These results suggest that calyculin A specifically affects SH2 domain-mediated protein-protein interactions and that Lyn does not bind to a susceptible SH2 domain. Furthermore, the data pres ented is consistent with the existence of a calyculin A-sensitive phos phatase or tyrosine kinase that may be a critical regulator of p130cas tyrosine phosphorylation.