POSSIBLE V-CRK-INDUCED TRANSFORMATION THROUGH ACTIVATION OF SRC KINASES

p47(gag-crk) (v-Crk) encoded by avian sarcoma virus CT10, causes an el evation of tyrosine phosphorylation of several cellular proteins, The lack of a protein tyrosine kinase domain in v-Crk suggests its co-oper ation with cellular protein-tyrosine kinase activity, We have shown th at suppression of a certain fraction of c-Src activity by Csk may requ ire the binding of Csk to tyrosine phosphorylated paxillin. In this st udy, we detected co-immunoprecipitation of tyrosine phosphorylated pax illin with v-Crk in CT10-transformed chicken embryo fibroblasts (CEF), and demonstrated that v-Crk binding to paxillin can inhibit Csk bindi ng to paxillin. A phosphotyrosine peptide, which can inhibit v-Crk bin ding to paxillin, did not inhibit Csk, binding to paxillin, suggesting that v-Crk and Csk bind to different tyrosine-phosphorylated sites in paxillin. We also found that the kinase activity of the endogenous c- Src in CEF is elevated severalfold after CT10-transformation, We there fore suggest that the competitive binding of overexpressed v-Crk affec ts an efficient interaction of Csk with tyrosine-phosphorylated paxill in in CT10 transformed CEF. This would result in a failure in the supp ression of the kinase activities of a population of c-Src and other Sr c family protein-tyrosine kinases as well, and these kinases may then contribute to the phosphorylation of cellular proteins in CT10-transfo rmed CEF.