The two major sites of cbl tyrosine phosphorylation in abl-transformed cells select the crkL SH2 domain

We recently found that the 120-kD protein product of the c-cbl oncogene is tyrosine phosphorylated in tumor cells generated by bcr-abl or v-abl and that p120(cbl) will associate with these proteins bl vivo, We also found an oncogenic form of cbl protein in the 70Z/3 pre-B cell lymphoma which exhibits deregulated tyrosine phosphorylation. These findings have led us to broaden our study of cbl's involvement in abl-mediated tumorigenesis. Here we show by immunodepletion that cbl is the major 120-kD tyrosine phosphorylated protein in cells which express activated forms of the abl oncogene. We also demonstrate that tyrosine phosphorylation of p120(cbl) in bcr-abl transformed cells does not alter its subcellular localization. In addition we show that the oncogenic 70Z/3 form of cbl exhibits enhanced tyrosine phosphorylation in v-abl infected cells and that cbl is heavily tyrosine phosphorylated in hemopoietic cells transformed by v-src. Finally this study identifies two sites that are essential for the tyrosine phosphorylation of cbl in abl-transformed cells. These sites conform to the preferred abl kinase substrate sequence of YXXP and we show that following phosphorylation they mediate an association with the crkL SH2 domain.