THE PRODUCT OF THE CBL ONCOGENE FORMS STABLE COMPLEXES IN-VIVO WITH ENDOGENOUS CRK IN A TYROSINE PHOSPHORYLATION-DEPENDENT MANNER

The cellular homologs of the v-Crk oncogene product are composed exclu sively of Src homology region 2 (SH2) and SH3 domains. v-Crk overexpre ssion in fibroblasts causes cell transformation and elevated tyrosine phosphorylation of specific cellular proteins. Among these proteins is a 130-kDa protein, identified as p130(cas), that forms a stable compl ex in vivo with v-Crk. We have explored the role of endogenous Crk pro teins in Bcr-Abl-transformed cells. In the K562 human chronic myelogen ous leukemia cell line, p130(cas) is not tyrosine phosphorylated or bo und to Crk Instead, Crk proteins predominantly associate with the tyro sine-phosphorylated proto-oncogene product of Cbl. In vitro analysis s howed that this interaction is mediated by the SH2 domain of Crk and c an be inhibited with a phosphopeptide containing the Crk-SH2 binding m otif. In NIH 3T3 cells transformed by Bcr-Abl, c-Cbl becomes strongly tyrosine phosphorylated and associates with c-Crk. The complex between c-Crk and c-Cbl is also seen upon T-cell receptor cross-linking or wi th the transforming, tyrosine-phosphorylated c-Cbl. These results indi cate that Crk binds to c-Cbl in a tyrosine phosphorylation-dependent m anner, suggesting a physiological role for the Crk-c-Cbl complex in Bc r-Abl tyrosine phosphorylation-mediated transformation.