Mutation of the c-Cbl TKB domain binding site on the Met receptor tyrosine kinase converts it into a transforming protein

The c-CbI protooncogene is a negative regulator for several receptor tyrosine kinases (RTKs) through its ability to promote their polyubiquitination. Hence, uncoupling c-CbI from RTKs may lead to their deregulation. In testing this, we show that c-CbI promotes ubiquitination of the Met RTK. This requires the c-Cbl tyrosine kinase binding (TKB) domain and a juxtamembrane tyrosine residue on Met. This tyrosine provides a direct binding site for the c-CbI TKB domain, and is absent in the rearranged oncogenic Tpr-Met variant. A Met receptor, where the juxtamembrane tyrosine is replaced by phenylalanine, is not ubiquitinated and has transforming activity in fibroblast and epithelial cells. We propose the uncoupling of c-CbI from RTKs as a mechanism contributing to their oncogenic activation.