Crk family adaptor proteins trans-activate c-Abl kinase

Background: c-Abl kinase is activated in response to a variety of biologica l stimuli. Crk family adaptor proteins can interact physically with c-Abl a nd be involved in the activation of c-Abl kinase. Results: We report that the Crk family of adaptor proteins act as trans-act ing activators of c-Abl kinase. The interaction of the amino-terminal Src-h omology (SH) 3 domain of c-Crk and the proline-rich motifs of c-Abl is an e ssential step for the phosphorylation of c-Crk by c-Abl, as well as the act ivation of c-Abl by c-Crk. The activation of c-Abl by c-Crk is negatively r egulated by phosphorylation of the tyrosine 221 of c-Crk. Our data suggest that, in the absence of phosphorylation of the tyrosine Y221, the SH2 domai n of c-Crk becomes free to bind to target molecules while the carboxyl-term inal SH3 domain of c-Crk binds to the proline-rich region of c-Abl, inducin g the activation of c-Abl by c-Crk. Conclusions: This study suggests that the Crk family functions as trans-act ing activators of c-Abl kinase. The phosphorylation of c-Crk may regulate c -Abl kinase.