EVIDENCE THAT DOCK180 UP-REGULATES SIGNALS FROM THE CRKII-P130(CAS) COMPLEX

DOCR180 is one of the two principal proteins bound to the SH3 domain o f the adaptor protein CrkII. Here, we have studied the involvement of DOCR180 in integrin signaling. DOCR180 was neither phosphorylated nor bound to CrkII in quiescent NIH 3T3 cells and 3Y1 cells. We found that DOCR180 was phosphorylated and bound to CrkII in MH 3T3 cells stimula ted with integrin and also in 3Y1 cells transformed by v-src or v-crk. The binding of DOCK180 to CrkII correlated with the binding of CrkII to p130(Cas), which is a major CrkII SH2 domain-binding protein at foc al adhesions. In a reconstitution experiment, expression of DOCK180 in duced hyperphosphorylation of p130(Cas) and a concomitant increase in the amount of CrkII bound to p130(Cas). Similarly, binding of DOCK180 to CrkII was also enhanced by the coexpression of p130(Cas). Finally, we found that coexpression of p130(Cas) and CrkII with DOCR180 induced local membrane spreading and accumulation of DOCK180-CrkII-p130(Cas) complexes at focal adhesions. These findings suggest that DOCK180 posi tively regulates signaling from integrins to CrkII-p130(Cas) complexes at focal adhesions.