TYROSINE PHOSPHORYLATION OF P130(CAS) AND CORTACTIN ACCOMPANIES INTEGRIN-MEDIATED CELL-ADHESION TO EXTRACELLULAR-MATRIX

We show in this report that two v-src substrate proteins, p130(Cas) and cortactin, become tyrosine-phosphoryIated during integrin-mediated cell adhesion to extracellular matrix substrata and upon cell attachment onto immobilized anti-integrin antibodies. This tyrosine phosphorylation does not occur when cells attach to polylysine or through antibodies against major histocompatibility complex. It also does not take place when adhesion-mediated reorganization of the actin cytoskeleton is inhibited with cytochalasin D. Tyrosine phosphorylation of p130(Cas) and cortactin coincides with tyrosine phosphorylation of focal adhesion kinase during integrin-mediated cell adhesion but is independent of cell adhesion in v-src-transformed cells. The tyrosine-phosphorylated sites in p130(Cas) and cortactin may serve as binding sites for proteins containing Src homology 2 domains, as is the case with two other integrin-regulated docking proteins, focal adhesion kinase and paxillin. Thus, these results suggest that ligand binding of integrins regulates the tyrosine phosphorylation state of multiple docking proteins, These proteins may mediate anchorage dependence of growth; their misregulation in v-src-transformed and other tumorigenic cells may be responsible for the anchorage independence of such cells.