COMPLEXES OF FOCAL ADHESION KINASE (FAK) AND CRK-ASSOCIATED SUBSTRATE(P130(CAS)) ARE ELEVATED IN CYTOSKELETON-ASSOCIATED FRACTIONS FOLLOWING ADHESION AND SRC TRANSFORMATION - REQUIREMENTS FOR SRC KINASE-ACTIVITY AND FAK PROLINE-RICH MOTIFS

The focal adhesion kinase (FAK) and Crk-associated substrate, p130(Cas ) (Gas), have been implicated in diverse signaling pathways including those mediated by integrins, G-protein-coupled receptors, tyrosine kin ase receptors, and the v-src and v-crk oncogenes. The recent identific ation of a direct interaction between FAK and Cas prompted the examina tion of potential regulation of FAX . Cas complexes by factors that re sult in concomitant increase in their phosphotyrosine content, namely cell adhesion and transformation by Src. Both conditions resulted in e levated FAK . Cas complex levels in nonionic detergent-insoluble fract ions, indicating increased association with the cytoskeleton. For acti vated Src, this effect requires an active Src catalytic domain but not its Src homology 2 (SH2) or Src homology 3 (SH3) domains. FAK kinase domain tyrosines 576 and 577 are also required, suggesting that direct phosphorylation of these sites by Src may influence the solubility an d/or stability of the complex. FAK-Cas association was only observed i n the context of Cas binding to at least one of two distinct proline-r ich sites on FAK. These findings firmly establish a direct interaction between FAK and Cas and demonstrate that Src can influence the subcel lular localization of the complex by a tyrosine phosphorylation-depend ent mechanism.