ASSOCIATION OF PHOSPHATIDYLINOSITOL 3-KINASE, VIA THE SH2 DOMAINS OF P85, WITH FOCAL ADHESION KINASE IN POLYOMA MIDDLE T-TRANSFORMED FIBROBLASTS

Focal adhesion kinase (FAK), a non-receptor protein tyrosine kinase, b ecomes activated and phosphorylated on tyrosine in cells transformed w ith v-src. By cytoimmunofluorescence a sub-fraction of the p85 subunit of phosphoinositide 3-kinase (PI 3-kinase) localized in focal adhesio n plaques. We examined the possibility that FAK associates with PI 3-k inase. In fibroblasts transformed with polyoma middle t, PI 3-kinase a ctivity co-immunoprecipitated with pp125(FAK) using two different anti bodies against this protein. pp125(FAK) from middle t-transformed cell s associated with a glutathione-S-transferase fusion protein containin g the 85-kDa subunit of phosphatidylinositol 3-kinase. Both of the SH2 domains and the SH3 domain of p85 also formed complexes with pp125(FA K) in vitro. Phosphopeptides that bind to the SH2 domains completely b locked the binding of full-length p85 to pp125(FAK), while a peptide t hat binds to the SH3 domain was ineffective, indicating that the assoc iation between p85 and pp125(FAK) is mediated by the SH2 domains of p8 5.