THE V-SRC SH3-DOMAIN BINDS PHOSPHATIDYLINOSITOL 3'-KINASE

Fibroblasts transformed by v-src or by related oncogenes encoding activated tyrosine kinases contain elevated levels of polyphosphoinositides with phosphate at the D-3 position of the inositol ring, as a result of the activation of phosphatidylinositol (PI) 3'-kinase. v-src-transformed cells also contain increased levels of PI 3'-kinase activity immunoprecipitable with anti-phosphotyrosine antibodies; furthermore, PI 3'-kinase can be detected in association with the v-Src tyrosine kinase. To identify regions of v-Src that can interact with PI 3'-kinase, the v-Src SH2 and SH3 domains were expressed in bacteria and incubated with lysates of normal chicken embryo fibroblasts. In vitro, the v-Src SH3 domain, but not the SH2 domain, bound PI 3'-kinase in lysates of uninfected chicken embryo fibroblasts. Substitutions of two highly conserved SH3 residues implicated in ligand binding abolished the ability of the v-Src SH3 domain to associate with PI 3'-kinase. Furthermore, the v-Src SH3 domain bound in vitro to the amino-terminal region of the p85alpha subunit of PI 3'-kinase. These results suggest that the v-Src SH3 domain may mediate an interaction between the v-Src tyrosine kinase and PI 3'-kinase, by direct binding to p85.