V-CRK-INDUCED CELL-TRANSFORMATION - CHANGES IN FOCAL ADHESION COMPOSITION AND SIGNALING

v-Crk is an oncogene product in which a viral Gag sequence is fused to a cellular Crk sequence, It contains one SH2 and one SH3 domain, To g ain insight into the molecular mechanisms underlying v-Crk-induced cel l transformation, we studied the subcellular localization and molecula r interactions of v-Crk in v-Crk-transformed NIH-3T3 cells. Our result s show that v-Crk specifically localizes to focal adhesions where it i nduces protein tyrosine phosphorylation, Subcellular fractionation stu dies indicated that. a significant amount of v-Crk is present in the c ytoskeletal cell fraction, a fraction that includes focal adhesions, T yrosine phosphorylated proteins, including p130(CAS), were also predom inantly found in the cytoskeletal fraction, We show that v-Crk induces a translocation of p130(CAS) to, the cytoskeleton, which is accompani ed by hyperphosphorylation of this protein. Mutational analyses showed that a functional v-Crk SH2 domain is required for the localization o f v-Crk in focal adhesions, Functional v-Crk SH2 and SH3 domains were both found to be required for the observed increase in tyrosine phosph orylation of focal adhesion proteins and for the translocation and hyp erphosphorylation of p130(CAS), v-Crk immunoprecipitation studies reve aled that cytoskeleton-associated v-Crk interacts with both p130(CAS) and an unidentified tyrosine kinase. These findings suggest the format ion of a focal adhesion-located complex consisting of v-Crk, a tyrosin e kinase and p130(CAS), which may lead to the hyperphosphorylation of p130(CAS). These specific and localized signaling events may represent initial steps in the process of v-Crk-induced cell transformation.