Negative regulation of FAK signaling by SOCS proteins

Focal adhesion kinase (FAK) becomes activated upon integrin‐mediated cell adhesion and controls cellular responses to the engagement of integrins, including cell migration and survival. We show here that a coordinated signaling by integrins and growth factor receptors induces expression of suppressor of cytokine signaling‐3 (SOCS‐3) and subsequent interaction between endogenous FAK and SOCS‐3 proteins in 3T3 fibroblasts. Cotransfection studies demonstrated that SOCS‐3, and also SOCS‐1, interact with FAK in a FAK‐Y397‐dependent manner, and that both the Src homology 2 (SH2) and the kinase inhibitory region (KIR) domains of the SOCS proteins contribute to FAK binding. SOCS‐1 and SOCS‐3 were found to inhibit FAK‐associated kinase activity in vitro and tyrosine phosphorylation of FAK in cells. The SOCS proteins also promoted polyubiquitination and degradation of FAK in a SOCS box‐dependent manner and inhibited FAK‐dependent signaling events, such as cell motility on fibronectin. These studies suggest a negative role of SOCS proteins in FAK signaling, and for a previously unidentified regulatory mechanism for FAK function.