Negative Regulation of focal adhesion kinase through phosphorylation at Tyrosine 407

Abstract

Focal adhesion kinase (FAK) is a non receptor protein-tyrosine kinase (PTK) localized at focal contacts to regulate integrin signaling events, cell cycle progression and cell migration. The ability of FAK to transduce downstream signals depends on its phosphorylation at tyrosine residue. In contrast to other tyrosine residues, the function of phosphorylation at Tyrosine 407 (Tyr-407) remains unknown. FAK phosphorylation at Tyr-407 in NIH3T3 cells was increased after serum starvation, while phosphorylation at Tyr-397 decreased. FAK phosphorylation at Tyr-407 was diminished when cells were detached and increased after plating on various extracellular matrix (ECM), suggesting adhesion dependency. In addition, the non phosphorylatable mutant FAK Y407F increased tyrosine phosphorylations of FAK and paxillin, and its kinase activity based on in vitro kinase assay. Consistently, FAK-null NIH3T3 cells transfected with Y407F mutant showed increased autophosphorylation of FAK, together with increased proliferation and migration. Taken together, these data suggest that FAK phosphorylation at Tyr-407 negatively regulates the activity and functions of FAK.