Focal adhesion kinase is negatively regulated by phosphorylation at tyrosine 407

Focal adhesion kinase ( FAK) mediates signal transduction in response to multiple extracellular inputs via tyrosine phosphorylation at specific residues. Although several tyrosine phosphorylation events have been linked to FAK activation and downstream signal transduction, the function of FAK phosphorylation at Tyr(407) was previously unknown. Here, we show for the first time that phosphorylation of FAK Tyr(407) increases during serum starvation, contact inhibition, and cell cycle arrest, all conditions under which activating FAK Tyr(397) phosphorylation decreases. Transfection of NIH3T3 cells with a phosphorylationmimicking FAK 407E mutant decreased autophosphorylation at Tyr(397) and inhibited bothFAKkinase activity in vitro and FAK- mediated functions such as cell adhesion, spreading, proliferation, and migration. The opposite effects were observed in cells transfected with nonphosphorylatable mutant FAK F-407. Taken together, these data suggest the novel concept that FAK Tyr(407) phosphorylation negatively regulates the enzymatic and biological activities of FAK.