Role of Src-specific phosphorylation site on focal adhesion kinase for senescence-associated apoptosis resistance

A decreased apoptotic response toward noxious stress is an issuing characteristic of the aging phenotype. Hydrogen peroxide or staurosporine induced apoptosis readily in young cells but not in senescent cells. We showed that focal adhesion kinase (FAK) expression and its phosphorylation at Tyr³⁹⁷, autophosphorylation site for focal adhesion formation, and Tyr⁵⁷⁷, Src-dependent phosphorylation site, were both increased in senescent cells. Moreover, FAK was inactivated proteolytically by apoptotic stimuli in young cells, but not in senescent cells. In addition, senescent cells whose FAK expression was downregulated by siRNA showed the increased level of apoptosis by staurosporine treatment via caspase-3 activation but not by hydrogen peroxide treatment. Interestingly dephosphorylation at Tyr⁵⁷⁷ of FAK by PP2 treatment, Src-family kinase inhibitor, induced the apoptosis by staurosporine in senescent cells but dephosphorylation at Tyr³⁹⁷ by downregulation of caveolin-1 was not affected. These data suggest that FAK might differently regulate apoptosis and focal adhesion formation through site-specific tyrosine phosphorylation in senescent cells. Both authors contributed equally to this work.