Suppression of ultraviolet irradiation-induced apoptosis by overexpression of focal adhesion kinase in Madin-Darby canine kidney cells.

Focal adhesion kinase (FAK) has been implicated to play a role in suppression of apoptosis. In this study, we have demonstrated that UV irradiation induced cleavage of FAK and two of its interacting proteins Src and p130(Cas) in Madin-Darby canine kidney cells, concomitant with an increase in cell death. The cleavage of these proteins upon UV irradiation was completely inhibited by ZVAD-FMK, a broad range inhibitor of caspases, and apparently delayed by Bcl2 overexpression. To examine if FAK plays a role in suppressing UV-induced apoptosis, stable Madin-Darby canine kidney cell lines overexpressing FAK were established. Our results showed that a marked (30-40%) increase in cell survival upon UV irradiation was achieved by this strategy. In our efforts to determine the mechanism by which FAK transduces survival signals to the downstream, we found that a FAK mutant deficient in binding to phosphatidylinositol 3-kinase failed to promote cell survival. Moreover, the expression of the Src homology 3 domain of p130(Cas), which competed with endogenous p130(Cas) for FAK binding, abrogated the FAK-promoted cell survival. Together, these results suggest that the integrity of FAK and its binding to phosphatidylinositol 3-kinase and p130(Cas) are required for FAK to exert its antiapoptotic function.