Anti-apoptotic Role of Focal Adhesion Kinase (FAK)

Abstract

Focal adhesion kinase (FAK) has an anti-apoptotic role in anchorage-dependent cells via an unknown mechanism. To elucidate the role of FAK in anti-apoptosis, we have established several FAK cDNA-transfected HL-60 cell lines and examined whether FAK-transfected cells have resistance to apoptotic stimuli. FAK-transfected HL-60 (HL-60/FAK) cells were highly resistant to apoptosis induced with hydrogen peroxide (1 mm) and etoposide (50 microg/ml) compared with the parental HL-60 cells or the vector-transfected cells, when determined using viability assay, DNA fragmentation, and flow cytometry analysis. Because no proteolytic cleavage of pro-caspase 3 to mature caspase 3 fragment was observed in HL-60/FAK cells, FAK was presumed to inhibit an upstream signal pathway leading to the activation of caspase 3. HL-60/FAK activated the phosphatidylinositide 3'-OH-kinase-Akt survival pathway and exhibited significant activation of NF-kappaB with marked induction of inhibitor-of-apoptosis proteins (IAPs: cIAP-1, cIAP-2, XIAP), regardless of the hydrogen peroxide-treated or untreated conditions, whereas no significant IAPs were detected in the parental or vector-transfected HL-60 cells. Apoptotic agents induced higher NF-kappaB activation in HL-60/FAK cells than in HL-60/Vect cells, and it appeared that sustained NF-kappaB activation is critical to the anti-apoptotic states in HL-60/FAK cells. Mutagenesis of FAK cDNA revealed that Y397 and Y925, which are involved in the tyrosine-phosphorylation sites, were prerequisite for the anti-apoptotic activity as well as induction of IAPs, and that K454, which is involved in the kinase activity, was also required for the full anti-apoptotic activity of FAK. Taken together, we have demonstrated definitively that FAK-transfected HL-60 cells, otherwise sensitive to apoptosis, become resistant to the apoptotic stimuli. We conclude that FAK activates the phosphatidylinositide 3'-OH-kinase-Akt survival pathway with the concomitant activation of NF-kB and induction of IAPs, which ultimately inhibit apoptosis by inhibiting caspase-3 cascade.