Focal adhesion kinase mediates cell survival via NF-κB and ERK signaling pathways

Focal adhesion kinase ( FAK) is important to cellular functions such as proliferation, migration, and survival of anchorage- dependent cells. We investigated the role of FAK in modulating normal cellular responses, specifically cell survival in response to inflammatory stimuli and serum withdrawal, using FAK- knockout ( FAK(-/-)) embryonic fibroblasts. FAK(-/-) fibroblasts were more vulnerable to TNF-alpha- induced apoptosis, as measured by terminal deoxynucleotidyl transferase positivity. FAK(-/-) fibroblasts also demonstrated increased procaspase- 3 cleavage to p17 subunit, whereas this was undetectable in FAK(-/-) fibroblasts. Insulin receptor substrate- 1 expression was completely abolished and NF-kappa B activity was reduced, with a concomitant decrease in abundance of the anti- apoptotic protein Bcl- x(L) in FAK(-/-) cells. Upon serum withdrawal, FAK(-/-) cells exhibited marked attenuation of basal ERK phosphorylation, while FAK(-/-) cells, in contrast, maintained high basal ERK phosphorylation. Moreover, inhibition of ERK phosphorylation potentiated serum withdrawal- induced caspase- 3 activity. This was paralleled by increased insulin receptor substrate ( IRS)- 2 expression in FAK(-/-) cells, although both insulin- and IGF-1-mediated phosphorylation of Akt/ PKB and GSK-3 were impaired. This suggests that IRS-2 protects against apoptosis upon serum withdrawal via the ERK signaling pathway. The specific role of FAK to protect cells from apoptosis is regulated by activation and phosphorylation of NF-kappa B and interaction between activated growth factor anti-apoptotic signaling pathways involving both phosphatidylinositol 3- kinase/ Akt and MAPK/ ERK1/2. We demonstrate that FAK is necessary for upregulation of the anti- apoptotic NF-kappa B response, as well as for normal expression of growth factor signaling proteins. Thus we propose a novel role for FAK in protection from cytokine- mediated apoptosis.