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GROWTH, DIFFERENTIATION, AND APOPTOSIS

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

¹West Los Angeles Veterans Administration Medical Center, the ²Gonda (Goldschmied) Diabetes Center, Division of Endocrinology, Diabetes and Hypertension, David Geffen School of Medicine at UCLA, Los Angeles, California; and ³Department of Stomatology and Anatomy, University of California, San Francisco, California

Submitted 30 March 2006 ; accepted in final form 26 November 2006

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--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-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-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-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.

apoptosis; ERK1/2; insulin; TNF-; IGF-1

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