α5β1 integrin stimulates Bcl‐2 expression and cell survival through Akt, focal adhesion kinase, and Ca2+/calmodulin‐dependent protein kinase IV

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Abstract
CHO cells expressing α5β1 integrin are more resistant to apoptosis and express more Bcl-2 than the same cells engineered to express αvβ1 or cytoplasmically truncated α5Δcβ1 integrin as their main fibronectin receptor. The Bcl-2 up-regulation by α5β1 is mediated, at least in part, by the focal adhesion kinase (FAK) and phosphatidylinositol-3 kinase (PI3K)/Akt pathways. Here, we show that integrin-mediated activation of Ca2+/calmodulin-dependent protein kinase (CaMK) IV, and the NF-κB and CREB transcription factors also enhance the integrin-dependent regulation of Bcl-2 expression in the α5β1cells. A forkhead transcription factor, which is inactivated by Akt, blocked Bcl-2 expression. The FAK pathway was found to be defective in both the αvβ1 and α5Δcβ1 cells. These cell lines differed from one another in two Bcl-2-regulating pathways: adhesion through αvβ1 failed to activate Akt, allowing forkhead to suppress Bcl-2 transcription, whereas α5Δcβ1 did not activate NF-κB and CREB, presumably because CaMK IV was not activated. Our results indicate that three pathways, the FAK, PI3K/Akt, and CaMK IV mediate the survival-supporting activity of α5β1 integrin.