Beta-catenin promotes survival of renal epithelial cells by inhibiting Bax.

Ischemia activates Bax, a proapoptotic BCL2 protein, as well as the prosurvival beta-catenin/Wnt signaling pathway. To test the hypothesis that beta-catenin/Wnt signaling regulates Bax-mediated apoptosis after induction of metabolic stress, which occurs during renal ischemia, we infected immortalized and primary proximal tubular epithelial cells with adenovirus to express either constitutively active or dominant negative beta-catenin constructs. Constitutively active beta-catenin significantly decreased apoptosis and improved cell survival after metabolic stress. Furthermore, active beta-catenin decreased Bax activation, oligomerization, and translocation to mitochondria, and reduced both organelle membrane injury and apoptosis. Dominant negative beta-catenin had the opposite effects. Because Akt regulates Bax, we examined the effects of the beta-catenin mutants on Akt expression and activation. Constitutively active beta-catenin increased Akt-1 expression and activation before and after stress, and treatment with a phosphatidylinositol-3 kinase inhibitor antagonized the protective effects of beta-catenin on Akt activation, Bax inhibition, and cell survival. In addition, beta-catenin significantly increased the rate of phosphorylation at Bax serine(184), an Akt-specific target. Taken together, these results suggest that beta-catenin/Wnt signaling promotes survival of renal epithelial cells after metabolic stress, in part by inhibiting Bax in a phosphatidylinositol-3 kinase/Akt-dependent manner.