Adherens junction-dependent PI3K/Akt activation induces resistance to genotoxin-induced cell death in differentiated intestinal epithelial cells

The crypt–villi axis of intestinal mucosa maintains homeostasis by renewal of epithelia, and also exhibits different properties from undifferentiated to terminally differentiated cells. We investigated differential susceptibility to genotoxin-induced cell death, based on the degree of differentiation of epithelial cells, and its mechanism. Differentiation was induced by post-confluence culture in Caco-2 cells. Methyl methanesulfonate (MMS), a direct-acting DNA alkylating agent, was used for genotoxin-induced cell death. Compared to subconfluent Caco-2 cells, 7 days post-confluent cells showed resistance to MMS-induced cell death. With increasing expression of adherens junction components of E-cadherin and β-catenin, E-cadherin and p-Akt expression increased in 7 days post-confluent Caco-2 cells, and in human intestinal tissue, expression of E-cadherin and p-Akt also increased in the upper portion of villi, compared to the crypt. Inhibition of cell–cell adhesion using EGTA decreased Akt phosphorylation, which was reversed by calcium restoration. Akt phosphorylation by calcium-mediated cell–cell adhesion was more prominent in differentiated cells. In addition, treatment of a PI3K inhibitor, LY294002, inhibited Akt phosphorylation by calcium-mediated cell–cell adhesion. Finally, the differential sensitivity to MMS-induced cell death between subconfluent and 7 days post-confluent Caco-2 cells was eliminated by inhibiting cell–cell adhesion or PI3K. Our data demonstrated that cell adhesion-mediated PI3K/Akt activation could be one of the important mechanisms of resistance to genotoxin-induced cell death in differentiated epithelial cells.