Expression of α-catenin in α-catenin–deficient cells increases resistance to sphingosine-induced apoptosis

α-Catenin, an intracellular protein, associates with the COOH-terminal region of cadherin cell adhesion molecules through interactions with either β-catenin or γ-catenin (plakoglobin). The full activity of cadherins requires a linkage to the actin cytoskeleton mediated by catenins. We transfected α-catenin–deficient colon carcinoma cells with a series of α-catenin constructs to determine that α-catenin expression increases the resistance to apoptosis induced by sphingosine. Two groups of constructs, containing deletions in either the middle segment of the molecule or the COOH terminus, induced morphological changes, cell compaction, and decreases in cell death. In α-catenin–expressing cells, inhibition of cadherin cell adhesion by treatment with anti–E-cadherin antibodies did not decrease the cells viability. α-Catenin expression partially suppressed the downregulation of Bcl-xL and the activation of caspase 3. Expression of p27kip1 protein, an inhibitor of cyclin-dependent kinases, was increased by α-catenin expression in low density cell cultures. The increased levels of p27kip1 correlated with both increased resistance to cell death and morphological changes in transfectants containing deletion mutants. Transfection-mediated upregulation of p27kip1 decreases sphingosine-induced cell death in α-catenin–deficient cells. We postulate that α-catenin mediates transduction of signals from the cadherin–catenin complex to regulate the apoptotic cascade via p27kip1.