Cleavage of the cytoplasmic domain of the integrin beta3 subunit during endothelial cell apoptosis.

In this study, we report that the cytoplasmic domain of the integrin beta3 subunit is a target for limited proteolysis during apoptosis of human umbilical vein endothelial cells. Calpain inhibitors inhibited the cleavage of the beta3 cytoplasmic domain, indicating that calpain is required. Calpain-mediated proteolysis of fodrin was also detected, indicating that calpain is activated during endothelial cell apoptosis. A phosphatase inhibitor, sodium orthovanadate, inhibited endothelial cell apoptosis and cleavage beta3, suggesting that protein dephosphorylation preceded integrin cleavage in the apoptosis signaling pathway. beta3 cleavage was observed in cells that were viable, suggesting that it is an early event and not the consequence of post-death proteolysis. The extent of beta3 cleavage correlated with a loss in the capacity of cells to reattach to matrix proteins. Loss of reattachment capacity during apoptosis was significantly retarded by a calpain inhibitor. As the beta3 cytoplasmic domain is required for integrin signaling and interaction with the cytoskeleton, our results suggest that cleavage in the beta3 cytoplasmic domain by calpain or a calpain-like protease negatively regulates integrin-mediated adhesion, signaling, and cytoskeleton association.