CLEAVAGE OF THE CYTOPLASMIC DOMAIN OF THE INTEGRIN BETA(3)-SUBUNIT DURING ENDOTHELIAL-CELL APOPTOSIS

In this study, we report that the cytoplasmic domain of the integrin b eta(3) subunit is a target for limited proteolysis during apoptosis of human umbilical vein endothelial cells, Calpain inhibitors inhibited the cleavage of the beta(3) cytoplasmic domain, indicating that calpai n is required. Calpain-mediated proteolysis of fodrin was also detecte d, indicating that calpain is activated during endothelial cell apopto sis. A phosphatase inhibitor, sodium orthovanadate, inhibited endothel ial cell apoptosis and cleavage beta(3), suggesting that protein depho sphorylation preceded integrin cleavage in the apoptosis signaling pat hway. beta(3) cleavage was observed in cells that were viable, suggest ing that it is an early event and not the consequence of post-death pr oteolysis. The extent of beta(3) cleavage correlated with a loss in th e capacity of cells to reattach to matrix proteins. Loss of reattachme nt capacity during apoptosis was significantly retarded by a calpain i nhibitor. As the beta(3) cytoplasmic domain is required for integrin s ignaling and interaction with the cytoskeleton, our results suggest th at cleavage in the beta(3) cytoplasmic domain by calpain or a calpain- like protease negatively regulates integrin-mediated adhesion, signali ng, and cytoskeleton association.