Meredith J, Mu Z, Saido T, Du X
Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
J Biol Chem. 1998 Jul 31;273(31):19525-31. doi: 10.1074/jbc.273.31.19525.
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.
在本研究中，我们报告整合素β3亚基的胞质结构域是人类脐静脉内皮细胞凋亡过程中有限蛋白水解作用的靶点。钙蛋白酶抑制剂可抑制β3胞质结构域的裂解，表明需要钙蛋白酶。同时还检测到钙蛋白酶介导的血影蛋白的蛋白水解作用，表明钙蛋白酶在内皮细胞凋亡过程中被激活。一种磷酸酶抑制剂原钒酸钠可抑制内皮细胞凋亡并抑制β3的裂解，这表明在凋亡信号通路中蛋白去磷酸化先于整合素裂解。在存活细胞中观察到β3裂解，这表明它是一个早期事件，而非死亡后蛋白水解的结果。β3裂解的程度与细胞重新附着于基质蛋白的能力丧失相关。钙蛋白酶抑制剂可显著延缓凋亡过程中重新附着能力的丧失。由于整合素信号传导以及与细胞骨架相互作用需要β3胞质结构域，我们的结果表明，钙蛋白酶或类钙蛋白酶对β3胞质结构域的裂解会对整合素介导的黏附、信号传导及细胞骨架关联产生负向调节作用。
