Involvement of caspase-dependent activation of cytosolic phospholipase A2in tumor necrosis factor-induced apoptosis

Abstract

Tumor necrosis factor (TNF)-induced apoptosis is mediated by caspases, which are cysteine proteases related to interleukin 1β-converting enzyme. We report here that TNF-induced activation of caspases results in the cleavage and activation of cytosolic phospholipase A 2(cPLA 2) and that activated cPLA 2 contributes to apoptosis. Inhibition of caspases by expression of a cowpox virus-derived inhibitor, CrmA, or by a specific tetrapeptide inhibitor of CPP32/caspase-3, acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), inhibited TNF-induced activation of cPLA 2 and apoptosis. TNF-induced activation of cPLA 2 was accompanied by a cleavage of the 100-kDa cPLA 2 to a 70-kDa proteolytic fragment. This cleavage was inhibited by Ac-DEVD-CHO in a similar manner as that of poly(ADP)ribose polymerase, a known substrate of CPP32/caspase-3. Interestingly, specific inhibition of cPLA 2 enzyme activity by arachidonyl trifluoromethylketone (AACOCF 3) partially inhibited TNF-induced apoptosis without inhibition of caspase activity. Thus, our results suggest a novel caspase-dependent activation pathway for cPLA 2 during apoptosis and identify cPLA 2 as a mediator of TNF-induced cell death acting downstream of caspases.