Involvement of caspase-dependent activation of cytosolic phospholipase A(2) in tumor necrosis factor-induced apoptosis

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.