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 1 beta-converting enzyme. We report here that TNF-induced activation of caspases result s in the cleavage and activation of cytosolic phospholipase A(2) (cPLA (2)) and that activated cPLA(2) contributes to apoptosis, Inhibition o f caspases by expression of a cowpox virus-derived inhibitor, CrmA, or by a specific tetrapeptide inhibitor of CPP32/caspase-3, acetyl-Asp-G lu-Val-Asp-aldehyde (Ac-DEVD-CHO), inhibited TNF-induced activation of cPLA(2) and apoptosis. TNF-induced activation of cPLA(2) was accompan ied by a cleavage of the 100-kDa cPLA(2) to a 70-kDa proteolytic fragm ent. This cleavage was inhibited by Ac-DEVD-CHO in a similar manner as that of poly(ADP)ribose polymerase, a known substrate of CPP32/caspas e-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 re sults suggest a novel caspase-dependent activation pathway for cPLA(2) during apoptosis and identify cPLA(2) as a mediator of TNF-induced ce ll death acting downstream of caspases.