PED/PEA-15 is a recently cloned 15 kDa protein possessing a death effector domain (DED). In MCF-7 and HeLa cells, a fivefold overexpression of PED/PEA-15 blocked FasL and TNFalpha apoptotic effects. This effect of PED overexpression was blocked by inhibition of PKC activity. In MCF-7 and HeLa cell lysates, PED/PEA-15 co-precipitated with both FADD and FLICE. PED/PEA-15-FLICE association was inhibited by overexpression of the wild-type but not of a DED-deletion mutant of FADD. Simultaneous overexpression of PED/PEA-15 with FADD and FLICE inhibited FADD-FLICE co-precipitation by threefold. Based on cleavage of the FLICE substrate PARP, this inhibitory effect was paralleled by a threefold decline in FLICE activation in response to TNF-alpha. TNFalpha, in turn, reduces PED association with the endogenous FADD and FLICE of the cells. Thus, PED/PEA-15 is an endogenous protein inhibiting FAS and TNFR1-mediated apoptosis. At least in part, this function may involve displacement of FADD-FLICE binding through the death effector domain of PED/PEA-15.