TNFR80-DEPENDENT ENHANCEMENT OF TNFR60-INDUCED CELL-DEATH IS MEDIATEDBY TNFR-ASSOCIATED FACTOR-2 AND IS SPECIFIC FOR TNFR60

Costimulation of TNFR80 can strongly enhance TNFR60-induced cell death . In this study, we show that this enhancement is TNFR60 selective, as neither TNF-related apoptosis-inducing ligand/Apo2 ligand-, Apo1/Fas- , ceramide-, nor daunorubicin-mediated cell death was affected by cost imulation of TNFR80. We further demonstrate that TNFR-associated facto r 2 (TRAF2) is critically involved in both negative and positive regul ation of TNF-induced cell death. Overexpression of TRAF2 and of a TRAF 2 mutant, deficient in nuclear factor-kappa B activation, selectively desensitized and enhanced, respectively, TNFR60-induced cell death in HeLa cells, However, upon costimulation of TNFR80, which mediates acti vation of nuclear factor-kappa B and the c-Jun aminoterminal kinase vi a TRAF2, TNF-induced cell death is drastically enhanced in parental an d TRAF2-transfected, but not in TRAF2 (87-501)-transfected cells. Thes e data point to a critical role of TRAF2 in the apoptotic TNFR cross t alk, whereby the TNFPR80-dependent enhancement of TNFR60-induced cell death is due to TNFR80-mediated negative regulation of TRAF2 function( s). An interference with TRAF2 function was confirmed independently by analysis of c-Jun amino-terminal kinase activation via TNFR60 upon pr estimulation of TNFR80. We propose that the apoptotic TNFR cross talk is based on TNFR80-mediated abrogation of antiapoptotic TRAF2-dependen t signaling pathways initiated by TNFR60, but not Apo1/Fas or the apop totic TNF-related apoptosis-inducing ligand receptors.