Abstract 1267: The RING domain of TRAF2 inhibits TNFα-induced cell death independent of NF-κB activation

TNFα is a pleiotropic cytokine that activates both the pro-survival IKK/NF-κB and the pro-apoptotic FADD/caspase-8 pathways. TNF receptor associated factor 2 and 5 (TRAF2/5) contain N-terminal RING domains, and TRAF2/5 RING domain-mediated RIP1 ubiquitination is believed to be essential for NF-κB activation and inhibition of cell death in response to TNFα stimulation. In support of this notion, TRAF2/5 double knockout (TRAF2/5 DKO) cells are sensitive to TNFα-induced apoptosis. In addition, the RING domain-deleted TRAF2 (TRAF2-ΔR) has been widely used in the field as a dominant negative to block TNFα-induced JNK and IKK activation in transient overexpression systems. Here, we report that stable expression of TRAF2-ΔR in TRAF2/5 DKO cells at a physiological level completely restores normal TNFα-induced NF-κB activation, but that it neither restores RIP1 polyubiquitination nor inhibits cell death. We also found that the basal and inducible expression of anti-apoptotic proteins in TRAF2-ΔR-expressing cells is normal, yet these cells remain sensitive to TNFα-induced cell death because anti-apoptotic proteins were not recruited to the TNFR1 complex efficiently. This suggests that two events are required for the inhibition of TNFα-induced cell death: i) NF-κB-dependent expression of anti-apoptotic proteins such as cIAP1/2 and cFLIP; and ii) TRAF2 RING domain-dependent retention of cIAP1 in the TNFR1 complex. Ablation of either event leads to caspase-8 activation and cell death in response to TNFα stimulation. Our data also suggest that RIP1 ubiquitination is not essential for TNFα-induced NF-κB activation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1267.