Reactive oxygen species are downstream products of TRAF-mediated signal transduction

Members of the TNFR (tumor necrosis factor receptor) superfamily are involv ed in regulating activation and differentiation of cells as well as cell su rvival and programmed cell death/apoptosis. Multimerization of TNFRs can le ad to recruitment of TRAFs (TNFR-associated factors) by the receptors resul ting in activation of kinases and transcription factors, such as c-Jun N-te rminal kinase and nuclear factor kappaB (NF-kappaB). Signal transduction tr iggered by TNF-alpha also induces an increase in intracellular reactive oxy gen species (ROS). ROS have been suggested to play a role in NF-kappaB acti vation, which is thought to promote cell survival. However, oxidation of pr oteins and lipids by ROS can also result in apoptosis. The processes genera ting intracellular ROS and the mechanism(s) regulating the cellular redox s tatus have not been fully elucidated. We investigated whether TRAFs play a role in controlling intracellular ROS levels. Our results indicate that rec ruitment of TRAFs to the plasma membrane of human embryonic kidney (HEK) 29 3 cells is crucial for activation of signaling pathways, which regulate ROS production in mitochondria. TRAF-mediated changes in ROS levels enhanced N F-kappaB activation but were not dependent on NF-kappaB-inducing kinase. Co nsistent with its anti-apoptotic function, Bcl-x(L) interfered with TRAF-me diated ROS generation but not NF-kappaB activation. Taken together, our res ults suggest a novel role of TRAFs in signal transduction pathways triggere d by TNFR-related proteins, which balance cell survival and apoptosis by re gulating the electron transport in mitochondria.