Competition between TRAF2 and TRAF6 Regulates NF-κB Activation in Human B Lymphocytes

ObjectiveTo investigate the role of TNF receptor-associated factor 2 (TRAF-2) and TRAF6 in CD40-induced nuclear factor-κB (NF-κB) signaling pathway and whether CD40 signaling requires TRAF2.MethodsHuman B cell lines were transfected with plasmids expressing wild type TRAF2 or dominant negative TRAF2, TRAF2-shRNA, or TRAF6-shRNA. The activation of NF-κB was detected by Western blot, kinase assay, transfactor enzyme-linked immunosorbent assay (ELISA), and fluorescence resonance energy transfer (FRET). Analysis of the role of TRAF-2 and TRAF-6 in CD40-mediated NF-κB activity was examined following stimulation with recombinant CD154.ResultsTRAF2 induced activity of IκB-kinases (IKKα, IKKi/ɛ), phosphorylation of IκBα, as well as nuclear translocation and phosphorylation of p65/RelA. In contrast, TRAF6 strongly induced NF-κB activation and nuclear translocation of p65 as well as p50 and c-Rel. Engagement of CD154-induced nuclear translocation of p65 was inhibited by a TRAF6-shRNA, but conversely was enhanced by a TRAF2-shRNA. Examination of direct interactions between CD40 and TRAFs by FRET documented that both TRAF2 and TRAF6 directly interacted with CD40. However, the two TRAFs competed for CD40 binding.ConclusionsThese results indicate that TRAF2 can signal in human B cells, but it is not essential for CD40-mediated NF-κB activation.