Both amino- and carboxyl-terminal domains of TRAF3 negatively regulate NF-kappa B activation induced by OX40 signaling

OX40 is a member of the tumor necrosis factor receptor (TNF-R) superfamily. We observed that overexpression of OX40 activated NF-kappa B, which was in hibited by dominant negative forms of TRAF2, NF-kappa B-inducing kinase (NI K), and IkappaB kinase (IKR) alpha. This indicates that OX40 signaling lead s to NF-kappa B activation through the same cascade as TNF-R2. We then inve stigated the negative regulatory function of TRAF3 on OX40-induced NF-kappa B activation. TRAF3 blocked OX40-, TRAF2-induced NP-kappa B activation, bu t not NIK- and IKK alpha-induced NF-kappa B activation, indicating that TRA F3 blocks the pathway between TRAF2 and NIK. C-terminal deletion mutants as well as the N-terminal deletion mutant of TRAF3 inhibited NP-kappa B activ ation induced by OX40 or TRAF2. Since TRAF3 bound to OX40 through the C-ter minal TRAF domain, the C-terminal domain is likely to work as a dominant ne gative mutant to compete the recruitment of TRAF2 to the receptor, which tr ansmits the signal from OX40 to the downstream, NIK kinase. On the other ha nd, the N-terminal domain of TRAF3 seems to affect the downstream of TRAF2 binding. Thus, it is suggested that TRAF3 actively inhibits NF-kappa B acti vation induced by OX40. (C) 2000 Academic Press.