The Binding Site for TRAF2 and TRAF3 but Not for TRAF6 Is Essential for CD40-Mediated Immunoglobulin Class Switching (original) (raw)

respectively, bind TRAF1 and TRAF5. The intracellular domain of murine CD40, like that of human CD40, has Children's Hospital and Department of Pediatrics a proline-rich membrane proximal region (aa 222-230), a conserved TRAF6 binding motif, RQDPQE (aa 234-239), Harvard Medical School 2 Immunopathology Unit and a 32 aa stretch (aa 247-278) that is 100% homologous to aa 246-277 of human CD40 and that contains the Massachusetts General Hospital Boston, Massachusetts 02115 TRAF2 and TRAF3 binding motif, PxQxT (aa 251-255). CD40 ligation in B cells causes activation of the MAP kinases JNK and p38 (Li et al., 1996) and of the transcription factor NFB (Berberich et al., 1994; Iciek et al., Summary 1997). Studies in B cell lines suggest that TRAF proteins play an important role in CD40 signaling. TRAF2 lacking To define the role of TRAF proteins in CD40-dependent isotype switching in B cells, we introduced wild-type an amino-terminal RING finger domain is a dominantnegative inhibitor of CD40 activation of NFB (Rothe et (WT) and mutant CD40 transgenes that lacked the binding motifs for TRAF6 (CD40⌬TRAF6), TRAF2 and TRAF3 al., 1995). TRAF2 and TRAF6 synergize in NFB activation (Lee et al., 1999; Tsukamoto et al., 1999). TRAF6, (CD40⌬TRAF2/3), or both (CD40⌬TRAFs) into B cells of CD40 Ϫ/Ϫ mice. The in vivo isotype switch defect in TRAF2, and TRAF3 all have been reported to be involved in JNK and p38 activation by CD40 (Grammer et al., CD40 Ϫ/Ϫ mice was fully corrected by WT and CD40⌬ TRAF6, partially by CD40⌬TRAF2/3, and not at all 1998; Leo et al., 1999a; Reinhard et al., 1997; Song et al., 1997; Sutherland et al., 1999). by CD40⌬TRAFs transgenes. CD40-mediated isotype switching, proliferation, and activation of p38, JNK,