TRAF3 Forms Heterotrimers with TRAF2 and Modulates Its Ability to Mediate NF-κB Activation

Abstract

A family of tumor necrosis factor receptor-associated factors (TRAFs 1-7) 1 functions as adaptor molecules for TNF receptor superfamily members by associating with the intracellular domain of these proteins and subsequently mediating downstream signaling events such as NF-B and AP-1 (1, 2). Biochemical approaches have revealed that TRAFs form homotypic multimers (3-6) as well as certain heterotypic multimers, such as those between TRAF1 and TRAF2 and between TRAF3 and TRAF5 (7-10).Previous reports have demonstrated that TRAF2 and -3 play an important role in cellular activation and differentiation following engagement of a variety of TNF receptor superfamily members such as CD40/TNFRSF5 (1), OX40/TNFRSF4 (11), LT␤R (12-14), XEDAR (15), BCMA/TNFRSF17 (16), and Fn14/ TWEAKR/TNFRSF12A (17, 18). The functional significance of TRAF2 and -3 in immune responses mediated by one or more of these TNF receptor superfamily molecules was revealed by experiments with mice that were genetically altered in expression of TRAF2 or -3. Experiments using mice transgenic for only the TRAF domain of TRAF2 (amino acids 245-501; TRAF2.dominant negative; Ref. 19) or mice genetically deficient in TRAF3 expression (20) revealed a role for both adaptor proteins in T cell-dependent humoral immune responses. Of note, mice expressing a dominant negative form of TRAF2 exhibited an expanded B cell compartment that was evidenced by splenomegaly and lymphadenopathy (21), whereas TRAF3Ϫ/Ϫ mice exhibited decreased numbers of B cell precursors (20). Examination of signaling mechanisms mediated by TRAF2 or -3 revealed that both adaptor proteins induce activation of the mitogen-activated protein kinase Jun N-terminal kinase (JNK) as well as playing a role in the regulation of . Importantly, a number of reports have indicated that TRAF3 inhibits NF-B activation induced by TRAF2 following engagement of TNF receptor superfamily members such as CD40/TNFRSF5 (29) and OX40/TNFRSF4 (30,31), but the precise mechanism of this observation has not been delineated. However, overexpression of wild-type TRAF3 has been shown to inhibit TRAF2-induced 31). Furthermore, proteolysis of TRAF3 by a pepstatin A inhibitable mechanism enhanced CD40-mediated NF-B activation (32), whereas TRAF2-induced degradation of TRAF3 enhanced . By contrast, expression of an alternatively spliced form of TRAF3 has been shown to activate 35). These findings suggest that a complex role for TRAF2 and TRAF3 in the regulation of NF-B, but the precise molecular mechanism has not been delineated. Importantly, no direct physical interaction between TRAF2 and TRAF3 has been documented to date.The purpose of the current study was to examine whether functional inhibition of TRAF2-induced NF-B activation was mediated by a direct interaction between TRAF2 and -3. Experiments utilizing one-and two-step FRET performed by confocal microscopy or flow cytometry clearly demonstrated that TRAF3 directly associates with TRAF2 and inhibits TRAF2-induced NF-B, but not AP-1, activation. MATERIALS AND METHODSPlas...

Activation-induced Tumor Necrosis Factor Receptor-associated Factor 3 (Traf3) Alternative Splicing Controls the Noncanonical Nuclear Factor κB Pathway and Chemokine Expression in Human T Cells

“…Earlier studies have shown that both the Traf and the RING domains are involved in Traf3-mediated ncNFB inhibition (21,22). The Traf domain is also required for the Traf3-NIK interaction (22,25), whereas the Traf3-Traf2 interaction could not be mapped to one domain alone (36), suggesting a more complex interaction surface. This could make the Traf3-Traf2 interaction susceptible for a regulation by an internal deletion as we observe in Traf3DE8.…”

TRAF4 acts as a silencer in TLR-mediated signaling through the association with TRAF6 and TRIF

“…Recently, it has been demonstrated that TRAF3, another family member, directly associates with p40 phox and mediates CD40-induced production of ROS in B cells [25]. Moreover, He et al [26] clearly demonstrated that TRAF3 forms heterotrimers with TRAF2, which modulate TRAF2-induced NF-jB activation. This finding, together with our results showing the interaction between p47 phox , TRAF4, TRAF6, and TRIF, indicates the cytosolic NADPH oxidase complex is likely to regulate immune cell activation signaling through a novel TRAF-TRAF dimerization-dependent mechanism.…”

A CD40 Kozak sequence polymorphism and susceptibility to antibody-mediated autoimmune conditions: the role of CD40 tissue-specific expression

“…Even though the signaling pathways of activation of CD40 in thyrocytes have not yet been examined, these can be postulated based on data from studies of activation of necrosis factor kappa B (NFkB) by transforming growth factor-beta (TGF-b) in Graves' thyrocytes, 49 as well as of CD40 signaling in other cell types. [50][51][52][53][54][55][56][57][58][59] According to our intrinsic hypothesis, CD40 ligand more readily activates CD40, overexpressed on the surface of thyrocytes in individuals harboring the CC genotype. Once activated, CD40 receptors multimerize, recruiting TNF-receptor associated factors (TRAFs) to their cytoplasmic tails.…”

“…Downstream of the initial receptor ligation, TRAFs recruit and activate kinases such as inhibitor of k-B (IkB) kinase (IKK), leading to activation of NFkB pathway. NFkB is able to turn on transcription of a number of genes including cytokines, chemokines and adhesion molecules, which could augment thyroidal inflammation [50][51][52][53][54][55][56][57][58][59] (Figure 4b). Moreover, activation of the CD40 pathway has been shown to activate anti-apoptotic pathways in several non-lympho- The intrinsic thyroidal CD40 model.…”