TRAF3 is a TNF receptor (see 191190) family adaptor protein with regulatory roles in immune and other cell types (summary by Li et al., 2019).

CD40 (109535) is a member of the tumor necrosis factor receptor (TNFR) family. The short cytoplasmic domain of CD40 contains a region with limited homology to the conserved cytosolic death domain of TNFR1 (191190) and FAS (134637). Using a yeast 2-hybrid assay with the cytoplasmic domain of CD40 as bait, Hu et al. (1994) isolated B-cell cDNAs encoding a protein that they called CD40-binding protein (CD40bp). The predicted CD40bp protein contains a RING finger DNA-binding motif, a cys/his-rich region, and a coiled-coil domain. Like TRAF1 (601711) and TRAF2 (601895), both TNFR2 (75-kD TNFR; 191191)-binding proteins, CD40bp contains a C-terminal TRAF domain. In vitro translated CD40bp has an apparent molecular mass of 64 kD. Coimmunoprecipitation studies indicated that CD40bp interacts with CD40 in human B cells. Hu et al. (1994) suggested that CD40bp, along with TRAF1 and TRAF2, comprise a family of proteins that associate with the cytoplasmic faces of the TNFR family and have in common a TRAF domain.

Independently, Sato et al. (1995) and Cheng et al. (1995) identified CD40bp, designating it CAP1 (CD40-associated protein-1) and CRAF1 (CD40 receptor-associated factor 1), respectively. Sato et al. (1995) demonstrated that CAP1 binds specifically to the cytoplasmic domain of CD40, but not to that of TNFR1, TNFR2, or FAS. The C-terminal TRAF domain of CAP1 was sufficient to mediate binding to CD40 and homodimerization. Cheng et al. (1995) isolated mouse and human CRAF1 cDNAs. The predicted 568-amino acid human protein is 96% identical to mouse CRAF1. These authors divided the TRAF domain into 2 regions: TRAF-N, the more N-terminal coiled-coil subdomain, and TRAF-C, which was necessary and sufficient for CRAF1 to interact with CD40. Overexpression of a truncated cDNA encoding the entire TRAF domain of CRAF1 inhibited CD40-mediated upregulation of the CD23 (151445) gene, which suggested to Cheng et al. (1995) that CRAF1 participates in CD40 signaling.

Gross (2012) mapped the TRAF3 gene to chromosome 14q32.32 based on an alignment of the TRAF3 sequence (GenBank BC075086) with the genomic sequence (GRCh37).

The cytoplasmic C terminus of the Epstein-Barr virus latent infection membrane protein-1 (LMP1) is essential for B lymphocyte growth transformation. LMP1 is an integral membrane protein that has transforming effects in nonlymphoid cells, and may act by constitutively activating a common cellular growth factor receptor pathway. Mosialos et al. (1995) found that CD40bp, which they called LAP1 (LMP1-associated protein-1), interacted with the LMP1 C-terminal domain. Expression of LMP1 caused LAP1 and TRAF1 (EBI6) to localize to LMP1 clusters in lymphoblast plasma membranes, and LMP1 coimmunoprecipitated with these proteins in cell extracts. LAP1 bound to the cytoplasmic domains of CD40 and LT-beta-R (600979) in vitro, and associated with p80 (TNFR2) in vivo. Northern blot analysis revealed that LAP1 was expressed as a full-length 2.8-kb mRNA and an alternatively spliced 1.8-kb mRNA in all tissues tested. Mosialos et al. (1995) concluded that the interaction of LAP1 with LMP1 and with the cytoplasmic domains of TNFR family members is evidence for a central role of this protein as an effector of cell growth or death signaling pathways.

Dadgostar et al. (2003) determined that the coiled-coil domain of mouse T3jam (608255) interacted with the isoleucine zipper domain of Traf3. T3jam did not associate with other Traf family members. Coexpression of T3jam and Traf3 recruited Traf3 to the detergent-insoluble fraction, and T3jam and Traf3 synergistically activated JNK (601158), but not nuclear factor kappa-B (see 164011).

To dissect biochemically Toll-like receptor signaling, Hacker et al. (2006) established a system for isolating signaling complexes assembled by dimerized adaptors. Using MyD88 (602170) as a prototypic adaptor, they identified TRAF3 as a new component of Toll/interleukin-1 receptor signaling complexes that is recruited along with TRAF6 (602355). Using myeloid cells from Traf3- and Traf6-deficient mice, Hacker et al. (2006) demonstrated that TRAF3 is essential for the induction of type I interferons and the antiinflammatory cytokine interleukin-10 (IL10; 124092), but is dispensable for expression of proinflammatory cytokines. In fact, Traf3-deficient cells overproduced proinflammatory cytokines owing to defective Il10 production. Despite their structural similarity, the functions of TRAF3 and TRAF6 are largely distinct. TRAF3 is also recruited to the adaptor TRIF (607601) and is required for marshalling the protein kinase TBK1 (604834) into Toll/interleukin-1 receptor signaling complexes, thereby explaining its unique role in activation of the interferon response.

Oganesyan et al. (2006) demonstrated that cells lacking TRAF3 are defective in type I interferon responses activated by several different Toll-like receptors. Furthermore, they showed that TRAF3 associates with the Toll-like receptor adaptors TRIF and IRAK1 (300283), as well as downstream IRF3/7 kinases TBK1 and IKK-epsilon (IKKE, or IKBKE; 605048), suggesting that TRAF3 serves as a critical link between Toll-like receptor adaptors and downstream regulatory kinases important for IRF activation. In addition to TLR stimulation, Oganesyan et al. (2006) showed that TRAF3-deficient fibroblasts are defective in their type I interferon response to direct infection with vesicular stomatitis virus, indicating that TRAF3 is also an important component of TLR-independent viral recognition pathways. Oganesyan et al. (2006) concluded that TRAF3 is a major regulator of type I interferon production and the innate antiviral response.

Production of type I interferon is a critical host defense triggered by pattern-recognition receptors (PRRs) of the innate immune system. Kayagaki et al. (2007) demonstrated that reduction of DUBA (300713) augmented the PRR-induced type I interferon response in transfected HEK293 cells, whereas ectopic expression of DUBA had the converse effect. DUBA bound TRAF3, an adaptor protein essential for type I interferon response. TRAF3 is an E3 ubiquitin ligase that preferentially assembled lys63-linked polyubiquitin chains in cotransfection assays. DUBA selectively cleaved the lys63-linked polyubiquitin chains on TRAF3, resulting in its dissociation from the downstream signaling complex containing TBK1. A discrete ubiquitin interaction motif within DUBA was required for efficient deubiquitination of TRAF3 and optimal suppression of type I interferon. Kayagaki et al. (2007) concluded that their data identified DUBA as a negative regulator of innate immune responses.

Cytokine signaling is thought to require assembly of multicomponent signaling complexes at cytoplasmic segments of membrane-embedded receptors, in which receptor-proximal protein kinases are activated. Matsuzawa et al. (2008) reported that, upon ligation, CD40 formed a complex containing adaptor molecules TRAF2 and TRAF3, ubiquitin-conjugating enzyme UBC13 (UBE2N; 603679), cellular inhibitor of apoptosis protein-1 (CIAP1, or BIRC2; 601712) and -2 (CIAP2, or BIRC3; 601721), IKK-gamma (IKBKG; 300248), and MEKK1 (MAP3K1; 600982). TRAF2, UBC13, and IKK-gamma were required for complex assembly and activation of MEKK1 and MAP kinase cascades. However, the kinases were not activated unless the complex was translocated from the membrane to the cytosol upon CIAP1/CIAP2-induced degradation of TRAF3. Matsuzawa et al. (2008) proposed that this 2-stage signaling mechanism may apply to other innate immune receptors and may account for spatial and temporal separation of MAPK and IKK signaling.

Hu et al. (2013) identified the deubiquitinase OTUD7B (611748) as a pivotal regulator of the noncanonical NF-kappa-B pathway. OTUD7B deficiency in mice has no appreciable effect on canonical NF-kappa-B activation but causes hyperactivation of noncanonical NF-kappa-B. In response to noncanonical NF-kappa-B stimuli, OTUD7B binds and deubiquitinates TRAF3, thereby inhibiting TRAF3 proteolysis and preventing aberrant noncanonical NF-kappa-B activation. Consequently, the OTUD7B deficiency results in B-cell hyperresponsiveness to antigens, lymphoid follicular hyperplasia in the intestinal mucosa, and elevated host-defense ability against an intestinal bacterial pathogen, Citrobacter rodentium. Hu et al. (2013) concluded that their findings established OTUD7B as a crucial regulator of signal-induced noncanonical NF-kappa-B activation, and indicated a mechanism of immune regulation that involves OTUD7B-mediated deubiquitination and stabilization of TRAF3.

The herpes simplex virus-1 (HSV-1) tegument protein UL36 contains an N-terminal deubiquitinase (DUB) motif called UL36 ubiquitin-specific protease (UL36USP). By expressing UL36USP in human embryonic kidney cells, Wang et al. (2013) identified host pathways affected by HSV-1 infection that resulted in inhibition of IFNB (147640) expression. UL36USP inhibited Sendai virus (SeV)-induced IRF3 (603734) dimerization and activation and transcription of IFNB. Mutation analysis confirmed that the DUB activity of UL36USP1 was required to block IFNB production. UL36USP also inhibited IFNB promoter activity induced by overexpression of the RIGI (DDX58; 609631) N terminus or MAVS (609676), but not TBK1, IKKE, or the active form of IRF3. UL36USP deubiquitinated TRAF3 and prevented recruitment of TBK1. Cells infected with recombinant HSV-1 lacking UL36USP DUB activity produced more IFNB than cells infected with wildtype HSV-1. Wang et al. (2013) concluded that HSV-1 UL36USP removes polyubiquitin chains on TRAF3 and counteracts the IFNB pathway.

Using transfected HEK293T cells, Chen et al. (2015) showed that overexpression of RNF166 (617178) enhanced activation of the IFNB promoter after infection with SeV. Knockdown of RNF166 in HEK293T cells inhibited IFNB promoter activation, IFNB transcription, and IFNB secretion in response to SeV infection. Similar results were observed with knockdown of RNF166 in HeLa cells. RNF166 interacted with TRAF3 and TRAF6, and knockdown of RNF166 suppressed SeV-induced ubiquitination of TRAF3 and TRAF6. Chen et al. (2015) proposed that RNF166 positively regulates RNA virus-triggered IFNB production by enhancing ubiquitination of TRAF3 and TRAF6.

Using primary Cd4 (186940) T cells isolated from Traf -/- mice, Arkee et al. (2024) showed that Traf3 deficiency led to impaired Akt (164730) activation and thus to impaired in vitro skewing of Cd4 T cells into T-helper-1 (Th1) and Th2 fates. Further analysis revealed that Traf3 enhanced activation of Stat6 (601512), thereby promoting differentiation of Cd4 T cells toward the Th2 fate. Traf3 promoted Stat6 activation by regulating recruitment of the inhibitory molecule Ptp1b (PTPN1; 176885) to the Il4r (147781) signaling complex in a manner that required integration of T-cell receptor (TCR; see 186880)-Cd28 (186760)- and Il4r-mediated signals.

Immunodeficiency 132A

Perez de Diego et al. (2010) investigated an 18-year-old French female with immunodeficiency-132A (IMD132A; 614849) who had suffered from herpes simplex encephalitis (HSE) at age 4 years and who lacked mutations in either the UNC93B1 (608204) or TLR3 (603029) genes. They identified a de novo heterozygous missense mutation in the TRAF3 gene (R118W; 601896.0001). RT-PCR analysis of patient cells detected normal levels of TRAF3 mRNA, but Western blot analysis showed severely reduced levels of TRAF3 protein at about 17.5% of control values. This suggested that the mutation prevents stable TRAF3 protein production and also has an effect on the amount of wildtype protein generated from the other allele. Responsiveness to TLR3 agonists was impaired in patient fibroblasts, as indicated by deficient NFKB (see 164011) activation and poor production of IFNB, IFNL (IL29; 607403), and IL6 (147620), consistent with a loss of function. Expression of wildtype and mutant alleles in cell lines showed that mutant TRAF3 acted in a dominant-negative manner. TRAF3-deficient fibroblasts had impaired type I and type III IFN-dependent control of viruses and deficient responses through the TNFR (e.g., TNFRSF5; 109535) pathways. Perez de Diego et al. (2010) concluded that, whereas complete Traf3 deficiency is neonatal lethal in mice, decreases in TRAF3 production and function result in predisposition to HSE, a condition that is usually fatal if untreated.

In a 51-year-old woman of Asian descent with IMD132A manifest as chronic pulmonary Mycobacterium abscessus infection, Liew et al. (2022) identified a heterozygous missense mutation in the TRAF3 gene (R338W; 601896.0002). The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing. Familial segregation studies were not performed. In gnomAD, the frequency of the variant allele was 2.78 x 10(-5). Western blot analysis of patients cells showed decreased TRAF3 expression in response to stimulation with poly I:C and LPS. Further studies in mouse RAW 264.7 cells transfected with both mutant and wildtype TRAF3 resulted in attenuated TNFA (191160) production in response to LPS and M. abscessus. The findings were consistent with a dominant-negative effect. The patient had Mycobacterium abscessus and later developed superimposed Pseudomonas aeruginosa and Aspergillus fumigatus pneumonia.

Immunodeficiency-132B

In 9 affected individuals from 5 unrelated families with immunodeficiency-132B (IMD132B; 621096), Rae et al. (2022) identified heterozygous frameshift or nonsense mutations in the TRAF3 gene (601896.0003-601896.0006). The mutations, which were found by various methods, were confirmed by Sanger sequencing and segregated with the disorder in all families except family E, which had only 1 affected individual; DNA from other family E members was not available. The mutations occurred de novo in families A and D, and was transmitted in an autosomal dominant pattern in families B and C. The mutations occurred throughout the gene. Two (Q114X and R163X) were located in zinc finger domains. Patient peripheral blood mononuclear cells showed decreased TRAF3 mRNA and protein levels, consistent with haploinsufficiency. No truncated TRAF3 protein products were detected in any of the patients. The authors hypothesized that the 50% reduction of TRAF3 may be due to ubiquitin-mediated proteasomal degradation of TRAF3 from the wildtype allele due to a reduced TRAF3:TRAF2-cIAP1/2 ratio. Detailed studies of patient B cells showed hyperactivity of the NFKB pathway (which may contribute to autoimmunity), elevated gene expression signatures associated with enhanced BCR signaling, and upregulation of genes involved in inflammatory responses (JAK/STAT3, IL6). Mutant B cells had evidence of increased mitochondrial respiration. In addition, TRAF3 haploinsufficiency caused complex changes in patient T-cell subsets such as CD4+ T-cell lymphopenia, reduced naive T cells, increased T(reg) and circulating T follicular helper cells, and mild impairment of T-cell receptor signaling strength. The overall findings were consistent with immune dysregulation resulting at least in part from altered B and T cell numbers and function.

In 3 patients from 2 unrelated families with IMD132B, Urban et al. (2024) identified 2 different heterozygous nonsense mutations in the TRAF3 gene. An affected woman (P1) inherited an R163X mutation (601896.0006) from her affected mother (P2), and an unrelated Argentinian man (P3) carried a de novo heterozygous nonsense mutation (Q407X; 601896.0007). Analysis of cells from the patients with the R163X mutation showed that the mutant TRAF3 mRNA was partially degraded. Western blot analysis from P1 showed only a single band corresponding to wildtype TRAF3. Analysis of cells from P3 indicated that the mutant mRNA escaped nonsense-mediated mRNA decay, and Western blot showed an abnormal band that could correspond to an expressed truncated TRAF3 protein. Functional studies of the variants were not performed. All 3 patients had been previously diagnosed with common variable immunodeficiency (CVID). The patients were part of a retrospective study of 800 patients with inborn errors of immunity who underwent genetic analysis through next-generation sequencing or exome sequencing.

Associations Pending Confirmation

Braggio et al. (2009) identified biallelic inactivation of TRAF3 in 3 (5.3%) of 57 Waldenstrom macroglobulinemia (WM; see 153600) samples. TRAF3 inactivation was associated with transcriptional activation of NF-kappa-B (NFKB1; 164011). In addition, 1 of 24 patients with a 6q deletion had an inactivating somatic mutation in TNFAIP3 (191163), another negative regulator of NF-kappa-B. Monoallelic deletions of chromosome 6q23, including the TNFAIP3 gene, were identified in 38% of patients, suggesting that haploinsufficiency can predispose to the development of WM. The results indicated that mutational activation of the NF-kappa-B pathway plays a role in the pathogenesis of WM.

Mikula et al. (2001) reported that mice lacking Craf1 died at midgestation with placenta and liver anomalies. The livers were hypocellular, but hepatoblast proliferation was not impaired. Fibroblast and hemopoietic cell proliferation was poor due to increased apoptosis with greater sensitivity to apoptotic stimuli, such as Fasl (TNFSF6; 134638)/Fas activation. Mikula et al. (2001) concluded that the essential function of CRAF1 is to counteract apoptosis using effectors distinct from the MEK/ERK (see 601795) cascade.

By generating mice deficient in Traf3 specifically in regulatory T (Treg) cells, Chang et al. (2014) showed that Traf3 was dispensable for homeostasis of Treg cells but was critical for regulation of follicular Treg (TFR) cell generation and germinal center reactions. Mice lacking Traf3 in Treg cells had severe inhibition of antigen-stimulated activation of TFR cells, coupled with deregulated activation of T follicular helper (TFH) cells and heightened germinal center reactions, with elevated production of high-affinity antibodies of the IgG subtypes. Chang et al. (2014) concluded that TRAF3 is a signaling factor that mediates the effector functions of Treg cells, particularly in the control of humoral immune responses, and that TRAF3 is involved in induction of ICOS (604558) as a result of impaired ERK activation.

Li et al. (2019) found that mice with Traf3 conditional deletion in mesenchymal progenitor cells (MPCs) appeared normal and had normal trabecular bone volume. However, mutant mice developed early-onset osteoporosis due to age-related reduction of bone formation and age-related increase in bone resorption. In young mice, Traf3 prevented beta-catenin (CTNNB1; 116806) degradation in MPCs and maintained osteoblast formation. However, Traf3 protein levels decreased during aging when Tgfb1 (190180) was released from resorbing bone. Tgfb1 induced degradation of Traf3 in MPCs by inducing Traf3 ubiquitination and lysosomal degradation, thereby inhibiting osteoblast formation through Gsk3b (605004)-mediated degradation of beta-catenin. Thus, Traf3 positively regulated MPC differentiation into osteoblasts. Traf3 limited Rankl (TNFSF11; 602642) expression by MPCs, and consequently, Traf3 deletion in MPCs activated Nfkb Rela (164014) and Relb (604758) to promote Rankl expression and enhance bone destruction.