🧬 Aging Wiki

traf6

Properties1
aliasesTNF receptor-associated factor 6, RING finger protein 85, RNF85, interleukin-1 signal transducer

14 min read

TRAF6

TRAF6 (TNF receptor-associated factor 6; UniProt Q9Y4K3; gene TRAF6) is an E3 ubiquitin ligase and adaptor protein that serves as the convergence hub for IL-1R/TLR, RANK, CD40, and NGF receptor signaling. Its defining biochemical function — assembly of K63-linked polyubiquitin chains on IRAK1 and itself — converts receptor-proximal phosphorylation events into a non-degradative ubiquitin scaffold that recruits and activates the TAK1 kinase complex, triggering NF-κB and MAPK cascades. In the aging context, TRAF6 is the key enzymatic node through which chronic low-grade IL-1 signaling in aged tissue amplifies inflammaging, and through which RANKL-driven TRAF6 activity mediates age-related bone resorption.

TRAF6 is the canonical example of a non-kinase adaptor in the IL-1/TLR cascade and the prototypical RING-type E3 ligase for K63-linked chain synthesis. See il-1-signaling for the full pathway context (R27, verified).

Identity

  • UniProt: Q9Y4K3 (TRAF6_HUMAN)
  • NCBI Gene: 7189
  • HGNC: 12036 (symbol: TRAF6)
  • Ensembl: ENSG00000175104
  • Length: 522 amino acids (canonical isoform)
  • Gene synonym: RNF85 (RING finger protein 85) — reflects the E3 ligase annotation
  • Mouse ortholog: Traf6 (well-conserved; Traf6-/- mouse phenotype is a primary evidence source)

Domain architecture

TRAF6 has a modular architecture organized from N- to C-terminus into four functional units 1:

RegionPositions (aa)Function
RING-type zinc finger70–109E3 catalytic domain; recruits UBC13 (UBE2N); required for K63-chain assembly
TRAF-type zinc finger 1150–202Structural; contributes to oligomerization scaffold
TRAF-type zinc finger 2203–259Structural; zinc-coordinating
Coiled-coil288–348Self-association; TRAF6 trimerization; receptor-complex nucleation
MATH domain (TRAF-C)350–499Receptor recognition; binds PxExxAr/Ac motifs on IRAK1, IRAK2, RANK cytoplasmic tail, CD40, EDAR

The RING domain (aa 70–109) is the catalytic core. It physically contacts the E2-conjugating enzyme UBC13 (UBE2N) via a conserved surface; this interaction is required for K63-linked chain elongation 2. TRAF6 can form RING homodimers and heterodimers with TRAF2/TRAF3/TRAF5, potentially broadening its E2 engagement repertoire 3.

The MATH domain is the receptor-binding interface. It recognizes a degenerate peptide motif (PxExxAr/Ac) present in cytoplasmic tails of RANK, CD40, and EDAR, as well as in the phosphorylated C-terminal region of IRAK1 following IRAK4-mediated phosphorylation.

Post-translational modifications: Auto-ubiquitination at Lys-124 and Lys-319 (K63-linked, auto-catalytic, activated by receptor engagement); sumoylation at Lys-124, Lys-142, Lys-453 (SUMO1; modulates nuclear function) 1.

Mechanism: K63-linked ubiquitin chain assembly

TRAF6’s central enzymatic function — confirmed by the landmark Deng et al. 2000 Cell study — is the synthesis of K63-linked polyubiquitin chains via a heterodimeric E2 complex 4:

IRAK4 activation → IRAK1/IRAK2 phosphorylation
  → phospho-IRAK1 dissociates from receptor complex
  → IRAK1 PxExxAr motif recruits TRAF6 MATH domain
  → TRAF6 oligomerizes (trimer of dimers) around the IRAK1·receptor scaffold
  → TRAF6 RING domain engages UBC13/UEV1A (UBE2N/UBE2V1) E2 heterodimer
  → K63-linked polyubiquitin chains assembled on TRAF6 (auto) and IRAK1 (trans)
  → unanchored and substrate-anchored K63-chains recruit TAB2/TAB3
      (TAK1-associated proteins with NZF ubiquitin-binding domains)
  → TAB2/TAB3 → TAK1 (MAP3K7) activation
      ├─ IKK arm: TAK1 → IKKβ → IκBα phosphorylation (Ser32/Ser36)
      │             → IκBα proteasomal degradation → NF-κB nuclear translocation
      └─ MAPK arm: TAK1 → MKK3/6 → p38; MKK4/7 → JNK → AP-1

Critical mechanistic distinction: K63-linked chains are non-degradative — they function as protein-scaffolding signals rather than proteasome-targeting signals (which require K48-linked chains). This allows TRAF6 to activate kinase cascades without destroying its substrate. The E2 partner determines chain linkage specificity: UBC13/UEV1A is the K63-specific E2; without this partner, TRAF6 cannot assemble K63 chains and IL-1 NF-κB activation is abolished 4.

Negative regulation: A20 (TNFAIP3) removes K63-ubiquitin chains from TRAF6, acting as the primary ubiquitin-editing brake on this axis (see il-1-signaling § Negative regulation). A20 expression is itself NF-κB-induced, forming a negative feedback loop. needs-replication — age-associated decline in A20 expression efficiency in macrophages has been proposed as a mechanism for exaggerated TRAF6 signaling in aged tissue, but direct quantitative data are limited 5.

Pathway membership and receptor contexts

TRAF6 operates in at least four distinct receptor systems, giving it an unusually broad functional scope:

Receptor/pathwayLigand/signalDownstream outputAging relevance
IL-1R1 / TLRIL-1α, IL-1β / PAMPs, DAMPsNF-κB, JNK, p38SASP amplification; inflammaging signal relay
RANKRANKL (TNFSF11)NF-κB, JNK, MAPK → NFATc1Osteoclast differentiation; age-related bone resorption
CD40CD40L (TNFSF5)NF-κB → B-cell activation, immunoglobulin switchingImmune aging; germinal center dysfunction
EDAREDA-A1NF-κB → ectodermal organ developmentDevelopmental; aging relevance minimal
NGF receptor (p75NTR)NGFNF-κB, apoptosisNeural survival; aging relevance under investigation

For IL-1/TLR signaling, see il-1-signaling (verified, R27) for the full cascade diagram. For RANK and osteoclast signaling, the TRAF6 link is described below.

RANK pathway and bone aging

In the RANK → NF-κB axis, TRAF6 plays the identical E3 ligase role it plays downstream of IL-1R: it is recruited to the phosphorylated cytoplasmic tail of RANK via the MATH domain (RANK contains a PxExxAr motif) and assembles K63-linked chains that activate TAK1 → NF-κB → NFATc1 transcription, driving osteoclast differentiation and activation.

Genetic validation (mouse): Two independent Traf6-/- mouse studies established the bone phenotype:

  • Lomaga et al. 1999 (Genes & Development, doi:10.1101/gad.13.8.1015): Traf6-/- mice developed severe osteopetrosis with radio-opaque long bones, absent tooth eruption, and 20–30% deficits in body mass and length. Crucially, osteoclast numbers (TRAP+ cells/mm²) were comparable to wild-type — the osteoclasts were present but non-functional, lacking ruffled borders and attachment zones and withdrawn from the bone surface. Perinatal survival was reduced (only 11% of pups at 2 weeks were homozygous knockouts vs. expected Mendelian 25%); surviving mice died prematurely within weeks. IL-1-induced NF-κB activation was impaired and JNK/SAPK activation was absent in TRAF6-/- cells; CD40-stimulated B-cell proliferation failed; LPS-stimulated B-cell proliferation was dramatically inhibited and macrophage iNOS induction was impaired. T-cell proliferative responses to anti-CD3ε and concanavalin A were not significantly different from wild type 6.
  • Naito et al. 1999 (Genes to Cells, doi:10.1046/j.1365-2443.1999.00265.x): Independent Traf6-/- line confirmed osteopetrosis; showed osteoclast precursors cannot differentiate to functional osteoclasts in response to ODF (later identified as RANKL) 7.

Aging bone connection: In aged humans, RANKL:OPG ratio increases in bone marrow, driving excess osteoclast activity → net bone resorption → osteoporosis. TRAF6 is the intracellular mediator of this RANK-to-NF-κB signal. The approved anti-RANKL antibody denosumab interrupts this axis upstream of TRAF6 (at the RANKL → RANK receptor level) and is a first-line treatment for postmenopausal osteoporosis. No TRAF6-directed drug has reached clinical development for osteoporosis.

DimensionStatus
Pathway conserved in humans?yes — RANK/TRAF6/NF-κB axis is conserved; human loss-of-function TRAF6 mutations cause ectodermal dysplasia
Phenotype (bone resorption) conserved in humans?yes — RANKL blockade (denosumab) reduces fracture risk in RCTs (postmenopausal women, n>7000)
Replicated in humans?partial — TRAF6 specifically not targeted; RANK/RANKL denosumab data validate the upstream axis

needs-human-replication — no clinical trial has directly targeted TRAF6 in the bone-aging context.

Aging connection

TRAF6 in inflammaging

In aged tissue, constitutively elevated DAMPs (mtDNA, oxidized lipids, AGEs) and SASP-derived IL-1α/IL-1β provide chronic low-grade ligand input to IL-1R1 and TLRs. TRAF6 is the convergence point at which these receptor signals are amplified into NF-κB-driven transcription of pro-inflammatory cytokines (IL-6, IL-8, TNF-α, further IL-1β) 8. This creates a self-sustaining loop: SASP cytokines → IL-1R1 → TRAF6 → NF-κB → more SASP cytokines.

The TRAF6-ubiquitin axis also integrates with the mTOR pathway: TRAF6-mediated K63 ubiquitination of AKT has been reported to regulate AKT membrane recruitment and activation (UniProt Q9Y4K3; interactors include AKT1/2/3) 1, creating a crosstalk between the inflammatory and nutrient-sensing axes in aged tissue. needs-replication — the functional significance of TRAF6–AKT ubiquitination in the aging context has not been directly tested.

A20 (TNFAIP3), the principal deubiquitinase that removes K63-chains from TRAF6, accumulates excessively in aged mouse lung macrophages and impairs NFκB and MAPK activation in response to bacterial challenge 5. This is somewhat paradoxical: excess A20 activity blunts pathogen-induced TRAF6 signaling, while insufficient A20 would enhance inflammaging TRAF6 signaling. The net outcome depends on the stimulus context (pathogen vs. sterile DAMP). This context-dependence is an unresolved question in aging immunology. contradictory-evidence

Pharmacology

No FDA-approved drug directly targets TRAF6. The druggability tier is 3 (aging context: high-quality research probes exist; no clinical-stage drug; upstream or downstream targets are clinically addressed by approved agents).

AgentTargetStageNotes
DenosumabRANKL (upstream of TRAF6)FDA-approvedOsteoporosis, bone metastases; validates the RANK→TRAF6 axis in humans but does not inhibit TRAF6 itself
C25-140TRAF6–UBC13 protein interactionPreclinicalFirst-in-class small-molecule disruptor of TRAF6–Ubc13 (UBE2N) interaction; reduced NF-κB activation and ameliorated psoriasis (IMQ model, ~1.5 mg/kg topical, n=8/group) and RA (CIA model, 6/10/14 mg/kg IP × 14 days) in mouse models 9; not in human trials
Peptidomimetic inhibitorsTRAF6 MATH domain (receptor-binding surface)Research onlyBlock TRAF6–RANK and TRAF6–CD40 interactions; no published in vivo aging data

C25-140 mechanism: Binds directly to TRAF6 (confirmed by NMR) and disrupts the physical protein–protein contact between the TRAF6 RING domain and the UBC13 (UBE2N) E2-conjugating enzyme, preventing K63-chain assembly without directly blocking TRAF6 adaptor function. C25-140 does not inhibit the Ubc13–Uev1a interaction itself. Selectivity note: C25-140 also inhibits cIAP1, another RING-type E3 ligase that generates K63-linked chains; it does not inhibit K48-chain E3 ligases (MDM2, TRIM63, MURF), SUMO ligase RNF4, or HECT E3 ligases (ITCH, E6AP), and does not inhibit E1–E2 reactions for any of 9 tested E2 enzymes. The compound is therefore selective for K63-chain-generating RING E3s rather than being pan-TRAF6-specific. Whether this selectivity profile reduces inflammaging in vivo — and whether it translates to humans — is untested 9. needs-human-replication

Druggability-tier rationale (tier 3): TRAF6 has no approved aging-relevant drug and no active clinical trials for an aging indication. However, the TRAF6–UBC13 interface has been validated as a high-quality preclinical target with C25-140 (JBC 2018, PubMed 29950522, 73 citations), meeting the Open Targets criterion for “high-quality preclinical probe.” Upstream agents (denosumab for RANK) and downstream agents (NF-κB pathway) have clinical validation. A TRAF6-specific aging-context drug remains a near-future target, not a current clinical asset.

Key interactors

Per UniProt Q9Y4K3 (experimental evidence channel):

  • UBE2N / UBC13 — E2 K63-specific; required for K63-chain assembly (RING–E2 interface)
  • UBE2V1 / UEV1A — UBC13 co-factor; non-catalytic; required for K63-chain specificity
  • IRAK1 — substrate; K63-ubiquitinated by TRAF6 after phospho-activation by IRAK4
  • IRAK4 — upstream kinase that phosphorylates IRAK1 → TRAF6 recruitment (see irak4)
  • MAP3K7 / TAK1 — downstream effector kinase; recruited via TAB2/TAB3 K63-ubiquitin recognition (see tak1)
  • IKBKG / NEMO — IKK complex scaffolding subunit; K63-ubiquitin also recruits NEMO
  • SQSTM1 / p62 — ubiquitin-binding adaptor; links TRAF6-generated K63 chains to autophagy cargo recognition (see p62)
  • MAVS — mitochondrial antiviral signaling protein; TRAF6 also mediates MAVS-induced NF-κB (antiviral RIG-I/MDA5 pathway)

Open questions and gaps

  • Selectivity of TRAF6 inhibition in aging vs. immunosuppression: TRAF6 is required for normal IL-1, TLR, CD40, and RANK signaling. A global TRAF6 inhibitor would suppress all these — raising the same infection-risk concern seen with canakinumab in CANTOS (fatal infection rate ~1.7× placebo). Whether a partial or context-specific TRAF6 inhibitor strategy is viable remains unresolved. no-mechanism
  • TRAF6 redundancy: TRAF2, TRAF3, and TRAF5 share MATH-domain receptor-binding surfaces and can form heterodimers with TRAF6 3. The degree to which these family members compensate for TRAF6 loss in specific aging tissues is not well characterized. needs-replication
  • K63-ubiquitin chain reading mechanisms in aged cells: Whether the efficiency of TAB2/TAB3 (K63-chain readers) or K63-chain removal (A20) changes with cell aging is incompletely characterized. needs-replication
  • Direct TRAF6 inhibition vs. upstream/downstream targeting: Given that denosumab (upstream) and NF-κB inhibitors (downstream) both have clinical precedent, the therapeutic niche for TRAF6-specific inhibition in aging is not defined. no-mechanism
  • GTEx-aging correlation: TRAF6 mRNA expression correlation with chronological age across GTEx tissues has not been queried. Field populated as null. needs-canonical-id
  • Mendelian randomization: No published MR study using TRAF6 genetic instruments for aging outcomes identified. Filed as not-tested.

Cross-references

  • il-1-signaling — verified pathway page (R27); TRAF6 is described at position 4 in the adaptor chain
  • irak4 — immediate upstream activator (R28 sibling, being seeded in parallel)
  • myd88 — upstream adaptor (R28 sibling)
  • tak1 — immediate downstream effector recruited by K63-ubiquitin scaffold (R28 sibling)
  • nf-kb — primary downstream transcription factor
  • chronic-inflammation — hallmark MOC; TRAF6 is a core enzymatic driver
  • p62 — ubiquitin-binding adaptor that reads TRAF6-generated K63-chains in autophagy context
  • cellular-senescence — SASP amplification via TRAF6/NF-κB loop
  • sasp — TRAF6-mediated NF-κB drives SASP gene transcription
  • ubiquitin-proteasome-system — pathway stub; TRAF6 belongs to the K63-ubiquitin axis (non-degradative branch)
  • rank-signaling — bone-resorption pathway; TRAF6 is the canonical RANK effector (implicit stub)

Implicit stubs created by this page:

Limitations and gaps

  • Open Targets druggability-tier: Verified 2026-05-07 via GraphQL API (ENSG00000175104). No approved SM/AB/PR drug, no clinical-stage compound, no high-quality SM pocket registered. PROTAC signals present (UniProt ubiquitination = true; Database ubiquitination = true; half-life data = true). Tier 3 confirmed: C25-140 (Brenke 2018) is a published research probe meeting the tier-3 criterion, though not yet catalogued by Open Targets as a high-quality ligand.
  • GenAge ID: Not found during seeding; TRAF6 may not have a GenAge entry. needs-canonical-id
  • GTEx aging correlation: Not queried; null in frontmatter. Populate per sops/finding-tissue-expression.md. needs-canonical-id
  • Ubiquitin-proteasome-system pathway page: Listed as “verified, exists” in task brief but not found in pathways/ directory. Wikilink preserved as implicit stub; verify on next lint pass.

Footnotes

Footnotes

  1. UniProt Q9Y4K3 (TRAF6_HUMAN), accessed 2026-05-07 · manually curated Swiss-Prot entry; domain positions (RING 70-109, MATH 350-499), PTMs (K124/K319 auto-ubiquitination; K124/K142/K453 sumoylation), interactors (UBE2N, UBE2V1, IRAK1, IRAK4, MAP3K7, SQSTM1) from experimental evidence channel ↩ ↩2 ↩3

  2. doi:10.1016/s0014-5793(04)00505-8 · FEBS Lett 2004 · in-vitro · TRAF6 RING finger domain mediates physical interaction with Ubc13; 3 direct citations; archive: not yet locally available (closed access) ↩

  3. doi:10.1016/j.jmb.2021.166844 · Das A et al. · J Mol Biol 2021 · in-vitro (structural, cryo-EM/X-ray) · structure of TRAF5-TRAF6 RING heterodimer; shows TRAF6 heterodimerizes with TRAF2/TRAF3/TRAF5; coiled-coil linker cooperates with TRAF6 to promote chain assembly; PMID 33539883; archive: not checked ↩ ↩2

  4. doi:10.1016/s0092-8674(00)00126-4 · Deng L et al. · Cell 2000 · in-vitro (biochemistry, cell-free IKK activation assay, co-immunoprecipitation, MALDI-TOF peptide fingerprinting) · foundational study establishing that TRAF6 requires a dimeric E2 complex (Ubc13/Uev1A = TRIKA1) to assemble K63-linked polyubiquitin chains for IKK complex activation; Ubc13 Cys-87 active site mutation abolishes IKK activation; Uev1A depletion abolishes TRAF6-mediated IKK activation; K63-chain assembly confirmed by Ub-mutant rescue experiments; 1855 citations; local PDF verified 2026-05-07 ↩ ↩2

  5. doi:10.1016/j.exger.2014.01.007 · Hinojosa CA et al. · Exp Gerontol 2014 · in-vivo (C57BL/6 mice; young 4 mo, mature 12 mo, aged 21 mo; alveolar macrophage) · A20 (TNFAIP3) protein significantly elevated in lungs and alveolar macrophages of aged vs. young mice (P<0.05); elevated A20 blunts NF-κB/MAPK response to S. pneumoniae serotype 4 TIGR4 challenge; dietary fish oil (4%, 2 months) reduced lung A20 and produced ~100-fold reduction in bacterial lung burden at 24 h post-challenge; PMC3989429; local download failed (green OA); verified via PMC full text 2026-05-07 · needs-human-replication ↩ ↩2

  6. doi:10.1101/gad.13.8.1015 · Lomaga MA et al. · Genes & Development 1999 · in-vivo (mouse, Traf6-/- germline KO; 129J ES cells → C57BL/6 blastocysts) · severe osteopetrosis with radio-opaque long bones and absent tooth eruption; osteoclasts present in normal numbers (TRAP+ cells/mm² comparable to WT) but non-functional (lack ruffled borders, withdrawn from bone surface); 11% pup survival at 2 wk (vs. expected 25% Mendelian); IL-1-induced NF-κB impaired, JNK/SAPK absent; CD40-stimulated B-cell proliferation absent; LPS B-cell proliferation inhibited; macrophage iNOS impaired; T-cell proliferative responses not significantly different from WT; 1266 citations; OA (diamond); PMC316636; local PDF verified 2026-05-07 ↩

  7. doi:10.1046/j.1365-2443.1999.00265.x · Naito A et al. · Genes to Cells 1999 · in-vivo (mouse, independent Traf6-/- line) · confirms osteopetrosis; osteoclast precursors cannot differentiate to functional osteoclasts in response to RANKL (ODF); B-cell and lymph node organogenesis defects; 634 citations; archive: pending download ↩

  8. Cross-reference to il-1-signaling (verified 2026-05-07); TRAF6 signal transduction arrows confirmed against Wesche 1997 (doi:10.1016/s1074-7613(00)80402-1) and Dinarello 2011 (doi:10.1182/blood-2010-07-273417) as cited there ↩

  9. doi:10.1074/jbc.RA118.002649 · Brenke JK et al. · J Biol Chem 2018 · in-vitro + in-vivo (mouse IMQ-psoriasis n=8/group; CIA-RA model 6/10/14 mg/kg IP ×14 days) · C25-140 binds TRAF6 directly (NMR confirmed) and disrupts TRAF6–Ubc13 PPI, reducing TRAF6-mediated K63-chain assembly; also inhibits cIAP1 (another K63 RING E3) but not K48-chain E3s, HECT E3s, or E1–E2 reactions; reduced NF-κB activation in MEF, Jurkat, and primary human PBMCs; ameliorated IMQ-psoriasis and CIA-RA in mouse models; 73 citations; PMC6109917; local PDF verified 2026-05-07 ↩ ↩2

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