| Background |
TRAFs (TNF receptor-associated factors) are a family of multifunctional adaptor proteins that bind to surface receptors and recruit additional proteins to form multiprotein signaling complexes capable of promoting cellular responses Members of the TRAF family share a common carboxy-terminal "TRAF domain", which mediates interactions with associated proteins; many also contain amino-terminal Zinc/RING finger motifs. The first TRAFs identified, TRAF1 and TRAF2, were found by virtue of their interactions with the cytoplasmic domain of TNF-receptor 2 (TNFRII) The six known TRAFs (TRAF1-6) act as adaptor proteins for a wide range of cell surface receptors and participate in the regulation of cell survival, proliferation, differentiation, and stress responses.TRAF6 plays a critical role in innate and adaptive immunity, bone metabolism, and development of certain tissues including the nervous system TRAF6 deficiency results in osteopetrosis and defective IL-1, CD40, and LPS signaling as well as defects in neuronal development Unlike other TRAF family members that mediate signaling through TNF, TRAF6 has unique binding activities that result in signaling responses from the interleukin-1 receptor (IL-1R) toll-like receptor, CD40, RANK, and p75 neurotrophin receptor. TRAF6 associates directly with CD40 and RANK, and indirectly with IL-1R/TLR through IRAK. This leads to activation of NF-κB and MAP kinase signaling pathways through downstream association with the TAB/TAK-1 complex. TRAF6 also activates Src family nonreceptor tyrosine kinases leading to Akt activation.
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