UBE2O negatively regulates TRAF6-mediated NF-κB activation by inhibiting TRAF6 polyubiquitination

Tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) is a key regulator of the activation of transcription factor NF-kappa B by the interleuldn-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily. Recruitment of TRAF6 to the receptor-associated IRAK1-IRAK4-MyD88 adaptor protein complex induces lysine 63 (K63) autopolyubiquitination of TRAF6, which leads to further recruitment of downstream regulators, such as TAB2/3 and TAK1, and subsequently triggers NF-kappa B activation. Here, we identified the putative E2 ubiquitin-conjugating (UBC) enzyme UBE2O as a novel negative regulator of TRAF6-dependent NF-kappa B signaling. We found that UBE2O binds to TRAF6 to inhibit its K63-polyubiquitination, and to prevent the activation of NF-kappa B by IL-1 beta and lipopolysaccharides (LPS). We further show that the inhibitory effect of UBE2O is independent of its carboxy-terminal UBC domain. In contrast, we found that UBE2O acts to disrupt the IL-1 beta-induced association of TRAF6 with MyD88. These results provide novel insight into the regulation of signaling by IL-1R/TLR and TRAF6.