The E3 ubiquitin ligase TRIM21 forms a complex with p62 and TRAF6 and promotes degradation of TRAF6 (P1176)

Abstract

Abstract NF-κB signaling pathway plays a pivotal role in inflammatory response, and its excessive activation causes systemic inflammatory disorder, such as systemic lupus erythematosus (SLE). TRIM21, one of the tripartite motif (TRIM) family members, is an E3 ubiquitin ligase that functions in both innate and acquired immunity. It is also an autoantigen known as Ro52/SS-A, which is observed in patients with SLE. Recent studies, including Trim21 gene disruption studies, suggest that TRIM21 is a negative regulator for NF-κB-dependent proinflammatory cytokine production. However, the molecular mechanism still remains to be clarified. Here we report that TRIM21 interacted with tumor necrosis factor-associated factor 6 (TRAF6), an essential adaptor protein for Toll-like receptor/interleukin 1 receptor (TLR/IL-1R)-mediated activation of NF-κB signaling pathway. The TRIM21-TRAF6 interaction was indirect and mediated by a scaffold protein, p62/sequestosome 1. TRIM21-overexpressed fibroblast cell line showed decreased expression of TRAF6 as compared to the control cells. TRIM21 promoted not only K63-linked ubiquitylation but also K48-linked ubiquitylation of TRAF6 in the presence of p62. Furthermore proteasome inhibitor MG132 increased the ubiquitylated TRAF6 proteins. These data suggest that the function of TRIM21 as a negative regulator for NF-κB signaling is attributed to the proteasome-mediated degradation of TRAF6.