TRAF6 distinctively mediates MyD88‐ and IRAK‐1‐induced activation of NF‐κB

MyD88 and IL‐1R‐associated kinase 1 (IRAK‐1) play crucial roles as adaptor molecules in signal transduction of the TLR/IL‐1R superfamily, and it is known that expression of these proteins leads to the activation of NF‐κB in a TNFR‐associated factor 6 (TRAF6)‐dependent manner. We found in this study, however, that a dominant‐negative mutant of TRAF6, lacking the N‐terminal RING and zinc‐finger domain, did not inhibit IRAK‐1‐induced activation of NF‐κB in human embryonic kidney 293 cells, although the TRAF6 mutant strongly suppressed the MyD88‐induced activation. The dominant‐negative mutant of TRAF6 did not affect the IRAK‐1‐induced activation, regardless of the expression level of IRAK‐1. In contrast, small interfering RNA silencing of TRAF6 expression inhibited MyD88‐induced and IRAK‐1‐induced activation, and supplementation with the TRAF6 dominant‐negative mutant did not restore the IRAK‐1‐induced activation. Expression of IRAK‐1, but not MyD88, induced the oligomerization of TRAF6, and IRAK‐1 and the TRAF6 dominant‐negative mutant were associated with TRAF6. These results indicate that TRAF6 is involved but with different mechanisms in MyD88‐induced and IRAK‐induced activation of NF‐κB and suggest that TRAF6 uses a distinctive mechanism to activate NF‐κB depending on signals.