Toll-like receptor 3-mediated activation of NF-kappaB and IRF3 diverges at Toll-IL-1 receptor domain-containing adapter inducing IFN-beta.
We have previously shown that double-stranded RNA-triggered, Toll-like receptor 3 (TLR3)-mediated signaling is independent of MyD88, IRAK4, and IRAK. Instead, TRAF6, TAK1, and TAB2 are recruited to TLR3 on poly(I.C) stimulation. TRAF6-TAK1-TAB2 are then translocated to the cytosol where TAK1 is phosphorylated and activated, leading to the activation of IkappaB kinase and NFkappaB. The present study addressed two important questions: (i) How are TRAF6, TAK1, and TAB2 recruited to TLR3? (ii) Are TRAF6, TAK1, and TAB2 also required for TLR3-mediated IRF3 activation? Recently, a novel Toll-IL-1 receptor (TIR)-containing adapter, TIR domain-containing adapter inducing IFN-beta (TRIF), was shown to play a critical role in TLR3-mediated activation of NF-kappaB and IRF3. We found that TLR3 recruits TRAF6 via adapter TRIF through a TRAF6-binding sequence in TRIF (PEEMSW, amino acids 250-255). Mutation of this TRAF6-binding sequence abolished the interaction of TRIF with TRAF6, but not with TLR3. Interestingly, mutation of the TRAF6-binding site of TRIF only abolished its ability to activate NF-kappaB but not IRF3, suggesting that TLR3-mediated activation of NF-kappaB and IRF3 might bifurcate at TRIF. In support of this finding, we showed that DN-TRAF6 and DN-TAK1 blocked poly(I.C)-induced NF-kappaB but not IRF3 activation. Furthermore, whereas poly(I.C)-induced NF-kappaB activation is completely abolished inTRAF6-/- MEFs, the signal-induced activation of IRF3 is TRAF6 independent. In conclusion, TRIF recruits TRAF6-TAK1-TAB2 to TLR3 through its TRAF6-binding site, which is required for NF-kappaB but not IRF3 activation. Therefore, double-stranded RNA-induced TLR3/TRIF-mediated NF-kappaB and IRF3 activation diverge at TRIF.
University of Toronto, Toronto, ON, Canada M5G 2M9.
Zhengfan
Z
Jiang
Tak W
TW
Mak
Ganes
G
Sen
Xiaoxia
X
Li
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D050838:Interferon Regulatory Factor-3; D053592:Interleukin-1 Receptor-Associated Kinases; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008954:Models, Biological; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism; D015398:Signal Transduction; D048029:TNF Receptor-Associated Factor 6; D051196:Toll-Like Receptor 3; D051193:Toll-Like Receptors; D014157:Transcription Factors / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000943:Antigens, Differentiation; D004268:DNA-Binding Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; C507779:MYD88 protein, human; D008562:Membrane Glycoproteins; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D011506:Proteins; D012330:RNA, Double-Stranded; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; C470409:TICAM1 protein, human; C495344:TLR3 protein, human; D048029:TNF Receptor-Associated Factor 6; D051196:Toll-Like Receptor 3; D051193:Toll-Like Receptors; D014157:Transcription Factors; D011494:Protein Kinases; C507773:IRAK4 protein, human; D053592:Interleukin-1 Receptor-Associated Kinases