TRIF mediates Toll-like receptor 5-induced signaling in intestinal epithelial cells.
Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. Here, we found that TRIF is involved in mediating TLR5-induced nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), specifically JNK1/2 and ERK1/2, activation in intestinal epithelial cells. TLR5 activation by flagellin permits the physical interaction between TLR5 and TRIF in human colonic epithelial cells (NCM460), whereas TLR5 does not interact with TRAM upon flagellin stimulation. Both primary intestinal epithelial cells from TRIF-KO mice and TRIF-silenced NCM460 cells significantly reduced flagellin-induced NFκB (p105 and p65), JNK1/2, and ERK1/2 activation compared with control cells. However, p38 activation by flagellin was preserved in these TRIF-deficient cells. TRIF-KO intestinal epithelial cells exhibited substantially reduced inflammatory cytokine (keratinocyte-derived cytokine, macrophage inflammatory protein 3α, and IL-6) expression upon flagellin, whereas control cells from TRIF-WT mice showed robust cytokine expression by flagellin. Compare with TRIF-WT mice, TRIF-KO mice were resistant to in vivo intestinal inflammatory responses: flagellin-mediated exacerbation of colonic inflammation and dextran sulfate sodium-induced experimental colitis. We conclude that in addition to MyD88, TRIF mediates TLR5-dependent responses and, thereby regulates inflammatory responses elicited by flagellin/TLR5 engagement. Our findings suggest an important role of TRIF in regulating host-microbial communication via TLR5 in the gut epithelium.
Choi
Yoon Jeong
YJ
Division of Digestive Diseases, David Geffen School of Medicine, UCLA, Los Angeles, California 90095, USA.
Im
Eunok
E
Chung
Hyo Kyun
HK
Pothoulakis
Charalabos
C
Rhee
Sang Hoon
SH
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D048670:MAP Kinase Kinase 4; D020928:Mitogen-Activated Protein Kinases; D016328:NF-kappa B; D051198:Toll-Like Receptor 5; C476286:Ticam1 protein, mouse; C470409:TICAM1 protein, human