Lipopolysaccharide stimulates the MyD88-independent pathway and results in activation of IFN-regulatory factor 3 and the expression of a subset of lipopolysaccharide-inducible genes.
Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor (TLR) 4, a member of the TLR family that participates in pathogen recognition. TLRs recruit a cytoplasmic protein, MyD88, upon pathogen recognition, mediating its function for immune responses. Two major pathways for LPS have been suggested in recent studies, which are referred to as MyD88-dependent and -independent pathways. We report in this study the characterization of the MyD88-independent pathway via TLR4. MyD88-deficient cells failed to produce inflammatory cytokines in response to LPS, whereas they responded to LPS by activating IFN-regulatory factor 3 as well as inducing the genes containing IFN-stimulated regulatory elements such as IP-10. In contrast, a lipopeptide that activates TLR2 had no ability to activate IFN-regulatory factor 3. The MyD88-independent pathway was also activated in cells lacking both MyD88 and TNFR-associated factor 6. Thus, TLR4 signaling is composed of at least two distinct pathways, a MyD88-dependent pathway that is critical to the induction of inflammatory cytokines and a MyD88/TNFR-associated factor 6-independent pathway that regulates induction of IP-10.
Kawai
T
T
Department of Host Defense, Research Institute for Microbial Diseases, Japan Science and Technology Corporation, Osaka University, Osaka, Japan.
Takeuchi
O
O
Fujita
T
T
Inoue
J
J
Mühlradt
P F
PF
Sato
S
S
Hoshino
K
K
Akira
S
S
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D054357:Chemokine CXCL10; D019743:Chemokines, CXC / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D029721:Drosophila Proteins; D017353:Gene Deletion; D050838:Interferon Regulatory Factor-3; D007372:Interferons / Q000502:physiology; D008050:Lipid A / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000378:metabolism; D011506:Proteins / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000378:metabolism; D011971:Receptors, Immunologic; D020218:Response Elements; D015398:Signal Transduction; D048029:TNF Receptor-Associated Factor 6; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology; D015533:Transcriptional Activation
D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D054357:Chemokine CXCL10; D019743:Chemokines, CXC; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D050838:Interferon Regulatory Factor-3; C494233:Irf3 protein, mouse; D008050:Lipid A; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D011506:Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D048029:TNF Receptor-Associated Factor 6; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014157:Transcription Factors; D007372:Interferons