title: IRAK4 kinase activity is not required for induction of endotoxin tolerance but contributes to TLR2-mediated tolerance.
abstract: Prior exposure to LPS induces "endotoxin tolerance" that reprograms TLR4 responses to subsequent LPS challenge by altering expression of inflammatory mediators. Endotoxin tolerance is thought to limit the excessive cytokine storm and prevent tissue damage during sepsis but renders the host immunocompromised and susceptible to secondary infections. Tolerance initiated via one TLR can affect cellular responses to challenge via the same TLR ("homotolerance") or through different TLRs ("heterotolerance"). IRAK4, an essential component of the MyD88-dependent pathway, functions as a kinase and an adapter, activating subsets of divergent signaling pathways. In this study, we addressed mechanistically the role of IRAK4 kinase activity in TLR4- and TLR2-induced tolerance using macrophages from WT versus IRAK4(KDKI) mice. Whereas IRAK4 kinase deficiency decreased LPS signaling, it did not prevent endotoxin tolerance, as endotoxin pretreatment of WT and IRAK4(KDKI) macrophages inhibited LPS-induced MAPK phosphorylation, degradation of IκB-α and recruitment of p65 to the TNF-α promoter, expression of proinflammatory cytokines, and increased levels of A20 and IRAK-M. Pretreatment of WT macrophages with Pam3Cys, a TLR2-TLR1 agonist, ablated p-p38 and p-JNK in response to challenge with Pam3Cys and LPS, whereas IRAK4(KDKI) macrophages exhibited attenuated TLR2-elicited homo- and heterotolerance at the level of MAPK activation. Thus, IRAK4 kinase activity is not required for the induction of endotoxin tolerance but contributes significantly to TLR2-elicited homo- and heterotolerance.
authors.affiliation: 1.University of Connecticut Health Center, ARB Bldg., Rm. E6032, 263 Farmington Ave., Farmington, CT 06030, USA. medvedev@uchc.edu
authors.forename: Yanbao
authors.initials: Y
authors.lastname: Xiong
authors.forename: Meghan
authors.initials: M
authors.lastname: Pennini
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Vogel
authors.forename: Andrei E
authors.initials: AE
authors.lastname: Medvedev
mesh_terms: D000818:Animals; D003546:Cysteine Endopeptidases; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D004361:Drug Tolerance; D004731:Endotoxins / Q000276:immunology* / Q000633:toxicity; D004789:Enzyme Activation; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D007153:Immunologic Deficiency Syndromes / Q000235:genetics / Q000276:immunology; D053592:Interleukin-1 Receptor-Associated Kinases / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000633:toxicity*; D008074:Lipoproteins / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000502:physiology; D016328:NF-kappa B / Q000378:metabolism; D000081207:Primary Immunodeficiency Diseases; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000819:agonists / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000502:physiology*; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D016207:Cytokines; D004268:DNA-Binding Proteins; D004731:Endotoxins; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D008074:Lipoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C061108:N-palmitoyl-S-(2,3-bis(palmitoyloxy)propyl)cysteinyl-seryl-lysyl-lysyl-lysyl-lysine; C044101:endotoxin, Escherichia coli; D044767:Ubiquitin-Protein Ligases; D053592:Interleukin-1 Receptor-Associated Kinases; C507772:Irak3 protein, mouse; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D003546:Cysteine Endopeptidases; C513261:Tnfaip3 protein, mouse
keywords: Toll-like receptors; inflammation; innate immunity; lipopolysaccharide; signal transduction