title: Toll-like receptor 4 and Toll-IL-1 receptor domain-containing adapter protein (TIRAP)/myeloid differentiation protein 88 adapter-like (Mal) contribute to maximal IL-6 expression in macrophages.
abstract: Previous studies have shown that engagement of Toll-like receptors (TLR) 2 and 4 can induce macrophages to express a variety of proinflammatory cytokines. We have recently demonstrated that TLR2 agonists poorly induce a subset of TLR4-inducible proinflammatory genes (e.g., inducible protein (IP)-10, inducible NO synthase (iNOS), monocyte chemoattractant protein-5, IL-12p40), due in part to differential activation of IFN-beta production and phosphorylation of the transcription factor STAT1. TLR4, but not TLR2, agonists can induce IFN-beta expression via a mechanism that requires the adapter protein Toll-IL-1R domain-containing adapter protein (TIRAP)/myeloid differentiation protein 88 (MyD88) adapter-like (Mal), but not the adapter protein MyD88. Thus, the failure of TLR2 agonists to induce STAT1-dependent genes results, in part, from their failure to induce the expression of IFN-beta. In this study, we show that IL-6 expression is also preferentially induced by activation of TLR4. TLR4-dependent induction of IL-6 expression did require Toll-IL-1R domain-containing adapter protein (TIRAP)/MyD88 adapter-like (Mal), but unlike iNOS and IP-10, it did not require the expression of IFN-beta. Although exogenous IFN-beta and IFN-gamma could synergize with TLR2 agonists to restore high levels of iNOS expression and NO production, these IFNs could not synergize with TLR2 agonists to induce high levels of IL-6. Similarly, neutralizing anti-IFN Abs could block iNOS gene expression in LPS-stimulated murine macrophages, whereas these Abs had little effect on IL-6 gene expression in these cells. Together, these studies demonstrate that IL-6, like iNOS and IP-10, is differentially expressed in macrophages stimulated via TLR2 vs TLR4, although these differences appear to arise from distinct signaling mechanisms.
authors.affiliation: Pulmonary Center, School of Medicine, Boston University, Boston, MA 02118, USA.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Schilling
authors.forename: Karen
authors.initials: K
authors.lastname: Thomas
authors.forename: Kathryn
authors.initials: K
authors.lastname: Nixdorff
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Vogel
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Fenton
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D000943:Antigens, Differentiation / Q000502:physiology*; D001426:Bacterial Proteins / Q000494:pharmacology; D001854:Bone Marrow Cells / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D003545:Cysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D029721:Drosophila Proteins; D004357:Drug Synergism; D007370:Interferon Type I / Q000378:metabolism / Q000502:physiology; D016899:Interferon-beta / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008074:Lipoproteins / Q000494:pharmacology; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000819:agonists / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D053594:Myeloid Differentiation Factor 88; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D014176:Protein Biosynthesis; D011506:Proteins / Q000502:physiology; D011956:Receptors, Cell Surface / Q000819:agonists / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*; D017472:Receptors, Interleukin-1 / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D019892:eIF-2 Kinase / Q000172:deficiency / Q000235:genetics / Q000502:physiology
chemical_list: C079336:58 kDa tumor necrosis factor-inducing protein, Mycobacterium tuberculosis; D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D007370:Interferon Type I; D015850:Interleukin-6; D008070:Lipopolysaccharides; D008074:Lipoproteins; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D011506:Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D017472:Receptors, Interleukin-1; C499045:TIRAP protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D016899:Interferon-beta; D007371:Interferon-gamma; C069172:2,3-bis(palmitoyloxy)-2-propyl-1-palmitoylcysteine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D019892:eIF-2 Kinase; D003545:Cysteine