title: Multiple signaling pathways contribute to synergistic TLR ligand-dependent cytokine gene expression in human monocyte-derived macrophages and dendritic cells.
abstract: TLRs are innate immune receptors that recognize pathogen-associated structures. Binding of ligands to different TLRs can induce the production of proinflammatory cytokines in a synergistic manner. We have analyzed the molecular mechanisms of synergy in TLR ligand-stimulated human monocyte-derived macrophages and dendritic cells (moDCs). Stimulation of moDCs with the TLR8 ligand together with the TLR3 or TLR4 ligand led to synergistic IL-6, IL-10, IL-12, and TNF-alpha mRNA expression and cytokine production. DNA-binding assays showed that TLR3 and TLR8 stimulation induced binding of multiple IFN regulatory factor (IRF) and STAT transcription factors to the IL-12p35 gene promoter IFN-stimulated response element in moDCs and macrophages but with different binding profiles and kinetics. We also demonstrate that NF-kappaB, MAPKs and PI-3K pathways have an important role in TLR-induced cytokine gene expression, as pharmacological inhibitors of these signaling pathways inhibited TLR3, TLR4, and TLR8 ligand-induced cytokine mRNA expression and protein production. Especially, synergistic IL-12p70 production was abolished completely in NF-kappaB, MAPK p38, and PI-3K inhibitor-treated moDCs. Our data suggest that TLR-dependent, synergistic cytokine gene expression results from enhanced activation and cooperation among NF-kappaB, IRF, MAPK, PI-3K, and STAT signaling pathways.
authors.affiliation: Department of Viral Diseases and Immunology, National Public Health Institute, Helsinki, Finland. sanna.makela@ktl.fi
authors.forename: Sanna M
authors.initials: SM
authors.lastname: Mäkelä
authors.forename: Mari
authors.initials: M
authors.lastname: Strengell
authors.forename: Taija E
authors.initials: TE
authors.lastname: Pietilä
authors.forename: Pamela
authors.initials: P
authors.lastname: Osterlund
authors.forename: Ilkka
authors.initials: I
authors.lastname: Julkunen
mesh_terms: D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics*; D003713:Dendritic Cells / Q000378:metabolism*; D006801:Humans; D050835:Interferon Regulatory Factors / Q000378:metabolism; D008024:Ligands; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D020239:Receptor Cross-Talk; D050791:STAT Transcription Factors / Q000378:metabolism; D015398:Signal Transduction; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors / Q000378:metabolism*
chemical_list: D016207:Cytokines; D050835:Interferon Regulatory Factors; D008024:Ligands; D016328:NF-kappa B; D012333:RNA, Messenger; D050791:STAT Transcription Factors; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors; D019869:Phosphatidylinositol 3-Kinases