title: Suppressor of cytokine signaling (SOCS) proteins indirectly regulate toll-like receptor signaling in innate immune cells.
abstract: Suppressor of cytokine signaling (SOCS) proteins constitute a class of negative regulators for Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathways. These intracellular proteins are induced by cytokine signaling, but they can also be induced by stimulation of Toll-like receptors (TLR). It has even been suggested that SOCS proteins are important negative regulators of TLR signaling. Here we have elucidated the nature of the regulatory role of SOCS in TLR signaling. Induction of SOCS-3 and cytokine-inducible Src homology 2-containing protein (CIS) by TLR stimulation was strictly dependent on MyD88 but showed differing needs in case of SOCS-1. However, induction of SOCS proteins by TLR ligands was independent of type I interferon. In macrophages overexpressing SOCS, we were not able to observe an inhibitory effect of SOCS-1, SOCS-2, SOCS-3, or CIS on prototypical TLR target genes such as tumor necrosis factor-alpha. However, we found that TLR-2, TLR-3, TLR-4, and TLR-9 stimulation induced interferon-beta (IFN-beta), which is able to exert auto- and paracrine signaling, leading to the activation of secondary genes like IP-10. SOCS-1 and, to a lesser extent, SOCS-3 and CIS were able to inhibit this indirect signaling pathway following TLR stimulation, whereas neither MAP kinase nor NF kappa B signaling were affected. However, STAT-1 tyrosine phosphorylation following TLR triggering was severely impaired by SOCS-1 overexpression. Thus, our data suggest that SOCS proteins induced by TLR stimulation limit the extent of TLR signaling by inhibiting type I IFN signaling but not the main NF kappa B pathway.
authors.affiliation: Institute of Medical Microbiology and Hygiene, Philipps-University Marburg, 35037 Marburg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Baetz
authors.forename: Markus
authors.initials: M
authors.lastname: Frey
authors.forename: Klaus
authors.initials: K
authors.lastname: Heeg
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Dalpke
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000943:Antigens, Differentiation / Q000502:physiology; D001854:Bone Marrow Cells; D019013:CD40 Antigens / Q000032:analysis; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D054357:Chemokine CXCL10; D019743:Chemokines, CXC / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D015870:Gene Expression; D007370:Interferon Type I / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000502:physiology*; D011971:Receptors, Immunologic / Q000172:deficiency / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D019013:CD40 Antigens; D002352:Carrier Proteins; D054357:Chemokine CXCL10; D019743:Chemokines, CXC; D004268:DNA-Binding Proteins; D007370:Interferon Type I; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; C491590:Socs1 protein, mouse; C491409:Socs2 protein, mouse; C491411:Socs3 protein, mouse; C494080:Stat1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015534:Trans-Activators; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha