title: Re-examination of the role of suppressor of cytokine signaling 1 (SOCS1) in the regulation of toll-like receptor signaling.
abstract: Suppressor of cytokine signaling 1 (SOCS1) is an obligate negative regulator of cytokine signaling and most importantly in vivo, signaling via the interferon-gamma (IFN-gamma) receptor. SOCS1, via its Src homology 2 domain, binds to phosphotyrosine residues in its targets, reducing the amplitude of signaling from cytokine receptors. SOCS1 is also implicated in blocking Toll-like receptor (TLR) signaling in macrophages activated by TLR agonists such as lipopolysaccharide (LPS), thus regulating multiple steps in the activation of innate immune responses. To rigorously test this, we isolated macrophages from Socs1-/- mice on multiple genetic backgrounds. We found no evidence that SOCS1 blocked TLR-activated pathways, endotoxin tolerance, or nitric oxide production. However, Socs1-/-;IFN-gamma-/- mice were extremely susceptible to LPS challenge, confirming previous findings. Because LPS induces IFN-beta production from macrophages, we tested whether SOCS1 regulates IFN-alpha/beta receptor signaling. We find that SOCS1 is required to inhibit IFN-alpha/beta receptor signaling in vitro. Furthermore, the absence of a single allele encoding TYK2, a JAK (Janus kinase) family member essential IFN-alpha/beta receptor signaling, rescued Socs1-/- mice from early lethality, even in the presence of IFN-gamma. We conclude that previous reports linking SOCS1 to TLR signaling are most likely due to effects on IFN-alpha/beta receptor signaling.
authors.affiliation: Howard Hughes Medical Institute, Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Gingras
authors.forename: Evan
authors.initials: E
authors.lastname: Parganas
authors.forename: Antoine
authors.initials: A
authors.lastname: de Pauw
authors.forename: James N
authors.initials: JN
authors.lastname: Ihle
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Murray
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020672:I-kappa B Proteins / Q000378:metabolism; D007371:Interferon-gamma / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D008562:Membrane Glycoproteins / Q000819:agonists / Q000502:physiology*; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D000072000:NF-KappaB Inhibitor alpha; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D053633:Receptor, Interferon alpha-beta; D011956:Receptors, Cell Surface / Q000819:agonists / Q000502:physiology*; D017471:Receptors, Interferon / Q000037:antagonists & inhibitors / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053634:TYK2 Kinase; D051193:Toll-Like Receptors; D015534:Trans-Activators / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C000606205:Nfkbia protein, mouse; D011956:Receptors, Cell Surface; D017471:Receptors, Interferon; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; C491590:Socs1 protein, mouse; C494080:Stat1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D051193:Toll-Like Receptors; D015534:Trans-Activators; D000072000:NF-KappaB Inhibitor alpha; D053633:Receptor, Interferon alpha-beta; D007371:Interferon-gamma; D011505:Protein-Tyrosine Kinases; D053634:TYK2 Kinase; C499356:Tyk2 protein, mouse; D048049:Extracellular Signal-Regulated MAP Kinases