Toll-like receptors discriminate between different pathogen-associated molecules and activate signaling cascades that lead to immune responses. The specificity of Toll-like receptor signaling occurs by means of adaptor proteins containing Toll–interleukin 1 receptor (TIR) domains. Activating functions have been assigned to four TIR adaptors: MyD88, Mal, TRIF and TRAM. Here we characterize a fifth TIR adaptor, SARM, as a negative regulator of TRIF-dependent Toll-like receptor signaling. Expression of SARM blocked gene induction 'downstream' of TRIF but not of MyD88. SARM associated with TRIF, and 'knockdown' of endogenous SARM expression by interfering RNA led to enhanced TRIF-dependent cytokine and chemokine induction. Thus, the fifth mammalian TIR adaptor SARM is a negative regulator of Toll-like receptor signaling.
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Beutler, B. Inferences, questions and possibilities in Toll-like receptor signalling. Nature 430, 257–263 (2004).
Moynagh, P.N. TLR signalling and activation of IRFs: revisiting old friends from the NF-κB pathway. Trends Immunol. 26, 469–476 (2005).
O'Neill, L.A.J., Fitzgerald, K. & Bowie, A.G. The Toll-IL-1 receptor adaptor family grows to five members. Trends Immunol. 24, 286–289 (2003).
Yamamoto, M. et al. Role of adaptor TRIF in the MyD88-independent Toll-like receptor signalling pathway. Science 301, 640–643 (2003).
McGettrick, A.F. & O'Neill, L.A. The expanding family of MyD88-like adaptors in Toll-like receptor signal transduction. Mol. Immunol. 41, 577–582 (2004).
Fitzgerald, K.A. et al. Mal (MyD88-adapter-like) is required for Toll-like receptor-4 signal transduction. Nature 413, 78–83 (2001).
Horng, T., Barton, G.M. & Medzhitov, R. TIRAP: an adapter molecule in the Toll signaling pathway. Nat. Immunol. 2, 835–841 (2001).
Oshiumi, H., Matsumoto, M., Funami, K., Akazawa, T. & Seya, T. TICAM-1, an adaptor molecule that participates in Toll-like receptor 3–mediated interferon-β induction. Nat. Immunol. 4, 161–167 (2003).
Yamamoto, M. et al. Cutting edge: a novel Toll/IL-1 receptor domain-containing adapter that preferentially activates the IFN-β promoter in the Toll-like receptor signalling. J. Immunol. 169, 6668–6672 (2002).
Hoebe, K. et al. Identification of Lps2 as a key transducer of MyD88-independent TIR signalling. Nature 424, 743–748 (2003).
Fitzgerald, K.A. et al. LPS-TLR4 signaling to IRF-3/7 and NF-κB involves the Toll adapters TRAM and TRIF. J. Exp. Med. 198, 1043–1055 (2003).
Mink, M., Fogelgren, B., Olszewski, K., Maroy, P. & Csiszar, K. A novel human gene (SARM) at chromosome 17q11 encodes a protein with a SAM motif and structural similarity to Armadillo/β-catenin that is conserved in mouse, Drosophila, and Caenorhabditis elegans. Genomics 74, 234–244 (2001).
Couillault, C. et al. TLR-independent control of innate immunity in Caenorhabditis elegans by the TIR domain adaptor protein TIR-1, an ortholog of human SARM. Nat. Immunol. 5, 488–494 (2004).
Liberati, N.T. et al. Requirement for a conserved Toll/interleukin-1 resistance domain protein in the Caenorhabditis elegans immune response. Proc. Natl. Acad. Sci. USA 101, 6593–6598 (2004).
Chuang, C.F. & Bargmann, C.I.A. Toll-interleukin 1 repeat protein at the synapse specifies asymmetric odorant receptor expression via ASK1 MAPKKK signalling. Genes Dev. 19, 270–281 (2005).
Kaiser, W.J. & Offermann, M.K. Apoptosis induced by the toll-like receptor adaptor TRIF is dependent on its receptor interacting protein homotypic interaction motif. J. Immunol. 174, 4942–4952 (2005).
Wald, D. et al. SIGIRR, a negative regulator of Toll-like receptor-interleukin 1 receptor signalling. Nat. Immunol. 4, 920–927 (2003).
Brint, E.K. et al. ST2 is an inhibitor of interleukin 1 receptor and Toll-like receptor 4 signaling and maintains endotoxin tolerance. Nat. Immunol. 5, 373–379 (2004).
Meylan, E. et al. Cardif is an adaptor protein in the RIG-I antiviral pathway and is targeted by hepatitis C virus. Nature 437, 1167–1172 (2005).
Yoneyama, M. et al. The RNA helicase RIG-I has an essential function in double-stranded RNA-induced innate antiviral responses. Nat. Immunol. 5, 730–737 (2004).
Clemens, M.J. PKR–a protein kinase regulated by double-stranded RNA. Int. J. Biochem. Cell Biol. 29, 945–949 (1997).
Honda, K. et al. IRF-7 is the master regulator of type-I interferon-dependent immune responses. Nature 434, 772–777 (2005).
Kawai, T. et al., Interferon-α induction through Toll-like receptors involves a direct interaction of IRF7 with MyD88 and TRAF6. Nat Immunol. 5, 1061–1068 (2004).
Honda, K. et al. Role of a transductional-transcriptional processor complex involving MyD88 and IRF-7 in Toll-like receptor signalling. Proc. Natl. Acad. Sci. USA 101, 15416–15421 (2004).
Meylan, E. et al. RIP1 is an essential mediator of Toll-like receptor 3-induced NF-κB activation. Nat. Immunol. 5, 503–507 (2004).
Fitzgerald, K.A. et al. IKKε and TBK1 are essential components of the IRF3 signaling pathway. Nat. Immunol. 4, 491–496 (2003).
Stack, J. et al. Vaccinia virus protein A46R targets multiple Toll-like-interleukin-1 receptor adaptors and contributes to virulence. J. Exp. Med. 201, 1007–1018 (2005).
Kariko, K. et al. Exogenous siRNA mediates sequence-independent gene suppression by signaling through Toll-like receptor 3. Cells Tissues Organs 177, 132–138 (2004).
Hoebe, K. et al. Upregulation of costimulatory molecules induced by lipopolysaccharide and double-stranded RNA occurs by Trif-dependent and Trif-independent pathways. Nat. Immunol. 4, 1162–1164 (2003).
Weighardt, H. et al. Identification of a TLR4- and TRIF-dependent activation program of dendritic cells. Eur. J. Immunol. 34, 558–564 (2004).
Li, K. et al. Immune evasion by hepatitis C virus NS3/4A protease-mediated cleavage of the Toll-like receptor 3 adaptor protein TRIF. Proc. Natl. Acad. Sci. USA 102, 2992–2997 (2005).
Liew, F.Y., Xu, D., Brint, E.K. & O'Neill, L.A. Negative regulation of toll-like receptor-mediated immune responses. Nat. Rev. Immunol. 5, 446–58 (2005).
Sato, S. et al. Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF) associates with TNF receptor-associated factor 6 and TANK-binding kinase 1, and activates two distinct transcription factors, NF-κB and IFN-regulatory factor-3, in the Toll-like receptor signaling. J. Immunol. 171, 4304–4310 (2003).
Kim, C.A. & Bowie, J.U. SAM domains: uniform structure, diversity of function. Trends Biochem. Sci. 28, 625–628 (2003).
Muzio, M., Ni, J., Feng, P. & Dixit, V.M. IRAK (Pelle) family member IRAK-2 and MyD88 as proximal mediators of IL-1 signaling. Science 278, 1612–1615 (1997).
Supported by the Irish Research Council for Science, Engineering and Technology and Science Foundation Ireland (Investigator Programme; 02/IN.1/B192).
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