title: Poxvirus protein N1L targets the I-kappaB kinase complex, inhibits signaling to NF-kappaB by the tumor necrosis factor superfamily of receptors, and inhibits NF-kappaB and IRF3 signaling by toll-like receptors.
abstract: Poxviruses encode proteins that suppress host immune responses, including secreted decoy receptors for pro-inflammatory cytokines such as interleukin-1 (IL-1) and the vaccinia virus proteins A46R and A52R that inhibit intracellular signaling by members of the IL-1 receptor (IL-1R) and Toll-like receptor (TLR) family. In vivo, the TLRs mediate the innate immune response by serving as pathogen recognition receptors, whose oligomerized intracellular Toll/IL-1 receptor (TIR) domains can initiate innate immune signaling. A family of TIR domain-containing adapter molecules transduces signals from engaged receptors that ultimately activate NF-kappaB and/or interferon regulatory factor 3 (IRF3) to induce pro-inflammatory cytokines. Data base searches detected a significant similarity between the N1L protein of vaccinia virus and A52R, a poxvirus inhibitor of TIR signaling. Compared with other poxvirus virulence factors, the poxvirus N1L protein strongly affects virulence in vivo; however, the precise target of N1L was previously unknown. Here we show that N1L suppresses NF-kappaB activation following engagement of Toll/IL-1 receptors, tumor necrosis factor receptors, and lymphotoxin receptors. N1L inhibited receptor-, adapter-, TRAF-, and IKK-alpha and IKK-beta-dependent signaling to NF-kappaB. N1L associated with several components of the multisubunit I-kappaB kinase complex, most strongly associating with the kinase, TANK-binding kinase 1 (TBK1). Together these findings are consistent with the hypothesis that N1L disrupts signaling to NF-kappaB by Toll/IL-1Rs and TNF superfamily receptors by targeting the IKK complex for inhibition. Furthermore, N1L inhibited IRF3 signaling, which is also regulated by TBK1. These studies define a role for N1L as an immunomodulator of innate immunity by targeting components of NF-kappaB and IRF3 signaling pathways.
authors.affiliation: Viral Immune Evasion Group, Department of Biochemistry, Trinity College, Dublin 2, Ireland.
authors.forename: Gary
authors.initials: G
authors.lastname: DiPerna
authors.forename: Julianne
authors.initials: J
authors.lastname: Stack
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Bowie
authors.forename: Annemarie
authors.initials: A
authors.lastname: Boyd
authors.forename: Girish
authors.initials: G
authors.lastname: Kotwal
authors.forename: Zhouning
authors.initials: Z
authors.lastname: Zhang
authors.forename: Sheila
authors.initials: S
authors.lastname: Arvikar
authors.forename: Eicke
authors.initials: E
authors.lastname: Latz
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Fitzgerald
authors.forename: William L
authors.initials: WL
authors.lastname: Marshall
mesh_terms: D002460:Cell Line; D016207:Cytokines / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D017930:Genes, Reporter; D005822:Genetic Vectors; D006801:Humans; D051550:I-kappa B Kinase; D050838:Interferon Regulatory Factor-3; D007375:Interleukin-1 / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011212:Poxviridae / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction; D051193:Toll-Like Receptors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry / Q000502:physiology*
chemical_list: D016207:Cytokines; D004268:DNA-Binding Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D007375:Interleukin-1; D008562:Membrane Glycoproteins; C464479:N1L protein, Vaccinia virus; D016328:NF-kappa B; D011956:Receptors, Cell Surface; D051193:Toll-Like Receptors; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D017346:Protein Serine-Threonine Kinases; C403191:TBK1 protein, human; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human