title: 2'-O methylation of the viral mRNA cap by West Nile virus evades ifit1-dependent and -independent mechanisms of host restriction in vivo.
abstract: Prior studies have shown that 2'-O methyltransferase activity of flaviviruses, coronaviruses, and poxviruses promotes viral evasion of Ifit1, an interferon-stimulated innate immune effector protein. Viruses lacking 2'-O methyltransferase activity exhibited attenuation in primary macrophages that was rescued in cells lacking Ifit1 gene expression. Here, we examined the role of Ifit1 in restricting pathogenesis in vivo of wild type WNV (WNV-WT) and a mutant in the NS5 gene (WNV-E218A) lacking 2'-O methylation of the 5' viral RNA cap. While deletion of Ifit1 had marginal effects on WNV-WT pathogenesis, WNV-E218A showed increased replication in peripheral tissues of Ifit1⁻/⁻ mice after subcutaneous infection, yet this failed to correlate with enhanced infection in the brain or lethality. In comparison, WNV-E218A was virulent after intracranial infection as judged by increased infection in different regions of the central nervous system (CNS) and a greater than 16,000-fold decrease in LD(50) values in Ifit1⁻/⁻ compared to wild type mice. Ex vivo infection experiments revealed cell-type specific differences in the ability of an Ifit1 deficiency to complement the replication defect of WNV-E218A. In particular, WNV-E218A infection was impaired in both wild type and Ifit1⁻/⁻ brain microvascular endothelial cells, which are believed to participate in blood-brain barrier (BBB) regulation of virus entry into the CNS. A deficiency of Ifit1 also was associated with increased neuronal death in vivo, which was both cell-intrinsic and mediated by immunopathogenic CD8⁺ T cells. Our results suggest that virulent strains of WNV have largely evaded the antiviral effects of Ifit1, and viral mutants lacking 2'-O methylation are controlled in vivo by Ifit1-dependent and -independent mechanisms in different cell types.
authors.affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United Stated of America.
authors.forename: Kristy J
authors.initials: KJ
authors.lastname: Szretter
authors.forename: Brian P
authors.initials: BP
authors.lastname: Daniels
authors.forename: Hyelim
authors.initials: H
authors.lastname: Cho
authors.forename: Maria D
authors.initials: MD
authors.lastname: Gainey
authors.forename: Wayne M
authors.initials: WM
authors.lastname: Yokoyama
authors.forename: Michael
authors.initials: M
authors.lastname: Gale
authors.forename: Herbert W
authors.initials: HW
authors.lastname: Virgin
authors.forename: Robyn S
authors.initials: RS
authors.lastname: Klein
authors.forename: Ganes C
authors.initials: GC
authors.lastname: Sen
authors.forename: Michael S
authors.initials: MS
authors.lastname: Diamond
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001812:Blood-Brain Barrier / Q000821:virology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000821:virology; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D002490:Central Nervous System / Q000821:virology; D042783:Endothelial Cells / Q000378:metabolism / Q000821:virology*; D005260:Female; D007113:Immunity, Innate; D007370:Interferon Type I / Q000235:genetics / Q000276:immunology; D008264:Macrophages / Q000276:immunology / Q000821:virology; D008745:Methylation; D008780:Methyltransferases / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism; D016601:RNA-Binding Proteins; D017361:Viral Nonstructural Proteins / Q000235:genetics; D014779:Virus Replication; D014901:West Nile Fever / Q000276:immunology / Q000378:metabolism / Q000821:virology; D014902:West Nile virus / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C092573:Ifit1 protein, mouse; D007370:Interferon Type I; C096041:NS5 protein, flavivirus; D012315:RNA Caps; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D017361:Viral Nonstructural Proteins; D008780:Methyltransferases