title: Inhibition of interferon-stimulated JAK-STAT signaling by a tick-borne flavivirus and identification of NS5 as an interferon antagonist.
abstract: The tick-borne encephalitis (TBE) complex of viruses, genus Flavivirus, can cause severe encephalitis, meningitis, and/or hemorrhagic fevers. Effective interferon (IFN) responses are critical to recovery from infection with flaviviruses, and the mosquito-borne flaviviruses can inhibit this response. However, little is known about interactions between IFN signaling and TBE viruses. Langat virus (LGTV), a member of the TBE complex of viruses, was found to be highly sensitive to the antiviral effects of IFN. However, LGTV infection inhibited IFN-induced expression of a reporter gene driven by either IFN-alpha/beta- or IFN-gamma-responsive promoters. This indicated that LGTV can inhibit the IFN-mediated JAK-STAT (Janus kinase-signal transducer and activator of transcription) pathway of signal transduction. The mechanism of inhibition was due to blocks in the phosphorylation of both Janus kinases, Jak1 and Tyk2, during IFN-alpha signaling and at least a failure of Jak1 phosphorylation following IFN-gamma stimulation. To determine the viral protein(s) responsible, we individually expressed all nonstructural (NS) proteins and examined their ability to inhibit signal transduction. Expression of NS5 alone inhibited STAT1 phosphorylation in response to IFN, thus identifying NS5 as a potential IFN antagonist. Examination of interactions between NS5 and cellular proteins revealed that NS5 associated with IFN-alpha/beta and -gamma receptor complexes. Importantly, inhibition of JAK-STAT signaling and NS5-IFN receptor interactions were demonstrated in LGTV-infected human monocyte-derived dendritic cells, important target cells for early virus replication. Because NS5 may interfere with both innate and acquired immune responses to virus infection, this protein may have a significant role in viral pathogenesis.
authors.affiliation: Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, NIAID, NIH, Hamilton, MT 59840, USA. sbest@niaid.nih.gov
authors.forename: Sonja M
authors.initials: SM
authors.lastname: Best
authors.forename: Keely L
authors.initials: KL
authors.lastname: Morris
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Shannon
authors.forename: Shelly J
authors.initials: SJ
authors.lastname: Robertson
authors.forename: Dana N
authors.initials: DN
authors.lastname: Mitzel
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Park
authors.forename: Elena
authors.initials: E
authors.lastname: Boer
authors.forename: James B
authors.initials: JB
authors.lastname: Wolfinbarger
authors.forename: Marshall E
authors.initials: ME
authors.lastname: Bloom
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003713:Dendritic Cells / Q000378:metabolism / Q000821:virology; D015536:Down-Regulation; D004669:Encephalitis Viruses, Tick-Borne / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D016898:Interferon-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism; D016899:Interferon-beta / Q000037:antagonists & inhibitors / Q000378:metabolism; D007371:Interferon-gamma / Q000037:antagonists & inhibitors / Q000378:metabolism; D007372:Interferons / Q000037:antagonists & inhibitors* / Q000378:metabolism; D053613:Janus Kinase 1; D008780:Methyltransferases / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D017471:Receptors, Interferon / Q000378:metabolism; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000378:metabolism / Q000494:pharmacology*; D014774:Virulence; D014779:Virus Replication / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D016898:Interferon-alpha; C096041:NS5 protein, flavivirus; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; D015534:Trans-Activators; D017361:Viral Nonstructural Proteins; D016899:Interferon-beta; D007371:Interferon-gamma; D007372:Interferons; D008780:Methyltransferases; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; D053613:Janus Kinase 1