The NS5 protein of the virulent West Nile virus NY99 strain is a potent antagonist of type I interferon-mediated JAK-STAT signaling.
Flaviviruses transmitted by arthropods represent a tremendous disease burden for humans, causing millions of infections annually. All vector-borne flaviviruses studied to date suppress host innate responses to infection by inhibiting alpha/beta interferon (IFN-alpha/beta)-mediated JAK-STAT signal transduction. The viral nonstructural protein NS5 of some flaviviruses functions as the major IFN antagonist, associated with inhibition of IFN-dependent STAT1 phosphorylation (pY-STAT1) or with STAT2 degradation. West Nile virus (WNV) infection prevents pY-STAT1 although a role for WNV NS5 in IFN antagonism has not been fully explored. Here, we report that NS5 from the virulent NY99 strain of WNV prevented pY-STAT1 accumulation, suppressed IFN-dependent gene expression, and rescued the growth of a highly IFN-sensitive virus (Newcastle disease virus) in the presence of IFN, suggesting that this protein can function as an efficient IFN antagonist. In contrast, NS5 from Kunjin virus (KUN), a naturally attenuated subtype of WNV, was a poor suppressor of pY-STAT1. Mutation of a single residue in KUN NS5 to the analogous residue in WNV-NY99 NS5 (S653F) rendered KUN NS5 an efficient inhibitor of pY-STAT1. Incorporation of this mutation into recombinant KUN resulted in 30-fold greater inhibition of JAK-STAT signaling than with the wild-type virus and enhanced KUN replication in the presence of IFN. Thus, a naturally occurring mutation is associated with the function of NS5 in IFN antagonism and may influence virulence of WNV field isolates.
Laurent-Rolle
Maudry
M
Laboratory of Virology, Rocky Mountain Laboratories, 903 S. Fourth St., Hamilton, MT 59840, USA.
Boer
Elena F
EF
Lubick
Kirk J
KJ
Wolfinbarger
James B
JB
Carmody
Aaron B
AB
Rockx
Barry
B
Liu
Wenjun
W
Ashour
Joseph
J
Shupert
W Lesley
WL
Holbrook
Michael R
MR
Barrett
Alan D
AD
Mason
Peter W
PW
Bloom
Marshall E
ME
García-Sastre
Adolfo
A
Khromykh
Alexander A
AA
Best
Sonja M
SM
D000818:Animals; D002522:Chlorocebus aethiops; D006801:Humans; D007370:Interferon Type I / Q000037:antagonists & inhibitors*; D053612:Janus Kinases / Q000037:antagonists & inhibitors*; D050794:STAT1 Transcription Factor / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000502:physiology*; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000502:physiology*; D014902:West Nile virus / Q000502:physiology
D007370:Interferon Type I; C080107:NS4B protein, flavivirus; C096041:NS5 protein, flavivirus; D050794:STAT1 Transcription Factor; D017361:Viral Nonstructural Proteins; D053612:Janus Kinases