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Journal of Virology, June 2001, p. 5090-5098, Vol. 75, No. 11
Department of Microbiology, School of
Medicine,1 and Regional Primate Research
Center,2 University of Washington, Seattle,
Washington 98195, and Department of
Microbiology3 and Graduate Degree
Program in Molecular and Cellular Biology,4
Arizona State University, Tempe, Arizona 85287
Received 8 December 2000/Accepted 2 March 2001
The NS5A nonstructural protein of hepatitis C virus (HCV) has been
shown to inhibit the cellular interferon (IFN)-induced protein kinase R
(PKR). PKR mediates the host IFN-induced antiviral response at least in
part by inhibiting mRNA translation initiation through phosphorylation
of the
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.11.5090-5098.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Regulation of mRNA Translation and Cellular
Signaling by Hepatitis C Virus Nonstructural Protein NS5A

subunit of eukaryotic initiation factor 2 (eIF2
). We thus
examined the effect of NS5A inhibition of PKR on mRNA translation
within the context of virus infection by using a recombinant vaccinia
virus (VV)-based assay. The VV E3L protein is a potent inhibitor of
PKR. Accordingly, infection of IFN-pretreated HeLa S3 cells with an
E3L-deficient VV (VV
E3L) resulted in increased phosphorylation
levels of both PKR and eIF2
. IFN-pretreated cells infected with VV
in which the E3L locus was replaced with the
NS5A gene (VVNS5A) displayed diminished phosphorylation of
PKR and eIF2
in a transient manner. We also observed an increase in
activation of p38 mitogen-activated protein kinase in IFN-pretreated cells infected with VV
E3L, consistent with reports that p38 lies downstream of the PKR pathway. Furthermore, these cells exhibited increased phosphorylation of the cap-binding initiation factor 4E
(eIF4E), which is downstream of the p38 pathway. Importantly, these
effects were reduced in cells infected with VVNS5A. NS5A was also found
to inhibit activation of the p38-eIF4E pathway in epidermal growth
factor-treated cells stably expressing NS5A. NS5A-induced inhibition of
eIF2
and eIF4E phosphorylation may exert counteracting effects on
mRNA translation. Indeed, IFN-pretreated cells infected with VVNS5A
exhibited a partial and transient restoration of cellular and viral
mRNA translation compared with IFN-pretreated cells infected with
VV
E3L. Taken together, these results support the role of NS5A as a
PKR inhibitor and suggest a potential mechanism by which HCV might
maintain global mRNA translation rate during early virus infection
while favoring cap-independent translation of HCV mRNA during late infection.
*
Corresponding author. Mailing address: Department of
Microbiology, Box 358070, University of Washington, Seattle, WA 98195. Phone: (206) 732-6135. Fax: (206) 732-6055. E-mail:
honey{at}u.washington.edu.
Present address: Infectious Diseases Research, Eli Lilly and
Company, Lilly Corporate Center, Indianapolis, IN 46285.
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