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Journal of Virology, February 2008, p. 1665-1678, Vol. 82, No. 4
0022-538X/08/$08.00+0 doi:10.1128/JVI.02113-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Identification of Three Interferon-Inducible Cellular Enzymes That Inhibit the Replication of Hepatitis C Virus
Dong Jiang,1
Haitao Guo,1
Chunxiao Xu,3
Jinhong Chang,1,3
Baohua Gu,1
Lijuan Wang,1
Timothy M. Block,1,2 and
Ju-Tao Guo1*
Drexel Institute for Biotechnology and Virology Research, Department of Microbiology and Immunology, Drexel University College of Medicine,1
Institute for Hepatitis Virus Research, Hepatitis B Foundation, 3805 Old Easton Road, Doylestown, Pennsylvania 18902,2
Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, Pennsylvania 191113
Received 24 September 2007/
Accepted 30 November 2007
Hepatitis C virus (HCV) infection is a common cause of chronic hepatitis and is currently treated with alpha interferon (IFN-
)-based therapies. However, the underlying mechanism of IFN-
therapy remains to be elucidated. To identify the cellular proteins that mediate the antiviral effects of IFN-
, we created a HEK293-based cell culture system to inducibly express individual interferon-stimulated genes (ISGs) and determined their antiviral effects against HCV. By screening 29 ISGs that are induced in Huh7 cells by IFN-
and/or up-regulated in HCV-infected livers, we discovered that viperin, ISG20, and double-stranded RNA-dependent protein kinase (PKR) noncytolytically inhibited the replication of HCV replicons. Mechanistically, inhibition of HCV replication by ISG20 and PKR depends on their 3'-5' exonuclease and protein kinase activities, respectively. Moreover, our work, for the first time, provides strong evidence suggesting that viperin is a putative radical S-adenosyl-L-methionine (SAM) enzyme. In addition to demonstrating that the antiviral activity of viperin depends on its radical SAM domain, which contains conserved motifs to coordinate [4Fe-4S] cluster and cofactor SAM and is essential for its enzymatic activity, mutagenesis studies also revealed that viperin requires an aromatic amino acid residue at its C terminus for proper antiviral function. Furthermore, although the N-terminal 70 amino acid residues of viperin are not absolutely required, deletion of this region significantly compromises its antiviral activity against HCV. Our findings suggest that viperin represents a novel antiviral pathway that works together with other antiviral proteins, such as ISG20 and PKR, to mediate the IFN response against HCV infection.
* Corresponding author. Mailing address: Drexel Institute for Biotechnology and Virology Research, Department of Microbiology and Immunology, Drexel University College of Medicine, 3805 Old Easton Road, Doylestown, PA 18902. Phone: (215) 489-4929. Fax: (215) 489-4920. E-mail:
jg362{at}drexel.edu
Published ahead of print on 12 December 2007.
Journal of Virology, February 2008, p. 1665-1678, Vol. 82, No. 4
0022-538X/08/$08.00+0 doi:10.1128/JVI.02113-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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