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Journal of Virology, May 2009, p. 4365-4375, Vol. 83, No. 9
0022-538X/09/$08.00+0     doi:10.1128/JVI.02148-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

NSs Protein of Rift Valley Fever Virus Induces the Specific Degradation of the Double-Stranded RNA-Dependent Protein Kinase{triangledown}

Matthias Habjan,1,{dagger} Andreas Pichlmair,1,2,{dagger} Richard M. Elliott,3 Anna K. Överby,1 Timo Glatter,4,5 Matthias Gstaiger,4,5 Giulio Superti-Furga,2 Hermann Unger,6 and Friedemann Weber1*

Department of Virology, University of Freiburg, Freiburg, Germany,1 CeMM-Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria,2 Centre for Biomolecular Sciences, School of Biology, University of St. Andrews, Fife, United Kingdom,3 Institute of Molecular Systems Biology, Zurich, Switzerland,4 Competence Center for Systems Physiology and Metabolic Diseases, Zurich, Switzerland,5 Laboratory for Tropical Veterinary Medicine, University of Veterinary Medicine, Vienna, Austria6

Received 11 October 2008/ Accepted 23 January 2009

Rift Valley fever virus (RVFV) continues to cause large outbreaks of acute febrile and often fatal illness among humans and domesticated animals in Africa, Saudi Arabia, and Yemen. The high pathogenicity of this bunyavirus is mainly due to the viral protein NSs, which was shown to prevent transcriptional induction of the antivirally active type I interferons (alpha/beta interferon [IFN-{alpha}/β]). Viruses lacking the NSs gene induce synthesis of IFNs and are therefore attenuated, whereas the noninducing wild-type RVFV strains can only be inhibited by pretreatment with IFN. We demonstrate here in vitro and in vivo that a substantial part of the antiviral activity of IFN against RVFV is due to a double-stranded RNA-dependent protein kinase (PKR). PKR-mediated virus inhibition, however, was much more pronounced for the strain Clone 13 with NSs deleted than for the NSs-expressing strain ZH548. In vivo, Clone 13 was nonpathogenic for wild-type (wt) mice but could regain pathogenicity if mice lacked the PKR gene. ZH548, in contrast, killed both wt and PKR knockout mice indiscriminately. ZH548 was largely resistant to the antiviral properties of PKR because RVFV NSs triggered the specific degradation of PKR via the proteasome. The NSs proteins of the related but less virulent sandfly fever Sicilian virus and La Crosse virus, in contrast, had no such anti-PKR activity despite being efficient suppressors of IFN induction. Our data suggest that RVFV NSs has gained an additional anti-IFN function that may explain the extraordinary pathogenicity of this virus.

* Corresponding author. Mailing address: Department of Virology, University of Freiburg, Hermann-Herder Str. 11, Freiburg 79104, Germany. Phone: 49-761-203-6614. Fax: 49-761-203-6634. E-mail: friedemann.weber{at}uniklinik-freiburg.de

{triangledown} Published ahead of print on 11 February 2009.

{dagger} M.H. and A.P. contributed equally to this study.

Journal of Virology, May 2009, p. 4365-4375, Vol. 83, No. 9
0022-538X/09/$08.00+0     doi:10.1128/JVI.02148-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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