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Journal of Virology, March 2009, p. 2178-2187, Vol. 83, No. 5
0022-538X/09/$08.00+0     doi:10.1128/JVI.01787-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Reovirus µ2 Protein Inhibits Interferon Signaling through a Novel Mechanism Involving Nuclear Accumulation of Interferon Regulatory Factor 9

Jennifer Zurney,¹ Takeshi Kobayashi,^2,3, Geoffrey H. Holm,^2,3, Terence S. Dermody,^2,3,4 and Barbara Sherry^1,5*

Department of Microbiology, North Carolina State University, Raleigh, North Carolina,¹ Departments of Pediatrics,² Microbiology and Immunology,⁴ the Elizabeth B. Lamb Center for Pediatric Research, Vanderbilt University School of Medicine, Nashville, Tennessee,³ Department of Molecular Biomedical Sciences, North Carolina State University, North Carolina⁵

Received 25 August 2008/ Accepted 12 December 2008

The secreted cytokine alpha/beta interferon (IFN-/β) binds its receptor to activate the Jak-STAT signal transduction pathway, leading to formation of the heterotrimeric IFN-stimulated gene factor 3 (ISGF3) transcription complex for induction of IFN-stimulated genes (ISGs) and establishment of an antiviral state. Many viruses have evolved countermeasures to inhibit the IFN pathway, thereby subverting the innate antiviral response. Here, we demonstrate that the mildly myocarditic reovirus type 1 Lang (T1L), but not the nonmyocarditic reovirus type 3 Dearing, represses IFN induction of a subset of ISGs and that this repressor function segregates with the T1L M1 gene. Concordantly, the T1L M1 gene product, µ2, dramatically inhibits IFN-β-induced reporter gene expression. Surprisingly, T1L infection does not degrade components of the ISGF3 complex or interfere with STAT1 or STAT2 nuclear translocation as has been observed for other viruses. Instead, infection with T1L or reassortant or recombinant viruses containing the T1L M1 gene results in accumulation of interferon regulatory factor 9 (IRF9) in the nucleus. This effect has not been previously described for any virus and suggests that µ2 modulates IRF9 interactions with STATs for both ISGF3 function and nuclear export. The M1 gene is a determinant of virus strain-specific differences in the IFN response, which are linked to virus strain-specific differences in induction of murine myocarditis. We find that virus-induced myocarditis is associated with repression of IFN function, providing new insights into the pathophysiology of this disease. Together, these data provide the first report of an increase in IRF9 nuclear accumulation associated with viral subversion of the IFN response and couple virus strain-specific differences in IFN antagonism to the pathogenesis of viral myocarditis.

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* Corresponding author. Mailing address: Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606. Phone: (919) 515-4480. Fax: (919) 513-7301. E-mail: barbara_sherry{at}ncsu.edu

Published ahead of print on 24 December 2008.

Present address: Institute for Virus Research, Kyoto University, Kyoto, Japan.

Present address: Department of Biology, Colgate University, Hamilton, NY.

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Journal of Virology, March 2009, p. 2178-2187, Vol. 83, No. 5
0022-538X/09/$08.00+0     doi:10.1128/JVI.01787-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.