title: A Rhesus Rhadinovirus Viral Interferon (IFN) Regulatory Factor Is Virion Associated and Inhibits the Early IFN Antiviral Response.
abstract: The interferon (IFN) response is the earliest host immune response dedicated to combating viral infection. As such, viruses have evolved strategies to subvert this potent antiviral response. Two closely related gammaherpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV) and rhesus macaque rhadinovirus (RRV), are unique in that they express viral homologues to cellular interferon regulatory factors (IRFs), termed viral IRFs (vIRFs). Cellular IRFs are a family of transcription factors that are particularly important for the transcription of type I IFNs. Here, we demonstrate a strategy employed by RRV to ensure rapid inhibition of virus-induced type I IFN induction. We found that RRV vIRF R6, when expressed ectopically, interacts with a transcriptional coactivator, CREB-binding protein (CBP), in the nucleus. As a result, phosphorylated IRF3, an important transcriptional regulator in beta interferon (IFN-β) transcription, fails to effectively bind to the IFN-β promoter, thus inhibiting the activation of IFN-β genes. In addition, we found R6 within RRV virion particles via immunoelectron microscopy and, furthermore, that virion-associated R6 is capable of inhibiting the type I IFN response by preventing efficient binding of IRF3/CBP complexes to the IFN-β promoter in the context of infection. The work shown here is the first example of a vIRF being associated with either the KSHV or RRV virion. The presence of this immunomodulatory protein in the RRV virion provides the virus with an immediate mechanism to evade the host IFN response, thus enabling the virus to effectively establish an infection within the host.
  
  
  OBJECTIVE
  Kaposi's sarcoma-associated herpesvirus (KSHV) and the closely related rhesus macaque rhadinovirus (RRV) are the only viruses known to encode viral homologues to cellular interferon regulatory factors (IRFs), known as vIRFs. In KSHV, these proteins have been shown to play major roles in a variety of cellular processes and are particularly important in the evasion of the host type I interferon (IFN) response. In this study, we delineate the immunomodulatory mechanism of an RRV vIRF and its ability to assist the virus in rapid immune evasion by being prepackaged within the virion, thus providing evidence, for the first time, of a virion-associated vIRF. This work further contributes to our understanding of the mechanisms behind immunomodulation by the RRV vIRFs during infection.
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA Vaccine and Gene Therapy Institute, Beaverton, Oregon, USA.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Morin
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA Vaccine and Gene Therapy Institute, Beaverton, Oregon, USA Department of Global Health, University of Washington, Seattle, Washington, USA.
authors.forename: Bridget A
authors.initials: BA
authors.lastname: Robinson
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA Vaccine and Gene Therapy Institute, Beaverton, Oregon, USA Department of Human Genetics, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Kelsey S
authors.initials: KS
authors.lastname: Rogers
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA Vaccine and Gene Therapy Institute, Beaverton, Oregon, USA Division of Pathobiology and Immunology, Oregon National Primate Research Center, Beaverton, Oregon, USA wongs@ohsu.edu.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Wong
mesh_terms: D000818:Animals; D050882:CREB-Binding Protein / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D006566:Herpesviridae Infections / Q000235:genetics / Q000276:immunology* / Q000821:virology; D054884:Host-Pathogen Interactions; D006801:Humans; D057131:Immune Evasion; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000276:immunology; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000276:immunology*; D016899:Interferon-beta / Q000235:genetics / Q000276:immunology*; D008253:Macaca mulatta; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018144:Rhadinovirus / Q000235:genetics / Q000276:immunology*; D014764:Viral Proteins / Q000235:genetics / Q000276:immunology*; D014771:Virion / Q000235:genetics / Q000276:immunology*
chemical_list: D050838:Interferon Regulatory Factor-3; D050835:Interferon Regulatory Factors; D014764:Viral Proteins; C413486:viral interferon regulatory factors; D016899:Interferon-beta; D050882:CREB-Binding Protein