title: Inhibition of antiviral innate immunity by birnavirus VP3 protein via blockage of viral double-stranded RNA binding to the host cytoplasmic RNA detector MDA5.
abstract: Chicken MDA5 (chMDA5), the sole known pattern recognition receptor for cytoplasmic viral RNA in chickens, initiates type I interferon (IFN) production. Infectious bursal disease virus (IBDV) evades host innate immunity, but the mechanism is unclear. We report here that IBDV inhibited antiviral innate immunity via the chMDA5-dependent signaling pathway. IBDV infection did not induce efficient type I interferon (IFN) production but antagonized the antiviral activity of beta interferon (IFN-β) in DF-1 cells pretreated with IFN-α/β. Dual-luciferase assays and inducible expression systems demonstrated that IBDV protein VP3 significantly inhibited IFN-β expression stimulated by naked IBDV genomic double-stranded RNA (dsRNA). The VP3 protein competed strongly with chMDA5 to bind IBDV genomic dsRNA in vitro and in vivo, and VP3 from other birnaviruses also bound dsRNA. Site-directed mutagenesis confirmed that deletion of the VP3 dsRNA binding domain restored IFN-β expression. Our data demonstrate that VP3 inhibits antiviral innate immunity by blocking binding of viral genomic dsRNA to MDA5.
  
  
  OBJECTIVE
  MDA5, a known pattern recognition receptor and cytoplasmic viral RNA sensor, plays a critical role in host antiviral innate immunity. Many pathogens escape or inhibit the host antiviral immune response, but the mechanisms involved are unclear for most pathogens. We report here that birnaviruses inhibit host antiviral innate immunity via the MDA5-dependent signaling pathway. The antiviral innate immune system involving IFN-β did not function effectively during birnavirus infection, and the viral protein VP3 significantly inhibited IFN-β expression stimulated by naked viral genomic dsRNA. We also show that VP3 blocks MDA5 binding to viral genomic dsRNA in vitro and in vivo. Our data reveal that birnavirus-encoded viral protein VP3 is an inhibitor of the antiviral innate immune response and inhibits the antiviral innate immune response via the MDA5-dependent signaling pathway.
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Chengjin
authors.initials: C
authors.lastname: Ye
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Lu
authors.initials: L
authors.lastname: Jia
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Yanting
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Boli
authors.initials: B
authors.lastname: Hu
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Lun
authors.initials: L
authors.lastname: Wang
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China.
authors.forename: Xingmeng
authors.initials: X
authors.lastname: Lu
authors.affiliation: Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, People's Republic of China College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, People's Republic of China jyzhou@zju.edu.cn.
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics* / Q000276:immunology / Q000494:pharmacology; D001667:Binding, Competitive; D002460:Cell Line; D002645:Chickens; D053487:DEAD-box RNA Helicases / Q000235:genetics* / Q000276:immunology / Q000494:pharmacology; D015967:Gene Expression Regulation, Viral; D054884:Host-Pathogen Interactions; D057131:Immune Evasion; D007113:Immunity, Innate / Q000187:drug effects*; D007243:Infectious bursal disease virus / Q000235:genetics / Q000276:immunology*; D016899:Interferon-beta / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000276:immunology; D011485:Protein Binding; D012330:RNA, Double-Stranded / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology; D012367:RNA, Viral / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction; D015678:Viral Structural Proteins / Q000235:genetics* / Q000276:immunology / Q000494:pharmacology
chemical_list: D030161:Avian Proteins; D012330:RNA, Double-Stranded; D012367:RNA, Viral; C478244:VP3 protein, infectious bursal disease virus; D015678:Viral Structural Proteins; D016899:Interferon-beta; D053487:DEAD-box RNA Helicases