title: Role of N Terminus-Truncated NS1 Proteins of Influenza A Virus in Inhibiting IRF3 Activation.
abstract: The NS1 protein encoded by influenza A virus antagonizes the interferon response through various mechanisms, including blocking cellular mRNA maturation by binding the cellular CPSF30 3' end processing factor and/or suppressing the activation of interferon regulatory factor 3 (IRF3). In the present study, we identified two truncated NS1 proteins that are translated from internal AUGs at positions 235 and 241 of the NS1 open reading frame. We analyzed the cellular localization and function of the N-truncated NS1 proteins encoded by two influenza A virus strains, Udorn/72/H3N2 (Ud) and Puerto Rico/8/34/H1N1 (PR8). The NS1 protein of PR8, but not Ud, inhibits the activation of IRF3, whereas the NS1 protein of Ud, but not PR8, binds CPSF30. The truncated PR8 NS1 proteins are localized in the cytoplasm, whereas the full-length PR8 NS1 protein is localized in the nucleus. The infection of cells with a PR8 virus expressing an NS1 protein containing mutations of the two in-frame AUGs results in both the absence of truncated NS1 proteins and the reduced inhibition of activation of IRF3 and beta interferon (IFN-β) transcription. The expression of the truncated PR8 NS1 protein by itself enhances the inhibition of the activation of IRF3 and IFN-β transcription in Ud virus-infected cells. These results demonstrate that truncated PR8 NS1 proteins contribute to the inhibition of activation of this innate immune response. In contrast, the N-truncated NS1 proteins of the Ud strain, like the full-length NS1 protein, are localized in the nucleus, and mutation of the two in-frame AUGs has no effect on the activation of IRF3 and IFN-β transcription.
  
  
  OBJECTIVE
  Influenza A virus causes pandemics and annual epidemics in the human population. The viral NS1 protein plays a critical role in suppressing type I interferon expression. In the present study, we identified two novel truncated NS1 proteins that are translated from the second and third in-frame AUG codons in the NS1 open reading frame. The N-terminally truncated NS1 encoded by the H1N1 PR8 strain of influenza virus that suppresses IRF3 activation is localized primarily in the cytoplasm. We demonstrate that this truncated NS1 protein by itself enhances this suppression, demonstrating that some strains of influenza A virus express truncated forms of the NS1 protein that function in the inhibition of cytoplasmic antiviral events.
authors.affiliation: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Taoyuan, Taiwan rlkuo@mail.cgu.edu.tw rkrug@austin.utexas.edu.|Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Rei-Lin
authors.initials: RL
authors.lastname: Kuo
authors.affiliation: Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Li-Hsin
authors.initials: LH
authors.lastname: Li
authors.affiliation: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Sue-Jane
authors.initials: SJ
authors.lastname: Lin
authors.affiliation: Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Zong-Hua
authors.initials: ZH
authors.lastname: Li
authors.affiliation: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Department of Computer Science and Information Engineering, School of Electrical and Computer Engineering, College of Engineering, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Guang-Wu
authors.initials: GW
authors.lastname: Chen
authors.affiliation: Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Cheng-Kai
authors.initials: CK
authors.lastname: Chang
authors.affiliation: Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Yi-Ren
authors.initials: YR
authors.lastname: Wang
authors.affiliation: Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Ee-Hong
authors.initials: EH
authors.lastname: Tam
authors.affiliation: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Department of Computer Science and Information Engineering, School of Electrical and Computer Engineering, College of Engineering, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Yu-Nong
authors.initials: YN
authors.lastname: Gong
authors.affiliation: Department of Molecular Biosciences, Center for Infectious Diseases, Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas, USA rlkuo@mail.cgu.edu.tw rkrug@austin.utexas.edu.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Krug
authors.affiliation: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Department of Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Clinical Virology Laboratory, Linkou Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Shin-Ru
authors.initials: SR
authors.lastname: Shih
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D018387:Codon, Initiator; D004195:Disease Models, Animal; D054884:Host-Pathogen Interactions; D006801:Humans; D009980:Influenza A virus / Q000502:physiology*; D007251:Influenza, Human / Q000378:metabolism / Q000821:virology; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism*; D016899:Interferon-beta / Q000235:genetics; D051379:Mice; D009154:Mutation; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D014158:Transcription, Genetic; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018387:Codon, Initiator; C085820:INS1 protein, influenza virus; D050838:Interferon Regulatory Factor-3; D017361:Viral Nonstructural Proteins; D016899:Interferon-beta