title: NS1 Protein Amino Acid Changes D189N and V194I Affect Interferon Responses, Thermosensitivity, and Virulence of Circulating H3N2 Human Influenza A Viruses.
abstract: Influenza virus NS1 protein is a nonstructural, multifunctional protein that counteracts host innate immune responses, modulating virus pathogenesis. NS1 protein variability in subjects infected with H3N2 influenza A viruses (IAVs) during the 2010/2011 season was analyzed, and amino acid changes in residues 86, 189, and 194 were found. The consequences of these mutations for the NS1-mediated inhibition of IFN responses and the pathogenesis of the virus were evaluated, showing that NS1 mutations D189N and V194I impaired the ability of the NS1 protein to inhibit general gene expression, most probably because these mutations decreased the binding of NS1 to the cleavage and polyadenylation specificity factor 30 (CPSF30). A recombinant A/Puerto Rico/8/34 (PR8) H1N1 virus encoding the H3N2 NS1-D189N protein was slightly attenuated, whereas the virus encoding the H3N2 NS1-V194I protein was further attenuated in mice. The higher attenuation of this virus could not be explained by differences in the ability of the two NS1 proteins to counteract host innate immune responses, indicating that another factor must be responsible. In fact, we showed that the virus encoding the H3N2 NS1-V194I protein demonstrated a temperature-sensitive (ts) phenotype, providing a most likely explanation for the stronger attenuation observed. As far as we know, this is the first description of a mutation in NS1 residue 194 conferring a ts phenotype. These studies are relevant in order to identify new residues important for NS1 functions and in human influenza virus surveillance to assess mutations affecting the pathogenicity of circulating viruses.IMPORTANCEInfluenza viral infections represent a serious public health problem, with influenza virus causing a contagious respiratory disease that is most effectively prevented through vaccination. The multifunctional nonstructural protein 1 (NS1) is the main viral factor counteracting the host antiviral response. Therefore, influenza virus surveillance to identify new mutations in the NS1 protein affecting the pathogenicity of the circulating viruses is highly important. In this work, we evaluated amino acid variability in the NS1 proteins from H3N2 human seasonal viruses and the effect of the mutations on innate immune responses and virus pathogenesis. NS1 mutations D189N and V194I impaired the ability of the NS1 protein to inhibit general gene expression, and recombinant viruses harboring these mutations were attenuated in a mouse model of influenza infection. Interestingly, a virus encoding the H3N2 NS1-V194I protein demonstrated a temperature-sensitive phenotype, further attenuating the virusin vivo.
authors.affiliation: Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA.
authors.forename: Aitor
authors.initials: A
authors.lastname: Nogales
authors.affiliation: Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA.
authors.forename: Luis
authors.initials: L
authors.lastname: Martinez-Sobrido
authors.affiliation: David H. Smith Center for Vaccine Biology and Immunology, University of Rochester, Rochester, New York, USA David_Topham@URMC.rochester.edu Marta_Lopez@URMC.rochester.edu.|Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA.
authors.forename: David J
authors.identifier: http://orcid.org/0000-0002-9435-8673
authors.initials: DJ
authors.lastname: Topham
authors.affiliation: David H. Smith Center for Vaccine Biology and Immunology, University of Rochester, Rochester, New York, USA David_Topham@URMC.rochester.edu Marta_Lopez@URMC.rochester.edu.|Department of Microbiology and Immunology, University of Rochester, Rochester, New York, USA.
authors.forename: Marta L
authors.initials: ML
authors.lastname: DeDiego
mesh_terms: D000072283:A549 Cells; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002522:Chlorocebus aethiops; D039223:Cleavage And Polyadenylation Specificity Factor / Q000378:metabolism; D004285:Dogs; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007113:Immunity, Innate; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology* / Q000472:pathogenicity; D007251:Influenza, Human / Q000276:immunology / Q000821:virology*; D007372:Interferons / Q000096:biosynthesis / Q000235:genetics; D061985:Madin Darby Canine Kidney Cells; D008810:Mice, Inbred C57BL; D050296:Microbial Viability; D011485:Protein Binding; D014176:Protein Biosynthesis; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000235:genetics* / Q000502:physiology; D014774:Virulence; D014779:Virus Replication
chemical_list: C000594014:CPSF4 protein, human; D039223:Cleavage And Polyadenylation Specificity Factor; C085820:INS1 protein, influenza virus; D017361:Viral Nonstructural Proteins; D007372:Interferons
keywords: NS1 protein; antiviral response; influenza virus; innate immunity; pathogenesis; virus-host interactions