title: Amino acid substitutions in PB1 of avian influenza viruses influence pathogenicity and transmissibility in chickens.
abstract: Amino acid substitutions were introduced into avian influenza virus PB1 in order to characterize the interaction between polymerase activity and pathogenicity. Previously, we used recombinant viruses containing the hemagglutinin (HA) and neuraminidase (NA) genes from the highly pathogenic avian influenza virus (HPAIV) H5N1 strain and other internal genes from two low-pathogenicity avian influenza viruses isolated from chicken and wild-bird hosts (LP and WB, respectively) to demonstrate that the pathogenicity of highly pathogenic avian influenza viruses (HPAIVs) of subtype H5N1 in chickens is regulated by the PB1 gene (Y. Uchida et al., J. Virol. 86:2686-2695, 2012, doi:http://dx.doi.org/10.1128/JVI.06374-11). In the present study, we introduced a C38Y substitution into WB PB1 and demonstrated that this substitution increased both polymerase activity in DF-1 cells in vitro and the pathogenicity of the recombinant viruses in chickens. The V14A substitution in LP PB1 reduced polymerase activity but did not affect pathogenicity in chickens. Interestingly, the V14A substitution reduced viral shedding and transmissibility. These studies demonstrate that increased polymerase activity correlates directly with enhanced pathogenicity, while decreased polymerase activity does not always correlate with pathogenicity and requires further analysis.
  
  
  OBJECTIVE
  We identified 2 novel amino acid substitutions in the avian influenza virus PB1 gene that affect the characteristics of highly pathogenic avian influenza viruses (HPAIVs) of the H5N1 subtype, such as viral replication and polymerase activity in vitro and pathogenicity and transmissibly in chickens. An amino acid substitution at residue 38 in PB1 directly affected pathogenicity in chickens and was associated with changes in polymerase activity in vitro. A substitution at residue 14 reduced polymerase activity in vitro, while its effects on pathogenicity and transmissibility depended on the constellation of internal genes.
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan Zoonotic Diseases Collaboration Center (ZDCC), Chatuchak, Bangkok, Thailand.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Uchida
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan.
authors.forename: Taichiro
authors.initials: T
authors.lastname: Tanikawa
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Maeda
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan Zoonotic Diseases Collaboration Center (ZDCC), Chatuchak, Bangkok, Thailand.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Takemae
authors.affiliation: Influenza and Prion Disease Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan Zoonotic Diseases Collaboration Center (ZDCC), Chatuchak, Bangkok, Thailand taksaito@affrc.go.jp.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Saito
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002645:Chickens; D053124:Influenza A Virus, H5N1 Subtype / Q000235:genetics / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000401:mortality / Q000635:transmission* / Q000821:virology; D016865:Reassortant Viruses / Q000235:genetics / Q000472:pathogenicity*; D016019:Survival Analysis; D019562:Viral Load; D014764:Viral Proteins / Q000235:genetics*; D014774:Virulence; D014779:Virus Replication; D017201:Virus Shedding
chemical_list: D014764:Viral Proteins; C077346:influenza virus polymerase basic protein 1