title: Mutations in polymerase genes enhanced the virulence of 2009 pandemic H1N1 influenza virus in mice.
abstract: Influenza A virus can infect a wide variety of animal species with illness ranging from mild to severe, and is a continual cause for concern. Genetic mutations that occur either naturally or during viral adaptation in a poorly susceptible host are key mechanisms underlying the evolution and virulence of influenza A virus. Here, the variants containing PA-A36T or PB2-H357N observed in the mouse-adapted descendants of 2009 pandemic H1N1 virus (pH1N1), A/Sichuan/1/2009 (SC), were characterized. Both mutations enhanced polymerase activity in mammalian cells. These effects were confirmed using recombinant SC virus containing polymerase genes with wild type (WT) or mutant PA or PB2. The PA-A36T mutant showed enhanced growth property compared to the WT in both human A549 cells and porcine PK15 cells in vitro, without significant effect on viral propagation in murine LA-4 cells and pathogenicity in mice; however, it did enhance the lung virus titer. PB2-H357N variant demonstrated growth ability comparable to the WT in A549 cells, but replicated well in PK15, LA-4 cells and in mice with an enhanced pathogenic phenotype. Despite such mutations are rare in nature, they could be observed in avian H5 and H7 subtype viruses which were currently recognized to pose potential threat to human. Our findings indicated that pH1N1 may adapt well in mammals when acquiring these mutations. Therefore, future molecular epidemiological surveillance should include scrutiny of both markers because of their potential impact on pathogenesis.
authors.affiliation: Chinese National Influenza Center, National Institute for Viral Disease Control and Prevention, China CDC, Beijing, People's Republic of China.
authors.forename: Wenfei
authors.initials: W
authors.lastname: Zhu
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhu
authors.forename: Kun
authors.initials: K
authors.lastname: Qin
authors.forename: Zaijiang
authors.initials: Z
authors.lastname: Yu
authors.forename: Rongbao
authors.initials: R
authors.lastname: Gao
authors.forename: Huiyan
authors.initials: H
authors.lastname: Yu
authors.forename: Jianfang
authors.initials: J
authors.lastname: Zhou
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D004285:Dogs; D005260:Female; D005814:Genes, Viral; D049674:History, 21st Century; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000201:enzymology / Q000235:genetics* / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology / Q000266:history / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009976:Orthomyxoviridae Infections / Q000821:virology*; D058873:Pandemics / Q000266:history; D020641:Polymorphism, Single Nucleotide; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics* / Q000378:metabolism; D011995:Recombination, Genetic; D013552:Swine; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D014774:Virulence / Q000235:genetics / Q000502:physiology; D014779:Virus Replication
chemical_list: C061290:PA protein, influenza viruses; C057027:PB2 protein, Influenzavirus A; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase