title: The avian-origin PB1 gene segment facilitated replication and transmissibility of the H3N2/1968 pandemic influenza virus.
abstract: The H2N2/1957 and H3N2/1968 pandemic influenza viruses emerged via the exchange of genomic RNA segments between human and avian viruses. The avian hemagglutinin (HA) allowed the hybrid viruses to escape preexisting immunity in the human population. Both pandemic viruses further received the PB1 gene segment from the avian parent (Y. Kawaoka, S. Krauss, and R. G. Webster, J Virol 63:4603-4608, 1989), but the biological significance of this observation was not understood. To assess whether the avian-origin PB1 segment provided pandemic viruses with some selective advantage, either on its own or via cooperation with the homologous HA segment, we modeled by reverse genetics the reassortment event that led to the emergence of the H3N2/1968 pandemic virus. Using seasonal H2N2 virus A/California/1/66 (Cal) as a surrogate precursor human virus and pandemic virus A/Hong Kong/1/68 (H3N2) (HK) as a source of avian-derived PB1 and HA gene segments, we generated four reassortant recombinant viruses and compared pairs of viruses which differed solely by the origin of PB1. Replacement of the PB1 segment of Cal by PB1 of HK facilitated viral polymerase activity, replication efficiency in human cells, and contact transmission in guinea pigs. A combination of PB1 and HA segments of HK did not enhance replicative fitness of the reassortant virus compared with the single-gene PB1 reassortant. Our data suggest that the avian PB1 segment of the 1968 pandemic virus served to enhance viral growth and transmissibility, likely by enhancing activity of the viral polymerase complex.
  
  
  OBJECTIVE
  Despite the high impact of influenza pandemics on human health, some mechanisms underlying the emergence of pandemic influenza viruses still are poorly understood. Thus, it was unclear why both H2N2/1957 and H3N2/1968 reassortant pandemic viruses contained, in addition to the avian HA, the PB1 gene segment of the avian parent. Here, we addressed this long-standing question by modeling the emergence of the H3N2/1968 virus from its putative human and avian precursors. We show that the avian PB1 segment increased activity of the viral polymerase and facilitated viral replication. Our results suggest that in addition to the acquisition of antigenically novel HA (i.e., antigenic shift), enhanced viral polymerase activity is required for the emergence of pandemic influenza viruses from their seasonal human precursors.
authors: Institute of Virology, Philipps University, Marburg, Germany.
authors: Isabel
authors: I
authors: Wendel
authors: Institute of Virology, University Medical Center Freiburg, Freiburg, Germany.
authors: Dennis
authors: D
authors: Rubbenstroth
authors: Institute of Virology, Philipps University, Marburg, Germany.
authors: Jennifer
authors: J
authors: Doedt
authors: Institute of Virology, University Medical Center Freiburg, Freiburg, Germany.
authors: Georg
authors: G
authors: Kochs
authors: German Lung Research Center, Justus Liebig University, Giessen, Germany.
authors: Jochen
authors: J
authors: Wilhelm
authors: Institute of Virology, University Medical Center Freiburg, Freiburg, Germany.
authors: Peter
authors: P
authors: Staeheli
authors: Institute of Virology, Philipps University, Marburg, Germany.
authors: Hans-Dieter
authors: HD
authors: Klenk
authors: Institute of Virology, Philipps University, Marburg, Germany matrosov@staff.uni-marburg.de.
authors: Mikhail
authors: M
authors: Matrosovich
mesh_terms: D000818:Animals; D001483:Base Sequence; D001717:Birds; D004196:Disease Outbreaks / Q000266:history*; D004285:Dogs; D006168:Guinea Pigs; D057809:HEK293 Cells; D049673:History, 20th Century; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype; D005585:Influenza in Birds / Q000453:epidemiology* / Q000635:transmission* / Q000821:virology; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D061985:Madin Darby Canine Kidney Cells; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D059386:Reverse Genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014764:Viral Proteins / Q000235:genetics* / Q000502:physiology; D015047:Zoonoses / Q000453:epidemiology* / Q000635:transmission* / Q000821:virology
chemical_list: D014764:Viral Proteins; C077346:influenza virus polymerase basic protein 1
references: J Gen Virol. 2000 May;81(Pt 5):1283-91
references: 10769071
references: Rev Med Virol. 2011 Sep;21(5):262-84
references: 21706672
references: J Infect. 2000 May;40(3):218-28
references: 10908015
references: Arch Virol. 2001 Dec;146(12):2275-89
references: 11811679
references: Virology. 2004 Oct 10;328(1):101-19
references: 15380362
references: J Virol. 1989 Nov;63(11):4603-8
references: 2795713
references: Microbiol Rev. 1992 Mar;56(1):152-79
references: 1579108
references: Emerg Infect Dis. 2006 Jan;12(1):9-14
references: 16494710
references: Virol J. 2006;3:63
references: 16945126
references: Virology. 2007 May 10;361(2):384-90
references: 17207830
references: Arch Virol. 2007;152(6):1139-45
references: 17294090
references: J Virol. 2008 Jan;82(2):596-601
references: 17942553
references: Proc Natl Acad Sci U S A. 2008 Feb 26;105(8):3064-9
references: 18287069
references: PLoS Pathog. 2008 May;4(5):e1000072
references: 18497857
references: Annu Rev Microbiol. 2008;62:403-24
references: 18785841
references: Proc Natl Acad Sci U S A. 2009 Jan 13;106(2):588-92
references: 19114663
references: PLoS One. 2009;4(5):e5658
references: 19462010
references: Proc Natl Acad Sci U S A. 2009 Jul 14;106(28):11709-12
references: 19597152
references: J Virol. 2009 Aug;83(16):8021-31
references: 19494001
references: Virus Res. 2010 Jan;147(1):145-8
references: 19879908
references: Cell Host Microbe. 2010 Jun 25;7(6):440-51
references: 20542248
references: J Virol. 2010 Nov;84(21):11219-26
references: 20739532
references: Rev Med Virol. 2010 Nov;20(6):380-91
references: 20853340
references: Emerg Infect Dis. 2011 Feb;17(2):200-8
references: 21291589
references: Bioessays. 2011 Mar;33(3):180-8
references: 21319184
references: J Antimicrob Chemother. 2011 Mar;66(3):466-70
references: 21172786
references: J Gen Virol. 2011 Jul;92(Pt 7):1645-9
references: 21471324
references: PLoS One. 2011;6(6):e20823
references: 21695145
references: Curr Opin Virol. 2011 Dec;1(6):635-42
references: 22440921
references: J Virol. 2013 Feb;87(3):1912-5
references: 23192869
references: Acta Virol. 2013;57(2):113-22
references: 23600869
references: Virology. 2013 Jun 5;440(2):97-104
references: 23545143
references: Proc Natl Acad Sci U S A. 2013 Oct 1;110(40):E3840-8
references: 24043788
references: Mol Biol Evol. 2013 Dec;30(12):2725-9
references: 24132122
references: Proc Natl Acad Sci U S A. 2014 Jun 3;111(22):8107-12
references: 24778238
references: J Virol. 2014 Aug;88(16):8971-80
references: 24872588
references: Trends Microbiol. 2014 Aug;22(8):446-55
references: 24798745
references: Curr Top Microbiol Immunol. 2014;385:377-401
references: 25007845
references: Proc Natl Acad Sci U S A. 2000 May 23;97(11):6108-13
references: 10801978