Inefficient control of host gene expression by the 2009 pandemic H1N1 influenza A virus NS1 protein.
In 2009, a novel swine-origin H1N1 influenza A virus emerged. Here, we characterize the multifunctional NS1 protein of this human pandemic virus in order to understand factors that may contribute to replication efficiency or pathogenicity. Although the 2009 H1N1 virus NS1 protein (2009/NS1) is an effective interferon antagonist, we found that this NS1 (unlike those of previous human-adapted influenza A viruses) is unable to block general host gene expression in human or swine cells. This property could be restored in 2009/NS1 by replacing R108, E125, and G189 with residues corresponding to human virus consensus. Mechanistically, these previously undescribed mutations acted by increasing binding of 2009/NS1 to the cellular pre-mRNA processing protein CPSF30. A recombinant 2009 H1N1 influenza A virus (A/California/04/09) expressing NS1 with these gain-of-function substitutions was more efficient than the wild type at antagonizing host innate immune responses in primary human epithelial cells. However, such mutations had no significant effect on virus replication in either human or swine tissue culture substrates. Surprisingly, in a mouse model of pathogenicity, the mutant virus appeared to cause less morbidity, and was cleared faster, than the wild type. The mutant virus also demonstrated reduced titers in the upper respiratory tracts of ferrets; however, contact and aerosol transmissibility of the virus was unaffected. Our data highlight a potential human adaptation of NS1 that seems absent in "classically derived" swine-origin influenza A viruses, including the 2009 H1N1 virus. We discuss the impact that a natural future gain of this NS1 function may have on the new pandemic virus in humans.
Hale
Benjamin G
BG
Department of Microbiology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
Steel
John
J
Medina
Rafael A
RA
Manicassamy
Balaji
B
Ye
Jianqiang
J
Hickman
Danielle
D
Hai
Rong
R
Schmolke
Mirco
M
Lowen
Anice C
AC
Perez
Daniel R
DR
García-Sastre
Adolfo
A
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004196:Disease Outbreaks; D005289:Ferrets; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007113:Immunity, Innate; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000821:virology*; D007372:Interferons / Q000276:immunology; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000276:immunology / Q000821:virology*; D016415:Sequence Alignment; D013552:Swine; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000276:immunology; D014779:Virus Replication
C085820:INS1 protein, influenza virus; D017361:Viral Nonstructural Proteins; D007372:Interferons
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