Amino acid substitutions V63I or A37S/I61T/V63I/V100A in the PA N-terminal domain increase the virulence of H7N7 influenza A virus

Abstract

The PA N-terminal domain (PA-Nter) is essential for viral transcription and replication. Here we identified PA-Nter substitutions A37S, I61T, V63I and V100A in recently emerged avian influenza A viruses (IAVs) with potential effect on virus pathogenicity and/or host adaptation. We introduced the identified PA-Nter substitutions into avian H7N7 IAV by reverse genetics. Our results showed that single substitution V63I and combined substitutions, I61T/V63I and A37S/I61T/V63I/V100A (Mfour), significantly increased virus growth capacity in mammalian cells. Meanwhile, these substitutions conferred higher virus transcription/replication capacity by producing more mRNA, cRNA and vRNA. Consistently, the polymerase activity and the endonuclease activity were enhanced by these PA-Nter substitutions. Notably, substitutions V63I and Mfour strongly increased virus replication and virulence in mice. Collectively, our findings demonstrated that the PA-Nter substitutions V63I and Mfour enhanced IAV pathogenicity through modification of the polymerase activity and the endonuclease activity, which added to the evolving knowledge of IAV virulence determinants.

HA stabilization promotes replication and transmission of swine H1N1 gamma influenza viruses in ferrets

“…All culturing media were supplemented with 10% HyClone standard fetal bovine serum (FBS, Life Technologies) and 1% penicillin/streptomycin (P/S, Thermo Fisher Scientific). All cells were grown at 37°C with 5% CO 2 ( Hu et al, 2016 ; Hu et al, 2017a ). Cell lines were authenticated by short-tandem repeat profiling and tested free of mycoplasma contamination.…”

“…Fifty-five H1N1 influenza A viruses (IAVs) (2009–2016) were propagated in MDCK cells less than three passages with 1 μg/ml tosylsulfonyl phenylalanyl chloromethyl ketone (TPCK)-treated trypsin, as described previously ( Hu et al, 2016 ). The four viruses used in ferret experiments (G15, P4, P19, and P24) were recovered from swine and then passaged two times in MDCK cells before the experiments reported here.…”

“…The four viruses used in ferret experiments (G15, P4, P19, and P24) were recovered from swine and then passaged two times in MDCK cells before the experiments reported here. Recombinant viruses used in this study were generated using reverse genetics using the HA and NA genes from the indicated viruses along with internal genes from A/TN/2009, and were propagated in MDCK cells less than three passages ( Hu et al, 2016 ; Hu et al, 2017b ; Russier et al, 2016 ).…”

Full-length genome sequences of the first H9N2 avian influenza viruses isolated in the Northeast of Algeria

“…Algerian strains harbored three PA substitutions V100I, K312R and S409N, associated with adaptation to mammals [ 14 , 28 , 82 ] (Table 5 ). The unique aa substitutions such as V63I, T97I, K142N/E, S421I and R443K, which increase AIV polymerase activity, replication in mammalian cells and virus virulence in mice, were however not detected [ 61 , 83 – 85 ]. Among the aa associated with increased virulence, PA protein of current Algerian strains shared three, 127 V, 550 L and 672 L, different molecular markers of virulence [ 14 , 28 , 59 ].…”

Risk of Environmental Exposure to H7N9 Influenza Virus via Airborne and Surface Routes in a Live Poultry Market in Hebei, China

“…Recent studies found that the H7N9 AIV has adapted to mammals through many mutations. Sha et al reported that mutations in PB2 (E627K), NA (R294K) and PA (V100A) were significantly correlated with increased mortality, while other mutations in HA (N276D) and PB2 (N559T) were distinctly correlated with mild cases (Gao et al, 2009;Wu et al, 2013;Li et al, 2014;Hu et al, 2016;Sha et al, 2016). Overall, the transmissibility of H7N9 to mammals and the lack of preexisting immunity to H7N9 in humans suggested that H7N9 viruses might pose a potential pandemic threat to humans through further mammalian adaptation.…”