The NS1 Gene Contributes to the Virulence of H5N1 Avian Influenza Viruses

Abstract

In the present study, we explored the genetic basis underlying the virulence and host range of two H5N1 influenza viruses in chickens. A/goose/Guangdong/1/96 (GS/GD/1/96) is a highly pathogenic virus for chickens, whereas A/goose/Guangdong/2/96 (GS/GD/2/96) is unable to replicate in chickens. These two H5N1 viruses differ in sequence by only five amino acids mapping to the PA, NP, M1, and NS1 genes. We used reverse genetics to create four single-gene recombinants that contained one of the sequence-differing genes from nonpathogenic GS/GD/2/96 and the remaining seven gene segments from highly pathogenic GS/GD/1/96. We determined that the NS1 gene of GS/GD/2/96 inhibited the replication of GS/GD/1/96 in chickens, while the substitution of the PA, NP, or M gene did not change the highly pathogenic properties of GS/GD/1/96. Conversely, of the recombinant viruses generated in the GS/GD/2/96 background, only the virus containing the NS1 gene of GS/GD/1/96 was able to replicate and cause disease and death in chickens. The single-amino-acid difference in the sequence of these two NS1 genes resides at position 149. We demonstrate that a recombinant virus expressing the GS/GD/1/96 NS1 protein with Ala149 is able to antagonize the induction of interferon protein levels in chicken embryo fibroblasts (CEFs), but a recombinant virus carrying a Val149 substitution is not capable of the same effect. These results indicate that the NS1 gene is critical for the pathogenicity of avian influenza virus in chickens and that the amino acid residue Ala149 correlates with the ability of these viruses to antagonize interferon induction in CEFs.

Prevalence of the C-terminal truncations of NS1 in avian influenza A viruses and effect on virulence and replication of a highly pathogenic H7N1 virus in chickens

“…Contribution of the NS1 to the virulence of an H5N1 virus 4 as well as to the virulence of a historic HPAIV H7N1 with NS gene segment from HPAIV H5N1 24 has been described. Our findings indicate that NS1 variation did not play a significant role in virulence of the Italian H7N1 viruses in chickens and major virulence markers reside outside the NS1 gene.…”

“…Although virulence of HPAIV is a complex multigenic trait in nature, 2,3 in some H5N1 and H7N9 viruses mutations in the gene encoding the non-structural protein 1 (NS1) contribute to virus virulence in chickens. [4][5][6] NS1 is a multifunctional protein encoded by the smallest segment 8 of AIV encompassing typically 890 nucleotides. In birds, NS1 can appear in 2 distinct alleles, where allele A is more common than allele B.…”

Avian Influenza Virus A/HK/483/97(H5N1) NS1 Protein Induces Apoptosis in Human Airway Epithelial Cells

“…It has also been shown previously that NS1 proteins encoded by different strains may have different abilities to induce apoptosis (3,30). Furthermore, there are reports showing that the H5N1 NS1 gene can circumvent the host antiviral cytokine responses and contribute to the virulence of H5N1 avian influenza viruses (25,43).…”

Loss of stress response as a consequence of viral infection: implications for disease and therapy

“…Additionally, the oncolytic effect of NDV is enhanced by influenza protein NS1 (Mansour et al 2011). The NS1 protein of the highly pathogenic avian H5N1 influenza virus is currently believed to be responsible for the increased virulence of the strain (Li et al 2006). Relevantly, NS1 inhibits cleavage of Hsp70 premRNAs, blocking the formation of mature mRNAs (Shimizu et al 1999).…”