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Modulation of Influenza A virus NS1 expression reveals prioritization of host response antagonism at single-cell resolution

ABSTRACT: Influenza A virus (IAV) is an important human respiratory pathogen that causes significant seasonal epidemics and potential devastating pandemics. As part of its life cycle, IAV encodes the multifunctional protein NS1, that, among many roles, prevents immune detection and limits interferon (IFN) production. As different host immune pathways exert different selective pressures against IAV as replication progresses, we expect a prioritization in the host immune antagonism by NS1. In this work, we profiled bulk transcriptomic differences in a primary bronchial epithelial cell model facing IAV infections at distinct NS1 levels. We further demonstrated that the intracellular NS1 levels in-part shapes the host response heterogeneity at single cell level. We found that modulation of NS1 levels reveal a ranking in its inhibitory roles: modest NS1 expression is sufficient to inhibit immune detection, and thus the expression of pro-inflammatory cytokines (including IFNs), but higher levels are required to inhibit IFN signaling and ISG expression. Lastly, inhibition of chaperones related to the unfolded protein response requires the highest amount of NS1, often associated with later stages of viral replication. This work demystifies some of the multiple functions ascribed to IAV NS1, highlighting the prioritization of NS1 in antagonizing the different pathways involved in the host response to IAV infection.

ORGANISM(S): Homo sapiens

PROVIDER: GSE243730 | GEO | 2023/09/25

REPOSITORIES: GEO

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Project description:Gene transcription effects of mutations in the infuenza virus A/Hong Kong/1/1968(H3N2) nonstructural 1 NS1 gene in infected human A549 (lung epithilium) cells Influenza A/Hong Kong/156/1997(H5N1) virus NS1 gene mutations F103L and M106I both increase IFN antagonism, virulence and cytoplasmic localization but differ in binding to RIG-I and CPSF30 (manuscript submitted to Virology Journal). Human cells were infected with influenza viruses mutants with specific gain of function mutations in the NS1 gene in order to assess the affects of each mutation on host gene expression. Human (A549) and mouse (M1) cells were infected at a multiplicity of infection of 2 (infectious viruses/cell) and incubated for 8 hr before collection of total RNA and microarray anlaysis using the Affymetrix platforms. Samples were compared in triplicate to mock PBS infected (uninfected) cells to detecte dysregulated genes for A/HK/1/1968(H3N2) wt, and the following NS1 gene mutants: F103L, M106I, M106V, and F103L + M106I. Background: The genetic basis for avian to mammalian host switching in influenza A virus is largely unknown. The human A/HK/156/1997(H5N1) virus that transmitted from poultry possesses NS1 gene mutations F103L + M106I that are virulence determinants in the mouse model of pneumonia; however their individual roles have not been determined. The emergent A/Shanghai/1/2013(H7N9)-like viruses also possess these mutations which may contribute to their virulence and ability to switch species. Methods: NS1 mutant viruses were constructed by reverse genetics and site directed mutagenesis on human and mouse-adapted backbones. Mouse infections assessed virulence, virus yield, tissue infection, and IFN induction. NS1 protein proprieties were assessed for subcellular distribution, IFN antagonism (mouse and human), CPSF30 and RIG-I domain binding, effect on host gene transcription (microarray); and the natural prevalence of 103L and 106I mutants was assessed. Results: Each of the F103L and M106I mutations contributes additively to virulence to reduce the lethal dose by >800 and >3,200 fold respectively by mediating alveolar tissue infection with >100 fold increased infectious yields. The 106I NS1 mutant lost CPSF binding but the 103L mutant maintained binding that correlated with an increased general decrease in host gene expression in human but not mouse cells. Each mutation positively modulated the inhibition of IFN induction in mouse cells and activation of the IFN-M-NM-2 promoter in human cells but not in combination in human cells indicating negative epistasis. Each of the F103L and M106I mutations restored a defect in cytoplasmic localization of H5N1 NS1 in mouse cells. Human H1N1 and H3N2 NS1 proteins bound to the CARD, helicase and RD RIG-I domains, whereas the H5N1 NS1 with the same consensus 103F and 106M mutations did not bind these domains, which was partially or totally restored by the F103L or M106I mutations respectively. Conclusions: The F103L and M106I mutations in the H5N1 NS1 protein each increased IFN antagonism and mediated interstitial pneumonia in mice that was associated with increased cytoplasmic localization and altered host factor binding. These mutations may contribute to the ability of previous HPAI H5N1 and recent LPAI H7N9 viruses to switch hosts and cause severe disease in mammals. Triplicate biological replicates of mock PBS treated (uninfected) cells to detecte dysregulated genes for A/HK/1/1968(H3N2) wt, and the following NS1 gene mutants: F103L, M106I, M106V, and F103L + M106I. Cells were infected at a multiplicty of infection of 2 and cells were incubated for 8 hr at 37 C for 8 hrs before RNA extraction and analysis of 3 biological replicates relative to mock PBS infected cells.

Project description:The NS1 protein of influenza A virus (IAV) is a multifunctional virulence factor. Mouse adaptive mutations in the NS1 protein of the human isolate A/Hong Kong/1/1968(H3N2) (HK) have been previously reported to increase virulence, viral fitness, and interferon antagonism, but differ in binding to post-transcriptional processing factor CPSF30. Because nuclear trafficking is a major genetic determinant of influenza virus host adaptation, we assessed subcellular localization and host gene expression of NS1 adaptive mutations. Recombinant HK viruses with adaptive mutations in the NS1 gene were assessed for NS1 protein subcellular localization in mouse and human cells using confocal microscopy and cellular fractionation. HK-wt virus NS1 partitioned equivalently between the cytoplasm and nucleus in human cells but was defective in cytoplasmic localization in mouse cells. The adaptive mutations either increased the proportion or abundance of NS1 in the cytoplasm, and/or the nucleus. NS1 mutations that increased cytoplasmic distribution identified a putative second nuclear export signal (NES) spanning aa positions 98-106 LSEDWFMLM, (mutation sites in bold); with the strongest effect seen for mutation M106I. The putative NES in the NS3 protein was associated with cytoplasmic localization. The host gene expression profile of the adaptive mutants was determined by microarray analysis of infected mouse cells to show either high or low gene regulation (HGR or LGR) phenotypes that mapped to the amino-terminal and the carboxy-terminal regions respectively. The HGR and LGR mutations were predominantly down regulating versus up regulating respectively. The greatest effect on host gene expression in the HGR group correlated with the ability of the NS1 protein to bind CPSF30. To our knowledge this is the first report of roles of adaptive NS1 mutations that affect intracellular localization and regulation of host gene expression. biological triplicates of mock infected mouse M1 cells; cells infected with A/HK/1/1968(H3N2) wt and NS1 mtuatn with mutaions, D2N, V23A, L98S, L98S + M106I, F103L, M106V, M106V + M124I, D125G, V180A, V226I, M106I, and R227K. Cells were infected at a multiplicty of infection of 2 and cels were incubated for 8 hr at 37 C for 8 hrs before RNA extraction and analysis relative to mock PBS infected cells.

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Modulation of Influenza A virus NS1 expression reveals prioritization of host response antagonism at single-cell resolution

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