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The NS1 protein of a human influenza virus inhibits type I interferon production and the induction of antiviral responses in primary human dendritic and respiratory epithelial cells.

ABSTRACT: The NS1 protein of the influenza A virus is a potent virulence factor that inhibits type I interferon (IFN) synthesis, allowing the virus to overcome host defenses and replicate efficiently. However, limited studies have been conducted on NS1 function using human virus strains and primary human cells. We used NS1 truncated mutant influenza viruses derived from the human isolate influenza A/TX/91 (TX WT, where WT is wild type) to study the functions of NS1 in infected primary cells. Infection of primary differentiated human tracheo-bronchial epithelial cells with an NS1 truncated mutant demonstrated limited viral replication and enhanced type I IFN induction. Additionally, human dendritic cells (DCs) infected with human NS1 mutant viruses showed higher levels of activation and stimulated naïve T-cells better than TX WT virus-infected DCs. We also compared infections of DCs with TX WT and our previously characterized laboratory strain A/PR/8/34 (PR8) and its NS1 knockout strain, deltaNS1. TX WT-infected DCs displayed higher viral replication than PR8 but had decreased antiviral gene expression at late time points and reduced naïve T-cell stimulation compared to PR8 infections, suggesting an augmented inhibition of IFN production and human DC activation. Our findings show that human-derived influenza A viruses have a high capacity to inhibit the antiviral state in a human system, and here we have evaluated the possible mechanism of this inhibition. Lastly, C-terminal truncations in the NS1 protein of human influenza virus are sufficient to make the virus attenuated and more immunogenic, supporting its use as a live attenuated influenza vaccine in humans.

SUBMITTER: Haye K

PROVIDER: S-EPMC2698524 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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The NS1 protein of a human influenza virus inhibits type I interferon production and the induction of antiviral responses in primary human dendritic and respiratory epithelial cells.

Haye Kester K Burmakina Svetlana S Moran Thomas T García-Sastre Adolfo A Fernandez-Sesma Ana A

Journal of virology 20090429 13

The NS1 protein of the influenza A virus is a potent virulence factor that inhibits type I interferon (IFN) synthesis, allowing the virus to overcome host defenses and replicate efficiently. However, limited studies have been conducted on NS1 function using human virus strains and primary human cells. We used NS1 truncated mutant influenza viruses derived from the human isolate influenza A/TX/91 (TX WT, where WT is wild type) to study the functions of NS1 in infected primary cells. Infection of ...[more]

PMID: 19403682

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Project description:The nonstructural protein 1 (NS1) of influenza A viruses is an important virulence factor that controls host cell immune responses. In human cells, NS1 proteins inhibit the induction of type I interferon by several mechanisms, including potentially, by preventing the activation of the retinoic acid-inducible gene I (RIG-I) receptor by the ubiquitin ligase tripartite motif-containing protein 25 (TRIM25). It is unclear whether the inhibition of human TRIM25 is a universal function of all influenza A NS1 proteins or is strain dependent. It is also unclear if NS1 proteins similarly target the TRIM25 of mallard ducks, a natural reservoir host of avian influenza viruses with a long coevolutionary history and unique disease dynamics. To answer these questions, we compared the ability of five different NS1 proteins to interact with human and duck TRIM25 using coimmunoprecipitation and microscopy and assessed the consequence of this on RIG-I ubiquitination and signaling in both species. We show that NS1 proteins from low-pathogenic and highly pathogenic avian influenza viruses potently inhibit RIG-I ubiquitination and reduce interferon promoter activity and interferon-beta protein secretion in transfected human cells, while the NS1 of the mouse-adapted PR8 strain does not. However, all the NS1 proteins, when cloned into recombinant viruses, suppress interferon in infected alveolar cells. In contrast, avian NS1 proteins do not suppress duck RIG-I ubiquitination and interferon promoter activity, despite interacting with duck TRIM25. IMPORTANCE Influenza A viruses are a major cause of human and animal disease. Periodically, avian influenza viruses from wild waterfowl, such as ducks, pass through intermediate agricultural hosts and emerge into the human population as zoonotic diseases with high mortality rates and epidemic potential. Because of their coevolution with influenza A viruses, ducks are uniquely resistant to influenza disease compared to other birds, animals, and humans. Here, we investigate a mechanism of influenza A virus interference in an important antiviral signaling pathway that is orthologous in humans and ducks. We show that NS1 proteins from four avian influenza strains can block the coactivation and signaling of the human RIG-I antiviral receptor, while none block the coactivation and signaling of duck RIG-I. Understanding host-pathogen dynamics in the natural reservoir will contribute to our understanding of viral disease mechanisms, viral evolution, and the pressures that drive it, which benefits global surveillance and outbreak prevention.

Project description:Influenza NS1 protein is the main viral protein counteracting host innate immune responses, allowing the virus to efficiently replicate in interferon (IFN)-competent systems. In this study, we analyzed NS1 protein variability within influenza A (IAV) H3N2 viruses infecting humans during the 2012-2013 season. We also evaluated the impact of the mutations on the ability of NS1 proteins to inhibit host innate immune responses and general gene expression. Surprisingly, a previously unidentified mutation in the double-stranded RNA (dsRNA)-binding domain (I64T) decreased NS1-mediated general inhibition of host protein synthesis by decreasing its interaction with cleavage and polyadenylation specificity factor 30 (CPSF30), leading to increased innate immune responses after viral infection. Notably, a recombinant A/Puerto Rico/8/34 H1N1 virus encoding the H3N2 NS1-T64 protein was highly attenuated in mice, most likely because of its ability to induce higher antiviral IFN responses at early times after infection and because this virus is highly sensitive to the IFN-induced antiviral state. Interestingly, using peripheral blood mononuclear cells (PBMCs) collected at the acute visit (2 to 3 days after infection), we show that the subject infected with the NS1-T64 attenuated virus has diminished responses to interferon and to interferon induction, suggesting why this subject could be infected with this highly IFN-sensitive virus. These data demonstrate the importance of influenza virus surveillance in identifying new mutations in the NS1 protein, affecting its ability to inhibit innate immune responses and, as a consequence, the pathogenicity of the virus. IMPORTANCE:Influenza A and B viruses are one of the most common causes of respiratory infections in humans, causing 1 billion infections and between 300,000 and 500,000 deaths annually. Influenza virus surveillance to identify new mutations in the NS1 protein affecting innate immune responses and, as a consequence, the pathogenicity of the circulating viruses is highly relevant. Here, we analyzed amino acid variability in the NS1 proteins from human seasonal viruses and the effect of the mutations in innate immune responses and virus pathogenesis. A previously unidentified mutation in the dsRNA-binding domain decreased NS1-mediated general inhibition of host protein synthesis and the interaction of the protein with CPSF30. This mutation led to increased innate immune responses after viral infection, augmented IFN sensitivity, and virus attenuation in mice. Interestingly, using PBMCs, the subject infected with the virus encoding the attenuating mutation induced decreased antiviral responses, suggesting why this subject could be infected with this virus.

Dataset Information

The NS1 protein of a human influenza virus inhibits type I interferon production and the induction of antiviral responses in primary human dendritic and respiratory epithelial cells.

Publications

The NS1 protein of a human influenza virus inhibits type I interferon production and the induction of antiviral responses in primary human dendritic and respiratory epithelial cells.

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