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Russell AB, Elshina E, Kowalsky JR, Te Velthuis AJW, Bloom JD. Single-Cell Virus Sequencing of Influenza Infections That Trigger Innate Immunity. J Virol 2019; 93:e00500-19. [PMID: 31068418 PMCID: PMC6600203 DOI: 10.1128/jvi.00500-19] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2019] [Accepted: 04/29/2019] [Indexed: 12/21/2022] Open
Abstract
Influenza virus-infected cells vary widely in their expression of viral genes and only occasionally activate innate immunity. Here, we develop a new method to assess how the genetic variation in viral populations contributes to this heterogeneity. We do this by determining the transcriptome and full-length sequences of all viral genes in single cells infected with a nominally "pure" stock of influenza virus. Most cells are infected by virions with defects, some of which increase the frequency of innate-immune activation. These immunostimulatory defects are diverse and include mutations that perturb the function of the viral polymerase protein PB1, large internal deletions in viral genes, and failure to express the virus's interferon antagonist NS1. However, immune activation remains stochastic in cells infected by virions with these defects and occasionally is triggered even by virions that express unmutated copies of all genes. Our work shows that the diverse spectrum of defects in influenza virus populations contributes to-but does not completely explain-the heterogeneity in viral gene expression and immune activation in single infected cells.IMPORTANCE Because influenza virus has a high mutation rate, many cells are infected by mutated virions. But so far, it has been impossible to fully characterize the sequence of the virion infecting any given cell, since conventional techniques such as flow cytometry and single-cell transcriptome sequencing (scRNA-seq) only detect if a protein or transcript is present, not its sequence. Here we develop a new approach that uses long-read PacBio sequencing to determine the sequences of virions infecting single cells. We show that viral genetic variation explains some but not all of the cell-to-cell variability in viral gene expression and innate immune induction. Overall, our study provides the first complete picture of how viral mutations affect the course of infection in single cells.
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Affiliation(s)
- Alistair B Russell
- Basic Sciences and Computational Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Elizaveta Elshina
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Jacob R Kowalsky
- Basic Sciences and Computational Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Aartjan J W Te Velthuis
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Jesse D Bloom
- Basic Sciences and Computational Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
- Department of Genome Sciences, University of Washington, Seattle, Washington, USA
- Howard Hughes Medical Institute, Seattle, Washington, USA
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PA-X antagonises MAVS-dependent accumulation of early type I interferon messenger RNAs during influenza A virus infection. Sci Rep 2019; 9:7216. [PMID: 31076606 PMCID: PMC6510759 DOI: 10.1038/s41598-019-43632-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 04/18/2019] [Indexed: 12/21/2022] Open
Abstract
The sensing of viral nucleic acids by the innate immune system activates a potent antiviral response in the infected cell, a key component of which is the expression of genes encoding type I interferons (IFNs). Many viruses counteract this response by blocking the activation of host nucleic acid sensors. The evolutionarily conserved influenza A virus (IAV) protein PA-X has been implicated in suppressing the host response to infection, including the expression of type I IFNs. Here, we characterise this further using a PA-X-deficient virus of the mouse-adapted PR8 strain to study activation of the innate immune response in a mouse model of the early response to viral infection. We show that levels of Ifna4 and Ifnb1 mRNAs in the lungs of infected mice were elevated in the absence of PA-X and that this was completely dependent on MAVS. This therefore suggests a role for PA-X in preventing the accumulation of early type I IFN mRNAs in the lung during IAV infection.
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Oishi K, Yamayoshi S, Kawaoka Y. Identification of Amino Acid Residues in Influenza A Virus PA-X That Contribute to Enhanced Shutoff Activity. Front Microbiol 2019; 10:432. [PMID: 30894843 PMCID: PMC6414799 DOI: 10.3389/fmicb.2019.00432] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/19/2019] [Indexed: 01/07/2023] Open
Abstract
The influenza virus protein PA-X modulates the host immune responses and viral pathogenicity through suppression of host protein expression. The endonuclease active site in the N-terminal region, the basic amino acid cluster in the C-terminal PA-X-specific region, and N-terminal acetylation of PA-X by NatB are important for the shutoff activity of PA-X. Here, we focused on the shutoff activity of PA-X derived from the A/California/04/2009 and A/WSN/33 viruses because these two PA-X proteins differ in their shutoff activity. Mutagenesis analysis revealed that proline and serine at positions 28 and 65, respectively, play a central role in this difference. Furthermore, we found that P28 and S65 also affect the shutoff activity of PA-X derived from other influenza virus subtypes. These data demonstrate that P28 and S65 contribute to enhanced shutoff activity of PA-X.
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Affiliation(s)
- Kohei Oishi
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan
| | - Seiya Yamayoshi
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan
| | - Yoshihiro Kawaoka
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin–Madison, Madison, WI, United States
- Department of Special Pathogens, International Research Center for Infectious Diseases, Institute of Medical Science, University of Tokyo, Tokyo, Japan
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54
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Mutation of Influenza A Virus PA-X Decreases Pathogenicity in Chicken Embryos and Can Increase the Yield of Reassortant Candidate Vaccine Viruses. J Virol 2019; 93:JVI.01551-18. [PMID: 30381488 PMCID: PMC6321911 DOI: 10.1128/jvi.01551-18] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/25/2018] [Indexed: 01/08/2023] Open
Abstract
Influenza A virus is a widespread pathogen that affects both humans and a variety of animal species, causing regular epidemics and sporadic pandemics, with major public health and economic consequences. A better understanding of virus biology is therefore important. The primary control measure is vaccination, which for humans mostly relies on antigens produced in eggs from PR8-based viruses bearing the glycoprotein genes of interest. However, not all reassortants replicate well enough to supply sufficient virus antigen for demand. The significance of our research lies in identifying that mutation of the PA-X gene in the PR8 strain of virus can improve antigen yield, potentially by decreasing the pathogenicity of the virus in embryonated eggs. The PA-X protein of influenza A virus has roles in host cell shutoff and viral pathogenesis. While most strains are predicted to encode PA-X, strain-dependent variations in activity have been noted. We found that PA-X protein from the A/PR/8/34 (PR8) strain had significantly lower repressive activity against cellular gene expression than PA-X proteins from the avian strains A/turkey/England/50-92/91 (H5N1) (T/E) and A/chicken/Rostock/34 (H7N1). Loss of normal PA-X expression, either by mutation of the frameshift site or by truncating the X open reading frame (ORF), had little effect on the infectious virus titer of PR8 or PR8 7:1 reassortants with T/E segment 3 grown in embryonated hens’ eggs. However, in both virus backgrounds, mutation of PA-X led to decreased embryo mortality and lower overall pathology, effects that were more pronounced in the PR8 strain than in the T/E reassortant, despite the low shutoff activity of the PR8 PA-X. Purified PA-X mutant virus particles displayed an increased ratio of hemagglutinin (HA) to nucleoprotein (NP) and M1 compared to values for their wild-type (WT) counterparts, suggesting altered virion composition. When the PA-X gene was mutated in the background of poorly growing PR8 6:2 vaccine reassortant analogues containing the HA and neuraminidase (NA) segments from H1N1 2009 pandemic viruses or from an avian H7N3 strain, HA yield increased up to 2-fold. This suggests that the PR8 PA-X protein may harbor a function unrelated to host cell shutoff and that disruption of the PA-X gene has the potential to improve the HA yield of vaccine viruses. IMPORTANCE Influenza A virus is a widespread pathogen that affects both humans and a variety of animal species, causing regular epidemics and sporadic pandemics, with major public health and economic consequences. A better understanding of virus biology is therefore important. The primary control measure is vaccination, which for humans mostly relies on antigens produced in eggs from PR8-based viruses bearing the glycoprotein genes of interest. However, not all reassortants replicate well enough to supply sufficient virus antigen for demand. The significance of our research lies in identifying that mutation of the PA-X gene in the PR8 strain of virus can improve antigen yield, potentially by decreasing the pathogenicity of the virus in embryonated eggs.
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55
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Nogales A, Martinez-Sobrido L, Topham DJ, DeDiego ML. Modulation of Innate Immune Responses by the Influenza A NS1 and PA-X Proteins. Viruses 2018; 10:v10120708. [PMID: 30545063 PMCID: PMC6315843 DOI: 10.3390/v10120708] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Revised: 12/06/2018] [Accepted: 12/08/2018] [Indexed: 12/14/2022] Open
Abstract
Influenza A viruses (IAV) can infect a broad range of animal hosts, including humans. In humans, IAV causes seasonal annual epidemics and occasional pandemics, representing a serious public health and economic problem, which is most effectively prevented through vaccination. The defense mechanisms that the host innate immune system provides restrict IAV replication and infection. Consequently, to successfully replicate in interferon (IFN)-competent systems, IAV has to counteract host antiviral activities, mainly the production of IFN and the activities of IFN-induced host proteins that inhibit virus replication. The IAV multifunctional proteins PA-X and NS1 are virulence factors that modulate the innate immune response and virus pathogenicity. Notably, these two viral proteins have synergistic effects in the inhibition of host protein synthesis in infected cells, although using different mechanisms of action. Moreover, the control of innate immune responses by the IAV NS1 and PA-X proteins is subject to a balance that can determine virus pathogenesis and fitness, and recent evidence shows co-evolution of these proteins in seasonal viruses, indicating that they should be monitored for enhanced virulence. Importantly, inhibition of host gene expression by the influenza NS1 and/or PA-X proteins could be explored to develop improved live-attenuated influenza vaccines (LAIV) by modulating the ability of the virus to counteract antiviral host responses. Likewise, both viral proteins represent a reasonable target for the development of new antivirals for the control of IAV infections. In this review, we summarize the role of IAV NS1 and PA-X in controlling the antiviral response during viral infection.
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Affiliation(s)
- Aitor Nogales
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
- Centro de Investigación en Sanidad Animal (CISA)-INIA, Valdeolmos, 28130 Madrid, Spain.
| | - Luis Martinez-Sobrido
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
| | - David J Topham
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
- David H. Smith Center for Vaccine Biology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
| | - Marta L DeDiego
- Department of Microbiology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
- David H. Smith Center for Vaccine Biology and Immunology, University of Rochester, Rochester, New York, NY 14642, USA.
- Department of Molecular and Cell Biology, Centro Nacional de Biotecnología (CNB-CSIC), Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain.
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56
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Specificity and functional interplay between influenza virus PA-X and NS1 shutoff activity. PLoS Pathog 2018; 14:e1007465. [PMID: 30496325 PMCID: PMC6289448 DOI: 10.1371/journal.ppat.1007465] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 12/11/2018] [Accepted: 11/12/2018] [Indexed: 12/20/2022] Open
Abstract
Influenza A viruses modulate host antiviral responses to promote viral growth and pathogenicity. Through viral PA-X and NS1 proteins, the virus is capable of suppressing host protein synthesis, termed "host shutoff." Although both proteins are known to induce general shutoff, specificity of target genes and their functional interplay in mediating host shutoff are not fully elucidated. In this study, we generated four recombinant influenza A/California/04/2009 (pH1N1) viruses containing mutations affecting the expression of active PA-X and NS1. We analyzed viral growth, general shutoff activity, specificity of mRNA targets, and viral gene expressions. Our results showed that PA-X was the major contributor in reducing general host protein expression in the virus-infected cells. Intriguingly, our transcriptomic analysis from infected human airway A549 cells indicate that shutoff-active NS1 specifically targeted host mRNAs related to interferon (IFN) signaling pathways and cytokine release. Specificity of target mRNAs was less evident in PA-X, although it preferentially degraded genes associated with cellular protein metabolism and protein repair. Interestingly, in the presence of shutoff-active NS1, PA-X also degraded viral mRNAs, especially NS segments. The virus expressing shutoff-active NS1 with reduced amount of PA-X expression most efficiently suppressed antiviral and innate immune responses in human cells, indicating that influenza virus needs to optimize the contribution of these two shutoff proteins to circumvent host responses for its optimum growth.
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57
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The Endonucleolytic RNA Cleavage Function of nsp1 of Middle East Respiratory Syndrome Coronavirus Promotes the Production of Infectious Virus Particles in Specific Human Cell Lines. J Virol 2018; 92:JVI.01157-18. [PMID: 30111568 DOI: 10.1128/jvi.01157-18] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Accepted: 08/11/2018] [Indexed: 01/10/2023] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) nsp1 suppresses host gene expression in expressed cells by inhibiting translation and inducing endonucleolytic cleavage of host mRNAs, the latter of which leads to mRNA decay. We examined the biological functions of nsp1 in infected cells and its role in virus replication by using wild-type MERS-CoV and two mutant viruses with specific mutations in the nsp1; one mutant lacked both biological functions, while the other lacked the RNA cleavage function but retained the translation inhibition function. In Vero cells, all three viruses replicated efficiently with similar replication kinetics, while wild-type virus induced stronger host translational suppression and host mRNA degradation than the mutants, demonstrating that nsp1 suppressed host gene expression in infected cells. The mutant viruses replicated less efficiently than wild-type virus in Huh-7 cells, HeLa-derived cells, and 293-derived cells, the latter two of which stably expressed a viral receptor protein. In 293-derived cells, the three viruses accumulated similar levels of nsp1 and major viral structural proteins and did not induce IFN-β and IFN-λ mRNAs; however, both mutants were unable to generate intracellular virus particles as efficiently as wild-type virus, leading to inefficient production of infectious viruses. These data strongly suggest that the endonucleolytic RNA cleavage function of the nsp1 promoted MERS-CoV assembly and/or budding in a 293-derived cell line. MERS-CoV nsp1 represents the first CoV gene 1 protein that plays an important role in virus assembly/budding and is the first identified viral protein whose RNA cleavage-inducing function promotes virus assembly/budding.IMPORTANCE MERS-CoV represents a high public health threat. Because CoV nsp1 is a major viral virulence factor, uncovering the biological functions of MERS-CoV nsp1 could contribute to our understanding of MERS-CoV pathogenicity and spur development of medical countermeasures. Expressed MERS-CoV nsp1 suppresses host gene expression, but its biological functions for virus replication and effects on host gene expression in infected cells are largely unexplored. We found that nsp1 suppressed host gene expression in infected cells. Our data further demonstrated that nsp1, which was not detected in virus particles, promoted virus assembly or budding in a 293-derived cell line, leading to efficient virus replication. These data suggest that nsp1 plays an important role in MERS-CoV replication and possibly affects virus-induced diseases by promoting virus particle production in infected hosts. Our data, which uncovered an unexpected novel biological function of nsp1 in virus replication, contribute to further understanding of the MERS-CoV replication strategies.
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58
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Narkpuk J, Jongkaewwattana A, Teeravechyan S. The avian influenza virus PA segment mediates strain-specific antagonism of BST-2/tetherin. Virology 2018; 525:161-169. [PMID: 30290311 PMCID: PMC7172379 DOI: 10.1016/j.virol.2018.09.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 09/19/2018] [Accepted: 09/21/2018] [Indexed: 12/26/2022]
Abstract
BST-2 is an antiviral protein described as a powerful cross-species transmission barrier for simian immunodeficiency viruses. Influenza viruses appear to interact with BST-2, raising the possibility that BST-2 may be a barrier for cross-species transmission. An MDCK-based cell line expressing human BST-2 was generated to study human-derived A/Puerto Rico/8/36 (H1N1; PR8) as well as two low pathogenic avian influenza viruses (subtypes H4N6 and H6N1). The H4N6 and H6N1 viruses were less affected by BST-2 expression than PR8, due to their ability to decrease BST-2 levels, a function localized to the PA segment of both avian viruses. Experiments with PA-mutant and -chimeric viruses confirmed that the avian PA segment conferred BST-2 downregulation and antagonism. These results indicate a species-specific ability of PA from low pathogenic avian viruses to mitigate human BST-2 antiviral activity, suggesting that BST-2 is unlikely to be a general cross-species barrier to transmission of such viruses to humans.
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Affiliation(s)
- Jaraspim Narkpuk
- Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park Phaholyothin Rd, Klong 1, Klong Luang, Pathumthani 12120, Thailand
| | - Anan Jongkaewwattana
- Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park Phaholyothin Rd, Klong 1, Klong Luang, Pathumthani 12120, Thailand
| | - Samaporn Teeravechyan
- Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park Phaholyothin Rd, Klong 1, Klong Luang, Pathumthani 12120, Thailand.
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59
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Smyth RP, Negroni M, Lever AM, Mak J, Kenyon JC. RNA Structure-A Neglected Puppet Master for the Evolution of Virus and Host Immunity. Front Immunol 2018; 9:2097. [PMID: 30283444 PMCID: PMC6156135 DOI: 10.3389/fimmu.2018.02097] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2018] [Accepted: 08/24/2018] [Indexed: 11/13/2022] Open
Abstract
The central dogma of molecular biology describes the flow of genetic information from DNA to protein via an RNA intermediate. For many years, RNA has been considered simply as a messenger relaying information between DNA and proteins. Recent advances in next generation sequencing technology, bioinformatics, and non-coding RNA biology have highlighted the many important roles of RNA in virtually every biological process. Our understanding of RNA biology has been further enriched by a number of significant advances in probing RNA structures. It is now appreciated that many cellular and viral biological processes are highly dependent on specific RNA structures and/or sequences, and such reliance will undoubtedly impact on the evolution of both hosts and viruses. As a contribution to this special issue on host immunity and virus evolution, it is timely to consider how RNA sequences and structures could directly influence the co-evolution between hosts and viruses. In this manuscript, we begin by stating some of the basic principles of RNA structures, followed by describing some of the critical RNA structures in both viruses and hosts. More importantly, we highlight a number of available new tools to predict and to evaluate novel RNA structures, pointing out some of the limitations readers should be aware of in their own analyses.
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Affiliation(s)
- Redmond P Smyth
- Helmholtz Institute for RNA-based Infection Research, Würzburg, Germany.,Faculty of Medicine, University of Würzburg, Würzburg, Germany
| | - Matteo Negroni
- Université de Strasbourg, CNRS, Architecture et Réactivité de l'ARN, UPR9002, F-67000, Strasbourg, France
| | - Andrew M Lever
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom.,Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Johnson Mak
- Institute for Glycomics, Griffith University, Gold Coast, QLD, Australia
| | - Julia C Kenyon
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom.,Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.,Homerton College, Cambridge, United Kingdom
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60
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Functional Evolution of the 2009 Pandemic H1N1 Influenza Virus NS1 and PA in Humans. J Virol 2018; 92:JVI.01206-18. [PMID: 30021892 DOI: 10.1128/jvi.01206-18] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 07/12/2018] [Indexed: 12/12/2022] Open
Abstract
In 2009, a pandemic H1N1 influenza A virus (IAV) (pH1N1) emerged in the human population from swine causing a pandemic. Importantly, this virus is still circulating in humans seasonally. To analyze the evolution of pH1N1 in humans, we sequenced viral genes encoding proteins inhibiting general gene expression (nonstructural protein 1 [NS1] and PA-X) from circulating seasonal viruses and compared them to the viruses isolated at the origin of the pandemic. Recent pH1N1 viruses contain amino acid changes in the NS1 protein (E55K, L90I, I123V, E125D, K131E, and N205S), as previously described (A. M. Clark, A. Nogales, L. Martinez-Sobrido, D. J. Topham, and M. L. DeDiego, J Virol 91:e00721-17, 2017, https://doi.org/10.1128/JVI.00721-17), and amino acid changes in the PA-X protein (V100I, N204S, R221Q, and L229S). These amino acid differences between early and more recent pH1N1 isolates are responsible for increased NS1-mediated inhibition of host gene expression and decreased PA-X-mediated shutoff, including innate immune response genes. In addition, currently circulating pH1N1 viruses have acquired amino acid changes in the PA protein (V100I, P224S, N321K, I330V, and R362K). A recombinant pH1N1 virus containing PA, PA-X, and NS1 genes from currently circulating viruses is fitter in replication in cultured cells and in mice and is slightly more pathogenic than the original ancestor pH1N1 virus. These results demonstrate the need to monitor the evolution of pH1N1 in humans for mutations in the viral genome that could result in enhanced virulence. Importantly, these results further support our previous findings suggesting that inhibition of global gene expression mediated by NS1 and PA-X proteins is subject to a balance which can determine virus pathogenesis and fitness.IMPORTANCE IAVs emerge in humans from animal reservoirs, causing unpredictable pandemics. One of these pandemics was caused by an H1N1 virus in 2009, and this virus is still circulating seasonally. To analyze host-virus adaptations likely affecting influenza virus pathogenesis, protein amino acid sequences from viruses circulating at the beginning of the pandemic and those circulating currently were compared. Currently circulating viruses have incorporated amino acid changes in two viral proteins (NS1 and PA-X), affecting innate immune responses, and in the PA gene. These amino acid differences led to increased NS1-mediated and decreased PA-X-mediated inhibition of host gene expression. A recombinant pH1N1 virus containing PA, PA-X, and NS1 genes from recently circulating viruses is fitter in replication in tissue culture cells and in mice, and the virus is more pathogenic in vivo Importantly, these results suggest that a balance in the abilities of NS1 and PA-X to induce host shutoff is beneficial for IAVs.
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61
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Levene RE, Gaglia MM. Host Shutoff in Influenza A Virus: Many Means to an End. Viruses 2018; 10:E475. [PMID: 30189604 PMCID: PMC6165434 DOI: 10.3390/v10090475] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 08/31/2018] [Accepted: 09/01/2018] [Indexed: 12/21/2022] Open
Abstract
Influenza A virus carries few of its own proteins, but uses them effectively to take control of the infected cells and avoid immune responses. Over the years, host shutoff, the widespread down-regulation of host gene expression, has emerged as a key process that contributes to cellular takeover in infected cells. Interestingly, multiple mechanisms of host shutoff have been described in influenza A virus, involving changes in translation, RNA synthesis and stability. Several viral proteins, notably the non-structural protein NS1, the RNA-dependent RNA polymerase and the endoribonuclease PA-X have been implicated in host shutoff. This multitude of host shutoff mechanisms indicates that host shutoff is an important component of the influenza A virus replication cycle. Here we review the various mechanisms of host shutoff in influenza A virus and the evidence that they contribute to immune evasion and/or viral replication. We also discuss what the purpose of having multiple mechanisms may be.
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Affiliation(s)
- Rachel Emily Levene
- Graduate Program in Molecular Microbiology, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA 02111, USA.
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Ave, Boston, MA 02111, USA.
| | - Marta Maria Gaglia
- Graduate Program in Molecular Microbiology, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA 02111, USA.
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Ave, Boston, MA 02111, USA.
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62
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Hu J, Ma C, Liu X. PA-X: a key regulator of influenza A virus pathogenicity and host immune responses. Med Microbiol Immunol 2018; 207:255-269. [PMID: 29974232 PMCID: PMC7086933 DOI: 10.1007/s00430-018-0548-z] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Accepted: 06/28/2018] [Indexed: 02/07/2023]
Abstract
PA-X, a fusion protein belonging to influenza A viruses (IAVs), integrating the N-terminal 191 amino acids of PA gene and the ribosomal frame-shifting product that lengthens out to 41 or 61 amino acids. Since its discovery in 2012, multiple functions have been attributed to this small protein, including a process, where wide-spread protein synthesis in infected host cells is shut down (called host shutoff), and viral replication, polymerase activity, viral-induced cell apoptosis, PA nuclear localization, and virulence are modulated. However, many of its proposed functions may be specific to strain, subtype, host, or cell line. In this review, we start by describing the well-defined global host-shutoff ability of PA-X and the potential mechanisms underlying it. We move on to the role played by PA-X in modulating innate and acquired immune responses in the host. We then systematically discuss the role played by PA-X in modulating the virulence of influenza viruses of different subtypes and host origins, and finish with a general overview of the research advances made in identifying the host cell partners that interact with PA-X. To uncover possible clues about the differential effects of PA-X in modulating viral virulence, we focus on systemically evaluating polymorphisms in PA-X from various viral subtypes and hosts, including avian and human H5N1, H5N6, H9N2, and H7N9 viruses. Finally, we conclude with a proposition regarding the possible future research directions for this important protein.
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Affiliation(s)
- Jiao Hu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, 225009, Jiangsu Province, China
- Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, Jiangsu, China
- Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture of China (26116120), Yangzhou University, Yangzhou, China
| | - Chunxi Ma
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, 225009, Jiangsu Province, China
- Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, Jiangsu, China
- Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture of China (26116120), Yangzhou University, Yangzhou, China
| | - Xiufan Liu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, 225009, Jiangsu Province, China.
- Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, Jiangsu, China.
- Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agri-food Safety and Quality, Ministry of Agriculture of China (26116120), Yangzhou University, Yangzhou, China.
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Klemm C, Boergeling Y, Ludwig S, Ehrhardt C. Immunomodulatory Nonstructural Proteins of Influenza A Viruses. Trends Microbiol 2018; 26:624-636. [PMID: 29373257 DOI: 10.1016/j.tim.2017.12.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Revised: 12/07/2017] [Accepted: 12/15/2017] [Indexed: 12/23/2022]
Abstract
Influenza epidemics and pandemics still represent a severe public health threat and cause significant morbidity and mortality worldwide. As intracellular parasites, influenza viruses are strongly dependent on the host cell machinery. To ensure efficient production of progeny viruses, viral proteins extensively interfere with cellular signalling pathways to inhibit antiviral responses or to activate virus-supportive functions. Here, we review various functions of the influenza virus nonstructural proteins NS1, PB1-F2, and PA-X in infected cells and how post-transcriptional modifications of these proteins affect the viral life cycle. Furthermore, we discuss newly discovered interactions between these proteins and the antiviral interferon response.
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Affiliation(s)
- Carolin Klemm
- Institute of Virology Muenster (IVM), Westfaelische Wilhelms-University Muenster, Von-Esmarch-Str. 56, D-48149 Muenster, Germany
| | - Yvonne Boergeling
- Institute of Virology Muenster (IVM), Westfaelische Wilhelms-University Muenster, Von-Esmarch-Str. 56, D-48149 Muenster, Germany
| | - Stephan Ludwig
- Institute of Virology Muenster (IVM), Westfaelische Wilhelms-University Muenster, Von-Esmarch-Str. 56, D-48149 Muenster, Germany
| | - Christina Ehrhardt
- Institute of Virology Muenster (IVM), Westfaelische Wilhelms-University Muenster, Von-Esmarch-Str. 56, D-48149 Muenster, Germany.
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64
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Chaisri U, Chaicumpa W. Evolution of Therapeutic Antibodies, Influenza Virus Biology, Influenza, and Influenza Immunotherapy. BIOMED RESEARCH INTERNATIONAL 2018; 2018:9747549. [PMID: 29998138 PMCID: PMC5994580 DOI: 10.1155/2018/9747549] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 03/19/2018] [Accepted: 03/31/2018] [Indexed: 02/07/2023]
Abstract
This narrative review article summarizes past and current technologies for generating antibodies for passive immunization/immunotherapy. Contemporary DNA and protein technologies have facilitated the development of engineered therapeutic monoclonal antibodies in a variety of formats according to the required effector functions. Chimeric, humanized, and human monoclonal antibodies to antigenic/epitopic myriads with less immunogenicity than animal-derived antibodies in human recipients can be produced in vitro. Immunotherapy with ready-to-use antibodies has gained wide acceptance as a powerful treatment against both infectious and noninfectious diseases. Influenza, a highly contagious disease, precipitates annual epidemics and occasional pandemics, resulting in high health and economic burden worldwide. Currently available drugs are becoming less and less effective against this rapidly mutating virus. Alternative treatment strategies are needed, particularly for individuals at high risk for severe morbidity. In a setting where vaccines are not yet protective or available, human antibodies that are broadly effective against various influenza subtypes could be highly efficacious in lowering morbidity and mortality and controlling unprecedented epidemic/pandemic. Prototypes of human single-chain antibodies to several conserved proteins of influenza virus with no Fc portion (hence, no ADE effect in recipients) are available. These antibodies have high potential as a novel, safe, and effective anti-influenza agent.
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Affiliation(s)
- Urai Chaisri
- Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Wanpen Chaicumpa
- Center of Research Excellence on Therapeutic Proteins and Antibody Engineering, Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
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65
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Hashem AM, Azhar EI, Shalhoub S, Abujamel TS, Othman NA, Al Zahrani AB, Abdullah HM, Al-Alawi MM, Sindi AA. Genetic characterization and diversity of circulating influenza A/H1N1pdm09 viruses isolated in Jeddah, Saudi Arabia between 2014 and 2015. Arch Virol 2018; 163:1219-1230. [PMID: 29396684 DOI: 10.1007/s00705-018-3732-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Accepted: 12/19/2017] [Indexed: 12/28/2022]
Abstract
The emerged influenza A/H1N1pdm09 viruses have replaced the previously circulating seasonal H1N1 viruses. The close antigenic properties of these viruses to the 1918 H1N1 pandemic viruses and their post-pandemic evolution pattern could further enhance their adaptation and pathogenicity in humans representing a major public health threat. Given that data on the dynamics and evolution of these viruses in Saudi Arabia is sparse we investigated the genetic diversity of circulating influenza A/H1N1pdm09 viruses from Jeddah, Saudi Arabia, by analyzing 39 full genomes from isolates obtained between 2014-2015, from patients with varying symptoms. Phylogenetic analysis of all gene segments and concatenated genomes showed similar topologies and co-circulation of clades 6b, 6b.1 and 6b.2, with clade 6b.1 being the most predominate since 2015. Most viruses were more closely related to the vaccine strain (Michigan/45/2015) recommended for the 2017/2018 season, than to the California/07/2009 strain. Low sequence variability was observed in the haemagglutinin protein compared to the neuraminidase protein. Resistance to neuraminidase inhibitors was limited as only one isolate had the H275Y substitution. Interestingly, two isolates had short PA-X proteins of 206 amino acids compared to the 232 amino acid protein found in most influenza A/H1N1pdm09 viruses. Together, the co-circulation of several clades and the predominance of clade 6b.1, despite its low circulation in Asia in 2015, suggests multiple introductions most probably during the mass gathering events of Hajj and Umrah. Jeddah represents the main port of entry to the holy cities of Makkah and Al-Madinah, emphasizing the need for vigilant surveillance in the kingdom.
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MESH Headings
- Amino Acid Substitution
- Female
- Genetic Variation
- Genome, Viral
- Hemagglutinin Glycoproteins, Influenza Virus/genetics
- Humans
- Influenza A Virus, H1N1 Subtype/classification
- Influenza A Virus, H1N1 Subtype/genetics
- Influenza A Virus, H1N1 Subtype/isolation & purification
- Influenza, Human/epidemiology
- Influenza, Human/transmission
- Influenza, Human/virology
- Male
- Nasopharynx/virology
- Neuraminidase/genetics
- Phylogeny
- RNA, Viral/genetics
- Saudi Arabia/epidemiology
- Seasons
- Sequence Analysis, DNA
- Viral Proteins/genetics
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Affiliation(s)
- Anwar M Hashem
- Special Infectious Agent Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
- Department of Medical Microbiology and Parasitology, Faculty of Medicine, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
| | - Esam I Azhar
- Special Infectious Agent Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
- Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
| | - Sarah Shalhoub
- Division of Infectious Diseases, Department of Medicine, King Fahd Armed Forces Hospital, Jeddah, Kingdom of Saudi Arabia
| | - Turki S Abujamel
- Special Infectious Agent Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
- Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Norah A Othman
- Special Infectious Agent Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Abdulwahab B Al Zahrani
- Molecular Diagnostics Laboratory, King Fahd Armed Forces Hospital, Jeddah, Kingdom of Saudi Arabia
| | - Hanan M Abdullah
- Students' Research and Innovation Unit, Faculty of Medicine, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Maha M Al-Alawi
- Special Infectious Agent Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
- Department of Medical Microbiology and Parasitology, Faculty of Medicine, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
- Infection Control and Environmental Health Unit, Faculty of Medicine, King Abdulaziz University Hospital, Jeddah, Kingdom of Saudi Arabia
| | - Anees A Sindi
- Department of Anesthesia and Critical Care, Faculty of Medicine, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
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66
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Oishi K, Yamayoshi S, Kawaoka Y. Identification of novel amino acid residues of influenza virus PA-X that are important for PA-X shutoff activity by using yeast. Virology 2018; 516:71-75. [PMID: 29331676 DOI: 10.1016/j.virol.2018.01.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Revised: 01/03/2018] [Accepted: 01/05/2018] [Indexed: 10/18/2022]
Abstract
The influenza A virus protein PA-X comprises an N-terminal PA region and a C-terminal PA-X-specific region. PA-X suppresses host gene expression, termed shutoff, via mRNA cleavage. Although the endonuclease active site in the N-terminal PA region of PA-X and basic amino acids in the C-terminal PA-X-specific region are known to be important for PA-X shutoff activity, other amino acids may also play a role. Here, we used yeast to identify novel amino acids of PA-X that are important for PA-X shutoff activity. Unlike wild-type PA-X, most PA-X mutants predominantly localized in the cytoplasm, indicating that these mutations decreased the shutoff activity of PA-X by affecting PA-X translocation to the nucleus. Mapping of the identified amino acids onto the N-terminal structure of PA revealed that some of them likely contribute to the formation of the endonuclease active site of PA.
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Affiliation(s)
- Kohei Oishi
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan
| | - Seiya Yamayoshi
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan.
| | - Yoshihiro Kawaoka
- Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan; Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, WI 53711, United States; Department of Special Pathogens, International Research Center for Infectious Diseases, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan.
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67
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Bera BC, Virmani N, Kumar N, Anand T, Pavulraj S, Rash A, Elton D, Rash N, Bhatia S, Sood R, Singh RK, Tripathi BN. Genetic and codon usage bias analyses of polymerase genes of equine influenza virus and its relation to evolution. BMC Genomics 2017; 18:652. [PMID: 28830350 PMCID: PMC5568313 DOI: 10.1186/s12864-017-4063-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 08/15/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Equine influenza is a major health problem of equines worldwide. The polymerase genes of influenza virus have key roles in virus replication, transcription, transmission between hosts and pathogenesis. Hence, the comprehensive genetic and codon usage bias of polymerase genes of equine influenza virus (EIV) were analyzed to elucidate the genetic and evolutionary relationships in a novel perspective. RESULTS The group - specific consensus amino acid substitutions were identified in all polymerase genes of EIVs that led to divergence of EIVs into various clades. The consistent amino acid changes were also detected in the Florida clade 2 EIVs circulating in Europe and Asia since 2007. To study the codon usage patterns, a total of 281,324 codons of polymerase genes of EIV H3N8 isolates from 1963 to 2015 were systemically analyzed. The polymerase genes of EIVs exhibit a weak codon usage bias. The ENc-GC3s and Neutrality plots indicated that natural selection is the major influencing factor of codon usage bias, and that the impact of mutation pressure is comparatively minor. The methods for estimating host imposed translation pressure suggested that the polymerase acidic (PA) gene seems to be under less translational pressure compared to polymerase basic 1 (PB1) and polymerase basic 2 (PB2) genes. The multivariate statistical analysis of polymerase genes divided EIVs into four evolutionary diverged clusters - Pre-divergent, Eurasian, Florida sub-lineage 1 and 2. CONCLUSIONS Various lineage specific amino acid substitutions observed in all polymerase genes of EIVs and especially, clade 2 EIVs underwent major variations which led to the emergence of a phylogenetically distinct group of EIVs originating from Richmond/1/07. The codon usage bias was low in all the polymerase genes of EIVs that was influenced by the multiple factors such as the nucleotide compositions, mutation pressure, aromaticity and hydropathicity. However, natural selection was the major influencing factor in defining the codon usage patterns and evolution of polymerase genes of EIVs.
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Affiliation(s)
- Bidhan Ch Bera
- National Research Centre on Equines, Sirsa Road, Hisar, Haryana, India
| | - Nitin Virmani
- National Research Centre on Equines, Sirsa Road, Hisar, Haryana, India.
| | - Naveen Kumar
- National Institute of High Security Animal Diseases, Hathai Kheda Dam Road, Anand Nagar, Bhopal, Madhya Pradesh, India
| | - Taruna Anand
- National Research Centre on Equines, Sirsa Road, Hisar, Haryana, India
| | - S Pavulraj
- National Research Centre on Equines, Sirsa Road, Hisar, Haryana, India
| | - Adam Rash
- Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, CB8 7UU, UK
| | - Debra Elton
- Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, CB8 7UU, UK
| | - Nicola Rash
- Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, CB8 7UU, UK
| | - Sandeep Bhatia
- National Institute of High Security Animal Diseases, Hathai Kheda Dam Road, Anand Nagar, Bhopal, Madhya Pradesh, India
| | - Richa Sood
- National Institute of High Security Animal Diseases, Hathai Kheda Dam Road, Anand Nagar, Bhopal, Madhya Pradesh, India
| | - Raj Kumar Singh
- Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, India
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68
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PA-X protein decreases replication and pathogenicity of swine influenza virus in cultured cells and mouse models. Vet Microbiol 2017. [PMID: 28622865 DOI: 10.1016/j.vetmic.2017.05.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Swine influenza viruses have been circulating in pigs throughout world and might be potential threats to human health. PA-X protein is a newly discovered protein produced from the PA gene by ribosomal frameshifting and the effects of PA-X on the 1918 H1N1, the pandemic 2009 H1N1, the highly pathogenic avian H5N1 and the avian H9N2 influenza viruses have been reported. However, the role of PA-X in the pathogenesis of swine influenza virus is still unknown. In this study, we rescued the H1N1 wild-type (WT) classical swine influenza virus (A/Swine/Guangdong/1/2011 (H1N1)) and H1N1 PA-X deficient virus containing mutations at the frameshift motif, and compared their replication properties and pathogenicity of swine influenza virus in vitro and in vivo. Our results show that the expression of PA-X inhibits virus replication and polymerase activity in cultured cells and decreases virulence in mouse models. Therefore, our study demonstrates that PA-X protein acts as a negative virulence regulator for classical H1N1 swine influenza virus and decreases virulence by inhibiting viral replication and polymerase activity, deepening our understanding of the pathogenesis of swine influenza virus.
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69
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Xu G, Zhang X, Liu Q, Bing G, Hu Z, Sun H, Xiong X, Jiang M, He Q, Wang Y, Pu J, Guo X, Yang H, Liu J, Sun Y. PA-X protein contributes to virulence of triple-reassortant H1N2 influenza virus by suppressing early immune responses in swine. Virology 2017; 508:45-53. [PMID: 28494344 DOI: 10.1016/j.virol.2017.05.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 05/03/2017] [Accepted: 05/04/2017] [Indexed: 12/22/2022]
Abstract
Previous studies have identified a functional role of PA-X for influenza viruses in mice and avian species; however, its role in swine remains unknown. Toward this, we constructed PA-X deficient virus (Sw-FS) in the background of a Triple-reassortment (TR) H1N2 swine influenza virus (SIV) to assess the impact of PA-X in viral virulence in pigs. Expression of PA-X in TR H1N2 SIV enhanced viral replication and host protein synthesis shutoff, and inhibited the mRNA levels of type I IFNs and proinflammatory cytokines in porcine cells. A delay of proinflammatory responses was observed in lungs of pigs infected by wild type SIV (Sw-WT) compared to Sw-FS. Furthermore, Sw-WT virus replicated and transmitted more efficiently than Sw-FS in pigs. These results highlight the importance of PA-X in the moderation of virulence and immune responses of TR SIV in swine, which indicated that PA-X is a pro-virulence factor in TR SIV in pigs.
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Affiliation(s)
- Guanlong Xu
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China; China Institute of Veterinary Drug Control, Beijing, China
| | - Xuxiao Zhang
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Qinfang Liu
- Department of Avian Infectious Disease, Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Guoxia Bing
- China Animal Disease Control Center, Beijing, China
| | - Zhe Hu
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Honglei Sun
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Xin Xiong
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Ming Jiang
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Qiming He
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Yu Wang
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Juan Pu
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Xin Guo
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Hanchun Yang
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Jinhua Liu
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China
| | - Yipeng Sun
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China.
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70
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Lee J, Yu H, Li Y, Ma J, Lang Y, Duff M, Henningson J, Liu Q, Li Y, Nagy A, Bawa B, Li Z, Tong G, Richt JA, Ma W. Impacts of different expressions of PA-X protein on 2009 pandemic H1N1 virus replication, pathogenicity and host immune responses. Virology 2017; 504:25-35. [PMID: 28142079 DOI: 10.1016/j.virol.2017.01.015] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2016] [Revised: 01/20/2017] [Accepted: 01/21/2017] [Indexed: 12/16/2022]
Abstract
Although several studies have investigated the functions of influenza PA-X, the impact of different expressions of PA-X protein including full-length, truncated or PA-X deficient forms on virus replication, pathogenicity and host response remains unclear. Herein, we generated two mutated viruses expressing a full-length or deficient PA-X protein based on the A/California/04/2009 (H1N1) virus that expresses a truncated PA-X to understand three different expressions of PA-X protein on virus replication, pathogenicity and host immune responses. The results showed that expression of either full-length or truncated PA-X protein enhanced viral replication and pathogenicity as well as reduced host innate immune response in mice by host shutoff activity when compared to the virus expressing the deficient PA-X form. Furthermore, the full-length PA-X expression exhibited a greater effect on virus pathogenicity than the truncated PA-X form. Our results provide novel insights of PA-X on viral replication, pathogenicity and host immune responses.
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Affiliation(s)
- Jinhwa Lee
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Hai Yu
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA; Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Yonghai Li
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Jingjiao Ma
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Yuekun Lang
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Michael Duff
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Jamie Henningson
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Qinfang Liu
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA; Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Yuhao Li
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Abdou Nagy
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Bhupinder Bawa
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Zejun Li
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Guangzhi Tong
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Juergen A Richt
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA
| | - Wenjun Ma
- Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, USA.
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Deep Sequencing of Influenza A Virus from a Human Challenge Study Reveals a Selective Bottleneck and Only Limited Intrahost Genetic Diversification. J Virol 2016; 90:11247-11258. [PMID: 27707932 PMCID: PMC5126380 DOI: 10.1128/jvi.01657-16] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 09/29/2016] [Indexed: 01/06/2023] Open
Abstract
Knowledge of influenza virus evolution at the point of transmission and at the intrahost level remains limited, particularly for human hosts. Here, we analyze a unique viral data set of next-generation sequencing (NGS) samples generated from a human influenza challenge study wherein 17 healthy subjects were inoculated with cell- and egg-passaged virus. Nasal wash samples collected from 7 of these subjects were successfully deep sequenced. From these, we characterized changes in the subjects' viral populations during infection and identified differences between the virus in these samples and the viral stock used to inoculate the subjects. We first calculated pairwise genetic distances between the subjects' nasal wash samples, the viral stock, and the influenza virus A/Wisconsin/67/2005 (H3N2) reference strain used to generate the stock virus. These distances revealed that considerable viral evolution occurred at various points in the human challenge study. Further quantitative analyses indicated that (i) the viral stock contained genetic variants that originated and likely were selected for during the passaging process, (ii) direct intranasal inoculation with the viral stock resulted in a selective bottleneck that reduced nonsynonymous genetic diversity in the viral hemagglutinin and nucleoprotein, and (iii) intrahost viral evolution continued over the course of infection. These intrahost evolutionary dynamics were dominated by purifying selection. Our findings indicate that rapid viral evolution can occur during acute influenza infection in otherwise healthy human hosts when the founding population size of the virus is large, as is the case with direct intranasal inoculation. IMPORTANCE Influenza viruses circulating among humans are known to rapidly evolve over time. However, little is known about how influenza virus evolves across single transmission events and over the course of a single infection. To address these issues, we analyze influenza virus sequences from a human challenge experiment that initiated infection with a cell- and egg-passaged viral stock, which appeared to have adapted during its preparation. We find that the subjects' viral populations differ genetically from the viral stock, with subjects' viral populations having lower representation of the amino-acid-changing variants that arose during viral preparation. We also find that most of the viral evolution occurring over single infections is characterized by further decreases in the frequencies of these amino-acid-changing variants and that only limited intrahost genetic diversification through new mutations is apparent. Our findings indicate that influenza virus populations can undergo rapid genetic changes during acute human infections.
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72
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Jacqueline C, Bourfia Y, Hbid H, Sorci G, Thomas F, Roche B. Interactions between immune challenges and cancer cells proliferation: timing does matter! EVOLUTION MEDICINE AND PUBLIC HEALTH 2016; 2016:299-311. [PMID: 27535084 PMCID: PMC5046994 DOI: 10.1093/emph/eow025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Indexed: 12/17/2022]
Abstract
The immune system is a key component of malignant cell control and it is also involved in the elimination of pathogens that threaten the host. Despite our body is permanently exposed to a myriad of pathogens, the interference of such infections with the immune responses against cancer has been poorly investigated. Through a mathematical model, we show that the frequency, the duration and the action (positive or negative) of immune challenges may significantly impact tumor proliferation. First, we observe that a long immunosuppressive challenge increases accumulation of cancerous cells only if it occurs 14 years after the beginning of immunosenescence. However, short immune challenges result in an even greater accumulation of cancerous cells for the same total duration of immunosuppression. Finally, we show that short challenges of immune activation could lead to a slightly decrease in cancerous cell accumulation compared to a long one. Our results predict that frequent and acute immune challenges could have a different and in some extent higher impact on cancer risk than persistent ones even they have been much less studied in cancer epidemiology. These results are discussed regarding the existing empirical evidences and we suggest potential novel indirect role of infectious diseases on cancer incidence which should be investigated to improve prevention strategies against cancer.
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Affiliation(s)
- Camille Jacqueline
- CREEC, 911 Avenue Agropolis, BP 64501, Montpellier, Cedex 5 34394, France MIVEGEC, UMR IRD/CNRS/UM 5290, 911 Avenue Agropolis, BP 64501, Montpellier, Cedex 5 34394, France
| | - Youssef Bourfia
- Laboratoire Jacques-Louis Lions (LJLL), UMR 7598 Université Pierre et Marie Curie (UPMC), Paris 6, Boîte courrier 187, ;Paris, Cedex 05 75252, France Université Cadi Ayyad Laboratoire de Mathématiques et Dynamique de Populations, Cadi Ayyad University, Marrakech, Morocco
| | - Hassan Hbid
- Université Cadi Ayyad Laboratoire de Mathématiques et Dynamique de Populations, Cadi Ayyad University, Marrakech, Morocco International Center for Mathematical and Computational Modeling of Complex Systems (UMI IRD/UPMC UMMISCO), 32 Avenue Henri Varagnat, Bondy Cedex 93143, France
| | - Gabriele Sorci
- BiogéoSciences, CNRS UMR 6282, Université de Bourgogne, 6 Boulevard Gabriel, Dijon 21000, France
| | - Frédéric Thomas
- CREEC, 911 Avenue Agropolis, BP 64501, Montpellier, Cedex 5 34394, France MIVEGEC, UMR IRD/CNRS/UM 5290, 911 Avenue Agropolis, BP 64501, Montpellier, Cedex 5 34394, France
| | - Benjamin Roche
- CREEC, 911 Avenue Agropolis, BP 64501, Montpellier, Cedex 5 34394, France International Center for Mathematical and Computational Modeling of Complex Systems (UMI IRD/UPMC UMMISCO), 32 Avenue Henri Varagnat, Bondy Cedex 93143, France
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73
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Li Q, Yuan X, Wang Q, Chang G, Wang F, Liu R, Zheng M, Chen G, Wen J, Zhao G. Interactomic landscape of PA-X-chicken protein complexes of H5N1 influenza A virus. J Proteomics 2016; 148:20-5. [DOI: 10.1016/j.jprot.2016.07.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 06/22/2016] [Accepted: 07/11/2016] [Indexed: 12/19/2022]
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74
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Antigenic Fingerprinting of Antibody Response in Humans following Exposure to Highly Pathogenic H7N7 Avian Influenza Virus: Evidence for Anti-PA-X Antibodies. J Virol 2016; 90:9383-93. [PMID: 27512055 DOI: 10.1128/jvi.01408-16] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Accepted: 08/01/2016] [Indexed: 12/18/2022] Open
Abstract
UNLABELLED Infections with H7 highly pathogenic avian influenza (HPAI) viruses remain a major public health concern. Adaptation of low-pathogenic H7N7 to highly pathogenic H7N7 in Europe in 2015 raised further alarm for a potential pandemic. An in-depth understanding of antibody responses to HPAI H7 virus following infection in humans could provide important insight into virus gene expression as well as define key protective and serodiagnostic targets. Here we used whole-genome gene fragment phage display libraries (GFPDLs) expressing peptides of 15 to 350 amino acids across the complete genome of the HPAI H7N7 A/Netherlands/33/03 virus. The hemagglutinin (HA) antibody epitope repertoires of 15 H7N7-exposed humans identified clear differences between individuals with no hemagglutination inhibition (HI) titers (<1:10) and those with HI titers of >1:40. Several potentially protective H7N7 epitopes close to the HA receptor binding domain (RBD) and neuraminidase (NA) catalytic site were identified. Surface plasmon resonance (SPR) analysis identified a strong correlation between HA1 (but not HA2) binding antibodies and H7N7 HI titers. A proportion of HA1 binding in plasma was contributed by IgA antibodies. Antibodies against the N7 neuraminidase were less frequent but targeted sites close to the sialic acid binding site. Importantly, we identified strong antibody reactivity against PA-X, a putative virulence factor, in most H7N7-exposed individuals, providing the first evidence for in vivo expression of PA-X and its recognition by the immune system during human influenza A virus infection. This knowledge can help inform the development and selection of the most effective countermeasures for prophylactic as well as therapeutic treatments of HPAI H7N7 avian influenza virus. IMPORTANCE An outbreak of pathogenic H7N7 virus occurred in poultry farms in The Netherlands in 2003. Severe outcome included conjunctivitis, influenza-like illness, and one lethal infection. In this study, we investigated convalescent-phase sera from H7N7-exposed individuals by using a whole-genome phage display library (H7N7-GFPDL) to explore the complete repertoire of post-H7N7-exposure antibodies. PA-X is a recently identified influenza virus virulence protein generated by ribosomal frameshifting in segment 3 of influenza virus coding for PA. However, PA-X expression during influenza virus infection in humans is unknown. We identified strong antibody reactivity against PA-X in most H7N7-exposed individuals (but not in unexposed adults), providing the first evidence for in vivo expression of PA-X and its recognition by the immune system during human infection with pathogenic H7N7 avian influenza virus.
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75
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Hayashi T, Chaimayo C, McGuinness J, Takimoto T. Critical Role of the PA-X C-Terminal Domain of Influenza A Virus in Its Subcellular Localization and Shutoff Activity. J Virol 2016; 90:7131-7141. [PMID: 27226377 PMCID: PMC4984632 DOI: 10.1128/jvi.00954-16] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Accepted: 05/22/2016] [Indexed: 12/31/2022] Open
Abstract
UNLABELLED PA-X is a recently identified influenza virus protein that is composed of the PA N-terminal 191 amino acids and unique C-terminal 41 or 61 residues. We and others showed that PA-X has a strong ability to suppress host protein synthesis via host mRNA decay, which is mediated by endonuclease activity in its N-terminal domain (B. W. Jagger, H. M. Wise, J. C. Kash, K. A. Walters, N. M. Wills, Y. L. Xiao, R. L. Dunfee, L. M. Schwartzman, A. Ozinsky, G. L. Bell, R. M. Dalton, A. Lo, S. Efstathiou, J. F. Atkins, A. E. Firth, J. K. Taubenberger, and P. Digard, 2012, Science 337:199-204, http://dx.doi.org/10.1126/science.1222213, and E. A. Desmet, K. A. Bussey, R. Stone, and T. Takimoto, 2013, J Virol 87:3108-3118, http://dx.doi.org/10.1128/JVI.02826-12). However, the mechanism of host mRNA degradation, especially where and how PA-X targets mRNAs, has not been analyzed. In this study, we determined the localization of PA-X and the role of the C-terminal unique region in shutoff activity. Quantitative subcellular localization analysis revealed that PA-X was located equally in both cytoplasm and nucleus. By characterizing a series of PA-X C-terminal deletion mutants, we found that the first 9 amino acids were sufficient for nuclear localization, but an additional 6 residues were required to induce the maximum shutoff activity observed with intact PA-X. Importantly, forced nuclear localization of the PA-X C-terminal deletion mutant enhanced shutoff activity, highlighting the ability of nuclear PA-X to degrade host mRNAs more efficiently. However, PA-X also inhibited luciferase expression from transfected mRNAs synthesized in vitro, suggesting that PA-X also degrades mRNAs in the cytoplasm. Among the basic amino acids in the PA-X C-terminal region, 3 residues, 195K, 198K, and 199R, were identified as key residues for inducing host shutoff and nuclear localization. Overall, our data indicate a critical role for the 15 residues in the PA-X C-terminal domain in degrading mRNAs in both the cytoplasm and nucleus. IMPORTANCE Influenza A viruses express PA-X proteins to suppress global host gene expression, including host antiviral genes, to allow efficient viral replication in infected cells. However, little is known about how PA-X induces host shutoff. In this study, we showed that PA-X localized equally in both the cytoplasm and nucleus of the cells, but the nuclear localization of PA-X mediated by its C-terminal region has a significant impact on shutoff activity. Three basic residues at the C-terminal region play a critical role in nuclear localization, but additional basic residues were required for maximum shutoff activity. Our findings indicate that PA-X targets and degrades mRNAs in both the nucleus and cytoplasm, and that the first 15 residues of the PA-X unique C-terminal region play a critical role in shutoff activity.
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Affiliation(s)
- Tsuyoshi Hayashi
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
| | - Chutikarn Chaimayo
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
- Department of Microbiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - James McGuinness
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
| | - Toru Takimoto
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
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76
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Affiliation(s)
- Tsuyoshi Hayashi
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
| | - Chutikarn Chaimayo
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
| | - Toru Takimoto
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
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77
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Feng KH, Sun M, Iketani S, Holmes EC, Parrish CR. Comparing the functions of equine and canine influenza H3N8 virus PA-X proteins: Suppression of reporter gene expression and modulation of global host gene expression. Virology 2016; 496:138-146. [PMID: 27314620 DOI: 10.1016/j.virol.2016.06.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Revised: 05/10/2016] [Accepted: 06/01/2016] [Indexed: 12/30/2022]
Abstract
The influenza PA-X protein is translated from the PA open reading frame from frameshifting and suppresses cellular gene expression due to its ribonuclease activity. We further defined the functional roles of PA-X by comparing PA-X proteins from two related viruses - equine influenza (EIV) and canine influenza (CIV) H3N8 - that differ in a C-terminal truncation and internal mutations. In vitro reporter gene assays revealed that both proteins were able to suppress gene expression. Interestingly, EIV PA-X demonstrated ~50% greater activity compared to CIV PA-X, and we identified the mutations that caused this difference. We used RNA-seq to evaluate the effects of PA-X on host gene expression after transfection into cultured cells. There were no significant differences in this property between EIV and CIV PA-X proteins, but expression of either resulted in the up-regulation of genes when compared to controls, most notably immunity-related proteins, trafficking proteins, and transcription factors.
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Affiliation(s)
- Kurtis H Feng
- Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Miao Sun
- Computational and Systems Biology 5, Genome Institute of Singapore, Republic of Singapore
| | - Sho Iketani
- Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Edward C Holmes
- Marie Bashir Institute for Infectious Diseases and Biosecurity, Charles Perkins Centre, School of Biological Sciences and Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia
| | - Colin R Parrish
- Department of Microbiology and Immunology, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
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78
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Hu J, Mo Y, Gao Z, Wang X, Gu M, Liang Y, Cheng X, Hu S, Liu W, Liu H, Chen S, Liu X, Peng D, Liu X. PA-X-associated early alleviation of the acute lung injury contributes to the attenuation of a highly pathogenic H5N1 avian influenza virus in mice. Med Microbiol Immunol 2016; 205:381-95. [PMID: 27289459 PMCID: PMC7086737 DOI: 10.1007/s00430-016-0461-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 05/31/2016] [Indexed: 12/18/2022]
Abstract
PA-X is a novel discovered accessory protein encoded by the PA mRNA. Our previous study demonstrated that PA-X decreases the virulence of a highly pathogenic H5N1 strain A/Chicken/Jiangsu/k0402/2010 in mice. However, the underlying mechanism of virulence attenuation associated with PA-X is still unknown. In this study, we compared two PA-X-deficient mutant viruses and the parental virus in terms of induction of pathology and manipulation of host response in the mouse lung, stimulation of cell death and PA nuclear accumulation. We first found that down-regulated PA-X expression markedly aggravated the acute lung injury of the infected mice early on day 1 post-infection (p.i.). We then determined that loss of PA-X expression induced higher levels of cytokines, chemokines and complement-derived peptides (C3a and C5a) in the lung, especially at early time point’s p.i. In addition, in vitro assays showed that the PA-X-deficient viruses enhanced cell death and increased expression of reactive oxygen species (ROS) in mammalian cells. Moreover, we also found that PA nuclear accumulation of the PA-X-null viruses accelerated in MDCK cells. These results demonstrate that PA-X decreases the level of complement components, ROS, cell death and inflammatory response, which may together contribute to the alleviated lung injury and the attenuation of the virulence of H5N1 virus in mice.
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Affiliation(s)
- Jiao Hu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Yiqun Mo
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Zhao Gao
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Xiaoquan Wang
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Min Gu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Yanyan Liang
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Xin Cheng
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Shunlin Hu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Wenbo Liu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Huimou Liu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Sujuan Chen
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Xiaowen Liu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Daxing Peng
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China
| | - Xiufan Liu
- Animal Infectious Disease Laboratory, School of Veterinary Medicine, Yangzhou University, 48 East Wenhui Road, Yangzhou, Jiangsu Province, 225009, China. .,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonosis, Yangzhou University, Yangzhou, 225009, China.
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79
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DesRochers BL, Chen RE, Gounder AP, Pinto AK, Bricker T, Linton CN, Rogers CD, Williams GD, Webby RJ, Boon ACM. Residues in the PB2 and PA genes contribute to the pathogenicity of avian H7N3 influenza A virus in DBA/2 mice. Virology 2016; 494:89-99. [PMID: 27105450 DOI: 10.1016/j.virol.2016.04.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 04/08/2016] [Accepted: 04/11/2016] [Indexed: 12/22/2022]
Abstract
Replication and transmission of avian influenza virus in humans poses a pandemic threat. The molecular determinants that facilitate this process are not well understood. We used DBA/2 mice to identify viral factors that mediate the difference in pathogenesis between a virulent (H7N3) and a non-virulent (H7N9) avian influenza virus from North America. In vitro and in vivo characterization of reassortant viruses identified the PB2 and PA polymerase genes as major determinants of H7N3 pathogenesis. Analysis of individual residues in the PB2 and PA genes identified position 358 (E358V) in PB2 and positions 190 (P190S) and 400 (Q400P) in PA that reduced the virulence of H7N3 virus. The E358V and P190S substitutions also caused reduced inflammation after infection. Our results suggest that specific residues in the polymerase proteins PB2 and PA are important for replication and virulence of avian influenza viruses in a mammalian host.
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Affiliation(s)
- Brittany L DesRochers
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Rita E Chen
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Anshu P Gounder
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Amelia K Pinto
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Traci Bricker
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Camille N Linton
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Corianne D Rogers
- Department of Infectious Diseases, St. Jude Children׳s Research Hospital, Memphis, TN 38105, USA
| | - Graham D Williams
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Richard J Webby
- Department of Infectious Diseases, St. Jude Children׳s Research Hospital, Memphis, TN 38105, USA
| | - Adrianus C M Boon
- Departments of Internal Medicine, Molecular Microbiology, and Pathology and Immunology, Washington University School of Medicine, St Louis, MO 63110, USA.
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80
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Shutoff of Host Gene Expression in Influenza A Virus and Herpesviruses: Similar Mechanisms and Common Themes. Viruses 2016; 8:102. [PMID: 27092522 PMCID: PMC4848596 DOI: 10.3390/v8040102] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 04/04/2016] [Accepted: 04/09/2016] [Indexed: 12/14/2022] Open
Abstract
The ability to shut off host gene expression is a shared feature of many viral infections, and it is thought to promote viral replication by freeing host cell machinery and blocking immune responses. Despite the molecular differences between viruses, an emerging theme in the study of host shutoff is that divergent viruses use similar mechanisms to enact host shutoff. Moreover, even viruses that encode few proteins often have multiple mechanisms to affect host gene expression, and we are only starting to understand how these mechanisms are integrated. In this review we discuss the multiplicity of host shutoff mechanisms used by the orthomyxovirus influenza A virus and members of the alpha- and gamma-herpesvirus subfamilies. We highlight the surprising similarities in their mechanisms of host shutoff and discuss how the different mechanisms they use may play a coordinated role in gene regulation.
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81
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De A, Sarkar T, Nandy A. Bioinformatics studies of Influenza A hemagglutinin sequence data indicate recombination-like events leading to segment exchanges. BMC Res Notes 2016; 9:222. [PMID: 27083561 PMCID: PMC4832483 DOI: 10.1186/s13104-016-2017-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 03/31/2016] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND The influenza genome is highly variable due primarily to two mechanisms: antigenic drift and antigenic shift. A third mechanism for genetic change, known as copy choice or template switching, can arise during replication when, if two viral strains infect a cell, a part of a gene from the second viral strain can be copied into the growing progeny of a gene of the first viral strain as replacement leading to a new variety of the virus. This template switching between the same genes of the two strains is known as homologous recombination. While genetic drift and shift are well-understood, the presence or absence of intra-segment homologous recombination in influenza genomes is controversial. CONTEXT AND PURPOSE OF STUDY We are interested to study the possibility of subunit-wise homologous recombination. The idea is that where well-defined subunits are separated by consensus sequences, it might be possible for template switching to take place at such junctions. The influenza hemagglutinin gene has basically two subunits, HA1 and HA2, with HA1 being mostly surface exposed and containing the active site for binding to cells, while HA2 secures the hemagglutinin to the viral coat. We undertook a thorough search of the major human infecting influenza hemagglutinin gene sequences, viz., the H1N1, H5N1, H3N2 and H7N9 subtypes, over the period 2010-2014 in Asia to determine if certain sequences could be identified that had HA1 from a previous strain and HA2 from another. RESULTS Our search yielded several instances where sequence identities between segments of various strains could be interpreted as indicating possibilities of segment exchange. In some cases, on closer examination they turn out to differ by a few mutations in each segment, due perhaps to the short time span of our database. CONCLUSIONS AND POTENTIAL IMPLICATIONS The study reported here, and in combination with our earlier observations on the neuraminidase, shows that subunit-wise recombination-like events in the influenza genes may be occurring more often than have been accounted for and merits further detailed studies.
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Affiliation(s)
- Antara De
- Centre for Interdisciplinary Research and Education, 404B Jodhpur Park, Kolkata, 700068, India.
| | - Tapati Sarkar
- Physics Department, Jadavpur University, Jadavpur, Kolkata, 700032, India
| | - Ashesh Nandy
- Centre for Interdisciplinary Research and Education, 404B Jodhpur Park, Kolkata, 700068, India
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82
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Pathogenicity of Genetically Similar, H5N1 Highly Pathogenic Avian Influenza Virus Strains in Chicken and the Differences in Sensitivity among Different Chicken Breeds. PLoS One 2016; 11:e0153649. [PMID: 27078641 PMCID: PMC4841636 DOI: 10.1371/journal.pone.0153649] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 03/03/2016] [Indexed: 12/18/2022] Open
Abstract
Differences in the pathogenicity of genetically closely related H5N1 highly pathogenic avian influenza viruses (HPAIVs) were evaluated in White Leghorn chickens. These viruses varied in the clinical symptoms they induced, including lethality, virus shedding, and replication in host tissues. A comparison of the host responses in the lung, brain, and spleen suggested that the differences in viral replication efficiency were related to the host cytokine response at the early phase of infection, especially variations in the proinflammatory cytokine IL-6. Based on these findings, we inoculated the virus that showed the mildest pathogenicity among the five tested, A/pigeon/Thailand/VSMU-7-NPT/2004, into four breeds of Thai indigenous chicken, Phadu-Hung-Dang (PHD), Chee, Dang, and Luang-Hung-Khao (LHK), to explore effects of genetic background on host response. Among these breeds, Chee, Dang, and LHK showed significantly longer survival times than White Leghorns. Virus shedding from dead Thai indigenous chickens was significantly lower than that from White Leghorns. Although polymorphisms were observed in the Mx and MHC class I genes, there was no significant association between the polymorphisms in these loci and resistance to HPAIV.
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83
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Truncation of C-terminal 20 amino acids in PA-X contributes to adaptation of swine influenza virus in pigs. Sci Rep 2016; 6:21845. [PMID: 26912401 PMCID: PMC4766433 DOI: 10.1038/srep21845] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 01/28/2016] [Indexed: 01/20/2023] Open
Abstract
The PA-X protein is a fusion protein incorporating the N-terminal 191 amino acids of the PA protein with a short C-terminal sequence encoded by an overlapping ORF (X-ORF) in segment 3 that is accessed by + 1 ribosomal frameshifting, and this X-ORF exists in either full length or a truncated form (either 61-or 41-condons). Genetic evolution analysis indicates that all swine influenza viruses (SIVs) possessed full-length PA-X prior to 1985, but since then SIVs with truncated PA-X have gradually increased and become dominant, implying that truncation of this protein may contribute to the adaptation of influenza virus in pigs. To verify this hypothesis, we constructed PA-X extended viruses in the background of a "triple-reassortment" H1N2 SIV with truncated PA-X, and evaluated their biological characteristics in vitro and in vivo. Compared with full-length PA-X, SIV with truncated PA-X had increased viral replication in porcine cells and swine respiratory tissues, along with enhanced pathogenicity, replication and transmissibility in pigs. Furthermore, we found that truncation of PA-X improved the inhibition of IFN-I mRNA expression. Hereby, our results imply that truncation of PA-X may contribute to the adaptation of SIV in pigs.
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84
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Khaperskyy DA, Schmaling S, Larkins-Ford J, McCormick C, Gaglia MM. Selective Degradation of Host RNA Polymerase II Transcripts by Influenza A Virus PA-X Host Shutoff Protein. PLoS Pathog 2016; 12:e1005427. [PMID: 26849127 PMCID: PMC4744033 DOI: 10.1371/journal.ppat.1005427] [Citation(s) in RCA: 93] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 01/10/2016] [Indexed: 11/30/2022] Open
Abstract
Influenza A viruses (IAVs) inhibit host gene expression by a process known as host shutoff. Host shutoff limits host innate immune responses and may also redirect the translation apparatus to the production of viral proteins. Multiple IAV proteins regulate host shutoff, including PA-X, a ribonuclease that remains incompletely characterized. We report that PA-X selectively targets host RNA polymerase II (Pol II) transcribed mRNAs, while sparing products of Pol I and Pol III. Interestingly, we show that PA-X can also target Pol II-transcribed RNAs in the nucleus, including non-coding RNAs that are not destined to be translated, and reporter transcripts with RNA hairpin structures that block ribosome loading. Transcript degradation likely occurs in the nucleus, as PA-X is enriched in the nucleus and its nuclear localization correlates with reduction in target RNA levels. Complete degradation of host mRNAs following PA-X-mediated endonucleolytic cleavage is dependent on the host 5’->3’-exonuclease Xrn1. IAV mRNAs are structurally similar to host mRNAs, but are synthesized and modified at the 3’ end by the action of the viral RNA-dependent RNA polymerase complex. Infection of cells with wild-type IAV or a recombinant PA-X-deficient virus revealed that IAV mRNAs resist PA-X-mediated degradation during infection. At the same time, loss of PA-X resulted in changes in the synthesis of select viral mRNAs and a decrease in viral protein accumulation. Collectively, these results significantly advance our understanding of IAV host shutoff, and suggest that the PA-X causes selective degradation of host mRNAs by discriminating some aspect of Pol II-dependent RNA biogenesis in the nucleus. All viruses depend on host components to convert viral mRNAs into proteins. Several viruses, including influenza A virus, encode factors that trigger RNA destruction. The influenza A virus factor that serves in this capacity is known as PA-X. PA-X limits accumulation of host mRNAs and proteins in infected cells and suppresses host responses to infection, but to date its precise mechanism of action remains obscure. Here we report that PA-X selectively targets cellular mRNAs, while sparing viral mRNAs, thereby compromising host gene expression and ensuring priority access of viral mRNAs to the protein synthesis machinery. We demonstrate that complete degradation of mRNAs cut by PA-X is dependent on the host factor Xrn1 and that PA-X likely works in the cell’s nuclei. Interestingly, PA-X targeting appears to be selective for products of host RNA polymerase II, and canonical mRNA processing is required for cleavage. Even though viral mRNAs are spared from PA-X-mediated degradation, PA-X-deficient viruses displayed defects in the synthesis of certain viral mRNAs and decreased viral protein accumulation. Thus, PA-X-mediated host shutoff influences the efficiency of viral gene expression. These studies significantly advance our understanding of this important viral host shutoff protein and may provide future opportunities to limit the pathogenesis of influenza A virus infection.
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Affiliation(s)
- Denys A. Khaperskyy
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Summer Schmaling
- Department of Molecular Biology and Microbiology and Graduate Program in Molecular Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Jonah Larkins-Ford
- Department of Molecular Biology and Microbiology and Graduate Program in Molecular Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Craig McCormick
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
- * E-mail: (CM); (MMG)
| | - Marta M. Gaglia
- Department of Molecular Biology and Microbiology and Graduate Program in Molecular Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America
- * E-mail: (CM); (MMG)
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85
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Bavagnoli L, Cucuzza S, Campanini G, Rovida F, Paolucci S, Baldanti F, Maga G. The novel influenza A virus protein PA-X and its naturally deleted variant show different enzymatic properties in comparison to the viral endonuclease PA. Nucleic Acids Res 2015; 43:9405-17. [PMID: 26384413 PMCID: PMC4627086 DOI: 10.1093/nar/gkv926] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 09/07/2015] [Indexed: 12/18/2022] Open
Abstract
The PA protein of Influenza A virus (IAV) encoded by segment 3 acts as a specialized RNA endonuclease in the transcription of the viral genome. The same genomic segment encodes for a second shorter protein, termed PA-X, with the first 191 N-terminal aminoacids (aa) identical to PA, but with a completely different C-ter domain of 61 aa, due to a ribosomal frameshifting. In addition, it has been shown that several IAV isolates encode for a naturally truncated PA-X variant, PAXΔC20, missing the last 20 aa. The biochemical properties of PA-X and PAXΔC20 have been poorly investigated so far. Here, we have carried out an enzymatic characterization of PA-X and its naturally deleted form, in comparison with PA from the human IAV strain A/WSN/33 (H1N1). Our results showed, to the best of our knowledge for the first time, that PA-X possesses an endonucleolytic activity. Both PA and PA-X preferentially cut single stranded RNA regions, but with some differences. In addition, we showed that PAXΔC20 has severely reduced nuclease activity. These results point to a previously undetected role of the last C-ter 20 aa for the catalytic activity of PA-X and support distinct roles for these proteins in the viral life cycle.
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Affiliation(s)
- Laura Bavagnoli
- Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy
| | - Stefano Cucuzza
- Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy
| | - Giulia Campanini
- Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy
| | - Francesca Rovida
- Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy
| | - Stefania Paolucci
- Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy
| | - Fausto Baldanti
- Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy
| | - Giovanni Maga
- Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy
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86
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Mapping of a Region of the PA-X Protein of Influenza A Virus That Is Important for Its Shutoff Activity. J Virol 2015; 89:8661-5. [PMID: 26041295 DOI: 10.1128/jvi.01132-15] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 05/28/2015] [Indexed: 01/10/2023] Open
Abstract
Influenza A virus PA-X comprises an N-terminal PA endonuclease domain and a C-terminal PA-X-specific domain. PA-X reduces host and viral mRNA accumulation via its endonuclease function. Here, we found that the N-terminal 15 amino acids, particularly six basic amino acids, in the C-terminal PA-X-specific region are important for PA-X shutoff activity. These six basic amino acids enabled a PA deletion mutant to suppress protein expression at a level comparable to that of wild-type PA-X.
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87
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Identification of Influenza A Virus PB2 Residues Involved in Enhanced Polymerase Activity and Virus Growth in Mammalian Cells at Low Temperatures. J Virol 2015; 89:8042-9. [PMID: 26018156 DOI: 10.1128/jvi.00901-15] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Accepted: 05/18/2015] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED Mutations in the polymerase genes are known to play a major role in avian influenza virus adaptation to mammalian hosts. Despite having avian origin PA and PB2, the 2009 pandemic H1N1 virus (pH1N1) can replicate well in mammalian respiratory tracts, suggesting that these proteins have acquired mutations for efficient growth in humans. We have previously shown that PA from the pH1N1 virus A/California/04/09 (Cal) strongly enhances activity of an otherwise avian polymerase complex derived from A/chicken/Nanchang/3-120/01 (Nan) in mammalian cells. However, this enhancement was observed at 37°C but not at the lower temperature of 34°C. An additional introduction of Cal PB2 enhanced activity at 34°C, suggesting the presence of unidentified residues in Cal PB2 that are required for efficient growth at low temperature. Here, we sought to determine the key PB2 residues which confer enhanced polymerase activity and virus growth in human cells at low temperature. Using a reporter gene assay, we identified novel mutations, PB2 V661A and V683T/A684S, which are involved in enhanced Cal polymerase activity at low temperature. The PB2 T271A mutation, which we previously reported, also contributed to enhanced activity. The growth of recombinant Cal containing PB2 with Nan residues 271T/661V/683V/684A was strongly reduced in human cells compared to wild-type virus at low temperature. Among the four residues, 271A and 684S are conserved in human and pH1N1 viruses but not in avian viruses, suggesting an important role in mammalian adaptation of pH1N1 virus. IMPORTANCE The PB2 protein plays a key role in the host adaptation, cold sensitivity, and pathogenesis of influenza A virus. Despite containing an avian origin PB2 lacking the mammalian adaptive mutations 627K or 701N, pH1N1 influenza virus strains can replicate efficiently in the low temperature upper respiratory tract of mammals, suggesting the presence of unknown mutations in the pH1N1 PB2 protein responsible for its low temperature adaptation. Here, in addition to PB2 271A, which has been shown to increase polymerase activity, we identified novel PB2 residues 661A and 683T/684S in pH1N1 which confer enhanced polymerase activity and virus growth in mammalian cells especially at low temperature. Our findings suggest that the presence of these PB2 residues contributes to efficient replication of the pH1N1 virus in the upper respiratory tract, which resulted in efficient human-to-human transmission of this virus.
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