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Gaucherand L, Iyer A, Gilabert I, Rycroft CH, Gaglia MM. Cut site preference allows influenza A virus PA-X to discriminate between host and viral mRNAs. Nat Microbiol 2023; 8:1304-1317. [PMID: 37349586 PMCID: PMC10690756 DOI: 10.1038/s41564-023-01409-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 05/10/2023] [Indexed: 06/24/2023]
Abstract
Many viruses block host gene expression to take over the infected cell. This process, termed host shutoff, is thought to promote viral replication by preventing antiviral responses and redirecting cellular resources to viral processes. Several viruses from divergent families accomplish host shutoff through RNA degradation by endoribonucleases. However, viruses also need to ensure expression of their own genes. The influenza A virus endoribonuclease PA-X solves this problem by sparing viral mRNAs and some host RNAs necessary for viral replication. To understand how PA-X distinguishes between RNAs, we characterized PA-X cut sites transcriptome-wide using 5' rapid amplification of complementary DNA ends coupled to high-throughput sequencing. This analysis, along with RNA structure predictions and validation experiments using reporters, shows that PA-Xs from multiple influenza strains preferentially cleave RNAs at GCUG tetramers in hairpin loops. Importantly, GCUG tetramers are enriched in the human but not the influenza transcriptome. Moreover, optimal PA-X cut sites inserted in the influenza A virus genome are quickly selected against during viral replication in cells. This finding suggests that PA-X evolved these cleavage characteristics to preferentially target host over viral mRNAs in a manner reminiscent of cellular self versus non-self discrimination.
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Affiliation(s)
- Lea Gaucherand
- Program in Molecular Microbiology, Tufts University Graduate School of Biomedical Sciences, Boston, MA, USA
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA, USA
- Architecture et Réactivité de l'ARN, Institut de Biologie Moléculaire et Cellulaire du CNRS, Université de Strasbourg, Strasbourg, France
| | - Amrita Iyer
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA, USA
| | - Isabel Gilabert
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA, USA
- Faculty of Experimental Sciences, Universidad Francisco de Vitoria, Madrid, Spain
| | - Chris H Rycroft
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
- Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Department of Mathematics, University of Wisconsin-Madison, Madison, WI, USA
| | - Marta M Gaglia
- Program in Molecular Microbiology, Tufts University Graduate School of Biomedical Sciences, Boston, MA, USA.
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA, USA.
- Institute for Molecular Virology and Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, Madison, WI, USA.
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Hu Y, Chen X, Ling Y, Zhou K, Han M, Wang X, Yue M, Li Y. Influenza A virus inhibits TET2 expression by endoribonuclease PA-X to attenuate type I interferon signaling and promote viral replication. PLoS Pathog 2023; 19:e1011550. [PMID: 37498975 PMCID: PMC10409264 DOI: 10.1371/journal.ppat.1011550] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2023] [Revised: 08/08/2023] [Accepted: 07/10/2023] [Indexed: 07/29/2023] Open
Abstract
Influenza A virus (IAV) expresses several accessory proteins to limit host anti-viral restriction factors to facilitate viral replication. The Ten-Eleven Translocation 2 (TET2) is a methylcytosine dioxygenase that promotes DNA demethylation by catalyzing the oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), which plays a vital role in hematopoiesis and immunity. Here we report that TET2 is a host restriction factor that limits IAV replication. But IAV endoribonuclease PA-X is able to remove the replication restriction by binding to TET2 mRNA and driving TET2 mRNA degradation to reduce TET2 expression during infection. Genetic inactivation of TET2 markedly enhances IAV replication in vitro and in vivo. Mechanistically, we found that TET2 regulates demethylation and transcription of STAT1 and some interferon-stimulated genes (ISGs), including ISG15, ISG20, and IFIT5, so the loss of TET2 greatly impairs type I Interferon signaling. Furthermore, we confirmed that TET2-mediated demethylation of the STAT1 gene is critical for interferon anti-viral activity. Our study demonstrates that the host TET2 is essential to the innate immune response against IAV infection.
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Affiliation(s)
- Yixiang Hu
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Hainan Institute of Zhejiang University, Sanya, Hainan, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
| | - Xinru Chen
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
| | - Yuehuan Ling
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
| | - Kun Zhou
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
| | - Meiqing Han
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Hainan Institute of Zhejiang University, Sanya, Hainan, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
| | - Xingbo Wang
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
| | - Min Yue
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Hainan Institute of Zhejiang University, Sanya, Hainan, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
- State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, National Medical Center for Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Yan Li
- Department of Veterinary Medicine & Institute of Preventive Veterinary Sciences, Zhejiang University College of Animal Sciences, Hangzhou, Zhejiang, China
- Hainan Institute of Zhejiang University, Sanya, Hainan, China
- Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang, China
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Abstract
Many viruses induce shutoff of host gene expression (host shutoff) as a strategy to take over cellular machinery and evade host immunity. Without host shutoff activity, these viruses generally replicate poorly in vivo, attesting to the importance of this antiviral strategy. In this review, we discuss one particularly advantageous way for viruses to induce host shutoff: triggering widespread host messenger RNA (mRNA) decay. Viruses can trigger increased mRNA destruction either directly, by encoding RNA cleaving or decapping enzymes, or indirectly, by activating cellular RNA degradation pathways. We review what is known about the mechanism of action of several viral RNA degradation factors. We then discuss the consequences of widespread RNA degradation on host gene expression and on the mechanisms of immune evasion, highlighting open questions. Answering these questions is critical to understanding how viral RNA degradation factors regulate host gene expression and how this process helps viruses evade host responses and replicate.
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Affiliation(s)
- Léa Gaucherand
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, and Graduate Program in Molecular Microbiology, Tufts Graduate School of Biomedical Sciences, Tufts University, Boston, Massachusetts, USA;
| | - Marta Maria Gaglia
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, and Graduate Program in Molecular Microbiology, Tufts Graduate School of Biomedical Sciences, Tufts University, Boston, Massachusetts, USA;
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Amino Acid Residues Involved in Inhibition of Host Gene Expression by Influenza A/Brevig Mission/1/1918 PA-X. Microorganisms 2021; 9:microorganisms9051109. [PMID: 34065592 PMCID: PMC8160905 DOI: 10.3390/microorganisms9051109] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 05/19/2021] [Accepted: 05/19/2021] [Indexed: 12/12/2022] Open
Abstract
The influenza A virus (IAV) PA-X protein is a virulence factor that selectively degrades host mRNAs leading to protein shutoff. This function modulates host inflammation, antiviral responses, cell apoptosis, and pathogenesis. In this work we describe a novel approach based on the use of bacteria and plasmid encoding of the PA-X gene under the control of the bacteriophage T7 promoter to identify amino acid residues important for A/Brevig Mission/1/1918 H1N1 PA-X’s shutoff activity. Using this system, we have identified PA-X mutants encoding single or double amino acid changes, which diminish its host shutoff activity, as well as its ability to counteract interferon responses upon viral infection. This novel bacteria-based approach could be used for the identification of viral proteins that inhibit host gene expression as well as the amino acid residues responsible for inhibition of host gene expression.
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Identification of amino acid residues required for inhibition of host gene expression by influenza A/Viet Nam/1203/2004 H5N1 PA-X. J Virol 2021; 96:e0040821. [PMID: 33853954 DOI: 10.1128/jvi.00408-21] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PA-X is a non-structural protein of influenza A virus (IAV), which is encoded by the polymerase acidic (PA) N-terminal region that contains a C-terminal +1 frameshifted sequence. IAV PA-X protein modulates virus-induced host innate immune responses and viral pathogenicity via suppression of host gene expression or cellular shutoff, through cellular mRNA cleavage. Highly pathogenic avian influenza viruses (HPAIV) of the H5N1 subtype naturally infect different avian species, they have an enormous economic impact in the poultry farming, and they also have zoonotic and pandemic potential, representing a risk to human public health. In the present study, we describe a novel bacteria-based approach to identify amino acid residues in the PA-X protein of the HPAIV A/Viet Nam/1203/2004 H5N1 that are important for its ability to inhibit host protein expression or cellular shutoff activity. Identified PA-X mutants displayed a reduced shutoff activity as compared to that of the wild-type (WT) A/Viet Nam/1203/2004 H5N1 PA-X protein. Notably, this new bacteria-based screening allowed us to identify amino acid residues widely distributed over the entire N-terminal region of PA-X. Furthermore, we found that some of the residues affecting A/Viet Nam/1203/2004 H5N1 PA-X host shutoff activity also affect PA polymerase activity in a minigenome assay. This information could be used for the rational design of new and more effective compounds with antiviral activity against IAV. Moreover, our results demonstrate the feasibility of using this bacteria-based approach to identify amino acid residues important for the activity of viral proteins to inhibit host gene expression. IMPORTANCE Highly pathogenic avian influenza viruses (HPAIV) continue to pose a huge threat to global animal and human health. Despite of the limited genome size of Influenza A virus (IAV), the virus encodes eight main viral structural proteins and multiple accessory non-structural proteins, depending on the IAV type, subtype or strain. One of the IAV accessory proteins, PA-X, is encoded by the polymerase acidic (PA) protein and is involved in pathogenicity through the modulation of IAV-induced host inflammatory and innate immune responses. However, the molecular mechanism(s) of IAV PA-X regulation of the host immune response is not well understood. In this work, we used, for the first time, a bacteria-based approach for the identification of amino acids important for the ability of IAV PA-X to induce host shutoff activity and describe novel residues relevant for its ability to inhibit host gene expression, and their contribution in PA polymerase activity.
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The influenza A virus host shutoff factor PA-X is rapidly turned over in a strain-specific manner. J Virol 2021; 95:JVI.02312-20. [PMID: 33504608 PMCID: PMC8103685 DOI: 10.1128/jvi.02312-20] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The influenza A endoribonuclease PA-X regulates virulence and transmission of the virus by reducing host gene expression and thus regulating immune responses to influenza A virus. Despite this key function in viral biology, the levels of PA-X protein remain markedly low during infection, and previous results suggest that these low levels are not solely the result of regulation of the level of translation and RNA stability. How PA-X is regulated post-translationally remains unknown. We now report that the PA-X protein is rapidly turned over. PA-X from multiple viral strains are short-lived, although the half-life of PA-X ranges from ∼30 minutes to ∼3.5 hours depending on the strain. Moreover, sequences in the variable PA-X C-terminal domain are primarily responsible for regulating PA-X half-life, although the N-terminal domain also accounts for some differences among strains. Interestingly, we find that the PA-X from the 2009 pandemic H1N1 strain has a longer half-life compared to the other variants we tested. This PA-X isoform has been reported to have a higher host shutoff activity, suggesting a role for protein turnover in regulating PA-X activity. Collectively, this study reveals a novel regulatory mechanism of PA-X protein levels that may impact host shutoff activity during influenza A virus infection.IMPORTANCE The PA-X protein from influenza A virus reduces host immune responses to infection through suppressing host gene expression, including genes encoding the antiviral response. Thus, it plays a central role in influenza A virus biology. Despite its key function, PA-X was only discovered in 2012 and much remains to be learned including how PA-X activity is regulated to promote optimal levels of viral infection. In this study, we reveal that PA-X protein levels are very low likely because of rapid turnover. We show that instability is a conserved property among PA-X variants from different strains of influenza A virus, but that the half-lives of PA-X variants differ. Moreover, the longer half-life of PA-X from the 2009 pandemic H1N1 strain correlates with its reported higher activity. Therefore, PA-X stability may be a way to regulate its activity and may contribute to the differential virulence of influenza A virus strains.
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