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Meng F, Yan T, Dahal K, Lu R. Unbiased genetic screen identifies Caenorhabditis elegans genes conserved for nodavirus genome replication. Virology 2022; 577:91-98. [PMID: 36332529 PMCID: PMC10234093 DOI: 10.1016/j.virol.2022.09.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 09/25/2022] [Accepted: 09/29/2022] [Indexed: 11/06/2022]
Abstract
All RNA viruses produce and use RNA-dependent RNA polymerases (RdRPs) for their genome replication. Efficient viral genome replication also requires host factors which often function as co-factors of viral RdRP. To identify host factors required for nodavirus genome replication, we carried out an unbiased genetic screen in Caenorhabditis elegans mutants defective in antiviral RNA interference. This genetic screen utilized a self-replicating GFP-tagged viral replicon, derived from flock house virus, as a reporter for the loss of viral genome replication. Upon completing the screen, 16 candidate alleles were isolated and assigned to 14 candidate genes through genetic complementation. Interestingly, 4 of the candidate genes were also found to be required for the genome replication of Orsay virus, a nodavirus that naturally infects C. elegans. Our unbiased genetic screen therefore has led to the identification of a set of worm genes conserved for nodavirus genome replication.
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Affiliation(s)
- Fei Meng
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70810, USA
| | - Teng Yan
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70810, USA
| | - Krishna Dahal
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70810, USA
| | - Rui Lu
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, 70810, USA.
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Lindenbach BD. Reinventing positive-strand RNA virus reverse genetics. Adv Virus Res 2022; 112:1-29. [PMID: 35840179 PMCID: PMC9273853 DOI: 10.1016/bs.aivir.2022.03.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
Reverse genetics is the prospective analysis of how genotype determines phenotype. In a typical experiment, a researcher alters a viral genome, then observes the phenotypic outcome. Among RNA viruses, this approach was first applied to positive-strand RNA viruses in the mid-1970s and over nearly 50 years has become a powerful and widely used approach for dissecting the mechanisms of viral replication and pathogenesis. During this time the global health importance of two virus groups, flaviviruses (genus Flavivirus, family Flaviviridae) and betacoronaviruses (genus Betacoronavirus, subfamily Orthocoronavirinae, family Coronaviridae), have dramatically increased, yet these viruses have genomes that are technically challenging to manipulate. As a result, several new techniques have been developed to overcome these challenges. Here I briefly review key historical aspects of positive-strand RNA virus reverse genetics, describe some recent reverse genetic innovations, particularly as applied to flaviviruses and coronaviruses, and discuss their benefits and limitations within the larger context of rigorous genetic analysis.
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Mao K, Breen P, Ruvkun G. Mitochondrial dysfunction induces RNA interference in C. elegans through a pathway homologous to the mammalian RIG-I antiviral response. PLoS Biol 2020; 18:e3000996. [PMID: 33264285 PMCID: PMC7735679 DOI: 10.1371/journal.pbio.3000996] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 12/14/2020] [Accepted: 11/09/2020] [Indexed: 12/27/2022] Open
Abstract
RNA interference (RNAi) is an antiviral pathway common to many eukaryotes that detects and cleaves foreign nucleic acids. In mammals, mitochondrially localized proteins such as mitochondrial antiviral signaling (MAVS), retinoic acid-inducible gene I (RIG-I), and melanoma differentiation-associated protein 5 (MDA5) mediate antiviral responses. Here, we report that mitochondrial dysfunction in Caenorhabditis elegans activates RNAi-directed silencing via induction of a pathway homologous to the mammalian RIG-I helicase viral response pathway. The induction of RNAi also requires the conserved RNA decapping enzyme EOL-1/DXO. The transcriptional induction of eol-1 requires DRH-1 as well as the mitochondrial unfolded protein response (UPRmt). Upon mitochondrial dysfunction, EOL-1 is concentrated into foci that depend on the transcription of mitochondrial RNAs that may form double-stranded RNA (dsRNA), as has been observed in mammalian antiviral responses. Enhanced RNAi triggered by mitochondrial dysfunction is necessary for the increase in longevity that is induced by mitochondrial dysfunction. Surveillance of mitochondrial dysfunction in the nematode Caenorhabditis elegans triggers the activation of an RNA interference pathway to mediate antiviral defense, in a manner homologous to the mammalian RIG-I helicase viral response pathway.
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Affiliation(s)
- Kai Mao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Peter Breen
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Gary Ruvkun
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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A Yeast Suppressor Screen Used To Identify Mammalian SIRT1 as a Proviral Factor for Middle East Respiratory Syndrome Coronavirus Replication. J Virol 2019; 93:JVI.00197-19. [PMID: 31142674 PMCID: PMC6675885 DOI: 10.1128/jvi.00197-19] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Accepted: 05/21/2019] [Indexed: 02/08/2023] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) initially emerged in 2012 and has since been responsible for over 2,300 infections, with a case fatality ratio of approximately 35%. We have used the highly characterized model system of Saccharomyces cerevisiae to investigate novel functional interactions between viral proteins and eukaryotic cells that may provide new avenues for antiviral intervention. We identify a functional link between the MERS-CoV ORF4a proteins and the YDL042C/SIR2 yeast gene. The mammalian homologue of SIR2 is SIRT1, an NAD-dependent histone deacetylase. We demonstrate for the first time that SIRT1 is a proviral factor for MERS-CoV replication and that ORF4a has a role in modulating its activity in mammalian cells. Viral proteins must intimately interact with the host cell machinery during virus replication. Here, we used the yeast Saccharomyces cerevisiae as a system to identify novel functional interactions between viral proteins and eukaryotic cells. Our work demonstrates that when the Middle East respiratory syndrome coronavirus (MERS-CoV) ORF4a accessory gene is expressed in yeast it causes a slow-growth phenotype. ORF4a has been characterized as an interferon antagonist in mammalian cells, and yet yeast lack an interferon system, suggesting further interactions between ORF4a and eukaryotic cells. Using the slow-growth phenotype as a reporter of ORF4a function, we utilized the yeast knockout library collection to perform a suppressor screen where we identified the YDL042C/SIR2 yeast gene as a suppressor of ORF4a function. The mammalian homologue of SIR2 is SIRT1, an NAD-dependent histone deacetylase. We found that when SIRT1 was inhibited by either chemical or genetic manipulation, there was reduced MERS-CoV replication, suggesting that SIRT1 is a proviral factor for MERS-CoV. Moreover, ORF4a inhibited SIRT1-mediated modulation of NF-κB signaling, demonstrating a functional link between ORF4a and SIRT1 in mammalian cells. Overall, the data presented here demonstrate the utility of yeast studies for identifying genetic interactions between viral proteins and eukaryotic cells. We also demonstrate for the first time that SIRT1 is a proviral factor for MERS-CoV replication and that ORF4a has a role in modulating its activity in cells. IMPORTANCE Middle East respiratory syndrome coronavirus (MERS-CoV) initially emerged in 2012 and has since been responsible for over 2,300 infections, with a case fatality ratio of approximately 35%. We have used the highly characterized model system of Saccharomyces cerevisiae to investigate novel functional interactions between viral proteins and eukaryotic cells that may provide new avenues for antiviral intervention. We identify a functional link between the MERS-CoV ORF4a proteins and the YDL042C/SIR2 yeast gene. The mammalian homologue of SIR2 is SIRT1, an NAD-dependent histone deacetylase. We demonstrate for the first time that SIRT1 is a proviral factor for MERS-CoV replication and that ORF4a has a role in modulating its activity in mammalian cells.
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Garcia-Ruiz H. Susceptibility Genes to Plant Viruses. Viruses 2018; 10:E484. [PMID: 30201857 PMCID: PMC6164914 DOI: 10.3390/v10090484] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 08/28/2018] [Accepted: 09/07/2018] [Indexed: 12/26/2022] Open
Abstract
Plant viruses use cellular factors and resources to replicate and move. Plants respond to viral infection by several mechanisms, including innate immunity, autophagy, and gene silencing, that viruses must evade or suppress. Thus, the establishment of infection is genetically determined by the availability of host factors necessary for virus replication and movement and by the balance between plant defense and viral suppression of defense responses. Host factors may have antiviral or proviral activities. Proviral factors condition susceptibility to viruses by participating in processes essential to the virus. Here, we review current advances in the identification and characterization of host factors that condition susceptibility to plant viruses. Host factors with proviral activity have been identified for all parts of the virus infection cycle: viral RNA translation, viral replication complex formation, accumulation or activity of virus replication proteins, virus movement, and virion assembly. These factors could be targets of gene editing to engineer resistance to plant viruses.
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Affiliation(s)
- Hernan Garcia-Ruiz
- Nebraska Center for Virology, Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68503, USA.
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The RNA Capping Enzyme Domain in Protein A is Essential for Flock House Virus Replication. Viruses 2018; 10:v10090483. [PMID: 30205593 PMCID: PMC6165433 DOI: 10.3390/v10090483] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 09/05/2018] [Accepted: 09/05/2018] [Indexed: 01/18/2023] Open
Abstract
The nodavirus flock house virus (FHV) and the alphavirus Semliki Forest virus (SFV) show evolutionarily intriguing similarities in their replication complexes and RNA capping enzymes. In this study, we first established an efficient FHV trans-replication system in mammalian cells, which disjoins protein expression from viral RNA synthesis. Following transfection, FHV replicase protein A was associated with mitochondria, whose outer surface displayed pouch-like invaginations with a ‘neck’ structure opening towards the cytoplasm. In mitochondrial pellets from transfected cells, high-level synthesis of both genomic and subgenomic RNA was detected in vitro and the newly synthesized RNA was of positive polarity. Secondly, we initiated the study of the putative RNA capping enzyme domain in protein A by mutating the conserved amino acids H93, R100, D141, and W215. RNA replication was abolished for all mutants inside cells and in vitro except for W215A, which showed reduced replication. Transfection of capped RNA template did not rescue the replication activity of the mutants. Comparing the efficiency of SFV and FHV trans-replication systems, the FHV system appeared to produce more RNA. Using fluorescent marker proteins, we demonstrated that both systems could replicate in the same cell. This work may facilitate the comparative analysis of FHV and SFV replication.
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Abstract
Tobacco mosaic virus and other tobamoviruses have served as models for studying the mechanisms of viral RNA replication. In tobamoviruses, genomic RNA replication occurs via several steps: (a) synthesis of viral replication proteins by translation of the genomic RNA; (b) translation-coupled binding of the replication proteins to a 5'-terminal region of the genomic RNA; (c) recruitment of the genomic RNA by replication proteins onto membranes and formation of a complex with host proteins TOM1 and ARL8; (d) synthesis of complementary (negative-strand) RNA in the complex; and (e) synthesis of progeny genomic RNA. This article reviews current knowledge on tobamovirus RNA replication, particularly regarding how the genomic RNA is specifically selected as a replication template and how the replication proteins are activated. We also focus on the roles of the replication proteins in evading or suppressing host defense systems.
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Affiliation(s)
- Kazuhiro Ishibashi
- Plant and Microbial Research Unit, Division of Plant and Microbial Sciences, Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), Tsukuba 305-8602, Japan ,
| | - Masayuki Ishikawa
- Plant and Microbial Research Unit, Division of Plant and Microbial Sciences, Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), Tsukuba 305-8602, Japan ,
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Abstract
Viruses have evolved intricate mechanisms to gain entry into the host cell. Identification of host proteins that serve as viral receptors has enabled insights into virus particle internalization, host and tissue tropism, and viral pathogenesis. In this review we discuss the most commonly employed methods for virus receptor discovery, specifically highlighting the use of forward genetic screens in human haploid cells. The ability to generate true knockout alleles at high saturation provides a sensitive means to study virus-host interactions. To illustrate the power of such haploid genetic screens, we highlight the discovery of the lysosomal proteins NPC1 and LAMP1 as intracellular receptors for Ebola virus and Lassa virus, respectively. From these studies emerges the notion that receptor usage by these viruses is highly dynamic, involving a programmed switch from cell surface receptor to intracellular receptor. Broad application of genetic knockout approaches will chart functional landscapes of receptors and endocytic pathways hijacked by viruses.
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Affiliation(s)
- Sirika Pillay
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305; ,
| | - Jan E Carette
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305; ,
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Sasvari Z, Alatriste Gonzalez P, Nagy PD. Tombusvirus-yeast interactions identify conserved cell-intrinsic viral restriction factors. FRONTIERS IN PLANT SCIENCE 2014; 5:383. [PMID: 25157258 PMCID: PMC4127529 DOI: 10.3389/fpls.2014.00383] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Accepted: 07/18/2014] [Indexed: 05/23/2023]
Abstract
To combat viral infections, plants possess innate and adaptive immune pathways, such as RNA silencing, R gene and recessive gene-mediated resistance mechanisms. However, it is likely that additional cell-intrinsic restriction factors (CIRF) are also involved in limiting plant virus replication. This review discusses novel CIRFs with antiviral functions, many of them RNA-binding proteins or affecting the RNA binding activities of viral replication proteins. The CIRFs against tombusviruses have been identified in yeast (Saccharomyces cerevisiae), which is developed as an advanced model organism. Grouping of the identified CIRFs based on their known cellular functions and subcellular localization in yeast reveals that TBSV replication is limited by a wide variety of host gene functions. Yeast proteins with the highest connectivity in the network map include the well-characterized Xrn1p 5'-3' exoribonuclease, Act1p actin protein and Cse4p centromere protein. The protein network map also reveals an important interplay between the pro-viral Hsp70 cellular chaperone and the antiviral co-chaperones, and possibly key roles for the ribosomal or ribosome-associated factors. We discuss the antiviral functions of selected CIRFs, such as the RNA binding nucleolin, ribonucleases, WW-domain proteins, single- and multi-domain cyclophilins, TPR-domain co-chaperones and cellular ion pumps. These restriction factors frequently target the RNA-binding region in the viral replication proteins, thus interfering with the recruitment of the viral RNA for replication and the assembly of the membrane-bound viral replicase. Although many of the characterized CIRFs act directly against TBSV, we propose that the TPR-domain co-chaperones function as "guardians" of the cellular Hsp70 chaperone system, which is subverted efficiently by TBSV for viral replicase assembly in the absence of the TPR-domain co-chaperones.
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Affiliation(s)
| | | | - Peter D. Nagy
- *Correspondence: Peter D. Nagy, Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, KY 40546, USA e-mail:
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Chasman D, Gancarz B, Hao L, Ferris M, Ahlquist P, Craven M. Inferring host gene subnetworks involved in viral replication. PLoS Comput Biol 2014; 10:e1003626. [PMID: 24874113 PMCID: PMC4038467 DOI: 10.1371/journal.pcbi.1003626] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 02/06/2014] [Indexed: 12/16/2022] Open
Abstract
Systematic, genome-wide loss-of-function experiments can be used to identify host factors that directly or indirectly facilitate or inhibit the replication of a virus in a host cell. We present an approach that combines an integer linear program and a diffusion kernel method to infer the pathways through which those host factors modulate viral replication. The inputs to the method are a set of viral phenotypes observed in single-host-gene mutants and a background network consisting of a variety of host intracellular interactions. The output is an ensemble of subnetworks that provides a consistent explanation for the measured phenotypes, predicts which unassayed host factors modulate the virus, and predicts which host factors are the most direct interfaces with the virus. We infer host-virus interaction subnetworks using data from experiments screening the yeast genome for genes modulating the replication of two RNA viruses. Because a gold-standard network is unavailable, we assess the predicted subnetworks using both computational and qualitative analyses. We conduct a cross-validation experiment in which we predict whether held-aside test genes have an effect on viral replication. Our approach is able to make high-confidence predictions more accurately than several baselines, and about as well as the best baseline, which does not infer mechanistic pathways. We also examine two kinds of predictions made by our method: which host factors are nearest to a direct interaction with a viral component, and which unassayed host genes are likely to be involved in viral replication. Multiple predictions are supported by recent independent experimental data, or are components or functional partners of confirmed relevant complexes or pathways. Integer program code, background network data, and inferred host-virus subnetworks are available at http://www.biostat.wisc.edu/~craven/chasman_host_virus/.
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Affiliation(s)
- Deborah Chasman
- Department of Computer Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
- Department of Biostatistics and Medical Informatics, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
| | - Brandi Gancarz
- Luminex Corporation, Madison, Wisconsin, United States of America
- Institute for Molecular Virology, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
| | - Linhui Hao
- Institute for Molecular Virology, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
- Howard Hughes Medical Institute, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
| | - Michael Ferris
- Department of Computer Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
| | - Paul Ahlquist
- Institute for Molecular Virology, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
- Howard Hughes Medical Institute, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
- Morgridge Institute for Research, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
| | - Mark Craven
- Department of Computer Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
- Department of Biostatistics and Medical Informatics, University of Wisconsin–Madison, Madison, Wisconsin, United States of America
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