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Ferron F, Lescar J. The Phlebovirus Ribonucleoprotein: An Overview. Methods Mol Biol 2024; 2824:259-280. [PMID: 39039418 DOI: 10.1007/978-1-0716-3926-9_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/24/2024]
Abstract
In negative strand RNA viruses, ribonucleoproteins, not naked RNA, constitute the template used by the large protein endowed with polymerase activity for replicating and transcribing the viral genome. Here we give an overview of the structures and functions of the ribonucleoprotein from phleboviruses. The nucleocapsid monomer, which constitutes the basic structural unit, possesses a flexible arm allowing for a conformational switch between a closed monomeric state and the formation of a polymeric filamentous structure competent for viral RNA binding and encapsidation in the open state of N. The modes of N-N oligomerization as well as interactions with vRNA are described. Finally, recent advances in tomography open exciting perspectives for a more complete understanding of N-L interactions and the design of specific antiviral compounds.
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Affiliation(s)
- François Ferron
- Aix Marseille Univ, CNRS - Architecture et Fonction des Macromolécules Biologiques (AFMB) UMR7257, Marseille, France.
- European Virus Bioinformatics Center, Jena, Germany.
| | - Julien Lescar
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
- NTU Institute of Structural Biology, Nanyang Technological University, Experimental Medicine Building, Singapore, Singapore.
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2
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Tercero B, Terasaki K, Narayanan K, Makino S. Mechanistic insight into the efficient packaging of antigenomic S RNA into Rift Valley fever virus particles. Front Cell Infect Microbiol 2023; 13:1132757. [PMID: 36875526 PMCID: PMC9978001 DOI: 10.3389/fcimb.2023.1132757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 02/06/2023] [Indexed: 02/18/2023] Open
Abstract
Rift Valley fever virus (RVFV), a bunyavirus, has a single-stranded, negative-sense tri-segmented RNA genome, consisting of L, M and S RNAs. An infectious virion carries two envelope glycoproteins, Gn and Gc, along with ribonucleoprotein complexes composed of encapsidated viral RNA segments. The antigenomic S RNA, which serves as the template of the mRNA encoding a nonstructural protein, NSs, an interferon antagonist, is also efficiently packaged into RVFV particles. An interaction between Gn and viral ribonucleoprotein complexes, including the direct binding of Gn to viral RNAs, drives viral RNA packaging into RVFV particles. To understand the mechanism of efficient antigenomic S RNA packaging in RVFV, we identified the regions in viral RNAs that directly interact with Gn by performing UV-crosslinking and immunoprecipitation of RVFV-infected cell lysates with anti-Gn antibody followed by high-throughput sequencing analysis (CLIP-seq analysis). Our data suggested the presence of multiple Gn-binding sites in RVFV RNAs, including a prominent Gn-binding site within the 3' noncoding region of the antigenomic S RNA. We found that the efficient packaging of antigenomic S RNA was abrogated in a RVFV mutant lacking a part of this prominent Gn-binding site within the 3' noncoding region. Also, the mutant RVFV, but not the parental RVFV, triggered the early induction of interferon-β mRNA expression after infection. These data suggest that the direct binding of Gn to the RNA element within the 3' noncoding region of the antigenomic S RNA promoted the efficient packaging of antigenomic S RNA into virions. Furthermore, the efficient packaging of antigenomic S RNA into RVFV particles, driven by the RNA element, facilitated the synthesis of viral mRNA encoding NSs immediately after infection, resulting in the suppression of interferon-β mRNA expression.
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Affiliation(s)
- Breanna Tercero
- Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, TX, United States
| | - Kaori Terasaki
- Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, TX, United States
- Institute for Human Infections and Immunity, The University of Texas Medical Branch, Galveston, TX, United States
| | - Krishna Narayanan
- Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, TX, United States
| | - Shinji Makino
- Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, TX, United States
- Institute for Human Infections and Immunity, The University of Texas Medical Branch, Galveston, TX, United States
- Center for Biodefense and Emerging Infectious Diseases, The University of Texas Medical Branch, Galveston, TX, United States
- UTMB Center for Tropical Diseases, The University of Texas Medical Branch, Galveston, TX, United States
- The Sealy Institute for Vaccine Sciences, The University of Texas Medical Branch, Galveston, TX, United States
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3
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Bracci N, de la Fuente C, Saleem S, Pinkham C, Narayanan A, García-Sastre A, Balaraman V, Richt JA, Wilson W, Kehn-Hall K. Rift Valley fever virus Gn V5-epitope tagged virus enables identification of UBR4 as a Gn interacting protein that facilitates Rift Valley fever virus production. Virology 2022; 567:65-76. [PMID: 35032865 PMCID: PMC8877469 DOI: 10.1016/j.virol.2021.12.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 11/15/2021] [Accepted: 12/31/2021] [Indexed: 02/03/2023]
Abstract
Rift Valley fever virus (RVFV) is an arbovirus that was first reported in the Rift Valley of Kenya which causes significant disease in humans and livestock. RVFV is a tri-segmented, negative-sense RNA virus consisting of a L, M, and S segments with the M segment encoding the glycoproteins Gn and Gc. Host factors that interact with Gn are largely unknown. To this end, two viruses containing an epitope tag (V5) on the Gn protein in position 105 or 229 (V5Gn105 and V5Gn229) were generated using the RVFV MP-12 vaccine strain as a backbone. The V5-tag insertion minimally impacted Gn functionality as measured by replication kinetics, Gn localization, and antibody neutralization assays. A proteomics-based approach was used to identify novel Gn-binding host proteins, including the E3 ubiquitin-protein ligase, UBR4. Depletion of UBR4 resulted in a significant decrease in RVFV titers and a reduction in viral RNA production.
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Affiliation(s)
- Nicole Bracci
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University,National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University
| | - Cynthia de la Fuente
- The National Institutes of Health, National Institute of Allergy and Infectious Diseases, DEA,National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University
| | - Sahar Saleem
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University
| | - Chelsea Pinkham
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University
| | - Aarthi Narayanan
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University
| | | | - Velmurugan Balaraman
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University
| | - Juergen A. Richt
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University
| | - William Wilson
- National Bio and Agro-Defense Facility, Agricultural Research Service, USDA
| | - Kylene Kehn-Hall
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University,National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University,Center for Zoonotic and Arthropod-borne Pathogens, Virginia Polytechnic Institute and State University,Corresponding Author: Kylene Kehn-Hall, Ph.D., Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Integrated Life Sciences Building, 1981 Kraft Drive, Blacksburg, VA 24060 USA,
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4
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Alem F, Olanrewaju AA, Omole S, Hobbs HE, Ahsan N, Matulis G, Brantner CA, Zhou W, Petricoin EF, Liotta LA, Caputi M, Bavari S, Wu Y, Kashanchi F, Hakami RM. Exosomes originating from infection with the cytoplasmic single-stranded RNA virus Rift Valley fever virus (RVFV) protect recipient cells by inducing RIG-I mediated IFN-B response that leads to activation of autophagy. Cell Biosci 2021; 11:220. [PMID: 34953502 PMCID: PMC8710069 DOI: 10.1186/s13578-021-00732-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 12/12/2021] [Indexed: 12/12/2022] Open
Abstract
Background Although multiple studies have demonstrated a role for exosomes during virus infections, our understanding of the mechanisms by which exosome exchange regulates immune response during viral infections and affects viral pathogenesis is still in its infancy. In particular, very little is known for cytoplasmic single-stranded RNA viruses such as SARS-CoV-2 and Rift Valley fever virus (RVFV). We have used RVFV infection as a model for cytoplasmic single-stranded RNA viruses to address this gap in knowledge. RVFV is a highly pathogenic agent that causes RVF, a zoonotic disease for which no effective therapeutic or approved human vaccine exist. Results We show here that exosomes released from cells infected with RVFV (designated as EXi-RVFV) serve a protective role for the host and provide a mechanistic model for these effects. Our results show that treatment of both naïve immune cells (U937 monocytes) and naïve non-immune cells (HSAECs) with EXi-RVFV induces a strong RIG-I dependent activation of IFN-B. We also demonstrate that this strong anti-viral response leads to activation of autophagy in treated cells and correlates with resistance to subsequent viral infection. Since we have shown that viral RNA genome is associated with EXi-RVFV, RIG-I activation might be mediated by the presence of packaged viral RNA sequences. Conclusions Using RVFV infection as a model for cytoplasmic single-stranded RNA viruses, our results show a novel mechanism of host protection by exosomes released from infected cells (EXi) whereby the EXi activate RIG-I to induce IFN-dependent activation of autophagy in naïve recipient cells including monocytes. Because monocytes serve as reservoirs for RVFV replication, this EXi-RVFV-induced activation of autophagy in monocytes may work to slow down or halt viral dissemination in the infected organism. These findings offer novel mechanistic insights that may aid in future development of effective vaccines or therapeutics, and that may be applicable for a better molecular understanding of how exosome release regulates innate immune response to other cytoplasmic single-stranded RNA viruses. Supplementary Information The online version contains supplementary material available at 10.1186/s13578-021-00732-z.
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Affiliation(s)
- Farhang Alem
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Adeyemi A Olanrewaju
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Samson Omole
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Heather E Hobbs
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Noor Ahsan
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA.,Lentigen Technology, Inc., Gaithersburg, MD, USA
| | - Graham Matulis
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Christine A Brantner
- Nanofabrication and Imaging Center, George Washington University, Washington, DC, USA
| | - Weidong Zhou
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, VA, USA
| | - Emanuel F Petricoin
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, VA, USA
| | - Lance A Liotta
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, VA, USA
| | - Massimo Caputi
- Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, USA
| | | | - Yuntao Wu
- School of Systems Biology, George Mason University, Manassas, VA, USA.,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA
| | - Fatah Kashanchi
- School of Systems Biology, George Mason University, Manassas, VA, USA
| | - Ramin M Hakami
- School of Systems Biology, George Mason University, Manassas, VA, USA. .,Center for Infectious Disease Research (Formerly, National Center for Biodefense and Infectious Diseases), George Mason University, Manassas, VA, USA.
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5
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Hayashi M, Schultz EP, Lanchy JM, Lodmell JS. Time-Resolved Analysis of N-RNA Interactions during RVFV Infection Shows Qualitative and Quantitative Shifts in RNA Encapsidation and Packaging. Viruses 2021; 13:2417. [PMID: 34960686 PMCID: PMC8704896 DOI: 10.3390/v13122417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/28/2021] [Accepted: 11/29/2021] [Indexed: 11/16/2022] Open
Abstract
Rift Valley fever virus (RVFV) is a negative-sense, tripartite RNA virus that is endemic to Africa and the Arabian Peninsula. It can cause severe disease and mortality in humans and domestic livestock and is a concern for its potential to spread more globally. RVFV's nucleocapsid protein (N) is an RNA-binding protein that is necessary for viral transcription, replication, and the production of nascent viral particles. We have conducted crosslinking, immunoprecipitation, and sequencing (CLIP-seq) to characterize N interactions with host and viral RNAs during infection. In parallel, to precisely measure intracellular N levels, we employed multiple reaction monitoring mass spectrometry (MRM-MS). Our results show that N binds mostly to host RNAs at early stages of infection, yielding nascent virus particles of reduced infectivity. The expression of N plateaus 10 h post-infection, whereas the intracellular viral RNA concentration continues to increase. Moreover, the virions produced later in infection have higher infectivity. Taken together, the detailed examination of these N-RNA interactions provides insight into how the regulated expression of N and viral RNA produces both infectious and incomplete, noninfectious particles.
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Affiliation(s)
- Miyuki Hayashi
- Department of Chemistry and Biochemistry, University of Montana, Missoula, MT 59812, USA;
- Center for Biomolecular Structure and Dynamics, Missoula, MT 59812, USA;
| | - Eric P. Schultz
- Center for Biomolecular Structure and Dynamics, Missoula, MT 59812, USA;
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA;
| | - Jean-Marc Lanchy
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA;
| | - J. Stephen Lodmell
- Center for Biomolecular Structure and Dynamics, Missoula, MT 59812, USA;
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA;
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6
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Characterization of the Molecular Interactions That Govern the Packaging of Viral RNA Segments into Rift Valley Fever Phlebovirus Particles. J Virol 2021; 95:e0042921. [PMID: 33952635 DOI: 10.1128/jvi.00429-21] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Rift Valley fever phlebovirus (RVFV) has a single-stranded, negative-sense RNA genome, consisting of L, M, and S segments. The virion carries two envelope glycoproteins, Gn and Gc, along with ribonucleoprotein complexes (RNPs), composed of encapsidated genomes carrying N protein and the viral polymerase, L protein. A quantitative analysis of the profile of viral RNA segments packaged into RVFV particles showed that all three genomic RNA segments had similar packaging abilities, whereas among antigenomic RNA segments, the antigenomic S RNA, which serves as the template for the transcription of mRNA expressing the RVFV virulence factor, NSs, displayed a significantly higher packaging ability. To delineate the factor(s) governing the packaging of RVFV RNA segments, we characterized the interactions between Gn and viral RNPs in RVFV-infected cells. Coimmunoprecipitation analysis demonstrated the interaction of Gn with N protein, L protein, and viral RNAs in RVFV-infected cells. Furthermore, UV-cross-linking and immunoprecipitation analysis revealed, for the first time in bunyaviruses, the presence of a direct interaction between Gn and all the viral RNA segments in RVFV-infected cells. Notably, analysis of the ability of Gn to bind to RVFV RNA segments indicated a positive correlation with their respective packaging abilities and highlighted a binding preference of Gn for antigenomic S RNA, among the antigenomic RNA segments, suggesting the presence of a selection mechanism for antigenomic S RNA incorporation into infectious RVFV particles. Collectively, the results of our study illuminate the importance of a direct interaction between Gn and viral RNA segments in determining their efficiency of incorporation into RVFV particles. IMPORTANCE Rift Valley fever phlebovirus, a bunyavirus, is a mosquito-borne, segmented RNA virus that can cause severe disease in humans and ruminants. An essential step in RVFV life cycle is the packaging of viral RNA segments to produce infectious virus particles for dissemination to new hosts. However, there are key gaps in knowledge regarding the mechanisms that regulate viral RNA packaging efficiency in bunyaviruses. Our studies investigating the mechanism of RNA packaging in RVFV revealed the presence of a direct interaction between the viral envelope glycoprotein, Gn, and the viral RNA segments in infected cells, for the first time in bunyaviruses. Furthermore, our data strongly indicate a critical role for the direct interaction between Gn and viral RNAs in determining the efficiency of incorporation of viral RNA segments into RVFV particles. Clarifying the fundamental mechanisms of RNA packaging in RVFV would be valuable for the development of antivirals and live-attenuated vaccines.
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7
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Bermúdez-Méndez E, Katrukha EA, Spruit CM, Kortekaas J, Wichgers Schreur PJ. Visualizing the ribonucleoprotein content of single bunyavirus virions reveals more efficient genome packaging in the arthropod host. Commun Biol 2021; 4:345. [PMID: 33753850 PMCID: PMC7985392 DOI: 10.1038/s42003-021-01821-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 02/09/2021] [Indexed: 01/31/2023] Open
Abstract
Bunyaviruses have a genome that is divided over multiple segments. Genome segmentation complicates the generation of progeny virus, since each newly formed virus particle should preferably contain a full set of genome segments in order to disseminate efficiently within and between hosts. Here, we combine immunofluorescence and fluorescence in situ hybridization techniques to simultaneously visualize bunyavirus progeny virions and their genomic content at single-molecule resolution in the context of singly infected cells. Using Rift Valley fever virus and Schmallenberg virus as prototype tri-segmented bunyaviruses, we show that bunyavirus genome packaging is influenced by the intracellular viral genome content of individual cells, which results in greatly variable packaging efficiencies within a cell population. We further show that bunyavirus genome packaging is more efficient in insect cells compared to mammalian cells and provide new insights on the possibility that incomplete particles may contribute to bunyavirus spread as well.
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Affiliation(s)
- Erick Bermúdez-Méndez
- Department of Virology, Wageningen Bioveterinary Research, Lelystad, The Netherlands
- Laboratory of Virology, Wageningen University, Wageningen, The Netherlands
| | - Eugene A Katrukha
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Cindy M Spruit
- Department of Virology, Wageningen Bioveterinary Research, Lelystad, The Netherlands
- Department of Chemical Biology & Drug Discovery, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
| | - Jeroen Kortekaas
- Department of Virology, Wageningen Bioveterinary Research, Lelystad, The Netherlands
- Laboratory of Virology, Wageningen University, Wageningen, The Netherlands
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8
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Molecular aspects of Rift Valley fever virus and the emergence of reassortants. Virus Genes 2018; 55:1-11. [PMID: 30426314 DOI: 10.1007/s11262-018-1611-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 11/03/2018] [Indexed: 10/27/2022]
Abstract
Rift Valley fever phlebovirus (RVFV) is a mosquito-transmitted pathogen endemic to sub-Saharan Africa and the Arabian Peninsula. RVFV is a threat to both animal and human health and has costly economic consequences mainly related to livestock production and trade. Competent hosts and vectors for RVFV are widespread, existing outside of endemic countries including the USA. Thus, the possibility of RVFV spreading to the USA or other countries worldwide is of significant concern. RVFV (genus Phlebovirus) is comprised of an enveloped virion containing a three-segmented, negative-stranded RNA genome that is able to undergo genetic reassortment. Reassortment has the potential to produce viruses that are more pathogenic, easily transmissible, and that have wider vector or host range. This is especially concerning because of the wide use of live attenuated vaccine strains throughout endemic countries. This review focuses on the molecular aspects of RVFV, genetic diversity of RVFV strains, and RVFV reassortment.
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9
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Wichgers Schreur PJ, Kormelink R, Kortekaas J. Genome packaging of the Bunyavirales. Curr Opin Virol 2018; 33:151-155. [PMID: 30227361 DOI: 10.1016/j.coviro.2018.08.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2018] [Revised: 08/17/2018] [Accepted: 08/28/2018] [Indexed: 11/18/2022]
Abstract
The order Bunyavirales comprises nine families of enveloped, negative-strand RNA viruses. Depending on the family and genus, bunyaviruses (i.e. now referring to all members of the Bunyavirales) contain genomes consisting of two to six segments. Each genome segment is encapsidated by multiple copies of the nucleocapsid (N) protein and one or a few molecules of the viral polymerase, forming so-called ribonucleoproteins (RNPs). Incorporation of RNPs into virions is mediated by the interaction of N with the cytoplasmic tails of the structural glycoproteins. Although some selectivity exists in the packaging of RNPs into virions, which seems to be driven by the 5' and 3'-untranslated regions of the genomic RNA segments, evidence is accumulating that bunyavirus genome packaging is a stochastic process.
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Affiliation(s)
| | - Richard Kormelink
- Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
| | - Jeroen Kortekaas
- Wageningen Bioveterinary Research, Houtribweg 39, 8221 RA Lelystad, The Netherlands; Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
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10
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Lundu T, Tsuda Y, Ito R, Shimizu K, Kobayashi S, Yoshii K, Yoshimatsu K, Arikawa J, Kariwa H. Targeting of severe fever with thrombocytopenia syndrome virus structural proteins to the ERGIC (endoplasmic reticulum Golgi intermediate compartment) and Golgi complex. Biomed Res 2018; 39:27-38. [PMID: 29467349 DOI: 10.2220/biomedres.39.27] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV) is a newly emerged phlebovirus identified in China, Japan, and South Korea. Phlebovirus glycoproteins (GP) play a key role in targeting viral structural components to the budding compartments in the ER-Golgi intermediate compartment (ERGIC) and Golgi complex. However, the role of SFTSV GP in targeting structural proteins to the ERGIC and Golgi complex remains unresolved. In this study, we show that SFTSV GP plays a significant role in targeting RNA-dependent RNA polymerase (L) and nucleocapsid protein (NP) to the budding sites. Confocal microscopy was used to investigate the subcellular localization of SFTSV structural proteins. In SFTSV-infected cells, GP and L localized to the ER, ERGIC and Golgi complex, whereas NP localized to the ERGIC and Golgi complex. In addition, GP colocalized with L and NP in infected cells. In cells singly transfected with GP, L or NP, GP localized to the same subcellular compartments as in infected cells. However, L or NP alone did not localize to the ER, ERGIC, or Golgi complex. Cotransfection experiments showed that GP altered the localization of L to the ERGIC and Golgi complex but not that of NP. Interestingly, plasmid-expressed NP fused with a hemagglutinin tag localized to the ERGIC and Golgi complex when expressed in SFTSV-infected cells and colocalised with GP, suggesting that GP plays a role in the subcellular localization of L and NP in infected cells. Thus, the SFTSV structural components start to assemble at the ERGIC to Golgi complex. GP is required for transporting L and NP to the ERGIC and Golgi complex. In addition, targeting of NP requires interaction with other factors besides GP.
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Affiliation(s)
- Tapiwa Lundu
- Laboratory of Public Health, Department of Preventive Veterinary Science, Division of Veterinary Medicine, Graduate School of Veterinary Medicine, Hokkaido University.,Department of Biomedical Sciences, School of Veterinary Medicine, University of Zambia
| | - Yoshimi Tsuda
- Laboratory of Microbiology and Infectious Diseases, Department of Microbiology and Immunology, Faculty of Medicine, Hokkaido University
| | - Ryo Ito
- Laboratory of Microbiology and Infectious Diseases, Department of Microbiology and Immunology, Faculty of Medicine, Hokkaido University
| | - Kenta Shimizu
- Laboratory of Microbiology and Infectious Diseases, Department of Microbiology and Immunology, Faculty of Medicine, Hokkaido University
| | - Shintaro Kobayashi
- Laboratory of Public Health, Department of Preventive Veterinary Science, Division of Veterinary Medicine, Faculty of Veterinary Medicine, Hokkaido University
| | - Kentaro Yoshii
- Laboratory of Public Health, Department of Preventive Veterinary Science, Division of Veterinary Medicine, Faculty of Veterinary Medicine, Hokkaido University
| | - Kumiko Yoshimatsu
- Laboratory of Microbiology and Infectious Diseases, Department of Microbiology and Immunology, Faculty of Medicine, Hokkaido University
| | - Jiro Arikawa
- Laboratory of Microbiology and Infectious Diseases, Department of Microbiology and Immunology, Faculty of Medicine, Hokkaido University
| | - Hiroaki Kariwa
- Laboratory of Public Health, Department of Preventive Veterinary Science, Division of Veterinary Medicine, Faculty of Veterinary Medicine, Hokkaido University
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11
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Atkins C, Freiberg AN. Recent advances in the development of antiviral therapeutics for Rift Valley fever virus infection. Future Virol 2017; 12:651-665. [PMID: 29181086 DOI: 10.2217/fvl-2017-0060] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 07/26/2017] [Indexed: 12/25/2022]
Abstract
Rift Valley fever virus (RVFV) is a mosquito-borne bunyavirus endemic to sub-Saharan Africa and the Arabian Peninsula and the etiological agent of Rift Valley fever. Rift Valley fever is a disease of major public health and economic concern, affecting livestock and humans. In ruminants, RVFV infection is characterized by high mortality rates in newborns and near 100% abortion rates in pregnant animals. Infection in humans is typically manifested as a self-limiting febrile illness, but can lead to severe and fatal hepatitis, encephalitis, hemorrhagic fever or retinitis with partial or complete blindness. Currently, there are no specific treatment options available for RVFV infection. This review presents a summary of the therapeutic approaches that have been explored on the treatment of RVFV infection.
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Affiliation(s)
- Colm Atkins
- Department of Pathology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,Department of Pathology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA
| | - Alexander N Freiberg
- Department of Pathology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,The Sealy Center for Vaccine Development, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,The Center for Biodefense & Emerging Infectious Diseases, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,Department of Pathology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,The Sealy Center for Vaccine Development, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA.,The Center for Biodefense & Emerging Infectious Diseases, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555, USA
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Sorafenib Impedes Rift Valley Fever Virus Egress by Inhibiting Valosin-Containing Protein Function in the Cellular Secretory Pathway. J Virol 2017; 91:JVI.00968-17. [PMID: 28794043 DOI: 10.1128/jvi.00968-17] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Accepted: 08/04/2017] [Indexed: 12/20/2022] Open
Abstract
There is an urgent need for therapeutic development to combat infections caused by Rift Valley fever virus (RVFV), which causes devastating disease in both humans and animals. In an effort to repurpose drugs for RVFV treatment, our previous studies screened a library of FDA-approved drugs. The most promising candidate identified was the hepatocellular and renal cell carcinoma drug sorafenib. Mechanism-of-action studies indicated that sorafenib targeted a late stage in virus infection and caused a buildup of virions within cells. In addition, small interfering RNA (siRNA) knockdown studies suggested that nonclassical targets of sorafenib are important for the propagation of RVFV. Here we extend our previous findings to identify the mechanism by which sorafenib inhibits the release of RVFV virions from the cell. Confocal microscopy imaging revealed that glycoprotein Gn colocalizes and accumulates within the endoplasmic reticulum (ER) and the transport of Gn from the Golgi complex to the host cell membrane is reduced. Transmission electron microscopy demonstrated that sorafenib caused virions to be present inside large vacuoles inside the cells. p97/valosin-containing protein (VCP), which is involved in membrane remodeling in the secretory pathway and a known target of sorafenib, was found to be important for RVFV egress. Knockdown of VCP resulted in decreased RVFV replication, reduced Gn Golgi complex localization, and increased Gn ER accumulation. The intracellular accumulation of RVFV virions was also observed in cells transfected with siRNA targeting VCP. Collectively, these data indicate that sorafenib causes a disruption in viral egress by targeting VCP and the secretory pathway, resulting in a buildup of virions within dilated ER vesicles.IMPORTANCE In humans, symptoms of RVFV infection mainly include a self-limiting febrile illness. However, in some cases, infected individuals can also experience hemorrhagic fever, neurological disorders, liver failure, and blindness, which could collectively be lethal. The ability of RVFV to expand geographically outside sub-Saharan Africa is of concern, particularly to the Americas, where native mosquito species are capable of virus transmission. Currently, there are no FDA-approved therapeutics to treat RVFV infection, and thus, there is an urgent need to understand the mechanisms by which the virus hijacks the host cell machinery to replicate. The significance of our research is in identifying the cellular target of sorafenib that inhibits RVFV propagation, so that this information can be used as a tool for the further development of therapeutics used to treat RVFV infection.
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Wichgers Schreur PJ, Kortekaas J. Single-Molecule FISH Reveals Non-selective Packaging of Rift Valley Fever Virus Genome Segments. PLoS Pathog 2016; 12:e1005800. [PMID: 27548280 PMCID: PMC4993503 DOI: 10.1371/journal.ppat.1005800] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 07/09/2016] [Indexed: 12/28/2022] Open
Abstract
The bunyavirus genome comprises a small (S), medium (M), and large (L) RNA segment of negative polarity. Although genome segmentation confers evolutionary advantages by enabling genome reassortment events with related viruses, genome segmentation also complicates genome replication and packaging. Accumulating evidence suggests that genomes of viruses with eight or more genome segments are incorporated into virions by highly selective processes. Remarkably, little is known about the genome packaging process of the tri-segmented bunyaviruses. Here, we evaluated, by single-molecule RNA fluorescence in situ hybridization (FISH), the intracellular spatio-temporal distribution and replication kinetics of the Rift Valley fever virus (RVFV) genome and determined the segment composition of mature virions. The results reveal that the RVFV genome segments start to replicate near the site of infection before spreading and replicating throughout the cytoplasm followed by translocation to the virion assembly site at the Golgi network. Despite the average intracellular S, M and L genome segments approached a 1:1:1 ratio, major differences in genome segment ratios were observed among cells. We also observed a significant amount of cells lacking evidence of M-segment replication. Analysis of two-segmented replicons and four-segmented viruses subsequently confirmed the previous notion that Golgi recruitment is mediated by the Gn glycoprotein. The absence of colocalization of the different segments in the cytoplasm and the successful rescue of a tri-segmented variant with a codon shuffled M-segment suggested that inter-segment interactions are unlikely to drive the copackaging of the different segments into a single virion. The latter was confirmed by direct visualization of RNPs inside mature virions which showed that the majority of virions lack one or more genome segments. Altogether, this study suggests that RVFV genome packaging is a non-selective process. The bunyavirus family is one of the largest virus families on Earth, of which several members cause severe disease in humans, animals or plants. Little is known about the mechanisms that facilitate the production of infectious bunyavirus virions, which should contain at least one copy of the small (S), medium (M) and large (L) genome segment. In this study, we investigated the genome packaging process of the Rift Valley fever virus (RVFV) by visualizing individual genome segments inside infected cells and virions. Experiments performed with wild-type virus, two- and four-segmented variants, and a variant with a codon-shuffled M segment showed that the production of infectious virions is a non-selective process and is unlikely to involve the formation of a supramolecular viral RNA complex. These observations have broad implications for understanding the bunyavirus replication cycle and may facilitate the development of new vaccines and the identification of novel antiviral targets.
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Affiliation(s)
- Paul J Wichgers Schreur
- Department of Virology, Central Veterinary Institute, part of Wageningen University and Research Centre, Lelystad, The Netherlands
| | - Jeroen Kortekaas
- Department of Virology, Central Veterinary Institute, part of Wageningen University and Research Centre, Lelystad, The Netherlands
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The Role of Phlebovirus Glycoproteins in Viral Entry, Assembly and Release. Viruses 2016; 8:v8070202. [PMID: 27455305 PMCID: PMC4974537 DOI: 10.3390/v8070202] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 07/13/2016] [Accepted: 07/14/2016] [Indexed: 01/08/2023] Open
Abstract
Bunyaviruses are enveloped viruses with a tripartite RNA genome that can pose a serious threat to animal and human health. Members of the Phlebovirus genus of the family Bunyaviridae are transmitted by mosquitos and ticks to humans and include highly pathogenic agents like Rift Valley fever virus (RVFV) and severe fever with thrombocytopenia syndrome virus (SFTSV) as well as viruses that do not cause disease in humans, like Uukuniemi virus (UUKV). Phleboviruses and other bunyaviruses use their envelope proteins, Gn and Gc, for entry into target cells and for assembly of progeny particles in infected cells. Thus, binding of Gn and Gc to cell surface factors promotes viral attachment and uptake into cells and exposure to endosomal low pH induces Gc-driven fusion of the viral and the vesicle membranes. Moreover, Gn and Gc facilitate virion incorporation of the viral genome via their intracellular domains and Gn and Gc interactions allow the formation of a highly ordered glycoprotein lattice on the virion surface. Studies conducted in the last decade provided important insights into the configuration of phlebovirus Gn and Gc proteins in the viral membrane, the cellular factors used by phleboviruses for entry and the mechanisms employed by phlebovirus Gc proteins for membrane fusion. Here, we will review our knowledge on the glycoprotein biogenesis and the role of Gn and Gc proteins in the phlebovirus replication cycle.
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Suda Y, Fukushi S, Tani H, Murakami S, Saijo M, Horimoto T, Shimojima M. Analysis of the entry mechanism of Crimean-Congo hemorrhagic fever virus, using a vesicular stomatitis virus pseudotyping system. Arch Virol 2016; 161:1447-54. [PMID: 26935918 PMCID: PMC7087235 DOI: 10.1007/s00705-016-2803-1] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 02/21/2016] [Indexed: 11/24/2022]
Abstract
Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease causing severe hemorrhagic symptoms with a nearly 30 % case-fatality rate in humans. The experimental use of CCHF virus (CCHFV), which causes CCHF, requires high-biosafety-level (BSL) containment. In contrast, pseudotyping of various viral glycoproteins (GPs) onto vesicular stomatitis virus (VSV) can be used in facilities with lower BSL containment, and this has facilitated studies on the viral entry mechanism and the measurement of neutralizing activity, especially for highly pathogenic viruses. In the present study, we generated high titers of pseudotyped VSV bearing the CCHFV envelope GP and analyzed the mechanisms involved in CCHFV infection. A partial deletion of the CCHFV GP cytoplasmic domain increased the titer of the pseudotyped VSV, the entry mechanism of which was dependent on the CCHFV envelope GP. Using the pseudotype virus, DC-SIGN (a calcium-dependent [C-type] lectin cell-surface molecule) was revealed to enhance viral infection and act as an entry factor for CCHFV.
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Affiliation(s)
- Yuto Suda
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.,Special Pathogens Laboratory, Department of Virology I, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama, Tokyo, 208-0011, Japan
| | - Shuetsu Fukushi
- Special Pathogens Laboratory, Department of Virology I, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama, Tokyo, 208-0011, Japan
| | - Hideki Tani
- Special Pathogens Laboratory, Department of Virology I, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama, Tokyo, 208-0011, Japan
| | - Shin Murakami
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan
| | - Masayuki Saijo
- Special Pathogens Laboratory, Department of Virology I, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama, Tokyo, 208-0011, Japan
| | - Taisuke Horimoto
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan
| | - Masayuki Shimojima
- Special Pathogens Laboratory, Department of Virology I, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama, Tokyo, 208-0011, Japan. shimoji-@nih.go.jp
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Ndiaye EH, Fall G, Gaye A, Bob NS, Talla C, Diagne CT, Diallo D, B A Y, Dia I, Kohl A, Sall AA, Diallo M. Vector competence of Aedes vexans (Meigen), Culex poicilipes (Theobald) and Cx. quinquefasciatus Say from Senegal for West and East African lineages of Rift Valley fever virus. Parasit Vectors 2016; 9:94. [PMID: 26897521 PMCID: PMC4761212 DOI: 10.1186/s13071-016-1383-y] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 02/16/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Rift Valley fever virus (RVFV; Phlebovirus, Bunyaviridae) is a mosquito-borne, zoonotic pathogen. In Senegal, RVFV was first isolated in 1974 from Aedes dalzieli (Theobald) and thereafter from Ae. fowleri (de Charmoy), Ae. ochraceus Theobald, Ae. vexans (Meigen), Culex poicilipes (Theobald), Mansonia africana (Theobald) and Ma. uniformis (Theobald). However, the vector competence of these local species has never been demonstrated making hypothetical the transmission cycle proposed for West Africa based on serological data and mosquito isolates. METHODS Aedes vexans and Cx. poicilipes, two common mosquito species most frequently associated with RVFV in Senegal, and Cx. quinquefasciatus, the most common domestic species, were assessed after oral feeding with three RVFV strains of the West and East/central African lineages. Fully engorged mosquitoes (420 Ae. vexans, 563 Cx. quinquefasciatus and 380 Cx. poicilipes) were maintained at 27 ± 1 °C and 70-80% relative humidity. The saliva, legs/wings and bodies were tested individually for the RVFV genome using real-time RT-PCR at 5, 10, 15 and 20 days post exposure (dpe) to estimate the infection, dissemination, and transmission rates. Genotypic characterisation of the 3 strains used were performed to identify factors underlying the different patterns of transmission. RESULTS The infection rates varied between 30.0-85.0% for Ae. vexans, 3.3-27% for Cx. quinquefasciatus and 8.3-46.7% for Cx. poicilipes, and the dissemination rates varied between 10.5-37% for Ae. vexans, 9.5-28.6% for Cx. quinquefasciatus and 3.0-40.9% for Cx. poicilipes. However only the East African lineage was transmitted, with transmission rates varying between 13.3-33.3% in Ae. vexans, 50% in Cx. quinquefasciatus and 11.1% in Cx. poicilipes. Culex mosquitoes were less susceptible to infection than Ae. vexans. Compared to other strains, amino acid variation in the NSs M segment proteins of the East African RVFV lineage human-derived strain SH172805, might explain the differences in transmission potential. CONCLUSION Our findings revealed that all the species tested were competent for RVFV with a significant more important role of Ae. vexans compared to Culex species and a highest potential of the East African lineage to be transmitted.
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Affiliation(s)
- El Hadji Ndiaye
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal. .,Université Cheikh Anta Diop de Dakar, Département de Biologie Animale, Faculté des Sciences et Techniques, Dakar, Senegal.
| | - Gamou Fall
- Institut Pasteur de Dakar, Unité des Arbovirus et Virus de Fièvres hémorragiques, Dakar, Senegal.
| | - Alioune Gaye
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal. .,Université Cheikh Anta Diop de Dakar, Département de Biologie Animale, Faculté des Sciences et Techniques, Dakar, Senegal.
| | - Ndeye Sakha Bob
- Institut Pasteur de Dakar, Unité des Arbovirus et Virus de Fièvres hémorragiques, Dakar, Senegal.
| | - Cheikh Talla
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal.
| | - Cheikh Tidiane Diagne
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal. .,Université Cheikh Anta Diop de Dakar, Département de Biologie Animale, Faculté des Sciences et Techniques, Dakar, Senegal.
| | - Diawo Diallo
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal.
| | - Yamar B A
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal.
| | - Ibrahima Dia
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal.
| | - Alain Kohl
- MRC-University of Glasgow Centre for Virus Research, Glasgow, G61 1QH, Scotland, UK.
| | - Amadou Alpha Sall
- Institut Pasteur de Dakar, Unité des Arbovirus et Virus de Fièvres hémorragiques, Dakar, Senegal.
| | - Mawlouth Diallo
- Unité d'Entomologie Médicale, Institut Pasteur de Dakar, 36 Avenue Pasteur, BP 220, Dakar, Senegal.
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Mudhasani R, Tran JP, Retterer C, Kota KP, Whitehouse CA, Bavari S. Protein Kinase R Degradation Is Essential for Rift Valley Fever Virus Infection and Is Regulated by SKP1-CUL1-F-box (SCF)FBXW11-NSs E3 Ligase. PLoS Pathog 2016; 12:e1005437. [PMID: 26837067 PMCID: PMC4737497 DOI: 10.1371/journal.ppat.1005437] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 01/13/2016] [Indexed: 12/11/2022] Open
Abstract
Activated protein kinase R (PKR) plays a vital role in antiviral defense primarily by inhibiting protein synthesis and augmenting interferon responses. Many viral proteins have adopted unique strategies to counteract the deleterious effects of PKR. The NSs (Non-structural s) protein which is encoded by Rift Valley fever virus (RVFV) promotes early PKR proteasomal degradation through a previously undefined mechanism. In this study, we demonstrate that NSs carries out this activity by assembling the SCF (SKP1-CUL1-F-box)FBXW11 E3 ligase. NSs binds to the F-box protein, FBXW11, via the six amino acid sequence DDGFVE called the degron sequence and recruits PKR through an alternate binding site to the SCFFBXW11 E3 ligase. We further show that disrupting the assembly of the SCFFBXW11-NSs E3 ligase with MLN4924 (a small molecule inhibitor of SCF E3 ligase activity) or NSs degron viral mutants or siRNA knockdown of FBXW11 can block PKR degradation. Surprisingly, under these conditions when PKR degradation was blocked, NSs was essential and sufficient to activate PKR causing potent inhibition of RVFV infection by suppressing viral protein synthesis. These antiviral effects were antagonized by the loss of PKR expression or with a NSs deleted mutant virus. Therefore, early PKR activation by disassembly of SCFFBXW11-NSs E3 ligase is sufficient to inhibit RVFV infection. Furthermore, FBXW11 and BTRC are the two homologues of the βTrCP (Beta-transducin repeat containing protein) gene that were previously described to be functionally redundant. However, in RVFV infection, among the two homologues of βTrCP, FBXW11 plays a dominant role in PKR degradation and is the limiting factor in the assembly of the SCFFBXW11 complex. Thus, FBXW11 serves as a master regulator of RVFV infection by promoting PKR degradation. Overall these findings provide new insights into NSs regulation of PKR activity and offer potential opportunities for therapeutic intervention of RVFV infection. Rift Valley fever (RVF) is a severe disease caused by infection with the Rift Valley fever virus (RVFV) that affects humans and livestock and occurs in large epidemics. Currently there are no FDA-approved drugs or vaccines to treat RVF. Many viruses have evolved unique strategies to overcome host immune responses in order to establish infection. One protein of RVFV called NSs is responsible for over-powering cellular antiviral defenses. NSs is known to degrade double-stranded (ds) RNA-dependent protein kinase (PKR), but neither the mechanism nor the functional significance of this activity has been fully understood. In this study we show that NSs promotes PKR degradation by recruiting PKR to the E3 ligase complex called SCF (SKP1-CUL1-F-box)FBXW11. A short stretch of six amino acids called the degron sequence in NSs regulates the NSs- FBXW11 interaction and is required for the assembly of the SCFFBXW11 complex. We further show that disruption of the SCFFBXW11-NSs complex, with either a small molecule or with NSs degron viral mutants, can block PKR degradation. Surprisingly, when NSs mediated PKR degradation was blocked, NSs was essential and sufficient to activate PKR, causing potent inhibition of RVFV infection by suppressing viral protein synthesis. Therefore early PKR activation induced by inactivation of the SCFFBXW11 is sufficient to induce potent inhibition of RVFV infection. These findings may provide new molecular targets for therapeutic intervention of this important disease.
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Affiliation(s)
- Rajini Mudhasani
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Julie P. Tran
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Cary Retterer
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Krishna P. Kota
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
- Perkin Elmer, Waltham, Massachusetts, United States of America
| | - Chris A. Whitehouse
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Sina Bavari
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
- * E-mail:
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Mudhasani R, Kota KP, Retterer C, Tran JP, Whitehouse CA, Bavari S. High content image-based screening of a protease inhibitor library reveals compounds broadly active against Rift Valley fever virus and other highly pathogenic RNA viruses. PLoS Negl Trop Dis 2014; 8:e3095. [PMID: 25144302 PMCID: PMC4140764 DOI: 10.1371/journal.pntd.0003095] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Accepted: 07/03/2014] [Indexed: 12/20/2022] Open
Abstract
High content image-based screening was developed as an approach to test a protease inhibitor small molecule library for antiviral activity against Rift Valley fever virus (RVFV) and to determine their mechanism of action. RVFV is the causative agent of severe disease of humans and animals throughout Africa and the Arabian Peninsula. Of the 849 compounds screened, 34 compounds exhibited ≥50% inhibition against RVFV. All of the hit compounds could be classified into 4 distinct groups based on their unique chemical backbone. Some of the compounds also showed broad antiviral activity against several highly pathogenic RNA viruses including Ebola, Marburg, Venezuela equine encephalitis, and Lassa viruses. Four hit compounds (C795-0925, D011-2120, F694-1532 and G202-0362), which were most active against RVFV and showed broad-spectrum antiviral activity, were selected for further evaluation for their cytotoxicity, dose response profile, and mode of action using classical virological methods and high-content imaging analysis. Time-of-addition assays in RVFV infections suggested that D011-2120 and G202-0362 targeted virus egress, while C795-0925 and F694-1532 inhibited virus replication. We showed that D011-2120 exhibited its antiviral effects by blocking microtubule polymerization, thereby disrupting the Golgi complex and inhibiting viral trafficking to the plasma membrane during virus egress. While G202-0362 also affected virus egress, it appears to do so by a different mechanism, namely by blocking virus budding from the trans Golgi. F694-1532 inhibited viral replication, but also appeared to inhibit overall cellular gene expression. However, G202-0362 and C795-0925 did not alter any of the morphological features that we examined and thus may prove to be good candidates for antiviral drug development. Overall this work demonstrates that high-content image analysis can be used to screen chemical libraries for new antivirals and to determine their mechanism of action and any possible deleterious effects on host cellular biology. Rift Valley fever (RVF) is an arthropod-borne viral zoonosis that occurs in large parts of sub-Saharan and North Africa and in 2000 emerged outside the African continent for the first time, raising concerns that it could further expand its geographical range. The disease in humans can result in encephalitis or hemorrhagic fever and in ruminants often results in abortion in pregnant females. Due to the lack of a licensed and commercially available vaccine, efforts to discover effective antiviral drugs are underway. Drug discovery using high content image-based screening is an effective tool that has been successfully used to identify new drugs. In this study, we developed an image-based assay to identify compounds active against RVF virus and other highly pathogenic human viruses. We demonstrated the usefulness of our image-based high content assay in identifying potential RVF antivirals by screening a small subset of chemical compounds for inhibition of RVF virus in a human cell line (HeLa) and partially characterized their mechanism of action within infected cells. The methods we developed in this study will be useful in discovering new effective drugs to combat Rift Valley fever.
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Affiliation(s)
- Rajini Mudhasani
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Krishna P. Kota
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Cary Retterer
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Julie P. Tran
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Chris A. Whitehouse
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
| | - Sina Bavari
- Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America
- * E-mail:
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Creation of Rift Valley fever viruses with four-segmented genomes reveals flexibility in bunyavirus genome packaging. J Virol 2014; 88:10883-93. [PMID: 25008937 DOI: 10.1128/jvi.00961-14] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
UNLABELLED Bunyavirus genomes comprise a small (S), a medium (M), and a large (L) RNA segment of negative polarity. Although the untranslated regions have been shown to comprise signals required for transcription, replication, and encapsidation, the mechanisms that drive the packaging of at least one S, M, and L segment into a single virion to generate infectious virus are largely unknown. One of the most important members of the Bunyaviridae family that causes devastating disease in ruminants and occasionally humans is the Rift Valley fever virus (RVFV). We studied the flexibility of RVFV genome packaging by splitting the glycoprotein precursor gene, encoding the (NSm)GnGc polyprotein, into two individual genes encoding either (NSm)Gn or Gc. Using reverse genetics, six viruses with a segmented glycoprotein precursor gene were rescued, varying from a virus comprising two S-type segments in the absence of an M-type segment to a virus consisting of four segments (RVFV-4s), of which three are M-type. Despite that all virus variants were able to grow in mammalian cell lines, they were unable to spread efficiently in cells of mosquito origin. Moreover, in vivo studies demonstrated that RVFV-4s is unable to cause disseminated infection and disease in mice, even in the presence of the main virulence factor NSs, but induced a protective immune response against a lethal challenge with wild-type virus. In summary, splitting bunyavirus glycoprotein precursor genes provides new opportunities to study bunyavirus genome packaging and offers new methods to develop next-generation live-attenuated bunyavirus vaccines. IMPORTANCE Rift Valley fever virus (RVFV) causes devastating disease in ruminants and occasionally humans. Virions capable of productive infection comprise at least one copy of the small (S), medium (M), and large (L) RNA genome segments. The M segment encodes a glycoprotein precursor (GPC) protein that is cotranslationally cleaved into Gn and Gc, which are required for virus entry and fusion. We studied the flexibility of RVFV genome packaging and developed experimental live-attenuated vaccines by applying a unique strategy based on the splitting of the GnGc open reading frame. Several RVFV variants, varying from viruses comprising two S-type segments to viruses consisting of four segments (RVFV-4s), of which three are M-type, could be rescued and were shown to induce a rapid protective immune response. Altogether, the segmentation of bunyavirus GPCs provides a new method for studying bunyavirus genome packaging and facilitates the development of novel live-attenuated bunyavirus vaccines.
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