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Martin V, Guerra B, Hernaez B, Kappler-Gratias S, Gallardo F, Guerra M, Andres G, Alejo A. A novel live DNA tagging system for African swine fever virus shows that bisbenzimide Hoechst 33342 can effectively block its replication. Antiviral Res 2024; 230:105973. [PMID: 39168188 DOI: 10.1016/j.antiviral.2024.105973] [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] [Received: 04/29/2024] [Revised: 07/26/2024] [Accepted: 07/29/2024] [Indexed: 08/23/2024]
Abstract
African swine fever virus (ASFV) infection causes a frequently fatal disease in domestic swine that has affected more than 50 countries worldwide since 2021, with a major impact on animal welfare and economy. The development of effective vaccines or antivirals against this disease are urgently required for its effective control. Live detection of viral replication has been used as a tool for the screening and characterization of antiviral compounds in other dsDNA genome containing viruses. Here, we have adapted the ANCHOR fluorescent DNA labelling system to ASFV by constructing and characterizing a novel recombinant virus. We show that this virus is viable and effectively tags viral DNA replication sites, which can be detected and quantified in real time. Further, we have used high content cell microscopy to test the antiviral activity of bisbenzimide compounds and show that Hoechst 33342 has specific anti-ASFV activity. We expect this novel tool to be useful both in the further study of ASFV replication as in the screening of new specific antiviral compounds.
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Affiliation(s)
- Veronica Martin
- Centro de Investigación en Sanidad Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Consejo Superior de Investigaciones Científicas, 28130, Valdeolmos, Madrid, Spain.
| | - Beatriz Guerra
- Centro de Investigación en Sanidad Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Consejo Superior de Investigaciones Científicas, 28130, Valdeolmos, Madrid, Spain.
| | - Bruno Hernaez
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28049, Cantoblanco, Madrid, Spain.
| | | | - Franck Gallardo
- NeoVirTech SAS, 1 Place Pierre Potier, 31000, Toulouse, France.
| | - Milagros Guerra
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28049, Cantoblanco, Madrid, Spain.
| | - German Andres
- Centro de Investigación en Sanidad Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Consejo Superior de Investigaciones Científicas, 28130, Valdeolmos, Madrid, Spain.
| | - Ali Alejo
- Centro de Investigación en Sanidad Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Consejo Superior de Investigaciones Científicas, 28130, Valdeolmos, Madrid, Spain.
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Yin D, Shi B, Geng R, Liu Y, Gong L, Shao H, Qian K, Chen H, Qin A. Function investigation of p11.5 in ASFV infection. Virol Sin 2024; 39:469-477. [PMID: 38789040 PMCID: PMC11279770 DOI: 10.1016/j.virs.2024.05.007] [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] [Received: 11/29/2023] [Accepted: 05/17/2024] [Indexed: 05/26/2024] Open
Abstract
Virus replication relies on complex interactions between viral proteins. In the case of African swine fever virus (ASFV), only a few such interactions have been identified so far. In this study, we demonstrate that ASFV protein p72 interacts with p11.5 using co-immunoprecipitation and liquid chromatography-mass spectrometry (LC-MS). It was found that protein p72 interacts specifically with p11.5 at sites amino acids (aa) 1-216 of p72 and aa 1-68 of p11.5. To assess the importance of p11.5 in ASFV infection, we developed a recombinant virus (ASFVGZΔA137R) by deleting the A137R gene from the ASFVGZ genome. Compared with ASFVGZ, the infectious progeny virus titers of ASFVGZΔA137R were reduced by approximately 1.0 logs. In addition, we demonstrated that the growth defect was partially attributable to a higher genome copies-to-infectious virus titer ratios produced in ASFVGZΔA137R-infected MA104 cells than in those infected with ASFVGZ. This finding suggests that MA104 cells infected with ASFVGZΔA137R may generate larger quantities of noninfectious particles. Importantly, we found that p11.5 did not affect virus-cell binding or endocytosis. Collectively, we show for the first time the interaction between ASFV p72 and p11.5. Our results effectively provide the relevant information of the p11.5 protein. These results extend our understanding of complex interactions between viral proteins, paving the way for further studies of the potential mechanisms and pathogenesis of ASFV infection.
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Affiliation(s)
- Dan Yin
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China
| | - Bin Shi
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China
| | - Renhao Geng
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China
| | - Yingnan Liu
- Shanghai Veterinary Research Institute, CAAS, Shanghai, 200241, China
| | - Lang Gong
- South China Agricultural University, Guangzhou 510642, China
| | - Hongxia Shao
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China
| | - Kun Qian
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China.
| | - Hongjun Chen
- Shanghai Veterinary Research Institute, CAAS, Shanghai, 200241, China.
| | - Aijian Qin
- Ministry of Education Key Laboratory for Avian Preventive Medicine, Yangzhou University, Jiangsu 225009, China; Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Jiangsu 225009, China; Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Jiangsu 225009, China.
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Tng PYL, Al-Adwani L, Pauletto E, Hui JYK, Netherton CL. Capsid-Specific Antibody Responses of Domestic Pigs Immunized with Low-Virulent African Swine Fever Virus. Vaccines (Basel) 2023; 11:1577. [PMID: 37896980 PMCID: PMC10611099 DOI: 10.3390/vaccines11101577] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 10/03/2023] [Accepted: 10/09/2023] [Indexed: 10/29/2023] Open
Abstract
African swine fever (ASF) is a lethal disease in pigs that has grave socio-economic implications worldwide. For the development of vaccines against the African swine fever virus (ASFV), immunogenic antigens that generate protective immune responses need to be identified. There are over 150 viral proteins-many of which are uncharacterized-and humoral immunity to ASFV has not been closely examined. To profile antigen-specific antibody responses, we developed luciferase-linked antibody capture assays (LACAs) for a panel of ASFV capsid proteins and screened sera from inbred and outbred animals that were previously immunized with low-virulent ASFV before challenge with virulent ASFV. Antibodies to B646L/p72, D117L/p17, M1249L, and E120R/p14.5 were detected in this study; however, we were unable to detect B438L-specific antibodies. Anti-B646L/p72 and B602L antibodies were associated with recovery from disease after challenges with genotype I OUR T88/1 but not genotype II Georgia 2007/1. Antibody responses against M1249L and E120R/p14.5 were observed in animals with reduced clinical signs and viremia. Here, we present LACAs as a tool for the targeted profiling of antigen-specific antibody responses to inform vaccine development.
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Affiliation(s)
- Priscilla Y. L. Tng
- The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK; (L.A.-A.); (E.P.); (J.Y.K.H.)
| | - Laila Al-Adwani
- The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK; (L.A.-A.); (E.P.); (J.Y.K.H.)
| | - Egle Pauletto
- The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK; (L.A.-A.); (E.P.); (J.Y.K.H.)
- The Institute of Medical Sciences, Foresterhill, University of Aberdeen, Aberdeen AB25 2ZD, UK
| | - Joshua Y. K. Hui
- The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK; (L.A.-A.); (E.P.); (J.Y.K.H.)
| | - Christopher L. Netherton
- The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK; (L.A.-A.); (E.P.); (J.Y.K.H.)
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Zheng X, Nie S, Feng WH. Regulation of antiviral immune response by African swine fever virus (ASFV). Virol Sin 2022; 37:157-167. [PMID: 35278697 PMCID: PMC9170969 DOI: 10.1016/j.virs.2022.03.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 03/07/2022] [Indexed: 12/13/2022] Open
Abstract
African swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease with a high mortality approaching 100% in domestic pigs. ASF is an endemic in countries in sub-Saharan Africa. Now, it has been spreading to many countries, especially in Asia and Europe. Due to the fact that there is no commercial vaccine available for ASF to provide sustainable prevention, the disease has spread rapidly worldwide and caused great economic losses in swine industry. The knowledge gap of ASF virus (ASFV) pathogenesis and immune evasion is the main factor to limit the development of safe and effective ASF vaccines. Here, we will summarize the molecular mechanisms of how ASFV interferes with the host innate and adaptive immune responses. An in-depth understanding of ASFV immune evasion strategies will provide us with rational design of ASF vaccines.
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Affiliation(s)
- Xiaojie Zheng
- State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Department of Microbiology and Immunology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Shengming Nie
- State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Department of Microbiology and Immunology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Wen-Hai Feng
- State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China; Department of Microbiology and Immunology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
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5
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African Swine Fever Virus E120R Protein Inhibits Interferon Beta Production by Interacting with IRF3 To Block Its Activation. J Virol 2021; 95:e0082421. [PMID: 34190598 DOI: 10.1128/jvi.00824-21] [Citation(s) in RCA: 61] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
African swine fever is a devastating disease of swine caused by African swine fever virus (ASFV). The pathogenesis of the disease remains largely unknown, leaving the spread of the disease uncontrolled in many countries and regions. Here, we identified E120R, a structural protein of ASFV, as a key virulence factor and late-phase-expressed protein of the virus. E120R revealed an activity to suppress the host antiviral response through blocking beta interferon (IFN-β) production, and the amino acids (aa) at sites 72 and 73 (amino acids 72-73) in the C-terminal domain were essential for this function. E120R interacted with interferon regulatory factor 3 (IRF3) and interfered with the recruitment of IRF3 to TANK-binding kinase 1 (TBK1), which in turn suppressed IRF3 phosphorylation, decreasing interferon production. A recombinant mutant ASFV was further constructed to confirm the claimed mechanism. The ASFV lacking the complete E120R region could not be rescued, whereas the virus could tolerate the deletion of the 72nd and 73rd residues in E120R (ASFV E120R-Δ72-73aa). ASFV E120R with the two-amino-acid deletion failed to interact with IRF3 during ASFV E120R-Δ72-73aa infection, and the viral infection activated IRF3 phosphorylation highly and induced more robust type I interferon production than its parental ASFV. An unbiased transcriptome-wide analysis of gene expression also confirmed that considerably more IFN-stimulated genes (ISGs) were detected in ASFV E120R-Δ72-73aa-infected porcine alveolar macrophages (PAMs) than in wild-type ASFV-infected PAMs. Together, our findings have identified a novel mechanism evolved by ASFV to inhibit the host antiviral response, and they provide a new target for guiding the development of ASFV live-attenuated vaccine. IMPORTANCE African swine fever is a highly contagious animal disease affecting the pig industry worldwide, which has brought enormous economic losses. Infection by the causative agent, African swine fever virus (ASFV), causes severe immunosuppression during viral infection, contributing to serious clinical manifestations. Therefore, identification of the viral proteins involved in immunosuppression is critical for ASFV vaccine design and development. Here, for the first time, we demonstrated that E120R protein, a structural protein of ASFV, played an important role in suppression of interferon regulatory factor 3 (IRF3) phosphorylation and type I interferon production by binding to IRF3 and blocking the recruitment of IRF3 to TANK-binding kinase 1 (TBK1). Deletion of the crucial binding sites in E120R critically increased the interferon response during ASFV infection. This study explored a novel antagonistic mechanism of ASFV, which is critical for guiding the development of ASFV live-attenuated vaccines.
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6
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Yoo D, Kim H, Lee JY, Yoo HS. African swine fever: Etiology, epidemiological status in Korea, and perspective on control. J Vet Sci 2020; 21:e38. [PMID: 32233141 PMCID: PMC7113569 DOI: 10.4142/jvs.2020.21.e38] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 02/18/2020] [Accepted: 02/19/2020] [Indexed: 12/22/2022] Open
Abstract
African swine fever (ASF), caused by the ASF virus, a member of the Asfarviridae family, is one of the most important diseases in the swine industry due to its clinical and economic impacts. Since the first report of ASF a century ago, ample information has become available, but prevention and treatment measures are still inadequate. Two waves of epizootic outbreaks have occurred worldwide. While the first wave of the epizootic outbreak was controlled in most of the infected areas, the second wave is currently active in the European and Asian continents, causing severe economic losses to the pig industry. There are different patterns of spreading in the outbreaks between those in European and Asian countries. Prevention and control of ASF are very difficult due to the lack of available vaccines and effective therapeutic measures. However, recent outbreaks in South Korea have been successfully controlled on swine farms, although feral pigs are periodically being found to be positive for the ASF virus. Therefore, we would like to share our story regarding the preparation and application of control measures. The success in controlling ASF on farms in South Korea is largely due to the awareness and education of swine farmers and practitioners, the early detection of infected animals, the implementation of strict control policies by the government, and widespread sharing of information among stakeholders. Based on the experience gained from the outbreaks in South Korea, this review describes the current understanding of the ASF virus and its pathogenic mechanisms, epidemiology, and control.
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Affiliation(s)
- Dongwan Yoo
- Department of Pathobiology, College of Veterinary Medicine, University of Illinois-Urbana-Champaign, Urbana, IL 61802, USA.,Department of Infectious Diseases, College of Veterinary Medicine, Seoul National University, Seoul 08826, Korea
| | | | - Joo Young Lee
- Choong Ang Vaccine Laboratories Co. (Ltd.), Daejeon 34055, Korea
| | - Han Sang Yoo
- Department of Infectious Diseases, College of Veterinary Medicine, Seoul National University, Seoul 08826, Korea.
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Jaing C, Rowland RRR, Allen JE, Certoma A, Thissen JB, Bingham J, Rowe B, White JR, Wynne JW, Johnson D, Gaudreault NN, Williams DT. Gene expression analysis of whole blood RNA from pigs infected with low and high pathogenic African swine fever viruses. Sci Rep 2017; 7:10115. [PMID: 28860602 PMCID: PMC5579198 DOI: 10.1038/s41598-017-10186-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 08/04/2017] [Indexed: 11/09/2022] Open
Abstract
African swine fever virus (ASFV) is a macrophage-tropic virus responsible for ASF, a transboundary disease that threatens swine production world-wide. Since there are no vaccines available to control ASF after an outbreak, obtaining an understanding of the virus-host interaction is important for developing new intervention strategies. In this study, a whole transcriptomic RNA-Seq method was used to characterize differentially expressed genes in pigs infected with a low pathogenic ASFV isolate, OUR T88/3 (OURT), or the highly pathogenic Georgia 2007/1 (GRG). After infection, pigs infected with OURT showed no or few clinical signs; whereas, GRG produced clinical signs consistent with acute ASF. RNA-Seq detected the expression of ASFV genes from the whole blood of the GRG, but not the OURT pigs, consistent with the pathotypes of these strains and the replication of GRG in circulating monocytes. Even though GRG and OURT possess different pathogenic properties, there was significant overlap in the most upregulated host genes. A small number of differentially expressed microRNAs were also detected in GRG and OURT pigs. These data confirm previous studies describing the response of macrophages and lymphocytes to ASFV infection, as well as reveal unique gene pathways upregulated in response to infection with GRG.
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Affiliation(s)
- Crystal Jaing
- Physical & Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States of America.
| | - Raymond R R Rowland
- Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, Kansas, United States of America
| | - Jonathan E Allen
- Computation Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States of America
| | - Andrea Certoma
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - James B Thissen
- Physical & Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States of America
| | - John Bingham
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - Brenton Rowe
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - John R White
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - James W Wynne
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - Dayna Johnson
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
| | - Natasha N Gaudreault
- Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, Kansas, United States of America
| | - David T Williams
- CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia
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9
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Dixon LK, Chapman DAG, Netherton CL, Upton C. African swine fever virus replication and genomics. Virus Res 2012; 173:3-14. [PMID: 23142553 DOI: 10.1016/j.virusres.2012.10.020] [Citation(s) in RCA: 418] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Revised: 10/19/2012] [Accepted: 10/19/2012] [Indexed: 01/03/2023]
Abstract
African swine fever virus (ASFV) is a large icosahedral DNA virus which replicates predominantly in the cytoplasm of infected cells. The ASFV double-stranded DNA genome varies in length from about 170 to 193 kbp depending on the isolate and contains between 150 and 167 open reading frames. These are closely spaced and read from both DNA strands. The virus genome termini are covalently closed by imperfectly base-paired hairpin loops that are present in two forms that are complimentary and inverted with respect to each other. Adjacent to the termini are inverted arrays of different tandem repeats. Head to head concatemeric genome replication intermediates have been described. A similar mechanism of replication to Poxviruses has been proposed for ASFV. Virus genome transcription occurs independently of the host RNA polymerase II and virus particles contain all of the enzymes and factors required for early gene transcription. DNA replication begins in perinuclear factory areas about 6h post-infection although an earlier stage of nuclear DNA synthesis has been reported. The virus genome encodes enzymes required for transcription and replication of the virus genome and virion structural proteins. Enzymes that are involved in a base excision repair pathway may be an adaptation to enable virus replication in the oxidative environment of the macrophage cytoplasm. Other ASFV genes encode factors involved in evading host defence systems and modulating host cell function. Variation between the genomes of different ASFV isolates is most commonly due to gain or loss of members of multigene families, MGFs 100, 110, 300, 360, 505/530 and family p22. These are located within the left terminal 40kbp and right terminal 20kbp. ASFV is the only member of the Asfarviridae, which is one of the families within the nucleocytoplasmic large DNA virus superfamily.
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Affiliation(s)
- Linda K Dixon
- The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey GU24 0NF, United Kingdom.
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Sánchez‐Vizcaíno JM, Martínez‐López B, Martínez‐Avilés M, Martins C, Boinas F, Vialc L, Michaud V, Jori F, Etter E, Albina E, Roger F. Scientific review on African Swine Fever. ACTA ACUST UNITED AC 2009. [DOI: 10.2903/sp.efsa.2009.en-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
| | | | | | - Carlos Martins
- Faculdade de Medicina Veterinaria, Universidade Técnica de Lisboa, (FMV‐UTL)
| | - Fernando Boinas
- Faculdade de Medicina Veterinaria, Universidade Técnica de Lisboa, (FMV‐UTL)
| | - Laurence Vialc
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
| | - Vincent Michaud
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
| | - Ferran Jori
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
| | - Eric Etter
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
| | - Emmanuel Albina
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
| | - François Roger
- Centre de Cooperation Internationale en Recherche Agronomique pour le Développement (CIRAD)
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The African swine fever virus virion membrane protein pE248R is required for virus infectivity and an early postentry event. J Virol 2009; 83:12290-300. [PMID: 19793823 DOI: 10.1128/jvi.01333-09] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The African swine fever virus (ASFV) protein pE248R, encoded by the gene E248R, is a late structural component of the virus particle. The protein contains intramolecular disulfide bonds and has been previously identified as a substrate of the ASFV-encoded redox system. Its amino acid sequence contains a putative myristoylation site and a hydrophobic transmembrane region near its carboxy terminus. We show here that the protein pE248R is myristoylated during infection and associates with the membrane fraction in infected cells, behaving as an integral membrane protein. Furthermore, the protein localizes at the inner envelope of the virus particles in the cytoplasmic factories. The function of the protein pE248R in ASFV replication was investigated by using a recombinant virus that inducibly expresses the gene E248R. Under repressive conditions, the ASFV polyproteins pp220 and pp62 are normally processed and virus particles with morphology indistinguishable from that of those produced in a wild-type infection or under permissive conditions are generated. Moreover, the mutant virus particles can exit the cell as does the parental virus. However, the infectivity of the pE248R-deficient virions was reduced at least 100-fold. An investigation of the defect of the mutant virus indicated that neither virus binding nor internalization was affected by the absence of the protein pE248R, but a cytopathic effect was not induced and early and late gene expression was impaired, indicating that the protein is required for some early postentry event.
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Abstract
African swine fever virus (ASFV) is a large, intracytoplasmically-replicating DNA arbovirus and the sole member of the family Asfarviridae. It is the etiologic agent of a highly lethal hemorrhagic disease of domestic swine and therefore extensively studied to elucidate the structures, genes, and mechanisms affecting viral replication in the host, virus-host interactions, and viral virulence. Increasingly apparent is the complexity with which ASFV replicates and interacts with the host cell during infection. ASFV encodes novel genes involved in host immune response modulation, viral virulence for domestic swine, and in the ability of ASFV to replicate and spread in its tick vector. The unique nature of ASFV has contributed to a broader understanding of DNA virus/host interactions.
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Affiliation(s)
- E R Tulman
- Department of Pathobiology and Veterinary Science, Center of Excellence for Vaccine Research, University of Connecticut, Storrs 06269, USA.
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Abstract
Increasing evidence points to the importance of the interferon (IFN) response in determining the host range and virulence of African swine fever virus (ASFV). Infection with attenuated strains of ASFV leads to the upregulation of genes controlled by IFN pathways, including myxovirus resistance (Mx) genes that are potent effectors of the antiviral state. Mx gene products are known to inhibit the replication of many negative-sense single-stranded RNA viruses, as well as double-stranded RNA viruses, positive-sense single-stranded RNA viruses, and the reverse-transcribing DNA virus hepatitis B virus. Here, we provide data that extend the known range of viruses inhibited by Mx to include the large double-stranded DNA viruses. Stably transfected Vero cells expressing human MxA protein did not support ASFV plaque formation, and virus replication in these cells was reduced 100-fold compared with that in control cells. In contrast, ASFV replication in cells expressing MxB protein or a mutant MxA protein was similar to that in control Vero cells. There was a drastic reduction in ASFV late protein synthesis in MxA-expressing cells, correlating with the results of previous work on the effect of IFN on viral replication. Strikingly, the inhibition of ASFV replication was linked to the recruitment of MxA protein to perinuclear viral assembly sites, where the protein surrounded the virus factories. Interactions between ASFV and MxA were similar to those seen between MxA and different RNA viruses, suggesting a common inhibitory mechanism.
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14
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Netherton C, Moffat K, Brooks E, Wileman T. A guide to viral inclusions, membrane rearrangements, factories, and viroplasm produced during virus replication. Adv Virus Res 2007; 70:101-82. [PMID: 17765705 PMCID: PMC7112299 DOI: 10.1016/s0065-3527(07)70004-0] [Citation(s) in RCA: 164] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Virus replication can cause extensive rearrangement of host cell cytoskeletal and membrane compartments leading to the “cytopathic effect” that has been the hallmark of virus infection in tissue culture for many years. Recent studies are beginning to redefine these signs of viral infection in terms of specific effects of viruses on cellular processes. In this chapter, these concepts have been illustrated by describing the replication sites produced by many different viruses. In many cases, the cellular rearrangements caused during virus infection lead to the construction of sophisticated platforms in the cell that concentrate replicase proteins, virus genomes, and host proteins required for replication, and thereby increase the efficiency of replication. Interestingly, these same structures, called virus factories, virus inclusions, or virosomes, can recruit host components that are associated with cellular defences against infection and cell stress. It is possible that cellular defence pathways can be subverted by viruses to generate sites of replication. The recruitment of cellular membranes and cytoskeleton to generate virus replication sites can also benefit viruses in other ways. Disruption of cellular membranes can, for example, slow the transport of immunomodulatory proteins to the surface of infected cells and protect against innate and acquired immune responses, and rearrangements to cytoskeleton can facilitate virus release.
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Affiliation(s)
- Christopher Netherton
- Vaccinology Group, Pirbright Laboratories, Institute for Animal Health, Surrey, United Kingdom
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15
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Epifano C, Krijnse-Locker J, Salas ML, Rodríguez JM, Salas J. The African swine fever virus nonstructural protein pB602L is required for formation of the icosahedral capsid of the virus particle. J Virol 2006; 80:12260-70. [PMID: 17035321 PMCID: PMC1676282 DOI: 10.1128/jvi.01323-06] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
African swine fever virus (ASFV) protein pB602L has been described as a molecular chaperone for the correct folding of the major capsid protein p72. We have studied the function of protein pB602L during the viral assembly process by using a recombinant ASFV, vB602Li, which inducibly expresses the gene coding for this protein. We show that protein pB602L is a late nonstructural protein, which, in contrast with protein p72, is excluded from the viral factory. Repression of protein pB602L synthesis inhibits the proteolytic processing of the two viral polyproteins pp220 and pp62 and leads to a decrease in the levels of protein p72 and a delocalization of the capsid protein pE120R. As shown by electron microscopy analysis of cells infected with the recombinant virus vB602Li, the viral assembly process is severely altered in the absence of protein pB602L, with the generation of aberrant "zipper-like" structures instead of icosahedral virus particles. These "zipper-like" structures are similar to those found in cells infected under restrictive conditions with the recombinant virus vA72 inducibly expressing protein p72. Immunoelectron microscopy studies show that the abnormal forms generated in the absence of protein pB602L contain the inner envelope protein p17 and the two polyproteins but lack the capsid proteins p72 and pE120R. These findings indicate that protein pB602L is essential for the assembly of the icosahedral capsid of the virus particle.
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Affiliation(s)
- Carolina Epifano
- Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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16
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Epifano C, Krijnse-Locker J, Salas ML, Salas J, Rodríguez JM. Generation of filamentous instead of icosahedral particles by repression of African swine fever virus structural protein pB438L. J Virol 2006; 80:11456-66. [PMID: 17005638 PMCID: PMC1642605 DOI: 10.1128/jvi.01468-06] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mechanisms involved in the construction of the icosahedral capsid of the African swine fever virus (ASFV) particle are not well understood at present. Capsid formation requires protein p72, the major capsid component, but other viral proteins are likely to play also a role in this process. We have examined the function of the ASFV structural protein pB438L, encoded by gene B438L, in virus morphogenesis. We show that protein pB438L associates with membranes during the infection, behaving as an integral membrane protein. Using a recombinant ASFV that inducibly expresses protein pB438L, we have determined that this structural protein is essential for the formation of infectious virus particles. In the absence of the protein, the virus assembly sites contain, instead of icosahedral particles, large aberrant tubular structures of viral origin as well as bilobulate forms that present morphological similarities with the tubules. The filamentous particles, which possess an aberrant core shell domain and an inner envelope, are covered by a capsid-like layer that, although containing the major capsid protein p72, does not acquire icosahedral morphology. This capsid, however, is to some extent functional, as the filamentous particles can move from the virus assembly sites to the plasma membrane and exit the cell by budding. The finding that, in the absence of protein pB438L, the viral particles formed have a tubular structure in which the icosahedral symmetry is lost supports a role for this protein in the construction or stabilization of the icosahedral vertices of the virus particle.
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Affiliation(s)
- Carolina Epifano
- Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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17
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Alfonso P, Quetglas JI, Escribano JM, Alonso C. Protein pE120R of African swine fever virus is post-translationally acetylated as revealed by post-source decay MALDI mass spectrometry. Virus Genes 2006; 35:81-5. [PMID: 16964554 DOI: 10.1007/s11262-006-0015-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2006] [Accepted: 05/08/2006] [Indexed: 12/11/2022]
Abstract
Post-translational modification of proteins is a key regulatory event in many cellular processes. African swine fever virus (ASFV) is a large DNA virus that contains about 150 open reading frames (ORF) which encode for more than 150 polypeptides, most of them without assigned function. Two-dimensional gel electrophoresis (2DE) followed by Post-Source Decay Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (PSD-MALDI-MS) revealed that ASFV protein pE120R, essential for virus transport from assembly sites to plasma membranes, is acetylated at the N-terminal Ala residue during infection. To our knowledge, this is the first acetylated ASFV protein described and this modification might be relevant to ASFV life cycle since many viruses use the acetylation signaling pathway as a primary target for viral proteins after infection.
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Affiliation(s)
- Patricia Alfonso
- Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Ctra de la Coruña Km 7, 28040, Madrid, Spain
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18
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Andrés G, García-Escudero R, Salas ML, Rodríguez JM. Repression of African swine fever virus polyprotein pp220-encoding gene leads to the assembly of icosahedral core-less particles. J Virol 2002; 76:2654-66. [PMID: 11861832 PMCID: PMC135994 DOI: 10.1128/jvi.76.6.2654-2666.2002] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
African swine fever virus (ASFV) polyprotein pp220, encoded by the CP2475L gene, is an N-myristoylated precursor polypeptide that, after proteolytic processing, gives rise to the major structural proteins p150, p37, p34, and p14. These proteins localize at the core shell, a matrix-like virus domain placed between the DNA-containing nucleoid and the inner envelope. In this study, we have examined the role of polyprotein pp220 in virus morphogenesis by means of an ASFV recombinant, v220i, containing an inducible copy of the CP2475L gene regulated by the Escherichia coli repressor-operator system. Under conditions that repress pp220 expression, the virus yield of v220i was about 2.6 log units lower than that of the parental virus or of the recombinant grown under permissive conditions. Electron microscopy revealed that pp220 repression leads to the assembly of icosahedral particles virtually devoid of the core structure. Analysis of recombinant v220i by immunoelectron microscopy, immunoblotting, and DNA hybridization showed that mutant particles essentially lack, besides the pp220-derived products, a number of major core proteins as well as the viral DNA. On the other hand, transient expression of the CP2475L gene in COS cells showed that polyprotein pp220 assembles into electron-dense membrane-bound coats, whereas a mutant nonmyristoylated version of pp220 does not associate with cellular membranes but forms large cytoplasmic aggregates. Together, these findings indicate that polyprotein pp220 is essential for the core assembly and suggest that its myristoyl moiety may function as a membrane-anchoring signal to bind the developing core shell to the inner viral envelope.
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Affiliation(s)
- Germán Andrés
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
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19
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Andrés G, García-Escudero R, Viñuela E, Salas ML, Rodríguez JM. African swine fever virus structural protein pE120R is essential for virus transport from assembly sites to plasma membrane but not for infectivity. J Virol 2001; 75:6758-68. [PMID: 11435554 PMCID: PMC114402 DOI: 10.1128/jvi.75.15.6758-6768.2001] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2001] [Accepted: 05/02/2001] [Indexed: 11/20/2022] Open
Abstract
This report examines the role of African swine fever virus (ASFV) structural protein pE120R in virus replication. Immunoelectron microscopy revealed that protein pE120R localizes at the surface of the intracellular virions. Consistent with this, coimmunoprecipitation assays showed that protein pE120R binds to the major capsid protein p72. Moreover, it was found that, in cells infected with an ASFV recombinant that inducibly expresses protein p72, the incorporation of pE120R into the virus particle is dependent on p72 expression. Protein pE120R was also studied using an ASFV recombinant in which E120R gene expression is regulated by the Escherichia coli lac repressor-operator system. In the absence of inducer, pE120R expression was reduced about 100-fold compared to that obtained with the parental virus or the recombinant virus grown under permissive conditions. One-step virus growth curves showed that, under conditions that repress pE120R expression, the titer of intracellular progeny was similar to the total virus yield obtained under permissive conditions, whereas the extracellular virus yield was about 100-fold lower than in control infections. Immunofluorescence and electron microscopy demonstrated that, under restrictive conditions, intracellular mature virions are properly assembled but remain confined to the replication areas. Altogether, these results indicate that pE120R is necessary for virus dissemination but not for virus infectivity. The data also suggest that protein pE120R might be involved in the microtubule-mediated transport of ASFV particles from the viral factories to the plasma membrane.
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Affiliation(s)
- G Andrés
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Facultad de Ciencias, Cantoblanco, 28049 Madrid, Spain.
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20
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Galindo I, Viñuela E, Carrascosa AL. Characterization of the african swine fever virus protein p49: a new late structural polypeptide. J Gen Virol 2000; 81:59-65. [PMID: 10640542 DOI: 10.1099/0022-1317-81-1-59] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The open reading frame B438L, located within the EcoRI B fragment of the African swine fever virus genome, is predicted to encode a protein of 438 amino acids with a molecular mass of 49.3 kDa. It presents a cell attachment RGD (Arg-Gly-Asp) motif but no other significant similarity to protein sequences in databases. Northern blot and primer extension analysis showed that B438L is transcribed only at late times during virus infection. The B438L gene product has been expressed in Escherichia coli, purified and used as an antigen for antibody production. The rabbit antiserum specific for pB438L recognized a protein of about 49 kDa in virus-infected cell extracts. This protein was synthesized late in infection by all the virus strains tested, was located in cytoplasmic virus factories and appeared as a structural component of purified virus particles.
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Affiliation(s)
- I Galindo
- Centro de Biología Molecular 'Severo Ochoa' (CSIC-UAM), Universidad Autónoma de Madrid, 28049 Madrid, Spain
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21
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Brookes SM, Hyatt AD, Wise T, Parkhouse RM. Intracellular virus DNA distribution and the acquisition of the nucleoprotein core during African swine fever virus particle assembly: ultrastructural in situ hybridisation and DNase-gold labelling. Virology 1998; 249:175-88. [PMID: 9740789 DOI: 10.1006/viro.1998.9308] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
African swine fever virus (ASFV) is a large complex icosahedral double-stranded DNA virus that replicates in the cytoplasm of susceptible cells. Assembly of new virus particles occurs within the perinuclear viroplasm bodies known as virus factories. Two types of virus particle are routinely observed: "fulls," which are particles with an electron-dense DNA-containing nucleoid, and "empties," which consist of the virus protein and membrane icosahedral shell but are without the incorporation of the virus genome. The objective of this study was to understand ASFV morphogenesis by determining the distribution of intracellular viral DNA in the virus factory and during virus particle assembly. The ultrastructural localisation of DNA within ASFV-infected cells was achieved using two complementary methods: with an ASFV-specific DNA probe to the major capsid protein (p73) gene (B646L) hybridised in situ or through detection of all forms of DNA (viral and cellular) with gold-labelled DNase. Conditions for in situ hybridisation at the electron microscopic level were optimised for infected cells in two Lowicryl resins (K4M and HM20) and using two nonradioactive probe labels (digoxygenin and biotin). The morphological data indicate that the viral DNA, perhaps from specialised storage sites within the factory, begins to condense into a pronucleoid and is then inserted, at a single vertex, into an "empty" particle. Further maturation of the viral particle, including closure of the narrow opening in the icosahedron, gives rise to "intermediate" particles, where the nucleoprotein core undergoes additional consolidation to produce the characteristic mature or "full" virions. The site of particle closure may represent a "weak point" at one vertex, but the mechanisms and structures involved in the packaging and release of the virus genome via such a port are yet to be determined.
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Affiliation(s)
- S M Brookes
- Institute for Animal Health, Ash Road, Pirbright, Surrey, GU24 ONF, United Kingdom.
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22
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Cobbold C, Wileman T. The major structural protein of African swine fever virus, p73, is packaged into large structures, indicative of viral capsid or matrix precursors, on the endoplasmic reticulum. J Virol 1998; 72:5215-23. [PMID: 9573294 PMCID: PMC110101 DOI: 10.1128/jvi.72.6.5215-5223.1998] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
African swine fever virus (ASFV) is a large enveloped DNA virus that shares the striking icosahedral symmetry of iridoviruses. To understand the mechanism of assembly of ASFV, we have been studying the biosynthesis and subcellular distribution of p73, the major structural protein of ASFV. Sucrose density sedimentation of lysates prepared from infected cells showed that newly synthesized p73 was incorporated into a complex with a size of 150 to 250 kDa. p73 synthesized by in vitro translation migrated at 70 kDa, suggesting that cellular and/or viral proteins are required for the formation of the 150- to 250-kDa complex. During a 2-h chase, approximately 50% of the newly synthesized pool of p73 bound to the endoplasmic reticulum (ER). During this period, the membrane-bound pool of p73, but not the cytosolic pool, formed large complexes of approximately 50,000 kDa. The complexes were formed via assembly intermediates, and the entire membrane-associated pool of p73 was incorporated into the 50,000-kDa complex within 2 h. The 50,000-kDa complexes containing p73 were also detected in virions secreted from cells. Immunoprecipitation of sucrose gradients with sera taken from hyperimmune pigs suggested that p73 was the major component of the 50,000-kDa complex. It is possible, therefore, that the complex contains between 600 and 700 copies of p73. The kinetics of complex formation and envelopment of p73 were similar, and complex formation and envelopment were both reversibly inhibited by cycloheximide, suggesting a functional link between complex assembly and ASFV envelopment. A protease protection assay detected 50,000-kDa complexes on the inside and outside of the membranes forming the viral envelope. The identification of a complex containing p73 beneath the envelope of ASFV suggests that p73 may be a component of the inner core shell or matrix of ASFV. The outer pool may represent p73 within the outer capsid layer of the virus. In summary, the data suggest that the assembly of the inner core matrix and outer capsid of ASFV takes place on the ER membrane during envelopment and that these structures are not preassembled in the cytosol.
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Affiliation(s)
- C Cobbold
- Division of Immunology, Institute for Animal Health, Pirbright Laboratory, Surrey, England
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23
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García-Escudero R, Andrés G, Almazán F, Viñuela E. Inducible gene expression from African swine fever virus recombinants: analysis of the major capsid protein p72. J Virol 1998; 72:3185-95. [PMID: 9580160 PMCID: PMC109780 DOI: 10.1128/jvi.72.4.3185-3195.1998] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A method to study the function of individual African swine fever virus (ASFV) gene products utilizing the Escherichia coli lac repressor-operator system has been developed. Recombinant viruses containing both the lacI gene encoding the lac repressor and a strong virus late promoter modified by the insertion of one or two copies of the lac operator sequence at various positions were constructed. The ability of each modified promoter to regulate expression of the firefly luciferase gene was assayed in the presence and in the absence of the inducer isopropyl beta-D-thiogalactoside (IPTG). Induction and repression of gene activity were dependent on the position(s) of the operator(s) with respect to the promoter and on the number of operators inserted. The ability of this system to regulate the expression of ASFV genes was analyzed by constructing a recombinant virus inducibly expressing the major capsid protein p72. Electron microscopy analysis revealed that under nonpermissive conditions, electron-dense membrane-like structures accumulated in the viral factories and capsid formation was inhibited. Induction of p72 expression allowed the progressive building of the capsid on these structures, leading to assembly of ASFV particles. The results of this report demonstrate that the transferred inducible expression system is a powerful tool for analyzing the function of ASFV genes.
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Affiliation(s)
- R García-Escudero
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Cientificas-Universidad Autónoma de Madrid), Facultad de Ciencias, Cantoblanco, Spain
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Rouiller I, Brookes SM, Hyatt AD, Windsor M, Wileman T. African swine fever virus is wrapped by the endoplasmic reticulum. J Virol 1998; 72:2373-87. [PMID: 9499098 PMCID: PMC109537 DOI: 10.1128/jvi.72.3.2373-2387.1998] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
African swine fever (ASF) virus is a large DNA virus that shares the striking icosahedral symmetry of iridoviruses and the genomic organization of poxviruses. Both groups of viruses have a complex envelope structure. In this study, the mechanism of formation of the inner envelope of ASF virus was investigated. Examination of thin cryosections by electron microscopy showed two internal membranes in mature intracellular virions and all structural intermediates. These membranes were in continuity with intracellular membrane compartments, suggesting that the virus gained two membranes from intracellular membrane cisternae. Immunogold electron microscopy showed the viral structural protein p17 and resident membrane proteins of the endoplasmic reticulum (ER) within virus assembly sites, virus assembly intermediates, and mature virions. Resident ER proteins were also detected by Western blotting of isolated virions. The data suggested the ASF virus was wrapped by the ER. Analysis of the published sequence of ASF virus (R. J. Yanez et al., Virology 208:249-278, 1995) revealed a reading frame, XP124L, that encoded a protein predicted to translocate into the lumen of the ER. Pulse-chase immunoprecipitation and glycosylation analysis of pXP124L, the product of the XP124L gene, showed that pXP124L was retained in the ER lumen after synthesis. When analyzed by immunogold electron microscopy, pXP124L localized to virus assembly intermediates and fully assembled virions. Western blot analysis detected pXP124L in virions isolated from Percoll gradients. The packaging of pXP124L from the lumen of the ER into the virion is consistent with ASF virus being wrapped by ER cisternae: a mechanism which explains the presence of two membranes in the viral envelope.
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Affiliation(s)
- I Rouiller
- Division of Immunology, Pirbright Laboratories, Institute for Animal Health, Surrey, England
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