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Dai X, Zhang X, Ostrikov K, Abrahamyan L. Host receptors: the key to establishing cells with broad viral tropism for vaccine production. Crit Rev Microbiol 2020; 46:147-168. [PMID: 32202955 PMCID: PMC7113910 DOI: 10.1080/1040841x.2020.1735992] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Cell culture-based vaccine technology is a flexible and convenient approach for vaccine production that requires adaptation of the vaccine strains to the new cells. Driven by the motivation to develop a broadly permissive cell line for infection with a wide range of viruses, we identified a set of the most relevant host receptors involved in viral attachment and entry. This identification was done through a review of different viral entry pathways and host cell lines, and in the context of the Baltimore classification of viruses. In addition, we indicated the potential technical problems and proposed some solutions regarding how to modify the host cell genome in order to meet industrial requirements for mass production of antiviral vaccines. Our work contributes to a finer understanding of the importance of breaking the host–virus recognition specificities for the possibility of creating a cell line feasible for the production of vaccines against a broad spectrum of viruses.
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Affiliation(s)
- Xiaofeng Dai
- Wuxi School of Medicine, Jiangnan University, Wuxi, China
| | - Xuanhao Zhang
- School of Biotechnology, Jiangnan University, Wuxi, China
| | - Kostya Ostrikov
- School of Chemistry and Physics and Institute for Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
| | - Levon Abrahamyan
- Faculty of Veterinary Medicine, Swine and Poultry Infectious Diseases Research Center (CRIPA), Research Group on Infectious Diseases in Production Animals (GREMIP), Université de Montréal, Saint-Hyacinthe, Canada
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2
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Chen J, Wu Y, Wu XD, Zhou J, Liang XD, Baloch AS, Qiu YF, Gao S, Zhou B. The R614E mutation of mouse Mx1 protein contributes to the novel antiviral activity against classical swine fever virus. Vet Microbiol 2020; 243:108621. [PMID: 32273007 DOI: 10.1016/j.vetmic.2020.108621] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 02/24/2020] [Accepted: 02/24/2020] [Indexed: 01/07/2023]
Abstract
Mx proteins are interferon-induced GTPases that have broad antiviral activity against a wide range of RNA and DNA viruses. We previously demonstrated that porcine Mx1 protein (poMx1) inhibited the replication of classical swine fever virus (CSFV), an economically important Pestivirus, and that mouse Mx1 did so as well. It is unknown why the nucleus-localizing mouse Mx1 inhibits CSFV replication which occurs in the cytoplasm. To the end, we assessed the anti-CSFV actions of wild type mouse Mx1 and seven previously reported mutants (K49A, G83R, A222V, A516V, G540E, R614E and ΔL4) and identified the molecular mechanism of R614E action against CSFV replication. A series of experiments revealed that mmMx1 (R614E) mutant reposted to the cytoplasm and interacted with the CSFV nucleocapsid protein (Core), thereby inhibiting viral replication. These findings broaden our understanding of the function of Mx protein family members against CSFV and suggest that the relative conservation of Mx1 among species is the basis of broad-spectrum antiviral properties.
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Affiliation(s)
- Jing Chen
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Yue Wu
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Xu-Dan Wu
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Jing Zhou
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Xiao-Dong Liang
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Abdul Sattar Baloch
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China
| | - Ya-Feng Qiu
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, 200241, China
| | - Song Gao
- the Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, and Collaborative Innovation Center for Cancer Medicine, Guangzhou, 510060, China
| | - Bin Zhou
- MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
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Structures and Functions of Pestivirus Glycoproteins: Not Simply Surface Matters. Viruses 2015; 7:3506-29. [PMID: 26131960 PMCID: PMC4517112 DOI: 10.3390/v7072783] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 06/11/2015] [Accepted: 06/18/2015] [Indexed: 12/21/2022] Open
Abstract
Pestiviruses, which include economically important animal pathogens such as bovine viral diarrhea virus and classical swine fever virus, possess three envelope glycoproteins, namely Erns, E1, and E2. This article discusses the structures and functions of these glycoproteins and their effects on viral pathogenicity in cells in culture and in animal hosts. E2 is the most important structural protein as it interacts with cell surface receptors that determine cell tropism and induces neutralizing antibody and cytotoxic T-lymphocyte responses. All three glycoproteins are involved in virus attachment and entry into target cells. E1-E2 heterodimers are essential for viral entry and infectivity. Erns is unique because it possesses intrinsic ribonuclease (RNase) activity that can inhibit the production of type I interferons and assist in the development of persistent infections. These glycoproteins are localized to the virion surface; however, variations in amino acids and antigenic structures, disulfide bond formation, glycosylation, and RNase activity can ultimately affect the virulence of pestiviruses in animals. Along with mutations that are driven by selection pressure, antigenic differences in glycoproteins influence the efficacy of vaccines and determine the appropriateness of the vaccines that are currently being used in the field.
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Xu D, Song L, Wang H, Xu X, Wang T, Lu L. Proteomic analysis of cellular protein expression profiles in response to grass carp reovirus infection. FISH & SHELLFISH IMMUNOLOGY 2015; 44:515-524. [PMID: 25783000 DOI: 10.1016/j.fsi.2015.03.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 03/04/2015] [Accepted: 03/06/2015] [Indexed: 06/04/2023]
Abstract
Grass carp (Ctenopharyngodon idella) hemorrhagic disease, caused by grass carp reovirus (GCRV), is emerging as a serious problem in grass carp aquaculture. To better understand the molecular responses to GCRV infection, two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization tandem mass spectroscopy were performed to investigate altered proteins in C. idella kidney (CIK) cells. Differentially expressed proteins in mock infected CIK cells and GCRV-infected CIK cells were compared. Twenty-three differentially expressed spots were identified (22 upregulated spots and 1 downregulated spot), which included cytoskeleton proteins, macromolecular biosynthesis-associated proteins, stress response proteins, signal transduction proteins, energy metabolism-associated proteins and ubiquitin proteasome pathway-associated proteins. Moreover, 10 of the corresponding genes of the differentially expressed proteins were quantified by real-time reverse transcription polymerase chain reaction to examine their transcriptional profiles. The T cell internal antigen 1 (TIA1) and Ras-GTPase-activating SH3-domain-binding protein1 (G3BP1) of the cellular stress granule pathway from grass carp C. idella (designated as CiTIA1 and CiG3BP1) were upregulated and downregulated during GCRV infection, respectively. The full-length cDNA of CiTIA1 was 2753 bp, with an open reading frame (ORF) of 1155bp, which encodes a putative 385-amino acid protein. The 2271 bp full-length cDNA of CiG3BP1 comprised an ORF of 1455 bp that encodes a putative 485-amino acid protein. Phylogenetic analysis revealed that the complete ORFs of CiTIA1 and CiG3BP1 were very similar to zebrafish and well-characterized mammalian homologs. The expressions of the cellular proteins CiTIA1 and CiG3BP1 in response to GCRV were validated by western blotting, which indicated that the GCRV should unlink TIA1 aggregation and stress granule formation. This study provides useful information on the proteomic and cellular stress granule pathway's responses to GCRV infection, which adds to our understanding of viral pathogenesis.
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Affiliation(s)
- Dan Xu
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China
| | - Lang Song
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China
| | - Hao Wang
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China
| | - Xiaoyan Xu
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China
| | - Tu Wang
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China
| | - Liqun Lu
- Key Laboratory of Aquatic Genetic Resources of the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, PR China.
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Dräger C, Beer M, Blome S. Porcine complement regulatory protein CD46 and heparan sulfates are the major factors for classical swine fever virus attachment in vitro. Arch Virol 2015; 160:739-46. [PMID: 25559665 DOI: 10.1007/s00705-014-2313-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 12/13/2014] [Indexed: 11/30/2022]
Abstract
Classical swine fever virus (CSFV) is the causative agent of a severe multi-systemic disease of pigs. While several aspects of virus-host-interaction are known, the early steps of infection remain unclear. For the closely related bovine viral diarrhea virus (BVDV), a cellular receptor is known: bovine complement regulatory protein CD46. Given that these two pestiviruses are closely related, porcine CD46 is also a candidate receptor for CSFV. In addition to CD46, cell-culture-adapted CSFV strains have been shown to use heparan sulfates as an additional cellular factor. In the present study, the interaction of field-type and cell-culture-adapted CSFV with a permanent porcine cell line or primary macrophages was assessed using anti-porcine CD46 monoclonal antibodies and a heparan-sulfate-blocking compound, DSTP-27. The influence of receptor blocking was assessed using virus titration and quantitative PCR. Treatment of cells with monoclonal antibodies against porcine CD46 led to a reduction of viral growth in both cell types. The effect was most pronounced with field-type CSFV. The blocking could be enhanced by addition of DSTP-27, especially for cell-culture-adapted CSFV. The combined use of both blocking agents led to a significant reduction of viral growth but was also not able to abolish infection completely. The results obtained in this study showed that both porcine CD46 and heparan sulfates play a major role in the initial steps of CSFV infection. Additional receptors might also play a role for attachment and entry; however, their impact is obviously limited in vitro in comparison to CD46 and heparan sulfates.
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Affiliation(s)
- Carolin Dräger
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Suedufer 10, 17493, Greifswald, Insel Riems, Germany
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Molecular characterization of E2 glycoprotein of classical swine fever virus: adaptation and propagation in porcine kidney cells. In Vitro Cell Dev Biol Anim 2015; 51:441-6. [DOI: 10.1007/s11626-014-9859-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 12/14/2014] [Indexed: 10/24/2022]
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He F, Ling L, Liao Y, Li S, Han W, Zhao B, Sun Y, Qiu HJ. Beta-actin interacts with the E2 protein and is involved in the early replication of classical swine fever virus. Virus Res 2014; 179:161-8. [DOI: 10.1016/j.virusres.2013.10.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 10/18/2013] [Accepted: 10/21/2013] [Indexed: 10/26/2022]
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Van Gennip H, Miedema G, Moormann R, Van Rijn P. Functionality of Chimeric E2 Glycoproteins of BVDV and CSFV in Virus Replication. Virology (Auckl) 2008. [DOI: 10.4137/vrt.s589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
An intriguing difference between the E2 glycoprotein of CSFV and the other groups of pestiviruses (nonCSFV) is a lack of two cysteine residues on positions cysteine 751 and 798. Other groups of pestivirus are not restricted to one species as swine, whereas CSFV is restricted to swine and wild boar. We constructed chimeric CSFV/BVDV E2 genes based on a 2D model of E2 proposed by van Rijn et al. (van Rijn et al. 1994, J Virol 68, 3934–42) and confirmed their expression by immunostaining of plasmid-transfected SK6 cells. No equivalents for the antigenic units B/C and A were found on E2 of BVDVII. This indicates major structural differences in E2. However, the immunodominant BVDVII domain A, containing epitopes with essential amino acids between position 760–764, showed to be dependent on the presence of the region defined by amino acids 684 to 796. As for the A domain of CSFV, the BVDVII A-like domain seemed to function as a separate unit. These combined domains in E2 proved to be the only combination which was functional in viral background of CSFV C-strain. The fitness of this virus (vflc36BVDVII 684–796) seemed to be reduced compared to vflc9 (with the complete antigenic region of BVDVII).
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Affiliation(s)
- H.G.P. Van Gennip
- Central Veterinary Institute of (CVI) of Wageningen UR, P.O. Box 2004, 8203 AA Lelystad, The Netherlands
| | - G.K.W Miedema
- Central Veterinary Institute of (CVI) of Wageningen UR, P.O. Box 2004, 8203 AA Lelystad, The Netherlands
| | - R.J.M. Moormann
- Central Veterinary Institute of (CVI) of Wageningen UR, P.O. Box 2004, 8203 AA Lelystad, The Netherlands
| | - P.A Van Rijn
- Central Veterinary Institute of (CVI) of Wageningen UR, P.O. Box 2004, 8203 AA Lelystad, The Netherlands
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Silflow RM, Degel PM, Harmsen AG. Bronchoalveolar immune defense in cattle exposed to primary and secondary challenge with bovine viral diarrhea virus. Vet Immunol Immunopathol 2005; 103:129-39. [PMID: 15626468 DOI: 10.1016/j.vetimm.2004.09.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Revised: 08/03/2004] [Accepted: 09/01/2004] [Indexed: 11/18/2022]
Abstract
To evaluate immune defense mechanisms against bovine viral diarrhea virus (BVDV), four calves received primary and secondary intrabronchial infections with the cytopathic, type I Singer strain of BVDV. The cellular and humoral responses to these site-specific infections with BVDV were monitored by sequential bronchoalveolar lavages (BAL) conducted prior to infection (day 0, non-infected controls) and on days 4, 7, 10, 17 (day 31, secondary infection), 35, 38, 41, 48 and 62 post-infection. Peak quantities of BVDV were recovered from BAL on day 4. BVDV clearance from the lung was complete between days 17 and 31. Immune clearance of BVDV from the lower airways upon secondary infection was swift, within 4 days, and sustained throughout a 1-month period. Total numbers of BAL CD4(+) and CD8(+) T-lymphocytes increased >200-fold by day 10, and increased to levels >70-fold higher than background by 4 days after a secondary BVDV infection. gammadelta(+) T-lymphocytes increased 100-fold by day 7 and remained at levels at least 10-fold higher than pre-infection throughout the study. B-lymphocytes increased to levels 30-fold greater than pre-infection levels by day 10, and further increased to levels 100-fold higher following secondary BVDV infection. Activation (defined by the phenotype CD25(+)/CD62L(-)) and memory (defined by the phenotype CD45RO(+)/CD45R(-)) profiles of lymphocytes in the lower airways were characterized. Activated subpopulations of CD4(+) and CD8(+) cells increased nearly 300- and 150-fold, respectively, by day 10, and to levels 100- and 50-fold 4 days after the secondary infection. Memory subpopulations of CD4(+) and CD8(+) cells increased to levels 170- and 120-fold, respectively, by day 10, and to levels approximately 400- and 300-fold, respectively, 7 days after the secondary infection. The primary antibody response consisted of increased titers of anti-BVDV-specific IgA in bronchoalveolar lavage fluid (BALF). A strong secondary antibody response with high levels of anti-BVDV-specific IgA and IgG in BALF before day 4 post-secondary BVDV infection, likely contributed, along with cellular defenses, to the rapid clearance of virus from the lung upon secondary exposure. These results demonstrate that primary infection of the bovine lung with BVDV initiates cell-mediated immune responses capable of clearing the virus within 2-3 weeks. Furthermore, populations of immune-activated and memory T-lymphocytes, combined with BVDV-specific antibody production, contribute to rapid BVDV clearance upon secondary exposure to the virus.
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Affiliation(s)
- Ronald M Silflow
- Department of Veterinary Molecular Biology, Montana State University, PO Box 173610, Bozeman, MT 59717-3610, USA.
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Buckwold VE, Beer BE, Donis RO. Bovine viral diarrhea virus as a surrogate model of hepatitis C virus for the evaluation of antiviral agents. Antiviral Res 2003; 60:1-15. [PMID: 14516916 DOI: 10.1016/s0166-3542(03)00174-8] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The identification and development of new antiviral agents that can be used to combat hepatitis C virus (HCV) infection has been complicated by both technical and logistic issues. There are few, if any, robust methods by which HCV virions can be grown in vitro. The development of HCV RNA replicons has been a great breakthrough that has allowed for the undertaking of significant screening efforts to identify inhibitors of HCV intracellular replication. However, since replicons do not undergo a complete replication cycle, drug screening programs and mechanism of action studies based solely on these assays will not identify compounds targeting either early (virion attachment, entry, uncoating) or late (virion assembly, egress) stages of the viral replication cycle. Drugs that negatively affect the infectivity of new virions will also not be identified using HCV RNA replicons. Bovine viral diarrhea virus (BVDV) shares a similar structural organization with HCV, and both viruses generally cause chronic long-term infections in their respective hosts. The BVDV surrogate model is attractive, since it is a virus-based system. It is easy to culture the virus in vitro, molecular clones are available for genetic studies, and the virus undergoes a complete replication cycle. Like HCV, BVDV utilizes the LDL receptor to enter cells, uses a functionally similar internal ribosome entry site (IRES) for translation, uses an NS4A cofactor with its homologous NS3 protease, has a similar NS3 helicase/NTPase, a mechanistically similar NS5B RNA-dependent RNA polymerase, and a seemingly equivalent mechanism of virion maturation, assembly and egress. While the concordance between drugs active in either BVDV or HCV is largely unknown at this time, BVDV remains a popular model system with which drugs can be evaluated for potential antiviral activity against HCV and in studies of drug mechanism of action.
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Affiliation(s)
- Victor E Buckwold
- Infectious Disease Research Department, Southern Research Institute, 431 Aviation Way, Frederick MD 21701, USA.
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Grummer B, Beer M, Liebler-Tenorio E, Greiser-Wilke I. Localization of viral proteins in cells infected with bovine viral diarrhoea virus. J Gen Virol 2001; 82:2597-2605. [PMID: 11602770 DOI: 10.1099/0022-1317-82-11-2597] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bovine viral diarrhoea virus (BVDV) is a member of the genus Pestivirus within the family Flaviviridae. In this report, protein localization studies were performed to assess the mechanism for the release of mature virus particles from infected cells. Since BVDV is an enveloped virus, budding from either intra- or extracellular membranes is feasible. A prerequisite for the latter mechanism is the integration of viral glycoproteins into the host cell membrane. Using monoclonal antibodies (MAbs) directed against the viral envelope glycoproteins E2 and E(RNS), no specific signals were detected on the surface of BVDV-infected cells by indirect fluorescence, confocal microscopy or fluorescence-activated cell sorter analyses. Furthermore, biotin-labelled cell surface proteins of virus-infected and non-infected cells were not detected by immunoprecipitation using MAbs directed against E(RNS) and E2 or the non-structural protein NS2-3. None of these proteins was detected on the cell surface. In addition, to analyse the intracellular localization of the two viral glycoproteins E(RNS) and E2 and the non-structural proteins NS2-3 and NS3, subcellular fractionation of virus-infected cells followed by radioimmunoprecipitation with the MAbs were performed. These results led to the conclusion that the BVDV envelope glycoproteins E(RNS) and E2 as well as the non-structural proteins NS2-3 and NS3 were almost quantitatively associated with intracellular membranes. These findings indicate that BVDV is released by budding into the cisternae of the endoplasmic reticulum and that there seems to be no correlation between the location and function of the analysed proteins.
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Affiliation(s)
- B Grummer
- Institutes of Virology1 and Pathology3, School of Veterinary Medicine Hannover, Buenteweg 17, 30559 Hannover, Germany
| | - M Beer
- Federal Research Centre for Virus Diseases of Animals, Institute for Diagnostic Virology, Boddenblick 5a, 17498 Insel Riems, Germany2
| | - E Liebler-Tenorio
- Federal Research Centre for Virus Diseases of Animals, Institute for Diagnostic Virology, Boddenblick 5a, 17498 Insel Riems, Germany2
| | - I Greiser-Wilke
- Institutes of Virology1 and Pathology3, School of Veterinary Medicine Hannover, Buenteweg 17, 30559 Hannover, Germany
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Hulst MM, van Gennip HG, Vlot AC, Schooten E, de Smit AJ, Moormann RJ. Interaction of classical swine fever virus with membrane-associated heparan sulfate: role for virus replication in vivo and virulence. J Virol 2001; 75:9585-95. [PMID: 11559790 PMCID: PMC114529 DOI: 10.1128/jvi.75.20.9585-9595.2001] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Passage of native classical swine fever virus (CSFV) in cultured swine kidney cells (SK6 cells) selects virus variants that attach to the surface of cells by interaction with membrane-associated heparan sulfate (HS). A Ser-to-Arg change in the C terminus of envelope glycoprotein E(rns) (amino acid 476 in the open reading frame of CSFV) is responsible for selection of these HS-binding virus variants (M. M. Hulst, H. G. P. van Gennip, and R. J. M. Moormann, J. Virol. 74:9553-9561, 2000). In this investigation we studied the role of binding of CSFV to HS in vivo. Using reverse genetics, an HS-independent recombinant virus (S-ST virus) with Ser(476) and an HS-dependent recombinant virus (S-RT virus) with Arg(476) were constructed. Animal experiments indicated that this adaptive Ser-to-Arg mutation had no effect on the virulence of CSFV. Analysis of viruses reisolated from pigs infected with these recombinant viruses indicated that replication in vivo introduced no mutations in the genes of the envelope proteins E(rns), E1, and E2. However, the blood of one of the three pigs infected with the S-RT virus contained also a low level of virus particles that, when grown under a methylcellulose overlay, produced relative large plaques, characteristic of an HS-independent virus. Sequence analysis of such a large-plaque phenotype showed that Arg(476) was mutated back to Ser(476). Removal of HS from the cell surface and addition of heparin to the medium inhibited infection of cultured (SK6) and primary swine kidney cells with S-ST virus reisolated from pigs by about 70% whereas infection with the administered S-ST recombinant virus produced in SK6 cells was not affected. Furthermore, E(rns) S-ST protein, produced in insect cells, could bind to immobilized heparin and to HS chains on the surface of SK6 cells. These results indicated that S-ST virus generated in pigs is able to infect cells by an HS-dependent mechanism. Binding of concanavalin A (ConA) to virus particles stimulated the infection of SK6 cells with S-ST virus produced in these cells by 12-fold; in contrast, ConA stimulated infection with S-ST virus generated in pigs no more than 3-fold. This suggests that the surface properties of S-ST virus reisolated from pigs are distinct from those of S-ST virus produced in cell culture. We postulate that due to these surface properties, in vivo-generated CSFV is able to infect cells by an HS-dependent mechanism. Infection studies with the HS-dependent S-RT virus, however, indicated that interaction with HS did not mediate infection of lung macrophages, indicating that alternative receptors are also involved in the attachment of CSFV to cells.
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Affiliation(s)
- M M Hulst
- Institute for Animal Science and Health, Research Branch Houtribweg, NL-8200 AB Lelystad, The Netherlands.
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