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Koshizuka T, Kondo H, Kato H, Takahashi K. Human cytomegalovirus UL42 protein inhibits the degradation of glycoprotein B through inhibition of Nedd4 family ubiquitin E3 ligases. Microbiol Immunol 2021; 65:472-480. [PMID: 34260096 DOI: 10.1111/1348-0421.12932] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Revised: 07/06/2021] [Accepted: 07/12/2021] [Indexed: 11/29/2022]
Abstract
Human cytomegalovirus (HCMV) is a globally ubiquitous pathogen and causes congenital infection as well as opportunistic infection in immunocompromised patients. The HCMV UL42 gene encodes a membrane protein that regulates the function of Nedd4 family ubiquitin E3 ligases through its PPxY motif. As HCMV envelope glycoprotein B (gB) also has a PPxY motif at its C-terminal cytoplasmic domain, we examined whether there was any relationship between UL42 protein with gB. Among the Nedd4 family proteins, Nedd4, Nedd4L, and Itch induced the degradation of gB in transiently expressing cells. The degradation of gB by Nedd4 was inhibited by proteasome inhibitor MG132, lysosome inhibitor chloroquine, and the co-expression of UL42 proteins. Among those Nedd4 family proteins, Itch was re-localized by the co-expression of gB to the perinuclear region of the cytoplasm. A co-immunoprecipitation assay demonstrated an interaction between gB and Itch through its PPxY motif. The 150 kDa gB precursor was aberrantly ubiquitinated, and the total amount of gB was quickly decreased in the absence of UL42. Our results indicate that UL42 prevent the degradation of gB by the inhibition of Nedd4 family proteins. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Tetsuo Koshizuka
- Department of Microbiology and Immunology, Gifu Pharmaceutical University, Gifu, Japan
| | - Hiroki Kondo
- Department of Microbiology and Immunology, Gifu Pharmaceutical University, Gifu, Japan
| | - Hiroki Kato
- Department of Microbiology and Immunology, Gifu Pharmaceutical University, Gifu, Japan
| | - Keita Takahashi
- Department of Microbiology and Immunology, Gifu Pharmaceutical University, Gifu, Japan
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2
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Lučin P, Jug Vučko N, Karleuša L, Mahmutefendić Lučin H, Blagojević Zagorac G, Lisnić B, Pavišić V, Marcelić M, Grabušić K, Brizić I, Lukanović Jurić S. Cytomegalovirus Generates Assembly Compartment in the Early Phase of Infection by Perturbation of Host-Cell Factors Recruitment at the Early Endosome/Endosomal Recycling Compartment/Trans-Golgi Interface. Front Cell Dev Biol 2020; 8:563607. [PMID: 33042998 PMCID: PMC7516400 DOI: 10.3389/fcell.2020.563607] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 08/18/2020] [Indexed: 12/02/2022] Open
Abstract
Beta-herpesviruses develop a unique structure within the infected cell known as an assembly compartment (AC). This structure, as large as the nucleus, is composed of host-cell-derived membranous elements. The biogenesis of the AC and its contribution to the final stages of beta-herpesvirus assembly are still unclear. In this study, we performed a spatial and temporal analysis of the AC in cells infected with murine CMV (MCMV), a member of the beta-herpesvirus family, using a panel of markers that characterize membranous organelle system. Out of 64 markers that were analyzed, 52 were cytosolic proteins that are recruited to membranes as components of membrane-shaping regulatory cascades. The analysis demonstrates that MCMV infection extensively reorganizes interface between early endosomes (EE), endosomal recycling compartment (ERC), and the trans-Golgi network (TGN), resulting in expansion of various EE-ERC-TGN intermediates that fill the broad area of the inner AC. These intermediates are displayed as over-recruitment of host-cell factors that control membrane flow at the EE-ERC-TGN interface. Most of the reorganization is accomplished in the early (E) phase of infection, indicating that the AC biogenesis is controlled by MCMV early genes. Although it is known that CMV infection affects the expression of a large number of host-cell factors that control membranous system, analysis of the host-cell transcriptome and protein expression in the E phase of infection demonstrated no sufficiently significant alteration in expression levels of analyzed markers. Thus, our study demonstrates that MCMV-encoded early phase function targets recruitment cascades of host cell-factors that control membranous flow at the EE-ERC-TGN interface in order to initiate the development of the AC.
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Affiliation(s)
- Pero Lučin
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia.,University North, University Center Varaždin, Varaždin, Croatia
| | - Natalia Jug Vučko
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Ljerka Karleuša
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Hana Mahmutefendić Lučin
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia.,University North, University Center Varaždin, Varaždin, Croatia
| | - Gordana Blagojević Zagorac
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia.,University North, University Center Varaždin, Varaždin, Croatia
| | - Berislav Lisnić
- Department of Histology and Embryology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Valentino Pavišić
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Marina Marcelić
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Kristina Grabušić
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Ilija Brizić
- Department of Histology and Embryology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Silvija Lukanović Jurić
- Department of Physiology and Immunology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
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3
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Wang YQ, Zhao XY. Human Cytomegalovirus Primary Infection and Reactivation: Insights From Virion-Carried Molecules. Front Microbiol 2020; 11:1511. [PMID: 32765441 PMCID: PMC7378892 DOI: 10.3389/fmicb.2020.01511] [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] [Received: 03/30/2020] [Accepted: 06/10/2020] [Indexed: 12/12/2022] Open
Abstract
Human cytomegalovirus (HCMV), a ubiquitous beta-herpesvirus, is able to establish lifelong latency after initial infection. Periodical reactivation occurs after immunosuppression, remaining a major cause of death in immunocompromised patients. HCMV has to reach a structural and functional balance with the host at its earliest entry. Virion-carried mediators are considered to play pivotal roles in viral adaptation into a new cellular environment upon entry. Additionally, one clear difference between primary infection and reactivation is the idea that virion-packaged factors are already formed such that those molecules can be used swiftly by the virus. In contrast, virion-carried mediators have to be transcribed and translated; thus, they are not readily available during reactivation. Hence, understanding virion-carried molecules helps to elucidate HCMV reactivation. In this article, the impact of virion-packaged molecules on viral structure, biological behavior, and viral life cycle will be reviewed.
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Affiliation(s)
- Yu-Qing Wang
- Peking University People's Hospital, Peking University Institute of Hematology, National Clinical Research Center for Hematologic Disease, Key Laboratory of Hematopoietic Stem Cell Transplantation, Beijing, China.,PKU-THU Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiang-Yu Zhao
- Peking University People's Hospital, Peking University Institute of Hematology, National Clinical Research Center for Hematologic Disease, Key Laboratory of Hematopoietic Stem Cell Transplantation, Beijing, China
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4
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Lopes PH, van den Berg CW, Tambourgi DV. Sphingomyelinases D From Loxosceles Spider Venoms and Cell Membranes: Action on Lipid Rafts and Activation of Endogenous Metalloproteinases. Front Pharmacol 2020; 11:636. [PMID: 32477123 PMCID: PMC7237637 DOI: 10.3389/fphar.2020.00636] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 04/21/2020] [Indexed: 01/01/2023] Open
Abstract
Loxosceles spider venom contains Sphingomyelinase D (SMase D), the key toxin causing pathology. SMase D hydrolyzes the main component of lipid rafts, sphingomyelin, which changes the membrane microenvironment resulting in the activation of endogenous metalloproteinase from the ADAMs family. Alterations in membrane microenvironment of lipid rafts contribute to the activation of several cell surface molecules. Serine proteinases convertases acting on the pro-domain of membrane metalloproteinases, such as ADAMs, increase the cleavage and the release of proteins ectodomains and receptors located at the cell surface areas containing lipid rafts. We, therefore, investigated the interaction of SMases D with these membrane microdomains (lipid rafts) in human keratinocytes, to better understand the molecular mechanism of SMases D action, and identify the ADAM(s) responsible for the cleavage of cell surface molecules. Using specific inhibitors, we observed that ADAMs 10 and 17 are activated in the cell membrane after SMase D action. Furthermore, proproteins convertases, such as furin, are involved in the SMase D induced ADAMs activation. One of the signaling pathways that may be involved in the activation of these proteases is the MAPK pathway, since phosphorylation of ERK1/2 was observed in cells treated with SMase D. Confocal analysis showed a strong colocalization between SMase D and GM1 ganglioside present in rafts. Analysis of structural components of rafts, such as caveolin-1 and flotillin-1, showed that the action of SMase D on cell membranes leads to a reduction in caveolin-1, which is possibly degraded by toxin-induced superoxide production in cells. The action of the toxin also results in flotilin-1 increased detection in the cell membrane. These results indicate that SMases D from Loxosceles venoms alter membrane rafts structure, leading to the activation of membrane bound proteases, which may explain why the lipase action of this toxin can result in proteolytic cleavage of cell surface proteins, ultimately leading to pathology.
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Affiliation(s)
| | - Carmen W. van den Berg
- Centre for Medical Education, School of Medicine, Cardiff University, Cardiff, United Kingdom
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5
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Izaguirre G. The Proteolytic Regulation of Virus Cell Entry by Furin and Other Proprotein Convertases. Viruses 2019; 11:v11090837. [PMID: 31505793 PMCID: PMC6784293 DOI: 10.3390/v11090837] [Citation(s) in RCA: 101] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 09/03/2019] [Accepted: 09/06/2019] [Indexed: 12/11/2022] Open
Abstract
A wide variety of viruses exploit furin and other proprotein convertases (PCs) of the constitutive protein secretion pathway in order to regulate their cell entry mechanism and infectivity. Surface proteins of enveloped, as well as non-enveloped, viruses become processed by these proteases intracellularly during morphogenesis or extracellularly after egress and during entry in order to produce mature virions activated for infection. Although viruses also take advantage of other proteases, it is when some viruses become reactive with PCs that they may develop high pathogenicity. Besides reacting with furin, some viruses may also react with the PCs of the other specificity group constituted by PC4/PC5/PACE4/PC7. The targeting of PCs for inhibition may result in a useful strategy to treat infections with some highly pathogenic viruses. A wide variety of PC inhibitors have been developed and tested for their antiviral activity in cell-based assays.
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Affiliation(s)
- Gonzalo Izaguirre
- College of Dentistry, University of Illinois at Chicago, Chicago, IL 60612, USA.
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6
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Böttcher-Friebertshäuser E, Garten W, Klenk HD. Characterization of Proprotein Convertases and Their Involvement in Virus Propagation. ACTIVATION OF VIRUSES BY HOST PROTEASES 2018. [PMCID: PMC7122180 DOI: 10.1007/978-3-319-75474-1_9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
| | - Wolfgang Garten
- Institut für Virologie, Philipps Universität, Marburg, Germany
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7
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Stangherlin LM, de Paula FN, Icimoto MY, Ruiz LGP, Nogueira ML, Braz ASK, Juliano L, da Silva MCC. Positively Selected Sites at HCMV gB Furin Processing Region and Their Effects in Cleavage Efficiency. Front Microbiol 2017; 8:934. [PMID: 28588572 PMCID: PMC5441137 DOI: 10.3389/fmicb.2017.00934] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2017] [Accepted: 05/08/2017] [Indexed: 12/16/2022] Open
Abstract
Human cytomegalovirus is a ubiquitous infectious agent that affects mainly immunosuppressed, fetuses, and newborns. The virus has several polymorphic regions, in particular in the envelope glycoproteins. The UL55 gene encodes the glycoprotein B that has a variable region, containing a furin cleavage site and according to the variability different genotypes are characterized. Here we investigated variability and existence of selective pressure on the UL55 variable region containing the furin cleavage site in 213 clinical sequences from patients worldwide. We showed the occurrence of positive selective pressure on gB codons 461 and 462, near the furin cleavage site. Cleavage analysis of synthesized peptides demonstrated that most mutations confer better cleavage by furin, suggesting that evolution is acting in order to increase the efficiency cleavage and supporting the hypothesis that gB processing is important in the host. We also demonstrated that peptides containing sequences, that characterize genotypes gB2 and 3, are differentially cleaved by furin. Our data demonstrate for the first time that variability in the cleavage site is related to degree of gB processing by furin.
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Affiliation(s)
- Lucas M Stangherlin
- Center for Natural Sciences and Humanities, Federal University of ABCSanto André, Brazil
| | - Felipe N de Paula
- Center for Natural Sciences and Humanities, Federal University of ABCSanto André, Brazil.,Pasteur InstituteSão Paulo, Brazil
| | - Marcelo Y Icimoto
- Department of Biophysics, Paulista Medical School, Federal University of São PauloSão Paulo, Brazil
| | - Leonardo G P Ruiz
- Medical School of São José do Rio PretoSão José do Rio Preto, Brazil
| | | | - Antônio S K Braz
- Center for Natural Sciences and Humanities, Federal University of ABCSanto André, Brazil
| | - Luiz Juliano
- Department of Biophysics, Paulista Medical School, Federal University of São PauloSão Paulo, Brazil
| | - Maria C C da Silva
- Center for Natural Sciences and Humanities, Federal University of ABCSanto André, Brazil
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8
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Virion Glycoprotein-Mediated Immune Evasion by Human Cytomegalovirus: a Sticky Virus Makes a Slick Getaway. Microbiol Mol Biol Rev 2016; 80:663-77. [PMID: 27307580 DOI: 10.1128/mmbr.00018-16] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The prototypic herpesvirus human cytomegalovirus (CMV) exhibits the extraordinary ability to establish latency and maintain a chronic infection throughout the life of its human host. This is even more remarkable considering the robust adaptive immune response elicited by infection and reactivation from latency. In addition to the ability of CMV to exist in a quiescent latent state, its persistence is enabled by a large repertoire of viral proteins that subvert immune defense mechanisms, such as NK cell activation and major histocompatibility complex antigen presentation, within the cell. However, dissemination outside the cell presents a unique existential challenge to the CMV virion, which is studded with antigenic glycoprotein complexes targeted by a potent neutralizing antibody response. The CMV virion envelope proteins, which are critical mediators of cell attachment and entry, possess various characteristics that can mitigate the humoral immune response and prevent viral clearance. Here we review the CMV glycoprotein complexes crucial for cell attachment and entry and propose inherent properties of these proteins involved in evading the CMV humoral immune response. These include viral glycoprotein polymorphism, epitope competition, Fc receptor-mediated endocytosis, glycan shielding, and cell-to-cell spread. The consequences of CMV virion glycoprotein-mediated immune evasion have a major impact on persistence of the virus in the population, and a comprehensive understanding of these evasion strategies will assist in designing effective CMV biologics and vaccines to limit CMV-associated disease.
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9
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Manghera A, McLean GR. Human cytomegalovirus vaccination: progress and perspectives of recombinant gB. Future Virol 2016. [DOI: 10.2217/fvl-2016-0039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
A vaccine for Human cytomegalovirus (HCMV) remains a high priority as complications following infection are observed in immunocompromised individuals and in congenitally infected neonates. Numerous preclinical and clinical studies have investigated vaccine strategies ranging from live attenuated preparations, nucleic acid-based approaches and recombinant delivery systems to subunit vaccines. These have defined the importance of both cell-mediated and humoral immunity to viral gB in the control of HCMV infection. This review will cover clinical trials investigating vaccine approaches that have incorporated gB and discuss the future perspectives of the recombinant gB subunit vaccine for HCMV.
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Affiliation(s)
- Avneet Manghera
- National Heart & Lung Institute, Imperial College London, London, UK
| | - Gary R McLean
- National Heart & Lung Institute, Imperial College London, London, UK
- Cellular & Molecular Immunology Research Centre, London Metropolitan University, London, UK
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10
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Omotuyi OI, Hamada T. Human furin Cys198 imposes dihedral and positional restraints on His194 for optimal Ser386-proton transfer. J Biomol Struct Dyn 2015; 33:2442-51. [DOI: 10.1080/07391102.2015.1041552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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11
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Crystal Structure of the Human Cytomegalovirus Glycoprotein B. PLoS Pathog 2015; 11:e1005227. [PMID: 26484870 PMCID: PMC4617298 DOI: 10.1371/journal.ppat.1005227] [Citation(s) in RCA: 109] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 09/23/2015] [Indexed: 12/21/2022] Open
Abstract
Human cytomegalovirus (HCMV), a dsDNA, enveloped virus, is a ubiquitous pathogen that establishes lifelong latent infections and caused disease in persons with compromised immune systems, e.g., organ transplant recipients or AIDS patients. HCMV is also a leading cause of congenital viral infections in newborns. Entry of HCMV into cells requires the conserved glycoprotein B (gB), thought to function as a fusogen and reported to bind signaling receptors. gB also elicits a strong immune response in humans and induces the production of neutralizing antibodies although most anti-gB Abs are non-neutralizing. Here, we report the crystal structure of the HCMV gB ectodomain determined to 3.6-Å resolution, which is the first atomic-level structure of any betaherpesvirus glycoprotein. The structure of HCMV gB resembles the postfusion structures of HSV-1 and EBV homologs, establishing it as a new member of the class III viral fusogens. Despite structural similarities, each gB has a unique domain arrangement, demonstrating structural plasticity of gB that may accommodate virus-specific functional requirements. The structure illustrates how extensive glycosylation of the gB ectodomain influences antibody recognition. Antigenic sites that elicit neutralizing antibodies are more heavily glycosylated than those that elicit non-neutralizing antibodies, which suggest that HCMV gB uses glycans to shield neutralizing epitopes while exposing non-neutralizing epitopes. This glycosylation pattern may have evolved to direct the immune response towards generation of non-neutralizing antibodies thus helping HCMV to avoid clearance. HCMV gB structure provides a starting point for elucidation of its antigenic and immunogenic properties and aid in the design of recombinant vaccines and monoclonal antibody therapies. Human cytomegalovirus (HCMV) establishes lifelong infection in a majority of the world’s population and causes disease in neonates and the immunocompromised patients such as organ transplant recipients or persons with AIDS. There is no vaccine against HCMV, and current HCMV antivirals are toxic and an increasing prevalence of resistance. Glycoprotein B (gB), displayed on the viral surface is a major viral immunogen and is necessary for viral penetration into cells. The crystal structure of gB reported here provides a detailed 3D map of gB. A thick glycan layer covers a large surface area, which may explain why anti-gB neutralizing antibodies are relatively rare. The structure is expected to aid in the development of a HCMV vaccine and monoclonal antibody therapies.
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12
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Li Q, Wilkie AR, Weller M, Liu X, Cohen JI. THY-1 Cell Surface Antigen (CD90) Has an Important Role in the Initial Stage of Human Cytomegalovirus Infection. PLoS Pathog 2015; 11:e1004999. [PMID: 26147640 PMCID: PMC4492587 DOI: 10.1371/journal.ppat.1004999] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 06/03/2015] [Indexed: 01/01/2023] Open
Abstract
Human cytomegalovirus (HCMV) infects about 50% of the US population, is the leading infectious cause of birth defects, and is considered the most important infectious agent in transplant recipients. The virus infects many cell types in vivo and in vitro. While previous studies have identified several cellular proteins that may function at early steps of infection in a cell type dependent manner, the mechanism of virus entry is still poorly understood. Using a computational biology approach, correlating gene expression with virus infectivity in 54 cell lines, we identified THY-1 as a putative host determinant for HCMV infection in these cells. With a series of loss-of-function, gain-of-function and protein-protein interaction analyses, we found that THY-1 mediates HCMV infection at the entry step and is important for infection that occurs at a low m.o.i. THY-1 antibody that bound to the cell surface blocked HCMV during the initial 60 minutes of infection in a dose-dependent manner. Down-regulation of THY-1 with siRNA impaired infectivity occurred during the initial 60 minutes of inoculation. Both THY-1 antibody and siRNA inhibited HCMV-induced activation of the PI3-K/Akt pathway required for entry. Soluble THY-1 protein blocked HCMV infection during, but not after, virus internalization. Expression of exogenous THY-1 enhanced entry in cells expressing low levels of the protein. THY-1 interacted with HCMV gB and gH and may form a complex important for entry. However, since gB and gH have previously been shown to interact, it is uncertain if THY-1 directly binds to both of these proteins. Prior observations that THY-1 (a) interacts with αVβ3 integrin and recruits paxillin (implicated in HCMV entry), (b) regulates leukocyte extravasation (critical for HCMV viremia), and (c) is expressed on many cells targeted for HCMV infection including epithelial and endothelial cells, fibroblast, and CD34+/CD38- stem cells, all support a role for THY-1 as an HCMV entry mediator in a cell type dependent manner. THY-1 may function through a complex setting, that would include viral gB and gH, and other cellular factors, thus links virus entry with signaling in host cells that ultimately leads to virus infection.
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Affiliation(s)
- Qingxue Li
- Medical Virology Section, Laboratory of Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Adrian R. Wilkie
- Medical Virology Section, Laboratory of Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Melodie Weller
- Secretory Physiology Section, Molecular Physiology and Therapeutics Branch, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Xueqiao Liu
- Medical Virology Section, Laboratory of Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jeffrey I. Cohen
- Medical Virology Section, Laboratory of Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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13
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Lilja AE, Mason PW. The next generation recombinant human cytomegalovirus vaccine candidates—Beyond gB. Vaccine 2012; 30:6980-90. [DOI: 10.1016/j.vaccine.2012.09.056] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 09/07/2012] [Accepted: 09/22/2012] [Indexed: 11/16/2022]
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14
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Sharma S, Wisner TW, Johnson DC, Heldwein EE. HCMV gB shares structural and functional properties with gB proteins from other herpesviruses. Virology 2012; 435:239-49. [PMID: 23089254 DOI: 10.1016/j.virol.2012.09.024] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 09/19/2012] [Accepted: 09/23/2012] [Indexed: 12/16/2022]
Abstract
Glycoprotein B (gB) facilitates HCMV entry into cells by binding receptors and mediating membrane fusion. The crystal structures of gB ectodomains from HSV-1 and EBV are available, but little is known about the HCMV gB structure. Using multiangle light scattering and electron microscopy, we show here that HCMV gB ectodomain is a trimer with the overall shape similar to HSV-1 and EBV gB ectodomains. HCMV gB ectodomain forms rosettes similar to rosettes formed by EBV gB and the postfusion forms of other viral fusogens. Substitution of several bulky hydrophobic residues within the putative fusion loops with more hydrophilic residues reduced rosette formation and abolished cell fusion. We propose that like gB proteins from HSV-1 and EBV, HCMV gB has two internal hydrophobic fusion loops that likely interact with target membranes. Our work establishes structural and functional similarities between gB proteins from three subfamilies of herpesviruses.
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Affiliation(s)
- Sapna Sharma
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA
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15
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Mutagenesis of varicella-zoster virus glycoprotein B: putative fusion loop residues are essential for viral replication, and the furin cleavage motif contributes to pathogenesis in skin tissue in vivo. J Virol 2009; 83:7495-506. [PMID: 19474103 DOI: 10.1128/jvi.00400-09] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycoprotein B (gB), the most conserved protein in the family Herpesviridae, is essential for the fusion of viral and cellular membranes. Information about varicella-zoster virus (VZV) gB is limited, but homology modeling showed that the structure of VZV gB was similar to that of herpes simplex virus (HSV) gB, including the putative fusion loops. In contrast to HSV gB, VZV gB had a furin recognition motif ([R]-X-[KR]-R-|-X, where | indicates the position at which the polypeptide is cleaved) at residues 491 to 494, thought to be required for gB cleavage into two polypeptides. To investigate their contribution, the putative primary fusion loop or the furin recognition motif was mutated in expression constructs and in the context of the VZV genome. Substitutions in the primary loop, W180G and Y185G, plus the deletion mutation Delta491RSRR494 and point mutation 491GSGG494 in the furin recognition motif did not affect gB expression or cellular localization in transfected cells. Infectious VZV was recovered from parental Oka (pOka)-bacterial artificial chromosomes that had either the Delta491RSRR494 or 491GSGG494 mutation but not the point mutations W180G and Y185G, demonstrating that residues in the primary loop of gB were essential but gB cleavage was not required for VZV replication in vitro. Virion morphology, protein localization, plaque size, and replication were unaffected for the pOka-gBDelta491RSRR494 or pOka-gB491GSGG494 virus compared to pOka in vitro. However, deletion of the furin recognition motif caused attenuation of VZV replication in human skin xenografts in vivo. This is the first evidence that cleavage of a herpesvirus fusion protein contributes to viral pathogenesis in vivo, as seen for fusion proteins in other virus families.
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16
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Sorem J, Longnecker R. Cleavage of Epstein-Barr virus glycoprotein B is required for full function in cell-cell fusion with both epithelial and B cells. J Gen Virol 2009; 90:591-595. [PMID: 19218203 DOI: 10.1099/vir.0.007237-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glycoprotein B (gB) homologues within the herpesvirus family display high sequence conservation, and a number of gB homologues contain a cleavage motif R-X-K/R-R recognized by the cellular protease furin. Epstein-Barr virus (EBV) gB contains this motif and cleaved gB is found in EBV virions. To determine the functional significance of this cleavage motif in EBV gB, a deletion mutant (gB Deltafurin) was created lacking the motif. This cleavage mutant was expressed well in cell culture but was not cleaved. Experiments examining gB Deltafurin in a cell-fusion assay revealed that fusion was reduced by 52 % in epithelial and 28 % in B cells when compared with wild-type EBV gB. This decrease in cell-cell fusion is similar to that observed with multiple alphaherpesvirus gB cleavage mutants and supports a conserved function for cleaved gB.
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Affiliation(s)
- Jessica Sorem
- Department of Microbiology and Immunology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Richard Longnecker
- Department of Microbiology and Immunology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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17
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Duan T, Wang XF, Xiao SY, Gu SY, Liang MF. Recombinant human IgG antibodies against human cytomegalovirus. BIOMEDICAL AND ENVIRONMENTAL SCIENCES : BES 2008; 21:372-380. [PMID: 19133610 DOI: 10.1016/s0895-3988(08)60057-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
OBJECTIVE To study the passive immunization with human monoclonal antibodies as for prophylaxis of human cytomegalovirus (HCMV) infection. METHODS Fab monoclonal antibodies to HCMV were recovered by repertoire cloning of mRNA from a HCMV infected individual. Antigen binding specificity, CDR sequence of V(H) and V(L) and neutralizing activity on HCMV AD169 stain were analyzed in vitro. The light and heavy chain Fd fragment genes of Fab antibodies were further cloned into a recombinant baculovirus expression vector pAC-kappa-Fc to express intact IgG. Secreted products were purified with affinity chromatography using protein G. RESULTS SDS-PAGE and Western blot confirmed the expression of the intact IgG. Immuno-blotting and -precipitation were used to identify HCMV proteins. One Fab monoclonal antibody recognized a conformational HCMV protein. CONCLUSION IgG antibodies can neutralize the HCMV AD169 strain efficiently at a titer of 2.5 microg/mL and may prove valuable for passive immunoprophylaxis against HCMV infection in humans.
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Affiliation(s)
- Tao Duan
- Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 100052, China
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18
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Galdiero S, Vitiello M, D'Isanto M, Falanga A, Cantisani M, Browne H, Pedone C, Galdiero M. The identification and characterization of fusogenic domains in herpes virus glycoprotein B molecules. Chembiochem 2008; 9:758-67. [PMID: 18311743 DOI: 10.1002/cbic.200700457] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The molecular mechanism of entry of herpes viruses requires a multicomponent fusion system. Virus entry and cell-cell fusion of Herpes simplex virus (HSV) requires four glycoproteins: gD, gB and gH/gL. The role of gB remained elusive until recently, when the crystal structure of HSV-1 gB became available. Glycoprotein B homologues represent the most highly conserved group of herpes virus glycoproteins; however, despite the high degree of sequence and structural conservation, differences in post-translational processing are observed for different members of this virus family. Whereas gB of HSV is not proteolytically processed after oligomerization, most other gB homologues are cleaved by a cellular protease into subunits that remain linked through disulfide bonds. Proteolytic cleavage is common for activation of many other viral fusion proteins, so it remains difficult to envisage a common role for different herpes virus gB structures in the fusion mechanism. We selected bovine herpes virus type 1 (BoHV-1) and herpes simplex virus type 1 (HSV-1) as representative viruses expressing cleaved and uncleaved gBs, and have screened their amino acid sequences for regions of highly interfacial hydrophobicity. Synthetic peptides corresponding to such regions were tested for their ability to induce the fusion of large unilamellar vesicles and to inhibit herpes virus infection. These results underline that several regions of the gB protein are involved in the mechanism of membrane interaction.
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Affiliation(s)
- Stefania Galdiero
- Department of Biological Sciences, Division of Biostructures, University of Naples Federico II, Via Mezzocannone 16, 80134 Napoli, Italy
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19
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Cleavage of group 1 coronavirus spike proteins: how furin cleavage is traded off against heparan sulfate binding upon cell culture adaptation. J Virol 2008; 82:6078-83. [PMID: 18400867 DOI: 10.1128/jvi.00074-08] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
A longstanding enigmatic feature of the group 1 coronaviruses is the uncleaved phenotype of their spike protein, an exceptional property among class I fusion proteins. Here, however, we show that some group 1 coronavirus spike proteins carry a furin enzyme recognition motif and can actually be cleaved, as demonstrated for a feline coronavirus. Interestingly, this feature can be lost during cell culture adaptation by a single mutation in the cleavage motif; this, however, preserves a heparan sulfate binding motif and renders infection by the virus heparan sulfate dependent. We identified a similar cell culture adaptation for the human coronavirus OC43.
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20
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Okazaki K. Proteolytic cleavage of glycoprotein B is dispensable for in vitro replication, but required for syncytium formation of pseudorabies virus. J Gen Virol 2007; 88:1859-1865. [PMID: 17554016 DOI: 10.1099/vir.0.82610-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Glycoprotein B (gB) is the most conserved glycoprotein among herpesviruses and it plays important roles in virus infectivity. In most herpesviruses, including pseudorabies virus (PRV), gB is cleaved by a cellular protease into two disulfide-linked subunits. In the present study, I found that the PRV gB generated in human colon carcinoma LoVo cells, which lack the ubiquitous protease furin, remained in the uncleaved form and the virus replicated in these cells without cell fusion. The uncleaved gB was converted into its subunits after furin digestion. The virus also replicated in Madin-Darby bovine kidney cells without cell fusion in the presence of a furin inhibitor, whereas distinct syncytia were formed in the absence of the inhibitor. LoVo cells constitutively expressing furin showed cell fusion when they were infected with the virus. Penetration kinetics assays revealed that the virus carrying uncleaved gB penetrated the cells at the same rate as the virus carrying cleaved gB. These results indicate that PRV gB is cleaved by furin and that the cleavage is dispensable for virus replication in vitro. Furthermore, gB cleavage is involved in syncytium formation but not in penetration kinetics, suggesting that different mechanisms operate between cell-cell fusion and virus-cell fusion by PRV.
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Affiliation(s)
- Katsunori Okazaki
- Department of Immunology and Microbiology, Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-Tobetsu 061-0293, Japan
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21
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Reap EA, Dryga SA, Morris J, Rivers B, Norberg PK, Olmsted RA, Chulay JD. Cellular and humoral immune responses to alphavirus replicon vaccines expressing cytomegalovirus pp65, IE1, and gB proteins. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2007; 14:748-55. [PMID: 17442845 PMCID: PMC1951075 DOI: 10.1128/cvi.00037-07] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Development of vaccines against cytomegalovirus (CMV) is an important public health priority. We used a propagation-defective, single-cycle RNA replicon vector system derived from an attenuated strain of an alphavirus, Venezuelan equine encephalitis virus, to produce virus-like replicon particles (VRP) expressing various combinations of pp65, IE1, or gB proteins of human CMV. Protein expression in VRP-infected cells was highest with single-promoter replicons expressing pp65, IE1, a pp65/IE1 fusion protein, or the extracellular domain of gB and with double-promoter replicons expressing pp65 and IE1. Protein expression was lower with double- and triple-promoter replicons expressing gB, especially the full-length form of gB. BALB/c mice immunized with VRP expressing gB developed high titers of neutralizing antibody to CMV, and mice immunized with VRP expressing pp65, IE1, or a pp65/IE1 fusion protein developed robust antigen-specific T-cell responses as measured by gamma interferon enzyme-linked immunospot assay. Three overlapping immunodominant pp65 peptides contained a nine-amino-acid sequence (LGPISGHVL) that matches the consensus binding motif for a major histocompatibility complex H2-D(d) T-cell epitope. These data provide the basis for further development and clinical evaluation of an alphavirus replicon vaccine for CMV expressing the pp65, IE1, and gB proteins.
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Affiliation(s)
- Elizabeth A Reap
- AlphaVax, Inc., 2 Triangle Drive, P.O. Box 110307, Research Triangle Park, NC 27709-0307, USA.
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22
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Coppola JM, Hamilton CA, Bhojani MS, Larsen MJ, Ross BD, Rehemtulla A. Identification of inhibitors using a cell-based assay for monitoring Golgi-resident protease activity. Anal Biochem 2007; 364:19-29. [PMID: 17316541 PMCID: PMC1995463 DOI: 10.1016/j.ab.2007.01.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Revised: 01/09/2007] [Accepted: 01/12/2007] [Indexed: 01/01/2023]
Abstract
Noninvasive real-time quantification of cellular protease activity allows monitoring of enzymatic activity and identification of activity modulators within the protease's natural milieu. We developed a protease activity assay based on differential localization of a recombinant reporter consisting of a Golgi retention signal and a protease cleavage sequence fused to alkaline phosphatase (AP). When expressed in mammalian cells, this protein localizes to Golgi bodies and, on protease-mediated cleavage, AP translocates to the extracellular medium where its activity is measured. We used this system to monitor the Golgi-associated protease furin, a pluripotent enzyme with a key role in tumorigenesis, viral propagation of avian influenza, ebola, and HIV as well as in activation of anthrax, pseudomonas, and diphtheria toxins. This technology was adapted for high-throughput screening of 39,000-compound small molecule libraries, leading to identification of furin inhibitors. Furthermore, this strategy was used to identify inhibitors of another Golgi protease, the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE). BACE cleavage of the APP leads to formation of the Abeta peptide, a key event that leads to Alzheimer's disease. In conclusion, we describe a customizable noninvasive technology for real-time assessment of Golgi protease activity used to identify inhibitors of furin and BACE.
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Affiliation(s)
- Julia M. Coppola
- Department of Biological Chemistry, University of Michigan Medical School, Life Sciences Institute, Ann Arbor MI 48109
| | - Christin A. Hamilton
- Department of Radiation Oncology, University of Michigan Medical School, Life Sciences Institute, Ann Arbor MI 48109
| | - Mahaveer S. Bhojani
- Department of Radiation Oncology, University of Michigan Medical School, Life Sciences Institute, Ann Arbor MI 48109
| | - Martha J. Larsen
- Center for Chemical Genomics, Life Sciences Institute, Ann Arbor MI 48109
| | - Brian D. Ross
- Department of Biological Chemistry, University of Michigan Medical School, Life Sciences Institute, Ann Arbor MI 48109
| | - Alnawaz Rehemtulla
- Department of Radiation Oncology, University of Michigan Medical School, Life Sciences Institute, Ann Arbor MI 48109
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23
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Gillet L, Gill MB, Colaco S, Smith CM, Stevenson PG. Murine gammaherpesvirus-68 glycoprotein B presents a difficult neutralization target to monoclonal antibodies derived from infected mice. J Gen Virol 2006; 87:3515-3527. [PMID: 17098966 PMCID: PMC2884974 DOI: 10.1099/vir.0.82313-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Persistent viruses disseminate from immune hosts. They must therefore resist neutralization by antibody. Murine gammaherpesvirus-68 (MHV-68) represents an accessible model with which to address how resistance to neutralization is achieved and how overcoming it might improve infection control. The MHV-68 glycoprotein B (gB), like that of other herpesviruses, is a virion protein that is essential for infectivity. As such, it presents a potential neutralization target. In order to test whether virus-induced antibodies reduce virion infectivity by binding to gB, monoclonal antibodies (mAbs) were derived from MHV-68-infected mice. gB-specific mAbs were common, but only an IgM specific for the gB N terminus reduced virion infectivity significantly. It inhibited MHV-68 entry into BHK-21 cells at a post-binding step that was linked closely to membrane fusion. Reducing the mAb to IgM monomers compromised neutralization severely, suggesting that a pentameric structure was crucial to its function. Antibody treatment never blocked BHK-21 cell infection completely and blocked the infection of NMuMG epithelial cells hardly at all. Virions saturated with antibody also remained infectious to mice. Thus, the MHV-68 gB presents at best a very difficult target for antibody-mediated neutralization.
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Affiliation(s)
- Laurent Gillet
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Michael B Gill
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Susanna Colaco
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Christopher M Smith
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Philip G Stevenson
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
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24
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Heldwein EE, Lou H, Bender FC, Cohen GH, Eisenberg RJ, Harrison SC. Crystal structure of glycoprotein B from herpes simplex virus 1. Science 2006; 313:217-20. [PMID: 16840698 DOI: 10.1126/science.1126548] [Citation(s) in RCA: 443] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Glycoprotein B (gB) is the most conserved component of the complex cell-entry machinery of herpes viruses. A crystal structure of the gB ectodomain from herpes simplex virus type 1 reveals a multidomain trimer with unexpected homology to glycoprotein G from vesicular stomatitis virus (VSV G). An alpha-helical coiled-coil core relates gB to class I viral membrane fusion glycoproteins; two extended beta hairpins with hydrophobic tips, homologous to fusion peptides in VSV G, relate gB to class II fusion proteins. Members of both classes accomplish fusion through a large-scale conformational change, triggered by a signal from a receptor-binding component. The domain connectivity within a gB monomer would permit such a rearrangement, including long-range translocations linked to viral and cellular membranes.
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Affiliation(s)
- Ekaterina E Heldwein
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 320 Longwood Avenue, Boston, MA 02115, USA.
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25
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Meulendyke KA, Wurth MA, McCann RO, Dutch RE. Endocytosis plays a critical role in proteolytic processing of the Hendra virus fusion protein. J Virol 2005; 79:12643-9. [PMID: 16188966 PMCID: PMC1235849 DOI: 10.1128/jvi.79.20.12643-12649.2005] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Hendra virus fusion (F) protein is synthesized as a precursor protein, F(0), which is proteolytically processed to the mature form, F(1) + F(2). Unlike the case for the majority of paramyxovirus F proteins, the processing event is furin independent, does not require the addition of exogenous proteases, is not affected by reductions in intracellular Ca(2+), and is strongly affected by conditions that raise the intracellular pH (C. T. Pager, M. A. Wurth, and R. E. Dutch, J. Virol. 78:9154-9163, 2004). The Hendra virus F protein cytoplasmic tail contains a consensus motif for endocytosis, YXXPhi. To analyze the potential role of endocytosis in the processing and membrane fusion promotion of the Hendra virus F protein, mutation of tyrosine 525 to alanine (Hendra virus F Y525A) or phenylalanine (Hendra virus F Y525F) was performed. The rate of endocytosis of Hendra virus F Y525A was significantly reduced compared to that of the wild-type (wt) F protein, confirming the functional importance of the endocytosis motif. An intermediate level of endocytosis was observed for Hendra virus F Y525F. Surprisingly, dramatic reductions in the rate of proteolytic processing were observed for Hendra virus F Y525A, although initial transport to the cell surface was not affected. The levels of surface expression for both Hendra virus F Y525A and Hendra virus F Y525F were higher than that of the wt protein, and these mutants displayed enhanced syncytium formation. These results suggest that endocytosis is critically important for Hendra virus F protein cleavage, representing a new paradigm for proteolytic processing of paramyxovirus F proteins.
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Affiliation(s)
- Kelly Ann Meulendyke
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, 40536-0509, USA
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26
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Volchkov VE, Volchkova VA, Dolnik O, Feldmann H, Klenk HD. Polymorphism of Filovirus Glycoproteins. Adv Virus Res 2005; 64:359-81. [PMID: 16139600 DOI: 10.1016/s0065-3527(05)64011-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Viktor E Volchkov
- Biologie des Filovirus, Claude Bernard University Lyon, INSERM U412 69365 Lyon, France
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27
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Abstract
Murine gammaherpesvirus 68 (MHV-68) glycoprotein B (gB) was identified in purified virions by immunoblotting, immunoprecipitation, and immunoelectron microscopy. It was synthesized as a 120-kDa precursor in infected cells and cleaved into 65-kDa and 55-kDa disulfide-linked subunits close to the time of virion release. The N-linked glycans on the cleaved, virion gB remained partially endoglycosidase H sensitive. The processing of MHV-68 gB therefore appears similar to that of Kaposi's sarcoma-associated herpesvirus gB and human cytomegalovirus gB.
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Affiliation(s)
- Filipa B Lopes
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge CB2 1QP, United Kingdom
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28
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Moll M, Diederich S, Klenk HD, Czub M, Maisner A. Ubiquitous activation of the Nipah virus fusion protein does not require a basic amino acid at the cleavage site. J Virol 2004; 78:9705-12. [PMID: 15331703 PMCID: PMC514977 DOI: 10.1128/jvi.78.18.9705-9712.2004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nipah virus (NiV), a highly pathogenic paramyxovirus, causes a systemic infection in vivo and is able to replicate in cultured cells of many species and organs. Such pantropic paramyxoviruses generally encode fusion (F) proteins with multibasic cleavage sites activated by furin or other ubiquitous intracellular host cell proteases. In contrast, NiV has an F protein with a single arginine (R109) at the cleavage site, as is the case with paramyxoviruses that are activated by trypsin-like proteases only present in specific cells or tissues and therefore only cause localized infections. Unlike these viruses, cleavage of the NiV F protein is ubiquitous and does not require the addition of exogenous proteases in cell culture. To determine the importance of the amino acid sequence at the NiV F protein cleavage site for ubiquitous activation, we generated NiV F proteins with mutations around R109. Surprisingly, neither the exchange of amino acids upstream of R109 nor replacement of the basic residue itself interfered with F cleavage. Thus, R109 is not essential for F cleavage and activation. Our data demonstrate that NiV F-protein activation depends on a novel type of proteolytic cleavage that has not yet been described for any other paramyxovirus F protein. NiV F activation is mediated by a ubiquitous protease that requires neither a monobasic nor a multibasic cleavage site and therefore differs from the furin- or trypsin-like proteases known to activate other ortho- and paramyxovirus fusion proteins.
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Affiliation(s)
- Markus Moll
- Institut für Virologie, Robert-Koch-Str. 17, 35037 Marburg, Germany
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29
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Pager CT, Wurth MA, Dutch RE. Subcellular localization and calcium and pH requirements for proteolytic processing of the Hendra virus fusion protein. J Virol 2004; 78:9154-63. [PMID: 15308711 PMCID: PMC506929 DOI: 10.1128/jvi.78.17.9154-9163.2004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Proteolytic cleavage of the Hendra virus fusion (F) protein results in the formation of disulfide-linked F1 and F2 subunits, with cleavage occurring after residue K109 in the sequence GDVK/L. This unusual cleavage site and efficient propagation of Hendra virus in a furin-deficient cell line indicate that the Hendra F protein is not cleaved by furin, the protease responsible for proteolytic activation of many viral fusion proteins. To identify the subcellular site of Hendra F processing, Vero cells transfected with pCAGGS-Hendra F or pCAGGS-SV5 F were metabolically labeled and chased in the absence and presence of inhibitors of exocytosis. The addition of carbonyl-cyanide-3-chlorophenylhydrazone, monensin, brefeldin A, or NaF-AlCl3 or incubation of cells at 20 degrees C all inhibited processing of the Hendra F protein, suggesting that cleavage of Hendra F occurs either in secretory vesicles budding from the trans-Golgi network or at the cell surface. In contrast to proteolytic cleavage of the simian virus 5 (SV5) F protein by the Ca(2+)-dependent protease furin, proteolytic cleavage of the Hendra F protein was not significantly inhibited by decreases in Ca2+ levels following incubation with EGTA or A23187. However, in the presence of weak amines and H+ V-ATPase inhibitors, known to raise intracellular pH, cleavage of Hendra F protein was inhibited while processing of the SV5 F protein was not significantly affected. The subcellular location, sensitivity to pH changes, and decreased Ca2+ requirement suggest that the protease responsible for cleavage of Hendra F protein differs from proteases previously shown to be involved in the processing of other viral glycoproteins.
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Affiliation(s)
- Cara Theresia Pager
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky 40536-0298, USA
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30
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Mavinakere MS, Colberg-Poley AM. Internal cleavage of the human cytomegalovirus UL37 immediate-early glycoprotein and divergent trafficking of its proteolytic fragments. J Gen Virol 2004; 85:1989-1994. [PMID: 15218184 DOI: 10.1099/vir.0.80094-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human cytomegalovirus UL37 gene encodes at least three isoforms, which share N-terminal UL37 exon 1 (UL37x1) sequences. UL37 proteins traffic dually into the endoplasmic reticulum (ER) and to mitochondria. Trafficking of the UL37 glycoprotein (gpUL37) in relation to its post-translational processing was investigated. gpUL37 is internally cleaved in the ER and its products traffic differentially. Its C-terminal fragment (UL37(COOH)) is ER-localized and N-glycosylated. Unlike conventional ER signal sequences, its N-terminal fragment is stable and traffics to mitochondria. Inhibition of N-glycosylation did not block pUL37 cleavage and dramatically decreased the levels of but not of UL37(COOH). pUL37(M), which differs from gpUL37 by the lack of residues 178-262 and hence the UL37x3 consensus signal peptidase cleavage site, traffics into the ER and mitochondria, but is neither cleaved nor N-glycosylated. This finding of a relationship between ER processing and mitochondrial importation of UL37 proteins is unique for herpesvirus proteins.
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Affiliation(s)
- Manohara S Mavinakere
- Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, George Washington University, School of Medicine and Health Sciences, 111 Michigan Avenue NW, Washington, DC 20010, USA
| | - Anamaris M Colberg-Poley
- Department of Pediatrics, George Washington University, School of Medicine and Health Sciences, 111 Michigan Avenue NW, Washington, DC 20010, USA
- Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, George Washington University, School of Medicine and Health Sciences, 111 Michigan Avenue NW, Washington, DC 20010, USA
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31
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de Haan CAM, Stadler K, Godeke GJ, Bosch BJ, Rottier PJM. Cleavage inhibition of the murine coronavirus spike protein by a furin-like enzyme affects cell-cell but not virus-cell fusion. J Virol 2004; 78:6048-54. [PMID: 15141003 PMCID: PMC415802 DOI: 10.1128/jvi.78.11.6048-6054.2004] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cleavage of the mouse hepatitis coronavirus strain A59 spike protein was blocked in a concentration-dependent manner by a peptide furin inhibitor, indicating that furin or a furin-like enzyme is responsible for this process. While cell-cell fusion was clearly affected by preventing spike protein cleavage, virus-cell fusion was not, indicating that these events have different requirements.
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Affiliation(s)
- Cornelis A M de Haan
- Virology Division, Department of Infectious Diseases & Immunology, Yalelaan 1, 3584CL Utrecht, The Netherlands.
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32
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Xiang Y, Moss B. Molluscum contagiosum virus interleukin-18 (IL-18) binding protein is secreted as a full-length form that binds cell surface glycosaminoglycans through the C-terminal tail and a furin-cleaved form with only the IL-18 binding domain. J Virol 2003; 77:2623-30. [PMID: 12552001 PMCID: PMC141116 DOI: 10.1128/jvi.77.4.2623-2630.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Some poxviruses and their mammalian hosts encode homologous proteins that bind interleukin-18 (IL-18) with high affinity and inhibit IL-18-mediated immune responses. MC54L, the IL-18 binding protein of the human poxvirus that causes molluscum contagiosum, is unique in having a C-terminal tail of nearly 100 amino acids that is dispensable for IL-18 binding. When recombinant MC54L was expressed and purified via a C-terminal six-histidine tag, a shorter fragment was detected in addition to the full-length protein. This C-terminal fragment resulted from the cleavage of MC54L by cellular furin, as it was greatly diminished when furin was specifically inhibited or when a furin-deficient cell line was used for expression. Furthermore, the N- and C-terminal fragments of MC54L were generated by cleavage of the recombinant protein with furin in vitro. The furin cleavage site was mapped within a 32-amino-acid segment that is C terminal to the IL-18 binding domain. Full-length MC54L, but not the N-terminal IL-18 binding fragment, bound to cells and to purified heparin and other glycosaminoglycans that are commonly found on the cell surface and in the extracellular matrix. MC54L bound to heparin with a nanomolar K(d) and could simultaneously bind to IL-18. Their different glycosaminoglycan and cell binding properties may allow the long and short forms of MC54L to inactivate IL-18 near the site of infection and at more distal locations, respectively.
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Affiliation(s)
- Yan Xiang
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases/National Institutes of Health, 4 Center Drive, Bethesda, MD 20892-0445, USA
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Rockwell NC, Krysan DJ, Komiyama T, Fuller RS. Precursor processing by kex2/furin proteases. Chem Rev 2002; 102:4525-48. [PMID: 12475200 DOI: 10.1021/cr010168i] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Nathan C Rockwell
- Department of Biological Chemistry, University of Michigan Medical Center, Room 5413 Med Sci I, 1301 East Catherine, Ann Arbor Michigan 48109, USA
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Hasegawa H, Tatsumi M, Ogawa-Goto K, Takahashi H, Kojima A, Iwasaki T, Kurata T, Sata T, Takeuchi T, Sheehy N, Sawa H, Nagashima K, Hall WW. Processing of the HTLV-II envelope precursor glycoprotein gp63 by furin is essential for cell fusion activity. AIDS Res Hum Retroviruses 2002; 18:1253-60. [PMID: 12487813 DOI: 10.1089/088922202320886299] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
To investigate the relationship between the fusogenic properties of HTLV-II and the processing of the envelope precursor glycoprotein gp63, recombinant cowpox virus expressing this protein was used to infect a range of cell lines derived from different species. Syncytium formation and gp63 processing were observed in all cells with the exception of LoVo cells, which are known to have a dysfunctional form of the endoprotease, furin. Furin has been shown to be necessary for the processing of a number of viral envelope glycoproteins, and gp63 contains a consensus sequence (305)Arg-Arg-Arg-Arg, which is a furin substrate motif. Pulse-chase studies demonstrated gp63 processing in Vero but not in LoVo cells. In addition it could be shown that expression of recombinant furin restored the processing of gp63 to gp46 in LoVo cells, and this resulted in syncytium formation. Our findings suggest that furin plays a pivotal role in cleavage of the HTLV-II envelope gp63, which in turn is a prerequisite for the fusogenic properties of the virus.
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Affiliation(s)
- Hideki Hasegawa
- Department of Pathology, National Institute of Infectious Diseases, Tokyo, Japan
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35
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Murata T, Goshima F, Takakuwa H, Nishiyama Y. Excretion of herpes simplex virus type 2 glycoprotein D into the culture medium. J Gen Virol 2002; 83:2791-2795. [PMID: 12388815 DOI: 10.1099/0022-1317-83-11-2791] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glycoprotein D (gD) of herpes simplex virus type 2 (HSV-2) was excreted from infected cells into the medium. Peptide mapping analysis and lectin binding assays suggested that the gD in the medium is secreted after full glycosylation and cleavage at its C terminus. Release of HSV-2 gD was inhibited by addition of either tunicamycin or brefeldin A, suggesting that the gD in the medium was secreted through the endoplasmic reticulum and Golgi apparatus.
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Affiliation(s)
- Takayuki Murata
- Laboratory of Virology, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan1
| | - Fumi Goshima
- Laboratory of Virology, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan1
| | - Hiroki Takakuwa
- Laboratory of Virology, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan1
| | - Yukihiro Nishiyama
- Laboratory of Virology, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan1
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36
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Strive T, Borst E, Messerle M, Radsak K. Proteolytic processing of human cytomegalovirus glycoprotein B is dispensable for viral growth in culture. J Virol 2002; 76:1252-64. [PMID: 11773401 PMCID: PMC135784 DOI: 10.1128/jvi.76.3.1252-1264.2002] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycoprotein B (gB) of human cytomegalovirus (HCMV), which is considered essential for the viral life cycle, is proteolytically processed during maturation. Since gB homologues of several other herpesviruses remain uncleaved, the relevance of this property of HCMV gB for viral infectivity is unclear. Here we report on the construction of a viral mutant in which the recognition site of gB for the cellular endoprotease furin was destroyed. Because mutagenesis of essential proteins may result in a lethal phenotype, a replication-deficient HCMV gB-null genome encoding enhanced green fluorescent protein was constructed, and complementation by mutant gBs was initially evaluated in transient-cotransfection assays. Cotransfection of plasmids expressing authentic gB or gB with a mutated cleavage site (gB-DeltaFur) led to the formation of green fluorescent miniplaques which were considered to result from one cycle of phenotypic complementation of the gB-null genome. To verify these results, two recombinant HCMV genomes were constructed: HCMV-BAC-DeltaMhdI, with a deletion of hydrophobic domain 1 of gB that appeared to be essential for viral growth in the cotransfection experiments, and HCMV-BACDeltaFur, in which the gB cleavage site was mutated by amino acid substitution. Consistent with the results of the cotransfection assays, only the DeltaFur mutant replicated in human fibroblasts, showing growth kinetics comparable to that of wild-type virus. gB in mutant-infected cells was uncleaved, whereas glycosylation and transport to the cell surface were not impaired. Extracellular mutant virus contained exclusively uncleaved gB, indicating that proteolytic processing of gB is dispensable for viral replication in cell culture.
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Affiliation(s)
- Tanja Strive
- Institut für Virologie der Philipps-Universität, 35037 Marburg, Germany
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37
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38
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Westenberg M, Wang H, IJkel WFJ, Goldbach RW, Vlak JM, Zuidema D. Furin is involved in baculovirus envelope fusion protein activation. J Virol 2002; 76:178-84. [PMID: 11739683 PMCID: PMC135720 DOI: 10.1128/jvi.76.1.178-184.2002] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV) Se8 gene was recently shown to encode the viral envelope fusion (F) protein. A 60-kDa C-terminal subunit (F1) of the 76-kDa primary translation product of this gene was found to be the major envelope protein of SeMNPV budded virus (BV) (W. F. J. IJkel, M. Westenberg, R. W. Goldbach, G. W. Blissard, J. M. Vlak, and D. Zuidema, Virology 275:30-41, 2000). A specific inhibitor was used to show that furin is involved in cleavage of the precursor envelope fusion (F0) protein. BV produced in the presence of the inhibitor possesses the uncleaved F0 protein, while an F protein with a mutation in the furin cleavage site was translocated to the plasma membrane but lost its fusogenic activity. These results indicate that cleavage of F0 is required to activate the SeMNPV F protein and is necessary for BV infectivity. Specific antibodies against F1 and against the putative N terminus (F2) of the primary translation product were used to show that the F protein is BV specific and that BVs contain both the 60- (F1) and 21-kDa (F2) cleavage products. In nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis both subunits migrate as a single 80-kDa protein, indicating that the subunits remain associated by a disulfide linkage. In addition, the presence of the F protein predominantly as a monomer suggests that disulfide links are not involved in oligomerization. Thus, the envelope fusion protein from group II nucleopolyhedroviruses of baculoviruses has properties similar to those of proteins from a number of vertebrate viruses.
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Affiliation(s)
- Marcel Westenberg
- Laboratory of Virology, Wageningen University and Research Center, 6709 PD Wageningen, The Netherlands
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39
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Hingley ST, Leparc-Goffart I, Seo SH, Tsai JC, Weiss SR. The virulence of mouse hepatitis virus strain A59 is not dependent on efficient spike protein cleavage and cell-to-cell fusion. J Neurovirol 2002; 8:400-10. [PMID: 12402166 PMCID: PMC7095328 DOI: 10.1080/13550280260422703] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The cleavage and fusion properties of recombinant murine hepatitis viruses (MHV) were examined to assess the role of the cleavage signal in determining the extent of S protein cleavage, and the correlation between cleavage and induction of cell-to-cell fusion. Targeted recombination was used to introduce amino acid substitutions into the cleavage signal of the fusion glycoprotein (spike or S protein) of MHV strain A59. The recombinants were then used to address the question of the importance of S protein cleavage and viral-mediated cell-to-cell fusion on pathogenicity. Our data indicate that cleavage of spike is not solely determined by the amino acid sequence at the cleavage site, but may also depend on sequences removed from the cleavage site. In addition, efficient cell-to-cell fusion is not necessary for virulence.
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Affiliation(s)
- Susan T Hingley
- Department of Pathology, Microbiology and Immunology, Philadelphia College of Osteopathic Medicine, Philadelphia, Pennsylvania 19131, USA.
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40
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Feldmann H, Volchkov VE, Volchkova VA, Ströher U, Klenk HD. Biosynthesis and role of filoviral glycoproteins. J Gen Virol 2001; 82:2839-2848. [PMID: 11714958 DOI: 10.1099/0022-1317-82-12-2839] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Heinz Feldmann
- Canadian Science Centre for Human and Animal Health, 1015 Arlington Street, Winnipeg, Manitoba, CanadaR3E 3R21
| | - Viktor E Volchkov
- Biologie des Filovirus, Claude Bernard University Lyon-1, 46 Allée d'Italie, 69007 Lyon, France2
| | - Valentina A Volchkova
- Biologie des Filovirus, Claude Bernard University Lyon-1, 46 Allée d'Italie, 69007 Lyon, France2
| | - Ute Ströher
- Institut für Virologie, Philipps-Universität, Robert-Koch-Str. 17, D-35037 Marburg, Germany3
| | - Hans-Dieter Klenk
- Institut für Virologie, Philipps-Universität, Robert-Koch-Str. 17, D-35037 Marburg, Germany3
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41
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Scheffczik H, Kraus I, Kiermayer S, Bogner E, Holzenburg A, Garten W, Eickmann M. Multimerization potential of the cytoplasmic domain of the human cytomegalovirus glycoprotein B. FEBS Lett 2001; 506:113-6. [PMID: 11591382 DOI: 10.1016/s0014-5793(01)02891-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In the present study the coding sequence of the cytoplasmic tail of the human cytomegalovirus glycoprotein B (gB) was expressed. The secondary structure of the purified recombinant protein was analyzed by circular dichroism, and the quaternary structure was investigated by gel permeation chromatography, and electron microscopy. Our data indicate that the cytoplasmic gB domain contains alpha-helix structures and assembles into tetramers, suggesting that the authentic gB may represent a homotetramer.
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42
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Sugrue RJ, Brown C, Brown G, Aitken J, McL Rixon HW. Furin cleavage of the respiratory syncytial virus fusion protein is not a requirement for its transport to the surface of virus-infected cells. J Gen Virol 2001; 82:1375-1386. [PMID: 11369882 DOI: 10.1099/0022-1317-82-6-1375] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The intracellular cleavage of respiratory syncytial virus (RSV) fusion (F) protein by furin was examined. In RSV-infected LoVo cells, which express an inactive form of furin, and in RSV-infected Vero cells treated with the furin inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone (dec-RVKR-cmk), the F protein was expressed as a non-cleaved 73 kDa species. In both cases the F protein was initially expressed as an endoglycosidase H (Endo H)-sensitive precursor (F0(EHs)) which was modified approximately 40 min post-synthesis by the addition of complex carbohydrates to produce the Endo H-resistant form (F0(EHr)). The size and glycosylation state of F0(EHr) were identical to a transient intermediate form of non-cleaved F protein which was detected in RSV-infected Vero cells in the absence of inhibitor. Cell surface biotinylation and surface immunofluorescence staining showed that F0(EHr) was present on the surface of RSV-infected cells. RSV filaments have been shown to be the predominant form of the budding virus that is detected during virus replication. Analysis of the RSV-infected cells using scanning electron microscopy (SEM) showed that, in the presence of dec-RVKR-cmk, virus budding was impaired, producing fewer and much smaller viral filaments than in untreated cells. A comparison of immunofluorescence and SEM data showed that F0(EHr) was routed to the surface of virus-infected cells but not located in these smaller structures. Our findings suggest that activation of the F protein is required for the efficient formation of RSV filaments.
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Affiliation(s)
- Richard J Sugrue
- MRC Virology Unit, Institute of Virology, Church Street, G11 5JR, Glasgow, UK1
| | - Craig Brown
- MRC Virology Unit, Institute of Virology, Church Street, G11 5JR, Glasgow, UK1
| | - Gaie Brown
- MRC Virology Unit, Institute of Virology, Church Street, G11 5JR, Glasgow, UK1
| | - James Aitken
- Division of Virology, University of Glasgow, Institute of Virology, Church Street, G11 5JR, Glasgow, UK2
| | - Helen W McL Rixon
- MRC Virology Unit, Institute of Virology, Church Street, G11 5JR, Glasgow, UK1
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43
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Marshall GS, Li M, Stout GG, Louthan MV, Duliège AM, Burke RL, Hunt LA. Antibodies to the major linear neutralizing domains of cytomegalovirus glycoprotein B among natural seropositives and CMV subunit vaccine recipients. Viral Immunol 2001; 13:329-41. [PMID: 11016597 DOI: 10.1089/08828240050144653] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The gB protein (gpUL55) of human cytomegalovirus (CMV) contains C-terminal (AD-1) and N-terminal (AD-2) linear immunodominant neutralizing domains. To measure antibodies to these epitopes, a modified protein (delta-gB) lacking heavily glycosylated intervening regions, the transmembrane domain, and the cytoplasmic domain, was expressed in recombinant baculovirus-infected cells. Eighty-six percent of 600 naturally CMV-seropositive individuals and 93% of 121 gB vaccine recipients had antibodies to delta-gB as detected by enzyme-linked immunosorbent assay (ELISA). The antibody level in vaccinees (median optical density [OD] = 1.73) exceeded that in natural seropositives (median OD = 0.94; p < .0001). Eleven percent of 95 natural seropositives and 7% of 120 gB vaccinees lacked A-gB antibodies but had neutralizing activity. Among subjects with delta-gB antibody, there were weak correlations between antibody level and neutralizing titer. These data suggest that antibodies to linear neutralizing gB domains are highly prevalent in naturally-infected individuals and regularly develop in gB vaccinees. However, for some individuals, discontinuous and/or linear epitopes not represented on delta-gB may be more important in the generation of neutralizing responses.
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Affiliation(s)
- G S Marshall
- Department of Pediatrics, University of Louisville School of Medicine, Kentucky 40202, USA.
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44
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IJkel WF, Westenberg M, Goldbach RW, Blissard GW, Vlak JM, Zuidema D. A novel baculovirus envelope fusion protein with a proprotein convertase cleavage site. Virology 2000; 275:30-41. [PMID: 11017785 DOI: 10.1006/viro.2000.0483] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The entry mechanism of Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV), a group II NPV, in cultured cells was examined. SeMNPV budded virus (BV) enters by endocytosis as do the BVs of the group I NPVs, Autographa californica (Ac) MNPV and Orgyia pseudotsugata (Op) MNPV. In group I NPVs, upon infection acidification of the endosome triggers fusion of the viral and endosomal membrane, which is mediated by the BV envelope glycoprotein GP64. However, the SeMNPV genome lacks a homolog of GP64 envelope fusion protein (EFP). A functional homolog of the OpMNPV GP64 EFP was identified in SeMNPV ORF8 (Se8; 76 kDa) and appeared to be the major BV envelope protein. Surprisingly, a 60-kDa cleavage product of this protein is present in the BV envelope. A furin-like proprotein convertase cleavage site (R-X-K/R-R) was identified immediately upstream of the N-terminus of the mature Se8 protein and this site was also conserved in the Lymantria dispar (Ld) MNPV homolog (Ld130) of Se8. Syncytium formation assays showed that Se8 and Ld130 alone were sufficient to mediate membrane fusion upon acidification of the medium. Furthermore, C-terminal GFP-fusion proteins of Se8 and Ld130 were primarily localized in the plasma membrane of insect cells. This is consistent with their fusogenic activity and supports the conclusion that the Se8 gene product is a functional homolog of the GP64 EFP.
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Affiliation(s)
- W F IJkel
- Laboratory of Virology, Wageningen University and Research Center, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
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45
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Sanchez V, Sztul E, Britt WJ. Human cytomegalovirus pp28 (UL99) localizes to a cytoplasmic compartment which overlaps the endoplasmic reticulum-golgi-intermediate compartment. J Virol 2000; 74:3842-51. [PMID: 10729158 PMCID: PMC111892 DOI: 10.1128/jvi.74.8.3842-3851.2000] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Although the assembly of herpesviruses has remained an active area of investigation, considerable controversy continues to surround the cellular location of tegument and envelope acquisition. This controversy is particularly evident when the proposed pathways for alpha- and beta-herpesvirus assembly are compared. We have approached this aspect of human cytomegalovirus (HCMV) assembly, specifically, envelopment, by investigating the intracellular trafficking of viral tegument proteins which localize in the cytoplasms of infected cells. In this study we have demonstrated that the virion tegument protein pp28 (UL99), a true late protein, was membrane associated as a result of myristoylation. A mutation in this protein which prevented incorporation of [(3)H]myristic acid also altered the detergent solubility and intracellular distribution of the protein when it was expressed in transfected cells. Using a panel of markers for intracellular compartments, we could localize the expression of wild-type pp28 to an intracellular compartment which colocalized with the endoplasmic reticulum-Golgi-intermediate compartment (ERGIC), a dynamic compartment of the secretory pathway which interfaces with both the ER and Golgi apparatus. The localization of this viral tegument protein within an early secretory compartment of the cell provided further evidence that the assembly of the HCMV tegument likely includes a cytoplasmic phase. Because pp28 has been shown to be localized to a cytoplasmic assembly compartment in HCMV-infected cells, our findings also suggested that viral tegument protein interactions within the secretory pathway may have an important role in the assembly of the virion.
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Affiliation(s)
- V Sanchez
- Departments of Pediatrics, The University of Alabama at Birmingham, Birmingham, Alabama, USA
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46
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Jean F, Thomas L, Molloy SS, Liu G, Jarvis MA, Nelson JA, Thomas G. A protein-based therapeutic for human cytomegalovirus infection. Proc Natl Acad Sci U S A 2000; 97:2864-9. [PMID: 10681468 PMCID: PMC16021 DOI: 10.1073/pnas.050504297] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Current antiviral strategies target viral gene products. Although initially successful, their severe toxicity and susceptibility to circumvention by the generation of drug-resistant variants limit their usefulness. By contrast, the central role of the host cell serine endoprotease furin in the proteolytic activation of numerous pathogens points to the endoprotease as a strategic target for therapeutics. Herein, we show that the production of infectious human cytomegalovirus is dramatically reduced by exogenous addition of a bioengineered serpin, alpha(1)-PDX. This protein is a potent and selective furin inhibitor (K(i) = 0.6 nM) and is 10-fold more effective than currently used antiherpetic agents in cell-culture models. The requirement of furin for the processing of envelope glycoproteins from many pathogenic viruses and for the activation of several bacterial toxins suggests that selective inhibitors of furin have potential as broad-based anti-pathogens.
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Affiliation(s)
- F Jean
- Vollum Institute, and Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97201, USA
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47
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Singh J, Compton T. Characterization of a panel of insertion mutants in human cytomegalovirus glycoprotein B. J Virol 2000; 74:1383-92. [PMID: 10627549 PMCID: PMC111473 DOI: 10.1128/jvi.74.3.1383-1392.2000] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycoprotein B (gB; gpUL55) of human cytomegalovirus (HCMV) plays a critical role in virus entry and cell-to-cell spread of infection. To define the structure-function relationships in gB, a panel of linker-insertion mutations was generated throughout the coding region. This strategy yielded a panel of 22 mutants with four amino acid insertions and 3 large truncation mutants. Assessment of the mutant proteins' biosynthetic properties and folding patterns analyzed in context with predicted secondary features revealed novel insights into gB's structure and trafficking properties. All of the insertion mutants were able to assemble into oligomers, suggesting that oligomerization is tolerant of small insertions and/or that multiple regions of the protein may be involved. Computer algorithm predictions of gB's secondary structure indicate that the furin-recognized cleavage site falls within an exposed loop. This loop may be particularly sensitive to structural alterations, since insertions upstream and downstream of the cleavage site rendered the mutant proteins cleavage defective. In addition, a strong correlation existed between terminal folding and cleavage of gB. Interestingly, terminal folding was not correlated with delivery to the cell surface but may influence the rate of transport to the cell surface. Nine mutants, containing insertions in both the extracellular and intracellular portions of gB, retained wild-type structural properties. This panel of characterized gB mutants, the first of this type for an HCMV protein, will be a useful tool in dissecting the role of gB during HCMV infection.
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Affiliation(s)
- J Singh
- Department of Medical Microbiology and Immunology, University of Wisconsin, Madison, Wisconsin 53706, USA
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48
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Sanchez V, Greis KD, Sztul E, Britt WJ. Accumulation of virion tegument and envelope proteins in a stable cytoplasmic compartment during human cytomegalovirus replication: characterization of a potential site of virus assembly. J Virol 2000; 74:975-86. [PMID: 10623760 PMCID: PMC111618 DOI: 10.1128/jvi.74.2.975-986.2000] [Citation(s) in RCA: 267] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The assembly of human cytomegalovirus (HCMV) is thought to be similar to that which has been proposed for alphaherpesviruses and involve envelopment of tegumented subviral particles at the nuclear membrane followed by export from the cell by a poorly defined pathway. However, several studies have shown that at least two tegument virion proteins remain in the cytoplasm during the HCMV replicative cycle, thereby suggesting that HCMV cannot acquire its final envelope at the nuclear envelope. We investigated the assembly of HCMV by determining the intracellular trafficking of the abundant tegument protein pp150 (UL32) in productively infected human fibroblasts. Our results indicated that pp150 remained within the cytoplasm throughout the replicative cycle of HCMV and accumulated in a stable, juxtanuclear structure late in infection. Image analysis using a variety of cell protein-specific antibodies indicated that the pp150-containing structure was not a component of the endoplasmic reticulum, (ER), ER-Golgi intermediate compartment, cis or medial Golgi, or lysosomes. Partial colocalization of the structure was noted with the trans-Golgi network, and it appeared to lie in close proximity to the microtubule organizing center. Two additional tegument proteins (pp28 and pp65) and three envelope glycoproteins (gB, gH, and gp65) localized in this same structure late infection. This compartment appeared to be relatively stable since pp150, pp65, and the processed form of gB could be coisolated following cell fractionation. Our findings indicated that pp150 was expressed exclusively within the cytoplasm throughout the infectious cycle of HCMV and that the accumulation of the pp150 in this cytoplasmic structure was accompanied by at least five other virion proteins. These results suggested the possibility that this virus-induced structure represented a cytoplasmic site of virus assembly.
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Affiliation(s)
- V Sanchez
- Departments of Pediatrics, The University of Alabama at Birmingham, Birmingham, Alabama 35233, USA
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49
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Tugizov S, Maidji E, Xiao J, Pereira L. An acidic cluster in the cytosolic domain of human cytomegalovirus glycoprotein B is a signal for endocytosis from the plasma membrane. J Virol 1999; 73:8677-88. [PMID: 10482621 PMCID: PMC112888 DOI: 10.1128/jvi.73.10.8677-8688.1999] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We previously reported that human cytomegalovirus (CMV) glycoprotein B (gB) is transported to apical membranes in CMV-infected polarized retinal pigment epithelial (ARPE-19) cells and in Madin-Darby canine kidney (MDCK) epithelial cells constitutively expressing gB. The cytosolic domain of gB contains a cluster of acidic amino acids, a motif that plays a pivotal role in vectorial trafficking in polarized epithelial cells and may also function as a signal for entry into the endocytic pathway. Here we compared gB internalization and recycling to the plasma membrane in CMV-infected human fibroblasts (HF) and ARPE-19 cells by using antibody-internalization experiments. Immunofluorescence and quantitative assays showed that gB was internalized from the cell surface into clathrin-coated transport vesicles and then recycled to the plasma membrane. gB colocalized with clathrin-coated vesicles containing the transferrin receptor in the early endocytic/recycling pathway, indicating that gB traffics in this pathway. The specific role of the acidic cluster in regulating the sorting of gB-containing vesicles in the early endocytic/recycling pathway was examined in MDCK cells expressing mutated gB derivatives. Immunofluorescence assays showed that derivatives lacking the acidic cluster were impaired in internalization and failed to recycle. These findings, together with our earlier observation that the acidic cluster is a key determinant for targeting gB molecules to apical membranes in epithelial cells, establish that this signal is recognized by cellular proteins that participate in polarized sorting and transport in the early endocytic/recycling pathway.
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Affiliation(s)
- S Tugizov
- Department of Stomatology, School of Dentistry, University of California San Francisco, San Francisco, California 94143-0512, USA
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50
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Feldmann H, Volchkov VE, Volchkova VA, Klenk HD. The glycoproteins of Marburg and Ebola virus and their potential roles in pathogenesis. ARCHIVES OF VIROLOGY. SUPPLEMENTUM 1999; 15:159-69. [PMID: 10470276 DOI: 10.1007/978-3-7091-6425-9_11] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Filoviruses cause systemic infections that can lead to severe hemorrhagic fever in human and non-human primates. The primary target of the virus appears to be the mononuclear phagocytic system. As the virus spreads through the organism, the spectrum of target cells increases to include endothelial cells, fibroblasts, hepatocytes, and many other cells. There is evidence that the filovirus glycoprotein plays an important role in cell tropism, spread of infection, and pathogenicity. Biosynthesis of the glycoprotein forming the spikes on the virion surface involves cleavage by the host cell protease furin into two disulfide linked subunits GP1 and GP2. GP1 is also shed in soluble form from infected cells. Different strains of Ebola virus show variations in the cleavability of the glycoprotein, that may account for differences in pathogenicity, as has been observed with influenza viruses and paramyxoviruses. Expression of the spike glycoprotein of Ebola virus, but not of Marburg virus, requires transcriptional editing. Unedited GP mRNA yields the nonstructural glycoprotein sGP, which is secreted extensively from infected cells. Whether the soluble glycoproteins GP1 and sGP interfere with the humoral immune response and other defense mechanisms remains to be determined.
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Affiliation(s)
- H Feldmann
- Institut für Virologie, Philipps-Universität Marburg, Germany
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