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Brenner S, Braun B, Read C, Weil T, Walther P, Schrader T, Münch J, von Einem J. The Molecular Tweezer CLR01 Inhibits Antibody-Resistant Cell-to-Cell Spread of Human Cytomegalovirus. Viruses 2021; 13:v13091685. [PMID: 34578265 PMCID: PMC8472163 DOI: 10.3390/v13091685] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 08/20/2021] [Accepted: 08/23/2021] [Indexed: 02/06/2023] Open
Abstract
Human cytomegalovirus (HCMV) uses two major ways for virus dissemination: infection by cell-free virus and direct cell-to-cell spread. Neutralizing antibodies can efficiently inhibit infection by cell-free virus but mostly fail to prevent cell-to-cell transmission. Here, we show that the ‘molecular tweezer’ CLR01, a broad-spectrum antiviral agent, is not only highly active against infection with cell-free virus but most remarkably inhibits antibody-resistant direct cell-to-cell spread of HCMV. The inhibition of cell-to-cell spread by CLR01 was not limited to HCMV but was also shown for the alphaherpesviruses herpes simplex viruses 1 and 2 (HSV-1, -2). CLR01 is a rapid acting small molecule that inhibits HCMV entry at the attachment and penetration steps. Electron microscopy of extracellular virus particles indicated damage of the viral envelope by CLR01, which likely impairs the infectivity of virus particles. The rapid inactivation of viral particles by CLR01, the viral envelope as the main target, and the inhibition of virus entry at different stages are presumably the key to inhibition of cell-free virus infection and cell-to-cell spread by CLR01. Importance: While cell-free spread enables the human cytomegalovirus (HCMV) and other herpesviruses to transmit between hosts, direct cell-to-cell spread is thought to be more relevant for in vivo dissemination within infected tissues. Cell-to-cell spread is resistant to neutralizing antibodies, thus contributing to the maintenance of virus infection and virus dissemination in the presence of an intact immune system. Therefore, it would be therapeutically interesting to target this mode of spread in order to treat severe HCMV infections and to prevent dissemination of virus within the infected host. The molecular tweezer CLR01 exhibits broad-spectrum antiviral activity against a number of enveloped viruses and efficiently blocks antibody-resistant cell-to-cell spread of HCMV, thus representing a novel class of small molecules with promising antiviral activity.
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Affiliation(s)
- Sina Brenner
- Institute of Virology, Ulm University Medical Center, 89081 Ulm, Germany; (S.B.); (B.B.); (C.R.)
| | - Berenike Braun
- Institute of Virology, Ulm University Medical Center, 89081 Ulm, Germany; (S.B.); (B.B.); (C.R.)
| | - Clarissa Read
- Institute of Virology, Ulm University Medical Center, 89081 Ulm, Germany; (S.B.); (B.B.); (C.R.)
- Central Facility for Electron Microscopy, Ulm University, 89081 Ulm, Germany;
| | - Tatjana Weil
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany; (T.W.); (J.M.)
| | - Paul Walther
- Central Facility for Electron Microscopy, Ulm University, 89081 Ulm, Germany;
| | - Thomas Schrader
- Faculty of Chemistry, University of Duisburg-Essen, 45117 Essen, Germany;
| | - Jan Münch
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany; (T.W.); (J.M.)
- Core Facility Functional Peptidomics, Ulm University Medical Center, 89081 Ulm, Germany
| | - Jens von Einem
- Institute of Virology, Ulm University Medical Center, 89081 Ulm, Germany; (S.B.); (B.B.); (C.R.)
- Correspondence: ; Tel.: +49-(0)731-500-65104; Fax: +49-(0)731-500-65102
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Rand U, Kubsch T, Kasmapour B, Cicin-Sain L. A Novel Triple-Fluorescent HCMV Strain Reveals Gene Expression Dynamics and Anti-Herpesviral Drug Mechanisms. Front Cell Infect Microbiol 2021; 10:536150. [PMID: 33489928 PMCID: PMC7820782 DOI: 10.3389/fcimb.2020.536150] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 11/25/2020] [Indexed: 11/15/2022] Open
Abstract
Human Cytomegalovirus (HCMV) infection may result in severe outcomes in immunocompromised individuals such as AIDS patients, transplant recipients, and neonates. To date, no vaccines are available and there are only few drugs for anti-HCMV therapy. Adverse effects and the continuous emergence of drug-resistance strains require the identification of new drug candidates in the near future. Identification and characterization of such compounds and biological factors requires sensitive and reliable detection techniques of HCMV infection, gene expression and spread. In this work, we present and validate a novel concept for multi-reporter herpesviruses, identified through iterative testing of minimally invasive mutations. We integrated up to three fluorescence reporter genes into replication-competent HCMV strains, generating reporter HCMVs that allow the visualization of replication cycle stages of HCMV, namely the immediate early (IE), early (E), and late (L) phase. Fluorescent proteins with clearly distinguishable emission spectra were linked by 2A peptides to essential viral genes, allowing bicistronic expression of the viral and the fluorescent protein without major effects on viral fitness. By using this triple color reporter HCMV, we monitored gene expression dynamics of the IE, E, and L genes by measuring the fluorescent signal of the viral gene-associated fluorophores within infected cell populations and at high temporal resolution. We demonstrate distinct inhibitory profiles of foscarnet, fomivirsen, phosphonoacetic acid, ganciclovir, and letermovir reflecting their mode-of-action. In conclusion, our data argues that this experimental approach allows the identification and characterization of new drug candidates in a single step.
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Affiliation(s)
- Ulfert Rand
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany
| | - Tobias Kubsch
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany
| | - Bahram Kasmapour
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany.,German Centre for Infection Research (DZIF), Hannover-Braunschweig Site, Braunschweig, Germany
| | - Luka Cicin-Sain
- Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany.,German Centre for Infection Research (DZIF), Hannover-Braunschweig Site, Braunschweig, Germany.,Centre for Individualised Infection Medicine (CIIM), A Joint Venture of Helmholtz Centre for Infection Research (HZI) and Hannover Medical School (MHH), Braunschweig, Germany.,Cluster of Excellence RESIST (EXC 2155), Hannover Medical School (MHH), Hannover, Germany
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3
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Böffert R, Businger R, Preiß H, Ehmann D, Truffault V, Simon C, Ruetalo N, Hamprecht K, Müller P, Wehkamp J, Schindler M. The human α-defensin-derived peptide HD5(1-9) inhibits cellular attachment and entry of human cytomegalovirus. Antiviral Res 2020; 177:104779. [PMID: 32209394 DOI: 10.1016/j.antiviral.2020.104779] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 03/13/2020] [Accepted: 03/18/2020] [Indexed: 10/24/2022]
Abstract
Human cytomegalovirus (HCMV) infection causes severe illness in newborns and immunocompromised patients. Since treatment options are limited there is an unmet need for new therapeutic approaches. Defensins are cationic peptides, produced by various human tissues, which serve as antimicrobial effectors of the immune system. Furthermore, some defensins are proteolytically cleaved, resulting in the generation of smaller fragments with increased activity. Together, this led us to hypothesize that defensin-derived peptides are natural human inhibitors of virus infection with low toxicity. We screened several human defensin HNP4- and HD5-derived peptides and found HD5(1-9) to be antiviral without toxicity at high concentrations. HD5(1-9) inhibited HCMV cellular attachment and thereby entry and was active against primary as well as a multiresistant HCMV isolate. Moreover, cysteine and arginine residues were identified to mediate the antiviral activity of HD5(1-9). Altogether, defensin-derived peptides, in particular HD5(1-9), qualify as promising candidates for further development as a novel class of HCMV entry inhibitors.
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Affiliation(s)
- Rebecca Böffert
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Ramona Businger
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Hannes Preiß
- Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany
| | - Dirk Ehmann
- Department for Internal Medicine I, University Hospital Tübingen, Tübingen, Germany
| | | | - Claudia Simon
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Natalia Ruetalo
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Klaus Hamprecht
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Patrick Müller
- Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany; Translational Oncology Division, University Hospital Tübingen, Tübingen, Germany
| | - Jan Wehkamp
- Department for Internal Medicine I, University Hospital Tübingen, Tübingen, Germany
| | - Michael Schindler
- Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany.
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4
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Abdellatif ME, Sinzger C, Walther P. Investigating HCMV entry into host cells by STEM tomography. J Struct Biol 2018; 204:406-419. [DOI: 10.1016/j.jsb.2018.10.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 10/17/2018] [Accepted: 10/18/2018] [Indexed: 11/17/2022]
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5
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Large-Scale Screening of HCMV-Seropositive Blood Donors Indicates that HCMV Effectively Escapes from Antibodies by Cell-Associated Spread. Viruses 2018; 10:v10090500. [PMID: 30223489 PMCID: PMC6163834 DOI: 10.3390/v10090500] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 09/07/2018] [Accepted: 09/12/2018] [Indexed: 12/16/2022] Open
Abstract
Immunoglobulins are only moderately effective for the treatment of human cytomegalovirus (HCMV) infections, possibly due to ineffectiveness against cell-associated virus spread. To overcome this limitation, we aimed to identify individuals with exceptional antibodies in their plasma that can efficiently block the cell-associated spread of HCMV. A Gaussia luciferase-secreting mutant of the cell-associated HCMV strain Merlin was generated, and luciferase activity evaluated as a readout for the extent of cell-associated focal spread. This reporter virus-based assay was then applied to screen plasma samples from 8400 HCMV-seropositive individuals for their inhibitory effect, including direct-acting antiviral drugs as positive controls. None of the plasmas reduced virus spread to the level of these controls. Even the top-scoring samples that partially reduced luciferase activity in the screening assay failed to inhibit focal growth when reevaluated with a more accurate, immunofluorescence-based assay. Selected sera with high neutralizing capacity against free viruses were analyzed separately, and none of them prevented the focal spread of three recent clinical HCMV isolates nor reduced the number of particles transmitted, as demonstrated with a fluorescent Merlin mutant. We concluded that donors with cell-to-cell-spread-inhibiting plasma are nonexistent or extremely rare, emphasizing cell-associated spread as a highly efficient immune escape mechanism of HCMV.
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Falk JJ, Winkelmann M, Stöhr D, Alt M, Schrezenmeier H, Krawczyk A, Lotfi R, Sinzger C. Identification of Elite Neutralizers With Broad and Potent Neutralizing Activity Against Human Cytomegalovirus (HCMV) in a Population of HCMV-Seropositive Blood Donors. J Infect Dis 2018; 218:876-885. [DOI: 10.1093/infdis/jiy229] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 04/16/2018] [Indexed: 11/14/2022] Open
Affiliation(s)
| | - Martina Winkelmann
- Institute for Clinical Transfusion Medicine and Immunogenetics Ulm, German Red Cross Blood-Transfusion Service Baden-Württemberg–Hessen and University Hospital, Ulm, Germany
| | - Dagmar Stöhr
- Institute for Virology, Ulm University Medical Center, Ulm, Germany
| | - Mira Alt
- Institute for Virology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Hubert Schrezenmeier
- Institute for Clinical Transfusion Medicine and Immunogenetics Ulm, German Red Cross Blood-Transfusion Service Baden-Württemberg–Hessen and University Hospital, Ulm, Germany
- Institute for Transfusion Medicine, Ulm University, Ulm, Germany
| | - Adalbert Krawczyk
- Institute for Virology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Ramin Lotfi
- Institute for Clinical Transfusion Medicine and Immunogenetics Ulm, German Red Cross Blood-Transfusion Service Baden-Württemberg–Hessen and University Hospital, Ulm, Germany
- Institute for Transfusion Medicine, Ulm University, Ulm, Germany
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7
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Kasmapour B, Kubsch T, Rand U, Eiz-Vesper B, Messerle M, Vondran FWR, Wiegmann B, Haverich A, Cicin-Sain L. Myeloid Dendritic Cells Repress Human Cytomegalovirus Gene Expression and Spread by Releasing Interferon-Unrelated Soluble Antiviral Factors. J Virol 2018; 92:e01138-17. [PMID: 29046460 PMCID: PMC5730771 DOI: 10.1128/jvi.01138-17] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 10/03/2017] [Indexed: 12/21/2022] Open
Abstract
Cytomegalovirus (CMV) is a betaherpesvirus that latently infects most adult humans worldwide and is a major cause of morbidity and mortality in immunocompromised hosts. Latent human CMV (HCMV) is believed to reside in precursors of myeloid-lineage leukocytes and monocytes, which give rise to macrophages and dendritic cells (DC). We report here that human monocyte-derived DC (mo-DC) suppress HCMV infection in coculture with infected fibroblast target cells in a manner dependent on the effector-to-target ratio. Intriguingly, optimal activation of mo-DC was achieved under coculture conditions and not by direct infection with HCMV, implying that mo-DC may recognize unique molecular patterns on, or within, infected fibroblasts. We show that HCMV is controlled by secreted factors that act by priming defenses in target cells rather than by direct viral neutralization, but we excluded a role for interferons (IFNs) in this control. The expression of lytic viral genes in infected cells and the progression of infection were significantly slowed, but this effect was reversible, indicating that the control of infection depended on the transient induction of antiviral effector molecules in target cells. Using immediate early or late-phase reporter HCMVs, we show that soluble factors secreted in the cocultures suppress HCMV replication at both stages of the infection and that their antiviral effects are robust and comparable in numerous batches of mo-DC as well as in primary fibroblasts and stromal cells.IMPORTANCE Human cytomegalovirus is a widespread opportunistic pathogen that can cause severe disease and complications in vulnerable individuals. This includes newborn children, HIV AIDS patients, and transplant recipients. Although the majority of healthy humans carry this virus throughout their lives without symptoms, it is not exactly clear which tissues in the body are the main reservoirs of latent virus infection or how the delicate balance between the virus and the immune system is maintained over an individual's lifetime. Here, for the first time, we provide evidence for a novel mechanism of direct virus control by a subset of human innate immune cells called dendritic cells, which are regarded as a major site of virus latency and reactivation. Our findings may have important implications in HCMV disease prevention as well as in development of novel therapeutic approaches.
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Affiliation(s)
- Bahram Kasmapour
- Immune Ageing and Chronic Infections Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Tobias Kubsch
- Immune Ageing and Chronic Infections Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Ulfert Rand
- Immune Ageing and Chronic Infections Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Britta Eiz-Vesper
- Institute for Transfusion Medicine, Hannover Medical School, Hannover, Germany
| | - Martin Messerle
- Institute of Virology, Hannover Medical School, Hannover, Germany
| | - Florian W R Vondran
- Department of General, Visceral and Transplant Surgery, Hannover Medical School, Hannover, Germany
- German Centre for Infection Research, Partner Site Hannover-Braunschweig, Braunschweig, Germany
| | - Bettina Wiegmann
- Department of Cardiothoracic, Transplantation and Vascular Surgery, Hannover Medical School, Hannover, Germany
| | - Axel Haverich
- Department of Cardiothoracic, Transplantation and Vascular Surgery, Hannover Medical School, Hannover, Germany
| | - Luka Cicin-Sain
- Immune Ageing and Chronic Infections Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute of Virology, Hannover Medical School, Hannover, Germany
- German Centre for Infection Research, Partner Site Hannover-Braunschweig, Braunschweig, Germany
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8
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Stegmann C, Hochdorfer D, Lieber D, Subramanian N, Stöhr D, Laib Sampaio K, Sinzger C. A derivative of platelet-derived growth factor receptor alpha binds to the trimer of human cytomegalovirus and inhibits entry into fibroblasts and endothelial cells. PLoS Pathog 2017; 13:e1006273. [PMID: 28403220 PMCID: PMC5389858 DOI: 10.1371/journal.ppat.1006273] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 03/06/2017] [Indexed: 12/03/2022] Open
Abstract
Human cytomegalovirus (HCMV) is a widely distributed herpesvirus that causes significant morbidity in immunocompromised hosts. Inhibitors of viral DNA replication are available, but adverse effects limit their use. Alternative antiviral strategies may include inhibition of entry. We show that soluble derivatives of the platelet-derived growth factor receptor alpha (PDGFR-alpha), a putative receptor of HCMV, can inhibit HCMV infection of various cell types. A PDGFR-alpha-Fc fusion protein binds to and neutralizes cell-free virus particles at an EC50 of 10–30 ng/ml. Treatment of particles reduced both attachment to and fusion with cells. In line with the latter, PDGFR-alpha-Fc was also effective when applied postattachment. A peptide scan of the extracellular domain of PDGFR-alpha identified a 40mer peptide that inhibits infection at an EC50 of 1–2 nmol/ml. Both, peptide and fusion protein, were effective against various HCMV strains and are hence promising candidates for the development of novel anti-HCMV therapies. Human cytomegalovirus (HCMV) depends on expression of platelet-derived growth factor receptor alpha (PDGFR-alpha) for infection of fibroblasts whereas this cell surface protein is not required for infection of endothelial cells. Surprisingly, pretreatment of HCMV with a soluble derivative of PDGFR-alpha prevents infection of both cell types, most probably via specific binding to the trimeric gH/gL/pUL74 complex. While adsorption is inhibited in both cell types, an additional penetration block occurs only in fibroblasts. The finding that an essential molecular interaction of HCMV with fibroblasts can be subverted for inhibition of the virus provides an antiviral strategy that may be hard to circumvent by the virus.
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Affiliation(s)
- Cora Stegmann
- Institute of Virology, University of Ulm, Ulm, Germany
| | | | - Diana Lieber
- Institute of Virology, University of Ulm, Ulm, Germany
| | | | - Dagmar Stöhr
- Institute of Virology, University of Ulm, Ulm, Germany
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Hochdorfer D, Florin L, Sinzger C, Lieber D. Tetraspanin CD151 Promotes Initial Events in Human Cytomegalovirus Infection. J Virol 2016; 90:6430-42. [PMID: 27147745 PMCID: PMC4936157 DOI: 10.1128/jvi.00145-16] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 04/26/2016] [Indexed: 01/21/2023] Open
Abstract
UNLABELLED Human cytomegalovirus (HCMV), a betaherpesvirus, can cause life-threatening disease in immunocompromised individuals. Viral envelope glycoproteins that mediate binding to and penetration into target cells have been identified previously. In contrast, cellular proteins supporting HCMV during entry are largely unknown. In order to systematically identify host genes affecting initial steps of HCMV infection, a targeted RNA interference screen of 96 cellular genes was performed in endothelial cells by use of a virus strain expressing the full set of known glycoprotein H and L (gH/gL) complexes. The approach yielded five proviral host factors from different protein families and eight antiviral host factors, mostly growth factor receptors. The tetraspanin CD151 was uncovered as a novel proviral host factor and was analyzed further. Like endothelial cells, fibroblasts were also less susceptible to HCMV infection after CD151 depletion. Virus strains with different sets of gH/gL complexes conferring either broad or narrow cell tropism were equally impaired. Infection of CD151-depleted cells by a fluorescent virus with differentially labeled capsid and envelope proteins revealed a role of CD151 in viral penetration but not in adsorption to the cell. In conclusion, the tetraspanin CD151 has emerged as a novel host factor in HCMV entry and as a putative antiviral target. IMPORTANCE At present, the events at the virus-cell interface and the cellular proteins involved during the HCMV entry steps are scarcely understood. In this study, several host factors with putative roles in this process were identified. The tetraspanin CD151 was discovered as a previously unrecognized proviral host factor for HCMV and was found to support viral penetration into the target cells. The findings of this study shed light on the cellular contribution during the initial steps of HCMV infection and open a new direction in HCMV research.
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Affiliation(s)
| | - Luise Florin
- Department of Medical Microbiology and Hygiene, University Medical Center of the Johannes Gutenberg University, Mainz, Germany
| | | | - Diana Lieber
- Institute of Virology, Ulm University Medical Center, Ulm, Germany
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10
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Borst EM, Bauerfeind R, Binz A, Stephan TM, Neuber S, Wagner K, Steinbrück L, Sodeik B, Lenac Roviš T, Jonjić S, Messerle M. The Essential Human Cytomegalovirus Proteins pUL77 and pUL93 Are Structural Components Necessary for Viral Genome Encapsidation. J Virol 2016; 90:5860-5875. [PMID: 27009952 PMCID: PMC4907240 DOI: 10.1128/jvi.00384-16] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 03/15/2016] [Indexed: 12/27/2022] Open
Abstract
UNLABELLED Several essential viral proteins are proposed to participate in genome encapsidation of human cytomegalovirus (HCMV), among them pUL77 and pUL93, which remain largely uncharacterized. To gain insight into their properties, we generated an HCMV mutant expressing a pUL77-monomeric enhanced green fluorescent protein (mGFP) fusion protein and a pUL93-specific antibody. Immunoblotting demonstrated that both proteins are incorporated into capsids and virions. Conversely to data suggesting internal translation initiation sites within the UL93 open reading frame (ORF), we provide evidence that pUL93 synthesis commences at the first start codon. In infected cells, pUL77-mGFP was found in nuclear replication compartments and dot-like structures, colocalizing with capsid proteins. Immunogold labeling of nuclear capsids revealed that pUL77 is present on A, B, and C capsids. Pulldown of pUL77-mGFP revealed copurification of pUL93, indicating interaction between these proteins, which still occurred when capsid formation was prevented. Correct subnuclear distribution of pUL77-mGFP required pUL93 as well as the major capsid protein (and thus probably the presence of capsids), but not the tegument protein pp150 or the encapsidation protein pUL52, demonstrating that pUL77 nuclear targeting occurs independently of the formation of DNA-filled capsids. When pUL77 or pUL93 was missing, generation of unit-length genomes was not observed, and only empty B capsids were produced. Taken together, these results show that pUL77 and pUL93 are capsid constituents needed for HCMV genome encapsidation. Therefore, the task of pUL77 seems to differ from that of its alphaherpesvirus orthologue pUL25, which exerts its function subsequent to genome cleavage-packaging. IMPORTANCE The essential HCMV proteins pUL77 and pUL93 were suggested to be involved in viral genome cleavage-packaging but are poorly characterized both biochemically and functionally. By producing a monoclonal antibody against pUL93 and generating an HCMV mutant in which pUL77 is fused to a fluorescent protein, we show that pUL77 and pUL93 are capsid constituents, with pUL77 being similarly abundant on all capsid types. Each protein is required for genome encapsidation, as the absence of either pUL77 or pUL93 results in a genome packaging defect with the formation of empty capsids only. This distinguishes pUL77 from its alphaherpesvirus orthologue pUL25, which is enriched on DNA-filled capsids and exerts its function after the viral DNA is packaged. Our data for the first time describe an HCMV mutant with a fluorescent capsid and provide insight into the roles of pUL77 and pUL93, thus contributing to a better understanding of the HCMV encapsidation network.
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Affiliation(s)
- Eva Maria Borst
- Institute for Virology, Hannover Medical School, Hannover, Germany
| | - Rudolf Bauerfeind
- Institute for Cell Biology, Hannover Medical School, Hannover, Germany
| | - Anne Binz
- Institute for Virology, Hannover Medical School, Hannover, Germany
| | | | - Sebastian Neuber
- Institute for Virology, Hannover Medical School, Hannover, Germany
| | - Karen Wagner
- Institute for Virology, Hannover Medical School, Hannover, Germany
| | - Lars Steinbrück
- Institute for Virology, Hannover Medical School, Hannover, Germany
| | - Beate Sodeik
- Institute for Virology, Hannover Medical School, Hannover, Germany
- German Center for Infection Research (DZIF), Partner Site Hannover-Braunschweig, Germany
| | - Tihana Lenac Roviš
- Department of Histology and Embryology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Stipan Jonjić
- Department of Histology and Embryology, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
| | - Martin Messerle
- Institute for Virology, Hannover Medical School, Hannover, Germany
- German Center for Infection Research (DZIF), Partner Site Hannover-Braunschweig, Germany
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11
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Krömmelbein N, Wiebusch L, Schiedner G, Büscher N, Sauer C, Florin L, Sehn E, Wolfrum U, Plachter B. Adenovirus E1A/E1B Transformed Amniotic Fluid Cells Support Human Cytomegalovirus Replication. Viruses 2016; 8:v8020037. [PMID: 26848680 PMCID: PMC4776192 DOI: 10.3390/v8020037] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 01/22/2016] [Accepted: 01/28/2016] [Indexed: 11/30/2022] Open
Abstract
The human cytomegalovirus (HCMV) replicates to high titers in primary human fibroblast cell cultures. A variety of primary human cells and some tumor-derived cell lines do also support permissive HCMV replication, yet at low levels. Cell lines established by transfection of the transforming functions of adenoviruses have been notoriously resistant to HCMV replication and progeny production. Here, we provide first-time evidence that a permanent cell line immortalized by adenovirus type 5 E1A and E1B (CAP) is supporting the full HCMV replication cycle and is releasing infectious progeny. The CAP cell line had previously been established from amniotic fluid cells which were likely derived from membranes of the developing fetus. These cells can be grown under serum-free conditions. HCMV efficiently penetrated CAP cells, expressed its immediate-early proteins and dispersed restrictive PML-bodies. Viral DNA replication was initiated and viral progeny became detectable by electron microscopy in CAP cells. Furthermore, infectious virus was released from CAP cells, yet to lower levels compared to fibroblasts. Subviral dense bodies were also secreted from CAP cells. The results show that E1A/E1B expression in transformed cells is not generally repressive to HCMV replication and that CAP cells may be a good substrate for dense body based vaccine production.
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Affiliation(s)
- Natascha Krömmelbein
- Institute for Virology, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
| | - Lüder Wiebusch
- Department of Pediatric Molecular Biology, Charité University Medical Centre Berlin, D-10117 Berlin, Germany.
| | | | - Nicole Büscher
- Institute for Virology, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
| | - Caroline Sauer
- Institute for Virology, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
| | - Luise Florin
- Institute for Medical Microbiology and Hygiene, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
| | - Elisabeth Sehn
- Institute for Zoology, Johannes Gutenberg-University Mainz, D-55099 Mainz, Germany.
| | - Uwe Wolfrum
- Institute for Zoology, Johannes Gutenberg-University Mainz, D-55099 Mainz, Germany.
| | - Bodo Plachter
- Institute for Virology, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
- Research Center for Immunotherapy, University Medical Center of the Johannes Gutenberg-University Mainz, D-55131 Mainz, Germany.
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