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Abstract
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The
Ebolaviruses are members of the family Filoviridae (“filoviruses”) and cause severe hemhorragic fever
with human case fatality rates as high as 90%. Infection requires
attachment of the viral particle to cells and triggering of membrane
fusion between the host and viral membranes, a process that occurs
in the host endosome and is facilitated by the envelope glycoprotein
(GP). One potential strategy for therapeutic intervention is the development
of agents (antibodies, peptides, and small molecules) that can interfere
with viral entry aspects such as attachment, uptake, priming, or membrane
fusion. This paper highlights recent developments in the discovery
and evaluation of therapeutic entry inhibitors and identifies opportunities
moving forward.
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Affiliation(s)
- Elisabeth K. Nyakatura
- Department
of Biochemistry, Albert Einstein College of Medicine, 1300 Morris
Park Avenue, Bronx, New York 10461, United States
| | - Julia C. Frei
- Department
of Biochemistry, Albert Einstein College of Medicine, 1300 Morris
Park Avenue, Bronx, New York 10461, United States
| | - Jonathan R. Lai
- Department
of Biochemistry, Albert Einstein College of Medicine, 1300 Morris
Park Avenue, Bronx, New York 10461, United States
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252
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Abstract
Ebola virus is an enveloped virus with filamentous structure and causes a severe hemorrhagic fever in human and nonhuman primates. Host cell entry is the first essential step in the viral life cycle, which has been extensively studied as one of the therapeutic targets. A virus factor of cell entry is a surface glycoprotein (GP), which is an only essential viral protein in the step, as well as the unique particle structure. The virus also interacts with a lot of host factors to successfully enter host cells. Ebola virus at first binds to cell surface proteins and internalizes into cells, followed by trafficking through endosomal vesicles to intracellular acidic compartments. There, host proteases process GPs, which can interact with an intracellular receptor. Then, under an appropriate circumstance, viral and endosomal membranes are fused, which is enhanced by major structural changes of GPs, to complete host cell entry. Recently the basic research of Ebola virus infection mechanism has markedly progressed, largely contributed by identification of host factors and detailed structural analyses of GPs. This article highlights the mechanism of Ebola virus host cell entry, including recent findings.
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253
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Fujimori T, Grabiec AM, Kaur M, Bell TJ, Fujino N, Cook PC, Svedberg FR, MacDonald AS, Maciewicz RA, Singh D, Hussell T. The Axl receptor tyrosine kinase is a discriminator of macrophage function in the inflamed lung. Mucosal Immunol 2015; 8:1021-1030. [PMID: 25603826 PMCID: PMC4430298 DOI: 10.1038/mi.2014.129] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 12/01/2014] [Indexed: 02/04/2023]
Abstract
Much of the biology surrounding macrophage functional specificity has arisen through examining inflammation-induced polarizing signals, but this also occurs in homeostasis, requiring tissue-specific environmental triggers that influence macrophage phenotype and function. The TAM receptor family of receptor tyrosine kinases (Tyro3, Axl and MerTK) mediates the non-inflammatory removal of apoptotic cells by phagocytes through the bridging phosphatidylserine-binding molecules growth arrest-specific 6 (Gas6) or Protein S. We show that one such TAM receptor (Axl) is exclusively expressed on mouse airway macrophages, but not interstitial macrophages and other lung leukocytes, under homeostatic conditions and is constitutively ligated to Gas6. Axl expression is potently induced by granulocyte-macrophage colony-stimulating factor expressed in the healthy and inflamed airway, and by type I interferon or Toll-like receptor-3 stimulation on human and mouse macrophages, indicating potential involvement of Axl in apoptotic cell removal under inflammatory conditions. Indeed, an absence of Axl does not cause sterile inflammation in health, but leads to exaggerated lung inflammatory disease upon influenza infection. These data imply that Axl allows specific identification of airway macrophages, and that its expression is critical for macrophage functional compartmentalization in the airspaces or lung interstitium. We propose that this may be a critical feature to prevent excessive inflammation because of secondary necrosis of apoptotic cells that have not been cleared by efferocytosis.
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Affiliation(s)
- T Fujimori
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - A M Grabiec
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - M Kaur
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK ,grid.462482.e0000 0004 0417 0074University of Manchester NIHR Translational Research Facility, Manchester Academic Health Science Centre, University Hospital of South Manchester Foundation Trust, Manchester, UK
| | - T J Bell
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - N Fujino
- grid.418151.80000 0001 1519 6403AstraZeneca R&D Mölndal, Mölndal, Sweden
| | - P C Cook
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - F R Svedberg
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - A S MacDonald
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
| | - R A Maciewicz
- grid.418151.80000 0001 1519 6403AstraZeneca R&D Mölndal, Mölndal, Sweden
| | - D Singh
- grid.462482.e0000 0004 0417 0074University of Manchester NIHR Translational Research Facility, Manchester Academic Health Science Centre, University Hospital of South Manchester Foundation Trust, Manchester, UK
| | - T Hussell
- grid.5379.80000000121662407Manchester Collaborative Centre for Inflammation Research, Manchester University, Core Technology Facility, Manchester, UK
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254
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Cruz-Oliveira C, Freire JM, Conceição TM, Higa LM, Castanho MARB, Da Poian AT. Receptors and routes of dengue virus entry into the host cells. FEMS Microbiol Rev 2014; 39:155-70. [PMID: 25725010 DOI: 10.1093/femsre/fuu004] [Citation(s) in RCA: 230] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Dengue is the most prevalent arthropod-borne viral disease, caused by dengue virus, a member of the Flaviviridae family. Its worldwide incidence is now a major health problem, with 2.5 billion people living in risk areas. In this review, we integrate the structural rearrangements of each viral protein and their functions in all the steps of virus entry into the host cells. We describe in detail the putative receptors and attachment factors in mammalian and mosquito cells, and the recognition of viral immunocomplexes via Fcγ receptor in immune cells. We also discuss that virus internalization might occur through distinct entry pathways, including clathrin-mediated or non-classical clathrin-independent endocytosis, depending on the host cell and virus serotype or strain. The implications of viral maturation in virus entry are also explored. Finally, we discuss the mechanisms of viral genome access to the cytoplasm. This includes the role of low pH-induced conformational changes in the envelope protein that mediate membrane fusion, and original insights raised by our recent work that supports the hypothesis that capsid protein would also be an active player in this process, acting on viral genome translocation into the cytoplasm.
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Affiliation(s)
- Christine Cruz-Oliveira
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902, Brazil
| | - João Miguel Freire
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisbon, Portugal
| | - Thaís M Conceição
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902, Brazil
| | - Luiza M Higa
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902, Brazil
| | - Miguel A R B Castanho
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisbon, Portugal
| | - Andrea T Da Poian
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-902, Brazil
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255
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Cerny D, Haniffa M, Shin A, Bigliardi P, Tan BK, Lee B, Poidinger M, Tan EY, Ginhoux F, Fink K. Selective susceptibility of human skin antigen presenting cells to productive dengue virus infection. PLoS Pathog 2014; 10:e1004548. [PMID: 25474532 PMCID: PMC4256468 DOI: 10.1371/journal.ppat.1004548] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 11/01/2014] [Indexed: 12/11/2022] Open
Abstract
Dengue is a growing global concern with 390 million people infected each year. Dengue virus (DENV) is transmitted by mosquitoes, thus host cells in the skin are the first point of contact with the virus. Human skin contains several populations of antigen-presenting cells which could drive the immune response to DENV in vivo: epidermal Langerhans cells (LCs), three populations of dermal dendritic cells (DCs), and macrophages. Using samples of normal human skin we detected productive infection of CD14+ and CD1c+ DCs, LCs and dermal macrophages, which was independent of DC-SIGN expression. LCs produced the highest viral titers and were less sensitive to IFN-β. Nanostring gene expression data showed significant up-regulation of IFN-β, STAT-1 and CCL5 upon viral exposure in susceptible DC populations. In mice infected intra-dermally with DENV we detected parallel populations of infected DCs originating from the dermis and migrating to the skin-draining lymph nodes. Therefore dermal DCs may simultaneously facilitate systemic spread of DENV and initiate the adaptive anti-viral immune response. Dengue virus (DENV) is transmitted by mosquitoes with skin as point of entry for the virus. Here, we investigated DENV infection in primary human skin cells and their initial immune response. Using skin from normal human donors for infection with DENV in vitro we identified antigen-presenting cells (APCs) as main targets of DENV. Further analysis showed that only distinct subsets of dendritic cells (DCs) and macrophages were infected and efficiently produced viral progeny. Langerhans cells were most susceptible to infection despite lacking DC-SIGN, a previously described DENV receptor. Infection of the other DC subsets and macrophages was also independent of DC-SIGN expression. Genes of the interferon pathway and CCL5, a chemokine attracting immune cells to sites of inflammation, were highly up-regulated in the infected DC subsets. Using a mouse infection model, we showed that murine dermal DCs were also susceptible to DENV and migrated to draining lymph nodes. At the same time infiltrating monocytes differentiated into monocyte-derived cells at the site of infection and became an additional target for DENV in vivo. These data demonstrate that DENV differentially infects and activates primary human skin APCs and that infected cell types individually contribute to inflammation and the adaptive response.
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Affiliation(s)
- Daniela Cerny
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
- School of Biological Sciences, Nanyang Technological University, Singapore
| | - Muzlifah Haniffa
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Amanda Shin
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
| | - Paul Bigliardi
- Institute of Molecular Biology, Agency for Science, Technology and Research, Singapore
- Division of Rheumatology, University Medicine Cluster, National University Health System, Singapore
| | - Bien Keem Tan
- Department of Plastic Surgery, Singapore General Hospital, Singapore
| | - Bernett Lee
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
| | - Michael Poidinger
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
| | - Ern Yu Tan
- Department of General Surgery, Tan Tock Seng Hospital, Singapore
| | - Florent Ginhoux
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
| | - Katja Fink
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore
- * E-mail:
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256
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Martinez FO, Gordon S. The evolution of our understanding of macrophages and translation of findings toward the clinic. Expert Rev Clin Immunol 2014; 11:5-13. [PMID: 25434688 DOI: 10.1586/1744666x.2015.985658] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
'There is at bottom only one genuinely scientific treatment for all diseases, and that is to stimulate the phagocytes,' so declaimed Sir Ralph Bloomfield Bonington in The Doctor's Dilemma, Act 1, by George Bernard Shaw (1906). More often nowadays, the need is to calm the phagocytes, given their role in inflammation and tissue damage. In spite of the growth of cellular and molecular information gained from studies in macrophage cell culture, mouse models and, to a lesser extent, human investigations, and the importance of macrophages in pathogenesis in a wide range of chronic disease processes, there is still a substantial shortfall in terms of clinical applications. In this review, we summarize concepts derived from macrophage studies and suggest possible properties suitable for diagnosis, prognosis and selective targeting of macrophage pathogenic functions.
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Affiliation(s)
- Fernando O Martinez
- Botnar Research Centre, University of Oxford, Windmill Road, Oxford, OX3 7LD, UK
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257
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Kuroda M, Fujikura D, Noyori O, Kajihara M, Maruyama J, Miyamoto H, Yoshida R, Takada A. A polymorphism of the TIM-1 IgV domain: implications for the susceptibility to filovirus infection. Biochem Biophys Res Commun 2014; 455:223-8. [PMID: 25449273 PMCID: PMC7124303 DOI: 10.1016/j.bbrc.2014.10.144] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Accepted: 10/29/2014] [Indexed: 01/17/2023]
Abstract
TIM-1 genes were compared among African green monkey kidney cell lines. Vero E6-derived TIM-1 has increased potential to promote filovirus entry. The IgV domain is primarily involved in TIM-1-mediated filovirus entry. A single amino acid in the IgV domain is crucial for the increased ability of TIM-1. TIM-1 polymorphism may affect the cell susceptibility to filovirus infection.
Filoviruses, including Ebola and Marburg viruses, cause severe hemorrhagic fever in humans and nonhuman primates with mortality rates of up to 90%. Human T-cell immunoglobulin and mucin domain 1 (TIM-1) is one of the host proteins that have been shown to promote filovirus entry into cells. In this study, we cloned TIM-1 genes from three different African green monkey kidney cell lines (Vero E6, COS-1, and BSC-1) and found that TIM-1 of Vero E6 had a 23-amino acid deletion and 6 amino acid substitutions compared with those of COS-1 and BSC-1. Interestingly, Vero E6 TIM-1 had a greater ability to promote the infectivity of vesicular stomatitis viruses pseudotyped with filovirus glycoproteins than COS-1-derived TIM-1. We further found that the increased ability of Vero E6 TIM-1 to promote virus infectivity was most likely due to a single amino acid difference between these TIM-1s. These results suggest that a polymorphism of the TIM-1 molecules is one of the factors that influence cell susceptibility to filovirus infection, providing a new insight into the molecular basis for the filovirus host range.
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Affiliation(s)
- Makoto Kuroda
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Daisuke Fujikura
- Division of Infection and Immunity, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Osamu Noyori
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Masahiro Kajihara
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Junki Maruyama
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Hiroko Miyamoto
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Reiko Yoshida
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan
| | - Ayato Takada
- Division of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 001-0020, Japan; Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo 001-0020, Japan; School of Veterinary Medicine, The University of Zambia, P.O. Box 32379, Lusaka, Zambia.
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258
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Misasi J, Sullivan NJ. Camouflage and misdirection: the full-on assault of ebola virus disease. Cell 2014; 159:477-86. [PMID: 25417101 DOI: 10.1016/j.cell.2014.10.006] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Indexed: 01/30/2023]
Abstract
Ebolaviruses cause a severe hemorrhagic fever syndrome that is rapidly fatal to humans and nonhuman primates. Ebola protein interactions with host cellular proteins disrupt type I and type II interferon responses, RNAi antiviral responses, antigen presentation, T-cell-dependent B cell responses, humoral antibodies, and cell-mediated immunity. This multifaceted approach to evasion and suppression of innate and adaptive immune responses in their target hosts leads to the severe immune dysregulation and "cytokine storm" that is characteristic of fatal ebolavirus infection. Here, we highlight some of the processes by which Ebola interacts with its mammalian hosts to evade antiviral defenses.
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Affiliation(s)
- John Misasi
- Boston Children's Hospital, Department of Medicine, Division of Infectious Diseases, Boston, MA 02115, USA
| | - Nancy J Sullivan
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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259
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Abstract
TIM proteins are known to promote viral entry into host cells. Unexpectedly, a recent study has shown that TIM proteins also inhibit HIV-1 release from the host cell by directly binding to phosphatidylserine exposed on the virus surface, providing details on a new role of TIM proteins in HIV replication.
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Affiliation(s)
- Jiri Vlach
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Jamil S Saad
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294.
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260
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Moller-Tank S, Maury W. Phosphatidylserine receptors: enhancers of enveloped virus entry and infection. Virology 2014; 468-470:565-580. [PMID: 25277499 PMCID: PMC4252826 DOI: 10.1016/j.virol.2014.09.009] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Revised: 07/15/2014] [Accepted: 09/08/2014] [Indexed: 12/23/2022]
Abstract
A variety of both RNA and DNA viruses envelop their capsids in a lipid bilayer. One of the more recently appreciated benefits this envelope is incorporation of phosphatidylserine (PtdSer). Surface exposure of PtdSer disguises viruses as apoptotic bodies; tricking cells into engulfing virions. This mechanism is termed apoptotic mimicry. Several PtdSer receptors have been identified to enhance virus entry and we have termed this group of proteins PtdSer-mediated virus entry enhancing receptors or PVEERs. These receptors enhance entry of a range of enveloped viruses. Internalization of virions by PVEERs provides a broad mechanism of entry with little investment by the virus itself. PVEERs may allow some viruses to attach to cells, thereby making viral glycoprotein/cellular receptor interactions more probable. Alternatively, other viruses may rely entirely on PVEERs for internalization into endosomes. This review provides an overview of PtdSer receptors that serve as PVEERs and the biology behind virion/PVEER interaction. Phosphatidylserine (PtdSer) receptors can mediate entry of enveloped viruses. PtdSer is present on the outer leaflet of the virion envelope. PtdSer receptors are expressed on a variety of primary cells and cell lines. Characteristics of PtdSer receptors that mediate virus entry are defined.
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Affiliation(s)
- Sven Moller-Tank
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
| | - Wendy Maury
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA.
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261
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Bird SW, Kirkegaard K, Agbandje-McKenna M, Freed EO. The ins and outs of viral infection: keystone meeting review. Viruses 2014; 6:3652-62. [PMID: 25256395 PMCID: PMC4189043 DOI: 10.3390/v6093652] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2014] [Revised: 09/23/2014] [Accepted: 09/23/2014] [Indexed: 12/14/2022] Open
Abstract
Newly observed mechanisms for viral entry, assembly, and exit are challenging our current understanding of the replication cycle of different viruses. To address and better understand these mechanisms, a Keystone Symposium was organized in the snowy mountains of Colorado (“The Ins and Outs of Viral Infection: Entry, Assembly, Exit, and Spread”; 30 March–4 April 2014, Beaver Run Resort, Breckenridge, Colorado, organized by Karla Kirkegaard, Mavis Agbandje-McKenna, and Eric O. Freed). The meeting served to bring together cell biologists, structural biologists, geneticists, and scientists expert in viral pathogenesis to discuss emerging mechanisms of viral ins and outs. The conference was organized around different phases of the viral replication cycle, including cell entry, viral assembly and post-assembly maturation, virus structure, cell exit, and virus spread. This review aims to highlight important topics and themes that emerged during the conference.
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Affiliation(s)
- Sara W Bird
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Karla Kirkegaard
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Mavis Agbandje-McKenna
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA.
| | - Eric O Freed
- Virus-Cell Interaction Section, HIV Drug Resistance Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA.
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262
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Mazzon M, Mercer J. Lipid interactions during virus entry and infection. Cell Microbiol 2014; 16:1493-502. [PMID: 25131438 PMCID: PMC4265854 DOI: 10.1111/cmi.12340] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Revised: 07/26/2014] [Accepted: 08/01/2014] [Indexed: 12/14/2022]
Abstract
For entry and infection viruses have developed numerous strategies to subjugate indispensable cellular factors and functions. Host cell lipids and cellular lipid synthesis machinery are no exception. Not only do viruses exploit existing lipid signalling and modifications for virus entry and trafficking, they also reprogram lipid synthesis, metabolism, and compartmentalization for assembly and egress. Here we review these various concepts and highlight recent progress in understanding viral interactions with host cell lipids during entry and assembly.
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Affiliation(s)
- Michela Mazzon
- MRC-Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK
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263
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Abstract
Accumulating evidence indicates that T-cell immunoglobulin (Ig) and mucin domain (TIM) proteins play critical roles in viral infections. Herein, we report that the TIM-family proteins strongly inhibit HIV-1 release, resulting in diminished viral production and replication. Expression of TIM-1 causes HIV-1 Gag and mature viral particles to accumulate on the plasma membrane. Mutation of the phosphatidylserine (PS) binding sites of TIM-1 abolishes its ability to block HIV-1 release. TIM-1, but to a much lesser extent PS-binding deficient mutants, induces PS flipping onto the cell surface; TIM-1 is also found to be incorporated into HIV-1 virions. Importantly, TIM-1 inhibits HIV-1 replication in CD4-positive Jurkat cells, despite its capability of up-regulating CD4 and promoting HIV-1 entry. In addition to TIM-1, TIM-3 and TIM-4 also block the release of HIV-1, as well as that of murine leukemia virus (MLV) and Ebola virus (EBOV); knockdown of TIM-3 in differentiated monocyte-derived macrophages (MDMs) enhances HIV-1 production. The inhibitory effects of TIM-family proteins on virus release are extended to other PS receptors, such as Axl and RAGE. Overall, our study uncovers a novel ability of TIM-family proteins to block the release of HIV-1 and other viruses by interaction with virion- and cell-associated PS. Our work provides new insights into a virus-cell interaction that is mediated by TIMs and PS receptors.
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264
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Tsou WI, Nguyen KQN, Calarese DA, Garforth SJ, Antes AL, Smirnov SV, Almo SC, Birge RB, Kotenko SV. Receptor tyrosine kinases, TYRO3, AXL, and MER, demonstrate distinct patterns and complex regulation of ligand-induced activation. J Biol Chem 2014; 289:25750-63. [PMID: 25074926 DOI: 10.1074/jbc.m114.569020] [Citation(s) in RCA: 183] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
TYRO3, AXL, and MER receptors (TAMs) are three homologous type I receptor-tyrosine kinases that are activated by endogenous ligands, protein S (PROS1) and growth arrest-specific gene 6 (GAS6). These ligands can either activate TAMs as soluble factors, or, in turn, opsonize phosphatidylserine (PS) on apoptotic cells (ACs) and serve as bridging molecules between ACs and TAMs. Abnormal expression and activation of TAMs have been implicated in promoting proliferation and survival of cancer cells, as well as in suppressing anti-tumor immunity. Despite the fact that TAM receptors share significant similarity, little is known about the specificity of interaction between TAM receptors and their ligands, particularly in the context of ACs, and about the functional diversity of TAM receptors. To study ligand-mediated activation of TAMs, we generated a series of reporter cell lines expressing chimeric TAM receptors. Using this system, we found that each TAM receptor has a unique pattern of interaction with and activation by GAS6 and PROS1, which is also differentially affected by the presence of ACs, PS-containing lipid vesicles and enveloped virus. We also demonstrated that γ-carboxylation of ligands is essential for the full activation of TAMs and that soluble immunoglobulin-like TAM domains act as specific ligand antagonists. These studies demonstrate that, despite their similarity, TYRO3, AXL, and MER are likely to perform distinct functions in both immunoregulation and the recognition and removal of ACs.
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Affiliation(s)
- Wen-I Tsou
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and Center for Immunity and Inflammation, New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey 07103, and
| | - Khanh-Quynh N Nguyen
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and
| | | | | | - Anita L Antes
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and
| | - Sergey V Smirnov
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and Center for Immunity and Inflammation, New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey 07103, and
| | - Steve C Almo
- the Department of Biochemistry and Albert Einstein Cancer Center, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461
| | - Raymond B Birge
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and
| | - Sergei V Kotenko
- From the Department of Biochemistry and Molecular Biology, University Hospital Cancer Center and Center for Immunity and Inflammation, New Jersey Medical School, Rutgers Biomedical and Health Sciences, Newark, New Jersey 07103, and
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265
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Feng Z, Hirai-Yuki A, McKnight KL, Lemon SM. Naked Viruses That Aren't Always Naked: Quasi-Enveloped Agents of Acute Hepatitis. Annu Rev Virol 2014; 1:539-60. [PMID: 26958733 DOI: 10.1146/annurev-virology-031413-085359] [Citation(s) in RCA: 115] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Historically, viruses were considered to be either enveloped or nonenveloped. However, recent work on hepatitis A virus and hepatitis E virus challenges this long-held tenet. Whereas these human pathogens are shed in feces as naked nonenveloped virions, recent studies indicate that both circulate in the blood completely masked in membranes during acute infection. These membrane-wrapped virions are as infectious as their naked counterparts, although they do not express a virally encoded protein on their surface, thus distinguishing them from conventional enveloped viruses. The absence of a viral fusion protein implies that these quasi-enveloped virions have unique mechanisms for entry into cells. Like true enveloped viruses, however, these phylogenetically distinct viruses usurp components of the host ESCRT system to hijack host cell membranes and noncytolytically exit infected cells. The membrane protects these viruses from neutralizing antibodies, facilitating dissemination within the host, whereas nonenveloped virions shed in feces are stable in the environment, allowing for epidemic transmission.
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Affiliation(s)
- Zongdi Feng
- Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292;
| | - Asuka Hirai-Yuki
- Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292;
| | - Kevin L McKnight
- Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292;
| | - Stanley M Lemon
- Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292;
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266
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Stahelin RV. Membrane binding and bending in Ebola VP40 assembly and egress. Front Microbiol 2014; 5:300. [PMID: 24995005 PMCID: PMC4061899 DOI: 10.3389/fmicb.2014.00300] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 05/31/2014] [Indexed: 11/13/2022] Open
Abstract
Lipid-enveloped viruses contain a lipid bilayer coat that protects their genome and helps to facilitate entry into the host cell. Filoviruses are lipid-enveloped viruses that have up to 90% clinical fatality and include Marbug (MARV) and Ebola (EBOV). These pleomorphic filamentous viruses enter the host cell through their membrane-embedded glycoprotein and then replicate using just seven genes encoded in their negative-sense RNA genome. EBOV budding occurs from the inner leaflet of the plasma membrane (PM) and is driven by the matrix protein VP40, which is the most abundantly expressed protein of the virus. VP40 expressed in mammalian cells alone can trigger budding of filamentous virus-like particles (VLPs) that are nearly indistinguishable from authentic EBOV. VP40, such as matrix proteins from other viruses, has been shown to bind anionic lipid membranes. However, how VP40 selectively interacts with the inner leaflet of the PM and assembles into a filamentous lipid enveloped particle is mostly unknown. This article describes what is known regarding VP40 membrane interactions and what answers will fill the gaps.
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Affiliation(s)
- Robert V Stahelin
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-South Bend South Bend, IN, USA ; Department of Chemistry and Biochemistry, Eck Institute for Global Health, University of Notre Dame Notre Dame, IN, USA
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267
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Abstract
UNLABELLED At least five New World (NW) arenaviruses cause hemorrhagic fevers in South America. These pathogenic clade B viruses, as well as nonpathogenic arenaviruses of the same clade, use transferrin receptor 1 (TfR1) of their host species to enter cells. Pathogenic viruses are distinguished from closely related nonpathogenic ones by their additional ability to utilize human TfR1 (hTfR1). Here, we investigate the receptor usage of North American arenaviruses, whose entry proteins share greatest similarity with those of the clade B viruses. We show that all six North American arenaviruses investigated utilize host species TfR1 orthologs and present evidence consistent with arenavirus-mediated selection pressure on the TfR1 of the North American arenavirus host species. Notably, one of these viruses, AV96010151, closely related to the prototype Whitewater Arroyo virus (WWAV), entered cells using hTfR1, consistent with a role for a WWAV-like virus in three fatal human infections whose causative agent has not been identified. In addition, modest changes were sufficient to convert hTfR1 into a functional receptor for most of these viruses, suggesting that a minor alteration in virus entry protein may allow these viruses to use hTfR1. Our data establish TfR1 as a cellular receptor for North American arenaviruses, highlight an "arms race" between these viruses and their host species, support the association of North American arenavirus with fatal human infections, and suggest that these viruses have a higher potential to emerge and cause human diseases than has previously been appreciated. IMPORTANCE hTfR1 use is a key determinant for a NW arenavirus to cause hemorrhagic fevers in humans. All known pathogenic NW arenaviruses are transmitted in South America by their host rodents. North American arenaviruses are generally considered nonpathogenic, but some of these viruses have been tentatively implicated in human fatalities. We show that these North American arenaviruses use the TfR1 orthologs of their rodent host species and identify TfR1 polymorphisms suggesting an ongoing "arms race" between these viruses and their hosts. We also show that a close relative of a North American arenavirus suggested to have caused human fatalities, the Whitewater Arroyo species complex virus AV96010151, uses human TfR1. Moreover, we present data that imply that modest changes in other North American arenaviruses might allow these viruses to infect humans. Collectively, our data suggest that North American arenaviruses have a higher potential to cause human disease than previously assumed.
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268
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Abstract
UNLABELLED T-cell immunoglobulin and mucin domain 1 (TIM-1) and other TIM family members were recently identified as phosphatidylserine (PtdSer)-mediated virus entry-enhancing receptors (PVEERs). These proteins enhance entry of Ebola virus (EBOV) and other viruses by binding PtdSer on the viral envelope, concentrating virus on the cell surface, and promoting subsequent internalization. The PtdSer-binding activity of the immunoglobulin-like variable (IgV) domain is essential for both virus binding and internalization by TIM-1. However, TIM-3, whose IgV domain also binds PtdSer, does not effectively enhance virus entry, indicating that other domains of TIM proteins are functionally important. Here, we investigate the domains supporting enhancement of enveloped virus entry, thereby defining the features necessary for a functional PVEER. Using a variety of chimeras and deletion mutants, we found that in addition to a functional PtdSer-binding domain PVEERs require a stalk domain of sufficient length, containing sequences that promote an extended structure. Neither the cytoplasmic nor the transmembrane domain of TIM-1 is essential for enhancing virus entry, provided the protein is still plasma membrane bound. Based on these defined characteristics, we generated a mimic lacking TIM sequences and composed of annexin V, the mucin-like domain of α-dystroglycan, and a glycophosphatidylinositol anchor that functioned as a PVEER to enhance transduction of virions displaying Ebola, Chikungunya, Ross River, or Sindbis virus glycoproteins. This identification of the key features necessary for PtdSer-mediated enhancement of virus entry provides a basis for more effective recognition of unknown PVEERs. IMPORTANCE T-cell immunoglobulin and mucin domain 1 (TIM-1) and other TIM family members are recently identified phosphatidylserine (PtdSer)-mediated virus entry-enhancing receptors (PVEERs). These proteins enhance virus entry by binding the phospholipid, PtdSer, present on the viral membrane. While it is known that the PtdSer binding is essential for the PVEER function of TIM-1, TIM-3 shares this binding activity but does not enhance virus entry. No comprehensive studies have been done to characterize the other domains of TIM-1. In this study, using a variety of chimeric proteins and deletion mutants, we define the features necessary for a functional PVEER. With these features in mind, we generated a TIM-1 mimic using functionally similar domains from other proteins. This mimic, like TIM-1, effectively enhanced transduction. These studies provide insight into the key features necessary for PVEERs and will allow for more effective identification of unknown PVEERs.
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269
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Primary human macrophages serve as vehicles for vaccinia virus replication and dissemination. J Virol 2014; 88:6819-31. [PMID: 24696488 DOI: 10.1128/jvi.03726-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
UNLABELLED Human monocytic and professional antigen-presenting cells have been reported only to exhibit abortive infections with vaccinia virus (VACV). We found that monocyte-derived macrophages (MDMs), including granulocyte macrophage colony-stimulating factor (GM-CSF)-polarized M1 and macrophage colony-stimulating factor (M-CSF)-polarized M2, but not human AB serum-derived cells, were permissive to VACV replication. The titers of infectious virions in both cell-free supernatants and cellular lysates of infected M1 and M2 markedly increased in a time-dependent manner. The majority of virions produced in permissive MDMs were extracellular enveloped virions (EEV), a secreted form of VACV associated with long-range virus dissemination, and were mainly found in the culture supernatant. Infected MDMs formed VACV factories, actin tails, virion-associated branching structures, and cell linkages, indicating that MDMs are able to initiate de novo synthesis of viral DNA and promote virus release. VACV replication was sensitive to inhibitors against the Akt and Erk1/2 pathways that can be activated by VACV infection and M-CSF stimulation. Classical activation of MDMs by lipopolysaccharide (LPS) plus gamma interferon (IFN-γ) stimulation caused no effect on VACV replication, while alternative activation of MDMs by interleukin-10 (IL-10) or LPS-plus-IL-1β treatment significantly decreased VACV production. The IL-10-mediated suppression of VACV replication was largely due to Stat3 activation, as a Stat3 inhibitor restored virus production to levels observed without IL-10 stimulation. In conclusion, our data demonstrate that primary human macrophages are permissive to VACV replication. After infection, these cells produce EEV for long-range dissemination and also form structures associated with virions which may contribute to cell-cell spread. IMPORTANCE Our results provide critical information to the burgeoning fields of cancer-killing (oncolytic) virus therapy with vaccinia virus (VACV). One type of macrophage (M2) is considered a common presence in tumors and is associated with poor prognosis. Our results demonstrate a preference for VACV replication in M2 macrophages and could assist in designing treatments and engineering poxviruses with special considerations for their effect on M2 macrophage-containing tumors. Additionally, this work highlights the importance of macrophages in the field of vaccine development using poxviruses as vectors. The understanding of the dynamics of poxvirus-infected foci is central in understanding the effectiveness of the immune response to poxvirus-mediated vaccine vectors. Monocytic cells have been found to be an important part of VACV skin lesions in mice in controlling the infection as well as mediating virus transport out of infected foci.
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270
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Shibata T, Habiel DM, Coelho AL, Kunkel SL, Lukacs NW, Hogaboam CM. Axl receptor blockade ameliorates pulmonary pathology resulting from primary viral infection and viral exacerbation of asthma. THE JOURNAL OF IMMUNOLOGY 2014; 192:3569-81. [PMID: 24659691 DOI: 10.4049/jimmunol.1302766] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Viruses use Tyro3, Axl, and Mertk (TAM) receptor tyrosine kinases to infect and modulate the immune properties of various cell types, which led us to investigate whether TAM receptor activation affected primary viral infection and viral exacerbation of asthma in experimental models. In these lung-specific models, we observed that Axl was the most abundantly induced TAM receptor protein. During primary respiratory syncytial virus (RSV) infection, anti-Axl mAb treatment significantly increased the number of IFN-γ-producing T cells and NK cells and significantly suppressed RSV replication and whole lung levels of IL-4 and IL-13. Intrapulmonary H1N1 infection induced lethal pulmonary inflammation, but anti-Axl mAb treatment of infected mice significantly increased the number of IFN-β-producing macrophages and dendritic cells and significantly suppressed neutrophil infiltration. Consequently, the lethal effect of H1N1 infection in this model was significantly reduced in the mAb-treated group compared with the IgG control-treated group. Targeting Axl also inhibited airway hyperresponsiveness, IL-4 and IL-13 production, and goblet cell metaplasia in an Aspergillus fumigatus-induced asthma model. Finally, infection of mice with RSV during fungal asthma significantly exacerbated airway inflammation, goblet cell metaplasia, and airway remodeling, but all of these features in this viral exacerbation model were ameliorated by anti-Axl mAb treatment. Taken together, these results demonstrate that Axl modulates the pulmonary immune response during viral and/or allergic pathology, and they also suggest that targeting this TAM receptor might provide a novel therapeutic approach in these infectious diseases.
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Affiliation(s)
- Takehiko Shibata
- Immunology Program, Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109
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271
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Bhattacharyya S, Zagórska A, Lew ED, Shrestha B, Rothlin CV, Naughton J, Diamond MS, Lemke G, Young JAT. Enveloped viruses disable innate immune responses in dendritic cells by direct activation of TAM receptors. Cell Host Microbe 2014; 14:136-47. [PMID: 23954153 DOI: 10.1016/j.chom.2013.07.005] [Citation(s) in RCA: 168] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 05/21/2013] [Accepted: 06/14/2013] [Indexed: 01/21/2023]
Abstract
Upon activation by the ligands Gas6 and Protein S, Tyro3/Axl/Mer (TAM) receptor tyrosine kinases promote phagocytic clearance of apoptotic cells and downregulate immune responses initiated by Toll-like receptors and type I interferons (IFNs). Many enveloped viruses display the phospholipid phosphatidylserine on their membranes, through which they bind Gas6 and Protein S and engage TAM receptors. We find that ligand-coated viruses activate TAM receptors on dendritic cells (DCs), dampen type I IFN signaling, and thereby evade host immunity and promote infection. Upon virus challenge, TAM-deficient DCs display type I IFN responses that are elevated in comparison to wild-type cells. As a consequence, TAM-deficient DCs are relatively resistant to infection by flaviviruses and pseudotyped retroviruses, but infection can be restored with neutralizing type I IFN antibodies. Correspondingly, a TAM kinase inhibitor antagonizes the infection of wild-type DCs. Thus, TAM receptors are engaged by viruses in order to attenuate type I IFN signaling and represent potential therapeutic targets.
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Affiliation(s)
- Suchita Bhattacharyya
- Nomis Center for Immunobiology and Microbial Pathogenesis, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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272
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Abstract
UNLABELLED We recently demonstrated that a soluble protein, Gas6, can facilitate viral entry by bridging viral envelope phosphatidylserine to Axl, a receptor tyrosine kinase expressed on target cells. The interaction between phosphatidylserine, Gas6, and Axl was originally shown to be a molecular mechanism through which phagocytes recognize phosphatidylserine exposed on dead cells. Since our initial report, several groups have confirmed that Axl/Gas6, as well as other phosphatidylserine receptors, facilitate entry of dengue, West Nile, and Ebola viruses. Virus binding by viral envelope phosphatidylserine is now a viral entry mechanism generalized to many families of viruses. In addition to Axl/Gas6, various molecules are known to recognize phosphatidylserine; however, the effects of these molecules on virus binding and entry have not been comprehensively evaluated and compared. In this study, we examined most of the known human phosphatidylserine-recognizing molecules, including MFG-E8, TIM-1, -3, and -4, CD300a, BAI1, and stabilin-1 and -2, for their abilities to facilitate virus binding and infection. Using pseudotyped lentiviral vectors, we found that a soluble phosphatidylserine-binding protein, MFG-E8, enhances transduction. Cell surface receptors TIM-1 and -4 also enhance virus binding/transduction. The extent of enhancement by these molecules varies, depending on the type of pseudotyping envelope proteins. Mutated MFG-E8, which binds viral envelope phosphatidylserine without bridging virus to cells, but, surprisingly, not annexin V, which has been used to block phagocytosis of dead cells by concealing phosphatidylserine, efficiently blocks these phosphatidylserine-dependent viral entry mechanisms. These results provide insight into understanding the role of viral envelope phosphatidylserine in viral infection. IMPORTANCE Envelope phosphatidylserine has previously been shown to be important for replication of various envelope viruses, but details of this mechanism(s) were unclear. We were the first to report that a bifunctional serum protein, Gas6, bridges envelope phosphatidylserine to a cell surface receptor, Axl. Recent studies demonstrated that many envelope viruses, including vaccinia, dengue, West Nile, and Ebola viruses, utilize Axl/Gas6 to facilitate their entry, suggesting that the phosphatidylserine-mediated viral entry mechanism can be shared by various enveloped viruses. In addition to Axl/Gas6, various molecules are known to recognize phosphatidylserine; however, the effects of these molecules on virus binding and entry have not been comprehensively evaluated and compared. In this study, we examined most human phosphatidylserine-recognizing molecules for their abilities to facilitate viral infection. The results provide insights into the role(s) of envelope phosphatidylserine in viral infection, which can be applicable to the development of novel antiviral reagents that block phosphatidylserine-mediated viral entry.
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273
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Abstract
UNLABELLED Ebola virus (EBOV) entry requires the virion surface-associated glycoprotein (GP) that is composed of a trimer of heterodimers (GP1/GP2). The GP1 subunit contains two heavily glycosylated domains, the glycan cap and the mucin-like domain (MLD). The glycan cap contains only N-linked glycans, whereas the MLD contains both N- and O-linked glycans. Site-directed mutagenesis was performed on EBOV GP1 to systematically disrupt N-linked glycan sites to gain an understanding of their role in GP structure and function. All 15 N-glycosylation sites of EBOV GP1 could be removed without compromising the expression of GP. The loss of these 15 glycosylation sites significantly enhanced pseudovirion transduction in Vero cells, which correlated with an increase in protease sensitivity. Interestingly, exposing the receptor-binding domain (RBD) by removing the glycan shield did not allow interaction with the endosomal receptor, NPC1, indicating that the glycan cap/MLD domains mask RBD residues required for binding. The effects of the loss of GP1 N-linked glycans on Ca(2+)-dependent (C-type) lectin (CLEC)-dependent transduction were complex, and the effect was unique for each of the CLECs tested. Surprisingly, EBOV entry into murine peritoneal macrophages was independent of GP1 N-glycans, suggesting that CLEC-GP1 N-glycan interactions are not required for entry into this important primary cell. Finally, the removal of all GP1 N-glycans outside the MLD enhanced antiserum and antibody sensitivity. In total, our results provide evidence that the conserved N-linked glycans on the EBOV GP1 core protect GP from antibody neutralization despite the negative impact the glycans have on viral entry efficiency. IMPORTANCE Filovirus outbreaks occur sporadically throughout central Africa, causing high fatality rates among the general public and health care workers. These unpredictable hemorrhagic fever outbreaks are caused by multiple species of Ebola viruses, as well as Marburg virus. While filovirus vaccines and therapeutics are being developed, there are no licensed products. The sole viral envelope glycoprotein, which is a principal immunogenic target, contains a heavy shield of glycans surrounding the conserved receptor-binding domain. We find that disruption of this shield through targeted mutagenesis leads to an increase in cell entry, protease sensitivity, and antiserum/antibody sensitivity but is not sufficient to allow virion binding to the intracellular receptor NPC1. Therefore, our studies provide evidence that filoviruses maintain glycoprotein glycosylation to protect against proteases and antibody neutralization at the expense of efficient entry. Our results unveil interesting insights into the unique entry process of filoviruses and potential immune evasion tactics of the virus.
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274
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Flavivirus entry receptors: an update. Viruses 2013; 6:69-88. [PMID: 24381034 PMCID: PMC3917432 DOI: 10.3390/v6010069] [Citation(s) in RCA: 238] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 12/12/2013] [Accepted: 12/12/2013] [Indexed: 12/15/2022] Open
Abstract
Flaviviruses enter host cells by endocytosis initiated when the virus particles interact with cell surface receptors. The current model suggests that flaviviruses use at least two different sets of molecules for infectious entry: attachment factors that concentrate and/or recruit viruses on the cell surface and primary receptor(s) that bind to virions and direct them to the endocytic pathway. Here, we present the currently available knowledge regarding the flavivirus receptors described so far with specific attention to C-type lectin receptors and the phosphatidylserine receptors, T-cell immunoglobulin and mucin domain (TIM) and TYRO3, AXL and MER (TAM). Their role in flavivirus attachment and entry as well as their implication in the virus biology will be discussed in depth.
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275
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Replication cycle and molecular biology of the West Nile virus. Viruses 2013; 6:13-53. [PMID: 24378320 PMCID: PMC3917430 DOI: 10.3390/v6010013] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 12/12/2013] [Accepted: 12/12/2013] [Indexed: 12/27/2022] Open
Abstract
West Nile virus (WNV) is a member of the genus Flavivirus in the family Flaviviridae. Flaviviruses replicate in the cytoplasm of infected cells and modify the host cell environment. Although much has been learned about virion structure and virion-endosomal membrane fusion, the cell receptor(s) used have not been definitively identified and little is known about the early stages of the virus replication cycle. Members of the genus Flavivirus differ from members of the two other genera of the family by the lack of a genomic internal ribosomal entry sequence and the creation of invaginations in the ER membrane rather than double-membrane vesicles that are used as the sites of exponential genome synthesis. The WNV genome 3' and 5' sequences that form the long distance RNA-RNA interaction required for minus strand initiation have been identified and contact sites on the 5' RNA stem loop for NS5 have been mapped. Structures obtained for many of the viral proteins have provided information relevant to their functions. Viral nonstructural protein interactions are complex and some may occur only in infected cells. Although interactions between many cellular proteins and virus components have been identified, the functions of most of these interactions have not been delineated.
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276
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Abstract
Several arenaviruses, chiefly Lassa virus (LASV), cause hemorrhagic fever (HF) disease in humans and pose a great public health concern in the regions in which they are endemic. Moreover, evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen of clinical significance. The limited existing armamentarium to combat human-pathogenic arenaviruses underscores the importance of developing novel antiarenaviral drugs, a task that would be facilitated by the identification and characterization of virus-host cell factor interactions that contribute to the arenavirus life cycle. A genome-wide small interfering RNA (siRNA) screen identified sodium hydrogen exchanger 3 (NHE3) as required for efficient multiplication of LCMV in HeLa cells, but the mechanisms by which NHE activity contributed to the life cycle of LCMV remain unknown. Here we show that treatment with the NHE inhibitor 5-(N-ethyl-N-isopropyl) amiloride (EIPA) resulted in a robust inhibition of LCMV multiplication in both rodent (BHK-21) and human (A549) cells. EIPA-mediated inhibition was due not to interference with virus RNA replication, gene expression, or budding but rather to a blockade of virus cell entry. EIPA also inhibited cell entry mediated by the glycoproteins of the HF arenaviruses LASV and Junin virus (JUNV). Pharmacological and genetic studies revealed that cell entry of LCMV in A549 cells depended on actin remodeling and Pak1, suggesting a macropinocytosis-like cell entry pathway. Finally, zoniporide, an NHE inhibitor being explored as a therapeutic agent to treat myocardial infarction, inhibited LCMV propagation in culture cells. Our findings indicate that targeting NHEs could be a novel strategy to combat human-pathogenic arenaviruses.
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277
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Abstract
TAM receptors promote apoptotic cell uptake and function as inflammation suppressors. Many viruses mimic apoptotic cells, thus exploiting TAM receptors for attachment and entry. In this issue of Cell Host & Microbe, Bhattacharyya et al. show that TAM binding by enveloped viruses also induces receptor signaling to suppress cellular interferon responses.
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Affiliation(s)
- Sonja M Best
- Laboratory of Virology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840, USA.
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278
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Abstract
The cell surface receptor T cell immunoglobulin mucin domain 1 (TIM-1) dramatically enhances filovirus infection of epithelial cells. Here, we showed that key phosphatidylserine (PtdSer) binding residues of the TIM-1 IgV domain are critical for Ebola virus (EBOV) entry through direct interaction with PtdSer on the viral envelope. PtdSer liposomes but not phosphatidylcholine liposomes competed with TIM-1 for EBOV pseudovirion binding and transduction. Further, annexin V (AnxV) substituted for the TIM-1 IgV domain, supporting a PtdSer-dependent mechanism. Our findings suggest that TIM-1-dependent uptake of EBOV occurs by apoptotic mimicry. Additionally, TIM-1 enhanced infection of a wide range of enveloped viruses, including alphaviruses and a baculovirus. As further evidence of the critical role of enveloped-virion-associated PtdSer in TIM-1-mediated uptake, TIM-1 enhanced internalization of pseudovirions and virus-like proteins (VLPs) lacking a glycoprotein, providing evidence that TIM-1 and PtdSer-binding receptors can mediate virus uptake independent of a glycoprotein. These results provide evidence for a broad role of TIM-1 as a PtdSer-binding receptor that mediates enveloped-virus uptake. Utilization of PtdSer-binding receptors may explain the wide tropism of many of these viruses and provide new avenues for controlling their virulence.
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279
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Kim HY, Chang YJ, Chuang YT, Lee HH, Kasahara DI, Martin T, Hsu JT, Savage PB, Shore SA, Freeman GJ, Dekruyff RH, Umetsu DT. T-cell immunoglobulin and mucin domain 1 deficiency eliminates airway hyperreactivity triggered by the recognition of airway cell death. J Allergy Clin Immunol 2013; 132:414-25.e6. [PMID: 23672783 DOI: 10.1016/j.jaci.2013.03.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 03/21/2013] [Accepted: 03/25/2013] [Indexed: 10/26/2022]
Abstract
BACKGROUND Studies of asthma have been limited by a poor understanding of how nonallergic environmental exposures, such as air pollution and infection, are translated in the lung into inflammation and wheezing. OBJECTIVE Our goal was to understand the mechanism of nonallergic asthma that leads to airway hyperreactivity (AHR), a cardinal feature of asthma independent of adaptive immunity. METHOD We examined mouse models of experimental asthma in which AHR was induced by respiratory syncytial virus infection or ozone exposure using mice deficient in T-cell immunoglobulin and mucin domain 1 (TIM1/HAVCR1), an important asthma susceptibility gene. RESULTS TIM1(-/-) mice did not have airways disease when infected with RSV or when repeatedly exposed to ozone, a major component of air pollution. On the other hand, the TIM1(-/-) mice had allergen-induced experimental asthma, as previously shown. The RSV- and ozone-induced pathways were blocked by treatment with caspase inhibitors, indicating an absolute requirement for programmed cell death and apoptosis. TIM-1-expressing, but not TIM-1-deficient, natural killer T cells responded to apoptotic airway epithelial cells by secreting cytokines, which mediated the development of AHR. CONCLUSION We defined a novel pathway in which TIM-1, a receptor for phosphatidylserine expressed by apoptotic cells, drives the development of asthma by sensing and responding to injured and apoptotic airway epithelial cells.
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Affiliation(s)
- Hye Young Kim
- Division of Immunology and Allergy, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
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