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Sainova I, Kolyovska V, Ilieva I, Markova T, Dimitrova-Dikanarova D, Hadjiolova R. The Development of Methods for the Production of New Molecular Vaccines and Appropriate RNA Fragments to Counteract Unwanted Genes: A Pilot Study. Vaccines (Basel) 2023; 11:1226. [PMID: 37515042 PMCID: PMC10386085 DOI: 10.3390/vaccines11071226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 06/22/2023] [Accepted: 07/04/2023] [Indexed: 07/30/2023] Open
Abstract
The potential of viruses as appropriate vectors for the development of new therapeutic strategies, as well as for the design of molecular (DNA, RNA, and/or protein) vaccines via substitution of nucleotide sequences, has been proven. Among the most appropriate DNA and/or RNA fragments, members belonging to families Parvoviridae (particularly adeno-associated virus, AAV) and Poxviridae have frequently been suggested for this purpose. In previous studies, the vaccine avipoxvirus strains FK (fowl) and Dessau (pigeon) have been proven able to infect mammalian cells (as well as avian cells), and to replicate productively in a small number of them; thus, we may be able to adapt them using incubation, and in these conditions. Additionally, we have previously proved, based on AAV recombinant DNA vectors, that it is possible to transfer appropriate genes of interest via mouse embryonic stem cells (mESCs). In the current study, we develop methods for the application of the same vaccine avipoxviral strains, based on the AAV DNA genome recombinant constructs, to be used for gene transfer in cells, for the transfer of DNA and/or RNA fragments (for the suppression of unwanted viral and/or cellular genes), and for the production of molecular (DNA, RNA, and/or protein) anti-cancer and anti-viral vaccines. To this end, sub-populations of embryonic mammalian cells infected with the two forms of both vaccine avipoxviral strains were frozen in the presence of cryo-protector dimethylsulfoxide (DMSO), subsequently thawed, and re-incubated. In most cases, the titers of the intra-cellular forms of the two strains were higher than those of their extra-cellular forms. These data were explained by the probable existence of the intra-cellular forms as different sub-forms, including those integrated in the cellular genome proviruses at a given stage of the cellular infection, and suggest the possibility of transferring nucleotide (DNA and/or RNA) fragments between cellular and viral genomes; this is due to the influence of activated fusion processes on DMSO, as well as drastic temperature variations.
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Affiliation(s)
- Iskra Sainova
- Institute of Experimental Morphology, Pathology and Anthropology with Museum (IEMPAM) to Bulgarian Academy of Sciences (BAS), 1113 Sofia, Bulgaria
| | - Vera Kolyovska
- Institute of Experimental Morphology, Pathology and Anthropology with Museum (IEMPAM) to Bulgarian Academy of Sciences (BAS), 1113 Sofia, Bulgaria
| | - Iliana Ilieva
- Institute of Experimental Morphology, Pathology and Anthropology with Museum (IEMPAM) to Bulgarian Academy of Sciences (BAS), 1113 Sofia, Bulgaria
| | - Tzvetanka Markova
- Department of Pharmacology and Toxicology, Medical University of Sofia, 1431 Sofia, Bulgaria
| | | | - Radka Hadjiolova
- Department of Pathophysiology, Medical University of Sofia, 1431 Sofia, Bulgaria
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2
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Xu C, Ren XH, Han D, Peng Y, Lei JJ, Yu LX, Liu LJ, Xu WC, Cheng SX. Precise Detection on Cell-Cell Fusion by a Facile Molecular Beacon-Based Method. Anal Chem 2022; 94:17334-17340. [PMID: 36456915 DOI: 10.1021/acs.analchem.2c04852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Cell-cell fusion studies provide an experimental platform for evaluating disease progression and investigating cell infection. However, to realize sensitive and quantitative detection on cell-cell fusion is still a challenge. Herein, we report a facile molecular beacon (MB)-based method for precise detection on cell-cell fusion. By transfection of the spike protein (S protein) and enhanced green fluorescent protein (EGFP) in HEK 293 cells, the virus-mimicking fusogenic effector cells 293-S-EGFP cells were constructed to interact with target cells. Before mixing the effector cells with the target cells, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression in 293-S-EGFP cells was silenced, and the MB for GAPDH mRNA detection was delivered into the GAPDH silenced 293-S-EGFP cells. Once cell-cell fusion occurred, MB migrated from the GAPDH silenced effector cells to the target cells and hybridized with GAPDH mRNA in the target cells to induce fluorescence emission. The cell-cell fusion can be easily visualized and quantitated by fluorescence microscopy and flow cytometry. The fluorescence intensity is strongly dependent on the number of fused target cells. This MB-based method can easily identify the differences in the cell fusions for various target cells with different angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) expression levels, resulting in dramatically different fluorescence intensities in fused target cells. Our study provides a convenient and efficient quantitative detection approach to study cell-cell fusion.
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Affiliation(s)
- Chang Xu
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Xiao-He Ren
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Di Han
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
| | - Yan Peng
- Department of Pharmacy, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Jin-Ju Lei
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Luo-Xiao Yu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Ling-Juan Liu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Wei-Chao Xu
- Cancer Center, The Renmin Hospital of Wuhan University, Wuhan 430060, P. R. China
| | - Si-Xue Cheng
- Key Laboratory of Biomedical Polymers of Ministry of Education, Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
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3
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Chiliveri SC, Louis JM, Best RB, Bax A. Real-time Exchange of the Lipid-bound Intermediate and Post-fusion States of the HIV-1 gp41 Ectodomain. J Mol Biol 2022; 434:167683. [PMID: 35700771 PMCID: PMC9378563 DOI: 10.1016/j.jmb.2022.167683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Revised: 06/03/2022] [Accepted: 06/08/2022] [Indexed: 11/17/2022]
Abstract
The envelope glycoprotein gp41 of the HIV-1 virus mediates its entry into the host cell. During this process, gp41 undergoes large conformational changes and the energy released in the remodeling events is utilized to overcome the barrier associated with fusing the viral and host membranes. Although the structural intermediates of this fusion process are attractive targets for drug development, no detailed high-resolution structural information or quantitative thermodynamic characterization are available. By measuring the dynamic equilibrium between the lipid-bound intermediate and the post-fusion six-helical bundle (6HB) states of the gp41 ectodomain in the presence of bilayer membrane mimetics, we derived both the reaction kinetics and energies associated with these two states by solution NMR spectroscopy. At equilibrium, an exchange time constant of about 12 seconds at 38 °C is observed, and the post-fusion conformation is energetically more stable than the lipid-bound state by 3.4 kcal mol-1. The temperature dependence of the kinetics indicates that the folding occurs through a high-energy transition state which may resemble a 5HB structure. The energetics and kinetics of gp41 folding in the context of membrane bilayers provide a molecular basis for an improved understanding of viral membrane fusion.
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Affiliation(s)
- Sai Chaitanya Chiliveri
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. https://twitter.com/SaiChiliveri
| | - John M Louis
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ad Bax
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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4
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Linder A, Hornung V. Inflammasomes in T cells. J Mol Biol 2021; 434:167275. [PMID: 34599941 DOI: 10.1016/j.jmb.2021.167275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 09/21/2021] [Accepted: 09/22/2021] [Indexed: 02/06/2023]
Abstract
The concept of non-self recognition through germ-line encoded pattern recognition receptors (PRRs) has been well-established for professional innate immune cells. However, there is growing evidence that also T cells employ PRRs and associated effector functions in response to certain non-self or damage signals. Inflammasomes constitute a special subgroup of PRRs that is hardwired to a signaling cascade that culminates in the activation of caspase-1. Active caspase-1 processes pro-inflammatory cytokines of the IL-1 family and also triggers a lytic programmed cell death pathway known as pyroptosis. An increasing body of literature suggests that inflammasomes are also functional in T cells. On the one hand, conventional inflammasome signaling cascades have been described that operate similarly to pathways characterized in innate immune cells. On the other hand, unconventional functions have been suggested, in which certain inflammasome components play a role in unrelated processes, such as cell fate decisions and functions of T helper cells. In this review, we discuss our current knowledge on inflammasome functions in T cells and the biological implications of these findings for health and disease.
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Affiliation(s)
- Andreas Linder
- Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universität München, Munich, Germany; Department of Medicine II, University Hospital, Ludwig-Maximilians-Universität München, Munich, Germany. https://twitter.com/AndreasLinder7
| | - Veit Hornung
- Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universität München, Munich, Germany.
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5
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Yuan Y, Jacobs CA, Llorente Garcia I, Pereira PM, Lawrence SP, Laine RF, Marsh M, Henriques R. Single-Molecule Super-Resolution Imaging of T-Cell Plasma Membrane CD4 Redistribution upon HIV-1 Binding. Viruses 2021; 13:142. [PMID: 33478139 PMCID: PMC7835772 DOI: 10.3390/v13010142] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 01/14/2021] [Accepted: 01/15/2021] [Indexed: 12/21/2022] Open
Abstract
The first step of cellular entry for the human immunodeficiency virus type-1 (HIV-1) occurs through the binding of its envelope protein (Env) with the plasma membrane receptor CD4 and co-receptor CCR5 or CXCR4 on susceptible cells, primarily CD4+ T cells and macrophages. Although there is considerable knowledge of the molecular interactions between Env and host cell receptors that lead to successful fusion, the precise way in which HIV-1 receptors redistribute to sites of virus binding at the nanoscale remains unknown. Here, we quantitatively examine changes in the nanoscale organisation of CD4 on the surface of CD4+ T cells following HIV-1 binding. Using single-molecule super-resolution imaging, we show that CD4 molecules are distributed mostly as either individual molecules or small clusters of up to 4 molecules. Following virus binding, we observe a local 3-to-10-fold increase in cluster diameter and molecule number for virus-associated CD4 clusters. Moreover, a similar but smaller magnitude reorganisation of CD4 was also observed with recombinant gp120. For one of the first times, our results quantify the nanoscale CD4 reorganisation triggered by HIV-1 on host CD4+ T cells. Our quantitative approach provides a robust methodology for characterising the nanoscale organisation of plasma membrane receptors in general with the potential to link spatial organisation to function.
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Affiliation(s)
- Yue Yuan
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
| | - Caron A. Jacobs
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town 7925, South Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape Town, Cape Town 7925, South Africa
| | | | - Pedro M. Pereira
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
- Bacterial Cell Biology, MOSTMICRO, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal
| | - Scott P. Lawrence
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
| | - Romain F. Laine
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
- The Francis Crick Institute, London NW1 1AT, UK
| | - Mark Marsh
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
| | - Ricardo Henriques
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (Y.Y.); (C.A.J.); (P.M.P.); (S.P.L.)
- The Francis Crick Institute, London NW1 1AT, UK
- Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal
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6
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Gale P. How virus size and attachment parameters affect the temperature sensitivity of virus binding to host cells: Predictions of a thermodynamic model for arboviruses and HIV. MICROBIAL RISK ANALYSIS 2020; 15:100104. [PMID: 32292808 PMCID: PMC7110232 DOI: 10.1016/j.mran.2020.100104] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2019] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 05/14/2023]
Abstract
Virus binding to host cells involves specific interactions between viral (glyco)proteins (GP) and host cell surface receptors (Cr) (protein or sialic acid (SA)). The magnitude of the enthalpy of association changes with temperature according to the change in heat capacity (ΔCp) on GP/Cr binding, being little affected for avian influenza virus (AIV) haemagglutinin (HA) binding to SA (ΔCp = 0 kJ/mol/K) but greatly affected for HIV gp120 binding to CD4 receptor (ΔCp = -5.0 kJ/mol/K). A thermodynamic model developed here predicts that values of ΔCp from 0 to ~-2.0 kJ/mol/K have relatively little impact on the temperature sensitivity of the number of mosquito midgut cells with bound arbovirus, while intermediate values of ΔCp of ~-3.0 kJ/mol/K give a peak binding at a temperature of ~20 °C as observed experimentally for Western equine encephalitis virus. More negative values of ΔCp greatly decrease arbovirus binding at temperatures below ~20 °C. Thus to promote transmission at low temperatures, arboviruses may benefit from ΔCp ~ 0 kJ/mol/K as for HA/SA and it is interesting that bluetongue virus binds to SA in midge midguts. Large negative values of ΔCp as for HIV gp120:CD4 diminish binding at 37 °C. Of greater importance, however, is the decrease in entropy of the whole virus (ΔSa_immob) on its immobilisation on the host cell surface. ΔSa_immob presents a repulsive force which the enthalpy-driven GP/Cr interactions weakened at higher temperatures struggle to overcome. ΔSa_immob is more negative (less favourable) for larger diameter viruses which therefore show diminished binding at higher temperatures than smaller viruses. It is proposed that small size phenotype through a less negative ΔSa_immob is selected for viruses infecting warmer hosts thus explaining the observation that virion volume decreases with increasing host temperature from 0 °C to 40 °C in the case of dsDNA viruses. Compared to arboviruses which also infect warm-blooded vertebrates, HIV is large at 134 nm diameter and thus would have a large negative ΔSa_immob which would diminish its binding at human body temperature. It is proposed that prior non-specific binding of HIV through attachment factors takes much of the entropy loss for ΔSa_immob so enhancing subsequent specific gp120:CD4 binding at 37 °C. This is consistent with the observation that HIV attachment factors are not essential but augment infection. Antiviral therapies should focus on increasing virion size, for example through binding of zinc oxide nanoparticles to herpes simplex virus, hence making ΔSa_immob more negative, and thus reducing binding affinity at 37 °C.
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Key Words
- AIV, avian influenza virus
- Antivirals
- BBF, brush border fragments from midgut
- BTV, bluetongue virus
- C.VT, number of host cells with bound virus at temperature T
- CD4, host cell receptor for HIV
- Cp, heat capacity at constant pressure
- Cr, host cell receptor
- Ctotal, number of host cells which can bind virus in a given volume of host fluid (midgut or blood)
- DENV, Dengue virus
- EA, activation energy
- EBOV, Zaire ebolavirus
- EM, electron microscopy
- Entropy
- Env, HIV gp120 trimer envelope protein which binds to a single CD4 molecule
- FcT, fraction of arthropod midgut cells with bound virus at temperature T
- GP, viral (glyco)protein on virus surface that binds to Cr
- HA, haemagglutinin
- HIV, human immunodeficiency virus
- HSV-2, herpes simplex virus type 2
- Heat capacity
- Ka_virus_T, association constant for binding of virus to host cells at temperature T
- Kd_receptor_T, dissociation constant for GP from Cr at temperature T
- Kd_virus, dissociation constant for virus from host cell
- M, molar (moles dm-3)
- R, ideal gas constant
- SA, sialic acid
- SIV, simian immunodeficiency virus
- Temperature
- Vfree, virus not bound to cells
- Virus size
- Vtotal, virus challenge dose in volume of host fluid
- WEEV, Western equine encephalitis virus
- WNV, West Nile virus
- ZnOT, zinc oxide tetrapod
- n, number of GP/Cr contacts made on virus binding to cell
- pcompleteT, probability given a virion has bound to the surface of a midgut cell that that midgut cell becomes infected and that its progeny viruses go on to infect the salivary gland so completing the arthropod infection process within the life time of the arthropod at temperature T
- ptransmissionT, probability of successful infection of the arthropod salivary glands after oral exposure at temperature T
- ΔCp, change in heat capacity
- ΔGa_virus_T, change in Gibbs free energy on association of virus and host cell at temperature T
- ΔHa_receptor_T, change in enthalpy for binding of virus GP to host Cr receptor at a temperature T
- ΔHa_virus_T, change in enthalpy for binding of virus to host cell at temperature T
- ΔSa_immob, change in entropy on immobilization of whole virus to cell surface
- ΔSa_non_specific, change in entropy on immobilization of virus to cell surface through non-specific binding
- ΔSa_receptor_T, change in entropy for binding of virus GP to host Cr receptor
- ΔSa_specific, change in entropy on immobilization of virus to cell surface through specific GP/Cr-driven binding
- ΔSa_virus_T, change in entropy for binding of virus to host cell at temperature T
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Affiliation(s)
- Paul Gale
- Independent Scientist, 15 Weare Close, Portland, Dorset, DT5 1JP, United Kingdom
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7
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He W, Huang L, Feng Y, Liang F, Ding W, Wang W. Highly integrated microfluidic device for cell pairing, fusion and culture. BIOMICROFLUIDICS 2019; 13:054109. [PMID: 31893009 PMCID: PMC6932852 DOI: 10.1063/1.5124705] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 09/30/2019] [Indexed: 05/02/2023]
Abstract
In this study, we proposed a microfluidic device with compact structures integrating multiple modalities for cell capture, pairing, fusion, and culture. The microfluidic device is composed of upper and lower parts. The lower part configured with electrodes and capture wells is used for cell trapping/pairing/fusion, while the upper part configured with corresponding culture wells is used for cell culture. Dielectrophoresis is used to enable accurate cell trapping and pairing in capture wells. Moreover, the paired cells are fused flexibly by either electrical pulses or polyethylene glycol (PEG) buffer. The fused cells are then transferred to culture wells for on-chip culture simply by flipping the device. Using the device and HeLa cells, we demonstrated pairing efficiency of ∼78% and fusion efficiencies of ∼ 26% for electrical fusion or ∼ 21% for PEG fusion, and successful cell proliferation and migration after 72 h on-chip culture. We believe that this multifunction-integrated but structure-simplified microfluidic device would largely facilitate cell fusion oriented tasks.
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Affiliation(s)
- Weihua He
- State Key Laboratory of Precision Measurement Technology and Instrument, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
| | - Liang Huang
- School of Instrument Science and Opto-Electronics Engineering, Hefei University of Technology, Hefei 230009, China
| | - Yongxiang Feng
- State Key Laboratory of Precision Measurement Technology and Instrument, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
| | - Fei Liang
- State Key Laboratory of Precision Measurement Technology and Instrument, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
| | - Wei Ding
- State Key Laboratory of Precision Measurement Technology and Instrument, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
| | - Wenhui Wang
- State Key Laboratory of Precision Measurement Technology and Instrument, Department of Precision Instrument, Tsinghua University, Beijing 100084, China
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Zou X, Yuan M, Zhang T, Wei H, Xu S, Jiang N, Zheng N, Wu Z. Extracellular vesicles expressing a single-chain variable fragment of an HIV-1 specific antibody selectively target Env + tissues. Theranostics 2019; 9:5657-5671. [PMID: 31534509 PMCID: PMC6735399 DOI: 10.7150/thno.33925] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2019] [Accepted: 07/09/2019] [Indexed: 12/26/2022] Open
Abstract
Rationale: Antiretroviral therapy can effectively suppress HIV-1 replication in the peripheral blood to an undetectable level. However, elimination of the latent virus in reservoirs remains a challenge and is a major obstacle in the treatment of HIV-1-infected patients. Exosomes exhibit huge promise as an endogenous drug delivery nanosystem for delivering drugs to solid tissues given their unique properties, including low immunogenicity, innate stability, high delivery efficiency, and most importantly the ability to penetrate solid tissues due to their lipophilic properties. Methods: We engineered and expressed the scFv of a high affinity HIV-1-specific monoclonal antibody, 10E8, on the exosomal surface (10E8scFv-exos). Subsequently, the 10E8scFv-exos were loaded with curcumin (Cur), a chemical that kills HIV-1-infected cells, or miR-143, an apoptosis-inducing miRNA. We tested the ability of 10E8scFv-exos to deliver cargo to Env+ target cells and tissues, as well as their ability to suppress HIV-1 infection. Results: 10E8scFv-exos efficiently targeted CHO cells expressing a trimeric gp140 on their surface (Env+ cells) in vitro, as demonstrated by confocal imaging and flow cytometry. 10E8scFv-exos loaded with Cur or miR-143 showed specific killing of Env+ cells. In addition, 10E8scFv-exos loaded with Cur or miR-143 could suppress p24 expression in an HIV-1 latency cell line ACH2 and in PBMCs from an ART-treated HIV-1-infected patient. In an NCG mouse model grafted with tumorigenic Env+ CHO cells and which had developed solid tissue tumors, intravenously injected 10E8scFv-exos targeted the Env-expressing tissues and delivered Cur to induce a strong suppression of the Env+ tumor growth with low toxicity. Conclusion: In principle, engineered exosomes can deliver anti-HIV agents to solid tissues by specifically targeting cells expressing viral envelop proteins and inducing cell killing, suggesting that such an approach could be developed for eradicating virus-infected cells in tissue reservoirs.
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Affiliation(s)
- Xue Zou
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
| | - Meng Yuan
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
| | - Tongyu Zhang
- Model Animal Research Center, Nanjing University, China
| | - Hongxia Wei
- Department of infectious disease, The Second Hospital of Nanjing, Nanjing University of Chinese Medicine
| | - Shijie Xu
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
| | - Na Jiang
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
| | - Nan Zheng
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
- State Key Laboratory of Analytical Chemistry for Life Science, Nanjing University, Nanjing, China
- Medical School, Jiangsu Key Laboratory of Molecular Medicine, Nanjing University, Nanjing, China
| | - Zhiwei Wu
- Center for Public Health Research, Medical School, Nanjing University, Nanjing, China
- State Key Laboratory of Analytical Chemistry for Life Science, Nanjing University, Nanjing, China
- Medical School, Jiangsu Key Laboratory of Molecular Medicine, Nanjing University, Nanjing, China
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9
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Tai CJ, Li CL, Tai CJ, Wang CK, Lin LT. Early Viral Entry Assays for the Identification and Evaluation of Antiviral Compounds. J Vis Exp 2015:e53124. [PMID: 26555014 DOI: 10.3791/53124] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Cell-based systems are useful for discovering antiviral agents. Dissecting the viral life cycle, particularly the early entry stages, allows a mechanistic approach to identify and evaluate antiviral agents that target specific steps of the viral entry. In this report, the methods of examining viral inactivation, viral attachment, and viral entry/fusion as antiviral assays for such purposes are described, using hepatitis C virus as a model. These assays should be useful for discovering novel antagonists/inhibitors to early viral entry and help expand the scope of candidate antiviral agents for further drug development.
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Affiliation(s)
- Chen-Jei Tai
- Department of Chinese Medicine, Taipei Medical University Hospital; Department of Obstetrics and Gynecology, School of Medicine, College of Medicine, Taipei Medical University
| | - Chia-Lin Li
- Department of Microbiology and Immunology, School of Medicine, College of Medicine, Taipei Medical University
| | - Cheng-Jeng Tai
- Division of Hematology and Oncology, Department of Internal Medicine, Taipei Medical University Hospital; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University
| | - Chien-Kai Wang
- Department of Obstetrics and Gynecology, School of Medicine, College of Medicine, Taipei Medical University; Division of Hematology and Oncology, Department of Internal Medicine, Taipei Medical University Hospital
| | - Liang-Tzung Lin
- Department of Microbiology and Immunology, School of Medicine, College of Medicine, Taipei Medical University; Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University;
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10
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Mengistu M, Ray K, Lewis GK, DeVico AL. Antigenic properties of the human immunodeficiency virus envelope glycoprotein gp120 on virions bound to target cells. PLoS Pathog 2015; 11:e1004772. [PMID: 25807494 PMCID: PMC4373872 DOI: 10.1371/journal.ppat.1004772] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Accepted: 03/02/2015] [Indexed: 12/17/2022] Open
Abstract
The HIV-1 envelope glycoprotein, gp120, undergoes multiple molecular interactions and structural rearrangements during the course of host cell attachment and viral entry, which are being increasingly defined at the atomic level using isolated proteins. In comparison, antigenic markers of these dynamic changes are essentially unknown for single HIV-1 particles bound to target cells. Such markers should indicate how neutralizing and/or non-neutralizing antibodies might interdict infection by either blocking infection or sensitizing host cells for elimination by Fc-mediated effector function. Here we address this deficit by imaging fluorescently labeled CCR5-tropic HIV-1 pseudoviruses using confocal and superresolution microscopy to track the exposure of neutralizing and non-neutralizing epitopes as they appear on single HIV-1 particles bound to target cells. Epitope exposure was followed under conditions permissive or non-permissive for viral entry to delimit changes associated with virion binding from those associated with post-attachment events. We find that a previously unexpected array of gp120 epitopes is exposed rapidly upon target cell binding. This array comprises both neutralizing and non-neutralizing epitopes, the latter being hidden on free virions yet capable of serving as potent targets for Fc-mediated effector function. Under non-permissive conditions for viral entry, both neutralizing and non-neutralizing epitope exposures were relatively static over time for the majority of bound virions. Under entry-permissive conditions, epitope exposure patterns changed over time on subsets of virions that exhibited concurrent variations in virion contents. These studies reveal that bound virions are distinguished by a broad array of both neutralizing and non-neutralizing gp120 epitopes that potentially sensitize a freshly engaged target cell for destruction by Fc-mediated effector function and/or for direct neutralization at a post-binding step. The elucidation of these epitope exposure patterns during viral entry will help clarify antibody-mediated inhibition of HIV-1 as it is measured in vitro and in vivo. A major strategy for blocking HIV-1 infection is to target antiviral antibodies or drugs to sites of vulnerability on the surface proteins of the virus. It is a relatively straightforward matter to explore these sites on the surfaces of free HIV-1 particles or on isolated viral envelope antigens. However, one difficulty presented by HIV-1 is that its surface proteins are flexible and change shape once the virus has attached to its host cell. To date, it has been difficult to predict how cell-bound HIV-1 exposes its sites of vulnerability. Yet the antiviral activities of certain antibodies indirectly suggest that there must be unique sites on cell-bound HIV-1 that are not found on free virus. Here, we use new techniques and tools to determine how HIV-1 exposes unique sites of vulnerability after attaching to host cells. We find that the virus exposes a remarkable array of these sites, including ones previously believed hidden. These exposure patterns explain the antiviral activities of various anti-HIV-1 antibodies and provide a new view of how HIV-1 might interact with the immune system. Our study also provides insights for how to target HIV-1 with antiviral antibodies, vaccines, or antiviral agents.
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Affiliation(s)
- Meron Mengistu
- The Institute of Human Virology of the University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- * E-mail: (MM); (ALD)
| | - Krishanu Ray
- Center for Fluorescence Spectroscopy of the University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - George K. Lewis
- The Institute of Human Virology of the University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Anthony L. DeVico
- The Institute of Human Virology of the University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- * E-mail: (MM); (ALD)
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Rozenfeld JH, Duarte EL, Ruysschaert JM, Lonez C, Lamy MT. Structural characterization of novel cationic diC16-amidine bilayers: Evidence for partial interdigitation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:127-33. [DOI: 10.1016/j.bbamem.2014.10.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Revised: 09/25/2014] [Accepted: 10/02/2014] [Indexed: 11/26/2022]
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12
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Jinno-Oue A, Tanaka A, Shimizu N, Mori T, Sugiura N, Kimata K, Isomura H, Hoshino H. Inhibitory effect of chondroitin sulfate type E on the binding step of human T-cell leukemia virus type 1. AIDS Res Hum Retroviruses 2013; 29:621-9. [PMID: 23033806 DOI: 10.1089/aid.2012.0156] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Cell surface heparan sulfate proteoglycans (HSPGs) are involved in the binding and entry of human T-cell leukemia virus type 1 (HTLV-1) into host cells, while sulfated polysaccharides such as heparin inhibit HTLV-1 infection. Chondroitin sulfate proteoglycans (CSPGs) are classified as another major type of proteoglycans. Here, we examined the effect of four types of chondroitin sulfate (CS) on HTLV-1 infection. Accordingly, a human T cell line, MOLT-4, was inoculated with cell-free HTLV-1 in the presence or absence of soluble CS, and the synthesis of reverse-transcribed HTLV-1 DNA within cells 20 h after inoculation was detected using polymerase chain reaction (PCR). Among the four types of CS (A, C, D, and E), the E type (CSE), which was derived from the squid cartilage, exhibited anti-HTLV-1 activity. Furthermore, we observed that CSE directly interacted with recombinant HTLV-1 envelope (Env) proteins and inhibited the binding of HTLV-1 virions to MOLT-4 cells, indicating that the interaction between Env and CSE plays a significant role in its anti-HTLV-1 activity. In addition, CSE inhibited syncytium formation that was induced by HTLV-1-producing cells. When CSE was mixed with the synthetic fusion inhibitor peptide corresponding to the ectodomain of the Env transmembrane subunit (TM) gp21, the HTLV-1 infection was further inhibited when compared with the inhibitory effect of each compound alone. Thus, further elucidation of the in vitro antiviral mechanism of CSE shown in this study will lead to the development of CSE-like molecules for the entry inhibition of HTLV-1.
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Affiliation(s)
- Atsushi Jinno-Oue
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Atsushi Tanaka
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Nobuaki Shimizu
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Takahisa Mori
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Nobuo Sugiura
- Institute for Molecular Science of Medicine, Aichi Medical University, Aichi, Japan
| | - Koji Kimata
- Institute for Molecular Science of Medicine, Aichi Medical University, Aichi, Japan
| | - Hiroki Isomura
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
| | - Hiroo Hoshino
- Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, Gunma, Japan
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Guo H, Sun X, Yan L, Shao L, Fang Q. The NS16 protein of aquareovirus-C is a fusion-associated small transmembrane (FAST) protein, and its activity can be enhanced by the nonstructural protein NS26. Virus Res 2012. [PMID: 23201583 DOI: 10.1016/j.virusres.2012.11.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Orthoreoviruses and aquareoviruses represent two different genera in the family Reoviridae, but they share many common characteristics in structural organization and pathogenesis. Similar to fusogenic orthoreoviruses, aquareoviruses can induce cell-cell fusion and multinucleated syncytium formation. Sequence analysis indicated that the nonstructural protein NS16 might be a fusion protein responsible for aquareovirus-C (AqRV-C) syncytiogenesis. To understand the basis of AqRV-C in syncytium formation, the properties of NS16 in mediating cell-cell fusion were investigated in this study. Bioinformatics analysis indicated that NS16 shares basic structural motifs with reovirus fusion-associated small transmembrane (FAST) proteins. However, the relative arrangement of these predicted structural motifs is different from the identified FAST proteins, suggesting that NS16 may present a new member of the FAST protein family. Further transfection assays showed that NS16 was able to induce cell-cell fusion. Nevertheless, the fusion activity was less efficient in comparison with that of the viral infection. In addition, NS16 was defined to display an N-terminus-outside/C-terminus-inside orientation, and the N-terminal ectodomain was critical for effective fusion. Moreover, immunofluorescence assays revealed that NS16 colocalized with nonstructural protein NS26 in cotransfected cells. And the enhanced fusion efficiency could be detected when NS16 was coexpressed with NS26, implying that NS26 may participate in cell-cell fusion through cooperation with NS16 in aquareovirus infection. Our study provided a basis for further characterization of cell-cell fusion mediated by AqRV-C.
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Affiliation(s)
- Hong Guo
- State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China
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14
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Oliveira TR, Duarte EL, Lamy MT, Vandenbranden M, Ruysschaert JM, Lonez C. Temperature-dependence of cationic lipid bilayer intermixing: possible role of interdigitation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:4640-4647. [PMID: 22332736 DOI: 10.1021/la3001569] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this work, we investigated the properties of a fusogenic cationic lipid, diC14-amidine, and show that this lipid possesses per se the capacity to adopt either an interdigitated structure (below and around its transition temperature) or a lamellar structure (above the transition temperature). To provide experimental evidence of this lipid bilayer organization, phospholipids spin-labeled at different positions of the hydrocarbon chain were incorporated into the membrane and their electron spin resonance (ESR) spectra were recorded at different temperatures. For comparison, similar experiments were performed with dimyristoyl phosphatidylcholine, a zwitterionic lipid (DMPC) which adopts a bilayer organization over a broad temperature range. Lipid mixing between diC14-amidine and asolectin liposomes was more efficient below (10-15 °C) than above the transition temperature (above 25 °C). This temperature-dependent "fusogenic" activity of diC14-amidine liposomes is opposite to what has been observed so far for peptides or virus-induced fusion. Altogether, our data suggest that interdigitation is a highly fusogenic state and that interdigitation-mediated fusion occurs via an unusual temperature-dependent mechanism that remains to be deciphered.
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Affiliation(s)
- Tiago R Oliveira
- Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
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HIV-1 clinical isolates resistant to CCR5 antagonists exhibit delayed entry kinetics that are corrected in the presence of drug. J Virol 2011; 86:1119-28. [PMID: 22090117 DOI: 10.1128/jvi.06421-11] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
HIV CCR5 antagonists select for env gene mutations that enable virus entry via drug-bound coreceptor. To investigate the mechanisms responsible for viral adaptation to drug-bound coreceptor-mediated entry, we studied viral isolates from three participants who developed CCR5 antagonist resistance during treatment with vicriviroc (VCV), an investigational small-molecule CCR5 antagonist. VCV-sensitive and -resistant viruses were isolated from one HIV subtype C- and two subtype B-infected participants; VCV-resistant isolates had mutations in the V3 loop of gp120 and were cross-resistant to TAK-779, an investigational antagonist, and maraviroc (MVC). All three resistant isolates contained a 306P mutation but had variable mutations elsewhere in the V3 stem. We used a virus-cell β-lactamase (BlaM) fusion assay to determine the entry kinetics of recombinant viruses that incorporated full-length VCV-sensitive and -resistant envelopes. VCV-resistant isolates exhibited delayed entry rates in the absence of drug, relative to pretherapy VCV-sensitive isolates. The addition of drug corrected these delays. These findings were generalizable across target cell types with a range of CD4 and CCR5 surface densities and were observed when either population-derived or clonal envelopes were used to construct recombinant viruses. V3 loop mutations alone were sufficient to restore virus entry in the presence of drug, and the accumulation of V3 mutations during VCV therapy led to progressively higher rates of viral entry. We propose that the restoration of pre-CCR5 antagonist therapy HIV entry kinetics drives the selection of V3 loop mutations and may represent a common mechanism that underlies the emergence of CCR5 antagonist resistance.
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16
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Yi HA, Diaz-Aguilar B, Bridon D, Quraishi O, Jacobs A. Permanent inhibition of viral entry by covalent entrapment of HIV gp41 on the virus surface. Biochemistry 2011; 50:6966-72. [PMID: 21736372 DOI: 10.1021/bi201014b] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
HIV entry occurs by concerted conformational changes in the envelope protein complex on the surface of the virus. This complex is made up of a trimer of heterodimers of two subunits: surface subunit, gp120, and transmembrane subunit, gp41. Conformational changes in the envelope complex allow gp41 to mediate membrane fusion leading to exposure of two gp41 regions: N-heptad repeat (NHR) and C-heptad repeat (CHR). Peptides from the NHR or the CHR have been found to inhibit HIV entry. Herein we show that we can covalently inhibit HIV viral entry by permanently trapping the gp41 intermediate on the virus surface using a covalently reactive group on inhibitory peptides. This is evidence showing that vulnerable conformational intermediates exist transiently during HIV viral entry, and the details presented herein will facilitate development of envelope as a target for therapeutics and potential chemopreventive agents that could disable the virus before contact with the host cell.
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Affiliation(s)
- Hyun Ah Yi
- Department of Microbiology and Immunology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York 14214, United States
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17
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Yee M, Konopka K, Balzarini J, Düzgüneş N. Inhibition of HIV-1 Env-Mediated Cell-Cell Fusion by Lectins, Peptide T-20, and Neutralizing Antibodies. Open Virol J 2011; 5:44-51. [PMID: 21660189 PMCID: PMC3109660 DOI: 10.2174/1874357901105010044] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2010] [Revised: 03/04/2011] [Accepted: 03/08/2011] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND Broadly cross-reactive, neutralizing human monoclonal antibodies, including 2F5, 2G12, 4E10 and IgG1 b12, can inhibit HIV-1 infection in vitro at very low concentrations. We examined the ability of these antibodies to inhibit cell-cell fusion between Clone69TRevEnv cells induced to express the viral envelope proteins, gp120/gp41 (Env), and highly CD4-positive SupT1 cells. The cells were loaded with green and red-orange cytoplasmic fluorophores, and fusion was monitored by fluorescence microscopy. RESULTS Cell-cell fusion was inhibited completely by the carbohydrate binding proteins (CBPs), Hippeastrum hybrid (Amaryllis) agglutinin (HHA), and Galanthus nivalis (Snowdrop) agglutinin (GNA), and by the peptide, T-20, at relatively low concentrations. Anti-gp120 and anti-gp41 antibodies, at concentrations much higher than those required for neutralization, were not particularly effective in inhibiting fusion. Monoclonal antibodies b12, m14 IgG and 2G12 had moderate inhibitory activity; the IC(50) of 2G12 was about 80 µg/ml. Antibodies 4E10 and 2F5 had no inhibitory activity at the concentrations tested. CONCLUSIONS These observations raise concerns about the ability of neutralizing antibodies to inhibit the spread of viral genetic material from infected cells to uninfected cells via cell-cell fusion. The interaction of gp120/gp41 with cell membrane CD4 may be different in cell-cell and virus-cell membrane fusion reactions, and may explain the differential effects of antibodies in these two systems. The fluorescence assay described here may be useful in high throughput screening of potential HIV fusion inhibitors.
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Affiliation(s)
- Michael Yee
- Department of Biomedical Sciences, University of the Pacific Arthur A. Dugoni School of Dentistry, San Francisco, CA 94115, USA
| | - Krystyna Konopka
- Department of Biomedical Sciences, University of the Pacific Arthur A. Dugoni School of Dentistry, San Francisco, CA 94115, USA
| | - Jan Balzarini
- Rega Institute for Medical Research, Catholic University of Leuven, Leuven, Belgium
| | - Nejat Düzgüneş
- Department of Biomedical Sciences, University of the Pacific Arthur A. Dugoni School of Dentistry, San Francisco, CA 94115, USA
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18
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Decreased CD4 and wide-ranging expression of other immune receptors after HIV-envelope-mediated formation of syncytia in vitro. Arch Virol 2010; 155:1205-16. [PMID: 20508956 DOI: 10.1007/s00705-010-0704-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Accepted: 05/13/2010] [Indexed: 10/19/2022]
Abstract
In human HIV infection, multinucleated cells (syncytia) are formed by fusion of HIV-infected cells with CD4+ cells. In order to examine possible functional implications of syncytia formation for the immune response, the expression of important surface molecules by T-cell syncytia and surrounding cells that remain unfused (bystander cells) was analyzed in cocultures of HIV-Env- and CD4-expressing E6 Jurkat T cells. Fusion partners were differentially labeled with lipophilic probes, and syncytia and bystander cells were identified by flow cytometry. The cellular phenotype and response to activation stimulus after fusion were analyzed with antibodies coupled to third-party fluorochromes. Cocultured unfused E6 cells showed a marked decrease in CD4 expression, suggesting the selective recruitment of cells strongly expressing CD4 into syncytia. However, the incorporated CD4 was not detected in the syncytia, whereas the range of expression of CD28, ICAM-1, CXCR4 and CD3 was wider than that of unfused cells. Limited expression of CD4 in the bystander unfused population, as well as in the newly formed syncytia, would result in limitation of further viral entry and a failure to identify these cells, and it could partially contribute to functional impairment and a decrease in the number of CD4+ T cells in AIDS. Most of the syncytia were viable and expressed CD25 and IL-2 in response to activation by phorbol myristate acetate (PMA) and ionomicyn. Thus, syncytia populations harboring widely heterogeneous levels of receptors would constitute a potential source of anomalous immune function.
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19
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An antibody directed against the fusion peptide of Junin virus envelope glycoprotein GPC inhibits pH-induced membrane fusion. J Virol 2010; 84:6119-29. [PMID: 20392854 DOI: 10.1128/jvi.02700-09] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The arenavirus envelope glycoprotein (GPC) initiates infection in the host cell through pH-induced fusion of the viral and endosomal membranes. As in other class I viral fusion proteins, this process proceeds through a structural reorganization in GPC in which the ectodomain of the transmembrane fusion subunit (G2) engages the host cell membrane and subsequently refolds to form a highly stable six-helix bundle structure that brings the two membranes into apposition for fusion. Here, we describe a G2-directed monoclonal antibody, F100G5, that prevents membrane fusion by binding to an intermediate form of the protein on the fusion pathway. Inhibition of syncytium formation requires that F100G5 be present concomitant with exposure of GPC to acidic pH. We show that F100G5 recognizes neither the six-helix bundle nor the larger trimer-of-hairpins structure in the postfusion form of G2. Rather, Western blot analysis using recombinant proteins and a panel of alanine-scanning GPC mutants revealed that F100G5 binding is dependent on an invariant lysine residue (K283) near the N terminus of G2, in the so-called fusion peptide that inserts into the host cell membrane during the fusion process. The F100G5 epitope is located in the internal segment of the bipartite GPC fusion peptide, which also contains four conserved cysteine residues, raising the possibility that this fusion peptide may be highly structured. Collectively, our studies indicate that F100G5 identifies an on-path intermediate form of GPC. Binding to the transiently exposed fusion peptide may interfere with G2 insertion into the host cell membrane. Strategies to effectively target fusion peptide function in the endosome may lead to novel classes of antiviral agents.
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Koch P, Lampe M, Godinez WJ, Müller B, Rohr K, Kräusslich HG, Lehmann MJ. Visualizing fusion of pseudotyped HIV-1 particles in real time by live cell microscopy. Retrovirology 2009; 6:84. [PMID: 19765276 PMCID: PMC2762461 DOI: 10.1186/1742-4690-6-84] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 09/18/2009] [Indexed: 11/10/2022] Open
Abstract
Background Most retroviruses enter their host cells by fusing the viral envelope with the plasma membrane. Although the protein machinery promoting fusion has been characterized extensively, the dynamics of the process are largely unknown. Results We generated human immunodeficiency virus-1 (HIV-1) particles pseudotyped with the envelope (Env) protein of ecotropic murine leukemia virus eMLV to study retrovirus entry at the plasma membrane using live-cell microscopy. This Env protein mediates highly efficient pH independent fusion at the cell surface and can be functionally tagged with a fluorescent protein. To detect fusion events, double labeled particles carrying one fluorophor in Env and the other in the matrix (MA) domain of Gag were generated and characterized. Fusion events were defined as loss of Env signal after virus-cell contact. Single particle tracking of >20,000 individual traces in two color channels recorded 28 events of color separation, where particles lost the Env protein, with the MA layer remaining stable at least for a short period. Fourty-five events were detected where both colors were lost simultaneously. Importantly, the first type of event was never observed when particles were pseudotyped with a non-fusogenic Env. Conclusion These results reveal rapid retroviral fusion at the plasma membrane and permit studies of the immediate post-fusion events.
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Affiliation(s)
- Peter Koch
- Department of Virology, Universitätsklinikum Heidelberg, Heidelberg, Germany.
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21
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HIV enters cells via endocytosis and dynamin-dependent fusion with endosomes. Cell 2009; 137:433-44. [PMID: 19410541 DOI: 10.1016/j.cell.2009.02.046] [Citation(s) in RCA: 508] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2008] [Revised: 01/03/2009] [Accepted: 02/25/2009] [Indexed: 10/20/2022]
Abstract
Enveloped viruses that rely on a low pH-dependent step for entry initiate infection by fusing with acidic endosomes, whereas the entry sites for pH-independent viruses, such as HIV-1, have not been defined. These viruses have long been assumed to fuse directly with the plasma membrane. Here we used population-based measurements of the viral content delivery into the cytosol and time-resolved imaging of single viruses to demonstrate that complete HIV-1 fusion occurred in endosomes. In contrast, viral fusion with the plasma membrane did not progress beyond the lipid mixing step. HIV-1 underwent receptor-mediated internalization long before endosomal fusion, thus minimizing the surface exposure of conserved viral epitopes during fusion and reducing the efficacy of inhibitors targeting these epitopes. We also show that, strikingly, endosomal fusion is sensitive to a dynamin inhibitor, dynasore. These findings imply that HIV-1 infects cells via endocytosis and envelope glycoprotein- and dynamin-dependent fusion with intracellular compartments.
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Melikyan GB. Common principles and intermediates of viral protein-mediated fusion: the HIV-1 paradigm. Retrovirology 2008; 5:111. [PMID: 19077194 PMCID: PMC2633019 DOI: 10.1186/1742-4690-5-111] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Accepted: 12/10/2008] [Indexed: 12/20/2022] Open
Abstract
Enveloped viruses encode specialized fusion proteins which promote the merger of viral and cell membranes, permitting the cytosolic release of the viral cores. Understanding the molecular details of this process is essential for antiviral strategies. Recent structural studies revealed a stunning diversity of viral fusion proteins in their native state. In spite of this diversity, the post-fusion structures of these proteins share a common trimeric hairpin motif in which the amino- and carboxy-terminal hydrophobic domains are positioned at the same end of a rod-shaped molecule. The converging hairpin motif, along with biochemical and functional data, implies that disparate viral proteins promote membrane merger via a universal "cast-and-fold" mechanism. According to this model, fusion proteins first anchor themselves to the target membrane through their hydrophobic segments and then fold back, bringing the viral and cellular membranes together and forcing their merger. However, the pathways of protein refolding and the mechanism by which this refolding is coupled to membrane rearrangements are still not understood. The availability of specific inhibitors targeting distinct steps of HIV-1 entry permitted the identification of key conformational states of its envelope glycoprotein en route to fusion. These studies provided functional evidence for the direct engagement of the target membrane by HIV-1 envelope glycoprotein prior to fusion and revealed the role of partially folded pre-hairpin conformations in promoting the pore formation.
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Affiliation(s)
- Gregory B Melikyan
- Institute of Human Virology, Department of Microbiology and Immunology, University of Maryland School of Medicine, 725 W, Lombard St, Baltimore, MD 21201, USA.
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23
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Anzinger JJ, Olinger GG, Spear GT. Donor variability in HIV binding to peripheral blood mononuclear cells. Virol J 2008; 5:95. [PMID: 18706090 PMCID: PMC2538508 DOI: 10.1186/1743-422x-5-95] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Accepted: 08/15/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND HIV infection of cells varies greatly between individuals, with multiple steps in the replication cycle potentially contributing to the variability. Although entry and post-entry variability of HIV infection levels in cells has been demonstrated, variability in HIV binding has not been examined. In this study, we examined variability of HIV binding to peripheral blood mononuclear cells (PBMC) from different donors. RESULTS HIV binding to PBMC varied up to 3.9-fold between individuals and was independent of CD4. Replication of HIV in donor PBMC required CD4 and paralleled virus binding trends of donor PBMC. To assess the stability of virus binding phenotypes over time, HIV was bound to donors with low- and high-binding phenotypes. The binding phenotypes were maintained when tested weekly over a 4-week period for 3 of 4 donors, while one high-binding donor decreased to lower binding on the 4th week. The low- and high-binding phenotypes were also preserved across different HIV strains. Experiments performed to determine if there was an association between HIV binding levels and specific cell subset levels within PBMC showed no correlation, suggesting that HIV binds to multiple cell subsets. CONCLUSION These results show that differences exist in HIV binding to donor PBMC. Our data also show that HIV binding to donor PBMC is CD4-independent and can change over time, suggesting that virus binding variability is due to differences in the expression of changeable cell-surface host factors. Taken together, this study highlights the impact of cell-surface factors in HIV binding to, and infection of, PBMC which likely represents an important step in HIV infection in vivo.
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Affiliation(s)
- Joshua J Anzinger
- Section of Experimental Atherosclerosis, National Heart, Lung, and Blood Institute, National Institutes of Health, 10 Center Drive, Building 10, Room 5N111, Bethesda, Maryland 20892, USA.
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Teeravechyan S, Suphaphiphat P, Essex M, Lee TH. Relative concordance of human immunodeficiency virus oligomeric and monomeric envelope in CCR5 coreceptor usage. Virology 2008; 370:443-50. [PMID: 17936869 DOI: 10.1016/j.virol.2007.09.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 09/11/2007] [Accepted: 09/11/2007] [Indexed: 10/22/2022]
Abstract
A major difference between binding and fusion assays commonly used to study the human immunodeficiency virus (HIV) envelope is the use of monomeric envelope for the former assay and oligomeric envelope for the latter. Due to discrepancies in their readouts for some mutants, envelope regions involved in CCR5 coreceptor usage were systematically studied to determine whether the discordance is due to inherent differences between the two assays or whether it genuinely reflects functional differences at each entry step. By adding the binding inhibitor TAK-779 to delay coreceptor binding kinetics in the fusion assay, the readouts were found comparable between the assays for the mutants analysed in this study. Our finding indicates that monomeric binding reflects oligomeric envelope-CCR5 interaction, thus discordant results between binding and fusion assays do not necessarily indicate differences in coreceptor usage by oligomeric envelope and monomeric gp120.
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Affiliation(s)
- Samaporn Teeravechyan
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, 651 Huntington Avenue, Boston, MA 02115, USA
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Harada S, Monde K, Tanaka Y, Kimura T, Maeda Y, Yusa K. Neutralizing antibodies decrease the envelope fluidity of HIV-1. Virology 2008; 370:142-50. [PMID: 17900650 DOI: 10.1016/j.virol.2007.08.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Revised: 08/06/2007] [Accepted: 08/17/2007] [Indexed: 11/28/2022]
Abstract
For successful penetration of HIV-1, the formation of a fusion pore may be required in order to accumulate critical numbers of fusion-activated gp41 with the help of fluidization of the plasma membrane and viral envelope. An increase in temperature to 40 degrees C after viral adsorption at 25 degrees C enhanced the infectivity by 1.4-fold. The enhanced infectivity was inhibited by an anti-CXCR4 peptide, T140, and anti-V3 monoclonal antibodies (0.5beta and 694/98-D) by post-attachment neutralization, but not by non-neutralizing antibodies (670-30D and 246-D) specific for the C5 of gp120 and cluster I of gp41, respectively. Anti-HLA-II and an anti-HTLV-I gp46 antibody, LAT27, neutralized the molecule-carrying HIV-1(C-2(MT-2)). The anti-V3 antibodies suppressed the fluidity of the HIV-1(C-2) envelope, whereas the non-neutralizing antibodies did not. The anti-HLA-II antibody decreased the envelope fluidity of HIV-1(C-2(MT-2)), but not that of HIV-1(C-2). Therefore, fluidity suppression by these antibodies represents an important neutralization mechanism, in addition to inhibition of viral attachment.
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Affiliation(s)
- Shinji Harada
- Department of Medical Virology, Graduate School of Medical Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
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26
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Mirsaliotis A, Nurkiyanova K, Lamb D, Kuo CWS, Brighty DW. Resistance to neutralization by antibodies targeting the coiled coil of fusion-active envelope is a common feature of retroviruses. J Biol Chem 2007; 282:36724-35. [PMID: 17940280 DOI: 10.1074/jbc.m706827200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The human T-cell leukemia virus transmembrane glycoprotein (TM) is a typical class 1 membrane fusion protein and a subunit of the viral envelope glycoprotein complex. Following activation, the TM undergoes conformational transitions from a native nonfusogenic state to a fusion-active pre-hairpin intermediate that subsequently resolves to a compact trimer-of-hairpins or six-helix bundle. Disruption of these structural transitions inhibits membrane fusion and viral entry and validates TM as an anti-viral and vaccine target. To investigate the immunological properties of fusion-active TM, we have generated a panel of monoclonal antibodies that recognize the coiled-coil domain of the pre-hairpin intermediate. Antibody reactivity is highly sensitive to the conformation of the coiled coil as binding is dramatically reduced or lost on denatured antigen. Moreover, a unique group of antibodies are 100-1000-fold more reactive with the coiled coil than the trimer-of-hairpins form of TM. The antibodies recognize virally expressed envelope, and significantly, some selectively bind to envelope only under conditions that promote membrane fusion. Most importantly, many of the antibodies potently block six-helix bundle formation in vitro. Nevertheless, viral envelope was remarkably resistant to neutralization by antibodies directed to the coiled coil. The data imply that the coiled coil of viral envelope is poorly exposed to antibody during membrane fusion. We suggest that resistance to neutralization by antibodies directed to fusion-associated structures is a common property of retroviral TM and perhaps of other viral class I fusion proteins. These observations have significant implications for vaccine design.
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Affiliation(s)
- Antonis Mirsaliotis
- Biomedical Research Centre, Ninewells Hospital and Medical School, the University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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27
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Jacobs A, Quraishi O, Huang X, Bousquet-Gagnon N, Nault G, Francella N, Alvord WG, Pham N, Soucy C, Robitaille M, Bridon D, Blumenthal R. A covalent inhibitor targeting an intermediate conformation of the fusogenic subunit of the HIV-1 envelope complex. J Biol Chem 2007; 282:32406-13. [PMID: 17726011 DOI: 10.1074/jbc.m705577200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Peptide inhibitors corresponding to sequences in the six helix bundle structure of the fusogenic portion (gp41) of the HIV envelope glycoprotein have been successfully implemented in preventing HIV entry. These peptides bind to regions in HIV gp41 transiently exposed during the fusion reaction. In an effort to improve upon these entry inhibitors, we have successfully designed and tested peptide analogs composed of chemical spacers and reactive moieties positioned strategically to facilitate covalent attachment. Using a temperature-arrested state prime wash in vitro assay we show evidence for the trapping of a pre-six helix bundle fusion intermediate by a covalent reaction with the specific anti-HIV-1 peptide. This is the first demonstration of the trapping of an intermediate conformation of a viral envelope glycoprotein during the fusion process that occurs in live cells. The permanent specific attachment of the covalent inhibitor is projected to improve the pharmacokinetics of administration in vivo and thereby improve the long-term sustainability of peptide entry inhibitor therapy and help to expand its applicability beyond salvage therapy.
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Affiliation(s)
- Amy Jacobs
- Center for Cancer Research Nanobiology Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702, USA
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28
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Melikyan GB, Platt EJ, Kabat D. The role of the N-terminal segment of CCR5 in HIV-1 Env-mediated membrane fusion and the mechanism of virus adaptation to CCR5 lacking this segment. Retrovirology 2007; 4:55. [PMID: 17686153 PMCID: PMC1995219 DOI: 10.1186/1742-4690-4-55] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Accepted: 08/08/2007] [Indexed: 02/05/2023] Open
Abstract
Background HIV-1 envelope glycoprotein (Env) induces membrane fusion as a result of sequential binding to CD4 and chemokine receptors (CCR5 or CXCR4). The critical determinants of CCR5 coreceptor function are the N-terminal domain (Nt) and the second extracellular loop. However, mutations in gp120 adapt HIV-1 to grow on cells expressing the N-terminally truncated CCR5(Δ18) (Platt et al., J. Virol. 2005, 79: 4357–68). Results We have functionally characterized the adapted Env (designated Env(NYP)) using a quantitative cell-cell fusion assay. The rate of fusion with target cells expressing wild-type CCR5 and the resistance to fusion inhibitors was virtually identical for wild-type Env and Env(NYP), implying that the coreceptor affinity had not increased as a result of adaptation. In contrast, Env(NYP)-induced fusion with cells expressing CCR5(Δ18) occurred at a slower rate and was extremely sensitive to the CCR5 binding inhibitor, Sch-C. Resistance to Sch-C drastically increased after pre-incubation of Env(NYP)- and CCR5(Δ18)-expressing cells at a temperature that was not permissive to fusion. This indicates that ternary Env(NYP)-CD4-CCR5(Δ18) complexes accumulate at sub-threshold temperature and that low-affinity interactions with the truncated coreceptor are sufficient for triggering conformational changes in the gp41 of Env(NYP) but not in wild-type Env. We also demonstrated that the ability of CCR5(Δ18) to support fusion and infection mediated by wild-type Env can be partially reconstituted in the presence of a synthetic sulfated peptide corresponding to the CCR5 Nt. Pre-incubation of wild-type Env- and CCR5(Δ18)-expressing cells with the sulfated peptide at sub-threshold temperature markedly increased the efficiency of fusion. Conclusion We propose that, upon binding the Nt region of CCR5, wild-type Env acquires the ability to productively engage the extracellular loop(s) of CCR5 – an event that triggers gp41 refolding and membrane merger. The adaptive mutations in Env(NYP) enable it to more readily release its hold on gp41, even when it interacts weakly with a severely damaged coreceptor in the absence of the sulfopeptide.
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Affiliation(s)
- Gregory B Melikyan
- Institute of Human Virology, University of Maryland School of Medicine.725 W. Lombard St., Baltimore, MD 21201, USA
| | - Emily J Platt
- Department of Biochemistry and Molecular Biology, Oregon Health and Science, University, Portland, OR 97239, USA
| | - David Kabat
- Department of Biochemistry and Molecular Biology, Oregon Health and Science, University, Portland, OR 97239, USA
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29
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Gattegno T, Mittal A, Valansi C, Nguyen KC, Hall DH, Chernomordik LV, Podbilewicz B. Genetic control of fusion pore expansion in the epidermis of Caenorhabditis elegans. Mol Biol Cell 2007; 18:1153-66. [PMID: 17229888 PMCID: PMC1838987 DOI: 10.1091/mbc.e06-09-0855] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2006] [Revised: 01/02/2007] [Accepted: 01/08/2007] [Indexed: 11/11/2022] Open
Abstract
Developmental cell fusion is found in germlines, muscles, bones, placentae, and stem cells. In Caenorhabditis elegans 300 somatic cells fuse during development. Although there is extensive information on the early intermediates of viral-induced and intracellular membrane fusion, little is known about late stages in membrane fusion. To dissect the pathway of cell fusion in C. elegans embryos, we use genetic and kinetic analyses using live-confocal and electron microscopy. We simultaneously monitor the rates of multiple cell fusions in developing embryos and find kinetically distinct stages of initiation and completion of membrane fusion in the epidermis. The stages of cell fusion are differentially blocked or retarded in eff-1 and idf-1 mutants. We generate kinetic cell fusion maps for embryos grown at different temperatures. Different sides of the same cell differ in their fusogenicity: the left and right membrane domains are fusion-incompetent, whereas the anterior and posterior membrane domains fuse with autonomous kinetics in embryos. All but one cell pair can initiate the formation of the largest syncytium. The first cell fusion does not trigger a wave of orderly fusions in either direction. Ultrastructural studies show that epidermal syncytiogenesis require eff-1 activities to initiate and expand membrane merger.
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Affiliation(s)
- Tamar Gattegno
- *Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Aditya Mittal
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892; and
| | - Clari Valansi
- *Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Ken C.Q. Nguyen
- Center for C. elegans Anatomy, Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | - David H. Hall
- Center for C. elegans Anatomy, Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Leonid V. Chernomordik
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892; and
| | - Benjamin Podbilewicz
- *Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892; and
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30
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Mirsaliotis A, Nurkiyanova K, Lamb D, Woof JM, Brighty DW. Conformation-specific antibodies targeting the trimer-of-hairpins motif of the human T-cell leukemia virus type 1 transmembrane glycoprotein recognize the viral envelope but fail to neutralize viral entry. J Virol 2007; 81:6019-31. [PMID: 17376912 PMCID: PMC1900303 DOI: 10.1128/jvi.02544-06] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Human T-cell leukemia virus type 1 (HTLV-1) entry into cells is dependent upon the viral envelope glycoprotein-catalyzed fusion of the viral and cellular membranes. Following receptor activation of the envelope, the transmembrane glycoprotein (TM) is thought to undergo a series of fusogenic conformational transitions through a rod-like prehairpin intermediate to a compact trimer-of-hairpins structure. Importantly, synthetic peptides that interfere with the conformational changes of TM are potent inhibitors of membrane fusion and HTLV-1 entry, suggesting that TM is a valid target for antiviral therapy. To assess the utility of TM as a vaccine target and to explore further the function of TM in HTLV-1 pathogenesis, we have begun to examine the immunological properties of TM. Here we demonstrate that a recombinant trimer-of-hairpins form of the TM ectodomain is strongly immunogenic. Monoclonal antibodies raised against the TM immunogen specifically bind to trimeric forms of TM, including structures thought to be important for membrane fusion. Importantly, these antibodies recognize the envelope on virally infected cells but, surprisingly, fail to neutralize envelope-mediated membrane fusion or infection by pseudotyped viral particles. Our data imply that, even in the absence of overt membrane fusion, there are multiple forms of TM on virally infected cells and that some of these display fusion-associated structures. Finally, we demonstrate that many of the antibodies possess the ability to recruit complement to TM, suggesting that envelope-derived immunogens capable of eliciting a combination of neutralizing and complement-fixing antibodies would be of value as subunit vaccines for intervention in HTLV infections.
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Affiliation(s)
- Antonis Mirsaliotis
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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31
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Henderson HI, Hope TJ. The temperature arrested intermediate of virus-cell fusion is a functional step in HIV infection. Virol J 2006; 3:36. [PMID: 16725045 PMCID: PMC1482684 DOI: 10.1186/1743-422x-3-36] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2006] [Accepted: 05/25/2006] [Indexed: 11/10/2022] Open
Abstract
HIV entry occurs via membrane-mediated fusion of virus and target cells. Interactions between gp120 and cellular co-receptors lead to both the formation of fusion pores and release of the HIV genome into target cells. Studies using cell-cell fusion assays have demonstrated that a temperature-arrested state (TAS) can generate a stable intermediate in fusion related events. Other studies with MLV pseudotyped with HIV envelope also found that a temperature sensitive intermediate could be generated as revealed by the loss of a fluorescently labeled membrane. However, such an intermediate has never been analyzed in the context of virus infection. Therefore, we used virus-cell infection with replication competent HIV to gain insights into virus-cell fusion. We find that the TAS is an intermediate in the process culminating in the HIV infection of a target cell. In the virion-cell TAS, CD4 has been engaged, the heptad repeats of gp41 are exposed and the complex is kinetically predisposed to interact with coreceptor to complete the fusion event leading to infection.
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Affiliation(s)
- Hamani I Henderson
- University of Illinois @ Chicago, Department of Microbiology and Immunology, Chicago, IL 60612, USA
| | - Thomas J Hope
- Northwestern University Department of Cell and Molecular Biology, Chicago, IL 60611, USA
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32
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Furuta RA, Nishikawa M, Fujisawa JI. Real-time analysis of human immunodeficiency virus type 1 Env-mediated membrane fusion by fluorescence resonance energy transfer. Microbes Infect 2006; 8:520-32. [PMID: 16300985 DOI: 10.1016/j.micinf.2005.08.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2005] [Revised: 08/12/2005] [Accepted: 08/16/2005] [Indexed: 10/25/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env)-mediated membrane fusion occurs as a sequence of events that is triggered by CD4 binding to the Env gp120 subunit. In this study, we analyzed the dynamics of Env-mediated membrane fusion at the single-cell level using fluorescent fusion proteins and confocal laser fluorescent microscopy. Either enhanced cyan or yellow fluorescent protein (CFP and YFP, respectively) was fused to the end of the cytoplasmic regions of the HIV-1 receptors (CD4 and CCR5) and Env proteins. Real-time imaging of membrane fusion mediated by these recombinant proteins revealed that the kinetics of fusion in our system was faster than that previously reported. Analysis of the receptor interaction by fluorescence resonance energy transfer (FRET) at the single-cell level demonstrated a tendency for oligomerization of CD4-CD4, but not of CD4-CCR5, in the absence of Env-expressing cells. However, when Env-expressing cells attached to the receptor cells, FRET produced by CD4-CCR5 interaction was increased; the FRET intensity began to decline before the formation of the fusion pore. These changes in FRET may represent the temporal association of these receptors, triggered by gp120 binding, and their dissociation during the formation of the fusion pore. In addition, the FRET analysis of receptor interactions in the presence of fusion inhibitors showed that not only inhibitors acting on CCR5 but also the gp41-derived peptide T-20 interfered with CD4-CCR5 interaction during fusion. These data suggest that T-20 could affect the formation of Env-receptors complexes during the membrane fusion.
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Affiliation(s)
- Rika A Furuta
- Department of Microbiology, Kansai Medical University, 15-10 Fumizono-cho, Moriguchi, Osaka 570-8506, Japan
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33
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Dimmock NJ. The complex antigenicity of a small external region of the C-terminal tail of the HIV-1 gp41 envelope protein: a lesson in epitope analysis. Rev Med Virol 2005; 15:365-81. [PMID: 16106492 DOI: 10.1002/rmv.476] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The newly discovered external tail loop within the C-terminal tail of the gp41 transmembrane subunit of the HIV-1 envelope protein comprises approximately 40 residues, and within this are 18-residues ((734)PDRPEGIEEEGGERDRDR(751)) that include three antibody-reactive regions. The antigenicity is complex, and changes according to the biological context of the gp41. It is thus of interest both to the HIV specialist and protein immunologists. The antibody-reactive region, centred on the sequence ERDRD, encompasses three distinct epitopes which are expressed in different combinations on infected cells, wt virions, prefusion virion-cell complexes, and a neutralising antibody escape mutant virion. In addition ERDRD-specific antibodies have one or more antiviral activities, and variously neutralise the infectivity of free virions, neutralise virions already attached to the target cell, reduce the production of infectious progeny, and inhibit the ability of infected cells to fuse with non-infected cells. Antibodies to PDRPEG and IEEE have no apparent antiviral activity even though the footprints of the IEEE- and ERDRD-specific antibodies overlap. This review marshals the available experimental data with the aim of understanding the significance of the gp41 tail loop to the HIV-1 life cycle, and its relevance to potential anti-viral measures. There are lessons here, too, that are relevant to the comprehension of the antigenicity of short protein segments in general.
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Affiliation(s)
- Nigel J Dimmock
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
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34
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Subramanian RP, Dunn JE, Geraghty RJ. The nectin-1alpha transmembrane domain, but not the cytoplasmic tail, influences cell fusion induced by HSV-1 glycoproteins. Virology 2005; 339:176-91. [PMID: 16005040 PMCID: PMC1360157 DOI: 10.1016/j.virol.2005.05.031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2005] [Revised: 04/06/2005] [Accepted: 05/25/2005] [Indexed: 12/28/2022]
Abstract
Nectin-1 is a receptor for herpes simplex virus (HSV), a member of the immunoglobulin superfamily, and a cellular adhesion molecule. To study domains of nectin-1alpha involved in cell fusion, we measured the ability of nectin-1alpha/nectin-2alpha chimeras, nectin-1alpha/CD4 chimeras, and transmembrane domain and cytoplasmic tail mutants of nectin-1alpha to promote cell fusion induced by HSV-1 glycoproteins. Our results demonstrate that only chimeras and mutants containing the entire V-like domain and a link to the plasma membrane conferred cell-fusion activity. The transmembrane domain and cytoplasmic tail of nectin-1 were not required for any viral receptor or cell adhesion function tested. Cellular cytoplasmic factors that bind to the nectin-1alpha cytoplasmic tail, therefore, did not influence virus entry or cell fusion. Interestingly, the efficiency of cell fusion was reduced when membrane-spanning domains of nectin-1alpha and gD were replaced by glycosylphosphatidylinositol tethers, indicating that transmembrane domains may play a modulatory role in the gD/nectin-1alpha interaction in fusion.
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Affiliation(s)
| | | | - Robert J. Geraghty
- *To whom correspondence and reprint requests should be addressed at University of Kentucky, Department of Microbiology, Immunology, and Molecular Genetics, 800 Rose St., UKMC MS415, Lexington, KY 40536-0298. Telephone: (859)257-5147 Fax:(859)257-8994 E-mail:
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35
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Mkrtchyan SR, Markosyan RM, Eadon MT, Moore JP, Melikyan GB, Cohen FS. Ternary complex formation of human immunodeficiency virus type 1 Env, CD4, and chemokine receptor captured as an intermediate of membrane fusion. J Virol 2005; 79:11161-9. [PMID: 16103167 PMCID: PMC1193594 DOI: 10.1128/jvi.79.17.11161-11169.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus (HIV) Env-induced fusion is highly temperature dependent. When effector and target cells were coincubated at 37 degrees C, there was a kinetic delay before fusion commenced. When effector and target cells were coincubated for varied times at 23 degrees C, a temperature that does not permit fusion, a temperature-arrested stage was created. Raising temperature to 37 degrees C from the 23 degrees C intermediate eliminated the kinetic delay. Inhibitors (T22, AMD3100, and Sch-C) that block fusion by binding chemokine receptors were added after creating the intermediate so as to assess the extent of engagement between gp120 and chemokine receptors at that stage. For both CXCR4 and CCR5 as coreceptors, increasingly long times of coincubation at 23 degrees C reduced the efficacy of the coreceptor-binding inhibitors in blocking fusion. This implies that an increasing number of ternary Env/CD4/coreceptor complexes form over time at 23 degrees C. It also shows that ternary complex formation has a lower temperature threshold than the downstream steps that include Env folding into a six-helix bundle; this provides an experimental means to separate coreceptor binding by gp120 from the subsequent refolding of gp41 into a six-helix bundle structure. As the time of cell coincubation at 23 degrees C was prolonged, more cells quickly fused upon the raising of the temperature to 37 degrees C, and the increase quantitatively correlated with the greater percentage of fusion that was resistant to drugs. Therefore the pronounced kinetic delay in HIV Env-induced fusion is caused predominantly by the time needed for ternary complexes to form.
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Affiliation(s)
- Samvel R Mkrtchyan
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612, USA
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36
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Harada S, Yusa K, Monde K, Akaike T, Maeda Y. Influence of membrane fluidity on human immunodeficiency virus type 1 entry. Biochem Biophys Res Commun 2005; 329:480-6. [PMID: 15737612 DOI: 10.1016/j.bbrc.2005.02.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Indexed: 11/25/2022]
Abstract
For penetration of human immunodeficiency virus type 1 (HIV-1), formation of fusion-pores might be required for accumulating critical numbers of fusion-activated gp41, followed by multiple-site binding of gp120 with receptors, with the help of fluidization of the plasma membrane and viral envelope. Correlation between HIV-1 infectivity and fluidity was observed by treatment of fluidity-modulators, indicating that infectivity was dependent on fluidity. A 5% decrease in fluidity suppressed the HIV-1 infectivity by 56%. Contrarily, a 5% increase in fluidity augmented the infectivity by 2.4-fold. An increased temperature of 40 degrees C or treatment of 0.2% xylocaine after viral adsorption at room temperature enhanced the infectivity by 2.6- and 1.5-fold, respectively. These were inhibited by anti-CXCR4 peptide, implying that multiple-site binding was accelerated at 40 degrees C or by xylocaine. Thus, fluidity of both the plasma membrane and viral envelope was required to form the fusion-pore and to complete the entry of HIV-1.
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Affiliation(s)
- Shinji Harada
- Department of Medical Virology, Graduate School of Medical Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
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37
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Abstract
Cells of the immune system communicate via the formation of receptor-containing adhesive junctions termed immunological synapses. Recently, retroviruses have been shown to subvert this process in order to pass directly from infected to uninfected immune cells. Such cell-cell viral dissemination appears to function by triggering existing cellular pathways involved in antigen presentation and T-cell communication. This mode of viral spread has important consequences for both the virus and the host cells in terms of viral pathogenesis and viral resistance to immune and therapeutic intervention. This review summarises the current knowledge concerning virological synapses induced by retroviruses.
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Affiliation(s)
- Clare Jolly
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE.
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38
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Abstract
Every enveloped virus fuses its membrane with a host cell membrane, thereby releasing its genome into the cytoplasm and initiating the viral replication cycle. In each case, one or a small set of viral surface transmembrane glycoproteins mediates fusion. Viral fusion proteins vary in their mode of activation and in structural class. These features combine to yield many different fusion mechanisms. Despite their differences, common principles for how fusion proteins function are emerging: In response to an activating trigger, the metastable fusion protein converts to an extended, in some cases rodlike structure, which inserts into the target membrane via its fusion peptide. A subsequent conformational change causes the fusion protein to fold back upon itself, thereby bringing its fusion peptide and its transmembrane domain-and their attached target and viral membranes-into intimate contact. Fusion ensues as the initial lipid stalk progresses through local hemifusion, and then opening and enlargement of a fusion pore. Here we review recent advances in our understanding of how fusion proteins are activated, how fusion proteins change conformation during fusion, and what is happening to the lipids during fusion. We also briefly discuss the therapeutic potential of fusion inhibitors in treating viral infections.
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Affiliation(s)
- Mark Marsh
- Cell Biology Unit, MRC-LMCB, University College London, Gower Street, London, WC1E 6BT UK
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39
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Jolly C, Kashefi K, Hollinshead M, Sattentau QJ. HIV-1 cell to cell transfer across an Env-induced, actin-dependent synapse. ACTA ACUST UNITED AC 2004; 199:283-93. [PMID: 14734528 PMCID: PMC2211771 DOI: 10.1084/jem.20030648] [Citation(s) in RCA: 476] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Direct cell–cell transfer is an efficient mechanism of viral dissemination within an infected host, and human immunodeficiency virus 1 (HIV-1) can exploit this mode of spread. Receptor recognition by HIV-1 occurs via interactions between the viral surface envelope glycoprotein (Env), gp120, and CD4 and a chemokine receptor, CCR5 or CXCR4. Here, we demonstrate that the binding of CXCR4-using HIV-1–infected effector T cells to primary CD4+/CXCR4+ target T cells results in rapid recruitment to the interface of CD4, CXCR4, talin, and lymphocyte function–associated antigen 1 on the target cell, and of Env and Gag on the effector cell. Recruitment of these membrane molecules into polarized clusters was dependent on Env engagement of CD4 and CXCR4 and required remodelling of the actin cytoskeleton. Transfer of Gag from effector to target cell was observed by 1 h after conjugate formation, was independent of cell–cell fusion, and was probably mediated by directed virion fusion with the target cell. We propose that receptor engagement by Env directs the rapid, actin-dependent recruitment of HIV receptors and adhesion molecules to the interface, resulting in a stable adhesive junction across which HIV infects the target cell.
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Affiliation(s)
- Clare Jolly
- The Sir William Dunn School of Pathology, University of Oxford, UK
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40
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Gallo SA, Clore GM, Louis JM, Bewley CA, Blumenthal R. Temperature-dependent intermediates in HIV-1 envelope glycoprotein-mediated fusion revealed by inhibitors that target N- and C-terminal helical regions of HIV-1 gp41. Biochemistry 2004; 43:8230-3. [PMID: 15209519 DOI: 10.1021/bi049957v] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Peptides derived from the N- (N-HR) and C- (C-HR) terminal heptad repeat regions adjacent to the fusion peptide and transmembrane domains, respectively, of human immunodeficiency virus (HIV)-1 gp41 inhibit HIV-1 viral envelope glycoproteins (Env)-mediated cell fusion specifically. The mechanism of HIV-1 Env-mediated cell fusion and its inhibition by agents that target the N- and C-HR regions was investigated. Priming experiments with Env-expressing cells indicate that the N-HR region but not the C-HR region is exposed by treatment with sCD4 at 31 degrees C, whereas both the N- and C-HR regions are exposed at 37 degrees C.
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Affiliation(s)
- Stephen A Gallo
- Laboratory of Experimental and Computational Biology, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA
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Harada S, Akaike T, Yusa K, Maeda Y. Adsorption and infectivity of human immunodeficiency virus type 1 are modified by the fluidity of the plasma membrane for multiple-site binding. Microbiol Immunol 2004; 48:347-55. [PMID: 15107546 DOI: 10.1111/j.1348-0421.2004.tb03516.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Based on the assumption that fluidity of the plasma membrane and viral envelope is necessary for recruiting additional receptors and ligands to the initial attachment site for "multiple-site binding," we determined the effect of increased temperature on viral infectivity. Infection of human immunodeficiency virus type 1 (HIV-1) and a pseudotyped luciferase-expressing chimeric virus using MAGI and GHOST/CXCR4 cells showed that in 1 hr of viral adsorption the extent of virus infection and the amount of tightly adsorbed viruses depended on temperature; and that membrane fluidity increased according to increased temperature. Augmented infection was observed as post-attachment enhancement (PAE) when cells were washed and incubated at 40 C for 1 hr after viral adsorption. PAE was completely inhibited by 1 micro M of anti-CXCR4 peptide T140, and addition of T140 at 20 min resulted in a gradual loss of inhibition of PAE, indicating the need for a 30 to 40 min timelag to ensure tight multiple-site binding. These data suggest that the accumulation of gp120 and receptor complex (multiple-site binding) was needed to complete the infection. Treatments of cells with 0.05% Tween 20 or 2 micro g/ml of anti-HLA-II antibody resulted in increases or decreases, respectively, of attached viruses and the infectivity. As well, Tween 20 and anti-HLAII antibody enhanced and suppressed the fluidity of the plasma membrane, respectively. Amounts of adsorbed viruses and degrees of viral infectivity correlated with the intensity of fluidity of the plasma membrane, probably due to the formation of multiple-site binding.
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Affiliation(s)
- Shinji Harada
- Department of Medical Virology, Graduate School of Medical Sciences, Kumamoto University, Japan.
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42
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Qian Z, Wang H, Empig C, Anderson WF, Albritton LM. Complementation of a binding-defective retrovirus by a host cell receptor mutant. J Virol 2004; 78:5766-72. [PMID: 15140974 PMCID: PMC415786 DOI: 10.1128/jvi.78.11.5766-5772.2004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The entry of ecotropic murine leukemia virus (MLV) into cells requires the interaction of the envelope protein (Env) with its receptor, mouse cationic amino acid transporter 1 (mATRC1). An aspartic acid-to-lysine change at position 84 (D84K) of ecotropic Moloney MLV Env abolishes virus binding and infection. We recently identified lysine 234 (rK234) in mATRC1 as a residue that influences virus binding and infection. Here we show that D84K virus infection increased 3,000-fold on cells expressing receptor with an rK234A change and 100,000-fold on cells expressing an rK234D change. The stronger complementation of D84K virus infection by rK234D than by the rK234A receptor suggests that although the major reason for loss of infection of D84K and D84R virus is due to steric hindrance and charge repulsion, the loss of an interaction of D84 with receptor appears to contribute as well. Taken together, these results indicate that D84 is very close to rK234 of mATRC1 in the bound complex and there is likely an interaction between them. The definitive localization of the receptor binding site on SU should facilitate the design of chimeric envelope proteins that target infection to new receptors by replacing the receptor binding site with an exogenous ligand sequence.
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Affiliation(s)
- Zhaohui Qian
- Department of Molecular Sciences, University of Tennessee Health Science Center, 858 Madison Ave., Room G01, Memphis, TN 38163, USA
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43
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Rawat SS, Eaton J, Gallo SA, Martin TD, Ablan S, Ratnayake S, Viard M, KewalRamani VN, Wang JM, Blumenthal R, Puri A. Functional expression of CD4, CXCR4, and CCR5 in glycosphingolipid-deficient mouse melanoma GM95 cells and susceptibility to HIV-1 envelope glycoprotein-triggered membrane fusion. Virology 2004; 318:55-65. [PMID: 14972535 DOI: 10.1016/j.virol.2003.08.042] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2003] [Revised: 08/19/2003] [Accepted: 08/28/2003] [Indexed: 11/27/2022]
Abstract
We had previously reported that glycosphingolipids (GSL) support human immunodeficiency virus type 1 (HIV-1) entry. In this study, we further examined this issue by expressing HIV-1 receptors in GSL-deficient GM95 cells. GM95 cells expressing low levels of CD4 and CXCR4 or CCR5 did not support HIV-1 Env-mediated fusion. However, higher expression of these receptors rendered GM95 cells highly susceptible to fusion with cells expressing appropriate HIV-1 envelope glycoproteins (HIV-1 Envs). The GM95 cells exhibited a different fusion phenotype when compared with GSL(+) NIH3T3 cells bearing similar receptor levels. Fusion of GM95 targets expressing higher levels of CD4 and coreceptors occurred at 25 degrees C and was sensitive to cholesterol depletion or disruption of the cytoskeleton. In contrast, the fusion threshold of NIH3T3CD4X4/R5 targets was at >/=28 degrees C as previously reported and was insensitive to cholesterol depletion or cytoskeletal network disruption. On the basis of these observations, we propose that target membrane GSLs support HIV-1 Env-mediated fusion at low density of receptors by stabilizing receptor pools in natural targets.
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Affiliation(s)
- Satinder S Rawat
- Laboratory of Experimental and Computational Biology, Center for Cancer Research, NCI-Frederick, National Institutes of Health, Frederick, MD 21702-1201, USA
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44
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Tailor CS, Lavillette D, Marin M, Kabat D. Cell surface receptors for gammaretroviruses. Curr Top Microbiol Immunol 2003; 281:29-106. [PMID: 12932075 DOI: 10.1007/978-3-642-19012-4_2] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Evidence obtained during the last few years has greatly extended our understanding of the cell surface receptors that mediate infections of retroviruses and has provided many surprising insights. In contrast to other cell surface components such as lectins or proteoglycans that influence infections indirectly by enhancing virus adsorption onto specific cells, the true receptors induce conformational changes in the viral envelope glycoproteins that are essential for infection. One surprise is that all of the cell surface receptors for gamma-retroviruses are proteins that have multiple transmembrane (TM) sequences, compatible with their identification in known instances as transporters for important solutes. In striking contrast, almost all other animal viruses use receptors that exclusively have single TM sequences, with the sole proven exception we know of being the coreceptors used by lentiviruses. This evidence strongly suggests that virus genera have been prevented because of their previous evolutionary adaptations from switching their specificities between single-TM and multi-TM receptors. This evidence also implies that gamma-retroviruses formed by divergent evolution from a common origin millions of years ago and that individual viruses have occasionally jumped between species (zoonoses) while retaining their commitment to using the orthologous receptor of the new host. Another surprise is that many gamma-retroviruses use not just one receptor but pairs of closely related receptors as alternatives. This appears to have enhanced viral survival by severely limiting the likelihood of host escape mutations. All of the receptors used by gamma-retroviruses contain hypervariable regions that are often heavily glycosylated and that control the viral host range properties, consistent with the idea that these sequences are battlegrounds of virus-host coevolution. However, in contrast to previous assumptions, we propose that gamma-retroviruses have become adapted to recognize conserved sites that are important for the receptor's natural function and that the hypervariable sequences have been elaborated by the hosts as defense bulwarks that surround the conserved viral attachment sites. Previously, it was believed that binding to receptors directly triggers a series of conformational changes in the viral envelope glycoproteins that culminate in fusion of the viral and cellular membranes. However, new evidence suggests that gamma-retroviral association with receptors triggers an obligatory interaction or cross-talk between envelope glycoproteins on the viral surface. If this intermediate step is prevented, infection fails. Conversely, in several circumstances this cross-talk can be induced in the absence of a cell surface receptor for the virus, in which case infection can proceed efficiently. This new evidence strongly implies that the role of cell surface receptors in infections of gamma-retroviruses (and perhaps of other enveloped animal viruses) is more complex and interesting than was previously imagined. Recently, another gammaretroviral receptor with multiple transmembrane sequences was cloned. See Prassolov, Y., Zhang, D., Ivanov, D., Lohler, J., Ross, S.R., and Stocking, C. Sodium-dependent myo-inositol transporter 1 is a receptor for Mus cervicolor M813 murine leukemia virus.
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Affiliation(s)
- C S Tailor
- Infection, Immunity Injury and Repair Program, Hospital for Sick Children, Toronto, ON M5G 1XB, Canada
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Abstract
Entry of HIV-1 virions into cells is a complex and dynamic process carried out by envelope (Env) glycoproteins on the surface of the virion that promote the thermodynamically unfavorable fusion of highly stable viral and target cell membranes. Insight gained from studies of the mechanism of viral entry allowed insight into the design of novel inhibitors of HIV-1 entry, several of which are now in clinical trials. This review highlights the mechanism by which viral and cellular proteins mediate entry of HIV-1 into permissive cells, with an emphasis on targeting this process in the design of novel therapies that target distinct steps of the entry process, including antagonizing receptor binding events and blocking conformational changes intimately involved in membrane fusion.
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Affiliation(s)
- T C Pierson
- Department of Microbiology, University of Pennsylvania, 301C Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
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Labrijn AF, Poignard P, Raja A, Zwick MB, Delgado K, Franti M, Binley J, Vivona V, Grundner C, Huang CC, Venturi M, Petropoulos CJ, Wrin T, Dimitrov DS, Robinson J, Kwong PD, Wyatt RT, Sodroski J, Burton DR. Access of antibody molecules to the conserved coreceptor binding site on glycoprotein gp120 is sterically restricted on primary human immunodeficiency virus type 1. J Virol 2003; 77:10557-65. [PMID: 12970440 PMCID: PMC228502 DOI: 10.1128/jvi.77.19.10557-10565.2003] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Anti-human immunodeficiency virus type 1 (HIV-1) antibodies whose binding to gp120 is enhanced by CD4 binding (CD4i antibodies) are generally considered nonneutralizing for primary HIV-1 isolates. However, a novel CD4i-specific Fab fragment, X5, has recently been found to neutralize a wide range of primary isolates. To investigate the precise nature of the extraordinary neutralizing ability of Fab X5, we evaluated the abilities of different forms (immunoglobulin G [IgG], Fab, and single-chain Fv) of X5 and other CD4i monoclonal antibodies to neutralize a range of primary HIV-1 isolates. Our results show that, for a number of isolates, the size of the neutralizing agent is inversely correlated with its ability to neutralize. Thus, the poor ability of CD4i-specific antibodies to neutralize primary isolates is due, at least in part, to steric factors that limit antibody access to the gp120 epitopes. Studies of temperature-regulated neutralization or fusion-arrested intermediates suggest that the steric effects are important in limiting the binding of IgG to the viral envelope glycoproteins after HIV-1 has engaged CD4 on the target cell membrane. The results identify hurdles in using CD4i epitopes as targets for antibody-mediated neutralization in vaccine design but also indicate that the CD4i regions could be efficiently targeted by small molecule entry inhibitors.
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Affiliation(s)
- Aran F Labrijn
- Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA
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Gallo SA, Finnegan CM, Viard M, Raviv Y, Dimitrov A, Rawat SS, Puri A, Durell S, Blumenthal R. The HIV Env-mediated fusion reaction. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1614:36-50. [PMID: 12873764 DOI: 10.1016/s0005-2736(03)00161-5] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The current general model of HIV viral entry involves the binding of the trimeric viral envelope glycoprotein gp120/gp41 to cell surface receptor CD4 and chemokine co-receptor CXCR4 or CCR5, which triggers conformational changes in the envelope proteins. Gp120 then dissociates from gp41, allowing for the fusion peptide to be inserted into the target membrane and the pre-hairpin configuration of the ectodomain to form. The C-terminal heptad repeat region and the leucine/isoleucine zipper region then form the thermostable six-helix coiled-coil, which drives the membrane merger and eventual fusion. This model needs updating, as there has been a wealth of data produced in the last few years concerning HIV entry, including target cell dependencies, fusion kinetic data, and conformational intermediates. A more complete model must include the involvement of membrane microdomains, actin polymerization, glycosphingolipids, and possibly CD4 and chemokine signaling in entry. In addition, kinetic experiments involving the addition of fusion inhibitors have revealed some of the rate-limiting steps in this process, adding a temporal component to the model. A review of these data that may require an updated version of the original model is presented here.
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Affiliation(s)
- Stephen A Gallo
- Laboratory of Experimental and Computational Biology, Center for Cancer Research, NCI-Frederick, National Institute of Health, Miller Drive, Frederick, MD 21702-1201, USA
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48
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Gómez-Treviño A, Castel S, López-Iglesias C, Cortadellas N, Comas-Riu J, Mercadé E. Effects of adenovirus-mediated SV5 fusogenic glycoprotein expression on tumor cells. J Gene Med 2003; 5:483-92. [PMID: 12797113 DOI: 10.1002/jgm.371] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND The fusogenic (F) membrane glycoprotein of the paramyxovirus SV5 allows virus to enter host cells and mediates fusion between neighboring cells, which leads to cell death. F glycoprotein is synthesized as an inactive precursor (F(0)) that is cleaved by cellular protease furine to form the active heterodimer F(1) + F(2). The active protein can induce syncytium formation in the absence of another integral glycoprotein (HN), a property that appears to be unique among paramyxoviruses. METHODOLOGY We constructed a non-replicative adenovirus to express SV5 F protein in tumor cells, and its fusion capacity was analyzed by fluorescent and confocal microscopy. Cell viability and bystander effect were compared with the thymidine kinase/ganciclovir suicide gene therapy. The structure of F-expressing cells was studied using electron microscopy. RESULTS F glycoprotein expression induced syncytium formation to a maximum at 72 h, after which syncytia progressively lost viability and detached. The cell membrane was disrupted while nuclear structure was preserved. Over-expression of SV5 F protein in tumor cells led to high cytotoxicity comparable with that associated with the thymidine kinase/ganciclovir. A potent bystander killing effect was detected until the ratio of F-transduced to non-transduced cells was 1 : 100. CONCLUSIONS These results indicate that the fusogenic glycoprotein of the paramyxovirus SV5 could be used to eliminate tumor cells and may encourage studies aimed at modifying its selectivity and combining its expression with other cytotoxic strategies to improve their efficacy.
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Affiliation(s)
- A Gómez-Treviño
- Department of Microbiology, University of Barcelona, 08028 Barcelona, Spain
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49
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Lin X, Derdeyn CA, Blumenthal R, West J, Hunter E. Progressive truncations C terminal to the membrane-spanning domain of simian immunodeficiency virus Env reduce fusogenicity and increase concentration dependence of Env for fusion. J Virol 2003; 77:7067-77. [PMID: 12768026 PMCID: PMC156184 DOI: 10.1128/jvi.77.12.7067-7077.2003] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The simian immunodeficiency virus (SIV) transmembrane (TM) protein, gp41, has multiple functions, which include anchoring the glycoprotein complex in the lipid envelope of the virus and mediating fusion of the virus and host cell membranes. Recently, a series of mutants of the SIVmac239 TM protein that have truncations at the carboxyl terminus of the membrane-spanning domain (MSD) have been characterized (J. T. West, P. Johnston, S. R. Dubay, and E. Hunter, J. Virol. 75:9601-9612, 2001). These mutants retained membrane anchorage but demonstrated reduced fusogenicity and infectivity as the MSD length was shortened. We have established a novel three-color fluorescence assay, which allows qualitative confocal and quantitative flow cytometric analyses, to further characterize the nature of the fusion defect in five of the MSD mutants: TM185, TM186, TM187, TM188, and TM189. Our analysis showed that each mutant could mediate complete lipid and aqueous dye transfer at early time points after effector and target cell mixing. No hemifusion with only lipid dye flux was detected. However, another intermediate fusion stage, which appears to involve small-fusion-pore formation that allowed small aqueous dye transfer but prevented the exchange of large cytoplasmic components, was identified infrequently in mutant-Env-expressing cell and target cell mixtures. Quantitative flow cytometric analysis of these mutants demonstrated that the TM187, TM188, and TM189 mutants were significantly more fusogenic than TM185 and TM186 but remained significantly impaired compared to the wild type. Moreover, fusion efficiency showed an increased dependence on the expression level of glycoproteins, suggesting that, for these mutants, formation of an active fusion complex was an increasingly stochastic event.
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Affiliation(s)
- Xiaoxu Lin
- Department of Microbiology, The University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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50
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Binley JM, Cayanan CS, Wiley C, Schülke N, Olson WC, Burton DR. Redox-triggered infection by disulfide-shackled human immunodeficiency virus type 1 pseudovirions. J Virol 2003; 77:5678-84. [PMID: 12719560 PMCID: PMC154040 DOI: 10.1128/jvi.77.10.5678-5684.2003] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2002] [Accepted: 02/14/2003] [Indexed: 11/20/2022] Open
Abstract
We previously described a human immunodeficiency virus type 1 (HIV-1) envelope mutant that introduces a disulfide bridge between the gp120 surface proteins and gp41 transmembrane proteins (J. M. Binley, R. W. Sanders, B. Clas, N. Schuelke, A. Master, Y. Guo, F. Kajumo, D. J. Anselma, P. J. Maddon, W. C. Olson, and J. P. Moore, J. Virol. 74:627-643, 2000). Here we produced pseudovirions bearing the mutant envelope and a reporter gene to examine the mutant's infectious properties. These pseudovirions attach to cells expressing CD4 and coreceptor but infect only when triggered with reducing agent, implying that gp120-gp41 dissociation is necessary for infection. Further studies suggested that virus entry was arrested after CD4 and coreceptor engagement. By measuring the activities of various entry inhibitors against the arrested intermediate, we found that gp120-targeting inhibitors typically act prior to virus attachment, whereas gp41 inhibitors are able to act postattachment. Unexpectedly, a significant fraction of antibodies in HIV-1-positive sera neutralized virus postattachment, suggesting that downstream fusion events and structures figure prominently in the host immune response. Overall, this disulfide-shackled virus is a unique tool with potential utility in vaccine design, drug discovery, and elucidation of the HIV-1 entry process.
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Affiliation(s)
- James M Binley
- Departments of Immunology and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
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