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Abstract
Human and simian immunodeficiency viruses (HIVs and SIVs, respectively) encode several small proteins (Vif, Vpr, Nef, Vpu, and Vpx) that are called accessory because they are not generally required for viral replication in cell culture. However, they play complex and important roles for viral immune evasion and spread in vivo. Here, we discuss the diverse functions and the relevance of the viral protein U (Vpu) that is expressed from a bicistronic RNA during the late stage of the viral replication cycle and found only in HIV-1 and closely related SIVs. It is well established that Vpu counteracts the restriction factor tetherin, mediates degradation of the primary viral CD4 receptors, and inhibits activation of the transcription factor nuclear factor kappa B. Recent studies identified additional activities and provided new insights into the sophisticated mechanisms by which Vpu enhances and prolongs the release of fully infectious viral particles. In addition, it has been shown that Vpu prevents superinfection not only by degrading CD4 but also by modulating DNA repair mechanisms to promote degradation of nuclear viral complementary DNA in cells that are already productively infected.
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Affiliation(s)
- Meta Volcic
- Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany;
| | - Lisa Wiesmüller
- Division of Gynecological Oncology, Department of Obstetrics and Gynecology, Ulm University Medical Center, Ulm, Germany
| | - Frank Kirchhoff
- Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany;
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2
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Prévost J, Anand SP, Rajashekar JK, Zhu L, Richard J, Goyette G, Medjahed H, Gendron-Lepage G, Chen HC, Chen Y, Horwitz JA, Grunst MW, Zolla-Pazner S, Haynes BF, Burton DR, Flavell RA, Kirchhoff F, Hahn BH, Smith AB, Pazgier M, Nussenzweig MC, Kumar P, Finzi A. HIV-1 Vpu restricts Fc-mediated effector functions in vivo. Cell Rep 2022; 41:111624. [PMID: 36351384 PMCID: PMC9703018 DOI: 10.1016/j.celrep.2022.111624] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 09/02/2022] [Accepted: 10/17/2022] [Indexed: 11/09/2022] Open
Abstract
Non-neutralizing antibodies (nnAbs) can eliminate HIV-1-infected cells via antibody-dependent cellular cytotoxicity (ADCC) and were identified as a correlate of protection in the RV144 vaccine trial. Fc-mediated effector functions of nnAbs were recently shown to alter the course of HIV-1 infection in vivo using a vpu-defective virus. Since Vpu is known to downregulate cell-surface CD4, which triggers conformational changes in the viral envelope glycoprotein (Env), we ask whether the lack of Vpu expression was linked to the observed nnAbs activity. We find that restoring Vpu expression greatly reduces nnAb recognition of infected cells, rendering them resistant to ADCC. Moreover, administration of nnAbs in humanized mice reduces viral loads only in animals infected with a vpu-defective but not with a wild-type virus. CD4-mimetics administration, known to "open" Env and expose nnAb epitopes, renders wild-type viruses sensitive to nnAbs Fc-effector functions. This work highlights the importance of Vpu-mediated evasion of humoral responses.
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Affiliation(s)
- Jérémie Prévost
- Centre de Recherche du CHUM, Montreal, QC H2X 0A9, Canada; Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, QC H2X 0A9, Canada.
| | - Sai Priya Anand
- Centre de Recherche du CHUM, Montreal, QC H2X 0A9, Canada; Department of Microbiology and Immunology, McGill University, Montreal, QC H3A 2B4, Canada
| | - Jyothi Krishnaswamy Rajashekar
- Department of Internal Medicine, Section of Infectious Diseases, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Li Zhu
- Department of Internal Medicine, Section of Infectious Diseases, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Jonathan Richard
- Centre de Recherche du CHUM, Montreal, QC H2X 0A9, Canada; Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, QC H2X 0A9, Canada
| | | | | | | | - Hung-Ching Chen
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
| | - Yaozong Chen
- Infectious Diseases Division, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4712, USA
| | - Joshua A Horwitz
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Michael W Grunst
- Department of Internal Medicine, Section of Infectious Diseases, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Susan Zolla-Pazner
- Department of Medicine, Division of Infectious Diseases, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Barton F Haynes
- Duke Human Vaccine Institute, Departments of Medicine and Immunology, Duke University School of Medicine, Durham, NC 27710, USA; Consortium for HIV/AIDS Vaccine Development (CHAVD), Duke University, Durham, NC 27710, USA
| | - Dennis R Burton
- Department of Immunology and Microbiology, The Scripps Research Institute, La Jolla, CA 92037, USA; Consortium for HIV/AIDS Vaccine Development (CHAVD), The Scripps Research Institute, La Jolla, CA 92037, USA; Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology, Harvard University, Cambridge, MA 02139, USA
| | - Richard A Flavell
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06519, USA
| | - Frank Kirchhoff
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany
| | - Beatrice H Hahn
- Departments of Medicine and Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6076, USA
| | - Amos B Smith
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
| | - Marzena Pazgier
- Infectious Diseases Division, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4712, USA
| | - Michel C Nussenzweig
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Priti Kumar
- Department of Internal Medicine, Section of Infectious Diseases, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Andrés Finzi
- Centre de Recherche du CHUM, Montreal, QC H2X 0A9, Canada; Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, QC H2X 0A9, Canada; Department of Microbiology and Immunology, McGill University, Montreal, QC H3A 2B4, Canada.
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Prévost J, Richard J, Gasser R, Medjahed H, Kirchhoff F, Hahn BH, Kappes JC, Ochsenbauer C, Duerr R, Finzi A. Detection of the HIV-1 Accessory Proteins Nef and Vpu by Flow Cytometry Represents a New Tool to Study Their Functional Interplay within a Single Infected CD4 + T Cell. J Virol 2022; 96:e0192921. [PMID: 35080425 PMCID: PMC8941894 DOI: 10.1128/jvi.01929-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 01/16/2022] [Indexed: 11/20/2022] Open
Abstract
The HIV-1 Nef and Vpu accessory proteins are known to protect infected cells from antibody-dependent cellular cytotoxicity (ADCC) responses by limiting exposure of CD4-induced (CD4i) envelope (Env) epitopes at the cell surface. Although both proteins target the host receptor CD4 for degradation, the extent of their functional redundancy is unknown. Here, we developed an intracellular staining technique that permits the intracellular detection of both Nef and Vpu in primary CD4+ T cells by flow cytometry. Using this method, we show that the combined expression of Nef and Vpu predicts the susceptibility of HIV-1-infected primary CD4+ T cells to ADCC by HIV+ plasma. We also show that Vpu cannot compensate for the absence of Nef, thus providing an explanation for why some infectious molecular clones that carry a LucR reporter gene upstream of Nef render infected cells more susceptible to ADCC responses. Our method thus represents a new tool to dissect the biological activity of Nef and Vpu in the context of other host and viral proteins within single infected CD4+ T cells. IMPORTANCE HIV-1 Nef and Vpu exert several biological functions that are important for viral immune evasion, release, and replication. Here, we developed a new method allowing simultaneous detection of these accessory proteins in their native form together with some of their cellular substrates. This allowed us to show that Vpu cannot compensate for the lack of a functional Nef, which has implications for studies that use Nef-defective viruses to study ADCC responses.
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Affiliation(s)
- Jérémie Prévost
- Centre de Recherche du CHUM, Montreal, Quebec, Canada
- Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, Quebec, Canada
| | - Jonathan Richard
- Centre de Recherche du CHUM, Montreal, Quebec, Canada
- Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, Quebec, Canada
| | - Romain Gasser
- Centre de Recherche du CHUM, Montreal, Quebec, Canada
- Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, Quebec, Canada
| | | | - Frank Kirchhoff
- Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany
| | - Beatrice H. Hahn
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Department Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - John C. Kappes
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Christina Ochsenbauer
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Ralf Duerr
- Department of Microbiology, New York University School of Medicine, New York, New York, USA
| | - Andrés Finzi
- Centre de Recherche du CHUM, Montreal, Quebec, Canada
- Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, Quebec, Canada
- Department of Microbiology and Immunology, McGill University, Montreal, Quebec, Canada
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Lewinski MK, Jafari M, Zhang H, Opella SJ, Guatelli J. Membrane Anchoring by a C-terminal Tryptophan Enables HIV-1 Vpu to Displace Bone Marrow Stromal Antigen 2 (BST2) from Sites of Viral Assembly. J Biol Chem 2015; 290:10919-33. [PMID: 25759385 DOI: 10.1074/jbc.m114.630095] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Indexed: 12/28/2022] Open
Abstract
The restriction factor BST2 (tetherin) prevents the release of enveloped viruses from the host cell and is counteracted by HIV-1 Vpu. Vpu and BST2 interact directly via their transmembrane domains. This interaction enables Vpu to induce the surface down-regulation and the degradation of BST2, but neither of these activities fully accounts for the ability of Vpu to enhance virion release. During a study of naturally occurring Vpu proteins, we found that a tryptophan residue near the Vpu C terminus is particularly important for enhancing virion release. Vpu proteins with a W76G polymorphism degraded and down-regulated BST2 from the cell surface, yet they inefficiently stimulated virion release. Here we explore the mechanism of this anomaly. We find that Trp-76 is critical for the ability of Vpu to displace BST2 from sites of viral assembly in the plane of the plasma membrane. This effect does not appear to involve a general reorganization of the membrane microdomains associated with virion assembly, but rather is a specific effect of Vpu on BST2. Using NMR spectroscopy, we find that the cytoplasmic domain of Vpu and Trp-76 specifically interact with lipids. Moreover, paramagnetic relaxation enhancement studies show that Trp-76 inserts into the lipid. These data are consistent with a model whereby Trp-76 anchors the C terminus of the cytoplasmic tail of Vpu to the plasma membrane, enabling the movement of Vpu-bound BST2 away from viral assembly sites.
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Affiliation(s)
- Mary K Lewinski
- From the Departments of Medicine and the Veterans Affairs San Diego Healthcare System, San Diego, California 92161
| | | | - Hua Zhang
- Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0679 and
| | - Stanley J Opella
- Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0679 and
| | - John Guatelli
- From the Departments of Medicine and the Veterans Affairs San Diego Healthcare System, San Diego, California 92161
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Activities of transmitted/founder and chronic clade B HIV-1 Vpu and a C-terminal polymorphism specifically affecting virion release. J Virol 2014; 88:5062-78. [PMID: 24574397 DOI: 10.1128/jvi.03472-13] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
UNLABELLED Acute HIV-1 infection is characterized by a type I interferon response, resulting in the induction of host restriction factors. HIV-1 has evolved to counteract these factors, and one such adaptation, the ability of Vpu to counteract BST2/tetherin, is associated with the evolution of simian immunodeficiency virus (SIVcpz) into pandemic group M human immunodeficiency virus type 1 (HIV-1). During transmission between individuals, very few viruses or even a single virus, the "transmitted/founder" (T/F) virus, gives rise to the new infection, but in the new host the selective pressure of the immune response yields the diverse "quasispecies" of chronic infection. Here we examine the functional characteristics of Vpu proteins encoded by T/F viruses compared to acute and chronic viruses from longitudinally sampled subjects. The studied T/F Vpu proteins showed a trend toward optimized CD4 downregulation compared to chronic Vpu proteins but did not differ substantially in their ability to downregulate BST2 or enhance virion release, although individual clones from each group were impaired in these activities. Analysis of the functionally impaired clones identified a C-terminal residue, W76, as important specifically for Vpu enhancement of virion release. Primary Vpu clones encoding a W76G polymorphism, or site-directed mutants encoding a W76G substitution, were impaired in their ability to enhance virion release, but they were not defective for BST2 surface downregulation. Conversely, the virion release function of impaired primary clones was restored by creating a G76W substitution. The identification of W76 as important for virion release enhancement that is independent of BST2 surface downregulation supports the potential to mechanistically separate these functions of Vpu. IMPORTANCE To establish infection in a host, HIV-1 must evade the host's immune response, including the production of antiviral factors. HIV-1 encodes proteins that antagonize these defenses, including Vpu. Vpu counteracts the host protein BST2, which blocks the release of progeny viruses from the host cell. To determine the importance of Vpu activity to HIV-1 transmission, this study assessed the functionality of Vpu from viruses isolated soon after transmission ("transmitted/founder" viruses) compared to isolates from chronic infection. Although the anti-BST2 activity of Vpu proteins from the tested transmitted/founder viruses did not differ from the activity of the chronic Vpu proteins, the transmitted/founder Vpu proteins trended toward having superior activity against another host protein, CD4. Further, this study identified an amino acid near the C terminus of Vpu that is specifically important for Vpu's ability to enhance the release of progeny virus from the host cell, supporting the notion of a new mechanism for this function of Vpu.
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Miyakawa K, Sawasaki T, Matsunaga S, Tokarev A, Quinn G, Kimura H, Nomaguchi M, Adachi A, Yamamoto N, Guatelli J, Ryo A. Interferon-Induced SCYL2 Limits Release of HIV-1 by Triggering PP2A-Mediated Dephosphorylation of the Viral Protein Vpu. Sci Signal 2012; 5:ra73. [PMID: 23047923 DOI: 10.1126/scisignal.2003212] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Kei Miyakawa
- Department of Microbiology, Yokohama City University School of Medicine, Kanagawa 236-0004, Japan
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Andrew AJ, Kao S, Strebel K. C-terminal hydrophobic region in human bone marrow stromal cell antigen 2 (BST-2)/tetherin protein functions as second transmembrane motif. J Biol Chem 2011; 286:39967-81. [PMID: 21937450 DOI: 10.1074/jbc.m111.287011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BST-2/CD317/HM1.24/tetherin is a host factor that inhibits the release of HIV-1 and other enveloped viruses. Structurally, tetherin consists of an N-terminal transmembrane (TM) region, a central coiled coil motif, and a putative C-terminal glycosylphosphatidylinositol (GPI) anchor motif. A current working model proposes that BST-2 inhibits virus release by physically tethering viral particles to the cell surface via its TM motif and GPI anchor. Here we analyzed the functional importance of the C-terminal GPI anchor motif in BST-2. We replaced the GPI anchor motif in BST-2 with the TM regions of several surface markers and found that the TM motifs of CD40 and transferrin receptor, but not that of CD45, could functionally substitute for a GPI anchor in BST-2. Conversely, replacing the TM region of CD4 by the putative GPI anchor signal of human BST-2 resulted in proper membrane targeting and surface expression of the chimeric protein, indicating that the BST-2 GPI anchor signal can function as a bona fide TM region. In fact, attempts to demonstrate GPI anchor modification of human BST-2 by biochemical methods failed. Our results demonstrate that the putative C-terminal GPI anchor motif in human BST-2 fulfills the requirements of a bona fide TM motif, leading us to propose that human BST-2 may in fact contain a second TM segment rather than a GPI anchor.
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Affiliation(s)
- Amy J Andrew
- Laboratory of Molecular Microbiology, Viral Biochemistry Section, NIAID, National Institutes of Health, Bethesda, Maryland 20892-0460, USA
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Gustin JK, Moses AV, Früh K, Douglas JL. Viral takeover of the host ubiquitin system. Front Microbiol 2011; 2:161. [PMID: 21847386 PMCID: PMC3147166 DOI: 10.3389/fmicb.2011.00161] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 07/14/2011] [Indexed: 01/29/2023] Open
Abstract
Like the other more well-characterized post-translational modifications (phosphorylation, methylation, acetylation, acylation, etc.), the attachment of the 76 amino acid ubiquitin (Ub) protein to substrates has been shown to govern countless cellular processes. As obligate intracellular parasites, viruses have evolved the capability to commandeer many host processes in order to maximize their own survival, whether it be to increase viral production or to ensure the long-term survival of latently infected host cells. The first evidence that viruses could usurp the Ub system came from the DNA tumor viruses and Adenoviruses, each of which use Ub to dysregulate the host cell cycle (Scheffner et al., 1990; Querido et al., 2001). Today, the list of viruses that utilize Ub includes members from almost every viral class, encompassing both RNA and DNA viruses. Among these, there are examples of Ub usage at every stage of the viral life cycle, involving both ubiquitination and de-ubiquitination. In addition to viruses that merely modify the host Ub system, many of the large DNA viruses encode their own Ub modifying machinery. In this review, we highlight the latest discoveries regarding the myriad ways that viruses utilize Ub to their advantage.
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Affiliation(s)
- Jean K Gustin
- Vaccine and Gene Therapy Institute, Oregon Health & Science University Beaverton, OR, USA
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Yoshida T, Kao S, Strebel K. Identification of Residues in the BST-2 TM Domain Important for Antagonism by HIV-1 Vpu Using a Gain-of-Function Approach. Front Microbiol 2011; 2:35. [PMID: 21687426 PMCID: PMC3109345 DOI: 10.3389/fmicb.2011.00035] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Accepted: 02/09/2011] [Indexed: 11/29/2022] Open
Abstract
The HIV-1 Vpu protein enhances the release of viral particles from the cell-surface in a cell-type specific manner. In the absence of Vpu, nascent virions remain tethered to the cell-surface in restricted cell-types. Recently, the human host factor BST-2/CD317/tetherin was found to be responsible for the inhibition of virus release. It was also reported that HIV-1 Vpu can target human BST-2 but is unable to interfere with the function of murine or simian BST-2. We performed a gain-of-function study to determine which of the differences between human and rhesus BST-2 account for the differential sensitivity to Vpu. We transferred human BST-2 sequences into rhesus BST-2 and assessed the resulting chimeras for inhibition of HIV-1 virus release and sensitivity to Vpu. We found that rhesus BST-2 carrying the transmembrane (TM) domain of human BST-2 is susceptible to HIV-1 Vpu. Finally, a single-amino-acid change in the rhesus BST-2 TM domain was sufficient to confer Vpu sensitivity.
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Affiliation(s)
- Takeshi Yoshida
- Viral Biochemistry Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health Bethesda, MD, USA
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Tisoncik JR, Guo Y, Cordero KS, Yu J, Wang J, Cao Y, Rong L. Identification of critical residues of influenza neuraminidase in viral particle release. Virol J 2011; 8:14. [PMID: 21232128 PMCID: PMC3033838 DOI: 10.1186/1743-422x-8-14] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Accepted: 01/13/2011] [Indexed: 12/14/2022] Open
Abstract
Background Influenza neuraminidase (NA) is essential for virus release from its host cells and it is one of the targets for structure-based antiviral drug design. Results In this report, we established a pseudoviral particle release assay to study NA function, which is based on lentiviral particles pseudotyped with influenza glycoproteins HA and NA as a surrogate system. Through an extensive molecular analysis, we sought to characterize important residues governing NA function. We identified five residues of NA, 234, 241, 257, 286 and 345, four of which (except 345) map away from the active site of NA when projected onto the three-dimensional structure of avian influenza H5N1 NA, and substitutions of these residues adversely affected the NA-mediated viral particle release, suggesting that these residues are critical for NA enzymatic activity. Conclusion Through extensive chimeric and mutational analyses, we have identified several residues, which map away from the active site and are critical for NA function. These findings provide new insights into NA-mediated pseudoviral particle release and may have important implications in drug design and therapeutics against influenza infection.
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Affiliation(s)
- Jennifer R Tisoncik
- Department of Microbiology and Immunology, University of Illinois at Chicago, Chicago, IL 60612, USA
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Dubé M, Bego MG, Paquay C, Cohen ÉA. Modulation of HIV-1-host interaction: role of the Vpu accessory protein. Retrovirology 2010; 7:114. [PMID: 21176220 PMCID: PMC3022690 DOI: 10.1186/1742-4690-7-114] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Accepted: 12/22/2010] [Indexed: 11/10/2022] Open
Abstract
Viral protein U (Vpu) is a type 1 membrane-associated accessory protein that is unique to human immunodeficiency virus type 1 (HIV-1) and a subset of related simian immunodeficiency virus (SIV). The Vpu protein encoded by HIV-1 is associated with two primary functions during the viral life cycle. First, it contributes to HIV-1-induced CD4 receptor downregulation by mediating the proteasomal degradation of newly synthesized CD4 molecules in the endoplasmic reticulum (ER). Second, it enhances the release of progeny virions from infected cells by antagonizing Tetherin, an interferon (IFN)-regulated host restriction factor that directly cross-links virions on host cell-surface. This review will mostly focus on recent advances on the role of Vpu in CD4 downregulation and Tetherin antagonism and will discuss how these two functions may have impacted primate immunodeficiency virus cross-species transmission and the emergence of pandemic strain of HIV-1.
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Affiliation(s)
- Mathieu Dubé
- Laboratory of Human Retrovirology, Institut de Recherches Cliniques de Montréal, 110, Avenue des Pins Ouest, Montreal, Quebec, Canada H2W 1R7
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12
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Andrew A, Strebel K. The interferon-inducible host factor bone marrow stromal antigen 2/tetherin restricts virion release, but is it actually a viral restriction factor? J Interferon Cytokine Res 2010; 31:137-44. [PMID: 21166593 DOI: 10.1089/jir.2010.0108] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Viruses face a variety of obstacles when infecting a new host. The past few years have brought exciting new insights into the function of restriction factors, which form part of the host's innate immune system. One of the most recently identified restriction factors is bone marrow stromal antigen 2 (BST-2)/tetherin. BST-2 is an interferon-inducible gene whose expression dramatically reduces the release of viruses from infected cells. This effect of BST-2 is not specific to human immunodeficiency virus but affects a broad range of enveloped viruses. Since the identification of BST-2 as a restriction factor in 2008, much progress has been made in understanding the molecular properties and functional characteristics of this host factor. The goal of this review was to provide an update on our current understanding of the role of BST-2 in regulating virus release and to discuss its role in controlling virus spread during productive infection with special emphasis on human immunodeficiency virus-1.
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Affiliation(s)
- Amy Andrew
- Laboratory of Molecular Microbiology, Viral Biochemistry Section, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, Maryland 90892-0460, USA
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Andrew A, Strebel K. HIV-1 Vpu targets cell surface markers CD4 and BST-2 through distinct mechanisms. Mol Aspects Med 2010; 31:407-17. [PMID: 20858517 PMCID: PMC2967615 DOI: 10.1016/j.mam.2010.08.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Accepted: 08/09/2010] [Indexed: 10/19/2022]
Abstract
Vpu is a small integral membrane protein encoded by HIV-1 and some SIV isolates. The protein is known to induce degradation of the viral receptor molecule CD4 and to enhance the release of newly formed virions from the cell surface. Vpu accomplishes these two functions through two distinct mechanisms. In the case of CD4, Vpu acts as a molecular adaptor to connect CD4 to an E3 ubiquitin ligase complex resulting in CD4 degradation by cellular proteasomes. This requires signals located in Vpu's cytoplasmic domain. Enhancement of virus release on the other hand involves the neutralization of a cellular host factor, BST-2 (also known as CD317, HM1.24, or tetherin) and requires Vpu's TM domain. The current review discusses recent advances on the role of Vpu in controlling degradation of CD4 and in regulating virus release.
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Affiliation(s)
- Amy Andrew
- Laboratory of Molecular Microbiology, Viral Biochemistry Section, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892-0460, USA
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14
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Andrew AJ, Miyagi E, Kao S, Strebel K. The formation of cysteine-linked dimers of BST-2/tetherin is important for inhibition of HIV-1 virus release but not for sensitivity to Vpu. Retrovirology 2009; 6:80. [PMID: 19737401 PMCID: PMC2754425 DOI: 10.1186/1742-4690-6-80] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 09/08/2009] [Indexed: 02/03/2023] Open
Abstract
Background The Human Immunodeficiency virus type 1 (HIV-1) Vpu protein enhances virus release from infected cells and induces proteasomal degradation of CD4. Recent work identified BST-2/CD317 as a host factor that inhibits HIV-1 virus release in a Vpu sensitive manner. A current working model proposes that BST-2 inhibits virus release by tethering viral particles to the cell surface thereby triggering their subsequent endocytosis. Results Here we defined structural properties of BST-2 required for inhibition of virus release and for sensitivity to Vpu. We found that BST-2 is modified by N-linked glycosylation at two sites in the extracellular domain. However, N-linked glycosylation was not important for inhibition of HIV-1 virus release nor did it affect surface expression or sensitivity to Vpu. Rodent BST-2 was previously found to form cysteine-linked dimers. Analysis of single, double, or triple cysteine mutants revealed that any one of three cysteine residues present in the BST-2 extracellular domain was sufficient for BST-2 dimerization, for inhibition of virus release, and sensitivity to Vpu. In contrast, BST-2 lacking all three cysteines in its ectodomain was unable to inhibit release of wild type or Vpu-deficient HIV-1 virions. This defect was not caused by a gross defect in BST-2 trafficking as the mutant protein was expressed at the cell surface of transfected 293T cells and was down-modulated by Vpu similar to wild type BST-2. Conclusion While BST-2 glycosylation was functionally irrelevant, formation of cysteine-linked dimers appeared to be important for inhibition of virus release. However lack of dimerization did not prevent surface expression or Vpu sensitivity of BST-2, suggesting Vpu sensitivity and inhibition of virus release are separable properties of BST-2.
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Affiliation(s)
- Amy J Andrew
- Laboratory of Molecular Microbiology, Viral Biochemistry Section, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, Maryland 20892-0460, USA.
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15
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Vpu antagonizes BST-2-mediated restriction of HIV-1 release via beta-TrCP and endo-lysosomal trafficking. PLoS Pathog 2009; 5:e1000450. [PMID: 19478868 PMCID: PMC2679223 DOI: 10.1371/journal.ppat.1000450] [Citation(s) in RCA: 267] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Accepted: 04/27/2009] [Indexed: 12/19/2022] Open
Abstract
The interferon-induced transmembrane protein BST-2/CD317 (tetherin) restricts the release of diverse enveloped viruses from infected cells. The HIV-1 accessory protein Vpu antagonizes this restriction by an unknown mechanism that likely involves the down-regulation of BST-2 from the cell surface. Here, we show that the optimal removal of BST-2 from the plasma membrane by Vpu requires the cellular protein β-TrCP, a substrate adaptor for a multi-subunit SCF E3 ubiquitin ligase complex and a known Vpu-interacting protein. β-TrCP is also required for the optimal enhancement of virion-release by Vpu. Mutations in the DSGxxS β-TrCP binding-motif of Vpu impair both the down-regulation of BST-2 and the enhancement of virion-release. Such mutations also confer dominant-negative activity, consistent with a model in which Vpu links BST-2 to β-TrCP. Optimal down-regulation of BST-2 from the cell surface by Vpu also requires the endocytic clathrin adaptor AP-2, although the rate of endocytosis is not increased; these data suggest that Vpu induces post-endocytic membrane trafficking events whose net effect is the removal of BST-2 from the cell surface. In addition to its marked effect on cell-surface levels, Vpu modestly decreases the total cellular levels of BST-2. The decreases in cell-surface and intracellular BST-2 are inhibited by bafilomycin A1, an inhibitor of endosomal acidification; these data suggest that Vpu induces late endosomal targeting and partial degradation of BST-2 in lysosomes. The Vpu-mediated decrease in surface expression is associated with reduced co-localization of BST-2 and the virion protein Gag along the plasma membrane. Together, the data support a model in which Vpu co-opts the β-TrCP/SCF E3 ubiquitin ligase complex to induce endosomal trafficking events that remove BST-2 from its site of action as a virion-tethering factor. The cellular protein BST-2 prevents newly formed particles of HIV-1 and other enveloped viruses from escaping the infected cell. HIV-1 encodes the protein Vpu to counteract this host defense, but the mechanism of this antagonism is currently unknown. Here, the data suggest that Vpu recruits the cellular protein β-TrCP to modulate the trafficking of BST-2 within internal cellular membranes, removing BST-2 from its apparent site of action at the cell surface. These results add a new example to the growing paradigm of viral counteraction of so-called “restriction factors,” proteins that provide an innate defense against viruses, by co-option of cellular regulatory assemblies known as multi-subunit ubiquitin ligases.
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16
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Nef-induced CD4 endocytosis in human immunodeficiency virus type 1 host cells: role of p56lck kinase. J Virol 2009; 83:7117-28. [PMID: 19439470 DOI: 10.1128/jvi.01648-08] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) Nef interferes with the endocytic machinery to modulate the cell surface expression of CD4. However, the basal trafficking of CD4 is governed by different rules in the target cells of HIV-1: whereas CD4 is rapidly internalized from the cell surface in myeloid cells, CD4 is stabilized at the plasma membrane through its interaction with the p56(lck) kinase in lymphoid cells. In this study, we showed that Nef was able to downregulate CD4 in both lymphoid and myeloid cell lines but that an increase in the internalization rate of CD4 could be observed only in lymphoid cells. Expression of p56(lck) in nonlymphoid CD4-expressing cells restores the ability of Nef in order to increase the internalization rate of CD4. Concurrent with this observation, the expression of a p56(lck)-binding-deficient mutant of CD4 in lymphoid cells abrogates the Nef-induced acceleration of CD4 internalization. We also show that the expression of Nef causes a decrease in the association of p56(lck) with cell surface-expressed CD4. Regardless of the presence of p56(lck), the downregulation of CD4 by Nef was followed by CD4 degradation. Our results imply that Nef uses distinct mechanisms to downregulate the cell surface expression levels of CD4 in either lymphoid or myeloid target cells of HIV-1.
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17
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Vpu enhances HIV-1 virus release in the absence of Bst-2 cell surface down-modulation and intracellular depletion. Proc Natl Acad Sci U S A 2009; 106:2868-73. [PMID: 19196977 DOI: 10.1073/pnas.0813223106] [Citation(s) in RCA: 190] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
HIV-1 Vpu enhances the release of virions from infected cells. Recent work identified Bst-2/CD317/tetherin as a host factor whose inhibitory activity on viral release is counteracted by Vpu. A current working model proposes that Bst-2 inhibits virus release by tethering viral particles to the cell surface. Here, we analyzed endogenous Bst-2 with respect to its effect on virus release from HeLa cells, T cells, and macrophages. We noted significant cell type-dependent variation in Bst-2 expression. Vpu caused a reduction in Bst-2 expression in transfected HeLa cells and long-term infected macrophages. However, Vpu expression did not result in cell surface down-modulation of Bst-2 or a reduction in intracellular Bst-2 expression in CEMx174 or H9 cells, yet virus replication in these cells was Vpu-responsive. Surprisingly, Bst-2 was undetectable in cell-free virions that were recovered from the surface of HeLa cells by physical shearing, suggesting that a tethering model may not explain all of the functional properties of Bst-2. Taken together we conclude that enhancement of virus release by Vpu does not, at least in CEMx174 and H9 cells, require cell surface down-modulation or intracellular depletion of Bst-2, nor does it entail exclusion of Bst-2 from viral particles.
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Van Duyne R, Kehn-Hall K, Klase Z, Easley R, Heydarian M, Saifuddin M, Wu W, Kashanchi F. Retroviral proteomics and interactomes: intricate balances of cell survival and viral replication. Expert Rev Proteomics 2008; 5:507-28. [PMID: 18532916 DOI: 10.1586/14789450.5.3.507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Overall changes in the host cellular proteome upon retroviral infection intensify from the initial entry of the virus to the incorporation of viral DNA into the host genome, and finally to the consistent latent state of infection. The host cell reacts to both the entry of viral elements and the manipulation of host cellular machinery, resulting in a cascade of signaling events and pathway activation. Cell type- and tissue-specific responses are also characteristic of infection and can be classified based on the differential expression of genes and proteins between normal and disease states. The characterization of differentially expressed proteins upon infection is also critical in identifying potential biomarkers within infected bodily fluids. Biomarkers can be used to monitor the progression of infection, track the effectiveness of specific treatments and characterize the mechanisms of disease pathogenesis. Standard proteomic approaches have been applied to monitor the changes in global protein expression and localization in infected cells, tissues and fluids. Here we report on recent investigations into the characterization of proteomes in response to retroviral infection.
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Affiliation(s)
- Rachel Van Duyne
- The George Washington University, Department of Microbiology, Immunology, & Tropical Medicine, 2300 I Street, NW, Washington, DC 20037, USA.
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19
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Nomaguchi M, Fujita M, Adachi A. Role of HIV-1 Vpu protein for virus spread and pathogenesis. Microbes Infect 2008; 10:960-7. [PMID: 18672082 DOI: 10.1016/j.micinf.2008.07.006] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Vpu is an accessory viral protein almost unique to HIV-1 among primate immunodeficiency viruses, and has two major functions: degradation of the CD4 molecule in endoplasmic reticulum and enhancement of virion release from cells. Recent identification of a novel host restriction factor, tetherin, as a Vpu-antagonist suggests that Vpu contributes to virus spread by facilitating progeny virion production. This review focuses on the two distinct functions of Vpu and summarizes current knowledge on its virological role in the HIV-1 life cycle.
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Affiliation(s)
- Masako Nomaguchi
- Department of Virology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima-shi, Tokushima, 770-8503, Japan
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20
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Valiathan RR, Resh MD. Differential control of CXCR4 and CD4 downregulation by HIV-1 Gag. Virol J 2008; 5:23. [PMID: 18267010 PMCID: PMC2262066 DOI: 10.1186/1743-422x-5-23] [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: 01/25/2008] [Accepted: 02/11/2008] [Indexed: 11/10/2022] Open
Abstract
Background The ESCRT (endosomal sorting complex required for transport) machinery functions to sort cellular receptors into the lumen of the multivesicular body (MVB) prior to lysosomal degradation. ESCRT components can also be recruited by enveloped viruses to sites of viral assembly where they have been proposed to mediate viral egress. For example, HIV-1 budding is dependent on Gag-mediated recruitment of the cellular ESCRTs-I, -III, AIP1/Alix and Vps4 proteins. Viral recruitment of ESCRT proteins could therefore impact on host cell processes such as receptor downregulation. Results Here we show that downregulation of the HIV-1 co-receptor, CXCR4, by its ligand SDF-1, is ESCRT-I dependent. Expression of HIV-1 Gag attenuated downregulation of CXCR4, resulting in accumulation of undegraded receptors within intracellular compartments. The effect of Gag was dependent on an ESCRT-I interacting motif within the C-terminal p6 region of Gag. In contrast, PMA-induced downregulation of the HIV-1 receptor CD4 was independent of ESCRT-I and Vps4; HIV-1 Gag had no effect on this process. Conclusion These results establish that the HIV-1 receptor, CD4, and co-receptor, CXCR4 are differentially regulated by ESCRT proteins. HIV-1 Gag selectively modulates protein sorting at the MVB, interfering with ESCRT-I dependent but not ESCRT-I independent processes.
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21
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Klase ZA, Van Duyne R, Kashanchi F. Identification of potential drug targets using genomics and proteomics: a systems approach. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2008; 56:327-68. [PMID: 18086417 DOI: 10.1016/s1054-3589(07)56011-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Zachary A Klase
- Department of Biochemistry, Medical Center, The George Washington University, Washington, DC 20037, USA
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22
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Poon B, Chang MA, Chen ISY. Vpr is required for efficient Nef expression from unintegrated human immunodeficiency virus type 1 DNA. J Virol 2007; 81:10515-23. [PMID: 17652391 PMCID: PMC2045493 DOI: 10.1128/jvi.00947-07] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Unintegrated human immunodeficiency virus (HIV) DNA are viral DNA products formed naturally during HIV replication. While the integrated proviral DNA form is transcriptionally active and results in productive infection, unintegrated DNA is also capable of expression of viral RNA and proteins. Previously, we showed that HIV Vpr enhances expression from integrase-defective HIV. Here we show that Vpr activation of expression is partially dependent upon the presence of a transcriptionally active HIV promoter and results in increased transcription of unspliced gag and spliced nef viral RNA. While Tat is detectable during infection with integrase-defective HIV, Tat levels are not affected by the presence of Vpr. Mutation studies reveal that Tat is dispensable for the Vpr-mediated enhancement of expression from unintegrated DNA. We find that virion-associated Vpr is sufficient for Nef expression from unintegrated viral DNA, resulting in the efficient downregulation of CD4 from the surface of infected cells. These results provide a mechanism by which Nef expression from unintegrated HIV type 1 DNA expression occurs.
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MESH Headings
- CD4 Antigens/genetics
- Cell Line
- DNA, Viral/genetics
- Down-Regulation
- Gene Expression Regulation, Viral
- Gene Products, nef/genetics
- Gene Products, tat/genetics
- Gene Products, vpr/genetics
- Gene Products, vpr/metabolism
- HIV-1/genetics
- Humans
- Mutation
- Promoter Regions, Genetic
- Transcription, Genetic
- Transcriptional Activation
- Virus Integration
- Virus Replication/genetics
- nef Gene Products, Human Immunodeficiency Virus
- tat Gene Products, Human Immunodeficiency Virus
- vpr Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- Betty Poon
- Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine at UCLA, UCLA AIDS Institute and Jonsson Comprehensive CAncer Center, 11-934 Factor Building, 10833 Le Conte Avenue, Los Angeles, CA 90095-1678, USA
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23
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Wildum S, Schindler M, Münch J, Kirchhoff F. Contribution of Vpu, Env, and Nef to CD4 down-modulation and resistance of human immunodeficiency virus type 1-infected T cells to superinfection. J Virol 2006; 80:8047-59. [PMID: 16873261 PMCID: PMC1563805 DOI: 10.1128/jvi.00252-06] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) utilizes Vpu, Env, and Nef to down-modulate its primary CD4 receptor from the cell surface, and this function seems to be critical for the pathogenesis of AIDS. The physiological relevance of CD4 down-modulation, however, is currently not well understood. In the present study, we analyzed the kinetics of CD4 down-modulation and the susceptibility of HIV-1-infected T cells to superinfection using proviral HIV-1 constructs containing individual and combined defects in vpu, env, and nef and expressing red or green fluorescent proteins. T cells infected with HIV-1 mutants containing functional nef genes expressed low surface levels of CD4 from the first moment that viral gene expression became detectable. In comparison, Vpu and Env had only minor to moderate effects on CD4 during later stages of infection. Consistent with these quantitative differences, Nef inhibited superinfection more efficiently than Vpu and Env. Notably, nef alleles from AIDS patients were more effective in preventing superinfection than those derived from a nonprogressor of HIV-1 infection. Our data suggest that protection against X4-tropic HIV-1 superinfection involves both CD4-independent and CD4-dependent mechanisms of HIV-1 Nef. X4 was effectively down-regulated by simian immunodeficiency virus and HIV-2 but not by HIV-1 Nef proteins. Thus, maximal protection seems to involve an as-yet-unknown mechanism that is independent of CD4 or coreceptor down-modulation. Finally, we demonstrate that superinfected primary T cells show enhanced levels of apoptosis. Accordingly, one reason that HIV-1 inhibits CD4 surface expression and superinfection is to prevent premature cell death in order to expand the period of effective virus production.
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Affiliation(s)
- Steffen Wildum
- Department of Virology, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany
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24
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Basmaciogullari S, Pacheco B, Bour S, Sodroski J. Specific interaction of CXCR4 with CD4 and CD8alpha: functional analysis of the CD4/CXCR4 interaction in the context of HIV-1 envelope glycoprotein-mediated membrane fusion. Virology 2006; 353:52-67. [PMID: 16808956 DOI: 10.1016/j.virol.2006.05.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2006] [Revised: 03/23/2006] [Accepted: 05/24/2006] [Indexed: 11/18/2022]
Abstract
We investigated possible interactions between HIV-1 receptor (CD4) and the main coreceptors CXCR4 and CCR5. We found that CD4 and CXCR4 coexpressed in 293T cells form a complex that can be immunoprecipitated with antibodies directed against the extracellular domain of either protein. Mutagenesis revealed that the CD4/CXCR4 interaction maps to two previously uncharacterized basic motifs in the cytoplasmic domain of CD4. HIV-1 envelope glycoprotein-mediated membrane fusion was found to be independent of the ability of CD4 and CXCR4 to interact, whether fusion was studied in a virus-cell or a cell-cell model. However, this interaction might explain the adaptation of HIV-1 to CXCR4 as an alternative to CCR5. We found that CXCR4 also interacts with the cytoplasmic domain of CD8alpha in a way that is similar to the CD4/CXCR4 interaction. The CD4/CXCR4 and CD8alpha/CXCR4 interactions may thus be involved in cellular signaling pathways shared by the CD4 and CD8alpha molecules.
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Hanna Z, Priceputu E, Hu C, Vincent P, Jolicoeur P. HIV-1 Nef mutations abrogating downregulation of CD4 affect other Nef functions and show reduced pathogenicity in transgenic mice. Virology 2006; 346:40-52. [PMID: 16310238 DOI: 10.1016/j.virol.2005.10.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Revised: 08/01/2005] [Accepted: 10/04/2005] [Indexed: 11/15/2022]
Abstract
HIV-1 Nef has the ability to downmodulate CD4 cell surface expression. Several studies have shown that CD4 downregulation is required for efficient virus replication and high infectivity. However, the pathophysiological relevance of this phenomenon in vivo, independently of its role in sustaining high virus loads, remains unclear. We studied the impact of the CD4 downregulation function of Nef on its pathogenesis in vivo, in the absence of viral replication, in the CD4C/HIV transgenic (Tg) mouse model. Two independent Nef mutants (RD35/36AA and D174K), known to abrogate CD4 downregulation, were tested in Tg mice. Flow cytometry analysis showed that downregulation of murine CD4 was severely decreased or abrogated on Tg T cells expressing respectively Nef(RD35/36AA) and Nef(D174K). Similarly, the severe depletion of double-positive CD4+CD8+ and of single-positive CD4+CD8- thymocytes, usually observed with Nef(Wt), was not detected in Nef(RD35/36AA) and Nef(D174K) Tg mice. However, both mutant Tg mice showed a partial depletion of peripheral CD4+ T cells. This was accompanied, as previously reported for Net(Wt) Tg mice, by the presence of an activated/memory-like phenotype (CD69+, CD25+, CD44+, CD45RB(Low), CD62(Low)) of CD4+ T cells expressing Nef(RD35/36AA) and to a lesser extent Nef(D174K). In addition, both mutants retained the ability to block CD4+ T cell proliferation in vitro after anti-CD3 stimulation, but not to enhance apoptosis/death of CD4+ T cells. Therefore, it appears that Nef-mediated CD4 downregulation is associated with thymic defects, but segregates independently of the activated/memory-like phenotype, of the partial depletion and of the impaired in vitro proliferation of peripheral CD4+ T cells. Histopathological assessment revealed the total absence of or decrease severity and frequency of organ AIDS-like diseases (lung, heart and kidney pathologies) in respectively Nef(RD35/36AA) and Nef(D174K) Tg mice, relative to those developing in Nef(Wt) Tg mice. Our data suggest that the RD35/36AA and D174K mutations affect other Nef functions, namely those involved in the development of lung and kidney diseases, in addition to their known role in CD4 downregulation. Similarly, in HIV-1-infected individuals, loss of CD4 downregulation by Nef alleles may reflect their lower intrinsic pathogenicity, independently of their effects on virus replication.
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Affiliation(s)
- Zaher Hanna
- Laboratory of Molecular Biology, Clinical Research Institute of Montreal, 110 Pine Avenue West, Montreal, Quebec, Canada H2W 1R7.
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26
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Ye Z, Harmison GG, Ragheb JA, Schubert M. Targeted infection of HIV-1 Env expressing cells by HIV(CD4/CXCR4) vectors reveals a potential new rationale for HIV-1 mediated down-modulation of CD4. Retrovirology 2005; 2:80. [PMID: 16371160 PMCID: PMC1352389 DOI: 10.1186/1742-4690-2-80] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Accepted: 12/21/2005] [Indexed: 12/04/2022] Open
Abstract
Background Efficient targeted gene transfer and cell type specific transgene expression are important for the safe and effective expression of transgenes in vivo. Enveloped viral vectors allow insertion of exogenous membrane proteins into their envelopes, which could potentially aid in the targeted transduction of specific cell types. Our goal was to specifically target cells that express the T cell tropic HIV-1 envelope protein (Env) using the highly specific interaction of Env with its cellular receptor (CD4) inserted into the envelope of an HIV-1-based viral vector. Results To generate HIV-1-based vectors carrying the CD4 molecule in their envelope, the CD4 ectodomain was fused to diverse membrane anchors and inserted together with the HIV-1 coreceptor CXCR4 into the envelopes of HIV-1 vector particles. Independent of the type of CD4 anchor, all chimeric CD4 proteins inserted into HIV-1 vector envelopes and the resultant HIV(CD4/CXCR4) particles were able to selectively confer neomycin resistance to cells expressing the fusogenic T cell tropic HIV-1 Env protein. Unexpectedly, in the absence of Env on the target cells, all vector particles carrying the CD4 ectodomain anchored in their envelope adhered to various cell types without infecting these cells. This cell adhesion was very avid. It was independent of the presence of Env on the target cell, the type of CD4 anchor or the presence of CXCR4 on the particle. In mixed cell populations with defined ratios of Env+/Env- cells, the targeted transduction of Env+ cells by HIV(CD4/CXCR4) particles was diminished in proportion to the number of Env- cells. Conclusion Vector diversion caused by a strong, non-selective cell binding of CD4+-vector particles effectively prevents the targeted transduction of HIV-1 Env expressing cells in mixed cell populations. This Env-independent cell adhesion severely limits the effective use of targeted HIV(CD4/CXCR4) vectors designed to interfere with HIV-1 replication in vivo. Importantly, the existence of this newly described and remarkably strong CD4-dependent cell adhesion suggests that the multiple viral efforts to reduce CD4 cell surface expression may, in part, be to prevent cell adhesion to non-target cells and thereby to increase the infectivity of viral progeny. Preventing CD4 down-modulation by HIV-1 might be an effective component of a multi-faceted antiviral strategy.
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Affiliation(s)
- Zhiping Ye
- Molecular Virology and Neurogenetics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rm. 4S-18, 5625 Fishers Lane, Bethesda, MD 20892-9403, USA
- Laboratory of Pediatric and Respiratory Viral Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, Bldg. 29A, 8800 Rockville Pike, Bethesda, MD 20892, USA
| | - George G Harmison
- Molecular Virology and Neurogenetics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rm. 4S-18, 5625 Fishers Lane, Bethesda, MD 20892-9403, USA
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bldg. 35, Rm. 2A1012, 35 Convent Drive, Bethesda, MD 20892-3705, USA
| | - Jack A Ragheb
- Clinical and Molecular Immunology Section, National Eye Institute, National Institutes of Health, Bldg. 10, Rm. 10N113A, 10 Center Drive, Bethesda, MD 20892-1857, USA
| | - Manfred Schubert
- Molecular Virology and Neurogenetics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rm. 4S-18, 5625 Fishers Lane, Bethesda, MD 20892-9403, USA
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Sierra S, Kupfer B, Kaiser R. Basics of the virology of HIV-1 and its replication. J Clin Virol 2005; 34:233-44. [PMID: 16198625 DOI: 10.1016/j.jcv.2005.09.004] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Accepted: 09/02/2005] [Indexed: 11/17/2022]
Abstract
Human immunodeficiency virus is undoubtedly the causative agent of AIDS. The understanding of HIV-1 pathogenesis is essential to develop and maintain antiretroviral treatment and vaccination. Since the first isolation of HIV-1 in cell culture, thousands of publications dealing with HIV and/or AIDS per year were released. In this review we give a basic overview of the virology of HIV-1 including the functions of the different HIV-1 proteins required for effective viral replication. Moreover, we summarize the interactive processes between HIV-1 and its target cells. Finally, the HIV-1 specific immune response and the current status of antiretroviral therapy are briefly described in this review.
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Affiliation(s)
- Saleta Sierra
- Institute of Virology, University of Cologne, Fürst-Pückler Str. 56, D-50935 Cologne, Germany
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Abstract
Human immunodeficiency virus generates the accessory proteins Nef, viral infectivity factor (Vif), viral protein R, and viral protein U or viral protein X during viral replication in host cells. Although the significance of these accessory proteins is often lost in vitro, they are essential for viral pathogenesis in vivo. Therefore, these proteins have much potential as antiviral targets. Recent data reveal Vif perturbs an ill-defined antiviral pathway in host cells allowing HIV replication. These data highlight a common feature among HIV accessory proteins in manipulating the host to aid viral pathogenesis. Therefore, these new insights into Vif and other HIV accessory proteins are reviewed, emphasizing host cell interactions and new targets for therapeutic intervention.
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Affiliation(s)
- Jenny L Anderson
- Department of Microbiology and Immunology, The University of Illinois at Chicago, Chicago, IL 60612, USA.
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Chan WE, Lin HH, Chen SSL. Wild-type-like viral replication potential of human immunodeficiency virus type 1 envelope mutants lacking palmitoylation signals. J Virol 2005; 79:8374-87. [PMID: 15956582 PMCID: PMC1143725 DOI: 10.1128/jvi.79.13.8374-8387.2005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Palmitoylation of the cytoplasmic domain of the human immunodeficiency type virus type 1 (HIV-1) envelope (Env) transmembrane protein, gp41, has been implicated in Env targeting to detergent-resistant lipid rafts, Env incorporation into the virus, and viral infectivity. In contrast, we provide evidence here to show that HIV-1 infectivity, Env targeting to lipid rafts, and Env incorporation into the virus are independent of cytoplasmic tail palmitoylation. The T-cell (T)-tropic HXB2-based virus, which utilizes CXCR4 as the entry coreceptor, carrying a Cys-to-Ser mutation at residue 764 or 837 or at both replicated with wild-type (WT) virus replication kinetics in CD4+ T cells. The properties of Env expression, precursor processing, cell surface expression, and Env incorporation of these three mutant viruses were normal compared to those of the WT virus. These three mutant Env proteins all effectively mediated one-cycle virus infection. When the Cys residues were replaced by Ala residues, all single and double mutants still retained the phenotypes of infectivity, Env incorporation, and lipid raft localization of the WT Env. When Cys-to-Ala substitutions were introduced into the macrophage (M)-tropic ConB virus, which utilizes CCR5 as the coreceptor, these mutations did not affect the replication potential, Env phenotypes, lipid raft targeting, or Env assembly into the virus of the WT Env. These T- and M-tropic mutants also productively replicated in human primary CD4+ T cells. Moreover, mutations at both Cys residues significantly reduced the level of palmitoylation of the Env. Our results together support the notion that palmitoylation of the cytoplasmic tail of the HIV-1 Env is not essential for the HIV-1 virus life cycle.
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Affiliation(s)
- Woan-Eng Chan
- Institute of Biomedical Sciences, Academia Sinica, 128 Yen-Chiu-Yuan Road, Section 2, Nankang, Taipei 11529, Taiwan, Republic of China
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30
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Pacyniak E, Gomez ML, Gomez LM, Mulcahy ER, Jackson M, Hout DR, Wisdom BJ, Stephens EB. Identification of a region within the cytoplasmic domain of the subtype B Vpu protein of human immunodeficiency virus type 1 (HIV-1) that is responsible for retention in the golgi complex and its absence in the Vpu protein from a subtype C HIV-1. AIDS Res Hum Retroviruses 2005; 21:379-94. [PMID: 15929700 DOI: 10.1089/aid.2005.21.379] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The structure of the Vpu protein of human immunodeficiency virus type 1 (HIV-1) is composed of a short Nterminal domain (NTD), a transmembrane domain (TM), and a cytoplasmic domain (CD). Previous studies have shown that the Vpu protein from subtype B HIV-1 is transported predominantly to the rough endoplasmic reticulum (RER)/Golgi complex compartments of the cell and is not incorporated into virions. Using a previously described VpuEGFP reporter system in which the Vpu protein was fused to the gene for enhanced green fluorescent protein (EGFP), we showed that the subtype B Vpu fusion protein was localized to the RER/Golgi region of the cell, similar to the native protein. In the present study, we show that fusion of the subtype C Vpu to EGFP results in a fusion protein that is transported to the cell surface. Using this reporter system, chimeric Vpu proteins in which the CD of the subtype B and C proteins were exchanged showed that the CD was sufficient for targeting the subtype B protein to the Golgi complex of the cell. Following identification of the cytoplasmic domain as being responsible for intracellular targeting, we then generated a series of mutants in which 13, 23, 31, 38, 51, and 56 amino acids were deleted from the cytoplasmic domain of subtype B Vpu. These deletion mutants were analyzed by SDS-PAGE for size, for membrane localization, and intracellular localization by confocal fluorescence microscopy. Our results indicate that the mutant with the carboxyl-terminal 13 amino acids deleted was still localized to the Golgi complex but mutants with 23, 31, 38, 51, and 56 amino acids from the carboxyl-terminus of the subtype B Vpu were transported to the cell surface. These results suggest that a signal for the retention of the subtype B Vpu within the Golgi complex resides in the second alpha-helical domain.
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Affiliation(s)
- Erik Pacyniak
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
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31
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Pham HM, Argañaraz ER, Groschel B, Trono D, Lama J. Lentiviral vectors interfering with virus-induced CD4 down-modulation potently block human immunodeficiency virus type 1 replication in primary lymphocytes. J Virol 2004; 78:13072-81. [PMID: 15542659 PMCID: PMC524995 DOI: 10.1128/jvi.78.23.13072-13081.2004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2004] [Accepted: 07/28/2004] [Indexed: 11/20/2022] Open
Abstract
CD4 down-modulation is essential for the production of human immunodeficiency virus (HIV) infectious particles. Disease progression correlates with enhanced viral induced CD4 down-modulation, and a subset of long-term nonprogressors carry viruses defective in this function. Despite multiple pieces of evidence highlighting the importance of this function in viral pathogenesis in vivo, to date, HIV-induced CD4 down-modulation has not been used as a target for intervention. We describe here HIV-based vectors that deliver truncated CD4 molecules resistant to down-modulation by the viral products Nef and Vpu. Infection of cells previously transduced with these vectors proceeded normally, and viral particles were released in normal amounts. However, the infectivity of the released virions was reduced 1,000-fold. Lentiviral vectors expressing truncated CD4 molecules were efficient at blocking HIV-1 infectivity and replication in several cell lines and in CD4-positive primary lymphocytes. The findings presented here provide proof-of-principle that approaches targeting the virus-induced CD4 down-modulation may constitute the basis for novel anti-HIV therapies.
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Affiliation(s)
- Hang M Pham
- La Jolla Institute for Molecular Medicine, 4570 Executive Dr., Suite 100, San Diego, CA 92121, USA
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32
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Hsu K, Seharaseyon J, Dong P, Bour S, Marbán E. Mutual functional destruction of HIV-1 Vpu and host TASK-1 channel. Mol Cell 2004; 14:259-67. [PMID: 15099524 DOI: 10.1016/s1097-2765(04)00183-2] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2003] [Revised: 03/01/2004] [Accepted: 03/03/2004] [Indexed: 01/28/2023]
Abstract
Sequence analysis predicted significant structural homology between the HIV-1 accessory protein Vpu and the N-terminal region of TASK-1, a mammalian background K(+) channel. If the homology resulted from molecular piracy during HIV-1 evolution, these two proteins may have important functional interactions. Here we demonstrate that TASK and Vpu physically interact in cultured cells and in AIDS lymphoid tissues. The functional consequences were potentially destructive for both components: Vpu abolished TASK-1 current, while overexpressing TASK led to a marked impairment of Vpu's ability to enhance viral particle release. Further, the first 40 amino acids of TASK-1 (part of the homology to Vpu) were capable of enhancing HIV-1 particle release. This virus-host interaction may influence HIV-1/AIDS progression, as well as electrical signaling in infected host tissues.
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Affiliation(s)
- Kate Hsu
- Institute of Molecular Cardiobiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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33
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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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34
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Coadou G, Gharbi-Benarous J, Megy S, Bertho G, Evrard-Todeschi N, Segeral E, Benarous R, Girault JP. NMR Studies of the Phosphorylation Motif of the HIV-1 Protein Vpu Bound to the F-Box Protein β-TrCP. Biochemistry 2003; 42:14741-51. [PMID: 14674748 DOI: 10.1021/bi035207u] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A protein-protein association regulated by phosphorylation of serine is examined by NMR studies. Degradation of the HIV receptor CD4 by the proteasome, mediated by the HIV-1 protein Vpu, is crucial for the release of fully infectious virions. Phosphorylation of Vpu at two sites, Ser52 and Ser56, on the motif DSGXXS is required for the interaction of Vpu with the ubiquitin ligase SCF-betaTrCP which triggers CD4 degradation by the proteasome. This motif is conserved in several signaling proteins known to be degraded by the proteasome. To elucidate the basis of beta-TrCP recognition, the bound conformation of the P-Vpu(41-62) peptide was determined by using NMR and MD. The TRNOE intensities provided distance constraints which were used in simulated annealing. The beta-TrCP-bound structure of P-Vpu was found to be similar to the structure of the free peptide in solution and to the structure recognized by its antibody. Residues 50-57 formed a bend while the phosphate groups are pointing away. The binding fragment was studied by STD-NMR spectroscopy. The phosphorylated motif DpS(52)GNEpS(56) was found to make intimate contact with beta-TrCP, and pSer52 displays the strongest binding effect. It is suggested that Ser phosphorylation allows protein-protein association by electrostatic stabilization: an obvious negative binding region of Vpu was recognizable by positive residues (Arg and Lys) of the WD domain of beta-TrCP. The Ile46 residue was also found essential for interaction with the beta-TrCP protein. Leu45 and Ile46 side chains lie in close proximity to a hydrophobic pocket of the WD domain.
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Affiliation(s)
- Gaël Coadou
- Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR 8601 CNRS, Université René Descartes, Paris V, France
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35
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Otto C, Puffer BA, Pöhlmann S, Doms RW, Kirchhoff F. Mutations in the C3 region of human and simian immunodeficiency virus envelope have differential effects on viral infectivity, replication, and CD4-dependency. Virology 2003; 315:292-302. [PMID: 14585332 DOI: 10.1016/s0042-6822(03)00513-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Residues within the highly conserved C3 region of human and simian immunodeficiency virus (HIV, SIV) envelope proteins (Envs) bind directly to the cellular CD4 receptor. However, substitutions of D385, which is critical for CD4 engagement along with other changes such as G382R, G383R, frequently arise in SIV mac-infected macaques. We investigated the influence of substitutions in the SIVmac and HIV-1 C3 regions on viral entry, dependence on CD4, and replication. Mutations flanking the C3 region such as G382R or V388A enhanced and changes within the C3 region (i.e., G383R or D385N) impaired SIVmac infectivity. Several naturally occurring sequence variations in the SIVmac Env C3 region facilitated CD4-independent membrane fusion but abrogated viral replication, suggesting that efficient infection requires additional changes elsewhere in Env. Substitutions of S365R and D368G in the HIV-1 Env, which correspond to G382 and D385 in SIVmac Env, consistently impaired viral infectivity. In contrast, mutation of D368N resulted in a virus that could not spread in cells expressing low levels of CD4, but which replicated efficiently when high levels of CD4 were expressed. Thus, changes in the C3 region of HIV-1 or SIVmac Env can have differential effects on viral infectivity and CD4-dependency. We conclude that substitutions flanking the C3 region in SIVmac Env such as G382R or V388A represent one step toward adaptation to growth in target cells expressing low CD4 levels, whereas changes within the C3 region that disrupt CD4 binding might indicate the emergence of CD4-independent variants at later stages of infection, which could potentially broaden viral tropism.
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Affiliation(s)
- Claas Otto
- Department of Virology, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany
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36
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Abstract
Viroporins are a group of proteins that participate in several viral functions, including the promotion of release of viral particles from cells. These proteins also affect cellular functions, including the cell vesicle system, glycoprotein trafficking and membrane permeability. Viroporins are not essential for the replication of viruses, but their presence enhances virus growth. Comprising some 60-120 amino acids, viroporins have a hydrophobic transmembrane domain that interacts with and expands the lipid bilayer. Some viroporins also contain other motifs, such as basic amino acid residues or a domain rich in aromatic amino acids that confers on the protein the ability to interact with the interfacial lipid bilayer. Viroporin oligomerization gives rise to hydrophilic pores at the membranes of virus-infected cells. As the list of known viroporins steadily grows, recent research efforts focus on deciphering the actions of the viroporins poliovirus 2B, alphavirus 6K, HIV-1 Vpu and influenza virus M2. All these proteins can enhance the passage of ions and small molecules through membranes depending on their concentration gradient. Future work will lengthen the list of viroporins and will provide a deeper understanding of their mechanisms of action.
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Affiliation(s)
- Maria Eugenia Gonzalez
- Unidad de Expresión Viral, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Carretera de Majadahonda-Pozuelo Km 2, 28220 Majadahonda, Madrid, Spain.
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37
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Argañaraz ER, Schindler M, Kirchhoff F, Cortes MJ, Lama J. Enhanced CD4 down-modulation by late stage HIV-1 nef alleles is associated with increased Env incorporation and viral replication. J Biol Chem 2003; 278:33912-9. [PMID: 12816953 DOI: 10.1074/jbc.m303679200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Three viral proteins participate in the down-modulation of CD4 in human immunodeficiency virus type 1 (HIV-1)-infected cells. The underlying mechanisms have been extensively investigated. However, the physiological relevance of this phenomenon remains poorly understood. To address the role of CD4 down-modulation in HIV-1 pathogenesis in vivo, we have characterized the functional properties of nef alleles isolated from seven HIV-1-infected patients at either the stage of AIDS (late alleles) or during the asymptomatic phase of infection (early alleles). HIV-1 variants carrying these nef alleles showed striking differences in CD4 down-modulation, virus infectivity, and replication properties. Infection of T cells with late strains resulted in production of viral particles with enhanced infectivity, as compared with variants carrying early nef alleles. These differences in infectivity were observed only when viruses were produced in cells with high levels of the viral receptor, suggesting a functional link between CD4 levels and the ability of Nef to down-modulate CD4 and to enhance viral infectivity. Similarly, late nef alleles were substantially more active than early nef genes in stimulating HIV-1 replication in high CD4-positive cells, including primary lymphocytes, but not in cells expressing low levels of the CD4 receptor. Single-round assays showed that differences in infectivity between late and early strains are largely reduced when evaluated in target cells with high levels of CD4, suggesting that the inhibitory effect occurs at the entry step. Supporting this, enhanced CD4 down-modulation by late nef alleles was associated with higher levels of envelope incorporation into viral particles, a phenomenon that likely accounted for the augmented infectivity. Our data suggest a mechanistic link between the Nef-mediated CD4 down-modulation and the enhancement of replication in CD4-positive lymphocytes. As progression to disease occurs, HIV-1 Nef variants with enhanced ability to down-modulate CD4 are selected. These strains efficiently overcome the deleterious effects of CD4 and replicate more aggressively in CD4-positive primary lymphocytes. These results highlight the importance of the virus-induced CD4 down-modulation in HIV-1 pathogenesis.
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Affiliation(s)
- Enrique R Argañaraz
- Department of Medicine, School of Medicine, University of California, La Jolla, 92093, USA
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38
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Abstract
HIV produces structural, regulatory, and accessory proteins during viral replication in host cells. The accessory proteins include Nef, viral infectivity factor (Vif), viral protein R, and viral protein U or viral protein X. Although these accessory proteins are generally dispensable for viral replication in vitro, they are essential for viral pathogenesis in vivo. Consequently, there has been much interest in understanding how these accessory proteins function because this research may yield new antiviral targets to curb HIV pathogenesis in vivo. Therefore, this review highlights recent advances in understanding the HIV accessory proteins and emphasizes breakthrough insights into the elusive Vif protein and potential new targets for therapeutic intervention.
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Affiliation(s)
- Jenny L. Anderson
- Department of Microbiology and Immunology, The University of Illinois at Chicago, Chicago, IL 60612, USA.
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39
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Abstract
HIV accessory genes are expressed throughout the viral life cycle and regulate wide-ranging aspects of virus replication including viral infectivity (Vif and Nef), viral gene expression (Vpr) and progeny virion production (Vpu). While in many cases the molecular basis of accessory protein function is not fully understood, a consensus is emerging that these viral products are generally devoid of enzymatic activity and instead act as multifunctional adapters, subverting normal cellular processes to serve the needs of the virus. This review focuses on presenting our current knowledge of the HIV-1-specific Vpu protein and its essential role in regulating viral particle release, viral load and expression of the CD4 receptor.
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Affiliation(s)
- Stephan Bour
- Bioinformatics Core Facility, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 4, Center Drive, Room 337, Bethesda, MD 20892-0460, USA.
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40
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Levesque K, Zhao YS, Cohen EA. Vpu exerts a positive effect on HIV-1 infectivity by down-modulating CD4 receptor molecules at the surface of HIV-1-producing cells. J Biol Chem 2003; 278:28346-53. [PMID: 12746459 DOI: 10.1074/jbc.m300327200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human immunodeficiencey virus, type 1 (HIV-1) encodes three proteins, Nef, Vpu, and gp160, that down-modulate surface expression of the CD4 receptor during viral infection. In the present study, we have investigated the role of CD4 down-modulation in the HIV-1 infection cycle, primarily from the perspective of Vpu function. We report here that, like Nef, Vpu-mediated CD4 degradation modulates positively HIV-1 infectivity. Our data reveal that accumulation of CD4 at the cell surface of Vpu-deficient HIV-1-producing cells leads to an efficient recruitment of CD4 into virions and to an impairment of viral infectivity. This CD4-mediated inhibition of viral infectivity was not observed when a CD4 mutant unable to bind Env gp120 was used or when VSV-G glycoprotein was utilized to pseudotype viruses, suggesting that an interaction between CD4 and gp120 is required for interference. Indeed, protein analysis of Vpu-defective viral particles reveals that CD4 recruitment is associated with an increased formation of gp120-CD4 complexes at the virion surface. Interestingly, we did not detect any difference at the level of total virion-associated Env glycoproteins between wild-type and Vpu-defective virus, indicating that accumulation of CD4 at the cell surface and recruitment of CD4 into Vpu-defective HIV-1 particles exert a negative effect on viral infectivity, most likely by promoting the formation of nonfunctional gp120-CD4 complexes at the virion surface. Finally, we show that both Vpu- and Nef-induced CD4 down-modulation activities are required for production of fully infectious particles in CD4+ T cell lines and primary cells, an observation that has clear implications for viral spread in vivo.
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Affiliation(s)
- Karine Levesque
- Laboratoire de Rétrovirologie Humaine, Département de Microbiologie et Immunologie, Université de Montréal, Québec H3C 3J7, Canada
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41
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Tanaka M, Ueno T, Nakahara T, Sasaki K, Ishimoto A, Sakai H. Downregulation of CD4 is required for maintenance of viral infectivity of HIV-1. Virology 2003; 311:316-25. [PMID: 12842621 DOI: 10.1016/s0042-6822(03)00126-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Downregulation of virus receptors on the cell surface is considered to be important in preventing superinfection. HIV-1 encodes multiple gene products, Env, Vpu, and Nef, involved in downregulation of CD4, a major HIV-1 receptor. We found that simultaneous mutations in both vpu and nef severely impaired virus replication. We examined the involvement of CD4 downregulation mediated by Vpu and Nef in the modification of virus infectivity. The mutation in vpu increased CD4 incorporation into virions without affecting the Env content in it, inhibiting the attachment step of virions to the CD4-positive cell surface. Although a single mutation in nef suppresses virus infectivity via a CD4-independent mechanism, it could augment CD4 incorporation in virions in combination with a vpu mutation. These results indicated that CD4 downregulation was necessary for maintenance of Env function in the virion.
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Affiliation(s)
- Masakazu Tanaka
- Laboratory of Gene Analysis, Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8393, Japan
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42
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Bour S, Akari H, Miyagi E, Strebel K. Naturally occurring amino acid substitutions in the HIV-2 ROD envelope glycoprotein regulate its ability to augment viral particle release. Virology 2003; 309:85-98. [PMID: 12726729 DOI: 10.1016/s0042-6822(02)00128-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The envelope glycoprotein of HIV-2 ROD10 has the intriguing ability to enhance the rate of viral particle release from infected cells. However, not all HIV-2 envelope glycoproteins are active in this regard. Indeed, we have previously noted that, despite a high degree of identity with that of ROD10, the envelope protein of the ROD14 isolate was unable to enhance virus production. In this study, site-directed mutagenesis was employed to reveal that a single naturally occurring alanine-to-threonine substitution at position 598, located in the extracellular part of the TM subunit, fully accounted for the lack of activity of the ROD14 Env in HeLa and 12D7 cells. A second mutation at position 422, substituting a lysine residue in ROD10 for an arginine in ROD14, was additionally required for efficient virus release from infected H9 cells, suggesting cell-type-specific requirements for this activity. Interestingly, the ROD14 Env protein exhibited a trans-dominant negative effect on particle release by ROD10 Env, suggesting that the viral release activity of the HIV-2 ROD envelope protein may be regulated by its ability to assemble into functional oligomeric structures.
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Affiliation(s)
- Stephan Bour
- Viral Biochemistry Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-0460, USA.
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43
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Affiliation(s)
- C M Steffens
- Department of Microbiology and Immunology, University of Illinois at Chicago, Chicago, Illinois, USA
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44
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Ma C, Marassi FM, Jones DH, Straus SK, Bour S, Strebel K, Schubert U, Oblatt-Montal M, Montal M, Opella SJ. Expression, purification, and activities of full-length and truncated versions of the integral membrane protein Vpu from HIV-1. Protein Sci 2002; 11:546-57. [PMID: 11847278 PMCID: PMC2373459 DOI: 10.1110/ps.37302] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2001] [Revised: 11/21/2001] [Accepted: 11/28/2001] [Indexed: 10/16/2022]
Abstract
Vpu is an 81-residue accessory protein of HIV-1. Because it is a membrane protein, it presents substantial technical challenges for the characterization of its structure and function, which are of considerable interest because the protein enhances the release of new virus particles from cells infected with HIV-1 and induces the intracellular degradation of the CD4 receptor protein. The Vpu-mediated enhancement of the virus release rate from HIV-1-infected cells is correlated with the expression of an ion channel activity associated with the transmembrane hydrophobic helical domain. Vpu-induced CD4 degradation and, to a lesser extent, enhancement of particle release are both dependent on the phosphorylation of two highly conserved serine residues in the cytoplasmic domain of Vpu. To define the minimal folding units of Vpu and to identify their activities, we prepared three truncated forms of Vpu and compared their structural and functional properties to those of full-length Vpu (residues 2-81). Vpu(2-37) encompasses the N-terminal transmembrane alpha-helix; Vpu(2-51) spans the N-terminal transmembrane helix and the first cytoplasmic alpha-helix; Vpu(28-81) includes the entire cytoplasmic domain containing the two C-terminal amphipathic alpha-helices without the transmembrane helix. Uniformly isotopically labeled samples of the polypeptides derived from Vpu were prepared by expression of fusion proteins in E. coli and were studied in the model membrane environments of lipid micelles by solution NMR spectroscopy and oriented lipid bilayers by solid-state NMR spectroscopy. The assignment of backbone resonances enabled the secondary structure of the constructs corresponding to the transmembrane and the cytoplasmic domains of Vpu to be defined in micelle samples by solution NMR spectroscopy. Solid-state NMR spectra of the polypeptides in oriented lipid bilayers demonstrated that the topology of the domains is retained in the truncated polypeptides. The biological activities of the constructs of Vpu were evaluated. The ion channel activity is confined to the transmembrane alpha-helix. The C-terminal alpha-helices modulate or promote the oligomerization of Vpu in the membrane and stabilize the conductive state of the channel, in addition to their involvement in CD4 degradation.
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Affiliation(s)
- Che Ma
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
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45
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Cortés MJ, Wong-Staal F, Lama J. Cell surface CD4 interferes with the infectivity of HIV-1 particles released from T cells. J Biol Chem 2002; 277:1770-9. [PMID: 11704677 DOI: 10.1074/jbc.m109807200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The CD4 protein is required for the entry of human immunodeficiency virus (HIV) into target cells. Upon expression of the viral genome, three HIV-1 gene products participate in the removal of the primary viral receptor from the cell surface. To investigate the role of surface-CD4 in HIV replication, we have created a set of Jurkat cell lines which constitutively express surface levels of CD4 comparable to those found in peripheral blood lymphocytes and monocytes. Expression of low levels of CD4 on the surface of producer cells exerted an inhibitory effect on the infectivity of HIV-1 particles, whereas no differences in the amount of cell-free p24 antigen were observed. Higher levels of cell surface CD4 exerted a stronger inhibitory effect on infectivity, and also affected the release of free virus in experiments where the viral genomes were delivered by electrotransfection. The CD4-mediated inhibition of HIV-1 infectivity was not observed in experiments where the vesicular stomatitis virus G protein was used to pseudotype viruses, suggesting that an interaction between CD4 and gp120 is required for interference. In contrast, inhibition of particle release by high levels of cell-surface CD4 was not overcome by pseudotyping HIV-1 with foreign envelope proteins. Protein analysis of viral particles released from HIV-infected Jurkat-T cells revealed a CD4-dependent reduction in the incorporation of gp120. These results demonstrate that physiological levels of cell-surface CD4 interfere with HIV-1 replication in T cells by a mechanism that inhibits envelope incorporation into viral membranes, and therefore provide an explanation for the need to down-modulate the viral receptor in infected cells. Our findings have important implications for the spread of HIV in vivo and suggest that the CD4 down-modulation function may be an alternative target for therapeutic intervention.
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Affiliation(s)
- Maria José Cortés
- Departments of Medicine and Biology, University of California, San Diego, La Jolla, California 92093-0665
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Akari H, Bour S, Kao S, Adachi A, Strebel K. The human immunodeficiency virus type 1 accessory protein Vpu induces apoptosis by suppressing the nuclear factor kappaB-dependent expression of antiapoptotic factors. J Exp Med 2001; 194:1299-311. [PMID: 11696595 PMCID: PMC2195969 DOI: 10.1084/jem.194.9.1299] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Human immunodeficiency virus (HIV) type 1 Vpu is an integral membrane protein with a unique affinity for betaTrCP (TrCP), a key member of the SkpI-Cullin-F-box E3 ubiquitin ligase complex that is involved in the regulated degradation of cellular proteins, including IkappaB. Remarkably, Vpu is resistant to TrCP-mediated degradation and competitively inhibits TrCP-dependent degradation of IkappaB, resulting in the suppression of nuclear factor (NF)-kappaB activity in Vpu-expressing cells. We now report that Vpu, through its interaction with TrCP, potently contributes to the induction of apoptosis in HIV-infected T cells. Vpu-induced apoptosis is specific and independent of other viral proteins. Mutation of a TrCP-binding motif in Vpu abolishes its apoptogenic property, demonstrating a close correlation between this property of Vpu and its ability to inhibit NF-kappaB activity. The involvement of NF-kappaB in Vpu-induced apoptosis is further supported by the finding that the levels of antiapoptotic factors Bcl-xL, A1/Bfl-1, and TNF receptor-associated factor (TRAF)1, all of which are expressed in an NF-kappaB-dependent manner, are reduced and, at the same time, levels of active caspase-3 are elevated. Thus, Vpu induces apoptosis through activation of the caspase pathway by way of inhibiting the NF-kappaB-dependent expression of antiapoptotic genes.
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Affiliation(s)
- H Akari
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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Bour S, Perrin C, Akari H, Strebel K. The human immunodeficiency virus type 1 Vpu protein inhibits NF-kappa B activation by interfering with beta TrCP-mediated degradation of Ikappa B. J Biol Chem 2001; 276:15920-8. [PMID: 11278695 DOI: 10.1074/jbc.m010533200] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) Vpu protein binds to the CD4 receptor and induces its degradation by cytosolic proteasomes. This process involves the recruitment of human betaTrCP (TrCP), a key member of the SkpI-Cdc53-F-box E3 ubiquitin ligase complex that specifically interacts with phosphorylated Vpu molecules. Interestingly, Vpu itself, unlike other TrCP-interacting proteins, is not targeted for degradation by proteasomes. We now report that, by virtue of its affinity for TrCP and resistance to degradation, Vpu, but not a phosphorylation mutant unable to interact with TrCP, has a dominant negative effect on TrCP function. As a consequence, expression of Vpu in HIV-infected T cells or in HeLa cells inhibited TNF-alpha-induced degradation of IkappaB-alpha. Vpu did not inhibit TNF-alpha-mediated activation of the IkappaB kinase but instead interfered with the subsequent TrCP-dependent degradation of phosphorylated IkappaB-alpha. This resulted in a pronounced reduction of NF-kappaB activity. We also observed that in cells producing Vpu-defective virus, NF-kappaB activity was significantly increased even in the absence of cytokine stimulation. However, in the presence of Vpu, this HIV-mediated NF-kappaB activation was markedly reduced. These results suggest that Vpu modulates both virus- and cytokine-induced activation of NF-kappaB in HIV-1-infected cells.
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Affiliation(s)
- S Bour
- Laboratory of Molecular Microbiology, NIAID, National Institutes of Health, Bethesda, Maryland 20892-0460, USA
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Swann SA, Williams M, Story CM, Bobbitt KR, Fleis R, Collins KL. HIV-1 Nef blocks transport of MHC class I molecules to the cell surface via a PI 3-kinase-dependent pathway. Virology 2001; 282:267-77. [PMID: 11289809 DOI: 10.1006/viro.2000.0816] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
HIV causes a chronic infection by evading immune eradication. A key element of HIV immune escape is the HIV-1 Nef protein. Nef causes a reduction in the level of cell surface major histocompatibility complex class I (MHC-I) protein expression, thus protecting HIV-infected cells from anti-HIV cytotoxic T lymphocyte (CTL) recognition and killing. Nef also reduces cell surface levels of the HIV receptor, CD4, by accelerating endocytosis. We show here that endocytosis is not required for Nef-mediated downmodulation of MHC-I molecules. The main effect of Nef is to block transport of MHC-I molecules to the cell surface, leading to accumulation in intracellular organelles. Furthermore, the effect of Nef on MHC-I molecules (but not on CD4) requires phosphoinositide 3-kinase (PI 3-kinase) activity. We propose that Nef diverts MHC-1 proteins into a PI 3-kinase-dependent transport pathway that prevents expression on the cell surface.
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Affiliation(s)
- S A Swann
- Departments of Medicine and Microbiology and Immunology, The University of Michigan, Ann Arbor, Michigan 48109, USA
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Schaeffer E, Geleziunas R, Greene WC. Human immunodeficiency virus type 1 Nef functions at the level of virus entry by enhancing cytoplasmic delivery of virions. J Virol 2001; 75:2993-3000. [PMID: 11222724 PMCID: PMC115925 DOI: 10.1128/jvi.75.6.2993-3000.2001] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Nef protein of the type 1 human immunodeficiency virus (HIV-1) plays a key although poorly understood role in accelerating the progression of clinical disease in vivo. Nef exerts several biological effects in vitro, including enhancement of virion infectivity, downregulation of CD4 and major histocompatibility complex class I receptor expression, and modulation of various intracellular signaling pathways. The positive effect of Nef on virion infectivity requires its expression in the producer cell, although its effect is manifested in the subsequent target cell of infection. Prior studies suggest that Nef does not alter viral entry into target cells; nevertheless, it enhances proviral DNA synthesis, arguing for an action of Nef at the level of viral uncoating or reverse transcription. However, these early studies discounting an effect of Nef on virion entry may be confounded by the recent finding that HIV enters cells by both fusion and endocytosis. Using epifluorescence microscopy to monitor green fluorescent protein-Vpr-labeled HIV virion entry into HeLa cells, we find that endocytosis forms a very active pathway for virus uptake. Virions entering via the endocytic pathway do not support productive infection of the host cell, presumably reflecting their inability to escape from the endosomes. Conversely, our studies now demonstrate that HIV Nef significantly enhances CD4- and chemokine receptor-dependent entry of HIV virions into the cytoplasmic compartment of target cells. Mutations in Nef either impairing its ability to downregulate CD4 or disrupting its polyproline helix compromise virion entry into the cytoplasm. We conclude that Nef acts at least in part as a regulator of cytosolic viral entry and that this action contributes to its positive effects on viral infectivity.
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Affiliation(s)
- E Schaeffer
- Gladstone Institute of Virology and Immunology, University of California, San Francisco, California 94141, USA
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Bour S, Strebel K. HIV accessory proteins: multifunctional components of a complex system. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2001; 48:75-120. [PMID: 10987089 DOI: 10.1016/s1054-3589(00)48004-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
- S Bour
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-0460, USA
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