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Iwamoto Y, Ye AA, Shirazinejad C, Hurley JH, Drubin DG. Kinetic investigation reveals an HIV-1 Nef-dependent increase in AP-2 recruitment and productivity at endocytic sites. Mol Biol Cell 2024; 35:ar9. [PMID: 37938925 PMCID: PMC10881171 DOI: 10.1091/mbc.e23-04-0126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 10/24/2023] [Accepted: 11/02/2023] [Indexed: 11/10/2023] Open
Abstract
The HIV-1 accessory protein Nef hijacks clathrin adaptors to degrade or mislocalize host proteins involved in antiviral defenses. Here, using quantitative live-cell microscopy in genome-edited Jurkat cells, we investigate the impact of Nef on clathrin-mediated endocytosis (CME), a major pathway for membrane protein internalization in mammalian cells. Nef is recruited to CME sites on the plasma membrane, and this recruitment is associated with an increase in the recruitment and lifetime of the CME coat protein AP-2 and the late-arriving CME protein dynamin2. Furthermore, we find that CME sites that recruit Nef are more likely to recruit dynamin2 and transferrin, suggesting that Nef recruitment to CME sites promotes site maturation to ensure high efficiency in host protein downregulation. Implications of these observations for HIV-1 infection are discussed.
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Affiliation(s)
- Yuichiro Iwamoto
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - Anna A. Ye
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - Cyna Shirazinejad
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720
| | - James H. Hurley
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
- California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720
- Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720
| | - David G. Drubin
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
- California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720
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Iwamoto Y, Ye A, Shirazinejad C, Hurley JH, Drubin DG. Kinetic investigation reveals an HIV-1 Nef-dependent increase in AP-2 recruitment and productivity at endocytic sites. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.18.537262. [PMID: 37131815 PMCID: PMC10153213 DOI: 10.1101/2023.04.18.537262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Lentiviruses express non-enzymatic accessory proteins whose function is to subvert cellular machinery in the infected host. The HIV-1 accessory protein Nef hijacks clathrin adaptors to degrade or mislocalize host proteins involved in antiviral defenses. Here, we investigate the interaction between Nef and clathrin-mediated endocytosis (CME), a major pathway for membrane protein internalization in mammalian cells, using quantitative live-cell microscopy in genome-edited Jurkat cells. Nef is recruited to CME sites on the plasma membrane, and this recruitment correlates with an increase in the recruitment and lifetime of CME coat protein AP-2 and late-arriving CME protein dynamin2. Furthermore, we find that CME sites that recruit Nef are more likely to recruit dynamin2, suggesting that Nef recruitment to CME sites promotes CME site maturation to ensure high efficiency in host protein downregulation.
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Affiliation(s)
- Yuichiro Iwamoto
- Department of Molecular and Cell Biology, University of California Berkeley; Berkeley CA 94720, USA
| | - Anna Ye
- Department of Molecular and Cell Biology, University of California Berkeley; Berkeley CA 94720, USA
| | - Cyna Shirazinejad
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
| | - James H Hurley
- Department of Molecular and Cell Biology, University of California Berkeley; Berkeley CA 94720, USA
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
- Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - David G Drubin
- Department of Molecular and Cell Biology, University of California Berkeley; Berkeley CA 94720, USA
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
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3
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Kruize Z, van Nuenen AC, van Wijk SW, Girigorie AF, van Dort KA, Booiman T, Kootstra NA. Nef Obtained from Individuals with HIV-1 Vary in Their Ability to Antagonize SERINC3- and SERINC5-Mediated HIV-1 Restriction. Viruses 2021; 13:v13030423. [PMID: 33800773 PMCID: PMC8000780 DOI: 10.3390/v13030423] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 02/25/2021] [Accepted: 03/02/2021] [Indexed: 12/14/2022] Open
Abstract
Nef is a multifunctional viral protein that has the ability to downregulate cell surface molecules, including CD4 and major histocompatibility complex class I (MHC-I) and, as recently shown, also members of the serine incorporator family (SERINC). Here, we analyzed the impact of naturally occurring mutations in HIV-1 Nef on its ability to counteract SERINC restriction and the clinical course of infection. HIV-1 Nef sequences were obtained from 123 participants of the Amsterdam Cohort Studies and showed multiple amino acid variations and mutations. Most of the primary Nef proteins showed increased activity to counteract SERINC3 and SERINC5 as compared to NL4-3 Nef. Several mutations in Nef were associated with either an increased or decreased infectivity of Bal26-pseudotyped HIV-1 produced in the presence of SERINC3 or SERINC5. The 8R, 157N and R178G Nef mutations were shown to have an effect on disease progression. Survival analysis showed an accelerated disease progression of individuals infected with HIV-1 carrying arginine or asparagine at position 8 or 157 in Nef, respectively, or the R178G Nef mutation. Here, we observed that naturally occurring mutations in Nef affect the ability of Nef to counteract SERINC3- and SERINC5-mediated inhibition of viral infectivity. The majority of these Nef mutations had no significant effect on HIV-1 pathogenesis and only the 8R, 157N and R178G mutations were associated with disease course.
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Ecker M, Redpath GMI, Nicovich PR, Rossy J. Quantitative visualization of endocytic trafficking through photoactivation of fluorescent proteins. Mol Biol Cell 2021; 32:892-902. [PMID: 33534630 PMCID: PMC8108533 DOI: 10.1091/mbc.e20-10-0669] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Endocytic trafficking controls the density of molecules at the plasma membrane and by doing so, the cell surface profile, which in turn determines how cells interact with their environment. A full apprehension of any cellular process necessitates understanding how proteins associated with the plasma membrane are endocytosed, how they are sorted after internalization, and if and how they are recycled to the plasma membrane. To date, it is still difficult to experimentally gain access to this information, even more to do it in a quantitative way. Here we present a toolset based on photoactivation of fluorescent proteins that enabled us to generate quantitative information on endocytosis, incorporation into sorting and recycling endosomes, delivery from endosomes to the plasma membrane, and on the type of vesicles performing intracellular transport. We illustrate these approaches by revealing striking differences in the endocytic trafficking of T-cell receptor and CD4, which bind to the same molecule at the surface of antigen-presenting cells during T-cell activation.
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Affiliation(s)
- Manuela Ecker
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW 2052, Australia
| | - Gregory M I Redpath
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW 2052, Australia
| | | | - Jérémie Rossy
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW 2052, Australia.,Biotechnology Institute Thurgau (BITg) at the University of Konstanz, 8280 Kreuzlingen, Switzerland.,Department of Biology, University of Konstanz, 78457 Konstanz, Germany
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Two Functional Variants of AP-1 Complexes Composed of either γ2 or γ1 Subunits Are Independently Required for Major Histocompatibility Complex Class I Downregulation by HIV-1 Nef. J Virol 2020; 94:JVI.02039-19. [PMID: 31915283 DOI: 10.1128/jvi.02039-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Accepted: 01/01/2020] [Indexed: 11/20/2022] Open
Abstract
The HIV-1 accessory protein Nef downregulates the cell surface expression of major histocompatibility complex class I (MHC-I) molecules to facilitate virus spreading. The Nef-induced downregulation of MHC-I molecules such as HLA-A requires the clathrin adaptor protein 1 (AP-1) complex. The cooperative interaction of Nef, AP-1, and the cytosolic tail (CT) of HLA-A leads to a redirection of HLA-A targeting from the trans-Golgi network (TGN) to lysosomes for degradation. Although the γ-adaptin subunit of AP-1 has two distinct isoforms (γ1 and γ2), which may form two AP-1 complex variants, so far, only the importance of AP-1γ1 in MHC-I downregulation by Nef has been investigated. Here, we report that the AP-1γ2 isoform also participates in this process. We found that AP-1γ2 forms a complex with Nef and HLA-A2_CT and that this interaction depends on the Y320 residue in HLA-A2_CT and Nef expression. Moreover, Nef targets AP-1γ1 and AP-1γ2 to different compartments in T cells, and the depletion of either AP-1 variant impairs the Nef-mediated reduction of total endogenous HLA-A levels and rescues HLA-A levels on the cell surface. Finally, immunofluorescence and immunoelectron microscopy analyses reveal that the depletion of γ2 in T cells compromises both the Nef-mediated retention of HLA-A molecules in the TGN and targeting to multivesicular bodies/late endosomes. Altogether, these results show that in addition to AP-1γ1, Nef also requires the AP-1γ2 variant for efficient MHC-I downregulation.IMPORTANCE HIV-1 Nef mediates evasion of the host immune system by inhibiting MHC-I surface presentation of viral antigens. To achieve this goal, Nef modifies the intracellular trafficking of MHC-I molecules in several ways. Despite being the subject of intense study, the molecular details underlying these modifications are not yet fully understood. Adaptor protein 1 (AP-1) plays an essential role in the Nef-mediated downregulation of MHC-I molecules such as HLA-A in different cell types. However, AP-1 has two functionally distinct variants composed of either γ1 or γ2 subunit isoforms. Because previous studies on the role of AP-1 in MHC-I downregulation by Nef focused on AP-1γ1, an important open question is the participation of AP-1γ2 in this process. Here, we show that AP-1γ2 is also essential for Nef-mediated depletion of surface HLA-A molecules in T cells. Our results indicate that Nef hijacks AP-1γ2 to modify HLA-A intracellular transport, redirecting these proteins to lysosomes for degradation.
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Abstract
The accessory protein Nef of human immunodeficiency virus (HIV) is a primary determinant of viral pathogenesis. Nef is abundantly expressed during infection and reroutes a variety of cell surface proteins to disrupt host immunity and promote the viral replication cycle. Nef counteracts host defenses by sequestering and/or degrading its targets via the endocytic and secretory pathways. Nef does this by physically engaging a number of host trafficking proteins. Substantial progress has been achieved in identifying the targets of Nef, and a structural and mechanistic understanding of Nef's ability to command the protein trafficking machinery has recently started to coalesce. Comparative analysis of HIV and simian immunodeficiency virus (SIV) Nef proteins in the context of recent structural advances sheds further light on both viral evolution and the mechanisms whereby trafficking is hijacked. This review describes how advances in cell and structural biology are uncovering in growing detail how Nef subverts the host immune system, facilitates virus release, and enhances viral infectivity.
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Shi J, Xiong R, Zhou T, Su P, Zhang X, Qiu X, Li H, Li S, Yu C, Wang B, Ding C, Smithgall TE, Zheng YH. HIV-1 Nef Antagonizes SERINC5 Restriction by Downregulation of SERINC5 via the Endosome/Lysosome System. J Virol 2018; 92:e00196-18. [PMID: 29514909 PMCID: PMC5952139 DOI: 10.1128/jvi.00196-18] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Accepted: 03/01/2018] [Indexed: 12/11/2022] Open
Abstract
The primate lentiviral accessory protein Nef downregulates CD4 and major histocompatibility complex class I (MHC-I) from the cell surface via independent endosomal trafficking pathways to promote viral pathogenesis. In addition, Nef antagonizes a novel restriction factor, SERINC5 (Ser5), to increase viral infectivity. To explore the molecular mechanism of Ser5 antagonism by Nef, we determined how Nef affects Ser5 expression and intracellular trafficking in comparison to CD4 and MHC-I. We confirm that Nef excludes Ser5 from human immunodeficiency virus type 1 (HIV-1) virions by downregulating its cell surface expression via similar functional motifs required for CD4 downregulation. We find that Nef decreases both Ser5 and CD4 expression at steady-state levels, which are rescued by NH4Cl or bafilomycin A1 treatment. Nef binding to Ser5 was detected in living cells using a bimolecular fluorescence complementation assay, where Nef membrane association is required for interaction. In addition, Nef triggers rapid Ser5 internalization via receptor-mediated endocytosis and relocalizes Ser5 to Rab5+ early, Rab7+ late, and Rab11+ recycling endosomes. Manipulation of AP-2, Rab5, Rab7, and Rab11 expression levels affects the Nef-dependent Ser5 and CD4 downregulation. Moreover, although Nef does not promote Ser5 polyubiquitination, Ser5 downregulation relies on the ubiquitination pathway, and both K48- and K63-specific ubiquitin linkages are required for the downregulation. Finally, Nef promotes Ser5 colocalization with LAMP1, which is enhanced by bafilomycin A1 treatment, suggesting that Ser5 is targeted to lysosomes for destruction. We conclude that Nef uses a similar mechanism to downregulate Ser5 and CD4, which sorts Ser5 into a point-of-no-return degradative pathway to counteract its restriction.IMPORTANCE Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) express an accessory protein called Nef to promote viral pathogenesis. Nef drives immune escape in vivo through downregulation of CD4 and MHC-I from the host cell surface. Recently, Nef was reported to counteract a novel host restriction factor, Ser5, to increase viral infectivity. Nef downregulates cell surface Ser5, thus preventing its incorporation into virus particles, resulting in disruption of its antiviral activity. Here, we report mechanistic studies of Nef-mediated Ser5 downregulation in comparison to CD4 and MHC-I. We demonstrate that Nef binds directly to Ser5 in living cells and that Nef-Ser5 interaction requires Nef association with the plasma membrane. Subsequently, Nef internalizes Ser5 from the plasma membrane via receptor-mediated endocytosis, and targets ubiquitinated Ser5 to endosomes and lysosomes for destruction. Collectively, these results provide new insights into our ongoing understanding of the Nef-Ser5 arms race in HIV-1 infection.
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Affiliation(s)
- Jing Shi
- Harbin Veterinary Research Institute, CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Ran Xiong
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Tao Zhou
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Peiyi Su
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Xihe Zhang
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Xusheng Qiu
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Hongmei Li
- Department of Pathology, Qiqihar Medical University, Qiqihar, China
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Sunan Li
- Harbin Veterinary Research Institute, CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Changqing Yu
- Harbin Veterinary Research Institute, CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Bin Wang
- Harbin Veterinary Research Institute, CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Chan Ding
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai, China
| | - Thomas E Smithgall
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Yong-Hui Zheng
- Harbin Veterinary Research Institute, CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences, Harbin, China
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
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SERINC as a Restriction Factor to Inhibit Viral Infectivity and the Interaction with HIV. J Immunol Res 2017; 2017:1548905. [PMID: 29359168 PMCID: PMC5735641 DOI: 10.1155/2017/1548905] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 10/22/2017] [Accepted: 11/02/2017] [Indexed: 12/16/2022] Open
Abstract
The serine incorporator 5 (SERINC5) is a recently discovered restriction factor that inhibits viral infectivity by preventing fusion. Retroviruses have developed strategies to counteract the action of SERINC5, such as the expression of proteins like negative regulatory factor (Nef), S2, and glycosylated Gag (glycoGag). These accessory proteins downregulate SERINC5 from the plasma membrane for subsequent degradation in the lysosomes. The observed variability in the action of SERINC5 suggests the participation of other elements like the envelope glycoprotein (Env) that modulates susceptibility of the virus towards SERINC5. The exact mechanism by which SERINC5 inhibits viral fusion has not yet been determined, although it has been proposed that it increases the sensitivity of the Env by exposing regions which are recognized by neutralizing antibodies. More studies are needed to understand the role of SERINC5 and to assess its utility as a therapeutic strategy.
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Tavares LA, da Silva EML, da Silva-Januário ME, Januário YC, de Cavalho JV, Czernisz ÉS, Mardones GA, daSilva LLP. CD4 downregulation by the HIV-1 protein Nef reveals distinct roles for the γ1 and γ2 subunits of the AP-1 complex in protein trafficking. J Cell Sci 2016; 130:429-443. [PMID: 27909244 DOI: 10.1242/jcs.192104] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 11/16/2016] [Indexed: 12/20/2022] Open
Abstract
The HIV accessory protein Nef is a major determinant of viral pathogenesis that facilitates viral particle release, prevents viral antigen presentation and increases infectivity of new virus particles. These functions of Nef involve its ability to remove specific host proteins from the surface of infected cells, including the CD4 receptor. Nef binds to the adaptor protein 2 (AP-2) and CD4 in clathrin-coated pits, forcing CD4 internalization and its subsequent targeting to lysosomes. Herein, we report that this lysosomal targeting requires a variant of AP-1 containing isoform 2 of γ-adaptin (AP1G2, hereafter γ2). Depletion of the γ2 or μ1A (AP1M1) subunits of AP-1, but not of γ1 (AP1G1), precludes Nef-mediated lysosomal degradation of CD4. In γ2-depleted cells, CD4 internalized by Nef accumulates in early endosomes and this alleviates CD4 removal from the cell surface. Depletion of γ2 also hinders EGFR-EGF-complex targeting to lysosomes, an effect that is not observed upon γ1 depletion. Taken together, our data provide evidence that the presence of γ1 or γ2 subunits delineates two distinct variants of AP-1 complexes, with different functions in protein sorting.
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Affiliation(s)
- Lucas A Tavares
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Eulália M L da Silva
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Mara E da Silva-Januário
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Yunan C Januário
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Julianne V de Cavalho
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Érika S Czernisz
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Gonzalo A Mardones
- Department of Physiology, School of Medicine, and Center for Interdisciplinary Studies of the Nervous System (CISNe), Universidad Austral de Chile, Valdivia 5110566, Chile
| | - Luis L P daSilva
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
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The Antagonism of HIV-1 Nef to SERINC5 Particle Infectivity Restriction Involves the Counteraction of Virion-Associated Pools of the Restriction Factor. J Virol 2016; 90:10915-10927. [PMID: 27681140 DOI: 10.1128/jvi.01246-16] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 09/21/2016] [Indexed: 11/20/2022] Open
Abstract
SERINC3 (serine incorporator 3) and SERINC5 are recently identified host cell inhibitors of HIV-1 particle infectivity that are counteracted by the viral pathogenesis factor Nef. Here we confirm that HIV-1 Nef, but not HIV-1 Vpu, antagonizes the particle infectivity restriction of SERINC5. SERINC5 antagonism occurred in parallel with other Nef activities, including cell surface receptor downregulation, trans-Golgi network targeting of Lck, and inhibition of host cell actin dynamics. Interaction motifs with host cell endocytic machinery and the Nef-associated kinase complex, as well as CD4 cytoplasmic tail/HIV-1 protease, were identified as essential Nef determinants for SERINC5 antagonism. Characterization of antagonism-deficient Nef mutants revealed that counteraction of SERINC5 occurs in the absence of retargeting of the restriction factor to intracellular compartments and reduction of SERINC5 cell surface density is insufficient for antagonism. Consistent with virion incorporation of SERINC5 being a prerequisite for its antiviral activity, the infectivity of HIV-1 particles produced in the absence of a SERINC5 antagonist decreased with increasing amounts of virion SERINC5. At low levels of SERINC5 expression, enhancement of virion infectivity by Nef was associated with reduced virion incorporation of SERINC5 and antagonism-defective Nef mutants failed to exclude SERINC5 from virions. However, at elevated levels of SERINC5 expression, Nef maintained infectious HIV particles, despite significant virion incorporation of the restriction factor. These results suggest that in addition to virion exclusion, Nef employs a cryptic mechanism to antagonize virion-associated SERINC5. The involvement of common determinants suggests that the antagonism of Nef to SERINC5 and the downregulation of cell surface CD4 by Nef involve related molecular mechanisms. IMPORTANCE HIV-1 Nef critically determines virus spread and disease progression in infected individuals by incompletely defined mechanisms. SERINC3 and SERINC5 were recently identified as potent inhibitors of HIV particle infectivity whose antiviral activity is antagonized by HIV-1 Nef. To address the mechanism of SERINC5 antagonism, we identified four molecular determinants of Nef antagonism that are all linked to the mechanism by which Nef downregulates cell surface CD4. Functional characterization of these mutants revealed that endosomal targeting and cell surface downregulation of SERINC5 are dispensable and insufficient for antagonism, respectively. In contrast, virion exclusion and antagonism of SERINC5 were correlated; however, Nef was also able to enhance the infectivity of virions that incorporated robust levels of SERINC5. These results suggest that the antagonism of HIV-1 Nef to SERINC5 restriction of virion infectivity is mediated by a dual mechanism that is related to CD4 downregulation.
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11
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Pereira EA, daSilva LLP. HIV-1 Nef: Taking Control of Protein Trafficking. Traffic 2016; 17:976-96. [PMID: 27161574 DOI: 10.1111/tra.12412] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 05/05/2016] [Accepted: 05/05/2016] [Indexed: 12/25/2022]
Abstract
The Nef protein of the human immunodeficiency virus is a crucial determinant of viral pathogenesis and disease progression. Nef is abundantly expressed early in infection and is thought to optimize the cellular environment for viral replication. Nef controls expression levels of various cell surface molecules that play important roles in immunity and virus life cycle, by directly interfering with the itinerary of these proteins within the endocytic and late secretory pathways. To exert these functions, Nef physically interacts with host proteins that regulate protein trafficking. In recent years, considerable progress was made in identifying host-cell-interacting partners for Nef, and the molecular machinery used by Nef to interfere with protein trafficking has started to be unraveled. Here, we briefly review the knowledge gained and discuss new findings regarding the mechanisms by which Nef modifies the intracellular trafficking pathways to prevent antigen presentation, facilitate viral particle release and enhance the infectivity of HIV-1 virions.
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Affiliation(s)
- Estela A Pereira
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Luis L P daSilva
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
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12
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Martínez-Bonet M, Palladino C, Briz V, Rudolph JM, Fackler OT, Relloso M, Muñoz-Fernandez MA, Madrid R. A Conserved GPG-Motif in the HIV-1 Nef Core Is Required for Principal Nef-Activities. PLoS One 2015; 10:e0145239. [PMID: 26700863 PMCID: PMC4689412 DOI: 10.1371/journal.pone.0145239] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Accepted: 11/30/2015] [Indexed: 12/26/2022] Open
Abstract
To find out new determinants required for Nef activity we performed a functional alanine scanning analysis along a discrete but highly conserved region at the core of HIV-1 Nef. We identified the GPG-motif, located at the 121–137 region of HIV-1 NL4.3 Nef, as a novel protein signature strictly required for the p56Lck dependent Nef-induced CD4-downregulation in T-cells. Since the Nef-GPG motif was dispensable for CD4-downregulation in HeLa-CD4 cells, Nef/AP-1 interaction and Nef-dependent effects on Tf-R trafficking, the observed effects on CD4 downregulation cannot be attributed to structure constraints or to alterations on general protein trafficking. Besides, we found that the GPG-motif was also required for Nef-dependent inhibition of ring actin re-organization upon TCR triggering and MHCI downregulation, suggesting that the GPG-motif could actively cooperate with the Nef PxxP motif for these HIV-1 Nef-related effects. Finally, we observed that the Nef-GPG motif was required for optimal infectivity of those viruses produced in T-cells. According to these findings, we propose the conserved GPG-motif in HIV-1 Nef as functional region required for HIV-1 infectivity and therefore with a potential interest for the interference of Nef activity during HIV-1 infection.
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Affiliation(s)
- Marta Martínez-Bonet
- Laboratorio de Inmunobiología Molecular, Instituto de Investigación Biomédica Gregorio Marañón (IISGM), 28007 Madrid, Spain
| | - Claudia Palladino
- Laboratorio de Inmunobiología Molecular, Instituto de Investigación Biomédica Gregorio Marañón (IISGM), 28007 Madrid, Spain
| | - Veronica Briz
- Laboratorio de Inmunobiología Molecular, Instituto de Investigación Biomédica Gregorio Marañón (IISGM), 28007 Madrid, Spain
| | - Jochen M. Rudolph
- Department of Infectious Diseases, Integrative Virology, University Hospital Heidelberg, Heidelberg, Germany
| | - Oliver T. Fackler
- Department of Infectious Diseases, Integrative Virology, University Hospital Heidelberg, Heidelberg, Germany
| | - Miguel Relloso
- Laboratorio de Inmunobiología Molecular, Instituto de Investigación Biomédica Gregorio Marañón (IISGM), 28007 Madrid, Spain
| | - Maria Angeles Muñoz-Fernandez
- Laboratorio de Inmunobiología Molecular, Instituto de Investigación Biomédica Gregorio Marañón (IISGM), 28007 Madrid, Spain
| | - Ricardo Madrid
- Departament of Virology. Centro de Biología Molecular Severo Ochoa, CSIC/UAM, Madrid, Spain
- * E-mail:
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Landi A, Timermans CG, Naessens E, Vanderstraeten H, Stove V, Verhasselt B. The human immunodeficiency virus (HIV) Rev-binding protein (HRB) is a co-factor for HIV-1 Nef-mediated CD4 downregulation. J Gen Virol 2015; 97:778-785. [PMID: 26701340 DOI: 10.1099/jgv.0.000382] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1)-mediated CD4 downregulation is an important determinant of viral replication in vivo. Research on cellular co-factors involved in this process could lead to the identification of potential therapeutic targets. We found that CD4 surface levels were significantly higher in HIV-1-infected cells knocked-down for the HIV Rev-binding protein (HRB) compared with control cells. HRB knock-down affected CD4 downregulation induced by Nef but not by HIV-1 Vpu. Interestingly, the knock-down of the related protein HRBL (HRB-like), but not of the HRB interaction partner EPS15 (epidermal growth factor receptor pathway substrate 15), increased CD4 levels in Vpu-expressing cells significantly. Both of these proteins are known to be involved in HIV-1-mediated CD4 downregulation as co-factors of HIV-1 Nef. These results identify HRB as a previously unknown co-factor for HIV-1 Nef-mediated CD4 downregulation and highlight differences with the related protein HRBL, which affects the CD4 downregulation in a dual role as co-factor of both HIV-1 Nef and Vpu.
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Affiliation(s)
- Alessia Landi
- Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium
| | | | - Evelien Naessens
- Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium
| | - Hanne Vanderstraeten
- Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium
| | - Veronique Stove
- Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium
| | - Bruno Verhasselt
- Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium
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14
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Percario ZA, Ali M, Mangino G, Affabris E. Nef, the shuttling molecular adaptor of HIV, influences the cytokine network. Cytokine Growth Factor Rev 2014; 26:159-73. [PMID: 25529283 DOI: 10.1016/j.cytogfr.2014.11.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 11/05/2014] [Indexed: 12/17/2022]
Abstract
Several viruses manipulate host innate immune responses to avoid immune recognition and improve viral replication and spreading. The viral protein Nef of Human Immunodeficiency Virus is mainly involved in this "hijacking" activity and is a well established virulence factor. In the last few years there have been remarkable advances in outlining a defined framework of its functions. In particular Nef appears to be a shuttling molecular adaptor able to exert its effects both on infected and non infected bystander cell. In addition it is emerging fact that it has an important impact on the chemo-cytokine network. Nef protein represents an interesting new target to develop therapeutic drugs for treatment of seropositive patients. In this review we have tried to provide a unifying view of the multiple functions of this viral protein on the basis of recently available experimental data.
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Affiliation(s)
| | - Muhammad Ali
- Department of Sciences, University Roma Tre, Rome, Italy
| | - Giorgio Mangino
- Department of Medico-Surgical Sciences and Biotechnologies, Sapienza University of Rome, Italy
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15
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de Carvalho JV, de Castro RO, da Silva EZM, Silveira PP, da Silva-Januário ME, Arruda E, Jamur MC, Oliver C, Aguiar RS, daSilva LLP. Nef neutralizes the ability of exosomes from CD4+ T cells to act as decoys during HIV-1 infection. PLoS One 2014; 9:e113691. [PMID: 25423108 PMCID: PMC4244142 DOI: 10.1371/journal.pone.0113691] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 10/27/2014] [Indexed: 01/09/2023] Open
Abstract
Nef is an HIV-1 accessory protein that promotes viral replication and pathogenesis. A key function of Nef is to ensure sustained depletion of CD4 and MHC-I molecules in infected cells by inducing targeting of these proteins to multivesicular bodies (MVBs), and ultimately to lysosomes for degradation. Nef also affects cellular secretory routes promoting its own secretion via exosomes. To better understand the effects of Nef on the exocytic pathway, we investigated whether this viral factor modifies the composition of exosomes released by T lymphocytes. We showed that both CD4 and MHC-I molecules are secreted in exosomes from T cells and that the expression of Nef reduces the amount of these proteins in exosomes. To investigate the functional role for this novel activity of Nef, we performed in vitro HIV-1 infection assays in the presence of distinct populations of exosomes. We demonstrated that exosomes released by CD4+ T cells, but not CD4− T cells, efficiently inhibit HIV-1 infection in vitro. Because CD4 is the main receptor for HIV-1 infection, these results suggest that CD4 molecules displayed on the surface of exosomes can bind to envelope proteins of HIV-1 hindering virus interaction with target cells and infection. Importantly, CD4-depleted exosomes released by CD4+ T cells expressing Nef have a reduced capacity to inhibit HIV-1 infection in vitro. These results provide evidence that Nef promotes HIV-1 infection by reducing the expression of CD4 in exosomes from infected cells, besides the original role of Nef in reducing the CD4 levels at the cell surface.
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Affiliation(s)
- Julianne V. de Carvalho
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Rodrigo O. de Castro
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Elaine Z. M. da Silva
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Paola P. Silveira
- Molecular Virology Laboratory, Department of Genetics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Mara E. da Silva-Januário
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Eurico Arruda
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Maria C. Jamur
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Constance Oliver
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
| | - Renato S. Aguiar
- Molecular Virology Laboratory, Department of Genetics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Luis L. P. daSilva
- Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil
- * E-mail:
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16
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Amorim NA, da Silva EML, de Castro RO, da Silva-Januário ME, Mendonça LM, Bonifacino JS, da Costa LJ, daSilva LLP. Interaction of HIV-1 Nef protein with the host protein Alix promotes lysosomal targeting of CD4 receptor. J Biol Chem 2014; 289:27744-56. [PMID: 25118280 DOI: 10.1074/jbc.m114.560193] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Nef is an accessory protein of human immunodeficiency viruses that promotes viral replication and progression to AIDS through interference with various host trafficking and signaling pathways. A key function of Nef is the down-regulation of the coreceptor CD4 from the surface of the host cells. Nef-induced CD4 down-regulation involves at least two independent steps as follows: acceleration of CD4 endocytosis by a clathrin/AP-2-dependent pathway and targeting of internalized CD4 to multivesicular bodies (MVBs) for eventual degradation in lysosomes. In a previous work, we found that CD4 targeting to the MVB pathway was independent of CD4 ubiquitination. Here, we report that this targeting depends on a direct interaction of Nef with Alix/AIP1, a protein associated with the endosomal sorting complexes required for transport (ESCRT) machinery that assists with cargo recruitment and intraluminal vesicle formation in MVBs. We show that Nef interacts with both the Bro1 and V domains of Alix. Depletion of Alix or overexpression of the Alix V domain impairs lysosomal degradation of CD4 induced by Nef. In contrast, the V domain overexpression does not prevent cell surface removal of CD4 by Nef or protein targeting to the canonical ubiquitination-dependent MVB pathway. We also show that the Nef-Alix interaction occurs in late endosomes that are enriched in internalized CD4. Together, our results indicate that Alix functions as an adaptor for the ESCRT-dependent, ubiquitin-independent targeting of CD4 to the MVB pathway induced by Nef.
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Affiliation(s)
- Nathaly A Amorim
- From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil
| | - Eulália M L da Silva
- From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil
| | - Rodrigo O de Castro
- From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil
| | - Mara E da Silva-Januário
- From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil
| | - Luiza M Mendonça
- the Department of Virology, Institute of Microbiology Paulo de Góes, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil, and
| | - Juan S Bonifacino
- the Cell Biology and Metabolism Program, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892
| | - Luciana J da Costa
- the Department of Virology, Institute of Microbiology Paulo de Góes, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil, and
| | - Luis L P daSilva
- From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil,
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Ren X, Park SY, Bonifacino JS, Hurley JH. How HIV-1 Nef hijacks the AP-2 clathrin adaptor to downregulate CD4. eLife 2014; 3:e01754. [PMID: 24473078 PMCID: PMC3901399 DOI: 10.7554/elife.01754] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The Nef protein of HIV-1 downregulates the cell surface co-receptor CD4 by hijacking the clathrin adaptor complex AP-2. The structural basis for the hijacking of AP-2 by Nef is revealed by a 2.9 Å crystal structure of Nef bound to the α and σ2 subunits of AP-2. Nef binds to AP-2 via its central loop (residues 149–179) and its core. The determinants for Nef binding include residues that directly contact AP-2 and others that stabilize the binding-competent conformation of the central loop. Residues involved in both direct and indirect interactions are required for the binding of Nef to AP-2 and for downregulation of CD4. These results lead to a model for the docking of the full AP-2 tetramer to membranes as bound to Nef, such that the cytosolic tail of CD4 is situated to interact with its binding site on Nef. DOI:http://dx.doi.org/10.7554/eLife.01754.001 Infection by a pathogen, such as a bacterium or virus, activates both the innate immune response—which is immediate but not specific to the pathogen—and the adaptive immune response, which is stronger and specific to the pathogen. White blood cells called CD4+ T helper cells play an important role in the early stages of the adaptive immune response by helping to activate and regulate other white blood cells that go on to eradicate the pathogen. HIV-1 is a retrovirus that infects immune cells that have the CD4 receptor on their surface, including CD4+ T helper cells. As the number of worker CD4+ T helper cells falls, the adaptive immune response gradually weakens, and the HIV-1 infected individual becomes increasingly susceptible to infection and disease. An individual is said to develop AIDS when either their CD4+ T helper cell count falls below 200 cells per microliter or they begin to experience specific diseases associated with the HIV-1 infection. In an effort to prevent and treat AIDS, researchers have worked to understand the HIV-1 genome and have developed medicines that target the enzymatic activity of viral proteins involved in viral replication. When used in combination, these drugs have helped to reduce transmission of HIV-1, and also to reduce deaths from the disease. However, worries about side effects and drug resistance mean that there is a need to develop new drugs. The HIV-1 genome codes for a number of accessory proteins, including a protein known as Nef that attacks the CD4+ T helper cells, removing the CD4 protein that gives the cells their name. This reduces the ability of the T cells to activate the immune system and allows the virus to spread. Nef acts by forming a complex with a protein called AP-2 in the T cells, and this complex then interacts with the CD4 proteins, causing them to be internalized and then destroyed inside the cells. Ren et al. have now worked out the structure of the Nef:AP-2 complex at the molecular level and identified the amino acid residues within the Nef protein that interact with the AP-2 protein. This allowed Ren et al. to propose a detailed model of the interaction between the complex and the CD4 protein, and how this leads to the protein being destroyed. This information could be used to develop drugs that work by blocking the amino residues on AP-2 that bind to Nef. Moreover, since these sites are not susceptible to rapid mutations, such drugs are less likely to encounter the problem of drug resistance. DOI:http://dx.doi.org/10.7554/eLife.01754.002
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Affiliation(s)
- Xuefeng Ren
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
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18
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Single-domain antibody-SH3 fusions for efficient neutralization of HIV-1 Nef functions. J Virol 2012; 86:4856-67. [PMID: 22345475 DOI: 10.1128/jvi.06329-11] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
HIV-1 Nef is essential for AIDS pathogenesis, but this viral protein is not targeted by antiviral strategies. The functions of Nef are largely related to perturbations of intracellular trafficking and signaling pathways through leucine-based and polyproline motifs that are required for interactions with clathrin-associated adaptor protein complexes and SH3 domain-containing proteins, such as the phagocyte-specific kinase Hck. We previously described a single-domain antibody (sdAb) targeting Nef and inhibiting many, but not all, of its biological activities. We now report a further development of this anti-Nef strategy through the demonstration of the remarkable inhibitory activity of artificial Nef ligands, called Neffins, comprised of the anti-Nef sdAb fused to modified SH3 domains. The Neffins inhibited all key activities of Nef, including Nef-mediated CD4 and major histocompatibility complex class I (MHC-I) cell surface downregulation and enhancement of virus infectivity. When expressed in T lymphocytes, Neffins specifically inhibited the Nef-induced mislocalization of the Lck kinase, which contributes to the alteration of the formation of the immunological synapse. In macrophages, Neffins inhibited the Nef-induced formation of multinucleated giant cells and podosome rosettes, and it counteracted the inhibitory activity of Nef on phagocytosis. Since we show here that these effects of Nef on macrophage and T cell functions were both dependent on the leucine-based and polyproline motifs, we confirmed that Neffins disrupted interactions of Nef with both AP complexes and Hck. These results demonstrate that it is possible to inhibit all functions of Nef, both in T lymphocytes and macrophages, with a single ligand that represents an efficient tool to develop new antiviral strategies targeting Nef.
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Abstract
The transmembrane domains (TMDs) of integral membrane proteins do not merely function as membrane anchors but play active roles in many important biological processes. The downregulation of the CD4 coreceptor by the Vpu protein of HIV-1 is a prime example of a process that is dependent on specific properties of TMDs. Here we report the identification of Trp22 in the Vpu TMD and Gly415 in the CD4 TMD as critical determinants of Vpu-induced targeting of CD4 to endoplasmic reticulum (ER)-associated degradation (ERAD). The two residues participate in different aspects of ERAD targeting. Vpu Trp22 is required to prevent assembly of Vpu into an inactive, oligomeric form and to promote CD4 polyubiquitination and subsequent recruitment of the VCP-UFD1L-NPL4 dislocase complex. In the presence of a Vpu Trp22 mutant, CD4 remains integrally associated with the ER membrane, suggesting that dislocation from the ER into the cytosol is impaired. CD4 Gly415, on the other hand, contributes to CD4-Vpu interactions. We also identify two residues, Val20 and Ser23, in the Vpu TMD that mediate retention of Vpu and, by extension, CD4 in the ER. These findings highlight the exploitation of several TMD-mediated mechanisms by HIV-1 Vpu in order to downregulate CD4 and thus promote viral pathogenesis.
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20
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Cheney L, Hou JC, Morrison S, Pessin J, Steigbigel RT. Nef inhibits glucose uptake in adipocytes and contributes to insulin resistance in human immunodeficiency virus type I infection. J Infect Dis 2011; 203:1824-31. [PMID: 21606541 DOI: 10.1093/infdis/jir170] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Human immunodeficiency virus (HIV) infection is associated with insulin resistance. HIV type 1 Nef downregulates cell surface protein expression, alters signal transduction, and interacts with the cytoskeleton and proteins involved in actin polymerization. These functions are required for glucose uptake by insulin-stimulated adipocytes. We sought to determine whether Nef alters adipocyte glucose homeostasis. Using radiolabeled glucose, we found that adipocytes exposed to recombinant Nef took in 42% less glucose after insulin stimulation than did control cells. This reduction resulted from a Nef-dependent inhibition of glucose transporter 4 (GLUT4) trafficking, as assessed by means of immunofluorescence microscopy. Immunoblot analysis revealed a decrease in phosphorylation of signal transducing proteins after Nef treatment, and fluorescence microscopy showed a dramatic alteration in cortical actin organization. We conclude that Nef interferes with insulin-stimulated processes in adipocytes. We have identified HIV Nef, which is detectable and antigenic in serum samples from HIV-infected people, as a novel contributor to the development of insulin resistance.
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Affiliation(s)
- Laura Cheney
- Department of Pharmacological Sciences, State University of New York at Stony Brook, NY 11794-8153, USA
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21
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Abstract
The Nef protein of HIV-1 is important for AIDS pathogenesis, but it is not targeted by current antiviral strategies. Here, we describe a single-domain antibody (sdAb) that binds to HIV-1 Nef with a high affinity (K(d) = 2 × 10(-9)M) and inhibited critical biologic activities of Nef both in vitro and in vivo. First, it interfered with the CD4 down-regulation activity of a broad panel of nef alleles through inhibition of the Nef effects on CD4 internalization from the cell surface. Second, it was able to interfere with the association of Nef with the cellular p21-activated kinase 2 as well as with the resulting inhibitory effect of Nef on actin remodeling. Third, it counteracted the Nef-dependent enhancement of virion infectivity and inhibited the positive effect of Nef on virus replication in peripheral blood mononuclear cells. Fourth, anti-Nef sdAb rescued Nef-mediated thymic CD4(+) T-cell maturation defects and peripheral CD4(+) T-cell activation in the CD4C/HIV-1(Nef) transgenic mouse model. Because all these Nef functions have been implicated in Nef effects on pathogenesis, this anti-Nef sdAb may represent an efficient tool to elucidate the molecular functions of Nef in the virus life cycle and could now help to develop new strategies for the control of AIDS.
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Affiliation(s)
- Derek Toomre
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002; ,
| | - Joerg Bewersdorf
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002; ,
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23
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Yi L, Rosales T, Rose JJ, Chowdhury B, Chaudhury B, Knutson JR, Venkatesan S. HIV-1 Nef binds a subpopulation of MHC-I throughout its trafficking itinerary and down-regulates MHC-I by perturbing both anterograde and retrograde trafficking. J Biol Chem 2010; 285:30884-905. [PMID: 20622010 DOI: 10.1074/jbc.m110.135947] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The HIV protein Nef is thought to mediate immune evasion and promote viral persistence in part by down-regulating major histocompatibility complex class I protein (MHC-I or HLA-I) from the cell surface. Two different models have been proposed to explain this phenomenon as follows: 1) stimulation of MHC-I retrograde trafficking from and aberrant recycling to the plasma membrane, and 2) inhibition of anterograde trafficking of newly synthesized HLA-I from the endoplasmic reticulum to the plasma membrane. We show here that Nef simultaneously uses both mechanisms to down-regulate HLA-I in peripheral blood mononuclear cells or HeLa cells. Consistent with this, we found by using fluorescence correlation spectroscopy that a third of diffusing HLA-I at the endoplasmic reticulum, Golgi/trans-Golgi network, and the plasma membrane (PM) was associated with Nef. The binding of Nef was similarly avid for native HLA-I and recombinant HLA-I A2 at the PM. Nef binding to HLA-I at the PM was sensitive to specific inhibition of endocytosis. It was also attenuated by cyclodextrin disruption of PM lipid micro-domain architecture, a change that also retarded lateral diffusion and induced large clusters of HLA-I. In all, our data support a model for Nef down-regulation of HLA-I that involves both major trafficking itineraries and persistent protein-protein interactions throughout the cell.
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Affiliation(s)
- Ling Yi
- Molecular and Cell Biology Unit, Laboratory of Molecular Immunology, NIAID, Laboratory of Molecular Biophysics, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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24
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Vérollet C, Zhang YM, Le Cabec V, Mazzolini J, Charrière G, Labrousse A, Bouchet J, Medina I, Biessen E, Niedergang F, Bénichou S, Maridonneau-Parini I. HIV-1 Nef Triggers Macrophage Fusion in a p61Hck- and Protease-Dependent Manner. THE JOURNAL OF IMMUNOLOGY 2010; 184:7030-9. [DOI: 10.4049/jimmunol.0903345] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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25
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Leontiev V, Hadany L. Regulated superinfection may help HIV adaptation on rugged landscape. INFECTION GENETICS AND EVOLUTION 2010; 10:505-10. [DOI: 10.1016/j.meegid.2010.02.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 02/16/2010] [Accepted: 02/18/2010] [Indexed: 10/19/2022]
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26
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Surface analysis of membrane dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:766-76. [DOI: 10.1016/j.bbamem.2009.09.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 09/18/2009] [Accepted: 09/20/2009] [Indexed: 11/18/2022]
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Vesicle traffic to the immunological synapse: a multifunctional process targeted by lymphotropic viruses. Curr Top Microbiol Immunol 2010; 340:191-207. [PMID: 19960315 DOI: 10.1007/978-3-642-03858-7_10] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The site of contact between T lymphocytes and antigen-presenting cells becomes, upon antigen recognition, an organized junction named the immunological synapse. Various T cell organelles polarize, together with microtubules, toward the antigen-presenting cell. Among them, intracellular vesicular compartments, such as the Golgi apparatus, the recycling endosomal compartment, or cytotoxic granules help to build the immunological synapse and ensure effector functions, such as polarized secretion of cytokines by helper T cells, or exocytosis of lytic granules by cytotoxic T cells. Lymphotropic retroviruses, such as the human immunodeficiency virus type 1, the human T cell leukemia virus type 1, or the Herpesvirus saimiri, can subvert some of the vesicle traffic mechanisms impeding the generation and function of the immunological synapses. This review focuses on the polarization of vesicle traffic, its regulation, and its role in maintaining the structure and function of the immunological synapse. We discuss how some lymphotropic viruses target the vesicle traffic in T lymphocytes, inhibiting the formation of immunological synapses and modulating the response of infected T cells.
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28
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daSilva LLP, Sougrat R, Burgos PV, Janvier K, Mattera R, Bonifacino JS. Human immunodeficiency virus type 1 Nef protein targets CD4 to the multivesicular body pathway. J Virol 2009; 83:6578-90. [PMID: 19403684 PMCID: PMC2698520 DOI: 10.1128/jvi.00548-09] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Accepted: 04/20/2009] [Indexed: 11/20/2022] Open
Abstract
The Nef protein of human immunodeficiency virus type 1 downregulates the CD4 coreceptor from the surface of host cells by accelerating the rate of CD4 endocytosis through a clathrin/AP-2 pathway. Herein, we report that Nef has the additional function of targeting CD4 to the multivesicular body (MVB) pathway for eventual delivery to lysosomes. This targeting involves the endosomal sorting complex required for transport (ESCRT) machinery. Perturbation of this machinery does not prevent removal of CD4 from the cell surface but precludes its lysosomal degradation, indicating that accelerated endocytosis and targeting to the MVB pathway are separate functions of Nef. We also show that both CD4 and Nef are ubiquitinated on lysine residues, but this modification is dispensable for Nef-induced targeting of CD4 to the MVB pathway.
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Affiliation(s)
- Luis L P daSilva
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Building 18T, Room 101, National Institutes of Health, Bethesda, MD 20892, USA
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29
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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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30
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A basic patch on alpha-adaptin is required for binding of human immunodeficiency virus type 1 Nef and cooperative assembly of a CD4-Nef-AP-2 complex. J Virol 2009; 83:2518-30. [PMID: 19129443 DOI: 10.1128/jvi.02227-08] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A critical function of the human immunodeficiency virus type 1 Nef protein is the downregulation of CD4 from the surfaces of infected cells. Nef is believed to act by linking the cytosolic tail of CD4 to the endocytic machinery, thereby increasing the rate of CD4 internalization. In support of this model, weak binary interactions between CD4, Nef, and the endocytic adaptor complex, AP-2, have been reported. In particular, dileucine and diacidic motifs in the C-terminal flexible loop of Nef have been shown to mediate binding to a combination of the alpha and sigma2 subunits of AP-2. Here, we report the identification of a potential binding site for the Nef diacidic motif on alpha-adaptin. This site comprises two basic residues, lysine-297 and arginine-340, on the alpha-adaptin trunk domain. The mutation of these residues specifically inhibits the ability of Nef to bind AP-2 and downregulate CD4. We also present evidence that the diacidic motif on Nef and the basic patch on alpha-adaptin are both required for the cooperative assembly of a CD4-Nef-AP-2 complex. This cooperativity explains how Nef is able to efficiently downregulate CD4 despite weak binary interactions between components of the tripartite complex.
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Laguette N, Benichou S, Basmaciogullari S. Human immunodeficiency virus type 1 Nef incorporation into virions does not increase infectivity. J Virol 2009; 83:1093-104. [PMID: 18987145 PMCID: PMC2612363 DOI: 10.1128/jvi.01633-08] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Accepted: 10/26/2008] [Indexed: 11/20/2022] Open
Abstract
The viral protein Nef contributes to the optimal infectivity of human and simian immunodeficiency viruses. The requirement for Nef during viral biogenesis particles suggests that Nef might play a role in this process. Alternatively, because Nef is incorporated into viruses, it might play a role when progeny virions reach target cells. We challenged these hypotheses by manipulating the amounts of Nef incorporated in viruses while keeping its expression level constant in producer cells. This was achieved by forcing the incorporation of Nef into viral particles by fusing a Vpr sequence to the C-terminal end of Nef. A cleavage site for the viral protease was introduced between Nef and Vpr to allow the release of Nef fragments from the fusion protein during virus maturation. We show that the resulting Nef-CS-Vpr fusion partially retains the ability of Nef to downregulate cell surface CD4 and that high amounts of Nef-CS-Vpr are incorporated into viral particles compared with what is seen for wild-type Nef. The fusion protein is processed during virion maturation and releases Nef fragments similar to those found in viruses produced in the presence of wild-type Nef. Unlike viruses produced in the presence of wild-type Nef, viruses produced in the presence of Nef-CS-Vpr do not have an increase in infectivity and are as poorly infectious as viruses produced in the absence of Nef. These findings demonstrate that the presence of Nef in viral particles is not sufficient to increase human immunodeficiency virus type 1 infectivity and suggest that Nef plays a role during the biogenesis of viral particles.
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Affiliation(s)
- Nadine Laguette
- Institut Cochin, CNRS UMR8104, Université Paris Descartes, Paris, France
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Trache A, Meininger GA. Total internal reflection fluorescence (TIRF) microscopy. ACTA ACUST UNITED AC 2008; Chapter 2:Unit 2A.2.1-2A.2.22. [PMID: 18729056 DOI: 10.1002/9780471729259.mc02a02s10] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Total internal reflection fluorescence (TIRF) microscopy represents a method of exciting and visualizing fluorophores present in the near-membrane region of live or fixed cells grown on coverslips. TIRF microscopy is based on the total internal reflection phenomenon that occurs when light passes from a high-refractive medium (e.g., glass) into a low-refractive medium (e.g., cell, water). The evanescent field produced by total internally reflected light excites the fluorescent molecules at the cell-substrate interface and is accompanied by minimal exposure of the remaining cell volume. This technique provides high-contrast fluorescence images, with very low background and virtually no out-of-focus light, ideal for visualization and spectroscopy of single-molecule fluorescence near a surface. This unit presents, in a concise manner, the principle of operation, instrument diversity, and TIRF microscopy applications for the study of biological samples.
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Affiliation(s)
- Andreea Trache
- Department of Systems Biology and Translational Medicine, College of Medicine, Texas A&M Health Science Center, College Station, Texas, USA
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Barbante A, Irons S, Hawes C, Frigerio L, Vitale A, Pedrazzini E. Anchorage to the cytosolic face of the endoplasmic reticulum membrane: a new strategy to stabilize a cytosolic recombinant antigen in plants. PLANT BIOTECHNOLOGY JOURNAL 2008; 6:560-75. [PMID: 18444969 DOI: 10.1111/j.1467-7652.2008.00342.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The levels of accumulation of recombinant vaccines in transgenic plants are protein specific and strongly influenced by the subcellular compartment of destination. The human immunodeficiency virus protein Nef (negative factor), a promising target for the development of an antiviral vaccine, is a cytosolic protein that accumulates to low levels in transgenic tobacco and is even more unstable when introduced into the secretory pathway, probably because of folding defects in the non-cytosolic environment. To improve Nef accumulation, a new strategy was developed to anchor the molecule to the cytosolic face of the endoplasmic reticulum (ER) membrane. For this purpose, the Nef sequence was fused to the C-terminal domain of mammalian ER cytochrome b5, a long-lived, tail-anchored (TA) protein. This consistently increased Nef accumulation by more than threefold in many independent transgenic tobacco plants. Real-time polymerase chain reaction of mRNA levels and protein pulse-chase analysis indicated that the increase was not caused by higher transcript levels but by enhanced protein stability. Subcellular fractionation and immunocytochemistry indicated that Nef-TA accumulated on the ER membrane. Over-expression of mammalian or plant ER cytochrome b5 caused the formation of stacked membrane structures, as observed previously in similar experiments performed in mammalian cells; however, Nef-TA did not alter membrane organization in tobacco cells. Finally, Nef could be removed in vitro by its tail-anchor, taking advantage of an engineered thrombin cleavage site. These results open up the way to use tail-anchors to improve foreign protein stability in the plant cytosol without perturbing cellular functions.
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MESH Headings
- Agrobacterium tumefaciens/genetics
- Amino Acid Sequence
- Animals
- Antigens, Viral/chemistry
- Antigens, Viral/genetics
- Antigens, Viral/metabolism
- Blotting, Western
- Cytochromes b5/chemistry
- Cytochromes b5/genetics
- Cytochromes b5/metabolism
- Cytosol/metabolism
- Cytosol/ultrastructure
- Endoplasmic Reticulum/metabolism
- Endoplasmic Reticulum/ultrastructure
- Fluorescent Antibody Technique
- Gene Products, nef/chemistry
- Gene Products, nef/genetics
- Gene Products, nef/metabolism
- Humans
- Microscopy, Confocal
- Microscopy, Electron, Transmission
- Molecular Sequence Data
- Plant Leaves/genetics
- Plant Leaves/metabolism
- Plant Leaves/ultrastructure
- Plants, Genetically Modified/genetics
- Plants, Genetically Modified/metabolism
- Plants, Genetically Modified/ultrastructure
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Nicotiana/genetics
- Nicotiana/metabolism
- Nicotiana/ultrastructure
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Affiliation(s)
- Alessandra Barbante
- Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche, Via Bassini 15, 20133 Milan, Italy
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Human immunodeficiency virus type 1 nef expression prevents AP-2-mediated internalization of the major histocompatibility complex class II-associated invariant chain. J Virol 2008; 82:8373-82. [PMID: 18596106 DOI: 10.1128/jvi.00670-08] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The lentiviral Nef protein has been studied extensively for its ability to induce the downregulation of several immunoreceptors on the surfaces of infected cells. However, Nef expression is unique in inducing highly effective upregulation of the major histocompatibility complex class II-associated chaperone invariant (Ii) chain complexes in different cell types. Under normal conditions, endocytosis of the Ii chain and other molecules, like the transferrin receptor and CD4, is rapid and AP-2 dependent. Human immunodeficiency virus type 1 (HIV-1) Nef expression strongly reduces the internalization of the Ii chain, enhances that of CD4, and does not modify transferrin uptake. The mutation of AP-2 binding motifs LL164 and DD174 in Nef leads to the inhibition of Ii chain upregulation. In AP-2-depleted cells, surface levels of the Ii chain are high and remain unmodified by Nef expression, further indicating that Nef regulates Ii chain internalization via the AP-2 pathway. Immunoprecipitation experiments revealed that the Ii chain can interact with Nef in a dileucine-dependent manner. Importantly, we have shown that Nef-induced CD4 downregulation and Ii chain upregulation are genetically distinguishable. We have identified natural nef alleles that have lost one of the two functions but not the other one. Moreover, we have characterized Nef mutant forms possessing a similar phenotype in the context of HIV-1 infection. Therefore, the Nef-induced accumulation of Ii chain complexes at the cell surface probably results from a complex mechanism leading to the impairment of AP-2-mediated endocytosis rather than from direct competition between Nef and the Ii chain for binding AP-2.
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Borck G, Mollà-Herman A, Boddaert N, Encha-Razavi F, Philippe A, Robel L, Desguerre I, Brunelle F, Benmerah A, Munnich A, Colleaux L. Clinical, cellular, and neuropathological consequences ofAP1S2mutations: further delineation of a recognizable X-linked mental retardation syndrome. Hum Mutat 2008; 29:966-74. [DOI: 10.1002/humu.20531] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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36
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Leontiev VV, Maury WJ, Hadany L. Drug induced superinfection in HIV and the evolution of drug resistance. INFECTION GENETICS AND EVOLUTION 2008; 8:40-50. [DOI: 10.1016/j.meegid.2007.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 09/22/2007] [Accepted: 09/24/2007] [Indexed: 11/25/2022]
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37
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A diacidic motif in human immunodeficiency virus type 1 Nef is a novel determinant of binding to AP-2. J Virol 2007; 82:1166-74. [PMID: 18032517 DOI: 10.1128/jvi.01874-07] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
A key function of the Nef protein of immunodeficiency viruses is the downregulation of the T-cell and macrophage coreceptor, CD4, from the surfaces of infected cells. CD4 downregulation depends on a conserved (D/E)XXXL(L/I)-type dileucine motif in the C-terminal, flexible loop of Nef, which mediates binding to the clathrin adaptor complexes AP-1, AP-2, and AP-3. We now report the identification of a consensus (D/E)D motif within this loop as a second, conserved determinant of interaction of Nef with AP-2, though not with AP-1 and AP-3. Mutations in this diacidic motif abrogate both AP-2 binding and CD4 downregulation. We also show that a dileucine motif from tyrosinase, both in its native context and in the context of Nef, can bind to AP-2 independently of a diacidic motif. These results thus identify a novel type of AP-2 interaction determinant, support the notion that AP-2 is the key clathrin adaptor for the downregulation of CD4 by Nef, and reveal a previously unrecognized diversity among dileucine sorting signals.
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38
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Burtey A, Schmid EM, Ford MGJ, Rappoport JZ, Scott MGH, Marullo S, Simon SM, McMahon HT, Benmerah A. The conserved isoleucine-valine-phenylalanine motif couples activation state and endocytic functions of beta-arrestins. Traffic 2007; 8:914-31. [PMID: 17547696 DOI: 10.1111/j.1600-0854.2007.00578.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Beta-arrestins (betaarrs) play a central role in the regulation of G-protein-coupled receptors (GPCRs). Their binding to phosphorylated activated GPCRs induces a conformational transition to an active state resulting in the release of their flexible C-terminal tail. Binding sites for clathrin and the adaptor protein (AP)-2 clathrin adaptor complex are then unmasked, which drive the recruitment of betaarrs-GPCR complexes into clathrin-coated pits (CCPs). A conserved isoleucine-valine-phenylalanine (IVF) motif of the C-terminal tail controls betaarr activation through intramolecular interactions. Here, we provide structural, biochemical and functional evidence in living cells that the IVF motif also controls binding to AP-2. While the F residue is directly involved in AP-2 binding, substitutions of I and V residues, markedly enhanced affinity for AP-2 resulting in active betaarr mutants, which are constitutively targeted to CCPs in the absence of any GPCR activation. Conformational change and endocytic functions of betaarrs thus appear to be coordinated via the complex molecular interactions established by the IVF motif.
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Affiliation(s)
- Anne Burtey
- Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), Paris, France
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39
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Abstract
Because of the discovery of coated pits and vesicles more than 40 years ago and the identification of clathrin as a major component of the coat, it has been assumed that clathrin-coated pits (CCPs) are responsible for the uptake of most plasma membrane receptors undergoing internalization. The recent molecular characterization of clathrin-independent routes of endocytosis confirms that several alternative endocytic pathways operate at the plasma membrane of mammalian cells. This heterogeneous view of endocytosis has been expanded still further by recent studies, suggesting that different subpopulations of CCPs responsible for the internalization of specific sets of cargo may coexist. In the present review, we have discussed the experimental evidence in favor or against the existence of distinct parallel clathrin-dependent pathways at the plasma membrane.
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Affiliation(s)
- Alexandre Benmerah
- Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), 75014 Paris, France, and INSERM, U567, 75014 Paris, France.
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40
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Sehgal PB, Mukhopadhyay S. Pulmonary arterial hypertension: a disease of tethers, SNAREs and SNAPs? Am J Physiol Heart Circ Physiol 2007; 293:H77-85. [PMID: 17416597 DOI: 10.1152/ajpheart.01386.2006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Histological and electron microscopic studies over the past four decades have highlighted "plump," "enlarged" endothelial, smooth muscle, and fibroblastic cellular elements with increased endoplasmic reticulum, Golgi stacks, and vacuolation in pulmonary arterial lesions in human and in experimental (hypoxia and monocrotaline) pulmonary arterial hypertension. However, the contribution of disrupted intracellular membrane trafficking in the pathobiology of this disease has received insufficient attention. Recent studies suggest a pathogenetic role of the disruption of intracellular trafficking of vasorelevant proteins and cell-surface receptors in the development of this disease. The purpose of this essay is to highlight the molecular regulation of vesicular trafficking by membrane tethers, SNAREs and SNAPs, and to suggest how their dysfunction, directly and/or indirectly, might contribute to development of pulmonary arterial hypertension in experimental models and in humans, including that due to mutations in bone morphogenetic receptor type 2.
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Affiliation(s)
- Pravin B Sehgal
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY 10595, USA.
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41
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Pizzato M, Helander A, Popova E, Calistri A, Zamborlini A, Palù G, Göttlinger HG. Dynamin 2 is required for the enhancement of HIV-1 infectivity by Nef. Proc Natl Acad Sci U S A 2007; 104:6812-7. [PMID: 17412836 PMCID: PMC1871867 DOI: 10.1073/pnas.0607622104] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nef is a virulence factor of HIV-1 and other primate lentiviruses that is crucial for rapid progression to AIDS. In cell culture, Nef increases the infectivity of HIV-1 progeny virions by an unknown mechanism. We now show that dynamin 2 (Dyn2), a key regulator of vesicular trafficking, is a binding partner of Nef that is required for its ability to increase viral infectivity. Dominant-negative Dyn2 or the depletion of Dyn2 by small interfering RNA potently inhibited the effect of Nef on HIV-1 infectivity. Furthermore, in Dyn2-depleted cells, this function of Nef could be rescued by ectopically expressed Dyn2 but not by Dyn1, a closely related isoform that does not bind Nef. The infectivity enhancement by Nef also depended on clathrin, because it was diminished in clathrin-depleted cells and profoundly inhibited in cells expressing the clathrin-binding domain of AP180, which blocks clathrin-coated pit formation but not clathrin-independent endocytosis. Together, these findings imply that the infectivity enhancement activity of Nef depends on Dyn2- and clathrin-mediated membrane invagination events.
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Affiliation(s)
- Massimo Pizzato
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
- Department of Histology, Microbiology, and Medical Biotechnologies, University of Padua, I-35121 Padua, Italy; and
- Department of Infectious Diseases, Division of Medicine, Imperial College London, London W2 1PG, United Kingdom
- To whom correspondence may be addressed. E-mail: or
| | - Anna Helander
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
| | - Elena Popova
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
| | - Arianna Calistri
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
- Department of Histology, Microbiology, and Medical Biotechnologies, University of Padua, I-35121 Padua, Italy; and
| | - Alessia Zamborlini
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
- Department of Histology, Microbiology, and Medical Biotechnologies, University of Padua, I-35121 Padua, Italy; and
| | - Giorgio Palù
- Department of Histology, Microbiology, and Medical Biotechnologies, University of Padua, I-35121 Padua, Italy; and
| | - Heinrich G. Göttlinger
- *Department of Cancer Immunology and AIDS, Dana–Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, MA 02115
- To whom correspondence may be addressed. E-mail: or
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Chaudhuri R, Lindwasser OW, Smith WJ, Hurley JH, Bonifacino JS. Downregulation of CD4 by human immunodeficiency virus type 1 Nef is dependent on clathrin and involves direct interaction of Nef with the AP2 clathrin adaptor. J Virol 2007; 81:3877-90. [PMID: 17267500 PMCID: PMC1866153 DOI: 10.1128/jvi.02725-06] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Accepted: 01/19/2007] [Indexed: 12/12/2022] Open
Abstract
Nef, an accessory protein of human and simian immunodeficiency viruses, is a critical determinant of pathogenesis that promotes the progression from infection to AIDS. The pathogenic effects of Nef are in large part dependent on its ability to downregulate the macrophage and T-cell coreceptor, CD4. It has been proposed that Nef induces downregulation by linking the cytosolic tail of CD4 to components of the host-cell protein trafficking machinery. To identify these components, we developed a novel Nef-CD4 downregulation system in Drosophila melanogaster S2 cells. We found that human immunodeficiency virus type 1 (HIV-1) Nef downregulates human CD4 in S2 cells and that this process is subject to the same sequence requirements as in human cells. An RNA interference screen targeting protein trafficking genes in S2 cells revealed a requirement for clathrin and the clathrin-associated, plasma membrane-localized AP2 complex in the downregulation of CD4. The requirement for AP2 was confirmed in the human cell line HeLa. We also used a yeast three-hybrid system and glutathione S-transferase pull-down analyses to demonstrate a robust, direct interaction between HIV-1 Nef and AP2. This interaction requires a dileucine motif in Nef that is also essential for downregulation of CD4. Together, these results support a model in which HIV-1 Nef downregulates CD4 by promoting its accelerated endocytosis by a clathrin/AP2 pathway.
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Affiliation(s)
- Rittik Chaudhuri
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, Bldg. 18T, Rm. 101, National Institutes of Health, Bethesda, MD 20892, USA
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Sehgal PB, Mukhopadhyay S. Dysfunctional intracellular trafficking in the pathobiology of pulmonary arterial hypertension. Am J Respir Cell Mol Biol 2007; 37:31-7. [PMID: 17363775 PMCID: PMC1899345 DOI: 10.1165/rcmb.2007-0066tr] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Discussions of the initiation of pulmonary arterial hypertension (PAH) in man and in experimental models have centered around intimal and medial proliferation in medium-sized pulmonary arteries. The histologic events are thought to include disordered proliferation of enlarged, vacuolated endothelial cells, neo-muscularization of the affected blood vessels, and vascular pruning. The discovery of the association of familial and sporadic PAH with mutations in BMPR2 has generated intense interest in cytokine receptor trafficking and function in the endothelial cell and how this might be disrupted to yield an enlarged proliferative cell phenotype. Nevertheless, considerations of the subcellular machinery of membrane trafficking in the endothelial cell and consequences of the disruption of this outward and inward membrane trafficking are largely absent from discussions of the pathobiology of PAH. Long-standing electron microscopy data in the PAH field has demonstrated marked disruptions of intracellular membrane trafficking in human and experimental PAH. Further, a role of the membrane-trafficking regulator Nef in simian HIV-induced PAH in macaques and in HIV-induced PAH in man is now evident. Additionally, monocrotaline and hypoxia are known to disrupt the function of Golgi tethers, SNAREs, SNAPs, and N-ethylmaleimide-sensitive factor ("the Golgi blockade hypothesis"). These results, along with recent reports demonstrating the trapping of PAH-associated human BMPR2 mutants in the Golgi, highlight the implications of disrupted intracellular membrane trafficking in the pathobiology of PAH. The purpose of this review is to present a brief overview of the molecular basis of intracellular trafficking and relate these considerations to the pathobiology of PAH.
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Affiliation(s)
- Pravin B Sehgal
- Basic Sciences Building, Department of Cell Biology & Anatomy, New York Medical College, Valhalla, NY 10595, USA.
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