101
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Vetter ML, Johnson ME, Antons AK, Unutmaz D, D'Aquila RT. Differences in APOBEC3G expression in CD4+ T helper lymphocyte subtypes modulate HIV-1 infectivity. PLoS Pathog 2009; 5:e1000292. [PMID: 19197360 PMCID: PMC2631133 DOI: 10.1371/journal.ppat.1000292] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2008] [Accepted: 01/08/2009] [Indexed: 01/01/2023] Open
Abstract
The cytidine deaminases APOBEC3G and APOBEC3F exert anti–HIV-1 activity that is countered by the HIV-1 vif protein. Based on potential transcription factor binding sites in their putative promoters, we hypothesized that expression of APOBEC3G and APOBEC3F would vary with T helper lymphocyte differentiation. Naive CD4+ T lymphocytes were differentiated to T helper type 1 (Th1) and 2 (Th2) effector cells by expression of transcription factors Tbet and GATA3, respectively, as well as by cytokine polarization. APOBEC3G and APOBEC3F RNA levels, and APOBEC3G protein levels, were higher in Th1 than in Th2 cells. T cell receptor stimulation further increased APOBEC3G and APOBEC3F expression in Tbet- and control-transduced, but not in GATA3-transduced, cells. Neutralizing anti–interferon-γ antibodies reduced both basal and T cell receptor-stimulated APOBEC3G and APOBEC3F expression in Tbet- and control-transduced cells. HIV-1 produced from Th1 cells had more virion APOBEC3G, and decreased infectivity, compared to virions produced from Th2 cells. These differences between Th1- and Th2-produced virions were greater for viruses lacking functional vif, but also seen with vif-positive viruses. Over-expression of APOBEC3G in Th2 cells decreased the infectivity of virions produced from Th2 cells, and reduction of APOBEC3G in Th1 cells increased infectivity of virions produced from Th1 cells, consistent with a causal role for APOBEC3G in the infectivity difference. These results indicate that APOBEC3G and APOBEC3F levels vary physiologically during CD4+ T lymphocyte differentiation, that interferon-γ contributes to this modulation, and that this physiological regulation can cause changes in infectivity of progeny virions, even in the presence of HIV-1 vif. Some host cell proteins can hinder, or restrict, the life cycle of HIV-1. APOBEC3G and APOBEC3F are cellular enzymes that decrease HIV-1's ability to replicate in a subsequent target cell if they are present in the virus particle. As a countermeasure, HIV-1 virion infectivity factor (vif) induces degradation of APOBEC3G and APOBEC3F, thereby preventing them from getting into the budding virus. Although vif-defective viruses cannot evade the antiviral effect of APOBEC3G, such viruses are very rarely present in HIV-1-infected humans. It is not yet known whether physiological variation in APOBEC3G and APOBEC3F expression in CD4+ T lymphocytes is substantial enough to reduce vif-positive HIV-1 infectivity. In this study, we found that T helper type 1 (Th1) cells, a subtype of CD4+ lymphocytes, expressed greater amounts of APOBEC3G and APOBEC3F than T helper type 2 (Th2) cells. This difference led to a difference in infectivity of HIV-1 produced from the two cell types, whether vif was expressed or not. These results demonstrate that physiological regulation of APOBEC3G does restrict vif-positive HIV-1, as well as vif-negative HIV-1. In addition, this study reveals biological factors regulating expression of these proteins that may be exploitable for new therapeutic or preventive strategies against HIV-1.
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Affiliation(s)
- Michael L. Vetter
- Department of Microbiology and Immunology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Megan E. Johnson
- Department of Microbiology and Immunology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Amanda K. Antons
- Department of Microbiology and Immunology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Derya Unutmaz
- Department of Microbiology, New York University, New York, New York, United States of America
| | - Richard T. D'Aquila
- Department of Microbiology and Immunology, Vanderbilt University, Nashville, Tennessee, United States of America
- Department of Medicine, Division of Infectious Diseases, Vanderbilt University, Nashville, Tennessee, United States of America
- * E-mail:
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102
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Induction of APOBEC3 in vivo causes increased restriction of retrovirus infection. J Virol 2009; 83:3486-95. [PMID: 19153238 DOI: 10.1128/jvi.02347-08] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
APOBEC3 proteins are important cellular factors that restrict infection by a number of viruses, including human immunodeficiency virus type 1 (HIV-1). Previously, we found that the mouse APOBEC3 (mA3) restricts infection by mouse mammary tumor virus (MMTV) in its natural host. Dendritic cells (DCs) are the first in vivo targets of MMTV infection. In this study, we demonstrate that mA3 expressed in target cells restricts MMTV infection in DCs ex vivo and in vivo. By comparing infection of DCs from mA3(+/+) and mA3(-/-) mice with one-hit viruses, we show that mA3 expression in target cells blocked MMTV infection at a postentry step and acted together with virion-packaged mA3 to inhibit infection. Similar results were obtained upon infection of mouse DCs with HIV-1 cores pseudotyped with vesicular stomatitis virus G protein. In addition, treatment of cells or mice with lipopolysaccharide (LPS) caused increased levels of mA3 expression and rendered them resistant to MMTV infection. Alpha interferon treatment had a similar effect. This LPS-induced resistance to infection was seen only in mA3(+/+) mice and not in mA3(-/-) mice, arguing that mA3 is the major anti-MMTV restriction factor that is induced upon DC maturation. Thus, increasing the levels of this intrinsic antiretroviral factor in vivo can lead to increased levels of restriction because of higher levels of both cell-intrinsic as well as virion-packaged APOBEC3.
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103
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Niewiadomska AM, Yu XF. Host restriction of HIV-1 by APOBEC3 and viral evasion through Vif. Curr Top Microbiol Immunol 2009; 339:1-25. [PMID: 20012521 DOI: 10.1007/978-3-642-02175-6_1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The arms race between virus and host is a constant battle. APOBEC3 proteins are known to be potent innate cellular defenses against both endogenous retroelements and diverse retroviruses. However, retroviruses have developed their own methods to launch counter-strikes. Most primate lentiviruses encode a protein called the viral infectivity factor (Vif). Vif induces targeted destruction of APOBEC3 proteins by hijacking the cellular ubiquitin-proteasome pathway. Here we review the research that led up to the identification of A3G, the mechanisms by which APOBEC3 proteins can inhibit retroelements, and the counter-mechanisms that HIV-1 Vif has developed to evade its antiviral activities.
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Affiliation(s)
- Anna Maria Niewiadomska
- Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
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104
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Bennett RP, Salter JD, Liu X, Wedekind JE, Smith HC. APOBEC3G subunits self-associate via the C-terminal deaminase domain. J Biol Chem 2008; 283:33329-36. [PMID: 18842592 PMCID: PMC2586250 DOI: 10.1074/jbc.m803726200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 10/03/2008] [Indexed: 11/06/2022] Open
Abstract
Human APOBEC3G (hA3G) is a cytidine deaminase active on HIV single-stranded DNA. Small angle x-ray scattering and molecular envelope restorations predicted a C-terminal dimeric model for RNA-depleted hA3G in solution. Each subunit was elongated, suggesting that individual domains of hA3G are solvent-exposed and therefore may interact with other macromolecules even as isolated substructures. In this study, co-immunoprecipitation and in-cell quenched fluorescence resonance energy transfer assays reveal that hA3G forms RNA-independent oligomers through interactions within its C terminus. Residues 209-336 were necessary and sufficient for homoligomerization. N-terminal domains of hA3G were unable to multimerize but remained functional for Gag and viral infectivity factor (Vif) interactions when expressed apart from the C terminus. These findings corroborate the small angle x-ray scattering structural model and are instructive for development of high throughput screens that target specific domains and their functions to identify HIV/AIDS therapeutics.
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MESH Headings
- APOBEC-3G Deaminase
- Cell Line
- Cytidine Deaminase/chemistry
- Cytidine Deaminase/genetics
- Cytidine Deaminase/metabolism
- DNA, Single-Stranded/chemistry
- DNA, Single-Stranded/genetics
- DNA, Single-Stranded/metabolism
- DNA, Viral/chemistry
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Dimerization
- HIV Core Protein p24/chemistry
- HIV Core Protein p24/genetics
- HIV Core Protein p24/metabolism
- HIV-1/chemistry
- HIV-1/genetics
- HIV-1/metabolism
- Humans
- Models, Molecular
- Protein Structure, Quaternary
- Protein Structure, Tertiary/physiology
- vif Gene Products, Human Immunodeficiency Virus/chemistry
- vif Gene Products, Human Immunodeficiency Virus/genetics
- vif Gene Products, Human Immunodeficiency Virus/metabolism
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Affiliation(s)
- Ryan P Bennett
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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105
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Double-stranded RNA analog poly(I:C) inhibits human immunodeficiency virus amplification in dendritic cells via type I interferon-mediated activation of APOBEC3G. J Virol 2008; 83:884-95. [PMID: 19004943 DOI: 10.1128/jvi.00023-08] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Human immunodeficiency virus (HIV) is taken up by and replicates in immature dendritic cells (imDCs), which can then transfer virus to T cells, amplifying the infection. Strategies known to boost DC function were tested for their ability to overcome this exploitation when added after HIV exposure. Poly(I:C), but not single-stranded RNA (ssRNA) or a standard DC maturation cocktail, elicited type I interferon (IFN) and interleukin-12 (IL-12) p70 production and the appearance of unique small (15- to 20-kDa) fragments of APOBEC3G (A3G) and impeded HIV(Bal) replication in imDCs when added up to 60 h after virus exposure. Comparable effects were mediated by recombinant alpha/beta IFN (IFN-alpha/beta). Neutralizing the anti-IFN-alpha/beta receptor reversed poly(I:C)-induced inhibition of HIV replication and blocked the appearance of the small A3G proteins. The poly(I:C)-induced appearance of small A3G proteins was not accompanied by significant differences in A3G mRNA or A3G monomer expression. Small interfering RNA (siRNA) knockdown of A3G could not be used to reverse the poly(I:C)-induced protective effect, since siRNAs nonspecifically activated the DCs, inducing the appearance of the small A3G proteins and inhibiting HIV infection. Notably, the appearance of small A3G proteins coincided with the shift of high-molecular-mass inactive A3G complexes to the low-molecular-mass (LMM) active A3G complexes. The unique immune stimulation by poly(I:C) with its antiviral effects on imDCs marked by the expression of IFN-alpha/beta and active LMM A3G renders poly(I:C) a promising novel strategy to combat early HIV infection in vivo.
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106
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Wang Y, Chen G, Yang Y, Hu Z, Chen X. A systems biology analysis of protein-protein interactions in the APOBEC family. Life Sci 2008; 83:521-30. [PMID: 18793652 DOI: 10.1016/j.lfs.2008.07.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Revised: 07/17/2008] [Accepted: 07/23/2008] [Indexed: 10/21/2022]
Abstract
AIMS The APOBEC (apolipoprotein B mRNA-editing catalytic polypeptide) family of cytidine deaminases inhibits the mobility of diverse retroviruses, retrotransposons and other viruses. This group of apolipoproteins is widely distributed in living organisms and plays a central role in diverse enzymatic pathways. Nevertheless, the interplay between APOBECs and innate immune proteins, as well as the role of APOBECs in protecting the host cell from viral infection are poorly understood. To elucidate the association between human APOBECs and immune system, a systems biology study was performed to identify various proteins involved in the function of APOBEC proteins. MAIN METHODS This identification utilized an integrated database and literature network of protein-protein interactions combined with nine microarray experiments. KEY FINDINGS Considering our systems biology data, we can infer some modes of action of APOBECs through interactions with proteins associated with the immune system. SIGNIFICANCE This study presents a comprehensive analysis of the APOBEC network, highlighting those proteins that have a higher probability of playing an important role with APOBECs in the innate immune system.
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Affiliation(s)
- Yi Wang
- College of Bioengineering, Chongqing University, Shapingba, Chongqing 400044, China
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107
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Ulenga NK, Dieng Sarr A, Hamel D, Sankale JL, Mboup S, Kanki PJ. The level of APOBEC3G (hA3G)-related G-to-A mutations does not correlate with viral load in HIV type 1-infected individuals. AIDS Res Hum Retroviruses 2008; 24:1285-90. [PMID: 18851679 DOI: 10.1089/aid.2008.0072] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The APOBEC family of mammalian cytidine deaminases, such as APOBEC3G (hA3G), has been demonstrated to function as a host viral restriction factor against HIV-1. hA3G has been shown to cause extensive G-to-A mutations in the HIV-1 genome, which may play a role in viral restriction. To investigate the role of G-to-A mutations in HIV-1 pathogenesis, we isolated, amplified, and sequenced HIV-1 sequences (vif, gag, and env) from 29 therapy-naive HIV-1-infected individuals. The levels of G-to-A mutations correlated with the expression levels of hA3G in the vif (rho = 0.438, p = 0.041) and the env regions (rho = 0.392, p = 0.038), but not in the gag region (rho = 0.131, p = 0.582). There is no correlation between viral load and the level of G-to-A mutations in the vif (rho = 0.144, p = 0.522), env (rho = 0.168, p = 0.391), or gag regions (rho = -0.254, p = 0.279). Taken together, these findings suggest that the hA3G-induced G-to-A mutations may not be the mechanism by which hA3G restricts or controls viral replication. Thus, hA3G might be restricting viral growth in infected individuals through a mechanism that is independent of the cytidine deaminase activities of hA3G.
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Affiliation(s)
- Nzovu K. Ulenga
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115
| | - Abdoulaye Dieng Sarr
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115
| | - Donald Hamel
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115
| | - Jean-Louis Sankale
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115
| | - Souleymane Mboup
- Laboratory of Bacteriology and Virology, Cheikh Anta Diop University, Dakar, Senegal
| | - Phyllis J. Kanki
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 02115
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108
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Fuqua CF, Akomeah R, Price JO, Adunyah SE. Involvement of ERK-1/2 in IL-21-induced cytokine production in leukemia cells and human monocytes. Cytokine 2008; 44:101-7. [PMID: 18707899 DOI: 10.1016/j.cyto.2008.06.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Revised: 06/06/2008] [Accepted: 06/27/2008] [Indexed: 01/15/2023]
Abstract
Cytokines play an important role in the immune system, and abnormalities in their production have been found in many human diseases. Interleukin-21 (IL-21), a type I cytokine produced by activated T cells, has diverse effects on the immune system, but its ability to induce production of other cytokines is not well delineated. Furthermore, the signaling pathway underlying its action is poorly understood. Here, we have evaluated IL-21-induced cytokine production in human monocytes and U937 leukemia cells. We found that IL-21 induces upregulation of a variety of cytokines from multiple cytokine families. We also found that IL-21 triggers rapid activation of ERK1/2. Neutralizing antibody to the IL-21R prevented both IL-21-induced cytokine production and IL-21-induced activation of ERK1/2. Inhibition of ERK1/2 activity by the ERK-selective inhibitor U0126 reverses the ability of IL-21 to upregulate cytokine production, suggesting that IL-21-induced cytokine production is dependent on ERK1/2 activation.
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Affiliation(s)
- C F Fuqua
- Department of Cancer Biology, Meharry Medical College, 1005 Dr. D.B. Todd Jr. Boulevard, Nashville, TN 37208, USA
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109
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Farrow MA, Sheehy AM. Vif and Apobec3G in the innate immune response to HIV: a tale of two proteins. Future Microbiol 2008; 3:145-54. [PMID: 18366335 DOI: 10.2217/17460913.3.2.145] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
It is now 26 years after the first published report on HIV, and the global epidemic continues unabated, with estimates of over 33 million people currently infected, worldwide. Development of targeted therapies aimed at perturbing the HIV life cycle can be achieved only with a detailed comprehension of the dynamics of virus-host interactions within the cell. One such critical virus-host interaction is the recently elucidated interplay between the viral Vif protein and the innate immune defense molecule Apobec3G. Apobec3G potently suppresses HIV replication, but Vif can alleviate this inhibition, rescuing viral infectivity. Early work describing the characterization of Vif and the cloning and identification of Apobec3G as an antiviral are discussed. Recent advances detailing the mechanisms of the Vif-Apobec3G regulatory circuit and our nascent understanding of Apobec3G endogenous function are also presented. Collectively, these studies have shed light on potential novel therapeutic strategies aimed at exploiting Apobec3G antiviral function to abrogate HIV replication.
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Affiliation(s)
- Melissa A Farrow
- College of the Holy Cross, Department of Biology, 1 College Street, Worcester, MA 01610, USA.
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110
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Jais JP, Haioun C, Molina TJ, Rickman DS, de Reynies A, Berger F, Gisselbrecht C, Brière J, Reyes F, Gaulard P, Feugier P, Labouyrie E, Tilly H, Bastard C, Coiffier B, Salles G, Leroy K. The expression of 16 genes related to the cell of origin and immune response predicts survival in elderly patients with diffuse large B-cell lymphoma treated with CHOP and rituximab. Leukemia 2008; 22:1917-24. [PMID: 18615101 DOI: 10.1038/leu.2008.188] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Gene expression profiles have been associated with clinical outcome in patients with diffuse large B-cell lymphoma (DLBCL) treated with anthracycline-containing chemotherapy. Using Affymetrix HU133A microarrays, we analyzed the lymphoma transcriptional profile of 30 patients treated with CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) and 23 patients treated with rituximab (R)-CHOP in the Groupe d'Etude des Lymphomes de l'Adulte clinical centers. We used this data set to select transcripts showing an association with progression-free survival in all patients or showing a differential effect in the two treatment groups. We performed real-time quantitative reverse transcription-PCR in the 23 R-CHOP samples of the screening set and an additional 44 R-CHOP samples set to evaluate the prognostic significance of these transcripts. In these 67 patients, the level of expression of 16 genes and the cell-of-origin classification were significantly associated with overall survival, independently of the International Prognostic Index. A multivariate model comprising four genes of the cell-of-origin signature (LMO2, MME, LPP and FOXP1) and two genes related to immune response, identified for their differential effects in R-CHOP patients (APOBEC3G and RAB33A), demonstrated a high predictive efficiency in this set of patients, suggesting that both features affect outcome in DLBCL patients receiving immunochemotherapy.
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Affiliation(s)
- J-P Jais
- Service de Biostatistique, AP-HP, hôpital Necker, Paris, France
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111
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Goila-Gaur R, Strebel K. HIV-1 Vif, APOBEC, and intrinsic immunity. Retrovirology 2008; 5:51. [PMID: 18577210 PMCID: PMC2443170 DOI: 10.1186/1742-4690-5-51] [Citation(s) in RCA: 270] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Accepted: 06/24/2008] [Indexed: 02/05/2023] Open
Abstract
Members of the APOBEC family of cellular cytidine deaminases represent a recently identified group of proteins that provide immunity to infection by retroviruses and protect the cell from endogenous mobile retroelements. Yet, HIV-1 is largely immune to the intrinsic antiviral effects of APOBEC proteins because it encodes Vif (viral infectivity factor), an accessory protein that is critical for in vivo replication of HIV-1. In the absence of Vif, APOBEC proteins are encapsidated by budding virus particles and either cause extensive cytidine to uridine editing of negative sense single-stranded DNA during reverse transcription or restrict virus replication through deaminase-independent mechanisms. Thus, the primary function of Vif is to prevent encapsidation of APOBEC proteins into viral particles. This is in part accomplished by the ability of Vif to induce the ubiquitin-dependent degradation of some of the APOBEC proteins. However, Vif is also able to prevent encapsidation of APOBEC3G and APOBEC3F through degradation-independent mechanism(s). The goal of this review is to recapitulate current knowledge of the functional interaction of HIV-1 and its Vif protein with the APOBEC3 subfamily of proteins and to summarize our present understanding of the mechanism of APOBEC3-dependent retrovirus restriction.
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Affiliation(s)
- Ritu Goila-Gaur
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 4/312, Bethesda, Maryland 20892-0460, USA.
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112
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Chiu YL, Greene WC. The APOBEC3 cytidine deaminases: an innate defensive network opposing exogenous retroviruses and endogenous retroelements. Annu Rev Immunol 2008; 26:317-53. [PMID: 18304004 DOI: 10.1146/annurev.immunol.26.021607.090350] [Citation(s) in RCA: 330] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
All retroviruses, including HIV-1, display species-specific patterns of infection. The impaired growth of these retroviruses in foreign and sometimes even in their natural hosts often stems from the action of potent host-encoded "viral restriction factors" that form important protective components of the innate immune system. The discovery of APOBEC3G and related cytidine deaminases as one class of host restriction factors and of the action of HIV-1 Vif as a specific APOBEC3G antagonist have stimulated intense scientific interest. This Vif-APOBEC3G axis now forms a very attractive target for development of an entirely new class of anti-HIV drugs. In this review, we summarize current understanding of the mechanism of action of the APOBEC3 family of enzymes, their intriguing regulation within cells, the impact of these enzymes on viral evolution and disease progression, and their roles in controlling not only the replication of exogenous retroviruses but also the retrotransposition of endogenous retroelements.
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Affiliation(s)
- Ya-Lin Chiu
- Gladstone Institute of Virology and Immunology, San Francisco, California 94158, USA.
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113
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Aguiar RS, Peterlin BM. APOBEC3 proteins and reverse transcription. Virus Res 2008; 134:74-85. [PMID: 18262674 DOI: 10.1016/j.virusres.2007.12.022] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2007] [Revised: 12/28/2007] [Accepted: 12/28/2007] [Indexed: 01/01/2023]
Abstract
The ability of members of the APOBEC3 (A3) family of proteins to confer intrinsic immunity to retroviral infection was recognized in several studies. More specifically, A3 proteins are cytidine deaminases (CDAs) that cause hypermutations of nascent retroviral genomes by deamination of cytidine residues. Although A3 proteins can restrict the replication of HIV, this inhibition is overcome by the viral infectivity factor (Vif). Inhibitory effects of APOBEC proteins are not limited to HIV but extend to other viruses and endogenous mobile genetic elements that share a reverse transcription process analogous to that of exogenous retroviruses. In sharp contrast, another conundrum of A3 proteins is that they inhibit viral replication even in the absence of CDA activity and recent advances have defined the inhibition of reverse transcriptase (RT) catalyzed DNA elongation reactions by A3 proteins. Together, these proteins provide strong and immediate intracellular immunity against incoming pathogens and restrict the movement of mobile genetic elements protecting the genome.
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Affiliation(s)
- Renato S Aguiar
- Department of Medicine, Microbiology and Immunology, University of California, San Francisco (UCSF), 533 Parnassus Avenue U422, San Francisco, CA 94143-0703, USA
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114
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Reverse transcriptase- and RNA packaging signal-dependent incorporation of APOBEC3G into hepatitis B virus nucleocapsids. J Virol 2008; 82:6852-61. [PMID: 18480459 DOI: 10.1128/jvi.00465-08] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
APOBEC3G (A3G) is a cytidine deaminase that can inhibit a wide range of retroviruses, including the para-retrovirus hepatitis B virus (HBV). The antiviral function of A3G depends on its incorporation into assembling viral particles. However, it remains enigmatic how A3G is specifically packaged into a variety of unrelated viruses. By adopting a native agarose gel electrophoresis assay that can specifically measure the levels of A3G incorporation into HBV nucleocapsids, we found that A3G is specifically packaged into replication-competent HBV nucleocapsids in a fashion that is dependent on both the viral reverse transcriptase (RT) and viral RNA packaging signal, epsilon. In contrast, A3G is not incorporated into empty capsids formed in the absence of RT or epsilon. We demonstrated that the packaged A3G was protected from protease digestion by the nucleocapsids, thus confirming its interior localization. We also showed that A3G could bind RT specifically in an RNA-independent manner, which may be responsible for mediating the specific incorporation of A3G into replication-competent nucleocapsids. Finally, we provide evidence that the N-terminal domain of A3G is required for packaging into HBV nucleocapsids.
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115
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Abstract
Cytokines are involved early in the pathogenesis of HIV infection and disease progression as a component of immunologic dysregulation and immunodeficiency and as determinants controlling virus replication. Several steps, before and after retroviral integration into host DNA in T cells and macrophages, are affected by cytokines whereas CCR5 and CXCR4 binding chemokines can interfere with viral entry. A growing number of potential players--including the gamma-common interleukin (IL)-7, IL-15, and IL-21 together with IL-17, IL-18, IL-19, IL-20, IL-23, and IL-27--are discussed in terms of their perturbation in HIV infection and of their effects on virus replication. Thus, an increasing intersection of HIV infection and the cytokine network represents a crucial determinant of virus replication and immunologic dysregulation and will likely play a key role in the development of effective strategies of HIV prevention and immunologic reconstitution.
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Affiliation(s)
- Massimo Alfano
- P2/P3 Laboratories, DIBIT, Via Olgettina n. 58, 20132, Milano, Italy
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116
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Kijak GH, Janini LM, Tovanabutra S, Sanders-Buell E, Arroyo MA, Robb ML, Michael NL, Birx DL, McCutchan FE. Variable contexts and levels of hypermutation in HIV-1 proviral genomes recovered from primary peripheral blood mononuclear cells. Virology 2008; 376:101-11. [PMID: 18436274 DOI: 10.1016/j.virol.2008.03.017] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2008] [Revised: 02/20/2008] [Accepted: 03/08/2008] [Indexed: 01/06/2023]
Abstract
APOBEC-mediated cytidine deamination of HIV-1 genomes during reverse transcription has been shown to be a potent mechanism of host restriction for HIV-1 infection ex vivo and in vitro. However, this defense system can be overcome by the viral protein Vif. Unlike other mechanisms of host restriction, the APOCEC-Vif interaction leaves an imprint on integrated proviruses in the form of G-->A hypermutation. In the current work we systematically studied levels, contexts, and patterns of HIV-1 hypermutation in vivo. The analysis of 24 full-genome HIV-1 sequences retrieved from primary PBMCs, representing infections with several HIV-1 clades, and the inclusion of 7 cognate pairs of hypermutated/non-hypermutated sequences derived from the same patient sample, provided a comprehensive view of the characteristics of APOBEC-mediated restriction in vivo. Levels of hypermutation varied nearly 5-fold among the studied proviruses. GpG motifs were most frequently affected (22/24 proviruses). Levels of hypermutation varied across the genome. The reported "twin peak" pattern of hypermutation was observed in 18/24 hypermutants, but the remainder exhibited singular non-conforming patterns. These data suggest considerable complexity in the interplay of host restriction and viral defense during HIV-1 infection.
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Affiliation(s)
- Gustavo H Kijak
- Henry M. Jackson Foundation for the Advancement of Military Medicine/US Military HIV Research Program, 1600 East Gude Drive, Rockville, Maryland 20850, USA.
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117
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Sirskyj D, Thèze J, Kumar A, Kryworuchko M. Disruption of the gamma c cytokine network in T cells during HIV infection. Cytokine 2008; 43:1-14. [PMID: 18417356 DOI: 10.1016/j.cyto.2008.03.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Revised: 02/05/2008] [Accepted: 03/03/2008] [Indexed: 01/03/2023]
Abstract
The common gamma chain (gammac)-sharing cytokines (IL's-2, 4, 7, 9, 15, and 21) play a vital role in the survival, proliferation, differentiation and function of T lymphocytes. As such, disruption of their signaling pathways would be expected to have severe consequences on the integrity of the immune system. Indeed, it appears that the signaling network of these cytokines is both disrupted and exploited by HIV at various stages of infection. IL-2 secretion and signaling downstream of its receptor are impaired in T cells from chronically-infected HIV+ patients. Elevated plasma IL-7 levels and decreased IL-7Ralpha expression in patient T cells results in significantly decreased responsiveness to this critical cytokine. Interestingly, IL-2 and IL-15 are also able to render CD4+ T cells permissive to HIV infection through their influence on the activity of the APOBEC3G deaminase enzyme. Herein, we describe the current state of knowledge on how the gammac cytokine network is affected during HIV infection, with a focus on how this impairs CD4+ and CD8+ T cell function while also benefiting the virus itself. We also address the use of cytokines as adjuncts to highly active antiretroviral therapy to bolster immune reconstitution in infected patients.
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Affiliation(s)
- Danylo Sirskyj
- Infectious Disease and Vaccine Research Centre, Children's Hospital of Eastern Ontario (CHEO)-Research Institute, Ottawa, Ontario, Canada
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118
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Role of APOBEC3G/F-mediated hypermutation in the control of human immunodeficiency virus type 1 in elite suppressors. J Virol 2007; 82:3125-30. [PMID: 18077705 DOI: 10.1128/jvi.01533-07] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While many studies show that the APOBEC3 family of cytidine deaminases can inhibit human immunodeficiency virus type 1 (HIV-1) replication, the clinical significance of this host defense mechanism is unclear. Elite suppressors are HIV-1-infected individuals who maintain viral loads below 50 copies/ml without antiretroviral therapy. To determine the role of APOBEC3G/F proteins in the control of viremia in these patients, we used a novel assay to measure the frequency of hypermutated proviral genomes. In most elite suppressors, the frequency was not significantly different than that observed in patients on highly active antiretroviral therapy. Thus, enhanced APOBEC3 activity alone cannot explain the ability of elite suppressors to control viremia.
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119
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Thielen BK, Klein KC, Walker LW, Rieck M, Buckner JH, Tomblingson GW, Lingappa JR. T cells contain an RNase-insensitive inhibitor of APOBEC3G deaminase activity. PLoS Pathog 2007; 3:1320-34. [PMID: 17892323 PMCID: PMC1993843 DOI: 10.1371/journal.ppat.0030135] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Accepted: 07/27/2007] [Indexed: 12/22/2022] Open
Abstract
The deoxycytidine deaminase APOBEC3G (A3G) is expressed in human T cells and inhibits HIV-1 replication. When transfected into A3G-deficient epithelial cell lines, A3G induces catastrophic hypermutation by deaminating the HIV-1 genome. Interestingly, studies suggest that endogenous A3G in T cells induces less hypermutation than would be expected. However, to date, the specific deaminase activity of endogenous A3G in human CD4+ T cells has not been examined directly. Here, we compared deaminase activity of endogenous and exogenous A3G in various human cell lines using a standard assay and a novel, quantitative, high-throughput assay. Exogenous A3G in epithelial cell lysates displayed deaminase activity only following RNase treatment, as expected given that A3G is known to form an enzymatically inactive RNA-containing complex. Surprisingly, comparable amounts of endogenous A3G from T cell lines or from resting or activated primary CD4+ T cells exhibited minimal deaminase activity, despite RNase treatment. Specific deaminase activity of endogenous A3G in H9, CEM, and other T cell lines was up to 36-fold lower than specific activity of exogenous A3G in epithelial-derived cell lines. Furthermore, RNase-treated T cell lysates conferred a dose-dependent inhibition to epithelial cell lysates expressing enzymatically active A3G. These studies suggest that T cells, unlike epithelial-derived cell lines, express an unidentified RNase-resistant factor that inhibits A3G deaminase activity. This factor could be responsible for reduced levels of hypermutation in T cells, and its identification and blockade could offer a means for increasing antiretroviral intrinsic immunity of T cells. APOBEC3G (A3G) is an antiviral enzyme that is expressed in human T cells and macrophages, which are the cell types infected by HIV. Early in the HIV life cycle, the HIV RNA genome is reverse transcribed into DNA. A3G can modify this DNA enzymatically, leading to high rates of mutation such that the virus can no longer replicate. To date, most studies of A3G's enzymatic activity have utilized cell lines (293T and HeLa) that can be transfected to express A3G but do not express it endogenously. A report of unexpectedly low levels of mutation in viral DNA from HIV-infected human T cells led us to investigate regulation of A3G enzymatic activity in T cells. We developed a high-throughput assay to compare the enzymatic activity of endogenous A3G in T cells versus transfected (exogenous) A3G. Surprisingly, enzymatic activity of A3G from human T cell lines and primary T cells was very low relative to A3G from transfected cells, even when corrected for A3G protein amount. Moreover, T cell lysates inhibited enzymatic activity of exogenously expressed A3G. These data suggest that enzymatic activity of endogenous A3G in human T cells is inhibited by an uncharacterized mechanism that may protect the host from this DNA mutator and could have important implications for A3G antiviral activity in vivo.
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Affiliation(s)
- Beth K Thielen
- Department of Pathobiology, University of Washington, Seattle, Washington, United States of America
| | - Kevin C Klein
- Department of Pathobiology, University of Washington, Seattle, Washington, United States of America
| | - Lorne W Walker
- Department of Pathobiology, University of Washington, Seattle, Washington, United States of America
| | - Mary Rieck
- Translational Research Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington, United States of America
| | - Jane H Buckner
- Translational Research Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington, United States of America
| | - Garrett W Tomblingson
- Department of Pathobiology, University of Washington, Seattle, Washington, United States of America
| | - Jaisri R Lingappa
- Department of Pathobiology, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- * To whom correspondence should be addressed. E-mail:
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120
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Human immunodeficiency virus type 1 Vif functionally interacts with diverse APOBEC3 cytidine deaminases and moves with them between cytoplasmic sites of mRNA metabolism. J Virol 2007; 82:987-98. [PMID: 17977970 DOI: 10.1128/jvi.01078-07] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vif(IIIB), which has been a standard model for the viral infectivity factor of human immunodeficiency virus type 1 (HIV-1), binds the cytidine deaminase APOBEC3G (A3G) and induces its degradation, thereby precluding its lethal incorporation into assembling virions. Additionally, Vif(IIIB) less efficiently degrades A3F, another potent anti-HIV-1 cytidine deaminase. Although the APOBEC3 paralogs A3A, A3B, and A3C have weaker anti-HIV-1 activities and are only partially degraded by Vif(IIIB), we found that Vif(IIIB) induces their emigration from the nucleus to the cytosol and thereby causes net increases in the cytosolic concentrations and anti-HIV-1 activities of A3A and A3B. In contrast, some other Vifs, exemplified by Vif(HXB2) and Vif(ELI-1), much more efficiently degrade and thereby neutralize all APOBEC3s. Studies focused mainly on A3F imply that it occurs associated with mRNA-PABP1 in translationally active polysomes and to a lesser extent in mRNA processing bodies (P-bodies). A3F appears to stabilize the P-bodies with which it is associated. A correspondingly small proportion of Vif(IIIB) also localizes in P-bodies in an A3F-dependent manner. Stress causes A3A, A3B, A3C, and A3F to colocalize efficiently with Vif(IIIB) and mRNA-PABP1 complexes in stress granules in a manner that is prevented by cycloheximide, an inhibitor of translational elongation. Coimmunoprecipitation studies suggest that Vifs from different HIV-1 isolates associate with all tested APOBEC3s. Thus, Vifs interact closely with structurally diverse APOBEC3s, with effects on their subcellular localization, degradation rates, and antiviral activities. Cytosolic APOBEC3-Vif complexes are predominantly bound to mRNAs that dynamically move between translationally active and storage or processing pools.
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121
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Piguet V, Steinman RM. The interaction of HIV with dendritic cells: outcomes and pathways. Trends Immunol 2007; 28:503-10. [PMID: 17950666 PMCID: PMC7106400 DOI: 10.1016/j.it.2007.07.010] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Revised: 07/27/2007] [Accepted: 07/27/2007] [Indexed: 12/20/2022]
Abstract
Dendritic cells (DCs), including Langerhans Cells (LCs), are probably among the earliest targets of HIV infection. Their localization in mucosal epithelia and in the T cell areas of lymphoid organs, as well as their crucial role in capturing antigens and initiating T cell responses, highlight their potential importance. Studies with cells in culture have addressed different outcomes of the HIV-–DC interaction, which include: direct productive infection of DC; carriage of virus by DC to CD4+ T cells; transfer of virus between DC and T cells at an infectious synapse; and immune evasion strategies of infected DC. Here we review the literature covering these areas, including current knowledge of underlying mechanisms or pathways.
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Affiliation(s)
- Vincent Piguet
- Department of Dermatology and Venereology, University Hospital and Medical School of Geneva, 24 Rue Micheli du Crest, 1211 Geneva, Switzerland.
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122
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Pion M, Stalder R, Correa R, Mangeat B, Towers GJ, Piguet V. Identification of an arsenic-sensitive block to primate lentiviral infection of human dendritic cells. J Virol 2007; 81:12086-90. [PMID: 17728230 PMCID: PMC2168788 DOI: 10.1128/jvi.00800-07] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Dendritic cells are central to the early events of human immunodeficiency virus type 1 (HIV-1) transmission, but HIV-1 infects dendritic cells inefficiently in vitro compared to activated CD4(+) T cells. There is a strong postentry restriction of HIV-1 infection in dendritic cells, partly mediated by the cellular restriction factor APOBEC3G. Here, we reveal that arsenic trioxide markedly increases HIV infection of immature and mature dendritic cells as well as blood-derived myeloid dendritic cells in an APOBEC3G- and TRIM5alpha-independent way. Our data suggest the presence of powerful, arsenic-sensitive antiviral activities in primary human immune cells of the dendritic cell lineage.
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Affiliation(s)
- Marjorie Pion
- Department of Dermatology and Venereology, Department of Microbiology and Molecular Medicine, University Hospital and Medical School of Geneva, 4-712, 24 Rue Micheli-du-Crest, 1211 Geneva, Switzerland
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123
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Argyris EG, Acheampong E, Wang F, Huang J, Chen K, Mukhtar M, Zhang H. The interferon-induced expression of APOBEC3G in human blood-brain barrier exerts a potent intrinsic immunity to block HIV-1 entry to central nervous system. Virology 2007; 367:440-51. [PMID: 17631933 PMCID: PMC2737467 DOI: 10.1016/j.virol.2007.06.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 05/21/2007] [Accepted: 06/06/2007] [Indexed: 12/28/2022]
Abstract
In the human genome, the APOBEC3 gene has expanded into a tandem array of genes termed APOBEC3A-H. Several members of this family have potent anti-HIV-1 activity. Here we demonstrate that APOBEC-3B/3C/3F and -3G are expressed in all major cellular components of the CNS. Moreover, we show that both interferon-alpha (IFN-alpha) and IFN-gamma significantly enhance the expression of APOBEC-3G/3F and drastically inhibit HIV-1 replication in primary human brain microvascular endothelial cells (BMVECs), the major component of blood-brain barrier (BBB). As the viral inhibition can be neutralized by APOBEC3G-specific siRNA, APOBEC3G plays a key role to mediate the anti-HIV-1 activity of IFN-alpha and/or IFN-gamma. Our findings suggest that, in addition to the restriction at viral entry level, the restriction from APOBEC3 family could account for the low-level replication of HIV-1 in BMVECs. The manipulation of IFN-APOBEC3 signaling pathway could be a potent therapeutic strategy to prevent HIV invasion to central nervous system (CNS).
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Affiliation(s)
- Elias G Argyris
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
| | - Edward Acheampong
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
| | - Fengxiang Wang
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
| | - Jialing Huang
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
| | - Keyang Chen
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
| | - Muhammad Mukhtar
- Drexel University-College of Medicine, Dept. of Microbiology and Immunology
| | - Hui Zhang
- Thomas Jefferson University, Dept. of Medicine, Division of Infectious Diseases, Center for Human Virology
- To whom correspondence should be addressed. Mailing Address: JAH334, 1040 Locust Street, Thomas Jefferson University, Philadelphia, PA, 19107. Tel: 215-503-0163. Fax: 215-923-1956.
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Muckenfuss H, Kaiser JK, Krebil E, Battenberg M, Schwer C, Cichutek K, Münk C, Flory E. Sp1 and Sp3 regulate basal transcription of the human APOBEC3G gene. Nucleic Acids Res 2007; 35:3784-96. [PMID: 17517765 PMCID: PMC1920263 DOI: 10.1093/nar/gkm340] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
APOBEC3G (A3G), a member of the recently discovered family of human cytidine deaminases, is expressed in peripheral blood lymphocytes and has been shown to be active against HIV-1 and other retroviruses. To gain new insights into the transcriptional regulation of this restriction factor, we cloned and characterized the promoter region of A3G. Transcriptional start sites were identified by 5′-rapid amplification of cDNA ends analysis. Luciferase reporter assays demonstrated that a 1025 bp A3G promoter sequence (from −959 to +66 relative to the major transcriptional start site) displayed constitutive promoter activity. In T cells, the A3G promoter was not inducible by mitogenic stimulation, interferon treatment or expression of HIV-1 proteins. Using a series of 5′ deletion promoter constructs in luciferase reporter assays, we identified a 180 bp region that was sufficient for full promoter activity. Transcriptional activity of this A3G core promoter was dependent on a GC-box (located at position −87/−78 relative to the major transcriptional start site) and was abolished after mutation of this DNA element. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays demonstrated that the identified GC-box represented a binding site for the ubiquitous transcription factors specificity protein (Sp) 1 and Sp3.
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Affiliation(s)
| | | | | | | | | | | | - Carsten Münk
- *To whom correspondence should be addressed. +49 6103 77 4000+49 6103 77 1255 Correspondence may also be addressed to Carsten Münk. +49 6103 77 4002+49 6103 77 1255
| | - Egbert Flory
- *To whom correspondence should be addressed. +49 6103 77 4000+49 6103 77 1255 Correspondence may also be addressed to Carsten Münk. +49 6103 77 4002+49 6103 77 1255
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125
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Ellery PJ, Tippett E, Chiu YL, Paukovics G, Cameron PU, Solomon A, Lewin SR, Gorry PR, Jaworowski A, Greene WC, Sonza S, Crowe SM. The CD16+Monocyte Subset Is More Permissive to Infection and Preferentially Harbors HIV-1 In Vivo. THE JOURNAL OF IMMUNOLOGY 2007; 178:6581-9. [PMID: 17475889 DOI: 10.4049/jimmunol.178.10.6581] [Citation(s) in RCA: 254] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
HIV-1 persists in peripheral blood monocytes in individuals receiving highly active antiretroviral therapy (HAART) with viral suppression, despite these cells being poorly susceptible to infection in vitro. Because very few monocytes harbor HIV-1 in vivo, we considered whether a subset of monocytes might be more permissive to infection. We show that a minor CD16+ monocyte subset preferentially harbors HIV-1 in infected individuals on HAART when compared with the majority of monocytes (CD14highCD16-). We confirmed this by in vitro experiments showing that CD16+ monocytes were more susceptible to CCR5-using strains of HIV-1, a finding that is associated with higher CCR5 expression on these cells. CD16+ monocytes were also more permissive to infection with a vesicular stomatitis virus G protein-pseudotyped reporter strain of HIV-1 than the majority of monocytes, suggesting that they are better able to support HIV-1 replication after entry. Consistent with this observation, high molecular mass complexes of apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G (APOBEC3G) were observed in CD16+ monocytes that were similar to those observed in highly permissive T cells. In contrast, CD14highCD16- monocytes contained low molecular mass active APOBEC3G, suggesting this is a mechanism of resistance to HIV-1 infection in these cells. Collectively, these data show that CD16+ monocytes are preferentially susceptible to HIV-1 entry, more permissive for replication, and constitute a continuing source of viral persistence during HAART.
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Affiliation(s)
- Philip J Ellery
- AIDS Pathogenesis and Clinical Research Program, Macfarlane Burnet Institute for Medical Research and Public Health, Melbourne, Victoria, Australia
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