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Hofmann S, Dehn S, Businger R, Bolduan S, Schneider M, Debyser Z, Brack-Werner R, Schindler M. Dual role of the chromatin-binding factor PHF13 in the pre- and post-integration phases of HIV-1 replication. Open Biol 2018; 7:rsob.170115. [PMID: 29021215 PMCID: PMC5666080 DOI: 10.1098/rsob.170115] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 09/08/2017] [Indexed: 12/23/2022] Open
Abstract
Viruses interact with multiple host cell factors. Some of these are required to promote viral propagation, others have roles in inhibiting infection. Here, we delineate the function of the cellular factor PHF13 (or SPOC1), a putative HIV-1 restriction factor. Early in the HIV-1 replication cycle PHF13 increased the number of integrated proviral copies and the number of infected cells. However, after HIV-1 integration, high levels of PHF13 suppressed viral gene expression. The antiviral activity of PHF13 is counteracted by the viral accessory protein Vpr, which mediates PHF13 degradation. Altogether, the transcriptional master regulator and chromatin binding protein PHF13 does not have purely repressive effects on HIV-1 replication, but also promotes viral integration. By the functional characterization of the dual role of PHF13 during the HIV-1 replication cycle, we reveal a surprising and intricate mechanism through which HIV-1 might regulate the switch from integration to viral gene expression. Furthermore, we identify PHF13 as a cellular target specifically degraded by HIV-1 Vpr.
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Affiliation(s)
- Stephan Hofmann
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Virology, Neuherberg, Germany
| | - Sandra Dehn
- Institute of Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Ramona Businger
- Institute of Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
| | - Sebastian Bolduan
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Virology, Neuherberg, Germany
| | - Martha Schneider
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Virology, Neuherberg, Germany
| | - Zeger Debyser
- Molecular Virology and Gene Therapy, KU Leuven, Leuven, Belgium
| | - Ruth Brack-Werner
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Virology, Neuherberg, Germany
| | - Michael Schindler
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Virology, Neuherberg, Germany .,Institute of Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany
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2
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Soares R, Rocha G, Meliço-Silvestre A, Gonçalves T. HIV1-viral protein R (Vpr) mutations: associated phenotypes and relevance for clinical pathologies. Rev Med Virol 2016; 26:314-29. [DOI: 10.1002/rmv.1889] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 04/11/2016] [Accepted: 04/13/2016] [Indexed: 11/08/2022]
Affiliation(s)
- Rui Soares
- FMUC-Faculdade de Medicina; Universidade de Coimbra; Coimbra Portugal
- CNC-Centro de Neurociências e Biologia Celular; Universidade de Coimbra; Coimbra Portugal
- IPO-Instituto Português de Oncologia Francisco Gentil; Coimbra Portugal
| | - Graça Rocha
- FMUC-Faculdade de Medicina; Universidade de Coimbra; Coimbra Portugal
- Departamento de Doenças Infeciosas Hospital Pediátrico de Coimbra; CHUC-Centro Hospitalar e Universitário de Coimbra; Coimbra Portugal
| | - António Meliço-Silvestre
- FMUC-Faculdade de Medicina; Universidade de Coimbra; Coimbra Portugal
- Departamento de Doenças Infeciosas; CHUC - Centro Hospitalar e Universitário de Coimbra; Coimbra Portugal
| | - Teresa Gonçalves
- FMUC-Faculdade de Medicina; Universidade de Coimbra; Coimbra Portugal
- CNC-Centro de Neurociências e Biologia Celular; Universidade de Coimbra; Coimbra Portugal
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3
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Cummings JS, Moreno-Nieves UY, Arnold V, Gilbert A, Yarbrough K, Didier C, Lévy Y, Barré-Sinoussi F, Scott-Algara D. Natural killer cell responses to dendritic cells infected by the ANRS HIV-1 vaccine candidate, MVAHIV. Vaccine 2014; 32:5577-84. [PMID: 25131736 DOI: 10.1016/j.vaccine.2014.07.094] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 06/27/2014] [Accepted: 07/31/2014] [Indexed: 12/24/2022]
Abstract
Innate mechanisms are critical for the development of the host immune responses to antigen. Particularly, early interaction between natural killer (NK) cells and dendritic cells (DC) greatly impacts the establishment of both innate and adaptive immune responses. In this study, using an autologous in vitro co-culture system we analyzed the NK cell response against MVAHIV-infected DC as well as the subsequent ability of these MVAHIV-primed NK cells to control HIV-1 infection in autologous DC. We found that NK cells responded early to MVAHIV- or MVAWT-infected DC in terms of degranulation and cytokine production. After a 4-day priming of NK cells by MVAHIV- or MVAWT-infected DC we observed an enhanced proliferation and modulation in the NK cell receptor repertoire expression. Interestingly, we found that MVAHIV-primed NK cells had a significant higher ability to control HIV-1 infection in autologous DC compared to MVAWT-primed NK cells; and this enhanced anti-HIV-1 activity appeared to be HIV-specific as MVAHIV-primed NK cells did not have a better ability to control other viral infections or respond against tumoral cells. Furthermore, we observed that NK cell receptors NKG2D and NKp46 modulate the priming of NK cells. This data provides evidence that in vitro NK cells can be primed by viral vector-infected DC, in the context of a NK/DC culture, to specifically target viral infected cells.
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Affiliation(s)
- Jean-Saville Cummings
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France.
| | - Uriel Y Moreno-Nieves
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France
| | - Vincent Arnold
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France.
| | - Adrien Gilbert
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France
| | - Kevin Yarbrough
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France
| | - Celine Didier
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France
| | - Yves Lévy
- INSERM U955, AP-HP, Groupe Henri-Mondor Albert-Chenevier, Immunologie Clinique, Créteil, France
| | - Françoise Barré-Sinoussi
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France
| | - Daniel Scott-Algara
- Institut Pasteur, Unité de Régulation des Infections Rétrovirales, 25 rue Dr Roux, 75015 Paris, France.
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4
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Kulkarni AG, Paranjape RS, Thakar MR. Higher Expression of Activating Receptors on Cytotoxic NK Cells is Associated with Early Control on HIV-1C Multiplication. Front Immunol 2014; 5:222. [PMID: 24904577 PMCID: PMC4032894 DOI: 10.3389/fimmu.2014.00222] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 05/01/2014] [Indexed: 12/02/2022] Open
Abstract
Natural killer (NK) cells may be important in modulating HIV replication in early course of HIV infection. The effector function of NK cells is finely tuned by a balance between signals delivered by activating and inhibitory receptors. However, the influence of expression of these receptors on the early course of HIV replication and subsequent disease progression is not explored in the context of HIV-1C infection. The expression pattern of activating (NKp46, NKp44, NKp30, NKG2D, and NKG2C) and inhibitory (CD158b, NKG2A, and ILT2) receptors was determined in 20 patients with recent HIV-1C infection within 3–7 months of acquiring HIV infection and was compared with the expression pattern in individuals with progressive (N = 12), non-progressive HIV-1C infection (LTNPs, N = 12) and healthy seronegative individuals (N = 20). The association of the expression of these receptors on the rate of disease progression was assessed using viral load set point of recently infected individuals as a marker of disease progression. The study showed that higher cytotoxic potency of NK cells was associated with low viral load set point in recent HIV infection (r = −0.701; p = 0.0006) and higher CD4 counts (r = 0.720; p = 0.001). The expression of activating receptors (NKp46, NKp30, and NKG2D) on cytotoxic NK cells but not on regulatory NK cells was also significantly associated with low viral set point (p < 0.01) and viral load in LTNPs and progressors (p < 0.01). The study also indicated that cytotoxic NK cells might show the ability to specifically lyse HIV infected CD4 cells. This data collectively showed that early and sustained higher expression of activating receptors on cytotoxic NK cells could be responsible for increased cytotoxicity, reduced viral burden, and thus delaying the disease progression. The study to identify the molecular mechanism of the expression of these receptors in HIV infection will be helpful in further understanding of NK cell mediated control in early HIV infection.
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Cullin4A and cullin4B are interchangeable for HIV Vpr and Vpx action through the CRL4 ubiquitin ligase complex. J Virol 2014; 88:6944-58. [PMID: 24719410 DOI: 10.1128/jvi.00241-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
UNLABELLED Human immunodeficiency virus (HIV) seizes control of cellular cullin-RING E3 ubiquitin ligases (CRLs) to promote viral replication. HIV-1 Vpr and HIV-2/simian immunodeficiency virus (SIV) Vpr and Vpx engage the cullin4 (CUL4)-containing ubiquitin ligase complex (CRL4) to cause polyubiquitination and proteasomal degradation of host proteins, including ones that block infection. HIV-1 Vpr engages CRL4 to trigger the degradation of uracil-N-glycosylase 2 (UNG2). Both HIV-1 Vpr and HIV-2/SIV Vpr tap CRL4 to initiate G2 cell cycle arrest. HIV-2/SIV Vpx secures CRL4 to degrade the antiviral protein SAMHD1. CRL4 includes either cullin4A (CUL4A) or cullin4B (CUL4B) among its components. Whether Vpr or Vpx relies on CUL4A, CUL4B, or both to act through CRL4 is not known. Reported structural, phenotypic, and intracellular distribution differences between the two CUL4 types led us to hypothesize that Vpr and Vpx employ these in a function-specific manner. Here we determined CUL4 requirements for HIV-1 and HIV-2/SIV Vpr-mediated G2 cell cycle arrest, HIV-1 Vpr-mediated UNG2 degradation, and HIV-2 Vpx-mediated SAMHD1 degradation. Surprisingly, CUL4A and CUL4B are exchangeable for CRL4-dependent Vpr and Vpx action, except in primary macrophages, where Vpx relies on both CUL4A and CUL4B for maximal SAMHD1 depletion. This work highlights the need to consider both CUL4 types for Vpr and Vpx functions and also shows that the intracellular distribution of CUL4A and CUL4B can vary by cell type. IMPORTANCE The work presented here shows for the first time that HIV Vpr and Vpx do not rely exclusively on CUL4A to cause ubiquitination through the CRL4 ubiquitin ligase complex. Furthermore, our finding that intracellular CUL4 and SAMHD1 distributions can vary with cell type provides the basis for reconciling previous disparate findings regarding the site of SAMHD1 depletion. Finally, our observations with primary immune cells provide insight into the cell biology of CUL4A and CUL4B that will help differentiate the functions of these similar proteins.
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6
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Hadi K, Walker LA, Guha D, Murali R, Watkins SC, Tarwater P, Srinivasan A, Ayyavoo V. Human immunodeficiency virus type 1 Vpr polymorphisms associated with progressor and nonprogressor individuals alter Vpr-associated functions. J Gen Virol 2013; 95:700-711. [PMID: 24300552 DOI: 10.1099/vir.0.059576-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Following infection with Human immunodeficiency virus 1 (HIV-1) there is a remarkable variation in virus replication and disease progression. Both host and viral factors have been implicated in the observed differences in disease status. Here, we focus on understanding the contribution of HIV-1 viral protein R (Vpr) by evaluating the disease-associated Vpr polymorphism and its biological functions from HIV-1 positive rapid progressor (RP) and long-term nonprogressor (LTNP) subjects. Results presented here show distinct variation in phenotypes of Vpr alleles from LTNP and RP subjects. Most notably, the polymorphism of Vpr at R36W and L68M associated with RP shows higher levels of oligomerization, and increased virus replication, whereas R77Q exhibits poor replication kinetics. Interestingly, we did not observe correlation with cell cycle arrest function. Together these results indicate that polymorphisms in Vpr in part may contribute to altered virus replication kinetics leading to the observed differences in disease progression in LTNP and RP groups.
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Affiliation(s)
- Kevin Hadi
- Department of Infectious Diseases and Microbiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15261, USA
| | - Leah A Walker
- Department of Infectious Diseases and Microbiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15261, USA
| | - Debjani Guha
- Department of Infectious Diseases and Microbiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15261, USA
| | - Ramachandran Murali
- Department of Biomedical Sciences, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Los Angeles, CA, USA
| | - Simon C Watkins
- Center for Biological Imaging, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Patrick Tarwater
- Paul L. Foster School of Medicine, Texas Tech University Health Science Center, El Paso, TX, USA
| | | | - Velpandi Ayyavoo
- Department of Infectious Diseases and Microbiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA 15261, USA
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7
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Casey Klockow L, Sharifi HJ, Wen X, Flagg M, Furuya AKM, Nekorchuk M, de Noronha CMC. The HIV-1 protein Vpr targets the endoribonuclease Dicer for proteasomal degradation to boost macrophage infection. Virology 2013; 444:191-202. [PMID: 23849790 DOI: 10.1016/j.virol.2013.06.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 06/09/2013] [Indexed: 12/13/2022]
Abstract
The HIV-1 protein Vpr enhances macrophage infection, triggers G2 cell cycle arrest, and targets cells for NK-cell killing. Vpr acts through the CRL4(DCAF1) ubiquitin ligase complex to cause G2 arrest and trigger expression of NK ligands. Corresponding ubiquitination targets have not been identified. UNG2 and SMUG1 are the only known substrates for Vpr-directed depletion through CRL4(DCAF1). Here we identify the endoribonuclease Dicer as a target of HIV-1 Vpr-directed proteasomal degradation through CRL4(DCAF1). We show that HIV-1 Vpr inhibits short hairpin RNA function as expected upon reduction of Dicer levels. Dicer inhibits HIV-1 replication in T cells. We demonstrate that Dicer also restricts HIV-1 replication in human monocyte-derived macrophages (MDM) and that reducing Dicer expression in MDMs enhances HIV-1 infection in a Vpr-dependent manner. Our results support a model in which Vpr complexes with human Dicer to boost its interaction with the CRL4(DCAF1) ubiquitin ligase complex and its subsequent degradation.
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Affiliation(s)
- Laurieann Casey Klockow
- Center for Immunology and Microbial Disease, Albany Medical College, 47 New Scotland Avenue, Albany, NY 12208, USA
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8
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Lam RA, Chwee JY, Le Bert N, Sauer M, Pogge von Strandmann E, Gasser S. Regulation of self-ligands for activating natural killer cell receptors. Ann Med 2013; 45:384-94. [PMID: 23701136 DOI: 10.3109/07853890.2013.792495] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Natural killer (NK) cells are able to lyse infected and tumor cells while sparing healthy cells. Recognition of diseased cells by NK cells is governed by several activating and inhibitory receptors. We review numerous pathways that have been implicated in the regulation of self-ligands for activating receptors, including NKG2D, DNAM-1, LFA-1, NKp30, NKp44, NKp46, NKp65, and NKp80 found on NK cells and some T cells. Understanding how the regulation of self-encoded ligand expression is regulated may provide novel avenues for future therapeutic approaches to infections and cancer.
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Affiliation(s)
- Runyi A Lam
- Immunology Programme, Centre for Life Sciences, Department of Microbiology, National University of Singapore 117456, Singapore
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9
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Richard J, Pham TNQ, Ishizaka Y, Cohen EA. Viral protein R upregulates expression of ULBP2 on uninfected bystander cells during HIV-1 infection of primary CD4+ T lymphocytes. Virology 2013; 443:248-56. [PMID: 23726848 DOI: 10.1016/j.virol.2013.04.037] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 03/12/2013] [Accepted: 04/30/2013] [Indexed: 11/26/2022]
Abstract
HIV-1 Vpr triggers NK cell-mediated lysis of infected cells by upregulating ULBP2, a ligand of the NKG2D receptor, through activation of the ATR-mediated DNA damage response. Herein, we demonstrate that Vpr augments ULBP2 expression on both infected and uninfected bystander cells during HIV-1 infection of primary CD4+ T lymphocytes. Indeed, the frequency of uninfected bystander cells expressing high levels of ULBP2 was elevated in a Vpr-dependent manner. Nevertheless, the same does not hold true for a Vpr mutant that is not packaged into virions, suggesting the involvement of virion-associated Vpr in this process. Additionally, we show that soluble Vpr has the ability to induce a DNA damage response and to augment cell-surface ULBP2 upon transducing target cells, including T cells, conditions known to promote NK cell-mediated killing. Overall, these findings suggest that Vpr could contribute to CD4+ T cell loss by rendering uninfected bystander cells susceptible to NK cell-mediated killing.
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Affiliation(s)
- Jonathan Richard
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada
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10
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Sandberg JK, Andersson SK, Bächle SM, Nixon DF, Moll M. HIV-1 Vpu interference with innate cell-mediated immune mechanisms. Curr HIV Res 2013; 10:327-33. [PMID: 22524181 PMCID: PMC3412205 DOI: 10.2174/157016212800792513] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2012] [Revised: 03/06/2012] [Accepted: 03/14/2012] [Indexed: 12/26/2022]
Abstract
The HIV-1 accessory protein Vpu is emerging as a viral factor with a range of activities devoted to counteracting host innate immunity. Here, we review recent findings concerning the role of Vpu in hampering activation of cellular immune responses mediated by CD1d-restricted invariant natural killer T (iNKT) cells and natural killer (NK) cells. The two key findings are that Vpu interferes with CD1d expression and antigen presentation, and also with expression of the NK cell activation ligand NK-T and B cell antigen (NTB-A). Both these activities are mechanistically distinct from CD4 and Tetherin (BST-2) down-modulation. We summarize the mechanistic insights gained into Vpu interference with CD1d and NTB-A, as well as important challenges going forward, and discuss these mechanisms in the context of the role that iNKT and NK cells play in HIV-1 immunity and immunopathogenesis.
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Affiliation(s)
- Johan K Sandberg
- Center for Infectious Medicine, Department of Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden.
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Zingoni A, Ardolino M, Santoni A, Cerboni C. NKG2D and DNAM-1 activating receptors and their ligands in NK-T cell interactions: role in the NK cell-mediated negative regulation of T cell responses. Front Immunol 2013; 3:408. [PMID: 23316196 PMCID: PMC3540764 DOI: 10.3389/fimmu.2012.00408] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Accepted: 12/17/2012] [Indexed: 11/13/2022] Open
Abstract
The negative regulation of adaptive immunity is relevant to maintain lymphocyte homeostasis. Several studies on natural killer (NK) cells have shown a previously unappreciated immunomodulatory role, as they can negatively regulate T cell-mediated immune responses by direct killing and by secretion of inhibitory cytokines. The molecular mechanisms of T cell suppression by NK cells, however, remained elusive. Only in the last few years has it become evident that, upon activation, human T cells express MICA-B, ULBP1-3, and PVR, ligands of the activating receptors NKG2D and DNAM-1, respectively. Their expression renders T cells targets of NK cell lysis, representing a new mechanism taking part to the negative regulation of T cell responses. Studies on the expression of NKG2D and DNAM-1 ligands on T cells have also contributed in understanding that the activation of ATM (ataxia-telangiectasia, mutated)/ATR (ATM/Rad3-related) kinases and the DNA damage response is a common pathway regulating the expression of activating ligands in different types of cells and under different conditions. The functional consequences of NKG2D and DNAM-1 ligand expression on activated T cells are discussed in the context of physiologic and pathologic processes such as infections, autoimmunity, and graft versus host disease.
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Affiliation(s)
- Alessandra Zingoni
- Department of Molecular Medicine, Istituto Pasteur-Fondazione Cenci Bolognetti, "Sapienza" University of Rome Rome, Italy
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12
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The role of HIV-1 Vpr in promoting the infection of nondividing cells and in cell cycle arrest. Curr Opin HIV AIDS 2012; 7:187-94. [PMID: 22274659 DOI: 10.1097/coh.0b013e32835049e0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
PURPOSE OF REVIEW The search for the role(s) that HIV-1 Vpr and its HIV2/SIV paralogs Vpr and Vpx play in viral infection and pathogenesis showed that all three engage CRL4 ubiquitin ligase complexes. This association triggers ubiquitination and degradation of cellular substrates. The identity of the ubiquitin ligase substrates is only now beginning to be revealed. This review focuses on recent work that has identified one such substrate and exposed new cellular restrictions to infection. RECENT FINDINGS Three groups have now described cellular factors that restrict HIV-1 infection in cells of the myeloid lineage. One of these factors, sterile alpha motif- and metal-dependent phosphohydrolase domain-containing protein 1 (SAMHD1), was shown to be depleted through the CRL4 ubiquitin ligase complex in the presence of HIV-2/SIV Vpx. The other restriction can be defeated by Vpx in the absence of at least one part of the ubiquitin ligase complex that triggers SAMHD1 depletion.Another group has shown that the previously described upregulation of natural killer-cell ligands on the surface of HIV-1-infected cells requires the actions of both the cytidine deaminase APOBEC3G and uracil-N-glycosylase 2 in association with HIV-1 Vpr. SUMMARY As more cellular interaction partners are identified for HIV-1 Vpr and its paralogs from other viruses, details are emerging about Vpr function. The recent findings have highlighted the existence of two new human proteins that can act to combat HIV infection and have revealed how HIV-1 proteins act in concert to modulate the interaction between natural killer cells and HIV-1 infected cells.
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