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Mbonye U, Karn J. The cell biology of HIV-1 latency and rebound. Retrovirology 2024; 21:6. [PMID: 38580979 PMCID: PMC10996279 DOI: 10.1186/s12977-024-00639-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2024] Open
Abstract
Transcriptionally latent forms of replication-competent proviruses, present primarily in a small subset of memory CD4+ T cells, pose the primary barrier to a cure for HIV-1 infection because they are the source of the viral rebound that almost inevitably follows the interruption of antiretroviral therapy. Over the last 30 years, many of the factors essential for initiating HIV-1 transcription have been identified in studies performed using transformed cell lines, such as the Jurkat T-cell model. However, as highlighted in this review, several poorly understood mechanisms still need to be elucidated, including the molecular basis for promoter-proximal pausing of the transcribing complex and the detailed mechanism of the delivery of P-TEFb from 7SK snRNP. Furthermore, the central paradox of HIV-1 transcription remains unsolved: how are the initial rounds of transcription achieved in the absence of Tat? A critical limitation of the transformed cell models is that they do not recapitulate the transitions between active effector cells and quiescent memory T cells. Therefore, investigation of the molecular mechanisms of HIV-1 latency reversal and LRA efficacy in a proper physiological context requires the utilization of primary cell models. Recent mechanistic studies of HIV-1 transcription using latently infected cells recovered from donors and ex vivo cellular models of viral latency have demonstrated that the primary blocks to HIV-1 transcription in memory CD4+ T cells are restrictive epigenetic features at the proviral promoter, the cytoplasmic sequestration of key transcription initiation factors such as NFAT and NF-κB, and the vanishingly low expression of the cellular transcription elongation factor P-TEFb. One of the foremost schemes to eliminate the residual reservoir is to deliberately reactivate latent HIV-1 proviruses to enable clearance of persisting latently infected cells-the "Shock and Kill" strategy. For "Shock and Kill" to become efficient, effective, non-toxic latency-reversing agents (LRAs) must be discovered. Since multiple restrictions limit viral reactivation in primary cells, understanding the T-cell signaling mechanisms that are essential for stimulating P-TEFb biogenesis, initiation factor activation, and reversing the proviral epigenetic restrictions have become a prerequisite for the development of more effective LRAs.
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Affiliation(s)
- Uri Mbonye
- Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
| | - Jonathan Karn
- Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
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2
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Abstract
Combinatory antiretroviral therapy (cART) reduces human immunodeficiency virus type 1 (HIV-1) replication but is not curative because cART interruption almost invariably leads to a rapid rebound of viremia due to the persistence of stable HIV-1-infected cellular reservoirs. These reservoirs are mainly composed of CD4+ T cells harboring replication-competent latent proviruses. A broadly explored approach to reduce the HIV-1 reservoir size, the shock and kill strategy, consists of reactivating HIV-1 gene expression from the latently infected cellular reservoirs (the shock), followed by killing of the virus-producing infected cells (the kill). Based on improved understanding of the multiple molecular mechanisms controlling HIV-1 latency, distinct classes of latency reversing agents (LRAs) have been studied for their efficiency to reactivate viral gene expression in in vitro and ex vivo cell models. Here, we provide an up-to-date review of these different mechanistic classes of LRAs and discuss optimizations of the shock strategy by combining several LRAs simultaneously or sequentially.
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Affiliation(s)
- Anthony Rodari
- Service of Molecular Virology, Department of Molecular Biology, Université Libre de Bruxelles (ULB), 6041 Gosselies, Belgium;
| | - Gilles Darcis
- Infectious Diseases Department, Liège University Hospital, 4000 Liège, Belgium
| | - Carine M Van Lint
- Service of Molecular Virology, Department of Molecular Biology, Université Libre de Bruxelles (ULB), 6041 Gosselies, Belgium;
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3
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Depicting HIV-1 Transcriptional Mechanisms: A Summary of What We Know. Viruses 2020; 12:v12121385. [PMID: 33287435 PMCID: PMC7761857 DOI: 10.3390/v12121385] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 11/26/2020] [Accepted: 12/01/2020] [Indexed: 12/19/2022] Open
Abstract
Despite the introduction of combinatory antiretroviral therapy (cART), HIV-1 infection cannot be cured and is still one of the major health issues worldwide. Indeed, as soon as cART is interrupted, a rapid rebound of viremia is observed. The establishment of viral latency and the persistence of the virus in cellular reservoirs constitute the main barrier to HIV eradication. For this reason, new therapeutic approaches have emerged to purge or restrain the HIV-1 reservoirs in order to cure infected patients. However, the viral latency is a multifactorial process that depends on various cellular mechanisms. Since these new therapies mainly target viral transcription, their development requires a detailed and precise understanding of the regulatory mechanism underlying HIV-1 transcription. In this review, we discuss the complex molecular transcriptional network regulating HIV-1 gene expression by focusing on the involvement of host cell factors that could be used as potential drug targets to design new therapeutic strategies and, to a larger extent, to reach an HIV-1 functional cure.
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4
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Mele AR, Marino J, Dampier W, Wigdahl B, Nonnemacher MR. HIV-1 Tat Length: Comparative and Functional Considerations. Front Microbiol 2020; 11:444. [PMID: 32265877 PMCID: PMC7105873 DOI: 10.3389/fmicb.2020.00444] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 03/02/2020] [Indexed: 12/22/2022] Open
Affiliation(s)
- Anthony R Mele
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States.,Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Jamie Marino
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States.,Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Will Dampier
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States.,Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States.,School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, United States
| | - Brian Wigdahl
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States.,Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States.,Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, United States
| | - Michael R Nonnemacher
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States.,Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, United States.,Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, United States
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5
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Zhang M, Liu X, Liu X, Li H, Sun W, Zhang Y. A pilot investigation of a urinary metabolic biomarker discovery in renal cell carcinoma. Int Urol Nephrol 2019; 52:437-446. [DOI: 10.1007/s11255-019-02332-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Accepted: 10/29/2019] [Indexed: 01/23/2023]
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6
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Murray LA, Combs AN, Rekapalli P, Cristea IM. Methods for characterizing protein acetylation during viral infection. Methods Enzymol 2019; 626:587-620. [PMID: 31606092 DOI: 10.1016/bs.mie.2019.06.030] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Lysine acetylation is a prevalent posttranslational modification that acts as a regulator of protein function, subcellular localization, and interactions. A growing body of work has highlighted the importance of temporal alterations in protein acetylation during infection with a range of human viruses. It has become clear that both cellular and viral proteins are decorated by lysine acetylations, and that these modifications contribute to core host defense and virus replication processes. Further defining the extent and dynamics of protein acetylation events during the progression of an infection can provide an important new perspective on the intricate mechanisms underlying the biology and pathogenesis of virus infections. Here, we provide protocols for identifying, quantifying, and probing the regulation of lysine acetylations during viral infection. We describe the use of acetyl-lysine immunoaffinity purification and quantitative mass spectrometry for assessing the cellular acetylome at different stages of an infection. As an alternative to traditional antibody-mediated western blotting, we discuss the benefits of targeted mass spectrometry approaches for detecting and quantifying site-specific acetylations on proteins of interest. Specifically, we provide a protocol using parallel reaction monitoring (PRM). We further discuss experimental considerations that are specific to studying viral infections. Finally, we provide a brief overview of the types of assays that can be employed to characterize the function of an acetylation event in the context of infection. As a method to interrogate the regulation of acetylation, we describe the Fluor de Lys assay for monitoring the enzymatic activities of deacetylases.
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Affiliation(s)
- Laura A Murray
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, NJ, United States
| | - Ashton N Combs
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, NJ, United States
| | - Pranav Rekapalli
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, NJ, United States
| | - Ileana M Cristea
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Princeton, NJ, United States.
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7
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Spector C, Mele AR, Wigdahl B, Nonnemacher MR. Genetic variation and function of the HIV-1 Tat protein. Med Microbiol Immunol 2019; 208:131-169. [PMID: 30834965 DOI: 10.1007/s00430-019-00583-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Accepted: 02/11/2019] [Indexed: 12/14/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) encodes a transactivator of transcription (Tat) protein, which has several functions that promote viral replication, pathogenesis, and disease. Amino acid variation within Tat has been observed to alter the functional properties of Tat and, depending on the HIV-1 subtype, may produce Tat phenotypes differing from viruses' representative of each subtype and commonly used in in vivo and in vitro experimentation. The molecular properties of Tat allow for distinctive functional activities to be determined such as the subcellular localization and other intracellular and extracellular functional aspects of this important viral protein influenced by variation within the Tat sequence. Once Tat has been transported into the nucleus and becomes engaged in transactivation of the long terminal repeat (LTR), various Tat variants may differ in their capacity to activate viral transcription. Post-translational modification patterns based on these amino acid variations may alter interactions between Tat and host factors, which may positively or negatively affect this process. In addition, the ability of HIV-1 to utilize or not utilize the transactivation response (TAR) element within the LTR, based on genetic variation and cellular phenotype, adds a layer of complexity to the processes that govern Tat-mediated proviral DNA-driven transcription and replication. In contrast, cytoplasmic or extracellular localization of Tat may cause pathogenic effects in the form of altered cell activation, apoptosis, or neurotoxicity. Tat variants have been shown to differentially induce these processes, which may have implications for long-term HIV-1-infected patient care in the antiretroviral therapy era. Future studies concerning genetic variation of Tat with respect to function should focus on variants derived from HIV-1-infected individuals to efficiently guide Tat-targeted therapies and elucidate mechanisms of pathogenesis within the global patient population.
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Affiliation(s)
- Cassandra Spector
- Department of Microbiology and Immunology, Drexel University College of Medicine, 245 N 15th St, Philadelphia, PA, 19102, USA
- Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Anthony R Mele
- Department of Microbiology and Immunology, Drexel University College of Medicine, 245 N 15th St, Philadelphia, PA, 19102, USA
- Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Brian Wigdahl
- Department of Microbiology and Immunology, Drexel University College of Medicine, 245 N 15th St, Philadelphia, PA, 19102, USA
- Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, USA
- Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA
| | - Michael R Nonnemacher
- Department of Microbiology and Immunology, Drexel University College of Medicine, 245 N 15th St, Philadelphia, PA, 19102, USA.
- Center for Molecular Virology and Translational Neuroscience, Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, PA, USA.
- Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.
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8
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Combinations of isoform-targeted histone deacetylase inhibitors and bryostatin analogues display remarkable potency to activate latent HIV without global T-cell activation. Sci Rep 2017; 7:7456. [PMID: 28785069 PMCID: PMC5547048 DOI: 10.1038/s41598-017-07814-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 07/05/2017] [Indexed: 12/26/2022] Open
Abstract
Current antiretroviral therapy (ART) for HIV/AIDS slows disease progression by reducing viral loads and increasing CD4 counts. Yet ART is not curative due to the persistence of CD4+ T-cell proviral reservoirs that chronically resupply active virus. Elimination of these reservoirs through the administration of synergistic combinations of latency reversing agents (LRAs), such as histone deacetylase (HDAC) inhibitors and protein kinase C (PKC) modulators, provides a promising strategy to reduce if not eradicate the viral reservoir. Here, we demonstrate that largazole and its analogues are isoform-targeted histone deacetylase inhibitors and potent LRAs. Significantly, these isoform-targeted HDAC inhibitors synergize with PKC modulators, namely bryostatin-1 analogues (bryologs). Implementation of this unprecedented LRA combination induces HIV-1 reactivation to unparalleled levels and avoids global T-cell activation within resting CD4+ T-cells.
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9
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Mbonye U, Karn J. Transcriptional control of HIV latency: cellular signaling pathways, epigenetics, happenstance and the hope for a cure. Virology 2014; 454-455:328-39. [PMID: 24565118 DOI: 10.1016/j.virol.2014.02.008] [Citation(s) in RCA: 178] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Revised: 01/23/2014] [Accepted: 02/07/2014] [Indexed: 02/06/2023]
Abstract
Replication-competent latent HIV-1 proviruses that persist in the genomes of a very small subset of resting memory T cells in infected individuals under life-long antiretroviral therapy present a major barrier towards viral eradication. Multiple molecular mechanisms are required to repress the viral trans-activating factor Tat and disrupt the regulatory Tat feedback circuit leading to the establishment of the latent viral reservoir. In particular, latency is due to a combination of transcriptional silencing of proviruses via host epigenetic mechanisms and restrictions on the expression of P-TEFb, an essential co-factor for Tat. Induction of latent proviruses in the presence of antiretroviral therapy is expected to enable clearance of latently infected cells by viral cytopathic effects and host antiviral immune responses. An in-depth comprehensive understanding of the molecular control of HIV-1 transcription should inform the development of optimal combinatorial reactivation strategies that are intended to purge the latent viral reservoir.
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Affiliation(s)
- Uri Mbonye
- Department of Molecular Biology and Microbiology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, United States
| | - Jonathan Karn
- Department of Molecular Biology and Microbiology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, United States.
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10
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Kumar S, Maiti S. The effect of N-acetylation and N-methylation of lysine residue of Tat peptide on its interaction with HIV-1 TAR RNA. PLoS One 2013; 8:e77595. [PMID: 24147034 PMCID: PMC3798303 DOI: 10.1371/journal.pone.0077595] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 09/06/2013] [Indexed: 12/25/2022] Open
Abstract
Post-translational modification (PTM) of RNA binding proteins (RBPs) play a very important role in determining their binding to cognate RNAs and therefore regulate the downstream effects. Lysine can undergo various PTMs and thereby contribute to the regulation of different cellular processes. It can be reversibly acetylated and methylated using a pool of respective enzymes, to act as a switch for controlling the binding efficiency of RBPs. Here we have delineated the thermodynamic and kinetic effects of N-acetylation and N-monomethylation of lysine on interaction between HIV-1 TAR RNA and its cognate binder Tat peptide ( a model system). Our results indicate that acetylation of lysine 50 (K50), leads to eight- fold reduction in binding affinity, originating exclusively from entropy changes whereas, lysine 51 (K51) acetylation resulted only in three fold decrease with large enthalpy-entropy compensation. The measurement of kinetic parameters indicated major change (4.5 fold) in dissociation rate in case of K50 acetylation however, K51 acetylation showed similar effect on both association and dissociation rates. In contrast, lysine methylation did not affect the binding affinity of Tat peptide to TAR RNA at K50, nonetheless three fold enhancement in binding affinity was observed at K51 position. In spite of large enthalpy-entropy compensation, lysine methylation seems to have more pronounced position specific effect on the kinetic parameters. In case of K50 methylation, simultaneous increase was observed in the rate of association and dissociation leaving binding affinity unaffected. The increased binding affinity for methylated Tat at K51 stems from faster association rate with slightly slower dissociation rate.
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Affiliation(s)
- Santosh Kumar
- Proteomics and Structural Biology Unit, CSIR-Institute of Genomics and Integrative Biology, CSIR, Delhi, India
| | - Souvik Maiti
- Proteomics and Structural Biology Unit, CSIR-Institute of Genomics and Integrative Biology, CSIR, Delhi, India
- CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, CSIR, Pune, India
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11
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Bromodomain proteins in HIV infection. Viruses 2013; 5:1571-86. [PMID: 23793227 PMCID: PMC3717722 DOI: 10.3390/v5061571] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 06/09/2013] [Accepted: 06/13/2013] [Indexed: 02/06/2023] Open
Abstract
Bromodomains are conserved protein modules of ~110 amino acids that bind acetylated lysine residues in histone and non-histone proteins. Bromodomains are present in many chromatin-associated transcriptional regulators and have been linked to diverse aspects of the HIV life cycle, including transcription and integration. Here, we review the role of bromodomain-containing proteins in HIV infection. We begin with a focus on acetylated viral factors, followed by a discussion of structural and biological studies defining the involvement of bromodomain proteins in the HIV life cycle. We end with an overview of promising new studies of bromodomain inhibitory compounds for the treatment of HIV latency.
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12
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Dhamija N, Rawat P, Mitra D. Epigenetic regulation of HIV-1 persistence and evolving strategies for virus eradication. Subcell Biochem 2013; 61:479-505. [PMID: 23150264 DOI: 10.1007/978-94-007-4525-4_21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Despite the intense effort put by researchers globally to understand Human Immunodeficiency Virus (HIV-1) pathogenesis since its discovery 30 years ago, the acquired knowledge till date is not good enough to eradicate HIV-1 from an infected individual. HIV-1 infects cells of the human immune system and integrates into the host cell genome thereby leading to persistent infection in these cells. Based on the activation status of the cells, the infection could be productive or result in latent infection. The current regimen used to treat HIV-1 infection in an AIDS patient includes combination of antiretroviral drugs called Highly Active Anti-Retroviral Therapy (HAART). A major challenge for the success of HAART has been these latent reservoirs of HIV which remain hidden and pose major hurdle for the eradication of virus. Combination of HAART therapy with simultaneous activation of latent reservoirs of HIV-1 seems to be the future of anti-retroviral therapy; however, this will require a much better understanding of the mechanisms and regulation of HIV-1 latency. In this chapter, we have tried to elaborate on HIV-1 latency, highlighting the strategies employed by the virus to ensure persistence in the host with specific focus on epigenetic regulation of latency. A complete understanding of HIV-1 latency will be extremely essential for ultimate eradication of HIV-1 from the human host.
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Affiliation(s)
- Neeru Dhamija
- National Centre for Cell Science, NCCS Complex, Pune University Campus, Ganeshkhind, Pune, 411007, India
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13
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Impact of Tat Genetic Variation on HIV-1 Disease. Adv Virol 2012; 2012:123605. [PMID: 22899925 PMCID: PMC3414192 DOI: 10.1155/2012/123605] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 05/14/2012] [Indexed: 01/08/2023] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) promoter or long-terminal repeat (LTR) regulates viral gene expression by interacting with multiple viral and host factors. The viral transactivator protein Tat plays an important role in transcriptional activation of HIV-1 gene expression. Functional domains of Tat and its interaction with transactivation response element RNA and cellular transcription factors have been examined. Genetic variation within tat of different HIV-1 subtypes has been shown to affect the interaction of the viral transactivator with cellular and/or viral proteins, influencing the overall level of transcriptional activation as well as its action as a neurotoxic protein. Consequently, the genetic variability within tat may impact the molecular architecture of functional domains of the Tat protein that may impact HIV pathogenesis and disease. Tat as a therapeutic target for anti-HIV drugs has also been discussed.
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14
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Tripathy MK, Abbas W, Herbein G. Epigenetic regulation of HIV-1 transcription. Epigenomics 2012; 3:487-502. [PMID: 22126207 DOI: 10.2217/epi.11.61] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
After entry into the target cell and reverse transcription, HIV-1 genes are integrated into the host genome. It is now well established that the viral promoter activity is directly governed by its chromatin environment. Nuc-1, a nucleosome located immediately downstream of the HIV-1 transcriptional initiation site directly impedes long-terminal repeat (LTR) activity. Epigenetic modifications and disruption of Nuc-1 are a prerequisite to the activation of LTR-driven transcription and viral expression. The compaction of chromatin and its permissiveness for transcription are directly dependent on the post-translational modifications of histones such as acetylation, methylation, phosphorylation and ubiquitination. Understanding the molecular mechanisms underlying HIV-1 transcriptional silencing and activation is thus a major challenge in the fight against AIDS and will certainly lead to new therapeutic tools.
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Affiliation(s)
- Manoj Kumar Tripathy
- Department of Virology, University of Franche-Comté, EA4266, IFR133 INSERM, CHU Besançon, Besançon, France
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15
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Abstract
Foamy viruses (FVs) are distinct members of the retrovirus (RV) family. In this chapter, the molecular regulation of foamy viral transcription, splicing, polyadenylation, and RNA export will be compared in detail to the orthoretroviruses. Foamy viral transcription is regulated in early and late phases, which are separated by the usage of two promoters. The viral transactivator protein Tas activates both promoters. The nature of this early-late switch and the molecular mechanism used by Tas are unique among RVs. RVs duplicate the long terminal repeats (LTRs) during reverse transcription. These LTRs carry both a promoter region and functional poly(A) sites. In order to express full-length transcripts, RVs have to silence the poly(A) signal in the 5' LTR and to activate it in the 3' LTR. FVs have a unique R-region within these LTRs with a major splice donor (MSD) at +51 followed by a poly(A) signal. FVs use a MSD-dependent mechanism to inactivate the polyadenylation. Most RVs express all their genes from a single primary transcript. In order to allow expression of more than one gene from this RNA, differential splicing is extensively used in complex RVs. The splicing pattern of FV is highly complex. In contrast to orthoretroviruses, FVs synthesize the Pol precursor protein from a specific and spliced transcript. The LTR and IP-derived primary transcripts are spliced into more than 15 different mRNA species. Since the RNA ratios have to be balanced, a tight regulation of splicing is required. Cellular quality control mechanisms retain and degrade unspliced or partially spliced RNAs in the nucleus. In this review, I compare the RNA export pathways used by orthoretroviruses with the distinct RNA export pathway used by FV. All these steps are highly regulated by host and viral factors and set FVs apart from all other RVs.
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Affiliation(s)
- Jochen Bodem
- Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany
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16
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Charbonneau J, Gendron K, Ferbeyre G, Brakier-Gingras L. The 5' UTR of HIV-1 full-length mRNA and the Tat viral protein modulate the programmed -1 ribosomal frameshift that generates HIV-1 enzymes. RNA (NEW YORK, N.Y.) 2012; 18:519-529. [PMID: 22286970 PMCID: PMC3285939 DOI: 10.1261/rna.030346.111] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Accepted: 12/01/2011] [Indexed: 05/31/2023]
Abstract
Translation of the full-length messenger RNA (mRNA) of the human immunodeficiency virus type 1 (HIV-1) generates the precursor of the viral enzymes via a programmed -1 ribosomal frameshift. Here, using dual-luciferase reporters, we investigated whether the highly structured 5' untranslated region (UTR) of this mRNA, which interferes with translation initiation, can modulate HIV-1 frameshift efficiency. We showed that, when the 5' UTR of HIV-1 mRNA occupies the 5' end of the reporter mRNA, HIV-1 frameshift efficiency is increased about fourfold in Jurkat T-cells, compared with a control dual-luciferase reporter with a short unstructured 5' UTR. This increase was related to an interference with cap-dependent translation initiation by the TAR-Poly(A) region at the 5' end of the messenger. HIV-1 mRNA 5' UTR also contains an internal ribosome entry site (IRES), but we showed that, when the cap-dependent initiation mode is available, the IRES is not used or is weakly used. However, when the ribosomes have to use the IRES to translate the dual-luciferase reporter, the frameshift efficiency is comparable to that of the control dual-luciferase reporter. The decrease in cap-dependent initiation and the accompanying increase in frameshift efficiency caused by the 5' UTR of HIV-1 mRNA is antagonized, in a dose-dependent way, by the Tat viral protein. Tat also stimulates the IRES-dependent initiation and decreases the corresponding frameshift efficiency. A model is presented that accounts for the variations in frameshift efficiency depending on the 5' UTR and the presence of Tat, and it is proposed that a range of frameshift efficiencies is compatible with the virus replication.
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Affiliation(s)
- Johanie Charbonneau
- Département de biochimie, Université de Montréal, Montréal, Québec, Canada, H3T 1J4
| | - Karine Gendron
- Département de biochimie, Université de Montréal, Montréal, Québec, Canada, H3T 1J4
- Centre de recherche, Hôpital Ste-Justine, Montréal, Québec, Canada, H3T 1C5
| | - Gerardo Ferbeyre
- Département de biochimie, Université de Montréal, Montréal, Québec, Canada, H3T 1J4
| | - Léa Brakier-Gingras
- Département de biochimie, Université de Montréal, Montréal, Québec, Canada, H3T 1J4
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17
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Choudhary SK, Margolis DM. Curing HIV: Pharmacologic approaches to target HIV-1 latency. Annu Rev Pharmacol Toxicol 2011; 51:397-418. [PMID: 21210747 DOI: 10.1146/annurev-pharmtox-010510-100237] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
HIV-1 infection persists even after years of antiretroviral therapy (ART). Although ART can halt viral replication and thereby reduce viremia to clinically undetectable levels, proviral latency established within the host genome remains largely unaffected by ART and can replenish systemic infection following interruption of therapy. Pharmacologic strategies, which not only target viral replication but also deplete proviral infection, are required for successful clearance of HIV-1 infection. This review highlights the current understanding of molecular mechanisms that establish and maintain HIV-1 latency in its major reservoir, the resting memory CD4(+) T cell. We also identify the molecular targets that might be exploited to induce HIV-1 expression, remove epigenetic restrictions, or enhance effective transcription. Finally, we discuss the potential pharmacologic approaches toward targeting viral persistence in different cellular and anatomical reservoirs to achieve a cure of HIV-1 infection.
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Affiliation(s)
- Shailesh K Choudhary
- Departments of Medicine, University of North Carolina at Chapel Hill, 27599, USA
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Zou W, Wang Z, Liu Y, Fan Y, Zhou BY, Yang XF, He JJ. Involvement of p300 in constitutive and HIV-1 Tat-activated expression of glial fibrillary acidic protein in astrocytes. Glia 2010; 58:1640-8. [PMID: 20578042 DOI: 10.1002/glia.21038] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
HIV-1 Tat protein is an important pathogenic factor in HIV-1-associated neurological diseases. One hallmark of HIV-1 infection of the central nervous system (CNS) is astrocytosis, which is characterized by elevated glial fibrillary acidic protein (GFAP) expression in astrocytes. We have shown that Tat activates GFAP expression in astrocytes [Zhou et al., (2004) Mol Cell Neurosci 27:296-305] and that GFAP is an important regulator of Tat neurotoxicity [Zou et al., (2007) Am J Pathol 171:1293-1935]. However, the underlying mechanisms for Tat-mediated GFAP up-regulation are not understood. In this study, we reported concurrent up-regulation of adenovirus E1a-associated 300 kDa protein p300 and GFAP in Tat-expressing human astrocytoma cells and primary astrocytes. We showed that p300 was indeed induced by Tat expression and HIV-1 infection and that the induction occurred at the transcriptional level through the cis-acting elements of early growth response 1 (egr-1) within its promoter. Using siRNA, we further showed that p300 regulated both constitutive and Tat-mediated GFAP expression. Moreover, we showed that ectopic expression of p300 potentiated Tat transactivation activity and increased proliferation of HIV-1-infected astrocytes, but had little effect on HIV-1 replication in these cells. Taken together, these results demonstrate for the first time that Tat is a positive regulator of p300 expression, which in turn regulates GFAP expression, and suggest that the Tat-Egr-1-p300-GFAP axis likely contributes to Tat neurotoxicity and predisposes astrocytes to be an HIV-1 sanctuary in the CNS.
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Affiliation(s)
- Wei Zou
- Department of Internal Medicine, Division of Infectious Diseases, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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19
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Muniz L, Egloff S, Ughy B, Jády BE, Kiss T. Controlling cellular P-TEFb activity by the HIV-1 transcriptional transactivator Tat. PLoS Pathog 2010; 6:e1001152. [PMID: 20976203 PMCID: PMC2954905 DOI: 10.1371/journal.ppat.1001152] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Accepted: 09/13/2010] [Indexed: 11/18/2022] Open
Abstract
The human immunodeficiency virus 1 (HIV-1) transcriptional transactivator (Tat) is essential for synthesis of full-length transcripts from the integrated viral genome by RNA polymerase II (Pol II). Tat recruits the host positive transcription elongation factor b (P-TEFb) to the HIV-1 promoter through binding to the transactivator RNA (TAR) at the 5′-end of the nascent HIV transcript. P-TEFb is a general Pol II transcription factor; its cellular activity is controlled by the 7SK small nuclear RNA (snRNA) and the HEXIM1 protein, which sequester P-TEFb into transcriptionally inactive 7SK/HEXIM/P-TEFb snRNP. Besides targeting P-TEFb to HIV transcription, Tat also increases the nuclear level of active P-TEFb through promoting its dissociation from the 7SK/HEXIM/P-TEFb RNP by an unclear mechanism. In this study, by using in vitro and in vivo RNA-protein binding assays, we demonstrate that HIV-1 Tat binds with high specificity and efficiency to an evolutionarily highly conserved stem-bulge-stem motif of the 5′-hairpin of human 7SK snRNA. The newly discovered Tat-binding motif of 7SK is structurally and functionally indistinguishable from the extensively characterized Tat-binding site of HIV TAR and importantly, it is imbedded in the HEXIM-binding elements of 7SK snRNA. We show that Tat efficiently replaces HEXIM1 on the 7SK snRNA in vivo and therefore, it promotes the disassembly of the 7SK/HEXIM/P-TEFb negative transcriptional regulatory snRNP to augment the nuclear level of active P-TEFb. This is the first demonstration that HIV-1 specifically targets an important cellular regulatory RNA, most probably to promote viral transcription and replication. Demonstration that the human 7SK snRNA carries a TAR RNA-like Tat-binding element that is essential for the normal transcriptional regulatory function of 7SK questions the viability of HIV therapeutic approaches based on small drugs blocking the Tat-binding site of HIV TAR. Expression and replication of the human immunodeficiency virus (HIV) is supported by the viral transcriptional transactivator (Tat) that recruits the host positive transcription elongation factor b (P-TEFb) to the promoter of the integrated viral genome. Here, we demonstrate that HIV Tat specifically and efficiently binds to the host 7SK small nuclear RNA (snRNA) that is a negative regulator of P-TEFb. Although HIV Tat has been reported to interact with a plethora of host factors, our results indicate that the 7SK transcriptional regulatory snRNA is a major and important cellular target of HIV Tat. We demonstrate that binding of Tat to the 7SK snRNA disrupts the 7SK-P-TEFb negative transcriptional regulatory complex and releases active P-TEFb. Thus, we propose that Tat not only targets P-TEFb for HIV transcription, but also modulates the nuclear level of active P-TEFb in HIV-infected cells.
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Affiliation(s)
- Lisa Muniz
- Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109 CNRS, Université Paul Sabatier, Toulouse, France
| | - Sylvain Egloff
- Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109 CNRS, Université Paul Sabatier, Toulouse, France
| | - Bettina Ughy
- Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109 CNRS, Université Paul Sabatier, Toulouse, France
- Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
| | - Beáta E. Jády
- Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109 CNRS, Université Paul Sabatier, Toulouse, France
| | - Tamás Kiss
- Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109 CNRS, Université Paul Sabatier, Toulouse, France
- Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
- * E-mail:
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Sobhian B, Laguette N, Yatim A, Nakamura M, Levy Y, Kiernan R, Benkirane M. HIV-1 Tat assembles a multifunctional transcription elongation complex and stably associates with the 7SK snRNP. Mol Cell 2010; 38:439-51. [PMID: 20471949 DOI: 10.1016/j.molcel.2010.04.012] [Citation(s) in RCA: 312] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 02/17/2010] [Accepted: 04/08/2010] [Indexed: 01/16/2023]
Abstract
HIV-1 transactivator Tat has greatly contributed to our understanding of transcription elongation by RNAPII. We purified HIV-1 Tat-associated factors from HeLa nuclear extract and show that Tat forms two distinct and stable complexes. Tatcom1 consists of the core active P-TEFb, MLL-fusion partners involved in leukemia (AF9, AFF4, AFF1, ENL, and ELL), and PAF1 complex. Importantly, Tatcom1 formation relies on P-TEFb while optimal CDK9 CTD-kinase activity is AF9 dependent. MLL-fusion partners and PAF1 are required for Tat transactivation. Tatcom2 is composed of CDK9, CycT1, and 7SK snRNP lacking HEXIM. Tat remodels 7SK snRNP by interacting directly with 7SK RNA, leading to the formation of a stress-resistant 7SK snRNP particle. Besides the identification of factors required for Tat transactivation and important for P-TEFb function, our data show a coordinated control of RNAPII elongation by different classes of transcription elongation factors associated in a single complex and acting at the same promoter.
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Affiliation(s)
- Bijan Sobhian
- Laboratoire de Virologie Moléculaire, Institut de Génétique Humaine, CNRS-UPR1142, Montpellier, France.
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21
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Colin L, Van Lint C. Molecular control of HIV-1 postintegration latency: implications for the development of new therapeutic strategies. Retrovirology 2009; 6:111. [PMID: 19961595 PMCID: PMC2797771 DOI: 10.1186/1742-4690-6-111] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2009] [Accepted: 12/04/2009] [Indexed: 02/07/2023] Open
Abstract
The persistence of HIV-1 latent reservoirs represents a major barrier to virus eradication in infected patients under HAART since interruption of the treatment inevitably leads to a rebound of plasma viremia. Latency establishes early after infection notably (but not only) in resting memory CD4+ T cells and involves numerous host and viral trans-acting proteins, as well as processes such as transcriptional interference, RNA silencing, epigenetic modifications and chromatin organization. In order to eliminate latent reservoirs, new strategies are envisaged and consist of reactivating HIV-1 transcription in latently-infected cells, while maintaining HAART in order to prevent de novo infection. The difficulty lies in the fact that a single residual latently-infected cell can in theory rekindle the infection. Here, we review our current understanding of the molecular mechanisms involved in the establishment and maintenance of HIV-1 latency and in the transcriptional reactivation from latency. We highlight the potential of new therapeutic strategies based on this understanding of latency. Combinations of various compounds used simultaneously allow for the targeting of transcriptional repression at multiple levels and can facilitate the escape from latency and the clearance of viral reservoirs. We describe the current advantages and limitations of immune T-cell activators, inducers of the NF-κB signaling pathway, and inhibitors of deacetylases and histone- and DNA- methyltransferases, used alone or in combinations. While a solution will not be achieved by tomorrow, the battle against HIV-1 latent reservoirs is well- underway.
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Affiliation(s)
- Laurence Colin
- Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles (ULB), Gosselies, Belgium.
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22
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Su Y, Deng G, Gai Y, Li Y, Gao Y, Du J, Geng Y, Chen Q, Qiao W. Comparative functional analysis of Jembrana disease virus Tat protein on lentivirus long terminal repeat promoters: evidence for flexibility at its N-terminus. Virol J 2009; 6:179. [PMID: 19860923 PMCID: PMC2775740 DOI: 10.1186/1743-422x-6-179] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2009] [Accepted: 10/28/2009] [Indexed: 11/11/2022] Open
Abstract
Background Jembrana disease virus (JDV) encodes a potent regulatory protein Tat that strongly stimulates viral expression by transactivating the long terminal repeat (LTR) promoter. JDV Tat (jTat) promotes the transcription from its own LTR as well as non-cognate LTRs, by recruiting host transcription factors and facilitating transcriptional elongation. Here, we compared the sequence requirements of jTat for transactivation of JDV, bovine immunodeficiency virus (BIV) and human immunodeficiency virus (HIV) LTRs. Results In this study, we identified the minimal protein sequence for LTR activation using jTat truncation mutants. We found that jTat N-terminal residues were indispensable for transactivating the HIV LTR. In contrast, transactivation of BIV and JDV LTRs depended largely on an arginine-rich motif and some flanking residues. Competitive inhibition assay and knockdown analysis showed that P-TEFb was required for jTat-mediated LTR transactivation, and a mammalian two-hybrid assay revealed the robust interaction of jTat with cyclin T1. In addition, HIV LTR transactivation was largely affected by fusion protein at the jTat N-terminus despite the fact that the cyclin T1-binding affinity was not altered. Furthermore, the jTat N-terminal sequence enabled HIV Tat to transactivate BIV and JDV LTRs, suggesting the flexibility at the jTat N-terminus. Conclusion This study showed the distinct sequence requirements of jTat for HIV, BIV and JDV LTR activation. Residues responsible for interaction with cyclin T1 and transactivation response element are the key determinants for transactivation of its cognate LTR. N-terminal residues in jTat may compensate for transactivation of the HIV LTR, based on the flexibility.
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Affiliation(s)
- Yang Su
- Key Laboratory of Molecular Microbiology and Biotechnology (Ministry of Education), College of Life Sciences, Nankai University, Tianjin 300071, China.
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23
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Romani B, Engelbrecht S, Glashoff RH. Functions of Tat: the versatile protein of human immunodeficiency virus type 1. J Gen Virol 2009; 91:1-12. [PMID: 19812265 DOI: 10.1099/vir.0.016303-0] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [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) Tat is a multifunctional protein that contributes to several pathological symptoms of HIV-1 infection as well as playing a critical role in virus replication. Tat is a robust transactivating protein that induces a variety of effects by altering the expression levels of cellular and viral genes. The functions of Tat are therefore primarily related to its role in modulation of gene expression. In this review the functions of HIV-1 Tat that have been well documented, as well as a number of novel functions that have been proposed for this protein, are discussed. Since some of the functions of Tat vary in different cell types in a concentration-dependent manner and because Tat sometimes exerts the same activity through different pathways, study of this protein has at times yielded conflicting and controversial results. Due to its pivotal role in viral replication and in disease pathogenesis, Tat and the cellular pathways targeted by Tat are potential targets for new anti-HIV drugs.
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Affiliation(s)
- Bizhan Romani
- Division of Medical Virology, Department of Pathology, University of Stellenbosch, Tygerberg 7505, South Africa.
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Gautier VW, Gu L, O'Donoghue N, Pennington S, Sheehy N, Hall WW. In vitro nuclear interactome of the HIV-1 Tat protein. Retrovirology 2009; 6:47. [PMID: 19454010 PMCID: PMC2702331 DOI: 10.1186/1742-4690-6-47] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Accepted: 05/19/2009] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND One facet of the complexity underlying the biology of HIV-1 resides not only in its limited number of viral proteins, but in the extensive repertoire of cellular proteins they interact with and their higher-order assembly. HIV-1 encodes the regulatory protein Tat (86-101aa), which is essential for HIV-1 replication and primarily orchestrates HIV-1 provirus transcriptional regulation. Previous studies have demonstrated that Tat function is highly dependent on specific interactions with a range of cellular proteins. However they can only partially account for the intricate molecular mechanisms underlying the dynamics of proviral gene expression. To obtain a comprehensive nuclear interaction map of Tat in T-cells, we have designed a proteomic strategy based on affinity chromatography coupled with mass spectrometry. RESULTS Our approach resulted in the identification of a total of 183 candidates as Tat nuclear partners, 90% of which have not been previously characterised. Subsequently we applied in silico analysis, to validate and characterise our dataset which revealed that the Tat nuclear interactome exhibits unique signature(s). First, motif composition analysis highlighted that our dataset is enriched for domains mediating protein, RNA and DNA interactions, and helicase and ATPase activities. Secondly, functional classification and network reconstruction clearly depicted Tat as a polyvalent protein adaptor and positioned Tat at the nexus of a densely interconnected interaction network involved in a range of biological processes which included gene expression regulation, RNA biogenesis, chromatin structure, chromosome organisation, DNA replication and nuclear architecture. CONCLUSION We have completed the in vitro Tat nuclear interactome and have highlighted its modular network properties and particularly those involved in the coordination of gene expression by Tat. Ultimately, the highly specialised set of molecular interactions identified will provide a framework to further advance our understanding of the mechanisms of HIV-1 proviral gene silencing and activation.
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Affiliation(s)
- Virginie W Gautier
- UCD-Centre for Research in Infectious Diseases, School of Medicine and Medical Science, University College Dublin (UCD), Belfield, Dublin 4, Ireland.
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25
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Tat acetylation modulates assembly of a viral-host RNA-protein transcription complex. Proc Natl Acad Sci U S A 2009; 106:3101-6. [PMID: 19223581 DOI: 10.1073/pnas.0900012106] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
HIV-1 Tat enhances viral transcription elongation by forming a ribonucleoprotein complex with transactivating responsive (TAR) RNA and P-TEFb, an elongation factor composed of cyclin T1 (CycT1) and Cdk9 that phosphorylates the C-terminal domain of RNA polymerase II. Previous studies have shown that Lys-28 in the activation domain (AD) of Tat is essential for HIV-1 transcription and replication and is acetylated by p300/CBP-associated factor (PCAF), but the mechanistic basis of the Lys-28 requirement is unknown. Here, we show that Lys-28 acetylation modulates the affinity and stability of HIV-1 Tat-CycT1-TAR complexes by enhancing an interaction with the CycT1 Tat-TAR recognition motif. High-affinity assembly correlates strongly with stimulation of transcription elongation in vitro and Tat activation in vivo. In marked contrast, bovine lentiviral Tat proteins have evolved a high-affinity TAR interaction that does not require PCAF-mediated acetylation of the Tat AD or CycT1 for RNA binding, whereas HIV-2 Tat has evolved an intermediate mechanism that uses a duplicated TAR element and CycT1 to enhance RNA affinity and consequently transcription activation. The coevolution of Tat acetylation, CycT1 dependence, and TAR binding affinity is seen in viral replication assays using Tat proteins that rely on CycT1 for TAR binding but are acetylation deficient, where compensatory mutations rapidly accrue in TAR to generate high-affinity, CycT1-independent complexes reminiscent of the bovine viruses. Thus, lysine acetylation can be used to modulate and evolve the strength of a viral-host RNA-protein complex, thereby tuning the levels of transcription elongation.
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Van Duyne R, Kehn-Hall K, Klase Z, Easley R, Heydarian M, Saifuddin M, Wu W, Kashanchi F. Retroviral proteomics and interactomes: intricate balances of cell survival and viral replication. Expert Rev Proteomics 2008; 5:507-28. [PMID: 18532916 DOI: 10.1586/14789450.5.3.507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Overall changes in the host cellular proteome upon retroviral infection intensify from the initial entry of the virus to the incorporation of viral DNA into the host genome, and finally to the consistent latent state of infection. The host cell reacts to both the entry of viral elements and the manipulation of host cellular machinery, resulting in a cascade of signaling events and pathway activation. Cell type- and tissue-specific responses are also characteristic of infection and can be classified based on the differential expression of genes and proteins between normal and disease states. The characterization of differentially expressed proteins upon infection is also critical in identifying potential biomarkers within infected bodily fluids. Biomarkers can be used to monitor the progression of infection, track the effectiveness of specific treatments and characterize the mechanisms of disease pathogenesis. Standard proteomic approaches have been applied to monitor the changes in global protein expression and localization in infected cells, tissues and fluids. Here we report on recent investigations into the characterization of proteomes in response to retroviral infection.
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Affiliation(s)
- Rachel Van Duyne
- The George Washington University, Department of Microbiology, Immunology, & Tropical Medicine, 2300 I Street, NW, Washington, DC 20037, USA.
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27
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Klase ZA, Van Duyne R, Kashanchi F. Identification of potential drug targets using genomics and proteomics: a systems approach. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2008; 56:327-68. [PMID: 18086417 DOI: 10.1016/s1054-3589(07)56011-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Zachary A Klase
- Department of Biochemistry, Medical Center, The George Washington University, Washington, DC 20037, USA
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28
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Sharma A, Awasthi S, Harrod CK, Matlock EF, Khan S, Xu L, Chan S, Yang H, Thammavaram CK, Rasor RA, Burns DK, Skiest DJ, Van Lint C, Girard AM, McGee M, Monnat RJ, Harrod R. The Werner Syndrome Helicase Is a Cofactor for HIV-1 Long Terminal Repeat Transactivation and Retroviral Replication. J Biol Chem 2007; 282:12048-57. [PMID: 17317667 DOI: 10.1074/jbc.m608104200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Werner syndrome helicase (WRN) participates in DNA replication, double strand break repair, telomere maintenance, and p53 activation. Mutations of wrn cause Werner syndrome (WS), an autosomal recessive premature aging disorder associated with cancer predisposition, atherosclerosis, and other aging related symptoms. Here, we report that WRN is a novel cofactor for HIV-1 replication. Immortalized human WRN(-/-) WS fibroblasts, lacking a functional wrn gene, are impaired for basal and Tat-activated HIV-1 transcription. Overexpression of wild-type WRN transactivates the HIV-1 long terminal repeat (LTR) in the absence of Tat, and WRN cooperates with Tat to promote high-level LTR transactivation. Ectopic WRN induces HIV-1 p24(Gag) production and retroviral replication in HIV-1-infected H9(HIV-1IIIB) lymphocytes. A dominant-negative helicase-minus mutant, WRN(K577M), inhibits LTR transactivation and HIV-1 replication. Inhibition of endogenous WRN, through co-expression of WRN(K577M), diminishes recruitment of p300/CREB-binding protein-associated factor (PCAF) and positive transcription elongation factor b (P-TEFb) to Tat/transactivation response-RNA complexes, and immortalized WRN(-/-) WS fibroblasts exhibit comparable defects in recruitment of PCAF and P-TEFb to the HIV-1 LTR. Our results demonstrate that WRN is a novel cellular cofactor for HIV-1 replication and suggest that the WRN helicase participates in the recruitment of PCAF/P-TEFb-containing transcription complexes. WRN may be a plausible target for antiretroviral therapy.
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Affiliation(s)
- Anima Sharma
- Laboratory of Molecular Virology, Department of Biological Sciences, Southern Methodist University, Dallas, Texas 75275-0376, USA
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Gatignol A. Transcription of HIV: Tat and cellular chromatin. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2007; 55:137-59. [PMID: 17586314 DOI: 10.1016/s1054-3589(07)55004-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Anne Gatignol
- Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research,, Department of Microbiology & Immunology and Experimental Medicine, McGill University, Montréal, Québec, Canada
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Ranjbar S, Rajsbaum R, Goldfeld AE. Transactivator of transcription from HIV type 1 subtype E selectively inhibits TNF gene expression via interference with chromatin remodeling of the TNF locus. THE JOURNAL OF IMMUNOLOGY 2006; 176:4182-90. [PMID: 16547255 DOI: 10.4049/jimmunol.176.7.4182] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The transactivator of transcription (Tat) protein is essential for efficient HIV type 1 (HIV-1) replication and is involved in the transcriptional regulation of the host immune response gene, TNF. In this study, we demonstrate that Tat proteins from representative HIV-1 subtype E isolates, but not from subtypes B or C, selectively inhibit TNF gene transcription and protein production in CD4(+) Jurkat T cells. Strikingly, we show that this repression is due to a tryptophan at residue 32 of Tat E and is secondary to interference with recruitment of the histone acetyltransferase P/CAF to the TNF promoter and with chromatin remodeling of the TNF locus. This study presents a novel mechanism by which HIV-1 manipulates a host immune response gene that is important in its own replication. Moreover, these results demonstrate a new mechanism by which the TNF gene is regulated via chromatin remodeling secondary to viral infection.
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Affiliation(s)
- Shahin Ranjbar
- CBR Institute for Biomedical Research, Harvard Medical School, Boston, MA 02115, USA
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31
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Berro R, Kehn K, de la Fuente C, Pumfery A, Adair R, Wade J, Colberg-Poley AM, Hiscott J, Kashanchi F. Acetylated Tat regulates human immunodeficiency virus type 1 splicing through its interaction with the splicing regulator p32. J Virol 2006; 80:3189-204. [PMID: 16537587 PMCID: PMC1440361 DOI: 10.1128/jvi.80.7.3189-3204.2006] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) potent transactivator Tat protein mediates pleiotropic effects on various cell functions. Posttranslational modification of Tat affects its activity during viral transcription. Tat binds to TAR and subsequently becomes acetylated on lysine residues by histone acetyltransferases. Novel protein-protein interaction domains on acetylated Tat are then established, which are necessary for both sustained transcriptional activation of the HIV-1 promoter and viral transcription elongation. In this study, we investigated the identity of proteins that preferentially bound acetylated Tat. Using a proteomic approach, we identified a number of proteins that preferentially bound AcTat, among which p32, a cofactor of splicing factor ASF/SF-2, was identified. We found that p32 was recruited to the HIV-1 genome, suggesting a mechanism by which acetylation of Tat may inhibit HIV-1 splicing needed for the production of full-length transcripts. Using Tat from different clades, harboring a different number of acetylation sites, as well as Tat mutated at lysine residues, we demonstrated that Tat acetylation affected splicing in vivo. Finally, using confocal microscopy, we found that p32 and Tat colocalize in vivo in HIV-1-infected cells.
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Affiliation(s)
- Reem Berro
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Kylene Kehn
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Cynthia de la Fuente
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Anne Pumfery
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Richard Adair
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - John Wade
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Anamaris M. Colberg-Poley
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - John Hiscott
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
| | - Fatah Kashanchi
- Genetics Program, The George Washington University, Washington, D.C. 20037, Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine, Washington, D.C. 20037, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, D.C. 20010, Howard Florey Institute, University of Melbourne, Victoria 3010, Australia, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada, The Institute for Genomic Research, Rockville, Maryland 20850
- Corresponding author. Mailing address: The George Washington University, 2300 I St., NW, Ross Hall, Room 551, Washington, DC 20037. Phone: (202) 994-1781. Fax: (202) 994-1780. E-mail:
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32
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Tréand C, du Chéné I, Brès V, Kiernan R, Benarous R, Benkirane M, Emiliani S. Requirement for SWI/SNF chromatin-remodeling complex in Tat-mediated activation of the HIV-1 promoter. EMBO J 2006; 25:1690-9. [PMID: 16601680 PMCID: PMC1440843 DOI: 10.1038/sj.emboj.7601074] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Accepted: 03/08/2006] [Indexed: 11/09/2022] Open
Abstract
Activation of the human immunodeficiency virus type-1 (HIV-1) promoter in infected cells requires the sequential recruitment of several cellular factors to facilitate the formation of a processive elongation complex. The nucleosomal reorganization of the HIV-1 long terminal repeat (LTR) observed upon Tat stimulation suggests that chromatin-remodeling complexes could play a role during this process. Here, we reported that Tat interacts directly with Brm, a DNA-dependent ATPase subunit of the SWI/SNF chromatin-remodeling complex, to activate the HIV-1 LTR. Inhibition of Brm via small interfering RNAs impaired Tat-mediated transactivation of an integrated HIV-1 promoter. Furthermore, Brm is recruited in vivo to the HIV-1 LTR in a Tat-dependent manner. Interestingly, we found that Tat/Brm interaction is regulated by Tat lysine 50 acetylation. These data show the requirement of Tat-mediated recruitment of SWI/SNF chromatin-remodeling complex to HIV-1 promoter in the activation of the LTR.
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Affiliation(s)
- Céline Tréand
- Institut Cochin, Département de Génétique et Développement, Paris, France
- Inserm, U567, Paris, France
- CNRS, UMR 8104, Paris, France
- Université Paris 5, Faculté de Médecine René Descartes, UM 3, Paris, France
| | - Isaure du Chéné
- Institut de Génétique Humaine, CNRSUPR1142, Montpellier, France
| | - Vanessa Brès
- Institut de Génétique Humaine, CNRSUPR1142, Montpellier, France
| | | | - Richard Benarous
- Institut Cochin, Département de Génétique et Développement, Paris, France
- Inserm, U567, Paris, France
- CNRS, UMR 8104, Paris, France
- Université Paris 5, Faculté de Médecine René Descartes, UM 3, Paris, France
| | | | - Stéphane Emiliani
- Institut Cochin, Département de Génétique et Développement, Paris, France
- Inserm, U567, Paris, France
- CNRS, UMR 8104, Paris, France
- Université Paris 5, Faculté de Médecine René Descartes, UM 3, Paris, France
- Institut Cochin, Département Maladies Infectieuses, 27 rue du faubourg Saint Jacques, Gustave Roussy, 75014 Paris, France. Tel.: +33 1 40 51 65 76; Fax: +33 1 40 51 65 70; E-mail:
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33
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Pantano S, Marcello A, Ferrari A, Gaudiosi D, Sabò A, Pellegrini V, Beltram F, Giacca M, Carloni P. Insights on HIV-1 Tat:P/CAF bromodomain molecular recognition from in vivo experiments and molecular dynamics simulations. Proteins 2006; 62:1062-73. [PMID: 16362936 DOI: 10.1002/prot.20805] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Structural and functional studies indicate that, through its bromodomain, the cellular acetyltransferase P/CAF binds the acetylated Tat protein of human immunodeficiency virus type 1 (HIV-1) and promotes transcriptional activation of the integrated provirus. Based on the NMR structure of P/CAF complexed with an acetylated Tat peptide, here we use molecular dynamics simulations to construct a model describing the interaction between full length Tat and the P/CAF bromodomain. Our calculations show that the protein-protein interface involves hydrophobic interactions between the P/CAF ZA loop and the Tat core domain. In particular, tyrosines 760 and 761 of P/CAF, two residues that are highly conserved in most known bromodomains, play an essential role for the binding. Fluorescence resonance energy transfer (FRET) experiments performed in this work demonstrate that P/CAF proteins in which these tyrosines are mutated into hydrophilic residues neither bind to Tat inside the cells nor mediate Tat transactivation. The combination of theoretical and in vivo studies provides new insights into the specificity of bromodomain recognition.
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Affiliation(s)
- Sergio Pantano
- International School for Advanced Studies, INFM-DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste, Italy
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34
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Li L, Li HS, Pauza CD, Bukrinsky M, Zhao RY. Roles of HIV-1 auxiliary proteins in viral pathogenesis and host-pathogen interactions. Cell Res 2005; 15:923-34. [PMID: 16354571 DOI: 10.1038/sj.cr.7290370] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Active host-pathogen interactions take place during infection of human immunodeficiency virus type 1 (HIV-1). Outcomes of these interactions determine the efficiency of viral infection and subsequent disease progression. HIV-infected cells respond to viral invasion with various defensive strategies such as innate, cellular and humoral immune antiviral mechanisms. On the other hand, the virus has also developed various offensive tactics to suppress these host cellular responses. Among many of the viral offensive strategies, HIV-1 viral auxiliary proteins (Tat, Rev, Nef, Vif, Vpr and Vpu) play important roles in the host-pathogen interaction and thus have significant impacts on the outcome of HIV infection. One of the best examples is the interaction of Vif with a host cytidine deaminase APOBEC3G. Although specific roles of other auxiliary proteins are not as well described as Vif-APOBEC3G interaction, it is the goal of this brief review to summarize some of the preliminary findings with the hope to stimulate further discussion and investigation in this exhilarating area of research.
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Affiliation(s)
- Lin Li
- Department of Pathology, Institute of Human Virology,University of Maryland, Baltimore, MD 21201, USA
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35
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Desfosses Y, Solis M, Sun Q, Grandvaux N, Van Lint C, Burny A, Gatignol A, Wainberg MA, Lin R, Hiscott J. Regulation of human immunodeficiency virus type 1 gene expression by clade-specific Tat proteins. J Virol 2005; 79:9180-91. [PMID: 15994812 PMCID: PMC1168763 DOI: 10.1128/jvi.79.14.9180-9191.2005] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The major group of human immunodeficiency virus type 1 (HIV-1) strains that comprise the current global pandemic have diversified during their worldwide spread into at least 10 distinct subtypes, or clades. Subtype C predominates in sub-Saharan Africa and is responsible for the majority of worldwide HIV-1 infections, subtype B predominates in North America and Europe, and subtype E is prevalent in Southeast Asia. Significant amino acid variations have been observed among the clade-specific Tat proteins. For the present study, we examined clade-specific interactions between Tat, transactivation-responsive (TAR) element, and P-TEFb proteins and how these interactions may modulate the efficiency of HIV-1 transcription. Clade-specific Tat proteins significantly modified viral gene expression. Tat proteins derived from HIV-1 clades C and E were strong transactivators of long terminal repeat (LTR) activity; Tat E also had a longer half-life than the other Tat proteins and interacted more efficiently with the stem-loop TAR element. Chimeric Tat proteins harboring the Tat E activation domain were strong transactivators of LTR expression. While Tat B, C, and E were able to rescue a Tat-defective HIV-1 proviral clone, Tat E was significantly more efficient at rescue than Tat C, possibly due to the relative stability of the Tat protein. Swapping the activation domains of Tat B, C, and E identified the cyclin T1 association domain as a critical determinant of the transactivation efficiency and of Tat-defective HIV-1 provirus rescue.
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Affiliation(s)
- Yan Desfosses
- McGill AIDS Center, Lady Davis Institute for Medical Research, Jewish General Hospital, McGill University, 3755 Cote Ste. Catherine, Montreal, Quebec, Canada H3T1E2
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36
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Hetzer C, Dormeyer W, Schnölzer M, Ott M. Decoding Tat: the biology of HIV Tat posttranslational modifications. Microbes Infect 2005; 7:1364-9. [PMID: 16046164 DOI: 10.1016/j.micinf.2005.06.003] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2005] [Accepted: 04/29/2005] [Indexed: 10/25/2022]
Abstract
The Tat protein is a viral transactivator that activates HIV transcription through complex interactions with RNA and host cell factors. Tat undergoes multiple posttranslational modifications that regulate the dynamics and complexity of these interactions. The biology of these modifications and their role in Tat function are reviewed.
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Affiliation(s)
- Claudia Hetzer
- Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
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37
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Marcello A, Lusic M, Pegoraro G, Pellegrini V, Beltram F, Giacca M. Nuclear organization and the control of HIV-1 transcription. Gene 2004; 326:1-11. [PMID: 14729258 DOI: 10.1016/j.gene.2003.10.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The regulation of transcription of the human immunodeficiency virus (HIV) is a complex event of significant pathological relevance, which recapitulates general concepts of cellular transcription with some peculiarities. The viral promoter is embedded in a chromatin structure that exerts powerful repression on transcription; activation of gene expression relies on the combined activity of a series of cellular factors that respond to different external stimuli, and on the function of a single viral regulatory protein, the Tat transactivator. Transcriptional activation is consequent to both chromatin remodeling and to the recruitment of elongation-competent RNA polymerase II complexes onto the integrated promoter, two events that require the coordinate, but transient, assembly of different protein complexes. Application of optical imaging techniques now allows us to appreciate the spatial and temporal evolvement of these reactions in vivo. The picture that is emerging is not only descriptive, but also relevant to the understanding of the regulation of the process. In particular, it appears that the confinement of biomolecules within specific subcellular compartments represents a way to control and coordinate the assembly of functional complexes that regulate viral gene expression.
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Affiliation(s)
- Alessandro Marcello
- Molecular Medicine Laboratory, International Centre for Genetic Engineering and Biotechnology, Area Science Park, Padriciano 99, 34012 Trieste, Italy
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38
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Xie B, Calabro V, Wainberg MA, Frankel AD. Selection of TAR RNA-binding chameleon peptides by using a retroviral replication system. J Virol 2004; 78:1456-63. [PMID: 14722301 PMCID: PMC321383 DOI: 10.1128/jvi.78.3.1456-1463.2004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The interaction between the arginine-rich motif (ARM) of the human immunodeficiency virus (HIV) Tat protein and TAR RNA is essential for Tat activation and viral replication. Two related lentiviruses, bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV), also require Tat ARM-TAR interactions to mediate activation, but the viruses have evolved different RNA-binding strategies. Interestingly, the JDV ARM can act as a "chameleon," adopting both the HIV and BIV TAR binding modes. To examine how RNA-protein interactions may evolve in a viral context and possibly to identify peptides that recognize HIV TAR in novel ways, we devised a retroviral system based on HIV replication to amplify and select for RNA binders. We constructed a combinatorial peptide library based on the BIV Tat ARM and identified peptides that, like the JDV Tat ARM, also function through HIV TAR, revealing unexpected sequence characteristics of an RNA-binding chameleon. The results suggest that a retroviral screening approach may help identify high-affinity TAR binders and may provide new insights into the evolution of RNA-protein interactions.
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Affiliation(s)
- Baode Xie
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California 94143-2280, USA
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39
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Apolloni A, Hooker CW, Mak J, Harrich D. Human immunodeficiency virus type 1 protease regulation of tat activity is essential for efficient reverse transcription and replication. J Virol 2003; 77:9912-21. [PMID: 12941901 PMCID: PMC224567 DOI: 10.1128/jvi.77.18.9912-9921.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) Tat protein enhances reverse transcription, but it is not known whether Tat acts directly on the reverse transcription complex or through indirect mechanisms. Since processing of Tat by HIV protease (PR) might mask its presence and, at least in part, explain this lack of data, we asked whether Tat can be cleaved by PR. We used a rabbit reticulocyte lysate (RRL) system to make Tat and PR. HIV-1 PR is expressed as a Gag-Pol fusion protein, and a PR-inactivated Gag-Pol is also expressed as a control. We showed that Tat is specifically cleaved in the presence of PR, producing a protein of approximately 5 kDa. This result suggested that the cleavage site was located in or near the Tat basic domain (amino acids 49 to 57), which we have previously shown to be important in reverse transcription. We created a panel of alanine-scanning mutations from amino acids 45 to 54 in Tat and evaluated functional parameters, including transactivation, reverse transcription, and cleavage by HIV-1 PR. We showed that amino acids 49 to 52 (RKKR) are absolutely required for Tat function in reverse transcription, that mutation of this domain blocks cleavage by HIV-1 PR, and that other pairwise mutations in this region modulate reverse transcription and proteolysis in strikingly similar degrees. Mutation of Tat Y47G48 to AA also down-regulated Tat-stimulated reverse transcription but had little effect on transactivation or proteolysis by HIV PR, suggesting that Y47 is critical for reverse transcription. We altered the tat gene of the laboratory strain NL4-3 to Y47D and Y47N so that overlapping reading frames were not affected and showed that Y47D greatly diminished virus replication and conveyed a reverse transcription defect. We hypothesize that a novel, cleaved form of Tat is present in the virion and that it requires Y47 for its role in support of efficient reverse transcription.
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Affiliation(s)
- Ann Apolloni
- HIV-1 Research Unit, Sir Albert Sakzewski Virus Research Centre, Royal Children's Hospital, Herston, Australia
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40
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Brigati C, Giacca M, Noonan DM, Albini A. HIV Tat, its TARgets and the control of viral gene expression. FEMS Microbiol Lett 2003; 220:57-65. [PMID: 12644228 DOI: 10.1016/s0378-1097(03)00067-3] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The human immunodeficiency virus (HIV-1) (transactivator of transcription (Tat)) protein is a pleiotropic factor that induces a broad range of biological effects in numerous cell types. At the HIV promoter, Tat is a powerful transactivator of gene expression, which acts by both inducing chromatin remodeling and by recruiting elongation-competent transcriptional complexes onto the viral LTR. Besides these transcriptional activities, Tat is released outside the cells and interacts with different cell membrane-associated receptors. Finally, extracellular Tat can be internalized by cells through an active endocytosis process. Here we discuss some of the molecular mechanisms involved in intracellular and extracellular Tat function.
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MESH Headings
- Acetylation
- Acetyltransferases/metabolism
- Bacteriophage lambda/genetics
- Chromatin/genetics
- Chromatin/metabolism
- Endocytosis
- Extracellular Space/metabolism
- Gene Expression Regulation, Viral
- Gene Products, tat/physiology
- Genes, tat
- HIV Long Terminal Repeat
- HIV-1/genetics
- Histone Acetyltransferases
- Histones/metabolism
- Humans
- Intracellular Fluid/metabolism
- Models, Biological
- Positive Transcriptional Elongation Factor B
- Promoter Regions, Genetic/genetics
- Protein Processing, Post-Translational
- Protein Serine-Threonine Kinases/metabolism
- RNA Polymerase II/metabolism
- RNA, Messenger/biosynthesis
- RNA, Viral/metabolism
- Receptors, Virus/physiology
- Regulatory Sequences, Nucleic Acid
- Saccharomyces cerevisiae Proteins/metabolism
- Transcriptional Activation
- tat Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- Claudio Brigati
- Molecular Oncology Laboratory, National Cancer Research Institute, c/o Centro di Biotecnologie Avanzante, Largo Rosanna Benzi 10, 16132 Genova, Italy
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41
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Abstract
It is becoming clear that the post-translational modification of histone and non-histone proteins by acetylation is part of an important cellular signaling process controlling a wide variety of functions in both the nucleus and the cytoplasm. Recent investigations designate this signaling pathway as one of the primary targets of viral proteins after infection. Indeed, specific viral proteins have acquired the capacity to interact with cellular acetyltransferases (HATs) and deacetylases (HDACs) and consequently to disrupt normal acetylation signaling pathways, thereby affecting viral and cellular gene expression. Here we review the targeting of cellular HATs and HDACs by viral proteins and highlight different strategies adopted by viruses to control cellular acetylation signaling and to accomplish their life cycle.
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Affiliation(s)
- Cécile Caron
- Laboratoire de Biologie Moléculaire et Cellulaire de la Différenciation--Equipe chromatine et expression des gènes, Institut Albert Bonniot, France
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42
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Brès V, Tagami H, Péloponèse JM, Loret E, Jeang KT, Nakatani Y, Emiliani S, Benkirane M, Kiernan RE. Differential acetylation of Tat coordinates its interaction with the co-activators cyclin T1 and PCAF. EMBO J 2002; 21:6811-9. [PMID: 12486002 PMCID: PMC139090 DOI: 10.1093/emboj/cdf669] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The HIV-1 transactivator protein, Tat, is an atypical transcriptional activator that functions through binding, not to DNA, but to a short leader RNA, TAR. Although details of its functional mechanism are still unknown, emerging findings suggest that Tat serves primarily to adapt co-activator complexes such as p300, PCAF and P-TEFb to the HIV-1 long terminal repeat. Hence, an understanding of how Tat interacts with these cofactors is crucial. It has recently been shown that acetylation at a single lysine, residue 50, regulated the association of Tat with PCAF. Here, we report that in the absence of Tat acetylation, PCAF binds to amino acids 20-40 within Tat. Interestingly, acetylation of Tat at Lys28 abrogates Tat-PCAF interaction. Acetylation at Lys50 creates a new site for binding to PCAF and dictates the formation of a ternary complex of Tat-PCAF-P-TEFb. Thus, differential lysine acetylation of Tat coordinates the interactions with its co-activators, cyclin T1 and PCAF. Our results may help in understanding the ordered recruitment of Tat co-activators to the HIV-1 promoter.
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Affiliation(s)
- Vanessa Brès
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Hideaki Tagami
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Jean-Marie Péloponèse
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Erwan Loret
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Kuan-Teh Jeang
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Yoshihiro Nakatani
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Stephane Emiliani
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Monsef Benkirane
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
| | - Rosemary E. Kiernan
- Laboratoire de Virologie Moléculaire et Transfert de Gène, Institut de Génétique Humaine, CNRS UPR1142, Montpellier, Laboratoire d’Ingenierie des Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS UPR 9027, Marseille, Institut Cochin, Departement des Maladies Infectieuses, Paris, France, Laboratory of Molecular Virology, NIAID, NIH, Bethesda, MD and Dana Farber Cancer Research Center, Boston, MA, USA Corresponding author e-mail:
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