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Ruhanya V, Jacobs GB, Paul RH, Joska JA, Seedat S, Nyandoro G, Glashoff RH, Engelbrecht S. HIV-1 subtype C Tat exon-1 amino acid residue 24K is a signature for neurocognitive impairment. J Neurovirol 2022; 28:392-403. [PMID: 35394614 DOI: 10.1007/s13365-022-01073-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 02/11/2022] [Accepted: 03/10/2022] [Indexed: 10/18/2022]
Abstract
Variation and differential selection pressures on Tat genes have been shown to alter the biological function of the protein, resulting in pathological consequences in a number of organs including the brain. We evaluated the impact of genetic variation and selection pressure on 147 HIV-1 subtype C Tat exon 1 sequences from monocyte-depleted peripheral lymphocytes on clinical diagnosis of neurocognitive impairment. Genetic analyses identified two signature amino acid residues, lysine at codon 24 (24K) with a frequency of 43.4% and arginine at codon 29 (29R) with a frequency of 34.0% in individuals with HIV-associated neurocognitive impairment. The analyses also revealed two signature residues, asparagine, 24 N (31.9%), and histidine, 29H (21.3%), in individuals without neurocognitive impairment. Both codons, 24 and 29, were associated with high entropy but only codon 29 was under positive selection. The presence of signature K24 increased by 2.08 times the risk of neurocognitive impairment, 3.15 times higher proviral load, and 69% lower absolute CD4 T-cell count compared to those without the signature. The results support a linkage between HIV-1 C Tat N24K polymorphism, proviral load, immunosuppression, and neurocognitive impairment. The signature may induce more neurotoxic effects, which contributes to establishment and severity of HIV-associated neurocognitive impairment.
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Affiliation(s)
- Vurayai Ruhanya
- Division of Medical Virology, Stellenbosch University, Francie van Zijl Avenue, Cape Town, 8000, South Africa. .,Department of Medical Microbiology, Harare, Zimbabwe.
| | - Graeme Brendon Jacobs
- Division of Medical Virology, Stellenbosch University, Francie van Zijl Avenue, Cape Town, 8000, South Africa
| | - Robert H Paul
- Department of Psychology and Behavioral Neuroscience, University of Missouri-St Louis, University Boulevard, St Louis, USA
| | - John A Joska
- MRC Unit of Anxiety & Stress Disorders, Department of Psychiatry & Mental Health, University of Cape Town, Cape Town, South Africa
| | - Soraya Seedat
- MRC Unit of Anxiety & Stress Disorders, Department of Psychiatry, University of Stellenbosch, Cape Town, South Africa
| | | | - Richard H Glashoff
- Division of Medical Microbiology, Stellenbosch University, Cape Town, South Africa.,National Health Laboratory Service (NHLS), Tygerberg Business Unit, Cape Town, South Africa
| | - Susan Engelbrecht
- Division of Medical Virology, Stellenbosch University, Francie van Zijl Avenue, Cape Town, 8000, South Africa.,National Health Laboratory Service (NHLS), Tygerberg Business Unit, Cape Town, South Africa
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2
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Sonti S, Sharma AL, Tyagi M. HIV-1 persistence in the CNS: Mechanisms of latency, pathogenesis and an update on eradication strategies. Virus Res 2021; 303:198523. [PMID: 34314771 DOI: 10.1016/j.virusres.2021.198523] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 07/14/2021] [Accepted: 07/17/2021] [Indexed: 12/20/2022]
Abstract
Despite four decades of research into the human immunodeficiency virus (HIV-1), a successful strategy to eradicate the virus post-infection is lacking. The major reason for this is the persistence of the virus in certain anatomical reservoirs where it can become latent and remain quiescent for as long as the cellular reservoir is alive. The Central Nervous System (CNS), in particular, is an intriguing anatomical compartment that is tightly regulated by the blood-brain barrier. Targeting the CNS viral reservoir is a major challenge owing to the decreased permeability of drugs into the CNS and the cellular microenvironment that facilitates the compartmentalization and evolution of the virus. Therefore, despite effective antiretroviral (ARV) treatment, virus persists in the CNS, and leads to neurological and neurocognitive deficits. To date, viral eradication strategies fail to eliminate the virus from the CNS. To facilitate the improvement of the existing elimination strategies, as well as the development of potential therapeutic targets, the aim of this review is to provide an in-depth understanding of HIV latency in CNS and the onset of HIV-1 associated neurological disorders.
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Affiliation(s)
- Shilpa Sonti
- Center for Translational Medicine, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA
| | | | - Mudit Tyagi
- Center for Translational Medicine, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.
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3
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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: 38] [Impact Index Per Article: 7.6] [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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4
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Abstract
BACKGROUND The viral transactivator Tat protein is a key modulator of HIV-1 replication, as it regulates transcriptional elongation from the integrated proviral genome. Tat recruits the human transcription elongation factor b, and other host proteins, such as the super elongation complex, to activate the cellular RNA polymerase II, normally stalled shortly after transcription initiation at the HIV promoter. By means of a complex set of interactions with host cellular factors, Tat determines the fate of viral activity within the infected cell. The virus will either actively replicate to promote dissemination in blood and tissues, or become dormant mostly in memory CD4+ T cells, as part of a small but long-living latent reservoir, the main obstacle for HIV eradication. OBJECTIVE In this review, we summarize recent advances in the understanding of the multi-step mechanism that regulates Tat-mediated HIV-1 transcription and RNA polymerase II release, to promote viral transcription elongation. Early events of the human transcription elongation factor b release from the inhibitory 7SK small nuclear ribonucleoprotein complex and its recruitment to the HIV promoter will be discussed. Specific roles of the super elongation complex subunits during transcription elongation, and insight on recently identified cellular factors and mechanisms regulating HIV latency will be detailed. CONCLUSION Understanding the complexity of HIV transcriptional regulation by host factors may open the door for development of novel strategies to eradicate the resilient latent reservoir.
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Affiliation(s)
- Guillaume Mousseau
- The Scripps Research Institute, Department of Immunology and Microbiology, 130 Scripps Way, Jupiter, FL 33458. United States
| | - Susana T Valente
- The Scripps Research Institute, Department of Immunology and Microbiology, 130 Scripps Way, Jupiter, FL 33458. United States
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5
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Abstract
Antiretroviral therapy (ART) inhibits HIV-1 replication, but the virus persists in latently infected resting memory CD4+ T cells susceptible to viral reactivation. The virus-encoded early gene product Tat activates transcription of the viral genome and promotes exponential viral production. Here we show that the Tat inhibitor didehydro-cortistatin A (dCA), unlike other antiretrovirals, reduces residual levels of viral transcription in several models of HIV latency, breaks the Tat-mediated transcriptional feedback loop, and establishes a nearly permanent state of latency, which greatly diminishes the capacity for virus reactivation. Importantly, treatment with dCA induces inactivation of viral transcription even after its removal, suggesting that the HIV promoter is epigenetically repressed. Critically, dCA inhibits viral reactivation upon CD3/CD28 or prostratin stimulation of latently infected CD4+ T cells from HIV-infected subjects receiving suppressive ART. Our results suggest that inclusion of a Tat inhibitor in current ART regimens may contribute to a functional HIV-1 cure by reducing low-level viremia and preventing viral reactivation from latent reservoirs. Antiretroviral therapy (ART) reduces HIV-1 replication to very low levels, but the virus persists in latently infected memory CD4+ T cells, representing a long-lasting source of resurgent virus upon ART interruption. Based on the mode of action of didehydro-cortistatin A (dCA), a Tat-dependent transcription inhibitor, our work highlights an alternative approach to current HIV-1 eradication strategies to decrease the latent reservoir. In our model, dCA blocks the Tat feedback loop initiated after low-level basal reactivation, blocking transcriptional elongation and hence viral production from latently infected cells. Therefore, dCA combined with ART would be aimed at delaying or halting ongoing viral replication, reactivation, and replenishment of the latent viral reservoir. Thus, the latent pool of cells in an infected individual would be stabilized, and death of the long-lived infected memory T cells would result in a continuous decay of this pool over time, possibly culminating in the long-awaited sterilizing cure.
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Abstract
The establishment of HIV-1 latency can result from limiting levels of transcription initiation or elongation factors, restrictive chromatin modifications, transcriptional interference, and insufficient Tat activity. Since the viral protein Tat can counteract many of these factors, we hypothesized that the presence of exogenous Tat during infection might inhibit the establishment of latency. This was explored using a Jurkat model of latency establishment and reactivation. PCR and reverse transcriptase PCR (RT-PCR) confirmed the latent state in this model and showed evidence of transcriptional interference. To address our hypothesis, cells undergoing infection were first exposed to either purified recombinant Tat or a transactivation-negative mutant. Only the former resulted in a modest inhibition of the establishment of latency. Next, Jurkat cells stably expressing intracellular Tat were used in our latency model to avoid limitations of Tat delivery. Experiments confirmed that intracellular Tat expression did not affect the susceptibility of these cells to viral infection. Eight weeks after infection, Jurkat cells expressing Tat harbored up to 1,700-fold fewer (P < 0.01) latent viruses than Jurkat cells that did not express Tat. Additionally, Tat delivered by a second virus was sufficient to reactivate most of the latent population. Our results suggest that inhibition of the establishment of latent infection is theoretically possible. In a hypothetical scenario of therapy that induces viral gene expression during acute infection, activation of viruses which would otherwise have entered latency could occur while concurrent highly active antiretroviral therapy (HAART) would prevent further viral spread, potentially decreasing the size of the established latent reservoir.
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Hoque M, Shamanna RA, Guan D, Pe'ery T, Mathews MB. HIV-1 replication and latency are regulated by translational control of cyclin T1. J Mol Biol 2011; 410:917-32. [PMID: 21763496 DOI: 10.1016/j.jmb.2011.03.060] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Revised: 03/24/2011] [Accepted: 03/25/2011] [Indexed: 11/29/2022]
Abstract
Human immunodeficiency virus (HIV) exploits cellular proteins during its replicative cycle and latent infection. The positive transcription elongation factor b (P-TEFb) is a key cellular transcription factor critical for these viral processes and is a drug target. During viral replication, P-TEFb is recruited via interactions of its cyclin T1 subunit with the HIV Tat (transactivator of transcription) protein and TAR (transactivation response) element. Through RNA silencing and over-expression experiments, we discovered that nuclear factor 90 (NF90), a cellular RNA binding protein, regulates P-TEFb expression. NF90 depletion reduced cyclin T1 protein levels by inhibiting translation initiation. Regulation was mediated by the 3' untranslated region of cyclin T1 mRNA independently of microRNAs. Cyclin T1 induction is involved in the escape of HIV-1 from latency. We show that the activation of viral replication by phorbol ester in latently infected monocytic cells requires the posttranscriptional induction of NF90 and cyclin T1, implicating NF90 in protein kinase C signaling pathways. This investigation reveals a novel mechanism of cyclin T1 regulation and establishes NF90 as a regulator of HIV-1 replication during both productive infection and induction from latency.
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Affiliation(s)
- Mainul Hoque
- Department of Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, PO Box 1709, Newark, NJ 07101-1709, USA
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8
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Recovery of replication-competent residual HIV-1 from plasma of a patient receiving prolonged, suppressive highly active antiretroviral therapy. J Virol 2010; 84:8348-52. [PMID: 20519388 DOI: 10.1128/jvi.00362-10] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The clinical significance of persistent residual viremia in patients on prolonged highly active antiretroviral therapy (HAART) is not clear. Moreover, it remains to be demonstrated whether residual viremia consists of viruses capable of spreading infection in vivo upon termination of therapy. Using residual viral RNAs (vRNAs) isolated from a HAART-treated patient's plasma, we cloned full-length viral genomes and found that most of them could produce infectious, replication-competent HIVs when transfected into TZM-bl cells, suggesting that residual viruses produced in the absence of therapy can initiate fresh cycles of infection and spread in host cells. The data further indicate that residual viremia may pose a major concern with regard to the emergence of drug-resistant HIVs during periods of low adherence to therapy.
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Hoque M, Mathews MB, Pe'ery T. Progranulin (granulin/epithelin precursor) and its constituent granulin repeats repress transcription from cellular promoters. J Cell Physiol 2010; 223:224-33. [PMID: 20054825 DOI: 10.1002/jcp.22031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Progranulin (also known as granulin/epithelin precursor, GEP) is composed of seven granulin/epithelin repeats (granulins) and functions both as a full-length protein and as individual granulins. It is a secretory protein but a substantial amount of GEP is found inside cells, some in complexes with positive transcription elongation factor b (P-TEFb). GEP and certain granulins interact with the cyclin T1 subunit of P-TEFb, and with its HIV-1 Tat co-factor, leading to repression of transcription from the HIV promoter. We show that GEP lacking the signal peptide (GEPspm) remains inside cells and, like wild-type GEP, interacts with cyclin T1 and Tat. GEPspm represses transcription from the HIV-1 promoter at the RNA level. Granulins that bind cyclin T1 are phosphorylated by P-TEFb in vivo and in vitro on serine residues. GEPspm and those granulins that interact with cyclin T1 also inhibit transcription from cellular cad and c-myc promoters, which are highly dependent on P-TEFb, but not from the PCNA promoter. In addition, GEPspm and granulins repress transcriptional activation by VP16 or c-Myc, proteins that bind and recruit P-TEFb to responsive promoters. These data suggest that intracellular GEP is a promoter-specific transcriptional repressor that modulates the function of cellular and viral transcription factors.
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Affiliation(s)
- Mainul Hoque
- Department of Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, Newark, New Jersey, USA
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10
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Epigenetic silencing of human immunodeficiency virus (HIV) transcription by formation of restrictive chromatin structures at the viral long terminal repeat drives the progressive entry of HIV into latency. J Virol 2008; 82:12291-303. [PMID: 18829756 DOI: 10.1128/jvi.01383-08] [Citation(s) in RCA: 244] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The molecular mechanisms utilized by human immunodeficiency virus (HIV) to enter latency are poorly understood. Following the infection of Jurkat T cells with lentiviral vectors that express Tat in cis, gene expression is progressively silenced. Silencing is greatly enhanced when the lentiviral vectors carry an attenuated Tat gene with the H13L mutation. Individual clones of lentivirus-infected cells showed a wide range of shutdown rates, with the majority showing a 50% silencing frequency between 30 to 80 days. The silenced clones characteristically contained a small fraction (0 to 15%) of activated cells that continued to express d2EGFP. When d2EGFP(+) and d2EGFP(-) cell populations were isolated from the shutdown clones, they quickly reverted to the original distribution of inactive and active cells, suggesting that the d2EGFP(+) cells arise from stochastic fluctuations in gene expression. The detailed analysis of transcription initiation and elongation using chromatin immunoprecipitation (ChIP) assays confirms that Tat levels are restricted in the latently infected cells but gradually rise during proviral reactivation. ChIP assays using clones of latently infected cells demonstrate that the latent proviruses carry high levels of deacetylated histones and trimethylated histones. In contrast, the cellular genes IkappaB alpha and GAPDH had high levels of acetylated histones and no trimethylated histones. The levels of trimethylated histone H3 and HP1-alpha associated with HIV proviruses fell rapidly after tumor necrosis factor alpha activation. The progressive shutdown of HIV transcription following infection suggests that epigenetic mechanisms targeting chromatin structures selectively restrict HIV transcription initiation. This decreases Tat production below the levels that are required to sustain HIV gene expression.
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11
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Wang Q, Young TM, Mathews MB, Pe’ery T. Developmental regulators containing the I-mfa domain interact with T cyclins and Tat and modulate transcription. J Mol Biol 2007; 367:630-46. [PMID: 17289077 PMCID: PMC1868487 DOI: 10.1016/j.jmb.2007.01.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2006] [Revised: 12/21/2006] [Accepted: 01/04/2007] [Indexed: 11/28/2022]
Abstract
Positive transcription elongation factor b (P-TEFb) complexes, composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1 or T2, are engaged by many cellular transcription regulators that activate or inhibit transcription from specific promoters. The related I-mfa (inhibitor of MyoD family a) and HIC (human I-mfa-domain-containing) proteins function in myogenic differentiation and embryonic development by participating in the Wnt signaling pathway. We report that I-mfa is a novel regulator of P-TEFb. Both HIC and I-mfa interact through their homologous I-mfa domains with cyclin T1 and T2 at two binding sites. One site is the regulatory histidine-rich domain that interacts with CDK9 substrates including RNA polymerase II. The second site contains a lysine and arginine-rich motif that is highly conserved between the two T cyclins. This site overlaps and includes the previously identified Tat/TAR recognition motif of cyclin T1 required for activation of human immunodeficiency virus type 1 (HIV-1) transcription. HIC and I-mfa can serve as substrates for P-TEFb. Their I-mfa domains also bind the activation domain of HIV-1 Tat and inhibit Tat- and P-TEFb-dependent transcription from the HIV-1 promoter. This transcriptional repression is cell-type specific and can operate via Tat and cyclin T1. Genomic and sequence comparisons indicate that the I-mf and HIC genes, as well as flanking genes, diverged from a duplicated chromosomal region. Our findings link I-mfa and HIC to viral replication, and suggest that P-TEFb is modulated in the Wnt signaling pathway.
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Affiliation(s)
- Qi Wang
- Department of Biochemistry and Molecular Biology, New Jersey Medical School
- Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 185 South Orange Ave., Newark, NJ 07103-2714
| | - Tara M. Young
- Department of Biochemistry and Molecular Biology, New Jersey Medical School
| | - Michael B. Mathews
- Department of Biochemistry and Molecular Biology, New Jersey Medical School
- Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 185 South Orange Ave., Newark, NJ 07103-2714
| | - Tsafi Pe’ery
- Department of Biochemistry and Molecular Biology, New Jersey Medical School
- Department of Medicine, New Jersey Medical School
- Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 185 South Orange Ave., Newark, NJ 07103-2714
- *Corresponding author: Ph:(973) 972-8763; Fax:(973) 972-5594 E-mail:
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12
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Sahu GK, Lee K, Ji J, Braciale V, Baron S, Cloyd MW. A novel in vitro system to generate and study latently HIV-infected long-lived normal CD4+ T-lymphocytes. Virology 2006; 355:127-37. [PMID: 16919704 DOI: 10.1016/j.virol.2006.07.020] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2006] [Revised: 03/13/2006] [Accepted: 07/11/2006] [Indexed: 11/30/2022]
Abstract
Studies of mechanisms of HIV-latency and its reactivation in long-lived resting CD4+ T-lymphocytes in patients have been limited due to the very low frequency of these cells ( approximately 1-10 cells per 10(6) CD4+ T-cells). To circumvent this obstacle, an in vitro culture system for post-activation long-term survival of normal CD4+ T-cells in a quiescent (non-cycling) state was developed and used to generate latently infected, long-lived quiescent CD4+ T-cells from HIV-infected, activated normal CD4+ T-lymphocytes. This yielded a frequency of approximately 5x10(4) latently infected cells per 10(6) cells in culture, which is approximately 10(3)- to 10(4)-fold higher than that available from patients. Moreover, 5-10% of long-term surviving non-cycling T-cells were found to make infectious HIV continuously at low levels, showing that HIV production from infected T-cells does not require full cellular activation. This model system should facilitate studies of long-lived, latently infected and persistently HIV-producing quiescent normal CD4+ T-lymphocytes.
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Affiliation(s)
- Gautam K Sahu
- Department of Microbiology and Immunology, The University of Texas Medical Branch, 301 University Blvd, BSB #3.132, Galveston, TX 77555, USA
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13
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Hoque M, Tian B, Mathews MB, Pe'ery T. Granulin and granulin repeats interact with the Tat.P-TEFb complex and inhibit Tat transactivation. J Biol Chem 2005; 280:13648-57. [PMID: 15653695 DOI: 10.1074/jbc.m409575200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cellular positive transcription elongation factor b (P-TEFb), containing cyclin T1 and cyclin-dependent kinase 9 (CDK9), interacts with the human immunodeficiency virus, type 1 (HIV-1) regulatory protein Tat to enable viral transcription and replication. Cyclin T1 is an unusually long cyclin and is engaged by cellular regulatory proteins. Previous studies showed that the granulin/epithelin precursor (GEP) binds the histidine-rich region of cyclin T1 and inhibits P-TEFb function. GEP is composed of repeats that vary in sequence and properties. GEP also binds directly to Tat. Here we show that GEP and some of its constituent granulin repeats can inhibit HIV-1 transcription via Tat without directly binding to cyclin T1. The interactions of granulins with Tat and cyclin T1 differ with respect to their binding sites and divalent cation requirements, and we identified granulin repeats that bind differentially to Tat and cyclin T1. Granulins DE and E bind Tat but do not interact directly with cyclin T1. These granulins are present in complexes with Tat and P-TEFb in which Tat forms a bridge between the cellular proteins. Granulins DE and E repress transcription from the HIV-1 LTR and gene expression from the viral genome, raising the possibility of developing granulin-based inhibitors of viral infection.
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Affiliation(s)
- Mainul Hoque
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103-2714, USA
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14
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Young TM, Wang Q, Pe'ery T, Mathews MB. The human I-mfa domain-containing protein, HIC, interacts with cyclin T1 and modulates P-TEFb-dependent transcription. Mol Cell Biol 2003; 23:6373-84. [PMID: 12944466 PMCID: PMC193714 DOI: 10.1128/mcb.23.18.6373-6384.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Positive transcription elongation factor b (P-TEFb) hyperphosphorylates the carboxy-terminal domain of RNA polymerase II, permitting productive transcriptional elongation. The cyclin T1 subunit of P-TEFb engages cellular transcription factors as well as the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. To identify potential P-TEFb regulators, we conducted a yeast two-hybrid screen with cyclin T1 as bait. Among the proteins isolated was the human I-mfa domain-containing protein (HIC). HIC has been reported to modulate expression from both cellular and viral promoters via its C-terminal cysteine-rich domain, which is similar to the inhibitor of MyoD family a (I-mfa) protein. We show that HIC binds cyclin T1 in yeast and mammalian cells and that it interacts with intact P-TEFb in mammalian cell extracts. The interaction involves the I-mfa domain of HIC and the regulatory histidine-rich region of cyclin T1. HIC also binds Tat via its I-mfa domain, although the sequence requirements are different. HIC colocalizes with cyclin T1 in nuclear speckle regions and with Tat in the nucleolus. Expression of the HIC cDNA modulates Tat transactivation of the HIV-1 long terminal repeat (LTR) in a cell type-specific fashion. It is mildly inhibitory in CEM cells but stimulates gene expression in HeLa, COS, and NIH 3T3 cells. The isolated I-mfa domain acts as a dominant negative inhibitor. Activation of the HIV-1 LTR by HIC in NIH 3T3 cells occurs at the RNA level and is mediated by direct interactions with P-TEFb.
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Affiliation(s)
- Tara M Young
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07013-2714, USA
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15
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Reza SM, Shen LM, Mukhopadhyay R, Rosetti M, Pe'ery T, Mathews MB. A naturally occurring substitution in human immunodeficiency virus Tat increases expression of the viral genome. J Virol 2003; 77:8602-6. [PMID: 12857933 PMCID: PMC165250 DOI: 10.1128/jvi.77.15.8602-8606.2003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A natural amino acid substitution in the human immunodeficiency virus type 1 (HIV-1) transcriptional activator Tat increases its activity and compensates for deleterious mutations elsewhere in the Tat protein. Substitution of asparagine for threonine 23 increases Tat transactivation of the HIV-1 promoter and the binding of Tat to the cellular kinase positive transcription elongation factor b (P-TEFb). Of nine other position 23 mutations tested, only the serine substitution retained wild-type activity. Correspondingly, asparagine is the most frequent amino acid at this position in HIV-1 isolates, followed by threonine and serine. Asparagine is prevalent in Tat proteins of viruses in clades A, C, and D, which are major etiologic agents of AIDS. We suggest that selection for asparagine in position 23 confers an advantage to the virus, since it can compensate for deleterious mutations in Tat. It may also support the replication of otherwise less fit drug-resistant viruses and permit the emergence of virulent strains.
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Affiliation(s)
- Syed M Reza
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 01701, USA
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Hoque M, Young TM, Lee CG, Serrero G, Mathews MB, Pe'ery T. The growth factor granulin interacts with cyclin T1 and modulates P-TEFb-dependent transcription. Mol Cell Biol 2003; 23:1688-702. [PMID: 12588988 PMCID: PMC151712 DOI: 10.1128/mcb.23.5.1688-1702.2003] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.
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Affiliation(s)
- Mainul Hoque
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07013-1709, USA
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