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Gatignol A, Duarte M, Daviet L, Chang YN, Jeang KT. Sequential steps in Tat trans-activation of HIV-1 mediated through cellular DNA, RNA, and protein binding factors. Gene Expr 2018; 5:217-28. [PMID: 8723388 PMCID: PMC6138028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The regulation of HIV expression is controlled by the activity of the Long Terminal Repeat (LTR). Trans-activation by the virally encoded Tat protein is one of the main mechanisms of LTR activation. Tat binds to its target, TAR RNA, and cellular proteins that bind the LTR, Tat, or TAR RNA are important components of the trans-activation process. We will review the factors that have been characterized for a possible involvement in this mechanism. Whereas LTR binding proteins consist of Sp1 and TBP, a large number of factors that bind TAR RNA have been isolated. We have previously cloned two of them by RNA probe recognition: TRBP and La. We have shown that the in vitro and in vivo binding of TRBP to TAR RNA correlates with a constant expression of the protein during HIV-1 infection. Several proteins that interact with Tat have mainly positive, but some negative, effects on trans-activation. Genetic studies have defined that human chromosome 12 encodes a protein that will allow trans-activation in rodent cells. The binding and the functional data about these proteins suggest sequential steps for the Tat trans-activation mechanism. Each of these intracellular molecular events could be the target for molecular intervention against the virus.
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MESH Headings
- Amino Acid Sequence
- Base Sequence
- Cloning, Molecular
- DNA, Complementary/genetics
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Gene Products, tat/genetics
- Gene Products, tat/metabolism
- HIV Long Terminal Repeat
- HIV-1/genetics
- HIV-1/metabolism
- HeLa Cells
- Humans
- Models, Biological
- Molecular Sequence Data
- Protein Binding
- RNA, Viral/genetics
- RNA, Viral/metabolism
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Transcriptional Activation
- tat Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- A Gatignol
- Unité 332 INSERM, Institut Cochin de Génétique Moléculaire, Paris, France
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2
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Cavalieri V, Baiamonte E, Lo Iacono M. Non-Primate Lentiviral Vectors and Their Applications in Gene Therapy for Ocular Disorders. Viruses 2018; 10:E316. [PMID: 29890733 PMCID: PMC6024700 DOI: 10.3390/v10060316] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Revised: 06/06/2018] [Accepted: 06/07/2018] [Indexed: 12/18/2022] Open
Abstract
Lentiviruses have a number of molecular features in common, starting with the ability to integrate their genetic material into the genome of non-dividing infected cells. A peculiar property of non-primate lentiviruses consists in their incapability to infect and induce diseases in humans, thus providing the main rationale for deriving biologically safe lentiviral vectors for gene therapy applications. In this review, we first give an overview of non-primate lentiviruses, highlighting their common and distinctive molecular characteristics together with key concepts in the molecular biology of lentiviruses. We next examine the bioengineering strategies leading to the conversion of lentiviruses into recombinant lentiviral vectors, discussing their potential clinical applications in ophthalmological research. Finally, we highlight the invaluable role of animal organisms, including the emerging zebrafish model, in ocular gene therapy based on non-primate lentiviral vectors and in ophthalmology research and vision science in general.
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Affiliation(s)
- Vincenzo Cavalieri
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), University of Palermo, Viale delle Scienze Edificio 16, 90128 Palermo, Italy.
- Advanced Technologies Network (ATeN) Center, University of Palermo, Viale delle Scienze Edificio 18, 90128 Palermo, Italy.
| | - Elena Baiamonte
- Campus of Haematology Franco e Piera Cutino, Villa Sofia-Cervello Hospital, 90146 Palermo, Italy.
| | - Melania Lo Iacono
- Campus of Haematology Franco e Piera Cutino, Villa Sofia-Cervello Hospital, 90146 Palermo, Italy.
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3
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Vanti M, Gallastegui E, Respaldiza I, Rodríguez-Gil A, Gómez-Herreros F, Jimeno-González S, Jordan A, Chávez S. Yeast genetic analysis reveals the involvement of chromatin reassembly factors in repressing HIV-1 basal transcription. PLoS Genet 2009; 5:e1000339. [PMID: 19148280 PMCID: PMC2613532 DOI: 10.1371/journal.pgen.1000339] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Accepted: 12/12/2008] [Indexed: 12/22/2022] Open
Abstract
Rebound of HIV viremia after interruption of anti-retroviral therapy is due to the small population of CD4+ T cells that remain latently infected. HIV-1 transcription is the main process controlling post-integration latency. Regulation of HIV-1 transcription takes place at both initiation and elongation levels. Pausing of RNA polymerase II at the 5' end of HIV-1 transcribed region (5'HIV-TR), which is immediately downstream of the transcription start site, plays an important role in the regulation of viral expression. The activation of HIV-1 transcription correlates with the rearrangement of a positioned nucleosome located at this region. These two facts suggest that the 5'HIV-TR contributes to inhibit basal transcription of those HIV-1 proviruses that remain latently inactive. However, little is known about the cell elements mediating the repressive role of the 5'HIV-TR. We performed a genetic analysis of this phenomenon in Saccharomyces cerevisiae after reconstructing a minimal HIV-1 transcriptional system in this yeast. Unexpectedly, we found that the critical role played by the 5'HIV-TR in maintaining low levels of basal transcription in yeast is mediated by FACT, Spt6, and Chd1, proteins so far associated with chromatin assembly and disassembly during ongoing transcription. We confirmed that this group of factors plays a role in HIV-1 postintegration latency in human cells by depleting the corresponding human orthologs with shRNAs, both in HIV latently infected cell populations and in particular single-integration clones, including a latent clone with a provirus integrated in a highly transcribed gene. Our results indicate that chromatin reassembly factors participate in the establishment of the equilibrium between activation and repression of HIV-1 when it integrates into the human genome, and they open the possibility of considering these factors as therapeutic targets of HIV-1 latency.
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Affiliation(s)
- Manuela Vanti
- Departamento de Genética, Universidad de Sevilla, Seville, Spain
| | - Edurne Gallastegui
- Centre de Regulació Genòmica, Universitat Pompeu Fabra, Barcelona, Spain
| | - Iñaki Respaldiza
- Departamento de Genética, Universidad de Sevilla, Seville, Spain
| | | | | | | | - Albert Jordan
- Centre de Regulació Genòmica, Universitat Pompeu Fabra, Barcelona, Spain
| | - Sebastián Chávez
- Departamento de Genética, Universidad de Sevilla, Seville, Spain
- * E-mail:
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St-Louis MC, Cojocariu M, Archambault D. The molecular biology of bovine immunodeficiency virus: a comparison with other lentiviruses. Anim Health Res Rev 2005; 5:125-43. [PMID: 15984320 DOI: 10.1079/ahr200496] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Bovine immunodeficiency virus (BIV) was first isolated in 1969 from a cow, R-29, with a wasting syndrome. The virus isolated induced the formation of syncytia in cell cultures and was structurally similar to maedi-visna virus. Twenty years later, it was demonstrated that the bovine R-29 isolate was indeed a lentivirus with striking similarity to the human immunodeficiency virus. Like other lentiviruses, BIV has a complex genomic structure characterized by the presence of several regulatory/accessory genes that encode proteins, some of which are involved in the regulation of virus gene expression. This manuscript aims to review biological and, more particularly, molecular aspects of BIV, with emphasis on regulatory/accessory viral genes/proteins, in comparison with those of other lentiviruses.
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Affiliation(s)
- Marie-Claude St-Louis
- University of Québec at Montréal, Department of Biological Sciences, Montréal, Québec, Canada
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5
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Raha T, Cheng SWG, Green MR. HIV-1 Tat stimulates transcription complex assembly through recruitment of TBP in the absence of TAFs. PLoS Biol 2005; 3:e44. [PMID: 15719058 PMCID: PMC546330 DOI: 10.1371/journal.pbio.0030044] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2004] [Accepted: 12/06/2004] [Indexed: 11/19/2022] Open
Abstract
The human immunodeficiency virus type I (HIV-1) transactivator protein Tat is an unusual transcriptional activator that is thought to act solely by promoting RNA polymerase II processivity. Here we study the mechanism of Tat action by analyzing transcription complex (TC) assembly in vivo using chromatin immunoprecipitation assays. We find, unexpectedly, that like typical activators Tat dramatically stimulates TC assembly. Surprisingly, however, the TC formed on the HIV-1 long terminal repeat is atypical and contains TATA-box-binding protein (TBP) but not TBP-associated factors (TAFs). Tat function involves direct interaction with the cellular cofactor positive transcription elongation factor b (P-TEFb). Artificial tethering of P-TEFb subunits to HIV-1 promoter DNA or nascent RNA indicates that P-TEFb is responsible for directing assembly of a TC containing TBP but not TAFs. On the basis of this finding, we identify P-TEFb-dependent cellular promoters that also recruit TBP in the absence of TAFs. Thus, in mammalian cells transcription of protein-coding genes involves alternative TCs that differ by the presence or absence of TAFs.
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Affiliation(s)
- Tamal Raha
- 1Howard Hughes Medical Institute, Programs in Gene Function and Expression and Molecular MedicineUniversity of Massachusetts Medical School, Worcester, MassachusettsUnited States of America
| | - S. W. Grace Cheng
- 1Howard Hughes Medical Institute, Programs in Gene Function and Expression and Molecular MedicineUniversity of Massachusetts Medical School, Worcester, MassachusettsUnited States of America
| | - Michael R Green
- 1Howard Hughes Medical Institute, Programs in Gene Function and Expression and Molecular MedicineUniversity of Massachusetts Medical School, Worcester, MassachusettsUnited States of America
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6
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Ching YP, Chun ACS, Chin KT, Zhang ZQ, Jeang KT, Jin DY. Specific TATAA and bZIP requirements suggest that HTLV-I Tax has transcriptional activity subsequent to the assembly of an initiation complex. Retrovirology 2004; 1:18. [PMID: 15285791 PMCID: PMC509288 DOI: 10.1186/1742-4690-1-18] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2004] [Accepted: 07/30/2004] [Indexed: 11/21/2022] Open
Abstract
Background Human T-cell leukemia virus type I (HTLV-I) Tax protein is a transcriptional regulator of viral and cellular genes. In this study we have examined in detail the determinants for Tax-mediated transcriptional activation. Results Whereas previously the LTR enhancer elements were thought to be the sole Tax-targets, herein, we find that the core HTLV-I TATAA motif also provides specific responsiveness not seen with either the SV40 or the E1b TATAA boxes. When enhancer elements which can mediate Tax-responsiveness were compared, the authentic HTLV-I 21-bp repeats were found to be the most effective. Related bZIP factors such as CREB, ATF4, c-Jun and LZIP are often thought to recognize the 21-bp repeats equivalently. However, amongst bZIP factors, we found that CREB, by far, is preferred by Tax for activation. When LTR transcription was reconstituted by substituting either κB or serum response elements in place of the 21-bp repeats, Tax activated these surrogate motifs using surfaces which are different from that utilized for CREB interaction. Finally, we employed artificial recruitment of TATA-binding protein to the HTLV-I promoter in "bypass" experiments to show for the first time that Tax has transcriptional activity subsequent to the assembly of an initiation complex at the promoter. Conclusions Optimal activation of the HTLV-I LTR by Tax specifically requires the core HTLV-I TATAA promoter, CREB and the 21-bp repeats. In addition, we also provide the first evidence for transcriptional activity of Tax after the recruitment of TATA-binding protein to the promoter.
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Affiliation(s)
- Yick-Pang Ching
- Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong, China
- Department of Pathology, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Abel CS Chun
- Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - King-Tung Chin
- Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Zhi-Qing Zhang
- National Key Laboratory for Molecular Virology, Institute of Virology, 100 Yingxin Street, Beijing 100052, China
| | | | - Dong-Yan Jin
- Laboratory of Molecular Microbiology, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892-0460, USA
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7
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Gatignol A, Jeang KT. Tat as a transcriptional activator and a potential therapeutic target for HIV-1. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2001; 48:209-27. [PMID: 10987092 DOI: 10.1016/s1054-3589(00)48007-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- A Gatignol
- U529 INSERM, Institut Cochin de Génétique Moléculaire, Paris, France
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8
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Daviet L, Bois F, Battisti PL, Gatignol A. Identification of limiting steps for efficient trans-activation of HIV-1 promoter by Tat in Saccharomyces cerevisiae. J Biol Chem 1998; 273:28219-28. [PMID: 9774443 DOI: 10.1074/jbc.273.43.28219] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellular context is an important determinant for the activity of Tat, the trans-activator of human immunodeficiency virus (HIV). We have investigated HIV-1 promoter expression and trans-activation in Saccharomyces cerevisiae to provide clues about the limiting steps for Tat activity in this organism. A minimal 43-nucleotide HIV promoter (HIV43) has the activity of a weak yeast promoter in the presence or absence of various enhancer binding sites (bs), whereas the entire long terminal repeat is not expressed. None of these constructs could be trans-activated by Tat. Fusion proteins Gal4 binding domain (BD)-Tat48 and Gal4BD-Tat72 are active with different efficiencies on various yeast promoters that have Gal4 bs. They have 70 and 50% of Gal4 wild type activity on hybrid HIV promoters fused to Gal4 bs only in the presence of AP1 bs. This study shows that trans-activation of the HIV-1 promoter by Tat occurs in yeast when Tat is targeted to the promoter and a functional enhancer activity is present. Sp1 function and Tat transfer from the RNA to the promoter are two major elements for in vivo trans-activation of HIV-1 that are defective in S. cerevisiae but can be replaced by functional equivalents.
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Affiliation(s)
- L Daviet
- Unité 332, INSERM, Institut Cochin de Génétique Moléculaire, 22, rue Méchain, 75014 Paris, France
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Chun RF, Semmes OJ, Neuveut C, Jeang KT. Modulation of Sp1 phosphorylation by human immunodeficiency virus type 1 Tat. J Virol 1998; 72:2615-29. [PMID: 9525578 PMCID: PMC109697 DOI: 10.1128/jvi.72.4.2615-2629.1998] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We previously reported (K. T. Jeang, R. Chun, N. H. Lin, A. Gatignol, C. G. Glabe, and H. Fan, J. Virol. 67: 6224-6233, 1993) that human immunodeficiency virus type 1 (HIV-1) Tat and Sp1 form a protein-protein complex. Here, we have characterized the physical interaction and a functional consequence of Tat-Sp1 contact. Using in vitro protein chromatography, we mapped the region in Tat that contacts Sp1 to amino acids 30 to 55. We found that in cell-free reactions, Tat augmented double-stranded DNA-dependent protein kinase (DNA-PK)-mediated Sp1 phosphorylation in a contact-dependent manner. Tat mutants that do not bind Sp1 failed to influence phosphorylation of the latter. In complementary experiments, we also found that Tat forms protein-protein contacts with DNA-PK. We confirmed that in HeLa and Jurkat cells, Tat expression indeed increased the intracellular amount of phosphorylated Sp1 in a manner consistent with the results of cell-free assays. Furthermore, using two phosphatase inhibitors and a kinase inhibitor, we demonstrated a modulation of reporter gene expression as a consequence of changes in Sp1 phosphorylation. Taken together, these findings suggest that activity at the HIV-1 promoter is influenced by phosphorylation of Sp1 which is affected by Tat and DNA-PK.
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Affiliation(s)
- R F Chun
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institutes of Allergy and Infectious Diseases, Bethesda, Maryland 20892-0460, USA
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10
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Abstract
Tat of HIV-2 (Tat-2) requires host cellular factors for optimal function. We show that transactivation by Tat-2 of the HIV promoter requires cis-acting binding sites for Sp1 or Sp1 brought to the promoter via a heterologous system. We demonstrate that an activation domain in Tat-2 consists of one of two potential alpha-helices in the amino-terminal region, the cysteine-rich region, and the core region and that this independent activation domain requires cis-acting Sp1-binding sites for function. Tat-2 interacts with Sp1 in in vitro binding assays, and these interactions require basic residues outside of the Tat-2 activation domain. The regions in Sp1 sufficient for functional synergy with Tat are the Sp1 activation domains, while the DNA-binding region is dispensable. Substitution mutations of a glutamine-rich region in one Sp1 activation domain, which eliminate interactions with a TBP-associated factor, also significantly decrease synergy with Tat. Thus, the functional synergy between Tat-2 and Sp1 localizes to domains in each activator that interact with components of the transcription complex. We suggest that these interactions, rather than direct Tat/Sp1 binding, result in highly processive RNA polymerase II complexes and full-length viral transcripts.
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Affiliation(s)
- A S Pagtakhan
- Department of Medicine, Veterans Administration Medical Center, San Francisco, California, USA
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11
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Yang L, Morris GF, Lockyer JM, Lu M, Wang Z, Morris CB. Distinct transcriptional pathways of TAR-dependent and TAR-independent human immunodeficiency virus type-1 transactivation by Tat. Virology 1997; 235:48-64. [PMID: 9300036 DOI: 10.1006/viro.1997.8672] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Tat stimulates HIV-1 gene expression during transcription initiation and elongation. Tat functions primarily through specific interactions with TAR RNA and several putative cellular cofactors to increase the processivity of RNA polymerase II complexes during HIV-1 transcription elongation. Although HIV-1 transactivation by Tat in most cell types requires intact TAR sequences, previous reports demonstrate that Tat transactivates HIV-1 long terminal repeat (LTR)-directed gene expression in several central nervous system-derived astrocytic/glial cell lines in the absence of TAR. Within this study, transient expression assays performed in the astrocytic/glial cell line, U87-MG, confirm that kappa B elements within the HIV-1 LTR mediate TAR-independent transactivation by Tat and demonstrate additionally that distinct amino acid residues within the cysteine-rich activation domain of Tat are required for TAR-independent versus TAR-dependent transactivation. Established U87-MG cell lines expressing a transdominant negative mutant of I kappa B alpha, I kappa B alpha delta N, fail to support TAR-independent transactivation by Tat, suggesting that binding of NF-kappa B to kappa B enhancer elements within the HIV-1 LTR is necessary for Tat-mediated transactivation in the absence of TAR. Ribonucleic acid protection analyses of promoter-proximal and -distal transcripts derived from TAR-deleted and TAR-containing HIV-1 LTR reporter constructs in U87-MG cells indicate that the predominant effect of Tat during TAR-independent transactivation occurs at the lavel of transcription initiation, whereas a prominent elongation effect of Tat is observed in the presence of TAR. These data suggest an alternative regulatory pathway for Tat transactivation in specific cells derived from the central nervous system that is independent of TAR and that requires direct or indirect interaction of Tat with NF-kappa B-binding sites in the HIV-1 LTR.
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Affiliation(s)
- L Yang
- School of Biology, Georgia Institute of Technology, Atlanta 30332, USA
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12
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Pendergrast PS, Hernandez N. RNA-targeted activators, but not DNA-targeted activators, repress the synthesis of short transcripts at the human immunodeficiency virus type 1 long terminal repeat. J Virol 1997; 71:910-7. [PMID: 8995607 PMCID: PMC191138 DOI: 10.1128/jvi.71.2.910-917.1997] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) promoter directs the synthesis of two types of RNA molecules: full-length transcripts, whose synthesis is activated by the viral activator Tat, and short transcripts, whose synthesis is dependent on the inducer of short transcripts (IST), a bipartite DNA element located in large part downstream of the HIV-1 transcriptional start site. In the absence of Tat, short transcripts constitute the large majority of the RNA molecules synthesized from the HIV-1 promoter. In the presence of Tat, synthesis of the short transcripts is repressed and synthesis of the full-length transcripts is activated. Tat is unique among transcriptional activators in acting through an RNA target, the TAR element. However, Tat has been shown to activate transcription from a DNA target when fused to the appropriate DNA binding domain, raising the question of why Tat has been directed to the RNA. Here we have compared the abilities of Tat and other RNA- and DNA-bound activators to stimulate transcription from the HIV-1 promoter. We show that DNA-targeted activators, including DNA-targeted Tat, activate the synthesis of both short and long transcripts, while RNA-targeted Tat and another RNA-targeted activator activate the synthesis of full-length transcripts but specifically repress that of short transcripts. The unique ability of RNA-targeted activators to down-regulate short transcript synthesis suggests that Tat is directed to the RNA specifically for the purpose of repressing short transcripts.
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Affiliation(s)
- P S Pendergrast
- Howard Hughes Medical Institute and Cold Spring Harbor Laboratory, New York 11724, USA
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Panagiotidis CA, Lium EK, Silverstein SJ. Physical and functional interactions between herpes simplex virus immediate-early proteins ICP4 and ICP27. J Virol 1997; 71:1547-57. [PMID: 8995681 PMCID: PMC191212 DOI: 10.1128/jvi.71.2.1547-1557.1997] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The ordered expression of herpes simplex virus type 1 (HSV-1) genes, during the course of a productive infection, requires the action of the virus immediate-early regulatory proteins. Using a protein interaction assay, we demonstrate specific in vitro protein-protein interactions between ICP4 and ICP27, two immediate-early proteins of HSV-1 that are essential for virus replication. We map multiple points of contact between these proteins. Furthermore, by coimmunoprecipitation experiments, we demonstrate the following. (i) ICP4-ICP27 complexes are present in extracts from HSV-1 infected cells. (ii) ICP27 binds preferentially to less modified forms of ICP4, a protein that is extensively modified posttranslationally. We also demonstrate, by performing electrophoretic mobility shift assays and supershifts with monoclonal antibodies to ICP4 or ICP27, that both proteins are present in a DNA-protein complex with a noncanonical ICP4 binding site present in the HSV thymidine kinase (TK) gene. ICP4, in extracts from cells infected with ICP27-deficient viruses, is impaired in its ability to form complexes with the TK site but not with the canonical site from the alpha4 gene. However, ICP4 is able to form complexes with the TK probe, in the absence of ICP27, when overproduced in mammalian cells or expressed in bacteria. These data suggest that the inability of ICP4 from infected cell extracts to bind the TK probe in the absence of ICP27 does not reflect a requirement for the physical presence of ICP27 in the complex. Rather, they imply that ICP27 is likely to modulate the DNA binding activity of ICP4 by affecting its posttranslational modification status. Therefore, we propose that ICP27, in addition to its established role as a posttranscriptional regulator of virus gene expression, may also modulate transcription either through direct or indirect interactions with HSV regulatory regions, or through its ability to modulate the DNA binding activity of ICP4.
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Affiliation(s)
- C A Panagiotidis
- Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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14
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Neuveut C, Jeang KT. Recombinant human immunodeficiency virus type 1 genomes with tat unconstrained by overlapping reading frames reveal residues in Tat important for replication in tissue culture. J Virol 1996; 70:5572-81. [PMID: 8764071 PMCID: PMC190517 DOI: 10.1128/jvi.70.8.5572-5581.1996] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) Tat is essential for virus replication and is a potent trans activator of viral gene expression. Evidence suggests that Tat also influences virus infectivity and cytopathicity. Extensive structure-function studies of Tat in subgenomic settings with point mutagenesis and transient transfection readouts have been performed. These reporter assays have defined certain amino acid residues as being important for trans activation of reporter plasmids. However, they have not directly addressed functions related to virus replication. Here, we have studied Tat structure-function in the setting of replicating viruses. We characterized mutations that emerged in Tat during HIV-1 infections of T lymphocytes. To ensure that the selection pressure for change was directed toward protein function, we constructed HIV-Is in which the Tat reading frame was freed from constraints exerted by overlapping with the reading frames of vpr, rev, and env. When these recombinant viruses were passaged in T cells, 26 novel nucleotide changes in tat were observed from sequencing of 220 independently isolated clones. Recloning of these changes into a pNL4-3 molecular background allowed for the characterization of residues in Tat important for virus replication. Interestingly, many of the changes that affected replication when they were assayed in transient trans activation of plasmid reporters were found to be relatively neutral. We conclude that the structure-function of Tat in virus replication is incompletely reflected by activity measurements based only on subgenomic transient transfections.
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Affiliation(s)
- C Neuveut
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892-0460, USA
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15
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Li XY, Green MR. Intramolecular inhibition of activating transcription factor-2 function by its DNA-binding domain. Genes Dev 1996; 10:517-27. [PMID: 8598283 DOI: 10.1101/gad.10.5.517] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
ATF-2 is a cellular basic region-leucine zipper (bZIP) transcription factor that can mediate diverse transcriptional responses, including activation by the adenovirus Ela protein. ATF-2 contains an activation domain, required for transcriptional activity, but in the absence of an appropriate inducer, full-length ATF-2 is transcriptionally inactive. Here we have investigated the mechanism underlying this regulated inhibition of ATF-2 transcriptional activity. We show that the region of ATF-2 that suppresses the activation region is the bZIP DNA-binding domain and that maximal inhibition requires both the basic region and leucine zipper subdomains. Inhibition is activation domain specific: The ATF-2 bZIP suppresses the ATF-2 and the related Ela activation domains but not acidic- and glutamine-rich activation domains. In vitro protein interaction assays demonstrate that the ATF-2 activation domain and bZIP specifically bind to one another. Finally, we show that bZIP-mediated inhibition can be modulated in a cell-type-specific manner by another sequence element within ATF-2. On the basis of these and other data, we propose that the ATF-2 bZIP and activation domain are engaged in an inhibitory intramolecular interaction and that inducers of ATF-2 disrupt this interaction to activate transcription.
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Affiliation(s)
- X Y Li
- Howard Hughes Medical Institute, University of Massachusetts Medical Center, Worcester, Massachusetts 01605, USA
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16
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Hoffman DW, White SW. NMR analysis of the trans-activation response (TAR) RNA element of equine infectious anemia virus. Nucleic Acids Res 1995; 23:4058-65. [PMID: 7479065 PMCID: PMC307343 DOI: 10.1093/nar/23.20.4058] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Transcription of lentiviral DNA in the host cell is regulated by an interaction between the viral TAR RNA stem-loop and the viral Tat protein. Here we present a model of the three-dimensional structure of the TAR RNA stem-loop of the equine infectious anemia virus (EIAV), derived from two- and three-dimensional NMR data. This 25 nucleotide RNA consists of an A-form helical stem capped by two U-G base pairs and a four-nucleotide loop. Two loop cytidines are stacked into the loop interior and likely form a non-Watson-Crick C-C base-pair. The two nucleotides at the top of the loop, U13 and G14, appear to be excluded from the interior of the loop and solvent exposed. It is significant that now for the EIAV TAR-Tat system, three-dimensional structures are now known for both the RNA and protein components.
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Affiliation(s)
- D W Hoffman
- Department of Chemistry and Biochemistry, University of Texas at Austin 78712, USA
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