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Taube R, Peterlin BM. Lost in transcription: molecular mechanisms that control HIV latency. Viruses 2013; 5:902-27. [PMID: 23518577 PMCID: PMC3705304 DOI: 10.3390/v5030902] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 03/15/2013] [Accepted: 03/18/2013] [Indexed: 02/06/2023] Open
Abstract
Highly active antiretroviral therapy (HAART) has limited the replication and spread of the human immunodeficiency virus (HIV). However, despite treatment, HIV infection persists in latently infected reservoirs, and once therapy is interrupted, viral replication rebounds quickly. Extensive efforts are being directed at eliminating these cell reservoirs. This feat can be achieved by reactivating latent HIV while administering drugs that prevent new rounds of infection and allow the immune system to clear the virus. However, current approaches to HIV eradication have not been effective. Moreover, as HIV latency is multifactorial, the significance of each of its molecular mechanisms is still under debate. Among these, transcriptional repression as a result of reduced levels and activity of the positive transcription elongation factor b (P-TEFb: CDK9/cyclin T) plays a significant role. Therefore, increasing levels of P-TEFb expression and activity is an excellent strategy to stimulate viral gene expression. This review summarizes the multiple steps that cause HIV to enter into latency. It positions the interplay between transcriptionally active and inactive host transcriptional activators and their viral partner Tat as valid targets for the development of new strategies to reactivate latent viral gene expression and eradicate HIV.
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Affiliation(s)
- Ran Taube
- The Shraga Segal Department of Microbiology Immunology and Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105, Israel
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +972-8-6479858; Fax: +972-8-6479953
| | - Boris Matija Peterlin
- Department of Medicine, Microbiology and Immunology, Rosalind Russell Medical Research Center, University of California at San Francisco, San Francisco, CA 94143, USA; E-Mail:
- Department of Virology, Haartman Institute, University of Helsinki, 00014 Helsinki, Finland
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Ying H, Zhang Y, Zhou X, Qu X, Wang P, Liu S, Lu D, Zhu H. Selective histonedeacetylase inhibitor M344 intervenes in HIV-1 latency through increasing histone acetylation and activation of NF-kappaB. PLoS One 2012; 7:e48832. [PMID: 23166597 PMCID: PMC3499534 DOI: 10.1371/journal.pone.0048832] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Accepted: 10/05/2012] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Histone deacetylase (HDAC) inhibitors present an exciting new approach to activate HIV production from latently infected cells to potentially enhance elimination of these cells and achieve a cure. M344, a novel HDAC inhibitor, shows robust activity in a variety of cancer cells and relatively low toxicity compared to trichostatin A (TSA). However, little is known about the effects and action mechanism of M344 in inducing HIV expression in latently infected cells. METHODOLOGY/PRINCIPAL FINDINGS Using the Jurkat T cell model of HIV latency, we demonstrate that M344 effectively reactivates HIV-1 gene expression in latently infected cells. Moreover, M344-mediated activation of the latent HIV LTR can be strongly inhibited by a NF-κB inhibitor aspirin. We further show that M344 acts by increasing the acetylation of histone H3 and histone H4 at the nucleosome 1 (nuc-1) site of the HIV-1 long terminal repeat (LTR) and by inducing NF-κB p65 nuclear translocation and direct RelA DNA binding at the nuc-1 region of the HIV-1 LTR. We also found that M344 synergized with prostratin to activate the HIV-1 LTR promoter in latently infected cells. CONCLUSIONS/SIGNIFICANCE These results suggest the potential of M344 in anti-latency therapies and an important role for histone modifications and NF-κB transcription factors in regulating HIV-1 LTR gene expression.
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Affiliation(s)
- Hao Ying
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Yuhao Zhang
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Xin Zhou
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Xiying Qu
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Pengfei Wang
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Sijie Liu
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Daru Lu
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
| | - Huanzhang Zhu
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, China
- * E-mail:
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53
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Ramakrishnan R, Chiang K, Liu H, Budhiraja S, Donahue H, Rice AP. Making a Short Story Long: Regulation of P-TEFb and HIV-1 Transcriptional Elongation in CD4+ T Lymphocytes and Macrophages. BIOLOGY 2012; 1:94-115. [PMID: 24832049 PMCID: PMC4011037 DOI: 10.3390/biology1010094] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 06/07/2012] [Accepted: 06/11/2012] [Indexed: 12/22/2022]
Abstract
Productive transcription of the integrated HIV-1 provirus is restricted by cellular factors that inhibit RNA polymerase II elongation. The viral Tat protein overcomes this by recruiting a general elongation factor, P-TEFb, to the TAR RNA element that forms at the 5' end of nascent viral transcripts. P-TEFb exists in multiple complexes in cells, and its core consists of a kinase, Cdk9, and a regulatory subunit, either Cyclin T1 or Cyclin T2. Tat binds directly to Cyclin T1 and thereby targets the Cyclin T1/P-TEFb complex that phosphorylates the CTD of RNA polymerase II and the negative factors that inhibit elongation, resulting in efficient transcriptional elongation. P-TEFb is tightly regulated in cells infected by HIV-1-CD4+ T lymphocytes and monocytes/macrophages. A number of mechanisms have been identified that inhibit P-TEFb in resting CD4+ T lymphocytes and monocytes, including miRNAs that repress Cyclin T1 protein expression and dephosphorylation of residue Thr186 in the Cdk9 T-loop. These repressive mechanisms are overcome upon T cell activation and macrophage differentiation when the permissivity for HIV-1 replication is greatly increased. This review will summarize what is currently known about mechanisms that regulate P-TEFb and how this regulation impacts HIV-1 replication and latency.
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Affiliation(s)
- Rajesh Ramakrishnan
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Karen Chiang
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Hongbing Liu
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Sona Budhiraja
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Hart Donahue
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Andrew P Rice
- Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
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54
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Cellular GCN5 is a novel regulator of human adenovirus E1A-conserved region 3 transactivation. J Virol 2012; 86:8198-209. [PMID: 22623781 DOI: 10.1128/jvi.00289-12] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The largest isoform of adenovirus early region 1A (E1A) contains a unique region termed conserved region 3 (CR3). This region activates viral gene expression by recruiting cellular transcription machinery to the early viral promoters. Recent studies have suggested that there is an optimal level of E1A-dependent transactivation required by human adenovirus (hAd) during infection and that this may be achieved via functional cross talk between the N termini of E1A and CR3. The N terminus of E1A binds GCN5, a cellular lysine acetyltransferase (KAT). We have identified a second independent interaction of E1A with GCN5 that is mediated by CR3, which requires residues 178 to 188 in hAd5 E1A. GCN5 was recruited to the viral genome during infection in an E1A-dependent manner, and this required both GCN5 interaction sites on E1A. Ectopic expression of GCN5 repressed transactivation by both E1A CR3 and full-length E1A. In contrast, RNA interference (RNAi) depletion of GCN5 or treatment with the KAT inhibitor cyclopentylidene-[4-(4'-chlorophenyl)thiazol-2-yl]hydrazone (CPTH2) resulted in increased E1A CR3 transactivation. Moreover, activation of the adenovirus E4 promoter by E1A was increased during infection of homozygous GCN5 KAT-defective (hat/hat) mouse embryonic fibroblasts (MEFs) compared to wild-type control MEFs. Enhanced histone H3 K9/K14 acetylation at the viral E4 promoter required the newly identified binding site for GCN5 within CR3 and correlated with repression and reduced occupancy by phosphorylated RNA polymerase II. Treatment with CPTH2 during infection also reduced virus yield. These data identify GCN5 as a new negative regulator of transactivation by E1A and suggest that its KAT activity is required for optimal virus replication.
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55
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Abstract
The introduction of highly active antiretroviral therapy (HAART) has been an important breakthrough in the treatment of HIV-1 infection and has also a powerful tool to upset the equilibrium of viral production and HIV-1 pathogenesis. Despite the advent of potent combinations of this therapy, the long-lived HIV-1 reservoirs like cells from monocyte-macrophage lineage and resting memory CD4+ T cells which are established early during primary infection constitute a major obstacle to virus eradication. Further HAART interruption leads to immediate rebound viremia from latent reservoirs. This paper focuses on the essentials of the molecular mechanisms for the establishment of HIV-1 latency with special concern to present and future possible treatment strategies to completely purge and target viral persistence in the reservoirs.
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56
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Ramakrishnan R, Rice AP. Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway. J Cell Physiol 2012; 227:609-17. [PMID: 21448926 DOI: 10.1002/jcp.22760] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Eukaryotic RNA polymerase II transcriptional elongation is a tightly regulated process and is dependent upon positive transcription elongation factor-b (P-TEFb). The core P-TEFb complex is composed of Cdk9 and Cyclin T and is essential for the expression of most protein coding genes. Cdk9 kinase function is dependent upon phosphorylation of Thr186 in its T-loop. In this study, we examined kinases and signaling pathways that influence Cdk9 T-loop phosphorylation. Using an RNAi screen in HeLa cells, we found that Cdk9 T-loop phosphorylation is regulated by Ca(2+)/calmodulin-dependent kinase 1D (CaMK1D). Using small molecules inhibitors in HeLa cells and primary CD4(+) T lymphocytes, we found that the Ca(2+) signaling pathway is required for Cdk9 T-loop phosphorylation. Inhibition of Ca(2+) signaling led to dephosphorylation of Thr186 on Cdk9. In reporter plasmid assays, inhibition of the Ca(2+) signaling pathway repressed the PCNA promoter and HIV-1 Tat transactivation of the HIV-1 LTR, but not HTLV-1 Tax transactivation of the HTLV-1 LTR, suggesting that perturbation of the Ca(2+) pathway and reduction of Cdk9 T-loop phosphorylation inhibits transcription units that have a rigorous requirement for P-TEFb function.
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Affiliation(s)
- Rajesh Ramakrishnan
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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57
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Kovacic P. Novel electrostatic mechanism for mode of action by N-acetylated proteins: cell signaling and phosphorylation. J Recept Signal Transduct Res 2011; 31:193-8. [PMID: 21619447 DOI: 10.3109/10799893.2011.577784] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Although extensive literature exists for N-acetylated proteins, scant knowledge is available concerning resultant mode of action. This review presents a novel mechanism based on electrostatics and cell signaling. There is substantial increase in the amide dipole and electrostatic field (EF) in contrast with the primary amino of the lysine precursor. The EF might serve as a bridge in electron transfer and cell signaling or energetics may play a role. The relationship between N-acetylation and phosphorylation is addressed. EFs may be important in the case of phosphates. Involvement of cell signaling is addressed including mechanistic aspects. As is the case for many aspects of bioaction, an integrated approach involving electrochemistry and cell signaling seems reasonable.
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Affiliation(s)
- Peter Kovacic
- Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA 92182, USA.
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58
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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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59
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Acetylation of a conserved lysine residue in the ATP binding pocket of p38 augments its kinase activity during hypertrophy of cardiomyocytes. Mol Cell Biol 2011; 31:2349-63. [PMID: 21444723 DOI: 10.1128/mcb.01205-10] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Like phosphorylation, acetylation of lysine residues within a protein is considered a biologically relevant modification that controls the activity of target proteins. During stress of cells, massive protein acetylation takes place. Here, we show that p38 mitogen-activated protein kinase (MAPK), which controls many biological functions during stress, is reversibly acetylated by PCAF/p300 and HDAC3. We identified two acetylated lysine residues, K152 and K53, located in the substrate binding domain and in the ATP-binding pocket of p38, respectively. Acetylation of lysine 53 enhanced the activity of p38 by increasing its affinity for ATP binding. The enhanced acetylation and activation of p38 were found to be in parallel with reduced intracellular ATP levels in cardiomyocytes under stress, as well as in vivo models of cardiac hypertrophy. Thus, our data show, for the first time, that p38 activity is critically regulated by, in addition to phosphorylation, reversible acetylation of a lysine residue, which is conserved in other kinases, implying the possibility of a similar mechanism regulating their activity.
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Functional characterization of a new member of the Cdk9 family in Aspergillus nidulans. EUKARYOTIC CELL 2010; 9:1901-12. [PMID: 20952582 DOI: 10.1128/ec.00384-09] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cdk9-like kinases in complex with T-type cyclins are essential components of the eukaryotic transcription elongation machinery. The full spectrum of Cdk9/cyclin T targets, as well as the specific consequences of phosphorylations, is still largely undefined. We identify and characterize here a Cdk9 kinase (PtkA) in the filamentous ascomycete Aspergillus nidulans. Deletion of ptkA had a lethal effect in later stages of vegetative growth and completely impeded asexual development. Overexpression of ptkA affected directionality of polarized growth and the initiation of new branching sites. A green fluorescent protein-tagged PtkA version localized inside the nucleus during interphase, supporting a role of PtkA in transcription elongation, as observed in other organisms. We also identified a putative cyclin T homolog, PchA, in the A. nidulans genome and confirmed its interaction with PtkA in vivo. Surprisingly, the Pcl-like cyclin PclA, previously described to be involved in asexual development, was also found to interact with PtkA, indicating a possible role of PtkA in linking transcriptional activity with development and/or morphogenesis in A. nidulans. This is the first report of a Cdk9 kinase interacting with a Pcl-like cyclin, revealing interesting new aspects about the involvement of this Cdk-subfamily in differential gene expression.
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61
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Galatioto J, Mascareno E, Siddiqui MAQ. CLP-1 associates with MyoD and HDAC to restore skeletal muscle cell regeneration. J Cell Sci 2010; 123:3789-95. [PMID: 20940258 DOI: 10.1242/jcs.073387] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Emerging evidence suggests that eukaryotic gene transcription is regulated primarily at the elongation stage by association and dissociation of the inhibitory protein cardiac lineage protein 1 (CLP-1/HEXIM1) from the positive transcription elongation factor b (P-TEFb) complex. It was reported recently that P-TEFb interacts with skeletal muscle-specific regulatory factor, MyoD, suggesting a linkage between CLP-1-mediated control of transcription and skeletal myogenesis. To examine this, we produced CLP-1 knockdown skeletal muscle C2C12 cells by homologous recombination, and demonstrated that the C2C12 CLP-1 +/- cells failed to differentiate when challenged by low serum in the medium. We also showed that CLP-1 interacts with both MyoD and histone deacetylases (HDACs) maximally at the early stage of differentiation of C2C12 cells. This led us to hypothesize that the association might be crucial to inhibition of MyoD-target proliferative genes. Chromatin immunoprecipitation analysis revealed that the CLP-1/MyoD/HDAC complex binds to the promoter of the cyclin D1 gene, which is downregulated in differentiated muscle cells. These findings suggest a novel transcriptional paradigm whereby CLP-1, in conjunction with MyoD and HDAC, acts to inhibit growth-related gene expression, a requirement for myoblasts to exit the cell cycle and transit to myotubes.
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Affiliation(s)
- Josephine Galatioto
- Department of Cell Biology, Center for Cardiovascular and Muscle Research, State University of New York Downstate Medical Center, Brooklyn, New York, NY 11203, USA
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62
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Krystof V, Chamrád I, Jorda R, Kohoutek J. Pharmacological targeting of CDK9 in cardiac hypertrophy. Med Res Rev 2010; 30:646-66. [PMID: 19757441 DOI: 10.1002/med.20172] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cardiac hypertrophy allows the heart to adapt to workload, but persistent or unphysiological stimulus can result in pump failure. Cardiac hypertrophy is characterized by an increase in the size of differentiated cardiac myocytes. At the molecular level, growth of cells is linked to intensive transcription and translation. Several cyclin-dependent kinases (CDKs) have been identified as principal regulators of transcription, and among these CDK9 is directly associated with cardiac hypertrophy. CDK9 phosphorylates the C-terminal domain of RNA polymerase II and thus stimulates the elongation phase of transcription. Chronic activation of CDK9 causes not only cardiac myocyte enlargement but also confers predisposition to heart failure. Due to the long interest of molecular oncologists and medicinal chemists in CDKs as potential targets of anticancer drugs, a portfolio of small-molecule inhibitors of CDK9 is available. Recent determination of CDK9's crystal structure now allows the development of selective inhibitors and their further optimization in terms of biochemical potency and selectivity. CDK9 may therefore constitute a novel target for drugs against cardiac hypertrophy.
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Affiliation(s)
- Vladimír Krystof
- Faculty of Science, Laboratory of Growth Regulators, Palacký University & Institute of Experimental Botany AS CR, Slechtitelů 11, Olomouc 783 71, Czech Republic.
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63
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Hoehenwarter W, Chen Y, Recuenco-Munoz L, Wienkoop S, Weckwerth W. Functional analysis of proteins and protein species using shotgun proteomics and linear mathematics. Amino Acids 2010; 41:329-41. [PMID: 20602127 DOI: 10.1007/s00726-010-0669-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2010] [Accepted: 06/16/2010] [Indexed: 12/16/2022]
Abstract
Covalent post-translational modification of proteins is the primary modulator of protein function in the cell. It greatly expands the functional potential of the proteome compared to the genome. In the past few years shotgun proteomics-based research, where the proteome is digested into peptides prior to mass spectrometric analysis has been prolific in this area. It has determined the kinetics of tens of thousands of sites of covalent modification on an equally large number of proteins under various biological conditions and uncovered a transiently active regulatory network that extends into diverse branches of cellular physiology. In this review, we discuss this work in light of the concept of protein speciation, which emphasizes the entire post-translationally modified molecule and its interactions and not just the modification site as the functional entity. Sometimes, particularly when considering complex multisite modification, all of the modified molecular species involved in the investigated condition, the protein species must be completely resolved for full understanding. We present a mathematical technique that delivers a good approximation for shotgun proteomics data.
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Affiliation(s)
- Wolfgang Hoehenwarter
- Department of Molecular Systems Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
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64
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Cho S, Schroeder S, Ott M. CYCLINg through transcription: posttranslational modifications of P-TEFb regulate transcription elongation. Cell Cycle 2010; 9:1697-705. [PMID: 20436276 DOI: 10.4161/cc.9.9.11346] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The cyclin T/CDK9 complex, also called positive transcription elongation factor b (P-TEFb) phosphorylates the C-terminal domain of the large fragment of the RNA polymerase II. This action is a hallmark of the transition from transcription initiation to elongation. P-TEFb is itself modified by phosphorylation and ubiquitination. Recently, the core components of P-TEFb, cyclin T1 and CDK9, were identified as novel substrates of histone acetyltransferases. Here, we review how posttranslational modifications regulate the activity of the P-TEFb complex and discuss how acetylation of the complex optimizes transcription elongation in the context of other posttranslational modifications.
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Affiliation(s)
- Sungyoo Cho
- Gladstone Institute of Virology and Immunology, University of California, San Francisco, San Francisco, CA, USA
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65
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Massari S, Daelemans D, Barreca ML, Knezevich A, Sabatini S, Cecchetti V, Marcello A, Pannecouque C, Tabarrini O. A 1,8-naphthyridone derivative targets the HIV-1 Tat-mediated transcription and potently inhibits the HIV-1 replication. J Med Chem 2010; 53:641-8. [PMID: 19958026 DOI: 10.1021/jm901211d] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The emergence of multidrug resistant HIV-1 strains and the inability of the HAART to eradicate HIV-1 virus from infected patients demand new drugs able to interfere with an alternative step of the replicative cycle. The naphthyridone 3 (HM13N), described in the present study, is a promising anti-HIV agent due to its ability to inhibit the HIV-1 Tat-mediated transcription and the potent antiviral activity observed in acutely, chronically, and latently infected cells. The absence of any tendency to select for resistance mutations in vitro adds to the potential clinical value of this type of compounds, especially as these compounds are drug-like and obey the Lipinski rules.
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Affiliation(s)
- Serena Massari
- Dipartimento di Chimica e Tecnologia del Farmaco, Università di Perugia, Via del Liceo 1, 06123 Perugia, Italy
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66
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Mateo F, Vidal-Laliena M, Canela N, Zecchin A, Martínez-Balbás M, Agell N, Giacca M, Pujol MJ, Bachs O. The transcriptional co-activator PCAF regulates cdk2 activity. Nucleic Acids Res 2010; 37:7072-84. [PMID: 19773423 PMCID: PMC2790897 DOI: 10.1093/nar/gkp777] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Cyclin dependent kinases (cdks) regulate cell cycle progression and transcription. We report here that the transcriptional co-activator PCAF directly interacts with cdk2. This interaction is mainly produced during S and G2/M phases of the cell cycle. As a consequence of this association, PCAF inhibits the activity of cyclin/cdk2 complexes. This effect is specific for cdk2 because PCAF does not inhibit either cyclin D3/cdk6 or cyclin B/cdk1 activities. The inhibition is neither competitive with ATP, nor with the substrate histone H1 suggesting that somehow PCAF disturbs cyclin/cdk2 complexes. We also demonstrate that overexpression of PCAF in the cells inhibits cdk2 activity and arrests cell cycle progression at S and G2/M. This blockade is dependent on cdk2 because it is rescued by the simultaneous overexpression of this kinase. Moreover, we also observed that PCAF acetylates cdk2 at lysine 33. As this lysine is essential for the interaction with ATP, acetylation of this residue inhibits cdk2 activity. Thus, we report here that PCAF inhibits cyclin/cdk2 activity by two different mechanisms: (i) by somehow affecting cyclin/cdk2 interaction and (ii) by acetylating K33 at the catalytic pocket of cdk2. These findings identify a previously unknown mechanism that regulates cdk2 activity.
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Affiliation(s)
- Francesca Mateo
- Department of Cell Biology, Immunology and Neurosciences, Faculty of Medicine, University of Barcelona, Spain
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67
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Coley W, Kehn-Hall K, Van Duyne R, Kashanchi F. Novel HIV-1 therapeutics through targeting altered host cell pathways. Expert Opin Biol Ther 2009; 9:1369-82. [PMID: 19732026 DOI: 10.1517/14712590903257781] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The emergence of drug-resistant HIV-1 strains presents a challenge for the design of new drugs. Anti-HIV compounds currently in use are the subject of advanced clinical trials using either HIV-1 reverse transcriptase, viral protease or integrase inhibitors. Recent studies show an increase in the number of HIV-1 variants resistant to anti-retroviral agents in newly infected individuals. Targeting host cell factors involved in the regulation of HIV-1 replication might be one way to combat HIV-1 resistance to the currently available anti-viral agents. A specific inhibition of HIV-1 gene expression could be expected from the development of compounds targeting host cell factors that participate in the activation of the HIV-1 LTR promoter. Here we discuss how targeting the host can be accomplished either by using small molecules to alter the function of the host's proteins such as p53 or cdk9, or by utilizing new advances in siRNA therapies to knock down essential host factors such as CCR5 and CXCR4. Finally, we will discuss how the viral protein interactomes should be used to better design therapeutics against HIV-1.
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Affiliation(s)
- William Coley
- George Washington University, School of Medicine, Department of Microbiology, Immunology and Tropical Medicine, Washington, DC 20037, USA
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68
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Coiras M, López-Huertas MR, Pérez-Olmeda M, Alcamí J. Understanding HIV-1 latency provides clues for the eradication of long-term reservoirs. Nat Rev Microbiol 2009; 7:798-812. [PMID: 19834480 DOI: 10.1038/nrmicro2223] [Citation(s) in RCA: 216] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
HIV-1 can infect both activated and resting, non-dividing cells, following which the viral genome can be permanently integrated into a host cell chromosome. Latent HIV-1 reservoirs are established early during primary infection and constitute a major barrier to eradication, even in the presence of highly active antiretroviral therapy. This Review analyses the molecular mechanisms that are necessary for the establishment of HIV-1 latency and their relationships with different cellular and anatomical reservoirs, and discusses the current treatment strategies for targeting viral persistence in reservoirs, their main limitations and future perspectives.
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Affiliation(s)
- Mayte Coiras
- AIDS Immunopathology Unit, National Centre of Microbiology, Instituto de Salud Carlos III, 28220 Majadahonda, Madrid, Spain.
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69
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Ramakrishnan R, Dow EC, Rice AP. Characterization of Cdk9 T-loop phosphorylation in resting and activated CD4(+) T lymphocytes. J Leukoc Biol 2009; 86:1345-50. [PMID: 19741158 DOI: 10.1189/jlb.0509309] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The cellular kinase complex P-TEFb is composed of Cdk9 and cyclin T, and it is required for expression of most protein-coding genes by RNAP II. Cdk9 has been shown recently to be activated in cis by autophosphorylation of Thr186 in its T-loop. Using a phosphospecific Cdk9 antibody, we examined the level of Cdk9 T-loop phosphorylation in resting and activated CD4(+) T lymphocytes. Cdk9 T-loop phosphorylation was found to be low-to-undetectable in resting CD4(+) T lymphocytes, and upon activation by distinct stimuli, there is a rapid (<1 h) increase in pCdk9 that does not require protein synthesis. The low level of Cdk9 T-loop phosphorylation was not to be a result of the absence of an associated regulatory cyclin partner. These observations suggest that autophosphorylation of the Cdk9 T-loop is repressed in resting CD4(+) T lymphocytes. The low level of T-loop phosphorylation in resting cells is also reflected in a low level of phosphorylation of Ser2 in the carboxyl terminal domain of RNAP II, suggesting that lack of Cdk9 T-loop autophosphorylation may limit RNAP II elongation in quiescent CD4(+) T lymphocytes.
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Affiliation(s)
- Rajesh Ramakrishnan
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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70
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Abstract
Regulation of gene expression is essential to all aspects of physiological processes in single-cell as well as multicellular organisms. It gives ultimately cells the ability to efficiently respond to extra- and intracellular stimuli participating in cell cycle, growth, differentiation and survival. Regulation of gene expression is executed primarily at the level of transcription of specific mRNAs by RNA polymerase II (RNAPII), typically in several distinct phases. Among them, transcription elongation is positively regulated by the positive transcription elongation factor b (P-TEFb), consisting of CDK9 and cyclin T1, T2 or K. P-TEFb enables transition from abortive to productive transcription elongation by phosphorylating carboxyl-terminal domain (CTD) in RNAPII and negative transcription elongation factors. Over the years, we have learned a great deal about molecular composition of P-TEFb complexes, their assembly and their role in transcription of specific genes, but function of P-TEFb in other physiological processes was not apparent until just recently. In light of emerging discoveries connecting P-TEFb to regulation of cell cycle, development and several diseases, I would like to discuss these observations as well as future perspectives.
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Affiliation(s)
- Jiri Kohoutek
- Veterinary Research Institute, Hudcova 70, 621 00 Brno, Czech Republic.
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71
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Lusic M, Manganaro L, Vardabasso C, Gutierrez MI, Giacca M. Spatial juxtaposition of HIV-1 provirus with PML and KAKA bodies as revealed by 3D Immuno DNA FISH. Retrovirology 2009. [PMCID: PMC2767037 DOI: 10.1186/1742-4690-6-s2-p52] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
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72
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Easley R, Van Duyne R, Coley W, Guendel I, Dadgar S, Kehn-Hall K, Kashanchi F. Chromatin dynamics associated with HIV-1 Tat-activated transcription. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2009; 1799:275-85. [PMID: 19716452 DOI: 10.1016/j.bbagrm.2009.08.008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2009] [Revised: 08/14/2009] [Accepted: 08/20/2009] [Indexed: 02/07/2023]
Abstract
Chromatin remodeling is an essential event for HIV-1 transcription. Over the last two decades this field of research has come to the forefront, as silencing of the HIV-1 provirus through chromatin modifications has been linked to latency. Here, we focus on chromatin remodeling, especially in relation to the transactivator Tat, and review the most important and newly emerging studies that investigate remodeling mechanisms. We begin by discussing covalent modifications that can alter chromatin structure including acetylation, deacetylation, and methylation, as well as topics addressing the interplay between chromatin remodeling and splicing. Next, we focus on complexes that use the energy of ATP to remove or secure nucleosomes and can additionally act to control HIV-1 transcription. Finally, we cover recent literature on viral microRNAs which have been shown to alter chromatin structure by inducing methylation or even by remodeling nucleosomes.
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Affiliation(s)
- Rebecca Easley
- The George Washington University Medical Center, Department of Microbiology, Immunology, and Tropical Medicine, Washington, DC 20037, USA
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73
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Choudhary C, Kumar C, Gnad F, Nielsen ML, Rehman M, Walther TC, Olsen JV, Mann M. Lysine acetylation targets protein complexes and co-regulates major cellular functions. Science 2009; 325:834-40. [PMID: 19608861 DOI: 10.1126/science.1175371] [Citation(s) in RCA: 3133] [Impact Index Per Article: 208.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Lysine acetylation is a reversible posttranslational modification of proteins and plays a key role in regulating gene expression. Technological limitations have so far prevented a global analysis of lysine acetylation's cellular roles. We used high-resolution mass spectrometry to identify 3600 lysine acetylation sites on 1750 proteins and quantified acetylation changes in response to the deacetylase inhibitors suberoylanilide hydroxamic acid and MS-275. Lysine acetylation preferentially targets large macromolecular complexes involved in diverse cellular processes, such as chromatin remodeling, cell cycle, splicing, nuclear transport, and actin nucleation. Acetylation impaired phosphorylation-dependent interactions of 14-3-3 and regulated the yeast cyclin-dependent kinase Cdc28. Our data demonstrate that the regulatory scope of lysine acetylation is broad and comparable with that of other major posttranslational modifications.
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Affiliation(s)
- Chunaram Choudhary
- Proteomics and Signal Transduction, Max Planck Institute for Biochemistry, Martinsried, Germany
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74
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Chou JW, Bushel PR. Discernment of possible mechanisms of hepatotoxicity via biological processes over-represented by co-expressed genes. BMC Genomics 2009; 10:272. [PMID: 19538742 PMCID: PMC2706894 DOI: 10.1186/1471-2164-10-272] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 06/18/2009] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Hepatotoxicity is a form of liver injury caused by exposure to stressors. Genomic-based approaches have been used to detect changes in transcription in response to hepatotoxicants. However, there are no straightforward ways of using co-expressed genes anchored to a phenotype or constrained by the experimental design for discerning mechanisms of a biological response. RESULTS Through the analysis of a gene expression dataset containing 318 liver samples from rats exposed to hepatotoxicants and leveraging alanine aminotransferase (ALT), a serum enzyme indicative of liver injury as the phenotypic marker, we identified biological processes and molecular pathways that may be associated with mechanisms of hepatotoxicity. Our analysis used an approach called Coherent Co-expression Biclustering (cc-Biclustering) for clustering a subset of genes through a coherent (consistency) measure within each group of samples representing a subset of experimental conditions. Supervised biclustering identified 87 genes co-expressed and correlated with ALT in all the samples exposed to the chemicals. None of the over-represented pathways related to liver injury. However, biclusters with subsets of samples exposed to one of the 7 hepatotoxicants, but not to a non-toxic isomer, contained co-expressed genes that represented pathways related to a stress response. Unsupervised biclustering of the data resulted in 1) four to five times more genes within the bicluster containing all the samples exposed to the chemicals, 2) biclusters with co-expression of genes that discerned 1,4 dichlorobenzene (a non-toxic isomer at low and mid doses) from the other chemicals, pathways and biological processes that underlie liver injury and 3) a bicluster with genes up-regulated in an early response to toxic exposure. CONCLUSION We obtained clusters of co-expressed genes that over-represented biological processes and molecular pathways related to hepatotoxicity in the rat. The mechanisms involved in the response of the liver to the exposure to 1,4-dichlorobenzene suggest non-genotoxicity whereas the exposure to the hepatotoxicants could be DNA damaging leading to overall genomic instability and activation of cell cycle check point signaling. In addition, key pathways and biological processes representative of an inflammatory response, energy production and apoptosis were impacted by the hepatotoxicant exposures that manifested liver injury in the rat.
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Affiliation(s)
- Jeff W Chou
- Biostatistics Branch, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, USA.
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75
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Bolstad ESD, Anderson AC. In pursuit of virtual lead optimization: pruning ensembles of receptor structures for increased efficiency and accuracy during docking. Proteins 2009; 75:62-74. [PMID: 18781587 DOI: 10.1002/prot.22214] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Representing receptors as ensembles of protein conformations during docking is a powerful method to approximate protein flexibility and increase the accuracy of the resulting ranked list of compounds. Unfortunately, docking compounds against a large number of ensemble members can increase computational cost and time investment. In this article, we present an efficient method to evaluate and select the most contributive ensemble members prior to docking for targets with a conserved core of residues that bind a ligand moiety. We observed that ensemble members that preserve the geometry of the active site core are most likely to place ligands in the active site with a conserved orientation, generally rank ligands correctly and increase interactions with the receptor. A relative distance approach is used to quantify the preservation of the three-dimensional interatomic distances of the conserved ligand-binding atoms and prune large ensembles quickly. In this study, we investigate dihydrofolate reductase as an example of a protein with a conserved core; however, this method for accurately selecting relevant ensemble members a priori can be applied to any system with a conserved ligand-binding core, including HIV-1 protease, kinases, and acetylcholinesterase. Representing a drug target as a pruned ensemble during in silico screening should increase the accuracy and efficiency of high-throughput analyses of lead analogs.
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Affiliation(s)
- Erin S D Bolstad
- Department of Pharmaceutical Sciences, University of Connecticut, Storrs, Connecticut 06269, USA
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76
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Acetylation of cyclin T1 regulates the equilibrium between active and inactive P-TEFb in cells. EMBO J 2009; 28:1407-17. [PMID: 19387490 DOI: 10.1038/emboj.2009.99] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Accepted: 03/20/2009] [Indexed: 12/23/2022] Open
Abstract
The elongation competence of the RNA polymerase II complex is critically dependent on the positive transcription elongation factor b (P-TEFb). P-TEFb exists in two forms in cells, an active form composed of cyclin T1 and CDK9 and an inactive form, in which cyclin T1/CDK9 is sequestered by Hexim1 and 7SK snRNA. Here, we report that partitioning of active and inactive P-TEFb is regulated by acetylation of cyclin T1. Cyclin T1 acetylation triggers dissociation of Hexim1 and 7SK snRNA from cyclin T1/CDK9 and activates the transcriptional activity of P-TEFb. This activation is lost in P-TEFb complexes containing cyclin T1 that can no longer be acetylated. An acetylation-deficient cyclin T1 mutant dominantly suppresses NF-kappaB-mediated activation of the interleukin-8 promoter but continues to synergize normally with the HIV Tat protein to transactivate the HIV long terminal repeat. These findings support the model that acetylation of cyclin T1 serves as a physiological switch that liberates P-TEFb from its endogenous inhibitors Hexim1 and 7SK snRNA, but is not required for the cooperative action with HIV Tat.
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77
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Brasier AR. Expanding role of cyclin dependent kinases in cytokine inducible gene expression. Cell Cycle 2008; 7:2661-6. [PMID: 18728388 DOI: 10.4161/cc.7.17.6594] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The Positive Transcriptional Elongation Factor b (P-TEFb), a heterodimer of CDK9 and Cyclin T1, is widely implicated in control of basal gene expression. Here, P-TEFb is involved in transitioning paused RNA polymerase II to enter productive transcriptional elongation mode by phosphorylating negative elongation factors and Ser(2) of the heptad repeat in the RNA Pol II COOH terminal domain (CTD). This perspective will examine recent work in two unrelated inducible signaling pathways that illustrate the central role of P-TEFb in mediating cytokine inducible transcription networks. Specifically, P-TEFb has been recently discovered to play a key role in TNF-inducible NFkappaB activation and IL-6-inducible STAT3 signaling. In these signaling cascades, P-TEFb forms protein complexes with the activated nuclear RelA and STAT3 transcription factor in the cellular nucleoplasm, an association important for P-TEFb's promoter targeting. Studies using siRNA-mediated knockdown and/or selective CDK inhibitors show that P-TEFb plays a functional role in activation of a subset of NFkappaB-dependent targets and all STAT3-dependent genes studied to date. Interestingly, cytokine inducible genes that are sensitive to P-TEFb inhibition share an induction mechanism requiring inducible RNA Pol II recruitment. Chromatin immunoprecipitation studies have preliminarily indicated that this recruitment is dependent on CDK enzymatic activity. The potential of inhibiting P-TEFb as an anti-inflammatory therapy in innate immunity and systemic inflammation will be discussed.
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Affiliation(s)
- Allan R Brasier
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas 77555-1060, USA.
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