Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P23193 (transcription elongation factor)
 739 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Positive transcription elongation factor b (P-TEFb) plays an important role in stimulating RNA polymerase II elongation for viral and cellular gene expression. P-TEFb is found in cells in either an active, low-molecular-weight (LMW) form or an inactive, high-molecular-weight (HMW) form. We report here that human T-lymphotropic virus type 1 (HTLV-1) Tax interacts with the cyclin T1 subunit of P-TEFb, forming a distinct Tax/P-TEFb LMW complex. We demonstrate that Tax can play a role in regulating the amount of HMW complex present in the cell by decreasing the binding of 7SK snRNP/HEXIM1 to P-TEFb. This is seen both in vitro using purified Tax protein and in vivo in cells transduced with Tax expression constructs. Further, we find that a peptide of cyclin T1 spanning the Tax binding domain inhibits the ability of Tax to disrupt HMW P-TEFb complexes. These results suggest that the direct interaction of Tax with cyclin T1 can dissociate P-TEFb from the P-TEFb/7SK snRNP/HEXIM1 complex for activation of the viral long terminal repeat (LTR). We also show that Tax competes with Brd4 for P-TEFb binding. Chromatin immunoprecipitation (ChIP) assays demonstrated that Brd4 and P-TEFb are associated with the basal HTLV-1 LTR, while Tax and P-TEFb are associated with the activated template. Furthermore, the knockdown of Brd4 by small interfering RNA (siRNA) activates the HTLV-1 LTR promoter, which results in an increase in viral expression and production. Our studies have identified Tax as a regulator of P-TEFb that is capable of affecting the balance between its association with the large inactive complex and the small active complex.
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PMID:Human T-lymphotropic virus type 1 Tax protein complexes with P-TEFb and competes for Brd4 and 7SK snRNP/HEXIM1 binding. 2092 76

Actin is a key regulator of RNA polymerase (Pol) II-dependent transcription. Positive transcription elongation factor b (P-TEFb), a Cdk9/cyclin T1 heterodimer, has been reported to play a critical role in transcription elongation. However, the relationship between actin and P-TEFb is still not clear. In this study, actin was found to interact with Cdk9, a catalytic subunit of P-TEFb, in elongation complexes. Using immunofluorescence and immunoprecipitation assays, Cdk9 was found to bind to G-actin through the conserved Thr-186 in the T-loop. Overexpression and in vitro kinase assays showed that G-actin promotes P-TEFb-dependent phosphorylation of the Pol II C-terminal domain. An in vitro transcription experiment revealed that the interaction between G-actin and Cdk9 stimulated Pol II transcription elongation. ChIP and immobilized template assays indicated that actin recruited Cdk9 to a transcriptional template in vivo and in vitro. Using cytokine IL-6-inducible p21 gene expression system, we revealed that actin recruited Cdk9 to endogenous gene. Moreover, overexpression of actin and Cdk9 increased histone H3 acetylation and acetylized histone H3 binding to a transcriptional template through the interaction with histone acetyltransferase, p300. Taken together, our results suggested that actin participates in transcription elongation by recruiting Cdk9 for phosphorylation of the Pol II C-terminal domain, and the actin-Cdk9 interaction promotes chromatin remodeling.
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PMID:G-actin participates in RNA polymerase II-dependent transcription elongation by recruiting positive transcription elongation factor b (P-TEFb). 2137 66

Transcription of the human immunodeficiency virus type 1 (HIV-1) requires the interaction of the cyclin T1 (CycT1) subunit of a host cellular factor, positive transcription elongation factor b, with the viral Tat protein at the transactivation response (TAR) element of nascent viral transcripts. The involvement of the interaction between Tat and CycT1 is known to be through the Tat-TAR recognition motif (TRM) on CycT1. Here, we have further characterized this molecular interaction and clarified the role of the CycT1 N-terminal region in Tat action. We found crucial and distinctive roles of Q46, Q50 and F176 of human CycT1 protein in Tat-mediated transcription by creating various Ala substitution mutants of CycT1 based on its three-dimensional structure. We confirmed the involvement of these amino acid residues in binding to Tat with Q46 and Q50, and to a lesser extent with F176, by in vitro pull-down assay. Relative transactivation activities of wild-type CycT1 chimeras and mutant derivatives on the HIV-1 long terminal repeat were determined by luciferase reporter assays. Whereas CycT1 Q46A alone had impaired transcriptional activity, the CycT1(Q46A)-Tat chimeric protein retained almost full activity of the wild-type CycT1. However, CycT1 mutants (C261Y, Q50A or F176A) or their chimeric counterparts had lost the transactivation capacity. Moreover, a triple-mutant chimera containing Q46A, Q50A and F176A mutations completely abolished the transcriptional activity, indicating that these amino acid residues are involved through distinct mechanisms. These findings provide new insights for the development of anti-HIV drugs.
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PMID:Functional characterization of human cyclin T1 N-terminal region for human immunodeficiency virus-1 Tat transcriptional activation. 2176 94

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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PMID:HIV-1 replication and latency are regulated by translational control of cyclin T1. 2176 96

The essential transactivator function of the HIV Tat protein is regulated by multiple posttranslational modifications. Although individual modifications are well characterized, their crosstalk and dynamics of occurrence during the HIV transcription cycle remain unclear.We examine interactions between two critical modifications within the RNA-binding domain of Tat: monomethylation of lysine 51 (K51) mediated by Set7/9/KMT7, an early event in the Tat transactivation cycle that strengthens the interaction of Tat with TAR RNA, and acetylation of lysine 50 (K50) mediated by p300/KAT3B, a later process that dissociates the complex formed by Tat, TAR RNA and the cyclin T1 subunit of the positive transcription elongation factor b (P-TEFb). We find K51 monomethylation inhibited in synthetic Tat peptides carrying an acetyl group at K50 while acetylation can occur in methylated peptides, albeit at a reduced rate. To examine whether Tat is subject to sequential monomethylation and acetylation in cells, we performed mass spectrometry on immunoprecipitated Tat proteins and generated new modification-specific Tat antibodies against monomethylated/acetylated Tat. No bimodified Tat protein was detected in cells pointing to a demethylation step during the Tat transactivation cycle. We identify lysine-specific demethylase 1 (LSD1/KDM1) as a Tat K51-specific demethylase, which is required for the activation of HIV transcription in latently infected T cells. LSD1/KDM1 and its cofactor CoREST associates with the HIV promoter in vivo and activate Tat transcriptional activity in a K51-dependent manner. In addition, small hairpin RNAs directed against LSD1/KDM1 or inhibition of its activity with the monoamine oxidase inhibitor phenelzine suppresses the activation of HIV transcription in latently infected T cells.Our data support the model that a LSD1/KDM1/CoREST complex, normally known as a transcriptional suppressor, acts as a novel activator of HIV transcription through demethylation of K51 in Tat. Small molecule inhibitors of LSD1/KDM1 show therapeutic promise by enforcing HIV latency in infected T cells.
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PMID:Activation of HIV transcription by the viral Tat protein requires a demethylation step mediated by lysine-specific demethylase 1 (LSD1/KDM1). 2187 70

The positive transcription elongation factor b (P-TEFb) exists in two forms in cells as follows: an inactive form where the core components cyclin T1 and CDK9 are incorporated in the 7SK small nuclear ribonucleoprotein complex containing the inhibitory molecule HEXIM1, and an active form, part of which associates with the bromodomain-containing protein BRD4. Here, we define a novel interaction between P-TEFb and BRD4 involving tri-acetylated cyclin T1 (acK380, acK386, and acK309) and the second bromodomain in BRD4. This interaction is observed with the short splice variant of BRD4 (amino acids 1-722) lacking a previously defined C-terminal P-TEFb-interacting domain (PID). Notably, P-TEFb complexes associated with short BRD4 contain HEXIM1 and 7SK snRNA, implicating the PID in the liberation of P-TEFb from the 7SK small nuclear ribonucleoprotein complex (7SK snPNP). Overexpression of the PID alone in cells dissociates HEXIM1 and 7SK snRNA from P-TEFb, but it is not sufficient to activate P-TEFb-dependent transcription of the HIV LTR. Our data support a model where two BRD4 domains, the second bromodomain and the PID, bind P-TEFb and are required for full transcriptional activation of P-TEFb response genes.
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PMID:Two-pronged binding with bromodomain-containing protein 4 liberates positive transcription elongation factor b from inactive ribonucleoprotein complexes. 2208 42

Thirteen years ago, human cyclin T1 was identified as part of the positive transcription elongation factor b (P-TEFb) and the long-sought host cofactor for the HIV-1 transactivator Tat. Recent years have brought new insights into the intricate regulation of P-TEFb function and its relationship with Tat, revealing novel mechanisms for controlling HIV transcription and fueling new efforts to overcome the barrier of transcriptional latency in eradicating HIV. Moreover, the improved understanding of HIV and Tat forms a basis for studying transcription elongation control in general. Here, we review advances in HIV transcription research with a focus on the growing family of cellular P-TEFb complexes, structural insights into the interactions between Tat, P-TEFb, and TAR RNA, and the multifaceted regulation of these interactions by posttranscriptional modifications of Tat.
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PMID:The control of HIV transcription: keeping RNA polymerase II on track. 2210 Jan 59

HIV transcription is regulated at the step of elongation by the viral Tat protein and the cellular positive transcription elongation factor b (P-TEFb; Cdk9/cyclin T1). Herein, a human cyclin T1 mutant, cyclin T1-U7, which contains four substitutions and one deletion in the N-terminal cyclin box, was stably expressed in HeLa cells. HIV transcription was efficiently inhibited in HeLa-HA-CycT1-U7 stable cells. Cyclin T1-U7 bound Tat but did not modulate its expression levels, which remained high. Importantly cyclin T1-U7 failed to interact with Cdk9 or HEXIM1 and did not interfere with endogenous P-TEFb activity to stimulate MEF2C or NFkB mediated transcription. In a T cell line and primary CD4+ cells, cyclin T1-U7 also inhibited HIV transcription. We conclude that cyclin T1-U7 sequesters Tat from P-TEFb and inhibits HIV transcription. Importantly, N-terminal residues in cyclin T1 are specifically involved in the binding of cyclin T1 to HEXIM1 but not to Tat.
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PMID:Functional characterization of a human cyclin T1 mutant reveals a different binding surface for Tat and HEXIM1. 2234 81

Human positive transcription elongation factor b (P-TEFb) phosphorylates RNA polymerase II and regulatory proteins to trigger elongation of many gene transcripts. The HIV-1 Tat protein selectively recruits P-TEFb as part of a super elongation complex (SEC) organized on a flexible AFF1 or AFF4 scaffold. To understand this specificity and determine if scaffold binding alters P-TEFb conformation, we determined the structure of a tripartite complex containing the recognition regions of P-TEFb and AFF4. AFF4 meanders over the surface of the P-TEFb cyclin T1 (CycT1) subunit but makes no stable contacts with the CDK9 kinase subunit. Interface mutations reduced CycT1 binding and AFF4-dependent transcription. AFF4 is positioned to make unexpected direct contacts with HIV Tat, and Tat enhances P-TEFb affinity for AFF4. These studies define the mechanism of scaffold recognition by P-TEFb and reveal an unanticipated intersubunit pocket on the AFF4 SEC that potentially represents a target for therapeutic intervention against HIV/AIDS. DOI:http://dx.doi.org/10.7554/eLife.00327.001.
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PMID:The AFF4 scaffold binds human P-TEFb adjacent to HIV Tat. 2347 Nov 3

A variety of cellular factors participates in the HIV-1 life cycle. Among them is the well characterized cyclin T1 (CYCT1). CycT1 binds to cyclin-dependent kinase 9 (CDK9) and forms the positive transcription elongation factor-b (P-TEFb). P-TEFb is then recruited by HIV-1 TAT to the HIV-1 long terminal repeat (LTR) promoter and subsequently leads to phosphorylation of the C-terminal domain of RNA polymerase II (pol II), enhanced processivity of pol II, and transcription of a full-length HIV-1 RNA. In this study, we report the identification of a new CYCT1 splice variant, designated as CYCT1b, and accordingly we renamed CYCT1 as CYCT1a. CYCT1b was detected in several cell lines, including primary human CD4 T cells, and its expression was subject to cell cycle regulation. Similar to CYCT1a, CYCT1b was primarily localized in the nucleus. CYCT1b expression was found to be inversely correlated with HIV-1 gene expression and replication. This inverse correlation appeared to involve TAT transactivation, CDK9 binding, and subsequent recruitment of P-TEFb to the HIV-1 LTR promoter and pol II C-terminal domain phosphorylation. In agreement with these findings, CYCT1b expression led to direct inhibition of TAT-transactivated transcription of the HIV-1 LTR promoter. Taken together, these results show that the newly identified CYCT1b splice variant inhibits HIV-1 transcription and may provide new clues for the development of anti-HIV strategies.
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PMID:Inhibition of HIV-1 transcription and replication by a newly identified cyclin T1 splice variant. 2356 10


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