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

Tat stimulation of HIV-1 transcriptional elongation is species-specific and is believed to require a specific cellular cofactor present in many human and primate cells but not in nonpermissive rodent cells. Human P-TEFb, composed of Cdk9 and cyclin T1, is a general transcription elongation factor that phosphorylates the C-terminal domain of RNA polymerase II. Previous studies have also implicated P-TEFb as a Tat-specific cellular cofactor and, in particular, human cyclin T1 as responsible for the species-specific Tat activation. To obtain functional evidence in support of these hypotheses, we generated and examined the activities of human-rodent "hybrid" P-TEFb complexes. We found that P-TEFb complexes containing human cyclin T1 complexed with either human or rodent Cdk9 supported Tat transactivation and interacted with the Tat activation domain and the HIV-1 TAR RNA element to form TAR loop-dependent ribonucleoprotein complexes. Although a stable complex containing rodent cyclin T1 and human Cdk9 was capable of phosphorylating CTD and mediating basal HIV-1 elongation, it failed to interact with Tat and to mediate Tat transactivation, indicating that the abilities of P-TEFb to support basal elongation and Tat activation can be separated. Together, our data indicated that the specific interaction of human P-TEFb with Tat/TAR, mostly through cyclin T1, is crucial for P-TEFb to mediate a Tat-specific and species-restricted activation of HIV-1 transcription. Amino acid residues unique to human Cdk9 also contributed partially to the formation of the P-TEFb-Tat-TAR complex. Moreover, the cyclin box of cyclin T1 and its immediate flanking region are largely responsible for the specific P-TEFb-Tat interaction.
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PMID:Specific interaction of Tat with the human but not rodent P-TEFb complex mediates the species-specific Tat activation of HIV-1 transcription. 1007 79

Phosphorylation of the carboxyl-terminal domain (CTD) of RNA polymerase II (RNAPII) is an important step in transcription and the positive transcription elongation factor b (P-TEFb) has been proposed to facilitate elongation at many genes. The P-TEFb contains a catalytic subunit (Cdk9) that, in association with a cyclin subunit (cyclinT1), has the ability to phosphorylate the CTD substrate in vitro. Here, we demonstrate that cyclinT1/Cdk9-mediated transcription requires CTD-containing RNAPII, suggesting that the CTD is the major target of the cyclinT1/Cdk9 complex in vivo. Unlike Cdk7 and Cdk8, two other cyclin-dependent kinases that are capable of phosphorylating the CTD in vitro, we found that only the Cdk9 activates gene expression in a catalysis-dependent manner. Finally, unlike cyclinT1 and T2, we found that the targeted recruitment to promoter DNA of cyclinK (a recently described alternative partner of Cdk9) does not stimulate transcription in vivo. Collectively, our data strongly indicate that the P-TEFb kinase subunits cyclinT/Cdk9 are specifically involved in transcription and the CTD domain of RNAPII is the major functional target of this complex in vivo.
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PMID:Transcriptional activity of positive transcription elongation factor b kinase in vivo requires the C-terminal domain of RNA polymerase II. 1097 44

The human positive transcription elongation factor P-TEFb, consisting of a CDK9/cyclin T1 heterodimer, functions as both a general and an HIV-1 Tat-specific transcription factor. P-TEFb activates transcription by phosphorylating RNA polymerase (Pol) II, leading to the formation of processive elongation complexes. As a Tat cofactor, P-TEFb stimulates HIV-1 transcription by interacting with Tat and the transactivating responsive (TAR) RNA structure located at the 5' end of the nascent viral transcript. Here we identified 7SK, an abundant and evolutionarily conserved small nuclear RNA (snRNA) of unknown function, as a specific P-TEFb-associated factor. 7SK inhibits general and HIV-1 Tat-specific transcriptional activities of P-TEFb in vivo and in vitro by inhibiting the kinase activity of CDK9 and preventing recruitment of P-TEFb to the HIV-1 promoter. 7SK is efficiently dissociated from P-TEFb by treatment of cells with ultraviolet irradiation and actinomycin D. As these two agents have been shown to significantly enhance HIV-1 transcription and phosphorylation of Pol II (refs 6,7,8), our data provide a mechanistic explanation for their stimulatory effects. The 7SK/P-TEFb interaction may serve as a principal control point for the induction of cellular and HIV-1 viral gene expression during stress-related responses. Our studies demonstrate the involvement of an snRNA in controlling the activity of a Cdk-cyclin kinase.
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PMID:The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription. 1171 32

Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.
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PMID:The growth factor granulin interacts with cyclin T1 and modulates P-TEFb-dependent transcription. 1258 88

The positive transcription elongation factor b (P-TEFb), comprising CDK9 and cyclin T, stimulates transcription of cellular and viral genes by phosphorylating RNA polymerase II. A major portion of nuclear P-TEFb is sequestered and inactivated by the coordinated actions of the 7SK snRNA and the HEXIM1 protein, whose induced dissociation from P-TEFb is crucial for stress-induced transcription and pathogenesis of cardiac hypertrophy. The 7SK.P-TEFb interaction, which can occur independently of HEXIM1 and does not by itself inhibit P-TEFb, recruits HEXIM1 for P-TEFb inactivation. To study the control of this interaction, we established an in vitro system that reconstituted the specific interaction of P-TEFb with 7SK but not other snRNAs. Using this system, together with an in vivo binding assay, we show that the phosphorylation of CDK9, on possibly the conserved Thr-186 in the T-loop, was crucial for the 7SK.P-TEFb interaction. This phosphorylation was not caused by CDK9 autophosphorylation or the general CDK-activating kinase CAK, but rather by a novel HeLa nuclear kinase. Furthermore, the stress-induced disruption of the 7SK.P-TEFb interaction was not caused by any prohibitive changes in 7SK but by the dephosphorylation of P-TEFb, leading to the loss of the key phosphorylation important for 7SK binding. Thus, the phosphorylated P-TEFb is tagged for inhibition through association with 7SK. We discuss the implications of this mechanism in controlling P-TEFb activity during normal and stress-induced transcription.
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PMID:Phosphorylated positive transcription elongation factor b (P-TEFb) is tagged for inhibition through association with 7SK snRNA. 1462 2

Acidic or type IIB transcriptional activation domains (AADs) increase rates of initiation as well as elongation of transcription. For the former effects, AADs bind general transcription factors and larger coactivator complexes, which position RNA polymerase II (RNAPII) at sites of initiation of transcription. For the latter effects, their ubiquitylation plays an important role. In this study, this posttranslational modification increased the binding between a prototypic AAD and the positive transcription elongation factor b (P-TEFb), which contains a C-type cyclin (CycT1, CycT2, or CycK) and Cdk9. By phosphorylating negative elongation factors and the C-terminal domain of RNAPII, P-TEFb modifies the transcription complex for efficient elongation and cotranscriptional processing of mRNA. Indeed, the activation domain of VP16 and ubiquitin bound the cyclin boxes and the C terminus in CycT1, respectively. Moreover, the artificial fusion of ubiquitin with VP16 not only increased its activity via DNA and RNA, which was reflected in increased ratios of elongated to initiated transcripts, but rescued the deleterious substitution of alanine for phenylalanine at position 442 in its AAD. Thus, the ubiquitylation of AADs increases their interaction with P-TEFb and augments rates of elongation of transcription.
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PMID:VP16 and ubiquitin; binding of P-TEFb via its activation domain and ubiquitin facilitates elongation of transcription of target genes. 1529 79

The active form of the positive transcription elongation factor b (P-TEFb) consists of cyclin T and the kinase Cdk9. P-TEFb stimulates transcription by phosphorylating the C-terminal domain of RNA polymerase II. It becomes inactivated when associated in a tetrameric complex with the abundant 7SK small nuclear RNA and the recently identified protein Hexim1. In this study, we identified a stable and soluble C-terminal domain (residues 255-359) in Hexim1 of 12.5-kDa size that binds the cyclin boxes of Cyclin T1. Functional assays in HeLa cells showed that this cyclin T-binding domain (TBD) is required for the binding of Hexim1 to P-TEFb and inhibition of transcriptional activity in vivo. Analytical gel filtration and GST pull-down experiments revealed that both full-length Hexim1 and the TBD are homodimers. Isothermal titration calorimetry yielded a weak multimer for the TBD with a multimerization constant of 1.3 x 10(3) m. The binding affinity between the TBD and cyclin T1 was analyzed with fluorescence spectroscopy methods, using a dansyl-based fluorescence label at position G257C. Equilibrium fluorescence titration and stopped flow fast kinetics yield a dissociation constant of 1.2 mum. Finally, we tested the effect of the HIV-1 Tat protein on the cyclin T1-TBD complex formation. GST pull-down experiments and size exclusion chromatography exhibit a mutually exclusive binding of the two effectors to cyclin T1. Our data suggest a model where HIV-1 Tat competes with Hexim1 for cyclin T1 binding, thus releasing P-TEFb from the inactive complex to stimulate the transcription of HIV-1 gene expression.
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PMID:Identification of a cyclin T-binding domain in Hexim1 and biochemical analysis of its binding competition with HIV-1 Tat. 1585 66

The positive transcription elongation factor b (P-TEFb), a complex of Cdk9 and cyclin T1/T2, stimulates transcription by phosphorylating RNA polymerase II. The 7SK small nuclear RNA, in cooperation with HEXIM1 protein, functions as a general polymerase II transcription regulator by sequestering P-TEFb into a large kinase-inactive 7SK/HEXIM1/P-TEFb complex. Here, determination and characterization of the functionally essential elements of human 7SK snRNA directing HEXIM1 and P-TEFb binding led to a new model for the assembly of the 7SK/HEXIM1/P-TEFb regulatory complex. We demonstrate that two structurally and functionally distinct protein binding elements located in the 5'- and 3'-terminal hairpins of 7SK support the in vivo recruitment of HEXIM1 and P-TEFb. Consistently, a minimal regulatory RNA composed of the 5' and 3' hairpins of 7SK can modulate polymerase II transcription in HeLa cells. HEXIM1 binds independently and specifically to the G24-C48/G60-C87 distal segment of the 5' hairpin of 7SK. Binding of HEXIM1 is a prerequisite for association of P-TEFb with the G302-C324 apical region of the 3' hairpin of 7SK that is highly reminiscent of the human immunodeficiency virus transactivation-responsive RNA.
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PMID:Regulation of polymerase II transcription by 7SK snRNA: two distinct RNA elements direct P-TEFb and HEXIM1 binding. 1638 53

The positive transcription elongation factor b (P-TEFb) stimulates transcriptional elongation by phosphorylating the carboxy-terminal domain of RNA polymerase II and antagonizing the effects of negative elongation factors. Not only is P-TEFb essential for transcription of the vast majority of cellular genes, but it is also a critical host cellular cofactor for the expression of the human immunodeficiency virus (HIV) type 1 genome. Given its important role in globally affecting transcription, P-TEFb's activity is dynamically controlled by both positive and negative regulators in order to achieve a functional equilibrium in sync with the overall transcriptional demand as well as the proliferative state of cells. Notably, this equilibrium can be shifted toward either the active or inactive state in response to diverse physiological stimuli that can ultimately affect the cellular decision between growth and differentiation. In this review, we examine the mechanisms by which the recently identified positive (the bromodomain protein Brd4) and negative (the noncoding 7SK small nuclear RNA and the HEXIM1 protein) regulators of P-TEFb affect the P-TEFb-dependent transcriptional elongation. We also discuss the consequences of perturbations of the dynamic associations of these regulators with P-TEFb in relation to the pathogenesis and progression of several major human diseases, such as cardiac hypertrophy, breast cancer, and HIV infection.
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PMID:The Yin and Yang of P-TEFb regulation: implications for human immunodeficiency virus gene expression and global control of cell growth and differentiation. 1695 64

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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PMID:P-TEFb- the final frontier. 1972 44


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