Activation and function of cyclin T–Cdk9 (positive transcription elongation factor-b) in cardiac muscle-cell hypertrophy

Sano, Motoaki; Abdellatif, Maha; Oh, Hidemasa; Xie, Min; Bagella, Luigi; Giordano, Antonio; Michael, Lloyd H.; DeMayo, Francesco J.; Schneider, Michael

doi:10.1038/nm778

Cited by 228 publications

(286 citation statements)

References 45 publications

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“…fraction of P-TEFb in response to stress signals and environmental stimuli can lead to a significant induction of the overall P-TEFb activity in the cell. Consistent with these ideas, it has been noticed that although CDK9 and CycT1 are fairly abundant in the cell, the amount of the transcriptionally active P-TEFb appears to be limiting in a variety of cell types and under different conditions (8,24,37). Finally, by targeting CDK9 with the phosphorylated T-loop and consequently an "open" conformation, 7SK/HEXIM1 may physically block the access to the catalytic center, thereby inhibiting the CDK9 kinase.…”

Section: Discussionmentioning

confidence: 81%

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Phosphorylated Positive Transcription Elongation Factor b (P-TEFb) Is Tagged for Inhibition through Association with 7SK snRNA

Chen

Yang

Zhou

2004

Journal of Biological Chemistry

162

213

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The positive transcription elongation factor b (PTEFb), 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 stressinduced transcription and pathogenesis of cardiac hypertrophy. The 7SK⅐P-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 7SK⅐P-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 7SK⅐P-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.7SK is an abundant (2 ϫ 10 5 copies/cell) and evolutionarily conserved small nuclear RNA (snRNA) 1 of ϳ330 nucleotides (1-4). It is transcribed by RNA polymerase (Pol) III from one or more genes belonging to a family of interspersed repeats in the mammalian genome (2, 5). The high conservation and abundance of 7SK suggest an important physiological function of this RNA. In searching for nuclear factors that can bind to and regulate the activity of human positive transcription elongation factor b (P-TEFb), we and others (6, 7) have identified 7SK as a specific P-TEFb-associated factor. Consisting of CDK9 and cyclin T1 (CycT1) (8, 9), P-TEFb strongly enhances the processivity of RNA Pol II by phosphorylating the C-terminal domain (CTD) of Pol II and antagonizing the actions of negative elongation factors (10 -13). Studies employing RNA interference in Caenorhabditis elegans and a pharmacological inhibitor of CDK9 in mammalian cells implicate P-TEFb as essential for expression of most protein-coding genes (10, 14).P-TEFb also functions as a specific host cellular cofactor for the HIV-1 Tat protein. Stimulation of Pol II elongation is essential for HIV transcription, during which P-TEFb is recruited to the nascent mRNA by Tat (15, 16). Tat binds to CycT1 and recruits P-TEFb through formation of a stable ternary complex containing P-TEFb, Tat, and the HIV TAR RNA structure located at the 5Ј-end of the nascent viral transcript. Once recruited, P-TEFb phosphorylates the CTD and stimulates the production of the full-l...

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Section: Discussionmentioning

confidence: 81%

“…P-TEFb activity is limiting for normal cardiac growth. Hypertrophic signals induce the dissociation of 7SK (presumably also HEXIM1) from P-TEFb, activating P-TEFb to stimulate Pol II transcription (23,24).…”

mentioning

confidence: 99%

Phosphorylated Positive Transcription Elongation Factor b (P-TEFb) Is Tagged for Inhibition through Association with 7SK snRNA

Chen

Yang

Zhou

2004

Journal of Biological Chemistry

162

213

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“…However, genetic disruption of the CLP-1 gene, which is a mouse homologue of HEXIM1, is reported to result in embryonic lethality with marked cardiac hypertrophy (33). Moreover, it is separately shown that hyperactivation of P-TEFb in cardiac myocytes produces cardiac hypertrophy (34). It is therefore likely that HEXIM1 plays an important role in cardiac development and disease pathogenesis.…”

Section: Discussionmentioning

confidence: 99%

HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b

Shimizu

Ouchida

Yoshikawa

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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The HEXIM1 protein has been shown to form a protein-RNA complex composed of 7SK small nuclear RNA and positive transcription elongation factor b (P-TEFb), which is composed of cyclindependent kinase 9 (CDK9) and cyclin T1, and to inhibit the kinase activity of CDK9, thereby suppressing RNA polymerase II-dependent transcriptional elongation. Here, we biochemically demonstrate that HEXIM1 forms a distinct complex with glucocorticoid receptor (GR) without RNA, CDK9, or cyclin T1. HEXIM1, through its arginine-rich nuclear localization signal, directly associates with the ligand-binding domain of GR. Introduction of HEXIM1 short interfering RNA and adenovirus-mediated exogenous expression of HEXIM1 positively and negatively modulated glucocorticoidresponsive gene activation, respectively. In the nucleus, HEXIM1 was shown to localize in a distinct compartment from that of the p160 coactivator transcriptional intermediary factor 2. Overexpression of HEXIM1 decreased ligand-dependent association between GR and transcriptional intermediary factor 2. Antisense-mediated disruption of 7SK blunted the negative effect of HEXIM1 on arylhydrocarbon receptor-dependent transcription but not on GRmediated one, indicating that a class of transcription factors are direct targets of HEXIM1. These results indicate that HEXIM1 has dual roles in transcriptional regulation: inhibition of transcriptional elongation dependent on 7SK RNA and positive transcription elongation factor b and interference with the sequence-specific transcription factor GR via a direct protein-protein interaction. Moreover, the fact that the central nuclear localization signal of HEXIM1 is essential for both of these actions may argue the crosstalk of these functions.nuclear receptor ͉ RNA-binding protein ͉ ribonucleoprotein ͉ steroid ͉ nuclear localization signal T ranscription is a complex multistep process that relies on highly coordinated actions of a number of cis-and transacting elements (1-3). RNA polymerase II (RNAP II), as the central player in transcription of class II genes, carries out a series of events that include promoter binding, transcription initiation, promoter escape, transcription elongation, and transcription termination. During transcription by RNAP II, phosphorylation of the C-terminal domain of the largest subunit of RNAP II by positive transcription elongation factor b (P-TEFb), which is composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1, is crucial for the transition from the abortive to the productive phase of transcriptional elongation, leading to the generation of full-length RNA transcripts. P-TEFb has been shown to lose its ability to phosphorylate the C-terminal domain when associated with 7SK RNA, a 330-nt small nuclear RNA (4-6).HEXIM1 was first identified as a protein whose expression is induced in vascular smooth muscle cells (VSMC) in response to hexamethylene bisacetamide (HMBA) treatment (7, 8). The HEXIM1 protein consists of 359 amino acids and is tentatively divided into three regions: an N-terminal proline-rich ...

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“…During pathological remodeling, the heart also undergoes a shift in its mode of energy utilization from oxidative toward glycolytic, which may further contribute to cardiac demise (19). Modulation of RNA polymerase II activity by cyclin-dependent protein kinases has been shown to contribute to many of the abovementioned processes in the diseased heart (20).…”

Section: Transcriptional Remodeling Of the Hypertrophic And Failing Hmentioning

confidence: 99%

Toward transcriptional therapies for the failing heart: chemical screens to modulate genes

McKinsey¹,

Olson²

2005

J. Clin. Invest.

117

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In response to acute and chronic stresses, the heart frequently undergoes a remodeling process that is accompanied by myocyte hypertrophy, impaired contractility, and pump failure, often culminating in sudden death. The existence of redundant signaling pathways that trigger heart failure poses challenges for therapeutic intervention. Cardiac remodeling is associated with the activation of a pathological gene program that weakens cardiac performance. Thus, targeting the disease process at the level of gene expression represents a potentially powerful therapeutic approach. In this review, we describe strategies for normalizing gene expression in the failing heart with small molecules that control signal transduction pathways directed at transcription factors and associated chromatin-modifying enzymes.

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Activation and function of cyclin T–Cdk9 (positive transcription elongation factor-b) in cardiac muscle-cell hypertrophy

Cited by 228 publications

References 45 publications

Phosphorylated Positive Transcription Elongation Factor b (P-TEFb) Is Tagged for Inhibition through Association with 7SK snRNA

Phosphorylated Positive Transcription Elongation Factor b (P-TEFb) Is Tagged for Inhibition through Association with 7SK snRNA

HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b

Toward transcriptional therapies for the failing heart: chemical screens to modulate genes

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