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)

Tat activation of HIV-1 transcription is mediated by human transcription elongation factor P-TEFb, which interacts with Tat and phosphorylates the C-terminal domain of RNA polymerase II. The catalytic subunit of the P-TEFb complex, Cdk9, has been shown to interact with cyclin T and several other proteins of unknown identity. Consequently, the exact subunit composition of active P-TEFb has not been determined. Here we report the affinity purification and identification of the Cdk9-associated proteins. In addition to forming a heterodimer with cyclin T1, Cdk9 interacted with the molecular chaperone Hsp70 or a kinase-specific chaperone complex, Hsp90/Cdc37, to form two separate chaperone-Cdk9 complexes. Although the Cdk9/cyclin T1 dimer was exceptionally stable and produced slowly in the cell, free and unprotected Cdk9 appeared to be degraded rapidly. Several lines of evidence indicate the heterodimer of Cdk9/cyclin T1 to be the mature, active form of P-TEFb responsible for phosphorylation of the C-terminal domain of RNA polymerase II interaction with the Tat activation domain, and mediation of Tat activation of HIV-1 transcription. Pharmacological inactivation of Hsp90/Cdc37 function by geldanamycin revealed an essential role for the chaperone-Cdk9 complexes in generation of Cdk9/cyclin T1. Our data suggest a previously unrecognized chaperone-dependent pathway involving the sequential actions of Hsp70 and Hsp90/Cdc37 in the stabilization/folding of Cdk9 as well as the assembly of an active Cdk9/cyclin T1 complex responsible for P-TEFb-mediated Tat transactivation.
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PMID:Requirement for a kinase-specific chaperone pathway in the production of a Cdk9/cyclin T1 heterodimer responsible for P-TEFb-mediated tat stimulation of HIV-1 transcription. 1061 16

The HIV trans-activator Tat recruits the host transcription elongation factor P-TEFb to stimulate proviral transcription. Phosphorylation of Thr-186 on the activation loop (T-loop) of cyclin-dependent kinase 9 (CDK9) is essential for its kinase activity and assembly of CDK9 and cyclin T1 (CycT1) to form functional P-TEFb. Phosphorylation of a second highly conserved T-loop site, Ser-175, alters the competitive binding of Tat and the host recruitment factor bromodomain containing 4 (BRD4) to P-TEFb. Here, we investigated the intracellular mechanisms that regulate these key phosphorylation events required for HIV transcription. Molecular dynamics simulations revealed that the CDK9/CycT1 interface is stabilized by intramolecular hydrogen bonding of pThr-186 by an arginine triad and Glu-96 of CycT1. Arginine triad substitutions that disrupted CDK9/CycT1 assembly accumulated Thr-186-dephosphorylated CDK9 associated with the cytoplasmic Hsp90/Cdc37 chaperone. The Hsp90/Cdc37/CDK9 complex was also present in resting T cells, which lack CycT1. Hsp90 inhibition in primary T cells blocked P-TEFb assembly, disrupted Thr-186 phosphorylation, and suppressed proviral reactivation. The selective CDK7 inhibitor THZ1 blocked CDK9 phosphorylation at Ser-175, and in vitro kinase assays confirmed that CDK7 activity is principally responsible for Ser-175 phosphorylation. Mutation of Ser-175 to Lys had no effect on CDK9 kinase activity or P-TEFb assembly but strongly suppressed both HIV expression and BRD4 binding. We conclude that the transfer of CDK9 from the Hsp90/Cdc37 complex induced by Thr-186 phosphorylation is a key step in P-TEFb biogenesis. Furthermore, we demonstrate that CDK7-mediated Ser-175 phosphorylation is a downstream nuclear event essential for facilitating CDK9 T-loop interactions with Tat.
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PMID:Cyclin-dependent kinase 7 (CDK7)-mediated phosphorylation of the CDK9 activation loop promotes P-TEFb assembly with Tat and proviral HIV reactivation. 2974 42

The positive transcription elongation factor b (P-TEFb), composed of CDK9 and cyclin T, stimulates transcriptional elongation by RNA polymerase (Pol) II and regulates cell growth and differentiation. Recently, we demonstrated that P-TEFb also controls the expression of EMT regulators to promote breast cancer progression. In the nucleus, more than half of P-TEFb are sequestered in the inactive-state 7SK snRNP complex. Here, we show that the assembly of the 7SK snRNP is preceded by an intermediate complex between HEXIM1 and P-TEFb that allows transfer of the kinase active P-TEFb from Hsp90 to 7SK snRNP for its suppression. Down-regulation of HEXIM1 locks P-TEFb in the Hsp90 complex, keeping it in the active state to enhance breast cancer progression, but also rendering the cells highly sensitive to Hsp90 inhibition. Because HEXIM1 is often down-regulated in human triple-negative breast cancer (TNBC), these cells are particularly sensitive to Hsp90 inhibition. Our study provides a mechanistic explanation for the increased sensitivity of TNBC to Hsp90 inhibition.
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PMID:HEXIM1 controls P-TEFb processing and regulates drug sensitivity in triple-negative breast cancer. 3252 Jun 33