Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Combinations of cytokines are known to reactivate transcription and replication of latent human immunodeficiency virus type 1 (HIV-1) proviruses in resting CD4(+) T lymphocytes isolated from infected individuals. Transcription of the HIV-1 provirus by RNA polymerase II is strongly stimulated by the viral Tat protein. Tat function is mediated by a cellular protein kinase known as TAK (cyclin T1/P-TEFb) that is composed of Cdk9 and cyclin T1. We have found that treatment of peripheral blood lymphocytes and purified resting CD4(+) T lymphocytes with the combination of interleukin-2 (IL-2), IL-6, and tumor necrosis factor alpha resulted in an increase in Cdk9 and cyclin T1 protein levels and an increase in TAK enzymatic activity. The cytokine induction of TAK in resting CD4(+) T lymphocytes did not appear to require proliferation of lymphocytes. These results suggest that induction of TAK by cytokines secreted in the microenvironment of lymphoid tissue may be involved in the reactivation of HIV-1 in CD4(+) T lymphocytes harboring a latent provirus.
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PMID:Induction of TAK (cyclin T1/P-TEFb) in purified resting CD4(+) T lymphocytes by combination of cytokines. 1168 14

The human immunodeficiency virus type 1 (HIV-1) Tat protein activates transcription elongation by stimulating the Tat-activated kinase (TAK/p-TEFb), a protein kinase composed of CDK9 and its cyclin partner, cyclin T1. CDK9 is able to hyperphosphorylate the carboxyl-terminal domain (CTD) of the large subunit of RNA polymerase during elongation. In addition to TAK, the transcription elongation factor Spt5 is required for the efficient activation of transcriptional elongation by Tat. To study the role of Spt5 in HIV transcription in more detail, we have developed a three-stage Tat-dependent transcription assay that permits the isolation of active preinitiation complexes, early-stage elongation complexes, and Tat-activated elongation complexes. Spt5 is recruited in the transcription complex shortly after initiation. After recruitment of Tat during elongation through the transactivation response element RNA, CDK9 is activated and induces hyperphosphorylation of Spt5 in parallel to the hyperphosphorylation of the CTD of RNA polymerase II. However, immunodepletion experiments demonstrate that Spt5 is not required for Tat-dependent activation of the kinase. Chase experiments using the Spt5-depleted extracts demonstrate that Spt5 is not required for early elongation. However, Spt5 plays an important role in late elongation by preventing the premature dissociation of RNA from the transcription complex at terminator sequences and reducing the amount of polymerase pausing at arrest sites, including bent DNA sequences. This novel biochemical function of Spt5 is analogous to the function of NusG, an elongation factor found in Escherichia coli that enhances RNA polymerase stability on templates and shows sequence similarity to Spt5.
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PMID:Spt5 cooperates with human immunodeficiency virus type 1 Tat by preventing premature RNA release at terminator sequences. 1180

The human immunodeficiency virus type 1 (HIV-1) Tat protein is essential for viral replication and stimulates transcription of the integrated provirus by recruiting the kinase complex TAK/P-TEFb, composed of cyclin T1 (CycT1) and Cdk9, to the viral TAR RNA element. TAK/P-TEFb phosphorylates the RNA polymerase II complex and stimulates transcriptional elongation. In this report, we investigated the regulation of TAK/P-TEFb in primary human macrophages, a major target cell of HIV infection. While Cdk9 levels remained constant, CycT1 protein expression in freshly isolated monocytes was very low, increased early during macrophage differentiation, and, unexpectedly, decreased to very low levels after about 1 week in culture. The kinase activity of TAK/P-TEFb paralleled the changes in CycT1 protein expression. RNA analysis indicated that the transient induction of CycT1 protein expression involves a posttranscriptional mechanism. In transient transfection assays, the ability of Tat to transactivate the HIV long terminal repeat (LTR) in the late differentiated macrophages was greatly diminished relative to its ability to transactivate the HIV LTR in early differentiated cells, strongly suggesting that CycT1 is limiting for Tat function in late differentiated macrophages. Interestingly, lipopolysaccharide, a component of the cell wall of gram-negative bacteria, reinduced CycT1 expression late in macrophage differentiation. These results raise the possibility that regulation of CycT1 expression may be involved in establishing latent infection in macrophages and that opportunistic infection may reactivate the virus by inducing CycT1 expression.
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PMID:Transient induction of cyclin T1 during human macrophage differentiation regulates human immunodeficiency virus type 1 Tat transactivation function. 1236


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