Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

P-TEFb is a key regulator of the process controlling the processivity of RNA polymerase II and possesses a kinase activity that can phosphorylate the carboxy-terminal domain of the largest subunit of RNA polymerase II. Here we report the cloning of the small subunit of Drosophila P-TEFb and the finding that it encodes a Cdc2-related protein kinase. Sequence comparison suggests that a protein with 72% identity, PITALRE, could be the human homolog of the Drosophila protein. Functional homology was suggested by transcriptional analysis of an RNA polymerase II promoter with HeLa nuclear extract depleted of PITALRE. Because the depleted extract lost the ability to produce long DRB-sensitive transcripts and this loss was reversed by the addition of purified Drosophila P-TEFb, we propose that PITALRE is a component of human P-TEFb. In addition, we found that PITALRE associated with the activation domain of HIV-1 Tat, indicating that P-TEFb is a Tat-associated kinase (TAK). An in vitro transcription assay demonstrates that the effect of Tat on transcription elongation requires P-TEFb and suggests that the enhancement of transcriptional processivity by Tat is attributable to enhanced function of P-TEFb on the HIV-1 LTR.
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PMID:Transcription elongation factor P-TEFb is required for HIV-1 tat transactivation in vitro. 933 25

To identify novel inhibitors of transcriptional activation by the HIV Tat protein, we used a combination of in vitro and in vivo Tat-dependent transcription assays to screen >100,000 compounds. All compounds identified blocked Tat-dependent stimulation of transcriptional elongation. Analysis of a panel of structurally diverse inhibitors indicated that their target is the human homolog of Drosophila positive transcription elongation factor b (P-TEFb). Loss of Tat transactivation in extracts depleted of the kinase subunit of human P-TEFb, PITALRE, was reversed by addition of partially purified human P-TEFb. Transfection experiments with wild-type or kinase knockout PITALRE demonstrated that P-TEFb is required for Tat function. Our results suggest that P-TEFb represents an attractive target for the development of novel HIV therapeutics.
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PMID:P-TEFb kinase is required for HIV Tat transcriptional activation in vivo and in vitro. 933 26

We have previously identified a cellular protein kinase activity termed TAK that specifically associates with the HIV types 1 and 2 Tat proteins. TAK hyperphosphorylates the carboxyl-terminal domain of the large subunit of RNA polymerase II in vitro in a manner believed to activate transcription [Herrmann, C. H. & Rice, A. P. (1995) J. Virol. 69, 1612-1620]. We show here that the catalytic subunit of TAK is a known human kinase previously named PITALRE, which is a member of the cyclin-dependent family of proteins. We also show that TAK activity is elevated upon activation of peripheral blood mononuclear cells and peripheral blood lymphocytes and upon differentiation of U1 and U937 promonocytic cell lines to macrophages. Therefore, in HIV-infected individuals TAK may be induced in T cells following activation and in macrophages following differentiation, thus contributing to high levels of viral transcription and the escape from latency of transcriptionally silent proviruses.
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PMID:TAK, an HIV Tat-associated kinase, is a member of the cyclin-dependent family of protein kinases and is induced by activation of peripheral blood lymphocytes and differentiation of promonocytic cell lines. 935 49

The human cdc2-related kinase PITALRE is the catalytic component of TAK, the Tat-associated kinase. Previously, we have proposed that TAK is a cellular factor that mediates Tat transactivation function. Here we demonstrate that transient overexpression of PITALRE specifically squelches Tat-1 activation of both a transfected and an integrated human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR), suggesting that PITALRE mediates Tat function as a multiprotein complex. A catalytic mutant of PITALRE, D167N, was found to be more efficient than wild-type PITALRE in squelching Tat transactivation. Neither wild-type PITALRE nor D167N was able to squelch transactivation of the human T-cell leukemia type 1 LTR by the Tax protein. Additionally, we show that artificial targeting of PITALRE to a nascent RNA element, in the absence of Tat, activated HIV-1 LTR expression. These results indicate that a PITALRE-containing complex mediates transactivation by Tat and suggest that Tat proteins function by localizing such a PITALRE-containing complex to the site of the transcribing provirus.
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PMID:PITALRE, the catalytic subunit of TAK, is required for human immunodeficiency virus Tat transactivation in vivo. 955 39

During transcription of mRNA genes, there is a correlation between the phosphorylation state of the C-terminal domain (CTD) of the large subunit of RNA polymerase II (RNAP II) and the ability of the RNAP II complex to processively transcribe the gene. To examine the involvement of CTD phosphorylation in modulation of RNAP II function, we have analyzed the ability of a known CTD kinase, human Cdk8, to modulate HIV-1 LTR-driven gene expression upon directed targeting to a promoter-proximal nascent RNA element. The results indicated that Cdk8, when localized to an RNA element, activates gene expression in a catalysis-dependent manner. Also, Cdk8 targeted to RNA was observed to act in a synergystic manner with DNA-targeted Sp1 but not with DNA-targeted HIV-1 Tat, suggesting that RNA-targeted Cdk8 acts on similar rate limiting post-initiation events as Tat. As recent observations suggest that Tat/TAR-mediated transcription of the proviral genome of HIV depends on specific phosphorylation of RNAP II in its CTD by the Tat-associated kinase (TAK/p-TEFb/Cdk9), our results indicate that Cdk8 shares with Cdk9 the ability to modulate transcription upon targeting to a nascent RNA element.
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PMID:Targeting of CDK8 to a promoter-proximal RNA element demonstrates catalysis-dependent activation of gene expression. 968 96

HIV-1 Tat activates transcription through binding to human cyclin T1, a regulatory subunit of the TAK/P-TEFb CTD kinase complex. Here we show that the cyclin domain of hCycT1 is necessary and sufficient to interact with Tat and promote cooperative binding to TAR RNA in vitro, as well as mediate Tat transactivation in vivo. A Tat:TAR recognition motif (TRM) was identified at the carboxy-terminal edge of the cyclin domain, and we show that hCycT1 can interact simultaneously with Tat and CDK9 on TAR RNA in vitro. Alanine-scanning mutagenesis of the hCycT1 TRM identified residues that are critical for the interaction with Tat and others that are required specifically for binding of the complex to TAR RNA. Interestingly, we find that the interaction between Tat and hCycT1 requires zinc as well as essential cysteine residues in both proteins. Cloning and characterization of the murine CycT1 protein revealed that it lacks a critical cysteine residue (C261) and forms a weak, zinc-independent complex with HIV-1 Tat that greatly reduces binding to TAR RNA. A point mutation in mCycT1 (Y261C) restores high-affinity, zinc-dependent binding to Tat and TAR in vitro, and rescues Tat transactivation in vivo. Although overexpression of hCycT1 in NIH3T3 cells strongly enhances transcription from an integrated proviral promoter, we find that this fails to overcome all blocks to productive HIV-1 infection in murine cells.
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PMID:The interaction between HIV-1 Tat and human cyclin T1 requires zinc and a critical cysteine residue that is not conserved in the murine CycT1 protein. 983 4

The human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR) initiates transcription efficiently but produces only short transcripts in the absence of the trans-activator protein, Tat. To determine whether a cellular enhancer could provide the signals required to recruit an elongation-competent polymerase to the HIV-1 LTR, the B cell-specific immunoglobulin heavy chain gene enhancer (IgHE) was inserted upstream of the LTR. The enhancer increased transcription in the absence of Tat between 6- and 7-fold in transfected B cells, but the full-length transcripts remained at basal levels in HeLa cells, where the enhancer is inactive. RNase-protection studies showed that initiation levels in the presence and absence of the enhancer were constant, but the enhancer significantly increased the elongation capacity of the polymerases. Tat-stimulated elongation is strongly inhibited by the nucleoside analogue 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), which inhibits the Tat-associated kinase, TAK (CDK9). However, polymerases initiating transcription from LTRs carrying the enhancer were able to efficiently elongate in the presence of DRB. Specific repression of TAK by expression in trans of the CDK9 kinase also inhibited Tat-stimulated elongation but did not inhibit enhancer-dependent transcription significantly. Thus, the activation of polymerase processivity by the IgHE involves a unique mechanism which is independent of TAK.
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PMID:Stimulation of Tat-associated kinase-independent transcriptional elongation from the human immunodeficiency virus type-1 long terminal repeat by a cellular enhancer. 1006 3

CDK9 is a cdc2-related kinase protein. Previously named PITALRE, this protein is a serine-threonine kinase involved in many physiological processes. Unlike most of the cdc2-like kinases, its activity is not cell cycle-regulated. CDK9 acts preferentially in processes different from cell-cycle regulation, such as differentiation. Its cyclin partners, cyclins of T family, recently have been isolated. CDK9 immunoprecipitates with several unidentified polypeptides that may regulate its kinase activity. CDK9 has been shown to associate with the HIV-Tat protein, suggesting a possible involvement in AIDS. CDK9 recently was shown to be responsible for the kinase activity associated with the TAK complex and with the P-TEFb complex, suggesting activity also in the transcription process.
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PMID:CDK9 (PITALRE): a multifunctional cdc2-related kinase. 1009 3

The beta-chemokine receptor CCR5 is considered to be an attractive target for inhibition of macrophage-tropic (CCR5-using or R5) HIV-1 replication because individuals having a nonfunctional receptor (a homozygous 32-bp deletion in the CCR5 coding region) are apparently normal but resistant to infection with R5 HIV-1. In this study, we found that TAK-779, a nonpeptide compound with a small molecular weight (Mr 531.13), antagonized the binding of RANTES (regulated on activation, normal T cell expressed and secreted) to CCR5-expressing Chinese hamster ovary cells and blocked CCR5-mediated Ca2+ signaling at nanomolar concentrations. The inhibition of beta-chemokine receptors by TAK-779 appeared to be specific to CCR5 because the compound antagonized CCR2b to a lesser extent but did not affect CCR1, CCR3, or CCR4. Consequently, TAK-779 displayed highly potent and selective inhibition of R5 HIV-1 replication without showing any cytotoxicity to the host cells. The compound inhibited the replication of R5 HIV-1 clinical isolates as well as a laboratory strain at a concentration of 1.6-3.7 nM in peripheral blood mononuclear cells, though it was totally inactive against T-cell line-tropic (CXCR4-using or X4) HIV-1.
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PMID:A small-molecule, nonpeptide CCR5 antagonist with highly potent and selective anti-HIV-1 activity. 1031 47

Actinomycin D and alpha-amanitin are commonly used to inhibit transcription. Unexpectedly, however, the transcription of the human immunodeficiency virus (HIV-1) long terminal repeats (LTR) is shown to be activated at the level of elongation, in human and murine cells exposed to these drugs, whereas the Rous sarcoma virus LTR, the human cytomegalovirus immediate early gene (CMV), and the HSP70 promoters are repressed. Activation of the HIV LTR is independent of the NFkappaB and TAR sequences and coincides with an enhanced average phosphorylation of the C-terminal domain (CTD) from the largest subunit of RNA polymerase II. Both the HIV-1 LTR activation and the bulk CTD phosphorylation enhancement are prevented by several CTD kinase inhibitors, including 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole. The efficacies of the various compounds to block CTD phosphorylation and transcription in vivo correlate with their capacities to inhibit the CDK9/PITALRE kinase in vitro. Hence, the positive transcription elongation factor, P-TEFb, is likely to contribute to the average CTD phosphorylation in vivo and to the activation of the HIV-1 LTR induced by actinomycin D.
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PMID:The transcriptional inhibitors, actinomycin D and alpha-amanitin, activate the HIV-1 promoter and favor phosphorylation of the RNA polymerase II C-terminal domain. 1034 61


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