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)

Tat stimulates HIV-1 gene expression during transcription initiation and elongation. Tat functions primarily through specific interactions with TAR RNA and several putative cellular cofactors to increase the processivity of RNA polymerase II complexes during HIV-1 transcription elongation. Although HIV-1 transactivation by Tat in most cell types requires intact TAR sequences, previous reports demonstrate that Tat transactivates HIV-1 long terminal repeat (LTR)-directed gene expression in several central nervous system-derived astrocytic/glial cell lines in the absence of TAR. Within this study, transient expression assays performed in the astrocytic/glial cell line, U87-MG, confirm that kappa B elements within the HIV-1 LTR mediate TAR-independent transactivation by Tat and demonstrate additionally that distinct amino acid residues within the cysteine-rich activation domain of Tat are required for TAR-independent versus TAR-dependent transactivation. Established U87-MG cell lines expressing a transdominant negative mutant of I kappa B alpha, I kappa B alpha delta N, fail to support TAR-independent transactivation by Tat, suggesting that binding of NF-kappa B to kappa B enhancer elements within the HIV-1 LTR is necessary for Tat-mediated transactivation in the absence of TAR. Ribonucleic acid protection analyses of promoter-proximal and -distal transcripts derived from TAR-deleted and TAR-containing HIV-1 LTR reporter constructs in U87-MG cells indicate that the predominant effect of Tat during TAR-independent transactivation occurs at the lavel of transcription initiation, whereas a prominent elongation effect of Tat is observed in the presence of TAR. These data suggest an alternative regulatory pathway for Tat transactivation in specific cells derived from the central nervous system that is independent of TAR and that requires direct or indirect interaction of Tat with NF-kappa B-binding sites in the HIV-1 LTR.
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PMID:Distinct transcriptional pathways of TAR-dependent and TAR-independent human immunodeficiency virus type-1 transactivation by Tat. 930 36

Tat protein mediates transactivation of human immunodeficiency virus type 1 (HIV-1), which results in more-efficient transcript elongation. Since phosphorylation of C-terminal domain (CTD) of RNA polymerase II correlates with its enhanced processivity, we studied the properties of a Tat-associated CTD kinase derived from mitogenically stimulated human primary T lymphocytes (TTK). TTK binds to full-length Tat and specifically phosphorylates CTD and CDK2. This dual kinase activity is characteristic of CDK-activating kinase (CAK). The CTD kinase activity is induced upon mitogenic stimulation of primary T lymphocytes. Fractionation of T-cell lysate demonstrates that Tat-associated CTD kinase activity elutes in two peaks. About 60% of Tat-associated CTD kinase copurifies with CDK2 kinase activity and contains the CAK components CDK7 and cyclin H. The rest of Tat-associated kinase is free of CDK2 kinase activity and the CAK components and thus may represent a novel CTD kinase. The kinase activities of TTK are blocked by the adenosine analog 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) as well as by the kinase inhibitor H8 at concentrations known to block transcript elongation. Importantly, the Tat-associated kinase markedly induced CAK. We suggest that the mechanism of Tat-mediated processive transcription of the HIV-1 promoter includes a Tat-associated CAK activator.
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PMID:A human primary T-lymphocyte-derived human immunodeficiency virus type 1 Tat-associated kinase phosphorylates the C-terminal domain of RNA polymerase II and induces CAK activity. 931 22

Maximal human immunodeficiency virus type 1 (HIV-1) gene expression requires specific cellular factors in addition to the virus-encoded trans-activator protein Tat and the RNA element TAR. We developed a functional assay, based on transcriptional activation in vitro, to identify these cellular factors. Here, we describe the purification and molecular cloning of CA150, a nuclear protein that is associated with the human RNA polymerase II holoenzyme and is involved in Tat-dependent HIV-1 transcriptional activation. The sequence of CA150 contains an extensive glutamine- and alanine-rich repeat that is found in transcriptional modulators such as GAL11 and SSN6 in Saccharomyces cerevisiae and Zeste in Drosophila melanogaster. Immunodepletion of CA150 abolished Tat trans activation in vitro. Moreover, overexpression of a mutant CA150 protein specifically and dramatically decreased Tat-mediated activation of the HIV-1 promoter in vivo, strongly suggesting a role for CA150 in HIV-1 gene regulation. Immunoprecipitation experiments demonstrated that both CA150 and Tat associate with the RNA polymerase II holoenzyme. Furthermore, we found that functional Tat associates with the holoenzyme whereas activation-deficient Tat mutants do not. Thus, we propose that Tat action is transduced via an RNA polymerase II holoenzyme that contains CA150.
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PMID:CA150, a nuclear protein associated with the RNA polymerase II holoenzyme, is involved in Tat-activated human immunodeficiency virus type 1 transcription. 931 62

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

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

Intracellular applications of ribozymes have been limited partly by the availability of suitable high-expression systems. For RNA effectors, consideration of an RNA virus vector system for delivery and expression is reasonable. We show that alphavirus replicons can be highly efficient nonintegrating ribozyme-expressing vectors. Using a hammerhead ribozyme targeted to a highly conserved sequence in the U5 region of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat, we demonstrate that a full-length 8.3-kb Semliki Forest virus ribozyme (SFVRz) chimeric RNA maintains catalytic activity. SFVRz is packaged into viral particles, and these particles transduce mammalian cells efficiently. SFVRz-transduced BHK cells were found to produce large amounts of genomic and subgenomic forms of ribozyme-containing RNAs that are functional in cleaving a U5-tagged mRNA. The RNase protection assay shows that HIV-1 U5-chloramphenicol acetyltransferase mRNA expressed intracellularly from an RNA polymerase II promoter is quantitatively eliminated in SFVRz-transduced BHK cells.
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PMID:Efficient expression by an alphavirus replicon of a functional ribozyme targeted to human immunodeficiency virus type 1. 937 37

Artificial recruitment of TATA-binding protein (TBP) to many eukaryotic promoters bypasses DNA-bound activator function. The human immunodeficiency virus type 1 (HIV-1) Tat is an unconventional activator that up-regulates transcription from the HIV-1 long terminal repeat (LTR) through binding to a nascent RNA sequence, TAR. Because this LTR and its cognate activator have atypical features compared to a standard RNA polymerase II (RNAP II) transcriptional unit, the precise limiting steps for HIV-1 transcription and how Tat resolves these limitations remain incompletely understood. We thus constructed human TBP fused to the DNA-binding domain of GAL4 to determine whether recruitment of TBP is one rate-limiting step in HIV-1 LTR transcription and whether Tat functions to recruit TBP. As a control, we compared the activity of the adenovirus E1b promoter. Our findings indicate that TBP tethering to the E1b promoter fully effected transcription to the same degree achievable with the potent GAL4-VP16 activator. By contrast, TBP recruitment to the HIV-1 LTR, although necessary for conferring Tat responsiveness, did not bypass a physical need for Tat in achieving activated transcription. These results document that the HIV-1 and the E1b promoters are transcriptionally limited at different steps; the major rate-limiting step for E1b is recruitment of TBP, while activation of the HIV-1 LTR requires steps in addition to TBP recruitment. We suggest that Tat acts to accelerate rate-limiting steps after TBP recruitment.
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PMID:Promoter activity of Tat at steps subsequent to TATA-binding protein recruitment. 937 21

Tat of HIV-2 (Tat-2) requires host cellular factors for optimal function. We show that transactivation by Tat-2 of the HIV promoter requires cis-acting binding sites for Sp1 or Sp1 brought to the promoter via a heterologous system. We demonstrate that an activation domain in Tat-2 consists of one of two potential alpha-helices in the amino-terminal region, the cysteine-rich region, and the core region and that this independent activation domain requires cis-acting Sp1-binding sites for function. Tat-2 interacts with Sp1 in in vitro binding assays, and these interactions require basic residues outside of the Tat-2 activation domain. The regions in Sp1 sufficient for functional synergy with Tat are the Sp1 activation domains, while the DNA-binding region is dispensable. Substitution mutations of a glutamine-rich region in one Sp1 activation domain, which eliminate interactions with a TBP-associated factor, also significantly decrease synergy with Tat. Thus, the functional synergy between Tat-2 and Sp1 localizes to domains in each activator that interact with components of the transcription complex. We suggest that these interactions, rather than direct Tat/Sp1 binding, result in highly processive RNA polymerase II complexes and full-length viral transcripts.
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PMID:Interactions between Tat of HIV-2 and transcription factor Sp1. 940 May 95

Transcriptional interference between adjacent genes has been demonstrated in a variety of biological systems. To study this process in RNA polymerase II (pol II) transcribed genes we have analysed the effect of transcription on tandem HIV-1 promoters integrated into the genome of HeLa cells. We show that transcriptional activation at the upstream promoter reduces transcription from the downstream promoter, as compared with basal transcription conditions (in the absence of an activator). Furthermore, insertion of a strong transcriptional termination element between the two promoters alleviates this transcriptional interference, resulting in elevated levels of transcription from the downstream promoter. Actual protein interactions with the downstream (occluded) promoter were analysed by in vivo footprinting. Binding of Sp1 transcription factors to the occluded promoter was reduced, when compared with the footprint pattern of the promoter protected by the terminator. This suggests that promoter occlusion is due to disruption of certain transcription factors and that it can be blocked by an intervening transcriptional terminator. Chromatin mapping with DNase I indicates that a factor binds to the termination element under both basal and induced conditions.
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PMID:Transcriptional interference perturbs the binding of Sp1 to the HIV-1 promoter. 946 40

Replication of HIV-1 requires the viral Tat protein, which increases the extent of transcription elongation by RNA polymerase II after activation at the single viral long terminal repeat (LTR) promoter. This effect of Tat on transcription requires Tat interactions with a 5' region (TAR) in nascent transcripts as well as Tat-specific cofactors. The present study identifies a cellular protein, TIP30, that interacts with Tat and with an SRB-containing RNA polymerase II complex both in vivo and in vitro. Coexpression of TIP30 specifically enhances transactivation by Tat in transfected cells, and immunodepletion of TIP30 from nuclear extracts abolishes Tat-activated transcription without affecting Tat-independent transcription. These results implicate TIP30 as a specific coactivator that may enhance formation of a Tat-RNA polymerase II holoenzyme complex.
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PMID:A cofactor, TIP30, specifically enhances HIV-1 Tat-activated transcription. 948 53


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