Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human immunodeficiency virus type 1 (HIV-1) RNA contains an extended hairpin structure at the 5' end (the TAR element) that is essential for viral replication. The upper part of the stem-loop structure binds the virally encoded transcriptional activator protein Tat and cellular co-factors, but no clear function for the lower stem region has been established. Here, we report that mutant HIV-1 viruses with base substitutions in the lower stem region are dead, most likely at the level of transcription from an integrated provirus. By using large amounts of these mutant DNA constructs for transfections, revertant viruses with a great variety of genetic changes (point mutations, short deletions) could be isolated in prolonged culture experiments that lasted over 6 months. The pattern and evolution of these changes supported the notion that base-pairing of the lower stem region is essential for optimal HIV-1 replication. The functional and genetic plasticities of this RNA domain and the HIV-1 long terminal repeat promoter are discussed.
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PMID:Evolution of a disrupted TAR RNA hairpin structure in the HIV-1 virus. 801 64

The p53 tumor suppressor gene product, a sequence-specific DNA-binding protein, has been shown to act as a transcriptional activator and repressor both in vitro and in vivo. Consistent with its role in regulating transcription are recent observations that the N-terminal acidic domain of p53 binds directly to the TATA box-binding protein subunit of the general transcription factor, TF IID. It is now demonstrated that wild-type p53 (wt-p53) inhibits human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR)-directed chloramphenicol acetyltransferase activity in a cotransfection assay system. Importantly, this effect of wt-p53 on the HIV-1 LTR was also demonstrated by in vitro transcription assays. In addition, the Sp1 sites and the TATA box of the HIV-1 LTR are demonstrated to be the primary sites involved with p53-induced effects on this viral promoter. The upstream elements of the HIV-1 LTR, including the nuclear factor kappa B (NF-kappa B) binding sites, decrease the p53-induced inhibitory effects on viral transcription. In the presence of the HIV-1 TAR sequence and Tat protein, the HIV-1 LTR also becomes less sensitive to wt-p53-induced inhibition. By using a retroviral vector delivery system, mutant forms of p53 genes were expressed in two HIV-1 latently infected cell lines, ACH-2 and U1. In the ACH-2 cell line, which is now demonstrated to contain an endogenous mutant form of p53 (amino acid 248, Arg to Gln), additional mutant p53 proteins did not alter HIV-1 replication. In U1 cells, which completely lack endogenous p53, overexpression of mutant p53 led to an increase in HIV-1 replication. Thus, these data indicate a possible functional role for wt-p53 and mutant p53 proteins in the control of HIV-1 replication patterns and proviral latency.
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PMID:The tumor suppressor protein p53 strongly alters human immunodeficiency virus type 1 replication. 820 5

Human immunodeficiency virus (HIV-1) gene expression is activated by the viral TAT protein that interacts with an RNA sequence, TAR, located at the 5' end of all viral mRNAs. TAT functions primarily as a transcriptional activator in mammalian cells. However, in Xenopus oocytes TAT functions primarily as a translational activator. TAR is an RNA structure comprising a partially base-paired stem, a tripyrimidine bulge in the upper stem, and an unpaired six-nucleotide loop. In vitro, TAT binds directly to the bulge with no requirement for the loop. In vivo, however, mutations in the loop abolish TAT activation of transcription and translation, implying a requirement for TAR-binding cellular factors. We now provide genetic evidence for the presence of two TAR-specific cellular factors in Xenopus oocytes. These factors display independent and mutually exclusive interactions with either the loop or the bulge region of TAR. Furthermore, by using in vivo RNA competition assays we show that the cellular factors regulate the accessibility of the TAT binding site. The fact that Xenopus oocytes contain factors that specifically interact with a human viral RNA sequence might indicate that the TAT/TAR interaction is subverting a conserved pathway in the cell.
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PMID:HIV-1 TAR RNA-binding proteins control TAT activation of translation in Xenopus oocytes. 842 67

The biological activity of the human immunodeficiency virus type 1 (HIV-1) Tat (Tat1) transcriptional activator requires the recruitment of a Tat1-CyclinT1 (CycT1) complex to the TAR RNA target encoded within the viral long terminal repeat (LTR). While other primate immunodeficiency viruses, such as HIV-2 and mandrill simian immunodeficiency virus (SIVmnd), also encode Tat proteins that activate transcription via RNA targets, these proteins differ significantly, both from each other and from Tat1, in terms of their ability to activate transcription directed by LTR promoter elements found in different HIV and SIV isolates. Here, we show that CycT1 also serves as an essential cofactor for HIV-2 Tat (Tat2) and SIVmnd Tat (Tat-M) function. Moreover, the CycT1 complex formed by each Tat protein displays a distinct RNA target specificity that accurately predicts the level of activation observed with a particular LTR. While Tat2 and Tat-M share the ability of Tat1 to bind to CycT1, they differ from Tat1 in that they are also able to bind to the related but distinct CycT2. However, the resultant Tat-CycT2 complexes fail to bind TAR and are therefore abortive. Surprisingly, mutation of a single residue in CycT2 (asparagine 260 to cysteine) rescues the ability of CycT2 to bind Tat1 and also activates not only TAR binding by all three Tat-CycT2 complexes but also Tat function. Therefore, the RNA target specificity of different Tat-CycT1 complexes is modulated by natural sequence variation in both the viral Tat transcriptional activator and in the host cell CycT molecule recruited by Tat. Further, the RNA target specificity of the resultant Tat-CycT1 complex accurately predicts the ability of that complex to activate transcription from a given LTR promoter element.
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PMID:Analysis of the effect of natural sequence variation in Tat and in cyclin T on the formation and RNA binding properties of Tat-cyclin T complexes. 1036 29

Human immunodeficiency virus type 1 (HIV-1) is unique in that it encodes its own transcriptional activator Tat, which specifically binds to the viral mRNA sequence TAR (transactivation response) element and activates viral transcription at the step of elongation as well as initiation. We recently reported that fluoroquinoline derivatives inhibited HIV-1 replication most likely by blocking viral transcription. In this report, we investigated the mechanism of action of one such compound 7-(3, 4-dehydro-4-phenyl-1-piperidinyl)-1, 4-dihydro-6-fluoro-1-methyl-8-trifluoromethyl-4-oxoquinoline-3-carbox ylic acid (K-37). We demonstrated that K-37 inhibited not only Tat but also other RNA-dependent transactivators. No effect was observed with DNA-dependent transactivators such as p65 (NF-kappaB) and Gal4VP16. Moreover, K-37 did not inhibit carboxyl-terminal domain (CTD)-kinase activities of CDK-activating kinase (CAK) and positive transcription elongation factor b (P-TEFb), which are known to be involved in Tat-mediated transactivation at the step of transcriptional elongation. It is suggested that RNA-mediated transactivation may involve a common unknown factor to which K-37 directly interacts. Since K-37 did not appear to block DNA-mediated transactivation and thus did not show strong nonspecific cytotoxicity as reported previously, K-37 and its derivative compounds are considered to be feasible candidates for a novel AIDS therapy.
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PMID:Inhibition of the RNA-dependent transactivation and replication of human immunodeficiency virus type 1 by a fluoroquinoline derivative K-37. 1087 84

The HIV-1 transactivator protein, Tat, is an atypical transcriptional activator that functions through binding, not to DNA, but to a short leader RNA, TAR. Although details of its functional mechanism are still unknown, emerging findings suggest that Tat serves primarily to adapt co-activator complexes such as p300, PCAF and P-TEFb to the HIV-1 long terminal repeat. Hence, an understanding of how Tat interacts with these cofactors is crucial. It has recently been shown that acetylation at a single lysine, residue 50, regulated the association of Tat with PCAF. Here, we report that in the absence of Tat acetylation, PCAF binds to amino acids 20-40 within Tat. Interestingly, acetylation of Tat at Lys28 abrogates Tat-PCAF interaction. Acetylation at Lys50 creates a new site for binding to PCAF and dictates the formation of a ternary complex of Tat-PCAF-P-TEFb. Thus, differential lysine acetylation of Tat coordinates the interactions with its co-activators, cyclin T1 and PCAF. Our results may help in understanding the ordered recruitment of Tat co-activators to the HIV-1 promoter.
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PMID:Differential acetylation of Tat coordinates its interaction with the co-activators cyclin T1 and PCAF. 1248 2

The HIV transcriptional activator Tat is acetylated by p300 at a single lysine residue in the TAR RNA binding domain. We have generated monoclonal and polyclonal antibodies specific for the acetylated form of Tat (AcTat). Microinjection of anti-AcTat antibodies inhibited Tat-mediated transactivation in cells. Similarly, the p300 inhibitor Lys-CoA and siRNA specific for p300 suppressed Tat transcriptional activity. Full-length synthetic AcTat bound to TAR RNA with the same affinity as unacetylated Tat, but formation of a Tat-TAR-CyclinT1 ternary complex was completely inhibited in the presence of AcTat. We propose that Tat acetylation may help in dissociating the Tat cofactor CyclinT1 from TAR RNA and serve to transfer Tat onto the elongating RNA polymerase II.
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PMID:Acetylation of Tat defines a cyclinT1-independent step in HIV transactivation. 1288 2

The targeting of RNA for the design of novel anti-viral compounds has until now proceeded largely without incorporating direct input from structure-based design methodology, partly because of lack of structural data, and complications arising from substrate flexibility. We propose a paradigm to explain the physical mechanism for ligand-induced refolding of trans-activation response element (TAR RNA) from human immunodeficiency virus 1 (HIV-1). Based upon Poisson-Boltzmann analysis of the TAR structure, as bound by a peptide derived from the transcriptional activator protein, Tat, our hypothesis shows that two specific electrostatic interactions are necessary to stabilise the conformation. This result contradicts the belief that a single argininamide residue is responsible for stabilising the TAR fold, as well as the conventional wisdom that electrostatic interactions with RNA are non-specific or dominated by phosphates. We test this hypothesis by using NMR and computational methods to model the interaction of a series of novel inhibitors of the in vitro RNA-binding activities for a peptide derived from Tat. A subset of inhibitors, including the bis-guanidine compound rbt203 and its analogues, induce a conformation in TAR similar to that brought about by the protein. Comparison of the interactions of two of these ligands with the RNA and structure-activity relationships observed within the compound series, confirm the importance of the two specific electrostatic interactions in the stabilisation of the Tat-bound RNA conformation. This work illustrates how the use of medicinal chemistry and structural analysis can provide a rational basis for prediction of ligand-induced conformational change, a necessary step towards the application of structure-based methods in the design of novel RNA or protein-binding drugs.
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PMID:Rational design of inhibitors of HIV-1 TAR RNA through the stabilisation of electrostatic "hot spots". 1475 49

The targeting of RNA for the design of novel anti-viral compounds represents an area of vast potential. We have used NMR and computational methods to model the interaction of a series of synthetic inhibitors of the in vitro RNA binding activities of a peptide derived from the transcriptional activator protein, Tat, from human immunodeficiency virus type 1. Inhibition has been measured through the monitering of fluorescence resonance energy transfer between fluorescently labeled peptide and RNA components. A series of compounds containing a bi-aryl heterocycle as one of the three substituents on a benzylic scaffold, induce a novel, inactive TAR conformation by stacking between base-pairs at the site of a three-base bulge within TAR. The development of this series resulted in an enhancement in potency (with Ki < 100 nM in an in vitro assay) and the removal of problematic guanidinium moieties. Ligands from this series can act as inhibitors of Tat-induced transcription in a cell-free system. This study validates the drug design strategy of using a ligand to target the RNA receptor in a non-functional conformation.
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PMID:Structure-based drug design targeting an inactive RNA conformation: exploiting the flexibility of HIV-1 TAR RNA. 1509 77

The HIV transcriptional activator Tat enhances the processivity of RNA polymerase II by recruiting the CyclinT1/CDK9 complex to the TAR RNA element. In addition, Tat synergizes with the histone acetyltransferase p300 and is acetylated by p300 at a single lysine residue (K50) in the TAR RNA binding domain. We have recently reported that this post-translational modification is necessary for the interaction and transcriptional synergy of Tat with the transcriptional coactivator PCAF. We have further studied the relevance of Tat acetylation during HIV transcription and generated antibodies specific for acetylated Tat (AcTat). Microinjection of anti-AcTat antibodies inhibited Tat-mediated transactivation in cells. Similarly, the specific p300 inhibitor Lys-CoA and short inhibitory RNAs specific for p300 suppressed Tat transcriptional activity. Full-length synthetic AcTat bound to TAR RNA and CyclinT1 with high affinity, but formation of the Tat-TAR-CyclinT1 ternary complex was inhibited when K50 was acetylated. Our data collectively show that Tat acetylation by p300 defines a critical step in Tat transactivation that serves to disrupt the Tat/TAR/CyclinT1 complex and helps in recruiting PCAF to the elongating RNA polymerase II.
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PMID:Tat acetylation: a regulatory switch between early and late phases in HIV transcription elongation. 1517 Dec 54


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