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)

The tumor suppressor p53 is a nuclear phosphoprotein with characteristics of a transcription factor. It displays sequence-specific DNA binding, contains a potent transactivation domain, and has been implicated as both a transcriptional activator and a repressor. Transcription of the human hsp70 gene is stimulated by adenovirus E1a protein. This E1a transactivation of the hsp70 promoter is mediated by CCAAT binding factor (CBF). It is demonstrated here that p53 both represses transcription from the human hsp70 promoter and also interacts with CBF. Thus, the repression of the hsp70 promoter by p53 may be mediated by direct protein-protein interaction with CBF. These results suggest that protein-protein interaction between p53 and specific transcription factors may be an additional mechanism by which p53 regulates gene expression.
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PMID:Regulation of the human hsp70 promoter by p53. 841

The human p53 tumor suppressor gene product can activate transcription by RNA polymerase II in the yeast, Saccharomyces cerevisiae, as well as in human cells. Several viral transcriptional activator proteins have been shown to directly contact TBP, the TATA box-binding subunit of the general initiation factor, TFIID. In this report, we use protein affinity chromatography to show that the cellular transcription factor, p53, interacts directly and specifically with yeast TBP. The TBP binding domain of p53 was localized to its N-terminal 73 amino acids. This highly acidic portion of p53 functions as a transcriptional activation domain and is deleted in some tumors induced by the Friend leukemia virus. A human tumor-derived oncogenic point mutation of p53, which lies outside the activation domain of p53, but reduces its ability to activate transcription, greatly reduced the ability of p53 to bind yeast TBP in vitro. This mutation probably affects the overall conformation of the protein and indirectly interferes with the ability of p53 to contact TBP and activate transcription. In contrast, a mutated oncogenic form of p53 that is unaffected in its ability to activate transcription bound yeast TBP as well as wild type p53. The human TBP activity in a HeLa extract also bound to the activation domain of p53. Our data support a general model in which DNA-bound activator proteins activate transcription by interacting with TBP.
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PMID:Direct interaction between the transcriptional activation domain of human p53 and the TATA box-binding protein. 842 1

The p53 tumour suppressor gene is the most widely mutated gene in human tumorigenesis. p53 encodes a transcriptional activator whose targets may include genes that regulate genomic stability, the cellular response to DNA damage, and cell-cycle progression. Introduction of wild-type p53 into cell lines that have lost endogenous p53 function can cause growth arrest or induce a process of cell death known as apoptosis. During normal development, self-reactive thymocytes undergo negative selection by apoptosis, which can also be induced in immature thymocytes by other stimuli, including exposure to glucocorticoids and ionizing radiation. Although normal negative selection involves signalling through the T-cell receptor, the induction of apoptosis by other stimuli is poorly understood. We have investigated the requirement for p53 during apoptosis in mouse thymocytes. We report here that immature thymocytes lacking p53 die normally when exposed to compounds that may mimic T-cell receptor engagement and to glucocorticoids but are resistant to the lethal effects of ionizing radiation. These results demonstrate that p53 is required for radiation-induced cell death in the thymus but is not necessary for all forms of apoptosis.
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PMID:p53 is required for radiation-induced apoptosis in mouse thymocytes. 847 14

We used a yeast-based genetic assay, the two-hybrid system, to characterize the domain of the tumor-suppressor p53 involved in oligomerization. This assay relies on the reconstitution of the function of a transcriptional activator, the yeast GAL4 protein, via the interaction of a protein fused to the DNA-binding domain of GAL4 with a protein fused to the transcriptional activation domain of GAL4. We show by a reconstruction experiment that this approach could detect the interaction of p53 deleted for its N-terminal activation domain with SV40 large T antigen. We then searched a library of human proteins present as activation domain hybrids for proteins that can interact with the hybrid of p53 with the DNA-binding domain. This search identified 36 plasmids containing the p53 gene, representing 10 different classes. These results provide an additional in vivo demonstration of p53 oligomerization. The smallest p53 fragment identified from screening the library contained only amino acids 331-393, indicating that this small C-terminal fragment is sufficient to mediate oligomerization. In addition, a mutant p53 protein could bind to the wild-type protein in this assay, providing support for the idea that mutant forms of p53 act in a dominant-negative manner through C-terminal oligomerization with the wild type.
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PMID:Use of the two-hybrid system to identify the domain of p53 involved in oligomerization. 850 89

Accumulating evidence supports the hypothesis that tumor-suppressor p53 can act as a transcriptional activator. Insertion of high-affinity p53 DNA binding sites upstream of a promoter yields a p53-responsive vector. Chimeric proteins fusing p53 and the GAL4 DNA-binding domain demonstrate the presence of a transcriptional activating domain in the N-terminus of p53. GAL4-p53 chimeras constructed using naturally occurring p53 mutations at either codon 141 (Tyr-141) or 175 (His-175) of p53 had little ability to activate the reporter gene; in contrast, mutations at either codon 248 (Trp-248) or 273 (His-273) produced greater transcriptional activities than did wild-type p53. GAL4 chimeras can be used to analyse interactions between different domains of p53 and between different p53 alleles; a DNA binding site is defined, and a simple measurement can be made of function. We had expected that coexpression of GAL4 chimeras and p53 alleles would squelch transcriptional activation downstream of GAL binding sites. Surprisingly, coexpression of either p53 (Trp-248) or (His-273) with the GALA-p53 (wild-type, His-273, Trp-248, His-175, Tyr-141) effectors conferred an increase in transcriptional activation as compared with the effector alone. Oligomerization of p53 alleles with GAL4-p53 chimeras could underlie this effect, leading to an increase in transcription-activating motifs near the promoter. To test this possibility, we constructed a GAL4-p53 C-terminal chimera with p53 residues 160-393, lacking the transcriptional activating domain but retaining regions believed to be important in p53 oligomerization. Neither GAL4-p53 (C-terminus) nor p53 expression vectors were able to transactivate G5E1B-CAT alone. Both p53 (His-273) and (Trp-248) co-expressed with GAL4-p53 (C-terminus) were able to transactivate the G5E1B-CAT reporter gene; in contrast, p53 (Tyr-141) was not able to activate transcription. p53 (Tyr-141/His-273) behaved as a dominant negative mutant and inhibited the ability of the combination of p53 (His-273) and GAL4-p53 (C-terminus) to stimulate the reporter gene. Double immunoprecipitation by sequentially using GAL4 and p53 antibodies showed that p53 (His-273) and (Tyr-141/His-273), but not p53 (Tyr-141), can efficiently oligomerize in vivo to the C-terminal region of p53. Transcriptional activating function of p53 may be modulated by oligomerization; some mutations, such as His-273 and Trp-248, participate in these functions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mutant p53 proteins have diverse intracellular abilities to oligomerize and activate transcription. 851 Sep 27

The wild-type p53 protein is a transcriptional activator implicated in the control of cellular growth-related gene expression. Here, using a number of different cell lines and transient-transfection-transcription assays, we demonstrate that at low levels, wild-type p53 transactivates the human proliferating cell nuclear antigen (PCNA) promoter. When expressed at a similar level, the tumor-derived p53 mutants did not transactivate the PCNA promoter. We identified a p53-binding site on the human PCNA promoter with which p53 interacts sequence specifically. When placed on a heterologous synthetic promoter, the binding site functions as a wild-type p53 response element in either orientation. Deletion of the p53-binding site renders the PCNA promoter p53 nonresponsive, showing that wild-type p53 transactivates the PCNA promoter by binding to the site. At a higher concentration, wild-type p53 inhibits the PCNA promoter but p53 mutants activate. Transactivation by p53 mutants does not require the p53-binding site. These observations suggest that moderate elevation of the cellular wild-type p53 level induces PCNA production to help in DNA repair.
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PMID:Wild-type human p53 transactivates the human proliferating cell nuclear antigen promoter. 852 44

The transcription factor c-Fos is a short-lived cellular protein. The levels of the protein fluctuate significantly and abruptly during changing pathophysiological conditions. Thus, it is clear that degradation of the protein plays an important role in its tightly regulated activity. We examined the involvement of the ubiquitin pathway in c-Fos breakdown. Using a mutant cell line, ts20, that harbors a thermolabile ubiquitin-activating enzyme, E1, we demonstrate that impaired function of the ubiquitin system stabilizes c-Fos in vivo. In vitro, we reconstituted a cell-free system and demonstrated that the protein is multiply ubiquitinated. The adducts serve as essential intermediates for degradation by the 26S proteasome. We show that both conjugation and degradation are significantly stimulated by c-Jun, with which c-Fos forms the active heterodimeric transcriptional activator AP-1. Analysis of the enzymatic cascade involved in the conjugation process reveals that the ubiquitin-carrier protein E2-F1 and its human homolog UbcH5, which target the tumor suppressor p53 for degradation, are also involved in c-Fos recognition. The E2 enzyme acts along with a novel species of ubiquitin-protein ligase, E3. This enzyme is distinct from other known E3s, including E3 alpha/UBR1, E3 beta, and E6-AP. We have purified the novel enzyme approximately 350-fold and demonstrated that it is a homodimer with an apparent molecular mass of approximately 280 kDa. It contains a sulfhydryl group that is essential for its activity, presumably for anchoring activated ubiquitin as an intermediate thioester prior to its transfer to the substrate. Taken together, our in vivo and in vitro studies strongly suggest that c-Fos is degraded in the cell by the ubiquitin-proteasome proteolytic pathway in a process that requires a novel recognition enzyme.
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PMID:Degradation of the proto-oncogene product c-Fos by the ubiquitin proteolytic system in vivo and in vitro: identification and characterization of the conjugating enzymes. 852 78

The p53 tumor suppressor gene has been implicated in the induction of apoptosis in several cell systems. We have recently reported than transiently-transfected wt p53 is capable of inducing apoptosis in certain transformed cell lines. We demonstrated by quantitative analysis using flow cytometry that apoptosis was restricted to the population expressing wt, but not mutant, p53. In the present study we use this model system to analyse the functional domain of p53 in the induction of apoptosis. Several constructs expressing mutations or deletions in the C-terminal oligomerization domain, the N-terminal transactivation domain or the central DNA-binding domain were introduced into HeLa cells, and the ability of the expressed proteins to induce apoptosis was evaluated. All the functional domains were found to be necessary for the induction of apoptosis. In addition, cycloheximide and actinomycin D inhibited wt p53-induced apoptosis. We therefore conclude that p53 acts in this cell system, at least in part, as a transcriptional activator in the induction of apoptosis.
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PMID:Transcriptional activation plays a role in the induction of apoptosis by transiently transfected wild-type p53. 857 Jan 69

Tumor suppressor protein p53 binds to DNA in a sequence-specific manner and activates transcription from promoters near its binding site. It is also known to repress promoters lacking the p53-binding site. In this study, we demonstrate that p53 can act as a transcriptional activator or repressor in vivo using the same reporter with the DNA-binding site CON and these effects depend on the amount of p53 expressed. Both in Saos2 and Cos7 cells, lower concentrations of p53 lead to activation and higher concentrations lead to repression of the model promoter containing the consensus p53-binding site CON. The N-terminal part of p53 is necessary for the transcriptional activation. It is not needed, however, for the repression of the same promoter, indicating that different domains of p53 are involved in activation and repression.
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PMID:Protein p53 modulates transcription from a promoter containing its binding site in a concentration-dependent manner. 857 41

The tumor suppressor p53 plays a role in mediating a G1 arrest (for example, in response to DNA damage), in the cellular commitment to apoptosis and in suppression of transformation. The mechanism of action of p53 in each of these biological outcomes is likely to be overlapping. Current data indicate that p53 functions as a sequence specific transcriptional activator. p53 can also repress transcription from certain promoters. One way in which p53 mediates a G1 arrest after DNA damage appears to be clear. Cells exposed to ionizing radiation show elevated levels of p53 protein. The increase in p53 levels is thought to be responsible for the increase in the cyclin-dependent kinase (cdk) inhibitor p21 mediated through the p53 binding sites in the p21 promoter. With regard to the ability of p53 to suppress transformation, there is data suggesting that p53 functions other than, or in addition to, its transcriptional activation function may be necessary. Similar data exist for p53-dependent apoptosis. Recently a role for p53 at another level of gene regulation, namely, translational regulation has been proposed. p53 associates with various components of the translation machinery and has been implicated in the translational regulation of both the p53 and CDK4 mRNAs. Here we will summarize the evidence suggesting a role for p53 in translation and how this regulation might be achieved.
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PMID:p53 and translational control. 860 71


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