Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oncogene activation has been suggested to play some role in determining the hormone independency of tumors. In order to study the role of protein kinase C in mediating the inhibition of the glucocorticoid-dependent transcription from the Mouse Mammary Tumor Virus (MMTV)-Long Terminal Repeat induced by overexpressed activated ras oncogene, we studied the effects of protein kinase C activators [the tumor promoting phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA)] and inhibitors [1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7)] on the dexamethasone (DEX)-mediated activation of a MMTV-Long Terminal Repeat-chloramphenicol acetyltransferase (pMMTV-CAT) chimeric reporter gene transiently transfected into NIH-3T3 cells and in Ha-ras-transformed fibroblasts (T24-NIH-3T3). TPA (30 ng/ml) together with DEX (0.1 microM) treatment of NIH-3T3 cells resulted in a significant decrease of CAT activity from pMMTV-CAT, compared to DEX treatment alone. The addition of H-7 (40 microM) was able to overcome the TPA-induced inhibition of DEX-dependent transcription from pMMTV-CAT. DEX-dependent expression of pMMTV-CAT was significantly reduced in T24-NIH-3T3 with respect to wild-type NIH-3T3 cells. Treatment of T24-NIH-3T3 cells with either H-7 or TPA significantly enhanced or decreased, respectively, the DEX-dependent expression of pMMTV-CAT. TPA and/or H-7 did not affect CAT activity from either pMMTV-CAT in the absence of DEX or from CAT gene under the control of the SV40 promoter. Similar glucocorticoid receptor sites and binding affinities were observed in T24-NIH-3T3 or TPA-treated NIH-3T3 cells compared to wild-type untreated cells. Our data suggest that activation of PKC is involved in the reduced transcriptional regulatory activity of glucocorticoid hormone induced by overexpressed Ha-ras oncogene in NIH-3T3 fibroblasts.
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PMID:Tumor-promoting phorbol ester and ras oncogene expression inhibit the glucocorticoid-dependent transcription from the mouse mammary tumor virus long terminal repeat. 255

Glucocorticoids regulate transcription of specific genes through the interaction of glucocorticoid hormone receptor complexes with DNA binding sites called glucocorticoid response elements (GREs). The GRE consensus sequence has been defined to be the imperfect palindromic sequence 5'-GGTACANNNTGTTCT-3', the most highly conserved portion being the 5'-TGTTCT-3' hexamer. We have identified 5 potential GREs in the 5' upstream noncoding region of the mouse c-Ha-ras oncogene, two with the same hexanucleotide sequence and three with a similar sequence. When subcloned fragments of the mouse c-Ha-ras 5' upstream region (containing the 2 hexamer GREs of exact homology) were fused to the chloramphenicol acetyltransferase (CAT) reporter gene and transfected into HeLa cells, CAT expression driven from the ras promoter was induced up to 3-fold in the presence of dexamethasone. To determine whether the 5' upstream region of the mouse Ha-ras gene was capable of specifically interacting with the glucocorticoid receptor complex, we performed Southwestern blot analysis showing that cloned DNA fragments from the 5' upstream region of the mouse c-Ha-ras gene were able to bind a 97 kDa protein in whole cell extracts from both primary SENCAR mouse epidermal cells and HeLa G cells. Immunodepletion of the epidermal cell extract with a monoclonal antibody to the glucocorticoid receptor verified that the 97 kDa protein bound by the Ha-ras 5' region was indeed the glucocorticoid receptor protein. Our results demonstrate that the upstream noncoding region of the mouse c-Ha-ras gene binds the glucocorticoid receptor. Furthermore, the presence of glucocorticoids enhances the transcription of the mouse Ha-ras promoter region in a transient gene expression assay.
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PMID:Binding of the 97 kDa glucocorticoid receptor to the 5' upstream flanking region of the mouse c-Ha-ras oncogene. 268 59

The activity of the mouse mammary tumor virus promoter was assessed in various sequence contexts with a transient transfection assay in which promoter activity was determined by way of expression of a linked gene encoding chloramphenicol acetyltransferase, as well as by direct analysis of RNA transcripts. The results indicate that the proviral long terminal repeat contains a negative transcriptional control element in addition to the glucocorticoid-responsive transcriptional enhancer that has been described previously. The negative element is able to function in both orientations and, at least to some extent, at multiple positions with respect to the regulated transcription unit. The effects on gene expression cannot be explained by alterations in transfection efficiency. The element has been localized to a 91 base pair fragment located immediately 5' of binding sites for the glucocorticoid receptor protein that have been defined in vitro. The role of the negative element may be to repress the inherent activity of the proviral promoter in the absence of glucocorticoids, resulting in an increased ratio of gene expression in the presence and absence of hormone.
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PMID:Transcriptional repression of a hormone-responsive promoter. 282 88

The upstream regulatory region of the human papilloma virus-16 (HPV-16) genomic DNA contains a sequence element with a large degree of homology to the partially palindromic sequence GGTACANNNTGTTCT, which is the consensus sequence of the glucocorticoid responsive elements of known genes regulated by this steroid hormone. DNase I and dimethylsulfate protection experiments reveal the binding of this sequence by rat glucocorticoid receptor protein. A 400-bp DNA segment centrally containing this sequence confers strong inducibility by dexamethasone to the promoter p97 of HPV-16 and to the Herpes simplex virus thymidine kinase promoter, as judged by chloramphenicol acetyltransferase activity and RNase protection assays. The same DNA segment, that does not contain the consensus sequences of all papilloma viruses relevant for E2 protein-mediated transcription enhancement, functions in an enhancer-like fashion in addition to its glucocorticoid responsive action. This hormone-independent transcription enhancement is absent in human MCF7 cells, but is strong in human HeLa cells where the combined activity of the constitutive and the steroid hormone-dependent enhancer elements stimulate transcription by a factor of 500. This cell type specificity of the HPV-16 enhancer may be responsible for the tissue tropism of the virus. These observations and the presence of numerous homologies to known enhancers of cellular and viral genes suggest a complex pattern of activation of the human papilloma virus-16 promoters.
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PMID:The upstream regulatory region of the human papilloma virus-16 contains an E2 protein-independent enhancer which is specific for cervical carcinoma cells and regulated by glucocorticoid hormones. 282 35

The actions of polycyclic aromatic hydrocarbons and glucocorticoids to regulate the expression of cytochrome P450c were investigated using cultured fetal rat hepatocytes. Cytochrome P450c mRNA content, determined by Northern blot analysis, was induced in cells treated with 1,2-benzanthracene from levels undetectable in untreated cells. When dexamethasone was included in the culture medium together with 1,2-benzanthracene there was a further 2-fold increase in the induction of cytochrome P450c mRNA. The concentration of dexamethasone required for a half-maximal increase in cytochrome P450c mRNA content was approximately 10(-9) M. By nuclear run-on transcription assays, treatment with 1,2-benzanthracene induced cytochrome P450c transcription 5.3-fold over untreated cells. In the presence of dexamethasone and 1,2-benzanthracene, there was a further 2-fold increase in cytochrome P450c transcription. Southwestern blotting and exonuclease footprinting methods have identified binding interactions of a purified glucocorticoid receptor fraction with portions of the cytochrome P450c gene within the first intron. Using a chimeric plasmid containing the first intron, the first exon, and 824 bp of 5'-flanking region of the cytochrome P450c gene, chloramphenicol acetyltransferase activity was induced in transfected HepG2 hepatoma cells by the addition of 1,2-benzanthracene. The addition of dexamethasone induced a further 2.2-fold increase in activity. Deletion of the first intron within the chimeric plasmid abolished responsiveness to dexamethasone. It is concluded that glucocorticoids act together with polycyclic aromatic hydrocarbons to increase the levels of cytochrome P450c expressed in the fetal rat hepatocyte, and that this action is mediated by the glucocorticoid receptor. A glucocorticoid responsive element, which binds the glucocorticoid receptor, has been identified within the first intron of the cytochrome P450c gene. These results suggest that glucocorticoids play a significant role in the response of the hepatic cytochrome P450c gene to xenobiotics.
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PMID:Glucocorticoid regulation of the rat cytochrome P450c (P450IA1) gene: receptor binding within intron I. 291 50

Synthesis of rat alpha 1-acid glycoprotein (AGP), one of the major inflammation-induced plasma proteins, is positively regulated by dexamethasone. To define the dexamethasone-responsive genetic element, we isolated and tested AGP gene sequences for the ability to confer glucocorticoid induction to the bacterial chloramphenicol acetyltransferase (CAT) gene in L cells. A 141-base-pair region of the AGP gene, including 120 base pairs of DNA upstream from the start site of transcription and 21 base pairs of the 5' untranslated region, was sufficient for maximal CAT gene induction by dexamethasone. To localize more precisely the AGP glucocorticoid-responsive element, parts of this 141-base-pair region were inserted 5' to either an AGP promoter-CAT gene or a human triosephosphate isomerase promoter-CAT gene, both of which lacked a response to the steroid. The AGP gene region between 120 and 42 base pairs upstream from the start site of transcription was found to mediate maximal dexamethasone induction of CAT enzyme levels. This result was unexpected because this region does not contain sequence homologies to known glucocorticoid receptor-binding sites and those AGP gene regions that lay further upstream and were homologous to other glucocorticoid receptor-binding sites were inactive in the CAT assay. The fact that the AGP gene region mediating dexamethasone regulation was distinct from the transcribed region indicates that glucocorticoids increase AGP gene expression primarily at the transcriptional rather than the posttranscriptional level.
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PMID:Localization of DNA sequences involved in dexamethasone-dependent expression of the rat alpha 1-acid glycoprotein gene. 302 39

The DNA sequences which interact with the estrogen receptor and which mediate the estrogenic regulation of prolactin gene transcription have been investigated by the use of receptor-DNA-binding experiments and gene transfer studies. Nitrocellulose filter binding assays using highly purified estrogen receptor and cloned fragments of the 5'-flanking region of the rat prolactin gene demonstrate that the receptor selectively binds to DNA sequences located between nucleotides -1713 and -1532 with respect to the transcription initiation site. The binding of the estrogen receptor to this region of the prolactin gene was strongly dependent on receptor concentration, suggesting that receptor dimers may be important in DNA binding. These data demonstrate that the selective binding of purified estrogen receptor to specific sequences of the rat prolactin gene is an intrinsic property of the receptor and is not due to the interaction of receptor with other proteins. The role of specific prolactin gene sequences in mediating the estrogenic regulation of prolactin gene transcription was confirmed by the use of prolactin-chloramphenicol acetyltransferase fusion genes. These studies demonstrated that sequences upstream of position -1532 are required for estrogen responsiveness. Furthermore, the region of the prolactin gene at -1713 to -1495 was able to confer estrogen responsiveness on the thymidine kinase promoter. Exonuclease III protection experiments further localized the receptor-binding sequences to positions -1587 to -1563. Comparison of the nucleotide sequence of the region of the prolactin gene which binds the estrogen receptor with the sequence of other estrogen-responsive genes suggested the presence of the conserved sequence [sequence in text], which shows similarity to sequences thought to mediate glucocorticoid receptor effects on transcription.
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PMID:Identification of an estrogen-responsive element from the 5'-flanking region of the rat prolactin gene. 348 34

Transcription of the gene coding for tryptophan oxygenase (TO) in rat liver is induced 10-fold by glucocorticoids. To identify DNA elements mediating the glucocorticoid-regulated expression of the TO gene we transfected mouse L cells with a fusion gene consisting of 1.95 kb TO 5'-flanking sequences linked to the coding sequence of the gene for chloramphenicol acetyltransferase (CAT). CAT assay and RNA mapping experiments demonstrate that both transient and stable expression of the TO-CAT fusion gene are inducible by dexamethasone. Analysis of transcripts from 5'-deletion mutants identifies two glucocorticoid-responsive elements (GRE), located 450 bp and 1.2 kb upstream of the cap site. The purified rat glucocorticoid receptor binds to the sequence of each GRE as evidenced from footprinting experiments. Interestingly the protected sequence of the proximal footprint is by itself not sufficient for sequence induction, but requires sequences located immediately upstream.
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PMID:Glucocorticoid induction of the rat tryptophan oxygenase gene is mediated by two widely separated glucocorticoid-responsive elements. 358 68

The induction by dexamethasone of rat liver CYP3A1 differs from classical glucocorticoid gene regulation in part because both glucocorticoids and antiglucocorticoids such as pregnenolone 16 alpha-carbonitrile (PCN) induce CYP3A1 through transcriptional gene activation. In the present study, we transiently expressed in primary cultures of rat hepatocytes plasmids consisting of CYP3A1 5'-flanking sequences fused to a chloramphenicol acetyltransferase reporter plasmid. Deletional analysis identified a 78-base pair (bp) element located approximately 135 bp upstream of the transcriptional start site that was inducible by treatment of the cultures with dexamethasone or PCN and was induced synergistically by dexamethasone plus PCN. Nuclear extract from control rat liver protected two regions within the 78-bp sequence against digestion with DNase I. The same two regions were protected when nuclear extracts from dexamethasone-treated animals were used. Analysis of both of the "footprints" (FP1 and FP2) failed to reveal a classical sequence for the glucocorticoid-responsive element. A 33-bp element that includes FP1 sequences inserted into the chloramphenicol acetyltransferase reporter plasmid and transiently expressed in rat hepatocytes conferred a profile of dexamethasone and PCN induction similar to that of the 78-bp element. However, an Escherichia coli expressed glucocorticoid receptor protein failed to protect sequences within FP1 in DNase I footprinting experiments and failed to change its mobility in gel shift assays. Moreover, as judged by the gel shift assay, the specific protein binding to this fragment was the same whether nuclear extracts from the liver of untreated or dexamethasone-treated rats were used. We conclude that the activation of CYP3A1 gene transcription by glucocorticoids may involve proteins already bound to the controlling element in the CYP3A1 gene through a mechanism in which GR in the presence of hormone does not bind directly to CYP3A1 DNA.
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PMID:A novel cis-acting element in a liver cytochrome P450 3A gene confers synergistic induction by glucocorticoids plus antiglucocorticoids. 749 21

To understand the function of cysteines, we have substituted cysteines 638, 643, and 665 by serine in the hormone-binding domain (HBD) of the human glucocorticoid receptor (hGR). In hormone-binding assays using [3H]dexamethasone, hGR C643S and hGR C665S exhibited wild type receptor Kd of 2.5 nM and hGR C665SM666L displayed a Kd of 3.7 nM, while hGR C638S exhibited a Kd of 162 pM, a 15-fold higher affinity. The affinity of hGR C638S for RU486 was 10-fold higher, and the mutants C643S and C665S bound RU486 with a 10-fold lower affinity when compared to wild type GR. While C665S bound aldosterone with very high relative affinity, the double mutant C665SM666L failed to bind aldosterone. The expression of wild type, mutant, and truncated hGRs in vitro showed an identical level of expression of the cloned receptors. Similar levels of expression of the receptors were observed in transfected cells, both by immunoprecipitation and by Western blotting. Transcription activation of the chimeric reporter gene mouse mammary tumor virus-chloramphenicol acetyltransferase (MMTV-CAT) with hGR C638S was 4-fold higher than the level observed with wild type hGR in the presence of dexamethasone. In the presence of RU486, hGR C638S induced MMTV-CAT 25-fold compared to the highest levels observed with wild type hGR and RU486. Even though the hGR C665S stimulated transcription with aldosterone, hGR C665SM666L did not. DNA-receptor interaction analyses by gel mobility shift assay demonstrated that the increased transactivation potential of hGR C638S was due to its intense interaction with DNA. These findings suggest that C638 and C665 are involved in maintaining specificity to glucocorticoids.
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PMID:Cysteines 638 and 665 in the hormone binding domain of human glucocorticoid receptor define the specificity to glucocorticoids. 757 14


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