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)

The mRNA for transforming growth factor beta 3 (TGF-beta 3) includes a long (1.1-kb) 5' noncoding region which exerts a potent inhibitory effect on translational efficiency. We now report that many human breast cancer cell lines (T47-D, SK-BR-3, ZR-75-1, and BT-474) express two mRNA species for TGF-beta 3: the 3.5-kb transcript previously described as the only TGF-beta 3 mRNA species in cells and a novel 2.6-kb transcript which lacks approximately 870 nucleotides from the 5' noncoding region. The 5' end of the shorter transcript was sequenced, establishing it to be a 5' truncation of the full-length TGF-beta 3 transcript. Estradiol decreased mRNA levels of both TGF-beta 3 mRNA transcripts to an equivalent degree in estrogen receptor-positive cells. In contrast, the synthetic progestin gestodene altered the relative abundance of the two transcripts, preferentially diminishing the expression of the 2.6-kb transcript. The potential for enhanced mRNA translation attributable to the shorter 5' noncoding region was evaluated by transfection of cells with chimeric plasmid constructs in which the transcription unit consisted of coding sequence for chloramphenicol acetyltransferase downstream of the 5' noncoding sequence from TGF-beta 3. The translational efficiency of chloramphenicol acetyltransferase-encoding mRNA containing the shorter 5' noncoding region of the 2.6-kb TGF-beta 3 transcript was approximately seven times greater than with the full-length 5' noncoding region of TGF-beta 3. Polysome analysis of TGF-beta 3 mRNA in SK-BR-3 cells supported the hypothesis that the 2.6-kb transcript was more actively engaged in translation.
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PMID:Enhanced translational efficiency of a novel transforming growth factor beta 3 mRNA in human breast cancer cells. 826 30

17 beta-Estradiol (E2) induces cathepsin D mRNA levels and intracellular levels of immunoreactive protein in MCF-7 human breast cancer cells. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alone does not affect cathepsin D gene expression in this cell line; however, in cells cotreated with TCDD and E2, TCDD inhibited E2-induced cathepsin D mRNA levels, the rate of gene transcription, and levels of immunoreactive protein. The inhibitory responses were observed within 30 to 120 min after the cells were treated with TCDD. TCDD also inhibited E2-induced secreted alkaline phosphatase activity in aryl hydrocarbon (Ah)-responsive MCF-7 and wild-type mouse Hepa 1c1c7 cells cotransfected with the human estrogen receptor (hER) and the pBC12/S1/pac plasmid, which contains the 5' promoter region (-296/+57) of the cathepsin D gene and an alkaline phosphatase reporter gene. The E2-responsive ER/Sp1 sequence (-199 to -165) in the cathepsin D 5' region contains an imperfect GTGCGTG (-175/-181) xenobiotic responsive element (XRE); the role of this sequence in Ah responsiveness was investigated in gel electrophoretic mobility shift assays and with plasmid constructs containing a wild-type ER/Sp1 oligonucleotide or a mutant ER/Sp1-"XRE" oligonucleotide containing two C-->A mutations in the XRE sequence (antisense strand). In plasmid constructs which contained a chloramphenicol acetyltransferase reporter gene and the wild-type ER/Sp1 promoter sequence, E2-induced chloramphenicol acetyltransferase activity and mRNA levels were inhibited by TCDD whereas no inhibition was observed with the mutant ER/Sp1-"XRE" plasmids. Electrophoretic mobility shift assays showed that the nuclear or transformed cytosolic Ah receptor complex blocked formation of the ER-Sp1 complex with the wild-type but not the ER/Sp1 mutant oligonucleotide. Moreover, incubation of the wild-type bromodeoxyuridine-substituted ER/Sp1 oligonucleotide with the nuclear Ah receptor complex gave a specifically bound cross-linked 200-kDa band. These data demonstrate that Ah receptor-mediated inhibition of E2-induced cathepsin D gene expression is due to disruption of the ER-Sp1 complex by targeted interaction with an overlapping XRE.
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PMID:Molecular mechanism of inhibition of estrogen-induced cathepsin D gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in MCF-7 cells. 852 36

Cultured mouse hepatoma Hepa lclc7 cells were treated with either estradiol or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or in combination to assess the role of estradiol in the process of Cypla-1 induction. Estradiol at a concentration as high as 1 microM slightly increased the activity of Cypla-1-specific 7-ethoxyresorufin O-deethylase (EROD); in contrast, TCDD-induced EROD activity and Cypla-1 mRNA levels were markedly reduced in the concomitant treatment of TCDD and estradiol in a dose-dependent manner. Treatment with tamoxifen, an anti-estrogen which acts through the estrogen receptor, did not affect the suppressive effects of estradiol on TCDD-induced EROD activity. Electrophoretic mobility shift assay using nuclear extract of cells revealed that estradiol reduced transformation of the Ah receptor to the form capable of specifically binding to an oligonucleotide containing dioxin-response element (DRE) sequence. Consistent with this, estradiol decreased TCDD-induced increased chloramphenicol acetyltransferase (CAT) activity from a DRE-containing CAT reporter plasmid after transient transfection into the cells. The levels of the cytosolic [3H]TCDD-Ah receptor complex were reduced by estradiol in competitive Ah receptor binding assay using [3H]TCDD. This study demonstrated that estradiol acts as an antagonist to TCDD and can regulate Cyp1a-1 expression in an Ah receptor-dependent manner but not through estradiol receptor in Hepa 1c1c7 cells.
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PMID:Suppressive effects of estradiol on 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated transcriptional activation of murine Cyp1a-1 in mouse hepatoma Hepa 1c1c7 cells. 1007 67

Serum apolipoprotein AI (apoAI) levels correlate with the risk of developing atherosclerosis. Previous studies have suggested that dehydroepiandrosterone (DHEA) lowers high-density lipoprotein (HDL)-cholesterol levels. We investigated whether or not DHEA may lower HDL-cholesterol levels by suppressing apoAI gene transcription in hepatocytes. ApoAI mRNA levels, assessed by Northern blotting, were suppressed in HepG2 cells treated with DHEA (34%) (10 microg/mL) or testosterone (36%) (T, 1 microg/mL). Estradiol alone (E2, 1 microg/mL) had relatively little effect on apoAI mRNA levels, while E2 in combination with DHEA prevented a decrease in apoAI mRNA levels compared to DHEA alone. To determine whether these effects were due to changes in apoAI gene transcription, HepG2 cells were transfected with a plasmid carrying the full-length promoter of the rat apoAI gene ligated into a chloramphenicol acetyltransferase (CAT) reporter construct. The plasmid pCMV.SPORT-beta-gal was included in each transfection to normalize the data to transfection efficiency. Cells were then cultured in the presence or absence of DHEA (10 microg/mL), T (1 microg/mL), 17alpha-methyltestosterone (MTT, 1 microg/mL), 5alpha-dihydrotestosterone (DHT, 1 microg/mL), E2 (1 microg/mL), or a combination of DHEA plus E2, T plus E2, MTT plus E2, and DHT plus E2, for 24 hours. CAT activity, relative to beta-galactosidase activity, was reduced by 19.6%, 57.6%, 38.6%, and 54.6% with DHEA, T, DHT, and MTT addition, respectively. E2 increased CAT activity by 43.8%. When the androgens (ie, DHEA, T, DHT, or MTT) were combined with E2, apoAI promoter activity was suppressed. We conclude, therefore, that androgens downregulate apoAI promoter activity in the presence or absence of E2. However, the changes in mRNA levels do not always reflect changes in promoter activity, suggesting that these steroids may have additional post-transcriptional effects on steady-state apoAI mRNA levels. It remains to be established if the transcriptional effects we observed are mediated through an androgen response element.
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PMID:Effects of dehydroepiandrosterone on rat apolipoprotein AI gene expression in the human hepatoma cell line, HepG2. 1188 77

As part of its mixtures program, the Agency for Toxic Substances and Disease Registry (ATSDR) supports in vitro and limited in vivo toxicity testing to further our understanding of the toxicity and health effects of chemical mixtures. There are increasing concerns that environmental chemicals adversely affect the health of humans and wildlife. These concerns have been augmented by the realization that exposure to chemicals often occurs to mixtures of these chemicals that may exhibit complex synergistic or antagonistic interactions. To address such concerns, we have conducted two studies with techniques that are being used increasingly in experimental toxicology. In the first study, six organochlorine pesticides (4,4 -DDT, 4,4 -DDD, 4,4 -DDE, aldrin, dieldrin, or endrin) were selected from the ATSDR Comprehensive Environmental Response, Compensation and Liability Act of 1980 (or Superfund) priority list and tested for their ability to modulate transcriptional activation of an estrogen-responsive reporter gene in transfected HeLa cells. In these assays, HeLa cells cotransfected with an expression vector encoding estrogen receptor and an estrogen-responsive chloramphenicol acetyltransferase (CAT) reporter plasmid were dosed with and without selected environmental chemicals either individually or in defined combinations. Estradiol consistently elicited 10- to 23-fold dose-dependent inductions in this assay. By contrast, all six of the organochlorine pesticides showed no detectable dose-related response when tested either individually or in binary combinations. Thus, these chemicals as binary mixtures do not exhibit any additional estrogenicity at the levels tested in these assays. In the second study, arsenic [As(V)], cadmium [Cd(II)], chromium [Cr(III, VI)], and lead [Pb(II)] were tested in a commercially developed assay system, CAT-Tox (L), to identify metal-responsive promoters and to determine whether the pattern of gene expression changed with a mixture of these metals. This assay employs a battery of recombinant HepG2 cell lines to test the transcriptional activation capacity of xenobiotics in any of 13 different signal-transduction pathways. Singly, As(V), Cd(II), Cr(III, VI), and Pb(II) produced complex induction profiles in these assays. However, no evidence of synergistic activity was detected with a mixture of Cd(II), Cr(III), and Pb(II). These results have shown metal activation of gene expression through several previously unreported signal-transduction pathways and thus suggest new directions for future studies into their biochemical mechanisms of toxicity. In conclusion, the (italic)in vitro(/italic) methods used in these studies provide insights into complex interactions that occur in cellular systems and could be used to identify biomarkers of exposure to other environmental chemical mixtures.
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PMID:Gene induction studies and toxicity of chemical mixtures. 1263 24

HIV-associated dementia results from neuronal loss and an alteration of neuronal function due to a loss of synapses. While HIV infection in astrocytes is limited, astrocytes exhibit a chronic nonproductive infection that can lead to the release of neurotoxic proteins. Additionally, infection can disrupt the normal neurotrophic role of astrocytes that results in neuronal death. Gonadal steroid hormones are known to act as trophic and protective factors in the brain under a variety of normal and pathological conditions. In the present study, to determine if estrogen plays a role in the ability of Tat to function as a transcriptional activator within astrocytes, we examined the effect of estrogen on regulation of viral transcription. We utilized an immortalized human astrocyte cell line (SVGA) stably transfected with a reporter plasmid containing the HIV-1IIIB LTR driving the chloramphenicol acetyltransferase (CAT) gene. The amount of transcriptional activity was measured by quantifying the amount of CAT produced. We determined that 17beta-estradiol treatment (1 nM) had no effect on basal LTR activity. Following transfection with a Tat-expressing plasmid, there was a 100-fold increase in CAT production. This induction was reduced by 40% in cells pretreated with 17beta-estradiol. 17beta- Estradiol only suppressed transcription stimulated by Tat. Furthermore, we determined that this effect was specific to 17beta-estradiol and estrogen receptor agonists. This activity was limited to astrocytes as no effect was observed in a monocytic cell line. Finally, the mechanism of action did not involve an alteration in levels of Cdk9 or Cyclin T1 proteins necessary for Tat activation of the HIV-1 LTR. This study demonstrates a novel activity of 17beta-estradiol in glial cells that could play a role in the maintenance of neuronal health during HIV infection of the central nervous system.
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PMID:Estradiol negatively regulates HIV-LTR promoter activity in glial cells. 1662 39

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