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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced cytochrome P450 IA1 activity in mouse primary hepatocyte cultures and mouse hepatoma Hepa-1 cells. Pretreatment with staurosporine, a protein kinase C inhibitor, inhibited TCDD-activated cytochrome P450 IA1 expression dose-dependently in both culture systems. Staurosporine also decreased P450IA1 protein synthesis which was detected using western immunoblot. Increased transcription of CYP1A1 gene by TCDD was also suppressed by staurosporine treatment. However, tyrphostin AG213, a specific tyrosine kinase inhibitor, had no effects on TCDD-induced cytochrome P450 expression. These results suggest that protein kinase C signal transduction may be involved in the cytochrome P450 induction mechanism by TCDD.
Biochem Mol Biol Int 1994 Apr
PMID:Suppression of TCDD-induced cytochrome P450 IA1 activity by staurosporine in mouse primary hepatocyte cultures and hepatoma cells. 806 18

Aryl hydrocarbons (AHs) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo[a]pyrene activate the sequence-specific DNA-binding activity of the AH receptor. In the rat hepatocyte-derived cell line LCS7, DNA-binding activity peaked after 30 min and was then down-regulated, reaching negligible levels by 2 h. Down-regulation could be blocked, and DNA-binding activity maintained at maximum for many hours by inhibiting protein or RNA synthesis, implying that down-regulation is a mediated process requiring a labile or inducible protein. CYP1A1 transcription and in vivo DNA-protein interactions at xenobiotic response elements were down-regulated in parallel with DNA-binding activity in nuclear extracts, and these changes could also be blocked by inhibitors of protein synthesis. The correlation between AH receptor DNA-binding activity, intensity of in vivo footprints at xenobiotic response elements, and CYP1A1 transcription rate implies that down-regulation of AH receptor DNA-binding activity is important in regulating CYP1A1 transcription and that receptor is required continuously to maintain transcription. This correlation extends to the murine hepatoma cell line Hepa-1c1c7, in which slower kinetics of activation and down-regulation of CYP1A1 transcription paralleled slower activation and down-regulation of AH receptor DNA-binding activity. The difference in kinetics between cell lines also implies that AH receptor DNA-binding activity is modulated by a mechanism that may be influenced by cell-specific regulatory pathways. The above observations in conjunction with mixing experiments and comparisons of cytoplasmic and nuclear extracts indicate that down-regulation of AH receptor DNA-binding activity is probably due either to degradation or to conversion of the receptor to form that is inactive in both DNA binding and transactivation.
Mol Cell Biol 1994 Sep
PMID:Down-regulation of nuclear aryl hydrocarbon receptor DNA-binding and transactivation functions: requirement for a labile or inducible factor. 806 2

Cultured murine hepatoma 1c1c7 cells were treated with either the actin filament-disrupting drug cytochalasin D or the microtubule inhibitors colchicine and nocadazole (NOC) to assess the role of the cytoskeleton in the process of cytochrome P450 Cyp1a-1 induction. Indirect fluorescence analyses demonstrated that microtubule or actin networks were disrupted within 1 hr of treatment and remained altered as long as cultures were maintained in the presence of the drugs. Treatment of cultures with cytochalasin D, colchicine, or NOC for 1 hr before the addition of dibenz[a,c]anthracene had no effect of Cyp1a-1 induction, as monitored by measurements of CYP1A1 mRNA. Pretreatment with NOC for > or = 18 hr produced populations of cells that had either a flat or rounded morphology. Both populations, when isolated 20-24 hr after NOC treatment, were arrested in the G2/M phase of the cell cycle (83-98% in G2/M versus approximately 7-10% in nontreated or solvent-treated cultures). Cyp1a-1 induction was suppressed in both of these populations, as monitored by measurement of CYP1A1 mRNA content (reductions of > 68%), 7-ethoxyresorufin O-deethylase activity (reductions of > 80%), or microsomal CYP1A1 protein content (reductions of > 80%). In contrast, overall [3H]leucine incorporation into protein was not affected. Cytosol prepared from these NOC-treated cultures bound approximately 39% of the radiolabeled 2,3,7,8-tetrachlorodibenzo-p-dioxin bound by cytosol isolated from solvent-treated cultures. Nuclear extracts prepared from cultures treated with NOC for 20-24 hr before in vivo exposure to inducer and cytoplasmic extracts isolated from similarly NOC-treated cultures that were exposed to inducer in vitro demonstrated reductions of > or = 54% and > or = 55%, respectively, in their abilities to bind to DNA, when analyzed by gel retardation analyses using an oligonucleotide corresponding to dioxin-responsive element D of the Cyp1a-1 gene. These studies suggest that ligand-dependent induction of Cyp1a-1 transcription is unaffected by short term disruption of the microfilament or microtubule network. However, long term exposure to microtubule inhibitors causes cells to pause in the G2/M stage of the cell cycle and modulates processes involved in the induction of Cyp1a-1 in these cells.
Mol Pharmacol 1994 May
PMID:Short and long term effects of cytoskeleton-disrupting drugs on cytochrome P450 Cyp1a-1 induction in murine hepatoma 1c1c7 cells: suppression by the microtubule inhibitor nocodazole. 819 Jan 10

Cytokines are thought to cause the depression of cytochrome P-450 (CYP)-associated drug metabolism in humans during inflammation and infection. We have examined the role of five cytokines, i.e., interleukin-1 beta, interleukin-4, interleukin-6, tumor necrosis factor-alpha, and interferon-gamma, on the expression of CYP1A2, CYP2C, CYP2E1, CYP3A, and epoxide hydrolase in primary human hepatocyte cultures. Steady state P-450 and epoxide hydrolase mRNA levels, as well as ethoxyresorufin-O-deethylase and nifedipine oxidation activities, which are mainly supported by CYP1A1/1A2 and CYP3A, respectively, were measured. Interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha were found to be the most potent depressors of P-450 enzymes. After 3 days of treatment, both mRNA levels and enzyme activities were depressed, typically by at least 40%, whatever the cytokine and the enzyme considered. Interferon-gamma also suppressed CYP1A2 and CYP2E1 mRNA levels and ethoxyresorufin-O-deethylase activity but had no effect on CYP3A and epoxide hydrolase mRNAs. In addition, interleukin-4 had the opposite effect, compared with other cytokines, on CYP2E1 mRNA, which was increased up to 5-fold; ethoxyresorufin-O-deethylase and nifedipine oxidation activities were not significantly affected. These results provide the first demonstration that various cytokines act directly on human hepatocytes to affect expression of major P-450 genes and that a wide range of responses can be observed among the enzymes for a given cytokine, suggesting that different regulatory mechanisms may be involved.
Mol Pharmacol 1993 Oct
PMID:Cytokines down-regulate expression of major cytochrome P-450 enzymes in adult human hepatocytes in primary culture. 823 20

In the present study, we developed a very sensitive, semiquantitative assay based on the reverse transcriptase-coupled polymerase chain reaction to measure, in a region-selective manner, mRNA expression patterns within the brain for microsomal epoxide hydrolase and several cytochrome P-450s (P-450s) known to be induced by prototypic agents in other tissues. The P-450s assessed included the polyaromatic hydrocarbon-inducible CYP1A1 and CYP1A2 systems, together with the phenobarbital-inducible P-450s, CYP2B1, CYP2B2, CYP3A1, which were examined 18 hr after a single intraperitoneal dose of the respective inducing agents. Highly region-specific patterns of expression were evident for P-450 mRNAs within the rat brain. In the control, uninduced brain, CYP1A1 mRNAs were readily detected in the striatum and in the hypothalamus, and to a lesser extent in the other regions examined. The regional pattern of expression was similar for CYP1A2; however, a major difference was noted in the olfactory bulbs, characterized by a relatively high level of CYP1A2 mRNA but correspondingly low levels of CYP1A1. Within the brain regions examined, the highest content of CYP2B1 and CYP2B2 mRNAs were present in the striatum and in the cerebellum, whereas CYP3A1 levels varied only slightly across the respective regions. In contrast to the P-450s, microsomal epoxide hydrolase mRNAs were expressed at relative homogeneous amounts throughout the brain. beta-Naphthoflavone markedly increased the CYP1A1 and CYP1A2 mRNA contents of each brain region investigated, although this agent did not affect levels of epoxide hydrolase. At 18 hr post-treatment with phenobarbital, an optimal time period for hepatic induction, brain expression was characterized by a complex pattern of effects, with increased levels noted for CYP2B1 mRNA content in the medulla oblongata, midbrain, and cortex, but decreased contents measured in the cerebellum, the hypothalamus, and the striatum. In each of these respective regions, CYP2B2 content was profoundly decreased whereas epoxide hydrolase expression was slightly increased by the same treatment. These results establish that the central nervous system actively expresses a number of different biotransformation gene products in a regional specific and inducer-dependent manner, and suggest that for tissues exhibiting low regenerative capacity, like the brain, such reactions are likely to be of critical toxicological significance.
Mol Pharmacol 1993 Nov
PMID:Regional distribution and expression modulation of cytochrome P-450 and epoxide hydrolase mRNAs in the rat brain. 824 22

alpha-Naphthoflavone (alpha NF) is a weak aryl hydrocarbon (Ah) receptor agonist and inhibits the induction of CYP1A1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin. It has been suggested that the Ah receptor antagonist activity is due to the formation of alpha NF-cytosolic Ah receptor complexes that fail to undergo transformation. This hypothesis is consistent with data obtained in this and other studies using alpha NF concentrations from 10 to 1000 nM. However, 10 microM alpha NF exhibited Ah receptor agonist activity in several assays. Incubation of rat hepatic cytosol with 10 microM alpha NF caused transformation of the Ah receptor, as determined in a gel retardation assay using a 32P-labeled oligonucleotide containing a single dioxin-responsive element (DRE). Incubation of rat hepatoma (H-4-II E) cells with 10 microM alpha NF not only resulted in the induction of CYP1A1 mRNA levels but also increased chloramphenicol acetyltransferase activity from a DRE-containing chloramphenicol acetyltransferase reporter plasmid. Moreover, the DRE-transformed cytosolic Ah receptor complex liganded with either alpha NF or 2,3,7,8-tetrachlorodibenzo-p-dioxin did not undergo significant dissociation at 4 degrees. These data confirm that alpha NF is an Ah receptor agonist and, based on the results of previous studies, exhibits partial antagonist activity via competition for receptor binding sites.
Mol Pharmacol 1993 Feb
PMID:alpha-Naphthoflavone-induced CYP1A1 gene expression and cytosolic aryl hydrocarbon receptor transformation. 838 8

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and 12-O-tetradecanoylphorbol-13-acetate (TPA) are both tumor promoters which act through different mechanisms. In MCF-7 human breast cancer cells, both TCDD and TPA inhibited constitutive and 17 beta-estradiol-induced cell proliferation but showed no apparent interactive effects. TCDD also inhibited the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) and induced CYP1A1 gene expression whereas TPA alone was inactive for these responses. Moreover, TPA did not modulate the TCDD-mediated antiestrogenic or induction responses and did not decrease levels of the nuclear Ah receptor complex as determined in a gel mobility shift assay using a 32P-dioxin responsive element (DRE). The interactions of TPA and TCDD on the metabolism of [13C]glucose to [13C]lactate was also investigated using 13C-nuclear magnetic resonance spectroscopy. The rate of formation of [13C]lactate from [13C]glucose in MCF-7 cells treated with DMSO (control), 1 nM 17 beta-estradiol, 1 nM TCDD, 1 nM TCDD plus 1 nM 17 beta-estradiol, and 0.1 ng/ml TPA plus 1 nM 17 beta-estradiol was 28, 48, 20, 22 and 50 fmol lactate formed/cell/h, respectively. Thus, TCDD, but not TPA, inhibited this estrogen-induced response. However, a comparison of the rate of lactate formation in cells treated with TCDD plus 17 beta-estradiol (22 fmol/cell/h) or TCDD plus 17 beta-estradiol plus TPA (61 fmol/cell/h) showed that TPA significantly inhibited the TCDD-mediated antiestrogenic response. The results of these studies in MCF-7 cells demonstrate that the interactions of TCDD and TPA are highly response-specific and do not involve TPA-mediated downregulation of the nuclear Ah receptor complex.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Interaction of 2,3,7,8-tetrachlorodibenzo-p-dioxin, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 17 beta-estradiol in MCF-7 human breast cancer cells. 838 72

In the presence of halogenated and polycyclic aromatic hydrocarbons, the CYP1A1 gene is regulated through induction after ligand binding to the cytosolic Ah receptor (AhR). Ligand-dependent AhR activation leads to nuclear translocation and binding of the receptor to dioxin-responsive element (DRE) sequences, an event that initiates transcriptional activation of the CYP1A1 gene. We recently established a human hepatoma cell line stably integrated with the human CYP1A1 promoter and 5'-flanking enhancer sequences fused to the firefly luciferase gene. This cell line, 101L, was used to determine whether the induction of CYP1A1 by omeprazole, a gastric proton pump inhibitor, is AhR mediated. Treatment of 101L cells with either 50 microM omeprazole or 5 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin for 12-72 hr resulted in maximal activity at 24 hr for both inducers. A dose-response curve for omeprazole induction at 24 hr was determined and the EC50 for omeprazole induction of the human CYP1A1 gene was estimated to be 100 microM. The induction of the CYP1A1 gene by omeprazole corresponds to increases in CYP1A1 mRNA. To examine whether omeprazole-initiated transcriptional activation of the CYP1A1 gene correlates with nuclear accumulation of the AhR, binding of nuclear proteins to the DRE was examined. When gel mobility shift assays were performed using nuclear extracts isolated from 101L cells treated with omeprazole or 2,3,7,8-tetrachlorodibenzo-p-dioxin, specific binding of the AhR to the DRE was observed. These studies demonstrate that omeprazole initiates AhR activation and that induction of the human CYP1A1 gene by omeprazole is AhR dependent.
Mol Pharmacol 1993 Apr
PMID:Nuclear uptake of the Ah (dioxin) receptor in response to omeprazole: transcriptional activation of the human CYP1A1 gene. 838 5

Immunoprecipitation experiments performed on cytosolic extracts of the mouse hepatoma cell line Hepa-1c1c7 (Hepa-1) confirm that the 9-S, unliganded, cytosolic aryl hydrocarbon (Ah) receptor complex contains the 90-kDa heat shock protein and the Ah receptor protein but reveal that it does not contain the Ah receptor nuclear translocator (ARNT) protein. These experiments confirm that the 6-S liganded form of the receptor identified in nuclear extracts of cells treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) contains the Ah receptor protein and ARNT but not the 90-kDa heat shock protein. The 6-S liganded Ah receptor complex activates transcription of the CYP1A1 gene via its binding to upstream xenobiotic-responsive elements (XREs). Treatment of cytosolic extracts of Hepa-1 cells with TCDD in vitro transforms the Ah receptor complex to the XRE-binding state. No such transformation occurs in a C- mutant deficient in ARNT activity. When in vitro synthesized ARNT was added concomitantly with TCDD to C- cytosolic extracts, it associated with the Ah receptor and restored Ah receptor-dependent XRE-binding activity to the extracts. Covalent cross-linking experiments in nuclear extracts of Hepa-1 and human LS180 cells treated with TCDD in vivo demonstrate that both ARNT and the Ah receptor bind directly to the XRE core sequence.
Mol Pharmacol 1993 Sep
PMID:Role of the aryl hydrocarbon receptor nuclear translocator protein in aryl hydrocarbon (dioxin) receptor action. 839 13

Rat CYP1A1 promoter activity was suppressed by the presence of a cis negative regulatory element (NRE) at position -843 to -746 in transiently transfected rat H4IIE and human HepG2 hepatoma cells. Removal of the NRE from the promoter-fusion gene constructs caused an increase in the basal promoter activity of 2-6-fold. Co-transfection of the NRE-containing or non-NRE-containing CYP1A1 promoter-fusion gene constructs with a cloned rat NRE, i.e., pNRE, into HepG2 cells caused a 2-fold or greater reduction in constitutive and induced promoter activities. 2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced expression of the endogenous human CYPA1 was also inhibited by transfection of pNRE into HepG2 cells. Deletion of the sequence from base pairs (bp) -658 to -269 in the NRE-containing construct caused a dramatic decrease of constitutive expression in transiently transfected HepG2 cells, compared with an identical construct that lacked the NRE. Deletion of the sequences between bp -658 and -158 in the CYP1A1 promoter did not affect reporter gene activity, indicating a second site of interaction. At least three different rat liver nuclear proteins bound to the rat NRE, as determined by gel mobility shift and DNase I footprinting assays. A 32-bp sequence within the rat NRE, with significant sequence identity to the 26-bp c-myc, fos/jun-octamer-binding, NRE, was protected from DNAse I cleavage by rat liver nuclear extracts. These data suggested a role for this region in the negative regulation of rat CYP1A1.
Mol Pharmacol 1993 Sep
PMID:Rat CYP1A1 negative regulatory element: biological activity and interaction with a protein from liver and hepatoma cells. 839 16


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