Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To determine the molecular mechanisms underlying the "cross talk" between the activity of 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), which binds to arylhydrocarbon receptor (AHR) and estradiol (E2)-liganded estrogen receptor (ER), we first examined the initial step of estrogen action, ligand binding to ER. None of the AHR ligands tested, i.e. TCDD, benzo[a]pyrene, 3,3',4,4',5-pentachlorobiphenyl, beta-naphthoflavone, or alpha-naphthoflavone, bound to ER alpha. We report the first examination of TCDD interaction with ER beta: TCDD did not displace E2 from ER beta. We then examined a second possible mechanism, i.e. direct inhibition of ER alpha binding to estrogen response elements (EREs) by the AHR/AHR nuclear translocator (ARNT) complex. The AHR/ARNT heterodimer did not bind either a full or half-site ERE. However, AHR/ARNT bound specifically to oligomers containing naturally occurring EREs derived from the human c-fos, pS2, and progesterone receptor (PR) gene promoters that include xenobiotic response element (XRE)-like sequences. In contrast, neither purified E2-liganded-ER from calf uterus or recombinant human ER alpha bound a consensus XRE. TCDD inhibited E2-activated reporter gene activity from a consensus ERE and from EREs in the pS2, PR, and Fos genes in transiently transfected MCF-7 human breast cancer cells. However, this inhibition was not reciprocal since E2 did not inhibit TCDD-stimulated luciferase activity from the CYP1A1 promoter in transiently transfected MCF-7 or human endometrial carcinoma HEC-1A cells. We propose that at least part of the mechanism by which the AHR/ARNT complex inhibits estrogen action is by competitively inhibiting ER alpha binding to imperfect ERE sites, adjacent to or overlapping XREs.
Mol Cell Endocrinol 1999 Nov 25
PMID:The aryl hydrocarbon receptor (AHR)/AHR nuclear translocator (ARNT) heterodimer interacts with naturally occurring estrogen response elements. 1061 2

Several cytochrome P450 (CYP) enzymes are expressed in the human lung, where they participate in metabolic inactivation and activation of numerous exogenous and endogenous compounds. In this study, the expression pattern of all known xenobiotic-metabolizing CYP genes was characterized in the human alveolar type II cell-derived A549 adenocarcinoma cell line using qualitative reverse transcriptase/polymerase chain reaction (RT-PCR). In addition, the mechanisms of induction by chemicals of members in the CYP1 and CYP3A subfamilies were assessed by quantitative RT-PCR. The expression of messenger RNAs (mRNAs) of CYPs 1A1, 1B1, 2B6, 2C, 2E1, 3A5, and 3A7 was detected in the A549 cells. The amounts of mRNAs of CYPs 1A2, 2A6, 2A7, 2A13, 2F1, 3A4, and 4B1 were below the limit of detection. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CYP1A1 and CYP1B1 mRNAs 56-fold and 2.5-fold, respectively. CYP3A5 was induced 8-fold by dexamethasone and 11-fold by phenobarbital. CYP3A4 was not induced by any of the typical CYP3A4 inducers used. The tyrosine kinase inhibitor genistein and the protein kinase C inhibitor staurosporine blocked TCDD-elicited induction of CYP1A1, but they did not affect CYP1B1 induction. Protein phosphatase inhibitors okadaic acid and calyculin A enhanced TCDD-induction of CYP1B1 slightly, but had negligible effects on CYP1A1 induction. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in human pulmonary epithelial cells and give the first indication of the induction of CYP3A5 by glucocorticoids in human lung cells. These results establish that having retained several characteristics of human lung epithelial cell CYP expression, the A549 lung cell line is a valuable model for mechanistic studies on induction of the pulmonary CYP system.
Am J Respir Cell Mol Biol 2000 Mar
PMID:Induction and regulation of xenobiotic-metabolizing cytochrome P450s in the human A549 lung adenocarcinoma cell line. 1069 73

Pulmonary cytochrome P450 monooxygenases metabolize xenobiotic chemicals, including those found in environmental tobacco smoke (ETS). Exposure to ETS beginning at birth has been shown to induce the P450 CYP1A1 by seven days of life. The effects of perinatal exposure to ETS of the rat lung on the expression of CYP1A1, 1B1, 2B1, and NADPH cytochrome P450 reductase were measured using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Timed pregnant dams and their pups were exposed to aged and diluted sidestream cigarette smoke (ADSS) as a surrogate for ETS for four hours/ day from gestational day 5 through postnatal day 21. For all genes analyzed, mRNA could be detected in the fetal lung beginning at gestational day 17 but were not altered by ADSS. In contrast, intraperitoneal injection of dams with beta-naphthoflavone significantly elevated both CYP1A1 and 1B1 at gestational day 21, indicating that these genes are inducible. Continued exposure to ADSS significantly induced CYP1A1 but not other P450 genes as early as one day after birth.. We conclude that (1) ADSS induces pulmonary CYP1A1 in the first day of life; (2) fetal cytochrome P450 genes are not induced by maternal exposure to ADSS; and (3) in the fetal lung, CYP1A1 and 1B1 can be induced by beta-naphthoflavone.
J Biochem Mol Toxicol 2000
PMID:Effect of in utero and postnatal exposure to environmental tobacco smoke on the developmental expression of pulmonary cytochrome P450 monooxygenases. 1071 27

We studied the long-term effects of streptozotocin-induced diabetes on tissue-specific cytochrome P450 (CYP) and glutathione-dependent (GSH-dependent) xenobiotic metabolism in rats. In addition, we also studied the effect of antidiabetic Momordica charantia (karela) fruit-extract feeding on the modulation of xenobiotic metabolism and oxidative stress in rats with diabetes. Our results have indicated an increase (35-50%) in CYP4A-dependent lauric acid hydroxylation in liver, kidney, and brain of diabetic rats. About a two-fold increase in CYP2E-dependent hepatic aniline hydroxylation and a 90-100% increase in CYP1A-dependent ethoxycoumarin-O-deethylase activities in kidney and brain were also observed. A significant increase (80%) in aminopyrene N-demethylase activity was observed only in rat kidney, and a decrease was observed in the liver and brain of diabetic rats. A significant increase (77%) in NADPH-dependent lipid peroxidation (LPO) in kidney of diabetic rats was also observed. On the other hand, a decrease in hepatic LPO was seen during chronic diabetes. During diabetes an increased expression of CYP1A1, CYP2E1, and CYP4A1 isoenzymes was also seen by Western blot analysis. Karela-juice feeding modulates the enzyme expression and catalytic activities in a tissue- and isoenzyme-specific manner. A marked decrease (65%) in hepatic GSH content and glutathione S-transferase (GST) activity and an increase (about two-fold) in brain GSH and GST activity was observed in diabetic rats. On the other hand, renal GST was markedly reduced, and GSH content was moderately higher than that of control rats. Western blot analyses using specific antibodies have confirmed the tissue-specific alterations in the expression of GST isoenzymes. Karela-juice feeding, in general, reversed the effect of chronic diabetes on the modulation of both P450-dependent monooxygenase activities and GSH-dependent oxidative stress related LPO and GST activities. These results have suggested that the modulation of xenobiotic metabolism and oxidative stress in various tissues may be related to altered metabolism of endogenous substrates and hormonal status during diabetes. The findings may have significant implications in elucidating the therapeutic use of antidiabetic drugs and management of Type 1 diabetes in chronic diabetic patients.
J Biochem Mol Toxicol 2000
PMID:Modulation of xenobiotic metabolism and oxidative stress in chronic streptozotocin-induced diabetic rats fed with Momordica charantia fruit extract. 1071 28

Carbofuran is a nematicide used in agricultural fields throughout the world. Indiscriminate use of this pesticide poses severe detrimental effects on our ecosystem. We have shown that it induces the CYP1A (cytochrome P4501A) monooxygenase enzyme system in cultured hepatocytes from Indian catfish, Heteropneustes fossilis (Bloch). We have quantified this induction by measuring the activity of the enzyme 7-ethoxyresorufin-O-deethylase (EROD), synthesized from CYP1A1 gene. The induction followed a dose-dependent relationship with carbofuran. The dose-dependent curve of EROD using carbofuran was very much similar with beta-napthoflavone, which is a known inducer of CYP1A1. Coexposure of these compounds to the culture media showed a synergistic effect on the enzyme activity. A blocker of aromatic hydrocarbon receptor, alpha-napthoflavone, blocked carbofuran-induced EROD activity in a dose-dependent manner. All these findings suggest that metabolism of carbofuran might be mediated by the CYP1A monooxygenase system through binding of the aromatic hydrocarbon receptor. We have also studied the superinduction phenomenon, which is a typical characteristic of the CYP1A gene in our system.
J Biochem Mol Toxicol 2000
PMID:Induction of CYP1A by carbofuran in primary culture of fish hepatocytes. 1078 98

Ishikawa endometrial cancer cells express the estrogen receptor (ER), and this study investigates aryl hydrocarbon receptor (AhR) expression and inhibitory AhR-ER crosstalk in this cell line. Treatment of Ishikawa cells with the AhR agonist [3H]2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) gave a radiolabeled nuclear complex that sedimented at 6.0 S in sucrose density gradients, and Western blot analysis confirmed that Ishikawa cells expressed human AhR and AhR nuclear translocator (Arnt) proteins. Treatment of Ishikawa cells with 10 nM TCDD induced a 9.7-fold increase in CYP1A1-dependent ethoxyresorufin O-deethylase (EROD) activity and a 10.5-fold increase in chloramphenicol acetyltransferase (CAT) activity in cells transfected with pRNH11c containing an Ah-responsive human CYP1A1 gene promoter insert (-1142 to +2434). Inhibitory AhR-ER crosstalk was investigated in Ishikawa cells using E2-induced cell proliferation and transcriptional activation assays in cells transfected with E2-responsive constructs containing promoter inserts from the progesterone receptor and vitellogenin A2 genes. AhR agonists including TCDD, benzo[a]pyrene (BaP) and 6-methyl-1,3,8-trichlorodibenzofuran, inhibited 32-47% of the E2-induced responses. In contrast, neither estrogen nor progesterone inhibited EROD activity induced by TCDD in Ishikawa cells, whereas inhibitory ER-AhR crosstalk was observed in ECC-1 endometrial cells suggesting that these interactions were cell context-dependent.
J Steroid Biochem Mol Biol 2000 Apr
PMID:Estrogen and aryl hydrocarbon receptor expression and crosstalk in human Ishikawa endometrial cancer cells. 1082 9

Cytochrome P450 enzymes catalyze the first step of the metabolism and subsequent elimination of hydrophobic xenobiotics. However, the activity of some isoforms, among them CYP1A1 and CYP2E1, may result in cellular insults such as oxidative stress and activation of procarcinogen compounds into reactive metabolites. The regulation of the expression of these enzymes is therefore important. We have previously shown that the CYP1A1 gene promoter was repressed by oxidative stress. We show here that the CYP2E1 gene promoter is down-regulated by exogenous H(2)O(2) addition and glutathione depletion. It is also repressed by the transfection of a CYP2E1 expression vector, which elicits an intracellular H(2)O(2) generation. This autoregulation is limited by catalase (which catalyzes the catabolism of H(2)O(2)), thus implying H(2)O(2) as a mediator of the negative feedback mechanism. Furthermore, we observed that the activity of CYP1A1 resulting either from the stimulation of the endogenous gene by benzo[a]pyrene treatment or from the transfection of an expression vector, repressed the activity of the CYP2E1 gene promoter. Conversely, CYP2E1 overexpression repressed the activity of the CYP1A1 gene promoter. In both cases, catalase and a specific inhibitor of one enzyme prevented the repression of the other. This suggests that the generation of H(2)O(2) during the catalytic cycle of these enzymes is a mediator of the cross-regulatory mechanisms. These novel repressive mechanisms of autoregulation and cross-regulation using H(2)O(2) as a common mediator may limit the potential toxicity resulting from high cytochrome P450 activity within the cell.
Mol Pharmacol 2000 Jun
PMID:A repressive cross-regulation between catalytic and promoter activities of the CYP1A1 and CYP2E1 genes: role of H(2)O(2). 1082 86

Previous studies from this laboratory have shown that L-tryptophan, after oxidation by either ultraviolet (UV) irradiation or ozone, causes induction of cytochrome P450 (CYP)1A1 mRNA, protein, and the corresponding 7-ethoxyresorufin O-deethylase (EROD) activity in wild type mouse hepatoma cells, Hepa lclc7 (Hepa-1), through the aryl hydrocarbon receptor (AhR). In the present study, we have examined the effect of temporary inhibition of protein synthesis by cycloheximide on oxidized tryptophan inducible CYP1A1 mRNA, protein, and EROD activity in Hepa-1 cells. The results demonstrate that combined exposure of wild-type Hepa-1 cells to either UV- or ozone-oxidized tryptophan and cycloheximide causes an increase in CYP1A1 mRNA, protein, and EROD activity, which is greater than the sum of the increases that were observed by exposure to each compound alone. The increase in EROD activity is dependent upon the dose and duration of cycloheximide treatment and is prolonged by actinomycin D when the latter compound was administered after removal of cycloheximide. Studies carried out to investigate the mechanism of this superinduction using various mutants of Hepa-1 cells, which are defective in either the AhR or AhR nuclear translocator protein indicated that the superinduction of oxidized tryptophan inducible EROD activity by cycloheximide occurs through the AhR. This is the first demonstration that oxidized tryptophan, in the presence of cycloheximide, causes superinduction of transcription of the Cyp1a1 gene with concomitant increase of CYP1A1 protein and EROD activity in Hepa-1 cells.
In Vitr Mol Toxicol 1999
PMID:Superinduction of Oxidized Tryptophan-Inducible Cytochrome P450 1A1 by Cycloheximide in Hepa lclc7 Cells. 1089 65

The aryl hydrocarbon receptor (AHR) contains signals for both nuclear import and nuclear export (NES). The purpose of the studies in this report was to determine the relationship between the nuclear export of the AHR and AHR-mediated gene regulation. Blockage of nuclear export in HepG2 cells with leptomycin B (LMB) resulted in increased levels of AHR-AHR nuclear translocator (ARNT) complex in the nucleus and correlative reductions in agonist-stimulated AHR degradation. However, LMB exposure inhibited agonist-mediated induction of numerous AHR-responsive reporter genes by 75 to 89% and also inhibited induction of endogenous CYP1A1. LMB did not transform the AHR to a ligand binding species or affect activation by TCDD (2, 3,7,8-tetrachlorodibenzo-p-dioxin). Mutagenesis of leucines 66 and 71 of the putative AHR NES resulted in a protein with reduced function in dimerization to ARNT and binding to DNA, while alanine substitution at leucine 69 (AHR(A69)) resulted in an AHR that bound with ARNT and associated with DNA. AHR(A69) protein injected directly into the nuclei of E36 cells remained nuclear following 6 h of agonist stimulation. In transient-transfection assays, AHR(A69) accumulated within the nucleus was not degraded efficiently following agonist exposure. Finally, AHR(A69) supported induction of AHR-responsive reporter genes in an agonist-dependent manner. These findings show that it is possible to generate an AHR protein defective in nuclear export that is functional in agonist-mediated gene induction. This implies that the negative effect of LMB on agonist-mediated gene induction is independent of the nuclear export of the AHR.
Mol Cell Biol 2000 Aug
PMID:Analysis of the complex relationship between nuclear export and aryl hydrocarbon receptor-mediated gene regulation. 1091 91

We investigated the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in prepubertal (PP) and adult (A) rat granulosa cells (GC) in vitro by examining the changes in estrogen secretion, aromatase enzyme activity and mRNAs for steroidogenic enzymes P450scc, 3beta-HSDI, P450arom; and for components of the AHR signaling pathway-CYP1A1, aromatic hydrocarbon receptor (AHR), and the AHR nuclear translocator protein (ARNT). In PP and A rat GC, TCDD (3.1 nM) reduced estrogen secretion at 48 h without altering aromatase enzyme activity. Addition of FSH (50 ng/ml) increased aromatase activity in GC with or without TCDD. FSH-induced aromatase activity was significantly reduced by TCDD (3.1 nM) at 48 h. Semi-quantitative RT-PCR showed a significant increase in CYP1A1 mRNA both at 24 and 48 h with TCAP, while a significant reduction in P450scc and P450arom mRNA was observed with competitive RT-PCR. All steroidogenic enzyme mRNAs were significantly lower in adults than in PP GC. We conclude that in rat GC, TCDD modulates the level of cytochrome P450 enzymes involved in the steroid biosynthetic cascade. This effect may be attributable to AHR interaction with dioxin-responsive elements present in the genes encoding these enzymes.
Mol Cell Endocrinol 2000 Jun
PMID:Demonstration of 2,3,7,8-tetrachlorodibenzo-p-dioxin attenuation of P450 steroidogenic enzyme mRNAs in rat granulosa cell in vitro by competitive reverse transcriptase-polymerase chain reaction assay. 1102 53


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