The Experts below are selected from a list of 510 Experts worldwide ranked by ideXlab platform
Mark E Hahn - One of the best experts on this subject based on the ideXlab platform.
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a ligand for the aryl Hydrocarbon receptor isolated from lung
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Jiasheng Song, Mark E Hahn, Margaret Clagettdame, Richard E Peterson, William M Westler, Rafal R Sicinski, Hector F DelucaAbstract:The aryl Hydrocarbon receptor (AHR) is a ligand-inducible transcription factor that is best known because it mediates the actions of polycyclic and Halogenated Aromatic Hydrocarbon environmental toxicants such as 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin. We report here the successful identification of an endogenous ligand for this receptor; ≈20 μg was isolated in pure form from 35 kg of porcine lung. Its structure was deduced as 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester from extensive physical measurements and quantum mechanical calculations. In a reporter gene assay, this ligand activates the AHR with a potency five times greater than that of β-naphthoflavone, a prototypical synthetic AHR ligand. 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester competes with 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin for binding to human, murine, and fish AHRs, thus showing that AHR activation is caused by direct receptor binding, and that recognition of this endogenous ligand is conserved from early vertebrates (fish) to humans.
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Halogenated Aromatic Hydrocarbon mediated porphyrin accumulation and induction of cytochrome p4501a in chicken embryo hepatocytes
Biochemical Pharmacology, 1997Co-Authors: Angela Lorenzen, Sean W Kennedy, Leonard J Bastien, Mark E HahnAbstract:Abstract Concentration-dependent induction of cytochrome P4501A (CYP1A) and intracellular porphyrin accumulation were observed following treatment of chicken embryo hepatocyte (CEH) cultures with 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3′,4,4′-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 2,3′,4,4′,5-pentachlorobiphenyl (PCB 118), 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126), 3,3′,4,4′,5,5′-hexachlorobiphenyl (PCB 169), and a commercial mixture of PCBs (Aroclor 1254). For these Halogenated Aromatic Hydrocarbons (HAHs), or mixture, maximal CYP1A activity [measured as ethoxyresorufin- O -deethylase (EROD) activity] and immunodetectable protein were observed at concentrations just prior to, or coincident with, the concentrations at which porphyrin accumulation became evident. Both immunodetectable CYP1A protein and catalytic activity decreased at high concentrations of these compounds, but the rate and extent of decrease of immunodetectable CYP1A protein varied. Time-course studies with PCB 77 indicated a decrease in potency and an increase in maximal CYP1A induction between 24 and 48 hr of exposure which may indicate in vitro metabolism of this HAH. Intracellular accumulation of total porphyrins without CYP1A induction, was observed for 2,2′,5,5′-tetrachlorobiphenyl (PCB 52), 2,2′,6,6′-tetrachlorobiphenyl (PCB 54), 2,2′,3,5′,6-pentachlorobiphenyl (PCB 95), 2,2′,4,5,5′-pentachlorobiphenyl (PCB 101), 2,2′,3,3′,6,6′-hexachlorobiphenyl (PCB 136), and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153). Overall, these results are consistent with a role for CYP1A induction and/or Ah receptor activation in porphyrin accumulation mediated by HAHs with a planar configuration, whereas those that are not planar may mediate porphyrin accumulation by a mechanism not involving induction of CYP1A.
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cytochrome p4501a induction and inhibition by 3 3 4 4 tetrachlorobiphenyl in an ah receptor containing fish hepatoma cell line plhc 1
Aquatic Toxicology, 1993Co-Authors: Mark E Hahn, Teresa M Lamb, Mary E Schultz, Roxanna M Smolowitz, John J StegemanAbstract:The induction of cytochrome P4501A1 (CYP1A1) in rat hepatoma cells has been used by some investigators to determine ‘dioxin equivalents’ in environmental samples, including extracts of fish tissues. However, the relative potency of inducing compounds may vary between species, suggesting the need for taxon-specific model systems. In this paper we present an initial characterization of CYP1A induction in one such system, a teleost liver cell line (PLHC-1) derived from a hepatocellular carcinoma of Poeciliopsis lucida (Hightower, L.E. and Renfro, J.L., 1988. J. Exp. Zool. 248, 290). Specific binding of the photoaffinity ligand 2-azido-3-[125I]iodo-7,8-dibromodibenzo-p-dioxin([125I]N3Br2DD) to proteins in PLHC-1 cytosol indicated the presence of the Ah receptor, which is known to control CYP1A induction in mammals. 3,3′,4,4′-Tetrachlorobiphenyl (TCB) induced a microsomal protein in PLHC-1 cells that was recognized by monoclonal antibody (MAb) 1-12-3 to scup CYP1A1 (P450E) on immunoblots. Immunohistochemical staining of whole cells with MAb 1-12-3 showed specific recognition of CYP1A induced by TCB. No staining was seen in untreated or vehicle-treated cells. There was an excellent quantitative correlation between amounts of CYP1A protein detected immunohistochemically and in immunoblots of cell homogenates. In a dose response experiment, maximal induction of ethoxyresorufin O-deethylase (EROD) activity occurred at 0.1 μM TCB; at higher concentrations (1 and 10 μM), EROD activity was reduced as compared to the activity at 0.1 μM TCB. In contrast, immunoreactive CYP1A protein increased with increasing TCB concentration up to 10 μM. The loss of EROD activity at high concentrations of TCB did not result from changes in cell number or viability. The apparent inhibition or inactivation of CYP1A catalytic activity by the higher concentrations of Halogenated biphenyls has been seen, but not generally recognized, both in vivo and in cultured cells from diverse vertebrate species. PLHC-1 cells may be a good model system for studying Ah receptor-mediated regulation of gene expression, for determining the fish-specific toxic or inducing potency of Halogenated Aromatic Hydrocarbon congeners, and for investigating the mechanism of CYP1A inhibition or inactivation by environmental contaminants such as TCB.
Hector F Deluca - One of the best experts on this subject based on the ideXlab platform.
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a ligand for the aryl Hydrocarbon receptor isolated from lung
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Jiasheng Song, Mark E Hahn, Margaret Clagettdame, Richard E Peterson, William M Westler, Rafal R Sicinski, Hector F DelucaAbstract:The aryl Hydrocarbon receptor (AHR) is a ligand-inducible transcription factor that is best known because it mediates the actions of polycyclic and Halogenated Aromatic Hydrocarbon environmental toxicants such as 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin. We report here the successful identification of an endogenous ligand for this receptor; ≈20 μg was isolated in pure form from 35 kg of porcine lung. Its structure was deduced as 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester from extensive physical measurements and quantum mechanical calculations. In a reporter gene assay, this ligand activates the AHR with a potency five times greater than that of β-naphthoflavone, a prototypical synthetic AHR ligand. 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester competes with 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin for binding to human, murine, and fish AHRs, thus showing that AHR activation is caused by direct receptor binding, and that recognition of this endogenous ligand is conserved from early vertebrates (fish) to humans.
John J Stegeman - One of the best experts on this subject based on the ideXlab platform.
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cytochrome p4501a induction and inhibition by 3 3 4 4 tetrachlorobiphenyl in an ah receptor containing fish hepatoma cell line plhc 1
Aquatic Toxicology, 1993Co-Authors: Mark E Hahn, Teresa M Lamb, Mary E Schultz, Roxanna M Smolowitz, John J StegemanAbstract:The induction of cytochrome P4501A1 (CYP1A1) in rat hepatoma cells has been used by some investigators to determine ‘dioxin equivalents’ in environmental samples, including extracts of fish tissues. However, the relative potency of inducing compounds may vary between species, suggesting the need for taxon-specific model systems. In this paper we present an initial characterization of CYP1A induction in one such system, a teleost liver cell line (PLHC-1) derived from a hepatocellular carcinoma of Poeciliopsis lucida (Hightower, L.E. and Renfro, J.L., 1988. J. Exp. Zool. 248, 290). Specific binding of the photoaffinity ligand 2-azido-3-[125I]iodo-7,8-dibromodibenzo-p-dioxin([125I]N3Br2DD) to proteins in PLHC-1 cytosol indicated the presence of the Ah receptor, which is known to control CYP1A induction in mammals. 3,3′,4,4′-Tetrachlorobiphenyl (TCB) induced a microsomal protein in PLHC-1 cells that was recognized by monoclonal antibody (MAb) 1-12-3 to scup CYP1A1 (P450E) on immunoblots. Immunohistochemical staining of whole cells with MAb 1-12-3 showed specific recognition of CYP1A induced by TCB. No staining was seen in untreated or vehicle-treated cells. There was an excellent quantitative correlation between amounts of CYP1A protein detected immunohistochemically and in immunoblots of cell homogenates. In a dose response experiment, maximal induction of ethoxyresorufin O-deethylase (EROD) activity occurred at 0.1 μM TCB; at higher concentrations (1 and 10 μM), EROD activity was reduced as compared to the activity at 0.1 μM TCB. In contrast, immunoreactive CYP1A protein increased with increasing TCB concentration up to 10 μM. The loss of EROD activity at high concentrations of TCB did not result from changes in cell number or viability. The apparent inhibition or inactivation of CYP1A catalytic activity by the higher concentrations of Halogenated biphenyls has been seen, but not generally recognized, both in vivo and in cultured cells from diverse vertebrate species. PLHC-1 cells may be a good model system for studying Ah receptor-mediated regulation of gene expression, for determining the fish-specific toxic or inducing potency of Halogenated Aromatic Hydrocarbon congeners, and for investigating the mechanism of CYP1A inhibition or inactivation by environmental contaminants such as TCB.
Luc Berghman - One of the best experts on this subject based on the ideXlab platform.
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2 3 7 8 tetrachlorodibenzo p dioxin elicits aryl Hydrocarbon receptor mediated apoptosis in the avian dt40 pre b cell line through activation of caspases 9 and 3
Comparative Biochemistry and Physiology C-toxicology & Pharmacology, 2004Co-Authors: Nahum Pueblaosorio, K S Ramos, M H Falahatpisheh, Roger Smith, Luc BerghmanAbstract:The Halogenated Aromatic Hydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known to induce immunotoxicity, but relatively little is known regarding its effects on B-lymphocytes, and on avian B-cells in particular. In this study, the avian bursal pre-B-cell line DT40 was exposed to TCDD ranging from 1 to 500 nM for 1 and 6 h. At 100 nM, TCDD caused a significant increase in the number of apoptotic cells, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) assay, and induced the expression of the chicken cytochrome P450 1A4 (CYP1A4) mRNA, a hallmark of TCDD exposure. TCDD induced transient upregulation of aryl Hydrocarbon receptor (AhR) mRNA. At 100 nM, both caspase 3 and caspase 9 were transiently upregulated after 1 h, but returned to normal levels after 6 h of exposure. Challenge with TCDD after AhR blockade with resveratrol, a competitive AhR antagonist, prevented changes in caspases 3 and 9 and in the AhR message itself, suggesting that the effects of TCDD were mediated via the AhR. TCDD did not cause significant changes in the relative gene expression of caspase 8, Bcl-2 and Bcl-xL. We conclude that avian DT40 pre-B-cells exposed to TCDD are susceptible to apoptosis, likely through activation of executioner caspase 3.
Rebecca J Van Beneden - One of the best experts on this subject based on the ideXlab platform.
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Halogenated Aromatic Hydrocarbon binding proteins identified in several invertebrate marine species
Aquatic Toxicology, 1997Co-Authors: David J Brown, George C Clarke, Rebecca J Van BenedenAbstract:Abstract The vertebrate aryl Hydrocarbon receptor (AhR) is a cytosolic protein which binds Halogenated Aromatic Hydrocarbons such as 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD). In vertebrates, the AhR-ligand complex, in association with other proteins, binds specific DNA sequences and modifies the expression of a number of genes. Most of the toxic effects of Halogenated Aromatic Hydrocarbon exposure are mediated through this receptor. A similar receptor system has not yet been identified in invertebrates. The current study investigated whether proteins which specifically bind Halogenated Aromatic Hydrocarbons were present in marine invertebrates. We used the photoaffinity TCDD-analog, 2- azido -3-[ 125 I] iodo -7,8- dibromodibenzo -p- dioxin ([ 125 I]N 3 Br 2 DpD), to detect the presence of cytosolic proteins which specifically bound this ligand. Specific binding was defined as labeling which could be competed off by an excess of unlabeled ligand. Eleven species of marine invertebrates were examined which represented six different phyla: Cnidaria, Mollusca, Annelida, Arthropoda, Chordata, and Echinodermata. Cytosols prepared from gill and gonad in the soft-shell clam ( Mya arenaria ), the eastern oyster ( Crassostrea virginica ), and hard-shell clam ( Mercenaria mercenaria ), as well as the hepatopancreas of the blue crab ( Callinectes sapidus ), contained proteins in the same size range (28–39 kDa) which were specifically labeled with the dioxin analog. No proteins of the size expected for vertebrate Ah receptors (95–146 kDa) were seen in any of the invertebrates. The biological function of these dioxin-binding proteins is not yet known.
