Contribution of the Ah receptor to the phenolic antioxidant-mediated expression of human and rat UDP-glucuronosyltransferase UGT1A6 in Caco-2 and rat hepatoma 5L cells

• Published in: Biochemical pharmacology Vol. 66; no. 5; pp. 841 - 847
• Main Authors: Münzel, Peter A., Schmohl, Stephan, Buckler, Felicitas, Jaehrling, Jan, Raschko, Frank T., Köhle, Christoph, Bock, Karl Walter
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.09.2003; Elsevier Science
• Subjects: 5' Flanking Region - drug effects; Ah receptor; Animals; Antioxidants - pharmacology; beta-Naphthoflavone - toxicity; Biological and medical sciences; Caco-2 Cells; Carcinoma, Hepatocellular; Environmental Pollutants - toxicity; Gene Expression - drug effects; Glucuronosyltransferase - genetics; Glucuronosyltransferase - metabolism; Human and rat UGT1A6; Humans; Hydroquinones - pharmacology; Medical sciences; Monosaccharide Transport Proteins; Pharmacology. Drug treatments; Polychlorinated Dibenzodioxins - toxicity; Rat hepatoma 5L cells; Rats; Receptors, Aryl Hydrocarbon - physiology; Species Specificity; TCDD; tert-Butylhydroquinone; Tumor Cells, Cultured; UDP-glucuronosyltransferase; NQO1; tBHQ; UGT; Caco-2 cells; UDP-glucuronosyltransferase; Rat hepatoma 5L cells; Arnt; TCDD; GST; AhR; XRE; Human and rat UGT1A6; tert-Butylhydroquinone; Ah receptor; ARE; Nrf2; Human; Rat; Human and rat UGTIA6; Enzyme; Transferases; Glycosyltransferases; Rodentia; Hepatic disease; Hepatocellular carcinoma; Pharmacology; Malignant tumor; Antioxidant; Vertebrata; Mammalia; Animal; Digestive diseases; Hexosyltransferases; Biological receptor
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(03)00389-7

UDP-glucuronosyltransferases (UGTs) represent major phase II enzymes of drug metabolism which are regulated in a tissue-specific manner by endogenous and environmental factors. Among the latter, aryl hydrocarbon receptor (AhR) agonists such as 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and phenolic antioxidants such as tert-butylhydroquinone (tBHQ) are known to induce the expression of human UGT1A6 in Caco-2 cells. While binding of the TCDD-activated AhR to one xenobiotic response element (XRE) in the 5′-flanking regulatory region of UGT1A6 was characterised previously, the mechanism responsible for tBHQ induction is unknown. Therefore, it was investigated whether antioxidant response elements (AREs) are involved in tBHQ induction of UGT1A6. Transfectants of 3 kb of its regulatory region and its deletion mutants were treated with tBHQ. These studies suggested a region with approximately 2-fold induction, including an ARE-like motif, 15 bp downstream of the previously characterised XRE. Transfectants of the point-mutated ARE-like motif showed marginally reduced response to tBHQ, but surprisingly, loss of response to TCDD, suggesting interference of flanking proteins with the AhR/Arnt complex. Coordinate responses of UGT activity after treatment with TCDD or tBHQ were also observed in rat hepatoma 5L cells, mutants without the AhR and with recomplemented AhR. The results suggest a contribution of the AhR pathway and of proteins binding to the XRE flanking region to the induction of human UGT1A6 by both AhR agonists and phenolic antioxidants.