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.

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.