Ritz, V.V.RitzLass, C.C.LassBamewitz, K.K.BamewitzZiemann, C.C.ZiemannRüdell, G.G.RüdellBauer, D.D.BauerSchmitz-Salue, C.C.Schmitz-SalueHirsch-Ernst, K.I.K.I.Hirsch-Ernst2022-03-102022-03-102007https://publica.fraunhofer.de/handle/publica/354710Rat UDP-glucuronosyltransferase UGT2B1 is involved in metabolism of endogenous and xenobiotic substrates, including opioids, testosterone and bisphenol A. UGT2B1 belongs to the spectrum of hepatic enzymes subject to induction by phenobarbital (PB). In primary rat hepatocyte cultures, UGT2B1 mRNA expression was maximally induced within 3 days by 1.5 mM phenobarbital (PB) or 100 µM permethrin, a pyrethroid acting as a PB-type inducer. Induction was repressed by the hepatotrophic growth factor EGF (16 nM) and by the prostaglandin E receptor agonist misoprostol (1-10 µg/ml), while induction was markedly enhanced in the presence of the antioxidant N-acetylcysteine (10 mM). Noteworthy, PB-dependent induction of cytochrome P450 CYP2B1 was also modulated by EGF, misoprostol or N-acetylcysteine, demonstrating coordinate regulation of UGT2B1 and CYP2B1 expression. To investigate molecular mechanisms of UGT2B1 gene regulation, primary rat hepatocytes were transfected with UGT2B1-luciferase reporter gene constructs and luciferase expression observed following treatment with modulators of UGT2B1 expression. It was shown that a 1311 bp UGT2B1-promoter fragment was responsive to PB-type inducers, as well as to modulators of induction, indicating that transcriptional regulation greatly contributed to control of UGT2B1 mRNA expression. Systematic UGT2B1 promoter deletion analysis revealed that a proximal fragment containing 239 bp of the 5´-UGT2B1 gene flank was sufficient in conferring responsiveness to PB-like inducers and modulators of induction. Comparison to the human CYP3A4 proximal promoter (that contains designated sites involved in xenobiotic responsiveness), suggests that a sequence within the proximal UGT2B1 promoter fragment, comprising a putative nuclear receptor binding site in close proximity to a C/EBP-alpha binding site, may be a target of PB-dependent activation. Striking parallels in regulation of UGT2B1 and CYP2B1 mRNA expression by PB-type inducers, cytokines, cellular redox status and prostaglandin E receptor stimulation, suggest that integrative molecular mechanisms for regulation of different xenobiotic metabolizing enzyme genes exist.enUGT2B1UDP-glucuronosyltransferaseenzyme610620conference paper