Coordinate regulation of the human UDP-glucuronosyltransferase 1A10 gene by aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor 2 (Nrf2)

Introduction: UDP-glucuronosyltransferases (UGTs) catalyze an important metabolic process in which many xenobiotics and endobiotics are converted to water soluble compounds facilitating elimination from the body. UGT1A10 is capable of glucuronidating a number of phenolic compounds, steroids and benzo[a]pyrene, which are associated with carcinogenesis and inflammation. Aim of this study was the characterization of transcriptional regulation of the human UGT1A10 gene by the 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) inducible transcription factor AhR and the tert-butyl hydroquinone (tBHQ) inducible factor Nrf2.

Methods: The UGT1A10 promoter was examined by induction experiments with TCDD and tBHQ via luciferase-assay in Kyse70 cells. DNA binding sites were characterized by site-directed mutagenesis and electrophoretic mobility shift assay (EMSA).

Results: TCDD-induction of the human UGT1A10 promoter led to a 7 fold and tBHQ-induction to a 2,3 fold increased luciferase expression. A xenobiotic response element (XRE), and binding of AhR was identified at position -101 and an antioxidant response element (ARE) and binding of Nrf2, was found at position -149. Interestingly, both TCDD- and tBHQ-inducibility were decreased by mutagenesis of the XRE-site. Similarly TCDD-inducibility as well as tBHQ-inducibility were reduced when the ARE-site was mutagenized. The binding of AhR and Nrf2 to both XRE and ARE was shown by EMSA super shift experiments and indicate a potential interaction between these two factors.

Conclusion: This is the first demonstration of coordinate regulation of human UGT1A10 by AhR and Nrf2. The specific binding sites for AhR and Nrf2 in the UGT1A10 promoter were identified. Because UGT1A10 plays a significant role in the elimination of carcinogenic compounds and drugs it may exert a protective role for the organism in situations of oxidative stress or environmental toxin exposure.