Cooperation of structurally different aryl hydrocarbon receptor agonists and β-catenin in the regulation of CYP1A expression

The ligand-activated nuclear receptor AhR (aryl hydrocarbon receptor) mediates the response of hepatocytes to various exogenous compounds. AhR is classically activated by planar, aromatic hydrocarbons, but also by other, structurally rather unrelated compounds. Recent data show that the canonical Wnt/beta-catenin signaling pathway is also involved in the regulation of hepatic zonal gene expression and drug metabolism in mammalian liver. Previous studies indicate that the loss of beta-catenin in hepatocytes diminishes the response to the AhR agonists 3-methylcholanthrene (3MC) in vivo and to 2,3,7,8-tetrachlorodibenzo-[p]-dioxin in vitro. The knockout of beta-catenin also impairs the zonal pattern of AhR target gene induction by 3MC. However, it is presently unknown whether the chemical nature of the AhR agonist influences the AhR/beta-catenin interaction. Moreover, no information is available about the dose-response curves of AhR activation in the absence or presence of Wnt/beta-catenin signaling. In the present study, we have analyzed AhR-dependent responses to different concentrations of structurally unrelated AhR agonists in vivo and in vitro. The results demonstrate that beta-catenin is essential to obtain the maximum AhR response. Moreover, using transgenic mouse models which allow for the ablation of beta-catenin at different age of mice, we demonstrate that the presence of beta-catenin, not postnatal developmental effects in beta-catenin-deficient livers, is responsible for the observed interplay of beta-catenin and the AhR. (C) 2014 Elsevier Ireland Ltd. All rights reserved.