TY - JOUR T1 - Constitutive androstane receptor 1 is constitutively bound to chromatin and 'primed' for transactivation in hepatocytes JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.118.113555 SP - mol.118.113555 AU - Michael McMahon AU - Shaohong Ding AU - Lourdes P Acosta-Jimenez AU - Remi Terranova AU - Marie-Apolline Gerard AU - Antonio Vitobello AU - Jonathan Moggs AU - Colin J Henderson AU - Charles R Wolf Y1 - 2018/01/01 UR - http://molpharm.aspetjournals.org/content/early/2018/10/25/mol.118.113555.abstract N2 - The constitutive androstane receptor (CAR) is a xenobiotic sensor expressed in hepatocytes that activates genes involved in drug metabolism, lipid homeostasis, and cell proliferation. Much progress has been made in understanding the mechanism of activation of human CAR by drugs and xenobiotics. However, many aspects of the activation pathway remain to be elucidated. In this report, we have used viral constructs to express human CAR, its splice variants, and mutant CAR forms in hepatocytes from Car-/- mice in vitro and in vivo. We demonstrate CAR expression rescued the ability of Car-/- hepatocytes to respond to a wide range of CAR activators including phenobarbital. Additionally, two major splice isoforms of human CAR, CAR2 and CAR3, were inactive with almost all the agents tested. In contrast to the current model of CAR activation ectopic CAR1 is constitutively localised in the nucleus and is loaded onto Cyp2b10 gene in the absence of an inducing agent. In studies to elucidate the role of threonine T38 in CAR regulation we found that the T38D mutant was inactive even in the presence of CAR activators. However, the T38A mutant, while not constitutively functional, was activated by CAR inducers, showing that Thr38 is not essential for CAR activation. Also, using the inhibitor erlotinib, we could not confirm a role for the epidermal growth factor receptor in CAR regulation. Our data suggest that CAR is constitutively bound to gene regulatory regions and is regulated by exogenous agents through a mechanism which involves protein phosphorylation in the nucleus. ER -