McMahon, Michael, Ding, Shaohong, Acosta Jimenez, Lourdes, Terranova, Remi, Gerard, Marie-Apolline, Vitobello, Antonio, Moggs, Jonathan, J. Henderson, Colin and Wolf, C. Roland (2018) CONSTITUTIVE ANDROSTANE RECEPTOR 1 IS CONSTITUTIVELY BOUND TO CHROMATIN AND ‘PRIMED’ FOR TRANSACTIVATION IN HEPATOCYTES. Molecular pharmacology. ISSN 1521-0111; 0026-895X

Abstract

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 was
activated by CAR inducers, showing that T38 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.

Item Type:	Article
Date Deposited:	11 Dec 2018 00:45
Last Modified:	11 Dec 2018 00:45
URI:	https://oak.novartis.com/id/eprint/36277