Constitutive Androstane Receptor (CAR) Activation and Intracellular Transport (2009- Present)

Investigator:  Matthew Stoner, University of Rhode Island
Mentor:  Karen Lounsbury, University of Vermont 

Abstract:  The constitutive androstane receptor (CAR) is unique among nuclear receptors because it is expressed almost exclusively in hepatocytes, remains in an active conformation in the cytoplasm and is activated by many chemicals with which it does not directly interact.  A prototypical activator of CAR is the sedative phenobarbital (PB), even though PB does not bind directly to CAR in the liver.  Besides PB, multiple neuroactive chemicals including other barbiturates, benzodiazepines and steroids are CAR activators in the liver; at the same time, these neuroactive chemicals bind to GABAA receptors in the central nervous system.  The primary hypothesis of this proposal is that hepatic GABAA receptors exist, and the perturbation of hepatic GABAA receptors is causally involved in CAR activation and CAR-target gene expression, followed by CAR return to homeostasis in the cytoplasm mediated by the non-classical adapter export protein calreticulin.  The Aims of this project are to: 1) Define the hepatocyte membrane chemical sensor upstream of CAR activation, and 2) Identify the key regulator of CAR nuclear export.  Human hepatocytes and transfected cells will be treated with various neuroactive chemicals, and experiments will be performed to analyze the subsequent intracellular compartmentalization of CAR.  Lentiviral infections of siRNAs and chimeric CAR-green fluorescent proteins in human hepatocytes and mouse livers will be used to gain a clearer understanding of CAR activation and intracellular transport.  Results from these studies will be used to better predict clinically relevant adverse drug-drug interactions.