Hepatobiliary ABC transporters: physiology, regulation and implications for disease.

The liver plays a key role in the metabolic conversion and elimination of endo- and xenobiotics. Hepatobiliary transport of many of these compounds is mediated by several ATP-binding cassette (ABC) transporters expressed at the canalicular membrane of the hepatocyte. Impaired function of these ABC transporters leads to impaired bile formation or cholestasis and mutations in these genes are associated with a variety of hereditary cholestatic syndromes. At the transcriptional level, these ABC transporters and the metabolizing enzymes involved in processing of their substrates are coordinately regulated by members of the nuclear receptor (NR) family of ligand-modulated transcription factors. In this review we will focus on ABC transporters involved in hepatobiliary excretion and how they are associated with hepatic physiology and disease states. We will also examine how NRs, acting as intracellular sensors for lipophilic molecules, regulate these ABC transporters and maintain metabolic homeostasis.