Regulation of the Function of the Human ABCG2 Multidrug Transporter by Cholesterol and Bile Acids: Effects of Mutations in Potential Substrate and Steroid Binding Sites

ABCG2 (ATP-binding cassette, subfamily G, member 2) is a plasma membrane glycoprotein that actively extrudes xenobiotics and endobiotics from the cells and causes multidrug resistance in cancer. In the liver, ABCG2 is expressed in the canalicular membrane of hepatocytes and excretes its substrates into the bile. ABCG2 is known to require high membrane cholesterol content for maximal activity, and by examining purified ABCG2 reconstituted in...