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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.

Telbisz, Ágnes and Hegedűs, Csilla and Váradi, András and Sarkadi, Balázs and Özvegy-Laczka, Csilla (2014) 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. DRUG METABOLISM AND DISPOSITION. pp. 1-36. ISSN 0090-9556

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Abstract

ABCG2 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 proteoliposomes, we have recently shown that cholesterol is an essential activator, while bile acids significantly modify the activity of this protein. In the present work, by using isolated insect cell membrane preparations expressing the human ABCG2 and its mutant variants, we have analyzed whether certain regions in this protein are involved in the sterol recognition. We found that replacing ABCG2-R482 with large amino acids does not affect cholesterol-dependence, while changes to small amino acids cause altered cholesterol sensitivity. When leucines in the potential steroid-binding element (SBE, aa 555-558) of ABCG2 were replaced by alanines, cholesterol-dependence of ABCG2 activity was strongly reduced, although the L558A mutant, when purified and reconstituted, still required cholesterol for full activity. Regarding the effects of bile acids in isolated membranes, we found that these compounds decreased ABCG2-ATPase in the absence of drug substrates, while did not significantly affect substrate-stimulated ATPase activity. The above ABCG2 mutant variants also altered bile acid sensitivity, although cholic acid and glycocholate are not transported by the protein. We suggest that the aforementioned two regions in ABCG2 are important for sterol sensing and may represent potential targets for pharmacological modulation of ABCG2 function.

Item Type: Article
Subjects: R Medicine / orvostudomány > RM Therapeutics. Pharmacology / terápia, gyógyszertan
SWORD Depositor: MTMT SWORD
Depositing User: MTMT SWORD
Date Deposited: 09 Jan 2014 13:08
Last Modified: 09 Jan 2014 13:08
URI: http://real.mtak.hu/id/eprint/8502

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