title: Intestinal cholesterol absorption: identification of different binding proteins for cholesterol and cholesterol absorption inhibitors in the enterocyte brush border membrane.
abstract: Absorption of cholesterol from the intestine is a central part of body cholesterol homeostasis. The molecular mechanisms of intestinal cholesterol absorption and the proteins mediating membrane transport are not known. We therefore aimed to identify the proteins involved in intestinal cholesterol absorption across the luminal brush border membrane of small intestinal enterocytes. By photoaffinity labeling using photoreactive derivatives of cholesterol and 2-azetidinone cholesterol absorption inhibitors, an 80-kDa and a 145-kDa integral membrane protein were identified as specific binding proteins for cholesterol and cholesterol absorption inhibitors, respectively, in the brush border membrane of small intestinal enterocytes. The 80-kDa cholesterol-binding protein did not interact with cholesterol absorption inhibitors and vice versa; cholesterol or plant sterols did not interfere with the 145-kDa molecular target for cholesterol absorption inhibitors. Both proteins showed an identical tissue distribution and were exclusively found at the anatomical sites of cholesterol absorption-duodenum, jejunum and ileum. Neither stomach, cecum, colon, rectum, kidney, liver nor fat tissue expressed the 80- or 145-kDa binding proteins for cholesterol and cholesterol absorption inhibitors. Both proteins are different from the hitherto described candidate proteins for the intestinal cholesterol transporter,-SR-BI, ABC G5/ABC G8 or ABC A1. Our data strongly suggest that intestinal cholesterol absorption is not facilitated by a single transporter protein but occurs by a complex machinery. Two specific binding proteins for cholesterol (80 kDa) and cholesterol absorption inhibitors (145 kDa) of the enterocyte brush border membrane are probable protein constituents of the mechanism responsible for the intestinal absorption of cholesterol.
authors.affiliation: Aventis Pharma Deutschland GmbH, DG Metabolic Diseases, Industriepark Höchst/Gebäude G 879, D-65926 Frankfurt am Main, Germany. Werner.Kramer@aventis.com
authors.forename: Werner
authors.initials: W
authors.lastname: Kramer
authors.forename: Frank
authors.initials: F
authors.lastname: Girbig
authors.forename: Daniel
authors.initials: D
authors.lastname: Corsiero
authors.forename: Katja
authors.initials: K
authors.lastname: Burger
authors.forename: Falk
authors.initials: F
authors.lastname: Fahrenholz
authors.forename: Christian
authors.initials: C
authors.lastname: Jung
authors.forename: Günter
authors.initials: G
authors.lastname: Müller
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002791:Cholesterol, Dietary / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D020895:Enterocytes / Q000648:ultrastructure; D007408:Intestinal Absorption / Q000187:drug effects*; D007421:Intestine, Small / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D015394:Molecular Structure; D008970:Molecular Weight; D011817:Rabbits; D013379:Substrate Specificity; D014018:Tissue Distribution
chemical_list: D000924:Anticholesteremic Agents; D002352:Carrier Proteins; D002791:Cholesterol, Dietary; D008565:Membrane Proteins