Epitope Insertion Favors a Six Transmembrane Domain Model for the Carboxy-Terminal Portion of the Multidrug Resistance-Associated Protein

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• 作者：Christina Kast and Philippe Gros
• 刊名：Biochemistry
• 出版年：1998
• 出版时间：February 24, 1998
• 年：1998
• 卷：37
• 期：8
• 页码：2305 - 2313
• 全文大小：125K
• 年卷期：v.37,no.8(February 24, 1998)
• ISSN：1520-4995

文摘

The overexpression of the multidrug resistance protein, MRP, inmammalian cells is associatedwith pleiotropic resistance to cytotoxic drugs. MRP is an integralmembrane protein which belongs tothe family of ATP-binding cassette transporters. Secondarystructure predictions combined withbiochemical analyses suggest that MRP encodes 11 transmembrane (TM)domains in the amino-terminalhalf of the protein and four or six transmembrane domains in thecarboxy-terminal half of the protein.To gain insight into the membrane topology of the carboxy-terminalhalf of MRP, small, antigenichemagglutinin (HA) epitopes (YPYDVPDYAS) were inserted within sixpredicted hydrophilic subfragmentsof this region (938, 1001, 1084, 1175, 1222, 1295). Theseepitope-tagged MRP variants were expressedin HeLa cells to evaluate their ability to confer resistance to thedrug etoposide (VP-16). Insertion of theHA epitopes at positions 938, 1001, and 1222 resulted in functionalproteins, while epitope insertion atpositions 1084, 1175, and 1295 abrogated MRP function. Theintracellular versus extracellular locationof the HA epitopes present in biologically active MRP variants was thenestablished in intact andpermeabilized cells by immunofluorescence using an anti-HA antibody.Epitopes inserted at positions1001 and 1222 were located on the extracellular side of the plasmamembrane, while the epitope insertedat position 938 was located intracellularly. These results areconsistent with a six TM rather than a fourTM domain model for the membrane portion of the carboxy-terminal halfof MRP.