title: Role of multiple drug resistance protein 1 in neutral but not acidic glycosphingolipid biosynthesis.
abstract: Transfection studies have implicated the multiple drug resistance pump, MDR1, as a glucosyl ceramide translocase within the Golgi complex (Lala, P., Ito, S., and Lingwood, C. A. (2000) J. Biol. Chem. 275, 6246-6251). We now show that MDR1 inhibitors, cyclosporin A or ketoconazole, inhibit neutral glycosphingolipid biosynthesis in 11 of 12 cell lines tested. The exception, HeLa cells, do not express MDR1. Microsomal lactosyl ceramide and globotriaosyl ceramide synthesis from endogenous or exogenously added liposomal glucosyl ceramide was inhibited by cyclosporin A, consistent with a direct role for MDR1/glucosyl ceramide translocase activity in their synthesis. In contrast, cellular ganglioside synthesis in the same cells, was unaffected by MDR1 inhibition, suggesting neutral and acid glycosphingolipids are synthesized from distinct precursor glycosphingolipid pools. Metabolic labeling in wild type and knock-out (MDR1a, 1b, MRP1) mouse fibroblasts showed the same loss of neutral glycosphingolipid (glucosyl ceramide, lactosyl ceramide) but not ganglioside (GM3) synthesis, confirming the proposed role for MDR1 translocase activity. Cryo-immunoelectron microscopy showed MDR1 was predominantly intracellular, largely in rab6-containing Golgi vesicles and Golgi cisternae, the site of glycosphingolipid synthesis. These studies identify MDR1 as the major glucosyl ceramide flippase required for neutral glycosphingolipid anabolism and demonstrate a previously unappreciated dichotomy between neutral and acid glycosphingolipid synthesis.
authors.affiliation: Research Institute and Department of Pediatric Laboratory Medicine, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: María Fabiana
authors.initials: MF
authors.lastname: De Rosa
authors.forename: Daniel
authors.initials: D
authors.lastname: Sillence
authors.forename: Cameron
authors.initials: C
authors.lastname: Ackerley
authors.forename: Clifford
authors.initials: C
authors.lastname: Lingwood
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D020384:Acidic Glycosphingolipids / Q000096:biosynthesis*; D000818:Animals; D001254:Astrocytoma; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D016572:Cyclosporine / Q000494:pharmacology; D004285:Dogs; D015870:Gene Expression; D005963:Glucosylceramides / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007654:Ketoconazole / Q000494:pharmacology; D007668:Kidney; D007790:Lactosylceramides / Q000096:biosynthesis; D008565:Membrane Proteins / Q000378:metabolism; D008579:Meningioma; D051379:Mice; D018345:Mice, Knockout; D016253:Microscopy, Immunoelectron; D020383:Neutral Glycosphingolipids / Q000096:biosynthesis*; D049294:Phospholipid Transfer Proteins; D011994:Recombinant Proteins; D014162:Transfection; D014281:Trihexosylceramides / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D020384:Acidic Glycosphingolipids; D002352:Carrier Proteins; D005963:Glucosylceramides; D007790:Lactosylceramides; D008565:Membrane Proteins; D020383:Neutral Glycosphingolipids; D049294:Phospholipid Transfer Proteins; D011994:Recombinant Proteins; D014281:Trihexosylceramides; C018549:globotriaosylceramide; D016572:Cyclosporine; D007654:Ketoconazole