title: Altered sphingolipid metabolism in multidrug-resistant ovarian cancer cells is due to uncoupling of glycolipid biosynthesis in the Golgi apparatus.
abstract: Multidrug-resistant tumor cells display enhanced levels of glucosylceramide. In this study, we investigated how this relates to the overall sphingolipid composition of multidrug-resistant ovarian carcinoma cells and which mechanisms are responsible for adapted sphingolipid metabolism. We found in multidrug-resistant cells substantially lower levels of lactosylceramide and gangliosides in sharp contrast to glucosylceramide, galactosylceramide, and sphingomyelin levels. This indicates a block in the glycolipid biosynthetic pathway at the level of lactosylceramide formation, with concomitant accumulation of glucosylceramide. A series of observations exclude regulation at the enzyme level as the underlying mechanism. First, reduced lactosylceramide formation occurred only in intact resistant cells whereas cell-free activity of lactosylceramide synthase was higher compared with the parental cells. Second, the level of lactosylceramide synthase gene expression was equal in both phenotypes. Third, glucosylceramide synthase (mRNA and protein) expression and activity were equal or lower in resistant cells. Based on the kinetics of sphingolipid metabolism, the observation that brefeldin A does not restore lactosylceramide synthesis, and altered localization of lactosylceramide synthase fused to green fluorescent protein, we conclude that lactosylceramide biosynthesis is highly uncoupled from glucosylceramide biosynthesis in the Golgi apparatus of resistant cells.
authors.affiliation: Groningen University Institute for Drug Exploration, Department of Membrane Cell Biology, University of Groningen, The Netherlands.
authors.forename: Robert Jan
authors.initials: RJ
authors.lastname: Veldman
authors.forename: Karin
authors.initials: K
authors.lastname: Klappe
authors.forename: John
authors.initials: J
authors.lastname: Hinrichs
authors.forename: Ina
authors.initials: I
authors.lastname: Hummel
authors.forename: Gieta
authors.initials: G
authors.lastname: van der Schaaf
authors.forename: Hannie
authors.initials: H
authors.lastname: Sietsma
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Kok
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD; D001692:Biological Transport; D002277:Carcinoma / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005260:Female; D005699:Galactosylceramides / Q000096:biosynthesis; D005700:Galactosyltransferases / Q000378:metabolism; D005963:Glucosylceramides / Q000096:biosynthesis / Q000378:metabolism; D006017:Glycolipids / Q000096:biosynthesis*; D006056:Golgi Apparatus / Q000201:enzymology / Q000378:metabolism*; D007700:Kinetics; D007790:Lactosylceramides / Q000096:biosynthesis; D008954:Models, Biological; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*; D013107:Sphingolipids / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D015703:Antigens, CD; D005699:Galactosylceramides; D005963:Glucosylceramides; D006017:Glycolipids; D007790:Lactosylceramides; D013107:Sphingolipids; C009744:CDw17 antigen; D005700:Galactosyltransferases; C039090:UDPgalactose-glucosylceramide galactosyltransferase