Vol. 62, Issue 2, 304-312, August 2002

Influence of Ceramide Metabolism on P-Glycoprotein Function in Immature Acute Myeloid Leukemia KG1a Cells

Isabelle Plo, Gustav Lehne, Karen Johanne Beckstrøm, Nicolas Maestre, Ali Bettaïeb, Guy Laurent, and Dominique Lautier

Institut National de la Santé et de la Recherche Médicale (INSERM) E9910, Institut Claudius Régaud, Toulouse, France (I.P., N.M., G.La., D.L.); Department of Clinical Pharmacology, Rikshospitalet University Hospital, Oslo, Norway (G.Le., K.J.B.); L'École Pratique des Hautes Études/INSERM U517, Mort Cellulaire et Cancer, UFR de Pharmacie, Dijon, France (A.B.); and Service d'Hématologie, Centre Hospitalier Universitaire Purpan, Toulouse, France (G.La.)

Previous studies have emphasized the role of glucosylceramide (Glu-Cer) synthase in multidrug resistance (MDR) regulation. However, the mechanism by which the inhibition of this enzyme results in increased drug retention and cytotoxicity remains unclear. In this study, we investigated the respective role of ceramide (Cer) accumulation and Glu-Cer derivatives depletion in MDR reversal effect of 1-phenyl-2-decanoylamino-3-morpholino-1-propanolol (PDMP), a Glu-Cer synthase inhibitor. We show here that treatment with PDMP resulted in increased rhodamine 123 (Rh123) retention and potent chemosensitization of P-glycoprotein (P-gp)-expressing cells, including KG1a cells, KG1a/200 cells, K562/138 cells, and K562/mdr-1 cells. Metabolic studies revealed that PDMP induced not only time-dependent Cer accumulation but also reduction of all glycosylated forms of Cer, including Glu-Cer, lactosylceramide (Lac-Cer), monosialo ganglioside (GM3) and disialo ganglioside (GD3). The influence of these metabolites on P-gp function was investigated by measuring Rh123 retention in PDMP-treated cells. P-gp function was found to be stimulated only by the addition of gangliosides in all resistant cell lines, whereas Glu-Cer, Lac-Cer, and Cer had no effect. Moreover, in KG1a/200 cells, GD3 and, to a lesser extent, GM3 were found to phosphorylate P-gp on serine residues. Altogether, these results suggest that, at least in leukemic cells, gangliosides depletion accounts for PDMP-mediated MDR reversal effect, and that gangliosides are important P-gp regulators perhaps through their capacity to modulate P-gp phosphorylation.