title: Ceramide is a competitive inhibitor of diacylglycerol kinase in vitro and in intact human leukemia (HL-60) cells.
abstract: Prior studies demonstrated that ceramide was phosphorylated by a novel Ca(2+)-dependent kinase distinct from diacylglycerol (DG) kinase in human myelogenous leukemia (HL-60) cells (Kolesnick, R. N., and Hemer, M. R. (1990) J. Biol. Chem. 265, 10900-10904). The present studies were initiated to determine whether mammalian DG kinase purified to homogeneity possessed phosphotransferase activity toward ceramide. A high molecular weight rat brain DG kinase demonstrated Mg(2+)-(but not Ca(2+)-) dependent DG kinase activity and did not phosphorylate ceramide in the presence of either cation. In contrast, ceramide served as a competitive inhibitor with an inhibition constant (Ki) 2-6-fold greater than the Km for DG. Inhibition was noncompetitive with respect to ATP and Mg2+. A cell-permeable ceramide, N-octanoyl sphingosine (C8-cer), was used to study effects of ceramide on DG kinase in intact HL-60 cells. C8-cer induced dose- and time-dependent increases in cellular DG levels. As little as 1 microM C8-cer increased DG from a basal level of 103 to 177 pmol.10(6) cells-1, and a maximal 2.9-fold elevation to 292 pmol.10(6) cells-1 occurred with 10 microM C8-cer. DG elevation was detected after 1 min, maximal by 7.5 min, and sustained for 30 min. The DG elevation was accompanied by a reduction in 32P incorporation in phosphatidic acid in cells short term-labeled with [32P]orthophosphoric acid, consistent with inhibition of DG kinase. In contrast, a similar elevation in the DG level induced by exogenous phospholipase C increased 32P incorporation into phosphatidic acid. C8-cer was not metabolized to sphingomyelin, indicating that DG was not generated through the phosphatidylcholine:ceramide cholinephosphotransferase reaction. DG elevation after C8-cer or phospholipase C treatment was sufficient to redistribute protein kinase C from cytosol to membrane. These findings provide evidence that ceramide may serve as a competitive inhibitor of DG kinase.
authors.affiliation: Laboratory of Signal Transduction, Cornell University Medical College, New York, New York 10021.
authors.forename: A
authors.initials: A
authors.lastname: Younes
authors.forename: D W
authors.initials: DW
authors.lastname: Kahn
authors.forename: J M
authors.initials: JM
authors.lastname: Besterman
authors.forename: R
authors.initials: R
authors.lastname: Bittman
authors.forename: H S
authors.initials: HS
authors.lastname: Byun
authors.forename: R N
authors.initials: RN
authors.lastname: Kolesnick
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001345:Autoradiography; D001921:Brain / Q000201:enzymology; D002518:Ceramides / Q000378:metabolism*; D019852:Diacylglycerol Kinase; D006801:Humans; D007938:Leukemia / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D010770:Phosphotransferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
chemical_list: D002518:Ceramides; D010712:Phosphatidic Acids; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D019852:Diacylglycerol Kinase; D008274:Magnesium