Effects of monensin on glycosphingolipid metabolism in cultured human proximal tubular cells.
Effects of monensin, a monovalent cationic ionophore which disrupts Golgi apparatus and its related functions, on glycosphingolipid (GSL) metabolism were investigated in cultured human proximal tubular (PT) cells. Monensin (10(-6) M) stimulated [3H]Gal incorporation into GlcCer, GalCer and LacCer by 8.5-fold and 15-fold, respectively, in PT cells as compared to control. In contrast, [3H]Gal incorporation into GbOse3Cer and GM3 remained unchanged and that into GbOse4Cer was decreased 2-fold as compared to control. GSL measured by HPLC revealed that in cells incubated with monensin, GlcCer, GalCer and LacCer levels were increased 1.6-fold and 7-fold, respectively, whereas GbOse3Cer and GbOse4Cer levels were decreased several folds. Cells incubated with monensin contained 2.5- to 3-fold higher activity of alpha-galactosidase, beta-galactosidase and beta-glucosidase than control, whereas the activity of UDP-gal: glucosylceramide galactosyltransferase (beta-GalT-2) was 8-fold lower than control cells. Cells incubated with monensin took up and degraded one-half as much 125I-LDL as that of control cells. In control cells, exogenously derived [3H]LacCer on LDL was rapidly taken up and catabolized to monoglycosylceramide, or it was used for the endogenous synthesis of globotriosylceramide (trihexosylceramide), globotetraosylceramide (tetrahexosylceramide) and a ganglioside, GM3. In contrast, cells incubated with monensin accumulated most of the [3H]LacCer-LDL. Exogenously derived [3H]LacCer on LDL was catabolized to GlcCer, but was not utilized, for the synthesis of globotriosylceramide, globotetraosylceramide and GM3 in cells incubated with monensin.(ABSTRACT TRUNCATED AT 250 WORDS)
Chatterjee
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Department of Pediatrics, Johns Hopkins University, School of Medicine, Baltimore, MD 21287-3654.
D002460:Cell Line; D002478:Cells, Cultured; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005700:Galactosyltransferases / Q000378:metabolism; D006028:Glycosphingolipids / Q000096:biosynthesis*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000378:metabolism; D001617:beta-Glucosidase / Q000378:metabolism
D006028:Glycosphingolipids; D008077:Lipoproteins, LDL; D008985:Monensin; D005700:Galactosyltransferases; D001617:beta-Glucosidase; D001616:beta-Galactosidase; D005690:Galactose