Neutral sphingomyelinase increases the binding, internalization, and degradation of low density lipoproteins and synthesis of cholesteryl ester in cultured human fibroblasts.
I have investigated the effects of human urinary neutral sphingomyelinase (N-SMase) (Chatterjee, S., and Ghosh, N. (1989) J. Biol. Chem. 264, 12554-12561) on the cell-surface binding, internalization, and degradation of 125I-low density lipoprotein (LDL) and on cholesteryl ester synthesis in cultured human fibroblasts. N-SMase exerted a concentration-dependent continuous stimulation of 125I-LDL cell-surface binding, internalization, and degradation in normal human fibroblasts. A 3-fold increase in binding, internalization, and degradation was observed at the maximum amount (600 units of N-SMase/ml) examined. This phenomenon was accompanied by a continuous stimulation of cholesteryl ester synthesis. A 5-fold increase in cholesteryl ester synthesis was observed after incubation for 4 h with N-SMase. Antibody against N-SMase and heat inactivation of N-SMase compromised the stimulatory effects of N-SMase on 125I-LDL metabolism and cholesteryl ester synthesis in these cells. Incubation of cells with phospholipase D and phospholipase C did not alter 125I-LDL binding, internalization, or degradation. This finding suggests that the stimulatory effects of N-SMase on LDL metabolism and on cholesteryl ester synthesis in fibroblasts is specific. Moreover, unlabeled LDL competitively displaced 125I-LDL from binding to N-SMase-treated cells. None of the precursors of sphingomyelin could mimic the stimulatory effects of N-SMase on 125I-LDL metabolism in these cells. Taken together, these studies suggest that one of the biological roles of N-SMase involves modulating LDL metabolism and cholesterol metabolism in fibroblasts.
Chatterjee
S
S
Department of Pediatrics, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21287-3654.
D002478:Cells, Cultured; D002788:Cholesterol Esters / Q000096:biosynthesis*; D002794:Choline / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000378:metabolism*; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D013107:Sphingolipids / Q000494:pharmacology; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology* / Q000652:urine; D013109:Sphingomyelins / Q000494:pharmacology; D013329:Structure-Activity Relationship
D002788:Cholesterol Esters; D008077:Lipoproteins, LDL; D013107:Sphingolipids; D013109:Sphingomyelins; D013108:Sphingomyelin Phosphodiesterase; D002794:Choline