title: 25-Hydroxycholesterol stimulates sphingomyelin synthesis in Chinese hamster ovary cells.
abstract: In several experimental and pathological conditions the cellular concentrations of cholesterol and sphingomyelin (SM) change coordinately. In an effort to identify factors mediating co-regulation, a class of suppressors of cholesterol synthesis, generically termed oxysterols, were tested for effects on sphingolipid synthesis in Chinese hamster ovary (CHO) cells. 25-Hydroxycholesterol was found to stimulate [3H]serine, [1-3H]palmitate, and [methyl-3H]choline incorporation into sphingomyelin 2- to 3-fold and increase sphingomyelin mass significantly, but did not influence synthesis of other major phospholipids. Maximal labeling of sphingomyelin by [3H]serine was observed 4-6 h after oxysterol addition, and coincided with inhibition of transcription of sterol-regulated genes and activation of cholesteryl ester synthesis. 25-Hydroxycholesterol dose-response curves for activation of sphingomyelin synthesis, suppression of sterol-regulated transcription, and activation of cholesteryl ester synthesis were also similar. Stimulation of SM and glucosylceramide synthesis was observed only with 25-hydroxycholesterol; other oxysterols and cholesterol were ineffective or inhibitory. The effects of 25-hydroxycholesterol on sphingolipid synthesis could not be reproduced by low density lipoprotein (LDL), whole serum, or non-lipoprotein cholesterol in the medium, and stimulation by 25-hydroxycholesterol was evident irrespective of a cholesterol source in the medium. 25-Hydroxycholesterol-treated CHO cells displayed enhanced conversion of [3H]sphinganine-labeled ceramide into sphingomyelin. Sphingomyelin synthesis from N-hexanoyl [3-3H]ceramide and N-hexanoyl [3-3H]dihydroceramide was also increased significantly. Consistent with enhanced ceramide conversion to sphingomyelin, ceramide mass was reduced by 20-40% in 25-hydroxycholesterol-treatment. However, in vitro activity of sphingomyelin synthase (assayed with short-chain ceramide) was not increased in membranes from oxysterol-treated cells. Stimulation of sphingolipid synthesis by 25-hydroxycholesterol is temporally related to effects of this oxysterol on cholesterol metabolism, and is the result of enhanced conversion of ceramide to SM.
authors.affiliation: Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: N D
authors.initials: ND
authors.lastname: Ridgway
mesh_terms: D000818:Animals; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism; D002788:Cholesterol Esters / Q000096:biosynthesis; D002794:Choline / Q000031:analogs & derivatives / Q000378:metabolism; D006224:Cricetinae; D003470:Culture Media; D006888:Hydroxycholesterols / Q000494:pharmacology*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics; D006904:Hydroxymethylglutaryl-CoA Synthase / Q000235:genetics; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics; D012694:Serine / Q000378:metabolism; D013109:Sphingomyelins / Q000096:biosynthesis*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D017855:Transferases (Other Substituted Phosphate Groups) / Q000378:metabolism; D014316:Tritium
chemical_list: D002518:Ceramides; D002788:Cholesterol Esters; D003470:Culture Media; D006888:Hydroxycholesterols; D010169:Palmitic Acids; D012333:RNA, Messenger; D011973:Receptors, LDL; D013109:Sphingomyelins; C017506:methylcholine; D014316:Tritium; D019308:Palmitic Acid; D012694:Serine; C007997:25-hydroxycholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D006904:Hydroxymethylglutaryl-CoA Synthase; D017855:Transferases (Other Substituted Phosphate Groups); C070186:phosphatidylcholine-ceramide phosphocholine transferase; D002794:Choline; D013110:Sphingosine; C005682:safingol