title: Differential effects of sphingomyelin hydrolysis and cholesterol transport on oxysterol-binding protein phosphorylation and Golgi localization.
abstract: The deposition of de novo synthesized and lipoprotein-derived cholesterol at the plasma membrane and transport to the endoplasmic reticulum is dependent on sphingomyelin (SM) content. Here we show that hydrolysis of plasma membrane SM in Chinese hamster ovary cells by exogenous bacterial sphingomyelinase resulted in enhanced cholesterol esterification at the endoplasmic reticulum and rapid dephosphorylation of the oxysterol-binding protein (OSBP), a cytosolic/Golgi receptor for oxysterols such as 25-hydroxycholesterol. After sphingomyelinase treatment, restoration of OSBP phosphorylation closely paralleled resynthesis of SM and down-regulation of cholesterol ester synthesis. SM hydrolysis activated an okadaic acid-sensitive phosphatase that was not stimulated in Chinese hamster ovary cells by short chain ceramides. Agents that specifically blocked sphingomyelinase-mediated delivery of cholesterol to acyl-CoA:cholesterol acyltransferase (U18666A) or promoted cholesterol efflux to the medium (cyclodextrin) did not inhibit OSBP dephosphorylation. SM hydrolysis also promoted OSBP translocation from a vesicular compartment to the Golgi apparatus. Cyclodextrin and U18666A also caused OSBP translocation to the Golgi apparatus, suggesting that OSBP movement is coupled to changes in the cholesterol content of the plasma membrane or Golgi apparatus. These results identify OSBP as a potential target of SM turnover and cholesterol mobilization at the plasma membrane and/or Golgi apparatus.
authors.affiliation: Atlantic Research Centre and Departments of Pediatrics and Biochemistry, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada. nridgway@is.dal.ca
authors.forename: N D
authors.initials: ND
authors.lastname: Ridgway
authors.forename: T A
authors.initials: TA
authors.lastname: Lagace
authors.forename: H W
authors.initials: HW
authors.lastname: Cook
authors.forename: D M
authors.initials: DM
authors.lastname: Byers
mesh_terms: D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D002518:Ceramides / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D006224:Cricetinae; D003505:Cyclodextrins / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000378:metabolism*; D006868:Hydrolysis; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011987:Receptors, Steroid / Q000378:metabolism*; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism*; D000098825:Oxysterol Binding Proteins
chemical_list: D000736:Androstenes; D002518:Ceramides; D002788:Cholesterol Esters; D003505:Cyclodextrins; D011987:Receptors, Steroid; D013109:Sphingomyelins; D000098825:Oxysterol Binding Proteins; D019319:Okadaic Acid; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; D002784:Cholesterol; D013108:Sphingomyelin Phosphodiesterase