title: Release of ceramide after membrane sphingomyelin hydrolysis decreases the basolateral secretion of triacylglycerol and apolipoprotein B in cultured human intestinal cells.
abstract: The effect of sphingomyelin hydrolysis on triacylglycerol-rich lipoprotein secretion was examined in the human intestinal cell line, CaCo-2. Addition of sphingomyelinase decreased sphingomyelin and phosphatidylethanolamine by 60 and 20%, respectively. Sphingomyelin hydrolysis decreased the basolateral secretion of triacylglycerol mass, newly synthesized triacylglycerol, and apo B mass. Pulse-chase experiments with [35S]methionine demonstrated a decrease in apo B synthesis and a marked decrease in apo B100 and apo B48 secretion without altering apo A1 secretion. Sphingomyelin hydrolysis did not change apo B mRNA levels nor apo B turnover. Phosphatidylcholine-specific phospholipase C did not decrease apo B synthesis or its basolateral secretion. Membrane protein kinase C (PKC) activity was decreased twofold after sphingomyelin hydrolysis. The PKC inhibitor staurosporine decreased apo B mass and newly synthesized apo B secretion. Sphingomyelinase and staurosporine together caused an additional decrease in apo B secretion suggesting that sphingomyelin hydrolysis decreased apo B secretion independently of its effect on PKC activity. Moreover, conditions that increase PKC activity did not increase apo B secretion. Cell-permeable analogs of ceramide decreased immunoreactive apo B secretion. Sphingosine was without effect. The hydrolysis of membrane sphingomyelin by intestinal or pancreatic neutral sphingomyelinase may lead to the accumulation of cellular ceramide, which, in turn, could inhibit triacylglycerol-rich lipoprotein secretion.
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City.
authors.forename: F J
authors.initials: FJ
authors.lastname: Field
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: E
authors.initials: E
authors.lastname: Born
authors.forename: B
authors.initials: B
authors.lastname: Dixon
authors.forename: S
authors.initials: S
authors.lastname: Mathur
mesh_terms: D001055:Apolipoproteins B / Q000096:biosynthesis / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002470:Cell Survival; D002518:Ceramides / Q000378:metabolism* / Q000494:pharmacology; D002788:Cholesterol Esters / Q000378:metabolism; D003110:Colonic Neoplasms; D006801:Humans; D006868:Hydrolysis; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008055:Lipids / Q000096:biosynthesis*; D008715:Methionine / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism*; D013462:Sulfur Radioisotopes; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014280:Triglycerides / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D001055:Apolipoproteins B; D002518:Ceramides; D002788:Cholesterol Esters; D008055:Lipids; D010743:Phospholipids; D012333:RNA, Messenger; D013109:Sphingomyelins; D013462:Sulfur Radioisotopes; D014280:Triglycerides; D008715:Methionine; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013108:Sphingomyelin Phosphodiesterase; D013755:Tetradecanoylphorbol Acetate