title: Acid sphingomyelinase activity is regulated by membrane lipids and facilitates cholesterol transfer by NPC2.
abstract: During endocytosis, membrane components move to intraluminal vesicles of the endolysosomal compartment for digestion. At the late endosomes, cholesterol is sorted out mainly by two sterol-binding proteins, Niemann-Pick protein type C (NPC)1 and NPC2. To study the NPC2-mediated intervesicular cholesterol transfer, we developed a liposomal assay system. (Abdul-Hammed, M., B. Breiden, M. A. Adebayo, J. O. Babalola, G. Schwarzmann, and K. Sandhoff. 2010. Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion. J. Lipid Res. 51: 1747-1760.) Anionic lipids stimulate cholesterol transfer between liposomes while SM inhibits it, even in the presence of anionic bis(monoacylglycero)phosphate (BMP). Preincubation of vesicles containing SM with acid sphingomyelinase (ASM) (SM phosphodiesterase, EC 3.1.4.12) results in hydrolysis of SM to ceramide (Cer), which enhances cholesterol transfer. Besides SM, ASM also cleaves liposomal phosphatidylcholine. Anionic phospholipids derived from the plasma membrane (phosphatidylglycerol and phosphatidic acid) stimulate SM and phosphatidylcholine hydrolysis by ASM more effectively than BMP, which is generated during endocytosis. ASM-mediated hydrolysis of liposomal SM was also stimulated by incorporation of diacylglycerol (DAG), Cer, and free fatty acids into the liposomal membranes. Conversely, phosphatidylcholine hydrolysis was inhibited by incorporation of cholesterol, Cer, DAG, monoacylglycerol, and fatty acids. Our data suggest that SM degradation by ASM is required for physiological secretion of cholesterol from the late endosomal compartment, and is a key regulator of endolysosomal lipid digestion.
authors.affiliation: LIMES Institute, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany Department of Chemistry, University of Ibadan, Ibadan, Nigeria.
authors.forename: Vincent O
authors.initials: VO
authors.lastname: Oninla
authors.affiliation: LIMES Institute, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany.
authors.forename: Bernadette
authors.initials: B
authors.lastname: Breiden
authors.affiliation: Department of Chemistry, University of Ibadan, Ibadan, Nigeria.
authors.forename: Jonathan O
authors.initials: JO
authors.lastname: Babalola
authors.affiliation: LIMES Institute, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany.
authors.forename: Konrad
authors.initials: K
authors.lastname: Sandhoff
mesh_terms: D000818:Animals; D001692:Biological Transport; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism*; D004705:Endocytosis; D011992:Endosomes / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008823:Micelles; D008954:Models, Biological; D010712:Phosphatidic Acids / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics / Q000378:metabolism*; D013109:Sphingomyelins / Q000737:chemistry / Q000378:metabolism*; D053835:Unilamellar Liposomes; D015854:Up-Regulation; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D008823:Micelles; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D011994:Recombinant Proteins; D013109:Sphingomyelins; D053835:Unilamellar Liposomes; D033921:Vesicular Transport Proteins; D002784:Cholesterol; C543066:SMPD1 protein, human; D013108:Sphingomyelin Phosphodiesterase
keywords: Niemann-Pick protein type C2; anionic phospholipids; cationic lipids; ceramide; diacylglycerol; phosphatidylcholine; sphingomyelin