title: Resistance to alkyl-lysophospholipid-induced apoptosis due to downregulated sphingomyelin synthase 1 expression with consequent sphingomyelin- and cholesterol-deficiency in lipid rafts.
abstract: The ALP (alkyl-lysophospholipid) edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine; Et-18-OCH3) induces apoptosis in S49 mouse lymphoma cells. To this end, ALP is internalized by lipid raft-dependent endocytosis and inhibits phosphatidylcholine synthesis. A variant cell-line, S49AR, which is resistant to ALP, was shown previously to be unable to internalize ALP via this lipid raft pathway. The reason for this uptake failure is not understood. In the present study, we show that S49AR cells are unable to synthesize SM (sphingomyelin) due to down-regulated SMS1 (SM synthase 1) expression. In parental S49 cells, resistance to ALP could be mimicked by small interfering RNA-induced SMS1 suppression, resulting in SM deficiency and blockage of raft-dependent internalization of ALP and induction of apoptosis. Similar results were obtained by treatment of the cells with myriocin/ISP-1, an inhibitor of general sphingolipid synthesis, or with U18666A, a cholesterol homoeostasis perturbing agent. U18666A is known to inhibit Niemann-Pick C1 protein-dependent vesicular transport of cholesterol from endosomal compartments to the trans-Golgi network and the plasma membrane. U18666A reduced cholesterol partitioning in detergent-resistant lipid rafts and inhibited SM synthesis in S49 cells, causing ALP resistance similar to that observed in S49AR cells. The results are explained by the strong physical interaction between (newly synthesized) SM and available cholesterol at the Golgi, where they facilitate lipid raft formation. We propose that ALP internalization by lipid-raft-dependent endocytosis represents the retrograde route of a constitutive SMS1- and lipid-raft-dependent membrane vesicular recycling process.
authors.affiliation: Division of Cellular Biochemistry, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: Arnold H
authors.initials: AH
authors.lastname: Van der Luit
authors.forename: Marianne
authors.initials: M
authors.lastname: Budde
authors.forename: Shuraila
authors.initials: S
authors.lastname: Zerp
authors.forename: Wendy
authors.initials: W
authors.lastname: Caan
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Klarenbeek
authors.forename: Marcel
authors.initials: M
authors.lastname: Verheij
authors.forename: Wim J
authors.initials: WJ
authors.lastname: Van Blitterswijk
mesh_terms: D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D002784:Cholesterol / Q000032:analysis / Q000378:metabolism; D015536:Down-Regulation; D004705:Endocytosis / Q000187:drug effects; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D021962:Membrane Microdomains / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009636:Norbornanes; D010742:Phospholipid Ethers / Q000378:metabolism / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D013109:Sphingomyelins / Q000032:analysis / Q000378:metabolism; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D017855:Transferases (Other Substituted Phosphate Groups) / Q000096:biosynthesis* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000736:Androstenes; D001952:Bridged-Ring Compounds; D005229:Fatty Acids, Monounsaturated; D009636:Norbornanes; D010742:Phospholipid Ethers; D034741:RNA, Small Interfering; D013109:Sphingomyelins; D013859:Thiocarbamates; D013871:Thiones; C026659:edelfosine; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; C046498:tricyclodecane-9-yl-xanthogenate; D002784:Cholesterol; D017855:Transferases (Other Substituted Phosphate Groups); C070186:phosphatidylcholine-ceramide phosphocholine transferase; C001996:thermozymocidin