Publications

• Developmentally regulated sphingolipid synthesis in African trypanosomes.

  Sutterwala S.S., Hsu F.F., Sevova E.S., Schwartz K.J., Zhang K., Key P., Turk J., Beverley S.M., Bangs J.D.

  Sphingolipids are essential components of eukaryotic membranes, and many unicellular eukaryotes, including kinetoplastid protozoa, are thought to synthesize exclusively inositol phosphorylceramide (IPC). Here we characterize sphingolipids from Trypanosoma brucei, and a trypanosome sphingolipid syn ... >> More

  Sphingolipids are essential components of eukaryotic membranes, and many unicellular eukaryotes, including kinetoplastid protozoa, are thought to synthesize exclusively inositol phosphorylceramide (IPC). Here we characterize sphingolipids from Trypanosoma brucei, and a trypanosome sphingolipid synthase gene family (TbSLS1-4) that is orthologous to Leishmania IPC synthase. Procyclic trypanosomes contain IPC, but also sphingomyelin, while surprisingly bloodstream-stage parasites contain sphingomyelin and ethanolamine phosphorylceramide (EPC), but no detectable IPC. In vivo fluorescent ceramide labelling confirmed stage-specific biosynthesis of both sphingomyelin and IPC. Expression of TbSLS4 in Leishmania resulted in production of sphingomyelin and EPC suggesting that the TbSLS gene family has bi-functional synthase activity. RNAi silencing of TbSLS1-4 in bloodstream trypanosomes led to rapid growth arrest and eventual cell death. Ceramide levels were increased more than threefold by silencing suggesting a toxic downstream effect mediated by this potent intracellular messenger. Topology predictions support a revised six-transmembrane domain model for the kinetoplastid sphingolipid synthases consistent with the proposed mammalian sphingomyelin synthase structure. This work reveals novel diversity and regulation in sphingolipid metabolism in this important group of human parasites. << Less

  Mol. Microbiol. 70:281-296(2008) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• The multigenic sphingomyelin synthase family.

  Tafesse F.G., Ternes P., Holthuis J.C.

  J Biol Chem 281:29421-29425(2006) [PubMed] [EuropePMC]

• Cell-free synthesis and functional characterization of sphingolipid synthases from parasitic trypanosomatid protozoa.

  Sevova E.S., Goren M.A., Schwartz K.J., Hsu F.F., Turk J., Fox B.G., Bangs J.D.

  The Trypanosoma brucei genome has four highly similar genes encoding sphingolipid synthases (TbSLS1-4). TbSLSs are polytopic membrane proteins that are essential for viability of the pathogenic bloodstream stage of this human protozoan parasite and, consequently, can be considered as potential dru ... >> More

  The Trypanosoma brucei genome has four highly similar genes encoding sphingolipid synthases (TbSLS1-4). TbSLSs are polytopic membrane proteins that are essential for viability of the pathogenic bloodstream stage of this human protozoan parasite and, consequently, can be considered as potential drug targets. TbSLS4 was shown previously to be a bifunctional sphingomyelin/ethanolamine phosphorylceramide synthase, whereas functions of the others were not characterized. Using a recently described liposome-supplemented cell-free synthesis system, which eliminates complications from background cellular activities, we now unambiguously define the enzymatic specificity of the entire gene family. TbSLS1 produces inositol phosphorylceramide, TbSLS2 produces ethanolamine phosphorylceramide, and TbSLS3 is bifunctional, like TbSLS4. These findings indicate that TbSLS1 is uniquely responsible for synthesis of inositol phosphorylceramide in insect stage parasites, in agreement with published expression array data (17). This approach also revealed that the Trypanosoma cruzi ortholog (TcSLS1) is a dedicated inositol phosphorylceramide synthase. The cell-free synthesis system allowed rapid optimization of the reaction conditions for these enzymes and site-specific mutagenesis to alter end product specificity. A single residue at position 252 (TbSLS1, Ser(252); TbSLS3, Phe(252)) strongly influences enzymatic specificity. We also have used this system to demonstrate that aureobasidin A, a potent inhibitor of fungal inositol phosphorylceramide synthases, does not significantly affect any of the TbSLS activities, consistent with the phylogenetic distance of these two clades of sphingolipid synthases. These results represent the first application of cell-free synthesis for the rapid preparation and functional annotation of integral membrane proteins and thus illustrate its utility in studying otherwise intractable enzyme systems. << Less

  J. Biol. Chem. 285:20580-20587(2010) [PubMed] [EuropePMC]

• Both sphingomyelin synthases SMS1 and SMS2 are required for sphingomyelin homeostasis and growth in human HeLa cells.

  Tafesse F.G., Huitema K., Hermansson M., van der Poel S., van den Dikkenberg J., Uphoff A., Somerharju P., Holthuis J.C.M.

  Sphingomyelin (SM) is a vital component of cellular membranes in organisms ranging from mammals to protozoa. Its production involves the transfer of phosphocholine from phosphatidylcholine to ceramide, yielding diacylglycerol in the process. The mammalian genome encodes two known SM synthase (SMS) ... >> More

  Sphingomyelin (SM) is a vital component of cellular membranes in organisms ranging from mammals to protozoa. Its production involves the transfer of phosphocholine from phosphatidylcholine to ceramide, yielding diacylglycerol in the process. The mammalian genome encodes two known SM synthase (SMS) isoforms, SMS1 and SMS2. However, the relative contributions of these enzymes to SM production in mammalian cells remained to be established. Here we show that SMS1 and SMS2 are co-expressed in a variety of cell types and function as the key Golgi- and plasma membrane-associated SM synthases in human cervical carcinoma HeLa cells, respectively. RNA interference-mediated depletion of either SMS1 or SMS2 caused a substantial decrease in SM production levels, an accumulation of ceramides, and a block in cell growth. Although SMS-depleted cells displayed a reduced SM content, external addition of SM did not restore growth. These results indicate that the biological role of SM synthases goes beyond formation of SM. << Less

  J. Biol. Chem. 282:17537-17547(2007) [PubMed] [EuropePMC]

• Sphingomyelin synthase SMS2 displays dual activity as ceramide phosphoethanolamine synthase.

  Ternes P., Brouwers J.F., van den Dikkenberg J., Holthuis J.C.

  Sphingolipids are vital components of eukaryotic membranes involved in the regulation of cell growth, death, intracellular trafficking, and the barrier function of the plasma membrane (PM). While sphingomyelin (SM) is the major sphingolipid in mammals, previous studies indicate that mammalian cell ... >> More

  Sphingolipids are vital components of eukaryotic membranes involved in the regulation of cell growth, death, intracellular trafficking, and the barrier function of the plasma membrane (PM). While sphingomyelin (SM) is the major sphingolipid in mammals, previous studies indicate that mammalian cells also produce the SM analog ceramide phosphoethanolamine (CPE). Little is known about the biological role of CPE or the enzyme(s) responsible for CPE biosynthesis. SM production is mediated by the SM synthases SMS1 in the Golgi and SMS2 at the PM, while a closely related enzyme, SMSr, has an unknown biochemical function. We now demonstrate that SMS family members display striking differences in substrate specificity, with SMS1 and SMSr being monofunctional enzymes with SM and CPE synthase activity, respectively, and SMS2 acting as a bifunctional enzyme with both SM and CPE synthase activity. In agreement with the PM residency of SMS2, we show that both SM and CPE synthase activities are enhanced at the surface of SMS2-overexpressing HeLa cells. Our findings reveal an unexpected diversity in substrate specificity among SMS family members that should enable the design of specific inhibitors to target the biological role of each enzyme individually. << Less

  J. Lipid Res. 50:2270-2277(2009) [PubMed] [EuropePMC]

  This publication is cited by 11 other entries.

• Expression cloning of a human cDNA restoring sphingomyelin synthesis and cell growth in sphingomyelin synthase-defective lymphoid cells.

  Yamaoka S., Miyaji M., Kitano T., Umehara H., Okazaki T.

  Sphingomyelin (SM) synthase has been assumed to be involved in both cell death and survival by regulating pro-apoptotic mediator ceramide and pro-survival mediator diacylglycerol. However, its precise functions are ambiguous due to the lack of molecular cloning of SM synthase gene(s). We isolated ... >> More

  Sphingomyelin (SM) synthase has been assumed to be involved in both cell death and survival by regulating pro-apoptotic mediator ceramide and pro-survival mediator diacylglycerol. However, its precise functions are ambiguous due to the lack of molecular cloning of SM synthase gene(s). We isolated WR19L/Fas-SM(-) mouse lymphoid cells, which show a defect of SM at the plasma membrane due to the lack of SM synthase activity and resistance to cell death induced by an SM-directed cytolytic protein lysenin. WR19L/Fas-SM(-) cells were also highly susceptible to methyl-beta-cyclodextrin (MbetaCD) as compared with the WR19L/Fas-SM(+) cells, which are capable of SM synthesis. By expression cloning method using WR19L/Fas-SM(-) cells and MbetaCD-based selection, we have succeeded in cloning of a human cDNA responsible for SM synthase activity. The cDNA encodes a peptide of 413 amino acids named SMS1 (putative molecular mass, 48.6 kDa), which contains a sterile alpha motif domain near the N-terminal region and four predicted transmembrane domains. WR19L/Fas-SM(-) cells expressing SMS1 cDNA (WR19L/Fas-SMS1) restored the resistance against MbetaCD, the accumulation of SM at the plasma membrane, and SM synthesis by transferring phosphocholine from phosphatidylcholine to ceramide. Furthermore, WR19L/Fas-SMS1 cells, as well as WR19L/Fas-SM(-) cells supplemented with exogenous SM, restored cell growth ability in serum-free conditions, where the growth of WR19L/Fas-SM(-) cells was severely inhibited. The results suggest that SMS1 is responsible for SM synthase activity in mammalian cells and plays a critical role in cell growth of mouse lymphoid cells. << Less

  J. Biol. Chem. 279:18688-18693(2004) [PubMed] [EuropePMC]

• Identification of a family of animal sphingomyelin synthases.

  Huitema K., Van Den Dikkenberg J., Brouwers J.F.H.M., Holthuis J.C.

  Sphingomyelin (SM) is a major component of animal plasma membranes. Its production involves the transfer of phosphocholine from phosphatidylcholine onto ceramide, yielding diacylglycerol as a side product. This reaction is catalysed by SM synthase, an enzyme whose biological potential can be judge ... >> More

  Sphingomyelin (SM) is a major component of animal plasma membranes. Its production involves the transfer of phosphocholine from phosphatidylcholine onto ceramide, yielding diacylglycerol as a side product. This reaction is catalysed by SM synthase, an enzyme whose biological potential can be judged from the roles of diacylglycerol and ceramide as anti- and proapoptotic stimuli, respectively. SM synthesis occurs in the lumen of the Golgi as well as on the cell surface. As no gene for SM synthase has been cloned so far, it is unclear whether different enzymes are present at these locations. Using a functional cloning strategy in yeast, we identified a novel family of integral membrane proteins exhibiting all enzymatic features previously attributed to animal SM synthase. Strikingly, human, mouse and Caenorhabditis elegans genomes each contain at least two different SM synthase (SMS) genes. Whereas human SMS1 is localised to the Golgi, SMS2 resides primarily at the plasma membrane. Collectively, these findings open up important new avenues for studying sphingolipid function in animals. << Less

  EMBO J. 23:33-44(2004) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.