Publications

• Two mammalian longevity assurance gene (LAG1) family members, trh1 and trh4, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.

  Riebeling C., Allegood J.C., Wang E., Merrill A.H. Jr., Futerman A.H.

  Overexpression of upstream of growth and differentiation factor 1 (uog1), a mammalian homolog of the yeast longevity assurance gene (LAG1), selectively induces the synthesis of stearoyl-containing sphingolipids in mammalian cells (Venkataraman, K., Riebeling, C., Bodennec, J., Riezman, H., Allegoo ... >> More

  Overexpression of upstream of growth and differentiation factor 1 (uog1), a mammalian homolog of the yeast longevity assurance gene (LAG1), selectively induces the synthesis of stearoyl-containing sphingolipids in mammalian cells (Venkataraman, K., Riebeling, C., Bodennec, J., Riezman, H., Allegood, J. C., Sullards, M. C., Merrill, A. H. Jr., and Futerman, A. H. (2002) J. Biol. Chem. 277, 35642-35649). Gene data base analysis subsequently revealed a new subfamily of proteins containing the Lag1p motif, previously characterized as translocating chain-associating membrane (TRAM) protein homologs (TRH). We now report that two additional members of this family regulate the synthesis of (dihydro)ceramides with specific fatty acid(s) when overexpressed in human embryonic kidney 293T cells. TRH1 or TRH4-overexpression elevated [3H](dihydro)ceramide synthesis from l-[3-3H]serine and the increase was not blocked by the (dihydro)ceramide synthase inhibitor, fumonisin B1 (FB1). Analysis of sphingolipids by liquid chromatography-electrospray tandem mass spectrometry revealed that TRH4 overexpression elevated mainly palmitic acid-containing sphingolipids whereas TRH1 overexpression increased mainly stearic acid and arachidic acid, which in both cases were further elevated upon incubation with FB1. A similar fatty acid specificity was obtained upon analysis of (dihydro)ceramide synthase activity in vitro using various fatty acyl-CoA substrates, although in a FB1-sensitive manner. Moreover, in homogenates from TRH4-overexpressing cells, sphinganine, rather than sphingosine was the preferred substrate, whereas no preference was seen in homogenates from TRH1-overexpressing cells. These findings lend support to our hypothesis (Venkataraman, K., and Futerman, A. H. (2002) FEBS Lett. 528, 3-4) that Lag1p family members regulate (dihydro)ceramide synthases responsible for production of sphingolipids containing different fatty acids. << Less

  J. Biol. Chem. 278:43452-43459(2003) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• 2-Hydroxy-ceramide synthesis by ceramide synthase family: enzymatic basis for the preference of FA chain length.

  Mizutani Y., Kihara A., Chiba H., Tojo H., Igarashi Y.

  Ceramide is unusually abundant in epidermal stratum corneum and is important for permeability barrier function. Ceramides in epidermis also comprise an unusual variety, including 2-hydroxy (alpha-hydroxy)-ceramide. Six mammalian ceramide synthase/longevity assurance homologue (CerS/LASS) family me ... >> More

  Ceramide is unusually abundant in epidermal stratum corneum and is important for permeability barrier function. Ceramides in epidermis also comprise an unusual variety, including 2-hydroxy (alpha-hydroxy)-ceramide. Six mammalian ceramide synthase/longevity assurance homologue (CerS/LASS) family members have been identified as synthases responsible for ceramide (CER) production. We reveal here that of the six, CerS3/LASS3 mRNA is the most predominantly expressed in keratinocytes. Moreover, its expression is increased upon differentiation. CerS family members have known substrate specificities for fatty acyl-CoA chain length and saturation, yet their abilities to produce 2-hydroxy-CER have not been examined. In the present study, we demonstrate that all CerS members can produce 2-hydroxy-CER when overproduced in HEK 293T cells. Each produced a 2-hydroxy-CER with a chain length similar to that of the respective nonhydroxy-CER produced. In HeLa cells overproducing the FA 2-hydroxylase FA2H, knock-down of CerS2 resulted in a reduction in total long-chain 2-hydroxy-CERs, confirming enzyme substrate specificity for chain length. In vitro CerS assays confirmed the ability of CerS1 to utilize 2-hydroxy-stearoyl-CoA as a substrate. These results suggest that all CerS members can synthesize 2-hydroxy-CER with specificity for 2-hydroxy-fatty acyl-CoA chain length and that CerS3 may be important in CER and 2-hydroxy-CER synthesis in epidermis. << Less

  J. Lipid Res. 49:2356-2364(2008) [PubMed] [EuropePMC]

  This publication is cited by 8 other entries.

• Kinetic characterization of mammalian ceramide synthases: determination of K(m) values towards sphinganine.

  Lahiri S., Lee H., Mesicek J., Fuks Z., Haimovitz-Friedman A., Kolesnick R.N., Futerman A.H.

  Ceramide is a key metabolite in the pathway of sphingolipid biosynthesis. In mammals, ceramide is synthesized by N-acylation of a sphingoid long-chain base by a family of ceramide synthases (CerS), each of which displays a high specificity towards acyl CoAs of different chain lengths. We now optim ... >> More

  Ceramide is a key metabolite in the pathway of sphingolipid biosynthesis. In mammals, ceramide is synthesized by N-acylation of a sphingoid long-chain base by a family of ceramide synthases (CerS), each of which displays a high specificity towards acyl CoAs of different chain lengths. We now optimize a previously-described assay for measuring CerS activity for use upon over-expression of mammalian CerS, and using these conditions, establish the K(m) value of each CerS towards sphinganine. Remarkably, the K(m) values towards sphinganine are all similar, ranging from 2 to 5microM, even for CerS proteins that are able to use more than one acyl CoA for ceramide synthesis (i.e. CerS4). The availability of this assay will permit further accurate characterization of the kinetic parameters of mammalian CerS proteins. << Less

  FEBS Lett. 581:5289-5294(2007) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Human homologues of LAG1 reconstitute Acyl-CoA-dependent ceramide synthesis in yeast.

  Guillas I., Jiang J.C., Vionnet C., Roubaty C., Uldry D., Chuard R., Wang J., Jazwinski S.M., Conzelmann A.

  Lag1p and Lac1p are two highly homologous membrane proteins of the endoplasmic reticulum. lag1delta lac1delta double mutants in Saccharomyces cerevisiae lack an acyl-CoA-dependent ceramide synthase and are either very sick or nonviable, depending on the genetic background. LAG1 and LAC1 are member ... >> More

  Lag1p and Lac1p are two highly homologous membrane proteins of the endoplasmic reticulum. lag1delta lac1delta double mutants in Saccharomyces cerevisiae lack an acyl-CoA-dependent ceramide synthase and are either very sick or nonviable, depending on the genetic background. LAG1 and LAC1 are members of a large eukaryotic gene family that shares the Lag1 motif, and some members of this family additionally contain a DNA-binding HOX homeodomain. Here we show that several human LAG1 homologues can rescue the viability of lag1delta lac1delta yeast cells and restore acyl-CoA-dependent ceramide and sphingolipid biosynthesis. When tested in a microsomal assay, Lac1p and Lag1p had a strong preference for C26:0-CoA over C24:0-CoA, C20-CoA, and C16-CoA, whereas some human homologues preferred C24:0-CoA and CoA derivatives with shorter fatty acids. This suggests that LAG1 proteins are related to substrate recognition and to the catalytic activity of ceramide synthase enzymes. CLN8, another human LAG1 homologue implicated in ceroid lipofuscinosis, could not restore viability to lag1delta lac1delta yeast mutants. << Less

  J. Biol. Chem. 278:37083-37091(2003) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Upstream of growth and differentiation factor 1 (uog1), a mammalian homolog of the yeast longevity assurance gene 1 (LAG1), regulates N-stearoyl-sphinganine (C18-(dihydro)ceramide) synthesis in a fumonisin B1-independent manner in mammalian cells.

  Venkataraman K., Riebeling C., Bodennec J., Riezman H., Allegood J.C., Sullards M.C., Merrill A.H. Jr., Futerman A.H.

  The longevity assurance gene (LAG1) and its homolog (LAC1) are required for acyl-CoA-dependent synthesis of ceramides containing very long acyl chain (e.g. C26) fatty acids in yeast, and a homolog of LAG1, ASC1, confers resistance in plants to fumonisin B(1), an inhibitor of ceramide synthesis. To ... >> More

  The longevity assurance gene (LAG1) and its homolog (LAC1) are required for acyl-CoA-dependent synthesis of ceramides containing very long acyl chain (e.g. C26) fatty acids in yeast, and a homolog of LAG1, ASC1, confers resistance in plants to fumonisin B(1), an inhibitor of ceramide synthesis. To understand further the mechanism of regulation of ceramide synthesis, we now characterize a mammalian homolog of LAG1, upstream of growth and differentiation factor-1 (uog1). cDNA clones of uog1 were obtained from expression sequence-tagged clones and sub-cloned into a mammalian expression vector. Transient transfection of human embryonic kidney 293T cells with uog1 followed by metabolic labeling with [4,5-(3)H]sphinganine or L-3-[(3)H]serine demonstrated that uog1 conferred fumonisin B(1) resistance with respect to the ability of the cells to continue to produce ceramide. Surprisingly, this ceramide was channeled into neutral glycosphingolipids but not into gangliosides. Electrospray tandem mass spectrometry confirmed the elevation in sphingolipids and revealed that the ceramides and neutral glycosphingolipids of uog1-transfected cells contain primarily stearic acid (C18), that this enrichment was further increased by FB(1), and that the amount of stearic acid in sphingomyelin was also increased. UOG1 was localized to the endoplasmic reticulum, demonstrating that the fatty acid selectivity and the fumonisin B(1) resistance are not due to a subcellular localization different from that found previously for ceramide synthase activity. Furthermore, in vitro assays of uog1-transfected cells demonstrated elevated ceramide synthase activity when stearoyl-CoA but not palmitoyl-CoA was used as substrate. We propose a role for UOG1 in regulating C18-ceramide (N-stearoyl-sphinganine) synthesis, and we note that not only is this the first case of ceramide formation in mammalian cells with such a high degree of fatty acid specificity, but also that the N-stearoyl-sphinganine produced by UOG1 most significantly impacts neutral glycosphingolipid synthesis. << Less

  J. Biol. Chem. 277:35642-35649(2002) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• LASS3 (longevity assurance homologue 3) is a mainly testis-specific (dihydro)ceramide synthase with relatively broad substrate specificity.

  Mizutani Y., Kihara A., Igarashi Y.

  The LASS (longevity assurance homologue) family members are highly conserved from yeasts to mammals. Five mouse and human LASS family members, namely LASS1, LASS2, LASS4, LASS5 and LASS6, have been identified and characterized. In the present study we cloned two transcriptional variants of hithert ... >> More

  The LASS (longevity assurance homologue) family members are highly conserved from yeasts to mammals. Five mouse and human LASS family members, namely LASS1, LASS2, LASS4, LASS5 and LASS6, have been identified and characterized. In the present study we cloned two transcriptional variants of hitherto-uncharacterized mouse LASS3 cDNA, which encode a 384-amino-acid protein (LASS3) and a 419-amino-acid protein (LASS3-long). In vivo, [3H]dihydrosphingosine labelling and electrospray-ionization MS revealed that overproduction of either LASS3 isoform results in increases in several ceramide species, with some preference toward those having middle-to long-chain-fatty acyl-CoAs. A similar substrate preference was observed in an in vitro (dihydro)ceramide synthase assay. These results indicate that LASS3 possesses (dihydro)ceramide synthesis activity with relatively broad substrate specificity. We also found that, except for a weak display in skin, LASS3 mRNA expression is limited almost solely to testis, implying that LASS3 plays an important role in this gland. << Less

  Biochem. J. 398:531-538(2006) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.

• Mammalian Lass6 and its related family members regulate synthesis of specific ceramides.

  Mizutani Y., Kihara A., Igarashi Y.

  The Lass (longevity-assurance homologue) family members, which are highly conserved among eukaryotes, function in ceramide synthesis. In the mouse, there are at least five Lass family members, Lass1, Lass2, Lass4, Lass5 and the hitherto uncharacterized Lass6. To investigate specific roles for each ... >> More

  The Lass (longevity-assurance homologue) family members, which are highly conserved among eukaryotes, function in ceramide synthesis. In the mouse, there are at least five Lass family members, Lass1, Lass2, Lass4, Lass5 and the hitherto uncharacterized Lass6. To investigate specific roles for each Lass member in ceramide synthesis, we cloned these five mouse proteins. Overproduction of any Lass protein in cultured cells resulted in an increase in cellular ceramide, but the ceramide species produced varied. Overproduction of Lass1 increased C18:0-ceramide levels preferentially, and overproduction of Lass2 and Lass4 increased levels of longer ceramides such as C22:0- and C24:0-ceramides. Lass5 and Lass6 produced shorter ceramide species (C14:0- and C16:0-ceramides); however, their substrate preferences towards saturated/unsaturated fatty acyl-CoA differed. In addition to differences in substrate preferences, we also demonstrated by Northern blotting that Lass family members are differentially expressed among tissues. Additionally, we found that Lass proteins differ with regard to glycosylation. Of the five members, only Lass2, Lass5 and Lass6 were N-glycosylated, each at their N-terminal Asn residue. The occurrence of N-glycosylation of some Lass proteins provides topological insight, indicating that the N-termini of Lass family members probably face the luminal side of the endoplasmic reticulum membrane. Furthermore, based on a proteinase K digestion assay, we demonstrated that the C-terminus of Lass6 faces the cytosolic side of the membrane. From these data we propose topology for the conserved Lag1 motif in Lass family members, namely that the N-terminal region faces the luminal side and the C-terminal region the cytosolic side of the endoplasmic reticulum membrane. << Less

  Biochem. J. 390:263-271(2005) [PubMed] [EuropePMC]

  This publication is cited by 7 other entries.