LASS5 is the predominant ceramide synthase isoform involved in de novo sphingolipid synthesis in lung epithelia

Abstract

Ceramide is a key bioactive mediator that inhibits surfactant phosphatidylcholine (PtdCho) synthesis in lung epithelia. Ceramide availability is governed by sphingomyelin (SM) hydrolysis, but less is known regarding its de novo synthesis. In this study, we observed that ceramide synthesis within murine lung epithelia was associated with high-level ceramide synthase (dihydroceramide synthase) activity. Longevity assurance homolog 5 (LASS5) was the predominant ceramide synthase isoform detected in lung epithelia, whereas relatively lower level expression was detected for the other five mammalian homologs. Pulmonary LASS5 was developmentally regulated, but its expression was spatially and gender nonspecific. Exogenously expressed LASS5 in lung epithelia was membrane-associated, triggering increased ceramide synthesis, whereas knockdown studies using fumonisin B1 or LASS5 small, interfering RNA reduced ceramide synthase activity by 78% or 45%, respectively. Overexpression of LASS5 also reduced PtdCho synthesis, but maximal inhibition was achieved when LASS5 was coexpressed with a plasmid encoding a neutral sphingomyelinase involved in SM hydrolysis.These results demonstrate that LASS5 is the major ceramide synthase gene product involved in sphingolipid production that may also regulate PtdCho metabolism in pulmonary epithelia. Ceramide is a key bioactive mediator that inhibits surfactant phosphatidylcholine (PtdCho) synthesis in lung epithelia. Ceramide availability is governed by sphingomyelin (SM) hydrolysis, but less is known regarding its de novo synthesis. In this study, we observed that ceramide synthesis within murine lung epithelia was associated with high-level ceramide synthase (dihydroceramide synthase) activity. Longevity assurance homolog 5 (LASS5) was the predominant ceramide synthase isoform detected in lung epithelia, whereas relatively lower level expression was detected for the other five mammalian homologs. Pulmonary LASS5 was developmentally regulated, but its expression was spatially and gender nonspecific. Exogenously expressed LASS5 in lung epithelia was membrane-associated, triggering increased ceramide synthesis, whereas knockdown studies using fumonisin B1 or LASS5 small, interfering RNA reduced ceramide synthase activity by 78% or 45%, respectively. Overexpression of LASS5 also reduced PtdCho synthesis, but maximal inhibition was achieved when LASS5 was coexpressed with a plasmid encoding a neutral sphingomyelinase involved in SM hydrolysis. These results demonstrate that LASS5 is the major ceramide synthase gene product involved in sphingolipid production that may also regulate PtdCho metabolism in pulmonary epithelia. Ceramide has emerged as a key signaling molecule involved in the inflammatory response, cell growth and differentiation, apoptosis, and cell senescence (1Barnes P.J. Ceramide lances the lungs.Nat. Med. 2004; 10: 130-131Crossref PubMed Scopus (18) Google Scholar, 2Hannun Y.A. Functions of ceramide in coordinating cellular responses to stress.Science. 1996; 274: 1855-1859Crossref PubMed Scopus (1515) Google Scholar, 3Obeid L.M. Linardic C.M. Karolak L.A. Hannun Y.A. Programmed cell death induced by ceramide.Science. 1993; 259: 1769-1771Crossref PubMed Scopus (1671) Google Scholar, 4Spiegel S. H. Merrill Jr, A. Sphingolipid metabolism and cell growth regulation.FASEB J. 1996; 10: 1388-1397Crossref PubMed Scopus (660) Google Scholar). In the lung, ceramide produces pulmonary injury in response to injurious cytokines and inflammatory mediators (1Barnes P.J. Ceramide lances the lungs.Nat. Med. 2004; 10: 130-131Crossref PubMed Scopus (18) Google Scholar). Ceramide potently induces programmed cell death in lung cells and inhibits the biosynthesis of phosphatidylcholine (PtdCho), the predominant phospholipid of alveolar surfactant (1Barnes P.J. Ceramide lances the lungs.Nat. Med. 2004; 10: 130-131Crossref PubMed Scopus (18) Google Scholar, 5Pettus B.J. Chalfant C.E. Hannun Y.A. Ceramide in apoptosis: an overview and current perspectives.Biochim. Biophys. Acta. 2002; 1585: 114-125Crossref PubMed Scopus (693) Google Scholar, 6Vivekananda J. Smith D. King R.J. Sphingomyelin metabolites inhibit sphingomyelin synthase and CTP:phosphocholine cytidylyltransferase.Am. J. Physiol. 2001; 281: L98-L107Google Scholar, 7Awasthi S. Vivekananda J. Awasthi V. Smith D. King R.J. CTP:phosphocholine cytidylyltransferase inhibition by ceramide via PKC-alpha, p38 MAPK, cPLA(2), and 5-lipoxygenase.Am. J. Physiol. 2001; 281: L108-L118Google Scholar, 8Ramos B. Mouedden M. El Claro E. Jackowski S. Inhibition of CTP:phosphocholine cytidylyltransferase by C(2)-ceramide and its relationship to apoptosis.Mol. Pharmacol. 2002; 62: 1068-1075Crossref PubMed Scopus (31) Google Scholar). Thus, there has been growing interest in investigations of the metabolic pathways for the generation of ceramide that might lead to newer strategies in manipulating the content of these bioactive sphingolipid products in mammalian cells. Prior studies have demonstrated that ceramides are metabolically derived, in part, from sphingomyelin (SM) hydrolysis (9Kolesnick R.N. Haimovitz-Friedman A. Fuks Z. The sphingomyelin signal transduction pathway mediates apoptosis for tumor necrosis factor, Fas, and ionizing radiation.Biochem. Cell Biol. 1994; 72: 471-474Crossref PubMed Scopus (143) Google Scholar). In this pathway, one of several membrane-associated sphingomyelinases (SMases) catalyze the rapid hydrolysis of SM to ceramide in response to a physiologic stress signal. These signals include tumor necrosis factor-α (TNF-α) and platelet-activating factor, which activate SMases, resulting in ceramide formation (9Kolesnick R.N. Haimovitz-Friedman A. Fuks Z. The sphingomyelin signal transduction pathway mediates apoptosis for tumor necrosis factor, Fas, and ionizing radiation.Biochem. Cell Biol. 1994; 72: 471-474Crossref PubMed Scopus (143) Google Scholar, 10Goggel R. Winoto-Morbach S. Vielhaber G. Imai Y. Lindner K. Brade L. Brade H. Ehlers S. Slutsky A.S. Schutze S. et al.PAF-mediated pulmonary edema: a new role for acid sphingomyelinase and ceramide.Nat. Med. 2004; 10: 155-160Crossref PubMed Scopus (273) Google Scholar). Furthermore, interruption of SMase activation using genetic or pharmacologic strategies attenuates lung injury, underscoring the observation that the SM hydrolysis pathway is a critical bioeffector mechanism for ceramide formation (10Goggel R. Winoto-Morbach S. Vielhaber G. Imai Y. Lindner K. Brade L. Brade H. Ehlers S. Slutsky A.S. Schutze S. et al.PAF-mediated pulmonary edema: a new role for acid sphingomyelinase and ceramide.Nat. Med. 2004; 10: 155-160Crossref PubMed Scopus (273) Google Scholar, 11Haimovitz-Friedman A. Cordon-Cardo C. Bayoumy S. Garzotto M. McLoughlin M. Gallily R. Edwards C.K.R. Schuchman E.H. Fuks Z. Kolesnick R. Lipopolysaccharide induces disseminated endothelial apoptosis requiring ceramide generation.J. Exp. Med. 1997; 186: 1831-1841Crossref PubMed Scopus (386) Google Scholar). Unlike SM hydrolysis, there is more limited information regarding ceramide generation via the de novo biosynthetic pathway. The first step in this pathway involves the condensation of serine with palmitoyl-CoA catalyzed by serine palmitoyltransferase (SPT; EC 2.3.1.50), generating 3-ketosphinganine. This product is immediately reduced to sphinganine by the enzyme 3-ketosphinganine reductase (EC 1.1.1.102). Acylation of sphinganine to dihydroceramide (or to ceramide if sphingosine is available) is catalyzed by ceramide synthase (dihydroceramide synthase, sphinganine N-acyltransferase, sphingosine N-acyltransferase; EC 2.3.1.24). Dihydroceramide, a physiologically inactive intermediate, is converted to bioactive ceramide by dihydroceramide desaturase. In this pathway, the molecular regulation of ceramide synthase may be of particular interest, as recent studies indicate that this enzyme is a metabolic target for TNF-α (12Meyer S.G. Groot H. de Liu J. Ginis I. Spatz M. Hallenbeck J.M. Xu J. Yeh C.H. Chen S. He L. et al.Cycloserine and threo-dihydrosphingosine inhibit TNF-alpha-induced cytotoxicity: evidence for the importance of de novo ceramide synthesis in TNF-alpha signaling.Biochim. Biophys. Acta. 2003; 1643: 1-4Crossref PubMed Scopus (37) Google Scholar, 13Liu J. Ginis I. Spatz M. Hallenbeck J.M. Xu J. Yeh C.H. Chen S. He L. Sensi S.L. Canzoniero L.M. et al.Hypoxic preconditioning protects cultured neurons against hypoxic stress via TNF-alpha and ceramide involvement of de novo ceramide biosynthesis in tumor necrosis factor-alpha/cycloheximide-induced cerebral endothelial cell death.Am. J. Physiol. 2000; 278: C144-C153Crossref PubMed Google Scholar, 14Xu J. Yeh C.H. Chen S. He L. Sensi S.L. Canzoniero L.M. Choi D.W. Hsu C.Y. Involvement of de novo ceramide biosynthesis in tumor necrosis factor-alpha/cycloheximide-induced cerebral endothelial cell death.J. Biol. Chem. 1998; 273: 16521-16526Abstract Full Text Full Text PDF PubMed Scopus (172) Google Scholar). Ceramide synthase has been partially purified, but very little is known about its enzymology and regulation (15Shimeno H. Soeda S. Sakamoto M. Kouchi T. Kowakame T. Kihara T. Partial purification and characterization of sphingosine N-acyltransferase (ceramide synthase) from bovine liver mitochondrion-rich fraction.Lipids. 1998; 33: 601-605Crossref PubMed Scopus (90) Google Scholar). The enzyme localizes to the endoplasmic reticulum, and its activity is inhibited by fumonisins, fungal inhibitors that produce pulmonary edema (16Mandon E.C. Ehses I. Rother J. Echten G. van Sandhoff K. Subcellular localization and membrane topology of serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase in mouse liver.J. Biol. Chem. 1992; 267: 11144-11148Abstract Full Text PDF PubMed Google Scholar, 17Gumprecht L.A. Beasley V.R. Weigel R.M. Parker H.M. Tumbleson M.E. Bacon C.W. Meredith F.I. Haschek W.M. Development of fumonisin-induced hepatotoxicity and pulmonary edema in orally dosed swine: morphological and biochemical alterations.Toxicol. Pathol. 1998; 26: 777-788Crossref PubMed Scopus (58) Google Scholar). Ceramide synthase effectively catalyzes N-transacylation of either sphinganine to form dihydroceramide or sphingosine to form ceramide and uses a multitude of fatty acyl-CoA species. These properties are indicative of the enzyme's relative substrate nonselectivity or reflect the existence of multiple isoenzymes (15Shimeno H. Soeda S. Sakamoto M. Kouchi T. Kowakame T. Kihara T. Partial purification and characterization of sphingosine N-acyltransferase (ceramide synthase) from bovine liver mitochondrion-rich fraction.Lipids. 1998; 33: 601-605Crossref PubMed Scopus (90) Google Scholar). Indeed, in mammalian cells, three known functional isoforms exist: longevity assurance homolog 1 (LASS1), LASS4, and LASS5. These isoforms are mammalian homologs of the yeast longevity assurance gene 1, proteins that regulate life span (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). Overexpression of these isoforms in cells ceramide isoform substrate (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, K. C. J. H. Allegood J.C. Merrill Jr., A.H. Futerman A.H. of growth and 1 (LASS1), a mammalian homolog of the yeast longevity assurance gene 1 synthesis in a fumonisin in mammalian Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). LASS4 and LASS5 are expressed in murine in to the expression of which is more for three isoforms are also detected in the lung (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). that a of to these mammalian isoforms have been and (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google the physiologic role of these isoforms is In of the pulmonary expression of isoforms with the of sphingolipid metabolites PtdCho synthesis in alveolar cells, we that ceramide synthase isoforms are expressed in the lung and are developmentally regulated, and of ceramide synthase de novo ceramide synthesis and PtdCho synthesis. The fumonisin B1 and from The cell was from the was from the of and and from The was from and from The was from The and from The small, interfering RNA and the from The was from The murine expression for LASS5 of and was from was from The and and cells from neutral was a from Liu B. Hannun Y.A. L.M. of neutral sphingomyelinase a of sphingomyelin involved in Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). was from from was from was by the of in the the of alveolar cells and from as D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar, K. of the CTP:phosphocholine cytidylyltransferase gene by J. 2004; PubMed Scopus Google Scholar). or with and and in 1 and or in The was for 5 to cells, and The was as enzyme alveolar cells or cells cultured in with and in studies cells within of In cells with a of that was the for as and for The was by for an 1 The was in with and for Ceramide synthase (dihydroceramide synthase) activity was in by of ceramide using the sphinganine or sphingosine K. C. J. H. Allegood J.C. Merrill Jr., A.H. Futerman A.H. of growth and 1 (LASS1), a mammalian homolog of the yeast longevity assurance gene 1 synthesis in a fumonisin in mammalian Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). in The sphingosine (or palmitoyl-CoA and of cellular in 1 and The was for The was by the of of cellular using rapid of and J. Physiol. PubMed Scopus Google Scholar). The was in of and to (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). using the using as a (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). The with an of enzyme activity was as the of 1 ceramide the Ceramide synthase activity was with to from to in the which was the in these SMase activity was as D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar). of epithelia and cells with or or with for to in cellular from of cellular using the of and rapid of and J. Physiol. PubMed Scopus Google to and the major sphingolipid using the (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). PtdCho was using the was by with known using and by using the as of lung Full Text PDF PubMed Google Scholar). PtdCho was by content the PtdCho by Jackowski S. necrosis factor-α inhibits expression of CTP:phosphocholine Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). lung and with a and cells in 1 of for RNA to the synthesis was using J. J. inhibit surfactant phosphatidylcholine synthesis via of CTP:phosphocholine Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). was as using the for for and for and for and for LASS4, and for LASS5, and and for and M. J. surfactant J. Biol. 2004; PubMed Scopus Google Scholar). was an using to the was in the as a for target and with using of and to be from to of RNA in the This in the The of of and and 1 of of in a of was using the of the by of and 1 The relative of the target gene was to that of the gene and expressed as relative The mouse expression was by the of and to the of the murine LASS5 gene for encoding the LASS5 was using using the with the and was using the one for and of and The product was from using the The product was for E. cells. The of the plasmid was by The was with and and from and to that was with the was with using cells cultured in in with of an a plasmid encoding murine LASS5, or a neutral cells with LASS5 plasmid in Cell for The resulting was to and the enzyme was to the The was and with the of by using of proteins using and using molecular to as Jackowski S. necrosis factor-α inhibits expression of CTP:phosphocholine Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). using or was by a in the of LASS5 for was using as a and with the and by one for of and 1 LASS5 was using the in the to the of was using the using of or LASS5 in cells for was using the with as a was using with a for multiple or a of Scholar). are as with first the biosynthesis of within murine lung epithelia. and alveolar epithelia with a substrate for sphingolipid and of this and SM was In cells cells within ceramide sphingosine and SM was observed to be lung cells metabolically sphingosine to cells also with with within or cells and cells of ceramide from sphingosine of the of These results demonstrate that murine lung epithelia ceramide from sphingolipid using a de novo pathway. also the existence of a functional N-acyltransferase for ceramide formation from lung epithelia effectively converted to ceramide and high-level de novo ceramide synthesis, was to ceramide synthase was to of known mammalian isoforms of ceramide LASS4, LASS5, and In cells, murine lung and cells, LASS5 was the predominant cells also ceramide synthase activity in the of (or that detected for in these cells D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar). ceramide synthase activity little cells and pulmonary D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar). to LASS5 expression in and cells, LASS5 was the predominant isoform in and lung and there gender in the expression of this lung are developmentally D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google and LASS5 was expressed in murine lung cells, we LASS5 and activity the and LASS5 a in lung, to lower in lung The for in enzyme activity with lung in of the that LASS5 is the major ceramide synthase activity. The studies indicate that in pulmonary epithelia, LASS5 was detected as the major of ceramide Thus, to this we LASS5 a encoding a to its expression in murine lung epithelia of cells with LASS5 plasmid to a in expression of the product with a in enzyme activity LASS5 was partially in cells, as by the increased enzyme by and a in enzyme activity in of ceramide synthase activity and the of enzyme detected within the membrane the role of LASS5 in ceramide synthase we pharmacologic and genetic strategies to sphingolipid with a plasmid or LASS5 plasmid with or a ceramide synthase Indeed, murine lung epithelia a ceramide synthase that was inhibited or cells with LASS5 ceramide synthase activity in cells of enzyme Thus, reduced activity the of LASS5 plasmid of the of these pharmacologic we to LASS5 expression using to LASS5 but a in enzyme activity These associated with a in LASS5 in LASS4 or and LASS5 also effectively reduced the of these these these that of LASS5 ceramide synthesis, whereas of its expression partially inhibits the production of the bioactive of ceramide is its the biosynthesis of Ceramide be in cells by the rapid of catalyzed by of SMase or LASS5 was to inhibit PtdCho synthesis. with a plasmid encoding neutral SMase or LASS5, or with and PtdCho was LASS5 expression reduced PtdCho by whereas of LASS5 with SMase a in PtdCho synthesis. In these SMase a in neutral SMase activity These results indicate that LASS5 is to inhibit phospholipid synthesis, but maximal is achieved in with the activation of SM hydrolysis. These of LASS5 associated with a in the of PtdCho in cells an to demonstrate that PtdCho synthesis is to SM synthesis, cells or cells with or LASS5 for of PtdCho with cells, cells with LASS5 a in of PtdCho synthesis and these for LASS5 the with the LASS5 knockdown that PtdCho synthesis and SM synthesis are physiologically Ceramide is a key mediator in the and have evidence that is the for surfactant phospholipid synthesis J. Smith D. King R.J. Sphingomyelin metabolites inhibit sphingomyelin synthase and CTP:phosphocholine cytidylyltransferase.Am. J. Physiol. 2001; 281: L98-L107Google Scholar, 8Ramos B. Mouedden M. El Claro E. Jackowski S. Inhibition of CTP:phosphocholine cytidylyltransferase by C(2)-ceramide and its relationship to apoptosis.Mol. Pharmacol. 2002; 62: 1068-1075Crossref PubMed Scopus (31) Google Scholar, of of TNF-alpha surfactant Physiol. 2000; PubMed Scopus Google Scholar, TNF-alpha ceramide apoptosis in alveolar J. Physiol. Google Scholar, M. M. Inhibition of phosphatidylcholine and biosynthesis in by J. PubMed Scopus Google Scholar, Jr., expression of tumor necrosis factor-α surfactant J. Physiol. 2002; Google Scholar). Thus, the of this was to via a de novo pathway, inhibits PtdCho production in lung epithelia. The new from these studies include the that lung epithelia in high-level de novo ceramide synthesis using that in lung cells is indicative of a N-acyltransferase mechanism catalyzed by a ceramide that LASS5 is the predominant isoform ceramide synthase activity that was developmentally in the and that PtdCho synthesis is with de novo ceramide synthesis. ceramide by SM has been in several investigations of ceramide synthesis are more limited as of the in this pathway have to be and cells and cells of and of the to dihydroceramide and but ceramide was detected as a major bioactive in pulmonary epithelia using Jr., expression of tumor necrosis factor-α surfactant J. Physiol. 2002; Google Scholar). Thus, is that ceramide is either from sphingosine or from sphinganine a ceramide In this for ceramide synthase within alveolar cells for that may be in the de novo sphingolipid pathway D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar). of this of of sphingolipid high-level ceramide synthase activity in lung epithelia might be as this enzyme as a target for the of bioactive LASS5 was the major ceramide synthase in cells but also within lung and alveolar LASS5 expression was the expression of mammalian isoforms that demonstrated to ceramide synthase activity and and also a of to ceramide synthase and The expression of LASS5 lung with a of the This is by and of alveolar the of and Google Scholar). in of role in apoptosis, is that LASS5 expression might in programmed cell death associated with condensation and alveolar lung L.M. R. L. in the of and J. Cell Biol. 1998; PubMed Scopus Google Scholar). In the LASS4, LASS5, and to LASS5 was observed to with for sphinganine sphingosine as a whereas LASS4 either sphingosine or sphinganine (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). observation by et (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google was that LASS4 or LASS5 in cells in with to a ceramide synthase increased ceramide and dihydroceramide the observed LASS4 or LASS5 expression These and indicate that ceramide or that in cells a product that In with this study, effectively reduced enzyme activity and ceramide synthesis in cells LASS5 and to using LASS5 LASS5 ceramide synthesis but or from other pulmonary ceramide synthase The also observed that LASS5 increased sphingolipid products (18Riebeling C. Allegood J.C. Wang E. Merrill Jr., A.H. Futerman A.H. Two mammalian longevity assurance gene (LAG1) family members, LASS4 and LASS5, regulate dihydroceramide synthesis using different fatty acyl-CoA donors.J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar). are relatively these results are cells are with that are with this fatty the and within the Thus, is that ceramide synthase activation in the lung might the availability of for in surfactant of ceramide is its to PtdCho synthesis. This is by studies that ceramide inhibit PtdCho and the activity of CTP:phosphocholine cytidylyltransferase the enzyme involved in PtdCho production J. Smith D. King R.J. Sphingomyelin metabolites inhibit sphingomyelin synthase and CTP:phosphocholine cytidylyltransferase.Am. J. Physiol. 2001; 281: L98-L107Google Scholar, M. M. Inhibition of phosphatidylcholine and biosynthesis in by J. PubMed Scopus Google Scholar, D. metabolic by ceramides and the with J. 2000; PubMed Google Scholar). in SMase also have increased surfactant PtdCho M. R. Schuchman E.H. in an acid mouse of J. Physiol. 2003; PubMed Scopus Google Scholar). ceramides have limited in the of inhibit PtdCho synthesis B. Mouedden M. El Claro E. Jackowski S. Inhibition of CTP:phosphocholine cytidylyltransferase by C(2)-ceramide and its relationship to apoptosis.Mol. Pharmacol. 2002; 62: 1068-1075Crossref PubMed Scopus (31) Google Scholar). ceramides from either SM hydrolysis or via de novo synthesis are for PtdCho we genetic strategies of encoding SMase or LASS5. Indeed, LASS5 expression in was to PtdCho synthesis, but inhibition was achieved with activation of the SM hydrolysis and ceramide of cells with to PtdCho synthesis. is that the observed in PtdCho synthesis LASS5 might be to an mechanism increased ceramide generation in cells activity. This enzyme from PtdCho to the generating SM D. Sphingomyelin metabolism is developmentally in J. Cell Biol. 1997; PubMed Scopus Google Scholar, C. Hannun Y.A. Sphingomyelin synthase, a of of ceramide and sphingomyelin synthase for the Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus (273) Google Scholar). that activity in cells was LASS5 and These as a of PtdCho synthesis with SM synthesis the ceramide synthase In studies that de novo ceramide synthesis in lung epithelia is catalyzed by a LASS5 expression of this enzyme also surfactant PtdCho studies be to these or by other sphingolipid metabolites that regulate with the PtdCho pathway. This was by the of and of of and