Mammalian ceramide synthases

Edited by Laszlo NagyDrosophila Ceramide Synthase (CerS) Schlank regulates both ceramide synthesis and fat metabolism. Schlank contains a catalytic lag1p motif and, like many CerS in other species, a homeodomain of unknown function. Here, we show that the Drosophila CerS Schlank is imported into the nucleus and requires two nuclear localization signals (NLSs) within its homeodomain and functional Importin-b import machinery. Expression of Schlank variants containing the homeodomain without functional lag1p motif rescued the fat metabolism phenotype of schlank mutants whereas a variant with a mutated NLS site did not rescue. Thus, the homeodomain of Schlank is involved in the regulation of lipid metabolism independent of the catalytic lag1p motif.Keywords: ceramide synthase; Drosophila; homeodomain; importin; lipid homeostasis; nuclear function Ceramides and sphingolipids are key intermediates in diverse cellular processes for growth, stress resistance, apoptosis, neurodegeneration, insulin function, and lipid homeostasis [1][2][3][4][5].In synthesis of ceramide, Ceramide Synthases (CerSs) acylate a sphingoid long-chain base (LCB) with a fatty acyl-CoA of distinct length to generate (dihydro) ceramide, the backbone of all complex sphAbbreviations aa, amino acid; ASAH1, acid ceramidase; ATF2, activating transcription factor 2; cDNA, complementary DNA; CerSs, ceramide synthases; dsRNA, double-stranded RNA; ER, endoplasmic reticulum; Gal4, galactose-responsive transcription factor; GFP, green fluorescent protein; GlcT-1, glucosylceramide synthase; H215D, change in a histidine at position 215 of schlank into glutamate; INM, inner nuclear membrane;

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“…The function of the homeodomain is still unknown [5,9,10,39]. Drosophila schlank encodes the only CerS family member in Drosophila.…”

Section: Discussionmentioning

confidence: 99%

Nuclear Drosophila CerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

et al. 2016

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“…growth factors and matrix metalloproteinases [33]. Peptides located at the C-terminus of secreted proteins can be liberated by furin and subsequently gain access to MHC-I in a TAP-independent way [30,32].Previously, we reported the TAP-independent presentation of a C-terminal peptide from the ceramide synthase Trh4, which is a multiple membrane-spanning protein in the ER [34][35][36]. This peptide was the first natural example of a C-terminal processing pathway of ER resident proteins, while previous studies suggested the existence of this route [37][38][39].…”

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confidence: 99%

Peptide transporter TAP mediates between competing antigen sources generating distinct surface MHC class I peptide repertoires

et al. 2011

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We recently described a category of TAP-independent peptide-epitopes that are selectively presented by cells with processing defects in the classical MHC class I (MHC-I) pathway. Here, we studied the ER-resident ceramide synthase Trh4 as a prototypic example of these neo-antigens and found that moderate inhibition of TAP permits cell surface presentation of the Trh4 peptide. The absence of this peptide from WT cells was not related to the binding or stability of the Trh4/D b complexes, or to the availability of MHC-I heavy chains, but rather to the limited expression of the antigen. Strongly elevated antigen levels were needed to reach comparable peptide display on WT as on TAP-deficient cells. Our data suggest that the normal influx of TAP-transported peptides in the ER during routine processing creates an efficient barrier for peptides from alternative processing routes. Impairment of TAP function, as commonly found in cancers and virus-infected cells, lowers this resistance allowing for MHC-I presentation of other peptide sources.Key words: Antigen processing . Cytotoxic T lymphocytes . Transporter associated with peptide processing Supporting Information available online IntroductionCytotoxic T lymphocytes (CTLs) are key effector cells of the adaptive immune system and circulate throughout the body in search of their cognate peptides that are presented by MHC class I (MHC-I) molecules. T-cell receptors determine the antigen specificity of CTLs and engagement with peptide/MHC-I complexes leads to their activation and elimination of target cells. Therefore, the process of MHC-I antigen processing and presentation, which operates in all nucleated cells of our body, is crucial for CTL immune surveillance [1][2][3]. The highly complex repertoire of MHC-I presented peptides reflects the total proteome of cells and derives from the physiological turnover of proteins, a process that is largely operated by the multicatalytic enzyme proteasome [4,5]. In addition to the proteasome, other proteolytic enzymes in the cytosol have been implicated in the liberation of peptides for MHC-I presentation, some of which can compensate for the lack of proteasome activity [1,6,7]. For instance, tripeptidyl peptidase II (TPPII), insulin-degrading enzyme (IDE), thimet oligopeptidase (TOP) and nardilysin have been implicated in the generation of some CTL epitopes [8][9][10]. However, the relative contributions of these novel peptidases and Ã These authors contributed equally to this work 3114their cooperation with the proteasome have not been fully characterized.The intermediate peptide products are rescued from total breakdown by these cytosolic proteases through translocation into the ER. Subsequently, peptides are trimmed and loaded into the grooves of MHC-I molecules, a dynamic process that is mediated by the peptide loading complex (PLC) consisting of MHC-I, b2m, ERp57, TAP, tapasin and chaperones [11][12][13]. The TAP peptide transport is operated by the heterodimer pump TAP1/TAP2, members of the ABC transporter family. The imp...

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“…The CerS2 null mice were generated as described (Levy & Futerman, 2010). The investigation was approved by the local ethics committee, the Institutional Review Board of the Ewha Womans University, and was in accordance with the Declaration of Helsinki, the Animal Care Guidelines of the Ewha Womans University, Medical School, and the National Institutes of Health Guide for the Care and Use of Laboratory Animals.…”

Section: Methodsmentioning

confidence: 99%

“…C6‐Ceramide also inhibited voltage‐gated K + currents and induced vasoconstriction in rat and human pulmonary arteries (Moral‐Sanz et al ., 2011). Ceramide, the backbone of all complex SLs, is synthesized by the N ‐acylation of a sphingoid long‐chain base by a family of six ceramide synthases (CerS; Levy & Futerman, 2010), each generating ceramides with a different acyl chain length. C18‐ceramide is generated by CerS1 and CerS4, and C16‐ceramide is generated by CerS5 and CerS6.…”

Section: Introductionmentioning

confidence: 99%

Altering sphingolipid composition with aging induces contractile dysfunction of gastric smooth muscle via K_C_a1.1 upregulation

Choi

Kim

et al. 2015

Aging Cell

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Summary KC a1.1 regulates smooth muscle contractility by modulating membrane potential, and age‐associated changes in KC a1.1 expression may contribute to the development of motility disorders of the gastrointestinal tract. Sphingolipids (SLs) are important structural components of cellular membranes whose altered composition may affect KC a1.1 expression. Thus, in this study, we examined whether altered SL composition due to aging may affect the contractility of gastric smooth muscle (GSM). We studied changes in ceramide synthases (CerS) and SL levels in the GSM of mice of varying ages and compared them with those in young CerS2‐null mice. The levels of C16‐ and C18‐ceramides, sphinganine, sphingosine, and sphingosine 1‐phosphate were increased, and levels of C22, C24:1 and C24 ceramides were decreased in the GSM of both aged wild‐type and young CerS2‐null mice. The altered SL composition upregulated KC a1.1 and increased KC a1.1 currents, while no change was observed in KC a1.1 channel activity. The upregulation of KC a1.1 impaired intracellular 2+ mobilization and decreased phosphorylated myosin light chain levels, causing GSM contractile dysfunction. Additionally, phosphoinositide 3‐kinase, protein kinase C ζ, c‐Jun N‐terminal kinases, and nuclear factor kappa‐B were found to be involved in KC a1.1 upregulation. Our findings suggest that age‐associated changes in SL composition or CerS2 ablation upregulate KC a1.1 via the phosphoinositide 3‐kinase/protein kinase C ζ/c‐Jun N‐terminal kinases/nuclear factor kappa‐B‐mediated pathway and impair 2+ mobilization, which thereby induces the contractile dysfunction of GSM. CerS2‐null mice exhibited similar effects to aged wild‐type mice; therefore, CerS2‐null mouse models may be utilized for investigating the pathogenesis of aging‐associated motility disorders.

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Mammalian ceramide synthases

Cited by 464 publications

References 82 publications

Nuclear Drosophila CerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

Nuclear Drosophila CerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

Peptide transporter TAP mediates between competing antigen sources generating distinct surface MHC class I peptide repertoires

Altering sphingolipid composition with aging induces contractile dysfunction of gastric smooth muscle via K_C_a1.1 upregulation

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Mammalian ceramide synthases

Cited by 464 publications

References 82 publications

Nuclear Drosophila CerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

Nuclear Drosophila CerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

Peptide transporter TAP mediates between competing antigen sources generating distinct surface MHC class I peptide repertoires

Altering sphingolipid composition with aging induces contractile dysfunction of gastric smooth muscle via KCa1.1 upregulation

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Altering sphingolipid composition with aging induces contractile dysfunction of gastric smooth muscle via K_C_a1.1 upregulation