Affinage

CERS5

Ceramide synthase 5 · UniProt Q8N5B7

Length
392 aa
Mass
45.8 kDa
Annotated
2026-06-09
12 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CERS5 (LASS5/TRH4) is an endoplasmic-reticulum-resident dihydroceramide synthase that selectively condenses palmitoyl-CoA with sphinganine to generate C16-ceramide (PMID:12912983). It is a bona fide, autonomous enzyme: HA-tagged CERS5 purified to near homogeneity retains full activity that is strictly phospholipid-dependent, highly selective for palmitoyl-CoA, and inhibited by fumonisin B1, establishing that no additional protein subunit is required for catalysis (PMID:16100120). CERS5 is the predominant ceramide synthase isoform in lung epithelia, where its C16-ceramide output suppresses surfactant phosphatidylcholine synthesis (PMID:15772421). The C16-ceramide it produces governs distinct downstream programs in a tissue-specific manner: hepatocyte CERS5 sustains cyp27a1 expression and the alternative bile acid pathway, restraining accumulation of fibrogenic hydrophobic bile acids (PMID:37216827), whereas its product is dispensable for skeletal muscle insulin resistance, unlike CerS1-derived C18-ceramide (PMID:35053322). Beyond catalysis, CERS5 physically interacts with succinate dehydrogenase subunit B (SDHB) through the SDHB C-terminus and the two proteins synergistically repress p53 and p21 reporter activity (PMID:27280497). CERS5 expression is transcriptionally controlled, being upregulated by 17β-estradiol/GPER1 signaling through AP-1 (c-Jun/c-Fos) at its promoter (PMID:25451689) and downregulated by fenretinide (PMID:28695226).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2003 High

    Whether CERS5/TRH4 was a ceramide synthase and which substrates it used was unknown; this work defined it as a dihydroceramide synthase with strict acyl-chain and sphingoid-base preference.

    Evidence Overexpression in HEK 293T, [3H]-serine metabolic labeling, LC-ESI-MS/MS lipidomics, and cell-free synthase assay with acyl-CoA panel plus fumonisin B1

    PMID:12912983

    Open questions at the time
    • Did not establish whether activity required partner proteins
    • Subcellular site of catalysis not directly resolved
  2. 2005 High

    It was unclear whether CERS5 catalysis is intrinsic or depends on accessory subunits; purification to homogeneity showed the enzyme is autonomous and lipid-dependent.

    Evidence Digitonin solubilization, immunoprecipitation/purification of HA-tagged LASS5, MS identity confirmation, reconstituted synthase assay with defined phospholipids and acyl-CoA

    PMID:16100120

    Open questions at the time
    • Catalytic residues and structural basis of palmitoyl-CoA selectivity not mapped
    • Regulation of activity in intact membranes not addressed
  3. 2005 Medium

    The physiological consequence of CERS5 activity in a specific tissue was undefined; it was identified as the dominant lung-epithelial isoform whose ceramide output suppresses surfactant phosphatidylcholine synthesis.

    Evidence siRNA knockdown and overexpression in lung epithelial cells, synthase activity assay, [14C]-PtdCho synthesis, membrane fractionation

    PMID:15772421

    Open questions at the time
    • Mechanism linking ceramide to PtdCho suppression not resolved
    • Residual ~55% activity after knockdown implies isoform redundancy
  4. 2014 Medium

    How CERS5 expression is regulated was unknown; estrogen/GPER1 signaling was shown to drive its promoter via AP-1.

    Evidence CerS5 promoter-luciferase with deletion/mutation constructs, GPER1 co-transfection, fulvestrant inhibition in MCF-7 and MDA-MB-231 cells

    PMID:25451689

    Open questions at the time
    • Downstream consequence of estrogen-induced CERS5 in breast cancer not defined
    • AP-1 binding shown by reporter, not endogenous chromatin occupancy
  5. 2016 Medium

    Whether CERS5 has functions beyond lipid synthesis was unaddressed; a physical interaction with SDHB linking it to p53/p21 repression was identified.

    Evidence Yeast and mammalian two-hybrid, GST pull-down, co-immunoprecipitation, co-localization in COS-7, p53/p21 luciferase reporters

    PMID:27280497

    Open questions at the time
    • Whether catalytic activity is required for transcriptional repression unknown
    • Functional consequence on endogenous p53 targets and SDH activity not tested
  6. 2017 Medium

    It was unclear whether fenretinide alters C16-ceramide enzymatically or transcriptionally; the drug was shown to downregulate Cers5 transcription rather than inhibit the enzyme.

    Evidence RT-PCR of Cers5 and ceramide mass spectrometry in fenretinide-treated CF lung epithelial lines

    PMID:28695226

    Open questions at the time
    • Transcription factors mediating fenretinide repression not identified
    • Single-method mechanistic link
  7. 2017 Low

    A possible link between CERS5-derived ceramide and metabolic signaling in endothelium was probed, indicating it negatively regulates AMPK target gene expression.

    Evidence siRNA knockdown in HUVECs with AMPK-alpha target gene expression analysis

    PMID:28424433

    Open questions at the time
    • Single siRNA knockdown with expression-only readout, no functional AMPK activity measurement
    • No rescue or orthogonal perturbation
  8. 2022 Medium

    Whether C16-ceramide is the species driving muscle insulin resistance was tested; CERS5 silencing failed to improve insulin signaling, excluding its product as the critical mediator.

    Evidence In vivo electroporation shRNA silencing in HFD-fed mouse gastrocnemius, insulin pathway and glucose uptake assays, ceramide quantification, with CerS1 comparison

    PMID:35053322

    Open questions at the time
    • Does not exclude roles in other insulin-target tissues
    • Negative result specific to skeletal muscle context
  9. 2023 Medium

    The hepatic role of CERS5 was undefined; conditional knockout revealed it protects against liver fibrosis by sustaining cyp27a1 and steering bile acid composition.

    Evidence Hepatocyte-specific CerS5 knockout mice on CDAHFD, RT-PCR/IHC/Western for fibrosis markers, RNA-seq, bile acid metabolomics

    PMID:37216827

    Open questions at the time
    • How C16-ceramide regulates cyp27a1 expression is not mechanistically resolved
    • Whether the SDHB/p53 axis contributes to the hepatic phenotype untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CERS5 catalytic output is mechanistically transduced into its varied downstream effects (PtdCho suppression, cyp27a1/bile acid control, p53/p21 repression) and whether the SDHB interaction depends on enzymatic activity remain unresolved.
  • No structural model of CERS5 or its catalytic mechanism
  • Causal chain from C16-ceramide to transcriptional and metabolic outputs not established
  • Catalysis-independent (scaffolding) functions not separated from enzymatic ones

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 2 GO:0016787 hydrolase activity 2
Localization
GO:0005783 endoplasmic reticulum 1
Pathway
R-HSA-1430728 Metabolism 4
Partners
SDHB

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 TRH4 (CERS5), when overexpressed in HEK 293T cells, elevates dihydroceramide synthesis selectively enriched in palmitic acid (C16), and in cell homogenates preferentially utilizes sphinganine (rather than sphingosine) as the sphingoid base substrate; in vitro dihydroceramide synthase activity using various fatty acyl-CoA substrates confirmed palmitoyl-CoA selectivity in a fumonisin B1-sensitive manner. Overexpression in HEK 293T cells, [3H]-serine metabolic labeling, LC-ESI-MS/MS lipidomics, in vitro dihydroceramide synthase activity assay with acyl-CoA substrates, fumonisin B1 inhibition The Journal of biological chemistry High 12912983
2005 LASS5 (CERS5) is a bona fide dihydroceramide synthase that does not require additional protein subunits for activity. HA-tagged LASS5 was solubilized with digitonin, immunoprecipitated to near homogeneity (single band by SDS-PAGE, identity confirmed by MS), and the purified protein retained dihydroceramide synthase activity that was strictly dependent on exogenous phospholipids, highly selective for palmitoyl-CoA as acyl donor, and inhibited by fumonisin B1. Immunoprecipitation/purification of HA-tagged LASS5, SDS-PAGE, mass spectrometry identity confirmation, in vitro dihydroceramide synthase activity reconstitution with defined lipid substrates, fumonisin B1 inhibition The Journal of biological chemistry High 16100120
2005 LASS5 (CERS5) is the predominant ceramide synthase isoform in lung epithelia; it is membrane-associated when exogenously expressed, and its knockdown by siRNA reduced ceramide synthase activity by ~45%, while fumonisin B1 reduced it by ~78%. Overexpression of LASS5 reduced phosphatidylcholine (PtdCho) synthesis, linking LASS5-driven ceramide production to inhibition of surfactant PtdCho metabolism. siRNA knockdown, overexpression in lung epithelial cells, ceramide synthase activity assay, [14C]-PtdCho synthesis measurement, subcellular fractionation (membrane association) Journal of lipid research Medium 15772421
2016 LASS5 (CERS5) physically interacts with succinate dehydrogenase subunit B (SDHB); the interaction was identified by yeast two-hybrid screen, confirmed by mammalian two-hybrid, GST pull-down, and co-immunoprecipitation assays. The C-terminal fragment of SDHB is required for binding. LASS5 and SDHB co-localize in COS-7 cells and synergistically repress p53 and p21 transcriptional reporter activity when co-expressed. Yeast two-hybrid screen, mammalian two-hybrid, GST pull-down, co-immunoprecipitation, co-localization (fluorescence microscopy), p53/p21 luciferase reporter assay Current molecular medicine Medium 27280497
2017 Fenretinide decreases long-chain ceramide (C16, synthesized by CerS5) levels and increases very long-chain ceramide levels in cystic fibrosis lung epithelial cell lines by transcriptionally downregulating Cers5 expression, not through direct enzymatic inhibition. RT-PCR/transcriptional analysis of Cers5 in CF lung epithelial cell lines treated with fenretinide, ceramide species quantification by mass spectrometry Journal of molecular medicine (Berlin, Germany) Medium 28695226
2014 17β-estradiol and GPER1 upregulate CerS5 promoter activity in MCF-7 breast cancer cells via activation of the AP-1 transcription factor (c-Jun/c-Fos dimerization), as demonstrated by promoter deletion and mutation constructs; this effect is blocked by the anti-estrogen fulvestrant. CerS5 promoter-luciferase reporter assays, promoter deletion and mutation constructs, co-transfection with GPER1, fulvestrant inhibition in MCF-7 and MDA-MB-231 cells Biochemical pharmacology Medium 25451689
2022 CerS5 silencing in mouse skeletal muscle (reducing C16:0-ceramide) did NOT improve insulin pathway activation or glucose uptake under high-fat diet conditions, in contrast to CerS1 silencing (which reduces C18:0-ceramide and does improve insulin sensitivity). This establishes that C16:0-ceramide generated by CerS5 is not the critical ceramide species driving skeletal muscle insulin resistance. In vivo electroporation-mediated shRNA-based gene silencing in gastrocnemius muscle of HFD-fed mice, insulin pathway activation assays, ceramide species quantification, glucose uptake measurement Cells Medium 35053322
2023 Hepatocyte-specific CerS5 knockout in mice fed a CDAHFD diet worsened liver fibrosis progression (increased α-SMA, COL1α, TGF-β) without affecting hepatic steatosis or inflammation. Mechanistically, CerS5 knockout decreased expression of cyp27a1 (a key enzyme in the alternative bile acid synthesis pathway), shifting the hepatic bile acid pool toward hydrophobic 12α-OH bile acids that promote fibrosis. Hepatocyte conditional CerS5 knockout mice, CDAHFD feeding, RT-PCR, IHC, Western blot for fibrosis/inflammation markers, RNA-seq transcriptome analysis, metabolomics for bile acid profiling Biochemical and biophysical research communications Medium 37216827
2017 Downregulation of LASS5/CERS5 by siRNA in HUVECs attenuated ceramide production and increased expression of AMPK-alpha target genes, suggesting CERS5-derived ceramide negatively regulates AMPK signaling in endothelial cells. siRNA-mediated gene silencing in HUVECs, differential gene expression analysis of AMPK-alpha and its target genes, AMPK activator treatment Turk Kardiyoloji Dernegi arsivi Low 28424433

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2003 Two mammalian longevity assurance gene (LAG1) family members, trh1 and trh4, regulate dihydroceramide synthesis using different fatty acyl-CoA donors. The Journal of biological chemistry 260 12912983
2005 LASS5 is a bona fide dihydroceramide synthase that selectively utilizes palmitoyl-CoA as acyl donor. The Journal of biological chemistry 110 16100120
2014 Ceramide synthases CerS4 and CerS5 are upregulated by 17β-estradiol and GPER1 via AP-1 in human breast cancer cells. Biochemical pharmacology 41 25451689
2005 LASS5 is the predominant ceramide synthase isoform involved in de novo sphingolipid synthesis in lung epithelia. Journal of lipid research 41 15772421
2017 Fenretinide differentially modulates the levels of long- and very long-chain ceramides by downregulating Cers5 enzyme: evidence from bench to bedside. Journal of molecular medicine (Berlin, Germany) 32 28695226
2022 CerS1 but Not CerS5 Gene Silencing, Improves Insulin Sensitivity and Glucose Uptake in Skeletal Muscle. Cells 12 35053322
2016 The MHC Class I Cancer-Associated Neoepitope Trh4 Linked with Impaired Peptide Processing Induces a Unique Noncanonical TCR Conformer. Journal of immunology (Baltimore, Md. : 1950) 11 26800871
2018 The Immunogenicity of a Proline-Substituted Altered Peptide Ligand toward the Cancer-Associated TEIPP Neoepitope Trh4 Is Unrelated to Complex Stability. Journal of immunology (Baltimore, Md. : 1950) 8 29507106
2016 LASS5 Interacts with SDHB and Synergistically Represses p53 and p21 Activity. Current molecular medicine 7 27280497
2024 Identification of CERS5 as a molecular biomarker in pan-cancer through multiple omics integrative analysis. Cellular signalling 5 38244710
2017 [Investigating the role of ceramide metabolism-associated CERS5 (LASS5) gene in atherosclerosis pathogenesis in endothelial cells]. Turk Kardiyoloji Dernegi arsivi : Turk Kardiyoloji Derneginin yayin organidir 2 28424433
2023 CerS5 deficiency promotes liver fibrosis development in non-alcoholic fatty liver disease. Biochemical and biophysical research communications 1 37216827

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