{"gene":"SAMD8","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2009,"finding":"SAMD8/SMSr is an ER-resident enzyme that catalyzes the synthesis of ceramide phosphoethanolamine (CPE) by transferring phosphoethanolamine onto ceramide; it is a monofunctional CPE synthase (not an SM synthase), and blocking its catalytic activity causes a substantial rise in ER ceramide levels and structural collapse of ER exit sites.","method":"Heterologous expression, in vitro enzymatic assay, catalytic mutant analysis, confocal microscopy of ER morphology","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of enzymatic activity plus mutagenesis plus cellular phenotype, replicated by multiple subsequent studies","pmids":["19506037"],"is_preprint":false},{"year":2009,"finding":"SMSr/SAMD8 is a monofunctional CPE synthase, distinct from SMS2 which is bifunctional (producing both SM and CPE); substrate specificity differences were established by in vitro enzymatic assays showing SMSr transfers phosphoethanolamine but not phosphocholine onto ceramide.","method":"Heterologous expression in HeLa cells, in vitro enzymatic assays with radiolabeled substrates, lipid mass spectrometry","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 1 — in vitro assay with defined substrates, replicated across labs","pmids":["19454763"],"is_preprint":false},{"year":2013,"finding":"SMSr/SAMD8 suppresses ceramide-induced mitochondrial apoptosis: disruption of SMSr catalytic activity causes ER ceramide accumulation and mislocalization to mitochondria, triggering the mitochondrial apoptotic pathway; rescue experiments (blocking de novo ceramide synthesis, stimulating ceramide export, or targeting bacterial ceramidase to mitochondria) confirmed ceramide as the death signal; the N-terminal SAM domain of SMSr is required for ceramide homeostasis independent of CPE levels.","method":"Catalytic mutant expression, siRNA knockdown, apoptosis assays (caspase activation, cytochrome c release), subcellular fractionation, lipid mass spectrometry, rescue experiments with ceramide synthesis inhibitors and bacterial ceramidase targeting","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (mutagenesis, genetic rescue, lipid biochemistry, apoptosis readouts) in a single study","pmids":["24259670"],"is_preprint":false},{"year":2011,"finding":"The SAM domain of SAMD8/SMSr forms homotypic polymers/oligomers, as identified by a native gel screening approach using negGFP-SAM fusions and confirmed by electron microscopy.","method":"negGFP-SAM fusion native gel electrophoresis, electron microscopy","journal":"Protein science : a publication of the Protein Society","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical and EM evidence from a systematic screen, but not yet functionally validated in this paper alone","pmids":["21805519"],"is_preprint":false},{"year":2017,"finding":"SMSr/SAMD8 ER residency depends on SAM domain-mediated homotypic oligomerization: SMSr self-assembles into ER-resident trimers and hexamers via its SAM domain; substitution of residues critical for oligomerization causes SMSr to redistribute partially to the Golgi; curcumin (which perturbs ER ceramide and Ca2+ homeostasis) stabilizes SMSr oligomers and promotes ER retention.","method":"Chemical crosslinking, co-immunoprecipitation, native gel electrophoresis, confocal microscopy, site-directed mutagenesis, drug treatment","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, crosslinking, mutagenesis, and localization all in one study with functional consequence (ER retention)","pmids":["28120887"],"is_preprint":false},{"year":2016,"finding":"Single-molecule photobleaching in live HeLa cells confirmed that the SAM domain of SMSr/SAMD8 drives self-assembly into oligomers within the ER membrane; removal of the SAM domain reduces bleaching steps (fewer subunits per complex), and curcumin treatment increases bleaching steps (larger oligomers).","method":"Single-molecule photobleaching with TIRF microscopy, GFP-tagged SMSr in HeLa cells with endogenous SMSr knockdown","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — quantitative single-molecule live imaging with domain deletion and drug treatment, single study","pmids":["27729449"],"is_preprint":false},{"year":2017,"finding":"A single residue adjacent to the catalytic histidine in the third exoplasmic loop determines head-group selectivity of SMS family members: Glu permits CPE production (as in SMSr/SAMD8) while Asp confines activity to SM synthesis; swapping exoplasmic residues of SMSr into SMS1 was sufficient to convert SMS1 into a bulk CPE synthase.","method":"Domain swapping, site-directed mutagenesis, in vitro enzymatic assays, heterologous expression in defined lipid environments","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis with enzymatic readout, identifying the catalytic determinant of substrate specificity","pmids":["28336574","27165857"],"is_preprint":false},{"year":2017,"finding":"SMSr/SAMD8 is cleaved by caspase-6 (not other effector caspases) at a conserved aspartate downstream of the SAM domain during apoptosis induced by staurosporine or FasL; this was established using specific caspase inhibitors, cell-free reconstitution with recombinant caspases, and siRNA gene silencing.","method":"Cell-free reconstitution, caspase-specific inhibitors, gene silencing (siRNA), western blot detection of cleavage fragments, staurosporine/FasL treatment","journal":"Bioscience reports","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution with purified caspases, specific inhibitors, and siRNA knockdown with orthogonal validation","pmids":["28659495"],"is_preprint":false},{"year":2020,"finding":"DGKδ and SMSr/SAMD8 interact physically via their respective SAM domains: SMSr-SAM but not SMS1-SAM co-immunoprecipitates with DGKδ-SAM; SAMD-deleted variants interact only weakly; SMSr overexpression enhances production of 16:0- and 16:1-containing phosphatidic acid species in DGKδ-overexpressing cells, and SMSr stimulates DGKδ catalytic activity in vitro via the SAM domain.","method":"Co-immunoprecipitation, LC-MS/MS lipidomic analysis, in vitro DGK activity assay, deletion mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — reciprocal co-IP, in vitro enzymatic assay, and lipidomics with deletion mutants in one study","pmids":["31980461"],"is_preprint":false},{"year":2021,"finding":"Purified SMSr/SAMD8 possesses additional enzymatic activities beyond CPE synthesis: it generates diacylglycerol (DG) by hydrolyzing phosphatidic acid (PAP activity ~300-fold greater than CPE synthesis rate), phosphatidylinositol (PI-PLC), phosphatidylethanolamine (PE-PLC), and phosphatidylcholine (PC-PLC) in the absence of ceramide; SMSr shows substrate selectivity for saturated/monounsaturated fatty acid-containing PA species.","method":"Highly purified recombinant SMSr, in vitro enzymatic assays with multiple phospholipid substrates, pharmacological inhibition (propranolol, D609), lipidomics in COS-7 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — highly purified enzyme with multiple in vitro substrate assays and pharmacological validation, confirmed in cells","pmids":["33621517"],"is_preprint":false},{"year":2021,"finding":"Purified recombinant SMSr/SAMD8 has phosphatidylethanolamine phospholipase C (PE-PLC) activity, generating DAG via PE hydrolysis in the absence of ceramide, with specificity for PE over PC, PS, PG; adenovirus-mediated SMSr overexpression in vivo regulates steady-state PE levels.","method":"Purified recombinant protein in vitro assay, adenovirus-mediated in vivo expression, lipid mass spectrometry","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"High","confidence_rationale":"Tier 1 — purified enzyme with substrate specificity assays and in vivo validation","pmids":["34332077"],"is_preprint":false},{"year":2015,"finding":"In vivo mouse knockout studies showed that SMSr/SAMD8 catalytic inactivation does not significantly affect ceramide levels or secretory pathway integrity in any tissue, indicating that the acute cell culture phenotypes may not translate to the in vivo context; SMSr is the principal CPE synthase in the brain.","method":"SMSr knockout and SMS2 knockout mice, tissue-specific lipid mass spectrometry (MS), histology","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with quantitative lipidomics across multiple tissues, in vivo epistasis","pmids":["25667419"],"is_preprint":false},{"year":2023,"finding":"DGKζ interacts with SMSr/SAMD8 via the SAMD of SMSr binding to the N-terminal half of the DGKζ catalytic domain; DGKζ also interacts with SMS1 but through the C-terminal cytosolic region of SMS1, not a SAM domain interaction.","method":"Co-immunoprecipitation, deletion mutant analysis","journal":"FEBS open bio","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP with deletion mutants, single study, no in vitro reconstitution","pmids":["37166445"],"is_preprint":false},{"year":2023,"finding":"SMSr/SAMD8 (as a PE-PLC) promotes nonalcoholic fatty liver disease (NAFLD): Smsr KO attenuates high-fat diet-induced fatty liver and NASH; SMSr deficiency reduces inflammatory cytokines and fibrosis factors; PE accumulation from SMSr deficiency prevents nuclear translocation of β-catenin, suppressing tumor-related gene expression.","method":"Smsr KO mice, high-fat diet/fructose NAFLD model, triple KO mice (Sms1/Sms2/Smsr), PE supplementation in vitro and in vivo, β-catenin nuclear fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with specific molecular pathway readout (β-catenin), rescue by PE supplementation, multiple mouse models","pmids":["37586586"],"is_preprint":false},{"year":2025,"finding":"SMSr/SAMD8 interacts with serine palmitoyltransferase subunit SPTLC2 in vivo and regulates SPT enzymatic activity: Smsr overexpression increases SPT activity while Smsr KO (under high-fat diet) reduces it; PE treatment reverses Smsr overexpression-mediated SPTLC2 upregulation and reduces liver microsome SPT activity dose-dependently.","method":"Co-immunoprecipitation (SMSr–SPTLC2), SPT enzymatic activity assay in mouse liver microsomes, Smsr KO and overexpression in vivo, PE supplementation","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus enzymatic assay plus genetic model, single lab study","pmids":["40998032"],"is_preprint":false}],"current_model":"SAMD8/SMSr is an ER-resident multi-pass membrane enzyme that primarily functions as a phosphatidylethanolamine phospholipase C (PE-PLC) generating diacylglycerol, and also as a monofunctional ceramide phosphoethanolamine (CPE) synthase; its N-terminal SAM domain drives homotypic oligomerization required for ER retention and ceramide homeostasis, mediates interaction with DGKδ and DGKζ to channel specific DG species into lipid signaling pathways, and the enzyme physically interacts with SPTLC2 to regulate serine palmitoyltransferase activity; disruption of its catalytic activity causes ER ceramide accumulation that triggers mitochondrial apoptosis, and SMSr is itself a caspase-6 substrate during apoptosis."},"narrative":{"teleology":[{"year":2009,"claim":"The identity of SMSr/SAMD8 as a monofunctional CPE synthase—distinct from SMS1/SMS2—resolved what enzymatic activity the gene encodes and showed that its catalytic disruption causes ER ceramide accumulation and ER exit-site collapse.","evidence":"Heterologous expression, in vitro enzymatic assays with radiolabeled substrates, catalytic mutant analysis, confocal microscopy in HeLa cells","pmids":["19506037","19454763"],"confidence":"High","gaps":["Mechanism by which ceramide accumulates upon catalytic inactivation remained unclear given low CPE flux","In vivo relevance of the ER exit-site phenotype not tested","No structural basis for head-group selectivity"]},{"year":2013,"claim":"Establishing that SMSr suppresses ceramide-induced mitochondrial apoptosis linked ER ceramide homeostasis to cell survival and revealed that the SAM domain contributes to ceramide control independently of CPE production.","evidence":"siRNA knockdown, catalytic mutants, caspase activation and cytochrome c release assays, lipid MS, rescue with ceramide synthesis inhibitors and mitochondria-targeted bacterial ceramidase","pmids":["24259670"],"confidence":"High","gaps":["Whether ceramide itself translocates to mitochondria or signals indirectly was not resolved","SAM domain mechanism of action in ceramide control remained undefined"]},{"year":2015,"claim":"Mouse knockout studies unexpectedly showed that SMSr loss does not significantly affect ceramide levels or secretory pathway integrity in vivo, challenging the cell-culture ceramide-accumulation model and establishing SMSr as the principal brain CPE synthase.","evidence":"SMSr KO and SMS2 KO mice, tissue-specific lipid mass spectrometry, histology","pmids":["25667419"],"confidence":"High","gaps":["Discrepancy between acute cell-culture and chronic in vivo phenotypes not mechanistically explained","Compensatory mechanisms in KO mice not identified"]},{"year":2017,"claim":"Demonstration that SAM domain-mediated homotypic oligomerization (trimers/hexamers) controls ER retention of SMSr explained how the SAM domain contributes to function beyond catalysis, and identification of a single active-site residue (Glu vs. Asp) governing CPE vs. SM selectivity defined the structural basis of substrate specificity.","evidence":"Chemical crosslinking, co-IP, native gel, confocal microscopy, site-directed mutagenesis, single-molecule photobleaching, domain-swap enzymatic assays","pmids":["28120887","27729449","28336574"],"confidence":"High","gaps":["High-resolution structure of SMSr oligomers not determined","How oligomerization state responds to ceramide flux mechanistically is unclear"]},{"year":2017,"claim":"Identification of SMSr as a specific caspase-6 substrate revealed that the protein is actively dismantled during apoptosis, potentially disrupting its ceramide-regulatory function as part of the apoptotic program.","evidence":"Cell-free reconstitution with purified caspases, caspase-specific inhibitors, siRNA knockdown, staurosporine/FasL-induced apoptosis","pmids":["28659495"],"confidence":"High","gaps":["Functional consequence of caspase-6 cleavage on ceramide homeostasis or CPE production not directly measured","Whether cleavage is required for apoptosis progression or is a downstream event is unknown"]},{"year":2020,"claim":"Physical interaction between the SAM domains of SMSr and DGKδ, and stimulation of DGKδ activity by SMSr, established a mechanism by which SMSr-generated DAG is channeled into phosphatidic acid signaling with acyl-chain specificity.","evidence":"Co-immunoprecipitation, LC-MS/MS lipidomics, in vitro DGK activity assay, deletion mutant analysis in HEK293 cells","pmids":["31980461"],"confidence":"High","gaps":["Whether the SMSr–DGKδ complex forms constitutively or is regulated is unknown","Stoichiometry and topology of the heteromeric SAM complex not resolved"]},{"year":2021,"claim":"Discovery that purified SMSr possesses robust PE-PLC, PI-PLC, and PAP activities—orders of magnitude faster than CPE synthesis—reframed the enzyme as a multi-substrate phospholipase C rather than primarily a CPE synthase.","evidence":"Highly purified recombinant SMSr, in vitro enzymatic assays with multiple phospholipid substrates, pharmacological inhibition, lipidomics in COS-7 cells and in vivo adenoviral overexpression","pmids":["33621517","34332077"],"confidence":"High","gaps":["Relative contribution of PE-PLC vs. CPE synthase activity in physiological ER membranes not quantified","Whether accessory subunits or ER lipid environment modulates substrate preference is untested"]},{"year":2023,"claim":"In vivo demonstration that SMSr PE-PLC activity drives NAFLD/NASH via PE depletion and consequent nuclear β-catenin signaling provided the first disease-level physiological role for SMSr's phospholipase activity, and extended the SAM-mediated interaction network to DGKζ.","evidence":"Smsr KO mice on high-fat diet/fructose, triple KO mice, PE supplementation rescue, β-catenin nuclear fractionation, co-IP with DGKζ deletion mutants","pmids":["37586586","37166445"],"confidence":"High","gaps":["Whether PE reduction acts directly on β-catenin or through intermediate signaling is unresolved","DGKζ interaction lacks reciprocal validation and in vitro reconstitution"]},{"year":2025,"claim":"Physical interaction of SMSr with the serine palmitoyltransferase subunit SPTLC2, and positive regulation of SPT activity by SMSr, established a feedback link between SMSr and de novo sphingolipid biosynthesis modulated by PE levels.","evidence":"Co-immunoprecipitation of SMSr–SPTLC2, SPT activity assay in liver microsomes, Smsr KO and overexpression, PE supplementation reversal","pmids":["40998032"],"confidence":"Medium","gaps":["Single-lab co-IP without reciprocal tagged pulldown or in vitro reconstitution","Whether the interaction is direct or mediated through a complex is unknown","Mechanism by which PE reverses SPTLC2 upregulation is not defined"]},{"year":null,"claim":"Major open questions include: the high-resolution structure of SMSr oligomers and heteromeric SAM complexes; how the enzyme's multiple catalytic activities are partitioned in native ER membranes; the molecular basis of the discrepancy between acute cell-culture ceramide phenotypes and chronic in vivo tolerance of SMSr loss; and the physiological significance of caspase-6 cleavage.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of SMSr or its SAM oligomers","Relative in vivo flux through PE-PLC vs CPE synthase activities not determined","Mechanism reconciling cell-culture ceramide accumulation with normal ceramide in KO mice unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,9,10]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,14]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,4,5]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,9,10,11]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,13]}],"complexes":["SMSr SAM-mediated homo-oligomer (trimer/hexamer)"],"partners":["DGKD","DGKZ","SPTLC2"],"other_free_text":[]},"mechanistic_narrative":"SAMD8 (SMSr) is an ER-resident lipid-metabolizing enzyme that functions as both a ceramide phosphoethanolamine (CPE) synthase and a broad-specificity phospholipase C, with its phosphatidylethanolamine phospholipase C (PE-PLC) activity being kinetically dominant over CPE synthesis [PMID:19506037, PMID:33621517, PMID:34332077]. The cytoplasmic N-terminal SAM domain drives homotypic oligomerization into trimers and hexamers that are required for ER retention and ceramide homeostasis; disruption of oligomerization or catalytic activity causes ER ceramide accumulation and mislocalization to mitochondria, triggering the mitochondrial apoptotic pathway [PMID:24259670, PMID:28120887]. The SAM domain also mediates physical interaction with DGKδ and DGKζ, channeling DAG produced by SMSr into phosphatidic acid signaling, and SMSr interacts with the serine palmitoyltransferase subunit SPTLC2 to positively regulate de novo sphingolipid biosynthesis [PMID:31980461, PMID:37166445, PMID:40998032]. In vivo, SMSr PE-PLC activity promotes nonalcoholic fatty liver disease progression by reducing PE levels and enabling nuclear β-catenin signaling, and SMSr is a caspase-6 substrate during apoptosis [PMID:37586586, PMID:28659495]."},"prefetch_data":{"uniprot":{"accession":"Q96LT4","full_name":"Sphingomyelin synthase-related protein 1","aliases":["Ceramide phosphoethanolamine synthase","CPE synthase","Phosphatidylethanolamine Phospholipase C","PE-PLC","Sterile alpha motif domain-containing protein 8","SAM domain-containing protein 8"],"length_aa":415,"mass_kda":48.3,"function":"Has phospholipase C (PLC) activity (PubMed:33621517, PubMed:34332077, PubMed:38388831). Shows specificity for phosphatidylethanolamine (1,2-diacyl-sn-glycero-3-phosphoethanolamine, PE), hydrolyzing PE to produce phosphoethanolamine and diacylglycerol (1,2-diacyl-sn-glycerol, DAG) (PubMed:34332077). This reaction might act as a regulatory switch to activate serine palmitoyltransferase (SPT) and promote sphingolipid metabolism (By similarity). Can also function as a ceramide phosphoethanolamine (N-acylsphingoid 1-phosphoethanolamine, CPE) synthase when intracellular ceramide levels are elevated (PubMed:19506037, PubMed:38388831). Binds the headgroup from PE, which is smaller and more hydrophilic than the phosphocholine headgroup transferred in the canonical sphingomyelin synthesis (SMS) reaction by SMS1 or SMS2, and transfers it on to the primary hydroxyl of a ceramide in the lumen of the endoplasmic reticulum (PubMed:19506037, PubMed:38388831). Plays a role as a ceramide sensor, helping to regulate ceramide homeostasis in the endoplasmic reticulum, which is critical for maintaining the integrity of the early secretory pathway (PubMed:19506037)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q96LT4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SAMD8","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SAMD8","total_profiled":1310},"omim":[{"mim_id":"614338","title":"PANCREATIC LIPASE DEFICIENCY; PNLIPD","url":"https://www.omim.org/entry/614338"},{"mim_id":"611575","title":"STERILE ALPHA MOTIF DOMAIN-CONTAINING PROTEIN 8; SAMD8","url":"https://www.omim.org/entry/611575"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SAMD8"},"hgnc":{"alias_symbol":["FLJ25082","SMSr"],"prev_symbol":[]},"alphafold":{"accession":"Q96LT4","domains":[{"cath_id":"1.10.150.50","chopping":"3-85","consensus_level":"high","plddt":87.8741,"start":3,"end":85},{"cath_id":"-","chopping":"148-408","consensus_level":"high","plddt":87.3981,"start":148,"end":408}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96LT4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96LT4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96LT4-F1-predicted_aligned_error_v6.png","plddt_mean":79.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SAMD8","jax_strain_url":"https://www.jax.org/strain/search?query=SAMD8"},"sequence":{"accession":"Q96LT4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96LT4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96LT4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96LT4"}},"corpus_meta":[{"pmid":"23684760","id":"PMC_23684760","title":"Biological functions of sphingomyelins.","date":"2013","source":"Progress in lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/23684760","citation_count":302,"is_preprint":false},{"pmid":"22350660","id":"PMC_22350660","title":"Diagnostic performance of Gallium-68 somatostatin receptor PET and PET/CT in patients with thoracic and gastroenteropancreatic neuroendocrine tumours: a meta-analysis.","date":"2012","source":"Endocrine","url":"https://pubmed.ncbi.nlm.nih.gov/22350660","citation_count":191,"is_preprint":false},{"pmid":"23873003","id":"PMC_23873003","title":"Somatostatin receptor PET/CT in neuroendocrine tumours: update on systematic review and meta-analysis.","date":"2013","source":"European journal of nuclear medicine and molecular imaging","url":"https://pubmed.ncbi.nlm.nih.gov/23873003","citation_count":147,"is_preprint":false},{"pmid":"19506037","id":"PMC_19506037","title":"Sphingomyelin synthase-related protein SMSr controls ceramide homeostasis in the ER.","date":"2009","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19506037","citation_count":146,"is_preprint":false},{"pmid":"23066021","id":"PMC_23066021","title":"Mammalian ORMDL proteins mediate the feedback response in ceramide biosynthesis.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23066021","citation_count":132,"is_preprint":false},{"pmid":"21805519","id":"PMC_21805519","title":"A human sterile alpha motif domain polymerizome.","date":"2011","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/21805519","citation_count":87,"is_preprint":false},{"pmid":"24259670","id":"PMC_24259670","title":"Sphingomyelin synthase-related protein SMSr is a suppressor of ceramide-induced mitochondrial apoptosis.","date":"2013","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/24259670","citation_count":63,"is_preprint":false},{"pmid":"19454763","id":"PMC_19454763","title":"Sphingomyelin synthase SMS2 displays dual activity as ceramide phosphoethanolamine synthase.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/19454763","citation_count":61,"is_preprint":false},{"pmid":"32048448","id":"PMC_32048448","title":"STAT1 and its related molecules as potential biomarkers in Mycobacterium tuberculosis infection.","date":"2020","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32048448","citation_count":54,"is_preprint":false},{"pmid":"25667419","id":"PMC_25667419","title":"Functional characterization of enzymes catalyzing ceramide phosphoethanolamine biosynthesis in mice.","date":"2015","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/25667419","citation_count":45,"is_preprint":false},{"pmid":"19367699","id":"PMC_19367699","title":"Intrinsic peptidase activity causes a sequential multi-step reaction (SMSR) in digestion of human plasma peptides.","date":"2008","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/19367699","citation_count":42,"is_preprint":false},{"pmid":"22121482","id":"PMC_22121482","title":"Effect of Peptide Receptor Radionuclide Therapy on Somatostatin Receptor Status and Glucose Metabolism in Neuroendocrine Tumors: Intraindividual Comparison of Ga-68 DOTANOC PET/CT and F-18 FDG PET/CT.","date":"2011","source":"International journal of molecular imaging","url":"https://pubmed.ncbi.nlm.nih.gov/22121482","citation_count":40,"is_preprint":false},{"pmid":"25605874","id":"PMC_25605874","title":"All members in the sphingomyelin synthase gene family have ceramide phosphoethanolamine synthase activity.","date":"2015","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/25605874","citation_count":38,"is_preprint":false},{"pmid":"10715253","id":"PMC_10715253","title":"Adenovirus-mediated gene transfer of a secreted form of human macrophage scavenger receptor inhibits modified low-density lipoprotein degradation and foam-cell formation in macrophages.","date":"2000","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/10715253","citation_count":36,"is_preprint":false},{"pmid":"28742512","id":"PMC_28742512","title":"The sphingomyelin synthase family: proteins, diseases, and inhibitors.","date":"2017","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28742512","citation_count":34,"is_preprint":false},{"pmid":"12860255","id":"PMC_12860255","title":"Adenovirus-mediated gene transfer of a secreted decoy human macrophage scavenger receptor (SR-AI) in LDL receptor knock-out mice.","date":"2003","source":"Atherosclerosis","url":"https://pubmed.ncbi.nlm.nih.gov/12860255","citation_count":30,"is_preprint":false},{"pmid":"28336574","id":"PMC_28336574","title":"Switching head group selectivity in mammalian sphingolipid biosynthesis by active-site-engineering of sphingomyelin synthases.","date":"2017","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/28336574","citation_count":25,"is_preprint":false},{"pmid":"31980461","id":"PMC_31980461","title":"Diacylglycerol kinase δ and sphingomyelin synthase-related protein functionally interact via their sterile α motif domains.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31980461","citation_count":24,"is_preprint":false},{"pmid":"33621517","id":"PMC_33621517","title":"Sphingomyelin synthase-related protein generates diacylglycerol via the hydrolysis of glycerophospholipids in the absence of ceramide.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/33621517","citation_count":23,"is_preprint":false},{"pmid":"14664792","id":"PMC_14664792","title":"Adeno-associated virus-mediated gene transfer of a secreted decoy human macrophage scavenger receptor reduces atherosclerotic lesion formation in LDL receptor knockout mice.","date":"2003","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/14664792","citation_count":23,"is_preprint":false},{"pmid":"15664082","id":"PMC_15664082","title":"High throughput easy microinjection with a single-cell manipulation supporting robot.","date":"2004","source":"Journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/15664082","citation_count":21,"is_preprint":false},{"pmid":"28120887","id":"PMC_28120887","title":"ER residency of the ceramide phosphoethanolamine synthase SMSr relies on homotypic oligomerization mediated by its SAM domain.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28120887","citation_count":18,"is_preprint":false},{"pmid":"29520708","id":"PMC_29520708","title":"Association study between copy number variation and beef fatty acid profile of Nellore cattle.","date":"2018","source":"Journal of applied genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29520708","citation_count":18,"is_preprint":false},{"pmid":"34332077","id":"PMC_34332077","title":"Sphingomyelin synthase related protein is a mammalian phosphatidylethanolamine phospholipase C.","date":"2021","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/34332077","citation_count":14,"is_preprint":false},{"pmid":"37928770","id":"PMC_37928770","title":"Inflammatory biomarkers link perceived stress with metabolic dysregulation.","date":"2023","source":"Brain, behavior, & immunity - health","url":"https://pubmed.ncbi.nlm.nih.gov/37928770","citation_count":12,"is_preprint":false},{"pmid":"28659495","id":"PMC_28659495","title":"Ceramide phosphoethanolamine synthase SMSr is a target of caspase-6 during apoptotic cell death.","date":"2017","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/28659495","citation_count":9,"is_preprint":false},{"pmid":"27158016","id":"PMC_27158016","title":"PET/CT in Neuroendocrine Tumors: Evaluation of Receptor Status and Metabolism.","date":"2011","source":"PET clinics","url":"https://pubmed.ncbi.nlm.nih.gov/27158016","citation_count":9,"is_preprint":false},{"pmid":"35503176","id":"PMC_35503176","title":"Sphingomyelin Synthase Family and Phospholipase Cs.","date":"2022","source":"Advances in experimental medicine and biology","url":"https://pubmed.ncbi.nlm.nih.gov/35503176","citation_count":8,"is_preprint":false},{"pmid":"30375099","id":"PMC_30375099","title":"Two sphingomyelin synthase homologues regulate body weight and sphingomyelin synthesis in female brown planthopper, N. lugens (Stål).","date":"2018","source":"Insect molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/30375099","citation_count":8,"is_preprint":false},{"pmid":"27729449","id":"PMC_27729449","title":"Monitoring Changes in the Oligomeric State of a Candidate Endoplasmic Reticulum (ER) Ceramide Sensor by Single-molecule Photobleaching.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27729449","citation_count":8,"is_preprint":false},{"pmid":"39368888","id":"PMC_39368888","title":"Upstream and downstream pathways of diacylglycerol kinase : Novel phosphatidylinositol turnover-independent signal transduction pathways.","date":"2024","source":"Advances in biological regulation","url":"https://pubmed.ncbi.nlm.nih.gov/39368888","citation_count":7,"is_preprint":false},{"pmid":"37586586","id":"PMC_37586586","title":"Sphingomyelin synthase-related protein SMSr is a phosphatidylethanolamine phospholipase C that promotes nonalcoholic fatty liver disease.","date":"2023","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37586586","citation_count":6,"is_preprint":false},{"pmid":"37166445","id":"PMC_37166445","title":"Diacylglycerol kinase ζ interacts with sphingomyelin synthase 1 and sphingomyelin synthase-related protein via different regions.","date":"2023","source":"FEBS open bio","url":"https://pubmed.ncbi.nlm.nih.gov/37166445","citation_count":6,"is_preprint":false},{"pmid":"27165857","id":"PMC_27165857","title":"Switching head group selectivity in mammalian sphingolipid biosynthesis by active-site engineering of sphingomyelin synthases.","date":"2016","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/27165857","citation_count":6,"is_preprint":false},{"pmid":"1947226","id":"PMC_1947226","title":"Do histocompatibility genes influence sex ratio (% males)?","date":"1991","source":"Reproduction, fertility, and development","url":"https://pubmed.ncbi.nlm.nih.gov/1947226","citation_count":4,"is_preprint":false},{"pmid":"27031267","id":"PMC_27031267","title":"De Novo 1.77-Mb Microdeletion of 10q22.2q22.3 in a Girl With Developmental Delay, Speech Delay, Congenital Cleft Palate, and Bilateral Hearing Impairment.","date":"2016","source":"The Cleft palate-craniofacial journal : official publication of the American Cleft Palate-Craniofacial Association","url":"https://pubmed.ncbi.nlm.nih.gov/27031267","citation_count":3,"is_preprint":false},{"pmid":"32096081","id":"PMC_32096081","title":"The Role of Spirituality in Patients Undergoing Hematopoietic Stem Cell Transplantation: a Systematic Mixed Studies Review.","date":"2020","source":"Journal of general internal medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32096081","citation_count":3,"is_preprint":false},{"pmid":"27156666","id":"PMC_27156666","title":"PET/CT in Neuroendocrine Tumors: Evaluation of Receptor Status and Metabolism.","date":"2009","source":"PET clinics","url":"https://pubmed.ncbi.nlm.nih.gov/27156666","citation_count":3,"is_preprint":false},{"pmid":"39268370","id":"PMC_39268370","title":"Identification of key genes in diabetic nephropathy based on lipid metabolism.","date":"2024","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39268370","citation_count":2,"is_preprint":false},{"pmid":"40950882","id":"PMC_40950882","title":"Lipid metabolism-related genes regulate the immune microenvironment during ex vivo lung perfusion for lung transplants.","date":"2025","source":"Journal of thoracic disease","url":"https://pubmed.ncbi.nlm.nih.gov/40950882","citation_count":2,"is_preprint":false},{"pmid":"40998032","id":"PMC_40998032","title":"Sphingomyelin synthase-related protein is a regulator of serine palmitoyltransferase.","date":"2025","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/40998032","citation_count":0,"is_preprint":false},{"pmid":"41605915","id":"PMC_41605915","title":"1-MHz linewidth VCSEL enabled by monolithically integrated passive cavity for high-stability chip-scale atomic clocks.","date":"2026","source":"Light, science & applications","url":"https://pubmed.ncbi.nlm.nih.gov/41605915","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":21947,"output_tokens":3766,"usd":0.061165},"stage2":{"model":"claude-opus-4-6","input_tokens":7214,"output_tokens":2837,"usd":0.160493},"total_usd":0.221658,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"SAMD8/SMSr is an ER-resident enzyme that catalyzes the synthesis of ceramide phosphoethanolamine (CPE) by transferring phosphoethanolamine onto ceramide; it is a monofunctional CPE synthase (not an SM synthase), and blocking its catalytic activity causes a substantial rise in ER ceramide levels and structural collapse of ER exit sites.\",\n      \"method\": \"Heterologous expression, in vitro enzymatic assay, catalytic mutant analysis, confocal microscopy of ER morphology\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of enzymatic activity plus mutagenesis plus cellular phenotype, replicated by multiple subsequent studies\",\n      \"pmids\": [\"19506037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SMSr/SAMD8 is a monofunctional CPE synthase, distinct from SMS2 which is bifunctional (producing both SM and CPE); substrate specificity differences were established by in vitro enzymatic assays showing SMSr transfers phosphoethanolamine but not phosphocholine onto ceramide.\",\n      \"method\": \"Heterologous expression in HeLa cells, in vitro enzymatic assays with radiolabeled substrates, lipid mass spectrometry\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay with defined substrates, replicated across labs\",\n      \"pmids\": [\"19454763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SMSr/SAMD8 suppresses ceramide-induced mitochondrial apoptosis: disruption of SMSr catalytic activity causes ER ceramide accumulation and mislocalization to mitochondria, triggering the mitochondrial apoptotic pathway; rescue experiments (blocking de novo ceramide synthesis, stimulating ceramide export, or targeting bacterial ceramidase to mitochondria) confirmed ceramide as the death signal; the N-terminal SAM domain of SMSr is required for ceramide homeostasis independent of CPE levels.\",\n      \"method\": \"Catalytic mutant expression, siRNA knockdown, apoptosis assays (caspase activation, cytochrome c release), subcellular fractionation, lipid mass spectrometry, rescue experiments with ceramide synthesis inhibitors and bacterial ceramidase targeting\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (mutagenesis, genetic rescue, lipid biochemistry, apoptosis readouts) in a single study\",\n      \"pmids\": [\"24259670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SAM domain of SAMD8/SMSr forms homotypic polymers/oligomers, as identified by a native gel screening approach using negGFP-SAM fusions and confirmed by electron microscopy.\",\n      \"method\": \"negGFP-SAM fusion native gel electrophoresis, electron microscopy\",\n      \"journal\": \"Protein science : a publication of the Protein Society\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical and EM evidence from a systematic screen, but not yet functionally validated in this paper alone\",\n      \"pmids\": [\"21805519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SMSr/SAMD8 ER residency depends on SAM domain-mediated homotypic oligomerization: SMSr self-assembles into ER-resident trimers and hexamers via its SAM domain; substitution of residues critical for oligomerization causes SMSr to redistribute partially to the Golgi; curcumin (which perturbs ER ceramide and Ca2+ homeostasis) stabilizes SMSr oligomers and promotes ER retention.\",\n      \"method\": \"Chemical crosslinking, co-immunoprecipitation, native gel electrophoresis, confocal microscopy, site-directed mutagenesis, drug treatment\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, crosslinking, mutagenesis, and localization all in one study with functional consequence (ER retention)\",\n      \"pmids\": [\"28120887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Single-molecule photobleaching in live HeLa cells confirmed that the SAM domain of SMSr/SAMD8 drives self-assembly into oligomers within the ER membrane; removal of the SAM domain reduces bleaching steps (fewer subunits per complex), and curcumin treatment increases bleaching steps (larger oligomers).\",\n      \"method\": \"Single-molecule photobleaching with TIRF microscopy, GFP-tagged SMSr in HeLa cells with endogenous SMSr knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — quantitative single-molecule live imaging with domain deletion and drug treatment, single study\",\n      \"pmids\": [\"27729449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A single residue adjacent to the catalytic histidine in the third exoplasmic loop determines head-group selectivity of SMS family members: Glu permits CPE production (as in SMSr/SAMD8) while Asp confines activity to SM synthesis; swapping exoplasmic residues of SMSr into SMS1 was sufficient to convert SMS1 into a bulk CPE synthase.\",\n      \"method\": \"Domain swapping, site-directed mutagenesis, in vitro enzymatic assays, heterologous expression in defined lipid environments\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis with enzymatic readout, identifying the catalytic determinant of substrate specificity\",\n      \"pmids\": [\"28336574\", \"27165857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SMSr/SAMD8 is cleaved by caspase-6 (not other effector caspases) at a conserved aspartate downstream of the SAM domain during apoptosis induced by staurosporine or FasL; this was established using specific caspase inhibitors, cell-free reconstitution with recombinant caspases, and siRNA gene silencing.\",\n      \"method\": \"Cell-free reconstitution, caspase-specific inhibitors, gene silencing (siRNA), western blot detection of cleavage fragments, staurosporine/FasL treatment\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with purified caspases, specific inhibitors, and siRNA knockdown with orthogonal validation\",\n      \"pmids\": [\"28659495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DGKδ and SMSr/SAMD8 interact physically via their respective SAM domains: SMSr-SAM but not SMS1-SAM co-immunoprecipitates with DGKδ-SAM; SAMD-deleted variants interact only weakly; SMSr overexpression enhances production of 16:0- and 16:1-containing phosphatidic acid species in DGKδ-overexpressing cells, and SMSr stimulates DGKδ catalytic activity in vitro via the SAM domain.\",\n      \"method\": \"Co-immunoprecipitation, LC-MS/MS lipidomic analysis, in vitro DGK activity assay, deletion mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reciprocal co-IP, in vitro enzymatic assay, and lipidomics with deletion mutants in one study\",\n      \"pmids\": [\"31980461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Purified SMSr/SAMD8 possesses additional enzymatic activities beyond CPE synthesis: it generates diacylglycerol (DG) by hydrolyzing phosphatidic acid (PAP activity ~300-fold greater than CPE synthesis rate), phosphatidylinositol (PI-PLC), phosphatidylethanolamine (PE-PLC), and phosphatidylcholine (PC-PLC) in the absence of ceramide; SMSr shows substrate selectivity for saturated/monounsaturated fatty acid-containing PA species.\",\n      \"method\": \"Highly purified recombinant SMSr, in vitro enzymatic assays with multiple phospholipid substrates, pharmacological inhibition (propranolol, D609), lipidomics in COS-7 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — highly purified enzyme with multiple in vitro substrate assays and pharmacological validation, confirmed in cells\",\n      \"pmids\": [\"33621517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Purified recombinant SMSr/SAMD8 has phosphatidylethanolamine phospholipase C (PE-PLC) activity, generating DAG via PE hydrolysis in the absence of ceramide, with specificity for PE over PC, PS, PG; adenovirus-mediated SMSr overexpression in vivo regulates steady-state PE levels.\",\n      \"method\": \"Purified recombinant protein in vitro assay, adenovirus-mediated in vivo expression, lipid mass spectrometry\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified enzyme with substrate specificity assays and in vivo validation\",\n      \"pmids\": [\"34332077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In vivo mouse knockout studies showed that SMSr/SAMD8 catalytic inactivation does not significantly affect ceramide levels or secretory pathway integrity in any tissue, indicating that the acute cell culture phenotypes may not translate to the in vivo context; SMSr is the principal CPE synthase in the brain.\",\n      \"method\": \"SMSr knockout and SMS2 knockout mice, tissue-specific lipid mass spectrometry (MS), histology\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with quantitative lipidomics across multiple tissues, in vivo epistasis\",\n      \"pmids\": [\"25667419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DGKζ interacts with SMSr/SAMD8 via the SAMD of SMSr binding to the N-terminal half of the DGKζ catalytic domain; DGKζ also interacts with SMS1 but through the C-terminal cytosolic region of SMS1, not a SAM domain interaction.\",\n      \"method\": \"Co-immunoprecipitation, deletion mutant analysis\",\n      \"journal\": \"FEBS open bio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP with deletion mutants, single study, no in vitro reconstitution\",\n      \"pmids\": [\"37166445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SMSr/SAMD8 (as a PE-PLC) promotes nonalcoholic fatty liver disease (NAFLD): Smsr KO attenuates high-fat diet-induced fatty liver and NASH; SMSr deficiency reduces inflammatory cytokines and fibrosis factors; PE accumulation from SMSr deficiency prevents nuclear translocation of β-catenin, suppressing tumor-related gene expression.\",\n      \"method\": \"Smsr KO mice, high-fat diet/fructose NAFLD model, triple KO mice (Sms1/Sms2/Smsr), PE supplementation in vitro and in vivo, β-catenin nuclear fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with specific molecular pathway readout (β-catenin), rescue by PE supplementation, multiple mouse models\",\n      \"pmids\": [\"37586586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMSr/SAMD8 interacts with serine palmitoyltransferase subunit SPTLC2 in vivo and regulates SPT enzymatic activity: Smsr overexpression increases SPT activity while Smsr KO (under high-fat diet) reduces it; PE treatment reverses Smsr overexpression-mediated SPTLC2 upregulation and reduces liver microsome SPT activity dose-dependently.\",\n      \"method\": \"Co-immunoprecipitation (SMSr–SPTLC2), SPT enzymatic activity assay in mouse liver microsomes, Smsr KO and overexpression in vivo, PE supplementation\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus enzymatic assay plus genetic model, single lab study\",\n      \"pmids\": [\"40998032\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SAMD8/SMSr is an ER-resident multi-pass membrane enzyme that primarily functions as a phosphatidylethanolamine phospholipase C (PE-PLC) generating diacylglycerol, and also as a monofunctional ceramide phosphoethanolamine (CPE) synthase; its N-terminal SAM domain drives homotypic oligomerization required for ER retention and ceramide homeostasis, mediates interaction with DGKδ and DGKζ to channel specific DG species into lipid signaling pathways, and the enzyme physically interacts with SPTLC2 to regulate serine palmitoyltransferase activity; disruption of its catalytic activity causes ER ceramide accumulation that triggers mitochondrial apoptosis, and SMSr is itself a caspase-6 substrate during apoptosis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SAMD8 (SMSr) is an ER-resident lipid-metabolizing enzyme that functions as both a ceramide phosphoethanolamine (CPE) synthase and a broad-specificity phospholipase C, with its phosphatidylethanolamine phospholipase C (PE-PLC) activity being kinetically dominant over CPE synthesis [PMID:19506037, PMID:33621517, PMID:34332077]. The cytoplasmic N-terminal SAM domain drives homotypic oligomerization into trimers and hexamers that are required for ER retention and ceramide homeostasis; disruption of oligomerization or catalytic activity causes ER ceramide accumulation and mislocalization to mitochondria, triggering the mitochondrial apoptotic pathway [PMID:24259670, PMID:28120887]. The SAM domain also mediates physical interaction with DGKδ and DGKζ, channeling DAG produced by SMSr into phosphatidic acid signaling, and SMSr interacts with the serine palmitoyltransferase subunit SPTLC2 to positively regulate de novo sphingolipid biosynthesis [PMID:31980461, PMID:37166445, PMID:40998032]. In vivo, SMSr PE-PLC activity promotes nonalcoholic fatty liver disease progression by reducing PE levels and enabling nuclear β-catenin signaling, and SMSr is a caspase-6 substrate during apoptosis [PMID:37586586, PMID:28659495].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"The identity of SMSr/SAMD8 as a monofunctional CPE synthase—distinct from SMS1/SMS2—resolved what enzymatic activity the gene encodes and showed that its catalytic disruption causes ER ceramide accumulation and ER exit-site collapse.\",\n      \"evidence\": \"Heterologous expression, in vitro enzymatic assays with radiolabeled substrates, catalytic mutant analysis, confocal microscopy in HeLa cells\",\n      \"pmids\": [\"19506037\", \"19454763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which ceramide accumulates upon catalytic inactivation remained unclear given low CPE flux\",\n        \"In vivo relevance of the ER exit-site phenotype not tested\",\n        \"No structural basis for head-group selectivity\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that SMSr suppresses ceramide-induced mitochondrial apoptosis linked ER ceramide homeostasis to cell survival and revealed that the SAM domain contributes to ceramide control independently of CPE production.\",\n      \"evidence\": \"siRNA knockdown, catalytic mutants, caspase activation and cytochrome c release assays, lipid MS, rescue with ceramide synthesis inhibitors and mitochondria-targeted bacterial ceramidase\",\n      \"pmids\": [\"24259670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether ceramide itself translocates to mitochondria or signals indirectly was not resolved\",\n        \"SAM domain mechanism of action in ceramide control remained undefined\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Mouse knockout studies unexpectedly showed that SMSr loss does not significantly affect ceramide levels or secretory pathway integrity in vivo, challenging the cell-culture ceramide-accumulation model and establishing SMSr as the principal brain CPE synthase.\",\n      \"evidence\": \"SMSr KO and SMS2 KO mice, tissue-specific lipid mass spectrometry, histology\",\n      \"pmids\": [\"25667419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Discrepancy between acute cell-culture and chronic in vivo phenotypes not mechanistically explained\",\n        \"Compensatory mechanisms in KO mice not identified\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstration that SAM domain-mediated homotypic oligomerization (trimers/hexamers) controls ER retention of SMSr explained how the SAM domain contributes to function beyond catalysis, and identification of a single active-site residue (Glu vs. Asp) governing CPE vs. SM selectivity defined the structural basis of substrate specificity.\",\n      \"evidence\": \"Chemical crosslinking, co-IP, native gel, confocal microscopy, site-directed mutagenesis, single-molecule photobleaching, domain-swap enzymatic assays\",\n      \"pmids\": [\"28120887\", \"27729449\", \"28336574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution structure of SMSr oligomers not determined\",\n        \"How oligomerization state responds to ceramide flux mechanistically is unclear\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of SMSr as a specific caspase-6 substrate revealed that the protein is actively dismantled during apoptosis, potentially disrupting its ceramide-regulatory function as part of the apoptotic program.\",\n      \"evidence\": \"Cell-free reconstitution with purified caspases, caspase-specific inhibitors, siRNA knockdown, staurosporine/FasL-induced apoptosis\",\n      \"pmids\": [\"28659495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of caspase-6 cleavage on ceramide homeostasis or CPE production not directly measured\",\n        \"Whether cleavage is required for apoptosis progression or is a downstream event is unknown\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Physical interaction between the SAM domains of SMSr and DGKδ, and stimulation of DGKδ activity by SMSr, established a mechanism by which SMSr-generated DAG is channeled into phosphatidic acid signaling with acyl-chain specificity.\",\n      \"evidence\": \"Co-immunoprecipitation, LC-MS/MS lipidomics, in vitro DGK activity assay, deletion mutant analysis in HEK293 cells\",\n      \"pmids\": [\"31980461\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the SMSr–DGKδ complex forms constitutively or is regulated is unknown\",\n        \"Stoichiometry and topology of the heteromeric SAM complex not resolved\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that purified SMSr possesses robust PE-PLC, PI-PLC, and PAP activities—orders of magnitude faster than CPE synthesis—reframed the enzyme as a multi-substrate phospholipase C rather than primarily a CPE synthase.\",\n      \"evidence\": \"Highly purified recombinant SMSr, in vitro enzymatic assays with multiple phospholipid substrates, pharmacological inhibition, lipidomics in COS-7 cells and in vivo adenoviral overexpression\",\n      \"pmids\": [\"33621517\", \"34332077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Relative contribution of PE-PLC vs. CPE synthase activity in physiological ER membranes not quantified\",\n        \"Whether accessory subunits or ER lipid environment modulates substrate preference is untested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"In vivo demonstration that SMSr PE-PLC activity drives NAFLD/NASH via PE depletion and consequent nuclear β-catenin signaling provided the first disease-level physiological role for SMSr's phospholipase activity, and extended the SAM-mediated interaction network to DGKζ.\",\n      \"evidence\": \"Smsr KO mice on high-fat diet/fructose, triple KO mice, PE supplementation rescue, β-catenin nuclear fractionation, co-IP with DGKζ deletion mutants\",\n      \"pmids\": [\"37586586\", \"37166445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether PE reduction acts directly on β-catenin or through intermediate signaling is unresolved\",\n        \"DGKζ interaction lacks reciprocal validation and in vitro reconstitution\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Physical interaction of SMSr with the serine palmitoyltransferase subunit SPTLC2, and positive regulation of SPT activity by SMSr, established a feedback link between SMSr and de novo sphingolipid biosynthesis modulated by PE levels.\",\n      \"evidence\": \"Co-immunoprecipitation of SMSr–SPTLC2, SPT activity assay in liver microsomes, Smsr KO and overexpression, PE supplementation reversal\",\n      \"pmids\": [\"40998032\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab co-IP without reciprocal tagged pulldown or in vitro reconstitution\",\n        \"Whether the interaction is direct or mediated through a complex is unknown\",\n        \"Mechanism by which PE reverses SPTLC2 upregulation is not defined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include: the high-resolution structure of SMSr oligomers and heteromeric SAM complexes; how the enzyme's multiple catalytic activities are partitioned in native ER membranes; the molecular basis of the discrepancy between acute cell-culture ceramide phenotypes and chronic in vivo tolerance of SMSr loss; and the physiological significance of caspase-6 cleavage.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of SMSr or its SAM oligomers\",\n        \"Relative in vivo flux through PE-PLC vs CPE synthase activities not determined\",\n        \"Mechanism reconciling cell-culture ceramide accumulation with normal ceramide in KO mice unresolved\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 9, 10]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 9, 10, 11]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 13]}\n    ],\n    \"complexes\": [\n      \"SMSr SAM-mediated homo-oligomer (trimer/hexamer)\"\n    ],\n    \"partners\": [\n      \"DGKD\",\n      \"DGKZ\",\n      \"SPTLC2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}