{"gene":"GNMT","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1998,"finding":"Crystal structure of apo-GNMT determined at 2.5 Å resolution, revealing it is a tetrameric enzyme (monomer 32,423 Da, 292 amino acids) with a three-domain monomer structure forming a square tetramer with a central channel; the apo structure shows only localized changes in the binding pocket residues compared to the AdoMet-bound form, confirming the catalytic mechanism of methyl transfer from S-adenosylmethionine to glycine producing S-adenosylhomocysteine and sarcosine.","method":"X-ray crystallography at 2.5 Å resolution (R-factor 21.9%)","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation of binding pocket","pmids":["9655336"],"is_preprint":false},{"year":2011,"finding":"GNMT expression increases hepatic folate concentration, induces folate-dependent homocysteine remethylation via methionine synthase, and improves folate retention in vivo; GNMT knockout mice show reduced hepatic folate and decreased methionine synthase expression, demonstrating GNMT is a major hepatic folate binding protein that regulates methylfolate-dependent metabolism.","method":"Stable isotopic tracers with GC/MS flux analysis; GNMT transgenic and knockout mouse models; Western blot for methionine synthase","journal":"Molecular medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (isotope tracing, transgenic/KO mice, enzyme quantification) in single study","pmids":["21210071"],"is_preprint":false},{"year":2013,"finding":"GNMT supports methylene-folate-dependent pyrimidine synthesis and formylfolate-dependent purine synthesis; loss of GNMT impairs nucleotide biosynthesis and increases uracil misincorporation into DNA; GNMT translocates into the nucleus during prolonged folate depletion, suggesting a direct role in DNA integrity maintenance.","method":"Stable isotopic tracers with GC/MS; GNMT overexpression in null cell lines; Gnmt wildtype, heterozygote, and knockout mouse models under varying folate conditions; uracil content in DNA assay","journal":"International journal of cancer","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (isotope tracing, KO mice, nuclear localization), replicated in both cell and animal models","pmids":["23922098"],"is_preprint":false},{"year":2014,"finding":"In Drosophila, the FOXO transcription factor dFoxO cell-autonomously upregulates Gnmt in the fat body in response to necrosis-driven Toll pathway activation; Gnmt upregulation increases sarcosine and reduces SAM levels, functioning as a rheostat for controlling energy loss during inflammatory and fasting conditions.","method":"Metabolomic analysis (hemolymph); genetic epistasis with apoptosis-deficient and Toll pathway mutants; fat body-specific manipulation in Drosophila","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in vivo with metabolomic readout, multiple genetic conditions tested","pmids":["24746817"],"is_preprint":false},{"year":2014,"finding":"GNMT deficiency in mice triggers NK cell activation, and TRAIL-producing NK cells promote liver injury and fibrogenesis through the TRAIL/DR5 axis; genetic ablation of TRAIL in GNMT-/- mice significantly attenuates chronic liver injury and fibrosis, placing GNMT upstream of NK cell-mediated TRAIL/DR5 signaling in liver homeostasis.","method":"Double knockout mice (TRAIL-/-/GNMT-/-); bile duct ligation model; in vivo DR5 silencing; NK cell depletion","journal":"Laboratory investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double KO and multiple in vivo interventions","pmids":["25531568"],"is_preprint":false},{"year":2017,"finding":"GNMT interacts with PREX2 (a PTEN inhibitor) and promotes its proteasomal degradation via the E3 ubiquitin ligase HectH9; depletion of GNMT or HectH9 results in PREX2 accumulation, AKT activation, and enhanced cell proliferation, placing GNMT as a regulator of the AKT signaling pathway through HectH9-mediated ubiquitination of PREX2.","method":"Co-immunoprecipitation to identify GNMT-PREX2 interaction; siRNA depletion of GNMT and HectH9; AKT phosphorylation assays; GNMT knockout mouse liver analysis; IHC in human HCC samples","journal":"International journal of cancer","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, KO mouse validation, mechanistic epistasis with defined AKT pathway readout","pmids":["28205209"],"is_preprint":false},{"year":2019,"finding":"GNMT functions as an essential regulator of mitochondrial Complex II (succinate dehydrogenase) activity in the electron transport chain; in NAFLD, GNMT is post-transcriptionally repressed by miR-873-5p, leading to mitochondrial dysfunction, and anti-miR-873-5p treatment restores GNMT expression and improves fatty acid β-oxidation.","method":"In vitro and in vivo NAFLD murine models; miR-873-5p target validation; mitochondrial Complex II activity assays; anti-miR therapeutic intervention","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — functional assay of Complex II activity linked to GNMT, but mechanistic interface details limited to single study","pmids":["31668391"],"is_preprint":false},{"year":2019,"finding":"Benzo[a]pyrene (BaP) treatment induces phosphorylation of GNMT at serine 9, which is required for GNMT nuclear translocation; mutation of serine 9 abolishes BaP-induced nuclear translocation and results in increased CYP1A1 expression; protein kinase C (PKC) and JNK may be the responsible kinases.","method":"LC-MS/MS phosphoproteomics; site-directed mutagenesis (S9A); nuclear translocation assay; CYP1A1 expression as functional readout","journal":"Journal of food and drug analysis","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis confirming specific phosphorylation site required for localization, with functional consequence; single lab","pmids":["30987732"],"is_preprint":false},{"year":2019,"finding":"MYC acts as a transcriptional repressor of GNMT by binding to the GNMT promoter; MYC overexpression suppresses GNMT promoter activity and protein expression, while MYC knockdown or pharmacological inhibition induces GNMT expression; PGG compound induces GNMT by suppressing MYC through both transcriptional repression and proteasome-independent protein degradation.","method":"Chromatin immunoprecipitation (ChIP) with anti-MYC antibody on GNMT promoter; luciferase reporter assay; shRNA knockdown; MYC overexpression; xenograft mouse model","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — ChIP directly demonstrating MYC binding to GNMT promoter, corroborated by reporter assays and in vivo xenograft","pmids":["30760754"],"is_preprint":false},{"year":2020,"finding":"GNMT, identified as a direct target of carnosine via cellular thermal shift assay (CETSA) and molecular docking, regulates the cellular SAM/SAH ratio; GNMT overexpression mimics carnosine's protective effects in reducing renal inflammation and fibrosis in diabetic nephropathy models, while GNMT knockdown abolishes these effects.","method":"Cellular thermal shift assay (CETSA); molecular docking; transient GNMT transfection; siRNA knockdown; in vivo DN mouse models","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2 — CETSA for direct binding, functional rescue and knockdown experiments; single lab","pmids":["33241846"],"is_preprint":false},{"year":2024,"finding":"In Drosophila fat body, GNMT protein levels are regulated by the nuclear ubiquitin-proteasome system (UPS) under conditions of SAM shortage (starvation or inhibition of SAM synthesis); suppression of nuclear UPS-mediated GNMT degradation causes starvation tolerance and prevents SAM depletion, demonstrating that GNMT degradation via nuclear UPS is a mechanism for buffering SAM levels.","method":"Drosophila genetic models; nuclear UPS suppression; metabolic measurement of SAM levels; starvation tolerance assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with defined metabolic readout in vivo; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2024.08.21.609067"],"is_preprint":true},{"year":2024,"finding":"Aurora kinase A (AurA) promotes nuclear localization of FOXO3, which drives GNMT expression; AurA inhibition increases GNMT activity and SAM consumption, reducing H3K4me3 and H3K36me3 on Il6 and Tnf gene regions, thereby dampening trained immunity; this places GNMT downstream of the mTOR-FOXO3 axis in regulating SAM-dependent histone methylation.","method":"ATAC-seq; RNA-seq; metabolomic analysis of SAM; ChIP for H3K4me3/H3K36me3; AurA inhibitor treatment; macrophage trained immunity model","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (epigenomics, metabolomics, ChIP) in single preprint study","pmids":["bio_10.1101_2024.11.11.622956"],"is_preprint":true},{"year":2025,"finding":"Choline upregulates GNMT expression through the AMPK/Myc/GNMT signaling axis; AMPK activation reduces Myc (a negative transcriptional regulator of GNMT), leading to increased GNMT expression; GNMT knockdown reverses choline's beneficial effects on lipid synthesis, fatty acid oxidation, lipoprotein assembly, and bile acid metabolism genes in hepatocytes.","method":"GNMT knockdown; AMPK inhibition; gene expression assays for lipid/bile acid metabolism genes; transcriptomic profiling","journal":"Stress biology","confidence":"Medium","confidence_rationale":"Tier 2 — KD with defined pathway epistasis, but single lab with limited mechanistic depth at molecular level","pmids":["41233636"],"is_preprint":false},{"year":2003,"finding":"Polymorphisms in the GNMT promoter region (short tandem repeat 1 and insertion/deletion polymorphism) cause allele-specific differences in GNMT transcriptional activity, as demonstrated by luciferase reporter and gel mobility shift assays; risk genotypes associated with lower GNMT expression are over-represented in tumor-adjacent tissues from HCC patients.","method":"Luciferase reporter gene assay; gel mobility shift assay (EMSA); loss of heterozygosity analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional assay of promoter variants, replicated by two complementary methods","pmids":["12566309"],"is_preprint":false}],"current_model":"GNMT is a tetrameric SAM-dependent methyltransferase that transfers a methyl group from SAM to glycine generating sarcosine and SAH, thereby regulating the cellular SAM/SAH ratio; it functions as a major hepatic folate-binding protein that supports both nucleotide biosynthesis and homocysteine remethylation, localizes to the nucleus upon phosphorylation at Ser9 by PKC/JNK in response to genotoxic stress, interacts with PREX2 to promote its HectH9-mediated proteasomal degradation and suppress AKT signaling, regulates mitochondrial Complex II activity, and is transcriptionally repressed by MYC and post-transcriptionally suppressed by miR-873-5p, with its own protein levels buffered through nuclear ubiquitin-proteasome-mediated degradation under SAM-limiting conditions."},"narrative":{"teleology":[{"year":1998,"claim":"Determination of the crystal structure of GNMT resolved how four identical subunits assemble into the functional tetramer and identified the SAM-binding pocket architecture, establishing the structural basis for its methyl transfer mechanism.","evidence":"X-ray crystallography of apo-GNMT at 2.5 Å resolution with comparison to AdoMet-bound form","pmids":["9655336"],"confidence":"High","gaps":["No structure of ternary complex with glycine substrate","Mechanism of inter-subunit allosteric communication unresolved","No structural basis for folate binding identified"]},{"year":2003,"claim":"Functional characterization of GNMT promoter polymorphisms established that allele-specific variation in transcriptional output is linked to hepatocellular carcinoma risk, positioning GNMT as a tumor suppressor gene whose reduced expression contributes to liver carcinogenesis.","evidence":"Luciferase reporter and EMSA assays of promoter variants; loss-of-heterozygosity analysis in HCC tissues","pmids":["12566309"],"confidence":"Medium","gaps":["Causal relationship between GNMT expression level and tumor initiation not demonstrated","No genome-wide association replication","Downstream oncogenic pathways linking reduced GNMT to HCC not defined"]},{"year":2011,"claim":"Demonstration that GNMT is a major hepatic folate-binding protein resolved how it integrates one-carbon metabolism by increasing folate retention and promoting methionine synthase-dependent homocysteine remethylation.","evidence":"Stable isotopic tracing with GC/MS in GNMT transgenic and knockout mouse models; Western blot quantification of methionine synthase","pmids":["21210071"],"confidence":"High","gaps":["Direct structural characterization of GNMT–folate binding interface absent","Relative contribution of GNMT folate-binding versus methyltransferase activity not separated"]},{"year":2013,"claim":"Establishing that GNMT supports both pyrimidine and purine synthesis through folate-dependent pathways, and translocates to the nucleus during folate depletion, expanded its role from SAM metabolism to genome integrity maintenance.","evidence":"Isotopic tracing in GNMT-overexpressing cells and Gnmt KO mice; uracil content measurement in genomic DNA; nuclear localization assays","pmids":["23922098"],"confidence":"High","gaps":["Nuclear function of GNMT beyond metabolic channeling undefined","Mechanism of folate-depletion-triggered nuclear import unknown at this stage"]},{"year":2014,"claim":"Cross-species work in Drosophila revealed that GNMT is transcriptionally upregulated by FOXO in response to inflammatory stress to consume SAM and produce sarcosine, establishing GNMT as a metabolic rheostat during energy stress; in parallel, mouse studies showed GNMT deficiency activates NK cell–TRAIL/DR5 signaling to drive liver fibrosis.","evidence":"Drosophila fat body genetic epistasis with metabolomics; double-knockout mice (TRAIL/GNMT) with bile duct ligation","pmids":["24746817","25531568"],"confidence":"High","gaps":["Whether FOXO-GNMT axis is conserved in mammalian liver not tested","How SAM depletion specifically activates NK cells in GNMT-null mice not established"]},{"year":2017,"claim":"Discovery that GNMT physically interacts with PREX2 and promotes its HectH9-mediated ubiquitination and proteasomal degradation revealed a non-enzymatic tumor-suppressive function through suppression of AKT signaling.","evidence":"Reciprocal co-immunoprecipitation; siRNA depletion of GNMT and HectH9; AKT phosphorylation assays; GNMT KO mouse liver; IHC in human HCC","pmids":["28205209"],"confidence":"High","gaps":["Whether GNMT methyltransferase activity is required for PREX2 interaction not tested","Structural basis of GNMT–PREX2–HectH9 tripartite complex unknown","Relative contribution of catalytic versus scaffolding tumor-suppressor functions unresolved"]},{"year":2019,"claim":"Three contemporaneous studies resolved distinct regulatory layers: MYC directly binds the GNMT promoter to repress transcription; miR-873-5p post-transcriptionally represses GNMT to impair mitochondrial Complex II activity in NAFLD; and phosphorylation at Ser9 by PKC/JNK is required for genotoxic-stress-induced nuclear translocation.","evidence":"ChIP with anti-MYC on GNMT promoter, reporter assays, xenograft model; miR-873-5p target validation with Complex II activity assays in NAFLD models; LC-MS/MS phosphoproteomics with S9A mutagenesis and CYP1A1 readout","pmids":["30760754","31668391","30987732"],"confidence":"High","gaps":["Mechanism by which GNMT regulates Complex II activity not molecularly defined","Whether nuclear GNMT has distinct substrates or functions beyond metabolic channeling unclear","Direct kinase assays for PKC/JNK phosphorylation of Ser9 not shown"]},{"year":2020,"claim":"Identification of GNMT as a direct target of the dipeptide carnosine via CETSA demonstrated that small-molecule binding can modulate GNMT's SAM/SAH regulatory function to reduce renal inflammation and fibrosis in diabetic nephropathy.","evidence":"CETSA and molecular docking for direct binding; GNMT overexpression/knockdown in diabetic nephropathy mouse models","pmids":["33241846"],"confidence":"Medium","gaps":["Binding site of carnosine on GNMT not structurally characterized","Whether carnosine modulates catalytic activity or protein stability not distinguished","Single-lab finding"]},{"year":2024,"claim":"Work in Drosophila and macrophage models extended the regulatory framework: GNMT protein is degraded by nuclear UPS under SAM shortage to buffer SAM levels, and the AurA–FOXO3 axis controls GNMT expression to regulate SAM-dependent histone methylation and trained immunity.","evidence":"Drosophila nuclear UPS suppression with SAM measurement (preprint); AurA inhibitor treatment with ATAC-seq, ChIP for H3K4me3/H3K36me3, and metabolomics in macrophages (preprint)","pmids":["bio_10.1101_2024.08.21.609067","bio_10.1101_2024.11.11.622956"],"confidence":"Medium","gaps":["Both studies are preprints awaiting peer review","E3 ligase responsible for nuclear GNMT degradation not identified","Whether GNMT-dependent histone methylation changes are direct or secondary to SAM pool depletion not resolved"]},{"year":2025,"claim":"Demonstration that choline upregulates GNMT through an AMPK/MYC axis linked GNMT to hepatic lipid metabolism, bile acid metabolism, and lipoprotein assembly, broadening its physiological role beyond one-carbon metabolism.","evidence":"GNMT knockdown combined with AMPK inhibition; transcriptomic profiling of lipid and bile acid metabolism genes in hepatocytes","pmids":["41233636"],"confidence":"Medium","gaps":["Direct enzymatic or metabolic mechanism connecting GNMT to lipid/bile acid pathways not defined","Single lab with limited molecular depth"]},{"year":null,"claim":"The structural basis of GNMT's non-catalytic interactions (PREX2, folate, Complex II), the identity of the E3 ligase mediating nuclear GNMT degradation in mammals, and whether nuclear GNMT has distinct substrates or chromatin-regulatory roles beyond SAM pool modulation remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of GNMT bound to PREX2 or folate","No mammalian validation of nuclear UPS-mediated GNMT degradation","Whether GNMT directly methylates nuclear substrates beyond glycine is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,3,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,6]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,7,10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,3,9,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,6,13]}],"complexes":[],"partners":["PREX2","HUWE1","MYC"],"other_free_text":[]},"mechanistic_narrative":"GNMT is a tetrameric S-adenosylmethionine (SAM)-dependent methyltransferase that catalyzes methyl transfer from SAM to glycine, producing sarcosine and S-adenosylhomocysteine (SAH), and thereby serves as a critical regulator of the cellular SAM/SAH ratio, folate metabolism, nucleotide biosynthesis, and epigenetic methylation. Structurally a homotetramer with a central channel, GNMT functions as a major hepatic folate-binding protein that promotes folate retention, methionine synthase-dependent homocysteine remethylation, and folate-dependent pyrimidine and purine synthesis, with its loss causing uracil misincorporation into DNA [PMID:9655336, PMID:21210071, PMID:23922098]. GNMT suppresses AKT signaling by interacting with PREX2 and promoting its HectH9-mediated proteasomal degradation, regulates mitochondrial Complex II activity, and undergoes phosphorylation-dependent (Ser9, via PKC/JNK) nuclear translocation in response to genotoxic stress [PMID:28205209, PMID:31668391, PMID:30987732]. GNMT expression is transcriptionally repressed by MYC, post-transcriptionally suppressed by miR-873-5p, and its protein levels are buffered through nuclear ubiquitin-proteasome-mediated degradation under SAM-limiting conditions; promoter polymorphisms that reduce GNMT expression are associated with hepatocellular carcinoma susceptibility [PMID:30760754, PMID:31668391, PMID:12566309]."},"prefetch_data":{"uniprot":{"accession":"Q14749","full_name":"Glycine N-methyltransferase","aliases":[],"length_aa":295,"mass_kda":32.7,"function":"Catalyzes the methylation of glycine by using S-adenosylmethionine (AdoMet) to form N-methylglycine (sarcosine) with the concomitant production of S-adenosylhomocysteine (AdoHcy), a reaction regulated by the binding of 5-methyltetrahydrofolate. Plays an important role in the regulation of methyl group metabolism by regulating the ratio between S-adenosyl-L-methionine and S-adenosyl-L-homocysteine","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q14749/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GNMT","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GNMT","total_profiled":1310},"omim":[{"mim_id":"606664","title":"GLYCINE N-METHYLTRANSFERASE DEFICIENCY","url":"https://www.omim.org/entry/606664"},{"mim_id":"606628","title":"GLYCINE N-METHYLTRANSFERASE; GNMT","url":"https://www.omim.org/entry/606628"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":278.9},{"tissue":"pancreas","ntpm":563.6}],"url":"https://www.proteinatlas.org/search/GNMT"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q14749","domains":[{"cath_id":"3.40.50.150","chopping":"25-179_248-292","consensus_level":"high","plddt":93.5772,"start":25,"end":292}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14749","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14749-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14749-F1-predicted_aligned_error_v6.png","plddt_mean":88.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GNMT","jax_strain_url":"https://www.jax.org/strain/search?query=GNMT"},"sequence":{"accession":"Q14749","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14749.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14749/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14749"}},"corpus_meta":[{"pmid":"24746817","id":"PMC_24746817","title":"Necrosis-driven 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metabolism","date":"2024-11-11","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.11.622956","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15904,"output_tokens":3553,"usd":0.050503},"stage2":{"model":"claude-opus-4-6","input_tokens":6943,"output_tokens":2967,"usd":0.163335},"total_usd":0.213838,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"Crystal structure of apo-GNMT determined at 2.5 Å resolution, revealing it is a tetrameric enzyme (monomer 32,423 Da, 292 amino acids) with a three-domain monomer structure forming a square tetramer with a central channel; the apo structure shows only localized changes in the binding pocket residues compared to the AdoMet-bound form, confirming the catalytic mechanism of methyl transfer from S-adenosylmethionine to glycine producing S-adenosylhomocysteine and sarcosine.\",\n      \"method\": \"X-ray crystallography at 2.5 Å resolution (R-factor 21.9%)\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation of binding pocket\",\n      \"pmids\": [\"9655336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GNMT expression increases hepatic folate concentration, induces folate-dependent homocysteine remethylation via methionine synthase, and improves folate retention in vivo; GNMT knockout mice show reduced hepatic folate and decreased methionine synthase expression, demonstrating GNMT is a major hepatic folate binding protein that regulates methylfolate-dependent metabolism.\",\n      \"method\": \"Stable isotopic tracers with GC/MS flux analysis; GNMT transgenic and knockout mouse models; Western blot for methionine synthase\",\n      \"journal\": \"Molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (isotope tracing, transgenic/KO mice, enzyme quantification) in single study\",\n      \"pmids\": [\"21210071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GNMT supports methylene-folate-dependent pyrimidine synthesis and formylfolate-dependent purine synthesis; loss of GNMT impairs nucleotide biosynthesis and increases uracil misincorporation into DNA; GNMT translocates into the nucleus during prolonged folate depletion, suggesting a direct role in DNA integrity maintenance.\",\n      \"method\": \"Stable isotopic tracers with GC/MS; GNMT overexpression in null cell lines; Gnmt wildtype, heterozygote, and knockout mouse models under varying folate conditions; uracil content in DNA assay\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (isotope tracing, KO mice, nuclear localization), replicated in both cell and animal models\",\n      \"pmids\": [\"23922098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In Drosophila, the FOXO transcription factor dFoxO cell-autonomously upregulates Gnmt in the fat body in response to necrosis-driven Toll pathway activation; Gnmt upregulation increases sarcosine and reduces SAM levels, functioning as a rheostat for controlling energy loss during inflammatory and fasting conditions.\",\n      \"method\": \"Metabolomic analysis (hemolymph); genetic epistasis with apoptosis-deficient and Toll pathway mutants; fat body-specific manipulation in Drosophila\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo with metabolomic readout, multiple genetic conditions tested\",\n      \"pmids\": [\"24746817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GNMT deficiency in mice triggers NK cell activation, and TRAIL-producing NK cells promote liver injury and fibrogenesis through the TRAIL/DR5 axis; genetic ablation of TRAIL in GNMT-/- mice significantly attenuates chronic liver injury and fibrosis, placing GNMT upstream of NK cell-mediated TRAIL/DR5 signaling in liver homeostasis.\",\n      \"method\": \"Double knockout mice (TRAIL-/-/GNMT-/-); bile duct ligation model; in vivo DR5 silencing; NK cell depletion\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double KO and multiple in vivo interventions\",\n      \"pmids\": [\"25531568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GNMT interacts with PREX2 (a PTEN inhibitor) and promotes its proteasomal degradation via the E3 ubiquitin ligase HectH9; depletion of GNMT or HectH9 results in PREX2 accumulation, AKT activation, and enhanced cell proliferation, placing GNMT as a regulator of the AKT signaling pathway through HectH9-mediated ubiquitination of PREX2.\",\n      \"method\": \"Co-immunoprecipitation to identify GNMT-PREX2 interaction; siRNA depletion of GNMT and HectH9; AKT phosphorylation assays; GNMT knockout mouse liver analysis; IHC in human HCC samples\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, KO mouse validation, mechanistic epistasis with defined AKT pathway readout\",\n      \"pmids\": [\"28205209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GNMT functions as an essential regulator of mitochondrial Complex II (succinate dehydrogenase) activity in the electron transport chain; in NAFLD, GNMT is post-transcriptionally repressed by miR-873-5p, leading to mitochondrial dysfunction, and anti-miR-873-5p treatment restores GNMT expression and improves fatty acid β-oxidation.\",\n      \"method\": \"In vitro and in vivo NAFLD murine models; miR-873-5p target validation; mitochondrial Complex II activity assays; anti-miR therapeutic intervention\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assay of Complex II activity linked to GNMT, but mechanistic interface details limited to single study\",\n      \"pmids\": [\"31668391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Benzo[a]pyrene (BaP) treatment induces phosphorylation of GNMT at serine 9, which is required for GNMT nuclear translocation; mutation of serine 9 abolishes BaP-induced nuclear translocation and results in increased CYP1A1 expression; protein kinase C (PKC) and JNK may be the responsible kinases.\",\n      \"method\": \"LC-MS/MS phosphoproteomics; site-directed mutagenesis (S9A); nuclear translocation assay; CYP1A1 expression as functional readout\",\n      \"journal\": \"Journal of food and drug analysis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis confirming specific phosphorylation site required for localization, with functional consequence; single lab\",\n      \"pmids\": [\"30987732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MYC acts as a transcriptional repressor of GNMT by binding to the GNMT promoter; MYC overexpression suppresses GNMT promoter activity and protein expression, while MYC knockdown or pharmacological inhibition induces GNMT expression; PGG compound induces GNMT by suppressing MYC through both transcriptional repression and proteasome-independent protein degradation.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) with anti-MYC antibody on GNMT promoter; luciferase reporter assay; shRNA knockdown; MYC overexpression; xenograft mouse model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP directly demonstrating MYC binding to GNMT promoter, corroborated by reporter assays and in vivo xenograft\",\n      \"pmids\": [\"30760754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GNMT, identified as a direct target of carnosine via cellular thermal shift assay (CETSA) and molecular docking, regulates the cellular SAM/SAH ratio; GNMT overexpression mimics carnosine's protective effects in reducing renal inflammation and fibrosis in diabetic nephropathy models, while GNMT knockdown abolishes these effects.\",\n      \"method\": \"Cellular thermal shift assay (CETSA); molecular docking; transient GNMT transfection; siRNA knockdown; in vivo DN mouse models\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CETSA for direct binding, functional rescue and knockdown experiments; single lab\",\n      \"pmids\": [\"33241846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In Drosophila fat body, GNMT protein levels are regulated by the nuclear ubiquitin-proteasome system (UPS) under conditions of SAM shortage (starvation or inhibition of SAM synthesis); suppression of nuclear UPS-mediated GNMT degradation causes starvation tolerance and prevents SAM depletion, demonstrating that GNMT degradation via nuclear UPS is a mechanism for buffering SAM levels.\",\n      \"method\": \"Drosophila genetic models; nuclear UPS suppression; metabolic measurement of SAM levels; starvation tolerance assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with defined metabolic readout in vivo; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.08.21.609067\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Aurora kinase A (AurA) promotes nuclear localization of FOXO3, which drives GNMT expression; AurA inhibition increases GNMT activity and SAM consumption, reducing H3K4me3 and H3K36me3 on Il6 and Tnf gene regions, thereby dampening trained immunity; this places GNMT downstream of the mTOR-FOXO3 axis in regulating SAM-dependent histone methylation.\",\n      \"method\": \"ATAC-seq; RNA-seq; metabolomic analysis of SAM; ChIP for H3K4me3/H3K36me3; AurA inhibitor treatment; macrophage trained immunity model\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (epigenomics, metabolomics, ChIP) in single preprint study\",\n      \"pmids\": [\"bio_10.1101_2024.11.11.622956\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Choline upregulates GNMT expression through the AMPK/Myc/GNMT signaling axis; AMPK activation reduces Myc (a negative transcriptional regulator of GNMT), leading to increased GNMT expression; GNMT knockdown reverses choline's beneficial effects on lipid synthesis, fatty acid oxidation, lipoprotein assembly, and bile acid metabolism genes in hepatocytes.\",\n      \"method\": \"GNMT knockdown; AMPK inhibition; gene expression assays for lipid/bile acid metabolism genes; transcriptomic profiling\",\n      \"journal\": \"Stress biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined pathway epistasis, but single lab with limited mechanistic depth at molecular level\",\n      \"pmids\": [\"41233636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Polymorphisms in the GNMT promoter region (short tandem repeat 1 and insertion/deletion polymorphism) cause allele-specific differences in GNMT transcriptional activity, as demonstrated by luciferase reporter and gel mobility shift assays; risk genotypes associated with lower GNMT expression are over-represented in tumor-adjacent tissues from HCC patients.\",\n      \"method\": \"Luciferase reporter gene assay; gel mobility shift assay (EMSA); loss of heterozygosity analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional assay of promoter variants, replicated by two complementary methods\",\n      \"pmids\": [\"12566309\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GNMT is a tetrameric SAM-dependent methyltransferase that transfers a methyl group from SAM to glycine generating sarcosine and SAH, thereby regulating the cellular SAM/SAH ratio; it functions as a major hepatic folate-binding protein that supports both nucleotide biosynthesis and homocysteine remethylation, localizes to the nucleus upon phosphorylation at Ser9 by PKC/JNK in response to genotoxic stress, interacts with PREX2 to promote its HectH9-mediated proteasomal degradation and suppress AKT signaling, regulates mitochondrial Complex II activity, and is transcriptionally repressed by MYC and post-transcriptionally suppressed by miR-873-5p, with its own protein levels buffered through nuclear ubiquitin-proteasome-mediated degradation under SAM-limiting conditions.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GNMT is a tetrameric S-adenosylmethionine (SAM)-dependent methyltransferase that catalyzes methyl transfer from SAM to glycine, producing sarcosine and S-adenosylhomocysteine (SAH), and thereby serves as a critical regulator of the cellular SAM/SAH ratio, folate metabolism, nucleotide biosynthesis, and epigenetic methylation. Structurally a homotetramer with a central channel, GNMT functions as a major hepatic folate-binding protein that promotes folate retention, methionine synthase-dependent homocysteine remethylation, and folate-dependent pyrimidine and purine synthesis, with its loss causing uracil misincorporation into DNA [PMID:9655336, PMID:21210071, PMID:23922098]. GNMT suppresses AKT signaling by interacting with PREX2 and promoting its HectH9-mediated proteasomal degradation, regulates mitochondrial Complex II activity, and undergoes phosphorylation-dependent (Ser9, via PKC/JNK) nuclear translocation in response to genotoxic stress [PMID:28205209, PMID:31668391, PMID:30987732]. GNMT expression is transcriptionally repressed by MYC, post-transcriptionally suppressed by miR-873-5p, and its protein levels are buffered through nuclear ubiquitin-proteasome-mediated degradation under SAM-limiting conditions; promoter polymorphisms that reduce GNMT expression are associated with hepatocellular carcinoma susceptibility [PMID:30760754, PMID:31668391, PMID:12566309].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Determination of the crystal structure of GNMT resolved how four identical subunits assemble into the functional tetramer and identified the SAM-binding pocket architecture, establishing the structural basis for its methyl transfer mechanism.\",\n      \"evidence\": \"X-ray crystallography of apo-GNMT at 2.5 Å resolution with comparison to AdoMet-bound form\",\n      \"pmids\": [\"9655336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of ternary complex with glycine substrate\", \"Mechanism of inter-subunit allosteric communication unresolved\", \"No structural basis for folate binding identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Functional characterization of GNMT promoter polymorphisms established that allele-specific variation in transcriptional output is linked to hepatocellular carcinoma risk, positioning GNMT as a tumor suppressor gene whose reduced expression contributes to liver carcinogenesis.\",\n      \"evidence\": \"Luciferase reporter and EMSA assays of promoter variants; loss-of-heterozygosity analysis in HCC tissues\",\n      \"pmids\": [\"12566309\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal relationship between GNMT expression level and tumor initiation not demonstrated\", \"No genome-wide association replication\", \"Downstream oncogenic pathways linking reduced GNMT to HCC not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstration that GNMT is a major hepatic folate-binding protein resolved how it integrates one-carbon metabolism by increasing folate retention and promoting methionine synthase-dependent homocysteine remethylation.\",\n      \"evidence\": \"Stable isotopic tracing with GC/MS in GNMT transgenic and knockout mouse models; Western blot quantification of methionine synthase\",\n      \"pmids\": [\"21210071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural characterization of GNMT–folate binding interface absent\", \"Relative contribution of GNMT folate-binding versus methyltransferase activity not separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that GNMT supports both pyrimidine and purine synthesis through folate-dependent pathways, and translocates to the nucleus during folate depletion, expanded its role from SAM metabolism to genome integrity maintenance.\",\n      \"evidence\": \"Isotopic tracing in GNMT-overexpressing cells and Gnmt KO mice; uracil content measurement in genomic DNA; nuclear localization assays\",\n      \"pmids\": [\"23922098\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear function of GNMT beyond metabolic channeling undefined\", \"Mechanism of folate-depletion-triggered nuclear import unknown at this stage\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Cross-species work in Drosophila revealed that GNMT is transcriptionally upregulated by FOXO in response to inflammatory stress to consume SAM and produce sarcosine, establishing GNMT as a metabolic rheostat during energy stress; in parallel, mouse studies showed GNMT deficiency activates NK cell–TRAIL/DR5 signaling to drive liver fibrosis.\",\n      \"evidence\": \"Drosophila fat body genetic epistasis with metabolomics; double-knockout mice (TRAIL/GNMT) with bile duct ligation\",\n      \"pmids\": [\"24746817\", \"25531568\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FOXO-GNMT axis is conserved in mammalian liver not tested\", \"How SAM depletion specifically activates NK cells in GNMT-null mice not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that GNMT physically interacts with PREX2 and promotes its HectH9-mediated ubiquitination and proteasomal degradation revealed a non-enzymatic tumor-suppressive function through suppression of AKT signaling.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation; siRNA depletion of GNMT and HectH9; AKT phosphorylation assays; GNMT KO mouse liver; IHC in human HCC\",\n      \"pmids\": [\"28205209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GNMT methyltransferase activity is required for PREX2 interaction not tested\", \"Structural basis of GNMT–PREX2–HectH9 tripartite complex unknown\", \"Relative contribution of catalytic versus scaffolding tumor-suppressor functions unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Three contemporaneous studies resolved distinct regulatory layers: MYC directly binds the GNMT promoter to repress transcription; miR-873-5p post-transcriptionally represses GNMT to impair mitochondrial Complex II activity in NAFLD; and phosphorylation at Ser9 by PKC/JNK is required for genotoxic-stress-induced nuclear translocation.\",\n      \"evidence\": \"ChIP with anti-MYC on GNMT promoter, reporter assays, xenograft model; miR-873-5p target validation with Complex II activity assays in NAFLD models; LC-MS/MS phosphoproteomics with S9A mutagenesis and CYP1A1 readout\",\n      \"pmids\": [\"30760754\", \"31668391\", \"30987732\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which GNMT regulates Complex II activity not molecularly defined\", \"Whether nuclear GNMT has distinct substrates or functions beyond metabolic channeling unclear\", \"Direct kinase assays for PKC/JNK phosphorylation of Ser9 not shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of GNMT as a direct target of the dipeptide carnosine via CETSA demonstrated that small-molecule binding can modulate GNMT's SAM/SAH regulatory function to reduce renal inflammation and fibrosis in diabetic nephropathy.\",\n      \"evidence\": \"CETSA and molecular docking for direct binding; GNMT overexpression/knockdown in diabetic nephropathy mouse models\",\n      \"pmids\": [\"33241846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site of carnosine on GNMT not structurally characterized\", \"Whether carnosine modulates catalytic activity or protein stability not distinguished\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Work in Drosophila and macrophage models extended the regulatory framework: GNMT protein is degraded by nuclear UPS under SAM shortage to buffer SAM levels, and the AurA–FOXO3 axis controls GNMT expression to regulate SAM-dependent histone methylation and trained immunity.\",\n      \"evidence\": \"Drosophila nuclear UPS suppression with SAM measurement (preprint); AurA inhibitor treatment with ATAC-seq, ChIP for H3K4me3/H3K36me3, and metabolomics in macrophages (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.08.21.609067\", \"bio_10.1101_2024.11.11.622956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Both studies are preprints awaiting peer review\", \"E3 ligase responsible for nuclear GNMT degradation not identified\", \"Whether GNMT-dependent histone methylation changes are direct or secondary to SAM pool depletion not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstration that choline upregulates GNMT through an AMPK/MYC axis linked GNMT to hepatic lipid metabolism, bile acid metabolism, and lipoprotein assembly, broadening its physiological role beyond one-carbon metabolism.\",\n      \"evidence\": \"GNMT knockdown combined with AMPK inhibition; transcriptomic profiling of lipid and bile acid metabolism genes in hepatocytes\",\n      \"pmids\": [\"41233636\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct enzymatic or metabolic mechanism connecting GNMT to lipid/bile acid pathways not defined\", \"Single lab with limited molecular depth\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of GNMT's non-catalytic interactions (PREX2, folate, Complex II), the identity of the E3 ligase mediating nuclear GNMT degradation in mammals, and whether nuclear GNMT has distinct substrates or chromatin-regulatory roles beyond SAM pool modulation remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of GNMT bound to PREX2 or folate\", \"No mammalian validation of nuclear UPS-mediated GNMT degradation\", \"Whether GNMT directly methylates nuclear substrates beyond glycine is untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 3, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 7, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 3, 9, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 6, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PREX2\",\n      \"HUWE1\",\n      \"MYC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}