{"gene":"SLC37A4","run_date":"2026-06-10T07:46:33","timeline":{"discoveries":[{"year":2025,"finding":"Cryo-EM structures of human SLC37A4 in four functional states reveal conformational transitions between lumen-facing and cytoplasm-facing states. A conserved substrate-binding pocket alternately accommodates G6P and Pi through electrostatic complementarity and domain-dependent interactions, establishing the antiport mechanism. The inhibitor S-4048 sterically occludes the cytoplasmic entry pathway by trapping the transporter in a cytoplasm-facing conformation.","method":"Cryo-EM structure determination, mutational analysis, molecular dynamics simulations, functional transport assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures in four states combined with mutagenesis, MD simulations, and functional assays in a single rigorous study","pmids":["41225049"],"is_preprint":false},{"year":2023,"finding":"SLC37A4 encodes the endoplasmic reticulum glucose-6-phosphate transporter (G6PT) that transports G6P from the cytosol across the ER membrane, where it is hydrolyzed by glucose-6-phosphatase (G6PC1). In neutrophils, G6PT transports 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) into the ER for hydrolysis by G6PC3, preventing accumulation of this hexokinase inhibitor; loss of G6PT function causes neutrophil dysfunction via 1,5-AG6P accumulation.","method":"Biochemical analysis of G6PT deficiency in GSD1b patients, mechanistic dissection via metabolite measurement and SGLT2 inhibitor treatment rescue experiments","journal":"Diagnostics (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic dissection using patient samples and pharmacological rescue, replicated across patient cohorts but primarily from a single review/analysis paper","pmids":["37238286"],"is_preprint":false},{"year":2021,"finding":"A dominant heterozygous truncating mutation (p.Arg423*) in SLC37A4 abolishes the ER retention signal of the glucose-6-phosphate transporter, causing mislocalization of the mutant protein to a non-Golgi compartment (possibly ER exit sites) and altering Golgi morphology and reducing intraluminal Golgi pH, resulting in a congenital disorder of glycosylation with abnormal serum N-glycans.","method":"CRISPR base-edited hepatoma cell line harboring the mutation, immunofluorescence localization, N-glycan profiling of patient serum and cell lines, iPSC-derived models","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — isogenic cell model with CRISPR editing, orthogonal localization and glycan analyses, confirmed in independent patient cohort (second patient report PMID 33728255)","pmids":["33964207","33728255"],"is_preprint":false},{"year":2020,"finding":"A single dominant mutation in SLC37A4 abolishes the ER retention signal of the glucose-6-phosphate transporter and generates a weak Golgi retention signal, causing intracellular mislocalization to the Golgi and resulting in a congenital disorder of glycosylation rather than glycogen storage disease.","method":"Identification and functional characterization of the mutation, subcellular localization studies","journal":"Molecular genetics and metabolism reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — localization experiments with functional consequence demonstrated, single lab but supported by independent replication in PMID 33964207","pmids":["32884905"],"is_preprint":false},{"year":2019,"finding":"In a human kidney cell model with CRISPR/Cas9-introduced SLC37A4 deficiency, SLC37A4 loss triggers ER stress and the unfolded protein response (UPR), with suppression of ATF4, DDIT3, and HSPA5 under chronic stress, but ultimately induces apoptosis through decreased BCL2/BAX ratio, suggesting renal dysfunction in GSD1b is partly mediated by ER stress and increased apoptosis.","method":"CRISPR/Cas9-mediated gene editing of SLC37A4 in Flp-In T-REx-293 cells, RT-qPCR analysis of UPR and apoptosis markers","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with defined cellular phenotype and pathway markers, but single lab and single cell-line model","pmids":["30951856"],"is_preprint":false},{"year":2024,"finding":"SLC37A4 localizes to the endoplasmic reticulum in gingival epithelial cells. SLC37A4 knockout decreases expression of the transcription factor HMX3, which in turn reduces JAM1 (junctional adhesion molecule 1) expression at tight junctions, increasing epithelial permeability to LPS and peptidoglycan. HMX3 overexpression rescues JAM1 expression in SLC37A4-knockout cells.","method":"SLC37A4 knockout in immortalized human gingival epithelial cells, immunofluorescence localization, RT-qPCR, siRNA knockdown, HMX3 overexpression rescue, 3D multilayered epithelial tissue permeability assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined pathway (SLC37A4→HMX3→JAM1) and functional permeability readout, rescue experiment, single lab","pmids":["39433915"],"is_preprint":false},{"year":2025,"finding":"SRSF9, an RNA splicing factor capable of liquid-liquid phase separation via its RS domain, promotes skipping of SLC37A4 exon 7 in oral cancer cells, generating a truncated isoform SLC37A4-S. This truncated isoform enhances proliferation, metastatic potential, and cisplatin resistance. Disruption of SRSF9 phase separation (by inhibitors or RS-domain mutants) prevents the aberrant splicing of SLC37A4.","method":"Semi-quantitative RT-PCR, minigene reporter assay, FRAP, live-cell immunofluorescence, siRNA knockdown, CCK8, EdU, transwell invasion assays, in vivo subcutaneous tumor models","journal":"Journal of advanced research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods establishing SRSF9→SLC37A4 splicing regulation with functional readouts, single lab","pmids":["40064440"],"is_preprint":false},{"year":2020,"finding":"In leukocytes from a GSD-Ib patient harboring the novel p.P119L SLC37A4 mutation, loss of SLC37A4 function causes increased ER stress markers (sXBP-1, BIP, CHOP mRNA), elevated BAX mRNA, and increased caspase-3 activity, suggesting that SLC37A4 deficiency-induced ER stress and apoptosis contribute to leukocytopenia.","method":"Whole-exome sequencing, RT-qPCR of UPR and apoptosis markers in patient leukocytes, caspase-3 activity assay","journal":"Molecular genetics & genomic medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single patient sample, single lab, no functional rescue or isogenic control","pmids":["33280276"],"is_preprint":false}],"current_model":"SLC37A4 encodes an ER-resident multitransmembrane antiporter that transports glucose-6-phosphate (G6P) from the cytosol into the ER lumen in exchange for inorganic phosphate (Pi), using a conserved substrate-binding pocket that alternates between cytoplasm-facing and lumen-facing conformational states; in neutrophils it also transports 1,5-anhydroglucitol-6-phosphate into the ER for detoxification by G6PC3, and a dominant truncating mutation that removes its ER retention signal mislocalizes the transporter to the Golgi, disrupting N-glycosylation rather than glycogen storage."},"narrative":{"mechanistic_narrative":"SLC37A4 encodes the endoplasmic reticulum glucose-6-phosphate transporter (G6PT), an ER membrane antiporter that imports cytosolic glucose-6-phosphate (G6P) into the ER lumen in exchange for inorganic phosphate, delivering G6P for hydrolysis by glucose-6-phosphatase [PMID:41225049, PMID:37238286]. Cryo-EM structures captured in four functional states define an alternating-access mechanism in which a single conserved substrate-binding pocket switches between cytoplasm-facing and lumen-facing conformations and selects G6P versus Pi by electrostatic complementarity, with the inhibitor S-4048 trapping a cytoplasm-facing state by occluding the cytosolic entry pathway [PMID:41225049]. Beyond bulk glucose metabolism, in neutrophils G6PT transports 1,5-anhydroglucitol-6-phosphate into the ER for detoxification by G6PC3, and its loss causes neutrophil dysfunction through accumulation of this hexokinase inhibitor [PMID:37238286]. The transporter is ER-retained, and a dominant truncating mutation (p.Arg423*) that abolishes its ER retention signal mislocalizes the protein toward the Golgi, perturbing Golgi morphology, lowering intraluminal pH, and producing a congenital disorder of glycosylation with abnormal serum N-glycans rather than glycogen storage disease [PMID:33964207, PMID:33728255, PMID:32884905]. SLC37A4 deficiency also triggers ER stress, the unfolded protein response, and apoptosis in renal and leukocyte models [PMID:30951856].","teleology":[{"year":2019,"claim":"Established that loss of SLC37A4 has cell-autonomous consequences beyond metabolic substrate handling, linking its deficiency to ER stress and cell death.","evidence":"CRISPR/Cas9 SLC37A4 knockout in Flp-In T-REx-293 kidney cells with RT-qPCR of UPR and apoptosis markers","pmids":["30951856"],"confidence":"Medium","gaps":["Single cell line and single lab","Did not connect ER stress to transport activity directly","No in vivo renal phenotype"]},{"year":2020,"claim":"Resolved why some SLC37A4 mutations cause glycosylation disease rather than glycogen storage disease, by showing a dominant mutation redirects the transporter from the ER to the Golgi.","evidence":"Mutation identification and subcellular localization studies","pmids":["32884905"],"confidence":"Medium","gaps":["Mechanism connecting mislocalization to glycosylation defects not fully resolved","Single lab"]},{"year":2020,"claim":"Reinforced the ER-stress/apoptosis axis of SLC37A4 deficiency in patient-derived material, implicating it in the leukocytopenia of GSD-Ib.","evidence":"Whole-exome sequencing and RT-qPCR/caspase assays in leukocytes from a single GSD-Ib patient (p.P119L)","pmids":["33280276"],"confidence":"Low","gaps":["Single patient sample with no isogenic control or rescue","Correlative marker data only","Cannot separate transporter loss from secondary effects"]},{"year":2021,"claim":"Defined the molecular basis of the SLC37A4-CDG by showing the p.Arg423* truncation removes the ER retention signal, mislocalizing the transporter and disrupting Golgi function and N-glycosylation.","evidence":"CRISPR base-edited isogenic hepatoma cells, immunofluorescence, serum/cell N-glycan profiling, iPSC-derived models, confirmed in an independent patient","pmids":["33964207","33728255"],"confidence":"High","gaps":["Exact non-Golgi compartment of mislocalization not definitively identified","Causal chain from mislocalization to Golgi pH change incomplete"]},{"year":2023,"claim":"Extended SLC37A4 substrate scope beyond G6P, showing it imports 1,5-anhydroglucitol-6-phosphate for detoxification in neutrophils, explaining neutrophil dysfunction in GSD1b.","evidence":"Biochemical analysis of GSD1b patient samples, metabolite measurement, and SGLT2-inhibitor rescue","pmids":["37238286"],"confidence":"Medium","gaps":["Primarily a review/analysis paper","Direct transport assay of 1,5-AG6P not shown in this entry","Tissue-specific substrate preferences unclear"]},{"year":2024,"claim":"Identified a non-metabolic, epithelial-barrier role wherein SLC37A4 supports tight-junction integrity through an HMX3-JAM1 axis.","evidence":"SLC37A4 knockout in human gingival epithelial cells, RT-qPCR, siRNA, HMX3 overexpression rescue, 3D epithelial permeability assay","pmids":["39433915"],"confidence":"Medium","gaps":["Link between transporter activity and HMX3 transcription unexplained","Single lab and cell system","Physiological relevance in vivo untested"]},{"year":2025,"claim":"Determined the atomic transport mechanism, capturing four conformational states that establish G6P/Pi antiport via a single alternating-access binding pocket and revealing the inhibitor S-4048's mode of action.","evidence":"Cryo-EM in four states with mutagenesis, MD simulations, and functional transport assays","pmids":["41225049"],"confidence":"High","gaps":["Structural basis for 1,5-AG6P transport not addressed","Regulation of conformational cycling in vivo unknown"]},{"year":2025,"claim":"Showed SLC37A4 is itself a regulated splicing target, with SRSF9-driven exon 7 skipping generating an oncogenic truncated isoform in oral cancer.","evidence":"RT-PCR, minigene reporter, FRAP, siRNA, proliferation/invasion assays, and in vivo tumor models","pmids":["40064440"],"confidence":"Medium","gaps":["Functional/transport properties of SLC37A4-S not characterized","Mechanism linking the isoform to proliferation unresolved","Single lab"]},{"year":null,"claim":"How SLC37A4's transport function mechanistically connects to its diverse downstream phenotypes — ER stress, glycosylation, epithelial barrier, and cancer isoform behavior — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified link between transport activity and ER-stress signaling","Transport properties of disease-associated isoforms uncharacterized","Tissue-specific substrate range incompletely defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2,4,5]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2,3]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[4]}],"complexes":[],"partners":["G6PC1","G6PC3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O43826","full_name":"Glucose-6-phosphate exchanger SLC37A4","aliases":["Glucose-5-phosphate transporter","Glucose-6-phosphate translocase","Solute carrier family 37 member 4","Transformation-related gene 19 protein","TRG-19"],"length_aa":429,"mass_kda":46.4,"function":"Inorganic phosphate and glucose-6-phosphate antiporter of the endoplasmic reticulum. Transports cytoplasmic glucose-6-phosphate into the lumen of the endoplasmic reticulum and translocates inorganic phosphate into the opposite direction (PubMed:33964207). Forms with glucose-6-phosphatase the complex responsible for glucose production through glycogenolysis and gluconeogenesis. Hence, it plays a central role in homeostatic regulation of blood glucose levels","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/O43826/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC37A4"},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000137700","cell_line_id":"CID001347","localizations":[{"compartment":"golgi","grade":3}],"interactors":[{"gene":"ZNRF2","stoichiometry":10.0},{"gene":"ARL3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001347","total_profiled":1310},"omim":[{"mim_id":"621384","title":"DEVELOPMENTAL DELAY WITH VARIABLE CARDIAC AND RENAL CONGENITAL ANOMALIES AND DYSMORPHIC FACIES; DEDCRF","url":"https://www.omim.org/entry/621384"},{"mim_id":"619525","title":"CONGENITAL DISORDER OF GLYCOSYLATION, TYPE IIw; CDG2W","url":"https://www.omim.org/entry/619525"},{"mim_id":"612541","title":"NEUTROPENIA, SEVERE CONGENITAL, 4, AUTOSOMAL RECESSIVE; SCN4","url":"https://www.omim.org/entry/612541"},{"mim_id":"611034","title":"SOLUTE CARRIER FAMILY 17 (ORGANIC ANION TRANSPORTER), MEMBER 3; SLC17A3","url":"https://www.omim.org/entry/611034"},{"mim_id":"608094","title":"SOLUTE CARRIER FAMILY 37 (SUGAR-PHOSPHATE TRANSPORTER), MEMBER 1; SLC37A1","url":"https://www.omim.org/entry/608094"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"kidney","ntpm":47.5},{"tissue":"liver","ntpm":134.4}],"url":"https://www.proteinatlas.org/search/SLC37A4"},"hgnc":{"alias_symbol":["GSD1b","GSD1c","GSD1d","G6PT","SPX4"],"prev_symbol":["G6PT1","G6PT2","G6PT3"]},"alphafold":{"accession":"O43826","domains":[{"cath_id":"1.20.1250.20","chopping":"9-195","consensus_level":"high","plddt":85.9215,"start":9,"end":195},{"cath_id":"1.20.1250.20","chopping":"218-415","consensus_level":"high","plddt":85.6418,"start":218,"end":415}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43826","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43826-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43826-F1-predicted_aligned_error_v6.png","plddt_mean":85.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC37A4","jax_strain_url":"https://www.jax.org/strain/search?query=SLC37A4"},"sequence":{"accession":"O43826","fasta_url":"https://rest.uniprot.org/uniprotkb/O43826.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43826/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43826"}},"corpus_meta":[{"pmid":"30911122","id":"PMC_30911122","title":"Nitrate-NRT1.1B-SPX4 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metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/19321372","citation_count":0,"is_preprint":false},{"pmid":"41771245","id":"PMC_41771245","title":"Decoding genetic complexity in glycogen storage diseases: three novel variants in SLC37A4, GAA, and PHKG2 identified in an Iranian cohort.","date":"2026","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/41771245","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15579,"output_tokens":2315,"usd":0.040731,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9400,"output_tokens":2897,"usd":0.059713,"stage2_stop_reason":"end_turn"},"total_usd":0.100444,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structures of human SLC37A4 in four functional states reveal conformational transitions between lumen-facing and cytoplasm-facing states. A conserved substrate-binding pocket alternately accommodates G6P and Pi through electrostatic complementarity and domain-dependent interactions, establishing the antiport mechanism. The inhibitor S-4048 sterically occludes the cytoplasmic entry pathway by trapping the transporter in a cytoplasm-facing conformation.\",\n      \"method\": \"Cryo-EM structure determination, mutational analysis, molecular dynamics simulations, functional transport assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures in four states combined with mutagenesis, MD simulations, and functional assays in a single rigorous study\",\n      \"pmids\": [\"41225049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SLC37A4 encodes the endoplasmic reticulum glucose-6-phosphate transporter (G6PT) that transports G6P from the cytosol across the ER membrane, where it is hydrolyzed by glucose-6-phosphatase (G6PC1). In neutrophils, G6PT transports 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) into the ER for hydrolysis by G6PC3, preventing accumulation of this hexokinase inhibitor; loss of G6PT function causes neutrophil dysfunction via 1,5-AG6P accumulation.\",\n      \"method\": \"Biochemical analysis of G6PT deficiency in GSD1b patients, mechanistic dissection via metabolite measurement and SGLT2 inhibitor treatment rescue experiments\",\n      \"journal\": \"Diagnostics (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic dissection using patient samples and pharmacological rescue, replicated across patient cohorts but primarily from a single review/analysis paper\",\n      \"pmids\": [\"37238286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A dominant heterozygous truncating mutation (p.Arg423*) in SLC37A4 abolishes the ER retention signal of the glucose-6-phosphate transporter, causing mislocalization of the mutant protein to a non-Golgi compartment (possibly ER exit sites) and altering Golgi morphology and reducing intraluminal Golgi pH, resulting in a congenital disorder of glycosylation with abnormal serum N-glycans.\",\n      \"method\": \"CRISPR base-edited hepatoma cell line harboring the mutation, immunofluorescence localization, N-glycan profiling of patient serum and cell lines, iPSC-derived models\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — isogenic cell model with CRISPR editing, orthogonal localization and glycan analyses, confirmed in independent patient cohort (second patient report PMID 33728255)\",\n      \"pmids\": [\"33964207\", \"33728255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A single dominant mutation in SLC37A4 abolishes the ER retention signal of the glucose-6-phosphate transporter and generates a weak Golgi retention signal, causing intracellular mislocalization to the Golgi and resulting in a congenital disorder of glycosylation rather than glycogen storage disease.\",\n      \"method\": \"Identification and functional characterization of the mutation, subcellular localization studies\",\n      \"journal\": \"Molecular genetics and metabolism reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — localization experiments with functional consequence demonstrated, single lab but supported by independent replication in PMID 33964207\",\n      \"pmids\": [\"32884905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In a human kidney cell model with CRISPR/Cas9-introduced SLC37A4 deficiency, SLC37A4 loss triggers ER stress and the unfolded protein response (UPR), with suppression of ATF4, DDIT3, and HSPA5 under chronic stress, but ultimately induces apoptosis through decreased BCL2/BAX ratio, suggesting renal dysfunction in GSD1b is partly mediated by ER stress and increased apoptosis.\",\n      \"method\": \"CRISPR/Cas9-mediated gene editing of SLC37A4 in Flp-In T-REx-293 cells, RT-qPCR analysis of UPR and apoptosis markers\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with defined cellular phenotype and pathway markers, but single lab and single cell-line model\",\n      \"pmids\": [\"30951856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SLC37A4 localizes to the endoplasmic reticulum in gingival epithelial cells. SLC37A4 knockout decreases expression of the transcription factor HMX3, which in turn reduces JAM1 (junctional adhesion molecule 1) expression at tight junctions, increasing epithelial permeability to LPS and peptidoglycan. HMX3 overexpression rescues JAM1 expression in SLC37A4-knockout cells.\",\n      \"method\": \"SLC37A4 knockout in immortalized human gingival epithelial cells, immunofluorescence localization, RT-qPCR, siRNA knockdown, HMX3 overexpression rescue, 3D multilayered epithelial tissue permeability assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined pathway (SLC37A4→HMX3→JAM1) and functional permeability readout, rescue experiment, single lab\",\n      \"pmids\": [\"39433915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SRSF9, an RNA splicing factor capable of liquid-liquid phase separation via its RS domain, promotes skipping of SLC37A4 exon 7 in oral cancer cells, generating a truncated isoform SLC37A4-S. This truncated isoform enhances proliferation, metastatic potential, and cisplatin resistance. Disruption of SRSF9 phase separation (by inhibitors or RS-domain mutants) prevents the aberrant splicing of SLC37A4.\",\n      \"method\": \"Semi-quantitative RT-PCR, minigene reporter assay, FRAP, live-cell immunofluorescence, siRNA knockdown, CCK8, EdU, transwell invasion assays, in vivo subcutaneous tumor models\",\n      \"journal\": \"Journal of advanced research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods establishing SRSF9→SLC37A4 splicing regulation with functional readouts, single lab\",\n      \"pmids\": [\"40064440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In leukocytes from a GSD-Ib patient harboring the novel p.P119L SLC37A4 mutation, loss of SLC37A4 function causes increased ER stress markers (sXBP-1, BIP, CHOP mRNA), elevated BAX mRNA, and increased caspase-3 activity, suggesting that SLC37A4 deficiency-induced ER stress and apoptosis contribute to leukocytopenia.\",\n      \"method\": \"Whole-exome sequencing, RT-qPCR of UPR and apoptosis markers in patient leukocytes, caspase-3 activity assay\",\n      \"journal\": \"Molecular genetics & genomic medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single patient sample, single lab, no functional rescue or isogenic control\",\n      \"pmids\": [\"33280276\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC37A4 encodes an ER-resident multitransmembrane antiporter that transports glucose-6-phosphate (G6P) from the cytosol into the ER lumen in exchange for inorganic phosphate (Pi), using a conserved substrate-binding pocket that alternates between cytoplasm-facing and lumen-facing conformational states; in neutrophils it also transports 1,5-anhydroglucitol-6-phosphate into the ER for detoxification by G6PC3, and a dominant truncating mutation that removes its ER retention signal mislocalizes the transporter to the Golgi, disrupting N-glycosylation rather than glycogen storage.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC37A4 encodes the endoplasmic reticulum glucose-6-phosphate transporter (G6PT), an ER membrane antiporter that imports cytosolic glucose-6-phosphate (G6P) into the ER lumen in exchange for inorganic phosphate, delivering G6P for hydrolysis by glucose-6-phosphatase [#0, #1]. Cryo-EM structures captured in four functional states define an alternating-access mechanism in which a single conserved substrate-binding pocket switches between cytoplasm-facing and lumen-facing conformations and selects G6P versus Pi by electrostatic complementarity, with the inhibitor S-4048 trapping a cytoplasm-facing state by occluding the cytosolic entry pathway [#0]. Beyond bulk glucose metabolism, in neutrophils G6PT transports 1,5-anhydroglucitol-6-phosphate into the ER for detoxification by G6PC3, and its loss causes neutrophil dysfunction through accumulation of this hexokinase inhibitor [#1]. The transporter is ER-retained, and a dominant truncating mutation (p.Arg423*) that abolishes its ER retention signal mislocalizes the protein toward the Golgi, perturbing Golgi morphology, lowering intraluminal pH, and producing a congenital disorder of glycosylation with abnormal serum N-glycans rather than glycogen storage disease [#2, #3]. SLC37A4 deficiency also triggers ER stress, the unfolded protein response, and apoptosis in renal and leukocyte models [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2019,\n      \"claim\": \"Established that loss of SLC37A4 has cell-autonomous consequences beyond metabolic substrate handling, linking its deficiency to ER stress and cell death.\",\n      \"evidence\": \"CRISPR/Cas9 SLC37A4 knockout in Flp-In T-REx-293 kidney cells with RT-qPCR of UPR and apoptosis markers\",\n      \"pmids\": [\"30951856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line and single lab\", \"Did not connect ER stress to transport activity directly\", \"No in vivo renal phenotype\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved why some SLC37A4 mutations cause glycosylation disease rather than glycogen storage disease, by showing a dominant mutation redirects the transporter from the ER to the Golgi.\",\n      \"evidence\": \"Mutation identification and subcellular localization studies\",\n      \"pmids\": [\"32884905\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting mislocalization to glycosylation defects not fully resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Reinforced the ER-stress/apoptosis axis of SLC37A4 deficiency in patient-derived material, implicating it in the leukocytopenia of GSD-Ib.\",\n      \"evidence\": \"Whole-exome sequencing and RT-qPCR/caspase assays in leukocytes from a single GSD-Ib patient (p.P119L)\",\n      \"pmids\": [\"33280276\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single patient sample with no isogenic control or rescue\", \"Correlative marker data only\", \"Cannot separate transporter loss from secondary effects\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the molecular basis of the SLC37A4-CDG by showing the p.Arg423* truncation removes the ER retention signal, mislocalizing the transporter and disrupting Golgi function and N-glycosylation.\",\n      \"evidence\": \"CRISPR base-edited isogenic hepatoma cells, immunofluorescence, serum/cell N-glycan profiling, iPSC-derived models, confirmed in an independent patient\",\n      \"pmids\": [\"33964207\", \"33728255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact non-Golgi compartment of mislocalization not definitively identified\", \"Causal chain from mislocalization to Golgi pH change incomplete\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended SLC37A4 substrate scope beyond G6P, showing it imports 1,5-anhydroglucitol-6-phosphate for detoxification in neutrophils, explaining neutrophil dysfunction in GSD1b.\",\n      \"evidence\": \"Biochemical analysis of GSD1b patient samples, metabolite measurement, and SGLT2-inhibitor rescue\",\n      \"pmids\": [\"37238286\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Primarily a review/analysis paper\", \"Direct transport assay of 1,5-AG6P not shown in this entry\", \"Tissue-specific substrate preferences unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a non-metabolic, epithelial-barrier role wherein SLC37A4 supports tight-junction integrity through an HMX3-JAM1 axis.\",\n      \"evidence\": \"SLC37A4 knockout in human gingival epithelial cells, RT-qPCR, siRNA, HMX3 overexpression rescue, 3D epithelial permeability assay\",\n      \"pmids\": [\"39433915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between transporter activity and HMX3 transcription unexplained\", \"Single lab and cell system\", \"Physiological relevance in vivo untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Determined the atomic transport mechanism, capturing four conformational states that establish G6P/Pi antiport via a single alternating-access binding pocket and revealing the inhibitor S-4048's mode of action.\",\n      \"evidence\": \"Cryo-EM in four states with mutagenesis, MD simulations, and functional transport assays\",\n      \"pmids\": [\"41225049\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for 1,5-AG6P transport not addressed\", \"Regulation of conformational cycling in vivo unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed SLC37A4 is itself a regulated splicing target, with SRSF9-driven exon 7 skipping generating an oncogenic truncated isoform in oral cancer.\",\n      \"evidence\": \"RT-PCR, minigene reporter, FRAP, siRNA, proliferation/invasion assays, and in vivo tumor models\",\n      \"pmids\": [\"40064440\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional/transport properties of SLC37A4-S not characterized\", \"Mechanism linking the isoform to proliferation unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SLC37A4's transport function mechanistically connects to its diverse downstream phenotypes — ER stress, glycosylation, epithelial barrier, and cancer isoform behavior — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified link between transport activity and ER-stress signaling\", \"Transport properties of disease-associated isoforms uncharacterized\", \"Tissue-specific substrate range incompletely defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2, 4, 5]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"G6PC1\", \"G6PC3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}