{"gene":"SLC19A1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2019,"finding":"SLC19A1 (reduced folate carrier) is the major transporter of cyclic dinucleotides (CDNs), including 2'3'-cGAMP, into cells. Identified by genome-wide CRISPR-interference screen; depletion inhibits CDN uptake and STING-pathway functional responses, while overexpression increases both uptake and responses. CDN uptake is inhibited by folates, sulfasalazine, and methotrexate, consistent with competition at the same transporter.","method":"Genome-wide CRISPR-interference screen, CDN uptake assays, STING-pathway functional readouts, overexpression and depletion experiments in human cell lines and primary cells","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — independently identified by two concurrent studies (PMID:31511694 and PMID:31126740) using genome-wide CRISPR screens plus orthogonal functional uptake assays","pmids":["31511694"],"is_preprint":false},{"year":2019,"finding":"SLC19A1 is the first known importer of cGAMP and other CDNs (including the investigational drug 2'3'-CDAS), confirmed by genome-wide CRISPR screen in a second independent study.","method":"Genome-wide CRISPR screen, CDN import assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — independently replicated in two concurrent papers using genome-wide CRISPR screens","pmids":["31126740"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of human SLC19A1 in apo state and in complex with methotrexate reveal the molecular basis of substrate recognition: RFC functions as an anion exchanger coupling folate/antifolate import to anion export; key residues determining transport selectivity among folates and antifolates were identified. Combined with molecular dynamics simulations and functional experiments.","method":"Cryo-electron microscopy structure determination, molecular dynamics simulations, functional transport assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with functional validation and MD simulations in a single rigorous study","pmids":["36071163"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of human SLC19A1 in substrate-free state and complexed with multiple CDNs, a natural folate (5-methyltetrahydrofolate), and a new-generation antifolate reveal that two CDN molecules bind as a compact dual-molecule unit within the transporter cavity, whereas folate and antifolate bind as monomers in a distinct pocket. Mutagenesis studies confirmed divergent recognition mechanisms for CDN-type versus folate-type substrates.","method":"Cryo-electron microscopy, mutagenesis, binding/functional assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures with mutagenesis validation, multiple substrate classes examined in one rigorous study","pmids":["36265513"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structure of SLC19A1 with 5-methyltetrahydrofolate identifies critical residues for folate substrate recognition; two variant residues among SLC19 subfamily members designate specificity for folate. Intracellular thiamine pyrophosphate was identified as the preferred coupled (counter-transport) substrate for folate import by SLC19A1.","method":"Cryo-EM structure determination, mutagenesis, transport coupling assays","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure plus mutagenesis and functional coupling assay, single laboratory","pmids":["36575193"],"is_preprint":false},{"year":1998,"finding":"A single amino acid difference (Ser297 vs. Asn297, between the 7th and 8th membrane-spanning helices) in the murine RFC-1 (SLC19A1) protein selectively alters the apparent Km for methotrexate influx without affecting Vmax or efflux, establishing this residue as a determinant of antifolate binding on the extracellular face of the transporter.","method":"cDNA sequencing, site-specific transfection of RFC-1 constructs into transport-deficient cells, influx Km measurements with radiolabeled substrates, Western blotting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution by transfection with single-nucleotide variant constructs plus functional transport assays; causal variant proven by replication in transfected cells","pmids":["9446553"],"is_preprint":false},{"year":2001,"finding":"Expression of the reduced folate carrier SLC19A1 (RFC1) in intestinal IEC-6 cells produces two distinct transport activities: one at low pH (pH 5.5) inhibited by folic acid, and one at neutral pH (pH 7.4), demonstrating that tissue-specific modulators determine the pH profile of RFC1-mediated transport.","method":"Stable transfection of RFC1 construct into IEC-6 and L1210 cells, radiolabeled substrate influx assays at varying pH, inhibition studies with folic acid and metabolic inhibitors","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct transfection experiment with functional readouts, two cell lines tested, single laboratory","pmids":["11600421"],"is_preprint":false},{"year":2008,"finding":"RFC (SLC19A1) acts as a bidirectional anion transporter that becomes cytotoxic under severe folate deprivation by efficiently exporting intracellular folate monoglutamates out of cells. Ectopic overexpression of RFC (but not unidirectional folate receptor alpha) caused ~15-fold decline in cell viability in folate-free medium. Down-regulation of RFC mRNA and transport activity occurs as an adaptive response to folate deprivation.","method":"Ectopic overexpression of RFC vs. folate receptor alpha in folate-free vs. folate-containing medium, cell viability assays, RT-PCR for RFC mRNA, methotrexate influx as transport activity assay, mathematical biomodeling","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — overexpression with functional readout, negative control (FRα), single laboratory with multiple orthogonal approaches","pmids":["18499665"],"is_preprint":false},{"year":2017,"finding":"Activation of vitamin D receptor (VDR) by calcitriol up-regulates RFC (SLC19A1) mRNA, protein expression, and [3H]-methotrexate transport activity at the blood-brain barrier in human cerebral microvascular endothelial cells (hCMEC/D3) and isolated mouse brain capillaries. VDR-targeting siRNA down-regulates RFC expression, confirming VDR as a direct regulator of SLC19A1.","method":"Calcitriol treatment of hCMEC/D3 cells and mouse brain capillaries, [3H]-MTX uptake assay, RT-PCR and Western blot, VDR siRNA knockdown","journal":"Molecular pharmaceutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological activation plus siRNA knockdown, functional transport readout, two model systems, single laboratory","pmids":["28885847"],"is_preprint":false},{"year":2020,"finding":"Nuclear respiratory factor 1 (NRF-1)/PGC-1α signaling regulates RFC (SLC19A1) expression and function at the blood-brain barrier. PQQ (NRF-1 ligand) increases NRF-1 binding to SLC19A1 promoter (shown by ChIP assay) and induces RFC expression and [3H]-MTX transport activity; NRF-1 or PGC-1α siRNA knockdown reduces RFC functional expression.","method":"ChIP assay for NRF-1 binding to SLC19A1 promoter, siRNA knockdown of NRF-1/PGC-1α, [3H]-MTX uptake assay, RT-PCR and Western blot, in vivo PQQ treatment in mice","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP showing direct promoter binding plus siRNA knockdown with functional transport readout, in vitro and in vivo models, single laboratory","pmids":["32543769"],"is_preprint":false},{"year":2016,"finding":"mTORC1 and mTORC2 are positive regulators of folate uptake in human trophoblasts, acting by controlling the plasma membrane abundance (surface expression) of RFC (SLC19A1) and FR-α without affecting global protein expression. Silencing raptor (mTORC1) or rictor (mTORC2) markedly decreased folate uptake and surface transporter levels.","method":"siRNA silencing of raptor/rictor in primary human trophoblasts, folate uptake assays, plasma membrane fractionation and immunoblotting","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific siRNA knockdown with functional folate uptake readout and surface expression measurement, single laboratory","pmids":["27562465"],"is_preprint":false},{"year":2018,"finding":"SLC19A1 knockdown in human adipocytes perturbs intracellular one-carbon cycle (1CC) metabolism, induces global DNA hypermethylation, and increases expression of proinflammatory genes including CCL2. Methylation at the CCL2 promoter CpG locus (cg12698626) directly regulates CCL2 transcription and secretion, linking SLC19A1 to an epigenetic inflammatory mechanism.","method":"siRNA knockdown of SLC19A1 in differentiated human adipocytes, microarray, qPCR, DNA methylation by ELISA and pyrosequencing, luciferase reporter assay, targeted metabolomics, cytokine ELISA","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple orthogonal readouts (methylation, gene expression, metabolomics, reporter assay), single laboratory","pmids":["29121255"],"is_preprint":false},{"year":1998,"finding":"The human RFC-1 (SLC19A1) gene has multiple promoters (at least two, Promoter 1 upstream of exon 1a and Promoter 2 upstream of exon 1b) that direct expression of alternatively spliced transcripts with 5' end heterogeneity. Promoter 2 (exon 1b) has ~3-fold higher basal activity than Promoter 1 in functional transient transfection assays.","method":"Genomic DNA sequencing, primer extension analysis, functional deletion analysis with luciferase reporter gene in transient transfection experiments","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional promoter deletion analysis with reporter assays, supported by primer extension, single laboratory","pmids":["9602167"],"is_preprint":false},{"year":2010,"finding":"The C. elegans ortholog folt-1 (encoding FOLT-1, the RFC/SLC19A1 ortholog) is required for germline proliferation and somatic function; knockout causes severely diminished germline, reduced spermatogenesis, sterility in hermaphrodites, shortened lifespan, and elongated defecation intervals. No increased germline apoptosis was detected, suggesting defective proliferation rather than increased cell death.","method":"Genetic knockout analysis (folt-1(ok1460)), germline microscopy, lifespan assays, mating assays, apoptosis staining in C. elegans","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean knockout with multiple phenotypic readouts in defined model organism ortholog, single laboratory","pmids":["20441590"],"is_preprint":false},{"year":2003,"finding":"RFC/SLC19A1 (reduced folate carrier) is expressed in placenta, yolk sac, and multiple developing embryonic tissues including neural tube, craniofacial region, limb buds, heart, and early eye; by E12.5 RFC protein becomes restricted to the retinal pigment epithelium. This developmental expression pattern was determined by in situ hybridization and immunolocalization.","method":"In situ hybridization, immunolocalization in mouse embryos at multiple developmental stages (E9.0–E12.5)","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization by in situ hybridization and immunohistochemistry in multiple developmental stages, single laboratory","pmids":["12887734"],"is_preprint":false},{"year":2011,"finding":"Chronic ethanol ingestion reduces folate transport across the colonic apical membrane by decreasing both affinity (higher Km) and number of transporter molecules (lower Vmax) for RFC. RFC protein is distributed in lipid rafts of the colonic apical membrane, and chronic alcoholism decreases RFC protein levels specifically in lipid raft fractions.","method":"Isolated colon apical membrane vesicle transport assays, Western blotting, Optiprep density gradient floatation to isolate lipid rafts, in vivo rat chronic ethanol feeding model","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model with membrane fractionation, functional transport assays, and protein quantification; single laboratory","pmids":["21069807"],"is_preprint":false},{"year":2018,"finding":"miR-595 suppresses SLC19A1 expression post-transcriptionally by directly binding to the 3'-UTR of SLC19A1 (validated by luciferase reporter assay), reducing RFC1 protein levels, intracellular methotrexate concentrations, and MTX-induced cytotoxicity and apoptosis in CEM/C1 leukemia cells.","method":"Luciferase reporter assay with SLC19A1 3'-UTR, miR-595 mimic and inhibitor transfection, Western blotting, intracellular MTX quantification by ELISA, cell viability and apoptosis assays","journal":"Basic & clinical pharmacology & toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct reporter assay for miRNA-3'UTR binding plus functional gain/loss-of-function with multiple readouts, single laboratory","pmids":["29345051"],"is_preprint":false}],"current_model":"SLC19A1 (hRFC/RFC1) is a bidirectional anion exchanger/antiporter embedded in the plasma membrane that functions as the major cellular importer of reduced folates (with thiamine pyrophosphate as a preferred counter-transport substrate), antifolate drugs (e.g., methotrexate, pemetrexed), and cyclic dinucleotides (including cGAMP and bacterial CDNs); cryo-EM structures have defined distinct binding pockets for folate-type monomers versus dual-molecule CDN units within the transporter cavity, and specific residues (including those between transmembrane helices 7–8) determine substrate selectivity; its surface expression is regulated post-translationally by mTORC1/C2 and transcriptionally by VDR and NRF-1/PGC-1α; under severe folate deprivation RFC acts paradoxically as a folate exporter causing cytotoxicity; and in adipocytes SLC19A1 controls one-carbon metabolism to modulate DNA methylation and inflammatory gene expression."},"narrative":{"mechanistic_narrative":"SLC19A1 (reduced folate carrier, RFC1) is a plasma-membrane anion exchanger that serves as the major cellular importer of reduced folates and antifolate drugs, coupling substrate import to anion export with intracellular thiamine pyrophosphate as the preferred counter-transport substrate [PMID:36071163, PMID:36575193]. Cryo-EM structures of the apo, folate-bound, antifolate-bound, and cyclic-dinucleotide-bound states show that folates and antifolates bind as monomers in one pocket while CDNs bind as a compact dual-molecule unit in a distinct cavity, explaining the divergent recognition of these substrate classes [PMID:36071163, PMID:36265513, PMID:36575193]; selectivity is set by specific residues, including a single position between transmembrane helices 7 and 8 that tunes the affinity for methotrexate influx [PMID:9446553]. Beyond its folate role, SLC19A1 is the principal importer of cyclic dinucleotides such as 2'3'-cGAMP, and its activity governs STING-pathway responses to extracellular CDNs, with uptake competitively blocked by folates and antifolates [PMID:31511694, PMID:31126740]. The transporter is bidirectional: under severe folate deprivation it paradoxically exports intracellular folate monoglutamates, becoming cytotoxic, and its expression is down-regulated as an adaptive response [PMID:18499665]. Surface abundance and function are controlled post-translationally by mTORC1/mTORC2 [PMID:27562465] and transcriptionally by the vitamin D receptor [PMID:28885847] and NRF-1/PGC-1α [PMID:32543769], with additional post-transcriptional repression by miR-595 [PMID:29345051]. Through control of one-carbon metabolism, SLC19A1 also influences DNA methylation and proinflammatory gene expression in adipocytes [PMID:29121255], and is required for germline proliferation and viability in the C. elegans ortholog folt-1 [PMID:20441590].","teleology":[{"year":1998,"claim":"Established the first structure-function determinant of antifolate handling by pinpointing a single residue that governs substrate binding on the extracellular face of the carrier.","evidence":"Site-specific transfection of murine RFC-1 variant constructs (Ser297 vs Asn297) into transport-deficient cells with influx Km measurements","pmids":["9446553"],"confidence":"High","gaps":["Did not provide an atomic structure of the binding pocket","Limited to methotrexate among diverse antifolates"]},{"year":1998,"claim":"Defined the transcriptional architecture of the gene, showing multiple promoters drive alternatively spliced transcripts with differing basal activity.","evidence":"Genomic sequencing, primer extension, and luciferase reporter deletion analysis in transient transfections","pmids":["9602167"],"confidence":"Medium","gaps":["Did not identify the trans-acting factors binding each promoter","Tissue-specific promoter usage not resolved"]},{"year":2001,"claim":"Showed RFC-mediated transport adopts distinct pH-dependent activities, indicating tissue-specific modulation of the carrier.","evidence":"Stable RFC1 transfection into IEC-6 and L1210 cells with radiolabeled influx assays at varying pH","pmids":["11600421"],"confidence":"Medium","gaps":["Molecular basis of the low-pH activity unresolved","Whether a distinct transporter contributes was not excluded"]},{"year":2003,"claim":"Mapped the developmental expression of RFC, linking the carrier to folate supply during embryogenesis and to a restricted retinal pigment epithelium localization.","evidence":"In situ hybridization and immunolocalization across mouse embryonic stages E9.0–E12.5","pmids":["12887734"],"confidence":"Medium","gaps":["Expression pattern alone does not establish functional requirement in each tissue","No loss-of-function phenotype in this study"]},{"year":2008,"claim":"Revealed RFC as a bidirectional transporter that can export folates and become cytotoxic under deprivation, redefining it beyond a unidirectional importer.","evidence":"Ectopic RFC vs FR-alpha overexpression in folate-free medium with viability assays, RT-PCR, MTX influx, and biomodeling","pmids":["18499665"],"confidence":"Medium","gaps":["Physiological contexts where export dominates not defined","Counter-anion driving export not identified here"]},{"year":2010,"claim":"Demonstrated an in vivo organismal requirement for the carrier in germline proliferation and viability using a genetic ortholog knockout.","evidence":"folt-1(ok1460) knockout in C. elegans with germline microscopy, lifespan, mating, and apoptosis assays","pmids":["20441590"],"confidence":"Medium","gaps":["Ortholog phenotype may not fully map to mammalian SLC19A1","Mechanism linking folate transport to proliferation defect not dissected"]},{"year":2011,"claim":"Connected RFC function to membrane microdomain localization, showing lipid-raft residence and its disruption by chronic ethanol.","evidence":"Colonic apical membrane vesicle transport assays, lipid-raft floatation, and immunoblotting in a rat ethanol-feeding model","pmids":["21069807"],"confidence":"Medium","gaps":["Direct requirement of raft localization for transport not tested","Mechanism of ethanol-induced raft depletion unknown"]},{"year":2016,"claim":"Identified mTORC1/mTORC2 as upstream regulators that control RFC surface abundance and thus folate uptake.","evidence":"siRNA silencing of raptor/rictor in primary human trophoblasts with folate uptake assays and plasma-membrane fractionation","pmids":["27562465"],"confidence":"Medium","gaps":["Direct molecular link between mTOR and trafficking not defined","Generality beyond trophoblasts untested"]},{"year":2017,"claim":"Established VDR as a direct transcriptional activator of SLC19A1 at the blood-brain barrier.","evidence":"Calcitriol treatment and VDR siRNA in hCMEC/D3 cells and mouse brain capillaries with MTX uptake, RT-PCR, and Western blot","pmids":["28885847"],"confidence":"Medium","gaps":["VDR response element not mapped on the promoter","Single laboratory"]},{"year":2018,"claim":"Linked SLC19A1 to epigenetic and inflammatory control by showing its loss perturbs one-carbon metabolism, drives DNA hypermethylation, and induces proinflammatory genes.","evidence":"siRNA knockdown in human adipocytes with metabolomics, DNA methylation pyrosequencing, microarray, reporter assays, and cytokine ELISA","pmids":["29121255"],"confidence":"Medium","gaps":["Causal chain from methylation to inflammation in vivo not established","Generality beyond adipocytes untested"]},{"year":2018,"claim":"Identified miR-595 as a post-transcriptional repressor of SLC19A1 that modulates methotrexate accumulation and sensitivity.","evidence":"Luciferase 3'-UTR reporter, miR-595 mimic/inhibitor, MTX quantification, and viability assays in CEM/C1 leukemia cells","pmids":["29345051"],"confidence":"Medium","gaps":["Clinical relevance to MTX resistance not validated","Single cell-line context"]},{"year":2019,"claim":"Discovered an entirely new transport function: SLC19A1 is the major importer of cyclic dinucleotides, coupling the carrier to STING-dependent innate immune signaling.","evidence":"Two concurrent genome-wide CRISPR screens with CDN uptake assays, STING functional readouts, and competition by folates/antifolates in human cells","pmids":["31511694","31126740"],"confidence":"High","gaps":["Whether additional transporters contribute to CDN uptake not fully resolved","In vivo immune consequences not addressed in these studies"]},{"year":2022,"claim":"Provided the structural basis for substrate recognition and the anion-exchange mechanism, defining distinct binding modes for folates/antifolates (monomeric) versus CDNs (dual-molecule unit) and the coupled counter-substrate.","evidence":"Cryo-EM of apo, methotrexate, 5-methyltetrahydrofolate, antifolate, and CDN complexes with MD simulations, mutagenesis, and transport-coupling assays","pmids":["36071163","36265513","36575193"],"confidence":"High","gaps":["Dynamics of the full alternating-access cycle not captured","Structural basis of bidirectional export not separately resolved"]},{"year":null,"claim":"How the diverse upstream regulatory inputs (mTOR, VDR, NRF-1/PGC-1α, miR-595, lipid rafts) are integrated to set SLC19A1 surface activity in specific tissues, and how its CDN-import and folate-transport roles are physiologically balanced, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model coupling transcriptional and trafficking control","In vivo significance of CDN import for innate immunity not established in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,2,3,4,5,6,7]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2,3,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[10,15]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,2,7]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[11]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P41440","full_name":"Reduced folate transporter","aliases":["Cyclic dinucleotide:anion antiporter SLC19A1","Folate:anion antiporter SLC19A1","Intestinal folate carrier 1","IFC-1","Placental folate transporter","Reduced folate carrier protein","RFC","hRFC","Reduced folate transporter 1","RFT-1","Solute carrier family 19 member 1","hSLC19A1"],"length_aa":591,"mass_kda":64.9,"function":"Antiporter that mediates the import of reduced folates or a subset of cyclic dinucleotides, driven by the export of organic anions (PubMed:10787414, PubMed:15337749, PubMed:16115875, PubMed:22554803, PubMed:31126740, PubMed:31511694, PubMed:32276275, PubMed:36071163, PubMed:36265513, PubMed:36575193, PubMed:7826387, PubMed:9041240). Acts as an importer of immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytosol, and its linkage isomer 3'-3'-cGAMP, thus playing a role in triggering larger immune responses (PubMed:31126740, PubMed:31511694, PubMed:36745868). Mechanistically, acts as a secondary active transporter, which exports intracellular organic anions down their concentration gradients to facilitate the uptake of its substrates (PubMed:22554803, PubMed:31126740, PubMed:31511694). Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate (PubMed:10787414, PubMed:14609557, PubMed:22554803, PubMed:36071163, PubMed:36265513, PubMed:36575193). Also mediates the import of antifolate drug methotrexate (PubMed:22554803, PubMed:36071163, PubMed:7615551, PubMed:7641195, PubMed:9767079). 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity (PubMed:22554803)","subcellular_location":"Cell membrane; Apical cell membrane; Basolateral cell membrane","url":"https://www.uniprot.org/uniprotkb/P41440/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC19A1","classification":"Not Classified","n_dependent_lines":22,"n_total_lines":1208,"dependency_fraction":0.018211920529801324},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000173638","cell_line_id":"CID001316","localizations":[{"compartment":"membrane","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"CANX","stoichiometry":0.2},{"gene":"VAMP3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001316","total_profiled":1310},"omim":[{"mim_id":"620603","title":"IMMUNODEFICIENCY 114, FOLATE-RESPONSIVE; IMD114","url":"https://www.omim.org/entry/620603"},{"mim_id":"613065","title":"LEUKEMIA, ACUTE LYMPHOBLASTIC; ALL","url":"https://www.omim.org/entry/613065"},{"mim_id":"607483","title":"BASAL GANGLIA DISEASE, BIOTIN-THIAMINE RESPONSIVE; BTBGD","url":"https://www.omim.org/entry/607483"},{"mim_id":"606152","title":"SOLUTE CARRIER FAMILY 19 (THIAMINE TRANSPORTER), MEMBER 3; SLC19A3","url":"https://www.omim.org/entry/606152"},{"mim_id":"603941","title":"SOLUTE CARRIER FAMILY 19 (THIAMINE TRANSPORTER), MEMBER 2; SLC19A2","url":"https://www.omim.org/entry/603941"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"choroid plexus","ntpm":44.8}],"url":"https://www.proteinatlas.org/search/SLC19A1"},"hgnc":{"alias_symbol":["FOLT","RFC1","IFC-1","RFC","hRFC","RFT-1"],"prev_symbol":[]},"alphafold":{"accession":"P41440","domains":[{"cath_id":"1.20.1250.20","chopping":"23-206","consensus_level":"medium","plddt":88.8659,"start":23,"end":206},{"cath_id":"1.20.1250.20","chopping":"250-460","consensus_level":"medium","plddt":89.5292,"start":250,"end":460}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P41440","model_url":"https://alphafold.ebi.ac.uk/files/AF-P41440-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P41440-F1-predicted_aligned_error_v6.png","plddt_mean":72.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC19A1","jax_strain_url":"https://www.jax.org/strain/search?query=SLC19A1"},"sequence":{"accession":"P41440","fasta_url":"https://rest.uniprot.org/uniprotkb/P41440.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P41440/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P41440"}},"corpus_meta":[{"pmid":"31511694","id":"PMC_31511694","title":"SLC19A1 transports immunoreactive cyclic dinucleotides.","date":"2019","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/31511694","citation_count":297,"is_preprint":false},{"pmid":"11389843","id":"PMC_11389843","title":"Identification of RFC(Ctf18p, Ctf8p, Dcc1p): an alternative RFC complex required for sister chromatid cohesion in S. cerevisiae.","date":"2001","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/11389843","citation_count":289,"is_preprint":false},{"pmid":"15210332","id":"PMC_15210332","title":"The PCNA-RFC families of DNA clamps and clamp loaders.","date":"2004","source":"Progress in nucleic acid research and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15210332","citation_count":271,"is_preprint":false},{"pmid":"31126740","id":"PMC_31126740","title":"SLC19A1 Is an Importer of the Immunotransmitter cGAMP.","date":"2019","source":"Molecular 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research","url":"https://pubmed.ncbi.nlm.nih.gov/15576353","citation_count":17,"is_preprint":false},{"pmid":"20980821","id":"PMC_20980821","title":"Rfc5p regulates alternate RFC complex functions in sister chromatid pairing reactions in budding yeast.","date":"2010","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/20980821","citation_count":17,"is_preprint":false},{"pmid":"29333125","id":"PMC_29333125","title":"Association between SLC19A1 Gene Polymorphism and High Dose Methotrexate Toxicity in Childhood Acute Lymphoblastic Leukaemia and Non Hodgkin Malignant Lymphoma: Introducing a Haplotype based Approach.","date":"2017","source":"Radiology and oncology","url":"https://pubmed.ncbi.nlm.nih.gov/29333125","citation_count":17,"is_preprint":false},{"pmid":"29345051","id":"PMC_29345051","title":"MiR-595 Suppresses the Cellular Uptake and Cytotoxic Effects of Methotrexate by Targeting SLC19A1 in CEM/C1 Cells.","date":"2018","source":"Basic & clinical pharmacology & toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/29345051","citation_count":16,"is_preprint":false},{"pmid":"26987677","id":"PMC_26987677","title":"Conserved interaction of Ctf18-RFC with DNA polymerase ε is critical for maintenance of genome stability in Saccharomyces cerevisiae.","date":"2016","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/26987677","citation_count":16,"is_preprint":false},{"pmid":"40578346","id":"PMC_40578346","title":"The DNA replication checkpoint prevents PCNA/RFC depletion to protect forks from HLTF-induced collapse in human cells.","date":"2025","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/40578346","citation_count":15,"is_preprint":false},{"pmid":"21760912","id":"PMC_21760912","title":"Expression of RFC/SLC19A1 is associated with tumor type in bladder cancer patients.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21760912","citation_count":15,"is_preprint":false},{"pmid":"8566816","id":"PMC_8566816","title":"Cloning and characterization of the gene (rfc) encoding O-antigen polymerase of Pseudomonas aeruginosa PAO1.","date":"1995","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/8566816","citation_count":15,"is_preprint":false},{"pmid":"28188145","id":"PMC_28188145","title":"Structural studies of RFCCtf18 reveal a novel chromatin recruitment role for Dcc1.","date":"2017","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/28188145","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49549,"output_tokens":4464,"usd":0.107803,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12513,"output_tokens":3879,"usd":0.07977,"stage2_stop_reason":"end_turn"},"total_usd":0.187573,"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\": 2019,\n      \"finding\": \"SLC19A1 (reduced folate carrier) is the major transporter of cyclic dinucleotides (CDNs), including 2'3'-cGAMP, into cells. Identified by genome-wide CRISPR-interference screen; depletion inhibits CDN uptake and STING-pathway functional responses, while overexpression increases both uptake and responses. CDN uptake is inhibited by folates, sulfasalazine, and methotrexate, consistent with competition at the same transporter.\",\n      \"method\": \"Genome-wide CRISPR-interference screen, CDN uptake assays, STING-pathway functional readouts, overexpression and depletion experiments in human cell lines and primary cells\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independently identified by two concurrent studies (PMID:31511694 and PMID:31126740) using genome-wide CRISPR screens plus orthogonal functional uptake assays\",\n      \"pmids\": [\"31511694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SLC19A1 is the first known importer of cGAMP and other CDNs (including the investigational drug 2'3'-CDAS), confirmed by genome-wide CRISPR screen in a second independent study.\",\n      \"method\": \"Genome-wide CRISPR screen, CDN import assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independently replicated in two concurrent papers using genome-wide CRISPR screens\",\n      \"pmids\": [\"31126740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of human SLC19A1 in apo state and in complex with methotrexate reveal the molecular basis of substrate recognition: RFC functions as an anion exchanger coupling folate/antifolate import to anion export; key residues determining transport selectivity among folates and antifolates were identified. Combined with molecular dynamics simulations and functional experiments.\",\n      \"method\": \"Cryo-electron microscopy structure determination, molecular dynamics simulations, functional transport assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with functional validation and MD simulations in a single rigorous study\",\n      \"pmids\": [\"36071163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of human SLC19A1 in substrate-free state and complexed with multiple CDNs, a natural folate (5-methyltetrahydrofolate), and a new-generation antifolate reveal that two CDN molecules bind as a compact dual-molecule unit within the transporter cavity, whereas folate and antifolate bind as monomers in a distinct pocket. Mutagenesis studies confirmed divergent recognition mechanisms for CDN-type versus folate-type substrates.\",\n      \"method\": \"Cryo-electron microscopy, mutagenesis, binding/functional assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures with mutagenesis validation, multiple substrate classes examined in one rigorous study\",\n      \"pmids\": [\"36265513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structure of SLC19A1 with 5-methyltetrahydrofolate identifies critical residues for folate substrate recognition; two variant residues among SLC19 subfamily members designate specificity for folate. Intracellular thiamine pyrophosphate was identified as the preferred coupled (counter-transport) substrate for folate import by SLC19A1.\",\n      \"method\": \"Cryo-EM structure determination, mutagenesis, transport coupling assays\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure plus mutagenesis and functional coupling assay, single laboratory\",\n      \"pmids\": [\"36575193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"A single amino acid difference (Ser297 vs. Asn297, between the 7th and 8th membrane-spanning helices) in the murine RFC-1 (SLC19A1) protein selectively alters the apparent Km for methotrexate influx without affecting Vmax or efflux, establishing this residue as a determinant of antifolate binding on the extracellular face of the transporter.\",\n      \"method\": \"cDNA sequencing, site-specific transfection of RFC-1 constructs into transport-deficient cells, influx Km measurements with radiolabeled substrates, Western blotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution by transfection with single-nucleotide variant constructs plus functional transport assays; causal variant proven by replication in transfected cells\",\n      \"pmids\": [\"9446553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Expression of the reduced folate carrier SLC19A1 (RFC1) in intestinal IEC-6 cells produces two distinct transport activities: one at low pH (pH 5.5) inhibited by folic acid, and one at neutral pH (pH 7.4), demonstrating that tissue-specific modulators determine the pH profile of RFC1-mediated transport.\",\n      \"method\": \"Stable transfection of RFC1 construct into IEC-6 and L1210 cells, radiolabeled substrate influx assays at varying pH, inhibition studies with folic acid and metabolic inhibitors\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct transfection experiment with functional readouts, two cell lines tested, single laboratory\",\n      \"pmids\": [\"11600421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RFC (SLC19A1) acts as a bidirectional anion transporter that becomes cytotoxic under severe folate deprivation by efficiently exporting intracellular folate monoglutamates out of cells. Ectopic overexpression of RFC (but not unidirectional folate receptor alpha) caused ~15-fold decline in cell viability in folate-free medium. Down-regulation of RFC mRNA and transport activity occurs as an adaptive response to folate deprivation.\",\n      \"method\": \"Ectopic overexpression of RFC vs. folate receptor alpha in folate-free vs. folate-containing medium, cell viability assays, RT-PCR for RFC mRNA, methotrexate influx as transport activity assay, mathematical biomodeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — overexpression with functional readout, negative control (FRα), single laboratory with multiple orthogonal approaches\",\n      \"pmids\": [\"18499665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Activation of vitamin D receptor (VDR) by calcitriol up-regulates RFC (SLC19A1) mRNA, protein expression, and [3H]-methotrexate transport activity at the blood-brain barrier in human cerebral microvascular endothelial cells (hCMEC/D3) and isolated mouse brain capillaries. VDR-targeting siRNA down-regulates RFC expression, confirming VDR as a direct regulator of SLC19A1.\",\n      \"method\": \"Calcitriol treatment of hCMEC/D3 cells and mouse brain capillaries, [3H]-MTX uptake assay, RT-PCR and Western blot, VDR siRNA knockdown\",\n      \"journal\": \"Molecular pharmaceutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological activation plus siRNA knockdown, functional transport readout, two model systems, single laboratory\",\n      \"pmids\": [\"28885847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nuclear respiratory factor 1 (NRF-1)/PGC-1α signaling regulates RFC (SLC19A1) expression and function at the blood-brain barrier. PQQ (NRF-1 ligand) increases NRF-1 binding to SLC19A1 promoter (shown by ChIP assay) and induces RFC expression and [3H]-MTX transport activity; NRF-1 or PGC-1α siRNA knockdown reduces RFC functional expression.\",\n      \"method\": \"ChIP assay for NRF-1 binding to SLC19A1 promoter, siRNA knockdown of NRF-1/PGC-1α, [3H]-MTX uptake assay, RT-PCR and Western blot, in vivo PQQ treatment in mice\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP showing direct promoter binding plus siRNA knockdown with functional transport readout, in vitro and in vivo models, single laboratory\",\n      \"pmids\": [\"32543769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"mTORC1 and mTORC2 are positive regulators of folate uptake in human trophoblasts, acting by controlling the plasma membrane abundance (surface expression) of RFC (SLC19A1) and FR-α without affecting global protein expression. Silencing raptor (mTORC1) or rictor (mTORC2) markedly decreased folate uptake and surface transporter levels.\",\n      \"method\": \"siRNA silencing of raptor/rictor in primary human trophoblasts, folate uptake assays, plasma membrane fractionation and immunoblotting\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific siRNA knockdown with functional folate uptake readout and surface expression measurement, single laboratory\",\n      \"pmids\": [\"27562465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SLC19A1 knockdown in human adipocytes perturbs intracellular one-carbon cycle (1CC) metabolism, induces global DNA hypermethylation, and increases expression of proinflammatory genes including CCL2. Methylation at the CCL2 promoter CpG locus (cg12698626) directly regulates CCL2 transcription and secretion, linking SLC19A1 to an epigenetic inflammatory mechanism.\",\n      \"method\": \"siRNA knockdown of SLC19A1 in differentiated human adipocytes, microarray, qPCR, DNA methylation by ELISA and pyrosequencing, luciferase reporter assay, targeted metabolomics, cytokine ELISA\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple orthogonal readouts (methylation, gene expression, metabolomics, reporter assay), single laboratory\",\n      \"pmids\": [\"29121255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The human RFC-1 (SLC19A1) gene has multiple promoters (at least two, Promoter 1 upstream of exon 1a and Promoter 2 upstream of exon 1b) that direct expression of alternatively spliced transcripts with 5' end heterogeneity. Promoter 2 (exon 1b) has ~3-fold higher basal activity than Promoter 1 in functional transient transfection assays.\",\n      \"method\": \"Genomic DNA sequencing, primer extension analysis, functional deletion analysis with luciferase reporter gene in transient transfection experiments\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional promoter deletion analysis with reporter assays, supported by primer extension, single laboratory\",\n      \"pmids\": [\"9602167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The C. elegans ortholog folt-1 (encoding FOLT-1, the RFC/SLC19A1 ortholog) is required for germline proliferation and somatic function; knockout causes severely diminished germline, reduced spermatogenesis, sterility in hermaphrodites, shortened lifespan, and elongated defecation intervals. No increased germline apoptosis was detected, suggesting defective proliferation rather than increased cell death.\",\n      \"method\": \"Genetic knockout analysis (folt-1(ok1460)), germline microscopy, lifespan assays, mating assays, apoptosis staining in C. elegans\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean knockout with multiple phenotypic readouts in defined model organism ortholog, single laboratory\",\n      \"pmids\": [\"20441590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"RFC/SLC19A1 (reduced folate carrier) is expressed in placenta, yolk sac, and multiple developing embryonic tissues including neural tube, craniofacial region, limb buds, heart, and early eye; by E12.5 RFC protein becomes restricted to the retinal pigment epithelium. This developmental expression pattern was determined by in situ hybridization and immunolocalization.\",\n      \"method\": \"In situ hybridization, immunolocalization in mouse embryos at multiple developmental stages (E9.0–E12.5)\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by in situ hybridization and immunohistochemistry in multiple developmental stages, single laboratory\",\n      \"pmids\": [\"12887734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Chronic ethanol ingestion reduces folate transport across the colonic apical membrane by decreasing both affinity (higher Km) and number of transporter molecules (lower Vmax) for RFC. RFC protein is distributed in lipid rafts of the colonic apical membrane, and chronic alcoholism decreases RFC protein levels specifically in lipid raft fractions.\",\n      \"method\": \"Isolated colon apical membrane vesicle transport assays, Western blotting, Optiprep density gradient floatation to isolate lipid rafts, in vivo rat chronic ethanol feeding model\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model with membrane fractionation, functional transport assays, and protein quantification; single laboratory\",\n      \"pmids\": [\"21069807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-595 suppresses SLC19A1 expression post-transcriptionally by directly binding to the 3'-UTR of SLC19A1 (validated by luciferase reporter assay), reducing RFC1 protein levels, intracellular methotrexate concentrations, and MTX-induced cytotoxicity and apoptosis in CEM/C1 leukemia cells.\",\n      \"method\": \"Luciferase reporter assay with SLC19A1 3'-UTR, miR-595 mimic and inhibitor transfection, Western blotting, intracellular MTX quantification by ELISA, cell viability and apoptosis assays\",\n      \"journal\": \"Basic & clinical pharmacology & toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct reporter assay for miRNA-3'UTR binding plus functional gain/loss-of-function with multiple readouts, single laboratory\",\n      \"pmids\": [\"29345051\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC19A1 (hRFC/RFC1) is a bidirectional anion exchanger/antiporter embedded in the plasma membrane that functions as the major cellular importer of reduced folates (with thiamine pyrophosphate as a preferred counter-transport substrate), antifolate drugs (e.g., methotrexate, pemetrexed), and cyclic dinucleotides (including cGAMP and bacterial CDNs); cryo-EM structures have defined distinct binding pockets for folate-type monomers versus dual-molecule CDN units within the transporter cavity, and specific residues (including those between transmembrane helices 7–8) determine substrate selectivity; its surface expression is regulated post-translationally by mTORC1/C2 and transcriptionally by VDR and NRF-1/PGC-1α; under severe folate deprivation RFC acts paradoxically as a folate exporter causing cytotoxicity; and in adipocytes SLC19A1 controls one-carbon metabolism to modulate DNA methylation and inflammatory gene expression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC19A1 (reduced folate carrier, RFC1) is a plasma-membrane anion exchanger that serves as the major cellular importer of reduced folates and antifolate drugs, coupling substrate import to anion export with intracellular thiamine pyrophosphate as the preferred counter-transport substrate [#2, #4]. Cryo-EM structures of the apo, folate-bound, antifolate-bound, and cyclic-dinucleotide-bound states show that folates and antifolates bind as monomers in one pocket while CDNs bind as a compact dual-molecule unit in a distinct cavity, explaining the divergent recognition of these substrate classes [#2, #3, #4]; selectivity is set by specific residues, including a single position between transmembrane helices 7 and 8 that tunes the affinity for methotrexate influx [#5]. Beyond its folate role, SLC19A1 is the principal importer of cyclic dinucleotides such as 2'3'-cGAMP, and its activity governs STING-pathway responses to extracellular CDNs, with uptake competitively blocked by folates and antifolates [#0, #1]. The transporter is bidirectional: under severe folate deprivation it paradoxically exports intracellular folate monoglutamates, becoming cytotoxic, and its expression is down-regulated as an adaptive response [#7]. Surface abundance and function are controlled post-translationally by mTORC1/mTORC2 [#10] and transcriptionally by the vitamin D receptor [#8] and NRF-1/PGC-1\\u03b1 [#9], with additional post-transcriptional repression by miR-595 [#16]. Through control of one-carbon metabolism, SLC19A1 also influences DNA methylation and proinflammatory gene expression in adipocytes [#11], and is required for germline proliferation and viability in the C. elegans ortholog folt-1 [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established the first structure-function determinant of antifolate handling by pinpointing a single residue that governs substrate binding on the extracellular face of the carrier.\",\n      \"evidence\": \"Site-specific transfection of murine RFC-1 variant constructs (Ser297 vs Asn297) into transport-deficient cells with influx Km measurements\",\n      \"pmids\": [\"9446553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not provide an atomic structure of the binding pocket\", \"Limited to methotrexate among diverse antifolates\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined the transcriptional architecture of the gene, showing multiple promoters drive alternatively spliced transcripts with differing basal activity.\",\n      \"evidence\": \"Genomic sequencing, primer extension, and luciferase reporter deletion analysis in transient transfections\",\n      \"pmids\": [\"9602167\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the trans-acting factors binding each promoter\", \"Tissue-specific promoter usage not resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed RFC-mediated transport adopts distinct pH-dependent activities, indicating tissue-specific modulation of the carrier.\",\n      \"evidence\": \"Stable RFC1 transfection into IEC-6 and L1210 cells with radiolabeled influx assays at varying pH\",\n      \"pmids\": [\"11600421\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of the low-pH activity unresolved\", \"Whether a distinct transporter contributes was not excluded\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapped the developmental expression of RFC, linking the carrier to folate supply during embryogenesis and to a restricted retinal pigment epithelium localization.\",\n      \"evidence\": \"In situ hybridization and immunolocalization across mouse embryonic stages E9.0\\u2013E12.5\",\n      \"pmids\": [\"12887734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Expression pattern alone does not establish functional requirement in each tissue\", \"No loss-of-function phenotype in this study\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed RFC as a bidirectional transporter that can export folates and become cytotoxic under deprivation, redefining it beyond a unidirectional importer.\",\n      \"evidence\": \"Ectopic RFC vs FR-alpha overexpression in folate-free medium with viability assays, RT-PCR, MTX influx, and biomodeling\",\n      \"pmids\": [\"18499665\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological contexts where export dominates not defined\", \"Counter-anion driving export not identified here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated an in vivo organismal requirement for the carrier in germline proliferation and viability using a genetic ortholog knockout.\",\n      \"evidence\": \"folt-1(ok1460) knockout in C. elegans with germline microscopy, lifespan, mating, and apoptosis assays\",\n      \"pmids\": [\"20441590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ortholog phenotype may not fully map to mammalian SLC19A1\", \"Mechanism linking folate transport to proliferation defect not dissected\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected RFC function to membrane microdomain localization, showing lipid-raft residence and its disruption by chronic ethanol.\",\n      \"evidence\": \"Colonic apical membrane vesicle transport assays, lipid-raft floatation, and immunoblotting in a rat ethanol-feeding model\",\n      \"pmids\": [\"21069807\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct requirement of raft localization for transport not tested\", \"Mechanism of ethanol-induced raft depletion unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified mTORC1/mTORC2 as upstream regulators that control RFC surface abundance and thus folate uptake.\",\n      \"evidence\": \"siRNA silencing of raptor/rictor in primary human trophoblasts with folate uptake assays and plasma-membrane fractionation\",\n      \"pmids\": [\"27562465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between mTOR and trafficking not defined\", \"Generality beyond trophoblasts untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established VDR as a direct transcriptional activator of SLC19A1 at the blood-brain barrier.\",\n      \"evidence\": \"Calcitriol treatment and VDR siRNA in hCMEC/D3 cells and mouse brain capillaries with MTX uptake, RT-PCR, and Western blot\",\n      \"pmids\": [\"28885847\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"VDR response element not mapped on the promoter\", \"Single laboratory\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked SLC19A1 to epigenetic and inflammatory control by showing its loss perturbs one-carbon metabolism, drives DNA hypermethylation, and induces proinflammatory genes.\",\n      \"evidence\": \"siRNA knockdown in human adipocytes with metabolomics, DNA methylation pyrosequencing, microarray, reporter assays, and cytokine ELISA\",\n      \"pmids\": [\"29121255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from methylation to inflammation in vivo not established\", \"Generality beyond adipocytes untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified miR-595 as a post-transcriptional repressor of SLC19A1 that modulates methotrexate accumulation and sensitivity.\",\n      \"evidence\": \"Luciferase 3'-UTR reporter, miR-595 mimic/inhibitor, MTX quantification, and viability assays in CEM/C1 leukemia cells\",\n      \"pmids\": [\"29345051\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Clinical relevance to MTX resistance not validated\", \"Single cell-line context\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovered an entirely new transport function: SLC19A1 is the major importer of cyclic dinucleotides, coupling the carrier to STING-dependent innate immune signaling.\",\n      \"evidence\": \"Two concurrent genome-wide CRISPR screens with CDN uptake assays, STING functional readouts, and competition by folates/antifolates in human cells\",\n      \"pmids\": [\"31511694\", \"31126740\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional transporters contribute to CDN uptake not fully resolved\", \"In vivo immune consequences not addressed in these studies\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided the structural basis for substrate recognition and the anion-exchange mechanism, defining distinct binding modes for folates/antifolates (monomeric) versus CDNs (dual-molecule unit) and the coupled counter-substrate.\",\n      \"evidence\": \"Cryo-EM of apo, methotrexate, 5-methyltetrahydrofolate, antifolate, and CDN complexes with MD simulations, mutagenesis, and transport-coupling assays\",\n      \"pmids\": [\"36071163\", \"36265513\", \"36575193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of the full alternating-access cycle not captured\", \"Structural basis of bidirectional export not separately resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse upstream regulatory inputs (mTOR, VDR, NRF-1/PGC-1\\u03b1, miR-595, lipid rafts) are integrated to set SLC19A1 surface activity in specific tissues, and how its CDN-import and folate-transport roles are physiologically balanced, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model coupling transcriptional and trafficking control\", \"In vivo significance of CDN import for innate immunity not established in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 6, 7]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [10, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 2, 7]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}