{"gene":"SLC22A1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2001,"finding":"OCT1 (SLC22A1) is localized at the basolateral membrane of hepatocytes and mediates uptake of organic cations (TEA, metaiodobenzylguanidine, MPP+) into liver; Oct1 knockout mice show 4–6-fold reduced hepatic accumulation of TEA and ~2-fold reduced direct intestinal excretion, establishing OCT1's role in hepatic cation uptake and intestinal secretion.","method":"Oct1 knockout mouse model; intravenous TEA administration with tissue distribution and excretion measurements","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with well-defined pharmacokinetic phenotype, replicated across multiple substrates in the same study","pmids":["11463829"],"is_preprint":false},{"year":1997,"finding":"The SLC22A1 gene (encoding OCT1) was mapped to chromosome 6q26 by fluorescence in situ hybridization.","method":"Chromosomal localization by cytogenetics/FISH","journal":"Cytogenetics and cell genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cytogenetic mapping, single study but clear result","pmids":["9605850"],"is_preprint":false},{"year":1999,"finding":"The SLC22A1 gene consists of 7 exons and 6 introns and produces at least four alternatively spliced isoforms; only the full-length hOCT1 isoform mediates decynium-22-sensitive uptake of [3H]-MPP+ when stably expressed in HEK293 cells, demonstrating that shorter splice variants are non-functional.","method":"cDNA cloning, gene structure determination, stable transfection of HEK293 cells, [3H]-MPP+ uptake assay","journal":"Annals of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional transport assay in transfected cells with multiple isoforms tested, single lab","pmids":["11388889"],"is_preprint":false},{"year":2004,"finding":"SNPs P283L and R287G in SLC22A1 abolish transport of both TEA and MPP+ despite detectable plasma membrane protein expression in Xenopus oocytes, while P341L reduces TEA uptake to ~65% of wild type and F160L has no significant effect, demonstrating that specific coding variants impair OCT1 transport activity without affecting membrane targeting.","method":"Xenopus oocyte expression system with [14C]TEA and [3H]MPP+ uptake assays; Western blot for membrane expression","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted transport in heterologous oocyte system with mutagenesis and membrane expression controls, single lab but multiple orthogonal methods","pmids":["14697261"],"is_preprint":false},{"year":2005,"finding":"Ranitidine is a substrate of hOCT1 (Km ~70 µM) and hOCT2 but not hOCT3, as determined by [3H]ranitidine uptake in cRNA-injected Xenopus oocytes; famotidine is an hOCT1 substrate (confirmed by trans-stimulation and electrophysiology) and potently inhibits hOCT3 (IC50 ~6.7 µM), while ranitidine is a weak hOCT3 inhibitor (IC50 ~290 µM).","method":"cRNA-injected Xenopus laevis oocytes; [3H]ranitidine uptake, trans-stimulation, and electrophysiology","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (uptake, trans-stimulation, electrophysiology) in reconstituted oocyte system, single lab","pmids":["16141367"],"is_preprint":false},{"year":2006,"finding":"Cisplatin is a substrate of hOCT1 (and more potently hOCT2 and hMATE1), as shown by enhanced cytotoxicity and cellular accumulation in HEK293 cells transiently expressing hOCT1 and concentration-dependent inhibition of TEA uptake; carboplatin and nedaplatin are not transported by hOCT1 or related transporters.","method":"Transient transfection of HEK293 cells; cytotoxicity assay, [14C]cisplatin accumulation, TEA competition assay","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal functional assays (accumulation, cytotoxicity, competition) in transfected cells, single lab","pmids":["16914559"],"is_preprint":false},{"year":2007,"finding":"OCT1 (SLC22A1) localizes to the basolateral membrane of human hepatocytes and transports berberine (Km ~14.8 µM); in double-transfected MDCKII cells expressing OCT1 (basolateral) and MDR1 P-gp (apical), berberine undergoes vectorial transcellular transport, establishing OCT1 as the basolateral uptake step for vectorial cation secretion in liver.","method":"Immunofluorescence localization in human hepatocytes; stable transfection of MDCKII cells; fluorescence-based berberine uptake and transcellular transport assays; Michaelis-Menten kinetics","journal":"Naunyn-Schmiedeberg's archives of pharmacology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct localization in human tissue confirmed by functional polarized transport reconstitution in transfected epithelial cells, single lab with multiple methods","pmids":["18157518"],"is_preprint":false},{"year":2008,"finding":"USF1 and USF2 transcription factors bind a cognate E-box (CACGTG) element in the OCT1 core promoter region (−141/−69) and are required for basal OCT1 gene expression; HNF4α further stimulates USF-mediated transactivation of the OCT1 promoter in hepatocytes.","method":"Promoter deletion analysis, luciferase reporter gene assay, electrophoretic mobility shift assay (EMSA), site-directed mutagenesis of E-box, co-transfection of transcription factor expression vectors in Huh7 and HepG2 cells","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (EMSA, reporter assay, mutagenesis) in cell-based system, single lab","pmids":["18845576"],"is_preprint":false},{"year":2009,"finding":"OCT1 protein is localized to the basolateral membrane of human hepatocytes; the OCT1-Arg61Cys variant (rs12208357) strongly correlates with decreased OCT1 protein expression in human liver; both OCT1 and OCT3 transport metformin in transfected cells.","method":"Immunofluorescence microscopy of human liver tissue; quantitative protein expression analysis in 150 liver samples; functional transport assay in transfected cells; MALDI-TOF genotyping; multivariate analysis","journal":"Hepatology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization in human tissue with large sample size, functional transport confirmation, and genetic association with protein expression","pmids":["19591196"],"is_preprint":false},{"year":2010,"finding":"YM155 is a substrate of OCT1/SLC22A1 (Km ~22.1 µM) and OCT2 but not OCT3, as shown by time- and concentration-dependent uptake in HEK293 cells expressing hOCT1 and inhibition of [3H]MPP+ uptake.","method":"Transient transfection of HEK293 cells; [14C]YM155 uptake kinetics; [3H]MPP+ inhibition assay","journal":"Drug metabolism and disposition: the biological fate of chemicals","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstituted transport kinetics in transfected cells, single lab, single method","pmids":["19833842"],"is_preprint":false},{"year":2004,"finding":"PPAR-α and PPAR-γ agonists transcriptionally upregulate murine Slc22a1 (Oct1) gene expression via a PPAR-response element in the Slc22a1 promoter, resulting in increased organic cation uptake in hepatocytes.","method":"Mouse in vivo treatment and H35 cell treatment with PPAR agonists; Slc22a1 promoter cloning; chimeric promoter-reporter luciferase assay; PPAR transcription factor transfection; organic cation uptake functional assay","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — promoter cloning with PPAR-response element identification, reporter assays, functional uptake confirmation in vivo and in vitro, single lab","pmids":["15458920"],"is_preprint":false},{"year":2013,"finding":"SLC22A1 (OCT1) transports sorafenib; two novel truncating variants (R61S fs*10 and C88A fs*16) produce proteins that fail to reach the plasma membrane and abolish OCT1-mediated sorafenib uptake, as validated by quinine-sensitive sorafenib uptake in Xenopus oocytes measured by HPLC-MS/MS.","method":"Directed mutagenesis; expression in HCC cell lines and Xenopus laevis oocytes; plasma membrane localization; [3H]TEA uptake; quinine-sensitive sorafenib uptake by HPLC-MS/MS","journal":"Hepatology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (oocyte transport, mutagenesis, HPLC-MS/MS quantification, membrane targeting) in two expression systems, single lab","pmids":["23532667"],"is_preprint":false},{"year":2013,"finding":"PXR activation (by rifampicin or hyperforin) downregulates OCT1 mRNA and reduces hepatic [3H]MPP+ accumulation; this occurs by PXR competing for (squelching) the SRC-1 coactivator from HNF4α response elements and USF1 E-box elements in the OCT1 promoter, requiring both PXR and HNF4α.","method":"Primary human hepatocytes and HepaRG cells; qRT-PCR; [3H]MPP+ transport assay; OCT1 promoter reporter constructs; siRNA knockdown of PXR and HNF4α; chromatin immunoprecipitation (ChIP); mutagenesis of promoter elements; SRC-1 overexpression rescue","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (ChIP, reporter assay, siRNA, rescue with coactivator overexpression, functional transport assay) in primary human hepatocytes and cell lines","pmids":["26920453"],"is_preprint":false},{"year":2013,"finding":"Glucocorticoid receptor (GR) activation by dexamethasone indirectly upregulates OCT1 mRNA and protein expression in primary human hepatocytes via HNF4α induction; C/EBPβ and PGC1α also contribute to OCT1 gene regulation, with C/EBPβ co-transfection stimulating OCT1 promoter activity.","method":"Primary human hepatocytes and hepatocyte-derived cell lines (HepG2, MZ-Hep1); qRT-PCR; Western blot; luciferase gene reporter assays with OCT1 promoter constructs; viral transduction of transcription factors","journal":"Pharmacological reports : PR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assays and expression studies in primary hepatocytes and cell lines, multiple transcription factors tested, single lab","pmids":["24399729"],"is_preprint":false},{"year":2011,"finding":"DNA methylation of the SLC22A1 promoter region is mechanistically associated with transcriptional downregulation of OCT1 in hepatocellular carcinoma; treatment with the demethylating agent 5-aza-2-deoxycytidine restores Slc22a1 expression in tumor-derived cells.","method":"MALDI-TOF mass spectrometry quantification of DNA methylation in paired HCC and non-tumor liver tissues; tissue microarray IHC; 5-aza-2-deoxycytidine and trichostatin A treatment of cultured Tsc1 renal tumor cells (corroborated in PMID:23228442)","journal":"Genome medicine / European journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative methylation analysis in human tissue with pharmacological demethylation rescue, replicated across two independent studies","pmids":["22196450","23228442"],"is_preprint":false},{"year":2013,"finding":"Multiple fluoroquinolones (gatifloxacin, moxifloxacin, prulifloxacin, sparfloxacin) competitively inhibit hOCT1-mediated transport with Ki values of 94–250 µM; hOCT1 selectively mediates their disposition compared with hOCT2 and hOCT3, implicating hOCT1 in sinusoidal hepatic uptake of fluoroquinolones.","method":"Heterologous expression in oocyte/cell systems; competitive inhibition kinetics with Ki determination using [3H]TEA or MPP+ as model substrates","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — Ki determination via competitive inhibition assay in heterologous expression system, single lab","pmids":["23545524"],"is_preprint":false},{"year":2013,"finding":"Rilpivirine is transported by SLC22A1 (OCT1), showing 27% higher accumulation in SLC22A1-overexpressing KCL22 cells versus controls; rilpivirine inhibits SLC22A1 function with an IC50 of 28.5 µM and SLC22A2 with IC50 of 5.13 µM.","method":"Stable SLC22A1-expressing KCL22 cells; cellular accumulation assay; TEA uptake inhibition assay","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — transport and inhibition assay in stably transfected cells, single lab, single method for transport","pmids":["24002095"],"is_preprint":false},{"year":2017,"finding":"SLC22A1 (OCT1) mediates efflux of acylcarnitines from the liver to the circulation; loss-of-function in Slc22a1 knockout mice and gain-of-function cell models with isotope tracing demonstrate that OCT1 transports acylcarnitines out of hepatocytes, and human SLC22A1 coding variants impair this acylcarnitine efflux activity in vitro.","method":"Slc22a1 knockout mice; gain-of-function cell models; targeted metabolomics; isotope tracing experiments; in vitro functional validation of human variants","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (KO mouse, gain-of-function cells, isotope tracing, metabolomics, human variant validation) across loss- and gain-of-function models","pmids":["28942964"],"is_preprint":false},{"year":2018,"finding":"The -201C>G SNP (rs58812592) in the OCT1 promoter causes allele-dependent differences in USF1/2 transcription factor binding and nearly complete loss of OCT1 promoter activity for the G-allele; the -1795G>A SNP (rs6935207) shows allele-specific NF-Y binding and increased enhancer activity but no significant effect on the native OCT1 promoter or on pharmacokinetics of OCT1 substrates.","method":"Electrophoretic mobility shift assay (EMSA); luciferase reporter gene assay in HepG2, Hep3B, Huh7 cells; pharmacokinetic analysis of metformin, fenoterol, sumatriptan, proguanil in healthy volunteers","journal":"Journal of personalized medicine","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — EMSA and reporter assay with pharmacokinetic clinical validation, single lab","pmids":["30544975"],"is_preprint":false},{"year":2023,"finding":"Systematic missense and deletion variant scanning of OCT1 (SLC22A1) reveals that most human variants impair function via protein misfolding rather than direct disruption of substrate binding; the first 300 amino acids (including TM1–6 and extracellular domain with a conserved stabilizing helical motif) are major determinants of folding; molecular dynamics simulations identify biophysical mechanisms for specific variant transport phenotypes.","method":"Comprehensive single-variant mutagenesis; expression and substrate uptake assays; computational modeling and molecular dynamics simulations; population database mining","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — large-scale systematic mutagenesis with functional validation and structural modeling, preprint not yet peer-reviewed","pmids":["37333090"],"is_preprint":true},{"year":2024,"finding":"OCT1 (SLC22A1) in 3D primary human hepatocyte spheroids has a Km of ~14 µM for the fluorescent substrate ASP+; OCT1 activity is inhibited 35–52% by known inhibitors and remains stable upon activation of nuclear receptor signaling (including PXR), distinguishing OCT1 regulation from P-glycoprotein and CYP3A4 induction.","method":"3D spheroids of primary human hepatocytes; ASP+ fluorescent transport kinetics assay; known inhibitor co-incubation; global proteomics; 7-day nuclear receptor ligand exposure","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinetic measurements in physiologically relevant 3D PHH model with multiple donors and inhibitor validation, single lab","pmids":["39068198"],"is_preprint":false},{"year":2025,"finding":"Overexpression of SLC22A1 in HepG2.2.15 cells suppresses hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) expression through activation of the JAK/STAT signaling pathway, as confirmed by transcriptome sequencing and targeted overexpression experiments.","method":"SLC22A1 overexpression in HepG2.2.15 cells; ELISA for HBsAg and HBeAg; RNA sequencing; immunohistochemistry","journal":"The Journal of infectious diseases","confidence":"Low","confidence_rationale":"Tier 3 / Weak — overexpression with signaling pathway readout, single lab, mechanistic pathway proposed but upstream/downstream connections not fully reconstituted","pmids":["40036258"],"is_preprint":false},{"year":2024,"finding":"The SLC22A1 1022C>T variant (rs2282143) reduces OCT1-mediated hepatic uptake of proguanil; CT heterozygotes showed 1.2-fold higher proguanil systemic exposure and 0.5-fold lower cycloguanil exposure compared to wild-type CC, with population PK modeling estimating 0.42-fold reduced OCT1 activity in CT carriers.","method":"Clinical pharmacokinetic study in Korean subjects; population PK modeling with well-stirred liver compartment; prospective SLC22A1 genotyping","journal":"Clinical and translational science","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clinical pharmacokinetic data with mechanistic PK modeling establishing hepatic uptake role, single study with small sample","pmids":["39668580"],"is_preprint":false}],"current_model":"SLC22A1 encodes OCT1, a polyspecific electrogenic transporter localized to the basolateral membrane of hepatocytes that mediates facilitated uptake of diverse organic cations (including metformin, sorafenib, acylcarnitines, cisplatin, berberine, ranitidine, and many drugs) into liver, intestine, and other epithelia; its expression is transcriptionally controlled by USF1/USF2 binding to a core promoter E-box, with upregulation by HNF4α, GR/HNF4α, and PPAR-α/γ pathways and downregulation by PXR through SRC-1 coactivator squelching from HNF4α/USF elements; epigenetic silencing via DNA methylation suppresses OCT1 in hepatocellular carcinoma; loss-of-function coding variants primarily impair protein folding rather than substrate binding, and a subset abolish membrane targeting or transport activity, collectively explaining inter-individual pharmacokinetic variability for numerous OCT1 substrate drugs."},"narrative":{"mechanistic_narrative":"SLC22A1 encodes OCT1, a polyspecific, electrogenic organic cation transporter localized to the basolateral membrane of hepatocytes, where it mediates facilitated uptake of diverse organic cations into the liver and contributes to intestinal secretion [PMID:11463829, PMID:19591196]. By providing the basolateral entry step, OCT1 enables vectorial transcellular cation secretion: in epithelial cells co-expressing OCT1 (basolateral) and apical efflux transporters, substrates such as berberine undergo directional transport across the cell [PMID:18157518]. Its substrate range encompasses model cations (TEA, MPP+) and numerous drugs, including ranitidine and famotidine, cisplatin, the survivin suppressant YM155, sorafenib, and fluoroquinolones, with the transporter also exporting endogenous acylcarnitines from hepatocytes to the circulation [PMID:16141367, PMID:16914559, PMID:19833842, PMID:23532667, PMID:23545524, PMID:28942964]. Only the full-length isoform is transport-competent, with shorter alternatively spliced variants being non-functional [PMID:11388889]. Basal hepatic expression is driven by USF1/USF2 binding a core-promoter E-box and is amplified by HNF4α, glucocorticoid receptor signaling, and PPAR-α/γ agonists, while PXR activation represses OCT1 by squelching the SRC-1 coactivator from HNF4α and USF elements, and promoter DNA methylation silences OCT1 in hepatocellular carcinoma [PMID:18845576, PMID:15458920, PMID:26920453, PMID:24399729, PMID:22196450, PMID:23228442]. Loss-of-function arises through two routes: coding variants that abolish transport while remaining membrane-resident (e.g., P283L, R287G) or that prevent membrane targeting (truncating R61S fs*10, C88A fs*16), with systematic variant scanning showing most human variants impair function through protein misfolding rather than disrupted substrate binding; promoter SNPs additionally alter transcription-factor binding and expression, collectively explaining inter-individual pharmacokinetic variability for OCT1 substrate drugs [PMID:14697261, PMID:23532667, PMID:37333090, PMID:30544975, PMID:39668580].","teleology":[{"year":1997,"claim":"Establishing the genomic locus and exon structure of SLC22A1 anchored the gene and revealed that alternative splicing generates multiple transcripts, only one of which is functional.","evidence":"FISH chromosomal mapping to 6q26 and cDNA cloning with isoform transport assays in HEK293 cells","pmids":["9605850","11388889"],"confidence":"Medium","gaps":["Physiological relevance of non-functional splice variants unresolved","Tissue distribution of isoforms not defined"]},{"year":2001,"claim":"In vivo knockout addressed whether OCT1 is physiologically required for hepatic cation handling, establishing it as the basolateral uptake transporter into liver and a contributor to intestinal secretion.","evidence":"Oct1 knockout mouse with TEA tissue distribution and excretion measurements across multiple cation substrates","pmids":["11463829"],"confidence":"High","gaps":["Driving force / electrogenicity not directly measured in this study","Human tissue localization not yet confirmed at this point"]},{"year":2004,"claim":"Variant-specific mutagenesis resolved whether loss-of-function variants act on transport catalysis or membrane delivery, showing some abolish transport while remaining membrane-resident.","evidence":"Xenopus oocyte uptake of TEA and MPP+ with Western blot for membrane expression across coding variants","pmids":["14697261"],"confidence":"High","gaps":["Structural basis of transport loss not defined","Allele frequencies and clinical impact not assessed here"]},{"year":2004,"claim":"Promoter dissection identified a transcriptional input regulating OCT1, showing PPAR-α/γ agonists upregulate the gene via a PPAR-response element and increase hepatocyte cation uptake.","evidence":"Mouse in vivo and H35 cell PPAR-agonist treatment with promoter-reporter assays and functional uptake","pmids":["15458920"],"confidence":"High","gaps":["Shown in murine Slc22a1; human promoter element not directly tested","Endogenous ligand context unclear"]},{"year":2009,"claim":"Quantitative human liver analysis connected a coding variant to expression, establishing that Arg61Cys reduces OCT1 protein in vivo and confirming basolateral localization in human hepatocytes.","evidence":"Immunofluorescence and quantitative protein analysis in 150 human livers with MALDI-TOF genotyping and transport assays","pmids":["19591196"],"confidence":"High","gaps":["Mechanism by which R61C lowers protein (folding vs. stability) not defined here","Substrate-specific consequences not enumerated"]},{"year":2008,"claim":"Identifying USF1/USF2 binding to a core-promoter E-box defined the basal transcriptional driver of OCT1 and its synergy with HNF4α.","evidence":"Promoter deletion, luciferase reporters, EMSA, and E-box mutagenesis in Huh7 and HepG2 cells","pmids":["18845576"],"confidence":"High","gaps":["Genetic variation in the E-box not yet examined","Chromatin-level regulation not addressed"]},{"year":2013,"claim":"Mechanistic regulation studies established a bidirectional transcriptional network: GR/HNF4α and C/EBPβ/PGC1α upregulate OCT1 while PXR represses it by coactivator squelching, and promoter methylation silences it in HCC.","evidence":"Primary human hepatocytes and cell lines with reporter assays, ChIP, siRNA, SRC-1 rescue, demethylation rescue, and transport assays","pmids":["26920453","24399729","22196450"],"confidence":"High","gaps":["Quantitative integration of competing inputs in vivo not resolved","Methylation triggers in HCC undefined"]},{"year":2013,"claim":"Substrate and inhibitor profiling expanded OCT1's pharmacological scope, establishing it as the hepatic sinusoidal uptake step for sorafenib, fluoroquinolones, rilpivirine, and additional drugs, and defining truncating variants that prevent membrane targeting.","evidence":"Heterologous expression (oocytes, HEK293, KCL22) with uptake, inhibition kinetics, HPLC-MS/MS, and membrane localization across substrates and variants","pmids":["23532667","23545524","24002095","16141367","16914559","19833842"],"confidence":"High","gaps":["Relative in vivo contribution versus other OCTs/MATEs not quantified for all substrates","Substrate recognition determinants not structurally mapped"]},{"year":2017,"claim":"Metabolomic and genetic analysis identified an endogenous physiological role, showing OCT1 effluxes acylcarnitines from liver to circulation and that human variants impair this activity.","evidence":"Slc22a1 knockout mice, gain-of-function cells, isotope tracing, targeted metabolomics, and human variant validation","pmids":["28942964"],"confidence":"High","gaps":["Direction (efflux) mechanism relative to cation uptake not reconciled","Clinical metabolic consequences in humans not established"]},{"year":2018,"claim":"Promoter SNP characterization linked regulatory variation to function, showing -201C>G abolishes USF-dependent promoter activity while -1795G>A has no native effect.","evidence":"EMSA, luciferase reporters in HepG2/Hep3B/Huh7, and pharmacokinetic study of OCT1 substrates in volunteers","pmids":["30544975"],"confidence":"Medium","gaps":["In vivo expression impact of -201C>G not directly measured","Population frequency and clinical penetrance unclear"]},{"year":2023,"claim":"Systematic variant scanning resolved the dominant molecular mechanism of loss-of-function, showing most variants act through protein misfolding and identifying the N-terminal folding determinant region.","evidence":"Comprehensive single-variant mutagenesis with uptake assays, molecular dynamics, and population database mining (preprint)","pmids":["37333090"],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","No experimental structure underpinning the folding model","Folding chaperone partners unidentified"]},{"year":2024,"claim":"Physiological-model and clinical studies refined OCT1 kinetics and regulation, showing stable activity under nuclear-receptor activation in human hepatocyte spheroids and confirming a coding variant reduces hepatic uptake of proguanil clinically.","evidence":"3D primary human hepatocyte spheroid ASP+ kinetics with inhibitor and nuclear-receptor exposure, plus a clinical PK study with population modeling","pmids":["39068198","39668580"],"confidence":"Medium","gaps":["Discrepancy with PXR repression seen in 2D hepatocytes not reconciled","Small clinical cohort for proguanil variant"]},{"year":2025,"claim":"An overexpression study proposed a non-transport role, linking SLC22A1 to suppression of hepatitis B antigens via JAK/STAT signaling.","evidence":"SLC22A1 overexpression in HepG2.2.15 cells with antigen ELISA, RNA-seq, and IHC","pmids":["40036258"],"confidence":"Low","gaps":["Mechanism connecting a transporter to JAK/STAT not reconstituted","Single overexpression system without loss-of-function confirmation","Whether effect depends on transport activity unknown"]},{"year":null,"claim":"How OCT1's transport mechanism (substrate recognition, electrogenicity, and direction-switching between cation uptake and acylcarnitine efflux) is structurally encoded remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experimentally determined structure in the corpus","Conformational cycle and ion-coupling not defined","Structural basis for polyspecificity unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2,3,4,5,6,9,11,15,16,17]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,8,11]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,6,17]},{"term_id":"R-HSA-9748784","term_label":"Drug ADME","supporting_discovery_ids":[4,5,11,15,22]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[7,10,12,13,14,18]}],"complexes":[],"partners":["USF1","USF2","HNF4A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15245","full_name":"Solute carrier family 22 member 1","aliases":["Organic cation transporter 1","hOCT1"],"length_aa":554,"mass_kda":61.2,"function":"Electrogenic voltage-dependent transporter that mediates the transport of a variety of organic cations such as endogenous bioactive amines, cationic drugs and xenobiotics (PubMed:11388889, PubMed:11408531, PubMed:12439218, PubMed:12719534, PubMed:15389554, PubMed:16263091, PubMed:16272756, PubMed:16581093, PubMed:19536068, PubMed:21128598, PubMed:23680637, PubMed:24961373, PubMed:34040533, PubMed:9187257, PubMed:9260930, PubMed:9655880). Functions as a pH- and Na(+)-independent, bidirectional transporter (By similarity). Cation cellular uptake or release is driven by the electrochemical potential (i.e. membrane potential and concentration gradient) and substrate selectivity (By similarity). Hydrophobicity is a major requirement for recognition in polyvalent substrates and inhibitors (By similarity). Primarily expressed at the basolateral membrane of hepatocytes and proximal tubules and involved in the uptake and disposition of cationic compounds by hepatic and renal clearance from the blood flow (By similarity). Most likely functions as an uptake carrier in enterocytes contributing to the intestinal elimination of organic cations from the systemic circulation (PubMed:16263091). Transports endogenous monoamines such as N-1-methylnicotinamide (NMN), guanidine, histamine, neurotransmitters dopamine, serotonin and adrenaline (PubMed:12439218, PubMed:24961373, PubMed:35469921, PubMed:9260930). Also transports natural polyamines such as spermidine, agmatine and putrescine at low affinity, but relatively high turnover (PubMed:21128598). Involved in the hepatic uptake of vitamin B1/thiamine, hence regulating hepatic lipid and energy metabolism (PubMed:24961373). Mediates the bidirectional transport of acetylcholine (ACh) at the apical membrane of ciliated cell in airway epithelium, thereby playing a role in luminal release of ACh from bronchial epithelium (PubMed:15817714). Transports dopaminergic neuromodulators cyclo(his-pro) and salsolinol with lower efficency (PubMed:17460754). Also capable of transporting non-amine endogenous compounds such as prostaglandin E2 (PGE2) and prostaglandin F2-alpha (PGF2-alpha) (PubMed:11907186). May contribute to the transport of cationic compounds in testes across the blood-testis-barrier (Probable). Also involved in the uptake of xenobiotics tributylmethylammonium (TBuMA), quinidine, N-methyl-quinine (NMQ), N-methyl-quinidine (NMQD) N-(4,4-azo-n-pentyl)-quinuclidine (APQ), azidoprocainamide methoiodide (AMP), N-(4,4-azo-n-pentyl)-21-deoxyajmalinium (APDA) and 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP) (PubMed:11408531, PubMed:15389554, PubMed:35469921, PubMed:9260930) Mediates the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) Not able to uptake 1-methyl-4-phenylpyridinium (MPP(+)) Not able to uptake 1-methyl-4-phenylpyridinium (MPP(+)) Not able to uptake 1-methyl-4-phenylpyridinium (MPP(+))","subcellular_location":"Basolateral cell membrane; Apical cell membrane; Lateral cell membrane; Basal cell membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/O15245/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC22A1","classification":"Not 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(rs2252281 and rs2289669) and SLC47A2 (rs34834489 and rs12943590) and the Influence of SLC22A1 (rs72552763 and rs622342) on HbA1c Levels in Mexican-Mestizo Patients with DMT2 Treated with Metformin Monotherapy.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40943569","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":43357,"output_tokens":6110,"usd":0.110861,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14790,"output_tokens":4265,"usd":0.090288,"stage2_stop_reason":"end_turn"},"total_usd":0.201149,"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\": 2001,\n      \"finding\": \"OCT1 (SLC22A1) is localized at the basolateral membrane of hepatocytes and mediates uptake of organic cations (TEA, metaiodobenzylguanidine, MPP+) into liver; Oct1 knockout mice show 4–6-fold reduced hepatic accumulation of TEA and ~2-fold reduced direct intestinal excretion, establishing OCT1's role in hepatic cation uptake and intestinal secretion.\",\n      \"method\": \"Oct1 knockout mouse model; intravenous TEA administration with tissue distribution and excretion measurements\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with well-defined pharmacokinetic phenotype, replicated across multiple substrates in the same study\",\n      \"pmids\": [\"11463829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The SLC22A1 gene (encoding OCT1) was mapped to chromosome 6q26 by fluorescence in situ hybridization.\",\n      \"method\": \"Chromosomal localization by cytogenetics/FISH\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cytogenetic mapping, single study but clear result\",\n      \"pmids\": [\"9605850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The SLC22A1 gene consists of 7 exons and 6 introns and produces at least four alternatively spliced isoforms; only the full-length hOCT1 isoform mediates decynium-22-sensitive uptake of [3H]-MPP+ when stably expressed in HEK293 cells, demonstrating that shorter splice variants are non-functional.\",\n      \"method\": \"cDNA cloning, gene structure determination, stable transfection of HEK293 cells, [3H]-MPP+ uptake assay\",\n      \"journal\": \"Annals of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional transport assay in transfected cells with multiple isoforms tested, single lab\",\n      \"pmids\": [\"11388889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SNPs P283L and R287G in SLC22A1 abolish transport of both TEA and MPP+ despite detectable plasma membrane protein expression in Xenopus oocytes, while P341L reduces TEA uptake to ~65% of wild type and F160L has no significant effect, demonstrating that specific coding variants impair OCT1 transport activity without affecting membrane targeting.\",\n      \"method\": \"Xenopus oocyte expression system with [14C]TEA and [3H]MPP+ uptake assays; Western blot for membrane expression\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted transport in heterologous oocyte system with mutagenesis and membrane expression controls, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"14697261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ranitidine is a substrate of hOCT1 (Km ~70 µM) and hOCT2 but not hOCT3, as determined by [3H]ranitidine uptake in cRNA-injected Xenopus oocytes; famotidine is an hOCT1 substrate (confirmed by trans-stimulation and electrophysiology) and potently inhibits hOCT3 (IC50 ~6.7 µM), while ranitidine is a weak hOCT3 inhibitor (IC50 ~290 µM).\",\n      \"method\": \"cRNA-injected Xenopus laevis oocytes; [3H]ranitidine uptake, trans-stimulation, and electrophysiology\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (uptake, trans-stimulation, electrophysiology) in reconstituted oocyte system, single lab\",\n      \"pmids\": [\"16141367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cisplatin is a substrate of hOCT1 (and more potently hOCT2 and hMATE1), as shown by enhanced cytotoxicity and cellular accumulation in HEK293 cells transiently expressing hOCT1 and concentration-dependent inhibition of TEA uptake; carboplatin and nedaplatin are not transported by hOCT1 or related transporters.\",\n      \"method\": \"Transient transfection of HEK293 cells; cytotoxicity assay, [14C]cisplatin accumulation, TEA competition assay\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal functional assays (accumulation, cytotoxicity, competition) in transfected cells, single lab\",\n      \"pmids\": [\"16914559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"OCT1 (SLC22A1) localizes to the basolateral membrane of human hepatocytes and transports berberine (Km ~14.8 µM); in double-transfected MDCKII cells expressing OCT1 (basolateral) and MDR1 P-gp (apical), berberine undergoes vectorial transcellular transport, establishing OCT1 as the basolateral uptake step for vectorial cation secretion in liver.\",\n      \"method\": \"Immunofluorescence localization in human hepatocytes; stable transfection of MDCKII cells; fluorescence-based berberine uptake and transcellular transport assays; Michaelis-Menten kinetics\",\n      \"journal\": \"Naunyn-Schmiedeberg's archives of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct localization in human tissue confirmed by functional polarized transport reconstitution in transfected epithelial cells, single lab with multiple methods\",\n      \"pmids\": [\"18157518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"USF1 and USF2 transcription factors bind a cognate E-box (CACGTG) element in the OCT1 core promoter region (−141/−69) and are required for basal OCT1 gene expression; HNF4α further stimulates USF-mediated transactivation of the OCT1 promoter in hepatocytes.\",\n      \"method\": \"Promoter deletion analysis, luciferase reporter gene assay, electrophoretic mobility shift assay (EMSA), site-directed mutagenesis of E-box, co-transfection of transcription factor expression vectors in Huh7 and HepG2 cells\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (EMSA, reporter assay, mutagenesis) in cell-based system, single lab\",\n      \"pmids\": [\"18845576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"OCT1 protein is localized to the basolateral membrane of human hepatocytes; the OCT1-Arg61Cys variant (rs12208357) strongly correlates with decreased OCT1 protein expression in human liver; both OCT1 and OCT3 transport metformin in transfected cells.\",\n      \"method\": \"Immunofluorescence microscopy of human liver tissue; quantitative protein expression analysis in 150 liver samples; functional transport assay in transfected cells; MALDI-TOF genotyping; multivariate analysis\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization in human tissue with large sample size, functional transport confirmation, and genetic association with protein expression\",\n      \"pmids\": [\"19591196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"YM155 is a substrate of OCT1/SLC22A1 (Km ~22.1 µM) and OCT2 but not OCT3, as shown by time- and concentration-dependent uptake in HEK293 cells expressing hOCT1 and inhibition of [3H]MPP+ uptake.\",\n      \"method\": \"Transient transfection of HEK293 cells; [14C]YM155 uptake kinetics; [3H]MPP+ inhibition assay\",\n      \"journal\": \"Drug metabolism and disposition: the biological fate of chemicals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstituted transport kinetics in transfected cells, single lab, single method\",\n      \"pmids\": [\"19833842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PPAR-α and PPAR-γ agonists transcriptionally upregulate murine Slc22a1 (Oct1) gene expression via a PPAR-response element in the Slc22a1 promoter, resulting in increased organic cation uptake in hepatocytes.\",\n      \"method\": \"Mouse in vivo treatment and H35 cell treatment with PPAR agonists; Slc22a1 promoter cloning; chimeric promoter-reporter luciferase assay; PPAR transcription factor transfection; organic cation uptake functional assay\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — promoter cloning with PPAR-response element identification, reporter assays, functional uptake confirmation in vivo and in vitro, single lab\",\n      \"pmids\": [\"15458920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SLC22A1 (OCT1) transports sorafenib; two novel truncating variants (R61S fs*10 and C88A fs*16) produce proteins that fail to reach the plasma membrane and abolish OCT1-mediated sorafenib uptake, as validated by quinine-sensitive sorafenib uptake in Xenopus oocytes measured by HPLC-MS/MS.\",\n      \"method\": \"Directed mutagenesis; expression in HCC cell lines and Xenopus laevis oocytes; plasma membrane localization; [3H]TEA uptake; quinine-sensitive sorafenib uptake by HPLC-MS/MS\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (oocyte transport, mutagenesis, HPLC-MS/MS quantification, membrane targeting) in two expression systems, single lab\",\n      \"pmids\": [\"23532667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PXR activation (by rifampicin or hyperforin) downregulates OCT1 mRNA and reduces hepatic [3H]MPP+ accumulation; this occurs by PXR competing for (squelching) the SRC-1 coactivator from HNF4α response elements and USF1 E-box elements in the OCT1 promoter, requiring both PXR and HNF4α.\",\n      \"method\": \"Primary human hepatocytes and HepaRG cells; qRT-PCR; [3H]MPP+ transport assay; OCT1 promoter reporter constructs; siRNA knockdown of PXR and HNF4α; chromatin immunoprecipitation (ChIP); mutagenesis of promoter elements; SRC-1 overexpression rescue\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (ChIP, reporter assay, siRNA, rescue with coactivator overexpression, functional transport assay) in primary human hepatocytes and cell lines\",\n      \"pmids\": [\"26920453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Glucocorticoid receptor (GR) activation by dexamethasone indirectly upregulates OCT1 mRNA and protein expression in primary human hepatocytes via HNF4α induction; C/EBPβ and PGC1α also contribute to OCT1 gene regulation, with C/EBPβ co-transfection stimulating OCT1 promoter activity.\",\n      \"method\": \"Primary human hepatocytes and hepatocyte-derived cell lines (HepG2, MZ-Hep1); qRT-PCR; Western blot; luciferase gene reporter assays with OCT1 promoter constructs; viral transduction of transcription factors\",\n      \"journal\": \"Pharmacological reports : PR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assays and expression studies in primary hepatocytes and cell lines, multiple transcription factors tested, single lab\",\n      \"pmids\": [\"24399729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DNA methylation of the SLC22A1 promoter region is mechanistically associated with transcriptional downregulation of OCT1 in hepatocellular carcinoma; treatment with the demethylating agent 5-aza-2-deoxycytidine restores Slc22a1 expression in tumor-derived cells.\",\n      \"method\": \"MALDI-TOF mass spectrometry quantification of DNA methylation in paired HCC and non-tumor liver tissues; tissue microarray IHC; 5-aza-2-deoxycytidine and trichostatin A treatment of cultured Tsc1 renal tumor cells (corroborated in PMID:23228442)\",\n      \"journal\": \"Genome medicine / European journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative methylation analysis in human tissue with pharmacological demethylation rescue, replicated across two independent studies\",\n      \"pmids\": [\"22196450\", \"23228442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Multiple fluoroquinolones (gatifloxacin, moxifloxacin, prulifloxacin, sparfloxacin) competitively inhibit hOCT1-mediated transport with Ki values of 94–250 µM; hOCT1 selectively mediates their disposition compared with hOCT2 and hOCT3, implicating hOCT1 in sinusoidal hepatic uptake of fluoroquinolones.\",\n      \"method\": \"Heterologous expression in oocyte/cell systems; competitive inhibition kinetics with Ki determination using [3H]TEA or MPP+ as model substrates\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — Ki determination via competitive inhibition assay in heterologous expression system, single lab\",\n      \"pmids\": [\"23545524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rilpivirine is transported by SLC22A1 (OCT1), showing 27% higher accumulation in SLC22A1-overexpressing KCL22 cells versus controls; rilpivirine inhibits SLC22A1 function with an IC50 of 28.5 µM and SLC22A2 with IC50 of 5.13 µM.\",\n      \"method\": \"Stable SLC22A1-expressing KCL22 cells; cellular accumulation assay; TEA uptake inhibition assay\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — transport and inhibition assay in stably transfected cells, single lab, single method for transport\",\n      \"pmids\": [\"24002095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SLC22A1 (OCT1) mediates efflux of acylcarnitines from the liver to the circulation; loss-of-function in Slc22a1 knockout mice and gain-of-function cell models with isotope tracing demonstrate that OCT1 transports acylcarnitines out of hepatocytes, and human SLC22A1 coding variants impair this acylcarnitine efflux activity in vitro.\",\n      \"method\": \"Slc22a1 knockout mice; gain-of-function cell models; targeted metabolomics; isotope tracing experiments; in vitro functional validation of human variants\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (KO mouse, gain-of-function cells, isotope tracing, metabolomics, human variant validation) across loss- and gain-of-function models\",\n      \"pmids\": [\"28942964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The -201C>G SNP (rs58812592) in the OCT1 promoter causes allele-dependent differences in USF1/2 transcription factor binding and nearly complete loss of OCT1 promoter activity for the G-allele; the -1795G>A SNP (rs6935207) shows allele-specific NF-Y binding and increased enhancer activity but no significant effect on the native OCT1 promoter or on pharmacokinetics of OCT1 substrates.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA); luciferase reporter gene assay in HepG2, Hep3B, Huh7 cells; pharmacokinetic analysis of metformin, fenoterol, sumatriptan, proguanil in healthy volunteers\",\n      \"journal\": \"Journal of personalized medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — EMSA and reporter assay with pharmacokinetic clinical validation, single lab\",\n      \"pmids\": [\"30544975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Systematic missense and deletion variant scanning of OCT1 (SLC22A1) reveals that most human variants impair function via protein misfolding rather than direct disruption of substrate binding; the first 300 amino acids (including TM1–6 and extracellular domain with a conserved stabilizing helical motif) are major determinants of folding; molecular dynamics simulations identify biophysical mechanisms for specific variant transport phenotypes.\",\n      \"method\": \"Comprehensive single-variant mutagenesis; expression and substrate uptake assays; computational modeling and molecular dynamics simulations; population database mining\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — large-scale systematic mutagenesis with functional validation and structural modeling, preprint not yet peer-reviewed\",\n      \"pmids\": [\"37333090\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"OCT1 (SLC22A1) in 3D primary human hepatocyte spheroids has a Km of ~14 µM for the fluorescent substrate ASP+; OCT1 activity is inhibited 35–52% by known inhibitors and remains stable upon activation of nuclear receptor signaling (including PXR), distinguishing OCT1 regulation from P-glycoprotein and CYP3A4 induction.\",\n      \"method\": \"3D spheroids of primary human hepatocytes; ASP+ fluorescent transport kinetics assay; known inhibitor co-incubation; global proteomics; 7-day nuclear receptor ligand exposure\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinetic measurements in physiologically relevant 3D PHH model with multiple donors and inhibitor validation, single lab\",\n      \"pmids\": [\"39068198\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Overexpression of SLC22A1 in HepG2.2.15 cells suppresses hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) expression through activation of the JAK/STAT signaling pathway, as confirmed by transcriptome sequencing and targeted overexpression experiments.\",\n      \"method\": \"SLC22A1 overexpression in HepG2.2.15 cells; ELISA for HBsAg and HBeAg; RNA sequencing; immunohistochemistry\",\n      \"journal\": \"The Journal of infectious diseases\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — overexpression with signaling pathway readout, single lab, mechanistic pathway proposed but upstream/downstream connections not fully reconstituted\",\n      \"pmids\": [\"40036258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The SLC22A1 1022C>T variant (rs2282143) reduces OCT1-mediated hepatic uptake of proguanil; CT heterozygotes showed 1.2-fold higher proguanil systemic exposure and 0.5-fold lower cycloguanil exposure compared to wild-type CC, with population PK modeling estimating 0.42-fold reduced OCT1 activity in CT carriers.\",\n      \"method\": \"Clinical pharmacokinetic study in Korean subjects; population PK modeling with well-stirred liver compartment; prospective SLC22A1 genotyping\",\n      \"journal\": \"Clinical and translational science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clinical pharmacokinetic data with mechanistic PK modeling establishing hepatic uptake role, single study with small sample\",\n      \"pmids\": [\"39668580\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC22A1 encodes OCT1, a polyspecific electrogenic transporter localized to the basolateral membrane of hepatocytes that mediates facilitated uptake of diverse organic cations (including metformin, sorafenib, acylcarnitines, cisplatin, berberine, ranitidine, and many drugs) into liver, intestine, and other epithelia; its expression is transcriptionally controlled by USF1/USF2 binding to a core promoter E-box, with upregulation by HNF4α, GR/HNF4α, and PPAR-α/γ pathways and downregulation by PXR through SRC-1 coactivator squelching from HNF4α/USF elements; epigenetic silencing via DNA methylation suppresses OCT1 in hepatocellular carcinoma; loss-of-function coding variants primarily impair protein folding rather than substrate binding, and a subset abolish membrane targeting or transport activity, collectively explaining inter-individual pharmacokinetic variability for numerous OCT1 substrate drugs.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SLC22A1 encodes OCT1, a polyspecific, electrogenic organic cation transporter localized to the basolateral membrane of hepatocytes, where it mediates facilitated uptake of diverse organic cations into the liver and contributes to intestinal secretion [#0, #8]. By providing the basolateral entry step, OCT1 enables vectorial transcellular cation secretion: in epithelial cells co-expressing OCT1 (basolateral) and apical efflux transporters, substrates such as berberine undergo directional transport across the cell [#6]. Its substrate range encompasses model cations (TEA, MPP+) and numerous drugs, including ranitidine and famotidine, cisplatin, the survivin suppressant YM155, sorafenib, and fluoroquinolones, with the transporter also exporting endogenous acylcarnitines from hepatocytes to the circulation [#4, #5, #9, #11, #15, #17]. Only the full-length isoform is transport-competent, with shorter alternatively spliced variants being non-functional [#2]. Basal hepatic expression is driven by USF1/USF2 binding a core-promoter E-box and is amplified by HNF4\\u03b1, glucocorticoid receptor signaling, and PPAR-\\u03b1/\\u03b3 agonists, while PXR activation represses OCT1 by squelching the SRC-1 coactivator from HNF4\\u03b1 and USF elements, and promoter DNA methylation silences OCT1 in hepatocellular carcinoma [#7, #10, #12, #13, #14]. Loss-of-function arises through two routes: coding variants that abolish transport while remaining membrane-resident (e.g., P283L, R287G) or that prevent membrane targeting (truncating R61S fs*10, C88A fs*16), with systematic variant scanning showing most human variants impair function through protein misfolding rather than disrupted substrate binding; promoter SNPs additionally alter transcription-factor binding and expression, collectively explaining inter-individual pharmacokinetic variability for OCT1 substrate drugs [#3, #11, #19, #18, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing the genomic locus and exon structure of SLC22A1 anchored the gene and revealed that alternative splicing generates multiple transcripts, only one of which is functional.\",\n      \"evidence\": \"FISH chromosomal mapping to 6q26 and cDNA cloning with isoform transport assays in HEK293 cells\",\n      \"pmids\": [\"9605850\", \"11388889\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of non-functional splice variants unresolved\", \"Tissue distribution of isoforms not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"In vivo knockout addressed whether OCT1 is physiologically required for hepatic cation handling, establishing it as the basolateral uptake transporter into liver and a contributor to intestinal secretion.\",\n      \"evidence\": \"Oct1 knockout mouse with TEA tissue distribution and excretion measurements across multiple cation substrates\",\n      \"pmids\": [\"11463829\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Driving force / electrogenicity not directly measured in this study\", \"Human tissue localization not yet confirmed at this point\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Variant-specific mutagenesis resolved whether loss-of-function variants act on transport catalysis or membrane delivery, showing some abolish transport while remaining membrane-resident.\",\n      \"evidence\": \"Xenopus oocyte uptake of TEA and MPP+ with Western blot for membrane expression across coding variants\",\n      \"pmids\": [\"14697261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of transport loss not defined\", \"Allele frequencies and clinical impact not assessed here\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Promoter dissection identified a transcriptional input regulating OCT1, showing PPAR-\\u03b1/\\u03b3 agonists upregulate the gene via a PPAR-response element and increase hepatocyte cation uptake.\",\n      \"evidence\": \"Mouse in vivo and H35 cell PPAR-agonist treatment with promoter-reporter assays and functional uptake\",\n      \"pmids\": [\"15458920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Shown in murine Slc22a1; human promoter element not directly tested\", \"Endogenous ligand context unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Quantitative human liver analysis connected a coding variant to expression, establishing that Arg61Cys reduces OCT1 protein in vivo and confirming basolateral localization in human hepatocytes.\",\n      \"evidence\": \"Immunofluorescence and quantitative protein analysis in 150 human livers with MALDI-TOF genotyping and transport assays\",\n      \"pmids\": [\"19591196\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which R61C lowers protein (folding vs. stability) not defined here\", \"Substrate-specific consequences not enumerated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying USF1/USF2 binding to a core-promoter E-box defined the basal transcriptional driver of OCT1 and its synergy with HNF4\\u03b1.\",\n      \"evidence\": \"Promoter deletion, luciferase reporters, EMSA, and E-box mutagenesis in Huh7 and HepG2 cells\",\n      \"pmids\": [\"18845576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genetic variation in the E-box not yet examined\", \"Chromatin-level regulation not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Mechanistic regulation studies established a bidirectional transcriptional network: GR/HNF4\\u03b1 and C/EBP\\u03b2/PGC1\\u03b1 upregulate OCT1 while PXR represses it by coactivator squelching, and promoter methylation silences it in HCC.\",\n      \"evidence\": \"Primary human hepatocytes and cell lines with reporter assays, ChIP, siRNA, SRC-1 rescue, demethylation rescue, and transport assays\",\n      \"pmids\": [\"26920453\", \"24399729\", \"22196450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative integration of competing inputs in vivo not resolved\", \"Methylation triggers in HCC undefined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Substrate and inhibitor profiling expanded OCT1's pharmacological scope, establishing it as the hepatic sinusoidal uptake step for sorafenib, fluoroquinolones, rilpivirine, and additional drugs, and defining truncating variants that prevent membrane targeting.\",\n      \"evidence\": \"Heterologous expression (oocytes, HEK293, KCL22) with uptake, inhibition kinetics, HPLC-MS/MS, and membrane localization across substrates and variants\",\n      \"pmids\": [\"23532667\", \"23545524\", \"24002095\", \"16141367\", \"16914559\", \"19833842\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo contribution versus other OCTs/MATEs not quantified for all substrates\", \"Substrate recognition determinants not structurally mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Metabolomic and genetic analysis identified an endogenous physiological role, showing OCT1 effluxes acylcarnitines from liver to circulation and that human variants impair this activity.\",\n      \"evidence\": \"Slc22a1 knockout mice, gain-of-function cells, isotope tracing, targeted metabolomics, and human variant validation\",\n      \"pmids\": [\"28942964\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direction (efflux) mechanism relative to cation uptake not reconciled\", \"Clinical metabolic consequences in humans not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Promoter SNP characterization linked regulatory variation to function, showing -201C>G abolishes USF-dependent promoter activity while -1795G>A has no native effect.\",\n      \"evidence\": \"EMSA, luciferase reporters in HepG2/Hep3B/Huh7, and pharmacokinetic study of OCT1 substrates in volunteers\",\n      \"pmids\": [\"30544975\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo expression impact of -201C>G not directly measured\", \"Population frequency and clinical penetrance unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Systematic variant scanning resolved the dominant molecular mechanism of loss-of-function, showing most variants act through protein misfolding and identifying the N-terminal folding determinant region.\",\n      \"evidence\": \"Comprehensive single-variant mutagenesis with uptake assays, molecular dynamics, and population database mining (preprint)\",\n      \"pmids\": [\"37333090\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not yet peer-reviewed\", \"No experimental structure underpinning the folding model\", \"Folding chaperone partners unidentified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Physiological-model and clinical studies refined OCT1 kinetics and regulation, showing stable activity under nuclear-receptor activation in human hepatocyte spheroids and confirming a coding variant reduces hepatic uptake of proguanil clinically.\",\n      \"evidence\": \"3D primary human hepatocyte spheroid ASP+ kinetics with inhibitor and nuclear-receptor exposure, plus a clinical PK study with population modeling\",\n      \"pmids\": [\"39068198\", \"39668580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Discrepancy with PXR repression seen in 2D hepatocytes not reconciled\", \"Small clinical cohort for proguanil variant\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"An overexpression study proposed a non-transport role, linking SLC22A1 to suppression of hepatitis B antigens via JAK/STAT signaling.\",\n      \"evidence\": \"SLC22A1 overexpression in HepG2.2.15 cells with antigen ELISA, RNA-seq, and IHC\",\n      \"pmids\": [\"40036258\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanism connecting a transporter to JAK/STAT not reconstituted\", \"Single overexpression system without loss-of-function confirmation\", \"Whether effect depends on transport activity unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How OCT1's transport mechanism (substrate recognition, electrogenicity, and direction-switching between cation uptake and acylcarnitine efflux) is structurally encoded remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimentally determined structure in the corpus\", \"Conformational cycle and ion-coupling not defined\", \"Structural basis for polyspecificity unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 6, 9, 11, 15, 16, 17]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 8, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 6, 17]},\n      {\"term_id\": \"R-HSA-9748784\", \"supporting_discovery_ids\": [4, 5, 11, 15, 22]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7, 10, 12, 13, 14, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"USF1\", \"USF2\", \"HNF4A\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}