{"gene":"NR1I2","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":1998,"finding":"SXR (NR1I2) is a novel nuclear receptor that activates transcription in response to a diversity of natural and synthetic compounds by forming a heterodimer with RXR, which binds to response elements present in steroid-inducible cytochrome P-450 genes; it is expressed in tissues where CYP catabolic enzymes are expressed.","method":"Receptor cloning, transient transfection reporter assays, heterodimer binding assays, tissue expression analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 — original discovery paper with multiple orthogonal methods, >700 citations, replicated widely","pmids":["9784494"],"is_preprint":false},{"year":2000,"finding":"Targeted disruption of the mouse PXR (NR1I2 ortholog) gene abolishes induction of CYP3A by prototypic inducers (dexamethasone, PCN), and transgenic expression of activated SXR constitutively upregulates CYP3A and confers xenobiotic protection; species origin of the receptor determines species-specific CYP3A inducibility.","method":"PXR knockout mice, transgenic humanized mice, pharmacokinetic and gene expression studies","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — genetic KO and transgenic rescue with clear phenotypic readout, >500 citations","pmids":["10935643"],"is_preprint":false},{"year":2001,"finding":"SXR/PXR (NR1I2) serves as a functional bile acid receptor; activation is necessary and sufficient to induce CYP3A enzymes and confer resistance to hepatotoxic lithocholic acid (LCA); established using knockout and transgenic animal combinations.","method":"Cell-based activation assays, knockout mice, transgenic mice, toxicity rescue experiments","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic KO plus transgenic rescue with defined mechanistic readout, >600 citations","pmids":["11248086"],"is_preprint":false},{"year":2001,"finding":"SXR (NR1I2) regulates drug efflux by activating MDR1 (P-glycoprotein/ABCB1) expression in addition to CYP3A4; paclitaxel activates SXR and enhances P-glycoprotein-mediated drug clearance, while docetaxel does not activate SXR due to its inability to displace transcriptional corepressors; ET-743 suppresses MDR1 transcription by acting as an SXR inhibitor.","method":"Reporter gene assays, corepressor displacement assays, pharmacokinetic studies","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal mechanistic assays, >700 citations","pmids":["11329060"],"is_preprint":false},{"year":2000,"finding":"SXR/PXR (NR1I2) can regulate CYP2B via adaptive recognition of the phenobarbital response element (PBRE) in cultured cells and transgenic mice; conversely, CAR activates CYP3A through SXR/PXR response elements, revealing reciprocal cross-regulation between these xenobiotic receptors.","method":"Transfection reporter assays in cultured cells, transgenic mouse gene expression studies","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — cell-based and in vivo genetic experiments with defined mechanistic readout, >390 citations","pmids":["11114890"],"is_preprint":false},{"year":2003,"finding":"HNF4α is critically required for PXR- and CAR-mediated transcriptional activation of CYP3A4; a specific cis-acting element in the CYP3A4 enhancer confers HNF4α binding enabling PXR/CAR-mediated gene activation; conditional deletion of Hnf4α in mice reduces basal and inducible CYP3A expression.","method":"Reporter assays identifying HNF4α binding element, conditional knockout mice, ChIP","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1–2 — promoter element mapping, genetic KO, and ChIP; >370 citations","pmids":["12514743"],"is_preprint":false},{"year":2003,"finding":"Vitamin K2 binds to and activates SXR (NR1I2) and induces expression of the SXR target gene CYP3A4; vitamin K2 induces osteoblast markers through SXR in osteosarcoma cells, an effect absent in cells from PXR-null mice, establishing SXR as a mediator of bone homeostasis.","method":"Ligand-binding assays, reporter gene assays, qRT-PCR, primary osteocytes from PXR knockout mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — binding assay plus genetic KO validation with defined phenotype, >290 citations","pmids":["12920130"],"is_preprint":false},{"year":2010,"finding":"Genome-wide ChIP-Seq of hepatic PXR binding in mouse liver revealed that the most frequent PXR DNA-binding motif is an AGTTCA-like direct repeat with a 4 bp spacer (DR-4) and a novel DR-(5n+4) pattern; PXR binding overlaps with histone-H3K4-di-methylation (active gene mark) but not with repressive marks; PXR agonist increases PXR binding at drug-metabolizing enzyme and transporter gene loci, and mRNA induction is absent in PXR-null mice.","method":"ChIP-Seq, ChIP-on-chip for histone marks and DNA methylation, PXR-null mouse comparison","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide in vivo binding mapped with genetic null validation","pmids":["20693526"],"is_preprint":false},{"year":2006,"finding":"PXR (NR1I2) induces CYP27A1 in intestinal (but not liver) cells via a functional PXR binding site in the CYP27A1 gene; rifampicin-activated PXR recruits steroid receptor coactivator 1 (SRC-1) to CYP27A1 chromatin, demonstrated by ChIP; this creates an intestine-specific PXR/CYP27A1/LXRα pathway regulating cholesterol efflux.","method":"Reporter gene assays with PXR binding site mutation, ChIP assay, CYP27A1 mRNA/protein quantification","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 — binding site identification, ChIP demonstrating coactivator recruitment, and functional metabolite measurement","pmids":["17088262"],"is_preprint":false},{"year":2016,"finding":"PXR (NR1I2) undergoes acetylation on lysine residues; increased acetylation stimulates SUMOylation of PXR to support active transcriptional suppression (SUMO-acetyl switch); pharmacologic inhibition of de-acetylation with TSA alters subcellular localization of PXR and suppresses its transactivation capacity; PXR associates with the HDAC3/SMRT complex that controls its acetylation/SUMOylation status.","method":"Cell-based assays with primary hepatocytes, PTM identification, TSA pharmacologic inhibition, co-immunoprecipitation of HDAC3/SMRT complex, subcellular localization imaging","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — multiple PTM methods with functional validation and localization consequence","pmids":["26883953"],"is_preprint":false},{"year":2011,"finding":"Metformin suppresses PXR (NR1I2)-mediated CYP3A4 expression in human hepatocytes and in vivo in wild-type but not Pxr-null mice; the mechanism involves disruption of PXR's interaction with the coactivator steroid receptor coactivator-1 (SRC1), independent of the PXR ligand binding pocket and independently of AMPK or SHP.","method":"Reporter gene assays, qRT-PCR in human hepatocytes and Pxr-null mice, two-hybrid coactivator interaction assay","journal":"Biochemical pharmacology","confidence":"High","confidence_rationale":"Tier 2 — genetic null mouse validation plus mechanistic coactivator interaction assay","pmids":["21920351"],"is_preprint":false},{"year":2009,"finding":"Activation of SXR (NR1I2) inhibits proliferation of breast cancer cells (MCF-7, ZR-75-1) through G1/S arrest and apoptosis; the mechanism requires SXR-dependent induction of iNOS and NO production, which stabilizes p53 and upregulates p21, PUMA, and BAX; siRNA knockdown of SXR abolished iNOS induction.","method":"siRNA knockdown, cell proliferation assays, qRT-PCR, western blotting, iNOS inhibition experiments","journal":"BMC cancer","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA validation with pathway epistasis established, single lab","pmids":["19123943"],"is_preprint":false},{"year":2004,"finding":"Highly chlorinated PCBs antagonize human SXR (NR1I2) while activating rodent PXR, inhibiting target gene induction in humans; this differential effect is species-specific and suggests that PCB exposure can blunt the human xenobiotic detoxification response.","method":"Reporter gene activation assays, ligand-binding competition assays, species-comparative cell-based assays","journal":"Environmental health perspectives","confidence":"Medium","confidence_rationale":"Tier 3 — cell-based assays with species comparison, single lab","pmids":["14754570"],"is_preprint":false},{"year":2000,"finding":"PXR (NR1I2) binds as a heterodimer with RXR to xenobiotic response elements in CYP3A gene promoters and is selectively expressed in liver and intestine, the same tissues in which CYP3A gene expression is induced; species-specific activation by rifampicin vs. PCN correlates with species-specific CYP3A induction.","method":"Cloning, electrophoretic mobility shift assays (EMSA), reporter gene assays, pharmacokinetic studies","journal":"Toxicology","confidence":"High","confidence_rationale":"Tier 2 — DNA binding and reporter assays with species-specificity mechanistic demonstration, widely replicated","pmids":["11090943"],"is_preprint":false},{"year":2021,"finding":"PXR (NR1I2) activation impairs hepatic glucose metabolism by inhibiting the HNF4α–GLUT2 pathway; PXR overexpression downregulates HNF4α and GLUT2, reducing glucose uptake; silencing PXR or overexpressing HNF4α reverses this effect; liver-specific Hnf4α deletion combined with PCN-activated PXR impairs glucose tolerance and hepatic glucose uptake in mice.","method":"PXR overexpression/silencing, HNF4α overexpression/silencing, promoter activity assays, ChIP for HNF4α recruitment, liver-specific Hnf4α knockout mice","journal":"Acta pharmaceutica Sinica. B","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal genetic methods with in vivo validation","pmids":["35646519"],"is_preprint":false},{"year":2016,"finding":"PXR transcript variant 1 (PXR1) interacts with p53, whereas transcript variant 3 (PXR3) does not; PXR1 and PXR4 mRNA are downregulated by methylation in cancerous tissue; PXR transcript variants have differential transcriptional activity and differential effects on cellular proliferation.","method":"Protein-protein interaction assays, methylation analysis, ectopic overexpression, transcriptional activity assays","journal":"Acta pharmaceutica Sinica. B","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, moderate mechanistic follow-up on isoform-specific interactions","pmids":["27709012"],"is_preprint":false},{"year":2013,"finding":"PXR (NR1I2) is modified by acetylation on lysine residues, phosphorylation, SUMOylation, and ubiquitination as post-translational modifications; these PTMs modulate PXR activity, sub-cellular localization, protein-binding partners, and stability in hepatic regulation of CYP genes.","method":"Review synthesizing PTM identification via mass spectrometry, mutagenesis, and biochemical assays from multiple studies","journal":"Current drug metabolism","confidence":"Medium","confidence_rationale":"Tier 3 — review synthesizing multiple PTM findings; individual experiments referenced are Tier 2","pmids":["24329114"],"is_preprint":false},{"year":2022,"finding":"Panaxytriol upregulates CYP3A4 by promoting PXR dissociation from HSP90α and enhancing PXR binding to RXRα; at high concentrations, CAR also participates via a similar HSP90α-to-RXRα switch; CAR antagonizes PXR binding to RXRα and attenuates panaxytriol-induced CYP3A4 upregulation.","method":"Co-immunoprecipitation, western blot, qPCR, immunofluorescence nuclear translocation, hCAR silencing in HepG2 cells","journal":"Phytomedicine : international journal of phytotherapy and phytopharmacology","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP and siRNA knockdown with nuclear translocation readout, single lab","pmids":["35417848"],"is_preprint":false},{"year":2006,"finding":"Retinoids activate the RXR/SXR (NR1I2)-mediated pathway and induce endogenous CYP3A4 enzyme activity in human hepatoma Huh7 cells; acid-form retinoids (9-cis-RA, 13-cis-RA, all-trans-RA) activate this pathway with potency comparable to or greater than rifampin; RXR may serve as a silent or active partner of SXR depending on the ligand.","method":"Transient transfection reporter assays in CV-1 and Huh7 cells using ER-6 response elements, CYP3A4 enzyme activity assays","journal":"Toxicological sciences : an official journal of the Society of Toxicology","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based reporter and enzyme activity assays, single lab","pmids":["16632523"],"is_preprint":false},{"year":2016,"finding":"Human PXR (NR1I2) promotes Mycobacterium tuberculosis survival inside macrophages by enhancing foamy macrophage formation and abrogating phagolysosomal fusion, inflammation, and apoptosis; mycobacterial cell wall lipids (mycolic acids) interact with the PXR ligand binding domain; expression of human PXR in transgenic mice promotes M. tuberculosis survival in vivo.","method":"Human monocyte-derived macrophage infection assays, ligand-binding domain interaction studies, hPXR-transgenic mice in vivo infection model","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 — LBD binding plus in vivo transgenic mouse model validation, single lab","pmids":["27233963"],"is_preprint":false},{"year":2015,"finding":"RXRα/PXR (NR1I2)/CAR signaling pathways mediate nonylphenol-induced apoptosis and neurotoxicity in mouse hippocampal neurons; siRNA knockdown of Pxr reduced nonylphenol-induced caspase-3 activation and LDH release; nonylphenol induced nuclear translocation of PXR in neurons.","method":"siRNA knockdown, immunofluorescence, caspase-3 and LDH assays in primary hippocampal neuronal cultures","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with phenotypic rescue and localization data, single lab","pmids":["26643981"],"is_preprint":false},{"year":2010,"finding":"Vinblastine induces CYP3A4 via an NR1I2 (PXR)-dependent mechanism; cell-based reporter gene assays showed weak activation of human and mouse full-length NR1I2 but no effect on NR1I3 (CAR); CYP3A4 protein induction was confirmed by western blot in treated cells, and midazolam clearance increased in cancer patients treated with vinblastine.","method":"Clinical pharmacokinetic study, western blot, reporter gene assays in HepG2 and NIH3T3 cells","journal":"The Annals of pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 2 — clinical plus in vitro mechanistic evidence, receptor-selectivity established","pmids":["20959500"],"is_preprint":false},{"year":2016,"finding":"Acetylated deoxycholic acid (DCA 3,12-diacetate) and cholic acid (CA 3,7,12-triacetate) are potent ligands of PXR (NR1I2); DCA 3,12-diacetate induces PXR target genes CYP3A4, CYP2B6, and ABCB1/MDR1, established by TR-FRET binding assay and reporter gene assays.","method":"Reporter gene assays in HepG2 cells, TR-FRET ligand-binding assay with recombinant PXR, RT-PCR of target genes in HepaRG cells","journal":"Toxicology letters","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding assay plus functional reporter and target gene assays, single lab","pmids":["27871908"],"is_preprint":false}],"current_model":"NR1I2 (PXR/SXR) is a ligand-activated nuclear receptor that, upon binding a broad range of steroids, bile acids, dietary compounds, and xenobiotics, heterodimerizes with RXR and binds to DR-3, DR-4, and ER-6 response elements in target gene promoters/enhancers to transcriptionally induce CYP3A4, CYP2B6, MDR1/ABCB1, and other phase I/II drug-metabolizing enzymes and transporters; its activity is further modulated by coactivator recruitment (e.g., SRC-1), corepressor displacement, and post-translational modifications including acetylation, SUMOylation, phosphorylation, and ubiquitination, with acetylation promoting SUMOylation via an HDAC3/SMRT complex to actively suppress target gene expression."},"narrative":{"teleology":[{"year":1998,"claim":"The cloning of SXR/PXR established the existence of a nuclear receptor that could respond to structurally diverse xenobiotics and steroids and explained how CYP3A genes are coordinately induced in liver and intestine.","evidence":"Receptor cloning, transient transfection reporter assays with heterodimer binding, tissue expression profiling","pmids":["9784494"],"confidence":"High","gaps":["Crystal structure of the ligand-binding domain was not yet available","In vivo necessity not yet demonstrated genetically"]},{"year":2000,"claim":"Genetic loss-of-function (PXR knockout) and gain-of-function (humanized SXR transgenic) mouse models proved that NR1I2 is necessary and sufficient for CYP3A induction in vivo, and that the receptor's species origin dictates species-specific drug induction profiles.","evidence":"PXR-null mice, constitutively activated human SXR transgenic mice, pharmacokinetic and gene expression analysis","pmids":["10935643","11090943"],"confidence":"High","gaps":["Mechanism of species-specific ligand selectivity at the structural level was unclear","Full spectrum of endogenous ligands unknown"]},{"year":2001,"claim":"Discovery that NR1I2 functions as an endogenous bile acid sensor and that it regulates drug efflux transporter MDR1/ABCB1 broadened its role from a xenobiotic receptor to a coordinator of both phase I metabolism and phase III efflux, and established corepressor displacement as a mechanism gating target gene activation.","evidence":"Bile acid activation assays, lithocholic acid hepatotoxicity rescue in PXR-null/transgenic mice, corepressor displacement assays for MDR1 activation","pmids":["11248086","11329060","11114890"],"confidence":"High","gaps":["Relative contribution of PXR vs. FXR in bile acid homeostasis not fully delineated","Corepressor identity at MDR1 not fully characterized"]},{"year":2003,"claim":"Identification of HNF4α as an essential cooperating transcription factor at the CYP3A4 enhancer and of vitamin K2 as a physiological NR1I2 ligand that mediates bone homeostasis expanded the regulatory framework and functional scope beyond detoxification.","evidence":"CYP3A4 promoter element mapping with HNF4α ChIP, Hnf4α conditional knockout mice, vitamin K2 ligand-binding assays with PXR-null osteocyte validation","pmids":["12514743","12920130"],"confidence":"High","gaps":["Whether HNF4α is required at all NR1I2 target genes was unknown","Bone-specific NR1I2 target gene program not characterized genome-wide"]},{"year":2006,"claim":"Demonstration that NR1I2 recruits SRC-1 to CYP27A1 chromatin in intestinal cells linked PXR to cholesterol efflux via a tissue-specific PXR→CYP27A1→LXRα axis, and retinoid activation revealed that RXR can serve as an active signaling partner in the heterodimer.","evidence":"ChIP for SRC-1 at CYP27A1, reporter assays with PXR binding-site mutation, retinoid-mediated reporter activation and CYP3A4 enzyme assays","pmids":["17088262","16632523"],"confidence":"High","gaps":["In vivo contribution of this intestinal cholesterol pathway not tested by genetic ablation","Structural basis for permissive vs. silent RXR partnering with PXR unresolved"]},{"year":2010,"claim":"Genome-wide ChIP-Seq of hepatic PXR binding defined DR-4 as the dominant binding motif, discovered a novel DR-(5n+4) motif, and showed PXR occupancy correlates with active histone marks, providing the first cistromic map of this receptor.","evidence":"ChIP-Seq and ChIP-on-chip for histone marks in mouse liver, PXR-null mouse comparison, agonist treatment","pmids":["20693526"],"confidence":"High","gaps":["Human liver cistrome not yet mapped","Mechanism of chromatin remodeling by PXR not addressed"]},{"year":2011,"claim":"Metformin was shown to suppress PXR-mediated CYP3A4 expression by disrupting the PXR–SRC-1 coactivator interaction without competing at the ligand-binding pocket, establishing a ligand-independent mechanism of PXR inhibition.","evidence":"Two-hybrid coactivator assay, qRT-PCR in human hepatocytes, PXR-null mouse validation","pmids":["21920351"],"confidence":"High","gaps":["Direct binding site of metformin on PXR not mapped","Clinical relevance for drug–drug interactions via PXR suppression not established in controlled trials"]},{"year":2016,"claim":"Characterization of PXR post-translational modifications revealed an acetylation–SUMOylation switch controlled by the HDAC3/SMRT complex that converts PXR from activator to active repressor, and mycobacterial lipid activation of PXR was found to promote intracellular M. tuberculosis survival by blocking phagolysosomal fusion.","evidence":"PTM identification, TSA pharmacologic inhibition, co-IP of HDAC3/SMRT, hPXR-transgenic mouse M. tuberculosis infection model, macrophage infection assays","pmids":["26883953","27233963"],"confidence":"High","gaps":["Specific lysine residues governing the SUMO-acetyl switch were not all mapped","Whether PXR-mediated immune evasion extends to other intracellular pathogens is unknown","In vivo relevance of PXR SUMOylation to drug metabolism phenotype untested"]},{"year":2021,"claim":"PXR activation was shown to impair hepatic glucose homeostasis by down-regulating HNF4α and GLUT2, establishing a PXR–HNF4α negative regulatory loop with metabolic consequences beyond xenobiotic handling.","evidence":"PXR overexpression/silencing, HNF4α ChIP, liver-specific Hnf4α knockout mice with PXR agonist treatment, glucose tolerance tests","pmids":["35646519"],"confidence":"High","gaps":["Molecular mechanism by which PXR down-regulates HNF4α expression not fully defined","Long-term metabolic consequences of chronic PXR activation in humans not established"]},{"year":null,"claim":"A comprehensive human liver and intestine cistrome for NR1I2, the structural basis for its uniquely promiscuous ligand recognition, and the quantitative contribution of each PTM to NR1I2 activity in physiological contexts remain to be established.","evidence":"","pmids":[],"confidence":"Low","gaps":["Human tissue-specific NR1I2 cistrome not mapped","No integrated structural–dynamics model explaining the breadth of ligand recognition","Relative in vivo importance of acetylation, SUMOylation, phosphorylation, and ubiquitination is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,3,4,5,7,8]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,7,13]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2,6,19,22]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,7,9,17,20]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,3,4,5,7,8]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,6,8,14,22]},{"term_id":"R-HSA-9748784","term_label":"Drug ADME","supporting_discovery_ids":[1,3,21]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,11,14]}],"complexes":["PXR/RXR heterodimer","HDAC3/SMRT corepressor complex"],"partners":["RXRA","NCOA1","NCOR2","HDAC3","HNF4A","TP53","HSP90AA1","NR1I3"],"other_free_text":[]},"mechanistic_narrative":"NR1I2 (PXR/SXR) is a ligand-activated nuclear receptor that serves as a master regulator of xenobiotic and endobiotic detoxification, coordinating the transcriptional induction of phase I/II drug-metabolizing enzymes and efflux transporters in liver and intestine. Upon binding a structurally diverse array of ligands—including steroids, bile acids, vitamin K2, retinoids, and xenobiotics—NR1I2 heterodimerizes with RXR and binds DR-4 and related response elements in target gene promoters to activate CYP3A4, CYP2B6, MDR1/ABCB1, and CYP27A1, with coactivator SRC-1 recruitment required for full transactivation and HNF4α acting as an essential cooperating factor at CYP3A4 [PMID:9784494, PMID:10935643, PMID:11248086, PMID:11329060, PMID:12514743, PMID:17088262]. NR1I2 activity is further tuned by post-translational modifications including acetylation, SUMOylation, phosphorylation, and ubiquitination, wherein an acetylation-dependent SUMO switch mediated by the HDAC3/SMRT complex converts NR1I2 from a transcriptional activator to a repressor [PMID:26883953]. Beyond drug metabolism, NR1I2 modulates hepatic glucose homeostasis by repressing the HNF4α–GLUT2 axis, influences cholesterol efflux through an intestine-specific CYP27A1/LXRα pathway, and affects innate immune responses by promoting foamy macrophage formation during mycobacterial infection [PMID:35646519, PMID:17088262, PMID:27233963]."},"prefetch_data":{"uniprot":{"accession":"O75469","full_name":"Nuclear receptor subfamily 1 group I member 2","aliases":["Orphan nuclear receptor PAR1","Orphan nuclear receptor PXR","Pregnane X receptor","Steroid and xenobiotic receptor","SXR"],"length_aa":434,"mass_kda":49.8,"function":"Nuclear receptor that acts as a transcription factor regulating genes involved in the metabolism and excretion of xenobiotics, drugs, and endogenous compounds. Activated by a broad range of endogenous steroids (e.g. pregnenolone, progesterone) and xenobiotics, including the antibiotic rifampicin and certain plant-derived metabolites. Upon ligand binding, translocates to the nucleus, forms a heterodimer with the retinoid X receptor/RXR, and binds to response elements in target promoters, leading to transcriptional activation. Target genes include cytochrome P450 enzymes such as CYP3A4 and ATP-binding cassette transporters including ABCB1/MDR1","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/O75469/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NR1I2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NR1I2","total_profiled":1310},"omim":[{"mim_id":"607623","title":"NPC INTRACELLULAR CHOLESTEROL TRANSPORTER 1; NPC1","url":"https://www.omim.org/entry/607623"},{"mim_id":"604843","title":"SOLUTE CARRIER ORGANIC ANION TRANSPORTER FAMILY, MEMBER 1B1; SLCO1B1","url":"https://www.omim.org/entry/604843"},{"mim_id":"603826","title":"NUCLEAR RECEPTOR SUBFAMILY 1, GROUP H, MEMBER 4; NR1H4","url":"https://www.omim.org/entry/603826"},{"mim_id":"603065","title":"NUCLEAR RECEPTOR SUBFAMILY 1, GROUP I, MEMBER 2; NR1I2","url":"https://www.omim.org/entry/603065"},{"mim_id":"600338","title":"ARYLACETAMIDE DEACETYLASE; AADAC","url":"https://www.omim.org/entry/600338"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"intestine","ntpm":29.4},{"tissue":"liver","ntpm":44.3}],"url":"https://www.proteinatlas.org/search/NR1I2"},"hgnc":{"alias_symbol":["ONR1","PXR","BXR","SXR","PAR2"],"prev_symbol":[]},"alphafold":{"accession":"O75469","domains":[{"cath_id":"3.30.50.10","chopping":"51-125","consensus_level":"high","plddt":91.7448,"start":51,"end":125},{"cath_id":"1.10.565.10","chopping":"146-175_193-209_235-296_313-430","consensus_level":"high","plddt":95.3365,"start":146,"end":430}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75469","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75469-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75469-F1-predicted_aligned_error_v6.png","plddt_mean":85.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NR1I2","jax_strain_url":"https://www.jax.org/strain/search?query=NR1I2"},"sequence":{"accession":"O75469","fasta_url":"https://rest.uniprot.org/uniprotkb/O75469.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75469/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75469"}},"corpus_meta":[{"pmid":"9784494","id":"PMC_9784494","title":"SXR, a novel steroid and xenobiotic-sensing nuclear receptor.","date":"1998","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/9784494","citation_count":783,"is_preprint":false},{"pmid":"11329060","id":"PMC_11329060","title":"The orphan nuclear receptor SXR coordinately regulates drug metabolism and efflux.","date":"2001","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/11329060","citation_count":705,"is_preprint":false},{"pmid":"11248086","id":"PMC_11248086","title":"An essential role for nuclear receptors SXR/PXR in detoxification of cholestatic bile acids.","date":"2001","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/11248086","citation_count":616,"is_preprint":false},{"pmid":"10935643","id":"PMC_10935643","title":"Humanized xenobiotic response in mice expressing nuclear receptor 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phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35417848","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":44734,"output_tokens":5498,"usd":0.108336},"stage2":{"model":"claude-opus-4-6","input_tokens":9137,"output_tokens":2905,"usd":0.177465},"total_usd":0.285801,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"SXR (NR1I2) is a novel nuclear receptor that activates transcription in response to a diversity of natural and synthetic compounds by forming a heterodimer with RXR, which binds to response elements present in steroid-inducible cytochrome P-450 genes; it is expressed in tissues where CYP catabolic enzymes are expressed.\",\n      \"method\": \"Receptor cloning, transient transfection reporter assays, heterodimer binding assays, tissue expression analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — original discovery paper with multiple orthogonal methods, >700 citations, replicated widely\",\n      \"pmids\": [\"9784494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Targeted disruption of the mouse PXR (NR1I2 ortholog) gene abolishes induction of CYP3A by prototypic inducers (dexamethasone, PCN), and transgenic expression of activated SXR constitutively upregulates CYP3A and confers xenobiotic protection; species origin of the receptor determines species-specific CYP3A inducibility.\",\n      \"method\": \"PXR knockout mice, transgenic humanized mice, pharmacokinetic and gene expression studies\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO and transgenic rescue with clear phenotypic readout, >500 citations\",\n      \"pmids\": [\"10935643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SXR/PXR (NR1I2) serves as a functional bile acid receptor; activation is necessary and sufficient to induce CYP3A enzymes and confer resistance to hepatotoxic lithocholic acid (LCA); established using knockout and transgenic animal combinations.\",\n      \"method\": \"Cell-based activation assays, knockout mice, transgenic mice, toxicity rescue experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus transgenic rescue with defined mechanistic readout, >600 citations\",\n      \"pmids\": [\"11248086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SXR (NR1I2) regulates drug efflux by activating MDR1 (P-glycoprotein/ABCB1) expression in addition to CYP3A4; paclitaxel activates SXR and enhances P-glycoprotein-mediated drug clearance, while docetaxel does not activate SXR due to its inability to displace transcriptional corepressors; ET-743 suppresses MDR1 transcription by acting as an SXR inhibitor.\",\n      \"method\": \"Reporter gene assays, corepressor displacement assays, pharmacokinetic studies\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal mechanistic assays, >700 citations\",\n      \"pmids\": [\"11329060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SXR/PXR (NR1I2) can regulate CYP2B via adaptive recognition of the phenobarbital response element (PBRE) in cultured cells and transgenic mice; conversely, CAR activates CYP3A through SXR/PXR response elements, revealing reciprocal cross-regulation between these xenobiotic receptors.\",\n      \"method\": \"Transfection reporter assays in cultured cells, transgenic mouse gene expression studies\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based and in vivo genetic experiments with defined mechanistic readout, >390 citations\",\n      \"pmids\": [\"11114890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"HNF4α is critically required for PXR- and CAR-mediated transcriptional activation of CYP3A4; a specific cis-acting element in the CYP3A4 enhancer confers HNF4α binding enabling PXR/CAR-mediated gene activation; conditional deletion of Hnf4α in mice reduces basal and inducible CYP3A expression.\",\n      \"method\": \"Reporter assays identifying HNF4α binding element, conditional knockout mice, ChIP\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — promoter element mapping, genetic KO, and ChIP; >370 citations\",\n      \"pmids\": [\"12514743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Vitamin K2 binds to and activates SXR (NR1I2) and induces expression of the SXR target gene CYP3A4; vitamin K2 induces osteoblast markers through SXR in osteosarcoma cells, an effect absent in cells from PXR-null mice, establishing SXR as a mediator of bone homeostasis.\",\n      \"method\": \"Ligand-binding assays, reporter gene assays, qRT-PCR, primary osteocytes from PXR knockout mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — binding assay plus genetic KO validation with defined phenotype, >290 citations\",\n      \"pmids\": [\"12920130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Genome-wide ChIP-Seq of hepatic PXR binding in mouse liver revealed that the most frequent PXR DNA-binding motif is an AGTTCA-like direct repeat with a 4 bp spacer (DR-4) and a novel DR-(5n+4) pattern; PXR binding overlaps with histone-H3K4-di-methylation (active gene mark) but not with repressive marks; PXR agonist increases PXR binding at drug-metabolizing enzyme and transporter gene loci, and mRNA induction is absent in PXR-null mice.\",\n      \"method\": \"ChIP-Seq, ChIP-on-chip for histone marks and DNA methylation, PXR-null mouse comparison\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide in vivo binding mapped with genetic null validation\",\n      \"pmids\": [\"20693526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PXR (NR1I2) induces CYP27A1 in intestinal (but not liver) cells via a functional PXR binding site in the CYP27A1 gene; rifampicin-activated PXR recruits steroid receptor coactivator 1 (SRC-1) to CYP27A1 chromatin, demonstrated by ChIP; this creates an intestine-specific PXR/CYP27A1/LXRα pathway regulating cholesterol efflux.\",\n      \"method\": \"Reporter gene assays with PXR binding site mutation, ChIP assay, CYP27A1 mRNA/protein quantification\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — binding site identification, ChIP demonstrating coactivator recruitment, and functional metabolite measurement\",\n      \"pmids\": [\"17088262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PXR (NR1I2) undergoes acetylation on lysine residues; increased acetylation stimulates SUMOylation of PXR to support active transcriptional suppression (SUMO-acetyl switch); pharmacologic inhibition of de-acetylation with TSA alters subcellular localization of PXR and suppresses its transactivation capacity; PXR associates with the HDAC3/SMRT complex that controls its acetylation/SUMOylation status.\",\n      \"method\": \"Cell-based assays with primary hepatocytes, PTM identification, TSA pharmacologic inhibition, co-immunoprecipitation of HDAC3/SMRT complex, subcellular localization imaging\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple PTM methods with functional validation and localization consequence\",\n      \"pmids\": [\"26883953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Metformin suppresses PXR (NR1I2)-mediated CYP3A4 expression in human hepatocytes and in vivo in wild-type but not Pxr-null mice; the mechanism involves disruption of PXR's interaction with the coactivator steroid receptor coactivator-1 (SRC1), independent of the PXR ligand binding pocket and independently of AMPK or SHP.\",\n      \"method\": \"Reporter gene assays, qRT-PCR in human hepatocytes and Pxr-null mice, two-hybrid coactivator interaction assay\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic null mouse validation plus mechanistic coactivator interaction assay\",\n      \"pmids\": [\"21920351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Activation of SXR (NR1I2) inhibits proliferation of breast cancer cells (MCF-7, ZR-75-1) through G1/S arrest and apoptosis; the mechanism requires SXR-dependent induction of iNOS and NO production, which stabilizes p53 and upregulates p21, PUMA, and BAX; siRNA knockdown of SXR abolished iNOS induction.\",\n      \"method\": \"siRNA knockdown, cell proliferation assays, qRT-PCR, western blotting, iNOS inhibition experiments\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA validation with pathway epistasis established, single lab\",\n      \"pmids\": [\"19123943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Highly chlorinated PCBs antagonize human SXR (NR1I2) while activating rodent PXR, inhibiting target gene induction in humans; this differential effect is species-specific and suggests that PCB exposure can blunt the human xenobiotic detoxification response.\",\n      \"method\": \"Reporter gene activation assays, ligand-binding competition assays, species-comparative cell-based assays\",\n      \"journal\": \"Environmental health perspectives\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cell-based assays with species comparison, single lab\",\n      \"pmids\": [\"14754570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PXR (NR1I2) binds as a heterodimer with RXR to xenobiotic response elements in CYP3A gene promoters and is selectively expressed in liver and intestine, the same tissues in which CYP3A gene expression is induced; species-specific activation by rifampicin vs. PCN correlates with species-specific CYP3A induction.\",\n      \"method\": \"Cloning, electrophoretic mobility shift assays (EMSA), reporter gene assays, pharmacokinetic studies\",\n      \"journal\": \"Toxicology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — DNA binding and reporter assays with species-specificity mechanistic demonstration, widely replicated\",\n      \"pmids\": [\"11090943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PXR (NR1I2) activation impairs hepatic glucose metabolism by inhibiting the HNF4α–GLUT2 pathway; PXR overexpression downregulates HNF4α and GLUT2, reducing glucose uptake; silencing PXR or overexpressing HNF4α reverses this effect; liver-specific Hnf4α deletion combined with PCN-activated PXR impairs glucose tolerance and hepatic glucose uptake in mice.\",\n      \"method\": \"PXR overexpression/silencing, HNF4α overexpression/silencing, promoter activity assays, ChIP for HNF4α recruitment, liver-specific Hnf4α knockout mice\",\n      \"journal\": \"Acta pharmaceutica Sinica. B\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic methods with in vivo validation\",\n      \"pmids\": [\"35646519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PXR transcript variant 1 (PXR1) interacts with p53, whereas transcript variant 3 (PXR3) does not; PXR1 and PXR4 mRNA are downregulated by methylation in cancerous tissue; PXR transcript variants have differential transcriptional activity and differential effects on cellular proliferation.\",\n      \"method\": \"Protein-protein interaction assays, methylation analysis, ectopic overexpression, transcriptional activity assays\",\n      \"journal\": \"Acta pharmaceutica Sinica. B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, moderate mechanistic follow-up on isoform-specific interactions\",\n      \"pmids\": [\"27709012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PXR (NR1I2) is modified by acetylation on lysine residues, phosphorylation, SUMOylation, and ubiquitination as post-translational modifications; these PTMs modulate PXR activity, sub-cellular localization, protein-binding partners, and stability in hepatic regulation of CYP genes.\",\n      \"method\": \"Review synthesizing PTM identification via mass spectrometry, mutagenesis, and biochemical assays from multiple studies\",\n      \"journal\": \"Current drug metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review synthesizing multiple PTM findings; individual experiments referenced are Tier 2\",\n      \"pmids\": [\"24329114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Panaxytriol upregulates CYP3A4 by promoting PXR dissociation from HSP90α and enhancing PXR binding to RXRα; at high concentrations, CAR also participates via a similar HSP90α-to-RXRα switch; CAR antagonizes PXR binding to RXRα and attenuates panaxytriol-induced CYP3A4 upregulation.\",\n      \"method\": \"Co-immunoprecipitation, western blot, qPCR, immunofluorescence nuclear translocation, hCAR silencing in HepG2 cells\",\n      \"journal\": \"Phytomedicine : international journal of phytotherapy and phytopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP and siRNA knockdown with nuclear translocation readout, single lab\",\n      \"pmids\": [\"35417848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Retinoids activate the RXR/SXR (NR1I2)-mediated pathway and induce endogenous CYP3A4 enzyme activity in human hepatoma Huh7 cells; acid-form retinoids (9-cis-RA, 13-cis-RA, all-trans-RA) activate this pathway with potency comparable to or greater than rifampin; RXR may serve as a silent or active partner of SXR depending on the ligand.\",\n      \"method\": \"Transient transfection reporter assays in CV-1 and Huh7 cells using ER-6 response elements, CYP3A4 enzyme activity assays\",\n      \"journal\": \"Toxicological sciences : an official journal of the Society of Toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based reporter and enzyme activity assays, single lab\",\n      \"pmids\": [\"16632523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Human PXR (NR1I2) promotes Mycobacterium tuberculosis survival inside macrophages by enhancing foamy macrophage formation and abrogating phagolysosomal fusion, inflammation, and apoptosis; mycobacterial cell wall lipids (mycolic acids) interact with the PXR ligand binding domain; expression of human PXR in transgenic mice promotes M. tuberculosis survival in vivo.\",\n      \"method\": \"Human monocyte-derived macrophage infection assays, ligand-binding domain interaction studies, hPXR-transgenic mice in vivo infection model\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — LBD binding plus in vivo transgenic mouse model validation, single lab\",\n      \"pmids\": [\"27233963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RXRα/PXR (NR1I2)/CAR signaling pathways mediate nonylphenol-induced apoptosis and neurotoxicity in mouse hippocampal neurons; siRNA knockdown of Pxr reduced nonylphenol-induced caspase-3 activation and LDH release; nonylphenol induced nuclear translocation of PXR in neurons.\",\n      \"method\": \"siRNA knockdown, immunofluorescence, caspase-3 and LDH assays in primary hippocampal neuronal cultures\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with phenotypic rescue and localization data, single lab\",\n      \"pmids\": [\"26643981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Vinblastine induces CYP3A4 via an NR1I2 (PXR)-dependent mechanism; cell-based reporter gene assays showed weak activation of human and mouse full-length NR1I2 but no effect on NR1I3 (CAR); CYP3A4 protein induction was confirmed by western blot in treated cells, and midazolam clearance increased in cancer patients treated with vinblastine.\",\n      \"method\": \"Clinical pharmacokinetic study, western blot, reporter gene assays in HepG2 and NIH3T3 cells\",\n      \"journal\": \"The Annals of pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clinical plus in vitro mechanistic evidence, receptor-selectivity established\",\n      \"pmids\": [\"20959500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Acetylated deoxycholic acid (DCA 3,12-diacetate) and cholic acid (CA 3,7,12-triacetate) are potent ligands of PXR (NR1I2); DCA 3,12-diacetate induces PXR target genes CYP3A4, CYP2B6, and ABCB1/MDR1, established by TR-FRET binding assay and reporter gene assays.\",\n      \"method\": \"Reporter gene assays in HepG2 cells, TR-FRET ligand-binding assay with recombinant PXR, RT-PCR of target genes in HepaRG cells\",\n      \"journal\": \"Toxicology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assay plus functional reporter and target gene assays, single lab\",\n      \"pmids\": [\"27871908\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NR1I2 (PXR/SXR) is a ligand-activated nuclear receptor that, upon binding a broad range of steroids, bile acids, dietary compounds, and xenobiotics, heterodimerizes with RXR and binds to DR-3, DR-4, and ER-6 response elements in target gene promoters/enhancers to transcriptionally induce CYP3A4, CYP2B6, MDR1/ABCB1, and other phase I/II drug-metabolizing enzymes and transporters; its activity is further modulated by coactivator recruitment (e.g., SRC-1), corepressor displacement, and post-translational modifications including acetylation, SUMOylation, phosphorylation, and ubiquitination, with acetylation promoting SUMOylation via an HDAC3/SMRT complex to actively suppress target gene expression.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NR1I2 (PXR/SXR) is a ligand-activated nuclear receptor that serves as a master regulator of xenobiotic and endobiotic detoxification, coordinating the transcriptional induction of phase I/II drug-metabolizing enzymes and efflux transporters in liver and intestine. Upon binding a structurally diverse array of ligands—including steroids, bile acids, vitamin K2, retinoids, and xenobiotics—NR1I2 heterodimerizes with RXR and binds DR-4 and related response elements in target gene promoters to activate CYP3A4, CYP2B6, MDR1/ABCB1, and CYP27A1, with coactivator SRC-1 recruitment required for full transactivation and HNF4α acting as an essential cooperating factor at CYP3A4 [PMID:9784494, PMID:10935643, PMID:11248086, PMID:11329060, PMID:12514743, PMID:17088262]. NR1I2 activity is further tuned by post-translational modifications including acetylation, SUMOylation, phosphorylation, and ubiquitination, wherein an acetylation-dependent SUMO switch mediated by the HDAC3/SMRT complex converts NR1I2 from a transcriptional activator to a repressor [PMID:26883953]. Beyond drug metabolism, NR1I2 modulates hepatic glucose homeostasis by repressing the HNF4α–GLUT2 axis, influences cholesterol efflux through an intestine-specific CYP27A1/LXRα pathway, and affects innate immune responses by promoting foamy macrophage formation during mycobacterial infection [PMID:35646519, PMID:17088262, PMID:27233963].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"The cloning of SXR/PXR established the existence of a nuclear receptor that could respond to structurally diverse xenobiotics and steroids and explained how CYP3A genes are coordinately induced in liver and intestine.\",\n      \"evidence\": \"Receptor cloning, transient transfection reporter assays with heterodimer binding, tissue expression profiling\",\n      \"pmids\": [\"9784494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of the ligand-binding domain was not yet available\", \"In vivo necessity not yet demonstrated genetically\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Genetic loss-of-function (PXR knockout) and gain-of-function (humanized SXR transgenic) mouse models proved that NR1I2 is necessary and sufficient for CYP3A induction in vivo, and that the receptor's species origin dictates species-specific drug induction profiles.\",\n      \"evidence\": \"PXR-null mice, constitutively activated human SXR transgenic mice, pharmacokinetic and gene expression analysis\",\n      \"pmids\": [\"10935643\", \"11090943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of species-specific ligand selectivity at the structural level was unclear\", \"Full spectrum of endogenous ligands unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Discovery that NR1I2 functions as an endogenous bile acid sensor and that it regulates drug efflux transporter MDR1/ABCB1 broadened its role from a xenobiotic receptor to a coordinator of both phase I metabolism and phase III efflux, and established corepressor displacement as a mechanism gating target gene activation.\",\n      \"evidence\": \"Bile acid activation assays, lithocholic acid hepatotoxicity rescue in PXR-null/transgenic mice, corepressor displacement assays for MDR1 activation\",\n      \"pmids\": [\"11248086\", \"11329060\", \"11114890\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of PXR vs. FXR in bile acid homeostasis not fully delineated\", \"Corepressor identity at MDR1 not fully characterized\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of HNF4α as an essential cooperating transcription factor at the CYP3A4 enhancer and of vitamin K2 as a physiological NR1I2 ligand that mediates bone homeostasis expanded the regulatory framework and functional scope beyond detoxification.\",\n      \"evidence\": \"CYP3A4 promoter element mapping with HNF4α ChIP, Hnf4α conditional knockout mice, vitamin K2 ligand-binding assays with PXR-null osteocyte validation\",\n      \"pmids\": [\"12514743\", \"12920130\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HNF4α is required at all NR1I2 target genes was unknown\", \"Bone-specific NR1I2 target gene program not characterized genome-wide\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstration that NR1I2 recruits SRC-1 to CYP27A1 chromatin in intestinal cells linked PXR to cholesterol efflux via a tissue-specific PXR→CYP27A1→LXRα axis, and retinoid activation revealed that RXR can serve as an active signaling partner in the heterodimer.\",\n      \"evidence\": \"ChIP for SRC-1 at CYP27A1, reporter assays with PXR binding-site mutation, retinoid-mediated reporter activation and CYP3A4 enzyme assays\",\n      \"pmids\": [\"17088262\", \"16632523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of this intestinal cholesterol pathway not tested by genetic ablation\", \"Structural basis for permissive vs. silent RXR partnering with PXR unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Genome-wide ChIP-Seq of hepatic PXR binding defined DR-4 as the dominant binding motif, discovered a novel DR-(5n+4) motif, and showed PXR occupancy correlates with active histone marks, providing the first cistromic map of this receptor.\",\n      \"evidence\": \"ChIP-Seq and ChIP-on-chip for histone marks in mouse liver, PXR-null mouse comparison, agonist treatment\",\n      \"pmids\": [\"20693526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human liver cistrome not yet mapped\", \"Mechanism of chromatin remodeling by PXR not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Metformin was shown to suppress PXR-mediated CYP3A4 expression by disrupting the PXR–SRC-1 coactivator interaction without competing at the ligand-binding pocket, establishing a ligand-independent mechanism of PXR inhibition.\",\n      \"evidence\": \"Two-hybrid coactivator assay, qRT-PCR in human hepatocytes, PXR-null mouse validation\",\n      \"pmids\": [\"21920351\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding site of metformin on PXR not mapped\", \"Clinical relevance for drug–drug interactions via PXR suppression not established in controlled trials\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Characterization of PXR post-translational modifications revealed an acetylation–SUMOylation switch controlled by the HDAC3/SMRT complex that converts PXR from activator to active repressor, and mycobacterial lipid activation of PXR was found to promote intracellular M. tuberculosis survival by blocking phagolysosomal fusion.\",\n      \"evidence\": \"PTM identification, TSA pharmacologic inhibition, co-IP of HDAC3/SMRT, hPXR-transgenic mouse M. tuberculosis infection model, macrophage infection assays\",\n      \"pmids\": [\"26883953\", \"27233963\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lysine residues governing the SUMO-acetyl switch were not all mapped\", \"Whether PXR-mediated immune evasion extends to other intracellular pathogens is unknown\", \"In vivo relevance of PXR SUMOylation to drug metabolism phenotype untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"PXR activation was shown to impair hepatic glucose homeostasis by down-regulating HNF4α and GLUT2, establishing a PXR–HNF4α negative regulatory loop with metabolic consequences beyond xenobiotic handling.\",\n      \"evidence\": \"PXR overexpression/silencing, HNF4α ChIP, liver-specific Hnf4α knockout mice with PXR agonist treatment, glucose tolerance tests\",\n      \"pmids\": [\"35646519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which PXR down-regulates HNF4α expression not fully defined\", \"Long-term metabolic consequences of chronic PXR activation in humans not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive human liver and intestine cistrome for NR1I2, the structural basis for its uniquely promiscuous ligand recognition, and the quantitative contribution of each PTM to NR1I2 activity in physiological contexts remain to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Human tissue-specific NR1I2 cistrome not mapped\", \"No integrated structural–dynamics model explaining the breadth of ligand recognition\", \"Relative in vivo importance of acetylation, SUMOylation, phosphorylation, and ubiquitination is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 7, 8]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 7, 13]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2, 6, 19, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 7, 9, 17, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 7, 8]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 6, 8, 14, 22]},\n      {\"term_id\": \"R-HSA-9748784\", \"supporting_discovery_ids\": [1, 3, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 11, 14]}\n    ],\n    \"complexes\": [\n      \"PXR/RXR heterodimer\",\n      \"HDAC3/SMRT corepressor complex\"\n    ],\n    \"partners\": [\n      \"RXRA\",\n      \"NCOA1\",\n      \"NCOR2\",\n      \"HDAC3\",\n      \"HNF4A\",\n      \"TP53\",\n      \"HSP90AA1\",\n      \"NR1I3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}