{"gene":"EDNRB","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2016,"finding":"Crystal structure of human EDNRB in ligand-free form and in complex with endothelin-1 revealed that transmembrane helices 1, 2, 6, and 7 move to envelop the entire endothelin peptide in a virtually irreversible manner; agonist-induced conformational changes propagate to the G-protein coupling interface and induce flexibility in TM6, elucidating the activation mechanism and isopeptide selectivity between ET-1 and ET-3.","method":"X-ray crystallography with mutation analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with mutagenesis functional validation","pmids":["27595334"],"is_preprint":false},{"year":2017,"finding":"Crystal structures of human EDNRB bound to clinical antagonist bosentan and ETB-selective analog K-8794 showed that bosentan sterically prevents the inward movement of TM6, exerting antagonistic activity; the K-8794-bound structure revealed water-mediated hydrogen-bonding network at the transmembrane core and weak negative allosteric modulation by Na+ ions.","method":"X-ray crystallography (3.6 Å and 2.2 Å resolution)","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structures with detailed mechanistic interpretation","pmids":["28805809"],"is_preprint":false},{"year":2018,"finding":"Crystal structures of human EDNRB in complex with ET-3 and the partial agonist IRL1620 revealed that disruption of water-mediated interactions between W6.48 and D2.50 is critical for full receptor activation; IRL1620 preserves these hydrogen-bonding interactions partially, explaining its partial agonistic effect.","method":"X-ray crystallography with functional analysis (IP accumulation assays)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with orthogonal functional validation of partial agonism","pmids":["30413709"],"is_preprint":false},{"year":2020,"finding":"Crystal structure of human EDNRB in complex with sarafotoxin S6b at 3.0 Å resolution revealed the binding mode of an endothelin-like peptide and, combined with molecular dynamics simulations, provided structural insight into sarafotoxin subtype selectivity.","method":"X-ray crystallography and molecular dynamics simulations","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with MD simulation","pmids":["32001000"],"is_preprint":false},{"year":1995,"finding":"EDNRB on vascular smooth muscle cells mediates vasoconstriction in human resistance (forearm) and capacitance (hand vein) vessels in vivo, demonstrated using selective ETB agonists endothelin-3 and sarafotoxin S6c by intra-arterial infusion.","method":"In vivo pharmacology (intra-arterial infusion of selective agonists in humans)","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — controlled in vivo human study with selective agonists/antagonists, replicated across vessel beds","pmids":["7634449"],"is_preprint":false},{"year":1992,"finding":"EDNRB activation mediates both vasodilation (transient, endothelium-dependent) and vasoconstriction (sustained) in vivo, demonstrated using the selective ETB agonist sarafotoxin S6c in rats.","method":"In vivo pharmacology (selective ETB agonist administration in rats)","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — selective agonist with clear dual functional readout in vivo, widely replicated","pmids":["1323294"],"is_preprint":false},{"year":2000,"finding":"EDNRB activation in the thick ascending limb of the loop of Henle decreases NaCl (chloride) flux by stimulating NO release through an intracellular calcium-dependent mechanism; this effect is blocked by the ETB antagonist BQ-788 and the NOS inhibitor L-NAME, but not by the ETA antagonist BQ-610.","method":"Isolated tubule perfusion assay with selective antagonists and NOS inhibitors","journal":"American journal of physiology. Renal physiology","confidence":"High","confidence_rationale":"Tier 2 — isolated tubule functional assay with multiple selective pharmacological tools","pmids":["10919853"],"is_preprint":false},{"year":2008,"finding":"Renal medullary EDNRB activation induces diuresis and natriuresis through a NOS1 → cGMP → PKG signaling pathway; effects absent in ETB receptor-deficient rats and blocked by selective NOS1 inhibition or PKG inhibition.","method":"In vivo renal medullary infusion in anesthetized rats, ETB-deficient rat model, selective pharmacological inhibitors","journal":"American journal of physiology. Renal physiology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout model combined with selective pharmacological dissection in vivo","pmids":["18305094"],"is_preprint":false},{"year":1999,"finding":"EDNRB activation leads to phosphorylation and activation of the Na+/H+ exchanger isoform 3 (NHE3) on multiple threonine and serine residues, with this phosphorylation being ETB receptor-specific (not mediated by ETA) and correlating with increased antiporter activity.","method":"Overexpression of ETB in OKP cells, immunoprecipitation, alkaline phosphatase treatment, amiloride-sensitive transport assay","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical phosphorylation assay with receptor-specificity controls and functional correlation","pmids":["10199826"],"is_preprint":false},{"year":1996,"finding":"EDNRB activation increases NHE3 activity via two parallel pathways: a Ca2+-dependent pathway (50%) and a tyrosine kinase pathway (50%) involving cytoskeletal focal adhesion proteins (paxillin, p125FAK) and a membrane-associated p210 tyrosine kinase; disruption of focal adhesions by cytochalasin D blocks focal adhesion protein phosphorylation but not antiporter activation, implicating p210 in the tyrosine kinase pathway.","method":"Pharmacological inhibitors in OKP cells stably expressing ETB, immunoprecipitation of phosphoproteins","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal inhibitor approaches with immunoprecipitation in defined cell system","pmids":["8843705"],"is_preprint":false},{"year":1997,"finding":"EDNRB undergoes rapid ligand-induced phosphorylation (within 5 min) leading to fast desensitization (>80% activity lost within 5 min), whereas ETA does not undergo ligand-induced phosphorylation and shows sustained activation; receptor internalization kinetics are identical for both subtypes, suggesting phosphorylation-dependent and internalization-independent desensitization mechanisms for EDNRB.","method":"Inositol phosphate accumulation assay, receptor phosphorylation assay, internalization assay in HEK cells expressing human receptors","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays in defined cell system, subtype specificity rigorously established","pmids":["9341224"],"is_preprint":false},{"year":1992,"finding":"EDNRB activation in rat glomeruli increases cGMP production via an L-arginine/nitric oxide-dependent mechanism that activates soluble guanylate cyclase; the ETA-selective antagonist BQ-123 has no effect, confirming ETB mediation.","method":"Glomerular cGMP accumulation assay with L-NNA, methylene blue, L-arginine, BQ-123, extracellular Ca2+ chelation","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — functional assay with multiple pharmacological tools establishing NO-cGMP pathway","pmids":["1336308"],"is_preprint":false},{"year":1995,"finding":"EDNRB activation promotes proliferation and migration of endothelial cells (bovine adrenal capillary and human umbilical vein endothelial cells) via an autocrine mechanism; the ETB-selective full agonist ET-(16-21) mimics the effect, and the ETB antagonist IRL-1038 blocks ET-3-induced and ET-(16-21)-induced migration, whereas the ETA antagonist BQ-123 is not effective.","method":"DNA synthesis, cell counting, cell migration assays with selective agonists and antagonists","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple readouts with selective pharmacological tools and negative controls","pmids":["7653633"],"is_preprint":false},{"year":2008,"finding":"EDNRB on pulmonary vascular endothelium mediates ET-1-induced impairment of alveolar fluid reabsorption via NO generation (cGMP-independent) leading to down-regulation of alveolar epithelial Na,K-ATPase activity and plasma membrane abundance; this requires endothelial-epithelial cell interaction and does not occur through direct action of ET-1 on alveolar epithelial cells.","method":"Isolated perfused rat lung, ETB-deficient transgenic rats, endothelial-epithelial co-culture, 86Rb+ uptake (Na,K-ATPase assay), L-NAME and guanylate cyclase inhibitor pharmacology","journal":"American journal of respiratory and critical care medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic ETB-deficient animal combined with mechanistic co-culture and pharmacological dissection","pmids":["18948426"],"is_preprint":false},{"year":1999,"finding":"Genetic and pharmacological disruption of EDNRB increases basal arterial blood pressure in mice by approximately 20 mmHg; the depressor effect of endogenous ET via EDNRB under basal conditions is partly mediated by prostacyclin (blocked by indomethacin) rather than nitric oxide.","method":"ETB gene-targeted mice (ETB-/s), ETB antagonist BQ-788, indomethacin, L-NMMA, ETA antagonist BQ-123","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — genetic model combined with selective pharmacology, functional blood pressure readout","pmids":["10198387"],"is_preprint":false},{"year":1993,"finding":"EDNRB is localized by immunohistochemistry primarily to vascular endothelium in kidney, adrenal gland, lung, cerebellum, and pituitary gland; tissue distribution varies (lung ~70% ETB, testis <2% ETB), established using a subtype-specific antiserum that immunoprecipitates only ETB.","method":"Subtype-specific rabbit antiserum, Western blot, immunoprecipitation, immunohistochemistry","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — specific antiserum validated by immunoprecipitation, localization with functional context","pmids":["8476120"],"is_preprint":false},{"year":1995,"finding":"Active-site mutagenesis of ETB (Asp147Ala in TM2) abolishes ET-1 and ET-3 activation of phospholipase C without altering ligand binding affinity, demonstrating that Asp147 is required for transmembrane signal transduction but not for ligand recognition in EDNRB.","method":"Site-directed mutagenesis of human ETB expressed in COS cells, inositol phosphate accumulation assay, radioligand binding","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis combined with functional assay dissecting binding from signaling","pmids":["7698331"],"is_preprint":false},{"year":2002,"finding":"Genetic epistasis between RET and EDNRB in Hirschsprung disease was demonstrated by non-complementation of aganglionosis in mouse intercrosses between Ret null and Ednrb hypomorphic piebald alleles, placing EDNRB in a gene interaction network with RET during enteric nervous system development.","method":"Genome-wide association in Mennonite trios, mouse intercross genetic epistasis analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in mouse intercross combined with human association study","pmids":["12355085"],"is_preprint":false},{"year":2019,"finding":"EDNRB transcription in the enteric nervous system is directly regulated by transcription factors GATA2, SOX10, and NKX2.5; RET and EDNRB share GATA2 and SOX10 as common regulators, and these TFs are in turn controlled by EDNRB and RET in a dose-dependent feedback manner, explaining the mechanistic basis for RET-EDNRB epistasis in Hirschsprung disease.","method":"Chromatin immunoprecipitation, transactivation assays, human and mouse cellular models, animal models","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — ChIP plus transactivation assays with multiple cell and animal model validation","pmids":["31313802"],"is_preprint":false},{"year":2017,"finding":"SOX10 and ZEB2 transcription factors directly activate the EDNRB promoter, and two copies of Zeb2 are required for EDN3/EDNRB signaling to prevent neuronal differentiation of enteric progenitor cells; overexpression of EDNRB in Zeb2-heterozygous EPCs rescues the inhibition of neuronal differentiation, placing EDNRB downstream of SOX10/ZEB2 transcriptional control.","method":"Transactivation assays, ChIP, retroviral EDNRB overexpression in enteric progenitor cell cultures, mouse double mutant analysis","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — ChIP + transactivation + functional rescue experiments with genetic mouse validation","pmids":["28063956"],"is_preprint":false},{"year":2006,"finding":"EDNRB genetically interacts with Sox10 and Edn3 during enteric nervous system and melanocyte development; double mutant (Sox10;Ednrb) mice show more severe aganglionosis and melanocyte defects than single mutants, with increased apoptosis in vagal neural crest cells outside the gut but no increase in cell proliferation or differentiation defects within the stomach.","method":"Genetic mouse double-mutant phenotypic analysis, apoptosis and proliferation assays, immunohistochemistry","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis using double-mutant mouse models with cellular phenotype quantification","pmids":["16650841"],"is_preprint":false},{"year":2000,"finding":"Big endothelin-1-induced diuresis and natriuresis are mediated mainly by EDNRB activation coupled to nitric oxide production; selective ETB antagonist A-192621.1 abolished these renal excretory responses, and effects were similarly blocked by L-NAME (NOS inhibitor).","method":"In vivo anesthetized rat pharmacology with selective ETB antagonist and NOS inhibitor","journal":"Hypertension","confidence":"High","confidence_rationale":"Tier 2 — selective pharmacological blockade in vivo with convergent evidence from two mechanistically distinct inhibitors","pmids":["10720587"],"is_preprint":false},{"year":1997,"finding":"Mouse EDNRB with a proline mutation in the fifth transmembrane domain causes a recessive lethal phenotype (white coat, megacolon), identifying this transmembrane proline as critical for EDNRB function in neural crest-derived melanocyte and enteric neuron development.","method":"Molecular characterization of induced alleles in mice (radiation/chemical mutagenesis), sequencing, Northern blot","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple alleles characterized molecularly with defined in vivo phenotypes","pmids":["9371807"],"is_preprint":false},{"year":2015,"finding":"EDNRB activation mediates vasogenic edema formation after status epilepticus via eNOS-mediated MMP-9 activation leading to ZO-1 tight junction protein degradation in endothelial cells; BQ788 (ETB antagonist) attenuates SE-induced vasogenic edema by inhibiting this eNOS/MMP-9/ZO-1 axis.","method":"Rat SE model, ETB antagonist BQ788, western blot for eNOS/MMP-9/ZO-1, BBB permeability assay","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — single lab with pharmacological and biochemical dissection but no genetic model validation","pmids":["26232046"],"is_preprint":false},{"year":2005,"finding":"AT1 receptors physically interact with EDNRB (co-immunoprecipitation) in renal proximal tubule cells and regulate ETB receptor expression and surface membrane localization; angiotensin II via AT1 receptors increases ETB receptor expression in WKY but not SHR cells, and this impaired interaction may contribute to hypertension in SHRs.","method":"Immunoblotting, confocal colocalization, co-immunoprecipitation, cell surface membrane fractionation in immortalized RPT cells","journal":"Hypertension","confidence":"Medium","confidence_rationale":"Tier 3 — co-immunoprecipitation with functional follow-up, single lab","pmids":["16144989"],"is_preprint":false},{"year":2005,"finding":"EDNRB activation decreases AT1 receptor protein expression in renal proximal tubule cells via direct receptor interaction (co-immunoprecipitation); ETB receptor agonist BQ3020 also increased AT1 receptor phosphorylation in WKY but decreased it in SHR cells, demonstrating aberrant ETB-AT1 cross-regulation in hypertension.","method":"Co-immunoprecipitation, immunoblotting, receptor phosphorylation in immortalized RPT cells from WKY and SHR","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 3 — co-immunoprecipitation with functional consequences, single lab","pmids":["16014039"],"is_preprint":false},{"year":2009,"finding":"D3 dopamine receptors physically interact with EDNRB (co-immunoprecipitation) in renal proximal tubule cells; D3 receptor activation increases ETB receptor expression and augments ETB-mediated inhibition of Na+/K+-ATPase in WKY cells, but this regulation is impaired in SHR cells where D3/ETB co-immunoprecipitation is markedly reduced.","method":"Co-immunoprecipitation, immunoblotting, Na+/K+-ATPase activity assay in RPT cells","journal":"American journal of hypertension","confidence":"Medium","confidence_rationale":"Tier 3 — co-immunoprecipitation with functional Na+/K+-ATPase readout, single lab","pmids":["19390510"],"is_preprint":false},{"year":2008,"finding":"ET-1-mediated apoptosis of retinal ganglion cells (RGC-5 cells) is mediated by EDNRB, involving cytochrome c release, JNK phosphorylation, and upregulation of ETB receptor expression; this was confirmed in ETB receptor-deficient rats where ET-1-induced apoptosis was markedly attenuated.","method":"ETB-deficient rat model, flow cytometry, cytochrome c western blot, JNK phosphorylation, ETB antagonist BQ788","journal":"Canadian journal of physiology and pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic ETB-deficient rat plus pharmacological confirmation, single lab","pmids":["18516102"],"is_preprint":false},{"year":2001,"finding":"EDNRB promoter CpG island methylation silences gene expression; treatment with 5-aza-2'-deoxycytidine restores all four EDNRB transcripts, and a low-methylation region immediately 5' to the transcription start site correlates with expression of the proximal transcript, while downstream methylation does not block initiation.","method":"Bisulfite sequencing, 5-aza-2'-deoxycytidine treatment, RT-PCR expression analysis in normal and tumor cells","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct methylation-expression correlation with pharmacological reversal, single lab","pmids":["11309363"],"is_preprint":false},{"year":2017,"finding":"EDN3/EDNRB signaling is required for melanocyte stem cell (McSC) activation and regeneration of follicular and epidermal melanocytes after epilation; genetic and pharmacological disruption of EDNRB significantly blocks epilation-induced melanocyte regeneration and skin/hair hyperpigmentation, with EDN3 upregulation occurring in the dermal papilla and epidermis after epilation.","method":"Genetic EDNRB disruption and pharmacological blockade in mice, immunohistochemistry","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — genetic plus pharmacological disruption with defined cellular phenotype","pmids":["28779103"],"is_preprint":false},{"year":2001,"finding":"ETB receptor activation inhibits platelet aggregation ex vivo in mice via ETB-dependent prostacyclin generation (COX-2 pathway); BQ-788 (ETB antagonist) abolishes this inhibitory effect, and indomethacin or tranylcypromine (prostacyclin synthase inhibitor) markedly reduces it.","method":"Ex vivo platelet aggregation assay in mice, selective ETB agonist IRL-1620, antagonist BQ-788, cyclooxygenase inhibitors","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — selective agonist/antagonist plus enzymatic inhibitors with clear mechanistic dissection","pmids":["11181435"],"is_preprint":false},{"year":2013,"finding":"Neural crest cell-specific deletion of Ednrb in mice results in decreased neuronal density and altered neurotransmitter expression (increased nNOS and VIP, decreased ChAT) in the ganglionated colon proximal to the aganglionic region, demonstrating that EDNRB function in neural crest cells is required for normal enteric nervous system organization.","method":"Neural crest cell-specific conditional Ednrb knockout mice, immunohistochemistry, neuronal counting","journal":"Neurogastroenterology and motility","confidence":"Medium","confidence_rationale":"Tier 2 — cell-type-specific genetic knockout with defined cellular/neurochemical phenotype","pmids":["23360229"],"is_preprint":false}],"current_model":"EDNRB is a class A G-protein-coupled receptor (GPCR) for endothelin peptides whose crystal structures reveal that agonist binding causes transmembrane helices 1, 2, 6, and 7 to envelope the ligand, disrupting a W6.48–D2.50 hydrogen-bonding network to propagate conformational changes to the G-protein interface, while Asp147 in TM2 is required for phospholipase C signal transduction but not ligand binding; activated EDNRB signals through Ca2+ and tyrosine kinase pathways to phosphorylate NHE3 and stimulate NO (via NOS1/eNOS) → cGMP → PKG cascades mediating natriuresis, diuresis, and vasodilation, undergoes rapid agonist-induced phosphorylation and desensitization distinct from ETA, is transcriptionally controlled by SOX10/GATA2/ZEB2/NKX2.5 in the developing enteric nervous system where it interacts epistatically with RET to permit neural crest colonization of the gut, and is silenced by promoter CpG hypermethylation in multiple cancers."},"narrative":{"teleology":[{"year":1992,"claim":"Establishing that EDNRB is a dual-function vascular receptor: selective ETB agonists demonstrated that a single receptor subtype mediates both transient endothelium-dependent vasodilation and sustained vasoconstriction, and that the vasodilatory arm operates through an NO→cGMP pathway.","evidence":"In vivo selective agonist (sarafotoxin S6c) pharmacology in rats; glomerular cGMP assays with NOS/guanylate cyclase inhibitors","pmids":["1323294","1336308"],"confidence":"High","gaps":["Downstream signaling intermediates between EDNRB and NOS activation were not identified","Cell-type-specific contributions (endothelial vs. smooth muscle) not genetically separated"]},{"year":1995,"claim":"Defining the tissue distribution and signal-transduction requirements of EDNRB: immunohistochemistry localized the receptor predominantly to vascular endothelium across organs, mutagenesis of Asp147 in TM2 separated ligand binding from PLC coupling, and human studies confirmed ETB-mediated vasoconstriction in resistance and capacitance vessels.","evidence":"Subtype-specific antiserum immunohistochemistry; site-directed mutagenesis of human ETB in COS cells with IP accumulation and radioligand binding; intra-arterial selective agonist infusion in human subjects","pmids":["8476120","7698331","7634449"],"confidence":"High","gaps":["Structural basis for why Asp147 couples to G-protein signaling was unknown","Endothelial versus smooth muscle ETB contributions not genetically dissected in vivo"]},{"year":1996,"claim":"Identifying the downstream effector pathways by which EDNRB regulates epithelial Na⁺/H⁺ exchange: EDNRB-specific activation of NHE3 proceeds through parallel Ca²⁺-dependent and tyrosine kinase (p210/paxillin/p125FAK) pathways, revealing a bifurcating intracellular signaling architecture.","evidence":"Pharmacological inhibitors and immunoprecipitation in OKP cells stably expressing ETB","pmids":["8843705"],"confidence":"High","gaps":["Identity of the p210 tyrosine kinase was unknown","Whether these pathways operate in native renal tubule cells was not shown"]},{"year":1997,"claim":"Demonstrating that EDNRB undergoes rapid agonist-induced phosphorylation causing fast desensitization distinct from ETA, and that a TM5 proline is critical for receptor function in neural crest development.","evidence":"Phosphorylation/IP accumulation/internalization assays in HEK cells; molecular characterization of radiation/chemical mutagenesis alleles in mice with white coat/megacolon phenotype","pmids":["9341224","9371807"],"confidence":"High","gaps":["Kinases responsible for EDNRB phosphorylation were not identified","Whether the TM5 proline mutation affects folding versus signaling was unresolved"]},{"year":1999,"claim":"Establishing EDNRB as a tonic vasodepressor: gene-targeted ETB-knockout mice showed ~20 mmHg elevated blood pressure, with the depressor effect partly mediated by prostacyclin rather than NO, and EDNRB-specific NHE3 phosphorylation was mapped to multiple Thr/Ser residues.","evidence":"ETB gene-targeted mice with selective pharmacological dissection; immunoprecipitation and alkaline phosphatase in OKP-ETB cells","pmids":["10198387","10199826"],"confidence":"High","gaps":["Specific NHE3 phosphorylation sites were not individually mutated","Relative contribution of renal versus vascular EDNRB to blood pressure was unresolved"]},{"year":2000,"claim":"Delineating the renal tubular mechanism: EDNRB on thick ascending limb cells decreases NaCl reabsorption through Ca²⁺-dependent NOS activation, and big-ET-1-induced natriuresis/diuresis is abolished by selective ETB blockade or NOS inhibition.","evidence":"Isolated tubule perfusion with BQ-788/L-NAME; in vivo ETB antagonist and NOS inhibitor infusion in anesthetized rats","pmids":["10919853","10720587"],"confidence":"High","gaps":["NOS isoform responsible in the thick ascending limb was not specified","Whether EDNRB acts on apical or basolateral membrane was not determined"]},{"year":2001,"claim":"Revealing epigenetic silencing of EDNRB: promoter CpG island methylation was shown to repress all four EDNRB transcripts, with demethylation restoring expression, and EDNRB-dependent prostacyclin generation was found to inhibit platelet aggregation.","evidence":"Bisulfite sequencing and 5-aza-dC treatment in normal and tumor cells; ex vivo platelet aggregation with selective ETB agonist/antagonist and COX inhibitors","pmids":["11309363","11181435"],"confidence":"Medium","gaps":["Cancer types and in vivo consequences of EDNRB methylation were not broadly surveyed","Whether COX-2-dependent prostacyclin is the sole antiplatelet mediator was not settled"]},{"year":2002,"claim":"Establishing genetic epistasis between EDNRB and RET in Hirschsprung disease: intercross of Ret-null and Ednrb-hypomorphic mice produced non-complementation of aganglionosis, placing both genes in a shared pathway for enteric nervous system colonization.","evidence":"Genome-wide association in Mennonite trios; mouse Ret/Ednrb intercross epistasis analysis","pmids":["12355085"],"confidence":"High","gaps":["Molecular mechanism of RET–EDNRB pathway convergence was unknown","Whether the epistasis is cell-autonomous in neural crest cells was not shown"]},{"year":2006,"claim":"Revealing that EDNRB and Sox10 genetically interact to promote neural crest cell survival: double-mutant mice showed enhanced aganglionosis and increased apoptosis in vagal neural crest cells, linking EDNRB signaling to anti-apoptotic function during gut colonization.","evidence":"Sox10/Ednrb double-mutant mouse phenotypic analysis with apoptosis quantification","pmids":["16650841"],"confidence":"High","gaps":["Anti-apoptotic effectors downstream of EDNRB in neural crest cells were not identified","Whether the apoptosis phenotype is cell-autonomous was not definitively resolved"]},{"year":2008,"claim":"Refining the renal signaling cascade and identifying a pulmonary paracrine function: medullary EDNRB signals through NOS1→cGMP→PKG to drive natriuresis/diuresis, while pulmonary endothelial EDNRB impairs alveolar fluid clearance via NO-dependent (cGMP-independent) downregulation of epithelial Na,K-ATPase.","evidence":"In vivo renal infusion in ETB-deficient rats with NOS1/PKG inhibitors; isolated perfused lung from ETB-deficient rats with co-culture and Na,K-ATPase assays","pmids":["18305094","18948426"],"confidence":"High","gaps":["The cGMP-independent NO effector in alveolar epithelium was not identified","How NOS1 versus eNOS are differentially engaged across tissues was not addressed"]},{"year":2016,"claim":"Solving the structural basis of endothelin recognition: the crystal structure of EDNRB in apo and ET-1-bound forms showed that TM1/2/6/7 move to envelop the entire peptide, creating near-irreversible binding, and revealed flexibility in TM6 linked to G-protein coupling.","evidence":"X-ray crystallography with mutation analysis (Nature)","pmids":["27595334"],"confidence":"High","gaps":["Active-state structure with a G-protein or arrestin was not obtained","Structural basis for isopeptide selectivity at the single-residue level was incompletely resolved"]},{"year":2017,"claim":"Elucidating antagonist mechanisms and transcriptional control of EDNRB: crystal structures showed bosentan blocks TM6 inward movement while Na⁺ acts as a weak negative allosteric modulator; SOX10 and ZEB2 were shown to directly activate the EDNRB promoter, with EDNRB functioning downstream of ZEB2 to inhibit premature neuronal differentiation of enteric progenitors.","evidence":"X-ray crystallography of bosentan- and K-8794-bound EDNRB; ChIP, transactivation, and retroviral EDNRB rescue in Zeb2-heterozygous enteric progenitor cultures","pmids":["28805809","28063956"],"confidence":"High","gaps":["Whether Na⁺ allosteric modulation is physiologically relevant was not established","Full enhancer/promoter architecture governing tissue-specific EDNRB expression was not mapped"]},{"year":2018,"claim":"Defining the structural switch for full versus partial agonism: the ET-3- and IRL1620-bound crystal structures showed that full agonism requires disruption of the W6.48–D2.50 water-mediated hydrogen bond network, which partial agonists preserve.","evidence":"X-ray crystallography with IP accumulation assays","pmids":["30413709"],"confidence":"High","gaps":["Dynamics of water network disruption during activation were not captured","How partial agonism translates to biased signaling profiles was not explored"]},{"year":2019,"claim":"Completing the transcriptional circuit: GATA2, SOX10, and NKX2.5 were shown to directly regulate EDNRB transcription, and EDNRB and RET reciprocally feed back on these shared transcription factors, providing the molecular explanation for RET–EDNRB epistasis in Hirschsprung disease.","evidence":"Chromatin immunoprecipitation and transactivation assays in human and mouse cellular/animal models","pmids":["31313802"],"confidence":"High","gaps":["Quantitative dose–response relationship of the feedback loop was not modeled","Whether additional transcription factors contribute in specific ENS progenitor subtypes is unknown"]},{"year":null,"claim":"Major unresolved questions include the active-state structure of EDNRB in complex with a G-protein or β-arrestin, the identity of kinases mediating rapid EDNRB phosphorylation and desensitization, the mechanistic basis for tissue-specific engagement of NOS1 versus eNOS, and the functional consequences of EDNRB promoter methylation in cancer progression in vivo.","evidence":"","pmids":[],"confidence":"High","gaps":["No active-state GPCR–transducer complex structure available","Kinases for agonist-induced EDNRB phosphorylation unidentified","In vivo cancer consequences of EDNRB methylation not causally tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,5,6,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,9,25,26]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,5,15,24]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,6,7,9,16]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[17,18,19,20,31]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[17,22,28]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[6,7,8,21]}],"complexes":[],"partners":["RET","SOX10","ZEB2","GATA2","NKX2.5","NHE3","AGTR1","DRD3"],"other_free_text":[]},"mechanistic_narrative":"EDNRB is a class A G-protein-coupled receptor for endothelin peptides that mediates vasodilation, vasoconstriction, natriuresis, and diuresis depending on tissue context, and is essential for neural crest-derived melanocyte and enteric neuron development. Crystal structures show that agonist binding causes transmembrane helices 1, 2, 6, and 7 to envelop the endothelin peptide, disrupting a W6.48–D2.50 water-mediated hydrogen-bonding network to propagate conformational changes to the G-protein interface; Asp147 in TM2 is required for phospholipase C activation but not ligand binding [PMID:27595334, PMID:30413709, PMID:7698331]. Activated EDNRB signals through Ca²⁺ and tyrosine kinase pathways to phosphorylate NHE3 and stimulates a NO→cGMP→PKG cascade that drives renal sodium and water excretion and endothelium-dependent vasodilation, undergoes rapid agonist-induced phosphorylation producing desensitization kinetically distinct from ETA, and genetically interacts with RET during enteric nervous system colonization under the transcriptional control of SOX10, ZEB2, GATA2, and NKX2.5—with loss-of-function mutations causing Hirschsprung disease and pigmentation defects [PMID:18305094, PMID:9341224, PMID:12355085, PMID:28063956]. EDNRB promoter CpG hypermethylation silences expression in multiple cancers, reversible by demethylating agents [PMID:11309363]."},"prefetch_data":{"uniprot":{"accession":"P24530","full_name":"Endothelin receptor type B","aliases":["Endothelin receptor non-selective type"],"length_aa":442,"mass_kda":49.6,"function":"Non-specific receptor for endothelin 1, 2, and 3. 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agonist-induced conformational changes propagate to the G-protein coupling interface and induce flexibility in TM6, elucidating the activation mechanism and isopeptide selectivity between ET-1 and ET-3.\",\n      \"method\": \"X-ray crystallography with mutation analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with mutagenesis functional validation\",\n      \"pmids\": [\"27595334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structures of human EDNRB bound to clinical antagonist bosentan and ETB-selective analog K-8794 showed that bosentan sterically prevents the inward movement of TM6, exerting antagonistic activity; the K-8794-bound structure revealed water-mediated hydrogen-bonding network at the transmembrane core and weak negative allosteric modulation by Na+ ions.\",\n      \"method\": \"X-ray crystallography (3.6 Å and 2.2 Å resolution)\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structures with detailed mechanistic interpretation\",\n      \"pmids\": [\"28805809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structures of human EDNRB in complex with ET-3 and the partial agonist IRL1620 revealed that disruption of water-mediated interactions between W6.48 and D2.50 is critical for full receptor activation; IRL1620 preserves these hydrogen-bonding interactions partially, explaining its partial agonistic effect.\",\n      \"method\": \"X-ray crystallography with functional analysis (IP accumulation assays)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with orthogonal functional validation of partial agonism\",\n      \"pmids\": [\"30413709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structure of human EDNRB in complex with sarafotoxin S6b at 3.0 Å resolution revealed the binding mode of an endothelin-like peptide and, combined with molecular dynamics simulations, provided structural insight into sarafotoxin subtype selectivity.\",\n      \"method\": \"X-ray crystallography and molecular dynamics simulations\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with MD simulation\",\n      \"pmids\": [\"32001000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"EDNRB on vascular smooth muscle cells mediates vasoconstriction in human resistance (forearm) and capacitance (hand vein) vessels in vivo, demonstrated using selective ETB agonists endothelin-3 and sarafotoxin S6c by intra-arterial infusion.\",\n      \"method\": \"In vivo pharmacology (intra-arterial infusion of selective agonists in humans)\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — controlled in vivo human study with selective agonists/antagonists, replicated across vessel beds\",\n      \"pmids\": [\"7634449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"EDNRB activation mediates both vasodilation (transient, endothelium-dependent) and vasoconstriction (sustained) in vivo, demonstrated using the selective ETB agonist sarafotoxin S6c in rats.\",\n      \"method\": \"In vivo pharmacology (selective ETB agonist administration in rats)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective agonist with clear dual functional readout in vivo, widely replicated\",\n      \"pmids\": [\"1323294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"EDNRB activation in the thick ascending limb of the loop of Henle decreases NaCl (chloride) flux by stimulating NO release through an intracellular calcium-dependent mechanism; this effect is blocked by the ETB antagonist BQ-788 and the NOS inhibitor L-NAME, but not by the ETA antagonist BQ-610.\",\n      \"method\": \"Isolated tubule perfusion assay with selective antagonists and NOS inhibitors\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isolated tubule functional assay with multiple selective pharmacological tools\",\n      \"pmids\": [\"10919853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Renal medullary EDNRB activation induces diuresis and natriuresis through a NOS1 → cGMP → PKG signaling pathway; effects absent in ETB receptor-deficient rats and blocked by selective NOS1 inhibition or PKG inhibition.\",\n      \"method\": \"In vivo renal medullary infusion in anesthetized rats, ETB-deficient rat model, selective pharmacological inhibitors\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout model combined with selective pharmacological dissection in vivo\",\n      \"pmids\": [\"18305094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"EDNRB activation leads to phosphorylation and activation of the Na+/H+ exchanger isoform 3 (NHE3) on multiple threonine and serine residues, with this phosphorylation being ETB receptor-specific (not mediated by ETA) and correlating with increased antiporter activity.\",\n      \"method\": \"Overexpression of ETB in OKP cells, immunoprecipitation, alkaline phosphatase treatment, amiloride-sensitive transport assay\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical phosphorylation assay with receptor-specificity controls and functional correlation\",\n      \"pmids\": [\"10199826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"EDNRB activation increases NHE3 activity via two parallel pathways: a Ca2+-dependent pathway (50%) and a tyrosine kinase pathway (50%) involving cytoskeletal focal adhesion proteins (paxillin, p125FAK) and a membrane-associated p210 tyrosine kinase; disruption of focal adhesions by cytochalasin D blocks focal adhesion protein phosphorylation but not antiporter activation, implicating p210 in the tyrosine kinase pathway.\",\n      \"method\": \"Pharmacological inhibitors in OKP cells stably expressing ETB, immunoprecipitation of phosphoproteins\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal inhibitor approaches with immunoprecipitation in defined cell system\",\n      \"pmids\": [\"8843705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"EDNRB undergoes rapid ligand-induced phosphorylation (within 5 min) leading to fast desensitization (>80% activity lost within 5 min), whereas ETA does not undergo ligand-induced phosphorylation and shows sustained activation; receptor internalization kinetics are identical for both subtypes, suggesting phosphorylation-dependent and internalization-independent desensitization mechanisms for EDNRB.\",\n      \"method\": \"Inositol phosphate accumulation assay, receptor phosphorylation assay, internalization assay in HEK cells expressing human receptors\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays in defined cell system, subtype specificity rigorously established\",\n      \"pmids\": [\"9341224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"EDNRB activation in rat glomeruli increases cGMP production via an L-arginine/nitric oxide-dependent mechanism that activates soluble guanylate cyclase; the ETA-selective antagonist BQ-123 has no effect, confirming ETB mediation.\",\n      \"method\": \"Glomerular cGMP accumulation assay with L-NNA, methylene blue, L-arginine, BQ-123, extracellular Ca2+ chelation\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional assay with multiple pharmacological tools establishing NO-cGMP pathway\",\n      \"pmids\": [\"1336308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"EDNRB activation promotes proliferation and migration of endothelial cells (bovine adrenal capillary and human umbilical vein endothelial cells) via an autocrine mechanism; the ETB-selective full agonist ET-(16-21) mimics the effect, and the ETB antagonist IRL-1038 blocks ET-3-induced and ET-(16-21)-induced migration, whereas the ETA antagonist BQ-123 is not effective.\",\n      \"method\": \"DNA synthesis, cell counting, cell migration assays with selective agonists and antagonists\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple readouts with selective pharmacological tools and negative controls\",\n      \"pmids\": [\"7653633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"EDNRB on pulmonary vascular endothelium mediates ET-1-induced impairment of alveolar fluid reabsorption via NO generation (cGMP-independent) leading to down-regulation of alveolar epithelial Na,K-ATPase activity and plasma membrane abundance; this requires endothelial-epithelial cell interaction and does not occur through direct action of ET-1 on alveolar epithelial cells.\",\n      \"method\": \"Isolated perfused rat lung, ETB-deficient transgenic rats, endothelial-epithelial co-culture, 86Rb+ uptake (Na,K-ATPase assay), L-NAME and guanylate cyclase inhibitor pharmacology\",\n      \"journal\": \"American journal of respiratory and critical care medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic ETB-deficient animal combined with mechanistic co-culture and pharmacological dissection\",\n      \"pmids\": [\"18948426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Genetic and pharmacological disruption of EDNRB increases basal arterial blood pressure in mice by approximately 20 mmHg; the depressor effect of endogenous ET via EDNRB under basal conditions is partly mediated by prostacyclin (blocked by indomethacin) rather than nitric oxide.\",\n      \"method\": \"ETB gene-targeted mice (ETB-/s), ETB antagonist BQ-788, indomethacin, L-NMMA, ETA antagonist BQ-123\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic model combined with selective pharmacology, functional blood pressure readout\",\n      \"pmids\": [\"10198387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"EDNRB is localized by immunohistochemistry primarily to vascular endothelium in kidney, adrenal gland, lung, cerebellum, and pituitary gland; tissue distribution varies (lung ~70% ETB, testis <2% ETB), established using a subtype-specific antiserum that immunoprecipitates only ETB.\",\n      \"method\": \"Subtype-specific rabbit antiserum, Western blot, immunoprecipitation, immunohistochemistry\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific antiserum validated by immunoprecipitation, localization with functional context\",\n      \"pmids\": [\"8476120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Active-site mutagenesis of ETB (Asp147Ala in TM2) abolishes ET-1 and ET-3 activation of phospholipase C without altering ligand binding affinity, demonstrating that Asp147 is required for transmembrane signal transduction but not for ligand recognition in EDNRB.\",\n      \"method\": \"Site-directed mutagenesis of human ETB expressed in COS cells, inositol phosphate accumulation assay, radioligand binding\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis combined with functional assay dissecting binding from signaling\",\n      \"pmids\": [\"7698331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Genetic epistasis between RET and EDNRB in Hirschsprung disease was demonstrated by non-complementation of aganglionosis in mouse intercrosses between Ret null and Ednrb hypomorphic piebald alleles, placing EDNRB in a gene interaction network with RET during enteric nervous system development.\",\n      \"method\": \"Genome-wide association in Mennonite trios, mouse intercross genetic epistasis analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in mouse intercross combined with human association study\",\n      \"pmids\": [\"12355085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"EDNRB transcription in the enteric nervous system is directly regulated by transcription factors GATA2, SOX10, and NKX2.5; RET and EDNRB share GATA2 and SOX10 as common regulators, and these TFs are in turn controlled by EDNRB and RET in a dose-dependent feedback manner, explaining the mechanistic basis for RET-EDNRB epistasis in Hirschsprung disease.\",\n      \"method\": \"Chromatin immunoprecipitation, transactivation assays, human and mouse cellular models, animal models\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus transactivation assays with multiple cell and animal model validation\",\n      \"pmids\": [\"31313802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SOX10 and ZEB2 transcription factors directly activate the EDNRB promoter, and two copies of Zeb2 are required for EDN3/EDNRB signaling to prevent neuronal differentiation of enteric progenitor cells; overexpression of EDNRB in Zeb2-heterozygous EPCs rescues the inhibition of neuronal differentiation, placing EDNRB downstream of SOX10/ZEB2 transcriptional control.\",\n      \"method\": \"Transactivation assays, ChIP, retroviral EDNRB overexpression in enteric progenitor cell cultures, mouse double mutant analysis\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + transactivation + functional rescue experiments with genetic mouse validation\",\n      \"pmids\": [\"28063956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EDNRB genetically interacts with Sox10 and Edn3 during enteric nervous system and melanocyte development; double mutant (Sox10;Ednrb) mice show more severe aganglionosis and melanocyte defects than single mutants, with increased apoptosis in vagal neural crest cells outside the gut but no increase in cell proliferation or differentiation defects within the stomach.\",\n      \"method\": \"Genetic mouse double-mutant phenotypic analysis, apoptosis and proliferation assays, immunohistochemistry\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis using double-mutant mouse models with cellular phenotype quantification\",\n      \"pmids\": [\"16650841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Big endothelin-1-induced diuresis and natriuresis are mediated mainly by EDNRB activation coupled to nitric oxide production; selective ETB antagonist A-192621.1 abolished these renal excretory responses, and effects were similarly blocked by L-NAME (NOS inhibitor).\",\n      \"method\": \"In vivo anesthetized rat pharmacology with selective ETB antagonist and NOS inhibitor\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective pharmacological blockade in vivo with convergent evidence from two mechanistically distinct inhibitors\",\n      \"pmids\": [\"10720587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mouse EDNRB with a proline mutation in the fifth transmembrane domain causes a recessive lethal phenotype (white coat, megacolon), identifying this transmembrane proline as critical for EDNRB function in neural crest-derived melanocyte and enteric neuron development.\",\n      \"method\": \"Molecular characterization of induced alleles in mice (radiation/chemical mutagenesis), sequencing, Northern blot\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple alleles characterized molecularly with defined in vivo phenotypes\",\n      \"pmids\": [\"9371807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"EDNRB activation mediates vasogenic edema formation after status epilepticus via eNOS-mediated MMP-9 activation leading to ZO-1 tight junction protein degradation in endothelial cells; BQ788 (ETB antagonist) attenuates SE-induced vasogenic edema by inhibiting this eNOS/MMP-9/ZO-1 axis.\",\n      \"method\": \"Rat SE model, ETB antagonist BQ788, western blot for eNOS/MMP-9/ZO-1, BBB permeability assay\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab with pharmacological and biochemical dissection but no genetic model validation\",\n      \"pmids\": [\"26232046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"AT1 receptors physically interact with EDNRB (co-immunoprecipitation) in renal proximal tubule cells and regulate ETB receptor expression and surface membrane localization; angiotensin II via AT1 receptors increases ETB receptor expression in WKY but not SHR cells, and this impaired interaction may contribute to hypertension in SHRs.\",\n      \"method\": \"Immunoblotting, confocal colocalization, co-immunoprecipitation, cell surface membrane fractionation in immortalized RPT cells\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-immunoprecipitation with functional follow-up, single lab\",\n      \"pmids\": [\"16144989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"EDNRB activation decreases AT1 receptor protein expression in renal proximal tubule cells via direct receptor interaction (co-immunoprecipitation); ETB receptor agonist BQ3020 also increased AT1 receptor phosphorylation in WKY but decreased it in SHR cells, demonstrating aberrant ETB-AT1 cross-regulation in hypertension.\",\n      \"method\": \"Co-immunoprecipitation, immunoblotting, receptor phosphorylation in immortalized RPT cells from WKY and SHR\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-immunoprecipitation with functional consequences, single lab\",\n      \"pmids\": [\"16014039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"D3 dopamine receptors physically interact with EDNRB (co-immunoprecipitation) in renal proximal tubule cells; D3 receptor activation increases ETB receptor expression and augments ETB-mediated inhibition of Na+/K+-ATPase in WKY cells, but this regulation is impaired in SHR cells where D3/ETB co-immunoprecipitation is markedly reduced.\",\n      \"method\": \"Co-immunoprecipitation, immunoblotting, Na+/K+-ATPase activity assay in RPT cells\",\n      \"journal\": \"American journal of hypertension\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-immunoprecipitation with functional Na+/K+-ATPase readout, single lab\",\n      \"pmids\": [\"19390510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ET-1-mediated apoptosis of retinal ganglion cells (RGC-5 cells) is mediated by EDNRB, involving cytochrome c release, JNK phosphorylation, and upregulation of ETB receptor expression; this was confirmed in ETB receptor-deficient rats where ET-1-induced apoptosis was markedly attenuated.\",\n      \"method\": \"ETB-deficient rat model, flow cytometry, cytochrome c western blot, JNK phosphorylation, ETB antagonist BQ788\",\n      \"journal\": \"Canadian journal of physiology and pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic ETB-deficient rat plus pharmacological confirmation, single lab\",\n      \"pmids\": [\"18516102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"EDNRB promoter CpG island methylation silences gene expression; treatment with 5-aza-2'-deoxycytidine restores all four EDNRB transcripts, and a low-methylation region immediately 5' to the transcription start site correlates with expression of the proximal transcript, while downstream methylation does not block initiation.\",\n      \"method\": \"Bisulfite sequencing, 5-aza-2'-deoxycytidine treatment, RT-PCR expression analysis in normal and tumor cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct methylation-expression correlation with pharmacological reversal, single lab\",\n      \"pmids\": [\"11309363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"EDN3/EDNRB signaling is required for melanocyte stem cell (McSC) activation and regeneration of follicular and epidermal melanocytes after epilation; genetic and pharmacological disruption of EDNRB significantly blocks epilation-induced melanocyte regeneration and skin/hair hyperpigmentation, with EDN3 upregulation occurring in the dermal papilla and epidermis after epilation.\",\n      \"method\": \"Genetic EDNRB disruption and pharmacological blockade in mice, immunohistochemistry\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic plus pharmacological disruption with defined cellular phenotype\",\n      \"pmids\": [\"28779103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ETB receptor activation inhibits platelet aggregation ex vivo in mice via ETB-dependent prostacyclin generation (COX-2 pathway); BQ-788 (ETB antagonist) abolishes this inhibitory effect, and indomethacin or tranylcypromine (prostacyclin synthase inhibitor) markedly reduces it.\",\n      \"method\": \"Ex vivo platelet aggregation assay in mice, selective ETB agonist IRL-1620, antagonist BQ-788, cyclooxygenase inhibitors\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — selective agonist/antagonist plus enzymatic inhibitors with clear mechanistic dissection\",\n      \"pmids\": [\"11181435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Neural crest cell-specific deletion of Ednrb in mice results in decreased neuronal density and altered neurotransmitter expression (increased nNOS and VIP, decreased ChAT) in the ganglionated colon proximal to the aganglionic region, demonstrating that EDNRB function in neural crest cells is required for normal enteric nervous system organization.\",\n      \"method\": \"Neural crest cell-specific conditional Ednrb knockout mice, immunohistochemistry, neuronal counting\",\n      \"journal\": \"Neurogastroenterology and motility\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific genetic knockout with defined cellular/neurochemical phenotype\",\n      \"pmids\": [\"23360229\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EDNRB is a class A G-protein-coupled receptor (GPCR) for endothelin peptides whose crystal structures reveal that agonist binding causes transmembrane helices 1, 2, 6, and 7 to envelope the ligand, disrupting a W6.48–D2.50 hydrogen-bonding network to propagate conformational changes to the G-protein interface, while Asp147 in TM2 is required for phospholipase C signal transduction but not ligand binding; activated EDNRB signals through Ca2+ and tyrosine kinase pathways to phosphorylate NHE3 and stimulate NO (via NOS1/eNOS) → cGMP → PKG cascades mediating natriuresis, diuresis, and vasodilation, undergoes rapid agonist-induced phosphorylation and desensitization distinct from ETA, is transcriptionally controlled by SOX10/GATA2/ZEB2/NKX2.5 in the developing enteric nervous system where it interacts epistatically with RET to permit neural crest colonization of the gut, and is silenced by promoter CpG hypermethylation in multiple cancers.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EDNRB is a class A G-protein-coupled receptor for endothelin peptides that mediates vasodilation, vasoconstriction, natriuresis, and diuresis depending on tissue context, and is essential for neural crest-derived melanocyte and enteric neuron development. Crystal structures show that agonist binding causes transmembrane helices 1, 2, 6, and 7 to envelop the endothelin peptide, disrupting a W6.48–D2.50 water-mediated hydrogen-bonding network to propagate conformational changes to the G-protein interface; Asp147 in TM2 is required for phospholipase C activation but not ligand binding [PMID:27595334, PMID:30413709, PMID:7698331]. Activated EDNRB signals through Ca²⁺ and tyrosine kinase pathways to phosphorylate NHE3 and stimulates a NO→cGMP→PKG cascade that drives renal sodium and water excretion and endothelium-dependent vasodilation, undergoes rapid agonist-induced phosphorylation producing desensitization kinetically distinct from ETA, and genetically interacts with RET during enteric nervous system colonization under the transcriptional control of SOX10, ZEB2, GATA2, and NKX2.5—with loss-of-function mutations causing Hirschsprung disease and pigmentation defects [PMID:18305094, PMID:9341224, PMID:12355085, PMID:28063956]. EDNRB promoter CpG hypermethylation silences expression in multiple cancers, reversible by demethylating agents [PMID:11309363].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that EDNRB is a dual-function vascular receptor: selective ETB agonists demonstrated that a single receptor subtype mediates both transient endothelium-dependent vasodilation and sustained vasoconstriction, and that the vasodilatory arm operates through an NO→cGMP pathway.\",\n      \"evidence\": \"In vivo selective agonist (sarafotoxin S6c) pharmacology in rats; glomerular cGMP assays with NOS/guanylate cyclase inhibitors\",\n      \"pmids\": [\"1323294\", \"1336308\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates between EDNRB and NOS activation were not identified\", \"Cell-type-specific contributions (endothelial vs. smooth muscle) not genetically separated\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Defining the tissue distribution and signal-transduction requirements of EDNRB: immunohistochemistry localized the receptor predominantly to vascular endothelium across organs, mutagenesis of Asp147 in TM2 separated ligand binding from PLC coupling, and human studies confirmed ETB-mediated vasoconstriction in resistance and capacitance vessels.\",\n      \"evidence\": \"Subtype-specific antiserum immunohistochemistry; site-directed mutagenesis of human ETB in COS cells with IP accumulation and radioligand binding; intra-arterial selective agonist infusion in human subjects\",\n      \"pmids\": [\"8476120\", \"7698331\", \"7634449\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for why Asp147 couples to G-protein signaling was unknown\", \"Endothelial versus smooth muscle ETB contributions not genetically dissected in vivo\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying the downstream effector pathways by which EDNRB regulates epithelial Na⁺/H⁺ exchange: EDNRB-specific activation of NHE3 proceeds through parallel Ca²⁺-dependent and tyrosine kinase (p210/paxillin/p125FAK) pathways, revealing a bifurcating intracellular signaling architecture.\",\n      \"evidence\": \"Pharmacological inhibitors and immunoprecipitation in OKP cells stably expressing ETB\",\n      \"pmids\": [\"8843705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the p210 tyrosine kinase was unknown\", \"Whether these pathways operate in native renal tubule cells was not shown\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstrating that EDNRB undergoes rapid agonist-induced phosphorylation causing fast desensitization distinct from ETA, and that a TM5 proline is critical for receptor function in neural crest development.\",\n      \"evidence\": \"Phosphorylation/IP accumulation/internalization assays in HEK cells; molecular characterization of radiation/chemical mutagenesis alleles in mice with white coat/megacolon phenotype\",\n      \"pmids\": [\"9341224\", \"9371807\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases responsible for EDNRB phosphorylation were not identified\", \"Whether the TM5 proline mutation affects folding versus signaling was unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing EDNRB as a tonic vasodepressor: gene-targeted ETB-knockout mice showed ~20 mmHg elevated blood pressure, with the depressor effect partly mediated by prostacyclin rather than NO, and EDNRB-specific NHE3 phosphorylation was mapped to multiple Thr/Ser residues.\",\n      \"evidence\": \"ETB gene-targeted mice with selective pharmacological dissection; immunoprecipitation and alkaline phosphatase in OKP-ETB cells\",\n      \"pmids\": [\"10198387\", \"10199826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific NHE3 phosphorylation sites were not individually mutated\", \"Relative contribution of renal versus vascular EDNRB to blood pressure was unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Delineating the renal tubular mechanism: EDNRB on thick ascending limb cells decreases NaCl reabsorption through Ca²⁺-dependent NOS activation, and big-ET-1-induced natriuresis/diuresis is abolished by selective ETB blockade or NOS inhibition.\",\n      \"evidence\": \"Isolated tubule perfusion with BQ-788/L-NAME; in vivo ETB antagonist and NOS inhibitor infusion in anesthetized rats\",\n      \"pmids\": [\"10919853\", \"10720587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"NOS isoform responsible in the thick ascending limb was not specified\", \"Whether EDNRB acts on apical or basolateral membrane was not determined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Revealing epigenetic silencing of EDNRB: promoter CpG island methylation was shown to repress all four EDNRB transcripts, with demethylation restoring expression, and EDNRB-dependent prostacyclin generation was found to inhibit platelet aggregation.\",\n      \"evidence\": \"Bisulfite sequencing and 5-aza-dC treatment in normal and tumor cells; ex vivo platelet aggregation with selective ETB agonist/antagonist and COX inhibitors\",\n      \"pmids\": [\"11309363\", \"11181435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cancer types and in vivo consequences of EDNRB methylation were not broadly surveyed\", \"Whether COX-2-dependent prostacyclin is the sole antiplatelet mediator was not settled\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing genetic epistasis between EDNRB and RET in Hirschsprung disease: intercross of Ret-null and Ednrb-hypomorphic mice produced non-complementation of aganglionosis, placing both genes in a shared pathway for enteric nervous system colonization.\",\n      \"evidence\": \"Genome-wide association in Mennonite trios; mouse Ret/Ednrb intercross epistasis analysis\",\n      \"pmids\": [\"12355085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of RET–EDNRB pathway convergence was unknown\", \"Whether the epistasis is cell-autonomous in neural crest cells was not shown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Revealing that EDNRB and Sox10 genetically interact to promote neural crest cell survival: double-mutant mice showed enhanced aganglionosis and increased apoptosis in vagal neural crest cells, linking EDNRB signaling to anti-apoptotic function during gut colonization.\",\n      \"evidence\": \"Sox10/Ednrb double-mutant mouse phenotypic analysis with apoptosis quantification\",\n      \"pmids\": [\"16650841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Anti-apoptotic effectors downstream of EDNRB in neural crest cells were not identified\", \"Whether the apoptosis phenotype is cell-autonomous was not definitively resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Refining the renal signaling cascade and identifying a pulmonary paracrine function: medullary EDNRB signals through NOS1→cGMP→PKG to drive natriuresis/diuresis, while pulmonary endothelial EDNRB impairs alveolar fluid clearance via NO-dependent (cGMP-independent) downregulation of epithelial Na,K-ATPase.\",\n      \"evidence\": \"In vivo renal infusion in ETB-deficient rats with NOS1/PKG inhibitors; isolated perfused lung from ETB-deficient rats with co-culture and Na,K-ATPase assays\",\n      \"pmids\": [\"18305094\", \"18948426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The cGMP-independent NO effector in alveolar epithelium was not identified\", \"How NOS1 versus eNOS are differentially engaged across tissues was not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Solving the structural basis of endothelin recognition: the crystal structure of EDNRB in apo and ET-1-bound forms showed that TM1/2/6/7 move to envelop the entire peptide, creating near-irreversible binding, and revealed flexibility in TM6 linked to G-protein coupling.\",\n      \"evidence\": \"X-ray crystallography with mutation analysis (Nature)\",\n      \"pmids\": [\"27595334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Active-state structure with a G-protein or arrestin was not obtained\", \"Structural basis for isopeptide selectivity at the single-residue level was incompletely resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Elucidating antagonist mechanisms and transcriptional control of EDNRB: crystal structures showed bosentan blocks TM6 inward movement while Na⁺ acts as a weak negative allosteric modulator; SOX10 and ZEB2 were shown to directly activate the EDNRB promoter, with EDNRB functioning downstream of ZEB2 to inhibit premature neuronal differentiation of enteric progenitors.\",\n      \"evidence\": \"X-ray crystallography of bosentan- and K-8794-bound EDNRB; ChIP, transactivation, and retroviral EDNRB rescue in Zeb2-heterozygous enteric progenitor cultures\",\n      \"pmids\": [\"28805809\", \"28063956\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Na⁺ allosteric modulation is physiologically relevant was not established\", \"Full enhancer/promoter architecture governing tissue-specific EDNRB expression was not mapped\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defining the structural switch for full versus partial agonism: the ET-3- and IRL1620-bound crystal structures showed that full agonism requires disruption of the W6.48–D2.50 water-mediated hydrogen bond network, which partial agonists preserve.\",\n      \"evidence\": \"X-ray crystallography with IP accumulation assays\",\n      \"pmids\": [\"30413709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of water network disruption during activation were not captured\", \"How partial agonism translates to biased signaling profiles was not explored\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Completing the transcriptional circuit: GATA2, SOX10, and NKX2.5 were shown to directly regulate EDNRB transcription, and EDNRB and RET reciprocally feed back on these shared transcription factors, providing the molecular explanation for RET–EDNRB epistasis in Hirschsprung disease.\",\n      \"evidence\": \"Chromatin immunoprecipitation and transactivation assays in human and mouse cellular/animal models\",\n      \"pmids\": [\"31313802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative dose–response relationship of the feedback loop was not modeled\", \"Whether additional transcription factors contribute in specific ENS progenitor subtypes is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the active-state structure of EDNRB in complex with a G-protein or β-arrestin, the identity of kinases mediating rapid EDNRB phosphorylation and desensitization, the mechanistic basis for tissue-specific engagement of NOS1 versus eNOS, and the functional consequences of EDNRB promoter methylation in cancer progression in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No active-state GPCR–transducer complex structure available\", \"Kinases for agonist-induced EDNRB phosphorylation unidentified\", \"In vivo cancer consequences of EDNRB methylation not causally tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 5, 6, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 9, 25, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 5, 15, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 6, 7, 9, 16]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [17, 18, 19, 20, 31]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [17, 22, 28]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [6, 7, 8, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"RET\",\n      \"SOX10\",\n      \"ZEB2\",\n      \"GATA2\",\n      \"NKX2.5\",\n      \"NHE3\",\n      \"AGTR1\",\n      \"DRD3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}