{"gene":"PTGER4","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1998,"finding":"EP4-deficient mice die neonatally due to patent ductus arteriosus remaining open; in situ hybridization showed EP4 mRNA is strongly expressed in the ductus arteriosus, establishing EP4 as essential for postnatal closure of this vessel.","method":"Gene targeting (knockout mice), histological examination, in situ hybridization","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined vascular phenotype, replicated in multiple papers referencing this finding, direct localization by in situ hybridization","pmids":["9600059"],"is_preprint":false},{"year":1996,"finding":"The human EP4 receptor gene spans ~22 kb with three exons; the promoter lacks a TATA box but is GC-rich and contains SP1, AP2, and CCAAT motifs; two related EP4 pseudogenes exist in the human genome. The coding region splits at transmembrane domain 6 by an intron, a structure conserved with thromboxane, PGI, and PGD receptors.","method":"Genomic cloning, sequencing, Southern blot, Northern blot","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct genomic sequencing and structural determination, independently consistent with rabbit and rat gene structure papers","pmids":["8661119"],"is_preprint":false},{"year":1996,"finding":"Rabbit EP4 receptor expressed in COS-1 cells couples to Gs and stimulates cAMP production; it is insensitive to butaprost (EP2-selective) but responds to misoprostol-free acid; highly expressed in intestine, uterus, thymus, kidney glomeruli, and adrenal cortex.","method":"cDNA library cloning, heterologous expression in COS-1 cells, cAMP assay, RNase protection assay, in situ hybridization","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted receptor in heterologous cells with direct cAMP measurement and binding profile; consistent with subsequent characterizations","pmids":["8780252"],"is_preprint":false},{"year":2003,"finding":"EP4 (unlike EP2) activates not only Gs/PKA/cAMP but also phosphatidylinositol 3-kinase (PI3K), leading to ERK1/2 activation and induction of the transcription factor EGR-1; EP4 can also stimulate T-cell factor (Tcf)-mediated transcriptional activity via both PKA and PI3K.","method":"Pharmacological and cell signaling assays (PI3K inhibitors, ERK assays, reporter gene assays)","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection in cell lines with pathway inhibitors; single lab review compilation, but findings confirmed by subsequent mechanistic papers","pmids":["14607241"],"is_preprint":false},{"year":2002,"finding":"EP4-deficient mice develop severe DSS-induced colitis with mucosal barrier dysfunction, epithelial loss, crypt damage, and CD4+ T cell proliferation, while deficiency in DP, EP1, EP2, EP3, FP, IP, or TP does not. EP4 maintains intestinal homeostasis by preserving mucosal integrity and downregulating immune response.","method":"Prostanoid receptor knockout mice panel, DSS colitis model, pharmacological agonist/antagonist treatment, DNA microarray, in vitro lamina propria mononuclear cell assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — receptor-specific KO compared across 8 receptor-deficient lines, pharmacological rescue, multiple orthogonal methods","pmids":["11927615"],"is_preprint":false},{"year":2001,"finding":"In rat sensory neurons, EP3C and EP4 receptor subtypes mediate PGE2-induced cAMP production and augmentation of substance P and CGRP release; antisense knockdown of both EP3C and EP4 (but not individual subtypes alone) abolishes PGE2-stimulated cAMP and peptide release.","method":"RT-PCR, antisense oligonucleotide knockdown, cAMP assay, immunoreactive peptide release assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — antisense knockdown with specific phenotypic rescue, multiple orthogonal readouts in primary neurons","pmids":["11278900"],"is_preprint":false},{"year":2004,"finding":"In colon adenocarcinoma CT26 cells, PGE2-EP4 receptor signaling promotes cell proliferation via PI3K/ERK activation; EP4-selective agonist PGE1-OH rescues anti-proliferative effects of COX inhibition specifically through this pathway.","method":"COX inhibitor rescue experiments, EP-selective agonists, PI3K/ERK inhibitors, cell proliferation assays, in vivo tumor model","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological dissection with receptor-selective agonist rescue, pathway inhibitors, and in vivo validation","pmids":["15123663"],"is_preprint":false},{"year":2006,"finding":"EP4 receptor expression increases in DRG neurons after peripheral inflammation; EP4 antagonist or shRNA knockdown attenuates inflammatory thermal and mechanical hypersensitivity; EP4 mediates PGE2-induced sensitization of capsaicin-evoked currents in DRG neurons in vitro.","method":"Immunohistochemistry, intrathecal shRNA knockdown, behavioral pain testing, whole-cell patch-clamp electrophysiology, EP4 antagonist (AH23848)","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo shRNA knockdown plus pharmacological antagonism plus electrophysiological validation in primary neurons","pmids":["16966471"],"is_preprint":false},{"year":2006,"finding":"Enforced EP4 overexpression in adenoma cells (RG/C2) confers stimulation of growth by high doses of PGE2 and promotes anchorage-independent growth, demonstrating that EP4 receptor level determines the tumorigenic response to PGE2 in colorectal cancer progression.","method":"Forced EP4 expression in cell lines, growth assay, soft agar anchorage-independence assay, immunohistochemistry of human specimens","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function overexpression with defined phenotypic readout, single lab","pmids":["16540660"],"is_preprint":false},{"year":2006,"finding":"EP4 receptor antagonism (AH23848 or ONO-AE3-208) reduces breast cancer lung colonization and spontaneous metastasis; EP4 gene silencing by shRNA also reduces metastasis; EP4 antagonism inhibited PGE2-induced tumor cell migration in vitro.","method":"EP4 antagonists, shRNA gene silencing, in vivo metastasis assays, in vitro chemotaxis assay","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological and genetic (shRNA) EP4 inhibition, both in vivo and in vitro, multiple labs replicated metastasis findings","pmids":["16540639"],"is_preprint":false},{"year":2007,"finding":"EP4 mediates PGE2-induced endothelial cell migration and tubulogenesis via ERK (not PKA) signaling; EP4-null endothelial cells fail to migrate or form tubes in response to PGE2 or EP4-selective agonists; EP4 also promotes angiogenesis in vivo in a sponge assay.","method":"Adenocre-mediated EP4 deletion in primary endothelial cells (EP4 flox/flox), ERK/PKA inhibitors, migration and tubulogenesis assays, in vivo angiogenesis sponge assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic deletion plus pathway inhibitor dissection, both in vitro and in vivo endpoints","pmids":["17401137"],"is_preprint":false},{"year":2007,"finding":"EP4 mediates PGE2-dependent cell survival in Jurkat T cells via the PI3K/AKT pathway (not PKA); EP4 antagonist abolishes PGE2 protection from camptothecin-induced apoptosis.","method":"Pharmacological EP receptor antagonists, PI3K/AKT and PKA inhibitors, caspase-3 assay, flow cytometry","journal":"Prostaglandins & other lipid mediators","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pharmacological dissection with multiple pathway inhibitors in a single cell line, mechanistic pathway placement","pmids":["17259077"],"is_preprint":false},{"year":2008,"finding":"Macrophage-specific EP4 deficiency increases macrophage apoptosis in response to proapoptotic stimuli and reduces early atherosclerosis; EP4 promotes macrophage survival through the PI3K/Akt and NF-κB pathways.","method":"Fetal liver cell transplantation (bone marrow chimeras), LDLR-/- atherosclerosis model, apoptosis assays, Western blot for p-Akt/p-Bad/NF-κB","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional hematopoietic KO with in vivo disease endpoint and mechanistic pathway analysis","pmids":["19041765"],"is_preprint":false},{"year":2008,"finding":"EP4 receptor functions as a negative regulator of B cell proliferation in response to BCR signaling; EP4 knockdown accelerates lymphoma spread in mice, while overexpression is protective; EP4 and PGE2-EP4 signaling target a similar set of activating genes in B cells.","method":"Stable shRNA knockdown and overexpression in B cell lymphoma, in vivo tumor spread assay, gene expression analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments with in vivo validation and transcriptomics","pmids":["19075289"],"is_preprint":false},{"year":2009,"finding":"PGE2-EP4 signaling on T cells and dendritic cells promotes TH1 cell differentiation and amplifies IL-23-mediated TH17 cell expansion in vitro; EP4-selective antagonist in vivo decreases TH1 and TH17 accumulation and suppresses EAE and contact hypersensitivity.","method":"In vitro T cell differentiation assays with EP4-selective agonists/antagonists, in vivo EAE and CHS models with EP4 antagonist treatment","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic cell-based experiments plus two distinct in vivo disease models, high-profile journal","pmids":["19465928"],"is_preprint":false},{"year":2009,"finding":"PGE2 signaling through EP4 on FSP1+ fibroblasts (not EP1 or EP2) induces RANKL expression to promote osteoclastogenesis and periprosthetic osteolysis; conditional fibroblast-specific EP4 knockout abrogates RANKL upregulation and osteolysis.","method":"EP receptor knockout mice panel, conditional FSP1-Cre EP4 knockout, wear debris mouse model, in vitro PGE2 stimulation of fibroblasts","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO compared across three receptor KO lines, in vitro and in vivo convergent results","pmids":["19419302"],"is_preprint":false},{"year":2009,"finding":"EP4 receptor exhibits functional selectivity: PGE2 most selectively activates Gαs, PGF2α and PGE1-OH show bias toward Gαi1 and β-arrestin respectively; EP4 can couple to Gαs, Gαi, and recruit β-arrestin with distinct potency/efficacy profiles depending on ligand.","method":"Bioluminescence resonance energy transfer (BRET) assays for Gαs, Gαi, and β-arrestin2 in living cells","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct BRET measurement of G protein coupling in live cells, systematic panel of ligands, single lab","pmids":["19584306"],"is_preprint":false},{"year":2011,"finding":"PGE2 promotes angiogenesis via EP4 coupling to Gαs/cAMP/PKA Cγ; knockdown of EP4 or PKA catalytic subunit γ attenuates tube formation; downstream PKA substrates Rap1A, HSPB6, and eNOS promote angiogenesis while RhoA and GSK3β (inactivated by PKA) suppress it.","method":"siRNA knockdown of EP4 and PKA subunits, EP receptor subtype-selective agonists/antagonists, in vitro tube formation, ex vivo aortic ring assay, in vivo angiogenesis assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic (siRNA) and pharmacological dissection with multiple in vitro and in vivo angiogenesis endpoints","pmids":["21926356"],"is_preprint":false},{"year":2011,"finding":"EP4 (not EP2 or IP) is the primary receptor mediating COX-2-dependent stimulation of renin expression in response to furosemide-induced macula densa activation; EP4-/- mice show ~70% reduction in renin stimulation.","method":"Genetic knockout mice for COX-2, mPGES1, mPGES2, EP2, EP4, and IP receptors; furosemide treatment; real-time RT-PCR for renin mRNA","journal":"American journal of physiology. Renal physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — comparison across multiple receptor and enzyme KO lines with quantitative molecular endpoint","pmids":["21835766"],"is_preprint":false},{"year":2012,"finding":"MiR-101 post-transcriptionally represses EP4 receptor expression by binding the 3'-UTR; ectopic miR-101 reduces EP4 protein, cell proliferation and motility; EP4 overexpression rescues cells from miR-101 tumor-suppressive effects; EP4 silencing phenocopies miR-101.","method":"Luciferase 3'-UTR reporter assay with wild-type and mutant constructs, miR-101 transfection, qRT-PCR, Western blot, cell proliferation and motility assays, co-transfection rescue","journal":"Cancer biology & therapy","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct 3'-UTR reporter assay with mutagenesis, multiple epistatic rescue experiments, single lab","pmids":["22353936"],"is_preprint":false},{"year":2012,"finding":"EP4 signaling through β-arrestin1 upregulates Akt signaling to protect colonic mucosal integrity; β-arrestin1-deficient mice show worsened DSS-colitis with reduced PI3K/p-Akt; PGE2 upregulates β-arrestin1 expression via EP4 both in vivo and in vitro.","method":"β-arrestin1 KO mice, DSS colitis model, siRNA knockdown of β-arr1 in HCT116 cells, Western blot for PI3K/Akt","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and siRNA loss-of-function with in vivo disease model, single lab, mechanistic pathway placement","pmids":["28432343"],"is_preprint":false},{"year":2012,"finding":"In immature B cells (WEHI 231), EP4 activation increases cAMP/PKA, stabilizes NF-κB1 p105, inhibits IκBα phosphorylation, and sequesters NF-κB p65 in the cytoplasm; PI3K is not involved in EP4 signaling in this cell type, contrasting with other cell types.","method":"cAMP ELISA, Western blot for VASP/ERK/IκBα/p105 phosphorylation, fluorescence microscopy for p65 localization, pharmacological EP receptor agonists/antagonists","journal":"The Journal of pharmacy and pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling readouts in single cell line, pharmacological characterization, single lab","pmids":["22775212"],"is_preprint":false},{"year":2013,"finding":"PGE2 regulates pancreatic stellate cell proliferation, migration, invasion, and extracellular matrix/MMP gene expression exclusively through the EP4 receptor (not EP1, EP2, or EP3); EP4 siRNA and EP4-selective antagonists abrogate these effects.","method":"siRNA knockdown of EP4, EP-selective antagonists, MTS proliferation assay, Boyden chamber migration/invasion assay, RT-PCR for matrix genes","journal":"Pancreas","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EP receptor subtype specificity established by siRNA and multiple antagonists, single lab","pmids":["23090667"],"is_preprint":false},{"year":2015,"finding":"EP4 receptor deletion in myeloid cells (using LysM-Cre) markedly inhibits adenoma number and size in ApcMin/+ mice, with decreased mTOR and ERK activation; either genetic or pharmacologic EP4 inhibition drives macrophages/DCs to an anti-tumorigenic M1 phenotype.","method":"Myeloid-specific conditional EP4 knockout (LysM-Cre), ApcMin/+ intestinal polyp model, EP4 pharmacological inhibitor, macrophage polarization assays, mTOR/ERK signaling analysis","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with genetic and pharmacological convergence, in vivo tumor endpoint with mechanistic pathway readout","pmids":["26378024"],"is_preprint":false},{"year":2016,"finding":"COX-2 induces breast cancer stem-like cells via EP4-mediated PI3K/AKT activation of NOTCH and WNT signaling; PI3K/AKT or NOTCH/WNT inhibitors block COX-2/EP4-induced stem cell induction; EP4 antagonist or knockdown reverses all stem-like cell markers and metastasis.","method":"COX-2 overexpression, EP4 antagonist and siRNA knockdown, PI3K/AKT/NOTCH/WNT pathway inhibitors, spheroid formation, ALDH activity, xenograft tumor metastasis models","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological EP4 inhibition with multiple orthogonal readouts, in vivo validation, epistatic pathway dissection","pmids":["27301070"],"is_preprint":false},{"year":2016,"finding":"EP4 activation in the collecting duct operates downstream of vasopressin via PGE2, and upstream of the (pro)renin receptor (PRR), forming a linear AVP/PGE2/EP4/PRR pathway that regulates AQP2 expression and urine concentrating capability; EP4 antagonist and PRR decoy peptide both impair AVP-induced AQP2 expression.","method":"Intrarenal infusion of EP4 antagonist and PRR decoy peptide in rats, collecting duct-specific PRR knockout mice, primary inner medullary CD cell culture, water deprivation model","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic KO plus pharmacological intervention in vivo and in vitro, linear pathway established by sequential blockade","pmids":["27000064"],"is_preprint":false},{"year":2017,"finding":"PGA2 signals through EP4 (identified as a novel PGA2 receptor by pharmacological and molecular screening) to activate Rap1/Rac1 GTPase and PKA targets (VE-cadherin, p120-catenin, ZO-1, cortactin, VASP) enhancing endothelial barrier; it also suppresses NF-κB and ICAM1/VCAM1 expression. Endothelial-specific EP4 knockout abolishes barrier protection in vivo.","method":"Pharmacological and siRNA EP receptor screening, endothelial-specific EP4 knockout mice, two models of acute lung injury, barrier permeability assays, cytoskeleton/junction protein analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — endothelial-specific conditional KO validated by multiple pharmacological approaches and two in vivo injury models","pmids":["28428256"],"is_preprint":false},{"year":2017,"finding":"EP4 promotes invadopodia-mediated ECM degradation and invasion of breast cancer cells through EGFR-dependent signaling; EP4 agonist increases invadopodia and matrix degradation in vitro and in vivo xenografts; EGFR tyrosine kinase inhibition abrogates EP4-mediated matrix degradation.","method":"EP4 agonist and antagonist treatment, 2D invadopodia assay, 3D invasion assay, EGFR kinase inhibitor epistasis, intravital microscopy, xenograft mouse model","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological epistasis with EGFR inhibitor, in vitro and in vivo endpoints, single lab","pmids":["28094049"],"is_preprint":false},{"year":2019,"finding":"EP4 activates PI3K and induces Ca2+ influx through Orai1 (without STIM1 involvement); EP4 forms a complex with Orai1 and TRPC1 (shown by co-immunoprecipitation); Orai1-mediated Ca2+ influx leads to ERK phosphorylation and MMP-2/9 activation promoting oral cancer cell migration; Orai1 knockdown abolishes EP4-induced ERK activation.","method":"Co-immunoprecipitation, siRNA knockdown of EP4 and Orai1, Ca2+ imaging, ERK phosphorylation assay, cell migration assay, in vivo lung metastasis model","journal":"Cancer science","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP for complex identification, reciprocal genetic knockdown experiments with mechanistic pathway dissection, in vivo metastasis validation","pmids":["31755615"],"is_preprint":false},{"year":2019,"finding":"In ankylosing spondylitis Th17 cells, EP4 drives Th17 expansion through upregulation of IL-23 receptor, suppression of the RORγt inhibitor FoxO1, and enhancement of STAT3 phosphorylation; EP4 creates a positive feedback loop enhancing its own expression in AS Th17 cells.","method":"Quantitative RT-PCR, flow cytometry, Western blot for EP4 protein, EP4-specific agonist functional assay in primary Th17 cells from AS, RA, PsA patients and healthy controls","journal":"Arthritis research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional agonist studies in primary human cells with molecular pathway readouts (STAT3, FoxO1, IL-23R), single lab","pmids":["31253169"],"is_preprint":false},{"year":2019,"finding":"COX-1/mPGES-1-derived PGE2 acts via endothelial EP4 to protect against myocardial ischemia/reperfusion injury; endothelium-restricted Ep4 deletion impairs microcirculation and exacerbates MI/R injury irrespective of EP4 agonism.","method":"mPges-1 knockout, endothelium-restricted Ep4 conditional knockout mice, MI/R model, microvascular perfusion imaging, leukocyte-endothelial interaction assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with multiple in vivo endpoints, combined with upstream enzyme KO","pmids":["31015404"],"is_preprint":false},{"year":2020,"finding":"Cryo-EM structure of EP4 coupled to heterotrimeric Gs protein at 3.3 Å resolution reveals that compared with other class A GPCRs, the TM6 outward shift is smaller; instead, the Gs C-terminal helix inserts toward TM2 with an extended hook structure; conserved prostanoid receptor residues Phe54(2.39) and Trp327(7.51) form these unique contacts.","method":"Cryo-electron microscopy (cryo-EM) structure determination at 3.3 Å global resolution","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct cryo-EM structure at near-atomic resolution defining G protein coupling mechanism","pmids":["33264604"],"is_preprint":false},{"year":2020,"finding":"Endothelial cell-specific EP4 deletion elevates blood pressure while EC-specific EP4 overexpression reduces it; EP4 maintains BP homeostasis by promoting eNOS phosphorylation at Ser1177 and NO production primarily via the AMPK pathway; mesenteric arteries of EC-EP4-/- mice show increased vasoconstrictor and reduced vasodilatory responses abolished by eNOS inhibition.","method":"EC-specific EP4 knockout and overexpression mice, blood pressure measurement, vascular reactivity assay, eNOS phosphorylation Western blot, AMPK pathway analysis, l-NAME pharmacology","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain- and loss-of-function conditional mouse models with mechanistic pathway (AMPK/eNOS) validation","pmids":["32641583"],"is_preprint":false},{"year":2020,"finding":"EP4/AC/cAMP/PKA signaling mediates GRK2 translocation to the plasma membrane, where GRK2 dissociates from ERK1/2 and loses its inhibitory effect on ERK, thus promoting PGE2-induced angiogenesis; GRK2 siRNA inhibits PGE2-induced endothelial migration and tube formation; Lys220 and Ser685 of GRK2 are important for GRK2 translocation and angiogenic function.","method":"siRNA knockdown of GRK2 and EP4, GRK2 mutant constructs, cAMP FRET assay, ERK co-precipitation, in vivo Matrigel angiogenesis assay with GRK2-deficient aortic segments","journal":"Clinical science (London, England : 1979)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockdown, site-directed mutants of GRK2, ex vivo and in vivo angiogenesis models, mechanistic pathway placement","pmids":["31967309"],"is_preprint":false},{"year":2021,"finding":"PTGER4+ intestinal macrophages promote epithelial barrier regeneration; Csf1r-iCre Ptger4fl/fl mice show defective mucosal healing in DSS colitis; mechanistically, PGE2 triggers CXCL1 secretion from monocyte-derived PTGER4+ macrophages via MAPK signaling, and CXCL1 drives epithelial cell differentiation and proliferation from regenerating crypts.","method":"Macrophage-specific conditional EP4 knockout (Csf1r-iCre), DSS colitis model, MAPK pathway analysis, liposome-encapsulated MAPK agonist therapeutic rescue, epithelial organoid differentiation assay","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with mechanistic rescue using MAPK agonist, organoid assay validates CXCL1 effector mechanism","pmids":["33558271"],"is_preprint":false},{"year":2021,"finding":"TNF-α impairs EP4 signaling by recruiting TRAF2 to the plasma membrane, where TRAF2 interacts with and translocates GRK2, causing EP4 desensitization and internalization and reducing cAMP production; TRAF2 siRNA prevents GRK2 translocation and restores EP4 membrane expression and cAMP.","method":"cAMP FRET biosensor, co-immunoprecipitation of TRAF2-GRK2, siRNA knockdown of TRAF2, Western blot for EP4 membrane distribution, primary human fibroblast-like synoviocytes","journal":"Acta pharmacologica Sinica","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP for complex identification, FRET-based real-time cAMP measurement, siRNA epistasis in primary human cells","pmids":["33859345"],"is_preprint":false},{"year":2022,"finding":"PGE2 acts via EP4 on osteoclasts (specifically via EP4, not EP2 alone) to promote OA progression; tissue-specific EP4 knockout in osteoclasts (EP4LysM) reduces OA progression, osteophyte formation, OA-related pain, Netrin-1 secretion, CGRP+ sensory innervation, PDGF-BB expression, and type H blood vessel formation; EP4 signals through Gαs/PI3K/AKT/MAPK in osteoclasts.","method":"Osteoclast-specific EP4 conditional knockout (LysM-Cre), DMM OA model, pain behavior testing, immunofluorescence for nerve innervation and vasculature, Gαs/PI3K/AKT/MAPK pathway analysis, novel EP4 antagonist HL-43","journal":"Bone research","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with multiple in vivo disease endpoints and molecular pathway validation, pharmacological confirmation with novel antagonist","pmids":["35260562"],"is_preprint":false},{"year":2022,"finding":"Cartilage-specific EP4 deletion promotes chondrogenesis and cartilage anabolism, suppresses catabolism and hypertrophy, and reduces joint pain; EP4 regulates cartilage anabolism through cAMP/PKA/CREB/Sox9 signaling; EP4 antagonist HL-43 reproduces these effects in multiple cartilage defect models.","method":"Cartilage-specific EP4 conditional knockout, microfracture and DMM surgery models, aging model, human cartilage explants, cAMP/PKA/CREB/Sox9 signaling analysis","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 2 / Strong — cartilage-specific conditional KO with multiple disease models, human tissue validation, mechanistic pathway dissection","pmids":["35256606"],"is_preprint":false},{"year":2022,"finding":"PGE2-EP2/EP4 signaling simultaneously promotes NF-κB-driven active inflammation in myeloid cells and drives the mregDC-Treg axis for Treg recruitment and activation, creating immunosuppression in the tumor microenvironment; dual EP2/EP4 inhibition required to reverse both arms.","method":"Immune checkpoint inhibitor-insensitive mouse cancer model, single-cell RNA sequencing, pharmacological EP2/EP4 antagonists","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — single-cell transcriptomics plus pharmacological intervention in in vivo tumor model; dual signaling axis mechanistically established","pmids":["35675777"],"is_preprint":false},{"year":2003,"finding":"The rat EP4 gene has three exons separated by two introns; a GC-rich/Sp1 binding site within the first 80 bases of the transcription start site is required for constitutive EP4 transcription; mutation of the Sp1 site at -78 to -66 abolishes promoter activity; three Sp1 sites cooperate to enhance transcription.","method":"Genomic cloning, Northern blot, luciferase reporter constructs with deletion and site-specific mutations, identification of transcription start site","journal":"American journal of obstetrics and gynecology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis of Sp1 sites in reporter constructs directly defines transcriptional control element","pmids":["14634592"],"is_preprint":false},{"year":2008,"finding":"EP4 transcription in glioblastoma T98G cells is driven by Sp1 binding sites at -197 to -160 of the human EP4 promoter; troglitazone and sulindac sulfide suppress EP4 expression by activating MEK/ERK, which phosphorylates Sp1 reducing its DNA binding (confirmed by ChIP); reversal by MEK inhibitor PD98059 establishes Sp1 phosphorylation as the suppression mechanism.","method":"Luciferase reporter assays with Sp1 site mutations, ChIP assay for Sp1 binding, immunoprecipitation-Western blot for Sp1 phosphorylation, MEK/ERK inhibitor (PD98059) rescue","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — ChIP and mutagenesis directly confirm Sp1-dependent promoter mechanism; orthogonal pharmacological validation","pmids":["18346464"],"is_preprint":false},{"year":2012,"finding":"EP4 signaling in DRG neurons promotes EP4 externalization (trafficking from Golgi and recycling endosomes to plasma membrane); inhibitors of anterograde secretory pathway, protein synthesis, or recycling suppress PGE2-induced EP4 surface expression; complete Freund's adjuvant-induced inflammation increases cell-surface EP4 levels via COX-2/PGE2/EP4 signaling in vivo.","method":"Pharmacological inhibitors of secretory pathway/recycling, cell-surface biotinylation, intracellular cAMP sequential treatment assay, CFA inflammation model, COX-2 inhibitor treatment","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — subcellular trafficking established by pathway inhibitors and surface biotinylation, in vivo inflammation model, single lab","pmids":["23265688"],"is_preprint":false},{"year":2015,"finding":"EP4 receptor deletion in macrophages (conditional KO) renders macrophages less susceptible to M2 polarization; EP4 agonist enhances M2 polarization and improves glucose tolerance and insulin sensitivity in obese db/db mice by promoting M2 macrophage polarization via PPARδ; PPARδ antagonism suppresses EP4-mediated M2 polarization.","method":"EP4-selective agonist in db/db mice, peritoneal macrophage M1/M2 polarization assay with EP4-KO macrophages, PPARδ antagonist epistasis, adipose tissue histology and cytokine analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO macrophages plus PPARδ epistasis, in vivo metabolic endpoints, single lab","pmids":["26308623"],"is_preprint":false},{"year":2023,"finding":"EP4 blockade abrogates Yes-associated protein 1 (YAP)-driven pro-metastatic factor expression in pancreatic cancer cells in vitro and reduces YAP activity in vivo; EP4-YAP signaling axis is a pro-metastatic pathway in pancreatic cancer.","method":"EP4 antagonist L001, YAP activity reporter assay, in vivo hepatic metastasis model, Western blot for YAP targets","journal":"Molecules (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological EP4 inhibition with YAP pathway readout in vitro and in vivo, single lab","pmids":["35208999"],"is_preprint":false}],"current_model":"PTGER4/EP4 is a Gαs-coupled class A GPCR (cryo-EM structure resolved at 3.3 Å) that primarily signals via cAMP/PKA but also engages PI3K/AKT, ERK, β-arrestin, and Gαi in a ligand- and cell-type-dependent (functionally selective) manner; it regulates diverse processes including ductus arteriosus closure, intestinal homeostasis, inflammatory T cell differentiation (TH1/TH17), sensory neuron sensitization, angiogenesis via ERK/PKA-dependent endothelial migration, bone remodeling via RANKL induction in fibroblasts and cAMP/PKA/CREB/Sox9 in chondrocytes, macrophage survival through PI3K/Akt/NF-κB, renin secretion, blood pressure through AMPK/eNOS, and tumor progression through PI3K/ERK, NOTCH/WNT, and YAP pathways; receptor desensitization is mediated by GRK2 translocation (promoted by TRAF2 in inflammatory conditions) and by β-arrestin recruitment, while EP4 surface expression in neurons is dynamically regulated by PGE2-driven anterograde trafficking from Golgi and recycling endosomes."},"narrative":{"mechanistic_narrative":"PTGER4 (EP4) is a Gαs-coupled class A prostaglandin E2 receptor that translates PGE2 signals into diverse physiological and pathological programs spanning vascular development, mucosal homeostasis, immune cell differentiation, sensory sensitization, bone and cartilage remodeling, and tumor progression [PMID:9600059, PMID:11927615, PMID:19465928]. Cryo-EM of the EP4–Gs complex shows an atypically small TM6 outward shift, with the Gs C-terminal helix inserting toward TM2 via an extended hook and contacts from conserved prostanoid-receptor residues Phe54(2.39) and Trp327(7.51) [PMID:33264604]. Beyond canonical Gαs/cAMP/PKA output, EP4 displays pronounced functional selectivity, coupling additionally to Gαi and recruiting β-arrestin with ligand-dependent potency, and engaging PI3K/AKT and ERK1/2 cascades that diverge by cell type [PMID:19584306, PMID:14607241, PMID:17259077]. These branches drive distinct outputs: PKA-dependent eNOS, Rap1A and HSPB6 activation supports angiogenesis and endothelial barrier integrity while suppressing RhoA/GSK3β and NF-κB [#17, #26_skip]. EP4 sustains intestinal homeostasis—maintaining mucosal integrity through β-arrestin1/Akt signaling and, in PTGER4+ macrophages, driving CXCL1-mediated epithelial regeneration via MAPK [PMID:11927615, PMID:28432343, PMID:33558271]; promotes TH1 and IL-23-amplified TH17 differentiation [PMID:19465928, PMID:31253169]; mediates inflammatory sensory neuron sensitization [PMID:16966471]; and in tumors couples PGE2 to proliferation, migration, metastasis, and stemness via PI3K/ERK, NOTCH/WNT, EGFR/invadopodia, Orai1-dependent Ca2+/ERK, and YAP pathways [PMID:15123663, PMID:16540639, PMID:27301070, PMID:28094049, PMID:31755615, PMID:35208999]. In bone and joint tissue EP4 induces RANKL in fibroblasts and signals through cAMP/PKA/CREB/Sox9 in chondrocytes and Gαs/PI3K/AKT/MAPK in osteoclasts to control remodeling and osteoarthritis [PMID:19419302, PMID:35260562, PMID:35256606]. EP4 also controls renal renin expression and an AVP/PGE2/EP4/PRR axis governing AQP2, and maintains blood pressure via endothelial AMPK/eNOS [PMID:21835766, PMID:27000064, PMID:32641583]. Receptor signaling is constrained by GRK2 translocation and β-arrestin recruitment—GRK2 movement being promoted by TRAF2 under TNF-α—while neuronal surface EP4 is dynamically supplied by PGE2-driven anterograde trafficking from Golgi and recycling endosomes [PMID:31967309, PMID:33859345, PMID:23265688]. EP4 transcription is governed by GC-rich, TATA-less Sp1-dependent promoter elements and is post-transcriptionally repressed by miR-101 [PMID:14634592, PMID:18346464, PMID:22353936]. Genetic ablation establishes that EP4 is essential for postnatal closure of the ductus arteriosus [PMID:9600059].","teleology":[{"year":1996,"claim":"Establishing the receptor's identity and basic coupling answered whether EP4 was a distinct Gs-coupled PGE2 receptor with a defined gene architecture.","evidence":"Genomic cloning of the human gene plus heterologous expression of rabbit EP4 in COS-1 cells with cAMP assays and binding profiling","pmids":["8661119","8780252"],"confidence":"High","gaps":["No structural basis for Gs coupling at this stage","Other signaling branches not yet probed"]},{"year":1998,"claim":"Knockout established a non-redundant developmental requirement, showing EP4 is essential for postnatal ductus arteriosus closure.","evidence":"Gene-targeted EP4-null mice with histology and in situ hybridization","pmids":["9600059"],"confidence":"High","gaps":["Mechanism linking EP4 signaling to ductal smooth muscle closure not defined","Did not address adult/tissue-specific roles"]},{"year":2002,"claim":"A panel of prostanoid receptor knockouts pinpointed EP4 as the specific receptor maintaining intestinal mucosal homeostasis.","evidence":"Eight-receptor KO comparison in DSS colitis with microarray and lamina propria cell assays","pmids":["11927615"],"confidence":"High","gaps":["Downstream effector pathway for barrier protection not yet identified","Cell type responsible not resolved"]},{"year":2003,"claim":"Pharmacological dissection showed EP4 signals beyond cAMP/PKA, engaging PI3K/ERK/EGR-1 and Tcf transcription, distinguishing it from EP2.","evidence":"Pathway inhibitor and reporter assays in cell lines","pmids":["14607241"],"confidence":"Medium","gaps":["Receptor-proximal mechanism of PI3K engagement undefined","Compiled from cell-line studies, not genetic"]},{"year":2006,"claim":"Genetic and pharmacological inhibition established EP4 as a driver of tumor cell proliferation, migration, and metastasis via PI3K/ERK.","evidence":"shRNA silencing and EP4 antagonists in colon and breast cancer with in vivo metastasis models","pmids":["15123663","16540660","16540639"],"confidence":"High","gaps":["Direct receptor-effector coupling for migration not resolved","Tumor microenvironment contributions not yet separated"]},{"year":2007,"claim":"Conditional deletion and pathway inhibitors revealed branch-specific outputs—ERK-dependent angiogenesis and PI3K/AKT-dependent survival—clarifying functional divergence.","evidence":"EP4-flox endothelial deletion with migration/tube assays and pharmacological dissection in Jurkat T cells","pmids":["17401137","17259077"],"confidence":"High","gaps":["What dictates ERK vs PKA vs PI3K branch selection unresolved","Jurkat survival study limited to one cell line"]},{"year":2009,"claim":"Direct BRET measurement demonstrated ligand-biased functional selectivity, showing EP4 couples to Gαs, Gαi, and β-arrestin with distinct ligand-dependent profiles.","evidence":"BRET assays for Gαs, Gαi, and β-arrestin2 across a ligand panel in living cells","pmids":["19584306"],"confidence":"High","gaps":["Structural basis of biased coupling not defined","Single-lab characterization"]},{"year":2009,"claim":"Cell-type-specific studies mapped EP4 onto immune differentiation and bone remodeling, defining TH1/TH17 promotion and fibroblast RANKL induction.","evidence":"EP4 agonist/antagonist T-cell differentiation assays with EAE/CHS models and FSP1-Cre fibroblast EP4 KO in osteolysis","pmids":["19465928","19419302","19075289"],"confidence":"High","gaps":["Transcriptional effectors downstream of EP4 in T cells incompletely mapped","B-cell vs T-cell opposing roles not mechanistically reconciled"]},{"year":2011,"claim":"Genetic dissection placed EP4 in defined linear signaling chains for angiogenesis (PKA Cγ→Rap1A/HSPB6/eNOS) and renal renin control.","evidence":"siRNA of EP4 and PKA subunits with angiogenesis assays; multi-KO renin expression study","pmids":["21926356","21835766"],"confidence":"High","gaps":["How PKA substrate selection is achieved unclear","Renin mechanism downstream of EP4 not detailed"]},{"year":2012,"claim":"Studies of EP4 regulation defined post-transcriptional control by miR-101, β-arrestin1-dependent mucosal protection, and cell-type-divergent NF-κB outputs.","evidence":"3'-UTR luciferase mutagenesis, β-arrestin1 KO colitis model, and signaling readouts in immature B cells","pmids":["22353936","28432343","22775212"],"confidence":"Medium","gaps":["Why PI3K is dispensable in some cell types unexplained","β-arrestin1 colitis study single lab"]},{"year":2016,"claim":"Integrating EP4 into renal and cancer networks defined the AVP/PGE2/EP4/PRR–AQP2 axis and EP4-driven PI3K/AKT activation of NOTCH/WNT for cancer stemness.","evidence":"Sequential pharmacological/genetic blockade in collecting duct; epistatic pathway inhibitors with stemness and metastasis readouts","pmids":["27000064","27301070"],"confidence":"High","gaps":["Linkage from EP4 to PRR molecularly undefined","How EP4 selects stemness program not resolved"]},{"year":2017,"claim":"EP4 was shown to operate through additional effectors—EGFR-dependent invadopodia, and PGA2-activated Rap1/Rac1 endothelial barrier protection—broadening its agonist and effector repertoire.","evidence":"EGFR inhibitor epistasis with invasion assays; endothelial-specific EP4 KO in acute lung injury with PGA2 screening","pmids":["28094049","28428256"],"confidence":"Medium","gaps":["Mechanism of EP4-EGFR transactivation undefined","PGA2 as EP4 ligand needs broader confirmation"]},{"year":2019,"claim":"Complex-level and tissue-specific analyses revealed an EP4-Orai1/TRPC1 Ca2+ signaling module and an endothelial EP4 cardioprotective role.","evidence":"Co-IP and reciprocal knockdown with Ca2+ imaging in oral cancer; endothelium-restricted Ep4 KO in MI/R injury; AS Th17 functional studies","pmids":["31755615","31015404","31253169"],"confidence":"High","gaps":["Stoichiometry of EP4-Orai1-TRPC1 complex unknown","Th17 feedback mechanism single lab"]},{"year":2020,"claim":"Structural and desensitization studies defined the Gs-coupling architecture and the GRK2 translocation mechanism controlling EP4 signaling and angiogenesis.","evidence":"3.3 Å cryo-EM of EP4-Gs; siRNA and GRK2 mutant analysis with cAMP FRET and angiogenesis assays; reciprocal endothelial EP4 BP models","pmids":["33264604","31967309","32641583"],"confidence":"High","gaps":["Structures of biased/Gi-coupled states absent","How GRK2 dissociation from ERK is regulated unclear"]},{"year":2021,"claim":"Mechanistic studies tied EP4 desensitization to TNF-α/TRAF2-driven GRK2 translocation and identified PTGER4+ macrophage CXCL1-mediated epithelial regeneration.","evidence":"Co-IP of TRAF2-GRK2 with cAMP FRET in synoviocytes; Csf1r-iCre EP4 KO with organoid and MAPK-agonist rescue in colitis","pmids":["33859345","33558271"],"confidence":"High","gaps":["How TRAF2 is recruited to EP4 vicinity not detailed","CXCL1 receptor on epithelium not defined here"]},{"year":2022,"claim":"Joint and tumor studies established EP4 cartilage cAMP/PKA/CREB/Sox9 and osteoclast Gαs/PI3K/AKT/MAPK programs and an EP2/EP4 immunosuppressive axis in tumors.","evidence":"Cartilage- and osteoclast-specific EP4 KO with OA models and antagonist HL-43; scRNA-seq with dual EP2/EP4 antagonists in tumor model","pmids":["35256606","35260562","35675777"],"confidence":"High","gaps":["Cross-talk between cartilage and osteoclast EP4 programs unresolved","Relative EP2 vs EP4 contributions to immunosuppression not separated"]},{"year":2023,"claim":"EP4 was linked to YAP-driven pro-metastatic signaling in pancreatic cancer, extending its tumor effector repertoire.","evidence":"EP4 antagonist with YAP reporter and hepatic metastasis model","pmids":["35208999"],"confidence":"Medium","gaps":["Molecular link between EP4 and YAP activation undefined","Single-lab pharmacological study"]},{"year":null,"claim":"How ligand identity and cellular context select among EP4's Gαs/Gαi/β-arrestin/PI3K/ERK/Ca2+ branches to produce opposing outputs in different tissues remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unified structural/biochemical model of biased signaling across cell types","Determinants of pro- vs anti-tumor and pro- vs anti-inflammatory outputs unclear","Structures of non-Gs coupled states unavailable"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[2,16,31]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[35,41]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[41]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[41]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,16,31]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,14,23,38]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,9,24,28]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,10,17]}],"complexes":[],"partners":["GNAS","ARRB1","GRK2","TRAF2","ORAI1","TRPC1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P35408","full_name":"Prostaglandin E2 receptor EP4 subtype","aliases":["Prostanoid EP4 receptor"],"length_aa":488,"mass_kda":53.1,"function":"Receptor for prostaglandin E2 (PGE2). The activity of this receptor is mediated by G(s) proteins that stimulate adenylate cyclase. Has a relaxing effect on smooth muscle. May play an important role in regulating renal hemodynamics, intestinal epithelial transport, adrenal aldosterone secretion, and uterine function","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P35408/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTGER4","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTGER4","total_profiled":1310},"omim":[{"mim_id":"615770","title":"ATRIAL FIBRILLATION, FAMILIAL, 15; ATFB15","url":"https://www.omim.org/entry/615770"},{"mim_id":"612381","title":"INFLAMMATORY BOWEL DISEASE 23; IBD23","url":"https://www.omim.org/entry/612381"},{"mim_id":"612380","title":"INFLAMMATORY BOWEL DISEASE 22; IBD22","url":"https://www.omim.org/entry/612380"},{"mim_id":"612354","title":"INFLAMMATORY BOWEL DISEASE 21; IBD21","url":"https://www.omim.org/entry/612354"},{"mim_id":"612288","title":"INFLAMMATORY BOWEL DISEASE 20; IBD20","url":"https://www.omim.org/entry/612288"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":81.0},{"tissue":"pancreas","ntpm":51.1}],"url":"https://www.proteinatlas.org/search/PTGER4"},"hgnc":{"alias_symbol":["EP4"],"prev_symbol":[]},"alphafold":{"accession":"P35408","domains":[{"cath_id":"1.20.1070.10","chopping":"22-232_258-350","consensus_level":"high","plddt":87.515,"start":22,"end":350}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P35408","model_url":"https://alphafold.ebi.ac.uk/files/AF-P35408-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P35408-F1-predicted_aligned_error_v6.png","plddt_mean":70.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTGER4","jax_strain_url":"https://www.jax.org/strain/search?query=PTGER4"},"sequence":{"accession":"P35408","fasta_url":"https://rest.uniprot.org/uniprotkb/P35408.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P35408/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P35408"}},"corpus_meta":[{"pmid":"19465928","id":"PMC_19465928","title":"Prostaglandin E2-EP4 signaling promotes immune inflammation through Th1 cell differentiation and Th17 cell expansion.","date":"2009","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/19465928","citation_count":458,"is_preprint":false},{"pmid":"11927615","id":"PMC_11927615","title":"The prostaglandin receptor EP4 suppresses colitis, mucosal damage and CD4 cell activation in the gut.","date":"2002","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/11927615","citation_count":407,"is_preprint":false},{"pmid":"14607241","id":"PMC_14607241","title":"EP2 and EP4 prostanoid receptor signaling.","date":"2003","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/14607241","citation_count":366,"is_preprint":false},{"pmid":"9600059","id":"PMC_9600059","title":"Patent ductus arteriosus and neonatal death in prostaglandin receptor EP4-deficient mice.","date":"1998","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/9600059","citation_count":253,"is_preprint":false},{"pmid":"23776144","id":"PMC_23776144","title":"The prostanoid EP4 receptor and its signaling pathway.","date":"2013","source":"Pharmacological reviews","url":"https://pubmed.ncbi.nlm.nih.gov/23776144","citation_count":220,"is_preprint":false},{"pmid":"16966471","id":"PMC_16966471","title":"Prostaglandin E2 receptor EP4 contributes to inflammatory pain hypersensitivity.","date":"2006","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/16966471","citation_count":197,"is_preprint":false},{"pmid":"11278900","id":"PMC_11278900","title":"Prostaglandin receptor subtypes, EP3C and EP4, mediate the prostaglandin E2-induced cAMP production and sensitization of sensory neurons.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11278900","citation_count":155,"is_preprint":false},{"pmid":"27544059","id":"PMC_27544059","title":"Validation of the SHOX2/PTGER4 DNA Methylation Marker Panel for Plasma-Based Discrimination between Patients with Malignant and Nonmalignant Lung Disease.","date":"2016","source":"Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/27544059","citation_count":140,"is_preprint":false},{"pmid":"23523686","id":"PMC_23523686","title":"E-type prostanoid receptor 4 (EP4) in disease and therapy.","date":"2013","source":"Pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/23523686","citation_count":134,"is_preprint":false},{"pmid":"15123663","id":"PMC_15123663","title":"Colon carcinoma cell growth is associated with prostaglandin E2/EP4 receptor-evoked ERK activation.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15123663","citation_count":131,"is_preprint":false},{"pmid":"16540639","id":"PMC_16540639","title":"Prostaglandin E receptor EP4 antagonism inhibits breast cancer metastasis.","date":"2006","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/16540639","citation_count":122,"is_preprint":false},{"pmid":"16540660","id":"PMC_16540660","title":"Increased EP4 receptor expression in colorectal cancer progression promotes cell growth and anchorage independence.","date":"2006","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/16540660","citation_count":121,"is_preprint":false},{"pmid":"35260562","id":"PMC_35260562","title":"PGE2 activates EP4 in subchondral bone osteoclasts to regulate osteoarthritis.","date":"2022","source":"Bone research","url":"https://pubmed.ncbi.nlm.nih.gov/35260562","citation_count":118,"is_preprint":false},{"pmid":"17401137","id":"PMC_17401137","title":"Prostaglandin E2-EP4 receptor promotes endothelial cell migration via ERK activation and angiogenesis in vivo.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17401137","citation_count":116,"is_preprint":false},{"pmid":"21926356","id":"PMC_21926356","title":"PGE2 promotes angiogenesis through EP4 and PKA Cγ pathway.","date":"2011","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/21926356","citation_count":113,"is_preprint":false},{"pmid":"35675777","id":"PMC_35675777","title":"PGE2-EP2/EP4 signaling elicits immunosuppression by driving the mregDC-Treg axis in inflammatory tumor microenvironment.","date":"2022","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/35675777","citation_count":107,"is_preprint":false},{"pmid":"27301070","id":"PMC_27301070","title":"COX-2 Induces Breast Cancer Stem Cells via EP4/PI3K/AKT/NOTCH/WNT Axis.","date":"2016","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/27301070","citation_count":107,"is_preprint":false},{"pmid":"19041765","id":"PMC_19041765","title":"Macrophage EP4 deficiency increases apoptosis and suppresses early atherosclerosis.","date":"2008","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/19041765","citation_count":97,"is_preprint":false},{"pmid":"19584306","id":"PMC_19584306","title":"Functional selectivity of natural and synthetic prostaglandin EP4 receptor ligands.","date":"2009","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/19584306","citation_count":95,"is_preprint":false},{"pmid":"33558271","id":"PMC_33558271","title":"Prostaglandin E2 receptor PTGER4-expressing macrophages promote intestinal epithelial barrier regeneration upon inflammation.","date":"2021","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/33558271","citation_count":74,"is_preprint":false},{"pmid":"27000064","id":"PMC_27000064","title":"Antidiuretic Action of Collecting Duct (Pro)Renin Receptor Downstream of Vasopressin and PGE2 Receptor EP4.","date":"2016","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/27000064","citation_count":72,"is_preprint":false},{"pmid":"21697732","id":"PMC_21697732","title":"Anti-inflammation therapy by activation of prostaglandin EP4 receptor in cardiovascular and other inflammatory diseases.","date":"2012","source":"Journal of cardiovascular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/21697732","citation_count":64,"is_preprint":false},{"pmid":"19419302","id":"PMC_19419302","title":"PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis.","date":"2009","source":"Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research","url":"https://pubmed.ncbi.nlm.nih.gov/19419302","citation_count":64,"is_preprint":false},{"pmid":"19075289","id":"PMC_19075289","title":"Prostaglandin E2 regulates B cell proliferation through a candidate tumor suppressor, Ptger4.","date":"2008","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/19075289","citation_count":63,"is_preprint":false},{"pmid":"19494202","id":"PMC_19494202","title":"The role of PGE2 receptor EP4 in pathologic ocular angiogenesis.","date":"2009","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/19494202","citation_count":63,"is_preprint":false},{"pmid":"29596308","id":"PMC_29596308","title":"EP4 as a Therapeutic Target for Aggressive Human Breast Cancer.","date":"2018","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/29596308","citation_count":62,"is_preprint":false},{"pmid":"17259077","id":"PMC_17259077","title":"EP4 mediates PGE2 dependent cell survival through the PI3 kinase/AKT pathway.","date":"2007","source":"Prostaglandins & other lipid mediators","url":"https://pubmed.ncbi.nlm.nih.gov/17259077","citation_count":62,"is_preprint":false},{"pmid":"31015404","id":"PMC_31015404","title":"The cyclooxygenase-1/mPGES-1/endothelial prostaglandin EP4 receptor pathway constrains myocardial ischemia-reperfusion injury.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31015404","citation_count":58,"is_preprint":false},{"pmid":"15869929","id":"PMC_15869929","title":"Osteopenia and impaired fracture healing in aged EP4 receptor knockout mice.","date":"2005","source":"Bone","url":"https://pubmed.ncbi.nlm.nih.gov/15869929","citation_count":56,"is_preprint":false},{"pmid":"22570740","id":"PMC_22570740","title":"Inhibition of EP4 signaling attenuates aortic aneurysm formation.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22570740","citation_count":55,"is_preprint":false},{"pmid":"18792778","id":"PMC_18792778","title":"Antagonism of the prostaglandin E receptor EP4 inhibits metastasis and enhances NK function.","date":"2008","source":"Breast cancer research and treatment","url":"https://pubmed.ncbi.nlm.nih.gov/18792778","citation_count":54,"is_preprint":false},{"pmid":"9214685","id":"PMC_9214685","title":"Detection of EP2, EP4, and FP receptors in human ciliary epithelial and ciliary muscle cells.","date":"1997","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/9214685","citation_count":52,"is_preprint":false},{"pmid":"8780252","id":"PMC_8780252","title":"Cloning and expression of the rabbit prostaglandin EP4 receptor.","date":"1996","source":"The American journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/8780252","citation_count":51,"is_preprint":false},{"pmid":"21365278","id":"PMC_21365278","title":"EP4 receptor stimulation down-regulates human eosinophil function.","date":"2011","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/21365278","citation_count":50,"is_preprint":false},{"pmid":"29067176","id":"PMC_29067176","title":"Grapiprant: an EP4 prostaglandin receptor antagonist and novel therapy for pain and inflammation.","date":"2015","source":"Veterinary medicine and science","url":"https://pubmed.ncbi.nlm.nih.gov/29067176","citation_count":48,"is_preprint":false},{"pmid":"17593083","id":"PMC_17593083","title":"Characteristic Ber-EP4 and EMA expression in sebaceoma is immunohistochemically distinct from basal cell carcinoma.","date":"2007","source":"Histopathology","url":"https://pubmed.ncbi.nlm.nih.gov/17593083","citation_count":47,"is_preprint":false},{"pmid":"26308623","id":"PMC_26308623","title":"The Prostaglandin E2 Receptor EP4 Regulates Obesity-Related Inflammation and Insulin Sensitivity.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26308623","citation_count":46,"is_preprint":false},{"pmid":"22353936","id":"PMC_22353936","title":"MicroRNA-101 (miR-101) post-transcriptionally regulates the expression of EP4 receptor in colon cancers.","date":"2012","source":"Cancer biology & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/22353936","citation_count":44,"is_preprint":false},{"pmid":"23090667","id":"PMC_23090667","title":"Prostaglandin E2 regulates pancreatic stellate cell activity via the EP4 receptor.","date":"2013","source":"Pancreas","url":"https://pubmed.ncbi.nlm.nih.gov/23090667","citation_count":43,"is_preprint":false},{"pmid":"33264604","id":"PMC_33264604","title":"Cryo-EM Structure of the Prostaglandin E Receptor EP4 Coupled to G Protein.","date":"2020","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/33264604","citation_count":40,"is_preprint":false},{"pmid":"26378024","id":"PMC_26378024","title":"Prostaglandin E receptor 4 (EP4) promotes colonic tumorigenesis.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26378024","citation_count":39,"is_preprint":false},{"pmid":"33190014","id":"PMC_33190014","title":"EP4 receptor as a novel promising therapeutic target in colon cancer.","date":"2020","source":"Pathology, research and practice","url":"https://pubmed.ncbi.nlm.nih.gov/33190014","citation_count":38,"is_preprint":false},{"pmid":"23300802","id":"PMC_23300802","title":"PTGER4 expression-modulating polymorphisms in the 5p13.1 region predispose to Crohn's disease and affect NF-κB and XBP1 binding sites.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23300802","citation_count":38,"is_preprint":false},{"pmid":"28432343","id":"PMC_28432343","title":"COX-1/PGE2/EP4 alleviates mucosal injury by upregulating β-arr1-mediated Akt signaling in colitis.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28432343","citation_count":38,"is_preprint":false},{"pmid":"28428256","id":"PMC_28428256","title":"Regulation of lung endothelial permeability and inflammatory responses by prostaglandin A2: role of EP4 receptor.","date":"2017","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/28428256","citation_count":38,"is_preprint":false},{"pmid":"35256606","id":"PMC_35256606","title":"A novel prostaglandin E receptor 4 (EP4) small molecule antagonist induces articular cartilage regeneration.","date":"2022","source":"Cell discovery","url":"https://pubmed.ncbi.nlm.nih.gov/35256606","citation_count":37,"is_preprint":false},{"pmid":"31253169","id":"PMC_31253169","title":"Prostaglandin receptor EP4 expression by Th17 cells is associated with high disease activity in ankylosing spondylitis.","date":"2019","source":"Arthritis research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/31253169","citation_count":36,"is_preprint":false},{"pmid":"16289620","id":"PMC_16289620","title":"Lipopolysaccharide stimulates the production of prostaglandin E2 and the receptor Ep4 in osteoblasts.","date":"2005","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/16289620","citation_count":36,"is_preprint":false},{"pmid":"14634592","id":"PMC_14634592","title":"Expression and regulation of the rat prostaglandin E2 receptor type 4 (EP4) in pregnant cervical tissue.","date":"2003","source":"American journal of obstetrics and gynecology","url":"https://pubmed.ncbi.nlm.nih.gov/14634592","citation_count":35,"is_preprint":false},{"pmid":"21835766","id":"PMC_21835766","title":"A major role for the EP4 receptor in regulation of renin.","date":"2011","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/21835766","citation_count":35,"is_preprint":false},{"pmid":"32641583","id":"PMC_32641583","title":"Endothelial cell prostaglandin E2 receptor EP4 is essential for blood pressure homeostasis.","date":"2020","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/32641583","citation_count":34,"is_preprint":false},{"pmid":"31967309","id":"PMC_31967309","title":"CP-25 inhibits PGE2-induced angiogenesis by down-regulating EP4/AC/cAMP/PKA-mediated GRK2 translocation.","date":"2020","source":"Clinical science (London, England : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/31967309","citation_count":34,"is_preprint":false},{"pmid":"23265688","id":"PMC_23265688","title":"Prostaglandin E2/EP4 signalling facilitates EP4 receptor externalization in primary sensory neurons in vitro and in vivo.","date":"2012","source":"Pain","url":"https://pubmed.ncbi.nlm.nih.gov/23265688","citation_count":34,"is_preprint":false},{"pmid":"37559947","id":"PMC_37559947","title":"Dual Blockade of EP2 and EP4 Signaling is Required for Optimal Immune Activation and Antitumor Activity Against Prostaglandin-Expressing Tumors.","date":"2023","source":"Cancer research communications","url":"https://pubmed.ncbi.nlm.nih.gov/37559947","citation_count":33,"is_preprint":false},{"pmid":"22595380","id":"PMC_22595380","title":"Prostaglandin receptor EP4 in abdominal aortic aneurysms.","date":"2012","source":"The American journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/22595380","citation_count":32,"is_preprint":false},{"pmid":"8661119","id":"PMC_8661119","title":"The structure of the prostaglandin EP4 receptor gene and related pseudogenes.","date":"1996","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8661119","citation_count":31,"is_preprint":false},{"pmid":"26830476","id":"PMC_26830476","title":"The Roles of EP4 Prostanoid Receptors in Cancer Malignancy Signaling.","date":"2016","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/26830476","citation_count":29,"is_preprint":false},{"pmid":"18346464","id":"PMC_18346464","title":"Regulation of EP4 expression via the Sp-1 transcription factor: inhibition of expression by anti-cancer agents.","date":"2008","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/18346464","citation_count":28,"is_preprint":false},{"pmid":"29522761","id":"PMC_29522761","title":"Overexpression of prostaglandin E2 EP4 receptor improves cardiac function after myocardial infarction.","date":"2018","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/29522761","citation_count":27,"is_preprint":false},{"pmid":"31755615","id":"PMC_31755615","title":"Prostaglandin E2 receptor EP4 regulates cell migration through Orai1.","date":"2019","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/31755615","citation_count":26,"is_preprint":false},{"pmid":"33662689","id":"PMC_33662689","title":"DNA methylation of PTGER4 in peripheral blood plasma helps to distinguish between lung cancer, benign pulmonary nodules and chronic obstructive pulmonary disease patients.","date":"2021","source":"European journal of cancer (Oxford, England : 1990)","url":"https://pubmed.ncbi.nlm.nih.gov/33662689","citation_count":26,"is_preprint":false},{"pmid":"33668160","id":"PMC_33668160","title":"Prostaglandin E2 Receptor 4 (EP4) as a Therapeutic Target to Impede Breast Cancer-Associated Angiogenesis and Lymphangiogenesis.","date":"2021","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/33668160","citation_count":25,"is_preprint":false},{"pmid":"25510249","id":"PMC_25510249","title":"Activation of prostaglandin E2-EP4 signaling reduces chemokine production in adipose tissue.","date":"2014","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/25510249","citation_count":25,"is_preprint":false},{"pmid":"28611444","id":"PMC_28611444","title":"EP4 inhibition attenuates the development of diabetic and non-diabetic experimental kidney disease.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28611444","citation_count":24,"is_preprint":false},{"pmid":"37457723","id":"PMC_37457723","title":"PGE2-EP2/EP4 signaling elicits mesoCAR T cell immunosuppression in pancreatic cancer.","date":"2023","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/37457723","citation_count":23,"is_preprint":false},{"pmid":"26439841","id":"PMC_26439841","title":"EP4 Receptor-Associated Protein in Macrophages Ameliorates Colitis and Colitis-Associated Tumorigenesis.","date":"2015","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/26439841","citation_count":23,"is_preprint":false},{"pmid":"30138657","id":"PMC_30138657","title":"COX-2/EP2-EP4/β-catenin signaling regulates patulin-induced intestinal cell proliferation and inflammation.","date":"2018","source":"Toxicology and applied pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30138657","citation_count":23,"is_preprint":false},{"pmid":"31645712","id":"PMC_31645712","title":"Epithelial EP4 plays an essential role in maintaining homeostasis in colon.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31645712","citation_count":23,"is_preprint":false},{"pmid":"23364535","id":"PMC_23364535","title":"Significance of divergent expression of prostaglandin EP4 and EP3 receptors in human prostate cancer.","date":"2013","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/23364535","citation_count":23,"is_preprint":false},{"pmid":"22695889","id":"PMC_22695889","title":"Genetic variability of prostaglandin E2 receptor subtype EP4 gene in aspirin-intolerant chronic urticaria.","date":"2012","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22695889","citation_count":23,"is_preprint":false},{"pmid":"28094049","id":"PMC_28094049","title":"EP4 receptor promotes invadopodia and invasion in human breast cancer.","date":"2017","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/28094049","citation_count":22,"is_preprint":false},{"pmid":"30619314","id":"PMC_30619314","title":"mPGES-1-Mediated Production of PGE2 and EP4 Receptor Sensing Regulate T Cell Colonic Inflammation.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30619314","citation_count":22,"is_preprint":false},{"pmid":"32321307","id":"PMC_32321307","title":"Excessive EP4 Signaling in Smooth Muscle Cells Induces Abdominal Aortic Aneurysm by Amplifying Inflammation.","date":"2020","source":"Arteriosclerosis, thrombosis, and vascular biology","url":"https://pubmed.ncbi.nlm.nih.gov/32321307","citation_count":22,"is_preprint":false},{"pmid":"25329458","id":"PMC_25329458","title":"Prostaglandin E2 prevents hyperosmolar-induced human mast cell activation through prostanoid receptors EP2 and EP4.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25329458","citation_count":22,"is_preprint":false},{"pmid":"11444589","id":"PMC_11444589","title":"Molecular cloning and functional characterization of the canine prostaglandin E2 receptor EP4 subtype.","date":"2001","source":"Prostaglandins & other lipid mediators","url":"https://pubmed.ncbi.nlm.nih.gov/11444589","citation_count":22,"is_preprint":false},{"pmid":"36318114","id":"PMC_36318114","title":"Prostaglandin PGE2 Receptor EP4 Regulates Microglial Phagocytosis and Increases Susceptibility to Diet-Induced Obesity.","date":"2023","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/36318114","citation_count":21,"is_preprint":false},{"pmid":"28465762","id":"PMC_28465762","title":"Paricalcitol Pretreatment Attenuates Renal Ischemia-Reperfusion Injury via Prostaglandin E2 Receptor EP4 Pathway.","date":"2017","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/28465762","citation_count":21,"is_preprint":false},{"pmid":"23902376","id":"PMC_23902376","title":"EP4 and EP2 receptor activation of protein kinase A by prostaglandin E2 impairs macrophage phagocytosis of Clostridium sordellii.","date":"2013","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/23902376","citation_count":21,"is_preprint":false},{"pmid":"26639895","id":"PMC_26639895","title":"Role of EP2 and EP4 receptors in airway microvascular leak induced by prostaglandin E2.","date":"2016","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/26639895","citation_count":21,"is_preprint":false},{"pmid":"28899736","id":"PMC_28899736","title":"Characterization of genome-wide copy number aberrations in colonic mixed adenoneuroendocrine carcinoma and neuroendocrine carcinoma reveals recurrent amplification of PTGER4 and MYC genes.","date":"2017","source":"Human pathology","url":"https://pubmed.ncbi.nlm.nih.gov/28899736","citation_count":20,"is_preprint":false},{"pmid":"30191681","id":"PMC_30191681","title":"Evidence for PTGER4, PSCA, and MBOAT7 as risk genes for gastric cancer on the genome and transcriptome level.","date":"2018","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30191681","citation_count":19,"is_preprint":false},{"pmid":"37232020","id":"PMC_37232020","title":"Complementary roles of EP2 and EP4 receptors in malignant glioma.","date":"2023","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/37232020","citation_count":19,"is_preprint":false},{"pmid":"38088451","id":"PMC_38088451","title":"PGE2-EP4 signaling steers cDC2 maturation toward the induction of suppressive T-cell responses.","date":"2024","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/38088451","citation_count":19,"is_preprint":false},{"pmid":"26538147","id":"PMC_26538147","title":"PTGER4 gene variant rs76523431 is a candidate risk factor for radiological joint damage in rheumatoid arthritis patients: a genetic study of six cohorts.","date":"2015","source":"Arthritis research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/26538147","citation_count":18,"is_preprint":false},{"pmid":"21600299","id":"PMC_21600299","title":"Prostaglandin EP4 receptor enhances BCR-induced apoptosis of immature B cells.","date":"2011","source":"Prostaglandins & other lipid mediators","url":"https://pubmed.ncbi.nlm.nih.gov/21600299","citation_count":18,"is_preprint":false},{"pmid":"18437696","id":"PMC_18437696","title":"EP4 agonist accelerates osteoinduction and degradation of beta-tricalcium phosphate by stimulating osteoclastogenesis.","date":"2009","source":"Journal of biomedical materials research. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/18437696","citation_count":18,"is_preprint":false},{"pmid":"33859345","id":"PMC_33859345","title":"TNF-α impairs EP4 signaling through the association of TRAF2-GRK2 in primary fibroblast-like synoviocytes.","date":"2021","source":"Acta pharmacologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/33859345","citation_count":17,"is_preprint":false},{"pmid":"22775212","id":"PMC_22775212","title":"EP4 receptor signalling in immature B cells involves cAMP and NF-κB dependent pathways.","date":"2012","source":"The Journal of pharmacy and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/22775212","citation_count":16,"is_preprint":false},{"pmid":"9888433","id":"PMC_9888433","title":"Expression of prostaglandin receptors EP4 and FP in human lens epithelial cells.","date":"1999","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/9888433","citation_count":16,"is_preprint":false},{"pmid":"29129801","id":"PMC_29129801","title":"Activating prostaglandin E2 receptor subtype EP4 increases secreted mucin from airway goblet cells.","date":"2017","source":"Pulmonary pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/29129801","citation_count":16,"is_preprint":false},{"pmid":"26188701","id":"PMC_26188701","title":"Prostanoids regulate angiogenesis acting primarily on IP and EP4 receptors.","date":"2015","source":"Microvascular research","url":"https://pubmed.ncbi.nlm.nih.gov/26188701","citation_count":16,"is_preprint":false},{"pmid":"25461458","id":"PMC_25461458","title":"EP2 and EP4 receptors mediate PGE2 induced relaxation in murine colonic circular muscle: pharmacological characterization.","date":"2014","source":"Pharmacological research","url":"https://pubmed.ncbi.nlm.nih.gov/25461458","citation_count":16,"is_preprint":false},{"pmid":"33275302","id":"PMC_33275302","title":"Crosstalk between the COX2-PGE2-EP4 signaling pathway and primary cilia in osteoblasts after mechanical stimulation.","date":"2020","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/33275302","citation_count":15,"is_preprint":false},{"pmid":"32186754","id":"PMC_32186754","title":"EP4 activation ameliorates liver ischemia/reperfusion injury via ERK1/2‑GSK3β‑dependent MPTP inhibition.","date":"2020","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32186754","citation_count":15,"is_preprint":false},{"pmid":"35208999","id":"PMC_35208999","title":"A Novel Small Molecular Prostaglandin Receptor EP4 Antagonist, L001, Suppresses Pancreatic Cancer Metastasis.","date":"2022","source":"Molecules (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/35208999","citation_count":14,"is_preprint":false},{"pmid":"28239768","id":"PMC_28239768","title":"Prostaglandin E2 EP4 Receptor Activation Attenuates Neuroinflammation and Early Brain Injury Induced by Subarachnoid Hemorrhage in Rats.","date":"2017","source":"Neurochemical research","url":"https://pubmed.ncbi.nlm.nih.gov/28239768","citation_count":14,"is_preprint":false},{"pmid":"19934343","id":"PMC_19934343","title":"The cyclooxygenase inhibitor sulindac sulfide inhibits EP4 expression and suppresses the growth of glioblastoma cells.","date":"2009","source":"Cancer prevention research (Philadelphia, Pa.)","url":"https://pubmed.ncbi.nlm.nih.gov/19934343","citation_count":14,"is_preprint":false},{"pmid":"32447215","id":"PMC_32447215","title":"Prostaglandin E receptor EP4 stimulates lymphangiogenesis to promote mucosal healing during DSS-induced colitis.","date":"2020","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/32447215","citation_count":13,"is_preprint":false},{"pmid":"28603634","id":"PMC_28603634","title":"Analgesic and anti-inflammatory properties of novel, selective, and potent EP4 receptor antagonists.","date":"2017","source":"Pharmacology research & perspectives","url":"https://pubmed.ncbi.nlm.nih.gov/28603634","citation_count":13,"is_preprint":false},{"pmid":"18684231","id":"PMC_18684231","title":"EP4 and EP2 receptor subtypes involved in colonic secretion in rat.","date":"2008","source":"Basic & clinical pharmacology & toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/18684231","citation_count":13,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54865,"output_tokens":10927,"usd":0.16425,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":21931,"output_tokens":5533,"usd":0.12399,"stage2_stop_reason":"end_turn"},"total_usd":0.28824,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"EP4-deficient mice die neonatally due to patent ductus arteriosus remaining open; in situ hybridization showed EP4 mRNA is strongly expressed in the ductus arteriosus, establishing EP4 as essential for postnatal closure of this vessel.\",\n      \"method\": \"Gene targeting (knockout mice), histological examination, in situ hybridization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined vascular phenotype, replicated in multiple papers referencing this finding, direct localization by in situ hybridization\",\n      \"pmids\": [\"9600059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The human EP4 receptor gene spans ~22 kb with three exons; the promoter lacks a TATA box but is GC-rich and contains SP1, AP2, and CCAAT motifs; two related EP4 pseudogenes exist in the human genome. The coding region splits at transmembrane domain 6 by an intron, a structure conserved with thromboxane, PGI, and PGD receptors.\",\n      \"method\": \"Genomic cloning, sequencing, Southern blot, Northern blot\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct genomic sequencing and structural determination, independently consistent with rabbit and rat gene structure papers\",\n      \"pmids\": [\"8661119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Rabbit EP4 receptor expressed in COS-1 cells couples to Gs and stimulates cAMP production; it is insensitive to butaprost (EP2-selective) but responds to misoprostol-free acid; highly expressed in intestine, uterus, thymus, kidney glomeruli, and adrenal cortex.\",\n      \"method\": \"cDNA library cloning, heterologous expression in COS-1 cells, cAMP assay, RNase protection assay, in situ hybridization\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted receptor in heterologous cells with direct cAMP measurement and binding profile; consistent with subsequent characterizations\",\n      \"pmids\": [\"8780252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"EP4 (unlike EP2) activates not only Gs/PKA/cAMP but also phosphatidylinositol 3-kinase (PI3K), leading to ERK1/2 activation and induction of the transcription factor EGR-1; EP4 can also stimulate T-cell factor (Tcf)-mediated transcriptional activity via both PKA and PI3K.\",\n      \"method\": \"Pharmacological and cell signaling assays (PI3K inhibitors, ERK assays, reporter gene assays)\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection in cell lines with pathway inhibitors; single lab review compilation, but findings confirmed by subsequent mechanistic papers\",\n      \"pmids\": [\"14607241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"EP4-deficient mice develop severe DSS-induced colitis with mucosal barrier dysfunction, epithelial loss, crypt damage, and CD4+ T cell proliferation, while deficiency in DP, EP1, EP2, EP3, FP, IP, or TP does not. EP4 maintains intestinal homeostasis by preserving mucosal integrity and downregulating immune response.\",\n      \"method\": \"Prostanoid receptor knockout mice panel, DSS colitis model, pharmacological agonist/antagonist treatment, DNA microarray, in vitro lamina propria mononuclear cell assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — receptor-specific KO compared across 8 receptor-deficient lines, pharmacological rescue, multiple orthogonal methods\",\n      \"pmids\": [\"11927615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In rat sensory neurons, EP3C and EP4 receptor subtypes mediate PGE2-induced cAMP production and augmentation of substance P and CGRP release; antisense knockdown of both EP3C and EP4 (but not individual subtypes alone) abolishes PGE2-stimulated cAMP and peptide release.\",\n      \"method\": \"RT-PCR, antisense oligonucleotide knockdown, cAMP assay, immunoreactive peptide release assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — antisense knockdown with specific phenotypic rescue, multiple orthogonal readouts in primary neurons\",\n      \"pmids\": [\"11278900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In colon adenocarcinoma CT26 cells, PGE2-EP4 receptor signaling promotes cell proliferation via PI3K/ERK activation; EP4-selective agonist PGE1-OH rescues anti-proliferative effects of COX inhibition specifically through this pathway.\",\n      \"method\": \"COX inhibitor rescue experiments, EP-selective agonists, PI3K/ERK inhibitors, cell proliferation assays, in vivo tumor model\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological dissection with receptor-selective agonist rescue, pathway inhibitors, and in vivo validation\",\n      \"pmids\": [\"15123663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EP4 receptor expression increases in DRG neurons after peripheral inflammation; EP4 antagonist or shRNA knockdown attenuates inflammatory thermal and mechanical hypersensitivity; EP4 mediates PGE2-induced sensitization of capsaicin-evoked currents in DRG neurons in vitro.\",\n      \"method\": \"Immunohistochemistry, intrathecal shRNA knockdown, behavioral pain testing, whole-cell patch-clamp electrophysiology, EP4 antagonist (AH23848)\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo shRNA knockdown plus pharmacological antagonism plus electrophysiological validation in primary neurons\",\n      \"pmids\": [\"16966471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Enforced EP4 overexpression in adenoma cells (RG/C2) confers stimulation of growth by high doses of PGE2 and promotes anchorage-independent growth, demonstrating that EP4 receptor level determines the tumorigenic response to PGE2 in colorectal cancer progression.\",\n      \"method\": \"Forced EP4 expression in cell lines, growth assay, soft agar anchorage-independence assay, immunohistochemistry of human specimens\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function overexpression with defined phenotypic readout, single lab\",\n      \"pmids\": [\"16540660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EP4 receptor antagonism (AH23848 or ONO-AE3-208) reduces breast cancer lung colonization and spontaneous metastasis; EP4 gene silencing by shRNA also reduces metastasis; EP4 antagonism inhibited PGE2-induced tumor cell migration in vitro.\",\n      \"method\": \"EP4 antagonists, shRNA gene silencing, in vivo metastasis assays, in vitro chemotaxis assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological and genetic (shRNA) EP4 inhibition, both in vivo and in vitro, multiple labs replicated metastasis findings\",\n      \"pmids\": [\"16540639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"EP4 mediates PGE2-induced endothelial cell migration and tubulogenesis via ERK (not PKA) signaling; EP4-null endothelial cells fail to migrate or form tubes in response to PGE2 or EP4-selective agonists; EP4 also promotes angiogenesis in vivo in a sponge assay.\",\n      \"method\": \"Adenocre-mediated EP4 deletion in primary endothelial cells (EP4 flox/flox), ERK/PKA inhibitors, migration and tubulogenesis assays, in vivo angiogenesis sponge assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic deletion plus pathway inhibitor dissection, both in vitro and in vivo endpoints\",\n      \"pmids\": [\"17401137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"EP4 mediates PGE2-dependent cell survival in Jurkat T cells via the PI3K/AKT pathway (not PKA); EP4 antagonist abolishes PGE2 protection from camptothecin-induced apoptosis.\",\n      \"method\": \"Pharmacological EP receptor antagonists, PI3K/AKT and PKA inhibitors, caspase-3 assay, flow cytometry\",\n      \"journal\": \"Prostaglandins & other lipid mediators\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pharmacological dissection with multiple pathway inhibitors in a single cell line, mechanistic pathway placement\",\n      \"pmids\": [\"17259077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Macrophage-specific EP4 deficiency increases macrophage apoptosis in response to proapoptotic stimuli and reduces early atherosclerosis; EP4 promotes macrophage survival through the PI3K/Akt and NF-κB pathways.\",\n      \"method\": \"Fetal liver cell transplantation (bone marrow chimeras), LDLR-/- atherosclerosis model, apoptosis assays, Western blot for p-Akt/p-Bad/NF-κB\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional hematopoietic KO with in vivo disease endpoint and mechanistic pathway analysis\",\n      \"pmids\": [\"19041765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"EP4 receptor functions as a negative regulator of B cell proliferation in response to BCR signaling; EP4 knockdown accelerates lymphoma spread in mice, while overexpression is protective; EP4 and PGE2-EP4 signaling target a similar set of activating genes in B cells.\",\n      \"method\": \"Stable shRNA knockdown and overexpression in B cell lymphoma, in vivo tumor spread assay, gene expression analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments with in vivo validation and transcriptomics\",\n      \"pmids\": [\"19075289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PGE2-EP4 signaling on T cells and dendritic cells promotes TH1 cell differentiation and amplifies IL-23-mediated TH17 cell expansion in vitro; EP4-selective antagonist in vivo decreases TH1 and TH17 accumulation and suppresses EAE and contact hypersensitivity.\",\n      \"method\": \"In vitro T cell differentiation assays with EP4-selective agonists/antagonists, in vivo EAE and CHS models with EP4 antagonist treatment\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic cell-based experiments plus two distinct in vivo disease models, high-profile journal\",\n      \"pmids\": [\"19465928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PGE2 signaling through EP4 on FSP1+ fibroblasts (not EP1 or EP2) induces RANKL expression to promote osteoclastogenesis and periprosthetic osteolysis; conditional fibroblast-specific EP4 knockout abrogates RANKL upregulation and osteolysis.\",\n      \"method\": \"EP receptor knockout mice panel, conditional FSP1-Cre EP4 knockout, wear debris mouse model, in vitro PGE2 stimulation of fibroblasts\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO compared across three receptor KO lines, in vitro and in vivo convergent results\",\n      \"pmids\": [\"19419302\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"EP4 receptor exhibits functional selectivity: PGE2 most selectively activates Gαs, PGF2α and PGE1-OH show bias toward Gαi1 and β-arrestin respectively; EP4 can couple to Gαs, Gαi, and recruit β-arrestin with distinct potency/efficacy profiles depending on ligand.\",\n      \"method\": \"Bioluminescence resonance energy transfer (BRET) assays for Gαs, Gαi, and β-arrestin2 in living cells\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct BRET measurement of G protein coupling in live cells, systematic panel of ligands, single lab\",\n      \"pmids\": [\"19584306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PGE2 promotes angiogenesis via EP4 coupling to Gαs/cAMP/PKA Cγ; knockdown of EP4 or PKA catalytic subunit γ attenuates tube formation; downstream PKA substrates Rap1A, HSPB6, and eNOS promote angiogenesis while RhoA and GSK3β (inactivated by PKA) suppress it.\",\n      \"method\": \"siRNA knockdown of EP4 and PKA subunits, EP receptor subtype-selective agonists/antagonists, in vitro tube formation, ex vivo aortic ring assay, in vivo angiogenesis assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic (siRNA) and pharmacological dissection with multiple in vitro and in vivo angiogenesis endpoints\",\n      \"pmids\": [\"21926356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"EP4 (not EP2 or IP) is the primary receptor mediating COX-2-dependent stimulation of renin expression in response to furosemide-induced macula densa activation; EP4-/- mice show ~70% reduction in renin stimulation.\",\n      \"method\": \"Genetic knockout mice for COX-2, mPGES1, mPGES2, EP2, EP4, and IP receptors; furosemide treatment; real-time RT-PCR for renin mRNA\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — comparison across multiple receptor and enzyme KO lines with quantitative molecular endpoint\",\n      \"pmids\": [\"21835766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MiR-101 post-transcriptionally represses EP4 receptor expression by binding the 3'-UTR; ectopic miR-101 reduces EP4 protein, cell proliferation and motility; EP4 overexpression rescues cells from miR-101 tumor-suppressive effects; EP4 silencing phenocopies miR-101.\",\n      \"method\": \"Luciferase 3'-UTR reporter assay with wild-type and mutant constructs, miR-101 transfection, qRT-PCR, Western blot, cell proliferation and motility assays, co-transfection rescue\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct 3'-UTR reporter assay with mutagenesis, multiple epistatic rescue experiments, single lab\",\n      \"pmids\": [\"22353936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EP4 signaling through β-arrestin1 upregulates Akt signaling to protect colonic mucosal integrity; β-arrestin1-deficient mice show worsened DSS-colitis with reduced PI3K/p-Akt; PGE2 upregulates β-arrestin1 expression via EP4 both in vivo and in vitro.\",\n      \"method\": \"β-arrestin1 KO mice, DSS colitis model, siRNA knockdown of β-arr1 in HCT116 cells, Western blot for PI3K/Akt\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and siRNA loss-of-function with in vivo disease model, single lab, mechanistic pathway placement\",\n      \"pmids\": [\"28432343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In immature B cells (WEHI 231), EP4 activation increases cAMP/PKA, stabilizes NF-κB1 p105, inhibits IκBα phosphorylation, and sequesters NF-κB p65 in the cytoplasm; PI3K is not involved in EP4 signaling in this cell type, contrasting with other cell types.\",\n      \"method\": \"cAMP ELISA, Western blot for VASP/ERK/IκBα/p105 phosphorylation, fluorescence microscopy for p65 localization, pharmacological EP receptor agonists/antagonists\",\n      \"journal\": \"The Journal of pharmacy and pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling readouts in single cell line, pharmacological characterization, single lab\",\n      \"pmids\": [\"22775212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PGE2 regulates pancreatic stellate cell proliferation, migration, invasion, and extracellular matrix/MMP gene expression exclusively through the EP4 receptor (not EP1, EP2, or EP3); EP4 siRNA and EP4-selective antagonists abrogate these effects.\",\n      \"method\": \"siRNA knockdown of EP4, EP-selective antagonists, MTS proliferation assay, Boyden chamber migration/invasion assay, RT-PCR for matrix genes\",\n      \"journal\": \"Pancreas\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EP receptor subtype specificity established by siRNA and multiple antagonists, single lab\",\n      \"pmids\": [\"23090667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"EP4 receptor deletion in myeloid cells (using LysM-Cre) markedly inhibits adenoma number and size in ApcMin/+ mice, with decreased mTOR and ERK activation; either genetic or pharmacologic EP4 inhibition drives macrophages/DCs to an anti-tumorigenic M1 phenotype.\",\n      \"method\": \"Myeloid-specific conditional EP4 knockout (LysM-Cre), ApcMin/+ intestinal polyp model, EP4 pharmacological inhibitor, macrophage polarization assays, mTOR/ERK signaling analysis\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with genetic and pharmacological convergence, in vivo tumor endpoint with mechanistic pathway readout\",\n      \"pmids\": [\"26378024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"COX-2 induces breast cancer stem-like cells via EP4-mediated PI3K/AKT activation of NOTCH and WNT signaling; PI3K/AKT or NOTCH/WNT inhibitors block COX-2/EP4-induced stem cell induction; EP4 antagonist or knockdown reverses all stem-like cell markers and metastasis.\",\n      \"method\": \"COX-2 overexpression, EP4 antagonist and siRNA knockdown, PI3K/AKT/NOTCH/WNT pathway inhibitors, spheroid formation, ALDH activity, xenograft tumor metastasis models\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological EP4 inhibition with multiple orthogonal readouts, in vivo validation, epistatic pathway dissection\",\n      \"pmids\": [\"27301070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"EP4 activation in the collecting duct operates downstream of vasopressin via PGE2, and upstream of the (pro)renin receptor (PRR), forming a linear AVP/PGE2/EP4/PRR pathway that regulates AQP2 expression and urine concentrating capability; EP4 antagonist and PRR decoy peptide both impair AVP-induced AQP2 expression.\",\n      \"method\": \"Intrarenal infusion of EP4 antagonist and PRR decoy peptide in rats, collecting duct-specific PRR knockout mice, primary inner medullary CD cell culture, water deprivation model\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic KO plus pharmacological intervention in vivo and in vitro, linear pathway established by sequential blockade\",\n      \"pmids\": [\"27000064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PGA2 signals through EP4 (identified as a novel PGA2 receptor by pharmacological and molecular screening) to activate Rap1/Rac1 GTPase and PKA targets (VE-cadherin, p120-catenin, ZO-1, cortactin, VASP) enhancing endothelial barrier; it also suppresses NF-κB and ICAM1/VCAM1 expression. Endothelial-specific EP4 knockout abolishes barrier protection in vivo.\",\n      \"method\": \"Pharmacological and siRNA EP receptor screening, endothelial-specific EP4 knockout mice, two models of acute lung injury, barrier permeability assays, cytoskeleton/junction protein analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endothelial-specific conditional KO validated by multiple pharmacological approaches and two in vivo injury models\",\n      \"pmids\": [\"28428256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"EP4 promotes invadopodia-mediated ECM degradation and invasion of breast cancer cells through EGFR-dependent signaling; EP4 agonist increases invadopodia and matrix degradation in vitro and in vivo xenografts; EGFR tyrosine kinase inhibition abrogates EP4-mediated matrix degradation.\",\n      \"method\": \"EP4 agonist and antagonist treatment, 2D invadopodia assay, 3D invasion assay, EGFR kinase inhibitor epistasis, intravital microscopy, xenograft mouse model\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological epistasis with EGFR inhibitor, in vitro and in vivo endpoints, single lab\",\n      \"pmids\": [\"28094049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"EP4 activates PI3K and induces Ca2+ influx through Orai1 (without STIM1 involvement); EP4 forms a complex with Orai1 and TRPC1 (shown by co-immunoprecipitation); Orai1-mediated Ca2+ influx leads to ERK phosphorylation and MMP-2/9 activation promoting oral cancer cell migration; Orai1 knockdown abolishes EP4-induced ERK activation.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of EP4 and Orai1, Ca2+ imaging, ERK phosphorylation assay, cell migration assay, in vivo lung metastasis model\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP for complex identification, reciprocal genetic knockdown experiments with mechanistic pathway dissection, in vivo metastasis validation\",\n      \"pmids\": [\"31755615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In ankylosing spondylitis Th17 cells, EP4 drives Th17 expansion through upregulation of IL-23 receptor, suppression of the RORγt inhibitor FoxO1, and enhancement of STAT3 phosphorylation; EP4 creates a positive feedback loop enhancing its own expression in AS Th17 cells.\",\n      \"method\": \"Quantitative RT-PCR, flow cytometry, Western blot for EP4 protein, EP4-specific agonist functional assay in primary Th17 cells from AS, RA, PsA patients and healthy controls\",\n      \"journal\": \"Arthritis research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional agonist studies in primary human cells with molecular pathway readouts (STAT3, FoxO1, IL-23R), single lab\",\n      \"pmids\": [\"31253169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"COX-1/mPGES-1-derived PGE2 acts via endothelial EP4 to protect against myocardial ischemia/reperfusion injury; endothelium-restricted Ep4 deletion impairs microcirculation and exacerbates MI/R injury irrespective of EP4 agonism.\",\n      \"method\": \"mPges-1 knockout, endothelium-restricted Ep4 conditional knockout mice, MI/R model, microvascular perfusion imaging, leukocyte-endothelial interaction assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with multiple in vivo endpoints, combined with upstream enzyme KO\",\n      \"pmids\": [\"31015404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cryo-EM structure of EP4 coupled to heterotrimeric Gs protein at 3.3 Å resolution reveals that compared with other class A GPCRs, the TM6 outward shift is smaller; instead, the Gs C-terminal helix inserts toward TM2 with an extended hook structure; conserved prostanoid receptor residues Phe54(2.39) and Trp327(7.51) form these unique contacts.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) structure determination at 3.3 Å global resolution\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct cryo-EM structure at near-atomic resolution defining G protein coupling mechanism\",\n      \"pmids\": [\"33264604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Endothelial cell-specific EP4 deletion elevates blood pressure while EC-specific EP4 overexpression reduces it; EP4 maintains BP homeostasis by promoting eNOS phosphorylation at Ser1177 and NO production primarily via the AMPK pathway; mesenteric arteries of EC-EP4-/- mice show increased vasoconstrictor and reduced vasodilatory responses abolished by eNOS inhibition.\",\n      \"method\": \"EC-specific EP4 knockout and overexpression mice, blood pressure measurement, vascular reactivity assay, eNOS phosphorylation Western blot, AMPK pathway analysis, l-NAME pharmacology\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain- and loss-of-function conditional mouse models with mechanistic pathway (AMPK/eNOS) validation\",\n      \"pmids\": [\"32641583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EP4/AC/cAMP/PKA signaling mediates GRK2 translocation to the plasma membrane, where GRK2 dissociates from ERK1/2 and loses its inhibitory effect on ERK, thus promoting PGE2-induced angiogenesis; GRK2 siRNA inhibits PGE2-induced endothelial migration and tube formation; Lys220 and Ser685 of GRK2 are important for GRK2 translocation and angiogenic function.\",\n      \"method\": \"siRNA knockdown of GRK2 and EP4, GRK2 mutant constructs, cAMP FRET assay, ERK co-precipitation, in vivo Matrigel angiogenesis assay with GRK2-deficient aortic segments\",\n      \"journal\": \"Clinical science (London, England : 1979)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockdown, site-directed mutants of GRK2, ex vivo and in vivo angiogenesis models, mechanistic pathway placement\",\n      \"pmids\": [\"31967309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PTGER4+ intestinal macrophages promote epithelial barrier regeneration; Csf1r-iCre Ptger4fl/fl mice show defective mucosal healing in DSS colitis; mechanistically, PGE2 triggers CXCL1 secretion from monocyte-derived PTGER4+ macrophages via MAPK signaling, and CXCL1 drives epithelial cell differentiation and proliferation from regenerating crypts.\",\n      \"method\": \"Macrophage-specific conditional EP4 knockout (Csf1r-iCre), DSS colitis model, MAPK pathway analysis, liposome-encapsulated MAPK agonist therapeutic rescue, epithelial organoid differentiation assay\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with mechanistic rescue using MAPK agonist, organoid assay validates CXCL1 effector mechanism\",\n      \"pmids\": [\"33558271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TNF-α impairs EP4 signaling by recruiting TRAF2 to the plasma membrane, where TRAF2 interacts with and translocates GRK2, causing EP4 desensitization and internalization and reducing cAMP production; TRAF2 siRNA prevents GRK2 translocation and restores EP4 membrane expression and cAMP.\",\n      \"method\": \"cAMP FRET biosensor, co-immunoprecipitation of TRAF2-GRK2, siRNA knockdown of TRAF2, Western blot for EP4 membrane distribution, primary human fibroblast-like synoviocytes\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP for complex identification, FRET-based real-time cAMP measurement, siRNA epistasis in primary human cells\",\n      \"pmids\": [\"33859345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PGE2 acts via EP4 on osteoclasts (specifically via EP4, not EP2 alone) to promote OA progression; tissue-specific EP4 knockout in osteoclasts (EP4LysM) reduces OA progression, osteophyte formation, OA-related pain, Netrin-1 secretion, CGRP+ sensory innervation, PDGF-BB expression, and type H blood vessel formation; EP4 signals through Gαs/PI3K/AKT/MAPK in osteoclasts.\",\n      \"method\": \"Osteoclast-specific EP4 conditional knockout (LysM-Cre), DMM OA model, pain behavior testing, immunofluorescence for nerve innervation and vasculature, Gαs/PI3K/AKT/MAPK pathway analysis, novel EP4 antagonist HL-43\",\n      \"journal\": \"Bone research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with multiple in vivo disease endpoints and molecular pathway validation, pharmacological confirmation with novel antagonist\",\n      \"pmids\": [\"35260562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cartilage-specific EP4 deletion promotes chondrogenesis and cartilage anabolism, suppresses catabolism and hypertrophy, and reduces joint pain; EP4 regulates cartilage anabolism through cAMP/PKA/CREB/Sox9 signaling; EP4 antagonist HL-43 reproduces these effects in multiple cartilage defect models.\",\n      \"method\": \"Cartilage-specific EP4 conditional knockout, microfracture and DMM surgery models, aging model, human cartilage explants, cAMP/PKA/CREB/Sox9 signaling analysis\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cartilage-specific conditional KO with multiple disease models, human tissue validation, mechanistic pathway dissection\",\n      \"pmids\": [\"35256606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PGE2-EP2/EP4 signaling simultaneously promotes NF-κB-driven active inflammation in myeloid cells and drives the mregDC-Treg axis for Treg recruitment and activation, creating immunosuppression in the tumor microenvironment; dual EP2/EP4 inhibition required to reverse both arms.\",\n      \"method\": \"Immune checkpoint inhibitor-insensitive mouse cancer model, single-cell RNA sequencing, pharmacological EP2/EP4 antagonists\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — single-cell transcriptomics plus pharmacological intervention in in vivo tumor model; dual signaling axis mechanistically established\",\n      \"pmids\": [\"35675777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The rat EP4 gene has three exons separated by two introns; a GC-rich/Sp1 binding site within the first 80 bases of the transcription start site is required for constitutive EP4 transcription; mutation of the Sp1 site at -78 to -66 abolishes promoter activity; three Sp1 sites cooperate to enhance transcription.\",\n      \"method\": \"Genomic cloning, Northern blot, luciferase reporter constructs with deletion and site-specific mutations, identification of transcription start site\",\n      \"journal\": \"American journal of obstetrics and gynecology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis of Sp1 sites in reporter constructs directly defines transcriptional control element\",\n      \"pmids\": [\"14634592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"EP4 transcription in glioblastoma T98G cells is driven by Sp1 binding sites at -197 to -160 of the human EP4 promoter; troglitazone and sulindac sulfide suppress EP4 expression by activating MEK/ERK, which phosphorylates Sp1 reducing its DNA binding (confirmed by ChIP); reversal by MEK inhibitor PD98059 establishes Sp1 phosphorylation as the suppression mechanism.\",\n      \"method\": \"Luciferase reporter assays with Sp1 site mutations, ChIP assay for Sp1 binding, immunoprecipitation-Western blot for Sp1 phosphorylation, MEK/ERK inhibitor (PD98059) rescue\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — ChIP and mutagenesis directly confirm Sp1-dependent promoter mechanism; orthogonal pharmacological validation\",\n      \"pmids\": [\"18346464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EP4 signaling in DRG neurons promotes EP4 externalization (trafficking from Golgi and recycling endosomes to plasma membrane); inhibitors of anterograde secretory pathway, protein synthesis, or recycling suppress PGE2-induced EP4 surface expression; complete Freund's adjuvant-induced inflammation increases cell-surface EP4 levels via COX-2/PGE2/EP4 signaling in vivo.\",\n      \"method\": \"Pharmacological inhibitors of secretory pathway/recycling, cell-surface biotinylation, intracellular cAMP sequential treatment assay, CFA inflammation model, COX-2 inhibitor treatment\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — subcellular trafficking established by pathway inhibitors and surface biotinylation, in vivo inflammation model, single lab\",\n      \"pmids\": [\"23265688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"EP4 receptor deletion in macrophages (conditional KO) renders macrophages less susceptible to M2 polarization; EP4 agonist enhances M2 polarization and improves glucose tolerance and insulin sensitivity in obese db/db mice by promoting M2 macrophage polarization via PPARδ; PPARδ antagonism suppresses EP4-mediated M2 polarization.\",\n      \"method\": \"EP4-selective agonist in db/db mice, peritoneal macrophage M1/M2 polarization assay with EP4-KO macrophages, PPARδ antagonist epistasis, adipose tissue histology and cytokine analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO macrophages plus PPARδ epistasis, in vivo metabolic endpoints, single lab\",\n      \"pmids\": [\"26308623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"EP4 blockade abrogates Yes-associated protein 1 (YAP)-driven pro-metastatic factor expression in pancreatic cancer cells in vitro and reduces YAP activity in vivo; EP4-YAP signaling axis is a pro-metastatic pathway in pancreatic cancer.\",\n      \"method\": \"EP4 antagonist L001, YAP activity reporter assay, in vivo hepatic metastasis model, Western blot for YAP targets\",\n      \"journal\": \"Molecules (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological EP4 inhibition with YAP pathway readout in vitro and in vivo, single lab\",\n      \"pmids\": [\"35208999\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTGER4/EP4 is a Gαs-coupled class A GPCR (cryo-EM structure resolved at 3.3 Å) that primarily signals via cAMP/PKA but also engages PI3K/AKT, ERK, β-arrestin, and Gαi in a ligand- and cell-type-dependent (functionally selective) manner; it regulates diverse processes including ductus arteriosus closure, intestinal homeostasis, inflammatory T cell differentiation (TH1/TH17), sensory neuron sensitization, angiogenesis via ERK/PKA-dependent endothelial migration, bone remodeling via RANKL induction in fibroblasts and cAMP/PKA/CREB/Sox9 in chondrocytes, macrophage survival through PI3K/Akt/NF-κB, renin secretion, blood pressure through AMPK/eNOS, and tumor progression through PI3K/ERK, NOTCH/WNT, and YAP pathways; receptor desensitization is mediated by GRK2 translocation (promoted by TRAF2 in inflammatory conditions) and by β-arrestin recruitment, while EP4 surface expression in neurons is dynamically regulated by PGE2-driven anterograde trafficking from Golgi and recycling endosomes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTGER4 (EP4) is a Gαs-coupled class A prostaglandin E2 receptor that translates PGE2 signals into diverse physiological and pathological programs spanning vascular development, mucosal homeostasis, immune cell differentiation, sensory sensitization, bone and cartilage remodeling, and tumor progression [#0, #4, #14]. Cryo-EM of the EP4–Gs complex shows an atypically small TM6 outward shift, with the Gs C-terminal helix inserting toward TM2 via an extended hook and contacts from conserved prostanoid-receptor residues Phe54(2.39) and Trp327(7.51) [#31]. Beyond canonical Gαs/cAMP/PKA output, EP4 displays pronounced functional selectivity, coupling additionally to Gαi and recruiting β-arrestin with ligand-dependent potency, and engaging PI3K/AKT and ERK1/2 cascades that diverge by cell type [#16, #3, #11]. These branches drive distinct outputs: PKA-dependent eNOS, Rap1A and HSPB6 activation supports angiogenesis and endothelial barrier integrity while suppressing RhoA/GSK3β and NF-κB [#17, #26_skip]. EP4 sustains intestinal homeostasis—maintaining mucosal integrity through β-arrestin1/Akt signaling and, in PTGER4+ macrophages, driving CXCL1-mediated epithelial regeneration via MAPK [#4, #20, #34]; promotes TH1 and IL-23-amplified TH17 differentiation [#14, #29]; mediates inflammatory sensory neuron sensitization [#7]; and in tumors couples PGE2 to proliferation, migration, metastasis, and stemness via PI3K/ERK, NOTCH/WNT, EGFR/invadopodia, Orai1-dependent Ca2+/ERK, and YAP pathways [#6, #9, #24, #27, #28, #43]. In bone and joint tissue EP4 induces RANKL in fibroblasts and signals through cAMP/PKA/CREB/Sox9 in chondrocytes and Gαs/PI3K/AKT/MAPK in osteoclasts to control remodeling and osteoarthritis [#15, #36, #37]. EP4 also controls renal renin expression and an AVP/PGE2/EP4/PRR axis governing AQP2, and maintains blood pressure via endothelial AMPK/eNOS [#18, #25, #32]. Receptor signaling is constrained by GRK2 translocation and β-arrestin recruitment—GRK2 movement being promoted by TRAF2 under TNF-α—while neuronal surface EP4 is dynamically supplied by PGE2-driven anterograde trafficking from Golgi and recycling endosomes [#33, #35, #41]. EP4 transcription is governed by GC-rich, TATA-less Sp1-dependent promoter elements and is post-transcriptionally repressed by miR-101 [#39, #40, #19]. Genetic ablation establishes that EP4 is essential for postnatal closure of the ductus arteriosus [#0].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Establishing the receptor's identity and basic coupling answered whether EP4 was a distinct Gs-coupled PGE2 receptor with a defined gene architecture.\",\n      \"evidence\": \"Genomic cloning of the human gene plus heterologous expression of rabbit EP4 in COS-1 cells with cAMP assays and binding profiling\",\n      \"pmids\": [\"8661119\", \"8780252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for Gs coupling at this stage\", \"Other signaling branches not yet probed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Knockout established a non-redundant developmental requirement, showing EP4 is essential for postnatal ductus arteriosus closure.\",\n      \"evidence\": \"Gene-targeted EP4-null mice with histology and in situ hybridization\",\n      \"pmids\": [\"9600059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking EP4 signaling to ductal smooth muscle closure not defined\", \"Did not address adult/tissue-specific roles\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"A panel of prostanoid receptor knockouts pinpointed EP4 as the specific receptor maintaining intestinal mucosal homeostasis.\",\n      \"evidence\": \"Eight-receptor KO comparison in DSS colitis with microarray and lamina propria cell assays\",\n      \"pmids\": [\"11927615\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector pathway for barrier protection not yet identified\", \"Cell type responsible not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Pharmacological dissection showed EP4 signals beyond cAMP/PKA, engaging PI3K/ERK/EGR-1 and Tcf transcription, distinguishing it from EP2.\",\n      \"evidence\": \"Pathway inhibitor and reporter assays in cell lines\",\n      \"pmids\": [\"14607241\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor-proximal mechanism of PI3K engagement undefined\", \"Compiled from cell-line studies, not genetic\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Genetic and pharmacological inhibition established EP4 as a driver of tumor cell proliferation, migration, and metastasis via PI3K/ERK.\",\n      \"evidence\": \"shRNA silencing and EP4 antagonists in colon and breast cancer with in vivo metastasis models\",\n      \"pmids\": [\"15123663\", \"16540660\", \"16540639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct receptor-effector coupling for migration not resolved\", \"Tumor microenvironment contributions not yet separated\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Conditional deletion and pathway inhibitors revealed branch-specific outputs—ERK-dependent angiogenesis and PI3K/AKT-dependent survival—clarifying functional divergence.\",\n      \"evidence\": \"EP4-flox endothelial deletion with migration/tube assays and pharmacological dissection in Jurkat T cells\",\n      \"pmids\": [\"17401137\", \"17259077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What dictates ERK vs PKA vs PI3K branch selection unresolved\", \"Jurkat survival study limited to one cell line\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Direct BRET measurement demonstrated ligand-biased functional selectivity, showing EP4 couples to Gαs, Gαi, and β-arrestin with distinct ligand-dependent profiles.\",\n      \"evidence\": \"BRET assays for Gαs, Gαi, and β-arrestin2 across a ligand panel in living cells\",\n      \"pmids\": [\"19584306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of biased coupling not defined\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Cell-type-specific studies mapped EP4 onto immune differentiation and bone remodeling, defining TH1/TH17 promotion and fibroblast RANKL induction.\",\n      \"evidence\": \"EP4 agonist/antagonist T-cell differentiation assays with EAE/CHS models and FSP1-Cre fibroblast EP4 KO in osteolysis\",\n      \"pmids\": [\"19465928\", \"19419302\", \"19075289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional effectors downstream of EP4 in T cells incompletely mapped\", \"B-cell vs T-cell opposing roles not mechanistically reconciled\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Genetic dissection placed EP4 in defined linear signaling chains for angiogenesis (PKA Cγ→Rap1A/HSPB6/eNOS) and renal renin control.\",\n      \"evidence\": \"siRNA of EP4 and PKA subunits with angiogenesis assays; multi-KO renin expression study\",\n      \"pmids\": [\"21926356\", \"21835766\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PKA substrate selection is achieved unclear\", \"Renin mechanism downstream of EP4 not detailed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Studies of EP4 regulation defined post-transcriptional control by miR-101, β-arrestin1-dependent mucosal protection, and cell-type-divergent NF-κB outputs.\",\n      \"evidence\": \"3'-UTR luciferase mutagenesis, β-arrestin1 KO colitis model, and signaling readouts in immature B cells\",\n      \"pmids\": [\"22353936\", \"28432343\", \"22775212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Why PI3K is dispensable in some cell types unexplained\", \"β-arrestin1 colitis study single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Integrating EP4 into renal and cancer networks defined the AVP/PGE2/EP4/PRR–AQP2 axis and EP4-driven PI3K/AKT activation of NOTCH/WNT for cancer stemness.\",\n      \"evidence\": \"Sequential pharmacological/genetic blockade in collecting duct; epistatic pathway inhibitors with stemness and metastasis readouts\",\n      \"pmids\": [\"27000064\", \"27301070\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Linkage from EP4 to PRR molecularly undefined\", \"How EP4 selects stemness program not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"EP4 was shown to operate through additional effectors—EGFR-dependent invadopodia, and PGA2-activated Rap1/Rac1 endothelial barrier protection—broadening its agonist and effector repertoire.\",\n      \"evidence\": \"EGFR inhibitor epistasis with invasion assays; endothelial-specific EP4 KO in acute lung injury with PGA2 screening\",\n      \"pmids\": [\"28094049\", \"28428256\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of EP4-EGFR transactivation undefined\", \"PGA2 as EP4 ligand needs broader confirmation\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Complex-level and tissue-specific analyses revealed an EP4-Orai1/TRPC1 Ca2+ signaling module and an endothelial EP4 cardioprotective role.\",\n      \"evidence\": \"Co-IP and reciprocal knockdown with Ca2+ imaging in oral cancer; endothelium-restricted Ep4 KO in MI/R injury; AS Th17 functional studies\",\n      \"pmids\": [\"31755615\", \"31015404\", \"31253169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of EP4-Orai1-TRPC1 complex unknown\", \"Th17 feedback mechanism single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Structural and desensitization studies defined the Gs-coupling architecture and the GRK2 translocation mechanism controlling EP4 signaling and angiogenesis.\",\n      \"evidence\": \"3.3 Å cryo-EM of EP4-Gs; siRNA and GRK2 mutant analysis with cAMP FRET and angiogenesis assays; reciprocal endothelial EP4 BP models\",\n      \"pmids\": [\"33264604\", \"31967309\", \"32641583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of biased/Gi-coupled states absent\", \"How GRK2 dissociation from ERK is regulated unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Mechanistic studies tied EP4 desensitization to TNF-α/TRAF2-driven GRK2 translocation and identified PTGER4+ macrophage CXCL1-mediated epithelial regeneration.\",\n      \"evidence\": \"Co-IP of TRAF2-GRK2 with cAMP FRET in synoviocytes; Csf1r-iCre EP4 KO with organoid and MAPK-agonist rescue in colitis\",\n      \"pmids\": [\"33859345\", \"33558271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TRAF2 is recruited to EP4 vicinity not detailed\", \"CXCL1 receptor on epithelium not defined here\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Joint and tumor studies established EP4 cartilage cAMP/PKA/CREB/Sox9 and osteoclast Gαs/PI3K/AKT/MAPK programs and an EP2/EP4 immunosuppressive axis in tumors.\",\n      \"evidence\": \"Cartilage- and osteoclast-specific EP4 KO with OA models and antagonist HL-43; scRNA-seq with dual EP2/EP4 antagonists in tumor model\",\n      \"pmids\": [\"35256606\", \"35260562\", \"35675777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cross-talk between cartilage and osteoclast EP4 programs unresolved\", \"Relative EP2 vs EP4 contributions to immunosuppression not separated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"EP4 was linked to YAP-driven pro-metastatic signaling in pancreatic cancer, extending its tumor effector repertoire.\",\n      \"evidence\": \"EP4 antagonist with YAP reporter and hepatic metastasis model\",\n      \"pmids\": [\"35208999\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between EP4 and YAP activation undefined\", \"Single-lab pharmacological study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ligand identity and cellular context select among EP4's Gαs/Gαi/β-arrestin/PI3K/ERK/Ca2+ branches to produce opposing outputs in different tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unified structural/biochemical model of biased signaling across cell types\", \"Determinants of pro- vs anti-tumor and pro- vs anti-inflammatory outputs unclear\", \"Structures of non-Gs coupled states unavailable\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [2, 16, 31]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [2, 16, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [35, 41]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [41]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 16, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 14, 23, 38]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 9, 24, 28]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 10, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GNAS\", \"ARRB1\", \"GRK2\", \"TRAF2\", \"ORAI1\", \"TRPC1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}