{"gene":"PTH1R","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2009,"finding":"A beta-arrestin-biased agonist (D-Trp12,Tyr34)-PTH(7-34) selectively activates beta-arrestin2 but not G protein signaling through PTH1R, and in beta-arrestin2-null mice the anabolic bone formation evoked by this biased agonist is ablated, demonstrating that PTH1R can signal through a distinct beta-arrestin2-dependent pathway to promote trabecular bone formation without stimulating bone resorption.","method":"Biased agonist pharmacology in vivo; beta-arrestin2 knockout mice with bone mineral density measurement","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with defined cellular phenotype, biased agonist tool, replicated in vivo","pmids":["20368153"],"is_preprint":false},{"year":2016,"finding":"SNX27 binds directly to the C-terminal PDZ-binding motif of PTH1R and couples it to the retromer trafficking complex for endosomal sorting; depletion of SNX27 or retromer augments intracellular PTH1R signaling in endosomes and impairs bone mineralization in osteoblasts lacking SNX27.","method":"Direct binding assay, crystal structure of SNX27-PTHR PDZ motif complex, SNX27 KO osteoblasts with signaling and mineralization readouts, SNX27-KO mouse skeletal phenotype","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 — structural validation with binding, KO phenotype, functional consequence in osteoblasts","pmids":["26912788"],"is_preprint":false},{"year":2011,"finding":"PTH(1-34) stimulation induces transient PTHR ubiquitination followed by deubiquitination mediated by the PTHR-specific deubiquitinating enzyme USP2, enabling receptor recycling; in contrast, PTH(7-34) induces sustained PTHR ubiquitination without USP2 induction, leading to proteasomal degradation of the receptor.","method":"Ubiquitination assays, recycling/degradation assays, USP2 overexpression rescue, ligand treatment in cell lines","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (ubiquitination, recycling, degradation, overexpression rescue) in single study","pmids":["21898592"],"is_preprint":false},{"year":2016,"finding":"Mass spectrometry identified nine phosphorylation sites in the C-terminal tail of PTH1R; two clusters (Ser489-Ser495 and Ser501-Thr506) are responsible for PTH(1-34)-induced phosphorylation. Ser503 and Thr504 in the second cluster account for ~70% of arrestin3 recruitment and are key determinants for arrestin3 interaction with the receptor, as shown by FRET and BRET assays.","method":"Mass spectrometry phosphosite mapping, alanine mutagenesis, FRET/BRET arrestin3 recruitment assays","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — MS identification plus mutagenesis plus two resonance energy transfer assays","pmids":["27623777"],"is_preprint":false},{"year":2006,"finding":"PTH1R forms a complex with importin alpha1 and importin beta in osteoblast-like cells, as demonstrated by immunoprecipitation and PTH-affinity chromatography, indicating that these transport proteins mediate nuclear import of PTH1R. Nuclear PTH1R localization is restricted to the nucleoplasm and is associated with specific stages of the cell cycle.","method":"Immunoprecipitation, affinity chromatography, immunofluorescence/deconvolution microscopy","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal IP and affinity chromatography, but single lab","pmids":["16574786"],"is_preprint":false},{"year":2007,"finding":"PTH1R nuclear-cytoplasmic shuttling depends on importin-alpha/beta for nuclear import and CRM1/exportin1 for nuclear export; importin-beta siRNA knockdown reduces nuclear PTH1R, and leptomycin B (CRM1 inhibitor) causes nuclear accumulation. Serum starvation favors nuclear localization, while PTHrP or serum re-addition promotes cytoplasmic localization.","method":"siRNA knockdown, CRM1 inhibitor (leptomycin B), co-immunoprecipitation, immunofluorescence microscopy, nuclear fractionation","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (siRNA, pharmacological inhibitor, co-IP, fractionation) with functional localization consequence","pmids":["17317770"],"is_preprint":false},{"year":2009,"finding":"PTH agonist and antagonist induce distinct conformational changes at the extracellular-facing interface of transmembrane domains TM5 and TM6 of PTH1R; engineered disulfide bond formation showed TM5/TM6 move relative to each other upon agonist binding but not antagonist binding, providing physicochemical evidence for the receptor activation mechanism.","method":"Engineered disulfide bond cross-linking strategy, cell membrane preparations, 18 double-cysteine PTHR1 mutants","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with systematic mutagenesis revealing activation mechanism","pmids":["19063682"],"is_preprint":false},{"year":2016,"finding":"An orally active small-molecule agonist (PCO371) acts as a full agonist of PTH1R but not PTH2R; chimeric receptor analysis identified Pro415 of PTH1R as critical for PCO371-mediated activation, indicating a distinct binding mode from peptide ligands.","method":"PTH1R-PTHR2 chimeric receptor analysis, cAMP assays, in vivo rat models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — chimeric receptor mutagenesis plus in vitro activity assay plus in vivo validation","pmids":["27857062"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of PTH- and ABL-bound PTH1R-Gs complexes reveal similar overall conformations but notable differences in the receptor ECD regions and peptide C-terminal portions; 3D variability analysis and site-directed mutagenesis show PTH-bound complexes display less motion and greater tolerance to mutations, providing molecular basis for the longer signaling duration of teriparatide (PTH) vs. abaloparatide (ABL).","method":"Cryo-EM structure determination, 3D variability analysis, site-directed mutagenesis, signaling assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures with mutagenesis and signaling assay validation, single paper with multiple orthogonal methods","pmids":["36271004"],"is_preprint":false},{"year":2022,"finding":"RAMP2 acts as a specific allosteric modulator of PTH1R, shifting it to a preactivated state that permits faster ligand-dependent activation; RAMP2 modulates PTH1R downstream signaling in an agonist-dependent manner, increasing PTH-mediated Gi3 signaling sensitivity and enhancing β-arrestin2 recruitment by both PTH and PTHrP.","method":"Optical biosensors (BRET/FRET), homology modeling, co-expression of RAMP2 with PTH1R","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biosensor assays with structural modeling in single study","pmids":["35914163"],"is_preprint":false},{"year":2023,"finding":"MMP14 cleaves the extracellular domain of PTH1R in hypertrophic chondrocyte-derived osteoblasts, dampening PTH signaling; in HC lineage-specific Mmp14 null mice, PTH1R signaling is enhanced and bone formation is increased, demonstrating MMP14 as a negative regulator of PTH1R signaling intensity in the osteoblast lineage.","method":"HC lineage-specific Mmp14 conditional knockout, single-cell transcriptomics, in vitro cleavage assay, PTH 1-34 treatment in mutant mice","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro cleavage assay plus conditional KO with defined bone phenotype and signaling readout","pmids":["36892459"],"is_preprint":false},{"year":2019,"finding":"An ECD-binding antibody (ECD-scFvhFc) targeting the α1 helix of the PTH1R extracellular domain potently inhibits β-arrestin-2 recruitment after PTH(1-34) activation without affecting Gs-mediated cAMP signaling, representing pathway-selective inhibition of PTH1R signaling.","method":"Phage display antibody generation, hydrogen-deuterium exchange mass spectrometry epitope mapping, β-arrestin-2 recruitment assay, Gs signaling assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — HDX-MS epitope mapping plus orthogonal signaling assays demonstrating biased inhibition","pmids":["31594997"],"is_preprint":false},{"year":2020,"finding":"Kindlin-2 interacts with the C-terminal cytoplasmic domain of PTH1R via residues aa 474-475 and with Gsα, functioning as an intrinsic component of the PTH1R signaling complex; Kindlin-2 loss suppresses PTH-induced cAMP production and CREB phosphorylation in osteoblasts, and haploinsufficiency of both Kindlin-2 and Pth1r significantly decreases bone mass.","method":"Co-immunoprecipitation, haploinsufficiency double-mutant epistasis in mice, cAMP/CREB signaling assays in osteoblasts, osteoblast-specific conditional KO","journal":"Signal transduction and targeted therapy","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, epistasis in vivo, defined signaling readouts","pmids":["33361757"],"is_preprint":false},{"year":2022,"finding":"Mechanical stimulation (fluid flow) causes redistribution of PTH1R along the entire primary cilium of osteocytic MLO-Y4 cells; PTH1R and primary cilia signaling are both required for FF-mediated inhibition of osteoclast recruitment and differentiation via modulation of CXCL5 and IL-6 secretion from osteocytes.","method":"siRNA knockdown of PTH1R and primary cilia, fluid flow stimulation, proteomic analysis, live imaging, neutralizing antibodies, osteoclast migration/differentiation assays","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 2 — siRNA knockdown with defined cellular phenotype, proteomic identification of downstream mediators, localization tied to function","pmids":["35933642"],"is_preprint":false},{"year":2015,"finding":"Mechanical stimulation (hypotonic shock or pulsatile fluid flow) activates PTH1R-dependent signaling in osteocytic MLO-Y4 cells to prevent apoptosis; this involves calcium signaling (blocked by verapamil), PLC (blocked by U73122), and PKA, as well as β-catenin stabilization and nuclear ERK translocation. Hypotonic shock rapidly stimulates Ca2+ transients in PTH1R-overexpressing HEK-293 cells even in the absence of PTHrP ligand, indicating PTH1R acts as a mechanosensor.","method":"PTH1R siRNA knockdown, PTH1R overexpression in HEK-293 cells, pharmacological inhibitors, calcium imaging, apoptosis assays in MLO-Y4 osteocytes","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 — siRNA KD plus overexpression plus pharmacological inhibitors plus Ca2+ imaging with defined apoptosis phenotype","pmids":["25529820"],"is_preprint":false},{"year":2010,"finding":"PTHrP increases MKP-1 (MAPK phosphatase-1) expression in differentiated osteoblasts via PTH1R activation through PKA and PKC pathways; MKP-1 then dephosphorylates pERK1/2 and down-regulates cyclin D1, inducing growth arrest in mature osteoblasts and mediating anabolic actions of PTH1R.","method":"MKP-1 overexpression, immunodepletion, in vitro pERK1/2 dephosphorylation assay with cell extracts, PKA/PKC inhibitors, in vivo PTH treatment with bone formation markers","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including in vitro dephosphorylation assay, immunodepletion, pathway inhibitors, in vivo validation","pmids":["19892016"],"is_preprint":false},{"year":2016,"finding":"PTH1R mutations identified in PFE patients (e.g., Gly452Glu) are functionally inactive in G-protein/cAMP signaling; PTH1R/Gly452Glu acts as a dominant negative on wild-type PTH1R signaling and is retained intracellularly rather than expressed at the cell surface, abolishing coupling to TRESK K+ channels.","method":"cAMP ELISA, Western blot (VASP phosphorylation), confocal microscopy, electrophysiological recordings in Xenopus oocytes, co-transfection with WT and mutant PTH1R","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays (cAMP, phosphorylation, imaging, electrophysiology) demonstrating dominant-negative mechanism","pmids":["27898723"],"is_preprint":false},{"year":2023,"finding":"Eiken syndrome PTH1R mutation R485X (truncation of C-terminal tail) increases basal cAMP signaling and decreases β-arrestin2 recruitment upon ligand stimulation; mutations E35K and Y134S weaken PTHrP binding, impairing β-arrestin2 recruitment and desensitization of cAMP response to PTHrP but not PTH, supporting a critical role for β-arrestin in PTH1R-regulated bone formation.","method":"Cell-based cAMP signaling assays, β-arrestin2 recruitment assays, ligand binding assays for multiple Eiken PTH1R mutants","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants tested with orthogonal assays (cAMP, arrestin recruitment, binding) in single rigorous study","pmids":["37268817"],"is_preprint":false},{"year":2021,"finding":"PTH1R is expressed in Leydig cells of the testis and epididymal epithelial cells; activation of PTH1R by abaloparatide alleviates inflammation-induced epididymitis/orchitis mainly through the Gq and β-arrestin-1 signaling pathways, as demonstrated by attenuated anti-inflammatory effects in Gnaq+/- and Arrb1-/- mouse models.","method":"Gnaq heterozygous and Arrb1 knockout mouse models, pharmacological activation with abaloparatide, inflammatory challenge models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — two distinct genetic KO models delineating specific pathway contributions","pmids":["34740971"],"is_preprint":false},{"year":2020,"finding":"Functional analysis of PFE-associated PTH1R variants P119L and P132L revealed severe reduction in N-linked glycosylation and markedly decreased affinity for PTH1-34, leading to severely impaired cAMP accumulation upon stimulation; these variants also failed to induce RANKL expression in osteoblastic cells derived from PFE patient iPSCs.","method":"Lentiviral expression in HeLa cells, N-linked glycosylation analysis, ligand binding assays, cAMP accumulation assays, iPSC disease modeling with osteoblastic differentiation","journal":"Journal of dental research","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal biochemical assays plus iPSC-based disease model","pmids":["31986066"],"is_preprint":false},{"year":2016,"finding":"N-cadherin reduces LRP6-PTH1R interaction and endocytosis in response to PTH, blunting PTH-induced suppression of sclerostin/SOST through impaired MEF2 downregulation; deletion of N-cadherin in osteocytes (Cdh2ΔDmp1 mice) accentuates iPTH-induced SOST suppression and bone anabolic effects.","method":"N-cadherin overexpression, immunoblot/qPCR for SOST/MEF2, co-IP for LRP6-PTHR1, Dmp1-Cre conditional Cdh2 KO mice with iPTH treatment","journal":"Annals of the New York Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro co-IP plus conditional KO in vivo, but single lab","pmids":["27723935"],"is_preprint":false},{"year":2010,"finding":"PTH1R receptors are localized at the basolateral plasma membrane of proximal and distal tubule epithelial cells in human kidney and at the plasma membrane of osteocytes and osteoblasts (but not osteoclasts) in bone, as established by a validated anti-PTH1R antibody showing translocation of receptor immunostaining after agonist exposure.","method":"Anti-peptide antibody characterization (western blot, cell surface staining of transfected cells, agonist-induced translocation, preadsorption controls), immunohistochemistry of 320 human tumors and normal tissues","journal":"European journal of endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — validated antibody with multiple specificity controls, direct localization with functional agonist-induced translocation","pmids":["20156969"],"is_preprint":false},{"year":2023,"finding":"PTH1R activation by a novel PTH analog (MY-1) promotes keratinocyte migration and epithelial-mesenchymal transition in wound healing through the PTHR1-PI3K/AKT signaling axis, as demonstrated by siRNA knockdown of PTHR1 abolishing PI3K/AKT activation in HaCaT cells.","method":"siRNA knockdown of PTHR1, PI3K/AKT pathway analysis by western blot, migration and EMT assays, in vivo wound models with GelMA hydrogel delivery","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown with defined signaling and phenotypic readouts, in vitro and in vivo","pmids":["37612710"],"is_preprint":false},{"year":2010,"finding":"Impaired phosphorylation/internalization of PTH1R (phosphorylation-deficient knock-in mice) results in sustained cyclin D1 downregulation in osteoblasts compared to wild-type, indicating that receptor phosphorylation and subsequent internalization regulate the duration of intracellular signaling responses including ERK1/2 and cyclin D1 in bone cells.","method":"Phosphorylation-deficient PTH1R knock-in mouse model, primary calvarial osteoblast culture, pERK1/2 and cyclin D1 assays","journal":"The Journal of endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic knock-in model with defined in vitro and in vivo signaling readouts, single lab","pmids":["20929987"],"is_preprint":false},{"year":2023,"finding":"Loss of Zfp467 in osteogenic precursors leads to increased nuclear translocation of NFκB1, which binds the P2 promoter of Pth1r and increases its transcription, creating a positive feedback loop; PTH suppresses Zfp467 primarily via the cAMP/PKA pathway downstream of PTH1R.","method":"Conditional KO (Prrx1Cre;Zfp467), dual fluorescence reporter assays, confocal immunofluorescence, PKA inhibitor, Pth1r siRNA, cAMP production assays","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal approaches (reporter assay, confocal, pharmacological, genetic) demonstrating feedback mechanism","pmids":["37159501"],"is_preprint":false},{"year":2017,"finding":"IL-17 upregulates N-cadherin which disrupts PTH1R/LRP-6 interaction, thereby inhibiting Wnt signaling and promoting bone loss; combination of PTH(1-34) with anti-IL17 reduces PTH1R expression and has synergistic bone-protective effects in ovariectomized mice, placing IL-17 upstream of the PTHR1/LRP-6/Wnt axis.","method":"Immunofluorescence analysis, anti-IL17 antibody treatment plus iPTH in OVX mice, bone mineral density measurement","journal":"Bone","confidence":"Low","confidence_rationale":"Tier 3 — immunofluorescence only for PTHR1/LRP-6 disruption, mechanistic details inferred rather than directly demonstrated","pmids":["28935557"],"is_preprint":false},{"year":2018,"finding":"Hyperstimulation of CaSR by biomimetic hydroxyapatite causes temporal downregulation of PTH1R in human BM-derived MSCs, inhibiting chondrogenic differentiation; rescuing PTH1R expression with PTH(1-34) partially restores chondrogenesis, demonstrating cross-talk between CaSR and PTH1R in controlling MSC ossification pathway choice.","method":"CaSR knockdown, PTH(1-34) rescue experiments, chondrogenic differentiation assays, in vivo ectopic implantation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — CaSR KD plus PTH1R rescue with in vitro and in vivo validation","pmids":["29915064"],"is_preprint":false},{"year":2015,"finding":"Conditional deletion of PTH1R in limb mesenchyme (Prx1-Cre;PTH1R fl/fl) causes symphalangism (digit joint fusion) due to failure of epiphyseal growth plate formation and replacement of cartilage by bone, demonstrating a novel role for PTH1R signaling in digit formation and segmentation distinct from its known role in long bone growth plates.","method":"Prx1-Cre conditional PTH1R KO mice, histomorphometry, comparison with Ihh conditional KO and Jansen transgenic rescue","journal":"Bone","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined skeletal phenotype, epistasis with rescue transgenic attempted","pmids":["26620087"],"is_preprint":false},{"year":2017,"finding":"Loss of RAMP2 in mice decreases PTH1R expression and causes a blunted response to systemic PTH administration, providing in vivo evidence that RAMP2 regulates PTH1R expression and function.","method":"Ramp2 KO mice, PTH administration, gene expression analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with defined in vivo PTH response, but correlation between RAMP2 loss and PTH1R expression without direct binding demonstration","pmids":["28727763"],"is_preprint":false},{"year":2008,"finding":"Three PTHR1 missense mutations identified in Ollier disease enchondromas (G121E, A122T, R255H) impair receptor function by reducing either PTH binding affinity or receptor expression at the cell surface, establishing loss-of-function as the mechanistic basis for PTHR1-associated enchondromatosis.","method":"Functional assays of receptor-ligand affinity and cell surface expression in patient-derived mutation-expressing cells","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional characterization of mutations with binding and surface expression assays","pmids":["18559376"],"is_preprint":false},{"year":1999,"finding":"Zebrafish PTH1R ortholog (zPTH1R) binds PTH, PTHrP, and fuguPTHrP with high affinity (IC50 1.2-3.5 nM) and efficiently stimulates cAMP accumulation and inositol phosphate (IP) production when expressed in COS-7 cells, establishing dual G-protein coupling (Gs and Gq).","method":"COS-7 cell expression, radioligand competition binding, cAMP accumulation assay, inositol phosphate accumulation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution in heterologous expression system with binding and two distinct signaling assays","pmids":["10497171"],"is_preprint":false}],"current_model":"PTH1R is a class B GPCR that binds PTH and PTHrP at its extracellular domain and signals primarily through Gs/cAMP/PKA and Gq/PLC/calcium pathways, with agonist-induced phosphorylation of specific C-terminal tail residues (Ser489-Ser495, Ser501-Thr506) driving β-arrestin2/3 recruitment, receptor internalization, endosomal signaling, and ubiquitin-dependent sorting between recycling (promoted by USP2 deubiquitinase) and proteasomal degradation; RAMP2 acts as an allosteric modulator shifting PTH1R to a preactivated state, SNX27-retromer couples the receptor to endosomal recycling in osteoblasts, importin-α/β and CRM1 mediate nuclear-cytoplasmic shuttling, MMP14 proteolytically dampens signaling by cleaving the extracellular domain, and biased agonism through the β-arrestin2 pathway selectively drives trabecular bone anabolism without bone resorption."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing that PTH1R dually couples to Gs (cAMP) and Gq (inositol phosphate) pathways resolved the fundamental question of which G-protein effectors transduce PTH/PTHrP binding into intracellular signals.","evidence":"Heterologous expression in COS-7 cells with radioligand binding and parallel cAMP/IP accumulation assays using zebrafish PTH1R ortholog","pmids":["10497171"],"confidence":"High","gaps":["Relative contributions of Gs vs. Gq to specific physiological outputs were not dissected","No structural basis for dual coupling was provided"]},{"year":2006,"claim":"Demonstrating that PTH1R forms complexes with importin-α1/β and localizes to the nucleoplasm during specific cell-cycle stages revealed an unexpected non-canonical trafficking route for a GPCR, raising questions about nuclear functions.","evidence":"Immunoprecipitation, PTH-affinity chromatography, and deconvolution microscopy in osteoblast-like cells","pmids":["16574786"],"confidence":"Medium","gaps":["Nuclear function of PTH1R was not established","Only one cell type examined"]},{"year":2007,"claim":"Identifying importin-α/β for nuclear import and CRM1 for nuclear export defined the molecular machinery controlling PTH1R nuclear-cytoplasmic shuttling and showed that serum/PTHrP availability regulates this partitioning.","evidence":"Importin-β siRNA, CRM1 inhibitor leptomycin B, co-IP, and nuclear fractionation","pmids":["17317770"],"confidence":"High","gaps":["Biological consequence of nuclear PTH1R accumulation remains unknown","Mechanism by which PTHrP promotes cytoplasmic relocalization not resolved"]},{"year":2008,"claim":"Functional characterization of Ollier disease-associated PTHR1 mutations established that enchondromatosis arises from loss-of-function—reduced ligand binding or surface expression—rather than constitutive activation.","evidence":"Receptor-ligand affinity and cell-surface expression assays for G121E, A122T, R255H mutants","pmids":["18559376"],"confidence":"Medium","gaps":["Only three mutations characterized; not all Ollier patients carry PTHR1 mutations","Downstream signaling of mutants not fully profiled"]},{"year":2009,"claim":"Engineered disulfide cross-linking across TM5 and TM6 revealed that agonist—but not antagonist—binding induces relative movement of these helices, providing the first physicochemical model of PTH1R activation conformational change.","evidence":"Systematic double-cysteine mutagenesis with disulfide bond formation in cell membrane preparations","pmids":["19063682"],"confidence":"High","gaps":["Full activation mechanism including intracellular conformational changes was not resolved","No high-resolution structure available at this time"]},{"year":2009,"claim":"A β-arrestin-biased agonist that activates β-arrestin2 but not G-protein signaling promoted trabecular bone formation without stimulating resorption, proving that PTH1R supports pathway-selective anabolic signaling in vivo.","evidence":"Biased agonist (D-Trp12,Tyr34)-PTH(7-34) in β-arrestin2 knockout mice with bone density measurements","pmids":["20368153"],"confidence":"High","gaps":["Downstream effectors of β-arrestin2-dependent anabolism not identified","Whether biased signaling is translatable to humans was unknown"]},{"year":2010,"claim":"Demonstrating that PTH1R phosphorylation-deficient knock-in mice show sustained cyclin D1 downregulation and that PTHrP/PKA/PKC induces MKP-1 to dephosphorylate ERK1/2 established receptor phosphorylation and internalization as critical timers of intracellular signaling duration in osteoblasts.","evidence":"Phosphorylation-deficient PTH1R knock-in mouse calvarial osteoblasts; MKP-1 overexpression and immunodepletion with pERK1/2 dephosphorylation assays and PKA/PKC inhibitors","pmids":["20929987","19892016"],"confidence":"High","gaps":["Identity of the kinase(s) phosphorylating PTH1R C-tail in vivo not established at this point","Relative contribution of ERK vs. other pathways to growth arrest not fully delineated"]},{"year":2011,"claim":"Discovery that PTH(1-34) triggers transient ubiquitination followed by USP2-mediated deubiquitination for receptor recycling, while PTH(7-34) causes sustained ubiquitination and proteasomal degradation, established ubiquitin editing as a ligand-dependent switch governing PTH1R fate.","evidence":"Ubiquitination assays, recycling/degradation assays, and USP2 overexpression rescue in cell lines","pmids":["21898592"],"confidence":"High","gaps":["E3 ligase responsible for PTH1R ubiquitination not identified","Whether USP2 regulation occurs in vivo in bone was not shown"]},{"year":2015,"claim":"PTH1R was shown to function as a mechanosensor in osteocytes: fluid flow or hypotonic shock activated PTH1R-dependent calcium, PLC, PKA, β-catenin, and ERK signaling to prevent apoptosis, even without exogenous ligand, while conditional limb deletion caused symphalangism, revealing non-canonical ligand-independent activation and essential roles in digit segmentation.","evidence":"PTH1R siRNA/overexpression with calcium imaging and apoptosis assays in MLO-Y4 osteocytes; Prx1-Cre conditional PTH1R KO mice with skeletal phenotyping","pmids":["25529820","26620087"],"confidence":"High","gaps":["Molecular mechanism by which mechanical force activates PTH1R without ligand not defined","Whether mechanosensory role is separable from IHH signaling axis in digit formation unclear"]},{"year":2016,"claim":"Mass spectrometry mapping of nine C-tail phosphosites and mutagenesis showing that Ser503/Thr504 account for ~70% of arrestin3 recruitment defined the phosphorylation code governing PTH1R-arrestin interaction, while SNX27-retromer was identified as the endosomal recycling machinery coupling PTH1R back to the surface in osteoblasts.","evidence":"MS phosphosite mapping with alanine mutagenesis and FRET/BRET arrestin recruitment; SNX27 PDZ-PTHR crystal structure, SNX27 KO osteoblasts with signaling and mineralization readouts","pmids":["27623777","26912788"],"confidence":"High","gaps":["Whether phosphosite code differs between PTH and PTHrP stimulation not tested","How SNX27-retromer is regulated in response to different ligands unknown"]},{"year":2016,"claim":"PFE-causing mutations such as Gly452Glu were shown to be functionally inactive, retained intracellularly, and dominant-negative on wild-type PTH1R, while Pro415 was identified as critical for selective activation by the small-molecule agonist PCO371, defining both disease mechanisms and a novel pharmacological binding mode.","evidence":"cAMP/VASP assays, confocal microscopy, electrophysiology for PFE mutants; chimeric PTH1R/PTH2R analysis and in vivo validation for PCO371","pmids":["27898723","27857062"],"confidence":"High","gaps":["Structural basis for dominant-negative effect not resolved","PCO371 binding site not visualized at atomic resolution"]},{"year":2019,"claim":"An ECD-binding antibody selectively blocked β-arrestin-2 recruitment without affecting Gs/cAMP signaling, demonstrating that the extracellular domain of PTH1R allosterically controls pathway selectivity and can be targeted for biased modulation.","evidence":"Phage display antibody with HDX-MS epitope mapping, parallel β-arrestin-2 and Gs signaling assays","pmids":["31594997"],"confidence":"High","gaps":["In vivo consequence of ECD-selective inhibition not tested","Whether ECD antibody affects internalization kinetics not assessed"]},{"year":2020,"claim":"Kindlin-2 was identified as a scaffolding partner that binds both the PTH1R C-terminal domain and Gsα, and Kindlin-2 haploinsufficiency combined with Pth1r haploinsufficiency synergistically reduced bone mass, establishing Kindlin-2 as an intrinsic component of the PTH1R signaling complex in osteoblasts.","evidence":"Reciprocal co-IP, osteoblast-specific Kindlin-2 conditional KO, epistatic double-haploinsufficiency in mice, cAMP/CREB assays","pmids":["33361757"],"confidence":"High","gaps":["Whether Kindlin-2 affects β-arrestin branch of PTH1R signaling not tested","Structural interface between Kindlin-2 and PTH1R not mapped at residue level"]},{"year":2021,"claim":"PTH1R was found to function in Leydig and epididymal epithelial cells, where abaloparatide-mediated anti-inflammatory effects required both Gq and β-arrestin-1, extending the receptor's physiological roles beyond bone and mineral metabolism.","evidence":"Gnaq heterozygous and Arrb1 knockout mouse models with inflammatory challenge","pmids":["34740971"],"confidence":"High","gaps":["Downstream effectors of Gq/β-arrestin-1 anti-inflammatory signaling in reproductive tract not identified","Whether this is pharmacologically relevant in humans unknown"]},{"year":2022,"claim":"Cryo-EM structures of PTH- and ABL-bound PTH1R–Gs complexes revealed that PTH forms a more rigid complex with greater tolerance to ECD mutations, explaining the longer signaling duration of PTH versus abaloparatide, while RAMP2 was shown to allosterically shift PTH1R toward a preactivated state enhancing Gi3 sensitivity and β-arrestin2 recruitment.","evidence":"Cryo-EM with 3D variability analysis and site-directed mutagenesis; BRET/FRET optical biosensors for RAMP2 co-expression studies","pmids":["36271004","35914163"],"confidence":"High","gaps":["Structure of RAMP2-PTH1R complex not determined","How RAMP2 modulates Gi3 coupling at the structural level is unknown"]},{"year":2023,"claim":"Eiken syndrome mutations were shown to increase basal cAMP or impair PTHrP-selective β-arrestin2 recruitment, while MMP14 was identified as a proteolytic negative regulator cleaving the PTH1R ectodomain in hypertrophic chondrocyte-derived osteoblasts, and a Zfp467-NFκB1 axis was found to transcriptionally upregulate Pth1r, revealing multiple layers of receptor regulation in skeletal cells.","evidence":"Signaling/binding assays for Eiken mutants; conditional Mmp14 KO with cleavage assay and bone phenotype; conditional Zfp467 KO with reporter assays and PKA inhibitors","pmids":["37268817","36892459","37159501"],"confidence":"High","gaps":["MMP14 cleavage site on PTH1R ECD not mapped at residue resolution","Whether Zfp467-dependent transcriptional regulation operates in cell types beyond osteogenic precursors is unknown"]},{"year":null,"claim":"The nuclear function of PTH1R, the structural basis of RAMP2 allosteric modulation, the E3 ubiquitin ligase for PTH1R, and the mechanism of ligand-independent mechanosensory activation remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No function assigned to nuclear PTH1R despite established import/export machinery","E3 ligase for PTH1R ubiquitination not identified","Structural mechanism of mechanosensory activation without ligand not determined","RAMP2-PTH1R complex structure not solved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,6,8,30]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[14]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[21,16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4,5]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[13]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,6,7,8,9,12,30]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[27,10]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,5]}],"complexes":[],"partners":["ARRB2","SNX27","RAMP2","FERMT2","USP2","MMP14","KPNA1","KPNB1"],"other_free_text":[]},"mechanistic_narrative":"PTH1R is a class B G protein-coupled receptor that transduces parathyroid hormone (PTH) and PTH-related peptide (PTHrP) signals to regulate bone formation, mineral ion homeostasis, and skeletal patterning through dual coupling to Gs/cAMP/PKA and Gq/PLC/calcium pathways [PMID:10497171, PMID:26620087]. Agonist-induced phosphorylation of C-terminal tail residues Ser503/Thr504 drives β-arrestin recruitment, receptor internalization, and endosomal signaling, while ubiquitin-dependent sorting—modulated by the deubiquitinase USP2—determines whether the receptor recycles (via SNX27-retromer) or undergoes proteasomal degradation [PMID:27623777, PMID:21898592, PMID:26912788]. β-Arrestin-biased agonism through PTH1R selectively stimulates trabecular bone anabolism without bone resorption, and receptor signaling is allosterically tuned by RAMP2, scaffolded by Kindlin-2/Gsα, negatively regulated by MMP14-mediated ectodomain cleavage, and subject to importin-α/β-dependent nuclear-cytoplasmic shuttling [PMID:20368153, PMID:35914163, PMID:33361757, PMID:36892459, PMID:17317770]. Loss-of-function PTH1R mutations cause primary failure of eruption (PFE) and Eiken syndrome, while specific enchondromatosis-associated mutations impair ligand binding or surface expression [PMID:27898723, PMID:37268817, PMID:18559376]."},"prefetch_data":{"uniprot":{"accession":"Q03431","full_name":"Parathyroid hormone/parathyroid hormone-related peptide receptor","aliases":["PTH/PTHrP type I receptor","PTH/PTHr receptor","Parathyroid hormone 1 receptor","PTH1 receptor"],"length_aa":593,"mass_kda":66.4,"function":"G-protein-coupled receptor for parathyroid hormone (PTH) and for parathyroid hormone-related peptide (PTHLH) (PubMed:10913300, PubMed:18375760, PubMed:19674967, PubMed:27160269, PubMed:30975883, PubMed:35932760, PubMed:8397094). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors, such as adenylate cyclase (cAMP) (PubMed:30975883, PubMed:35932760). PTH1R is coupled to G(s) G alpha proteins and mediates activation of adenylate cyclase activity (PubMed:20172855, PubMed:30975883, PubMed:35932760). PTHLH dissociates from PTH1R more rapidly than PTH; as consequence, the cAMP response induced by PTHLH decays faster than the response induced by PTH (PubMed:35932760)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q03431/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTH1R","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTH1R","total_profiled":1310},"omim":[{"mim_id":"618162","title":"SPONDYLOEPIMETAPHYSEAL DYSPLASIA, KRAKOW TYPE; SEMDK","url":"https://www.omim.org/entry/618162"},{"mim_id":"614776","title":"SIK FAMILY KINASE 3; SIK3","url":"https://www.omim.org/entry/614776"},{"mim_id":"614569","title":"MULTIPLE ENCHONDROMATOSIS, MAFFUCCI TYPE","url":"https://www.omim.org/entry/614569"},{"mim_id":"607733","title":"SCRIBBLE PLANAR CELL POLARITY PROTEIN; SCRIB","url":"https://www.omim.org/entry/607733"},{"mim_id":"606553","title":"SOLUTE CARRIER FAMILY 9, MEMBER 3, REGULATOR 2; SLC9A3R2","url":"https://www.omim.org/entry/606553"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"kidney","ntpm":583.6}],"url":"https://www.proteinatlas.org/search/PTH1R"},"hgnc":{"alias_symbol":[],"prev_symbol":["PTHR","PTHR1"]},"alphafold":{"accession":"Q03431","domains":[{"cath_id":"4.10.1240.10","chopping":"35-53_103-174","consensus_level":"medium","plddt":90.3735,"start":35,"end":174},{"cath_id":"1.20.1070.10","chopping":"176-472","consensus_level":"high","plddt":82.4554,"start":176,"end":472}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q03431","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q03431-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q03431-F1-predicted_aligned_error_v6.png","plddt_mean":70.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTH1R","jax_strain_url":"https://www.jax.org/strain/search?query=PTH1R"},"sequence":{"accession":"Q03431","fasta_url":"https://rest.uniprot.org/uniprotkb/Q03431.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q03431/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q03431"}},"corpus_meta":[{"pmid":"12595692","id":"PMC_12595692","title":"Proteomic 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PTH1R.","date":"2021","source":"Endocrine reviews","url":"https://pubmed.ncbi.nlm.nih.gov/33564837","citation_count":84,"is_preprint":false},{"pmid":"10497171","id":"PMC_10497171","title":"Zebrafish express the common parathyroid hormone/parathyroid hormone-related peptide receptor (PTH1R) and a novel receptor (PTH3R) that is preferentially activated by mammalian and fugufish parathyroid hormone-related peptide.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10497171","citation_count":79,"is_preprint":false},{"pmid":"18440674","id":"PMC_18440674","title":"Safety and immunogenicity of recombinant low-dosage HIV-1 A vaccine candidates vectored by plasmid pTHr DNA or modified vaccinia virus Ankara (MVA) in humans in East Africa.","date":"2008","source":"Vaccine","url":"https://pubmed.ncbi.nlm.nih.gov/18440674","citation_count":76,"is_preprint":false},{"pmid":"20152661","id":"PMC_20152661","title":"Primary failure of eruption and PTH1R: the importance of a genetic diagnosis for orthodontic treatment planning.","date":"2010","source":"American journal of orthodontics and dentofacial orthopedics : official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics","url":"https://pubmed.ncbi.nlm.nih.gov/20152661","citation_count":69,"is_preprint":false},{"pmid":"18559376","id":"PMC_18559376","title":"PTHR1 mutations associated with Ollier disease result in receptor loss of function.","date":"2008","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18559376","citation_count":64,"is_preprint":false},{"pmid":"15525660","id":"PMC_15525660","title":"Recessive mutations in PTHR1 cause contrasting skeletal dysplasias in Eiken and Blomstrand syndromes.","date":"2004","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/15525660","citation_count":62,"is_preprint":false},{"pmid":"27857062","id":"PMC_27857062","title":"Identification of an orally active small-molecule PTHR1 agonist for the treatment of hypoparathyroidism.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27857062","citation_count":56,"is_preprint":false},{"pmid":"20156969","id":"PMC_20156969","title":"Immunohistochemical identification of the PTHR1 parathyroid hormone receptor in normal and neoplastic human tissues.","date":"2010","source":"European journal of endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/20156969","citation_count":52,"is_preprint":false},{"pmid":"33361757","id":"PMC_33361757","title":"Kindlin-2 regulates skeletal homeostasis by modulating PTH1R in mice.","date":"2020","source":"Signal transduction and targeted therapy","url":"https://pubmed.ncbi.nlm.nih.gov/33361757","citation_count":47,"is_preprint":false},{"pmid":"15523647","id":"PMC_15523647","title":"Enchondromatosis (Ollier disease, Maffucci syndrome) is not caused by the PTHR1 mutation p.R150C.","date":"2004","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/15523647","citation_count":47,"is_preprint":false},{"pmid":"26912788","id":"PMC_26912788","title":"Sorting nexin 27 couples PTHR trafficking to retromer for signal regulation in osteoblasts during bone growth.","date":"2016","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/26912788","citation_count":46,"is_preprint":false},{"pmid":"8020952","id":"PMC_8020952","title":"Cloning of a parathyroid hormone/parathyroid hormone-related peptide receptor (PTHR) cDNA from a rat osteosarcoma (UMR 106) cell line: chromosomal assignment of the gene in the human, mouse, and rat genomes.","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8020952","citation_count":46,"is_preprint":false},{"pmid":"31382618","id":"PMC_31382618","title":"Inhibition of Ihh Reverses Temporomandibular Joint Osteoarthritis via a PTH1R Signaling Dependent Mechanism.","date":"2019","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31382618","citation_count":45,"is_preprint":false},{"pmid":"22312238","id":"PMC_22312238","title":"The bone-protective effect of genistein in the animal model of bilateral ovariectomy: roles of phytoestrogens and PTH/PTHR1 against post-menopausal osteoporosis.","date":"2011","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/22312238","citation_count":45,"is_preprint":false},{"pmid":"21404329","id":"PMC_21404329","title":"Exome resequencing combined with linkage analysis identifies novel PTH1R variants in primary failure of tooth eruption in 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trial to evaluate the safety and immunogenicity of the pTHr.HIVA DNA and MVA.HIVA vaccines in a prime-boost strategy to induce HIV-1 specific T-cell responses in healthy volunteers.","date":"2008","source":"Vaccine","url":"https://pubmed.ncbi.nlm.nih.gov/18812202","citation_count":42,"is_preprint":false},{"pmid":"19892016","id":"PMC_19892016","title":"Distinct roles for mitogen-activated protein kinase phosphatase-1 (MKP-1) and ERK-MAPK in PTH1R signaling during osteoblast proliferation and differentiation.","date":"2010","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/19892016","citation_count":42,"is_preprint":false},{"pmid":"24300310","id":"PMC_24300310","title":"Novel mutations in PTH1R associated with primary failure of eruption and osteoarthritis.","date":"2013","source":"Journal of dental research","url":"https://pubmed.ncbi.nlm.nih.gov/24300310","citation_count":41,"is_preprint":false},{"pmid":"23135290","id":"PMC_23135290","title":"Thymoquinone blocks pSer/pThr recognition by Plk1 Polo-box domain as a phosphate mimic.","date":"2012","source":"ACS chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/23135290","citation_count":40,"is_preprint":false},{"pmid":"23771181","id":"PMC_23771181","title":"Expanding the spectrum of PTH1R mutations in patients with primary failure of tooth eruption.","date":"2013","source":"Clinical oral investigations","url":"https://pubmed.ncbi.nlm.nih.gov/23771181","citation_count":40,"is_preprint":false},{"pmid":"25043296","id":"PMC_25043296","title":"Knockdown of PTHR1 in osteosarcoma cells decreases invasion and growth and increases tumor differentiation in vivo.","date":"2014","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/25043296","citation_count":39,"is_preprint":false},{"pmid":"24058597","id":"PMC_24058597","title":"Identification of six novel PTH1R mutations in families with a history of primary failure of tooth eruption.","date":"2013","source":"PloS 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Kieferorthopadie","url":"https://pubmed.ncbi.nlm.nih.gov/24825834","citation_count":28,"is_preprint":false},{"pmid":"12220122","id":"PMC_12220122","title":"Expression of parathyroid hormone-related peptide (PthrP) and its receptor (PTH1R) during the histogenesis of cartilage and bone in the chicken mandibular process.","date":"2002","source":"Journal of anatomy","url":"https://pubmed.ncbi.nlm.nih.gov/12220122","citation_count":28,"is_preprint":false},{"pmid":"16574786","id":"PMC_16574786","title":"Type 1 parathyroid hormone receptor (PTH1R) nuclear trafficking: association of PTH1R with importin alpha1 and beta.","date":"2006","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/16574786","citation_count":28,"is_preprint":false},{"pmid":"35126319","id":"PMC_35126319","title":"PTH1R Actions on Bone Using the cAMP/Protein Kinase A Pathway.","date":"2022","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/35126319","citation_count":27,"is_preprint":false},{"pmid":"29867773","id":"PMC_29867773","title":"Parathyroid Hormone-Related Protein Negatively Regulates Tumor Cell Dormancy Genes in a PTHR1/Cyclic AMP-Independent Manner.","date":"2018","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/29867773","citation_count":26,"is_preprint":false},{"pmid":"35933642","id":"PMC_35933642","title":"PTH1R translocation to primary cilia in mechanically-stimulated ostecytes prevents osteoclast formation via regulation of CXCL5 and IL-6 secretion.","date":"2022","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/35933642","citation_count":26,"is_preprint":false},{"pmid":"31594997","id":"PMC_31594997","title":"Modulation of PTH1R signaling by an ECD binding antibody results in inhibition of β-arrestin 2 coupling.","date":"2019","source":"Scientific 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agonist pharmacology in vivo; beta-arrestin2 knockout mice with bone mineral density measurement\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular phenotype, biased agonist tool, replicated in vivo\",\n      \"pmids\": [\"20368153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SNX27 binds directly to the C-terminal PDZ-binding motif of PTH1R and couples it to the retromer trafficking complex for endosomal sorting; depletion of SNX27 or retromer augments intracellular PTH1R signaling in endosomes and impairs bone mineralization in osteoblasts lacking SNX27.\",\n      \"method\": \"Direct binding assay, crystal structure of SNX27-PTHR PDZ motif complex, SNX27 KO osteoblasts with signaling and mineralization readouts, SNX27-KO mouse skeletal phenotype\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural validation with binding, KO phenotype, functional consequence in osteoblasts\",\n      \"pmids\": [\"26912788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PTH(1-34) stimulation induces transient PTHR ubiquitination followed by deubiquitination mediated by the PTHR-specific deubiquitinating enzyme USP2, enabling receptor recycling; in contrast, PTH(7-34) induces sustained PTHR ubiquitination without USP2 induction, leading to proteasomal degradation of the receptor.\",\n      \"method\": \"Ubiquitination assays, recycling/degradation assays, USP2 overexpression rescue, ligand treatment in cell lines\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ubiquitination, recycling, degradation, overexpression rescue) in single study\",\n      \"pmids\": [\"21898592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mass spectrometry identified nine phosphorylation sites in the C-terminal tail of PTH1R; two clusters (Ser489-Ser495 and Ser501-Thr506) are responsible for PTH(1-34)-induced phosphorylation. Ser503 and Thr504 in the second cluster account for ~70% of arrestin3 recruitment and are key determinants for arrestin3 interaction with the receptor, as shown by FRET and BRET assays.\",\n      \"method\": \"Mass spectrometry phosphosite mapping, alanine mutagenesis, FRET/BRET arrestin3 recruitment assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — MS identification plus mutagenesis plus two resonance energy transfer assays\",\n      \"pmids\": [\"27623777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PTH1R forms a complex with importin alpha1 and importin beta in osteoblast-like cells, as demonstrated by immunoprecipitation and PTH-affinity chromatography, indicating that these transport proteins mediate nuclear import of PTH1R. Nuclear PTH1R localization is restricted to the nucleoplasm and is associated with specific stages of the cell cycle.\",\n      \"method\": \"Immunoprecipitation, affinity chromatography, immunofluorescence/deconvolution microscopy\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal IP and affinity chromatography, but single lab\",\n      \"pmids\": [\"16574786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PTH1R nuclear-cytoplasmic shuttling depends on importin-alpha/beta for nuclear import and CRM1/exportin1 for nuclear export; importin-beta siRNA knockdown reduces nuclear PTH1R, and leptomycin B (CRM1 inhibitor) causes nuclear accumulation. Serum starvation favors nuclear localization, while PTHrP or serum re-addition promotes cytoplasmic localization.\",\n      \"method\": \"siRNA knockdown, CRM1 inhibitor (leptomycin B), co-immunoprecipitation, immunofluorescence microscopy, nuclear fractionation\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (siRNA, pharmacological inhibitor, co-IP, fractionation) with functional localization consequence\",\n      \"pmids\": [\"17317770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PTH agonist and antagonist induce distinct conformational changes at the extracellular-facing interface of transmembrane domains TM5 and TM6 of PTH1R; engineered disulfide bond formation showed TM5/TM6 move relative to each other upon agonist binding but not antagonist binding, providing physicochemical evidence for the receptor activation mechanism.\",\n      \"method\": \"Engineered disulfide bond cross-linking strategy, cell membrane preparations, 18 double-cysteine PTHR1 mutants\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with systematic mutagenesis revealing activation mechanism\",\n      \"pmids\": [\"19063682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"An orally active small-molecule agonist (PCO371) acts as a full agonist of PTH1R but not PTH2R; chimeric receptor analysis identified Pro415 of PTH1R as critical for PCO371-mediated activation, indicating a distinct binding mode from peptide ligands.\",\n      \"method\": \"PTH1R-PTHR2 chimeric receptor analysis, cAMP assays, in vivo rat models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chimeric receptor mutagenesis plus in vitro activity assay plus in vivo validation\",\n      \"pmids\": [\"27857062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of PTH- and ABL-bound PTH1R-Gs complexes reveal similar overall conformations but notable differences in the receptor ECD regions and peptide C-terminal portions; 3D variability analysis and site-directed mutagenesis show PTH-bound complexes display less motion and greater tolerance to mutations, providing molecular basis for the longer signaling duration of teriparatide (PTH) vs. abaloparatide (ABL).\",\n      \"method\": \"Cryo-EM structure determination, 3D variability analysis, site-directed mutagenesis, signaling assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures with mutagenesis and signaling assay validation, single paper with multiple orthogonal methods\",\n      \"pmids\": [\"36271004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAMP2 acts as a specific allosteric modulator of PTH1R, shifting it to a preactivated state that permits faster ligand-dependent activation; RAMP2 modulates PTH1R downstream signaling in an agonist-dependent manner, increasing PTH-mediated Gi3 signaling sensitivity and enhancing β-arrestin2 recruitment by both PTH and PTHrP.\",\n      \"method\": \"Optical biosensors (BRET/FRET), homology modeling, co-expression of RAMP2 with PTH1R\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biosensor assays with structural modeling in single study\",\n      \"pmids\": [\"35914163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MMP14 cleaves the extracellular domain of PTH1R in hypertrophic chondrocyte-derived osteoblasts, dampening PTH signaling; in HC lineage-specific Mmp14 null mice, PTH1R signaling is enhanced and bone formation is increased, demonstrating MMP14 as a negative regulator of PTH1R signaling intensity in the osteoblast lineage.\",\n      \"method\": \"HC lineage-specific Mmp14 conditional knockout, single-cell transcriptomics, in vitro cleavage assay, PTH 1-34 treatment in mutant mice\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro cleavage assay plus conditional KO with defined bone phenotype and signaling readout\",\n      \"pmids\": [\"36892459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"An ECD-binding antibody (ECD-scFvhFc) targeting the α1 helix of the PTH1R extracellular domain potently inhibits β-arrestin-2 recruitment after PTH(1-34) activation without affecting Gs-mediated cAMP signaling, representing pathway-selective inhibition of PTH1R signaling.\",\n      \"method\": \"Phage display antibody generation, hydrogen-deuterium exchange mass spectrometry epitope mapping, β-arrestin-2 recruitment assay, Gs signaling assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — HDX-MS epitope mapping plus orthogonal signaling assays demonstrating biased inhibition\",\n      \"pmids\": [\"31594997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Kindlin-2 interacts with the C-terminal cytoplasmic domain of PTH1R via residues aa 474-475 and with Gsα, functioning as an intrinsic component of the PTH1R signaling complex; Kindlin-2 loss suppresses PTH-induced cAMP production and CREB phosphorylation in osteoblasts, and haploinsufficiency of both Kindlin-2 and Pth1r significantly decreases bone mass.\",\n      \"method\": \"Co-immunoprecipitation, haploinsufficiency double-mutant epistasis in mice, cAMP/CREB signaling assays in osteoblasts, osteoblast-specific conditional KO\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, epistasis in vivo, defined signaling readouts\",\n      \"pmids\": [\"33361757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mechanical stimulation (fluid flow) causes redistribution of PTH1R along the entire primary cilium of osteocytic MLO-Y4 cells; PTH1R and primary cilia signaling are both required for FF-mediated inhibition of osteoclast recruitment and differentiation via modulation of CXCL5 and IL-6 secretion from osteocytes.\",\n      \"method\": \"siRNA knockdown of PTH1R and primary cilia, fluid flow stimulation, proteomic analysis, live imaging, neutralizing antibodies, osteoclast migration/differentiation assays\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with defined cellular phenotype, proteomic identification of downstream mediators, localization tied to function\",\n      \"pmids\": [\"35933642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mechanical stimulation (hypotonic shock or pulsatile fluid flow) activates PTH1R-dependent signaling in osteocytic MLO-Y4 cells to prevent apoptosis; this involves calcium signaling (blocked by verapamil), PLC (blocked by U73122), and PKA, as well as β-catenin stabilization and nuclear ERK translocation. Hypotonic shock rapidly stimulates Ca2+ transients in PTH1R-overexpressing HEK-293 cells even in the absence of PTHrP ligand, indicating PTH1R acts as a mechanosensor.\",\n      \"method\": \"PTH1R siRNA knockdown, PTH1R overexpression in HEK-293 cells, pharmacological inhibitors, calcium imaging, apoptosis assays in MLO-Y4 osteocytes\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD plus overexpression plus pharmacological inhibitors plus Ca2+ imaging with defined apoptosis phenotype\",\n      \"pmids\": [\"25529820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PTHrP increases MKP-1 (MAPK phosphatase-1) expression in differentiated osteoblasts via PTH1R activation through PKA and PKC pathways; MKP-1 then dephosphorylates pERK1/2 and down-regulates cyclin D1, inducing growth arrest in mature osteoblasts and mediating anabolic actions of PTH1R.\",\n      \"method\": \"MKP-1 overexpression, immunodepletion, in vitro pERK1/2 dephosphorylation assay with cell extracts, PKA/PKC inhibitors, in vivo PTH treatment with bone formation markers\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including in vitro dephosphorylation assay, immunodepletion, pathway inhibitors, in vivo validation\",\n      \"pmids\": [\"19892016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PTH1R mutations identified in PFE patients (e.g., Gly452Glu) are functionally inactive in G-protein/cAMP signaling; PTH1R/Gly452Glu acts as a dominant negative on wild-type PTH1R signaling and is retained intracellularly rather than expressed at the cell surface, abolishing coupling to TRESK K+ channels.\",\n      \"method\": \"cAMP ELISA, Western blot (VASP phosphorylation), confocal microscopy, electrophysiological recordings in Xenopus oocytes, co-transfection with WT and mutant PTH1R\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays (cAMP, phosphorylation, imaging, electrophysiology) demonstrating dominant-negative mechanism\",\n      \"pmids\": [\"27898723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Eiken syndrome PTH1R mutation R485X (truncation of C-terminal tail) increases basal cAMP signaling and decreases β-arrestin2 recruitment upon ligand stimulation; mutations E35K and Y134S weaken PTHrP binding, impairing β-arrestin2 recruitment and desensitization of cAMP response to PTHrP but not PTH, supporting a critical role for β-arrestin in PTH1R-regulated bone formation.\",\n      \"method\": \"Cell-based cAMP signaling assays, β-arrestin2 recruitment assays, ligand binding assays for multiple Eiken PTH1R mutants\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants tested with orthogonal assays (cAMP, arrestin recruitment, binding) in single rigorous study\",\n      \"pmids\": [\"37268817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PTH1R is expressed in Leydig cells of the testis and epididymal epithelial cells; activation of PTH1R by abaloparatide alleviates inflammation-induced epididymitis/orchitis mainly through the Gq and β-arrestin-1 signaling pathways, as demonstrated by attenuated anti-inflammatory effects in Gnaq+/- and Arrb1-/- mouse models.\",\n      \"method\": \"Gnaq heterozygous and Arrb1 knockout mouse models, pharmacological activation with abaloparatide, inflammatory challenge models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two distinct genetic KO models delineating specific pathway contributions\",\n      \"pmids\": [\"34740971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Functional analysis of PFE-associated PTH1R variants P119L and P132L revealed severe reduction in N-linked glycosylation and markedly decreased affinity for PTH1-34, leading to severely impaired cAMP accumulation upon stimulation; these variants also failed to induce RANKL expression in osteoblastic cells derived from PFE patient iPSCs.\",\n      \"method\": \"Lentiviral expression in HeLa cells, N-linked glycosylation analysis, ligand binding assays, cAMP accumulation assays, iPSC disease modeling with osteoblastic differentiation\",\n      \"journal\": \"Journal of dental research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical assays plus iPSC-based disease model\",\n      \"pmids\": [\"31986066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"N-cadherin reduces LRP6-PTH1R interaction and endocytosis in response to PTH, blunting PTH-induced suppression of sclerostin/SOST through impaired MEF2 downregulation; deletion of N-cadherin in osteocytes (Cdh2ΔDmp1 mice) accentuates iPTH-induced SOST suppression and bone anabolic effects.\",\n      \"method\": \"N-cadherin overexpression, immunoblot/qPCR for SOST/MEF2, co-IP for LRP6-PTHR1, Dmp1-Cre conditional Cdh2 KO mice with iPTH treatment\",\n      \"journal\": \"Annals of the New York Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro co-IP plus conditional KO in vivo, but single lab\",\n      \"pmids\": [\"27723935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PTH1R receptors are localized at the basolateral plasma membrane of proximal and distal tubule epithelial cells in human kidney and at the plasma membrane of osteocytes and osteoblasts (but not osteoclasts) in bone, as established by a validated anti-PTH1R antibody showing translocation of receptor immunostaining after agonist exposure.\",\n      \"method\": \"Anti-peptide antibody characterization (western blot, cell surface staining of transfected cells, agonist-induced translocation, preadsorption controls), immunohistochemistry of 320 human tumors and normal tissues\",\n      \"journal\": \"European journal of endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — validated antibody with multiple specificity controls, direct localization with functional agonist-induced translocation\",\n      \"pmids\": [\"20156969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTH1R activation by a novel PTH analog (MY-1) promotes keratinocyte migration and epithelial-mesenchymal transition in wound healing through the PTHR1-PI3K/AKT signaling axis, as demonstrated by siRNA knockdown of PTHR1 abolishing PI3K/AKT activation in HaCaT cells.\",\n      \"method\": \"siRNA knockdown of PTHR1, PI3K/AKT pathway analysis by western blot, migration and EMT assays, in vivo wound models with GelMA hydrogel delivery\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with defined signaling and phenotypic readouts, in vitro and in vivo\",\n      \"pmids\": [\"37612710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Impaired phosphorylation/internalization of PTH1R (phosphorylation-deficient knock-in mice) results in sustained cyclin D1 downregulation in osteoblasts compared to wild-type, indicating that receptor phosphorylation and subsequent internalization regulate the duration of intracellular signaling responses including ERK1/2 and cyclin D1 in bone cells.\",\n      \"method\": \"Phosphorylation-deficient PTH1R knock-in mouse model, primary calvarial osteoblast culture, pERK1/2 and cyclin D1 assays\",\n      \"journal\": \"The Journal of endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic knock-in model with defined in vitro and in vivo signaling readouts, single lab\",\n      \"pmids\": [\"20929987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of Zfp467 in osteogenic precursors leads to increased nuclear translocation of NFκB1, which binds the P2 promoter of Pth1r and increases its transcription, creating a positive feedback loop; PTH suppresses Zfp467 primarily via the cAMP/PKA pathway downstream of PTH1R.\",\n      \"method\": \"Conditional KO (Prrx1Cre;Zfp467), dual fluorescence reporter assays, confocal immunofluorescence, PKA inhibitor, Pth1r siRNA, cAMP production assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (reporter assay, confocal, pharmacological, genetic) demonstrating feedback mechanism\",\n      \"pmids\": [\"37159501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-17 upregulates N-cadherin which disrupts PTH1R/LRP-6 interaction, thereby inhibiting Wnt signaling and promoting bone loss; combination of PTH(1-34) with anti-IL17 reduces PTH1R expression and has synergistic bone-protective effects in ovariectomized mice, placing IL-17 upstream of the PTHR1/LRP-6/Wnt axis.\",\n      \"method\": \"Immunofluorescence analysis, anti-IL17 antibody treatment plus iPTH in OVX mice, bone mineral density measurement\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — immunofluorescence only for PTHR1/LRP-6 disruption, mechanistic details inferred rather than directly demonstrated\",\n      \"pmids\": [\"28935557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Hyperstimulation of CaSR by biomimetic hydroxyapatite causes temporal downregulation of PTH1R in human BM-derived MSCs, inhibiting chondrogenic differentiation; rescuing PTH1R expression with PTH(1-34) partially restores chondrogenesis, demonstrating cross-talk between CaSR and PTH1R in controlling MSC ossification pathway choice.\",\n      \"method\": \"CaSR knockdown, PTH(1-34) rescue experiments, chondrogenic differentiation assays, in vivo ectopic implantation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CaSR KD plus PTH1R rescue with in vitro and in vivo validation\",\n      \"pmids\": [\"29915064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Conditional deletion of PTH1R in limb mesenchyme (Prx1-Cre;PTH1R fl/fl) causes symphalangism (digit joint fusion) due to failure of epiphyseal growth plate formation and replacement of cartilage by bone, demonstrating a novel role for PTH1R signaling in digit formation and segmentation distinct from its known role in long bone growth plates.\",\n      \"method\": \"Prx1-Cre conditional PTH1R KO mice, histomorphometry, comparison with Ihh conditional KO and Jansen transgenic rescue\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined skeletal phenotype, epistasis with rescue transgenic attempted\",\n      \"pmids\": [\"26620087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of RAMP2 in mice decreases PTH1R expression and causes a blunted response to systemic PTH administration, providing in vivo evidence that RAMP2 regulates PTH1R expression and function.\",\n      \"method\": \"Ramp2 KO mice, PTH administration, gene expression analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined in vivo PTH response, but correlation between RAMP2 loss and PTH1R expression without direct binding demonstration\",\n      \"pmids\": [\"28727763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Three PTHR1 missense mutations identified in Ollier disease enchondromas (G121E, A122T, R255H) impair receptor function by reducing either PTH binding affinity or receptor expression at the cell surface, establishing loss-of-function as the mechanistic basis for PTHR1-associated enchondromatosis.\",\n      \"method\": \"Functional assays of receptor-ligand affinity and cell surface expression in patient-derived mutation-expressing cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional characterization of mutations with binding and surface expression assays\",\n      \"pmids\": [\"18559376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Zebrafish PTH1R ortholog (zPTH1R) binds PTH, PTHrP, and fuguPTHrP with high affinity (IC50 1.2-3.5 nM) and efficiently stimulates cAMP accumulation and inositol phosphate (IP) production when expressed in COS-7 cells, establishing dual G-protein coupling (Gs and Gq).\",\n      \"method\": \"COS-7 cell expression, radioligand competition binding, cAMP accumulation assay, inositol phosphate accumulation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution in heterologous expression system with binding and two distinct signaling assays\",\n      \"pmids\": [\"10497171\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTH1R is a class B GPCR that binds PTH and PTHrP at its extracellular domain and signals primarily through Gs/cAMP/PKA and Gq/PLC/calcium pathways, with agonist-induced phosphorylation of specific C-terminal tail residues (Ser489-Ser495, Ser501-Thr506) driving β-arrestin2/3 recruitment, receptor internalization, endosomal signaling, and ubiquitin-dependent sorting between recycling (promoted by USP2 deubiquitinase) and proteasomal degradation; RAMP2 acts as an allosteric modulator shifting PTH1R to a preactivated state, SNX27-retromer couples the receptor to endosomal recycling in osteoblasts, importin-α/β and CRM1 mediate nuclear-cytoplasmic shuttling, MMP14 proteolytically dampens signaling by cleaving the extracellular domain, and biased agonism through the β-arrestin2 pathway selectively drives trabecular bone anabolism without bone resorption.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PTH1R is a class B G protein-coupled receptor that transduces parathyroid hormone (PTH) and PTH-related peptide (PTHrP) signals to regulate bone formation, mineral ion homeostasis, and skeletal patterning through dual coupling to Gs/cAMP/PKA and Gq/PLC/calcium pathways [PMID:10497171, PMID:26620087]. Agonist-induced phosphorylation of C-terminal tail residues Ser503/Thr504 drives β-arrestin recruitment, receptor internalization, and endosomal signaling, while ubiquitin-dependent sorting—modulated by the deubiquitinase USP2—determines whether the receptor recycles (via SNX27-retromer) or undergoes proteasomal degradation [PMID:27623777, PMID:21898592, PMID:26912788]. β-Arrestin-biased agonism through PTH1R selectively stimulates trabecular bone anabolism without bone resorption, and receptor signaling is allosterically tuned by RAMP2, scaffolded by Kindlin-2/Gsα, negatively regulated by MMP14-mediated ectodomain cleavage, and subject to importin-α/β-dependent nuclear-cytoplasmic shuttling [PMID:20368153, PMID:35914163, PMID:33361757, PMID:36892459, PMID:17317770]. Loss-of-function PTH1R mutations cause primary failure of eruption (PFE) and Eiken syndrome, while specific enchondromatosis-associated mutations impair ligand binding or surface expression [PMID:27898723, PMID:37268817, PMID:18559376].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that PTH1R dually couples to Gs (cAMP) and Gq (inositol phosphate) pathways resolved the fundamental question of which G-protein effectors transduce PTH/PTHrP binding into intracellular signals.\",\n      \"evidence\": \"Heterologous expression in COS-7 cells with radioligand binding and parallel cAMP/IP accumulation assays using zebrafish PTH1R ortholog\",\n      \"pmids\": [\"10497171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of Gs vs. Gq to specific physiological outputs were not dissected\", \"No structural basis for dual coupling was provided\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that PTH1R forms complexes with importin-α1/β and localizes to the nucleoplasm during specific cell-cycle stages revealed an unexpected non-canonical trafficking route for a GPCR, raising questions about nuclear functions.\",\n      \"evidence\": \"Immunoprecipitation, PTH-affinity chromatography, and deconvolution microscopy in osteoblast-like cells\",\n      \"pmids\": [\"16574786\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear function of PTH1R was not established\", \"Only one cell type examined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying importin-α/β for nuclear import and CRM1 for nuclear export defined the molecular machinery controlling PTH1R nuclear-cytoplasmic shuttling and showed that serum/PTHrP availability regulates this partitioning.\",\n      \"evidence\": \"Importin-β siRNA, CRM1 inhibitor leptomycin B, co-IP, and nuclear fractionation\",\n      \"pmids\": [\"17317770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biological consequence of nuclear PTH1R accumulation remains unknown\", \"Mechanism by which PTHrP promotes cytoplasmic relocalization not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Functional characterization of Ollier disease-associated PTHR1 mutations established that enchondromatosis arises from loss-of-function—reduced ligand binding or surface expression—rather than constitutive activation.\",\n      \"evidence\": \"Receptor-ligand affinity and cell-surface expression assays for G121E, A122T, R255H mutants\",\n      \"pmids\": [\"18559376\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Only three mutations characterized; not all Ollier patients carry PTHR1 mutations\", \"Downstream signaling of mutants not fully profiled\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Engineered disulfide cross-linking across TM5 and TM6 revealed that agonist—but not antagonist—binding induces relative movement of these helices, providing the first physicochemical model of PTH1R activation conformational change.\",\n      \"evidence\": \"Systematic double-cysteine mutagenesis with disulfide bond formation in cell membrane preparations\",\n      \"pmids\": [\"19063682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full activation mechanism including intracellular conformational changes was not resolved\", \"No high-resolution structure available at this time\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"A β-arrestin-biased agonist that activates β-arrestin2 but not G-protein signaling promoted trabecular bone formation without stimulating resorption, proving that PTH1R supports pathway-selective anabolic signaling in vivo.\",\n      \"evidence\": \"Biased agonist (D-Trp12,Tyr34)-PTH(7-34) in β-arrestin2 knockout mice with bone density measurements\",\n      \"pmids\": [\"20368153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effectors of β-arrestin2-dependent anabolism not identified\", \"Whether biased signaling is translatable to humans was unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that PTH1R phosphorylation-deficient knock-in mice show sustained cyclin D1 downregulation and that PTHrP/PKA/PKC induces MKP-1 to dephosphorylate ERK1/2 established receptor phosphorylation and internalization as critical timers of intracellular signaling duration in osteoblasts.\",\n      \"evidence\": \"Phosphorylation-deficient PTH1R knock-in mouse calvarial osteoblasts; MKP-1 overexpression and immunodepletion with pERK1/2 dephosphorylation assays and PKA/PKC inhibitors\",\n      \"pmids\": [\"20929987\", \"19892016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the kinase(s) phosphorylating PTH1R C-tail in vivo not established at this point\", \"Relative contribution of ERK vs. other pathways to growth arrest not fully delineated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery that PTH(1-34) triggers transient ubiquitination followed by USP2-mediated deubiquitination for receptor recycling, while PTH(7-34) causes sustained ubiquitination and proteasomal degradation, established ubiquitin editing as a ligand-dependent switch governing PTH1R fate.\",\n      \"evidence\": \"Ubiquitination assays, recycling/degradation assays, and USP2 overexpression rescue in cell lines\",\n      \"pmids\": [\"21898592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase responsible for PTH1R ubiquitination not identified\", \"Whether USP2 regulation occurs in vivo in bone was not shown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"PTH1R was shown to function as a mechanosensor in osteocytes: fluid flow or hypotonic shock activated PTH1R-dependent calcium, PLC, PKA, β-catenin, and ERK signaling to prevent apoptosis, even without exogenous ligand, while conditional limb deletion caused symphalangism, revealing non-canonical ligand-independent activation and essential roles in digit segmentation.\",\n      \"evidence\": \"PTH1R siRNA/overexpression with calcium imaging and apoptosis assays in MLO-Y4 osteocytes; Prx1-Cre conditional PTH1R KO mice with skeletal phenotyping\",\n      \"pmids\": [\"25529820\", \"26620087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which mechanical force activates PTH1R without ligand not defined\", \"Whether mechanosensory role is separable from IHH signaling axis in digit formation unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Mass spectrometry mapping of nine C-tail phosphosites and mutagenesis showing that Ser503/Thr504 account for ~70% of arrestin3 recruitment defined the phosphorylation code governing PTH1R-arrestin interaction, while SNX27-retromer was identified as the endosomal recycling machinery coupling PTH1R back to the surface in osteoblasts.\",\n      \"evidence\": \"MS phosphosite mapping with alanine mutagenesis and FRET/BRET arrestin recruitment; SNX27 PDZ-PTHR crystal structure, SNX27 KO osteoblasts with signaling and mineralization readouts\",\n      \"pmids\": [\"27623777\", \"26912788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether phosphosite code differs between PTH and PTHrP stimulation not tested\", \"How SNX27-retromer is regulated in response to different ligands unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"PFE-causing mutations such as Gly452Glu were shown to be functionally inactive, retained intracellularly, and dominant-negative on wild-type PTH1R, while Pro415 was identified as critical for selective activation by the small-molecule agonist PCO371, defining both disease mechanisms and a novel pharmacological binding mode.\",\n      \"evidence\": \"cAMP/VASP assays, confocal microscopy, electrophysiology for PFE mutants; chimeric PTH1R/PTH2R analysis and in vivo validation for PCO371\",\n      \"pmids\": [\"27898723\", \"27857062\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for dominant-negative effect not resolved\", \"PCO371 binding site not visualized at atomic resolution\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"An ECD-binding antibody selectively blocked β-arrestin-2 recruitment without affecting Gs/cAMP signaling, demonstrating that the extracellular domain of PTH1R allosterically controls pathway selectivity and can be targeted for biased modulation.\",\n      \"evidence\": \"Phage display antibody with HDX-MS epitope mapping, parallel β-arrestin-2 and Gs signaling assays\",\n      \"pmids\": [\"31594997\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo consequence of ECD-selective inhibition not tested\", \"Whether ECD antibody affects internalization kinetics not assessed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Kindlin-2 was identified as a scaffolding partner that binds both the PTH1R C-terminal domain and Gsα, and Kindlin-2 haploinsufficiency combined with Pth1r haploinsufficiency synergistically reduced bone mass, establishing Kindlin-2 as an intrinsic component of the PTH1R signaling complex in osteoblasts.\",\n      \"evidence\": \"Reciprocal co-IP, osteoblast-specific Kindlin-2 conditional KO, epistatic double-haploinsufficiency in mice, cAMP/CREB assays\",\n      \"pmids\": [\"33361757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Kindlin-2 affects β-arrestin branch of PTH1R signaling not tested\", \"Structural interface between Kindlin-2 and PTH1R not mapped at residue level\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"PTH1R was found to function in Leydig and epididymal epithelial cells, where abaloparatide-mediated anti-inflammatory effects required both Gq and β-arrestin-1, extending the receptor's physiological roles beyond bone and mineral metabolism.\",\n      \"evidence\": \"Gnaq heterozygous and Arrb1 knockout mouse models with inflammatory challenge\",\n      \"pmids\": [\"34740971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effectors of Gq/β-arrestin-1 anti-inflammatory signaling in reproductive tract not identified\", \"Whether this is pharmacologically relevant in humans unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Cryo-EM structures of PTH- and ABL-bound PTH1R–Gs complexes revealed that PTH forms a more rigid complex with greater tolerance to ECD mutations, explaining the longer signaling duration of PTH versus abaloparatide, while RAMP2 was shown to allosterically shift PTH1R toward a preactivated state enhancing Gi3 sensitivity and β-arrestin2 recruitment.\",\n      \"evidence\": \"Cryo-EM with 3D variability analysis and site-directed mutagenesis; BRET/FRET optical biosensors for RAMP2 co-expression studies\",\n      \"pmids\": [\"36271004\", \"35914163\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of RAMP2-PTH1R complex not determined\", \"How RAMP2 modulates Gi3 coupling at the structural level is unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Eiken syndrome mutations were shown to increase basal cAMP or impair PTHrP-selective β-arrestin2 recruitment, while MMP14 was identified as a proteolytic negative regulator cleaving the PTH1R ectodomain in hypertrophic chondrocyte-derived osteoblasts, and a Zfp467-NFκB1 axis was found to transcriptionally upregulate Pth1r, revealing multiple layers of receptor regulation in skeletal cells.\",\n      \"evidence\": \"Signaling/binding assays for Eiken mutants; conditional Mmp14 KO with cleavage assay and bone phenotype; conditional Zfp467 KO with reporter assays and PKA inhibitors\",\n      \"pmids\": [\"37268817\", \"36892459\", \"37159501\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MMP14 cleavage site on PTH1R ECD not mapped at residue resolution\", \"Whether Zfp467-dependent transcriptional regulation operates in cell types beyond osteogenic precursors is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The nuclear function of PTH1R, the structural basis of RAMP2 allosteric modulation, the E3 ubiquitin ligase for PTH1R, and the mechanism of ligand-independent mechanosensory activation remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No function assigned to nuclear PTH1R despite established import/export machinery\", \"E3 ligase for PTH1R ubiquitination not identified\", \"Structural mechanism of mechanosensory activation without ligand not determined\", \"RAMP2-PTH1R complex structure not solved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 6, 8, 30]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [21, 16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 6, 7, 8, 9, 12, 30]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [27, 10]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ARRB2\",\n      \"SNX27\",\n      \"RAMP2\",\n      \"FERMT2\",\n      \"USP2\",\n      \"MMP14\",\n      \"KPNA1\",\n      \"KPNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}