{"gene":"PROKR2","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2006,"finding":"PKR2 knockout mice exhibit hypoplasia of the olfactory bulb and severe atrophy of the reproductive system, with absence of GnRH neurons in the hypothalamus and reduced plasma testosterone and gonadotropin levels, establishing that PROKR2 signaling is essential for olfactory bulb development and GnRH neuron positioning/function.","method":"Targeted gene knockout (Pkr2-/- mice), immunohistochemistry, hormone assays, mRNA quantification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype replicated across multiple readouts (histology, hormone levels, IHC); consistent with independent Prokr2-null mouse paper (PMID:18052978)","pmids":["16537498"],"is_preprint":false},{"year":2007,"finding":"Prokr2 null mice lose precision in circadian locomotor activity onset and show redistribution of activity across circadian night and depressed nocturnal body temperature, but their SCN circadian oscillator remains intact; demonstrating PROKR2 is required for SCN-to-behavior circadian output but not for cellular timekeeping or light entrainment.","method":"Targeted null mutation, locomotor activity monitoring under LD and DD, bioluminescence real-time imaging of SCN slices","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with multiple orthogonal phenotypic readouts (activity, temperature, ex vivo SCN bioluminescence) distinguishing output from oscillator function","pmids":["17202262"],"is_preprint":false},{"year":2007,"finding":"Prokr2 null mice show decreased OB volume, reduced BrdU+ proliferating cells, TUNEL+ cells in the glomerular layer, decreased TH+ neurons, accumulation of doublecortin+ neuroblasts in the RMS, and Prokr2-deficient neurosphere cells fail to migrate toward PROK2 in vitro; establishing PROKR2 as necessary for neuronal progenitor migration and differentiation into the olfactory bulb.","method":"Prokr2 null mouse analysis, BrdU labeling, TUNEL, immunohistochemistry, in vitro neurosphere migration assay","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vivo and in vitro methods establishing migration defect mechanistically","pmids":["18052978"],"is_preprint":false},{"year":2008,"finding":"Ten KS-associated PROKR2 missense mutations impair receptor signaling via distinct mechanisms: three (L173R, W178S, P290S) impair cell surface targeting; one (Q210R) abolishes ligand binding; five (R85C, R85H, R164Q, R268C, V331M) impair G protein coupling; none exert dominant negative effects on co-expressed wild-type receptor.","method":"Site-directed mutagenesis of recombinant murine Prokr2, transfection in HEK-293 cells, intracellular calcium release assay, cell surface expression assays","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with functional assays across ten mutations, multiple orthogonal readouts (signaling, trafficking, ligand binding), dominant-negative testing","pmids":["18826963"],"is_preprint":false},{"year":2011,"finding":"The R164Q disease-causing mutation in the second intracellular loop (IL2) of PKR2 abolishes signaling without affecting cell surface expression or ligand binding; R164 is required for interaction of the IL2 loop with Gαq, Gαi, and Gα16 proteins, and a positive charge at position 164 is essential; R164Q also reduces ligand-induced endocytosis.","method":"Site-directed mutagenesis, transfection assays, G-protein binding studies, endocytosis assays, charge-substitution series","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with direct G-protein binding assay, multiple charge variants tested, mechanistic resolution of trafficking vs. coupling defects","pmids":["21454486"],"is_preprint":false},{"year":2014,"finding":"Wild-type PROKR2 activates Gq, Gs, and Gi/o signaling pathways and recruits β-arrestins; KS-associated mutations cause pathway-selective signaling bias: R85C, R85H, R164Q, V331M lose Gq signaling but retain β-arrestin recruitment; R80C activates all three G proteins but cannot recruit β-arrestins; R268C can recruit β-arrestins and activate Gq/Gs but not Gi/o.","method":"Transfection in HEK-293 cells, pathway-specific signaling assays (Gq, Gs, Gi/o, β-arrestin recruitment), site-directed mutagenesis","journal":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple signaling pathways assayed in parallel, systematic mutation analysis, mechanistic biased agonism characterized","pmids":["24830383"],"is_preprint":false},{"year":2014,"finding":"PKR2 endocytosis is GRK2-dependent and clathrin-dependent, but β-arrestin-independent; PKC activation can also induce PKR2 endocytosis but is not necessary for ligand-induced endocytosis; PK2-induced ERK1/2 activation requires Gβγ subunits and PLC-β/MEK but not receptor internalization or PKC.","method":"Dominant-negative constructs, siRNA knockdown, pharmacological inhibitors, ERK1/2 phosphorylation assays, endocytosis assays in transfected cells","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mechanistic dissection using multiple perturbations (dominant negatives, siRNA, inhibitors) across two distinct processes (internalization and ERK activation), single lab","pmids":["24509228"],"is_preprint":false},{"year":2014,"finding":"The small molecule PKR2 antagonist A457 rescues cell surface expression and function of the P290S trafficking-deficient mutant but not W178S or G234D mutants; glycerol (chemical chaperone) rescues surface expression and signaling of both P290S and W178S mutants.","method":"Pharmacological rescue with small molecule antagonist and chemical chaperone, cell surface expression assays, functional signaling assays in transfected cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct pharmacological rescue experiments with functional readout, two distinct rescue strategies tested, single lab","pmids":["24753254"],"is_preprint":false},{"year":2015,"finding":"Snapin is a novel binding partner of PKR2, interacting via the PKR2 C-terminus (YFK 343-345 and HWR 351-353 motifs) and two α-helix domains of Snapin; disruption of Snapin-PKR2 interaction does not affect PKR2 signaling but increases ligand-induced receptor degradation, indicating Snapin regulates PKR2 trafficking/stability.","method":"Yeast two-hybrid screening, GST pull-down, co-immunoprecipitation, mutagenesis mapping of interaction motifs","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — interaction confirmed by three methods (Y2H, GST-PD, Co-IP) with mutagenesis to map motifs, functional consequence assessed, single lab","pmids":["26687946"],"is_preprint":false},{"year":2013,"finding":"The distal region of the third intracellular loop (IL3) of PROKR2 differentially controls receptor trafficking and G-protein coupling: deletion of RRK (270-272) abolishes cell surface expression, whereas deletion of RKR (264-266) preserves surface expression but causes loss of G-protein coupling; charged residue at V274 is required for normal surface expression.","method":"Site-directed mutagenesis, deletion analysis, cell surface expression assays, functional signaling assays in transfected cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — systematic deletion and substitution mutagenesis with mechanistic dissection of trafficking vs. coupling, single lab","pmids":["23969157"],"is_preprint":false},{"year":2018,"finding":"IHH-associated PROKR2 mutations L218P and R270H disrupt Gαq-dependent signaling while maintaining normal Gαs and ERK1/2 signaling; GST pull-down demonstrated that R270H specifically disrupts the interaction of intracellular loop 3 of PROKR2 with Gαq but not Gαs protein, establishing that selective Gα-coupling disruption underlies biased signaling in some mutations.","method":"Site-directed mutagenesis, pathway-specific signaling assays, GST pull-down with Gαq and Gαs proteins","journal":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical demonstration of selective Gα binding disruption by pull-down combined with multiple signaling pathway assays, mechanistic resolution at the level of individual protein interactions","pmids":["30576231"],"is_preprint":false},{"year":2013,"finding":"Multiple PROKR2 missense variants differentially affect Gq (IP/Ca2+) and Gs (cAMP) signaling pathways: variants T260M, R268C, V331M show preserved cAMP response but impaired IP signaling; L173R and V274D lack cAMP response; V334M (gain of expression) elevates EC50 for both pathways; demonstrating single allelic variants can selectively or differentially impair distinct PROKR2 signaling cascades.","method":"Transfection in HEK-293 cells, IP/Ca2+ assay (Gq), cAMP accumulation assay (Gs), surface expression quantification","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — parallel measurement of two independent signaling pathways for multiple variants, single lab","pmids":["24276467"],"is_preprint":false},{"year":2008,"finding":"Transgenic overexpression of PKR2 in cardiomyocytes induces eccentric cardiac hypertrophy (increased hypertrophic gene expression, increased heart-to-body weight ratio, increased cardiomyocyte length) and vascular leakage through mislocalization of tight junction protein ZO-1, without inducing angiogenesis; conditioned media from PKR2-overexpressing cardioblasts recapitulates impaired ZO-1 localization in endothelial cells, indicating paracrine signaling.","method":"Transgenic mouse generation, morphological and echocardiographic analysis, immunofluorescence for ZO-1, vascular leakage assay, conditioned media experiment in H5V endothelial cells","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic model with multiple orthogonal readouts plus in vitro conditioned media validation, single lab","pmids":["18806277"],"is_preprint":false},{"year":2019,"finding":"PROK2/PROKR2 signaling is required for both tangential and radial migration of olfactory bulb interneurons; Prokr2 is expressed in postmitotic immature interneurons in the SVZ-RMS-OB; loss of Prok2 or Prokr2 causes loss of ~75% of GABAergic interneurons in the OB due to migration failure.","method":"Prokr2-LacZ knockin mice, Prok2-EGFP transgenic mice, cell lineage analysis, in situ hybridization, quantitative cell counting","journal":"The Journal of comparative neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent knockin/transgenic models with multiple orthogonal analyses (reporter gene, ISH, quantitative histology) establishing cell-type identity and migration requirement","pmids":["31132148"],"is_preprint":false},{"year":2021,"finding":"N-linked glycosylation at position N27 of PKR2 is required for plasma membrane localization and signaling; glycosylation at position N7 selectively reduces PKR2 signaling through Gαs without impairing Gαq/11 signaling; MRAP2 prevents PKR2 from trafficking to the plasma membrane.","method":"Site-directed mutagenesis of glycosylation sites, cell surface expression assays, pathway-specific signaling assays (Gαs/cAMP, Gαq/Ca2+)","journal":"Frontiers in neuroscience","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct mutagenesis of specific glycosylation sites with functional and localization readouts, pathway selectivity established, single lab","pmids":["34483834"],"is_preprint":false},{"year":2022,"finding":"Trafficking-defective P290S PROKR2 mutant cycles between the ER and Golgi rather than reaching the cell surface; both WT and P290S mutant undergo ER-associated degradation, but the mutant is degraded to greater extent; the post-ER cycling of the mutant to the Golgi reduces ER stress; distinct interactomes were identified for WT versus P290S PROKR2.","method":"Interactome analysis (MS), ER-associated degradation assays, ER-to-Golgi trafficking assays, ER stress measurements, pharmacological perturbations","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (interactomics, degradation assays, trafficking assays, ER stress measurements) in a single rigorous study establishing post-ER quality control mechanism","pmids":["35173048"],"is_preprint":false},{"year":2017,"finding":"A heterozygous frameshift PROKR2 mutation generating a truncated receptor lacking two transmembrane domains and the C-terminal tail has no intrinsic signaling activity in vitro, but cells co-expressing this mutant with wild-type PROKR2 show markedly exaggerated ligand-induced Ca2+ responses, establishing a paradoxical gain-of-function mechanism via enhancement of wild-type receptor activity.","method":"Frameshift mutation identification, in vitro signaling assays (Ca2+ response) in cells transfected with mutant alone or co-transfected with wild-type PROKR2","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct co-transfection experiment demonstrating gain-of-function mechanism, single lab, novel mechanism validated functionally","pmids":["28338294"],"is_preprint":false},{"year":2018,"finding":"In vitro co-transfection of mutant with wild-type PROKR2 (modeling heterozygosity) identified 15/34 IGD-associated variants as loss-of-function including 3 novel dominant negatives, while only 4/25 control variants were LoF; variants LoF in ≥2 signaling assays under co-transfection conditions were more likely disease-associated, revealing dominant-negative and dominant mechanisms not detected by mutant-alone assays.","method":"Co-transfection assays modeling heterozygosity, three parallel signaling pathway assays, comparison of 59 variants","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — systematic in vitro functional assays across three pathways with co-transfection modeling; single lab but large variant series","pmids":["29161432"],"is_preprint":false},{"year":2010,"finding":"C. trachomatis infection increases PROKR2 mRNA in fallopian tube epithelial cells via TLR2 ligation and NFκB activation; transfection with dominant-negative TLR2 or IκBα abrogated the C. trachomatis-induced PROKR2 upregulation, placing PROKR2 downstream of TLR2/NFκB in this inflammatory signaling cascade.","method":"C. trachomatis infection of fallopian tube explants and OE-E6/E7 cell line, dominant-negative TLR2 and IκBα transfection, mRNA quantification","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dominant-negative constructs establish epistatic pathway position, two orthogonal interventions, single lab","pmids":["21224062"],"is_preprint":false},{"year":2021,"finding":"EG-VEGF activates ERK1/2 signaling and upregulates MMP-2 and MMP-9 in HTR-8/SVneo trophoblast cells, promoting cell migration and invasion; anti-PROKR2 antibody (but not anti-PROKR1) suppresses ERK1/2 activation and inhibits EG-VEGF-stimulated migration and invasion, establishing PROKR2 as the receptor mediating EG-VEGF-induced trophoblast invasion via ERK1/2/MMP pathway.","method":"Antibody blocking of PROKR2 and PROKR1 in HTR-8/SVneo cells, ERK1/2 phosphorylation assay, MMP-2/9 qRT-PCR and western blot, wound-healing and invasion assays","journal":"Acta medica Okayama","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody-mediated receptor blockade with multiple functional readouts (signaling + invasion), single lab","pmids":["34955534"],"is_preprint":false},{"year":2019,"finding":"Pkr2-null mice show reduced nociceptive sensitization to heat (46-48°C), capsaicin, and protons (TRPV1 agonists), and reduced response to cold and mustard oil (TRPA1 agonists); DRG culture analysis shows the percentage of Bv8-responsive neurons also responsive to mustard oil is much higher in PKR1-/- than PKR2-/- mice, establishing functional interactions between PKR2 and both TRPV1 and TRPA1 in nociception.","method":"Pkr2-/- mouse behavioral nociception assays, DRG primary neuron culture, capsaicin/proton/mustard oil/cold stimulation, comparison with PKR1-/- mice","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with multiple nociceptive paradigms, comparison with paralog KO provides specificity evidence, single lab","pmids":["31883821"],"is_preprint":false},{"year":2025,"finding":"TRPV1 physically interacts with PKR2; in the presence of snapin, the strength of the TRPV1-PKR2 interaction is increased; TRPV1 modulates PKR2 activation, subcellular localization, and β-arrestin-2 recruitment, and regulates PK2-induced mechanical allodynia in vivo.","method":"Co-immunoprecipitation/interaction mapping, snapin co-expression experiments, PKR2 localization and signaling assays, in vivo allodynia assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct physical interaction mapped with functional consequences on signaling and in vivo behavior, multiple readouts, single lab","pmids":["40139621"],"is_preprint":false},{"year":2022,"finding":"Blockage of Gαq signaling, but not the MAPK/ERK pathway, inhibits PROK2-induced migration of PROKR2-expressing cells, establishing that Gαq is the primary downstream effector of PROKR2 mediating GnRH neuron migration-related signaling relevant to IHH pathogenesis.","method":"Pathway-specific pharmacological inhibition combined with cell migration assay in PROKR2-expressing cells","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct pathway inhibition with migration readout in a defined cellular system, single lab","pmids":["36694982"],"is_preprint":false}],"current_model":"PROKR2 is a G protein-coupled receptor that binds prokineticin 2 (PROK2) and signals through multiple G protein subtypes (Gq, Gs, Gi/o) as well as β-arrestins; it is essential for GnRH neuron migration to the hypothalamus and olfactory bulb morphogenesis (established by knockout mice), mediates circadian behavioral output from the SCN without being required for the oscillator itself, drives neuronal progenitor migration in the rostral migratory stream via Gαq-dependent signaling, and undergoes GRK2/clathrin-dependent internalization regulated by interacting partners including snapin (which stabilizes the receptor) and TRPV1 (which modulates its activation and β-arrestin recruitment); disease-causing missense mutations impair receptor function through distinct mechanisms—defective trafficking to the plasma membrane, loss of ligand binding, or selective disruption of coupling to specific Gα proteins—sometimes producing biased signaling rather than complete loss of function."},"narrative":{"mechanistic_narrative":"PROKR2 is a G protein-coupled receptor for prokineticin 2 (PROK2) that is essential for the migration and positioning of GnRH neurons and olfactory bulb interneurons, linking it directly to reproductive and olfactory development [PMID:16537498, PMID:18052978, PMID:31132148]. Knockout mice lack hypothalamic GnRH neurons, show olfactory bulb hypoplasia, and lose roughly three-quarters of OB GABAergic interneurons because postmitotic immature neuroblasts fail to migrate from the SVZ-RMS toward PROK2 [PMID:16537498, PMID:18052978, PMID:31132148]; this migratory function is driven principally by Gαq signaling rather than the MAPK/ERK arm [PMID:36694982]. Beyond development, PROKR2 transduces SCN circadian output to behavior without being required for the cellular oscillator itself [PMID:17202262] and contributes to nociceptive sensitization through functional coupling to TRPV1 and TRPA1 channels [PMID:31883821]. Mechanistically, wild-type PROKR2 activates Gq, Gs, and Gi/o and recruits β-arrestins, and disease-associated missense mutations partition into distinct functional defects—impaired plasma-membrane trafficking, loss of ligand binding, or selective uncoupling from individual Gα proteins—frequently producing biased signaling rather than complete loss of function [PMID:18826963, PMID:24830383, PMID:30576231]. Intracellular determinants of these behaviors have been mapped: a positively charged residue in IL2 (R164) is required for coupling to Gαq, Gαi, and Gα16 [PMID:21454486], and distinct motifs of IL3 separately govern surface trafficking versus G-protein coupling [PMID:23969157]. Receptor surface delivery additionally depends on N-linked glycosylation at N27 and is negatively regulated by MRAP2, while the trafficking-defective P290S mutant cycles between ER and Golgi and undergoes enhanced ER-associated degradation [PMID:34483834, PMID:35173048]. PROKR2 internalizes via a GRK2- and clathrin-dependent, β-arrestin-independent route, and its stability and trafficking are modulated by the binding partner snapin and by TRPV1 [PMID:24509228, PMID:26687946, PMID:40139621]. Some disease alleles act dominantly, including a truncated receptor that paradoxically enhances wild-type receptor activity and additional dominant-negative variants revealed only under co-expression with wild-type receptor [PMID:28338294, PMID:29161432].","teleology":[{"year":2006,"claim":"Established the developmental requirement for PROKR2 by showing its loss eliminates hypothalamic GnRH neurons and disrupts olfactory bulb formation, defining the receptor's physiological role.","evidence":"Targeted knockout mice with IHC, hormone assays, and mRNA quantification","pmids":["16537498"],"confidence":"High","gaps":["Did not resolve which downstream G-protein pathway mediates the developmental defect","Did not distinguish cell-autonomous migration from survival effects"]},{"year":2007,"claim":"Separated PROKR2's role in circadian behavioral output from the timekeeping oscillator, showing it conveys SCN signals to behavior without being required for the clock.","evidence":"Null mice with locomotor/temperature monitoring and ex vivo SCN bioluminescence imaging","pmids":["17202262"],"confidence":"High","gaps":["Did not identify the target neurons receiving the PROKR2-dependent output signal","Mechanism of output coupling unresolved"]},{"year":2008,"claim":"Defined PROKR2 as a chemoattractant receptor for neuronal progenitor migration into the olfactory bulb, showing Prokr2-deficient cells fail to migrate toward PROK2.","evidence":"Null mouse histology with BrdU/TUNEL and in vitro neurosphere migration assays","pmids":["18052978"],"confidence":"High","gaps":["Did not define the intracellular signaling effector for migration","Did not separate proliferation from migration contributions to OB volume"]},{"year":2008,"claim":"First systematic functional triage of KS-associated mutations, showing missense variants impair the receptor through three distinct mechanisms—trafficking, ligand binding, or coupling—without dominant-negative effects.","evidence":"Site-directed mutagenesis of ten mutations with calcium, surface-expression, and co-expression assays in HEK-293 cells","pmids":["18826963"],"confidence":"High","gaps":["Tested only Gq/calcium signaling, missing pathway-selective defects","Did not assess heterozygous co-expression beyond dominant-negative screening for this readout"]},{"year":2008,"claim":"Revealed a peripheral, paracrine action of PROKR2 in the heart, where cardiomyocyte overexpression causes hypertrophy and vascular leakage via ZO-1 mislocalization.","evidence":"Transgenic mice with echocardiography, ZO-1 immunofluorescence, and endothelial conditioned-media experiments","pmids":["18806277"],"confidence":"Medium","gaps":["Overexpression model may not reflect endogenous receptor levels","Paracrine mediator linking PKR2 signaling to ZO-1 not identified"]},{"year":2011,"claim":"Pinpointed an IL2 residue (R164) as a charge-dependent determinant of G-protein coupling, resolving how a disease mutation abolishes signaling without trafficking or ligand-binding defects.","evidence":"Charge-substitution mutagenesis with direct Gα binding and endocytosis assays","pmids":["21454486"],"confidence":"High","gaps":["Structural basis of the IL2-Gα interaction not determined","Did not address β-arrestin coupling at this residue"]},{"year":2013,"claim":"Mapped IL3 as a bifunctional segment in which separate motifs independently govern trafficking versus G-protein coupling.","evidence":"Deletion and substitution mutagenesis with surface-expression and signaling assays","pmids":["23969157"],"confidence":"Medium","gaps":["Single lab; structural mechanism of the RKR/RRK switch unresolved","Did not connect IL3 motifs to specific Gα subtypes"]},{"year":2013,"claim":"Demonstrated that single disease alleles can differentially impair Gq versus Gs cascades, refining mutation interpretation beyond binary loss-of-function.","evidence":"Parallel IP/Ca2+ and cAMP assays across multiple variants in HEK-293 cells","pmids":["24276467"],"confidence":"Medium","gaps":["Single lab; did not test β-arrestin recruitment","Functional consequences in neurons not assessed"]},{"year":2014,"claim":"Established PROKR2 as a multi-G-protein receptor exhibiting mutation-induced biased agonism, with distinct alleles selectively losing Gq, β-arrestin, or Gi/o coupling.","evidence":"Parallel Gq/Gs/Gi/o and β-arrestin recruitment assays with systematic mutagenesis","pmids":["24830383"],"confidence":"High","gaps":["Physiological readout of each biased profile not established in vivo","Structural basis of biased coupling unresolved"]},{"year":2014,"claim":"Defined the internalization route and an ERK-activation mechanism, showing endocytosis is GRK2/clathrin-dependent but β-arrestin-independent while ERK requires Gβγ and PLC-β/MEK.","evidence":"Dominant-negative constructs, siRNA, inhibitors, and ERK/endocytosis assays in transfected cells","pmids":["24509228"],"confidence":"High","gaps":["Single lab; in vivo relevance of these routes not tested","Adaptor linking GRK2 to clathrin not identified"]},{"year":2014,"claim":"Provided proof-of-concept for pharmacological rescue of trafficking-defective mutants, with mutant-specific responsiveness to a small-molecule pharmacochaperone versus a chemical chaperone.","evidence":"Rescue with antagonist A457 and glycerol, surface-expression and signaling readouts","pmids":["24753254"],"confidence":"Medium","gaps":["Single lab; rescue not demonstrated in vivo","Mechanism of mutant-selective rescue not resolved"]},{"year":2015,"claim":"Identified snapin as a C-terminal binding partner that regulates receptor stability rather than signaling, expanding the trafficking-control machinery.","evidence":"Yeast two-hybrid, GST pull-down, Co-IP, and motif-mapping mutagenesis","pmids":["26687946"],"confidence":"Medium","gaps":["Single lab; physiological role of snapin in PROKR2 function not tested in vivo","How snapin slows ligand-induced degradation mechanistically unclear"]},{"year":2017,"claim":"Uncovered a paradoxical gain-of-function mechanism in which a signaling-dead truncated receptor enhances wild-type receptor activity, challenging simple loss-of-function interpretation.","evidence":"Co-transfection of frameshift mutant with wild-type PROKR2 and Ca2+ signaling assays","pmids":["28338294"],"confidence":"Medium","gaps":["Single lab; molecular basis of WT enhancement not defined","In vivo phenotype of the gain-of-function allele not established"]},{"year":2018,"claim":"Showed that co-expression assays modeling heterozygosity reveal dominant-negative and dominant alleles missed by mutant-alone testing, improving variant pathogenicity classification.","evidence":"Co-transfection of 59 variants across three signaling pathways","pmids":["29161432"],"confidence":"Medium","gaps":["Single lab; in vitro classification not validated against clinical penetrance","Structural basis of dominant-negative interference not resolved"]},{"year":2018,"claim":"Demonstrated biochemically that selective disruption of IL3-Gαq binding underlies biased signaling, with R270H losing Gαq but retaining Gαs/ERK.","evidence":"GST pull-down with Gαq and Gαs plus pathway-specific signaling assays","pmids":["30576231"],"confidence":"High","gaps":["Structural model of the IL3-Gαq interface not determined","In vivo consequence of selective Gαq loss not tested"]},{"year":2019,"claim":"Established the cell-type identity and migratory requirement of PROKR2 in OB interneurons, localizing expression to postmitotic neuroblasts and quantifying interneuron loss upon disruption.","evidence":"Prokr2-LacZ knockin and Prok2-EGFP transgenic mice with lineage analysis, ISH, and cell counting","pmids":["31132148"],"confidence":"High","gaps":["Did not define the intracellular signaling pathway for tangential vs radial migration","Source and gradient of PROK2 guiding migration not mapped"]},{"year":2021,"claim":"Identified glycosylation as a trafficking and pathway-selectivity determinant, with N27 required for surface delivery and N7 selectively tuning Gαs signaling, and MRAP2 as a negative trafficking regulator.","evidence":"Glycosylation-site mutagenesis with surface-expression and Gαs/Gαq signaling assays","pmids":["34483834"],"confidence":"Medium","gaps":["Single lab; MRAP2 regulation not validated in neurons in vivo","Mechanism by which N7 glycan biases Gαs unresolved"]},{"year":2021,"claim":"Defined PROKR2 as the receptor mediating EG-VEGF-induced trophoblast invasion via ERK1/2 and MMP-2/9 upregulation, extending its role to placentation.","evidence":"Antibody blockade of PROKR2 vs PROKR1 in HTR-8/SVneo cells with signaling and invasion assays","pmids":["34955534"],"confidence":"Medium","gaps":["Single lab; in vivo placental requirement not tested","Did not establish G-protein link to the ERK/MMP cascade in this context"]},{"year":2022,"claim":"Resolved the post-ER quality-control fate of a trafficking-defective mutant, showing P290S cycles between ER and Golgi, undergoes enhanced ERAD, and assembles a distinct interactome.","evidence":"Mass-spec interactomics, ERAD and ER-to-Golgi trafficking assays, and ER stress measurements","pmids":["35173048"],"confidence":"High","gaps":["Specific chaperones controlling the ER-Golgi cycle not pinpointed functionally","Whether other trafficking mutants share this fate not established"]},{"year":2022,"claim":"Identified Gαq as the primary effector for PROKR2-driven cell migration, mechanistically linking the migration phenotype to a specific signaling arm relevant to IHH.","evidence":"Pathway-specific pharmacological inhibition with migration assays in PROKR2-expressing cells","pmids":["36694982"],"confidence":"Medium","gaps":["Single lab; not validated in primary GnRH neurons","Downstream cytoskeletal effectors of Gαq not identified"]},{"year":2025,"claim":"Established a physical and functional TRPV1-PROKR2 interaction, strengthened by snapin, that modulates receptor activation, localization, β-arrestin recruitment, and pain behavior, integrating PROKR2 into nociceptive channel signaling.","evidence":"Co-IP/interaction mapping, snapin co-expression, signaling/localization assays, and in vivo allodynia assay","pmids":["40139621"],"confidence":"Medium","gaps":["Single lab; structural basis of the TRPV1-PROKR2 interface not determined","Whether the interaction occurs in defined sensory neuron subtypes in vivo not resolved"]},{"year":null,"claim":"How PROKR2's diverse signaling outputs (Gq, Gs, Gi/o, β-arrestin) are selected and spatially organized in vivo to produce its distinct developmental, circadian, and nociceptive functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of PROKR2 or its Gα/effector complexes","Tissue-specific determinants of biased signaling not mapped","Endogenous regulation by MRAP2, snapin, and TRPV1 not validated in native cells in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[3,5,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[16,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,9,14]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[15]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,6,10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,2,13]},{"term_id":"R-HSA-9909396","term_label":"Circadian clock","supporting_discovery_ids":[1]}],"complexes":[],"partners":["PROK2","GNAQ","GRK2","SNAPIN","TRPV1","MRAP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NFJ6","full_name":"Prokineticin receptor 2","aliases":["G-protein coupled receptor 73-like 1","G-protein coupled receptor I5E","GPR73b","GPRg2"],"length_aa":384,"mass_kda":44.0,"function":"Receptor for prokineticin 2. Exclusively coupled to the G(q) subclass of heteromeric G proteins. 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olfactory bulb and severe atrophy of the reproductive system, with absence of GnRH neurons in the hypothalamus and reduced plasma testosterone and gonadotropin levels, establishing that PROKR2 signaling is essential for olfactory bulb development and GnRH neuron positioning/function.\",\n      \"method\": \"Targeted gene knockout (Pkr2-/- mice), immunohistochemistry, hormone assays, mRNA quantification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype replicated across multiple readouts (histology, hormone levels, IHC); consistent with independent Prokr2-null mouse paper (PMID:18052978)\",\n      \"pmids\": [\"16537498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Prokr2 null mice lose precision in circadian locomotor activity onset and show redistribution of activity across circadian night and depressed nocturnal body temperature, but their SCN circadian oscillator remains intact; demonstrating PROKR2 is required for SCN-to-behavior circadian output but not for cellular timekeeping or light entrainment.\",\n      \"method\": \"Targeted null mutation, locomotor activity monitoring under LD and DD, bioluminescence real-time imaging of SCN slices\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with multiple orthogonal phenotypic readouts (activity, temperature, ex vivo SCN bioluminescence) distinguishing output from oscillator function\",\n      \"pmids\": [\"17202262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Prokr2 null mice show decreased OB volume, reduced BrdU+ proliferating cells, TUNEL+ cells in the glomerular layer, decreased TH+ neurons, accumulation of doublecortin+ neuroblasts in the RMS, and Prokr2-deficient neurosphere cells fail to migrate toward PROK2 in vitro; establishing PROKR2 as necessary for neuronal progenitor migration and differentiation into the olfactory bulb.\",\n      \"method\": \"Prokr2 null mouse analysis, BrdU labeling, TUNEL, immunohistochemistry, in vitro neurosphere migration assay\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vivo and in vitro methods establishing migration defect mechanistically\",\n      \"pmids\": [\"18052978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ten KS-associated PROKR2 missense mutations impair receptor signaling via distinct mechanisms: three (L173R, W178S, P290S) impair cell surface targeting; one (Q210R) abolishes ligand binding; five (R85C, R85H, R164Q, R268C, V331M) impair G protein coupling; none exert dominant negative effects on co-expressed wild-type receptor.\",\n      \"method\": \"Site-directed mutagenesis of recombinant murine Prokr2, transfection in HEK-293 cells, intracellular calcium release assay, cell surface expression assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with functional assays across ten mutations, multiple orthogonal readouts (signaling, trafficking, ligand binding), dominant-negative testing\",\n      \"pmids\": [\"18826963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The R164Q disease-causing mutation in the second intracellular loop (IL2) of PKR2 abolishes signaling without affecting cell surface expression or ligand binding; R164 is required for interaction of the IL2 loop with Gαq, Gαi, and Gα16 proteins, and a positive charge at position 164 is essential; R164Q also reduces ligand-induced endocytosis.\",\n      \"method\": \"Site-directed mutagenesis, transfection assays, G-protein binding studies, endocytosis assays, charge-substitution series\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with direct G-protein binding assay, multiple charge variants tested, mechanistic resolution of trafficking vs. coupling defects\",\n      \"pmids\": [\"21454486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Wild-type PROKR2 activates Gq, Gs, and Gi/o signaling pathways and recruits β-arrestins; KS-associated mutations cause pathway-selective signaling bias: R85C, R85H, R164Q, V331M lose Gq signaling but retain β-arrestin recruitment; R80C activates all three G proteins but cannot recruit β-arrestins; R268C can recruit β-arrestins and activate Gq/Gs but not Gi/o.\",\n      \"method\": \"Transfection in HEK-293 cells, pathway-specific signaling assays (Gq, Gs, Gi/o, β-arrestin recruitment), site-directed mutagenesis\",\n      \"journal\": \"FASEB journal : official publication of the Federation of American Societies for Experimental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple signaling pathways assayed in parallel, systematic mutation analysis, mechanistic biased agonism characterized\",\n      \"pmids\": [\"24830383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PKR2 endocytosis is GRK2-dependent and clathrin-dependent, but β-arrestin-independent; PKC activation can also induce PKR2 endocytosis but is not necessary for ligand-induced endocytosis; PK2-induced ERK1/2 activation requires Gβγ subunits and PLC-β/MEK but not receptor internalization or PKC.\",\n      \"method\": \"Dominant-negative constructs, siRNA knockdown, pharmacological inhibitors, ERK1/2 phosphorylation assays, endocytosis assays in transfected cells\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mechanistic dissection using multiple perturbations (dominant negatives, siRNA, inhibitors) across two distinct processes (internalization and ERK activation), single lab\",\n      \"pmids\": [\"24509228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The small molecule PKR2 antagonist A457 rescues cell surface expression and function of the P290S trafficking-deficient mutant but not W178S or G234D mutants; glycerol (chemical chaperone) rescues surface expression and signaling of both P290S and W178S mutants.\",\n      \"method\": \"Pharmacological rescue with small molecule antagonist and chemical chaperone, cell surface expression assays, functional signaling assays in transfected cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct pharmacological rescue experiments with functional readout, two distinct rescue strategies tested, single lab\",\n      \"pmids\": [\"24753254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Snapin is a novel binding partner of PKR2, interacting via the PKR2 C-terminus (YFK 343-345 and HWR 351-353 motifs) and two α-helix domains of Snapin; disruption of Snapin-PKR2 interaction does not affect PKR2 signaling but increases ligand-induced receptor degradation, indicating Snapin regulates PKR2 trafficking/stability.\",\n      \"method\": \"Yeast two-hybrid screening, GST pull-down, co-immunoprecipitation, mutagenesis mapping of interaction motifs\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — interaction confirmed by three methods (Y2H, GST-PD, Co-IP) with mutagenesis to map motifs, functional consequence assessed, single lab\",\n      \"pmids\": [\"26687946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The distal region of the third intracellular loop (IL3) of PROKR2 differentially controls receptor trafficking and G-protein coupling: deletion of RRK (270-272) abolishes cell surface expression, whereas deletion of RKR (264-266) preserves surface expression but causes loss of G-protein coupling; charged residue at V274 is required for normal surface expression.\",\n      \"method\": \"Site-directed mutagenesis, deletion analysis, cell surface expression assays, functional signaling assays in transfected cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic deletion and substitution mutagenesis with mechanistic dissection of trafficking vs. coupling, single lab\",\n      \"pmids\": [\"23969157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IHH-associated PROKR2 mutations L218P and R270H disrupt Gαq-dependent signaling while maintaining normal Gαs and ERK1/2 signaling; GST pull-down demonstrated that R270H specifically disrupts the interaction of intracellular loop 3 of PROKR2 with Gαq but not Gαs protein, establishing that selective Gα-coupling disruption underlies biased signaling in some mutations.\",\n      \"method\": \"Site-directed mutagenesis, pathway-specific signaling assays, GST pull-down with Gαq and Gαs proteins\",\n      \"journal\": \"FASEB journal : official publication of the Federation of American Societies for Experimental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical demonstration of selective Gα binding disruption by pull-down combined with multiple signaling pathway assays, mechanistic resolution at the level of individual protein interactions\",\n      \"pmids\": [\"30576231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Multiple PROKR2 missense variants differentially affect Gq (IP/Ca2+) and Gs (cAMP) signaling pathways: variants T260M, R268C, V331M show preserved cAMP response but impaired IP signaling; L173R and V274D lack cAMP response; V334M (gain of expression) elevates EC50 for both pathways; demonstrating single allelic variants can selectively or differentially impair distinct PROKR2 signaling cascades.\",\n      \"method\": \"Transfection in HEK-293 cells, IP/Ca2+ assay (Gq), cAMP accumulation assay (Gs), surface expression quantification\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — parallel measurement of two independent signaling pathways for multiple variants, single lab\",\n      \"pmids\": [\"24276467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Transgenic overexpression of PKR2 in cardiomyocytes induces eccentric cardiac hypertrophy (increased hypertrophic gene expression, increased heart-to-body weight ratio, increased cardiomyocyte length) and vascular leakage through mislocalization of tight junction protein ZO-1, without inducing angiogenesis; conditioned media from PKR2-overexpressing cardioblasts recapitulates impaired ZO-1 localization in endothelial cells, indicating paracrine signaling.\",\n      \"method\": \"Transgenic mouse generation, morphological and echocardiographic analysis, immunofluorescence for ZO-1, vascular leakage assay, conditioned media experiment in H5V endothelial cells\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic model with multiple orthogonal readouts plus in vitro conditioned media validation, single lab\",\n      \"pmids\": [\"18806277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PROK2/PROKR2 signaling is required for both tangential and radial migration of olfactory bulb interneurons; Prokr2 is expressed in postmitotic immature interneurons in the SVZ-RMS-OB; loss of Prok2 or Prokr2 causes loss of ~75% of GABAergic interneurons in the OB due to migration failure.\",\n      \"method\": \"Prokr2-LacZ knockin mice, Prok2-EGFP transgenic mice, cell lineage analysis, in situ hybridization, quantitative cell counting\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent knockin/transgenic models with multiple orthogonal analyses (reporter gene, ISH, quantitative histology) establishing cell-type identity and migration requirement\",\n      \"pmids\": [\"31132148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"N-linked glycosylation at position N27 of PKR2 is required for plasma membrane localization and signaling; glycosylation at position N7 selectively reduces PKR2 signaling through Gαs without impairing Gαq/11 signaling; MRAP2 prevents PKR2 from trafficking to the plasma membrane.\",\n      \"method\": \"Site-directed mutagenesis of glycosylation sites, cell surface expression assays, pathway-specific signaling assays (Gαs/cAMP, Gαq/Ca2+)\",\n      \"journal\": \"Frontiers in neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct mutagenesis of specific glycosylation sites with functional and localization readouts, pathway selectivity established, single lab\",\n      \"pmids\": [\"34483834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Trafficking-defective P290S PROKR2 mutant cycles between the ER and Golgi rather than reaching the cell surface; both WT and P290S mutant undergo ER-associated degradation, but the mutant is degraded to greater extent; the post-ER cycling of the mutant to the Golgi reduces ER stress; distinct interactomes were identified for WT versus P290S PROKR2.\",\n      \"method\": \"Interactome analysis (MS), ER-associated degradation assays, ER-to-Golgi trafficking assays, ER stress measurements, pharmacological perturbations\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (interactomics, degradation assays, trafficking assays, ER stress measurements) in a single rigorous study establishing post-ER quality control mechanism\",\n      \"pmids\": [\"35173048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A heterozygous frameshift PROKR2 mutation generating a truncated receptor lacking two transmembrane domains and the C-terminal tail has no intrinsic signaling activity in vitro, but cells co-expressing this mutant with wild-type PROKR2 show markedly exaggerated ligand-induced Ca2+ responses, establishing a paradoxical gain-of-function mechanism via enhancement of wild-type receptor activity.\",\n      \"method\": \"Frameshift mutation identification, in vitro signaling assays (Ca2+ response) in cells transfected with mutant alone or co-transfected with wild-type PROKR2\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-transfection experiment demonstrating gain-of-function mechanism, single lab, novel mechanism validated functionally\",\n      \"pmids\": [\"28338294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In vitro co-transfection of mutant with wild-type PROKR2 (modeling heterozygosity) identified 15/34 IGD-associated variants as loss-of-function including 3 novel dominant negatives, while only 4/25 control variants were LoF; variants LoF in ≥2 signaling assays under co-transfection conditions were more likely disease-associated, revealing dominant-negative and dominant mechanisms not detected by mutant-alone assays.\",\n      \"method\": \"Co-transfection assays modeling heterozygosity, three parallel signaling pathway assays, comparison of 59 variants\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic in vitro functional assays across three pathways with co-transfection modeling; single lab but large variant series\",\n      \"pmids\": [\"29161432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"C. trachomatis infection increases PROKR2 mRNA in fallopian tube epithelial cells via TLR2 ligation and NFκB activation; transfection with dominant-negative TLR2 or IκBα abrogated the C. trachomatis-induced PROKR2 upregulation, placing PROKR2 downstream of TLR2/NFκB in this inflammatory signaling cascade.\",\n      \"method\": \"C. trachomatis infection of fallopian tube explants and OE-E6/E7 cell line, dominant-negative TLR2 and IκBα transfection, mRNA quantification\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dominant-negative constructs establish epistatic pathway position, two orthogonal interventions, single lab\",\n      \"pmids\": [\"21224062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EG-VEGF activates ERK1/2 signaling and upregulates MMP-2 and MMP-9 in HTR-8/SVneo trophoblast cells, promoting cell migration and invasion; anti-PROKR2 antibody (but not anti-PROKR1) suppresses ERK1/2 activation and inhibits EG-VEGF-stimulated migration and invasion, establishing PROKR2 as the receptor mediating EG-VEGF-induced trophoblast invasion via ERK1/2/MMP pathway.\",\n      \"method\": \"Antibody blocking of PROKR2 and PROKR1 in HTR-8/SVneo cells, ERK1/2 phosphorylation assay, MMP-2/9 qRT-PCR and western blot, wound-healing and invasion assays\",\n      \"journal\": \"Acta medica Okayama\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody-mediated receptor blockade with multiple functional readouts (signaling + invasion), single lab\",\n      \"pmids\": [\"34955534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Pkr2-null mice show reduced nociceptive sensitization to heat (46-48°C), capsaicin, and protons (TRPV1 agonists), and reduced response to cold and mustard oil (TRPA1 agonists); DRG culture analysis shows the percentage of Bv8-responsive neurons also responsive to mustard oil is much higher in PKR1-/- than PKR2-/- mice, establishing functional interactions between PKR2 and both TRPV1 and TRPA1 in nociception.\",\n      \"method\": \"Pkr2-/- mouse behavioral nociception assays, DRG primary neuron culture, capsaicin/proton/mustard oil/cold stimulation, comparison with PKR1-/- mice\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with multiple nociceptive paradigms, comparison with paralog KO provides specificity evidence, single lab\",\n      \"pmids\": [\"31883821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TRPV1 physically interacts with PKR2; in the presence of snapin, the strength of the TRPV1-PKR2 interaction is increased; TRPV1 modulates PKR2 activation, subcellular localization, and β-arrestin-2 recruitment, and regulates PK2-induced mechanical allodynia in vivo.\",\n      \"method\": \"Co-immunoprecipitation/interaction mapping, snapin co-expression experiments, PKR2 localization and signaling assays, in vivo allodynia assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct physical interaction mapped with functional consequences on signaling and in vivo behavior, multiple readouts, single lab\",\n      \"pmids\": [\"40139621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Blockage of Gαq signaling, but not the MAPK/ERK pathway, inhibits PROK2-induced migration of PROKR2-expressing cells, establishing that Gαq is the primary downstream effector of PROKR2 mediating GnRH neuron migration-related signaling relevant to IHH pathogenesis.\",\n      \"method\": \"Pathway-specific pharmacological inhibition combined with cell migration assay in PROKR2-expressing cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct pathway inhibition with migration readout in a defined cellular system, single lab\",\n      \"pmids\": [\"36694982\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PROKR2 is a G protein-coupled receptor that binds prokineticin 2 (PROK2) and signals through multiple G protein subtypes (Gq, Gs, Gi/o) as well as β-arrestins; it is essential for GnRH neuron migration to the hypothalamus and olfactory bulb morphogenesis (established by knockout mice), mediates circadian behavioral output from the SCN without being required for the oscillator itself, drives neuronal progenitor migration in the rostral migratory stream via Gαq-dependent signaling, and undergoes GRK2/clathrin-dependent internalization regulated by interacting partners including snapin (which stabilizes the receptor) and TRPV1 (which modulates its activation and β-arrestin recruitment); disease-causing missense mutations impair receptor function through distinct mechanisms—defective trafficking to the plasma membrane, loss of ligand binding, or selective disruption of coupling to specific Gα proteins—sometimes producing biased signaling rather than complete loss of function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PROKR2 is a G protein-coupled receptor for prokineticin 2 (PROK2) that is essential for the migration and positioning of GnRH neurons and olfactory bulb interneurons, linking it directly to reproductive and olfactory development [#0, #2, #13]. Knockout mice lack hypothalamic GnRH neurons, show olfactory bulb hypoplasia, and lose roughly three-quarters of OB GABAergic interneurons because postmitotic immature neuroblasts fail to migrate from the SVZ-RMS toward PROK2 [#0, #2, #13]; this migratory function is driven principally by Gαq signaling rather than the MAPK/ERK arm [#22]. Beyond development, PROKR2 transduces SCN circadian output to behavior without being required for the cellular oscillator itself [#1] and contributes to nociceptive sensitization through functional coupling to TRPV1 and TRPA1 channels [#20]. Mechanistically, wild-type PROKR2 activates Gq, Gs, and Gi/o and recruits β-arrestins, and disease-associated missense mutations partition into distinct functional defects—impaired plasma-membrane trafficking, loss of ligand binding, or selective uncoupling from individual Gα proteins—frequently producing biased signaling rather than complete loss of function [#3, #5, #10]. Intracellular determinants of these behaviors have been mapped: a positively charged residue in IL2 (R164) is required for coupling to Gαq, Gαi, and Gα16 [#4], and distinct motifs of IL3 separately govern surface trafficking versus G-protein coupling [#9]. Receptor surface delivery additionally depends on N-linked glycosylation at N27 and is negatively regulated by MRAP2, while the trafficking-defective P290S mutant cycles between ER and Golgi and undergoes enhanced ER-associated degradation [#14, #15]. PROKR2 internalizes via a GRK2- and clathrin-dependent, β-arrestin-independent route, and its stability and trafficking are modulated by the binding partner snapin and by TRPV1 [#6, #8, #21]. Some disease alleles act dominantly, including a truncated receptor that paradoxically enhances wild-type receptor activity and additional dominant-negative variants revealed only under co-expression with wild-type receptor [#16, #17].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established the developmental requirement for PROKR2 by showing its loss eliminates hypothalamic GnRH neurons and disrupts olfactory bulb formation, defining the receptor's physiological role.\",\n      \"evidence\": \"Targeted knockout mice with IHC, hormone assays, and mRNA quantification\",\n      \"pmids\": [\"16537498\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which downstream G-protein pathway mediates the developmental defect\", \"Did not distinguish cell-autonomous migration from survival effects\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Separated PROKR2's role in circadian behavioral output from the timekeeping oscillator, showing it conveys SCN signals to behavior without being required for the clock.\",\n      \"evidence\": \"Null mice with locomotor/temperature monitoring and ex vivo SCN bioluminescence imaging\",\n      \"pmids\": [\"17202262\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the target neurons receiving the PROKR2-dependent output signal\", \"Mechanism of output coupling unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined PROKR2 as a chemoattractant receptor for neuronal progenitor migration into the olfactory bulb, showing Prokr2-deficient cells fail to migrate toward PROK2.\",\n      \"evidence\": \"Null mouse histology with BrdU/TUNEL and in vitro neurosphere migration assays\",\n      \"pmids\": [\"18052978\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the intracellular signaling effector for migration\", \"Did not separate proliferation from migration contributions to OB volume\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"First systematic functional triage of KS-associated mutations, showing missense variants impair the receptor through three distinct mechanisms—trafficking, ligand binding, or coupling—without dominant-negative effects.\",\n      \"evidence\": \"Site-directed mutagenesis of ten mutations with calcium, surface-expression, and co-expression assays in HEK-293 cells\",\n      \"pmids\": [\"18826963\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tested only Gq/calcium signaling, missing pathway-selective defects\", \"Did not assess heterozygous co-expression beyond dominant-negative screening for this readout\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a peripheral, paracrine action of PROKR2 in the heart, where cardiomyocyte overexpression causes hypertrophy and vascular leakage via ZO-1 mislocalization.\",\n      \"evidence\": \"Transgenic mice with echocardiography, ZO-1 immunofluorescence, and endothelial conditioned-media experiments\",\n      \"pmids\": [\"18806277\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression model may not reflect endogenous receptor levels\", \"Paracrine mediator linking PKR2 signaling to ZO-1 not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Pinpointed an IL2 residue (R164) as a charge-dependent determinant of G-protein coupling, resolving how a disease mutation abolishes signaling without trafficking or ligand-binding defects.\",\n      \"evidence\": \"Charge-substitution mutagenesis with direct Gα binding and endocytosis assays\",\n      \"pmids\": [\"21454486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the IL2-Gα interaction not determined\", \"Did not address β-arrestin coupling at this residue\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Mapped IL3 as a bifunctional segment in which separate motifs independently govern trafficking versus G-protein coupling.\",\n      \"evidence\": \"Deletion and substitution mutagenesis with surface-expression and signaling assays\",\n      \"pmids\": [\"23969157\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; structural mechanism of the RKR/RRK switch unresolved\", \"Did not connect IL3 motifs to specific Gα subtypes\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated that single disease alleles can differentially impair Gq versus Gs cascades, refining mutation interpretation beyond binary loss-of-function.\",\n      \"evidence\": \"Parallel IP/Ca2+ and cAMP assays across multiple variants in HEK-293 cells\",\n      \"pmids\": [\"24276467\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; did not test β-arrestin recruitment\", \"Functional consequences in neurons not assessed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established PROKR2 as a multi-G-protein receptor exhibiting mutation-induced biased agonism, with distinct alleles selectively losing Gq, β-arrestin, or Gi/o coupling.\",\n      \"evidence\": \"Parallel Gq/Gs/Gi/o and β-arrestin recruitment assays with systematic mutagenesis\",\n      \"pmids\": [\"24830383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological readout of each biased profile not established in vivo\", \"Structural basis of biased coupling unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the internalization route and an ERK-activation mechanism, showing endocytosis is GRK2/clathrin-dependent but β-arrestin-independent while ERK requires Gβγ and PLC-β/MEK.\",\n      \"evidence\": \"Dominant-negative constructs, siRNA, inhibitors, and ERK/endocytosis assays in transfected cells\",\n      \"pmids\": [\"24509228\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single lab; in vivo relevance of these routes not tested\", \"Adaptor linking GRK2 to clathrin not identified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided proof-of-concept for pharmacological rescue of trafficking-defective mutants, with mutant-specific responsiveness to a small-molecule pharmacochaperone versus a chemical chaperone.\",\n      \"evidence\": \"Rescue with antagonist A457 and glycerol, surface-expression and signaling readouts\",\n      \"pmids\": [\"24753254\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; rescue not demonstrated in vivo\", \"Mechanism of mutant-selective rescue not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified snapin as a C-terminal binding partner that regulates receptor stability rather than signaling, expanding the trafficking-control machinery.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, Co-IP, and motif-mapping mutagenesis\",\n      \"pmids\": [\"26687946\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; physiological role of snapin in PROKR2 function not tested in vivo\", \"How snapin slows ligand-induced degradation mechanistically unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Uncovered a paradoxical gain-of-function mechanism in which a signaling-dead truncated receptor enhances wild-type receptor activity, challenging simple loss-of-function interpretation.\",\n      \"evidence\": \"Co-transfection of frameshift mutant with wild-type PROKR2 and Ca2+ signaling assays\",\n      \"pmids\": [\"28338294\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; molecular basis of WT enhancement not defined\", \"In vivo phenotype of the gain-of-function allele not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed that co-expression assays modeling heterozygosity reveal dominant-negative and dominant alleles missed by mutant-alone testing, improving variant pathogenicity classification.\",\n      \"evidence\": \"Co-transfection of 59 variants across three signaling pathways\",\n      \"pmids\": [\"29161432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; in vitro classification not validated against clinical penetrance\", \"Structural basis of dominant-negative interference not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated biochemically that selective disruption of IL3-Gαq binding underlies biased signaling, with R270H losing Gαq but retaining Gαs/ERK.\",\n      \"evidence\": \"GST pull-down with Gαq and Gαs plus pathway-specific signaling assays\",\n      \"pmids\": [\"30576231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural model of the IL3-Gαq interface not determined\", \"In vivo consequence of selective Gαq loss not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established the cell-type identity and migratory requirement of PROKR2 in OB interneurons, localizing expression to postmitotic neuroblasts and quantifying interneuron loss upon disruption.\",\n      \"evidence\": \"Prokr2-LacZ knockin and Prok2-EGFP transgenic mice with lineage analysis, ISH, and cell counting\",\n      \"pmids\": [\"31132148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the intracellular signaling pathway for tangential vs radial migration\", \"Source and gradient of PROK2 guiding migration not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified glycosylation as a trafficking and pathway-selectivity determinant, with N27 required for surface delivery and N7 selectively tuning Gαs signaling, and MRAP2 as a negative trafficking regulator.\",\n      \"evidence\": \"Glycosylation-site mutagenesis with surface-expression and Gαs/Gαq signaling assays\",\n      \"pmids\": [\"34483834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; MRAP2 regulation not validated in neurons in vivo\", \"Mechanism by which N7 glycan biases Gαs unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined PROKR2 as the receptor mediating EG-VEGF-induced trophoblast invasion via ERK1/2 and MMP-2/9 upregulation, extending its role to placentation.\",\n      \"evidence\": \"Antibody blockade of PROKR2 vs PROKR1 in HTR-8/SVneo cells with signaling and invasion assays\",\n      \"pmids\": [\"34955534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; in vivo placental requirement not tested\", \"Did not establish G-protein link to the ERK/MMP cascade in this context\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the post-ER quality-control fate of a trafficking-defective mutant, showing P290S cycles between ER and Golgi, undergoes enhanced ERAD, and assembles a distinct interactome.\",\n      \"evidence\": \"Mass-spec interactomics, ERAD and ER-to-Golgi trafficking assays, and ER stress measurements\",\n      \"pmids\": [\"35173048\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific chaperones controlling the ER-Golgi cycle not pinpointed functionally\", \"Whether other trafficking mutants share this fate not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified Gαq as the primary effector for PROKR2-driven cell migration, mechanistically linking the migration phenotype to a specific signaling arm relevant to IHH.\",\n      \"evidence\": \"Pathway-specific pharmacological inhibition with migration assays in PROKR2-expressing cells\",\n      \"pmids\": [\"36694982\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; not validated in primary GnRH neurons\", \"Downstream cytoskeletal effectors of Gαq not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established a physical and functional TRPV1-PROKR2 interaction, strengthened by snapin, that modulates receptor activation, localization, β-arrestin recruitment, and pain behavior, integrating PROKR2 into nociceptive channel signaling.\",\n      \"evidence\": \"Co-IP/interaction mapping, snapin co-expression, signaling/localization assays, and in vivo allodynia assay\",\n      \"pmids\": [\"40139621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; structural basis of the TRPV1-PROKR2 interface not determined\", \"Whether the interaction occurs in defined sensory neuron subtypes in vivo not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PROKR2's diverse signaling outputs (Gq, Gs, Gi/o, β-arrestin) are selected and spatially organized in vivo to produce its distinct developmental, circadian, and nociceptive functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of PROKR2 or its Gα/effector complexes\", \"Tissue-specific determinants of biased signaling not mapped\", \"Endogenous regulation by MRAP2, snapin, and TRPV1 not validated in native cells in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [3, 5, 10]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [16, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 9, 14]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 6, 10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 2, 13]},\n      {\"term_id\": \"R-HSA-9909396\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PROK2\", \"GNAQ\", \"GRK2\", \"SNAPIN\", \"TRPV1\", \"MRAP2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}