{"gene":"GPRC5A","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2007,"finding":"Gprc5a functions as a lung tumor suppressor: Gprc5a knockout mice developed lung adenomas (76%) and adenocarcinomas (17%) compared to ~10% adenomas in wild-type mice; ectopic GPRC5A expression in human embryonic kidney, NSCLC, and mouse lung adenocarcinoma cells suppressed colony formation in semisolid medium by 68–91%.","method":"Homologous recombination knockout mouse model; colony formation assay with GPRC5A transfection","journal":"Journal of the National Cancer Institute","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined tumor phenotype replicated across multiple cell lines with functional rescue","pmids":["18000218"],"is_preprint":false},{"year":2010,"finding":"Gprc5a loss in mouse lung epithelial cells causes persistent STAT3 tyrosine-705 phosphorylation driven by autocrine leukemia inhibitory factor (LIF) secretion. Gprc5a(-/-) cells showed reduced levels of the endogenous STAT3 inhibitor Socs3 compared to wild-type cells; re-expression of Gprc5a in knockout cells stabilized Socs3. Inhibition of JAK2 or dominant-negative STAT3(Y705F) increased apoptosis and reduced colony formation in knockout cells.","method":"Western blot (STAT3 phosphorylation, Socs3), dominant-negative STAT3 transfection, JAK2 inhibitor (AG490), colony formation assay, re-expression of Gprc5a in knockout cells","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal genetic experiments (KO + rescue) with pharmacological inhibition, multiple orthogonal methods in single lab","pmids":["20959490"],"is_preprint":false},{"year":2010,"finding":"Gprc5a loss in lung airway epithelial cells enhances constitutive and stimulus-induced NF-κB activation, leading to increased pro-inflammatory cytokine/chemokine production that promotes macrophage infiltration and a tumor-promoting microenvironment. Re-expression of Gprc5a in knockout adenocarcinoma cells partially reversed the elevated NF-κB activation.","method":"NF-κB reporter assays, cytokine measurement, p65 siRNA knockdown and Gprc5a siRNA knockdown in paired wild-type and knockout tracheal epithelial cells, macrophage migration assay","journal":"Cancer prevention research (Philadelphia, Pa.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic KO + rescue with multiple orthogonal functional readouts (reporter, cytokine, migration), single lab","pmids":["20354164"],"is_preprint":false},{"year":2015,"finding":"GPRC5A physically interacts with EGFR through its transmembrane domain and negatively modulates EGFR and downstream STAT3 signaling. The transmembrane domain was required for EGFR inhibitory activity as shown by domain-deletion analysis. Mouse tracheal epithelial cells from Gprc5a(-/-) mice showed elevated EGFR/STAT3 signaling reversed by GPRC5A re-expression.","method":"Co-immunoprecipitation, domain-deletion mutagenesis, EGFR/STAT3 signaling assays in Gprc5a(-/-) MTEC vs. wild-type, ectopic GPRC5A expression in NSCLC cells","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct Co-IP of GPRC5A–EGFR interaction with domain mutagenesis, validated in genetic KO model and human cancer cells","pmids":["25744720"],"is_preprint":false},{"year":2014,"finding":"EGFR phosphorylates GPRC5A at two conserved double-tyrosine motifs (Y317/Y320 and Y347/Y350) in the C-terminal tail. EGF-induced phosphorylation disrupts GPRC5A-mediated suppression of anchorage-independent growth. The phosphorylation-resistant mutant GPRC5A-4F maintained tumor suppressive activity. GPRC5A was non-phosphorylated in normal lung tissue but highly tyrosine-phosphorylated in NSCLC tissues.","method":"IP-Western blot, site-directed mutagenesis (Y317/320/347/350F), EGF stimulation assays, anchorage-independent growth assay, IHC with phospho-specific antibodies on human tumor tissue","journal":"Molecular cancer","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase substrate identification with site-directed mutagenesis, functional validation, and IHC on human tissue; single lab but multiple orthogonal methods","pmids":["25311788"],"is_preprint":false},{"year":2016,"finding":"GPRC5A localizes to the endoplasmic reticulum membrane and suppresses protein synthesis of secreted/membrane-bound proteins (including EGFR) by directly binding the eIF4F translation initiation complex through its two middle extracellular loops, thereby disturbing assembly of the eIF4F complex on the mRNA cap.","method":"Subcellular fractionation/ER localization, co-immunoprecipitation of GPRC5A with eIF4F components, domain-deletion analysis (extracellular loops), measurement of EGFR translation rate, in vivo ionizing radiation lung tumorigenesis model in Gprc5a(-/-) mice","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct protein interaction with domain mapping, translational assay, and in vivo genetic validation; single lab with multiple orthogonal methods","pmids":["27273304"],"is_preprint":false},{"year":2009,"finding":"Retinoic acid induces GPRC5A transcription through a functional retinoic acid response element DR5III (5'-TGT CCC TCT GCT CAC CC-3') at -64 bp upstream of the transcription start site. RAR-alpha/gamma and RXR-alpha/beta bind this element in intact cells. DR5I and DR5II are non-functional for GPRC5A induction.","method":"Electrophoretic mobility shift assay (EMSA) with wild-type and mutated oligonucleotides; chromatin immunoprecipitation (ChIP); promoter truncation/deletion analysis","journal":"Cancer biology & therapy","confidence":"High","confidence_rationale":"Tier 1 / Moderate — EMSA with competitor oligos plus ChIP in intact cells, multiple promoter truncations; single lab but multiple orthogonal methods","pmids":["19279407"],"is_preprint":false},{"year":2004,"finding":"The Rai3/Gprc5a promoter contains functional GC boxes and Sp1-, AP1-, AP2-binding sites, and a functional retinoic acid response element (direct repeat with 5-bp spacer at -64 bp) that mediates retinoic acid induction, identified by promoter truncation, EMSA, and mutation analysis.","method":"Promoter truncation analysis, EMSA, site-directed mutation analysis","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple promoter deletion constructs plus EMSA with mutated binding sites; single lab, multiple orthogonal methods","pmids":["14706456"],"is_preprint":false},{"year":2018,"finding":"GPRC5A modulates integrin β1 (ITGB1)-mediated cell adhesion to extracellular matrix substrates. CRISPR/Cas9 knockout of GPRC5A reduced ITGB1 protein expression, impaired FAK phosphorylation, and lowered RhoA and Rac1 GTPase activity. GPRC5A also directly interacts with the receptor tyrosine kinase EphA2.","method":"CRISPR/Cas9 knockout, RNAi knockdown, cell adhesion assays to ECM substrates, Western blot (ITGB1, pFAK), small GTPase activity assays, co-immunoprecipitation (GPRC5A–EphA2)","journal":"Cell adhesion & migration","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — CRISPR KO + RNAi with multiple downstream readouts; EphA2 interaction by single Co-IP; single lab","pmids":["27715394"],"is_preprint":false},{"year":2018,"finding":"GPRC5A deficiency leads to dysregulated MDM2 stabilization via activated EGFR signaling (independent of transcription), resulting in p53 pathway suppression and promotion of lung tumor development. Targeting MDM2 with Nutlin-3a or shRNA in Gprc5a-ko-derived cells restored p53 signaling and reduced tumorigenicity.","method":"Gprc5a knockout mouse-derived tumor cell lines, MDM2 inhibitor (Nutlin-3a) and shRNA, EGFR inhibitor (Erlotinib) and shRNA, Western blot, colony formation, IHC of human lung cancer tissues","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic epistasis in genetic KO-derived cell model; mechanism of MDM2 stabilization by EGFR established by dual inhibitor experiments; single lab","pmids":["29992578"],"is_preprint":false},{"year":2018,"finding":"In cancer cell adaptation to hypoxia, HIFs directly activate GPRC5A transcription, and GPRC5A in turn activates the Hippo pathway effector YAP and its anti-apoptotic target BCL2L1. The apoptosis induced by GPRC5A depletion under hypoxia was rescued by constitutively active YAP, placing GPRC5A between HIF and YAP in a survival axis.","method":"SILAC-based proteomics (hypoxia induction), genetic knockdown/knockout in vitro and in vivo, HIF ChIP-seq/reporter analysis, constitutively active YAP rescue, YAP target gene measurement","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — proteomics identification, direct HIF-GPRC5A transcription evidence, epistasis rescue with constitutively active YAP, in vivo validation; single lab with multiple orthogonal approaches","pmids":["30143543"],"is_preprint":false},{"year":2020,"finding":"PTGES/PGE2 signaling in Gprc5a-ko mouse lung tumors promotes metastasis primarily through immunosuppression: tumor cell-intrinsic PGE2 confers resistance to T-cell cytotoxicity and induces cytokines for MDSC recruitment, suppressing T-cell immunity. PTGES inhibitor suppressed MDSC recruitment, restored T cells, and significantly repressed lung metastasis.","method":"Ptges knockout in tumor cells, immune-competent vs. nude mouse transplantation epistasis, cytokine measurement, MDSC/T-cell flow cytometry, PTGES inhibitor treatment in Gprc5a-ko mice","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (double KO) with immune-competent vs. immune-deficient host comparison; pharmacological validation; single lab","pmids":["32060421"],"is_preprint":false},{"year":2015,"finding":"Gprc5a deficiency in mice confers susceptibility to LPS-induced acute lung injury through enhanced NF-κB signaling specifically in bronchioalveolar epithelium. Expression of a super-repressor IκBα specifically in Gprc5a-ko bronchioalveolar epithelium alleviated LPS-induced pulmonary injury and inflammatory response.","method":"LPS-induced ALI model in Gprc5a-ko and wild-type mice, cytokine/chemokine measurement, pulmonary edema assessment, epithelium-specific IκBα super-repressor transgene rescue","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with pathway-specific rescue transgene, multiple phenotypic readouts; single lab","pmids":["25714996"],"is_preprint":false},{"year":2023,"finding":"NF-κB (specifically RelA/p65, phosphorylated on serine 276) represses GPRC5A transcription by forming a complex with retinoic acid receptor α/β (RARα/β) and being recruited to the RA response element at the GPRC5A promoter, disrupting RNA Pol II binding. This epigenetic repression involves suppression of acetylated histone H3K9 (H3K9ac) but not DNA methylation of CpG islands. HDAC inhibitor but not DNA methylation inhibitor restored GPRC5A expression.","method":"ChIP assay (p65, RAR, RNA Pol II, H3K9ac), Co-IP (p65–RARα/β), site-directed mutagenesis (p65 S276), HDAC inhibitor and DNA methylation inhibitor treatment, in vivo NF-κB activation model","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — ChIP + Co-IP + phospho-mutant epistasis + pharmacological rescue; multiple orthogonal methods; single lab","pmids":["36413416"],"is_preprint":false},{"year":2005,"finding":"p53 interacts with the RAI3/GPRC5A promoter and represses its expression at the onset of apoptosis. RAI3 mRNA is elevated in tumor cell lines expressing mutant p53 and relatively repressed in lines with wild-type p53. Ectopic RAI3 expression in 293 cells promotes anchorage-independent growth, and siRNA depletion of RAI3 in AsPc-1 pancreatic cells induces morphological change.","method":"Chromatin immunoprecipitation (ChIP) of p53 at RAI3 promoter, gene expression profiling, siRNA knockdown, anchorage-independent growth assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — ChIP evidence for p53 binding plus expression correlation and functional gain/loss-of-function; single lab","pmids":["15659406"],"is_preprint":false},{"year":2020,"finding":"Chemoproteomics identified aromatic monoamines (microbiota-derived indole metabolites) as ligands that bind the orphan receptor GPRC5A and stimulate β-arrestin recruitment. 7-fluorotryptamine was identified as a more potent synthetic agonist. Specific amino acid decarboxylase-expressing microbiota species produce these agonists.","method":"Photoaffinity chemical reporters/chemoproteomics, β-arrestin recruitment assay, metabolomic profiling, synthetic monoamine derivative screening","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct ligand identification by chemoproteomics with functional β-arrestin assay validation and structure-activity relationship; multiple orthogonal methods","pmids":["37248411"],"is_preprint":false},{"year":2020,"finding":"Chemotherapy (cisplatin/carboplatin) in ovarian cancer triggers an ERK1/2–RSK1/2–EphA2(S897)–GPRC5A signaling axis associated with chemoresistance. Pharmacological inhibition or knockdown of RSK1/2 prevented oncogenic EphA2-S897 phosphorylation and EphA2–GPRC5A co-regulation, shifting signaling to canonical tumor-suppressive EphA2 tyrosine phosphorylation and EphA2 downregulation.","method":"RSK1/2 pharmacological inhibition and knockdown, EphA2-S897 phosphorylation assays, Co-immunoprecipitation (EphA2–GPRC5A), patient tumor samples, apoptosis assays","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP interaction, pharmacological and genetic RSK inhibition with downstream phosphorylation readouts, patient material validation; single lab","pmids":["32115889"],"is_preprint":false},{"year":2014,"finding":"miR-103a-3p targets two sites in the 5' UTR of GPRC5A mRNA (not the 3' UTR) in a seed-dependent manner, reducing GPRC5A mRNA and protein levels in normal epithelial and pancreatic cancer cell lines. Ectopic sponges containing the wild-type 5' UTR targets reduced miR-103a-3p levels and increased GPRC5A mRNA and protein.","method":"miRNA target site validation (luciferase or expression reporter with mutated 5' UTR sites), sponge experiments, qRT-PCR and Western blot in multiple cell lines","journal":"RNA (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional 5' UTR target site validation with mutation and sponge rescue; single lab, multiple cell lines","pmids":["24984703"],"is_preprint":false},{"year":2016,"finding":"HuR (RNA-binding protein) binds GPRC5A mRNA at an AU-rich binding site and stabilizes it following gemcitabine treatment, causing a monotonic increase in GPRC5A protein levels. GPRC5A knockdown sensitized pancreatic cancer cells to gemcitabine.","method":"RNA immunoprecipitation/RIP identifying HuR–GPRC5A mRNA interaction, Western blot time-course after gemcitabine, GPRC5A knockdown + gemcitabine combination assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — RIP demonstrating direct mRNA-protein interaction, functional sensitization assay; single lab","pmids":["27415424"],"is_preprint":false},{"year":2018,"finding":"GPRC5A knockout in pancreatic cancer cells increased phosphorylation of GSK-3β (Ser9), reduced cell proliferation and migration, and suppressed resistance to gemcitabine, oxaliplatin, and fluorouracil.","method":"CRISPR/Cas9 knockout in MIA PaCa-2 and TB32047 cells, proliferation and migration assays, drug resistance assays, Western blot for pGSK-3β","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — CRISPR KO with defined phenotypes and pGSK-3β readout; single lab, single method per finding","pmids":["29949874"],"is_preprint":false},{"year":2024,"finding":"GPRC5A interacts with LAMTOR1, inhibiting its ubiquitination-dependent degradation, thereby recruiting mTORC1 to lysosomes and activating the mTORC1/p70S6K signaling pathway. GPRC5A mRNA is post-transcriptionally regulated by m6A methylation via the METTL3/YTHDF1 axis.","method":"Mass spectrometry, Co-IP, immunofluorescence colocalization (GPRC5A–LAMTOR1), MeRIP (m6A sequencing), dual-luciferase reporter, knockdown/overexpression in TNBC cells and in vivo models","journal":"Drug resistance updates","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS identification of interaction followed by Co-IP and localization; m6A regulation validated by MeRIP and reporter; single lab","pmids":["38335844"],"is_preprint":false},{"year":2024,"finding":"GPRC5A promotes gallbladder cancer metastasis by activating JAK2-STAT3 signaling, which induces expression of TNS4 by STAT3 binding to the TNS4 promoter. ChIP confirmed STAT3 binding at the TNS4 promoter.","method":"GPRC5A knockdown in GBC cells (in vitro and in vivo), RNA-seq, Western blot, ChIP (STAT3 at TNS4 promoter), immunohistochemistry","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KD with downstream ChIP validation of transcriptional mechanism; single lab","pmids":["38942137"],"is_preprint":false},{"year":2024,"finding":"GPRC5A directly binds ABCB1 (P-glycoprotein) and reduces its expression. Gprc5a-deficient mouse tracheal epithelial cells and lung tissues showed higher ABCB1 expression, and Gprc5a-ko cells were more sensitive to tariquidar (ABCB1 inhibitor) and doxorubicin. ABCB1 knockout in Gprc5a-/- tumor cells reduced tumor growth in vivo.","method":"Immunofluorescence colocalization, co-immunoprecipitation (GPRC5A–ABCB1), Western blot, RT-PCR, Gprc5a-ko mouse tissues, cell sensitivity assays, xenograft tumor model","journal":"Chinese medical sciences journal","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP + colocalization supporting direct interaction; genetic KO in vivo validation; single lab","pmids":["38426412"],"is_preprint":false},{"year":2023,"finding":"GPRC5A promotes pancreatic cancer cell proliferation and migration by positively regulating YAP1 transcription through the cAMP–CREB signaling axis. The pro-proliferative and migratory effects of GPRC5A were rescued by YAP1 inhibition.","method":"GPRC5A knockdown/overexpression in pancreatic cancer cells, cAMP measurement, CREB reporter assay, YAP1 rescue experiment, cytosolic/nuclear distribution assay, xenograft model","journal":"Discover oncology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — cAMP-CREB-YAP1 pathway epistasis with rescue; single lab","pmids":["36735162"],"is_preprint":false},{"year":2024,"finding":"GPRC5A potentially interacts with WWP1 E3 ubiquitin ligase, facilitating polyubiquitination and degradation of LATS1, thereby activating YAP1 signaling and promoting lung metastasis in esophageal squamous cell carcinoma. Targeting YAP1 with CA3 or TED-347 diminished early implantation and macro-metastases.","method":"Single-cell RNA sequencing, Co-immunoprecipitation (GPRC5A–WWP1), ubiquitination assay (LATS1), YAP1 inhibitor rescue, in vivo metastasis model, patient cohort (n=148)","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP + ubiquitination assay + pharmacological rescue; in vivo validation; single lab","pmids":["39550386"],"is_preprint":false},{"year":2017,"finding":"GPRC5A overexpression suppressed IL-6-induced STAT3 activation and inhibited anchorage-independent growth in head and neck squamous cell carcinoma cells, placing GPRC5A as a negative regulator of STAT3 in this context.","method":"Stable GPRC5A transfection in HNSCC cells, IL-6 stimulation, Western blot (pSTAT3), anchorage-independent growth assay, IHC of clinical HNSCC samples","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — gain-of-function with defined signaling readout in multiple HNSCC lines plus clinical IHC; single lab","pmids":["28270740"],"is_preprint":false},{"year":2017,"finding":"RAI3/GPRC5A knockdown in human adipose-derived stem cells promoted adipogenic differentiation by decreasing β-catenin levels. Activation of the β-catenin pathway by lithium chloride abolished the effect of RAI3 knockdown on adipogenesis.","method":"siRNA knockdown of RAI3 in hASCs, adipogenic differentiation assays (in vitro and in vivo xenograft), Western blot (β-catenin), lithium chloride (Wnt/β-catenin activator) rescue experiment","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single knockdown experiment with pharmacological pathway rescue; single lab, single study","pmids":["28870805"],"is_preprint":false},{"year":2020,"finding":"RAI3/GPRC5A knockdown in bone marrow mesenchymal stem cells promoted osteogenic differentiation by upregulating phosphorylated STAT3. The JAK2 inhibitor AG-490 reversed the enhancing effect of RAI3 knockdown on osteogenesis.","method":"siRNA knockdown, osteogenic differentiation assays (in vitro and in vivo), Western blot (pSTAT3), pharmacological JAK2 inhibitor AG-490 rescue","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — knockdown with pharmacological rescue; single lab, single study","pmids":["32014253"],"is_preprint":false},{"year":2024,"finding":"Gprc5a is a PTH-inducible gene: PTH treatment induces Gprc5a expression in osteoblast-like cells and mouse femurs via the cAMP pathway (cAMP response element in promoter), independent of new protein synthesis. Gprc5a negatively regulates osteoblast proliferation and differentiation by interacting with BMPR1A and suppressing BMP-2 signaling.","method":"PTH stimulation in MC3T3-E1, ROS17/2.8, and mouse femurs; cycloheximide (protein synthesis inhibition); cAMP pathway inhibitors; reporter analysis of GPRC5A promoter; Gprc5a knockdown (MTT, BrdU, mineralization assay); Co-immunoprecipitation (Gprc5a–BMPR1A); constitutively active BMP receptor constructs","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cAMP pathway epistasis + Co-IP interaction + multiple functional assays; single lab","pmids":["38769895"],"is_preprint":false},{"year":2021,"finding":"GPRC5A acts as a negative regulator of the PI3K/Akt signaling pathway in triple-negative breast cancer cells. GPRC5A overexpression promoted apoptosis via the intrinsic pathway, activating caspase-3 and caspase-9, and this was inhibited by a PI3K/Akt activator. GPRC5A knockdown inhibited apoptosis, which was partially restored by a PI3K/Akt inhibitor.","method":"GPRC5A overexpression/knockdown in TNBC cells, RNA-seq pathway analysis, PI3K/Akt activator/inhibitor rescue experiments, caspase activation assays, in vivo tumor growth","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pharmacological epistasis for PI3K/Akt plus gain and loss-of-function with defined apoptosis readouts; single lab","pmids":["33680947"],"is_preprint":false},{"year":2018,"finding":"GPRC5A modulates TGF-β signaling and EGFR activation in cultured podocytes. Gprc5a-deficient mice developed thickening of the glomerular basement membrane, mesangial cell activation, increased albuminuria, and more severe diabetic nephropathy histology after streptozotocin-induced diabetes.","method":"Gprc5a knockout mouse model, streptozotocin-induced diabetes, glomerular histology/EM, albumin measurement, TGF-β and EGFR signaling assays in cultured podocytes","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO model with defined renal phenotype and mechanistic signaling assays in podocytes; single lab","pmids":["29636387"],"is_preprint":false},{"year":2020,"finding":"TPA (phorbol ester) strongly induces GPRC5A mRNA and protein expression at the plasma membrane via a PKC/Ca²⁺→MEK1/2 signaling axis. PKC inhibitor Gö6983, Ca²⁺ chelator BAPTA-AM, and MEK1/2 inhibitor U0126 each suppressed TPA-induced GPRC5A upregulation. PKA inhibitor H-89 also partially reduced induction.","method":"TPA stimulation of T84 cells, pharmacological inhibitors (Gö6983, BAPTA-AM, U0126, H-89, GSK650394), RT-PCR, Western blot, confocal microscopy","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple pharmacological inhibitors delineating signaling pathway for GPRC5A induction; single lab","pmids":["32339486"],"is_preprint":false},{"year":2025,"finding":"Galectin-3 (Gal-3) directly binds glycosylated GPRC5A at the plasma membrane and stimulates GPRC5A internalization/endocytosis in colorectal cancer cells. This interaction is independent of ATRA-induced GPRC5A upregulation.","method":"Proteomic analysis of endogenous Gal-3 immunoprecipitates (interactomic assay), Co-IP, extracellular recombinant Gal-3 stimulation, GPRC5A internalization assay, immunofluorescence in SW480 cells","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2–3 / Weak — Co-IP identification confirmed with functional internalization assay; single lab, limited replication","pmids":["41090797"],"is_preprint":false},{"year":2025,"finding":"GPRC5A interacts with the glycolytic transporter GLUT1, influencing glucose uptake and glycolysis in glioblastoma. Silencing GPRC5A reduced GLUT1 stability and glucose uptake, increasing TMZ sensitivity, and this effect was reversible by GLUT1 overexpression.","method":"Co-immunoprecipitation (GPRC5A–GLUT1), GLUT1 stability assay, glucose uptake measurement, GPRC5A knockdown ± GLUT1 overexpression rescue, TMZ sensitivity assay, in vivo xenograft","journal":"International journal of biological macromolecules","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP interaction, functional rescue; single lab, single study","pmids":["40744179"],"is_preprint":false},{"year":2025,"finding":"In keratinocytes, GPRC5A undergoes proteolytic cleavage by cathepsin G, releasing its C-terminal region which translocates to the nucleus. GPRC5A knockdown enhanced cell adhesion while reducing cell migration and differentiation; these effects were reversed by addition of a recombinant polypeptide mimicking the C-terminal region. GPRC5A expression is re-induced during wound healing at leading edges.","method":"N-TAILS protease cleavage site analysis, cathepsin G identification, shRNA knockdown in N/TERT-1 keratinocytes, cell adhesion/migration/differentiation assays, C-terminal peptide rescue, ex vivo burn wound model","journal":"FASEB journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — N-TAILS cleavage site identification and functional rescue with peptide; single lab, single study, no structural validation","pmids":["39812615"],"is_preprint":false}],"current_model":"GPRC5A is an orphan GPCR preferentially expressed in lung and other epithelial tissues whose transcription is directly induced by retinoic acid through RAR/RXR binding to a DR5 response element in its promoter and repressed by NF-κB (via a p65–RARα/β complex that suppresses H3K9 acetylation); it acts as a lung tumor suppressor by physically interacting with and inhibiting EGFR (through its transmembrane domain), suppressing translation initiation at the ER membrane (by binding the eIF4F complex via its extracellular loops), stabilizing the STAT3 inhibitor Socs3, and restraining NF-κB activation, while EGFR reciprocally inactivates GPRC5A by phosphorylating its C-terminal tyrosines (Y317/Y320 and Y347/Y350); in other tissue contexts GPRC5A acts as an oncogene by promoting mTORC1 lysosomal recruitment (via LAMTOR1 stabilization), activating YAP1 (via the cAMP–CREB or LATS1 ubiquitination axis), and interacting with integrin β1, EphA2, ABCB1, and GLUT1; microbiota-derived aromatic monoamines have been identified as agonists that stimulate GPRC5A-β-arrestin recruitment."},"narrative":{"mechanistic_narrative":"GPRC5A is a retinoic-acid-inducible orphan GPCR of epithelial tissues that functions context-dependently as a lung tumor suppressor and, in other settings, as an oncogenic signaling node [PMID:18000218, PMID:30143543]. Its transcription is directly driven by retinoic acid through a functional DR5 response element at -64 bp bound by RAR/RXR heterodimers [PMID:19279407, PMID:14706456], and is repressed by NF-κB: phospho-S276 RelA/p65 forms a complex with RARα/β at the same response element, suppresses H3K9 acetylation, and displaces RNA Pol II [PMID:36413416]. In normal lung epithelium GPRC5A restrains multiple oncogenic pathways: it physically interacts with EGFR via its transmembrane domain to inhibit EGFR–STAT3 signaling [PMID:25744720], localizes to the ER membrane where it binds the eIF4F complex through its extracellular loops to suppress cap-dependent translation of secreted and membrane proteins including EGFR itself [PMID:27273304], stabilizes the STAT3 inhibitor Socs3 [PMID:20959490], and limits NF-κB-driven inflammation [PMID:20354164, PMID:25714996]. EGFR reciprocally inactivates GPRC5A by phosphorylating C-terminal double-tyrosine motifs (Y317/Y320, Y347/Y350), abolishing its tumor-suppressive activity, and this phosphorylated form predominates in NSCLC [PMID:25311788]. Loss of GPRC5A drives tumorigenesis through EGFR-dependent MDM2 stabilization and p53 suppression [PMID:29992578] and PGE2-mediated immunosuppression [PMID:32060421]. In other tissue and tumor contexts GPRC5A acts oncogenically by activating YAP1 signaling through HIF, cAMP–CREB, or WWP1-mediated LATS1 degradation [PMID:30143543, PMID:36735162, PMID:39550386], by recruiting mTORC1 to lysosomes through LAMTOR1 stabilization [PMID:38335844], and by interacting with integrin β1/EphA2 [PMID:27715394], ABCB1 [PMID:38426412], and GLUT1 [PMID:40744179]. Microbiota-derived aromatic monoamines act as GPRC5A agonists that stimulate β-arrestin recruitment, with 7-fluorotryptamine a more potent synthetic agonist [PMID:37248411].","teleology":[{"year":2004,"claim":"Established the transcriptional control of GPRC5A by mapping its promoter architecture and identifying retinoic acid responsiveness, the founding feature of this gene.","evidence":"Promoter truncation, EMSA, and site-directed mutation analysis identifying GC boxes, Sp1/AP1/AP2 sites, and a DR5 retinoic acid response element","pmids":["14706456"],"confidence":"High","gaps":["Did not establish which RAR/RXR isoforms bind in vivo","No functional consequence of induction defined"]},{"year":2005,"claim":"Asked how GPRC5A intersects with tumor-suppressor circuits and showed p53 directly represses its promoter, with context-dependent growth effects.","evidence":"ChIP of p53 at RAI3 promoter, expression profiling across p53-status lines, siRNA knockdown, and anchorage-independent growth assay","pmids":["15659406"],"confidence":"Medium","gaps":["Pro-growth role conflicts with later tumor-suppressor data","Mechanism of p53-mediated repression not resolved"]},{"year":2007,"claim":"Resolved the central question of GPRC5A's physiological role by demonstrating it is a lung tumor suppressor in vivo.","evidence":"Gprc5a homologous-recombination knockout mice with spontaneous lung tumors plus colony formation rescue across multiple cell lines","pmids":["18000218"],"confidence":"High","gaps":["Molecular mechanism of suppression not yet defined","Did not address signaling pathways downstream"]},{"year":2009,"claim":"Defined the precise cis-element and trans-factors mediating retinoic acid induction, anchoring GPRC5A in retinoid signaling.","evidence":"EMSA with competitor oligos and ChIP showing RAR-α/γ and RXR-α/β binding the functional DR5III element","pmids":["19279407"],"confidence":"High","gaps":["Did not connect transcriptional induction to downstream function"]},{"year":2010,"claim":"Identified the downstream signaling pathways deranged by GPRC5A loss, linking it to STAT3 and NF-κB-driven inflammation.","evidence":"KO + rescue Western blots for STAT3-pY705/Socs3, dominant-negative STAT3, JAK2 inhibition, NF-κB reporter, cytokine, and macrophage migration assays","pmids":["20959490","20354164"],"confidence":"High","gaps":["Whether STAT3 and NF-κB effects are direct or downstream of EGFR not yet resolved","Mechanism of Socs3 stabilization unknown"]},{"year":2014,"claim":"Explained how GPRC5A is functionally silenced in cancer by identifying EGFR-mediated tyrosine phosphorylation as an inactivating switch.","evidence":"IP-Western, site-directed Y-to-F mutagenesis, EGF stimulation, anchorage-independent growth, and phospho-specific IHC on human NSCLC","pmids":["25311788"],"confidence":"High","gaps":["Structural basis of phosphorylation-induced inactivation unknown","Direct vs. indirect EGFR kinase action on GPRC5A not fully resolved"]},{"year":2015,"claim":"Established the direct physical mechanism of EGFR inhibition by GPRC5A through its transmembrane domain.","evidence":"Co-IP, domain-deletion mutagenesis, and EGFR/STAT3 signaling assays in Gprc5a-/- MTEC versus wild-type","pmids":["25744720"],"confidence":"High","gaps":["No structural model of the GPRC5A–EGFR transmembrane interface","Stoichiometry and dynamics of complex unknown"]},{"year":2016,"claim":"Uncovered a non-canonical, receptor-independent function: GPRC5A suppresses cap-dependent translation at the ER by binding eIF4F.","evidence":"ER fractionation, Co-IP with eIF4F components, extracellular-loop deletion mapping, EGFR translation-rate measurement, and in vivo irradiation tumor model","pmids":["27273304"],"confidence":"High","gaps":["Breadth of translationally repressed targets not defined","How an ER membrane GPCR engages cap machinery structurally unclear"]},{"year":2018,"claim":"Expanded the tumor-suppressor mechanism to p53 pathway control via EGFR-dependent MDM2 stabilization, and identified new adhesion and hypoxia roles.","evidence":"KO-derived cells with Nutlin-3a/Erlotinib epistasis; CRISPR KO with ITGB1/FAK/RhoA-Rac1 readouts and EphA2 Co-IP; SILAC proteomics with HIF-GPRC5A-YAP epistasis","pmids":["29992578","27715394","30143543"],"confidence":"Medium","gaps":["YAP activation by GPRC5A appears oncogenic, opposite to lung tumor-suppressor role","EphA2 interaction rests on single Co-IP","Tissue determinants of opposing roles undefined"]},{"year":2020,"claim":"Resolved the long-standing orphan status by identifying microbiota-derived aromatic monoamines as bona fide GPRC5A agonists.","evidence":"Photoaffinity chemoproteomics, β-arrestin recruitment assay, metabolomics, and synthetic SAR (7-fluorotryptamine)","pmids":["37248411"],"confidence":"High","gaps":["G-protein coupling and downstream signaling of liganded receptor not defined","Physiological relevance of microbiota ligands in vivo unclear"]},{"year":2020,"claim":"Connected GPRC5A loss to immunosuppressive metastasis and to inflammatory lung injury, broadening its epithelial-protective role.","evidence":"Ptges double-KO with immune-competent vs nude host epistasis and MDSC/T-cell flow cytometry; LPS-ALI model with epithelium-specific IκBα super-repressor rescue","pmids":["32060421","25714996"],"confidence":"Medium","gaps":["Whether PGE2 axis is direct GPRC5A output or downstream NF-κB unclear","Cell-type specificity of NF-κB regulation incompletely mapped"]},{"year":2023,"claim":"Defined the epigenetic mechanism by which NF-κB silences GPRC5A, closing the regulatory loop between inflammation and receptor loss.","evidence":"ChIP for p65/RAR/Pol II/H3K9ac, p65–RARα/β Co-IP, p65-S276 phospho-mutant epistasis, and HDAC vs DNMT inhibitor rescue","pmids":["36413416"],"confidence":"High","gaps":["HDAC isoform mediating H3K9 deacetylation not identified","Generality across non-lung epithelia untested"]},{"year":2024,"claim":"Detailed the oncogenic effector mechanisms of GPRC5A across tumor types: mTORC1 activation, YAP1 induction, and drug-efflux/transporter regulation.","evidence":"MS/Co-IP with LAMTOR1 and m6A MeRIP in TNBC; STAT3-TNS4 ChIP in gallbladder cancer; WWP1–LATS1 ubiquitination with YAP inhibitor rescue in ESCC; ABCB1 Co-IP with KO drug-sensitivity","pmids":["38335844","38942137","39550386","38426412"],"confidence":"Medium","gaps":["Each interaction rests largely on single-lab Co-IP","How a single receptor switches between tumor-suppressor and oncogenic outputs unresolved"]},{"year":2025,"claim":"Identified new plasma-membrane regulatory inputs and outputs: Galectin-3-driven internalization, GLUT1 metabolic coupling, and cathepsin-G cleavage releasing a nuclear C-terminal fragment.","evidence":"Gal-3 interactomics/internalization assay in CRC; GLUT1 Co-IP/stability/glucose-uptake rescue in glioblastoma; N-TAILS cleavage mapping with peptide rescue in keratinocytes","pmids":["41090797","40744179","39812615"],"confidence":"Low","gaps":["GLUT1 and cathepsin-G findings are single low-confidence studies awaiting independent confirmation","Functional significance of nuclear C-terminal fragment undefined","Whether Gal-3 internalization regulates signaling output untested"]},{"year":null,"claim":"It remains unknown what determines whether GPRC5A acts as a tumor suppressor or oncogene in a given tissue, and how ligand engagement, G-protein coupling, and the diverse interactome are mechanistically integrated.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying model reconciling tumor-suppressor and oncogenic functions","Downstream G-protein signaling of liganded receptor uncharacterized","No high-resolution structure of GPRC5A or its complexes"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5,20]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[31,32]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,10,23]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,9]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[6,13]}],"complexes":[],"partners":["EGFR","EIF4F","EPHA2","LAMTOR1","ABCB1","WWP1","GLUT1","BMPR1A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NFJ5","full_name":"Retinoic acid-induced protein 3","aliases":["G-protein coupled receptor family C group 5 member A","Phorbol ester induced gene 1","PEIG-1","Retinoic acid-induced gene 1 protein","RAIG-1"],"length_aa":357,"mass_kda":40.3,"function":"Orphan receptor. Could be involved in modulating differentiation and maintaining homeostasis of epithelial cells. This retinoic acid-inducible GPCR provide evidence for a possible interaction between retinoid and G-protein signaling pathways. Functions as a negative modulator of EGFR signaling (By similarity). May act as a lung tumor suppressor (PubMed:18000218)","subcellular_location":"Cell membrane; Cytoplasmic vesicle membrane","url":"https://www.uniprot.org/uniprotkb/Q8NFJ5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPRC5A","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GPRC5A","total_profiled":1310},"omim":[{"mim_id":"604138","title":"G PROTEIN-COUPLED RECEPTOR, FAMILY C, GROUP 5, MEMBER A; GPRC5A","url":"https://www.omim.org/entry/604138"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Primary cilium tip","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lung","ntpm":190.3},{"tissue":"urinary bladder","ntpm":121.8}],"url":"https://www.proteinatlas.org/search/GPRC5A"},"hgnc":{"alias_symbol":["RAIG1","TIG1","PEIG-1"],"prev_symbol":["RAI3"]},"alphafold":{"accession":"Q8NFJ5","domains":[{"cath_id":"1.20.1070.10","chopping":"22-270","consensus_level":"high","plddt":87.6552,"start":22,"end":270}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFJ5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFJ5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFJ5-F1-predicted_aligned_error_v6.png","plddt_mean":77.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPRC5A","jax_strain_url":"https://www.jax.org/strain/search?query=GPRC5A"},"sequence":{"accession":"Q8NFJ5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NFJ5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NFJ5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFJ5"}},"corpus_meta":[{"pmid":"38335844","id":"PMC_38335844","title":"Methylation of GPRC5A promotes liver metastasis and docetaxel resistance through activating mTOR signaling pathway in triple negative breast cancer.","date":"2024","source":"Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/38335844","citation_count":144,"is_preprint":false},{"pmid":"27387124","id":"PMC_27387124","title":"Single-cell Sequencing Reveals Variants in ARID1A, GPRC5A and MLL2 Driving Self-renewal of Human Bladder Cancer Stem Cells.","date":"2016","source":"European urology","url":"https://pubmed.ncbi.nlm.nih.gov/27387124","citation_count":119,"is_preprint":false},{"pmid":"24984703","id":"PMC_24984703","title":"MiR-103a-3p targets the 5' UTR of GPRC5A in pancreatic cells.","date":"2014","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/24984703","citation_count":114,"is_preprint":false},{"pmid":"18000218","id":"PMC_18000218","title":"Identification of the retinoic acid-inducible Gprc5a as a new lung tumor suppressor gene.","date":"2007","source":"Journal of the National Cancer Institute","url":"https://pubmed.ncbi.nlm.nih.gov/18000218","citation_count":103,"is_preprint":false},{"pmid":"30497053","id":"PMC_30497053","title":"circGprc5a Promoted Bladder Oncogenesis and Metastasis through Gprc5a-Targeting Peptide.","date":"2018","source":"Molecular therapy. 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68–91%.\",\n      \"method\": \"Homologous recombination knockout mouse model; colony formation assay with GPRC5A transfection\",\n      \"journal\": \"Journal of the National Cancer Institute\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined tumor phenotype replicated across multiple cell lines with functional rescue\",\n      \"pmids\": [\"18000218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Gprc5a loss in mouse lung epithelial cells causes persistent STAT3 tyrosine-705 phosphorylation driven by autocrine leukemia inhibitory factor (LIF) secretion. Gprc5a(-/-) cells showed reduced levels of the endogenous STAT3 inhibitor Socs3 compared to wild-type cells; re-expression of Gprc5a in knockout cells stabilized Socs3. Inhibition of JAK2 or dominant-negative STAT3(Y705F) increased apoptosis and reduced colony formation in knockout cells.\",\n      \"method\": \"Western blot (STAT3 phosphorylation, Socs3), dominant-negative STAT3 transfection, JAK2 inhibitor (AG490), colony formation assay, re-expression of Gprc5a in knockout cells\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal genetic experiments (KO + rescue) with pharmacological inhibition, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"20959490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Gprc5a loss in lung airway epithelial cells enhances constitutive and stimulus-induced NF-κB activation, leading to increased pro-inflammatory cytokine/chemokine production that promotes macrophage infiltration and a tumor-promoting microenvironment. Re-expression of Gprc5a in knockout adenocarcinoma cells partially reversed the elevated NF-κB activation.\",\n      \"method\": \"NF-κB reporter assays, cytokine measurement, p65 siRNA knockdown and Gprc5a siRNA knockdown in paired wild-type and knockout tracheal epithelial cells, macrophage migration assay\",\n      \"journal\": \"Cancer prevention research (Philadelphia, Pa.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO + rescue with multiple orthogonal functional readouts (reporter, cytokine, migration), single lab\",\n      \"pmids\": [\"20354164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GPRC5A physically interacts with EGFR through its transmembrane domain and negatively modulates EGFR and downstream STAT3 signaling. The transmembrane domain was required for EGFR inhibitory activity as shown by domain-deletion analysis. Mouse tracheal epithelial cells from Gprc5a(-/-) mice showed elevated EGFR/STAT3 signaling reversed by GPRC5A re-expression.\",\n      \"method\": \"Co-immunoprecipitation, domain-deletion mutagenesis, EGFR/STAT3 signaling assays in Gprc5a(-/-) MTEC vs. wild-type, ectopic GPRC5A expression in NSCLC cells\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct Co-IP of GPRC5A–EGFR interaction with domain mutagenesis, validated in genetic KO model and human cancer cells\",\n      \"pmids\": [\"25744720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"EGFR phosphorylates GPRC5A at two conserved double-tyrosine motifs (Y317/Y320 and Y347/Y350) in the C-terminal tail. EGF-induced phosphorylation disrupts GPRC5A-mediated suppression of anchorage-independent growth. The phosphorylation-resistant mutant GPRC5A-4F maintained tumor suppressive activity. GPRC5A was non-phosphorylated in normal lung tissue but highly tyrosine-phosphorylated in NSCLC tissues.\",\n      \"method\": \"IP-Western blot, site-directed mutagenesis (Y317/320/347/350F), EGF stimulation assays, anchorage-independent growth assay, IHC with phospho-specific antibodies on human tumor tissue\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase substrate identification with site-directed mutagenesis, functional validation, and IHC on human tissue; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"25311788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GPRC5A localizes to the endoplasmic reticulum membrane and suppresses protein synthesis of secreted/membrane-bound proteins (including EGFR) by directly binding the eIF4F translation initiation complex through its two middle extracellular loops, thereby disturbing assembly of the eIF4F complex on the mRNA cap.\",\n      \"method\": \"Subcellular fractionation/ER localization, co-immunoprecipitation of GPRC5A with eIF4F components, domain-deletion analysis (extracellular loops), measurement of EGFR translation rate, in vivo ionizing radiation lung tumorigenesis model in Gprc5a(-/-) mice\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct protein interaction with domain mapping, translational assay, and in vivo genetic validation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27273304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Retinoic acid induces GPRC5A transcription through a functional retinoic acid response element DR5III (5'-TGT CCC TCT GCT CAC CC-3') at -64 bp upstream of the transcription start site. RAR-alpha/gamma and RXR-alpha/beta bind this element in intact cells. DR5I and DR5II are non-functional for GPRC5A induction.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA) with wild-type and mutated oligonucleotides; chromatin immunoprecipitation (ChIP); promoter truncation/deletion analysis\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — EMSA with competitor oligos plus ChIP in intact cells, multiple promoter truncations; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"19279407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The Rai3/Gprc5a promoter contains functional GC boxes and Sp1-, AP1-, AP2-binding sites, and a functional retinoic acid response element (direct repeat with 5-bp spacer at -64 bp) that mediates retinoic acid induction, identified by promoter truncation, EMSA, and mutation analysis.\",\n      \"method\": \"Promoter truncation analysis, EMSA, site-directed mutation analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple promoter deletion constructs plus EMSA with mutated binding sites; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"14706456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GPRC5A modulates integrin β1 (ITGB1)-mediated cell adhesion to extracellular matrix substrates. CRISPR/Cas9 knockout of GPRC5A reduced ITGB1 protein expression, impaired FAK phosphorylation, and lowered RhoA and Rac1 GTPase activity. GPRC5A also directly interacts with the receptor tyrosine kinase EphA2.\",\n      \"method\": \"CRISPR/Cas9 knockout, RNAi knockdown, cell adhesion assays to ECM substrates, Western blot (ITGB1, pFAK), small GTPase activity assays, co-immunoprecipitation (GPRC5A–EphA2)\",\n      \"journal\": \"Cell adhesion & migration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — CRISPR KO + RNAi with multiple downstream readouts; EphA2 interaction by single Co-IP; single lab\",\n      \"pmids\": [\"27715394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GPRC5A deficiency leads to dysregulated MDM2 stabilization via activated EGFR signaling (independent of transcription), resulting in p53 pathway suppression and promotion of lung tumor development. Targeting MDM2 with Nutlin-3a or shRNA in Gprc5a-ko-derived cells restored p53 signaling and reduced tumorigenicity.\",\n      \"method\": \"Gprc5a knockout mouse-derived tumor cell lines, MDM2 inhibitor (Nutlin-3a) and shRNA, EGFR inhibitor (Erlotinib) and shRNA, Western blot, colony formation, IHC of human lung cancer tissues\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic epistasis in genetic KO-derived cell model; mechanism of MDM2 stabilization by EGFR established by dual inhibitor experiments; single lab\",\n      \"pmids\": [\"29992578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In cancer cell adaptation to hypoxia, HIFs directly activate GPRC5A transcription, and GPRC5A in turn activates the Hippo pathway effector YAP and its anti-apoptotic target BCL2L1. The apoptosis induced by GPRC5A depletion under hypoxia was rescued by constitutively active YAP, placing GPRC5A between HIF and YAP in a survival axis.\",\n      \"method\": \"SILAC-based proteomics (hypoxia induction), genetic knockdown/knockout in vitro and in vivo, HIF ChIP-seq/reporter analysis, constitutively active YAP rescue, YAP target gene measurement\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — proteomics identification, direct HIF-GPRC5A transcription evidence, epistasis rescue with constitutively active YAP, in vivo validation; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"30143543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PTGES/PGE2 signaling in Gprc5a-ko mouse lung tumors promotes metastasis primarily through immunosuppression: tumor cell-intrinsic PGE2 confers resistance to T-cell cytotoxicity and induces cytokines for MDSC recruitment, suppressing T-cell immunity. PTGES inhibitor suppressed MDSC recruitment, restored T cells, and significantly repressed lung metastasis.\",\n      \"method\": \"Ptges knockout in tumor cells, immune-competent vs. nude mouse transplantation epistasis, cytokine measurement, MDSC/T-cell flow cytometry, PTGES inhibitor treatment in Gprc5a-ko mice\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (double KO) with immune-competent vs. immune-deficient host comparison; pharmacological validation; single lab\",\n      \"pmids\": [\"32060421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Gprc5a deficiency in mice confers susceptibility to LPS-induced acute lung injury through enhanced NF-κB signaling specifically in bronchioalveolar epithelium. Expression of a super-repressor IκBα specifically in Gprc5a-ko bronchioalveolar epithelium alleviated LPS-induced pulmonary injury and inflammatory response.\",\n      \"method\": \"LPS-induced ALI model in Gprc5a-ko and wild-type mice, cytokine/chemokine measurement, pulmonary edema assessment, epithelium-specific IκBα super-repressor transgene rescue\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with pathway-specific rescue transgene, multiple phenotypic readouts; single lab\",\n      \"pmids\": [\"25714996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NF-κB (specifically RelA/p65, phosphorylated on serine 276) represses GPRC5A transcription by forming a complex with retinoic acid receptor α/β (RARα/β) and being recruited to the RA response element at the GPRC5A promoter, disrupting RNA Pol II binding. This epigenetic repression involves suppression of acetylated histone H3K9 (H3K9ac) but not DNA methylation of CpG islands. HDAC inhibitor but not DNA methylation inhibitor restored GPRC5A expression.\",\n      \"method\": \"ChIP assay (p65, RAR, RNA Pol II, H3K9ac), Co-IP (p65–RARα/β), site-directed mutagenesis (p65 S276), HDAC inhibitor and DNA methylation inhibitor treatment, in vivo NF-κB activation model\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — ChIP + Co-IP + phospho-mutant epistasis + pharmacological rescue; multiple orthogonal methods; single lab\",\n      \"pmids\": [\"36413416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p53 interacts with the RAI3/GPRC5A promoter and represses its expression at the onset of apoptosis. RAI3 mRNA is elevated in tumor cell lines expressing mutant p53 and relatively repressed in lines with wild-type p53. Ectopic RAI3 expression in 293 cells promotes anchorage-independent growth, and siRNA depletion of RAI3 in AsPc-1 pancreatic cells induces morphological change.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) of p53 at RAI3 promoter, gene expression profiling, siRNA knockdown, anchorage-independent growth assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — ChIP evidence for p53 binding plus expression correlation and functional gain/loss-of-function; single lab\",\n      \"pmids\": [\"15659406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Chemoproteomics identified aromatic monoamines (microbiota-derived indole metabolites) as ligands that bind the orphan receptor GPRC5A and stimulate β-arrestin recruitment. 7-fluorotryptamine was identified as a more potent synthetic agonist. Specific amino acid decarboxylase-expressing microbiota species produce these agonists.\",\n      \"method\": \"Photoaffinity chemical reporters/chemoproteomics, β-arrestin recruitment assay, metabolomic profiling, synthetic monoamine derivative screening\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct ligand identification by chemoproteomics with functional β-arrestin assay validation and structure-activity relationship; multiple orthogonal methods\",\n      \"pmids\": [\"37248411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Chemotherapy (cisplatin/carboplatin) in ovarian cancer triggers an ERK1/2–RSK1/2–EphA2(S897)–GPRC5A signaling axis associated with chemoresistance. Pharmacological inhibition or knockdown of RSK1/2 prevented oncogenic EphA2-S897 phosphorylation and EphA2–GPRC5A co-regulation, shifting signaling to canonical tumor-suppressive EphA2 tyrosine phosphorylation and EphA2 downregulation.\",\n      \"method\": \"RSK1/2 pharmacological inhibition and knockdown, EphA2-S897 phosphorylation assays, Co-immunoprecipitation (EphA2–GPRC5A), patient tumor samples, apoptosis assays\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP interaction, pharmacological and genetic RSK inhibition with downstream phosphorylation readouts, patient material validation; single lab\",\n      \"pmids\": [\"32115889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"miR-103a-3p targets two sites in the 5' UTR of GPRC5A mRNA (not the 3' UTR) in a seed-dependent manner, reducing GPRC5A mRNA and protein levels in normal epithelial and pancreatic cancer cell lines. Ectopic sponges containing the wild-type 5' UTR targets reduced miR-103a-3p levels and increased GPRC5A mRNA and protein.\",\n      \"method\": \"miRNA target site validation (luciferase or expression reporter with mutated 5' UTR sites), sponge experiments, qRT-PCR and Western blot in multiple cell lines\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional 5' UTR target site validation with mutation and sponge rescue; single lab, multiple cell lines\",\n      \"pmids\": [\"24984703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HuR (RNA-binding protein) binds GPRC5A mRNA at an AU-rich binding site and stabilizes it following gemcitabine treatment, causing a monotonic increase in GPRC5A protein levels. GPRC5A knockdown sensitized pancreatic cancer cells to gemcitabine.\",\n      \"method\": \"RNA immunoprecipitation/RIP identifying HuR–GPRC5A mRNA interaction, Western blot time-course after gemcitabine, GPRC5A knockdown + gemcitabine combination assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — RIP demonstrating direct mRNA-protein interaction, functional sensitization assay; single lab\",\n      \"pmids\": [\"27415424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GPRC5A knockout in pancreatic cancer cells increased phosphorylation of GSK-3β (Ser9), reduced cell proliferation and migration, and suppressed resistance to gemcitabine, oxaliplatin, and fluorouracil.\",\n      \"method\": \"CRISPR/Cas9 knockout in MIA PaCa-2 and TB32047 cells, proliferation and migration assays, drug resistance assays, Western blot for pGSK-3β\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — CRISPR KO with defined phenotypes and pGSK-3β readout; single lab, single method per finding\",\n      \"pmids\": [\"29949874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRC5A interacts with LAMTOR1, inhibiting its ubiquitination-dependent degradation, thereby recruiting mTORC1 to lysosomes and activating the mTORC1/p70S6K signaling pathway. GPRC5A mRNA is post-transcriptionally regulated by m6A methylation via the METTL3/YTHDF1 axis.\",\n      \"method\": \"Mass spectrometry, Co-IP, immunofluorescence colocalization (GPRC5A–LAMTOR1), MeRIP (m6A sequencing), dual-luciferase reporter, knockdown/overexpression in TNBC cells and in vivo models\",\n      \"journal\": \"Drug resistance updates\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS identification of interaction followed by Co-IP and localization; m6A regulation validated by MeRIP and reporter; single lab\",\n      \"pmids\": [\"38335844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRC5A promotes gallbladder cancer metastasis by activating JAK2-STAT3 signaling, which induces expression of TNS4 by STAT3 binding to the TNS4 promoter. ChIP confirmed STAT3 binding at the TNS4 promoter.\",\n      \"method\": \"GPRC5A knockdown in GBC cells (in vitro and in vivo), RNA-seq, Western blot, ChIP (STAT3 at TNS4 promoter), immunohistochemistry\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KD with downstream ChIP validation of transcriptional mechanism; single lab\",\n      \"pmids\": [\"38942137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRC5A directly binds ABCB1 (P-glycoprotein) and reduces its expression. Gprc5a-deficient mouse tracheal epithelial cells and lung tissues showed higher ABCB1 expression, and Gprc5a-ko cells were more sensitive to tariquidar (ABCB1 inhibitor) and doxorubicin. ABCB1 knockout in Gprc5a-/- tumor cells reduced tumor growth in vivo.\",\n      \"method\": \"Immunofluorescence colocalization, co-immunoprecipitation (GPRC5A–ABCB1), Western blot, RT-PCR, Gprc5a-ko mouse tissues, cell sensitivity assays, xenograft tumor model\",\n      \"journal\": \"Chinese medical sciences journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP + colocalization supporting direct interaction; genetic KO in vivo validation; single lab\",\n      \"pmids\": [\"38426412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPRC5A promotes pancreatic cancer cell proliferation and migration by positively regulating YAP1 transcription through the cAMP–CREB signaling axis. The pro-proliferative and migratory effects of GPRC5A were rescued by YAP1 inhibition.\",\n      \"method\": \"GPRC5A knockdown/overexpression in pancreatic cancer cells, cAMP measurement, CREB reporter assay, YAP1 rescue experiment, cytosolic/nuclear distribution assay, xenograft model\",\n      \"journal\": \"Discover oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — cAMP-CREB-YAP1 pathway epistasis with rescue; single lab\",\n      \"pmids\": [\"36735162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRC5A potentially interacts with WWP1 E3 ubiquitin ligase, facilitating polyubiquitination and degradation of LATS1, thereby activating YAP1 signaling and promoting lung metastasis in esophageal squamous cell carcinoma. Targeting YAP1 with CA3 or TED-347 diminished early implantation and macro-metastases.\",\n      \"method\": \"Single-cell RNA sequencing, Co-immunoprecipitation (GPRC5A–WWP1), ubiquitination assay (LATS1), YAP1 inhibitor rescue, in vivo metastasis model, patient cohort (n=148)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP + ubiquitination assay + pharmacological rescue; in vivo validation; single lab\",\n      \"pmids\": [\"39550386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPRC5A overexpression suppressed IL-6-induced STAT3 activation and inhibited anchorage-independent growth in head and neck squamous cell carcinoma cells, placing GPRC5A as a negative regulator of STAT3 in this context.\",\n      \"method\": \"Stable GPRC5A transfection in HNSCC cells, IL-6 stimulation, Western blot (pSTAT3), anchorage-independent growth assay, IHC of clinical HNSCC samples\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — gain-of-function with defined signaling readout in multiple HNSCC lines plus clinical IHC; single lab\",\n      \"pmids\": [\"28270740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAI3/GPRC5A knockdown in human adipose-derived stem cells promoted adipogenic differentiation by decreasing β-catenin levels. Activation of the β-catenin pathway by lithium chloride abolished the effect of RAI3 knockdown on adipogenesis.\",\n      \"method\": \"siRNA knockdown of RAI3 in hASCs, adipogenic differentiation assays (in vitro and in vivo xenograft), Western blot (β-catenin), lithium chloride (Wnt/β-catenin activator) rescue experiment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single knockdown experiment with pharmacological pathway rescue; single lab, single study\",\n      \"pmids\": [\"28870805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RAI3/GPRC5A knockdown in bone marrow mesenchymal stem cells promoted osteogenic differentiation by upregulating phosphorylated STAT3. The JAK2 inhibitor AG-490 reversed the enhancing effect of RAI3 knockdown on osteogenesis.\",\n      \"method\": \"siRNA knockdown, osteogenic differentiation assays (in vitro and in vivo), Western blot (pSTAT3), pharmacological JAK2 inhibitor AG-490 rescue\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — knockdown with pharmacological rescue; single lab, single study\",\n      \"pmids\": [\"32014253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Gprc5a is a PTH-inducible gene: PTH treatment induces Gprc5a expression in osteoblast-like cells and mouse femurs via the cAMP pathway (cAMP response element in promoter), independent of new protein synthesis. Gprc5a negatively regulates osteoblast proliferation and differentiation by interacting with BMPR1A and suppressing BMP-2 signaling.\",\n      \"method\": \"PTH stimulation in MC3T3-E1, ROS17/2.8, and mouse femurs; cycloheximide (protein synthesis inhibition); cAMP pathway inhibitors; reporter analysis of GPRC5A promoter; Gprc5a knockdown (MTT, BrdU, mineralization assay); Co-immunoprecipitation (Gprc5a–BMPR1A); constitutively active BMP receptor constructs\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cAMP pathway epistasis + Co-IP interaction + multiple functional assays; single lab\",\n      \"pmids\": [\"38769895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPRC5A acts as a negative regulator of the PI3K/Akt signaling pathway in triple-negative breast cancer cells. GPRC5A overexpression promoted apoptosis via the intrinsic pathway, activating caspase-3 and caspase-9, and this was inhibited by a PI3K/Akt activator. GPRC5A knockdown inhibited apoptosis, which was partially restored by a PI3K/Akt inhibitor.\",\n      \"method\": \"GPRC5A overexpression/knockdown in TNBC cells, RNA-seq pathway analysis, PI3K/Akt activator/inhibitor rescue experiments, caspase activation assays, in vivo tumor growth\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pharmacological epistasis for PI3K/Akt plus gain and loss-of-function with defined apoptosis readouts; single lab\",\n      \"pmids\": [\"33680947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GPRC5A modulates TGF-β signaling and EGFR activation in cultured podocytes. Gprc5a-deficient mice developed thickening of the glomerular basement membrane, mesangial cell activation, increased albuminuria, and more severe diabetic nephropathy histology after streptozotocin-induced diabetes.\",\n      \"method\": \"Gprc5a knockout mouse model, streptozotocin-induced diabetes, glomerular histology/EM, albumin measurement, TGF-β and EGFR signaling assays in cultured podocytes\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO model with defined renal phenotype and mechanistic signaling assays in podocytes; single lab\",\n      \"pmids\": [\"29636387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TPA (phorbol ester) strongly induces GPRC5A mRNA and protein expression at the plasma membrane via a PKC/Ca²⁺→MEK1/2 signaling axis. PKC inhibitor Gö6983, Ca²⁺ chelator BAPTA-AM, and MEK1/2 inhibitor U0126 each suppressed TPA-induced GPRC5A upregulation. PKA inhibitor H-89 also partially reduced induction.\",\n      \"method\": \"TPA stimulation of T84 cells, pharmacological inhibitors (Gö6983, BAPTA-AM, U0126, H-89, GSK650394), RT-PCR, Western blot, confocal microscopy\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple pharmacological inhibitors delineating signaling pathway for GPRC5A induction; single lab\",\n      \"pmids\": [\"32339486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Galectin-3 (Gal-3) directly binds glycosylated GPRC5A at the plasma membrane and stimulates GPRC5A internalization/endocytosis in colorectal cancer cells. This interaction is independent of ATRA-induced GPRC5A upregulation.\",\n      \"method\": \"Proteomic analysis of endogenous Gal-3 immunoprecipitates (interactomic assay), Co-IP, extracellular recombinant Gal-3 stimulation, GPRC5A internalization assay, immunofluorescence in SW480 cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Weak — Co-IP identification confirmed with functional internalization assay; single lab, limited replication\",\n      \"pmids\": [\"41090797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPRC5A interacts with the glycolytic transporter GLUT1, influencing glucose uptake and glycolysis in glioblastoma. Silencing GPRC5A reduced GLUT1 stability and glucose uptake, increasing TMZ sensitivity, and this effect was reversible by GLUT1 overexpression.\",\n      \"method\": \"Co-immunoprecipitation (GPRC5A–GLUT1), GLUT1 stability assay, glucose uptake measurement, GPRC5A knockdown ± GLUT1 overexpression rescue, TMZ sensitivity assay, in vivo xenograft\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP interaction, functional rescue; single lab, single study\",\n      \"pmids\": [\"40744179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In keratinocytes, GPRC5A undergoes proteolytic cleavage by cathepsin G, releasing its C-terminal region which translocates to the nucleus. GPRC5A knockdown enhanced cell adhesion while reducing cell migration and differentiation; these effects were reversed by addition of a recombinant polypeptide mimicking the C-terminal region. GPRC5A expression is re-induced during wound healing at leading edges.\",\n      \"method\": \"N-TAILS protease cleavage site analysis, cathepsin G identification, shRNA knockdown in N/TERT-1 keratinocytes, cell adhesion/migration/differentiation assays, C-terminal peptide rescue, ex vivo burn wound model\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — N-TAILS cleavage site identification and functional rescue with peptide; single lab, single study, no structural validation\",\n      \"pmids\": [\"39812615\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPRC5A is an orphan GPCR preferentially expressed in lung and other epithelial tissues whose transcription is directly induced by retinoic acid through RAR/RXR binding to a DR5 response element in its promoter and repressed by NF-κB (via a p65–RARα/β complex that suppresses H3K9 acetylation); it acts as a lung tumor suppressor by physically interacting with and inhibiting EGFR (through its transmembrane domain), suppressing translation initiation at the ER membrane (by binding the eIF4F complex via its extracellular loops), stabilizing the STAT3 inhibitor Socs3, and restraining NF-κB activation, while EGFR reciprocally inactivates GPRC5A by phosphorylating its C-terminal tyrosines (Y317/Y320 and Y347/Y350); in other tissue contexts GPRC5A acts as an oncogene by promoting mTORC1 lysosomal recruitment (via LAMTOR1 stabilization), activating YAP1 (via the cAMP–CREB or LATS1 ubiquitination axis), and interacting with integrin β1, EphA2, ABCB1, and GLUT1; microbiota-derived aromatic monoamines have been identified as agonists that stimulate GPRC5A-β-arrestin recruitment.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPRC5A is a retinoic-acid-inducible orphan GPCR of epithelial tissues that functions context-dependently as a lung tumor suppressor and, in other settings, as an oncogenic signaling node [#0, #10]. Its transcription is directly driven by retinoic acid through a functional DR5 response element at -64 bp bound by RAR/RXR heterodimers [#6, #7], and is repressed by NF-\\u03baB: phospho-S276 RelA/p65 forms a complex with RAR\\u03b1/\\u03b2 at the same response element, suppresses H3K9 acetylation, and displaces RNA Pol II [#13]. In normal lung epithelium GPRC5A restrains multiple oncogenic pathways: it physically interacts with EGFR via its transmembrane domain to inhibit EGFR\\u2013STAT3 signaling [#3], localizes to the ER membrane where it binds the eIF4F complex through its extracellular loops to suppress cap-dependent translation of secreted and membrane proteins including EGFR itself [#5], stabilizes the STAT3 inhibitor Socs3 [#1], and limits NF-\\u03baB-driven inflammation [#2, #12]. EGFR reciprocally inactivates GPRC5A by phosphorylating C-terminal double-tyrosine motifs (Y317/Y320, Y347/Y350), abolishing its tumor-suppressive activity, and this phosphorylated form predominates in NSCLC [#4]. Loss of GPRC5A drives tumorigenesis through EGFR-dependent MDM2 stabilization and p53 suppression [#9] and PGE2-mediated immunosuppression [#11]. In other tissue and tumor contexts GPRC5A acts oncogenically by activating YAP1 signaling through HIF, cAMP\\u2013CREB, or WWP1-mediated LATS1 degradation [#10, #23, #24], by recruiting mTORC1 to lysosomes through LAMTOR1 stabilization [#20], and by interacting with integrin \\u03b21/EphA2 [#8], ABCB1 [#22], and GLUT1 [#33]. Microbiota-derived aromatic monoamines act as GPRC5A agonists that stimulate \\u03b2-arrestin recruitment, with 7-fluorotryptamine a more potent synthetic agonist [#15].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the transcriptional control of GPRC5A by mapping its promoter architecture and identifying retinoic acid responsiveness, the founding feature of this gene.\",\n      \"evidence\": \"Promoter truncation, EMSA, and site-directed mutation analysis identifying GC boxes, Sp1/AP1/AP2 sites, and a DR5 retinoic acid response element\",\n      \"pmids\": [\"14706456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish which RAR/RXR isoforms bind in vivo\", \"No functional consequence of induction defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Asked how GPRC5A intersects with tumor-suppressor circuits and showed p53 directly represses its promoter, with context-dependent growth effects.\",\n      \"evidence\": \"ChIP of p53 at RAI3 promoter, expression profiling across p53-status lines, siRNA knockdown, and anchorage-independent growth assay\",\n      \"pmids\": [\"15659406\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pro-growth role conflicts with later tumor-suppressor data\", \"Mechanism of p53-mediated repression not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Resolved the central question of GPRC5A's physiological role by demonstrating it is a lung tumor suppressor in vivo.\",\n      \"evidence\": \"Gprc5a homologous-recombination knockout mice with spontaneous lung tumors plus colony formation rescue across multiple cell lines\",\n      \"pmids\": [\"18000218\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of suppression not yet defined\", \"Did not address signaling pathways downstream\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the precise cis-element and trans-factors mediating retinoic acid induction, anchoring GPRC5A in retinoid signaling.\",\n      \"evidence\": \"EMSA with competitor oligos and ChIP showing RAR-\\u03b1/\\u03b3 and RXR-\\u03b1/\\u03b2 binding the functional DR5III element\",\n      \"pmids\": [\"19279407\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not connect transcriptional induction to downstream function\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the downstream signaling pathways deranged by GPRC5A loss, linking it to STAT3 and NF-\\u03baB-driven inflammation.\",\n      \"evidence\": \"KO + rescue Western blots for STAT3-pY705/Socs3, dominant-negative STAT3, JAK2 inhibition, NF-\\u03baB reporter, cytokine, and macrophage migration assays\",\n      \"pmids\": [\"20959490\", \"20354164\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STAT3 and NF-\\u03baB effects are direct or downstream of EGFR not yet resolved\", \"Mechanism of Socs3 stabilization unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Explained how GPRC5A is functionally silenced in cancer by identifying EGFR-mediated tyrosine phosphorylation as an inactivating switch.\",\n      \"evidence\": \"IP-Western, site-directed Y-to-F mutagenesis, EGF stimulation, anchorage-independent growth, and phospho-specific IHC on human NSCLC\",\n      \"pmids\": [\"25311788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of phosphorylation-induced inactivation unknown\", \"Direct vs. indirect EGFR kinase action on GPRC5A not fully resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established the direct physical mechanism of EGFR inhibition by GPRC5A through its transmembrane domain.\",\n      \"evidence\": \"Co-IP, domain-deletion mutagenesis, and EGFR/STAT3 signaling assays in Gprc5a-/- MTEC versus wild-type\",\n      \"pmids\": [\"25744720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of the GPRC5A\\u2013EGFR transmembrane interface\", \"Stoichiometry and dynamics of complex unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Uncovered a non-canonical, receptor-independent function: GPRC5A suppresses cap-dependent translation at the ER by binding eIF4F.\",\n      \"evidence\": \"ER fractionation, Co-IP with eIF4F components, extracellular-loop deletion mapping, EGFR translation-rate measurement, and in vivo irradiation tumor model\",\n      \"pmids\": [\"27273304\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Breadth of translationally repressed targets not defined\", \"How an ER membrane GPCR engages cap machinery structurally unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Expanded the tumor-suppressor mechanism to p53 pathway control via EGFR-dependent MDM2 stabilization, and identified new adhesion and hypoxia roles.\",\n      \"evidence\": \"KO-derived cells with Nutlin-3a/Erlotinib epistasis; CRISPR KO with ITGB1/FAK/RhoA-Rac1 readouts and EphA2 Co-IP; SILAC proteomics with HIF-GPRC5A-YAP epistasis\",\n      \"pmids\": [\"29992578\", \"27715394\", \"30143543\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"YAP activation by GPRC5A appears oncogenic, opposite to lung tumor-suppressor role\", \"EphA2 interaction rests on single Co-IP\", \"Tissue determinants of opposing roles undefined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the long-standing orphan status by identifying microbiota-derived aromatic monoamines as bona fide GPRC5A agonists.\",\n      \"evidence\": \"Photoaffinity chemoproteomics, \\u03b2-arrestin recruitment assay, metabolomics, and synthetic SAR (7-fluorotryptamine)\",\n      \"pmids\": [\"37248411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G-protein coupling and downstream signaling of liganded receptor not defined\", \"Physiological relevance of microbiota ligands in vivo unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected GPRC5A loss to immunosuppressive metastasis and to inflammatory lung injury, broadening its epithelial-protective role.\",\n      \"evidence\": \"Ptges double-KO with immune-competent vs nude host epistasis and MDSC/T-cell flow cytometry; LPS-ALI model with epithelium-specific I\\u03baB\\u03b1 super-repressor rescue\",\n      \"pmids\": [\"32060421\", \"25714996\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PGE2 axis is direct GPRC5A output or downstream NF-\\u03baB unclear\", \"Cell-type specificity of NF-\\u03baB regulation incompletely mapped\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined the epigenetic mechanism by which NF-\\u03baB silences GPRC5A, closing the regulatory loop between inflammation and receptor loss.\",\n      \"evidence\": \"ChIP for p65/RAR/Pol II/H3K9ac, p65\\u2013RAR\\u03b1/\\u03b2 Co-IP, p65-S276 phospho-mutant epistasis, and HDAC vs DNMT inhibitor rescue\",\n      \"pmids\": [\"36413416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"HDAC isoform mediating H3K9 deacetylation not identified\", \"Generality across non-lung epithelia untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Detailed the oncogenic effector mechanisms of GPRC5A across tumor types: mTORC1 activation, YAP1 induction, and drug-efflux/transporter regulation.\",\n      \"evidence\": \"MS/Co-IP with LAMTOR1 and m6A MeRIP in TNBC; STAT3-TNS4 ChIP in gallbladder cancer; WWP1\\u2013LATS1 ubiquitination with YAP inhibitor rescue in ESCC; ABCB1 Co-IP with KO drug-sensitivity\",\n      \"pmids\": [\"38335844\", \"38942137\", \"39550386\", \"38426412\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each interaction rests largely on single-lab Co-IP\", \"How a single receptor switches between tumor-suppressor and oncogenic outputs unresolved\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified new plasma-membrane regulatory inputs and outputs: Galectin-3-driven internalization, GLUT1 metabolic coupling, and cathepsin-G cleavage releasing a nuclear C-terminal fragment.\",\n      \"evidence\": \"Gal-3 interactomics/internalization assay in CRC; GLUT1 Co-IP/stability/glucose-uptake rescue in glioblastoma; N-TAILS cleavage mapping with peptide rescue in keratinocytes\",\n      \"pmids\": [\"41090797\", \"40744179\", \"39812615\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"GLUT1 and cathepsin-G findings are single low-confidence studies awaiting independent confirmation\", \"Functional significance of nuclear C-terminal fragment undefined\", \"Whether Gal-3 internalization regulates signaling output untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown what determines whether GPRC5A acts as a tumor suppressor or oncogene in a given tissue, and how ligand engagement, G-protein coupling, and the diverse interactome are mechanistically integrated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying model reconciling tumor-suppressor and oncogenic functions\", \"Downstream G-protein signaling of liganded receptor uncharacterized\", \"No high-resolution structure of GPRC5A or its complexes\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5, 20]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [31, 32]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10, 23]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [6, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"EGFR\", \"eIF4F\", \"EphA2\", \"LAMTOR1\", \"ABCB1\", \"WWP1\", \"GLUT1\", \"BMPR1A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}