{"gene":"KDELR2","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1992,"finding":"Overexpression of human ERD-2 (KDELR1) or its novel homolog ELP-1 (KDELR2) induces a brefeldin A-like phenotype, including redistribution of beta-COP to the cytosol, collapse of the Golgi into the ER, and block of anterograde traffic, indicating these receptors regulate retrograde Golgi-to-ER traffic.","method":"Overexpression in multiple cell types, immunofluorescence, subcellular fractionation, glycosylation assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, replicated across cell types, foundational study with 144 citations","pmids":["1316805"],"is_preprint":false},{"year":2020,"finding":"KDELR2 binds HSP47 (a KDEL-motif-containing ER chaperone) and mediates its retrograde COPI-dependent transport from cis-Golgi to ER; loss-of-function KDELR2 variants cause HSP47 to remain bound to collagen extracellularly, disrupting collagen fibril formation and causing osteogenesis imperfecta.","method":"Patient fibroblast analysis (Western blot, electron microscopy), crystal structure mapping of OI variants onto Gallus gallus KDELR2 structure, co-immunoprecipitation, collagen secretion assays","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 — structural mapping plus functional patient cell data plus multiple orthogonal methods; 51 citations","pmids":["33053334"],"is_preprint":false},{"year":2019,"finding":"KDELR2 overexpression retains ER chaperones calnexin and GRP78/BiP in the ER, competing with measles virus envelope proteins (H and F) for these chaperones, thereby reducing chaperone availability for viral glycoprotein folding and transport to the cell surface and limiting viral spread.","method":"Overexpression and silencing of KDELR2 in Vero and CEM-SS T cells, co-immunoprecipitation, viral titer assays, surface trafficking assays","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP plus functional silencing/overexpression, single lab","pmids":["30621148"],"is_preprint":false},{"year":2021,"finding":"HDAC3 transcriptionally activates KDELR2 via the transcription factor CREB1 (validated by ChIP assay and promoter binding); KDELR2 in turn protects the centrosomal protein POC5 from proteasomal degradation, accelerating cell cycle progression and promoting breast cancer proliferation.","method":"Transcriptome sequencing, ChIP assay, co-immunoprecipitation (KDELR2–POC5), flow cytometry (cell cycle), MTT assay, in vivo mouse tumor model","journal":"Cancer communications","confidence":"Medium","confidence_rationale":"Tier 2–3 — ChIP plus Co-IP plus in vivo validation, single lab, moderate evidence","pmids":["34146461"],"is_preprint":false},{"year":2020,"finding":"KDELR2 drives lung cancer invasion and metastasis by enhancing Golgi-mediated secretion; therapeutically inhibiting matrix metalloproteases (MMPs) suppresses KDELR2-mediated invasion, placing KDELR2 upstream of MMP secretion in the Golgi secretory pathway.","method":"Gain-of-function invasion screen, in vitro invasion assays, in vivo metastasis models, MMP inhibitor rescue experiments","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — unbiased screen with mechanistic follow-up including pharmacological rescue, single lab","pmids":["32753652"],"is_preprint":false},{"year":2019,"finding":"HIF1α directly binds the upstream promoter region of KDELR2 and transcriptionally activates it in glioblastoma cells, placing KDELR2 downstream of hypoxia signaling.","method":"ChIP-qPCR and luciferase reporter assay","journal":"Cellular and molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 — two orthogonal methods (ChIP + luciferase), single lab","pmids":["31342232"],"is_preprint":false},{"year":2021,"finding":"KDELR2 knockdown activates ER stress pathways including the CHOP pathway and phosphorylation of JNK and p38, leading to apoptosis; combination with temozolomide shows synergistic cytotoxicity through these ERS-dependent pathways in glioma cells.","method":"siRNA knockdown, Western blot (caspase-3, PARP, Bcl-2, Bax, JNK, p38, GRP78, CHOP, PERK, ATF4, ATF6), flow cytometry, CCK8 assay","journal":"Translational cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple pathway markers assessed by Western blot, functional apoptosis readouts, single lab","pmids":["35116653"],"is_preprint":false},{"year":2022,"finding":"KDELR2 regulates expression of KIF20A, which in turn stimulates expression of MMP2, MMP9, and MKI67, thereby enhancing Golgi-mediated MMP secretion to drive bladder cancer proliferation, migration, and invasion.","method":"siRNA knockdown, overexpression, Western blot, in vitro migration/invasion assays, in vivo tumor growth and lymph node metastasis models","journal":"Biological procedures online","confidence":"Low","confidence_rationale":"Tier 3 — functional assays with downstream readouts but indirect pathway placement, single lab","pmids":["36096734"],"is_preprint":false},{"year":2024,"finding":"KDELR2 promotes osteogenic differentiation of bone marrow mesenchymal stem cells by upregulating phospho-GSK3β (Ser9) and active β-catenin, activating the GSK3β/β-catenin (Wnt) signaling pathway; in vivo overexpression accelerates fracture healing.","method":"Lentiviral overexpression and knockdown, Western blot (active β-catenin, p-GSK3β), osteogenic differentiation assays, mouse fracture model","journal":"Cell and tissue research","confidence":"Low","confidence_rationale":"Tier 3 — pathway markers measured, functional in vivo data, but mechanism is indirect and single lab","pmids":["38470494"],"is_preprint":false},{"year":2024,"finding":"KDELR2 is required for MUC5AC hypersecretion in COPD airway epithelium; its expression is regulated upstream by ATF6 and IRE1α/XBP-1s ER stress signaling pathways, and KDELR2 knockdown reduces MUC5AC levels both in vivo and in vitro.","method":"siRNA knockdown in vitro, in vivo COPD rat model, co-localization (immunofluorescence), IRE1α inhibitor (4μ8C) treatment, Western blot","journal":"Journal of cellular and molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 — functional knockdown with in vivo corroboration, but mechanistic pathway placement is correlative","pmids":["39365189"],"is_preprint":false},{"year":2025,"finding":"Inhibition of KDELR2 in a minor fraction of tumor cells triggers robust macrophage and neutrophil infiltration into the tumor microenvironment, leading to complete regression of both immunogenic and non-immunogenic tumors independently of T cells; intratumoral siKDELR2 delivered by lipid nanoparticles recapitulates this effect.","method":"siRNA knockdown (in vivo lipid nanoparticle delivery), tumor regression assays, immune cell infiltration analysis, T cell depletion experiments","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 2 — in vivo functional data with mechanistic immune readouts, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.08.07.669177"],"is_preprint":true}],"current_model":"KDELR2 is a seven-transmembrane KDEL-motif receptor at the cis-Golgi that recognizes escaped ER-resident proteins (such as HSP47, GRP78/BiP, and calnexin) and mediates their COPI-dependent retrograde retrieval to the ER; its overexpression collapses Golgi structure and blocks anterograde traffic (BFA-like phenotype), its loss prevents HSP47 recycling causing it to remain bound to extracellular collagen and disrupt fibril formation (leading to osteogenesis imperfecta), and it is transcriptionally regulated by HDAC3/CREB1 and HIF1α; beyond its canonical retrieval function, KDELR2 has been shown to protect the centrosomal protein POC5 from degradation, enhance Golgi-mediated MMP secretion to drive cancer invasion, and modulate ER stress (CHOP/JNK/p38) and Wnt (GSK3β/β-catenin) signaling."},"narrative":{"teleology":[{"year":1992,"claim":"It was unknown whether additional KDEL receptors existed or how they influenced Golgi-to-ER traffic; overexpression of the novel KDELR2 (ELP-1) showed it could redistribute β-COP and collapse the Golgi into the ER, establishing KDELR2 as a bona fide retrograde trafficking regulator.","evidence":"Overexpression in multiple cell types with immunofluorescence, subcellular fractionation, and glycosylation assays","pmids":["1316805"],"confidence":"High","gaps":["Endogenous cargo specificity of KDELR2 versus KDELR1 was not resolved","Structural basis of KDEL peptide recognition by KDELR2 was unknown","Physiological consequence of KDELR2 loss of function was not tested"]},{"year":2019,"claim":"It was unclear what regulated KDELR2 expression; ChIP-qPCR and luciferase assays showed HIF1α directly binds the KDELR2 promoter, and separately, overexpression/silencing experiments demonstrated KDELR2 retains ER chaperones calnexin and GRP78, limiting their availability for measles virus glycoprotein folding.","evidence":"ChIP-qPCR and luciferase reporter (glioblastoma cells); co-immunoprecipitation and viral titer assays (Vero and T cells)","pmids":["31342232","30621148"],"confidence":"Medium","gaps":["Whether HIF1α-driven KDELR2 upregulation is sufficient to alter ER proteostasis in hypoxia was not tested","Direct binding of KDELR2 to calnexin or GRP78 KDEL motifs was not demonstrated biochemically"]},{"year":2020,"claim":"The physiological consequence of KDELR2 loss was unknown; patient-derived loss-of-function KDELR2 variants were shown to prevent HSP47 retrograde retrieval, causing extracellular HSP47-collagen retention and defective fibrillogenesis, establishing KDELR2 mutations as a cause of osteogenesis imperfecta.","evidence":"Patient fibroblast analysis, crystal structure mapping of OI variants onto KDELR2 structure, co-immunoprecipitation, collagen secretion assays","pmids":["33053334"],"confidence":"High","gaps":["Whether KDELR1 or KDELR3 can partially compensate for KDELR2 in HSP47 retrieval was not resolved","Full atomic structure of human KDELR2 bound to HSP47 KDEL peptide was not determined"]},{"year":2020,"claim":"Whether KDELR2 influenced secretory cargo beyond ER-resident proteins was unknown; a gain-of-function invasion screen identified KDELR2 as a driver of lung cancer metastasis through enhanced Golgi-mediated MMP secretion, establishing a pro-invasive function.","evidence":"Unbiased invasion screen, in vitro and in vivo metastasis assays, MMP inhibitor rescue","pmids":["32753652"],"confidence":"Medium","gaps":["The mechanism by which KDELR2 enhances anterograde MMP secretion from the Golgi was not defined","Whether this reflects altered COPI vesicle dynamics or a separate signaling function was not distinguished"]},{"year":2021,"claim":"How KDELR2 expression is controlled and whether it has non-canonical functions beyond cargo retrieval was unresolved; HDAC3/CREB1 was shown to transcriptionally activate KDELR2, and KDELR2 was found to protect the centrosomal protein POC5 from proteasomal degradation, accelerating cell cycle progression.","evidence":"ChIP assay (CREB1-KDELR2 promoter), co-immunoprecipitation (KDELR2–POC5), cell cycle analysis, in vivo breast cancer model","pmids":["34146461"],"confidence":"Medium","gaps":["How a Golgi-localized receptor protects a centrosomal protein from degradation is mechanistically unexplained","Whether KDELR2-POC5 interaction is direct or mediated through an adaptor was not established"]},{"year":2021,"claim":"Whether KDELR2 depletion triggers ER stress was unknown; knockdown activated CHOP, phospho-JNK, and phospho-p38, leading to apoptosis that synergized with temozolomide in glioma cells, linking KDELR2 to ER stress suppression.","evidence":"siRNA knockdown, Western blot for multiple UPR and MAPK markers, flow cytometry for apoptosis","pmids":["35116653"],"confidence":"Medium","gaps":["Whether ER stress results from general chaperone mislocalization or a specific KDELR2-dependent signal was not resolved","Synergy with temozolomide was shown only in one glioma cell line"]},{"year":2024,"claim":"Broader physiological roles of KDELR2 outside cancer remained unclear; KDELR2 was shown to promote osteogenic differentiation via GSK3β/β-catenin activation and to be required for MUC5AC hypersecretion in COPD airways downstream of ATF6 and IRE1α/XBP-1s.","evidence":"Overexpression/knockdown in mesenchymal stem cells and fracture model; siRNA and IRE1α inhibitor in COPD rat model","pmids":["38470494","39365189"],"confidence":"Low","gaps":["GSK3β/β-catenin activation by KDELR2 is correlative; direct mechanistic link is not established","Whether KDELR2 role in MUC5AC secretion reflects canonical retrieval function or a distinct secretory pathway remains unknown","Both findings are from single laboratories without independent replication"]},{"year":null,"claim":"It remains unknown how KDELR2's canonical retrograde retrieval activity relates to its reported non-canonical roles in MMP secretion, centrosomal protein stabilization, and Wnt signaling — specifically whether these functions reflect a unified COPI-dependent mechanism, Golgi-localized signaling, or independent activities.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of human KDELR2 with bound KDEL peptide exists","Functional redundancy among KDELR1, KDELR2, and KDELR3 is poorly characterized","The mechanism coupling KDELR2 to anterograde secretory cargo (MMPs, MUC5AC) is undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,4]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,4]}],"complexes":[],"partners":["HSP47","GRP78","POC5","CREB1","HDAC3"],"other_free_text":[]},"mechanistic_narrative":"KDELR2 is a seven-transmembrane receptor at the cis-Golgi that retrieves escaped ER-resident chaperones bearing KDEL motifs via COPI-dependent retrograde transport, thereby maintaining ER proteostasis and governing Golgi organization. Overexpression of KDELR2 redistributes β-COP to the cytosol and collapses Golgi structure into the ER, blocking anterograde traffic [PMID:1316805], while its loss prevents retrograde recycling of the collagen chaperone HSP47, causing HSP47 to persist on extracellular collagen fibrils and disrupt fibrillogenesis, resulting in osteogenesis imperfecta [PMID:33053334]. KDELR2 also retains ER chaperones calnexin and GRP78/BiP, limiting their availability for viral glycoprotein folding [PMID:30621148], and its depletion activates ER stress effectors CHOP, JNK, and p38 leading to apoptosis [PMID:35116653]. Beyond ER quality control, KDELR2 enhances Golgi-mediated MMP secretion to promote cancer cell invasion [PMID:32753652] and is transcriptionally regulated by HDAC3/CREB1 and HIF1α [PMID:34146461, PMID:31342232]."},"prefetch_data":{"uniprot":{"accession":"P33947","full_name":"ER lumen protein-retaining receptor 2","aliases":["ERD2-like protein 1","ELP-1","KDEL endoplasmic reticulum protein retention receptor 2","KDEL receptor 2"],"length_aa":212,"mass_kda":24.4,"function":"Membrane receptor that binds the K-D-E-L sequence motif in the C-terminal part of endoplasmic reticulum resident proteins and maintains their localization in that compartment by participating to their vesicle-mediated recycling back from the Golgi (PubMed:1325562, PubMed:18086916, PubMed:33053334). Binding is pH dependent, and is optimal at pH 5-5.4 (By similarity)","subcellular_location":"Endoplasmic reticulum membrane; Golgi apparatus membrane; Cytoplasmic vesicle, COPI-coated vesicle membrane","url":"https://www.uniprot.org/uniprotkb/P33947/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KDELR2","classification":"Not Classified","n_dependent_lines":23,"n_total_lines":1208,"dependency_fraction":0.01903973509933775},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KDELR2","total_profiled":1310},"omim":[{"mim_id":"619900","title":"KDEL ENDOPLASMIC RETICULUM PROTEIN RETENTION RECEPTOR 3; KDELR3","url":"https://www.omim.org/entry/619900"},{"mim_id":"619131","title":"OSTEOGENESIS IMPERFECTA, TYPE XXI; OI21","url":"https://www.omim.org/entry/619131"},{"mim_id":"609024","title":"KDEL ENDOPLASMIC RETICULUM PROTEIN RETENTION RECEPTOR 2; KDELR2","url":"https://www.omim.org/entry/609024"},{"mim_id":"131235","title":"KDEL ENDOPLASMIC RETICULUM PROTEIN RETENTION RECEPTOR 1; KDELR1","url":"https://www.omim.org/entry/131235"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/KDELR2"},"hgnc":{"alias_symbol":["ELP-1","ERD2.2"],"prev_symbol":[]},"alphafold":{"accession":"P33947","domains":[{"cath_id":"-","chopping":"2-207","consensus_level":"high","plddt":94.0694,"start":2,"end":207}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P33947","model_url":"https://alphafold.ebi.ac.uk/files/AF-P33947-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P33947-F1-predicted_aligned_error_v6.png","plddt_mean":93.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KDELR2","jax_strain_url":"https://www.jax.org/strain/search?query=KDELR2"},"sequence":{"accession":"P33947","fasta_url":"https://rest.uniprot.org/uniprotkb/P33947.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P33947/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P33947"}},"corpus_meta":[{"pmid":"1316805","id":"PMC_1316805","title":"A brefeldin A-like phenotype is induced by the overexpression of a human ERD-2-like protein, ELP-1.","date":"1992","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/1316805","citation_count":144,"is_preprint":false},{"pmid":"33053334","id":"PMC_33053334","title":"Interaction between KDELR2 and HSP47 as a Key Determinant in Osteogenesis Imperfecta Caused by Bi-allelic Variants in KDELR2.","date":"2020","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33053334","citation_count":51,"is_preprint":false},{"pmid":"34146461","id":"PMC_34146461","title":"KDELR2 promotes breast cancer proliferation via HDAC3-mediated cell cycle progression.","date":"2021","source":"Cancer communications (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/34146461","citation_count":40,"is_preprint":false},{"pmid":"32753652","id":"PMC_32753652","title":"IMPAD1 and KDELR2 drive invasion and metastasis by enhancing Golgi-mediated secretion.","date":"2020","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/32753652","citation_count":34,"is_preprint":false},{"pmid":"31342232","id":"PMC_31342232","title":"KDELR2 Promotes Glioblastoma Tumorigenesis Targeted by HIF1a via mTOR Signaling Pathway.","date":"2019","source":"Cellular and molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/31342232","citation_count":27,"is_preprint":false},{"pmid":"19014691","id":"PMC_19014691","title":"The C. elegans EMAP-like protein, ELP-1 is required for touch sensation and associates with microtubules and adhesion complexes.","date":"2008","source":"BMC developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/19014691","citation_count":24,"is_preprint":false},{"pmid":"36096734","id":"PMC_36096734","title":"KDELR2-KIF20A axis facilitates bladder cancer growth and metastasis by enhancing Golgi-mediated secretion.","date":"2022","source":"Biological procedures online","url":"https://pubmed.ncbi.nlm.nih.gov/36096734","citation_count":22,"is_preprint":false},{"pmid":"35116653","id":"PMC_35116653","title":"KDELR2 knockdown synergizes with temozolomide to induce glioma cell apoptosis through the CHOP and JNK/p38 pathways.","date":"2021","source":"Translational cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/35116653","citation_count":10,"is_preprint":false},{"pmid":"30621148","id":"PMC_30621148","title":"KDELR2 Competes with Measles Virus Envelope Proteins for Cellular Chaperones Reducing Their Chaperone-Mediated Cell Surface Transport.","date":"2019","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/30621148","citation_count":6,"is_preprint":false},{"pmid":"19582871","id":"PMC_19582871","title":"Loss of dystrophin and the microtubule-binding protein ELP-1 causes progressive paralysis and death of adult C. elegans.","date":"2009","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/19582871","citation_count":5,"is_preprint":false},{"pmid":"39691708","id":"PMC_39691708","title":"A new perspective on macrophage-targeted drug research: the potential of KDELR2 in bladder cancer immunotherapy.","date":"2024","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/39691708","citation_count":4,"is_preprint":false},{"pmid":"39365189","id":"PMC_39365189","title":"KDELR2 is necessary for chronic obstructive pulmonary disease airway Mucin5AC hypersecretion via an IRE1α/XBP-1s-dependent mechanism.","date":"2024","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39365189","citation_count":4,"is_preprint":false},{"pmid":"38470494","id":"PMC_38470494","title":"KDELR2 promotes bone marrow mesenchymal stem cell osteogenic differentiation via GSK3β/β-catenin signaling pathway.","date":"2024","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/38470494","citation_count":3,"is_preprint":false},{"pmid":"37939504","id":"PMC_37939504","title":"Chinese herb related molecules Catechins, Caudatin and Cucurbitacin-I inhibit the proliferation of glioblastoma by activating KDELR2-mediated endoplasmic reticulum stress.","date":"2023","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/37939504","citation_count":2,"is_preprint":false},{"pmid":"41251935","id":"PMC_41251935","title":"A pan-cancer analysis of the oncogenic role of KDELR2 in human cancers.","date":"2025","source":"Discover oncology","url":"https://pubmed.ncbi.nlm.nih.gov/41251935","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.07.669177","title":"Inhibition of KDEL receptors remodels the tumor microenvironment for robust T cell independent tumor regression","date":"2025-08-11","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.07.669177","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8970,"output_tokens":2686,"usd":0.0336},"stage2":{"model":"claude-opus-4-6","input_tokens":6076,"output_tokens":2464,"usd":0.13797},"total_usd":0.17157,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"Overexpression of human ERD-2 (KDELR1) or its novel homolog ELP-1 (KDELR2) induces a brefeldin A-like phenotype, including redistribution of beta-COP to the cytosol, collapse of the Golgi into the ER, and block of anterograde traffic, indicating these receptors regulate retrograde Golgi-to-ER traffic.\",\n      \"method\": \"Overexpression in multiple cell types, immunofluorescence, subcellular fractionation, glycosylation assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, replicated across cell types, foundational study with 144 citations\",\n      \"pmids\": [\"1316805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KDELR2 binds HSP47 (a KDEL-motif-containing ER chaperone) and mediates its retrograde COPI-dependent transport from cis-Golgi to ER; loss-of-function KDELR2 variants cause HSP47 to remain bound to collagen extracellularly, disrupting collagen fibril formation and causing osteogenesis imperfecta.\",\n      \"method\": \"Patient fibroblast analysis (Western blot, electron microscopy), crystal structure mapping of OI variants onto Gallus gallus KDELR2 structure, co-immunoprecipitation, collagen secretion assays\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structural mapping plus functional patient cell data plus multiple orthogonal methods; 51 citations\",\n      \"pmids\": [\"33053334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"KDELR2 overexpression retains ER chaperones calnexin and GRP78/BiP in the ER, competing with measles virus envelope proteins (H and F) for these chaperones, thereby reducing chaperone availability for viral glycoprotein folding and transport to the cell surface and limiting viral spread.\",\n      \"method\": \"Overexpression and silencing of KDELR2 in Vero and CEM-SS T cells, co-immunoprecipitation, viral titer assays, surface trafficking assays\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP plus functional silencing/overexpression, single lab\",\n      \"pmids\": [\"30621148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HDAC3 transcriptionally activates KDELR2 via the transcription factor CREB1 (validated by ChIP assay and promoter binding); KDELR2 in turn protects the centrosomal protein POC5 from proteasomal degradation, accelerating cell cycle progression and promoting breast cancer proliferation.\",\n      \"method\": \"Transcriptome sequencing, ChIP assay, co-immunoprecipitation (KDELR2–POC5), flow cytometry (cell cycle), MTT assay, in vivo mouse tumor model\",\n      \"journal\": \"Cancer communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — ChIP plus Co-IP plus in vivo validation, single lab, moderate evidence\",\n      \"pmids\": [\"34146461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KDELR2 drives lung cancer invasion and metastasis by enhancing Golgi-mediated secretion; therapeutically inhibiting matrix metalloproteases (MMPs) suppresses KDELR2-mediated invasion, placing KDELR2 upstream of MMP secretion in the Golgi secretory pathway.\",\n      \"method\": \"Gain-of-function invasion screen, in vitro invasion assays, in vivo metastasis models, MMP inhibitor rescue experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — unbiased screen with mechanistic follow-up including pharmacological rescue, single lab\",\n      \"pmids\": [\"32753652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HIF1α directly binds the upstream promoter region of KDELR2 and transcriptionally activates it in glioblastoma cells, placing KDELR2 downstream of hypoxia signaling.\",\n      \"method\": \"ChIP-qPCR and luciferase reporter assay\",\n      \"journal\": \"Cellular and molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal methods (ChIP + luciferase), single lab\",\n      \"pmids\": [\"31342232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KDELR2 knockdown activates ER stress pathways including the CHOP pathway and phosphorylation of JNK and p38, leading to apoptosis; combination with temozolomide shows synergistic cytotoxicity through these ERS-dependent pathways in glioma cells.\",\n      \"method\": \"siRNA knockdown, Western blot (caspase-3, PARP, Bcl-2, Bax, JNK, p38, GRP78, CHOP, PERK, ATF4, ATF6), flow cytometry, CCK8 assay\",\n      \"journal\": \"Translational cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple pathway markers assessed by Western blot, functional apoptosis readouts, single lab\",\n      \"pmids\": [\"35116653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KDELR2 regulates expression of KIF20A, which in turn stimulates expression of MMP2, MMP9, and MKI67, thereby enhancing Golgi-mediated MMP secretion to drive bladder cancer proliferation, migration, and invasion.\",\n      \"method\": \"siRNA knockdown, overexpression, Western blot, in vitro migration/invasion assays, in vivo tumor growth and lymph node metastasis models\",\n      \"journal\": \"Biological procedures online\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — functional assays with downstream readouts but indirect pathway placement, single lab\",\n      \"pmids\": [\"36096734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KDELR2 promotes osteogenic differentiation of bone marrow mesenchymal stem cells by upregulating phospho-GSK3β (Ser9) and active β-catenin, activating the GSK3β/β-catenin (Wnt) signaling pathway; in vivo overexpression accelerates fracture healing.\",\n      \"method\": \"Lentiviral overexpression and knockdown, Western blot (active β-catenin, p-GSK3β), osteogenic differentiation assays, mouse fracture model\",\n      \"journal\": \"Cell and tissue research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — pathway markers measured, functional in vivo data, but mechanism is indirect and single lab\",\n      \"pmids\": [\"38470494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KDELR2 is required for MUC5AC hypersecretion in COPD airway epithelium; its expression is regulated upstream by ATF6 and IRE1α/XBP-1s ER stress signaling pathways, and KDELR2 knockdown reduces MUC5AC levels both in vivo and in vitro.\",\n      \"method\": \"siRNA knockdown in vitro, in vivo COPD rat model, co-localization (immunofluorescence), IRE1α inhibitor (4μ8C) treatment, Western blot\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — functional knockdown with in vivo corroboration, but mechanistic pathway placement is correlative\",\n      \"pmids\": [\"39365189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Inhibition of KDELR2 in a minor fraction of tumor cells triggers robust macrophage and neutrophil infiltration into the tumor microenvironment, leading to complete regression of both immunogenic and non-immunogenic tumors independently of T cells; intratumoral siKDELR2 delivered by lipid nanoparticles recapitulates this effect.\",\n      \"method\": \"siRNA knockdown (in vivo lipid nanoparticle delivery), tumor regression assays, immune cell infiltration analysis, T cell depletion experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 — in vivo functional data with mechanistic immune readouts, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.08.07.669177\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"KDELR2 is a seven-transmembrane KDEL-motif receptor at the cis-Golgi that recognizes escaped ER-resident proteins (such as HSP47, GRP78/BiP, and calnexin) and mediates their COPI-dependent retrograde retrieval to the ER; its overexpression collapses Golgi structure and blocks anterograde traffic (BFA-like phenotype), its loss prevents HSP47 recycling causing it to remain bound to extracellular collagen and disrupt fibril formation (leading to osteogenesis imperfecta), and it is transcriptionally regulated by HDAC3/CREB1 and HIF1α; beyond its canonical retrieval function, KDELR2 has been shown to protect the centrosomal protein POC5 from degradation, enhance Golgi-mediated MMP secretion to drive cancer invasion, and modulate ER stress (CHOP/JNK/p38) and Wnt (GSK3β/β-catenin) signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KDELR2 is a seven-transmembrane receptor at the cis-Golgi that retrieves escaped ER-resident chaperones bearing KDEL motifs via COPI-dependent retrograde transport, thereby maintaining ER proteostasis and governing Golgi organization. Overexpression of KDELR2 redistributes β-COP to the cytosol and collapses Golgi structure into the ER, blocking anterograde traffic [PMID:1316805], while its loss prevents retrograde recycling of the collagen chaperone HSP47, causing HSP47 to persist on extracellular collagen fibrils and disrupt fibrillogenesis, resulting in osteogenesis imperfecta [PMID:33053334]. KDELR2 also retains ER chaperones calnexin and GRP78/BiP, limiting their availability for viral glycoprotein folding [PMID:30621148], and its depletion activates ER stress effectors CHOP, JNK, and p38 leading to apoptosis [PMID:35116653]. Beyond ER quality control, KDELR2 enhances Golgi-mediated MMP secretion to promote cancer cell invasion [PMID:32753652] and is transcriptionally regulated by HDAC3/CREB1 and HIF1α [PMID:34146461, PMID:31342232].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"It was unknown whether additional KDEL receptors existed or how they influenced Golgi-to-ER traffic; overexpression of the novel KDELR2 (ELP-1) showed it could redistribute β-COP and collapse the Golgi into the ER, establishing KDELR2 as a bona fide retrograde trafficking regulator.\",\n      \"evidence\": \"Overexpression in multiple cell types with immunofluorescence, subcellular fractionation, and glycosylation assays\",\n      \"pmids\": [\"1316805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Endogenous cargo specificity of KDELR2 versus KDELR1 was not resolved\",\n        \"Structural basis of KDEL peptide recognition by KDELR2 was unknown\",\n        \"Physiological consequence of KDELR2 loss of function was not tested\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"It was unclear what regulated KDELR2 expression; ChIP-qPCR and luciferase assays showed HIF1α directly binds the KDELR2 promoter, and separately, overexpression/silencing experiments demonstrated KDELR2 retains ER chaperones calnexin and GRP78, limiting their availability for measles virus glycoprotein folding.\",\n      \"evidence\": \"ChIP-qPCR and luciferase reporter (glioblastoma cells); co-immunoprecipitation and viral titer assays (Vero and T cells)\",\n      \"pmids\": [\"31342232\", \"30621148\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether HIF1α-driven KDELR2 upregulation is sufficient to alter ER proteostasis in hypoxia was not tested\",\n        \"Direct binding of KDELR2 to calnexin or GRP78 KDEL motifs was not demonstrated biochemically\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The physiological consequence of KDELR2 loss was unknown; patient-derived loss-of-function KDELR2 variants were shown to prevent HSP47 retrograde retrieval, causing extracellular HSP47-collagen retention and defective fibrillogenesis, establishing KDELR2 mutations as a cause of osteogenesis imperfecta.\",\n      \"evidence\": \"Patient fibroblast analysis, crystal structure mapping of OI variants onto KDELR2 structure, co-immunoprecipitation, collagen secretion assays\",\n      \"pmids\": [\"33053334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether KDELR1 or KDELR3 can partially compensate for KDELR2 in HSP47 retrieval was not resolved\",\n        \"Full atomic structure of human KDELR2 bound to HSP47 KDEL peptide was not determined\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether KDELR2 influenced secretory cargo beyond ER-resident proteins was unknown; a gain-of-function invasion screen identified KDELR2 as a driver of lung cancer metastasis through enhanced Golgi-mediated MMP secretion, establishing a pro-invasive function.\",\n      \"evidence\": \"Unbiased invasion screen, in vitro and in vivo metastasis assays, MMP inhibitor rescue\",\n      \"pmids\": [\"32753652\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The mechanism by which KDELR2 enhances anterograde MMP secretion from the Golgi was not defined\",\n        \"Whether this reflects altered COPI vesicle dynamics or a separate signaling function was not distinguished\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"How KDELR2 expression is controlled and whether it has non-canonical functions beyond cargo retrieval was unresolved; HDAC3/CREB1 was shown to transcriptionally activate KDELR2, and KDELR2 was found to protect the centrosomal protein POC5 from proteasomal degradation, accelerating cell cycle progression.\",\n      \"evidence\": \"ChIP assay (CREB1-KDELR2 promoter), co-immunoprecipitation (KDELR2–POC5), cell cycle analysis, in vivo breast cancer model\",\n      \"pmids\": [\"34146461\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How a Golgi-localized receptor protects a centrosomal protein from degradation is mechanistically unexplained\",\n        \"Whether KDELR2-POC5 interaction is direct or mediated through an adaptor was not established\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Whether KDELR2 depletion triggers ER stress was unknown; knockdown activated CHOP, phospho-JNK, and phospho-p38, leading to apoptosis that synergized with temozolomide in glioma cells, linking KDELR2 to ER stress suppression.\",\n      \"evidence\": \"siRNA knockdown, Western blot for multiple UPR and MAPK markers, flow cytometry for apoptosis\",\n      \"pmids\": [\"35116653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether ER stress results from general chaperone mislocalization or a specific KDELR2-dependent signal was not resolved\",\n        \"Synergy with temozolomide was shown only in one glioma cell line\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Broader physiological roles of KDELR2 outside cancer remained unclear; KDELR2 was shown to promote osteogenic differentiation via GSK3β/β-catenin activation and to be required for MUC5AC hypersecretion in COPD airways downstream of ATF6 and IRE1α/XBP-1s.\",\n      \"evidence\": \"Overexpression/knockdown in mesenchymal stem cells and fracture model; siRNA and IRE1α inhibitor in COPD rat model\",\n      \"pmids\": [\"38470494\", \"39365189\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"GSK3β/β-catenin activation by KDELR2 is correlative; direct mechanistic link is not established\",\n        \"Whether KDELR2 role in MUC5AC secretion reflects canonical retrieval function or a distinct secretory pathway remains unknown\",\n        \"Both findings are from single laboratories without independent replication\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how KDELR2's canonical retrograde retrieval activity relates to its reported non-canonical roles in MMP secretion, centrosomal protein stabilization, and Wnt signaling — specifically whether these functions reflect a unified COPI-dependent mechanism, Golgi-localized signaling, or independent activities.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of human KDELR2 with bound KDEL peptide exists\",\n        \"Functional redundancy among KDELR1, KDELR2, and KDELR3 is poorly characterized\",\n        \"The mechanism coupling KDELR2 to anterograde secretory cargo (MMPs, MUC5AC) is undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"HSP47\",\n      \"GRP78\",\n      \"POC5\",\n      \"CREB1\",\n      \"HDAC3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}