{"gene":"PCDH9","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":1998,"finding":"PCDH9 was identified as a novel protocadherin (calcium-dependent cell-cell adhesion protein) in the cadherin superfamily, predominantly expressed in brain with broader tissue expression than PCDH8, and with developmentally regulated expression patterns.","method":"Genomic cloning and characterization, expression analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — foundational molecular characterization by cloning and expression profiling, single study","pmids":["9787079"],"is_preprint":false},{"year":2013,"finding":"Restoration of PCDH9 expression in glioma cell lines (U87, U251) reduced tumor cell viability, induced apoptosis, caused G0/G1 cell cycle arrest, and suppressed colony formation and invasion; molecularly, PCDH9 upregulated Bax and downregulated Bcl-2 and cyclin D1.","method":"Lentiviral PCDH9 re-expression in glioma cell lines with cell viability, apoptosis, cell cycle, and invasion assays; Western blot for Bax, Bcl-2, cyclin D1","journal":"Journal of molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — clean gain-of-function with defined molecular readouts, single lab","pmids":["24214103"],"is_preprint":false},{"year":2015,"finding":"Pcdh9 knockout mice exhibit specific long-term social and object recognition deficits, sensorimotor developmental impairments, and structural changes in deep layers of sensory cortices where Pcdh9 is selectively expressed, establishing a role for Pcdh9 in sensory cortex development and cognitive memory functions.","method":"Chromosome substitution strain QTL mapping followed by Pcdh9 knockout mouse generation; behavioral (recognition, rotarod, sensory gating) and neuroanatomical assessments","journal":"Biological psychiatry","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO with multiple behavioral readouts and brain morphology analysis, replicated with QTL mapping","pmids":["25802080"],"is_preprint":false},{"year":2017,"finding":"Restored PCDH9 expression in hepatocellular carcinoma (HCC) cell lines inhibited tumor cell proliferation and xenograft tumor formation, and induced cell cycle arrest at G0/G1 phase; PCDH9 promoter is frequently methylated in primary HCC tissues, and its expression is restored by the DNA demethylation reagent 5-azacytidine.","method":"PCDH9 re-expression in HCC cell lines, xenograft assay, promoter methylation analysis, 5-azacytidine treatment, cell cycle analysis","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function with xenograft and cell cycle readouts plus epigenetic mechanism, single lab","pmids":["28791409"],"is_preprint":false},{"year":2017,"finding":"miR-215-5p dually inhibits PCDH9 expression in glioma by binding to both the promoter and 3'UTR of PCDH9, reducing PCDH9 mRNA and protein levels, thereby increasing glioma cell proliferation, clone formation, and in vitro migration while reducing apoptosis.","method":"miRNA overexpression, luciferase reporter assay for promoter and 3'UTR binding, RT-PCR, Western blot, cell proliferation and migration assays","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — luciferase reporter validation of dual binding sites plus functional rescue, single lab","pmids":["28055966"],"is_preprint":false},{"year":2019,"finding":"miR-200a-3p binds the 3'UTR of PCDH9 and decreases PCDH9 expression in ovarian cancer cells, promoting proliferation, colony formation, and invasion; restored PCDH9 expression inhibited the pro-proliferative effect of miR-200a-3p.","method":"Luciferase reporter assay for 3'UTR binding, RT-qPCR, Western blot, cell proliferation, colony formation, and invasion assays, rescue experiment","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 2 — luciferase validation of miRNA-target interaction plus functional rescue, single lab","pmids":["31632082"],"is_preprint":false},{"year":2022,"finding":"COP1 (RFWD2), a RING-finger E3 ubiquitin ligase, interacts with PCDH9 and promotes its Lys48-linked polyubiquitination and proteasomal degradation in glioma cells; COP1 protein level is inversely correlated with PCDH9 protein level in human glioma tissues.","method":"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescent co-localization, ubiquitination assay with K48-linkage specificity, proteasome inhibitor treatment","journal":"Molecular neurobiology","confidence":"High","confidence_rationale":"Tier 1–2 — yeast two-hybrid discovery confirmed by reciprocal Co-IP, ubiquitination assay with linkage specificity, and in vivo correlation","pmids":["35084653"],"is_preprint":false},{"year":2022,"finding":"PCDH9 overexpression in melanoma suppressed cell proliferation, invasion, and promoted apoptosis; overexpression downregulated RAC1, MMP2, and MMP9, and upregulated Pyk2 and Cyclin D1. PCDH9 knockdown had the opposite effects in vitro and promoted tumor growth in vivo.","method":"Lentiviral overexpression and knockdown in melanoma cell lines, PCR, Western blot, in vivo xenograft, circ_0084043-miR-134-5p sponging validated by dual-luciferase reporter","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — loss- and gain-of-function with defined molecular targets in vitro and in vivo, single lab","pmids":["36387162"],"is_preprint":false},{"year":2024,"finding":"PCDH9 undergoes proteolytic cleavage in gastric cancer cells; the intracellular domain (ICD) translocates to the nucleus where it interacts with DNA methyltransferase 1 (DNMT1) and increases DNMT1 activity, leading to hypermethylation of the CDH2 (N-cadherin) promoter and reduced CDH2 expression, thereby suppressing gastric cancer cell migration and in vivo metastasis.","method":"Subcellular fractionation, co-immunoprecipitation of PCDH9 ICD with DNMT1, DNMT1 activity assay, bisulfite sequencing of CDH2 promoter, migration and metastasis assays in vitro and in vivo","journal":"iScience","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (Co-IP, enzymatic activity assay, bisulfite sequencing, in vivo metastasis) establishing mechanistic pathway, single study","pmids":["38357662"],"is_preprint":false},{"year":2024,"finding":"Pcdh9 localizes predominantly at glutamatergic synapses in mouse hippocampus, with expression peaking in the first postnatal week. Pcdh9 KO neurons exhibit oversized presynaptic terminals and postsynaptic densities (PSD) in CA1, upregulation of synaptic genes (snRNA-seq), dysregulation of the SHANK2/CORTACTIN pathway, increased mEPSC amplitude, and reduced hippocampal network activity.","method":"Immunofluorescence localization, electron microscopy (ultrastructural analysis), single-nucleus RNA-seq, patch-clamp electrophysiology, biochemical pathway analysis in Pcdh9 KO mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1–2 — comprehensive multi-method study (EM ultrastructure, snRNA-seq, electrophysiology, biochemistry) in KO model","pmids":["39557582"],"is_preprint":false},{"year":2026,"finding":"Neuronal activity triggers MMP-dependent cleavage of PCDH9 at the synapse, generating a C-terminal fragment (CTF) that translocates to the nucleus; CTF overexpression promotes dendritic growth, increases spine density, and strengthens excitatory synaptic transmission, establishing an activity-dependent signaling role for PCDH9 linking synaptic activity to structural remodeling.","method":"Biochemical fractionation, MMP inhibitor treatment, immunohistochemistry in neuronal cultures, CTF overexpression with morphological and electrophysiological readouts","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemistry, pharmacological inhibition, functional overexpression), single lab","pmids":["41685090"],"is_preprint":false},{"year":2026,"finding":"RNF145, an E3 ubiquitin ligase upregulated in hepatocellular carcinoma, promotes HCC metastasis by ubiquitinating and degrading PCDH9; RNF145 knockdown abolished migratory and invasive capacities of HCC cells.","method":"Protein immunoprecipitation, Western blot, transwell migration and wound-healing assays, RNF145 knockdown","journal":"Oncology research","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus functional knockdown with defined cellular phenotype, single lab","pmids":["41613811"],"is_preprint":false}],"current_model":"PCDH9 is a δ1-protocadherin that functions at glutamatergic synapses to regulate synapse morphology and hippocampal network activity; it undergoes MMP-dependent activity-driven cleavage with nuclear translocation of its intracellular domain, where it modulates gene expression (e.g., suppressing CDH2 via DNMT1 activation), and is subject to proteasomal degradation via COP1- and RNF145-mediated Lys48-linked ubiquitination, while its promoter is epigenetically silenced by methylation and its mRNA repressed by multiple miRNAs, collectively establishing PCDH9 as a context-dependent tumor suppressor and synaptic organizer with dual extracellular adhesion and intracellular signaling functions."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing PCDH9 as a novel brain-enriched protocadherin resolved its identity within the cadherin superfamily and revealed developmentally regulated expression, setting the stage for functional studies.","evidence":"Genomic cloning, expression profiling across tissues and developmental stages","pmids":["9787079"],"confidence":"Medium","gaps":["No functional data; expression pattern alone does not establish mechanism","Protein-level validation not performed","No loss-of-function or gain-of-function experiments"]},{"year":2013,"claim":"Demonstrating that PCDH9 re-expression suppresses glioma cell viability, induces apoptosis, and arrests the cell cycle established PCDH9 as a candidate tumor suppressor and identified Bax/Bcl-2/cyclin D1 as downstream effectors.","evidence":"Lentiviral PCDH9 re-expression in U87/U251 glioma lines with viability, apoptosis, cell cycle, and invasion assays; Western blot","pmids":["24214103"],"confidence":"Medium","gaps":["Single lab, no in vivo validation","Direct versus indirect regulation of Bax/Bcl-2 not distinguished","Mechanism linking a cell-adhesion molecule to apoptotic signaling unknown"]},{"year":2015,"claim":"Pcdh9 knockout mice revealed that the gene is required for normal sensory cortex development and cognitive memory, providing the first in vivo loss-of-function evidence for a non-redundant neurological role.","evidence":"Pcdh9 KO mice generated via QTL-guided targeting; behavioral testing (social/object recognition, rotarod, sensory gating) and neuroanatomical analysis","pmids":["25802080"],"confidence":"High","gaps":["Synaptic and circuit-level mechanisms underlying behavioral deficits unresolved","Contribution of cell-autonomous versus non-autonomous functions unknown","No electrophysiological characterization"]},{"year":2017,"claim":"Discovery that the PCDH9 promoter is silenced by DNA methylation in HCC and that miR-215-5p represses PCDH9 via both promoter and 3′UTR binding in glioma established convergent epigenetic and post-transcriptional mechanisms for PCDH9 downregulation in cancer.","evidence":"Promoter methylation analysis and 5-azacytidine rescue in HCC; dual-luciferase reporter assays confirming miR-215-5p binding to PCDH9 promoter and 3′UTR in glioma","pmids":["28791409","28055966"],"confidence":"Medium","gaps":["Whether promoter methylation and miRNA repression act cooperatively in the same tumor type untested","Upstream signals driving methylation not identified","In vivo validation of miRNA-mediated repression lacking"]},{"year":2022,"claim":"Identification of COP1 as an E3 ligase that mediates Lys48-linked polyubiquitination and proteasomal degradation of PCDH9 revealed a post-translational mechanism controlling PCDH9 protein turnover in glioma.","evidence":"Yeast two-hybrid screen, reciprocal co-immunoprecipitation, K48-linkage-specific ubiquitination assay, proteasome inhibitor rescue, clinical correlation in glioma tissues","pmids":["35084653"],"confidence":"High","gaps":["Degron motif on PCDH9 recognized by COP1 not mapped","Whether COP1-mediated degradation occurs in neurons unknown","Relationship to PCDH9 cleavage-dependent signaling unaddressed"]},{"year":2024,"claim":"Demonstrating that the PCDH9 intracellular domain translocates to the nucleus and activates DNMT1 to silence CDH2 by promoter hypermethylation established a direct signaling pathway from PCDH9 cleavage to transcriptional reprogramming that suppresses metastasis.","evidence":"Subcellular fractionation, co-immunoprecipitation of ICD with DNMT1, DNMT1 activity assay, bisulfite sequencing of CDH2 promoter, in vivo metastasis assay in gastric cancer models","pmids":["38357662"],"confidence":"High","gaps":["Protease responsible for ICD release not identified in this study","Whether DNMT1 interaction occurs in neurons not tested","Genome-wide targets of PCDH9-ICD/DNMT1 beyond CDH2 unknown"]},{"year":2024,"claim":"Comprehensive characterization of Pcdh9 KO hippocampus resolved the synaptic phenotype: PCDH9 localizes to glutamatergic synapses and constrains synapse ultrastructure, with its loss causing enlarged synapses, increased mEPSC amplitude, reduced network activity, and SHANK2/CORTACTIN pathway dysregulation.","evidence":"Immunofluorescence, electron microscopy, single-nucleus RNA-seq, patch-clamp electrophysiology, and biochemical analysis in Pcdh9 KO mice","pmids":["39557582"],"confidence":"High","gaps":["Whether PCDH9 acts trans-synaptically or cell-autonomously at the synapse not fully resolved","Binding partner on the presynaptic side unknown","Rescue experiments to confirm cell-autonomy not performed"]},{"year":2026,"claim":"Identification of MMP-dependent, activity-triggered cleavage of PCDH9 at synapses, with the resulting CTF promoting dendritic growth and spine density, unified the proteolytic processing observed in cancer with a physiological activity-dependent signaling function in neurons.","evidence":"Biochemical fractionation, MMP inhibitor treatment, CTF overexpression with morphological and electrophysiological readouts in neuronal cultures","pmids":["41685090"],"confidence":"Medium","gaps":["Specific MMP isoform responsible not identified","Whether CTF nuclear targets in neurons overlap with DNMT1/CDH2 pathway unknown","Single lab; independent replication needed"]},{"year":2026,"claim":"RNF145 was identified as a second E3 ubiquitin ligase that ubiquitinates and degrades PCDH9 in hepatocellular carcinoma, providing a cancer-type-specific post-translational silencing mechanism.","evidence":"Co-immunoprecipitation, Western blot, transwell migration and wound-healing assays with RNF145 knockdown in HCC cells","pmids":["41613811"],"confidence":"Medium","gaps":["Ubiquitin chain linkage type not specified","Whether RNF145 and COP1 target overlapping or distinct pools of PCDH9 unknown","In vivo validation of RNF145-PCDH9 axis lacking"]},{"year":null,"claim":"Key unresolved questions include the identity of the specific extracellular binding partners of PCDH9 at synapses, the genome-wide transcriptional targets of the nuclear ICD beyond CDH2, the structural basis for PCDH9 homophilic or heterophilic interactions, and whether the ICD-DNMT1 signaling axis operates in neurons to link synaptic activity to epigenetic remodeling.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model for PCDH9 extracellular domain interactions","Genome-wide targets of ICD/DNMT1 complex not mapped","Trans-synaptic binding partner unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3,7,8]},{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,9,10]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8,10]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,9,10]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[0,8,9]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[1,7]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[6,11]}],"complexes":[],"partners":["COP1","DNMT1","RNF145","SHANK2","CORTACTIN"],"other_free_text":[]},"mechanistic_narrative":"PCDH9 is a δ1-protocadherin that functions as both a synaptic organizer in the brain and a context-dependent tumor suppressor in multiple cancer types. In the hippocampus, PCDH9 localizes to glutamatergic synapses where it constrains synapse size; Pcdh9 knockout mice display oversized presynaptic terminals and postsynaptic densities, increased mEPSC amplitude, reduced hippocampal network activity, dysregulation of the SHANK2/CORTACTIN pathway, and behavioral deficits in social and object recognition memory [PMID:39557582, PMID:25802080]. PCDH9 undergoes MMP-dependent, activity-driven proteolytic cleavage that releases its intracellular domain (ICD) for nuclear translocation, where the ICD interacts with DNMT1 to hypermethylate and silence CDH2, suppressing cell migration, and separately promotes dendritic growth and spine formation [PMID:38357662, PMID:41685090]. PCDH9 protein levels are regulated by COP1- and RNF145-mediated Lys48-linked ubiquitination and proteasomal degradation, and its expression is epigenetically silenced via promoter methylation and miRNA-mediated repression in glioma, hepatocellular carcinoma, and other cancers, where restoration of PCDH9 inhibits proliferation, invasion, and induces apoptosis [PMID:35084653, PMID:41613811, PMID:28791409, PMID:24214103]."},"prefetch_data":{"uniprot":{"accession":"Q9HC56","full_name":"Protocadherin-9","aliases":[],"length_aa":1237,"mass_kda":136.1,"function":"Potential calcium-dependent cell-adhesion protein","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9HC56/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PCDH9","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PCDH9","total_profiled":1310},"omim":[{"mim_id":"603581","title":"PROTOCADHERIN 9; PCDH9","url":"https://www.omim.org/entry/603581"},{"mim_id":"603580","title":"PROTOCADHERIN 8; PCDH8","url":"https://www.omim.org/entry/603580"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Centrosome","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":38.4}],"url":"https://www.proteinatlas.org/search/PCDH9"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9HC56","domains":[{"cath_id":"2.60.40.60","chopping":"22-132","consensus_level":"high","plddt":74.1331,"start":22,"end":132},{"cath_id":"2.60.40.60","chopping":"145-242","consensus_level":"high","plddt":89.137,"start":145,"end":242},{"cath_id":"2.60.40.60","chopping":"250-348","consensus_level":"high","plddt":90.4871,"start":250,"end":348},{"cath_id":"2.60.40.60","chopping":"356-459","consensus_level":"medium","plddt":90.9709,"start":356,"end":459},{"cath_id":"2.60.40.60","chopping":"467-562","consensus_level":"medium","plddt":92.751,"start":467,"end":562},{"cath_id":"2.60.40.60","chopping":"570-665","consensus_level":"high","plddt":91.2253,"start":570,"end":665},{"cath_id":"2.60.40.60","chopping":"673-799","consensus_level":"high","plddt":84.3947,"start":673,"end":799}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HC56","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HC56-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HC56-F1-predicted_aligned_error_v6.png","plddt_mean":67.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCDH9","jax_strain_url":"https://www.jax.org/strain/search?query=PCDH9"},"sequence":{"accession":"Q9HC56","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HC56.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HC56/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HC56"}},"corpus_meta":[{"pmid":"9787079","id":"PMC_9787079","title":"Characterization of two novel protocadherins (PCDH8 and PCDH9) localized on human chromosome 13 and mouse chromosome 14.","date":"1998","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/9787079","citation_count":68,"is_preprint":false},{"pmid":"30045829","id":"PMC_30045829","title":"Lnc-PCDH9-13:1 Is a Hypersensitive and Specific Biomarker for Early Hepatocellular Carcinoma.","date":"2018","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/30045829","citation_count":47,"is_preprint":false},{"pmid":"28990594","id":"PMC_28990594","title":"The Gene Encoding Protocadherin 9 (PCDH9), a Novel Risk Factor for Major Depressive Disorder.","date":"2017","source":"Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/28990594","citation_count":45,"is_preprint":false},{"pmid":"31632082","id":"PMC_31632082","title":"MiR-200a-3p promoted the malignant behaviors of ovarian cancer cells through regulating PCDH9.","date":"2019","source":"OncoTargets and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/31632082","citation_count":43,"is_preprint":false},{"pmid":"25802080","id":"PMC_25802080","title":"Genetic Mapping in Mice Reveals the Involvement of Pcdh9 in Long-Term Social and Object Recognition and Sensorimotor Development.","date":"2015","source":"Biological psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/25802080","citation_count":38,"is_preprint":false},{"pmid":"28055966","id":"PMC_28055966","title":"Dual inhibition of PCDH9 expression by miR-215-5p up-regulation in gliomas.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28055966","citation_count":29,"is_preprint":false},{"pmid":"28791409","id":"PMC_28791409","title":"PCDH9 acts as a tumor suppressor inducing tumor cell arrest at G0/G1 phase and is frequently methylated in hepatocellular carcinoma.","date":"2017","source":"Molecular medicine 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neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/41685090","citation_count":0,"is_preprint":false},{"pmid":"41613811","id":"PMC_41613811","title":"RNF145 Promotes Hepatocellular Carcinoma Metastasis through Ubiquitination and Degradation of PCDH9.","date":"2026","source":"Oncology research","url":"https://pubmed.ncbi.nlm.nih.gov/41613811","citation_count":0,"is_preprint":false},{"pmid":"40060108","id":"PMC_40060108","title":"The Interaction Between Family Functioning and the PCDH9 rs9540720 Polymorphism on Major Depressive Disorder in Chinese Freshmen.","date":"2025","source":"Psychology research and behavior management","url":"https://pubmed.ncbi.nlm.nih.gov/40060108","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14444,"output_tokens":3030,"usd":0.044391},"stage2":{"model":"claude-opus-4-6","input_tokens":6382,"output_tokens":2835,"usd":0.154177},"total_usd":0.198568,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"PCDH9 was identified as a novel protocadherin (calcium-dependent cell-cell adhesion protein) in the cadherin superfamily, predominantly expressed in brain with broader tissue expression than PCDH8, and with developmentally regulated expression patterns.\",\n      \"method\": \"Genomic cloning and characterization, expression analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — foundational molecular characterization by cloning and expression profiling, single study\",\n      \"pmids\": [\"9787079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Restoration of PCDH9 expression in glioma cell lines (U87, U251) reduced tumor cell viability, induced apoptosis, caused G0/G1 cell cycle arrest, and suppressed colony formation and invasion; molecularly, PCDH9 upregulated Bax and downregulated Bcl-2 and cyclin D1.\",\n      \"method\": \"Lentiviral PCDH9 re-expression in glioma cell lines with cell viability, apoptosis, cell cycle, and invasion assays; Western blot for Bax, Bcl-2, cyclin D1\",\n      \"journal\": \"Journal of molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean gain-of-function with defined molecular readouts, single lab\",\n      \"pmids\": [\"24214103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Pcdh9 knockout mice exhibit specific long-term social and object recognition deficits, sensorimotor developmental impairments, and structural changes in deep layers of sensory cortices where Pcdh9 is selectively expressed, establishing a role for Pcdh9 in sensory cortex development and cognitive memory functions.\",\n      \"method\": \"Chromosome substitution strain QTL mapping followed by Pcdh9 knockout mouse generation; behavioral (recognition, rotarod, sensory gating) and neuroanatomical assessments\",\n      \"journal\": \"Biological psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with multiple behavioral readouts and brain morphology analysis, replicated with QTL mapping\",\n      \"pmids\": [\"25802080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Restored PCDH9 expression in hepatocellular carcinoma (HCC) cell lines inhibited tumor cell proliferation and xenograft tumor formation, and induced cell cycle arrest at G0/G1 phase; PCDH9 promoter is frequently methylated in primary HCC tissues, and its expression is restored by the DNA demethylation reagent 5-azacytidine.\",\n      \"method\": \"PCDH9 re-expression in HCC cell lines, xenograft assay, promoter methylation analysis, 5-azacytidine treatment, cell cycle analysis\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with xenograft and cell cycle readouts plus epigenetic mechanism, single lab\",\n      \"pmids\": [\"28791409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"miR-215-5p dually inhibits PCDH9 expression in glioma by binding to both the promoter and 3'UTR of PCDH9, reducing PCDH9 mRNA and protein levels, thereby increasing glioma cell proliferation, clone formation, and in vitro migration while reducing apoptosis.\",\n      \"method\": \"miRNA overexpression, luciferase reporter assay for promoter and 3'UTR binding, RT-PCR, Western blot, cell proliferation and migration assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase reporter validation of dual binding sites plus functional rescue, single lab\",\n      \"pmids\": [\"28055966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"miR-200a-3p binds the 3'UTR of PCDH9 and decreases PCDH9 expression in ovarian cancer cells, promoting proliferation, colony formation, and invasion; restored PCDH9 expression inhibited the pro-proliferative effect of miR-200a-3p.\",\n      \"method\": \"Luciferase reporter assay for 3'UTR binding, RT-qPCR, Western blot, cell proliferation, colony formation, and invasion assays, rescue experiment\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase validation of miRNA-target interaction plus functional rescue, single lab\",\n      \"pmids\": [\"31632082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"COP1 (RFWD2), a RING-finger E3 ubiquitin ligase, interacts with PCDH9 and promotes its Lys48-linked polyubiquitination and proteasomal degradation in glioma cells; COP1 protein level is inversely correlated with PCDH9 protein level in human glioma tissues.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescent co-localization, ubiquitination assay with K48-linkage specificity, proteasome inhibitor treatment\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — yeast two-hybrid discovery confirmed by reciprocal Co-IP, ubiquitination assay with linkage specificity, and in vivo correlation\",\n      \"pmids\": [\"35084653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PCDH9 overexpression in melanoma suppressed cell proliferation, invasion, and promoted apoptosis; overexpression downregulated RAC1, MMP2, and MMP9, and upregulated Pyk2 and Cyclin D1. PCDH9 knockdown had the opposite effects in vitro and promoted tumor growth in vivo.\",\n      \"method\": \"Lentiviral overexpression and knockdown in melanoma cell lines, PCR, Western blot, in vivo xenograft, circ_0084043-miR-134-5p sponging validated by dual-luciferase reporter\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss- and gain-of-function with defined molecular targets in vitro and in vivo, single lab\",\n      \"pmids\": [\"36387162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCDH9 undergoes proteolytic cleavage in gastric cancer cells; the intracellular domain (ICD) translocates to the nucleus where it interacts with DNA methyltransferase 1 (DNMT1) and increases DNMT1 activity, leading to hypermethylation of the CDH2 (N-cadherin) promoter and reduced CDH2 expression, thereby suppressing gastric cancer cell migration and in vivo metastasis.\",\n      \"method\": \"Subcellular fractionation, co-immunoprecipitation of PCDH9 ICD with DNMT1, DNMT1 activity assay, bisulfite sequencing of CDH2 promoter, migration and metastasis assays in vitro and in vivo\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (Co-IP, enzymatic activity assay, bisulfite sequencing, in vivo metastasis) establishing mechanistic pathway, single study\",\n      \"pmids\": [\"38357662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Pcdh9 localizes predominantly at glutamatergic synapses in mouse hippocampus, with expression peaking in the first postnatal week. Pcdh9 KO neurons exhibit oversized presynaptic terminals and postsynaptic densities (PSD) in CA1, upregulation of synaptic genes (snRNA-seq), dysregulation of the SHANK2/CORTACTIN pathway, increased mEPSC amplitude, and reduced hippocampal network activity.\",\n      \"method\": \"Immunofluorescence localization, electron microscopy (ultrastructural analysis), single-nucleus RNA-seq, patch-clamp electrophysiology, biochemical pathway analysis in Pcdh9 KO mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — comprehensive multi-method study (EM ultrastructure, snRNA-seq, electrophysiology, biochemistry) in KO model\",\n      \"pmids\": [\"39557582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Neuronal activity triggers MMP-dependent cleavage of PCDH9 at the synapse, generating a C-terminal fragment (CTF) that translocates to the nucleus; CTF overexpression promotes dendritic growth, increases spine density, and strengthens excitatory synaptic transmission, establishing an activity-dependent signaling role for PCDH9 linking synaptic activity to structural remodeling.\",\n      \"method\": \"Biochemical fractionation, MMP inhibitor treatment, immunohistochemistry in neuronal cultures, CTF overexpression with morphological and electrophysiological readouts\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemistry, pharmacological inhibition, functional overexpression), single lab\",\n      \"pmids\": [\"41685090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"RNF145, an E3 ubiquitin ligase upregulated in hepatocellular carcinoma, promotes HCC metastasis by ubiquitinating and degrading PCDH9; RNF145 knockdown abolished migratory and invasive capacities of HCC cells.\",\n      \"method\": \"Protein immunoprecipitation, Western blot, transwell migration and wound-healing assays, RNF145 knockdown\",\n      \"journal\": \"Oncology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional knockdown with defined cellular phenotype, single lab\",\n      \"pmids\": [\"41613811\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCDH9 is a δ1-protocadherin that functions at glutamatergic synapses to regulate synapse morphology and hippocampal network activity; it undergoes MMP-dependent activity-driven cleavage with nuclear translocation of its intracellular domain, where it modulates gene expression (e.g., suppressing CDH2 via DNMT1 activation), and is subject to proteasomal degradation via COP1- and RNF145-mediated Lys48-linked ubiquitination, while its promoter is epigenetically silenced by methylation and its mRNA repressed by multiple miRNAs, collectively establishing PCDH9 as a context-dependent tumor suppressor and synaptic organizer with dual extracellular adhesion and intracellular signaling functions.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PCDH9 is a δ1-protocadherin that functions as both a synaptic organizer in the brain and a context-dependent tumor suppressor in multiple cancer types. In the hippocampus, PCDH9 localizes to glutamatergic synapses where it constrains synapse size; Pcdh9 knockout mice display oversized presynaptic terminals and postsynaptic densities, increased mEPSC amplitude, reduced hippocampal network activity, dysregulation of the SHANK2/CORTACTIN pathway, and behavioral deficits in social and object recognition memory [PMID:39557582, PMID:25802080]. PCDH9 undergoes MMP-dependent, activity-driven proteolytic cleavage that releases its intracellular domain (ICD) for nuclear translocation, where the ICD interacts with DNMT1 to hypermethylate and silence CDH2, suppressing cell migration, and separately promotes dendritic growth and spine formation [PMID:38357662, PMID:41685090]. PCDH9 protein levels are regulated by COP1- and RNF145-mediated Lys48-linked ubiquitination and proteasomal degradation, and its expression is epigenetically silenced via promoter methylation and miRNA-mediated repression in glioma, hepatocellular carcinoma, and other cancers, where restoration of PCDH9 inhibits proliferation, invasion, and induces apoptosis [PMID:35084653, PMID:41613811, PMID:28791409, PMID:24214103].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing PCDH9 as a novel brain-enriched protocadherin resolved its identity within the cadherin superfamily and revealed developmentally regulated expression, setting the stage for functional studies.\",\n      \"evidence\": \"Genomic cloning, expression profiling across tissues and developmental stages\",\n      \"pmids\": [\"9787079\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional data; expression pattern alone does not establish mechanism\", \"Protein-level validation not performed\", \"No loss-of-function or gain-of-function experiments\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that PCDH9 re-expression suppresses glioma cell viability, induces apoptosis, and arrests the cell cycle established PCDH9 as a candidate tumor suppressor and identified Bax/Bcl-2/cyclin D1 as downstream effectors.\",\n      \"evidence\": \"Lentiviral PCDH9 re-expression in U87/U251 glioma lines with viability, apoptosis, cell cycle, and invasion assays; Western blot\",\n      \"pmids\": [\"24214103\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, no in vivo validation\", \"Direct versus indirect regulation of Bax/Bcl-2 not distinguished\", \"Mechanism linking a cell-adhesion molecule to apoptotic signaling unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Pcdh9 knockout mice revealed that the gene is required for normal sensory cortex development and cognitive memory, providing the first in vivo loss-of-function evidence for a non-redundant neurological role.\",\n      \"evidence\": \"Pcdh9 KO mice generated via QTL-guided targeting; behavioral testing (social/object recognition, rotarod, sensory gating) and neuroanatomical analysis\",\n      \"pmids\": [\"25802080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Synaptic and circuit-level mechanisms underlying behavioral deficits unresolved\", \"Contribution of cell-autonomous versus non-autonomous functions unknown\", \"No electrophysiological characterization\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that the PCDH9 promoter is silenced by DNA methylation in HCC and that miR-215-5p represses PCDH9 via both promoter and 3′UTR binding in glioma established convergent epigenetic and post-transcriptional mechanisms for PCDH9 downregulation in cancer.\",\n      \"evidence\": \"Promoter methylation analysis and 5-azacytidine rescue in HCC; dual-luciferase reporter assays confirming miR-215-5p binding to PCDH9 promoter and 3′UTR in glioma\",\n      \"pmids\": [\"28791409\", \"28055966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether promoter methylation and miRNA repression act cooperatively in the same tumor type untested\", \"Upstream signals driving methylation not identified\", \"In vivo validation of miRNA-mediated repression lacking\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of COP1 as an E3 ligase that mediates Lys48-linked polyubiquitination and proteasomal degradation of PCDH9 revealed a post-translational mechanism controlling PCDH9 protein turnover in glioma.\",\n      \"evidence\": \"Yeast two-hybrid screen, reciprocal co-immunoprecipitation, K48-linkage-specific ubiquitination assay, proteasome inhibitor rescue, clinical correlation in glioma tissues\",\n      \"pmids\": [\"35084653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degron motif on PCDH9 recognized by COP1 not mapped\", \"Whether COP1-mediated degradation occurs in neurons unknown\", \"Relationship to PCDH9 cleavage-dependent signaling unaddressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrating that the PCDH9 intracellular domain translocates to the nucleus and activates DNMT1 to silence CDH2 by promoter hypermethylation established a direct signaling pathway from PCDH9 cleavage to transcriptional reprogramming that suppresses metastasis.\",\n      \"evidence\": \"Subcellular fractionation, co-immunoprecipitation of ICD with DNMT1, DNMT1 activity assay, bisulfite sequencing of CDH2 promoter, in vivo metastasis assay in gastric cancer models\",\n      \"pmids\": [\"38357662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Protease responsible for ICD release not identified in this study\", \"Whether DNMT1 interaction occurs in neurons not tested\", \"Genome-wide targets of PCDH9-ICD/DNMT1 beyond CDH2 unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Comprehensive characterization of Pcdh9 KO hippocampus resolved the synaptic phenotype: PCDH9 localizes to glutamatergic synapses and constrains synapse ultrastructure, with its loss causing enlarged synapses, increased mEPSC amplitude, reduced network activity, and SHANK2/CORTACTIN pathway dysregulation.\",\n      \"evidence\": \"Immunofluorescence, electron microscopy, single-nucleus RNA-seq, patch-clamp electrophysiology, and biochemical analysis in Pcdh9 KO mice\",\n      \"pmids\": [\"39557582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PCDH9 acts trans-synaptically or cell-autonomously at the synapse not fully resolved\", \"Binding partner on the presynaptic side unknown\", \"Rescue experiments to confirm cell-autonomy not performed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of MMP-dependent, activity-triggered cleavage of PCDH9 at synapses, with the resulting CTF promoting dendritic growth and spine density, unified the proteolytic processing observed in cancer with a physiological activity-dependent signaling function in neurons.\",\n      \"evidence\": \"Biochemical fractionation, MMP inhibitor treatment, CTF overexpression with morphological and electrophysiological readouts in neuronal cultures\",\n      \"pmids\": [\"41685090\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific MMP isoform responsible not identified\", \"Whether CTF nuclear targets in neurons overlap with DNMT1/CDH2 pathway unknown\", \"Single lab; independent replication needed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"RNF145 was identified as a second E3 ubiquitin ligase that ubiquitinates and degrades PCDH9 in hepatocellular carcinoma, providing a cancer-type-specific post-translational silencing mechanism.\",\n      \"evidence\": \"Co-immunoprecipitation, Western blot, transwell migration and wound-healing assays with RNF145 knockdown in HCC cells\",\n      \"pmids\": [\"41613811\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin chain linkage type not specified\", \"Whether RNF145 and COP1 target overlapping or distinct pools of PCDH9 unknown\", \"In vivo validation of RNF145-PCDH9 axis lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the specific extracellular binding partners of PCDH9 at synapses, the genome-wide transcriptional targets of the nuclear ICD beyond CDH2, the structural basis for PCDH9 homophilic or heterophilic interactions, and whether the ICD-DNMT1 signaling axis operates in neurons to link synaptic activity to epigenetic remodeling.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model for PCDH9 extracellular domain interactions\", \"Genome-wide targets of ICD/DNMT1 complex not mapped\", \"Trans-synaptic binding partner unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3, 7, 8]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 9, 10]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 9, 10]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [1, 7]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [6, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"COP1\",\n      \"DNMT1\",\n      \"RNF145\",\n      \"SHANK2\",\n      \"CORTACTIN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}