{"gene":"PCDH9","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1998,"finding":"PCDH9 is a member of the protocadherin subfamily of calcium-dependent cell-cell adhesion and recognition proteins. It is predominantly expressed in brain but also in a broader variety of tissues, with developmentally regulated expression patterns.","method":"Gene isolation, genomic organization analysis, expression profiling","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — foundational characterization paper with expression analysis across tissues and developmental stages, single lab","pmids":["9787079"],"is_preprint":false},{"year":2013,"finding":"Restoration of PCDH9 expression in glioma cell lines (U87 and U251) reduced tumor cell viability, induced apoptosis, caused G0/G1 cell cycle arrest, and suppressed colony formation and invasion. Molecularly, PCDH9 restoration upregulated Bax protein and downregulated Bcl-2 and cyclin D1.","method":"Lentiviral PCDH9 re-expression in glioma cell lines, cell viability assays, apoptosis assays, cell cycle analysis, invasion assays, Western blot","journal":"Journal of molecular neuroscience : MN","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — loss/gain-of-function with defined phenotypic readouts and molecular markers, single lab, multiple orthogonal methods","pmids":["24214103"],"is_preprint":false},{"year":2015,"finding":"Pcdh9 knockout mice exhibit specific long-term social and object recognition deficits, early touch-evoked biting, rotarod performance deficits, and sensory gating deficits. Structural changes were observed in deep layers of sensory cortices, where Pcdh9 is selectively expressed, implicating PCDH9 in sensory cortex development and long-term memory functions.","method":"Chromosome substitution strain QTL mapping, Pcdh9 knockout mouse generation, behavioral testing, gene expression analysis, brain morphology analysis","journal":"Biological psychiatry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO mouse with multiple defined behavioral and structural phenotypes, QTL mapping, independent orthogonal methods","pmids":["25802080"],"is_preprint":false},{"year":2017,"finding":"miR-215-5p suppresses PCDH9 expression in glioma by targeting both the promoter and 3'UTR of PCDH9 simultaneously (dual inhibition), leading to increased glioma cell proliferation, clone formation, migration, and reduced apoptosis.","method":"Luciferase reporter assays (promoter and 3'UTR), qRT-PCR, Western blot, cell proliferation, migration, and apoptosis assays in glioma cell lines","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — dual reporter assay evidence for binding sites, functional consequences shown, single lab","pmids":["28055966"],"is_preprint":false},{"year":2017,"finding":"PCDH9 promoter methylation leads to transcriptional silencing in hepatocellular carcinoma (HCC), and treatment with DNA demethylation agent 5-azacytidine restores PCDH9 expression. Restored PCDH9 expression inhibits HCC cell proliferation and xenograft tumor formation by inducing G0/G1 cell cycle arrest.","method":"Quantitative methylation analysis, 5-azacytidine treatment, PCDH9 re-expression, cell proliferation assays, xenograft tumor formation, cell cycle analysis","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epigenetic mechanism demonstrated with demethylation rescue, functional gain-of-function with defined phenotype, single lab","pmids":["28791409"],"is_preprint":false},{"year":2019,"finding":"miR-200a-3p directly binds the 3'-UTR of PCDH9 mRNA and decreases PCDH9 expression in ovarian cancer cells, thereby promoting ovarian cancer cell proliferation, colony formation, and invasion. Restoring PCDH9 expression inhibits the pro-proliferative effect of miR-200a-3p.","method":"Luciferase reporter assay (3'UTR), qRT-PCR, Western blot, cell proliferation, colony formation, invasion assays, rescue experiments","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — luciferase reporter confirms binding, rescue experiment confirms pathway position, single lab","pmids":["31632082"],"is_preprint":false},{"year":2022,"finding":"COP1 (RFWD2), a RING-finger E3 ubiquitin ligase, physically interacts with PCDH9 and promotes its Lys48-linked polyubiquitination and proteasomal degradation in glioma cells. COP1 protein levels are inversely correlated with PCDH9 protein levels in human glioma tissues.","method":"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assays, proteasome inhibitor experiments, Western blot, human glioma tissue analysis","journal":"Molecular neurobiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ubiquitination type defined (K48-linked), proteasomal degradation confirmed, discovery by yeast two-hybrid plus multiple orthogonal validations","pmids":["35084653"],"is_preprint":false},{"year":2022,"finding":"PCDH9 overexpression in melanoma inhibits cell proliferation and migration, downregulates RAC1, MMP2, and MMP9, and upregulates Pyk2 and Cyclin D1. The circ_0084043/miR-134-5p axis indirectly regulates PCDH9: circ_0084043 sponges miR-134-5p, thereby relieving miR-134-5p-mediated suppression of PCDH9. PCDH9 overexpression also inhibits melanoma tumor growth in vivo.","method":"Lentiviral overexpression/knockdown of PCDH9, proliferation/invasion/apoptosis assays, qRT-PCR, Western blot, in vivo xenograft, ceRNA luciferase reporter assays","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — functional effects shown in vitro and in vivo, ceRNA axis confirmed by reporter assay, single lab","pmids":["36387162"],"is_preprint":false},{"year":2024,"finding":"PCDH9 is cleaved in gastric cancer cells, generating an intracellular domain (ICD) that translocates to the nucleus. In the nucleus, the PCDH9 ICD interacts with DNA methyltransferase 1 (DNMT1) and increases DNMT1 activity, which leads to increased DNA methylation at the CDH2 (N-cadherin) promoter, downregulating CDH2 expression and thereby dampening gastric cancer cell migration and in vivo metastasis.","method":"Co-immunoprecipitation, nuclear fractionation, DNMT1 activity assays, DNA methylation analysis (promoter bisulfite), cell migration assays, in vivo metastasis models, correlation with patient tissue data","journal":"iScience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, enzymatic activity assay, DNA methylation mechanistic link, in vivo validation, multiple orthogonal methods in single study","pmids":["38357662"],"is_preprint":false},{"year":2024,"finding":"PCDH9 primarily localizes at glutamatergic synapses in the mouse hippocampus CA1 region, with expression peaking in the first week after birth. Pcdh9 KO neurons exhibit oversized presynaptic terminals and postsynaptic densities, widespread upregulation of synaptic genes (by snRNA-seq), dysregulation of the SHANK2/CORTACTIN pathway, increased miniature excitatory postsynaptic currents (mEPSC), and reduced network activity in CA1.","method":"Pcdh9 KO mice, electron microscopy (ultrastructural), single-nucleus RNA-seq, electrophysiology (mEPSC recordings), biochemical fractionation/localization, network activity recordings","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — KO mouse with ultrastructural, transcriptomic, electrophysiological, and biochemical multi-level characterization in one rigorous study","pmids":["39557582"],"is_preprint":false},{"year":2026,"finding":"Neuronal activity triggers Matrix Metalloprotease (MMP)-dependent cleavage of PCDH9, generating a C-terminal fragment (CTF) that translocates to the nucleus. Overexpression of the PCDH9 CTF promotes dendritic growth, increases spine density, and strengthens excitatory synaptic transmission, identifying PCDH9 CTF as an activity-dependent signaling molecule linking synaptic activity to structural and functional remodeling.","method":"Biochemical fractionation, immunohistochemistry, MMP inhibitor treatment, neuronal cultures, CTF overexpression, dendritic morphology analysis, spine density quantification, electrophysiology","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical and immunohistochemical evidence for cleavage and nuclear translocation, functional overexpression phenotype, single lab, single study","pmids":["41685090"],"is_preprint":false},{"year":2026,"finding":"RNF145, an E3 ubiquitin ligase, physically interacts with PCDH9 and promotes its ubiquitination and subsequent proteasomal degradation, thereby facilitating hepatocellular carcinoma cell migration and invasion. Knockdown of RNF145 abolishes migratory and invasive capacities of HCC cells.","method":"Co-immunoprecipitation, Western blot, ubiquitination assays, transwell migration/invasion assays, wound-healing assay, RNF145 knockdown","journal":"Oncology research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP demonstrates interaction, ubiquitination assay confirms substrate relationship, functional consequence shown with knockdown, single lab","pmids":["41613811"],"is_preprint":false}],"current_model":"PCDH9 is a δ1-protocadherin cell-adhesion molecule predominantly expressed at glutamatergic synapses in the brain, where it shapes excitatory synapse morphology (via SHANK2/CORTACTIN pathway), glutamatergic transmission, and long-term recognition memory; neuronal activity triggers MMP-dependent cleavage of PCDH9, and the resulting intracellular C-terminal fragment translocates to the nucleus where it promotes dendritic growth and spine density; in cancer contexts, PCDH9 acts as a tumor suppressor whose nuclear ICD interacts with DNMT1 to methylate and silence the CDH2 promoter, suppressing metastasis, while its protein levels are regulated by E3 ubiquitin ligases COP1 and RNF145 via Lys48-linked polyubiquitination and proteasomal degradation; additionally, PCDH9 expression is post-transcriptionally suppressed by multiple miRNAs (miR-215-5p, miR-200a-3p, miR-134-5p) and epigenetically silenced by promoter methylation in several cancers."},"narrative":{"mechanistic_narrative":"PCDH9 is a calcium-dependent protocadherin cell-adhesion molecule predominantly expressed in brain that organizes excitatory synapses and supports long-term recognition memory [PMID:9787079, PMID:25802080, PMID:39557582]. At glutamatergic synapses in hippocampal CA1, PCDH9 constrains synaptic architecture: its loss produces oversized presynaptic terminals and postsynaptic densities, dysregulates the SHANK2/CORTACTIN pathway, and increases miniature excitatory postsynaptic currents while reducing network activity [PMID:39557582]. PCDH9 also functions as a signaling receptor that is processed by regulated proteolysis—neuronal activity drives MMP-dependent cleavage of PCDH9, releasing a C-terminal/intracellular fragment that translocates to the nucleus and promotes dendritic growth, spine density, and synaptic strengthening [PMID:41685090]. In cancer, PCDH9 acts as a tumor suppressor; re-expression induces apoptosis, G0/G1 arrest, and reduced proliferation and invasion across glioma and hepatocellular carcinoma models [PMID:24214103, PMID:28791409]. Its nuclear intracellular domain interacts with DNMT1 to stimulate methylation of the CDH2 (N-cadherin) promoter, silencing CDH2 and suppressing migration and metastasis [PMID:38357662]. PCDH9 abundance is controlled by E3 ubiquitin ligases COP1/RFWD2 and RNF145, which drive its polyubiquitination and proteasomal degradation [PMID:35084653, PMID:41613811], while its expression is suppressed post-transcriptionally by multiple miRNAs and epigenetically by promoter methylation [PMID:28055966, PMID:31632082, PMID:36387162, PMID:28791409].","teleology":[{"year":1998,"claim":"Established PCDH9 as a member of the protocadherin family of calcium-dependent cell-cell adhesion proteins with brain-predominant, developmentally regulated expression, framing it as a candidate neural recognition molecule.","evidence":"Gene isolation, genomic organization, and tissue/developmental expression profiling","pmids":["9787079"],"confidence":"Medium","gaps":["No functional or mechanistic role demonstrated","Adhesion partners and homophilic/heterophilic specificity unaddressed"]},{"year":2013,"claim":"Identified a tumor-suppressor function by showing that restoring PCDH9 in glioma cells halts proliferation and invasion, opening a cancer biology axis distinct from its neural role.","evidence":"Lentiviral PCDH9 re-expression in U87/U251 glioma lines with viability, apoptosis, cell cycle, invasion, and marker Western blots","pmids":["24214103"],"confidence":"Medium","gaps":["Molecular mechanism of growth suppression not defined","Bax/Bcl-2/cyclin D1 changes correlative, not causally dissected"]},{"year":2015,"claim":"Demonstrated in vivo that PCDH9 is required for long-term social and object recognition memory and sensory cortex development, establishing its physiological neural function.","evidence":"Pcdh9 knockout mice from QTL mapping with behavioral testing and brain morphology analysis","pmids":["25802080"],"confidence":"High","gaps":["Synaptic/cellular mechanism underlying behavioral deficits not resolved at this stage","Molecular pathways downstream of PCDH9 unidentified"]},{"year":2017,"claim":"Showed that PCDH9 is silenced in cancers by two converging regulatory routes—miRNA targeting and promoter methylation—explaining how its tumor-suppressor function is lost.","evidence":"miR-215-5p dual promoter/3'UTR luciferase reporters in glioma; quantitative methylation and 5-azacytidine rescue in hepatocellular carcinoma with functional assays","pmids":["28055966","28791409"],"confidence":"Medium","gaps":["Mechanism of dual promoter+3'UTR miRNA targeting unusual and not structurally explained","Tumor-suppressor effector pathway still undefined"]},{"year":2019,"claim":"Extended the miRNA-suppression model to ovarian cancer, reinforcing post-transcriptional control of PCDH9 as a recurring oncogenic strategy.","evidence":"miR-200a-3p 3'UTR luciferase reporter, expression assays, and PCDH9-restoration rescue in ovarian cancer cells","pmids":["31632082"],"confidence":"Medium","gaps":["Single lab, single cancer type","Downstream effectors of PCDH9 in ovarian cancer not defined"]},{"year":2022,"claim":"Identified the first post-translational regulator of PCDH9 stability, COP1, defining ubiquitin-proteasome control of PCDH9 protein levels in glioma.","evidence":"Yeast two-hybrid, reciprocal Co-IP, K48-linked ubiquitination assays, proteasome inhibition, and inverse correlation in human glioma tissue","pmids":["35084653"],"confidence":"High","gaps":["Ubiquitination site(s) on PCDH9 not mapped","Whether cleavage and degradation are coupled not addressed"]},{"year":2024,"claim":"Defined the nuclear effector mechanism of PCDH9: a cleaved intracellular domain binds and activates DNMT1 to methylate and silence the CDH2 promoter, providing a molecular basis for metastasis suppression.","evidence":"Co-IP, nuclear fractionation, DNMT1 activity and promoter bisulfite assays, migration and in vivo metastasis models in gastric cancer","pmids":["38357662"],"confidence":"High","gaps":["Protease generating the cancer-context ICD not identified","Generality of CDH2 silencing across tumor types untested"]},{"year":2024,"claim":"Resolved the synaptic mechanism behind PCDH9's memory role, localizing it to glutamatergic synapses and showing it constrains synapse size and excitatory transmission via the SHANK2/CORTACTIN pathway.","evidence":"Pcdh9 KO mice with EM ultrastructure, snRNA-seq, mEPSC and network recordings, and biochemical localization in hippocampal CA1","pmids":["39557582"],"confidence":"High","gaps":["Direct biochemical link between PCDH9 and SHANK2/CORTACTIN not established","Trans-synaptic adhesion partners unidentified"]},{"year":2026,"claim":"Connected synaptic activity to nuclear signaling by showing neuronal-activity-driven MMP cleavage of PCDH9 releases a CTF that promotes dendritic and spine remodeling, unifying adhesion and intracellular signaling functions.","evidence":"Biochemical fractionation, MMP inhibitor treatment, immunohistochemistry, CTF overexpression with morphology and electrophysiology in neurons","pmids":["41685090"],"confidence":"Medium","gaps":["Specific MMP and cleavage site not identified","Nuclear targets of the neuronal CTF not defined","Relationship to the DNMT1-binding cancer ICD unclear"]},{"year":2026,"claim":"Identified a second E3 ligase, RNF145, that degrades PCDH9, linking its loss to hepatocellular carcinoma migration and invasion and broadening proteasomal control of PCDH9 across cancers.","evidence":"Co-IP, ubiquitination assays, and transwell/wound-healing assays with RNF145 knockdown in HCC cells","pmids":["41613811"],"confidence":"Medium","gaps":["Ubiquitin linkage type not specified","Whether COP1 and RNF145 act redundantly or in distinct contexts unknown"]},{"year":null,"claim":"It remains unknown which protease(s) generate the nuclear fragment in neurons versus cancer cells and whether the activity-dependent CTF and the DNMT1-binding tumor-suppressor ICD are the same proteolytic product acting through a shared nuclear program.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Cleavage protease identity and site uncharacterized in both contexts","Trans-synaptic adhesion partner(s) of full-length PCDH9 not identified","No structural model of the ICD-DNMT1 interaction"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[8,10]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[9]},{"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":[9,2]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,8]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[8]}],"complexes":[],"partners":["DNMT1","COP1","RNF145"],"other_free_text":[]}},"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 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It is predominantly expressed in brain but also in a broader variety of tissues, with developmentally regulated expression patterns.\",\n      \"method\": \"Gene isolation, genomic organization analysis, expression profiling\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — foundational characterization paper with expression analysis across tissues and developmental stages, single lab\",\n      \"pmids\": [\"9787079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Restoration of PCDH9 expression in glioma cell lines (U87 and U251) reduced tumor cell viability, induced apoptosis, caused G0/G1 cell cycle arrest, and suppressed colony formation and invasion. Molecularly, PCDH9 restoration upregulated Bax protein and downregulated Bcl-2 and cyclin D1.\",\n      \"method\": \"Lentiviral PCDH9 re-expression in glioma cell lines, cell viability assays, apoptosis assays, cell cycle analysis, invasion assays, Western blot\",\n      \"journal\": \"Journal of molecular neuroscience : MN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — loss/gain-of-function with defined phenotypic readouts and molecular markers, single lab, multiple orthogonal methods\",\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, early touch-evoked biting, rotarod performance deficits, and sensory gating deficits. Structural changes were observed in deep layers of sensory cortices, where Pcdh9 is selectively expressed, implicating PCDH9 in sensory cortex development and long-term memory functions.\",\n      \"method\": \"Chromosome substitution strain QTL mapping, Pcdh9 knockout mouse generation, behavioral testing, gene expression analysis, brain morphology analysis\",\n      \"journal\": \"Biological psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO mouse with multiple defined behavioral and structural phenotypes, QTL mapping, independent orthogonal methods\",\n      \"pmids\": [\"25802080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"miR-215-5p suppresses PCDH9 expression in glioma by targeting both the promoter and 3'UTR of PCDH9 simultaneously (dual inhibition), leading to increased glioma cell proliferation, clone formation, migration, and reduced apoptosis.\",\n      \"method\": \"Luciferase reporter assays (promoter and 3'UTR), qRT-PCR, Western blot, cell proliferation, migration, and apoptosis assays in glioma cell lines\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — dual reporter assay evidence for binding sites, functional consequences shown, single lab\",\n      \"pmids\": [\"28055966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PCDH9 promoter methylation leads to transcriptional silencing in hepatocellular carcinoma (HCC), and treatment with DNA demethylation agent 5-azacytidine restores PCDH9 expression. Restored PCDH9 expression inhibits HCC cell proliferation and xenograft tumor formation by inducing G0/G1 cell cycle arrest.\",\n      \"method\": \"Quantitative methylation analysis, 5-azacytidine treatment, PCDH9 re-expression, cell proliferation assays, xenograft tumor formation, cell cycle analysis\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epigenetic mechanism demonstrated with demethylation rescue, functional gain-of-function with defined phenotype, single lab\",\n      \"pmids\": [\"28791409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"miR-200a-3p directly binds the 3'-UTR of PCDH9 mRNA and decreases PCDH9 expression in ovarian cancer cells, thereby promoting ovarian cancer cell proliferation, colony formation, and invasion. Restoring PCDH9 expression inhibits the pro-proliferative effect of miR-200a-3p.\",\n      \"method\": \"Luciferase reporter assay (3'UTR), qRT-PCR, Western blot, cell proliferation, colony formation, invasion assays, rescue experiments\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — luciferase reporter confirms binding, rescue experiment confirms pathway position, single lab\",\n      \"pmids\": [\"31632082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"COP1 (RFWD2), a RING-finger E3 ubiquitin ligase, physically interacts with PCDH9 and promotes its Lys48-linked polyubiquitination and proteasomal degradation in glioma cells. COP1 protein levels are inversely correlated with PCDH9 protein levels in human glioma tissues.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescence co-localization, ubiquitination assays, proteasome inhibitor experiments, Western blot, human glioma tissue analysis\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ubiquitination type defined (K48-linked), proteasomal degradation confirmed, discovery by yeast two-hybrid plus multiple orthogonal validations\",\n      \"pmids\": [\"35084653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PCDH9 overexpression in melanoma inhibits cell proliferation and migration, downregulates RAC1, MMP2, and MMP9, and upregulates Pyk2 and Cyclin D1. The circ_0084043/miR-134-5p axis indirectly regulates PCDH9: circ_0084043 sponges miR-134-5p, thereby relieving miR-134-5p-mediated suppression of PCDH9. PCDH9 overexpression also inhibits melanoma tumor growth in vivo.\",\n      \"method\": \"Lentiviral overexpression/knockdown of PCDH9, proliferation/invasion/apoptosis assays, qRT-PCR, Western blot, in vivo xenograft, ceRNA luciferase reporter assays\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — functional effects shown in vitro and in vivo, ceRNA axis confirmed by reporter assay, single lab\",\n      \"pmids\": [\"36387162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCDH9 is cleaved in gastric cancer cells, generating an intracellular domain (ICD) that translocates to the nucleus. In the nucleus, the PCDH9 ICD interacts with DNA methyltransferase 1 (DNMT1) and increases DNMT1 activity, which leads to increased DNA methylation at the CDH2 (N-cadherin) promoter, downregulating CDH2 expression and thereby dampening gastric cancer cell migration and in vivo metastasis.\",\n      \"method\": \"Co-immunoprecipitation, nuclear fractionation, DNMT1 activity assays, DNA methylation analysis (promoter bisulfite), cell migration assays, in vivo metastasis models, correlation with patient tissue data\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, enzymatic activity assay, DNA methylation mechanistic link, in vivo validation, multiple orthogonal methods in single study\",\n      \"pmids\": [\"38357662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCDH9 primarily localizes at glutamatergic synapses in the mouse hippocampus CA1 region, with expression peaking in the first week after birth. Pcdh9 KO neurons exhibit oversized presynaptic terminals and postsynaptic densities, widespread upregulation of synaptic genes (by snRNA-seq), dysregulation of the SHANK2/CORTACTIN pathway, increased miniature excitatory postsynaptic currents (mEPSC), and reduced network activity in CA1.\",\n      \"method\": \"Pcdh9 KO mice, electron microscopy (ultrastructural), single-nucleus RNA-seq, electrophysiology (mEPSC recordings), biochemical fractionation/localization, network activity recordings\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — KO mouse with ultrastructural, transcriptomic, electrophysiological, and biochemical multi-level characterization in one rigorous study\",\n      \"pmids\": [\"39557582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Neuronal activity triggers Matrix Metalloprotease (MMP)-dependent cleavage of PCDH9, generating a C-terminal fragment (CTF) that translocates to the nucleus. Overexpression of the PCDH9 CTF promotes dendritic growth, increases spine density, and strengthens excitatory synaptic transmission, identifying PCDH9 CTF as an activity-dependent signaling molecule linking synaptic activity to structural and functional remodeling.\",\n      \"method\": \"Biochemical fractionation, immunohistochemistry, MMP inhibitor treatment, neuronal cultures, CTF overexpression, dendritic morphology analysis, spine density quantification, electrophysiology\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical and immunohistochemical evidence for cleavage and nuclear translocation, functional overexpression phenotype, single lab, single study\",\n      \"pmids\": [\"41685090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"RNF145, an E3 ubiquitin ligase, physically interacts with PCDH9 and promotes its ubiquitination and subsequent proteasomal degradation, thereby facilitating hepatocellular carcinoma cell migration and invasion. Knockdown of RNF145 abolishes migratory and invasive capacities of HCC cells.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, ubiquitination assays, transwell migration/invasion assays, wound-healing assay, RNF145 knockdown\",\n      \"journal\": \"Oncology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP demonstrates interaction, ubiquitination assay confirms substrate relationship, functional consequence shown with knockdown, single lab\",\n      \"pmids\": [\"41613811\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCDH9 is a δ1-protocadherin cell-adhesion molecule predominantly expressed at glutamatergic synapses in the brain, where it shapes excitatory synapse morphology (via SHANK2/CORTACTIN pathway), glutamatergic transmission, and long-term recognition memory; neuronal activity triggers MMP-dependent cleavage of PCDH9, and the resulting intracellular C-terminal fragment translocates to the nucleus where it promotes dendritic growth and spine density; in cancer contexts, PCDH9 acts as a tumor suppressor whose nuclear ICD interacts with DNMT1 to methylate and silence the CDH2 promoter, suppressing metastasis, while its protein levels are regulated by E3 ubiquitin ligases COP1 and RNF145 via Lys48-linked polyubiquitination and proteasomal degradation; additionally, PCDH9 expression is post-transcriptionally suppressed by multiple miRNAs (miR-215-5p, miR-200a-3p, miR-134-5p) and epigenetically silenced by promoter methylation in several cancers.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PCDH9 is a calcium-dependent protocadherin cell-adhesion molecule predominantly expressed in brain that organizes excitatory synapses and supports long-term recognition memory [#0, #2, #9]. At glutamatergic synapses in hippocampal CA1, PCDH9 constrains synaptic architecture: its loss produces oversized presynaptic terminals and postsynaptic densities, dysregulates the SHANK2/CORTACTIN pathway, and increases miniature excitatory postsynaptic currents while reducing network activity [#9]. PCDH9 also functions as a signaling receptor that is processed by regulated proteolysis—neuronal activity drives MMP-dependent cleavage of PCDH9, releasing a C-terminal/intracellular fragment that translocates to the nucleus and promotes dendritic growth, spine density, and synaptic strengthening [#10]. In cancer, PCDH9 acts as a tumor suppressor; re-expression induces apoptosis, G0/G1 arrest, and reduced proliferation and invasion across glioma and hepatocellular carcinoma models [#1, #4]. Its nuclear intracellular domain interacts with DNMT1 to stimulate methylation of the CDH2 (N-cadherin) promoter, silencing CDH2 and suppressing migration and metastasis [#8]. PCDH9 abundance is controlled by E3 ubiquitin ligases COP1/RFWD2 and RNF145, which drive its polyubiquitination and proteasomal degradation [#6, #11], while its expression is suppressed post-transcriptionally by multiple miRNAs and epigenetically by promoter methylation [#3, #5, #7, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established PCDH9 as a member of the protocadherin family of calcium-dependent cell-cell adhesion proteins with brain-predominant, developmentally regulated expression, framing it as a candidate neural recognition molecule.\",\n      \"evidence\": \"Gene isolation, genomic organization, and tissue/developmental expression profiling\",\n      \"pmids\": [\"9787079\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional or mechanistic role demonstrated\", \"Adhesion partners and homophilic/heterophilic specificity unaddressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified a tumor-suppressor function by showing that restoring PCDH9 in glioma cells halts proliferation and invasion, opening a cancer biology axis distinct from its neural role.\",\n      \"evidence\": \"Lentiviral PCDH9 re-expression in U87/U251 glioma lines with viability, apoptosis, cell cycle, invasion, and marker Western blots\",\n      \"pmids\": [\"24214103\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of growth suppression not defined\", \"Bax/Bcl-2/cyclin D1 changes correlative, not causally dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated in vivo that PCDH9 is required for long-term social and object recognition memory and sensory cortex development, establishing its physiological neural function.\",\n      \"evidence\": \"Pcdh9 knockout mice from QTL mapping with behavioral testing and brain morphology analysis\",\n      \"pmids\": [\"25802080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Synaptic/cellular mechanism underlying behavioral deficits not resolved at this stage\", \"Molecular pathways downstream of PCDH9 unidentified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed that PCDH9 is silenced in cancers by two converging regulatory routes—miRNA targeting and promoter methylation—explaining how its tumor-suppressor function is lost.\",\n      \"evidence\": \"miR-215-5p dual promoter/3'UTR luciferase reporters in glioma; quantitative methylation and 5-azacytidine rescue in hepatocellular carcinoma with functional assays\",\n      \"pmids\": [\"28055966\", \"28791409\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of dual promoter+3'UTR miRNA targeting unusual and not structurally explained\", \"Tumor-suppressor effector pathway still undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended the miRNA-suppression model to ovarian cancer, reinforcing post-transcriptional control of PCDH9 as a recurring oncogenic strategy.\",\n      \"evidence\": \"miR-200a-3p 3'UTR luciferase reporter, expression assays, and PCDH9-restoration rescue in ovarian cancer cells\",\n      \"pmids\": [\"31632082\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, single cancer type\", \"Downstream effectors of PCDH9 in ovarian cancer not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the first post-translational regulator of PCDH9 stability, COP1, defining ubiquitin-proteasome control of PCDH9 protein levels in glioma.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP, K48-linked ubiquitination assays, proteasome inhibition, and inverse correlation in human glioma tissue\",\n      \"pmids\": [\"35084653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitination site(s) on PCDH9 not mapped\", \"Whether cleavage and degradation are coupled not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the nuclear effector mechanism of PCDH9: a cleaved intracellular domain binds and activates DNMT1 to methylate and silence the CDH2 promoter, providing a molecular basis for metastasis suppression.\",\n      \"evidence\": \"Co-IP, nuclear fractionation, DNMT1 activity and promoter bisulfite assays, migration and in vivo metastasis models in gastric cancer\",\n      \"pmids\": [\"38357662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Protease generating the cancer-context ICD not identified\", \"Generality of CDH2 silencing across tumor types untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the synaptic mechanism behind PCDH9's memory role, localizing it to glutamatergic synapses and showing it constrains synapse size and excitatory transmission via the SHANK2/CORTACTIN pathway.\",\n      \"evidence\": \"Pcdh9 KO mice with EM ultrastructure, snRNA-seq, mEPSC and network recordings, and biochemical localization in hippocampal CA1\",\n      \"pmids\": [\"39557582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between PCDH9 and SHANK2/CORTACTIN not established\", \"Trans-synaptic adhesion partners unidentified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Connected synaptic activity to nuclear signaling by showing neuronal-activity-driven MMP cleavage of PCDH9 releases a CTF that promotes dendritic and spine remodeling, unifying adhesion and intracellular signaling functions.\",\n      \"evidence\": \"Biochemical fractionation, MMP inhibitor treatment, immunohistochemistry, CTF overexpression with morphology and electrophysiology in neurons\",\n      \"pmids\": [\"41685090\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific MMP and cleavage site not identified\", \"Nuclear targets of the neuronal CTF not defined\", \"Relationship to the DNMT1-binding cancer ICD unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified a second E3 ligase, RNF145, that degrades PCDH9, linking its loss to hepatocellular carcinoma migration and invasion and broadening proteasomal control of PCDH9 across cancers.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, and transwell/wound-healing assays with RNF145 knockdown in HCC cells\",\n      \"pmids\": [\"41613811\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin linkage type not specified\", \"Whether COP1 and RNF145 act redundantly or in distinct contexts unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown which protease(s) generate the nuclear fragment in neurons versus cancer cells and whether the activity-dependent CTF and the DNMT1-binding tumor-suppressor ICD are the same proteolytic product acting through a shared nuclear program.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cleavage protease identity and site uncharacterized in both contexts\", \"Trans-synaptic adhesion partner(s) of full-length PCDH9 not identified\", \"No structural model of the ICD-DNMT1 interaction\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [9, 2]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DNMT1\", \"COP1\", \"RNF145\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}