{"gene":"USP40","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2019,"finding":"USP40 deubiquitinates CFLARL (c-FLIPL) via K48-linked deubiquitination, stabilizing it from proteasomal degradation. GMEB1 acts as a bridge protein that promotes USP40 binding to CFLARL, and USP40 knockdown prevents GMEB1-mediated CFLARL stabilization, inhibiting DISC formation and caspase-8 activation in non-small cell lung cancer cells.","method":"Co-immunoprecipitation, GST pull-down assay, immunofluorescence, flow cytometry, western blotting, shRNA knockdown","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP and functional knockdown with defined phenotype, single lab","pmids":["31046799"],"is_preprint":false},{"year":2017,"finding":"USP40 localizes to the intermediate filament protein nestin in glomerular endothelial cells and podocytes; immunoprecipitation confirmed direct protein-protein binding of USP40 with nestin, and USP40 siRNA knockdown reduced nestin levels. USP40 morphant zebrafish displayed disorganized glomeruli with disrupted glomerular permeability, indicating USP40 is required for glomerular integrity through modulation of intermediate filament homeostasis.","method":"Immunoprecipitation, immunofluorescence/confocal microscopy, siRNA knockdown, zebrafish morpholino knockdown, permeability assay","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus loss-of-function with defined permeability phenotype, single lab","pmids":["28148530"],"is_preprint":false},{"year":2022,"finding":"USP40 deubiquitinates HINT1 (histidine triad nucleotide-binding protein 1), preventing its degradation and thereby stabilizing p53. USP40 is bound to and co-localizes with nestin in podocytes, and USP40 gene knockdown in cultured podocytes reduces HINT1 and p53 protein expression. In a mouse FSGS model, HINT1 upregulation precedes upregulation of USP40, p53, and nestin.","method":"Co-immunoprecipitation, gene knockdown, western blotting, immunofluorescence, USP40 knockout mouse model","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — functional knockdown plus KO mouse with mechanistic pathway placement, single lab","pmids":["35605301"],"is_preprint":false},{"year":2024,"finding":"USP40 deubiquitinates HSP90β and inactivates it, thereby preventing endothelial barrier disruption; mechanistically, USP40 reduces RhoA activation, myosin light chain and cofilin phosphorylation, NF-κB activation, ICAM1 expression, and leukocyte-endothelial adhesion. Global and EC-specific USP40 knockout in mice exacerbated experimental lung injury, while lentiviral USP40 gene transfer was protective.","method":"Unbiased proteomic approach, Co-immunoprecipitation, ubiquitination assay, EC-specific knockout mice, lentiviral gene transfer, transendothelial electrical resistance assay, western blotting","journal":"Experimental & molecular medicine","confidence":"High","confidence_rationale":"Tier 1-2 — unbiased substrate identification, in vivo KO and rescue, multiple orthogonal methods, single lab","pmids":["38307937"],"is_preprint":false},{"year":2024,"finding":"USP40 protects against LPS-induced endothelial dysfunction and lung injury through activation of USP40-mediated HSP90β deubiquitination. IAA (indole-3-acetic acid) acts as an activator of USP40, reducing HSP90 ubiquitination. The protective effects of IAA were abolished in USP40-deficient endothelial cells and in USP40 EC-specific knockout (USP40cdh5-ECKO) mice.","method":"Transendothelial electrical resistance assay, ubiquitination assay, USP40 EC-specific knockout mice, siRNA knockdown, western blotting","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo EC-specific KO with pharmacological rescue, single lab","pmids":["38761166"],"is_preprint":false},{"year":2024,"finding":"USP40 interacts with YAP and removes K48-linked polyubiquitination at YAP K252 and K315 sites, thereby stabilizing YAP and promoting HCC cell proliferation, migration, and stemness. In turn, YAP transcriptionally activates USP40, forming a positive feedback loop. Stiffness-induced USP40 upregulation was abolished by YAP knockdown.","method":"Co-immunoprecipitation, ubiquitination assay, site-directed mutagenesis (K252/K315 sites), RNA sequencing, knockdown/overexpression, in vivo xenograft","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 1-2 — ubiquitination site mutagenesis, functional knockdown/rescue, in vivo model, single lab with multiple orthogonal methods","pmids":["38537774"],"is_preprint":false},{"year":2024,"finding":"USP40 interacts with Claudin1 and inhibits its polyubiquitination, thereby stabilizing Claudin1 protein levels and promoting HCC cell proliferation, migration, and stemness.","method":"Co-immunoprecipitation, ubiquitination assay, immunofluorescence, RT-qPCR, western blotting, knockdown/overexpression","journal":"Biology direct","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ubiquitination assay with functional knockdown, single lab","pmids":["38308285"],"is_preprint":false}],"current_model":"USP40 is a deubiquitinating enzyme that stabilizes multiple substrates (CFLARL, HINT1, HSP90β, YAP, Claudin1, Nestin-associated proteins) via removal of K48-linked polyubiquitin chains, with identified roles in endothelial barrier integrity (through HSP90β inactivation and suppression of RhoA/MLC/NF-κB signaling), podocyte homeostasis (through HINT1/p53 stabilization), and cancer cell proliferation (through YAP and Claudin1 stabilization), while being regulated by bridging partners such as GMEB1 and small molecules such as IAA."},"narrative":{"teleology":[{"year":2017,"claim":"Whether USP40 had any physiological role in vivo was unknown; demonstration that USP40 binds nestin in glomerular cells and that its loss disrupts glomerular permeability in zebrafish established USP40 as a regulator of kidney filtration barrier integrity.","evidence":"Immunoprecipitation, siRNA knockdown in podocytes, and zebrafish morpholino knockdown with permeability assays","pmids":["28148530"],"confidence":"Medium","gaps":["Deubiquitination activity toward nestin was not directly demonstrated","Mechanism linking USP40 loss to nestin reduction (direct deubiquitination vs. indirect stabilization) was not resolved","Mammalian in vivo kidney phenotype not yet tested"]},{"year":2019,"claim":"Whether USP40 had catalytic substrates was unresolved; identification of CFLARL (c-FLIPL) as a USP40 substrate, with GMEB1 acting as a bridging factor, established USP40 as a K48-directed deubiquitinase that regulates DISC formation and apoptotic signaling in NSCLC cells.","evidence":"Co-immunoprecipitation, GST pull-down, shRNA knockdown, and flow cytometry in NSCLC cell lines","pmids":["31046799"],"confidence":"Medium","gaps":["Single-lab study; independent replication absent","Catalytic-dead mutant control not reported","In vivo relevance for apoptosis regulation not tested"]},{"year":2022,"claim":"How USP40 supports podocyte homeostasis mechanistically was unclear; showing that USP40 deubiquitinates HINT1, preventing its degradation and sustaining p53 expression, linked USP40 catalytic activity to a defined tumor-suppressor signaling axis in podocytes.","evidence":"Co-immunoprecipitation, gene knockdown in cultured podocytes, USP40 knockout mouse, and FSGS disease model","pmids":["35605301"],"confidence":"Medium","gaps":["Direct ubiquitin-chain type specificity for HINT1 not defined","Whether HINT1 stabilization is the sole mechanism underlying the glomerular phenotype is unknown","Rescue experiment restoring USP40 in KO podocytes not reported"]},{"year":2024,"claim":"Establishing the endothelial-intrinsic function of USP40 and its substrate in vascular barrier regulation, unbiased proteomics identified HSP90β as a direct USP40 substrate whose deubiquitination suppresses RhoA/MLC/NF-κB signaling; endothelial-specific knockout exacerbated lung injury while gene transfer rescued it, and the small molecule IAA was shown to activate USP40-dependent HSP90β deubiquitination.","evidence":"Unbiased proteomics, Co-IP, ubiquitination assays, global and EC-specific KO mice, lentiviral rescue, TEER assays, IAA pharmacological activation in KO mice","pmids":["38307937","38761166"],"confidence":"High","gaps":["Structural basis of IAA-mediated USP40 activation is unknown","Whether HSP90β deubiquitination is activating or inactivating in other cell types is not resolved","USP40 catalytic-domain crystal structure not available"]},{"year":2024,"claim":"Whether USP40 contributes to oncogenesis was untested; identification of YAP (at K252/K315) and Claudin1 as USP40 substrates, and discovery of a YAP→USP40 transcriptional positive-feedback loop, established USP40 as a driver of HCC cell proliferation, migration, and stemness.","evidence":"Co-IP, ubiquitination assays, site-directed mutagenesis, RNA-seq, knockdown/overexpression, in vivo xenograft, and mechanical stiffness models in HCC cells","pmids":["38537774","38308285"],"confidence":"High","gaps":["Whether YAP and Claudin1 stabilization are independent or epistatic is not resolved","Relevance to patient HCC survival or in vivo genetic models (conditional KO) not established","Selectivity of USP40 for YAP versus other Hippo pathway components not tested"]},{"year":null,"claim":"No structural or biochemical reconstitution data exist for USP40; the catalytic mechanism, substrate selectivity determinants, and regulation of USP40 enzymatic activity remain undefined at the molecular level.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of USP40","In vitro reconstitution of deubiquitinase activity with purified components not reported","Relative specificity across its multiple identified substrates has not been compared under standardized conditions"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,3,4,5,6]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,5,6]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,3,5,6]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,6]}],"complexes":[],"partners":["HSP90AB1","YAP1","CFLAR","HINT1","CLDN1","NES","GMEB1"],"other_free_text":[]},"mechanistic_narrative":"USP40 is a deubiquitinating enzyme that stabilizes diverse substrates by removing K48-linked polyubiquitin chains, thereby preventing their proteasomal degradation, with established roles in endothelial barrier integrity, podocyte homeostasis, and hepatocellular carcinoma progression. In endothelial cells, USP40 deubiquitinates and inactivates HSP90β, suppressing RhoA/MLC signaling and NF-κB–dependent ICAM1 expression; global and endothelial-specific USP40 knockout in mice exacerbates experimental lung injury, while lentiviral USP40 gene transfer or the small-molecule activator indole-3-acetic acid (IAA) is protective [PMID:38307937, PMID:38761166]. In podocytes, USP40 co-localizes with nestin and stabilizes HINT1, thereby sustaining p53 expression; USP40 loss in zebrafish disrupts glomerular permeability [PMID:28148530, PMID:35605301]. In hepatocellular carcinoma, USP40 deubiquitinates YAP at K252/K315 and stabilizes Claudin1, promoting tumor cell proliferation, migration, and stemness through a YAP–USP40 positive-feedback loop [PMID:38537774, PMID:38308285]."},"prefetch_data":{"uniprot":{"accession":"Q9NVE5","full_name":"Ubiquitin carboxyl-terminal hydrolase 40","aliases":["Deubiquitinating enzyme 40","Ubiquitin thioesterase 40","Ubiquitin-specific-processing protease 40"],"length_aa":1235,"mass_kda":140.1,"function":"Deubiquitinating enzyme that plays a key role in maintaining endothelial cell (EC) barrier integrity and regulating apoptosis and inflammation. Stabilizes Claudin-1/CLDN1 by cleaving its polyubiquitin chains, thereby protecting tight junction structure (PubMed:38308285). Prevents EC barrier disruption by inhibiting RhoA activation and reducing phosphorylation of myosin light chain and cofilin. Suppresses EC inflammation by inhibiting NF-kappa-B activation, decreasing ICAM1 expression, and reducing leukocyte adhesion to ECs (PubMed:38307937). Mediates these protective effects in part via deubiquitination and inactivation of heat shock protein 90-beta/HSP90AB1 (PubMed:38307937). Targets CFLAR for 'Lys-48'-linked deubiquitination, stabilizing its protein levels. This interaction is facilitated by the adapter protein GMEB1, which enhances USP40-CFLAR binding. Through CFLAR stabilization, USP40 inhibits pro-caspase-8 activation and protects against apoptosis (PubMed:31046799). Additionally, USP40 stabilizes HINT1, an activator of p53/TP53, thereby maintaining p53/TP53 levels and sustaining the HINT1-p53/TP53 axis (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9NVE5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/USP40","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/USP40","total_profiled":1310},"omim":[{"mim_id":"610570","title":"UBIQUITIN-SPECIFIC PROTEASE 40; USP40","url":"https://www.omim.org/entry/610570"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Focal adhesion sites","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/USP40"},"hgnc":{"alias_symbol":["FLJ10785"],"prev_symbol":[]},"alphafold":{"accession":"Q9NVE5","domains":[{"cath_id":"-","chopping":"43-159_453-517","consensus_level":"medium","plddt":86.6859,"start":43,"end":517},{"cath_id":"3.90.70.10","chopping":"165-297","consensus_level":"medium","plddt":92.5384,"start":165,"end":297},{"cath_id":"-","chopping":"360-406","consensus_level":"high","plddt":87.5302,"start":360,"end":406},{"cath_id":"3.10.20.90","chopping":"529-639","consensus_level":"high","plddt":85.4417,"start":529,"end":639},{"cath_id":"3.10.20.90","chopping":"641-728","consensus_level":"high","plddt":72.2184,"start":641,"end":728},{"cath_id":"3.10.20.90","chopping":"748-838","consensus_level":"medium","plddt":82.7569,"start":748,"end":838},{"cath_id":"3.10.20.90","chopping":"841-919","consensus_level":"medium","plddt":82.9695,"start":841,"end":919},{"cath_id":"3.10.20.90","chopping":"928-944_982-1064","consensus_level":"medium","plddt":82.3349,"start":928,"end":1064},{"cath_id":"3.10.20.90","chopping":"1066-1137_1150-1196","consensus_level":"medium","plddt":84.5782,"start":1066,"end":1196}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NVE5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NVE5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NVE5-F1-predicted_aligned_error_v6.png","plddt_mean":76.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=USP40","jax_strain_url":"https://www.jax.org/strain/search?query=USP40"},"sequence":{"accession":"Q9NVE5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NVE5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NVE5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NVE5"}},"corpus_meta":[{"pmid":"16917932","id":"PMC_16917932","title":"Genetic evidence for ubiquitin-specific proteases USP24 and USP40 as candidate genes for late-onset Parkinson disease.","date":"2006","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/16917932","citation_count":52,"is_preprint":false},{"pmid":"31046799","id":"PMC_31046799","title":"Glucocorticoid modulatory element-binding protein 1 (GMEB1) interacts with the de-ubiquitinase USP40 to stabilize CFLARL and inhibit apoptosis in human non-small cell lung cancer cells.","date":"2019","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/31046799","citation_count":26,"is_preprint":false},{"pmid":"38537774","id":"PMC_38537774","title":"USP40 promotes hepatocellular carcinoma progression through a YAP/USP40 positive feedback loop.","date":"2024","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/38537774","citation_count":14,"is_preprint":false},{"pmid":"38761166","id":"PMC_38761166","title":"Indole-3-Acetic Acid Protects Against Lipopolysaccharide-induced Endothelial Cell Dysfunction and Lung Injury through the Activation of USP40.","date":"2024","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38761166","citation_count":13,"is_preprint":false},{"pmid":"28148530","id":"PMC_28148530","title":"USP40 gene knockdown disrupts glomerular permeability in zebrafish.","date":"2017","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/28148530","citation_count":13,"is_preprint":false},{"pmid":"22923019","id":"PMC_22923019","title":"Association analysis of single-nucleotide polymorphisms of USP24 and USP40 with Parkinson's disease in the Han Chinese population.","date":"2012","source":"European neurology","url":"https://pubmed.ncbi.nlm.nih.gov/22923019","citation_count":11,"is_preprint":false},{"pmid":"38307937","id":"PMC_38307937","title":"The deubiquitinase USP40 preserves endothelial integrity by targeting the heat shock protein HSP90β.","date":"2024","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38307937","citation_count":9,"is_preprint":false},{"pmid":"35605301","id":"PMC_35605301","title":"USP40 deubiquitinates HINT1 and stabilizes p53 in podocyte damage.","date":"2022","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/35605301","citation_count":9,"is_preprint":false},{"pmid":"38308285","id":"PMC_38308285","title":"USP40 promotes hepatocellular carcinoma cell proliferation, migration and stemness by deubiquitinating and stabilizing Claudin1.","date":"2024","source":"Biology direct","url":"https://pubmed.ncbi.nlm.nih.gov/38308285","citation_count":9,"is_preprint":false},{"pmid":"31933881","id":"PMC_31933881","title":"A detrimental mutation on USP40 unlocks the tumorigenesis in a rare case of lung cancer.","date":"2019","source":"International journal of clinical and experimental pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31933881","citation_count":4,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.05.03.652026","title":"<i>In silico</i> analysis and Predictive linkage of Deubiquitinating Enzymes underlying Early Development","date":"2025-05-08","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.03.652026","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7078,"output_tokens":1917,"usd":0.024994},"stage2":{"model":"claude-opus-4-6","input_tokens":5194,"output_tokens":2010,"usd":0.11433},"total_usd":0.139324,"stage1_batch_id":"msgbatch_01BparvgRZ9S2LMidvaoo86K","stage2_batch_id":"msgbatch_01NkBfv9SVZWthhS7j6mU6G3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"USP40 deubiquitinates CFLARL (c-FLIPL) via K48-linked deubiquitination, stabilizing it from proteasomal degradation. GMEB1 acts as a bridge protein that promotes USP40 binding to CFLARL, and USP40 knockdown prevents GMEB1-mediated CFLARL stabilization, inhibiting DISC formation and caspase-8 activation in non-small cell lung cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down assay, immunofluorescence, flow cytometry, western blotting, shRNA knockdown\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and functional knockdown with defined phenotype, single lab\",\n      \"pmids\": [\"31046799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP40 localizes to the intermediate filament protein nestin in glomerular endothelial cells and podocytes; immunoprecipitation confirmed direct protein-protein binding of USP40 with nestin, and USP40 siRNA knockdown reduced nestin levels. USP40 morphant zebrafish displayed disorganized glomeruli with disrupted glomerular permeability, indicating USP40 is required for glomerular integrity through modulation of intermediate filament homeostasis.\",\n      \"method\": \"Immunoprecipitation, immunofluorescence/confocal microscopy, siRNA knockdown, zebrafish morpholino knockdown, permeability assay\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus loss-of-function with defined permeability phenotype, single lab\",\n      \"pmids\": [\"28148530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP40 deubiquitinates HINT1 (histidine triad nucleotide-binding protein 1), preventing its degradation and thereby stabilizing p53. USP40 is bound to and co-localizes with nestin in podocytes, and USP40 gene knockdown in cultured podocytes reduces HINT1 and p53 protein expression. In a mouse FSGS model, HINT1 upregulation precedes upregulation of USP40, p53, and nestin.\",\n      \"method\": \"Co-immunoprecipitation, gene knockdown, western blotting, immunofluorescence, USP40 knockout mouse model\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional knockdown plus KO mouse with mechanistic pathway placement, single lab\",\n      \"pmids\": [\"35605301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP40 deubiquitinates HSP90β and inactivates it, thereby preventing endothelial barrier disruption; mechanistically, USP40 reduces RhoA activation, myosin light chain and cofilin phosphorylation, NF-κB activation, ICAM1 expression, and leukocyte-endothelial adhesion. Global and EC-specific USP40 knockout in mice exacerbated experimental lung injury, while lentiviral USP40 gene transfer was protective.\",\n      \"method\": \"Unbiased proteomic approach, Co-immunoprecipitation, ubiquitination assay, EC-specific knockout mice, lentiviral gene transfer, transendothelial electrical resistance assay, western blotting\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — unbiased substrate identification, in vivo KO and rescue, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"38307937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP40 protects against LPS-induced endothelial dysfunction and lung injury through activation of USP40-mediated HSP90β deubiquitination. IAA (indole-3-acetic acid) acts as an activator of USP40, reducing HSP90 ubiquitination. The protective effects of IAA were abolished in USP40-deficient endothelial cells and in USP40 EC-specific knockout (USP40cdh5-ECKO) mice.\",\n      \"method\": \"Transendothelial electrical resistance assay, ubiquitination assay, USP40 EC-specific knockout mice, siRNA knockdown, western blotting\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo EC-specific KO with pharmacological rescue, single lab\",\n      \"pmids\": [\"38761166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP40 interacts with YAP and removes K48-linked polyubiquitination at YAP K252 and K315 sites, thereby stabilizing YAP and promoting HCC cell proliferation, migration, and stemness. In turn, YAP transcriptionally activates USP40, forming a positive feedback loop. Stiffness-induced USP40 upregulation was abolished by YAP knockdown.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, site-directed mutagenesis (K252/K315 sites), RNA sequencing, knockdown/overexpression, in vivo xenograft\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ubiquitination site mutagenesis, functional knockdown/rescue, in vivo model, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"38537774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP40 interacts with Claudin1 and inhibits its polyubiquitination, thereby stabilizing Claudin1 protein levels and promoting HCC cell proliferation, migration, and stemness.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, immunofluorescence, RT-qPCR, western blotting, knockdown/overexpression\",\n      \"journal\": \"Biology direct\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ubiquitination assay with functional knockdown, single lab\",\n      \"pmids\": [\"38308285\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"USP40 is a deubiquitinating enzyme that stabilizes multiple substrates (CFLARL, HINT1, HSP90β, YAP, Claudin1, Nestin-associated proteins) via removal of K48-linked polyubiquitin chains, with identified roles in endothelial barrier integrity (through HSP90β inactivation and suppression of RhoA/MLC/NF-κB signaling), podocyte homeostasis (through HINT1/p53 stabilization), and cancer cell proliferation (through YAP and Claudin1 stabilization), while being regulated by bridging partners such as GMEB1 and small molecules such as IAA.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"USP40 is a deubiquitinating enzyme that stabilizes diverse substrates by removing K48-linked polyubiquitin chains, thereby preventing their proteasomal degradation, with established roles in endothelial barrier integrity, podocyte homeostasis, and hepatocellular carcinoma progression. In endothelial cells, USP40 deubiquitinates and inactivates HSP90β, suppressing RhoA/MLC signaling and NF-κB–dependent ICAM1 expression; global and endothelial-specific USP40 knockout in mice exacerbates experimental lung injury, while lentiviral USP40 gene transfer or the small-molecule activator indole-3-acetic acid (IAA) is protective [PMID:38307937, PMID:38761166]. In podocytes, USP40 co-localizes with nestin and stabilizes HINT1, thereby sustaining p53 expression; USP40 loss in zebrafish disrupts glomerular permeability [PMID:28148530, PMID:35605301]. In hepatocellular carcinoma, USP40 deubiquitinates YAP at K252/K315 and stabilizes Claudin1, promoting tumor cell proliferation, migration, and stemness through a YAP–USP40 positive-feedback loop [PMID:38537774, PMID:38308285].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether USP40 had any physiological role in vivo was unknown; demonstration that USP40 binds nestin in glomerular cells and that its loss disrupts glomerular permeability in zebrafish established USP40 as a regulator of kidney filtration barrier integrity.\",\n      \"evidence\": \"Immunoprecipitation, siRNA knockdown in podocytes, and zebrafish morpholino knockdown with permeability assays\",\n      \"pmids\": [\"28148530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Deubiquitination activity toward nestin was not directly demonstrated\",\n        \"Mechanism linking USP40 loss to nestin reduction (direct deubiquitination vs. indirect stabilization) was not resolved\",\n        \"Mammalian in vivo kidney phenotype not yet tested\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether USP40 had catalytic substrates was unresolved; identification of CFLARL (c-FLIPL) as a USP40 substrate, with GMEB1 acting as a bridging factor, established USP40 as a K48-directed deubiquitinase that regulates DISC formation and apoptotic signaling in NSCLC cells.\",\n      \"evidence\": \"Co-immunoprecipitation, GST pull-down, shRNA knockdown, and flow cytometry in NSCLC cell lines\",\n      \"pmids\": [\"31046799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study; independent replication absent\",\n        \"Catalytic-dead mutant control not reported\",\n        \"In vivo relevance for apoptosis regulation not tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"How USP40 supports podocyte homeostasis mechanistically was unclear; showing that USP40 deubiquitinates HINT1, preventing its degradation and sustaining p53 expression, linked USP40 catalytic activity to a defined tumor-suppressor signaling axis in podocytes.\",\n      \"evidence\": \"Co-immunoprecipitation, gene knockdown in cultured podocytes, USP40 knockout mouse, and FSGS disease model\",\n      \"pmids\": [\"35605301\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct ubiquitin-chain type specificity for HINT1 not defined\",\n        \"Whether HINT1 stabilization is the sole mechanism underlying the glomerular phenotype is unknown\",\n        \"Rescue experiment restoring USP40 in KO podocytes not reported\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Establishing the endothelial-intrinsic function of USP40 and its substrate in vascular barrier regulation, unbiased proteomics identified HSP90β as a direct USP40 substrate whose deubiquitination suppresses RhoA/MLC/NF-κB signaling; endothelial-specific knockout exacerbated lung injury while gene transfer rescued it, and the small molecule IAA was shown to activate USP40-dependent HSP90β deubiquitination.\",\n      \"evidence\": \"Unbiased proteomics, Co-IP, ubiquitination assays, global and EC-specific KO mice, lentiviral rescue, TEER assays, IAA pharmacological activation in KO mice\",\n      \"pmids\": [\"38307937\", \"38761166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of IAA-mediated USP40 activation is unknown\",\n        \"Whether HSP90β deubiquitination is activating or inactivating in other cell types is not resolved\",\n        \"USP40 catalytic-domain crystal structure not available\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Whether USP40 contributes to oncogenesis was untested; identification of YAP (at K252/K315) and Claudin1 as USP40 substrates, and discovery of a YAP→USP40 transcriptional positive-feedback loop, established USP40 as a driver of HCC cell proliferation, migration, and stemness.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, site-directed mutagenesis, RNA-seq, knockdown/overexpression, in vivo xenograft, and mechanical stiffness models in HCC cells\",\n      \"pmids\": [\"38537774\", \"38308285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether YAP and Claudin1 stabilization are independent or epistatic is not resolved\",\n        \"Relevance to patient HCC survival or in vivo genetic models (conditional KO) not established\",\n        \"Selectivity of USP40 for YAP versus other Hippo pathway components not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No structural or biochemical reconstitution data exist for USP40; the catalytic mechanism, substrate selectivity determinants, and regulation of USP40 enzymatic activity remain undefined at the molecular level.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No crystal or cryo-EM structure of USP40\",\n        \"In vitro reconstitution of deubiquitinase activity with purified components not reported\",\n        \"Relative specificity across its multiple identified substrates has not been compared under standardized conditions\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 5, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 3, 5, 6]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"HSP90AB1\",\n      \"YAP1\",\n      \"CFLAR\",\n      \"HINT1\",\n      \"CLDN1\",\n      \"NES\",\n      \"GMEB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}