{"gene":"EPN1","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2009,"finding":"Epsin 1 (EPN1) and epsin 2 (EPN2) together act as specialized endocytic adaptors required for Notch signaling activation in mammals; combined loss of both genes causes embryonic lethality at E9.5-E10 with severe reduction of Notch primary target gene expression, recapitulating global Notch signaling impairment, while housekeeping clathrin-mediated endocytosis remains intact in double-knockout cells.","method":"Genetic double knockout in mice, embryo phenotyping, Notch target gene expression analysis, endocytosis assays in derived cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic DKO with specific Notch pathway readout, housekeeping endocytosis controls, replicated developmental phenotype","pmids":["19666558"],"is_preprint":false},{"year":2013,"finding":"Endothelial epsins (EPN1/EPN2) function to downregulate VEGFR2 by mediating activated VEGFR2 internalization and degradation; genetic reduction of VEGFR2 in endothelial epsin-deleted mice rescues aberrant angiogenesis, restoring normal VEGF signaling, EC proliferation, EC migration, and EC network formation.","method":"Conditional endothelial-specific DKO mice, genetic epistasis with VEGFR2 heterozygosity, in vitro angiogenesis assays with primary endothelial cells, in vivo wound healing and tumor angiogenesis assays","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple in vivo and in vitro orthogonal assays, mechanism specifically placed at VEGFR2 internalization and degradation","pmids":["24311377"],"is_preprint":false},{"year":2013,"finding":"In C. elegans, epsin (EPN-1) plays a role in apoptotic cell engulfment by promoting actin polymerization during pseudopod extension; CHC-1 is recruited to extending pseudopods in an EPN-1-dependent manner, and epistasis analysis places epn-1 and chc-1 in the same engulfment pathway as ced-1, ced-6, and dyn-1. CED-1 signaling is required for pseudopod enrichment of EPN-1 and CHC-1.","method":"RNAi inactivation in C. elegans, genetic epistasis, live imaging of pseudopod localization, cofilin partial suppression assay","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis and localization data from single lab, multiple orthogonal methods, C. elegans ortholog","pmids":["23861060"],"is_preprint":false},{"year":2020,"finding":"Podocyte-specific triple knockout of Epn1, Epn2, and Epn3 in mice causes increased albuminuria and foot process effacement, with reduced activation of Cdc42 and SRF, resulting in diminished β1 integrin expression; epsins maintain podocyte function through the Cdc42–SRF–β1 integrin signaling axis.","method":"Podocyte-specific triple KO mice, albuminuria measurements, primary podocyte isolation, cell adhesion/spreading assays, Cdc42 and SRF activity assays, β1 integrin expression analysis","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean tissue-specific genetic KO with multiple orthogonal readouts placing EPN1 in the Cdc42-SRF-β1 integrin pathway","pmids":["33051360"],"is_preprint":false},{"year":2023,"finding":"EPN1 recruits clathrin to ubiquitinated TCR microclusters at the immunological synapse to enable trans-endocytosis of pMHC-TCR conjugates from the antigen-presenting cell; this occurs after an earlier HRS/STAM2-mediated clathrin recruitment step that drives ectocytic vesicle release, demonstrating that EPN1 coordinates the endocytic fate of TCR through sequential adaptor recruitment.","method":"Live-cell imaging at immunological synapse, sequential recruitment analysis, functional perturbation experiments distinguishing ecto- and endocytic fates","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live imaging with functional pathway placement, single lab, mechanistic dissection of sequential adaptor roles","pmids":["36730202"],"is_preprint":false},{"year":2024,"finding":"ITSN1 (intersectin1) recruits epsin1 (EPN1) as part of a CME adaptor protein interaction network; artificially targeting ITSN1 to the mitochondrial surface was sufficient to assemble puncta containing EPN1, AP2, EPS15, FCHO2, and dynamin2, demonstrating that ITSN1 organizes EPN1-containing endocytic protein complexes. ITSN1 can form puncta and recruit dynamin2 independently of EPN1.","method":"Genome-edited live-cell imaging, mitochondrial targeting assay, ITSN1 knockdown with endocytic protein recruitment analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ectopic targeting reconstitution and KD experiments in genome-edited cells, single lab, two orthogonal approaches","pmids":["39580802"],"is_preprint":false},{"year":2024,"finding":"The ENTH domain of epsin-1 (EPN1) has membrane vesiculation activity, demonstrated using a single-particle analysis assay with free-floating liposomes at physiologically relevant protein concentrations, consistent with its established role in membrane curvature generation during endocytosis.","method":"In vitro liposome vesiculation assay (single-particle fluorescence), biophysical reconstitution","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution of ENTH domain membrane vesiculation, single lab, single method","pmids":["39324332"],"is_preprint":false},{"year":2024,"finding":"UBE2C-mediated monoubiquitination of SNAT2 at K59 inhibits K63-linked polyubiquitination at K33, increasing SNAT2 membrane protein levels by suppressing EPN1-mediated endocytosis of SNAT2; this crosstalk promotes glutamine uptake, VEGFC secretion, and lymphangiogenesis in bladder cancer.","method":"Ubiquitination mutagenesis, co-IP, membrane fractionation, siRNA knockdown of EPN1, in vitro and in vivo tumor models, patient-derived xenograft","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic mutagenesis of ubiquitination sites linked to EPN1-dependent endocytosis by KD, single lab, multiple orthogonal methods","pmids":["38949026"],"is_preprint":false},{"year":2021,"finding":"In C. elegans, loss of the epsin homolog epn-1 causes levamisole hypersensitivity and has opposing effects on postsynaptic receptor levels: increased abundance of L-type acetylcholine receptors (L-AChRs) and decreased abundance of GABAA receptors at the neuromuscular junction, indicating that EPN-1 mediates endocytosis of these receptor subtypes differentially.","method":"C. elegans genome-wide RNAi screen, pharmacological levamisole assay, receptor abundance measurements","journal":"G3 (Bethesda, Md.)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — RNAi knockdown with receptor level readouts, single lab, single method, no direct mechanistic dissection","pmids":["33713125"],"is_preprint":false}],"current_model":"EPN1 (epsin 1) is a specialized endocytic adaptor protein whose ENTH domain drives membrane curvature and vesiculation; it mediates ubiquitinated cargo internalization (including activated VEGFR2 and ubiquitinated SNAT2), recruits clathrin to specific cargo microclusters (e.g., TCR at the immunological synapse), participates in clathrin-mediated endocytosis site assembly as part of intersectin1-organized protein networks, and is specifically required for Notch signaling activation and podocyte homeostasis (via the Cdc42-SRF-β1 integrin axis) in mammals, while playing a conserved role in actin-dependent phagocytic engulfment downstream of CED-1 signaling in C. elegans."},"narrative":{"mechanistic_narrative":"EPN1 (epsin 1) is a specialized endocytic adaptor that couples membrane deformation to the selective internalization of ubiquitinated and clustered cell-surface cargo [PMID:19666558, PMID:39324332]. Its ENTH domain drives membrane vesiculation, generating the curvature required for endocytic budding [PMID:39324332]. EPN1 operates within clathrin-mediated endocytosis adaptor networks: intersectin1 (ITSN1) recruits EPN1 together with AP2, EPS15, FCHO2, and dynamin2 into organized endocytic puncta [PMID:39580802], and EPN1 itself recruits clathrin to specific cargo, including ubiquitinated TCR microclusters at the immunological synapse to enable trans-endocytosis of pMHC-TCR conjugates [PMID:36730202]. Functionally, EPN1 (acting redundantly with EPN2/EPN3) mediates internalization and degradation of activated VEGFR2 to downregulate angiogenic signaling [PMID:24311377], internalizes ubiquitinated SNAT2 to control its membrane abundance [PMID:38949026], and is specifically required for Notch signaling activation during development, distinct from housekeeping endocytosis [PMID:19666558]. In podocytes, epsins sustain cell function through the Cdc42-SRF-β1 integrin signaling axis [PMID:33051360]. A conserved role is seen in C. elegans, where the epsin homolog EPN-1 promotes actin-dependent pseudopod extension during apoptotic cell engulfment downstream of CED-1 signaling [PMID:23861060].","teleology":[{"year":2009,"claim":"Established that epsins are not merely generic endocytic adaptors but are specifically required for a defined signaling pathway, answering whether their function is dispensable or cargo-selective.","evidence":"Genetic EPN1/EPN2 double knockout in mice with Notch target gene readouts and housekeeping endocytosis controls","pmids":["19666558"],"confidence":"High","gaps":["Does not define the molecular step (ligand vs receptor side) at which epsins enable Notch activation","Redundancy between EPN1 and EPN2 not separated"]},{"year":2013,"claim":"Placed epsin function at a specific cargo, showing it controls receptor signaling output by mediating activated receptor internalization and degradation.","evidence":"Endothelial-specific DKO mice with genetic epistasis to VEGFR2 heterozygosity plus in vitro and in vivo angiogenesis assays","pmids":["24311377"],"confidence":"High","gaps":["Direct physical EPN1-VEGFR2 interaction and ubiquitin-dependence not biochemically resolved here","Role of individual epsin paralogs not separated"]},{"year":2013,"claim":"Revealed a conserved, actin-linked role for epsin beyond classical clathrin endocytosis, in apoptotic cell engulfment downstream of corpse-recognition signaling.","evidence":"RNAi inactivation, genetic epistasis, and live imaging of pseudopod localization in C. elegans","pmids":["23861060"],"confidence":"Medium","gaps":["Molecular link between EPN-1 and the actin machinery not defined","C. elegans ortholog; mammalian conservation of this engulfment role not tested"]},{"year":2020,"claim":"Connected epsin loss to a tissue-level homeostatic phenotype and a defined downstream signaling axis, broadening epsin function from cargo trafficking to cytoskeletal/adhesion signaling.","evidence":"Podocyte-specific triple KO mice with Cdc42/SRF activity assays, β1 integrin expression, and adhesion/spreading assays","pmids":["33051360"],"confidence":"High","gaps":["Mechanism linking epsin endocytic activity to Cdc42-SRF activation not resolved","Requires triple knockout, leaving paralog-specific contributions unclear"]},{"year":2021,"claim":"Indicated cargo-selective endocytic regulation of neurotransmitter receptors, showing epsin differentially controls surface abundance of distinct receptor subtypes.","evidence":"Genome-wide RNAi screen with levamisole pharmacology and receptor abundance measurements in C. elegans","pmids":["33713125"],"confidence":"Low","gaps":["RNAi knockdown with abundance readouts only; no direct mechanistic dissection","Opposing effects on L-AChR vs GABAA receptors are unexplained","Single lab, single method"]},{"year":2023,"claim":"Resolved how EPN1 directs cargo fate, showing it recruits clathrin to ubiquitinated TCR microclusters to specify endocytosis within a sequence of adaptor handoffs.","evidence":"Live-cell imaging at the immunological synapse with sequential recruitment analysis and functional perturbation distinguishing ecto- vs endocytic fates","pmids":["36730202"],"confidence":"Medium","gaps":["Direct EPN1 ubiquitin-binding requirement at TCR not biochemically isolated","Single lab; generality beyond TCR not addressed"]},{"year":2024,"claim":"Defined the architectural context of EPN1 recruitment, showing ITSN1 organizes an EPN1-containing CME adaptor network and can recruit it de novo.","evidence":"Genome-edited live-cell imaging with ectopic mitochondrial targeting reconstitution and ITSN1 knockdown","pmids":["39580802"],"confidence":"Medium","gaps":["Direct ITSN1-EPN1 binding interface not mapped","Functional consequence of ITSN1-dependent EPN1 recruitment for cargo not tested"]},{"year":2024,"claim":"Provided direct biophysical confirmation that the ENTH domain itself deforms membranes, grounding the cell-biological adaptor role in an intrinsic membrane-shaping activity.","evidence":"In vitro single-particle liposome vesiculation assay with the isolated ENTH domain at physiological concentrations","pmids":["39324332"],"confidence":"Medium","gaps":["Single in vitro method; in-cell contribution relative to other curvature drivers not quantified"]},{"year":2024,"claim":"Linked EPN1-mediated endocytosis to metabolic and tumor phenotypes via ubiquitin-code crosstalk controlling cargo surface levels.","evidence":"Ubiquitination site mutagenesis, co-IP, membrane fractionation, EPN1 siRNA, and in vivo/PDX bladder cancer tumor models","pmids":["38949026"],"confidence":"Medium","gaps":["Direct EPN1 recognition of K63-polyubiquitinated SNAT2 not demonstrated","Single lab"]},{"year":null,"claim":"How EPN1 achieves cargo selectivity and is partitioned among its paralogs (EPN2/EPN3) across tissues and pathways remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No isolated EPN1-specific (paralog-resolved) loss-of-function across the characterized pathways","Structural basis for selective ubiquitinated-cargo recognition not established in this corpus","Mechanistic link between endocytic activity and downstream signaling axes (Cdc42-SRF, Notch) not bridged"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5,0]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,1,7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5,1,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3]}],"complexes":[],"partners":["ITSN1","CLTC","AP2","EPS15","FCHO2","DNM2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y6I3","full_name":"Epsin-1","aliases":["EH domain-binding mitotic phosphoprotein","EPS-15-interacting protein 1"],"length_aa":576,"mass_kda":60.3,"function":"Binds to membranes enriched in phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Modifies membrane curvature and facilitates the formation of clathrin-coated invaginations (By similarity). Regulates receptor-mediated endocytosis (PubMed:10393179, PubMed:10557078)","subcellular_location":"Cytoplasm; Cell membrane; Nucleus; Membrane, clathrin-coated pit","url":"https://www.uniprot.org/uniprotkb/Q9Y6I3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EPN1","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000063245","cell_line_id":"CID000525","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"membrane","grade":3}],"interactors":[{"gene":"H1FX","stoichiometry":4.0},{"gene":"CLTA","stoichiometry":0.2},{"gene":"CSNK2A2","stoichiometry":0.2},{"gene":"HIST2H2AA3;HIST2H2AC","stoichiometry":0.2},{"gene":"HIST1H4A","stoichiometry":0.2},{"gene":"RPS27A;UBC;UBB;UBA52","stoichiometry":0.2},{"gene":"HIST1H2BN;HIST1H2BM;HIST1H2BH;HIST2H2BF;HIST1H2BC;HIST1H2BD;HIST1H2BK;H2BFS","stoichiometry":0.2},{"gene":"MAP4","stoichiometry":0.2},{"gene":"PHGDH","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000525","total_profiled":1310},"omim":[{"mim_id":"607265","title":"CLATHRIN INTERACTOR 1; CLINT1","url":"https://www.omim.org/entry/607265"},{"mim_id":"607264","title":"EPSIN 3; EPN3","url":"https://www.omim.org/entry/607264"},{"mim_id":"607263","title":"EPSIN 2; EPN2","url":"https://www.omim.org/entry/607263"},{"mim_id":"607262","title":"EPSIN 1; EPN1","url":"https://www.omim.org/entry/607262"},{"mim_id":"605801","title":"RALA-BINDING PROTEIN 1; RALBP1","url":"https://www.omim.org/entry/605801"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EPN1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9Y6I3","domains":[{"cath_id":"1.25.40.90","chopping":"4-159","consensus_level":"high","plddt":91.422,"start":4,"end":159}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6I3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6I3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6I3-F1-predicted_aligned_error_v6.png","plddt_mean":63.84},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EPN1","jax_strain_url":"https://www.jax.org/strain/search?query=EPN1"},"sequence":{"accession":"Q9Y6I3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y6I3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y6I3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6I3"}},"corpus_meta":[{"pmid":"19666558","id":"PMC_19666558","title":"Embryonic arrest at midgestation and disruption of Notch signaling produced by the absence of both epsin 1 and epsin 2 in mice.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19666558","citation_count":96,"is_preprint":false},{"pmid":"23409203","id":"PMC_23409203","title":"Mosquito cellular factors and functions in mediating the infectious entry of chikungunya virus.","date":"2013","source":"PLoS neglected tropical diseases","url":"https://pubmed.ncbi.nlm.nih.gov/23409203","citation_count":58,"is_preprint":false},{"pmid":"24311377","id":"PMC_24311377","title":"Genetic reduction of vascular endothelial growth factor receptor 2 rescues aberrant angiogenesis caused by epsin deficiency.","date":"2013","source":"Arteriosclerosis, thrombosis, and vascular biology","url":"https://pubmed.ncbi.nlm.nih.gov/24311377","citation_count":42,"is_preprint":false},{"pmid":"23861060","id":"PMC_23861060","title":"Phagocytic receptor signaling regulates 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Peutz-Jeghers hamartoma to the putative PJS locus at 19q13.4 and mutation analysis of candidate genes in polyp and STK11-negative PJS cases.","date":"2004","source":"Genes, chromosomes & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/15287029","citation_count":20,"is_preprint":false},{"pmid":"38949026","id":"PMC_38949026","title":"UBE2C-induced crosstalk between mono- and polyubiquitination of SNAT2 promotes lymphatic metastasis in bladder cancer.","date":"2024","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/38949026","citation_count":16,"is_preprint":false},{"pmid":"37698381","id":"PMC_37698381","title":"Methylome and proteome integration in human skeletal muscle uncover group and individual responses to high-intensity interval training.","date":"2023","source":"FASEB journal : official publication of the Federation of American Societies for Experimental 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signaling impairment, while housekeeping clathrin-mediated endocytosis remains intact in double-knockout cells.\",\n      \"method\": \"Genetic double knockout in mice, embryo phenotyping, Notch target gene expression analysis, endocytosis assays in derived cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic DKO with specific Notch pathway readout, housekeeping endocytosis controls, replicated developmental phenotype\",\n      \"pmids\": [\"19666558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Endothelial epsins (EPN1/EPN2) function to downregulate VEGFR2 by mediating activated VEGFR2 internalization and degradation; genetic reduction of VEGFR2 in endothelial epsin-deleted mice rescues aberrant angiogenesis, restoring normal VEGF signaling, EC proliferation, EC migration, and EC network formation.\",\n      \"method\": \"Conditional endothelial-specific DKO mice, genetic epistasis with VEGFR2 heterozygosity, in vitro angiogenesis assays with primary endothelial cells, in vivo wound healing and tumor angiogenesis assays\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple in vivo and in vitro orthogonal assays, mechanism specifically placed at VEGFR2 internalization and degradation\",\n      \"pmids\": [\"24311377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In C. elegans, epsin (EPN-1) plays a role in apoptotic cell engulfment by promoting actin polymerization during pseudopod extension; CHC-1 is recruited to extending pseudopods in an EPN-1-dependent manner, and epistasis analysis places epn-1 and chc-1 in the same engulfment pathway as ced-1, ced-6, and dyn-1. CED-1 signaling is required for pseudopod enrichment of EPN-1 and CHC-1.\",\n      \"method\": \"RNAi inactivation in C. elegans, genetic epistasis, live imaging of pseudopod localization, cofilin partial suppression assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis and localization data from single lab, multiple orthogonal methods, C. elegans ortholog\",\n      \"pmids\": [\"23861060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Podocyte-specific triple knockout of Epn1, Epn2, and Epn3 in mice causes increased albuminuria and foot process effacement, with reduced activation of Cdc42 and SRF, resulting in diminished β1 integrin expression; epsins maintain podocyte function through the Cdc42–SRF–β1 integrin signaling axis.\",\n      \"method\": \"Podocyte-specific triple KO mice, albuminuria measurements, primary podocyte isolation, cell adhesion/spreading assays, Cdc42 and SRF activity assays, β1 integrin expression analysis\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean tissue-specific genetic KO with multiple orthogonal readouts placing EPN1 in the Cdc42-SRF-β1 integrin pathway\",\n      \"pmids\": [\"33051360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"EPN1 recruits clathrin to ubiquitinated TCR microclusters at the immunological synapse to enable trans-endocytosis of pMHC-TCR conjugates from the antigen-presenting cell; this occurs after an earlier HRS/STAM2-mediated clathrin recruitment step that drives ectocytic vesicle release, demonstrating that EPN1 coordinates the endocytic fate of TCR through sequential adaptor recruitment.\",\n      \"method\": \"Live-cell imaging at immunological synapse, sequential recruitment analysis, functional perturbation experiments distinguishing ecto- and endocytic fates\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live imaging with functional pathway placement, single lab, mechanistic dissection of sequential adaptor roles\",\n      \"pmids\": [\"36730202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITSN1 (intersectin1) recruits epsin1 (EPN1) as part of a CME adaptor protein interaction network; artificially targeting ITSN1 to the mitochondrial surface was sufficient to assemble puncta containing EPN1, AP2, EPS15, FCHO2, and dynamin2, demonstrating that ITSN1 organizes EPN1-containing endocytic protein complexes. ITSN1 can form puncta and recruit dynamin2 independently of EPN1.\",\n      \"method\": \"Genome-edited live-cell imaging, mitochondrial targeting assay, ITSN1 knockdown with endocytic protein recruitment analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ectopic targeting reconstitution and KD experiments in genome-edited cells, single lab, two orthogonal approaches\",\n      \"pmids\": [\"39580802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The ENTH domain of epsin-1 (EPN1) has membrane vesiculation activity, demonstrated using a single-particle analysis assay with free-floating liposomes at physiologically relevant protein concentrations, consistent with its established role in membrane curvature generation during endocytosis.\",\n      \"method\": \"In vitro liposome vesiculation assay (single-particle fluorescence), biophysical reconstitution\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution of ENTH domain membrane vesiculation, single lab, single method\",\n      \"pmids\": [\"39324332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBE2C-mediated monoubiquitination of SNAT2 at K59 inhibits K63-linked polyubiquitination at K33, increasing SNAT2 membrane protein levels by suppressing EPN1-mediated endocytosis of SNAT2; this crosstalk promotes glutamine uptake, VEGFC secretion, and lymphangiogenesis in bladder cancer.\",\n      \"method\": \"Ubiquitination mutagenesis, co-IP, membrane fractionation, siRNA knockdown of EPN1, in vitro and in vivo tumor models, patient-derived xenograft\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic mutagenesis of ubiquitination sites linked to EPN1-dependent endocytosis by KD, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38949026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In C. elegans, loss of the epsin homolog epn-1 causes levamisole hypersensitivity and has opposing effects on postsynaptic receptor levels: increased abundance of L-type acetylcholine receptors (L-AChRs) and decreased abundance of GABAA receptors at the neuromuscular junction, indicating that EPN-1 mediates endocytosis of these receptor subtypes differentially.\",\n      \"method\": \"C. elegans genome-wide RNAi screen, pharmacological levamisole assay, receptor abundance measurements\",\n      \"journal\": \"G3 (Bethesda, Md.)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — RNAi knockdown with receptor level readouts, single lab, single method, no direct mechanistic dissection\",\n      \"pmids\": [\"33713125\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EPN1 (epsin 1) is a specialized endocytic adaptor protein whose ENTH domain drives membrane curvature and vesiculation; it mediates ubiquitinated cargo internalization (including activated VEGFR2 and ubiquitinated SNAT2), recruits clathrin to specific cargo microclusters (e.g., TCR at the immunological synapse), participates in clathrin-mediated endocytosis site assembly as part of intersectin1-organized protein networks, and is specifically required for Notch signaling activation and podocyte homeostasis (via the Cdc42-SRF-β1 integrin axis) in mammals, while playing a conserved role in actin-dependent phagocytic engulfment downstream of CED-1 signaling in C. elegans.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"EPN1 (epsin 1) is a specialized endocytic adaptor that couples membrane deformation to the selective internalization of ubiquitinated and clustered cell-surface cargo [#0, #6]. Its ENTH domain drives membrane vesiculation, generating the curvature required for endocytic budding [#6]. EPN1 operates within clathrin-mediated endocytosis adaptor networks: intersectin1 (ITSN1) recruits EPN1 together with AP2, EPS15, FCHO2, and dynamin2 into organized endocytic puncta [#5], and EPN1 itself recruits clathrin to specific cargo, including ubiquitinated TCR microclusters at the immunological synapse to enable trans-endocytosis of pMHC-TCR conjugates [#4]. Functionally, EPN1 (acting redundantly with EPN2/EPN3) mediates internalization and degradation of activated VEGFR2 to downregulate angiogenic signaling [#1], internalizes ubiquitinated SNAT2 to control its membrane abundance [#7], and is specifically required for Notch signaling activation during development, distinct from housekeeping endocytosis [#0]. In podocytes, epsins sustain cell function through the Cdc42-SRF-\\u03b21 integrin signaling axis [#3]. A conserved role is seen in C. elegans, where the epsin homolog EPN-1 promotes actin-dependent pseudopod extension during apoptotic cell engulfment downstream of CED-1 signaling [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established that epsins are not merely generic endocytic adaptors but are specifically required for a defined signaling pathway, answering whether their function is dispensable or cargo-selective.\",\n      \"evidence\": \"Genetic EPN1/EPN2 double knockout in mice with Notch target gene readouts and housekeeping endocytosis controls\",\n      \"pmids\": [\"19666558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define the molecular step (ligand vs receptor side) at which epsins enable Notch activation\", \"Redundancy between EPN1 and EPN2 not separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed epsin function at a specific cargo, showing it controls receptor signaling output by mediating activated receptor internalization and degradation.\",\n      \"evidence\": \"Endothelial-specific DKO mice with genetic epistasis to VEGFR2 heterozygosity plus in vitro and in vivo angiogenesis assays\",\n      \"pmids\": [\"24311377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical EPN1-VEGFR2 interaction and ubiquitin-dependence not biochemically resolved here\", \"Role of individual epsin paralogs not separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a conserved, actin-linked role for epsin beyond classical clathrin endocytosis, in apoptotic cell engulfment downstream of corpse-recognition signaling.\",\n      \"evidence\": \"RNAi inactivation, genetic epistasis, and live imaging of pseudopod localization in C. elegans\",\n      \"pmids\": [\"23861060\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between EPN-1 and the actin machinery not defined\", \"C. elegans ortholog; mammalian conservation of this engulfment role not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected epsin loss to a tissue-level homeostatic phenotype and a defined downstream signaling axis, broadening epsin function from cargo trafficking to cytoskeletal/adhesion signaling.\",\n      \"evidence\": \"Podocyte-specific triple KO mice with Cdc42/SRF activity assays, \\u03b21 integrin expression, and adhesion/spreading assays\",\n      \"pmids\": [\"33051360\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking epsin endocytic activity to Cdc42-SRF activation not resolved\", \"Requires triple knockout, leaving paralog-specific contributions unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Indicated cargo-selective endocytic regulation of neurotransmitter receptors, showing epsin differentially controls surface abundance of distinct receptor subtypes.\",\n      \"evidence\": \"Genome-wide RNAi screen with levamisole pharmacology and receptor abundance measurements in C. elegans\",\n      \"pmids\": [\"33713125\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"RNAi knockdown with abundance readouts only; no direct mechanistic dissection\", \"Opposing effects on L-AChR vs GABAA receptors are unexplained\", \"Single lab, single method\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved how EPN1 directs cargo fate, showing it recruits clathrin to ubiquitinated TCR microclusters to specify endocytosis within a sequence of adaptor handoffs.\",\n      \"evidence\": \"Live-cell imaging at the immunological synapse with sequential recruitment analysis and functional perturbation distinguishing ecto- vs endocytic fates\",\n      \"pmids\": [\"36730202\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct EPN1 ubiquitin-binding requirement at TCR not biochemically isolated\", \"Single lab; generality beyond TCR not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the architectural context of EPN1 recruitment, showing ITSN1 organizes an EPN1-containing CME adaptor network and can recruit it de novo.\",\n      \"evidence\": \"Genome-edited live-cell imaging with ectopic mitochondrial targeting reconstitution and ITSN1 knockdown\",\n      \"pmids\": [\"39580802\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ITSN1-EPN1 binding interface not mapped\", \"Functional consequence of ITSN1-dependent EPN1 recruitment for cargo not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided direct biophysical confirmation that the ENTH domain itself deforms membranes, grounding the cell-biological adaptor role in an intrinsic membrane-shaping activity.\",\n      \"evidence\": \"In vitro single-particle liposome vesiculation assay with the isolated ENTH domain at physiological concentrations\",\n      \"pmids\": [\"39324332\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single in vitro method; in-cell contribution relative to other curvature drivers not quantified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked EPN1-mediated endocytosis to metabolic and tumor phenotypes via ubiquitin-code crosstalk controlling cargo surface levels.\",\n      \"evidence\": \"Ubiquitination site mutagenesis, co-IP, membrane fractionation, EPN1 siRNA, and in vivo/PDX bladder cancer tumor models\",\n      \"pmids\": [\"38949026\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct EPN1 recognition of K63-polyubiquitinated SNAT2 not demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How EPN1 achieves cargo selectivity and is partitioned among its paralogs (EPN2/EPN3) across tissues and pathways remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No isolated EPN1-specific (paralog-resolved) loss-of-function across the characterized pathways\", \"Structural basis for selective ubiquitinated-cargo recognition not established in this corpus\", \"Mechanistic link between endocytic activity and downstream signaling axes (Cdc42-SRF, Notch) not bridged\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5, 0]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 1, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5, 1, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ITSN1\", \"CLTC\", \"AP2\", \"EPS15\", \"FCHO2\", \"DNM2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}