{"gene":"RBSN","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2008,"finding":"Drosophila Rabenosyn-5 (Rbsn-5) acts as a Rab5 effector that bridges an interaction between Rab5 and the Sec1/Munc18-family protein Vps45, which in turn targets the syntaxin Avalanche (Avl); all four proteins localize specifically to early endosomes and are required for vesicle fusion to form early endosomes, with loss leading to neoplastic tumor formation due to loss of epithelial polarity.","method":"Genetic null mutants, ultrastructural analysis, co-immunoprecipitation, localization studies in Drosophila","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction mapping, ultrastructural phenotypic analysis, multiple orthogonal methods (genetics, EM, co-IP, localization), replicated across multiple mutant alleles","pmids":["18685079"],"is_preprint":false},{"year":2008,"finding":"Drosophila Rbsn-5 is required for maintaining microtubule polarity in oocytes and for pole plasm assembly; long Osk recruits endosomal proteins including Rbsn-5 and stimulates endocytosis, and in rbsn-5 mutant oocytes ectopic Osk induces aberrant F-actin aggregates, indicating Rbsn-5 acts downstream of Osk to promote endosomal cycling which reorganizes F-actin to anchor pole plasm components to the cortex.","method":"Genetic loss-of-function (rbsn-5 null mutants), immunofluorescence, live imaging, epistasis analysis in Drosophila oocytes","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with defined phenotypic readout, multiple mutant analyses, confirmed downstream positioning in pole plasm assembly pathway","pmids":["18272590"],"is_preprint":false},{"year":2010,"finding":"Rbsn-5 regulates endocytosis at the apical side of the Drosophila wing epithelium and is required for planar cell polarity (PCP); during planar polarization, Rbsn-5 is recruited to apical cell boundaries and redistributes along the proximodistal axis in an Fmi-dependent manner; loss of Rbsn-5 causes intracellular accumulation of PCP protein Fmi and PCP defects including aberrant cell packing, hair orientation and formation.","method":"Loss-of-function genetics, immunofluorescence, live imaging, localization analysis in Drosophila wing epithelium","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — defined genetic loss-of-function with specific cellular phenotype, co-localization, and pathway placement, single lab with multiple orthogonal readouts","pmids":["20534670"],"is_preprint":false},{"year":2009,"finding":"In Drosophila wing primordial cells, Rbsn-5 mediates PI3K(III)-dependent regulation of beta-integrin and Fasciclin III (Fas III) localization at distinct membrane domains, but does not mediate PI3K(III)-dependent regulation of DE-cadherin and Flamingo, indicating Rbsn-5 acts downstream of PI3K(III) for only a subset of cargo.","method":"Loss-of-function genetics (rbsn-5 mutant), RNAi knockdown of Vps15, immunofluorescence in Drosophila wing cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with specific cargo readout, single lab, multiple cargo comparisons","pmids":["19798413"],"is_preprint":false},{"year":2011,"finding":"Rbsn-5 (Rab5/Rbsn-5-dependent endocytic pathway) and Mon2 act downstream of long Osk in Drosophila pole plasm assembly; Rbsn-5 promotes formation of specialized vesicles in response to long Osk, and Mon2 acts on these vesicles as a scaffold to instruct actin nucleators Cappuccino and Spire to remodel the actin cytoskeleton for anchoring pole plasm components to the cortex.","method":"Genetic loss-of-function, epistasis analysis, immunofluorescence in Drosophila oocytes","journal":"Bioarchitecture","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined cellular phenotype, corroborates prior work, single lab review/follow-up","pmids":["21922042"],"is_preprint":false},{"year":2014,"finding":"A homozygous missense mutation (p.Gly425Arg) in human RBSN (ZFYVE20) results in expression and localization of Rbsn-5 in wild-type manner but causes a 50% decrease in transferrin accumulation (correctable by wild-type allele transfection), impaired cell proliferation, and cytoskeletal and lysosomal abnormalities, demonstrating a functional defect in the early endocytic pathway.","method":"Patient fibroblast studies, transferrin uptake assay, wild-type rescue transfection, whole exome sequencing confirmed by Sanger sequencing","journal":"Orphanet journal of rare diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional rescue experiment in patient cells with defined endocytic readout, multiple cellular phenotypes assessed, single lab","pmids":["25233840"],"is_preprint":false},{"year":2022,"finding":"Two RBSN missense variants (p.Arg180Gly and p.Gly183Arg) in the FYVE domain abrogate binding to phosphatidylinositol 3-phosphate (PI3P) and prevent RBSN translocation to early endosomes; mutant p.Gly183Arg patient fibroblasts show accumulation of cargo tagged for lysosomal degradation while endosomal recycling is unaltered, indicating these are separation-of-function alleles causing a delay in endosomal maturation without affecting recycling.","method":"Exome sequencing, patient fibroblast cellular/biochemical studies, PI3P binding assays, cargo trafficking assays, subcellular localization","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — PI3P binding assay (in vitro biochemistry), patient cell localization, cargo trafficking with separation-of-function genetic alleles, multiple orthogonal methods in single study","pmids":["35652444"],"is_preprint":false},{"year":2021,"finding":"Drosophila Rabenosyn-5 (Rbsn) binds to the HOPS and CORVET complexes primarily via their shared subunit Vps18, with the interaction mapping to the 773-854 region of Vps18; this Rbsn-Vps18 interaction is required for endosomal transport (but dispensable for autophagy), and Vps18 also participates in beta1 integrin recycling through binding to Rbsn and Vps45.","method":"Co-immunoprecipitation, interaction mapping, genetic rescue experiments in Drosophila","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction mapping with domain identification, genetic rescue assays, single lab with multiple orthogonal methods","pmids":["33781757"],"is_preprint":false},{"year":2024,"finding":"Human Rbsn interacts with CDC42 and functions as a GTPase activating protein (GAP), thereby inhibiting CDC42 activity and suppressing filopodia formation and lung cancer cell migration/invasion; Akt phosphorylates Rbsn at Thr253, and this phosphorylation negates the inhibitory effect of Rbsn on CDC42 activity.","method":"Co-immunoprecipitation, GAP activity assay, phosphorylation site mutagenesis, filopodia formation assay, knockdown/overexpression in lung cancer cells","journal":"Cancer gene therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GAP activity assay with mutagenesis, co-IP, and cellular phenotype, single lab with multiple orthogonal methods","pmids":["39075137"],"is_preprint":false}],"current_model":"Rabenosyn-5 (RBSN/ZFYVE20) is a conserved multi-domain endosomal protein that acts as a Rab5 effector: it binds PI3P via its FYVE domain to localize to early endosomes, bridges Rab5 to the SM protein Vps45 (which targets syntaxin/SNARE machinery) to drive vesicle fusion and early endosome formation, interacts with HOPS/CORVET complexes via Vps18 for endolysosomal transport, and plays separation-of-function roles in cargo recycling versus lysosomal degradation; additionally, it acts as a CDC42 GAP to suppress filopodia formation, a function negated by Akt-mediated phosphorylation at Thr253."},"narrative":{"mechanistic_narrative":"Rabenosyn-5 (RBSN/ZFYVE20) is a conserved multi-domain endosomal protein that organizes early endocytic trafficking as a Rab5 effector, bridging Rab5 to the Sec1/Munc18 protein Vps45, which in turn targets the syntaxin SNARE machinery to drive vesicle fusion and early endosome formation [PMID:18685079]. Membrane targeting depends on its FYVE domain binding phosphatidylinositol 3-phosphate (PI3P): FYVE-domain variants abolish PI3P binding and prevent translocation to early endosomes [PMID:35652444]. Beyond early endosome biogenesis, RBSN engages the HOPS and CORVET tethering complexes through their shared subunit Vps18, an interaction required for endosomal transport and beta1-integrin recycling but dispensable for autophagy [PMID:33781757]. RBSN supports distinct, separable cargo fates: separation-of-function alleles cause accumulation of cargo destined for lysosomal degradation while leaving endosomal recycling intact, indicating it gates endosomal maturation independently of recycling [PMID:35652444]. In humans, RBSN acts downstream of PI3K(III) in endocytic regulation, and a homozygous missense mutation reduces transferrin uptake, impairs proliferation, and produces cytoskeletal and lysosomal abnormalities, establishing a disease-associated defect in the early endocytic pathway [PMID:25233840, PMID:19798413]. RBSN also functions as a CDC42 GTPase-activating protein that suppresses filopodia formation and lung cancer cell migration, an inhibitory activity negated by Akt phosphorylation at Thr253 [PMID:39075137]. In Drosophila, this trafficking activity underlies tissue-level outcomes, including epithelial polarity maintenance, planar cell polarity, and pole plasm assembly through endosomal cycling that remodels the actin cytoskeleton [PMID:18685079, PMID:20534670, PMID:18272590].","teleology":[{"year":2008,"claim":"Established the core molecular logic of RBSN as a Rab5 effector that physically bridges Rab5 to the fusion machinery, answering how early endosomes are formed from incoming vesicles.","evidence":"Genetic null mutants, ultrastructural EM, co-immunoprecipitation and localization in Drosophila","pmids":["18685079"],"confidence":"High","gaps":["Structural basis of the Rab5-Rbsn-5-Vps45 bridge not resolved","Mammalian conservation of the bridging mechanism not tested here"]},{"year":2008,"claim":"Linked RBSN-dependent endosomal cycling to cytoskeletal organization, showing it acts downstream of Oskar to reorganize F-actin and anchor pole plasm.","evidence":"Genetic loss-of-function and epistasis with imaging in Drosophila oocytes","pmids":["18272590"],"confidence":"High","gaps":["Direct molecular link between endosomal cycling and actin remodeling not defined","Cargo mediating actin effects not identified"]},{"year":2009,"claim":"Defined RBSN as a cargo-selective effector downstream of PI3K(III), regulating only a subset of membrane proteins.","evidence":"rbsn-5 mutant and Vps15 RNAi with cargo-specific immunofluorescence in Drosophila wing cells","pmids":["19798413"],"confidence":"Medium","gaps":["Basis of cargo selectivity unknown","Single tissue context"]},{"year":2010,"claim":"Connected RBSN-mediated apical endocytosis to planar cell polarity, showing it is recruited to cell boundaries and required for PCP protein trafficking.","evidence":"Loss-of-function genetics, localization and live imaging in Drosophila wing epithelium","pmids":["20534670"],"confidence":"High","gaps":["Mechanism of Fmi-dependent redistribution unresolved","Direct interaction with PCP machinery not shown"]},{"year":2011,"claim":"Refined the pole plasm model by placing RBSN-generated vesicles upstream of Mon2-directed actin nucleator scaffolding.","evidence":"Genetic loss-of-function and epistasis in Drosophila oocytes","pmids":["21922042"],"confidence":"Medium","gaps":["Vesicle identity and composition not characterized","Follow-up/review corroboration rather than new mechanism"]},{"year":2014,"claim":"Provided the first human disease link, demonstrating a missense mutation causes a functional early-endocytic defect rescuable by wild-type allele.","evidence":"Patient fibroblast transferrin uptake, wild-type rescue transfection, exome sequencing","pmids":["25233840"],"confidence":"Medium","gaps":["Molecular mechanism by which p.Gly425Arg impairs function unknown","Single patient/family"]},{"year":2021,"claim":"Identified the HOPS/CORVET tethering complexes as RBSN partners via Vps18, distinguishing endosomal transport from autophagy functions.","evidence":"Co-IP, interaction mapping, and genetic rescue in Drosophila","pmids":["33781757"],"confidence":"Medium","gaps":["Whether RBSN-Vps18 binding is conserved in human cells not tested here","Structural detail beyond the 773-854 region absent"]},{"year":2022,"claim":"Resolved the membrane-targeting requirement and separated cargo degradation from recycling, defining FYVE/PI3P-dependent endosomal maturation as a distinct RBSN function.","evidence":"PI3P binding assays, patient fibroblast localization and cargo trafficking with separation-of-function alleles","pmids":["35652444"],"confidence":"High","gaps":["How degradation cargo is selectively gated remains undefined","Recycling pathway components engaged by RBSN not enumerated"]},{"year":2024,"claim":"Uncovered a non-trafficking activity of RBSN as a CDC42 GAP regulated by Akt phosphorylation, linking it to cytoskeletal dynamics and cancer cell motility.","evidence":"Co-IP, GAP activity assay, Thr253 phosphosite mutagenesis, filopodia and migration assays in lung cancer cells","pmids":["39075137"],"confidence":"Medium","gaps":["Relationship between GAP activity and endosomal function unclear","Structural basis of GAP catalysis not defined","Single cancer cell context"]},{"year":null,"claim":"How RBSN coordinates its endosomal tethering/fusion role with its CDC42 GAP activity, and how these are integrated by upstream signaling, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model integrating FYVE, Rab5/Vps45, Vps18, and CDC42 GAP functions","Functional crosstalk between trafficking and GAP roles untested","Tissue-specific consequences of each activity not delineated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,8]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,6]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,6,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8]}],"complexes":[],"partners":["RAB5","VPS45","VPS18","CDC42","AKT","STX7"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H1K0","full_name":"Rabenosyn-5","aliases":["110 kDa protein","FYVE finger-containing Rab5 effector protein rabenosyn-5","RAB effector RBSN","Zinc finger FYVE domain-containing protein 20"],"length_aa":784,"mass_kda":88.9,"function":"Rab4/Rab5 effector protein acting in early endocytic membrane fusion and membrane trafficking of recycling endosomes. Required for endosome fusion either homotypically or with clathrin coated vesicles. Plays a role in the lysosomal trafficking of CTSD/cathepsin D from the Golgi to lysosomes. Also promotes the recycling of transferrin directly from early endosomes to the plasma membrane. Binds phospholipid vesicles containing phosphatidylinositol 3-phosphate (PtdInsP3) (PubMed:11062261, PubMed:11788822, PubMed:15020713). Plays a role in the recycling of transferrin receptor to the plasma membrane (PubMed:22308388)","subcellular_location":"Cell membrane; Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9H1K0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RBSN","classification":"Not Classified","n_dependent_lines":362,"n_total_lines":1208,"dependency_fraction":0.2996688741721854},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000131381","cell_line_id":"CID000553","localizations":[{"compartment":"big_aggregates","grade":3},{"compartment":"cytoplasmic","grade":1}],"interactors":[{"gene":"VPS45","stoichiometry":10.0},{"gene":"PDHA1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000553","total_profiled":1310},"omim":[{"mim_id":"620939","title":"MYELOFIBROSIS, CONGENITAL, WITH ANEMIA, NEUTROPENIA, DEVELOPMENTAL DELAY, AND OCULAR ABNORMALITIES; MFANDO","url":"https://www.omim.org/entry/620939"},{"mim_id":"620937","title":"KARIMINEJAD NEURODEVELOPMENTAL SYNDROME; KAREVS","url":"https://www.omim.org/entry/620937"},{"mim_id":"609511","title":"RABENOSYN, RAB EFFECTOR; RBSN","url":"https://www.omim.org/entry/609511"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RBSN"},"hgnc":{"alias_symbol":[],"prev_symbol":["ZFYVE20"]},"alphafold":{"accession":"Q9H1K0","domains":[{"cath_id":"3.30.40.10","chopping":"136-210_246-271","consensus_level":"high","plddt":89.3759,"start":136,"end":271},{"cath_id":"1.20.58,1.10.132","chopping":"275-378","consensus_level":"high","plddt":90.1674,"start":275,"end":378},{"cath_id":"4.10.860,1.10.287","chopping":"744-782","consensus_level":"medium","plddt":87.6523,"start":744,"end":782}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H1K0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H1K0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H1K0-F1-predicted_aligned_error_v6.png","plddt_mean":67.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RBSN","jax_strain_url":"https://www.jax.org/strain/search?query=RBSN"},"sequence":{"accession":"Q9H1K0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H1K0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H1K0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H1K0"}},"corpus_meta":[{"pmid":"18272590","id":"PMC_18272590","title":"The endocytic pathway acts downstream of Oskar in Drosophila germ plasm assembly.","date":"2008","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/18272590","citation_count":139,"is_preprint":false},{"pmid":"27899655","id":"PMC_27899655","title":"Visualization of self-delivering hydrophobically modified siRNA cellular internalization.","date":"2016","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27899655","citation_count":105,"is_preprint":false},{"pmid":"18685079","id":"PMC_18685079","title":"Regulation of early endosomal entry by the Drosophila tumor suppressors Rabenosyn and Vps45.","date":"2008","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/18685079","citation_count":75,"is_preprint":false},{"pmid":"20534670","id":"PMC_20534670","title":"A novel function for the Rab5 effector Rabenosyn-5 in planar cell polarity.","date":"2010","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/20534670","citation_count":35,"is_preprint":false},{"pmid":"25233840","id":"PMC_25233840","title":"Single point mutation in Rabenosyn-5 in a female with intractable seizures and evidence of defective endocytotic trafficking.","date":"2014","source":"Orphanet journal of rare diseases","url":"https://pubmed.ncbi.nlm.nih.gov/25233840","citation_count":23,"is_preprint":false},{"pmid":"19798413","id":"PMC_19798413","title":"Membrane protein location-dependent regulation by PI3K (III) and rabenosyn-5 in Drosophila wing cells.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19798413","citation_count":18,"is_preprint":false},{"pmid":"10644962","id":"PMC_10644962","title":"Proinflammatory cytokine expression of IL-1beta and TNF-alpha by human osteoblast-like MG-63 cells upon exposure to silicon nitride in vitro.","date":"2000","source":"Journal of biomedical materials research","url":"https://pubmed.ncbi.nlm.nih.gov/10644962","citation_count":16,"is_preprint":false},{"pmid":"24718986","id":"PMC_24718986","title":"Clathrin heavy chain plays multiple roles in polarizing the Drosophila oocyte downstream of Bic-D.","date":"2014","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/24718986","citation_count":15,"is_preprint":false},{"pmid":"21922042","id":"PMC_21922042","title":"Oskar-induced endocytic activation and actin remodeling for anchorage of the Drosophila germ plasm.","date":"2011","source":"Bioarchitecture","url":"https://pubmed.ncbi.nlm.nih.gov/21922042","citation_count":14,"is_preprint":false},{"pmid":"25644331","id":"PMC_25644331","title":"Programmed cell death 6 interacting protein (PDCD6IP) and Rabenosyn-5 (ZFYVE20) are potential urinary biomarkers for upper gastrointestinal cancer.","date":"2015","source":"Proteomics. Clinical applications","url":"https://pubmed.ncbi.nlm.nih.gov/25644331","citation_count":11,"is_preprint":false},{"pmid":"33781757","id":"PMC_33781757","title":"Identification of New Interactions between Endolysosomal Tethering Factors.","date":"2021","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/33781757","citation_count":5,"is_preprint":false},{"pmid":"39075137","id":"PMC_39075137","title":"Rabenosyn-5 suppresses non-small cell lung cancer metastasis via inhibiting CDC42 activity.","date":"2024","source":"Cancer gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/39075137","citation_count":3,"is_preprint":false},{"pmid":"40546800","id":"PMC_40546800","title":"Combined Oxaliplatin with 5-Fluorouracil for Effective Chemotherapy Against Gastric Cancer in Animal Model.","date":"2025","source":"International journal of nanomedicine","url":"https://pubmed.ncbi.nlm.nih.gov/40546800","citation_count":2,"is_preprint":false},{"pmid":"39323841","id":"PMC_39323841","title":"Silencing GDI2 inhibits proliferation, migration and invasion of colorectal cancer through activation of p53 signaling pathway.","date":"2024","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/39323841","citation_count":1,"is_preprint":false},{"pmid":"35652444","id":"PMC_35652444","title":"RABENOSYN separation-of-function mutations uncouple endosomal recycling from lysosomal degradation, causing a distinct Mendelian disorder.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35652444","citation_count":0,"is_preprint":false},{"pmid":"41473159","id":"PMC_41473159","title":"Identifying sepsis susceptibility genes in post-surgical patients using an artificial intelligence approach.","date":"2025","source":"Frontiers in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41473159","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10252,"output_tokens":2582,"usd":0.034743,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9713,"output_tokens":3019,"usd":0.06202,"stage2_stop_reason":"end_turn"},"total_usd":0.096763,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"Drosophila Rabenosyn-5 (Rbsn-5) acts as a Rab5 effector that bridges an interaction between Rab5 and the Sec1/Munc18-family protein Vps45, which in turn targets the syntaxin Avalanche (Avl); all four proteins localize specifically to early endosomes and are required for vesicle fusion to form early endosomes, with loss leading to neoplastic tumor formation due to loss of epithelial polarity.\",\n      \"method\": \"Genetic null mutants, ultrastructural analysis, co-immunoprecipitation, localization studies in Drosophila\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction mapping, ultrastructural phenotypic analysis, multiple orthogonal methods (genetics, EM, co-IP, localization), replicated across multiple mutant alleles\",\n      \"pmids\": [\"18685079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Drosophila Rbsn-5 is required for maintaining microtubule polarity in oocytes and for pole plasm assembly; long Osk recruits endosomal proteins including Rbsn-5 and stimulates endocytosis, and in rbsn-5 mutant oocytes ectopic Osk induces aberrant F-actin aggregates, indicating Rbsn-5 acts downstream of Osk to promote endosomal cycling which reorganizes F-actin to anchor pole plasm components to the cortex.\",\n      \"method\": \"Genetic loss-of-function (rbsn-5 null mutants), immunofluorescence, live imaging, epistasis analysis in Drosophila oocytes\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with defined phenotypic readout, multiple mutant analyses, confirmed downstream positioning in pole plasm assembly pathway\",\n      \"pmids\": [\"18272590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Rbsn-5 regulates endocytosis at the apical side of the Drosophila wing epithelium and is required for planar cell polarity (PCP); during planar polarization, Rbsn-5 is recruited to apical cell boundaries and redistributes along the proximodistal axis in an Fmi-dependent manner; loss of Rbsn-5 causes intracellular accumulation of PCP protein Fmi and PCP defects including aberrant cell packing, hair orientation and formation.\",\n      \"method\": \"Loss-of-function genetics, immunofluorescence, live imaging, localization analysis in Drosophila wing epithelium\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined genetic loss-of-function with specific cellular phenotype, co-localization, and pathway placement, single lab with multiple orthogonal readouts\",\n      \"pmids\": [\"20534670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Drosophila wing primordial cells, Rbsn-5 mediates PI3K(III)-dependent regulation of beta-integrin and Fasciclin III (Fas III) localization at distinct membrane domains, but does not mediate PI3K(III)-dependent regulation of DE-cadherin and Flamingo, indicating Rbsn-5 acts downstream of PI3K(III) for only a subset of cargo.\",\n      \"method\": \"Loss-of-function genetics (rbsn-5 mutant), RNAi knockdown of Vps15, immunofluorescence in Drosophila wing cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with specific cargo readout, single lab, multiple cargo comparisons\",\n      \"pmids\": [\"19798413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Rbsn-5 (Rab5/Rbsn-5-dependent endocytic pathway) and Mon2 act downstream of long Osk in Drosophila pole plasm assembly; Rbsn-5 promotes formation of specialized vesicles in response to long Osk, and Mon2 acts on these vesicles as a scaffold to instruct actin nucleators Cappuccino and Spire to remodel the actin cytoskeleton for anchoring pole plasm components to the cortex.\",\n      \"method\": \"Genetic loss-of-function, epistasis analysis, immunofluorescence in Drosophila oocytes\",\n      \"journal\": \"Bioarchitecture\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined cellular phenotype, corroborates prior work, single lab review/follow-up\",\n      \"pmids\": [\"21922042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A homozygous missense mutation (p.Gly425Arg) in human RBSN (ZFYVE20) results in expression and localization of Rbsn-5 in wild-type manner but causes a 50% decrease in transferrin accumulation (correctable by wild-type allele transfection), impaired cell proliferation, and cytoskeletal and lysosomal abnormalities, demonstrating a functional defect in the early endocytic pathway.\",\n      \"method\": \"Patient fibroblast studies, transferrin uptake assay, wild-type rescue transfection, whole exome sequencing confirmed by Sanger sequencing\",\n      \"journal\": \"Orphanet journal of rare diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional rescue experiment in patient cells with defined endocytic readout, multiple cellular phenotypes assessed, single lab\",\n      \"pmids\": [\"25233840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Two RBSN missense variants (p.Arg180Gly and p.Gly183Arg) in the FYVE domain abrogate binding to phosphatidylinositol 3-phosphate (PI3P) and prevent RBSN translocation to early endosomes; mutant p.Gly183Arg patient fibroblasts show accumulation of cargo tagged for lysosomal degradation while endosomal recycling is unaltered, indicating these are separation-of-function alleles causing a delay in endosomal maturation without affecting recycling.\",\n      \"method\": \"Exome sequencing, patient fibroblast cellular/biochemical studies, PI3P binding assays, cargo trafficking assays, subcellular localization\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — PI3P binding assay (in vitro biochemistry), patient cell localization, cargo trafficking with separation-of-function genetic alleles, multiple orthogonal methods in single study\",\n      \"pmids\": [\"35652444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Drosophila Rabenosyn-5 (Rbsn) binds to the HOPS and CORVET complexes primarily via their shared subunit Vps18, with the interaction mapping to the 773-854 region of Vps18; this Rbsn-Vps18 interaction is required for endosomal transport (but dispensable for autophagy), and Vps18 also participates in beta1 integrin recycling through binding to Rbsn and Vps45.\",\n      \"method\": \"Co-immunoprecipitation, interaction mapping, genetic rescue experiments in Drosophila\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction mapping with domain identification, genetic rescue assays, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"33781757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Human Rbsn interacts with CDC42 and functions as a GTPase activating protein (GAP), thereby inhibiting CDC42 activity and suppressing filopodia formation and lung cancer cell migration/invasion; Akt phosphorylates Rbsn at Thr253, and this phosphorylation negates the inhibitory effect of Rbsn on CDC42 activity.\",\n      \"method\": \"Co-immunoprecipitation, GAP activity assay, phosphorylation site mutagenesis, filopodia formation assay, knockdown/overexpression in lung cancer cells\",\n      \"journal\": \"Cancer gene therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GAP activity assay with mutagenesis, co-IP, and cellular phenotype, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"39075137\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Rabenosyn-5 (RBSN/ZFYVE20) is a conserved multi-domain endosomal protein that acts as a Rab5 effector: it binds PI3P via its FYVE domain to localize to early endosomes, bridges Rab5 to the SM protein Vps45 (which targets syntaxin/SNARE machinery) to drive vesicle fusion and early endosome formation, interacts with HOPS/CORVET complexes via Vps18 for endolysosomal transport, and plays separation-of-function roles in cargo recycling versus lysosomal degradation; additionally, it acts as a CDC42 GAP to suppress filopodia formation, a function negated by Akt-mediated phosphorylation at Thr253.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Rabenosyn-5 (RBSN/ZFYVE20) is a conserved multi-domain endosomal protein that organizes early endocytic trafficking as a Rab5 effector, bridging Rab5 to the Sec1/Munc18 protein Vps45, which in turn targets the syntaxin SNARE machinery to drive vesicle fusion and early endosome formation [#0]. Membrane targeting depends on its FYVE domain binding phosphatidylinositol 3-phosphate (PI3P): FYVE-domain variants abolish PI3P binding and prevent translocation to early endosomes [#6]. Beyond early endosome biogenesis, RBSN engages the HOPS and CORVET tethering complexes through their shared subunit Vps18, an interaction required for endosomal transport and beta1-integrin recycling but dispensable for autophagy [#7]. RBSN supports distinct, separable cargo fates: separation-of-function alleles cause accumulation of cargo destined for lysosomal degradation while leaving endosomal recycling intact, indicating it gates endosomal maturation independently of recycling [#6]. In humans, RBSN acts downstream of PI3K(III) in endocytic regulation, and a homozygous missense mutation reduces transferrin uptake, impairs proliferation, and produces cytoskeletal and lysosomal abnormalities, establishing a disease-associated defect in the early endocytic pathway [#5, #3]. RBSN also functions as a CDC42 GTPase-activating protein that suppresses filopodia formation and lung cancer cell migration, an inhibitory activity negated by Akt phosphorylation at Thr253 [#8]. In Drosophila, this trafficking activity underlies tissue-level outcomes, including epithelial polarity maintenance, planar cell polarity, and pole plasm assembly through endosomal cycling that remodels the actin cytoskeleton [#0, #2, #1].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established the core molecular logic of RBSN as a Rab5 effector that physically bridges Rab5 to the fusion machinery, answering how early endosomes are formed from incoming vesicles.\",\n      \"evidence\": \"Genetic null mutants, ultrastructural EM, co-immunoprecipitation and localization in Drosophila\",\n      \"pmids\": [\"18685079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the Rab5-Rbsn-5-Vps45 bridge not resolved\", \"Mammalian conservation of the bridging mechanism not tested here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked RBSN-dependent endosomal cycling to cytoskeletal organization, showing it acts downstream of Oskar to reorganize F-actin and anchor pole plasm.\",\n      \"evidence\": \"Genetic loss-of-function and epistasis with imaging in Drosophila oocytes\",\n      \"pmids\": [\"18272590\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between endosomal cycling and actin remodeling not defined\", \"Cargo mediating actin effects not identified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined RBSN as a cargo-selective effector downstream of PI3K(III), regulating only a subset of membrane proteins.\",\n      \"evidence\": \"rbsn-5 mutant and Vps15 RNAi with cargo-specific immunofluorescence in Drosophila wing cells\",\n      \"pmids\": [\"19798413\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Basis of cargo selectivity unknown\", \"Single tissue context\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected RBSN-mediated apical endocytosis to planar cell polarity, showing it is recruited to cell boundaries and required for PCP protein trafficking.\",\n      \"evidence\": \"Loss-of-function genetics, localization and live imaging in Drosophila wing epithelium\",\n      \"pmids\": [\"20534670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of Fmi-dependent redistribution unresolved\", \"Direct interaction with PCP machinery not shown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Refined the pole plasm model by placing RBSN-generated vesicles upstream of Mon2-directed actin nucleator scaffolding.\",\n      \"evidence\": \"Genetic loss-of-function and epistasis in Drosophila oocytes\",\n      \"pmids\": [\"21922042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Vesicle identity and composition not characterized\", \"Follow-up/review corroboration rather than new mechanism\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided the first human disease link, demonstrating a missense mutation causes a functional early-endocytic defect rescuable by wild-type allele.\",\n      \"evidence\": \"Patient fibroblast transferrin uptake, wild-type rescue transfection, exome sequencing\",\n      \"pmids\": [\"25233840\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism by which p.Gly425Arg impairs function unknown\", \"Single patient/family\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified the HOPS/CORVET tethering complexes as RBSN partners via Vps18, distinguishing endosomal transport from autophagy functions.\",\n      \"evidence\": \"Co-IP, interaction mapping, and genetic rescue in Drosophila\",\n      \"pmids\": [\"33781757\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RBSN-Vps18 binding is conserved in human cells not tested here\", \"Structural detail beyond the 773-854 region absent\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the membrane-targeting requirement and separated cargo degradation from recycling, defining FYVE/PI3P-dependent endosomal maturation as a distinct RBSN function.\",\n      \"evidence\": \"PI3P binding assays, patient fibroblast localization and cargo trafficking with separation-of-function alleles\",\n      \"pmids\": [\"35652444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How degradation cargo is selectively gated remains undefined\", \"Recycling pathway components engaged by RBSN not enumerated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Uncovered a non-trafficking activity of RBSN as a CDC42 GAP regulated by Akt phosphorylation, linking it to cytoskeletal dynamics and cancer cell motility.\",\n      \"evidence\": \"Co-IP, GAP activity assay, Thr253 phosphosite mutagenesis, filopodia and migration assays in lung cancer cells\",\n      \"pmids\": [\"39075137\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between GAP activity and endosomal function unclear\", \"Structural basis of GAP catalysis not defined\", \"Single cancer cell context\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RBSN coordinates its endosomal tethering/fusion role with its CDC42 GAP activity, and how these are integrated by upstream signaling, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model integrating FYVE, Rab5/Vps45, Vps18, and CDC42 GAP functions\", \"Functional crosstalk between trafficking and GAP roles untested\", \"Tissue-specific consequences of each activity not delineated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 6, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RAB5\", \"VPS45\", \"VPS18\", \"CDC42\", \"AKT\", \"STX7\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}