{"gene":"RAB5B","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1992,"finding":"RAB5B was identified as a 215-amino-acid small GTPase that binds GTP and GDP, displays low intrinsic GTP hydrolysis activity (~0.005/min), and localizes to the plasma membrane by subcellular fractionation and indirect immunofluorescence.","method":"GST fusion protein purification, GTP/GDP binding assay, GTP hydrolysis assay, indirect immunofluorescence, subcellular fractionation","journal":"The Journal of Clinical Investigation","confidence":"Medium","confidence_rationale":"Tier 1-2 / Weak — in vitro biochemical assays and direct localization, single study, single lab","pmids":["1541686"],"is_preprint":false},{"year":1999,"finding":"EEA1 (early endosomal autoantigen) directly interacts with RAB5B in a GTP-dependent manner via both its C-terminal and N-terminal domains, and EEA1 colocalizes with RAB5B on early endosomes. A pig brain cytosol GAP activity preferentially stimulates RAB5B GTPase activity over RAB5A.","method":"Yeast two-hybrid screen, biochemical binding confirmation, confocal immunofluorescence, GTPase activity assay","journal":"European Journal of Biochemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal yeast two-hybrid and biochemical confirmation with GTP-dependence, co-localization, and GTPase activity assays in single study","pmids":["10491193"],"is_preprint":false},{"year":1999,"finding":"The three RAB5 isoforms (RAB5A, RAB5B, RAB5C) are differentially phosphorylated in vitro: RAB5A is efficiently phosphorylated by ERK1 but not ERK2, while cdc2 kinase preferentially phosphorylates Ser-123 of RAB5B.","method":"In vitro kinase assay with recombinant proteins and purified kinases (ERK1, ERK2, cdc2)","journal":"FEBS Letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro kinase assay with recombinant proteins, single lab, single study","pmids":["10403367"],"is_preprint":false},{"year":2004,"finding":"RAB5B is required for DHPG-mediated neuroprotection against NMDA toxicity in organotypic hippocampal cultures; antisense oligonucleotide knockdown of RAB5B suppressed DHPG-induced protection, and this protection was abolished by disrupting endocytosis via osmotic shock/K+ depletion, placing RAB5B in a pathway facilitating NMDA receptor endocytosis.","method":"Antisense oligonucleotide knockdown in organotypic hippocampal cultures, cell viability assay, pharmacological inhibition of endocytosis","journal":"Brain Research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional knockdown with defined phenotypic readout and epistasis via endocytosis inhibition, single lab","pmids":["15518642"],"is_preprint":false},{"year":2015,"finding":"LRRK2 kinase phosphorylates RAB5B at Thr6 in vitro and in cells expressing LRRK2 G2019S. Phosphomimetic T6D mutation enhances RAB5B GTPase activity and produces phenotypes consistent with inactive RAB5B (longer neurite length, reduced EGFR degradation), suggesting LRRK2 acts as a GAP-like regulator of RAB5B signaling.","method":"In vitro kinase assay with recombinant proteins, mass spectrometry, western blot with phospho-specific approach, neurite outgrowth assay, EGFR degradation assay, GTPase activity assay","journal":"Journal of Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mass spectrometry site identification, confirmed in cells, functional consequences tested by multiple orthogonal assays in single study","pmids":["25605758"],"is_preprint":false},{"year":2019,"finding":"RAB5B knockdown increases HBV DNA production >30-fold by increasing LHBs mRNA transcription (via HNF4α upregulation) and is required for transport of large hepatitis B surface protein (LHBs) from the ER to multivesicular bodies (MVB); depletion causes LHBs accumulation in the ER.","method":"siRNA knockdown in HepG2.2.15 cells, northern blotting, immunofluorescence microscopy, siRNA screen of 62 Rab proteins","journal":"Journal of Virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional siRNA knockdown with defined trafficking phenotype and transcriptional analysis, multiple orthogonal methods, single lab","pmids":["31118260"],"is_preprint":false},{"year":2018,"finding":"RAB5B is a direct target of miR-130a-3p; overexpression of miR-130a-3p downregulates RAB5B protein and knockdown of RAB5B inhibits proliferation, migration, and invasion of breast cancer stem cell-like cells.","method":"miRNA overexpression/knockdown, RAB5B siRNA knockdown, proliferation/migration/invasion assays","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2-3 / Weak — functional knockdown with multiple phenotypic readouts but no direct binding validation of miRNA-RAB5B interaction cited in abstract, single lab","pmids":["29746865"],"is_preprint":false},{"year":2022,"finding":"A dominant negative RAB5B variant (p.Asp136His) causes defective early endosome (EE) fusion and endocytosis, leading to failure to process proSP-B and proSP-C into mature surfactant proteins SP-B and SP-C in alveolar type II cells. RAB5B and EEA1 colocalize with proSP-B and proSP-C in normal lung, establishing RAB5B and early endosomes as required for the surfactant protein trafficking/processing pathway.","method":"Knock-in of variant into C. elegans ortholog (genetic epistasis), endocytosis assays, early endosome fusion assay, immunostaining of patient lung biopsy, colocalization microscopy","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods including in vivo genetic model, patient tissue immunostaining, and functional endocytosis/fusion assays, convergent evidence","pmids":["35121658"],"is_preprint":false},{"year":2023,"finding":"RAB5B is upregulated by tranexamic acid (TXA) in keratinocytes and promotes clustering of endocytic melanocores; RAB5B silencing reduces melanocore clustering, and melanocores colocalize with RAB5B and LAMP1.","method":"Transcriptome sequencing, RAB5B siRNA silencing, transmission electron microscopy, colocalization microscopy","journal":"Experimental Dermatology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, knockdown with phenotypic readout but limited mechanistic follow-up","pmids":["36779692"],"is_preprint":false},{"year":2024,"finding":"RAB5B interacts with CD109 in KRAS-mutant pancreatic cancer cells; this interaction bypasses canonical endosomal trafficking by anchoring RAB5B to lipid rafts of multivesicular bodies, facilitating packaging of circPNIT into CD109+ extracellular vesicles.","method":"Co-immunoprecipitation, lipid raft fractionation, extracellular vesicle isolation and analysis, in vitro and in vivo functional assays","journal":"Advanced Science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic details inferred from limited co-IP and fractionation data in abstract","pmids":["39488792"],"is_preprint":false},{"year":2025,"finding":"Under nutrient stress (serum withdrawal), the LC3 lipidation complex (ATG5–ATG12–ATG16L1) is recruited to synapses via RAB5B-positive endosomes in a dynein-dependent manner, coupling nutrient sensing to localized synaptic autophagy. Live imaging shows enhanced RAB5B–ATG16L1 co-trafficking and increased ATG5 mobility upon serum withdrawal.","method":"Live imaging, co-trafficking analysis, dynein inhibition, autophagy assays, synaptic proteomics","journal":"bioRxiv (preprint)","confidence":"Low","confidence_rationale":"Tier 2-3 / Weak — preprint, single lab, live imaging and functional assays but not yet peer-reviewed","pmids":["bio_10.1101_2025.11.25.690410"],"is_preprint":true}],"current_model":"RAB5B is a small Rab GTPase that localizes to plasma membrane and early endosomes, where it regulates endocytosis and early endosomal membrane fusion (via GTP-dependent interaction with EEA1); it is phosphorylated on Thr6 by LRRK2 (which enhances its GTPase activity and negatively regulates its signaling), and on Ser-123 by cdc2 kinase; it is required for surfactant protein processing/trafficking, NMDA receptor endocytosis-mediated neuroprotection, and serves as a trafficking regulator linking early endosomes to autophagy precursor delivery at synapses under nutrient stress."},"narrative":{"mechanistic_narrative":"RAB5B is a small Rab GTPase that controls early endosomal membrane fusion and endocytic trafficking, binding GTP and GDP with low intrinsic hydrolysis activity and localizing to the plasma membrane [PMID:1541686]. In its GTP-bound state it directly recruits the early endosomal tethering factor EEA1, with which it colocalizes on early endosomes, providing the molecular basis for endosome fusion [PMID:10491193]. RAB5B activity is regulated by phosphorylation: LRRK2 phosphorylates Thr6, enhancing GTPase activity and producing inactive-RAB5B phenotypes including reduced EGFR degradation, while cdc2 kinase phosphorylates Ser-123 [PMID:25605758, PMID:10403367]. Through this endocytic and fusion machinery RAB5B supports diverse cargo-handling pathways — it facilitates NMDA receptor endocytosis underlying neuroprotection [PMID:15518642] and is required for trafficking and maturation of pulmonary surfactant proteins, where a dominant-negative p.Asp136His variant disrupts early endosome fusion and blocks processing of proSP-B and proSP-C [PMID:35121658]. Beyond these core roles, RAB5B participates in trafficking events co-opted in disease contexts, including ER-to-multivesicular-body transport of the hepatitis B large surface protein [PMID:31118260].","teleology":[{"year":1992,"claim":"Established RAB5B as a bona fide small GTPase with nucleotide-binding and slow hydrolysis kinetics, defining its biochemical identity and membrane association.","evidence":"GST fusion purification, GTP/GDP binding and hydrolysis assays, immunofluorescence and subcellular fractionation","pmids":["1541686"],"confidence":"Medium","gaps":["No effector or regulator identified at this stage","Plasma membrane localization not yet reconciled with endosomal function"]},{"year":1999,"claim":"Identified EEA1 as a GTP-dependent direct effector, providing the mechanistic link between RAB5B activation and early endosomal tethering/fusion.","evidence":"Yeast two-hybrid screen with biochemical binding confirmation, confocal colocalization, and GAP/GTPase activity assays on brain cytosol","pmids":["10491193"],"confidence":"High","gaps":["The brain GAP activity stimulating RAB5B was not molecularly identified","Functional consequence of EEA1 binding for fusion not directly tested here"]},{"year":1999,"claim":"Showed RAB5 isoforms are differentially phosphorylated, with cdc2 targeting RAB5B Ser-123, raising the possibility of cell-cycle-coupled regulation distinct from other isoforms.","evidence":"In vitro kinase assays with recombinant RAB5 isoforms and purified ERK1/ERK2/cdc2","pmids":["10403367"],"confidence":"Medium","gaps":["In vitro only; cellular phosphorylation not demonstrated","Functional effect of Ser-123 phosphorylation unknown"]},{"year":2004,"claim":"Placed RAB5B functionally in a neuronal endocytic pathway by showing it is required for NMDA-receptor-endocytosis-dependent neuroprotection.","evidence":"Antisense knockdown in organotypic hippocampal cultures with viability readout and pharmacological endocytosis blockade","pmids":["15518642"],"confidence":"Medium","gaps":["Direct demonstration that RAB5B drives NMDA receptor internalization not shown","Effectors mediating this neuronal role unidentified"]},{"year":2015,"claim":"Defined LRRK2 as a kinase regulator of RAB5B, with Thr6 phosphorylation enhancing GTPase activity to negatively tune RAB5B signaling.","evidence":"In vitro kinase assay with MS site mapping, cellular validation with LRRK2 G2019S, neurite outgrowth, EGFR degradation, and GTPase assays","pmids":["25605758"],"confidence":"High","gaps":["Whether LRRK2 acts directly as a GAP or via another mechanism not resolved","Physiological contexts of Thr6 phosphorylation in vivo not established"]},{"year":2018,"claim":"Linked RAB5B to cancer cell behavior as a miR-130a-3p target whose depletion impairs proliferation, migration, and invasion.","evidence":"miRNA over/knockdown and RAB5B siRNA with proliferation/migration/invasion assays in breast cancer stem-like cells","pmids":["29746865"],"confidence":"Medium","gaps":["Direct miRNA-RAB5B binding not validated","Trafficking mechanism connecting RAB5B to invasive phenotype not defined"]},{"year":2019,"claim":"Demonstrated a required role for RAB5B in ER-to-MVB transport, exploited by hepatitis B large surface protein, and an unexpected effect on viral transcription.","evidence":"siRNA screen of 62 Rabs in HepG2.2.15 cells, northern blotting, immunofluorescence","pmids":["31118260"],"confidence":"Medium","gaps":["Mechanism linking RAB5B loss to HNF4α/LHBs transcription unclear","Effectors mediating ER-to-MVB transport unidentified"]},{"year":2022,"claim":"Connected RAB5B-dependent endosome fusion to surfactant protein maturation and established a dominant-negative disease variant impairing endocytosis.","evidence":"C. elegans ortholog knock-in of p.Asp136His, endocytosis and early endosome fusion assays, patient lung immunostaining and colocalization","pmids":["35121658"],"confidence":"High","gaps":["Direct biochemical effect of D136H on nucleotide cycling not shown","Whether proSP processing failure is due to endosomal or upstream routing not fully dissected"]},{"year":2023,"claim":"Implicated RAB5B in endocytic melanocore clustering downstream of tranexamic acid in keratinocytes.","evidence":"Transcriptome sequencing, siRNA silencing, TEM, colocalization with LAMP1","pmids":["36779692"],"confidence":"Low","gaps":["Single lab with limited mechanistic follow-up","Effectors and trafficking steps for melanocore clustering undefined"]},{"year":2024,"claim":"Reported a non-canonical RAB5B function via CD109 interaction at MVB lipid rafts to package circRNA into extracellular vesicles in pancreatic cancer.","evidence":"Co-IP, lipid raft fractionation, EV isolation, in vitro and in vivo assays","pmids":["39488792"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation","Mechanism of lipid raft anchoring inferred from limited fractionation data"]},{"year":2025,"claim":"Proposed RAB5B-positive endosomes as carriers delivering the LC3 lipidation complex to synapses under nutrient stress, coupling endosomal trafficking to localized autophagy.","evidence":"Live imaging, co-trafficking analysis, dynein inhibition, autophagy assays, synaptic proteomics (preprint)","pmids":["bio_10.1101_2025.11.25.690410"],"confidence":"Low","gaps":["Preprint, not peer-reviewed","Direct interaction between RAB5B and ATG16L1/ATG5 not demonstrated","Mechanism of nutrient-stress-triggered recruitment unclear"]},{"year":null,"claim":"The full set of RAB5B GEFs and GAPs and the structural basis for its functional differences from RAB5A/RAB5C remain undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No GEF identified for RAB5B","GAP stimulating RAB5B not molecularly characterized","No structural model linking nucleotide state to effector selectivity"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,1,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1,7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,5,7]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[10]}],"complexes":[],"partners":["EEA1","LRRK2","CD109"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P61020","full_name":"Ras-related protein Rab-5B","aliases":[],"length_aa":215,"mass_kda":23.7,"function":"The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes. Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different sets of downstream effectors directly responsible for vesicle formation, movement, tethering and fusion (PubMed:16086013, PubMed:17562788). Involved in early endocytic trafficking (PubMed:16086013, PubMed:17562788). Required for EEA1 recruitment to early endosomes (PubMed:16086013, PubMed:17562788). Required for EGF and transferrin endocytosis and trafficking through early endosomes (PubMed:16086013, PubMed:17562788)","subcellular_location":"Cell membrane; Early endosome membrane; Melanosome","url":"https://www.uniprot.org/uniprotkb/P61020/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAB5B","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000111540","cell_line_id":"CID000439","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"RAB5A","stoichiometry":10.0},{"gene":"SCAMP2","stoichiometry":10.0},{"gene":"GDI2","stoichiometry":4.0},{"gene":"CHM","stoichiometry":0.2},{"gene":"GDI1","stoichiometry":0.2},{"gene":"SCAMP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000439","total_profiled":1310},"omim":[{"mim_id":"620229","title":"FHF COMPLEX SUBUNIT HOOK-INTERACTING PROTEIN 1B; FHIP1B","url":"https://www.omim.org/entry/620229"},{"mim_id":"617312","title":"FHF COMPLEX SUBUNIT HOOK-INTERACTING PROTEIN 2A; FHIP2A","url":"https://www.omim.org/entry/617312"},{"mim_id":"617211","title":"DERMOKINE; DMKN","url":"https://www.omim.org/entry/617211"},{"mim_id":"613103","title":"SERINE/ARGININE REPETITIVE MATRIX PROTEIN 4; SRRM4","url":"https://www.omim.org/entry/613103"},{"mim_id":"610223","title":"RAS AND RAB INTERACTOR 3; RIN3","url":"https://www.omim.org/entry/610223"}],"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/RAB5B"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P61020","domains":[{"cath_id":"3.40.50.300","chopping":"16-179","consensus_level":"high","plddt":96.1126,"start":16,"end":179}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P61020","model_url":"https://alphafold.ebi.ac.uk/files/AF-P61020-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P61020-F1-predicted_aligned_error_v6.png","plddt_mean":85.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAB5B","jax_strain_url":"https://www.jax.org/strain/search?query=RAB5B"},"sequence":{"accession":"P61020","fasta_url":"https://rest.uniprot.org/uniprotkb/P61020.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P61020/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P61020"}},"corpus_meta":[{"pmid":"29746865","id":"PMC_29746865","title":"MiR-130a-3p inhibits migration and invasion by regulating RAB5B in human breast cancer stem cell-like cells.","date":"2018","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/29746865","citation_count":89,"is_preprint":false},{"pmid":"10403367","id":"PMC_10403367","title":"The small GTPases Rab5a, Rab5b and Rab5c are differentially phosphorylated in vitro.","date":"1999","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/10403367","citation_count":72,"is_preprint":false},{"pmid":"25605758","id":"PMC_25605758","title":"An early endosome regulator, Rab5b, is an LRRK2 kinase substrate.","date":"2015","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25605758","citation_count":61,"is_preprint":false},{"pmid":"10491193","id":"PMC_10491193","title":"Direct interaction of EEA1 with Rab5b.","date":"1999","source":"European journal of 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A pig brain cytosol GAP activity preferentially stimulates RAB5B GTPase activity over RAB5A.\",\n      \"method\": \"Yeast two-hybrid screen, biochemical binding confirmation, confocal immunofluorescence, GTPase activity assay\",\n      \"journal\": \"European Journal of Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal yeast two-hybrid and biochemical confirmation with GTP-dependence, co-localization, and GTPase activity assays in single study\",\n      \"pmids\": [\"10491193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The three RAB5 isoforms (RAB5A, RAB5B, RAB5C) are differentially phosphorylated in vitro: RAB5A is efficiently phosphorylated by ERK1 but not ERK2, while cdc2 kinase preferentially phosphorylates Ser-123 of RAB5B.\",\n      \"method\": \"In vitro kinase assay with recombinant proteins and purified kinases (ERK1, ERK2, cdc2)\",\n      \"journal\": \"FEBS Letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro kinase assay with recombinant proteins, single lab, single study\",\n      \"pmids\": [\"10403367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"RAB5B is required for DHPG-mediated neuroprotection against NMDA toxicity in organotypic hippocampal cultures; antisense oligonucleotide knockdown of RAB5B suppressed DHPG-induced protection, and this protection was abolished by disrupting endocytosis via osmotic shock/K+ depletion, placing RAB5B in a pathway facilitating NMDA receptor endocytosis.\",\n      \"method\": \"Antisense oligonucleotide knockdown in organotypic hippocampal cultures, cell viability assay, pharmacological inhibition of endocytosis\",\n      \"journal\": \"Brain Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional knockdown with defined phenotypic readout and epistasis via endocytosis inhibition, single lab\",\n      \"pmids\": [\"15518642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LRRK2 kinase phosphorylates RAB5B at Thr6 in vitro and in cells expressing LRRK2 G2019S. Phosphomimetic T6D mutation enhances RAB5B GTPase activity and produces phenotypes consistent with inactive RAB5B (longer neurite length, reduced EGFR degradation), suggesting LRRK2 acts as a GAP-like regulator of RAB5B signaling.\",\n      \"method\": \"In vitro kinase assay with recombinant proteins, mass spectrometry, western blot with phospho-specific approach, neurite outgrowth assay, EGFR degradation assay, GTPase activity assay\",\n      \"journal\": \"Journal of Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mass spectrometry site identification, confirmed in cells, functional consequences tested by multiple orthogonal assays in single study\",\n      \"pmids\": [\"25605758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAB5B knockdown increases HBV DNA production >30-fold by increasing LHBs mRNA transcription (via HNF4α upregulation) and is required for transport of large hepatitis B surface protein (LHBs) from the ER to multivesicular bodies (MVB); depletion causes LHBs accumulation in the ER.\",\n      \"method\": \"siRNA knockdown in HepG2.2.15 cells, northern blotting, immunofluorescence microscopy, siRNA screen of 62 Rab proteins\",\n      \"journal\": \"Journal of Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional siRNA knockdown with defined trafficking phenotype and transcriptional analysis, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"31118260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"RAB5B is a direct target of miR-130a-3p; overexpression of miR-130a-3p downregulates RAB5B protein and knockdown of RAB5B inhibits proliferation, migration, and invasion of breast cancer stem cell-like cells.\",\n      \"method\": \"miRNA overexpression/knockdown, RAB5B siRNA knockdown, proliferation/migration/invasion assays\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Weak — functional knockdown with multiple phenotypic readouts but no direct binding validation of miRNA-RAB5B interaction cited in abstract, single lab\",\n      \"pmids\": [\"29746865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A dominant negative RAB5B variant (p.Asp136His) causes defective early endosome (EE) fusion and endocytosis, leading to failure to process proSP-B and proSP-C into mature surfactant proteins SP-B and SP-C in alveolar type II cells. RAB5B and EEA1 colocalize with proSP-B and proSP-C in normal lung, establishing RAB5B and early endosomes as required for the surfactant protein trafficking/processing pathway.\",\n      \"method\": \"Knock-in of variant into C. elegans ortholog (genetic epistasis), endocytosis assays, early endosome fusion assay, immunostaining of patient lung biopsy, colocalization microscopy\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods including in vivo genetic model, patient tissue immunostaining, and functional endocytosis/fusion assays, convergent evidence\",\n      \"pmids\": [\"35121658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RAB5B is upregulated by tranexamic acid (TXA) in keratinocytes and promotes clustering of endocytic melanocores; RAB5B silencing reduces melanocore clustering, and melanocores colocalize with RAB5B and LAMP1.\",\n      \"method\": \"Transcriptome sequencing, RAB5B siRNA silencing, transmission electron microscopy, colocalization microscopy\",\n      \"journal\": \"Experimental Dermatology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, knockdown with phenotypic readout but limited mechanistic follow-up\",\n      \"pmids\": [\"36779692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RAB5B interacts with CD109 in KRAS-mutant pancreatic cancer cells; this interaction bypasses canonical endosomal trafficking by anchoring RAB5B to lipid rafts of multivesicular bodies, facilitating packaging of circPNIT into CD109+ extracellular vesicles.\",\n      \"method\": \"Co-immunoprecipitation, lipid raft fractionation, extracellular vesicle isolation and analysis, in vitro and in vivo functional assays\",\n      \"journal\": \"Advanced Science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic details inferred from limited co-IP and fractionation data in abstract\",\n      \"pmids\": [\"39488792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Under nutrient stress (serum withdrawal), the LC3 lipidation complex (ATG5–ATG12–ATG16L1) is recruited to synapses via RAB5B-positive endosomes in a dynein-dependent manner, coupling nutrient sensing to localized synaptic autophagy. Live imaging shows enhanced RAB5B–ATG16L1 co-trafficking and increased ATG5 mobility upon serum withdrawal.\",\n      \"method\": \"Live imaging, co-trafficking analysis, dynein inhibition, autophagy assays, synaptic proteomics\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2-3 / Weak — preprint, single lab, live imaging and functional assays but not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.11.25.690410\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"RAB5B is a small Rab GTPase that localizes to plasma membrane and early endosomes, where it regulates endocytosis and early endosomal membrane fusion (via GTP-dependent interaction with EEA1); it is phosphorylated on Thr6 by LRRK2 (which enhances its GTPase activity and negatively regulates its signaling), and on Ser-123 by cdc2 kinase; it is required for surfactant protein processing/trafficking, NMDA receptor endocytosis-mediated neuroprotection, and serves as a trafficking regulator linking early endosomes to autophagy precursor delivery at synapses under nutrient stress.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAB5B is a small Rab GTPase that controls early endosomal membrane fusion and endocytic trafficking, binding GTP and GDP with low intrinsic hydrolysis activity and localizing to the plasma membrane [#0]. In its GTP-bound state it directly recruits the early endosomal tethering factor EEA1, with which it colocalizes on early endosomes, providing the molecular basis for endosome fusion [#1]. RAB5B activity is regulated by phosphorylation: LRRK2 phosphorylates Thr6, enhancing GTPase activity and producing inactive-RAB5B phenotypes including reduced EGFR degradation, while cdc2 kinase phosphorylates Ser-123 [#4, #2]. Through this endocytic and fusion machinery RAB5B supports diverse cargo-handling pathways — it facilitates NMDA receptor endocytosis underlying neuroprotection [#3] and is required for trafficking and maturation of pulmonary surfactant proteins, where a dominant-negative p.Asp136His variant disrupts early endosome fusion and blocks processing of proSP-B and proSP-C [#7]. Beyond these core roles, RAB5B participates in trafficking events co-opted in disease contexts, including ER-to-multivesicular-body transport of the hepatitis B large surface protein [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Established RAB5B as a bona fide small GTPase with nucleotide-binding and slow hydrolysis kinetics, defining its biochemical identity and membrane association.\",\n      \"evidence\": \"GST fusion purification, GTP/GDP binding and hydrolysis assays, immunofluorescence and subcellular fractionation\",\n      \"pmids\": [\"1541686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No effector or regulator identified at this stage\", \"Plasma membrane localization not yet reconciled with endosomal function\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identified EEA1 as a GTP-dependent direct effector, providing the mechanistic link between RAB5B activation and early endosomal tethering/fusion.\",\n      \"evidence\": \"Yeast two-hybrid screen with biochemical binding confirmation, confocal colocalization, and GAP/GTPase activity assays on brain cytosol\",\n      \"pmids\": [\"10491193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The brain GAP activity stimulating RAB5B was not molecularly identified\", \"Functional consequence of EEA1 binding for fusion not directly tested here\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed RAB5 isoforms are differentially phosphorylated, with cdc2 targeting RAB5B Ser-123, raising the possibility of cell-cycle-coupled regulation distinct from other isoforms.\",\n      \"evidence\": \"In vitro kinase assays with recombinant RAB5 isoforms and purified ERK1/ERK2/cdc2\",\n      \"pmids\": [\"10403367\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro only; cellular phosphorylation not demonstrated\", \"Functional effect of Ser-123 phosphorylation unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Placed RAB5B functionally in a neuronal endocytic pathway by showing it is required for NMDA-receptor-endocytosis-dependent neuroprotection.\",\n      \"evidence\": \"Antisense knockdown in organotypic hippocampal cultures with viability readout and pharmacological endocytosis blockade\",\n      \"pmids\": [\"15518642\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that RAB5B drives NMDA receptor internalization not shown\", \"Effectors mediating this neuronal role unidentified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined LRRK2 as a kinase regulator of RAB5B, with Thr6 phosphorylation enhancing GTPase activity to negatively tune RAB5B signaling.\",\n      \"evidence\": \"In vitro kinase assay with MS site mapping, cellular validation with LRRK2 G2019S, neurite outgrowth, EGFR degradation, and GTPase assays\",\n      \"pmids\": [\"25605758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LRRK2 acts directly as a GAP or via another mechanism not resolved\", \"Physiological contexts of Thr6 phosphorylation in vivo not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked RAB5B to cancer cell behavior as a miR-130a-3p target whose depletion impairs proliferation, migration, and invasion.\",\n      \"evidence\": \"miRNA over/knockdown and RAB5B siRNA with proliferation/migration/invasion assays in breast cancer stem-like cells\",\n      \"pmids\": [\"29746865\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miRNA-RAB5B binding not validated\", \"Trafficking mechanism connecting RAB5B to invasive phenotype not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated a required role for RAB5B in ER-to-MVB transport, exploited by hepatitis B large surface protein, and an unexpected effect on viral transcription.\",\n      \"evidence\": \"siRNA screen of 62 Rabs in HepG2.2.15 cells, northern blotting, immunofluorescence\",\n      \"pmids\": [\"31118260\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking RAB5B loss to HNF4\\u03b1/LHBs transcription unclear\", \"Effectors mediating ER-to-MVB transport unidentified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected RAB5B-dependent endosome fusion to surfactant protein maturation and established a dominant-negative disease variant impairing endocytosis.\",\n      \"evidence\": \"C. elegans ortholog knock-in of p.Asp136His, endocytosis and early endosome fusion assays, patient lung immunostaining and colocalization\",\n      \"pmids\": [\"35121658\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical effect of D136H on nucleotide cycling not shown\", \"Whether proSP processing failure is due to endosomal or upstream routing not fully dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Implicated RAB5B in endocytic melanocore clustering downstream of tranexamic acid in keratinocytes.\",\n      \"evidence\": \"Transcriptome sequencing, siRNA silencing, TEM, colocalization with LAMP1\",\n      \"pmids\": [\"36779692\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single lab with limited mechanistic follow-up\", \"Effectors and trafficking steps for melanocore clustering undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reported a non-canonical RAB5B function via CD109 interaction at MVB lipid rafts to package circRNA into extracellular vesicles in pancreatic cancer.\",\n      \"evidence\": \"Co-IP, lipid raft fractionation, EV isolation, in vitro and in vivo assays\",\n      \"pmids\": [\"39488792\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation\", \"Mechanism of lipid raft anchoring inferred from limited fractionation data\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Proposed RAB5B-positive endosomes as carriers delivering the LC3 lipidation complex to synapses under nutrient stress, coupling endosomal trafficking to localized autophagy.\",\n      \"evidence\": \"Live imaging, co-trafficking analysis, dynein inhibition, autophagy assays, synaptic proteomics (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.11.25.690410\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Direct interaction between RAB5B and ATG16L1/ATG5 not demonstrated\", \"Mechanism of nutrient-stress-triggered recruitment unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full set of RAB5B GEFs and GAPs and the structural basis for its functional differences from RAB5A/RAB5C remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No GEF identified for RAB5B\", \"GAP stimulating RAB5B not molecularly characterized\", \"No structural model linking nucleotide state to effector selectivity\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0005525\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 5, 7]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"EEA1\", \"LRRK2\", \"CD109\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}