{"gene":"RABIF","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2017,"finding":"RABIF functions as a Rab-stabilizing holdase chaperone rather than a guanine nucleotide exchange factor (GEF). In the absence of RABIF, Rab10 is rapidly degraded by the proteasome despite normal synthesis. Restoration of Rab10 expression rescues exocytosis defects, bypassing the requirement for RABIF. RABIF also stabilizes Rab8 and Rab13, suggesting holdase chaperone activity is a general feature of Rab regulation.","method":"Genome-wide CRISPR genetic screen to identify RABIF as a positive regulator of exocytosis; RABIF knockout in adipocytes; proteasome inhibition rescue experiments; Rab10 re-expression rescue of GLUT4 exocytosis defects","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (CRISPR screen, KO phenotype, rescue by Rab10 re-expression, proteasome inhibition) in a single rigorous study establishing a novel molecular mechanism","pmids":["28894007"],"is_preprint":false},{"year":2020,"finding":"RABIF co-translationally associates with nascent RAB13 protein at peripheral protrusions of migrating cells. This co-translational RABIF-RAB13 association at the cell periphery is required for directing RAB13 GTPase activity to promote cell migration, but is not required for overall RAB13 protein distribution or membrane association.","method":"Specific prevention of RAB13 RNA localization to protrusions; co-translational interaction assays; cell migration assays with localization-deficient RNA constructs","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab with multiple orthogonal methods (RNA localization manipulation, co-translational interaction, functional migration readout), but not independently replicated","pmids":["32946136"],"is_preprint":false},{"year":2019,"finding":"RAB10 and its chaperone RABIF are required for optimal L. pneumophila replication and ER recruitment to the Legionella-containing vacuole (LCV) in human macrophage-like cells.","method":"Genome-wide CRISPR-Cas9 screen in U937 human monocyte/macrophage-like cells; secondary targeted screens; functional validation of LCV ER recruitment","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen with secondary validation, single lab, mechanistic placement of RABIF in RAB10-dependent ER recruitment to LCV","pmids":["31540829"],"is_preprint":false},{"year":2017,"finding":"Stratum, the Drosophila homolog of mammalian RABIF/MSS4, acts upstream of Rab8 GTPase to restrict basement membrane protein deposition to the basal side of epithelial cells. Loss of Stratum causes missecretion of BM proteins to the apical side.","method":"Drosophila genetics; loss-of-function analysis; epistasis placing Rab8 downstream of Stratum in basal BM protein restriction pathway","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Drosophila ortholog with defined cellular phenotype, single lab","pmids":["28228250"],"is_preprint":false},{"year":2024,"finding":"RABIF depletion attenuates the STOML2-PARL-PGAM5 axis-mediated mitophagy in hepatocellular carcinoma cells, leading to reduced mitochondrial ROS production and consequent alleviation of HIF1α-mediated downregulation of glycolytic genes (HK1, HKDC1, LDHB). RABIF also regulates glucose uptake by controlling RAB10 expression.","method":"RABIF knockdown/knockout in HCC cells in vitro and in vivo; mitophagy pathway component analysis; mitochondrial ROS measurement; glycolytic gene expression analysis; glucose uptake assays","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular assays (KO in vitro/in vivo, pathway component analysis, metabolic readouts) in a single lab","pmids":["39414994"],"is_preprint":false},{"year":2024,"finding":"RABIF knockdown suppresses hepatoma cell migration and clone formation capability, and these effects can be rescued by RABIF overexpression, establishing RABIF as a positive regulator of hepatoma cell malignant behaviors.","method":"Transwell migration assay; colony formation assay; RABIF knockdown and overexpression rescue in hepatoma cell lines","journal":"Recent patents on anti-cancer drug discovery","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single study, basic cellular assays without detailed molecular pathway placement","pmids":["37644748"],"is_preprint":false},{"year":2021,"finding":"miR-491-5p directly targets RABIF to downregulate RABIF-mediated cancer stemness, drug resistance, cell invasion, and pulmonary metastasis via matrix metalloproteinase (MMP) signaling in triple-negative breast cancer cells.","method":"miRNA target validation for RABIF; functional assays for stemness, drug resistance, invasion, and in vivo pulmonary metastasis with RABIF manipulation","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited mechanistic detail in abstract regarding direct RABIF-MMP connection, no reconstitution or structural data","pmids":["34685504"],"is_preprint":false}],"current_model":"RABIF/MSS4 is a Rab-stabilizing holdase chaperone (not a GEF) that prevents proteasomal degradation of newly synthesized Rab GTPases including Rab10, Rab8, and Rab13; it co-translationally associates with nascent Rab13 at cell protrusions to direct its GTPase activity for cell migration, and through Rab10 stabilization supports GLUT4 exocytosis, ER recruitment to pathogen-containing vacuoles, and regulation of mitophagy and glycolysis in cancer cells."},"narrative":{"mechanistic_narrative":"RABIF/MSS4 is a Rab-stabilizing holdase chaperone that protects newly synthesized Rab GTPases from proteasomal degradation, rather than acting as a guanine nucleotide exchange factor [PMID:28894007]. In its absence, Rab10 is rapidly degraded by the proteasome despite normal synthesis, and re-expression of Rab10 bypasses the requirement for RABIF in exocytosis, establishing that RABIF acts upstream of Rab function by maintaining Rab protein levels; this chaperone activity extends to Rab8 and Rab13 [PMID:28894007]. RABIF can co-translationally associate with nascent RAB13 at peripheral protrusions of migrating cells, an interaction that directs RAB13 GTPase activity to promote cell migration without altering overall RAB13 distribution [PMID:32946136]. Through its stabilization of Rab10, RABIF supports diverse Rab-dependent membrane trafficking events, including ER recruitment to the Legionella-containing vacuole during L. pneumophila replication in macrophages [PMID:31540829] and, in hepatocellular carcinoma cells, glucose uptake and the STOML2-PARL-PGAM5 mitophagy axis that modulates mitochondrial ROS and HIF1α-dependent glycolytic gene expression [PMID:39414994]. The Drosophila homolog Stratum acts upstream of Rab8 to restrict basement membrane protein secretion to the basal epithelial surface, consistent with a conserved role in Rab-mediated trafficking [PMID:28228250]. Beyond these chaperone and trafficking roles, no structural model of RABIF or its Rab-binding interface has been characterized in the available corpus.","teleology":[{"year":2017,"claim":"Reclassified RABIF from a presumed nucleotide exchange factor to a holdase chaperone, answering what its actual molecular role in Rab biology is and why its loss disrupts exocytosis.","evidence":"Genome-wide CRISPR screen for exocytosis regulators plus RABIF knockout in adipocytes, proteasome-inhibition rescue, and Rab10 re-expression rescue of GLUT4 exocytosis","pmids":["28894007"],"confidence":"High","gaps":["No structural basis for how RABIF recognizes and shields nascent Rabs","Whether all Rab family members are clients or only a defined subset is undefined","Stoichiometry and dynamics of the RABIF-Rab interaction not resolved"]},{"year":2017,"claim":"Established conservation of the RABIF-Rab axis by showing the Drosophila homolog Stratum acts upstream of Rab8 to spatially direct secretion, indicating the chaperone-Rab relationship governs polarized trafficking.","evidence":"Drosophila loss-of-function genetics and epistasis placing Rab8 downstream of Stratum in basal basement-membrane protein restriction","pmids":["28228250"],"confidence":"Medium","gaps":["Whether Stratum stabilizes Rab8 by the same holdase mechanism shown for mammalian RABIF is not directly demonstrated","Single-lab genetic study without biochemical reconstitution"]},{"year":2019,"claim":"Placed RABIF in host-pathogen biology by showing its Rab10-dependent role is required for ER recruitment to the Legionella-containing vacuole, extending the chaperone's relevance to intracellular bacterial replication.","evidence":"Genome-wide CRISPR-Cas9 screen in U937 macrophage-like cells with secondary screens and LCV ER-recruitment validation","pmids":["31540829"],"confidence":"Medium","gaps":["Does not establish whether the requirement is solely through Rab10 stabilization or additional clients","Single-lab screen-based placement without direct biochemistry"]},{"year":2020,"claim":"Revealed a spatially regulated, co-translational mode of action: RABIF associates with nascent RAB13 at protrusions to direct GTPase activity for migration, distinguishing local functional targeting from bulk protein stabilization.","evidence":"Manipulation of RAB13 RNA localization to protrusions, co-translational interaction assays, and migration assays with localization-deficient constructs","pmids":["32946136"],"confidence":"Medium","gaps":["Mechanism by which co-translational binding directs GTPase activity is undefined","Not independently replicated","Unclear if co-translational engagement applies to other Rab clients such as Rab10/Rab8"]},{"year":2024,"claim":"Connected RABIF to cancer metabolism, showing that via Rab10 control of glucose uptake and the STOML2-PARL-PGAM5 mitophagy axis it modulates mitochondrial ROS and HIF1α-driven glycolytic gene expression in hepatocellular carcinoma.","evidence":"RABIF knockdown/knockout in HCC cells in vitro and in vivo, mitophagy pathway component analysis, ROS measurement, glycolytic gene expression, and glucose uptake assays","pmids":["39414994"],"confidence":"Medium","gaps":["Whether RABIF acts on the mitophagy axis directly or solely through Rab10 stabilization is not separated","Causal ordering between mitophagy changes and glycolytic remodeling not fully resolved"]},{"year":2021,"claim":"Implicated RABIF in tumor aggressiveness, showing miR-491-5p directly represses RABIF to reduce stemness, drug resistance, invasion, and metastasis via MMP signaling in triple-negative breast cancer.","evidence":"miRNA target validation plus functional assays for stemness, drug resistance, invasion, and in vivo pulmonary metastasis","pmids":["34685504"],"confidence":"Low","gaps":["Direct mechanistic link between RABIF and MMP signaling not reconstituted","Single-lab study with limited molecular detail","No connection drawn to RABIF's chaperone activity"]},{"year":null,"claim":"The structural basis for RABIF's holdase recognition of nascent Rabs and the full client repertoire across the Rab family remain undefined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of RABIF or its Rab-binding interface","Complete set of Rab clients beyond Rab8/Rab10/Rab13 unknown","Mechanism coupling chaperone binding to nucleotide state and GTPase activity unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0]}],"complexes":[],"partners":["RAB10","RAB8","RAB13"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P47224","full_name":"Guanine nucleotide exchange factor MSS4","aliases":["Rab-interacting factor"],"length_aa":123,"mass_kda":13.8,"function":"Guanine-nucleotide-releasing protein that acts on members of the SEC4/YPT1/RAB subfamily. Stimulates GDP release from both YPT1, RAB3A and RAB10, but is less active on these proteins than on the SEC4 protein (PubMed:31540829). Might play a general role in vesicular transport","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P47224/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RABIF","classification":"Not Classified","n_dependent_lines":365,"n_total_lines":1208,"dependency_fraction":0.3021523178807947},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000183155","cell_line_id":"CID000451","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"WDR48","stoichiometry":0.2},{"gene":"ZNF148","stoichiometry":0.2},{"gene":"RAB1B;RAB1C","stoichiometry":0.2},{"gene":"RAB13","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000451","total_profiled":1310},"omim":[{"mim_id":"603417","title":"RAB-INTERACTING FACTOR; RABIF","url":"https://www.omim.org/entry/603417"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Microtubules","reliability":"Approved"},{"location":"Cytokinetic bridge","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RABIF"},"hgnc":{"alias_symbol":["mss4"],"prev_symbol":["RASGRF3"]},"alphafold":{"accession":"P47224","domains":[{"cath_id":"2.170.150.10","chopping":"8-123","consensus_level":"high","plddt":90.6473,"start":8,"end":123}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P47224","model_url":"https://alphafold.ebi.ac.uk/files/AF-P47224-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P47224-F1-predicted_aligned_error_v6.png","plddt_mean":89.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RABIF","jax_strain_url":"https://www.jax.org/strain/search?query=RABIF"},"sequence":{"accession":"P47224","fasta_url":"https://rest.uniprot.org/uniprotkb/P47224.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P47224/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P47224"}},"corpus_meta":[{"pmid":"31540829","id":"PMC_31540829","title":"Systematic Identification of Host Cell Regulators of Legionella pneumophila Pathogenesis Using a Genome-wide CRISPR Screen.","date":"2019","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/31540829","citation_count":73,"is_preprint":false},{"pmid":"28894007","id":"PMC_28894007","title":"RABIF/MSS4 is a Rab-stabilizing holdase chaperone required for GLUT4 exocytosis.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/28894007","citation_count":54,"is_preprint":false},{"pmid":"33540684","id":"PMC_33540684","title":"Analysis of m6A RNA Methylation-Related Genes in Liver Hepatocellular Carcinoma and Their Correlation with Survival.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33540684","citation_count":53,"is_preprint":false},{"pmid":"32946136","id":"PMC_32946136","title":"RNA localization and co-translational interactions control RAB13 GTPase function and cell migration.","date":"2020","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/32946136","citation_count":40,"is_preprint":false},{"pmid":"28228250","id":"PMC_28228250","title":"Stratum, a Homolog of the Human GEF Mss4, Partnered with Rab8, Controls the Basal Restriction of Basement Membrane Proteins in Epithelial Cells.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/28228250","citation_count":26,"is_preprint":false},{"pmid":"34685504","id":"PMC_34685504","title":"Identification of the Novel Tumor Suppressor Role of FOCAD/miR-491-5p to Inhibit Cancer Stemness, Drug Resistance and Metastasis via Regulating RABIF/MMP Signaling in Triple Negative Breast Cancer.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/34685504","citation_count":13,"is_preprint":false},{"pmid":"26740525","id":"PMC_26740525","title":"PINCAGE: probabilistic integration of cancer genomics data for perturbed gene identification and sample classification.","date":"2016","source":"Bioinformatics (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/26740525","citation_count":13,"is_preprint":false},{"pmid":"39414994","id":"PMC_39414994","title":"RABIF promotes hepatocellular carcinoma progression through regulation of mitophagy and glycolysis.","date":"2024","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/39414994","citation_count":11,"is_preprint":false},{"pmid":"37644748","id":"PMC_37644748","title":"Identification of the Roles of Coagulation-related Signature and its Key Factor RABIF in Hepatoma Cell Malignancy.","date":"2024","source":"Recent patents on anti-cancer drug discovery","url":"https://pubmed.ncbi.nlm.nih.gov/37644748","citation_count":3,"is_preprint":false},{"pmid":"19232337","id":"PMC_19232337","title":"Novel real-time PCR assay for rapid prenatal diagnosis of Down syndrome: a prospective study of 563 amniocytes.","date":"2009","source":"Clinical biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19232337","citation_count":3,"is_preprint":false},{"pmid":"39644349","id":"PMC_39644349","title":"CRISPR-Cas9 screening identified novel subtypes of cutaneous melanoma based on essential cancer genes.","date":"2024","source":"Archives of dermatological research","url":"https://pubmed.ncbi.nlm.nih.gov/39644349","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7748,"output_tokens":1798,"usd":0.025107,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8672,"output_tokens":2680,"usd":0.05518,"stage2_stop_reason":"end_turn"},"total_usd":0.080287,"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\": 2017,\n      \"finding\": \"RABIF functions as a Rab-stabilizing holdase chaperone rather than a guanine nucleotide exchange factor (GEF). In the absence of RABIF, Rab10 is rapidly degraded by the proteasome despite normal synthesis. Restoration of Rab10 expression rescues exocytosis defects, bypassing the requirement for RABIF. RABIF also stabilizes Rab8 and Rab13, suggesting holdase chaperone activity is a general feature of Rab regulation.\",\n      \"method\": \"Genome-wide CRISPR genetic screen to identify RABIF as a positive regulator of exocytosis; RABIF knockout in adipocytes; proteasome inhibition rescue experiments; Rab10 re-expression rescue of GLUT4 exocytosis defects\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (CRISPR screen, KO phenotype, rescue by Rab10 re-expression, proteasome inhibition) in a single rigorous study establishing a novel molecular mechanism\",\n      \"pmids\": [\"28894007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RABIF co-translationally associates with nascent RAB13 protein at peripheral protrusions of migrating cells. This co-translational RABIF-RAB13 association at the cell periphery is required for directing RAB13 GTPase activity to promote cell migration, but is not required for overall RAB13 protein distribution or membrane association.\",\n      \"method\": \"Specific prevention of RAB13 RNA localization to protrusions; co-translational interaction assays; cell migration assays with localization-deficient RNA constructs\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab with multiple orthogonal methods (RNA localization manipulation, co-translational interaction, functional migration readout), but not independently replicated\",\n      \"pmids\": [\"32946136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAB10 and its chaperone RABIF are required for optimal L. pneumophila replication and ER recruitment to the Legionella-containing vacuole (LCV) in human macrophage-like cells.\",\n      \"method\": \"Genome-wide CRISPR-Cas9 screen in U937 human monocyte/macrophage-like cells; secondary targeted screens; functional validation of LCV ER recruitment\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen with secondary validation, single lab, mechanistic placement of RABIF in RAB10-dependent ER recruitment to LCV\",\n      \"pmids\": [\"31540829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Stratum, the Drosophila homolog of mammalian RABIF/MSS4, acts upstream of Rab8 GTPase to restrict basement membrane protein deposition to the basal side of epithelial cells. Loss of Stratum causes missecretion of BM proteins to the apical side.\",\n      \"method\": \"Drosophila genetics; loss-of-function analysis; epistasis placing Rab8 downstream of Stratum in basal BM protein restriction pathway\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Drosophila ortholog with defined cellular phenotype, single lab\",\n      \"pmids\": [\"28228250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RABIF depletion attenuates the STOML2-PARL-PGAM5 axis-mediated mitophagy in hepatocellular carcinoma cells, leading to reduced mitochondrial ROS production and consequent alleviation of HIF1α-mediated downregulation of glycolytic genes (HK1, HKDC1, LDHB). RABIF also regulates glucose uptake by controlling RAB10 expression.\",\n      \"method\": \"RABIF knockdown/knockout in HCC cells in vitro and in vivo; mitophagy pathway component analysis; mitochondrial ROS measurement; glycolytic gene expression analysis; glucose uptake assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular assays (KO in vitro/in vivo, pathway component analysis, metabolic readouts) in a single lab\",\n      \"pmids\": [\"39414994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RABIF knockdown suppresses hepatoma cell migration and clone formation capability, and these effects can be rescued by RABIF overexpression, establishing RABIF as a positive regulator of hepatoma cell malignant behaviors.\",\n      \"method\": \"Transwell migration assay; colony formation assay; RABIF knockdown and overexpression rescue in hepatoma cell lines\",\n      \"journal\": \"Recent patents on anti-cancer drug discovery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single study, basic cellular assays without detailed molecular pathway placement\",\n      \"pmids\": [\"37644748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"miR-491-5p directly targets RABIF to downregulate RABIF-mediated cancer stemness, drug resistance, cell invasion, and pulmonary metastasis via matrix metalloproteinase (MMP) signaling in triple-negative breast cancer cells.\",\n      \"method\": \"miRNA target validation for RABIF; functional assays for stemness, drug resistance, invasion, and in vivo pulmonary metastasis with RABIF manipulation\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited mechanistic detail in abstract regarding direct RABIF-MMP connection, no reconstitution or structural data\",\n      \"pmids\": [\"34685504\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RABIF/MSS4 is a Rab-stabilizing holdase chaperone (not a GEF) that prevents proteasomal degradation of newly synthesized Rab GTPases including Rab10, Rab8, and Rab13; it co-translationally associates with nascent Rab13 at cell protrusions to direct its GTPase activity for cell migration, and through Rab10 stabilization supports GLUT4 exocytosis, ER recruitment to pathogen-containing vacuoles, and regulation of mitophagy and glycolysis in cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RABIF/MSS4 is a Rab-stabilizing holdase chaperone that protects newly synthesized Rab GTPases from proteasomal degradation, rather than acting as a guanine nucleotide exchange factor [#0]. In its absence, Rab10 is rapidly degraded by the proteasome despite normal synthesis, and re-expression of Rab10 bypasses the requirement for RABIF in exocytosis, establishing that RABIF acts upstream of Rab function by maintaining Rab protein levels; this chaperone activity extends to Rab8 and Rab13 [#0]. RABIF can co-translationally associate with nascent RAB13 at peripheral protrusions of migrating cells, an interaction that directs RAB13 GTPase activity to promote cell migration without altering overall RAB13 distribution [#1]. Through its stabilization of Rab10, RABIF supports diverse Rab-dependent membrane trafficking events, including ER recruitment to the Legionella-containing vacuole during L. pneumophila replication in macrophages [#2] and, in hepatocellular carcinoma cells, glucose uptake and the STOML2-PARL-PGAM5 mitophagy axis that modulates mitochondrial ROS and HIF1\\u03b1-dependent glycolytic gene expression [#4]. The Drosophila homolog Stratum acts upstream of Rab8 to restrict basement membrane protein secretion to the basal epithelial surface, consistent with a conserved role in Rab-mediated trafficking [#3]. Beyond these chaperone and trafficking roles, no structural model of RABIF or its Rab-binding interface has been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Reclassified RABIF from a presumed nucleotide exchange factor to a holdase chaperone, answering what its actual molecular role in Rab biology is and why its loss disrupts exocytosis.\",\n      \"evidence\": \"Genome-wide CRISPR screen for exocytosis regulators plus RABIF knockout in adipocytes, proteasome-inhibition rescue, and Rab10 re-expression rescue of GLUT4 exocytosis\",\n      \"pmids\": [\"28894007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for how RABIF recognizes and shields nascent Rabs\", \"Whether all Rab family members are clients or only a defined subset is undefined\", \"Stoichiometry and dynamics of the RABIF-Rab interaction not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established conservation of the RABIF-Rab axis by showing the Drosophila homolog Stratum acts upstream of Rab8 to spatially direct secretion, indicating the chaperone-Rab relationship governs polarized trafficking.\",\n      \"evidence\": \"Drosophila loss-of-function genetics and epistasis placing Rab8 downstream of Stratum in basal basement-membrane protein restriction\",\n      \"pmids\": [\"28228250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Stratum stabilizes Rab8 by the same holdase mechanism shown for mammalian RABIF is not directly demonstrated\", \"Single-lab genetic study without biochemical reconstitution\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed RABIF in host-pathogen biology by showing its Rab10-dependent role is required for ER recruitment to the Legionella-containing vacuole, extending the chaperone's relevance to intracellular bacterial replication.\",\n      \"evidence\": \"Genome-wide CRISPR-Cas9 screen in U937 macrophage-like cells with secondary screens and LCV ER-recruitment validation\",\n      \"pmids\": [\"31540829\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish whether the requirement is solely through Rab10 stabilization or additional clients\", \"Single-lab screen-based placement without direct biochemistry\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed a spatially regulated, co-translational mode of action: RABIF associates with nascent RAB13 at protrusions to direct GTPase activity for migration, distinguishing local functional targeting from bulk protein stabilization.\",\n      \"evidence\": \"Manipulation of RAB13 RNA localization to protrusions, co-translational interaction assays, and migration assays with localization-deficient constructs\",\n      \"pmids\": [\"32946136\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which co-translational binding directs GTPase activity is undefined\", \"Not independently replicated\", \"Unclear if co-translational engagement applies to other Rab clients such as Rab10/Rab8\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected RABIF to cancer metabolism, showing that via Rab10 control of glucose uptake and the STOML2-PARL-PGAM5 mitophagy axis it modulates mitochondrial ROS and HIF1\\u03b1-driven glycolytic gene expression in hepatocellular carcinoma.\",\n      \"evidence\": \"RABIF knockdown/knockout in HCC cells in vitro and in vivo, mitophagy pathway component analysis, ROS measurement, glycolytic gene expression, and glucose uptake assays\",\n      \"pmids\": [\"39414994\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RABIF acts on the mitophagy axis directly or solely through Rab10 stabilization is not separated\", \"Causal ordering between mitophagy changes and glycolytic remodeling not fully resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Implicated RABIF in tumor aggressiveness, showing miR-491-5p directly represses RABIF to reduce stemness, drug resistance, invasion, and metastasis via MMP signaling in triple-negative breast cancer.\",\n      \"evidence\": \"miRNA target validation plus functional assays for stemness, drug resistance, invasion, and in vivo pulmonary metastasis\",\n      \"pmids\": [\"34685504\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Direct mechanistic link between RABIF and MMP signaling not reconstituted\", \"Single-lab study with limited molecular detail\", \"No connection drawn to RABIF's chaperone activity\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis for RABIF's holdase recognition of nascent Rabs and the full client repertoire across the Rab family remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of RABIF or its Rab-binding interface\", \"Complete set of Rab clients beyond Rab8/Rab10/Rab13 unknown\", \"Mechanism coupling chaperone binding to nucleotide state and GTPase activity unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RAB10\", \"RAB8\", \"RAB13\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}