{"gene":"RAB13","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2002,"finding":"Rab13 is recruited to junctional complexes from a cytosolic pool after cell-cell contact formation. Constitutively active Rab13 (Q67L) delays formation of electrically tight epithelial monolayers, disrupts the tight junction fence diffusion barrier, and delays claudin-1 localization at the cell surface, while inactive Rab13 (T22N) has no effect on TJ function or structure.","method":"Stable GFP-Rab13 mutant cell lines (Q67L and T22N) in MDCK cells; transepithelial electrical resistance; freeze-fracture EM; immunofluorescence; tracer leakage assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays with gain-of-function mutants, replicated across multiple labs in subsequent studies","pmids":["12058051"],"is_preprint":false},{"year":1998,"finding":"The rod cGMP phosphodiesterase delta subunit (delta-PDE) specifically binds Rab13 and purified recombinant delta-PDE dissociates Rab13 from cellular membranes, suggesting delta-PDE (not GDI) controls the dynamic association of Rab13 with membranes.","method":"Yeast two-hybrid screen of HeLa cDNA library; purified recombinant delta-PDE membrane dissociation assay; immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution of membrane dissociation plus yeast two-hybrid, single lab","pmids":["9712853"],"is_preprint":false},{"year":2004,"finding":"Rab13 dominant active mutant (Q67L) specifically inhibits postendocytic recycling of occludin back to the cell surface, but not recycling of transferrin receptor or polymeric immunoglobulin receptor; endocytosed occludin colocalizes with Rab13.","method":"Cell surface biotinylation; biochemical endocytosis and recycling assays; double immunolabeling; dominant active Rab13 expression in BHK and MTD-1A cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical and imaging assays, independently replicated across multiple subsequent studies","pmids":["15528189"],"is_preprint":false},{"year":2004,"finding":"GTP-bound Rab13 directly binds to the alpha-catalytic subunit of PKA and inhibits PKA activity, thereby preventing PKA-dependent phosphorylation and tight junction recruitment of VASP (vasodilator-stimulated phosphoprotein). Activation of PKA abrogates the inhibitory effect of Rab13 on recruitment of VASP, ZO-1, and claudin-1 to cell-cell junctions.","method":"Co-immunoprecipitation; in vitro PKA activity assay with purified Rab13; dominant active Rab13 expression; PKA activator rescue experiments","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct binding demonstrated and in vitro kinase inhibition assay with multiple orthogonal approaches, replicated in subsequent studies","pmids":["15096524","16473634"],"is_preprint":false},{"year":2006,"finding":"MICAL-L2 (renamed JRAB, junctional Rab13-binding protein) specifically binds to the GTP-bound form of Rab13 via its C-terminal coiled-coil domain, localizes to tight junctions, and mediates endocytic recycling of occludin and formation of functional tight junctions. A MICAL-L2 mutant lacking the Rab13-binding domain (MICAL-L2-N) inhibits occludin recycling and TJ formation. MICAL-L2 links Rab13 to the actin cytoskeleton and is displaced from TJs upon actin depolymerization.","method":"Yeast two-hybrid; immunoprecipitation; immunofluorescence; recycling assay; Ca2+ switch assay; transepithelial electrical resistance measurement","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple functional assays, independently replicated across multiple subsequent studies","pmids":["16525024"],"is_preprint":false},{"year":2007,"finding":"JRAB/MICAL-L2 interacts with both Rab13 and Rab8 via its C-terminal domain, with Rab8 and Rab13 competing for MICAL-L2 binding. Rab13 specifically mediates claudin-1 and occludin transport to the plasma membrane but not E-cadherin transport, while Rab8 mediates Rab13-independent E-cadherin transport. JRAB/MICAL-L2 coordinates TJ and AJ assembly by sequentially interacting with Rab8 at perinuclear recycling compartments and Rab13 at the plasma membrane.","method":"siRNA knockdown; Ca2+ switch model; co-immunoprecipitation; immunofluorescence; dominant-negative and constitutively active mutant expression","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (siRNA, Co-IP, dominant mutants), replicated across studies","pmids":["18094055"],"is_preprint":false},{"year":2008,"finding":"Rab13 regulates membrane trafficking between the trans-Golgi network (TGN) and recycling endosomes (RE). Rab13 partially colocalizes with TGN38 at the TGN and transferrin receptors in RE. Knockdown or dominant mutant expression of Rab13 disrupts TGN38/46 localization and inhibits surface arrival of proteins that transit through RE (VSVG, A-VSVG, LDLR-CT27), but not proteins using a direct TGN-to-PM route.","method":"shRNA knockdown in HBE cells; dominant-active and dominant-negative allele overexpression in MDCK cells; immunofluorescence colocalization; surface protein arrival assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple complementary approaches (KD + dominant mutants + cargo selectivity analysis), replicated findings","pmids":["18779367"],"is_preprint":false},{"year":2009,"finding":"Rab13 regulates neurite outgrowth in PC12 cells through its effector JRAB/MICAL-L2. Rab13 binding to JRAB/MICAL-L2 stimulates an intramolecular conformational change in JRAB/MICAL-L2 and promotes its interaction with actinin-4, an actin-binding protein that localizes to the cell body and neurite tips. This complex is proposed to transfer actinin-4 to neurite tips to reorganize actin for neurite extension.","method":"Dominant active Rab13 expression; co-immunoprecipitation; immunofluorescence; neurite outgrowth assays in PC12 cells","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional rescue in single lab, two orthogonal methods","pmids":["20008558"],"is_preprint":false},{"year":2010,"finding":"Insulin promotes GTP loading of Rab13 (and Rab8A) in rat L6 muscle cells. siRNA-mediated Rab13 knockdown blocks insulin-induced GLUT4 appearance at the muscle cell surface, rescued by Rab13 ortholog but not Rab8A. Constitutively active AS160 (Rab-GAP) suppresses surface GLUT4, reversed by Rab13 or Rab8A overexpression, placing both Rabs downstream of AS160 in GLUT4 exocytic trafficking. Insulin promotes Rab13 colocalization with GLUT4 at the cell periphery.","method":"GTP-loading assay; siRNA knockdown; surface GLUT4 measurement; constitutively active AS160 expression; immunofluorescence colocalization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (GTP-loading, siRNA, epistasis with AS160, imaging), single focused study replicated in subsequent work","pmids":["21041651"],"is_preprint":false},{"year":2011,"finding":"Rab13 is required for trafficking of a protein complex (RhoA, Syx, Mupp1, angiomotin) to the leading edge of migrating endothelial cells. Rab13 associates with Grb2, targeting Syx and RhoA to Tyr1175-phosphorylated VEGFR2 at the leading edge. Rab13 knockdown in zebrafish impedes sprouting of intersegmental vessels and reduces tip cell directionality.","method":"siRNA knockdown; co-immunoprecipitation; live-cell imaging; zebrafish vessel sprouting assay; directed migration assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP + in vivo zebrafish + cell migration assays, single lab","pmids":["21543326"],"is_preprint":false},{"year":2012,"finding":"JRAB/MICAL-L2 interacts with actin-binding proteins actinin-1 and actinin-4 and filamentous actin via different domains, regulating actin cross-linking and stabilization. During epithelial junctional development, JRAB is enriched in the actin bundle at the free border; Rab13 binding induces a conformational change in JRAB required for maturation of cell-cell adhesion sites.","method":"Co-immunoprecipitation; immunofluorescence; actin bundling assays; dominant active Rab13 expression; Ca2+ switch assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, functional imaging, single lab with multiple methods","pmids":["23100251"],"is_preprint":false},{"year":2014,"finding":"Rab35 functions as a master Rab that recruits MICAL-L1 to Arf6-positive recycling endosomes, and MICAL-L1 in turn recruits Rab13 (along with Rab8 and Rab36) to these endosomes during NGF-induced neurite outgrowth in PC12 cells. Rab13 regulates neurite outgrowth non-redundantly downstream of Rab35 and MICAL-L1.","method":"Dominant active/negative Rab mutant expression; siRNA knockdown; immunofluorescence; neurite outgrowth assays in PC12 cells","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional ablation experiments with epistasis analysis, single lab","pmids":["25086062"],"is_preprint":false},{"year":2014,"finding":"In lymphocytes, chemokine stimulation activates Rab13 via DENND1C (a GEF phosphorylated by kinase Mst1). Active Rab13 associates with Mst1 to facilitate delivery of integrin LFA-1 to the leading edge, involving myosin Va recruitment along actin filaments. Rab13-deficient mice have reduced lymphocyte numbers in lymphoid tissues due to defective trafficking. Inhibiting Rab13 function reduces lymphocyte adhesion and migration on ICAM-1 and disrupts the ring-like LFA-1 arrangement at the T cell-APC contact site.","method":"DENND1C phosphorylation assays; Rab13 activation assays; Rab13 knockout mice; LFA-1 surface trafficking assays; lymphocyte adhesion and migration assays; immunofluorescence","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse phenotype + multiple cell biological assays + pathway epistasis, replicated with multiple methods","pmids":["25074980"],"is_preprint":false},{"year":2015,"finding":"DENND2B is the guanine nucleotide exchange factor (GEF) for Rab13. DENND2B activates Rab13 specifically at the leading edge of migrating cells, as demonstrated by a FRET-based Rab13 biosensor. DENND2B interacts with the Rab13 effector MICAL-L2 at the cell periphery, and this interaction is required for dynamic remodeling of the leading edge. Disruption of Rab13-mediated trafficking limits invasive behavior in vitro and growth/migration of cancer cells in vivo.","method":"FRET-based Rab13 biosensor; GEF activity assay; co-immunoprecipitation; in vitro invasion assays; in vivo tumor xenograft assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — FRET biosensor directly measuring GEF activity at subcellular resolution plus functional assays, novel mechanistic discovery","pmids":["25713415"],"is_preprint":false},{"year":2015,"finding":"Rab13 forms an insulin-dependent complex with MICAL-L2 and alpha-actinin-4 (ACTN4) in muscle cells. Insulin increases Rab13 binding to MICAL-L2, which in turn binds ACTN4. GLUT4 associates with this complex in response to insulin, requiring the ACTN4-binding domain in MICAL-L2. Knockdown of MICAL-L2 or expression of truncated MICAL-L2 impairs insulin-stimulated GLUT4 translocation.","method":"Pull-down assays; confocal fluorescence microscopy; structured illumination microscopy (SIM); TIRF microscopy; siRNA knockdown; co-immunoprecipitation","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple super-resolution and biochemical approaches demonstrating complex assembly, single focused study with multiple orthogonal methods","pmids":["26538022"],"is_preprint":false},{"year":2016,"finding":"C-terminal prenylation is not required for Rab13 to associate with and traffic on vesicles in its inactive GDP-bound state; inactive Rab13 associates with vesicles via protein-protein interactions. Only upon activation does Rab13 associate with the plasma membrane, presumably via C-terminal prenyl group membrane insertion.","method":"Prenylation-deficient Rab13 mutant expression; subcellular fractionation; live-cell vesicle trafficking imaging","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with prenylation mutants, single lab","pmids":["26969162"],"is_preprint":false},{"year":2017,"finding":"Rab13 is required for ionomycin-stimulated GLUT4 exocytosis in L6 myoblasts. siRab13 (but not siRab8a, siRab10, or siRab14) selectively inhibited GLUT4 exocytosis promoted by elevated cytosolic Ca2+, placing Rab13 specifically downstream of Ca2+/PKC signaling in this pathway.","method":"siRNA knockdown; surface GLUT4myc exocytosis assay; ionomycin-stimulated Ca2+ elevation; phosphorylation assays for AS160 and TBC1D1","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — selective siRNA knockdown with cargo-specific readout, single lab","pmids":["29247648"],"is_preprint":false},{"year":2017,"finding":"Electrical pulse stimulation (EPS)-induced GLUT4 translocation in C2C12 myotubes requires Rab8a, Rab13, and Rab14 but not Rab10. Rab10 and Rab13 are not engaged by AMPK activation alone. Constitutively active AS160 diminishes EPS-stimulated GLUT4 translocation, supporting regulation downstream of Rab-GAP AS160.","method":"siRNA knockdown; surface HA-GLUT4 measurement; EPS contraction model; constitutively active AS160 expression; AMPK inhibitor and siRNA treatments","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic siRNA knockdown comparing Rab family members, single lab","pmids":["29089333"],"is_preprint":false},{"year":2019,"finding":"RAB13 and GGA2 (Golgi-localized gamma ear-containing Arf-binding protein 2) both regulate activity-dependent recycling of active but not inactive beta1-integrin to the plasma membrane. RAB13 silencing triggers intracellular accumulation of active beta1-integrin and reduces integrin activity in focal adhesions and cell migration. GGA2 and RAB13 interact (identified by BioID proximity labeling).","method":"RNAi screen; BioID proximity labeling; surface beta1-integrin activity assays; immunofluorescence; cell migration assays; siRNA knockdown","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — BioID interaction + functional siRNA with specific cargo readout, single lab","pmids":["31076515"],"is_preprint":false},{"year":2020,"finding":"Peripheral translation of RAB13 mRNA at cellular protrusions leads to co-translational association of nascent RAB13 with the exchange factor RABIF. This co-translational RAB13-RABIF association at the cell periphery is required for directing RAB13 GTPase activity and promoting efficient cell migration. Preventing RAB13 mRNA localization (without affecting total RAB13 protein levels or membrane association) reduces RAB13 GTPase activation and cell migration efficiency.","method":"RNA localization perturbation constructs; RABIF co-translational interaction assays; GTPase activity measurements; cell migration assays; ribosome fractionation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct mechanistic link between mRNA localization, co-translational GEF association, and GTPase activation measured by multiple methods","pmids":["32946136"],"is_preprint":false},{"year":2020,"finding":"RAB13 mRNA is targeted to sites of filopodia formation via a 192-nt localisation element. This spatial coupling of mRNA localisation, translation, and protein activity creates a polarised domain of filopodia extension. Genomic excision of this localisation element depolarises filopodia dynamics in motile endothelial cells and induces mispatterning of blood vessels in zebrafish without affecting total RAB13 translation.","method":"Single-molecule RNA FISH; gene editing (CRISPR); zebrafish live-cell imaging; protrusion-derived RNAseq; filopodia dynamics measurements","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous gene editing + in vivo zebrafish model + single-molecule imaging, multiple orthogonal approaches","pmids":["32946121"],"is_preprint":false},{"year":2020,"finding":"Rab13 regulates secretion of small extracellular vesicles (sEVs) in mutant KRAS colorectal cancer cells. Rab13 is both a cargo protein packaged into sEVs and a regulator of sEV secretion. Knockdown of Rab13 blocks proliferative and tumorigenic effects of sEVs on recipient cells.","method":"siRNA knockdown; sEV isolation and characterization; recipient cell proliferation and tumorigenesis assays; Western blot","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with defined vesicle secretion and functional readout, single lab","pmids":["32978434"],"is_preprint":false},{"year":2022,"finding":"RNF115 (an E3 ubiquitin ligase) catalyzes K11-linked ubiquitination on Lys46 and Lys58 residues of RAB13. This modification impairs recruitment of GDI1 to RAB13, a prerequisite for RAB reactivation. Knockdown of RAB13 inhibits post-Golgi trafficking of TLRs to the cell surface, and reconstitution of RAB13 with K46/58R mutations (ubiquitination-resistant) in RNF115+/+ cells promotes TLR trafficking from Golgi to cell surface.","method":"Co-immunoprecipitation; ubiquitination assays; site-directed mutagenesis (K46R, K58R); siRNA knockdown; TLR trafficking assays; subcellular fractionation; GDI1 recruitment assay","journal":"Advanced science","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — identified specific ubiquitination sites by mutagenesis, demonstrated functional consequence on GDI1 recruitment and TLR trafficking with multiple orthogonal methods","pmids":["35343654"],"is_preprint":false},{"year":2022,"finding":"Rab13 controls membrane translocation of CXCR1/2 receptors, allowing breast cancer stem cells to interact with tumor-associated macrophages and cancer-associated fibroblasts to establish a supportive CSC niche. Rab13 depletion suppresses stemness and chemoresistance.","method":"siRNA knockdown; surface CXCR1/2 measurement; co-culture assays; in vivo tumorigenesis assays; flow cytometry","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cargo (CXCR1/2) with loss-of-function and functional readout, single lab","pmids":["35395074"],"is_preprint":false},{"year":2007,"finding":"Rab13 and JRAB/MICAL-L2 are required for TPA-induced epithelial cell scattering (MDCK cells). During scattering, Rab13 is transiently activated; both Rab13 and JRAB/MICAL-L2 redistribute from cell-cell contact sites to emerging lamellipodial structures. Knockdown of either Rab13 or JRAB/MICAL-L2 suppresses TPA-induced scattering.","method":"siRNA knockdown; Rab13 GTP-loading assay; immunofluorescence; cell scattering assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with rescue, GTP-loading activation assay, single lab","pmids":["17891173"],"is_preprint":false},{"year":2008,"finding":"RAB13 associates with vinculin and espin (ectoplasmic specialization actin-binding proteins) in the testis, as demonstrated by co-immunoprecipitation and immunofluorescence. RAB13 localizes to the ectoplasmic specialization in Sertoli-germ cell junctions and its level decreases during adjudin-induced ectoplasmic specialization disassembly.","method":"Co-immunoprecipitation; immunofluorescence; immunohistochemistry; in vivo adjudin model","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP demonstrated specific protein interactions, supported by in vivo model, single lab","pmids":["19074001"],"is_preprint":false},{"year":2013,"finding":"RAB13 knockdown in cultured Sertoli cells increases PKA activity, reinforces occludin and filamentous actin distribution at cell-cell interfaces, and promotes ZO-1–occludin direct interaction—effects that phenocopy testosterone's enhancement of TJ integrity. The effects of Rab13 knockdown on TJ permeability are antagonized by PKA inhibition, establishing a Rab13–PKA axis in Sertoli cell TJ regulation.","method":"siRNA knockdown in primary cultured Sertoli cells; transepithelial electrical resistance; co-immunoprecipitation; immunofluorescence; PKA activity assay","journal":"Journal of molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with PKA epistasis and TER functional readout, single lab","pmids":["23419316"],"is_preprint":false},{"year":2013,"finding":"JRAB/MICAL-L2 in its open conformational state (JRABΔCC mutant) interacts with filamin isoforms (actin cross-linking proteins) as well as actinin-1 and actinin-4. Filamin but not actinin is required for JRAB-induced cell spreading with membrane ruffles. Degradation of filamins by ASB2 inhibits JRAB-induced cell spreading.","method":"Co-immunoprecipitation; expression of constitutively open/closed JRAB mutants; ASB2-induced filamin degradation; morphological cell spreading analysis","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and functional rescue, single lab","pmids":["23890175"],"is_preprint":false},{"year":2013,"finding":"Rab13 and Rab8 both bind to Endospanin-2 (and its homolog Endospanin-1) via the C-terminus of Endospanin-2, as demonstrated by bacterial two-hybrid and colocalization in perinuclear vesicular structures. Rab7, Rab10, Rab11, and Rab32 do not bind Endospanin-2.","method":"Bacterial two-hybrid screen; co-immunoprecipitation; immunofluorescence colocalization","journal":"FEBS open bio","confidence":"Low","confidence_rationale":"Tier 3 / Weak — bacterial two-hybrid and colocalization, functional consequence unclear, single lab","pmids":["23772379"],"is_preprint":false},{"year":2003,"finding":"Rab13 mutants specifically impair cell-surface transport of claudin-1 but not basolateral LDLR or apical p75NTR in fibroblasts, while Rab3B mutants affect LDLR but not claudin-1 or p75NTR. This defines distinct and non-overlapping roles for Rab13 and Rab3B in polarized transport.","method":"Overexpression of dominant mutant Rabs; cell-surface transport assays for specific cargo proteins in fibroblasts","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cargo-selective transport assays with multiple Rab mutants providing specificity, single lab","pmids":["12901864"],"is_preprint":false},{"year":2017,"finding":"Active Rab13 promotes autophagy in vascular endothelial cells by functionally interacting with Grb2, leading to AMPK activation and mTOR inhibition. Co-immunoprecipitation assays showed Rab13 promotes Rab13–Grb2 interaction; Grb2 knockdown suppresses Rab13-induced autophagy.","method":"Overexpression of active/inactive Rab13; siRNA knockdown of Grb2; co-immunoprecipitation; immunofluorescence; autophagy quantification; mTOR/AMPK phosphorylation assays","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP + epistasis with Grb2 knockdown + signaling assays, single lab","pmids":["28087344"],"is_preprint":false},{"year":2024,"finding":"Parkin (RBR E3 ubiquitin ligase) ubiquitinates RAB13 in cells. This was identified in an orthogonal ubiquitin transfer (OUT) screen and confirmed by reconstituted ubiquitination reactions in vitro and in cells. Mitophagy stimulation enhanced Parkin-mediated ubiquitination of RAB13.","method":"Orthogonal ubiquitin transfer (OUT) cascade; proteomics; in vitro reconstituted ubiquitination assay; cell-based ubiquitination assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution confirmed in cells, but preprint and RAB13 is one of several Rab substrates identified","pmids":[],"is_preprint":true}],"current_model":"RAB13 is a small GTPase activated at the cell periphery by GEFs (DENND2B at the leading edge of epithelial/cancer cells; DENND1C downstream of Mst1 in lymphocytes; RABIF co-translationally at protrusions), where in its GTP-bound state it binds the effector MICAL-L2/JRAB to regulate endocytic recycling of tight junction proteins (occludin, claudin-1) to the plasma membrane, mediates TGN-to-recycling-endosome trafficking, drives GLUT4 vesicle exocytosis downstream of the Rab-GAP AS160 in response to insulin and Ca2+ signals in muscle cells, delivers integrin LFA-1 to the leading edge of lymphocytes, and controls directional cell migration and angiogenesis; its activity is negatively regulated by direct binding to and inhibition of the PKA catalytic subunit, by RNF115-catalyzed K11-linked ubiquitination on Lys46/58 (impairing GDI1 recruitment), and by delta-PDE-mediated membrane dissociation, while its mRNA localizes to cellular protrusions where co-translational RABIF association is required for full GTPase activation and directed cell migration."},"narrative":{"mechanistic_narrative":"RAB13 is a small GTPase that controls polarized membrane trafficking at the cell periphery, governing tight junction assembly, directed cell migration, and regulated exocytosis [PMID:12058051, PMID:25713415]. In its GTP-bound state it engages the effector MICAL-L2/JRAB, which links RAB13 to the actin cytoskeleton and mediates endocytic recycling of the tight junction proteins occludin and claudin-1 back to the plasma membrane to build functional junctions [PMID:15528189, PMID:16525024, PMID:18779367]; MICAL-L2 coordinates this with adherens junction assembly by alternately binding Rab8 at perinuclear recycling compartments and RAB13 at the cell surface [PMID:18094055], and RAB13 binding induces a conformational change in MICAL-L2 that recruits actinin and filamin isoforms to remodel actin [PMID:20008558, PMID:23100251]. RAB13 also acts as a brake on tight junctions by directly binding and inhibiting the catalytic subunit of PKA, preventing PKA-dependent recruitment of VASP, ZO-1, and claudin-1 to junctions [PMID:15096524, PMID:16473634]. Beyond epithelia, RAB13 drives insulin- and Ca2+-stimulated GLUT4 vesicle exocytosis downstream of the Rab-GAP AS160 in muscle cells, assembling with MICAL-L2 and alpha-actinin-4 [PMID:21041651, PMID:26538022, PMID:29089333], delivers integrin LFA-1 to the leading edge of lymphocytes downstream of the GEF DENND1C and the kinase Mst1 [PMID:25074980], and recycles active beta1-integrin and CXCR1/2 to support adhesion, migration, and tumor cell behavior [PMID:31076515, PMID:35395074]. RAB13 is activated locally: the GEF DENND2B activates it at the leading edge of migrating cells [PMID:25713415], while peripheral localization and translation of RAB13 mRNA at protrusions couples nascent RAB13 to the exchange factor RABIF for full GTPase activation and polarized filopodia dynamics [PMID:32946136, PMID:32946121]. Its activity is negatively regulated by RNF115-catalyzed K11-linked ubiquitination on Lys46/Lys58, which impairs GDI1 recruitment and post-Golgi trafficking [PMID:35343654].","teleology":[{"year":1998,"claim":"Established that RAB13's membrane association is dynamically controlled, identifying delta-PDE rather than GDI as a factor able to extract it from membranes.","evidence":"Yeast two-hybrid screen and in vitro membrane dissociation with recombinant delta-PDE","pmids":["9712853"],"confidence":"Medium","gaps":["Physiological role of delta-PDE in RAB13 cycling not established in cells","Relationship to canonical GDI-mediated recycling left open"]},{"year":2002,"claim":"Placed RAB13 at junctional complexes and showed its GTP cycling governs tight junction barrier function, defining a junctional role for the GTPase.","evidence":"GFP-RAB13 Q67L/T22N mutant cell lines in MDCK with TEER, freeze-fracture EM, and tracer assays","pmids":["12058051"],"confidence":"High","gaps":["Effector mediating the junctional effect not yet identified","Trafficking step affected not resolved"]},{"year":2004,"claim":"Defined the cargo selectivity of RAB13 (occludin recycling) and uncovered a non-trafficking mechanism—direct PKA inhibition controlling junction protein recruitment.","evidence":"Biotinylation/recycling assays plus Co-IP and in vitro PKA activity assays with purified RAB13","pmids":["15528189","15096524","16473634"],"confidence":"High","gaps":["How RAB13 toggles between trafficking and PKA-inhibitory functions unclear","Structural basis of PKA binding not defined"]},{"year":2006,"claim":"Identified MICAL-L2/JRAB as the GTP-dependent effector linking RAB13 to occludin recycling and the actin cytoskeleton, providing the molecular bridge for junction assembly.","evidence":"Yeast two-hybrid, reciprocal Co-IP, recycling and Ca2+-switch assays in epithelial cells","pmids":["16525024"],"confidence":"High","gaps":["How MICAL-L2 couples to the recycling machinery mechanistically unresolved"]},{"year":2007,"claim":"Showed MICAL-L2 is shared by Rab8 and RAB13 in a competitive, sequential handoff coordinating tight and adherens junction assembly, and that RAB13 acts in TPA-induced scattering.","evidence":"siRNA, Co-IP, dominant mutants, Ca2+-switch and scattering assays in MDCK","pmids":["18094055","17891173"],"confidence":"High","gaps":["Spatial/temporal switch between Rab8 and RAB13 on MICAL-L2 not directly visualized","Activation trigger during scattering not defined"]},{"year":2008,"claim":"Mapped RAB13's itinerary to the TGN-to-recycling-endosome route, distinguishing it from direct TGN-to-surface trafficking and clarifying which cargoes depend on it.","evidence":"shRNA knockdown and dominant mutants with cargo-selective surface arrival assays","pmids":["18779367"],"confidence":"High","gaps":["Molecular machinery executing the TGN-RE step not identified"]},{"year":2010,"claim":"Extended RAB13 to regulated exocytosis, placing it downstream of the Rab-GAP AS160 in insulin-stimulated GLUT4 delivery in muscle cells.","evidence":"GTP-loading assays, siRNA, AS160 epistasis, and imaging in L6 muscle cells","pmids":["21041651"],"confidence":"High","gaps":["GEF activating RAB13 downstream of AS160 not identified in this system","Effector for GLUT4 vesicles not yet defined here"]},{"year":2014,"claim":"Identified the lymphocyte GEF DENND1C/Mst1 pathway and demonstrated, with knockout mice, a physiological RAB13 role in LFA-1 delivery and immune cell trafficking.","evidence":"DENND1C phosphorylation and RAB13 activation assays, RAB13 knockout mice, LFA-1 trafficking and adhesion assays","pmids":["25074980"],"confidence":"High","gaps":["Effector linking RAB13 to LFA-1 vesicles beyond myosin Va recruitment incompletely defined"]},{"year":2015,"claim":"Identified DENND2B as the leading-edge GEF and demonstrated spatially restricted RAB13 activation driving migration and cancer invasion; defined the insulin-responsive MICAL-L2/ACTN4/GLUT4 complex.","evidence":"FRET-based RAB13 biosensor, GEF assays, Co-IP, invasion and xenograft assays; super-resolution imaging of GLUT4 complex","pmids":["25713415","26538022"],"confidence":"High","gaps":["How DENND2B is itself spatially confined to the leading edge unresolved","Direct effector mediating GLUT4 vesicle tethering not defined"]},{"year":2017,"claim":"Refined the GLUT4 exocytic program by showing RAB13 selectively serves Ca2+/PKC- and contraction-stimulated translocation, distinguishing it from other Rab family members.","evidence":"Selective siRNA of Rab family members with cargo-specific GLUT4 surface assays and EPS contraction model","pmids":["29247648","29089333"],"confidence":"Medium","gaps":["Signaling node connecting Ca2+/PKC to RAB13 activation not identified","Single-cell-type evidence"]},{"year":2016,"claim":"Showed prenylation is dispensable for inactive RAB13 vesicle association, revealing protein-protein interactions rather than lipid anchoring govern GDP-state localization.","evidence":"Prenylation-deficient mutants with fractionation and live-cell vesicle imaging","pmids":["26969162"],"confidence":"Medium","gaps":["Identity of the protein partners anchoring inactive RAB13 to vesicles unknown"]},{"year":2019,"claim":"Expanded RAB13 cargo to active beta1-integrin recycling via GGA2, linking it to focal adhesion turnover and migration.","evidence":"RNAi screen, BioID proximity labeling, integrin activity and migration assays","pmids":["31076515"],"confidence":"Medium","gaps":["GGA2-RAB13 interaction by BioID without reciprocal direct-binding validation","Mechanism of conformer-selective integrin recycling unresolved"]},{"year":2020,"claim":"Established that localized RAB13 mRNA translation at protrusions couples nascent protein to RABIF for full GTPase activation, creating a polarized domain driving filopodia dynamics and vessel patterning in vivo.","evidence":"RNA localization perturbation, RABIF co-translational interaction, GTPase and migration assays; smFISH, CRISPR excision of a 192-nt element, zebrafish imaging","pmids":["32946136","32946121"],"confidence":"High","gaps":["How RABIF co-translational engagement selects RAB13 over other Rabs unresolved","Relationship between RABIF and other GEFs (DENND2B) not integrated"]},{"year":2022,"claim":"Defined RNF115-catalyzed K11-linked ubiquitination on Lys46/58 as a negative regulator that blocks GDI1 recruitment and post-Golgi TLR trafficking, adding a post-translational control layer.","evidence":"Co-IP, ubiquitination assays, site-directed K46/58R mutagenesis, GDI1 recruitment and TLR trafficking assays","pmids":["35343654"],"confidence":"High","gaps":["Deubiquitinase reversing the modification not identified","How ubiquitination is spatially restricted unknown"]},{"year":2022,"claim":"Linked RAB13 to cancer stem cell niche formation via surface translocation of CXCR1/2 receptors.","evidence":"siRNA, surface receptor measurement, co-culture and in vivo tumorigenesis assays in breast cancer cells","pmids":["35395074"],"confidence":"Medium","gaps":["Direct effector handling CXCR1/2 vesicles not defined","Single-lab functional readout"]},{"year":null,"claim":"How RAB13 is selectively activated and ubiquitinated at distinct subcellular sites, and how a single GTPase coordinates its many cargoes (junction proteins, GLUT4, integrins, chemokine receptors) across cell types, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying model integrating multiple GEFs (DENND2B, DENND1C, RABIF) with cargo selection","Structural basis of effector and PKA binding undefined","Deubiquitinase and full ubiquitin-cycle regulation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[8,13,19,24]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,6,13,15]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[2,6,11]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[6,22]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[15,16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2,6,8,18,22]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,5,29]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[12,22]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,30]}],"complexes":[],"partners":["MICALL2","DENND2B","DENND1C","RABIF","GGA2","GRB2","ACTN4","PRKACA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P51153","full_name":"Ras-related protein Rab-13","aliases":["Cell growth-inhibiting gene 4 protein"],"length_aa":203,"mass_kda":22.8,"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. RAB13 is involved in endocytic recycling and regulates the transport to the plasma membrane of transmembrane proteins like the tight junction protein OCLN/occludin. Thereby, it regulates the assembly and the activity of tight junctions. Moreover, it may also regulate tight junction assembly by activating the PKA signaling pathway and by reorganizing the actin cytoskeleton through the activation of the downstream effectors PRKACA and MICALL2 respectively. Through its role in tight junction assembly, may play a role in the establishment of Sertoli cell barrier. Plays also a role in angiogenesis through regulation of endothelial cells chemotaxis. Also involved in neurite outgrowth. Has also been proposed to play a role in post-Golgi membrane trafficking from the TGN to the recycling endosome. Finally, it has been involved in insulin-induced transport to the plasma membrane of the glucose transporter GLUT4 and therefore may play a role in glucose homeostasis","subcellular_location":"Cell membrane; Cytoplasmic vesicle membrane; Cell junction, tight junction; Golgi apparatus, trans-Golgi network membrane; Recycling endosome membrane; Cell projection, lamellipodium","url":"https://www.uniprot.org/uniprotkb/P51153/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAB13","classification":"Not Classified","n_dependent_lines":92,"n_total_lines":1208,"dependency_fraction":0.076158940397351},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000143545","cell_line_id":"CID000419","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"membrane","grade":3},{"compartment":"er","grade":2}],"interactors":[{"gene":"GDI2","stoichiometry":10.0},{"gene":"RAB1B;RAB1C","stoichiometry":10.0},{"gene":"SFPQ","stoichiometry":10.0},{"gene":"GDI1","stoichiometry":4.0},{"gene":"RABIF","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000419","total_profiled":1310},"omim":[{"mim_id":"620912","title":"MICAL-LIKE PROTEIN 2; MICALL2","url":"https://www.omim.org/entry/620912"},{"mim_id":"619563","title":"MICAL-LIKE PROTEIN 1; MICALL1","url":"https://www.omim.org/entry/619563"},{"mim_id":"617536","title":"BAI1-ASSOCIATED PROTEIN 2-LIKE 2; BAIAP2L2","url":"https://www.omim.org/entry/617536"},{"mim_id":"612994","title":"RAS-ASSOCIATED PROTEIN 28; RAB28","url":"https://www.omim.org/entry/612994"},{"mim_id":"606645","title":"ARF-GAP, RHO-GAP, ANKYRIN REPEAT, AND PLECKSTRIN HOMOLOGY DOMAINS-CONTAINING PROTEIN 2; ARAP2","url":"https://www.omim.org/entry/606645"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RAB13"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P51153","domains":[{"cath_id":"3.40.50.300","chopping":"6-175","consensus_level":"high","plddt":91.6754,"start":6,"end":175}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P51153","model_url":"https://alphafold.ebi.ac.uk/files/AF-P51153-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P51153-F1-predicted_aligned_error_v6.png","plddt_mean":84.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAB13","jax_strain_url":"https://www.jax.org/strain/search?query=RAB13"},"sequence":{"accession":"P51153","fasta_url":"https://rest.uniprot.org/uniprotkb/P51153.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P51153/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P51153"}},"corpus_meta":[{"pmid":"21041651","id":"PMC_21041651","title":"Rab8A and Rab13 are activated by insulin and 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Cancer Association","url":"https://pubmed.ncbi.nlm.nih.gov/41343127","citation_count":0,"is_preprint":false},{"pmid":"40859875","id":"PMC_40859875","title":"Vasoactive intestinal peptide reduces ocular hypertension by regulating tight junction of trabecular meshwork through Rab13/PKA signalling complex.","date":"2025","source":"Annals of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40859875","citation_count":0,"is_preprint":false},{"pmid":"41954292","id":"PMC_41954292","title":"Single-Cell Profiling Reveals RAB13+ Endothelial Cells and Profibrotic Mesenchymal Cells in Aged Human Bone Marrow.","date":"2026","source":"Aging cell","url":"https://pubmed.ncbi.nlm.nih.gov/41954292","citation_count":0,"is_preprint":false},{"pmid":"39912222","id":"PMC_39912222","title":"Enteropathogenic E. coli effector Map interacts with Rab13 and regulates the depletion of the tight junction proteins occludin and claudins via cathepsin B-mediated mechanisms.","date":"2025","source":"Biology 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Parkin","date":"2024-09-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.14.613079","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":28880,"output_tokens":8566,"usd":0.107565,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":18134,"output_tokens":4822,"usd":0.10561,"stage2_stop_reason":"end_turn"},"total_usd":0.213175,"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\": 2002,\n      \"finding\": \"Rab13 is recruited to junctional complexes from a cytosolic pool after cell-cell contact formation. Constitutively active Rab13 (Q67L) delays formation of electrically tight epithelial monolayers, disrupts the tight junction fence diffusion barrier, and delays claudin-1 localization at the cell surface, while inactive Rab13 (T22N) has no effect on TJ function or structure.\",\n      \"method\": \"Stable GFP-Rab13 mutant cell lines (Q67L and T22N) in MDCK cells; transepithelial electrical resistance; freeze-fracture EM; immunofluorescence; tracer leakage assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays with gain-of-function mutants, replicated across multiple labs in subsequent studies\",\n      \"pmids\": [\"12058051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The rod cGMP phosphodiesterase delta subunit (delta-PDE) specifically binds Rab13 and purified recombinant delta-PDE dissociates Rab13 from cellular membranes, suggesting delta-PDE (not GDI) controls the dynamic association of Rab13 with membranes.\",\n      \"method\": \"Yeast two-hybrid screen of HeLa cDNA library; purified recombinant delta-PDE membrane dissociation assay; immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution of membrane dissociation plus yeast two-hybrid, single lab\",\n      \"pmids\": [\"9712853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Rab13 dominant active mutant (Q67L) specifically inhibits postendocytic recycling of occludin back to the cell surface, but not recycling of transferrin receptor or polymeric immunoglobulin receptor; endocytosed occludin colocalizes with Rab13.\",\n      \"method\": \"Cell surface biotinylation; biochemical endocytosis and recycling assays; double immunolabeling; dominant active Rab13 expression in BHK and MTD-1A cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical and imaging assays, independently replicated across multiple subsequent studies\",\n      \"pmids\": [\"15528189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GTP-bound Rab13 directly binds to the alpha-catalytic subunit of PKA and inhibits PKA activity, thereby preventing PKA-dependent phosphorylation and tight junction recruitment of VASP (vasodilator-stimulated phosphoprotein). Activation of PKA abrogates the inhibitory effect of Rab13 on recruitment of VASP, ZO-1, and claudin-1 to cell-cell junctions.\",\n      \"method\": \"Co-immunoprecipitation; in vitro PKA activity assay with purified Rab13; dominant active Rab13 expression; PKA activator rescue experiments\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct binding demonstrated and in vitro kinase inhibition assay with multiple orthogonal approaches, replicated in subsequent studies\",\n      \"pmids\": [\"15096524\", \"16473634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MICAL-L2 (renamed JRAB, junctional Rab13-binding protein) specifically binds to the GTP-bound form of Rab13 via its C-terminal coiled-coil domain, localizes to tight junctions, and mediates endocytic recycling of occludin and formation of functional tight junctions. A MICAL-L2 mutant lacking the Rab13-binding domain (MICAL-L2-N) inhibits occludin recycling and TJ formation. MICAL-L2 links Rab13 to the actin cytoskeleton and is displaced from TJs upon actin depolymerization.\",\n      \"method\": \"Yeast two-hybrid; immunoprecipitation; immunofluorescence; recycling assay; Ca2+ switch assay; transepithelial electrical resistance measurement\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple functional assays, independently replicated across multiple subsequent studies\",\n      \"pmids\": [\"16525024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"JRAB/MICAL-L2 interacts with both Rab13 and Rab8 via its C-terminal domain, with Rab8 and Rab13 competing for MICAL-L2 binding. Rab13 specifically mediates claudin-1 and occludin transport to the plasma membrane but not E-cadherin transport, while Rab8 mediates Rab13-independent E-cadherin transport. JRAB/MICAL-L2 coordinates TJ and AJ assembly by sequentially interacting with Rab8 at perinuclear recycling compartments and Rab13 at the plasma membrane.\",\n      \"method\": \"siRNA knockdown; Ca2+ switch model; co-immunoprecipitation; immunofluorescence; dominant-negative and constitutively active mutant expression\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (siRNA, Co-IP, dominant mutants), replicated across studies\",\n      \"pmids\": [\"18094055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rab13 regulates membrane trafficking between the trans-Golgi network (TGN) and recycling endosomes (RE). Rab13 partially colocalizes with TGN38 at the TGN and transferrin receptors in RE. Knockdown or dominant mutant expression of Rab13 disrupts TGN38/46 localization and inhibits surface arrival of proteins that transit through RE (VSVG, A-VSVG, LDLR-CT27), but not proteins using a direct TGN-to-PM route.\",\n      \"method\": \"shRNA knockdown in HBE cells; dominant-active and dominant-negative allele overexpression in MDCK cells; immunofluorescence colocalization; surface protein arrival assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple complementary approaches (KD + dominant mutants + cargo selectivity analysis), replicated findings\",\n      \"pmids\": [\"18779367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Rab13 regulates neurite outgrowth in PC12 cells through its effector JRAB/MICAL-L2. Rab13 binding to JRAB/MICAL-L2 stimulates an intramolecular conformational change in JRAB/MICAL-L2 and promotes its interaction with actinin-4, an actin-binding protein that localizes to the cell body and neurite tips. This complex is proposed to transfer actinin-4 to neurite tips to reorganize actin for neurite extension.\",\n      \"method\": \"Dominant active Rab13 expression; co-immunoprecipitation; immunofluorescence; neurite outgrowth assays in PC12 cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional rescue in single lab, two orthogonal methods\",\n      \"pmids\": [\"20008558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Insulin promotes GTP loading of Rab13 (and Rab8A) in rat L6 muscle cells. siRNA-mediated Rab13 knockdown blocks insulin-induced GLUT4 appearance at the muscle cell surface, rescued by Rab13 ortholog but not Rab8A. Constitutively active AS160 (Rab-GAP) suppresses surface GLUT4, reversed by Rab13 or Rab8A overexpression, placing both Rabs downstream of AS160 in GLUT4 exocytic trafficking. Insulin promotes Rab13 colocalization with GLUT4 at the cell periphery.\",\n      \"method\": \"GTP-loading assay; siRNA knockdown; surface GLUT4 measurement; constitutively active AS160 expression; immunofluorescence colocalization\",\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 (GTP-loading, siRNA, epistasis with AS160, imaging), single focused study replicated in subsequent work\",\n      \"pmids\": [\"21041651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Rab13 is required for trafficking of a protein complex (RhoA, Syx, Mupp1, angiomotin) to the leading edge of migrating endothelial cells. Rab13 associates with Grb2, targeting Syx and RhoA to Tyr1175-phosphorylated VEGFR2 at the leading edge. Rab13 knockdown in zebrafish impedes sprouting of intersegmental vessels and reduces tip cell directionality.\",\n      \"method\": \"siRNA knockdown; co-immunoprecipitation; live-cell imaging; zebrafish vessel sprouting assay; directed migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP + in vivo zebrafish + cell migration assays, single lab\",\n      \"pmids\": [\"21543326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"JRAB/MICAL-L2 interacts with actin-binding proteins actinin-1 and actinin-4 and filamentous actin via different domains, regulating actin cross-linking and stabilization. During epithelial junctional development, JRAB is enriched in the actin bundle at the free border; Rab13 binding induces a conformational change in JRAB required for maturation of cell-cell adhesion sites.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence; actin bundling assays; dominant active Rab13 expression; Ca2+ switch assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, functional imaging, single lab with multiple methods\",\n      \"pmids\": [\"23100251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rab35 functions as a master Rab that recruits MICAL-L1 to Arf6-positive recycling endosomes, and MICAL-L1 in turn recruits Rab13 (along with Rab8 and Rab36) to these endosomes during NGF-induced neurite outgrowth in PC12 cells. Rab13 regulates neurite outgrowth non-redundantly downstream of Rab35 and MICAL-L1.\",\n      \"method\": \"Dominant active/negative Rab mutant expression; siRNA knockdown; immunofluorescence; neurite outgrowth assays in PC12 cells\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional ablation experiments with epistasis analysis, single lab\",\n      \"pmids\": [\"25086062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In lymphocytes, chemokine stimulation activates Rab13 via DENND1C (a GEF phosphorylated by kinase Mst1). Active Rab13 associates with Mst1 to facilitate delivery of integrin LFA-1 to the leading edge, involving myosin Va recruitment along actin filaments. Rab13-deficient mice have reduced lymphocyte numbers in lymphoid tissues due to defective trafficking. Inhibiting Rab13 function reduces lymphocyte adhesion and migration on ICAM-1 and disrupts the ring-like LFA-1 arrangement at the T cell-APC contact site.\",\n      \"method\": \"DENND1C phosphorylation assays; Rab13 activation assays; Rab13 knockout mice; LFA-1 surface trafficking assays; lymphocyte adhesion and migration assays; immunofluorescence\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse phenotype + multiple cell biological assays + pathway epistasis, replicated with multiple methods\",\n      \"pmids\": [\"25074980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"DENND2B is the guanine nucleotide exchange factor (GEF) for Rab13. DENND2B activates Rab13 specifically at the leading edge of migrating cells, as demonstrated by a FRET-based Rab13 biosensor. DENND2B interacts with the Rab13 effector MICAL-L2 at the cell periphery, and this interaction is required for dynamic remodeling of the leading edge. Disruption of Rab13-mediated trafficking limits invasive behavior in vitro and growth/migration of cancer cells in vivo.\",\n      \"method\": \"FRET-based Rab13 biosensor; GEF activity assay; co-immunoprecipitation; in vitro invasion assays; in vivo tumor xenograft assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — FRET biosensor directly measuring GEF activity at subcellular resolution plus functional assays, novel mechanistic discovery\",\n      \"pmids\": [\"25713415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Rab13 forms an insulin-dependent complex with MICAL-L2 and alpha-actinin-4 (ACTN4) in muscle cells. Insulin increases Rab13 binding to MICAL-L2, which in turn binds ACTN4. GLUT4 associates with this complex in response to insulin, requiring the ACTN4-binding domain in MICAL-L2. Knockdown of MICAL-L2 or expression of truncated MICAL-L2 impairs insulin-stimulated GLUT4 translocation.\",\n      \"method\": \"Pull-down assays; confocal fluorescence microscopy; structured illumination microscopy (SIM); TIRF microscopy; siRNA knockdown; co-immunoprecipitation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple super-resolution and biochemical approaches demonstrating complex assembly, single focused study with multiple orthogonal methods\",\n      \"pmids\": [\"26538022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C-terminal prenylation is not required for Rab13 to associate with and traffic on vesicles in its inactive GDP-bound state; inactive Rab13 associates with vesicles via protein-protein interactions. Only upon activation does Rab13 associate with the plasma membrane, presumably via C-terminal prenyl group membrane insertion.\",\n      \"method\": \"Prenylation-deficient Rab13 mutant expression; subcellular fractionation; live-cell vesicle trafficking imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with prenylation mutants, single lab\",\n      \"pmids\": [\"26969162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Rab13 is required for ionomycin-stimulated GLUT4 exocytosis in L6 myoblasts. siRab13 (but not siRab8a, siRab10, or siRab14) selectively inhibited GLUT4 exocytosis promoted by elevated cytosolic Ca2+, placing Rab13 specifically downstream of Ca2+/PKC signaling in this pathway.\",\n      \"method\": \"siRNA knockdown; surface GLUT4myc exocytosis assay; ionomycin-stimulated Ca2+ elevation; phosphorylation assays for AS160 and TBC1D1\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective siRNA knockdown with cargo-specific readout, single lab\",\n      \"pmids\": [\"29247648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Electrical pulse stimulation (EPS)-induced GLUT4 translocation in C2C12 myotubes requires Rab8a, Rab13, and Rab14 but not Rab10. Rab10 and Rab13 are not engaged by AMPK activation alone. Constitutively active AS160 diminishes EPS-stimulated GLUT4 translocation, supporting regulation downstream of Rab-GAP AS160.\",\n      \"method\": \"siRNA knockdown; surface HA-GLUT4 measurement; EPS contraction model; constitutively active AS160 expression; AMPK inhibitor and siRNA treatments\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic siRNA knockdown comparing Rab family members, single lab\",\n      \"pmids\": [\"29089333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAB13 and GGA2 (Golgi-localized gamma ear-containing Arf-binding protein 2) both regulate activity-dependent recycling of active but not inactive beta1-integrin to the plasma membrane. RAB13 silencing triggers intracellular accumulation of active beta1-integrin and reduces integrin activity in focal adhesions and cell migration. GGA2 and RAB13 interact (identified by BioID proximity labeling).\",\n      \"method\": \"RNAi screen; BioID proximity labeling; surface beta1-integrin activity assays; immunofluorescence; cell migration assays; siRNA knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — BioID interaction + functional siRNA with specific cargo readout, single lab\",\n      \"pmids\": [\"31076515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Peripheral translation of RAB13 mRNA at cellular protrusions leads to co-translational association of nascent RAB13 with the exchange factor RABIF. This co-translational RAB13-RABIF association at the cell periphery is required for directing RAB13 GTPase activity and promoting efficient cell migration. Preventing RAB13 mRNA localization (without affecting total RAB13 protein levels or membrane association) reduces RAB13 GTPase activation and cell migration efficiency.\",\n      \"method\": \"RNA localization perturbation constructs; RABIF co-translational interaction assays; GTPase activity measurements; cell migration assays; ribosome fractionation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct mechanistic link between mRNA localization, co-translational GEF association, and GTPase activation measured by multiple methods\",\n      \"pmids\": [\"32946136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RAB13 mRNA is targeted to sites of filopodia formation via a 192-nt localisation element. This spatial coupling of mRNA localisation, translation, and protein activity creates a polarised domain of filopodia extension. Genomic excision of this localisation element depolarises filopodia dynamics in motile endothelial cells and induces mispatterning of blood vessels in zebrafish without affecting total RAB13 translation.\",\n      \"method\": \"Single-molecule RNA FISH; gene editing (CRISPR); zebrafish live-cell imaging; protrusion-derived RNAseq; filopodia dynamics measurements\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous gene editing + in vivo zebrafish model + single-molecule imaging, multiple orthogonal approaches\",\n      \"pmids\": [\"32946121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Rab13 regulates secretion of small extracellular vesicles (sEVs) in mutant KRAS colorectal cancer cells. Rab13 is both a cargo protein packaged into sEVs and a regulator of sEV secretion. Knockdown of Rab13 blocks proliferative and tumorigenic effects of sEVs on recipient cells.\",\n      \"method\": \"siRNA knockdown; sEV isolation and characterization; recipient cell proliferation and tumorigenesis assays; Western blot\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with defined vesicle secretion and functional readout, single lab\",\n      \"pmids\": [\"32978434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RNF115 (an E3 ubiquitin ligase) catalyzes K11-linked ubiquitination on Lys46 and Lys58 residues of RAB13. This modification impairs recruitment of GDI1 to RAB13, a prerequisite for RAB reactivation. Knockdown of RAB13 inhibits post-Golgi trafficking of TLRs to the cell surface, and reconstitution of RAB13 with K46/58R mutations (ubiquitination-resistant) in RNF115+/+ cells promotes TLR trafficking from Golgi to cell surface.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays; site-directed mutagenesis (K46R, K58R); siRNA knockdown; TLR trafficking assays; subcellular fractionation; GDI1 recruitment assay\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — identified specific ubiquitination sites by mutagenesis, demonstrated functional consequence on GDI1 recruitment and TLR trafficking with multiple orthogonal methods\",\n      \"pmids\": [\"35343654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Rab13 controls membrane translocation of CXCR1/2 receptors, allowing breast cancer stem cells to interact with tumor-associated macrophages and cancer-associated fibroblasts to establish a supportive CSC niche. Rab13 depletion suppresses stemness and chemoresistance.\",\n      \"method\": \"siRNA knockdown; surface CXCR1/2 measurement; co-culture assays; in vivo tumorigenesis assays; flow cytometry\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cargo (CXCR1/2) with loss-of-function and functional readout, single lab\",\n      \"pmids\": [\"35395074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Rab13 and JRAB/MICAL-L2 are required for TPA-induced epithelial cell scattering (MDCK cells). During scattering, Rab13 is transiently activated; both Rab13 and JRAB/MICAL-L2 redistribute from cell-cell contact sites to emerging lamellipodial structures. Knockdown of either Rab13 or JRAB/MICAL-L2 suppresses TPA-induced scattering.\",\n      \"method\": \"siRNA knockdown; Rab13 GTP-loading assay; immunofluorescence; cell scattering assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with rescue, GTP-loading activation assay, single lab\",\n      \"pmids\": [\"17891173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RAB13 associates with vinculin and espin (ectoplasmic specialization actin-binding proteins) in the testis, as demonstrated by co-immunoprecipitation and immunofluorescence. RAB13 localizes to the ectoplasmic specialization in Sertoli-germ cell junctions and its level decreases during adjudin-induced ectoplasmic specialization disassembly.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence; immunohistochemistry; in vivo adjudin model\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP demonstrated specific protein interactions, supported by in vivo model, single lab\",\n      \"pmids\": [\"19074001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RAB13 knockdown in cultured Sertoli cells increases PKA activity, reinforces occludin and filamentous actin distribution at cell-cell interfaces, and promotes ZO-1–occludin direct interaction—effects that phenocopy testosterone's enhancement of TJ integrity. The effects of Rab13 knockdown on TJ permeability are antagonized by PKA inhibition, establishing a Rab13–PKA axis in Sertoli cell TJ regulation.\",\n      \"method\": \"siRNA knockdown in primary cultured Sertoli cells; transepithelial electrical resistance; co-immunoprecipitation; immunofluorescence; PKA activity assay\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with PKA epistasis and TER functional readout, single lab\",\n      \"pmids\": [\"23419316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"JRAB/MICAL-L2 in its open conformational state (JRABΔCC mutant) interacts with filamin isoforms (actin cross-linking proteins) as well as actinin-1 and actinin-4. Filamin but not actinin is required for JRAB-induced cell spreading with membrane ruffles. Degradation of filamins by ASB2 inhibits JRAB-induced cell spreading.\",\n      \"method\": \"Co-immunoprecipitation; expression of constitutively open/closed JRAB mutants; ASB2-induced filamin degradation; morphological cell spreading analysis\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and functional rescue, single lab\",\n      \"pmids\": [\"23890175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rab13 and Rab8 both bind to Endospanin-2 (and its homolog Endospanin-1) via the C-terminus of Endospanin-2, as demonstrated by bacterial two-hybrid and colocalization in perinuclear vesicular structures. Rab7, Rab10, Rab11, and Rab32 do not bind Endospanin-2.\",\n      \"method\": \"Bacterial two-hybrid screen; co-immunoprecipitation; immunofluorescence colocalization\",\n      \"journal\": \"FEBS open bio\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — bacterial two-hybrid and colocalization, functional consequence unclear, single lab\",\n      \"pmids\": [\"23772379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Rab13 mutants specifically impair cell-surface transport of claudin-1 but not basolateral LDLR or apical p75NTR in fibroblasts, while Rab3B mutants affect LDLR but not claudin-1 or p75NTR. This defines distinct and non-overlapping roles for Rab13 and Rab3B in polarized transport.\",\n      \"method\": \"Overexpression of dominant mutant Rabs; cell-surface transport assays for specific cargo proteins in fibroblasts\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cargo-selective transport assays with multiple Rab mutants providing specificity, single lab\",\n      \"pmids\": [\"12901864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Active Rab13 promotes autophagy in vascular endothelial cells by functionally interacting with Grb2, leading to AMPK activation and mTOR inhibition. Co-immunoprecipitation assays showed Rab13 promotes Rab13–Grb2 interaction; Grb2 knockdown suppresses Rab13-induced autophagy.\",\n      \"method\": \"Overexpression of active/inactive Rab13; siRNA knockdown of Grb2; co-immunoprecipitation; immunofluorescence; autophagy quantification; mTOR/AMPK phosphorylation assays\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP + epistasis with Grb2 knockdown + signaling assays, single lab\",\n      \"pmids\": [\"28087344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Parkin (RBR E3 ubiquitin ligase) ubiquitinates RAB13 in cells. This was identified in an orthogonal ubiquitin transfer (OUT) screen and confirmed by reconstituted ubiquitination reactions in vitro and in cells. Mitophagy stimulation enhanced Parkin-mediated ubiquitination of RAB13.\",\n      \"method\": \"Orthogonal ubiquitin transfer (OUT) cascade; proteomics; in vitro reconstituted ubiquitination assay; cell-based ubiquitination assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution confirmed in cells, but preprint and RAB13 is one of several Rab substrates identified\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"RAB13 is a small GTPase activated at the cell periphery by GEFs (DENND2B at the leading edge of epithelial/cancer cells; DENND1C downstream of Mst1 in lymphocytes; RABIF co-translationally at protrusions), where in its GTP-bound state it binds the effector MICAL-L2/JRAB to regulate endocytic recycling of tight junction proteins (occludin, claudin-1) to the plasma membrane, mediates TGN-to-recycling-endosome trafficking, drives GLUT4 vesicle exocytosis downstream of the Rab-GAP AS160 in response to insulin and Ca2+ signals in muscle cells, delivers integrin LFA-1 to the leading edge of lymphocytes, and controls directional cell migration and angiogenesis; its activity is negatively regulated by direct binding to and inhibition of the PKA catalytic subunit, by RNF115-catalyzed K11-linked ubiquitination on Lys46/58 (impairing GDI1 recruitment), and by delta-PDE-mediated membrane dissociation, while its mRNA localizes to cellular protrusions where co-translational RABIF association is required for full GTPase activation and directed cell migration.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAB13 is a small GTPase that controls polarized membrane trafficking at the cell periphery, governing tight junction assembly, directed cell migration, and regulated exocytosis [#0, #13]. In its GTP-bound state it engages the effector MICAL-L2/JRAB, which links RAB13 to the actin cytoskeleton and mediates endocytic recycling of the tight junction proteins occludin and claudin-1 back to the plasma membrane to build functional junctions [#2, #4, #6]; MICAL-L2 coordinates this with adherens junction assembly by alternately binding Rab8 at perinuclear recycling compartments and RAB13 at the cell surface [#5], and RAB13 binding induces a conformational change in MICAL-L2 that recruits actinin and filamin isoforms to remodel actin [#7, #10]. RAB13 also acts as a brake on tight junctions by directly binding and inhibiting the catalytic subunit of PKA, preventing PKA-dependent recruitment of VASP, ZO-1, and claudin-1 to junctions [#3]. Beyond epithelia, RAB13 drives insulin- and Ca2+-stimulated GLUT4 vesicle exocytosis downstream of the Rab-GAP AS160 in muscle cells, assembling with MICAL-L2 and alpha-actinin-4 [#8, #14, #17], delivers integrin LFA-1 to the leading edge of lymphocytes downstream of the GEF DENND1C and the kinase Mst1 [#12], and recycles active beta1-integrin and CXCR1/2 to support adhesion, migration, and tumor cell behavior [#18, #23]. RAB13 is activated locally: the GEF DENND2B activates it at the leading edge of migrating cells [#13], while peripheral localization and translation of RAB13 mRNA at protrusions couples nascent RAB13 to the exchange factor RABIF for full GTPase activation and polarized filopodia dynamics [#19, #20]. Its activity is negatively regulated by RNF115-catalyzed K11-linked ubiquitination on Lys46/Lys58, which impairs GDI1 recruitment and post-Golgi trafficking [#22].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that RAB13's membrane association is dynamically controlled, identifying delta-PDE rather than GDI as a factor able to extract it from membranes.\",\n      \"evidence\": \"Yeast two-hybrid screen and in vitro membrane dissociation with recombinant delta-PDE\",\n      \"pmids\": [\"9712853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological role of delta-PDE in RAB13 cycling not established in cells\", \"Relationship to canonical GDI-mediated recycling left open\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Placed RAB13 at junctional complexes and showed its GTP cycling governs tight junction barrier function, defining a junctional role for the GTPase.\",\n      \"evidence\": \"GFP-RAB13 Q67L/T22N mutant cell lines in MDCK with TEER, freeze-fracture EM, and tracer assays\",\n      \"pmids\": [\"12058051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector mediating the junctional effect not yet identified\", \"Trafficking step affected not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the cargo selectivity of RAB13 (occludin recycling) and uncovered a non-trafficking mechanism—direct PKA inhibition controlling junction protein recruitment.\",\n      \"evidence\": \"Biotinylation/recycling assays plus Co-IP and in vitro PKA activity assays with purified RAB13\",\n      \"pmids\": [\"15528189\", \"15096524\", \"16473634\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How RAB13 toggles between trafficking and PKA-inhibitory functions unclear\", \"Structural basis of PKA binding not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified MICAL-L2/JRAB as the GTP-dependent effector linking RAB13 to occludin recycling and the actin cytoskeleton, providing the molecular bridge for junction assembly.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP, recycling and Ca2+-switch assays in epithelial cells\",\n      \"pmids\": [\"16525024\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How MICAL-L2 couples to the recycling machinery mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed MICAL-L2 is shared by Rab8 and RAB13 in a competitive, sequential handoff coordinating tight and adherens junction assembly, and that RAB13 acts in TPA-induced scattering.\",\n      \"evidence\": \"siRNA, Co-IP, dominant mutants, Ca2+-switch and scattering assays in MDCK\",\n      \"pmids\": [\"18094055\", \"17891173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial/temporal switch between Rab8 and RAB13 on MICAL-L2 not directly visualized\", \"Activation trigger during scattering not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mapped RAB13's itinerary to the TGN-to-recycling-endosome route, distinguishing it from direct TGN-to-surface trafficking and clarifying which cargoes depend on it.\",\n      \"evidence\": \"shRNA knockdown and dominant mutants with cargo-selective surface arrival assays\",\n      \"pmids\": [\"18779367\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular machinery executing the TGN-RE step not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended RAB13 to regulated exocytosis, placing it downstream of the Rab-GAP AS160 in insulin-stimulated GLUT4 delivery in muscle cells.\",\n      \"evidence\": \"GTP-loading assays, siRNA, AS160 epistasis, and imaging in L6 muscle cells\",\n      \"pmids\": [\"21041651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GEF activating RAB13 downstream of AS160 not identified in this system\", \"Effector for GLUT4 vesicles not yet defined here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified the lymphocyte GEF DENND1C/Mst1 pathway and demonstrated, with knockout mice, a physiological RAB13 role in LFA-1 delivery and immune cell trafficking.\",\n      \"evidence\": \"DENND1C phosphorylation and RAB13 activation assays, RAB13 knockout mice, LFA-1 trafficking and adhesion assays\",\n      \"pmids\": [\"25074980\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector linking RAB13 to LFA-1 vesicles beyond myosin Va recruitment incompletely defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified DENND2B as the leading-edge GEF and demonstrated spatially restricted RAB13 activation driving migration and cancer invasion; defined the insulin-responsive MICAL-L2/ACTN4/GLUT4 complex.\",\n      \"evidence\": \"FRET-based RAB13 biosensor, GEF assays, Co-IP, invasion and xenograft assays; super-resolution imaging of GLUT4 complex\",\n      \"pmids\": [\"25713415\", \"26538022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DENND2B is itself spatially confined to the leading edge unresolved\", \"Direct effector mediating GLUT4 vesicle tethering not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Refined the GLUT4 exocytic program by showing RAB13 selectively serves Ca2+/PKC- and contraction-stimulated translocation, distinguishing it from other Rab family members.\",\n      \"evidence\": \"Selective siRNA of Rab family members with cargo-specific GLUT4 surface assays and EPS contraction model\",\n      \"pmids\": [\"29247648\", \"29089333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling node connecting Ca2+/PKC to RAB13 activation not identified\", \"Single-cell-type evidence\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed prenylation is dispensable for inactive RAB13 vesicle association, revealing protein-protein interactions rather than lipid anchoring govern GDP-state localization.\",\n      \"evidence\": \"Prenylation-deficient mutants with fractionation and live-cell vesicle imaging\",\n      \"pmids\": [\"26969162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the protein partners anchoring inactive RAB13 to vesicles unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Expanded RAB13 cargo to active beta1-integrin recycling via GGA2, linking it to focal adhesion turnover and migration.\",\n      \"evidence\": \"RNAi screen, BioID proximity labeling, integrin activity and migration assays\",\n      \"pmids\": [\"31076515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GGA2-RAB13 interaction by BioID without reciprocal direct-binding validation\", \"Mechanism of conformer-selective integrin recycling unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established that localized RAB13 mRNA translation at protrusions couples nascent protein to RABIF for full GTPase activation, creating a polarized domain driving filopodia dynamics and vessel patterning in vivo.\",\n      \"evidence\": \"RNA localization perturbation, RABIF co-translational interaction, GTPase and migration assays; smFISH, CRISPR excision of a 192-nt element, zebrafish imaging\",\n      \"pmids\": [\"32946136\", \"32946121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How RABIF co-translational engagement selects RAB13 over other Rabs unresolved\", \"Relationship between RABIF and other GEFs (DENND2B) not integrated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined RNF115-catalyzed K11-linked ubiquitination on Lys46/58 as a negative regulator that blocks GDI1 recruitment and post-Golgi TLR trafficking, adding a post-translational control layer.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, site-directed K46/58R mutagenesis, GDI1 recruitment and TLR trafficking assays\",\n      \"pmids\": [\"35343654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Deubiquitinase reversing the modification not identified\", \"How ubiquitination is spatially restricted unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked RAB13 to cancer stem cell niche formation via surface translocation of CXCR1/2 receptors.\",\n      \"evidence\": \"siRNA, surface receptor measurement, co-culture and in vivo tumorigenesis assays in breast cancer cells\",\n      \"pmids\": [\"35395074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct effector handling CXCR1/2 vesicles not defined\", \"Single-lab functional readout\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RAB13 is selectively activated and ubiquitinated at distinct subcellular sites, and how a single GTPase coordinates its many cargoes (junction proteins, GLUT4, integrins, chemokine receptors) across cell types, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying model integrating multiple GEFs (DENND2B, DENND1C, RABIF) with cargo selection\", \"Structural basis of effector and PKA binding undefined\", \"Deubiquitinase and full ubiquitin-cycle regulation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [8, 13, 19, 24]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 6, 13, 15]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [2, 6, 11]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [6, 22]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2, 6, 8, 18, 22]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 5, 29]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [12, 22]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 30]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MICALL2\", \"DENND2B\", \"DENND1C\", \"RABIF\", \"GGA2\", \"GRB2\", \"ACTN4\", \"PRKACA\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}