TBC1D10B

TBC1D10B (EPI64B) is a TBC-domain Rab GTPase-activating protein (RabGAP) with broad substrate specificity that orchestrates membrane identity transitions during endocytic recycling, exocytosis, phagocytosis, and cargo sorting. It catalyzes GTP hydrolysis on Rab3A, Rab22A, Rab27A, Rab27B, and Rab35 in vitro and in cells, with catalytic arginine residue R134 essential for activity (PMID:19077034, PMID:23671284, PMID:22226746). At clathrin-coated pits, ARF6-dependent recruitment of TBC1D10B suppresses Rab35 until vesicle scission, whereupon its departure triggers switch-like Rab35 activation and OCRL-mediated PtdIns(4,5)P₂ hydrolysis on newborn endosomes; a BAG3–HSP70 complex attenuates TBC1D10B activity to sustain RAB35-dependent ESCRT-mediated tau clearance (PMID:26725203, PMID:22226746, PMID:35000752). TBC1D10B also localizes to apical microvilli where its loss disrupts microvillar and junctional architecture, regulates tubular endosome formation through Rab22A inactivation, and modulates Fcγ receptor–mediated phagocytosis downstream of the Rit1 GTPase (PMID:34757852, PMID:40241313, PMID:39084876).

1. 2008 High

   Establishing TBC1D10B as a bona fide RabGAP: it was unknown whether TBC1D10B possessed catalytic activity, and in vitro assays demonstrated broad specificity toward Rab3A, Rab22A, Rab27A, and Rab35, with the R134K mutation ablating activity, proving the catalytic TBC domain is functional.

   Evidence In vitro GTPase assays with purified Rab proteins and catalytically dead R134K mutant in mammalian cells

   PMID:19077034

   Open questions at the time

   • In vivo substrate selectivity undetermined
   • No structural basis for broad specificity
   • Regulation of TBC1D10B activity itself unknown
2. 2011 Medium

   An early hint that TBC1D10B functions in membrane defense: siRNA depletion increased intracellular Salmonella replication, revealing a host-restrictive role, though the Rab substrate and mechanism were not identified.

   Evidence SILAC proteomics of Golgi-enriched fractions combined with siRNA knockdown and bacterial replication assay in human epithelial cells

   PMID:21919203

   Open questions at the time

   • No direct Rab substrate identified in this context
   • Mechanism of bacterial restriction unknown
   • Single study without independent replication
3. 2012 High

   Placing TBC1D10B in the ARF6–Rab35 signaling axis: it was unclear how Rab35 is inactivated at endocytic membranes, and this work showed ARF6 recruits TBC1D10B to clathrin-coated pits to suppress Rab35, linking it to endocytic recycling and cytokinesis.

   Evidence Co-IP, epistasis with constitutively active/dominant-negative ARF6 and Rab35 mutants, endocytic recycling and cytokinesis assays in mammalian cells

   PMID:22226746

   Open questions at the time

   • Direct structural interaction between ARF6 and TBC1D10B not mapped
   • Relative contribution of TBC1D10B versus paralogs (EPI64/EPI64C) to Rab35 inactivation unclear
4. 2013 High

   Demonstrating tissue-specific substrate usage: in pancreatic acinar cells TBC1D10B acts as a Rab27B-selective GAP to regulate exocytic amylase secretion, establishing that its broad in vitro specificity translates to context-dependent selectivity in vivo.

   Evidence Adenoviral overexpression and catalytic mutants in isolated mouse pancreatic acini, GTP-Rab27B pull-down, amylase secretion assay

   PMID:23671284

   Open questions at the time

   • How TBC1D10B discriminates Rab27B from Rab3D in acinar cells not resolved
   • Upstream signals directing TBC1D10B to exocytic granules unknown
5. 2015 High

   Revealing the spatial logic of Rab35 activation: the disappearance of TBC1D10B from clathrin-coated vesicles immediately after scission was shown to be the trigger for switch-like Rab35 activation and OCRL recruitment, providing a timer mechanism for endosomal PtdIns(4,5)P₂ hydrolysis and cargo sorting.

   Evidence Live-cell imaging with temporal resolution of vesicle scission, siRNA knockdown, CI-MPR cargo sorting readout

   PMID:26725203

   Open questions at the time

   • Mechanism of TBC1D10B dissociation from vesicles at scission not identified
   • Whether this timing mechanism operates in all cell types unknown
6. 2019 Medium

   Extending TBC1D10B function to receptor signaling: overexpression in endothelial cells attenuated VEGFR2/NRP1 surface expression and Erk/p38 signaling, suggesting a role in receptor trafficking that influences angiogenic responses.

   Evidence Overexpression in endothelial cells, western blotting, tube formation assay, immunofluorescence

   PMID:31527750

   Open questions at the time

   • Rab substrate responsible for VEGFR2 trafficking not identified
   • Only overexpression; loss-of-function not tested
   • Single lab observation
7. 2021 High

   Identifying a chaperone-based suppression mechanism: BAG3–HSP70 complex binds TBC1D10B and attenuates its GAP activity toward RAB35, maintaining RAB35 in its active state to drive HRS recruitment and ESCRT-mediated endosomal tau clearance — connecting TBC1D10B to neurodegeneration-relevant proteostasis.

   Evidence Mass spectrometry interactome, co-IP, live-cell endosomal imaging, validation in P301S tau transgenic mice and human AD brain

   PMID:35000752

   Open questions at the time

   • Direct biochemical reconstitution of BAG3–HSP70 inhibition of TBC1D10B GAP activity not shown
   • Whether this mechanism operates in neurons in vivo not directly tested
8. 2021 Medium

   Establishing an apical morphogenesis role: TBC1D10B localizes to epithelial microvilli via its RabGAP domains, and CRISPR knockout reduces microvilli and disrupts apical junctions, linking its GAP activity to apical membrane organization.

   Evidence CRISPR/Cas9 knockout in Jeg-3 and Caco2 cells, domain mapping, immunofluorescence

   PMID:34757852

   Open questions at the time

   • Rab8 and Rab35 involvement inferred but not directly measured
   • Mechanism linking GAP activity to microvillar assembly unknown
   • In vivo relevance in intestinal or placental epithelium not tested
9. 2024 Medium

   Placing TBC1D10B downstream of Rit1 in phagocytosis: Rit1 GTPase promotes TBC1D10B dissociation from phagocytic cups, relieving its inhibitory effect on Fcγ receptor-mediated phagosome formation — revealing both GAP-dependent and GAP-independent inhibitory mechanisms.

   Evidence Live-cell imaging, Rit1 knockout and GTPase-locked mutants, TBC1D10B overexpression/knockout, phagosome quantification in RAW264 macrophages

   PMID:39084876

   Open questions at the time

   • Rab substrate at the phagocytic cup not identified
   • GAP-independent inhibitory mechanism molecularly undefined
   • Single macrophage cell line used
10. 2025 Medium

    Identifying Rab22A as the functional substrate for tubular endosome biogenesis: a systematic screen showed TBC1D10B is required for tubular endosome formation in a GAP-dependent manner, with active Rab22A as its principal target in this context.

    Evidence Comprehensive TBC/RabGAP siRNA screen, overexpression, active-Rab22A pull-down, fluorescence microscopy in HeLa cells

    PMID:40241313

    Open questions at the time

    • Direct in vitro reconstitution of Rab22A GAP activity in this system not shown
    • How tubular endosome formation serves downstream trafficking unknown
    • Relationship between Rab22A and Rab35 regulation by TBC1D10B at endosomes unresolved

• Key unresolved questions include: the structural basis for TBC1D10B's broad yet context-dependent Rab selectivity, the molecular mechanism of its GAP-independent inhibition of phagocytosis, whether its loss contributes to human disease, and how upstream signals (ARF6, Rit1, BAG3–HSP70) are integrated to coordinate its activity across different membrane compartments.
• No crystal or cryo-EM structure available
• No Mendelian or somatic disease association established by direct evidence
• Integrated signaling logic across ARF6/Rit1/BAG3 inputs not modeled