TBC1D10B

TBC1D10B (EPI64B) is a broad-specificity Rab-GTPase-activating protein that uses its catalytic TBC domain to accelerate GTP hydrolysis on multiple Rab isoforms—including Rab3A, Rab22A, Rab27A, and Rab35—thereby switching these traffic regulators off; an active-site R134K substitution abolishes this activity, defining the TBC domain as the catalytic unit (PMID:19077034). Its best-defined cellular role is in endocytic membrane trafficking, where it functions as an effector of ARF6 that is recruited to clathrin-coated pits to restrain Rab35; the spatially controlled disappearance of TBC1D10B from newly formed clathrin-coated vesicles after scission permits switch-like Rab35 activation and downstream OCRL recruitment, and loss of this regulation produces endocytic recycling and cytokinesis defects (PMID:22226746, PMID:26725203). Through its GAP activity it also shapes endosomal architecture, being required for tubular endosome formation via inactivation of Rab22A (PMID:40241313), and it controls regulated secretion as a Rab27B GAP that enhances amylase release in pancreatic acinar cells (PMID:23671284). At epithelial apical surfaces TBC1D10B localizes to microvilli through a domain spanning its RabGAP region and supports apical microvillar density, acting redundantly with the paralog EPI64A (PMID:34757852). Beyond core trafficking, a BAG3–HSP70 complex sequesters TBC1D10B to attenuate its inactivation of RAB35, sustaining ESCRT-dependent endosomal tau clearance—a function whose colocalization is reduced in Alzheimer's disease brains (PMID:35000752), and TBC1D10B is released from phagocytic cups in a Rit1 GTPase-dependent manner to regulate FcγR-mediated phagocytosis (PMID:39084876).

1. 2008 High

   Established that TBC1D10B is a catalytically active, broad-specificity RabGAP rather than an orphan TBC-domain protein, defining its molecular activity and substrate range.

   Evidence In vitro GTPase assays across multiple Rabs plus R134K active-site mutant and Rab3A exclusion assay in PC12 cells

   PMID:19077034

   Open questions at the time

   • Did not establish which Rab is the physiological substrate in any given cell type
   • No structural basis for substrate selectivity
2. 2012 High

   Placed TBC1D10B in a signaling cascade as an ARF6 effector that negatively regulates Rab35 at clathrin-coated pits, linking its GAP activity to endocytic recycling and cytokinesis.

   Evidence Epistasis with dominant GTPase mutants, Co-IP, and live-cell imaging in human cells

   PMID:22226746

   Open questions at the time

   • Mechanism of ARF6-dependent recruitment not resolved at structural level
   • Did not address other Rab substrates in this context
3. 2013 High

   Showed TBC1D10B acts as a Rab27B GAP controlling regulated secretion, demonstrating a context-specific physiological substrate distinct from Rab35.

   Evidence Adenoviral overexpression, GTP-Rab pulldown, amylase secretion assays, GAP-dead rescue, Rab27A-knockout mice in pancreatic acinar cells

   PMID:23671284

   Open questions at the time

   • Whether endogenous TBC1D10B levels limit secretion not shown
   • Selectivity for Rab27B over Rab3D mechanism unexplained
4. 2015 High

   Resolved how a constitutive Rab35 inhibitor permits Rab35 activation, showing spatial removal of TBC1D10B from newborn vesicles generates a switch-like Rab35-OCRL response.

   Evidence Live-cell imaging of CCV dynamics with depletion/overexpression and Rab35/OCRL localization (independent lab)

   PMID:26725203

   Open questions at the time

   • Trigger for TBC1D10B disappearance from vesicles not defined
   • Direct OCRL link is downstream of Rab35, not of TBC1D10B itself
5. 2019 Medium

   Linked TBC1D10B to VEGFR2 signaling and angiogenesis, contrasting its action with paralog TBC1D10A.

   Evidence Overexpression in endothelial cells with ERK1/2 and p38 phospho-Western, immunofluorescence, and tube formation assay

   PMID:31527750

   Open questions at the time

   • No substrate identification or GAP-dead control
   • Effect shown only by overexpression, not loss-of-function
6. 2021 Medium

   Defined a role at epithelial apical surfaces, showing TBC1D10B supports microvillar density redundantly with EPI64A and localizes via its RabGAP-spanning domain without binding EBP50.

   Evidence CRISPR/Cas9 single and double knockouts, immunofluorescence, and domain mapping in Jeg-3 cells

   PMID:34757852

   Open questions at the time

   • Causal Rab substrate (Rab8/Rab35) at microvilli inferred, not directly demonstrated
   • Functional consequence of microvillar loss not assessed
7. 2021 High

   Identified a regulatory mechanism in which BAG3-HSP70 sequesters TBC1D10B to sustain RAB35 activity and ESCRT-dependent tau clearance, connecting its GAP regulation to neurodegeneration.

   Evidence Mass spectrometry, reciprocal Co-IP, GTP-RAB35 assays, live imaging, P301S mouse and human AD brain immunohistochemistry

   PMID:35000752

   Open questions at the time

   • Whether reduced BAG3-TBC1D10B colocalization is cause or consequence of AD pathology unresolved
   • Stoichiometry of the BAG3-HSP70-TBC1D10B complex not defined
8. 2024 Medium

   Placed TBC1D10B downstream of Rit1 in macrophage phagocytosis, showing GTP-Rit1-driven dissociation from phagocytic cups regulates FcγR-mediated phagosome formation in both GAP-dependent and -independent ways.

   Evidence Live-cell imaging, Rit1 and TBC1D10B knockouts, GTP/GDP-locked Rit1 mutants in RAW264 macrophages

   PMID:39084876

   Open questions at the time

   • GAP-independent mechanism of phagocytosis regulation undefined
   • Direct Rit1-TBC1D10B physical interaction not biochemically established
9. 2025 Medium

   Identified Rab22A as a probable physiological substrate by showing TBC1D10B is required for tubular endosome formation through Rab22A inactivation.

   Evidence TBC/Rab-GAP siRNA screen, overexpression, GTP-Rab22A pulldown, and tubular endosome imaging in HeLa cells

   PMID:40241313

   Open questions at the time

   • Why both knockdown and overexpression reduce tubular endosomes mechanistically unclear
   • Relationship to Rab35-based functions not integrated

• How TBC1D10B's broad in vitro substrate range is restricted to specific Rabs in specific compartments, and what governs its recruitment versus removal, remains unresolved.
• No structural model of substrate selectivity
• Determinants of compartment-specific recruitment unknown
• Integration of secretory, endosomal, phagocytic, and neurodegenerative roles into one regulatory logic missing