TBC1D10A

TBC1D10A (EPI64) is a TBC-domain RabGAP that couples microvillar architecture to membrane trafficking and regulated secretion at the apical plasma membrane (PMID:11285285, PMID:17145964). It is targeted to microvilli through its C-terminal DTYL motif, which binds the first PDZ domain of the scaffold EBP50; uncoupling EPI64 from EBP50 or mislocalizing its TBC domain abolishes both its localization and the integrity of microvilli (PMID:11285285, PMID:17145964). Through its catalytic TBC domain it functions as a GAP for multiple Rab GTPases—Rab27A, where it drives melanosome aggregation and, in parotid acinar cells, controls Rab27-dependent amylase exocytosis (PMID:16923811, PMID:21832089); Rab35, where it suppresses histamine-evoked Weibel-Palade body exocytosis and negatively regulates NDP52-dependent xenophagy and mitophagy while controlling ciliary length and ciliary Rab35 localization (PMID:28566286, PMID:28848034, PMID:31432619); and Rab8a, which it recruits for inactivation via the effector JFC1 (PMID:22219378). In parallel its TBC domain binds and stabilizes Arf6-GTP, linking its GAP activity to Arf6-dependent actin-coated vacuole formation and microvillar remodeling (PMID:17145964, PMID:22219378). In pancreatic β-cells EPI64 is recruited downstream of PI3K/PIP3 by the Arf6-GEF ARNO to regulate endocytosis following insulin secretion (PMID:26683831). Beyond these Rab/Arf activities, EPI64 also exhibits RasGAP activity (PMID:23248241).

1. 2001 High

   Established how an uncharacterized microvillar TBC protein is targeted to its site of action, defining the scaffold interaction that anchors EPI64 to microvilli.

   Evidence Affinity chromatography from placental microvilli with PDZ binding assays and DTYL-motif mutagenesis

   PMID:11285285

   Open questions at the time

   • Did not define a catalytic substrate or GAP target
   • Functional consequence of microvillar localization unresolved at this stage
2. 2006 High

   Resolved the catalytic identity of EPI64 by showing its TBC domain is a specific Rab27A-GAP, linking it to organelle (melanosome) transport.

   Evidence TBC-protein functional screen in melanocytes, GTP-Rab27A trapping, in vitro Rab27A-GAP assay, and catalytic-domain mutagenesis

   PMID:16923811

   Open questions at the time

   • Physiological relevance in secretory tissues not yet shown
   • Other potential Rab substrates not surveyed
3. 2006 High

   Connected EPI64's GAP scaffold to microvillar structure and revealed a second small-GTPase activity, showing its TBC domain binds and elevates Arf6-GTP.

   Evidence High-resolution imaging, EBP50 knockdown, dominant constructs, and direct TBC-domain–Arf6-GTP binding/GTP-level assays

   PMID:17145964

   Open questions at the time

   • Mechanism by which Arf6-GTP binding is reconciled with GAP catalysis unclear
   • Whether Arf6 binding requires Rab inactivation not resolved
4. 2011 High

   Demonstrated that EPI64's Rab27-GAP activity is physiologically required for regulated exocytosis in a native secretory cell.

   Evidence Fractionation, anti-TBC antibody inhibition in permeabilized parotid acinar cells, antisense knockdown, and amylase release assays

   PMID:21832089

   Open questions at the time

   • Upstream signals controlling EPI64 expression beyond isoproterenol not defined
   • Direct in vivo Rab27 GTP measurement in this tissue limited
5. 2012 High

   Expanded the trafficking model by showing EPI64 inactivates Rab8a through effector-mediated recruitment, coordinating Arf6 and Rab8a pathways.

   Evidence GAP-dead overexpression, Rab8-GTP pull-down, and direct binding of the EPI64 C-terminus to JFC1

   PMID:22219378

   Open questions at the time

   • Whether Rab8a recruitment via JFC1 occurs in physiological cell types untested
   • Relationship to Rab27 inactivation events unclear
6. 2012 Medium

   Identified an additional enzymatic dimension by showing all EPI64-family members possess RasGAP activity in cells.

   Evidence FRET Ras sensors, Bos pull-down for active Ras, and time-lapse FRET in COS-7 cells

   PMID:23248241

   Open questions at the time

   • No in vitro reconstitution with purified proteins
   • Physiological context of RasGAP activity not defined
7. 2015 Medium

   Placed EPI64 in a lipid-signaling-regulated endocytic pathway in β-cells, downstream of PIP3-recruited ARNO.

   Evidence Co-IP of EPI64 with ARNO, PI3K inhibition, and glucose-stimulated endocytosis assays in β-cells

   PMID:26683831

   Open questions at the time

   • Single-lab co-IP without reciprocal structural mapping
   • Which Rab/Arf substrate executes the endocytic step unclear
8. 2017 High

   Established Rab35 as a substrate and tied EPI64 to vascular secretion and selective autophagy regulation.

   Evidence RabGAP screen for WPB exocytosis, reciprocal co-IP, GAP-dead and Rab35(Q67A) rescue, knockdown; NDP52 recruitment and mitophagy assays

   PMID:28566286 PMID:28848034

   Open questions at the time

   • Direct in vitro Rab35-GAP kinetics not reported
   • How EPI64 selects Rab35 versus Rab27/Rab8a substrates in vivo unresolved
9. 2019 Medium

   Extended Rab35 regulation to the cilium, linking EPI64 to ciliary length control and ciliary Rab35 localization.

   Evidence siRNA knockdown, GFP-TBC1D10A ciliary live imaging, and cilium length measurements

   PMID:31432619

   Open questions at the time

   • Mechanism coupling Rab35 inactivation to length control unclear
   • Single-lab localization data
10. 2019 Low

    Proposed additional substrate (RAB13) and an upstream β-cell receptor (IRR), broadening but not yet solidifying the regulatory network.

    Evidence Colocalization with RAB13/VEGFR2 and Erk signaling assays; EPI64-interactor identification with IRR knockdown endocytosis assays

    PMID:31353211 PMID:31527750

    Open questions at the time

    • No direct GAP activity assay for RAB13
    • EPI64–IRR interaction detection method not specified; single-lab, unreplicated

• How EPI64 selects among its multiple Rab substrates (Rab27A, Rab35, Rab8a, RAB13) and integrates concurrent Arf6 and Ras activities at distinct membranes remains unresolved.
• No structural model distinguishing substrate engagement
• Spatial/temporal logic of competing GAP activities undefined
• No loss-of-function organismal phenotype reported in the corpus