RAB8B

RAB8B is a small Rab GTPase that controls multiple vesicular trafficking steps at the plasma membrane and secretory/endosomal pathways (PMID:24035388, PMID:24213529, PMID:11278749). It acts redundantly with RAB8A to mediate apical, but not basolateral, transport in polarized cells in vivo, where double knockout disrupts apical marker localization; additional loss of Rab10 in this background impairs ciliogenesis (PMID:24213529). RAB8B engages effectors in a guanine-nucleotide-dependent manner: it binds the TPR-domain protein TRIP8b through its GTP-bound state to stimulate regulated cAMP-induced ACTH secretion (PMID:11278749). It is also required for caveolin-dependent endocytosis of LRP6, thereby promoting Wnt/β-catenin signaling and induction of Wnt target genes (PMID:24035388). RAB8B further participates in trans-Golgi trafficking at cochlear ribbon synapses through interaction with the deafness protein otoferlin (PMID:18772196). In hepatocytes, RAB8B supports autophagosome/lysosome formation and lipophagy and is a direct target of LXRα-induced let-7a and miR-34a microRNAs (PMID:32557804).

1. 2001 High

   Established the first RAB8B effector and a functional role, showing that RAB8B couples to the secretory machinery through a nucleotide-state-dependent interaction.

   Evidence Yeast two-hybrid, in vitro binding, co-IP with GTP/GDP-binding mutants, and ACTH secretion assay in AtT20 cells

   PMID:11278749

   Open questions at the time

   • Mechanism by which TRIP8b stimulates secretion downstream of RAB8B is not resolved
   • Endogenous vesicle population controlled by the RAB8B–TRIP8b complex not defined
2. 2003 Low

   Linked RAB8B expression to junction assembly and cytoskeletal networks in the testis, but without direct perturbation of RAB8B.

   Evidence RT-PCR, immunohistochemistry, cytoskeletal co-fractionation, and germ cell co-culture in primary rat Sertoli cells

   PMID:12639940

   Open questions at the time

   • Correlative expression data only; no loss-of-function for RAB8B
   • Causal role in adherens junction assembly not established
3. 2008 Medium

   Identified otoferlin as a RAB8B partner, placing RAB8B in trans-Golgi trafficking at cochlear ribbon synapses.

   Evidence Yeast two-hybrid (cochlear cDNA library), co-localization in HEK293, and reciprocal co-IP of native cochlear proteins

   PMID:18772196

   Open questions at the time

   • Functional consequence of the RAB8B–otoferlin interaction for hair cell secretion untested
   • Single lab; no in vivo RAB8B perturbation in the cochlea
4. 2008 Low

   Characterized molecular determinants of the TRIP8b TPR domain that govern RAB8B binding specificity.

   Evidence In vitro binding assays and interface mutagenesis comparing TRIP8b and Pex5p

   PMID:18346465

   Open questions at the time

   • No cellular functional readout for RAB8B in this study
   • Physiological relevance of binding-affinity changes not tested
5. 2013 High

   Demonstrated that RAB8B is required for caveolar endocytosis of LRP6 and for Wnt/β-catenin signal activation, defining a receptor-internalization role.

   Evidence RNAi screen, siRNA depletion, overexpression rescue, β-catenin and Wnt target gene assays, and Xenopus/zebrafish morphant models

   PMID:24035388

   Open questions at the time

   • Whether RAB8B acts directly on caveolar carriers or via an effector is unresolved
   • Generality across Wnt receptor types not defined
6. 2013 High

   Established functional redundancy of RAB8B with RAB8A in apical transport in vivo and a combinatorial role with Rab10 in ciliogenesis.

   Evidence Rab8b-KO and Rab8a/Rab8b double-KO mice, apical/basolateral marker immunofluorescence, Rab10 knockdown, and cilia frequency analysis

   PMID:24213529

   Open questions at the time

   • Specific cargo and effectors mediating apical delivery not identified
   • Non-redundant RAB8B-specific functions not separated from RAB8A
7. 2016 Medium

   Showed RAB8B routes West Nile virus particles from recycling endosomes to the plasma membrane for egress.

   Evidence RNAi knockdown, viral release quantification, and co-localization with recycling endosome markers

   PMID:26817838

   Open questions at the time

   • Direct interaction with viral components not shown
   • Effector linking RAB8B to recycling-endosome exocytosis unknown
8. 2021 Medium

   Placed RAB8B under transcriptional/microRNA control by LXRα and tied its activity to autophagy and lipid metabolism in hepatocytes.

   Evidence LXRα-KO mice, ChIP, 3′UTR luciferase reporter, miRNA transfection, autophagy flux, and oxygen consumption assays

   PMID:32557804

   Open questions at the time

   • Molecular step by which RAB8B promotes autophagosome/lysosome formation not defined
   • Single lab; effectors in lipophagy unidentified
9. 2025 Low

   Implicated a PFKM–RAB8B axis in exosome release and chemoresistance in lung adenocarcinoma.

   Evidence Metabolomics, RAB8B expression modulation, exosome characterization, and apoptosis/glycolysis assays in chemoresistant LUAD cells

   PMID:42057963

   Open questions at the time

   • No direct PFKM–RAB8B binding or reconstitution shown
   • Mechanism connecting RAB8B to exosome biogenesis undefined
10. 2026 Low

    Suggested RAB8B modulates VAMP-3 clustering and trafficking to support SARS-CoV-2 infection.

    Evidence Molecular dynamics simulations and siRNA silencing in SARS-CoV-2-infected CaCo-2 cells with infection quantification

    PMID:42015392

    Open questions at the time

    • Direct control of VAMP-3 by RAB8B not mechanistically demonstrated
    • Computational predictions not validated by binding data

• The full set of RAB8B-specific GEFs, GAPs, and effectors that distinguish its functions from RAB8A across distinct trafficking routes remains undefined.
• No structural model of RAB8B effector complexes
• RAB8B-specific (non-redundant) cargo not catalogued
• Regulatory GEF/GAP network unmapped