DENND2B

DENND2B (ST5/p126) is a multi-substrate DENN-domain guanine nucleotide exchange factor (GEF) that spatially controls Rab and Rho GTPase signaling to direct membrane trafficking, cell migration, ciliogenesis, and cytokinesis (PMID:25713415, PMID:35196081, PMID:37454296). It activates Rab13 specifically at the leading edge of migrating cells, where it engages the Rab13 effector MICAL-L2 to remodel the cell periphery and drive epithelial invasion and tumor cell migration in vivo (PMID:25713415). A systematic GEF screen established that DENND2B additionally activates Rab10 to repress primary cilium formation and acts as a GEF for the non-Rab substrate RhoA to control cilium length, thereby coupling its catalytic activity to two parallel ciliogenesis pathways (PMID:35196081). At the intercellular cytokinetic bridge DENND2B serves as both GEF and effector for Rab35, and its loss delays abscission, producing F-actin accumulation, impaired ESCRT-III recruitment, chromatin bridges, multinucleation, and Aurora B/NoCut checkpoint activation (PMID:37454296). DENND2B also binds the endocytic adaptor intersectin-s to promote recycling of ligand-free EGFR; EGF-triggered phosphorylation by protein kinase D dissociates this complex and redirects EGFR to lysosomal degradation (PMID:29030480). The largest ST5 isoform, p126, binds the c-Abl SH3 domain through a proline-rich motif and activates ERK2/MAPK upstream of RAS, whereas the p70 isoform suppresses this pathway via a C-terminal inhibitory region and restores contact-regulated, flattened growth phenotypes (PMID:9632734, PMID:10692462, PMID:10229203). Monoallelic DENND2B variants cause a neurodevelopmental disorder with intellectual disability, epilepsy, and congenital anomalies, with patient variants confirmed as loss-of-function in zebrafish (PMID:40717498).

1. 1996 Medium

   Established how expression of the ST5 p70-encoding transcript is transcriptionally controlled, linking its loss to the tumorigenic state.

   Evidence Reporter assays with enhancer mutagenesis and EMSA for YY1/AP1 binding in HeLa-fibroblast hybrids

   PMID:8972856

   Open questions at the time

   • Does not define the protein function of p70
   • Mechanism connecting YY1 activity to tumorigenicity unresolved
2. 1998 Medium

   Defined the ST5 isoforms and showed the largest, p126, binds c-Abl and activates ERK2/MAPK, identifying an isoform-specific signaling role.

   Evidence In vitro SH3 binding, transient transfection ERK2 assays, and deletion mutagenesis in COS-7 cells

   PMID:9632734

   Open questions at the time

   • Direct enzymatic activity of p126 not defined
   • Physiological relevance of c-Abl interaction not tested in vivo
3. 1999 Medium

   Demonstrated that p70 expression alone is sufficient to restore non-transformed cell morphology and contact-regulated growth, establishing a tumor-suppressive cellular phenotype.

   Evidence Stable transfection of p70 into p70-negative fibroblasts with morphology and saturation density readouts

   PMID:10229203

   Open questions at the time

   • Molecular mechanism of growth suppression not defined
   • Single primary phenotypic method
4. 2000 Medium

   Placed p70 upstream of RAS in MAPK signaling and mapped its C-terminal inhibitory determinant, explaining the opposing activities of ST5 isoforms.

   Evidence Dominant-negative epistasis (RAS17N, MEKAA), deletion mutagenesis, and NIH-3T3 transformation assays

   PMID:10692462

   Open questions at the time

   • Direct molecular target of p70 in the RAS pathway unidentified
   • Structural basis of C-terminal inhibition unknown
5. 2009 Low

   Linked ST5 disruption to a CNS phenotype and characterized its expression in developing and adult brain, raising a neurodevelopmental role.

   Evidence FISH/sequencing of translocation breakpoints in a patient plus qPCR and in situ hybridization expression mapping

   PMID:19843505

   Open questions at the time

   • Association rests on a single patient with a translocation, not direct functional proof
   • No mechanism connecting ST5 loss to neural phenotypes
6. 2015 High

   Identified DENND2B as the Rab13 GEF and localized its activity to the leading edge, defining its role in trafficking-driven migration and invasion.

   Evidence FRET Rab biosensor, in vitro GEF assay, MICAL-L2 Co-IP, and knockdown invasion/migration with in vivo xenograft validation

   PMID:25713415

   Open questions at the time

   • Structural basis of substrate specificity not resolved
   • Upstream regulators of leading-edge recruitment not defined
7. 2017 High

   Connected DENND2B to receptor trafficking by showing it binds intersectin-s to recycle EGFR, and that PKD phosphorylation switches receptor fate toward degradation.

   Evidence Reciprocal Co-IP, PKD phosphorylation assay, and EGFR trafficking/knockdown readouts

   PMID:29030480

   Open questions at the time

   • PKD phosphorylation sites on DENND2B not mapped
   • Whether GEF activity is required for the recycling function not established
8. 2022 High

   Expanded DENND2B's substrate repertoire to Rab10 and RhoA and assigned distinct ciliary functions, showing one GEF coordinates parallel pathways.

   Evidence Systematic cellular GEF screen of 60 Rabs, RhoA GEF assay, and ciliogenesis knockdown phenotypes

   PMID:35196081

   Open questions at the time

   • How DENND2B selects between Rab and Rho substrates is unknown
   • Spatial regulation of the two ciliary pathways unresolved
9. 2023 High

   Demonstrated dual GEF/effector function toward Rab35 at the cytokinetic bridge, establishing a requirement for DENND2B in actin clearance and abscission.

   Evidence GEF assay, active-Rab35 pulldown, and siRNA knockdown with multinucleation, F-actin, ESCRT-III, and Aurora B readouts plus live imaging

   PMID:37454296

   Open questions at the time

   • How GEF and effector roles are temporally coordinated at the bridge unclear
   • Direct link between Rab35 activation and ESCRT-III recruitment mechanism not fully defined
10. 2026 Medium

    Established DENND2B as the cause of a monoallelic neurodevelopmental disorder, connecting its loss of function to human disease.

    Evidence Patient variant identification with in vivo zebrafish loss-of-function modelling of nine variants

    PMID:40717498

    Open questions at the time

    • Which GTPase pathway(s) underlie the neurodevelopmental phenotype not determined
    • Genotype-phenotype correlations across variants not resolved

• How DENND2B integrates its multiple GTPase substrates, isoform-specific MAPK roles, and EGFR trafficking into the neurodevelopmental disease mechanism remains unresolved.
• No structural model explaining multi-substrate specificity
• Disease-relevant substrate(s) in neural cells not identified
• Relationship between DENN GEF activity and isoform-specific MAPK modulation unclear