DENND1C

DENND1C is a DENN-domain Rab guanine nucleotide exchange factor (GEF) that activates both Rab13 and Rab35 in distinct cellular contexts to regulate actin-dependent membrane dynamics and cell migration (PMID:20937701, PMID:22072793, PMID:25074980). A unique C-terminal actin-binding motif, absent from paralogous DENND1A and DENND1B, directly tethers DENND1C to actin filaments, coupling Rab35 activation to fascin recruitment and the formation of protrusive membrane extensions (PMID:22072793). In lymphocytes, Mst1 kinase-dependent phosphorylation of DENND1C activates Rab13, which in turn drives myosin Va-dependent delivery of integrin LFA-1 to the leading edge to support adhesion and migration (PMID:25074980). DENND1C is also recruited to the IL-17R/Act1 signaling complex in airway smooth muscle cells, where it activates Rab35 to promote PKCα-dependent stress fiber formation and contraction (PMID:30683702).

1. 2010 High

   Systematic biochemical profiling established that DENND1C is a bona fide Rab GEF with specificity for Rab13, placing it within a family of 17 DENN-domain proteins that collectively activate 10 distinct Rabs.

   Evidence Family-wide GEF activity assays and subcellular localization across all human DENN-domain proteins

   PMID:20937701

   Open questions at the time

   • Whether DENND1C also activates Rabs other than Rab13 was not resolved in this screen
   • Upstream regulation of DENND1C GEF activity was unknown
   • Physiological cellular functions of DENND1C-Rab13 axis were uncharacterized
2. 2011 High

   DENND1C was shown to directly bind actin through a unique C-terminal motif and to activate Rab35 (not only Rab13), coupling Rab35 GEF activity to the actin cytoskeleton and driving fascin-dependent protrusive membrane extensions — a function not shared by DENND1A or DENND1B.

   Evidence Direct actin-binding assays, DENN-domain and actin-binding motif mutagenesis, colocalization microscopy, and cell morphology analysis

   PMID:22072793

   Open questions at the time

   • The relative contributions of Rab13 versus Rab35 activation by DENND1C in vivo were not delineated
   • Structural basis of the C-terminal actin-binding motif interaction was not determined
   • Cell-type specificity of DENND1C-driven protrusions was unexplored
3. 2014 High

   A signaling cascade was defined in which chemokine-stimulated Mst1 kinase phosphorylates DENND1C to activate Rab13, which then partners with Mst1 and myosin Va to deliver LFA-1 integrin to the leading edge for lymphocyte adhesion and migration.

   Evidence Phosphorylation assays, Rab13 activation assays, knockdown/inhibition with adhesion and migration readouts in T lymphocytes, and Rab13-knockout mice

   PMID:25074980

   Open questions at the time

   • The specific phosphorylation site(s) on DENND1C and their mechanistic effect on GEF activity were not fully resolved
   • Whether DENND1C phosphorylation similarly regulates Rab35 activation was untested
   • Contribution of DENND1C versus other Rab13 GEFs in lymphocyte biology in vivo was not dissected
4. 2019 Medium

   DENND1C was found to be recruited to the IL-17R/Act1 signaling complex in airway smooth muscle cells, linking IL-17A cytokine signaling to Rab35 activation, PKCα-dependent fascin phosphorylation, stress fiber formation, and enhanced contractility.

   Evidence Co-immunoprecipitation of DENND1C with IL-17R/Act1, Rab35 knockdown with contraction readouts, PKCα inhibitor experiments

   PMID:30683702

   Open questions at the time

   • Recruitment mechanism of DENND1C to the IL-17R/Act1 complex (direct binding vs. adaptor) was not defined
   • Findings are from a single laboratory and have not been independently replicated
   • Whether this pathway operates in other IL-17-responsive cell types was not tested
5. 2020 Medium

   Genetic knockout experiments clarified that DENND1C is dispensable for Rab35-dependent podocalyxin trafficking in epithelial cells, demonstrating that DENND1C's Rab35-GEF function is context-specific rather than universally required.

   Evidence CRISPR knockout of individual DENN-domain GEFs in MDCK cells with podocalyxin localization in 2D and 3D culture

   PMID:31992598

   Open questions at the time

   • The specific cell types and trafficking pathways where DENND1C is the essential Rab35 GEF remain incompletely mapped
   • Compensatory mechanisms among DENN-family GEFs were not tested
   • Negative result in one epithelial model does not exclude roles in other epithelial contexts

• The structural basis for DENND1C's dual Rab specificity (Rab13 and Rab35), the precise phosphorylation sites controlling its GEF activity, and the in vivo physiological consequences of DENND1C loss in whole organisms remain unresolved.
• No crystal or cryo-EM structure of DENND1C DENN domain bound to Rab13 or Rab35
• No DENND1C-knockout mouse phenotype reported
• How DENND1C GEF activity is switched between Rab13 and Rab35 substrates is unknown