ARHGAP17

ARHGAP17 (Rich1/Nadrin) is a BAR-domain-containing RhoGAP that spatiotemporally inactivates Cdc42, Rac1, and RhoA to control epithelial polarity, tight junction integrity, cell migration, invadopodia turnover, and Hippo pathway signaling. Its GAP domain stimulates GTP hydrolysis on Rho-family GTPases, while its BAR domain oligomerizes on lipid membranes, senses membrane curvature, and mediates recruitment to tight junctions via angiomotin (Amot) and to invadopodia via CIP4, enabling compartment-specific Cdc42 inactivation that drives invadopodia disassembly and maintains apical junction architecture (PMID:16678097, PMID:36571786, PMID:15240152). ARHGAP17 activity and stability are regulated by Src-family tyrosine phosphorylation, PKA/PKG-mediated phosphorylation at S702 (which disrupts CIP4 binding and suppresses migration), and CUL4-Wdr4-dependent ubiquitination and proteasomal degradation that controls Rac1-GTP levels during cerebellar granule neuron progenitor proliferation (PMID:24703939, PMID:26507661, PMID:36681682). Through competition with Merlin for Amot-p80 binding, ARHGAP17 activates the Hippo kinase cascade to inactivate YAP/TAZ, and it promotes TRIM21-mediated RhoA ubiquitination to modulate STAT3 signaling and tumor immune microenvironment polarization (PMID:35064101, PMID:41436617).

1. 2000 High

   Identification of ARHGAP17 as a multi-target RhoGAP established its fundamental enzymatic activity and linked it to actin remodeling and regulated exocytosis.

   Evidence In vitro GAP assays on RhoA/Rac1/Cdc42, NIH3T3 morphology, PC12 exocytosis with GAP-domain mutant

   PMID:10967100

   Open questions at the time

   • No structural basis for multi-GTPase recognition
   • Exocytosis mechanism limited to PC12 overexpression system
2. 2002 Medium

   Discovery of multiple splice variants with distinct C-termini and subcellular distributions revealed that isoform diversity enables tissue- and signal-specific functions, including nuclear translocation upon differentiation.

   Evidence Expression of deletion/variant constructs in PC12 cells, immunofluorescence, neurite outgrowth assay

   PMID:12358749

   Open questions at the time

   • Nuclear function of C-terminal fragment unknown
   • Endogenous isoform expression patterns not mapped across tissues
3. 2004 High

   Demonstration that the BAR domain binds membranes and tubulates liposomes through oligomerization established ARHGAP17 as a curvature-sensing protein, explaining how it is targeted to membrane compartments.

   Evidence Liposome tubulation assay with purified BAR domain, BS3 cross-linking showing oligomers

   PMID:15240152

   Open questions at the time

   • No structural model of BAR domain at atomic resolution
   • How BAR-domain membrane binding coordinates with GAP activity not tested
4. 2006 High

   The finding that ARHGAP17 is recruited to tight junctions via angiomotin to regulate Cdc42 placed it as a central regulator of epithelial polarity and junctional integrity.

   Evidence Reciprocal Co-IP with Amot, knockdown/dominant-negative in MDCK cells, tight junction and polarity assays

   PMID:16678097

   Open questions at the time

   • Structural basis of Amot–ARHGAP17 interaction not resolved
   • Whether ARHGAP17 acts at other junctional complexes (adherens junctions) untested
5. 2012 Medium

   Isoform-specific analysis in platelets showed that the BAR domain controls membrane targeting and GAP activity while distinct C-termini determine GTPase substrate selectivity, resolving how one gene regulates multiple Rho GTPases.

   Evidence Isoform-specific overexpression, platelet spreading on fibrinogen, Rho-GTP pull-down, BAR-domain deletion

   PMID:22975681

   Open questions at the time

   • Platelet-specific isoform ratios under physiological conditions not quantified
   • Whether BAR-domain regulation of GAP activity is autoinhibitory or allosteric not distinguished
6. 2014 Medium

   Src-family kinase phosphorylation was shown to differentially regulate GAP activity in an isoform-specific manner—activating Cdc42 inactivation via Nadrin5 while promoting RhoA/Rac1 activation via Nadrin2—establishing tyrosine phosphorylation as a key regulatory switch.

   Evidence Src/Lyn/Fyn overexpression and inhibition in platelets, isoform-specific Rho-GTP pull-down

   PMID:24703939

   Open questions at the time

   • Specific tyrosine phosphorylation sites not mapped by mass spectrometry
   • Physiological signals triggering isoform-selective phosphorylation not identified
7. 2015 High

   Two regulatory inputs were defined: PKA/PKG phosphorylation at S702 disrupts CIP4 binding to suppress migration, while GAP-mediated Cdc42/Rac1 inactivation attenuates PAK1-ERK1/2 signaling to arrest proliferation.

   Evidence Phos-tag gel mapping of S702, Co-IP disruption with PKA/PKG agonists, phospho-mutant migration assay; GTPase activity assay, phospho-western for PAK1/ERK1/2, cell cycle analysis

   PMID:26004135 PMID:26507661

   Open questions at the time

   • Whether S702 phosphorylation alters GAP catalytic activity directly not tested
   • Epistatic relationship between Src and PKA/PKG phosphorylation events unknown
8. 2016 High

   Arhgap17 knockout mice demonstrated in vivo requirement for epithelial barrier function, validating the tight junction role discovered in cell culture.

   Evidence Knockout mouse, paracellular permeability assay, junction protein immunofluorescence, DSS colitis model

   PMID:27229483

   Open questions at the time

   • Contribution of individual GTPase targets (Cdc42 vs. Rac1) to barrier defect not dissected in vivo
   • Phenotype in tissues beyond intestine not characterized
9. 2022 High

   Live imaging with a Cdc42 biosensor revealed that ARHGAP17 acts as a spatiotemporal switch at invadopodia—restricting Cdc42 to the core during assembly and then inactivating it to drive disassembly via CIP4-mediated translocation—while BAR-domain competition with Merlin for Amot-p80 activates the Hippo cascade to suppress YAP/TAZ.

   Evidence ARHGAP17-GFP live imaging, FRET Cdc42 biosensor, CIP4 interaction mutants, invadopodia turnover assay; Co-IP with BAR-domain deletion, YAP/TAZ activity and cancer stem cell assays

   PMID:35064101 PMID:36571786

   Open questions at the time

   • Structural basis for competitive Amot binding between ARHGAP17 BAR domain and Merlin not resolved
   • How invadopodia-localized and tight-junction-localized ARHGAP17 pools are distinguished is unclear
10. 2023 High

    Identification of CUL4-Wdr4 E3 ligase-mediated ubiquitination and degradation of ARHGAP17 established protein stability as a critical regulatory layer, with loss of Wdr4 stabilizing ARHGAP17, depleting Rac1-GTP, and causing cerebellar hypoplasia.

    Evidence In vitro and in vivo ubiquitination assay, Wdr4 knockout mouse, Rac1-GTP pull-down, granule neuron progenitor rescue

    PMID:36681682

    Open questions at the time

    • Ubiquitination sites on ARHGAP17 not mapped
    • Whether other E3 ligases also target ARHGAP17 not explored
11. 2025 Medium

    ARHGAP17 was shown to function beyond its GAP activity by bridging TRIM21 to RhoA, promoting RhoA ubiquitination and degradation, which reduces STAT3 phosphorylation and reprograms tumor-associated macrophages toward an anti-tumor M1-like phenotype.

    Evidence Co-IP of RICH1-TRIM21-RhoA complex, ubiquitination assay, STAT3 phospho-western, macrophage polarization in 4T1 mouse model

    PMID:41436617

    Open questions at the time

    • Whether ARHGAP17 GAP-independent adapter function extends to other E3 ligase substrates unknown
    • Direct binding interface between ARHGAP17 and TRIM21 not mapped
12. 2026 Medium

    Placement of NME1 upstream of ARHGAP17 defined a histidine-phosphorylation-dependent axis through which NME1 controls CDC42 activity, cytoskeletal state, and YAP phosphorylation via the Hippo pathway.

    Evidence PhastID proximity labeling, CDC42 activity assays, YAP phosphorylation and localization measurements

    PMID:41978798

    Open questions at the time

    • Whether NME1 directly phosphorylates ARHGAP17 or acts indirectly not determined
    • Histidine phosphorylation site(s) on ARHGAP17 not identified

• Key unresolved questions include the structural basis of BAR-domain autoinhibition of GAP activity, how ARHGAP17 pools are partitioned between tight junctions, invadopodia, and other compartments, and whether its GAP-independent adapter functions (e.g., TRIM21 bridging) represent a general mechanism.
• No high-resolution structure of full-length ARHGAP17
• Mechanism partitioning ARHGAP17 between distinct membrane compartments unknown
• Relative contribution of GAP-dependent vs. GAP-independent functions in vivo not dissected