ARHGAP4

ARHGAP4 is a multi-domain Rho GTPase-activating protein that integrates cytoskeletal regulation with the control of cell and axon motility (PMID:12414125, PMID:17804252). Recombinant ARHGAP4 stimulates the intrinsic GTPase activity of Rac1, Cdc42, and RhoA, establishing it as a functional GAP for multiple Rho-family members (PMID:12414125). Its modular architecture partitions these activities: the FCH domain directs localization to the leading edges of migrating cells and to axon growth cones, while the GAP domain and C-terminus are required for its inhibition of cell migration and axon outgrowth (PMID:17804252). Through its RhoGAP and SH3 domains, ARHGAP4 assembles a complex with the septins SEPT2 and SEPT9 that reorganizes focal adhesions and modulates integrin-β1–dependent migration and invasion (PMID:34524873), and it suppresses epithelial-to-mesenchymal transition and focal-adhesion–driven force generation, with Septin9 acting as a negative regulator that promotes EMT via FAK/Src signaling (PMID:32378260). Beyond its canonical GAP role, ARHGAP4 functions as a scaffolding and regulatory protein in cancer: it promotes ubiquitination of HDAC2 to suppress β-catenin activation and tumor cell invasion (PMID:30958531), binds p53 to repress DRAM1-dependent apoptosis in acute myeloid leukemia (PMID:37443303), and drives colorectal cancer stemness through a MYH9/β-catenin/c-Jun feedback loop (PMID:40817404). Its expression is suppressed by miR-939-5p (PMID:32021284).

1. 2002 High

   Established ARHGAP4 as a biochemically active GAP and placed it at the Golgi and motility structures, defining its candidate cellular context.

   Evidence In vitro GTPase assays with recombinant protein on Rac1/Cdc42/RhoA plus subcellular fractionation and immunofluorescence of endogenous protein

   PMID:12414125

   Open questions at the time

   • In vitro substrate preference among Rac1/Cdc42/RhoA not quantified
   • Functional consequence of Golgi/microtubule localization unresolved
2. 2007 Medium

   Mapped functional roles to specific domains, showing the FCH domain governs localization while the GAP domain and C-terminus drive motility inhibition.

   Evidence Domain-deletion structure/function analysis with live-cell migration and hippocampal axon outgrowth assays

   PMID:17804252

   Open questions at the time

   • Which Rho GTPase mediates the migration/axon phenotype in cells not established
   • Endogenous loss-of-function not tested (overexpression-based)
3. 2019 Medium

   Revealed a non-canonical scaffolding mechanism whereby ARHGAP4 promotes HDAC2 ubiquitination to restrain β-catenin and tumor invasion, and placed it upstream of the mTOR/HIF-1α Warburg axis.

   Evidence Co-IP, ubiquitination assay, siRNA knockdown, pharmacological rescue (CAY10683, XAV939, rapamycin, YC-1), invasion/migration and metabolic assays in pancreatic cancer cells

   PMID:30958531 PMID:31303760

   Open questions at the time

   • Whether ARHGAP4 has direct E3 ligase activity or recruits one is not defined
   • Link between GAP activity and HDAC2/β-catenin axis unresolved
4. 2020 Medium

   Identified upstream regulation by miR-939-5p and a septin-mediated route to EMT control, with Septin9 acting as a negative regulator via FAK/Src.

   Evidence Luciferase reporter target validation and rescue; RhoGAP siRNA screen, proteomics, traction force microscopy and 3D morphogenesis in mammary epithelial cells

   PMID:32021284 PMID:32378260

   Open questions at the time

   • Mechanism by which Septin9 inhibits ARHGAP4 not defined at molecular level
   • Direct ARHGAP4–Septin9 binding interface not mapped here
5. 2021 High

   Defined a direct ARHGAP4–SEPT2–SEPT9 complex and showed it bidirectionally controls integrin-β1–dependent focal adhesions and invasion.

   Evidence Reciprocal Co-IP with RhoGAP/SH3 domain mapping, siRNA knockdown, overexpression of multiple complex members, focal adhesion and migration/invasion assays

   PMID:34524873

   Open questions at the time

   • Stoichiometry and structural architecture of the complex unknown
   • Whether GAP catalytic activity is required for focal adhesion remodeling not tested
6. 2023 Medium

   Established a p53-binding, apoptosis-suppressing role in leukemia by placing ARHGAP4 upstream of p53/DRAM1.

   Evidence Co-IP (ARHGAP4-p53), siRNA knockdown, DRAM1 epistatic rescue, in vivo AML model and apoptosis/colony assays

   PMID:37443303

   Open questions at the time

   • Binding interface and effect of ARHGAP4 on p53 transcriptional activity not detailed
   • Relationship between GAP function and p53 regulation unknown
7. 2024 Low

   Extended ARHGAP4's pro-tumor/EMT activity to colon cancer (TGF-β/Smad) and to apoptosis/inflammation in ovarian granulosa cells (PI3K-Akt).

   Evidence siRNA knockdown with Western blotting for pathway and EMT markers; CCK-8, annexin-V/PI, ELISA in granulosa cells and clinical tissue

   PMID:38355537 PMID:38805788

   Open questions at the time

   • No direct binding or rescue experiments to establish causality
   • Context-dependent opposite roles (pro- vs anti-tumor) not reconciled
8. 2025 Medium

   Identified a MYH9/β-catenin/c-Jun positive feedback loop through which ARHGAP4 drives cancer stemness.

   Evidence Co-IP (ARHGAP4-MYH9), ChIP (c-Jun binding), FRAP, in vitro/in vivo stemness assays

   PMID:40817404

   Open questions at the time

   • How the GAP/scaffolding domains engage MYH9 not mapped
   • Reconciliation with ARHGAP4's β-catenin-suppressing role in pancreatic cancer unresolved

• It remains unresolved how ARHGAP4's canonical Rho-GAP catalytic activity mechanistically connects to its diverse scaffolding functions (HDAC2 ubiquitination, p53, MYH9), and why it acts as a migration suppressor in some contexts but a tumor/stemness driver in others.
• No structural model linking GAP and scaffolding activities
• Context-determinants of opposing phenotypes undefined
• In vivo physiological (non-cancer) function not established