{"gene":"ARHGAP21","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2007,"finding":"Crystal structure of ARF1(GTP)-bound form in complex with the Arf-binding domain (ArfBD) of ARHGAP21 at 2.1 Å resolution showed that ArfBD comprises a PH domain adjoining a C-terminal alpha helix, and that ARF1 interacts with both motifs through its switch regions, triggering structural rearrangement of the PH domain. Site-directed mutagenesis confirmed both the PH domain and helical motif are essential for ARF1 binding and Golgi recruitment of ARHGAP21.","method":"X-ray crystallography (2.1 Å) + site-directed mutagenesis + Golgi recruitment assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional mutagenesis validation, multiple orthogonal methods in one rigorous study","pmids":["17347647"],"is_preprint":false},{"year":2010,"finding":"β-arrestin 1 directly binds to ARHGAP21 in a region that transects the RhoA effector GAP domain, inhibiting its GAP function. This interaction is dynamically increased following angiotensin II stimulation of the type 1A receptor, and the complex modulates the temporal activation of RhoA leading to stress fiber formation. A cell-permeant peptide disrupting the β-arrestin 1/ARHGAP21 complex resulted in more active ARHGAP21, less efficient RhoA signaling, and attenuated stress fiber formation.","method":"Yeast two-hybrid screening, peptide array, in vitro binding, truncation analyses, co-immunoprecipitation, cell-permeant peptide inhibitor assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, in vitro binding, peptide array, and functional peptide inhibitor; multiple orthogonal methods in one study","pmids":["21173159"],"is_preprint":false},{"year":2009,"finding":"ARHGAP21 is expressed in nuclear and perinuclear regions of glioblastoma cell lines and interacts with the C-terminal region of FAK. ARHGAP21 depletion by shRNAi increases FAK phosphorylation and downstream signaling activation, increases Cdc42 activity, MMP-2 production, and cell migration, indicating ARHGAP21 negatively regulates FAK signaling and cell migration.","method":"shRNAi knockdown, pulldown assay (FAK C-terminal region), phosphorylation assays, cell migration assay","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulldown mapping of interaction domain plus KD with defined phenotypic readouts, single lab","pmids":["19268501"],"is_preprint":false},{"year":2008,"finding":"ARHGAP21 associates with PKCzeta and FAK in cardiac tissue and is redistributed to Z-lines and costameres after pressure overload. Co-transfection studies showed ARHGAP21 associates with PKCzeta-GST and endogenous FAK; pulldown assay confirmed ARHGAP21 binds the C-terminal region of FAK. ARHGAP21 binds to PKCzeta phosphorylated on Thr410 in sham and SHR rats, and to FAK phosphorylated on Tyr925 only in SHR.","method":"Co-transfection, pulldown assay, co-immunoprecipitation, immunofluorescence localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pulldown and Co-IP with phospho-specific interaction mapping, single lab, multiple methods","pmids":["18662671"],"is_preprint":false},{"year":2009,"finding":"Constitutively active Cdc42 or knockdown of the Cdc42-specific GAP ARHGAP21 inhibited retrograde transport of Shiga toxin to the Golgi apparatus. Shiga toxin addition greatly decreases levels of active Cdc42-GTP in an ARHGAP21-dependent manner, demonstrating that ARHGAP21 and Cdc42-based signaling regulates dynein-dependent retrograde transport.","method":"siRNA knockdown, constitutively active Cdc42 expression, Cdc42-GTP pull-down activity assay, fluorescence microscopy of toxin trafficking","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi epistasis with GTPase activity assay and trafficking readout, single lab","pmids":["19692570"],"is_preprint":false},{"year":2012,"finding":"ARHGAP21 presents GAP activity for RhoA and RhoC in PC3 prostate cancer cells (not just Cdc42), and its depletion results in decreased proliferation and increased migration. ARHGAP21 is localized in the nucleus and cytoplasm of prostate cancer cell lines.","method":"shRNA knockdown, RhoA/RhoC GTPase activity assay, cell proliferation and migration assays, subcellular fractionation/immunofluorescence","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct GAP activity assay for RhoA/RhoC plus KD phenotyping, single lab","pmids":["23200924"],"is_preprint":false},{"year":2012,"finding":"ARHGAP21 is transiently redistributed to cell-cell junctions 4 hours after initiation of cell-cell adhesion, where it interacts with Cdc42 and decreases Cdc42 activity. ARHGAP21 also interacts with α-tubulin and is essential for α-tubulin acetylation during epithelial-mesenchymal transition (EMT). Cells lacking ARHGAP21 show weaker cell-cell adhesions, increased migration, and diminished HGF-induced EMT.","method":"Co-immunoprecipitation, immunofluorescence (localization during adhesion), Cdc42 activity assay, shRNA knockdown, α-tubulin acetylation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, activity assay, and KD phenotyping with multiple readouts, single lab","pmids":["23235160"],"is_preprint":false},{"year":2012,"finding":"ARHGAP21 is post-translationally modified by SUMO2/3; co-immunoprecipitation and in vitro SUMOylation mapped the SUMOylation site to lysine K1443. A 250 kDa modified form of ARHGAP21 is differentially expressed among cell lines and human primary cells. ARHGAP21 co-localizes with SUMO2/3 in cytoplasm and membrane compartments.","method":"Co-immunoprecipitation, in vitro SUMOylation assay, mass spectrometry, immunofluorescence","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro SUMOylation with site mapping by mutagenesis/MS, single lab","pmids":["22922005"],"is_preprint":false},{"year":2012,"finding":"ARHGAP21 regulates Cdc42 activity to control transport of influenza virus neuraminidase (NA) to the cell surface. Depletion of ARHGAP21 or expression of constitutively active Cdc42 promoted NA transport to plasma membranes, while overexpression of ARHGAP21 or shRNA targeting Cdc42 decreased cell surface NA. Silencing ARHGAP21 increased influenza A virus replication.","method":"shRNA knockdown, constitutively active/dominant-negative mutant expression, surface NA quantification, viral replication assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via KD and constitutive mutants with functional transport readout, single lab","pmids":["22318733"],"is_preprint":false},{"year":2017,"finding":"PTEN controls 3D glandular morphogenesis through a membrane-associated β-arrestin1/ARHGAP21/Cdc42 scaffolding complex. PTEN knockdown impairs β-arrestin1 membrane localization and β-arrestin1-ARHGAP21 interactions, reducing Cdc42 activation and disrupting mitotic spindle orientation. Silencing of ARHGAP21 enhanced Cdc42 activation and rescued aberrant morphogenic processes of PTEN-deficient cultures. A membrane-binding defective mutant of PTEN C2 domain abrogated these rescue properties.","method":"siRNA knockdown, co-immunoprecipitation, Cdc42 activity assay, 3D morphogenesis assay, mitotic spindle orientation analysis, domain mutant rescue","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis with multiple KDs, Co-IP, activity assays, and domain mutant analysis; multiple orthogonal methods in a rigorous study","pmids":["28749339"],"is_preprint":false},{"year":2017,"finding":"Arhgap21 haploinsufficiency in mice leads to enhanced RhoC activity in bone marrow cells, impaired hematopoietic progenitor adhesion, enhanced mobilization of LSK and myeloid progenitors, and reduced erythroid commitment. ARHGAP21 knockdown in human CMP and MEP cells recapitulated decreased erythroid commitment, indicating Arhgap21 functions in hematopoiesis at least partially through RhoC inactivation.","method":"Haploinsufficient mouse model, RhoC-GTP pull-down assay, in vitro colony formation, in vivo transplantation, human primary cell knockdown","journal":"Stem cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function mouse model with RhoC activity assay and functional hematopoietic readouts, single lab","pmids":["29212046"],"is_preprint":false},{"year":2015,"finding":"ARHGAP21 co-localizes with actin in MIN6 beta cells and with insulin in neonatal pancreatic islets. Antisense-mediated knockdown of ARHGAP21 reduces F-actin polymerization, increases basal insulin secretion (but not GSIS), increases pERK1/2, and upregulates VAMP2 and SNAP25 gene expression, indicating ARHGAP21 regulates insulin secretion via actin rearrangement and pERK1/2 signaling.","method":"Antisense oligonucleotide knockdown, phalloidin staining (F-actin quantification), insulin secretion assay, Western blot (pERK1/2), RT-PCR, immunofluorescence","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with multiple mechanistic readouts (actin, signaling, gene expression), single lab","pmids":["25744409"],"is_preprint":false},{"year":2024,"finding":"In C. elegans, PAC-1/ARHGAP21 is enriched at cell contact sites in a manner dependent on afadin (AFD-1), and genetic interactions indicate afd-1 and pac-1 regulate epidermal morphogenesis through parallel mechanisms. E-cadherin is required for polarized distribution of AFD-1, which in turn promotes PAC-1/ARHGAP21 enrichment at cell contacts.","method":"Null mutation (genetic), RNAi, fluorescence localization, genetic epistasis analysis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis and localization in C. elegans ortholog model, single lab","pmids":["38556137"],"is_preprint":false},{"year":2026,"finding":"ARHGAP21 directly binds to filamin A (FLNA) via its PDZ domain interacting with the 1-1200 aa fragment of FLNA. ARHGAP21 also directly binds and recruits HSP90α to stabilize FLNA by inhibiting its ubiquitination and degradation. Overexpression of FLNA reversed the actin cytoskeleton remodeling-related suppression of tumor metastasis caused by ARHGAP21 knockdown in HCC cells.","method":"Co-immunoprecipitation, domain mapping (PDZ domain deletion/mutation), ubiquitination assay, rescue by FLNA overexpression, in vitro and in vivo migration/invasion assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding with domain mapping, ubiquitination assay, and functional rescue, single lab","pmids":["41957357"],"is_preprint":false},{"year":2023,"finding":"ARHGAP21 knockdown in NSCLC cells significantly decreased ubiquitination of β-catenin, upregulated N-cadherin, and activated the WNT signaling pathway by affecting expression of APC, GSK3β, and Axin, promoting cell migration and metastasis in vivo.","method":"siRNA knockdown, Western blot (β-catenin ubiquitination, pathway components), Transwell/wound healing migration assay, nude mouse tail-vein metastasis model","journal":"Nan fang yi ke da xue xue bao","confidence":"Low","confidence_rationale":"Tier 3 / Weak — KD with Western blot pathway analysis, single lab, no direct interaction assay between ARHGAP21 and WNT components","pmids":["37712268"],"is_preprint":false}],"current_model":"ARHGAP21 is a large multifunctional RhoGAP that is recruited to the Golgi by GTP-bound ARF1 (via a novel PH domain + α-helix ArfBD), where it negatively regulates Cdc42 (and also RhoA, RhoC) to control actin/Arp2/3 dynamics, vesicular trafficking, and cell-cell junction remodeling; its GAP activity is suppressed when β-arrestin 1 binds its GAP domain upon angiotensin II receptor activation, and it is further regulated by SUMO2/3 modification at K1443; it also scaffolds FAK and PKCζ signaling, binds α-tubulin to promote its acetylation during EMT, inhibits FLNA ubiquitination via HSP90α recruitment, and functions downstream of a PTEN–β-arrestin1 complex to orient the mitotic spindle during glandular morphogenesis."},"narrative":{"mechanistic_narrative":"ARHGAP21 is a large multifunctional Rho-family GTPase-activating protein that couples membrane and adhesion signaling to actin cytoskeletal remodeling, vesicular trafficking, and tissue morphogenesis [PMID:17347647, PMID:23235160]. It is recruited to the Golgi by GTP-bound ARF1 through a bipartite Arf-binding domain comprising a PH domain and an adjacent C-terminal alpha helix, both of which engage the ARF1 switch regions [PMID:17347647]. At its catalytic core it inactivates Cdc42, and also RhoA and RhoC, thereby controlling actin dynamics in contexts ranging from dynein-dependent retrograde transport of Shiga toxin to the Golgi and surface delivery of influenza neuraminidase [PMID:19692570, PMID:22318733], to cell-cell junction stability and HGF-induced epithelial-mesenchymal transition, where it additionally binds alpha-tubulin to promote its acetylation [PMID:23200924, PMID:23235160]. Its GAP activity is dynamically restrained by direct binding of beta-arrestin 1 across the GAP domain following angiotensin II receptor stimulation, gating RhoA-driven stress fiber formation [PMID:21173159], and the same beta-arrestin1/ARHGAP21/Cdc42 scaffold operates downstream of membrane-associated PTEN to orient the mitotic spindle during 3D glandular morphogenesis [PMID:28749339]. ARHGAP21 further acts as a scaffold for FAK and PKCzeta signaling to suppress cell migration [PMID:19268501, PMID:18662671], stabilizes filamin A by recruiting HSP90alpha through its PDZ domain to block FLNA ubiquitination [PMID:41957357], and is regulated by SUMO2/3 modification at lysine K1443 [PMID:22922005]. Through RhoC inactivation it controls hematopoietic progenitor adhesion, mobilization, and erythroid commitment [PMID:29212046].","teleology":[{"year":2007,"claim":"Established the structural basis for how ARHGAP21 is targeted to the Golgi, answering how an Arf GTPase localizes a RhoGAP to a membrane compartment.","evidence":"X-ray crystallography of the ARF1(GTP)-ArfBD complex with site-directed mutagenesis and Golgi recruitment assays","pmids":["17347647"],"confidence":"High","gaps":["Does not define which Rho GTPase is regulated at the Golgi","Does not address regulation of the GAP catalytic domain"]},{"year":2008,"claim":"Identified ARHGAP21 as a scaffold associating with PKCzeta and FAK that relocalizes upon cardiac mechanical stress, linking it to phospho-dependent signaling assemblies.","evidence":"Co-transfection, pulldown, Co-IP and immunofluorescence in cardiac tissue from sham and SHR rats","pmids":["18662671"],"confidence":"Medium","gaps":["Does not establish a catalytic or GTPase-dependent role in this context","Functional consequence of relocalization not tested"]},{"year":2009,"claim":"Demonstrated that ARHGAP21 negatively regulates FAK signaling and migration via Cdc42 in glioblastoma, connecting its GAP activity to invasive behavior.","evidence":"shRNAi knockdown with FAK pulldown, phosphorylation, Cdc42 activity, and migration assays","pmids":["19268501"],"confidence":"Medium","gaps":["Direct GAP-on-Cdc42 catalysis not separated from scaffolding","Single lab, single tumor type"]},{"year":2009,"claim":"Showed ARHGAP21-controlled Cdc42 inactivation is required for dynein-dependent retrograde transport to the Golgi, placing it in a trafficking pathway.","evidence":"siRNA, constitutively active Cdc42, Cdc42-GTP pulldown, and Shiga toxin trafficking microscopy","pmids":["19692570"],"confidence":"Medium","gaps":["Link to ARF1-dependent Golgi recruitment not directly tested","Mechanism connecting Cdc42 to dynein unresolved"]},{"year":2010,"claim":"Defined a direct regulatory mechanism: beta-arrestin1 binding across the GAP domain inhibits ARHGAP21 GAP activity downstream of a GPCR, timing RhoA activation.","evidence":"Yeast two-hybrid, peptide array, in vitro binding, truncation, Co-IP, and cell-permeant peptide inhibitor following angiotensin II stimulation","pmids":["21173159"],"confidence":"High","gaps":["Structural basis of GAP-domain occlusion not solved","Generalizability to other GPCRs unknown"]},{"year":2012,"claim":"Broadened the substrate repertoire to RhoA and RhoC and tied ARHGAP21 to proliferation/migration balance in prostate cancer.","evidence":"shRNA with RhoA/RhoC GTPase activity assays and proliferation/migration assays in PC3 cells","pmids":["23200924"],"confidence":"Medium","gaps":["Relative contribution of each GTPase to phenotype not dissected","No in vivo validation"]},{"year":2012,"claim":"Connected ARHGAP21 to cell-cell adhesion and EMT, showing it localizes to junctions, inactivates Cdc42 there, and binds alpha-tubulin to drive its acetylation.","evidence":"Co-IP, immunofluorescence during adhesion, Cdc42 activity assay, shRNA, alpha-tubulin acetylation assay","pmids":["23235160"],"confidence":"Medium","gaps":["Mechanism linking alpha-tubulin binding to acetylation unknown","Junctional recruitment signal not defined"]},{"year":2012,"claim":"Established ARHGAP21 as a post-translationally SUMOylated protein, mapping a defined modification site.","evidence":"Co-IP, in vitro SUMOylation, MS, and immunofluorescence mapping SUMO2/3 to K1443","pmids":["22922005"],"confidence":"Medium","gaps":["Functional consequence of SUMOylation on GAP activity not determined","Conditions inducing modification unclear"]},{"year":2012,"claim":"Showed ARHGAP21-mediated Cdc42 control gates surface delivery of a viral glycoprotein and restricts influenza replication, extending its trafficking role to host-pathogen interactions.","evidence":"shRNA, constitutively active/dominant-negative Cdc42, surface NA quantification, viral replication assay","pmids":["22318733"],"confidence":"Medium","gaps":["Compartment of action not pinpointed","Direct GAP catalysis vs scaffolding not separated"]},{"year":2015,"claim":"Implicated ARHGAP21 in regulated secretion, linking its actin control to insulin exocytosis machinery in beta cells.","evidence":"Antisense knockdown with F-actin quantification, insulin secretion, pERK1/2 Western, and RT-PCR in MIN6 cells/islets","pmids":["25744409"],"confidence":"Medium","gaps":["Which Rho GTPase mediates the actin effect not specified","pERK1/2 link mechanistically undefined"]},{"year":2017,"claim":"Integrated ARHGAP21 into a PTEN-driven scaffold controlling Cdc42-dependent spindle orientation and epithelial architecture.","evidence":"siRNA, Co-IP, Cdc42 activity, 3D morphogenesis, spindle orientation, and PTEN C2 domain mutant rescue","pmids":["28749339"],"confidence":"High","gaps":["How membrane-bound PTEN recruits the complex structurally unknown","Direct PTEN-ARHGAP21 vs beta-arrestin1-bridged contact not resolved"]},{"year":2017,"claim":"Demonstrated an in vivo physiological role via RhoC inactivation in hematopoiesis using a loss-of-function mouse.","evidence":"Arhgap21 haploinsufficient mice, RhoC-GTP pulldown, colony formation, transplantation, and human CMP/MEP knockdown","pmids":["29212046"],"confidence":"Medium","gaps":["Cell-intrinsic vs niche contributions not fully separated","Mechanism downstream of RhoC in erythroid commitment unclear"]},{"year":2024,"claim":"Showed the ortholog's contact-site enrichment depends on afadin and E-cadherin, defining how ARHGAP21 is recruited to junctions during morphogenesis.","evidence":"Null mutants, RNAi, localization, and genetic epistasis of PAC-1/ARHGAP21, AFD-1, and E-cadherin in C. elegans","pmids":["38556137"],"confidence":"Medium","gaps":["Conservation of afadin-dependent recruitment in mammals not tested","Direct vs indirect afadin interaction not defined"]},{"year":2026,"claim":"Revealed a GAP-independent function: ARHGAP21 stabilizes filamin A by recruiting HSP90alpha to block FLNA ubiquitination, controlling actin remodeling and metastasis.","evidence":"Co-IP, PDZ domain mapping, ubiquitination assay, FLNA-overexpression rescue, and migration/invasion assays in HCC","pmids":["41957357"],"confidence":"Medium","gaps":["How HSP90alpha recruitment inhibits the relevant E3 ligase unknown","Interplay with GAP activity not dissected"]},{"year":null,"claim":"How ARHGAP21's distinct activities — ARF1-dependent Golgi GAP function, beta-arrestin/PTEN-gated scaffolding, tubulin acetylation, and FLNA stabilization — are coordinated within a single protein and which dominate in a given cell type remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structure-function map across domains","Regulation linking SUMOylation, beta-arrestin binding, and substrate selectivity unknown","Direct disease-causing mutation not established in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,6,10]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,9,13]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[6,11,13]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,5]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6,9]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,9]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[4,8]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9,10,12]}],"complexes":["beta-arrestin1/ARHGAP21/Cdc42 scaffold"],"partners":["ARF1","ARRB1","PTK2","PRKCZ","CDC42","PTEN","FLNA","HSP90AA1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5T5U3","full_name":"Rho GTPase-activating protein 21","aliases":["Rho GTPase-activating protein 10","Rho-type GTPase-activating protein 21"],"length_aa":1958,"mass_kda":217.5,"function":"Functions as a GTPase-activating protein (GAP) for RHOA and CDC42. Downstream partner of ARF1 which may control Golgi apparatus structure and function. Also required for CTNNA1 recruitment to adherens junctions","subcellular_location":"Golgi apparatus membrane; Cell junction; Cytoplasmic vesicle membrane; Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/Q5T5U3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ARHGAP21","classification":"Not Classified","n_dependent_lines":15,"n_total_lines":1208,"dependency_fraction":0.012417218543046357},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000107863","cell_line_id":"CID000556","localizations":[{"compartment":"membrane","grade":3},{"compartment":"big_aggregates","grade":2},{"compartment":"cell_contact","grade":2},{"compartment":"cytoplasmic","grade":2}],"interactors":[{"gene":"PRR36","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"LMNB1","stoichiometry":0.2},{"gene":"MAP4K4","stoichiometry":0.2},{"gene":"MYO1E","stoichiometry":0.2},{"gene":"NCK1","stoichiometry":0.2},{"gene":"NECAP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000556","total_profiled":1310},"omim":[{"mim_id":"610590","title":"RHO GTPase-ACTIVATING PROTEIN 23; ARHGAP23","url":"https://www.omim.org/entry/610590"},{"mim_id":"609870","title":"RHO GTPase-ACTIVATING PROTEIN 21; ARHGAP21","url":"https://www.omim.org/entry/609870"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cell Junctions","reliability":"Approved"},{"location":"Actin filaments","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":74.7}],"url":"https://www.proteinatlas.org/search/ARHGAP21"},"hgnc":{"alias_symbol":["KIAA1424","ARHGAP10"],"prev_symbol":[]},"alphafold":{"accession":"Q5T5U3","domains":[{"cath_id":"2.30.42.10","chopping":"50-73_97-177","consensus_level":"high","plddt":81.3566,"start":50,"end":177},{"cath_id":"2.30.29.30","chopping":"931-1042_1052-1060","consensus_level":"medium","plddt":79.9372,"start":931,"end":1060},{"cath_id":"1.10.555.10","chopping":"1155-1340","consensus_level":"high","plddt":92.4513,"start":1155,"end":1340}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T5U3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T5U3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T5U3-F1-predicted_aligned_error_v6.png","plddt_mean":44.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARHGAP21","jax_strain_url":"https://www.jax.org/strain/search?query=ARHGAP21"},"sequence":{"accession":"Q5T5U3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5T5U3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5T5U3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T5U3"}},"corpus_meta":[{"pmid":"17347647","id":"PMC_17347647","title":"Structural basis for ARF1-mediated recruitment of ARHGAP21 to Golgi membranes.","date":"2007","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/17347647","citation_count":90,"is_preprint":false},{"pmid":"22318733","id":"PMC_22318733","title":"Transport of influenza virus neuraminidase (NA) to host cell surface is regulated by ARHGAP21 and Cdc42 proteins.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22318733","citation_count":65,"is_preprint":false},{"pmid":"23200924","id":"PMC_23200924","title":"ARHGAP21 is a RhoGAP for RhoA and RhoC with a role in proliferation and migration of prostate adenocarcinoma cells.","date":"2012","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/23200924","citation_count":57,"is_preprint":false},{"pmid":"21173159","id":"PMC_21173159","title":"β-Arrestin 1 inhibits the GTPase-activating protein function of ARHGAP21, promoting activation of RhoA following angiotensin II type 1A receptor stimulation.","date":"2010","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21173159","citation_count":56,"is_preprint":false},{"pmid":"23235160","id":"PMC_23235160","title":"ARHGAP21 protein, a new partner of α-tubulin involved in cell-cell adhesion formation and essential for epithelial-mesenchymal transition.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23235160","citation_count":46,"is_preprint":false},{"pmid":"19268501","id":"PMC_19268501","title":"ARHGAP21 modulates FAK activity and impairs glioblastoma cell migration.","date":"2009","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/19268501","citation_count":44,"is_preprint":false},{"pmid":"25691070","id":"PMC_25691070","title":"Genetic association of ARHGAP21 gene variant with mandibular prognathism.","date":"2015","source":"Journal of dental research","url":"https://pubmed.ncbi.nlm.nih.gov/25691070","citation_count":44,"is_preprint":false},{"pmid":"19692570","id":"PMC_19692570","title":"Retrograde Shiga toxin trafficking is regulated by ARHGAP21 and Cdc42.","date":"2009","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/19692570","citation_count":37,"is_preprint":false},{"pmid":"29856495","id":"PMC_29856495","title":"ARHGAP21 as a master regulator of multiple cellular processes.","date":"2018","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29856495","citation_count":21,"is_preprint":false},{"pmid":"29212046","id":"PMC_29212046","title":"Hematopoietic defects in response to reduced Arhgap21.","date":"2017","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/29212046","citation_count":19,"is_preprint":false},{"pmid":"18662671","id":"PMC_18662671","title":"ARHGAP21 associates with FAK and PKCzeta and is redistributed after cardiac pressure 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physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29574752","citation_count":10,"is_preprint":false},{"pmid":"31191459","id":"PMC_31191459","title":"Whole-Body ARHGAP21-Deficiency Improves Energetic Homeostasis in Lean and Obese Mice.","date":"2019","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/31191459","citation_count":9,"is_preprint":false},{"pmid":"31247150","id":"PMC_31247150","title":"ARHGAP21 deficiency impairs hepatic lipid metabolism and improves insulin signaling in lean and obese mice.","date":"2019","source":"Canadian journal of physiology and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/31247150","citation_count":8,"is_preprint":false},{"pmid":"38556137","id":"PMC_38556137","title":"C. elegans Afadin is required for epidermal morphogenesis and functionally interfaces with the cadherin-catenin complex and RhoGAP PAC-1/ARHGAP21.","date":"2024","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/38556137","citation_count":7,"is_preprint":false},{"pmid":"25744409","id":"PMC_25744409","title":"ARHGAP21 prevents abnormal insulin release through actin rearrangement in pancreatic islets from neonatal mice.","date":"2015","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/25744409","citation_count":5,"is_preprint":false},{"pmid":"33324349","id":"PMC_33324349","title":"ARHGAP21 Acts as an Inhibitor of the Glucose-Stimulated Insulin Secretion Process.","date":"2020","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/33324349","citation_count":4,"is_preprint":false},{"pmid":"36676763","id":"PMC_36676763","title":"ARHGAP21 Is Involved in the Carcinogenic Mechanism of Cholangiocarcinoma: A Study Based on Bioinformatic Analyses and Experimental Validation.","date":"2023","source":"Medicina (Kaunas, Lithuania)","url":"https://pubmed.ncbi.nlm.nih.gov/36676763","citation_count":4,"is_preprint":false},{"pmid":"34917608","id":"PMC_34917608","title":"Arhgap21 Deficiency Results in Increase of Osteoblastic Lineage Cells in the Murine Bone Marrow Microenvironment.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34917608","citation_count":2,"is_preprint":false},{"pmid":"37546884","id":"PMC_37546884","title":"C. elegans Afadin is required for epidermal morphogenesis and functionally interfaces with the cadherin-catenin complex and RhoGAP PAC-1/ARHGAP21.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37546884","citation_count":1,"is_preprint":false},{"pmid":"37712268","id":"PMC_37712268","title":"[ARHGAP21 inhibits epithelial-mesenchymal transition by inactivating the WNT signaling pathway in non-small cell lung cancer].","date":"2023","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/37712268","citation_count":0,"is_preprint":false},{"pmid":"41957357","id":"PMC_41957357","title":"ARHGAP21 enhances metastasis in hepatocellular carcinoma by inhibiting ubiquitination of filamin A.","date":"2026","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/41957357","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13592,"output_tokens":4140,"usd":0.051438,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12051,"output_tokens":4481,"usd":0.08614,"stage2_stop_reason":"end_turn"},"total_usd":0.137578,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of ARF1(GTP)-bound form in complex with the Arf-binding domain (ArfBD) of ARHGAP21 at 2.1 Å resolution showed that ArfBD comprises a PH domain adjoining a C-terminal alpha helix, and that ARF1 interacts with both motifs through its switch regions, triggering structural rearrangement of the PH domain. Site-directed mutagenesis confirmed both the PH domain and helical motif are essential for ARF1 binding and Golgi recruitment of ARHGAP21.\",\n      \"method\": \"X-ray crystallography (2.1 Å) + site-directed mutagenesis + Golgi recruitment assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional mutagenesis validation, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"17347647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"β-arrestin 1 directly binds to ARHGAP21 in a region that transects the RhoA effector GAP domain, inhibiting its GAP function. This interaction is dynamically increased following angiotensin II stimulation of the type 1A receptor, and the complex modulates the temporal activation of RhoA leading to stress fiber formation. A cell-permeant peptide disrupting the β-arrestin 1/ARHGAP21 complex resulted in more active ARHGAP21, less efficient RhoA signaling, and attenuated stress fiber formation.\",\n      \"method\": \"Yeast two-hybrid screening, peptide array, in vitro binding, truncation analyses, co-immunoprecipitation, cell-permeant peptide inhibitor assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, in vitro binding, peptide array, and functional peptide inhibitor; multiple orthogonal methods in one study\",\n      \"pmids\": [\"21173159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ARHGAP21 is expressed in nuclear and perinuclear regions of glioblastoma cell lines and interacts with the C-terminal region of FAK. ARHGAP21 depletion by shRNAi increases FAK phosphorylation and downstream signaling activation, increases Cdc42 activity, MMP-2 production, and cell migration, indicating ARHGAP21 negatively regulates FAK signaling and cell migration.\",\n      \"method\": \"shRNAi knockdown, pulldown assay (FAK C-terminal region), phosphorylation assays, cell migration assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulldown mapping of interaction domain plus KD with defined phenotypic readouts, single lab\",\n      \"pmids\": [\"19268501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ARHGAP21 associates with PKCzeta and FAK in cardiac tissue and is redistributed to Z-lines and costameres after pressure overload. Co-transfection studies showed ARHGAP21 associates with PKCzeta-GST and endogenous FAK; pulldown assay confirmed ARHGAP21 binds the C-terminal region of FAK. ARHGAP21 binds to PKCzeta phosphorylated on Thr410 in sham and SHR rats, and to FAK phosphorylated on Tyr925 only in SHR.\",\n      \"method\": \"Co-transfection, pulldown assay, co-immunoprecipitation, immunofluorescence localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pulldown and Co-IP with phospho-specific interaction mapping, single lab, multiple methods\",\n      \"pmids\": [\"18662671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Constitutively active Cdc42 or knockdown of the Cdc42-specific GAP ARHGAP21 inhibited retrograde transport of Shiga toxin to the Golgi apparatus. Shiga toxin addition greatly decreases levels of active Cdc42-GTP in an ARHGAP21-dependent manner, demonstrating that ARHGAP21 and Cdc42-based signaling regulates dynein-dependent retrograde transport.\",\n      \"method\": \"siRNA knockdown, constitutively active Cdc42 expression, Cdc42-GTP pull-down activity assay, fluorescence microscopy of toxin trafficking\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi epistasis with GTPase activity assay and trafficking readout, single lab\",\n      \"pmids\": [\"19692570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ARHGAP21 presents GAP activity for RhoA and RhoC in PC3 prostate cancer cells (not just Cdc42), and its depletion results in decreased proliferation and increased migration. ARHGAP21 is localized in the nucleus and cytoplasm of prostate cancer cell lines.\",\n      \"method\": \"shRNA knockdown, RhoA/RhoC GTPase activity assay, cell proliferation and migration assays, subcellular fractionation/immunofluorescence\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct GAP activity assay for RhoA/RhoC plus KD phenotyping, single lab\",\n      \"pmids\": [\"23200924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ARHGAP21 is transiently redistributed to cell-cell junctions 4 hours after initiation of cell-cell adhesion, where it interacts with Cdc42 and decreases Cdc42 activity. ARHGAP21 also interacts with α-tubulin and is essential for α-tubulin acetylation during epithelial-mesenchymal transition (EMT). Cells lacking ARHGAP21 show weaker cell-cell adhesions, increased migration, and diminished HGF-induced EMT.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence (localization during adhesion), Cdc42 activity assay, shRNA knockdown, α-tubulin acetylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, activity assay, and KD phenotyping with multiple readouts, single lab\",\n      \"pmids\": [\"23235160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ARHGAP21 is post-translationally modified by SUMO2/3; co-immunoprecipitation and in vitro SUMOylation mapped the SUMOylation site to lysine K1443. A 250 kDa modified form of ARHGAP21 is differentially expressed among cell lines and human primary cells. ARHGAP21 co-localizes with SUMO2/3 in cytoplasm and membrane compartments.\",\n      \"method\": \"Co-immunoprecipitation, in vitro SUMOylation assay, mass spectrometry, immunofluorescence\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro SUMOylation with site mapping by mutagenesis/MS, single lab\",\n      \"pmids\": [\"22922005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ARHGAP21 regulates Cdc42 activity to control transport of influenza virus neuraminidase (NA) to the cell surface. Depletion of ARHGAP21 or expression of constitutively active Cdc42 promoted NA transport to plasma membranes, while overexpression of ARHGAP21 or shRNA targeting Cdc42 decreased cell surface NA. Silencing ARHGAP21 increased influenza A virus replication.\",\n      \"method\": \"shRNA knockdown, constitutively active/dominant-negative mutant expression, surface NA quantification, viral replication assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via KD and constitutive mutants with functional transport readout, single lab\",\n      \"pmids\": [\"22318733\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PTEN controls 3D glandular morphogenesis through a membrane-associated β-arrestin1/ARHGAP21/Cdc42 scaffolding complex. PTEN knockdown impairs β-arrestin1 membrane localization and β-arrestin1-ARHGAP21 interactions, reducing Cdc42 activation and disrupting mitotic spindle orientation. Silencing of ARHGAP21 enhanced Cdc42 activation and rescued aberrant morphogenic processes of PTEN-deficient cultures. A membrane-binding defective mutant of PTEN C2 domain abrogated these rescue properties.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, Cdc42 activity assay, 3D morphogenesis assay, mitotic spindle orientation analysis, domain mutant rescue\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis with multiple KDs, Co-IP, activity assays, and domain mutant analysis; multiple orthogonal methods in a rigorous study\",\n      \"pmids\": [\"28749339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Arhgap21 haploinsufficiency in mice leads to enhanced RhoC activity in bone marrow cells, impaired hematopoietic progenitor adhesion, enhanced mobilization of LSK and myeloid progenitors, and reduced erythroid commitment. ARHGAP21 knockdown in human CMP and MEP cells recapitulated decreased erythroid commitment, indicating Arhgap21 functions in hematopoiesis at least partially through RhoC inactivation.\",\n      \"method\": \"Haploinsufficient mouse model, RhoC-GTP pull-down assay, in vitro colony formation, in vivo transplantation, human primary cell knockdown\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function mouse model with RhoC activity assay and functional hematopoietic readouts, single lab\",\n      \"pmids\": [\"29212046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ARHGAP21 co-localizes with actin in MIN6 beta cells and with insulin in neonatal pancreatic islets. Antisense-mediated knockdown of ARHGAP21 reduces F-actin polymerization, increases basal insulin secretion (but not GSIS), increases pERK1/2, and upregulates VAMP2 and SNAP25 gene expression, indicating ARHGAP21 regulates insulin secretion via actin rearrangement and pERK1/2 signaling.\",\n      \"method\": \"Antisense oligonucleotide knockdown, phalloidin staining (F-actin quantification), insulin secretion assay, Western blot (pERK1/2), RT-PCR, immunofluorescence\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with multiple mechanistic readouts (actin, signaling, gene expression), single lab\",\n      \"pmids\": [\"25744409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In C. elegans, PAC-1/ARHGAP21 is enriched at cell contact sites in a manner dependent on afadin (AFD-1), and genetic interactions indicate afd-1 and pac-1 regulate epidermal morphogenesis through parallel mechanisms. E-cadherin is required for polarized distribution of AFD-1, which in turn promotes PAC-1/ARHGAP21 enrichment at cell contacts.\",\n      \"method\": \"Null mutation (genetic), RNAi, fluorescence localization, genetic epistasis analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis and localization in C. elegans ortholog model, single lab\",\n      \"pmids\": [\"38556137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ARHGAP21 directly binds to filamin A (FLNA) via its PDZ domain interacting with the 1-1200 aa fragment of FLNA. ARHGAP21 also directly binds and recruits HSP90α to stabilize FLNA by inhibiting its ubiquitination and degradation. Overexpression of FLNA reversed the actin cytoskeleton remodeling-related suppression of tumor metastasis caused by ARHGAP21 knockdown in HCC cells.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping (PDZ domain deletion/mutation), ubiquitination assay, rescue by FLNA overexpression, in vitro and in vivo migration/invasion assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding with domain mapping, ubiquitination assay, and functional rescue, single lab\",\n      \"pmids\": [\"41957357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ARHGAP21 knockdown in NSCLC cells significantly decreased ubiquitination of β-catenin, upregulated N-cadherin, and activated the WNT signaling pathway by affecting expression of APC, GSK3β, and Axin, promoting cell migration and metastasis in vivo.\",\n      \"method\": \"siRNA knockdown, Western blot (β-catenin ubiquitination, pathway components), Transwell/wound healing migration assay, nude mouse tail-vein metastasis model\",\n      \"journal\": \"Nan fang yi ke da xue xue bao\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — KD with Western blot pathway analysis, single lab, no direct interaction assay between ARHGAP21 and WNT components\",\n      \"pmids\": [\"37712268\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARHGAP21 is a large multifunctional RhoGAP that is recruited to the Golgi by GTP-bound ARF1 (via a novel PH domain + α-helix ArfBD), where it negatively regulates Cdc42 (and also RhoA, RhoC) to control actin/Arp2/3 dynamics, vesicular trafficking, and cell-cell junction remodeling; its GAP activity is suppressed when β-arrestin 1 binds its GAP domain upon angiotensin II receptor activation, and it is further regulated by SUMO2/3 modification at K1443; it also scaffolds FAK and PKCζ signaling, binds α-tubulin to promote its acetylation during EMT, inhibits FLNA ubiquitination via HSP90α recruitment, and functions downstream of a PTEN–β-arrestin1 complex to orient the mitotic spindle during glandular morphogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARHGAP21 is a large multifunctional Rho-family GTPase-activating protein that couples membrane and adhesion signaling to actin cytoskeletal remodeling, vesicular trafficking, and tissue morphogenesis [#0, #6]. It is recruited to the Golgi by GTP-bound ARF1 through a bipartite Arf-binding domain comprising a PH domain and an adjacent C-terminal alpha helix, both of which engage the ARF1 switch regions [#0]. At its catalytic core it inactivates Cdc42, and also RhoA and RhoC, thereby controlling actin dynamics in contexts ranging from dynein-dependent retrograde transport of Shiga toxin to the Golgi and surface delivery of influenza neuraminidase [#4, #8], to cell-cell junction stability and HGF-induced epithelial-mesenchymal transition, where it additionally binds alpha-tubulin to promote its acetylation [#5, #6]. Its GAP activity is dynamically restrained by direct binding of beta-arrestin 1 across the GAP domain following angiotensin II receptor stimulation, gating RhoA-driven stress fiber formation [#1], and the same beta-arrestin1/ARHGAP21/Cdc42 scaffold operates downstream of membrane-associated PTEN to orient the mitotic spindle during 3D glandular morphogenesis [#9]. ARHGAP21 further acts as a scaffold for FAK and PKCzeta signaling to suppress cell migration [#2, #3], stabilizes filamin A by recruiting HSP90alpha through its PDZ domain to block FLNA ubiquitination [#13], and is regulated by SUMO2/3 modification at lysine K1443 [#7]. Through RhoC inactivation it controls hematopoietic progenitor adhesion, mobilization, and erythroid commitment [#10].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established the structural basis for how ARHGAP21 is targeted to the Golgi, answering how an Arf GTPase localizes a RhoGAP to a membrane compartment.\",\n      \"evidence\": \"X-ray crystallography of the ARF1(GTP)-ArfBD complex with site-directed mutagenesis and Golgi recruitment assays\",\n      \"pmids\": [\"17347647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define which Rho GTPase is regulated at the Golgi\", \"Does not address regulation of the GAP catalytic domain\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified ARHGAP21 as a scaffold associating with PKCzeta and FAK that relocalizes upon cardiac mechanical stress, linking it to phospho-dependent signaling assemblies.\",\n      \"evidence\": \"Co-transfection, pulldown, Co-IP and immunofluorescence in cardiac tissue from sham and SHR rats\",\n      \"pmids\": [\"18662671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish a catalytic or GTPase-dependent role in this context\", \"Functional consequence of relocalization not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that ARHGAP21 negatively regulates FAK signaling and migration via Cdc42 in glioblastoma, connecting its GAP activity to invasive behavior.\",\n      \"evidence\": \"shRNAi knockdown with FAK pulldown, phosphorylation, Cdc42 activity, and migration assays\",\n      \"pmids\": [\"19268501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct GAP-on-Cdc42 catalysis not separated from scaffolding\", \"Single lab, single tumor type\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed ARHGAP21-controlled Cdc42 inactivation is required for dynein-dependent retrograde transport to the Golgi, placing it in a trafficking pathway.\",\n      \"evidence\": \"siRNA, constitutively active Cdc42, Cdc42-GTP pulldown, and Shiga toxin trafficking microscopy\",\n      \"pmids\": [\"19692570\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link to ARF1-dependent Golgi recruitment not directly tested\", \"Mechanism connecting Cdc42 to dynein unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined a direct regulatory mechanism: beta-arrestin1 binding across the GAP domain inhibits ARHGAP21 GAP activity downstream of a GPCR, timing RhoA activation.\",\n      \"evidence\": \"Yeast two-hybrid, peptide array, in vitro binding, truncation, Co-IP, and cell-permeant peptide inhibitor following angiotensin II stimulation\",\n      \"pmids\": [\"21173159\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of GAP-domain occlusion not solved\", \"Generalizability to other GPCRs unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Broadened the substrate repertoire to RhoA and RhoC and tied ARHGAP21 to proliferation/migration balance in prostate cancer.\",\n      \"evidence\": \"shRNA with RhoA/RhoC GTPase activity assays and proliferation/migration assays in PC3 cells\",\n      \"pmids\": [\"23200924\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of each GTPase to phenotype not dissected\", \"No in vivo validation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected ARHGAP21 to cell-cell adhesion and EMT, showing it localizes to junctions, inactivates Cdc42 there, and binds alpha-tubulin to drive its acetylation.\",\n      \"evidence\": \"Co-IP, immunofluorescence during adhesion, Cdc42 activity assay, shRNA, alpha-tubulin acetylation assay\",\n      \"pmids\": [\"23235160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking alpha-tubulin binding to acetylation unknown\", \"Junctional recruitment signal not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established ARHGAP21 as a post-translationally SUMOylated protein, mapping a defined modification site.\",\n      \"evidence\": \"Co-IP, in vitro SUMOylation, MS, and immunofluorescence mapping SUMO2/3 to K1443\",\n      \"pmids\": [\"22922005\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of SUMOylation on GAP activity not determined\", \"Conditions inducing modification unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed ARHGAP21-mediated Cdc42 control gates surface delivery of a viral glycoprotein and restricts influenza replication, extending its trafficking role to host-pathogen interactions.\",\n      \"evidence\": \"shRNA, constitutively active/dominant-negative Cdc42, surface NA quantification, viral replication assay\",\n      \"pmids\": [\"22318733\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Compartment of action not pinpointed\", \"Direct GAP catalysis vs scaffolding not separated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Implicated ARHGAP21 in regulated secretion, linking its actin control to insulin exocytosis machinery in beta cells.\",\n      \"evidence\": \"Antisense knockdown with F-actin quantification, insulin secretion, pERK1/2 Western, and RT-PCR in MIN6 cells/islets\",\n      \"pmids\": [\"25744409\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which Rho GTPase mediates the actin effect not specified\", \"pERK1/2 link mechanistically undefined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Integrated ARHGAP21 into a PTEN-driven scaffold controlling Cdc42-dependent spindle orientation and epithelial architecture.\",\n      \"evidence\": \"siRNA, Co-IP, Cdc42 activity, 3D morphogenesis, spindle orientation, and PTEN C2 domain mutant rescue\",\n      \"pmids\": [\"28749339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How membrane-bound PTEN recruits the complex structurally unknown\", \"Direct PTEN-ARHGAP21 vs beta-arrestin1-bridged contact not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated an in vivo physiological role via RhoC inactivation in hematopoiesis using a loss-of-function mouse.\",\n      \"evidence\": \"Arhgap21 haploinsufficient mice, RhoC-GTP pulldown, colony formation, transplantation, and human CMP/MEP knockdown\",\n      \"pmids\": [\"29212046\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cell-intrinsic vs niche contributions not fully separated\", \"Mechanism downstream of RhoC in erythroid commitment unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed the ortholog's contact-site enrichment depends on afadin and E-cadherin, defining how ARHGAP21 is recruited to junctions during morphogenesis.\",\n      \"evidence\": \"Null mutants, RNAi, localization, and genetic epistasis of PAC-1/ARHGAP21, AFD-1, and E-cadherin in C. elegans\",\n      \"pmids\": [\"38556137\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conservation of afadin-dependent recruitment in mammals not tested\", \"Direct vs indirect afadin interaction not defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed a GAP-independent function: ARHGAP21 stabilizes filamin A by recruiting HSP90alpha to block FLNA ubiquitination, controlling actin remodeling and metastasis.\",\n      \"evidence\": \"Co-IP, PDZ domain mapping, ubiquitination assay, FLNA-overexpression rescue, and migration/invasion assays in HCC\",\n      \"pmids\": [\"41957357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How HSP90alpha recruitment inhibits the relevant E3 ligase unknown\", \"Interplay with GAP activity not dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ARHGAP21's distinct activities — ARF1-dependent Golgi GAP function, beta-arrestin/PTEN-gated scaffolding, tubulin acetylation, and FLNA stabilization — are coordinated within a single protein and which dominate in a given cell type remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated structure-function map across domains\", \"Regulation linking SUMOylation, beta-arrestin binding, and substrate selectivity unknown\", \"Direct disease-causing mutation not established in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 6, 10]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 9, 13]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [6, 11, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 9]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [4, 8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9, 10, 12]}\n    ],\n    \"complexes\": [\n      \"beta-arrestin1/ARHGAP21/Cdc42 scaffold\"\n    ],\n    \"partners\": [\n      \"ARF1\",\n      \"ARRB1\",\n      \"PTK2\",\n      \"PRKCZ\",\n      \"CDC42\",\n      \"PTEN\",\n      \"FLNA\",\n      \"HSP90AA1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}