{"gene":"ARHGAP44","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2009,"finding":"RICH2 (ARHGAP44) links CD317/tetherin to the apical actin cytoskeleton in polarized epithelial cells via a complex with EBP50 and ezrin. Knockdown of RICH2 causes loss of the apical actin network, loss of apical microvilli, increased basal actin bundles, and reduced cell height, phenocopying CD317 knockdown.","method":"siRNA knockdown, co-immunoprecipitation, confocal imaging of polarized epithelial cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction demonstrated, KD phenotype with defined cellular readout, independently convergent results from both CD317 and RICH2 KD","pmids":["19273615"],"is_preprint":false},{"year":2013,"finding":"Rich2 (ARHGAP44) is a Rac1-specific GAP that controls dendritic spine morphogenesis in hippocampal neurons. Overexpression increases spine size and decreases density; knockdown decreases both. The morphological changes are rescued by Rac1 inhibitor EHT 1864, placing Rich2 upstream of Rac1 in spine regulation.","method":"siRNA knockdown, overexpression, pharmacological Rac1 inhibition (EHT 1864) epistasis, miniature EPSC recording, immunofluorescence in cultured hippocampal neurons","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with Rac1 inhibitor rescue, multiple orthogonal readouts (morphology + electrophysiology), KD and OE in same system","pmids":["24352656"],"is_preprint":false},{"year":2013,"finding":"Rich2 (ARHGAP44) physically interacts with the postsynaptic scaffolding protein Shank3 in dendritic spines, and this interaction is increased during LTP. Rich2 functions as an endosomal recycling regulator controlling AMPA receptor GluA1 subunit exocytosis and spine enlargement during LTP. Disruption of the Rich2-Shank3 complex (via siRNA or interfering peptide) inhibits LTP-associated spine enlargement and GluA1 exocytosis.","method":"Proteomic screen, bioluminescence resonance energy transfer (BRET) microscopy, siRNA knockdown, interfering mimetic peptide, GluA1 exocytosis assay in cultured hippocampal neurons","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — BRET-based interaction in live cells, two independent disruption strategies (siRNA + peptide), functional readouts of LTP","pmids":["23739967"],"is_preprint":false},{"year":2014,"finding":"ArhGAP44 (ARHGAP44) contains an N-BAR domain that senses inward plasma membrane curvature generated by acto-myosin contractile forces at actin patches, recruiting the protein to nascent filopodia seed sites. The GAP domain then triggers local Rac-GTP hydrolysis, reducing actin polymerization and suppressing filopodia initiation in neurons. ArhGAP44 expression increases during neuronal development concurrent with decreased filopodia formation rate.","method":"Live-cell imaging, dominant-negative and constitutively active constructs, BAR domain membrane curvature binding assay, Rac-GTP pull-down, neuronal KD/OE with filopodia quantification","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — BAR domain curvature-sensing assay, Rac-GTP hydrolysis demonstrated, multiple orthogonal methods, domain-level dissection","pmids":["25498153"],"is_preprint":false},{"year":2016,"finding":"In RICH2 knockout mice, synaptic Rac1 is disinhibited in vivo, leading to increased multiple spine synapses in hippocampus and cerebellum, altered receptor composition, and impaired actin polymerization, consistent with RICH2 acting as a negative regulator of Rac1 at postsynaptic densities.","method":"RICH2 KO mouse model, immunohistochemistry, electron microscopy, biochemical Rac1-GTP pull-down, behavioral testing","journal":"Molecular brain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO with defined biochemical (Rac1-GTP) and structural phenotype, single lab","pmids":["26969129"],"is_preprint":false},{"year":2017,"finding":"Mutant p53 suppresses ARHGAP44 transcription, leading to elevated GTP-Cdc42 levels. Wild-type ARHGAP44 (but not GAP-dead R291A mutant) suppresses mutant-p53-mediated cell spreading and migration, establishing ARHGAP44 as a GAP for Cdc42 that restrains these behaviors.","method":"RNA-seq, RT-qPCR, Cdc42-GTP pull-down, overexpression of WT vs. R291A mutant ARHGAP44, cell spreading and migration assays","journal":"Science China. Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — active-site mutagenesis (R291A) validates GAP activity requirement, Cdc42-GTP biochemical assay, single lab","pmids":["28527113"],"is_preprint":false},{"year":2017,"finding":"In RICH2 KO mouse amygdala, RhoA (not Rac1) is disinhibited, associated with decreased actin polymerization capacity and reduced mature spines, indicating that RICH2 also negatively regulates RhoA signaling in this brain region.","method":"RICH2 KO mouse, RhoA-GTP pull-down, spine morphology analysis, c-fos immunostaining in amygdala","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO with RhoA-GTP biochemical readout, single lab, single brain region","pmids":["28642683"],"is_preprint":false},{"year":2019,"finding":"RICH2 co-immunoprecipitates with endogenous Cdc42, Rac1, and β-catenin in hepatocellular carcinoma cells. RICH2 overexpression inhibits filopodia formation in a Cdc42-dependent manner and suppresses tumor growth in vivo.","method":"Co-immunoprecipitation, filopodia assay, stable overexpression, in vivo xenograft","journal":"Frontiers in bioscience (Landmark edition)","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP with multiple substrates, in vivo confirmation, Cdc42-dependence established, single lab","pmids":["31136984"],"is_preprint":false},{"year":2020,"finding":"CD317 protects tumor cells from NK cell-mediated immunocytolysis through its association with RICH2, which modulates cytoskeletal flexibility to preserve membrane integrity against perforin.","method":"CD317 knockdown in tumor cells, NK and CAR-NK cytotoxicity assays, RICH2 interaction assessed, perforin sensitivity assay","journal":"Molecular immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic link to RICH2 inferred from CD317-RICH2 association and phenotype, no direct RICH2 KD or reconstitution for this specific finding","pmids":["33223223"],"is_preprint":false},{"year":2023,"finding":"Rich2/Arhgap44 is localized to postsynaptic densities via biochemical fractionation in mouse brain and is expressed in excitatory synapses of hippocampal CA1 at postnatal day 30, with nuclear accumulation also observed in cortical neurons at certain developmental stages.","method":"Immunohistochemistry, immunoblotting of tissue fractions, subcellular fractionation to postsynaptic density fraction","journal":"Developmental neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical fractionation establishing PSD localization in vivo, replicated across two brain regions and developmental time points, single lab","pmids":["36630934"],"is_preprint":false},{"year":2023,"finding":"RICH2 overexpression in glioma cells decreases mitochondrial number and calcium flow, reduces mitochondrial fusion via downregulation of MFN-1/MFN-2 and upregulation of Drp-1, reduces mitochondrial release from glioma cells into extracellular environment, and downregulates the MAPK/ERK/HIF-1 pathway.","method":"Fluorescence microscopy, qRT-PCR, Western blot, electrophysiology in nude mouse glioma model, single-cell calcium imaging","journal":"Neurobiology of disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, overexpression only, pathway modulation inferred from protein-level changes without direct mechanistic dissection of RICH2-mitochondria link","pmids":["37926169"],"is_preprint":false}],"current_model":"ARHGAP44 (RICH2) is a Rho-GAP protein with an N-BAR membrane curvature-sensing domain that inactivates Rac1 (and Cdc42) by stimulating GTP hydrolysis; it is enriched at postsynaptic densities where it forms a complex with Shank3 to regulate AMPA receptor recycling, dendritic spine morphogenesis, and LTP, and at the apical surface of polarized epithelial cells where it bridges CD317/tetherin to the actin cytoskeleton via EBP50 and ezrin to maintain microvilli."},"narrative":{"mechanistic_narrative":"ARHGAP44 (RICH2) is a Rho-family GTPase-activating protein that couples membrane geometry to actin remodeling, restraining Rac1, Cdc42, and RhoA signaling across neuronal and epithelial contexts [PMID:24352656, PMID:25498153, PMID:28527113, PMID:28642683]. Its N-BAR domain senses inward plasma membrane curvature generated by acto-myosin contractile forces, recruiting the protein to nascent filopodia sites where its GAP domain drives local Rac-GTP hydrolysis to suppress filopodia initiation in developing neurons [PMID:25498153]. As a Rac1-specific GAP it controls dendritic spine morphogenesis, with loss-of-function disinhibiting synaptic Rac1 in vivo and altering spine number and receptor composition [PMID:24352656, PMID:26969129]; at postsynaptic densities it forms an LTP-regulated complex with Shank3 that governs endosomal recycling and GluA1 AMPA-receptor exocytosis during spine enlargement [PMID:23739967, PMID:36630934]. In polarized epithelial cells ARHGAP44 links CD317/tetherin to the apical actin cytoskeleton through EBP50 and ezrin, maintaining the apical actin network and microvilli [PMID:19273615]. Its catalytic (R291A-sensitive) GAP activity toward Cdc42 restrains cell spreading and migration and is transcriptionally suppressed by mutant p53 [PMID:28527113].","teleology":[{"year":2009,"claim":"Established the first cellular role for RICH2 as a cytoskeletal adaptor, answering how the membrane protein CD317/tetherin is anchored to the apical actin network in polarized epithelia.","evidence":"siRNA knockdown, co-immunoprecipitation, and confocal imaging in polarized epithelial cells","pmids":["19273615"],"confidence":"High","gaps":["Did not test GAP activity or a specific Rho GTPase in this epithelial context","Direct binding stoichiometry within the EBP50/ezrin complex not resolved"]},{"year":2013,"claim":"Defined RICH2 as a Rac1-specific GAP acting upstream of Rac1 to control dendritic spine morphology, answering which GTPase mediates its synaptic function.","evidence":"Knockdown/overexpression with Rac1-inhibitor (EHT 1864) epistasis rescue, mEPSC recording, and immunofluorescence in cultured hippocampal neurons","pmids":["24352656"],"confidence":"High","gaps":["Did not address regulation of recruitment to spines","Did not distinguish Rac1 from other potential substrates biochemically"]},{"year":2013,"claim":"Identified the Shank3-RICH2 complex as an LTP-regulated machine controlling AMPA receptor recycling, connecting GAP function to synaptic plasticity output.","evidence":"Proteomic screen, BRET in live cells, siRNA and interfering peptide disruption, GluA1 exocytosis assay in hippocampal neurons","pmids":["23739967"],"confidence":"High","gaps":["Molecular basis of LTP-induced interaction increase not defined","Link between GAP catalysis and receptor exocytosis not directly dissected"]},{"year":2014,"claim":"Revealed the mechanistic logic of curvature-sensing, showing the N-BAR domain reads acto-myosin-generated membrane curvature to target GAP activity and suppress filopodia initiation.","evidence":"Live-cell imaging, dominant-negative/constitutively-active constructs, BAR-domain curvature binding assay, Rac-GTP pull-down in neurons","pmids":["25498153"],"confidence":"High","gaps":["In vivo relevance of curvature sensing not tested","Whether the same mechanism operates at spines or epithelial surfaces unknown"]},{"year":2016,"claim":"Confirmed RICH2 as an in vivo negative regulator of synaptic Rac1, linking its loss to structural and receptor-composition synaptic phenotypes.","evidence":"RICH2 knockout mouse with immunohistochemistry, electron microscopy, Rac1-GTP pull-down, and behavioral testing","pmids":["26969129"],"confidence":"Medium","gaps":["Single lab","Behavioral consequences not mechanistically tied to specific spine changes"]},{"year":2017,"claim":"Extended the substrate repertoire to Cdc42 and RhoA and placed RICH2 in a tumor-suppressive transcriptional circuit downstream of mutant p53.","evidence":"RNA-seq/RT-qPCR, Cdc42-GTP and RhoA-GTP pull-downs, WT vs GAP-dead R291A overexpression, cell spreading/migration assays, and amygdala KO analysis","pmids":["28527113","28642683"],"confidence":"Medium","gaps":["Region- and context-specificity of substrate choice (Rac1 vs Cdc42 vs RhoA) unexplained","Single lab for each substrate claim"]},{"year":2019,"claim":"Documented physical association with Cdc42, Rac1, and β-catenin in carcinoma cells and a Cdc42-dependent anti-tumor, anti-filopodia function in vivo.","evidence":"Co-immunoprecipitation, filopodia assay, stable overexpression, and xenograft in hepatocellular carcinoma cells","pmids":["31136984"],"confidence":"Medium","gaps":["β-catenin interaction functional significance not established","GAP-dependence of tumor suppression not formally tested here"]},{"year":2023,"claim":"Anchored RICH2 biochemically to the postsynaptic density in vivo and noted developmental nuclear accumulation, refining its subcellular localization.","evidence":"Subcellular fractionation, immunoblotting, and immunohistochemistry of mouse brain across regions and developmental stages","pmids":["36630934"],"confidence":"Medium","gaps":["Functional role of nuclear pool not addressed","Single lab"]},{"year":2023,"claim":"Reported a non-canonical effect of RICH2 overexpression on mitochondrial dynamics and MAPK/ERK/HIF-1 signaling in glioma.","evidence":"Fluorescence microscopy, qRT-PCR, Western blot, calcium imaging, and glioma mouse model (overexpression only)","pmids":["37926169"],"confidence":"Low","gaps":["Overexpression only, no loss-of-function","Direct molecular link between RICH2 and mitochondrial machinery not dissected","Not independently replicated"]},{"year":null,"claim":"How ARHGAP44 selects among Rac1, Cdc42, and RhoA in different cellular and tissue contexts, and how curvature sensing, scaffold binding, and transcriptional control are integrated, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of substrate selectivity","Mechanism coupling N-BAR recruitment to specific GTPase choice unknown","No unified model across neuronal, epithelial, and tumor contexts"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3,5]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,3,5]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,4]}],"complexes":["RICH2-Shank3 postsynaptic complex","CD317-EBP50-ezrin apical complex"],"partners":["SHANK3","CD317","EBP50","EZR","RAC1","CDC42","RHOA","CTNNB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q17R89","full_name":"Rho GTPase-activating protein 44","aliases":["NPC-A-10","Rho-type GTPase-activating protein RICH2","RhoGAP interacting with CIP4 homologs protein 2","RICH-2"],"length_aa":818,"mass_kda":89.2,"function":"GTPase-activating protein (GAP) that stimulates the GTPase activity of Rho-type GTPases. Thereby, controls Rho-type GTPases cycling between their active GTP-bound and inactive GDP-bound states. Acts as a GAP at least for CDC42 and RAC1 (PubMed:11431473). In neurons, is involved in dendritic spine formation and synaptic plasticity in a specific RAC1-GAP activity (By similarity). Limits the initiation of exploratory dendritic filopodia. Recruited to actin-patches that seed filopodia, binds specifically to plasma membrane sections that are deformed inward by acto-myosin mediated contractile forces. Acts through GAP activity on RAC1 to reduce actin polymerization necessary for filopodia formation (By similarity). In association with SHANK3, promotes GRIA1 exocytosis from recycling endosomes and spine morphological changes associated to long-term potentiation (By similarity)","subcellular_location":"Cell projection, dendritic spine; Recycling endosome; Presynapse; Cell projection, dendrite","url":"https://www.uniprot.org/uniprotkb/Q17R89/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ARHGAP44","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ARHGAP17","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ARHGAP44","total_profiled":1310},"omim":[{"mim_id":"617716","title":"RHO GTPase-ACTIVATING PROTEIN 44; ARHGAP44","url":"https://www.omim.org/entry/617716"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":24.1}],"url":"https://www.proteinatlas.org/search/ARHGAP44"},"hgnc":{"alias_symbol":["KIAA0672","RICH-2","RICH2"],"prev_symbol":[]},"alphafold":{"accession":"Q17R89","domains":[{"cath_id":"1.20.1270.60","chopping":"25-164_173-247","consensus_level":"high","plddt":91.1062,"start":25,"end":247},{"cath_id":"1.10.555.10","chopping":"258-445","consensus_level":"medium","plddt":90.5011,"start":258,"end":445}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q17R89","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q17R89-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q17R89-F1-predicted_aligned_error_v6.png","plddt_mean":65.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARHGAP44","jax_strain_url":"https://www.jax.org/strain/search?query=ARHGAP44"},"sequence":{"accession":"Q17R89","fasta_url":"https://rest.uniprot.org/uniprotkb/Q17R89.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q17R89/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q17R89"}},"corpus_meta":[{"pmid":"19273615","id":"PMC_19273615","title":"A CD317/tetherin-RICH2 complex plays a critical role in the organization of the subapical actin cytoskeleton in polarized epithelial cells.","date":"2009","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19273615","citation_count":112,"is_preprint":false},{"pmid":"34774561","id":"PMC_34774561","title":"Modulation of transforming growth factor-β-induced kidney fibrosis by leucine-rich ⍺-2 glycoprotein-1.","date":"2021","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/34774561","citation_count":81,"is_preprint":false},{"pmid":"23739967","id":"PMC_23739967","title":"Shank3-Rich2 interaction regulates AMPA receptor recycling and synaptic long-term potentiation.","date":"2013","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/23739967","citation_count":53,"is_preprint":false},{"pmid":"9722562","id":"PMC_9722562","title":"Structural and transglutaminase substrate properties of the small proline-rich 2 family of cornified cell envelope proteins.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9722562","citation_count":51,"is_preprint":false},{"pmid":"25498153","id":"PMC_25498153","title":"Dynamic recruitment of the curvature-sensitive protein ArhGAP44 to nanoscale membrane deformations limits exploratory filopodia initiation in neurons.","date":"2014","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/25498153","citation_count":46,"is_preprint":false},{"pmid":"24352656","id":"PMC_24352656","title":"Rho-GTPase-activating protein interacting with Cdc-42-interacting protein 4 homolog 2 (Rich2): a new Ras-related C3 botulinum toxin substrate 1 (Rac1) GTPase-activating protein that controls dendritic spine morphogenesis.","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24352656","citation_count":27,"is_preprint":false},{"pmid":"26969129","id":"PMC_26969129","title":"Enlarged dendritic spines and pronounced neophobia in mice lacking the PSD protein RICH2.","date":"2016","source":"Molecular brain","url":"https://pubmed.ncbi.nlm.nih.gov/26969129","citation_count":24,"is_preprint":false},{"pmid":"15232223","id":"PMC_15232223","title":"Estrogen regulates the expression of the small proline-rich 2 gene family in the mouse uterus.","date":"2004","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/15232223","citation_count":21,"is_preprint":false},{"pmid":"28527113","id":"PMC_28527113","title":"Mutant p53 promotes cell spreading and migration via ARHGAP44.","date":"2017","source":"Science China. Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/28527113","citation_count":16,"is_preprint":false},{"pmid":"28642683","id":"PMC_28642683","title":"Object Phobia and Altered RhoA Signaling in Amygdala of Mice Lacking RICH2.","date":"2017","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/28642683","citation_count":11,"is_preprint":false},{"pmid":"31136984","id":"PMC_31136984","title":"RICH2, a potential tumor suppressor in hepatocellular carcinoma.","date":"2019","source":"Frontiers in bioscience (Landmark edition)","url":"https://pubmed.ncbi.nlm.nih.gov/31136984","citation_count":8,"is_preprint":false},{"pmid":"33349937","id":"PMC_33349937","title":"Brewing rich 2-phenylethanol beer from cassava and its producing metabolisms in yeast.","date":"2021","source":"Journal of the science of food and agriculture","url":"https://pubmed.ncbi.nlm.nih.gov/33349937","citation_count":8,"is_preprint":false},{"pmid":"33223223","id":"PMC_33223223","title":"CD317 mediates immunocytolysis resistance by RICH2/cytoskeleton-dependent membrane protection.","date":"2020","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/33223223","citation_count":7,"is_preprint":false},{"pmid":"29904086","id":"PMC_29904086","title":"The evolution of phase constitution and microstructure in iron-rich 2:17-type Sm-Co magnets with high magnetic performance.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29904086","citation_count":7,"is_preprint":false},{"pmid":"34974809","id":"PMC_34974809","title":"Long non-coding RNA HOXA11 antisense RNA upregulates spermatogenesis-associated serine-rich 2-like to enhance cisplatin resistance in laryngeal squamous cell carcinoma by suppressing microRNA-518a.","date":"2022","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/34974809","citation_count":6,"is_preprint":false},{"pmid":"10462486","id":"PMC_10462486","title":"Acquisition of ordered conformation by the N-terminal domain of the human small proline rich 2 protein.","date":"1999","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10462486","citation_count":5,"is_preprint":false},{"pmid":"37926169","id":"PMC_37926169","title":"RICH2 decreases the mitochondrial number and affects mitochondrial localization in diffuse low-grade glioma-related epilepsy.","date":"2023","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/37926169","citation_count":4,"is_preprint":false},{"pmid":"36630934","id":"PMC_36630934","title":"Expression Analyses of Rich2/Arhgap44, a Rho Family GTPase-Activating Protein, during Mouse Brain Development.","date":"2023","source":"Developmental neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/36630934","citation_count":3,"is_preprint":false},{"pmid":"38031136","id":"PMC_38031136","title":"ARHGAP44-mediated regulation of the p53/C-myc/Cyclin D1 pathway in modulating the malignant biological behavior of osteosarcoma cells.","date":"2023","source":"Journal of orthopaedic surgery and research","url":"https://pubmed.ncbi.nlm.nih.gov/38031136","citation_count":2,"is_preprint":false},{"pmid":"28069446","id":"PMC_28069446","title":"RICH2 is implicated in viraemic control of HIV-1 in black South African individuals.","date":"2017","source":"Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/28069446","citation_count":2,"is_preprint":false},{"pmid":"28744747","id":"PMC_28744747","title":"Structural and inhibition analysis of novel sulfur-rich 2-mercaptobenzothiazole and 1,2,3-triazole ligands against Mycobacterium tuberculosis DprE1 enzyme.","date":"2017","source":"Journal of molecular modeling","url":"https://pubmed.ncbi.nlm.nih.gov/28744747","citation_count":2,"is_preprint":false},{"pmid":"40019798","id":"PMC_40019798","title":"Evidence of a novel gene locus ARHGAP44 for longitudinal change in hemoglobin A1c levels among subjects without diabetes from the Long Life Family Study.","date":"2025","source":"Physiological genomics","url":"https://pubmed.ncbi.nlm.nih.gov/40019798","citation_count":1,"is_preprint":false},{"pmid":"38826208","id":"PMC_38826208","title":"A Novel Gene ARHGAP44 for Longitudinal Changes in Glycated Hemoglobin (HbA1c) in Subjects without Type 2 Diabetes: Evidence from the Long Life Family Study (LLFS) and the Framingham Offspring Study (FOS).","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38826208","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13749,"output_tokens":2830,"usd":0.041848,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10092,"output_tokens":3227,"usd":0.065568,"stage2_stop_reason":"end_turn"},"total_usd":0.107416,"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\": 2009,\n      \"finding\": \"RICH2 (ARHGAP44) links CD317/tetherin to the apical actin cytoskeleton in polarized epithelial cells via a complex with EBP50 and ezrin. Knockdown of RICH2 causes loss of the apical actin network, loss of apical microvilli, increased basal actin bundles, and reduced cell height, phenocopying CD317 knockdown.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, confocal imaging of polarized epithelial cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction demonstrated, KD phenotype with defined cellular readout, independently convergent results from both CD317 and RICH2 KD\",\n      \"pmids\": [\"19273615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rich2 (ARHGAP44) is a Rac1-specific GAP that controls dendritic spine morphogenesis in hippocampal neurons. Overexpression increases spine size and decreases density; knockdown decreases both. The morphological changes are rescued by Rac1 inhibitor EHT 1864, placing Rich2 upstream of Rac1 in spine regulation.\",\n      \"method\": \"siRNA knockdown, overexpression, pharmacological Rac1 inhibition (EHT 1864) epistasis, miniature EPSC recording, immunofluorescence in cultured hippocampal neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with Rac1 inhibitor rescue, multiple orthogonal readouts (morphology + electrophysiology), KD and OE in same system\",\n      \"pmids\": [\"24352656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rich2 (ARHGAP44) physically interacts with the postsynaptic scaffolding protein Shank3 in dendritic spines, and this interaction is increased during LTP. Rich2 functions as an endosomal recycling regulator controlling AMPA receptor GluA1 subunit exocytosis and spine enlargement during LTP. Disruption of the Rich2-Shank3 complex (via siRNA or interfering peptide) inhibits LTP-associated spine enlargement and GluA1 exocytosis.\",\n      \"method\": \"Proteomic screen, bioluminescence resonance energy transfer (BRET) microscopy, siRNA knockdown, interfering mimetic peptide, GluA1 exocytosis assay in cultured hippocampal neurons\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — BRET-based interaction in live cells, two independent disruption strategies (siRNA + peptide), functional readouts of LTP\",\n      \"pmids\": [\"23739967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ArhGAP44 (ARHGAP44) contains an N-BAR domain that senses inward plasma membrane curvature generated by acto-myosin contractile forces at actin patches, recruiting the protein to nascent filopodia seed sites. The GAP domain then triggers local Rac-GTP hydrolysis, reducing actin polymerization and suppressing filopodia initiation in neurons. ArhGAP44 expression increases during neuronal development concurrent with decreased filopodia formation rate.\",\n      \"method\": \"Live-cell imaging, dominant-negative and constitutively active constructs, BAR domain membrane curvature binding assay, Rac-GTP pull-down, neuronal KD/OE with filopodia quantification\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — BAR domain curvature-sensing assay, Rac-GTP hydrolysis demonstrated, multiple orthogonal methods, domain-level dissection\",\n      \"pmids\": [\"25498153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In RICH2 knockout mice, synaptic Rac1 is disinhibited in vivo, leading to increased multiple spine synapses in hippocampus and cerebellum, altered receptor composition, and impaired actin polymerization, consistent with RICH2 acting as a negative regulator of Rac1 at postsynaptic densities.\",\n      \"method\": \"RICH2 KO mouse model, immunohistochemistry, electron microscopy, biochemical Rac1-GTP pull-down, behavioral testing\",\n      \"journal\": \"Molecular brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO with defined biochemical (Rac1-GTP) and structural phenotype, single lab\",\n      \"pmids\": [\"26969129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mutant p53 suppresses ARHGAP44 transcription, leading to elevated GTP-Cdc42 levels. Wild-type ARHGAP44 (but not GAP-dead R291A mutant) suppresses mutant-p53-mediated cell spreading and migration, establishing ARHGAP44 as a GAP for Cdc42 that restrains these behaviors.\",\n      \"method\": \"RNA-seq, RT-qPCR, Cdc42-GTP pull-down, overexpression of WT vs. R291A mutant ARHGAP44, cell spreading and migration assays\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — active-site mutagenesis (R291A) validates GAP activity requirement, Cdc42-GTP biochemical assay, single lab\",\n      \"pmids\": [\"28527113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In RICH2 KO mouse amygdala, RhoA (not Rac1) is disinhibited, associated with decreased actin polymerization capacity and reduced mature spines, indicating that RICH2 also negatively regulates RhoA signaling in this brain region.\",\n      \"method\": \"RICH2 KO mouse, RhoA-GTP pull-down, spine morphology analysis, c-fos immunostaining in amygdala\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO with RhoA-GTP biochemical readout, single lab, single brain region\",\n      \"pmids\": [\"28642683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RICH2 co-immunoprecipitates with endogenous Cdc42, Rac1, and β-catenin in hepatocellular carcinoma cells. RICH2 overexpression inhibits filopodia formation in a Cdc42-dependent manner and suppresses tumor growth in vivo.\",\n      \"method\": \"Co-immunoprecipitation, filopodia assay, stable overexpression, in vivo xenograft\",\n      \"journal\": \"Frontiers in bioscience (Landmark edition)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP with multiple substrates, in vivo confirmation, Cdc42-dependence established, single lab\",\n      \"pmids\": [\"31136984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD317 protects tumor cells from NK cell-mediated immunocytolysis through its association with RICH2, which modulates cytoskeletal flexibility to preserve membrane integrity against perforin.\",\n      \"method\": \"CD317 knockdown in tumor cells, NK and CAR-NK cytotoxicity assays, RICH2 interaction assessed, perforin sensitivity assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic link to RICH2 inferred from CD317-RICH2 association and phenotype, no direct RICH2 KD or reconstitution for this specific finding\",\n      \"pmids\": [\"33223223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Rich2/Arhgap44 is localized to postsynaptic densities via biochemical fractionation in mouse brain and is expressed in excitatory synapses of hippocampal CA1 at postnatal day 30, with nuclear accumulation also observed in cortical neurons at certain developmental stages.\",\n      \"method\": \"Immunohistochemistry, immunoblotting of tissue fractions, subcellular fractionation to postsynaptic density fraction\",\n      \"journal\": \"Developmental neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical fractionation establishing PSD localization in vivo, replicated across two brain regions and developmental time points, single lab\",\n      \"pmids\": [\"36630934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RICH2 overexpression in glioma cells decreases mitochondrial number and calcium flow, reduces mitochondrial fusion via downregulation of MFN-1/MFN-2 and upregulation of Drp-1, reduces mitochondrial release from glioma cells into extracellular environment, and downregulates the MAPK/ERK/HIF-1 pathway.\",\n      \"method\": \"Fluorescence microscopy, qRT-PCR, Western blot, electrophysiology in nude mouse glioma model, single-cell calcium imaging\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, overexpression only, pathway modulation inferred from protein-level changes without direct mechanistic dissection of RICH2-mitochondria link\",\n      \"pmids\": [\"37926169\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARHGAP44 (RICH2) is a Rho-GAP protein with an N-BAR membrane curvature-sensing domain that inactivates Rac1 (and Cdc42) by stimulating GTP hydrolysis; it is enriched at postsynaptic densities where it forms a complex with Shank3 to regulate AMPA receptor recycling, dendritic spine morphogenesis, and LTP, and at the apical surface of polarized epithelial cells where it bridges CD317/tetherin to the actin cytoskeleton via EBP50 and ezrin to maintain microvilli.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARHGAP44 (RICH2) is a Rho-family GTPase-activating protein that couples membrane geometry to actin remodeling, restraining Rac1, Cdc42, and RhoA signaling across neuronal and epithelial contexts [#1, #3, #5, #6]. Its N-BAR domain senses inward plasma membrane curvature generated by acto-myosin contractile forces, recruiting the protein to nascent filopodia sites where its GAP domain drives local Rac-GTP hydrolysis to suppress filopodia initiation in developing neurons [#3]. As a Rac1-specific GAP it controls dendritic spine morphogenesis, with loss-of-function disinhibiting synaptic Rac1 in vivo and altering spine number and receptor composition [#1, #4]; at postsynaptic densities it forms an LTP-regulated complex with Shank3 that governs endosomal recycling and GluA1 AMPA-receptor exocytosis during spine enlargement [#2, #9]. In polarized epithelial cells ARHGAP44 links CD317/tetherin to the apical actin cytoskeleton through EBP50 and ezrin, maintaining the apical actin network and microvilli [#0]. Its catalytic (R291A-sensitive) GAP activity toward Cdc42 restrains cell spreading and migration and is transcriptionally suppressed by mutant p53 [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established the first cellular role for RICH2 as a cytoskeletal adaptor, answering how the membrane protein CD317/tetherin is anchored to the apical actin network in polarized epithelia.\",\n      \"evidence\": \"siRNA knockdown, co-immunoprecipitation, and confocal imaging in polarized epithelial cells\",\n      \"pmids\": [\"19273615\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test GAP activity or a specific Rho GTPase in this epithelial context\", \"Direct binding stoichiometry within the EBP50/ezrin complex not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined RICH2 as a Rac1-specific GAP acting upstream of Rac1 to control dendritic spine morphology, answering which GTPase mediates its synaptic function.\",\n      \"evidence\": \"Knockdown/overexpression with Rac1-inhibitor (EHT 1864) epistasis rescue, mEPSC recording, and immunofluorescence in cultured hippocampal neurons\",\n      \"pmids\": [\"24352656\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address regulation of recruitment to spines\", \"Did not distinguish Rac1 from other potential substrates biochemically\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified the Shank3-RICH2 complex as an LTP-regulated machine controlling AMPA receptor recycling, connecting GAP function to synaptic plasticity output.\",\n      \"evidence\": \"Proteomic screen, BRET in live cells, siRNA and interfering peptide disruption, GluA1 exocytosis assay in hippocampal neurons\",\n      \"pmids\": [\"23739967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of LTP-induced interaction increase not defined\", \"Link between GAP catalysis and receptor exocytosis not directly dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed the mechanistic logic of curvature-sensing, showing the N-BAR domain reads acto-myosin-generated membrane curvature to target GAP activity and suppress filopodia initiation.\",\n      \"evidence\": \"Live-cell imaging, dominant-negative/constitutively-active constructs, BAR-domain curvature binding assay, Rac-GTP pull-down in neurons\",\n      \"pmids\": [\"25498153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of curvature sensing not tested\", \"Whether the same mechanism operates at spines or epithelial surfaces unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Confirmed RICH2 as an in vivo negative regulator of synaptic Rac1, linking its loss to structural and receptor-composition synaptic phenotypes.\",\n      \"evidence\": \"RICH2 knockout mouse with immunohistochemistry, electron microscopy, Rac1-GTP pull-down, and behavioral testing\",\n      \"pmids\": [\"26969129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Behavioral consequences not mechanistically tied to specific spine changes\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended the substrate repertoire to Cdc42 and RhoA and placed RICH2 in a tumor-suppressive transcriptional circuit downstream of mutant p53.\",\n      \"evidence\": \"RNA-seq/RT-qPCR, Cdc42-GTP and RhoA-GTP pull-downs, WT vs GAP-dead R291A overexpression, cell spreading/migration assays, and amygdala KO analysis\",\n      \"pmids\": [\"28527113\", \"28642683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Region- and context-specificity of substrate choice (Rac1 vs Cdc42 vs RhoA) unexplained\", \"Single lab for each substrate claim\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Documented physical association with Cdc42, Rac1, and β-catenin in carcinoma cells and a Cdc42-dependent anti-tumor, anti-filopodia function in vivo.\",\n      \"evidence\": \"Co-immunoprecipitation, filopodia assay, stable overexpression, and xenograft in hepatocellular carcinoma cells\",\n      \"pmids\": [\"31136984\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"β-catenin interaction functional significance not established\", \"GAP-dependence of tumor suppression not formally tested here\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Anchored RICH2 biochemically to the postsynaptic density in vivo and noted developmental nuclear accumulation, refining its subcellular localization.\",\n      \"evidence\": \"Subcellular fractionation, immunoblotting, and immunohistochemistry of mouse brain across regions and developmental stages\",\n      \"pmids\": [\"36630934\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of nuclear pool not addressed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Reported a non-canonical effect of RICH2 overexpression on mitochondrial dynamics and MAPK/ERK/HIF-1 signaling in glioma.\",\n      \"evidence\": \"Fluorescence microscopy, qRT-PCR, Western blot, calcium imaging, and glioma mouse model (overexpression only)\",\n      \"pmids\": [\"37926169\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Overexpression only, no loss-of-function\", \"Direct molecular link between RICH2 and mitochondrial machinery not dissected\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ARHGAP44 selects among Rac1, Cdc42, and RhoA in different cellular and tissue contexts, and how curvature sensing, scaffold binding, and transcriptional control are integrated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of substrate selectivity\", \"Mechanism coupling N-BAR recruitment to specific GTPase choice unknown\", \"No unified model across neuronal, epithelial, and tumor contexts\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0014069\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [\n      \"RICH2-Shank3 postsynaptic complex\",\n      \"CD317-EBP50-ezrin apical complex\"\n    ],\n    \"partners\": [\n      \"SHANK3\",\n      \"CD317\",\n      \"EBP50\",\n      \"EZR\",\n      \"RAC1\",\n      \"CDC42\",\n      \"RHOA\",\n      \"CTNNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}