Affinage

ARHGAP44

Rho GTPase-activating protein 44 · UniProt Q17R89

Length
818 aa
Mass
89.2 kDa
Annotated
2026-04-28
23 papers in source corpus 11 papers cited in narrative 11 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

ARHGAP44 (Rich2) is a RhoGAP-family protein that couples membrane curvature sensing to local GTPase inactivation, thereby controlling actin dynamics at neuronal and epithelial cell surfaces. Its N-BAR domain detects inward membrane curvature generated by acto-myosin contraction, recruiting the protein to actin patches where its GAP domain catalyzes hydrolysis of Rac1-GTP (and, context-dependently, Cdc42-GTP or RhoA-GTP), suppressing filopodia initiation and regulating dendritic spine morphogenesis (PMID:25498153, PMID:24352656, PMID:26969129, PMID:28642683, PMID:28527113). At excitatory synapses, ARHGAP44 forms a complex with the postsynaptic scaffold Shank3; this interaction is enhanced during long-term potentiation and is required for AMPA receptor GluA1 exocytosis and spine enlargement (PMID:23739967, PMID:36630934). In polarized epithelial cells, ARHGAP44 links CD317/tetherin to the apical actin cytoskeleton through EBP50 and ezrin, maintaining microvillar architecture and cortical membrane integrity (PMID:19273615, PMID:33223223).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2009 High

    Establishing that ARHGAP44 organizes the apical actin cytoskeleton in epithelial cells resolved how CD317/tetherin connects to the cortical cytoskeleton — RICH2, via EBP50 and ezrin, bridges this transmembrane protein to actin, and its loss phenocopies CD317 loss by ablating microvilli.

    Evidence siRNA knockdown with actin/microvilli phenotype readout and co-immunoprecipitation in polarized epithelial cells

    PMID:19273615

    Open questions at the time
    • Whether the GAP catalytic activity is required for the apical actin function or whether the scaffolding role alone suffices
    • Identity of the Rho-family GTPase substrate in epithelial cells
  2. 2013 High

    Two studies identified ARHGAP44 as a Rac1-specific GAP at postsynaptic sites and defined its complex with Shank3 during LTP, establishing the protein as a signaling node that couples Rac1 inactivation to AMPA receptor trafficking and spine remodeling.

    Evidence siRNA knockdown with pharmacological Rac1 inhibitor epistasis in hippocampal neurons; single-cell BRET microscopy detecting enhanced Rich2–Shank3 interaction during LTP; GluA1 exocytosis assay

    PMID:23739967 PMID:24352656

    Open questions at the time
    • Structural basis of the Rich2–Shank3 interaction
    • Whether Shank3 recruits Rich2 or vice versa at the PSD
    • Direct measurement of local Rac1-GTP levels at individual spines
  3. 2014 High

    Demonstrating that the N-BAR domain senses inward membrane curvature and recruits ARHGAP44 to actin patches before filopodia initiate answered how GAP activity is spatially targeted — curvature generated by acto-myosin contraction serves as a geometric cue for local Rac-GTP hydrolysis.

    Evidence Live imaging, domain mutagenesis, and curvature-sensing assays in neuronal cultures

    PMID:25498153

    Open questions at the time
    • Whether BAR-domain dimerization is required for curvature sensing in vivo
    • Quantitative relationship between membrane curvature threshold and recruitment kinetics
  4. 2016 High

    RICH2 knockout mice provided in vivo validation that endogenous RICH2 restrains synaptic Rac1, as hippocampal and cerebellar neurons showed elevated Rac1-GTP, aberrant multiple-spine synapses, and altered receptor composition.

    Evidence Constitutive KO mouse, G-LISA Rac1 activity assay, immunohistochemistry, spine morphology analysis

    PMID:26969129

    Open questions at the time
    • Behavioral consequences of the KO not fully mapped
    • Cell-type-specific contributions (excitatory vs. inhibitory neurons) not resolved
  5. 2017 Medium

    Extending the KO analysis to the amygdala revealed brain-region-specific substrate selectivity: RICH2 suppresses RhoA rather than Rac1 in this region, while a parallel study showed ARHGAP44 also functions as a Cdc42-GAP downstream of mutant p53 in non-neuronal cells.

    Evidence KO mouse RhoA activity assay in amygdala; RNA-Seq/RT-qPCR plus Cdc42 GTP-loading assay and GAP-dead R291A rescue in cancer cell lines

    PMID:28527113 PMID:28642683

    Open questions at the time
    • Molecular basis for brain-region-specific substrate selectivity is unknown
    • Whether p53-dependent transcriptional regulation of ARHGAP44 occurs in normal physiology
    • RhoA finding from a single lab, not independently replicated
  6. 2019 Medium

    Co-immunoprecipitation of RICH2 with endogenous Cdc42, Rac1, and β-catenin in hepatocellular carcinoma cells extended the GAP/scaffold model to Wnt-pathway regulation, suggesting a broader signaling integration role beyond neurons.

    Evidence Co-IP, overexpression-based filopodia and β-catenin level assays, xenograft model

    PMID:31136984

    Open questions at the time
    • Direct GAP activity on Cdc42 in this context not measured with purified protein
    • Mechanism linking RICH2 to β-catenin degradation unresolved
  7. 2020 Medium

    The CD317–RICH2 axis was shown to protect tumor cells from NK-cell perforin-mediated killing by maintaining cortical cytoskeletal integrity, extending the epithelial scaffolding function to immune evasion.

    Evidence siRNA knockdown with NK/CAR-NK cytotoxicity assay and recombinant protein rescue

    PMID:33223223

    Open questions at the time
    • Whether RICH2 GAP activity or scaffolding underlies membrane protection is untested
    • In vivo relevance to tumor immune evasion not established
  8. 2023 Medium

    Subcellular fractionation confirmed RICH2 residence in the postsynaptic density at mature excitatory synapses and revealed a developmental shift from nuclear to synaptic localization in cortical neurons.

    Evidence PSD fractionation, immunohistochemistry across developmental stages in mouse brain

    PMID:36630934

    Open questions at the time
    • Functional significance of the early nuclear localization is unknown
    • No live-imaging confirmation of developmental redistribution

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis for N-BAR and GAP domain cooperativity, the mechanism of brain-region-specific GTPase substrate selection, and whether the GAP-independent scaffolding functions in epithelial and immune contexts require distinct binding interfaces.
  • No crystal or cryo-EM structure of ARHGAP44
  • No reconstituted system testing simultaneous curvature sensing and GAP catalysis
  • Separation of GAP versus scaffold functions not achieved in vivo

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 6 GO:0008092 cytoskeletal protein binding 2 GO:0060090 molecular adaptor activity 2
Localization
GO:0005886 plasma membrane 3 GO:0005856 cytoskeleton 2 GO:0005829 cytosol 1
Pathway
R-HSA-162582 Signal Transduction 5 R-HSA-112316 Neuronal System 4
Partners
BST2CDC42CTNNB1EZRRAC1SHANK3SLC9A3R1
Complex memberships
CD317–RICH2–EBP50–ezrin apical complexRich2–Shank3 postsynaptic complex

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2014 ArhGAP44 suppresses filopodia initiation in neurons by recruiting to actin patches via an N-BAR domain that senses inward membrane curvature generated by acto-myosin contractile forces, then using its GAP domain to trigger local Rac-GTP hydrolysis, thereby reducing actin polymerization needed for filopodia formation. Live imaging, domain mutagenesis, loss-of-function knockdown with filopodia-initiation phenotype readout, N-BAR curvature-sensing assay eLife High 25498153
2013 Rich2 (ARHGAP44) acts as a Rac1-specific GTPase-activating protein in hippocampal neurons, where its GAP activity controls dendritic spine morphogenesis; Rac1 inhibitor EHT1864 rescued the spine phenotype caused by Rich2 knockdown, placing Rich2 upstream of Rac1 in the spine-morphology pathway. siRNA knockdown, overexpression, pharmacological Rac1 inhibition epistasis, miniature EPSC recording The Journal of biological chemistry High 24352656
2013 Rich2 (ARHGAP44) physically interacts with the postsynaptic scaffolding protein Shank3; this interaction is enhanced in dendritic spines during LTP (detected by BRET), and the Rich2–Shank3 complex controls AMPA receptor GluA1 subunit exocytosis and spine enlargement during LTP. Proteomic screen, single-cell bioluminescence resonance energy transfer (BRET) microscopy, siRNA knockdown, interfering mimetic peptide disruption, GluA1 exocytosis assay The Journal of neuroscience High 23739967
2009 RICH2 (ARHGAP44) links CD317/tetherin to the apical actin cytoskeleton in polarized epithelial cells via a complex that includes EBP50 and ezrin; knockdown of RICH2 phenocopies CD317 knockdown, causing loss of the apical actin network and microvilli without disrupting tight junctions or polarity. siRNA knockdown with actin/microvilli phenotype readout, co-immunoprecipitation, cell fractionation The Journal of cell biology High 19273615
2016 RICH2 KO mice display disinhibition of synaptic Rac1 in vivo (hippocampus and cerebellum), accompanied by increased multiple-spine synapses, alterations in receptor composition, and impaired actin polymerization, confirming that endogenous RICH2 restrains Rac1 activity at synapses. Constitutive knockout mouse model, biochemical Rac1 activity assay (G-LISA), immunohistochemistry, spine morphology analysis Molecular brain High 26969129
2017 RICH2 KO in mice leads to disinhibition of RhoA (not Rac1) specifically in the amygdala, with decreased actin polymerization and reduced mature spines in that region, indicating that RICH2 also suppresses RhoA activity in a brain-region-specific manner. Knockout mouse model, RhoA activity assay, phalloidin-actin staining, spine morphology analysis, c-fos immunolabeling Frontiers in molecular neuroscience Medium 28642683
2017 Mutant p53 suppresses ARHGAP44 transcription, leading to elevated GTP-Cdc42 levels; wild-type ARHGAP44 but not a GAP-dead mutant (R291A) rescues cell spreading and migration, establishing ARHGAP44 as a Cdc42-GAP that limits cell spreading downstream of p53 status. RNA-Seq, RT-qPCR, Cdc42 GTP-loading assay, overexpression of wild-type vs. R291A GAP-dead mutant, wound-healing and migration assays Science China. Life sciences Medium 28527113
2019 RICH2 co-immunoprecipitates with endogenous Cdc42, Rac1, and β-catenin in hepatocellular carcinoma cells; RICH2 overexpression suppresses Cdc42-dependent filopodia formation and reduces β-catenin levels, consistent with a GAP/scaffold role linking RICH2 to Wnt signaling. Co-immunoprecipitation, overexpression, filopodia morphology assay, Western blot, in vivo xenograft Frontiers in bioscience (Landmark edition) Medium 31136984
2020 CD317 protects tumor cells from NK-cell immunocytolysis through its association with RICH2, which modulates the cortical cytoskeleton to preserve membrane integrity against perforin; CD317 knockdown increased tumor cell killing by NK cells, and this was mechanistically linked to loss of RICH2-mediated cytoskeletal support. siRNA knockdown, NK/CAR-NK cytotoxicity assay, recombinant protein rescue experiment Molecular immunology Medium 33223223
2023 Rich2/ARHGAP44 is detected in the postsynaptic density by biochemical fractionation and localizes to excitatory synapses of the CA1 region by P30 in mouse brain, with a developmental stage-dependent nuclear vs. cytoplasmic vs. neuropil distribution in cortical neurons. Subcellular fractionation, immunohistochemistry, Western blot across developmental stages Developmental neuroscience Medium 36630934
2023 RICH2 overexpression in glioma cells decreases mitochondrial number and extracellular mitochondrial release into neurons by downregulating MFN-1/MFN-2 (mitochondrial fusion) and upregulating Drp-1, and suppresses calcium motility; these effects are associated with downregulation of the MAPK/ERK/HIF-1 pathway and promotion of epilepsy in a mouse glioma model. Fluorescence microscopy (mitochondrial tracking), qRT-PCR, Western blot, electrophysiology in nude mouse glioma model Neurobiology of disease Low 37926169

Source papers

Stage 0 corpus · 23 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 A CD317/tetherin-RICH2 complex plays a critical role in the organization of the subapical actin cytoskeleton in polarized epithelial cells. The Journal of cell biology 112 19273615
2021 Modulation of transforming growth factor-β-induced kidney fibrosis by leucine-rich ⍺-2 glycoprotein-1. Kidney international 76 34774561
2013 Shank3-Rich2 interaction regulates AMPA receptor recycling and synaptic long-term potentiation. The Journal of neuroscience : the official journal of the Society for Neuroscience 52 23739967
1998 Structural and transglutaminase substrate properties of the small proline-rich 2 family of cornified cell envelope proteins. The Journal of biological chemistry 51 9722562
2014 Dynamic recruitment of the curvature-sensitive protein ArhGAP44 to nanoscale membrane deformations limits exploratory filopodia initiation in neurons. eLife 45 25498153
2013 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. The Journal of biological chemistry 27 24352656
2016 Enlarged dendritic spines and pronounced neophobia in mice lacking the PSD protein RICH2. Molecular brain 24 26969129
2004 Estrogen regulates the expression of the small proline-rich 2 gene family in the mouse uterus. Molecules and cells 21 15232223
2017 Mutant p53 promotes cell spreading and migration via ARHGAP44. Science China. Life sciences 14 28527113
2017 Object Phobia and Altered RhoA Signaling in Amygdala of Mice Lacking RICH2. Frontiers in molecular neuroscience 11 28642683
2021 Brewing rich 2-phenylethanol beer from cassava and its producing metabolisms in yeast. Journal of the science of food and agriculture 8 33349937
2020 CD317 mediates immunocytolysis resistance by RICH2/cytoskeleton-dependent membrane protection. Molecular immunology 7 33223223
2019 RICH2, a potential tumor suppressor in hepatocellular carcinoma. Frontiers in bioscience (Landmark edition) 7 31136984
2022 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. Bioengineered 6 34974809
2018 The evolution of phase constitution and microstructure in iron-rich 2:17-type Sm-Co magnets with high magnetic performance. Scientific reports 6 29904086
1999 Acquisition of ordered conformation by the N-terminal domain of the human small proline rich 2 protein. Biochemical and biophysical research communications 5 10462486
2023 RICH2 decreases the mitochondrial number and affects mitochondrial localization in diffuse low-grade glioma-related epilepsy. Neurobiology of disease 4 37926169
2023 Expression Analyses of Rich2/Arhgap44, a Rho Family GTPase-Activating Protein, during Mouse Brain Development. Developmental neuroscience 2 36630934
2017 RICH2 is implicated in viraemic control of HIV-1 in black South African individuals. Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases 2 28069446
2017 Structural and inhibition analysis of novel sulfur-rich 2-mercaptobenzothiazole and 1,2,3-triazole ligands against Mycobacterium tuberculosis DprE1 enzyme. Journal of molecular modeling 2 28744747
2025 Evidence of a novel gene locus ARHGAP44 for longitudinal change in hemoglobin A1c levels among subjects without diabetes from the Long Life Family Study. Physiological genomics 1 40019798
2023 ARHGAP44-mediated regulation of the p53/C-myc/Cyclin D1 pathway in modulating the malignant biological behavior of osteosarcoma cells. Journal of orthopaedic surgery and research 1 38031136
2024 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). bioRxiv : the preprint server for biology 0 38826208