{"gene":"ARPC1B","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2004,"finding":"ARPC1B (p41-Arc) physically interacts with PAK1 both in vitro and in vivo, and PAK1 phosphorylates ARPC1B on threonine 21 within the first WD repeat. This phosphorylation regulates ARPC1B localization with the Arp2/3 complex at cortical nucleation regions and is required for both constitutive and growth-factor-induced cell motility.","method":"In vitro kinase assay, co-immunoprecipitation, site-directed mutagenesis (T21A), cell motility assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation assay with mutagenesis plus in vivo co-IP and functional motility readout in a single focused study","pmids":["14749719"],"is_preprint":false},{"year":2010,"finding":"ARPC1B colocalizes with gamma-tubulin at centrosomes and acts as both a physiological activator and substrate of Aurora A kinase. Aurora A phosphorylates ARPC1B on threonine 21; expression of wild-type but not non-phosphorylatable ARPC1B leads to Aurora A activation and abnormal centrosome amplification. Depletion of ARPC1B inhibits Aurora A activation at the centrosome and impairs mitotic entry.","method":"Immunofluorescence colocalization, in vitro kinase assay, Aurora A activity assay, siRNA depletion, overexpression of phosphomutant ARPC1B","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with phosphomutant validation plus functional cellular phenotypes in a single focused study","pmids":["20603326"],"is_preprint":false},{"year":2017,"finding":"Loss of ARPC1B in platelets abolishes Arp2/3 complex assembly (greatly reduced Arp2/3 complex detected in platelet lysates), causes aberrant platelet spreading consistent with loss of Arp2/3-dependent actin branching, and leads to microthrombocytopenia. Knockout of ARPC1B in megakaryocytic cells decreases proplatelet formation. Loss of ARPC1B is accompanied by compensatory upregulation of ARPC1A, but the two isoforms are not functionally interchangeable.","method":"Western blot of patient platelet lysates, platelet spreading assay, ARPC1B knockout in megakaryocytic cell lines, patient genetics (homozygous frameshift)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (patient proteomics, spreading assay, KO cell line), replicated in two unrelated patients","pmids":["28368018"],"is_preprint":false},{"year":2017,"finding":"ARPC1B is required for T cell and thrombocyte development in zebrafish; loss-of-function ARPC1B defects are rescued by wild-type human ARPC1B but not by the patient frameshift variant p.V208VfsX20, establishing the causality of this variant. ARPC1B expression is restricted to hematopoietic cells.","method":"Zebrafish ARPC1B morpholino knockdown / genetic loss-of-function, rescue with human ARPC1B cDNA versus mutant variant, whole-exome sequencing","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via rescue experiment in zebrafish with orthologous human construct, multiple developmental lineages assessed","pmids":["29127144"],"is_preprint":false},{"year":2018,"finding":"ARPC1B deficiency in T cells impairs Arp2/3-dependent actin-rich lamellipodia extension upon TCR stimulation, prevents immunological synapse assembly, and causes defective TCR-mediated proliferation and SDF1-α-directed migration. Lentiviral gene transfer of ARPC1B into patient-derived T cells restored ARPC1B expression and T-cell proliferation, confirming direct causality.","method":"Confocal microscopy (lamellipodia/immunological synapse), proliferation assays, migration assays, lentiviral gene correction, flow cytometry","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays plus lentiviral rescue in patient cells, replicated across six unrelated patients","pmids":["30254128"],"is_preprint":false},{"year":2019,"finding":"ARPC1B is required for CTL lamellipodia formation, actin reorganization at the immune synapse, and polarized lytic granule secretion. Additionally, ARPC1B is indispensable for retromer/WASH-dependent recycling of TCR, CD8, and GLUT1 to the plasma membrane; loss of ARPC1B causes depletion of these surface proteins, impaired T cell signaling and proliferation, and progressive CD8+ T cell loss.","method":"ARPC1B-deficient patient CTL assays, cytotoxicity assays, imaging of immune synapse, flow cytometry of surface TCR/CD8/GLUT1, retromer/WASH complex functional assessment","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (cytotoxicity, imaging, flow cytometry, vesicle recycling pathway) in patient cells, identifies two distinct mechanistic levels","pmids":["31710310"],"is_preprint":false},{"year":2021,"finding":"ARPC1B-containing Arp2/3 complexes are stimulated by WASP to nucleate branched actin networks. Despite ARPC1A upregulation, ARPC1B-deficient cells are incapable of WASP-mediated Arp2/3 nucleation, demonstrating that ARPC1B specifically mediates WASP-stimulated actin branching. Loss of this activity weakens the cortical F-actin cytoskeleton in B cells, increases BCR diffusion, and causes elevated tonic lipid signaling, oscillatory calcium release from the ER, and elevated phospho-Akt.","method":"Actin nucleation assay (WASP-stimulated), podosome formation assay in macrophages, lamellipodia assay in B cells, calcium imaging, BCR diffusion (single-molecule or FRAP), Akt phosphorylation, patient ARPC1B-deficient cells","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — actin nucleation assay directly testing WASP-ARP2/3 activity plus multiple downstream signaling readouts in patient-derived cells","pmids":["34673575"],"is_preprint":false},{"year":2021,"finding":"ARPC1B-deficient neutrophils show defective actin polymerization and are able to transmigrate through TNF-α-activated endothelium with decreased efficiency under physiological flow conditions but show severe impairment in subendothelial crawling, 3D collagen matrix migration, and vessel-on-a-chip locomotion, indicating that Arp2/3-dependent actin branching via ARPC1B is specifically required for post-transmigration migration modes.","method":"Flow-based neutrophil transmigration assay, subendothelial crawling assay, 3D collagen matrix migration, vessel-on-a-chip model, patient ARPC1B-deficient neutrophils","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional migration assays in patient-derived cells; single lab, no genetic rescue shown","pmids":["34135903"],"is_preprint":false},{"year":2021,"finding":"EVA1A promotes endothelial cell migration partly through ARPC1B as a downstream effector; siRNA-mediated knockdown of ARPC1B downstream of EVA1A ablates EVA1A-promoted migration. Proteomics revealed reduced Arpc1b levels when EVA1A is absent, and Rac1/Cdc42 GTPase activation is regulated by EVA1A upstream of Arpc1b.","method":"Proteomics, siRNA knockdown, transwell/scratch migration assays, Rac1/Cdc42 activation assay, Eva1a-/- mouse model","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — siRNA epistasis and proteomics place ARPC1B downstream of EVA1A/Rac1/Cdc42; single lab, no rescue","pmids":["31977009"],"is_preprint":false},{"year":2011,"finding":"Overexpression of ARPC1B (p41-Arc) in p53/Rb-deficient human osteosarcoma cells (SaOs-2) induces premature senescence, characterized by SA-β-galactosidase activity, irreversible cell cycle exit, and nuclear accumulation of actin filaments, demonstrating a p53/Rb-independent senescence-inducing role linked to actin cytoskeletal reorganization.","method":"ARPC1B overexpression in SaOs-2 cells, SA-β-gal assay, actin staining, cell cycle analysis","journal":"Experimental & molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single overexpression experiment, single lab, limited mechanistic follow-up","pmids":["21628992"],"is_preprint":false},{"year":2022,"finding":"ARPC1B interacts with IFI16 (via IFI16 Pyrin domain) and HuR (via RRM2 domain) in glioma stem cells, protecting both proteins from TRIM21-mediated ubiquitination and degradation, thereby sustaining NF-κB (via IFI16) and STAT3 (via HuR) signaling and maintaining the mesenchymal GSC phenotype and radioresistance.","method":"Co-immunoprecipitation, mass spectrometry, ubiquitination assay, deletion mutant constructs, in vitro and in vivo knockdown/overexpression, intracranial xenograft model","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with domain-mapping mutants plus ubiquitination assay; single lab","pmids":["36380368"],"is_preprint":false},{"year":2024,"finding":"ARPC1B in GBM tumor cells inhibits NEDD4L-mediated ubiquitination of STAT1 and promotes the USP7–STAT1 deubiquitinase interaction, thereby stabilizing STAT1, increasing IL-10 production, and inducing protumorigenic macrophage polarization that contributes to immune checkpoint blockade resistance.","method":"Co-immunoprecipitation (ARPC1B-STAT1-NEDD4L-USP7), ubiquitination assay, ARPC1B knockdown, GBM mouse models, ICB combination treatment","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus ubiquitination assay identifying E3 and DUB; single lab","pmids":["39841088"],"is_preprint":false},{"year":2024,"finding":"ARPC1B-deficient iPSC-derived neutrophils (iNeutrophils) show impaired migration and switch from pseudopod formation to elongated filopodia, indicating that ARPC1B/Arp2/3-dependent branched actin is specifically required for pseudopod-based motility. Additionally, ARPC1B deficiency in endothelium (blood vessel-on-a-chip) independently impairs neutrophil transmigration, with combined neutrophil+endothelial ARPC1B deficiency causing additive migration reduction.","method":"iPSC-derived ARPC1B-KO neutrophils, blood vessel-on-a-chip model, live-cell migration imaging, primary human ARPC1B-deficient endothelial cells","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — iPSC genetic model plus vessel-on-a-chip functional system; novel cell-intrinsic vs. extrinsic dissection; single lab","pmids":["38224139"],"is_preprint":false},{"year":2022,"finding":"ARPC1B deficiency in patients is associated with increased radiosensitivity, manifested as elevated chromatid-type chromosomal aberrations, increased γH2AX foci, and G2/M cell cycle arrest after ionizing radiation or bleomycin treatment, implicating ARPC1B/Arp2/3 in double-strand break clustering for homology-directed repair.","method":"Cytogenetic aberration assay, γH2AX immunofluorescence, cell cycle analysis (G2/M), radiomimetic bleomycin treatment in patient-derived cells","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal DNA-damage assays in patient-derived cells; single lab; mechanistic link to DSB repair pathway established by phenotypic convergence","pmids":["35967303"],"is_preprint":false},{"year":2025,"finding":"CK-636, a known Arp2/3 complex inhibitor, directly binds ARPC1B protein with high affinity as determined by surface plasmon resonance and molecular docking, providing a mechanistic basis for CK-636 activity and identifying ARPC1B as a druggable target in pancreatic cancer stem cells.","method":"Surface plasmon resonance (SPR), molecular docking, in vitro cytotoxicity, organoid cultures, in vivo xenograft/orthotopic models","journal":"Cell proliferation","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — SPR provides direct binding evidence; single lab, no mutagenesis validation of binding site","pmids":["40903212"],"is_preprint":false},{"year":2026,"finding":"ARPC1B binds IGF2BP3 and prevents its ubiquitination and degradation; IGF2BP3 in turn stabilizes HK2 mRNA, promoting glycolytic reprogramming in gastric cancer. Co-immunoprecipitation and RNA immunoprecipitation confirmed the ARPC1B–IGF2BP3 interaction and IGF2BP3–HK2 mRNA binding; HK2 overexpression rescued anti-glycolytic effects of ARPC1B knockdown.","method":"Co-immunoprecipitation, confocal microscopy, RNA immunoprecipitation, actinomycin D mRNA stability assay, ARPC1B KD/OE, in vivo xenograft","journal":"European journal of medical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus RNA-IP and mRNA stability assay with rescue experiment; single lab","pmids":["41803983"],"is_preprint":false},{"year":2026,"finding":"NAA30, an N-alpha-acetyltransferase, directly binds ARPC1B and N-terminally acetylates it; NAA30 knockdown enhances polyubiquitination and proteasomal degradation of ARPC1B, and re-expression of ARPC1B in NAA30-silenced ovarian cancer cells rescues malignant phenotypes, placing ARPC1B as the critical downstream effector of the NR2C2–NAA30 axis.","method":"Co-immunoprecipitation, IP–LC/MS, N-terminal acetylation modification omics, ubiquitination assay, ARPC1B re-expression rescue, dual-luciferase assay (for upstream NR2C2)","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — proteomics-identified acetylation with Co-IP and rescue; single lab","pmids":["41615304"],"is_preprint":false}],"current_model":"ARPC1B is a regulatory subunit of the Arp2/3 complex that is predominantly expressed in hematopoietic cells; it is phosphorylated on Thr21 by both PAK1 (regulating cortical actin localization and cell motility) and Aurora A (regulating centrosomal homeostasis and mitotic entry), N-terminally acetylated by NAA30 (protecting it from ubiquitin-mediated degradation), and specifically mediates WASP-stimulated branched actin nucleation—a function that cannot be compensated by the ARPC1A isoform—thereby controlling lamellipodia formation, immune synapse assembly, lytic granule secretion, neutrophil migration, B cell receptor tonic signaling, platelet spreading and proplatelet formation, and double-strand break repair, while in non-hematopoietic cancer contexts ARPC1B has additional non-actin scaffolding roles including stabilizing IFI16/HuR from TRIM21-mediated degradation, stabilizing STAT1 via USP7 interaction to drive IL-10/macrophage immunosuppression, and protecting IGF2BP3 from degradation to sustain glycolysis."},"narrative":{"mechanistic_narrative":"ARPC1B is a hematopoietically-enriched regulatory subunit of the Arp2/3 complex that mediates WASP-stimulated nucleation of branched actin networks, an activity that the ARPC1A isoform cannot compensate for despite its compensatory upregulation [PMID:28368018, PMID:34673575]. Loss of ARPC1B abolishes Arp2/3 complex assembly and disables WASP-dependent actin branching, weakening the cortical F-actin cytoskeleton and crippling actin-driven processes across immune and platelet lineages: lamellipodia extension, immunological synapse assembly, polarized lytic granule secretion, neutrophil pseudopod-based and post-transmigration migration, B-cell receptor confinement, and proplatelet formation [PMID:28368018, PMID:30254128, PMID:31710310, PMID:34673575, PMID:34135903, PMID:38224139]. In T cells, ARPC1B additionally supports retromer/WASH-dependent recycling of TCR, CD8, and GLUT1 to the plasma membrane, coupling its actin role to surface receptor homeostasis and signaling [PMID:31710310]. Patient frameshift mutations cause an inborn error of immunity with microthrombocytopenia, defective T-cell and thrombocyte development, and increased radiosensitivity; causality is established by rescue with wild-type but not mutant ARPC1B in zebrafish and in patient-derived T cells [PMID:28368018, PMID:29127144, PMID:30254128, PMID:35967303]. ARPC1B activity is tuned by Thr21 phosphorylation within its first WD repeat—by PAK1 to control cortical Arp2/3 localization and motility, and by Aurora A to govern centrosomal homeostasis and mitotic entry—and its abundance is stabilized against ubiquitin-mediated degradation by NAA30-dependent N-terminal acetylation [PMID:14749719, PMID:20603326, PMID:41615304]. In non-hematopoietic cancer contexts, ARPC1B exerts non-canonical scaffolding roles, stabilizing partner proteins (IFI16/HuR, STAT1, IGF2BP3) against ubiquitination to sustain oncogenic signaling, immunosuppression, and glycolytic reprogramming [PMID:36380368, PMID:39841088, PMID:41803983].","teleology":[{"year":2004,"claim":"Established that ARPC1B is a phosphoregulated subunit, showing PAK1 phosphorylates it on Thr21 to control its localization with Arp2/3 at cortical nucleation sites and cell motility.","evidence":"In vitro kinase assay, co-IP, T21A mutagenesis, and motility assays","pmids":["14749719"],"confidence":"High","gaps":["Did not address tissue specificity of this regulation","Did not test whether T21 phosphorylation alters actin nucleation kinetics directly"]},{"year":2010,"claim":"Revealed a second kinase axis where ARPC1B is both an activator and Thr21 substrate of Aurora A, linking it to centrosomal homeostasis and mitotic entry beyond cortical actin.","evidence":"Immunofluorescence colocalization with gamma-tubulin, in vitro kinase assay, Aurora A activity assay, siRNA depletion, phosphomutant overexpression","pmids":["20603326"],"confidence":"High","gaps":["Whether the centrosomal role depends on Arp2/3 complex assembly is unresolved","Relationship between the PAK1 and Aurora A Thr21 inputs not reconciled"]},{"year":2017,"claim":"Defined ARPC1B as a non-redundant, hematopoietically-restricted Arp2/3 subunit whose loss is causative for human disease, abolishing complex assembly and causing microthrombocytopenia and defective platelet/thrombocyte and T-cell development.","evidence":"Patient platelet proteomics, spreading assays, megakaryocyte KO cell lines, and zebrafish loss-of-function with human cDNA rescue versus mutant variant","pmids":["28368018","29127144"],"confidence":"High","gaps":["Molecular basis for ARPC1A's inability to substitute not defined at this stage","Did not establish the biochemical defect in actin nucleation"]},{"year":2018,"claim":"Localized the T-cell defect to Arp2/3-dependent lamellipodia and immunological synapse assembly, with lentiviral gene correction confirming cell-intrinsic causality.","evidence":"Confocal imaging, proliferation and migration assays, lentiviral rescue in patient T cells across six unrelated patients","pmids":["30254128"],"confidence":"High","gaps":["Did not address whether defects extend beyond actin to membrane trafficking"]},{"year":2019,"claim":"Uncovered a dual mechanism in CTLs whereby ARPC1B drives synapse actin and lytic granule secretion and also supports retromer/WASH-dependent surface recycling of TCR, CD8, and GLUT1.","evidence":"Patient CTL cytotoxicity, synapse imaging, surface receptor flow cytometry, and retromer/WASH functional assessment","pmids":["31710310"],"confidence":"High","gaps":["Direct molecular link between ARPC1B and the WASH/retromer machinery not mapped","Whether surface depletion is a primary or secondary consequence unclear"]},{"year":2021,"claim":"Provided the biochemical basis for ARPC1B's non-redundancy by showing it specifically mediates WASP-stimulated branched actin nucleation, the loss of which weakens cortical actin and dysregulates BCR tonic signaling.","evidence":"WASP-stimulated actin nucleation assays, podosome/lamellipodia assays, BCR diffusion (FRAP/single-molecule), calcium imaging, and phospho-Akt in patient cells","pmids":["34673575"],"confidence":"High","gaps":["Structural determinant of WASP-specific stimulation in ARPC1B vs ARPC1A not defined"]},{"year":2021,"claim":"Refined the neutrophil migration defect, showing ARPC1B/Arp2/3 branched actin is dispensable for transmigration efficiency but essential for subendothelial crawling and 3D matrix locomotion.","evidence":"Flow-based transmigration, subendothelial crawling, 3D collagen migration, and vessel-on-a-chip assays in patient neutrophils","pmids":["34135903"],"confidence":"Medium","gaps":["No genetic rescue performed","Single lab; molecular distinction between migration modes not resolved"]},{"year":2024,"claim":"Used a genetic iPSC model to attribute the migration defect to a switch from pseudopod to filopodia and dissected cell-intrinsic neutrophil from extrinsic endothelial contributions.","evidence":"ARPC1B-KO iPSC-derived neutrophils, primary deficient endothelial cells, and blood vessel-on-a-chip live imaging","pmids":["38224139"],"confidence":"Medium","gaps":["Single lab","Mechanism of the pseudopod-to-filopod switch not defined at molecular level"]},{"year":2022,"claim":"Extended ARPC1B function to genome maintenance, linking its deficiency to radiosensitivity, chromatid aberrations, and G2/M arrest, implicating Arp2/3-dependent actin in double-strand break repair.","evidence":"Cytogenetic aberration assays, gammaH2AX foci, and cell cycle analysis after ionizing radiation/bleomycin in patient cells","pmids":["35967303"],"confidence":"Medium","gaps":["Mechanistic link to DSB clustering inferred from phenotypic convergence, not direct","Single lab; no rescue"]},{"year":2026,"claim":"Identified post-translational control of ARPC1B abundance, showing NAA30-mediated N-terminal acetylation protects it from polyubiquitination and proteasomal degradation.","evidence":"Co-IP, IP-LC/MS, N-terminal acetylation omics, ubiquitination assay, and re-expression rescue in ovarian cancer cells","pmids":["41615304"],"confidence":"Medium","gaps":["Single lab","Whether acetylation affects Arp2/3 assembly or only stability is untested"]},{"year":2024,"claim":"Defined non-canonical scaffolding roles in cancer whereby ARPC1B stabilizes partner proteins against ubiquitination to sustain oncogenic and immunosuppressive signaling.","evidence":"Reciprocal Co-IP with domain mapping, ubiquitination assays, RNA-IP, and in vivo tumor/macrophage models for IFI16/HuR, STAT1, and IGF2BP3","pmids":["36380368","39841088","41803983"],"confidence":"Medium","gaps":["Each interaction shown by single lab","Whether these scaffolding roles require Arp2/3 complex incorporation is unknown","Generalizability beyond the specific tumor types not established"]},{"year":2025,"claim":"Demonstrated ARPC1B is directly druggable, with the Arp2/3 inhibitor CK-636 binding ARPC1B at high affinity, nominating it as a therapeutic target in cancer stem cells.","evidence":"Surface plasmon resonance, molecular docking, organoid cytotoxicity, and xenograft models in pancreatic cancer","pmids":["40903212"],"confidence":"Medium","gaps":["Binding site not validated by mutagenesis","Single lab"]},{"year":null,"claim":"It remains unresolved how a single subunit reconciles its canonical Arp2/3 branched-actin role with the distinct centrosomal, DNA-repair, and ubiquitin-protective scaffolding functions, and whether the cancer scaffolding roles operate independently of the Arp2/3 complex.","evidence":"No single study integrates the actin, mitotic, and scaffolding functions","pmids":[],"confidence":"Low","gaps":["No structural model distinguishing ARPC1B from ARPC1A function","Unknown whether scaffolding partners require Arp2/3 incorporation","Cross-talk between phosphorylation and acetylation control of ARPC1B undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,6]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,6]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[10,11,15]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,6]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[1]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5,6,7]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[2]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1]}],"complexes":["Arp2/3 complex"],"partners":["PAK1","AURKA","WASP","NAA30","IFI16","STAT1","IGF2BP3","USP7"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15143","full_name":"Actin-related protein 2/3 complex subunit 1B","aliases":["Arp2/3 complex 41 kDa subunit","p41-ARC"],"length_aa":372,"mass_kda":41.0,"function":"Component of the Arp2/3 complex, a multiprotein complex that mediates actin polymerization upon stimulation by nucleation-promoting factor (NPF) (PubMed:11741539, PubMed:9230079). The Arp2/3 complex mediates the formation of branched actin networks in the cytoplasm, providing the force for cell motility (PubMed:11741539, PubMed:9230079). In addition to its role in the cytoplasmic cytoskeleton, the Arp2/3 complex also promotes actin polymerization in the nucleus, thereby regulating gene transcription and repair of damaged DNA (PubMed:29925947). The Arp2/3 complex promotes homologous recombination (HR) repair in response to DNA damage by promoting nuclear actin polymerization, leading to drive motility of double-strand breaks (DSBs) (PubMed:29925947)","subcellular_location":"Cytoplasm, cytoskeleton; Nucleus","url":"https://www.uniprot.org/uniprotkb/O15143/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ARPC1B","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ARL6IP5","stoichiometry":10.0},{"gene":"ARPC3","stoichiometry":10.0},{"gene":"ACTR2","stoichiometry":4.0},{"gene":"ARPC2","stoichiometry":4.0},{"gene":"ACTB","stoichiometry":0.2},{"gene":"ACTG1","stoichiometry":0.2},{"gene":"ACTN4","stoichiometry":0.2},{"gene":"ARL6IP6","stoichiometry":0.2},{"gene":"BCAR1","stoichiometry":0.2},{"gene":"CALD1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ARPC1B","total_profiled":1310},"omim":[{"mim_id":"621450","title":"ACTIN-RELATED PROTEIN 2/3 COMPLEX, SUBUNIT 5-LIKE; ARPC5L","url":"https://www.omim.org/entry/621450"},{"mim_id":"617718","title":"IMMUNODEFICIENCY 71 WITH INFLAMMATORY DISEASE AND CONGENITAL THROMBOCYTOPENIA; IMD71","url":"https://www.omim.org/entry/617718"},{"mim_id":"604227","title":"ACTIN-RELATED PROTEIN 2/3 COMPLEX, SUBUNIT 5; ARPC5","url":"https://www.omim.org/entry/604227"},{"mim_id":"604226","title":"ACTIN-RELATED PROTEIN 2/3 COMPLEX, SUBUNIT 4; ARPC4","url":"https://www.omim.org/entry/604226"},{"mim_id":"604225","title":"ACTIN-RELATED PROTEIN 2/3 COMPLEX, SUBUNIT 3; ARPC3","url":"https://www.omim.org/entry/604225"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":288.1}],"url":"https://www.proteinatlas.org/search/ARPC1B"},"hgnc":{"alias_symbol":["ARC41","p40-ARC","p41-ARC"],"prev_symbol":[]},"alphafold":{"accession":"O15143","domains":[{"cath_id":"2.130.10.10","chopping":"212-287_322-372","consensus_level":"medium","plddt":95.5195,"start":212,"end":372}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15143","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15143-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15143-F1-predicted_aligned_error_v6.png","plddt_mean":92.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARPC1B","jax_strain_url":"https://www.jax.org/strain/search?query=ARPC1B"},"sequence":{"accession":"O15143","fasta_url":"https://rest.uniprot.org/uniprotkb/O15143.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15143/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15143"}},"corpus_meta":[{"pmid":"28368018","id":"PMC_28368018","title":"Loss of the Arp2/3 complex component ARPC1B causes platelet abnormalities and predisposes to inflammatory disease.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/28368018","citation_count":163,"is_preprint":false},{"pmid":"14749719","id":"PMC_14749719","title":"p41-Arc subunit of human Arp2/3 complex is a p21-activated kinase-1-interacting substrate.","date":"2004","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/14749719","citation_count":116,"is_preprint":false},{"pmid":"30254128","id":"PMC_30254128","title":"T-cell defects in patients with ARPC1B germline mutations account for combined immunodeficiency.","date":"2018","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/30254128","citation_count":98,"is_preprint":false},{"pmid":"31710310","id":"PMC_31710310","title":"Loss of ARPC1B impairs cytotoxic T lymphocyte maintenance and cytolytic activity.","date":"2019","source":"The Journal of clinical 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This phosphorylation regulates ARPC1B localization with the Arp2/3 complex at cortical nucleation regions and is required for both constitutive and growth-factor-induced cell motility.\",\n      \"method\": \"In vitro kinase assay, co-immunoprecipitation, site-directed mutagenesis (T21A), cell motility assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation assay with mutagenesis plus in vivo co-IP and functional motility readout in a single focused study\",\n      \"pmids\": [\"14749719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ARPC1B colocalizes with gamma-tubulin at centrosomes and acts as both a physiological activator and substrate of Aurora A kinase. Aurora A phosphorylates ARPC1B on threonine 21; expression of wild-type but not non-phosphorylatable ARPC1B leads to Aurora A activation and abnormal centrosome amplification. Depletion of ARPC1B inhibits Aurora A activation at the centrosome and impairs mitotic entry.\",\n      \"method\": \"Immunofluorescence colocalization, in vitro kinase assay, Aurora A activity assay, siRNA depletion, overexpression of phosphomutant ARPC1B\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with phosphomutant validation plus functional cellular phenotypes in a single focused study\",\n      \"pmids\": [\"20603326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of ARPC1B in platelets abolishes Arp2/3 complex assembly (greatly reduced Arp2/3 complex detected in platelet lysates), causes aberrant platelet spreading consistent with loss of Arp2/3-dependent actin branching, and leads to microthrombocytopenia. Knockout of ARPC1B in megakaryocytic cells decreases proplatelet formation. Loss of ARPC1B is accompanied by compensatory upregulation of ARPC1A, but the two isoforms are not functionally interchangeable.\",\n      \"method\": \"Western blot of patient platelet lysates, platelet spreading assay, ARPC1B knockout in megakaryocytic cell lines, patient genetics (homozygous frameshift)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (patient proteomics, spreading assay, KO cell line), replicated in two unrelated patients\",\n      \"pmids\": [\"28368018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ARPC1B is required for T cell and thrombocyte development in zebrafish; loss-of-function ARPC1B defects are rescued by wild-type human ARPC1B but not by the patient frameshift variant p.V208VfsX20, establishing the causality of this variant. ARPC1B expression is restricted to hematopoietic cells.\",\n      \"method\": \"Zebrafish ARPC1B morpholino knockdown / genetic loss-of-function, rescue with human ARPC1B cDNA versus mutant variant, whole-exome sequencing\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via rescue experiment in zebrafish with orthologous human construct, multiple developmental lineages assessed\",\n      \"pmids\": [\"29127144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ARPC1B deficiency in T cells impairs Arp2/3-dependent actin-rich lamellipodia extension upon TCR stimulation, prevents immunological synapse assembly, and causes defective TCR-mediated proliferation and SDF1-α-directed migration. Lentiviral gene transfer of ARPC1B into patient-derived T cells restored ARPC1B expression and T-cell proliferation, confirming direct causality.\",\n      \"method\": \"Confocal microscopy (lamellipodia/immunological synapse), proliferation assays, migration assays, lentiviral gene correction, flow cytometry\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays plus lentiviral rescue in patient cells, replicated across six unrelated patients\",\n      \"pmids\": [\"30254128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ARPC1B is required for CTL lamellipodia formation, actin reorganization at the immune synapse, and polarized lytic granule secretion. Additionally, ARPC1B is indispensable for retromer/WASH-dependent recycling of TCR, CD8, and GLUT1 to the plasma membrane; loss of ARPC1B causes depletion of these surface proteins, impaired T cell signaling and proliferation, and progressive CD8+ T cell loss.\",\n      \"method\": \"ARPC1B-deficient patient CTL assays, cytotoxicity assays, imaging of immune synapse, flow cytometry of surface TCR/CD8/GLUT1, retromer/WASH complex functional assessment\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (cytotoxicity, imaging, flow cytometry, vesicle recycling pathway) in patient cells, identifies two distinct mechanistic levels\",\n      \"pmids\": [\"31710310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ARPC1B-containing Arp2/3 complexes are stimulated by WASP to nucleate branched actin networks. Despite ARPC1A upregulation, ARPC1B-deficient cells are incapable of WASP-mediated Arp2/3 nucleation, demonstrating that ARPC1B specifically mediates WASP-stimulated actin branching. Loss of this activity weakens the cortical F-actin cytoskeleton in B cells, increases BCR diffusion, and causes elevated tonic lipid signaling, oscillatory calcium release from the ER, and elevated phospho-Akt.\",\n      \"method\": \"Actin nucleation assay (WASP-stimulated), podosome formation assay in macrophages, lamellipodia assay in B cells, calcium imaging, BCR diffusion (single-molecule or FRAP), Akt phosphorylation, patient ARPC1B-deficient cells\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — actin nucleation assay directly testing WASP-ARP2/3 activity plus multiple downstream signaling readouts in patient-derived cells\",\n      \"pmids\": [\"34673575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ARPC1B-deficient neutrophils show defective actin polymerization and are able to transmigrate through TNF-α-activated endothelium with decreased efficiency under physiological flow conditions but show severe impairment in subendothelial crawling, 3D collagen matrix migration, and vessel-on-a-chip locomotion, indicating that Arp2/3-dependent actin branching via ARPC1B is specifically required for post-transmigration migration modes.\",\n      \"method\": \"Flow-based neutrophil transmigration assay, subendothelial crawling assay, 3D collagen matrix migration, vessel-on-a-chip model, patient ARPC1B-deficient neutrophils\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional migration assays in patient-derived cells; single lab, no genetic rescue shown\",\n      \"pmids\": [\"34135903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EVA1A promotes endothelial cell migration partly through ARPC1B as a downstream effector; siRNA-mediated knockdown of ARPC1B downstream of EVA1A ablates EVA1A-promoted migration. Proteomics revealed reduced Arpc1b levels when EVA1A is absent, and Rac1/Cdc42 GTPase activation is regulated by EVA1A upstream of Arpc1b.\",\n      \"method\": \"Proteomics, siRNA knockdown, transwell/scratch migration assays, Rac1/Cdc42 activation assay, Eva1a-/- mouse model\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — siRNA epistasis and proteomics place ARPC1B downstream of EVA1A/Rac1/Cdc42; single lab, no rescue\",\n      \"pmids\": [\"31977009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Overexpression of ARPC1B (p41-Arc) in p53/Rb-deficient human osteosarcoma cells (SaOs-2) induces premature senescence, characterized by SA-β-galactosidase activity, irreversible cell cycle exit, and nuclear accumulation of actin filaments, demonstrating a p53/Rb-independent senescence-inducing role linked to actin cytoskeletal reorganization.\",\n      \"method\": \"ARPC1B overexpression in SaOs-2 cells, SA-β-gal assay, actin staining, cell cycle analysis\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single overexpression experiment, single lab, limited mechanistic follow-up\",\n      \"pmids\": [\"21628992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ARPC1B interacts with IFI16 (via IFI16 Pyrin domain) and HuR (via RRM2 domain) in glioma stem cells, protecting both proteins from TRIM21-mediated ubiquitination and degradation, thereby sustaining NF-κB (via IFI16) and STAT3 (via HuR) signaling and maintaining the mesenchymal GSC phenotype and radioresistance.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, ubiquitination assay, deletion mutant constructs, in vitro and in vivo knockdown/overexpression, intracranial xenograft model\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with domain-mapping mutants plus ubiquitination assay; single lab\",\n      \"pmids\": [\"36380368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ARPC1B in GBM tumor cells inhibits NEDD4L-mediated ubiquitination of STAT1 and promotes the USP7–STAT1 deubiquitinase interaction, thereby stabilizing STAT1, increasing IL-10 production, and inducing protumorigenic macrophage polarization that contributes to immune checkpoint blockade resistance.\",\n      \"method\": \"Co-immunoprecipitation (ARPC1B-STAT1-NEDD4L-USP7), ubiquitination assay, ARPC1B knockdown, GBM mouse models, ICB combination treatment\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus ubiquitination assay identifying E3 and DUB; single lab\",\n      \"pmids\": [\"39841088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ARPC1B-deficient iPSC-derived neutrophils (iNeutrophils) show impaired migration and switch from pseudopod formation to elongated filopodia, indicating that ARPC1B/Arp2/3-dependent branched actin is specifically required for pseudopod-based motility. Additionally, ARPC1B deficiency in endothelium (blood vessel-on-a-chip) independently impairs neutrophil transmigration, with combined neutrophil+endothelial ARPC1B deficiency causing additive migration reduction.\",\n      \"method\": \"iPSC-derived ARPC1B-KO neutrophils, blood vessel-on-a-chip model, live-cell migration imaging, primary human ARPC1B-deficient endothelial cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — iPSC genetic model plus vessel-on-a-chip functional system; novel cell-intrinsic vs. extrinsic dissection; single lab\",\n      \"pmids\": [\"38224139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ARPC1B deficiency in patients is associated with increased radiosensitivity, manifested as elevated chromatid-type chromosomal aberrations, increased γH2AX foci, and G2/M cell cycle arrest after ionizing radiation or bleomycin treatment, implicating ARPC1B/Arp2/3 in double-strand break clustering for homology-directed repair.\",\n      \"method\": \"Cytogenetic aberration assay, γH2AX immunofluorescence, cell cycle analysis (G2/M), radiomimetic bleomycin treatment in patient-derived cells\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal DNA-damage assays in patient-derived cells; single lab; mechanistic link to DSB repair pathway established by phenotypic convergence\",\n      \"pmids\": [\"35967303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CK-636, a known Arp2/3 complex inhibitor, directly binds ARPC1B protein with high affinity as determined by surface plasmon resonance and molecular docking, providing a mechanistic basis for CK-636 activity and identifying ARPC1B as a druggable target in pancreatic cancer stem cells.\",\n      \"method\": \"Surface plasmon resonance (SPR), molecular docking, in vitro cytotoxicity, organoid cultures, in vivo xenograft/orthotopic models\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — SPR provides direct binding evidence; single lab, no mutagenesis validation of binding site\",\n      \"pmids\": [\"40903212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ARPC1B binds IGF2BP3 and prevents its ubiquitination and degradation; IGF2BP3 in turn stabilizes HK2 mRNA, promoting glycolytic reprogramming in gastric cancer. Co-immunoprecipitation and RNA immunoprecipitation confirmed the ARPC1B–IGF2BP3 interaction and IGF2BP3–HK2 mRNA binding; HK2 overexpression rescued anti-glycolytic effects of ARPC1B knockdown.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy, RNA immunoprecipitation, actinomycin D mRNA stability assay, ARPC1B KD/OE, in vivo xenograft\",\n      \"journal\": \"European journal of medical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus RNA-IP and mRNA stability assay with rescue experiment; single lab\",\n      \"pmids\": [\"41803983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NAA30, an N-alpha-acetyltransferase, directly binds ARPC1B and N-terminally acetylates it; NAA30 knockdown enhances polyubiquitination and proteasomal degradation of ARPC1B, and re-expression of ARPC1B in NAA30-silenced ovarian cancer cells rescues malignant phenotypes, placing ARPC1B as the critical downstream effector of the NR2C2–NAA30 axis.\",\n      \"method\": \"Co-immunoprecipitation, IP–LC/MS, N-terminal acetylation modification omics, ubiquitination assay, ARPC1B re-expression rescue, dual-luciferase assay (for upstream NR2C2)\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — proteomics-identified acetylation with Co-IP and rescue; single lab\",\n      \"pmids\": [\"41615304\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARPC1B is a regulatory subunit of the Arp2/3 complex that is predominantly expressed in hematopoietic cells; it is phosphorylated on Thr21 by both PAK1 (regulating cortical actin localization and cell motility) and Aurora A (regulating centrosomal homeostasis and mitotic entry), N-terminally acetylated by NAA30 (protecting it from ubiquitin-mediated degradation), and specifically mediates WASP-stimulated branched actin nucleation—a function that cannot be compensated by the ARPC1A isoform—thereby controlling lamellipodia formation, immune synapse assembly, lytic granule secretion, neutrophil migration, B cell receptor tonic signaling, platelet spreading and proplatelet formation, and double-strand break repair, while in non-hematopoietic cancer contexts ARPC1B has additional non-actin scaffolding roles including stabilizing IFI16/HuR from TRIM21-mediated degradation, stabilizing STAT1 via USP7 interaction to drive IL-10/macrophage immunosuppression, and protecting IGF2BP3 from degradation to sustain glycolysis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARPC1B is a hematopoietically-enriched regulatory subunit of the Arp2/3 complex that mediates WASP-stimulated nucleation of branched actin networks, an activity that the ARPC1A isoform cannot compensate for despite its compensatory upregulation [#2, #6]. Loss of ARPC1B abolishes Arp2/3 complex assembly and disables WASP-dependent actin branching, weakening the cortical F-actin cytoskeleton and crippling actin-driven processes across immune and platelet lineages: lamellipodia extension, immunological synapse assembly, polarized lytic granule secretion, neutrophil pseudopod-based and post-transmigration migration, B-cell receptor confinement, and proplatelet formation [#2, #4, #5, #6, #7, #12]. In T cells, ARPC1B additionally supports retromer/WASH-dependent recycling of TCR, CD8, and GLUT1 to the plasma membrane, coupling its actin role to surface receptor homeostasis and signaling [#5]. Patient frameshift mutations cause an inborn error of immunity with microthrombocytopenia, defective T-cell and thrombocyte development, and increased radiosensitivity; causality is established by rescue with wild-type but not mutant ARPC1B in zebrafish and in patient-derived T cells [#2, #3, #4, #13]. ARPC1B activity is tuned by Thr21 phosphorylation within its first WD repeat—by PAK1 to control cortical Arp2/3 localization and motility, and by Aurora A to govern centrosomal homeostasis and mitotic entry—and its abundance is stabilized against ubiquitin-mediated degradation by NAA30-dependent N-terminal acetylation [#0, #1, #16]. In non-hematopoietic cancer contexts, ARPC1B exerts non-canonical scaffolding roles, stabilizing partner proteins (IFI16/HuR, STAT1, IGF2BP3) against ubiquitination to sustain oncogenic signaling, immunosuppression, and glycolytic reprogramming [#10, #11, #15].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that ARPC1B is a phosphoregulated subunit, showing PAK1 phosphorylates it on Thr21 to control its localization with Arp2/3 at cortical nucleation sites and cell motility.\",\n      \"evidence\": \"In vitro kinase assay, co-IP, T21A mutagenesis, and motility assays\",\n      \"pmids\": [\"14749719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address tissue specificity of this regulation\", \"Did not test whether T21 phosphorylation alters actin nucleation kinetics directly\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealed a second kinase axis where ARPC1B is both an activator and Thr21 substrate of Aurora A, linking it to centrosomal homeostasis and mitotic entry beyond cortical actin.\",\n      \"evidence\": \"Immunofluorescence colocalization with gamma-tubulin, in vitro kinase assay, Aurora A activity assay, siRNA depletion, phosphomutant overexpression\",\n      \"pmids\": [\"20603326\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the centrosomal role depends on Arp2/3 complex assembly is unresolved\", \"Relationship between the PAK1 and Aurora A Thr21 inputs not reconciled\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined ARPC1B as a non-redundant, hematopoietically-restricted Arp2/3 subunit whose loss is causative for human disease, abolishing complex assembly and causing microthrombocytopenia and defective platelet/thrombocyte and T-cell development.\",\n      \"evidence\": \"Patient platelet proteomics, spreading assays, megakaryocyte KO cell lines, and zebrafish loss-of-function with human cDNA rescue versus mutant variant\",\n      \"pmids\": [\"28368018\", \"29127144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis for ARPC1A's inability to substitute not defined at this stage\", \"Did not establish the biochemical defect in actin nucleation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Localized the T-cell defect to Arp2/3-dependent lamellipodia and immunological synapse assembly, with lentiviral gene correction confirming cell-intrinsic causality.\",\n      \"evidence\": \"Confocal imaging, proliferation and migration assays, lentiviral rescue in patient T cells across six unrelated patients\",\n      \"pmids\": [\"30254128\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether defects extend beyond actin to membrane trafficking\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Uncovered a dual mechanism in CTLs whereby ARPC1B drives synapse actin and lytic granule secretion and also supports retromer/WASH-dependent surface recycling of TCR, CD8, and GLUT1.\",\n      \"evidence\": \"Patient CTL cytotoxicity, synapse imaging, surface receptor flow cytometry, and retromer/WASH functional assessment\",\n      \"pmids\": [\"31710310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between ARPC1B and the WASH/retromer machinery not mapped\", \"Whether surface depletion is a primary or secondary consequence unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided the biochemical basis for ARPC1B's non-redundancy by showing it specifically mediates WASP-stimulated branched actin nucleation, the loss of which weakens cortical actin and dysregulates BCR tonic signaling.\",\n      \"evidence\": \"WASP-stimulated actin nucleation assays, podosome/lamellipodia assays, BCR diffusion (FRAP/single-molecule), calcium imaging, and phospho-Akt in patient cells\",\n      \"pmids\": [\"34673575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural determinant of WASP-specific stimulation in ARPC1B vs ARPC1A not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Refined the neutrophil migration defect, showing ARPC1B/Arp2/3 branched actin is dispensable for transmigration efficiency but essential for subendothelial crawling and 3D matrix locomotion.\",\n      \"evidence\": \"Flow-based transmigration, subendothelial crawling, 3D collagen migration, and vessel-on-a-chip assays in patient neutrophils\",\n      \"pmids\": [\"34135903\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No genetic rescue performed\", \"Single lab; molecular distinction between migration modes not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Used a genetic iPSC model to attribute the migration defect to a switch from pseudopod to filopodia and dissected cell-intrinsic neutrophil from extrinsic endothelial contributions.\",\n      \"evidence\": \"ARPC1B-KO iPSC-derived neutrophils, primary deficient endothelial cells, and blood vessel-on-a-chip live imaging\",\n      \"pmids\": [\"38224139\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism of the pseudopod-to-filopod switch not defined at molecular level\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended ARPC1B function to genome maintenance, linking its deficiency to radiosensitivity, chromatid aberrations, and G2/M arrest, implicating Arp2/3-dependent actin in double-strand break repair.\",\n      \"evidence\": \"Cytogenetic aberration assays, gammaH2AX foci, and cell cycle analysis after ionizing radiation/bleomycin in patient cells\",\n      \"pmids\": [\"35967303\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link to DSB clustering inferred from phenotypic convergence, not direct\", \"Single lab; no rescue\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified post-translational control of ARPC1B abundance, showing NAA30-mediated N-terminal acetylation protects it from polyubiquitination and proteasomal degradation.\",\n      \"evidence\": \"Co-IP, IP-LC/MS, N-terminal acetylation omics, ubiquitination assay, and re-expression rescue in ovarian cancer cells\",\n      \"pmids\": [\"41615304\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Whether acetylation affects Arp2/3 assembly or only stability is untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined non-canonical scaffolding roles in cancer whereby ARPC1B stabilizes partner proteins against ubiquitination to sustain oncogenic and immunosuppressive signaling.\",\n      \"evidence\": \"Reciprocal Co-IP with domain mapping, ubiquitination assays, RNA-IP, and in vivo tumor/macrophage models for IFI16/HuR, STAT1, and IGF2BP3\",\n      \"pmids\": [\"36380368\", \"39841088\", \"41803983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each interaction shown by single lab\", \"Whether these scaffolding roles require Arp2/3 complex incorporation is unknown\", \"Generalizability beyond the specific tumor types not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated ARPC1B is directly druggable, with the Arp2/3 inhibitor CK-636 binding ARPC1B at high affinity, nominating it as a therapeutic target in cancer stem cells.\",\n      \"evidence\": \"Surface plasmon resonance, molecular docking, organoid cytotoxicity, and xenograft models in pancreatic cancer\",\n      \"pmids\": [\"40903212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site not validated by mutagenesis\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how a single subunit reconciles its canonical Arp2/3 branched-actin role with the distinct centrosomal, DNA-repair, and ubiquitin-protective scaffolding functions, and whether the cancer scaffolding roles operate independently of the Arp2/3 complex.\",\n      \"evidence\": \"No single study integrates the actin, mitotic, and scaffolding functions\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model distinguishing ARPC1B from ARPC1A function\", \"Unknown whether scaffolding partners require Arp2/3 incorporation\", \"Cross-talk between phosphorylation and acetylation control of ARPC1B undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [10, 11, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5, 6, 7]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"Arp2/3 complex\"],\n    \"partners\": [\"PAK1\", \"AURKA\", \"WASP\", \"NAA30\", \"IFI16\", \"STAT1\", \"IGF2BP3\", \"USP7\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}