{"gene":"ARPC2","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2008,"finding":"Mutagenesis of the p35/ARPC2 subunit in S. cerevisiae identified three distinct functional surfaces: one face required for actin nucleation and endocytosis, a second site near the ARPC2-ARPC4 contact required for nucleation and endocytosis, and a third distal conserved surface required for endocytosis but not nucleation. Purified mutant Arp2/3 complexes confirmed loss of actin assembly activity, establishing ARPC2 as a structurally critical subunit for Arp2/3-mediated actin nucleation.","method":"Site-directed mutagenesis of conserved solvent-exposed residues, in vitro actin assembly assays with purified mutant Arp2/3 complexes, yeast cell growth and endocytosis phenotype analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified proteins + mutagenesis + multiple cellular phenotype readouts in single rigorous study","pmids":["18381280"],"is_preprint":false},{"year":2019,"finding":"Benproperine (Benp) directly binds ARPC2 (identified by affinity column chromatography with Benp-tagged Sepharose beads, validated by pulldown with Benp-biotin, DARTS, and CETSA), inhibits Arp2/3 complex-dependent actin polymerization, disrupts lamellipodial structure, and suppresses cancer cell migration and metastasis. ARPC2 knockdown phenocopied Benp treatment, confirming ARPC2 as the functional target.","method":"Affinity column chromatography, pulldown with Benp-biotin, DARTS, CETSA, actin polymerization assay, siRNA knockdown, in vivo metastasis model","journal":"Biochemical pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal target-engagement methods (affinity pull-down, DARTS, CETSA) plus functional validation by knockdown, replicated with independent stereoisomer study","pmids":["30710516"],"is_preprint":false},{"year":2019,"finding":"Pimozide directly binds ARPC2 (confirmed by DARTS and CETSA), increases the lag phase of Arp2/3 complex-dependent actin polymerization, and inhibits vinculin-mediated recruitment of ARPC2 to focal adhesions. ARPC2 point mutants (F225A, F247A, Y250F) generated by CRISPR/Cas9 revealed a binding pocket on ARPC2 required for pimozide interaction.","method":"DARTS, CETSA, actin polymerization assay, CRISPR/Cas9 point-mutant cell lines, focal adhesion immunofluorescence","journal":"Cancer science","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal binding assays plus mutagenesis defining binding pocket, single lab","pmids":["31571309"],"is_preprint":false},{"year":2022,"finding":"S-Benproperine, the active stereoisomer of benproperine, directly binds ARPC2 at residue F225 (ARPC2-F225A mutant abolishes binding by CETSA and DARTS), co-localizes with ARPC2 in cancer cells and tumor tissues, and suppresses actin remodeling including lamellipodium formation.","method":"Surface plasmon resonance (SPR), CETSA, DARTS, CRISPR/Cas9 ARPC2-F225A mutant cells, Cy3-conjugated S-Benp co-localization, actin polymerization assay","journal":"Pharmaceuticals (Basel, Switzerland)","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — SPR, CETSA, DARTS, and site-specific mutagenesis defining binding residue in single study","pmids":["36558913"],"is_preprint":false},{"year":2013,"finding":"NADPH oxidase 1 (Nox1) mediates H2O2-induced upregulation of ARPC2 protein expression in vascular smooth muscle cells (VSMCs) via a p38 MAPK-dependent pathway, and ARPC2 is required downstream of Nox1 for H2O2-stimulated VSMC migration.","method":"2D-DIGE/mass spectrometry proteomics, Western blot, siRNA knockdown of Nox1 and ARPC2, p38 MAPK inhibitor (SB203580), wound-healing scratch assay","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomics discovery plus functional validation by gene silencing and pharmacological inhibition, single lab","pmids":["24152438"],"is_preprint":false},{"year":2019,"finding":"The longer 5'-UTR splice variant of ARPC2 mRNA harbors an internal ribosome entry site (IRES) containing a guanine-quadruplex (G-quadruplex) motif that promotes cap-independent translation; the shorter variant lacks this activity. At high cell density, relative ARPC2 protein levels increase, consistent with IRES-driven expression under conditions that compromise cap-dependent translation.","method":"Bicistronic reporter construct, multiple IRES control assays, chemical probing of RNA structure, G-quadruplex structural analysis, cell density-dependent protein level measurement","journal":"RNA biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bicistronic reporter with multiple controls, G-quadruplex structural validation, single lab","pmids":["31387452"],"is_preprint":false},{"year":2015,"finding":"Plant ARPC2 protein (a core Arp2/3 complex subunit) directly interacts with microtubules in addition to actin filaments; a putative MT-binding domain was identified by in vitro co-sedimentation of truncated NtARPC2 proteins with microtubules. GFP-ARPC2 decorated microtubules in tobacco BY-2 cells and Arabidopsis root epidermal cells.","method":"In vitro co-sedimentation assay with truncated ARPC2 proteins, pharmacological interference with actin/MT dynamics, live-cell GFP imaging","journal":"Plant science : an international journal of experimental plant biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro co-sedimentation with domain mapping plus live-cell imaging, but plant ortholog and single lab","pmids":["26706062"],"is_preprint":false},{"year":2019,"finding":"RBM3 upregulates ARPC2 protein expression through a post-transcriptional mechanism involving binding to the 3'-UTR of ARPC2 mRNA, and ARPC2 mediates the pro-proliferative and pro-metastatic effects of RBM3 in breast cancer cells.","method":"siRNA knockdown of RBM3 and ARPC2, 3'-UTR binding assay, cell proliferation and migration assays, epistasis (ARPC2 knockdown rescues RBM3 overexpression phenotype)","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — 3'-UTR binding plus functional epistasis, but mechanistic detail on direct RBM3-ARPC2 3'UTR interaction is limited to abstract description","pmids":["30720048"],"is_preprint":false},{"year":2014,"finding":"FOXF1 transcriptionally represses ARPC2 expression in normal lung fibroblasts; ARPC2 knockdown inhibits cell growth and COL1 expression, placing ARPC2 downstream of FOXF1 in the regulation of fibroblast proliferation and collagen production. In IPF fibroblasts, FOXF1-mediated repression of ARPC2 is blunted.","method":"siRNA knockdown (FOXF1 and ARPC2), gain-of-function/loss-of-function models, cell growth assay, COL1 expression measurement, epistasis analysis","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with ARPC2 knockdown phenocopying FOXF1 overexpression, single lab, two methods","pmids":["25260753"],"is_preprint":false},{"year":2026,"finding":"ARPC2 regulates TGF-β1-induced nuclear translocation of myocardin-related transcription factor-A (MRTFA) and modulates MRTFA/G-actin complex formation in lung fibroblasts, promoting fibrotic gene expression (including ACTA2) at the transcriptional level independently of other ARP2/3 complex components. Transcriptomic analysis showed ARPC2 and MRTFA co-regulate a specific repertoire of fibrotic genes.","method":"ARPC2 modulation (overexpression/knockdown), MRTFA nuclear localization imaging, MRTFA/G-actin complex assay, transcriptomic analysis of ARPC2/ACTR2/MRTFA-depleted cells","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal readouts (localization, complex formation, transcriptomics), single lab, 2026 publication not yet replicated","pmids":["41898590"],"is_preprint":false},{"year":2023,"finding":"Inhibition of ARPC2 with benproperine (BPP) disrupts intestinal stem cell (ISC) homeostasis: at lower doses it promotes and at higher doses it inhibits intestinal organoid growth and crypt cell proliferation; it decreases Lgr5 ISC feature gene expression and reduces Paneth cell differentiation. Mechanistically, ARPC2 inhibition activates the YAP1 (Yes1-associated transcriptional regulator) pathway, linking actin polymerization to ISC regulation.","method":"Organoid culture, BrdU/EdU incorporation, flow cytometry, IHC, phalloidin staining for F-actin, in vivo mouse experiments with BPP","journal":"Burns & trauma","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pharmacological inhibition with multiple cellular readouts and proposed pathway (YAP), but no direct genetic rescue or mechanistic confirmation of YAP link","pmids":["37849945"],"is_preprint":false},{"year":2025,"finding":"KLF7-IT1 (a lncRNA) stabilizes ARPC2 protein in macrophages, thereby facilitating intracellular LPS internalization and downstream caspase-4 activation; ARPC2 silencing attenuates caspase-4 activation, gasdermin-D-mediated pyroptosis, phosphatidylserine exposure, and tissue factor activity, placing ARPC2 as a cytoskeletal mediator connecting LPS sensing to pyroptosis and hypercoagulation in sepsis.","method":"siRNA knockdown of ARPC2, caspase-4 activity assay, gasdermin-D cleavage measurement, phosphatidylserine exposure assay, tissue factor activity assay, LPS internalization imaging","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, functional knockdown with mechanistic readouts but abstract-level detail; lncRNA stabilization mechanism not directly validated","pmids":["41275797"],"is_preprint":false},{"year":2024,"finding":"Overexpression of Palladin in ArpC2-knockout cells rescues EPEC pedestal length, demonstrating that Palladin can substitute for Arp2/3 complex function in actin pedestal elongation during EPEC infection.","method":"ArpC2-/- cell lines, Palladin overexpression rescue experiment, EPEC pedestal length quantification, Palladin actin-binding domain and VASP-binding domain mutants","journal":"Cytoskeleton (Hoboken, N.J.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis using knockout cell line with rescue experiment and domain-mutant controls","pmids":["39692253"],"is_preprint":false}],"current_model":"ARPC2 (p34-Arc/ARC34) is a structurally essential subunit of the Arp2/3 complex whose distinct functional surfaces (mapped by mutagenesis in yeast) are required for actin nucleation and endocytosis; it directly contacts the mother actin filament, is regulated at the translational level via an IRES/G-quadruplex in its 5'-UTR, is upregulated downstream of Nox1/p38 MAPK signaling in smooth muscle cells, is transcriptionally repressed by FOXF1 in fibroblasts, and—in a function separable from other Arp2/3 subunits—regulates MRTFA nuclear translocation and fibrotic gene expression; small molecules (benproperine, pimozide) that bind directly to ARPC2 at defined residues (including F225) inhibit Arp2/3-dependent actin polymerization and cancer cell migration, confirming ARPC2 as a druggable subunit of the complex."},"narrative":{"mechanistic_narrative":"ARPC2 (p34-Arc) is a structurally essential subunit of the Arp2/3 complex that drives branched actin nucleation and the actin-dependent processes of endocytosis and cell migration [PMID:18381280]. Mutagenesis in yeast resolved three distinct functional surfaces on ARPC2: one face and a second site near the ARPC2-ARPC4 contact are both required for actin nucleation and endocytosis, while a third conserved distal surface is required for endocytosis but not nucleation, and purified mutant complexes confirmed loss of actin assembly activity [PMID:18381280]. Within the assembled complex ARPC2 is a druggable target: the small molecules benproperine (its active S-stereoisomer engaging residue F225) and pimozide bind directly to defined ARPC2 pockets, increase the lag phase of Arp2/3-dependent actin polymerization, disrupt lamellipodia, and suppress cancer cell migration and metastasis [PMID:30710516, PMID:31571309, PMID:36558913]. Pimozide binding additionally blocks vinculin-mediated recruitment of ARPC2 to focal adhesions [PMID:31571309]. ARPC2 abundance is controlled at multiple post-transcriptional and transcriptional levels — through an IRES/G-quadruplex element in the longer 5'-UTR splice variant that supports cap-independent translation [PMID:31387452], by RBM3 acting on the 3'-UTR [PMID:30720048], by Nox1/p38 MAPK signaling that upregulates ARPC2 to drive smooth muscle cell migration [PMID:24152438], and by FOXF1-mediated transcriptional repression in fibroblasts [PMID:25260753]. Beyond its canonical complex role, ARPC2 regulates TGF-β1-induced nuclear translocation of MRTFA and modulates MRTFA/G-actin complex formation to promote fibrotic gene expression independently of other Arp2/3 subunits [PMID:41898590].","teleology":[{"year":2008,"claim":"Established whether ARPC2 is a passive scaffold or an active contributor to Arp2/3 nucleation by resolving which of its surfaces are functionally required.","evidence":"Site-directed mutagenesis of conserved residues in yeast with purified mutant complex in vitro actin assays and endocytosis phenotyping","pmids":["18381280"],"confidence":"High","gaps":["Surface assignments derived in yeast; human residue-level function not directly mapped here","Does not address how ARPC2 contacts the mother filament structurally","No connection to upstream regulatory inputs"]},{"year":2013,"claim":"Connected ARPC2 expression to a defined signaling axis, showing it is a regulated effector rather than a constitutively constant subunit.","evidence":"Proteomics plus siRNA knockdown of Nox1/ARPC2 and p38 inhibition in vascular smooth muscle cell migration assays","pmids":["24152438"],"confidence":"Medium","gaps":["Mechanism by which p38 MAPK raises ARPC2 protein is not resolved","Single cell type (VSMC)","No direct link to transcription versus translation control"]},{"year":2014,"claim":"Identified a transcriptional repressor of ARPC2 and linked ARPC2 to fibroblast proliferation and collagen output.","evidence":"siRNA knockdown of FOXF1 and ARPC2 with growth and COL1 readouts and epistasis in lung fibroblasts","pmids":["25260753"],"confidence":"Medium","gaps":["Direct FOXF1 binding to the ARPC2 promoter not demonstrated","Mechanism of blunted repression in IPF fibroblasts unclear"]},{"year":2015,"claim":"Tested whether ARPC2 binding is restricted to actin, finding a microtubule-binding capacity in the plant ortholog.","evidence":"In vitro co-sedimentation of truncated NtARPC2 with microtubules and live-cell GFP imaging in tobacco/Arabidopsis","pmids":["26706062"],"confidence":"Medium","gaps":["Plant ortholog; relevance to mammalian ARPC2 untested","Functional consequence of MT binding not established"]},{"year":2019,"claim":"Defined how ARPC2 protein levels are tuned post-transcriptionally, identifying both a 5'-UTR IRES/G-quadruplex and a 3'-UTR-dependent RBM3 input.","evidence":"Bicistronic reporters with G-quadruplex structural probing; separately siRNA/3'-UTR binding and epistasis in breast cancer cells","pmids":["31387452","30720048"],"confidence":"Medium","gaps":["Physiological trigger for IRES switching beyond cell density not defined","Direct RBM3-3'UTR interaction described at abstract level","Relationship between the two regulatory layers untested"]},{"year":2019,"claim":"Validated ARPC2 as a directly druggable subunit by identifying small molecules that bind it and inhibit Arp2/3 actin polymerization and migration.","evidence":"Affinity pulldown, DARTS, CETSA, SPR, CRISPR point mutants (F225, F247, Y250) plus actin assays and knockdown across benproperine and pimozide studies","pmids":["30710516","31571309","36558913"],"confidence":"High","gaps":["Co-crystal structure of compound-bound ARPC2 not reported","Selectivity against other actin regulators not fully characterized"]},{"year":2024,"claim":"Probed the necessity of ARPC2/Arp2/3 in actin pedestal formation, showing Palladin can functionally substitute during EPEC infection.","evidence":"ArpC2-knockout cells rescued by Palladin overexpression with domain-mutant controls and pedestal length quantification","pmids":["39692253"],"confidence":"Medium","gaps":["Whether substitution generalizes beyond EPEC pedestals unknown","Does not address endogenous redundancy in normal cells"]},{"year":2026,"claim":"Revealed an Arp2/3-independent role for ARPC2 in transcriptional control of fibrosis via MRTFA.","evidence":"ARPC2 overexpression/knockdown with MRTFA nuclear localization imaging, MRTFA/G-actin complex assay, and transcriptomics of ARPC2/ACTR2/MRTFA-depleted cells","pmids":["41898590"],"confidence":"Medium","gaps":["Molecular basis of ARPC2 acting separately from other subunits unresolved","Single lab, recent and unreplicated","Direct ARPC2-MRTFA or ARPC2-G-actin interaction not defined"]},{"year":null,"claim":"How ARPC2 mechanistically uncouples from the Arp2/3 complex to perform its MRTFA-regulatory and microtubule-associated roles, and whether these are conserved in mammals, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural or biochemical model for Arp2/3-independent ARPC2 function","Mammalian relevance of MT binding untested","Integration of multiple regulatory inputs on ARPC2 abundance not assembled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,6]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[9,8]}],"complexes":["Arp2/3 complex"],"partners":["ARPC4","MRTFA","RBM3","VINCULIN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15144","full_name":"Actin-related protein 2/3 complex subunit 2","aliases":["Arp2/3 complex 34 kDa subunit","p34-ARC"],"length_aa":300,"mass_kda":34.3,"function":"Actin-binding component of the Arp2/3 complex, a multiprotein complex that mediates actin polymerization upon stimulation by nucleation-promoting factor (NPF) (PubMed:9230079). The Arp2/3 complex mediates the formation of branched actin networks in the cytoplasm, providing the force for cell motility (PubMed:9230079). Seems to contact the mother actin filament (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; Cell projection; Synapse, synaptosome; Nucleus","url":"https://www.uniprot.org/uniprotkb/O15144/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/ARPC2","classification":"Common Essential","n_dependent_lines":550,"n_total_lines":1208,"dependency_fraction":0.4552980132450331},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000163466","cell_line_id":"CID001775","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"membrane","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"ACTR2","stoichiometry":10.0},{"gene":"ARL6IP5","stoichiometry":10.0},{"gene":"ACTR3","stoichiometry":10.0},{"gene":"ARPC1A","stoichiometry":10.0},{"gene":"ARPC5L","stoichiometry":10.0},{"gene":"ARPC4-TTLL3;ARPC4","stoichiometry":10.0},{"gene":"ARPC5","stoichiometry":10.0},{"gene":"ARPC3","stoichiometry":10.0},{"gene":"USP22","stoichiometry":10.0},{"gene":"ARPC1B","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/target/CID001775","total_profiled":1310},"omim":[{"mim_id":"619857","title":"SPERMATOGENESIS-ASSOCIATED PROTEIN 3; SPATA3","url":"https://www.omim.org/entry/619857"},{"mim_id":"612381","title":"INFLAMMATORY BOWEL DISEASE 23; IBD23","url":"https://www.omim.org/entry/612381"},{"mim_id":"612261","title":"INFLAMMATORY BOWEL DISEASE 17; IBD17","url":"https://www.omim.org/entry/612261"},{"mim_id":"605035","title":"WASP PROTEIN FAMILY, MEMBER 1; WASF1","url":"https://www.omim.org/entry/605035"},{"mim_id":"604519","title":"INFLAMMATORY BOWEL DISEASE 3; IBD3","url":"https://www.omim.org/entry/604519"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ARPC2"},"hgnc":{"alias_symbol":["p34-Arc","ARC34"],"prev_symbol":[]},"alphafold":{"accession":"O15144","domains":[{"cath_id":"3.30.1460.20","chopping":"8-122","consensus_level":"high","plddt":96.9963,"start":8,"end":122},{"cath_id":"3.30.1460.20","chopping":"136-256","consensus_level":"high","plddt":95.6261,"start":136,"end":256}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15144","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15144-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15144-F1-predicted_aligned_error_v6.png","plddt_mean":93.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARPC2","jax_strain_url":"https://www.jax.org/strain/search?query=ARPC2"},"sequence":{"accession":"O15144","fasta_url":"https://rest.uniprot.org/uniprotkb/O15144.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15144/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15144"}},"corpus_meta":[{"pmid":"18836448","id":"PMC_18836448","title":"Sequence variants in IL10, ARPC2 and multiple other loci contribute to ulcerative colitis susceptibility.","date":"2008","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18836448","citation_count":485,"is_preprint":false},{"pmid":"30710516","id":"PMC_30710516","title":"Benproperine, an ARPC2 inhibitor, suppresses cancer cell migration and tumor metastasis.","date":"2019","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30710516","citation_count":43,"is_preprint":false},{"pmid":"31571309","id":"PMC_31571309","title":"Pimozide suppresses cancer cell migration and tumor metastasis through binding to ARPC2, a subunit of the Arp2/3 complex.","date":"2019","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/31571309","citation_count":38,"is_preprint":false},{"pmid":"31002363","id":"PMC_31002363","title":"ARPC2 promotes breast cancer proliferation and metastasis.","date":"2019","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/31002363","citation_count":29,"is_preprint":false},{"pmid":"25260753","id":"PMC_25260753","title":"Forkhead Box F1 represses cell growth and inhibits COL1 and ARPC2 expression in lung fibroblasts in vitro.","date":"2014","source":"American journal of physiology. 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sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41898590","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12397,"output_tokens":3734,"usd":0.046601,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11375,"output_tokens":2998,"usd":0.065912,"stage2_stop_reason":"end_turn"},"total_usd":0.112513,"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\": 2008,\n      \"finding\": \"Mutagenesis of the p35/ARPC2 subunit in S. cerevisiae identified three distinct functional surfaces: one face required for actin nucleation and endocytosis, a second site near the ARPC2-ARPC4 contact required for nucleation and endocytosis, and a third distal conserved surface required for endocytosis but not nucleation. Purified mutant Arp2/3 complexes confirmed loss of actin assembly activity, establishing ARPC2 as a structurally critical subunit for Arp2/3-mediated actin nucleation.\",\n      \"method\": \"Site-directed mutagenesis of conserved solvent-exposed residues, in vitro actin assembly assays with purified mutant Arp2/3 complexes, yeast cell growth and endocytosis phenotype analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified proteins + mutagenesis + multiple cellular phenotype readouts in single rigorous study\",\n      \"pmids\": [\"18381280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Benproperine (Benp) directly binds ARPC2 (identified by affinity column chromatography with Benp-tagged Sepharose beads, validated by pulldown with Benp-biotin, DARTS, and CETSA), inhibits Arp2/3 complex-dependent actin polymerization, disrupts lamellipodial structure, and suppresses cancer cell migration and metastasis. ARPC2 knockdown phenocopied Benp treatment, confirming ARPC2 as the functional target.\",\n      \"method\": \"Affinity column chromatography, pulldown with Benp-biotin, DARTS, CETSA, actin polymerization assay, siRNA knockdown, in vivo metastasis model\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal target-engagement methods (affinity pull-down, DARTS, CETSA) plus functional validation by knockdown, replicated with independent stereoisomer study\",\n      \"pmids\": [\"30710516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Pimozide directly binds ARPC2 (confirmed by DARTS and CETSA), increases the lag phase of Arp2/3 complex-dependent actin polymerization, and inhibits vinculin-mediated recruitment of ARPC2 to focal adhesions. ARPC2 point mutants (F225A, F247A, Y250F) generated by CRISPR/Cas9 revealed a binding pocket on ARPC2 required for pimozide interaction.\",\n      \"method\": \"DARTS, CETSA, actin polymerization assay, CRISPR/Cas9 point-mutant cell lines, focal adhesion immunofluorescence\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal binding assays plus mutagenesis defining binding pocket, single lab\",\n      \"pmids\": [\"31571309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"S-Benproperine, the active stereoisomer of benproperine, directly binds ARPC2 at residue F225 (ARPC2-F225A mutant abolishes binding by CETSA and DARTS), co-localizes with ARPC2 in cancer cells and tumor tissues, and suppresses actin remodeling including lamellipodium formation.\",\n      \"method\": \"Surface plasmon resonance (SPR), CETSA, DARTS, CRISPR/Cas9 ARPC2-F225A mutant cells, Cy3-conjugated S-Benp co-localization, actin polymerization assay\",\n      \"journal\": \"Pharmaceuticals (Basel, Switzerland)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — SPR, CETSA, DARTS, and site-specific mutagenesis defining binding residue in single study\",\n      \"pmids\": [\"36558913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NADPH oxidase 1 (Nox1) mediates H2O2-induced upregulation of ARPC2 protein expression in vascular smooth muscle cells (VSMCs) via a p38 MAPK-dependent pathway, and ARPC2 is required downstream of Nox1 for H2O2-stimulated VSMC migration.\",\n      \"method\": \"2D-DIGE/mass spectrometry proteomics, Western blot, siRNA knockdown of Nox1 and ARPC2, p38 MAPK inhibitor (SB203580), wound-healing scratch assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomics discovery plus functional validation by gene silencing and pharmacological inhibition, single lab\",\n      \"pmids\": [\"24152438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The longer 5'-UTR splice variant of ARPC2 mRNA harbors an internal ribosome entry site (IRES) containing a guanine-quadruplex (G-quadruplex) motif that promotes cap-independent translation; the shorter variant lacks this activity. At high cell density, relative ARPC2 protein levels increase, consistent with IRES-driven expression under conditions that compromise cap-dependent translation.\",\n      \"method\": \"Bicistronic reporter construct, multiple IRES control assays, chemical probing of RNA structure, G-quadruplex structural analysis, cell density-dependent protein level measurement\",\n      \"journal\": \"RNA biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bicistronic reporter with multiple controls, G-quadruplex structural validation, single lab\",\n      \"pmids\": [\"31387452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Plant ARPC2 protein (a core Arp2/3 complex subunit) directly interacts with microtubules in addition to actin filaments; a putative MT-binding domain was identified by in vitro co-sedimentation of truncated NtARPC2 proteins with microtubules. GFP-ARPC2 decorated microtubules in tobacco BY-2 cells and Arabidopsis root epidermal cells.\",\n      \"method\": \"In vitro co-sedimentation assay with truncated ARPC2 proteins, pharmacological interference with actin/MT dynamics, live-cell GFP imaging\",\n      \"journal\": \"Plant science : an international journal of experimental plant biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro co-sedimentation with domain mapping plus live-cell imaging, but plant ortholog and single lab\",\n      \"pmids\": [\"26706062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RBM3 upregulates ARPC2 protein expression through a post-transcriptional mechanism involving binding to the 3'-UTR of ARPC2 mRNA, and ARPC2 mediates the pro-proliferative and pro-metastatic effects of RBM3 in breast cancer cells.\",\n      \"method\": \"siRNA knockdown of RBM3 and ARPC2, 3'-UTR binding assay, cell proliferation and migration assays, epistasis (ARPC2 knockdown rescues RBM3 overexpression phenotype)\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — 3'-UTR binding plus functional epistasis, but mechanistic detail on direct RBM3-ARPC2 3'UTR interaction is limited to abstract description\",\n      \"pmids\": [\"30720048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"FOXF1 transcriptionally represses ARPC2 expression in normal lung fibroblasts; ARPC2 knockdown inhibits cell growth and COL1 expression, placing ARPC2 downstream of FOXF1 in the regulation of fibroblast proliferation and collagen production. In IPF fibroblasts, FOXF1-mediated repression of ARPC2 is blunted.\",\n      \"method\": \"siRNA knockdown (FOXF1 and ARPC2), gain-of-function/loss-of-function models, cell growth assay, COL1 expression measurement, epistasis analysis\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with ARPC2 knockdown phenocopying FOXF1 overexpression, single lab, two methods\",\n      \"pmids\": [\"25260753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ARPC2 regulates TGF-β1-induced nuclear translocation of myocardin-related transcription factor-A (MRTFA) and modulates MRTFA/G-actin complex formation in lung fibroblasts, promoting fibrotic gene expression (including ACTA2) at the transcriptional level independently of other ARP2/3 complex components. Transcriptomic analysis showed ARPC2 and MRTFA co-regulate a specific repertoire of fibrotic genes.\",\n      \"method\": \"ARPC2 modulation (overexpression/knockdown), MRTFA nuclear localization imaging, MRTFA/G-actin complex assay, transcriptomic analysis of ARPC2/ACTR2/MRTFA-depleted cells\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal readouts (localization, complex formation, transcriptomics), single lab, 2026 publication not yet replicated\",\n      \"pmids\": [\"41898590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Inhibition of ARPC2 with benproperine (BPP) disrupts intestinal stem cell (ISC) homeostasis: at lower doses it promotes and at higher doses it inhibits intestinal organoid growth and crypt cell proliferation; it decreases Lgr5 ISC feature gene expression and reduces Paneth cell differentiation. Mechanistically, ARPC2 inhibition activates the YAP1 (Yes1-associated transcriptional regulator) pathway, linking actin polymerization to ISC regulation.\",\n      \"method\": \"Organoid culture, BrdU/EdU incorporation, flow cytometry, IHC, phalloidin staining for F-actin, in vivo mouse experiments with BPP\",\n      \"journal\": \"Burns & trauma\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pharmacological inhibition with multiple cellular readouts and proposed pathway (YAP), but no direct genetic rescue or mechanistic confirmation of YAP link\",\n      \"pmids\": [\"37849945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KLF7-IT1 (a lncRNA) stabilizes ARPC2 protein in macrophages, thereby facilitating intracellular LPS internalization and downstream caspase-4 activation; ARPC2 silencing attenuates caspase-4 activation, gasdermin-D-mediated pyroptosis, phosphatidylserine exposure, and tissue factor activity, placing ARPC2 as a cytoskeletal mediator connecting LPS sensing to pyroptosis and hypercoagulation in sepsis.\",\n      \"method\": \"siRNA knockdown of ARPC2, caspase-4 activity assay, gasdermin-D cleavage measurement, phosphatidylserine exposure assay, tissue factor activity assay, LPS internalization imaging\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, functional knockdown with mechanistic readouts but abstract-level detail; lncRNA stabilization mechanism not directly validated\",\n      \"pmids\": [\"41275797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Overexpression of Palladin in ArpC2-knockout cells rescues EPEC pedestal length, demonstrating that Palladin can substitute for Arp2/3 complex function in actin pedestal elongation during EPEC infection.\",\n      \"method\": \"ArpC2-/- cell lines, Palladin overexpression rescue experiment, EPEC pedestal length quantification, Palladin actin-binding domain and VASP-binding domain mutants\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis using knockout cell line with rescue experiment and domain-mutant controls\",\n      \"pmids\": [\"39692253\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARPC2 (p34-Arc/ARC34) is a structurally essential subunit of the Arp2/3 complex whose distinct functional surfaces (mapped by mutagenesis in yeast) are required for actin nucleation and endocytosis; it directly contacts the mother actin filament, is regulated at the translational level via an IRES/G-quadruplex in its 5'-UTR, is upregulated downstream of Nox1/p38 MAPK signaling in smooth muscle cells, is transcriptionally repressed by FOXF1 in fibroblasts, and—in a function separable from other Arp2/3 subunits—regulates MRTFA nuclear translocation and fibrotic gene expression; small molecules (benproperine, pimozide) that bind directly to ARPC2 at defined residues (including F225) inhibit Arp2/3-dependent actin polymerization and cancer cell migration, confirming ARPC2 as a druggable subunit of the complex.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARPC2 (p34-Arc) is a structurally essential subunit of the Arp2/3 complex that drives branched actin nucleation and the actin-dependent processes of endocytosis and cell migration [#0]. Mutagenesis in yeast resolved three distinct functional surfaces on ARPC2: one face and a second site near the ARPC2-ARPC4 contact are both required for actin nucleation and endocytosis, while a third conserved distal surface is required for endocytosis but not nucleation, and purified mutant complexes confirmed loss of actin assembly activity [#0]. Within the assembled complex ARPC2 is a druggable target: the small molecules benproperine (its active S-stereoisomer engaging residue F225) and pimozide bind directly to defined ARPC2 pockets, increase the lag phase of Arp2/3-dependent actin polymerization, disrupt lamellipodia, and suppress cancer cell migration and metastasis [#1, #2, #3]. Pimozide binding additionally blocks vinculin-mediated recruitment of ARPC2 to focal adhesions [#2]. ARPC2 abundance is controlled at multiple post-transcriptional and transcriptional levels — through an IRES/G-quadruplex element in the longer 5'-UTR splice variant that supports cap-independent translation [#5], by RBM3 acting on the 3'-UTR [#7], by Nox1/p38 MAPK signaling that upregulates ARPC2 to drive smooth muscle cell migration [#4], and by FOXF1-mediated transcriptional repression in fibroblasts [#8]. Beyond its canonical complex role, ARPC2 regulates TGF-β1-induced nuclear translocation of MRTFA and modulates MRTFA/G-actin complex formation to promote fibrotic gene expression independently of other Arp2/3 subunits [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established whether ARPC2 is a passive scaffold or an active contributor to Arp2/3 nucleation by resolving which of its surfaces are functionally required.\",\n      \"evidence\": \"Site-directed mutagenesis of conserved residues in yeast with purified mutant complex in vitro actin assays and endocytosis phenotyping\",\n      \"pmids\": [\"18381280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Surface assignments derived in yeast; human residue-level function not directly mapped here\", \"Does not address how ARPC2 contacts the mother filament structurally\", \"No connection to upstream regulatory inputs\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connected ARPC2 expression to a defined signaling axis, showing it is a regulated effector rather than a constitutively constant subunit.\",\n      \"evidence\": \"Proteomics plus siRNA knockdown of Nox1/ARPC2 and p38 inhibition in vascular smooth muscle cell migration assays\",\n      \"pmids\": [\"24152438\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which p38 MAPK raises ARPC2 protein is not resolved\", \"Single cell type (VSMC)\", \"No direct link to transcription versus translation control\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified a transcriptional repressor of ARPC2 and linked ARPC2 to fibroblast proliferation and collagen output.\",\n      \"evidence\": \"siRNA knockdown of FOXF1 and ARPC2 with growth and COL1 readouts and epistasis in lung fibroblasts\",\n      \"pmids\": [\"25260753\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FOXF1 binding to the ARPC2 promoter not demonstrated\", \"Mechanism of blunted repression in IPF fibroblasts unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Tested whether ARPC2 binding is restricted to actin, finding a microtubule-binding capacity in the plant ortholog.\",\n      \"evidence\": \"In vitro co-sedimentation of truncated NtARPC2 with microtubules and live-cell GFP imaging in tobacco/Arabidopsis\",\n      \"pmids\": [\"26706062\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Plant ortholog; relevance to mammalian ARPC2 untested\", \"Functional consequence of MT binding not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined how ARPC2 protein levels are tuned post-transcriptionally, identifying both a 5'-UTR IRES/G-quadruplex and a 3'-UTR-dependent RBM3 input.\",\n      \"evidence\": \"Bicistronic reporters with G-quadruplex structural probing; separately siRNA/3'-UTR binding and epistasis in breast cancer cells\",\n      \"pmids\": [\"31387452\", \"30720048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological trigger for IRES switching beyond cell density not defined\", \"Direct RBM3-3'UTR interaction described at abstract level\", \"Relationship between the two regulatory layers untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Validated ARPC2 as a directly druggable subunit by identifying small molecules that bind it and inhibit Arp2/3 actin polymerization and migration.\",\n      \"evidence\": \"Affinity pulldown, DARTS, CETSA, SPR, CRISPR point mutants (F225, F247, Y250) plus actin assays and knockdown across benproperine and pimozide studies\",\n      \"pmids\": [\"30710516\", \"31571309\", \"36558913\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Co-crystal structure of compound-bound ARPC2 not reported\", \"Selectivity against other actin regulators not fully characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Probed the necessity of ARPC2/Arp2/3 in actin pedestal formation, showing Palladin can functionally substitute during EPEC infection.\",\n      \"evidence\": \"ArpC2-knockout cells rescued by Palladin overexpression with domain-mutant controls and pedestal length quantification\",\n      \"pmids\": [\"39692253\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether substitution generalizes beyond EPEC pedestals unknown\", \"Does not address endogenous redundancy in normal cells\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed an Arp2/3-independent role for ARPC2 in transcriptional control of fibrosis via MRTFA.\",\n      \"evidence\": \"ARPC2 overexpression/knockdown with MRTFA nuclear localization imaging, MRTFA/G-actin complex assay, and transcriptomics of ARPC2/ACTR2/MRTFA-depleted cells\",\n      \"pmids\": [\"41898590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of ARPC2 acting separately from other subunits unresolved\", \"Single lab, recent and unreplicated\", \"Direct ARPC2-MRTFA or ARPC2-G-actin interaction not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ARPC2 mechanistically uncouples from the Arp2/3 complex to perform its MRTFA-regulatory and microtubule-associated roles, and whether these are conserved in mammals, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural or biochemical model for Arp2/3-independent ARPC2 function\", \"Mammalian relevance of MT binding untested\", \"Integration of multiple regulatory inputs on ARPC2 abundance not assembled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 8]}\n    ],\n    \"complexes\": [\"Arp2/3 complex\"],\n    \"partners\": [\"ARPC4\", \"MRTFA\", \"RBM3\", \"Vinculin\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}