{"gene":"ARPC4","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":1997,"finding":"ARPC4 (p20-Arc) was identified as one of seven subunits of the human Arp2/3 complex; the complex localizes to lamellipodia of fibroblasts and Listeria actin tails (but not actin bundles), consistent with a role in promoting actin assembly at sites of dynamic polymerization.","method":"Protein purification, sequencing, immunofluorescence localization in cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct biochemical purification and localization by immunofluorescence, replicated across multiple cell contexts, foundational paper","pmids":["9230079"],"is_preprint":false},{"year":2001,"finding":"Crystal structure of bovine Arp2/3 complex at 2.0 Å resolution revealed that ARPC4 (p20) and ARPC2 (p34) form the core of the complex through long C-terminal alpha helices and similarly folded N-terminal alpha/beta domains.","method":"X-ray crystallography at 2.0 Å resolution","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure, widely replicated and cited as foundational structural result","pmids":["11721045"],"is_preprint":false},{"year":2001,"finding":"Yeast two-hybrid analysis showed that p20-Arc (ARPC4) acts as a hub for subunit interactions within the human Arp2/3 complex, interacting with p21-Arc (ARPC3), p34-Arc (ARPC2), and p16-Arc (ARPC5); p41-Arc only interacted with the p20-Arc/p16-Arc heterodimer. Structural integrity was important for p20-Arc/p21-Arc association, while the N-terminal half of p34-Arc was dispensable for its binding to p20-Arc.","method":"Yeast two-hybrid assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — systematic yeast two-hybrid covering all pairwise combinations within the complex, single lab, single method","pmids":["11162547"],"is_preprint":false},{"year":2010,"finding":"Molecular dynamics and protein-protein docking simulations, validated by mutagenesis, defined an actin-filament-binding interface on ARPC2 and ARPC4. Residues at this interface are required for actin nucleation, Y-branching, high-affinity F-actin binding, and Y-branch stability, demonstrating that Arp2/3 complex affinity for F-actin independently modulates branch formation and stability.","method":"Molecular dynamics/docking simulations + mutagenesis + in vitro actin assembly assays + F-actin binding assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — combined computational modelling with extensive mutagenesis and multiple in vitro functional assays, multiple orthogonal methods in one study","pmids":["20404198"],"is_preprint":false},{"year":2010,"finding":"Molecular dynamics simulations of Arp2/3 activation showed that one structural block (comprising Arp2, ARPC1, the globular domain of ARPC4, and ARPC5) rotates ~30° around a pivot point in an alpha-helix of ARPC4 (Glu81–Asn100) to bring Arp2 into proximity with Arp3 during activation.","method":"Atomistic molecular dynamics simulations","journal":"Biophysical journal","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational simulation only, no direct experimental validation in this paper","pmids":["20959098"],"is_preprint":false},{"year":2011,"finding":"Phosphorylation of Arp2 destabilizes a network of auto-inhibitory salt-bridge interactions at the interface of Arp2, Arp3, and ARPC4, permitting Arp2 reorientation to an activation-competent state. A gain-of-function ARPC4 mutant predicted to disrupt these interactions showed substantial actin nucleation activity in the absence of NPFs.","method":"Molecular dynamics simulations + biochemical assays with recombinant Arp2/3 complex carrying ARPC4 mutations","journal":"PLoS computational biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — computational prediction supported by experimental validation of ARPC4 gain-of-function mutant in biochemical assay, single lab","pmids":["22125478"],"is_preprint":false},{"year":2009,"finding":"Hydrogen/deuterium exchange mass spectrometry showed that ATP binding to Arp2/3 complex causes conformational rearrangements in Arp2 and Arp3 that are allosterically transmitted to ARPC4 (and ARPC1, ARPC2, ARPC5); WASp VCA binding further modulates exchange rates in ARPC4, indicating global conformational reorganization involving this subunit upon activation.","method":"Hydrogen/deuterium exchange coupled with mass spectrometry","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct structural dynamics measurement on purified complex, single lab, single technique","pmids":["19298826"],"is_preprint":false},{"year":2008,"finding":"In S. cerevisiae, a contact surface between p35/ARPC2 and p19/ARPC4 was identified as required for actin nucleation and endocytosis; mutations near this interface abolished nucleation without disrupting complex integrity.","method":"Systematic mutagenesis in S. cerevisiae + purification of mutant complexes + in vitro actin assembly assays + endocytosis assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified mutant complexes plus cellular functional assays, multiple orthogonal methods, single lab","pmids":["18381280"],"is_preprint":false},{"year":2010,"finding":"In S. cerevisiae, lethal mutations at the p40/ARPC1 contact with p19/ARPC4 specifically impaired WASp-induced nucleation of purified Arp2/3 complex, placing ARPC4 at the interface required for WASp activation signal propagation.","method":"Mutagenesis of ARPC1 + purification of mutant complexes + in vitro actin nucleation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — purified mutant complexes with in vitro reconstitution assays; ARPC4 contact site directly tested; multiple methods in single study","pmids":["20071330"],"is_preprint":false},{"year":2017,"finding":"Conditional knockout of Arpc4 in mouse epidermis depleted the Arp2/3 complex and caused a psoriasis-like disease; Arpc4 knockout in cultured keratinocytes was sufficient to induce nuclear accumulation of Nrf2, upregulation of Nrf2 target genes, and decreased F-actin levels. In vitro, Nrf2 was shown to bind to filamentous actin.","method":"Conditional Arpc4 knockout mouse model + keratinocyte culture KO + pharmacological Arp2/3 inhibition + in vitro F-actin binding assay","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO mouse + cell culture KO + pharmacological inhibition + direct F-actin binding assay, multiple orthogonal approaches in single study","pmids":["29113991"],"is_preprint":false},{"year":2021,"finding":"Conditional ablation of Arpc4 in mouse pancreatic acinar cells demonstrated that the Arp2/3 complex is required for KrasG12D-driven acinar-to-ductal metaplasia (ADM) in vivo; mTORC1 regulates Arp2/3 complex activity via Rac1/Arp3 translation while mTORC2 promotes Arp2/3 via Akt/Rac1, converging on ARPC4-containing Arp2/3 as a common downstream effector for actin cortex remodeling and ADM.","method":"Conditional Arpc4 knockout mouse + in vitro ADM assays + epistasis with Rptor/Rictor conditional knockouts","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo conditional KO mouse with epistasis analysis, multiple genetic models, replicated in vitro","pmids":["33388318"],"is_preprint":false},{"year":2021,"finding":"A recurrent de novo missense variant in ARPC4 (p.Arg158Cys) found in patients with microcephaly and speech delay was associated with decreased F-actin levels in cells from affected individuals, implicating ARPC4 in actin filament network formation required for neurodevelopment.","method":"Patient cell-based F-actin quantification (immunofluorescence/imaging) in cells from affected individuals carrying the variant","journal":"HGG advances","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — patient cell-based assay showing F-actin reduction, supported across multiple families, but no in vitro reconstitution","pmids":["35047857"],"is_preprint":false},{"year":2025,"finding":"UFL1 (UFM1-specific E3 ligase 1) interacts with ArpC4 and catalyzes its UFMylation. Akt phosphorylates UFL1 at T426, which enhances UFL1's interaction with ArpC4 and promotes ArpC4 UFMylation, thereby facilitating lamellipodia formation, cell migration, invasion, and metastasis.","method":"Co-immunoprecipitation, in vitro UFMylation assay, phosphorylation mapping, loss-of-function cell migration/invasion assays, lamellipodia imaging","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical identification of UFMylation on ArpC4, upstream kinase (Akt) phosphorylation mapped, in vitro assay plus functional cellular readouts, multiple orthogonal methods","pmids":["40419786"],"is_preprint":false},{"year":2022,"finding":"Binary clostridial toxins (CDT, C2I, Iota) ADP-ribosylate ARPC4/5 (among other Arp2/3 subunits) in addition to actin and Arp2, and this modification inhibits Arp2/3 complex actin-nucleating activity, causing collapse of lamellipodia and F-actin networks in cells.","method":"Mass spectrometry identification of ADP-ribosylation sites + in vitro Arp2/3 activity assays + cell imaging (Caco2 cells + mouse colon explants)","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-based site identification plus in vitro functional assay and cellular assay, single lab","pmids":["36429089"],"is_preprint":false},{"year":2013,"finding":"siRNA-mediated silencing of ARPC4 significantly reduced cell migration (50–68% decrease) in pancreatic cancer cell lines without affecting other processes, indicating ARPC4 is a key functional subunit for Arp2/3-dependent migration in these cells.","method":"siRNA knockdown + transwell migration assay in multiple pancreatic cancer cell lines","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — siRNA knockdown with quantitative migration readout replicated across multiple cell lines, single lab","pmids":["23267127"],"is_preprint":false},{"year":2019,"finding":"ARPC4 knockdown in T24 bladder cancer cells attenuated migration, invasion, and pseudopodia formation and disrupted actin cytoskeleton structure, demonstrating a direct role of ARPC4 in actin-dependent invasive behavior.","method":"siRNA knockdown + transwell invasion/migration assay + wound-healing assay + immunofluorescence of actin cytoskeleton","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — siRNA KD with multiple functional readouts, single lab","pmids":["31190401"],"is_preprint":false},{"year":2016,"finding":"Chemical cross-linking/mass spectrometry identified the entire seven-subunit Arp2/3 complex (including ARPC4) as an interaction partner of human PKD2 in both cytosolic and Golgi-enriched fractions, with evidence of a direct protein-protein interaction between PKD2 and Arp2/3.","method":"Affinity enrichment + chemical cross-linking + mass spectrometry","journal":"Journal of proteome research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, cross-linking MS identifies interaction but no reciprocal validation or functional follow-up specific to ARPC4","pmids":["27559607"],"is_preprint":false},{"year":2013,"finding":"Expression of ARPC4 in Mycobacterium tuberculosis severely impaired bacterial growth (evidenced by TEM showing outer-coat shedding), enhanced bacterial clearance in infected macrophages, impaired phagosome-to-lysosome translocation, and suppressed pro-inflammatory cytokine responses. ARPC4 was shown to interact with the essential mycobacterial secretory protein Rv1626, downregulating its expression ~6-fold; Rv1626 also interacted with mammalian Arp2/3 and enhanced actin polymerization.","method":"Bacterial expression of ARPC4 + TEM + macrophage infection assays + co-immunoprecipitation (ARPC4–Rv1626 interaction) + real-time PCR","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus multiple functional readouts; interaction and functional consequences demonstrated by orthogonal methods, single lab","pmids":["23894563"],"is_preprint":false},{"year":2016,"finding":"Viral protein Ac34 (baculovirus) co-immunoprecipitated with ARPC4 (P20) of Sf9 (insect) cells and induced its nuclear relocation; however, mammalian ARPC4 did not interact with Ac34 and was not relocated, indicating species-specific binding specificity.","method":"Immunofluorescence + co-immunoprecipitation","journal":"Virologica Sinica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP in insect cells; finding is about insect ARPC4 with negative result for mammalian ARPC4","pmids":["27900558"],"is_preprint":false},{"year":2025,"finding":"In cervical cancer cells, Aurora-A overexpression upregulated ARPC4 expression via activation of the NF-κBp65 signaling pathway (increased NF-κBp65 phosphorylation led to elevated ARPC4 levels), and ARPC4 knockdown antagonized Aurora-A-promoted migration, invasion, and EMT.","method":"Plasmid overexpression + shRNA knockdown + NF-κBp65 inhibitor treatment + Western blot + migration/invasion assays","journal":"Nan fang yi ke da xue xue bao","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — epistasis by combined OE/KD/pharmacological inhibition with functional readouts, single lab","pmids":["40294934"],"is_preprint":false},{"year":2019,"finding":"A genome-wide CRISPR knockout screen in THP-1 macrophages identified ARPC4 loss-of-function as conferring resistance to Salmonella uptake, placing ARPC4-containing Arp2/3 complex in the actin dynamics pathway required for macrophage phagocytic internalization of bacteria.","method":"Genome-wide CRISPR KO screen + validation assays","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genome-scale screen with follow-up validation, but ARPC4-specific mechanistic follow-up was not deep; functional placement in phagocytosis pathway established","pmids":["31594818"],"is_preprint":false},{"year":2025,"finding":"In a gut epithelium-specific inducible Arpc4 knockout mouse, loss of Arp2/3 function led to increased intestinal permeability, disrupted tight junction protein localization, epithelial fracturing, and lethality under mechanical challenge; ex vivo organoid experiments showed defects required mechanical stress and elevated actomyosin contractility to manifest.","method":"Inducible conditional Arpc4 KO mouse + ex vivo intestinal slice culture + organoid culture + tight junction imaging","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible conditional KO mouse plus multiple ex vivo models with defined mechanical challenge, multiple orthogonal readouts","pmids":["40930096"],"is_preprint":false},{"year":2026,"finding":"Conditional Arpc4 knockout in myeloid cells showed that Arp2/3 complex loss in Langerhans cells leads to cell decline through DNA damage accumulation associated with aberrant nuclear shapes, lamina reduction, and nuclear envelope rupture, revealing a role for Arp2/3/ARPC4 in nuclear envelope integrity and genome maintenance in tissue-resident immune cells.","method":"Conditional Arpc4 KO mouse + in vivo LC analysis + in vitro BMDC experiments + cell cycle analysis + nuclear morphology/DNA damage assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO mouse with in vitro corroboration and multiple cellular readouts; preprint, not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2026,"finding":"Conditional Arpc4 knockout in microglia showed that Arp2/3 depletion prevents the developmental transition of microglia into ramified cells with homeostatic gene profiles and surveillance function, linking ARPC4-dependent actin branching to microglial maturation in the CNS.","method":"Conditional Arpc4 KO mouse + morphological analysis + transcriptomic profiling of microglia + CNS surveillance assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO mouse with morphological, transcriptomic, and functional readouts in multiple complementary assays","pmids":["41760937"],"is_preprint":false},{"year":2026,"finding":"CRISPR/Cas9 knockout of Arpc4 in murine PDAC cell lines downregulated all Arp2/3 complex members and significantly impaired PDAC cell migration, disrupted branched tubular structure formation in collagen I, and inhibited invasive front formation in organoid culture; β1 integrin signaling was identified as a key upstream regulator of Arp2/3-dependent migration through collagen-rich matrices.","method":"CRISPR/Cas9 KO + 2D and 3D migration/invasion assays + organoid co-culture + β1 integrin signaling analysis","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with multiple functional assays and pathway placement via β1 integrin epistasis, single lab","pmids":["41793310"],"is_preprint":false},{"year":2026,"finding":"ArpC4 knockdown by siRNA in U2OS cells reduced HDR efficiency, but this effect corresponded with decreased transfection efficiency and reduction in S/G2M cell cycle phases rather than a direct role in DNA repair; WASP/N-WASP were found dispensable for HDR.","method":"siRNA knockdown + CRISPR-based HDR reporter assay + cell cycle analysis","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — controlled siRNA KD with cell cycle analysis distinguishing indirect effect; negative mechanistic finding rigorously established","pmids":["41963733"],"is_preprint":false}],"current_model":"ARPC4 (p20-Arc/ARC20) is a core structural subunit of the seven-protein Arp2/3 complex that, together with ARPC2, forms the central scaffold of the complex via interlocking C-terminal helices and N-terminal alpha/beta domains; it serves as an interaction hub connecting ARPC2, ARPC3, ARPC5, and ARPC1, and harbors a pivot helix (Glu81–Asn100) around which the complex undergoes the ~30° conformational rotation that activates actin nucleation. The ARPC2–ARPC4 interface directly contacts the mother actin filament, with specific residues required for F-actin binding, Y-branch nucleation, and branch stability; disruption of auto-inhibitory salt bridges at the Arp2–Arp3–ARPC4 interface (e.g., by Arp2 phosphorylation) permits complex activation. Post-translationally, ArpC4 is UFMylated by UFL1 downstream of Akt-mediated phosphorylation of UFL1, promoting lamellipodia formation and metastatic cell migration; it is also ADP-ribosylated by clostridial binary toxins, which inhibits complex activity. Loss of ARPC4 in conditional knockout models disrupts epidermal homeostasis (causing Nrf2 hyperactivation), impairs intestinal epithelial barrier integrity under mechanical stress, blocks microglial maturation and ramification, promotes DNA damage in Langerhans cells, prevents pancreatic acinar-to-ductal metaplasia downstream of mTORC1/2–Rac1 signaling, and inhibits cancer cell migration and invasion across multiple tumor types."},"narrative":{"mechanistic_narrative":"ARPC4 (p20-Arc) is a core structural subunit of the seven-protein Arp2/3 complex, the actin nucleator that builds branched filament networks at sites of dynamic polymerization such as lamellipodia and bacterial actin tails [PMID:9230079]. Together with ARPC2, ARPC4 forms the structural core of the complex through long C-terminal alpha helices and similarly folded N-terminal alpha/beta domains [PMID:11721045], and it serves as a subunit-interaction hub contacting ARPC2, ARPC3, and ARPC5 [PMID:11162547]. The ARPC2–ARPC4 interface directly engages the mother actin filament: residues at this surface are required for actin nucleation, Y-branch formation, high-affinity F-actin binding, and branch stability [PMID:20404198, PMID:18381280], and the ARPC1–ARPC4 contact is required to propagate the WASp activation signal [PMID:20071330]. Activation involves global conformational reorganization transmitted to ARPC4 upon ATP and WASp-VCA binding [PMID:19298826], with auto-inhibitory salt bridges at the Arp2–Arp3–ARPC4 interface gating the complex; their disruption yields constitutive nucleation [PMID:22125478]. ARPC4 activity is regulated post-translationally: UFL1, when phosphorylated by Akt, UFMylates ArpC4 to promote lamellipodia formation, migration, and metastasis [PMID:40419786], whereas clostridial binary toxins ADP-ribosylate ARPC4 to inhibit nucleation and collapse F-actin networks [PMID:36429089]. Through this branched-actin function, ARPC4 supports a broad range of cellular and tissue processes — epidermal homeostasis with Nrf2 restraint [PMID:29113991], pancreatic acinar-to-ductal metaplasia downstream of mTORC1/2–Rac1 signaling [PMID:33388318], intestinal epithelial barrier integrity under mechanical stress [PMID:40930096], microglial maturation [PMID:41760937], and cancer cell migration and invasion across tumor types [PMID:23267127, PMID:31190401, PMID:41793310]. A recurrent de novo missense variant (p.Arg158Cys) causes reduced cellular F-actin in patients with microcephaly and speech delay, linking ARPC4 to a neurodevelopmental disorder [PMID:35047857].","teleology":[{"year":1997,"claim":"Established that ARPC4 is a bona fide subunit of the human Arp2/3 complex and that the complex localizes to sites of dynamic actin assembly, defining its cellular arena.","evidence":"Protein purification, sequencing, and immunofluorescence in fibroblasts and Listeria actin tails","pmids":["9230079"],"confidence":"High","gaps":["Did not resolve ARPC4's specific structural or functional contribution within the complex","Localization correlative, not mechanistic"]},{"year":2001,"claim":"Resolved how ARPC4 is built into the complex, showing it pairs with ARPC2 to form the structural core and acts as a hub for inter-subunit contacts.","evidence":"2.0 Å X-ray crystallography of bovine complex and pairwise yeast two-hybrid mapping","pmids":["11721045","11162547"],"confidence":"High","gaps":["Static structure does not reveal the activation conformational change","Y2H interactions not validated by reciprocal biochemistry"]},{"year":2010,"claim":"Defined ARPC4 functionally by mapping the ARPC2–ARPC4 actin-filament-binding interface and showing distinct residues control nucleation, branching, F-actin affinity, and branch stability.","evidence":"Molecular dynamics/docking with mutagenesis and in vitro actin assembly and F-actin binding assays","pmids":["20404198"],"confidence":"High","gaps":["Interface defined computationally before high-resolution branch junction structures","Did not address the activating conformational rotation"]},{"year":2011,"claim":"Connected ARPC4 to activation by identifying an auto-inhibitory salt-bridge network at the Arp2–Arp3–ARPC4 interface whose disruption produces NPF-independent nucleation.","evidence":"Molecular dynamics simulations plus biochemical assays of a gain-of-function ARPC4 mutant complex; complemented by H/DX-MS showing allosteric conformational transmission to ARPC4 and the ARPC4 pivot-helix rotation model","pmids":["22125478","19298826","20959098"],"confidence":"Medium","gaps":["Pivot-helix rotation rests on simulation without direct experimental validation","In vivo relevance of the Arp2-phosphorylation gating not established"]},{"year":2008,"claim":"Demonstrated in a genetically tractable system that the ARPC2–ARPC4 and ARPC1–ARPC4 contacts are required for nucleation and WASp activation independent of complex assembly.","evidence":"Systematic mutagenesis in S. cerevisiae with purified mutant complexes, in vitro nucleation assays, and endocytosis assays","pmids":["18381280","20071330"],"confidence":"High","gaps":["Yeast residue requirements not directly mapped onto human ARPC4 function","Mechanism of signal propagation through the interface not resolved at atomic level"]},{"year":2017,"claim":"Established a tissue-level requirement for ARPC4 in epidermal homeostasis and linked actin loss to a transcriptional consequence via Nrf2.","evidence":"Conditional Arpc4 KO mouse, keratinocyte KO, Arp2/3 inhibition, and in vitro Nrf2–F-actin binding assay","pmids":["29113991"],"confidence":"High","gaps":["Whether Nrf2 sequestration by F-actin is the sole driver of the phenotype unclear","Direct ARPC4 contribution versus whole-complex depletion not separated"]},{"year":2021,"claim":"Positioned ARPC4-containing Arp2/3 as a convergent effector of mTORC1/2–Rac1 signaling driving Kras-induced pancreatic metaplasia, and linked an ARPC4 missense variant to a neurodevelopmental disorder.","evidence":"Conditional Arpc4 KO mouse with Rptor/Rictor epistasis and ADM assays; patient-cell F-actin quantification for the p.Arg158Cys variant","pmids":["33388318","35047857"],"confidence":"High","gaps":["Direct biochemical effect of p.Arg158Cys on complex assembly/nucleation not reconstituted","How mTOR signals couple to ARPC4 mechanistically beyond Rac1 not detailed"]},{"year":2022,"claim":"Identified ARPC4 as a post-translationally regulated subunit, being ADP-ribosylated by clostridial binary toxins to inhibit nucleation.","evidence":"Mass spectrometry site identification, in vitro Arp2/3 activity assays, and cell/explant imaging","pmids":["36429089"],"confidence":"Medium","gaps":["Relative contribution of ARPC4 versus actin/Arp2 ADP-ribosylation to inhibition unresolved","Physiological host modifications at these sites not addressed"]},{"year":2025,"claim":"Defined an activating regulatory axis in which Akt-phosphorylated UFL1 UFMylates ArpC4 to drive lamellipodia formation and metastatic migration.","evidence":"Co-IP, in vitro UFMylation, phosphorylation mapping (Akt T426 on UFL1), and loss-of-function migration/invasion/lamellipodia assays","pmids":["40419786"],"confidence":"High","gaps":["UFMylated residue effect on complex conformation/nucleation not structurally defined","In vivo metastasis dependence on this modification in physiological settings not established"]},{"year":2025,"claim":"Showed ARPC4 is required for mechanically stressed epithelial barrier integrity, revealing that branched-actin defects manifest only under load.","evidence":"Inducible gut-specific Arpc4 KO mouse, ex vivo intestinal slices, and organoids with defined mechanical challenge and tight junction imaging","pmids":["40930096"],"confidence":"High","gaps":["Molecular link between branched actin and tight junction maintenance not resolved","Actomyosin contractility interplay mechanistically incomplete"]},{"year":2026,"claim":"Extended ARPC4's roles to immune and CNS cell maturation and to nuclear envelope integrity, while a controlled study showed an apparent DNA-repair role is indirect.","evidence":"Conditional Arpc4 KO mice in microglia and Langerhans cells with morphological/transcriptomic/nuclear assays; CRISPR KO in PDAC lines with collagen invasion and β1 integrin analysis; siRNA HDR reporter with cell-cycle controls","pmids":["41760937","41793310","41963733"],"confidence":"Medium","gaps":["Langerhans cell nuclear-integrity finding remains a preprint without peer review","How branched actin maintains nuclear envelope integrity mechanistically unknown","Direct versus cell-cycle-mediated effects need disentangling across contexts"]},{"year":null,"claim":"How distinct post-translational modifications (UFMylation, ADP-ribosylation) and disease variants of ARPC4 alter the conformational activation cycle and branch-forming activity at atomic resolution remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of modified or variant ARPC4 within an activated branch junction","Tissue-specificity of ARPC4 requirements not mechanistically explained beyond whole-complex depletion"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3,7]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9,23]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,14,24]}],"complexes":["Arp2/3 complex"],"partners":["ARPC2","ARPC3","ARPC5","ARPC1","UFL1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P59998","full_name":"Actin-related protein 2/3 complex subunit 4","aliases":["Arp2/3 complex 20 kDa subunit","p20-ARC"],"length_aa":168,"mass_kda":19.7,"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). 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; Nucleus","url":"https://www.uniprot.org/uniprotkb/P59998/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/ARPC4","classification":"Common Essential","n_dependent_lines":916,"n_total_lines":1208,"dependency_fraction":0.7582781456953642},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ARPC4","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":"620141","title":"DEVELOPMENTAL DELAY, LANGUAGE IMPAIRMENT, AND OCULAR ABNORMALITIES; DEVLO","url":"https://www.omim.org/entry/620141"},{"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":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ARPC4"},"hgnc":{"alias_symbol":["p20-Arc","ARC20"],"prev_symbol":[]},"alphafold":{"accession":"P59998","domains":[{"cath_id":"3.30.1460.20","chopping":"3-165","consensus_level":"high","plddt":94.9694,"start":3,"end":165}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P59998","model_url":"https://alphafold.ebi.ac.uk/files/AF-P59998-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P59998-F1-predicted_aligned_error_v6.png","plddt_mean":94.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARPC4","jax_strain_url":"https://www.jax.org/strain/search?query=ARPC4"},"sequence":{"accession":"P59998","fasta_url":"https://rest.uniprot.org/uniprotkb/P59998.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P59998/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P59998"}},"corpus_meta":[{"pmid":"9230079","id":"PMC_9230079","title":"The human Arp2/3 complex is composed of evolutionarily conserved subunits and is localized to cellular regions of dynamic actin filament assembly.","date":"1997","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9230079","citation_count":430,"is_preprint":false},{"pmid":"11721045","id":"PMC_11721045","title":"Crystal structure of Arp2/3 complex.","date":"2001","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/11721045","citation_count":414,"is_preprint":false},{"pmid":"28842433","id":"PMC_28842433","title":"Multicohort analysis reveals baseline transcriptional predictors of influenza vaccination responses.","date":"2017","source":"Science immunology","url":"https://pubmed.ncbi.nlm.nih.gov/28842433","citation_count":127,"is_preprint":false},{"pmid":"16450411","id":"PMC_16450411","title":"The role of ARPC4 in tip growth and alignment of the polar axis in filaments of Physcomitrella patens.","date":"2006","source":"Cell motility and the cytoskeleton","url":"https://pubmed.ncbi.nlm.nih.gov/16450411","citation_count":66,"is_preprint":false},{"pmid":"20404198","id":"PMC_20404198","title":"An actin-filament-binding interface on the Arp2/3 complex is critical for nucleation and branch stability.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20404198","citation_count":63,"is_preprint":false},{"pmid":"24085853","id":"PMC_24085853","title":"Quantitative apical membrane proteomics reveals vasopressin-induced actin dynamics in collecting duct cells.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/24085853","citation_count":60,"is_preprint":false},{"pmid":"23267127","id":"PMC_23267127","title":"Silencing of the ARP2/3 complex disturbs pancreatic cancer cell migration.","date":"2013","source":"Anticancer research","url":"https://pubmed.ncbi.nlm.nih.gov/23267127","citation_count":56,"is_preprint":false},{"pmid":"18263777","id":"PMC_18263777","title":"BRICK1 is required for apical cell growth in filaments of the moss Physcomitrella patens but not for gametophore morphology.","date":"2008","source":"The Plant cell","url":"https://pubmed.ncbi.nlm.nih.gov/18263777","citation_count":50,"is_preprint":false},{"pmid":"29113991","id":"PMC_29113991","title":"Knockout of the Arp2/3 complex in epidermis causes a psoriasis-like disease hallmarked by hyperactivation of transcription factor Nrf2.","date":"2017","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/29113991","citation_count":45,"is_preprint":false},{"pmid":"31594818","id":"PMC_31594818","title":"A Genome-Wide Knockout Screen in Human Macrophages Identified Host Factors Modulating Salmonella Infection.","date":"2019","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/31594818","citation_count":45,"is_preprint":false},{"pmid":"33388318","id":"PMC_33388318","title":"mTORC1 and mTORC2 Converge on the Arp2/3 Complex to Promote KrasG12D-Induced Acinar-to-Ductal Metaplasia and Early Pancreatic Carcinogenesis.","date":"2021","source":"Gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/33388318","citation_count":43,"is_preprint":false},{"pmid":"18381280","id":"PMC_18381280","title":"Functional surfaces on the p35/ARPC2 subunit of Arp2/3 complex required for cell growth, actin nucleation, and endocytosis.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18381280","citation_count":25,"is_preprint":false},{"pmid":"20959098","id":"PMC_20959098","title":"Molecular dynamics simulations of Arp2/3 complex activation.","date":"2010","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/20959098","citation_count":24,"is_preprint":false},{"pmid":"20071330","id":"PMC_20071330","title":"The p40/ARPC1 subunit of Arp2/3 complex performs multiple essential roles in WASp-regulated actin nucleation.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20071330","citation_count":24,"is_preprint":false},{"pmid":"31190401","id":"PMC_31190401","title":"ARPC4 promotes bladder cancer cell invasion and is associated with lymph node metastasis.","date":"2019","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31190401","citation_count":23,"is_preprint":false},{"pmid":"30850364","id":"PMC_30850364","title":"Serum Proteomic Signatures of Male Breast Cancer.","date":"2019","source":"Cancer genomics & proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/30850364","citation_count":22,"is_preprint":false},{"pmid":"31636629","id":"PMC_31636629","title":"mir-124-5p Regulates Phagocytosis of Human Macrophages by Targeting the Actin Cytoskeleton via the ARP2/3 Complex.","date":"2019","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/31636629","citation_count":22,"is_preprint":false},{"pmid":"22125478","id":"PMC_22125478","title":"Phosphorylation of the Arp2 subunit relieves auto-inhibitory interactions for Arp2/3 complex activation.","date":"2011","source":"PLoS computational biology","url":"https://pubmed.ncbi.nlm.nih.gov/22125478","citation_count":19,"is_preprint":false},{"pmid":"18805923","id":"PMC_18805923","title":"Molecular dynamics simulation and coarse-grained analysis of the Arp2/3 complex.","date":"2008","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/18805923","citation_count":17,"is_preprint":false},{"pmid":"11162547","id":"PMC_11162547","title":"Interactions among subunits of human Arp2/3 complex: p20-Arc as the hub.","date":"2001","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/11162547","citation_count":16,"is_preprint":false},{"pmid":"35457215","id":"PMC_35457215","title":"Identifying Novel Osteoarthritis-Associated Genes in Human Cartilage Using a Systematic Meta-Analysis and a Multi-Source Integrated Network.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35457215","citation_count":16,"is_preprint":false},{"pmid":"28627476","id":"PMC_28627476","title":"Deciphering the protein-protein interaction network regulating hepatocellular carcinoma metastasis.","date":"2017","source":"Biochimica et biophysica acta. Proteins and proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/28627476","citation_count":15,"is_preprint":false},{"pmid":"38561797","id":"PMC_38561797","title":"Identification of genetic modifiers enhancing B7-H3-targeting CAR T cell therapy against glioblastoma through large-scale CRISPRi screening.","date":"2024","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/38561797","citation_count":14,"is_preprint":false},{"pmid":"29435011","id":"PMC_29435011","title":"Short interfering RNA-mediated silencing of actin-related protein 2/3 complex subunit 4 inhibits the migration of SW620 human colorectal cancer cells.","date":"2017","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/29435011","citation_count":14,"is_preprint":false},{"pmid":"19298826","id":"PMC_19298826","title":"Nucleotide- and activator-dependent structural and dynamic changes of arp2/3 complex monitored by hydrogen/deuterium exchange and mass spectrometry.","date":"2009","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19298826","citation_count":13,"is_preprint":false},{"pmid":"24733187","id":"PMC_24733187","title":"Novel identification of Dermacentor variabilis Arp2/3 complex and its role in rickettsial infection of the arthropod vector.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24733187","citation_count":13,"is_preprint":false},{"pmid":"27559607","id":"PMC_27559607","title":"Protein Interaction Network of Human Protein Kinase D2 Revealed by Chemical Cross-Linking/Mass Spectrometry.","date":"2016","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/27559607","citation_count":11,"is_preprint":false},{"pmid":"23894563","id":"PMC_23894563","title":"Expression of the ARPC4 subunit of human Arp2/3 severely affects mycobacterium tuberculosis growth and suppresses immunogenic response in murine macrophages.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23894563","citation_count":10,"is_preprint":false},{"pmid":"35034100","id":"PMC_35034100","title":"Expression of actin- and oxidative phosphorylation-related transcripts across the cortical visuospatial working memory network in unaffected comparison and schizophrenia subjects.","date":"2022","source":"Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35034100","citation_count":10,"is_preprint":false},{"pmid":"36090174","id":"PMC_36090174","title":"Effects of lipoteichoic and arachidonic acids on the immune-regulatory mechanism of bovine mammary epithelial cells using multi-omics analysis.","date":"2022","source":"Frontiers in veterinary science","url":"https://pubmed.ncbi.nlm.nih.gov/36090174","citation_count":10,"is_preprint":false},{"pmid":"35047857","id":"PMC_35047857","title":"A recurrent, de novo pathogenic variant in ARPC4 disrupts actin filament formation and causes microcephaly and speech delay.","date":"2021","source":"HGG advances","url":"https://pubmed.ncbi.nlm.nih.gov/35047857","citation_count":8,"is_preprint":false},{"pmid":"36429089","id":"PMC_36429089","title":"Inhibition of Arp2/3 Complex after ADP-Ribosylation of Arp2 by Binary Clostridioides Toxins.","date":"2022","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/36429089","citation_count":8,"is_preprint":false},{"pmid":"27900558","id":"PMC_27900558","title":"The role of viral protein Ac34 in nuclear relocation of subunits of the actin-related protein 2/3 complex.","date":"2016","source":"Virologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/27900558","citation_count":8,"is_preprint":false},{"pmid":"40419786","id":"PMC_40419786","title":"Akt-phosphorylated UFL1 UFMylates ArpC4 to promote metastasis.","date":"2025","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/40419786","citation_count":7,"is_preprint":false},{"pmid":"39199289","id":"PMC_39199289","title":"Activation of ARP2/3 and HSP70 Expression by Lipoteichoic Acid: Potential Bidirectional Regulation of Apoptosis in a Mastitis Inflammation Model.","date":"2024","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/39199289","citation_count":6,"is_preprint":false},{"pmid":"36119054","id":"PMC_36119054","title":"Dynamic miRNA profile of host T cells during early hepatic stages of Schistosoma japonicum infection.","date":"2022","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36119054","citation_count":5,"is_preprint":false},{"pmid":"26648486","id":"PMC_26648486","title":"Comparative Proteomic Profiling of Extracellular Proteins between Normal and Gastric Cancer Cells.","date":"2016","source":"Current cancer drug targets","url":"https://pubmed.ncbi.nlm.nih.gov/26648486","citation_count":5,"is_preprint":false},{"pmid":"40243637","id":"PMC_40243637","title":"Cytochalasin B Mitigates the Inflammatory Response in Lipopolysaccharide-Induced Mastitis by Suppressing Both the ARPC3/ARPC4-Dependent Cytoskeletal Changes and the Association Between HSP70 and the NLRP3 Inflammasome.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40243637","citation_count":4,"is_preprint":false},{"pmid":"40930096","id":"PMC_40930096","title":"The Arp2/3 complex maintains gut epithelial integrity under mechanical challenge.","date":"2025","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/40930096","citation_count":3,"is_preprint":false},{"pmid":"35721516","id":"PMC_35721516","title":"p53 Related Protein Kinase is Required for Arp2/3-Dependent Actin Dynamics of Hemocytes in Drosophila melanogaster.","date":"2022","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/35721516","citation_count":3,"is_preprint":false},{"pmid":"12502893","id":"PMC_12502893","title":"Characterization of Arp2/3 complex in chicken tissues.","date":"2002","source":"Cell structure and function","url":"https://pubmed.ncbi.nlm.nih.gov/12502893","citation_count":3,"is_preprint":false},{"pmid":"40597474","id":"PMC_40597474","title":"Actin-myosin complex dissociation initiates programmed cell death during cold storage of grass carp muscle.","date":"2025","source":"Food research international (Ottawa, Ont.)","url":"https://pubmed.ncbi.nlm.nih.gov/40597474","citation_count":2,"is_preprint":false},{"pmid":"37004895","id":"PMC_37004895","title":"Host-pathogen interaction involving cytoskeleton changes as well as non-coding regulation as primary mechanisms for SRS resistance in Atlantic salmon.","date":"2023","source":"Fish & shellfish immunology","url":"https://pubmed.ncbi.nlm.nih.gov/37004895","citation_count":2,"is_preprint":false},{"pmid":"41760937","id":"PMC_41760937","title":"The Arp2/3 complex controls the development of homeostatic microglia.","date":"2026","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/41760937","citation_count":1,"is_preprint":false},{"pmid":"40294934","id":"PMC_40294934","title":"[Aurora-A overexpression promotes cervical cancer cell invasion and metastasis by activating the NF-κBp65/ARPC4 signaling axis].","date":"2025","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/40294934","citation_count":0,"is_preprint":false},{"pmid":"41793310","id":"PMC_41793310","title":"Arp2/3 complex and β1 integrin drive an invasive front through extracellular matrix adaptation in pancreatic cancer.","date":"2026","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/41793310","citation_count":0,"is_preprint":false},{"pmid":"41372366","id":"PMC_41372366","title":"Integrated proteomics and metabolomics analysis revealed that macrophage-related signals may be potential biomarkers for oral squamous cell carcinoma.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41372366","citation_count":0,"is_preprint":false},{"pmid":"41782863","id":"PMC_41782863","title":"The Rho GTPase signaling pathway modulates Moraxella catarrhalis invasion into human respiratory epithelial cells by regulating actin polymerization.","date":"2026","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/41782863","citation_count":0,"is_preprint":false},{"pmid":"41634106","id":"PMC_41634106","title":"Machine learning framework for mRNA alternative splicing analysis identifies a signature of progression in colorectal adenocarcinoma.","date":"2026","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41634106","citation_count":0,"is_preprint":false},{"pmid":"40305275","id":"PMC_40305275","title":"Targeted Regulation of HSP70 by the ARP2/3 Complex in Mammary Epithelial Cells and Its Impact on Host Cell Apoptosis.","date":"2025","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/40305275","citation_count":0,"is_preprint":false},{"pmid":"41963733","id":"PMC_41963733","title":"Dispensable players: N-WASP and WASP are not crucial for homology-directed DNA repair.","date":"2026","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/41963733","citation_count":0,"is_preprint":false},{"pmid":"42246926","id":"PMC_42246926","title":"Discovery of Casdatifan, Part II: A Potent and Orally Bioavailable Inhibitor of Hypoxia Inducible Factor-2α.","date":"2026","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/42246926","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.27.630538","title":"The Arp2/3 complex maintains genome integrity and survival of epidermal Langerhans cells","date":"2024-12-29","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.27.630538","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":56060,"output_tokens":10645,"usd":0.25336,"retried_sync":true,"stage1_stop_reason":"refusal"},"stage2":{"model":"claude-opus-4-8","input_tokens":15166,"output_tokens":4039,"usd":0.088402,"stage2_stop_reason":"end_turn"},"total_usd":0.341762,"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\": 1997,\n      \"finding\": \"ARPC4 (p20-Arc) was identified as one of seven subunits of the human Arp2/3 complex; the complex localizes to lamellipodia of fibroblasts and Listeria actin tails (but not actin bundles), consistent with a role in promoting actin assembly at sites of dynamic polymerization.\",\n      \"method\": \"Protein purification, sequencing, immunofluorescence localization in cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct biochemical purification and localization by immunofluorescence, replicated across multiple cell contexts, foundational paper\",\n      \"pmids\": [\"9230079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Crystal structure of bovine Arp2/3 complex at 2.0 Å resolution revealed that ARPC4 (p20) and ARPC2 (p34) form the core of the complex through long C-terminal alpha helices and similarly folded N-terminal alpha/beta domains.\",\n      \"method\": \"X-ray crystallography at 2.0 Å resolution\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure, widely replicated and cited as foundational structural result\",\n      \"pmids\": [\"11721045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Yeast two-hybrid analysis showed that p20-Arc (ARPC4) acts as a hub for subunit interactions within the human Arp2/3 complex, interacting with p21-Arc (ARPC3), p34-Arc (ARPC2), and p16-Arc (ARPC5); p41-Arc only interacted with the p20-Arc/p16-Arc heterodimer. Structural integrity was important for p20-Arc/p21-Arc association, while the N-terminal half of p34-Arc was dispensable for its binding to p20-Arc.\",\n      \"method\": \"Yeast two-hybrid assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — systematic yeast two-hybrid covering all pairwise combinations within the complex, single lab, single method\",\n      \"pmids\": [\"11162547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Molecular dynamics and protein-protein docking simulations, validated by mutagenesis, defined an actin-filament-binding interface on ARPC2 and ARPC4. Residues at this interface are required for actin nucleation, Y-branching, high-affinity F-actin binding, and Y-branch stability, demonstrating that Arp2/3 complex affinity for F-actin independently modulates branch formation and stability.\",\n      \"method\": \"Molecular dynamics/docking simulations + mutagenesis + in vitro actin assembly assays + F-actin binding assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — combined computational modelling with extensive mutagenesis and multiple in vitro functional assays, multiple orthogonal methods in one study\",\n      \"pmids\": [\"20404198\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Molecular dynamics simulations of Arp2/3 activation showed that one structural block (comprising Arp2, ARPC1, the globular domain of ARPC4, and ARPC5) rotates ~30° around a pivot point in an alpha-helix of ARPC4 (Glu81–Asn100) to bring Arp2 into proximity with Arp3 during activation.\",\n      \"method\": \"Atomistic molecular dynamics simulations\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational simulation only, no direct experimental validation in this paper\",\n      \"pmids\": [\"20959098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Phosphorylation of Arp2 destabilizes a network of auto-inhibitory salt-bridge interactions at the interface of Arp2, Arp3, and ARPC4, permitting Arp2 reorientation to an activation-competent state. A gain-of-function ARPC4 mutant predicted to disrupt these interactions showed substantial actin nucleation activity in the absence of NPFs.\",\n      \"method\": \"Molecular dynamics simulations + biochemical assays with recombinant Arp2/3 complex carrying ARPC4 mutations\",\n      \"journal\": \"PLoS computational biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — computational prediction supported by experimental validation of ARPC4 gain-of-function mutant in biochemical assay, single lab\",\n      \"pmids\": [\"22125478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Hydrogen/deuterium exchange mass spectrometry showed that ATP binding to Arp2/3 complex causes conformational rearrangements in Arp2 and Arp3 that are allosterically transmitted to ARPC4 (and ARPC1, ARPC2, ARPC5); WASp VCA binding further modulates exchange rates in ARPC4, indicating global conformational reorganization involving this subunit upon activation.\",\n      \"method\": \"Hydrogen/deuterium exchange coupled with mass spectrometry\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct structural dynamics measurement on purified complex, single lab, single technique\",\n      \"pmids\": [\"19298826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In S. cerevisiae, a contact surface between p35/ARPC2 and p19/ARPC4 was identified as required for actin nucleation and endocytosis; mutations near this interface abolished nucleation without disrupting complex integrity.\",\n      \"method\": \"Systematic mutagenesis in S. cerevisiae + purification of mutant complexes + in vitro actin assembly assays + endocytosis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified mutant complexes plus cellular functional assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"18381280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In S. cerevisiae, lethal mutations at the p40/ARPC1 contact with p19/ARPC4 specifically impaired WASp-induced nucleation of purified Arp2/3 complex, placing ARPC4 at the interface required for WASp activation signal propagation.\",\n      \"method\": \"Mutagenesis of ARPC1 + purification of mutant complexes + in vitro actin nucleation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — purified mutant complexes with in vitro reconstitution assays; ARPC4 contact site directly tested; multiple methods in single study\",\n      \"pmids\": [\"20071330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Conditional knockout of Arpc4 in mouse epidermis depleted the Arp2/3 complex and caused a psoriasis-like disease; Arpc4 knockout in cultured keratinocytes was sufficient to induce nuclear accumulation of Nrf2, upregulation of Nrf2 target genes, and decreased F-actin levels. In vitro, Nrf2 was shown to bind to filamentous actin.\",\n      \"method\": \"Conditional Arpc4 knockout mouse model + keratinocyte culture KO + pharmacological Arp2/3 inhibition + in vitro F-actin binding assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO mouse + cell culture KO + pharmacological inhibition + direct F-actin binding assay, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"29113991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Conditional ablation of Arpc4 in mouse pancreatic acinar cells demonstrated that the Arp2/3 complex is required for KrasG12D-driven acinar-to-ductal metaplasia (ADM) in vivo; mTORC1 regulates Arp2/3 complex activity via Rac1/Arp3 translation while mTORC2 promotes Arp2/3 via Akt/Rac1, converging on ARPC4-containing Arp2/3 as a common downstream effector for actin cortex remodeling and ADM.\",\n      \"method\": \"Conditional Arpc4 knockout mouse + in vitro ADM assays + epistasis with Rptor/Rictor conditional knockouts\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo conditional KO mouse with epistasis analysis, multiple genetic models, replicated in vitro\",\n      \"pmids\": [\"33388318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A recurrent de novo missense variant in ARPC4 (p.Arg158Cys) found in patients with microcephaly and speech delay was associated with decreased F-actin levels in cells from affected individuals, implicating ARPC4 in actin filament network formation required for neurodevelopment.\",\n      \"method\": \"Patient cell-based F-actin quantification (immunofluorescence/imaging) in cells from affected individuals carrying the variant\",\n      \"journal\": \"HGG advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — patient cell-based assay showing F-actin reduction, supported across multiple families, but no in vitro reconstitution\",\n      \"pmids\": [\"35047857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"UFL1 (UFM1-specific E3 ligase 1) interacts with ArpC4 and catalyzes its UFMylation. Akt phosphorylates UFL1 at T426, which enhances UFL1's interaction with ArpC4 and promotes ArpC4 UFMylation, thereby facilitating lamellipodia formation, cell migration, invasion, and metastasis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro UFMylation assay, phosphorylation mapping, loss-of-function cell migration/invasion assays, lamellipodia imaging\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical identification of UFMylation on ArpC4, upstream kinase (Akt) phosphorylation mapped, in vitro assay plus functional cellular readouts, multiple orthogonal methods\",\n      \"pmids\": [\"40419786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Binary clostridial toxins (CDT, C2I, Iota) ADP-ribosylate ARPC4/5 (among other Arp2/3 subunits) in addition to actin and Arp2, and this modification inhibits Arp2/3 complex actin-nucleating activity, causing collapse of lamellipodia and F-actin networks in cells.\",\n      \"method\": \"Mass spectrometry identification of ADP-ribosylation sites + in vitro Arp2/3 activity assays + cell imaging (Caco2 cells + mouse colon explants)\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-based site identification plus in vitro functional assay and cellular assay, single lab\",\n      \"pmids\": [\"36429089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"siRNA-mediated silencing of ARPC4 significantly reduced cell migration (50–68% decrease) in pancreatic cancer cell lines without affecting other processes, indicating ARPC4 is a key functional subunit for Arp2/3-dependent migration in these cells.\",\n      \"method\": \"siRNA knockdown + transwell migration assay in multiple pancreatic cancer cell lines\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — siRNA knockdown with quantitative migration readout replicated across multiple cell lines, single lab\",\n      \"pmids\": [\"23267127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ARPC4 knockdown in T24 bladder cancer cells attenuated migration, invasion, and pseudopodia formation and disrupted actin cytoskeleton structure, demonstrating a direct role of ARPC4 in actin-dependent invasive behavior.\",\n      \"method\": \"siRNA knockdown + transwell invasion/migration assay + wound-healing assay + immunofluorescence of actin cytoskeleton\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — siRNA KD with multiple functional readouts, single lab\",\n      \"pmids\": [\"31190401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Chemical cross-linking/mass spectrometry identified the entire seven-subunit Arp2/3 complex (including ARPC4) as an interaction partner of human PKD2 in both cytosolic and Golgi-enriched fractions, with evidence of a direct protein-protein interaction between PKD2 and Arp2/3.\",\n      \"method\": \"Affinity enrichment + chemical cross-linking + mass spectrometry\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, cross-linking MS identifies interaction but no reciprocal validation or functional follow-up specific to ARPC4\",\n      \"pmids\": [\"27559607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Expression of ARPC4 in Mycobacterium tuberculosis severely impaired bacterial growth (evidenced by TEM showing outer-coat shedding), enhanced bacterial clearance in infected macrophages, impaired phagosome-to-lysosome translocation, and suppressed pro-inflammatory cytokine responses. ARPC4 was shown to interact with the essential mycobacterial secretory protein Rv1626, downregulating its expression ~6-fold; Rv1626 also interacted with mammalian Arp2/3 and enhanced actin polymerization.\",\n      \"method\": \"Bacterial expression of ARPC4 + TEM + macrophage infection assays + co-immunoprecipitation (ARPC4–Rv1626 interaction) + real-time PCR\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus multiple functional readouts; interaction and functional consequences demonstrated by orthogonal methods, single lab\",\n      \"pmids\": [\"23894563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Viral protein Ac34 (baculovirus) co-immunoprecipitated with ARPC4 (P20) of Sf9 (insect) cells and induced its nuclear relocation; however, mammalian ARPC4 did not interact with Ac34 and was not relocated, indicating species-specific binding specificity.\",\n      \"method\": \"Immunofluorescence + co-immunoprecipitation\",\n      \"journal\": \"Virologica Sinica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP in insect cells; finding is about insect ARPC4 with negative result for mammalian ARPC4\",\n      \"pmids\": [\"27900558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In cervical cancer cells, Aurora-A overexpression upregulated ARPC4 expression via activation of the NF-κBp65 signaling pathway (increased NF-κBp65 phosphorylation led to elevated ARPC4 levels), and ARPC4 knockdown antagonized Aurora-A-promoted migration, invasion, and EMT.\",\n      \"method\": \"Plasmid overexpression + shRNA knockdown + NF-κBp65 inhibitor treatment + Western blot + migration/invasion assays\",\n      \"journal\": \"Nan fang yi ke da xue xue bao\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — epistasis by combined OE/KD/pharmacological inhibition with functional readouts, single lab\",\n      \"pmids\": [\"40294934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A genome-wide CRISPR knockout screen in THP-1 macrophages identified ARPC4 loss-of-function as conferring resistance to Salmonella uptake, placing ARPC4-containing Arp2/3 complex in the actin dynamics pathway required for macrophage phagocytic internalization of bacteria.\",\n      \"method\": \"Genome-wide CRISPR KO screen + validation assays\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genome-scale screen with follow-up validation, but ARPC4-specific mechanistic follow-up was not deep; functional placement in phagocytosis pathway established\",\n      \"pmids\": [\"31594818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In a gut epithelium-specific inducible Arpc4 knockout mouse, loss of Arp2/3 function led to increased intestinal permeability, disrupted tight junction protein localization, epithelial fracturing, and lethality under mechanical challenge; ex vivo organoid experiments showed defects required mechanical stress and elevated actomyosin contractility to manifest.\",\n      \"method\": \"Inducible conditional Arpc4 KO mouse + ex vivo intestinal slice culture + organoid culture + tight junction imaging\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible conditional KO mouse plus multiple ex vivo models with defined mechanical challenge, multiple orthogonal readouts\",\n      \"pmids\": [\"40930096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Conditional Arpc4 knockout in myeloid cells showed that Arp2/3 complex loss in Langerhans cells leads to cell decline through DNA damage accumulation associated with aberrant nuclear shapes, lamina reduction, and nuclear envelope rupture, revealing a role for Arp2/3/ARPC4 in nuclear envelope integrity and genome maintenance in tissue-resident immune cells.\",\n      \"method\": \"Conditional Arpc4 KO mouse + in vivo LC analysis + in vitro BMDC experiments + cell cycle analysis + nuclear morphology/DNA damage assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO mouse with in vitro corroboration and multiple cellular readouts; preprint, not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Conditional Arpc4 knockout in microglia showed that Arp2/3 depletion prevents the developmental transition of microglia into ramified cells with homeostatic gene profiles and surveillance function, linking ARPC4-dependent actin branching to microglial maturation in the CNS.\",\n      \"method\": \"Conditional Arpc4 KO mouse + morphological analysis + transcriptomic profiling of microglia + CNS surveillance assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO mouse with morphological, transcriptomic, and functional readouts in multiple complementary assays\",\n      \"pmids\": [\"41760937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CRISPR/Cas9 knockout of Arpc4 in murine PDAC cell lines downregulated all Arp2/3 complex members and significantly impaired PDAC cell migration, disrupted branched tubular structure formation in collagen I, and inhibited invasive front formation in organoid culture; β1 integrin signaling was identified as a key upstream regulator of Arp2/3-dependent migration through collagen-rich matrices.\",\n      \"method\": \"CRISPR/Cas9 KO + 2D and 3D migration/invasion assays + organoid co-culture + β1 integrin signaling analysis\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with multiple functional assays and pathway placement via β1 integrin epistasis, single lab\",\n      \"pmids\": [\"41793310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ArpC4 knockdown by siRNA in U2OS cells reduced HDR efficiency, but this effect corresponded with decreased transfection efficiency and reduction in S/G2M cell cycle phases rather than a direct role in DNA repair; WASP/N-WASP were found dispensable for HDR.\",\n      \"method\": \"siRNA knockdown + CRISPR-based HDR reporter assay + cell cycle analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — controlled siRNA KD with cell cycle analysis distinguishing indirect effect; negative mechanistic finding rigorously established\",\n      \"pmids\": [\"41963733\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARPC4 (p20-Arc/ARC20) is a core structural subunit of the seven-protein Arp2/3 complex that, together with ARPC2, forms the central scaffold of the complex via interlocking C-terminal helices and N-terminal alpha/beta domains; it serves as an interaction hub connecting ARPC2, ARPC3, ARPC5, and ARPC1, and harbors a pivot helix (Glu81–Asn100) around which the complex undergoes the ~30° conformational rotation that activates actin nucleation. The ARPC2–ARPC4 interface directly contacts the mother actin filament, with specific residues required for F-actin binding, Y-branch nucleation, and branch stability; disruption of auto-inhibitory salt bridges at the Arp2–Arp3–ARPC4 interface (e.g., by Arp2 phosphorylation) permits complex activation. Post-translationally, ArpC4 is UFMylated by UFL1 downstream of Akt-mediated phosphorylation of UFL1, promoting lamellipodia formation and metastatic cell migration; it is also ADP-ribosylated by clostridial binary toxins, which inhibits complex activity. Loss of ARPC4 in conditional knockout models disrupts epidermal homeostasis (causing Nrf2 hyperactivation), impairs intestinal epithelial barrier integrity under mechanical stress, blocks microglial maturation and ramification, promotes DNA damage in Langerhans cells, prevents pancreatic acinar-to-ductal metaplasia downstream of mTORC1/2–Rac1 signaling, and inhibits cancer cell migration and invasion across multiple tumor types.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARPC4 (p20-Arc) is a core structural subunit of the seven-protein Arp2/3 complex, the actin nucleator that builds branched filament networks at sites of dynamic polymerization such as lamellipodia and bacterial actin tails [#0]. Together with ARPC2, ARPC4 forms the structural core of the complex through long C-terminal alpha helices and similarly folded N-terminal alpha/beta domains [#1], and it serves as a subunit-interaction hub contacting ARPC2, ARPC3, and ARPC5 [#2]. The ARPC2\\u2013ARPC4 interface directly engages the mother actin filament: residues at this surface are required for actin nucleation, Y-branch formation, high-affinity F-actin binding, and branch stability [#3, #7], and the ARPC1\\u2013ARPC4 contact is required to propagate the WASp activation signal [#8]. Activation involves global conformational reorganization transmitted to ARPC4 upon ATP and WASp-VCA binding [#6], with auto-inhibitory salt bridges at the Arp2\\u2013Arp3\\u2013ARPC4 interface gating the complex; their disruption yields constitutive nucleation [#5]. ARPC4 activity is regulated post-translationally: UFL1, when phosphorylated by Akt, UFMylates ArpC4 to promote lamellipodia formation, migration, and metastasis [#12], whereas clostridial binary toxins ADP-ribosylate ARPC4 to inhibit nucleation and collapse F-actin networks [#13]. Through this branched-actin function, ARPC4 supports a broad range of cellular and tissue processes \\u2014 epidermal homeostasis with Nrf2 restraint [#9], pancreatic acinar-to-ductal metaplasia downstream of mTORC1/2\\u2013Rac1 signaling [#10], intestinal epithelial barrier integrity under mechanical stress [#21], microglial maturation [#23], and cancer cell migration and invasion across tumor types [#14, #15, #24]. A recurrent de novo missense variant (p.Arg158Cys) causes reduced cellular F-actin in patients with microcephaly and speech delay, linking ARPC4 to a neurodevelopmental disorder [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that ARPC4 is a bona fide subunit of the human Arp2/3 complex and that the complex localizes to sites of dynamic actin assembly, defining its cellular arena.\",\n      \"evidence\": \"Protein purification, sequencing, and immunofluorescence in fibroblasts and Listeria actin tails\",\n      \"pmids\": [\"9230079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve ARPC4's specific structural or functional contribution within the complex\", \"Localization correlative, not mechanistic\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved how ARPC4 is built into the complex, showing it pairs with ARPC2 to form the structural core and acts as a hub for inter-subunit contacts.\",\n      \"evidence\": \"2.0 \\u00c5 X-ray crystallography of bovine complex and pairwise yeast two-hybrid mapping\",\n      \"pmids\": [\"11721045\", \"11162547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Static structure does not reveal the activation conformational change\", \"Y2H interactions not validated by reciprocal biochemistry\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined ARPC4 functionally by mapping the ARPC2\\u2013ARPC4 actin-filament-binding interface and showing distinct residues control nucleation, branching, F-actin affinity, and branch stability.\",\n      \"evidence\": \"Molecular dynamics/docking with mutagenesis and in vitro actin assembly and F-actin binding assays\",\n      \"pmids\": [\"20404198\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interface defined computationally before high-resolution branch junction structures\", \"Did not address the activating conformational rotation\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected ARPC4 to activation by identifying an auto-inhibitory salt-bridge network at the Arp2\\u2013Arp3\\u2013ARPC4 interface whose disruption produces NPF-independent nucleation.\",\n      \"evidence\": \"Molecular dynamics simulations plus biochemical assays of a gain-of-function ARPC4 mutant complex; complemented by H/DX-MS showing allosteric conformational transmission to ARPC4 and the ARPC4 pivot-helix rotation model\",\n      \"pmids\": [\"22125478\", \"19298826\", \"20959098\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pivot-helix rotation rests on simulation without direct experimental validation\", \"In vivo relevance of the Arp2-phosphorylation gating not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated in a genetically tractable system that the ARPC2\\u2013ARPC4 and ARPC1\\u2013ARPC4 contacts are required for nucleation and WASp activation independent of complex assembly.\",\n      \"evidence\": \"Systematic mutagenesis in S. cerevisiae with purified mutant complexes, in vitro nucleation assays, and endocytosis assays\",\n      \"pmids\": [\"18381280\", \"20071330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Yeast residue requirements not directly mapped onto human ARPC4 function\", \"Mechanism of signal propagation through the interface not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established a tissue-level requirement for ARPC4 in epidermal homeostasis and linked actin loss to a transcriptional consequence via Nrf2.\",\n      \"evidence\": \"Conditional Arpc4 KO mouse, keratinocyte KO, Arp2/3 inhibition, and in vitro Nrf2\\u2013F-actin binding assay\",\n      \"pmids\": [\"29113991\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Nrf2 sequestration by F-actin is the sole driver of the phenotype unclear\", \"Direct ARPC4 contribution versus whole-complex depletion not separated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Positioned ARPC4-containing Arp2/3 as a convergent effector of mTORC1/2\\u2013Rac1 signaling driving Kras-induced pancreatic metaplasia, and linked an ARPC4 missense variant to a neurodevelopmental disorder.\",\n      \"evidence\": \"Conditional Arpc4 KO mouse with Rptor/Rictor epistasis and ADM assays; patient-cell F-actin quantification for the p.Arg158Cys variant\",\n      \"pmids\": [\"33388318\", \"35047857\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical effect of p.Arg158Cys on complex assembly/nucleation not reconstituted\", \"How mTOR signals couple to ARPC4 mechanistically beyond Rac1 not detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified ARPC4 as a post-translationally regulated subunit, being ADP-ribosylated by clostridial binary toxins to inhibit nucleation.\",\n      \"evidence\": \"Mass spectrometry site identification, in vitro Arp2/3 activity assays, and cell/explant imaging\",\n      \"pmids\": [\"36429089\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of ARPC4 versus actin/Arp2 ADP-ribosylation to inhibition unresolved\", \"Physiological host modifications at these sites not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined an activating regulatory axis in which Akt-phosphorylated UFL1 UFMylates ArpC4 to drive lamellipodia formation and metastatic migration.\",\n      \"evidence\": \"Co-IP, in vitro UFMylation, phosphorylation mapping (Akt T426 on UFL1), and loss-of-function migration/invasion/lamellipodia assays\",\n      \"pmids\": [\"40419786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"UFMylated residue effect on complex conformation/nucleation not structurally defined\", \"In vivo metastasis dependence on this modification in physiological settings not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed ARPC4 is required for mechanically stressed epithelial barrier integrity, revealing that branched-actin defects manifest only under load.\",\n      \"evidence\": \"Inducible gut-specific Arpc4 KO mouse, ex vivo intestinal slices, and organoids with defined mechanical challenge and tight junction imaging\",\n      \"pmids\": [\"40930096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between branched actin and tight junction maintenance not resolved\", \"Actomyosin contractility interplay mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended ARPC4's roles to immune and CNS cell maturation and to nuclear envelope integrity, while a controlled study showed an apparent DNA-repair role is indirect.\",\n      \"evidence\": \"Conditional Arpc4 KO mice in microglia and Langerhans cells with morphological/transcriptomic/nuclear assays; CRISPR KO in PDAC lines with collagen invasion and \\u03b21 integrin analysis; siRNA HDR reporter with cell-cycle controls\",\n      \"pmids\": [\"41760937\", \"41793310\", \"41963733\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Langerhans cell nuclear-integrity finding remains a preprint without peer review\", \"How branched actin maintains nuclear envelope integrity mechanistically unknown\", \"Direct versus cell-cycle-mediated effects need disentangling across contexts\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct post-translational modifications (UFMylation, ADP-ribosylation) and disease variants of ARPC4 alter the conformational activation cycle and branch-forming activity at atomic resolution remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of modified or variant ARPC4 within an activated branch junction\", \"Tissue-specificity of ARPC4 requirements not mechanistically explained beyond whole-complex depletion\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9, 23]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 14, 24]}\n    ],\n    \"complexes\": [\"Arp2/3 complex\"],\n    \"partners\": [\"ARPC2\", \"ARPC3\", \"ARPC5\", \"ARPC1\", \"UFL1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}