{"gene":"ARPC5L","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2023,"finding":"ARPC5L specifically drives nuclear actin polymerization upon TCR activation in CD4 T cells, while ARPC5 is required for cytoplasmic actin dynamics. TCR-induced nuclear actin polymerization requires nuclear calcium-calmodulin signaling and N-WASP upstream of ARPC5L. In contrast, DNA replication stress-induced nuclear actin polymerization specifically requires ARPC5 but not ARPC5L.","method":"Reverse genetics (isoform-specific knockdown/knockout), live-cell imaging of nuclear and cytoplasmic actin polymerization in CD4 T cells, stimulus-specific perturbation experiments","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific genetic knockdown with distinct phenotypic readouts, multiple stimuli tested, pathway placement via calcium-calmodulin-N-WASP epistasis","pmids":["37162507"],"is_preprint":false},{"year":2023,"finding":"ArpC5L and ArpC5 differentially regulate Arp2/3 complex-dependent cell migration by defining structural stability of ArpC1 in branch junctions, determining protrusion characteristics, and affecting actin network ultrastructure. ArpC5 isoforms also differentially position Ena/VASP family actin elongators, which mediate isoform-specific effects on actin assembly, placing ArpC5/ArpC5L and Ena/VASP in a shared signaling pathway enhancing cell migration.","method":"Reverse genetics (isoform-specific knockouts), cellular structural biology (cryo-electron tomography of branch junctions), FRAP/protein dynamics measurements, fluorescence microscopy of actin network ultrastructure","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reverse genetics combined with cryo-ET structural analysis of branch junctions plus protein dynamics measurements; multiple orthogonal methods in one study","pmids":["36662867"],"is_preprint":false},{"year":2024,"finding":"Mutation of a mechanosensitive site between talin 1 rod-domain helix bundles R1 and R2 promotes binding of the Arp2/3 complex subunit ARPC5L to a cryptic site in talin, and this interaction mediates altered ECM stiffness sensing in cells. Cells bearing these talin mutations spread and exert tension on compliant substrates in an ARPC5L-dependent manner.","method":"Site-directed mutagenesis of talin 1, pull-down assays, cellular phenotype rescue experiments on compliant substrates, mouse genetic model (ascending aorta mechanics)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutagenesis-driven binding assay, cellular functional rescue, and in vivo mouse model; replicated in preprint and peer-reviewed publication by same group","pmids":["39167642","38328095"],"is_preprint":false},{"year":2024,"finding":"Tension applied to the talin rod domain via a DNA-based molecular clamp induces binding of ARPC5L to a cryptic site within the talin structure, as shown by pull-down assays, demonstrating that ARPC5L binding to talin is force-dependent.","method":"DNA-based molecular clamp device applying defined tension to talin fragment, pull-down assays, negative-stain electron microscopy","journal":"ACS nano","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — novel in vitro reconstitution device with structural validation; single lab, but orthogonal biochemical and EM methods; replicated in preprint","pmids":["39344156","38895381"],"is_preprint":false},{"year":2024,"finding":"In mammary epithelial cells (MCF10A), combined PI 3-kinase activation (H1047R) and KMT2D inactivation induces ARPC5L gene expression, and ARPC5L depletion fully abolishes the enhanced single-cell migration persistence exhibited by these double-mutant cells, placing ARPC5L-containing Arp2/3 complex downstream of these oncogenic signals in mediating migration.","method":"Genetic reconstitution (PI3K mutation + KMT2D knockout), ARPC5L siRNA depletion, single-cell migration assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean loss-of-function with specific migration phenotype, genetic epistasis placing ARPC5L downstream; single lab, single method per step","pmids":["38786098"],"is_preprint":false},{"year":2024,"finding":"Loss of Arpc5l (but not Arpc5) in the murine hematopoietic system does NOT cause intestinal inflammation or impair macrophage phagocytosis and bacterial killing, establishing that Arpc5l-containing Arp2/3 complexes are dispensable for mononuclear phagocyte function and host-microbiota homeostasis, in contrast to Arpc5.","method":"Conditional hematopoietic knockout mouse models for Arpc5 and Arpc5l, intestinal inflammation phenotyping, macrophage phagocytosis and bacterial killing assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean in vivo KO with specific cellular phenotype readouts; preprint, single lab, but rigorous genetic approach","pmids":["bio_10.1101_2024.07.18.604111"],"is_preprint":true},{"year":2016,"finding":"ARPC5L was identified as a component of PKD2 protein complexes in cytosolic and Golgi-enriched fractions, alongside the canonical Arp2/3 complex subunits, suggesting ARPC5L-containing Arp2/3 complexes interact with PKD2.","method":"Affinity enrichment combined with chemical cross-linking/mass spectrometry from cytosolic and Golgi subcellular fractions","journal":"Journal of proteome research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single cross-linking MS experiment; no functional follow-up on ARPC5L specifically; single lab","pmids":["27559607"],"is_preprint":false},{"year":2014,"finding":"ARPC5L was found to be dephosphorylated in osteosarcoma SaOS-2 cells treated with the Src inhibitor SI-83, concomitant with impaired cell migration and adhesion, suggesting that phosphorylation of ARPC5L may contribute to Src-driven cytoskeletal dynamics and metastatic behavior.","method":"Gel-based phosphoproteomics of SI-83-treated osteosarcoma cells, cell migration and adhesion assays","journal":"Molecular bioSystems","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single phosphoproteomics observation with no direct mechanistic follow-up on ARPC5L specifically; single lab, correlative","pmids":["24615350"],"is_preprint":false}],"current_model":"ARPC5L is an alternative isoform subunit of the Arp2/3 complex that confers distinct properties relative to its paralog ARPC5: it drives nuclear actin polymerization downstream of TCR/calcium-calmodulin-N-WASP signaling in CD4 T cells, regulates Arp2/3 branch junction stability and Ena/VASP positioning to fine-tune cell migration, binds to a cryptic mechanosensitive site in talin 1 in a force-dependent manner to mediate ECM stiffness sensing, and is required for PI3K/KMT2D-driven migration persistence in mammary epithelial cells, while being dispensable for macrophage phagocytosis and host-microbiota homeostasis."},"narrative":{"mechanistic_narrative":"ARPC5L is an alternative isoform subunit of the Arp2/3 actin-nucleating complex whose incorporation confers branch-specific properties distinct from its paralog ARPC5, allowing the same machinery to drive different actin-dependent processes depending on stimulus and context [PMID:36662867]. At the structural level, ARPC5L versus ARPC5 incorporation defines the stability of ARPC1 within branch junctions and tunes actin network ultrastructure and protrusion characteristics, and the two isoforms differentially position Ena/VASP family elongators to produce isoform-specific effects on migration [PMID:36662867]. ARPC5L confers stimulus selectivity in the nucleus: in CD4 T cells it drives TCR-induced nuclear actin polymerization downstream of nuclear calcium-calmodulin and N-WASP signaling, whereas replication-stress-induced nuclear actin requires ARPC5 instead [PMID:37162507]. ARPC5L also acts as a force-dependent partner of the focal-adhesion protein talin 1, binding a cryptic mechanosensitive site exposed between talin rod helix bundles R1 and R2 under tension to mediate ECM stiffness sensing and substrate-dependent cell spreading [PMID:39167642, PMID:38328095, PMID:39344156, PMID:38895381]. Functionally, ARPC5L-containing Arp2/3 complex is required for the enhanced single-cell migration persistence driven by combined PI3K activation and KMT2D loss in mammary epithelial cells [PMID:38786098], while it is dispensable for macrophage phagocytosis and host-microbiota homeostasis, a role specific to ARPC5 [PMID:bio_10.1101_2024.07.18.604111].","teleology":[{"year":2023,"claim":"Established that ARPC5L and ARPC5 are not redundant Arp2/3 subunits but partition actin-dependent functions by stimulus and subcellular compartment.","evidence":"Isoform-specific knockdown/knockout with live-cell imaging of nuclear and cytoplasmic actin and calcium-calmodulin/N-WASP epistasis in CD4 T cells","pmids":["37162507"],"confidence":"High","gaps":["Molecular basis for why ARPC5L versus ARPC5 is recruited to specific stimuli is unresolved","How nuclear N-WASP selectively activates ARPC5L-containing complexes is not defined"]},{"year":2023,"claim":"Resolved how isoform identity changes the Arp2/3 complex physically, linking ARPC5L incorporation to branch-junction stability, network ultrastructure, and Ena/VASP positioning.","evidence":"Isoform-specific knockouts combined with cryo-electron tomography of branch junctions and FRAP protein-dynamics measurements","pmids":["36662867"],"confidence":"High","gaps":["Structural determinants within ARPC5L responsible for differential ARPC1 stabilization not pinpointed","Mechanism coupling branch-junction stability to Ena/VASP recruitment unknown"]},{"year":2024,"claim":"Identified ARPC5L as a force-gated binding partner of talin 1, connecting the Arp2/3 subunit directly to mechanosensing at adhesions.","evidence":"Site-directed mutagenesis of the talin R1-R2 cryptic site, pull-down assays, cellular spreading/traction rescue on compliant substrates, and an aortic-mechanics mouse model","pmids":["39167642","38328095"],"confidence":"High","gaps":["Whether talin binds intact Arp2/3 complex or free ARPC5L is not established","Functional consequence of talin-ARPC5L binding for actin nucleation itself is undefined"]},{"year":2024,"claim":"Demonstrated directly that the talin-ARPC5L interaction is tension-dependent, confirming force as the trigger for cryptic-site exposure.","evidence":"DNA-based molecular clamp applying defined tension to a talin fragment, with pull-down assays and negative-stain EM","pmids":["39344156","38895381"],"confidence":"Medium","gaps":["Single-lab in vitro reconstitution; physiological force thresholds in cells not measured","Binding affinity and stoichiometry not quantified"]},{"year":2024,"claim":"Placed ARPC5L downstream of oncogenic PI3K/KMT2D signaling as an effector of migration persistence in epithelial cells.","evidence":"Genetic reconstitution of PI3K H1047R plus KMT2D knockout in MCF10A, ARPC5L siRNA depletion, single-cell migration assays","pmids":["38786098"],"confidence":"Medium","gaps":["Transcriptional route from KMT2D loss to ARPC5L induction not mapped","Single method per epistasis step"]},{"year":2024,"claim":"Defined the boundary of ARPC5L function by showing it is dispensable for phagocyte function, sharpening the division of labor with ARPC5 in vivo.","evidence":"Conditional hematopoietic Arpc5 and Arpc5l knockout mice with intestinal inflammation phenotyping and macrophage phagocytosis/killing assays (preprint)","pmids":["bio_10.1101_2024.07.18.604111"],"confidence":"Medium","gaps":["Preprint, single lab, not yet peer-reviewed","Does not test ARPC5L roles in other immune lineages"]},{"year":null,"claim":"How the cell selects ARPC5L- versus ARPC5-containing Arp2/3 complexes at specific stimuli, locations, and force regimes remains the central open question.","evidence":"No direct evidence in the available corpus","pmids":[],"confidence":"Low","gaps":["No mechanism for isoform-selective assembly or recruitment","Functional significance of reported PKD2 association and Src-dependent phosphorylation not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1]}],"complexes":["Arp2/3 complex"],"partners":["TLN1","ARPC1","WASL","PKD2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BPX5","full_name":"Actin-related protein 2/3 complex subunit 5-like protein","aliases":["Arp2/3 complex 16 kDa subunit 2","ARC16-2"],"length_aa":153,"mass_kda":16.9,"function":"May function as component of the Arp2/3 complex which is involved in regulation of actin polymerization and together with an activating nucleation-promoting factor (NPF) mediates the formation of branched actin networks","subcellular_location":"Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/Q9BPX5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ARPC5L","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ACTR2","stoichiometry":10.0},{"gene":"ARPC2","stoichiometry":10.0},{"gene":"ARPC3","stoichiometry":10.0},{"gene":"ACTB","stoichiometry":0.2},{"gene":"ACTG1","stoichiometry":0.2},{"gene":"ACTN4","stoichiometry":0.2},{"gene":"ARL8B","stoichiometry":0.2},{"gene":"CALD1","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ARPC5L","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":"604227","title":"ACTIN-RELATED PROTEIN 2/3 COMPLEX, SUBUNIT 5; ARPC5","url":"https://www.omim.org/entry/604227"}],"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/ARPC5L"},"hgnc":{"alias_symbol":["MGC3038","ARC16-2"],"prev_symbol":[]},"alphafold":{"accession":"Q9BPX5","domains":[{"cath_id":"1.25.40.190","chopping":"37-147","consensus_level":"medium","plddt":94.2438,"start":37,"end":147}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPX5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPX5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPX5-F1-predicted_aligned_error_v6.png","plddt_mean":89.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARPC5L","jax_strain_url":"https://www.jax.org/strain/search?query=ARPC5L"},"sequence":{"accession":"Q9BPX5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BPX5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BPX5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPX5"}},"corpus_meta":[{"pmid":"25947061","id":"PMC_25947061","title":"'Conceptualizing' the Endometrium: Identification of Conceptus-Derived Proteins During Early Pregnancy in Cattle.","date":"2015","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/25947061","citation_count":82,"is_preprint":false},{"pmid":"24480542","id":"PMC_24480542","title":"Defective minor spliceosome mRNA processing results in isolated familial growth hormone deficiency.","date":"2014","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/24480542","citation_count":78,"is_preprint":false},{"pmid":"36662867","id":"PMC_36662867","title":"ArpC5 isoforms regulate Arp2/3 complex-dependent protrusion through differential Ena/VASP positioning.","date":"2023","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/36662867","citation_count":22,"is_preprint":false},{"pmid":"37162507","id":"PMC_37162507","title":"ARPC5 isoforms and their regulation by calcium-calmodulin-N-WASP drive distinct Arp2/3-dependent actin remodeling events in CD4 T cells.","date":"2023","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/37162507","citation_count":19,"is_preprint":false},{"pmid":"24615350","id":"PMC_24615350","title":"Proteomics and phosphoproteomics provide insights into the mechanism of action of a novel pyrazolo[3,4-d]pyrimidine Src inhibitor in human osteosarcoma.","date":"2014","source":"Molecular bioSystems","url":"https://pubmed.ncbi.nlm.nih.gov/24615350","citation_count":18,"is_preprint":false},{"pmid":"39167642","id":"PMC_39167642","title":"Cellular stiffness sensing through talin 1 in tissue mechanical homeostasis.","date":"2024","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/39167642","citation_count":12,"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":"39344156","id":"PMC_39344156","title":"DNA-Based Molecular Clamp for Probing Protein Interactions and Structure under Force.","date":"2024","source":"ACS nano","url":"https://pubmed.ncbi.nlm.nih.gov/39344156","citation_count":7,"is_preprint":false},{"pmid":"38328095","id":"PMC_38328095","title":"Mechanosensing through talin 1 contributes to tissue mechanical homeostasis.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38328095","citation_count":2,"is_preprint":false},{"pmid":"38895381","id":"PMC_38895381","title":"A DNA-based molecular clamp for probing protein interactions and structure under force.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38895381","citation_count":2,"is_preprint":false},{"pmid":"38786098","id":"PMC_38786098","title":"PI 3-Kinase and the Histone Methyl-Transferase KMT2D Collaborate to Induce Arp2/3-Dependent Migration of Mammary Epithelial Cells.","date":"2024","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/38786098","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.07.18.604111","title":"Branched actin networks mediate macrophage-dependent host microbiota homeostasis","date":"2024-07-18","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.18.604111","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7256,"output_tokens":2182,"usd":0.027249,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9224,"output_tokens":2538,"usd":0.054785,"stage2_stop_reason":"end_turn"},"total_usd":0.082034,"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\": 2023,\n      \"finding\": \"ARPC5L specifically drives nuclear actin polymerization upon TCR activation in CD4 T cells, while ARPC5 is required for cytoplasmic actin dynamics. TCR-induced nuclear actin polymerization requires nuclear calcium-calmodulin signaling and N-WASP upstream of ARPC5L. In contrast, DNA replication stress-induced nuclear actin polymerization specifically requires ARPC5 but not ARPC5L.\",\n      \"method\": \"Reverse genetics (isoform-specific knockdown/knockout), live-cell imaging of nuclear and cytoplasmic actin polymerization in CD4 T cells, stimulus-specific perturbation experiments\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific genetic knockdown with distinct phenotypic readouts, multiple stimuli tested, pathway placement via calcium-calmodulin-N-WASP epistasis\",\n      \"pmids\": [\"37162507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ArpC5L and ArpC5 differentially regulate Arp2/3 complex-dependent cell migration by defining structural stability of ArpC1 in branch junctions, determining protrusion characteristics, and affecting actin network ultrastructure. ArpC5 isoforms also differentially position Ena/VASP family actin elongators, which mediate isoform-specific effects on actin assembly, placing ArpC5/ArpC5L and Ena/VASP in a shared signaling pathway enhancing cell migration.\",\n      \"method\": \"Reverse genetics (isoform-specific knockouts), cellular structural biology (cryo-electron tomography of branch junctions), FRAP/protein dynamics measurements, fluorescence microscopy of actin network ultrastructure\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reverse genetics combined with cryo-ET structural analysis of branch junctions plus protein dynamics measurements; multiple orthogonal methods in one study\",\n      \"pmids\": [\"36662867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mutation of a mechanosensitive site between talin 1 rod-domain helix bundles R1 and R2 promotes binding of the Arp2/3 complex subunit ARPC5L to a cryptic site in talin, and this interaction mediates altered ECM stiffness sensing in cells. Cells bearing these talin mutations spread and exert tension on compliant substrates in an ARPC5L-dependent manner.\",\n      \"method\": \"Site-directed mutagenesis of talin 1, pull-down assays, cellular phenotype rescue experiments on compliant substrates, mouse genetic model (ascending aorta mechanics)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutagenesis-driven binding assay, cellular functional rescue, and in vivo mouse model; replicated in preprint and peer-reviewed publication by same group\",\n      \"pmids\": [\"39167642\", \"38328095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Tension applied to the talin rod domain via a DNA-based molecular clamp induces binding of ARPC5L to a cryptic site within the talin structure, as shown by pull-down assays, demonstrating that ARPC5L binding to talin is force-dependent.\",\n      \"method\": \"DNA-based molecular clamp device applying defined tension to talin fragment, pull-down assays, negative-stain electron microscopy\",\n      \"journal\": \"ACS nano\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — novel in vitro reconstitution device with structural validation; single lab, but orthogonal biochemical and EM methods; replicated in preprint\",\n      \"pmids\": [\"39344156\", \"38895381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In mammary epithelial cells (MCF10A), combined PI 3-kinase activation (H1047R) and KMT2D inactivation induces ARPC5L gene expression, and ARPC5L depletion fully abolishes the enhanced single-cell migration persistence exhibited by these double-mutant cells, placing ARPC5L-containing Arp2/3 complex downstream of these oncogenic signals in mediating migration.\",\n      \"method\": \"Genetic reconstitution (PI3K mutation + KMT2D knockout), ARPC5L siRNA depletion, single-cell migration assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean loss-of-function with specific migration phenotype, genetic epistasis placing ARPC5L downstream; single lab, single method per step\",\n      \"pmids\": [\"38786098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Loss of Arpc5l (but not Arpc5) in the murine hematopoietic system does NOT cause intestinal inflammation or impair macrophage phagocytosis and bacterial killing, establishing that Arpc5l-containing Arp2/3 complexes are dispensable for mononuclear phagocyte function and host-microbiota homeostasis, in contrast to Arpc5.\",\n      \"method\": \"Conditional hematopoietic knockout mouse models for Arpc5 and Arpc5l, intestinal inflammation phenotyping, macrophage phagocytosis and bacterial killing assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean in vivo KO with specific cellular phenotype readouts; preprint, single lab, but rigorous genetic approach\",\n      \"pmids\": [\"bio_10.1101_2024.07.18.604111\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ARPC5L was identified as a component of PKD2 protein complexes in cytosolic and Golgi-enriched fractions, alongside the canonical Arp2/3 complex subunits, suggesting ARPC5L-containing Arp2/3 complexes interact with PKD2.\",\n      \"method\": \"Affinity enrichment combined with chemical cross-linking/mass spectrometry from cytosolic and Golgi subcellular fractions\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single cross-linking MS experiment; no functional follow-up on ARPC5L specifically; single lab\",\n      \"pmids\": [\"27559607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ARPC5L was found to be dephosphorylated in osteosarcoma SaOS-2 cells treated with the Src inhibitor SI-83, concomitant with impaired cell migration and adhesion, suggesting that phosphorylation of ARPC5L may contribute to Src-driven cytoskeletal dynamics and metastatic behavior.\",\n      \"method\": \"Gel-based phosphoproteomics of SI-83-treated osteosarcoma cells, cell migration and adhesion assays\",\n      \"journal\": \"Molecular bioSystems\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single phosphoproteomics observation with no direct mechanistic follow-up on ARPC5L specifically; single lab, correlative\",\n      \"pmids\": [\"24615350\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARPC5L is an alternative isoform subunit of the Arp2/3 complex that confers distinct properties relative to its paralog ARPC5: it drives nuclear actin polymerization downstream of TCR/calcium-calmodulin-N-WASP signaling in CD4 T cells, regulates Arp2/3 branch junction stability and Ena/VASP positioning to fine-tune cell migration, binds to a cryptic mechanosensitive site in talin 1 in a force-dependent manner to mediate ECM stiffness sensing, and is required for PI3K/KMT2D-driven migration persistence in mammary epithelial cells, while being dispensable for macrophage phagocytosis and host-microbiota homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARPC5L is an alternative isoform subunit of the Arp2/3 actin-nucleating complex whose incorporation confers branch-specific properties distinct from its paralog ARPC5, allowing the same machinery to drive different actin-dependent processes depending on stimulus and context [#1]. At the structural level, ARPC5L versus ARPC5 incorporation defines the stability of ARPC1 within branch junctions and tunes actin network ultrastructure and protrusion characteristics, and the two isoforms differentially position Ena/VASP family elongators to produce isoform-specific effects on migration [#1]. ARPC5L confers stimulus selectivity in the nucleus: in CD4 T cells it drives TCR-induced nuclear actin polymerization downstream of nuclear calcium-calmodulin and N-WASP signaling, whereas replication-stress-induced nuclear actin requires ARPC5 instead [#0]. ARPC5L also acts as a force-dependent partner of the focal-adhesion protein talin 1, binding a cryptic mechanosensitive site exposed between talin rod helix bundles R1 and R2 under tension to mediate ECM stiffness sensing and substrate-dependent cell spreading [#2, #3]. Functionally, ARPC5L-containing Arp2/3 complex is required for the enhanced single-cell migration persistence driven by combined PI3K activation and KMT2D loss in mammary epithelial cells [#4], while it is dispensable for macrophage phagocytosis and host-microbiota homeostasis, a role specific to ARPC5 [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2023,\n      \"claim\": \"Established that ARPC5L and ARPC5 are not redundant Arp2/3 subunits but partition actin-dependent functions by stimulus and subcellular compartment.\",\n      \"evidence\": \"Isoform-specific knockdown/knockout with live-cell imaging of nuclear and cytoplasmic actin and calcium-calmodulin/N-WASP epistasis in CD4 T cells\",\n      \"pmids\": [\"37162507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular basis for why ARPC5L versus ARPC5 is recruited to specific stimuli is unresolved\",\n        \"How nuclear N-WASP selectively activates ARPC5L-containing complexes is not defined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved how isoform identity changes the Arp2/3 complex physically, linking ARPC5L incorporation to branch-junction stability, network ultrastructure, and Ena/VASP positioning.\",\n      \"evidence\": \"Isoform-specific knockouts combined with cryo-electron tomography of branch junctions and FRAP protein-dynamics measurements\",\n      \"pmids\": [\"36662867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural determinants within ARPC5L responsible for differential ARPC1 stabilization not pinpointed\",\n        \"Mechanism coupling branch-junction stability to Ena/VASP recruitment unknown\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified ARPC5L as a force-gated binding partner of talin 1, connecting the Arp2/3 subunit directly to mechanosensing at adhesions.\",\n      \"evidence\": \"Site-directed mutagenesis of the talin R1-R2 cryptic site, pull-down assays, cellular spreading/traction rescue on compliant substrates, and an aortic-mechanics mouse model\",\n      \"pmids\": [\"39167642\", \"38328095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether talin binds intact Arp2/3 complex or free ARPC5L is not established\",\n        \"Functional consequence of talin-ARPC5L binding for actin nucleation itself is undefined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated directly that the talin-ARPC5L interaction is tension-dependent, confirming force as the trigger for cryptic-site exposure.\",\n      \"evidence\": \"DNA-based molecular clamp applying defined tension to a talin fragment, with pull-down assays and negative-stain EM\",\n      \"pmids\": [\"39344156\", \"38895381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab in vitro reconstitution; physiological force thresholds in cells not measured\",\n        \"Binding affinity and stoichiometry not quantified\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed ARPC5L downstream of oncogenic PI3K/KMT2D signaling as an effector of migration persistence in epithelial cells.\",\n      \"evidence\": \"Genetic reconstitution of PI3K H1047R plus KMT2D knockout in MCF10A, ARPC5L siRNA depletion, single-cell migration assays\",\n      \"pmids\": [\"38786098\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Transcriptional route from KMT2D loss to ARPC5L induction not mapped\",\n        \"Single method per epistasis step\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the boundary of ARPC5L function by showing it is dispensable for phagocyte function, sharpening the division of labor with ARPC5 in vivo.\",\n      \"evidence\": \"Conditional hematopoietic Arpc5 and Arpc5l knockout mice with intestinal inflammation phenotyping and macrophage phagocytosis/killing assays (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.07.18.604111\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint, single lab, not yet peer-reviewed\",\n        \"Does not test ARPC5L roles in other immune lineages\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the cell selects ARPC5L- versus ARPC5-containing Arp2/3 complexes at specific stimuli, locations, and force regimes remains the central open question.\",\n      \"evidence\": \"No direct evidence in the available corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No mechanism for isoform-selective assembly or recruitment\",\n        \"Functional significance of reported PKD2 association and Src-dependent phosphorylation not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"Arp2/3 complex\"],\n    \"partners\": [\"TLN1\", \"ARPC1\", \"WASL\", \"PKD2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}