{"gene":"PHACTR1","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2004,"finding":"PHACTR1 (Phactr-1) was identified as the founding member of a family of PP1-binding proteins that also bind cytoplasmic actin via RPEL motifs. Phactr-1 was shown to be a potent modulator of PP1 activity in vitro, and the protein is selectively expressed in brain with enrichment at synapses.","method":"Interaction cloning, in vitro PP1 activity assay, subcellular fractionation, immunohistochemistry in rat brain","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — original discovery paper with in vitro PP1 activity assay, interaction cloning, and synaptic localization by fractionation; foundational study replicated by subsequent work","pmids":["15107502"],"is_preprint":false},{"year":2011,"finding":"PHACTR1 depletion in HUVECs abolished tube formation and triggered apoptosis via death receptors DR4, DR5, and FAS in a caspase-8-dependent manner, establishing PHACTR1 as a key regulator of endothelial cell survival and tubulogenesis.","method":"siRNA knockdown in HUVECs, tube formation assay, flow cytometry for apoptosis, siRNA rescue with death-receptor and caspase-8 siRNAs","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 2–3 — clean loss-of-function with defined phenotypic readout and pathway placement via receptor-specific siRNA rescue; single lab","pmids":["21798305"],"is_preprint":false},{"year":2011,"finding":"PHACTR1 expression in HUVECs is induced by VEGF-A165 and is regulated specifically through NRP-1 and VEGF-R1 (but not NRP-2 or VEGF-R2). Upon VEGF stimulation, Phactr1 promotes tube formation and fine-tunes actin polymerization and lamellipodial dynamics; its depletion decreases PP1 activity and disrupts actin dynamics.","method":"siRNA knockdown of NRP-1, NRP-2, VEGFR1, VEGFR2; antagonist peptide blocking; PP1 activity assay; live-cell imaging of lamellipodia; tube formation assay in HUVECs","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple orthogonal approaches (receptor-specific knockdown, peptide antagonism, PP1 activity assay, live imaging); single lab","pmids":["21939755"],"is_preprint":false},{"year":2012,"finding":"G-actin binding by the three C-terminal RPEL motifs of Phactr1 is required for its cytoplasmic retention in resting cells. Rho-actin signalling (serum stimulation) depletes G-actin and promotes importin α-β-dependent nuclear accumulation of Phactr1. G-actin and importin α-β bind competitively to nuclear import signals flanking the RPEL motifs. Furthermore, G-actin and PP1 bind competitively to the Phactr1 C-terminal region, so that nuclear Phactr1 RPEL mutants that cannot bind G-actin induce aberrant actomyosin structures in a PP1-dependent manner. In CHL-1 melanoma cells, Phactr1 is required for stress fibre assembly, motility, and invasiveness.","method":"RPEL motif mutagenesis, importin binding assays, serum-stimulation nuclear accumulation assays, live-cell imaging, siRNA knockdown with motility/invasion assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal experiments (mutagenesis, competitive binding assays, functional rescue) in the same study; mechanistic model strongly supported","pmids":["22976292"],"is_preprint":false},{"year":2013,"finding":"TGF-β down-regulates miR-584 in breast cancer cells, relieving repression of PHACTR1 and thereby increasing PHACTR1 expression. Elevated PHACTR1 reorganizes the actin cytoskeleton and is required for TGF-β-induced breast cancer cell migration; overexpression of miR-584 or knockdown of PHACTR1 each blocked this migration.","method":"miRNA overexpression, siRNA knockdown, TGF-β stimulation, cell migration assays, phalloidin staining of actin cytoskeleton","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 — clean loss-of-function and gain-of-function with defined miRNA-mediated pathway; single lab","pmids":["23479725"],"is_preprint":false},{"year":2015,"finding":"Phactr-1 down-expression in endothelial cells activates focal adhesion kinase pathways (FAK/PYK2/Paxillin) and inhibits metabolic stress pathways (AMPK/CREB/eNOS), and induces expression of pro-atherogenic molecules including MMP regulators (TIMP-1/-2, RECK), oxidized LDL receptors (CD36, Clusterin), and inflammatory proteins (Thrombin, PAR-1, ADAM-9/-17).","method":"siRNA knockdown of Phactr1 in endothelial cells; antagonist peptide inhibition of VEGF-A165/NRP-1 interaction; Western blot and protein array profiling","journal":"Biochimie","confidence":"Low","confidence_rationale":"Tier 3 — broad protein expression profiling after knockdown without direct mechanistic dissection of individual pathways; single lab","pmids":["26362351"],"is_preprint":false},{"year":2015,"finding":"The CAD-risk SNP rs9349379 in intron 3 of PHACTR1 is an eQTL for PHACTR1 expression in human coronary arteries; alleles at this SNP are differentially bound by the MEF2 transcription factor, and CRISPR/Cas9 deletion of the MEF2-binding site in endothelial cells reduced PHACTR1 expression by ~35%.","method":"Genetic fine-mapping, eQTL analysis in human coronary arteries, electrophoretic mobility shift assay with endothelial cell extracts, CRISPR/Cas9 deletion","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 1–2 — eQTL confirmed in human tissue and CRISPR editing demonstrates direct regulatory link; multiple orthogonal methods","pmids":["25838425"],"is_preprint":false},{"year":2016,"finding":"PHACTR1 is expressed in human atherosclerotic plaque macrophages, foam cells, adventitial lymphocytes, and endothelial cells (but absent from vascular smooth muscle cells). Atherogenic stimuli (oxLDL, TNF-α) regulate PHACTR1 transcription; the CAD risk allele at rs9349379 is associated with reduced PHACTR1 expression in macrophages, paralleling the effect of inflammatory stimulation.","method":"Immunohistochemistry, qRT-PCR, immunoblotting, eQTL analysis in primary human macrophages","journal":"Atherosclerosis","confidence":"Medium","confidence_rationale":"Tier 2–3 — direct tissue immunohistochemistry and primary macrophage eQTL; multiple methods but primarily expression-level findings","pmids":["27187934"],"is_preprint":false},{"year":2017,"finding":"The CAD/MI risk SNP rs9349379 acts as a distal enhancer of endothelin-1 (EDN1) gene expression ~600 kb upstream. CRISPR-edited stem-cell-derived endothelial cells revealed that rs9349379 regulates EDN1 (not PHACTR1) expression in an aorta-specific enhancer context, providing a mechanistic link between this pleiotropic locus and vascular disease.","method":"CRISPR base editing in iPSC-derived endothelial cells, epigenomic chromatin analysis (H3K27ac, DNase I), eQTL mapping in aorta, reporter assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — CRISPR editing with functional readout in relevant cell type; replicated across epigenomic datasets; high-impact study","pmids":["28753427"],"is_preprint":false},{"year":2017,"finding":"Phactr1 is expressed in mouse brain in a developmental stage-dependent and tissue-dependent manner. In primary hippocampal neurons, Phactr1 is detected in axons, dendrites, and is enriched in synaptosomal and postsynaptic density fractions. In embryonic cortex, Phactr1 accumulates in the nucleus, whereas postnatally it distributes diffusely in the cell body.","method":"Western blotting, subcellular fractionation (synaptosomal/PSD), immunohistochemistry in mouse brain, immunofluorescence in cultured hippocampal neurons","journal":"Neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization experiments with fractionation and immunohistochemistry across developmental stages; single lab","pmids":["28803787"],"is_preprint":false},{"year":2017,"finding":"Phactr1 expression level positively correlates with vascular calcification severity in smooth muscle cells. Stable overexpression of Phactr1 in mESC-derived SMCs enhanced calcium phosphate deposition and osteogenic marker osteopontin expression, while knockdown reduced calcification.","method":"Stable lentiviral over- and under-expression of Phactr1 in mouse embryonic stem cell-derived SMCs; osteogenic medium calcification assay; alizarin red staining; RT-PCR for osteopontin","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2–3 — bidirectional gain/loss-of-function with molecular readout; single lab","pmids":["28720499"],"is_preprint":false},{"year":2018,"finding":"De novo missense mutations in PHACTR1 associated with West syndrome (infantile spasms) impair either actin binding (p.Leu500Pro, p.Asn479Ile, p.Ile518Asn) or PP1 binding (p.Arg521Cys) as determined by immunoprecipitation. Acute knockdown of mouse Phactr1 by in utero electroporation caused defects in cortical neuron migration rescued by wild-type but not mutant PHACTR1, and Phactr1-deficient excitatory neurons showed abnormal synaptic electrophysiological properties.","method":"Trio whole-exome sequencing, co-immunoprecipitation of mutant PHACTR1 with actin and PP1, in utero electroporation knockdown + rescue in mouse cortex, patch-clamp electrophysiology","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with in vivo electroporation rescue and electrophysiology; multiple orthogonal methods linking specific domains to cortical neuron migration and synaptic function","pmids":["30256902"],"is_preprint":false},{"year":2018,"finding":"PHACTR1 interacts with MRTF-A and with p65/NF-κB in coronary artery endothelial cells (co-immunoprecipitation). Knockdown of PHACTR1 attenuates nuclear translocation of p65 and NF-κB activity (without affecting IκBα or IKKα/β phosphorylation), reduces ox-LDL-induced ICAM-1, VCAM-1, and VE-cadherin expression, and reduces intracellular ROS. Knockdown of MRTF-A disrupts the PHACTR1–p65 interaction.","method":"Co-immunoprecipitation, siRNA knockdown, immunofluorescence for p65 nuclear translocation, flow cytometry for ROS, Western blotting for NF-κB pathway components","journal":"Atherosclerosis","confidence":"Medium","confidence_rationale":"Tier 2–3 — reciprocal co-IP and defined mechanistic pathway; single lab with multiple complementary assays","pmids":["30293016"],"is_preprint":false},{"year":2019,"finding":"Phactr1 physically links Slack (KCNT1) potassium channels to actin via co-immunoprecipitation. Co-expression of Phactr1 reduces Slack current amplitude in a manner dependent on the PP1-binding activity of Phactr1 and a conserved PKC phosphorylation site (S407) on Slack, establishing that Phactr1 regulates Slack channel activity by recruiting PP1 to dephosphorylate the channel.","method":"Co-immunoprecipitation, patch-clamp electrophysiology in Xenopus oocytes/HEK cells, Phactr1 PP1-binding mutant","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1–2 — electrophysiology with mutant dissection of PP1-binding vs. actin-binding requirements; mechanistically rigorous","pmids":["31914597"],"is_preprint":false},{"year":2020,"finding":"Crystal/high-resolution structures of the Phactr1/PP1 holoenzyme bound to dephosphorylated substrates IRSp53 and spectrin αII revealed that Phactr1 remodels PP1's hydrophobic groove to create a composite substrate-recognition surface. Substrate sequences C-terminal to the dephosphorylation site make intimate contacts with this composite surface, conferring sequence specificity and orders-of-magnitude enhanced reactivity toward specific substrates compared to apo-PP1 or other PP1 holoenzymes. Phosphoproteomic identification of Phactr1/PP1 substrates in fibroblasts and neurons included cytoskeletal components and regulators.","method":"X-ray crystallography (high-resolution structures of holoenzyme-product complexes), phosphoproteomics in mouse fibroblasts and neurons, in vitro dephosphorylation assays with mutagenesis of substrate contact residues","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with functional validation by mutagenesis and phosphoproteomics; mechanistically definitive","pmids":["32975518"],"is_preprint":false},{"year":2020,"finding":"Phactr1 deficiency in macrophages promotes M1 polarization, increased pro-inflammatory cytokine production, and enhanced foam cell formation driven by ox-LDL. Mechanistically, Phactr1 activates CREB signaling by directly binding to CREB and up-regulating phospho-CREB and KLF4 expression; KLF4 overexpression partially rescued the inflammatory and foam cell phenotypes of Phactr1-deficient macrophages.","method":"Phactr1-/-/Apoe-/- double-knockout mice, bone marrow transplantation, co-immunoprecipitation of Phactr1 with CREB, Western blot for phospho-CREB, KLF4 overexpression rescue, macrophage polarization assays","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2–3 — in vivo mouse model with bone marrow transplant and mechanistic co-IP; single lab","pmids":["32857129"],"is_preprint":false},{"year":2021,"finding":"PHACTR1 prevents dephosphorylation of myosin light chain (MLC), which is required for actin-mediated apoptotic cell engulfment (efferocytosis) by macrophages. The rs9349379-G/G risk genotype associates with lower PHACTR1 expression in human macrophages and impaired efferocytosis. Hematopoietic Phactr1 deletion in Ldlr-/- mice on a Western diet impaired lesional efferocytosis, increased plaque necrosis, and produced thinner fibrous caps.","method":"Human monocyte-derived macrophage efferocytosis assays, Ldlr-/- hematopoietic-specific Phactr1 knockout mouse model, Western diet atherosclerosis model, Western blot for phospho-MLC, plaque histology","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo mouse model combined with mechanistic phospho-MLC analysis and human macrophage validation; multiple orthogonal methods","pmids":["33630758"],"is_preprint":false},{"year":2021,"finding":"A de novo PHACTR1 missense mutation p.L519R reduces the affinity of PHACTR1 for G-actin and increases its propensity to form complexes with PP1 catalytic subunit (PPP1CA), leading to altered subcellular localization and increased cytoskeletal rearrangements, associated with multifocal epilepsy and infantile spasms.","method":"In vitro binding assays, subcellular localization analysis of mutant PHACTR1, functional cytoskeletal assays","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2–3 — in vitro binding and localization assays for a single variant; single case report with mechanistic follow-up","pmids":["33463715"],"is_preprint":false},{"year":2021,"finding":"Phactr1 negatively regulates osteogenesis and promotes adipogenesis of bone marrow mesenchymal stem cells via the RhoA/ROCK2 pathway. Phactr1 and ROCK2 physically interact (co-IP) during osteogenic differentiation, and ROCK2 inhibition (KD025) reproduces the Phactr1-overexpression phenotype of suppressed Runx2 and osteogenesis.","method":"Co-immunoprecipitation of Phactr1 and ROCK2, siRNA knockdown and lentiviral overexpression of Phactr1 in BMSCs, osteogenic/adipogenic differentiation assays, alizarin red/Oil red O staining, Western blot for RhoA/ROCK2/Runx2/C-EBPα","journal":"Journal of molecular histology","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP of Phactr1-ROCK2 and pharmacological ROCK2 inhibition rescue; single lab","pmids":["34709489"],"is_preprint":false},{"year":2023,"finding":"Endothelial PHACTR1 acts as a transcriptional corepressor of PPARγ under disturbed flow conditions. PHACTR1 is enriched in the nucleus of endothelial cells in disturbed-flow regions and shuttles to the cytoplasm under laminar flow. PHACTR1 binds PPARγ through corepressor motifs. Global or EC-specific Phactr1 knockout in ApoE-/- mice significantly reduced atherosclerosis, and PPARγ antagonist GW9662 abolished the protective effect.","method":"EC-specific and global Phactr1 knockout in ApoE-/- mice, partial carotid ligation atherosclerosis model, immunostaining for PHACTR1 localization under laminar vs. disturbed flow, RNA-seq of EC-enriched mRNA, PPARγ binding assays (corepressor motif), GW9662 pharmacological rescue","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo mouse KO model with pharmacological rescue and direct PPARγ binding; multiple orthogonal methods","pmids":["37199156"],"is_preprint":false},{"year":2023,"finding":"PHACTR1 overexpression promotes invasion, migration, and tumorigenicity of papillary thyroid carcinoma cells by increasing F-actin formation; disruption of F-actin assembly with swinholide A reversed the enhanced migration, placing PHACTR1 function upstream of F-actin polymerization in cancer cell motility.","method":"siRNA knockdown and cDNA overexpression in PTC cell lines, Transwell invasion/migration assays, phalloidin-F-actin fluorescence imaging, swinholide A pharmacological rescue","journal":"Heliyon","confidence":"Medium","confidence_rationale":"Tier 2–3 — bidirectional gain/loss-of-function with pharmacological pathway rescue; single lab","pmids":["37876444"],"is_preprint":false},{"year":2024,"finding":"BDNF stimulation of primary cortical neurons causes sustained downregulation of PHACTR1 (and PHACTR2/3 but not PHACTR4) mRNA via the ERK/MAPK pathway; this was blocked by the MEK inhibitor U0126, identifying ERK/MAPK as an upstream regulator of PHACTR1 gene expression in neurons.","method":"BDNF stimulation of primary cultured mouse cortical neurons, qRT-PCR for PHACTR family mRNAs, MEK inhibitor U0126 treatment","journal":"Drug discoveries & therapeutics","confidence":"Low","confidence_rationale":"Tier 3 — mRNA-level regulation with pharmacological inhibitor; no direct mechanistic dissection of the ERK-PHACTR1 link","pmids":["39183043"],"is_preprint":false},{"year":2024,"finding":"AlphaFold-Multimer modeling and analysis of PHACTR1 patient variants indicate that the RPEL3 domain serves as the binding interface for both G-actin and PPP1CA, and these two interactions are competitive. Missense variants in patients with infantile epileptic spasms syndrome map to the RPEL3 domain and impair either G-actin or PPP1CA binding.","method":"AlphaFold-Multimer structural prediction, whole-exome sequencing of nine PHACTR1-variant patients, genotype-phenotype correlation","journal":"Journal of medical genetics","confidence":"Low","confidence_rationale":"Tier 4 — primarily computational structural prediction; clinical genotype-phenotype correlation without in vitro binding validation","pmids":["38272663"],"is_preprint":false},{"year":2014,"finding":"Phactr1 binds directly to MRTF-A, MRTF-B, myocardin, and Phactr1 itself via RPEL-containing nuclear localization sequences, and is a direct target of the Rho-signaling inhibitor CCG-1423 (pull-down with CCG-1423-Sepharose). G-actin binding blocks CCG-1423 interaction with the NLS of RPEL proteins including Phactr1.","method":"CCG-1423-Sepharose affinity pull-down assay, competitive G-actin displacement assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2–3 — direct pull-down demonstrating Phactr1 as a CCG-1423 target; mechanistically relevant finding confirmed by competitive assay","pmids":["24558465"],"is_preprint":false},{"year":2026,"finding":"Multi-omics profiling (transcriptomics, proteomics, metabolomics, lipidomics) of PHACTR1 overexpression and knockdown in HT1080 cells revealed that PHACTR1 governs cell cycle progression (altering key regulatory proteins), regulates cellular iron-storage proteins (iron metabolism), and localizes to mitochondria where it modulates mitochondrial morphology and bioenergetics through a signaling axis involving AKAP1 and Drp1. Mitochondrial changes correlated with shifts in lipid metabolism.","method":"Multi-omics (transcriptomics, proteomics, metabolomics, lipidomics) in PHACTR1 OE/KD HT1080 cells; validation in primary human endothelial cells; mitochondrial localization confirmed; AKAP1/Drp1 interaction identified","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 — multi-omics with validation in primary cells and identification of mitochondrial signaling axis; single study but four orthogonal omics layers","pmids":["41554990"],"is_preprint":false},{"year":2025,"finding":"The CAD-risk SNP rs6903956 'A' allele enhances HOXA4/MEIS1 transcription factor binding at the locus to drive PHACTR1 transcriptional activation in endothelial cells. iPSC-derived endothelial cells with the 'A' allele show elevated PHACTR1 expression and, under pathological flow, elevated ICAM-1 expression and increased monocyte adhesion compared to the 'G' allele.","method":"Single-base editing of iPSC-derived endothelial cells, eQTL analysis, AlphaFold 3 in silico binding modeling, luciferase reporter assays, ICAM-1/monocyte adhesion assays under flow","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3–4 — preprint; computational structural modeling with functional reporter and cell assay validation; not yet peer-reviewed","pmids":["40654905"],"is_preprint":true},{"year":2024,"finding":"All four Phactr proteins (Phactr1–4) confer identical sequence specificities on their respective PP1 holoenzymes, as demonstrated by a PP1-PIP fusion approach. This establishes that the composite Phactr/PP1 substrate-recognition surface described for Phactr1 is a conserved property of the Phactr family.","method":"PP1-PIP fusion protein approach, substrate phosphoproteomics, in vitro dephosphorylation assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1–2 — rigorous biochemical approach extending the Phactr1/PP1 structural finding; preprint from same lab as the eLife 2020 structure paper","pmids":[],"is_preprint":true}],"current_model":"PHACTR1 is an RPEL-motif-containing protein that acts as a PP1 cofactor: it binds G-actin (via three C-terminal RPEL motifs) and PP1 competitively, such that Rho-signal-induced G-actin depletion drives importin α-β-dependent nuclear accumulation of PHACTR1, where it remodels PP1's hydrophobic groove to create a composite surface conferring sequence-specific dephosphorylation of cytoskeletal substrates (e.g., IRSp53, spectrin αII); in neurons it recruits PP1 to dephosphorylate and suppress Slack (KCNT1) channel activity, and in macrophages it maintains myosin light chain phosphorylation to support efferocytosis; in endothelial cells under disturbed flow it accumulates in the nucleus and acts as a PPARγ transcriptional corepressor to promote endothelial activation and atherosclerosis, while its expression is regulated upstream by VEGF/NRP-1/VEGFR1 signaling, TGF-β/miR-584, and the BDNF-ERK/MAPK axis, and by the CAD-risk SNP rs9349379 acting as an MEF2-dependent enhancer in coronary arteries."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing PHACTR1 as a PP1-binding, actin-associating protein enriched at synapses answered the initial question of what this brain-expressed protein does biochemically and where it acts.","evidence":"Interaction cloning, in vitro PP1 activity assay, subcellular fractionation and immunohistochemistry in rat brain","pmids":["15107502"],"confidence":"High","gaps":["No structural basis for PP1 or actin binding","No in vivo loss-of-function data","Neuronal substrates of PHACTR1/PP1 unknown"]},{"year":2011,"claim":"Demonstrating that VEGF/NRP-1/VEGFR1 signaling induces PHACTR1 in endothelial cells and that PHACTR1 is required for tubulogenesis, survival, and lamellipodial dynamics extended the protein's role beyond neurons into the vasculature and linked it to actin dynamics and PP1 activity in endothelial biology.","evidence":"siRNA knockdown in HUVECs with receptor-specific depletion, PP1 activity assays, tube formation and apoptosis assays, live-cell imaging","pmids":["21798305","21939755"],"confidence":"Medium","gaps":["Mechanism connecting PHACTR1 loss to death receptor activation unclear","No in vivo endothelial phenotype","Whether PP1 catalytic activity mediates tube formation not directly tested"]},{"year":2012,"claim":"Resolving how PHACTR1 shuttles between cytoplasm and nucleus answered the key regulatory question: G-actin binding to RPEL motifs competitively blocks both importin α–β-dependent nuclear import and PP1 binding, so Rho-driven G-actin depletion simultaneously drives nuclear entry and enables PP1 engagement.","evidence":"RPEL motif mutagenesis, competitive importin and PP1 binding assays, serum-stimulation nuclear accumulation, siRNA phenotyping in CHL-1 melanoma cells","pmids":["22976292"],"confidence":"High","gaps":["No structural resolution of competitive binding interfaces","Whether the mechanism operates equivalently in neurons vs. endothelial cells untested","Nuclear PP1 substrates not identified"]},{"year":2013,"claim":"Identifying TGF-β/miR-584 as an upstream regulatory axis for PHACTR1 expression established a mechanism by which PHACTR1-dependent actin reorganization drives TGF-β-induced cancer cell migration.","evidence":"miR-584 overexpression and PHACTR1 knockdown in breast cancer cells; TGF-β stimulation; phalloidin staining; migration assays","pmids":["23479725"],"confidence":"Medium","gaps":["Direct miR-584 binding site on PHACTR1 3'UTR not validated by reporter assay in this study","Whether PP1 activity is required for this migration phenotype unknown"]},{"year":2014,"claim":"Showing that PHACTR1 interacts with MRTF-A/B and myocardin via RPEL-containing NLS sequences, and is a direct target of Rho-pathway inhibitor CCG-1423, placed PHACTR1 within the broader RPEL-protein regulatory network.","evidence":"CCG-1423-Sepharose affinity pull-down, competitive G-actin displacement assay","pmids":["24558465"],"confidence":"Medium","gaps":["Functional consequence of PHACTR1–MRTF interaction not determined","Whether CCG-1423 inhibits PHACTR1 function in cells not tested"]},{"year":2015,"claim":"Identifying the CAD-risk SNP rs9349379 as a MEF2-dependent enhancer that controls PHACTR1 expression in coronary arteries connected human GWAS genetics to a specific cis-regulatory mechanism.","evidence":"eQTL analysis in human coronary arteries, EMSA, CRISPR/Cas9 deletion of MEF2 site in endothelial cells","pmids":["25838425"],"confidence":"High","gaps":["Whether reduced PHACTR1 expression is the causal mediator of CAD risk at this locus was contested by subsequent work implicating EDN1","No functional vascular phenotype tested"]},{"year":2017,"claim":"A landmark CRISPR base-editing study demonstrated that rs9349379 acts as a distal enhancer of EDN1 (not PHACTR1) in aortic endothelial cells, raising the possibility that the CAD risk at this locus is mediated through endothelin-1 rather than PHACTR1 in certain vascular beds.","evidence":"CRISPR base editing in iPSC-derived endothelial cells, H3K27ac and DNase I chromatin analysis, aorta eQTL mapping","pmids":["28753427"],"confidence":"High","gaps":["Cell-type and vascular-bed specificity of rs9349379 regulation not fully resolved","Does not exclude PHACTR1-mediated contributions in macrophages or non-aortic vessels"]},{"year":2018,"claim":"Identification of de novo PHACTR1 missense mutations causing West syndrome, with mutations selectively disrupting actin- or PP1-binding and failing to rescue cortical neuron migration, established PHACTR1 as a disease gene and demonstrated that both binding activities are essential for brain development.","evidence":"Trio WES, co-IP of mutant PHACTR1 with actin/PP1, in utero electroporation rescue in mouse cortex, patch-clamp electrophysiology","pmids":["30256902"],"confidence":"High","gaps":["Downstream substrates mediating migration and synaptic phenotypes not identified","Whether PP1 catalytic activity or scaffolding underlies the rescue not distinguished"]},{"year":2018,"claim":"Demonstrating that PHACTR1 interacts with MRTF-A and p65/NF-κB to promote nuclear translocation of p65 in endothelial cells provided a PP1-independent transcriptional mechanism for PHACTR1's pro-inflammatory role.","evidence":"Co-IP of PHACTR1 with MRTF-A and p65, siRNA knockdown, immunofluorescence for p65 translocation in coronary artery endothelial cells","pmids":["30293016"],"confidence":"Medium","gaps":["No reciprocal IP for PHACTR1–p65 direct binding","Mechanism by which PHACTR1 promotes p65 translocation without affecting IκBα unclear","Relationship to PP1 catalytic activity not tested"]},{"year":2019,"claim":"Electrophysiological evidence that PHACTR1 recruits PP1 to dephosphorylate the Slack (KCNT1) potassium channel at Ser407, reducing channel current, identified the first ion-channel substrate and demonstrated a neuronal signaling role for the PHACTR1/PP1 holoenzyme.","evidence":"Co-IP of PHACTR1 with Slack, patch-clamp electrophysiology in oocytes/HEK cells, PP1-binding mutant of PHACTR1","pmids":["31914597"],"confidence":"High","gaps":["In vivo neuronal consequence of Slack regulation by PHACTR1 not determined","Whether other PHACTR1/PP1 substrates exist in neurons not addressed beyond this channel"]},{"year":2020,"claim":"Crystal structures of the PHACTR1/PP1 holoenzyme with dephosphorylated substrates (IRSp53, spectrin αII) provided the definitive structural mechanism: PHACTR1 remodels PP1's hydrophobic groove to create a composite surface conferring sequence-specific substrate recognition and orders-of-magnitude enhanced catalytic efficiency.","evidence":"X-ray crystallography of holoenzyme–product complexes, phosphoproteomics in fibroblasts and neurons, mutagenesis of substrate-contact residues","pmids":["32975518"],"confidence":"High","gaps":["Full substrate repertoire in physiological contexts incompletely mapped","Whether actin-bound vs. PP1-bound pools have distinct substrate access in cells not resolved"]},{"year":2020,"claim":"Showing that macrophage PHACTR1 deficiency drives M1 polarization and foam cell formation via reduced CREB/KLF4 signaling provided a macrophage-intrinsic mechanism linking lower PHACTR1 to atherosclerosis progression.","evidence":"Phactr1−/−/Apoe−/− mice, bone marrow transplant, co-IP of PHACTR1 with CREB, KLF4 rescue","pmids":["32857129"],"confidence":"Medium","gaps":["Whether PHACTR1-CREB interaction is PP1-dependent not tested","Single lab finding awaiting independent replication"]},{"year":2021,"claim":"Demonstrating that PHACTR1 prevents MLC dephosphorylation to enable macrophage efferocytosis, and that the rs9349379 risk allele reduces PHACTR1 expression and efferocytic capacity, provided a direct mechanistic link between PHACTR1-directed PP1 activity, apoptotic cell clearance, and CAD risk.","evidence":"Human macrophage efferocytosis assays, hematopoietic-specific Phactr1 KO in Ldlr−/− mice on Western diet, phospho-MLC Western blot, plaque histology","pmids":["33630758"],"confidence":"High","gaps":["Paradox: PHACTR1 here prevents dephosphorylation of MLC whereas it promotes dephosphorylation of other substrates — mechanism of substrate selectivity in macrophages not resolved","Whether endothelial and macrophage PHACTR1 effects are additive in atherogenesis not tested in combined models"]},{"year":2023,"claim":"Identifying PHACTR1 as a flow-sensitive PPARγ transcriptional corepressor in endothelial cells resolved how nuclear PHACTR1 promotes endothelial activation: under disturbed flow it represses PPARγ anti-inflammatory target genes, and endothelial-specific deletion is atheroprotective.","evidence":"EC-specific and global Phactr1 KO in ApoE−/− mice, partial carotid ligation, immunostaining under flow, PPARγ binding assays, GW9662 pharmacological rescue","pmids":["37199156"],"confidence":"High","gaps":["Whether the corepressor function requires PP1 or is independent not determined","Identity of PPARγ target genes most relevant to atheroprotection not fully defined"]},{"year":2024,"claim":"Multi-omics profiling revealed that PHACTR1 localizes to mitochondria and modulates mitochondrial morphology and bioenergetics via an AKAP1/Drp1 axis, expanding PHACTR1's functional repertoire beyond the actin cytoskeleton and nucleus.","evidence":"Transcriptomics, proteomics, metabolomics, lipidomics in HT1080 OE/KD cells; validation in primary endothelial cells; mitochondrial localization confirmed","pmids":["41554990"],"confidence":"Medium","gaps":["Whether PP1 activity is required for mitochondrial effects not tested","AKAP1/Drp1 interaction with PHACTR1 not validated by reciprocal co-IP or mutagenesis","Single study; independent replication needed"]},{"year":null,"claim":"Major open questions include: how PHACTR1 differentially prevents dephosphorylation of MLC in macrophages while promoting dephosphorylation of other cytoskeletal substrates; the relative contributions of endothelial, macrophage, and smooth muscle cell PHACTR1 to CAD in vivo; the full neuronal substrate repertoire and how its disruption causes epileptic spasms; and whether the mitochondrial localization and AKAP1/Drp1 axis represent a physiologically significant function.","evidence":"","pmids":[],"confidence":"Low","gaps":["Substrate selectivity mechanism in distinct cell types unresolved","No combined tissue-specific KO studies for atherosclerosis","Neuronal substrates beyond Slack channel not validated in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,13,14,16]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3,4,20]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[19]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[13,14]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,9,19]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,9]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,4,20]},{"term_id":"GO:0005886","term_label":"plasma 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across vascular, immune, and neuronal contexts. In resting cells, G-actin binds the three C-terminal RPEL motifs to retain PHACTR1 in the cytoplasm; Rho-signal-driven G-actin depletion exposes importin α–β binding sites and triggers nuclear accumulation, simultaneously freeing the PP1-interaction surface because G-actin and PP1 bind competitively to the same region [PMID:22976292, PMID:32975518]. The PHACTR1/PP1 holoenzyme remodels PP1's hydrophobic groove to create a composite substrate-recognition surface that confers sequence-specific dephosphorylation of cytoskeletal targets such as IRSp53 and spectrin αII; in macrophages this activity maintains myosin light chain phosphorylation required for efferocytosis, while in neurons it recruits PP1 to suppress Slack (KCNT1) channel activity [PMID:32975518, PMID:33630758, PMID:31914597]. De novo missense mutations disrupting actin- or PP1-binding cause West syndrome (infantile epileptic spasms), with loss of PHACTR1 impairing cortical neuron migration and synaptic function [PMID:30256902]; in endothelial cells under disturbed flow, nuclear PHACTR1 acts as a PPARγ transcriptional corepressor to promote endothelial activation and atherosclerosis [PMID:37199156]."},"prefetch_data":{"uniprot":{"accession":"Q9C0D0","full_name":"Phosphatase and actin regulator 1","aliases":[],"length_aa":580,"mass_kda":66.3,"function":"Binds actin monomers (G actin) and plays a role in multiple processes including the regulation of actin cytoskeleton dynamics, actin stress fibers formation, cell motility and survival, formation of tubules by endothelial cells, and regulation of PPP1CA activity (PubMed:21798305, PubMed:21939755). Involved in the regulation of cortical neuron migration and dendrite arborization (By similarity)","subcellular_location":"Cytoplasm; Synapse; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9C0D0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PHACTR1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":77,"dependency_fraction":0.012987012987012988},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PHACTR1","total_profiled":1310},"omim":[{"mim_id":"618298","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 70; DEE70","url":"https://www.omim.org/entry/618298"},{"mim_id":"608726","title":"PHOSPHATASE AND ACTIN REGULATOR 4; PHACTR4","url":"https://www.omim.org/entry/608726"},{"mim_id":"608725","title":"PHOSPHATASE AND ACTIN REGULATOR 3; PHACTR3","url":"https://www.omim.org/entry/608725"},{"mim_id":"608724","title":"PHOSPHATASE AND ACTIN REGULATOR 2; PHACTR2","url":"https://www.omim.org/entry/608724"},{"mim_id":"608723","title":"PHOSPHATASE AND ACTIN REGULATOR 1; PHACTR1","url":"https://www.omim.org/entry/608723"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Plasma membrane","reliability":"Uncertain"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":21.5},{"tissue":"brain","ntpm":25.7}],"url":"https://www.proteinatlas.org/search/PHACTR1"},"hgnc":{"alias_symbol":["KIAA1733","dJ257A7.2"],"prev_symbol":["RPEL1"]},"alphafold":{"accession":"Q9C0D0","domains":[{"cath_id":"-","chopping":"548-580","consensus_level":"medium","plddt":91.8891,"start":548,"end":580},{"cath_id":"1.20.5","chopping":"449-481","consensus_level":"medium","plddt":96.4479,"start":449,"end":481},{"cath_id":"1.20.5","chopping":"486-520","consensus_level":"medium","plddt":93.6114,"start":486,"end":520}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9C0D0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9C0D0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9C0D0-F1-predicted_aligned_error_v6.png","plddt_mean":62.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PHACTR1","jax_strain_url":"https://www.jax.org/strain/search?query=PHACTR1"},"sequence":{"accession":"Q9C0D0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9C0D0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9C0D0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9C0D0"}},"corpus_meta":[{"pmid":"25420145","id":"PMC_25420145","title":"Common 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G-actin and importin α-β compete for binding to nuclear import signals at the N- and C-terminal RPEL motifs. G-actin and PP1 also bind competitively to the C-terminal region, and PHACTR1 C-terminal RPEL mutants that cannot bind G-actin induce aberrant actomyosin structures in a PP1-binding-dependent manner. In CHL-1 melanoma cells, PHACTR1 is required for stress fiber assembly, motility and invasiveness.\",\n      \"method\": \"Immunofluorescence localization, dominant-negative/mutant expression, co-immunoprecipitation, siRNA knockdown with phenotypic readouts (stress fiber assembly, motility, invasion)\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (localization, mutagenesis, competitive binding, functional KD) in a single rigorous study\",\n      \"pmids\": [\"22976292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Phactr1/PP1 holoenzyme acquires sequence specificity through structural remodeling: Phactr1 binding reshapes PP1's hydrophobic groove to create a composite surface adjacent to the catalytic site. Substrate sequences C-terminal to the dephosphorylation site make intimate contacts with this composite surface, which are required for efficient dephosphorylation. Neuronal and fibroblast substrates identified by phosphoproteomics include cytoskeletal components IRSp53 and spectrin αII; high-resolution structures of Phactr1/PP1 bound to dephosphorylated IRSp53 and spectrin αII were determined, and inversion of the phosphate in these product complexes supports the PPP-family catalytic mechanism. Phactr1/PP1 shows orders-of-magnitude enhanced reactivity toward its substrates compared with apo-PP1 or other PP1 holoenzymes.\",\n      \"method\": \"Phosphoproteomics substrate identification, X-ray crystallography (high-resolution holoenzyme-product structures), in vitro phosphatase assays with mutagenesis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, crystal structures with functional validation, and phosphoproteomics in a single study\",\n      \"pmids\": [\"32975518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR1 knockdown in HUVECs impairs tube formation and triggers apoptosis through death receptors DR4, DR5, and FAS (caspase-8-dependent pathway), which is reversed by siRNA silencing of these death receptors or caspase-8, establishing PHACTR1 as a regulator of endothelial cell survival and tubulogenesis.\",\n      \"method\": \"siRNA knockdown, rescue experiments with death receptor siRNAs and caspase-8 siRNA, tube formation assay, apoptosis assay\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with specific pathway rescue, but single lab\",\n      \"pmids\": [\"21798305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR1 expression in HUVECs is regulated downstream of VEGF-A165 via NRP-1 and VEGFR1 (but not NRP-2 or VEGFR2). PHACTR1 depletion decreases PP1 activity, disrupts actin polymerization fine-tuning, and impairs lamellipodial dynamics, thereby blocking VEGF-induced tubulogenesis.\",\n      \"method\": \"Receptor-specific siRNA depletion, antagonist peptide inhibition, PP1 activity assay, live-cell imaging of lamellipodia, tube formation assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (receptor KD, peptide inhibition, functional assays), single lab\",\n      \"pmids\": [\"21939755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TGF-β down-regulates miR-584 in breast cancer cells, relieving repression of PHACTR1; increased PHACTR1 expression is required for TGF-β-induced actin rearrangement and cell migration. Both miR-584 overexpression and PHACTR1 knockdown abolish TGF-β-induced migration and reorganize the actin cytoskeleton.\",\n      \"method\": \"miRNA overexpression, siRNA knockdown, migration assays, actin cytoskeleton staining\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function with defined phenotype, single lab\",\n      \"pmids\": [\"23479725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"De novo missense mutations in PHACTR1 (p.Leu500Pro, p.Asn479Ile, p.Ile518Asn) impair actin-binding activity, while p.Arg521Cys impairs PP1 binding. Acute Phactr1 knockdown in mouse cortex via in utero electroporation causes defects in cortical neuron migration, rescued by RNAi-resistant wild-type PHACTR1 but not by any of the four mutants. Electrophysiological analyses reveal abnormal synaptic properties in Phactr1-deficient excitatory cortical neurons.\",\n      \"method\": \"Immunoprecipitation (binding assays), in utero electroporation knockdown + mutant rescue, in vivo cortical migration analysis, electrophysiology\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-function mutagenesis combined with in vivo rescue experiments and electrophysiology, multiple orthogonal methods\",\n      \"pmids\": [\"30256902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Phactr1 physically links Slack (KCNT1) potassium channels to actin via co-immunoprecipitation, and co-expression of Phactr1 with wild-type Slack reduces current amplitude in a PP1-binding-dependent manner. A Phactr1 mutant that disrupts PP1 binding (but not actin binding) fails to alter Slack currents, and mutation of the conserved PKC phosphorylation site S407 on Slack abolishes Phactr1's regulatory effect.\",\n      \"method\": \"Co-immunoprecipitation, patch-clamp electrophysiology, site-directed mutagenesis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — electrophysiology with mutagenesis and co-IP, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"31914597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In macrophages, PHACTR1 prevents dephosphorylation of myosin light chain (MLC), which is necessary for apoptotic cell (AC) engulfment (efferocytosis). The rs9349379-G/G risk allele lowers PHACTR1 expression in human monocyte-derived macrophages, impairing efferocytosis. Hematopoietic Phactr1 targeting in Ldlr-/- mice on a Western diet impairs lesional efferocytosis, increases plaque necrosis, and produces thinner fibrous caps.\",\n      \"method\": \"Genotype-stratified human macrophage efferocytosis assays, siRNA knockdown in human and mouse macrophages, conditional hematopoietic KO mouse model, phospho-MLC western blotting\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO mouse model with defined cellular mechanism (MLC phosphorylation), validated in human primary cells and in vivo\",\n      \"pmids\": [\"33630758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial PHACTR1 functions as a PPARγ transcriptional corepressor: it binds PPARγ through corepressor motifs and is enriched in the nucleus of ECs under disturbed flow but shuttles to the cytoplasm under laminar flow. Global or EC-specific Phactr1 KO in Apoe-/- mice significantly inhibits atherosclerosis in disturbed-flow regions, and this protection is abolished by the PPARγ antagonist GW9662, confirming the PPARγ-dependent mechanism.\",\n      \"method\": \"EC-specific and global KO mouse models, partial carotid ligation, RNA sequencing, co-immunoprecipitation (PHACTR1-PPARγ binding), PPARγ antagonist rescue, siRNA KD in HUVECs\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with pharmacological rescue plus direct protein interaction, multiple orthogonal methods\",\n      \"pmids\": [\"37199156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PHACTR1 activates CREB signaling in macrophages by directly binding to CREB, upregulating CREB phosphorylation and inducing KLF4 expression, which promotes M2 macrophage polarization and inhibits foam cell formation; KLF4 overexpression partially rescues the excessive inflammation caused by Phactr1 deficiency.\",\n      \"method\": \"Co-immunoprecipitation (Phactr1-CREB direct binding), CREB phosphorylation western blot, Phactr1-/- Apoe-/- double-KO mouse atherosclerosis model, bone marrow transplant, KLF4 overexpression rescue\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus in vivo KO and rescue, but mechanistic link to CREB relies on single-method co-IP\",\n      \"pmids\": [\"32857129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PHACTR1 interacts with MRTF-A and with NF-κB p65 in human coronary artery endothelial cells (co-immunoprecipitation). Knockdown of PHACTR1 blocks nuclear translocation of p65 and attenuates NF-κB activity, oxidative stress (ROS/p47phox phosphorylation), and expression of ICAM-1, VCAM-1, and VE-cadherin. Knockdown of MRTF-A suppresses the PHACTR1–p65 interaction and blocks p65 nuclear translocation.\",\n      \"method\": \"Co-immunoprecipitation (PHACTR1 with MRTF-A and p65), siRNA knockdown, NF-κB reporter/immunofluorescence, flow cytometry (ROS)\",\n      \"journal\": \"Atherosclerosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP plus KD phenotype, single lab, no structural validation\",\n      \"pmids\": [\"30293016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PHACTR1 expression in smooth muscle cells modulates vascular calcification: stable overexpression enhances calcium phosphate deposition and osteopontin expression in mESC-derived SMCs, while knockdown decreases calcification, establishing a positive regulatory role of PHACTR1 in SMC mineralization.\",\n      \"method\": \"Stable overexpression and knockdown in mESCs differentiated into SMCs, calcium phosphate staining/quantification, RT-PCR for osteopontin\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function in differentiated cells with quantitative mineral readout\",\n      \"pmids\": [\"28720499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Phactr1 interacts with ROCK2 (by co-IP) during osteogenic differentiation of BMSCs, and activates RhoA/ROCK2 signaling to inhibit osteogenesis (reducing Runx2) while promoting adipogenesis (increasing C/EBPα); selective ROCK2 inhibition reverses these effects, confirming the RhoA/ROCK2 axis as the pathway through which PHACTR1 regulates BMSC fate.\",\n      \"method\": \"Co-immunoprecipitation (Phactr1-ROCK2), siRNA and lentiviral overexpression, selective ROCK2 inhibitor (KD025), Alizarin red and Oil red O staining, western blot\",\n      \"journal\": \"Journal of molecular histology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP plus pharmacological rescue, single lab\",\n      \"pmids\": [\"34709489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo PHACTR1 p.L519R mutation reduces affinity for G-actin and increases complex formation with the PP1 catalytic subunit, altering subcellular localization and increasing the ability to induce cytoskeletal rearrangements, consistent with a gain-of-function/dominant-negative mechanism causing multifocal epilepsy.\",\n      \"method\": \"In vitro binding assays (G-actin affinity), co-immunoprecipitation (PP1 binding), immunofluorescence localization, cytoskeletal phenotype assay\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays with functional phenotype, single lab\",\n      \"pmids\": [\"33463715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Phactr1 is detected in the synaptosomal and postsynaptic density fractions of mouse brain and is enriched in the nucleus of cortical neurons at embryonic stages, shifting to diffuse cytoplasmic/dendritic distribution postnatally, indicating spatiotemporally regulated nucleocytoplasmic shuttling in neurons consistent with its actin/PP1 regulatory roles.\",\n      \"method\": \"Subcellular fractionation (synaptosomal/PSD), immunohistochemistry, western blot during development\",\n      \"journal\": \"Neuroscience research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — localization by fractionation and IHC, no direct functional consequence tested\",\n      \"pmids\": [\"28803787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"BDNF stimulation of cortical neurons causes sustained downregulation of PHACTR1 (and PHACTR2/3) mRNA via the ERK/MAPK pathway, as shown by blockade with the MEK inhibitor U0126, revealing a neurotrophin-dependent transcriptional regulatory mechanism for PHACTR1 in neurons.\",\n      \"method\": \"Primary cortical neuron culture, BDNF stimulation, pharmacological ERK/MAPK inhibition (U0126), qRT-PCR\",\n      \"journal\": \"Drug discoveries & therapeutics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single pharmacological inhibitor approach, single lab, no direct mechanistic follow-up\",\n      \"pmids\": [\"39183043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Multi-omics profiling (transcriptomics, proteomics, metabolomics, lipidomics) of HT1080 cells with PHACTR1 overexpression or knockdown, validated in primary endothelial cells, reveals that PHACTR1 controls cell cycle progression (altering key regulatory proteins), iron metabolism (regulating iron-storage proteins), and mitochondrial morphology/bioenergetics through a signaling axis involving AKAP1 and Drp1, with associated shifts in lipid metabolism.\",\n      \"method\": \"Multi-omics (transcriptomics, proteomics, metabolomics, lipidomics) in gain/loss-of-function cells, validation in primary endothelial cells, mitochondrial morphology imaging\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal omics with orthogonal validation in primary cells, but novel findings without deep mechanistic dissection yet\",\n      \"pmids\": [\"41554990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The rs6903956 'A' risk allele enhances binding of HOXA4 and MEIS1 transcription factors to form a ternary complex that promotes transcriptional activation of PHACTR1 (cis-eQTL); single-base editing of iPSC-derived endothelial cells confirmed allele-specific regulation of PHACTR1 and EDN1. Under pathological flow, cells with the 'A' allele show elevated ICAM-1 and increased monocyte adhesion, linking PHACTR1 upregulation to endothelial inflammatory activation.\",\n      \"method\": \"Single-base editing of iPSC-ECs, eQTL analysis, AlphaFold3 in silico modeling, luciferase enhancer assay, ICAM-1/monocyte adhesion functional assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single-base editing plus functional assays, but preprint with in silico modeling component; not yet peer-reviewed\",\n      \"pmids\": [\"40654905\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PHACTR1 interacts with heat shock protein HSPA8 in endothelial cells (co-immunoprecipitation proteomics), and PHACTR1 overexpression reduces nitric oxide generation by inhibiting Akt/eNOS activation and induces NF-κB-dependent ICAM1/VCAM1 expression and monocyte adhesion.\",\n      \"method\": \"Proteomic co-IP (PHACTR1-HSPA8 interaction), RNA sequencing, ICAM1/VCAM1 expression assays, NO measurement, Akt/eNOS phosphorylation western blot, monocyte adhesion assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP for HSPA8 interaction; functional data is overexpression-based with limited mechanistic follow-up\",\n      \"pmids\": [\"36091033\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PHACTR1 is a G-actin- and PP1-binding cofactor that senses intracellular actin levels through RPEL motifs to control nucleocytoplasmic shuttling: in resting cells G-actin sequesters PHACTR1 in the cytoplasm, while Rho-actin signaling promotes importin α-β-dependent nuclear accumulation; in the nucleus, the Phactr1/PP1 holoenzyme acquires substrate sequence-specificity by remodeling PP1's hydrophobic groove to dephosphorylate cytoskeletal substrates (e.g., IRSp53, spectrin αII) and regulators such as myosin light chain, thereby controlling actomyosin assembly, efferocytosis in macrophages, cortical neuron migration, and Slack (KCNT1) channel activity, while also acting as a transcriptional corepressor of PPARγ in endothelial cells under disturbed flow to promote atherosclerosis.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries from KEPT papers only.\n\n**Key exclusions:**\n- Paper [45] (PMID:39000149) and [57]: circRNA hsa_circ_0002268 — case (B) alt-locus product\n- Paper [55] (PMID:36194484): RPEL1 gene in SLE — case (A) alias collision (different gene)\n- Paper [59] (bio_10.1101_2024.06.26.600760): ATM paper mentioning PHACTR1 only as a phosphopeptide hit — not a PHACTR1 mechanistic paper\n- Paper [60] (bio_10.1101_2024.09.23.614477): PP1-Neurabin paper; mentions Phactr1 for context but primary subject is Neurabin/Spinophilin — marginal; the finding about Phactr proteins having identical sequence specificities is worth including as it directly characterizes PHACTR1 holoenzyme\n- Papers [2],[3],[5] in gene2pubmed that are cDNA/genome sequencing projects, GWAS without mechanism, etc. — these are association studies, not mechanistic\n\nAll other papers about canonical PHACTR1 protein: KEEP (extracting only mechanistic findings).\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"PHACTR1 (Phactr-1) was identified as the founding member of a family of PP1-binding proteins that also bind cytoplasmic actin via RPEL motifs. Phactr-1 was shown to be a potent modulator of PP1 activity in vitro, and the protein is selectively expressed in brain with enrichment at synapses.\",\n      \"method\": \"Interaction cloning, in vitro PP1 activity assay, subcellular fractionation, immunohistochemistry in rat brain\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — original discovery paper with in vitro PP1 activity assay, interaction cloning, and synaptic localization by fractionation; foundational study replicated by subsequent work\",\n      \"pmids\": [\"15107502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR1 depletion in HUVECs abolished tube formation and triggered apoptosis via death receptors DR4, DR5, and FAS in a caspase-8-dependent manner, establishing PHACTR1 as a key regulator of endothelial cell survival and tubulogenesis.\",\n      \"method\": \"siRNA knockdown in HUVECs, tube formation assay, flow cytometry for apoptosis, siRNA rescue with death-receptor and caspase-8 siRNAs\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — clean loss-of-function with defined phenotypic readout and pathway placement via receptor-specific siRNA rescue; single lab\",\n      \"pmids\": [\"21798305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR1 expression in HUVECs is induced by VEGF-A165 and is regulated specifically through NRP-1 and VEGF-R1 (but not NRP-2 or VEGF-R2). Upon VEGF stimulation, Phactr1 promotes tube formation and fine-tunes actin polymerization and lamellipodial dynamics; its depletion decreases PP1 activity and disrupts actin dynamics.\",\n      \"method\": \"siRNA knockdown of NRP-1, NRP-2, VEGFR1, VEGFR2; antagonist peptide blocking; PP1 activity assay; live-cell imaging of lamellipodia; tube formation assay in HUVECs\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple orthogonal approaches (receptor-specific knockdown, peptide antagonism, PP1 activity assay, live imaging); single lab\",\n      \"pmids\": [\"21939755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"G-actin binding by the three C-terminal RPEL motifs of Phactr1 is required for its cytoplasmic retention in resting cells. Rho-actin signalling (serum stimulation) depletes G-actin and promotes importin α-β-dependent nuclear accumulation of Phactr1. G-actin and importin α-β bind competitively to nuclear import signals flanking the RPEL motifs. Furthermore, G-actin and PP1 bind competitively to the Phactr1 C-terminal region, so that nuclear Phactr1 RPEL mutants that cannot bind G-actin induce aberrant actomyosin structures in a PP1-dependent manner. In CHL-1 melanoma cells, Phactr1 is required for stress fibre assembly, motility, and invasiveness.\",\n      \"method\": \"RPEL motif mutagenesis, importin binding assays, serum-stimulation nuclear accumulation assays, live-cell imaging, siRNA knockdown with motility/invasion assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal experiments (mutagenesis, competitive binding assays, functional rescue) in the same study; mechanistic model strongly supported\",\n      \"pmids\": [\"22976292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TGF-β down-regulates miR-584 in breast cancer cells, relieving repression of PHACTR1 and thereby increasing PHACTR1 expression. Elevated PHACTR1 reorganizes the actin cytoskeleton and is required for TGF-β-induced breast cancer cell migration; overexpression of miR-584 or knockdown of PHACTR1 each blocked this migration.\",\n      \"method\": \"miRNA overexpression, siRNA knockdown, TGF-β stimulation, cell migration assays, phalloidin staining of actin cytoskeleton\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — clean loss-of-function and gain-of-function with defined miRNA-mediated pathway; single lab\",\n      \"pmids\": [\"23479725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Phactr-1 down-expression in endothelial cells activates focal adhesion kinase pathways (FAK/PYK2/Paxillin) and inhibits metabolic stress pathways (AMPK/CREB/eNOS), and induces expression of pro-atherogenic molecules including MMP regulators (TIMP-1/-2, RECK), oxidized LDL receptors (CD36, Clusterin), and inflammatory proteins (Thrombin, PAR-1, ADAM-9/-17).\",\n      \"method\": \"siRNA knockdown of Phactr1 in endothelial cells; antagonist peptide inhibition of VEGF-A165/NRP-1 interaction; Western blot and protein array profiling\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — broad protein expression profiling after knockdown without direct mechanistic dissection of individual pathways; single lab\",\n      \"pmids\": [\"26362351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The CAD-risk SNP rs9349379 in intron 3 of PHACTR1 is an eQTL for PHACTR1 expression in human coronary arteries; alleles at this SNP are differentially bound by the MEF2 transcription factor, and CRISPR/Cas9 deletion of the MEF2-binding site in endothelial cells reduced PHACTR1 expression by ~35%.\",\n      \"method\": \"Genetic fine-mapping, eQTL analysis in human coronary arteries, electrophoretic mobility shift assay with endothelial cell extracts, CRISPR/Cas9 deletion\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — eQTL confirmed in human tissue and CRISPR editing demonstrates direct regulatory link; multiple orthogonal methods\",\n      \"pmids\": [\"25838425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PHACTR1 is expressed in human atherosclerotic plaque macrophages, foam cells, adventitial lymphocytes, and endothelial cells (but absent from vascular smooth muscle cells). Atherogenic stimuli (oxLDL, TNF-α) regulate PHACTR1 transcription; the CAD risk allele at rs9349379 is associated with reduced PHACTR1 expression in macrophages, paralleling the effect of inflammatory stimulation.\",\n      \"method\": \"Immunohistochemistry, qRT-PCR, immunoblotting, eQTL analysis in primary human macrophages\",\n      \"journal\": \"Atherosclerosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct tissue immunohistochemistry and primary macrophage eQTL; multiple methods but primarily expression-level findings\",\n      \"pmids\": [\"27187934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The CAD/MI risk SNP rs9349379 acts as a distal enhancer of endothelin-1 (EDN1) gene expression ~600 kb upstream. CRISPR-edited stem-cell-derived endothelial cells revealed that rs9349379 regulates EDN1 (not PHACTR1) expression in an aorta-specific enhancer context, providing a mechanistic link between this pleiotropic locus and vascular disease.\",\n      \"method\": \"CRISPR base editing in iPSC-derived endothelial cells, epigenomic chromatin analysis (H3K27ac, DNase I), eQTL mapping in aorta, reporter assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — CRISPR editing with functional readout in relevant cell type; replicated across epigenomic datasets; high-impact study\",\n      \"pmids\": [\"28753427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Phactr1 is expressed in mouse brain in a developmental stage-dependent and tissue-dependent manner. In primary hippocampal neurons, Phactr1 is detected in axons, dendrites, and is enriched in synaptosomal and postsynaptic density fractions. In embryonic cortex, Phactr1 accumulates in the nucleus, whereas postnatally it distributes diffusely in the cell body.\",\n      \"method\": \"Western blotting, subcellular fractionation (synaptosomal/PSD), immunohistochemistry in mouse brain, immunofluorescence in cultured hippocampal neurons\",\n      \"journal\": \"Neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments with fractionation and immunohistochemistry across developmental stages; single lab\",\n      \"pmids\": [\"28803787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Phactr1 expression level positively correlates with vascular calcification severity in smooth muscle cells. Stable overexpression of Phactr1 in mESC-derived SMCs enhanced calcium phosphate deposition and osteogenic marker osteopontin expression, while knockdown reduced calcification.\",\n      \"method\": \"Stable lentiviral over- and under-expression of Phactr1 in mouse embryonic stem cell-derived SMCs; osteogenic medium calcification assay; alizarin red staining; RT-PCR for osteopontin\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — bidirectional gain/loss-of-function with molecular readout; single lab\",\n      \"pmids\": [\"28720499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"De novo missense mutations in PHACTR1 associated with West syndrome (infantile spasms) impair either actin binding (p.Leu500Pro, p.Asn479Ile, p.Ile518Asn) or PP1 binding (p.Arg521Cys) as determined by immunoprecipitation. Acute knockdown of mouse Phactr1 by in utero electroporation caused defects in cortical neuron migration rescued by wild-type but not mutant PHACTR1, and Phactr1-deficient excitatory neurons showed abnormal synaptic electrophysiological properties.\",\n      \"method\": \"Trio whole-exome sequencing, co-immunoprecipitation of mutant PHACTR1 with actin and PP1, in utero electroporation knockdown + rescue in mouse cortex, patch-clamp electrophysiology\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with in vivo electroporation rescue and electrophysiology; multiple orthogonal methods linking specific domains to cortical neuron migration and synaptic function\",\n      \"pmids\": [\"30256902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PHACTR1 interacts with MRTF-A and with p65/NF-κB in coronary artery endothelial cells (co-immunoprecipitation). Knockdown of PHACTR1 attenuates nuclear translocation of p65 and NF-κB activity (without affecting IκBα or IKKα/β phosphorylation), reduces ox-LDL-induced ICAM-1, VCAM-1, and VE-cadherin expression, and reduces intracellular ROS. Knockdown of MRTF-A disrupts the PHACTR1–p65 interaction.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, immunofluorescence for p65 nuclear translocation, flow cytometry for ROS, Western blotting for NF-κB pathway components\",\n      \"journal\": \"Atherosclerosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — reciprocal co-IP and defined mechanistic pathway; single lab with multiple complementary assays\",\n      \"pmids\": [\"30293016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Phactr1 physically links Slack (KCNT1) potassium channels to actin via co-immunoprecipitation. Co-expression of Phactr1 reduces Slack current amplitude in a manner dependent on the PP1-binding activity of Phactr1 and a conserved PKC phosphorylation site (S407) on Slack, establishing that Phactr1 regulates Slack channel activity by recruiting PP1 to dephosphorylate the channel.\",\n      \"method\": \"Co-immunoprecipitation, patch-clamp electrophysiology in Xenopus oocytes/HEK cells, Phactr1 PP1-binding mutant\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — electrophysiology with mutant dissection of PP1-binding vs. actin-binding requirements; mechanistically rigorous\",\n      \"pmids\": [\"31914597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal/high-resolution structures of the Phactr1/PP1 holoenzyme bound to dephosphorylated substrates IRSp53 and spectrin αII revealed that Phactr1 remodels PP1's hydrophobic groove to create a composite substrate-recognition surface. Substrate sequences C-terminal to the dephosphorylation site make intimate contacts with this composite surface, conferring sequence specificity and orders-of-magnitude enhanced reactivity toward specific substrates compared to apo-PP1 or other PP1 holoenzymes. Phosphoproteomic identification of Phactr1/PP1 substrates in fibroblasts and neurons included cytoskeletal components and regulators.\",\n      \"method\": \"X-ray crystallography (high-resolution structures of holoenzyme-product complexes), phosphoproteomics in mouse fibroblasts and neurons, in vitro dephosphorylation assays with mutagenesis of substrate contact residues\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with functional validation by mutagenesis and phosphoproteomics; mechanistically definitive\",\n      \"pmids\": [\"32975518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Phactr1 deficiency in macrophages promotes M1 polarization, increased pro-inflammatory cytokine production, and enhanced foam cell formation driven by ox-LDL. Mechanistically, Phactr1 activates CREB signaling by directly binding to CREB and up-regulating phospho-CREB and KLF4 expression; KLF4 overexpression partially rescued the inflammatory and foam cell phenotypes of Phactr1-deficient macrophages.\",\n      \"method\": \"Phactr1-/-/Apoe-/- double-knockout mice, bone marrow transplantation, co-immunoprecipitation of Phactr1 with CREB, Western blot for phospho-CREB, KLF4 overexpression rescue, macrophage polarization assays\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — in vivo mouse model with bone marrow transplant and mechanistic co-IP; single lab\",\n      \"pmids\": [\"32857129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PHACTR1 prevents dephosphorylation of myosin light chain (MLC), which is required for actin-mediated apoptotic cell engulfment (efferocytosis) by macrophages. The rs9349379-G/G risk genotype associates with lower PHACTR1 expression in human macrophages and impaired efferocytosis. Hematopoietic Phactr1 deletion in Ldlr-/- mice on a Western diet impaired lesional efferocytosis, increased plaque necrosis, and produced thinner fibrous caps.\",\n      \"method\": \"Human monocyte-derived macrophage efferocytosis assays, Ldlr-/- hematopoietic-specific Phactr1 knockout mouse model, Western diet atherosclerosis model, Western blot for phospho-MLC, plaque histology\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo mouse model combined with mechanistic phospho-MLC analysis and human macrophage validation; multiple orthogonal methods\",\n      \"pmids\": [\"33630758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo PHACTR1 missense mutation p.L519R reduces the affinity of PHACTR1 for G-actin and increases its propensity to form complexes with PP1 catalytic subunit (PPP1CA), leading to altered subcellular localization and increased cytoskeletal rearrangements, associated with multifocal epilepsy and infantile spasms.\",\n      \"method\": \"In vitro binding assays, subcellular localization analysis of mutant PHACTR1, functional cytoskeletal assays\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — in vitro binding and localization assays for a single variant; single case report with mechanistic follow-up\",\n      \"pmids\": [\"33463715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Phactr1 negatively regulates osteogenesis and promotes adipogenesis of bone marrow mesenchymal stem cells via the RhoA/ROCK2 pathway. Phactr1 and ROCK2 physically interact (co-IP) during osteogenic differentiation, and ROCK2 inhibition (KD025) reproduces the Phactr1-overexpression phenotype of suppressed Runx2 and osteogenesis.\",\n      \"method\": \"Co-immunoprecipitation of Phactr1 and ROCK2, siRNA knockdown and lentiviral overexpression of Phactr1 in BMSCs, osteogenic/adipogenic differentiation assays, alizarin red/Oil red O staining, Western blot for RhoA/ROCK2/Runx2/C-EBPα\",\n      \"journal\": \"Journal of molecular histology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP of Phactr1-ROCK2 and pharmacological ROCK2 inhibition rescue; single lab\",\n      \"pmids\": [\"34709489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial PHACTR1 acts as a transcriptional corepressor of PPARγ under disturbed flow conditions. PHACTR1 is enriched in the nucleus of endothelial cells in disturbed-flow regions and shuttles to the cytoplasm under laminar flow. PHACTR1 binds PPARγ through corepressor motifs. Global or EC-specific Phactr1 knockout in ApoE-/- mice significantly reduced atherosclerosis, and PPARγ antagonist GW9662 abolished the protective effect.\",\n      \"method\": \"EC-specific and global Phactr1 knockout in ApoE-/- mice, partial carotid ligation atherosclerosis model, immunostaining for PHACTR1 localization under laminar vs. disturbed flow, RNA-seq of EC-enriched mRNA, PPARγ binding assays (corepressor motif), GW9662 pharmacological rescue\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo mouse KO model with pharmacological rescue and direct PPARγ binding; multiple orthogonal methods\",\n      \"pmids\": [\"37199156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PHACTR1 overexpression promotes invasion, migration, and tumorigenicity of papillary thyroid carcinoma cells by increasing F-actin formation; disruption of F-actin assembly with swinholide A reversed the enhanced migration, placing PHACTR1 function upstream of F-actin polymerization in cancer cell motility.\",\n      \"method\": \"siRNA knockdown and cDNA overexpression in PTC cell lines, Transwell invasion/migration assays, phalloidin-F-actin fluorescence imaging, swinholide A pharmacological rescue\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — bidirectional gain/loss-of-function with pharmacological pathway rescue; single lab\",\n      \"pmids\": [\"37876444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"BDNF stimulation of primary cortical neurons causes sustained downregulation of PHACTR1 (and PHACTR2/3 but not PHACTR4) mRNA via the ERK/MAPK pathway; this was blocked by the MEK inhibitor U0126, identifying ERK/MAPK as an upstream regulator of PHACTR1 gene expression in neurons.\",\n      \"method\": \"BDNF stimulation of primary cultured mouse cortical neurons, qRT-PCR for PHACTR family mRNAs, MEK inhibitor U0126 treatment\",\n      \"journal\": \"Drug discoveries & therapeutics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mRNA-level regulation with pharmacological inhibitor; no direct mechanistic dissection of the ERK-PHACTR1 link\",\n      \"pmids\": [\"39183043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AlphaFold-Multimer modeling and analysis of PHACTR1 patient variants indicate that the RPEL3 domain serves as the binding interface for both G-actin and PPP1CA, and these two interactions are competitive. Missense variants in patients with infantile epileptic spasms syndrome map to the RPEL3 domain and impair either G-actin or PPP1CA binding.\",\n      \"method\": \"AlphaFold-Multimer structural prediction, whole-exome sequencing of nine PHACTR1-variant patients, genotype-phenotype correlation\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — primarily computational structural prediction; clinical genotype-phenotype correlation without in vitro binding validation\",\n      \"pmids\": [\"38272663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Phactr1 binds directly to MRTF-A, MRTF-B, myocardin, and Phactr1 itself via RPEL-containing nuclear localization sequences, and is a direct target of the Rho-signaling inhibitor CCG-1423 (pull-down with CCG-1423-Sepharose). G-actin binding blocks CCG-1423 interaction with the NLS of RPEL proteins including Phactr1.\",\n      \"method\": \"CCG-1423-Sepharose affinity pull-down assay, competitive G-actin displacement assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct pull-down demonstrating Phactr1 as a CCG-1423 target; mechanistically relevant finding confirmed by competitive assay\",\n      \"pmids\": [\"24558465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Multi-omics profiling (transcriptomics, proteomics, metabolomics, lipidomics) of PHACTR1 overexpression and knockdown in HT1080 cells revealed that PHACTR1 governs cell cycle progression (altering key regulatory proteins), regulates cellular iron-storage proteins (iron metabolism), and localizes to mitochondria where it modulates mitochondrial morphology and bioenergetics through a signaling axis involving AKAP1 and Drp1. Mitochondrial changes correlated with shifts in lipid metabolism.\",\n      \"method\": \"Multi-omics (transcriptomics, proteomics, metabolomics, lipidomics) in PHACTR1 OE/KD HT1080 cells; validation in primary human endothelial cells; mitochondrial localization confirmed; AKAP1/Drp1 interaction identified\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multi-omics with validation in primary cells and identification of mitochondrial signaling axis; single study but four orthogonal omics layers\",\n      \"pmids\": [\"41554990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The CAD-risk SNP rs6903956 'A' allele enhances HOXA4/MEIS1 transcription factor binding at the locus to drive PHACTR1 transcriptional activation in endothelial cells. iPSC-derived endothelial cells with the 'A' allele show elevated PHACTR1 expression and, under pathological flow, elevated ICAM-1 expression and increased monocyte adhesion compared to the 'G' allele.\",\n      \"method\": \"Single-base editing of iPSC-derived endothelial cells, eQTL analysis, AlphaFold 3 in silico binding modeling, luciferase reporter assays, ICAM-1/monocyte adhesion assays under flow\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3–4 — preprint; computational structural modeling with functional reporter and cell assay validation; not yet peer-reviewed\",\n      \"pmids\": [\"40654905\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"All four Phactr proteins (Phactr1–4) confer identical sequence specificities on their respective PP1 holoenzymes, as demonstrated by a PP1-PIP fusion approach. This establishes that the composite Phactr/PP1 substrate-recognition surface described for Phactr1 is a conserved property of the Phactr family.\",\n      \"method\": \"PP1-PIP fusion protein approach, substrate phosphoproteomics, in vitro dephosphorylation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — rigorous biochemical approach extending the Phactr1/PP1 structural finding; preprint from same lab as the eLife 2020 structure paper\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PHACTR1 is an RPEL-motif-containing protein that acts as a PP1 cofactor: it binds G-actin (via three C-terminal RPEL motifs) and PP1 competitively, such that Rho-signal-induced G-actin depletion drives importin α-β-dependent nuclear accumulation of PHACTR1, where it remodels PP1's hydrophobic groove to create a composite surface conferring sequence-specific dephosphorylation of cytoskeletal substrates (e.g., IRSp53, spectrin αII); in neurons it recruits PP1 to dephosphorylate and suppress Slack (KCNT1) channel activity, and in macrophages it maintains myosin light chain phosphorylation to support efferocytosis; in endothelial cells under disturbed flow it accumulates in the nucleus and acts as a PPARγ transcriptional corepressor to promote endothelial activation and atherosclerosis, while its expression is regulated upstream by VEGF/NRP-1/VEGFR1 signaling, TGF-β/miR-584, and the BDNF-ERK/MAPK axis, and by the CAD-risk SNP rs9349379 acting as an MEF2-dependent enhancer in coronary arteries.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PHACTR1 is a PP1 cofactor and G-actin sensor that couples Rho-actin signaling to phosphatase-dependent control of the cytoskeleton, transcription, and ion channel activity. Four RPEL motifs bind G-actin to retain PHACTR1 in the cytoplasm; Rho-driven actin polymerization releases this inhibition, permitting importin α-β-dependent nuclear import, while G-actin and PP1 compete for the C-terminal region so that nuclear PHACTR1 preferentially engages PP1, whose hydrophobic groove is remodeled to create a composite substrate-recognition surface that confers orders-of-magnitude selectivity for cytoskeletal substrates such as IRSp53 and spectrin αII [PMID:22976292, PMID:32975518]. Through PP1-dependent regulation of myosin light chain phosphorylation, PHACTR1 controls macrophage efferocytosis and atherosclerotic plaque stability, while in endothelial cells it acts as a flow-sensitive PPARγ transcriptional corepressor that promotes atherosclerosis under disturbed shear stress [PMID:33630758, PMID:37199156]. De novo missense mutations that disrupt actin or PP1 binding cause defective cortical neuron migration and are associated with epilepsy, and PHACTR1 also regulates Slack (KCNT1) channel currents in a PP1-binding-dependent manner [PMID:30256902, PMID:33463715, PMID:31914597].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing PHACTR1 as an endothelial survival factor downstream of VEGF/NRP-1/VEGFR1 signaling resolved how it is induced in vascular cells and showed that its loss triggers death-receptor-mediated apoptosis and disrupts actin-dependent lamellipodial dynamics during tubulogenesis.\",\n      \"evidence\": \"siRNA knockdown and receptor-specific depletion in HUVECs with tube formation, apoptosis, and PP1 activity assays\",\n      \"pmids\": [\"21798305\", \"21939755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking PHACTR1 loss to death receptor upregulation is unclear\", \"Whether PHACTR1's role in tubulogenesis is PP1-dependent versus actin scaffold-dependent was not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defining the RPEL-motif-based nucleocytoplasmic shuttling mechanism revealed how PHACTR1 senses intracellular actin levels: G-actin competes with both importin α-β and PP1 for binding, so Rho-driven actin polymerization simultaneously licenses nuclear import and PP1 engagement, explaining how cytoplasmic RPEL mutants generate aberrant actomyosin structures.\",\n      \"evidence\": \"Mutagenesis of four RPEL motifs, immunofluorescence localization, co-immunoprecipitation of competitive G-actin/importin/PP1 binding, siRNA knockdown in CHL-1 melanoma cells\",\n      \"pmids\": [\"22976292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of the G-actin–RPEL complex was not determined in this study\", \"Whether the four RPEL motifs have graded affinities with functional hierarchy was untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that TGF-β-induced migration requires PHACTR1 de-repression (via miR-584 downregulation) placed PHACTR1 in a signaling cascade linking extracellular cues to actin rearrangement in cancer cells.\",\n      \"evidence\": \"miR-584 overexpression and PHACTR1 knockdown in breast cancer cells with migration and actin staining\",\n      \"pmids\": [\"23479725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PHACTR1 acts through PP1 or actin binding in this context was not dissected\", \"In vivo relevance for metastasis untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of de novo PHACTR1 missense mutations that selectively disrupt actin or PP1 binding and fail to rescue cortical neuron migration established PHACTR1 as a neurodevelopmental gene whose dual binding activities are both essential for neuronal positioning.\",\n      \"evidence\": \"In utero electroporation knockdown and mutant rescue in mouse cortex, binding assays, electrophysiology\",\n      \"pmids\": [\"30256902\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific PP1 substrates mediating neuronal migration were not identified\", \"Whether synaptic defects are cell-autonomous was not fully resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that PHACTR1 physically links Slack (KCNT1) channels to actin and reduces channel currents in a PP1-binding-dependent manner through dephosphorylation of Slack S407 extended the PHACTR1/PP1 holoenzyme's substrate repertoire to ion channels.\",\n      \"evidence\": \"Co-immunoprecipitation, patch-clamp electrophysiology, site-directed mutagenesis of PP1-binding and Slack S407 sites\",\n      \"pmids\": [\"31914597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Phactr1 regulates Slack in vivo (neuronal context) was not tested\", \"Stoichiometry and structural basis of the Phactr1–Slack complex are unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Crystallographic resolution of the Phactr1/PP1 holoenzyme bound to dephosphorylated substrates (IRSp53, spectrin αII) revealed that Phactr1 remodels PP1's hydrophobic groove to generate a composite substrate-recognition surface, explaining how the holoenzyme achieves orders-of-magnitude selectivity over free PP1.\",\n      \"evidence\": \"X-ray crystallography of holoenzyme–product complexes, phosphoproteomics substrate identification, quantitative in vitro phosphatase assays with mutagenesis\",\n      \"pmids\": [\"32975518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the structural remodeling generalizes to other Phactr family members was not tested\", \"Full substrate scope in different cell types remains incomplete\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that PHACTR1 binds CREB directly to activate KLF4-dependent M2 macrophage polarization provided a transcription-regulatory mechanism distinct from its PP1 phosphatase role, linking it to anti-inflammatory macrophage function in atherosclerosis.\",\n      \"evidence\": \"Co-immunoprecipitation (Phactr1-CREB), Phactr1−/−Apoe−/− double-KO mouse model, bone marrow transplant, KLF4 rescue\",\n      \"pmids\": [\"32857129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CREB binding relies on a single co-IP without domain mapping\", \"Whether CREB activation requires PP1 catalytic activity was not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealing that PHACTR1 prevents MLC dephosphorylation to sustain actomyosin contractility required for macrophage efferocytosis, and that atherosclerosis risk allele rs9349379-G lowers PHACTR1 expression in human macrophages, connected a precise molecular mechanism to CAD-associated plaque instability.\",\n      \"evidence\": \"Genotype-stratified human macrophage assays, hematopoietic-specific KO in Ldlr−/− mice, phospho-MLC western blot\",\n      \"pmids\": [\"33630758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MLC is a direct Phactr1/PP1 substrate or regulated indirectly (e.g. via ROCK) was not resolved\", \"Contribution of efferocytosis defect relative to other macrophage functions in plaque progression is unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A de novo PHACTR1 p.L519R mutation that reduces G-actin affinity while enhancing PP1 complex formation supported a gain-of-function/dominant-negative mechanism for multifocal epilepsy, reinforcing the model that balanced actin/PP1 competition is critical for normal neuronal function.\",\n      \"evidence\": \"In vitro G-actin binding, co-IP for PP1, immunofluorescence, cytoskeletal phenotype in a patient-derived mutation\",\n      \"pmids\": [\"33463715\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single patient; independent replication in additional families or animal models lacking\", \"Electrophysiological consequence of this specific mutation was not characterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying PHACTR1 as a flow-sensitive PPARγ transcriptional corepressor in endothelial cells — nuclear under disturbed flow, cytoplasmic under laminar flow — and showing that EC-specific Phactr1 deletion is atheroprotective in a PPARγ-dependent manner established a direct transcriptional mechanism for the PHACTR1–atherosclerosis GWAS association.\",\n      \"evidence\": \"EC-specific and global Phactr1 KO in Apoe−/− mice, partial carotid ligation, co-IP of PHACTR1–PPARγ, GW9662 antagonist rescue, RNA-seq\",\n      \"pmids\": [\"37199156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PHACTR1–PPARγ corepressor interaction is undefined\", \"Relative contributions of endothelial vs. macrophage PHACTR1 to human CAD risk are unresolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Multi-omics profiling extended PHACTR1's functional reach beyond cytoskeleton and transcription to cell cycle control, iron metabolism, and mitochondrial morphology/bioenergetics via an AKAP1–Drp1 axis, revealing unexpectedly broad metabolic effects.\",\n      \"evidence\": \"Transcriptomics, proteomics, metabolomics, lipidomics in PHACTR1 gain/loss-of-function HT1080 cells validated in primary endothelial cells\",\n      \"pmids\": [\"41554990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"AKAP1/Drp1 mechanism is correlative; direct PHACTR1 interaction or PP1-dependence not shown\", \"Iron metabolism regulation is descriptive without identified substrates\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: (1) how the actin-sensing/PP1 engagement switch is structurally integrated at the full-length protein level, (2) what the complete substrate repertoire of the Phactr1/PP1 holoenzyme is across cell types, (3) whether MLC regulation is direct or indirect, and (4) how endothelial versus macrophage PHACTR1 functions independently contribute to human CAD risk.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full-length Phactr1 structure (with RPEL motifs and PP1) not determined\", \"Cell-type-specific substrate catalogs are incomplete\", \"Relative in vivo contributions of transcriptional corepressor versus phosphatase functions to disease phenotypes are unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 6, 7]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 5, 6, 13]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 8, 14]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 14]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 4, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 6, 9]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"complexes\": [\n      \"Phactr1/PP1 holoenzyme\"\n    ],\n    \"partners\": [\n      \"PPP1CA\",\n      \"ACTA1\",\n      \"KCNT1\",\n      \"PPARG\",\n      \"CREB1\",\n      \"ROCK2\",\n      \"RELA\",\n      \"MRTFA\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"PHACTR1 is an RPEL-motif-containing cofactor of protein phosphatase 1 (PP1) that couples Rho–actin signaling to substrate-specific dephosphorylation, transcriptional regulation, and cytoskeletal remodeling across vascular, immune, and neuronal contexts. In resting cells, G-actin binds the three C-terminal RPEL motifs to retain PHACTR1 in the cytoplasm; Rho-signal-driven G-actin depletion exposes importin α–β binding sites and triggers nuclear accumulation, simultaneously freeing the PP1-interaction surface because G-actin and PP1 bind competitively to the same region [PMID:22976292, PMID:32975518]. The PHACTR1/PP1 holoenzyme remodels PP1's hydrophobic groove to create a composite substrate-recognition surface that confers sequence-specific dephosphorylation of cytoskeletal targets such as IRSp53 and spectrin αII; in macrophages this activity maintains myosin light chain phosphorylation required for efferocytosis, while in neurons it recruits PP1 to suppress Slack (KCNT1) channel activity [PMID:32975518, PMID:33630758, PMID:31914597]. De novo missense mutations disrupting actin- or PP1-binding cause West syndrome (infantile epileptic spasms), with loss of PHACTR1 impairing cortical neuron migration and synaptic function [PMID:30256902]; in endothelial cells under disturbed flow, nuclear PHACTR1 acts as a PPARγ transcriptional corepressor to promote endothelial activation and atherosclerosis [PMID:37199156].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing PHACTR1 as a PP1-binding, actin-associating protein enriched at synapses answered the initial question of what this brain-expressed protein does biochemically and where it acts.\",\n      \"evidence\": \"Interaction cloning, in vitro PP1 activity assay, subcellular fractionation and immunohistochemistry in rat brain\",\n      \"pmids\": [\"15107502\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for PP1 or actin binding\", \"No in vivo loss-of-function data\", \"Neuronal substrates of PHACTR1/PP1 unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrating that VEGF/NRP-1/VEGFR1 signaling induces PHACTR1 in endothelial cells and that PHACTR1 is required for tubulogenesis, survival, and lamellipodial dynamics extended the protein's role beyond neurons into the vasculature and linked it to actin dynamics and PP1 activity in endothelial biology.\",\n      \"evidence\": \"siRNA knockdown in HUVECs with receptor-specific depletion, PP1 activity assays, tube formation and apoptosis assays, live-cell imaging\",\n      \"pmids\": [\"21798305\", \"21939755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting PHACTR1 loss to death receptor activation unclear\", \"No in vivo endothelial phenotype\", \"Whether PP1 catalytic activity mediates tube formation not directly tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolving how PHACTR1 shuttles between cytoplasm and nucleus answered the key regulatory question: G-actin binding to RPEL motifs competitively blocks both importin α–β-dependent nuclear import and PP1 binding, so Rho-driven G-actin depletion simultaneously drives nuclear entry and enables PP1 engagement.\",\n      \"evidence\": \"RPEL motif mutagenesis, competitive importin and PP1 binding assays, serum-stimulation nuclear accumulation, siRNA phenotyping in CHL-1 melanoma cells\",\n      \"pmids\": [\"22976292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural resolution of competitive binding interfaces\", \"Whether the mechanism operates equivalently in neurons vs. endothelial cells untested\", \"Nuclear PP1 substrates not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying TGF-β/miR-584 as an upstream regulatory axis for PHACTR1 expression established a mechanism by which PHACTR1-dependent actin reorganization drives TGF-β-induced cancer cell migration.\",\n      \"evidence\": \"miR-584 overexpression and PHACTR1 knockdown in breast cancer cells; TGF-β stimulation; phalloidin staining; migration assays\",\n      \"pmids\": [\"23479725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-584 binding site on PHACTR1 3'UTR not validated by reporter assay in this study\", \"Whether PP1 activity is required for this migration phenotype unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showing that PHACTR1 interacts with MRTF-A/B and myocardin via RPEL-containing NLS sequences, and is a direct target of Rho-pathway inhibitor CCG-1423, placed PHACTR1 within the broader RPEL-protein regulatory network.\",\n      \"evidence\": \"CCG-1423-Sepharose affinity pull-down, competitive G-actin displacement assay\",\n      \"pmids\": [\"24558465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of PHACTR1–MRTF interaction not determined\", \"Whether CCG-1423 inhibits PHACTR1 function in cells not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying the CAD-risk SNP rs9349379 as a MEF2-dependent enhancer that controls PHACTR1 expression in coronary arteries connected human GWAS genetics to a specific cis-regulatory mechanism.\",\n      \"evidence\": \"eQTL analysis in human coronary arteries, EMSA, CRISPR/Cas9 deletion of MEF2 site in endothelial cells\",\n      \"pmids\": [\"25838425\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether reduced PHACTR1 expression is the causal mediator of CAD risk at this locus was contested by subsequent work implicating EDN1\", \"No functional vascular phenotype tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"A landmark CRISPR base-editing study demonstrated that rs9349379 acts as a distal enhancer of EDN1 (not PHACTR1) in aortic endothelial cells, raising the possibility that the CAD risk at this locus is mediated through endothelin-1 rather than PHACTR1 in certain vascular beds.\",\n      \"evidence\": \"CRISPR base editing in iPSC-derived endothelial cells, H3K27ac and DNase I chromatin analysis, aorta eQTL mapping\",\n      \"pmids\": [\"28753427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type and vascular-bed specificity of rs9349379 regulation not fully resolved\", \"Does not exclude PHACTR1-mediated contributions in macrophages or non-aortic vessels\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of de novo PHACTR1 missense mutations causing West syndrome, with mutations selectively disrupting actin- or PP1-binding and failing to rescue cortical neuron migration, established PHACTR1 as a disease gene and demonstrated that both binding activities are essential for brain development.\",\n      \"evidence\": \"Trio WES, co-IP of mutant PHACTR1 with actin/PP1, in utero electroporation rescue in mouse cortex, patch-clamp electrophysiology\",\n      \"pmids\": [\"30256902\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream substrates mediating migration and synaptic phenotypes not identified\", \"Whether PP1 catalytic activity or scaffolding underlies the rescue not distinguished\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating that PHACTR1 interacts with MRTF-A and p65/NF-κB to promote nuclear translocation of p65 in endothelial cells provided a PP1-independent transcriptional mechanism for PHACTR1's pro-inflammatory role.\",\n      \"evidence\": \"Co-IP of PHACTR1 with MRTF-A and p65, siRNA knockdown, immunofluorescence for p65 translocation in coronary artery endothelial cells\",\n      \"pmids\": [\"30293016\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reciprocal IP for PHACTR1–p65 direct binding\", \"Mechanism by which PHACTR1 promotes p65 translocation without affecting IκBα unclear\", \"Relationship to PP1 catalytic activity not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Electrophysiological evidence that PHACTR1 recruits PP1 to dephosphorylate the Slack (KCNT1) potassium channel at Ser407, reducing channel current, identified the first ion-channel substrate and demonstrated a neuronal signaling role for the PHACTR1/PP1 holoenzyme.\",\n      \"evidence\": \"Co-IP of PHACTR1 with Slack, patch-clamp electrophysiology in oocytes/HEK cells, PP1-binding mutant of PHACTR1\",\n      \"pmids\": [\"31914597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo neuronal consequence of Slack regulation by PHACTR1 not determined\", \"Whether other PHACTR1/PP1 substrates exist in neurons not addressed beyond this channel\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Crystal structures of the PHACTR1/PP1 holoenzyme with dephosphorylated substrates (IRSp53, spectrin αII) provided the definitive structural mechanism: PHACTR1 remodels PP1's hydrophobic groove to create a composite surface conferring sequence-specific substrate recognition and orders-of-magnitude enhanced catalytic efficiency.\",\n      \"evidence\": \"X-ray crystallography of holoenzyme–product complexes, phosphoproteomics in fibroblasts and neurons, mutagenesis of substrate-contact residues\",\n      \"pmids\": [\"32975518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full substrate repertoire in physiological contexts incompletely mapped\", \"Whether actin-bound vs. PP1-bound pools have distinct substrate access in cells not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showing that macrophage PHACTR1 deficiency drives M1 polarization and foam cell formation via reduced CREB/KLF4 signaling provided a macrophage-intrinsic mechanism linking lower PHACTR1 to atherosclerosis progression.\",\n      \"evidence\": \"Phactr1−/−/Apoe−/− mice, bone marrow transplant, co-IP of PHACTR1 with CREB, KLF4 rescue\",\n      \"pmids\": [\"32857129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PHACTR1-CREB interaction is PP1-dependent not tested\", \"Single lab finding awaiting independent replication\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that PHACTR1 prevents MLC dephosphorylation to enable macrophage efferocytosis, and that the rs9349379 risk allele reduces PHACTR1 expression and efferocytic capacity, provided a direct mechanistic link between PHACTR1-directed PP1 activity, apoptotic cell clearance, and CAD risk.\",\n      \"evidence\": \"Human macrophage efferocytosis assays, hematopoietic-specific Phactr1 KO in Ldlr−/− mice on Western diet, phospho-MLC Western blot, plaque histology\",\n      \"pmids\": [\"33630758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Paradox: PHACTR1 here prevents dephosphorylation of MLC whereas it promotes dephosphorylation of other substrates — mechanism of substrate selectivity in macrophages not resolved\", \"Whether endothelial and macrophage PHACTR1 effects are additive in atherogenesis not tested in combined models\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying PHACTR1 as a flow-sensitive PPARγ transcriptional corepressor in endothelial cells resolved how nuclear PHACTR1 promotes endothelial activation: under disturbed flow it represses PPARγ anti-inflammatory target genes, and endothelial-specific deletion is atheroprotective.\",\n      \"evidence\": \"EC-specific and global Phactr1 KO in ApoE−/− mice, partial carotid ligation, immunostaining under flow, PPARγ binding assays, GW9662 pharmacological rescue\",\n      \"pmids\": [\"37199156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the corepressor function requires PP1 or is independent not determined\", \"Identity of PPARγ target genes most relevant to atheroprotection not fully defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Multi-omics profiling revealed that PHACTR1 localizes to mitochondria and modulates mitochondrial morphology and bioenergetics via an AKAP1/Drp1 axis, expanding PHACTR1's functional repertoire beyond the actin cytoskeleton and nucleus.\",\n      \"evidence\": \"Transcriptomics, proteomics, metabolomics, lipidomics in HT1080 OE/KD cells; validation in primary endothelial cells; mitochondrial localization confirmed\",\n      \"pmids\": [\"41554990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PP1 activity is required for mitochondrial effects not tested\", \"AKAP1/Drp1 interaction with PHACTR1 not validated by reciprocal co-IP or mutagenesis\", \"Single study; independent replication needed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include: how PHACTR1 differentially prevents dephosphorylation of MLC in macrophages while promoting dephosphorylation of other cytoskeletal substrates; the relative contributions of endothelial, macrophage, and smooth muscle cell PHACTR1 to CAD in vivo; the full neuronal substrate repertoire and how its disruption causes epileptic spasms; and whether the mitochondrial localization and AKAP1/Drp1 axis represent a physiologically significant function.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Substrate selectivity mechanism in distinct cell types unresolved\", \"No combined tissue-specific KO studies for atherosclerosis\", \"Neuronal substrates beyond Slack channel not validated in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 13, 14, 16]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3, 4, 20]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [13, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 9, 19]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 9]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 4, 20]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 13, 18, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [12, 15, 16]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 7, 16, 19]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [11, 13]}\n    ],\n    \"complexes\": [\n      \"PHACTR1/PP1 holoenzyme\"\n    ],\n    \"partners\": [\n      \"PPP1CA\",\n      \"ACTA1\",\n      \"KCNT1\",\n      \"PPARG\",\n      \"MRTFA\",\n      \"ROCK2\",\n      \"CREB1\",\n      \"AKAP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}