{"gene":"PHACTR1","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2012,"finding":"PHACTR1 contains four G-actin binding RPEL motifs (one N-terminal, three C-terminal) that control its subcellular localization: G-actin binding to the three C-terminal RPEL motifs retains PHACTR1 in the cytoplasm of resting cells, while Rho-actin signaling (serum stimulation) reduces free G-actin and promotes importin α-β-dependent nuclear accumulation of PHACTR1. G-actin and importin α-β bind competitively to nuclear import signals associated with the N- and C-terminal RPEL motifs. G-actin and PP1 also bind competitively to the PHACTR1 C-terminal region; RPEL mutants unable to bind G-actin constitutively accumulate in the nucleus and 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.","method":"Co-immunoprecipitation, site-directed mutagenesis of RPEL motifs, fluorescence microscopy of subcellular localization, importin competition assays, actin binding assays, cell motility/invasion assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (mutagenesis, competitive binding assays, localization studies, functional cellular assays) in a single rigorous study establishing the mechanistic model","pmids":["22976292"],"is_preprint":false},{"year":2020,"finding":"The Phactr1/PP1 holoenzyme has defined substrate specificity: Phactr1 binding remodels PP1's hydrophobic groove to create a composite surface adjacent to the catalytic site. High-resolution crystal structures of Phactr1/PP1 bound to dephosphorylated substrates IRSp53 and spectrin αII showed that substrate sequences C-terminal to the dephosphorylation site make intimate contacts with this composite Phactr1/PP1 surface, which are required for efficient dephosphorylation. Phactr1/PP1 exhibits orders-of-magnitude enhanced reactivity toward its substrates (identified by phosphoproteomics as cytoskeletal components including IRSp53 and spectrin αII) compared to apo-PP1 or other PP1 holoenzymes. Inversion of the phosphate in holoenzyme-product complexes supports the proposed PPP-family catalytic mechanism.","method":"X-ray crystallography (high-resolution structures of holoenzyme-product complexes), phosphoproteomics substrate identification, in vitro phosphatase activity assays, mutagenesis of substrate contact residues","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with functional validation by phosphoproteomics and in vitro assays, multiple orthogonal methods in one study","pmids":["32975518"],"is_preprint":false},{"year":2018,"finding":"De novo missense mutations in PHACTR1 (p.Leu500Pro, p.Asn479Ile, p.Ile518Asn) impair actin-binding activity of PHACTR1, while p.Arg521Cys impairs binding to PP1, as shown by immunoprecipitation. Acute knockdown of mouse Phactr1 by in utero electroporation causes defects in cortical neuron migration during corticogenesis, rescued by RNAi-resistant wild-type PHACTR1 but not by the four mutants. The p.Arg521Cys PP1-binding mutant has dominant-negative effects on dendritic development in vivo. Electrophysiological analyses revealed abnormal synaptic properties in Phactr1-deficient excitatory cortical neurons.","method":"Co-immunoprecipitation (actin and PP1 binding), in utero electroporation knockdown/rescue in mouse cortex, electrophysiology of cortical neurons","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays with multiple mutants, in vivo knockdown/rescue with defined phenotypic readouts, electrophysiology, multiple orthogonal methods","pmids":["30256902"],"is_preprint":false},{"year":2021,"finding":"PHACTR1 prevents dephosphorylation of myosin light chain (MLC), which is necessary for apoptotic cell (AC) engulfment by macrophages. The rs9349379-G/G risk allele is associated with lower PHACTR1 expression in human monocyte-derived macrophages, lower phospho-MLC, and impaired efferocytosis. Silencing PHACTR1 in human and mouse macrophages compromised AC engulfment. Hematopoietic Phactr1-targeted Ldlr-/- mice on Western diet showed impaired lesional efferocytosis, increased plaque necrosis, and thinner fibrous caps.","method":"siRNA knockdown of PHACTR1 in human/mouse macrophages, hematopoietic-specific genetic knockout (bone marrow transplant into Ldlr-/- mice), phospho-MLC western blotting, efferocytosis assays, histological analysis of atherosclerotic plaques","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic model with defined cellular phenotype, mechanistic link to MLC phosphorylation, multiple orthogonal methods (KO, KD, biochemistry, histology)","pmids":["33630758"],"is_preprint":false},{"year":2019,"finding":"Phactr1 regulates Slack (KCNT1) sodium-activated potassium channels via PP1: co-immunoprecipitation showed Phactr1 links channels to actin. Co-expression of Phactr1 with wild-type Slack channels reduces current amplitude; this effect is absent when the conserved PKC phosphorylation site S407 (which regulates current amplitude) is mutated. A Phactr1 mutant that disrupts PP1 binding but not actin binding fails to alter Slack currents, indicating regulation occurs through PP1 recruitment.","method":"Co-immunoprecipitation, patch-clamp electrophysiology, site-directed mutagenesis of Slack S407 and Phactr1 PP1-binding domain","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — electrophysiology with mutagenesis, co-IP, mechanistic dissection with multiple mutants in one study","pmids":["31914597"],"is_preprint":false},{"year":2011,"finding":"PHACTR-1 depletion in HUVECs inhibits tube formation and triggers apoptosis through death receptors DR4, DR5, and FAS; this apoptosis is reversed by death receptor siRNAs or caspase-8 siRNA. PHACTR-1 is an actin- and PP1-binding protein that controls PP1 activity and F-actin remodeling, and its expression is dependent on VEGF-A165.","method":"siRNA knockdown of PHACTR-1 and death receptors/caspase-8 in HUVECs, tube formation assay, apoptosis assays","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular phenotype and pathway rescue by death receptor siRNA, single lab","pmids":["21798305"],"is_preprint":false},{"year":2011,"finding":"PHACTR-1 expression is regulated downstream of VEGF-A165 via NRP-1 and VEGF-R1 (but not NRP-2 or VEGF-R2). PHACTR-1 depletion decreased PP1 activity, disrupted actin polymerization, and impaired lamellipodial dynamics in HUVECs. Upon VEGF-A165 stimulation, PHACTR-1 promotes formation and maintenance of cellular tubes through NRP-1 and VEGFR1.","method":"siRNA knockdown of NRP-1, NRP-2, VEGF-R1, VEGF-R2, and PHACTR-1 in HUVECs; VEGF-A165 receptor blocking peptides; PP1 activity assay; live-cell imaging of lamellipodial dynamics; tube formation assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple receptor knockdowns, peptide inhibitors, PP1 activity assay, and live imaging in one study, single lab","pmids":["21939755"],"is_preprint":false},{"year":2013,"finding":"TGF-β downregulates miR-584 in breast cancer cells, which leads to upregulation of PHACTR1 (a miR-584 target). PHACTR1 upregulation is required for TGF-β-induced actin rearrangement and cell migration; overexpression of miR-584 or knockdown of PHACTR1 causes drastic actin cytoskeleton reorganization and reduces TGF-β-induced cell migration.","method":"miRNA overexpression and knockdown, PHACTR1 siRNA knockdown, cell migration assays, actin cytoskeleton staining, luciferase reporter for miR-584/PHACTR1 interaction","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (miRNA OE, KD, migration assay, actin staining) in one study, single lab","pmids":["23479725"],"is_preprint":false},{"year":2018,"finding":"PHACTR1 interacts with MRTF-A and NF-κB p65 in human coronary artery endothelial cells (HCAECs) as shown by co-immunoprecipitation. Knockdown of PHACTR1 reduces MRTF-A-dependent nuclear translocation of p65 and attenuates NF-κB activity, reducing ICAM-1, VCAM-1, and VE-cadherin expression and intracellular ROS/p47phox phosphorylation induced by ox-LDL. Knockdown of MRTF-A disrupts the PHACTR1-p65 interaction.","method":"Co-immunoprecipitation (PHACTR1-MRTF-A, PHACTR1-p65), siRNA knockdown of PHACTR1 and MRTF-A, immunofluorescence for p65 nuclear translocation, flow cytometry for ROS, western blotting","journal":"Atherosclerosis","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP for protein interactions with functional knockdown phenotypes, single lab, multiple readouts","pmids":["30293016"],"is_preprint":false},{"year":2023,"finding":"Endothelial PHACTR1 acts as a transcriptional corepressor of PPARγ: PHACTR1 binds PPARγ through corepressor motifs. PHACTR1 is enriched in endothelial cell nuclei under disturbed flow conditions but shuttles to the cytoplasm under laminar flow. Global or EC-specific Phactr1 knockout in ApoE-/- mice significantly inhibits atherosclerosis in disturbed-flow regions. RNA sequencing identified PPARγ as the top transcription factor regulating differentially expressed genes upon Phactr1 depletion. PPARγ antagonist GW9662 abolishes the protective effects of Phactr1 KO on endothelial activation and atherosclerosis in vivo.","method":"EC-specific and global Phactr1 knockout mice (crossed with ApoE-/- on high-fat diet), RNA sequencing, immunostaining for PHACTR1 localization under different flow conditions, co-immunoprecipitation/binding assay for PHACTR1-PPARγ interaction, PPARγ pharmacological antagonism in vivo, siRNA knockdown in HUVECs","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo EC-specific KO with atherosclerosis phenotype, RNA-seq, protein interaction assay, pharmacological epistasis, multiple orthogonal methods","pmids":["37199156"],"is_preprint":false},{"year":2017,"finding":"PHACTR1 expression in smooth muscle cells modulates vascular calcification: overexpression of Phactr1 in mESC-derived SMCs enhances mineralization and increases osteopontin expression, while downregulation decreases calcification. This was demonstrated in both murine embryonic stem cell-derived SMCs and primary human aortic SMCs.","method":"Stable overexpression and knockdown of Phactr1 in mESCs differentiated to SMCs, osteogenic differentiation assay, calcium phosphate deposit quantification, RT-PCR for osteopontin, primary human aortic SMC validation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function in two cell systems with molecular marker readouts, single lab","pmids":["28720499"],"is_preprint":false},{"year":2017,"finding":"Phactr1 is expressed in developing mouse brain in a developmental stage- and tissue-dependent manner; it localizes to axons, dendrites, and synapses in primary hippocampal neurons and is enriched in synaptosomal and postsynaptic density fractions. In embryonic cortical neurons Phactr1 accumulates in the nucleus, whereas postnatally it distributes diffusely in the cell body.","method":"Western blotting with specific antibody, immunohistochemistry, subcellular fractionation (synaptosomal/PSD fractions), immunofluorescence in primary cultured hippocampal neurons","journal":"Neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — direct fractionation and imaging experiments establishing localization, but no functional consequence directly tested, single lab","pmids":["28803787"],"is_preprint":false},{"year":2021,"finding":"Phactr1 interacts with ROCK2 during osteogenic but not adipogenic differentiation of BMSCs (Co-IP). Phactr1 overexpression inhibits osteogenesis (suppresses Runx2 increase) and promotes adipogenesis (increases C/EBPα), while knockdown has opposite effects. ROCK2 inhibition with KD025 reverses Phactr1 effects on both differentiation pathways, placing Phactr1 upstream of RhoA/ROCK2 in BMSC fate determination.","method":"Co-immunoprecipitation (Phactr1-ROCK2), lentiviral overexpression and siRNA knockdown of Phactr1, ROCK2 inhibitor KD025, osteogenic/adipogenic differentiation assays (alizarin red, Oil Red O), western blotting for Runx2, C/EBPα, RhoA, ROCK2","journal":"Journal of molecular histology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP, pharmacological epistasis, gain/loss-of-function with differentiation markers, single lab","pmids":["34709489"],"is_preprint":false},{"year":2020,"finding":"Phactr1 deficiency in macrophages promotes M1 polarization and foam cell formation. Mechanistically, Phactr1 activates CREB signaling by directly binding to CREB, upregulating CREB phosphorylation and inducing KLF4 expression. KLF4 overexpression partially rescues the excessive inflammation and foam cell formation caused by Phactr1 deficiency. In Phactr1-/-Apoe-/- double-knockout mice, more severe atherosclerotic plaques with elevated proinflammatory cytokines were observed; bone marrow transplant experiments confirmed the protective effect is hematopoietic cell-autonomous.","method":"Co-immunoprecipitation (Phactr1-CREB binding), Phactr1-/- Apoe-/- double-knockout mice, bone marrow transplantation, macrophage polarization assays, KLF4 overexpression rescue, western blotting for CREB phosphorylation, foam cell assays","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP, in vivo KO with BM transplant, rescue experiment, single lab with multiple methods","pmids":["32857129"],"is_preprint":false},{"year":2021,"finding":"A de novo PHACTR1 missense variant (p.L519R) reduces G-actin binding affinity and increases complex formation with the PP1 catalytic subunit (PPP1CA), as shown by in vitro binding assays. This leads to altered subcellular localization of PHACTR1 and increased ability to induce cytoskeletal rearrangements.","method":"In vitro binding assays for G-actin and PP1 affinity, subcellular localization imaging of mutant vs. wild-type PHACTR1","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — in vitro binding assay with localization imaging for a single mutant, single lab, limited detail in abstract","pmids":["33463715"],"is_preprint":false},{"year":2015,"finding":"Phactr-1 downregulation in endothelial cells (via inhibition of VEGF-A165/NRP-1/VEGF-R1 signaling with antagonist peptides targeting VEGF exon 7 and 8 cysteine residues) induces expression of MMP regulators (TIMP-1/-2, RECK), inhibits focal adhesion kinases (FAK/PYK2/PAXILLIN) and metabolic stress pathways (AMPK/CREB/eNOS), and upregulates pro-atherogenic/pro-inflammatory factors including CD36, clusterin, cadherin-13, thrombin, PAR-1, ADAM-9/-17, thrombospondin-2, galectin-3, SSAO, and βIG-H3.","method":"Antagonist peptide inhibition of VEGF-A165/NRP-1/VEGFR-1, PHACTR1 knockdown in endothelial cells, proteomics/western blotting for downstream pathway components","journal":"Biochimie","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, indirect perturbation of PHACTR1, downstream readouts without direct mechanistic linkage to PHACTR1 function","pmids":["26362351"],"is_preprint":false},{"year":2022,"finding":"PHACTR1 overexpression in endothelial cells activates NF-κB-dependent ICAM1 and VCAM1 expression and reduces nitric oxide generation by inhibiting Akt/eNOS activation. A proteomic study validated that PHACTR1 interacts with HSPA8 (heat shock protein A8), which is associated with eNOS degradation.","method":"RNA sequencing after PHACTR1 OE/KD, NF-κB reporter assays, NO production assays, Akt/eNOS phosphorylation western blotting, co-immunoprecipitation/proteomics for PHACTR1-HSPA8 interaction","journal":"Frontiers in immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, proteomics interaction with limited validation, functional assays with OE without full mechanistic dissection","pmids":["36091033"],"is_preprint":false},{"year":2024,"finding":"BDNF stimulation of primary cortical neurons causes sustained downregulation of PHACTR1 (and PHACTR2/3 but not PHACTR4) mRNA, and this downregulation is blocked by the ERK/MAPK inhibitor U0126, establishing that BDNF regulates PHACTR1 expression through the ERK/MAPK pathway.","method":"BDNF stimulation of primary cultured cortical neurons, qRT-PCR for PHACTR family mRNA, pharmacological inhibition with U0126","journal":"Drug discoveries & therapeutics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pharmacological inhibition only, mRNA readout without protein or functional validation","pmids":["39183043"],"is_preprint":false},{"year":2023,"finding":"PHACTR1 promotes invasion and migration of papillary thyroid carcinoma cells by inducing F-actin formation; overexpression increases F-actin fluorescence intensity and promotes invasion/migration, while knockdown inhibits these processes. The pro-invasive effect of PHACTR1 overexpression is reversed by the F-actin disruptor swinholide A, confirming dependence on F-actin assembly.","method":"PHACTR1 siRNA knockdown and overexpression in PTC cell lines, invasion/migration assays (Transwell), F-actin staining, pharmacological disruption with swinholide A","journal":"Heliyon","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single rescue with pharmacological agent, no upstream mechanistic dissection","pmids":["37876444"],"is_preprint":false},{"year":2024,"finding":"Multi-omics profiling (transcriptomics, proteomics, metabolomics, lipidomics) of HT1080 cells with PHACTR1 overexpression or knockdown reveals that PHACTR1 governs cell cycle progression (altering key regulatory proteins), regulates cellular iron metabolism (including iron-storage proteins), and is detected within mitochondria where it directs mitochondrial morphology and bioenergetics through a signaling axis involving AKAP1 and Drp1.","method":"Multi-omics (transcriptomics, proteomics, metabolomics, lipidomics) in PHACTR1 OE/KD HT1080 cells; validation in primary endothelial cells; mitochondrial fractionation/localization; western blotting for AKAP1/Drp1","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multi-omics with orthogonal validation in primary cells, novel mitochondrial localization finding, single lab but multiple methods","pmids":["41554990"],"is_preprint":false},{"year":2024,"finding":"AlphaFold-Multimer modeling and analysis of PHACTR1 missense variants in patients indicates that the RPEL3 domain is the site of overlapping binding interfaces for G-actin and PP1 (PPP1CA), suggesting competition between G-actin and PP1 for PHACTR1 binding at this domain. Variants clustering at the PHACTR1-PPP1CA or PHACTR1-G-actin interfaces consistently cause infantile epileptic spasms syndrome.","method":"AlphaFold-Multimer structural prediction, genotype-phenotype correlation in patient cohort (whole-exome sequencing), domain-level variant analysis","journal":"Journal of medical genetics","confidence":"Low","confidence_rationale":"Tier 4 / Weak — primarily computational structural prediction; in vitro binding experiments referenced from prior work, not performed here","pmids":["38272663"],"is_preprint":false}],"current_model":"PHACTR1 is a G-actin- and PP1-binding protein whose subcellular localization (cytoplasmic vs. nuclear) is controlled by competitive binding of G-actin to its C-terminal RPEL motifs; upon Rho/actin signaling, reduced G-actin allows importin α-β-dependent nuclear accumulation where PHACTR1 acts as a PP1 cofactor that remodels the PP1 hydrophobic groove to confer sequence specificity toward cytoskeletal substrates (IRSp53, spectrin αII, MLC), regulates actomyosin assembly, controls cortical neuron migration and synaptic function, modulates Slack (KCNT1) channel activity via PP1-dependent dephosphorylation of S407, and functions in endothelial cells as a PPARγ transcriptional corepressor promoting NF-κB-dependent inflammation under disturbed flow, while in macrophages it supports efferocytosis by maintaining MLC phosphorylation."},"narrative":{"mechanistic_narrative":"PHACTR1 is a G-actin- and protein phosphatase 1 (PP1)-binding protein that couples Rho/actin signaling to substrate-specific dephosphorylation and actomyosin remodeling [PMID:22976292, PMID:32975518]. Its four RPEL motifs bind G-actin to retain it in the cytoplasm of resting cells; when Rho-actin signaling lowers free G-actin, importin α-β drives nuclear accumulation, with G-actin, importin, and PP1 competing for overlapping C-terminal/RPEL3 interfaces [PMID:22976292, PMID:38272663]. In the nucleus and cytoplasm PHACTR1 acts as a PP1 cofactor: binding remodels the PP1 hydrophobic groove into a composite surface that confers orders-of-magnitude enhanced, sequence-specific reactivity toward cytoskeletal substrates such as IRSp53 and spectrin αII [PMID:32975518]. Through this PP1-directed activity and its control of F-actin assembly, PHACTR1 governs stress fiber formation, cell motility and invasion [PMID:22976292], regulates myosin light chain phosphorylation required for macrophage efferocytosis [PMID:33630758], and tunes Slack (KCNT1) Na+-activated K+ channel currents via PP1-dependent dephosphorylation of channel residue S407 [PMID:31914597]. In the nervous system PHACTR1 is required for cortical neuron migration, dendritic development, and normal synaptic properties, and de novo missense mutations that selectively impair actin- or PP1-binding cause these neurodevelopmental defects, linking PHACTR1 to infantile epileptic spasms syndrome [PMID:30256902, PMID:38272663]. In the vasculature, endothelial PHACTR1 functions as a transcriptional corepressor of PPARγ and partners with MRTF-A and NF-κB p65 to promote disturbed-flow–dependent endothelial inflammation and atherosclerosis [PMID:30293016, PMID:37199156].","teleology":[{"year":2012,"claim":"Established the core regulatory logic of PHACTR1: how a single protein integrates actin signaling with PP1-dependent cytoskeletal remodeling through competitive G-actin/importin/PP1 binding at RPEL motifs.","evidence":"RPEL mutagenesis, competitive binding and importin assays, localization microscopy, and motility/invasion assays in melanoma cells","pmids":["22976292"],"confidence":"High","gaps":["Did not resolve atomic basis of substrate specificity","Physiological substrates beyond actomyosin not defined"]},{"year":2011,"claim":"Connected PHACTR1 to endothelial biology, showing its expression is VEGF-A165/NRP-1/VEGFR1-dependent and that it controls PP1 activity, F-actin, lamellipodial dynamics, and survival via death-receptor signaling.","evidence":"siRNA knockdown of PHACTR1 and receptors, blocking peptides, PP1 activity assays, tube formation and apoptosis assays in HUVECs","pmids":["21798305","21939755"],"confidence":"Medium","gaps":["Mechanism linking PHACTR1 loss to death receptor induction unresolved","Single-lab HUVEC system"]},{"year":2013,"claim":"Placed PHACTR1 in a TGF-β/miR-584 axis driving actin rearrangement and migration in cancer cells, indicating transcriptional/post-transcriptional control of PHACTR1 abundance shapes cytoskeletal output.","evidence":"miR-584 overexpression/knockdown, PHACTR1 siRNA, luciferase reporter, migration and actin staining in breast cancer cells","pmids":["23479725"],"confidence":"Medium","gaps":["Direct PP1/actin mechanism not dissected in this context","In vivo relevance untested"]},{"year":2017,"claim":"Extended PHACTR1 function to vascular cell fate and neuronal compartmentalization, showing it modulates SMC calcification and localizes to neuronal synapses and developing brain in a stage-dependent manner.","evidence":"Gain/loss-of-function in mESC-derived and human aortic SMCs; subcellular fractionation and immunofluorescence in hippocampal/cortical neurons","pmids":["28720499","28803787"],"confidence":"Medium","gaps":["No functional consequence tested for neuronal localization","Calcification mechanism downstream of PHACTR1 unclear"]},{"year":2018,"claim":"Demonstrated that PHACTR1 is required for cortical neuron migration and synaptic function and that disease mutations act by selectively disrupting actin- or PP1-binding, providing genotype-to-mechanism resolution.","evidence":"Reciprocal Co-IP binding assays of four mutants, in utero electroporation knockdown/rescue, electrophysiology in mouse cortex","pmids":["30256902"],"confidence":"High","gaps":["Synaptic substrate(s) of PHACTR1/PP1 not identified","Acute knockdown rather than germline model"]},{"year":2018,"claim":"Identified endothelial PHACTR1 as a partner of MRTF-A and NF-κB p65 that promotes p65 nuclear translocation and adhesion-molecule/ROS responses to ox-LDL, linking it to pro-inflammatory endothelial activation.","evidence":"Co-IP, PHACTR1/MRTF-A knockdown, p65 immunofluorescence and ROS flow cytometry in HCAECs","pmids":["30293016"],"confidence":"Medium","gaps":["Direct vs. PP1-dependent role in p65 regulation not separated","Single-lab Co-IP"]},{"year":2019,"claim":"Showed PHACTR1 channels PP1 activity to ion-channel regulation, dephosphorylating Slack (KCNT1) at S407 to modulate Na+-activated K+ currents.","evidence":"Co-IP, patch-clamp, and mutagenesis of Slack S407 and the PHACTR1 PP1-binding domain","pmids":["31914597"],"confidence":"High","gaps":["In vivo relevance of Slack regulation untested","Whether dephosphorylation is direct on S407 not crystallographically shown"]},{"year":2020,"claim":"Resolved the structural basis for PHACTR1/PP1 substrate specificity, showing PHACTR1 remodels the PP1 groove into a composite surface that reads sequences C-terminal to the dephosphorylation site.","evidence":"High-resolution crystal structures of holoenzyme-product complexes with IRSp53/spectrin αII, phosphoproteomics, in vitro phosphatase assays, contact-residue mutagenesis","pmids":["32975518"],"confidence":"High","gaps":["Full physiological substrate repertoire incomplete","Regulation of holoenzyme assembly in vivo not addressed"]},{"year":2020,"claim":"Defined a macrophage-autonomous, PP1-independent transcriptional route by which Phactr1 binds CREB to induce KLF4, restraining M1 polarization and foam cell formation and limiting atherosclerosis.","evidence":"Co-IP, Phactr1-/-Apoe-/- mice with bone marrow transplant, KLF4 rescue, polarization and foam cell assays","pmids":["32857129"],"confidence":"Medium","gaps":["Direct vs. indirect CREB binding not structurally defined","Relationship to PHACTR1's actin/PP1 functions unclear"]},{"year":2021,"claim":"Linked PHACTR1 to macrophage efferocytosis and plaque stability, showing it maintains MLC phosphorylation needed for apoptotic cell engulfment, with a human risk allele lowering its expression.","evidence":"siRNA in human/mouse macrophages, hematopoietic Phactr1-targeted Ldlr-/- mice, phospho-MLC blotting, efferocytosis and plaque histology","pmids":["33630758"],"confidence":"High","gaps":["Whether MLC is a direct PHACTR1/PP1 substrate or regulated indirectly","rs9349379 mechanism on expression not fully resolved"]},{"year":2021,"claim":"Added a ROCK2-coupled role for Phactr1 in BMSC fate and characterized a disease variant (L519R) that shifts the G-actin/PP1 binding balance toward PP1 and enhanced cytoskeletal activity.","evidence":"Co-IP with ROCK2, ROCK2 inhibitor epistasis, differentiation assays; in vitro G-actin/PP1 binding and localization of L519R","pmids":["34709489","33463715"],"confidence":"Medium","gaps":["Mechanistic link between Phactr1 and RhoA/ROCK2 directionality limited","Single-mutant binding study"]},{"year":2023,"claim":"Identified PHACTR1 as a flow-regulated transcriptional corepressor of PPARγ in endothelium that drives atherosclerosis specifically in disturbed-flow regions.","evidence":"EC-specific and global Phactr1 KO in ApoE-/- mice, RNA-seq, flow-dependent localization, PHACTR1-PPARγ binding, GW9662 epistasis in vivo","pmids":["37199156"],"confidence":"High","gaps":["How nuclear shuttling is sensed from flow not mechanistically tied to RPEL/actin in this study","Corepressor complex composition undefined"]},{"year":2023,"claim":"Provided a cancer-cell readout linking PHACTR1 to F-actin–dependent invasion in papillary thyroid carcinoma.","evidence":"Overexpression/knockdown with Transwell assays, F-actin staining, and swinholide A reversal in PTC lines","pmids":["37876444"],"confidence":"Low","gaps":["No upstream mechanistic dissection or PP1/actin-binding requirement tested","Single pharmacological rescue"]},{"year":2024,"claim":"Implicated PHACTR1 in mitochondrial morphology, bioenergetics, cell cycle, and iron metabolism, including an unexpected mitochondrial pool acting via AKAP1/Drp1.","evidence":"Multi-omics in HT1080 OE/KD cells with primary-cell validation, mitochondrial fractionation, AKAP1/Drp1 blotting","pmids":["41554990"],"confidence":"Medium","gaps":["Mechanism of mitochondrial targeting unknown","Causal links from omics correlations not fully established"]},{"year":2024,"claim":"Refined the structural model by mapping overlapping G-actin and PP1 (PPP1CA) interfaces to the RPEL3 domain and correlating interface variants with infantile epileptic spasms syndrome.","evidence":"AlphaFold-Multimer modeling with genotype-phenotype analysis of patient missense variants","pmids":["38272663"],"confidence":"Low","gaps":["Predictions are computational; binding not measured here","Variant functional consequences inferred, not directly assayed"]},{"year":null,"claim":"It remains unresolved how PHACTR1's actin/PP1-regulated cytoskeletal function, its CREB/PPARγ transcriptional roles, and its reported mitochondrial activity are mechanistically integrated within a single cell.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking PP1-dependent and transcriptional functions","Physiological substrate map beyond IRSp53/spectrin/MLC/Slack incomplete","Mechanism of mitochondrial localization undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,4]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,18]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,4]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[9,8]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,4]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,9,11]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,18]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[19]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,4]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,12]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[9,8,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,3,9]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,8,13]}],"complexes":["PHACTR1/PP1 (PPP1CA) holoenzyme"],"partners":["PPP1CA","ACTB","IRSP53","KCNT1","MRTF-A","RELA","PPARG","ROCK2"],"other_free_text":[]}},"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). 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G-actin and importin α-β bind competitively to nuclear import signals associated with the N- and C-terminal RPEL motifs. G-actin and PP1 also bind competitively to the PHACTR1 C-terminal region; RPEL mutants unable to bind G-actin constitutively accumulate in the nucleus and 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\": \"Co-immunoprecipitation, site-directed mutagenesis of RPEL motifs, fluorescence microscopy of subcellular localization, importin competition assays, actin binding assays, cell motility/invasion assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (mutagenesis, competitive binding assays, localization studies, functional cellular assays) in a single rigorous study establishing the mechanistic model\",\n      \"pmids\": [\"22976292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Phactr1/PP1 holoenzyme has defined substrate specificity: Phactr1 binding remodels PP1's hydrophobic groove to create a composite surface adjacent to the catalytic site. High-resolution crystal structures of Phactr1/PP1 bound to dephosphorylated substrates IRSp53 and spectrin αII showed that substrate sequences C-terminal to the dephosphorylation site make intimate contacts with this composite Phactr1/PP1 surface, which are required for efficient dephosphorylation. Phactr1/PP1 exhibits orders-of-magnitude enhanced reactivity toward its substrates (identified by phosphoproteomics as cytoskeletal components including IRSp53 and spectrin αII) compared to apo-PP1 or other PP1 holoenzymes. Inversion of the phosphate in holoenzyme-product complexes supports the proposed PPP-family catalytic mechanism.\",\n      \"method\": \"X-ray crystallography (high-resolution structures of holoenzyme-product complexes), phosphoproteomics substrate identification, in vitro phosphatase activity assays, mutagenesis of substrate contact residues\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with functional validation by phosphoproteomics and in vitro assays, multiple orthogonal methods in one study\",\n      \"pmids\": [\"32975518\"],\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 of PHACTR1, while p.Arg521Cys impairs binding to PP1, as shown by immunoprecipitation. Acute knockdown of mouse Phactr1 by in utero electroporation causes defects in cortical neuron migration during corticogenesis, rescued by RNAi-resistant wild-type PHACTR1 but not by the four mutants. The p.Arg521Cys PP1-binding mutant has dominant-negative effects on dendritic development in vivo. Electrophysiological analyses revealed abnormal synaptic properties in Phactr1-deficient excitatory cortical neurons.\",\n      \"method\": \"Co-immunoprecipitation (actin and PP1 binding), in utero electroporation knockdown/rescue in mouse cortex, electrophysiology of cortical neurons\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays with multiple mutants, in vivo knockdown/rescue with defined phenotypic readouts, electrophysiology, multiple orthogonal methods\",\n      \"pmids\": [\"30256902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PHACTR1 prevents dephosphorylation of myosin light chain (MLC), which is necessary for apoptotic cell (AC) engulfment by macrophages. The rs9349379-G/G risk allele is associated with lower PHACTR1 expression in human monocyte-derived macrophages, lower phospho-MLC, and impaired efferocytosis. Silencing PHACTR1 in human and mouse macrophages compromised AC engulfment. Hematopoietic Phactr1-targeted Ldlr-/- mice on Western diet showed impaired lesional efferocytosis, increased plaque necrosis, and thinner fibrous caps.\",\n      \"method\": \"siRNA knockdown of PHACTR1 in human/mouse macrophages, hematopoietic-specific genetic knockout (bone marrow transplant into Ldlr-/- mice), phospho-MLC western blotting, efferocytosis assays, histological analysis of atherosclerotic plaques\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic model with defined cellular phenotype, mechanistic link to MLC phosphorylation, multiple orthogonal methods (KO, KD, biochemistry, histology)\",\n      \"pmids\": [\"33630758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Phactr1 regulates Slack (KCNT1) sodium-activated potassium channels via PP1: co-immunoprecipitation showed Phactr1 links channels to actin. Co-expression of Phactr1 with wild-type Slack channels reduces current amplitude; this effect is absent when the conserved PKC phosphorylation site S407 (which regulates current amplitude) is mutated. A Phactr1 mutant that disrupts PP1 binding but not actin binding fails to alter Slack currents, indicating regulation occurs through PP1 recruitment.\",\n      \"method\": \"Co-immunoprecipitation, patch-clamp electrophysiology, site-directed mutagenesis of Slack S407 and Phactr1 PP1-binding domain\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — electrophysiology with mutagenesis, co-IP, mechanistic dissection with multiple mutants in one study\",\n      \"pmids\": [\"31914597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR-1 depletion in HUVECs inhibits tube formation and triggers apoptosis through death receptors DR4, DR5, and FAS; this apoptosis is reversed by death receptor siRNAs or caspase-8 siRNA. PHACTR-1 is an actin- and PP1-binding protein that controls PP1 activity and F-actin remodeling, and its expression is dependent on VEGF-A165.\",\n      \"method\": \"siRNA knockdown of PHACTR-1 and death receptors/caspase-8 in HUVECs, tube formation assay, apoptosis assays\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular phenotype and pathway rescue by death receptor siRNA, single lab\",\n      \"pmids\": [\"21798305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PHACTR-1 expression is regulated downstream of VEGF-A165 via NRP-1 and VEGF-R1 (but not NRP-2 or VEGF-R2). PHACTR-1 depletion decreased PP1 activity, disrupted actin polymerization, and impaired lamellipodial dynamics in HUVECs. Upon VEGF-A165 stimulation, PHACTR-1 promotes formation and maintenance of cellular tubes through NRP-1 and VEGFR1.\",\n      \"method\": \"siRNA knockdown of NRP-1, NRP-2, VEGF-R1, VEGF-R2, and PHACTR-1 in HUVECs; VEGF-A165 receptor blocking peptides; PP1 activity assay; live-cell imaging of lamellipodial dynamics; tube formation assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple receptor knockdowns, peptide inhibitors, PP1 activity assay, and live imaging in one study, single lab\",\n      \"pmids\": [\"21939755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TGF-β downregulates miR-584 in breast cancer cells, which leads to upregulation of PHACTR1 (a miR-584 target). PHACTR1 upregulation is required for TGF-β-induced actin rearrangement and cell migration; overexpression of miR-584 or knockdown of PHACTR1 causes drastic actin cytoskeleton reorganization and reduces TGF-β-induced cell migration.\",\n      \"method\": \"miRNA overexpression and knockdown, PHACTR1 siRNA knockdown, cell migration assays, actin cytoskeleton staining, luciferase reporter for miR-584/PHACTR1 interaction\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (miRNA OE, KD, migration assay, actin staining) in one study, single lab\",\n      \"pmids\": [\"23479725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PHACTR1 interacts with MRTF-A and NF-κB p65 in human coronary artery endothelial cells (HCAECs) as shown by co-immunoprecipitation. Knockdown of PHACTR1 reduces MRTF-A-dependent nuclear translocation of p65 and attenuates NF-κB activity, reducing ICAM-1, VCAM-1, and VE-cadherin expression and intracellular ROS/p47phox phosphorylation induced by ox-LDL. Knockdown of MRTF-A disrupts the PHACTR1-p65 interaction.\",\n      \"method\": \"Co-immunoprecipitation (PHACTR1-MRTF-A, PHACTR1-p65), siRNA knockdown of PHACTR1 and MRTF-A, immunofluorescence for p65 nuclear translocation, flow cytometry for ROS, western blotting\",\n      \"journal\": \"Atherosclerosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP for protein interactions with functional knockdown phenotypes, single lab, multiple readouts\",\n      \"pmids\": [\"30293016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial PHACTR1 acts as a transcriptional corepressor of PPARγ: PHACTR1 binds PPARγ through corepressor motifs. PHACTR1 is enriched in endothelial cell nuclei under disturbed flow conditions but shuttles to the cytoplasm under laminar flow. Global or EC-specific Phactr1 knockout in ApoE-/- mice significantly inhibits atherosclerosis in disturbed-flow regions. RNA sequencing identified PPARγ as the top transcription factor regulating differentially expressed genes upon Phactr1 depletion. PPARγ antagonist GW9662 abolishes the protective effects of Phactr1 KO on endothelial activation and atherosclerosis in vivo.\",\n      \"method\": \"EC-specific and global Phactr1 knockout mice (crossed with ApoE-/- on high-fat diet), RNA sequencing, immunostaining for PHACTR1 localization under different flow conditions, co-immunoprecipitation/binding assay for PHACTR1-PPARγ interaction, PPARγ pharmacological antagonism in vivo, siRNA knockdown in HUVECs\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo EC-specific KO with atherosclerosis phenotype, RNA-seq, protein interaction assay, pharmacological epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"37199156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PHACTR1 expression in smooth muscle cells modulates vascular calcification: overexpression of Phactr1 in mESC-derived SMCs enhances mineralization and increases osteopontin expression, while downregulation decreases calcification. This was demonstrated in both murine embryonic stem cell-derived SMCs and primary human aortic SMCs.\",\n      \"method\": \"Stable overexpression and knockdown of Phactr1 in mESCs differentiated to SMCs, osteogenic differentiation assay, calcium phosphate deposit quantification, RT-PCR for osteopontin, primary human aortic SMC validation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function in two cell systems with molecular marker readouts, single lab\",\n      \"pmids\": [\"28720499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Phactr1 is expressed in developing mouse brain in a developmental stage- and tissue-dependent manner; it localizes to axons, dendrites, and synapses in primary hippocampal neurons and is enriched in synaptosomal and postsynaptic density fractions. In embryonic cortical neurons Phactr1 accumulates in the nucleus, whereas postnatally it distributes diffusely in the cell body.\",\n      \"method\": \"Western blotting with specific antibody, immunohistochemistry, subcellular fractionation (synaptosomal/PSD fractions), immunofluorescence in primary cultured hippocampal neurons\",\n      \"journal\": \"Neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — direct fractionation and imaging experiments establishing localization, but no functional consequence directly tested, single lab\",\n      \"pmids\": [\"28803787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Phactr1 interacts with ROCK2 during osteogenic but not adipogenic differentiation of BMSCs (Co-IP). Phactr1 overexpression inhibits osteogenesis (suppresses Runx2 increase) and promotes adipogenesis (increases C/EBPα), while knockdown has opposite effects. ROCK2 inhibition with KD025 reverses Phactr1 effects on both differentiation pathways, placing Phactr1 upstream of RhoA/ROCK2 in BMSC fate determination.\",\n      \"method\": \"Co-immunoprecipitation (Phactr1-ROCK2), lentiviral overexpression and siRNA knockdown of Phactr1, ROCK2 inhibitor KD025, osteogenic/adipogenic differentiation assays (alizarin red, Oil Red O), western blotting for Runx2, C/EBPα, RhoA, ROCK2\",\n      \"journal\": \"Journal of molecular histology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP, pharmacological epistasis, gain/loss-of-function with differentiation markers, single lab\",\n      \"pmids\": [\"34709489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Phactr1 deficiency in macrophages promotes M1 polarization and foam cell formation. Mechanistically, Phactr1 activates CREB signaling by directly binding to CREB, upregulating CREB phosphorylation and inducing KLF4 expression. KLF4 overexpression partially rescues the excessive inflammation and foam cell formation caused by Phactr1 deficiency. In Phactr1-/-Apoe-/- double-knockout mice, more severe atherosclerotic plaques with elevated proinflammatory cytokines were observed; bone marrow transplant experiments confirmed the protective effect is hematopoietic cell-autonomous.\",\n      \"method\": \"Co-immunoprecipitation (Phactr1-CREB binding), Phactr1-/- Apoe-/- double-knockout mice, bone marrow transplantation, macrophage polarization assays, KLF4 overexpression rescue, western blotting for CREB phosphorylation, foam cell assays\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP, in vivo KO with BM transplant, rescue experiment, single lab with multiple methods\",\n      \"pmids\": [\"32857129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo PHACTR1 missense variant (p.L519R) reduces G-actin binding affinity and increases complex formation with the PP1 catalytic subunit (PPP1CA), as shown by in vitro binding assays. This leads to altered subcellular localization of PHACTR1 and increased ability to induce cytoskeletal rearrangements.\",\n      \"method\": \"In vitro binding assays for G-actin and PP1 affinity, subcellular localization imaging of mutant vs. wild-type PHACTR1\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — in vitro binding assay with localization imaging for a single mutant, single lab, limited detail in abstract\",\n      \"pmids\": [\"33463715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Phactr-1 downregulation in endothelial cells (via inhibition of VEGF-A165/NRP-1/VEGF-R1 signaling with antagonist peptides targeting VEGF exon 7 and 8 cysteine residues) induces expression of MMP regulators (TIMP-1/-2, RECK), inhibits focal adhesion kinases (FAK/PYK2/PAXILLIN) and metabolic stress pathways (AMPK/CREB/eNOS), and upregulates pro-atherogenic/pro-inflammatory factors including CD36, clusterin, cadherin-13, thrombin, PAR-1, ADAM-9/-17, thrombospondin-2, galectin-3, SSAO, and βIG-H3.\",\n      \"method\": \"Antagonist peptide inhibition of VEGF-A165/NRP-1/VEGFR-1, PHACTR1 knockdown in endothelial cells, proteomics/western blotting for downstream pathway components\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, indirect perturbation of PHACTR1, downstream readouts without direct mechanistic linkage to PHACTR1 function\",\n      \"pmids\": [\"26362351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PHACTR1 overexpression in endothelial cells activates NF-κB-dependent ICAM1 and VCAM1 expression and reduces nitric oxide generation by inhibiting Akt/eNOS activation. A proteomic study validated that PHACTR1 interacts with HSPA8 (heat shock protein A8), which is associated with eNOS degradation.\",\n      \"method\": \"RNA sequencing after PHACTR1 OE/KD, NF-κB reporter assays, NO production assays, Akt/eNOS phosphorylation western blotting, co-immunoprecipitation/proteomics for PHACTR1-HSPA8 interaction\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, proteomics interaction with limited validation, functional assays with OE without full mechanistic dissection\",\n      \"pmids\": [\"36091033\"],\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, and this downregulation is blocked by the ERK/MAPK inhibitor U0126, establishing that BDNF regulates PHACTR1 expression through the ERK/MAPK pathway.\",\n      \"method\": \"BDNF stimulation of primary cultured cortical neurons, qRT-PCR for PHACTR family mRNA, pharmacological inhibition with U0126\",\n      \"journal\": \"Drug discoveries & therapeutics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pharmacological inhibition only, mRNA readout without protein or functional validation\",\n      \"pmids\": [\"39183043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PHACTR1 promotes invasion and migration of papillary thyroid carcinoma cells by inducing F-actin formation; overexpression increases F-actin fluorescence intensity and promotes invasion/migration, while knockdown inhibits these processes. The pro-invasive effect of PHACTR1 overexpression is reversed by the F-actin disruptor swinholide A, confirming dependence on F-actin assembly.\",\n      \"method\": \"PHACTR1 siRNA knockdown and overexpression in PTC cell lines, invasion/migration assays (Transwell), F-actin staining, pharmacological disruption with swinholide A\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single rescue with pharmacological agent, no upstream mechanistic dissection\",\n      \"pmids\": [\"37876444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Multi-omics profiling (transcriptomics, proteomics, metabolomics, lipidomics) of HT1080 cells with PHACTR1 overexpression or knockdown reveals that PHACTR1 governs cell cycle progression (altering key regulatory proteins), regulates cellular iron metabolism (including iron-storage proteins), and is detected within mitochondria where it directs mitochondrial morphology and bioenergetics through a signaling axis involving AKAP1 and Drp1.\",\n      \"method\": \"Multi-omics (transcriptomics, proteomics, metabolomics, lipidomics) in PHACTR1 OE/KD HT1080 cells; validation in primary endothelial cells; mitochondrial fractionation/localization; western blotting for AKAP1/Drp1\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multi-omics with orthogonal validation in primary cells, novel mitochondrial localization finding, single lab but multiple methods\",\n      \"pmids\": [\"41554990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AlphaFold-Multimer modeling and analysis of PHACTR1 missense variants in patients indicates that the RPEL3 domain is the site of overlapping binding interfaces for G-actin and PP1 (PPP1CA), suggesting competition between G-actin and PP1 for PHACTR1 binding at this domain. Variants clustering at the PHACTR1-PPP1CA or PHACTR1-G-actin interfaces consistently cause infantile epileptic spasms syndrome.\",\n      \"method\": \"AlphaFold-Multimer structural prediction, genotype-phenotype correlation in patient cohort (whole-exome sequencing), domain-level variant analysis\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — primarily computational structural prediction; in vitro binding experiments referenced from prior work, not performed here\",\n      \"pmids\": [\"38272663\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PHACTR1 is a G-actin- and PP1-binding protein whose subcellular localization (cytoplasmic vs. nuclear) is controlled by competitive binding of G-actin to its C-terminal RPEL motifs; upon Rho/actin signaling, reduced G-actin allows importin α-β-dependent nuclear accumulation where PHACTR1 acts as a PP1 cofactor that remodels the PP1 hydrophobic groove to confer sequence specificity toward cytoskeletal substrates (IRSp53, spectrin αII, MLC), regulates actomyosin assembly, controls cortical neuron migration and synaptic function, modulates Slack (KCNT1) channel activity via PP1-dependent dephosphorylation of S407, and functions in endothelial cells as a PPARγ transcriptional corepressor promoting NF-κB-dependent inflammation under disturbed flow, while in macrophages it supports efferocytosis by maintaining MLC phosphorylation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PHACTR1 is a G-actin- and protein phosphatase 1 (PP1)-binding protein that couples Rho/actin signaling to substrate-specific dephosphorylation and actomyosin remodeling [#0, #1]. Its four RPEL motifs bind G-actin to retain it in the cytoplasm of resting cells; when Rho-actin signaling lowers free G-actin, importin \\u03b1-\\u03b2 drives nuclear accumulation, with G-actin, importin, and PP1 competing for overlapping C-terminal/RPEL3 interfaces [#0, #20]. In the nucleus and cytoplasm PHACTR1 acts as a PP1 cofactor: binding remodels the PP1 hydrophobic groove into a composite surface that confers orders-of-magnitude enhanced, sequence-specific reactivity toward cytoskeletal substrates such as IRSp53 and spectrin \\u03b1II [#1]. Through this PP1-directed activity and its control of F-actin assembly, PHACTR1 governs stress fiber formation, cell motility and invasion [#0], regulates myosin light chain phosphorylation required for macrophage efferocytosis [#3], and tunes Slack (KCNT1) Na+-activated K+ channel currents via PP1-dependent dephosphorylation of channel residue S407 [#4]. In the nervous system PHACTR1 is required for cortical neuron migration, dendritic development, and normal synaptic properties, and de novo missense mutations that selectively impair actin- or PP1-binding cause these neurodevelopmental defects, linking PHACTR1 to infantile epileptic spasms syndrome [#2, #20]. In the vasculature, endothelial PHACTR1 functions as a transcriptional corepressor of PPAR\\u03b3 and partners with MRTF-A and NF-\\u03baB p65 to promote disturbed-flow\\u2013dependent endothelial inflammation and atherosclerosis [#8, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established the core regulatory logic of PHACTR1: how a single protein integrates actin signaling with PP1-dependent cytoskeletal remodeling through competitive G-actin/importin/PP1 binding at RPEL motifs.\",\n      \"evidence\": \"RPEL mutagenesis, competitive binding and importin assays, localization microscopy, and motility/invasion assays in melanoma cells\",\n      \"pmids\": [\"22976292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve atomic basis of substrate specificity\", \"Physiological substrates beyond actomyosin not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected PHACTR1 to endothelial biology, showing its expression is VEGF-A165/NRP-1/VEGFR1-dependent and that it controls PP1 activity, F-actin, lamellipodial dynamics, and survival via death-receptor signaling.\",\n      \"evidence\": \"siRNA knockdown of PHACTR1 and receptors, blocking peptides, PP1 activity assays, tube formation and apoptosis assays in HUVECs\",\n      \"pmids\": [\"21798305\", \"21939755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking PHACTR1 loss to death receptor induction unresolved\", \"Single-lab HUVEC system\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed PHACTR1 in a TGF-\\u03b2/miR-584 axis driving actin rearrangement and migration in cancer cells, indicating transcriptional/post-transcriptional control of PHACTR1 abundance shapes cytoskeletal output.\",\n      \"evidence\": \"miR-584 overexpression/knockdown, PHACTR1 siRNA, luciferase reporter, migration and actin staining in breast cancer cells\",\n      \"pmids\": [\"23479725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PP1/actin mechanism not dissected in this context\", \"In vivo relevance untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended PHACTR1 function to vascular cell fate and neuronal compartmentalization, showing it modulates SMC calcification and localizes to neuronal synapses and developing brain in a stage-dependent manner.\",\n      \"evidence\": \"Gain/loss-of-function in mESC-derived and human aortic SMCs; subcellular fractionation and immunofluorescence in hippocampal/cortical neurons\",\n      \"pmids\": [\"28720499\", \"28803787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence tested for neuronal localization\", \"Calcification mechanism downstream of PHACTR1 unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that PHACTR1 is required for cortical neuron migration and synaptic function and that disease mutations act by selectively disrupting actin- or PP1-binding, providing genotype-to-mechanism resolution.\",\n      \"evidence\": \"Reciprocal Co-IP binding assays of four mutants, in utero electroporation knockdown/rescue, electrophysiology in mouse cortex\",\n      \"pmids\": [\"30256902\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Synaptic substrate(s) of PHACTR1/PP1 not identified\", \"Acute knockdown rather than germline model\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified endothelial PHACTR1 as a partner of MRTF-A and NF-\\u03baB p65 that promotes p65 nuclear translocation and adhesion-molecule/ROS responses to ox-LDL, linking it to pro-inflammatory endothelial activation.\",\n      \"evidence\": \"Co-IP, PHACTR1/MRTF-A knockdown, p65 immunofluorescence and ROS flow cytometry in HCAECs\",\n      \"pmids\": [\"30293016\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs. PP1-dependent role in p65 regulation not separated\", \"Single-lab Co-IP\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed PHACTR1 channels PP1 activity to ion-channel regulation, dephosphorylating Slack (KCNT1) at S407 to modulate Na+-activated K+ currents.\",\n      \"evidence\": \"Co-IP, patch-clamp, and mutagenesis of Slack S407 and the PHACTR1 PP1-binding domain\",\n      \"pmids\": [\"31914597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of Slack regulation untested\", \"Whether dephosphorylation is direct on S407 not crystallographically shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the structural basis for PHACTR1/PP1 substrate specificity, showing PHACTR1 remodels the PP1 groove into a composite surface that reads sequences C-terminal to the dephosphorylation site.\",\n      \"evidence\": \"High-resolution crystal structures of holoenzyme-product complexes with IRSp53/spectrin \\u03b1II, phosphoproteomics, in vitro phosphatase assays, contact-residue mutagenesis\",\n      \"pmids\": [\"32975518\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full physiological substrate repertoire incomplete\", \"Regulation of holoenzyme assembly in vivo not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a macrophage-autonomous, PP1-independent transcriptional route by which Phactr1 binds CREB to induce KLF4, restraining M1 polarization and foam cell formation and limiting atherosclerosis.\",\n      \"evidence\": \"Co-IP, Phactr1-/-Apoe-/- mice with bone marrow transplant, KLF4 rescue, polarization and foam cell assays\",\n      \"pmids\": [\"32857129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs. indirect CREB binding not structurally defined\", \"Relationship to PHACTR1's actin/PP1 functions unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked PHACTR1 to macrophage efferocytosis and plaque stability, showing it maintains MLC phosphorylation needed for apoptotic cell engulfment, with a human risk allele lowering its expression.\",\n      \"evidence\": \"siRNA in human/mouse macrophages, hematopoietic Phactr1-targeted Ldlr-/- mice, phospho-MLC blotting, efferocytosis and plaque histology\",\n      \"pmids\": [\"33630758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MLC is a direct PHACTR1/PP1 substrate or regulated indirectly\", \"rs9349379 mechanism on expression not fully resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Added a ROCK2-coupled role for Phactr1 in BMSC fate and characterized a disease variant (L519R) that shifts the G-actin/PP1 binding balance toward PP1 and enhanced cytoskeletal activity.\",\n      \"evidence\": \"Co-IP with ROCK2, ROCK2 inhibitor epistasis, differentiation assays; in vitro G-actin/PP1 binding and localization of L519R\",\n      \"pmids\": [\"34709489\", \"33463715\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between Phactr1 and RhoA/ROCK2 directionality limited\", \"Single-mutant binding study\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified PHACTR1 as a flow-regulated transcriptional corepressor of PPAR\\u03b3 in endothelium that drives atherosclerosis specifically in disturbed-flow regions.\",\n      \"evidence\": \"EC-specific and global Phactr1 KO in ApoE-/- mice, RNA-seq, flow-dependent localization, PHACTR1-PPAR\\u03b3 binding, GW9662 epistasis in vivo\",\n      \"pmids\": [\"37199156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How nuclear shuttling is sensed from flow not mechanistically tied to RPEL/actin in this study\", \"Corepressor complex composition undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a cancer-cell readout linking PHACTR1 to F-actin\\u2013dependent invasion in papillary thyroid carcinoma.\",\n      \"evidence\": \"Overexpression/knockdown with Transwell assays, F-actin staining, and swinholide A reversal in PTC lines\",\n      \"pmids\": [\"37876444\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No upstream mechanistic dissection or PP1/actin-binding requirement tested\", \"Single pharmacological rescue\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated PHACTR1 in mitochondrial morphology, bioenergetics, cell cycle, and iron metabolism, including an unexpected mitochondrial pool acting via AKAP1/Drp1.\",\n      \"evidence\": \"Multi-omics in HT1080 OE/KD cells with primary-cell validation, mitochondrial fractionation, AKAP1/Drp1 blotting\",\n      \"pmids\": [\"41554990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of mitochondrial targeting unknown\", \"Causal links from omics correlations not fully established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined the structural model by mapping overlapping G-actin and PP1 (PPP1CA) interfaces to the RPEL3 domain and correlating interface variants with infantile epileptic spasms syndrome.\",\n      \"evidence\": \"AlphaFold-Multimer modeling with genotype-phenotype analysis of patient missense variants\",\n      \"pmids\": [\"38272663\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Predictions are computational; binding not measured here\", \"Variant functional consequences inferred, not directly assayed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how PHACTR1's actin/PP1-regulated cytoskeletal function, its CREB/PPAR\\u03b3 transcriptional roles, and its reported mitochondrial activity are mechanistically integrated within a single cell.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking PP1-dependent and transcriptional functions\", \"Physiological substrate map beyond IRSp53/spectrin/MLC/Slack incomplete\", \"Mechanism of mitochondrial localization undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 18]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [9, 8]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 9, 11]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 18]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 12]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 8, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 3, 9]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 8, 13]}\n    ],\n    \"complexes\": [\n      \"PHACTR1/PP1 (PPP1CA) holoenzyme\"\n    ],\n    \"partners\": [\n      \"PPP1CA\",\n      \"ACTB\",\n      \"IRSp53\",\n      \"KCNT1\",\n      \"MRTF-A\",\n      \"RELA\",\n      \"PPARG\",\n      \"ROCK2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}