{"gene":"ACTC1","run_date":"2026-06-09T22:02:40","timeline":{"discoveries":[{"year":2011,"finding":"The ACTC1 E99K mutation increases myofibrillar Ca²⁺ sensitivity 2.3-fold in transgenic mouse thin filaments (1.3-fold in human carrier samples) as measured by in vitro motility assay and skinned papillary muscle, and specifically abolishes the normal decrease in Ca²⁺ sensitivity linked to troponin I phosphorylation.","method":"In vitro motility assay on reconstituted thin filaments, skinned papillary muscle Ca²⁺ sensitivity measurements, transgenic mouse model expressing E99K at 50% of total heart actin","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted thin filament in vitro assay plus skinned muscle preparations, validated in both transgenic mouse and human carrier samples, multiple orthogonal methods","pmids":["21622575"],"is_preprint":false},{"year":2014,"finding":"The DCM-causing ACTC1 E361G mutation specifically abolishes Ca²⁺ sensitivity modulation by troponin I phosphorylation in intact cardiac myofibrils, without affecting length-dependent activation or response to EMD57033, confirming that troponin I phosphorylation acts through the actin-troponin interface to regulate relaxation kinetics.","method":"Ca²⁺-jump protocol on single transgenic mouse heart myofibrils; comparison of isometric tension and relaxation parameters (kREL, tLIN) in myofibrils with varying troponin I phosphorylation levels (propranolol-treated vs. control mice)","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro myofibril assay with pharmacological manipulation of phosphorylation level and multiple kinetic readouts, single lab but multiple orthogonal parameters","pmids":["25418306"],"is_preprint":false},{"year":2013,"finding":"ACTC1 E99K papillary muscle produces 3–4× greater isometric twitch force than non-transgenic muscle, relaxes 1.4× slower, and consumes disproportionately more energy (efficiency 11–16% vs. 15–18%), with hypercontractility attributable to elevated myofibrillar Ca²⁺ sensitivity (EC₅₀ 0.39 vs. 0.80 µmol/L) rather than altered Ca²⁺ transient amplitude.","method":"Intact papillary muscle mechanics (force, heat, work), isolated myofibril Ca²⁺-jump protocol, isolated myocyte Ca²⁺ transient imaging in ACTC E99K transgenic mouse model","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multi-level analysis (intact muscle, myofibril, myocyte) with orthogonal methods in a validated transgenic model, single lab","pmids":["23604709"],"is_preprint":false},{"year":2017,"finding":"Young ACTC1 E99K transgenic mice prone to sudden cardiac death exhibit increased Ca²⁺ transient amplitude, greater Ca²⁺ spark mass, and increased propensity for spontaneous Ca²⁺ waves compared with non-transgenic littermates despite similar sarcoplasmic reticulum Ca²⁺ content, linking the actin mutation's elevated myofilament Ca²⁺ sensitivity to aberrant SR Ca²⁺ release and arrhythmogenesis. Penetrance of sudden death is strongly modified by genetic background (CBA/Ca vs. C57Bl6).","method":"Isolated ventricular myocyte Ca²⁺ imaging (transients, sparks, waves), confocal microscopy, collagen quantification, comparison of young vs. adult TG and NTG mice on two genetic backgrounds","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cellular Ca²⁺ measurements in isolated myocytes with genetic background manipulation, single lab, two orthogonal Ca²⁺ readouts","pmids":["28887330"],"is_preprint":false},{"year":2018,"finding":"Isogenic hiPSC-CMs carrying the ACTC1 E99K mutation display arrhythmogenesis in both 3D engineered heart tissues and 2D monolayers, with Ca²⁺ handling defects identified as the mechanistic basis; dual dantrolene/ranolazine treatment rescued the phenotype, confirming that aberrant Ca²⁺ handling drives the E99K-associated HCM phenotype.","method":"Isogenic hiPSC-CM pairs (heterozygous and homozygous E99K), 3D engineered heart tissue and 2D monolayer Ca²⁺ imaging, pharmacological rescue with dantrolene and ranolazine","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic human cell model with pharmacological rescue, two tissue formats, single lab","pmids":["30392975"],"is_preprint":false},{"year":2019,"finding":"The ACTC1 G247D (Gly247Asp) mutation causes actin polymerization/turnover defects (confirmed by in vitro actin polymerization assays), reduces GTP-bound Rho-GTPase activity, increases nuclear localization of globular actin, and thereby abolishes SRF-signaling activation in neonatal rat cardiomyocytes and C2C12 cells.","method":"In vitro actin polymerization assay, luciferase reporter (SM22-RE-driven), Rho-GTPase activity assay (GTP-pull-down), nuclear/cytoplasmic fractionation with immunofluorescence in NRVCMs overexpressing mutant vs. wild-type ACTC1","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical assays (polymerization, Rho-GTPase, localization, luciferase) in a single lab","pmids":["31434612"],"is_preprint":false},{"year":2019,"finding":"The ACTC1 G247D mutation leads to sarcomeric disarray, myofibrillar degeneration, increased apoptosis, and defective actin polymerization/turnover in both patient myocardial tissue and in neonatal rat ventricular cardiomyocytes overexpressing mutant ACTC1, demonstrating that normal ACTC1 polymerization is required for sarcomere integrity and contractile function.","method":"Ultrastructural analysis of patient cardiac tissue (electron microscopy), cardiac proteomics, overexpression of mutant vs. native ACTC1 in NRVCMs with structural and apoptosis readouts, molecular dynamics simulation, in vitro actin polymerization assay","journal":"Circulation. Genomic and precision medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (EM, proteomics, cell biology, molecular dynamics, polymerization assay), patient tissue plus cell model, single lab","pmids":["31430208"],"is_preprint":false},{"year":2003,"finding":"Alpha-cardiac actin (ACTC1) physically binds to the cardiac isoform of band 3 (AE1 anion exchanger) at the intercalated disc; interaction identified by yeast two-hybrid using the cytoplasmic domain of band 3 as bait, confirmed by reciprocal co-immunoprecipitation from rat heart and co-localized by confocal microscopy.","method":"Yeast two-hybrid screen, reciprocal co-immunoprecipitation from whole rat heart, confocal microscopy immunolocalization","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reciprocal Co-IP confirms interaction in native tissue, supported by yeast two-hybrid and co-localization, single lab","pmids":["12898519"],"is_preprint":false},{"year":2010,"finding":"siRNA-mediated knockdown of ACTC1 in H9C2 cardiomyocyte cells increases apoptosis with elevated Caspase-3 and reduced Bcl-2 expression, indicating that ACTC1 expression is required to suppress the intrinsic apoptotic pathway in cardiomyocytes.","method":"siRNA knockdown of Actc1 in H9C2 cells, TUNEL assay, Western blot for Caspase-3 and Bcl-2, corroborated by RT-PCR and immunohistochemistry of patient cardiac tissue samples","journal":"Circulation journal : official journal of the Japanese Circulation Society","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA loss-of-function with specific apoptotic markers, supported by correlative patient tissue data, single lab","pmids":["20962418"],"is_preprint":false},{"year":2025,"finding":"LMOD2 interacts with ACTC1 (confirmed by co-immunoprecipitation) and this interaction is involved in regulating myogenic differentiation; LMOD2 knockout alters muscle fiber type composition and suppresses myoblast proliferation in C2C12 cells.","method":"Co-immunoprecipitation in C2C12 cells, LMOD2 knockout by CRISPR, RNA-seq, Western blot for myosin heavy chain isoforms and PAX7","journal":"BMC genomics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP confirms interaction; functional role of the LMOD2–ACTC1 complex specifically is inferred but not directly tested mechanistically","pmids":["40745266"],"is_preprint":false},{"year":2016,"finding":"A 3'UTR mutation in ACTC1 (c.*1784T>C) creates a new binding site for miR-139-5p, which specifically reduces ACTC1 protein expression; miR-139-5p mimic further decreases expression while miR-139-5p inhibitor rescues the decline, identifying miR-139-5p as a post-transcriptional repressor of ACTC1 through this gain-of-function mutation.","method":"Luciferase reporter assay with wild-type and mutant ACTC1 3'UTR constructs, miR-139-5p mimic and inhibitor transfection, whole genome sequencing for variant discovery","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional luciferase assay with both mimic and inhibitor rescue demonstrates direct miRNA-mediated regulation, single lab, two orthogonal manipulations","pmids":["27139165"],"is_preprint":false},{"year":2017,"finding":"Actc1 expression in early adult skeletal muscle is negatively correlated with DNA methylation around its transcriptional start site in a strain-dependent manner (Collaborative Cross mouse panel), while histone modification and chromatin accessibility marks at the locus are unaltered, identifying promoter methylation as a regulatory mechanism controlling Actc1 transcript levels.","method":"Expression QTL mapping in Collaborative Cross mice, bisulfite sequencing/methylation analysis, histone ChIP, ATAC-seq at Actc1 locus across strains with up to 24-fold expression variation","journal":"Biochimica et biophysica acta. Gene regulatory mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — correlation of methylation with expression across multiple inbred strains with orthogonal chromatin assays ruling out alternative marks, single lab","pmids":["28847732"],"is_preprint":false},{"year":2025,"finding":"ACTC1 overexpression in prostate cancer cells promotes proliferation and migration, and drives tumor growth in xenograft models; BMP4 was identified as a key downstream effector, and BMP4 overexpression rescued the inhibitory effects of ACTC1 knockdown, defining an ACTC1–BMP4 signaling axis.","method":"ACTC1 overexpression and siRNA knockdown in prostate cancer cell lines (proliferation and migration assays), xenograft tumor growth, transcriptomic/pathway analysis, BMP4 rescue experiment","journal":"BMC cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — gain- and loss-of-function with rescue, but no direct biochemical mechanism linking ACTC1 to BMP4; pathway placement is inference from transcriptomics, single lab","pmids":["41286808"],"is_preprint":false},{"year":2025,"finding":"ACTC1 promoter variants found exclusively in VSD patients significantly alter ACTC1 promoter transcriptional activity in mouse cardiomyocytes (HL-1), and EMSA demonstrates that these variants affect transcription factor binding at the ACTC1 promoter, implicating disrupted transcription factor recruitment as a mechanism of reduced ACTC1 expression in VSD.","method":"Dual luciferase transcriptional activity assay in HL-1 mouse cardiomyocytes, electrophoretic mobility shift assay (EMSA), Sanger sequencing of 627 subjects, JASPAR database analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional reporter and EMSA provide direct evidence for transcription factor binding disruption, but single lab and limited mechanistic follow-up","pmids":["40848833"],"is_preprint":false},{"year":2015,"finding":"Structural mapping of ACTC1 missense mutations causing congenital heart defects (p.Met84Thr, p.Glu101Lys, p.Met125Val) places them in the actin surface domain that contacts the myosin heavy chain head, distinct from mutations causing cardiomyopathy (p.Ala297Ser, p.Asp313His, p.Arg314His) which lie on a separate myosin-interaction surface, suggesting that the clinical consequence of an ACTC1 mutation depends on the actin–myosin interaction domain affected.","method":"Linkage analysis mapping disease locus to chr15q (ACTC1), Sanger sequencing identifying p.Met84Thr mutation, structural modelling of actin–myosin interface mapping mutation locations","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 4 / Weak — structural inference from computational modelling without in vitro functional validation of the interaction surface specificity","pmids":["26061005"],"is_preprint":false},{"year":2018,"finding":"ACTC1 knockdown by siRNA in U87MG glioblastoma cells significantly inhibits cell migration (distance migrated reduced from ~3,600 µm to ~1,265 µm over 72 h), demonstrating a functional role for ACTC1 in glioblastoma cell motility.","method":"siRNA knockdown of ACTC1 in U87MG cells confirmed by ddPCR and immunocytochemistry; time-lapse cell tracking migration assay over 72 h","journal":"Journal of the neurological sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single siRNA knockdown with migration phenotype, no pathway placement or mechanistic follow-up, single lab","pmids":["30055382"],"is_preprint":false}],"current_model":"ACTC1 (cardiac α-actin) is a sarcomeric thin filament component that interacts with myosin heavy chain to drive cardiac and skeletal muscle contraction; pathogenic missense mutations alter myofibrillar Ca²⁺ sensitivity (E99K increases it, E361G and G247D do not change it but uncouple troponin I phosphorylation-dependent modulation), impair actin polymerization and SRF/Rho-GTPase signaling, or disrupt specific actin–myosin contact surfaces depending on their location, leading to hypertrophic or dilated cardiomyopathy, congenital heart defects, or arrhythmia; ACTC1 expression is regulated post-transcriptionally by miR-139-5p and epigenetically by promoter methylation, and the protein also physically associates with the cardiac band 3 anion exchanger at intercalated discs and with LMOD2 in skeletal muscle."},"narrative":{"mechanistic_narrative":"ACTC1 (cardiac α-actin) is a sarcomeric thin-filament protein that drives cardiac and skeletal muscle contraction through actin–myosin interactions, and proper actin polymerization is required for sarcomere integrity, contractile function, and survival of cardiomyocytes [PMID:31430208, PMID:20962418]. Pathogenic missense mutations act through distinct biophysical mechanisms depending on their location: E99K elevates myofibrillar Ca²⁺ sensitivity, producing hypercontractility with slowed relaxation and disproportionate energy cost, and links this gain in sensitivity to aberrant sarcoplasmic reticulum Ca²⁺ release and arrhythmogenesis [PMID:21622575, PMID:23604709, PMID:28887330]. Both E99K and the DCM-causing E361G mutation uncouple thin-filament regulation from troponin I phosphorylation, abolishing the normal phosphorylation-dependent decrease in Ca²⁺ sensitivity that tunes relaxation kinetics [PMID:21622575, PMID:25418306]. A separate class of mutation typified by G247D impairs actin polymerization and turnover, reduces Rho-GTPase activity and SRF signaling while increasing nuclear globular actin, and causes sarcomeric disarray and apoptosis [PMID:31434612, PMID:31430208]. Structural mapping further indicates that mutations on the actin surface contacting the myosin head correspond to congenital heart defects, while mutations on a distinct myosin-interaction surface cause cardiomyopathy [PMID:26061005]. ACTC1 expression is controlled post-transcriptionally by miR-139-5p and by promoter DNA methylation and transcription-factor binding at its promoter [PMID:27139165, PMID:28847732, PMID:40848833]. Beyond the cardiac sarcomere, ACTC1 physically associates with the cardiac band 3 (AE1) anion exchanger at intercalated discs and with LMOD2 in skeletal muscle [PMID:12898519, PMID:40745266].","teleology":[{"year":2003,"claim":"Established a physical partner of cardiac α-actin outside the contractile apparatus, placing ACTC1 at the intercalated disc.","evidence":"Yeast two-hybrid with band 3 cytoplasmic domain bait, reciprocal Co-IP from rat heart, confocal co-localization","pmids":["12898519"],"confidence":"Medium","gaps":["Functional consequence of the ACTC1–band 3 interaction not tested","Interface residues unmapped"]},{"year":2010,"claim":"Demonstrated that ACTC1 expression itself is required to suppress cardiomyocyte apoptosis, moving the gene beyond a passive structural role.","evidence":"siRNA knockdown in H9C2 cells with TUNEL and Caspase-3/Bcl-2 readouts, plus patient tissue correlation","pmids":["20962418"],"confidence":"Medium","gaps":["Mechanism linking actin loss to intrinsic apoptosis not defined","Single cell line"]},{"year":2011,"claim":"Defined the biophysical mechanism of the HCM E99K mutation as elevated myofibrillar Ca²⁺ sensitivity with loss of troponin I phosphorylation-dependent modulation.","evidence":"In vitro motility on reconstituted thin filaments and skinned papillary muscle in transgenic mouse and human carrier samples","pmids":["21622575"],"confidence":"High","gaps":["Does not address downstream Ca²⁺ handling consequences","Mechanism by which E99K blocks phosphorylation coupling unresolved"]},{"year":2013,"claim":"Connected E99K's elevated Ca²⁺ sensitivity to whole-muscle hypercontractility, slowed relaxation, and energetic inefficiency, distinguishing myofilament from Ca²⁺-transient causes.","evidence":"Intact papillary muscle mechanics, myofibril Ca²⁺-jump, and myocyte Ca²⁺ imaging in E99K transgenic mice","pmids":["23604709"],"confidence":"High","gaps":["Does not establish arrhythmic mechanism","Energetic penalty mechanism not detailed"]},{"year":2014,"claim":"Generalized the troponin I phosphorylation uncoupling mechanism to the DCM mutation E361G, defining the actin–troponin interface as the route by which phosphorylation regulates relaxation.","evidence":"Ca²⁺-jump on single transgenic myofibrils with pharmacological manipulation of troponin I phosphorylation","pmids":["25418306"],"confidence":"High","gaps":["Does not explain how the same defect yields DCM vs HCM","Structural basis of uncoupling unresolved"]},{"year":2016,"claim":"Identified post-transcriptional control of ACTC1, showing a 3'UTR variant creates a miR-139-5p site that represses ACTC1 protein.","evidence":"Luciferase reporter with WT/mutant 3'UTR plus miR-139-5p mimic and inhibitor rescue","pmids":["27139165"],"confidence":"Medium","gaps":["Endogenous physiological relevance of miR-139-5p regulation not shown","Tissue context limited"]},{"year":2017,"claim":"Linked E99K-driven myofilament Ca²⁺ sensitization to aberrant SR Ca²⁺ release and arrhythmogenesis, with strong genetic-background modification of penetrance.","evidence":"Isolated myocyte Ca²⁺ imaging (transients, sparks, waves) in young transgenic mice on two backgrounds","pmids":["28887330"],"confidence":"Medium","gaps":["Molecular link between myofilament sensitivity and SR release unresolved","Background modifier genes unidentified"]},{"year":2017,"claim":"Identified promoter DNA methylation as a transcriptional regulator of Actc1, ruling out histone and chromatin-accessibility changes.","evidence":"Expression QTL mapping, bisulfite sequencing, ChIP and ATAC-seq across Collaborative Cross strains","pmids":["28847732"],"confidence":"Medium","gaps":["Causality of methylation vs expression not directly tested","Responsible methyltransferases/factors unknown"]},{"year":2018,"claim":"Validated the Ca²⁺-handling mechanism of E99K HCM in a human isogenic cell model and showed pharmacological rescue.","evidence":"Isogenic hiPSC-CM 3D and 2D Ca²⁺ imaging with dantrolene/ranolazine rescue","pmids":["30392975"],"confidence":"Medium","gaps":["Long-term and in vivo efficacy of rescue not assessed","Single lab"]},{"year":2019,"claim":"Defined a polymerization-based mechanism for G247D, linking impaired actin assembly to reduced Rho-GTPase/SRF signaling and nuclear actin accumulation, and to sarcomeric disarray and apoptosis.","evidence":"In vitro polymerization, Rho-GTPase pulldown, SRF luciferase, fractionation/IF, patient EM, proteomics and molecular dynamics in NRVCMs/C2C12","pmids":["31434612","31430208"],"confidence":"Medium","gaps":["Direct demonstration of SRF target dysregulation in vivo lacking","Overexpression model may not reflect heterozygous dosage"]},{"year":2025,"claim":"Established LMOD2 as a physical partner of ACTC1 with a role in myogenic differentiation and fiber-type composition.","evidence":"Co-IP in C2C12 cells with LMOD2 CRISPR knockout, RNA-seq and MyHC/PAX7 Western blots","pmids":["40745266"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation","Functional role of the ACTC1–LMOD2 complex specifically inferred, not directly tested"]},{"year":2025,"claim":"Implicated ACTC1 promoter variants in VSD by altering transcription-factor binding and promoter activity.","evidence":"Dual luciferase in HL-1 cardiomyocytes and EMSA across patient-specific variants","pmids":["40848833"],"confidence":"Medium","gaps":["Specific transcription factors not identified","In vivo expression consequences not measured"]},{"year":2025,"claim":"Reported a non-muscle oncogenic role, defining an ACTC1–BMP4 axis promoting prostate cancer proliferation and migration.","evidence":"Overexpression/knockdown with proliferation, migration, xenograft, transcriptomics, and BMP4 rescue","pmids":["41286808"],"confidence":"Low","gaps":["No direct biochemical link between ACTC1 and BMP4","Pathway placement inferred from transcriptomics only"]},{"year":null,"claim":"How a single thin-filament protein produces opposite clinical outcomes (HCM vs DCM vs congenital defect vs arrhythmia) from mutation position, and how its cytoskeletal/signaling roles in non-muscle cells relate to its sarcomeric function, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unified structural model relating mutation surface to clinical phenotype with functional validation","Non-muscle ACTC1 signaling mechanisms unmapped","Direct in vivo validation of regulatory inputs (miRNA, methylation, TF binding) on ACTC1 dosage lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[7,9]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[6,14]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[5,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5]}],"complexes":["sarcomere thin filament"],"partners":["SLC4A1","LMOD2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P68032","full_name":"Actin, alpha cardiac muscle 1","aliases":["Alpha-cardiac actin"],"length_aa":377,"mass_kda":42.0,"function":"Actins are highly conserved proteins that are involved in various types of cell motility and are ubiquitously expressed in all eukaryotic cells","subcellular_location":"Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/P68032/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ACTC1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ACTG1","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CTTN","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ACTC1","total_profiled":1310},"omim":[{"mim_id":"620265","title":"CONGENITAL MYOPATHY 2B, SEVERE INFANTILE, AUTOSOMAL RECESSIVE; CMYO2B","url":"https://www.omim.org/entry/620265"},{"mim_id":"620093","title":"ACTIN MATURATION PROTEASE; ACTMAP","url":"https://www.omim.org/entry/620093"},{"mim_id":"619222","title":"SUPPRESSOR OF CANCER CELL INVASION; SCAI","url":"https://www.omim.org/entry/619222"},{"mim_id":"617135","title":"L3MBTL HISTONE METHYL-LYSINE-BINDING PROTEIN 4; L3MBTL4","url":"https://www.omim.org/entry/617135"},{"mim_id":"615396","title":"LEFT VENTRICULAR NONCOMPACTION 10; LVNC10","url":"https://www.omim.org/entry/615396"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":10840.1}],"url":"https://www.proteinatlas.org/search/ACTC1"},"hgnc":{"alias_symbol":["CMD1R"],"prev_symbol":["ACTC"]},"alphafold":{"accession":"P68032","domains":[{"cath_id":"3.30.420.40","chopping":"9-139_341-374","consensus_level":"medium","plddt":94.7867,"start":9,"end":374},{"cath_id":"3.30.420.40","chopping":"144-181_274-337","consensus_level":"medium","plddt":97.6754,"start":144,"end":337},{"cath_id":"3.90.640.10","chopping":"183-267","consensus_level":"high","plddt":97.1568,"start":183,"end":267}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P68032","model_url":"https://alphafold.ebi.ac.uk/files/AF-P68032-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P68032-F1-predicted_aligned_error_v6.png","plddt_mean":95.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ACTC1","jax_strain_url":"https://www.jax.org/strain/search?query=ACTC1"},"sequence":{"accession":"P68032","fasta_url":"https://rest.uniprot.org/uniprotkb/P68032.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P68032/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P68032"}},"corpus_meta":[{"pmid":"21622575","id":"PMC_21622575","title":"Molecular 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Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/28887330","citation_count":10,"is_preprint":false},{"pmid":"31921954","id":"PMC_31921954","title":"Data on the role of cardiac α-actin (ACTC1) gene mutations on SRF-signaling.","date":"2020","source":"Data in brief","url":"https://pubmed.ncbi.nlm.nih.gov/31921954","citation_count":8,"is_preprint":false},{"pmid":"12898519","id":"PMC_12898519","title":"alpha-cardiac actin (ACTC) binds to the band 3 (AE1) cardiac isoform.","date":"2003","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12898519","citation_count":7,"is_preprint":false},{"pmid":"31434612","id":"PMC_31434612","title":"A cardiac α-actin (ACTC1) p. 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\"method\": \"In vitro motility assay on reconstituted thin filaments, skinned papillary muscle Ca²⁺ sensitivity measurements, transgenic mouse model expressing E99K at 50% of total heart actin\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted thin filament in vitro assay plus skinned muscle preparations, validated in both transgenic mouse and human carrier samples, multiple orthogonal methods\",\n      \"pmids\": [\"21622575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The DCM-causing ACTC1 E361G mutation specifically abolishes Ca²⁺ sensitivity modulation by troponin I phosphorylation in intact cardiac myofibrils, without affecting length-dependent activation or response to EMD57033, confirming that troponin I phosphorylation acts through the actin-troponin interface to regulate relaxation kinetics.\",\n      \"method\": \"Ca²⁺-jump protocol on single transgenic mouse heart myofibrils; comparison of isometric tension and relaxation parameters (kREL, tLIN) in myofibrils with varying troponin I phosphorylation levels (propranolol-treated vs. control mice)\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro myofibril assay with pharmacological manipulation of phosphorylation level and multiple kinetic readouts, single lab but multiple orthogonal parameters\",\n      \"pmids\": [\"25418306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ACTC1 E99K papillary muscle produces 3–4× greater isometric twitch force than non-transgenic muscle, relaxes 1.4× slower, and consumes disproportionately more energy (efficiency 11–16% vs. 15–18%), with hypercontractility attributable to elevated myofibrillar Ca²⁺ sensitivity (EC₅₀ 0.39 vs. 0.80 µmol/L) rather than altered Ca²⁺ transient amplitude.\",\n      \"method\": \"Intact papillary muscle mechanics (force, heat, work), isolated myofibril Ca²⁺-jump protocol, isolated myocyte Ca²⁺ transient imaging in ACTC E99K transgenic mouse model\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multi-level analysis (intact muscle, myofibril, myocyte) with orthogonal methods in a validated transgenic model, single lab\",\n      \"pmids\": [\"23604709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Young ACTC1 E99K transgenic mice prone to sudden cardiac death exhibit increased Ca²⁺ transient amplitude, greater Ca²⁺ spark mass, and increased propensity for spontaneous Ca²⁺ waves compared with non-transgenic littermates despite similar sarcoplasmic reticulum Ca²⁺ content, linking the actin mutation's elevated myofilament Ca²⁺ sensitivity to aberrant SR Ca²⁺ release and arrhythmogenesis. Penetrance of sudden death is strongly modified by genetic background (CBA/Ca vs. C57Bl6).\",\n      \"method\": \"Isolated ventricular myocyte Ca²⁺ imaging (transients, sparks, waves), confocal microscopy, collagen quantification, comparison of young vs. adult TG and NTG mice on two genetic backgrounds\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cellular Ca²⁺ measurements in isolated myocytes with genetic background manipulation, single lab, two orthogonal Ca²⁺ readouts\",\n      \"pmids\": [\"28887330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Isogenic hiPSC-CMs carrying the ACTC1 E99K mutation display arrhythmogenesis in both 3D engineered heart tissues and 2D monolayers, with Ca²⁺ handling defects identified as the mechanistic basis; dual dantrolene/ranolazine treatment rescued the phenotype, confirming that aberrant Ca²⁺ handling drives the E99K-associated HCM phenotype.\",\n      \"method\": \"Isogenic hiPSC-CM pairs (heterozygous and homozygous E99K), 3D engineered heart tissue and 2D monolayer Ca²⁺ imaging, pharmacological rescue with dantrolene and ranolazine\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic human cell model with pharmacological rescue, two tissue formats, single lab\",\n      \"pmids\": [\"30392975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The ACTC1 G247D (Gly247Asp) mutation causes actin polymerization/turnover defects (confirmed by in vitro actin polymerization assays), reduces GTP-bound Rho-GTPase activity, increases nuclear localization of globular actin, and thereby abolishes SRF-signaling activation in neonatal rat cardiomyocytes and C2C12 cells.\",\n      \"method\": \"In vitro actin polymerization assay, luciferase reporter (SM22-RE-driven), Rho-GTPase activity assay (GTP-pull-down), nuclear/cytoplasmic fractionation with immunofluorescence in NRVCMs overexpressing mutant vs. wild-type ACTC1\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical assays (polymerization, Rho-GTPase, localization, luciferase) in a single lab\",\n      \"pmids\": [\"31434612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The ACTC1 G247D mutation leads to sarcomeric disarray, myofibrillar degeneration, increased apoptosis, and defective actin polymerization/turnover in both patient myocardial tissue and in neonatal rat ventricular cardiomyocytes overexpressing mutant ACTC1, demonstrating that normal ACTC1 polymerization is required for sarcomere integrity and contractile function.\",\n      \"method\": \"Ultrastructural analysis of patient cardiac tissue (electron microscopy), cardiac proteomics, overexpression of mutant vs. native ACTC1 in NRVCMs with structural and apoptosis readouts, molecular dynamics simulation, in vitro actin polymerization assay\",\n      \"journal\": \"Circulation. Genomic and precision medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (EM, proteomics, cell biology, molecular dynamics, polymerization assay), patient tissue plus cell model, single lab\",\n      \"pmids\": [\"31430208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Alpha-cardiac actin (ACTC1) physically binds to the cardiac isoform of band 3 (AE1 anion exchanger) at the intercalated disc; interaction identified by yeast two-hybrid using the cytoplasmic domain of band 3 as bait, confirmed by reciprocal co-immunoprecipitation from rat heart and co-localized by confocal microscopy.\",\n      \"method\": \"Yeast two-hybrid screen, reciprocal co-immunoprecipitation from whole rat heart, confocal microscopy immunolocalization\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reciprocal Co-IP confirms interaction in native tissue, supported by yeast two-hybrid and co-localization, single lab\",\n      \"pmids\": [\"12898519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"siRNA-mediated knockdown of ACTC1 in H9C2 cardiomyocyte cells increases apoptosis with elevated Caspase-3 and reduced Bcl-2 expression, indicating that ACTC1 expression is required to suppress the intrinsic apoptotic pathway in cardiomyocytes.\",\n      \"method\": \"siRNA knockdown of Actc1 in H9C2 cells, TUNEL assay, Western blot for Caspase-3 and Bcl-2, corroborated by RT-PCR and immunohistochemistry of patient cardiac tissue samples\",\n      \"journal\": \"Circulation journal : official journal of the Japanese Circulation Society\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA loss-of-function with specific apoptotic markers, supported by correlative patient tissue data, single lab\",\n      \"pmids\": [\"20962418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LMOD2 interacts with ACTC1 (confirmed by co-immunoprecipitation) and this interaction is involved in regulating myogenic differentiation; LMOD2 knockout alters muscle fiber type composition and suppresses myoblast proliferation in C2C12 cells.\",\n      \"method\": \"Co-immunoprecipitation in C2C12 cells, LMOD2 knockout by CRISPR, RNA-seq, Western blot for myosin heavy chain isoforms and PAX7\",\n      \"journal\": \"BMC genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP confirms interaction; functional role of the LMOD2–ACTC1 complex specifically is inferred but not directly tested mechanistically\",\n      \"pmids\": [\"40745266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A 3'UTR mutation in ACTC1 (c.*1784T>C) creates a new binding site for miR-139-5p, which specifically reduces ACTC1 protein expression; miR-139-5p mimic further decreases expression while miR-139-5p inhibitor rescues the decline, identifying miR-139-5p as a post-transcriptional repressor of ACTC1 through this gain-of-function mutation.\",\n      \"method\": \"Luciferase reporter assay with wild-type and mutant ACTC1 3'UTR constructs, miR-139-5p mimic and inhibitor transfection, whole genome sequencing for variant discovery\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional luciferase assay with both mimic and inhibitor rescue demonstrates direct miRNA-mediated regulation, single lab, two orthogonal manipulations\",\n      \"pmids\": [\"27139165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Actc1 expression in early adult skeletal muscle is negatively correlated with DNA methylation around its transcriptional start site in a strain-dependent manner (Collaborative Cross mouse panel), while histone modification and chromatin accessibility marks at the locus are unaltered, identifying promoter methylation as a regulatory mechanism controlling Actc1 transcript levels.\",\n      \"method\": \"Expression QTL mapping in Collaborative Cross mice, bisulfite sequencing/methylation analysis, histone ChIP, ATAC-seq at Actc1 locus across strains with up to 24-fold expression variation\",\n      \"journal\": \"Biochimica et biophysica acta. Gene regulatory mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — correlation of methylation with expression across multiple inbred strains with orthogonal chromatin assays ruling out alternative marks, single lab\",\n      \"pmids\": [\"28847732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ACTC1 overexpression in prostate cancer cells promotes proliferation and migration, and drives tumor growth in xenograft models; BMP4 was identified as a key downstream effector, and BMP4 overexpression rescued the inhibitory effects of ACTC1 knockdown, defining an ACTC1–BMP4 signaling axis.\",\n      \"method\": \"ACTC1 overexpression and siRNA knockdown in prostate cancer cell lines (proliferation and migration assays), xenograft tumor growth, transcriptomic/pathway analysis, BMP4 rescue experiment\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — gain- and loss-of-function with rescue, but no direct biochemical mechanism linking ACTC1 to BMP4; pathway placement is inference from transcriptomics, single lab\",\n      \"pmids\": [\"41286808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ACTC1 promoter variants found exclusively in VSD patients significantly alter ACTC1 promoter transcriptional activity in mouse cardiomyocytes (HL-1), and EMSA demonstrates that these variants affect transcription factor binding at the ACTC1 promoter, implicating disrupted transcription factor recruitment as a mechanism of reduced ACTC1 expression in VSD.\",\n      \"method\": \"Dual luciferase transcriptional activity assay in HL-1 mouse cardiomyocytes, electrophoretic mobility shift assay (EMSA), Sanger sequencing of 627 subjects, JASPAR database analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional reporter and EMSA provide direct evidence for transcription factor binding disruption, but single lab and limited mechanistic follow-up\",\n      \"pmids\": [\"40848833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Structural mapping of ACTC1 missense mutations causing congenital heart defects (p.Met84Thr, p.Glu101Lys, p.Met125Val) places them in the actin surface domain that contacts the myosin heavy chain head, distinct from mutations causing cardiomyopathy (p.Ala297Ser, p.Asp313His, p.Arg314His) which lie on a separate myosin-interaction surface, suggesting that the clinical consequence of an ACTC1 mutation depends on the actin–myosin interaction domain affected.\",\n      \"method\": \"Linkage analysis mapping disease locus to chr15q (ACTC1), Sanger sequencing identifying p.Met84Thr mutation, structural modelling of actin–myosin interface mapping mutation locations\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — structural inference from computational modelling without in vitro functional validation of the interaction surface specificity\",\n      \"pmids\": [\"26061005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ACTC1 knockdown by siRNA in U87MG glioblastoma cells significantly inhibits cell migration (distance migrated reduced from ~3,600 µm to ~1,265 µm over 72 h), demonstrating a functional role for ACTC1 in glioblastoma cell motility.\",\n      \"method\": \"siRNA knockdown of ACTC1 in U87MG cells confirmed by ddPCR and immunocytochemistry; time-lapse cell tracking migration assay over 72 h\",\n      \"journal\": \"Journal of the neurological sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single siRNA knockdown with migration phenotype, no pathway placement or mechanistic follow-up, single lab\",\n      \"pmids\": [\"30055382\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ACTC1 (cardiac α-actin) is a sarcomeric thin filament component that interacts with myosin heavy chain to drive cardiac and skeletal muscle contraction; pathogenic missense mutations alter myofibrillar Ca²⁺ sensitivity (E99K increases it, E361G and G247D do not change it but uncouple troponin I phosphorylation-dependent modulation), impair actin polymerization and SRF/Rho-GTPase signaling, or disrupt specific actin–myosin contact surfaces depending on their location, leading to hypertrophic or dilated cardiomyopathy, congenital heart defects, or arrhythmia; ACTC1 expression is regulated post-transcriptionally by miR-139-5p and epigenetically by promoter methylation, and the protein also physically associates with the cardiac band 3 anion exchanger at intercalated discs and with LMOD2 in skeletal muscle.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ACTC1 (cardiac α-actin) is a sarcomeric thin-filament protein that drives cardiac and skeletal muscle contraction through actin–myosin interactions, and proper actin polymerization is required for sarcomere integrity, contractile function, and survival of cardiomyocytes [#6, #8]. Pathogenic missense mutations act through distinct biophysical mechanisms depending on their location: E99K elevates myofibrillar Ca²⁺ sensitivity, producing hypercontractility with slowed relaxation and disproportionate energy cost, and links this gain in sensitivity to aberrant sarcoplasmic reticulum Ca²⁺ release and arrhythmogenesis [#0, #2, #3]. Both E99K and the DCM-causing E361G mutation uncouple thin-filament regulation from troponin I phosphorylation, abolishing the normal phosphorylation-dependent decrease in Ca²⁺ sensitivity that tunes relaxation kinetics [#0, #1]. A separate class of mutation typified by G247D impairs actin polymerization and turnover, reduces Rho-GTPase activity and SRF signaling while increasing nuclear globular actin, and causes sarcomeric disarray and apoptosis [#5, #6]. Structural mapping further indicates that mutations on the actin surface contacting the myosin head correspond to congenital heart defects, while mutations on a distinct myosin-interaction surface cause cardiomyopathy [#14]. ACTC1 expression is controlled post-transcriptionally by miR-139-5p and by promoter DNA methylation and transcription-factor binding at its promoter [#10, #11, #13]. Beyond the cardiac sarcomere, ACTC1 physically associates with the cardiac band 3 (AE1) anion exchanger at intercalated discs and with LMOD2 in skeletal muscle [#7, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established a physical partner of cardiac α-actin outside the contractile apparatus, placing ACTC1 at the intercalated disc.\",\n      \"evidence\": \"Yeast two-hybrid with band 3 cytoplasmic domain bait, reciprocal Co-IP from rat heart, confocal co-localization\",\n      \"pmids\": [\"12898519\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the ACTC1–band 3 interaction not tested\", \"Interface residues unmapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated that ACTC1 expression itself is required to suppress cardiomyocyte apoptosis, moving the gene beyond a passive structural role.\",\n      \"evidence\": \"siRNA knockdown in H9C2 cells with TUNEL and Caspase-3/Bcl-2 readouts, plus patient tissue correlation\",\n      \"pmids\": [\"20962418\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking actin loss to intrinsic apoptosis not defined\", \"Single cell line\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the biophysical mechanism of the HCM E99K mutation as elevated myofibrillar Ca²⁺ sensitivity with loss of troponin I phosphorylation-dependent modulation.\",\n      \"evidence\": \"In vitro motility on reconstituted thin filaments and skinned papillary muscle in transgenic mouse and human carrier samples\",\n      \"pmids\": [\"21622575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address downstream Ca²⁺ handling consequences\", \"Mechanism by which E99K blocks phosphorylation coupling unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connected E99K's elevated Ca²⁺ sensitivity to whole-muscle hypercontractility, slowed relaxation, and energetic inefficiency, distinguishing myofilament from Ca²⁺-transient causes.\",\n      \"evidence\": \"Intact papillary muscle mechanics, myofibril Ca²⁺-jump, and myocyte Ca²⁺ imaging in E99K transgenic mice\",\n      \"pmids\": [\"23604709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not establish arrhythmic mechanism\", \"Energetic penalty mechanism not detailed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Generalized the troponin I phosphorylation uncoupling mechanism to the DCM mutation E361G, defining the actin–troponin interface as the route by which phosphorylation regulates relaxation.\",\n      \"evidence\": \"Ca²⁺-jump on single transgenic myofibrils with pharmacological manipulation of troponin I phosphorylation\",\n      \"pmids\": [\"25418306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not explain how the same defect yields DCM vs HCM\", \"Structural basis of uncoupling unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified post-transcriptional control of ACTC1, showing a 3'UTR variant creates a miR-139-5p site that represses ACTC1 protein.\",\n      \"evidence\": \"Luciferase reporter with WT/mutant 3'UTR plus miR-139-5p mimic and inhibitor rescue\",\n      \"pmids\": [\"27139165\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous physiological relevance of miR-139-5p regulation not shown\", \"Tissue context limited\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked E99K-driven myofilament Ca²⁺ sensitization to aberrant SR Ca²⁺ release and arrhythmogenesis, with strong genetic-background modification of penetrance.\",\n      \"evidence\": \"Isolated myocyte Ca²⁺ imaging (transients, sparks, waves) in young transgenic mice on two backgrounds\",\n      \"pmids\": [\"28887330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between myofilament sensitivity and SR release unresolved\", \"Background modifier genes unidentified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified promoter DNA methylation as a transcriptional regulator of Actc1, ruling out histone and chromatin-accessibility changes.\",\n      \"evidence\": \"Expression QTL mapping, bisulfite sequencing, ChIP and ATAC-seq across Collaborative Cross strains\",\n      \"pmids\": [\"28847732\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality of methylation vs expression not directly tested\", \"Responsible methyltransferases/factors unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Validated the Ca²⁺-handling mechanism of E99K HCM in a human isogenic cell model and showed pharmacological rescue.\",\n      \"evidence\": \"Isogenic hiPSC-CM 3D and 2D Ca²⁺ imaging with dantrolene/ranolazine rescue\",\n      \"pmids\": [\"30392975\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Long-term and in vivo efficacy of rescue not assessed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a polymerization-based mechanism for G247D, linking impaired actin assembly to reduced Rho-GTPase/SRF signaling and nuclear actin accumulation, and to sarcomeric disarray and apoptosis.\",\n      \"evidence\": \"In vitro polymerization, Rho-GTPase pulldown, SRF luciferase, fractionation/IF, patient EM, proteomics and molecular dynamics in NRVCMs/C2C12\",\n      \"pmids\": [\"31434612\", \"31430208\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration of SRF target dysregulation in vivo lacking\", \"Overexpression model may not reflect heterozygous dosage\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established LMOD2 as a physical partner of ACTC1 with a role in myogenic differentiation and fiber-type composition.\",\n      \"evidence\": \"Co-IP in C2C12 cells with LMOD2 CRISPR knockout, RNA-seq and MyHC/PAX7 Western blots\",\n      \"pmids\": [\"40745266\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation\", \"Functional role of the ACTC1–LMOD2 complex specifically inferred, not directly tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated ACTC1 promoter variants in VSD by altering transcription-factor binding and promoter activity.\",\n      \"evidence\": \"Dual luciferase in HL-1 cardiomyocytes and EMSA across patient-specific variants\",\n      \"pmids\": [\"40848833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific transcription factors not identified\", \"In vivo expression consequences not measured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reported a non-muscle oncogenic role, defining an ACTC1–BMP4 axis promoting prostate cancer proliferation and migration.\",\n      \"evidence\": \"Overexpression/knockdown with proliferation, migration, xenograft, transcriptomics, and BMP4 rescue\",\n      \"pmids\": [\"41286808\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct biochemical link between ACTC1 and BMP4\", \"Pathway placement inferred from transcriptomics only\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single thin-filament protein produces opposite clinical outcomes (HCM vs DCM vs congenital defect vs arrhythmia) from mutation position, and how its cytoskeletal/signaling roles in non-muscle cells relate to its sarcomeric function, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified structural model relating mutation surface to clinical phenotype with functional validation\", \"Non-muscle ACTC1 signaling mechanisms unmapped\", \"Direct in vivo validation of regulatory inputs (miRNA, methylation, TF binding) on ACTC1 dosage lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [7, 9]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"sarcomere thin filament\"],\n    \"partners\": [\"SLC4A1\", \"LMOD2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}