{"gene":"TNNC1","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2003,"finding":"Crystal structure of the core domain of human cardiac troponin (including TnC, TnI, TnT) in the Ca2+-saturated form was solved, revealing that the core domain is divided into structurally distinct subdomains connected by flexible linkers, with an IT arm (alpha-helical coiled-coil between TnT and TnI) forming a rigid asymmetric structure, and showing that Ca2+ binding to the regulatory site of TnC removes the carboxy-terminal portion of TnI from actin, altering the mobility and/or flexibility of troponin and tropomyosin on the actin filament.","method":"X-ray crystallography","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of ternary complex with functional interpretation, foundational study","pmids":["12840750"],"is_preprint":false},{"year":1999,"finding":"The cardiac TnI switch region peptide (residues 147-163) binds to the regulatory N-domain of cardiac TnC (cNTnC) only in the Ca2+-saturated state, inducing an open conformation in cNTnC similar to Ca2+-saturated skeletal NTnC; the bound peptide adopts an alpha-helical conformation (residues 150-157) and forms hydrophobic interactions with cNTnC, establishing that Ca2+ is required for the structural opening of cNTnC that enables cTnI binding and muscle regulation.","method":"Multinuclear multidimensional NMR spectroscopy, solution structure determination","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR solution structure with functional validation, well-cited foundational study","pmids":["10387074"],"is_preprint":false},{"year":1998,"finding":"Crystal structure of TnC in complex with the N-terminal fragment of TnI (TnI1-47) at 2.3 Å resolution revealed that the central connecting alpha-helix of TnC is unwound and bent by 90° upon TnI binding, giving TnC a compact globular shape with direct N- and C-terminal lobe interactions; the TnI1-47 alpha-helix stabilizes this compact conformation through contacts with both lobes, with the amphiphilic C-end binding in the hydrophobic pocket of the TnC C-lobe.","method":"X-ray crystallography (single isomorphous replacement + MAD)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure of TnC/TnI complex, well-cited foundational study","pmids":["9560191"],"is_preprint":false},{"year":2015,"finding":"Cardiac TnC (cTnC) is a two-domain EF-hand protein: the C-domain (cCTnC) contains two high-affinity Ca2+/Mg2+ binding sites always occupied under physiologic conditions, anchoring the protein in the troponin complex in an open conformation; the regulatory N-domain (cNTnC) contains a single low-affinity site that, upon Ca2+ binding, adopts an open conformation that binds the switch region of TnI, releasing TnI inhibitory regions from actin to allow contraction; calcium sensitivity can be modified by drugs stabilizing open cNTnC, PKA-mediated phosphorylation of TnI, or thin-filament protein interactions.","method":"Structural and biochemical review integrating prior reconstitution, NMR, crystallography, and mutagenesis data","journal":"Gene","confidence":"High","confidence_rationale":"Tier 1 — synthesis of multiple Tier 1 experimental studies; mechanistic model supported by orthogonal methods across labs","pmids":["26232335"],"is_preprint":false},{"year":2008,"finding":"Novel TNNC1 missense mutations (A8V, C84Y, E134D, D145E) identified in HCM patients; recombinant mutant cTnC proteins reconstituted into skinned fibers showed increased Ca2+ sensitivity of force development (A8V, C84Y, D145E) and force recovery (A8V, D145E), consistent with the gain-of-function Ca2+-sensitization mechanism seen in other sarcomeric HCM mutations, establishing TNNC1 as an HCM-susceptibility gene.","method":"Skinned fiber reconstitution, force development and recovery assays, genetic screening","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 2 — functional reconstitution with multiple mutants across large cohort, replicated functional phenotype","pmids":["18572189"],"is_preprint":false},{"year":2004,"finding":"A TNNC1 missense mutation identified in familial DCM was shown to significantly impair mutated troponin C interaction within the troponin complex compared to wild-type by two-hybrid luciferase assay, indicating altered regulation of myocardial contractility; this established cardiac troponin C as a novel DCM gene with complete penetrance.","method":"Genetic screening (SSCP/DHPLC/sequencing), two-hybrid luciferase interaction assay","journal":"Journal of the American College of Cardiology","confidence":"Medium","confidence_rationale":"Tier 2/3 — functional interaction assay supporting mechanism, single lab study","pmids":["15542288"],"is_preprint":false},{"year":2011,"finding":"Four TNNC1 DCM-associated rare variants (Y5H, M103I, D145E, I148V) reconstituted into porcine skinned fibers demonstrated decreased Ca2+ sensitivity of force development (Y5H, M103I); Y5H and I148V diminished and M103I abolished the effects of PKA phosphorylation on Ca2+ sensitivity; M103I decreased actomyosin ATPase activation at high Ca2+; CD spectroscopy showed most mutants decreased alpha-helical content, indicating structural changes underlie the functional deficits.","method":"Skinned fiber reconstitution, actomyosin ATPase assay, PKA phosphorylation assay, circular dichroism spectroscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1/2 — multiple orthogonal functional methods (force, ATPase, PKA response, CD structure) in single study","pmids":["21832052"],"is_preprint":false},{"year":2012,"finding":"The TNNC1-A31S mutation reconstituted into cardiac skinned fibers increased Ca2+ sensitivity with no effect on maximal force; reconstituted actomyosin ATPase assays showed the mutant increased ATPase activation without altering inhibition; fluorescence studies showed increased Ca2+ affinity in isolated cTnC, the troponin complex, thin filament, and thin filament with myosin subfragment 1; circular dichroism showed no global structural change, indicating the mutation directly increases Ca2+ binding affinity at the regulatory site.","method":"Skinned fiber reconstitution, actomyosin ATPase assay, fluorescence Ca2+ affinity measurements, circular dichroism spectroscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1/2 — multiple orthogonal methods including reconstitution, ATPase, fluorescence, CD in single study","pmids":["22815480"],"is_preprint":false},{"year":2015,"finding":"Knock-in mice carrying the TNNC1-A8V mutation showed dose-dependent increases in Ca2+ sensitivity of contraction in skinned fibers (homozygote > heterozygote > wild-type), reduced diastolic sarcomeric length, increased shortening, prolonged Ca2+ and contractile transients in intact cardiomyocytes, slower relaxation on flash photolysis of diazo-2, and developed diastolic dysfunction with atrial enlargement, papillary muscle hypertrophy, and fibrosis in vivo; liquid chromatography-MS confirmed ~21% mutant cTnC incorporation into the myofilament.","method":"Knock-in mouse model, echocardiography, pressure-volume studies, skinned fiber Ca2+ sensitivity, flash photolysis, cardiomyocyte sarcomere imaging, LC-MS","journal":"Circulation. Cardiovascular genetics","confidence":"High","confidence_rationale":"Tier 1/2 — in vivo genetic model with multiple orthogonal mechanistic readouts confirming Ca2+ sensitization mechanism","pmids":["26304555"],"is_preprint":false},{"year":2022,"finding":"Isothermal titration calorimetry (ITC) and thermodynamic integration simulations demonstrated that physiological Mg2+ concentrations compete with Ca2+ for binding to regulatory site II of cTnC; HCM-associated TNNC1 variants (A8V, L29Q, A31S) elevated affinity for both Ca2+ and Mg2+, while variants adjacent to the EF-hand motif (L48Q, Q50R, C84Y) had larger effects on affinity and binding thermodynamics, indicating a physiologically significant role for Mg2+ in modulating Ca2+ sensitivity and contraction regulation.","method":"Isothermal titration calorimetry, thermodynamic integration molecular dynamics simulations","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 1 — rigorous biophysical assay with computational validation, single lab study","pmids":["35838319"],"is_preprint":false},{"year":2021,"finding":"A de novo TNNC1 point mutation (G34S) reconstituted into skinned cardiomyocytes and fibers and into reconstituted thin filaments caused functional and structural impairments including altered contractile function and disrupted structural integrity of thin filaments; interaction with actin and inter-subunit troponin interactions were affected; the protein quality control system was also impaired as shown in patient myocardial tissue; levosimendan and EGCG stabilized thin filament structure and partially ameliorated contractile function in vitro.","method":"Skinned cardiomyocyte and fiber functional assays, reconstituted thin filament structural analysis, patient tissue protein quality control assessment, drug treatment in vitro","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays including patient tissue, single study","pmids":["34502534"],"is_preprint":false},{"year":2014,"finding":"In ovarian cancer cells, MFAP5 stromal signaling activates a FAK/CREB/TNNC1 signaling pathway to promote cancer cell motility and invasion; siRNA knockdown of MFAP5 decreased TNNC1-dependent ovarian tumor growth and metastasis in vivo.","method":"siRNA knockdown, in vitro motility/invasion assays, in vivo mouse tumor model, signaling pathway analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2/3 — functional knockdown with in vivo validation, pathway placement via signaling assays","pmids":["25277212"],"is_preprint":false},{"year":2020,"finding":"TNNC1 knockout in SKOV-3-13 ovarian cancer cells (CRISPR/Cas9) reduced proliferation, colony formation, wound healing, migration, and invasion; TNNC1-KO decreased phosphorylated AKT (Ser-473 and Thr-308), reduced active GSK-3β, decreased SNAIL and SLUG nuclear localization, shifted EMT markers (decreased N-cadherin and vimentin, increased E-cadherin), and suppressed F-actin polymerization, establishing that TNNC1 overexpression drives ovarian cancer metastasis through AKT/GSK-3β/EMT and actin cytoskeletal pathways.","method":"CRISPR/Cas9 knockout, migration/invasion assays, western blot for pathway components, immunofluorescence for transcription factor localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined molecular and phenotypic readouts across multiple assays, single lab","pmids":["33592378"],"is_preprint":false},{"year":2020,"finding":"In lung adenocarcinoma cells, ectopic TNNC1 expression inhibited KRASG12D-mediated anchorage-independent growth, inhibited colony formation, induced DNA damage, cell cycle arrest, and apoptosis; KRAS suppression enhanced TNNC1 expression while KRAS pathway activation correlated with TNNC1 downregulation, and TNNC1 knockdown enhanced invasiveness in vitro, establishing TNNC1 as a tumor suppressor downstream of KRAS signaling.","method":"Ectopic overexpression, siRNA knockdown, anchorage-independent growth assay, colony formation, flow cytometry (cell cycle/apoptosis), DNA damage assay","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple functional assays with gain- and loss-of-function, single lab","pmids":["32638704"],"is_preprint":false},{"year":2020,"finding":"TNNC1 promotes gemcitabine resistance in NSCLC cells by activating cytoprotective autophagy; TNNC1 silencing reduced autophagy and chemoresistance while overexpression increased both; blocking autophagy with 3-methyladenine restored gemcitabine sensitivity; FOXO3 silencing in resistant cells rescued the autophagy reduction caused by TNNC1 knockdown, placing TNNC1 upstream of FOXO3 in a chemoresistance autophagy pathway.","method":"siRNA knockdown, viral overexpression, autophagy assays (LC3 punctate, 3-MA inhibition), flow cytometry, epistasis via FOXO3 silencing","journal":"Medical science monitor","confidence":"Medium","confidence_rationale":"Tier 2/3 — epistasis experiment placing TNNC1 upstream of FOXO3, multiple functional assays, single lab","pmids":["32946432"],"is_preprint":false},{"year":2020,"finding":"LukS-PV inhibits HCC cell migration by downregulating TNNC1, which in turn inhibits phosphorylation of PI3K/AKT, thereby suppressing HCC cell migration; TNNC1 acts upstream of the PI3K/AKT pathway in HCC cells.","method":"Scratch assay, qRT-PCR, western blot, RNA sequencing, quantitative proteomics, KEGG/GSEA pathway analysis","journal":"OncoTargets and therapy","confidence":"Low","confidence_rationale":"Tier 3 — pathway inference from expression changes and western blot, no direct rescue or reconstitution","pmids":["33116603"],"is_preprint":false},{"year":2024,"finding":"KDM5D (histone demethylase) suppresses H3K4me3 modification in the E2F1 promoter, reducing E2F1 expression; E2F1 normally binds to the TNNC1 promoter to activate its transcription (confirmed by ChIP and dual luciferase reporter assay); thus KDM5D represses TNNC1 transcription indirectly through E2F1, and this axis controls HCC cell proliferation, migration, and invasion.","method":"ChIP assay (H3K4me3 and E2F1 binding), dual luciferase reporter assay, overexpression, in vivo nude mouse tumor model","journal":"Antioxidants & redox signaling","confidence":"Medium","confidence_rationale":"Tier 2 — direct ChIP and luciferase assays establishing transcriptional regulation of TNNC1 by E2F1 downstream of KDM5D","pmids":["38504588"],"is_preprint":false},{"year":2024,"finding":"Molecular dynamics simulations of cardiac troponin containing the TNNC1 G159D mutation showed that silybin B, EGCG, and resveratrol restore the phosphorylation-induced change in the TnC helix A/B angle and interdomain angle to wild-type values, and in vitro single thin filament motility assays confirmed these small molecules restore PKA phosphorylation-dependent modulation of Ca2+ dissociation from cTnC (lusitropy); in intact transgenic cardiomyocytes, these compounds restored the dobutamine-induced increase in relaxation speed blunted by cardiomyopathy mutations.","method":"Molecular dynamics simulation, single thin filament in vitro motility assay, intact transgenic mouse and guinea pig cardiomyocyte experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1/2 — in vitro reconstitution + MD simulation + intact cell validation; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2024.05.09.593307"],"is_preprint":true}],"current_model":"TNNC1-encoded cardiac troponin C (cTnC) is the Ca2+-sensing component of the troponin complex: Ca2+ binding to its regulatory N-domain (site II) induces an open conformation that engages the TnI switch region (residues 147-163), releasing TnI inhibitory regions from actin to activate contraction; the C-domain anchors cTnC constitutively in the complex; HCM-associated mutations increase Ca2+ (and Mg2+) binding affinity causing gain-of-Ca2+-sensitivity, DCM-associated mutations decrease Ca2+ sensitivity and impair PKA phosphorylation responses, and in non-muscle contexts TNNC1 acts upstream of AKT/GSK-3β/EMT and FOXO3-autophagy pathways to regulate cancer cell motility and chemoresistance, with its transcription regulated by the KDM5D/E2F1 epigenetic axis."},"narrative":{"teleology":[{"year":1998,"claim":"How TnI anchors to TnC was unknown; crystallography revealed that TnI N-terminal binding causes a 90° bend in the TnC central helix, creating a compact conformation with direct inter-lobe contacts, establishing the structural basis of TnC–TnI anchoring.","evidence":"X-ray crystallography of TnC–TnI(1-47) complex at 2.3 Å","pmids":["9560191"],"confidence":"High","gaps":["Structure was of an isolated binary complex, not the full ternary troponin on actin","Ca²⁺-free state not captured"]},{"year":1999,"claim":"The mechanism by which Ca²⁺ couples TnC conformational change to TnI engagement was unclear; NMR showed that the TnI switch peptide binds TnC's regulatory N-domain only in the Ca²⁺-saturated state, inducing an open hydrophobic cleft, establishing Ca²⁺-gated TnI binding as the activation switch.","evidence":"Multinuclear multidimensional NMR solution structure of cNTnC with TnI switch peptide","pmids":["10387074"],"confidence":"High","gaps":["Study used isolated peptide rather than full-length TnI in the ternary complex","Kinetics of opening/closing not resolved"]},{"year":2003,"claim":"The architecture of the full ternary troponin core on the thin filament was unknown; the crystal structure revealed an IT arm coiled-coil and showed that Ca²⁺ binding to cTnC removes the TnI C-terminus from actin, providing the first atomic model of the activation mechanism in the complete core domain.","evidence":"X-ray crystallography of human cardiac troponin core domain (TnC/TnI/TnT) in Ca²⁺-saturated form","pmids":["12840750"],"confidence":"High","gaps":["Structure captured only the Ca²⁺-saturated state; apo transition not visualized","Tropomyosin and actin not present in the crystal"]},{"year":2004,"claim":"Whether TNNC1 mutations could cause cardiomyopathy was unknown; identification of a DCM-causing TNNC1 missense mutation that impairs troponin subunit interaction established TNNC1 as a dilated cardiomyopathy gene.","evidence":"Genetic screening of DCM families with two-hybrid luciferase interaction assay","pmids":["15542288"],"confidence":"Medium","gaps":["Functional data relied on a two-hybrid assay without reciprocal reconstitution in skinned fibers","Single family reported"]},{"year":2008,"claim":"How TNNC1 mutations produce HCM was unclear; reconstitution of four HCM-associated cTnC mutants into skinned fibers demonstrated increased Ca²⁺ sensitivity of force, establishing a gain-of-function Ca²⁺-sensitization mechanism parallel to other sarcomeric HCM genes.","evidence":"Skinned fiber reconstitution with recombinant mutant cTnC, force-pCa assays","pmids":["18572189"],"confidence":"High","gaps":["In vivo consequences not yet tested at this stage","Heterozygous dosage effects not modeled"]},{"year":2011,"claim":"The mechanistic basis of DCM-linked TNNC1 variants and their effect on β-adrenergic regulation was unexplored; skinned fiber and ATPase reconstitution showed DCM variants decrease Ca²⁺ sensitivity and impair or abolish PKA phosphorylation-dependent modulation, linking loss of lusitropy to DCM pathogenesis.","evidence":"Skinned fiber force, actomyosin ATPase, PKA phosphorylation, and CD spectroscopy with four DCM variants","pmids":["21832052"],"confidence":"High","gaps":["No in vivo animal model for DCM variants at the time","Structural mechanism of impaired PKA response not resolved at atomic level"]},{"year":2012,"claim":"Whether HCM mutations directly alter Ca²⁺ binding affinity versus downstream coupling was debated; fluorescence and reconstitution studies of A31S showed a direct increase in regulatory site Ca²⁺ affinity across increasing levels of thin filament complexity, pinpointing the defect to the Ca²⁺ binding step itself.","evidence":"Fluorescence Ca²⁺ titration in isolated cTnC, troponin complex, thin filament ± myosin S1; skinned fibers; CD","pmids":["22815480"],"confidence":"High","gaps":["Single mutation studied; generalizability to all HCM variants not confirmed","In vivo validation pending"]},{"year":2015,"claim":"Whether increased Ca²⁺ sensitivity in vitro translates to diastolic dysfunction in vivo was untested; TNNC1-A8V knock-in mice showed dose-dependent Ca²⁺ sensitization, prolonged relaxation, diastolic dysfunction, hypertrophy, and fibrosis, providing the first in vivo genetic proof of the gain-of-function HCM mechanism.","evidence":"Knock-in mouse model with echocardiography, pressure-volume loops, skinned fibers, flash photolysis, LC-MS","pmids":["26304555"],"confidence":"High","gaps":["Only one mutation modeled in vivo","Mutant cTnC incorporated at only ~21%, leaving natural dosage effects uncertain"]},{"year":2020,"claim":"TNNC1's role outside the sarcomere was emerging; CRISPR knockout in ovarian cancer cells demonstrated that TNNC1 activates AKT/GSK-3β signaling, promotes EMT, and drives F-actin remodeling to support invasion, while epistasis experiments in NSCLC placed TNNC1 upstream of FOXO3-dependent autophagy in chemoresistance.","evidence":"CRISPR/Cas9 KO (ovarian cancer), siRNA/overexpression with FOXO3 epistasis (NSCLC), migration/invasion assays, western blot","pmids":["33592378","32946432"],"confidence":"Medium","gaps":["Direct binding partners linking cTnC to AKT or FOXO3 are unidentified","Cancer findings are from cell lines; in vivo validation limited"]},{"year":2022,"claim":"Whether Mg²⁺ competition at the regulatory site is physiologically significant and affected by disease mutations was unresolved; ITC showed that HCM variants increase affinity for both Ca²⁺ and Mg²⁺ at site II, establishing Mg²⁺ as a relevant modulator of Ca²⁺ sensitivity and contraction regulation.","evidence":"Isothermal titration calorimetry and thermodynamic integration MD simulations","pmids":["35838319"],"confidence":"Medium","gaps":["Functional consequences of Mg²⁺ competition on force development not directly measured","Single-site measurements may not capture cooperativity on the thin filament"]},{"year":2024,"claim":"How TNNC1 transcription is regulated was unknown; ChIP and luciferase assays showed that E2F1 directly binds the TNNC1 promoter and is itself repressed by KDM5D-mediated H3K4me3 demethylation at the E2F1 locus, establishing a KDM5D/E2F1/TNNC1 transcriptional axis in hepatocellular carcinoma.","evidence":"ChIP for H3K4me3 and E2F1, dual luciferase reporter, overexpression, nude mouse xenograft","pmids":["38504588"],"confidence":"Medium","gaps":["Relevance of this transcriptional axis to cardiac tissue unknown","Whether E2F1-driven TNNC1 expression occurs in normal physiology or is cancer-specific is unclear"]},{"year":null,"claim":"Key open questions include: the structural basis of how individual cardiomyopathy mutations alter Mg²⁺/Ca²⁺ selectivity and PKA-responsiveness at atomic resolution; the direct molecular partners through which non-sarcomeric TNNC1 engages AKT and autophagy pathways; and whether pharmacological restoration of lusitropy (e.g., silybin B, EGCG) translates to therapeutic benefit in vivo.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of mutant cTnC in the apo-to-Ca²⁺ transition","Non-sarcomeric binding partners remain unidentified","No clinical trial data for Ca²⁺-sensitizer correction of TNNC1-linked cardiomyopathy"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3,4,6,7,8]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,2,10]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2,10,12]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,1,3,4,6,7,8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,5,6,8,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,12,14,15]}],"complexes":["cardiac troponin complex (cTnC/cTnI/cTnT)"],"partners":["TNNI3","TNNT2","ACTA1","TPM1","FOXO3","AKT1","E2F1"],"other_free_text":[]},"mechanistic_narrative":"TNNC1 encodes cardiac troponin C (cTnC), the Ca²⁺-sensing subunit of the cardiac troponin complex that transduces cytosolic Ca²⁺ signals into thin-filament activation and sarcomere contraction. Its regulatory N-domain (site II) binds Ca²⁺ to adopt an open conformation that engages the TnI switch peptide (residues 147–163), releasing the TnI inhibitory region from actin and permitting tropomyosin movement; the C-domain constitutively anchors cTnC in the troponin complex via two high-affinity Ca²⁺/Mg²⁺ sites [PMID:12840750, PMID:10387074, PMID:26232335]. Missense mutations in TNNC1 cause hypertrophic cardiomyopathy through gain-of-function increases in Ca²⁺ (and Mg²⁺) binding affinity and myofilament Ca²⁺ sensitivity, and dilated cardiomyopathy through decreased Ca²⁺ sensitivity and impaired PKA-phosphorylation responsiveness [PMID:18572189, PMID:21832052, PMID:26304555]. Outside the sarcomere, TNNC1 is transcriptionally regulated by the KDM5D/E2F1 axis and signals through AKT/GSK-3β/EMT and FOXO3-autophagy pathways to modulate cancer cell motility and chemoresistance [PMID:33592378, PMID:32946432, PMID:38504588]."},"prefetch_data":{"uniprot":{"accession":"P63316","full_name":"Troponin C, slow skeletal and cardiac muscles","aliases":[],"length_aa":161,"mass_kda":18.4,"function":"Troponin is the central regulatory protein of striated muscle contraction. Tn consists of three components: Tn-I which is the inhibitor of actomyosin ATPase, Tn-T which contains the binding site for tropomyosin and Tn-C. The binding of calcium to Tn-C abolishes the inhibitory action of Tn on actin filaments","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P63316/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TNNC1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TNNC1","total_profiled":1310},"omim":[{"mim_id":"615396","title":"LEFT VENTRICULAR NONCOMPACTION 10; LVNC10","url":"https://www.omim.org/entry/615396"},{"mim_id":"613243","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 13; CMH13","url":"https://www.omim.org/entry/613243"},{"mim_id":"611879","title":"CARDIOMYOPATHY, DILATED, 1Z; CMD1Z","url":"https://www.omim.org/entry/611879"},{"mim_id":"600958","title":"MYOSIN-BINDING PROTEIN C, CARDIAC; MYBPC3","url":"https://www.omim.org/entry/600958"},{"mim_id":"192600","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 1; CMH1","url":"https://www.omim.org/entry/192600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Actin filaments","reliability":"Approved"},{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":8750.1},{"tissue":"skeletal muscle","ntpm":19761.9},{"tissue":"tongue","ntpm":11563.6}],"url":"https://www.proteinatlas.org/search/TNNC1"},"hgnc":{"alias_symbol":[],"prev_symbol":["TNNC"]},"alphafold":{"accession":"P19429","domains":[{"cath_id":"1.20.5","chopping":"43-80","consensus_level":"medium","plddt":96.6466,"start":43,"end":80},{"cath_id":"1.20.5","chopping":"90-140","consensus_level":"medium","plddt":92.8155,"start":90,"end":140},{"cath_id":"1.20.5","chopping":"150-182","consensus_level":"medium","plddt":68.31,"start":150,"end":182}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P19429","model_url":"https://alphafold.ebi.ac.uk/files/AF-P19429-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P19429-F1-predicted_aligned_error_v6.png","plddt_mean":78.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TNNC1","jax_strain_url":"https://www.jax.org/strain/search?query=TNNC1"},"sequence":{"accession":"P19429","fasta_url":"https://rest.uniprot.org/uniprotkb/P19429.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P19429/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P19429"}},"corpus_meta":[{"pmid":"20215591","id":"PMC_20215591","title":"Coding sequence rare variants identified in MYBPC3, MYH6, TPM1, TNNC1, and TNNI3 from 312 patients with familial or idiopathic dilated cardiomyopathy.","date":"2010","source":"Circulation. 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The C-domain (cCTnC) contains two high-affinity Ca2+/Mg2+-binding sites that maintain an open conformation anchored to the troponin complex. The regulatory N-domain (cNTnC) contains a single low-affinity Ca2+-binding site; upon Ca2+ binding, cNTnC adopts an open conformation that engages the switch region of troponin I, displacing inhibitory regions of troponin I from actin to permit muscle contraction.\",\n      \"method\": \"Structural and biochemical characterization integrated from multiple prior studies; NMR and X-ray crystallography with functional validation\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural and biochemical mechanism replicated across many labs, well-established model\",\n      \"pmids\": [\"26232335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Novel TNNC1 missense mutations (A8V, C84Y, E134D, D145E) were identified in HCM patients; recombinant mutant cTnC proteins reconstituted into skinned fibers showed increased Ca2+ sensitivity of force development (A8V, C84Y, D145E) and force recovery (A8V, D145E), establishing that gain-of-Ca2+-sensitivity is the mechanistic consequence of these HCM-associated mutations.\",\n      \"method\": \"Recombinant protein reconstitution into skinned muscle fibers, Ca2+ sensitivity of force development assays\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with functional assays, multiple mutations tested, replicated in subsequent studies\",\n      \"pmids\": [\"18572189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DCM-associated TNNC1 rare variants (Y5H, M103I, D145E, I148V) reconstituted into skinned fibers showed decreased Ca2+ sensitivity of force development (Y5H, M103I). Variants Y5H and I148V diminished, and M103I abolished, the effects of PKA phosphorylation on Ca2+ sensitivity. M103I also decreased actomyosin ATPase activation. CD spectroscopy showed all mutants (except I148V in Ca2+/Mg2+ conditions) decreased α-helical content, indicating structural alterations underlie their functional effects.\",\n      \"method\": \"Recombinant mutant cTnC reconstitution into porcine papillary skinned fibers, actomyosin ATPase assay, circular dichroism spectroscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal in vitro methods (skinned fibers, ATPase, CD) on multiple variants\",\n      \"pmids\": [\"21832052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The HCM-associated TNNC1-A31S mutation increases Ca2+ affinity in isolated cTnC, the troponin complex, thin filament, and thin filament with myosin subfragment 1, and increases Ca2+ sensitivity of skinned fiber force development without affecting maximal contractile force. Reconstituted actomyosin ATPase assays showed increased activation without impaired inhibition. These effects directly alter myofilament Ca2+ sensitivity and may contribute to arrhythmogenesis.\",\n      \"method\": \"Fluorescence Ca2+-binding assays, skinned fiber reconstitution, actomyosin ATPase assay, circular dichroism\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal in vitro methods with rigorous controls\",\n      \"pmids\": [\"22815480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Knock-in mice carrying TNNC1-A8V show Ca2+ sensitivity of contraction in skinned fibers that increases with mutant gene dose (homozygote > heterozygote > WT). Intact cardiomyocytes show reduced diastolic sarcomeric length, increased shortening, and prolonged Ca2+ and contractile transients. Homozygous KI mice display decreased ventricular dimensions, diastolic dysfunction, and enhanced systolic function, with fibrosis and papillary muscle hypertrophy, demonstrating that increased Ca2+-binding affinity of the thin filament drives cellular remodeling and cardiomyopathy in vivo.\",\n      \"method\": \"Knock-in mouse model, echocardiography, pressure-volume studies, Ca2+ transient measurements, skinned fiber Ca2+ sensitivity assays, LC-MS for mutant protein incorporation\",\n      \"journal\": \"Circulation. Cardiovascular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo genetic model with multiple orthogonal functional readouts\",\n      \"pmids\": [\"26304555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Isothermal titration calorimetry (ITC) and thermodynamic integration simulations of HCM-associated TNNC1 variants (A8V, L29Q, A31S, L48Q, Q50R, C84Y) demonstrated that these mutations elevate the Ca2+ affinity of the regulatory site II of cNTnC and also increase Mg2+ affinity at the same site, revealing that physiological Mg2+ competes with Ca2+ for binding to the regulatory site and modifies the Ca2+-binding properties of HCM-associated cTnC variants.\",\n      \"method\": \"Isothermal titration calorimetry (ITC), thermodynamic integration (TI) molecular dynamics simulations\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ITC with computational validation, multiple variants tested\",\n      \"pmids\": [\"35838319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The de novo TNNC1 p.G34S mutation (causing non-compaction cardiomyopathy) impairs contractile function in skinned cardiomyocytes and fibers, disrupts interaction of TnC with actin and inter-subunit troponin interactions, and compromises the structural integrity of reconstituted thin filaments. Additionally, the protein quality control system is perturbed in patient myocardial tissue. Troponin-targeting agents levosimendan and EGCg partially restore structural integrity and contractile function in vitro.\",\n      \"method\": \"Skinned cardiomyocytes and fibers, reconstituted thin filaments, protein interaction assays, patient myocardial tissue analysis, in vitro drug treatment\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays but single study, patient tissue corroborates findings\",\n      \"pmids\": [\"34502534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In ovarian cancer cells, stromal MFAP5 activates a FAK/CREB/TNNC1 signalling pathway to promote cancer cell motility and invasion. Functional studies showed that this pathway mediates the effect of MFAP5 on metastatic potential, and siRNA-mediated knockdown of MFAP5 decreased ovarian tumour growth and metastasis in vivo.\",\n      \"method\": \"siRNA knockdown, in vitro motility/invasion assays, in vivo nanoparticle-siRNA delivery, pathway inhibitor studies\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays in vitro and in vivo, but TNNC1's direct molecular role in this non-muscle context is not fully resolved\",\n      \"pmids\": [\"25277212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRISPR/Cas9 knockout of TNNC1 in ovarian cancer cells reduces proliferation, migration, and invasion, and suppresses F-actin polymerization. TNNC1-KO cells show decreased phospho-AKT (Ser-473 and Thr-308) and inactive GSK-3β, with downstream reduction of SNAIL and SLUG and EMT markers (N-cadherin, vimentin) and increased E-cadherin, placing TNNC1 upstream of AKT/GSK-3β/EMT signaling in ovarian cancer.\",\n      \"method\": \"CRISPR/Cas9 knockout, western blot for pathway components, wound healing/migration/invasion assays, F-actin staining\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined pathway readouts, but non-muscle context and single study\",\n      \"pmids\": [\"33592378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KDM5D, a histone H3K4me3 demethylase, suppresses E2F1 expression by reducing H3K4me3 in the E2F1 promoter; E2F1 in turn directly binds the TNNC1 promoter (confirmed by ChIP and dual luciferase assay) and activates TNNC1 transcription in hepatocellular carcinoma. Thus TNNC1 is a transcriptional target of E2F1, regulated epigenetically via KDM5D-mediated H3K4 demethylation.\",\n      \"method\": \"ChIP assay (H3K4me3 modification at E2F1 promoter; E2F1 binding at TNNC1 promoter), dual luciferase reporter assay, western blot, KDM5D overexpression, in vivo nude mouse model\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ChIP and luciferase assays establish E2F1-TNNC1 promoter interaction, but single study in cancer cell line context\",\n      \"pmids\": [\"38504588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Nutraceuticals silybin B, resveratrol, and EGCG restore PKA phosphorylation-dependent modulation of Ca2+ dissociation from cTnC (lusitropy) that is uncoupled by cardiomyopathy mutations including TNNC1-G159D. Molecular dynamics simulations show these molecules intercalate between the N-terminal peptide of troponin I and troponin C in the unphosphorylated state, restoring the phosphorylation-induced change in the TnC helix A/B angle and interdomain angle to wild-type values.\",\n      \"method\": \"Single thin filament in vitro motility assays, molecular dynamics simulations, intact transgenic cardiomyocytes (ACTC E99K mouse, TNNT2 R92Q guinea pig)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution, MD simulations, and cell studies, but preprint and focused on drug mechanism\",\n      \"pmids\": [\"bio_10.1101_2024.05.09.593307\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TNNC1-encoded cardiac troponin C (cTnC) is the Ca2+-sensing subunit of the troponin complex in cardiac and slow-twitch skeletal muscle: its regulatory N-domain (cNTnC) binds a single Ca2+ ion at site II (also competed by physiological Mg2+) to adopt an open conformation that engages the troponin I switch region, releasing inhibitory constraints on actin and enabling actomyosin cross-bridge cycling; HCM-associated mutations (A8V, C84Y, A31S, etc.) increase Ca2+/Mg2+ affinity and Ca2+ sensitivity of force development, while DCM-associated mutations (Y5H, M103I) decrease Ca2+ sensitivity and impair PKA phosphorylation-dependent modulation of Ca2+ dissociation, with these functional alterations driving cardiac remodeling and disease as confirmed in knock-in mouse models.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure of the core domain of human cardiac troponin (including TnC, TnI, TnT) in the Ca2+-saturated form was solved, revealing that the core domain is divided into structurally distinct subdomains connected by flexible linkers, with an IT arm (alpha-helical coiled-coil between TnT and TnI) forming a rigid asymmetric structure, and showing that Ca2+ binding to the regulatory site of TnC removes the carboxy-terminal portion of TnI from actin, altering the mobility and/or flexibility of troponin and tropomyosin on the actin filament.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of ternary complex with functional interpretation, foundational study\",\n      \"pmids\": [\"12840750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The cardiac TnI switch region peptide (residues 147-163) binds to the regulatory N-domain of cardiac TnC (cNTnC) only in the Ca2+-saturated state, inducing an open conformation in cNTnC similar to Ca2+-saturated skeletal NTnC; the bound peptide adopts an alpha-helical conformation (residues 150-157) and forms hydrophobic interactions with cNTnC, establishing that Ca2+ is required for the structural opening of cNTnC that enables cTnI binding and muscle regulation.\",\n      \"method\": \"Multinuclear multidimensional NMR spectroscopy, solution structure determination\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR solution structure with functional validation, well-cited foundational study\",\n      \"pmids\": [\"10387074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Crystal structure of TnC in complex with the N-terminal fragment of TnI (TnI1-47) at 2.3 Å resolution revealed that the central connecting alpha-helix of TnC is unwound and bent by 90° upon TnI binding, giving TnC a compact globular shape with direct N- and C-terminal lobe interactions; the TnI1-47 alpha-helix stabilizes this compact conformation through contacts with both lobes, with the amphiphilic C-end binding in the hydrophobic pocket of the TnC C-lobe.\",\n      \"method\": \"X-ray crystallography (single isomorphous replacement + MAD)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure of TnC/TnI complex, well-cited foundational study\",\n      \"pmids\": [\"9560191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cardiac TnC (cTnC) is a two-domain EF-hand protein: the C-domain (cCTnC) contains two high-affinity Ca2+/Mg2+ binding sites always occupied under physiologic conditions, anchoring the protein in the troponin complex in an open conformation; the regulatory N-domain (cNTnC) contains a single low-affinity site that, upon Ca2+ binding, adopts an open conformation that binds the switch region of TnI, releasing TnI inhibitory regions from actin to allow contraction; calcium sensitivity can be modified by drugs stabilizing open cNTnC, PKA-mediated phosphorylation of TnI, or thin-filament protein interactions.\",\n      \"method\": \"Structural and biochemical review integrating prior reconstitution, NMR, crystallography, and mutagenesis data\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — synthesis of multiple Tier 1 experimental studies; mechanistic model supported by orthogonal methods across labs\",\n      \"pmids\": [\"26232335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Novel TNNC1 missense mutations (A8V, C84Y, E134D, D145E) identified in HCM patients; recombinant mutant cTnC proteins reconstituted into skinned fibers showed increased Ca2+ sensitivity of force development (A8V, C84Y, D145E) and force recovery (A8V, D145E), consistent with the gain-of-function Ca2+-sensitization mechanism seen in other sarcomeric HCM mutations, establishing TNNC1 as an HCM-susceptibility gene.\",\n      \"method\": \"Skinned fiber reconstitution, force development and recovery assays, genetic screening\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution with multiple mutants across large cohort, replicated functional phenotype\",\n      \"pmids\": [\"18572189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A TNNC1 missense mutation identified in familial DCM was shown to significantly impair mutated troponin C interaction within the troponin complex compared to wild-type by two-hybrid luciferase assay, indicating altered regulation of myocardial contractility; this established cardiac troponin C as a novel DCM gene with complete penetrance.\",\n      \"method\": \"Genetic screening (SSCP/DHPLC/sequencing), two-hybrid luciferase interaction assay\",\n      \"journal\": \"Journal of the American College of Cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — functional interaction assay supporting mechanism, single lab study\",\n      \"pmids\": [\"15542288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Four TNNC1 DCM-associated rare variants (Y5H, M103I, D145E, I148V) reconstituted into porcine skinned fibers demonstrated decreased Ca2+ sensitivity of force development (Y5H, M103I); Y5H and I148V diminished and M103I abolished the effects of PKA phosphorylation on Ca2+ sensitivity; M103I decreased actomyosin ATPase activation at high Ca2+; CD spectroscopy showed most mutants decreased alpha-helical content, indicating structural changes underlie the functional deficits.\",\n      \"method\": \"Skinned fiber reconstitution, actomyosin ATPase assay, PKA phosphorylation assay, circular dichroism spectroscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — multiple orthogonal functional methods (force, ATPase, PKA response, CD structure) in single study\",\n      \"pmids\": [\"21832052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The TNNC1-A31S mutation reconstituted into cardiac skinned fibers increased Ca2+ sensitivity with no effect on maximal force; reconstituted actomyosin ATPase assays showed the mutant increased ATPase activation without altering inhibition; fluorescence studies showed increased Ca2+ affinity in isolated cTnC, the troponin complex, thin filament, and thin filament with myosin subfragment 1; circular dichroism showed no global structural change, indicating the mutation directly increases Ca2+ binding affinity at the regulatory site.\",\n      \"method\": \"Skinned fiber reconstitution, actomyosin ATPase assay, fluorescence Ca2+ affinity measurements, circular dichroism spectroscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — multiple orthogonal methods including reconstitution, ATPase, fluorescence, CD in single study\",\n      \"pmids\": [\"22815480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Knock-in mice carrying the TNNC1-A8V mutation showed dose-dependent increases in Ca2+ sensitivity of contraction in skinned fibers (homozygote > heterozygote > wild-type), reduced diastolic sarcomeric length, increased shortening, prolonged Ca2+ and contractile transients in intact cardiomyocytes, slower relaxation on flash photolysis of diazo-2, and developed diastolic dysfunction with atrial enlargement, papillary muscle hypertrophy, and fibrosis in vivo; liquid chromatography-MS confirmed ~21% mutant cTnC incorporation into the myofilament.\",\n      \"method\": \"Knock-in mouse model, echocardiography, pressure-volume studies, skinned fiber Ca2+ sensitivity, flash photolysis, cardiomyocyte sarcomere imaging, LC-MS\",\n      \"journal\": \"Circulation. Cardiovascular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vivo genetic model with multiple orthogonal mechanistic readouts confirming Ca2+ sensitization mechanism\",\n      \"pmids\": [\"26304555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Isothermal titration calorimetry (ITC) and thermodynamic integration simulations demonstrated that physiological Mg2+ concentrations compete with Ca2+ for binding to regulatory site II of cTnC; HCM-associated TNNC1 variants (A8V, L29Q, A31S) elevated affinity for both Ca2+ and Mg2+, while variants adjacent to the EF-hand motif (L48Q, Q50R, C84Y) had larger effects on affinity and binding thermodynamics, indicating a physiologically significant role for Mg2+ in modulating Ca2+ sensitivity and contraction regulation.\",\n      \"method\": \"Isothermal titration calorimetry, thermodynamic integration molecular dynamics simulations\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — rigorous biophysical assay with computational validation, single lab study\",\n      \"pmids\": [\"35838319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo TNNC1 point mutation (G34S) reconstituted into skinned cardiomyocytes and fibers and into reconstituted thin filaments caused functional and structural impairments including altered contractile function and disrupted structural integrity of thin filaments; interaction with actin and inter-subunit troponin interactions were affected; the protein quality control system was also impaired as shown in patient myocardial tissue; levosimendan and EGCG stabilized thin filament structure and partially ameliorated contractile function in vitro.\",\n      \"method\": \"Skinned cardiomyocyte and fiber functional assays, reconstituted thin filament structural analysis, patient tissue protein quality control assessment, drug treatment in vitro\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays including patient tissue, single study\",\n      \"pmids\": [\"34502534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In ovarian cancer cells, MFAP5 stromal signaling activates a FAK/CREB/TNNC1 signaling pathway to promote cancer cell motility and invasion; siRNA knockdown of MFAP5 decreased TNNC1-dependent ovarian tumor growth and metastasis in vivo.\",\n      \"method\": \"siRNA knockdown, in vitro motility/invasion assays, in vivo mouse tumor model, signaling pathway analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — functional knockdown with in vivo validation, pathway placement via signaling assays\",\n      \"pmids\": [\"25277212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TNNC1 knockout in SKOV-3-13 ovarian cancer cells (CRISPR/Cas9) reduced proliferation, colony formation, wound healing, migration, and invasion; TNNC1-KO decreased phosphorylated AKT (Ser-473 and Thr-308), reduced active GSK-3β, decreased SNAIL and SLUG nuclear localization, shifted EMT markers (decreased N-cadherin and vimentin, increased E-cadherin), and suppressed F-actin polymerization, establishing that TNNC1 overexpression drives ovarian cancer metastasis through AKT/GSK-3β/EMT and actin cytoskeletal pathways.\",\n      \"method\": \"CRISPR/Cas9 knockout, migration/invasion assays, western blot for pathway components, immunofluorescence for transcription factor localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined molecular and phenotypic readouts across multiple assays, single lab\",\n      \"pmids\": [\"33592378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In lung adenocarcinoma cells, ectopic TNNC1 expression inhibited KRASG12D-mediated anchorage-independent growth, inhibited colony formation, induced DNA damage, cell cycle arrest, and apoptosis; KRAS suppression enhanced TNNC1 expression while KRAS pathway activation correlated with TNNC1 downregulation, and TNNC1 knockdown enhanced invasiveness in vitro, establishing TNNC1 as a tumor suppressor downstream of KRAS signaling.\",\n      \"method\": \"Ectopic overexpression, siRNA knockdown, anchorage-independent growth assay, colony formation, flow cytometry (cell cycle/apoptosis), DNA damage assay\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple functional assays with gain- and loss-of-function, single lab\",\n      \"pmids\": [\"32638704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TNNC1 promotes gemcitabine resistance in NSCLC cells by activating cytoprotective autophagy; TNNC1 silencing reduced autophagy and chemoresistance while overexpression increased both; blocking autophagy with 3-methyladenine restored gemcitabine sensitivity; FOXO3 silencing in resistant cells rescued the autophagy reduction caused by TNNC1 knockdown, placing TNNC1 upstream of FOXO3 in a chemoresistance autophagy pathway.\",\n      \"method\": \"siRNA knockdown, viral overexpression, autophagy assays (LC3 punctate, 3-MA inhibition), flow cytometry, epistasis via FOXO3 silencing\",\n      \"journal\": \"Medical science monitor\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — epistasis experiment placing TNNC1 upstream of FOXO3, multiple functional assays, single lab\",\n      \"pmids\": [\"32946432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LukS-PV inhibits HCC cell migration by downregulating TNNC1, which in turn inhibits phosphorylation of PI3K/AKT, thereby suppressing HCC cell migration; TNNC1 acts upstream of the PI3K/AKT pathway in HCC cells.\",\n      \"method\": \"Scratch assay, qRT-PCR, western blot, RNA sequencing, quantitative proteomics, KEGG/GSEA pathway analysis\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — pathway inference from expression changes and western blot, no direct rescue or reconstitution\",\n      \"pmids\": [\"33116603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KDM5D (histone demethylase) suppresses H3K4me3 modification in the E2F1 promoter, reducing E2F1 expression; E2F1 normally binds to the TNNC1 promoter to activate its transcription (confirmed by ChIP and dual luciferase reporter assay); thus KDM5D represses TNNC1 transcription indirectly through E2F1, and this axis controls HCC cell proliferation, migration, and invasion.\",\n      \"method\": \"ChIP assay (H3K4me3 and E2F1 binding), dual luciferase reporter assay, overexpression, in vivo nude mouse tumor model\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct ChIP and luciferase assays establishing transcriptional regulation of TNNC1 by E2F1 downstream of KDM5D\",\n      \"pmids\": [\"38504588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Molecular dynamics simulations of cardiac troponin containing the TNNC1 G159D mutation showed that silybin B, EGCG, and resveratrol restore the phosphorylation-induced change in the TnC helix A/B angle and interdomain angle to wild-type values, and in vitro single thin filament motility assays confirmed these small molecules restore PKA phosphorylation-dependent modulation of Ca2+ dissociation from cTnC (lusitropy); in intact transgenic cardiomyocytes, these compounds restored the dobutamine-induced increase in relaxation speed blunted by cardiomyopathy mutations.\",\n      \"method\": \"Molecular dynamics simulation, single thin filament in vitro motility assay, intact transgenic mouse and guinea pig cardiomyocyte experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro reconstitution + MD simulation + intact cell validation; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.05.09.593307\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TNNC1-encoded cardiac troponin C (cTnC) is the Ca2+-sensing component of the troponin complex: Ca2+ binding to its regulatory N-domain (site II) induces an open conformation that engages the TnI switch region (residues 147-163), releasing TnI inhibitory regions from actin to activate contraction; the C-domain anchors cTnC constitutively in the complex; HCM-associated mutations increase Ca2+ (and Mg2+) binding affinity causing gain-of-Ca2+-sensitivity, DCM-associated mutations decrease Ca2+ sensitivity and impair PKA phosphorylation responses, and in non-muscle contexts TNNC1 acts upstream of AKT/GSK-3β/EMT and FOXO3-autophagy pathways to regulate cancer cell motility and chemoresistance, with its transcription regulated by the KDM5D/E2F1 epigenetic axis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TNNC1 encodes cardiac troponin C (cTnC), the Ca²⁺-sensing subunit of the cardiac and slow-skeletal-muscle troponin complex that couples cytoplasmic Ca²⁺ transients to sarcomere activation. Its regulatory N-domain binds a single Ca²⁺ ion at site II—where physiological Mg²⁺ also competes—triggering an open conformation that engages the troponin I switch region, displacing inhibitory contacts from actin and permitting actomyosin cross-bridge cycling [PMID:26232335, PMID:35838319]. Gain-of-function TNNC1 mutations (A8V, C84Y, A31S) that increase Ca²⁺/Mg²⁺ affinity and myofilament Ca²⁺ sensitivity cause hypertrophic cardiomyopathy, as demonstrated by dose-dependent diastolic dysfunction and remodeling in A8V knock-in mice, whereas loss-of-function mutations (Y5H, M103I) that decrease Ca²⁺ sensitivity and impair PKA-phosphorylation-dependent lusitropy are associated with dilated cardiomyopathy [PMID:18572189, PMID:21832052, PMID:22815480, PMID:26304555]. Outside the myocardium, TNNC1 is transcriptionally activated by E2F1 and participates in AKT/GSK-3β/EMT signaling in cancer cells, where its knockout suppresses proliferation, migration, and F-actin polymerization [PMID:33592378, PMID:38504588].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"The discovery that HCM-associated TNNC1 missense mutations (A8V, C84Y, D145E) increase Ca²⁺ sensitivity of skinned-fiber force development established that gain-of-Ca²⁺-sensitivity is a unifying mechanistic consequence of cTnC mutations linked to hypertrophic cardiomyopathy.\",\n      \"evidence\": \"Recombinant mutant cTnC reconstituted into skinned muscle fibers with Ca²⁺–force relationship assays\",\n      \"pmids\": [\"18572189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo model to confirm remodeling consequences\", \"Mechanism by which increased Ca²⁺ sensitivity drives hypertrophy not resolved\", \"No assessment of Mg²⁺ competition at site II\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Characterization of DCM-associated TNNC1 variants (Y5H, M103I) revealed that the opposite functional defect—decreased Ca²⁺ sensitivity and impaired PKA-phosphorylation modulation—distinguishes dilated cardiomyopathy variants from HCM variants, establishing a bidirectional Ca²⁺-sensitivity paradigm for TNNC1 disease mutations.\",\n      \"evidence\": \"Skinned porcine papillary fibers, actomyosin ATPase assay, circular dichroism spectroscopy on multiple recombinant variants\",\n      \"pmids\": [\"21832052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo DCM model generated\", \"Structural basis for impaired PKA-dependent modulation not resolved at atomic level\", \"Effect on diastolic relaxation kinetics not measured\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that the HCM mutation A31S increases Ca²⁺ affinity at every level of thin-filament complexity—from isolated cTnC through the intact thin filament with myosin—established that the gain-of-function phenotype is preserved across reconstitution hierarchy, not an artifact of isolated protein studies.\",\n      \"evidence\": \"Fluorescence-based Ca²⁺ binding assays at multiple reconstitution levels, skinned fiber force measurements, actomyosin ATPase assays\",\n      \"pmids\": [\"22815480\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo confirmation of arrhythmogenesis\", \"Cooperative effects in intact myocardium not assessed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of TNNC1 as a downstream effector in a stromal MFAP5/FAK/CREB signaling axis in ovarian cancer revealed an unexpected non-muscle role for cTnC in promoting cancer cell motility and invasion.\",\n      \"evidence\": \"siRNA knockdown, motility/invasion assays, and in vivo nanoparticle-siRNA delivery in ovarian cancer models\",\n      \"pmids\": [\"25277212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target of cTnC in non-muscle cells unknown\", \"Whether cTnC functions via Ca²⁺ sensing or a distinct mechanism in cancer not resolved\", \"Single signaling pathway context\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The A8V knock-in mouse provided the first in vivo genetic proof that increased thin-filament Ca²⁺ affinity from a TNNC1 mutation is sufficient to drive dose-dependent diastolic dysfunction, fibrosis, and cardiac hypertrophy, closing the gap between in vitro Ca²⁺-sensitivity changes and disease phenotype.\",\n      \"evidence\": \"Knock-in mouse model with echocardiography, pressure-volume analysis, cardiomyocyte Ca²⁺ transients, skinned fiber assays, LC-MS confirmation of mutant protein incorporation\",\n      \"pmids\": [\"26304555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No equivalent DCM knock-in model for loss-of-function variants\", \"Molecular basis of prolonged Ca²⁺ transients not fully dissected\", \"Arrhythmia susceptibility not systematically evaluated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The G34S mutation causing non-compaction cardiomyopathy was shown to disrupt TnC–actin and inter-subunit troponin interactions, and to compromise thin-filament structural integrity, expanding the disease spectrum of TNNC1 mutations beyond HCM and DCM and revealing that some mutations cause structural rather than purely affinity-based defects.\",\n      \"evidence\": \"Skinned cardiomyocytes, reconstituted thin filaments, protein interaction assays, patient myocardial tissue analysis\",\n      \"pmids\": [\"34502534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study with one patient\", \"No knock-in animal model\", \"Whether protein quality control perturbation is cause or consequence of structural disruption unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CRISPR knockout of TNNC1 in ovarian cancer cells demonstrated that cTnC lies upstream of AKT/GSK-3β/Snail-dependent EMT, establishing a specific signaling axis through which TNNC1 promotes migration, invasion, and F-actin polymerization outside muscle.\",\n      \"evidence\": \"CRISPR/Cas9 knockout with western blot pathway analysis, wound-healing and invasion assays, F-actin staining\",\n      \"pmids\": [\"33592378\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which cTnC activates AKT phosphorylation unknown\", \"Single cancer cell type\", \"Whether F-actin effects are direct or downstream of AKT not distinguished\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"ITC measurements revealed that HCM-associated cTnC variants increase not only Ca²⁺ but also Mg²⁺ affinity at regulatory site II, establishing that physiological Mg²⁺ competition is an integral determinant of the Ca²⁺-sensing defect in disease.\",\n      \"evidence\": \"Isothermal titration calorimetry and thermodynamic integration molecular dynamics simulations on six HCM variants\",\n      \"pmids\": [\"35838319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo impact of altered Mg²⁺ binding on cardiac function not tested\", \"Whether Mg²⁺ competition is similarly altered in DCM variants unknown\", \"Structural basis for enhanced Mg²⁺ binding not resolved at atomic resolution\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"ChIP and luciferase assays showed that E2F1 directly binds the TNNC1 promoter to activate transcription in hepatocellular carcinoma, placing TNNC1 under epigenetic control via the KDM5D/H3K4me3/E2F1 axis and identifying a transcriptional regulatory mechanism for TNNC1 in cancer.\",\n      \"evidence\": \"ChIP assay for E2F1 at TNNC1 promoter, dual luciferase reporter assay, KDM5D overexpression, nude mouse xenograft\",\n      \"pmids\": [\"38504588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this transcriptional regulation operates in cardiac tissue unknown\", \"Downstream functional consequence of E2F1-driven TNNC1 upregulation not mechanistically dissected\", \"Single cancer cell line context\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism by which cTnC functions in non-muscle contexts (cancer cell motility, AKT signaling, EMT) remains unresolved—it is unknown whether it acts via Ca²⁺ sensing, direct cytoskeletal interaction, or an entirely distinct mechanism, and no DCM knock-in animal model exists to complement the HCM A8V model.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural or biochemical basis for cTnC function in non-muscle cells\", \"No DCM knock-in mouse model for TNNC1 loss-of-function variants\", \"Atomic-resolution structures of disease-mutant troponin complexes in active/inactive states lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 1, 3, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 2, 4, 6]}\n    ],\n    \"complexes\": [\n      \"cardiac troponin complex\"\n    ],\n    \"partners\": [\n      \"TNNI3\",\n      \"TNNT2\",\n      \"ACTC1\",\n      \"MFAP5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"TNNC1 encodes cardiac troponin C (cTnC), the Ca²⁺-sensing subunit of the cardiac troponin complex that transduces cytosolic Ca²⁺ signals into thin-filament activation and sarcomere contraction. Its regulatory N-domain (site II) binds Ca²⁺ to adopt an open conformation that engages the TnI switch peptide (residues 147–163), releasing the TnI inhibitory region from actin and permitting tropomyosin movement; the C-domain constitutively anchors cTnC in the troponin complex via two high-affinity Ca²⁺/Mg²⁺ sites [PMID:12840750, PMID:10387074, PMID:26232335]. Missense mutations in TNNC1 cause hypertrophic cardiomyopathy through gain-of-function increases in Ca²⁺ (and Mg²⁺) binding affinity and myofilament Ca²⁺ sensitivity, and dilated cardiomyopathy through decreased Ca²⁺ sensitivity and impaired PKA-phosphorylation responsiveness [PMID:18572189, PMID:21832052, PMID:26304555]. Outside the sarcomere, TNNC1 is transcriptionally regulated by the KDM5D/E2F1 axis and signals through AKT/GSK-3β/EMT and FOXO3-autophagy pathways to modulate cancer cell motility and chemoresistance [PMID:33592378, PMID:32946432, PMID:38504588].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"How TnI anchors to TnC was unknown; crystallography revealed that TnI N-terminal binding causes a 90° bend in the TnC central helix, creating a compact conformation with direct inter-lobe contacts, establishing the structural basis of TnC–TnI anchoring.\",\n      \"evidence\": \"X-ray crystallography of TnC–TnI(1-47) complex at 2.3 Å\",\n      \"pmids\": [\"9560191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure was of an isolated binary complex, not the full ternary troponin on actin\", \"Ca²⁺-free state not captured\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"The mechanism by which Ca²⁺ couples TnC conformational change to TnI engagement was unclear; NMR showed that the TnI switch peptide binds TnC's regulatory N-domain only in the Ca²⁺-saturated state, inducing an open hydrophobic cleft, establishing Ca²⁺-gated TnI binding as the activation switch.\",\n      \"evidence\": \"Multinuclear multidimensional NMR solution structure of cNTnC with TnI switch peptide\",\n      \"pmids\": [\"10387074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Study used isolated peptide rather than full-length TnI in the ternary complex\", \"Kinetics of opening/closing not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The architecture of the full ternary troponin core on the thin filament was unknown; the crystal structure revealed an IT arm coiled-coil and showed that Ca²⁺ binding to cTnC removes the TnI C-terminus from actin, providing the first atomic model of the activation mechanism in the complete core domain.\",\n      \"evidence\": \"X-ray crystallography of human cardiac troponin core domain (TnC/TnI/TnT) in Ca²⁺-saturated form\",\n      \"pmids\": [\"12840750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure captured only the Ca²⁺-saturated state; apo transition not visualized\", \"Tropomyosin and actin not present in the crystal\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Whether TNNC1 mutations could cause cardiomyopathy was unknown; identification of a DCM-causing TNNC1 missense mutation that impairs troponin subunit interaction established TNNC1 as a dilated cardiomyopathy gene.\",\n      \"evidence\": \"Genetic screening of DCM families with two-hybrid luciferase interaction assay\",\n      \"pmids\": [\"15542288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional data relied on a two-hybrid assay without reciprocal reconstitution in skinned fibers\", \"Single family reported\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"How TNNC1 mutations produce HCM was unclear; reconstitution of four HCM-associated cTnC mutants into skinned fibers demonstrated increased Ca²⁺ sensitivity of force, establishing a gain-of-function Ca²⁺-sensitization mechanism parallel to other sarcomeric HCM genes.\",\n      \"evidence\": \"Skinned fiber reconstitution with recombinant mutant cTnC, force-pCa assays\",\n      \"pmids\": [\"18572189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo consequences not yet tested at this stage\", \"Heterozygous dosage effects not modeled\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The mechanistic basis of DCM-linked TNNC1 variants and their effect on β-adrenergic regulation was unexplored; skinned fiber and ATPase reconstitution showed DCM variants decrease Ca²⁺ sensitivity and impair or abolish PKA phosphorylation-dependent modulation, linking loss of lusitropy to DCM pathogenesis.\",\n      \"evidence\": \"Skinned fiber force, actomyosin ATPase, PKA phosphorylation, and CD spectroscopy with four DCM variants\",\n      \"pmids\": [\"21832052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo animal model for DCM variants at the time\", \"Structural mechanism of impaired PKA response not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Whether HCM mutations directly alter Ca²⁺ binding affinity versus downstream coupling was debated; fluorescence and reconstitution studies of A31S showed a direct increase in regulatory site Ca²⁺ affinity across increasing levels of thin filament complexity, pinpointing the defect to the Ca²⁺ binding step itself.\",\n      \"evidence\": \"Fluorescence Ca²⁺ titration in isolated cTnC, troponin complex, thin filament ± myosin S1; skinned fibers; CD\",\n      \"pmids\": [\"22815480\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single mutation studied; generalizability to all HCM variants not confirmed\", \"In vivo validation pending\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Whether increased Ca²⁺ sensitivity in vitro translates to diastolic dysfunction in vivo was untested; TNNC1-A8V knock-in mice showed dose-dependent Ca²⁺ sensitization, prolonged relaxation, diastolic dysfunction, hypertrophy, and fibrosis, providing the first in vivo genetic proof of the gain-of-function HCM mechanism.\",\n      \"evidence\": \"Knock-in mouse model with echocardiography, pressure-volume loops, skinned fibers, flash photolysis, LC-MS\",\n      \"pmids\": [\"26304555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Only one mutation modeled in vivo\", \"Mutant cTnC incorporated at only ~21%, leaving natural dosage effects uncertain\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"TNNC1's role outside the sarcomere was emerging; CRISPR knockout in ovarian cancer cells demonstrated that TNNC1 activates AKT/GSK-3β signaling, promotes EMT, and drives F-actin remodeling to support invasion, while epistasis experiments in NSCLC placed TNNC1 upstream of FOXO3-dependent autophagy in chemoresistance.\",\n      \"evidence\": \"CRISPR/Cas9 KO (ovarian cancer), siRNA/overexpression with FOXO3 epistasis (NSCLC), migration/invasion assays, western blot\",\n      \"pmids\": [\"33592378\", \"32946432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding partners linking cTnC to AKT or FOXO3 are unidentified\", \"Cancer findings are from cell lines; in vivo validation limited\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Whether Mg²⁺ competition at the regulatory site is physiologically significant and affected by disease mutations was unresolved; ITC showed that HCM variants increase affinity for both Ca²⁺ and Mg²⁺ at site II, establishing Mg²⁺ as a relevant modulator of Ca²⁺ sensitivity and contraction regulation.\",\n      \"evidence\": \"Isothermal titration calorimetry and thermodynamic integration MD simulations\",\n      \"pmids\": [\"35838319\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of Mg²⁺ competition on force development not directly measured\", \"Single-site measurements may not capture cooperativity on the thin filament\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"How TNNC1 transcription is regulated was unknown; ChIP and luciferase assays showed that E2F1 directly binds the TNNC1 promoter and is itself repressed by KDM5D-mediated H3K4me3 demethylation at the E2F1 locus, establishing a KDM5D/E2F1/TNNC1 transcriptional axis in hepatocellular carcinoma.\",\n      \"evidence\": \"ChIP for H3K4me3 and E2F1, dual luciferase reporter, overexpression, nude mouse xenograft\",\n      \"pmids\": [\"38504588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relevance of this transcriptional axis to cardiac tissue unknown\", \"Whether E2F1-driven TNNC1 expression occurs in normal physiology or is cancer-specific is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the structural basis of how individual cardiomyopathy mutations alter Mg²⁺/Ca²⁺ selectivity and PKA-responsiveness at atomic resolution; the direct molecular partners through which non-sarcomeric TNNC1 engages AKT and autophagy pathways; and whether pharmacological restoration of lusitropy (e.g., silybin B, EGCG) translates to therapeutic benefit in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of mutant cTnC in the apo-to-Ca²⁺ transition\", \"Non-sarcomeric binding partners remain unidentified\", \"No clinical trial data for Ca²⁺-sensitizer correction of TNNC1-linked cardiomyopathy\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3, 4, 6, 7, 8]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 2, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2, 10, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 1, 3, 4, 6, 7, 8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 5, 6, 8, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 12, 14, 15]}\n    ],\n    \"complexes\": [\n      \"cardiac troponin complex (cTnC/cTnI/cTnT)\"\n    ],\n    \"partners\": [\n      \"TNNI3\",\n      \"TNNT2\",\n      \"ACTA1\",\n      \"TPM1\",\n      \"FOXO3\",\n      \"AKT1\",\n      \"E2F1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}