{"gene":"TPM2","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2002,"finding":"Two heterozygous missense mutations in TPM2 (beta-tropomyosin) affect conserved amino acids and are expressed at the mutant allele level; the mutations are predicted to affect tropomyosin dimer formation and actin-binding properties, establishing TPM2 mutations as a cause of nemaline myopathy.","method":"SSCP analysis, sequencing, expression analysis of mutant allele","journal":"Neuromuscular disorders : NMD","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — genetic identification with allele expression confirmed, but mechanistic inference about dimer/actin binding is speculative rather than directly assayed; replicated concept across multiple subsequent papers","pmids":["11738357"],"is_preprint":false},{"year":2007,"finding":"An in-frame deletion of Glu139 (p.Glu139del) in TPM2 disrupts the seven-amino acid repeat essential for the coiled-coil structure, impairing tropomyosin-actin interaction and causing cap disease; 2D-gel electrophoresis confirmed mutant protein incorporates into sarcomeric structures where it likely exerts a dominant-negative effect.","method":"Genetic sequencing, 2D-gel electrophoresis of patient muscle","journal":"Neuromuscular disorders : NMD","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — 2D-gel fractionation showing incorporation plus mechanistic inference; confirmed in independent case (PMID 19345583)","pmids":["17434307","19345583"],"is_preprint":false},{"year":2012,"finding":"Four disease-causing TPM2 mutations (in nemaline myopathy and cap myopathy) cause altered affinity of beta-tropomyosin for actin as measured by in vitro binding assays; two mutations also cause defective Ca2+ activation of contractility; two mutations cause altered protein conformation mapped to actin-binding regions.","method":"In vitro actin co-sedimentation assay, Ca2+-activation of contractility assay, conformation analysis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro biochemical assays with multiple mutations and multiple orthogonal readouts in one study","pmids":["22084935"],"is_preprint":false},{"year":2013,"finding":"The TPM2 p.K7del mutation reduces beta-tropomyosin affinity for actin, impairs incorporation into sarcomeres in C2C12 myotubes (mutant accumulates in nemaline rods), disrupts head-to-tail polymerization, and increases myofilament calcium sensitivity as measured by force in single dissected patient myofibres.","method":"Recombinant protein actin-binding assay, C2C12 myotube transfection, 2D-gel electrophoresis of patient muscle, single myofibre force measurements","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including in vitro binding, cell-based incorporation, and direct force measurement from patient tissue; replicated by independent cohort (PMID 23413262)","pmids":["23378224"],"is_preprint":false},{"year":2013,"finding":"Expression of p.K7del beta-tropomyosin in zebrafish disrupts thin filament localization and alters sarcomere length in vivo, consistent with impaired head-to-tail polymerization of TPM2 dimers.","method":"Zebrafish in vivo overexpression, fluorescence microscopy of sarcomere structure","journal":"Brain : a journal of neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo animal model with direct structural readout; single lab but corroborates PMID 23378224 findings","pmids":["23413262"],"is_preprint":false},{"year":2014,"finding":"Genotype-phenotype analysis of 53 TPM2-mutation families reveals that five TPM2 mutations cause increased Ca2+ sensitivity (hypercontractile molecular phenotype), correlated with joint contractures, while non-hypercontractile mutations correlate with axial contractures; in silico analysis indicates most mutations affect tropomyosin-actin association or head-to-tail binding.","method":"Ca2+ sensitivity measurements (from prior studies referenced), clinical correlation across 93 families, in silico structural prediction","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — large multi-family correlation integrating prior functional data; direct Ca2+ sensitivity measurements cited from earlier work; in silico predictions for novel variants","pmids":["24692096"],"is_preprint":false},{"year":2015,"finding":"The myopathy-causing Q147P mutation in beta-tropomyosin (TPM2) shifts tropomyosin strands closer to the center of the actin filament (open position) despite reduced actin affinity, increases the proportion of strong-binding myosin cross-bridges during ATPase cycle, and disrupts cooperation of actin and myosin heads.","method":"Polarized fluorimetry in reconstituted ghost muscle fibres, co-sedimentation assay for actin affinity","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution in ghost fibres with polarized fluorimetry; single lab, single paper","pmids":["26708479"],"is_preprint":false},{"year":2016,"finding":"Epigenetic silencing of TPM2 via promoter DNA methylation suppresses its expression in colorectal cancer; treatment with demethylation agent 5-AZA restores TPM2 expression; reconstitution of TPM2 suppresses cell proliferation and migration; loss of TPM2 is associated with RhoA activation.","method":"Promoter methylation analysis, 5-AZA demethylation assay, TPM2 overexpression/knockdown in cancer cell lines, proliferation/migration assays, RhoA activity measurement","journal":"Tumour biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (methylation, rescue, knockdown, RhoA assay) in single lab; mechanistic link to RhoA established by association not direct epistasis","pmids":["27333992"],"is_preprint":false},{"year":2017,"finding":"The Glu139del mutation in TPM2 does not alter tropomyosin affinity for actin but markedly increases tropomyosin flexibility, keeps tropomyosin strands near the inner domain of actin (blocked-position movement inhibited at low Ca2+), increases troponin-mediated switching on/off of actin monomers, and decreases strong myosin head binding at high Ca2+ while increasing it at relaxation—mechanistically explaining hypercontractile Ca2+ sensitivity and muscle weakness.","method":"Polarized fluorescence microscopy of reconstituted ghost fibres, actin affinity assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution + polarized fluorimetry; mechanistically detailed but single lab","pmids":["29196649"],"is_preprint":false},{"year":2017,"finding":"Knockdown of Tpm2.1 in MCF10A breast epithelial cells retards collective cell migration but increases single cell migration and invasion; this is associated with enhanced actomyosin contractility, increased E-cadherin/β-catenin expression, decreased AXL receptor tyrosine kinase, and is rescued by ROCK inhibition.","method":"siRNA/shRNA knockdown, wound healing and transwell migration/invasion assays, Western blotting, ROCK inhibitor treatment, spheroid re-plating assay","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (KD, rescue, inhibitor), defined pathway placement via ROCK; single lab","pmids":["29221121"],"is_preprint":false},{"year":2017,"finding":"Overexpression of Tpm2.1 in rat neuroepithelial cells enhances sensitivity to anoikis and to jasplakinolide-induced apoptosis; this is accompanied by enhanced mitochondrial depolarization and elevated levels of Bak, Mcl-1, Bcl-2, and phospho-p53 (Ser392); jasplakinolide treatment of Tpm2.1-overexpressing cells reduces Mcl-1, Bcl-2, and p53(Ser392).","method":"Tpm2.1 overexpression in rat cells, apoptosis assays (anoikis, jasplakinolide), mitochondrial membrane potential assay, Western blotting of apoptosis regulators","journal":"Cytoskeleton (Hoboken, N.J.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple apoptotic stimuli and protein-level readouts; single lab, mechanistic pathway partially defined","pmids":["28378936"],"is_preprint":false},{"year":2017,"finding":"The Arg91Gly mutation in TPM2 markedly decreases bending stiffness of beta-tropomyosin in thin filaments; during ATPase cycle, mutant tropomyosin remains near the open position allowing strong myosin head binding to actin even at low Ca2+, mechanistically explaining high Ca2+ sensitivity and contractures associated with this distal arthrogryposis mutation.","method":"Polarized fluorescence microscopy of reconstituted ghost fibres during ATPase cycle","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution with structural/dynamic readout; single lab, single method","pmids":["29097206"],"is_preprint":false},{"year":2017,"finding":"Smad4 SUMOylation (by E3 ligase PIAS1 at Lys-113 and Lys-159 in hippocampus) drives TPM2 upregulation; knockdown of TPM2 in rats impairs spatial learning and memory; TPM2 mRNA and protein increase after spatial training; the myopathy-associated TPM2-E122K mutation reduces TPM2 expression and impairs spatial memory in rats.","method":"SUMO site mutagenesis, rat hippocampal injection/knockdown, behavioral memory tests, Western blot, mRNA quantification","journal":"BMC biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SUMOylation site identified, KD with behavioral readout, mutation effect on expression; single lab but multiple methods","pmids":["29183317"],"is_preprint":false},{"year":2018,"finding":"The Glu41Lys (E41K) mutation in TPM2 inhibits troponin's ability to shift tropomyosin to the closed position at high Ca2+, restraining thin filament transition from 'off' to 'on' state; it also inhibits S1-driven shift to the open position and inhibits switching off of actin monomers at low Ca2+—explaining reduced Ca2+ sensitivity and muscle weakness in nemaline myopathy/cap disease.","method":"Polarized fluorescence microscopy of reconstituted ghost fibres during ATPase cycle","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — detailed reconstitution; single lab, single paper","pmids":["29792862"],"is_preprint":false},{"year":2019,"finding":"The R133W mutation in Tpm2.2 decreases the amount of strongly actin-bound myosin heads and number of switched-on actin monomers at high Ca2+, inhibits tropomyosin shifting towards the open position, and freezes mutant tropomyosin near the blocked position; at low Ca2+, fewer strongly-bound myosin heads contribute to low myofilament Ca2+-sensitivity—explaining muscle weakness in Sheldon-Hall syndrome.","method":"Polarized fluorescence microscopy of reconstituted ghost fibres (αβ-Tpm heterodimers and ββ-Tpm homodimers) during ATPase cycle","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution with two dimer types compared; single lab","pmids":["31864708"],"is_preprint":false},{"year":2021,"finding":"Mutations Q93H and E97K in Tpm2.2 both decrease actin affinity of homo- and heterodimers in vitro; Q93H strongly decreases actomyosin ATPase activation and reduces Ca2+ sensitivity (hypocontractile); E97K causes hyperactivation of ATPase and increased Ca2+ sensitivity (hypercontractile); both mutations alter tropomyosin dynamics on the filament.","method":"In vitro actin co-sedimentation, actomyosin ATPase assay, Ca2+ sensitivity measurements, trypsin susceptibility assay for dynamics","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple direct biochemical assays (binding, ATPase, Ca2+ sensitivity, conformation) for two mutations in one study","pmids":["33919826"],"is_preprint":false},{"year":2022,"finding":"Expression of dominant pathogenic TPM2 variants in Drosophila embryos significantly affected muscle development and function; transient overexpression disrupted mouse myotube morphogenesis in vitro and zebrafish muscle development in vivo, establishing disrupted myogenesis as a pathomechanism of TPM2 disorders.","method":"Drosophila muscle development assays, mouse myotube morphogenesis assay, zebrafish in vivo overexpression","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — three model systems used; single lab, multiple orthogonal organism models supporting same conclusion","pmids":["35579956"],"is_preprint":false},{"year":2023,"finding":"TPM2 competes with YAP1 for binding to PDLIM7 via its PDZ-binding motif; this competition prevents PDLIM7-mediated nuclear translocation of YAP1, sequestering YAP1 in the cytoplasm where it is phosphorylated at S127 and inactivated/degraded, thereby suppressing YAP1 target gene expression and prostate cancer progression.","method":"Co-immunoprecipitation, immunofluorescence localization, Western blotting (p-YAP1-S127), PDZ-binding motif deletion mutant, in vitro cell proliferation/invasion assays, xenograft tumor assay","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with domain mapping, localization, and in vivo xenograft; single lab","pmids":["36823643"],"is_preprint":false},{"year":2024,"finding":"Hypercontractile mutations D20H and E181K in Tpm2.2 alter the binding geometry and orientation of tropomyosin on actin (by FRET), stimulate myosin motor performance and accelerate product (ADP/Pi) release kinetics; hypocontractile mutations E41K and N202K inhibit actin activation of myosin ATPase, motor activity, and decelerate product release—demonstrating opposite mechanochemical effects on the cross-bridge cycle.","method":"FRET assays for Tpm orientation on actin, myosin ATPase assay, in vitro motility assay, single ATP turnover kinetics","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biochemical assays (FRET, ATPase, motility, single-turnover kinetics) with four mutations in one study","pmids":["38156416"],"is_preprint":false},{"year":2025,"finding":"At low Ca2+, all four pathogenic Tpm2.2 variants (D20H, E181K, E41K, N202K) inhibit troponin-regulated actomyosin ATPase without affecting troponin binding to actin; at activating Ca2+, hypocontractile mutants suppress ATPase and motor function while hypercontractile mutants enhance myosin-driven actin translocation; N-terminal mutations (D20H, E181K) enhance high-affinity Tpm2.2-troponin interactions; hypercontractile mutants increase Ca2+ sensitivity while hypocontractile mutants decrease it.","method":"In vitro actomyosin ATPase assay, in vitro motility assay, Tpm-troponin binding assay, Arrhenius analysis of temperature dependence","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal in vitro assays dissecting Tn-dependent and Tn-independent regulation; four mutations systematically compared in one study","pmids":["40657867"],"is_preprint":false},{"year":2025,"finding":"Cytoplasmic TPM2 isoforms (Tpm2.1, Tpm2.3, Tpm2.4) directly interact with fascin-1 (pull-down assay) and inhibit fascin-1-mediated actin bundling by reducing fascin-1 affinity for actin; Tpm2 occupancy on actin filaments partially displaces fascin-1; fascin-1 binding does not affect Tpm2 affinity for actin; Tpm2.4 shows highest actin and fascin-1 affinities; overexpression of Tpm2 isoforms in SAOS-2 LM5 cells reduces fascin co-localization with actin.","method":"High-speed centrifugation (actin affinity), low-speed centrifugation and fluorescence microscopy (bundling), pull-down assay (direct Tpm2-fascin interaction), confocal microscopy in SAOS-2 cells","journal":"Biological research","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct binding demonstrated by pull-down, functional consequences by multiple in vitro assays, and cell-based confirmation; multiple orthogonal methods in one study","pmids":["40887664"],"is_preprint":false},{"year":2025,"finding":"TPM2 overexpression in HTR-8/SVneo trophoblast cells enhances migration and invasion, suppresses IL-6, IL-1β, and IL-8 production, inhibits IκBα degradation, and blocks nuclear translocation of NF-κB p65, establishing TPM2 as a suppressor of NF-κB-mediated inflammation.","method":"TPM2 overexpression in trophoblast cells, migration/invasion assays, cytokine ELISA, Western blot for IκBα and p65 nuclear translocation","journal":"Tissue & cell","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple assays in single lab but no rescue or domain mapping; single paper","pmids":["41297249"],"is_preprint":false},{"year":2026,"finding":"Wild-type Tpm2.2 inhibits spontaneous actin polymerization; hypercontractile D20H and E181K further decrease polymerization rate; hypocontractile E41K and N202K stabilize filaments under actomyosin-driven conditions increasing filament length (abolished by troponin); all variants slightly decrease cofilin-2 affinity for F-actin; Tpm2.2-N202K inhibits cofilin-2-dependent depolymerization while E181K increases susceptibility; the Tpm2.2-troponin complex protects filaments from cofilin-2-induced disassembly.","method":"In vitro actin polymerization assay, filament stability and length measurement under actomyosin conditions, cofilin-2 binding and depolymerization assays, structural modeling","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — preprint; multiple in vitro assays but not yet peer-reviewed; single lab","pmids":["42239403"],"is_preprint":true}],"current_model":"TPM2-encoded beta-tropomyosin (Tpm2.2 in striated muscle) is an actin-binding coiled-coil protein that regulates muscle contraction by controlling tropomyosin strand positioning on the thin filament: it gates Ca2+-dependent transitions between blocked, closed, and open states to permit or inhibit myosin cross-bridge formation; disease-causing mutations alter actin affinity, tropomyosin flexibility and position, Ca2+ sensitivity, myosin ATPase kinetics, and filament dynamics in ways that produce either hyper- or hypocontractile phenotypes; cytoplasmic Tpm2 isoforms additionally regulate actin bundling by inhibiting fascin-1, modulate cell migration through actomyosin contractility and ROCK signaling, suppress YAP1 nuclear activity by competing with PDLIM7, and regulate apoptosis sensitivity through modulation of intrinsic apoptosis proteins."},"narrative":{"mechanistic_narrative":"TPM2 encodes beta-tropomyosin, an actin-binding coiled-coil protein that regulates striated muscle contraction by positioning tropomyosin strands on the thin filament and gating Ca2+-dependent transitions between blocked, closed, and open states that permit or inhibit myosin cross-bridge formation [PMID:22084935, PMID:26708479, PMID:38156416]. Pathogenic missense and in-frame deletion mutations cluster in actin-binding and head-to-tail polymerization regions and act through several biophysical mechanisms: reduced actin affinity and impaired sarcomeric incorporation [PMID:22084935, PMID:23378224], altered tropomyosin flexibility and azimuthal position on actin [PMID:29196649, PMID:29097206], and shifted equilibrium of the thin filament regulatory state [PMID:26708479, PMID:29792862, PMID:31864708]. These changes resolve into two opposing molecular phenotypes — hypercontractile variants that hold tropomyosin near the open position, increase Ca2+ sensitivity, accelerate myosin product release, and stimulate motor activity, versus hypocontractile variants that freeze tropomyosin near the blocked position, reduce Ca2+ sensitivity, and suppress actomyosin ATPase and motility [PMID:33919826, PMID:38156416, PMID:40657867]. Beyond steady-state regulation, Tpm2.2 controls thin filament dynamics by inhibiting spontaneous actin polymerization and modulating cofilin-2-mediated filament turnover, with the tropomyosin–troponin complex protecting filaments from disassembly [PMID:42239403]. Direct genetic and biochemical evidence establishes TPM2 mutations as a cause of nemaline myopathy, cap disease, distal arthrogryposis, and Sheldon-Hall syndrome [PMID:11738357, PMID:17434307, PMID:19345583, PMID:29097206, PMID:31864708], and disrupted myogenesis is itself a pathomechanism across model organisms [PMID:35579956]. Cytoplasmic Tpm2 isoforms perform distinct cytoskeletal roles: they directly bind and inhibit fascin-1-mediated actin bundling [PMID:40887664], regulate cell migration and invasion through actomyosin contractility and ROCK signaling [PMID:29221121], and suppress tumor progression by competing with YAP1 for PDLIM7 to retain YAP1 in the cytoplasm in its inactivated form [PMID:36823643].","teleology":[{"year":2002,"claim":"Established that TPM2 mutations cause human myopathy, framing beta-tropomyosin as a disease gene whose lesions likely act through dimer formation and actin binding.","evidence":"SSCP, sequencing and mutant-allele expression analysis in nemaline myopathy patients","pmids":["11738357"],"confidence":"Medium","gaps":["Effect on actin binding was predicted, not directly assayed","No biophysical measurement of the contractile defect"]},{"year":2007,"claim":"Showed that an in-frame deletion disrupting the coiled-coil heptad repeat incorporates into sarcomeres and likely acts dominant-negatively, linking structural disruption to cap disease.","evidence":"Genetic sequencing and 2D-gel electrophoresis of patient muscle","pmids":["17434307","19345583"],"confidence":"Medium","gaps":["Dominant-negative mechanism inferred rather than directly demonstrated","No reconstituted thin-filament functional readout"]},{"year":2012,"claim":"Provided the first direct biochemical demonstration that disease mutations alter actin affinity, Ca2+ activation, and protein conformation, moving from genetic association to assayed mechanism.","evidence":"In vitro actin co-sedimentation, Ca2+-activation of contractility, and conformation analysis of four mutations","pmids":["22084935"],"confidence":"High","gaps":["Did not resolve tropomyosin position on the filament","Cross-bridge cycle kinetics not measured"]},{"year":2013,"claim":"Connected reduced actin affinity to defective sarcomeric incorporation, nemaline rod formation, and altered force/Ca2+ sensitivity in patient fibres, and corroborated the polymerization defect in vivo.","evidence":"Recombinant binding assay, C2C12 transfection, single patient myofibre force measurement, and zebrafish overexpression","pmids":["23378224","23413262"],"confidence":"High","gaps":["Mechanism limited to one mutation (K7del)","Head-to-tail polymerization defect inferred from localization"]},{"year":2014,"claim":"Correlated molecular phenotype with clinical presentation across many families, establishing that increased Ca2+ sensitivity (hypercontractility) tracks with joint contractures.","evidence":"Genotype-phenotype analysis of TPM2-mutation families with in silico structural prediction","pmids":["24692096"],"confidence":"Medium","gaps":["Many variant effects predicted in silico, not measured","Ca2+ sensitivity data drawn from prior studies"]},{"year":2017,"claim":"Defined at the structural level how individual mutations reposition tropomyosin on actin and shift the blocked/closed/open equilibrium to produce hyper- or hypocontractile states.","evidence":"Polarized fluorescence microscopy of reconstituted ghost fibres during the ATPase cycle (Q147P, Glu139del, Arg91Gly)","pmids":["26708479","29196649","29097206"],"confidence":"Medium","gaps":["Each result from a single lab and method","Quantitative myosin kinetics not directly measured"]},{"year":2019,"claim":"Extended the positional model to additional weakness-causing mutations and compared heterodimer versus homodimer behavior, linking blocked-position freezing to low Ca2+ sensitivity.","evidence":"Polarized fluorescence microscopy of reconstituted ghost fibres (E41K, R133W; αβ and ββ dimers)","pmids":["29792862","31864708"],"confidence":"Medium","gaps":["Single-lab reconstitution data","In vivo relevance of homo- vs heterodimer differences unresolved"]},{"year":2021,"claim":"Systematically partitioned mutations into hyper- and hypocontractile classes using direct ATPase and Ca2+ sensitivity measurements, consolidating the two-class mechanistic model.","evidence":"Actin co-sedimentation, actomyosin ATPase, Ca2+ sensitivity, and trypsin-susceptibility assays (Q93H, E97K)","pmids":["33919826"],"confidence":"High","gaps":["Two mutations only","Did not address filament turnover or thin-filament assembly"]},{"year":2024,"claim":"Resolved the mechanochemical basis of the two phenotype classes, showing hypercontractile mutations accelerate and hypocontractile mutations decelerate myosin product release.","evidence":"FRET orientation assays, myosin ATPase, in vitro motility, and single-turnover kinetics (D20H, E181K, E41K, N202K)","pmids":["38156416"],"confidence":"High","gaps":["Performed without full troponin regulation in some readouts","Structural cause of orientation changes not solved"]},{"year":2025,"claim":"Dissected troponin-dependent versus troponin-independent regulation and mapped N-terminal mutations to enhanced tropomyosin-troponin affinity, refining how variants distort Ca2+-regulated switching.","evidence":"Actomyosin ATPase, in vitro motility, Tpm-troponin binding, and Arrhenius analysis of four variants","pmids":["40657867"],"confidence":"High","gaps":["Mechanism of N-terminal affinity enhancement unresolved","Effects measured in reconstituted not cellular systems"]},{"year":2025,"claim":"Established a non-muscle role for cytoplasmic Tpm2 isoforms as direct inhibitors of fascin-1-mediated actin bundling, distinguishing isoform-specific cytoskeletal regulation.","evidence":"Pull-down, co-sedimentation, bundling assays, and confocal microscopy in SAOS-2 cells","pmids":["40887664"],"confidence":"High","gaps":["Cellular consequences for migration/metastasis not directly tested","Structural basis of Tpm2-fascin competition unknown"]},{"year":2023,"claim":"Defined a tumor-suppressive signaling mechanism in which TPM2 competes with YAP1 for PDLIM7 to retain YAP1 in the cytoplasm in its phosphorylated, inactive state.","evidence":"Reciprocal Co-IP, PDZ-motif deletion mapping, immunofluorescence, and xenograft assays","pmids":["36823643"],"confidence":"Medium","gaps":["Single-lab finding","Link between cytoskeletal and signaling functions not integrated"]},{"year":2025,"claim":"Implicated TPM2 in regulating cell migration, invasion, apoptosis, and NF-κB-driven inflammation, indicating broad non-sarcomeric functions tied to actomyosin and signaling.","evidence":"Knockdown/overexpression with migration, apoptosis, ROCK-inhibitor, and cytokine/NF-κB readouts in epithelial, neuroepithelial, and trophoblast cells","pmids":["29221121","28378936","27333992","41297249"],"confidence":"Medium","gaps":["Mechanistic links established mostly by association","No domain mapping or rescue for several effects"]},{"year":null,"claim":"How the distinct sarcomeric, cytoskeletal-bundling, and signaling functions of TPM2 isoforms are integrated, and whether a unified structural framework explains both contractile and non-muscle roles, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking position changes to non-muscle isoform function","Isoform-specific in vivo functions not delineated","Cross-talk between actin-bundling and YAP/NF-κB signaling untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,3,6,18,20]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3,4,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[18,19,20,22]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,4,20]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[17,20]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[2,6,18,19]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,1,3,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[17,21]}],"complexes":["thin filament (actin-tropomyosin-troponin)"],"partners":["ACTA1","TNNT","FASCIN-1 (FSCN1)","PDLIM7","YAP1","COFILIN-2 (CFL2)"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07951","full_name":"Tropomyosin beta chain","aliases":["Beta-tropomyosin","Tropomyosin-2"],"length_aa":284,"mass_kda":32.9,"function":"Binds to actin filaments in muscle and non-muscle cells. Plays a central role, in association with the troponin complex, in the calcium dependent regulation of vertebrate striated muscle contraction. Smooth muscle contraction is regulated by interaction with caldesmon. In non-muscle cells is implicated in stabilizing cytoskeleton actin filaments. The non-muscle isoform may have a role in agonist-mediated receptor internalization","subcellular_location":"Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/P07951/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TPM2","classification":"Not Classified","n_dependent_lines":49,"n_total_lines":1208,"dependency_fraction":0.04056291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TPM2","total_profiled":1310},"omim":[{"mim_id":"618435","title":"ARTHROGRYPOSIS, DISTAL, TYPE 2B2; DA2B2","url":"https://www.omim.org/entry/618435"},{"mim_id":"615155","title":"STEEL SYNDROME; STLS","url":"https://www.omim.org/entry/615155"},{"mim_id":"613629","title":"PIEZO-TYPE MECHANOSENSITIVE ION CHANNEL COMPONENT 2; PIEZO2","url":"https://www.omim.org/entry/613629"},{"mim_id":"609285","title":"CONGENITAL MYOPATHY 23; CMYO23","url":"https://www.omim.org/entry/609285"},{"mim_id":"609273","title":"NEMALINE MYOPATHY 6; NEM6","url":"https://www.omim.org/entry/609273"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal 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analysis, sequencing, expression analysis of mutant allele\",\n      \"journal\": \"Neuromuscular disorders : NMD\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — genetic identification with allele expression confirmed, but mechanistic inference about dimer/actin binding is speculative rather than directly assayed; replicated concept across multiple subsequent papers\",\n      \"pmids\": [\"11738357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"An in-frame deletion of Glu139 (p.Glu139del) in TPM2 disrupts the seven-amino acid repeat essential for the coiled-coil structure, impairing tropomyosin-actin interaction and causing cap disease; 2D-gel electrophoresis confirmed mutant protein incorporates into sarcomeric structures where it likely exerts a dominant-negative effect.\",\n      \"method\": \"Genetic sequencing, 2D-gel electrophoresis of patient muscle\",\n      \"journal\": \"Neuromuscular disorders : NMD\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — 2D-gel fractionation showing incorporation plus mechanistic inference; confirmed in independent case (PMID 19345583)\",\n      \"pmids\": [\"17434307\", \"19345583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Four disease-causing TPM2 mutations (in nemaline myopathy and cap myopathy) cause altered affinity of beta-tropomyosin for actin as measured by in vitro binding assays; two mutations also cause defective Ca2+ activation of contractility; two mutations cause altered protein conformation mapped to actin-binding regions.\",\n      \"method\": \"In vitro actin co-sedimentation assay, Ca2+-activation of contractility assay, conformation analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro biochemical assays with multiple mutations and multiple orthogonal readouts in one study\",\n      \"pmids\": [\"22084935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The TPM2 p.K7del mutation reduces beta-tropomyosin affinity for actin, impairs incorporation into sarcomeres in C2C12 myotubes (mutant accumulates in nemaline rods), disrupts head-to-tail polymerization, and increases myofilament calcium sensitivity as measured by force in single dissected patient myofibres.\",\n      \"method\": \"Recombinant protein actin-binding assay, C2C12 myotube transfection, 2D-gel electrophoresis of patient muscle, single myofibre force measurements\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including in vitro binding, cell-based incorporation, and direct force measurement from patient tissue; replicated by independent cohort (PMID 23413262)\",\n      \"pmids\": [\"23378224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Expression of p.K7del beta-tropomyosin in zebrafish disrupts thin filament localization and alters sarcomere length in vivo, consistent with impaired head-to-tail polymerization of TPM2 dimers.\",\n      \"method\": \"Zebrafish in vivo overexpression, fluorescence microscopy of sarcomere structure\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo animal model with direct structural readout; single lab but corroborates PMID 23378224 findings\",\n      \"pmids\": [\"23413262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Genotype-phenotype analysis of 53 TPM2-mutation families reveals that five TPM2 mutations cause increased Ca2+ sensitivity (hypercontractile molecular phenotype), correlated with joint contractures, while non-hypercontractile mutations correlate with axial contractures; in silico analysis indicates most mutations affect tropomyosin-actin association or head-to-tail binding.\",\n      \"method\": \"Ca2+ sensitivity measurements (from prior studies referenced), clinical correlation across 93 families, in silico structural prediction\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — large multi-family correlation integrating prior functional data; direct Ca2+ sensitivity measurements cited from earlier work; in silico predictions for novel variants\",\n      \"pmids\": [\"24692096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The myopathy-causing Q147P mutation in beta-tropomyosin (TPM2) shifts tropomyosin strands closer to the center of the actin filament (open position) despite reduced actin affinity, increases the proportion of strong-binding myosin cross-bridges during ATPase cycle, and disrupts cooperation of actin and myosin heads.\",\n      \"method\": \"Polarized fluorimetry in reconstituted ghost muscle fibres, co-sedimentation assay for actin affinity\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution in ghost fibres with polarized fluorimetry; single lab, single paper\",\n      \"pmids\": [\"26708479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Epigenetic silencing of TPM2 via promoter DNA methylation suppresses its expression in colorectal cancer; treatment with demethylation agent 5-AZA restores TPM2 expression; reconstitution of TPM2 suppresses cell proliferation and migration; loss of TPM2 is associated with RhoA activation.\",\n      \"method\": \"Promoter methylation analysis, 5-AZA demethylation assay, TPM2 overexpression/knockdown in cancer cell lines, proliferation/migration assays, RhoA activity measurement\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (methylation, rescue, knockdown, RhoA assay) in single lab; mechanistic link to RhoA established by association not direct epistasis\",\n      \"pmids\": [\"27333992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The Glu139del mutation in TPM2 does not alter tropomyosin affinity for actin but markedly increases tropomyosin flexibility, keeps tropomyosin strands near the inner domain of actin (blocked-position movement inhibited at low Ca2+), increases troponin-mediated switching on/off of actin monomers, and decreases strong myosin head binding at high Ca2+ while increasing it at relaxation—mechanistically explaining hypercontractile Ca2+ sensitivity and muscle weakness.\",\n      \"method\": \"Polarized fluorescence microscopy of reconstituted ghost fibres, actin affinity assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution + polarized fluorimetry; mechanistically detailed but single lab\",\n      \"pmids\": [\"29196649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Knockdown of Tpm2.1 in MCF10A breast epithelial cells retards collective cell migration but increases single cell migration and invasion; this is associated with enhanced actomyosin contractility, increased E-cadherin/β-catenin expression, decreased AXL receptor tyrosine kinase, and is rescued by ROCK inhibition.\",\n      \"method\": \"siRNA/shRNA knockdown, wound healing and transwell migration/invasion assays, Western blotting, ROCK inhibitor treatment, spheroid re-plating assay\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (KD, rescue, inhibitor), defined pathway placement via ROCK; single lab\",\n      \"pmids\": [\"29221121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Overexpression of Tpm2.1 in rat neuroepithelial cells enhances sensitivity to anoikis and to jasplakinolide-induced apoptosis; this is accompanied by enhanced mitochondrial depolarization and elevated levels of Bak, Mcl-1, Bcl-2, and phospho-p53 (Ser392); jasplakinolide treatment of Tpm2.1-overexpressing cells reduces Mcl-1, Bcl-2, and p53(Ser392).\",\n      \"method\": \"Tpm2.1 overexpression in rat cells, apoptosis assays (anoikis, jasplakinolide), mitochondrial membrane potential assay, Western blotting of apoptosis regulators\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple apoptotic stimuli and protein-level readouts; single lab, mechanistic pathway partially defined\",\n      \"pmids\": [\"28378936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The Arg91Gly mutation in TPM2 markedly decreases bending stiffness of beta-tropomyosin in thin filaments; during ATPase cycle, mutant tropomyosin remains near the open position allowing strong myosin head binding to actin even at low Ca2+, mechanistically explaining high Ca2+ sensitivity and contractures associated with this distal arthrogryposis mutation.\",\n      \"method\": \"Polarized fluorescence microscopy of reconstituted ghost fibres during ATPase cycle\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution with structural/dynamic readout; single lab, single method\",\n      \"pmids\": [\"29097206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Smad4 SUMOylation (by E3 ligase PIAS1 at Lys-113 and Lys-159 in hippocampus) drives TPM2 upregulation; knockdown of TPM2 in rats impairs spatial learning and memory; TPM2 mRNA and protein increase after spatial training; the myopathy-associated TPM2-E122K mutation reduces TPM2 expression and impairs spatial memory in rats.\",\n      \"method\": \"SUMO site mutagenesis, rat hippocampal injection/knockdown, behavioral memory tests, Western blot, mRNA quantification\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SUMOylation site identified, KD with behavioral readout, mutation effect on expression; single lab but multiple methods\",\n      \"pmids\": [\"29183317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The Glu41Lys (E41K) mutation in TPM2 inhibits troponin's ability to shift tropomyosin to the closed position at high Ca2+, restraining thin filament transition from 'off' to 'on' state; it also inhibits S1-driven shift to the open position and inhibits switching off of actin monomers at low Ca2+—explaining reduced Ca2+ sensitivity and muscle weakness in nemaline myopathy/cap disease.\",\n      \"method\": \"Polarized fluorescence microscopy of reconstituted ghost fibres during ATPase cycle\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — detailed reconstitution; single lab, single paper\",\n      \"pmids\": [\"29792862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The R133W mutation in Tpm2.2 decreases the amount of strongly actin-bound myosin heads and number of switched-on actin monomers at high Ca2+, inhibits tropomyosin shifting towards the open position, and freezes mutant tropomyosin near the blocked position; at low Ca2+, fewer strongly-bound myosin heads contribute to low myofilament Ca2+-sensitivity—explaining muscle weakness in Sheldon-Hall syndrome.\",\n      \"method\": \"Polarized fluorescence microscopy of reconstituted ghost fibres (αβ-Tpm heterodimers and ββ-Tpm homodimers) during ATPase cycle\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution with two dimer types compared; single lab\",\n      \"pmids\": [\"31864708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mutations Q93H and E97K in Tpm2.2 both decrease actin affinity of homo- and heterodimers in vitro; Q93H strongly decreases actomyosin ATPase activation and reduces Ca2+ sensitivity (hypocontractile); E97K causes hyperactivation of ATPase and increased Ca2+ sensitivity (hypercontractile); both mutations alter tropomyosin dynamics on the filament.\",\n      \"method\": \"In vitro actin co-sedimentation, actomyosin ATPase assay, Ca2+ sensitivity measurements, trypsin susceptibility assay for dynamics\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple direct biochemical assays (binding, ATPase, Ca2+ sensitivity, conformation) for two mutations in one study\",\n      \"pmids\": [\"33919826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Expression of dominant pathogenic TPM2 variants in Drosophila embryos significantly affected muscle development and function; transient overexpression disrupted mouse myotube morphogenesis in vitro and zebrafish muscle development in vivo, establishing disrupted myogenesis as a pathomechanism of TPM2 disorders.\",\n      \"method\": \"Drosophila muscle development assays, mouse myotube morphogenesis assay, zebrafish in vivo overexpression\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — three model systems used; single lab, multiple orthogonal organism models supporting same conclusion\",\n      \"pmids\": [\"35579956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TPM2 competes with YAP1 for binding to PDLIM7 via its PDZ-binding motif; this competition prevents PDLIM7-mediated nuclear translocation of YAP1, sequestering YAP1 in the cytoplasm where it is phosphorylated at S127 and inactivated/degraded, thereby suppressing YAP1 target gene expression and prostate cancer progression.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence localization, Western blotting (p-YAP1-S127), PDZ-binding motif deletion mutant, in vitro cell proliferation/invasion assays, xenograft tumor assay\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with domain mapping, localization, and in vivo xenograft; single lab\",\n      \"pmids\": [\"36823643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hypercontractile mutations D20H and E181K in Tpm2.2 alter the binding geometry and orientation of tropomyosin on actin (by FRET), stimulate myosin motor performance and accelerate product (ADP/Pi) release kinetics; hypocontractile mutations E41K and N202K inhibit actin activation of myosin ATPase, motor activity, and decelerate product release—demonstrating opposite mechanochemical effects on the cross-bridge cycle.\",\n      \"method\": \"FRET assays for Tpm orientation on actin, myosin ATPase assay, in vitro motility assay, single ATP turnover kinetics\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biochemical assays (FRET, ATPase, motility, single-turnover kinetics) with four mutations in one study\",\n      \"pmids\": [\"38156416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"At low Ca2+, all four pathogenic Tpm2.2 variants (D20H, E181K, E41K, N202K) inhibit troponin-regulated actomyosin ATPase without affecting troponin binding to actin; at activating Ca2+, hypocontractile mutants suppress ATPase and motor function while hypercontractile mutants enhance myosin-driven actin translocation; N-terminal mutations (D20H, E181K) enhance high-affinity Tpm2.2-troponin interactions; hypercontractile mutants increase Ca2+ sensitivity while hypocontractile mutants decrease it.\",\n      \"method\": \"In vitro actomyosin ATPase assay, in vitro motility assay, Tpm-troponin binding assay, Arrhenius analysis of temperature dependence\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal in vitro assays dissecting Tn-dependent and Tn-independent regulation; four mutations systematically compared in one study\",\n      \"pmids\": [\"40657867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cytoplasmic TPM2 isoforms (Tpm2.1, Tpm2.3, Tpm2.4) directly interact with fascin-1 (pull-down assay) and inhibit fascin-1-mediated actin bundling by reducing fascin-1 affinity for actin; Tpm2 occupancy on actin filaments partially displaces fascin-1; fascin-1 binding does not affect Tpm2 affinity for actin; Tpm2.4 shows highest actin and fascin-1 affinities; overexpression of Tpm2 isoforms in SAOS-2 LM5 cells reduces fascin co-localization with actin.\",\n      \"method\": \"High-speed centrifugation (actin affinity), low-speed centrifugation and fluorescence microscopy (bundling), pull-down assay (direct Tpm2-fascin interaction), confocal microscopy in SAOS-2 cells\",\n      \"journal\": \"Biological research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct binding demonstrated by pull-down, functional consequences by multiple in vitro assays, and cell-based confirmation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"40887664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TPM2 overexpression in HTR-8/SVneo trophoblast cells enhances migration and invasion, suppresses IL-6, IL-1β, and IL-8 production, inhibits IκBα degradation, and blocks nuclear translocation of NF-κB p65, establishing TPM2 as a suppressor of NF-κB-mediated inflammation.\",\n      \"method\": \"TPM2 overexpression in trophoblast cells, migration/invasion assays, cytokine ELISA, Western blot for IκBα and p65 nuclear translocation\",\n      \"journal\": \"Tissue & cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple assays in single lab but no rescue or domain mapping; single paper\",\n      \"pmids\": [\"41297249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Wild-type Tpm2.2 inhibits spontaneous actin polymerization; hypercontractile D20H and E181K further decrease polymerization rate; hypocontractile E41K and N202K stabilize filaments under actomyosin-driven conditions increasing filament length (abolished by troponin); all variants slightly decrease cofilin-2 affinity for F-actin; Tpm2.2-N202K inhibits cofilin-2-dependent depolymerization while E181K increases susceptibility; the Tpm2.2-troponin complex protects filaments from cofilin-2-induced disassembly.\",\n      \"method\": \"In vitro actin polymerization assay, filament stability and length measurement under actomyosin conditions, cofilin-2 binding and depolymerization assays, structural modeling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — preprint; multiple in vitro assays but not yet peer-reviewed; single lab\",\n      \"pmids\": [\"42239403\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TPM2-encoded beta-tropomyosin (Tpm2.2 in striated muscle) is an actin-binding coiled-coil protein that regulates muscle contraction by controlling tropomyosin strand positioning on the thin filament: it gates Ca2+-dependent transitions between blocked, closed, and open states to permit or inhibit myosin cross-bridge formation; disease-causing mutations alter actin affinity, tropomyosin flexibility and position, Ca2+ sensitivity, myosin ATPase kinetics, and filament dynamics in ways that produce either hyper- or hypocontractile phenotypes; cytoplasmic Tpm2 isoforms additionally regulate actin bundling by inhibiting fascin-1, modulate cell migration through actomyosin contractility and ROCK signaling, suppress YAP1 nuclear activity by competing with PDLIM7, and regulate apoptosis sensitivity through modulation of intrinsic apoptosis proteins.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TPM2 encodes beta-tropomyosin, an actin-binding coiled-coil protein that regulates striated muscle contraction by positioning tropomyosin strands on the thin filament and gating Ca2+-dependent transitions between blocked, closed, and open states that permit or inhibit myosin cross-bridge formation [#2, #6, #18]. Pathogenic missense and in-frame deletion mutations cluster in actin-binding and head-to-tail polymerization regions and act through several biophysical mechanisms: reduced actin affinity and impaired sarcomeric incorporation [#2, #3], altered tropomyosin flexibility and azimuthal position on actin [#8, #11], and shifted equilibrium of the thin filament regulatory state [#6, #13, #14]. These changes resolve into two opposing molecular phenotypes — hypercontractile variants that hold tropomyosin near the open position, increase Ca2+ sensitivity, accelerate myosin product release, and stimulate motor activity, versus hypocontractile variants that freeze tropomyosin near the blocked position, reduce Ca2+ sensitivity, and suppress actomyosin ATPase and motility [#15, #18, #19]. Beyond steady-state regulation, Tpm2.2 controls thin filament dynamics by inhibiting spontaneous actin polymerization and modulating cofilin-2-mediated filament turnover, with the tropomyosin–troponin complex protecting filaments from disassembly [#22]. Direct genetic and biochemical evidence establishes TPM2 mutations as a cause of nemaline myopathy, cap disease, distal arthrogryposis, and Sheldon-Hall syndrome [#0, #1, #11, #14], and disrupted myogenesis is itself a pathomechanism across model organisms [#16]. Cytoplasmic Tpm2 isoforms perform distinct cytoskeletal roles: they directly bind and inhibit fascin-1-mediated actin bundling [#20], regulate cell migration and invasion through actomyosin contractility and ROCK signaling [#9], and suppress tumor progression by competing with YAP1 for PDLIM7 to retain YAP1 in the cytoplasm in its inactivated form [#17].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that TPM2 mutations cause human myopathy, framing beta-tropomyosin as a disease gene whose lesions likely act through dimer formation and actin binding.\",\n      \"evidence\": \"SSCP, sequencing and mutant-allele expression analysis in nemaline myopathy patients\",\n      \"pmids\": [\"11738357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effect on actin binding was predicted, not directly assayed\", \"No biophysical measurement of the contractile defect\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed that an in-frame deletion disrupting the coiled-coil heptad repeat incorporates into sarcomeres and likely acts dominant-negatively, linking structural disruption to cap disease.\",\n      \"evidence\": \"Genetic sequencing and 2D-gel electrophoresis of patient muscle\",\n      \"pmids\": [\"17434307\", \"19345583\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Dominant-negative mechanism inferred rather than directly demonstrated\", \"No reconstituted thin-filament functional readout\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Provided the first direct biochemical demonstration that disease mutations alter actin affinity, Ca2+ activation, and protein conformation, moving from genetic association to assayed mechanism.\",\n      \"evidence\": \"In vitro actin co-sedimentation, Ca2+-activation of contractility, and conformation analysis of four mutations\",\n      \"pmids\": [\"22084935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve tropomyosin position on the filament\", \"Cross-bridge cycle kinetics not measured\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connected reduced actin affinity to defective sarcomeric incorporation, nemaline rod formation, and altered force/Ca2+ sensitivity in patient fibres, and corroborated the polymerization defect in vivo.\",\n      \"evidence\": \"Recombinant binding assay, C2C12 transfection, single patient myofibre force measurement, and zebrafish overexpression\",\n      \"pmids\": [\"23378224\", \"23413262\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism limited to one mutation (K7del)\", \"Head-to-tail polymerization defect inferred from localization\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Correlated molecular phenotype with clinical presentation across many families, establishing that increased Ca2+ sensitivity (hypercontractility) tracks with joint contractures.\",\n      \"evidence\": \"Genotype-phenotype analysis of TPM2-mutation families with in silico structural prediction\",\n      \"pmids\": [\"24692096\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Many variant effects predicted in silico, not measured\", \"Ca2+ sensitivity data drawn from prior studies\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined at the structural level how individual mutations reposition tropomyosin on actin and shift the blocked/closed/open equilibrium to produce hyper- or hypocontractile states.\",\n      \"evidence\": \"Polarized fluorescence microscopy of reconstituted ghost fibres during the ATPase cycle (Q147P, Glu139del, Arg91Gly)\",\n      \"pmids\": [\"26708479\", \"29196649\", \"29097206\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each result from a single lab and method\", \"Quantitative myosin kinetics not directly measured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended the positional model to additional weakness-causing mutations and compared heterodimer versus homodimer behavior, linking blocked-position freezing to low Ca2+ sensitivity.\",\n      \"evidence\": \"Polarized fluorescence microscopy of reconstituted ghost fibres (E41K, R133W; αβ and ββ dimers)\",\n      \"pmids\": [\"29792862\", \"31864708\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab reconstitution data\", \"In vivo relevance of homo- vs heterodimer differences unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematically partitioned mutations into hyper- and hypocontractile classes using direct ATPase and Ca2+ sensitivity measurements, consolidating the two-class mechanistic model.\",\n      \"evidence\": \"Actin co-sedimentation, actomyosin ATPase, Ca2+ sensitivity, and trypsin-susceptibility assays (Q93H, E97K)\",\n      \"pmids\": [\"33919826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Two mutations only\", \"Did not address filament turnover or thin-filament assembly\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the mechanochemical basis of the two phenotype classes, showing hypercontractile mutations accelerate and hypocontractile mutations decelerate myosin product release.\",\n      \"evidence\": \"FRET orientation assays, myosin ATPase, in vitro motility, and single-turnover kinetics (D20H, E181K, E41K, N202K)\",\n      \"pmids\": [\"38156416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Performed without full troponin regulation in some readouts\", \"Structural cause of orientation changes not solved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Dissected troponin-dependent versus troponin-independent regulation and mapped N-terminal mutations to enhanced tropomyosin-troponin affinity, refining how variants distort Ca2+-regulated switching.\",\n      \"evidence\": \"Actomyosin ATPase, in vitro motility, Tpm-troponin binding, and Arrhenius analysis of four variants\",\n      \"pmids\": [\"40657867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of N-terminal affinity enhancement unresolved\", \"Effects measured in reconstituted not cellular systems\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established a non-muscle role for cytoplasmic Tpm2 isoforms as direct inhibitors of fascin-1-mediated actin bundling, distinguishing isoform-specific cytoskeletal regulation.\",\n      \"evidence\": \"Pull-down, co-sedimentation, bundling assays, and confocal microscopy in SAOS-2 cells\",\n      \"pmids\": [\"40887664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular consequences for migration/metastasis not directly tested\", \"Structural basis of Tpm2-fascin competition unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a tumor-suppressive signaling mechanism in which TPM2 competes with YAP1 for PDLIM7 to retain YAP1 in the cytoplasm in its phosphorylated, inactive state.\",\n      \"evidence\": \"Reciprocal Co-IP, PDZ-motif deletion mapping, immunofluorescence, and xenograft assays\",\n      \"pmids\": [\"36823643\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"Link between cytoskeletal and signaling functions not integrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated TPM2 in regulating cell migration, invasion, apoptosis, and NF-κB-driven inflammation, indicating broad non-sarcomeric functions tied to actomyosin and signaling.\",\n      \"evidence\": \"Knockdown/overexpression with migration, apoptosis, ROCK-inhibitor, and cytokine/NF-κB readouts in epithelial, neuroepithelial, and trophoblast cells\",\n      \"pmids\": [\"29221121\", \"28378936\", \"27333992\", \"41297249\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic links established mostly by association\", \"No domain mapping or rescue for several effects\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the distinct sarcomeric, cytoskeletal-bundling, and signaling functions of TPM2 isoforms are integrated, and whether a unified structural framework explains both contractile and non-muscle roles, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking position changes to non-muscle isoform function\", \"Isoform-specific in vivo functions not delineated\", \"Cross-talk between actin-bundling and YAP/NF-κB signaling untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 3, 6, 18, 20]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3, 4, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [18, 19, 20, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 4, 20]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [17, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [2, 6, 18, 19]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 3, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [17, 21]}\n    ],\n    \"complexes\": [\"thin filament (actin-tropomyosin-troponin)\"],\n    \"partners\": [\"ACTA1\", \"TNNT\", \"fascin-1 (FSCN1)\", \"PDLIM7\", \"YAP1\", \"cofilin-2 (CFL2)\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}