{"gene":"TAGLN","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":1987,"finding":"SM22 (TAGLN) was isolated and characterized as an abundant ~22 kDa protein from chicken gizzard smooth muscle, existing as a monomer at physiological ionic strength with a moderately asymmetric globular structure (~37% α-helix, ~31% β-sheet); it was shown not to share functional properties with myokinase, brain 23-kDa protein, or troponin I, establishing it as a novel smooth muscle protein.","method":"SDS-PAGE, sedimentation equilibrium, Stokes radius measurement, CD spectroscopy, purification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — rigorous biophysical characterization with multiple orthogonal methods on purified protein","pmids":["3818630"],"is_preprint":false},{"year":1987,"finding":"SM22 (TAGLN) is widely distributed in smooth muscles of birds and mammals (chicken and bovine aorta, pig carotid, uterus, intestine, gizzard, oesophagus) with molar abundance relative to actin of ~1:6 in bovine aorta; present only in trace amounts or absent in brain, liver, heart, and skeletal muscle.","method":"Immunoblotting with polyclonal antibody, 1D and 2D gel electrophoresis, purification from bovine aorta","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — multiple tissues, multiple methods, replicated across species","pmids":["3446186"],"is_preprint":false},{"year":1987,"finding":"The complete amino acid sequence of chicken gizzard SM22α was determined: a single polypeptide of 197 residues with Mr ~21,978 and net charge of +4.5 at neutral pH; no significant similarity to any known protein at the time, confirming it as a novel protein.","method":"Automated and manual Edman degradation sequencing of chemical and proteolytic fragments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing, complete primary structure determination","pmids":["3571244"],"is_preprint":false},{"year":1993,"finding":"Rat SM22 encodes a 201-amino acid protein (Mr 22,601) with 43% identity to calponin over a 181-aa overlap, particularly high (70%) identity at the C-terminal region of SM22 and the first repeat motif of calponin, establishing structural homology between SM22 and calponin.","method":"cDNA cloning, sequencing, sequence alignment","journal":"Gene","confidence":"High","confidence_rationale":"Tier 1 — direct cDNA cloning and sequence analysis establishing structural relationship","pmids":["8359698"],"is_preprint":false},{"year":1994,"finding":"A bovine aorta SM22 homolog (25-kDa) directly binds F-actin at a ratio of 1:6 actin monomers with a binding constant of 7.0 × 10^5 M⁻¹, and the interaction is Ca²⁺-sensitive: the protein associates with the membrane fraction in the presence of Ca²⁺ and dissociates with EGTA.","method":"Protein purification, F-actin cosedimentation assay, Ca²⁺-dependent membrane fractionation, partial sequence analysis","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro binding assay with defined stoichiometry and binding constant","pmids":["8117285"],"is_preprint":false},{"year":1995,"finding":"The murine SM22α gene promoter (441 bp of 5'-flanking sequence) containing two CArG/SRF boxes, a CACC box, and a MEF-2 binding site is necessary and sufficient to drive high-level transcription specifically in smooth muscle cells; deletion analysis defined the core promoter elements.","method":"Transient transfection, luciferase reporter assay, deletion analysis in primary rat aortic SMCs and A7r5 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted transcription with defined cis-elements, multiple deletion constructs","pmids":["7768949"],"is_preprint":false},{"year":2000,"finding":"Human SM22 (TAGLN) binds F-actin through multiple regions within its C-terminal domain: the region 170–186 is almost completely required, the segment 154–161 (KKAQEHKR) partially required, and residues beyond 151 are necessary; the N-terminal domain alone is insufficient. Phosphorylation of Ser-181 by protein kinase C greatly decreases actin binding, and a S181D phosphomimetic also reduces binding. In transfected airway myocytes, full-length SM22 colocalizes with actin filaments while truncated SM22-(1-151) does not.","method":"Site-directed mutagenesis, E. coli expression of His-tagged mutants, in vitro actin cosedimentation assay, PKC phosphorylation assay, immunofluorescence in transfected cells","journal":"Journal of applied physiology","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro binding with systematic mutagenesis and functional validation in cells","pmids":["11053353"],"is_preprint":false},{"year":2000,"finding":"SM22 (TAGLN) is identified as a novel protein kinase C (PKC) substrate in smooth muscle cells; phosphorylation by PKC in vitro was confirmed and, upon PKC activation in vivo, SM22 dissociates from the actin cytoskeleton and redistributes diffusely in the cytoplasm, demonstrating that PKC-mediated phosphorylation controls SM22 intracellular localization.","method":"In vitro PKC kinase assay, 2D gel electrophoresis, mass spectrometry identification, immunofluorescence in PKC-activated cells","journal":"Electrophoresis","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro kinase assay combined with in vivo localization change upon PKC activation","pmids":["10939458"],"is_preprint":false},{"year":2006,"finding":"SM22 (transgelin/TAGLN) represses MMP-9 expression by targeting the ERK/MAPK signaling pathway, leading to reduced AP-1 (c-Fos) binding to the proximal MMP-9 promoter AP-1 motif; this requires an intact N-terminal calponin homology domain. SM22 knockdown by siRNA elevates MMP-9 synthesis and invasion, while SM22 null mouse uterus shows strong MMP-9 immunoreactivity.","method":"Expression cloning, siRNA knockdown, overexpression in HT1080 cells, MMP-9 promoter deletion/mutation analysis, AP-1 reporter assay, nuclear extract EMSA for c-Fos binding, in vitro invasion assay, immunohistochemistry in SM22-null mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods: expression cloning, promoter mapping, mutagenesis, in vivo validation","pmids":["16835221"],"is_preprint":false},{"year":2008,"finding":"Yeast SM22 homolog Scp1 (ortholog of mammalian TAGLN) contains two distinct actin-binding domains that allow it to both bind and bundle F-actin without dimerization; live cell imaging showed Scp1 localizes to cortical actin patches during endocytosis and is required for movement of patches away from the plasma membrane. Loss of both Scp1 and fimbrin Sac6 dramatically increases patch lifetime, demonstrating that actin-bundling activity is critical for endocytosis.","method":"Live cell imaging of GFP-tagged mutants, in vitro actin bundling assays, genetic deletion and epistasis (scp1Δ sac6Δ double mutant), Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — reconstituted actin bundling + live imaging + genetic epistasis in yeast ortholog","pmids":["18400761"],"is_preprint":false},{"year":2010,"finding":"SM22 (TAGLN) disruption in vascular smooth muscle cells (VSMCs) promotes NF-κB pathway activation via increased reactive oxygen species (ROS) production involving NADPH oxidase (p47phox activation) and mitochondria (increased Sod2), leading to upregulation of proinflammatory genes (Vcam1, Icam1, Cx3cl1, Ccl2, Ptgs2) after arterial injury; ROS scavengers blocked NF-κB activation and gene induction.","method":"SM22 knockout mouse carotid denudation model, primary Sm22⁻/⁻ VSMCs, siRNA knockdown in PAC1 cells, ROS measurement, NF-κB activation assay, ROS scavenger rescue experiments","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — in vivo knockout + primary cell validation + pharmacological rescue with defined molecular pathway","pmids":["20224039"],"is_preprint":false},{"year":2010,"finding":"SM22 deficiency promotes chondrogenic conversion of VSMCs: loss of SM22 alters VSMC morphology with compromised stress fiber formation and increased actin dynamics, upregulates Sox9 mRNA and chondrogenic markers (type II collagen, aggrecan, BMP2), and downregulates myocardin and VSMC markers; this chondrogenic switch is mediated via ROS-NF-κB pathway activation.","method":"SM22 knockout mouse carotid denudation model, primary Sm22⁻/⁻ VSMCs, SM22 siRNA knockdown, immunostaining for chondrogenic markers, actin dynamics assay","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 — in vivo knockout + primary cells + mechanistic pathway identification","pmids":["21183509"],"is_preprint":false},{"year":2012,"finding":"Depletion of SM22 (TAGLN) in REF52 fibroblasts disrupts normal actin organization, increases cell motility, increases spontaneous podosome formation, and enhances Matrigel invasion; conversely, re-expression of SM22 in SM22-negative PC3 prostate cancer cells reduces Matrigel invasion. SM22-depleted cells also have reduced ROS under serum starvation stress.","method":"siRNA knockdown in REF52 fibroblasts, SM22 re-expression in PC3 cells, actin organization imaging, podosome quantification, Matrigel invasion assay, ROS measurement","journal":"BMC cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD/OE with defined cellular phenotypes, single lab","pmids":["22257561"],"is_preprint":false},{"year":2015,"finding":"SM22 (TAGLN) phosphorylation by Rho kinase (ROCK), but not PKC, inversely correlates with SM22-actin binding in smooth muscle cells; SM22 overexpression (pFLAG-SM22) causes relaxation in tonic IAS smooth muscle cells greater than in phasic RSM cells, while SM22 siRNA causes contraction in both cell types, indicating SM22 regulates basal tone via ROCK-induced phosphorylation affecting its actin binding.","method":"SM22 overexpression (pFLAG-SM22 transfection), siRNA knockdown, measurement of SMC length, phospho-SM22 western blot, Y-27632 (ROCK inhibitor) and Gö-6850 (PKC inhibitor) treatment","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — functional OE/KD with biochemical mechanism (phosphorylation-actin binding link), single lab","pmids":["25617350"],"is_preprint":false},{"year":2021,"finding":"TAGLN acts as a mechanosensitive gene in ovarian cancer cells: matrix stiffness upregulates TAGLN expression, TAGLN activates Src, and Src in turn feeds back on TAGLN in a regulation loop mediating stiffness-induced OC progression through the RhoA/ROCK pathway.","method":"Atomic force microscopy for stiffness measurement, polyacrylamide hydrogel system (soft vs. stiff), siRNA knockdown, western blot, immunofluorescence, in vivo xenograft","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — mechanosensitive function demonstrated with defined pathway, multiple in vitro and in vivo methods","pmids":["34538264"],"is_preprint":false},{"year":2021,"finding":"TAGLN is expressed in endothelial cells (ECs) and functions as a negative regulator of angiogenesis: TAGLN expression is activated during EC elongation in response to VEGF-A; genetic disruption of TAGLN in HUVECs augments angiogenic behaviors (tube formation, sprouting); similar results were obtained with TAGLN2 and TAGLN3 knockouts.","method":"Mouse ESC Tagln promoter-fluorescence reporter, VEGF-A stimulation, PI3K-Akt/mTORC1 inhibition, CRISPR genetic disruption in HUVECs, angiogenesis assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — genetic disruption with defined angiogenic phenotype, multiple approaches","pmids":["34338296"],"is_preprint":false},{"year":2021,"finding":"TRAF6 mediates mono-ubiquitination of TAGLN at K89 or K108 residues via the E2A-TRAF6 pair, leading to proteasomal degradation of TAGLN in prostate cancer cells. Loss of TAGLN activates NF-κB and Myc signaling pathways, promoting cancer cell proliferation and suppressing migration.","method":"In vitro ubiquitination assay screening >20 E2-E3 pairs, site-directed mutagenesis of ubiquitination sites, proteasome inhibitor rescue, western blot, siRNA/overexpression functional assays","journal":"Molecular cancer research","confidence":"High","confidence_rationale":"Tier 1 — in vitro ubiquitination reconstitution with mutagenesis of specific sites, functional consequences defined","pmids":["33771884"],"is_preprint":false},{"year":2021,"finding":"ALKBH5, an m6A demethylase, binds to m6A sites in TAGLN mRNA and reduces m6A methylation of TAGLN mRNA, thereby inhibiting its degradation and increasing TAGLN protein expression; elevated TAGLN then inhibits proliferation and migration of enteric neural crest cells, contributing to Hirschsprung's disease.","method":"MeRIP-qPCR, dual-luciferase reporter assay, ALKBH5 overexpression/knockdown, cell proliferation and migration assays, zebrafish overexpression model","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — MeRIP-qPCR defines writer/reader interaction, functional consequence in cells and zebrafish model","pmids":["33961858"],"is_preprint":false},{"year":2020,"finding":"TAGLN physically interacts with HMGA2, and TGF-β-induced TAGLN undergoes nuclear translocation; knockdown of TAGLN reverses TGF-β-induced EMT markers (E-cadherin loss, vimentin, fibronectin upregulation) and MMP2/MMP9 elevation in colorectal cancer cells; HMGA2 overexpression restores TGF-β effects suppressed by TAGLN inhibition in vitro and in vivo.","method":"Co-immunoprecipitation, siRNA knockdown, TGF-β treatment, western blot for EMT markers, migration/invasion assays, in vivo tumor growth experiment","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 3 — single Co-IP identifying TAGLN-HMGA2 interaction, supported by functional rescue experiments","pmids":["33116628"],"is_preprint":false},{"year":2007,"finding":"The C-terminal domain of SM22α (TAGLN) directly interacts with F-actin to participate in cytoskeleton reorganization in VSMCs: GST pull-down and co-immunoprecipitation confirmed SM22-actin interaction; immunofluorescence showed SM22α colocalizes with F-actin during VSMC redifferentiation, and SM22α distributes predominantly in F-actin fractions (not G-actin) during the contractile phenotype.","method":"GST pull-down assay, co-immunoprecipitation, western blot of F-actin/G-actin fractions, immunofluorescence in VSMCs undergoing phenotypic modulation","journal":"Chinese journal of applied physiology","confidence":"Medium","confidence_rationale":"Tier 2 — GST pull-down + co-IP + fractionation + localization in same study","pmids":["21162287"],"is_preprint":false},{"year":2025,"finding":"TAGLN regulates skin fibroblast motility and secretory function (invasion, migration, contraction, collagen secretion) through a mechano-metabolic axis: TAGLN activates the RhoA/ROCK2 pathway, which upregulates the glucose transporter SLC2A3, thereby affecting glycolysis in dermal fibroblasts. Targeting TAGLN reduced fibrosis in a bleomycin-induced mouse model.","method":"Transwell, wound healing, collagen gel contraction assay, immunofluorescence, RNA-seq, siRNA knockdown/overexpression, western blot, bleomycin mouse model","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — RNA-seq identifies downstream target (SLC2A3), pathway validation by multiple functional assays and in vivo","pmids":["39781462"],"is_preprint":false},{"year":2025,"finding":"NRF2 directly transcriptionally activates TAGLN: a functional antioxidant response element (ARE) was identified in the TAGLN promoter; ChIP confirmed NRF2 binding; TAGLN mediates NRF2-promoted ovarian cancer cell migration and EMT (E-cadherin down, N-cadherin up), as TAGLN siRNA reversed NRF2 overexpression effects on migration and EMT markers.","method":"Dual luciferase reporter assay, ChIP assay, siRNA knockdown, wound-healing and Transwell assays, western blot for EMT markers","journal":"Journal of ovarian research","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP + luciferase reporter + functional rescue establishes NRF2 as transcriptional writer for TAGLN","pmids":["41029755"],"is_preprint":false},{"year":2014,"finding":"TAGLN upregulation in NF1-associated MPNSTs is caused by hypomethylation of its promoter and subpromoter regions; TAGLN knockdown in MPNST cells decreases RAS-GTP and phospho-ERK1/2 activation, while TAGLN overexpression in normal NF1-deficient cells increases RAS and ERK1/2 activation, placing TAGLN as an activator of the RAS-MAPK pathway.","method":"DNA methylation analysis, siRNA knockdown, TAGLN overexpression, western blot for GTP-RAS and phospho-ERK1/2, immunohistochemistry","journal":"Oncology reports","confidence":"Medium","confidence_rationale":"Tier 2 — epigenetic mechanism identified + bidirectional functional manipulation of RAS-MAPK pathway","pmids":["25109740"],"is_preprint":false},{"year":2005,"finding":"Fission yeast Stg1, an SM22/transgelin-like protein (ortholog of mammalian TAGLN), crosslinks F-actin in vitro and localizes to actin patches; Stg1 overexpression causes cytokinesis defects by suppressing contractile ring formation and generating abnormal F-actin aggregates, implicating TAGLN orthologs in actin cytoskeleton organization and cytokinesis.","method":"In vitro F-actin crosslinking assay, fluorescence microscopy of actin patches, Stg1 overexpression phenotype analysis in fission yeast","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro biochemistry + in vivo genetic manipulation in yeast ortholog","pmids":["16256112"],"is_preprint":false},{"year":2003,"finding":"AVP induces and PDGF-BB suppresses SM22α expression in VSMCs through distinct signaling pathways: AVP activates both JNK and p38 MAPK and requires the proximal CArG boxes in the SM22α promoter and serum response factor (SRF) binding; PDGF suppression involves Raf, Ral-GDS, and PI3K activation downstream of Ras, independently of CArG boxes.","method":"Promoter-reporter assays, truncation analysis, CArG box mutagenesis, dominant-active and dominant-negative signaling constructs, SRF overexpression, kinase inhibitor experiments","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple promoter constructs and signaling pathway dissection, single lab","pmids":["12829429"],"is_preprint":false}],"current_model":"TAGLN (SM22α/transgelin) is a ~22 kDa actin-binding and actin-bundling protein that binds F-actin through multiple C-terminal domain regions (residues ~154–186 critical), stabilizes the actin cytoskeleton in smooth muscle and other cells, and is regulated by phosphorylation at Ser-181 by PKC and by ROCK — phosphorylation disrupts actin binding and causes cytoplasmic redistribution; it suppresses MMP-9 expression by dampening ERK/AP-1 signaling, restrains NF-κB/ROS-driven inflammation in VSMCs, is transcriptionally activated by SRF via CArG boxes and by NRF2 via an ARE, and is post-translationally degraded via TRAF6-mediated K89/K108 ubiquitination; in cancer contexts it can act as either a tumor suppressor or oncogene depending on cell type, partly through interactions with HMGA2 and the RhoA/ROCK2-SLC2A3 mechano-metabolic axis."},"narrative":{"teleology":[{"year":1987,"claim":"Identification and biophysical characterization of SM22 as a novel, abundant smooth-muscle-specific protein resolved its identity as distinct from all known muscle proteins, establishing it as a new cytoskeletal component to study.","evidence":"Purification from chicken gizzard smooth muscle with SDS-PAGE, sedimentation equilibrium, Stokes radius, CD spectroscopy; immunoblotting across bird and mammalian tissues","pmids":["3818630","3446186","3571244"],"confidence":"High","gaps":["No binding partner or function identified at this stage","Expression analysis limited to immunoblotting with one polyclonal antibody"]},{"year":1993,"claim":"Establishing structural homology between SM22 and calponin placed TAGLN within the calponin family and predicted actin-binding capability, framing subsequent biochemical studies.","evidence":"cDNA cloning and sequence alignment of rat SM22 vs. calponin showing 43% identity over 181 aa","pmids":["8359698"],"confidence":"High","gaps":["Functional similarity to calponin not yet tested","No direct actin-binding data at this point"]},{"year":1994,"claim":"Direct demonstration that SM22 binds F-actin with defined stoichiometry (1:6) and a Ca²⁺-sensitive membrane association answered the fundamental question of molecular function.","evidence":"F-actin cosedimentation assay with purified bovine aorta SM22 homolog, Ca²⁺-dependent membrane fractionation","pmids":["8117285"],"confidence":"High","gaps":["Actin-binding domain not mapped","Physiological relevance of Ca²⁺ sensitivity unclear"]},{"year":1995,"claim":"Mapping the SM22α promoter to CArG/SRF boxes explained smooth-muscle-specific transcription and provided the regulatory logic for lineage-restricted expression.","evidence":"Transient transfection with luciferase reporters and deletion constructs in primary rat aortic SMCs and A7r5 cells","pmids":["7768949"],"confidence":"High","gaps":["Contribution of MEF-2 and CACC elements not functionally separated","In vivo promoter activity not tested with transgenic models in this study"]},{"year":2000,"claim":"Systematic mutagenesis mapped the actin-binding interface to C-terminal residues 154–186 and identified PKC phosphorylation of Ser-181 as a switch that disrupts actin binding and relocalizes SM22 to the cytoplasm, establishing the first regulatory mechanism for TAGLN function.","evidence":"Site-directed mutagenesis, His-tagged mutant cosedimentation, PKC phosphorylation assay, immunofluorescence in transfected airway myocytes; in vitro PKC assay with mass spectrometry and in vivo localization in PKC-activated cells","pmids":["11053353","10939458"],"confidence":"High","gaps":["Identity of in vivo kinase(s) not resolved (PKC isoform specificity unclear)","Whether phosphorylation is reversible and by which phosphatase unknown"]},{"year":2003,"claim":"Demonstrating that AVP-induced SM22α expression requires SRF binding to CArG boxes while PDGF suppression operates through Ras effectors independently of CArG elements revealed dual and opposing signaling inputs converging on the SM22 promoter.","evidence":"Promoter-reporter truncation/mutation analysis, dominant-negative/active signaling constructs, SRF overexpression, kinase inhibitors in VSMCs","pmids":["12829429"],"confidence":"Medium","gaps":["Chromatin-level regulation not addressed","In vivo relevance of AVP/PDGF antagonism on SM22 not tested"]},{"year":2005,"claim":"Demonstrating that fission yeast and budding yeast SM22 orthologs crosslink/bundle F-actin and function in actin patch dynamics and endocytosis established evolutionary conservation of the actin-bundling mechanism and linked it to membrane trafficking.","evidence":"In vitro F-actin crosslinking, fluorescence microscopy of actin patches, overexpression phenotype in S. pombe (Stg1); live imaging, bundling assay, genetic epistasis with fimbrin in S. cerevisiae (Scp1)","pmids":["16256112","18400761"],"confidence":"High","gaps":["Whether mammalian TAGLN similarly functions in endocytic actin patches not tested","Structural basis of dual actin-binding domain architecture not resolved"]},{"year":2006,"claim":"Discovery that SM22 represses MMP-9 by inhibiting ERK/AP-1 signaling, validated in SM22-null mice, established TAGLN as a signaling modulator beyond a structural actin-binding protein.","evidence":"Expression cloning, siRNA, overexpression in HT1080, MMP-9 promoter deletion/EMSA, AP-1 reporter, invasion assay, SM22-null mouse immunohistochemistry","pmids":["16835221"],"confidence":"High","gaps":["Whether MMP-9 repression is direct or mediated through cytoskeletal changes not resolved","Calponin homology domain contribution to ERK inhibition not mechanistically explained"]},{"year":2010,"claim":"SM22 knockout in VSMCs revealed that TAGLN restrains NF-κB activation via suppression of ROS (NADPH oxidase/mitochondrial), and that its loss drives proinflammatory gene expression and chondrogenic transdifferentiation, expanding its role to vascular inflammation and cell fate.","evidence":"SM22 knockout mouse carotid injury model, primary Sm22−/− VSMCs, siRNA, ROS measurement, NF-κB assay, ROS scavenger rescue, immunostaining for chondrogenic markers","pmids":["20224039","21183509"],"confidence":"High","gaps":["Direct molecular target linking SM22 to NADPH oxidase suppression unknown","Whether chondrogenic conversion is reversible upon SM22 restoration not shown"]},{"year":2014,"claim":"Identification of TAGLN as an activator of RAS-MAPK signaling in NF1-associated tumors, upregulated by promoter hypomethylation, revealed a context-dependent oncogenic role contrasting its tumor-suppressive function elsewhere.","evidence":"DNA methylation analysis, siRNA knockdown and overexpression, GTP-RAS and phospho-ERK1/2 western blot in MPNST cells","pmids":["25109740"],"confidence":"Medium","gaps":["Mechanism by which TAGLN activates RAS-GTP loading not identified","Whether this is specific to NF1-deficient context not resolved"]},{"year":2015,"claim":"Establishing that ROCK (not only PKC) phosphorylates SM22 to regulate actin binding and smooth muscle basal tone added a second kinase input and linked TAGLN to RhoA/ROCK contractile signaling.","evidence":"SM22 overexpression/siRNA in IAS and RSM cells, phospho-SM22 western blot, ROCK inhibitor (Y-27632) and PKC inhibitor treatments, cell length measurement","pmids":["25617350"],"confidence":"Medium","gaps":["Specific ROCK phosphorylation site on SM22 not mapped","In vivo contribution of ROCK vs. PKC phosphorylation not quantified"]},{"year":2020,"claim":"Identification of a physical TAGLN–HMGA2 interaction and TGF-β-induced nuclear translocation of TAGLN revealed a non-cytoskeletal mechanism through which TAGLN promotes EMT in colorectal cancer.","evidence":"Co-immunoprecipitation, siRNA knockdown, TGF-β treatment, EMT marker western blot, in vivo tumor growth","pmids":["33116628"],"confidence":"Medium","gaps":["Single Co-IP without reciprocal validation or domain mapping","Mechanism of TAGLN nuclear translocation not defined","Whether TAGLN-HMGA2 interaction occurs in non-cancer contexts unknown"]},{"year":2021,"claim":"Multiple studies in 2021 expanded TAGLN regulation and function: TRAF6-mediated ubiquitination at K89/K108 was identified as the degradation pathway; ALKBH5-dependent m6A demethylation stabilizes TAGLN mRNA affecting enteric neural crest cells; TAGLN acts as a mechanosensor activating Src/RhoA/ROCK in ovarian cancer; and TAGLN negatively regulates angiogenesis in endothelial cells.","evidence":"In vitro ubiquitination reconstitution with mutagenesis (TRAF6); MeRIP-qPCR and zebrafish model (ALKBH5/m6A); AFM, hydrogels, siRNA, xenografts (mechanosensing); CRISPR disruption in HUVECs (angiogenesis)","pmids":["33771884","33961858","34538264","34338296"],"confidence":"Medium","gaps":["Whether TRAF6 ubiquitination is regulated by upstream signals unknown","m6A regulation shown only for Hirschsprung's context; generalizability unclear","Mechanosensor mechanism (how stiffness upregulates TAGLN) not defined"]},{"year":2025,"claim":"Identification of NRF2 as a direct transcriptional activator of TAGLN via an ARE element, and discovery of the TAGLN→RhoA/ROCK2→SLC2A3 mechano-metabolic axis in fibrosis, connected TAGLN to oxidative stress responses and glycolytic metabolism.","evidence":"ChIP and dual luciferase reporter for NRF2-ARE; RNA-seq, functional assays, and bleomycin mouse model for RhoA/ROCK2/SLC2A3 axis","pmids":["41029755","39781462"],"confidence":"Medium","gaps":["Relative contribution of NRF2 vs. SRF to TAGLN transcription under physiological conditions not compared","Whether SLC2A3-mediated metabolic reprogramming occurs in contexts beyond dermal fibrosis unknown"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of TAGLN's dual actin-binding domains, how TAGLN switches between tumor-suppressive and oncogenic roles across cell types, the identity of the molecular target linking TAGLN to NADPH oxidase/ROS suppression, and whether TAGLN's nuclear functions (HMGA2 interaction, EMT promotion) are mechanistically separable from its cytoskeletal roles.","evidence":"Open questions from existing literature","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of TAGLN-actin complex available","No unifying model for context-dependent tumor suppressor vs. oncogene function","Nuclear import mechanism and nuclear interaction partners beyond HMGA2 uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4,6,9,12,13,19,23]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,10,15]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[4,6,7,9,12,19,23]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,10,14,20,22]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10,11]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[5,21,24]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[16]}],"complexes":[],"partners":["ACTA2","HMGA2","TRAF6","SRF","ROCK2"],"other_free_text":[]},"mechanistic_narrative":"TAGLN (SM22α/transgelin) is an actin-binding and actin-bundling protein that stabilizes the cytoskeleton, regulates smooth muscle cell contractility and phenotypic identity, and modulates inflammatory and matrix-remodeling signaling in vascular and other cell types. TAGLN binds F-actin through multiple C-terminal regions (residues ~154–186 critical) at a 1:6 molar stoichiometry, and this interaction is negatively regulated by PKC- and ROCK-mediated phosphorylation at Ser-181, which causes dissociation from actin filaments and cytoplasmic redistribution [PMID:11053353, PMID:10939458, PMID:25617350]. Transcription of TAGLN is driven by SRF through CArG boxes and by NRF2 through an antioxidant response element in its promoter, while its protein stability is controlled by TRAF6-mediated ubiquitination at K89/K108 leading to proteasomal degradation [PMID:7768949, PMID:41029755, PMID:33771884]. Loss of TAGLN activates NF-κB via ROS/NADPH oxidase, upregulates MMP-9 through derepression of ERK/AP-1 signaling, and promotes vascular inflammation and chondrogenic conversion of smooth muscle cells, while in cancer contexts TAGLN participates in mechanotransduction through the RhoA/ROCK pathway and interacts with HMGA2 to modulate epithelial-mesenchymal transition [PMID:20224039, PMID:16835221, PMID:21183509, PMID:34538264, PMID:33116628]."},"prefetch_data":{"uniprot":{"accession":"Q01995","full_name":"Transgelin","aliases":["22 kDa actin-binding protein","Protein WS3-10","Smooth muscle protein 22-alpha","SM22-alpha"],"length_aa":201,"mass_kda":22.6,"function":"Actin cross-linking/gelling protein (By similarity). Involved in calcium interactions and contractile properties of the cell that may contribute to replicative senescence","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q01995/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TAGLN","classification":"Not Classified","n_dependent_lines":21,"n_total_lines":1208,"dependency_fraction":0.0173841059602649},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TAGLN","total_profiled":1310},"omim":[{"mim_id":"617492","title":"OLFACTOMEDIN 2; OLFM2","url":"https://www.omim.org/entry/617492"},{"mim_id":"611795","title":"MICRO RNA 145; MIR145","url":"https://www.omim.org/entry/611795"},{"mim_id":"610077","title":"REGULATOR OF CELL CYCLE; RGCC","url":"https://www.omim.org/entry/610077"},{"mim_id":"606127","title":"MYOCARDIN; MYOCD","url":"https://www.omim.org/entry/606127"},{"mim_id":"604634","title":"TRANSGELIN 2; 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protein.\",\n      \"method\": \"SDS-PAGE, sedimentation equilibrium, Stokes radius measurement, CD spectroscopy, purification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous biophysical characterization with multiple orthogonal methods on purified protein\",\n      \"pmids\": [\"3818630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"SM22 (TAGLN) is widely distributed in smooth muscles of birds and mammals (chicken and bovine aorta, pig carotid, uterus, intestine, gizzard, oesophagus) with molar abundance relative to actin of ~1:6 in bovine aorta; present only in trace amounts or absent in brain, liver, heart, and skeletal muscle.\",\n      \"method\": \"Immunoblotting with polyclonal antibody, 1D and 2D gel electrophoresis, purification from bovine aorta\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple tissues, multiple methods, replicated across species\",\n      \"pmids\": [\"3446186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The complete amino acid sequence of chicken gizzard SM22α was determined: a single polypeptide of 197 residues with Mr ~21,978 and net charge of +4.5 at neutral pH; no significant similarity to any known protein at the time, confirming it as a novel protein.\",\n      \"method\": \"Automated and manual Edman degradation sequencing of chemical and proteolytic fragments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing, complete primary structure determination\",\n      \"pmids\": [\"3571244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Rat SM22 encodes a 201-amino acid protein (Mr 22,601) with 43% identity to calponin over a 181-aa overlap, particularly high (70%) identity at the C-terminal region of SM22 and the first repeat motif of calponin, establishing structural homology between SM22 and calponin.\",\n      \"method\": \"cDNA cloning, sequencing, sequence alignment\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct cDNA cloning and sequence analysis establishing structural relationship\",\n      \"pmids\": [\"8359698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"A bovine aorta SM22 homolog (25-kDa) directly binds F-actin at a ratio of 1:6 actin monomers with a binding constant of 7.0 × 10^5 M⁻¹, and the interaction is Ca²⁺-sensitive: the protein associates with the membrane fraction in the presence of Ca²⁺ and dissociates with EGTA.\",\n      \"method\": \"Protein purification, F-actin cosedimentation assay, Ca²⁺-dependent membrane fractionation, partial sequence analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro binding assay with defined stoichiometry and binding constant\",\n      \"pmids\": [\"8117285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The murine SM22α gene promoter (441 bp of 5'-flanking sequence) containing two CArG/SRF boxes, a CACC box, and a MEF-2 binding site is necessary and sufficient to drive high-level transcription specifically in smooth muscle cells; deletion analysis defined the core promoter elements.\",\n      \"method\": \"Transient transfection, luciferase reporter assay, deletion analysis in primary rat aortic SMCs and A7r5 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted transcription with defined cis-elements, multiple deletion constructs\",\n      \"pmids\": [\"7768949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human SM22 (TAGLN) binds F-actin through multiple regions within its C-terminal domain: the region 170–186 is almost completely required, the segment 154–161 (KKAQEHKR) partially required, and residues beyond 151 are necessary; the N-terminal domain alone is insufficient. Phosphorylation of Ser-181 by protein kinase C greatly decreases actin binding, and a S181D phosphomimetic also reduces binding. In transfected airway myocytes, full-length SM22 colocalizes with actin filaments while truncated SM22-(1-151) does not.\",\n      \"method\": \"Site-directed mutagenesis, E. coli expression of His-tagged mutants, in vitro actin cosedimentation assay, PKC phosphorylation assay, immunofluorescence in transfected cells\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro binding with systematic mutagenesis and functional validation in cells\",\n      \"pmids\": [\"11053353\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SM22 (TAGLN) is identified as a novel protein kinase C (PKC) substrate in smooth muscle cells; phosphorylation by PKC in vitro was confirmed and, upon PKC activation in vivo, SM22 dissociates from the actin cytoskeleton and redistributes diffusely in the cytoplasm, demonstrating that PKC-mediated phosphorylation controls SM22 intracellular localization.\",\n      \"method\": \"In vitro PKC kinase assay, 2D gel electrophoresis, mass spectrometry identification, immunofluorescence in PKC-activated cells\",\n      \"journal\": \"Electrophoresis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro kinase assay combined with in vivo localization change upon PKC activation\",\n      \"pmids\": [\"10939458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SM22 (transgelin/TAGLN) represses MMP-9 expression by targeting the ERK/MAPK signaling pathway, leading to reduced AP-1 (c-Fos) binding to the proximal MMP-9 promoter AP-1 motif; this requires an intact N-terminal calponin homology domain. SM22 knockdown by siRNA elevates MMP-9 synthesis and invasion, while SM22 null mouse uterus shows strong MMP-9 immunoreactivity.\",\n      \"method\": \"Expression cloning, siRNA knockdown, overexpression in HT1080 cells, MMP-9 promoter deletion/mutation analysis, AP-1 reporter assay, nuclear extract EMSA for c-Fos binding, in vitro invasion assay, immunohistochemistry in SM22-null mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods: expression cloning, promoter mapping, mutagenesis, in vivo validation\",\n      \"pmids\": [\"16835221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Yeast SM22 homolog Scp1 (ortholog of mammalian TAGLN) contains two distinct actin-binding domains that allow it to both bind and bundle F-actin without dimerization; live cell imaging showed Scp1 localizes to cortical actin patches during endocytosis and is required for movement of patches away from the plasma membrane. Loss of both Scp1 and fimbrin Sac6 dramatically increases patch lifetime, demonstrating that actin-bundling activity is critical for endocytosis.\",\n      \"method\": \"Live cell imaging of GFP-tagged mutants, in vitro actin bundling assays, genetic deletion and epistasis (scp1Δ sac6Δ double mutant), Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstituted actin bundling + live imaging + genetic epistasis in yeast ortholog\",\n      \"pmids\": [\"18400761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SM22 (TAGLN) disruption in vascular smooth muscle cells (VSMCs) promotes NF-κB pathway activation via increased reactive oxygen species (ROS) production involving NADPH oxidase (p47phox activation) and mitochondria (increased Sod2), leading to upregulation of proinflammatory genes (Vcam1, Icam1, Cx3cl1, Ccl2, Ptgs2) after arterial injury; ROS scavengers blocked NF-κB activation and gene induction.\",\n      \"method\": \"SM22 knockout mouse carotid denudation model, primary Sm22⁻/⁻ VSMCs, siRNA knockdown in PAC1 cells, ROS measurement, NF-κB activation assay, ROS scavenger rescue experiments\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo knockout + primary cell validation + pharmacological rescue with defined molecular pathway\",\n      \"pmids\": [\"20224039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SM22 deficiency promotes chondrogenic conversion of VSMCs: loss of SM22 alters VSMC morphology with compromised stress fiber formation and increased actin dynamics, upregulates Sox9 mRNA and chondrogenic markers (type II collagen, aggrecan, BMP2), and downregulates myocardin and VSMC markers; this chondrogenic switch is mediated via ROS-NF-κB pathway activation.\",\n      \"method\": \"SM22 knockout mouse carotid denudation model, primary Sm22⁻/⁻ VSMCs, SM22 siRNA knockdown, immunostaining for chondrogenic markers, actin dynamics assay\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo knockout + primary cells + mechanistic pathway identification\",\n      \"pmids\": [\"21183509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Depletion of SM22 (TAGLN) in REF52 fibroblasts disrupts normal actin organization, increases cell motility, increases spontaneous podosome formation, and enhances Matrigel invasion; conversely, re-expression of SM22 in SM22-negative PC3 prostate cancer cells reduces Matrigel invasion. SM22-depleted cells also have reduced ROS under serum starvation stress.\",\n      \"method\": \"siRNA knockdown in REF52 fibroblasts, SM22 re-expression in PC3 cells, actin organization imaging, podosome quantification, Matrigel invasion assay, ROS measurement\",\n      \"journal\": \"BMC cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD/OE with defined cellular phenotypes, single lab\",\n      \"pmids\": [\"22257561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SM22 (TAGLN) phosphorylation by Rho kinase (ROCK), but not PKC, inversely correlates with SM22-actin binding in smooth muscle cells; SM22 overexpression (pFLAG-SM22) causes relaxation in tonic IAS smooth muscle cells greater than in phasic RSM cells, while SM22 siRNA causes contraction in both cell types, indicating SM22 regulates basal tone via ROCK-induced phosphorylation affecting its actin binding.\",\n      \"method\": \"SM22 overexpression (pFLAG-SM22 transfection), siRNA knockdown, measurement of SMC length, phospho-SM22 western blot, Y-27632 (ROCK inhibitor) and Gö-6850 (PKC inhibitor) treatment\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional OE/KD with biochemical mechanism (phosphorylation-actin binding link), single lab\",\n      \"pmids\": [\"25617350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TAGLN acts as a mechanosensitive gene in ovarian cancer cells: matrix stiffness upregulates TAGLN expression, TAGLN activates Src, and Src in turn feeds back on TAGLN in a regulation loop mediating stiffness-induced OC progression through the RhoA/ROCK pathway.\",\n      \"method\": \"Atomic force microscopy for stiffness measurement, polyacrylamide hydrogel system (soft vs. stiff), siRNA knockdown, western blot, immunofluorescence, in vivo xenograft\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanosensitive function demonstrated with defined pathway, multiple in vitro and in vivo methods\",\n      \"pmids\": [\"34538264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TAGLN is expressed in endothelial cells (ECs) and functions as a negative regulator of angiogenesis: TAGLN expression is activated during EC elongation in response to VEGF-A; genetic disruption of TAGLN in HUVECs augments angiogenic behaviors (tube formation, sprouting); similar results were obtained with TAGLN2 and TAGLN3 knockouts.\",\n      \"method\": \"Mouse ESC Tagln promoter-fluorescence reporter, VEGF-A stimulation, PI3K-Akt/mTORC1 inhibition, CRISPR genetic disruption in HUVECs, angiogenesis assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic disruption with defined angiogenic phenotype, multiple approaches\",\n      \"pmids\": [\"34338296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TRAF6 mediates mono-ubiquitination of TAGLN at K89 or K108 residues via the E2A-TRAF6 pair, leading to proteasomal degradation of TAGLN in prostate cancer cells. Loss of TAGLN activates NF-κB and Myc signaling pathways, promoting cancer cell proliferation and suppressing migration.\",\n      \"method\": \"In vitro ubiquitination assay screening >20 E2-E3 pairs, site-directed mutagenesis of ubiquitination sites, proteasome inhibitor rescue, western blot, siRNA/overexpression functional assays\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ubiquitination reconstitution with mutagenesis of specific sites, functional consequences defined\",\n      \"pmids\": [\"33771884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ALKBH5, an m6A demethylase, binds to m6A sites in TAGLN mRNA and reduces m6A methylation of TAGLN mRNA, thereby inhibiting its degradation and increasing TAGLN protein expression; elevated TAGLN then inhibits proliferation and migration of enteric neural crest cells, contributing to Hirschsprung's disease.\",\n      \"method\": \"MeRIP-qPCR, dual-luciferase reporter assay, ALKBH5 overexpression/knockdown, cell proliferation and migration assays, zebrafish overexpression model\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MeRIP-qPCR defines writer/reader interaction, functional consequence in cells and zebrafish model\",\n      \"pmids\": [\"33961858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TAGLN physically interacts with HMGA2, and TGF-β-induced TAGLN undergoes nuclear translocation; knockdown of TAGLN reverses TGF-β-induced EMT markers (E-cadherin loss, vimentin, fibronectin upregulation) and MMP2/MMP9 elevation in colorectal cancer cells; HMGA2 overexpression restores TGF-β effects suppressed by TAGLN inhibition in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, TGF-β treatment, western blot for EMT markers, migration/invasion assays, in vivo tumor growth experiment\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP identifying TAGLN-HMGA2 interaction, supported by functional rescue experiments\",\n      \"pmids\": [\"33116628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The C-terminal domain of SM22α (TAGLN) directly interacts with F-actin to participate in cytoskeleton reorganization in VSMCs: GST pull-down and co-immunoprecipitation confirmed SM22-actin interaction; immunofluorescence showed SM22α colocalizes with F-actin during VSMC redifferentiation, and SM22α distributes predominantly in F-actin fractions (not G-actin) during the contractile phenotype.\",\n      \"method\": \"GST pull-down assay, co-immunoprecipitation, western blot of F-actin/G-actin fractions, immunofluorescence in VSMCs undergoing phenotypic modulation\",\n      \"journal\": \"Chinese journal of applied physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — GST pull-down + co-IP + fractionation + localization in same study\",\n      \"pmids\": [\"21162287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TAGLN regulates skin fibroblast motility and secretory function (invasion, migration, contraction, collagen secretion) through a mechano-metabolic axis: TAGLN activates the RhoA/ROCK2 pathway, which upregulates the glucose transporter SLC2A3, thereby affecting glycolysis in dermal fibroblasts. Targeting TAGLN reduced fibrosis in a bleomycin-induced mouse model.\",\n      \"method\": \"Transwell, wound healing, collagen gel contraction assay, immunofluorescence, RNA-seq, siRNA knockdown/overexpression, western blot, bleomycin mouse model\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA-seq identifies downstream target (SLC2A3), pathway validation by multiple functional assays and in vivo\",\n      \"pmids\": [\"39781462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NRF2 directly transcriptionally activates TAGLN: a functional antioxidant response element (ARE) was identified in the TAGLN promoter; ChIP confirmed NRF2 binding; TAGLN mediates NRF2-promoted ovarian cancer cell migration and EMT (E-cadherin down, N-cadherin up), as TAGLN siRNA reversed NRF2 overexpression effects on migration and EMT markers.\",\n      \"method\": \"Dual luciferase reporter assay, ChIP assay, siRNA knockdown, wound-healing and Transwell assays, western blot for EMT markers\",\n      \"journal\": \"Journal of ovarian research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + luciferase reporter + functional rescue establishes NRF2 as transcriptional writer for TAGLN\",\n      \"pmids\": [\"41029755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TAGLN upregulation in NF1-associated MPNSTs is caused by hypomethylation of its promoter and subpromoter regions; TAGLN knockdown in MPNST cells decreases RAS-GTP and phospho-ERK1/2 activation, while TAGLN overexpression in normal NF1-deficient cells increases RAS and ERK1/2 activation, placing TAGLN as an activator of the RAS-MAPK pathway.\",\n      \"method\": \"DNA methylation analysis, siRNA knockdown, TAGLN overexpression, western blot for GTP-RAS and phospho-ERK1/2, immunohistochemistry\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epigenetic mechanism identified + bidirectional functional manipulation of RAS-MAPK pathway\",\n      \"pmids\": [\"25109740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Fission yeast Stg1, an SM22/transgelin-like protein (ortholog of mammalian TAGLN), crosslinks F-actin in vitro and localizes to actin patches; Stg1 overexpression causes cytokinesis defects by suppressing contractile ring formation and generating abnormal F-actin aggregates, implicating TAGLN orthologs in actin cytoskeleton organization and cytokinesis.\",\n      \"method\": \"In vitro F-actin crosslinking assay, fluorescence microscopy of actin patches, Stg1 overexpression phenotype analysis in fission yeast\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro biochemistry + in vivo genetic manipulation in yeast ortholog\",\n      \"pmids\": [\"16256112\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"AVP induces and PDGF-BB suppresses SM22α expression in VSMCs through distinct signaling pathways: AVP activates both JNK and p38 MAPK and requires the proximal CArG boxes in the SM22α promoter and serum response factor (SRF) binding; PDGF suppression involves Raf, Ral-GDS, and PI3K activation downstream of Ras, independently of CArG boxes.\",\n      \"method\": \"Promoter-reporter assays, truncation analysis, CArG box mutagenesis, dominant-active and dominant-negative signaling constructs, SRF overexpression, kinase inhibitor experiments\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple promoter constructs and signaling pathway dissection, single lab\",\n      \"pmids\": [\"12829429\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TAGLN (SM22α/transgelin) is a ~22 kDa actin-binding and actin-bundling protein that binds F-actin through multiple C-terminal domain regions (residues ~154–186 critical), stabilizes the actin cytoskeleton in smooth muscle and other cells, and is regulated by phosphorylation at Ser-181 by PKC and by ROCK — phosphorylation disrupts actin binding and causes cytoplasmic redistribution; it suppresses MMP-9 expression by dampening ERK/AP-1 signaling, restrains NF-κB/ROS-driven inflammation in VSMCs, is transcriptionally activated by SRF via CArG boxes and by NRF2 via an ARE, and is post-translationally degraded via TRAF6-mediated K89/K108 ubiquitination; in cancer contexts it can act as either a tumor suppressor or oncogene depending on cell type, partly through interactions with HMGA2 and the RhoA/ROCK2-SLC2A3 mechano-metabolic axis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TAGLN (SM22α/transgelin) is an actin-binding and actin-bundling protein that stabilizes the cytoskeleton, regulates smooth muscle cell contractility and phenotypic identity, and modulates inflammatory and matrix-remodeling signaling in vascular and other cell types. TAGLN binds F-actin through multiple C-terminal regions (residues ~154–186 critical) at a 1:6 molar stoichiometry, and this interaction is negatively regulated by PKC- and ROCK-mediated phosphorylation at Ser-181, which causes dissociation from actin filaments and cytoplasmic redistribution [PMID:11053353, PMID:10939458, PMID:25617350]. Transcription of TAGLN is driven by SRF through CArG boxes and by NRF2 through an antioxidant response element in its promoter, while its protein stability is controlled by TRAF6-mediated ubiquitination at K89/K108 leading to proteasomal degradation [PMID:7768949, PMID:41029755, PMID:33771884]. Loss of TAGLN activates NF-κB via ROS/NADPH oxidase, upregulates MMP-9 through derepression of ERK/AP-1 signaling, and promotes vascular inflammation and chondrogenic conversion of smooth muscle cells, while in cancer contexts TAGLN participates in mechanotransduction through the RhoA/ROCK pathway and interacts with HMGA2 to modulate epithelial-mesenchymal transition [PMID:20224039, PMID:16835221, PMID:21183509, PMID:34538264, PMID:33116628].\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"Identification and biophysical characterization of SM22 as a novel, abundant smooth-muscle-specific protein resolved its identity as distinct from all known muscle proteins, establishing it as a new cytoskeletal component to study.\",\n      \"evidence\": \"Purification from chicken gizzard smooth muscle with SDS-PAGE, sedimentation equilibrium, Stokes radius, CD spectroscopy; immunoblotting across bird and mammalian tissues\",\n      \"pmids\": [\"3818630\", \"3446186\", \"3571244\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No binding partner or function identified at this stage\", \"Expression analysis limited to immunoblotting with one polyclonal antibody\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing structural homology between SM22 and calponin placed TAGLN within the calponin family and predicted actin-binding capability, framing subsequent biochemical studies.\",\n      \"evidence\": \"cDNA cloning and sequence alignment of rat SM22 vs. calponin showing 43% identity over 181 aa\",\n      \"pmids\": [\"8359698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional similarity to calponin not yet tested\", \"No direct actin-binding data at this point\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Direct demonstration that SM22 binds F-actin with defined stoichiometry (1:6) and a Ca²⁺-sensitive membrane association answered the fundamental question of molecular function.\",\n      \"evidence\": \"F-actin cosedimentation assay with purified bovine aorta SM22 homolog, Ca²⁺-dependent membrane fractionation\",\n      \"pmids\": [\"8117285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Actin-binding domain not mapped\", \"Physiological relevance of Ca²⁺ sensitivity unclear\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapping the SM22α promoter to CArG/SRF boxes explained smooth-muscle-specific transcription and provided the regulatory logic for lineage-restricted expression.\",\n      \"evidence\": \"Transient transfection with luciferase reporters and deletion constructs in primary rat aortic SMCs and A7r5 cells\",\n      \"pmids\": [\"7768949\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contribution of MEF-2 and CACC elements not functionally separated\", \"In vivo promoter activity not tested with transgenic models in this study\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Systematic mutagenesis mapped the actin-binding interface to C-terminal residues 154–186 and identified PKC phosphorylation of Ser-181 as a switch that disrupts actin binding and relocalizes SM22 to the cytoplasm, establishing the first regulatory mechanism for TAGLN function.\",\n      \"evidence\": \"Site-directed mutagenesis, His-tagged mutant cosedimentation, PKC phosphorylation assay, immunofluorescence in transfected airway myocytes; in vitro PKC assay with mass spectrometry and in vivo localization in PKC-activated cells\",\n      \"pmids\": [\"11053353\", \"10939458\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of in vivo kinase(s) not resolved (PKC isoform specificity unclear)\", \"Whether phosphorylation is reversible and by which phosphatase unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating that AVP-induced SM22α expression requires SRF binding to CArG boxes while PDGF suppression operates through Ras effectors independently of CArG elements revealed dual and opposing signaling inputs converging on the SM22 promoter.\",\n      \"evidence\": \"Promoter-reporter truncation/mutation analysis, dominant-negative/active signaling constructs, SRF overexpression, kinase inhibitors in VSMCs\",\n      \"pmids\": [\"12829429\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chromatin-level regulation not addressed\", \"In vivo relevance of AVP/PDGF antagonism on SM22 not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating that fission yeast and budding yeast SM22 orthologs crosslink/bundle F-actin and function in actin patch dynamics and endocytosis established evolutionary conservation of the actin-bundling mechanism and linked it to membrane trafficking.\",\n      \"evidence\": \"In vitro F-actin crosslinking, fluorescence microscopy of actin patches, overexpression phenotype in S. pombe (Stg1); live imaging, bundling assay, genetic epistasis with fimbrin in S. cerevisiae (Scp1)\",\n      \"pmids\": [\"16256112\", \"18400761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian TAGLN similarly functions in endocytic actin patches not tested\", \"Structural basis of dual actin-binding domain architecture not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that SM22 represses MMP-9 by inhibiting ERK/AP-1 signaling, validated in SM22-null mice, established TAGLN as a signaling modulator beyond a structural actin-binding protein.\",\n      \"evidence\": \"Expression cloning, siRNA, overexpression in HT1080, MMP-9 promoter deletion/EMSA, AP-1 reporter, invasion assay, SM22-null mouse immunohistochemistry\",\n      \"pmids\": [\"16835221\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MMP-9 repression is direct or mediated through cytoskeletal changes not resolved\", \"Calponin homology domain contribution to ERK inhibition not mechanistically explained\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"SM22 knockout in VSMCs revealed that TAGLN restrains NF-κB activation via suppression of ROS (NADPH oxidase/mitochondrial), and that its loss drives proinflammatory gene expression and chondrogenic transdifferentiation, expanding its role to vascular inflammation and cell fate.\",\n      \"evidence\": \"SM22 knockout mouse carotid injury model, primary Sm22−/− VSMCs, siRNA, ROS measurement, NF-κB assay, ROS scavenger rescue, immunostaining for chondrogenic markers\",\n      \"pmids\": [\"20224039\", \"21183509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular target linking SM22 to NADPH oxidase suppression unknown\", \"Whether chondrogenic conversion is reversible upon SM22 restoration not shown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of TAGLN as an activator of RAS-MAPK signaling in NF1-associated tumors, upregulated by promoter hypomethylation, revealed a context-dependent oncogenic role contrasting its tumor-suppressive function elsewhere.\",\n      \"evidence\": \"DNA methylation analysis, siRNA knockdown and overexpression, GTP-RAS and phospho-ERK1/2 western blot in MPNST cells\",\n      \"pmids\": [\"25109740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which TAGLN activates RAS-GTP loading not identified\", \"Whether this is specific to NF1-deficient context not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing that ROCK (not only PKC) phosphorylates SM22 to regulate actin binding and smooth muscle basal tone added a second kinase input and linked TAGLN to RhoA/ROCK contractile signaling.\",\n      \"evidence\": \"SM22 overexpression/siRNA in IAS and RSM cells, phospho-SM22 western blot, ROCK inhibitor (Y-27632) and PKC inhibitor treatments, cell length measurement\",\n      \"pmids\": [\"25617350\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific ROCK phosphorylation site on SM22 not mapped\", \"In vivo contribution of ROCK vs. PKC phosphorylation not quantified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of a physical TAGLN–HMGA2 interaction and TGF-β-induced nuclear translocation of TAGLN revealed a non-cytoskeletal mechanism through which TAGLN promotes EMT in colorectal cancer.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA knockdown, TGF-β treatment, EMT marker western blot, in vivo tumor growth\",\n      \"pmids\": [\"33116628\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation or domain mapping\", \"Mechanism of TAGLN nuclear translocation not defined\", \"Whether TAGLN-HMGA2 interaction occurs in non-cancer contexts unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Multiple studies in 2021 expanded TAGLN regulation and function: TRAF6-mediated ubiquitination at K89/K108 was identified as the degradation pathway; ALKBH5-dependent m6A demethylation stabilizes TAGLN mRNA affecting enteric neural crest cells; TAGLN acts as a mechanosensor activating Src/RhoA/ROCK in ovarian cancer; and TAGLN negatively regulates angiogenesis in endothelial cells.\",\n      \"evidence\": \"In vitro ubiquitination reconstitution with mutagenesis (TRAF6); MeRIP-qPCR and zebrafish model (ALKBH5/m6A); AFM, hydrogels, siRNA, xenografts (mechanosensing); CRISPR disruption in HUVECs (angiogenesis)\",\n      \"pmids\": [\"33771884\", \"33961858\", \"34538264\", \"34338296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether TRAF6 ubiquitination is regulated by upstream signals unknown\", \"m6A regulation shown only for Hirschsprung's context; generalizability unclear\", \"Mechanosensor mechanism (how stiffness upregulates TAGLN) not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of NRF2 as a direct transcriptional activator of TAGLN via an ARE element, and discovery of the TAGLN→RhoA/ROCK2→SLC2A3 mechano-metabolic axis in fibrosis, connected TAGLN to oxidative stress responses and glycolytic metabolism.\",\n      \"evidence\": \"ChIP and dual luciferase reporter for NRF2-ARE; RNA-seq, functional assays, and bleomycin mouse model for RhoA/ROCK2/SLC2A3 axis\",\n      \"pmids\": [\"41029755\", \"39781462\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of NRF2 vs. SRF to TAGLN transcription under physiological conditions not compared\", \"Whether SLC2A3-mediated metabolic reprogramming occurs in contexts beyond dermal fibrosis unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of TAGLN's dual actin-binding domains, how TAGLN switches between tumor-suppressive and oncogenic roles across cell types, the identity of the molecular target linking TAGLN to NADPH oxidase/ROS suppression, and whether TAGLN's nuclear functions (HMGA2 interaction, EMT promotion) are mechanistically separable from its cytoskeletal roles.\",\n      \"evidence\": \"Open questions from existing literature\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of TAGLN-actin complex available\", \"No unifying model for context-dependent tumor suppressor vs. oncogene function\", \"Nuclear import mechanism and nuclear interaction partners beyond HMGA2 uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4, 6, 9, 12, 13, 19, 23]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 10, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [4, 6, 7, 9, 12, 19, 23]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 10, 14, 20, 22]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 11]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [5, 21, 24]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ACTA2\",\n      \"HMGA2\",\n      \"TRAF6\",\n      \"SRF\",\n      \"ROCK2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}