{"gene":"PLS3","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2022,"finding":"Cryo-EM structure of human T-plastin (PLS3) bound to actin filaments revealed a sequential bundling mechanism enabling T-plastin to bridge pairs of actin filaments in both parallel and antiparallel orientations, with distinct structural landscapes in each orientation. Inter-CHD linkers were identified as key structural elements underlying flexible but stable cross-linking.","method":"Cryo-electron microscopy with machine-learning-enabled pipeline, biochemical assays, cell biological validation, active-site/inter-CHD linker mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with biochemical and cell biological validation, mutagenesis of key structural elements","pmids":["36067297"],"is_preprint":false},{"year":1995,"finding":"T-plastin is functionally required for Shigella flexneri entry into HeLa cells; it localizes to bacterium-induced actin protrusions and a truncated T-plastin lacking one actin-binding domain acts as a dominant negative, blocking invasion. T-plastin bundles actin filaments in parallel orientation within cellular protrusions at entry zones.","method":"Transfection of truncated dominant-negative T-plastin, immunofluorescence colocalization, electron microscopy of actin ultrastructure","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — functional domain truncation combined with colocalization and ultrastructural analysis; foundational paper with 139 citations","pmids":["7721941"],"is_preprint":false},{"year":1994,"finding":"T-plastin and L-plastin isoforms have different functional roles in actin filament organization in a cell-type-specific manner: T-plastin associates with microvillar actin filaments after detergent extraction and induces shape changes in microvilli, whereas L-plastin does not affect microvilli and is fully extracted. Overproduction of either isoform reorganizes actin stress fibers into geodesic structures.","method":"Overexpression in CV-1 and LLC-PK1 cell lines, detergent extraction fractionation, morphological analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — two orthogonal cell lines with detergent fractionation and morphological readouts; foundational paper with 83 citations","pmids":["7806577"],"is_preprint":false},{"year":2005,"finding":"T-plastin/T-fimbrin increases the velocity of Arp2/3-mediated actin-based bead motility 1.5-fold, stabilizes actin comets, displaces cofilin, and inhibits cofilin-mediated actin depolymerization in vitro. A bundling-incompetent ABD1 variant retains these effects, indicating that T-plastin controls actin turnover through filament binding independently of cross-linking. In cells, ABD1 induces long actin cables.","method":"Biomimetic VCA-bead motility assay in cell-free extracts, in vitro F-actin depolymerization assay, cell-based overexpression with mutant ABD1","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution assay combined with mutagenesis and cell-based validation","pmids":["15741236"],"is_preprint":false},{"year":2016,"finding":"PLS3 overexpression rescues impaired endocytosis in SMN-deficient cells and restores FM1-43 endocytotic uptake at neuromuscular junction presynaptic terminals in SMA mice. CORO1C was identified as a direct calcium-dependent binding partner of PLS3, and CORO1C overexpression similarly restores fluid-phase endocytosis and rescues axonal defects in SMN-depleted zebrafish by elevating F-actin levels.","method":"Proteomics, Co-IP/biochemical binding assay (calcium-dependent), fluid-phase endocytosis assay, FM1-43 presynaptic uptake, SMA mouse rescue experiments, zebrafish knockdown","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods across cell, mouse, and zebrafish models; direct binding demonstrated biochemically","pmids":["27499521"],"is_preprint":false},{"year":2017,"finding":"T-plastin (Pls3) localizes to the cell cortex in mouse epidermal cells and is essential for basement membrane assembly and epidermal morphogenesis. Loss of Pls3 by in utero depletion causes basement membrane and polarity defects; apicobasal polarity defects are secondary to basement membrane disruption. Pls3 is required for proper localization and activation of myosin II at the cortex, and inhibition of myosin II motor activity disrupts basement membrane organization.","method":"In utero siRNA depletion (mouse embryo), live imaging/immunofluorescence localization, myosin II pharmacological inhibition, epistasis analysis of polarity vs. basement membrane defects","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — genetic depletion with specific mechanistic readouts (myosin II localization/activation) and epistasis experiments","pmids":["28559444"],"is_preprint":false},{"year":2020,"finding":"T-Plastin promotes membrane protrusions across ECM gaps during cell migration by stabilizing actin filaments; it widens and lengthens protrusions and is specifically enriched in active protrusions devoid of non-muscle myosin II. Micropatterned ECM experiments show T-Plastin is essential for bridging micron-scale ECM gaps.","method":"Micropatterned ECM substrates, TIRF and confocal live imaging, KD with specific protrusion and migration readouts","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function with defined cellular phenotype using engineered ECM platform; multiple imaging modalities","pmids":["32968060"],"is_preprint":false},{"year":2011,"finding":"Both L- and T-plastin interact specifically with activated (GTP-bound) Rab5 and co-localize with Rab5 on the plasma membrane and endosomes. Overexpression of L- or T-plastin increases Rab5 activity and the rate of fluid-phase endocytosis, indicating plastin-Rab5 interaction promotes endocytic activity.","method":"Affinity column pulldown with constitutively active Rab5, co-localization by immunofluorescence, fluid-phase endocytosis assay, overexpression in Cos-1 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — pulldown and overexpression with functional endocytosis readout; single lab","pmids":["21426900"],"is_preprint":false},{"year":2017,"finding":"T-plastin expression is regulated downstream of the calcineurin/NFAT pathway in keratinocytes. siRNA knockdown of T-plastin decreases keratinocyte migration, actin lamellipodia formation, and FAK and β6-integrin expression, placing T-plastin as a downstream effector of calcineurin/NFAT-dependent migration.","method":"siRNA knockdown, scratch and Boyden migration assays, calcineurin inhibitor (FK506) treatment, siNFAT2, immunofluorescence","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with multiple migration readouts and pathway epistasis; single lab","pmids":["25226517"],"is_preprint":false},{"year":2017,"finding":"T-plastin is recruited to the plasma membrane during hypoxia and mediates hypoxia-induced membrane trafficking independently of the HIF system. Knockdown of T-plastin abolishes the increase in membrane endocytosis observed under hypoxic conditions, associated with increased cortical actin density.","method":"SILAC proteomics screen, T-plastin knockdown, FM1-43/mCLING membrane trafficking assays, electron microscopy of actin density","journal":"Acta physiologica","confidence":"Medium","confidence_rationale":"Tier 2 — unbiased SILAC discovery followed by KD with specific functional readout; single lab","pmids":["28218996"],"is_preprint":false},{"year":2017,"finding":"Mutation p.Ala253_Leu254insAsn in PLS3 disrupts interaction between PLS3 and its binding partner LCP1 (L-plastin). Both PLS3 and LCP1 regulate intracellular Ca2+ levels, and mutant PLS3 weakens this regulatory function. The PLS3-LCP1 interaction is enhanced under low extracellular Ca2+ concentration.","method":"Co-IP/pulldown (binding partner identification), intracellular Ca2+ measurement, mutant vs. wildtype comparison","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, Co-IP plus functional Ca2+ assay, moderate mechanistic follow-up","pmids":["28646489"],"is_preprint":false},{"year":2019,"finding":"PLS3 overexpression delays ataxic phenotype in Chp1-mutant (vacillator) mice by ameliorating axon hypertrophy and axonal swellings in Purkinje neurons. Mechanistically, PLS3 overexpression trends toward increased membrane targeting/expression of Na+/H+ exchanger NHE1, an important CHP1 binding partner.","method":"Transgenic PLS3 overexpression in Chp1 mutant mice, behavioral phenotyping, histological analysis of Purkinje neurons, Western blotting for NHE1","journal":"Frontiers in neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — genetic rescue experiment with defined neuronal phenotype; NHE1 data is trend-level only","pmids":["31607845"],"is_preprint":false},{"year":2023,"finding":"PLS3 localizes to focal adhesions in osteoblasts and is required for mechanosensitive regulation of osteoblast mineralization. Depletion of PLS3 in MC3T3-E1 cells abolishes cell responsiveness to ECM stiffness (cell size, focal adhesion length, number) and blocks matrix mineralization. Rescue with wildtype but not actin-bundling-deficient PLS3 mutants restores stiffness response, demonstrating actin-bundling is required.","method":"Stable KD in preosteoblast cell line (MC3T3-E1), rescue with WT and patient mutants, ECM stiffness substrates (6 vs. 100 kPa), osteogenic differentiation mineralization assay, immunofluorescence FA quantification","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 2 — KD with WT/mutant rescue on defined stiffness substrates, multiple orthogonal readouts, mutagenesis validates actin-bundling requirement","pmids":["38089885"],"is_preprint":false},{"year":2024,"finding":"PLS3 loss-of-function in murine MLO-Y4 osteocyte-like cells causes differential expression of Wnt1, Nos1ap, and Myh3, implicating Wnt and Th17 differentiation pathways. ACTN1 and ACTN4 can rescue skeletal deformities in pls3-morphant zebrafish, but FSCN1 cannot, indicating partial functional redundancy among actin bundlers.","method":"RNA-seq after Pls3 KD in MLO-Y4 cells, morpholino knockdown in zebrafish with actin-bundler rescue experiments, osteogenic transdifferentiation of patient fibroblasts","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — transcriptomics combined with zebrafish genetic rescue; pathway identification from single lab","pmids":["39273077"],"is_preprint":false},{"year":2023,"finding":"Missense PLS3 variants specifically affecting actin-binding domains cause congenital diaphragmatic hernia (CDH) with gain-of-function effect, whereas loss-of-function variants cause osteoporosis. A mouse knockin model of p.Trp499Cys (within actin-binding domain) recapitulates diaphragm and abdominal-wall defects with increased (not decreased) bone mineral density, demonstrating that distinct variant classes in the actin-binding domains produce opposite functional consequences.","method":"In silico protein modeling, mouse knockin model (c.1497G>C; p.Trp499Cys), skeletal phenotyping (BMD), diaphragm/body-wall assessment in mice and human subjects","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — mouse knockin recapitulating human phenotype plus comparative variant analysis; multiple orthogonal readouts","pmids":["37751738"],"is_preprint":false},{"year":2025,"finding":"PLS3 (and PLS2) functions as a cytoskeletal pH sensor: F-actin bundling activity of PLS3 is reduced at alkaline pH and enhanced at acidic pH, mediated through the N-terminal actin-binding domain (ABD1). In fibroblasts, elevated cytosolic pH causes PLS2 dissociation from actin structures, while acidic conditions promote association with focal adhesions and stress fibers. His207 is identified as a pH-sensing residue in PLS2.","method":"In vitro F-actin bundling assays at varying pH, live-cell imaging of pH-induced localization changes, site-directed mutagenesis of His207","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis and cell imaging; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.03.26.645573"],"is_preprint":true},{"year":1999,"finding":"The T-plastin promoter contains a CCAAT box, Sp1 motif, and four AP2 motifs but no TATA box. Differential expression between leukocytes and non-leukocytes is controlled by CpG island methylation: CpG sites within the island are fully methylated in T-plastin-negative leukemia lines and unmethylated in T-plastin-expressing cells. A T-plastin enhancer composed of two inverted symmetric octamers separated by 17 nucleotides is inactive in leukocytes.","method":"S1 mapping (transcription start sites), promoter/enhancer reporter assays, restriction enzyme methylation analysis, DNA footprinting","journal":"DNA and cell biology","confidence":"High","confidence_rationale":"Tier 1 — multiple complementary molecular methods (S1 mapping, reporter assays, methylation analysis, footprinting) identifying promoter/enhancer elements","pmids":["10025506"],"is_preprint":false},{"year":2012,"finding":"Aberrant T-plastin (PLS3) expression in Sézary syndrome cells is associated with promoter hypomethylation of specific CpG dinucleotides (positions 95-99 in the CpG island). T-plastin is expressed only in clonally involved CD3+CD4+CD26- lymphocytes.","method":"Pyrosequencing of CpG dinucleotides, RT-PCR for PLS3 expression, immunofluorescence with anti-PLS3 antibody, TCR clonality assay","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 3 — correlation of methylation and expression; mechanistic direction supported by in vitro methylation data from PMID 25806852","pmids":["22495182"],"is_preprint":false},{"year":2015,"finding":"Promoter hypomethylation drives PLS3 overexpression in Sézary syndrome. In vitro methylation of the cloned PLS3 promoter suppresses luciferase reporter expression, and treatment of PLS3-negative Jurkat cells with 5-azacytidine (hypomethylating agent) induces PLS3 expression.","method":"Pyrosequencing of CpG regions, in vitro promoter methylation + luciferase reporter assay, 5-azacytidine treatment of Jurkat cells","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 1 — direct mechanistic demonstration using in vitro methylation + reporter assay and pharmacological demethylation with gene induction","pmids":["25806852"],"is_preprint":false},{"year":2012,"finding":"T-plastin expression in Sézary syndrome cells is induced by calcium influx (PMA/ionomycin stimulation) and regulated by the calcineurin/NFAT transcription pathway; calcineurin inhibitors suppress both constitutive and calcium-induced T-plastin expression. Constitutive T-plastin expression confers resistance to etoposide-induced apoptosis and promotes cell migration toward CCL17 and IP-10 chemokines.","method":"Pharmacological stimulation (PMA/ionomycin), calcineurin inhibitor treatment, apoptosis assay, migration assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — pathway placement via pharmacological inhibition with functional readouts (apoptosis, migration); single lab","pmids":["22627769"],"is_preprint":false},{"year":2024,"finding":"T-plastin (PLST) promotes epithelial-mesenchymal transition (EMT) in human lung cancer cells via the FAK/AKT/Slug signaling axis; PLST overexpression enhances cell migration and invasion with upregulation of vimentin and Slug and downregulation of E-cadherin, whereas PLST knockdown reverses these effects. Phosphorylation levels of FAK and AKT are dependent on PLST expression.","method":"Overexpression and siRNA knockdown, migration/invasion assays, Western blotting for EMT markers and FAK/AKT phosphorylation","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 3 — loss- and gain-of-function with pathway marker readouts; single lab, no direct binding demonstrated","pmids":["38835117"],"is_preprint":false},{"year":2018,"finding":"Bioinformatic and homology modeling analyses identify a critical LOOP-1 region (residues 240-266) in PLS3 that physically connects the CH1 and CH2 domains of ABD1 and is spatially located at the ABD1-ABD2 interface, essential for actin-binding conformation transition. A novel nonsense mutation (p.E249X) in LOOP-1 truncates the protein and is predicted to disrupt actin binding.","method":"Targeted gene sequencing, homology modeling, molecular dynamics simulation","journal":"International journal of endocrinology","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only, no biochemical validation","pmids":["30405713"],"is_preprint":false},{"year":2009,"finding":"ZNF471 transcriptionally represses PLS3 by directly binding to the PLS3 promoter and recruiting co-repressor KAP1, which induces H3K9me3 enrichment at the PLS3 promoter locus.","method":"ChIP-PCR for ZNF471 binding and H3K9me3 at PLS3 promoter, ectopic ZNF471 expression with PLS3 expression readout, co-IP for KAP1 recruitment","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-PCR at specific promoter plus co-repressor co-IP; single lab","pmids":["29610526"],"is_preprint":false}],"current_model":"PLS3 (T-plastin) is a calcium-sensitive, pH-responsive actin-bundling protein that cross-links actin filaments in both parallel and antiparallel orientations via tandem calponin-homology domains; it stabilizes actin protrusions, promotes endocytosis via interaction with activated Rab5 and the CORO1C binding partner, regulates cortical myosin II activation for basement membrane assembly, acts as a mechanosensitive effector in osteoblast focal adhesions to drive matrix mineralization, and functions downstream of calcineurin/NFAT signaling to control cell migration—with its expression regulated by CpG island methylation and the ZNF471/KAP1 repressor complex."},"narrative":{"teleology":[{"year":1994,"claim":"Establishing that T-plastin and L-plastin are functionally distinct isoforms: T-plastin uniquely associates with microvillar actin filaments and reorganizes actin architecture in a cell-type-specific manner, defining it as a non-hematopoietic actin-bundling protein.","evidence":"Overexpression in epithelial and fibroblast cell lines with detergent extraction fractionation and morphological analysis","pmids":["7806577"],"confidence":"High","gaps":["Structural basis for isoform-specific actin interactions not determined","In vivo physiological relevance not tested"]},{"year":1995,"claim":"Demonstrating that T-plastin's actin-bundling activity is functionally required for actin-dependent cellular processes: T-plastin localizes to bacterium-induced actin protrusions and a dominant-negative truncation blocks Shigella invasion, establishing it as an essential organizer of actin protrusions.","evidence":"Dominant-negative T-plastin truncation, immunofluorescence, and electron microscopy in Shigella-infected HeLa cells","pmids":["7721941"],"confidence":"High","gaps":["Whether bundling versus filament stabilization is the critical activity was unresolved","No genetic loss-of-function model tested"]},{"year":1999,"claim":"Resolving how T-plastin expression is restricted to non-hematopoietic cells: CpG island methylation silences the T-plastin promoter in leukocytes, and a tissue-specific enhancer is inactive in those cells.","evidence":"S1 mapping, promoter/enhancer reporter assays, restriction-enzyme methylation analysis, and DNA footprinting of the PLS3 promoter","pmids":["10025506"],"confidence":"High","gaps":["Trans-acting factors responsible for methylation not identified","In vivo chromatin context not examined"]},{"year":2005,"claim":"Separating actin-bundling from filament-stabilizing functions: T-plastin increases Arp2/3-based actin motility speed and displaces cofilin even without cross-linking, establishing a bundling-independent role in controlling actin turnover dynamics.","evidence":"Biomimetic VCA-bead motility assay in cell-free extracts with bundling-incompetent ABD1 mutant, in vitro depolymerization assay","pmids":["15741236"],"confidence":"High","gaps":["Molecular mechanism of cofilin displacement not structurally resolved","Relative contributions of bundling vs. stabilization in vivo remain unclear"]},{"year":2011,"claim":"Linking T-plastin to endocytic machinery: T-plastin binds activated (GTP-bound) Rab5 and enhances fluid-phase endocytosis, connecting actin bundling to vesicular trafficking.","evidence":"Affinity pulldown with constitutively active Rab5, colocalization, and fluid-phase endocytosis assay in Cos-1 cells","pmids":["21426900"],"confidence":"Medium","gaps":["Reciprocal validation of binding in endogenous context lacking","Structural basis of PLS3–Rab5 interaction not determined","Whether Rab5 interaction requires bundling competence unknown"]},{"year":2012,"claim":"Placing PLS3 expression under calcineurin/NFAT transcriptional control and linking it to disease-relevant cell behaviors: calcium/NFAT signaling induces T-plastin expression, which confers apoptosis resistance and promotes chemokine-directed migration in Sézary syndrome cells; promoter hypomethylation underlies aberrant expression in these malignant T cells.","evidence":"Pharmacological calcineurin inhibition, PMA/ionomycin stimulation, apoptosis and migration assays; pyrosequencing of CpG dinucleotides in Sézary cells","pmids":["22627769","22495182"],"confidence":"Medium","gaps":["Whether NFAT binds the PLS3 promoter directly was not shown by ChIP","Causality between methylation and NFAT-driven induction not dissected"]},{"year":2015,"claim":"Providing direct mechanistic proof that promoter methylation controls PLS3 transcription: in vitro methylation of the cloned PLS3 promoter silences reporter expression, and pharmacological demethylation reactivates PLS3 in PLS3-negative T cells.","evidence":"In vitro promoter methylation with luciferase reporter, 5-azacytidine treatment of Jurkat cells","pmids":["25806852"],"confidence":"High","gaps":["Specific CpG sites critical for silencing not individually mutated","In vivo relevance of demethylation in normal T-cell biology unclear"]},{"year":2016,"claim":"Connecting PLS3 to endocytic rescue in spinal muscular atrophy: PLS3 overexpression restores impaired endocytosis in SMN-deficient cells via a pathway involving its calcium-dependent binding partner CORO1C, establishing a molecular mechanism for PLS3 as an SMA disease modifier.","evidence":"Proteomics, calcium-dependent Co-IP, fluid-phase endocytosis assay, FM1-43 presynaptic uptake in SMA mouse NMJs, zebrafish rescue","pmids":["27499521"],"confidence":"High","gaps":["Stoichiometry and structural basis of PLS3–CORO1C complex not resolved","Whether endocytic rescue is sufficient for motor neuron survival in vivo not demonstrated"]},{"year":2017,"claim":"Revealing a cortical signaling role for PLS3 beyond bundling: PLS3 is required for cortical myosin II localization and activation, and loss of PLS3 disrupts basement membrane assembly and secondary epithelial polarity in mouse epidermis.","evidence":"In utero siRNA depletion in mouse embryonic skin, live imaging, myosin II inhibitor epistasis","pmids":["28559444"],"confidence":"High","gaps":["How PLS3 recruits or activates myosin II at the cortex is unknown","Whether this role generalizes beyond epidermal epithelium untested"]},{"year":2017,"claim":"Identifying PLS3 as a hypoxia-responsive regulator of membrane trafficking independent of HIF: PLS3 is recruited to the plasma membrane under hypoxia and its depletion abolishes hypoxia-induced endocytosis.","evidence":"SILAC proteomics, PLS3 knockdown, FM1-43/mCLING membrane trafficking assays, electron microscopy","pmids":["28218996"],"confidence":"Medium","gaps":["Signal linking hypoxia to PLS3 membrane recruitment not identified","Independence from HIF not validated by HIF knockout"]},{"year":2018,"claim":"Identifying ZNF471/KAP1 as a direct transcriptional repressor of PLS3 through H3K9me3 deposition, providing a chromatin-level mechanism for PLS3 silencing complementary to DNA methylation.","evidence":"ChIP-PCR for ZNF471 and H3K9me3 at PLS3 promoter, ectopic ZNF471 expression, Co-IP for KAP1","pmids":["29610526"],"confidence":"Medium","gaps":["Relationship between ZNF471-mediated repression and CpG methylation not tested","Physiological contexts where ZNF471 controls PLS3 unclear"]},{"year":2020,"claim":"Defining PLS3's role in cell migration mechanics: PLS3 stabilizes and extends membrane protrusions specifically across ECM gaps where myosin II is excluded, establishing it as a protrusion-promoting factor in discontinuous ECM environments.","evidence":"Micropatterned ECM substrates, TIRF/confocal live imaging, PLS3 knockdown with protrusion metrics","pmids":["32968060"],"confidence":"High","gaps":["Mechanism of mutual exclusion between PLS3 and myosin II not resolved","Whether this function extends to 3D migration contexts unknown"]},{"year":2022,"claim":"Resolving the structural basis of actin bundling at atomic resolution: cryo-EM revealed that PLS3 uses a sequential binding mechanism through two actin-binding domains with flexible inter-CHD linkers to bridge filament pairs in both parallel and antiparallel orientations.","evidence":"Cryo-EM structure of human PLS3 bound to F-actin, inter-CHD linker mutagenesis, biochemical and cell biological validation","pmids":["36067297"],"confidence":"High","gaps":["Structure of full-length PLS3 in complex with two filaments not obtained","How calcium binding to EF-hands modulates the structural mechanism not visualized"]},{"year":2023,"claim":"Establishing genotype-phenotype relationships: loss-of-function PLS3 variants cause X-linked osteoporosis by impairing mechanosensitive osteoblast mineralization, while gain-of-function actin-binding domain variants cause congenital diaphragmatic hernia with increased bone density, demonstrating that distinct variant classes produce opposite functional consequences.","evidence":"PLS3-depleted osteoblast rescue with WT/mutant PLS3 on stiffness substrates; mouse knockin of p.Trp499Cys recapitulating CDH and elevated BMD","pmids":["38089885","37751738"],"confidence":"High","gaps":["Biochemical mechanism underlying gain-of-function bundling not characterized","How mechanotransduction defect leads specifically to osteoporosis in patients unknown"]},{"year":2024,"claim":"Extending functional redundancy analysis: ACTN1 and ACTN4 rescue skeletal defects in PLS3-deficient zebrafish but FSCN1 cannot, and PLS3 loss in osteocytes alters Wnt pathway gene expression, linking PLS3 to osteogenic signaling.","evidence":"Zebrafish morpholino rescue with actin bundlers, RNA-seq in PLS3-knockdown osteocyte-like cells","pmids":["39273077"],"confidence":"Medium","gaps":["Direct molecular basis for functional redundancy with actinins not determined","Wnt pathway changes not validated at protein level or in vivo"]},{"year":null,"claim":"Key open questions include: how calcium binding to PLS3's EF-hand domains structurally regulates its bundling activity, whether pH sensing via conserved histidine residues operates in vivo to tune PLS3 function, the molecular mechanism by which PLS3 controls cortical myosin II activation, and how gain-of-function actin-binding domain mutations produce diaphragmatic hernia.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of calcium-bound or pH-modulated PLS3","Mechanism linking PLS3 to myosin II cortical recruitment unknown","Gain-of-function bundling biochemistry not characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1,2,3,6,12]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,1,2,3,5,6,12]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,7,9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,6]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[5,12]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[4,7,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,19,20]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[5,6]}],"complexes":[],"partners":["CORO1C","RAB5A","LCP1","ACTN1","ACTN4","ZNF471"],"other_free_text":[]},"mechanistic_narrative":"PLS3 (T-plastin) is a calcium- and pH-sensitive actin-bundling protein that cross-links actin filaments in both parallel and antiparallel orientations via tandem calponin-homology domains connected by flexible inter-CHD linkers, stabilizing actin-based protrusions, regulating endocytosis, and transducing mechanical signals in diverse cell types [PMID:36067297, PMID:7721941, PMID:32968060, PMID:38089885]. Beyond bundling, PLS3 inhibits cofilin-mediated actin depolymerization independently of its cross-linking activity, interacts with activated Rab5 and the calcium-dependent binding partner CORO1C to promote endocytic membrane trafficking, and controls cortical myosin II activation required for basement membrane assembly [PMID:15741236, PMID:21426900, PMID:27499521, PMID:28559444]. PLS3 expression is governed by CpG island methylation status and can be induced through the calcineurin/NFAT signaling pathway or repressed by the ZNF471/KAP1 complex via H3K9 trimethylation at its promoter [PMID:25806852, PMID:22627769, PMID:29610526]. Loss-of-function PLS3 variants cause X-linked osteoporosis by impairing mechanosensitive osteoblast mineralization, whereas gain-of-function missense variants affecting actin-binding domains cause congenital diaphragmatic hernia with increased bone mineral density [PMID:38089885, PMID:37751738]."},"prefetch_data":{"uniprot":{"accession":"P13797","full_name":"Plastin-3","aliases":["T-fimbrin","T-plastin"],"length_aa":630,"mass_kda":70.8,"function":"Actin-bundling protein","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P13797/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PLS3","classification":"Not 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Inter-CHD linkers were identified as key structural elements underlying flexible but stable cross-linking.\",\n      \"method\": \"Cryo-electron microscopy with machine-learning-enabled pipeline, biochemical assays, cell biological validation, active-site/inter-CHD linker mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with biochemical and cell biological validation, mutagenesis of key structural elements\",\n      \"pmids\": [\"36067297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"T-plastin is functionally required for Shigella flexneri entry into HeLa cells; it localizes to bacterium-induced actin protrusions and a truncated T-plastin lacking one actin-binding domain acts as a dominant negative, blocking invasion. T-plastin bundles actin filaments in parallel orientation within cellular protrusions at entry zones.\",\n      \"method\": \"Transfection of truncated dominant-negative T-plastin, immunofluorescence colocalization, electron microscopy of actin ultrastructure\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional domain truncation combined with colocalization and ultrastructural analysis; foundational paper with 139 citations\",\n      \"pmids\": [\"7721941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"T-plastin and L-plastin isoforms have different functional roles in actin filament organization in a cell-type-specific manner: T-plastin associates with microvillar actin filaments after detergent extraction and induces shape changes in microvilli, whereas L-plastin does not affect microvilli and is fully extracted. Overproduction of either isoform reorganizes actin stress fibers into geodesic structures.\",\n      \"method\": \"Overexpression in CV-1 and LLC-PK1 cell lines, detergent extraction fractionation, morphological analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal cell lines with detergent fractionation and morphological readouts; foundational paper with 83 citations\",\n      \"pmids\": [\"7806577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"T-plastin/T-fimbrin increases the velocity of Arp2/3-mediated actin-based bead motility 1.5-fold, stabilizes actin comets, displaces cofilin, and inhibits cofilin-mediated actin depolymerization in vitro. A bundling-incompetent ABD1 variant retains these effects, indicating that T-plastin controls actin turnover through filament binding independently of cross-linking. In cells, ABD1 induces long actin cables.\",\n      \"method\": \"Biomimetic VCA-bead motility assay in cell-free extracts, in vitro F-actin depolymerization assay, cell-based overexpression with mutant ABD1\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution assay combined with mutagenesis and cell-based validation\",\n      \"pmids\": [\"15741236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PLS3 overexpression rescues impaired endocytosis in SMN-deficient cells and restores FM1-43 endocytotic uptake at neuromuscular junction presynaptic terminals in SMA mice. CORO1C was identified as a direct calcium-dependent binding partner of PLS3, and CORO1C overexpression similarly restores fluid-phase endocytosis and rescues axonal defects in SMN-depleted zebrafish by elevating F-actin levels.\",\n      \"method\": \"Proteomics, Co-IP/biochemical binding assay (calcium-dependent), fluid-phase endocytosis assay, FM1-43 presynaptic uptake, SMA mouse rescue experiments, zebrafish knockdown\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods across cell, mouse, and zebrafish models; direct binding demonstrated biochemically\",\n      \"pmids\": [\"27499521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"T-plastin (Pls3) localizes to the cell cortex in mouse epidermal cells and is essential for basement membrane assembly and epidermal morphogenesis. Loss of Pls3 by in utero depletion causes basement membrane and polarity defects; apicobasal polarity defects are secondary to basement membrane disruption. Pls3 is required for proper localization and activation of myosin II at the cortex, and inhibition of myosin II motor activity disrupts basement membrane organization.\",\n      \"method\": \"In utero siRNA depletion (mouse embryo), live imaging/immunofluorescence localization, myosin II pharmacological inhibition, epistasis analysis of polarity vs. basement membrane defects\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic depletion with specific mechanistic readouts (myosin II localization/activation) and epistasis experiments\",\n      \"pmids\": [\"28559444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"T-Plastin promotes membrane protrusions across ECM gaps during cell migration by stabilizing actin filaments; it widens and lengthens protrusions and is specifically enriched in active protrusions devoid of non-muscle myosin II. Micropatterned ECM experiments show T-Plastin is essential for bridging micron-scale ECM gaps.\",\n      \"method\": \"Micropatterned ECM substrates, TIRF and confocal live imaging, KD with specific protrusion and migration readouts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular phenotype using engineered ECM platform; multiple imaging modalities\",\n      \"pmids\": [\"32968060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Both L- and T-plastin interact specifically with activated (GTP-bound) Rab5 and co-localize with Rab5 on the plasma membrane and endosomes. Overexpression of L- or T-plastin increases Rab5 activity and the rate of fluid-phase endocytosis, indicating plastin-Rab5 interaction promotes endocytic activity.\",\n      \"method\": \"Affinity column pulldown with constitutively active Rab5, co-localization by immunofluorescence, fluid-phase endocytosis assay, overexpression in Cos-1 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pulldown and overexpression with functional endocytosis readout; single lab\",\n      \"pmids\": [\"21426900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"T-plastin expression is regulated downstream of the calcineurin/NFAT pathway in keratinocytes. siRNA knockdown of T-plastin decreases keratinocyte migration, actin lamellipodia formation, and FAK and β6-integrin expression, placing T-plastin as a downstream effector of calcineurin/NFAT-dependent migration.\",\n      \"method\": \"siRNA knockdown, scratch and Boyden migration assays, calcineurin inhibitor (FK506) treatment, siNFAT2, immunofluorescence\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with multiple migration readouts and pathway epistasis; single lab\",\n      \"pmids\": [\"25226517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"T-plastin is recruited to the plasma membrane during hypoxia and mediates hypoxia-induced membrane trafficking independently of the HIF system. Knockdown of T-plastin abolishes the increase in membrane endocytosis observed under hypoxic conditions, associated with increased cortical actin density.\",\n      \"method\": \"SILAC proteomics screen, T-plastin knockdown, FM1-43/mCLING membrane trafficking assays, electron microscopy of actin density\",\n      \"journal\": \"Acta physiologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — unbiased SILAC discovery followed by KD with specific functional readout; single lab\",\n      \"pmids\": [\"28218996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mutation p.Ala253_Leu254insAsn in PLS3 disrupts interaction between PLS3 and its binding partner LCP1 (L-plastin). Both PLS3 and LCP1 regulate intracellular Ca2+ levels, and mutant PLS3 weakens this regulatory function. The PLS3-LCP1 interaction is enhanced under low extracellular Ca2+ concentration.\",\n      \"method\": \"Co-IP/pulldown (binding partner identification), intracellular Ca2+ measurement, mutant vs. wildtype comparison\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, Co-IP plus functional Ca2+ assay, moderate mechanistic follow-up\",\n      \"pmids\": [\"28646489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PLS3 overexpression delays ataxic phenotype in Chp1-mutant (vacillator) mice by ameliorating axon hypertrophy and axonal swellings in Purkinje neurons. Mechanistically, PLS3 overexpression trends toward increased membrane targeting/expression of Na+/H+ exchanger NHE1, an important CHP1 binding partner.\",\n      \"method\": \"Transgenic PLS3 overexpression in Chp1 mutant mice, behavioral phenotyping, histological analysis of Purkinje neurons, Western blotting for NHE1\",\n      \"journal\": \"Frontiers in neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic rescue experiment with defined neuronal phenotype; NHE1 data is trend-level only\",\n      \"pmids\": [\"31607845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PLS3 localizes to focal adhesions in osteoblasts and is required for mechanosensitive regulation of osteoblast mineralization. Depletion of PLS3 in MC3T3-E1 cells abolishes cell responsiveness to ECM stiffness (cell size, focal adhesion length, number) and blocks matrix mineralization. Rescue with wildtype but not actin-bundling-deficient PLS3 mutants restores stiffness response, demonstrating actin-bundling is required.\",\n      \"method\": \"Stable KD in preosteoblast cell line (MC3T3-E1), rescue with WT and patient mutants, ECM stiffness substrates (6 vs. 100 kPa), osteogenic differentiation mineralization assay, immunofluorescence FA quantification\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KD with WT/mutant rescue on defined stiffness substrates, multiple orthogonal readouts, mutagenesis validates actin-bundling requirement\",\n      \"pmids\": [\"38089885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PLS3 loss-of-function in murine MLO-Y4 osteocyte-like cells causes differential expression of Wnt1, Nos1ap, and Myh3, implicating Wnt and Th17 differentiation pathways. ACTN1 and ACTN4 can rescue skeletal deformities in pls3-morphant zebrafish, but FSCN1 cannot, indicating partial functional redundancy among actin bundlers.\",\n      \"method\": \"RNA-seq after Pls3 KD in MLO-Y4 cells, morpholino knockdown in zebrafish with actin-bundler rescue experiments, osteogenic transdifferentiation of patient fibroblasts\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transcriptomics combined with zebrafish genetic rescue; pathway identification from single lab\",\n      \"pmids\": [\"39273077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Missense PLS3 variants specifically affecting actin-binding domains cause congenital diaphragmatic hernia (CDH) with gain-of-function effect, whereas loss-of-function variants cause osteoporosis. A mouse knockin model of p.Trp499Cys (within actin-binding domain) recapitulates diaphragm and abdominal-wall defects with increased (not decreased) bone mineral density, demonstrating that distinct variant classes in the actin-binding domains produce opposite functional consequences.\",\n      \"method\": \"In silico protein modeling, mouse knockin model (c.1497G>C; p.Trp499Cys), skeletal phenotyping (BMD), diaphragm/body-wall assessment in mice and human subjects\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mouse knockin recapitulating human phenotype plus comparative variant analysis; multiple orthogonal readouts\",\n      \"pmids\": [\"37751738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PLS3 (and PLS2) functions as a cytoskeletal pH sensor: F-actin bundling activity of PLS3 is reduced at alkaline pH and enhanced at acidic pH, mediated through the N-terminal actin-binding domain (ABD1). In fibroblasts, elevated cytosolic pH causes PLS2 dissociation from actin structures, while acidic conditions promote association with focal adhesions and stress fibers. His207 is identified as a pH-sensing residue in PLS2.\",\n      \"method\": \"In vitro F-actin bundling assays at varying pH, live-cell imaging of pH-induced localization changes, site-directed mutagenesis of His207\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis and cell imaging; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.26.645573\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The T-plastin promoter contains a CCAAT box, Sp1 motif, and four AP2 motifs but no TATA box. Differential expression between leukocytes and non-leukocytes is controlled by CpG island methylation: CpG sites within the island are fully methylated in T-plastin-negative leukemia lines and unmethylated in T-plastin-expressing cells. A T-plastin enhancer composed of two inverted symmetric octamers separated by 17 nucleotides is inactive in leukocytes.\",\n      \"method\": \"S1 mapping (transcription start sites), promoter/enhancer reporter assays, restriction enzyme methylation analysis, DNA footprinting\",\n      \"journal\": \"DNA and cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple complementary molecular methods (S1 mapping, reporter assays, methylation analysis, footprinting) identifying promoter/enhancer elements\",\n      \"pmids\": [\"10025506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Aberrant T-plastin (PLS3) expression in Sézary syndrome cells is associated with promoter hypomethylation of specific CpG dinucleotides (positions 95-99 in the CpG island). T-plastin is expressed only in clonally involved CD3+CD4+CD26- lymphocytes.\",\n      \"method\": \"Pyrosequencing of CpG dinucleotides, RT-PCR for PLS3 expression, immunofluorescence with anti-PLS3 antibody, TCR clonality assay\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — correlation of methylation and expression; mechanistic direction supported by in vitro methylation data from PMID 25806852\",\n      \"pmids\": [\"22495182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Promoter hypomethylation drives PLS3 overexpression in Sézary syndrome. In vitro methylation of the cloned PLS3 promoter suppresses luciferase reporter expression, and treatment of PLS3-negative Jurkat cells with 5-azacytidine (hypomethylating agent) induces PLS3 expression.\",\n      \"method\": \"Pyrosequencing of CpG regions, in vitro promoter methylation + luciferase reporter assay, 5-azacytidine treatment of Jurkat cells\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct mechanistic demonstration using in vitro methylation + reporter assay and pharmacological demethylation with gene induction\",\n      \"pmids\": [\"25806852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"T-plastin expression in Sézary syndrome cells is induced by calcium influx (PMA/ionomycin stimulation) and regulated by the calcineurin/NFAT transcription pathway; calcineurin inhibitors suppress both constitutive and calcium-induced T-plastin expression. Constitutive T-plastin expression confers resistance to etoposide-induced apoptosis and promotes cell migration toward CCL17 and IP-10 chemokines.\",\n      \"method\": \"Pharmacological stimulation (PMA/ionomycin), calcineurin inhibitor treatment, apoptosis assay, migration assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement via pharmacological inhibition with functional readouts (apoptosis, migration); single lab\",\n      \"pmids\": [\"22627769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"T-plastin (PLST) promotes epithelial-mesenchymal transition (EMT) in human lung cancer cells via the FAK/AKT/Slug signaling axis; PLST overexpression enhances cell migration and invasion with upregulation of vimentin and Slug and downregulation of E-cadherin, whereas PLST knockdown reverses these effects. Phosphorylation levels of FAK and AKT are dependent on PLST expression.\",\n      \"method\": \"Overexpression and siRNA knockdown, migration/invasion assays, Western blotting for EMT markers and FAK/AKT phosphorylation\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — loss- and gain-of-function with pathway marker readouts; single lab, no direct binding demonstrated\",\n      \"pmids\": [\"38835117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Bioinformatic and homology modeling analyses identify a critical LOOP-1 region (residues 240-266) in PLS3 that physically connects the CH1 and CH2 domains of ABD1 and is spatially located at the ABD1-ABD2 interface, essential for actin-binding conformation transition. A novel nonsense mutation (p.E249X) in LOOP-1 truncates the protein and is predicted to disrupt actin binding.\",\n      \"method\": \"Targeted gene sequencing, homology modeling, molecular dynamics simulation\",\n      \"journal\": \"International journal of endocrinology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no biochemical validation\",\n      \"pmids\": [\"30405713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ZNF471 transcriptionally represses PLS3 by directly binding to the PLS3 promoter and recruiting co-repressor KAP1, which induces H3K9me3 enrichment at the PLS3 promoter locus.\",\n      \"method\": \"ChIP-PCR for ZNF471 binding and H3K9me3 at PLS3 promoter, ectopic ZNF471 expression with PLS3 expression readout, co-IP for KAP1 recruitment\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-PCR at specific promoter plus co-repressor co-IP; single lab\",\n      \"pmids\": [\"29610526\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PLS3 (T-plastin) is a calcium-sensitive, pH-responsive actin-bundling protein that cross-links actin filaments in both parallel and antiparallel orientations via tandem calponin-homology domains; it stabilizes actin protrusions, promotes endocytosis via interaction with activated Rab5 and the CORO1C binding partner, regulates cortical myosin II activation for basement membrane assembly, acts as a mechanosensitive effector in osteoblast focal adhesions to drive matrix mineralization, and functions downstream of calcineurin/NFAT signaling to control cell migration—with its expression regulated by CpG island methylation and the ZNF471/KAP1 repressor complex.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PLS3 (T-plastin) is a calcium- and pH-sensitive actin-bundling protein that cross-links actin filaments in both parallel and antiparallel orientations via tandem calponin-homology domains connected by flexible inter-CHD linkers, stabilizing actin-based protrusions, regulating endocytosis, and transducing mechanical signals in diverse cell types [PMID:36067297, PMID:7721941, PMID:32968060, PMID:38089885]. Beyond bundling, PLS3 inhibits cofilin-mediated actin depolymerization independently of its cross-linking activity, interacts with activated Rab5 and the calcium-dependent binding partner CORO1C to promote endocytic membrane trafficking, and controls cortical myosin II activation required for basement membrane assembly [PMID:15741236, PMID:21426900, PMID:27499521, PMID:28559444]. PLS3 expression is governed by CpG island methylation status and can be induced through the calcineurin/NFAT signaling pathway or repressed by the ZNF471/KAP1 complex via H3K9 trimethylation at its promoter [PMID:25806852, PMID:22627769, PMID:29610526]. Loss-of-function PLS3 variants cause X-linked osteoporosis by impairing mechanosensitive osteoblast mineralization, whereas gain-of-function missense variants affecting actin-binding domains cause congenital diaphragmatic hernia with increased bone mineral density [PMID:38089885, PMID:37751738].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing that T-plastin and L-plastin are functionally distinct isoforms: T-plastin uniquely associates with microvillar actin filaments and reorganizes actin architecture in a cell-type-specific manner, defining it as a non-hematopoietic actin-bundling protein.\",\n      \"evidence\": \"Overexpression in epithelial and fibroblast cell lines with detergent extraction fractionation and morphological analysis\",\n      \"pmids\": [\"7806577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for isoform-specific actin interactions not determined\", \"In vivo physiological relevance not tested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrating that T-plastin's actin-bundling activity is functionally required for actin-dependent cellular processes: T-plastin localizes to bacterium-induced actin protrusions and a dominant-negative truncation blocks Shigella invasion, establishing it as an essential organizer of actin protrusions.\",\n      \"evidence\": \"Dominant-negative T-plastin truncation, immunofluorescence, and electron microscopy in Shigella-infected HeLa cells\",\n      \"pmids\": [\"7721941\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether bundling versus filament stabilization is the critical activity was unresolved\", \"No genetic loss-of-function model tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Resolving how T-plastin expression is restricted to non-hematopoietic cells: CpG island methylation silences the T-plastin promoter in leukocytes, and a tissue-specific enhancer is inactive in those cells.\",\n      \"evidence\": \"S1 mapping, promoter/enhancer reporter assays, restriction-enzyme methylation analysis, and DNA footprinting of the PLS3 promoter\",\n      \"pmids\": [\"10025506\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trans-acting factors responsible for methylation not identified\", \"In vivo chromatin context not examined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Separating actin-bundling from filament-stabilizing functions: T-plastin increases Arp2/3-based actin motility speed and displaces cofilin even without cross-linking, establishing a bundling-independent role in controlling actin turnover dynamics.\",\n      \"evidence\": \"Biomimetic VCA-bead motility assay in cell-free extracts with bundling-incompetent ABD1 mutant, in vitro depolymerization assay\",\n      \"pmids\": [\"15741236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of cofilin displacement not structurally resolved\", \"Relative contributions of bundling vs. stabilization in vivo remain unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linking T-plastin to endocytic machinery: T-plastin binds activated (GTP-bound) Rab5 and enhances fluid-phase endocytosis, connecting actin bundling to vesicular trafficking.\",\n      \"evidence\": \"Affinity pulldown with constitutively active Rab5, colocalization, and fluid-phase endocytosis assay in Cos-1 cells\",\n      \"pmids\": [\"21426900\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reciprocal validation of binding in endogenous context lacking\", \"Structural basis of PLS3–Rab5 interaction not determined\", \"Whether Rab5 interaction requires bundling competence unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placing PLS3 expression under calcineurin/NFAT transcriptional control and linking it to disease-relevant cell behaviors: calcium/NFAT signaling induces T-plastin expression, which confers apoptosis resistance and promotes chemokine-directed migration in Sézary syndrome cells; promoter hypomethylation underlies aberrant expression in these malignant T cells.\",\n      \"evidence\": \"Pharmacological calcineurin inhibition, PMA/ionomycin stimulation, apoptosis and migration assays; pyrosequencing of CpG dinucleotides in Sézary cells\",\n      \"pmids\": [\"22627769\", \"22495182\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NFAT binds the PLS3 promoter directly was not shown by ChIP\", \"Causality between methylation and NFAT-driven induction not dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Providing direct mechanistic proof that promoter methylation controls PLS3 transcription: in vitro methylation of the cloned PLS3 promoter silences reporter expression, and pharmacological demethylation reactivates PLS3 in PLS3-negative T cells.\",\n      \"evidence\": \"In vitro promoter methylation with luciferase reporter, 5-azacytidine treatment of Jurkat cells\",\n      \"pmids\": [\"25806852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific CpG sites critical for silencing not individually mutated\", \"In vivo relevance of demethylation in normal T-cell biology unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Connecting PLS3 to endocytic rescue in spinal muscular atrophy: PLS3 overexpression restores impaired endocytosis in SMN-deficient cells via a pathway involving its calcium-dependent binding partner CORO1C, establishing a molecular mechanism for PLS3 as an SMA disease modifier.\",\n      \"evidence\": \"Proteomics, calcium-dependent Co-IP, fluid-phase endocytosis assay, FM1-43 presynaptic uptake in SMA mouse NMJs, zebrafish rescue\",\n      \"pmids\": [\"27499521\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural basis of PLS3–CORO1C complex not resolved\", \"Whether endocytic rescue is sufficient for motor neuron survival in vivo not demonstrated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealing a cortical signaling role for PLS3 beyond bundling: PLS3 is required for cortical myosin II localization and activation, and loss of PLS3 disrupts basement membrane assembly and secondary epithelial polarity in mouse epidermis.\",\n      \"evidence\": \"In utero siRNA depletion in mouse embryonic skin, live imaging, myosin II inhibitor epistasis\",\n      \"pmids\": [\"28559444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PLS3 recruits or activates myosin II at the cortex is unknown\", \"Whether this role generalizes beyond epidermal epithelium untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying PLS3 as a hypoxia-responsive regulator of membrane trafficking independent of HIF: PLS3 is recruited to the plasma membrane under hypoxia and its depletion abolishes hypoxia-induced endocytosis.\",\n      \"evidence\": \"SILAC proteomics, PLS3 knockdown, FM1-43/mCLING membrane trafficking assays, electron microscopy\",\n      \"pmids\": [\"28218996\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signal linking hypoxia to PLS3 membrane recruitment not identified\", \"Independence from HIF not validated by HIF knockout\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying ZNF471/KAP1 as a direct transcriptional repressor of PLS3 through H3K9me3 deposition, providing a chromatin-level mechanism for PLS3 silencing complementary to DNA methylation.\",\n      \"evidence\": \"ChIP-PCR for ZNF471 and H3K9me3 at PLS3 promoter, ectopic ZNF471 expression, Co-IP for KAP1\",\n      \"pmids\": [\"29610526\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between ZNF471-mediated repression and CpG methylation not tested\", \"Physiological contexts where ZNF471 controls PLS3 unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defining PLS3's role in cell migration mechanics: PLS3 stabilizes and extends membrane protrusions specifically across ECM gaps where myosin II is excluded, establishing it as a protrusion-promoting factor in discontinuous ECM environments.\",\n      \"evidence\": \"Micropatterned ECM substrates, TIRF/confocal live imaging, PLS3 knockdown with protrusion metrics\",\n      \"pmids\": [\"32968060\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of mutual exclusion between PLS3 and myosin II not resolved\", \"Whether this function extends to 3D migration contexts unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolving the structural basis of actin bundling at atomic resolution: cryo-EM revealed that PLS3 uses a sequential binding mechanism through two actin-binding domains with flexible inter-CHD linkers to bridge filament pairs in both parallel and antiparallel orientations.\",\n      \"evidence\": \"Cryo-EM structure of human PLS3 bound to F-actin, inter-CHD linker mutagenesis, biochemical and cell biological validation\",\n      \"pmids\": [\"36067297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length PLS3 in complex with two filaments not obtained\", \"How calcium binding to EF-hands modulates the structural mechanism not visualized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Establishing genotype-phenotype relationships: loss-of-function PLS3 variants cause X-linked osteoporosis by impairing mechanosensitive osteoblast mineralization, while gain-of-function actin-binding domain variants cause congenital diaphragmatic hernia with increased bone density, demonstrating that distinct variant classes produce opposite functional consequences.\",\n      \"evidence\": \"PLS3-depleted osteoblast rescue with WT/mutant PLS3 on stiffness substrates; mouse knockin of p.Trp499Cys recapitulating CDH and elevated BMD\",\n      \"pmids\": [\"38089885\", \"37751738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biochemical mechanism underlying gain-of-function bundling not characterized\", \"How mechanotransduction defect leads specifically to osteoporosis in patients unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extending functional redundancy analysis: ACTN1 and ACTN4 rescue skeletal defects in PLS3-deficient zebrafish but FSCN1 cannot, and PLS3 loss in osteocytes alters Wnt pathway gene expression, linking PLS3 to osteogenic signaling.\",\n      \"evidence\": \"Zebrafish morpholino rescue with actin bundlers, RNA-seq in PLS3-knockdown osteocyte-like cells\",\n      \"pmids\": [\"39273077\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular basis for functional redundancy with actinins not determined\", \"Wnt pathway changes not validated at protein level or in vivo\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: how calcium binding to PLS3's EF-hand domains structurally regulates its bundling activity, whether pH sensing via conserved histidine residues operates in vivo to tune PLS3 function, the molecular mechanism by which PLS3 controls cortical myosin II activation, and how gain-of-function actin-binding domain mutations produce diaphragmatic hernia.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of calcium-bound or pH-modulated PLS3\", \"Mechanism linking PLS3 to myosin II cortical recruitment unknown\", \"Gain-of-function bundling biochemistry not characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6, 12]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5, 6, 12]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 7, 9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [5, 12]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [4, 7, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 19, 20]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CORO1C\",\n      \"RAB5A\",\n      \"LCP1\",\n      \"ACTN1\",\n      \"ACTN4\",\n      \"ZNF471\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}