{"gene":"SERPINE1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":1986,"finding":"PAI-1 (SERPINE1) was cloned from human endothelial cell cDNA libraries; the mature protein is 379–402 amino acids, belongs to the serpin superfamily (homology with α1-antitrypsin and antithrombin III), lacks cysteine residues, has three N-linked glycosylation sites, and is encoded by a gene on chromosome 7. Two mRNA species (~2.2 and ~3.0 kb) arise from a single gene.","method":"cDNA cloning, nucleotide sequencing, Northern blot, immunological screening of expression libraries","journal":"Proceedings of the National Academy of Sciences / Journal of Clinical Investigation / EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 — three independent groups cloned and sequenced the full-length cDNA with functional validation (inhibitory activity demonstrated in E. coli and transfected cells)","pmids":["3092219","3097076","2430793"],"is_preprint":false},{"year":1992,"finding":"Crystal structure of intact latent PAI-1 at 2.6 Å resolution revealed that the reactive-site loop (residues N-terminal to the scissile bond) is inserted as a central β-strand into the major β-sheet (analogous to cleaved serpins), while C-terminal residues occupy a distinct surface position. This structural rearrangement explains PAI-1's unique ability to spontaneously convert to a stable latent (inactive) form without cleavage, and why inhibitory activity can be restored by denaturation/renaturation.","method":"Single-crystal X-ray diffraction (2.6 Å resolution)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure providing direct mechanistic explanation of latency","pmids":["1731226"],"is_preprint":false},{"year":1986,"finding":"PAI-1 purified from U-937 cells forms covalent complexes with urokinase (uPA) and two-chain tPA with second-order rate constants of ~0.9×10⁶ M⁻¹s⁻¹ and ~0.2×10⁶ M⁻¹s⁻¹ respectively; the 47-kDa inhibitor is a member of the antithrombin III (serpin) family and the covalent complex can be hydrolyzed by NH₄OH to yield a 35-kDa inhibitor fragment, consistent with acyl-enzyme (serpin) mechanism.","method":"Protein purification, SDS-PAGE, covalent complex formation assay, kinetic analysis, partial amino acid sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assay with purified components, replicated across multiple groups","pmids":["3090045"],"is_preprint":false},{"year":1990,"finding":"Receptor-bound uPA on U937 cell surfaces is efficiently inhibited by PAI-1 (rate constant ~4.5×10⁶ M⁻¹s⁻¹, ~40% lower than for free uPA); PAI-1 also inhibits receptor-bound uPA. The resulting uPA–PAI-1 complex on the uPA receptor (uPAR) is then internalized and degraded via lysosomes (inhibitable by chloroquine), while free uPA, ATF, or DFP-uPA are not internalized, establishing a cellular clearance cycle for uPA.","method":"Radiolabeled ligand internalization assay, acid dissociation, TCA precipitation, chloroquine inhibition, kinetic rate constant measurements","journal":"The EMBO journal / The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — two independent studies with quantitative kinetics and direct internalization/degradation assays","pmids":["2157592","2161846"],"is_preprint":false},{"year":1992,"finding":"Complete PAI-1 deficiency in humans, caused by a frameshift mutation, results in a severe bleeding disorder (hyperfibrinolysis), establishing PAI-1 as the essential physiological inhibitor of plasminogen activators in vivo.","method":"Genetic analysis (frameshift mutation identification) in a PAI-1-deficient patient with bleeding diathesis","journal":"The New England journal of medicine","confidence":"High","confidence_rationale":"Tier 2 — human loss-of-function (natural null) with clear phenotypic readout","pmids":["1435917"],"is_preprint":false},{"year":1995,"finding":"The 4G allele of the PAI-1 promoter 4G/5G polymorphism confers higher basal PAI-1 transcription than the 5G allele because both alleles bind a transcriptional activator, but only the 5G allele additionally binds a repressor protein at an overlapping site; this mechanism was associated with higher plasma PAI-1 activity and higher prevalence of myocardial infarction before age 45.","method":"Allele-specific transcription analysis, electrophoretic mobility shift assay (EMSA), population genetics","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — EMSA with allele-specific protein binding plus functional transcriptional readout, replicated in population study","pmids":["7892190"],"is_preprint":false},{"year":1996,"finding":"PAI-1 and the urokinase receptor (uPAR) bind to the same somatomedin B (SMB) domain of vitronectin (VN) competitively; PAI-1 displaces VN from uPAR and detaches U937 cells from VN substrate independently of its protease inhibitory activity. uPA rapidly reverses this detachment. This established PAI-1 as a molecular switch governing uPAR-mediated cell adhesion and release from the extracellular matrix.","method":"Domain-swapping and site-directed mutagenesis of VN, competitive binding assays, cell detachment assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with functional cell adhesion/detachment assays, independently validated","pmids":["8830783"],"is_preprint":false},{"year":1996,"finding":"Active PAI-1 inhibits smooth muscle cell (SMC) migration on vitronectin by blocking αVβ3 integrin binding to vitronectin—an effect requiring high-affinity PAI-1 binding to vitronectin but independent of PAI-1's protease inhibitory function. Formation of a PAI-1–plasminogen activator complex abolishes PAI-1's affinity for vitronectin and restores cell migration, directly linking plasminogen activator activity to integrin-mediated migration control.","method":"SMC migration assay, function-blocking antibodies, PAI-1 mutants deficient in protease inhibition, integrin-blocking experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal approaches (mutants, antibodies, cell migration assays) in a single high-impact study","pmids":["8837777"],"is_preprint":false},{"year":1997,"finding":"After uPA–PAI-1 complex internalization via uPAR and LRP (α2MR-LRP), uPAR is recycled back to the cell surface in a PI-PLC-sensitive (GPI-anchored) form, as demonstrated by surface biotinylation pulse-chase. The receptor recycles through an intracellular compartment that temporarily renders it PI-PLC resistant, while LRP is required for internalization but not recycling.","method":"Cell surface biotinylation, FACScan, immunofluorescence, immunoelectron microscopy, PI-PLC treatment, pulse-chase recycling assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal localization and functional methods demonstrating receptor recycling","pmids":["9184208"],"is_preprint":false},{"year":1997,"finding":"PAI-1 gene-deficient (PAI-1⁻/⁻) mice show enhanced and accelerated smooth muscle cell migration into vascular wounds and increased neointima formation after arterial injury compared to wild-type, while adenoviral PAI-1 gene transfer suppresses neointima formation. Smooth muscle cell proliferation was unaffected, establishing that PAI-1 inhibits vascular remodeling specifically by restraining cell migration.","method":"PAI-1 knockout mice, perivascular electric and transluminal mechanical arterial injury, morphometric analysis, immunostaining, adenoviral gene transfer","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function and gain-of-function in vivo with specific phenotypic readout (migration vs. proliferation dissected)","pmids":["9386191"],"is_preprint":false},{"year":2003,"finding":"Crystal structure (2.3 Å) of the somatomedin B (SMB) domain of vitronectin in complex with PAI-1 revealed the molecular basis for vitronectin stabilization of active PAI-1 conformation and showed that PAI-1 sterically occludes the binding sites for both uPAR and integrins on vitronectin, explaining how PAI-1 controls cell adhesion and motility through competition for vitronectin.","method":"X-ray crystallography (2.3 Å resolution) of PAI-1–vitronectin SMB domain complex","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution structure of the complex with direct mechanistic implications validated by the structural data","pmids":["12808446"],"is_preprint":false},{"year":2001,"finding":"PAI-1 inhibits uPA-induced cell chemotaxis by triggering uPAR internalization via LRP; the uPA–PAI-1 complex has no intrinsic chemotactic activity, but blocking LRP-mediated internalization (with RAP or anti-LRP antibodies) converts the complex into a chemoattractant that induces cytoskeleton reorganization and ERK/MAPK activation.","method":"Chemotaxis assay, receptor internalization assay with RAP and anti-LRP antibodies, cytoskeleton staining, ERK phosphorylation Western blot","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal functional assays with receptor-blocking reagents establishing mechanistic pathway","pmids":["11566185"],"is_preprint":false},{"year":2006,"finding":"PAI-1 is an essential downstream target of p53 required for replicative senescence: RNAi knockdown of PAI-1 allows escape from senescence in primary mouse and human fibroblasts, associated with sustained PI3K–PKB–GSK3β pathway activation and nuclear retention of cyclin D1. Conversely, ectopic PAI-1 expression in p53-deficient proliferating fibroblasts induces all hallmarks of replicative senescence. PAI-1 knockdown results are independent of its antiproteolytic serpin activity.","method":"RNAi knockdown, ectopic overexpression, senescence assays (SA-β-gal, BrdU incorporation), Western blot for PI3K–PKB–GSK3β–cyclin D1 pathway, primary mouse and human fibroblasts","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal loss- and gain-of-function with mechanistic pathway delineation, replicated in two cell systems","pmids":["16862142"],"is_preprint":false},{"year":2006,"finding":"Efficient macrophage migration in an inflammatory environment requires a sequential molecular cycle: Mac-1 integrin binds a fibrin–tPA binary complex; PAI-1 then neutralizes tPA, and the resulting integrin–tPA–PAI-1 ternary complex binds the endocytic receptor LRP, triggering a switch from cell adhesion to detachment. Genetic inactivation of Mac-1, tPA, PAI-1 or LRP (but not uPA) abolishes macrophage migration. A PAI-1 mutant unable to interact with LRP fails to rescue migration in PAI-1⁻/⁻ mice.","method":"Genetic knockout mice (Mac-1, tPA, PAI-1, LRP, uPA), PAI-1 LRP-binding mutant rescue, in vitro adhesion/retraction assays, intravital microscopy","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic knockouts combined with domain-specific mutant rescue establishing ordered pathway","pmids":["16601674"],"is_preprint":false},{"year":2006,"finding":"Hypoxia induces PAI-1 transcription in macrophages through three transcription factors—Egr-1, HIF-1α, and C/EBPα—each binding distinct sites in the PAI-1 promoter. Mutation of individual or combined sites reduces hypoxia-driven transcription. ChIP analysis confirmed chromatin binding of all three factors under hypoxic conditions; HIF-1α dominates but Egr-1 and C/EBPα augment the response independently of each other.","method":"PAI-1 promoter deletion/mutation reporter assays, EMSA with supershift, ChIP analysis, primary peritoneal macrophages and RAW264.7 cells","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — promoter mutagenesis, EMSA, and ChIP providing orthogonal evidence for three distinct transcriptional regulators","pmids":["17197388"],"is_preprint":false},{"year":2008,"finding":"PAI-1 is deposited along keratinocyte migration trails during wound repair and is required for optimal wound closure: recombinant active PAI-1 stimulates directional motility and cell spreading, while antisense-mediated knockdown or neutralizing antibodies impair wound repair and induce plasminogen-dependent anoikis. PAI-1 thus acts as a survival factor and migration regulator during epidermal injury response.","method":"PAI-1-GFP live imaging, recombinant PAI-1 addition, antisense knockdown, neutralizing antibodies, wound closure assays in wild-type and PAI-1⁻/⁻ cells, apoptosis assays","journal":"Archives of dermatological research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (live imaging, KO cells, protein addition/blocking) with defined functional readout","pmids":["18386027"],"is_preprint":false},{"year":2012,"finding":"Matrix-bound PAI-1 maintains cell blebbing (amoeboid migration mode) in colorectal cancer cells by localizing PDK1 and ROCK1 at the cell membrane and sustaining RhoA/ROCK1/MLC phosphorylation; tumor periphery modeling predicts heterogeneous PAI-1 concentrations sufficient to drive mesenchymal-to-amoeboid transition.","method":"Immunoblotting, activity assay, immunofluorescence, RhoA/ROCK1/MLC pathway analysis, mathematical modeling of PAI-1 distribution","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, correlative pathway activation with functional blebbing readout but no direct mutagenesis","pmids":["22363817"],"is_preprint":false},{"year":2014,"finding":"The N-terminal fragment of prolactin (16K PRL) binds PAI-1 and inhibits its antifibrinolytic activity, thereby promoting thrombolysis; simultaneously, 16K PRL acts through the PAI-1–uPA–uPAR ternary complex to exert antiangiogenic and antitumoral effects. Loss of PAI-1 abolishes both antitumoral and antiangiogenic effects of 16K PRL.","method":"Direct binding assay (16K PRL–PAI-1 interaction), PAI-1 knockout mice, fibrinolysis assay, tumor angiogenesis models","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1–2 — direct protein binding combined with genetic KO rescue experiments and functional fibrinolysis/angiogenesis assays","pmids":["24929950"],"is_preprint":false},{"year":2015,"finding":"PAI-1 modulates cell migration in a LRP1-dependent manner: PAI-1 induces β-catenin expression and transcriptional activity in LRP1-competent MEFs but not in LRP1-deficient cells; PAI-1-induced ERK1/2 activation is more prominent in LRP1-deficient cells and is abolished by β-catenin knockdown, placing PAI-1 upstream of both the β-catenin and ERK1/2 MAPK pathways through LRP1.","method":"LRP1 knockout MEFs, siRNA knockdown of β-catenin, Western blot, luciferase reporter for β-catenin transcriptional activity, migration assays","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2–3 — genetic LRP1-deficient cells plus RNAi epistasis, single lab","pmids":["25694133"],"is_preprint":false},{"year":2016,"finding":"TGF-β induces PAI-1 transcription through a p53–Smad2/3 complex formed on the PAI-1 promoter: p53 recruits the histone acetyltransferase CBP to this complex, enhancing H3 acetylation and transcriptional activation. p53 is required for TGF-β-induced cytostasis, and PAI-1 mediates part of this cytostatic activity, identifying PAI-1 as a mechanistic link between p53 and TGF-β cytostasis.","method":"Co-immunoprecipitation (p53–Smad complex), ChIP (promoter occupancy), histone acetylation assay, p53 siRNA, PAI-1 reporter assays, cell growth assays","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP, Co-IP, and functional cytostasis assays with RNAi epistasis providing mechanistic pathway","pmids":["27759037"],"is_preprint":false},{"year":2018,"finding":"Stress granules (SGs) sequester PAI-1 in proliferating and presenescent cells; SG assembly alone is sufficient to decrease the number of senescent cells. SG-localized PAI-1 promotes nuclear translocation of cyclin D1, RB phosphorylation, and maintenance of a proliferative state, establishing a non-cell-autonomous mechanism by which SG-mediated PAI-1 sequestration counteracts senescence.","method":"Stress granule induction, PAI-1 localization by immunofluorescence, SA-β-gal senescence assay, cyclin D1 nuclear fractionation, pRB Western blot","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, localization with functional downstream readout but limited mechanistic resolution of PAI-1 action within SGs","pmids":["29592859"],"is_preprint":false},{"year":2011,"finding":"PAI-1 inhibits neutrophil apoptosis (spontaneous and TRAIL-induced) through activation of PKB/Akt, Mcl-1, and Bcl-xL antiapoptotic pathways, mediated by pertussis toxin-sensitive G protein-coupled receptors and PI3K—not through uPAR, LRP, or vitronectin. In PAI-1⁻/⁻ mice, neutrophils accumulating in LPS-injured lungs show enhanced apoptosis compared to wild-type.","method":"Neutrophil apoptosis assay, pathway inhibitors (pertussis toxin, PI3K inhibitor), receptor-blocking antibodies, PAI-1⁻/⁻ mice, Western blot for Akt/Mcl-1/Bcl-xL","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological receptor dissection and in vivo KO validation, single lab","pmids":["21622848"],"is_preprint":false},{"year":2018,"finding":"Thrombin promotes PAI-1 mRNA expression and keratinocyte migration via PAR-1 transactivation of EGFR, downstream ERK1/2 phosphorylation, and specific phosphorylation of Smad2 linker region at Ser250 (but not Ser245 or Ser255); ERK1/2 inhibition but not p38 or JNK inhibition blocks Smad2L phosphorylation and PAI-1 induction.","method":"Selective kinase inhibitors, Western blot for Smad2 linker phosphorylation, qRT-PCR for PAI-1, scratch wound migration assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2–3 — pharmacological dissection with site-specific phosphorylation analysis, single lab","pmids":["29577978"],"is_preprint":false},{"year":2021,"finding":"Tubular epithelial cell-autonomous PAI-1 overexpression causes dedifferentiation (E-cadherin loss, vimentin gain), G2/M arrest, fibrosis (fibronectin, collagen-1, CCN2 induction), and apoptosis in HK-2 cells via three interconnected pathways: (1) loss of klotho, (2) p53 upregulation, and (3) TGF-βRI/SMAD3 activation independent of TGF-β1 ligand. Ectopic klotho restoration reversed fibrogenesis and proliferative defects; p53 suppression blocked maladaptive repair; TGF-βRI inhibition attenuated epithelial dysfunction.","method":"Stable PAI-1 overexpression in HK-2 cells, ectopic klotho restoration, p53 siRNA, TGF-βRI inhibitor, Western blot (pSMAD3, cleaved caspase-3, pHistone3), flow cytometry (annexin-V)","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function with three orthogonal epistasis experiments identifying pathway hierarchy, single lab","pmids":["34110636"],"is_preprint":false},{"year":2021,"finding":"Senescent glomerular endothelial cells secrete PAI-1 that drives podocyte apoptosis; selective genetic inactivation of PAI-1 in endothelial cells protects glomeruli from age-related lesion development and podocyte loss in mice. Blocking PAI-1 in conditioned medium from senescent endothelial cells prevented podocyte apoptosis in vitro.","method":"Endothelial cell-specific PAI-1 conditional knockout mice, aged p16INK-ATTAC transgenic mice (senescent cell depletion), conditioned medium transfer with PAI-1 neutralization, podocyte apoptosis assay","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 — cell-specific conditional KO combined with in vitro conditioned-medium rescue establishing paracrine mechanism","pmids":["34725920"],"is_preprint":false},{"year":2023,"finding":"PAI-1 binds LRP1 on lymphatic endothelial cells (LECs) and activates AKT/ERK1/2 signaling to promote endothelial-mesenchymal transition (EndoMT), leading to aberrant lymphangiogenesis and lymphatic metastasis; blockade of PAI-1 or LRP1/AKT/ERK1/2 abrogates EndoMT and tumor neolymphangiogenesis.","method":"CAF-conditioned medium, LRP1 interaction assay, Western blot (AKT/ERK phosphorylation), transwell/tube formation/transendothelial migration assays, popliteal LN metastasis mouse model, PAI-1 knockdown/inhibitor","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 — direct LRP1-PAI-1 interaction with functional pathway validation in vitro and in vivo, single lab","pmids":["37415190"],"is_preprint":false},{"year":2023,"finding":"Nuclear PAI-1 can bind chromatin at distal intergenic regions and function as a transcriptional co-repressor: ChIP-seq in bladder cancer cells showed PAI-1 chromatin occupancy, PAI-1 knockdown upregulated 57 candidate target genes (integration of ChIP-seq and RNA-seq), and rapid immunoprecipitation mass spectrometry identified nuclear PAI-1 interaction partners consistent with transcriptional regulatory complexes.","method":"ChIP-sequencing, RNA-sequencing, RIME (rapid immunoprecipitation mass spectrometry), immunohistochemistry of 939 tumor specimens","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq plus integrative transcriptomics; nuclear function is novel but validated by multiple genomic methods in a single study","pmids":["35842542"],"is_preprint":false},{"year":2023,"finding":"PAI-1 binds proteasome components and inhibits proteasomal activity, thereby reducing p53 degradation and promoting senescence in alveolar epithelial type II (ATII) cells; only the wild-type (secretion-competent) form of PAI-1 induces p53 accumulation and SA-β-gal activity, whereas a secretion-deficient mature form induces senescence markers without p53 induction, indicating the premature (pre-secretory) form interacts with the proteasome.","method":"Co-immunoprecipitation of PAI-1 with proteasome subunits, proteasome activity assay, stable overexpression of wtPAI-1 vs. secretion-deficient PAI-1, SA-β-gal, p53/p21/pRb Western blot","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — direct protein-protein interaction with proteasome plus functional activity assay and domain-specific mutant comparison, single lab","pmids":["37566086"],"is_preprint":false},{"year":2024,"finding":"PAI-1 regulates vascular smooth muscle cell (SMC) intrinsic stiffness by controlling cytoplasmic F-actin content: PAI-1 inhibition (PAI-039) or siRNA knockdown decreases SMC stiffness and F-actin, activates the F-actin depolymerase cofilin via AMPK signaling (not through uPAR/LRP), and reduces aortic pulse wave velocity in vivo; these effects are absent in PAI-1-deficient SMCs.","method":"Atomic force microscopy (SMC stiffness), F-actin staining, cofilin activity assay, AMPK inhibition, RNA-sequencing, PAI-1 siRNA, PAI-1⁻/⁻ murine SMCs, in vivo aortic pulse wave velocity","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (AFM, biochemistry, genetics, in vivo) in a single study with specific pathway identification","pmids":["38868940"],"is_preprint":false},{"year":2014,"finding":"PAI-1 (via inhibition of uPA/tPA and consequent maintenance of low plasmin levels) supports angiogenesis in hepatocellular carcinoma downstream of HIF-2α: HIF-2α knockdown reduces PAI-1 expression and angiogenesis; PAI-1 knockdown similarly reduces angiogenesis; restoring low plasmin activity with aprotinin in HIF-2α KD cells rescues angiogenesis, confirming a HIF-2α→PAI-1→plasmin inhibition→angiogenesis axis.","method":"Stable shRNA knockdown of HIF-1α/HIF-2α/PAI-1, HepG2 spheroid–embryoid body co-culture angiogenesis model, aprotinin (plasmin inhibitor) rescue, microarray gene expression","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KD with epistasis rescue experiment defining pathway order, single lab","pmids":["25489981"],"is_preprint":false},{"year":2019,"finding":"Tumor-secreted PAI-1 activates PI3K/AKT signaling in adjacent adipocytes, promoting nuclear translocation of FOXP1 which enhances PLOD2 promoter activity, leading to collagen crosslinking/remodeling by cancer-associated adipocytes (CAAs) that facilitates breast cancer invasion and metastasis.","method":"Co-culture proteomics, ELISA, ChIP assay (FOXP1 on PLOD2 promoter), Western blot (AKT/FOXP1), siRNA knockdown, 3D collagen invasion assay, in vivo co-implantation mouse model","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus functional pathway validation with in vivo model, single lab","pmids":["31170987"],"is_preprint":false},{"year":2014,"finding":"RNA aptamers (R10-4 and R10-2) that bind PAI-1 with nanomolar affinity inhibit PAI-1's antiproteolytic activity against tPA, prevent stable covalent complex formation between PAI-1 and tPA, and increase the amount of cleaved (substrate) PAI-1 in a concentration-dependent manner, demonstrating direct targeting of the tPA-docking site of PAI-1.","method":"SELEX aptamer selection, in vitro PAI-1 inhibition assay, covalent complex formation assay, dose-response analysis","journal":"Nucleic acid therapeutics","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro reconstitution with purified proteins and multiple functional readouts, single lab","pmids":["24922319"],"is_preprint":false},{"year":2014,"finding":"Vitronectin-binding (but not protease-inhibitory) activity of PAI-1 protects against cardiac fibrosis: in angiotensin II–infused mice, the non-vitronectin-binding PAI-1 variant (AK) increased cardiac fibrosis, fibroblast marker (periostin), and Col1 mRNA, while the vitronectin-binding but non-protease-inhibitory variant (RR) and control PAI-1 (CPAI) were protective. In cardiac fibroblasts, RR and CPAI reduced integrin β3 expression, vitronectin supernatant levels, and fibroblast adhesion to vitronectin, and preserved apoptotic over antiapoptotic/proliferative signaling.","method":"In vivo mouse cardiac fibrosis model with PAI-1 variant infusion, cardiac fibroblast culture with variant PAI-1 treatments, morphometry, qPCR, integrin/vitronectin assays","journal":"Laboratory investigation","confidence":"Medium","confidence_rationale":"Tier 2 — domain-specific PAI-1 variants dissecting two functional activities in vivo and in vitro, single lab","pmids":["24687120"],"is_preprint":false}],"current_model":"SERPINE1/PAI-1 is a secreted serpin that covalently inhibits tPA and uPA via an acyl-enzyme mechanism; its unique structural property of spontaneous conversion to a stable latent form (reactive-loop insertion into β-sheet A) is explained by its crystal structure. Beyond antiproteolytic function, PAI-1 controls cell adhesion and migration through competitive binding to the vitronectin SMB domain (blocking αVβ3 integrin and uPAR), drives uPAR/LRP-mediated endocytosis and recycling of uPA complexes, promotes replicative senescence as an essential p53 target gene (via suppression of PI3K–PKB–GSK3β–cyclin D1 signaling), regulates cytoskeletal stiffness in smooth muscle cells through AMPK-dependent cofilin activation, inhibits neutrophil apoptosis via G-protein/PI3K/Akt signaling, undergoes nuclear translocation to act as a transcriptional co-repressor, binds proteasome subunits to stabilize p53 in epithelial cells, and is transcriptionally regulated by TGF-β/p53–Smad complexes, HIF-2α, HIF-1α/Egr-1/C/EBPα (under hypoxia), and the 4G/5G promoter polymorphism that differentially recruits transcriptional activators and repressors."},"narrative":{"teleology":[{"year":1986,"claim":"Molecular cloning and biochemical characterization established PAI-1 as a serpin-family serine protease inhibitor that forms covalent complexes with uPA and tPA via an acyl-enzyme mechanism, defining its primary molecular activity.","evidence":"cDNA cloning from endothelial cells by three independent groups; purification and kinetic analysis of covalent complex formation with uPA/tPA","pmids":["3092219","3097076","2430793","3090045"],"confidence":"High","gaps":["No structural basis for PAI-1's unusual spontaneous loss of activity","No in vivo validation of physiological necessity"]},{"year":1990,"claim":"Demonstration that PAI-1 inhibits receptor-bound uPA and triggers internalization and lysosomal degradation of the uPA–PAI-1 complex via uPAR established the first cellular clearance mechanism for plasminogen activators.","evidence":"Radiolabeled ligand internalization assays on U937 cells with chloroquine inhibition and kinetic measurements","pmids":["2157592","2161846"],"confidence":"High","gaps":["Endocytic receptor mediating internalization not yet identified","Fate of uPAR after internalization unknown"]},{"year":1992,"claim":"The crystal structure of latent PAI-1 revealed that full reactive-loop insertion into β-sheet A without cleavage explains the serpin's unique spontaneous conversion to a stable inactive form, resolving a long-standing structural puzzle.","evidence":"X-ray crystallography at 2.6 Å resolution","pmids":["1731226"],"confidence":"High","gaps":["Structure of the active conformation and mechanism of latency transition not resolved","Vitronectin-mediated stabilization not structurally explained"]},{"year":1992,"claim":"Identification of a human frameshift mutation causing complete PAI-1 deficiency with severe bleeding confirmed PAI-1 as the essential in vivo inhibitor of plasminogen activators.","evidence":"Genetic analysis of a PAI-1-deficient patient with hyperfibrinolytic bleeding diathesis","pmids":["1435917"],"confidence":"High","gaps":["No systematic characterization of heterozygous carriers","Tissue-specific consequences of PAI-1 loss not defined"]},{"year":1995,"claim":"Characterization of the 4G/5G promoter polymorphism revealed that differential transcription factor binding (activator on both alleles, repressor only on 5G) explains allele-specific PAI-1 expression levels and associated cardiovascular risk.","evidence":"EMSA with allele-specific probes, transcription reporter assays, population study of myocardial infarction","pmids":["7892190"],"confidence":"High","gaps":["Identity of the repressor protein binding the 5G allele not determined","Causality between polymorphism and MI not established by the association study alone"]},{"year":1996,"claim":"Discovery that PAI-1 competes with uPAR and αVβ3 integrin for vitronectin binding—and that this is independent of protease inhibition—established a second major function: regulation of cell adhesion and migration through extracellular matrix interactions.","evidence":"Domain-swap mutagenesis of vitronectin, cell detachment assays, smooth muscle cell migration with PAI-1 mutants deficient in protease inhibition","pmids":["8830783","8837777"],"confidence":"High","gaps":["Atomic details of PAI-1–vitronectin interface not yet resolved","Relative contribution of anti-adhesive versus antiproteolytic function in vivo not quantified"]},{"year":1997,"claim":"Identification of LRP as the endocytic receptor for uPA–PAI-1 complexes and demonstration of uPAR recycling after internalization completed the cellular clearance cycle model and explained how cells regenerate uPA-binding capacity.","evidence":"Surface biotinylation pulse-chase, PI-PLC treatment, immunoelectron microscopy on U937 and HT1080 cells; PAI-1 knockout mice with arterial injury showing enhanced SMC migration rescued by adenoviral PAI-1","pmids":["9184208","9386191"],"confidence":"High","gaps":["Sorting signals directing uPAR recycling versus LRP/ligand degradation not defined","Whether other endocytic receptors contribute in specific tissues not tested"]},{"year":2003,"claim":"The crystal structure of PAI-1 bound to the vitronectin SMB domain provided the atomic basis for vitronectin stabilization of active PAI-1 and confirmed steric occlusion of integrin and uPAR binding sites, unifying the structural and cell-biological observations.","evidence":"X-ray crystallography at 2.3 Å resolution of the PAI-1–SMB domain complex","pmids":["12808446"],"confidence":"High","gaps":["Structure of the full-length vitronectin–PAI-1 complex not available","Dynamics of the active-to-latent transition in the presence of vitronectin not captured"]},{"year":2006,"claim":"Three studies collectively expanded PAI-1's role beyond fibrinolysis: PAI-1 was shown to be an essential p53 target enforcing replicative senescence via PI3K–PKB–GSK3β–cyclin D1 suppression, to orchestrate macrophage migration through a sequential Mac-1/tPA/PAI-1/LRP adhesion-to-detachment switch, and to be transcriptionally co-regulated by HIF-1α, Egr-1, and C/EBPα under hypoxia.","evidence":"RNAi knockdown and ectopic expression in fibroblasts with pathway analysis (senescence); multiple genetic knockouts with PAI-1 LRP-binding mutant rescue in vivo (macrophage migration); PAI-1 promoter mutagenesis, EMSA, and ChIP under hypoxia (transcription)","pmids":["16862142","16601674","17197388"],"confidence":"High","gaps":["Whether PAI-1's senescence function requires a specific receptor or is intracellular not resolved","Relative importance of each hypoxia-responsive element in different tissues not established","Mac-1/tPA/PAI-1/LRP pathway not tested in human macrophages"]},{"year":2014,"claim":"Multiple studies dissected PAI-1's dual functional domains in disease contexts: vitronectin-binding (not antiprotease) activity protects against cardiac fibrosis; PAI-1 supports HIF-2α-driven angiogenesis by maintaining low plasmin; and the prolactin fragment 16K PRL directly binds PAI-1 to modulate fibrinolysis and angiogenesis.","evidence":"PAI-1 domain-specific variants in mouse cardiac fibrosis model; epistatic shRNA knockdown with aprotinin rescue in HepG2 spheroids; direct 16K PRL–PAI-1 binding assay with PAI-1 KO mice","pmids":["24687120","25489981","24929950"],"confidence":"Medium","gaps":["Whether vitronectin-binding function is protective in non-cardiac fibrosis settings not tested","HIF-2α–PAI-1 axis validated only in hepatocellular carcinoma model","16K PRL–PAI-1 binding site not mapped"]},{"year":2016,"claim":"Elucidation of TGF-β-induced PAI-1 transcription through a p53–Smad2/3–CBP complex on the PAI-1 promoter mechanistically linked p53 and TGF-β cytostatic signaling, with PAI-1 as an effector mediating growth arrest.","evidence":"Co-immunoprecipitation of p53–Smad complex, ChIP for promoter occupancy, histone acetylation analysis, p53 siRNA epistasis","pmids":["27759037"],"confidence":"High","gaps":["Whether this complex operates in non-epithelial cell types not tested","Genome-wide p53–Smad co-regulation beyond PAI-1 not explored"]},{"year":2021,"claim":"Cell-autonomous and paracrine senescence functions of PAI-1 were defined: PAI-1 overexpression in tubular epithelial cells drives dedifferentiation and fibrosis through klotho loss, p53, and ligand-independent TGF-βRI/SMAD3 activation; meanwhile, senescent endothelial cell-secreted PAI-1 induces podocyte apoptosis in a paracrine manner, with endothelial-specific PAI-1 deletion protecting against age-related glomerular injury.","evidence":"Stable PAI-1 overexpression with epistasis (klotho rescue, p53 siRNA, TGF-βRI inhibitor) in HK-2 cells; endothelial cell-specific PAI-1 conditional KO mice with conditioned medium transfer","pmids":["34110636","34725920"],"confidence":"High","gaps":["Whether intracellular PAI-1 drives these effects through proteasome inhibition or another mechanism not fully resolved","Identity of the podocyte receptor for secreted PAI-1 unknown"]},{"year":2023,"claim":"Two novel intracellular functions were described: nuclear PAI-1 occupies distal intergenic chromatin regions and acts as a transcriptional co-repressor, and pre-secretory PAI-1 binds proteasome subunits to stabilize p53 and promote senescence in epithelial cells.","evidence":"ChIP-seq and RNA-seq integration with RIME in bladder cancer cells (nuclear function); co-immunoprecipitation with proteasome subunits and proteasome activity assay with wild-type versus secretion-deficient PAI-1 in ATII cells","pmids":["35842542","37566086"],"confidence":"Medium","gaps":["Nuclear PAI-1 chromatin-binding partners and co-repressor complex composition not fully defined","Proteasome interaction surfaces on PAI-1 not mapped","Both findings from single laboratories; independent replication pending"]},{"year":2024,"claim":"PAI-1 was shown to regulate vascular smooth muscle cell intrinsic stiffness by controlling F-actin content through AMPK-dependent cofilin activation, independent of uPAR/LRP, identifying a mechanotransduction function relevant to arterial stiffness.","evidence":"Atomic force microscopy, AMPK signaling analysis, PAI-1 siRNA and PAI-1−/− SMCs, in vivo aortic pulse wave velocity measurement","pmids":["38868940"],"confidence":"Medium","gaps":["Direct PAI-1 target upstream of AMPK not identified","Whether this mechanism operates in non-vascular cell types unknown","Single-lab finding awaiting independent validation"]},{"year":null,"claim":"Major unresolved questions include: the identity of the receptor(s) mediating PAI-1's intracellular senescence and anti-apoptotic functions (independent of uPAR/LRP/vitronectin), the structural basis for PAI-1's nuclear translocation and chromatin binding, and whether proteasome inhibition and transcriptional co-repression represent a unified intracellular mechanism or distinct activities.","evidence":"","pmids":[],"confidence":"Low","gaps":["No receptor identified for PAI-1's GPCR/PI3K-dependent anti-apoptotic signaling in neutrophils","Nuclear localization signal or import mechanism not characterized","Relationship between pre-secretory proteasome binding and nuclear chromatin occupancy not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,4,31]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6,7,10,32]},{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[6,7,10]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[26]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,6,7,10,15]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[6,7,10,15,16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[26,27]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[2,4,5]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[6,7,10,32]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12,18,19,21,25,30]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[12,21,24]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[14,29]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,8,11,13]}],"complexes":["uPA–PAI-1–uPAR–LRP1 endocytic complex","p53–Smad2/3–CBP transcriptional complex on PAI-1 promoter"],"partners":["PLAU","PLAT","VTN","LRP1","PLAUR","TP53","SMAD3"],"other_free_text":[]},"mechanistic_narrative":"SERPINE1 encodes plasminogen activator inhibitor 1 (PAI-1), a secreted serpin that functions as the principal physiological inhibitor of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators through covalent acyl-enzyme complex formation, thereby governing fibrinolysis, extracellular matrix remodeling, and cell migration [PMID:3090045, PMID:1435917]. A unique structural feature—spontaneous insertion of its reactive-center loop into β-sheet A without proteolytic cleavage—converts PAI-1 to a stable latent conformation, while vitronectin binding to the somatomedin B domain stabilizes the active state and simultaneously occludes integrin αVβ3 and uPAR binding sites, enabling PAI-1 to regulate cell adhesion and motility independently of its antiprotease activity [PMID:1731226, PMID:12808446, PMID:8837777]. PAI-1 drives LRP1-dependent endocytic clearance and recycling of uPA–uPAR complexes, controls macrophage and smooth muscle cell migration through integrin-to-LRP switching, and regulates vascular smooth muscle stiffness via AMPK–cofilin-mediated F-actin remodeling [PMID:9184208, PMID:16601674, PMID:38868940]. Beyond its extracellular roles, PAI-1 is a critical p53/TGF-β–Smad target gene that enforces replicative senescence by suppressing PI3K–PKB–GSK3β–cyclin D1 signaling, can translocate to the nucleus to act as a transcriptional co-repressor, and stabilizes p53 by binding and inhibiting proteasome subunits [PMID:16862142, PMID:27759037, PMID:35842542, PMID:37566086]."},"prefetch_data":{"uniprot":{"accession":"P05121","full_name":"Plasminogen activator inhibitor 1","aliases":["Endothelial plasminogen activator inhibitor","Serpin E1"],"length_aa":402,"mass_kda":45.1,"function":"Serine protease inhibitor. Inhibits TMPRSS7 (PubMed:15853774). Is a primary inhibitor of tissue-type plasminogen activator (PLAT) and urokinase-type plasminogen activator (PLAU). As PLAT inhibitor, it is required for fibrinolysis down-regulation and is responsible for the controlled degradation of blood clots (PubMed:17912461, PubMed:8481516, PubMed:9207454, PubMed:21925150). As PLAU inhibitor, it is involved in the regulation of cell adhesion and spreading (PubMed:9175705). Acts as a regulator of cell migration, independently of its role as protease inhibitor (PubMed:15001579, PubMed:9168821). It is required for stimulation of keratinocyte migration during cutaneous injury repair (PubMed:18386027). It is involved in cellular and replicative senescence (PubMed:16862142). Plays a role in alveolar type 2 cells senescence in the lung (By similarity). Is involved in the regulation of cementogenic differentiation of periodontal ligament stem cells, and regulates odontoblast differentiation and dentin formation during odontogenesis (PubMed:25808697, PubMed:27046084)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P05121/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SERPINE1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SERPINE1","total_profiled":1310},"omim":[{"mim_id":"621190","title":"MICRO RNA 617; MIR617","url":"https://www.omim.org/entry/621190"},{"mim_id":"615675","title":"MICRO RNA 301A; MIR301A","url":"https://www.omim.org/entry/615675"},{"mim_id":"614517","title":"BRAIN AND MUSCLE ARNT-LIKE PROTEIN 2; BMAL2","url":"https://www.omim.org/entry/614517"},{"mim_id":"613329","title":"PLASMINOGEN ACTIVATOR INHIBITOR-1 DEFICIENCY","url":"https://www.omim.org/entry/613329"},{"mim_id":"607378","title":"SERPINE1 mRNA-BINDING PROTEIN 1; SERBP1","url":"https://www.omim.org/entry/607378"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"blood vessel","ntpm":620.0},{"tissue":"placenta","ntpm":392.6}],"url":"https://www.proteinatlas.org/search/SERPINE1"},"hgnc":{"alias_symbol":["PAI"],"prev_symbol":["PLANH1","PAI1"]},"alphafold":{"accession":"P05121","domains":[{"cath_id":"3.30.497.10","chopping":"28-195_302-348","consensus_level":"medium","plddt":94.8264,"start":28,"end":348},{"cath_id":"2.30.39.10","chopping":"203-301_351-385","consensus_level":"medium","plddt":89.2776,"start":203,"end":385}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P05121","model_url":"https://alphafold.ebi.ac.uk/files/AF-P05121-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P05121-F1-predicted_aligned_error_v6.png","plddt_mean":88.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SERPINE1","jax_strain_url":"https://www.jax.org/strain/search?query=SERPINE1"},"sequence":{"accession":"P05121","fasta_url":"https://rest.uniprot.org/uniprotkb/P05121.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P05121/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P05121"}},"corpus_meta":[{"pmid":"2157592","id":"PMC_2157592","title":"Receptor-mediated 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release?","date":"1996","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/8830783","citation_count":397,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"3092219","id":"PMC_3092219","title":"Cloning and sequence of a cDNA coding for the human beta-migrating endothelial-cell-type plasminogen activator inhibitor.","date":"1986","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/3092219","citation_count":394,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16102055","id":"PMC_16102055","title":"PAI-1 and atherothrombosis.","date":"2005","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/16102055","citation_count":379,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"3097076","id":"PMC_3097076","title":"cDNA cloning of human plasminogen activator-inhibitor from endothelial cells.","date":"1986","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/3097076","citation_count":344,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"2430793","id":"PMC_2430793","title":"Endothelial plasminogen activator inhibitor (PAI): a new member of the Serpin gene family.","date":"1986","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/2430793","citation_count":335,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19501581","id":"PMC_19501581","title":"Hepatic insulin resistance, metabolic syndrome and cardiovascular disease.","date":"2009","source":"Clinical biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19501581","citation_count":334,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"20385790","id":"PMC_20385790","title":"Venous thrombosis risk associated with plasma hypofibrinolysis is explained by elevated plasma levels of TAFI and PAI-1.","date":"2010","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20385790","citation_count":294,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"9184208","id":"PMC_9184208","title":"Recycling of the urokinase receptor upon internalization of the uPA:serpin complexes.","date":"1997","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9184208","citation_count":273,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32826331","id":"PMC_32826331","title":"IL-6 trans-signaling induces plasminogen activator inhibitor-1 from vascular endothelial cells in cytokine release syndrome.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32826331","citation_count":267,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15146197","id":"PMC_15146197","title":"Transcriptome characterization elucidates signaling networks that control human ES cell growth and differentiation.","date":"2004","source":"Nature biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/15146197","citation_count":266,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"2161846","id":"PMC_2161846","title":"Inhibition of receptor-bound urokinase by plasminogen-activator inhibitors.","date":"1990","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2161846","citation_count":248,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15634264","id":"PMC_15634264","title":"Pleiotropic functions of plasminogen activator inhibitor-1.","date":"2005","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/15634264","citation_count":246,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"3090045","id":"PMC_3090045","title":"Purification and characterization of a plasminogen activator inhibitor from the histiocytic lymphoma cell line U-937.","date":"1986","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3090045","citation_count":233,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"1435917","id":"PMC_1435917","title":"Brief report: complete deficiency of plasminogen-activator inhibitor type 1 due to a frame-shift mutation.","date":"1992","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/1435917","citation_count":223,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"9386191","id":"PMC_9386191","title":"Inhibitory role of plasminogen activator inhibitor-1 in arterial wound healing and neointima formation: a gene targeting and gene transfer study in mice.","date":"1997","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/9386191","citation_count":223,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":52751,"output_tokens":10406,"usd":0.157171},"stage2":{"model":"claude-opus-4-6","input_tokens":14543,"output_tokens":4429,"usd":0.27516},"total_usd":0.862174,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":66187,"output_tokens":9226,"usd":0.168476},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":13544,"output_tokens":4261,"usd":0.261367}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1990,\n      \"finding\": \"The uPA-PAI-1 complex bound to the uPA receptor (uPAR) is internalized into cells and subsequently degraded in lysosomes, whereas free uPA, ATF, or DFP-treated uPA are not internalized. PAI-1 thus triggers receptor-mediated endocytosis and lysosomal degradation of uPA.\",\n      \"method\": \"Radioligand internalization assay at 4°C/37°C shift, acid dissociation to distinguish surface vs. internalized ligand, chloroquine inhibition of lysosomal degradation in U937 cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean mechanistic experiment with multiple controls (temperature shift, chloroquine, multiple ligand comparisons), replicated finding\",\n      \"pmids\": [\"2157592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure (2.3 Å) of the somatomedin B (SMB) domain of vitronectin in complex with PAI-1 reveals how vitronectin stabilizes the active conformation of PAI-1 and how PAI-1 sterically blocks vitronectin binding to cell-surface integrins and uPAR, thereby linking PAI-1's antifibrinolytic activity to its effects on cell adhesion and motility.\",\n      \"method\": \"X-ray crystallography at 2.3 Å resolution with structural analysis of binding interface\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional interpretation, independently foundational\",\n      \"pmids\": [\"12808446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PAI-1 competes with uPAR for binding to the somatomedin B (SMB) domain of vitronectin, thereby regulating uPAR-mediated cell adhesion; PAI-1 binding to the SMB domain also sterically hinders integrin access to the adjacent RGD sequence, affecting integrin-mediated adhesion.\",\n      \"method\": \"Cell adhesion assays, competitive binding studies with SMB domain of vitronectin\",\n      \"journal\": \"APMIS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — competitive binding assays with defined domain mapping, single lab\",\n      \"pmids\": [\"10190280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAI-1 inhibits uPA-induced chemotaxis by triggering internalization of uPAR via LRP; when uPAR internalization is blocked (by RAP or anti-LRP antibodies), the uPA-PAI-1 complex becomes chemoattractive and activates cytoskeletal reorganization and ERK/MAPK signaling.\",\n      \"method\": \"Chemotaxis assays, receptor internalization assays, antibody blocking of LRP, ERK phosphorylation immunoblot\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (chemotaxis, internalization, signaling), genetic/pharmacological blockade with rescue\",\n      \"pmids\": [\"11566185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PAI-1 forms a binary complex with tPA on fibrin; neutralization of tPA by PAI-1 enhances binding of the integrin (Mac-1)–protease–inhibitor complex to the endocytic receptor LRP, switching macrophages from adhesion to detachment and enabling directional migration. Genetic ablation of PAI-1 abrogates macrophage migration, restored only by wild-type PAI-1 but not a mutant unable to interact with LRP.\",\n      \"method\": \"In vitro adhesion/detachment assays, genetic knockout mice (Mac-1, tPA, PAI-1, LRP), rescue with PAI-1 mutant defective for LRP binding, intravital microscopy\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple KO models, mutant rescue, and in vitro/in vivo correlation; strong mechanistic placement in migration pathway\",\n      \"pmids\": [\"16601674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Hypoxia induces PAI-1 transcription in macrophages through the combinatorial action of three transcription factors—Egr-1, HIF-1α, and C/EBPα—each binding distinct sites in the PAI-1 promoter; mutation of any of these sites reduces hypoxia-induced transcriptional activity, and ChIP confirms their chromatin occupancy under hypoxic conditions.\",\n      \"method\": \"PAI-1 promoter deletion/mutation constructs, transient transfection luciferase assays, EMSA with supershift, ChIP in RAW264.7 macrophages and primary peritoneal macrophages\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — promoter mutagenesis combined with EMSA, supershift, and ChIP in multiple cell types\",\n      \"pmids\": [\"17197388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The transcription factor Net (a TCF/Ets family member) represses PAI-1 promoter activity by binding to Ets binding sites in the PAI-1 promoter independently of SRF; loss of Net increases PAI-1 expression and impairs cell migration, which is rescued by PAI-1 blocking antibody.\",\n      \"method\": \"Net knockout MEFs, PAI-1 promoter activity assays, ChIP/EMSA for Net binding, PAI-1 blocking antibody rescue of migration defect\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined phenotype, promoter binding, and antibody rescue constitute multiple orthogonal approaches\",\n      \"pmids\": [\"16314510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PAI-1 is deposited into keratinocyte migration trails and is required for optimal wound repair; addition of recombinant PAI-1 stimulates directional motility, enhances cell spreading, and rescues keratinocytes from plasminogen-induced anoikis, while PAI-1 knockdown or antibody blockade impairs wound closure.\",\n      \"method\": \"PAI-1-GFP live imaging, scrape-wound assays in WT and PAI-1−/− cells, recombinant PAI-1 addition, antisense knockdown with rescue, PAI-1 neutralizing antibodies\",\n      \"journal\": \"Archives of dermatological research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (imaging, KO, KD, recombinant protein rescue, antibody blockade) in one study\",\n      \"pmids\": [\"18386027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Wound-induced PAI-1 expression in keratinocytes is necessary to maintain basal epidermal cell phenotype and appropriate cell-substrate adhesion during injury repair; antisense-mediated PAI-1 knockdown impairs wound closure and is associated with increased suprabasal keratinocyte differentiation.\",\n      \"method\": \"Inducible antisense vector in HaCaT cells, scrape-wound assays, immunostaining for keratinocyte differentiation markers\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined KD phenotype with mechanistic readout, single lab\",\n      \"pmids\": [\"10896775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TGF-β induces PAI-1 transcription through a complex formed by p53 and Smad2/3 on the PAI-1 promoter, which recruits histone acetyltransferase CBP and enhances histone H3 acetylation; p53 is required for TGF-β-induced cytostasis, and PAI-1 mediates the cytostatic activity of TGF-β.\",\n      \"method\": \"ChIP, co-immunoprecipitation of p53/Smad complex, histone acetylation assays, PAI-1 promoter reporter assays, p53 knockdown experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP, co-IP, histone modification assay, and functional cytostasis readout in one study\",\n      \"pmids\": [\"27759037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAI-1 inhibits spontaneous and TRAIL-induced neutrophil apoptosis by activating antiapoptotic signaling (PKB/Akt, Mcl-1, Bcl-xL) through pertussis toxin-sensitive G protein-coupled receptors and PI3K; uPAR, LRP, and vitronectin are not involved in this antiapoptotic effect. PAI-1−/− mice show enhanced neutrophil apoptosis in LPS-induced acute lung injury.\",\n      \"method\": \"Neutrophil culture apoptosis assays, pharmacological inhibitors (pertussis toxin, PI3K inhibitors), immunoblot for signaling intermediates, PAI-1 knockout mice in vivo ALI model\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection of receptor pathway plus KO in vivo validation; multiple orthogonal approaches\",\n      \"pmids\": [\"21622848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Matrix-bound PAI-1 maintains cell blebbing (amoeboid migration mode) in colorectal cancer cells by localizing PDK1 and ROCK1 to the cell membrane and sustaining the RhoA/ROCK1/MLC-P signaling pathway.\",\n      \"method\": \"Immunoblotting, activity assays, immunofluorescence for PDK1/ROCK1 localization, RhoA/ROCK1/MLC-P pathway analysis in SW620 cells with PAI-1 manipulation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple signaling readouts and localization data, single lab\",\n      \"pmids\": [\"22363817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAI-1 promotes cell migration via LRP1-dependent activation of the β-catenin pathway and ERK1/2 MAPK; in LRP1-deficient MEFs, PAI-1-induced β-catenin expression and transcriptional activity are abolished, while ERK1/2 activation is paradoxically enhanced and is suppressed by β-catenin knockdown.\",\n      \"method\": \"WT and LRP1-deficient MEFs, proliferation and migration assays, β-catenin reporter assays, ERK1/2 immunoblot, β-catenin siRNA knockdown\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — LRP1-deficient cells with genetic rescue and multiple pathway readouts, single lab\",\n      \"pmids\": [\"25694133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"16K prolactin binds PAI-1 directly and thereby inhibits the PAI-1–uPA–uPAR ternary complex to exert antiangiogenic and antitumoral effects; loss of PAI-1 abrogates the antitumoral and antiangiogenic effects of 16K PRL, and 16K PRL also inhibits PAI-1's antifibrinolytic activity to promote thrombolysis.\",\n      \"method\": \"Direct binding assays between 16K PRL and PAI-1, PAI-1 knockout mouse experiments, in vivo tumor models, arterial clot lysis assays\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding established, PAI-1 KO genetic epistasis, multiple in vivo readouts in one study\",\n      \"pmids\": [\"24929950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HIF-2α (but not HIF-1α) induces PAI-1 expression as a target gene in hepatocellular carcinoma cells; PAI-1 in turn suppresses plasmin activity, which supports angiogenesis. Knockdown of either HIF-2α or PAI-1 reduces angiogenesis, and blocking plasmin in HIF-2α knockdown cells restores angiogenesis.\",\n      \"method\": \"Stable HIF-1α and HIF-2α knockdown HepG2 cells, HepG2 spheroid–embryoid body coculture angiogenesis model, microarray gene expression, PAI-1 knockdown, aprotinin (plasmin inhibitor) rescue\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD of upstream regulator, microarray identification of target, functional rescue with plasmin inhibitor; multiple orthogonal methods\",\n      \"pmids\": [\"25489981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Angiotensin II and its metabolites (Ang III, Ang IV) stimulate PAI-1 mRNA expression and protein release from human adipocytes in a dose- and time-dependent manner via the AT1 receptor; AT1 blockade abolishes this effect and reduces basal PAI-1 release, indicating autocrine/paracrine Ang II regulation of adipocyte PAI-1.\",\n      \"method\": \"Primary human adipocyte culture, PAI-1 ELISA and mRNA quantification, AT1 receptor blocker (candesartan) experiments\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor-specific pharmacological blockade with mRNA and protein readouts, single lab\",\n      \"pmids\": [\"11358950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Protein kinase C-β (PKC-β) mediates LDL- and Lp(a)-induced PAI-1 production in vascular endothelial cells; PKC-β1 translocates from cytosol to membrane after lipoprotein treatment, and selective PKC-β inhibition blocks PAI-1 production induced by both native and oxidized LDL and Lp(a).\",\n      \"method\": \"PKC activity assay, PKC-β-specific inhibitor (379196), calphostin C, immunofluorescence for PKC-β1 subcellular redistribution, PAI-1 ELISA in HUVEC and coronary artery ECs\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific inhibitor and translocation data with PAI-1 output, single lab\",\n      \"pmids\": [\"10751199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Oxidized HDL3 (but not native HDL3) induces PAI-1 mRNA expression and antigen release in endothelial cells via p38 MAPK activation and increased PAI-1 mRNA stability, without involving proximal promoter response elements.\",\n      \"method\": \"p38 and ERK1/2 inhibitors, transfection with PAI-1 promoter constructs, mRNA stability experiments, PAI-1 ELISA in endothelial cells\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase inhibitor dissection plus promoter and mRNA stability assays, single lab\",\n      \"pmids\": [\"15384983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TNFα induces PAI-1 expression in trophoblast cells via NF-κB activation; NF-κB binds the NF-κB recognition site in the PAI-1 promoter, and PAI-1 upregulation is responsible for TNFα-mediated restriction of trophoblast invasion, as shown by restoration of invasion with PAI-1 blocking antibodies.\",\n      \"method\": \"Western blot and Northern blot for PAI-1, EMSA for NF-κB binding to PAI-1 promoter, immunocytochemistry for p65 nuclear translocation, Matrigel invasion assay with PAI-1 blocking antibody rescue\",\n      \"journal\": \"Placenta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — promoter binding (EMSA), nuclear translocation, and functional antibody rescue constitute multiple orthogonal methods\",\n      \"pmids\": [\"16338458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Thrombin stimulates PAI-1 mRNA expression and keratinocyte migration via PAR-1 transactivation of EGFR, leading to ERK1/2-dependent phosphorylation of Smad2 linker region at Ser250; blocking either EGFR or ERK1/2 reduces both PAI-1 induction and migration.\",\n      \"method\": \"Western blot for Smad2L phosphorylation, selective kinase inhibitors (UO126, SB202190, SP600125), qRT-PCR for PAI-1 mRNA, scratch wound migration assay in HaCaT cells\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined signaling cascade with site-specific phosphorylation and pharmacological dissection, single lab\",\n      \"pmids\": [\"29577978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Stable PAI-1 overexpression in renal tubular epithelial cells promotes dedifferentiation, G2/M arrest, fibronectin/collagen-1/CCN2 induction, and apoptosis through loss of klotho, p53 upregulation, and activation of TGF-βRI–SMAD3 signaling; this occurs independently of uPA inhibitory activity. Ectopic klotho restoration reversed fibrogenesis, and genetic p53 suppression reversed the maladaptive repair.\",\n      \"method\": \"Stable PAI-1 overexpression in HK-2 cells, flow cytometry for cell cycle and apoptosis, immunoblot for pathway components, klotho ectopic expression rescue, p53 siRNA knockdown, TGF-βRI inhibitor\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — stable overexpression with multiple genetic rescues (klotho, p53 KD, TGF-βRI inhibition) defining pathway, multiple orthogonal readouts\",\n      \"pmids\": [\"34110636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PAI-1 is sequestered into stress granules (SGs) in proliferative and presenescent cells; SG-mediated sequestration of PAI-1 promotes nuclear translocation of cyclin D1, RB phosphorylation, and maintenance of a non-senescent proliferative state, demonstrating that PAI-1 promotes senescence and its compartmentalization counteracts this function.\",\n      \"method\": \"SG induction and disruption, immunofluorescence for PAI-1 localization in SGs, cyclin D1 nuclear translocation, RB phosphorylation immunoblot, SA-β-gal senescence assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — subcellular localization linked to functional senescence readout with multiple biochemical markers, single lab\",\n      \"pmids\": [\"29592859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PAI-1 binds to proteasome components and inhibits proteasome activity and p53 degradation in alveolar epithelial cells; this promotes cellular senescence (increased p21, decreased pRb, increased SA-β-gal activity). A secretion-deficient intracellular form of PAI-1 still induces senescence but does not induce p53, indicating the proteasome interaction requires the premature form of PAI-1.\",\n      \"method\": \"Co-immunoprecipitation of PAI-1 with proteasome components, proteasome activity assays, overexpression of WT vs. secretion-deficient PAI-1 mutant, immunoblot for p53/p21/pRb, SA-β-gal assay in A549 and primary mouse ATII cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — co-IP with functional proteasome activity assay and mutant PAI-1 dissection, multiple cell types\",\n      \"pmids\": [\"37566086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PAI-1 secreted by senescent glomerular endothelial cells drives podocyte apoptosis in aging kidney; selective inactivation of PAI-1 in endothelial cells in vivo protects glomeruli from lesion development and podocyte loss, and blocking PAI-1 in conditioned medium from senescent endothelial cells prevents podocyte apoptosis in vitro.\",\n      \"method\": \"Endothelial-specific PAI-1 knockout mice, conditioned medium transfer assays, PAI-1 blocking in vitro, p16INK-ATTAC senescent cell depletion mouse model\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — endothelial-specific KO in vivo plus in vitro conditioned medium rescue with multiple controls\",\n      \"pmids\": [\"34725920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RNA aptamers that bind PAI-1 with nanomolar affinity can inhibit PAI-1's antiproteolytic activity against tPA by preventing stable covalent complex formation between PAI-1 and tPA, and by promoting PAI-1 cleavage.\",\n      \"method\": \"SELEX aptamer selection, in vitro PAI-1 activity assays, covalent complex formation assays, dose-response analysis\",\n      \"journal\": \"Nucleic acid therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted inhibition assay with mechanistic characterization of covalent complex disruption, single lab\",\n      \"pmids\": [\"24922319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PAI-1 promotes vascular smooth muscle cell (SMC) intrinsic stiffness and cytoplasmic F-actin content; pharmacological or siRNA inhibition of PAI-1 decreases SMC stiffness by activating AMPK, which in turn activates cofilin (an F-actin depolymerase). In vivo PAI-039 treatment decreases aortic stiffness and tunica media F-actin content without altering collagen or elastin.\",\n      \"method\": \"Atomic force microscopy for SMC stiffness, F-actin staining, PAI-039 pharmacological inhibitor, PAI-1 siRNA, PAI-1-deficient murine SMCs, AMPK inhibition, cofilin activity assay, RNA sequencing, in vivo pulse wave velocity\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple genetic and pharmacological perturbations with mechanistic pathway (AMPK–cofilin) confirmed in vitro and in vivo\",\n      \"pmids\": [\"38868940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The PAI-1 binding site on vitronectin maps primarily to the N-terminal somatomedin B (SMB) domain, and the vitronectin-binding region on PAI-1 involves the area around α-helices E and F of PAI-1; at least one additional low-affinity PAI-1 binding site exists in the C-terminal region of vitronectin.\",\n      \"method\": \"Peptide mapping, domain deletion mutants, binding assays\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — binding site mapping by mutagenesis/domain analysis, review of multiple studies with partial resolution\",\n      \"pmids\": [\"12437099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Vitronectin-binding PAI-1 protects against cardiac fibrosis through interaction with fibroblasts: the vitronectin-binding function of PAI-1 (not its protease inhibitory function) reduces integrin β3 expression, vitronectin levels, and fibroblast adhesion to vitronectin, and preserves fibroblast apoptosis. The protease inhibitory function of PAI-1 promotes fibronectin accumulation by suppressing plasminogen activator/plasmin activities.\",\n      \"method\": \"Murine cardiac fibrosis model with Ang II infusion, PAI-1 variants (vitronectin-binding deficient AK, protease inhibitory deficient RR, and control CPAI), in vitro human cardiac fibroblast stimulation, periostin/collagen immunostaining, MMP and PA activity assays, integrin β3 immunoblot\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mechanistic dissection using functional PAI-1 mutants in vivo and in vitro, multiple pathway readouts\",\n      \"pmids\": [\"24687120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Tumor-secreted PAI-1 activates the PI3K/AKT pathway in adjacent adipocytes, promoting nuclear translocation of FOXP1 and transcriptional upregulation of PLOD2, which drives collagen remodeling (alignment) in cancer-associated adipocytes to facilitate breast cancer metastasis.\",\n      \"method\": \"Proteomics of co-culture media, ELISA, loss-of-function assays, qPCR, western blot, ChIP for FOXP1 at PLOD2 promoter, PAI-1 pharmacological blockade, 3D collagen invasion assay, in vivo breast cancer–adipose co-implantation model\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including ChIP, in vivo model, and pharmacological rescue identify complete signaling axis\",\n      \"pmids\": [\"31170987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CAF-derived PAI-1 promotes endothelial-mesenchymal transition (EndoMT) of lymphatic endothelial cells (LECs) by directly interacting with LRP1, activating AKT/ERK1/2 signaling, leading to enhanced lymphangiogenesis and lymphatic metastasis in cervical cancer; blockade of PAI-1 or LRP1/AKT/ERK1/2 abrogates EndoMT.\",\n      \"method\": \"Cytokine antibody arrays, ELISA, western blot, transwell/tube formation/transendothelial migration assays, PAI-1 and LRP1 inhibition, popliteal lymph node metastasis mouse model, immunohistochemistry\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — PAI-1–LRP1 interaction linked to defined signaling cascade with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"37415190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Estrogen (17β-estradiol) increases PAI-1 expression in endothelial cells through estrogen receptor α–G protein–PI3K–ROCK-II signaling, leading to c-Jun and c-Fos upregulation; estrogen-induced PAI-1 expression is required for estrogen-mediated endothelial cell horizontal migration.\",\n      \"method\": \"HUVEC culture with E2 treatment, pharmacological inhibitors (ERα antagonist, G protein inhibitor, PI3K inhibitor, ROCK-II inhibitor), western blot, PAI-1 siRNA, migration assay, ovariectomized rat in vivo model\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — signaling pathway dissected with multiple inhibitors plus in vivo validation, PAI-1 KD linking expression to migration, single lab\",\n      \"pmids\": [\"22389473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HDAC2 attenuates LPS-induced PAI-1 expression in macrophages via the c-Jun/PAI-1 pathway; HDAC2 knockdown increases nuclear translocation and DNA binding of c-Jun to the PAI-1 promoter, activating PAI-1 transcription. Inhibition of PAI-1 with TM5275 suppresses downstream TNF and MIP-2 expression.\",\n      \"method\": \"HDAC2 overexpression and knockdown, ChIP for c-Jun binding to PAI-1 promoter, nuclear translocation assay, PAI-1 inhibitor TM5275, ELISA for inflammatory cytokines in RAW264.7 and primary peritoneal macrophages\",\n      \"journal\": \"Journal of inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP for promoter binding plus gain/loss of function and downstream pathway readout, single lab\",\n      \"pmids\": [\"29344006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Nuclear PAI-1 in bladder cancer cells binds DNA at distal intergenic regions (demonstrated by ChIP-sequencing), acting as a transcriptional coregulator/silencer; PAI-1 downregulation upregulates numerous genes, and integration of ChIP-seq and RNA-seq identified 57 candidate PAI-1-regulated genes.\",\n      \"method\": \"ChIP-sequencing, RNA-sequencing after PAI-1 knockdown, rapid immunoprecipitation mass spectrometry, immunohistochemistry for nuclear PAI-1 localization in 939 bladder cancer specimens\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq demonstrates DNA binding, RNA-seq defines downstream targets; novel nuclear function, single lab\",\n      \"pmids\": [\"35842542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR4 activation by LPS in astrocytes stimulates a physical interaction between TLR4 and the non-receptor tyrosine kinase Fyn (confirmed by co-immunoprecipitation and co-localization), leading to PI3K/Akt/NF-κB pathway activation and PAI-1 induction; Src kinase inhibitor (PP2) or Fyn siRNA blocks this interaction and PAI-1 upregulation. Astrocyte-derived PAI-1 then inhibits tPA activity and suppresses neurite outgrowth.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, Fyn siRNA knockdown, PP2 inhibitor, PI3K/Akt/NF-κB pathway inhibitors, tPA activity assay in supernatants, neurite outgrowth assay with cortical neurons\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus genetic and pharmacological dissection with functional downstream tPA/neurite readout, single lab\",\n      \"pmids\": [\"25106729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"miR-30c directly targets the 3′ UTR of PAI-1 (SERPINE1) and negatively regulates its expression; hyperglycemia-induced repression of miR-30c in platelets increases PAI-1 expression and thrombus formation. In vivo lenti-miR-30c delivery decreases platelet PAI-1 and prolongs arterial occlusion time in high-fat diet-fed diabetic mice.\",\n      \"method\": \"Luciferase 3′ UTR reporter assays, qRT-PCR and western blot in human and mouse platelets, lentiviral miR-30c delivery in HFD mice, arterial thrombosis model, platelet depletion/reinfusion experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct 3′ UTR validation plus in vivo genetic delivery and platelet-specific PAI-1 ablation rescue\",\n      \"pmids\": [\"27819307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"miR-30c directly targets PAI-1 (SERPINE1) and ALK2 (ACVR1) 3′ UTRs; co-silencing of both PAI-1 and ALK2 (but not either alone) phenocopies the pro-adipogenic effect of miR-30c in human adipocyte differentiation.\",\n      \"method\": \"Luciferase 3′ UTR reporter assays, miR-30c overexpression, PAI-1 and ALK2 siRNA co-silencing, adipogenesis markers in hMADS cells\",\n      \"journal\": \"RNA biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — direct 3′ UTR reporter validation plus functional co-silencing experiment, single lab\",\n      \"pmids\": [\"21878751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The lncRNA LINC01468 recruits SERBP1 to enhance SERPINE1 (PAI-1) mRNA stability and interacts with USP5 to facilitate PAI-1 protein deubiquitylation, thereby increasing PAI-1 protein levels to promote lung adenocarcinoma progression.\",\n      \"method\": \"RIP assays, RNA stability assays, ubiquitination assays, co-immunoprecipitation of LINC01468-USP5, luciferase assays, in vitro functional assays, xenograft mouse models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mRNA stability and ubiquitination mechanisms validated by multiple biochemical assays, single lab\",\n      \"pmids\": [\"35387981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Deficiency of the antioxidative gas H2S in fibrotic lungs inactivates endothelial AMPK, leading to YAP activation and PAI-1 overexpression as an angiocrine factor that promotes lung fibrosis; metformin (AMPK activator) or H2S supplementation reverses lung fibrosis in an endothelial AMPK-dependent manner, and PAI-1 inhibitor (Tiplaxtinin) mitigates lung fibrosis.\",\n      \"method\": \"Endothelial AMPK-specific KO mice, metformin and H2S supplement treatment, PAI-1 inhibitor Tiplaxtinin, YAP signaling immunoblot, in vivo lung fibrosis models, human fibrotic lung tissue correlation\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — endothelial-specific KO in vivo plus pharmacological PAI-1 inhibition and multiple pathway readouts, single lab\",\n      \"pmids\": [\"38266576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FGFR2-activated JAK2/STAT3 signaling upregulates PAI-1 expression in colon cancer cells; phosphorylated STAT3 directly upregulates PAI-1, and cancer-cell-derived PAI-1 drives M2 macrophage polarization in the tumor microenvironment. In vivo, FGFR2 overexpression promotes M2 polarization that is rescued by PAI-1 inhibitor.\",\n      \"method\": \"JAK2/STAT3 pathway inhibition, STAT3 phosphorylation western blot, PAI-1 overexpression/knockdown, co-culture macrophage polarization assay, FGFR2-overexpressing tumor-bearing mouse model, PAI-1 inhibitor rescue\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined signaling axis with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"36781088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic or pharmacological reduction of PAI-1 activity ameliorates hyperlipidemia in vivo and RNA sequencing revealed that PAI-1 directly regulates transcription of genes involved in lipid homeostasis including PCSK9 and FGF21; in humans, genetic deficiency of PAI-1 is associated with reduced plasma PCSK9 levels.\",\n      \"method\": \"RNA sequencing of PAI-1-manipulated cells, in vivo pharmacological/genetic PAI-1 reduction in mice, plasma PCSK9 measurement in PAI-1-deficient humans\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA-seq with in vivo genetic/pharmacological validation and human genetic data, single lab\",\n      \"pmids\": [\"33432099\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SERPINE1/PAI-1 is a serine protease inhibitor (serpin) that covalently inhibits tPA and uPA to suppress fibrinolysis; it stabilizes its active conformation by binding the somatomedin B domain of vitronectin (crystal structure defined), competes with uPAR and integrins for vitronectin binding to regulate cell adhesion and migration, triggers receptor-mediated endocytosis and lysosomal degradation of the uPA–uPAR complex via LRP, promotes cellular senescence by inhibiting proteasomal p53 degradation and activating p53/p21/pRb, modulates amoeboid and mesenchymal cell migration through RhoA/ROCK1 and LRP1-β-catenin/ERK pathways, and is transcriptionally regulated by HIF-1α/Egr-1/C/EBPα (hypoxia), p53/Smad (TGF-β), NF-κB (TNFα), and post-transcriptionally by miR-30c targeting its 3′ UTR.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1986,\n      \"finding\": \"PAI-1 (SERPINE1) was cloned from human endothelial cell cDNA libraries; the mature protein is 379–402 amino acids, belongs to the serpin superfamily (homology with α1-antitrypsin and antithrombin III), lacks cysteine residues, has three N-linked glycosylation sites, and is encoded by a gene on chromosome 7. Two mRNA species (~2.2 and ~3.0 kb) arise from a single gene.\",\n      \"method\": \"cDNA cloning, nucleotide sequencing, Northern blot, immunological screening of expression libraries\",\n      \"journal\": \"Proceedings of the National Academy of Sciences / Journal of Clinical Investigation / EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — three independent groups cloned and sequenced the full-length cDNA with functional validation (inhibitory activity demonstrated in E. coli and transfected cells)\",\n      \"pmids\": [\"3092219\", \"3097076\", \"2430793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Crystal structure of intact latent PAI-1 at 2.6 Å resolution revealed that the reactive-site loop (residues N-terminal to the scissile bond) is inserted as a central β-strand into the major β-sheet (analogous to cleaved serpins), while C-terminal residues occupy a distinct surface position. This structural rearrangement explains PAI-1's unique ability to spontaneously convert to a stable latent (inactive) form without cleavage, and why inhibitory activity can be restored by denaturation/renaturation.\",\n      \"method\": \"Single-crystal X-ray diffraction (2.6 Å resolution)\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure providing direct mechanistic explanation of latency\",\n      \"pmids\": [\"1731226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"PAI-1 purified from U-937 cells forms covalent complexes with urokinase (uPA) and two-chain tPA with second-order rate constants of ~0.9×10⁶ M⁻¹s⁻¹ and ~0.2×10⁶ M⁻¹s⁻¹ respectively; the 47-kDa inhibitor is a member of the antithrombin III (serpin) family and the covalent complex can be hydrolyzed by NH₄OH to yield a 35-kDa inhibitor fragment, consistent with acyl-enzyme (serpin) mechanism.\",\n      \"method\": \"Protein purification, SDS-PAGE, covalent complex formation assay, kinetic analysis, partial amino acid sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay with purified components, replicated across multiple groups\",\n      \"pmids\": [\"3090045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Receptor-bound uPA on U937 cell surfaces is efficiently inhibited by PAI-1 (rate constant ~4.5×10⁶ M⁻¹s⁻¹, ~40% lower than for free uPA); PAI-1 also inhibits receptor-bound uPA. The resulting uPA–PAI-1 complex on the uPA receptor (uPAR) is then internalized and degraded via lysosomes (inhibitable by chloroquine), while free uPA, ATF, or DFP-uPA are not internalized, establishing a cellular clearance cycle for uPA.\",\n      \"method\": \"Radiolabeled ligand internalization assay, acid dissociation, TCA precipitation, chloroquine inhibition, kinetic rate constant measurements\",\n      \"journal\": \"The EMBO journal / The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — two independent studies with quantitative kinetics and direct internalization/degradation assays\",\n      \"pmids\": [\"2157592\", \"2161846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Complete PAI-1 deficiency in humans, caused by a frameshift mutation, results in a severe bleeding disorder (hyperfibrinolysis), establishing PAI-1 as the essential physiological inhibitor of plasminogen activators in vivo.\",\n      \"method\": \"Genetic analysis (frameshift mutation identification) in a PAI-1-deficient patient with bleeding diathesis\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human loss-of-function (natural null) with clear phenotypic readout\",\n      \"pmids\": [\"1435917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The 4G allele of the PAI-1 promoter 4G/5G polymorphism confers higher basal PAI-1 transcription than the 5G allele because both alleles bind a transcriptional activator, but only the 5G allele additionally binds a repressor protein at an overlapping site; this mechanism was associated with higher plasma PAI-1 activity and higher prevalence of myocardial infarction before age 45.\",\n      \"method\": \"Allele-specific transcription analysis, electrophoretic mobility shift assay (EMSA), population genetics\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — EMSA with allele-specific protein binding plus functional transcriptional readout, replicated in population study\",\n      \"pmids\": [\"7892190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PAI-1 and the urokinase receptor (uPAR) bind to the same somatomedin B (SMB) domain of vitronectin (VN) competitively; PAI-1 displaces VN from uPAR and detaches U937 cells from VN substrate independently of its protease inhibitory activity. uPA rapidly reverses this detachment. This established PAI-1 as a molecular switch governing uPAR-mediated cell adhesion and release from the extracellular matrix.\",\n      \"method\": \"Domain-swapping and site-directed mutagenesis of VN, competitive binding assays, cell detachment assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with functional cell adhesion/detachment assays, independently validated\",\n      \"pmids\": [\"8830783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Active PAI-1 inhibits smooth muscle cell (SMC) migration on vitronectin by blocking αVβ3 integrin binding to vitronectin—an effect requiring high-affinity PAI-1 binding to vitronectin but independent of PAI-1's protease inhibitory function. Formation of a PAI-1–plasminogen activator complex abolishes PAI-1's affinity for vitronectin and restores cell migration, directly linking plasminogen activator activity to integrin-mediated migration control.\",\n      \"method\": \"SMC migration assay, function-blocking antibodies, PAI-1 mutants deficient in protease inhibition, integrin-blocking experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal approaches (mutants, antibodies, cell migration assays) in a single high-impact study\",\n      \"pmids\": [\"8837777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"After uPA–PAI-1 complex internalization via uPAR and LRP (α2MR-LRP), uPAR is recycled back to the cell surface in a PI-PLC-sensitive (GPI-anchored) form, as demonstrated by surface biotinylation pulse-chase. The receptor recycles through an intracellular compartment that temporarily renders it PI-PLC resistant, while LRP is required for internalization but not recycling.\",\n      \"method\": \"Cell surface biotinylation, FACScan, immunofluorescence, immunoelectron microscopy, PI-PLC treatment, pulse-chase recycling assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal localization and functional methods demonstrating receptor recycling\",\n      \"pmids\": [\"9184208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PAI-1 gene-deficient (PAI-1⁻/⁻) mice show enhanced and accelerated smooth muscle cell migration into vascular wounds and increased neointima formation after arterial injury compared to wild-type, while adenoviral PAI-1 gene transfer suppresses neointima formation. Smooth muscle cell proliferation was unaffected, establishing that PAI-1 inhibits vascular remodeling specifically by restraining cell migration.\",\n      \"method\": \"PAI-1 knockout mice, perivascular electric and transluminal mechanical arterial injury, morphometric analysis, immunostaining, adenoviral gene transfer\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function and gain-of-function in vivo with specific phenotypic readout (migration vs. proliferation dissected)\",\n      \"pmids\": [\"9386191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure (2.3 Å) of the somatomedin B (SMB) domain of vitronectin in complex with PAI-1 revealed the molecular basis for vitronectin stabilization of active PAI-1 conformation and showed that PAI-1 sterically occludes the binding sites for both uPAR and integrins on vitronectin, explaining how PAI-1 controls cell adhesion and motility through competition for vitronectin.\",\n      \"method\": \"X-ray crystallography (2.3 Å resolution) of PAI-1–vitronectin SMB domain complex\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution structure of the complex with direct mechanistic implications validated by the structural data\",\n      \"pmids\": [\"12808446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAI-1 inhibits uPA-induced cell chemotaxis by triggering uPAR internalization via LRP; the uPA–PAI-1 complex has no intrinsic chemotactic activity, but blocking LRP-mediated internalization (with RAP or anti-LRP antibodies) converts the complex into a chemoattractant that induces cytoskeleton reorganization and ERK/MAPK activation.\",\n      \"method\": \"Chemotaxis assay, receptor internalization assay with RAP and anti-LRP antibodies, cytoskeleton staining, ERK phosphorylation Western blot\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional assays with receptor-blocking reagents establishing mechanistic pathway\",\n      \"pmids\": [\"11566185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PAI-1 is an essential downstream target of p53 required for replicative senescence: RNAi knockdown of PAI-1 allows escape from senescence in primary mouse and human fibroblasts, associated with sustained PI3K–PKB–GSK3β pathway activation and nuclear retention of cyclin D1. Conversely, ectopic PAI-1 expression in p53-deficient proliferating fibroblasts induces all hallmarks of replicative senescence. PAI-1 knockdown results are independent of its antiproteolytic serpin activity.\",\n      \"method\": \"RNAi knockdown, ectopic overexpression, senescence assays (SA-β-gal, BrdU incorporation), Western blot for PI3K–PKB–GSK3β–cyclin D1 pathway, primary mouse and human fibroblasts\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal loss- and gain-of-function with mechanistic pathway delineation, replicated in two cell systems\",\n      \"pmids\": [\"16862142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Efficient macrophage migration in an inflammatory environment requires a sequential molecular cycle: Mac-1 integrin binds a fibrin–tPA binary complex; PAI-1 then neutralizes tPA, and the resulting integrin–tPA–PAI-1 ternary complex binds the endocytic receptor LRP, triggering a switch from cell adhesion to detachment. Genetic inactivation of Mac-1, tPA, PAI-1 or LRP (but not uPA) abolishes macrophage migration. A PAI-1 mutant unable to interact with LRP fails to rescue migration in PAI-1⁻/⁻ mice.\",\n      \"method\": \"Genetic knockout mice (Mac-1, tPA, PAI-1, LRP, uPA), PAI-1 LRP-binding mutant rescue, in vitro adhesion/retraction assays, intravital microscopy\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic knockouts combined with domain-specific mutant rescue establishing ordered pathway\",\n      \"pmids\": [\"16601674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Hypoxia induces PAI-1 transcription in macrophages through three transcription factors—Egr-1, HIF-1α, and C/EBPα—each binding distinct sites in the PAI-1 promoter. Mutation of individual or combined sites reduces hypoxia-driven transcription. ChIP analysis confirmed chromatin binding of all three factors under hypoxic conditions; HIF-1α dominates but Egr-1 and C/EBPα augment the response independently of each other.\",\n      \"method\": \"PAI-1 promoter deletion/mutation reporter assays, EMSA with supershift, ChIP analysis, primary peritoneal macrophages and RAW264.7 cells\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — promoter mutagenesis, EMSA, and ChIP providing orthogonal evidence for three distinct transcriptional regulators\",\n      \"pmids\": [\"17197388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PAI-1 is deposited along keratinocyte migration trails during wound repair and is required for optimal wound closure: recombinant active PAI-1 stimulates directional motility and cell spreading, while antisense-mediated knockdown or neutralizing antibodies impair wound repair and induce plasminogen-dependent anoikis. PAI-1 thus acts as a survival factor and migration regulator during epidermal injury response.\",\n      \"method\": \"PAI-1-GFP live imaging, recombinant PAI-1 addition, antisense knockdown, neutralizing antibodies, wound closure assays in wild-type and PAI-1⁻/⁻ cells, apoptosis assays\",\n      \"journal\": \"Archives of dermatological research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (live imaging, KO cells, protein addition/blocking) with defined functional readout\",\n      \"pmids\": [\"18386027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Matrix-bound PAI-1 maintains cell blebbing (amoeboid migration mode) in colorectal cancer cells by localizing PDK1 and ROCK1 at the cell membrane and sustaining RhoA/ROCK1/MLC phosphorylation; tumor periphery modeling predicts heterogeneous PAI-1 concentrations sufficient to drive mesenchymal-to-amoeboid transition.\",\n      \"method\": \"Immunoblotting, activity assay, immunofluorescence, RhoA/ROCK1/MLC pathway analysis, mathematical modeling of PAI-1 distribution\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, correlative pathway activation with functional blebbing readout but no direct mutagenesis\",\n      \"pmids\": [\"22363817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The N-terminal fragment of prolactin (16K PRL) binds PAI-1 and inhibits its antifibrinolytic activity, thereby promoting thrombolysis; simultaneously, 16K PRL acts through the PAI-1–uPA–uPAR ternary complex to exert antiangiogenic and antitumoral effects. Loss of PAI-1 abolishes both antitumoral and antiangiogenic effects of 16K PRL.\",\n      \"method\": \"Direct binding assay (16K PRL–PAI-1 interaction), PAI-1 knockout mice, fibrinolysis assay, tumor angiogenesis models\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct protein binding combined with genetic KO rescue experiments and functional fibrinolysis/angiogenesis assays\",\n      \"pmids\": [\"24929950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAI-1 modulates cell migration in a LRP1-dependent manner: PAI-1 induces β-catenin expression and transcriptional activity in LRP1-competent MEFs but not in LRP1-deficient cells; PAI-1-induced ERK1/2 activation is more prominent in LRP1-deficient cells and is abolished by β-catenin knockdown, placing PAI-1 upstream of both the β-catenin and ERK1/2 MAPK pathways through LRP1.\",\n      \"method\": \"LRP1 knockout MEFs, siRNA knockdown of β-catenin, Western blot, luciferase reporter for β-catenin transcriptional activity, migration assays\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — genetic LRP1-deficient cells plus RNAi epistasis, single lab\",\n      \"pmids\": [\"25694133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TGF-β induces PAI-1 transcription through a p53–Smad2/3 complex formed on the PAI-1 promoter: p53 recruits the histone acetyltransferase CBP to this complex, enhancing H3 acetylation and transcriptional activation. p53 is required for TGF-β-induced cytostasis, and PAI-1 mediates part of this cytostatic activity, identifying PAI-1 as a mechanistic link between p53 and TGF-β cytostasis.\",\n      \"method\": \"Co-immunoprecipitation (p53–Smad complex), ChIP (promoter occupancy), histone acetylation assay, p53 siRNA, PAI-1 reporter assays, cell growth assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP, Co-IP, and functional cytostasis assays with RNAi epistasis providing mechanistic pathway\",\n      \"pmids\": [\"27759037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Stress granules (SGs) sequester PAI-1 in proliferating and presenescent cells; SG assembly alone is sufficient to decrease the number of senescent cells. SG-localized PAI-1 promotes nuclear translocation of cyclin D1, RB phosphorylation, and maintenance of a proliferative state, establishing a non-cell-autonomous mechanism by which SG-mediated PAI-1 sequestration counteracts senescence.\",\n      \"method\": \"Stress granule induction, PAI-1 localization by immunofluorescence, SA-β-gal senescence assay, cyclin D1 nuclear fractionation, pRB Western blot\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, localization with functional downstream readout but limited mechanistic resolution of PAI-1 action within SGs\",\n      \"pmids\": [\"29592859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAI-1 inhibits neutrophil apoptosis (spontaneous and TRAIL-induced) through activation of PKB/Akt, Mcl-1, and Bcl-xL antiapoptotic pathways, mediated by pertussis toxin-sensitive G protein-coupled receptors and PI3K—not through uPAR, LRP, or vitronectin. In PAI-1⁻/⁻ mice, neutrophils accumulating in LPS-injured lungs show enhanced apoptosis compared to wild-type.\",\n      \"method\": \"Neutrophil apoptosis assay, pathway inhibitors (pertussis toxin, PI3K inhibitor), receptor-blocking antibodies, PAI-1⁻/⁻ mice, Western blot for Akt/Mcl-1/Bcl-xL\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological receptor dissection and in vivo KO validation, single lab\",\n      \"pmids\": [\"21622848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Thrombin promotes PAI-1 mRNA expression and keratinocyte migration via PAR-1 transactivation of EGFR, downstream ERK1/2 phosphorylation, and specific phosphorylation of Smad2 linker region at Ser250 (but not Ser245 or Ser255); ERK1/2 inhibition but not p38 or JNK inhibition blocks Smad2L phosphorylation and PAI-1 induction.\",\n      \"method\": \"Selective kinase inhibitors, Western blot for Smad2 linker phosphorylation, qRT-PCR for PAI-1, scratch wound migration assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — pharmacological dissection with site-specific phosphorylation analysis, single lab\",\n      \"pmids\": [\"29577978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Tubular epithelial cell-autonomous PAI-1 overexpression causes dedifferentiation (E-cadherin loss, vimentin gain), G2/M arrest, fibrosis (fibronectin, collagen-1, CCN2 induction), and apoptosis in HK-2 cells via three interconnected pathways: (1) loss of klotho, (2) p53 upregulation, and (3) TGF-βRI/SMAD3 activation independent of TGF-β1 ligand. Ectopic klotho restoration reversed fibrogenesis and proliferative defects; p53 suppression blocked maladaptive repair; TGF-βRI inhibition attenuated epithelial dysfunction.\",\n      \"method\": \"Stable PAI-1 overexpression in HK-2 cells, ectopic klotho restoration, p53 siRNA, TGF-βRI inhibitor, Western blot (pSMAD3, cleaved caspase-3, pHistone3), flow cytometry (annexin-V)\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with three orthogonal epistasis experiments identifying pathway hierarchy, single lab\",\n      \"pmids\": [\"34110636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Senescent glomerular endothelial cells secrete PAI-1 that drives podocyte apoptosis; selective genetic inactivation of PAI-1 in endothelial cells protects glomeruli from age-related lesion development and podocyte loss in mice. Blocking PAI-1 in conditioned medium from senescent endothelial cells prevented podocyte apoptosis in vitro.\",\n      \"method\": \"Endothelial cell-specific PAI-1 conditional knockout mice, aged p16INK-ATTAC transgenic mice (senescent cell depletion), conditioned medium transfer with PAI-1 neutralization, podocyte apoptosis assay\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-specific conditional KO combined with in vitro conditioned-medium rescue establishing paracrine mechanism\",\n      \"pmids\": [\"34725920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PAI-1 binds LRP1 on lymphatic endothelial cells (LECs) and activates AKT/ERK1/2 signaling to promote endothelial-mesenchymal transition (EndoMT), leading to aberrant lymphangiogenesis and lymphatic metastasis; blockade of PAI-1 or LRP1/AKT/ERK1/2 abrogates EndoMT and tumor neolymphangiogenesis.\",\n      \"method\": \"CAF-conditioned medium, LRP1 interaction assay, Western blot (AKT/ERK phosphorylation), transwell/tube formation/transendothelial migration assays, popliteal LN metastasis mouse model, PAI-1 knockdown/inhibitor\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct LRP1-PAI-1 interaction with functional pathway validation in vitro and in vivo, single lab\",\n      \"pmids\": [\"37415190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Nuclear PAI-1 can bind chromatin at distal intergenic regions and function as a transcriptional co-repressor: ChIP-seq in bladder cancer cells showed PAI-1 chromatin occupancy, PAI-1 knockdown upregulated 57 candidate target genes (integration of ChIP-seq and RNA-seq), and rapid immunoprecipitation mass spectrometry identified nuclear PAI-1 interaction partners consistent with transcriptional regulatory complexes.\",\n      \"method\": \"ChIP-sequencing, RNA-sequencing, RIME (rapid immunoprecipitation mass spectrometry), immunohistochemistry of 939 tumor specimens\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq plus integrative transcriptomics; nuclear function is novel but validated by multiple genomic methods in a single study\",\n      \"pmids\": [\"35842542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PAI-1 binds proteasome components and inhibits proteasomal activity, thereby reducing p53 degradation and promoting senescence in alveolar epithelial type II (ATII) cells; only the wild-type (secretion-competent) form of PAI-1 induces p53 accumulation and SA-β-gal activity, whereas a secretion-deficient mature form induces senescence markers without p53 induction, indicating the premature (pre-secretory) form interacts with the proteasome.\",\n      \"method\": \"Co-immunoprecipitation of PAI-1 with proteasome subunits, proteasome activity assay, stable overexpression of wtPAI-1 vs. secretion-deficient PAI-1, SA-β-gal, p53/p21/pRb Western blot\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct protein-protein interaction with proteasome plus functional activity assay and domain-specific mutant comparison, single lab\",\n      \"pmids\": [\"37566086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PAI-1 regulates vascular smooth muscle cell (SMC) intrinsic stiffness by controlling cytoplasmic F-actin content: PAI-1 inhibition (PAI-039) or siRNA knockdown decreases SMC stiffness and F-actin, activates the F-actin depolymerase cofilin via AMPK signaling (not through uPAR/LRP), and reduces aortic pulse wave velocity in vivo; these effects are absent in PAI-1-deficient SMCs.\",\n      \"method\": \"Atomic force microscopy (SMC stiffness), F-actin staining, cofilin activity assay, AMPK inhibition, RNA-sequencing, PAI-1 siRNA, PAI-1⁻/⁻ murine SMCs, in vivo aortic pulse wave velocity\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (AFM, biochemistry, genetics, in vivo) in a single study with specific pathway identification\",\n      \"pmids\": [\"38868940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PAI-1 (via inhibition of uPA/tPA and consequent maintenance of low plasmin levels) supports angiogenesis in hepatocellular carcinoma downstream of HIF-2α: HIF-2α knockdown reduces PAI-1 expression and angiogenesis; PAI-1 knockdown similarly reduces angiogenesis; restoring low plasmin activity with aprotinin in HIF-2α KD cells rescues angiogenesis, confirming a HIF-2α→PAI-1→plasmin inhibition→angiogenesis axis.\",\n      \"method\": \"Stable shRNA knockdown of HIF-1α/HIF-2α/PAI-1, HepG2 spheroid–embryoid body co-culture angiogenesis model, aprotinin (plasmin inhibitor) rescue, microarray gene expression\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD with epistasis rescue experiment defining pathway order, single lab\",\n      \"pmids\": [\"25489981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Tumor-secreted PAI-1 activates PI3K/AKT signaling in adjacent adipocytes, promoting nuclear translocation of FOXP1 which enhances PLOD2 promoter activity, leading to collagen crosslinking/remodeling by cancer-associated adipocytes (CAAs) that facilitates breast cancer invasion and metastasis.\",\n      \"method\": \"Co-culture proteomics, ELISA, ChIP assay (FOXP1 on PLOD2 promoter), Western blot (AKT/FOXP1), siRNA knockdown, 3D collagen invasion assay, in vivo co-implantation mouse model\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus functional pathway validation with in vivo model, single lab\",\n      \"pmids\": [\"31170987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RNA aptamers (R10-4 and R10-2) that bind PAI-1 with nanomolar affinity inhibit PAI-1's antiproteolytic activity against tPA, prevent stable covalent complex formation between PAI-1 and tPA, and increase the amount of cleaved (substrate) PAI-1 in a concentration-dependent manner, demonstrating direct targeting of the tPA-docking site of PAI-1.\",\n      \"method\": \"SELEX aptamer selection, in vitro PAI-1 inhibition assay, covalent complex formation assay, dose-response analysis\",\n      \"journal\": \"Nucleic acid therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution with purified proteins and multiple functional readouts, single lab\",\n      \"pmids\": [\"24922319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Vitronectin-binding (but not protease-inhibitory) activity of PAI-1 protects against cardiac fibrosis: in angiotensin II–infused mice, the non-vitronectin-binding PAI-1 variant (AK) increased cardiac fibrosis, fibroblast marker (periostin), and Col1 mRNA, while the vitronectin-binding but non-protease-inhibitory variant (RR) and control PAI-1 (CPAI) were protective. In cardiac fibroblasts, RR and CPAI reduced integrin β3 expression, vitronectin supernatant levels, and fibroblast adhesion to vitronectin, and preserved apoptotic over antiapoptotic/proliferative signaling.\",\n      \"method\": \"In vivo mouse cardiac fibrosis model with PAI-1 variant infusion, cardiac fibroblast culture with variant PAI-1 treatments, morphometry, qPCR, integrin/vitronectin assays\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain-specific PAI-1 variants dissecting two functional activities in vivo and in vitro, single lab\",\n      \"pmids\": [\"24687120\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SERPINE1/PAI-1 is a secreted serpin that covalently inhibits tPA and uPA via an acyl-enzyme mechanism; its unique structural property of spontaneous conversion to a stable latent form (reactive-loop insertion into β-sheet A) is explained by its crystal structure. Beyond antiproteolytic function, PAI-1 controls cell adhesion and migration through competitive binding to the vitronectin SMB domain (blocking αVβ3 integrin and uPAR), drives uPAR/LRP-mediated endocytosis and recycling of uPA complexes, promotes replicative senescence as an essential p53 target gene (via suppression of PI3K–PKB–GSK3β–cyclin D1 signaling), regulates cytoskeletal stiffness in smooth muscle cells through AMPK-dependent cofilin activation, inhibits neutrophil apoptosis via G-protein/PI3K/Akt signaling, undergoes nuclear translocation to act as a transcriptional co-repressor, binds proteasome subunits to stabilize p53 in epithelial cells, and is transcriptionally regulated by TGF-β/p53–Smad complexes, HIF-2α, HIF-1α/Egr-1/C/EBPα (under hypoxia), and the 4G/5G promoter polymorphism that differentially recruits transcriptional activators and repressors.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SERPINE1 (PAI-1) is a serine protease inhibitor (serpin) that functions as the principal physiological inhibitor of tissue-type and urokinase-type plasminogen activators (tPA and uPA), thereby regulating fibrinolysis, extracellular matrix turnover, cell adhesion, migration, and senescence. PAI-1 forms covalent inhibitory complexes with tPA and uPA and triggers LRP-mediated endocytosis and lysosomal degradation of the uPA–uPAR complex, switching cells between adhesive and migratory states; its active conformation is stabilized by binding the somatomedin B domain of vitronectin, which simultaneously blocks integrin and uPAR access to vitronectin and modulates cell–matrix adhesion [PMID:2157592, PMID:12808446, PMID:16601674]. Intracellularly, PAI-1 binds proteasome components and inhibits proteasomal degradation of p53, activating the p53/p21/pRb senescence axis, while sequestration of PAI-1 into stress granules counteracts this pro-senescent function [PMID:37566086, PMID:29592859]. PAI-1 transcription is induced by HIF-1α/Egr-1/C/EBPα under hypoxia, by p53/Smad2/3 downstream of TGF-β, and by NF-κB in response to TNFα, and is post-transcriptionally repressed by miR-30c targeting its 3′ UTR [PMID:17197388, PMID:27759037, PMID:16338458, PMID:27819307].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Resolving how PAI-1 clears surface-bound uPA: demonstrating that PAI-1 binding to uPA on uPAR triggers receptor-mediated endocytosis and lysosomal degradation established PAI-1 as a regulator of surface protease turnover, not merely a soluble protease inhibitor.\",\n      \"evidence\": \"Radioligand internalization assay with temperature shift and chloroquine lysosomal inhibition in U937 cells\",\n      \"pmids\": [\"2157592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic receptor (later identified as LRP) not yet defined\", \"Fate of uPAR after internalization unclear\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Mapping the PAI-1–vitronectin interface to the somatomedin B domain and showing competitive exclusion of uPAR and integrins explained how PAI-1 couples protease inhibition to cell adhesion regulation.\",\n      \"evidence\": \"Competitive binding and cell adhesion assays with SMB domain of vitronectin; later confirmed at 2.3 Å by X-ray crystallography (2003)\",\n      \"pmids\": [\"10190280\", \"12808446\", \"12437099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural dynamics of PAI-1 conformational transition (active→latent) on vitronectin not fully resolved\", \"Low-affinity C-terminal vitronectin binding site function unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying LRP as the endocytic receptor that internalizes the uPA–PAI-1–uPAR complex linked PAI-1's protease inhibitory function to chemotaxis regulation and ERK/MAPK signaling.\",\n      \"evidence\": \"Chemotaxis assays with RAP and anti-LRP antibody blockade, ERK phosphorylation immunoblot\",\n      \"pmids\": [\"11566185\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How LRP engagement selects between ERK activation and receptor clearance not mechanistically defined\", \"Identity of downstream LRP signaling adaptors not established\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that PAI-1 forms a ternary complex with tPA and Mac-1 on fibrin and switches macrophages from adhesion to detachment via LRP established PAI-1 as a directional migration switch in vivo.\",\n      \"evidence\": \"Multiple KO mice (Mac-1, tPA, PAI-1, LRP), PAI-1 mutant rescue defective for LRP binding, intravital microscopy\",\n      \"pmids\": [\"16601674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism generalizes beyond macrophages to other leukocytes in vivo not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining the combinatorial transcriptional regulation of PAI-1 under hypoxia (HIF-1α, Egr-1, C/EBPα) and inflammation (NF-κB/TNFα) resolved how diverse stimuli converge on PAI-1 induction.\",\n      \"evidence\": \"Promoter mutagenesis, EMSA with supershift, ChIP in macrophages (hypoxia); EMSA and NF-κB nuclear translocation plus antibody rescue in trophoblasts (TNFα)\",\n      \"pmids\": [\"17197388\", \"16338458\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chromatin remodeling dynamics at the PAI-1 locus under combined stimuli not mapped\", \"Epigenetic regulation beyond histone acetylation not addressed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The transcriptional repressor Net (TCF/Ets family) was shown to tonically suppress PAI-1 transcription, and its loss increased PAI-1 and impaired migration — revealing that PAI-1 levels are set by a balance of activators and repressors.\",\n      \"evidence\": \"Net KO MEFs, ChIP/EMSA for Net binding to PAI-1 promoter, PAI-1 blocking antibody rescue of migration defect\",\n      \"pmids\": [\"16314510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Net integrates with HIF/NF-κB activators at the same promoter unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"PAI-1 deposition in keratinocyte migration trails and its requirement for wound closure and protection from plasminogen-induced anoikis established a physiological role in epithelial repair beyond hemostasis.\",\n      \"evidence\": \"PAI-1-GFP live imaging, PAI-1 KO and KD keratinocytes, recombinant PAI-1 rescue, antisense and antibody blockade in wound assays\",\n      \"pmids\": [\"18386027\", \"10896775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor mediating PAI-1's anti-anoikis effect in keratinocytes not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"PAI-1 was found to inhibit neutrophil apoptosis through a Gi-coupled receptor/PI3K/Akt pathway independent of uPAR, LRP, and vitronectin, revealing a receptor axis distinct from the canonical LRP-dependent pathway.\",\n      \"evidence\": \"Pertussis toxin and PI3K inhibitor blockade of PAI-1's antiapoptotic effect, PAI-1 KO mice with enhanced neutrophil apoptosis in acute lung injury\",\n      \"pmids\": [\"21622848\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the Gi-coupled receptor mediating PAI-1 antiapoptotic signaling not determined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of miR-30c as a direct post-transcriptional repressor of PAI-1 via 3′ UTR targeting connected metabolic dysregulation (hyperglycemia) to PAI-1-driven thrombosis.\",\n      \"evidence\": \"Luciferase 3′ UTR reporter assays, lentiviral miR-30c delivery in diabetic mice, arterial thrombosis model\",\n      \"pmids\": [\"27819307\", \"21878751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other miRNAs regulating PAI-1 not systematically evaluated\", \"Mechanism of hyperglycemia-induced miR-30c repression not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Matrix-bound PAI-1 was shown to maintain amoeboid blebbing via membrane localization of PDK1 and ROCK1, sustaining the RhoA/ROCK1/MLC pathway, demonstrating PAI-1 as a regulator of migration mode.\",\n      \"evidence\": \"Immunofluorescence for PDK1/ROCK1 localization and RhoA/ROCK1/MLC-P pathway analysis in SW620 colorectal cancer cells\",\n      \"pmids\": [\"22363817\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which matrix-bound PAI-1 recruits PDK1 to the membrane not established\", \"Not independently confirmed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Functional dissection of PAI-1 using vitronectin-binding-deficient and protease-inhibitory-deficient mutants showed that its vitronectin-binding function protects against cardiac fibrosis (by reducing integrin β3/fibroblast adhesion) while its protease-inhibitory function promotes fibronectin accumulation.\",\n      \"evidence\": \"PAI-1 functional mutants (AK, RR) in murine cardiac fibrosis model with Ang II infusion, human cardiac fibroblast assays\",\n      \"pmids\": [\"24687120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How these two separable functions are coordinated in vivo not understood\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating that TGF-β induces PAI-1 through a p53–Smad2/3–CBP complex on the PAI-1 promoter linked the tumor suppressor p53 to PAI-1-mediated cytostasis.\",\n      \"evidence\": \"ChIP, co-IP of p53/Smad complex, histone H3 acetylation assays, p53 knockdown blocking TGF-β cytostasis\",\n      \"pmids\": [\"27759037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether p53 mutations in cancer alter this TGF-β–PAI-1 axis not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"PAI-1 sequestration into stress granules was shown to promote cyclin D1 nuclear translocation and Rb phosphorylation, revealing that subcellular compartmentalization counteracts PAI-1's pro-senescent activity.\",\n      \"evidence\": \"SG induction/disruption, immunofluorescence for PAI-1 in SGs, cyclin D1 and RB phosphorylation readouts, SA-β-gal senescence assay\",\n      \"pmids\": [\"29592859\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis for PAI-1 recruitment to stress granules unknown\", \"Not independently confirmed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Intracellular (premature) PAI-1 was shown to bind proteasome components and inhibit proteasomal activity, stabilizing p53 and activating the p53/p21/pRb senescence axis, establishing a non-canonical intracellular mechanism distinct from its secreted antiprotease role.\",\n      \"evidence\": \"Co-IP of PAI-1 with proteasome components, proteasome activity assays, WT vs. secretion-deficient PAI-1 mutant comparison in A549 and primary mouse ATII cells\",\n      \"pmids\": [\"37566086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific proteasome subunit(s) bound by PAI-1 not identified\", \"Structural basis of proteasome inhibition unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Endothelial-specific PAI-1 KO revealed that senescent endothelial cell-secreted PAI-1 drives podocyte apoptosis in aging kidneys, establishing PAI-1 as a paracrine senescence effector.\",\n      \"evidence\": \"Endothelial-specific PAI-1 KO mice, conditioned medium transfer from senescent endothelial cells, PAI-1 blocking rescue\",\n      \"pmids\": [\"34725920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor on podocytes mediating PAI-1-induced apoptosis not identified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"ChIP-sequencing revealed nuclear PAI-1 binding to distal intergenic DNA regions in bladder cancer cells, suggesting a transcriptional coregulator/silencer role — a function entirely distinct from serpin activity.\",\n      \"evidence\": \"ChIP-seq, RNA-seq after PAI-1 knockdown, rapid immunoprecipitation mass spectrometry, nuclear PAI-1 IHC in 939 bladder cancer specimens\",\n      \"pmids\": [\"35842542\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"DNA-binding domain or motif specificity of PAI-1 not defined\", \"No reconstitution of transcriptional activity with purified components\", \"Not independently confirmed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"PAI-1 was shown to regulate vascular smooth muscle cell intrinsic stiffness through AMPK–cofilin-mediated F-actin remodeling, extending PAI-1's role to mechanobiology of the vascular wall.\",\n      \"evidence\": \"Atomic force microscopy, PAI-039 inhibitor, PAI-1 siRNA, PAI-1-deficient murine SMCs, AMPK/cofilin activity assays, in vivo pulse wave velocity\",\n      \"pmids\": [\"38868940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PAI-1 inhibits AMPK mechanistically is unclear\", \"Whether this is protease-inhibitory or vitronectin-binding dependent not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the identity of the Gi-coupled receptor mediating PAI-1's antiapoptotic signaling; the structural basis of intracellular PAI-1's proteasome inhibition; whether nuclear PAI-1's DNA-binding/transcriptional silencer function is direct or mediated through a chromatin-associated partner; and how PAI-1's protease-inhibitory vs. vitronectin-binding vs. intracellular functions are differentially deployed across tissue contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Gi-coupled receptor identity unknown\", \"Proteasome inhibition mechanism unresolved\", \"Nuclear DNA-binding specificity and functional significance require reconstitution\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 24, 27]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 24]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 4, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 7, 23, 27]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [21, 22]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [32]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 1, 24, 34]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10, 12, 25, 28, 29]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [34, 35, 36]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [10, 23]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [5, 21, 22, 37]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [2, 27, 28]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [5, 6, 9, 18, 31, 32]}\n    ],\n    \"complexes\": [\n      \"uPA–PAI-1–uPAR–LRP endocytic complex\",\n      \"tPA–PAI-1 binary complex\",\n      \"PAI-1–vitronectin (SMB domain) complex\"\n    ],\n    \"partners\": [\n      \"PLAU\",\n      \"PLAT\",\n      \"VTN\",\n      \"LRP1\",\n      \"PLAUR\",\n      \"SMAD3\",\n      \"TP53\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SERPINE1 encodes plasminogen activator inhibitor 1 (PAI-1), a secreted serpin that functions as the principal physiological inhibitor of tissue-type (tPA) and urokinase-type (uPA) plasminogen activators through covalent acyl-enzyme complex formation, thereby governing fibrinolysis, extracellular matrix remodeling, and cell migration [PMID:3090045, PMID:1435917]. A unique structural feature—spontaneous insertion of its reactive-center loop into β-sheet A without proteolytic cleavage—converts PAI-1 to a stable latent conformation, while vitronectin binding to the somatomedin B domain stabilizes the active state and simultaneously occludes integrin αVβ3 and uPAR binding sites, enabling PAI-1 to regulate cell adhesion and motility independently of its antiprotease activity [PMID:1731226, PMID:12808446, PMID:8837777]. PAI-1 drives LRP1-dependent endocytic clearance and recycling of uPA–uPAR complexes, controls macrophage and smooth muscle cell migration through integrin-to-LRP switching, and regulates vascular smooth muscle stiffness via AMPK–cofilin-mediated F-actin remodeling [PMID:9184208, PMID:16601674, PMID:38868940]. Beyond its extracellular roles, PAI-1 is a critical p53/TGF-β–Smad target gene that enforces replicative senescence by suppressing PI3K–PKB–GSK3β–cyclin D1 signaling, can translocate to the nucleus to act as a transcriptional co-repressor, and stabilizes p53 by binding and inhibiting proteasome subunits [PMID:16862142, PMID:27759037, PMID:35842542, PMID:37566086].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Molecular cloning and biochemical characterization established PAI-1 as a serpin-family serine protease inhibitor that forms covalent complexes with uPA and tPA via an acyl-enzyme mechanism, defining its primary molecular activity.\",\n      \"evidence\": \"cDNA cloning from endothelial cells by three independent groups; purification and kinetic analysis of covalent complex formation with uPA/tPA\",\n      \"pmids\": [\"3092219\", \"3097076\", \"2430793\", \"3090045\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for PAI-1's unusual spontaneous loss of activity\", \"No in vivo validation of physiological necessity\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Demonstration that PAI-1 inhibits receptor-bound uPA and triggers internalization and lysosomal degradation of the uPA–PAI-1 complex via uPAR established the first cellular clearance mechanism for plasminogen activators.\",\n      \"evidence\": \"Radiolabeled ligand internalization assays on U937 cells with chloroquine inhibition and kinetic measurements\",\n      \"pmids\": [\"2157592\", \"2161846\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic receptor mediating internalization not yet identified\", \"Fate of uPAR after internalization unknown\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"The crystal structure of latent PAI-1 revealed that full reactive-loop insertion into β-sheet A without cleavage explains the serpin's unique spontaneous conversion to a stable inactive form, resolving a long-standing structural puzzle.\",\n      \"evidence\": \"X-ray crystallography at 2.6 Å resolution\",\n      \"pmids\": [\"1731226\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the active conformation and mechanism of latency transition not resolved\", \"Vitronectin-mediated stabilization not structurally explained\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Identification of a human frameshift mutation causing complete PAI-1 deficiency with severe bleeding confirmed PAI-1 as the essential in vivo inhibitor of plasminogen activators.\",\n      \"evidence\": \"Genetic analysis of a PAI-1-deficient patient with hyperfibrinolytic bleeding diathesis\",\n      \"pmids\": [\"1435917\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No systematic characterization of heterozygous carriers\", \"Tissue-specific consequences of PAI-1 loss not defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Characterization of the 4G/5G promoter polymorphism revealed that differential transcription factor binding (activator on both alleles, repressor only on 5G) explains allele-specific PAI-1 expression levels and associated cardiovascular risk.\",\n      \"evidence\": \"EMSA with allele-specific probes, transcription reporter assays, population study of myocardial infarction\",\n      \"pmids\": [\"7892190\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the repressor protein binding the 5G allele not determined\", \"Causality between polymorphism and MI not established by the association study alone\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Discovery that PAI-1 competes with uPAR and αVβ3 integrin for vitronectin binding—and that this is independent of protease inhibition—established a second major function: regulation of cell adhesion and migration through extracellular matrix interactions.\",\n      \"evidence\": \"Domain-swap mutagenesis of vitronectin, cell detachment assays, smooth muscle cell migration with PAI-1 mutants deficient in protease inhibition\",\n      \"pmids\": [\"8830783\", \"8837777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic details of PAI-1–vitronectin interface not yet resolved\", \"Relative contribution of anti-adhesive versus antiproteolytic function in vivo not quantified\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of LRP as the endocytic receptor for uPA–PAI-1 complexes and demonstration of uPAR recycling after internalization completed the cellular clearance cycle model and explained how cells regenerate uPA-binding capacity.\",\n      \"evidence\": \"Surface biotinylation pulse-chase, PI-PLC treatment, immunoelectron microscopy on U937 and HT1080 cells; PAI-1 knockout mice with arterial injury showing enhanced SMC migration rescued by adenoviral PAI-1\",\n      \"pmids\": [\"9184208\", \"9386191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals directing uPAR recycling versus LRP/ligand degradation not defined\", \"Whether other endocytic receptors contribute in specific tissues not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The crystal structure of PAI-1 bound to the vitronectin SMB domain provided the atomic basis for vitronectin stabilization of active PAI-1 and confirmed steric occlusion of integrin and uPAR binding sites, unifying the structural and cell-biological observations.\",\n      \"evidence\": \"X-ray crystallography at 2.3 Å resolution of the PAI-1–SMB domain complex\",\n      \"pmids\": [\"12808446\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the full-length vitronectin–PAI-1 complex not available\", \"Dynamics of the active-to-latent transition in the presence of vitronectin not captured\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Three studies collectively expanded PAI-1's role beyond fibrinolysis: PAI-1 was shown to be an essential p53 target enforcing replicative senescence via PI3K–PKB–GSK3β–cyclin D1 suppression, to orchestrate macrophage migration through a sequential Mac-1/tPA/PAI-1/LRP adhesion-to-detachment switch, and to be transcriptionally co-regulated by HIF-1α, Egr-1, and C/EBPα under hypoxia.\",\n      \"evidence\": \"RNAi knockdown and ectopic expression in fibroblasts with pathway analysis (senescence); multiple genetic knockouts with PAI-1 LRP-binding mutant rescue in vivo (macrophage migration); PAI-1 promoter mutagenesis, EMSA, and ChIP under hypoxia (transcription)\",\n      \"pmids\": [\"16862142\", \"16601674\", \"17197388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PAI-1's senescence function requires a specific receptor or is intracellular not resolved\", \"Relative importance of each hypoxia-responsive element in different tissues not established\", \"Mac-1/tPA/PAI-1/LRP pathway not tested in human macrophages\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Multiple studies dissected PAI-1's dual functional domains in disease contexts: vitronectin-binding (not antiprotease) activity protects against cardiac fibrosis; PAI-1 supports HIF-2α-driven angiogenesis by maintaining low plasmin; and the prolactin fragment 16K PRL directly binds PAI-1 to modulate fibrinolysis and angiogenesis.\",\n      \"evidence\": \"PAI-1 domain-specific variants in mouse cardiac fibrosis model; epistatic shRNA knockdown with aprotinin rescue in HepG2 spheroids; direct 16K PRL–PAI-1 binding assay with PAI-1 KO mice\",\n      \"pmids\": [\"24687120\", \"25489981\", \"24929950\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether vitronectin-binding function is protective in non-cardiac fibrosis settings not tested\", \"HIF-2α–PAI-1 axis validated only in hepatocellular carcinoma model\", \"16K PRL–PAI-1 binding site not mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Elucidation of TGF-β-induced PAI-1 transcription through a p53–Smad2/3–CBP complex on the PAI-1 promoter mechanistically linked p53 and TGF-β cytostatic signaling, with PAI-1 as an effector mediating growth arrest.\",\n      \"evidence\": \"Co-immunoprecipitation of p53–Smad complex, ChIP for promoter occupancy, histone acetylation analysis, p53 siRNA epistasis\",\n      \"pmids\": [\"27759037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this complex operates in non-epithelial cell types not tested\", \"Genome-wide p53–Smad co-regulation beyond PAI-1 not explored\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cell-autonomous and paracrine senescence functions of PAI-1 were defined: PAI-1 overexpression in tubular epithelial cells drives dedifferentiation and fibrosis through klotho loss, p53, and ligand-independent TGF-βRI/SMAD3 activation; meanwhile, senescent endothelial cell-secreted PAI-1 induces podocyte apoptosis in a paracrine manner, with endothelial-specific PAI-1 deletion protecting against age-related glomerular injury.\",\n      \"evidence\": \"Stable PAI-1 overexpression with epistasis (klotho rescue, p53 siRNA, TGF-βRI inhibitor) in HK-2 cells; endothelial cell-specific PAI-1 conditional KO mice with conditioned medium transfer\",\n      \"pmids\": [\"34110636\", \"34725920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether intracellular PAI-1 drives these effects through proteasome inhibition or another mechanism not fully resolved\", \"Identity of the podocyte receptor for secreted PAI-1 unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Two novel intracellular functions were described: nuclear PAI-1 occupies distal intergenic chromatin regions and acts as a transcriptional co-repressor, and pre-secretory PAI-1 binds proteasome subunits to stabilize p53 and promote senescence in epithelial cells.\",\n      \"evidence\": \"ChIP-seq and RNA-seq integration with RIME in bladder cancer cells (nuclear function); co-immunoprecipitation with proteasome subunits and proteasome activity assay with wild-type versus secretion-deficient PAI-1 in ATII cells\",\n      \"pmids\": [\"35842542\", \"37566086\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear PAI-1 chromatin-binding partners and co-repressor complex composition not fully defined\", \"Proteasome interaction surfaces on PAI-1 not mapped\", \"Both findings from single laboratories; independent replication pending\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"PAI-1 was shown to regulate vascular smooth muscle cell intrinsic stiffness by controlling F-actin content through AMPK-dependent cofilin activation, independent of uPAR/LRP, identifying a mechanotransduction function relevant to arterial stiffness.\",\n      \"evidence\": \"Atomic force microscopy, AMPK signaling analysis, PAI-1 siRNA and PAI-1−/− SMCs, in vivo aortic pulse wave velocity measurement\",\n      \"pmids\": [\"38868940\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PAI-1 target upstream of AMPK not identified\", \"Whether this mechanism operates in non-vascular cell types unknown\", \"Single-lab finding awaiting independent validation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include: the identity of the receptor(s) mediating PAI-1's intracellular senescence and anti-apoptotic functions (independent of uPAR/LRP/vitronectin), the structural basis for PAI-1's nuclear translocation and chromatin binding, and whether proteasome inhibition and transcriptional co-repression represent a unified intracellular mechanism or distinct activities.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No receptor identified for PAI-1's GPCR/PI3K-dependent anti-apoptotic signaling in neutrophils\", \"Nuclear localization signal or import mechanism not characterized\", \"Relationship between pre-secretory proteasome binding and nuclear chromatin occupancy not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 4, 31]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6, 7, 10, 32]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [6, 7, 10]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 2, 6, 7, 10, 15]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [6, 7, 10, 15, 16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [26, 27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [2, 4, 5]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [6, 7, 10, 32]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 18, 19, 21, 25, 30]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12, 21, 24]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [14, 29]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 8, 11, 13]}\n    ],\n    \"complexes\": [\n      \"uPA–PAI-1–uPAR–LRP1 endocytic complex\",\n      \"p53–Smad2/3–CBP transcriptional complex on PAI-1 promoter\"\n    ],\n    \"partners\": [\n      \"PLAU\",\n      \"PLAT\",\n      \"VTN\",\n      \"LRP1\",\n      \"PLAUR\",\n      \"TP53\",\n      \"SMAD3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}