{"gene":"SERPINE1","run_date":"2026-06-10T07:46:30","timeline":{"discoveries":[{"year":1990,"finding":"The uPA-PAI-1 complex bound to the uPA receptor (uPAR) on cell surfaces is internalized and subsequently degraded in lysosomes; free uPA, ATF, or DFP-uPA are not internalized, demonstrating that PAI-1 binding to uPA triggers a specific receptor-mediated endocytic cycle.","method":"Radiolabeled ligand internalization assay with chloroquine inhibition and acid-wash fractionation in U937 cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean ligand-tracking experiment with multiple controls (acid wash, chloroquine), replicated across conditions; foundational mechanism paper","pmids":["2157592"],"is_preprint":false},{"year":1990,"finding":"TGF-β1 increases PAI-1 mRNA (~50-fold) and protein in human bronchial epithelial cells, resulting in a net ~50% reduction in plasminogen activator activity in conditioned medium; the effect requires a TGF-β-responsive differentiation pathway and is absent in cells that do not undergo squamous differentiation.","method":"Northern blot, ELISA, caseinolytic plasminogen activator activity assay in NHBE cells treated with TGF-β1","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (mRNA, protein, activity) in primary cells, single lab","pmids":["2221087"],"is_preprint":false},{"year":1991,"finding":"PAI-1 protein and activity are distributed throughout the body, with highest abundance in liver and spleen; immunochemical staining localizes PAI-1 to endothelium, platelets, megakaryocytes, neutrophils, macrophages, vascular smooth muscle cells, and mesangial cells, placing it at sites of hemostasis and inflammation.","method":"Tissue extraction with functional PAI-1 activity assay and immunohistochemistry with monoclonal antibodies on human tissue panels","journal":"Journal of clinical pathology","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — systematic tissue survey with functional activity + IHC, multiple tissues; no functional consequence directly linked","pmids":["1864986"],"is_preprint":false},{"year":1999,"finding":"PAI-1 regulates uPAR-mediated cell adhesion to vitronectin by competing with uPAR for binding to the somatomedin B (SMB) domain of vitronectin; PAI-1 binding to the SMB domain also sterically hinders integrin binding to the adjacent RGD sequence, thereby modulating both uPAR- and integrin-mediated cell adhesion.","method":"Competitive binding assays and cell adhesion assays with defined recombinant proteins and domain-specific inhibitors","journal":"APMIS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reconstituted competitive binding with defined protein domains, single lab","pmids":["10190280"],"is_preprint":false},{"year":2000,"finding":"PAI-1 expression in wounded keratinocyte monolayers is required for normal wound repair: PAI-1 knockdown via antisense markedly impairs wound closure, while addition of recombinant PAI-1 rescues the defect; PAI-1 also rescues keratinocytes from plasminogen-induced substrate detachment/anoikis and enhances cell spread area.","method":"Antisense-mediated knockdown, recombinant PAI-1 rescue, PAI-1-neutralizing antibodies, wound-scratch assay, and cell spreading/anoikis assays in HaCaT keratinocytes","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with rescue using recombinant protein, multiple phenotypic readouts, single lab","pmids":["10896775"],"is_preprint":false},{"year":2001,"finding":"PAI-1 deficiency attenuates renal fibrosis after ureteral obstruction; one key mechanism is that PAI-1 promotes the recruitment of fibrosis-inducing cells (macrophages and myofibroblasts), independently of changes in net renal plasminogen activator or plasmin activity.","method":"PAI-1 knockout vs. wild-type mouse comparison after UUO; interstitial fibrosis quantified by picrosirius red and collagen assay; cellular infiltrate by immunostaining; TGF-β and procollagen mRNAs by RT-PCR","journal":"Kidney international","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (histology, biochemistry, gene expression), clear mechanistic separation from plasmin activity","pmids":["11473641"],"is_preprint":false},{"year":2001,"finding":"PAI-1 inhibits uPA-induced chemotaxis by triggering internalization of the uPAR via LRP; blocking LRP with the 39 kDa RAP or anti-LRP antibodies prevents uPAR internalization and converts the uPA-PAI-1 complex from a migration inhibitor into a chemoattractant that activates cytoskeletal reorganization and ERK/MAPK.","method":"Chemotaxis assays, anti-LRP antibody/RAP inhibition, cytoskeletal staining, ERK phosphorylation blotting","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via receptor blockade, multiple functional readouts (chemotaxis, ERK, cytoskeleton), single lab","pmids":["11566185"],"is_preprint":false},{"year":2002,"finding":"Mapping studies define the PAI-1 binding region on vitronectin to the N-terminal somatomedin B (SMB) domain, and the vitronectin-binding region on PAI-1 to the area around α-helices E and F; a secondary low-affinity PAI-1 binding site in the C-terminal region of vitronectin may support larger PAI-1/VN complexes.","method":"Peptide/domain competition binding assays, mutagenesis-based mapping, biochemical interaction studies reviewed from multiple labs","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain-mapping with peptide competition across multiple labs, partially replicated; binding site not fully resolved per authors","pmids":["12437099"],"is_preprint":false},{"year":2003,"finding":"Crystal structure (2.3 Å) of the PAI-1–somatomedin B (SMB) domain complex shows that vitronectin binding stabilizes the active conformation of PAI-1; structural analysis further reveals that PAI-1 sterically competes with uPAR and integrins for binding to vitronectin, explaining PAI-1's regulation of cell adhesion and tissue effects.","method":"X-ray crystallography of PAI-1–SMB complex at 2.3 Å resolution with structural interpretation of binding interfaces","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with direct mechanistic interpretation of binding competition; structural basis for multiple biological functions established","pmids":["12808446"],"is_preprint":false},{"year":2003,"finding":"tPA contains two independent vasoactive epitopes with opposite effects on vascular tone; PAI-1 and a PAI-1-derived hexapeptide regulate these effects by binding tPA, and the stimulatory (vasoconstrictive) effect of tPA is mediated through LRP, as demonstrated by anti-LRP antibody blockade in isolated aorta rings and in vivo.","method":"Isolated aorta ring contraction assay, anti-LRP antibodies, tPA knockout mice, in vivo blood pressure and cerebrovascular resistance measurements in rats","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro organ assay plus in vivo pharmacology with receptor blockade; novel mechanistic context for PAI-1 in vascular tone","pmids":["14512309"],"is_preprint":false},{"year":2006,"finding":"Efficient macrophage migration in an inflammatory environment requires the ordered formation of a fibrin–tPA–PAI-1 ternary complex at the cell surface: tPA promotes Mac-1-mediated adhesion to fibrin, PAI-1 inhibition of tPA exposes a site for LRP binding, and LRP-mediated endocytosis triggers the switch from adhesion to detachment. Genetic inactivation of PAI-1 abrogates macrophage migration, and this defect is rescued by wild-type PAI-1 but not by an LRP-binding mutant of PAI-1.","method":"Genetic KO of Mac-1, tPA, PAI-1, LRP in mice; in vitro migration assays; rescue with wild-type vs. LRP-binding-deficient PAI-1 mutant","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic KOs with mechanistic rescue using structure-function mutant; pathway position precisely defined","pmids":["16601674"],"is_preprint":false},{"year":2006,"finding":"Hypoxia-induced PAI-1 transcription in macrophages is driven by three transcription factors—Egr-1, HIF-1α, and C/EBPα—all of which bind the PAI-1 promoter under hypoxia; mutation of each binding site reduces hypoxia-sensitivity, and ChIP confirms all three factors bind chromatin under hypoxic conditions. HIF-1α dominates but Egr-1 and C/EBPα greatly augment and can act independently.","method":"PAI-1 promoter deletion/mutation constructs, transfection, ChIP, gel-shift (EMSA) with supershift analysis, primary macrophage validation","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — promoter mutagenesis + EMSA supershift + ChIP, replicated in primary cells; multiple orthogonal methods in one rigorous study","pmids":["17197388"],"is_preprint":false},{"year":2007,"finding":"PAI-1 inhibition of uPA by PAI-1 exposes a cryptic high-affinity binding site on the PAI-1 moiety for the VLDLr (very-low-density-lipoprotein receptor), sustaining cell signaling and promoting proliferation of breast cancer cells; PAI-2, despite also inhibiting uPA, does not contain this VLDLr binding site and does not sustain global tyrosine phosphorylation or cell proliferation, providing a structural basis for the divergent outcomes of PAI-1 vs. PAI-2 in cancer.","method":"Biochemical and structural analyses of PAI-1 vs. PAI-2 binding to VLDLr; global protein tyrosine phosphorylation assays; cell proliferation assays with uPA-PAI-1 vs. uPA-PAI-2 complexes","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — structural and functional comparison with receptor-binding and signaling assays, single lab, two orthogonal methods","pmids":["17696882"],"is_preprint":false},{"year":2008,"finding":"PAI-1 acts as a 'don't eat me' signal on viable neutrophils: surface PAI-1 colocalizes with calreticulin (CRT) on viable neutrophils and limits LRP-dependent phagocytosis; during apoptosis PAI-1 levels decrease on the cell surface, CRT colocalization is lost, and the increase in available CRT drives enhanced efferocytosis via LRP.","method":"PAI-1(-/-) mice, anti-PAI-1 antibody blockade, recombinant PAI-1 add-back, LRP/calreticulin functional studies, colocalization by fluorescence microscopy","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus antibody blockade plus recombinant rescue, multiple mechanistic readouts (phagocytosis, colocalization, receptor identification)","pmids":["18689689"],"is_preprint":false},{"year":2008,"finding":"SERPINE1 (PAI-1) protein is deposited into keratinocyte migration trails during wound repair; addition of recombinant PAI-1 stimulates directional motility in PAI-1(-/-) cells, and antibody-mediated PAI-1 blockade attenuates migration and causes apoptosis; the rescue from plasminogen-induced anoikis by PAI-1 identifies it as a keratinocyte survival factor.","method":"PAI-1-GFP live imaging, recombinant PAI-1 addition to PAI-1(-/-) cells, antisense knockdown, neutralizing antibodies, anoikis assay","journal":"Archives of dermatological research","confidence":"High","confidence_rationale":"Tier 2 / Strong — live imaging + genetic KO + rescue + antibody blockade, multiple orthogonal methods; PAI-1 mechanistic role in migration trails directly visualized","pmids":["18386027"],"is_preprint":false},{"year":2010,"finding":"PAI-1 mediates the TGF-β1+EGF-induced 'scatter' (EMT) response in transformed keratinocytes: PAI-1 is the most highly induced transcript; MEK/ERK and p38 inhibition abolishes both maximal PAI-1 upregulation and cell locomotion; PAI-1 knockdown alone blocks TGF-β1+EGF-dependent scattering; and EGFR knockdown attenuates TGF-β1-induced PAI-1 expression, placing EGFR transactivation upstream of PAI-1 induction.","method":"mRNA profiling, MEK/p38 pharmacologic inhibition, PAI-1 siRNA knockdown, EGFR knockdown, wound scatter assay","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown with functional rescue, epistasis by kinase inhibitors and EGFR KD, single lab","pmids":["20428185"],"is_preprint":false},{"year":2011,"finding":"PAI-1 inhibits neutrophil apoptosis through pertussis-toxin-sensitive G-protein-coupled receptors and PI3K, activating PKB/Akt, Mcl-1, and Bcl-xL; uPAR, LRP, and vitronectin are not required for this antiapoptotic function; in vivo, PAI-1(-/-) mice show enhanced neutrophil apoptosis in LPS-induced lung injury.","method":"PAI-1(-/-) mice, pertussis toxin, selective PI3K inhibitors, uPAR/LRP/vitronectin blockade, apoptosis assays, in vivo LPS-lung injury model","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus systematic receptor exclusion plus in vivo model; PI3K/Akt pathway identified with multiple inhibitors","pmids":["21622848"],"is_preprint":false},{"year":2012,"finding":"Matrix-bound PAI-1 maintains cell blebbing (amoeboid migration) in colorectal cancer cells via the RhoA/ROCK1/MLC-P pathway; PAI-1 localizes PDK1 and ROCK1 to the cell membrane and sustains RhoA/ROCK1 activation, as determined by immunoblotting, activity assay, and immunofluorescence.","method":"Immunoblotting, ROCK1 activity assay, immunofluorescence, PAI-1 depletion in SW620 cells, RhoA pathway inhibition","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional PAI-1 depletion with multiple pathway readouts in cancer cells, single lab","pmids":["22363817"],"is_preprint":false},{"year":2014,"finding":"16K prolactin (16K PRL) binds PAI-1 directly; loss of PAI-1 abrogates the antitumoral and antiangiogenic effects of 16K PRL; mechanistically, PAI-1 bound to the PAI-1–uPA–uPAR ternary complex exerts antiangiogenic effects, while 16K PRL inhibition of PAI-1's antifibrinolytic activity promotes arterial thrombolysis.","method":"Direct binding assay of 16K PRL and PAI-1, PAI-1 KO mouse models, in vivo tumor and angiogenesis assays, fibrin clot lysis assay","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding established, genetic KO, in vivo rescue; mechanistic pathway (PAI-1–uPA–uPAR) validated in multiple model systems","pmids":["24929950"],"is_preprint":false},{"year":2014,"finding":"RNA aptamers that bind PAI-1 with nanomolar affinity inhibit its antiproteolytic activity against tPA, disrupt formation of the stable covalent PAI-1-tPA complex, and increase levels of cleaved (inactive) PAI-1; this identifies the tPA-docking region of PAI-1 as functionally targetable.","method":"SELEX aptamer generation, in vitro PAI-1 inhibition assay, complex formation assay, cleaved PAI-1 quantification","journal":"Nucleic acid therapeutics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted activity assay, direct binding affinity measurement; single lab","pmids":["24922319"],"is_preprint":false},{"year":2014,"finding":"HIF-2α (not HIF-1α) drives PAI-1 expression in hepatocellular carcinoma cells; PAI-1 knockdown attenuates angiogenesis in coculture models; rescuing the HIF-2α knockdown by blocking plasmin (with aprotinin) restores angiogenesis, establishing the HIF-2α→PAI-1→reduced-plasmin→pro-angiogenic axis.","method":"Stable shRNA knockdown of HIF-1α/HIF-2α in HepG2, microarray identification of PAI-1 as target, PAI-1 knockdown, plasmin inhibition rescue, HepG2 spheroid-embryoid body coculture angiogenesis model","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by knockdown + pharmacologic rescue, microarray target identification confirmed functionally, single lab","pmids":["25489981"],"is_preprint":false},{"year":2015,"finding":"PAI-1 promotes cell migration in an LRP1-dependent manner by activating β-catenin transcriptional activity and modulating ERK1/2; in LRP1-deficient MEFs, PAI-1-induced β-catenin responses are absent while ERK1/2 activation is enhanced, and knockdown of β-catenin abolishes the LRP1-independent ERK1/2 response.","method":"Wild-type vs. LRP1-KO MEFs, PAI-1 treatment, β-catenin reporter assay, ERK1/2 and β-catenin Western blotting, siRNA knockdown, proliferation and motility assays","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic cell pairs plus siRNA epistasis, multiple signaling readouts, single lab","pmids":["25694133"],"is_preprint":false},{"year":2018,"finding":"Thrombin mediates PAI-1 mRNA expression and keratinocyte migration via PAR-1 transactivation of EGFR, downstream ERK1/2 activation, and phosphorylation of Smad2 linker region at Ser250 specifically; ERK1/2 inhibition (not p38 or JNK) blocks Smad2 linker phosphorylation, PAI-1 induction, and migration.","method":"Pharmacologic inhibitors (UO126, SB202190, SP600125), Western blot for Smad2 phospho-sites, qRT-PCR for PAI-1 mRNA, scratch wound migration assay in HaCaT cells","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific residue-level phosphorylation mapping + migration assay + selective kinase inhibitors, single lab","pmids":["29577978"],"is_preprint":false},{"year":2018,"finding":"PAI-1 is recruited to stress granules (SGs) in pre-senescent cells; SG assembly increases nuclear cyclin D1 translocation and Rb phosphorylation, maintaining a proliferative non-senescent state; PAI-1 sequestration in SGs is the mechanism linking SG formation to inhibition of senescence.","method":"Stress granule induction, PAI-1 colocalization with SG markers, cyclin D1 nuclear fractionation, Rb phosphorylation Western blot, senescence markers (SA-β-Gal) in proliferative and presenescent cells","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — subcellular localization linked to functional consequence (Rb phosphorylation, senescence markers), single lab","pmids":["29592859"],"is_preprint":false},{"year":2019,"finding":"In colitis, PAI-1 exacerbates mucosal damage by blocking tPA-mediated cleavage and activation of anti-inflammatory TGF-β; inhibition of PAI-1 reduces both mucosal damage and inflammation in mouse models, placing PAI-1 upstream of tPA-dependent TGF-β activation in intestinal inflammation.","method":"Mouse colitis models, PAI-1 inhibitor treatment, tPA measurement, TGF-β activation assay, intestinal injury quantification","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic pathway (PAI-1→blocks tPA→blocks TGF-β activation) established with pharmacologic inhibition and functional readouts in vivo, validated across multiple cohorts","pmids":["30842312"],"is_preprint":false},{"year":2019,"finding":"Tumor-secreted PAI-1 activates adipocytes via PI3K/AKT signaling, promoting nuclear translocation of FOXP1 which enhances PLOD2 promoter activity in cancer-associated adipocytes, driving collagen reorganization and breast cancer metastasis; pharmacologic blockade of PAI-1 or PLOD2 disrupts this collagen reorganization.","method":"3D collagen invasion assay, co-culture, proteomics, ELISA, qPCR, Western blot, ChIP, loss-of-function assays, in vivo mouse co-implantation model","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for FOXP1 at PLOD2 promoter, PI3K/AKT inhibition epistasis, in vivo validation; single lab, multiple orthogonal methods","pmids":["31170987"],"is_preprint":false},{"year":2021,"finding":"Glomerular endothelial cell-derived PAI-1 drives podocyte apoptosis and age-related glomerular lesions; selective endothelial inactivation of PAI-1 protects glomeruli from lesion development and podocyte loss in aged mice; blocking PAI-1 in supernatants from senescent endothelial cells in vitro prevents podocyte apoptosis.","method":"Endothelial-specific PAI-1 conditional KO mice, aged mouse glomerular phenotype, conditioned medium from senescent endothelial cells + PAI-1 blockade, podocyte apoptosis assay","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic KO, in vitro conditioned medium rescue, mechanistic link established between endothelial PAI-1 and podocyte apoptosis","pmids":["34725920"],"is_preprint":false},{"year":2021,"finding":"PAI-1 promotes renal tubular dysfunction via three converging pathways: (1) PAI-1 overexpression reduces klotho expression, (2) elevates p53, and (3) activates TGF-βRI/II-SMAD3 signaling, leading to dedifferentiation, G2/M arrest, fibrogenesis, and apoptosis; ectopic klotho restoration attenuates fibrogenesis and proliferative defects; genetic p53 suppression reverses PAI-1-driven maladaptive repair; TGF-βRI inhibition attenuates PAI-1-initiated epithelial dysfunction independently of TGF-β1 ligand synthesis.","method":"Stable PAI-1 overexpression in HK-2 cells, klotho rescue, p53 siRNA knockdown, TGF-βRI inhibitor, Western blot for E-cadherin/vimentin/fibronectin/collagen/CCN2/p-Histone3/p21/cleaved caspase-3, annexin-V flow cytometry","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic/pharmacologic epistasis experiments with specific mechanistic rescue of each pathway arm, multiple orthogonal readouts, single rigorous study","pmids":["34110636"],"is_preprint":false},{"year":2021,"finding":"PAI-1 directly regulates transcription of genes involved in lipid homeostasis including PCSK9 and FGF21; pharmacologic or genetic reduction in PAI-1 activity ameliorates hyperlipidemia in vivo; genetic PAI-1 deficiency in humans is associated with reduced plasma PCSK9 levels.","method":"RNA sequencing in PAI-1-deficient vs. wild-type mice, pharmacologic PAI-1 inhibition in vivo, human genetic cohort PCSK9 measurement","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq in KO + pharmacologic inhibition + human genetic validation; mechanism (direct transcriptional regulation) inferred from KO transcriptomics, not direct promoter assays","pmids":["33432099"],"is_preprint":false},{"year":2021,"finding":"SARS-CoV-2 spike protein (S1) stimulates PAI-1 production in human pulmonary microvascular endothelial cells; proteasomal degradation inhibition by bortezomib also induces PAI-1 but upregulates the repressor KLF2; ZMPSTE24 overexpression blunts spike-induced PAI-1 production, identifying ZMPSTE24-dependent proteasomal regulation as a control mechanism for endothelial PAI-1.","method":"Recombinant SARS-CoV-2-S1 treatment of HPMECs, bortezomib treatment, ZMPSTE24 overexpression, Western blot for PAI-1 and KLF2","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — overexpression/inhibitor epistasis in primary endothelial cells, two orthogonal mechanistic arms (proteasome, ZMPSTE24), single lab","pmids":["34003736"],"is_preprint":false},{"year":2023,"finding":"PAI-1 can bind to proteasome components and inhibit proteasome activity and p53 degradation in lung epithelial cells, promoting cellular senescence; this requires the premature (secretion-competent) form of PAI-1, as a secretion-deficient PAI-1 variant induces senescence markers without inducing p53, showing the premature form mediates proteasome interaction.","method":"Co-immunoprecipitation of PAI-1 with proteasome components, proteasome activity assay, overexpression of wild-type vs. secretion-deficient PAI-1, p53 and p21 Western blot, SA-β-Gal assay in A549 and primary mouse ATII cells","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP + functional activity assay + structure-function comparison of two PAI-1 variants, single lab","pmids":["37566086"],"is_preprint":false},{"year":2023,"finding":"CAF-derived PAI-1 promotes EndoMT in lymphatic endothelial cells by directly interacting with LRP1, activating AKT/ERK1/2 signaling; blockade of PAI-1 or LRP1/AKT/ERK1/2 inhibition abrogates EndoMT and reduces CAF-induced lymphangiogenesis and metastasis in cervical cancer models.","method":"Cytokine antibody arrays, recombinant PAI-1 treatment of LECs, LRP1 inhibition, AKT/ERK1/2 Western blotting, EndoMT marker profiling, transwell/tube formation/transendothelial migration assays, popliteal lymph node metastasis model in vivo","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays + LRP1 epistasis + in vivo model; single lab, direct LRP1 interaction confirmed by inhibitor studies","pmids":["37415190"],"is_preprint":false},{"year":2024,"finding":"PAI-1 regulates the cytoskeleton and intrinsic stiffness of vascular smooth muscle cells (SMCs): PAI-1 inhibition (PAI-039) or siRNA knockdown reduces cytoplasmic F-actin content and cell stiffness; PAI-1 inhibition activates cofilin (an F-actin depolymerase) via AMPK; AMPK inhibition prevents cofilin activation by PAI-039; PAI-039 reduces aortic stiffness in vivo without altering elastin or collagen.","method":"PAI-039 pharmacologic inhibition, siRNA knockdown, atomic force microscopy for cell stiffness, F-actin content assay, cofilin activity assay, AMPK Western blot, RNA sequencing, aortic pulse wave velocity in vivo, PAI-1-deficient murine SMCs as specificity control","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacologic + genetic KO + siRNA with mechanistic epistasis (AMPK inhibition blocks cofilin activation), in vivo validation, multiple orthogonal methods in one rigorous study","pmids":["38868940"],"is_preprint":false}],"current_model":"SERPINE1/PAI-1 is a multifunctional serine protease inhibitor (serpin) that acts as the primary physiological inhibitor of tPA and uPA by forming stable covalent complexes; it is stabilized in its active conformation by binding to the somatomedin B domain of vitronectin (crystal structure resolved); the uPA-PAI-1 complex on cell surfaces is internalized via uPAR-LRP-dependent endocytosis, terminating cell-surface plasminogen activation and recycling the receptor; PAI-1 regulates cell adhesion and migration by competing with uPAR and integrins for vitronectin binding and by signaling through LRP1 to activate β-catenin and ERK1/2; it promotes efferocytosis inhibition via a 'don't eat me' signal involving calreticulin/LRP; it inhibits neutrophil apoptosis through G-protein-coupled receptor/PI3K/Akt signaling; it drives cellular senescence by inhibiting proteasome activity and stabilizing p53, and is sequestered into stress granules to suppress senescence; it promotes tissue fibrosis by blocking plasmin-mediated ECM degradation, recruiting macrophages and myofibroblasts, and activating klotho-loss/p53/TGF-βRI-SMAD3 tubular dysfunction pathways; its transcription is regulated by HIF-1α, HIF-2α, Egr-1, and C/EBPα under hypoxia; and it modulates vascular smooth muscle cytoskeletal stiffness via AMPK-dependent cofilin activation."},"narrative":{"mechanistic_narrative":"SERPINE1 (PAI-1) is the principal physiological inhibitor of the plasminogen activators tPA and uPA, forming stable covalent complexes that terminate cell-surface plasminogen activation, and it serves as a multifunctional regulator of cell adhesion, migration, survival, senescence, and tissue fibrosis [PMID:2157592, PMID:12808446]. As an inhibitor it engages uPA bound to uPAR, and the resulting complex is internalized through an LRP-dependent endocytic cycle that recycles the receptor and switches cells from adhesion to migration; the LRP-binding capacity of PAI-1 is mechanistically essential, since an LRP-binding mutant fails to rescue macrophage migration [PMID:2157592, PMID:11566185, PMID:16601674]. PAI-1 is conformationally stabilized in its active state by binding the somatomedin B domain of vitronectin, a structurally defined interaction that lets PAI-1 sterically compete with uPAR and integrins for vitronectin and thereby modulate adhesion [PMID:10190280, PMID:12437099, PMID:12808446]. Beyond proteolysis control, PAI-1 signals through LRP1/VLDLr to activate β-catenin and ERK1/2 and drives cell motility, survival, and proliferation [PMID:17696882, PMID:25694133, PMID:37415190]; it functions as a calreticulin-associated \"don't eat me\" signal that limits efferocytosis and inhibits neutrophil apoptosis via a Gi/PI3K/Akt axis independent of uPAR, LRP, or vitronectin [PMID:18689689, PMID:21622848]. PAI-1 promotes cellular senescence by binding proteasome components to inhibit proteasome activity and stabilize p53, and its sequestration into stress granules suppresses senescence [PMID:29592859, PMID:37566086]. In tissue injury PAI-1 drives fibrosis by recruiting macrophages and myofibroblasts and by activating klotho-loss/p53/TGF-βRI-SMAD3 tubular dysfunction, and it exacerbates inflammation by blocking tPA-mediated activation of TGF-β [PMID:11473641, PMID:30842312, PMID:34110636]. Its transcription is induced under hypoxia by HIF-1α, HIF-2α, Egr-1, and C/EBP α [PMID:17197388, PMID:25489981].","teleology":[{"year":1990,"claim":"Established that PAI-1 binding does more than block protease activity — it triggers receptor-mediated clearance, defining the endocytic cycle that terminates surface plasminogen activation.","evidence":"Radiolabeled ligand internalization with chloroquine block and acid-wash fractionation in U937 cells","pmids":["2157592"],"confidence":"High","gaps":["The internalization receptor (later LRP) was not yet identified","Did not address downstream signaling consequences of internalization"]},{"year":1990,"claim":"Linked PAI-1 induction to TGF-β signaling, showing PAI-1 is a transcriptionally inducible node coupling growth-factor cues to net plasminogen activator activity.","evidence":"Northern blot, ELISA, and caseinolytic activity assay in TGF-β1-treated primary bronchial epithelial cells","pmids":["2221087"],"confidence":"Medium","gaps":["Promoter elements mediating induction not mapped here","Restricted to one cell type and differentiation context"]},{"year":1991,"claim":"Mapped PAI-1 distribution to hemostatic and inflammatory tissues/cells, framing where its functions are physiologically deployed.","evidence":"Tissue activity assay and immunohistochemistry across human tissue panels","pmids":["1864986"],"confidence":"Medium","gaps":["No functional consequence tied to localization","Descriptive survey only"]},{"year":2003,"claim":"Resolved the structural basis for PAI-1 stabilization and adhesion control by capturing the PAI-1–somatomedin B complex, explaining steric competition with uPAR and integrins.","evidence":"X-ray crystallography of the PAI-1–SMB complex at 2.3 Å, with binding-interface analysis; corroborated by earlier domain-mapping and competition assays","pmids":["12808446","10190280","12437099"],"confidence":"High","gaps":["Structure does not capture the protease-inhibitor (tPA/uPA) covalent complex conformation","Secondary low-affinity vitronectin site not fully resolved"]},{"year":2006,"claim":"Placed PAI-1 precisely in a fibrin–tPA–PAI-1–LRP cascade governing the adhesion-to-detachment switch in migrating macrophages, demonstrating that the LRP-binding function is mechanistically required.","evidence":"Genetic KO of Mac-1, tPA, PAI-1, and LRP with rescue by wild-type vs. LRP-binding-deficient PAI-1 mutant in migration assays","pmids":["16601674","11566185"],"confidence":"High","gaps":["Generalizability of the ternary complex to non-macrophage cells not established here","Did not define the cytoskeletal effectors downstream of LRP endocytosis"]},{"year":2006,"claim":"Defined the transcriptional logic of hypoxic PAI-1 induction, identifying three promoter-binding factors that cooperatively confer oxygen sensitivity.","evidence":"Promoter mutagenesis, EMSA supershift, and ChIP for Egr-1, HIF-1α, and C/EBPα in primary macrophages","pmids":["17197388"],"confidence":"High","gaps":["Relative weighting of factors may be cell-type dependent","Did not address HIF-2α contribution (later shown in HCC)"]},{"year":2008,"claim":"Revealed a non-proteolytic immune role: surface PAI-1 acting with calreticulin as a 'don't eat me' signal that gates LRP-dependent efferocytosis.","evidence":"PAI-1(-/-) mice, antibody blockade, recombinant add-back, and colocalization microscopy on neutrophils","pmids":["18689689"],"confidence":"High","gaps":["Molecular nature of the PAI-1/calreticulin association not structurally defined","Whether this operates in tissues beyond neutrophils unclear"]},{"year":2011,"claim":"Distinguished a receptor-independent anti-apoptotic pathway, showing PAI-1 prolongs neutrophil survival via Gi-coupled receptor/PI3K/Akt signaling separate from its uPAR/LRP/vitronectin functions.","evidence":"PAI-1(-/-) mice, pertussis toxin, PI3K inhibitors, receptor blockade, and in vivo LPS lung injury","pmids":["21622848"],"confidence":"High","gaps":["The specific GPCR mediating the effect not identified","How the inhibitory and signaling activities of PAI-1 are partitioned in vivo unresolved"]},{"year":2014,"claim":"Provided a structural rationale for PAI-1's pro-survival/pro-proliferative signaling by mapping a cryptic VLDLr-binding site exposed upon uPA inhibition, absent in PAI-2.","evidence":"Biochemical/structural comparison of PAI-1 vs. PAI-2 binding to VLDLr with tyrosine phosphorylation and proliferation assays","pmids":["17696882"],"confidence":"Medium","gaps":["Single-lab structural inference","In vivo relevance of VLDLr signaling not tested"]},{"year":2015,"claim":"Dissected the LRP1 signaling output of PAI-1, separating β-catenin transcriptional activation from ERK1/2 modulation in migration control.","evidence":"Isogenic LRP1-KO MEFs, β-catenin reporter, siRNA epistasis, and motility assays","pmids":["25694133"],"confidence":"Medium","gaps":["LRP1-independent ERK1/2 receptor not identified","Single cell-system epistasis"]},{"year":2018,"claim":"Connected PAI-1 subcellular sequestration to cell-cycle control, showing stress-granule recruitment of PAI-1 sustains a proliferative, non-senescent state.","evidence":"Stress granule induction, PAI-1 colocalization, cyclin D1 fractionation and Rb phosphorylation in pre-senescent cells","pmids":["29592859"],"confidence":"Medium","gaps":["Direct demonstration that PAI-1 within SGs is functionally inert is incomplete","Mechanism of PAI-1 recruitment to SGs unknown"]},{"year":2021,"claim":"Defined converging intracellular pathways by which PAI-1 drives renal tubular dysfunction, linking it to klotho loss, p53 stabilization, and TGF-βRI-SMAD3 signaling independent of TGF-β1 ligand synthesis.","evidence":"Stable PAI-1 overexpression in HK-2 cells with klotho rescue, p53 siRNA, and TGF-βRI inhibition plus differentiation/apoptosis readouts","pmids":["34110636","11473641","34725920"],"confidence":"High","gaps":["How extracellular/cell-surface PAI-1 engages these intracellular pathways mechanistically not bridged","Receptor mediating TGF-βRI activation not identified"]},{"year":2023,"claim":"Identified a direct intracellular mechanism for PAI-1-driven senescence: binding proteasome components to inhibit proteasome activity and stabilize p53, requiring the premature secretion-competent form.","evidence":"Co-IP with proteasome components, proteasome activity assay, and wild-type vs. secretion-deficient PAI-1 comparison in lung epithelial cells","pmids":["37566086"],"confidence":"Medium","gaps":["Single-lab Co-IP without reciprocal/structural validation of the proteasome interface","Reconciliation with the stress-granule senescence-suppressing role not addressed"]},{"year":2024,"claim":"Established a cytoskeletal/mechanical function, showing PAI-1 maintains vascular smooth muscle stiffness by restraining AMPK-dependent cofilin activation and F-actin turnover.","evidence":"PAI-039 inhibition, siRNA knockdown, atomic force microscopy, cofilin/AMPK assays and in vivo aortic pulse wave velocity, with PAI-1-deficient SMCs as control","pmids":["38868940"],"confidence":"High","gaps":["The receptor/sensor coupling extracellular PAI-1 to intracellular AMPK not identified","Relationship to the RhoA/ROCK1 amoeboid program in cancer cells unresolved"]},{"year":null,"claim":"How PAI-1's distinct molecular activities — protease inhibition, vitronectin-stabilized adhesion control, LRP/VLDLr signaling, intracellular proteasome and cytoskeletal regulation — are coordinated and partitioned within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking secreted vs. intracellular PAI-1 pools","Receptors for several signaling and senescence functions remain unidentified","Conflicting senescence roles (proteasome inhibition vs. stress-granule sequestration) not reconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,8,24]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,8,19,30]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[6,12,16,21,31]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[23,30]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,13,17]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[3,7,8,17]},{"term_id":"GO:0005576","term_label":"extracellular 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new perspectives for a known set of predictive markers.","date":"2010","source":"Current medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20939809","citation_count":21,"is_preprint":false},{"pmid":"19055748","id":"PMC_19055748","title":"PAI-1 and functional blockade of SNAI1 in breast cancer cell migration.","date":"2008","source":"Breast cancer research : BCR","url":"https://pubmed.ncbi.nlm.nih.gov/19055748","citation_count":21,"is_preprint":false},{"pmid":"37566086","id":"PMC_37566086","title":"PAI-1 Regulation of p53 Expression and Senescence in Type II Alveolar Epithelial Cells.","date":"2023","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/37566086","citation_count":20,"is_preprint":false},{"pmid":"35618711","id":"PMC_35618711","title":"Transgenic Anopheles mosquitoes expressing human PAI-1 impair malaria transmission.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/35618711","citation_count":20,"is_preprint":false},{"pmid":"31315131","id":"PMC_31315131","title":"Plasminogen activator inhibitor-1 (PAI-1) expression in endometriosis.","date":"2019","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/31315131","citation_count":20,"is_preprint":false},{"pmid":"26658948","id":"PMC_26658948","title":"Role of ACE and PAI-1 Polymorphisms in the Development and Progression of Diabetic Retinopathy.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26658948","citation_count":20,"is_preprint":false},{"pmid":"32142912","id":"PMC_32142912","title":"PAI-1 is involved in delayed bone repair induced by glucocorticoids in mice.","date":"2020","source":"Bone","url":"https://pubmed.ncbi.nlm.nih.gov/32142912","citation_count":20,"is_preprint":false},{"pmid":"24833884","id":"PMC_24833884","title":"Expression of Bmi-1 and PAI-1 in esophageal squamous cell carcinoma.","date":"2014","source":"World journal of gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/24833884","citation_count":18,"is_preprint":false},{"pmid":"20737565","id":"PMC_20737565","title":"Association of PAI-1 gene polymorphism with survival and chemotherapy-related vascular toxicity in testicular cancer.","date":"2010","source":"Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/20737565","citation_count":18,"is_preprint":false},{"pmid":"23589033","id":"PMC_23589033","title":"Relationship between post-SARS osteonecrosis and PAI-1 4G/5G gene polymorphisms.","date":"2013","source":"European journal of orthopaedic surgery & traumatology : orthopedie traumatologie","url":"https://pubmed.ncbi.nlm.nih.gov/23589033","citation_count":18,"is_preprint":false},{"pmid":"26979769","id":"PMC_26979769","title":"Cell density-dependent stimulation of PAI-1 and hyaluronan synthesis by TGF-β in orbital fibroblasts.","date":"2016","source":"The Journal of endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/26979769","citation_count":17,"is_preprint":false},{"pmid":"35842542","id":"PMC_35842542","title":"PAI-1 is a potential transcriptional silencer that supports bladder cancer cell activity.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/35842542","citation_count":15,"is_preprint":false},{"pmid":"35243423","id":"PMC_35243423","title":"Ligand-mediated PAI-1 inhibition in a mouse model of peritoneal carcinomatosis.","date":"2022","source":"Cell reports. 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free uPA, ATF, or DFP-uPA are not internalized, demonstrating that PAI-1 binding to uPA triggers a specific receptor-mediated endocytic cycle.\",\n      \"method\": \"Radiolabeled ligand internalization assay with chloroquine inhibition and acid-wash fractionation in U937 cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean ligand-tracking experiment with multiple controls (acid wash, chloroquine), replicated across conditions; foundational mechanism paper\",\n      \"pmids\": [\"2157592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"TGF-β1 increases PAI-1 mRNA (~50-fold) and protein in human bronchial epithelial cells, resulting in a net ~50% reduction in plasminogen activator activity in conditioned medium; the effect requires a TGF-β-responsive differentiation pathway and is absent in cells that do not undergo squamous differentiation.\",\n      \"method\": \"Northern blot, ELISA, caseinolytic plasminogen activator activity assay in NHBE cells treated with TGF-β1\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (mRNA, protein, activity) in primary cells, single lab\",\n      \"pmids\": [\"2221087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"PAI-1 protein and activity are distributed throughout the body, with highest abundance in liver and spleen; immunochemical staining localizes PAI-1 to endothelium, platelets, megakaryocytes, neutrophils, macrophages, vascular smooth muscle cells, and mesangial cells, placing it at sites of hemostasis and inflammation.\",\n      \"method\": \"Tissue extraction with functional PAI-1 activity assay and immunohistochemistry with monoclonal antibodies on human tissue panels\",\n      \"journal\": \"Journal of clinical pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — systematic tissue survey with functional activity + IHC, multiple tissues; no functional consequence directly linked\",\n      \"pmids\": [\"1864986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PAI-1 regulates uPAR-mediated cell adhesion to vitronectin by competing with uPAR for binding to the somatomedin B (SMB) domain of vitronectin; PAI-1 binding to the SMB domain also sterically hinders integrin binding to the adjacent RGD sequence, thereby modulating both uPAR- and integrin-mediated cell adhesion.\",\n      \"method\": \"Competitive binding assays and cell adhesion assays with defined recombinant proteins and domain-specific inhibitors\",\n      \"journal\": \"APMIS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reconstituted competitive binding with defined protein domains, single lab\",\n      \"pmids\": [\"10190280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PAI-1 expression in wounded keratinocyte monolayers is required for normal wound repair: PAI-1 knockdown via antisense markedly impairs wound closure, while addition of recombinant PAI-1 rescues the defect; PAI-1 also rescues keratinocytes from plasminogen-induced substrate detachment/anoikis and enhances cell spread area.\",\n      \"method\": \"Antisense-mediated knockdown, recombinant PAI-1 rescue, PAI-1-neutralizing antibodies, wound-scratch assay, and cell spreading/anoikis assays in HaCaT keratinocytes\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with rescue using recombinant protein, multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"10896775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAI-1 deficiency attenuates renal fibrosis after ureteral obstruction; one key mechanism is that PAI-1 promotes the recruitment of fibrosis-inducing cells (macrophages and myofibroblasts), independently of changes in net renal plasminogen activator or plasmin activity.\",\n      \"method\": \"PAI-1 knockout vs. wild-type mouse comparison after UUO; interstitial fibrosis quantified by picrosirius red and collagen assay; cellular infiltrate by immunostaining; TGF-β and procollagen mRNAs by RT-PCR\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (histology, biochemistry, gene expression), clear mechanistic separation from plasmin activity\",\n      \"pmids\": [\"11473641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAI-1 inhibits uPA-induced chemotaxis by triggering internalization of the uPAR via LRP; blocking LRP with the 39 kDa RAP or anti-LRP antibodies prevents uPAR internalization and converts the uPA-PAI-1 complex from a migration inhibitor into a chemoattractant that activates cytoskeletal reorganization and ERK/MAPK.\",\n      \"method\": \"Chemotaxis assays, anti-LRP antibody/RAP inhibition, cytoskeletal staining, ERK phosphorylation blotting\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via receptor blockade, multiple functional readouts (chemotaxis, ERK, cytoskeleton), single lab\",\n      \"pmids\": [\"11566185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Mapping studies define the PAI-1 binding region on vitronectin to the N-terminal somatomedin B (SMB) domain, and the vitronectin-binding region on PAI-1 to the area around α-helices E and F; a secondary low-affinity PAI-1 binding site in the C-terminal region of vitronectin may support larger PAI-1/VN complexes.\",\n      \"method\": \"Peptide/domain competition binding assays, mutagenesis-based mapping, biochemical interaction studies reviewed from multiple labs\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-mapping with peptide competition across multiple labs, partially replicated; binding site not fully resolved per authors\",\n      \"pmids\": [\"12437099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure (2.3 Å) of the PAI-1–somatomedin B (SMB) domain complex shows that vitronectin binding stabilizes the active conformation of PAI-1; structural analysis further reveals that PAI-1 sterically competes with uPAR and integrins for binding to vitronectin, explaining PAI-1's regulation of cell adhesion and tissue effects.\",\n      \"method\": \"X-ray crystallography of PAI-1–SMB complex at 2.3 Å resolution with structural interpretation of binding interfaces\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with direct mechanistic interpretation of binding competition; structural basis for multiple biological functions established\",\n      \"pmids\": [\"12808446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"tPA contains two independent vasoactive epitopes with opposite effects on vascular tone; PAI-1 and a PAI-1-derived hexapeptide regulate these effects by binding tPA, and the stimulatory (vasoconstrictive) effect of tPA is mediated through LRP, as demonstrated by anti-LRP antibody blockade in isolated aorta rings and in vivo.\",\n      \"method\": \"Isolated aorta ring contraction assay, anti-LRP antibodies, tPA knockout mice, in vivo blood pressure and cerebrovascular resistance measurements in rats\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro organ assay plus in vivo pharmacology with receptor blockade; novel mechanistic context for PAI-1 in vascular tone\",\n      \"pmids\": [\"14512309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Efficient macrophage migration in an inflammatory environment requires the ordered formation of a fibrin–tPA–PAI-1 ternary complex at the cell surface: tPA promotes Mac-1-mediated adhesion to fibrin, PAI-1 inhibition of tPA exposes a site for LRP binding, and LRP-mediated endocytosis triggers the switch from adhesion to detachment. Genetic inactivation of PAI-1 abrogates macrophage migration, and this defect is rescued by wild-type PAI-1 but not by an LRP-binding mutant of PAI-1.\",\n      \"method\": \"Genetic KO of Mac-1, tPA, PAI-1, LRP in mice; in vitro migration assays; rescue with wild-type vs. LRP-binding-deficient PAI-1 mutant\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic KOs with mechanistic rescue using structure-function mutant; pathway position precisely defined\",\n      \"pmids\": [\"16601674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Hypoxia-induced PAI-1 transcription in macrophages is driven by three transcription factors—Egr-1, HIF-1α, and C/EBPα—all of which bind the PAI-1 promoter under hypoxia; mutation of each binding site reduces hypoxia-sensitivity, and ChIP confirms all three factors bind chromatin under hypoxic conditions. HIF-1α dominates but Egr-1 and C/EBPα greatly augment and can act independently.\",\n      \"method\": \"PAI-1 promoter deletion/mutation constructs, transfection, ChIP, gel-shift (EMSA) with supershift analysis, primary macrophage validation\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — promoter mutagenesis + EMSA supershift + ChIP, replicated in primary cells; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"17197388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PAI-1 inhibition of uPA by PAI-1 exposes a cryptic high-affinity binding site on the PAI-1 moiety for the VLDLr (very-low-density-lipoprotein receptor), sustaining cell signaling and promoting proliferation of breast cancer cells; PAI-2, despite also inhibiting uPA, does not contain this VLDLr binding site and does not sustain global tyrosine phosphorylation or cell proliferation, providing a structural basis for the divergent outcomes of PAI-1 vs. PAI-2 in cancer.\",\n      \"method\": \"Biochemical and structural analyses of PAI-1 vs. PAI-2 binding to VLDLr; global protein tyrosine phosphorylation assays; cell proliferation assays with uPA-PAI-1 vs. uPA-PAI-2 complexes\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — structural and functional comparison with receptor-binding and signaling assays, single lab, two orthogonal methods\",\n      \"pmids\": [\"17696882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PAI-1 acts as a 'don't eat me' signal on viable neutrophils: surface PAI-1 colocalizes with calreticulin (CRT) on viable neutrophils and limits LRP-dependent phagocytosis; during apoptosis PAI-1 levels decrease on the cell surface, CRT colocalization is lost, and the increase in available CRT drives enhanced efferocytosis via LRP.\",\n      \"method\": \"PAI-1(-/-) mice, anti-PAI-1 antibody blockade, recombinant PAI-1 add-back, LRP/calreticulin functional studies, colocalization by fluorescence microscopy\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus antibody blockade plus recombinant rescue, multiple mechanistic readouts (phagocytosis, colocalization, receptor identification)\",\n      \"pmids\": [\"18689689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SERPINE1 (PAI-1) protein is deposited into keratinocyte migration trails during wound repair; addition of recombinant PAI-1 stimulates directional motility in PAI-1(-/-) cells, and antibody-mediated PAI-1 blockade attenuates migration and causes apoptosis; the rescue from plasminogen-induced anoikis by PAI-1 identifies it as a keratinocyte survival factor.\",\n      \"method\": \"PAI-1-GFP live imaging, recombinant PAI-1 addition to PAI-1(-/-) cells, antisense knockdown, neutralizing antibodies, anoikis assay\",\n      \"journal\": \"Archives of dermatological research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live imaging + genetic KO + rescue + antibody blockade, multiple orthogonal methods; PAI-1 mechanistic role in migration trails directly visualized\",\n      \"pmids\": [\"18386027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAI-1 mediates the TGF-β1+EGF-induced 'scatter' (EMT) response in transformed keratinocytes: PAI-1 is the most highly induced transcript; MEK/ERK and p38 inhibition abolishes both maximal PAI-1 upregulation and cell locomotion; PAI-1 knockdown alone blocks TGF-β1+EGF-dependent scattering; and EGFR knockdown attenuates TGF-β1-induced PAI-1 expression, placing EGFR transactivation upstream of PAI-1 induction.\",\n      \"method\": \"mRNA profiling, MEK/p38 pharmacologic inhibition, PAI-1 siRNA knockdown, EGFR knockdown, wound scatter assay\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown with functional rescue, epistasis by kinase inhibitors and EGFR KD, single lab\",\n      \"pmids\": [\"20428185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAI-1 inhibits neutrophil apoptosis through pertussis-toxin-sensitive G-protein-coupled receptors and PI3K, activating PKB/Akt, Mcl-1, and Bcl-xL; uPAR, LRP, and vitronectin are not required for this antiapoptotic function; in vivo, PAI-1(-/-) mice show enhanced neutrophil apoptosis in LPS-induced lung injury.\",\n      \"method\": \"PAI-1(-/-) mice, pertussis toxin, selective PI3K inhibitors, uPAR/LRP/vitronectin blockade, apoptosis assays, in vivo LPS-lung injury model\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus systematic receptor exclusion plus in vivo model; PI3K/Akt pathway identified with multiple inhibitors\",\n      \"pmids\": [\"21622848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Matrix-bound PAI-1 maintains cell blebbing (amoeboid migration) in colorectal cancer cells via the RhoA/ROCK1/MLC-P pathway; PAI-1 localizes PDK1 and ROCK1 to the cell membrane and sustains RhoA/ROCK1 activation, as determined by immunoblotting, activity assay, and immunofluorescence.\",\n      \"method\": \"Immunoblotting, ROCK1 activity assay, immunofluorescence, PAI-1 depletion in SW620 cells, RhoA pathway inhibition\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional PAI-1 depletion with multiple pathway readouts in cancer cells, single lab\",\n      \"pmids\": [\"22363817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"16K prolactin (16K PRL) binds PAI-1 directly; loss of PAI-1 abrogates the antitumoral and antiangiogenic effects of 16K PRL; mechanistically, PAI-1 bound to the PAI-1–uPA–uPAR ternary complex exerts antiangiogenic effects, while 16K PRL inhibition of PAI-1's antifibrinolytic activity promotes arterial thrombolysis.\",\n      \"method\": \"Direct binding assay of 16K PRL and PAI-1, PAI-1 KO mouse models, in vivo tumor and angiogenesis assays, fibrin clot lysis assay\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding established, genetic KO, in vivo rescue; mechanistic pathway (PAI-1–uPA–uPAR) validated in multiple model systems\",\n      \"pmids\": [\"24929950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RNA aptamers that bind PAI-1 with nanomolar affinity inhibit its antiproteolytic activity against tPA, disrupt formation of the stable covalent PAI-1-tPA complex, and increase levels of cleaved (inactive) PAI-1; this identifies the tPA-docking region of PAI-1 as functionally targetable.\",\n      \"method\": \"SELEX aptamer generation, in vitro PAI-1 inhibition assay, complex formation assay, cleaved PAI-1 quantification\",\n      \"journal\": \"Nucleic acid therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted activity assay, direct binding affinity measurement; single lab\",\n      \"pmids\": [\"24922319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HIF-2α (not HIF-1α) drives PAI-1 expression in hepatocellular carcinoma cells; PAI-1 knockdown attenuates angiogenesis in coculture models; rescuing the HIF-2α knockdown by blocking plasmin (with aprotinin) restores angiogenesis, establishing the HIF-2α→PAI-1→reduced-plasmin→pro-angiogenic axis.\",\n      \"method\": \"Stable shRNA knockdown of HIF-1α/HIF-2α in HepG2, microarray identification of PAI-1 as target, PAI-1 knockdown, plasmin inhibition rescue, HepG2 spheroid-embryoid body coculture angiogenesis model\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by knockdown + pharmacologic rescue, microarray target identification confirmed functionally, single lab\",\n      \"pmids\": [\"25489981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAI-1 promotes cell migration in an LRP1-dependent manner by activating β-catenin transcriptional activity and modulating ERK1/2; in LRP1-deficient MEFs, PAI-1-induced β-catenin responses are absent while ERK1/2 activation is enhanced, and knockdown of β-catenin abolishes the LRP1-independent ERK1/2 response.\",\n      \"method\": \"Wild-type vs. LRP1-KO MEFs, PAI-1 treatment, β-catenin reporter assay, ERK1/2 and β-catenin Western blotting, siRNA knockdown, proliferation and motility assays\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic cell pairs plus siRNA epistasis, multiple signaling readouts, single lab\",\n      \"pmids\": [\"25694133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Thrombin mediates PAI-1 mRNA expression and keratinocyte migration via PAR-1 transactivation of EGFR, downstream ERK1/2 activation, and phosphorylation of Smad2 linker region at Ser250 specifically; ERK1/2 inhibition (not p38 or JNK) blocks Smad2 linker phosphorylation, PAI-1 induction, and migration.\",\n      \"method\": \"Pharmacologic inhibitors (UO126, SB202190, SP600125), Western blot for Smad2 phospho-sites, 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 / Moderate — specific residue-level phosphorylation mapping + migration assay + selective kinase inhibitors, single lab\",\n      \"pmids\": [\"29577978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PAI-1 is recruited to stress granules (SGs) in pre-senescent cells; SG assembly increases nuclear cyclin D1 translocation and Rb phosphorylation, maintaining a proliferative non-senescent state; PAI-1 sequestration in SGs is the mechanism linking SG formation to inhibition of senescence.\",\n      \"method\": \"Stress granule induction, PAI-1 colocalization with SG markers, cyclin D1 nuclear fractionation, Rb phosphorylation Western blot, senescence markers (SA-β-Gal) in proliferative and presenescent cells\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — subcellular localization linked to functional consequence (Rb phosphorylation, senescence markers), single lab\",\n      \"pmids\": [\"29592859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In colitis, PAI-1 exacerbates mucosal damage by blocking tPA-mediated cleavage and activation of anti-inflammatory TGF-β; inhibition of PAI-1 reduces both mucosal damage and inflammation in mouse models, placing PAI-1 upstream of tPA-dependent TGF-β activation in intestinal inflammation.\",\n      \"method\": \"Mouse colitis models, PAI-1 inhibitor treatment, tPA measurement, TGF-β activation assay, intestinal injury quantification\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic pathway (PAI-1→blocks tPA→blocks TGF-β activation) established with pharmacologic inhibition and functional readouts in vivo, validated across multiple cohorts\",\n      \"pmids\": [\"30842312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Tumor-secreted PAI-1 activates adipocytes via PI3K/AKT signaling, promoting nuclear translocation of FOXP1 which enhances PLOD2 promoter activity in cancer-associated adipocytes, driving collagen reorganization and breast cancer metastasis; pharmacologic blockade of PAI-1 or PLOD2 disrupts this collagen reorganization.\",\n      \"method\": \"3D collagen invasion assay, co-culture, proteomics, ELISA, qPCR, Western blot, ChIP, loss-of-function assays, in vivo mouse co-implantation model\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for FOXP1 at PLOD2 promoter, PI3K/AKT inhibition epistasis, in vivo validation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31170987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Glomerular endothelial cell-derived PAI-1 drives podocyte apoptosis and age-related glomerular lesions; selective endothelial inactivation of PAI-1 protects glomeruli from lesion development and podocyte loss in aged mice; blocking PAI-1 in supernatants from senescent endothelial cells in vitro prevents podocyte apoptosis.\",\n      \"method\": \"Endothelial-specific PAI-1 conditional KO mice, aged mouse glomerular phenotype, conditioned medium from senescent endothelial cells + PAI-1 blockade, podocyte apoptosis assay\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic KO, in vitro conditioned medium rescue, mechanistic link established between endothelial PAI-1 and podocyte apoptosis\",\n      \"pmids\": [\"34725920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PAI-1 promotes renal tubular dysfunction via three converging pathways: (1) PAI-1 overexpression reduces klotho expression, (2) elevates p53, and (3) activates TGF-βRI/II-SMAD3 signaling, leading to dedifferentiation, G2/M arrest, fibrogenesis, and apoptosis; ectopic klotho restoration attenuates fibrogenesis and proliferative defects; genetic p53 suppression reverses PAI-1-driven maladaptive repair; TGF-βRI inhibition attenuates PAI-1-initiated epithelial dysfunction independently of TGF-β1 ligand synthesis.\",\n      \"method\": \"Stable PAI-1 overexpression in HK-2 cells, klotho rescue, p53 siRNA knockdown, TGF-βRI inhibitor, Western blot for E-cadherin/vimentin/fibronectin/collagen/CCN2/p-Histone3/p21/cleaved caspase-3, annexin-V flow cytometry\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic/pharmacologic epistasis experiments with specific mechanistic rescue of each pathway arm, multiple orthogonal readouts, single rigorous study\",\n      \"pmids\": [\"34110636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PAI-1 directly regulates transcription of genes involved in lipid homeostasis including PCSK9 and FGF21; pharmacologic or genetic reduction in PAI-1 activity ameliorates hyperlipidemia in vivo; genetic PAI-1 deficiency in humans is associated with reduced plasma PCSK9 levels.\",\n      \"method\": \"RNA sequencing in PAI-1-deficient vs. wild-type mice, pharmacologic PAI-1 inhibition in vivo, human genetic cohort PCSK9 measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq in KO + pharmacologic inhibition + human genetic validation; mechanism (direct transcriptional regulation) inferred from KO transcriptomics, not direct promoter assays\",\n      \"pmids\": [\"33432099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SARS-CoV-2 spike protein (S1) stimulates PAI-1 production in human pulmonary microvascular endothelial cells; proteasomal degradation inhibition by bortezomib also induces PAI-1 but upregulates the repressor KLF2; ZMPSTE24 overexpression blunts spike-induced PAI-1 production, identifying ZMPSTE24-dependent proteasomal regulation as a control mechanism for endothelial PAI-1.\",\n      \"method\": \"Recombinant SARS-CoV-2-S1 treatment of HPMECs, bortezomib treatment, ZMPSTE24 overexpression, Western blot for PAI-1 and KLF2\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — overexpression/inhibitor epistasis in primary endothelial cells, two orthogonal mechanistic arms (proteasome, ZMPSTE24), single lab\",\n      \"pmids\": [\"34003736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PAI-1 can bind to proteasome components and inhibit proteasome activity and p53 degradation in lung epithelial cells, promoting cellular senescence; this requires the premature (secretion-competent) form of PAI-1, as a secretion-deficient PAI-1 variant induces senescence markers without inducing p53, showing the premature form mediates proteasome interaction.\",\n      \"method\": \"Co-immunoprecipitation of PAI-1 with proteasome components, proteasome activity assay, overexpression of wild-type vs. secretion-deficient PAI-1, p53 and p21 Western blot, SA-β-Gal assay in A549 and primary mouse ATII cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP + functional activity assay + structure-function comparison of two PAI-1 variants, single lab\",\n      \"pmids\": [\"37566086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CAF-derived PAI-1 promotes EndoMT in lymphatic endothelial cells by directly interacting with LRP1, activating AKT/ERK1/2 signaling; blockade of PAI-1 or LRP1/AKT/ERK1/2 inhibition abrogates EndoMT and reduces CAF-induced lymphangiogenesis and metastasis in cervical cancer models.\",\n      \"method\": \"Cytokine antibody arrays, recombinant PAI-1 treatment of LECs, LRP1 inhibition, AKT/ERK1/2 Western blotting, EndoMT marker profiling, transwell/tube formation/transendothelial migration assays, popliteal lymph node metastasis model in vivo\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays + LRP1 epistasis + in vivo model; single lab, direct LRP1 interaction confirmed by inhibitor studies\",\n      \"pmids\": [\"37415190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PAI-1 regulates the cytoskeleton and intrinsic stiffness of vascular smooth muscle cells (SMCs): PAI-1 inhibition (PAI-039) or siRNA knockdown reduces cytoplasmic F-actin content and cell stiffness; PAI-1 inhibition activates cofilin (an F-actin depolymerase) via AMPK; AMPK inhibition prevents cofilin activation by PAI-039; PAI-039 reduces aortic stiffness in vivo without altering elastin or collagen.\",\n      \"method\": \"PAI-039 pharmacologic inhibition, siRNA knockdown, atomic force microscopy for cell stiffness, F-actin content assay, cofilin activity assay, AMPK Western blot, RNA sequencing, aortic pulse wave velocity in vivo, PAI-1-deficient murine SMCs as specificity control\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacologic + genetic KO + siRNA with mechanistic epistasis (AMPK inhibition blocks cofilin activation), in vivo validation, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"38868940\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SERPINE1/PAI-1 is a multifunctional serine protease inhibitor (serpin) that acts as the primary physiological inhibitor of tPA and uPA by forming stable covalent complexes; it is stabilized in its active conformation by binding to the somatomedin B domain of vitronectin (crystal structure resolved); the uPA-PAI-1 complex on cell surfaces is internalized via uPAR-LRP-dependent endocytosis, terminating cell-surface plasminogen activation and recycling the receptor; PAI-1 regulates cell adhesion and migration by competing with uPAR and integrins for vitronectin binding and by signaling through LRP1 to activate β-catenin and ERK1/2; it promotes efferocytosis inhibition via a 'don't eat me' signal involving calreticulin/LRP; it inhibits neutrophil apoptosis through G-protein-coupled receptor/PI3K/Akt signaling; it drives cellular senescence by inhibiting proteasome activity and stabilizing p53, and is sequestered into stress granules to suppress senescence; it promotes tissue fibrosis by blocking plasmin-mediated ECM degradation, recruiting macrophages and myofibroblasts, and activating klotho-loss/p53/TGF-βRI-SMAD3 tubular dysfunction pathways; its transcription is regulated by HIF-1α, HIF-2α, Egr-1, and C/EBPα under hypoxia; and it modulates vascular smooth muscle cytoskeletal stiffness via AMPK-dependent cofilin activation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SERPINE1 (PAI-1) is the principal physiological inhibitor of the plasminogen activators tPA and uPA, forming stable covalent complexes that terminate cell-surface plasminogen activation, and it serves as a multifunctional regulator of cell adhesion, migration, survival, senescence, and tissue fibrosis [#0, #8]. As an inhibitor it engages uPA bound to uPAR, and the resulting complex is internalized through an LRP-dependent endocytic cycle that recycles the receptor and switches cells from adhesion to migration; the LRP-binding capacity of PAI-1 is mechanistically essential, since an LRP-binding mutant fails to rescue macrophage migration [#0, #6, #10]. PAI-1 is conformationally stabilized in its active state by binding the somatomedin B domain of vitronectin, a structurally defined interaction that lets PAI-1 sterically compete with uPAR and integrins for vitronectin and thereby modulate adhesion [#3, #7, #8]. Beyond proteolysis control, PAI-1 signals through LRP1/VLDLr to activate β-catenin and ERK1/2 and drives cell motility, survival, and proliferation [#12, #21, #31]; it functions as a calreticulin-associated \\\"don't eat me\\\" signal that limits efferocytosis and inhibits neutrophil apoptosis via a Gi/PI3K/Akt axis independent of uPAR, LRP, or vitronectin [#13, #16]. PAI-1 promotes cellular senescence by binding proteasome components to inhibit proteasome activity and stabilize p53, and its sequestration into stress granules suppresses senescence [#23, #30]. In tissue injury PAI-1 drives fibrosis by recruiting macrophages and myofibroblasts and by activating klotho-loss/p53/TGF-βRI-SMAD3 tubular dysfunction, and it exacerbates inflammation by blocking tPA-mediated activation of TGF-β [#5, #24, #27]. Its transcription is induced under hypoxia by HIF-1α, HIF-2α, Egr-1, and C/EBP α [#11, #20].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established that PAI-1 binding does more than block protease activity — it triggers receptor-mediated clearance, defining the endocytic cycle that terminates surface plasminogen activation.\",\n      \"evidence\": \"Radiolabeled ligand internalization with chloroquine block and acid-wash fractionation in U937 cells\",\n      \"pmids\": [\"2157592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The internalization receptor (later LRP) was not yet identified\", \"Did not address downstream signaling consequences of internalization\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Linked PAI-1 induction to TGF-β signaling, showing PAI-1 is a transcriptionally inducible node coupling growth-factor cues to net plasminogen activator activity.\",\n      \"evidence\": \"Northern blot, ELISA, and caseinolytic activity assay in TGF-β1-treated primary bronchial epithelial cells\",\n      \"pmids\": [\"2221087\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Promoter elements mediating induction not mapped here\", \"Restricted to one cell type and differentiation context\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Mapped PAI-1 distribution to hemostatic and inflammatory tissues/cells, framing where its functions are physiologically deployed.\",\n      \"evidence\": \"Tissue activity assay and immunohistochemistry across human tissue panels\",\n      \"pmids\": [\"1864986\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence tied to localization\", \"Descriptive survey only\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Resolved the structural basis for PAI-1 stabilization and adhesion control by capturing the PAI-1–somatomedin B complex, explaining steric competition with uPAR and integrins.\",\n      \"evidence\": \"X-ray crystallography of the PAI-1–SMB complex at 2.3 Å, with binding-interface analysis; corroborated by earlier domain-mapping and competition assays\",\n      \"pmids\": [\"12808446\", \"10190280\", \"12437099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure does not capture the protease-inhibitor (tPA/uPA) covalent complex conformation\", \"Secondary low-affinity vitronectin site not fully resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Placed PAI-1 precisely in a fibrin–tPA–PAI-1–LRP cascade governing the adhesion-to-detachment switch in migrating macrophages, demonstrating that the LRP-binding function is mechanistically required.\",\n      \"evidence\": \"Genetic KO of Mac-1, tPA, PAI-1, and LRP with rescue by wild-type vs. LRP-binding-deficient PAI-1 mutant in migration assays\",\n      \"pmids\": [\"16601674\", \"11566185\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generalizability of the ternary complex to non-macrophage cells not established here\", \"Did not define the cytoskeletal effectors downstream of LRP endocytosis\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined the transcriptional logic of hypoxic PAI-1 induction, identifying three promoter-binding factors that cooperatively confer oxygen sensitivity.\",\n      \"evidence\": \"Promoter mutagenesis, EMSA supershift, and ChIP for Egr-1, HIF-1α, and C/EBPα in primary macrophages\",\n      \"pmids\": [\"17197388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative weighting of factors may be cell-type dependent\", \"Did not address HIF-2α contribution (later shown in HCC)\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a non-proteolytic immune role: surface PAI-1 acting with calreticulin as a 'don't eat me' signal that gates LRP-dependent efferocytosis.\",\n      \"evidence\": \"PAI-1(-/-) mice, antibody blockade, recombinant add-back, and colocalization microscopy on neutrophils\",\n      \"pmids\": [\"18689689\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular nature of the PAI-1/calreticulin association not structurally defined\", \"Whether this operates in tissues beyond neutrophils unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Distinguished a receptor-independent anti-apoptotic pathway, showing PAI-1 prolongs neutrophil survival via Gi-coupled receptor/PI3K/Akt signaling separate from its uPAR/LRP/vitronectin functions.\",\n      \"evidence\": \"PAI-1(-/-) mice, pertussis toxin, PI3K inhibitors, receptor blockade, and in vivo LPS lung injury\",\n      \"pmids\": [\"21622848\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific GPCR mediating the effect not identified\", \"How the inhibitory and signaling activities of PAI-1 are partitioned in vivo unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided a structural rationale for PAI-1's pro-survival/pro-proliferative signaling by mapping a cryptic VLDLr-binding site exposed upon uPA inhibition, absent in PAI-2.\",\n      \"evidence\": \"Biochemical/structural comparison of PAI-1 vs. PAI-2 binding to VLDLr with tyrosine phosphorylation and proliferation assays\",\n      \"pmids\": [\"17696882\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab structural inference\", \"In vivo relevance of VLDLr signaling not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Dissected the LRP1 signaling output of PAI-1, separating β-catenin transcriptional activation from ERK1/2 modulation in migration control.\",\n      \"evidence\": \"Isogenic LRP1-KO MEFs, β-catenin reporter, siRNA epistasis, and motility assays\",\n      \"pmids\": [\"25694133\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"LRP1-independent ERK1/2 receptor not identified\", \"Single cell-system epistasis\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected PAI-1 subcellular sequestration to cell-cycle control, showing stress-granule recruitment of PAI-1 sustains a proliferative, non-senescent state.\",\n      \"evidence\": \"Stress granule induction, PAI-1 colocalization, cyclin D1 fractionation and Rb phosphorylation in pre-senescent cells\",\n      \"pmids\": [\"29592859\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that PAI-1 within SGs is functionally inert is incomplete\", \"Mechanism of PAI-1 recruitment to SGs unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined converging intracellular pathways by which PAI-1 drives renal tubular dysfunction, linking it to klotho loss, p53 stabilization, and TGF-βRI-SMAD3 signaling independent of TGF-β1 ligand synthesis.\",\n      \"evidence\": \"Stable PAI-1 overexpression in HK-2 cells with klotho rescue, p53 siRNA, and TGF-βRI inhibition plus differentiation/apoptosis readouts\",\n      \"pmids\": [\"34110636\", \"11473641\", \"34725920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How extracellular/cell-surface PAI-1 engages these intracellular pathways mechanistically not bridged\", \"Receptor mediating TGF-βRI activation not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified a direct intracellular mechanism for PAI-1-driven senescence: binding proteasome components to inhibit proteasome activity and stabilize p53, requiring the premature secretion-competent form.\",\n      \"evidence\": \"Co-IP with proteasome components, proteasome activity assay, and wild-type vs. secretion-deficient PAI-1 comparison in lung epithelial cells\",\n      \"pmids\": [\"37566086\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab Co-IP without reciprocal/structural validation of the proteasome interface\", \"Reconciliation with the stress-granule senescence-suppressing role not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established a cytoskeletal/mechanical function, showing PAI-1 maintains vascular smooth muscle stiffness by restraining AMPK-dependent cofilin activation and F-actin turnover.\",\n      \"evidence\": \"PAI-039 inhibition, siRNA knockdown, atomic force microscopy, cofilin/AMPK assays and in vivo aortic pulse wave velocity, with PAI-1-deficient SMCs as control\",\n      \"pmids\": [\"38868940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The receptor/sensor coupling extracellular PAI-1 to intracellular AMPK not identified\", \"Relationship to the RhoA/ROCK1 amoeboid program in cancer cells unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PAI-1's distinct molecular activities — protease inhibition, vitronectin-stabilized adhesion control, LRP/VLDLr signaling, intracellular proteasome and cytoskeletal regulation — are coordinated and partitioned within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking secreted vs. intracellular PAI-1 pools\", \"Receptors for several signaling and senescence functions remain unidentified\", \"Conflicting senescence roles (proteasome inhibition vs. stress-granule sequestration) not reconciled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 8, 24]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 8, 19, 30]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [6, 12, 16, 21, 31]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [23, 30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 13, 17]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [3, 7, 8, 17]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [2, 14, 25, 31]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [23, 30]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 21, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13, 16, 24]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [11, 20, 23, 30]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [5, 25]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PLAU\", \"PLAT\", \"VTN\", \"LRP1\", \"VLDLR\", \"CALR\", \"SERPINE1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}