{"gene":"SPINT1","run_date":"2026-06-10T07:46:40","timeline":{"discoveries":[{"year":2005,"finding":"HAI-1 (SPINT1) is required for matriptase activation: HAI-1 is co-translocated with matriptase to cell-cell junctions upon sphingosine 1-phosphate (S1P) stimulation, and HAI-1 knockdown or anti-HAI-1 antibody treatment causes spontaneous matriptase activation. Coexpression of wild-type HAI-1 (but not Kunitz domain 1 mutants) rescues matriptase trafficking to the cell surface in cells lacking endogenous HAI-1; catalytically defective matriptase mutants traffic normally without HAI-1, indicating HAI-1 prevents inappropriate matriptase proteolytic activity during synthesis and trafficking.","method":"siRNA knockdown, anti-HAI-1 monoclonal antibody treatment, co-expression of wild-type vs. Kunitz domain mutant HAI-1, immunofluorescence, Western blot, S1P stimulation assay","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (siRNA, antibody blockade, domain mutagenesis, co-expression rescue) in a single focused study with rigorous controls","pmids":["15800053"],"is_preprint":false},{"year":2003,"finding":"HAI-1B, a splice variant of HAI-1 containing an extra 16 amino acids adjacent to the C-terminus of KD1, potently inhibits HGFA (IC50=30.5 nM), matriptase (IC50=16.5 nM), and trypsin (IC50=2.4 nM), with weak inhibition of plasmin and plasma kallikrein, and no significant inhibition of plasminogen activators, coagulation enzymes, or activated protein C. P1 residue-directed mutagenesis demonstrated that inhibition is mediated exclusively by KD1 and not KD2.","method":"Soluble recombinant protein production, enzyme inhibition assays (IC50 determination against 16 serine proteases), P1 residue-directed mutagenesis of Kunitz domains","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with active-site mutagenesis across multiple proteases in a single rigorous study","pmids":["12815039"],"is_preprint":false},{"year":2005,"finding":"HAI-1 (SPINT1) is essential for branching morphogenesis of the chorioallantoic placenta in mice. Homozygous HAI-1-/- mice die at ~E10.5 with severely impaired labyrinth layer formation but intact spongiotrophoblast and giant cell layers, indicating a specific role in trophoblast branching rather than general placental cell identity.","method":"Homozygous gene knockout by homologous recombination in mice, histological analysis at E9.5 and E10.5","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with specific phenotypic readout, independently corroborated by a second HAI-1 KO mouse study (PMID:17174946)","pmids":["15964823"],"is_preprint":false},{"year":2006,"finding":"HAI-1 is essential for the integrity of basement membranes in the developing placental labyrinth. HAI-1-/- placentas show disrupted collagen IV and laminin-containing basement membranes at the trophoblast–allantoic mesoderm interface, resulting in failed vascularization. Matriptase and prostasin co-localize with HAI-1 in labyrinthine trophoblasts in wild-type placentas, and their localization and expression are unchanged in HAI-1-/- placentas, implying uncontrolled proteolytic activity of these enzymes underlies the basement membrane defects.","method":"Gene knockout mice, immunofluorescent staining of collagen IV and laminin, electron microscopy, immunohistochemistry","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — independent replication of HAI-1 KO phenotype with mechanistic protein localization data using multiple orthogonal methods","pmids":["17174946"],"is_preprint":false},{"year":2008,"finding":"HAI-1/SPINT1 is required for normal epidermal keratinization and hair development. Spint1-/- mice rescued from embryonic lethality (by blastocyst complementation) develop ichthyosis-like scaly skin with hyperkeratosis, acanthosis with enhanced Akt phosphorylation, and abnormal hair shafts. HAI-1 deficiency causes altered proteolytic processing of profilaggrin with impaired generation of filaggrin monomers.","method":"Blastocyst complementation rescue of Spint1-/- embryonic lethality, histology, immunoblot for profilaggrin/filaggrin processing, immunohistochemistry for Akt phosphorylation","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic rescue with specific biochemical readout (profilaggrin processing), multiple orthogonal methods","pmids":["18832587"],"is_preprint":false},{"year":2009,"finding":"Loss of HAI-1 (Spint1) in mice causes ichthyosis, acanthosis, and hypotrichosis through loss of suppression of a matriptase-dependent proteolytic pathway. Genetic epistasis: Spint1-deficient mice carrying a hypomorphic St14 (matriptase) allele survive normally with no histological abnormalities, demonstrating that matriptase suppression is the essential function of HAI-1 in postnatal tissue homeostasis.","method":"Genetic epistasis analysis using Spint1-/- × St14 hypomorphic double mutant mice, histological analysis, long-term survival monitoring","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis rescue experiment with comprehensive histological phenotyping","pmids":["19389929"],"is_preprint":false},{"year":2009,"finding":"HAI-1 mediates matriptase inhibition and complex formation selectively at the basolateral surface of polarized epithelial cells. Latent matriptase is targeted to the basolateral membrane; only matriptase–HAI-1 complexes (not latent matriptase) are detectable in seminal fluid and urine. In polarized Caco-2 cells, matriptase–HAI-1 complexes (but not latent matriptase) undergo transcytosis to the apical surface for secretion.","method":"Analysis of seminal fluid and urine for matriptase forms, polarized Caco-2 monolayer experiments, Western blot, immunohistochemistry of prostate and kidney","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with functional consequence, in vivo and in vitro orthogonal approaches in a single study","pmids":["19535514"],"is_preprint":false},{"year":2012,"finding":"HAI-1 (Spint1) is required for maintenance of intestinal epithelial integrity. Intestine-specific Spint1 deletion causes crypt abnormalities, increased apoptosis, elevated epithelial turnover, increased intestinal permeability, and endoplasmic reticulum stress in colonic crypts, and greatly worsens experimental colitis (DSS model) with significantly lower survival.","method":"Conditional KO using Villin-Cre × Spint1-LoxP mice, histology, TUNEL assay, intestinal permeability assay, electron microscopy, DSS colitis model","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal phenotypic readouts and disease model validation","pmids":["21840293"],"is_preprint":false},{"year":2012,"finding":"In HAI-1/SPINT1 deficiency, prostasin activation and pericellular serine protease activity are suppressed because cell-surface localization of matriptase is impaired. HAI-1/SPINT1 knockdown in BeWo trophoblast cells decreases cell-associated matriptase protein (without altering mRNA) and reduces laminin degradation activity, demonstrating that HAI-1 is required for cell-surface retention of matriptase to enable physiological activation of prostasin.","method":"siRNA knockdown of HAI-1 in BeWo cells, immunoblot for matriptase and prostasin, laminin degradation assay, immunohistochemistry of HAI-1-deficient mouse placentas","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with defined cellular phenotype and biochemical readout, single lab, two orthogonal approaches","pmids":["23248048"],"is_preprint":false},{"year":2012,"finding":"Reduced prostasin (CAP1/PRSS8) activity rescues both HAI-1 and HAI-2 deficiency-associated developmental defects by preventing matriptase activation. Hypomorphic Prss8 mutations restore placentation and normal development of HAI-1-deficient embryos. Biochemical analysis revealed that prostasin is required for conversion of the matriptase zymogen to active matriptase, while prostasin zymogen activation is matriptase-independent in placental tissues.","method":"Genetic epistasis analysis with compound mutant mice (HAI-1 or HAI-2 deficient × Prss8 hypomorph), biochemical analysis of matriptase and prostasin activation in placental tissue","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple genotype combinations plus biochemical validation of mechanism","pmids":["22952456"],"is_preprint":false},{"year":2014,"finding":"HAI-1 (SPINT1) regulates the activity of already-activated matriptase, whereas HAI-2 (not HAI-1) has an essential role in regulating prostasin-dependent matriptase zymogen activation. In genetically engineered mice, HAI-1 ablation does not affect matriptase in intestinal epithelial cells, but HAI-2 ablation causes loss of matriptase from both small and large intestine; gene silencing in Caco-2 cells shows this is due to accelerated matriptase activation and shedding caused by loss of prostasin regulation by HAI-2.","method":"Conditional KO mice (HAI-1 and HAI-2 ablation), gene silencing in Caco-2 monolayers, immunohistochemistry, Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic knockout and in vitro gene silencing with mechanistic biochemical follow-up, two orthogonal model systems","pmids":["24962579"],"is_preprint":false},{"year":2006,"finding":"Androgen receptor-mediated transcription and new protein synthesis are required for dihydrotestosterone (DHT)-induced matriptase activation and shedding in LNCaP prostate cancer cells. Activated matriptase is shed in complex with HAI-1; both latent matriptase and free HAI-1 are also shed. DHT-induced matriptase activation is blocked by the androgen antagonist bicalutamide, transcription inhibitor actinomycin D, and translation inhibitor cycloheximide.","method":"Hormone stimulation assays, pharmacological inhibitors (bicalutamide, actinomycin D, cycloheximide), Western blot, immunoprecipitation","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological inhibitors with defined biochemical readouts, single lab","pmids":["16467405"],"is_preprint":false},{"year":2010,"finding":"HAI-1 acts as a specific cell-surface binding protein and reservoir for active HGFA on the epithelial cell surface; active HGFA–HAI-1 complexes are rapidly released from the cell surface by IL-1β treatment with significant recovery of HGFA activity in culture supernatant, suggesting HAI-1 localizes HGFA to facilitate pericellular HGF activation in injured mucosa.","method":"Cell surface binding assays, immunoprecipitation, IL-1β stimulation experiments, enzyme activity assays in culture supernatant","journal":"Journal of gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP and cell-surface binding with functional enzyme activity readout, single lab","pmids":["12572861"],"is_preprint":false},{"year":2010,"finding":"Crystal structure of the KD1–HGFA complex reveals that HAI-1 KD1 inhibits HGFA by occupying the active site in a substrate-like manner, making contacts with all substrate specificity-determining loops and occupying subsites S1, S2, and S4. KD1 side chains occupying these sites are virtually superimposable on P1, P2, and P4 residues of a pro-HGF-derived substrate mimic.","method":"X-ray crystallography of KD1–HGFA complex, structural comparison with substrate analog-bound HGFA","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with substrate analog comparison providing atomic-level mechanism of inhibition","pmids":["20402765"],"is_preprint":false},{"year":2011,"finding":"When HAI-1 levels are insufficient, active matriptase forms a 140-kDa homodimer (in addition to a 100-kDa complex with unidentified inhibitors) as a mechanism to control its activity. The 140-kDa dimer contains two-chain activated matriptase, lacks gelatinolytic activity, and its levels are inversely correlated with the HAI-1:matriptase ratio, suggesting it may represent a matriptase autoactivation intermediate.","method":"Western blot, gel filtration/biochemical characterization of matriptase complexes, gelatin zymography, immunoprecipitation","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical methods characterizing novel complex, single lab","pmids":["22031598"],"is_preprint":false},{"year":2015,"finding":"γ-Catenin (Plakoglobin) reduces NSCLC cell migration in a p53-dependent manner by inducing HAI-1 (SPINT1) expression, which serves as an upstream inhibitor of c-MET signaling. Re-expression of γ-catenin sensitizes NSCLC cells to c-MET inhibitor-mediated growth inhibition.","method":"γ-Catenin expression in NSCLC cells, scratch and trans-well migration assays, Western blot for HAI-1 and c-MET pathway components, c-MET inhibitor treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — KO/OE with defined pathway placement (γ-catenin → HAI-1 → c-MET), multiple cell-based assays, single lab","pmids":["25925948"],"is_preprint":false},{"year":2016,"finding":"Matriptase and prostasin both form complexes with HAI-1 in human milk (and in milk-derived mammary epithelial cells), providing in vivo evidence that HAI-1 inhibits both proteases during lactation. HAI-1 is the primary inhibitor for both matriptase and prostasin in this context.","method":"Immunoaffinity purification, ion exchange chromatography, Western blot analysis of human milk fractions and milk-derived mammary epithelial cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo protein complex identification by biochemical purification, single lab, orthogonal purification methods","pmids":["27043831"],"is_preprint":false},{"year":2017,"finding":"Crystal structure and SAXS solution structure of soluble full-length HAI-1 extracellular domain (sHAI-1) reveal that it exists in a compact, auto-inhibited conformation in which the active site of Kunitz domain 1 is sterically blocked by neighboring structural elements. In the presence of target proteases, sHAI-1 adopts an extended conformation that disables auto-inhibition, explaining the lower inhibitory activity of full-length versus truncated HAI-1 fragments.","method":"X-ray crystallography, small-angle X-ray scattering (SAXS), enzyme inhibition assays comparing full-length vs. truncated HAI-1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure and SAXS with functional validation by inhibition assays, multiple orthogonal structural methods","pmids":["28348076"],"is_preprint":false},{"year":2017,"finding":"MMP-7 cleaves HAI-1 on the cancer cell surface, primarily between Gly451 and Leu452, releasing soluble HAI-1 (sHAI-1). This sHAI-1 induces homotypic cancer cell aggregation through the HAI-1 region corresponding to amino acids 141–249, which does not include the serine protease inhibitor domain. Cell-surface cholesterol sulfate is needed for sHAI-1 generation by MMP-7, but a cholesterol sulfate-independent MMP-7 action is critical for sHAI-1-mediated aggregation induction.","method":"Cell surface biotinylation, LC-MS/MS substrate identification, site-directed cleavage site mapping, cancer cell aggregation assays with recombinant sHAI-1 fragments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — mass spectrometry substrate identification, precise cleavage site mapping, functional cell aggregation assay with defined domain mapping","pmids":["29046355"],"is_preprint":false},{"year":2018,"finding":"HAI-1 (at cell surface) is a more effective inhibitor of extracellular matriptase proteolytic activity than HAI-2 (predominantly intracellular) because of differential subcellular localization. Both HAI-1 and HAI-2 promote matriptase expression and cell-surface translocation, but HAI-1 cell-surface expression allows it to efficiently capture active matriptase before shedding, whereas HAI-2's primarily intracellular localization prevents effective suppression of extracellular active matriptase.","method":"Immunohistochemistry, Western blot, cell surface biotinylation/avidin depletion, analysis of prostasin-matriptase complexes in human skin foreskin lysates","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization tied to functional consequence with biochemical verification, single lab","pmids":["29438412"],"is_preprint":false},{"year":2018,"finding":"TMPRSS11A-related enzymes human airway tryptase and DESC1, but not TMPRSS11A itself, are blocked by HAI-1 in their ability to activate influenza A virus hemagglutinin, demonstrating differential sensitivity of HA-activating TTSPs to HAI-1 inhibition.","method":"Cell-based HA cleavage assays, protease inhibition assays with recombinant HAI-1","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and cell-based inhibition assays with specific protease/inhibitor pairs, single lab","pmids":["29976755"],"is_preprint":false},{"year":2018,"finding":"HAI-1 (SPINT1) expression in tumor-associated macrophages is regulated by HIF-2α under hypoxia. HIF-2α-deficient bone marrow-derived macrophages show reduced Spint1 mRNA and protein secretion under hypoxia. Supernatants from HIF-2α KO macrophages (lacking Spint1) could activate pro-HGF to stimulate breast tumor cell proliferation, while wild-type macrophage supernatants containing Spint1 failed to do so.","method":"RNA-seq of sorted TAMs from HIF-2α LysM-/- vs. WT mice, RT-PCR, ELISA for secreted Spint1, pro-HGF activation assay in breast tumor cell proliferation","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq plus functional validation of Spint1 role in pro-HGF activation, single lab with multiple methods","pmids":["31436357"],"is_preprint":false},{"year":2018,"finding":"CDX2 transcription factor directly regulates both ST14 (matriptase) and SPINT1 (HAI-1) gene expression in intestinal cells through binding to CDX2-enriched enhancer elements identified by ChIP-seq. CDX2 is not required for basal ST14 and SPINT1 expression, but changes in CDX2 expression alter the ST14/SPINT1 mRNA ratio in a cell-type-dependent manner.","method":"siRNA KD of CDX2, promoter-reporter assays, CDX2 ChIP-seq analysis, RT-PCR","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq with promoter-reporter functional validation, multiple cell lines, single lab","pmids":["30087389"],"is_preprint":false},{"year":2018,"finding":"Grhl2 transcription factor directly binds to the Spint1 gene in developing mouse submandibular salivary gland (confirmed by ChIP-PCR), and Grhl2 knockdown suppresses SPINT1 expression concomitant with retardation of epithelial development and disorganized laminin deposition. Addition of recombinant SPINT1 protein rescues the suppressive effects of Grhl2 siRNA on epithelial development and laminin deposition.","method":"siRNA knockdown of Grhl2 in ex vivo SMG culture, RT-PCR for SPINT1 mRNA, ChIP-PCR for Grhl2 binding to Spint1 gene, recombinant SPINT1 rescue experiment","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — ChIP-PCR demonstrating direct TF binding, confirmed by rescue with recombinant protein, two orthogonal methods","pmids":["30193734"],"is_preprint":false},{"year":2020,"finding":"HAI-1 (and HAI-2) inhibits the zymogen form of matriptase in addition to the activated form. Using purified proteins and cell-based assays, HAI-1 inhibits matriptase zymogen activity toward peptide-based substrates and the natural protein substrates pro-HGF and pro-prostasin at concentrations comparable to inhibition of activated matriptase, suggesting interaction at the active site of the zymogen.","method":"In vitro enzyme inhibition assays with purified HAI-1 and matriptase zymogen, peptide substrate cleavage assay, pro-HGF and pro-prostasin cleavage assays, cell-based assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple natural substrates and cell-based confirmation, single lab","pmids":["32338287"],"is_preprint":false},{"year":2020,"finding":"HAI-1 deficiency increases prostasin proteolysis (through increased protein expression and zymogen activation) but paradoxically decreases matriptase proteolysis in HaCaT human keratinocytes. In HAI-1-deficient cells, all activated prostasin is found in complex with HAI-2, and matriptase zymogen activation and shedding are suppressed. This demonstrates that HAI-1 has opposite effects on matriptase versus prostasin proteolysis in keratinocytes.","method":"CRISPR/targeted HAI-1 deletion in HaCaT keratinocytes, Western blot for protease activation states, immunoprecipitation for complex formation","journal":"Human cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — targeted KO with multiple biochemical readouts, novel mechanistic finding with clear controls, single lab","pmids":["33486722"],"is_preprint":false},{"year":2021,"finding":"HAI-1 and HAI-2 differ in their subcellular targeting due to differences in their intracellular Arg/Lys-rich and EHLVY motifs. HAI-1 localizes both intracellularly and at the cell surface, while HAI-2 localizes predominantly in intracellular granules. Domain swap and point mutation studies combined with immunocytochemistry and cell surface biotinylation revealed these intrinsic sequence differences control the differential subcellular distribution.","method":"Domain swap constructs, site-directed point mutations, immunocytochemistry, cell surface biotinylation/avidin depletion, confocal microscopy","journal":"Human cell","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — mutagenesis combined with direct subcellular localization experiments defining the molecular determinants, multiple orthogonal methods","pmids":["34643933"],"is_preprint":false},{"year":2016,"finding":"HAI-1 loss in intestine-specific Spint1-deleted ApcMin/+ mice promotes intestinal carcinogenesis through NF-κB signaling activation, as evidenced by upregulation of inflammatory cytokines (TNF-α, IL-6), increased nuclear NF-κB translocation in normal mucosa and tumor tissues, and upregulation of NF-κB target urokinase-type plasminogen activator. Treatment with DHMEQ (NF-κB inhibitor) reduced intestinal tumor formation in these mice.","method":"Conditional intestinal Spint1 KO in ApcMin/+ background, RT-PCR and immunohistochemistry for NF-κB targets, DHMEQ pharmacological treatment experiment","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic model with pharmacological rescue and mechanistic pathway identification, single lab","pmids":["27612426"],"is_preprint":false},{"year":2024,"finding":"SPINT1 in pancreatic β cells controls glucose homeostasis by suppressing the serine protease HEPSIN. SPINT1 and HEPSIN interact in β cells; Hepsin silencing counteracts the downregulation of Mafa and Ins1 caused by Spint1 depletion. SPINT1 loss or HEPSIN overexpression reduces GLP1R-related cyclic AMP levels and Mafa expression. Spint1-disrupted mice show reduced Exendin-4-induced insulin secretion, and pancreas-specific Spint1 disruption diminishes islet size and mass, causing glucose intolerance.","method":"Spint1-lacZ knock-in mice, pancreas-specific Spint1 KO mice, siRNA gene silencing, co-immunoprecipitation (SPINT1–HEPSIN interaction), cAMP assays, Exendin-4 challenge, glucose tolerance tests, Western blot","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vivo KO with multiple functional readouts, Co-IP for direct interaction, pharmacological challenge, multiple orthogonal methods in a single study","pmids":["39627229"],"is_preprint":false},{"year":2024,"finding":"HAI-1 (SPINT1) loss in keratinocytes upregulates MMP-9 expression via NF-κB activation, leading to increased MMP gelatinolytic activity and disrupted epidermal basement membrane structure. Treatment of SPINT1 KO HaCaT cells with DHMEQ (NF-κB inhibitor) abrogates MMP-9 upregulation and associated gelatinolytic activity.","method":"SPINT1 KO HaCaT cells, gelatin zymography, Western blot, electron microscopy of Spint1-deleted skin, DHMEQ pharmacological inhibition","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined biochemical mechanism and pharmacological rescue, single lab, two orthogonal methods","pmids":["39730982"],"is_preprint":false},{"year":2004,"finding":"Decreased HAI-1 immunoreactivity in colorectal carcinoma cells results largely from enhanced ectodomain shedding of HAI-1. In contrast, at the invasion front, membrane-form HAI-1 is paradoxically enhanced, correlating with decreased E-cadherin expression and low proliferative activity (MIB-1 negative), revealing distinct regulation of membrane-bound versus shed HAI-1 in cancer progression.","method":"Immunohistochemistry with three anti-HAI-1 antibodies recognizing distinct epitopes, in situ hybridization for HAI-1 mRNA","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple antibody epitopes and ISH provide distinct mechanistic insight into ectodomain shedding, single lab","pmids":["15471558"],"is_preprint":false},{"year":2001,"finding":"HAI-1 functions as a cell-surface inhibitor and reservoir of HGFA in colorectal carcinoma, where HGF activation is significantly enhanced compared to normal mucosa. HAI-1 cell-surface binding of active HGFA may paradoxically ensure concentrated pericellular HGFA activity when shedding of the HAI-1/HGFA complex is upregulated.","method":"In vitro cell-surface HGFA binding assays, immunohistochemistry, enzyme activity assays in colorectal tissue extracts","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct cell-surface binding assay combined with tissue enzyme activity measurements and IHC, single lab","pmids":["11436357"],"is_preprint":false},{"year":2018,"finding":"An engineered bivalent HAI-1 KD1-based inhibitor (KD1 duplicated via domain replacement of inactive KD2, fused to antibody Fc) inhibits matriptase with a Ki of 70 ± 5 pM (120-fold improvement over natural HAI-1), inhibits pro-HGF activation by matriptase, and inhibits matriptase on cancer cells with greater than an order-of-magnitude higher efficacy than monomeric KD1. This establishes that HAI-1 KD1 is the minimal matriptase-binding domain and that KD2 is involved in negative regulation.","method":"Rational domain engineering, combinatorial library screening, in vitro enzyme inhibition assays (Ki determination), pro-HGF cleavage assay, cancer cell surface matriptase inhibition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with quantitative affinity measurement, multiple substrates/assays defining domain function","pmids":["29386351"],"is_preprint":false}],"current_model":"SPINT1 (HAI-1) is a membrane-anchored, multidomain Kunitz-type serine protease inhibitor whose primary cellular function is to tightly regulate the pericellular proteolytic activity of matriptase (ST14) and, to a lesser extent, prostasin (PRSS8) and HGFA: the crystal and SAXS structures of HAI-1 show it is auto-inhibited in full-length form (KD1 active site sterically blocked), becoming active upon engagement with target proteases; KD1 is the sole inhibitory domain responsible for potent inhibition of matriptase, HGFA, and prostasin; HAI-1 serves as a chaperone required for matriptase synthesis, intracellular trafficking, and surface localization, and also couples matriptase zymogen activation to immediate inhibition, forming shed matriptase–HAI-1 complexes; in vivo, HAI-1 is essential for placental labyrinth formation, postnatal epidermal barrier integrity, intestinal epithelial homeostasis, and pancreatic β-cell function (via HEPSIN suppression to maintain MAFA and insulin expression); HAI-1 also sequesters active HGFA on the cell surface to regulate pericellular HGF activation, and its loss triggers NF-κB-mediated upregulation of MMP-9 and urokinase, while its cell-surface localization (determined by intracellular Arg/Lys-rich and EHLVY targeting motifs) distinguishes it from the predominantly intracellular HAI-2 and renders it the default inhibitor of extracellular matriptase activity."},"narrative":{"mechanistic_narrative":"SPINT1 (HAI-1) is a membrane-anchored, multidomain Kunitz-type serine protease inhibitor that governs pericellular proteolysis at epithelial surfaces by controlling the activity of the type II transmembrane serine protease matriptase and its partner proteases [PMID:19389929, PMID:24962579]. Inhibitory activity resides exclusively in Kunitz domain 1 (KD1), which inhibits HGFA, matriptase, and trypsin while leaving plasminogen activators and coagulation enzymes untouched [PMID:12815039]; crystallography shows KD1 occupies the protease active site in a substrate-like manner across the S1, S2, and S4 subsites [PMID:20402765], and full-length HAI-1 exists in a compact auto-inhibited conformation in which the KD1 active site is sterically blocked until target-protease engagement triggers an extended, active conformation [PMID:28348076]. HAI-1 acts as a chaperone required for matriptase synthesis, cell-surface trafficking, and retention, preventing inappropriate proteolytic activity during biosynthesis, and it captures activated matriptase to form shed matriptase–HAI-1 complexes [PMID:15800053, PMID:19535514, PMID:23248048]; KD1 is the minimal matriptase-binding module while KD2 negatively regulates this interaction [PMID:29386351]. Genetic epistasis establishes that suppression of a matriptase- and prostasin-dependent proteolytic cascade is the essential physiological function of HAI-1 [PMID:19389929, PMID:22952456]. HAI-1 is essential in vivo for placental labyrinth basement-membrane integrity [PMID:15964823, PMID:17174946], postnatal epidermal keratinization and profilaggrin processing [PMID:18832587], intestinal epithelial homeostasis [PMID:21840293], and pancreatic β-cell glucose homeostasis, where it suppresses HEPSIN to sustain MAFA and insulin expression [PMID:39627229]. Loss of HAI-1 drives NF-κB–mediated upregulation of urokinase and MMP-9, linking proteolytic dysregulation to intestinal carcinogenesis and basement-membrane disruption [PMID:27612426, PMID:39730982]. Its cell-surface localization, dictated by intracellular Arg/Lys-rich and EHLVY targeting motifs, distinguishes it from the predominantly intracellular HAI-2 and makes HAI-1 the default inhibitor of extracellular matriptase activity [PMID:29438412, PMID:34643933].","teleology":[{"year":2003,"claim":"Established which proteases HAI-1 inhibits and localized inhibitory activity to a single domain, defining its target specificity.","evidence":"Recombinant soluble HAI-1B with IC50 determinations against 16 serine proteases and P1 active-site mutagenesis of both Kunitz domains","pmids":["12815039"],"confidence":"High","gaps":["Did not address regulation of HAI-1 inhibitory activity in the membrane-anchored full-length context","Cellular trafficking and chaperone roles not yet examined"]},{"year":2005,"claim":"Showed HAI-1 is not merely an inhibitor but a chaperone required for matriptase trafficking and surface localization, explaining why its loss causes spontaneous protease activation.","evidence":"siRNA knockdown, anti-HAI-1 antibody blockade, and KD1-mutant co-expression rescue with immunofluorescence in S1P-stimulated cells","pmids":["15800053"],"confidence":"High","gaps":["Molecular determinants of co-trafficking not mapped","Did not establish in vivo physiological consequence"]},{"year":2005,"claim":"Demonstrated an essential developmental requirement for HAI-1 in placental trophoblast branching, providing the first whole-organism phenotype.","evidence":"Homozygous Spint1 knockout mice with histology at E9.5–E10.5","pmids":["15964823"],"confidence":"High","gaps":["Did not identify the dysregulated protease responsible","Embryonic lethality precluded study of postnatal roles"]},{"year":2006,"claim":"Linked HAI-1 loss mechanistically to basement-membrane destruction, implicating uncontrolled matriptase/prostasin proteolysis in the placental phenotype.","evidence":"Knockout placentas analyzed by collagen IV/laminin immunofluorescence, EM, and protease co-localization","pmids":["17174946"],"confidence":"High","gaps":["Causal protease not formally identified by epistasis at this stage","Direct demonstration of excess proteolytic activity inferred from localization"]},{"year":2008,"claim":"Defined HAI-1's postnatal role in epidermal barrier formation and tied it to a specific biochemical substrate-processing event.","evidence":"Blastocyst-complementation rescue of lethality, histology, and immunoblot of profilaggrin/filaggrin processing","pmids":["18832587"],"confidence":"High","gaps":["Did not establish whether profilaggrin defect is direct or downstream of matriptase dysregulation","Akt activation mechanism not resolved"]},{"year":2009,"claim":"Genetic epistasis proved matriptase suppression is the essential function of HAI-1 in tissue homeostasis, anchoring the entire mechanistic model.","evidence":"Spint1-/- × St14 hypomorph double-mutant mice with histology and survival monitoring","pmids":["19389929"],"confidence":"High","gaps":["Did not address the contribution of prostasin or HGFA","Tissue-specific differences in protease dependence not resolved"]},{"year":2012,"claim":"Placed prostasin upstream as the matriptase zymogen activator and showed reducing prostasin rescues HAI-1 deficiency, refining the proteolytic cascade hierarchy.","evidence":"Compound mutant mice (HAI-1 or HAI-2 deficient × Prss8 hypomorph) with biochemical analysis of placental protease activation","pmids":["22952456"],"confidence":"High","gaps":["Did not resolve how prostasin zymogen is itself activated","Relative roles of HAI-1 vs HAI-2 in this cascade left for later work"]},{"year":2012,"claim":"Extended HAI-1's essential role to adult intestinal epithelium and disease susceptibility via conditional deletion.","evidence":"Villin-Cre × Spint1-LoxP conditional KO with permeability assays, TUNEL, EM, and DSS colitis model","pmids":["21840293"],"confidence":"High","gaps":["Did not delineate the signaling pathway driving epithelial turnover and ER stress","Causal protease in intestine not pinpointed here"]},{"year":2014,"claim":"Distinguished the non-redundant roles of HAI-1 versus HAI-2, showing HAI-1 controls activated matriptase while HAI-2 governs prostasin-driven zymogen activation.","evidence":"Conditional HAI-1 and HAI-2 knockout mice plus Caco-2 gene silencing with IHC and Western blot","pmids":["24962579"],"confidence":"High","gaps":["Mechanistic basis of the division of labor (localization vs intrinsic activity) not yet defined","Did not address compensatory regulation"]},{"year":2010,"claim":"Provided atomic-level mechanism of inhibition, showing KD1 mimics a substrate to occupy the HGFA active site.","evidence":"X-ray crystallography of the KD1–HGFA complex compared to a substrate analog","pmids":["20402765"],"confidence":"High","gaps":["Structure of full-length auto-inhibited HAI-1 not yet determined","Did not explain reduced potency of full-length inhibitor"]},{"year":2017,"claim":"Resolved why full-length HAI-1 is a weaker inhibitor than KD1 fragments by revealing a compact auto-inhibited conformation regulated by target-protease binding.","evidence":"Crystallography and SAXS of soluble full-length HAI-1 ectodomain with comparative inhibition assays","pmids":["28348076"],"confidence":"High","gaps":["In situ conformational switching at the membrane not directly visualized","Kinetics of the conformational transition not measured"]},{"year":2020,"claim":"Showed HAI-1 inhibits the matriptase zymogen as effectively as the active enzyme, expanding its regulatory window to pre-activation states.","evidence":"In vitro reconstitution with purified zymogen and natural substrates pro-HGF and pro-prostasin plus cell-based assays","pmids":["32338287"],"confidence":"High","gaps":["Structural basis of zymogen recognition not solved","Physiological significance of zymogen inhibition in vivo not tested"]},{"year":2021,"claim":"Identified the intracellular sequence motifs (Arg/Lys-rich and EHLVY) that direct HAI-1 to the cell surface, explaining its functional divergence from intracellular HAI-2.","evidence":"Domain-swap and point-mutation constructs with immunocytochemistry, surface biotinylation, and confocal microscopy","pmids":["34643933"],"confidence":"High","gaps":["Trafficking machinery recognizing these motifs not identified","Quantitative surface vs intracellular partitioning under physiological conditions not measured"]},{"year":2024,"claim":"Revealed a distinct HAI-1 function in pancreatic β cells, suppressing HEPSIN to maintain GLP1R signaling, MAFA, and insulin expression for glucose homeostasis.","evidence":"Spint1-lacZ knock-in and pancreas-specific KO mice, siRNA silencing, SPINT1–HEPSIN co-IP, cAMP assays, Exendin-4 challenge, and glucose tolerance tests","pmids":["39627229"],"confidence":"High","gaps":["Whether HEPSIN inhibition uses the same KD1 active-site mechanism not shown","Direct enzymatic inhibition of HEPSIN by HAI-1 not biochemically reconstituted"]},{"year":2024,"claim":"Connected HAI-1 loss to NF-κB-driven MMP-9 upregulation as the route to basement-membrane disruption in epidermis.","evidence":"SPINT1 KO HaCaT cells with gelatin zymography, Western blot, skin EM, and DHMEQ NF-κB inhibition","pmids":["39730982"],"confidence":"Medium","gaps":["How protease dysregulation activates NF-κB upstream not defined","single-cell-line mechanism not validated across epithelial tissues"]},{"year":null,"claim":"How the auto-inhibited-to-active conformational switch, chaperone trafficking, and tissue-specific protease targeting (matriptase, prostasin, HGFA, HEPSIN) are coordinately controlled at the membrane in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model linking conformational regulation to target selection","Determinants of context-specific protease choice (e.g., HEPSIN in β cells vs matriptase in epithelium) not 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Inhibits serine protease activity of ST14/matriptase in vitro (PubMed:28710277). 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Histochemistry Society","url":"https://pubmed.ncbi.nlm.nih.gov/16495474","citation_count":8,"is_preprint":false},{"pmid":"23393351","id":"PMC_23393351","title":"Expression of Hepatocyte growth factor activator inhibitor type-1 (HAI-1) in prostate cancer.","date":"2013","source":"Anticancer research","url":"https://pubmed.ncbi.nlm.nih.gov/23393351","citation_count":7,"is_preprint":false},{"pmid":"23979832","id":"PMC_23979832","title":"Down-regulation of HAI-1 is associated with poor-differentiation status of colorectal cancer.","date":"2013","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/23979832","citation_count":6,"is_preprint":false},{"pmid":"33486722","id":"PMC_33486722","title":"Targeted deletion of HAI-1 increases prostasin proteolysis but decreases matriptase proteolysis in human keratinocytes.","date":"2021","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/33486722","citation_count":5,"is_preprint":false},{"pmid":"39627229","id":"PMC_39627229","title":"Spint1 disruption in mouse pancreas leads to glucose intolerance and impaired insulin production involving HEPSIN/MAFA.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/39627229","citation_count":4,"is_preprint":false},{"pmid":"34643933","id":"PMC_34643933","title":"The difference in the intracellular Arg/Lys-rich and EHLVY motifs contributes to distinct subcellular distribution of HAI-1 versus HAI-2.","date":"2021","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/34643933","citation_count":4,"is_preprint":false},{"pmid":"34089062","id":"PMC_34089062","title":"Targeted HAI-2 deletion causes excessive proteolysis with prolonged active prostasin and depletion of HAI-1 monomer in intestinal but not epidermal epithelial cells.","date":"2021","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34089062","citation_count":4,"is_preprint":false},{"pmid":"40507942","id":"PMC_40507942","title":"SPINT1 Expressed in Epithelial Cells of Choroid Plexus in Human and Mouse Brains.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40507942","citation_count":3,"is_preprint":false},{"pmid":"30370662","id":"PMC_30370662","title":"3-Cl-AHPC inhibits pro-HGF maturation by inducing matriptase/HAI-1 complex formation.","date":"2018","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30370662","citation_count":3,"is_preprint":false},{"pmid":"37076641","id":"PMC_37076641","title":"HAI-1 is required for the novel role of FGFBP1 in maintenance of cell morphology and F-actin rearrangement in human keratinocytes.","date":"2023","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/37076641","citation_count":2,"is_preprint":false},{"pmid":"16909612","id":"PMC_16909612","title":"[HAI-1 expression in villous tissue of early gestational period in women].","date":"2006","source":"Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition","url":"https://pubmed.ncbi.nlm.nih.gov/16909612","citation_count":2,"is_preprint":false},{"pmid":"39730982","id":"PMC_39730982","title":"Loss of hepatocyte growth factor activator inhibitor type 1 (HAI-1) upregulates MMP-9 expression and induces degradation of the epidermal basement membrane.","date":"2024","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/39730982","citation_count":1,"is_preprint":false},{"pmid":"41140002","id":"PMC_41140002","title":"Overexpression of Matriptase-1 Inhibitor HAI-1 as an Effective Strategy to Reduce Proteolytic Clipping in Chinese Hamster Ovary Cells.","date":"2025","source":"Biotechnology journal","url":"https://pubmed.ncbi.nlm.nih.gov/41140002","citation_count":1,"is_preprint":false},{"pmid":"40299447","id":"PMC_40299447","title":"Engineered Expression of Hepatocyte Growth Factor Activator Inhibitor-1 (HAI-1) Reduces the Growth of Bladder Cancer Cells.","date":"2025","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/40299447","citation_count":1,"is_preprint":false},{"pmid":"30111395","id":"PMC_30111395","title":"[Expression and Clinical Significances of HGFA, Matriptase, HAI-1 and HAI-2 in Acute Myeloid Leukemia].","date":"2018","source":"Zhongguo shi yan xue ye xue za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/30111395","citation_count":1,"is_preprint":false},{"pmid":"16044910","id":"PMC_16044910","title":"[Effect of HAI-1 over-expression on in vitro growth and migration/motility of SW620 cells].","date":"2005","source":"Shi yan sheng wu xue bao","url":"https://pubmed.ncbi.nlm.nih.gov/16044910","citation_count":1,"is_preprint":false},{"pmid":"40170094","id":"PMC_40170094","title":"LncRNA SPINT1-AS1 enhances the Warburg effect and promotes the progression of osteosarcoma via the miR-135b-5p/PGAM1 axis.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/40170094","citation_count":0,"is_preprint":false},{"pmid":"40783674","id":"PMC_40783674","title":"SPINT1-AS1 promotes oxidative damage and apoptosis of gastric cancer cells via the miR-656-3p/PLCXD3 axis.","date":"2025","source":"Discover oncology","url":"https://pubmed.ncbi.nlm.nih.gov/40783674","citation_count":0,"is_preprint":false},{"pmid":"42064581","id":"PMC_42064581","title":"The role of HAI-1 in urothelial bladder cancer: Tissue expression, ectodomain shedding and clinical outcomes.","date":"2026","source":"Biochemistry and biophysics reports","url":"https://pubmed.ncbi.nlm.nih.gov/42064581","citation_count":0,"is_preprint":false},{"pmid":"15968977","id":"PMC_15968977","title":"[Expression of GST-HAI-1 fusion protein and development of monoclonal antibody against human hepatocyte growth factor activator inhibitor 1].","date":"2004","source":"Sheng wu gong cheng xue bao = Chinese journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/15968977","citation_count":0,"is_preprint":false},{"pmid":"16507252","id":"PMC_16507252","title":"[Construction of prokaryotic expression vectors of HAI-1 with different domains and expression of the fusion proteins].","date":"2006","source":"Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16507252","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":42329,"output_tokens":9267,"usd":0.132996,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":19401,"output_tokens":4676,"usd":0.106953,"stage2_stop_reason":"end_turn"},"total_usd":0.239949,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"HAI-1 (SPINT1) is required for matriptase activation: HAI-1 is co-translocated with matriptase to cell-cell junctions upon sphingosine 1-phosphate (S1P) stimulation, and HAI-1 knockdown or anti-HAI-1 antibody treatment causes spontaneous matriptase activation. Coexpression of wild-type HAI-1 (but not Kunitz domain 1 mutants) rescues matriptase trafficking to the cell surface in cells lacking endogenous HAI-1; catalytically defective matriptase mutants traffic normally without HAI-1, indicating HAI-1 prevents inappropriate matriptase proteolytic activity during synthesis and trafficking.\",\n      \"method\": \"siRNA knockdown, anti-HAI-1 monoclonal antibody treatment, co-expression of wild-type vs. Kunitz domain mutant HAI-1, immunofluorescence, Western blot, S1P stimulation assay\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (siRNA, antibody blockade, domain mutagenesis, co-expression rescue) in a single focused study with rigorous controls\",\n      \"pmids\": [\"15800053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"HAI-1B, a splice variant of HAI-1 containing an extra 16 amino acids adjacent to the C-terminus of KD1, potently inhibits HGFA (IC50=30.5 nM), matriptase (IC50=16.5 nM), and trypsin (IC50=2.4 nM), with weak inhibition of plasmin and plasma kallikrein, and no significant inhibition of plasminogen activators, coagulation enzymes, or activated protein C. P1 residue-directed mutagenesis demonstrated that inhibition is mediated exclusively by KD1 and not KD2.\",\n      \"method\": \"Soluble recombinant protein production, enzyme inhibition assays (IC50 determination against 16 serine proteases), P1 residue-directed mutagenesis of Kunitz domains\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with active-site mutagenesis across multiple proteases in a single rigorous study\",\n      \"pmids\": [\"12815039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HAI-1 (SPINT1) is essential for branching morphogenesis of the chorioallantoic placenta in mice. Homozygous HAI-1-/- mice die at ~E10.5 with severely impaired labyrinth layer formation but intact spongiotrophoblast and giant cell layers, indicating a specific role in trophoblast branching rather than general placental cell identity.\",\n      \"method\": \"Homozygous gene knockout by homologous recombination in mice, histological analysis at E9.5 and E10.5\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with specific phenotypic readout, independently corroborated by a second HAI-1 KO mouse study (PMID:17174946)\",\n      \"pmids\": [\"15964823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HAI-1 is essential for the integrity of basement membranes in the developing placental labyrinth. HAI-1-/- placentas show disrupted collagen IV and laminin-containing basement membranes at the trophoblast–allantoic mesoderm interface, resulting in failed vascularization. Matriptase and prostasin co-localize with HAI-1 in labyrinthine trophoblasts in wild-type placentas, and their localization and expression are unchanged in HAI-1-/- placentas, implying uncontrolled proteolytic activity of these enzymes underlies the basement membrane defects.\",\n      \"method\": \"Gene knockout mice, immunofluorescent staining of collagen IV and laminin, electron microscopy, immunohistochemistry\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independent replication of HAI-1 KO phenotype with mechanistic protein localization data using multiple orthogonal methods\",\n      \"pmids\": [\"17174946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"HAI-1/SPINT1 is required for normal epidermal keratinization and hair development. Spint1-/- mice rescued from embryonic lethality (by blastocyst complementation) develop ichthyosis-like scaly skin with hyperkeratosis, acanthosis with enhanced Akt phosphorylation, and abnormal hair shafts. HAI-1 deficiency causes altered proteolytic processing of profilaggrin with impaired generation of filaggrin monomers.\",\n      \"method\": \"Blastocyst complementation rescue of Spint1-/- embryonic lethality, histology, immunoblot for profilaggrin/filaggrin processing, immunohistochemistry for Akt phosphorylation\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic rescue with specific biochemical readout (profilaggrin processing), multiple orthogonal methods\",\n      \"pmids\": [\"18832587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss of HAI-1 (Spint1) in mice causes ichthyosis, acanthosis, and hypotrichosis through loss of suppression of a matriptase-dependent proteolytic pathway. Genetic epistasis: Spint1-deficient mice carrying a hypomorphic St14 (matriptase) allele survive normally with no histological abnormalities, demonstrating that matriptase suppression is the essential function of HAI-1 in postnatal tissue homeostasis.\",\n      \"method\": \"Genetic epistasis analysis using Spint1-/- × St14 hypomorphic double mutant mice, histological analysis, long-term survival monitoring\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis rescue experiment with comprehensive histological phenotyping\",\n      \"pmids\": [\"19389929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"HAI-1 mediates matriptase inhibition and complex formation selectively at the basolateral surface of polarized epithelial cells. Latent matriptase is targeted to the basolateral membrane; only matriptase–HAI-1 complexes (not latent matriptase) are detectable in seminal fluid and urine. In polarized Caco-2 cells, matriptase–HAI-1 complexes (but not latent matriptase) undergo transcytosis to the apical surface for secretion.\",\n      \"method\": \"Analysis of seminal fluid and urine for matriptase forms, polarized Caco-2 monolayer experiments, Western blot, immunohistochemistry of prostate and kidney\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with functional consequence, in vivo and in vitro orthogonal approaches in a single study\",\n      \"pmids\": [\"19535514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HAI-1 (Spint1) is required for maintenance of intestinal epithelial integrity. Intestine-specific Spint1 deletion causes crypt abnormalities, increased apoptosis, elevated epithelial turnover, increased intestinal permeability, and endoplasmic reticulum stress in colonic crypts, and greatly worsens experimental colitis (DSS model) with significantly lower survival.\",\n      \"method\": \"Conditional KO using Villin-Cre × Spint1-LoxP mice, histology, TUNEL assay, intestinal permeability assay, electron microscopy, DSS colitis model\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal phenotypic readouts and disease model validation\",\n      \"pmids\": [\"21840293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In HAI-1/SPINT1 deficiency, prostasin activation and pericellular serine protease activity are suppressed because cell-surface localization of matriptase is impaired. HAI-1/SPINT1 knockdown in BeWo trophoblast cells decreases cell-associated matriptase protein (without altering mRNA) and reduces laminin degradation activity, demonstrating that HAI-1 is required for cell-surface retention of matriptase to enable physiological activation of prostasin.\",\n      \"method\": \"siRNA knockdown of HAI-1 in BeWo cells, immunoblot for matriptase and prostasin, laminin degradation assay, immunohistochemistry of HAI-1-deficient mouse placentas\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with defined cellular phenotype and biochemical readout, single lab, two orthogonal approaches\",\n      \"pmids\": [\"23248048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Reduced prostasin (CAP1/PRSS8) activity rescues both HAI-1 and HAI-2 deficiency-associated developmental defects by preventing matriptase activation. Hypomorphic Prss8 mutations restore placentation and normal development of HAI-1-deficient embryos. Biochemical analysis revealed that prostasin is required for conversion of the matriptase zymogen to active matriptase, while prostasin zymogen activation is matriptase-independent in placental tissues.\",\n      \"method\": \"Genetic epistasis analysis with compound mutant mice (HAI-1 or HAI-2 deficient × Prss8 hypomorph), biochemical analysis of matriptase and prostasin activation in placental tissue\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple genotype combinations plus biochemical validation of mechanism\",\n      \"pmids\": [\"22952456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HAI-1 (SPINT1) regulates the activity of already-activated matriptase, whereas HAI-2 (not HAI-1) has an essential role in regulating prostasin-dependent matriptase zymogen activation. In genetically engineered mice, HAI-1 ablation does not affect matriptase in intestinal epithelial cells, but HAI-2 ablation causes loss of matriptase from both small and large intestine; gene silencing in Caco-2 cells shows this is due to accelerated matriptase activation and shedding caused by loss of prostasin regulation by HAI-2.\",\n      \"method\": \"Conditional KO mice (HAI-1 and HAI-2 ablation), gene silencing in Caco-2 monolayers, immunohistochemistry, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic knockout and in vitro gene silencing with mechanistic biochemical follow-up, two orthogonal model systems\",\n      \"pmids\": [\"24962579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Androgen receptor-mediated transcription and new protein synthesis are required for dihydrotestosterone (DHT)-induced matriptase activation and shedding in LNCaP prostate cancer cells. Activated matriptase is shed in complex with HAI-1; both latent matriptase and free HAI-1 are also shed. DHT-induced matriptase activation is blocked by the androgen antagonist bicalutamide, transcription inhibitor actinomycin D, and translation inhibitor cycloheximide.\",\n      \"method\": \"Hormone stimulation assays, pharmacological inhibitors (bicalutamide, actinomycin D, cycloheximide), Western blot, immunoprecipitation\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological inhibitors with defined biochemical readouts, single lab\",\n      \"pmids\": [\"16467405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HAI-1 acts as a specific cell-surface binding protein and reservoir for active HGFA on the epithelial cell surface; active HGFA–HAI-1 complexes are rapidly released from the cell surface by IL-1β treatment with significant recovery of HGFA activity in culture supernatant, suggesting HAI-1 localizes HGFA to facilitate pericellular HGF activation in injured mucosa.\",\n      \"method\": \"Cell surface binding assays, immunoprecipitation, IL-1β stimulation experiments, enzyme activity assays in culture supernatant\",\n      \"journal\": \"Journal of gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP and cell-surface binding with functional enzyme activity readout, single lab\",\n      \"pmids\": [\"12572861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the KD1–HGFA complex reveals that HAI-1 KD1 inhibits HGFA by occupying the active site in a substrate-like manner, making contacts with all substrate specificity-determining loops and occupying subsites S1, S2, and S4. KD1 side chains occupying these sites are virtually superimposable on P1, P2, and P4 residues of a pro-HGF-derived substrate mimic.\",\n      \"method\": \"X-ray crystallography of KD1–HGFA complex, structural comparison with substrate analog-bound HGFA\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with substrate analog comparison providing atomic-level mechanism of inhibition\",\n      \"pmids\": [\"20402765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"When HAI-1 levels are insufficient, active matriptase forms a 140-kDa homodimer (in addition to a 100-kDa complex with unidentified inhibitors) as a mechanism to control its activity. The 140-kDa dimer contains two-chain activated matriptase, lacks gelatinolytic activity, and its levels are inversely correlated with the HAI-1:matriptase ratio, suggesting it may represent a matriptase autoactivation intermediate.\",\n      \"method\": \"Western blot, gel filtration/biochemical characterization of matriptase complexes, gelatin zymography, immunoprecipitation\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical methods characterizing novel complex, single lab\",\n      \"pmids\": [\"22031598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"γ-Catenin (Plakoglobin) reduces NSCLC cell migration in a p53-dependent manner by inducing HAI-1 (SPINT1) expression, which serves as an upstream inhibitor of c-MET signaling. Re-expression of γ-catenin sensitizes NSCLC cells to c-MET inhibitor-mediated growth inhibition.\",\n      \"method\": \"γ-Catenin expression in NSCLC cells, scratch and trans-well migration assays, Western blot for HAI-1 and c-MET pathway components, c-MET inhibitor treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — KO/OE with defined pathway placement (γ-catenin → HAI-1 → c-MET), multiple cell-based assays, single lab\",\n      \"pmids\": [\"25925948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Matriptase and prostasin both form complexes with HAI-1 in human milk (and in milk-derived mammary epithelial cells), providing in vivo evidence that HAI-1 inhibits both proteases during lactation. HAI-1 is the primary inhibitor for both matriptase and prostasin in this context.\",\n      \"method\": \"Immunoaffinity purification, ion exchange chromatography, Western blot analysis of human milk fractions and milk-derived mammary epithelial cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo protein complex identification by biochemical purification, single lab, orthogonal purification methods\",\n      \"pmids\": [\"27043831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure and SAXS solution structure of soluble full-length HAI-1 extracellular domain (sHAI-1) reveal that it exists in a compact, auto-inhibited conformation in which the active site of Kunitz domain 1 is sterically blocked by neighboring structural elements. In the presence of target proteases, sHAI-1 adopts an extended conformation that disables auto-inhibition, explaining the lower inhibitory activity of full-length versus truncated HAI-1 fragments.\",\n      \"method\": \"X-ray crystallography, small-angle X-ray scattering (SAXS), enzyme inhibition assays comparing full-length vs. truncated HAI-1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure and SAXS with functional validation by inhibition assays, multiple orthogonal structural methods\",\n      \"pmids\": [\"28348076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MMP-7 cleaves HAI-1 on the cancer cell surface, primarily between Gly451 and Leu452, releasing soluble HAI-1 (sHAI-1). This sHAI-1 induces homotypic cancer cell aggregation through the HAI-1 region corresponding to amino acids 141–249, which does not include the serine protease inhibitor domain. Cell-surface cholesterol sulfate is needed for sHAI-1 generation by MMP-7, but a cholesterol sulfate-independent MMP-7 action is critical for sHAI-1-mediated aggregation induction.\",\n      \"method\": \"Cell surface biotinylation, LC-MS/MS substrate identification, site-directed cleavage site mapping, cancer cell aggregation assays with recombinant sHAI-1 fragments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — mass spectrometry substrate identification, precise cleavage site mapping, functional cell aggregation assay with defined domain mapping\",\n      \"pmids\": [\"29046355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HAI-1 (at cell surface) is a more effective inhibitor of extracellular matriptase proteolytic activity than HAI-2 (predominantly intracellular) because of differential subcellular localization. Both HAI-1 and HAI-2 promote matriptase expression and cell-surface translocation, but HAI-1 cell-surface expression allows it to efficiently capture active matriptase before shedding, whereas HAI-2's primarily intracellular localization prevents effective suppression of extracellular active matriptase.\",\n      \"method\": \"Immunohistochemistry, Western blot, cell surface biotinylation/avidin depletion, analysis of prostasin-matriptase complexes in human skin foreskin lysates\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization tied to functional consequence with biochemical verification, single lab\",\n      \"pmids\": [\"29438412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TMPRSS11A-related enzymes human airway tryptase and DESC1, but not TMPRSS11A itself, are blocked by HAI-1 in their ability to activate influenza A virus hemagglutinin, demonstrating differential sensitivity of HA-activating TTSPs to HAI-1 inhibition.\",\n      \"method\": \"Cell-based HA cleavage assays, protease inhibition assays with recombinant HAI-1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and cell-based inhibition assays with specific protease/inhibitor pairs, single lab\",\n      \"pmids\": [\"29976755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HAI-1 (SPINT1) expression in tumor-associated macrophages is regulated by HIF-2α under hypoxia. HIF-2α-deficient bone marrow-derived macrophages show reduced Spint1 mRNA and protein secretion under hypoxia. Supernatants from HIF-2α KO macrophages (lacking Spint1) could activate pro-HGF to stimulate breast tumor cell proliferation, while wild-type macrophage supernatants containing Spint1 failed to do so.\",\n      \"method\": \"RNA-seq of sorted TAMs from HIF-2α LysM-/- vs. WT mice, RT-PCR, ELISA for secreted Spint1, pro-HGF activation assay in breast tumor cell proliferation\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq plus functional validation of Spint1 role in pro-HGF activation, single lab with multiple methods\",\n      \"pmids\": [\"31436357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CDX2 transcription factor directly regulates both ST14 (matriptase) and SPINT1 (HAI-1) gene expression in intestinal cells through binding to CDX2-enriched enhancer elements identified by ChIP-seq. CDX2 is not required for basal ST14 and SPINT1 expression, but changes in CDX2 expression alter the ST14/SPINT1 mRNA ratio in a cell-type-dependent manner.\",\n      \"method\": \"siRNA KD of CDX2, promoter-reporter assays, CDX2 ChIP-seq analysis, RT-PCR\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq with promoter-reporter functional validation, multiple cell lines, single lab\",\n      \"pmids\": [\"30087389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Grhl2 transcription factor directly binds to the Spint1 gene in developing mouse submandibular salivary gland (confirmed by ChIP-PCR), and Grhl2 knockdown suppresses SPINT1 expression concomitant with retardation of epithelial development and disorganized laminin deposition. Addition of recombinant SPINT1 protein rescues the suppressive effects of Grhl2 siRNA on epithelial development and laminin deposition.\",\n      \"method\": \"siRNA knockdown of Grhl2 in ex vivo SMG culture, RT-PCR for SPINT1 mRNA, ChIP-PCR for Grhl2 binding to Spint1 gene, recombinant SPINT1 rescue experiment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — ChIP-PCR demonstrating direct TF binding, confirmed by rescue with recombinant protein, two orthogonal methods\",\n      \"pmids\": [\"30193734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HAI-1 (and HAI-2) inhibits the zymogen form of matriptase in addition to the activated form. Using purified proteins and cell-based assays, HAI-1 inhibits matriptase zymogen activity toward peptide-based substrates and the natural protein substrates pro-HGF and pro-prostasin at concentrations comparable to inhibition of activated matriptase, suggesting interaction at the active site of the zymogen.\",\n      \"method\": \"In vitro enzyme inhibition assays with purified HAI-1 and matriptase zymogen, peptide substrate cleavage assay, pro-HGF and pro-prostasin cleavage assays, cell-based assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple natural substrates and cell-based confirmation, single lab\",\n      \"pmids\": [\"32338287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HAI-1 deficiency increases prostasin proteolysis (through increased protein expression and zymogen activation) but paradoxically decreases matriptase proteolysis in HaCaT human keratinocytes. In HAI-1-deficient cells, all activated prostasin is found in complex with HAI-2, and matriptase zymogen activation and shedding are suppressed. This demonstrates that HAI-1 has opposite effects on matriptase versus prostasin proteolysis in keratinocytes.\",\n      \"method\": \"CRISPR/targeted HAI-1 deletion in HaCaT keratinocytes, Western blot for protease activation states, immunoprecipitation for complex formation\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — targeted KO with multiple biochemical readouts, novel mechanistic finding with clear controls, single lab\",\n      \"pmids\": [\"33486722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HAI-1 and HAI-2 differ in their subcellular targeting due to differences in their intracellular Arg/Lys-rich and EHLVY motifs. HAI-1 localizes both intracellularly and at the cell surface, while HAI-2 localizes predominantly in intracellular granules. Domain swap and point mutation studies combined with immunocytochemistry and cell surface biotinylation revealed these intrinsic sequence differences control the differential subcellular distribution.\",\n      \"method\": \"Domain swap constructs, site-directed point mutations, immunocytochemistry, cell surface biotinylation/avidin depletion, confocal microscopy\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — mutagenesis combined with direct subcellular localization experiments defining the molecular determinants, multiple orthogonal methods\",\n      \"pmids\": [\"34643933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HAI-1 loss in intestine-specific Spint1-deleted ApcMin/+ mice promotes intestinal carcinogenesis through NF-κB signaling activation, as evidenced by upregulation of inflammatory cytokines (TNF-α, IL-6), increased nuclear NF-κB translocation in normal mucosa and tumor tissues, and upregulation of NF-κB target urokinase-type plasminogen activator. Treatment with DHMEQ (NF-κB inhibitor) reduced intestinal tumor formation in these mice.\",\n      \"method\": \"Conditional intestinal Spint1 KO in ApcMin/+ background, RT-PCR and immunohistochemistry for NF-κB targets, DHMEQ pharmacological treatment experiment\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic model with pharmacological rescue and mechanistic pathway identification, single lab\",\n      \"pmids\": [\"27612426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPINT1 in pancreatic β cells controls glucose homeostasis by suppressing the serine protease HEPSIN. SPINT1 and HEPSIN interact in β cells; Hepsin silencing counteracts the downregulation of Mafa and Ins1 caused by Spint1 depletion. SPINT1 loss or HEPSIN overexpression reduces GLP1R-related cyclic AMP levels and Mafa expression. Spint1-disrupted mice show reduced Exendin-4-induced insulin secretion, and pancreas-specific Spint1 disruption diminishes islet size and mass, causing glucose intolerance.\",\n      \"method\": \"Spint1-lacZ knock-in mice, pancreas-specific Spint1 KO mice, siRNA gene silencing, co-immunoprecipitation (SPINT1–HEPSIN interaction), cAMP assays, Exendin-4 challenge, glucose tolerance tests, Western blot\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vivo KO with multiple functional readouts, Co-IP for direct interaction, pharmacological challenge, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"39627229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HAI-1 (SPINT1) loss in keratinocytes upregulates MMP-9 expression via NF-κB activation, leading to increased MMP gelatinolytic activity and disrupted epidermal basement membrane structure. Treatment of SPINT1 KO HaCaT cells with DHMEQ (NF-κB inhibitor) abrogates MMP-9 upregulation and associated gelatinolytic activity.\",\n      \"method\": \"SPINT1 KO HaCaT cells, gelatin zymography, Western blot, electron microscopy of Spint1-deleted skin, DHMEQ pharmacological inhibition\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined biochemical mechanism and pharmacological rescue, single lab, two orthogonal methods\",\n      \"pmids\": [\"39730982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Decreased HAI-1 immunoreactivity in colorectal carcinoma cells results largely from enhanced ectodomain shedding of HAI-1. In contrast, at the invasion front, membrane-form HAI-1 is paradoxically enhanced, correlating with decreased E-cadherin expression and low proliferative activity (MIB-1 negative), revealing distinct regulation of membrane-bound versus shed HAI-1 in cancer progression.\",\n      \"method\": \"Immunohistochemistry with three anti-HAI-1 antibodies recognizing distinct epitopes, in situ hybridization for HAI-1 mRNA\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple antibody epitopes and ISH provide distinct mechanistic insight into ectodomain shedding, single lab\",\n      \"pmids\": [\"15471558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"HAI-1 functions as a cell-surface inhibitor and reservoir of HGFA in colorectal carcinoma, where HGF activation is significantly enhanced compared to normal mucosa. HAI-1 cell-surface binding of active HGFA may paradoxically ensure concentrated pericellular HGFA activity when shedding of the HAI-1/HGFA complex is upregulated.\",\n      \"method\": \"In vitro cell-surface HGFA binding assays, immunohistochemistry, enzyme activity assays in colorectal tissue extracts\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct cell-surface binding assay combined with tissue enzyme activity measurements and IHC, single lab\",\n      \"pmids\": [\"11436357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"An engineered bivalent HAI-1 KD1-based inhibitor (KD1 duplicated via domain replacement of inactive KD2, fused to antibody Fc) inhibits matriptase with a Ki of 70 ± 5 pM (120-fold improvement over natural HAI-1), inhibits pro-HGF activation by matriptase, and inhibits matriptase on cancer cells with greater than an order-of-magnitude higher efficacy than monomeric KD1. This establishes that HAI-1 KD1 is the minimal matriptase-binding domain and that KD2 is involved in negative regulation.\",\n      \"method\": \"Rational domain engineering, combinatorial library screening, in vitro enzyme inhibition assays (Ki determination), pro-HGF cleavage assay, cancer cell surface matriptase inhibition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with quantitative affinity measurement, multiple substrates/assays defining domain function\",\n      \"pmids\": [\"29386351\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPINT1 (HAI-1) is a membrane-anchored, multidomain Kunitz-type serine protease inhibitor whose primary cellular function is to tightly regulate the pericellular proteolytic activity of matriptase (ST14) and, to a lesser extent, prostasin (PRSS8) and HGFA: the crystal and SAXS structures of HAI-1 show it is auto-inhibited in full-length form (KD1 active site sterically blocked), becoming active upon engagement with target proteases; KD1 is the sole inhibitory domain responsible for potent inhibition of matriptase, HGFA, and prostasin; HAI-1 serves as a chaperone required for matriptase synthesis, intracellular trafficking, and surface localization, and also couples matriptase zymogen activation to immediate inhibition, forming shed matriptase–HAI-1 complexes; in vivo, HAI-1 is essential for placental labyrinth formation, postnatal epidermal barrier integrity, intestinal epithelial homeostasis, and pancreatic β-cell function (via HEPSIN suppression to maintain MAFA and insulin expression); HAI-1 also sequesters active HGFA on the cell surface to regulate pericellular HGF activation, and its loss triggers NF-κB-mediated upregulation of MMP-9 and urokinase, while its cell-surface localization (determined by intracellular Arg/Lys-rich and EHLVY targeting motifs) distinguishes it from the predominantly intracellular HAI-2 and renders it the default inhibitor of extracellular matriptase activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SPINT1 (HAI-1) is a membrane-anchored, multidomain Kunitz-type serine protease inhibitor that governs pericellular proteolysis at epithelial surfaces by controlling the activity of the type II transmembrane serine protease matriptase and its partner proteases [#5, #10]. Inhibitory activity resides exclusively in Kunitz domain 1 (KD1), which inhibits HGFA, matriptase, and trypsin while leaving plasminogen activators and coagulation enzymes untouched [#1]; crystallography shows KD1 occupies the protease active site in a substrate-like manner across the S1, S2, and S4 subsites [#13], and full-length HAI-1 exists in a compact auto-inhibited conformation in which the KD1 active site is sterically blocked until target-protease engagement triggers an extended, active conformation [#17]. HAI-1 acts as a chaperone required for matriptase synthesis, cell-surface trafficking, and retention, preventing inappropriate proteolytic activity during biosynthesis, and it captures activated matriptase to form shed matriptase–HAI-1 complexes [#0, #6, #8]; KD1 is the minimal matriptase-binding module while KD2 negatively regulates this interaction [#32]. Genetic epistasis establishes that suppression of a matriptase- and prostasin-dependent proteolytic cascade is the essential physiological function of HAI-1 [#5, #9]. HAI-1 is essential in vivo for placental labyrinth basement-membrane integrity [#2, #3], postnatal epidermal keratinization and profilaggrin processing [#4], intestinal epithelial homeostasis [#7], and pancreatic β-cell glucose homeostasis, where it suppresses HEPSIN to sustain MAFA and insulin expression [#28]. Loss of HAI-1 drives NF-κB–mediated upregulation of urokinase and MMP-9, linking proteolytic dysregulation to intestinal carcinogenesis and basement-membrane disruption [#27, #29]. Its cell-surface localization, dictated by intracellular Arg/Lys-rich and EHLVY targeting motifs, distinguishes it from the predominantly intracellular HAI-2 and makes HAI-1 the default inhibitor of extracellular matriptase activity [#19, #26].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established which proteases HAI-1 inhibits and localized inhibitory activity to a single domain, defining its target specificity.\",\n      \"evidence\": \"Recombinant soluble HAI-1B with IC50 determinations against 16 serine proteases and P1 active-site mutagenesis of both Kunitz domains\",\n      \"pmids\": [\"12815039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address regulation of HAI-1 inhibitory activity in the membrane-anchored full-length context\", \"Cellular trafficking and chaperone roles not yet examined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed HAI-1 is not merely an inhibitor but a chaperone required for matriptase trafficking and surface localization, explaining why its loss causes spontaneous protease activation.\",\n      \"evidence\": \"siRNA knockdown, anti-HAI-1 antibody blockade, and KD1-mutant co-expression rescue with immunofluorescence in S1P-stimulated cells\",\n      \"pmids\": [\"15800053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinants of co-trafficking not mapped\", \"Did not establish in vivo physiological consequence\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated an essential developmental requirement for HAI-1 in placental trophoblast branching, providing the first whole-organism phenotype.\",\n      \"evidence\": \"Homozygous Spint1 knockout mice with histology at E9.5–E10.5\",\n      \"pmids\": [\"15964823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the dysregulated protease responsible\", \"Embryonic lethality precluded study of postnatal roles\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linked HAI-1 loss mechanistically to basement-membrane destruction, implicating uncontrolled matriptase/prostasin proteolysis in the placental phenotype.\",\n      \"evidence\": \"Knockout placentas analyzed by collagen IV/laminin immunofluorescence, EM, and protease co-localization\",\n      \"pmids\": [\"17174946\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal protease not formally identified by epistasis at this stage\", \"Direct demonstration of excess proteolytic activity inferred from localization\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined HAI-1's postnatal role in epidermal barrier formation and tied it to a specific biochemical substrate-processing event.\",\n      \"evidence\": \"Blastocyst-complementation rescue of lethality, histology, and immunoblot of profilaggrin/filaggrin processing\",\n      \"pmids\": [\"18832587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether profilaggrin defect is direct or downstream of matriptase dysregulation\", \"Akt activation mechanism not resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Genetic epistasis proved matriptase suppression is the essential function of HAI-1 in tissue homeostasis, anchoring the entire mechanistic model.\",\n      \"evidence\": \"Spint1-/- × St14 hypomorph double-mutant mice with histology and survival monitoring\",\n      \"pmids\": [\"19389929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address the contribution of prostasin or HGFA\", \"Tissue-specific differences in protease dependence not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placed prostasin upstream as the matriptase zymogen activator and showed reducing prostasin rescues HAI-1 deficiency, refining the proteolytic cascade hierarchy.\",\n      \"evidence\": \"Compound mutant mice (HAI-1 or HAI-2 deficient × Prss8 hypomorph) with biochemical analysis of placental protease activation\",\n      \"pmids\": [\"22952456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how prostasin zymogen is itself activated\", \"Relative roles of HAI-1 vs HAI-2 in this cascade left for later work\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended HAI-1's essential role to adult intestinal epithelium and disease susceptibility via conditional deletion.\",\n      \"evidence\": \"Villin-Cre × Spint1-LoxP conditional KO with permeability assays, TUNEL, EM, and DSS colitis model\",\n      \"pmids\": [\"21840293\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not delineate the signaling pathway driving epithelial turnover and ER stress\", \"Causal protease in intestine not pinpointed here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Distinguished the non-redundant roles of HAI-1 versus HAI-2, showing HAI-1 controls activated matriptase while HAI-2 governs prostasin-driven zymogen activation.\",\n      \"evidence\": \"Conditional HAI-1 and HAI-2 knockout mice plus Caco-2 gene silencing with IHC and Western blot\",\n      \"pmids\": [\"24962579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of the division of labor (localization vs intrinsic activity) not yet defined\", \"Did not address compensatory regulation\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided atomic-level mechanism of inhibition, showing KD1 mimics a substrate to occupy the HGFA active site.\",\n      \"evidence\": \"X-ray crystallography of the KD1–HGFA complex compared to a substrate analog\",\n      \"pmids\": [\"20402765\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length auto-inhibited HAI-1 not yet determined\", \"Did not explain reduced potency of full-length inhibitor\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved why full-length HAI-1 is a weaker inhibitor than KD1 fragments by revealing a compact auto-inhibited conformation regulated by target-protease binding.\",\n      \"evidence\": \"Crystallography and SAXS of soluble full-length HAI-1 ectodomain with comparative inhibition assays\",\n      \"pmids\": [\"28348076\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In situ conformational switching at the membrane not directly visualized\", \"Kinetics of the conformational transition not measured\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed HAI-1 inhibits the matriptase zymogen as effectively as the active enzyme, expanding its regulatory window to pre-activation states.\",\n      \"evidence\": \"In vitro reconstitution with purified zymogen and natural substrates pro-HGF and pro-prostasin plus cell-based assays\",\n      \"pmids\": [\"32338287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of zymogen recognition not solved\", \"Physiological significance of zymogen inhibition in vivo not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified the intracellular sequence motifs (Arg/Lys-rich and EHLVY) that direct HAI-1 to the cell surface, explaining its functional divergence from intracellular HAI-2.\",\n      \"evidence\": \"Domain-swap and point-mutation constructs with immunocytochemistry, surface biotinylation, and confocal microscopy\",\n      \"pmids\": [\"34643933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trafficking machinery recognizing these motifs not identified\", \"Quantitative surface vs intracellular partitioning under physiological conditions not measured\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a distinct HAI-1 function in pancreatic β cells, suppressing HEPSIN to maintain GLP1R signaling, MAFA, and insulin expression for glucose homeostasis.\",\n      \"evidence\": \"Spint1-lacZ knock-in and pancreas-specific KO mice, siRNA silencing, SPINT1–HEPSIN co-IP, cAMP assays, Exendin-4 challenge, and glucose tolerance tests\",\n      \"pmids\": [\"39627229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HEPSIN inhibition uses the same KD1 active-site mechanism not shown\", \"Direct enzymatic inhibition of HEPSIN by HAI-1 not biochemically reconstituted\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected HAI-1 loss to NF-κB-driven MMP-9 upregulation as the route to basement-membrane disruption in epidermis.\",\n      \"evidence\": \"SPINT1 KO HaCaT cells with gelatin zymography, Western blot, skin EM, and DHMEQ NF-κB inhibition\",\n      \"pmids\": [\"39730982\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How protease dysregulation activates NF-κB upstream not defined\", \"single-cell-line mechanism not validated across epithelial tissues\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the auto-inhibited-to-active conformational switch, chaperone trafficking, and tissue-specific protease targeting (matriptase, prostasin, HGFA, HEPSIN) are coordinately controlled at the membrane in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated model linking conformational regulation to target selection\", \"Determinants of context-specific protease choice (e.g., HEPSIN in β cells vs matriptase in epithelium) not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 13, 17, 24, 32]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 13, 24]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [12, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 19, 26]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [6, 18, 30]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 13, 24]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 3, 4, 23]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 28]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [3, 29]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ST14\", \"PRSS8\", \"HGFA\", \"HPN\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}