SPINK7

SPINK7 (ECRG2) is a Kazal-type serine protease inhibitor that safeguards epithelial barrier integrity and restrains inflammatory and tumor-invasive programs by neutralizing extracellular proteolytic activity (PMID:29875205, PMID:17602171). Its core biochemical activity is direct binding to and inhibition of urokinase plasminogen activator (uPA): SPINK7 engages the kringle domain of uPA, forms a complex with uPA·uPAR, and suppresses uPA/plasmin and MMP2 proteolysis (PMID:17602171, PMID:19717562, PMID:19796867). Through this inhibition it limits uPAR–β1 integrin association and downstream Src/MAP kinase signaling, and it blocks generation of the soluble uPAR fragment that engages FPRL1, thereby curbing cell migration and invasion and reducing in vivo metastasis (PMID:17602171, PMID:19717562, PMID:19796867). In epithelia, loss of SPINK7 unleashes uPA activity, driving uPAR-dependent eosinophil activation, barrier dysfunction, and TSLP production, with broad serine-protease inhibition reversing these defects (PMID:29875205); analogous protease-driven phenotypes underlie its protective roles in colitis and cutaneous wound healing, where SPINK7 loss elevates uPA, MMP2/9, and KLK5/7 activity and amplifies chemokine/cytokine output (PMID:33722746, PMID:40147022). SPINK7 expression is transcriptionally controlled by p53 in response to DNA damage and by the epithelial transcription factor OVOL1, the latter being degraded by IL-13–activated calpain-14 to suppress SPINK7 in eosinophilic esophagitis (PMID:32681017, PMID:42048165). Beyond protease inhibition, SPINK7 localizes to centrosomes and kinetochores to stabilize p53 and BUBR1 and preserve mitotic fidelity (PMID:18162463), and it promotes apoptosis by driving HuR ubiquitination to destabilize XIAP mRNA (PMID:26434587).

1. 2003 Medium

   Established the first molecular interaction and cellular activity for ECRG2, indicating a nuclear, growth-suppressive role in esophageal cancer cells.

   Evidence Yeast two-hybrid, GST pull-down, Co-IP, and confocal localization with proliferation/apoptosis assays in esophageal cancer cells

   PMID:12646258

   Open questions at the time

   • Functional significance of the MT2A interaction not mechanistically resolved
   • Nuclear localization not reconciled with later secreted protease-inhibitor role
   • Single-lab finding
2. 2007 High

   Defined SPINK7's biochemical activity as a direct uPA-binding inhibitor that suppresses proteolysis and metastasis, establishing it as a functional protease inhibitor.

   Evidence Binding assays, Co-IP from conditioned medium, plasmin substrate activity assay, in vitro invasion and tail-vein metastasis in nude mice

   PMID:17602171

   Open questions at the time

   • Did not map the binding site on uPA
   • Did not connect inhibition to downstream signaling
3. 2007 Medium

   Revealed a protease-independent role in mitotic fidelity, linking SPINK7 to p53 stabilization, centrosome integrity, and the spindle checkpoint.

   Evidence Immunofluorescence localization, siRNA knockdown, western blotting, CDK2 kinase assay, centrosome counting, and overexpression rescue

   PMID:18162463

   Open questions at the time

   • Molecular mechanism by which SPINK7 stabilizes p53 and BUBR1 unknown
   • How a protease inhibitor localizes to centrosomes/kinetochores unresolved
   • Single lab
4. 2009 High

   Mechanistically connected uPA inhibition to suppression of uPAR–β1 integrin/Src/MAPK signaling, explaining how SPINK7 limits cell migration.

   Evidence Domain-mapping binding, reciprocal Co-IP, siRNA depletion, Matrigel invasion, and Src/MAPK western blotting across cancer cell lines

   PMID:19717562

   Open questions at the time

   • Stoichiometry of the SPINK7·uPA·uPAR complex not defined
   • In vivo relevance of the signaling axis not tested
5. 2009 Medium

   Extended SPINK7's protease targets to MMP2 and showed it blocks uPAR cleavage and the sD2D3–FPRL1 migratory axis.

   Evidence uPA/plasmin and MMP2 activity assays, Co-IP, siRNA knockdown, and invasion assays in multiple cell lines

   PMID:19796867

   Open questions at the time

   • Direct versus indirect inhibition of MMP2 not distinguished
   • Single lab
6. 2015 High

   Identified an apoptosis-promoting mechanism via HuR ubiquitination and XIAP mRNA destabilization, and a cancer mutant that abolishes this activity.

   Evidence Co-IP, ubiquitination and mRNA-stability assays, caspase activation, and V30E mutant drug-resistance studies

   PMID:26434587

   Open questions at the time

   • How SPINK7 drives HuR ubiquitination (E3 ligase involvement) unresolved
   • Relationship between this activity and protease inhibition unclear
7. 2018 High

   Placed SPINK7 at the center of esophageal barrier homeostasis, showing its loss triggers uPA/uPAR-dependent eosinophil activation, barrier loss, and TSLP induction.

   Evidence siRNA silencing in esophageal epithelial cells, uPA activity assays, α1-antitrypsin rescue, and TSLP/PLAU genetic epistasis in vivo

   PMID:29875205

   Open questions at the time

   • Upstream regulators of SPINK7 in EoE not yet identified at this stage
   • Direct protease responsible for barrier loss not fully isolated
8. 2020 High

   Established SPINK7 as a direct DNA-damage-responsive p53 target gene, with a common defective promoter variant, linking it to genotoxic stress responses.

   Evidence Promoter-reporter luciferase assays, ChIP, RT-PCR, and knockout drug-survival assays

   PMID:32681017

   Open questions at the time

   • Physiological consequence of the population promoter variant not tested in vivo
   • Connection between p53-driven expression and protease-inhibitor function unexplored
9. 2021 Medium

   Demonstrated a protective immune-compartment role for SPINK7 in intestinal inflammation, expanding its function beyond epithelium to neutrophils.

   Evidence Spink7 KO mice, DSS colitis model, bone marrow reconstitution, and cytokine/chemokine profiling

   PMID:33722746

   Open questions at the time

   • Protease target driving the neutrophil phenotype not defined
   • Single lab
10. 2025 Medium

    Showed SPINK7 controls the resolution phase of wound healing by restraining a broad protease network (uPA, MMP2/9, KLK5/7) and shaping macrophage polarization.

    Evidence siRNA knockdown and KO mice in wound models, multi-protease activity assays, cytokine multiplex, and PAR2-inhibition epistasis

    PMID:40147022

    Open questions at the time

    • Direct versus indirect inhibition of each protease not separated
    • Mechanism linking protease control to M2 polarization unresolved
11. 2026 High

    Identified OVOL1 as a direct transcriptional activator of SPINK7 and a calpain-14/IL-13 axis that suppresses it, explaining SPINK7 loss in eosinophilic esophagitis.

    Evidence OVOL1 overexpression/depletion, promoter-reporter, nuclear localization assays, calpain-14 manipulation, barrier and TSLP readouts, and human biopsy correlation

    PMID:42048165

    Open questions at the time

    • Whether OVOL1 and p53 act combinatorially on the promoter not addressed
    • In vivo reversal of EoE by restoring SPINK7 not demonstrated

• How SPINK7's extracellular protease-inhibitory function mechanistically integrates with its intracellular roles in p53/BUBR1 stabilization, HuR/XIAP-driven apoptosis, and centrosome/kinetochore localization remains unresolved.
• No unified model reconciling secreted protease inhibition with nuclear/mitotic activities
• No structural model of SPINK7 protease complexes
• E3 ligase and direct partners for intracellular functions unidentified