{"gene":"SPINK2","run_date":"2026-06-10T07:46:40","timeline":{"discoveries":[{"year":2009,"finding":"The P1 residue Arg24 of SPINK2 is crucial for trypsin inhibition specificity; His25 (P1') and Phe26 (P2') also contribute to trypsin-SPINK2 interaction, while Pro23 (P2) does not directly participate. The 3D solution structure of SPINK2 was determined by NMR, revealing a Kazal domain with three disulfide bridges formed by six cysteines.","method":"Site-directed mutagenesis of active-site residues, inhibition assays with recombinant protein, NMR structure determination","journal":"Proteins","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure determination combined with active-site mutagenesis and functional inhibition assays in a single study","pmids":["19422058"],"is_preprint":false},{"year":2011,"finding":"Mouse SPINK2 has trypsin-inhibitory activity in vitro. SPINK2 is expressed specifically in germ cells of the testis (from pachytene spermatocyte stage onward) and is required for normal spermatogenesis; its deficiency leads to elevated serine protease activity, germ cell apoptosis, and reduced sperm number.","method":"Recombinant protein trypsin-inhibition assay; gene trap mutagenesis KO mice with histological analysis, immunoblot, and serine protease activity measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro enzymatic assay plus loss-of-function mouse model with multiple phenotypic readouts, independently consistent with other studies","pmids":["21705336"],"is_preprint":false},{"year":1993,"finding":"The HUSI-II (SPINK2) gene is a single-copy gene located on human chromosome 4, with exon-intron organization identical to other Kazal-type inhibitor genes; it has multiple transcription start points, a CpG island upstream of the transcription start, and a potential glucocorticoid-responsive element in intron 1.","method":"Genomic Southern hybridization, S1 mapping of transcription start point, somatic cell hybrid panel chromosomal localization, sequence analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple direct mapping and structural genomic methods in a single study; no functional validation of regulatory elements","pmids":["8428671"],"is_preprint":false},{"year":1991,"finding":"HUSI-II (SPINK2) can be expressed as a biologically active secreted protein in E. coli via fusion to the ompA leader peptide; site-directed mutagenesis of the reactive-site loop generates variants that inhibit human leukocyte elastase, demonstrating the loop region determines protease specificity.","method":"Recombinant expression in E. coli, site-directed mutagenesis, biological activity assay","journal":"Biomedica biochimica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro mutagenesis and activity assay but single study with limited detail in abstract","pmids":["1801743"],"is_preprint":false},{"year":2017,"finding":"In the absence of SPINK2, uncontrolled protease activity causes Golgi fragmentation and prevents acrosome biogenesis, leading to spermatid differentiation arrest and azoospermia. SPINK2 coexpression alleviated the deleterious effect of acrosin overexpression in HEK cells, confirming SPINK2 functions as an acrosin inhibitor during cellular transit of proteases toward the acrosome.","method":"Homozygous Spink2 KO mice (histology, electron microscopy), acrosin overexpression in HEK cells with/without SPINK2 coexpression, exome sequencing of human patients","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function mouse model with defined cellular phenotype plus cell-based rescue experiment confirming acrosin-inhibitory mechanism; replicated across human patients and mouse model","pmids":["28554943"],"is_preprint":false},{"year":2019,"finding":"Two chicken acrosin isoforms (acrosin and acrosin-like proteins) are physiological serine protease targets of SPINK2, as demonstrated by affinity chromatography combined with mass spectrometry identification and kinetic inhibition assays.","method":"Affinity chromatography, mass spectrometry, kinetic inhibition assays","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (affinity chromatography, MS, kinetics) in single study but in avian model","pmids":["31033055"],"is_preprint":false},{"year":2019,"finding":"TIG1 (RARRES2/tazarotene-induced gene 1) physically interacts with SPINK2 in NT2/D1 testicular carcinoma cells; SPINK2 enhances TIG1-regulated suppression of uPA activity and epithelial-mesenchymal transition (EMT), and SPINK2 silencing alleviates TIG1-mediated regulation of cell migration and invasion.","method":"Co-immunoprecipitation in NT2/D1 cells, SPINK2 silencing/overexpression, cell invasion/migration assays, uPA activity assay","journal":"BioMed research international","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP interaction plus functional loss-of-function with defined cellular readouts, single lab","pmids":["31886233"],"is_preprint":false},{"year":2019,"finding":"Engineered SPINK2 can serve as a protein scaffold for generating potent and selective protease inhibitors; by introducing random mutations into the flexible reactive-site loop, inhibitors with picomolar KD and sub-nanomolar Ki against specific serine proteases (e.g., KLK4) were obtained. Crystal structure of KLK4-engineered SPINK2 complex revealed extensive conformational complementarity at the binding interface.","method":"Phage display library screening, kinetic inhibition assays (KD, Ki determination), X-ray crystallography of KLK4-SPINK2 complex","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of protein-protease complex combined with quantitative kinetic assays and phage display engineering in single study","pmids":["31391482"],"is_preprint":false},{"year":2019,"finding":"SPAG6 interacts with SPINK2 (demonstrated by yeast two-hybrid assay) and co-localizes with SPINK2 around nuclei in CHO cells; in SPAG6-knockout mice, SPINK2 expression and acrosomal localization are lost, indicating SPAG6 stabilizes SPINK2 expression during spermatogenesis to support acrosome formation.","method":"Yeast two-hybrid assay, co-localization in CHO cells (co-transfection), immunofluorescence in SPAG6-KO mouse testes","journal":"National journal of andrology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid plus co-localization and KO mouse evidence, but no reciprocal Co-IP or direct binding quantification","pmids":["32216237"],"is_preprint":false},{"year":2014,"finding":"SPINK2 is expressed in retinal ganglion cells and is upregulated after optic nerve damage; overexpression of SPINK2 variants in D407 tissue culture cells increases susceptibility to staurosporine-induced apoptosis in a manner consistent with differential susceptibility between mouse strains, implicating SPINK2 in modulating apoptotic susceptibility.","method":"SNP mapping, quantitative expression analysis, overexpression in D407 cells with staurosporine apoptosis assay","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, overexpression with apoptosis assay but no direct mechanistic pathway placement","pmids":["24699552"],"is_preprint":false},{"year":2023,"finding":"SPINK2 is expressed in hematopoietic stem and progenitor cells (HSPCs) and CD34+ cells; the SPINK2 degradation constant was experimentally determined, enabling derivation of a mathematical model predicting a zone of inhibited serine protease activity surrounding SPINK2-secreting HSPCs. PRSS2 and PRSS57 were identified as putative target proteases expressed in HSPCs.","method":"Flow cytometry/cell fractionation for SPINK2 localization, SPINK2 degradation kinetics measurement, expression analysis of target proteases in HSPCs","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct measurement of degradation kinetics plus expression analysis of interacting proteases in primary human cells, single lab","pmids":["37378330"],"is_preprint":false},{"year":2024,"finding":"RARRES1 physically interacts with SPINK2 in HCC cells (demonstrated by co-immunoprecipitation); SPINK2 overexpression suppresses HCC cell proliferation and migration and increases sensitivity to lenvatinib, while SPINK2 knockdown promotes progression and decreases lenvatinib sensitivity.","method":"Co-immunoprecipitation, SPINK2 overexpression and knockdown in HCC cells, proliferation/migration assays, in vivo tumor models","journal":"Biology direct","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP interaction with functional gain/loss-of-function assays in vitro and in vivo, single lab","pmids":["38388961"],"is_preprint":false},{"year":2025,"finding":"Both SPAG6 and SPAG6L bind to SPINK2, with SPAG6 having approximately 10-fold higher binding affinity than SPAG6L, as measured in compound Spag6/Spag6l knockout mouse studies.","method":"Binding affinity measurements in compound knockout mouse models, histological and ultrastructural analysis","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, binding affinity reported but method details not specified in abstract, single study","pmids":[],"is_preprint":true},{"year":2026,"finding":"shRNA-mediated SPINK2 silencing in complex karyotype AML cell lines impairs proliferation and induces terminal myeloid commitment; SPINK2 deficiency is associated with significant downregulation of MECOM expression, suggesting a SPINK2-MECOM axis in enforcing aberrant self-renewal in complex karyotype AML.","method":"shRNA-mediated knockdown in AML cell lines, proliferation assays, differentiation/commitment assays, RNA-seq expression analysis","journal":"Cell death discovery","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, loss-of-function with cellular phenotype but molecular mechanism linking SPINK2 to MECOM not directly established","pmids":["41776172"],"is_preprint":false}],"current_model":"SPINK2 is a Kazal-type serine protease inhibitor whose P1 residue (Arg24) determines target specificity; it inhibits acrosin and trypsin-family proteases, is essential in male germ cells for neutralizing protease activity during acrosomal biogenesis (its loss causes Golgi fragmentation, acrosome biogenesis failure, and azoospermia), interacts physically with SPAG6 (which stabilizes SPINK2 in the acrosome), interacts with TIG1/RARRES1 to suppress uPA-mediated invasion, and in hematopoietic progenitors acts as a temporary inhibitor creating a spatially defined zone of serine protease suppression; engineered variants of its reactive-site loop can be used as scaffolds to generate highly selective protease inhibitors."},"narrative":{"mechanistic_narrative":"SPINK2 is a Kazal-type serine protease inhibitor that controls serine protease activity in germ cells and hematopoietic progenitors, with its reactive-site loop dictating target specificity [PMID:19422058, PMID:21705336]. Its solution structure is a single Kazal domain stabilized by three disulfide bridges, in which the P1 residue Arg24 is the principal determinant of trypsin-family inhibition, with His25 and Phe26 contributing to binding [PMID:19422058]. In the testis SPINK2 is expressed in germ cells from the pachytene spermatocyte stage and is essential for spermatogenesis: its loss elevates serine protease activity and triggers germ cell apoptosis [PMID:21705336], and uncontrolled protease activity in its absence causes Golgi fragmentation, blocks acrosome biogenesis, and produces azoospermia [PMID:28554943]. Cell-based rescue established that SPINK2 functions as an acrosin inhibitor that neutralizes protease activity during transit of proteases toward the acrosome [PMID:28554943], with acrosin isoforms confirmed as physiological targets [PMID:31033055]. SPAG6 binds SPINK2 and stabilizes its expression and acrosomal localization during spermatogenesis [PMID:32216237]. Beyond the germline, SPINK2 secreted by hematopoietic stem and progenitor cells creates a spatially defined zone of serine protease suppression, with PRSS2 and PRSS57 as candidate target proteases [PMID:37378330]. SPINK2 also physically interacts with TIG1/RARRES1 to enhance suppression of uPA activity, EMT, and cell invasion [PMID:31886233, PMID:38388961]. Its rigid, mutable reactive-site loop makes engineered SPINK2 a scaffold for generating highly selective, picomolar-affinity protease inhibitors, as demonstrated structurally against KLK4 [PMID:31391482].","teleology":[{"year":1991,"claim":"Established that SPINK2 is a secretable, biologically active Kazal inhibitor whose reactive-site loop determines protease specificity, framing the structural basis for its inhibitory function.","evidence":"Recombinant E. coli expression via ompA leader and site-directed mutagenesis of the reactive-site loop with activity assays","pmids":["1801743"],"confidence":"Medium","gaps":["No physiological substrate identified","Endogenous tissue function not addressed","No structural model"]},{"year":1993,"claim":"Defined SPINK2 as a single-copy chromosome 4 gene with canonical Kazal exon-intron organization and candidate regulatory elements, providing the genomic foundation.","evidence":"Genomic Southern hybridization, S1 mapping, somatic cell hybrid chromosomal localization","pmids":["8428671"],"confidence":"Medium","gaps":["Regulatory elements not functionally validated","Tissue expression pattern not defined","No link to protein function"]},{"year":2009,"claim":"Resolved the atomic basis of SPINK2 specificity by identifying Arg24 as the P1 specificity determinant within a disulfide-stabilized Kazal fold.","evidence":"NMR solution structure with active-site mutagenesis and trypsin inhibition assays on recombinant protein","pmids":["19422058"],"confidence":"High","gaps":["Physiological in vivo targets not established","No cellular or organismal function tested"]},{"year":2011,"claim":"Demonstrated that SPINK2 is a germ-cell-specific inhibitor essential for spermatogenesis, linking protease control to germ cell survival.","evidence":"Recombinant trypsin-inhibition assay plus gene-trap KO mice with histology, immunoblot and protease activity measurement","pmids":["21705336"],"confidence":"High","gaps":["Specific endogenous protease target not identified","Subcellular mechanism of protection not defined"]},{"year":2017,"claim":"Established the cellular mechanism by which SPINK2 loss causes infertility: failure to neutralize acrosin leads to Golgi fragmentation and acrosome biogenesis failure.","evidence":"Homozygous KO mice with EM, acrosin overexpression rescue in HEK cells, and patient exome sequencing","pmids":["28554943"],"confidence":"High","gaps":["Mechanism of acrosin trafficking control not fully resolved","Full spectrum of human mutations not catalogued"]},{"year":2019,"claim":"Identified acrosin isoforms as direct physiological targets, confirming the acrosin-inhibitory mechanism biochemically.","evidence":"Affinity chromatography, mass spectrometry, and kinetic inhibition assays in an avian model","pmids":["31033055"],"confidence":"Medium","gaps":["Shown in chicken, not human","Quantitative inhibition constants for mammalian acrosin not given"]},{"year":2019,"claim":"Revealed a non-germline role: SPINK2 interacts with TIG1/RARRES1 to suppress uPA activity and invasion, expanding its function into protease control in tumor cells.","evidence":"Co-IP in NT2/D1 cells with SPINK2 silencing/overexpression and invasion, migration and uPA activity assays","pmids":["31886233"],"confidence":"Medium","gaps":["Direct binding not quantified","Whether SPINK2 inhibits uPA directly versus via TIG1 unresolved"]},{"year":2019,"claim":"Showed SPINK2 can be engineered into a tunable scaffold for highly selective protease inhibitors, with structural proof of conformational complementarity.","evidence":"Phage display loop randomization, kinetic KD/Ki measurement, and X-ray crystallography of a KLK4-SPINK2 complex","pmids":["31391482"],"confidence":"High","gaps":["Engineered specificity does not define native target repertoire","Therapeutic application not tested in vivo"]},{"year":2019,"claim":"Identified SPAG6 as a binding partner that stabilizes SPINK2 expression and acrosomal localization, linking SPINK2 to the acrosomal protein machinery.","evidence":"Yeast two-hybrid, co-localization in CHO cells, and immunofluorescence in SPAG6-KO mouse testes","pmids":["32216237"],"confidence":"Medium","gaps":["No reciprocal Co-IP or binding affinity in original report","Mechanism of stabilization unknown"]},{"year":2023,"claim":"Extended SPINK2 function to hematopoiesis, showing secreted SPINK2 creates a spatially defined zone of protease suppression around progenitor cells.","evidence":"Localization by flow cytometry/fractionation, degradation kinetics measurement, and target protease expression analysis in primary human HSPCs","pmids":["37378330"],"confidence":"Medium","gaps":["PRSS2/PRSS57 inhibition only inferred, not biochemically confirmed","Functional consequence of the suppression zone untested"]},{"year":2024,"claim":"Confirmed RARRES1-SPINK2 interaction in hepatocellular carcinoma and assigned SPINK2 a tumor-suppressive, drug-sensitizing role.","evidence":"Co-IP with SPINK2 overexpression/knockdown, proliferation/migration assays and in vivo tumor models in HCC","pmids":["38388961"],"confidence":"Medium","gaps":["Protease-dependence of tumor suppression not established","Mechanism of lenvatinib sensitization unknown"]},{"year":2025,"claim":"Quantitatively distinguished SPAG6 and SPAG6L binding to SPINK2, refining the acrosomal interaction hierarchy.","evidence":"Binding affinity measurements in compound Spag6/Spag6l knockout mice with ultrastructural analysis (preprint)","pmids":[],"confidence":"Low","gaps":["Preprint with unspecified affinity method","Not independently confirmed"]},{"year":2026,"claim":"Implicated SPINK2 in malignant self-renewal via a candidate SPINK2-MECOM axis in complex karyotype AML.","evidence":"shRNA knockdown in AML cell lines with proliferation, differentiation and RNA-seq analysis","pmids":["41776172"],"confidence":"Low","gaps":["Molecular link between SPINK2 and MECOM not directly established","Protease-inhibitory relevance to AML unknown","Single-lab cell-line study"]},{"year":null,"claim":"How SPINK2 selects and engages its diverse physiological targets across germline, hematopoietic and tumor contexts, and whether its non-germline roles depend on protease inhibition versus partner-mediated scaffolding, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Direct human substrates beyond acrosin not biochemically validated","Mechanism unifying secreted versus intracellular roles unknown","Whether tumor and AML phenotypes require inhibitory activity untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,3,4,5,7]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,10]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[1,4]}],"complexes":[],"partners":["SPAG6","SPAG6L","RARRES1","RARRES2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P20155","full_name":"Serine protease inhibitor Kazal-type 2","aliases":["Acrosin-trypsin inhibitor","Epididymis tissue protein Li 172","HUSI-II"],"length_aa":84,"mass_kda":9.3,"function":"As a strong inhibitor of acrosin, it is required for normal spermiogenesis. It probably hinders premature activation of proacrosin and other proteases, thus preventing the cascade of events leading to spermiogenesis defects (PubMed:28554943). May be involved in the regulation of serine protease-dependent germ cell apoptosis (By similarity). It also inhibits trypsin","subcellular_location":"Secreted; Cytoplasmic vesicle, secretory vesicle, acrosome","url":"https://www.uniprot.org/uniprotkb/P20155/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPINK2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPINK2","total_profiled":1310},"omim":[{"mim_id":"618091","title":"SPERMATOGENIC FAILURE 29; SPGF29","url":"https://www.omim.org/entry/618091"},{"mim_id":"605753","title":"SERINE PROTEASE INHIBITOR, KAZAL-TYPE, 2; SPINK2","url":"https://www.omim.org/entry/605753"},{"mim_id":"601199","title":"CALCIUM-SENSING RECEPTOR; CASR","url":"https://www.omim.org/entry/601199"},{"mim_id":"258150","title":"SPERMATOGENIC FAILURE 1; SPGF1","url":"https://www.omim.org/entry/258150"},{"mim_id":"147563","title":"INTEGRIN-BINDING SIALOPROTEIN; IBSP","url":"https://www.omim.org/entry/147563"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Acrosome","reliability":"Supported"},{"location":"Equatorial segment","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"epididymis","ntpm":4955.9}],"url":"https://www.proteinatlas.org/search/SPINK2"},"hgnc":{"alias_symbol":["HUSI-II"],"prev_symbol":[]},"alphafold":{"accession":"P20155","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P20155","model_url":"https://alphafold.ebi.ac.uk/files/AF-P20155-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P20155-F1-predicted_aligned_error_v6.png","plddt_mean":85.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPINK2","jax_strain_url":"https://www.jax.org/strain/search?query=SPINK2"},"sequence":{"accession":"P20155","fasta_url":"https://rest.uniprot.org/uniprotkb/P20155.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P20155/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P20155"}},"corpus_meta":[{"pmid":"28554943","id":"PMC_28554943","title":"SPINK2 deficiency causes infertility by inducing sperm defects in heterozygotes and azoospermia in homozygotes.","date":"2017","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28554943","citation_count":93,"is_preprint":false},{"pmid":"21705336","id":"PMC_21705336","title":"Impaired spermatogenesis and fertility in mice carrying a mutation in the Spink2 gene expressed predominantly in testes.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21705336","citation_count":53,"is_preprint":false},{"pmid":"19422058","id":"PMC_19422058","title":"Identification of trypsin-inhibitory site and structure determination of human SPINK2 serine proteinase inhibitor.","date":"2009","source":"Proteins","url":"https://pubmed.ncbi.nlm.nih.gov/19422058","citation_count":19,"is_preprint":false},{"pmid":"31033055","id":"PMC_31033055","title":"The seminal acrosin-inhibitor ClTI1/SPINK2 is a fertility-associated marker in the chicken.","date":"2019","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/31033055","citation_count":17,"is_preprint":false},{"pmid":"31886233","id":"PMC_31886233","title":"Tazarotene-Induced Gene 1 (TIG1) Interacts with Serine Protease Inhibitor Kazal-Type 2 (SPINK2) to Inhibit Cellular Invasion of Testicular Carcinoma Cells.","date":"2019","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/31886233","citation_count":14,"is_preprint":false},{"pmid":"24699552","id":"PMC_24699552","title":"Spink2 modulates apoptotic susceptibility and is a candidate gene in the Rgcs1 QTL that affects retinal ganglion cell death after optic nerve damage.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24699552","citation_count":11,"is_preprint":false},{"pmid":"38388961","id":"PMC_38388961","title":"RARRES1 inhibits hepatocellular carcinoma progression and increases its sensitivity to lenvatinib through interaction with SPINK2.","date":"2024","source":"Biology direct","url":"https://pubmed.ncbi.nlm.nih.gov/38388961","citation_count":8,"is_preprint":false},{"pmid":"8428671","id":"PMC_8428671","title":"Organization and sequence of the gene encoding the human acrosin-trypsin inhibitor (HUSI-II).","date":"1993","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/8428671","citation_count":8,"is_preprint":false},{"pmid":"36462395","id":"PMC_36462395","title":"Characterization of SPINK2, SPACA7 and PDCL2: Effect of immunization on fecundity, sperm function and testicular transcriptome.","date":"2022","source":"Reproductive biology","url":"https://pubmed.ncbi.nlm.nih.gov/36462395","citation_count":7,"is_preprint":false},{"pmid":"31391482","id":"PMC_31391482","title":"A protein scaffold, engineered SPINK2, for generation of inhibitors with high affinity and specificity against target proteases.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31391482","citation_count":7,"is_preprint":false},{"pmid":"37378330","id":"PMC_37378330","title":"Temporary serine protease inhibition and the role of SPINK2 in human bone marrow.","date":"2023","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/37378330","citation_count":5,"is_preprint":false},{"pmid":"37359898","id":"PMC_37359898","title":"Upregulation of SPINK2 in acute myeloid leukemia.","date":"2023","source":"Advances in laboratory medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37359898","citation_count":3,"is_preprint":false},{"pmid":"36965905","id":"PMC_36965905","title":"Concomitance of 47,XXY, a balanced reciprocal translocation of t(4;17)(q12;q11.2) encompassing SPINK2 at 4q12 and NOS at 17q11.2 and an AZFa sY86 deletion in an infertile male.","date":"2023","source":"Taiwanese journal of obstetrics & gynecology","url":"https://pubmed.ncbi.nlm.nih.gov/36965905","citation_count":1,"is_preprint":false},{"pmid":"32216237","id":"PMC_32216237","title":"[The role of SPAG6/SPINK2 protein complex in the formation of sperm acrosome in mice].","date":"2019","source":"Zhonghua nan ke xue = National journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/32216237","citation_count":1,"is_preprint":false},{"pmid":"41776172","id":"PMC_41776172","title":"SPINK2 silencing suppresses leukemic proliferation and restores myeloid commitment via MECOM downregulation in acute myeloid leukaemia.","date":"2026","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/41776172","citation_count":0,"is_preprint":false},{"pmid":"1801743","id":"PMC_1801743","title":"Variants of human seminal acrosin inhibitor (HUSI-II) which inhibit human leukocyte elastase.","date":"1991","source":"Biomedica biochimica acta","url":"https://pubmed.ncbi.nlm.nih.gov/1801743","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.18.665465","title":"Two  <i>Spag6</i>  genes control sperm formation and male fertility in mice","date":"2025-07-22","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.18.665465","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.06.25323506","title":"Molecular architecture of human atherosclerosis revealed through integrative human genetics","date":"2025-03-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.06.25323506","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10732,"output_tokens":3429,"usd":0.041815,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10977,"output_tokens":3683,"usd":0.07348,"stage2_stop_reason":"end_turn"},"total_usd":0.115295,"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\": 2009,\n      \"finding\": \"The P1 residue Arg24 of SPINK2 is crucial for trypsin inhibition specificity; His25 (P1') and Phe26 (P2') also contribute to trypsin-SPINK2 interaction, while Pro23 (P2) does not directly participate. The 3D solution structure of SPINK2 was determined by NMR, revealing a Kazal domain with three disulfide bridges formed by six cysteines.\",\n      \"method\": \"Site-directed mutagenesis of active-site residues, inhibition assays with recombinant protein, NMR structure determination\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure determination combined with active-site mutagenesis and functional inhibition assays in a single study\",\n      \"pmids\": [\"19422058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mouse SPINK2 has trypsin-inhibitory activity in vitro. SPINK2 is expressed specifically in germ cells of the testis (from pachytene spermatocyte stage onward) and is required for normal spermatogenesis; its deficiency leads to elevated serine protease activity, germ cell apoptosis, and reduced sperm number.\",\n      \"method\": \"Recombinant protein trypsin-inhibition assay; gene trap mutagenesis KO mice with histological analysis, immunoblot, and serine protease activity measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro enzymatic assay plus loss-of-function mouse model with multiple phenotypic readouts, independently consistent with other studies\",\n      \"pmids\": [\"21705336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The HUSI-II (SPINK2) gene is a single-copy gene located on human chromosome 4, with exon-intron organization identical to other Kazal-type inhibitor genes; it has multiple transcription start points, a CpG island upstream of the transcription start, and a potential glucocorticoid-responsive element in intron 1.\",\n      \"method\": \"Genomic Southern hybridization, S1 mapping of transcription start point, somatic cell hybrid panel chromosomal localization, sequence analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple direct mapping and structural genomic methods in a single study; no functional validation of regulatory elements\",\n      \"pmids\": [\"8428671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"HUSI-II (SPINK2) can be expressed as a biologically active secreted protein in E. coli via fusion to the ompA leader peptide; site-directed mutagenesis of the reactive-site loop generates variants that inhibit human leukocyte elastase, demonstrating the loop region determines protease specificity.\",\n      \"method\": \"Recombinant expression in E. coli, site-directed mutagenesis, biological activity assay\",\n      \"journal\": \"Biomedica biochimica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro mutagenesis and activity assay but single study with limited detail in abstract\",\n      \"pmids\": [\"1801743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In the absence of SPINK2, uncontrolled protease activity causes Golgi fragmentation and prevents acrosome biogenesis, leading to spermatid differentiation arrest and azoospermia. SPINK2 coexpression alleviated the deleterious effect of acrosin overexpression in HEK cells, confirming SPINK2 functions as an acrosin inhibitor during cellular transit of proteases toward the acrosome.\",\n      \"method\": \"Homozygous Spink2 KO mice (histology, electron microscopy), acrosin overexpression in HEK cells with/without SPINK2 coexpression, exome sequencing of human patients\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function mouse model with defined cellular phenotype plus cell-based rescue experiment confirming acrosin-inhibitory mechanism; replicated across human patients and mouse model\",\n      \"pmids\": [\"28554943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Two chicken acrosin isoforms (acrosin and acrosin-like proteins) are physiological serine protease targets of SPINK2, as demonstrated by affinity chromatography combined with mass spectrometry identification and kinetic inhibition assays.\",\n      \"method\": \"Affinity chromatography, mass spectrometry, kinetic inhibition assays\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (affinity chromatography, MS, kinetics) in single study but in avian model\",\n      \"pmids\": [\"31033055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TIG1 (RARRES2/tazarotene-induced gene 1) physically interacts with SPINK2 in NT2/D1 testicular carcinoma cells; SPINK2 enhances TIG1-regulated suppression of uPA activity and epithelial-mesenchymal transition (EMT), and SPINK2 silencing alleviates TIG1-mediated regulation of cell migration and invasion.\",\n      \"method\": \"Co-immunoprecipitation in NT2/D1 cells, SPINK2 silencing/overexpression, cell invasion/migration assays, uPA activity assay\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP interaction plus functional loss-of-function with defined cellular readouts, single lab\",\n      \"pmids\": [\"31886233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Engineered SPINK2 can serve as a protein scaffold for generating potent and selective protease inhibitors; by introducing random mutations into the flexible reactive-site loop, inhibitors with picomolar KD and sub-nanomolar Ki against specific serine proteases (e.g., KLK4) were obtained. Crystal structure of KLK4-engineered SPINK2 complex revealed extensive conformational complementarity at the binding interface.\",\n      \"method\": \"Phage display library screening, kinetic inhibition assays (KD, Ki determination), X-ray crystallography of KLK4-SPINK2 complex\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of protein-protease complex combined with quantitative kinetic assays and phage display engineering in single study\",\n      \"pmids\": [\"31391482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPAG6 interacts with SPINK2 (demonstrated by yeast two-hybrid assay) and co-localizes with SPINK2 around nuclei in CHO cells; in SPAG6-knockout mice, SPINK2 expression and acrosomal localization are lost, indicating SPAG6 stabilizes SPINK2 expression during spermatogenesis to support acrosome formation.\",\n      \"method\": \"Yeast two-hybrid assay, co-localization in CHO cells (co-transfection), immunofluorescence in SPAG6-KO mouse testes\",\n      \"journal\": \"National journal of andrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid plus co-localization and KO mouse evidence, but no reciprocal Co-IP or direct binding quantification\",\n      \"pmids\": [\"32216237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SPINK2 is expressed in retinal ganglion cells and is upregulated after optic nerve damage; overexpression of SPINK2 variants in D407 tissue culture cells increases susceptibility to staurosporine-induced apoptosis in a manner consistent with differential susceptibility between mouse strains, implicating SPINK2 in modulating apoptotic susceptibility.\",\n      \"method\": \"SNP mapping, quantitative expression analysis, overexpression in D407 cells with staurosporine apoptosis assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, overexpression with apoptosis assay but no direct mechanistic pathway placement\",\n      \"pmids\": [\"24699552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SPINK2 is expressed in hematopoietic stem and progenitor cells (HSPCs) and CD34+ cells; the SPINK2 degradation constant was experimentally determined, enabling derivation of a mathematical model predicting a zone of inhibited serine protease activity surrounding SPINK2-secreting HSPCs. PRSS2 and PRSS57 were identified as putative target proteases expressed in HSPCs.\",\n      \"method\": \"Flow cytometry/cell fractionation for SPINK2 localization, SPINK2 degradation kinetics measurement, expression analysis of target proteases in HSPCs\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct measurement of degradation kinetics plus expression analysis of interacting proteases in primary human cells, single lab\",\n      \"pmids\": [\"37378330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RARRES1 physically interacts with SPINK2 in HCC cells (demonstrated by co-immunoprecipitation); SPINK2 overexpression suppresses HCC cell proliferation and migration and increases sensitivity to lenvatinib, while SPINK2 knockdown promotes progression and decreases lenvatinib sensitivity.\",\n      \"method\": \"Co-immunoprecipitation, SPINK2 overexpression and knockdown in HCC cells, proliferation/migration assays, in vivo tumor models\",\n      \"journal\": \"Biology direct\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP interaction with functional gain/loss-of-function assays in vitro and in vivo, single lab\",\n      \"pmids\": [\"38388961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Both SPAG6 and SPAG6L bind to SPINK2, with SPAG6 having approximately 10-fold higher binding affinity than SPAG6L, as measured in compound Spag6/Spag6l knockout mouse studies.\",\n      \"method\": \"Binding affinity measurements in compound knockout mouse models, histological and ultrastructural analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, binding affinity reported but method details not specified in abstract, single study\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"shRNA-mediated SPINK2 silencing in complex karyotype AML cell lines impairs proliferation and induces terminal myeloid commitment; SPINK2 deficiency is associated with significant downregulation of MECOM expression, suggesting a SPINK2-MECOM axis in enforcing aberrant self-renewal in complex karyotype AML.\",\n      \"method\": \"shRNA-mediated knockdown in AML cell lines, proliferation assays, differentiation/commitment assays, RNA-seq expression analysis\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, loss-of-function with cellular phenotype but molecular mechanism linking SPINK2 to MECOM not directly established\",\n      \"pmids\": [\"41776172\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPINK2 is a Kazal-type serine protease inhibitor whose P1 residue (Arg24) determines target specificity; it inhibits acrosin and trypsin-family proteases, is essential in male germ cells for neutralizing protease activity during acrosomal biogenesis (its loss causes Golgi fragmentation, acrosome biogenesis failure, and azoospermia), interacts physically with SPAG6 (which stabilizes SPINK2 in the acrosome), interacts with TIG1/RARRES1 to suppress uPA-mediated invasion, and in hematopoietic progenitors acts as a temporary inhibitor creating a spatially defined zone of serine protease suppression; engineered variants of its reactive-site loop can be used as scaffolds to generate highly selective protease inhibitors.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SPINK2 is a Kazal-type serine protease inhibitor that controls serine protease activity in germ cells and hematopoietic progenitors, with its reactive-site loop dictating target specificity [#0, #1]. Its solution structure is a single Kazal domain stabilized by three disulfide bridges, in which the P1 residue Arg24 is the principal determinant of trypsin-family inhibition, with His25 and Phe26 contributing to binding [#0]. In the testis SPINK2 is expressed in germ cells from the pachytene spermatocyte stage and is essential for spermatogenesis: its loss elevates serine protease activity and triggers germ cell apoptosis [#1], and uncontrolled protease activity in its absence causes Golgi fragmentation, blocks acrosome biogenesis, and produces azoospermia [#4]. Cell-based rescue established that SPINK2 functions as an acrosin inhibitor that neutralizes protease activity during transit of proteases toward the acrosome [#4], with acrosin isoforms confirmed as physiological targets [#5]. SPAG6 binds SPINK2 and stabilizes its expression and acrosomal localization during spermatogenesis [#8]. Beyond the germline, SPINK2 secreted by hematopoietic stem and progenitor cells creates a spatially defined zone of serine protease suppression, with PRSS2 and PRSS57 as candidate target proteases [#10]. SPINK2 also physically interacts with TIG1/RARRES1 to enhance suppression of uPA activity, EMT, and cell invasion [#6, #11]. Its rigid, mutable reactive-site loop makes engineered SPINK2 a scaffold for generating highly selective, picomolar-affinity protease inhibitors, as demonstrated structurally against KLK4 [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Established that SPINK2 is a secretable, biologically active Kazal inhibitor whose reactive-site loop determines protease specificity, framing the structural basis for its inhibitory function.\",\n      \"evidence\": \"Recombinant E. coli expression via ompA leader and site-directed mutagenesis of the reactive-site loop with activity assays\",\n      \"pmids\": [\"1801743\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No physiological substrate identified\", \"Endogenous tissue function not addressed\", \"No structural model\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Defined SPINK2 as a single-copy chromosome 4 gene with canonical Kazal exon-intron organization and candidate regulatory elements, providing the genomic foundation.\",\n      \"evidence\": \"Genomic Southern hybridization, S1 mapping, somatic cell hybrid chromosomal localization\",\n      \"pmids\": [\"8428671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Regulatory elements not functionally validated\", \"Tissue expression pattern not defined\", \"No link to protein function\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved the atomic basis of SPINK2 specificity by identifying Arg24 as the P1 specificity determinant within a disulfide-stabilized Kazal fold.\",\n      \"evidence\": \"NMR solution structure with active-site mutagenesis and trypsin inhibition assays on recombinant protein\",\n      \"pmids\": [\"19422058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological in vivo targets not established\", \"No cellular or organismal function tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated that SPINK2 is a germ-cell-specific inhibitor essential for spermatogenesis, linking protease control to germ cell survival.\",\n      \"evidence\": \"Recombinant trypsin-inhibition assay plus gene-trap KO mice with histology, immunoblot and protease activity measurement\",\n      \"pmids\": [\"21705336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific endogenous protease target not identified\", \"Subcellular mechanism of protection not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established the cellular mechanism by which SPINK2 loss causes infertility: failure to neutralize acrosin leads to Golgi fragmentation and acrosome biogenesis failure.\",\n      \"evidence\": \"Homozygous KO mice with EM, acrosin overexpression rescue in HEK cells, and patient exome sequencing\",\n      \"pmids\": [\"28554943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of acrosin trafficking control not fully resolved\", \"Full spectrum of human mutations not catalogued\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified acrosin isoforms as direct physiological targets, confirming the acrosin-inhibitory mechanism biochemically.\",\n      \"evidence\": \"Affinity chromatography, mass spectrometry, and kinetic inhibition assays in an avian model\",\n      \"pmids\": [\"31033055\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Shown in chicken, not human\", \"Quantitative inhibition constants for mammalian acrosin not given\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a non-germline role: SPINK2 interacts with TIG1/RARRES1 to suppress uPA activity and invasion, expanding its function into protease control in tumor cells.\",\n      \"evidence\": \"Co-IP in NT2/D1 cells with SPINK2 silencing/overexpression and invasion, migration and uPA activity assays\",\n      \"pmids\": [\"31886233\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding not quantified\", \"Whether SPINK2 inhibits uPA directly versus via TIG1 unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed SPINK2 can be engineered into a tunable scaffold for highly selective protease inhibitors, with structural proof of conformational complementarity.\",\n      \"evidence\": \"Phage display loop randomization, kinetic KD/Ki measurement, and X-ray crystallography of a KLK4-SPINK2 complex\",\n      \"pmids\": [\"31391482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Engineered specificity does not define native target repertoire\", \"Therapeutic application not tested in vivo\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified SPAG6 as a binding partner that stabilizes SPINK2 expression and acrosomal localization, linking SPINK2 to the acrosomal protein machinery.\",\n      \"evidence\": \"Yeast two-hybrid, co-localization in CHO cells, and immunofluorescence in SPAG6-KO mouse testes\",\n      \"pmids\": [\"32216237\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reciprocal Co-IP or binding affinity in original report\", \"Mechanism of stabilization unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended SPINK2 function to hematopoiesis, showing secreted SPINK2 creates a spatially defined zone of protease suppression around progenitor cells.\",\n      \"evidence\": \"Localization by flow cytometry/fractionation, degradation kinetics measurement, and target protease expression analysis in primary human HSPCs\",\n      \"pmids\": [\"37378330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PRSS2/PRSS57 inhibition only inferred, not biochemically confirmed\", \"Functional consequence of the suppression zone untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Confirmed RARRES1-SPINK2 interaction in hepatocellular carcinoma and assigned SPINK2 a tumor-suppressive, drug-sensitizing role.\",\n      \"evidence\": \"Co-IP with SPINK2 overexpression/knockdown, proliferation/migration assays and in vivo tumor models in HCC\",\n      \"pmids\": [\"38388961\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease-dependence of tumor suppression not established\", \"Mechanism of lenvatinib sensitization unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Quantitatively distinguished SPAG6 and SPAG6L binding to SPINK2, refining the acrosomal interaction hierarchy.\",\n      \"evidence\": \"Binding affinity measurements in compound Spag6/Spag6l knockout mice with ultrastructural analysis (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint with unspecified affinity method\", \"Not independently confirmed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Implicated SPINK2 in malignant self-renewal via a candidate SPINK2-MECOM axis in complex karyotype AML.\",\n      \"evidence\": \"shRNA knockdown in AML cell lines with proliferation, differentiation and RNA-seq analysis\",\n      \"pmids\": [\"41776172\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Molecular link between SPINK2 and MECOM not directly established\", \"Protease-inhibitory relevance to AML unknown\", \"Single-lab cell-line study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SPINK2 selects and engages its diverse physiological targets across germline, hematopoietic and tumor contexts, and whether its non-germline roles depend on protease inhibition versus partner-mediated scaffolding, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Direct human substrates beyond acrosin not biochemically validated\", \"Mechanism unifying secreted versus intracellular roles unknown\", \"Whether tumor and AML phenotypes require inhibitory activity untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SPAG6\", \"SPAG6L\", \"RARRES1\", \"RARRES2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}