{"gene":"KLK2","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2010,"finding":"KLK2 is the protease responsible for activating PSA (KLK3) zymogen, demonstrated in cell-based in vitro models (co-incubated cell clones), in vivo xenograft co-inoculation experiments, and PSA/KLK2 double-transgenic mice where double-transgenic animals produced more active PSA than single-transgenic animals.","method":"Cell-based co-incubation assays, subcutaneous xenograft co-inoculation, and prostate-targeted double-transgenic mouse models measuring free/total PSA ratios","journal":"The Prostate","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vitro and in vivo models across cell-based, xenograft, and transgenic systems, all converging on KLK2-mediated PSA activation","pmids":["20058238"],"is_preprint":false},{"year":2010,"finding":"KLK2 degrades IGFBP-3 into multiple small fragments with cleavage preferentially after Arg residues, consistent with its trypsin-like serine protease activity; cleavage sites were identified by mass spectrometry, and fragmentation was inhibited by KLK2-inhibiting peptides in a dose-dependent fashion.","method":"In vitro proteolysis assay with immunoblotting, two specific immunoassays (native vs. total IGFBP-3), mass spectrometry identification of cleavage sites, and KLK2-inhibiting peptide dose-response","journal":"Biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assay with mass spectrometry site mapping and peptide inhibitor confirmation, single lab but multiple orthogonal methods","pmids":["20180640"],"is_preprint":false},{"year":2008,"finding":"KLK2 enzymatic (proteolytic) activity can be specifically inhibited by peptides developed against it; peptide stability was improved by cyclization, enabling development of in vivo-applicable KLK2 inhibitors.","method":"Peptide-based enzymatic activity assays, in vitro peptide inhibition, peptide cyclization for stability improvement","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro activity assay with peptide inhibitors, single lab, abstract-level detail only","pmids":["18627344"],"is_preprint":false},{"year":2014,"finding":"KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance androgen receptor (AR) transactivation; KLK2 knockdown by siRNA caused increased apoptosis and G1-phase cell growth arrest, while KLK2 cDNA addition increased cell growth.","method":"KLK2 cDNA overexpression, KLK2-siRNA knockdown in LNCaP cells, colony formation assay, in vivo xenograft growth assay, AR transactivation reporter assay","journal":"Tumour biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function experiments with defined cellular phenotypes and AR transactivation mechanistic link, single lab with multiple assays","pmids":["24122203"],"is_preprint":false},{"year":2019,"finding":"A KLK2-FGFR2 fusion protein (identified in metastatic prostate cancer) activates downstream FGFR signaling pathways, promotes enhanced cell migration, and induces profound morphological changes when expressed in NIH3T3 cells; the fusion is sensitive to selective FGFR inhibitors (AZD-4547, BGJ398, JNJ-42756943, TAS-120, Ponatinib) but not Dovitinib.","method":"Targeted RNA-sequencing to identify fusion, retroviral transduction of NIH3T3 cells, migration assays, Western blots for downstream FGFR signaling activation, drug sensitivity assays","journal":"Prostate cancer and prostatic diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional characterization with multiple orthogonal methods (migration, signaling, drug sensitivity) in a cell model, single lab","pmids":["31043681"],"is_preprint":false},{"year":2024,"finding":"KLK2 cleaves the extracellular domain of IL-10 receptor chain-2 (IL-10R2) at the sequence SYRIF (residues 58–63), reducing IL-10R2 surface expression on macrophages and blunting IL-10-mediated anti-inflammatory signaling (decreased inhibition of nitric oxide, TNF-α, and IL-12 p40). KLK2 is fully active at pH 8.0–8.2 and is strongly activated by sodium citrate and glycosaminoglycans. KLK3 did not show the same effects.","method":"FRET peptide library screening to identify optimal substrate (SYRIF), flow cytometry (FACS) to measure IL-10R2 surface expression on bone-marrow-derived macrophages after KLK2 treatment, functional inflammatory assays measuring nitric oxide, TNF-α, and IL-12 p40; comparison with KLK3","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical substrate identification combined with cell-based functional validation using orthogonal readouts, with negative control (KLK3), single lab","pmids":["39106042"],"is_preprint":false},{"year":2025,"finding":"KLK2, previously considered a purely secreted serine protease with no cell-surface localization, has now been demonstrated to be expressed on the cell surface, making it targetable by antibody-based and other therapeutic modalities.","method":"Experimental demonstration of cell-surface localization (details attributed to a related article by Shen et al.)","journal":"Clinical cancer research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — editorial commentary citing a companion paper; cell-surface localization claim is referenced but experimental details not in this abstract","pmids":["40924642"],"is_preprint":false},{"year":2026,"finding":"KLK2 expression is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus and associated enhancer activation, as determined by epigenomic analysis of mCRPC patient samples; KLK2 expression is absent in neuroendocrine and AR-negative prostate cancer phenotypes.","method":"Transcriptomic and epigenomic profiling of 1095 mCRPC patient samples including ChIP/ATAC-seq-based analysis of AR/FOXA1/HOXB13 binding and enhancer activation, rapid autopsy cohort in situ studies","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — large multi-cohort epigenomic and transcriptomic analysis demonstrating mechanistic AR/FOXA1/HOXB13 co-regulation, but relies on correlative multi-omics rather than direct functional manipulation of KLK2 locus","pmids":["42189191"],"is_preprint":false},{"year":2002,"finding":"Alternative splicing of KLK2 involving inclusion of intronic sequences adjacent to exon 1 produces a novel protein (hK2-linked molecule, K-LM) that shares only the signal peptide with KLK2; the mature K-LM protein is entirely different from kallikreins and shows androgen-regulated prostate-specific expression similar to KLK2.","method":"Identification of splice variant mRNAs by molecular cloning, protein characterization, and androgen-stimulation expression analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — molecular cloning and expression analysis of splice variant, but functional role of K-LM protein not established; finding is about KLK2 gene structure/splicing","pmids":["11834722"],"is_preprint":false}],"current_model":"KLK2 is a prostate-specific trypsin-like serine protease whose transcription is strictly driven by androgen receptor (AR) in concert with FOXA1 and HOXB13; it activates the PSA (KLK3) zymogen, degrades IGFBP-3 at Arg residues to potentially promote IGF signaling, cleaves IL-10R2 on macrophages to dampen anti-inflammatory signaling, enhances AR transactivation in cooperation with the coregulator ARA70, can appear as an oncogenic KLK2-FGFR2 fusion that constitutively activates FGFR signaling, and — contrary to earlier assumptions — is also expressed on the prostate cancer cell surface, enabling antibody-based targeting strategies."},"narrative":{"mechanistic_narrative":"KLK2 is a prostate-specific, androgen-regulated trypsin-like serine protease that participates in prostate biology and prostate cancer through proteolytic processing of multiple substrates [PMID:20058238, PMID:20180640, PMID:39106042]. Its transcription is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus driving enhancer activation; consistent with this dependence, KLK2 expression is absent in AR-negative and neuroendocrine prostate cancer [PMID:42189191]. Enzymatically, KLK2 cleaves preferentially after arginine residues, activating the PSA (KLK3) zymogen [PMID:20058238], degrading IGFBP-3 into small fragments [PMID:20180640], and cleaving the extracellular domain of macrophage IL-10 receptor chain-2 (IL-10R2) at the SYRIF sequence to reduce IL-10R2 surface levels and blunt IL-10-mediated anti-inflammatory signaling, an activity favored at pH 8.0–8.2 and enhanced by sodium citrate and glycosaminoglycans [PMID:39106042]. Beyond proteolysis, KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance AR transactivation, with knockdown causing apoptosis and G1 arrest [PMID:24122203]. An oncogenic KLK2-FGFR2 fusion identified in metastatic disease constitutively activates FGFR signaling and is sensitive to selective FGFR inhibitors [PMID:31043681]. Its enzymatic activity can be specifically blocked by cyclized inhibitory peptides developed for in vivo application [PMID:18627344].","teleology":[{"year":2002,"claim":"Established that the KLK2 locus generates more than the canonical protease, revealing an alternatively spliced, androgen-regulated transcript encoding a distinct prostate-specific protein.","evidence":"Molecular cloning of splice-variant mRNAs and androgen-stimulation expression analysis","pmids":["11834722"],"confidence":"Medium","gaps":["Functional role of the K-LM protein not established","No protein-level activity or partner identified"]},{"year":2008,"claim":"Showed that KLK2 proteolytic activity is specifically druggable, providing chemical tools to dissect and inhibit its function in vivo.","evidence":"In vitro enzymatic activity assays with cyclized inhibitory peptides","pmids":["18627344"],"confidence":"Medium","gaps":["Abstract-level detail only","In vivo efficacy not demonstrated in this work","Substrate specificity of inhibition not defined"]},{"year":2010,"claim":"Resolved which protease activates the PSA zymogen by demonstrating KLK2-mediated PSA activation across orthogonal models, defining a key step in prostate kallikrein cascades.","evidence":"Cell co-incubation, xenograft co-inoculation, and PSA/KLK2 double-transgenic mice measuring free/total PSA","pmids":["20058238"],"confidence":"High","gaps":["Physiological/pathological consequence of PSA activation not addressed","Cleavage kinetics versus other activators not compared"]},{"year":2010,"claim":"Defined a substrate relevant to growth-factor signaling by mapping KLK2 cleavage of IGFBP-3, consistent with its trypsin-like Arg-directed specificity.","evidence":"In vitro proteolysis with immunoblot, native/total immunoassays, mass-spec site mapping, and peptide-inhibitor dose response","pmids":["20180640"],"confidence":"High","gaps":["Downstream effect on IGF signaling not directly demonstrated","Cellular relevance versus in vitro proteolysis not established"]},{"year":2014,"claim":"Linked KLK2 to prostate cancer cell proliferation through a non-proteolytic transcriptional mechanism, showing it enhances AR transactivation via ARA70.","evidence":"KLK2 cDNA overexpression and siRNA knockdown in LNCaP, colony formation, xenograft growth, and AR transactivation reporter assays","pmids":["24122203"],"confidence":"Medium","gaps":["Single lab","Mechanism of ARA70/AR cooperation not structurally defined","Whether proteolytic activity contributes to growth effect unclear"]},{"year":2019,"claim":"Identified an oncogenic KLK2-FGFR2 gene fusion as a driver event, connecting the androgen-driven locus to constitutive growth-factor receptor signaling.","evidence":"Targeted RNA-seq fusion discovery, retroviral expression in NIH3T3, migration/signaling assays, FGFR inhibitor sensitivity panel","pmids":["31043681"],"confidence":"Medium","gaps":["Frequency in patient populations not established","Functional studies in patient-derived prostate models lacking","Role of KLK2 portion in fusion activity undefined"]},{"year":2024,"claim":"Uncovered an immunomodulatory function by showing KLK2 cleaves IL-10R2 on macrophages to dampen anti-inflammatory signaling, with biochemical optima and a KLK3 negative control.","evidence":"FRET peptide-library substrate screen, FACS for IL-10R2 surface expression on BMDMs, inflammatory readouts (NO, TNF-alpha, IL-12 p40)","pmids":["39106042"],"confidence":"High","gaps":["In vivo relevance in the tumor microenvironment not shown","Source of KLK2 acting on macrophages not defined","Single lab"]},{"year":2026,"claim":"Mechanistically anchored KLK2 expression to AR/FOXA1/HOXB13 enhancer co-regulation across large mCRPC cohorts and showed loss in AR-negative/neuroendocrine disease.","evidence":"Transcriptomic/epigenomic profiling (ChIP/ATAC-seq) of 1095 mCRPC samples plus rapid autopsy in situ studies","pmids":["42189191"],"confidence":"Medium","gaps":["Correlative multi-omics rather than direct locus manipulation","Causality of individual factor binding not tested functionally"]},{"year":null,"claim":"Whether KLK2 cell-surface localization is a robust, generalizable feature enabling therapeutic targeting remains to be established with direct experimental detail.","evidence":"Editorial commentary referencing a companion paper for cell-surface localization","pmids":[],"confidence":"Low","gaps":["Experimental details of surface localization not in the cited commentary","Mechanism of membrane association of a secreted protease unknown","Targetability claim not independently validated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,5]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[3,7]}],"complexes":[],"partners":["KLK3","IGFBP3","IL10RB","AR","ARA70","FGFR2","FOXA1","HOXB13"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P20151","full_name":"Kallikrein-2","aliases":["Glandular kallikrein-1","hGK-1","Tissue kallikrein-2"],"length_aa":261,"mass_kda":28.7,"function":"Glandular kallikreins cleave Met-Lys and Arg-Ser bonds in kininogen to release Lys-bradykinin","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P20151/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KLK2","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/KLK2","total_profiled":1310},"omim":[{"mim_id":"611959","title":"PROSTATE CANCER, HEREDITARY, 15; HPC15","url":"https://www.omim.org/entry/611959"},{"mim_id":"605097","title":"SOLUTE CARRIER FAMILY 45, MEMBER 3; SLC45A3","url":"https://www.omim.org/entry/605097"},{"mim_id":"605096","title":"ANOCTAMIN 7; ANO7","url":"https://www.omim.org/entry/605096"},{"mim_id":"605094","title":"STEAP2 METALLOREDUCTASE; STEAP2","url":"https://www.omim.org/entry/605094"},{"mim_id":"604146","title":"SYNAPTOTAGMIN 7; SYT7","url":"https://www.omim.org/entry/604146"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"prostate","ntpm":530.8}],"url":"https://www.proteinatlas.org/search/KLK2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P20151","domains":[{"cath_id":"2.40.10.10","chopping":"30-258","consensus_level":"medium","plddt":97.4208,"start":30,"end":258}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P20151","model_url":"https://alphafold.ebi.ac.uk/files/AF-P20151-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P20151-F1-predicted_aligned_error_v6.png","plddt_mean":92.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KLK2","jax_strain_url":"https://www.jax.org/strain/search?query=KLK2"},"sequence":{"accession":"P20151","fasta_url":"https://rest.uniprot.org/uniprotkb/P20151.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P20151/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P20151"}},"corpus_meta":[{"pmid":"11834722","id":"PMC_11834722","title":"Unusual alternative splicing within the human kallikrein genes KLK2 and KLK3 gives rise to novel prostate-specific proteins.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11834722","citation_count":50,"is_preprint":false},{"pmid":"24122203","id":"PMC_24122203","title":"Human kallikrein 2 (KLK2) promotes prostate cancer cell growth via function as a modulator to promote the ARA70-enhanced androgen receptor transactivation.","date":"2014","source":"Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/24122203","citation_count":48,"is_preprint":false},{"pmid":"20058238","id":"PMC_20058238","title":"Prostate-specific antigen (PSA) is activated by KLK2 in prostate cancer ex vivo models and in prostate-targeted PSA/KLK2 double transgenic mice.","date":"2010","source":"The Prostate","url":"https://pubmed.ncbi.nlm.nih.gov/20058238","citation_count":33,"is_preprint":false},{"pmid":"25153390","id":"PMC_25153390","title":"Loss of miR-378 in prostate cancer, a common regulator of KLK2 and KLK4, correlates with aggressive disease phenotype and predicts the short-term relapse of the patients.","date":"2014","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25153390","citation_count":31,"is_preprint":false},{"pmid":"17085659","id":"PMC_17085659","title":"Variants of the hK2 protein gene (KLK2) are associated with serum hK2 levels and predict the presence of prostate cancer at biopsy.","date":"2006","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/17085659","citation_count":30,"is_preprint":false},{"pmid":"19823874","id":"PMC_19823874","title":"A comprehensive resequence analysis of the KLK15-KLK3-KLK2 locus on chromosome 19q13.33.","date":"2009","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19823874","citation_count":25,"is_preprint":false},{"pmid":"18627344","id":"PMC_18627344","title":"Development of peptides specifically modulating the activity of KLK2 and KLK3.","date":"2008","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18627344","citation_count":24,"is_preprint":false},{"pmid":"24270797","id":"PMC_24270797","title":"Genetic variation in KLK2 and KLK3 is associated with concentrations of hK2 and PSA in serum and seminal plasma in young men.","date":"2013","source":"Clinical chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24270797","citation_count":21,"is_preprint":false},{"pmid":"29614347","id":"PMC_29614347","title":"Discovery of novel transcripts of the human tissue kallikrein (KLK1) and kallikrein-related peptidase 2 (KLK2) in human cancer cells, exploiting Next-Generation Sequencing technology.","date":"2018","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/29614347","citation_count":15,"is_preprint":false},{"pmid":"23204305","id":"PMC_23204305","title":"Birth-and-death of KLK3 and KLK2 in primates: evolution driven by reproductive biology.","date":"2012","source":"Genome biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/23204305","citation_count":13,"is_preprint":false},{"pmid":"38396898","id":"PMC_38396898","title":"Genomic and Immunologic Correlates in Prostate Cancer with High Expression of KLK2.","date":"2024","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38396898","citation_count":11,"is_preprint":false},{"pmid":"20180640","id":"PMC_20180640","title":"Identification of IGFBP-3 fragments generated by KLK2 and prevention of fragmentation by KLK2-inhibiting peptides.","date":"2010","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20180640","citation_count":11,"is_preprint":false},{"pmid":"23359319","id":"PMC_23359319","title":"Genome-wide association study identifies loci at ATF7IP and KLK2 associated with percentage of circulating free PSA.","date":"2013","source":"Neoplasia (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/23359319","citation_count":10,"is_preprint":false},{"pmid":"31043681","id":"PMC_31043681","title":"Characterization of a KLK2-FGFR2 fusion gene in two cases of metastatic prostate cancer.","date":"2019","source":"Prostate cancer and prostatic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/31043681","citation_count":7,"is_preprint":false},{"pmid":"28216900","id":"PMC_28216900","title":"Trichosanthes kirilowii Exerts Androgenic Activity via Regulation of PSA and KLK2 in 22Rv1 Prostate Cancer Cells.","date":"2017","source":"Pharmacognosy magazine","url":"https://pubmed.ncbi.nlm.nih.gov/28216900","citation_count":3,"is_preprint":false},{"pmid":"23824286","id":"PMC_23824286","title":"Association of Polymorphism rs198977 in Human Kallikrein-2 Gene (KLK2) with Susceptibility of Prostate Cancer: A Meta-Analysis.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23824286","citation_count":2,"is_preprint":false},{"pmid":"37593117","id":"PMC_37593117","title":"KLK2 single-nucleotide polymorphism rs198977 is associated with increased susceptibility and hyperleukocytosis in AML.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37593117","citation_count":1,"is_preprint":false},{"pmid":"40924642","id":"PMC_40924642","title":"Drug Targets in Prostate Cancer: An Appetite for KLK2-Mediated Destruction.","date":"2025","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/40924642","citation_count":1,"is_preprint":false},{"pmid":"39106042","id":"PMC_39106042","title":"Extracellular Domain of IL-10 Receptor Chain-2 (IL-10R2) and Its Arginine-Containing Peptides Are Susceptible Substrates for Human Prostate Kallikrein-2 (KLK2).","date":"2024","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39106042","citation_count":1,"is_preprint":false},{"pmid":"41817312","id":"PMC_41817312","title":"Molecular Characterization of KLK2 RNA Expression in Prostate Cancer.","date":"2026","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/41817312","citation_count":0,"is_preprint":false},{"pmid":"42189191","id":"PMC_42189191","title":"Integrative Surface Antigen Profiling of KLK2 and STEAP1 in Advanced Prostate Cancer.","date":"2026","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/42189191","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12881,"output_tokens":2467,"usd":0.037824,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9618,"output_tokens":2871,"usd":0.059932,"stage2_stop_reason":"end_turn"},"total_usd":0.097756,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"KLK2 is the protease responsible for activating PSA (KLK3) zymogen, demonstrated in cell-based in vitro models (co-incubated cell clones), in vivo xenograft co-inoculation experiments, and PSA/KLK2 double-transgenic mice where double-transgenic animals produced more active PSA than single-transgenic animals.\",\n      \"method\": \"Cell-based co-incubation assays, subcutaneous xenograft co-inoculation, and prostate-targeted double-transgenic mouse models measuring free/total PSA ratios\",\n      \"journal\": \"The Prostate\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vitro and in vivo models across cell-based, xenograft, and transgenic systems, all converging on KLK2-mediated PSA activation\",\n      \"pmids\": [\"20058238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KLK2 degrades IGFBP-3 into multiple small fragments with cleavage preferentially after Arg residues, consistent with its trypsin-like serine protease activity; cleavage sites were identified by mass spectrometry, and fragmentation was inhibited by KLK2-inhibiting peptides in a dose-dependent fashion.\",\n      \"method\": \"In vitro proteolysis assay with immunoblotting, two specific immunoassays (native vs. total IGFBP-3), mass spectrometry identification of cleavage sites, and KLK2-inhibiting peptide dose-response\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assay with mass spectrometry site mapping and peptide inhibitor confirmation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20180640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KLK2 enzymatic (proteolytic) activity can be specifically inhibited by peptides developed against it; peptide stability was improved by cyclization, enabling development of in vivo-applicable KLK2 inhibitors.\",\n      \"method\": \"Peptide-based enzymatic activity assays, in vitro peptide inhibition, peptide cyclization for stability improvement\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro activity assay with peptide inhibitors, single lab, abstract-level detail only\",\n      \"pmids\": [\"18627344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance androgen receptor (AR) transactivation; KLK2 knockdown by siRNA caused increased apoptosis and G1-phase cell growth arrest, while KLK2 cDNA addition increased cell growth.\",\n      \"method\": \"KLK2 cDNA overexpression, KLK2-siRNA knockdown in LNCaP cells, colony formation assay, in vivo xenograft growth assay, AR transactivation reporter assay\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function experiments with defined cellular phenotypes and AR transactivation mechanistic link, single lab with multiple assays\",\n      \"pmids\": [\"24122203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A KLK2-FGFR2 fusion protein (identified in metastatic prostate cancer) activates downstream FGFR signaling pathways, promotes enhanced cell migration, and induces profound morphological changes when expressed in NIH3T3 cells; the fusion is sensitive to selective FGFR inhibitors (AZD-4547, BGJ398, JNJ-42756943, TAS-120, Ponatinib) but not Dovitinib.\",\n      \"method\": \"Targeted RNA-sequencing to identify fusion, retroviral transduction of NIH3T3 cells, migration assays, Western blots for downstream FGFR signaling activation, drug sensitivity assays\",\n      \"journal\": \"Prostate cancer and prostatic diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional characterization with multiple orthogonal methods (migration, signaling, drug sensitivity) in a cell model, single lab\",\n      \"pmids\": [\"31043681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KLK2 cleaves the extracellular domain of IL-10 receptor chain-2 (IL-10R2) at the sequence SYRIF (residues 58–63), reducing IL-10R2 surface expression on macrophages and blunting IL-10-mediated anti-inflammatory signaling (decreased inhibition of nitric oxide, TNF-α, and IL-12 p40). KLK2 is fully active at pH 8.0–8.2 and is strongly activated by sodium citrate and glycosaminoglycans. KLK3 did not show the same effects.\",\n      \"method\": \"FRET peptide library screening to identify optimal substrate (SYRIF), flow cytometry (FACS) to measure IL-10R2 surface expression on bone-marrow-derived macrophages after KLK2 treatment, functional inflammatory assays measuring nitric oxide, TNF-α, and IL-12 p40; comparison with KLK3\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical substrate identification combined with cell-based functional validation using orthogonal readouts, with negative control (KLK3), single lab\",\n      \"pmids\": [\"39106042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KLK2, previously considered a purely secreted serine protease with no cell-surface localization, has now been demonstrated to be expressed on the cell surface, making it targetable by antibody-based and other therapeutic modalities.\",\n      \"method\": \"Experimental demonstration of cell-surface localization (details attributed to a related article by Shen et al.)\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — editorial commentary citing a companion paper; cell-surface localization claim is referenced but experimental details not in this abstract\",\n      \"pmids\": [\"40924642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"KLK2 expression is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus and associated enhancer activation, as determined by epigenomic analysis of mCRPC patient samples; KLK2 expression is absent in neuroendocrine and AR-negative prostate cancer phenotypes.\",\n      \"method\": \"Transcriptomic and epigenomic profiling of 1095 mCRPC patient samples including ChIP/ATAC-seq-based analysis of AR/FOXA1/HOXB13 binding and enhancer activation, rapid autopsy cohort in situ studies\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — large multi-cohort epigenomic and transcriptomic analysis demonstrating mechanistic AR/FOXA1/HOXB13 co-regulation, but relies on correlative multi-omics rather than direct functional manipulation of KLK2 locus\",\n      \"pmids\": [\"42189191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Alternative splicing of KLK2 involving inclusion of intronic sequences adjacent to exon 1 produces a novel protein (hK2-linked molecule, K-LM) that shares only the signal peptide with KLK2; the mature K-LM protein is entirely different from kallikreins and shows androgen-regulated prostate-specific expression similar to KLK2.\",\n      \"method\": \"Identification of splice variant mRNAs by molecular cloning, protein characterization, and androgen-stimulation expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — molecular cloning and expression analysis of splice variant, but functional role of K-LM protein not established; finding is about KLK2 gene structure/splicing\",\n      \"pmids\": [\"11834722\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KLK2 is a prostate-specific trypsin-like serine protease whose transcription is strictly driven by androgen receptor (AR) in concert with FOXA1 and HOXB13; it activates the PSA (KLK3) zymogen, degrades IGFBP-3 at Arg residues to potentially promote IGF signaling, cleaves IL-10R2 on macrophages to dampen anti-inflammatory signaling, enhances AR transactivation in cooperation with the coregulator ARA70, can appear as an oncogenic KLK2-FGFR2 fusion that constitutively activates FGFR signaling, and — contrary to earlier assumptions — is also expressed on the prostate cancer cell surface, enabling antibody-based targeting strategies.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KLK2 is a prostate-specific, androgen-regulated trypsin-like serine protease that participates in prostate biology and prostate cancer through proteolytic processing of multiple substrates [#0, #1, #5]. Its transcription is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus driving enhancer activation; consistent with this dependence, KLK2 expression is absent in AR-negative and neuroendocrine prostate cancer [#7]. Enzymatically, KLK2 cleaves preferentially after arginine residues, activating the PSA (KLK3) zymogen [#0], degrading IGFBP-3 into small fragments [#1], and cleaving the extracellular domain of macrophage IL-10 receptor chain-2 (IL-10R2) at the SYRIF sequence to reduce IL-10R2 surface levels and blunt IL-10-mediated anti-inflammatory signaling, an activity favored at pH 8.0–8.2 and enhanced by sodium citrate and glycosaminoglycans [#5]. Beyond proteolysis, KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance AR transactivation, with knockdown causing apoptosis and G1 arrest [#3]. An oncogenic KLK2-FGFR2 fusion identified in metastatic disease constitutively activates FGFR signaling and is sensitive to selective FGFR inhibitors [#4]. Its enzymatic activity can be specifically blocked by cyclized inhibitory peptides developed for in vivo application [#2].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that the KLK2 locus generates more than the canonical protease, revealing an alternatively spliced, androgen-regulated transcript encoding a distinct prostate-specific protein.\",\n      \"evidence\": \"Molecular cloning of splice-variant mRNAs and androgen-stimulation expression analysis\",\n      \"pmids\": [\"11834722\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of the K-LM protein not established\", \"No protein-level activity or partner identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed that KLK2 proteolytic activity is specifically druggable, providing chemical tools to dissect and inhibit its function in vivo.\",\n      \"evidence\": \"In vitro enzymatic activity assays with cyclized inhibitory peptides\",\n      \"pmids\": [\"18627344\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Abstract-level detail only\", \"In vivo efficacy not demonstrated in this work\", \"Substrate specificity of inhibition not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved which protease activates the PSA zymogen by demonstrating KLK2-mediated PSA activation across orthogonal models, defining a key step in prostate kallikrein cascades.\",\n      \"evidence\": \"Cell co-incubation, xenograft co-inoculation, and PSA/KLK2 double-transgenic mice measuring free/total PSA\",\n      \"pmids\": [\"20058238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological/pathological consequence of PSA activation not addressed\", \"Cleavage kinetics versus other activators not compared\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined a substrate relevant to growth-factor signaling by mapping KLK2 cleavage of IGFBP-3, consistent with its trypsin-like Arg-directed specificity.\",\n      \"evidence\": \"In vitro proteolysis with immunoblot, native/total immunoassays, mass-spec site mapping, and peptide-inhibitor dose response\",\n      \"pmids\": [\"20180640\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effect on IGF signaling not directly demonstrated\", \"Cellular relevance versus in vitro proteolysis not established\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked KLK2 to prostate cancer cell proliferation through a non-proteolytic transcriptional mechanism, showing it enhances AR transactivation via ARA70.\",\n      \"evidence\": \"KLK2 cDNA overexpression and siRNA knockdown in LNCaP, colony formation, xenograft growth, and AR transactivation reporter assays\",\n      \"pmids\": [\"24122203\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism of ARA70/AR cooperation not structurally defined\", \"Whether proteolytic activity contributes to growth effect unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified an oncogenic KLK2-FGFR2 gene fusion as a driver event, connecting the androgen-driven locus to constitutive growth-factor receptor signaling.\",\n      \"evidence\": \"Targeted RNA-seq fusion discovery, retroviral expression in NIH3T3, migration/signaling assays, FGFR inhibitor sensitivity panel\",\n      \"pmids\": [\"31043681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Frequency in patient populations not established\", \"Functional studies in patient-derived prostate models lacking\", \"Role of KLK2 portion in fusion activity undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Uncovered an immunomodulatory function by showing KLK2 cleaves IL-10R2 on macrophages to dampen anti-inflammatory signaling, with biochemical optima and a KLK3 negative control.\",\n      \"evidence\": \"FRET peptide-library substrate screen, FACS for IL-10R2 surface expression on BMDMs, inflammatory readouts (NO, TNF-alpha, IL-12 p40)\",\n      \"pmids\": [\"39106042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance in the tumor microenvironment not shown\", \"Source of KLK2 acting on macrophages not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Mechanistically anchored KLK2 expression to AR/FOXA1/HOXB13 enhancer co-regulation across large mCRPC cohorts and showed loss in AR-negative/neuroendocrine disease.\",\n      \"evidence\": \"Transcriptomic/epigenomic profiling (ChIP/ATAC-seq) of 1095 mCRPC samples plus rapid autopsy in situ studies\",\n      \"pmids\": [\"42189191\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlative multi-omics rather than direct locus manipulation\", \"Causality of individual factor binding not tested functionally\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether KLK2 cell-surface localization is a robust, generalizable feature enabling therapeutic targeting remains to be established with direct experimental detail.\",\n      \"evidence\": \"Editorial commentary referencing a companion paper for cell-surface localization\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Experimental details of surface localization not in the cited commentary\", \"Mechanism of membrane association of a secreted protease unknown\", \"Targetability claim not independently validated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"KLK3\", \"IGFBP3\", \"IL10RB\", \"AR\", \"ARA70\", \"FGFR2\", \"FOXA1\", \"HOXB13\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}