{"gene":"CTSV","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":1998,"finding":"CTSV (cathepsin L2/cathepsin V) was cloned from a human brain cDNA library and identified as a novel cysteine proteinase with 78% amino acid identity to cathepsin L. Recombinant protein expressed in E. coli demonstrated proteolytic activity on the synthetic substrate Z-Phe-Arg-AMC, which was abolished by the cysteine proteinase inhibitor E-64 (trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane), confirming active-site cysteine-dependent catalysis. Expression was found predominantly in thymus and testis, with upregulation in colorectal and breast carcinomas.","method":"Recombinant protein expression, enzyme activity assay with synthetic substrate, inhibitor studies (E-64), Northern blot","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with active-site inhibitor validation, original cloning paper","pmids":["9563472"],"is_preprint":false},{"year":1998,"finding":"CTSV was independently identified as the major cysteine protease in human corneal epithelium. Recombinant CTSV expressed in a baculovirus system cleaved BSA and was inhibited by E-64 and leupeptin (cysteine proteinase inhibitors) but not by pepstatin A, PMSF, or EDTA, establishing it as a cysteine protease rather than aspartyl or serine protease.","method":"Baculovirus recombinant expression, enzyme activity assay on BSA substrate, class-specific inhibitor profiling, RT-PCR tissue distribution","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 1 — in vitro activity assay with inhibitor class discrimination, independent corroboration of cysteine protease mechanism","pmids":["9727401"],"is_preprint":false},{"year":1999,"finding":"Recombinant CTSV expressed in Pichia pastoris undergoes autocatalytic activation at acidic pH. Its S2 subsite specificity is intermediate between cathepsins L and S, accepting both aromatic and non-aromatic hydrophobic residues. CTSV is significantly more stable at mildly acidic and neutral pH than cathepsin L but less stable than cathepsin S. CTSV showed only weak collagenolytic activity (unlike cathepsin L). Chromosomal mapping placed CTSV at 9q22.2, adjacent to the cathepsin L locus, suggesting evolution from a common ancestor by gene duplication. A homology model revealed a neutral-to-weakly-positive electrostatic potential near the active site cleft, contrasting with cathepsin L's negative surface.","method":"Recombinant protein expression (Pichia pastoris), kinetic assays, pH stability assays, collagenolysis assay, class-specific inhibitor profiling, homology modeling, chromosomal mapping","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with multiple orthogonal biochemical methods and structural modeling","pmids":["10029531"],"is_preprint":false},{"year":2000,"finding":"The 1.6 Å resolution crystal structure of human CTSV was determined with an irreversible vinyl sulfone inhibitor bound at the active site. The fold is similar to the papain superfamily of cysteine proteases. Comparison of the active site with related proteases identified differences in the S2 and S3 subsites that distinguish CTSV from other family members and can be exploited for selective inhibitor design.","method":"X-ray crystallography (1.6 Å resolution), active-site inhibitor co-crystal","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with active-site occupancy","pmids":["11027133"],"is_preprint":false},{"year":2003,"finding":"CTSV is the dominant cysteine protease in cortical human thymic epithelial cells (TECs), while cathepsins L and S are restricted to dendritic and macrophage-like cells. Active CTSV in thymic lysosomal preparations was demonstrated by active-site labeling. Recombinant CTSV efficiently converts the invariant chain (Ii) into CLIP (class II-associated invariant chain peptide), identifying CTSV as the protease controlling MHC class II peptide loading in human thymus (analogous to cathepsin L in mouse). CTSV expression is significantly elevated in thymi of myasthenia gravis patients compared to healthy controls.","method":"Active-site labeling (activity-based probe), cell fractionation, recombinant protein in vitro Ii degradation assay, immunohistochemistry, Western blot","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of Ii→CLIP conversion plus active-site labeling in native thymic lysosomes","pmids":["12925692"],"is_preprint":false},{"year":2003,"finding":"CTSV (cathepsin L2) was identified as the stratum corneum thiol protease (SCTP) previously described in human epidermis. CTSV can hydrolyze corneodesmosin, a marker of corneocyte cohesion, implicating it in the desquamation process. Expression analysis showed CTSV is expressed as a pro-enzyme in lower epidermal layers and is partially activated in upper layers during keratinocyte differentiation.","method":"Protein purification/gel filtration, specific antibody immunoidentification, caseinolytic activity assay, corneodesmosin hydrolysis assay, RT-PCR","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical identification with functional substrate assay, single lab","pmids":["12648222"],"is_preprint":false},{"year":2003,"finding":"Hurpin (serpinB13/PI13), an intracellular serpin expressed in keratinocytes, potently and selectively inhibits cathepsin L (k_assoc = 4.6×10⁵ M⁻¹s⁻¹, SI = 1.7) but only inefficiently inhibits CTSV. Site-directed mutagenesis of the reactive center loop (P1-P1' bond Thr356-Ser357) confirmed the conventional serpin inhibitory mechanism. This establishes CTSV as resistant to hurpin-mediated serpin inhibition, in contrast to cathepsin L.","method":"In vitro inhibition kinetics, site-directed mutagenesis of serpin reactive center loop, recombinant protein assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — kinetic characterization with mutagenesis validation, defines CTSV substrate specificity boundary","pmids":["12809493"],"is_preprint":false},{"year":2004,"finding":"Macrophages express CTSV as a potent elastolytic cysteine protease — the most potent elastase activity yet described among human proteases. Approximately 60% of total macrophage elastolytic activity is attributable to cysteine proteases (cathepsins V, K, and S contributing equally). Two-thirds of this activity is extracellular and one-third intracellular, with the intracellular portion credited specifically to CTSV. Glycosaminoglycans (GAGs) such as chondroitin sulfate specifically inhibit the elastolytic activities of CTSV and cathepsin K via formation of specific cathepsin-GAG complexes, whereas cathepsin S is not inhibited. CTSV was detected in atherosclerotic plaque specimens.","method":"In vitro elastin degradation assays, macrophage cysteine protease activity profiling, GAG-cathepsin complex formation assay, activity-based inhibitors, plaque immunohistochemistry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of elastolytic activity with mechanistic GAG-inhibition studies and native macrophage activity profiling","pmids":["15192101"],"is_preprint":false},{"year":2004,"finding":"Transgenic keratinocyte-specific expression of CTSV (under the keratin 14 promoter) in cathepsin L knockout mice rescues both the skin phenotype (epidermal hyperplasia/hyperproliferation) and the hair loss phenotype. This genetic complementation demonstrates that CTSV can functionally substitute for cathepsin L in mouse epidermis and hair follicles, establishing a conserved keratinocyte-specific proteolytic function.","method":"Transgenic mouse generation, genetic epistasis (transgene rescue of KO phenotype), histological analysis of epidermis, hair follicle morphology","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via transgenic rescue of KO phenotype, clear functional readout","pmids":["15679121"],"is_preprint":false},{"year":2005,"finding":"Cystatin F, expressed in immune cells, tightly inhibits CTSV with a Ki of 0.17–0.35 nM (among the highest affinities measured), compared to ~30 nM for cathepsins S and H, and no inhibition of cathepsins C and X. This establishes CTSV as a preferred high-affinity target of cystatin F among lysosomal cysteine proteases.","method":"In vitro inhibition kinetics with recombinant proteins, Ki measurement","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 — quantitative kinetic characterization with recombinant proteins","pmids":["15752368"],"is_preprint":false},{"year":2006,"finding":"Cystatin M/E is a high-affinity inhibitor of CTSV (Ki = 0.47 nM) and cathepsin L (Ki = 1.78 nM). Site-directed mutagenesis of cystatin M/E identified that residue W135 is required for inhibition of CTSV and cathepsin L (W135A abolishes this activity) but not for legumain inhibition, while N64 is required for legumain inhibition but not for CTSV/cathepsin L inhibition. This demonstrates that papain-like cysteine proteases (including CTSV) and legumain are inhibited by two distinct, non-overlapping sites on cystatin M/E. Immunohistochemistry showed co-localization of cystatin M/E with CTSV in the stratum granulosum of human skin.","method":"In vitro inhibition kinetics, site-directed mutagenesis, immunohistochemistry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — kinetic characterization combined with mutagenesis identifying distinct binding sites","pmids":["16565075"],"is_preprint":false},{"year":2010,"finding":"CTSV immunoreactivity localizes to the nucleus in peri-nucleolar patterns in the anaplastic thyroid carcinoma cell line HTh74, as demonstrated by immunofluorescence and biochemical subcellular fractionation. Co-localization studies and in vitro degradation assays suggest nuclear CTSV variants may be involved in modification of DNA-associated proteins in thyroid malignancies. This is distinct from cathepsin L, which does not show nuclear localization in this context.","method":"Immunofluorescence, subcellular fractionation, in vitro degradation assay, co-localization microscopy","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — direct subcellular localization by orthogonal methods (IF + fractionation) with in vitro substrate degradation, single lab","pmids":["20536394"],"is_preprint":false},{"year":2012,"finding":"CTSV is N-glycosylated at two specific asparagine residues, Asn221 and Asn292, as confirmed by mass spectrometry and site-directed mutagenesis. N-glycosylation is required for proper lysosomal trafficking, secretion, and enzymatic activity of CTSV in HT1080 cells. Mutation of either glycosylation site disrupts these functions.","method":"Mass spectrometry (glycopeptide identification), site-directed mutagenesis of N-glycosylation sites, lysosomal trafficking assay, secretion assay, enzymatic activity assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — mass spectrometry identification combined with mutagenesis functional validation, multiple orthogonal readouts","pmids":["22967898"],"is_preprint":false},{"year":2013,"finding":"CTSV (CTSL2) is a direct transcriptional target of E2F1. E2F1 directly binds to the CTSL2 promoter, and CTSV is regulated by both exogenous and endogenous E2F1. RNAi-mediated knockdown of CTSV abrogates E2F1-induced apoptosis, reduces lysosomal membrane permeabilization (LMP), and prevents mitochondrial membrane depolarization. CTSV depletion also inhibits apoptosis induced by DNA-damage-activated endogenous E2F1 and by histone deacetylase inhibitors (HDACi), while overexpression of CTSV sensitizes cancer cells to HDACi. This places CTSV downstream of E2F1 in a pro-apoptotic pathway involving lysosomal membrane permeabilization.","method":"Chromatin immunoprecipitation (ChIP), RNAi knockdown, luciferase reporter assay, apoptosis assays, LMP measurement, mitochondrial membrane potential assay, overexpression","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — ChIP establishing direct E2F1-promoter binding, multiple orthogonal functional assays (KD + OE + LMP + mitochondrial depolarization)","pmids":["23542171"],"is_preprint":false},{"year":2020,"finding":"CTSV expression in renal cell carcinoma (RCC) is regulated by the EGFR-MEK-ERK signaling pathway. Praeruptorin B reduces CTSV mRNA and protein levels in RCC cells by inhibiting phosphorylation of EGFR, MEK, and ERK. EGF treatment upregulates CTSV expression via EGFR-MEK-ERK, and this is blocked by Praeruptorin B. Downregulation of CTSV correlates with reduced RCC cell migration and invasion, placing CTSV downstream of EGFR-MEK-ERK in a pro-metastatic signaling cascade.","method":"siRNA knockdown, Western blot, migration/invasion assays, EGF stimulation, pharmacological inhibition, RT-PCR","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pathway placement via EGF stimulation and pharmacological inhibition with functional readouts, single lab","pmids":["32331211"],"is_preprint":false},{"year":2021,"finding":"CTSV can cleave multiple sites on the SARS-CoV-2 spike protein, including within the S1/S2 region critical for viral activation and membrane fusion. Computational prediction of cleavage sites (PACMANS) was verified by molecular docking and immunoblotting, identifying CTSV as one of several cathepsins capable of processing the spike protein and potentially facilitating viral entry.","method":"Computational cleavage site prediction (PACMANS), molecular docking, immunoblotting","journal":"Protein science","confidence":"Low","confidence_rationale":"Tier 3-4 — primarily computational with limited immunoblot validation, no cell-based viral entry assay","pmids":["33786919"],"is_preprint":false},{"year":2022,"finding":"CTSV promotes bladder cancer cell proliferation through activation of the NF-κB inflammatory signaling pathway. Overexpression of CTSV increases NF-κB transcriptional activity as measured by dual-luciferase reporter assay, while CTSV deletion inhibits proliferation and viability in vitro and suppresses tumor growth in vivo. The proliferative effect of CTSV overexpression is restored to baseline by an NF-κB inhibitor.","method":"siRNA knockdown, overexpression, CCK8 and colony formation assays, dual-luciferase reporter (NF-κB), in vivo nude mouse xenograft, NF-κB inhibitor rescue","journal":"Bioengineered","confidence":"Medium","confidence_rationale":"Tier 2 — NF-κB reporter assay plus pharmacological rescue in vitro and in vivo, single lab","pmids":["35443863"],"is_preprint":false},{"year":2025,"finding":"In colorectal cancer cells, CTSV expression is controlled by the PKCα/PKCδ-ERK-Sp1 signaling axis. Trichodermin inhibits phosphorylation of PKCα, PKCδ, and ERK, which in turn reduces Sp1 transcriptional activity and CTSV expression. siRNA knockdown of either ERK or CTSV enhances the anti-migration and anti-invasion effects of trichodermin. PKC activator TPA rescues CTSV expression and cell migration/invasion, which is counteracted by trichodermin, placing CTSV downstream of PKC-ERK-Sp1 as a mediator of CRC metastatic behavior.","method":"siRNA knockdown, proteomic protease array, Western blot (phospho-PKC, phospho-ERK, Sp1), migration/invasion assays, pharmacological activation (TPA) and inhibition","journal":"Phytomedicine","confidence":"Medium","confidence_rationale":"Tier 2 — pathway placement by siRNA + pharmacological epistasis with functional invasion readouts, single lab","pmids":["40674912"],"is_preprint":false}],"current_model":"CTSV is a lysosomal cysteine protease of the papain superfamily, structurally characterized at 1.6 Å resolution, that undergoes autocatalytic activation at acidic pH and is trafficked to lysosomes in an N-glycosylation-dependent manner (at Asn221 and Asn292); it functions as the dominant Ii→CLIP-processing protease in human cortical thymic epithelial cells (analogous to cathepsin L in mouse), acts as a potent elastase in macrophages whose activity is regulated by GAG complexes, participates in keratinocyte/epidermal homeostasis, drives pro-apoptotic lysosomal membrane permeabilization downstream of E2F1, promotes cancer cell migration/invasion via EGFR-MEK-ERK and PKCα/δ-ERK-Sp1 pathways that upregulate CTSV expression, and activates NF-κB-dependent proliferation in bladder cancer; its activity is tightly regulated by endogenous inhibitors including cystatin M/E (Ki = 0.47 nM) and cystatin F (Ki ~0.2 nM)."},"narrative":{"teleology":[{"year":1998,"claim":"Cloning of CTSV from human brain and corneal cDNA libraries established it as a novel cysteine protease closely related to cathepsin L, resolving whether humans possess a second cathepsin L-like gene with tissue-restricted expression.","evidence":"Recombinant expression (E. coli and baculovirus), proteolytic activity on synthetic and protein substrates, class-specific inhibitor profiling (E-64, leupeptin), Northern blot tissue distribution","pmids":["9563472","9727401"],"confidence":"High","gaps":["Endogenous substrates unknown","No structural information","Intracellular trafficking mechanism undefined"]},{"year":1999,"claim":"Biochemical characterization revealed that CTSV undergoes autocatalytic activation at acidic pH and is more stable at neutral pH than cathepsin L, explaining how it can retain activity in extracellular or mildly acidic compartments and clarifying its functional distinction from cathepsin L.","evidence":"Kinetic and pH-stability assays with Pichia-expressed recombinant protein, chromosomal mapping to 9q22.2","pmids":["10029531"],"confidence":"High","gaps":["No crystal structure yet","In vivo substrates not identified","Mechanism of greater pH stability not structurally explained"]},{"year":2000,"claim":"Determination of the 1.6 Å crystal structure with a vinyl sulfone inhibitor resolved the molecular basis of CTSV's distinct substrate specificity by identifying S2 and S3 subsite differences from related cathepsins, enabling rational inhibitor design.","evidence":"X-ray crystallography with active-site inhibitor co-crystal","pmids":["11027133"],"confidence":"High","gaps":["No structure of CTSV with a physiological substrate or pro-domain","Dynamics of autocatalytic processing not captured"]},{"year":2003,"claim":"Three concurrent studies established CTSV's key physiological roles: it is the dominant Ii→CLIP-processing protease in human cortical thymic epithelial cells (the human counterpart of mouse cathepsin L in MHC class II antigen loading), it cleaves corneodesmosin during epidermal desquamation, and it is differentially resistant to the serpin hurpin compared with cathepsin L.","evidence":"Active-site labeling in thymic lysosomes plus in vitro Ii degradation reconstitution; corneodesmosin hydrolysis assay; inhibition kinetics with site-directed mutagenesis of hurpin reactive center loop","pmids":["12925692","12648222","12809493"],"confidence":"High","gaps":["No genetic loss-of-function in human thymus","Relative contribution to desquamation versus other proteases unresolved","In vivo regulation in thymus not addressed"]},{"year":2004,"claim":"CTSV was identified as the most potent human elastase described at that time in macrophages, with its activity specifically inhibited by glycosaminoglycans, and transgenic expression of CTSV rescued the skin and hair phenotype of cathepsin L–knockout mice, proving functional equivalence in the epidermis.","evidence":"In vitro elastin degradation and GAG-cathepsin complex assays in macrophages; transgenic K14-CTSV rescue in cathepsin L KO mice with histological analysis","pmids":["15192101","15679121"],"confidence":"High","gaps":["Structural basis of GAG-mediated inhibition undefined","In vivo elastolytic contribution in atherosclerosis not causally tested","CTSV-specific KO mouse not available"]},{"year":2005,"claim":"Quantitative kinetic analysis revealed that cystatin F is a sub-nanomolar inhibitor of CTSV (Ki ~0.2 nM), establishing CTSV as its preferred target and suggesting tight endogenous regulation in immune cells.","evidence":"In vitro Ki determination with recombinant cystatin F and CTSV","pmids":["15752368"],"confidence":"High","gaps":["Physiological consequence of cystatin F-CTSV interaction in immune cells not shown","In vivo relevance not tested"]},{"year":2006,"claim":"Cystatin M/E was shown to inhibit CTSV at sub-nanomolar affinity through a binding site distinct from its legumain-inhibitory interface, and co-localization in the stratum granulosum implied functional regulation during epidermal differentiation.","evidence":"Inhibition kinetics with site-directed mutagenesis (W135A, N64 variants), immunohistochemistry in human skin","pmids":["16565075"],"confidence":"High","gaps":["Functional consequence of cystatin M/E loss on CTSV activity in skin not tested in vivo","Relative importance versus other epidermal cystatin–cathepsin pairs unclear"]},{"year":2012,"claim":"Identification of Asn221 and Asn292 as N-glycosylation sites required for lysosomal trafficking and enzymatic activity resolved how CTSV is sorted to lysosomes and why glycosylation-deficient mutants are non-functional.","evidence":"Mass spectrometry glycopeptide mapping, site-directed mutagenesis, trafficking and activity assays in HT1080 cells","pmids":["22967898"],"confidence":"High","gaps":["Mannose-6-phosphate receptor dependence not formally tested","Contribution of each glycosylation site individually to trafficking versus stability not fully separated"]},{"year":2013,"claim":"Discovery that CTSV is a direct E2F1 transcriptional target required for E2F1-induced lysosomal membrane permeabilization and apoptosis placed CTSV in an oncogene-responsive cell death pathway and explained how lysosomal proteases connect to the intrinsic apoptosis program.","evidence":"ChIP for E2F1 at CTSL2 promoter, RNAi knockdown and overexpression with LMP and mitochondrial depolarization readouts, HDAC inhibitor sensitization","pmids":["23542171"],"confidence":"High","gaps":["Identity of CTSV substrates that trigger LMP or mitochondrial depolarization unknown","Whether this pathway operates in non-cancer cells not tested"]},{"year":2020,"claim":"Placing CTSV downstream of EGFR-MEK-ERK in renal cell carcinoma established that growth-factor signaling transcriptionally controls CTSV to promote cell migration and invasion, extending its pro-metastatic role beyond thyroid and colon cancers.","evidence":"EGF stimulation, pharmacological inhibition (Praeruptorin B), siRNA knockdown, migration/invasion assays in RCC cells","pmids":["32331211"],"confidence":"Medium","gaps":["Promoter-level mechanism of ERK-driven transcription not mapped","Independent replication in additional RCC models needed","In vivo metastasis assay not performed"]},{"year":2022,"claim":"Demonstration that CTSV activates NF-κB-dependent proliferation in bladder cancer (rescued by NF-κB inhibitor) identified a second downstream signaling pathway through which CTSV promotes tumor growth, distinct from the EGFR-ERK axis.","evidence":"Overexpression and knockdown with NF-κB dual-luciferase reporter, xenograft tumor growth in nude mice, NF-κB inhibitor rescue","pmids":["35443863"],"confidence":"Medium","gaps":["Mechanism by which a lysosomal protease activates NF-κB not defined","Direct versus indirect NF-κB activation not distinguished","Single cancer type tested"]},{"year":2025,"claim":"Identification of the PKCα/δ-ERK-Sp1 axis as a transcriptional regulator of CTSV in colorectal cancer provided a second upstream kinase cascade converging on CTSV expression, reinforcing its role as a convergent effector of multiple MAPK-dependent pro-invasive programs.","evidence":"Phospho-Western blots, siRNA epistasis (ERK, CTSV), TPA rescue, proteomic protease array, migration/invasion assays","pmids":["40674912"],"confidence":"Medium","gaps":["Sp1 binding to CTSV promoter not confirmed by ChIP","Overlap or redundancy with EGFR-ERK pathway not addressed","In vivo metastasis model lacking"]},{"year":null,"claim":"Major unresolved questions include the full repertoire of endogenous CTSV substrates in thymus and skin, the molecular mechanism by which CTSV triggers NF-κB activation and lysosomal membrane permeabilization, the phenotype of a CTSV-specific knockout in human or humanized models, and structural elucidation of CTSV–glycosaminoglycan inhibitory complexes.","evidence":"","pmids":[],"confidence":"High","gaps":["No CTSV-specific genetic knockout phenotype in a human-relevant model","No unbiased substrate profiling (e.g. TAILS/ATOMS) reported","Structural basis of GAG-mediated inhibition unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,4,5,7]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,2,5,7]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[4,12,13]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[7]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,9]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,16,17]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[12]}],"complexes":[],"partners":["CST6","CST7","E2F1","CD74"],"other_free_text":[]},"mechanistic_narrative":"CTSV (cathepsin L2) is a lysosomal papain-family cysteine protease that undergoes autocatalytic activation at acidic pH, possesses an S2 subsite specificity intermediate between cathepsins L and S, and requires N-glycosylation at Asn221 and Asn292 for proper lysosomal trafficking and enzymatic activity [PMID:10029531, PMID:22967898, PMID:11027133]. CTSV functions as the dominant protease converting invariant chain (Ii) to CLIP for MHC class II peptide loading in human cortical thymic epithelial cells, the most potent elastase in human macrophages (regulated by glycosaminoglycan complex formation), and a corneodesmosin-cleaving enzyme in epidermal desquamation that functionally substitutes for murine cathepsin L in transgenic rescue of cathepsin L–knockout skin and hair phenotypes [PMID:12925692, PMID:15192101, PMID:12648222, PMID:15679121]. Its activity is tightly controlled by endogenous inhibitors including cystatin F (Ki ~0.2 nM) and cystatin M/E (Ki = 0.47 nM), which bind through a site distinct from the legumain-inhibitory interface [PMID:15752368, PMID:16565075]. CTSV is a direct transcriptional target of E2F1 that drives pro-apoptotic lysosomal membrane permeabilization, and its expression is upregulated through EGFR-MEK-ERK and PKCα/δ-ERK-Sp1 cascades in cancer cells where it promotes migration, invasion, and NF-κB-dependent proliferation [PMID:23542171, PMID:32331211, PMID:40674912, PMID:35443863]."},"prefetch_data":{"uniprot":{"accession":"O60911","full_name":"Cathepsin L2","aliases":["Cathepsin U","Cathepsin V"],"length_aa":334,"mass_kda":37.3,"function":"Cysteine protease. May have an important role in corneal physiology","subcellular_location":"Lysosome","url":"https://www.uniprot.org/uniprotkb/O60911/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CTSV","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PMVK","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CTSV","total_profiled":1310},"omim":[{"mim_id":"609812","title":"MATURITY-ONSET DIABETES OF THE YOUNG, TYPE 8, WITH EXOCRINE DYSFUNCTION; MODY8","url":"https://www.omim.org/entry/609812"},{"mim_id":"603308","title":"CATHEPSIN V; CTSV","url":"https://www.omim.org/entry/603308"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoli fibrillar center","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":599.5}],"url":"https://www.proteinatlas.org/search/CTSV"},"hgnc":{"alias_symbol":["CTSU"],"prev_symbol":["CTSL2"]},"alphafold":{"accession":"O60911","domains":[{"cath_id":"3.90.70.10","chopping":"90-334","consensus_level":"high","plddt":95.4263,"start":90,"end":334},{"cath_id":"1.10.287","chopping":"24-72","consensus_level":"high","plddt":96.2943,"start":24,"end":72}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60911","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60911-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60911-F1-predicted_aligned_error_v6.png","plddt_mean":92.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CTSV","jax_strain_url":"https://www.jax.org/strain/search?query=CTSV"},"sequence":{"accession":"O60911","fasta_url":"https://rest.uniprot.org/uniprotkb/O60911.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60911/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60911"}},"corpus_meta":[{"pmid":"17869649","id":"PMC_17869649","title":"Polymorphisms in the cathepsin L2 (CTSL2) gene show association with type 1 diabetes and early-onset myasthenia gravis.","date":"2007","source":"Human immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17869649","citation_count":28,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32331211","id":"PMC_32331211","title":"Praeruptorin B Mitigates the Metastatic Ability of Human Renal Carcinoma Cells through Targeting CTSC and CTSV Expression.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32331211","citation_count":17,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"35443863","id":"PMC_35443863","title":"CTSV (cathepsin V) promotes bladder cancer progression by increasing NF-κB activity.","date":"2022","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/35443863","citation_count":17,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"17934903","id":"PMC_17934903","title":"Evaluation of the CTSL2 gene as a candidate gene for alopecia X in Pomeranians and Keeshonden.","date":"2007","source":"Animal biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/17934903","citation_count":7,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"23542171","id":"PMC_23542171","title":"CTSL2 is a pro-apoptotic target of E2F1 and a modulator of histone deacetylase inhibitor and DNA damage-induced apoptosis.","date":"2013","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/23542171","citation_count":7,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40674912","id":"PMC_40674912","title":"Trichodermin, an endophytic fungal sesquiterpene, suppresses colorectal cancer cell migration and invasion by targeting the PKC-ERK-Sp1-CTSV axis.","date":"2025","source":"Phytomedicine : international journal of phytotherapy and 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A novel clue for the role of cystatin M/E in epidermal cornification.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16565075","citation_count":91,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32707033","id":"PMC_32707033","title":"Kinase Interaction Network Expands Functional and Disease Roles of Human Kinases.","date":"2020","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/32707033","citation_count":88,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15164053","id":"PMC_15164053","title":"DNA sequence and analysis of human chromosome 9.","date":"2004","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/15164053","citation_count":86,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28515276","id":"PMC_28515276","title":"Assembly of the U5 snRNP component PRPF8 is controlled by the HSP90/R2TP chaperones.","date":"2017","source":"The Journal of cell 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functional apoptosis readouts) in a single study with rigorous controls\",\n      \"pmids\": [\"23542171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CTSL2/CTSV is required for histone deacetylase inhibitor (HDACi)-induced apoptosis in cancer cells; CTSL2 knockdown inhibits HDACi-induced cell death, while CTSL2 overexpression sensitizes cancer cells to HDACi.\",\n      \"method\": \"RNAi knockdown, ectopic overexpression, HDACi treatment with apoptosis assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic manipulation (KD and OE) with defined apoptotic phenotype\",\n      \"pmids\": [\"23542171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CTSV promotes bladder cancer cell proliferation through activation of the NF-κB signaling pathway; overexpression of CTSV increases NF-κB transcriptional activity, and this effect is reversed by an NF-κB inhibitor.\",\n      \"method\": \"CTSV overexpression and knockdown (in vitro and in vivo), dual-luciferase reporter assay, NF-κB inhibitor rescue, CCK8 and colony formation assays\",\n      \"journal\": \"Bioengineered\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — reporter assay plus loss- and gain-of-function in single study, but pathway placement relies on pharmacological inhibitor\",\n      \"pmids\": [\"35443863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CTSV expression in renal carcinoma cells is regulated downstream of the EGFR-MEK-ERK signaling pathway; Praeruptorin B reduces p-EGFR, p-MEK, and p-ERK levels and consequently downregulates CTSV protein and mRNA, inhibiting cell migration and invasion.\",\n      \"method\": \"Pharmacological inhibition of EGFR-MEK-ERK, Western blot, qRT-PCR, migration and invasion assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological approach with multiple readouts but no direct genetic epistasis or rescue\",\n      \"pmids\": [\"32331211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In colorectal cancer cells, CTSV expression is transcriptionally regulated by Sp1 downstream of PKCα/PKCδ-ERK signaling; siRNA knockdown of ERK or CTSV enhances the anti-migratory effects of trichodermin, and activation of PKC by TPA rescues CTSV expression, establishing a PKC-ERK-Sp1-CTSV axis controlling CRC cell migration and invasion.\",\n      \"method\": \"siRNA knockdown (ERK, CTSV), protease array, qRT-PCR, immunoblot, PKC activator (TPA) rescue, migration and invasion assays\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple orthogonal methods including siRNA epistasis and pharmacological rescue in a single study\",\n      \"pmids\": [\"40674912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The CTSL2/CTSV gene is associated with antigen presentation in human cortical thymic epithelial cells, as highlighted by genetic association of CTSL2 polymorphisms with type 1 diabetes and early-onset myasthenia gravis.\",\n      \"method\": \"Genetic association study (polymorphism genotyping in T1D families and MG patients)\",\n      \"journal\": \"Human immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — genetic association only, no direct mechanistic experiment on protein function\",\n      \"pmids\": [\"17869649\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSV (cathepsin V/CTSL2) is a lysosomal cysteine protease that acts downstream of E2F1 transcriptional activation to induce lysosomal membrane permeabilization and apoptosis, is required for HDACi-induced cell death, promotes cancer cell proliferation via NF-κB signaling, and its expression is regulated by EGFR-MEK-ERK and PKC-ERK-Sp1 signaling axes that control cell migration and invasion.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper before extracting discoveries.\n\n**Retrieved Papers Classification:**\n1. PMID:17869649 — KEEP (CTSV/CTSL2 in autoimmunity/thymus context)\n2. PMID:32331211 — KEEP (CTSV in RCC metastasis, EGFR-MEK-ERK pathway)\n3. PMID:35443863 — KEEP (CTSV in bladder cancer, NF-κB)\n4. PMID:17934903 — EXCLUDE (dog alopecia X, no mechanistic finding)\n5. PMID:23542171 — KEEP (CTSL2/CTSV as E2F1 target, apoptosis)\n6. PMID:40674912 — KEEP (CTSV in CRC, PKC-ERK-Sp1 axis)\n7. PMID:40275325 — EXCLUDE (oyster CgCTSL-2, symbol collision with non-orthologous organism)\n8. bio_10.1101_2025.08.01.668211 — EXCLUDE (planarian CTSL2, symbol collision)\n9. bio_10.1101_2025.11.26.690782 — EXCLUDE (CTSV is a computational method name, not the gene)\n\n**Curated Papers Classification:**\n- PMID:12477932 — EXCLUDE (genome/cDNA project, no mechanistic finding)\n- PMID:26186194 — EXCLUDE (interactome resource, no specific CTSV mechanism)\n- PMID:28514442 — EXCLUDE (interactome resource)\n- PMID:33961781 — EXCLUDE (interactome resource)\n- PMID:21873635 — EXCLUDE (GO annotation methods)\n- PMID:15489334 — EXCLUDE (MGC cDNA project)\n- PMID:26638075 — EXCLUDE (centrosome/cilia BioID, no CTSV mechanism)\n- PMID:35271311 — EXCLUDE (proteome cartography resource)\n- PMID:26344197 — EXCLUDE (metazoan complexes resource)\n- PMID:27173435 — EXCLUDE (cilia proteomics)\n- PMID:10029531 — KEEP (CTSV biochemical characterization)\n- PMID:15192101 — KEEP (CTSV elastolytic activity in macrophages)\n- PMID:17889653 — EXCLUDE (C. elegans SRP-6/calpains, not CTSV-specific)\n- PMID:23376485 — EXCLUDE (podocyte exosome proteomics, no CTSV mechanism)\n- PMID:9563472 — KEEP (CTSV/cathepsin L2 original cloning and characterization)\n- PMID:12925692 — KEEP (CTSV in invariant chain degradation, thymus)\n- PMID:16565075 — KEEP (cystatin M/E inhibition of CTSV)\n- PMID:32707033 — EXCLUDE (kinase interaction network)\n- PMID:15164053 — EXCLUDE (chromosome 9 sequence)\n- PMID:28515276 — EXCLUDE (PRPF8/U5 snRNP)\n- PMID:15752368 — KEEP (cystatin F inhibition of CTSV)\n- PMID:9727401 — KEEP (CTSV isolation and characterization in cornea)\n- PMID:12809493 — KEEP (hurpin/serpinB13 inhibition of CTSV)\n- PMID:33786919 — KEEP (CTSV cleavage of SARS-CoV-2 spike protein)\n- PMID:11027133 — KEEP (crystal structure of CTSV)\n- PMID:12648222 — KEEP (CTSV = stratum corneum thiol protease, desquamation)\n- PMID:20536394 — KEEP (nuclear localization of CTSV in thyroid carcinoma)\n- PMID:15679121 — KEEP (CTSV rescues cathepsin L KO skin phenotype)\n- PMID:31839598 — EXCLUDE (XL-MS tool, no CTSV mechanism)\n- PMID:22967898 — KEEP (N-glycosylation of CTSV controls activity and trafficking)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"CTSV (cathepsin L2/cathepsin V) was cloned from a human brain cDNA library and identified as a novel cysteine proteinase with 78% amino acid identity to cathepsin L. Recombinant protein expressed in E. coli demonstrated proteolytic activity on the synthetic substrate Z-Phe-Arg-AMC, which was abolished by the cysteine proteinase inhibitor E-64 (trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane), confirming active-site cysteine-dependent catalysis. Expression was found predominantly in thymus and testis, with upregulation in colorectal and breast carcinomas.\",\n      \"method\": \"Recombinant protein expression, enzyme activity assay with synthetic substrate, inhibitor studies (E-64), Northern blot\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with active-site inhibitor validation, original cloning paper\",\n      \"pmids\": [\"9563472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CTSV was independently identified as the major cysteine protease in human corneal epithelium. Recombinant CTSV expressed in a baculovirus system cleaved BSA and was inhibited by E-64 and leupeptin (cysteine proteinase inhibitors) but not by pepstatin A, PMSF, or EDTA, establishing it as a cysteine protease rather than aspartyl or serine protease.\",\n      \"method\": \"Baculovirus recombinant expression, enzyme activity assay on BSA substrate, class-specific inhibitor profiling, RT-PCR tissue distribution\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro activity assay with inhibitor class discrimination, independent corroboration of cysteine protease mechanism\",\n      \"pmids\": [\"9727401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Recombinant CTSV expressed in Pichia pastoris undergoes autocatalytic activation at acidic pH. Its S2 subsite specificity is intermediate between cathepsins L and S, accepting both aromatic and non-aromatic hydrophobic residues. CTSV is significantly more stable at mildly acidic and neutral pH than cathepsin L but less stable than cathepsin S. CTSV showed only weak collagenolytic activity (unlike cathepsin L). Chromosomal mapping placed CTSV at 9q22.2, adjacent to the cathepsin L locus, suggesting evolution from a common ancestor by gene duplication. A homology model revealed a neutral-to-weakly-positive electrostatic potential near the active site cleft, contrasting with cathepsin L's negative surface.\",\n      \"method\": \"Recombinant protein expression (Pichia pastoris), kinetic assays, pH stability assays, collagenolysis assay, class-specific inhibitor profiling, homology modeling, chromosomal mapping\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with multiple orthogonal biochemical methods and structural modeling\",\n      \"pmids\": [\"10029531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The 1.6 Å resolution crystal structure of human CTSV was determined with an irreversible vinyl sulfone inhibitor bound at the active site. The fold is similar to the papain superfamily of cysteine proteases. Comparison of the active site with related proteases identified differences in the S2 and S3 subsites that distinguish CTSV from other family members and can be exploited for selective inhibitor design.\",\n      \"method\": \"X-ray crystallography (1.6 Å resolution), active-site inhibitor co-crystal\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with active-site occupancy\",\n      \"pmids\": [\"11027133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CTSV is the dominant cysteine protease in cortical human thymic epithelial cells (TECs), while cathepsins L and S are restricted to dendritic and macrophage-like cells. Active CTSV in thymic lysosomal preparations was demonstrated by active-site labeling. Recombinant CTSV efficiently converts the invariant chain (Ii) into CLIP (class II-associated invariant chain peptide), identifying CTSV as the protease controlling MHC class II peptide loading in human thymus (analogous to cathepsin L in mouse). CTSV expression is significantly elevated in thymi of myasthenia gravis patients compared to healthy controls.\",\n      \"method\": \"Active-site labeling (activity-based probe), cell fractionation, recombinant protein in vitro Ii degradation assay, immunohistochemistry, Western blot\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of Ii→CLIP conversion plus active-site labeling in native thymic lysosomes\",\n      \"pmids\": [\"12925692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CTSV (cathepsin L2) was identified as the stratum corneum thiol protease (SCTP) previously described in human epidermis. CTSV can hydrolyze corneodesmosin, a marker of corneocyte cohesion, implicating it in the desquamation process. Expression analysis showed CTSV is expressed as a pro-enzyme in lower epidermal layers and is partially activated in upper layers during keratinocyte differentiation.\",\n      \"method\": \"Protein purification/gel filtration, specific antibody immunoidentification, caseinolytic activity assay, corneodesmosin hydrolysis assay, RT-PCR\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical identification with functional substrate assay, single lab\",\n      \"pmids\": [\"12648222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Hurpin (serpinB13/PI13), an intracellular serpin expressed in keratinocytes, potently and selectively inhibits cathepsin L (k_assoc = 4.6×10⁵ M⁻¹s⁻¹, SI = 1.7) but only inefficiently inhibits CTSV. Site-directed mutagenesis of the reactive center loop (P1-P1' bond Thr356-Ser357) confirmed the conventional serpin inhibitory mechanism. This establishes CTSV as resistant to hurpin-mediated serpin inhibition, in contrast to cathepsin L.\",\n      \"method\": \"In vitro inhibition kinetics, site-directed mutagenesis of serpin reactive center loop, recombinant protein assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — kinetic characterization with mutagenesis validation, defines CTSV substrate specificity boundary\",\n      \"pmids\": [\"12809493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Macrophages express CTSV as a potent elastolytic cysteine protease — the most potent elastase activity yet described among human proteases. Approximately 60% of total macrophage elastolytic activity is attributable to cysteine proteases (cathepsins V, K, and S contributing equally). Two-thirds of this activity is extracellular and one-third intracellular, with the intracellular portion credited specifically to CTSV. Glycosaminoglycans (GAGs) such as chondroitin sulfate specifically inhibit the elastolytic activities of CTSV and cathepsin K via formation of specific cathepsin-GAG complexes, whereas cathepsin S is not inhibited. CTSV was detected in atherosclerotic plaque specimens.\",\n      \"method\": \"In vitro elastin degradation assays, macrophage cysteine protease activity profiling, GAG-cathepsin complex formation assay, activity-based inhibitors, plaque immunohistochemistry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of elastolytic activity with mechanistic GAG-inhibition studies and native macrophage activity profiling\",\n      \"pmids\": [\"15192101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Transgenic keratinocyte-specific expression of CTSV (under the keratin 14 promoter) in cathepsin L knockout mice rescues both the skin phenotype (epidermal hyperplasia/hyperproliferation) and the hair loss phenotype. This genetic complementation demonstrates that CTSV can functionally substitute for cathepsin L in mouse epidermis and hair follicles, establishing a conserved keratinocyte-specific proteolytic function.\",\n      \"method\": \"Transgenic mouse generation, genetic epistasis (transgene rescue of KO phenotype), histological analysis of epidermis, hair follicle morphology\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via transgenic rescue of KO phenotype, clear functional readout\",\n      \"pmids\": [\"15679121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Cystatin F, expressed in immune cells, tightly inhibits CTSV with a Ki of 0.17–0.35 nM (among the highest affinities measured), compared to ~30 nM for cathepsins S and H, and no inhibition of cathepsins C and X. This establishes CTSV as a preferred high-affinity target of cystatin F among lysosomal cysteine proteases.\",\n      \"method\": \"In vitro inhibition kinetics with recombinant proteins, Ki measurement\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative kinetic characterization with recombinant proteins\",\n      \"pmids\": [\"15752368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cystatin M/E is a high-affinity inhibitor of CTSV (Ki = 0.47 nM) and cathepsin L (Ki = 1.78 nM). Site-directed mutagenesis of cystatin M/E identified that residue W135 is required for inhibition of CTSV and cathepsin L (W135A abolishes this activity) but not for legumain inhibition, while N64 is required for legumain inhibition but not for CTSV/cathepsin L inhibition. This demonstrates that papain-like cysteine proteases (including CTSV) and legumain are inhibited by two distinct, non-overlapping sites on cystatin M/E. Immunohistochemistry showed co-localization of cystatin M/E with CTSV in the stratum granulosum of human skin.\",\n      \"method\": \"In vitro inhibition kinetics, site-directed mutagenesis, immunohistochemistry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — kinetic characterization combined with mutagenesis identifying distinct binding sites\",\n      \"pmids\": [\"16565075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CTSV immunoreactivity localizes to the nucleus in peri-nucleolar patterns in the anaplastic thyroid carcinoma cell line HTh74, as demonstrated by immunofluorescence and biochemical subcellular fractionation. Co-localization studies and in vitro degradation assays suggest nuclear CTSV variants may be involved in modification of DNA-associated proteins in thyroid malignancies. This is distinct from cathepsin L, which does not show nuclear localization in this context.\",\n      \"method\": \"Immunofluorescence, subcellular fractionation, in vitro degradation assay, co-localization microscopy\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization by orthogonal methods (IF + fractionation) with in vitro substrate degradation, single lab\",\n      \"pmids\": [\"20536394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CTSV is N-glycosylated at two specific asparagine residues, Asn221 and Asn292, as confirmed by mass spectrometry and site-directed mutagenesis. N-glycosylation is required for proper lysosomal trafficking, secretion, and enzymatic activity of CTSV in HT1080 cells. Mutation of either glycosylation site disrupts these functions.\",\n      \"method\": \"Mass spectrometry (glycopeptide identification), site-directed mutagenesis of N-glycosylation sites, lysosomal trafficking assay, secretion assay, enzymatic activity assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mass spectrometry identification combined with mutagenesis functional validation, multiple orthogonal readouts\",\n      \"pmids\": [\"22967898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CTSV (CTSL2) is a direct transcriptional target of E2F1. E2F1 directly binds to the CTSL2 promoter, and CTSV is regulated by both exogenous and endogenous E2F1. RNAi-mediated knockdown of CTSV abrogates E2F1-induced apoptosis, reduces lysosomal membrane permeabilization (LMP), and prevents mitochondrial membrane depolarization. CTSV depletion also inhibits apoptosis induced by DNA-damage-activated endogenous E2F1 and by histone deacetylase inhibitors (HDACi), while overexpression of CTSV sensitizes cancer cells to HDACi. This places CTSV downstream of E2F1 in a pro-apoptotic pathway involving lysosomal membrane permeabilization.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), RNAi knockdown, luciferase reporter assay, apoptosis assays, LMP measurement, mitochondrial membrane potential assay, overexpression\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP establishing direct E2F1-promoter binding, multiple orthogonal functional assays (KD + OE + LMP + mitochondrial depolarization)\",\n      \"pmids\": [\"23542171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CTSV expression in renal cell carcinoma (RCC) is regulated by the EGFR-MEK-ERK signaling pathway. Praeruptorin B reduces CTSV mRNA and protein levels in RCC cells by inhibiting phosphorylation of EGFR, MEK, and ERK. EGF treatment upregulates CTSV expression via EGFR-MEK-ERK, and this is blocked by Praeruptorin B. Downregulation of CTSV correlates with reduced RCC cell migration and invasion, placing CTSV downstream of EGFR-MEK-ERK in a pro-metastatic signaling cascade.\",\n      \"method\": \"siRNA knockdown, Western blot, migration/invasion assays, EGF stimulation, pharmacological inhibition, RT-PCR\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement via EGF stimulation and pharmacological inhibition with functional readouts, single lab\",\n      \"pmids\": [\"32331211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CTSV can cleave multiple sites on the SARS-CoV-2 spike protein, including within the S1/S2 region critical for viral activation and membrane fusion. Computational prediction of cleavage sites (PACMANS) was verified by molecular docking and immunoblotting, identifying CTSV as one of several cathepsins capable of processing the spike protein and potentially facilitating viral entry.\",\n      \"method\": \"Computational cleavage site prediction (PACMANS), molecular docking, immunoblotting\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3-4 — primarily computational with limited immunoblot validation, no cell-based viral entry assay\",\n      \"pmids\": [\"33786919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CTSV promotes bladder cancer cell proliferation through activation of the NF-κB inflammatory signaling pathway. Overexpression of CTSV increases NF-κB transcriptional activity as measured by dual-luciferase reporter assay, while CTSV deletion inhibits proliferation and viability in vitro and suppresses tumor growth in vivo. The proliferative effect of CTSV overexpression is restored to baseline by an NF-κB inhibitor.\",\n      \"method\": \"siRNA knockdown, overexpression, CCK8 and colony formation assays, dual-luciferase reporter (NF-κB), in vivo nude mouse xenograft, NF-κB inhibitor rescue\",\n      \"journal\": \"Bioengineered\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — NF-κB reporter assay plus pharmacological rescue in vitro and in vivo, single lab\",\n      \"pmids\": [\"35443863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In colorectal cancer cells, CTSV expression is controlled by the PKCα/PKCδ-ERK-Sp1 signaling axis. Trichodermin inhibits phosphorylation of PKCα, PKCδ, and ERK, which in turn reduces Sp1 transcriptional activity and CTSV expression. siRNA knockdown of either ERK or CTSV enhances the anti-migration and anti-invasion effects of trichodermin. PKC activator TPA rescues CTSV expression and cell migration/invasion, which is counteracted by trichodermin, placing CTSV downstream of PKC-ERK-Sp1 as a mediator of CRC metastatic behavior.\",\n      \"method\": \"siRNA knockdown, proteomic protease array, Western blot (phospho-PKC, phospho-ERK, Sp1), migration/invasion assays, pharmacological activation (TPA) and inhibition\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement by siRNA + pharmacological epistasis with functional invasion readouts, single lab\",\n      \"pmids\": [\"40674912\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSV is a lysosomal cysteine protease of the papain superfamily, structurally characterized at 1.6 Å resolution, that undergoes autocatalytic activation at acidic pH and is trafficked to lysosomes in an N-glycosylation-dependent manner (at Asn221 and Asn292); it functions as the dominant Ii→CLIP-processing protease in human cortical thymic epithelial cells (analogous to cathepsin L in mouse), acts as a potent elastase in macrophages whose activity is regulated by GAG complexes, participates in keratinocyte/epidermal homeostasis, drives pro-apoptotic lysosomal membrane permeabilization downstream of E2F1, promotes cancer cell migration/invasion via EGFR-MEK-ERK and PKCα/δ-ERK-Sp1 pathways that upregulate CTSV expression, and activates NF-κB-dependent proliferation in bladder cancer; its activity is tightly regulated by endogenous inhibitors including cystatin M/E (Ki = 0.47 nM) and cystatin F (Ki ~0.2 nM).\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CTSV (cathepsin V/CTSL2) is a lysosomal cysteine protease that functions in apoptosis, cell proliferation, and cancer cell migration. CTSV is a direct transcriptional target of E2F1 and mediates E2F1-induced apoptosis by triggering lysosomal membrane permeabilization and subsequent mitochondrial membrane depolarization; accordingly, CTSV is required for histone deacetylase inhibitor (HDACi)-induced cell death in cancer cells [PMID:23542171]. In proliferative contexts, CTSV promotes bladder cancer cell growth through activation of NF-κB signaling [PMID:35443863], and its expression is transcriptionally controlled by EGFR-MEK-ERK and PKC-ERK-Sp1 signaling axes that drive cancer cell migration and invasion [PMID:32331211, PMID:40674912].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Genetic association linked CTSV to immune-relevant antigen presentation in thymic epithelial cells, raising the possibility that CTSV has functional roles beyond housekeeping proteolysis, but no direct mechanistic evidence was provided.\",\n      \"evidence\": \"Polymorphism genotyping in type 1 diabetes families and myasthenia gravis patients\",\n      \"pmids\": [\"17869649\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct mechanistic experiment on CTSV protein function was performed\",\n        \"Association does not establish a causal role in antigen presentation\",\n        \"Not independently replicated with functional validation\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The discovery that CTSV is a direct E2F1 transcriptional target that mediates apoptosis via lysosomal membrane permeabilization established the first defined signaling pathway placing CTSV as an effector protease in programmed cell death, and simultaneously showed CTSV is required for HDACi-induced cancer cell killing.\",\n      \"evidence\": \"ChIP and reporter assays for E2F1 binding to the CTSV promoter; RNAi knockdown and overexpression with measurement of LMP, mitochondrial depolarization, and apoptosis upon HDACi treatment\",\n      \"pmids\": [\"23542171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The specific CTSV substrate(s) responsible for LMP induction are not identified\",\n        \"Whether CTSV operates cell-autonomously or through secreted activity in this context is unresolved\",\n        \"In vivo validation of the E2F1-CTSV apoptotic axis is lacking\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that EGFR-MEK-ERK signaling controls CTSV expression expanded the regulatory landscape of CTSV beyond E2F1 and linked its expression to cancer cell migration and invasion phenotypes.\",\n      \"evidence\": \"Pharmacological inhibition of EGFR-MEK-ERK in renal carcinoma cells with Western blot, qRT-PCR, and migration/invasion assays\",\n      \"pmids\": [\"32331211\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No genetic epistasis experiments were performed to confirm pathway ordering\",\n        \"The transcription factor directly binding the CTSV promoter downstream of ERK was not identified in this study\",\n        \"Contribution of CTSV versus other cathepsins to invasion phenotype not delineated\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of NF-κB as a downstream effector of CTSV-driven proliferation revealed a pro-tumorigenic signaling output distinct from its apoptotic role, suggesting context-dependent functions.\",\n      \"evidence\": \"CTSV overexpression and knockdown in bladder cancer cells in vitro and in vivo, dual-luciferase NF-κB reporter, NF-κB inhibitor rescue\",\n      \"pmids\": [\"35443863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which CTSV activates NF-κB is unknown—whether through direct proteolytic processing of a pathway component or indirectly\",\n        \"Reliance on a pharmacological NF-κB inhibitor for epistasis limits specificity\",\n        \"How CTSV switches between pro-apoptotic and pro-proliferative roles in different cellular contexts is unexplained\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of Sp1 as the transcription factor downstream of PKC-ERK signaling that directly controls CTSV expression completed a defined signaling axis (PKC-ERK-Sp1-CTSV) governing cancer cell migration.\",\n      \"evidence\": \"siRNA knockdown of ERK and CTSV, PKC activator (TPA) rescue, protease array, qRT-PCR, and immunoblot in colorectal cancer cells\",\n      \"pmids\": [\"40674912\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct Sp1 binding to the CTSV promoter was not demonstrated by ChIP\",\n        \"Whether the PKC-ERK-Sp1 axis operates in non-cancer cell contexts is unknown\",\n        \"The proteolytic substrate(s) of CTSV that mediate its pro-migratory effect remain unidentified\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct proteolytic substrates of CTSV that mediate its apoptotic (LMP), proliferative (NF-κB), and migratory functions remain unidentified, and the molecular basis for its context-dependent switch between pro-death and pro-survival roles is unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No CTSV substrate has been biochemically identified and validated\",\n        \"No structural model explains CTSV substrate specificity relative to other cathepsin L family members\",\n        \"In vivo genetic models (knockout or conditional) have not been reported for cancer-relevant phenotypes\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"E2F1\",\n      \"SP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CTSV (cathepsin L2) is a lysosomal papain-family cysteine protease that undergoes autocatalytic activation at acidic pH, possesses an S2 subsite specificity intermediate between cathepsins L and S, and requires N-glycosylation at Asn221 and Asn292 for proper lysosomal trafficking and enzymatic activity [PMID:10029531, PMID:22967898, PMID:11027133]. CTSV functions as the dominant protease converting invariant chain (Ii) to CLIP for MHC class II peptide loading in human cortical thymic epithelial cells, the most potent elastase in human macrophages (regulated by glycosaminoglycan complex formation), and a corneodesmosin-cleaving enzyme in epidermal desquamation that functionally substitutes for murine cathepsin L in transgenic rescue of cathepsin L–knockout skin and hair phenotypes [PMID:12925692, PMID:15192101, PMID:12648222, PMID:15679121]. Its activity is tightly controlled by endogenous inhibitors including cystatin F (Ki ~0.2 nM) and cystatin M/E (Ki = 0.47 nM), which bind through a site distinct from the legumain-inhibitory interface [PMID:15752368, PMID:16565075]. CTSV is a direct transcriptional target of E2F1 that drives pro-apoptotic lysosomal membrane permeabilization, and its expression is upregulated through EGFR-MEK-ERK and PKCα/δ-ERK-Sp1 cascades in cancer cells where it promotes migration, invasion, and NF-κB-dependent proliferation [PMID:23542171, PMID:32331211, PMID:40674912, PMID:35443863].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Cloning of CTSV from human brain and corneal cDNA libraries established it as a novel cysteine protease closely related to cathepsin L, resolving whether humans possess a second cathepsin L-like gene with tissue-restricted expression.\",\n      \"evidence\": \"Recombinant expression (E. coli and baculovirus), proteolytic activity on synthetic and protein substrates, class-specific inhibitor profiling (E-64, leupeptin), Northern blot tissue distribution\",\n      \"pmids\": [\"9563472\", \"9727401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous substrates unknown\", \"No structural information\", \"Intracellular trafficking mechanism undefined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Biochemical characterization revealed that CTSV undergoes autocatalytic activation at acidic pH and is more stable at neutral pH than cathepsin L, explaining how it can retain activity in extracellular or mildly acidic compartments and clarifying its functional distinction from cathepsin L.\",\n      \"evidence\": \"Kinetic and pH-stability assays with Pichia-expressed recombinant protein, chromosomal mapping to 9q22.2\",\n      \"pmids\": [\"10029531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure yet\", \"In vivo substrates not identified\", \"Mechanism of greater pH stability not structurally explained\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Determination of the 1.6 Å crystal structure with a vinyl sulfone inhibitor resolved the molecular basis of CTSV's distinct substrate specificity by identifying S2 and S3 subsite differences from related cathepsins, enabling rational inhibitor design.\",\n      \"evidence\": \"X-ray crystallography with active-site inhibitor co-crystal\",\n      \"pmids\": [\"11027133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of CTSV with a physiological substrate or pro-domain\", \"Dynamics of autocatalytic processing not captured\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Three concurrent studies established CTSV's key physiological roles: it is the dominant Ii→CLIP-processing protease in human cortical thymic epithelial cells (the human counterpart of mouse cathepsin L in MHC class II antigen loading), it cleaves corneodesmosin during epidermal desquamation, and it is differentially resistant to the serpin hurpin compared with cathepsin L.\",\n      \"evidence\": \"Active-site labeling in thymic lysosomes plus in vitro Ii degradation reconstitution; corneodesmosin hydrolysis assay; inhibition kinetics with site-directed mutagenesis of hurpin reactive center loop\",\n      \"pmids\": [\"12925692\", \"12648222\", \"12809493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No genetic loss-of-function in human thymus\", \"Relative contribution to desquamation versus other proteases unresolved\", \"In vivo regulation in thymus not addressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"CTSV was identified as the most potent human elastase described at that time in macrophages, with its activity specifically inhibited by glycosaminoglycans, and transgenic expression of CTSV rescued the skin and hair phenotype of cathepsin L–knockout mice, proving functional equivalence in the epidermis.\",\n      \"evidence\": \"In vitro elastin degradation and GAG-cathepsin complex assays in macrophages; transgenic K14-CTSV rescue in cathepsin L KO mice with histological analysis\",\n      \"pmids\": [\"15192101\", \"15679121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of GAG-mediated inhibition undefined\", \"In vivo elastolytic contribution in atherosclerosis not causally tested\", \"CTSV-specific KO mouse not available\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Quantitative kinetic analysis revealed that cystatin F is a sub-nanomolar inhibitor of CTSV (Ki ~0.2 nM), establishing CTSV as its preferred target and suggesting tight endogenous regulation in immune cells.\",\n      \"evidence\": \"In vitro Ki determination with recombinant cystatin F and CTSV\",\n      \"pmids\": [\"15752368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of cystatin F-CTSV interaction in immune cells not shown\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Cystatin M/E was shown to inhibit CTSV at sub-nanomolar affinity through a binding site distinct from its legumain-inhibitory interface, and co-localization in the stratum granulosum implied functional regulation during epidermal differentiation.\",\n      \"evidence\": \"Inhibition kinetics with site-directed mutagenesis (W135A, N64 variants), immunohistochemistry in human skin\",\n      \"pmids\": [\"16565075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of cystatin M/E loss on CTSV activity in skin not tested in vivo\", \"Relative importance versus other epidermal cystatin–cathepsin pairs unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of Asn221 and Asn292 as N-glycosylation sites required for lysosomal trafficking and enzymatic activity resolved how CTSV is sorted to lysosomes and why glycosylation-deficient mutants are non-functional.\",\n      \"evidence\": \"Mass spectrometry glycopeptide mapping, site-directed mutagenesis, trafficking and activity assays in HT1080 cells\",\n      \"pmids\": [\"22967898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mannose-6-phosphate receptor dependence not formally tested\", \"Contribution of each glycosylation site individually to trafficking versus stability not fully separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that CTSV is a direct E2F1 transcriptional target required for E2F1-induced lysosomal membrane permeabilization and apoptosis placed CTSV in an oncogene-responsive cell death pathway and explained how lysosomal proteases connect to the intrinsic apoptosis program.\",\n      \"evidence\": \"ChIP for E2F1 at CTSL2 promoter, RNAi knockdown and overexpression with LMP and mitochondrial depolarization readouts, HDAC inhibitor sensitization\",\n      \"pmids\": [\"23542171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of CTSV substrates that trigger LMP or mitochondrial depolarization unknown\", \"Whether this pathway operates in non-cancer cells not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Placing CTSV downstream of EGFR-MEK-ERK in renal cell carcinoma established that growth-factor signaling transcriptionally controls CTSV to promote cell migration and invasion, extending its pro-metastatic role beyond thyroid and colon cancers.\",\n      \"evidence\": \"EGF stimulation, pharmacological inhibition (Praeruptorin B), siRNA knockdown, migration/invasion assays in RCC cells\",\n      \"pmids\": [\"32331211\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Promoter-level mechanism of ERK-driven transcription not mapped\", \"Independent replication in additional RCC models needed\", \"In vivo metastasis assay not performed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstration that CTSV activates NF-κB-dependent proliferation in bladder cancer (rescued by NF-κB inhibitor) identified a second downstream signaling pathway through which CTSV promotes tumor growth, distinct from the EGFR-ERK axis.\",\n      \"evidence\": \"Overexpression and knockdown with NF-κB dual-luciferase reporter, xenograft tumor growth in nude mice, NF-κB inhibitor rescue\",\n      \"pmids\": [\"35443863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which a lysosomal protease activates NF-κB not defined\", \"Direct versus indirect NF-κB activation not distinguished\", \"Single cancer type tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of the PKCα/δ-ERK-Sp1 axis as a transcriptional regulator of CTSV in colorectal cancer provided a second upstream kinase cascade converging on CTSV expression, reinforcing its role as a convergent effector of multiple MAPK-dependent pro-invasive programs.\",\n      \"evidence\": \"Phospho-Western blots, siRNA epistasis (ERK, CTSV), TPA rescue, proteomic protease array, migration/invasion assays\",\n      \"pmids\": [\"40674912\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sp1 binding to CTSV promoter not confirmed by ChIP\", \"Overlap or redundancy with EGFR-ERK pathway not addressed\", \"In vivo metastasis model lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the full repertoire of endogenous CTSV substrates in thymus and skin, the molecular mechanism by which CTSV triggers NF-κB activation and lysosomal membrane permeabilization, the phenotype of a CTSV-specific knockout in human or humanized models, and structural elucidation of CTSV–glycosaminoglycan inhibitory complexes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No CTSV-specific genetic knockout phenotype in a human-relevant model\", \"No unbiased substrate profiling (e.g. TAILS/ATOMS) reported\", \"Structural basis of GAG-mediated inhibition unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 4, 5, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [4, 12, 13]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0168256\", \"supporting_discovery_ids\": [4, 9]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 16, 17]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CST6\",\n      \"CST7\",\n      \"E2F1\",\n      \"CD74\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait — I need to fix the pathway entries. I accidentally included an invalid term_id `GO:0168256`. Let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"CTSV (cathepsin L2) is a lysosomal papain-family cysteine protease that undergoes autocatalytic activation at acidic pH, possesses an S2 subsite specificity intermediate between cathepsins L and S, and requires N-glycosylation at Asn221 and Asn292 for proper lysosomal trafficking and enzymatic activity [PMID:10029531, PMID:22967898, PMID:11027133]. CTSV functions as the dominant protease converting invariant chain (Ii) to CLIP for MHC class II peptide loading in human cortical thymic epithelial cells, the most potent elastase in human macrophages (regulated by glycosaminoglycan complex formation), and a corneodesmosin-cleaving enzyme in epidermal desquamation that functionally substitutes for murine cathepsin L in transgenic rescue of cathepsin L–knockout skin and hair phenotypes [PMID:12925692, PMID:15192101, PMID:12648222, PMID:15679121]. Its activity is tightly controlled by endogenous inhibitors including cystatin F (Ki ~0.2 nM) and cystatin M/E (Ki = 0.47 nM), which bind through a site distinct from the legumain-inhibitory interface [PMID:15752368, PMID:16565075]. CTSV is a direct transcriptional target of E2F1 that drives pro-apoptotic lysosomal membrane permeabilization, and its expression is upregulated through EGFR-MEK-ERK and PKCα/δ-ERK-Sp1 cascades in cancer cells where it promotes migration, invasion, and NF-κB-dependent proliferation [PMID:23542171, PMID:32331211, PMID:40674912, PMID:35443863].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Cloning of CTSV from human brain and corneal cDNA libraries established it as a novel cysteine protease closely related to cathepsin L, resolving whether humans possess a second cathepsin L-like gene with tissue-restricted expression.\",\n      \"evidence\": \"Recombinant expression (E. coli and baculovirus), proteolytic activity on synthetic and protein substrates, class-specific inhibitor profiling (E-64, leupeptin), Northern blot tissue distribution\",\n      \"pmids\": [\"9563472\", \"9727401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous substrates unknown\", \"No structural information\", \"Intracellular trafficking mechanism undefined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Biochemical characterization revealed that CTSV undergoes autocatalytic activation at acidic pH and is more stable at neutral pH than cathepsin L, explaining how it can retain activity in extracellular or mildly acidic compartments and clarifying its functional distinction from cathepsin L.\",\n      \"evidence\": \"Kinetic and pH-stability assays with Pichia-expressed recombinant protein, chromosomal mapping to 9q22.2\",\n      \"pmids\": [\"10029531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure yet\", \"In vivo substrates not identified\", \"Mechanism of greater pH stability not structurally explained\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Determination of the 1.6 Å crystal structure with a vinyl sulfone inhibitor resolved the molecular basis of CTSV's distinct substrate specificity by identifying S2 and S3 subsite differences from related cathepsins, enabling rational inhibitor design.\",\n      \"evidence\": \"X-ray crystallography with active-site inhibitor co-crystal\",\n      \"pmids\": [\"11027133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of CTSV with a physiological substrate or pro-domain\", \"Dynamics of autocatalytic processing not captured\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Three concurrent studies established CTSV's key physiological roles: it is the dominant Ii→CLIP-processing protease in human cortical thymic epithelial cells (the human counterpart of mouse cathepsin L in MHC class II antigen loading), it cleaves corneodesmosin during epidermal desquamation, and it is differentially resistant to the serpin hurpin compared with cathepsin L.\",\n      \"evidence\": \"Active-site labeling in thymic lysosomes plus in vitro Ii degradation reconstitution; corneodesmosin hydrolysis assay; inhibition kinetics with site-directed mutagenesis of hurpin reactive center loop\",\n      \"pmids\": [\"12925692\", \"12648222\", \"12809493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No genetic loss-of-function in human thymus\", \"Relative contribution to desquamation versus other proteases unresolved\", \"In vivo regulation in thymus not addressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"CTSV was identified as the most potent human elastase described at that time in macrophages, with its activity specifically inhibited by glycosaminoglycans, and transgenic expression of CTSV rescued the skin and hair phenotype of cathepsin L–knockout mice, proving functional equivalence in the epidermis.\",\n      \"evidence\": \"In vitro elastin degradation and GAG-cathepsin complex assays in macrophages; transgenic K14-CTSV rescue in cathepsin L KO mice with histological analysis\",\n      \"pmids\": [\"15192101\", \"15679121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of GAG-mediated inhibition undefined\", \"In vivo elastolytic contribution in atherosclerosis not causally tested\", \"CTSV-specific KO mouse not available\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Quantitative kinetic analysis revealed that cystatin F is a sub-nanomolar inhibitor of CTSV (Ki ~0.2 nM), establishing CTSV as its preferred target and suggesting tight endogenous regulation in immune cells.\",\n      \"evidence\": \"In vitro Ki determination with recombinant cystatin F and CTSV\",\n      \"pmids\": [\"15752368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of cystatin F-CTSV interaction in immune cells not shown\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Cystatin M/E was shown to inhibit CTSV at sub-nanomolar affinity through a binding site distinct from its legumain-inhibitory interface, and co-localization in the stratum granulosum implied functional regulation during epidermal differentiation.\",\n      \"evidence\": \"Inhibition kinetics with site-directed mutagenesis (W135A, N64 variants), immunohistochemistry in human skin\",\n      \"pmids\": [\"16565075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of cystatin M/E loss on CTSV activity in skin not tested in vivo\", \"Relative importance versus other epidermal cystatin-cathepsin pairs unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of Asn221 and Asn292 as N-glycosylation sites required for lysosomal trafficking and enzymatic activity resolved how CTSV is sorted to lysosomes and why glycosylation-deficient mutants are non-functional.\",\n      \"evidence\": \"Mass spectrometry glycopeptide mapping, site-directed mutagenesis, trafficking and activity assays in HT1080 cells\",\n      \"pmids\": [\"22967898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mannose-6-phosphate receptor dependence not formally tested\", \"Contribution of each glycosylation site individually to trafficking versus stability not fully separated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that CTSV is a direct E2F1 transcriptional target required for E2F1-induced lysosomal membrane permeabilization and apoptosis placed CTSV in an oncogene-responsive cell death pathway and explained how lysosomal proteases connect to the intrinsic apoptosis program.\",\n      \"evidence\": \"ChIP for E2F1 at CTSL2 promoter, RNAi knockdown and overexpression with LMP and mitochondrial depolarization readouts, HDAC inhibitor sensitization\",\n      \"pmids\": [\"23542171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of CTSV substrates that trigger LMP or mitochondrial depolarization unknown\", \"Whether this pathway operates in non-cancer cells not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Placing CTSV downstream of EGFR-MEK-ERK in renal cell carcinoma established that growth-factor signaling transcriptionally controls CTSV to promote cell migration and invasion, extending its pro-metastatic role beyond thyroid and colon cancers.\",\n      \"evidence\": \"EGF stimulation, pharmacological inhibition (Praeruptorin B), siRNA knockdown, migration/invasion assays in RCC cells\",\n      \"pmids\": [\"32331211\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Promoter-level mechanism of ERK-driven transcription not mapped\", \"Independent replication in additional RCC models needed\", \"In vivo metastasis assay not performed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstration that CTSV activates NF-κB-dependent proliferation in bladder cancer (rescued by NF-κB inhibitor) identified a second downstream signaling pathway through which CTSV promotes tumor growth, distinct from the EGFR-ERK axis.\",\n      \"evidence\": \"Overexpression and knockdown with NF-κB dual-luciferase reporter, xenograft tumor growth in nude mice, NF-κB inhibitor rescue\",\n      \"pmids\": [\"35443863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which a lysosomal protease activates NF-κB not defined\", \"Direct versus indirect NF-κB activation not distinguished\", \"Single cancer type tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of the PKCα/δ-ERK-Sp1 axis as a transcriptional regulator of CTSV in colorectal cancer provided a second upstream kinase cascade converging on CTSV expression, reinforcing its role as a convergent effector of multiple MAPK-dependent pro-invasive programs.\",\n      \"evidence\": \"Phospho-Western blots, siRNA epistasis (ERK, CTSV), TPA rescue, proteomic protease array, migration/invasion assays\",\n      \"pmids\": [\"40674912\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sp1 binding to CTSV promoter not confirmed by ChIP\", \"Overlap or redundancy with EGFR-ERK pathway not addressed\", \"In vivo metastasis model lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the full repertoire of endogenous CTSV substrates in thymus and skin, the molecular mechanism by which CTSV triggers NF-κB activation and lysosomal membrane permeabilization, the phenotype of a CTSV-specific knockout in human or humanized models, and structural elucidation of CTSV–glycosaminoglycan inhibitory complexes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No CTSV-specific genetic knockout phenotype in a human-relevant model\", \"No unbiased substrate profiling (e.g. TAILS/ATOMS) reported\", \"Structural basis of GAG-mediated inhibition unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 4, 5, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [4, 12, 13]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 16, 17]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CST6\",\n      \"CST7\",\n      \"E2F1\",\n      \"CD74\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}