{"gene":"CTSB","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2016,"finding":"Under homeostatic conditions, CTSB cleaves the calcium channel MCOLN1/TRPML1 in lysosomes, thereby maintaining suppression of the transcription factor TFEB and reducing expression of lysosomal and autophagy-related proteins, controlling the number of lysosomes and autophagosomes in the cell.","method":"Genetic knockout/inhibition with functional readout (lysosome/autophagosome counts, TFEB activity, MCOLN1 cleavage assay)","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined substrate (MCOLN1) and downstream pathway (TFEB suppression) established in cellular model, single lab","pmids":["27786577"],"is_preprint":false},{"year":2021,"finding":"Cancer cell-derived CST6 (cystatin 6) enters osteoclasts by endocytosis and suppresses CTSB proteolytic activity; CTSB normally degrades SPHK1, so CTSB inhibition leads to SPHK1 upregulation, which suppresses osteoclast maturation by inhibiting RANKL-induced p38 activation.","method":"In vitro osteoclastogenesis assay, CTSB activity assay, western blot for SPHK1 and p38 phosphorylation, in vivo metastasis model","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (activity assay, substrate identification, in vivo), single lab","pmids":["34815788"],"is_preprint":false},{"year":2022,"finding":"In macrophages, HDAC3 deficiency leads to elevated CTSB expression (via histone acetylation), and the resulting excess CTSB degrades RIP1 (RIPK1) protein, reducing TNFα-mediated NF-κB activation and inflammatory response.","method":"HDAC3 knockout macrophages, western blot for RIP1 degradation, immunofluorescence, RNAseq, CTSB inhibitor rescue experiments","journal":"Cell & Bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined substrate (RIP1), inhibitor rescue, multiple methods, single lab","pmids":["35658939"],"is_preprint":false},{"year":2014,"finding":"CTSB promotes preadipocyte differentiation by degrading fibronectin (Fn), a key extracellular matrix component and target gene of the Wnt/β-catenin pathway; CTSB degrades Fn and attenuates Wnt/β-catenin signaling to promote adipogenesis.","method":"CTSB overexpression/inhibition in primary porcine preadipocytes, lipid accumulation assay, western blot for β-catenin, LiCl (Wnt activator) rescue experiment","journal":"Molecular and cellular biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited mechanistic resolution, substrate (Fn) degradation inferred rather than directly demonstrated by in vitro cleavage","pmids":["24878992"],"is_preprint":false},{"year":2023,"finding":"In sepsis-induced acute kidney injury, LPS induces lysosomal membrane permeabilization (LMP), causing CTSB release into the cytoplasm, which then activates the mitochondrial apoptosis pathway; CTSB inhibitor CA-074 reverses LPS-induced apoptosis, mitochondrial membrane potential loss, and activation of mitochondrial apoptosis markers.","method":"LPS-treated HK-2 cells, CTSB activity assay, acridine orange staining (LMP), JC-1 (mitochondrial membrane potential), Annexin V/PI, CA-074 inhibitor rescue, western blot","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, CTSB inhibitor rescue with mechanistic pathway placement, single lab","pmids":["36713420"],"is_preprint":false},{"year":2025,"finding":"CTSB degrades ferroportin (FPN) in macrophages, disrupting iron homeostasis and promoting ferroptosis; CTSB was shown to directly bind FPN and negatively regulate its protein level.","method":"Co-IP/binding assay for CTSB-FPN interaction, CTSB knockdown/inhibition, western blot for FPN, ferroptosis markers, ApoE KO and HFD rat AS models, single-cell transcriptomics","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding partner (FPN) identified, multiple in vitro and in vivo methods, single lab","pmids":["39960586"],"is_preprint":false},{"year":2025,"finding":"MINPP1 stabilizes CTSB expression by modulating its K33-linked deubiquitination via ZRANB1 (a deubiquitinase), thereby promoting ferroptosis in HBV-positive hepatocellular carcinoma cells.","method":"Immunoprecipitation for ubiquitin modifications, immunofluorescence, CTSB K33-ubiquitination site mapping, in vivo tumor assays","journal":"Biology direct","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific ubiquitination linkage (K33) and writer/eraser identified (ZRANB1), multiple methods, single lab","pmids":["41035046"],"is_preprint":false},{"year":2025,"finding":"ETS1 transcription factor promotes the transcription of CTSB (and MMP13) during the differentiation of septoclasts from pericytes; ETS1 siRNA significantly reduced CTSB expression in primary septoclast cultures.","method":"RNA-seq of isolated septoclasts vs pericytes, ETS1 siRNA knockdown in primary cultures, RT-qPCR","journal":"Cell and tissue research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — transcriptional regulation identified by siRNA and RNA-seq, single lab, no direct ETS1-CTSB promoter binding confirmed","pmids":["40387924"],"is_preprint":false},{"year":2025,"finding":"METTL3 upregulates CTSB expression in chondrocytes through m6A methylation of CTSB mRNA; the protective effects of METTL3 silencing against IL-1β-induced chondrocyte injury depend on downstream CTSB downregulation.","method":"m6A RNA immunoprecipitation assay, dual-luciferase reporter assay, METTL3/CTSB siRNA knockdown, western blot, flow cytometry","journal":"Journal of orthopaedic surgery and research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — m6A modification of CTSB by METTL3 confirmed by MeRIP and luciferase assay, two orthogonal methods, single lab","pmids":["41466292"],"is_preprint":false},{"year":2025,"finding":"OGT-mediated O-GlcNAcylation of CTSB promotes its lysosomal retention and reduces its maturation; reduced O-GlcNAcylation (through OGT downregulation) lowers ROS, attenuates lysosomal membrane permeabilization, limits cytoplasmic CTSB leakage, and suppresses NLRP3 inflammasome activation in astrocytes.","method":"Co-IP for OGT-CTSB interaction, O-GlcNAcylation analysis, immunofluorescence for CTSB/LAMP1 colocalization, DHE staining for ROS, western blot","journal":"Journal of ethnopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PTM (O-GlcNAcylation) and writer (OGT) identified by Co-IP and modification analysis, multiple methods, single lab","pmids":["41391522"],"is_preprint":false},{"year":2020,"finding":"A gain-of-function missense mutation in CTSB results in increased cathepsin B endopeptidase proteolytic activity, as confirmed by a cathepsin B enzymatic assay, and causes palmoplantar keratoderma in a dominant fashion.","method":"Whole exome sequencing, cathepsin B enzymatic activity assay, protein structural modelling","journal":"Clinical and experimental dermatology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — enzymatic activity assay with disease-linked variant, supported by structural modelling, single case/single lab","pmids":["32683719"],"is_preprint":false},{"year":2017,"finding":"Duplicated enhancer region upstream of CTSB drives increased CTSB expression specifically in epidermal keratinocytes; the enhancer activity correlates with CTSB expression in differentiating keratinocytes, establishing CTSB overexpression as the cause of keratolytic winter erythema (KWE).","method":"Targeted resequencing, SNP array, whole-genome sequencing, enhancer activity reporter assay, qPCR, immunohistochemistry; segregation analysis in South African and Norwegian families","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — enhancer duplication identified and activity validated, replicated in two independent ethnic cohorts with multiple orthogonal methods","pmids":["28457472"],"is_preprint":false},{"year":2023,"finding":"Nuclear translocation of CTSB in retinoblastoma cells promotes DNA damage and cell cycle arrest by inhibiting BRCA1 expression, and activates the STAT3/STING1 pathway to induce lysosomal stress, ferroptosis, and autophagy.","method":"CTSB overexpression with nuclear translocation, comet assay (DNA damage), flow cytometry (cell cycle/apoptosis/ferroptosis), western blot for BRCA1 and STAT3/STING1 pathway, CCK-8, RT-qPCR","journal":"Molecular biotechnology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic claims (BRCA1 inhibition, STAT3/STING1) based on correlative western blot and knockdown, single lab, no direct CTSB-BRCA1 interaction shown","pmids":["38159170"],"is_preprint":false},{"year":2024,"finding":"Lysosomal CTSB activity is required for efficient phagolysosomal fusion and acidification in microglia; myeloid-specific CTSB knockdown in zebrafish led to dysmorphic microglia containing undigested dead cells and accumulation of apoptotic cells during brain development, phenocopied in Ctsb-deficient mice.","method":"Myeloid-specific CTSB knockdown in zebrafish, Ctsb global KO mice, live imaging of phagolysosomal fusion and acidification, apoptosis markers, behavioral assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two independent model organisms (zebrafish and mouse), live imaging of lysosomal function, defined cellular process (efferocytosis), single lab preprint","pmids":[],"is_preprint":true},{"year":2025,"finding":"Nervous system-specific double knockout of CtsB and CtsL in mice leads to selective loss of specific Purkinje cell subpopulations (phospholipase C β4-positive, Zebrin II-negative), ubiquitin-positive aggregate accumulation in Purkinje cell perikarya and axons reflecting impaired autophagy-lysosomal degradation, and neuronal loss in thalamic nuclei.","method":"Conditional double-knockout mice (Nestin-Cre; CTSBflox/flox; CTSLflox/flox), electron microscopy, immunohistochemistry, behavioral testing","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean conditional KO with defined cellular phenotype, electron microscopy confirmation, but CtsB and CtsL are ablated together making CtsB-specific contributions ambiguous","pmids":["40320169"],"is_preprint":false},{"year":2024,"finding":"Beauvericin (BEA) directly interacts with CTSB and acts as an uncompetitive inhibitor of its enzymatic activity; NMR analyses confirmed direct BEA-CTSB interaction, and enzyme kinetics established uncompetitive inhibition mechanism.","method":"NMR spectroscopy (direct interaction), enzyme kinetics (uncompetitive inhibition), molecular docking (binding site), CTSB activity assay in BMDCs and THP-1-derived DCs","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzyme kinetics with defined inhibition mechanism and NMR interaction validation, single lab preprint","pmids":[],"is_preprint":true},{"year":2025,"finding":"Elevated lysosomal CTSB and cytoplasmic CTSB leakage in mouse models of neurological lysosomal storage diseases (MPS IIIC and sialidosis) triggers amyloidogenesis in cortical neurons; CTSB-deficient MPS IIIC mice or animals treated with irreversible CTSB inhibitor E64 showed drastic reduction of Thioflavin-S/APP-positive amyloid deposits and restoration of autophagy.","method":"Ctsb knockout in MPS IIIC mouse model, chronic E64 (CTSB inhibitor) treatment, Thioflavin-S/APP staining, P62/LC3 puncta, behavioral assays, cytoplasmic CTSB localization","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal approaches (genetic KO and pharmacological inhibition) in two LSD models, defined amyloidogenic mechanism, single lab preprint","pmids":[],"is_preprint":true},{"year":2025,"finding":"Extralysosomal CTSB cleaves the C-terminal region of TAF1 (a core TFIID component) in oligodendrocytes during multiple sclerosis progression, impairing RNAPII promoter-proximal pausing and reducing expression of oligodendroglial myelination genes.","method":"Mass spectrometry/proteomics of MS brains, endoproteolysis assay for TAF1 cleavage by CTSB, Taf1 C-terminal deletion mouse model, brain transcriptomics, CTSB inhibitor experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — substrate (TAF1) identified and cleavage validated, in vivo model recapitulates transcriptomic consequences, single lab preprint","pmids":[],"is_preprint":true},{"year":2025,"finding":"AAV-mediated overexpression of CTSB in skeletal muscle of APP/PS1 Alzheimer's disease mice improves motor coordination, memory function, and adult hippocampal neurogenesis, and shifts hippocampal, muscle, and plasma proteomic profiles toward wild-type; wildtype mice receiving Ctsb muscle overexpression developed memory deficits.","method":"AAV-vector muscle overexpression in APP/PS1 mice, behavioral testing (memory, motor), hippocampal neurogenesis assay, multi-tissue proteomics","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 2 / Weak — in vivo functional rescue established but molecular mechanism of muscle-brain CTSB signaling not directly resolved, single lab preprint","pmids":[],"is_preprint":true},{"year":2025,"finding":"CTSB cleaves sialin (a lysosomal nitrate transporter) to generate a proteolytic fragment called Sialin2 that localizes to mitochondria and scaffolds LKB1-AMPK complexes to activate AMPK-dependent mitochondrial biogenesis.","method":"Cryo-EM structure of Sialin2, microscale thermophoresis (nitrate binding), CTSB cleavage assay, subcellular fractionation, Co-IP for LKB1-AMPK scaffold","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 1 / Weak — cryo-EM and in vitro cleavage assay described, but CTSB-specific cleavage mechanism is peripheral to the main paper focus; single lab preprint, mechanistic link to CTSB not fully validated","pmids":[],"is_preprint":true},{"year":2025,"finding":"CTSB promotes NLRP3-mediated pyroptosis in vascular endothelial cells (HUVECs) through NF-κB activation after being released from lysosomes upon lysosomal damage caused by Na+/Ca2+ overload; lentiviral CTSB overexpression increased and CTSB silencing decreased NLRP3-mediated pyroptosis.","method":"Lentiviral CTSB overexpression and silencing in HUVECs, western blot for NF-κB/NLRP3/GSDMD pathway, LDH/IL-1β release assay, ion overload measurement","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with pathway placement (NF-κB → NLRP3), multiple methods, single lab","pmids":["40058708"],"is_preprint":false}],"current_model":"CTSB is a lysosomal cysteine protease that, beyond bulk protein degradation, performs specific proteolytic functions including cleavage of MCOLN1/TRPML1 to suppress TFEB-dependent lysosomal biogenesis, degradation of substrates such as RIP1, FPN, fibronectin, and TAF1 in extra-lysosomal compartments, and activation of NLRP3 inflammasome signaling upon lysosomal membrane permeabilization; its activity is regulated by endogenous inhibitors (CST6), post-translational modifications (K33-linked ubiquitination via ZRANB1; O-GlcNAcylation via OGT), transcriptional control (by HDAC3 and ETS1), and its gene expression is upregulated by an enhancer duplication causing keratolytic winter erythema, placing CTSB at the intersection of autophagy, inflammation, cell death, and tissue homeostasis."},"narrative":{"mechanistic_narrative":"CTSB is a lysosomal cysteine endopeptidase whose proteolytic activity governs lysosomal homeostasis, autophagy, inflammation, and cell death across diverse tissues [PMID:27786577, PMID:36713420]. Within the lysosome it supports degradative function and organelle dynamics: it cleaves the calcium channel MCOLN1/TRPML1 to keep TFEB transcriptionally suppressed and thereby restrain lysosomal and autophagosome biogenesis [PMID:27786577], and its activity is required for efficient phagolysosomal fusion and acidification, enabling microglial clearance of apoptotic cells during brain development. Loss of CTSB-dependent autophagic-lysosomal degradation, shown in combined nervous-system CtsB/CtsL knockout mice, causes ubiquitin-positive aggregate accumulation and selective neuronal loss [PMID:40320169]. Beyond bulk turnover, CTSB executes specific cleavages of defined substrates: it degrades RIP1 to dampen TNFα-driven NF-κB signaling [PMID:35658939], degrades fibronectin to attenuate Wnt/β-catenin signaling during adipogenesis [PMID:24878992], binds and downregulates ferroportin to disrupt iron homeostasis and promote ferroptosis [PMID:39960586], degrades SPHK1 to control osteoclast maturation [PMID:34815788], and cleaves the TFIID component TAF1 to reprogram oligodendroglial transcription. Upon lysosomal membrane permeabilization, CTSB leaks into the cytoplasm where it activates the mitochondrial apoptosis pathway [PMID:36713420] and NF-κB–NLRP3 inflammasome/pyroptosis signaling [PMID:40058708], and contributes to neuronal amyloidogenesis in lysosomal storage disease models. CTSB abundance and localization are tightly regulated transcriptionally by HDAC3 and ETS1 [PMID:35658939, PMID:40387924], post-transcriptionally by METTL3-mediated m6A methylation [PMID:41466292], and post-translationally by ZRANB1-dependent K33-linked deubiquitination [PMID:41035046] and OGT-mediated O-GlcNAcylation, which promotes lysosomal retention and limits cytoplasmic leakage [PMID:41391522]. A duplicated upstream enhancer driving keratinocyte CTSB overexpression causes keratolytic winter erythema, and a gain-of-function missense variant increasing endopeptidase activity causes dominant palmoplantar keratoderma [PMID:28457472, PMID:32683719].","teleology":[{"year":2014,"claim":"Established that CTSB can act on an extracellular matrix substrate to shape a signaling pathway, linking its protease activity to fibronectin turnover and Wnt/β-catenin attenuation during adipocyte differentiation.","evidence":"CTSB overexpression/inhibition in primary porcine preadipocytes with lipid assays and β-catenin western blot, plus LiCl rescue","pmids":["24878992"],"confidence":"Low","gaps":["Fibronectin degradation inferred rather than shown by direct in vitro cleavage","single lab, single cell system"]},{"year":2016,"claim":"Defined a homeostatic lysosomal substrate for CTSB by showing it cleaves MCOLN1/TRPML1 to suppress TFEB, revealing CTSB as a negative regulator of lysosomal and autophagosome biogenesis rather than only a bulk-degradation enzyme.","evidence":"Genetic knockout/inhibition with lysosome/autophagosome counts, TFEB activity, and MCOLN1 cleavage readouts","pmids":["27786577"],"confidence":"Medium","gaps":["Single lab and cellular model","site of MCOLN1 cleavage not mapped"]},{"year":2017,"claim":"Connected CTSB dosage to human disease by identifying an upstream enhancer duplication that drives keratinocyte-specific CTSB overexpression as the cause of keratolytic winter erythema.","evidence":"Targeted/whole-genome sequencing, enhancer reporter assays, qPCR/IHC, and segregation in two ethnic cohorts","pmids":["28457472"],"confidence":"High","gaps":["Downstream keratinocyte substrates of excess CTSB not defined"]},{"year":2020,"claim":"Showed that a gain-of-function CTSB missense variant directly elevates endopeptidase activity and causes dominant palmoplantar keratoderma, complementing the dosage mechanism with an activity mechanism.","evidence":"Whole-exome sequencing, cathepsin B enzymatic assay, and structural modelling of a disease variant","pmids":["32683719"],"confidence":"Medium","gaps":["Single case/single lab","tissue-level pathogenic substrate not identified"]},{"year":2021,"claim":"Identified SPHK1 as a CTSB substrate in osteoclasts and showed CST6 entry suppresses CTSB, placing CTSB within a tumor-bone signaling axis controlling osteoclast maturation.","evidence":"In vitro osteoclastogenesis, CTSB activity assay, SPHK1/p38 western blots, and an in vivo metastasis model","pmids":["34815788"],"confidence":"Medium","gaps":["Direct CTSB-SPHK1 cleavage not biochemically mapped","single lab"]},{"year":2022,"claim":"Linked CTSB transcriptional control to inflammatory tone by showing HDAC3 represses CTSB and that excess CTSB degrades RIP1 to limit TNFα/NF-κB signaling in macrophages.","evidence":"HDAC3-knockout macrophages, RIP1 degradation western blots, RNAseq, and CTSB-inhibitor rescue","pmids":["35658939"],"confidence":"Medium","gaps":["RIP1 cleavage site not defined","single lab"]},{"year":2023,"claim":"Demonstrated the extra-lysosomal, lethal arm of CTSB by showing LMP-driven cytoplasmic CTSB release activates the mitochondrial apoptosis pathway in sepsis-associated kidney injury.","evidence":"LPS-treated HK-2 cells with LMP and mitochondrial-potential assays, apoptosis markers, and CA-074 inhibitor rescue","pmids":["36713420"],"confidence":"Medium","gaps":["Direct cytoplasmic substrate triggering apoptosis not identified","single lab"]},{"year":2023,"claim":"Reported a nuclear function for CTSB in retinoblastoma cells affecting BRCA1 expression and STAT3/STING1 signaling, raising the possibility of CTSB action outside lysosome and cytoplasm.","evidence":"CTSB overexpression with nuclear translocation, comet assay, flow cytometry, and pathway western blots","pmids":["38159170"],"confidence":"Low","gaps":["No direct CTSB-BRCA1 interaction shown; effects are correlative","mechanism of nuclear import unknown","single lab"]},{"year":2025,"claim":"Expanded the post-translational and transcriptional control of CTSB, identifying ZRANB1-dependent K33-linked deubiquitination, OGT-mediated O-GlcNAcylation controlling lysosomal retention/leakage, METTL3 m6A methylation, and ETS1-driven transcription.","evidence":"Ubiquitin/O-GlcNAc Co-IP and modification mapping, MeRIP and luciferase assays, ETS1 siRNA with RNA-seq across multiple cell systems","pmids":["41035046","41391522","41466292","40387924"],"confidence":"Medium","gaps":["ETS1-CTSB promoter binding not directly confirmed","each regulator characterized in a distinct disease context, generality unclear"]},{"year":2025,"claim":"Established CTSB as a driver of ferroptosis and inflammatory cell death by direct ferroportin binding/downregulation and by NF-κB–NLRP3 pyroptosis activation following lysosomal damage.","evidence":"CTSB-FPN Co-IP/binding with knockdown and ferroptosis markers in vivo, plus lentiviral CTSB gain/loss with NF-κB/NLRP3/GSDMD readouts in HUVECs","pmids":["39960586","40058708"],"confidence":"Medium","gaps":["Whether FPN is cleaved or only bound is unresolved","single lab per study"]},{"year":2025,"claim":"Tied CTSB to neurodegenerative and developmental brain phenotypes through autophagy-lysosomal degradation, microglial efferocytosis, and amyloidogenesis, while a TAF1-cleavage finding revealed a transcription-reprogramming role in oligodendrocytes.","evidence":"Conditional CtsB/CtsL double-KO mice with EM, zebrafish/mouse CTSB knockdown with live imaging (preprint), CTSB-KO/E64 in LSD models (preprint), and TAF1 cleavage assays with a Taf1-deletion mouse (preprint)","pmids":["40320169"],"confidence":"Medium","gaps":["CtsB-specific contribution ambiguous when ablated with CtsL","several findings are single-lab preprints","TAF1 cleavage site and access mechanism for nuclear/cytoplasmic CTSB unresolved"]},{"year":null,"claim":"How CTSB escapes the lysosome and accesses extra-lysosomal and nuclear substrates (RIP1, TAF1, FPN, BRCA1) in a regulated rather than purely damage-induced manner remains undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying model for CTSB compartmental trafficking to non-lysosomal substrates","direct cleavage sites for most substrates unmapped","muscle-to-brain CTSB signaling mechanism unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,10]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,5,17]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,9,13]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,20]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0,14]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,5,20]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,20]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,11]}],"complexes":[],"partners":["MCOLN1","RIPK1","SLC40A1","SPHK1","TAF1","CST6","ZRANB1","OGT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07858","full_name":"Cathepsin B","aliases":["APP secretase","APPS","Cathepsin B1"],"length_aa":339,"mass_kda":37.8,"function":"Thiol protease which is believed to participate in intracellular degradation and turnover of proteins (PubMed:12220505). Cleaves matrix extracellular phosphoglycoprotein MEPE (PubMed:12220505). Involved in the solubilization of cross-linked TG/thyroglobulin in the thyroid follicle lumen (By similarity). Has also been implicated in tumor invasion and metastasis (PubMed:3972105)","subcellular_location":"Lysosome; Melanosome; Secreted, extracellular space; Apical cell membrane","url":"https://www.uniprot.org/uniprotkb/P07858/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CTSB","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CTSB","total_profiled":1310},"omim":[{"mim_id":"619389","title":"SPINOCEREBELLAR ATAXIA, AUTOSOMAL RECESSIVE 29; SCAR29","url":"https://www.omim.org/entry/619389"},{"mim_id":"617322","title":"SH3KBP1-BINDING PROTEIN 1; SHKBP1","url":"https://www.omim.org/entry/617322"},{"mim_id":"616967","title":"THIOREDOXIN DOMAIN-CONTAINING PROTEIN 17; TXNDC17","url":"https://www.omim.org/entry/616967"},{"mim_id":"616064","title":"TUBULOINTERSTITIAL NEPHRITIS ANTIGEN-LIKE PROTEIN 1; TINAGL1","url":"https://www.omim.org/entry/616064"},{"mim_id":"610034","title":"VPS33A CORE SUBUNIT OF CORVET AND HOPS COMPLEXES; VPS33A","url":"https://www.omim.org/entry/610034"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"thyroid gland","ntpm":991.2}],"url":"https://www.proteinatlas.org/search/CTSB"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P07858","domains":[{"cath_id":"3.90.70.10","chopping":"27-336","consensus_level":"high","plddt":95.8157,"start":27,"end":336}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P07858","model_url":"https://alphafold.ebi.ac.uk/files/AF-P07858-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P07858-F1-predicted_aligned_error_v6.png","plddt_mean":92.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CTSB","jax_strain_url":"https://www.jax.org/strain/search?query=CTSB"},"sequence":{"accession":"P07858","fasta_url":"https://rest.uniprot.org/uniprotkb/P07858.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P07858/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P07858"}},"corpus_meta":[{"pmid":"27786577","id":"PMC_27786577","title":"Regulation of lysosomal dynamics and autophagy by CTSB/cathepsin B.","date":"2016","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/27786577","citation_count":173,"is_preprint":false},{"pmid":"34815788","id":"PMC_34815788","title":"CST6 protein and peptides inhibit breast cancer bone metastasis by suppressing CTSB activity and osteoclastogenesis.","date":"2021","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/34815788","citation_count":59,"is_preprint":false},{"pmid":"37141464","id":"PMC_37141464","title":"Apigenin Alleviated High-Fat-Diet-Induced Hepatic Pyroptosis by Mitophagy-ROS-CTSB-NLRP3 Pathway in Mice and AML12 Cells.","date":"2023","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37141464","citation_count":58,"is_preprint":false},{"pmid":"36713420","id":"PMC_36713420","title":"CTSB promotes sepsis-induced acute kidney injury through activating mitochondrial apoptosis pathway.","date":"2023","source":"Frontiers in 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channel MCOLN1/TRPML1 in lysosomes, thereby maintaining suppression of the transcription factor TFEB and reducing expression of lysosomal and autophagy-related proteins, controlling the number of lysosomes and autophagosomes in the cell.\",\n      \"method\": \"Genetic knockout/inhibition with functional readout (lysosome/autophagosome counts, TFEB activity, MCOLN1 cleavage assay)\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined substrate (MCOLN1) and downstream pathway (TFEB suppression) established in cellular model, single lab\",\n      \"pmids\": [\"27786577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cancer cell-derived CST6 (cystatin 6) enters osteoclasts by endocytosis and suppresses CTSB proteolytic activity; CTSB normally degrades SPHK1, so CTSB inhibition leads to SPHK1 upregulation, which suppresses osteoclast maturation by inhibiting RANKL-induced p38 activation.\",\n      \"method\": \"In vitro osteoclastogenesis assay, CTSB activity assay, western blot for SPHK1 and p38 phosphorylation, in vivo metastasis model\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (activity assay, substrate identification, in vivo), single lab\",\n      \"pmids\": [\"34815788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In macrophages, HDAC3 deficiency leads to elevated CTSB expression (via histone acetylation), and the resulting excess CTSB degrades RIP1 (RIPK1) protein, reducing TNFα-mediated NF-κB activation and inflammatory response.\",\n      \"method\": \"HDAC3 knockout macrophages, western blot for RIP1 degradation, immunofluorescence, RNAseq, CTSB inhibitor rescue experiments\",\n      \"journal\": \"Cell & Bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined substrate (RIP1), inhibitor rescue, multiple methods, single lab\",\n      \"pmids\": [\"35658939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CTSB promotes preadipocyte differentiation by degrading fibronectin (Fn), a key extracellular matrix component and target gene of the Wnt/β-catenin pathway; CTSB degrades Fn and attenuates Wnt/β-catenin signaling to promote adipogenesis.\",\n      \"method\": \"CTSB overexpression/inhibition in primary porcine preadipocytes, lipid accumulation assay, western blot for β-catenin, LiCl (Wnt activator) rescue experiment\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited mechanistic resolution, substrate (Fn) degradation inferred rather than directly demonstrated by in vitro cleavage\",\n      \"pmids\": [\"24878992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In sepsis-induced acute kidney injury, LPS induces lysosomal membrane permeabilization (LMP), causing CTSB release into the cytoplasm, which then activates the mitochondrial apoptosis pathway; CTSB inhibitor CA-074 reverses LPS-induced apoptosis, mitochondrial membrane potential loss, and activation of mitochondrial apoptosis markers.\",\n      \"method\": \"LPS-treated HK-2 cells, CTSB activity assay, acridine orange staining (LMP), JC-1 (mitochondrial membrane potential), Annexin V/PI, CA-074 inhibitor rescue, western blot\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, CTSB inhibitor rescue with mechanistic pathway placement, single lab\",\n      \"pmids\": [\"36713420\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CTSB degrades ferroportin (FPN) in macrophages, disrupting iron homeostasis and promoting ferroptosis; CTSB was shown to directly bind FPN and negatively regulate its protein level.\",\n      \"method\": \"Co-IP/binding assay for CTSB-FPN interaction, CTSB knockdown/inhibition, western blot for FPN, ferroptosis markers, ApoE KO and HFD rat AS models, single-cell transcriptomics\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding partner (FPN) identified, multiple in vitro and in vivo methods, single lab\",\n      \"pmids\": [\"39960586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MINPP1 stabilizes CTSB expression by modulating its K33-linked deubiquitination via ZRANB1 (a deubiquitinase), thereby promoting ferroptosis in HBV-positive hepatocellular carcinoma cells.\",\n      \"method\": \"Immunoprecipitation for ubiquitin modifications, immunofluorescence, CTSB K33-ubiquitination site mapping, in vivo tumor assays\",\n      \"journal\": \"Biology direct\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific ubiquitination linkage (K33) and writer/eraser identified (ZRANB1), multiple methods, single lab\",\n      \"pmids\": [\"41035046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ETS1 transcription factor promotes the transcription of CTSB (and MMP13) during the differentiation of septoclasts from pericytes; ETS1 siRNA significantly reduced CTSB expression in primary septoclast cultures.\",\n      \"method\": \"RNA-seq of isolated septoclasts vs pericytes, ETS1 siRNA knockdown in primary cultures, RT-qPCR\",\n      \"journal\": \"Cell and tissue research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — transcriptional regulation identified by siRNA and RNA-seq, single lab, no direct ETS1-CTSB promoter binding confirmed\",\n      \"pmids\": [\"40387924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL3 upregulates CTSB expression in chondrocytes through m6A methylation of CTSB mRNA; the protective effects of METTL3 silencing against IL-1β-induced chondrocyte injury depend on downstream CTSB downregulation.\",\n      \"method\": \"m6A RNA immunoprecipitation assay, dual-luciferase reporter assay, METTL3/CTSB siRNA knockdown, western blot, flow cytometry\",\n      \"journal\": \"Journal of orthopaedic surgery and research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — m6A modification of CTSB by METTL3 confirmed by MeRIP and luciferase assay, two orthogonal methods, single lab\",\n      \"pmids\": [\"41466292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"OGT-mediated O-GlcNAcylation of CTSB promotes its lysosomal retention and reduces its maturation; reduced O-GlcNAcylation (through OGT downregulation) lowers ROS, attenuates lysosomal membrane permeabilization, limits cytoplasmic CTSB leakage, and suppresses NLRP3 inflammasome activation in astrocytes.\",\n      \"method\": \"Co-IP for OGT-CTSB interaction, O-GlcNAcylation analysis, immunofluorescence for CTSB/LAMP1 colocalization, DHE staining for ROS, western blot\",\n      \"journal\": \"Journal of ethnopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PTM (O-GlcNAcylation) and writer (OGT) identified by Co-IP and modification analysis, multiple methods, single lab\",\n      \"pmids\": [\"41391522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A gain-of-function missense mutation in CTSB results in increased cathepsin B endopeptidase proteolytic activity, as confirmed by a cathepsin B enzymatic assay, and causes palmoplantar keratoderma in a dominant fashion.\",\n      \"method\": \"Whole exome sequencing, cathepsin B enzymatic activity assay, protein structural modelling\",\n      \"journal\": \"Clinical and experimental dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — enzymatic activity assay with disease-linked variant, supported by structural modelling, single case/single lab\",\n      \"pmids\": [\"32683719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Duplicated enhancer region upstream of CTSB drives increased CTSB expression specifically in epidermal keratinocytes; the enhancer activity correlates with CTSB expression in differentiating keratinocytes, establishing CTSB overexpression as the cause of keratolytic winter erythema (KWE).\",\n      \"method\": \"Targeted resequencing, SNP array, whole-genome sequencing, enhancer activity reporter assay, qPCR, immunohistochemistry; segregation analysis in South African and Norwegian families\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — enhancer duplication identified and activity validated, replicated in two independent ethnic cohorts with multiple orthogonal methods\",\n      \"pmids\": [\"28457472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Nuclear translocation of CTSB in retinoblastoma cells promotes DNA damage and cell cycle arrest by inhibiting BRCA1 expression, and activates the STAT3/STING1 pathway to induce lysosomal stress, ferroptosis, and autophagy.\",\n      \"method\": \"CTSB overexpression with nuclear translocation, comet assay (DNA damage), flow cytometry (cell cycle/apoptosis/ferroptosis), western blot for BRCA1 and STAT3/STING1 pathway, CCK-8, RT-qPCR\",\n      \"journal\": \"Molecular biotechnology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic claims (BRCA1 inhibition, STAT3/STING1) based on correlative western blot and knockdown, single lab, no direct CTSB-BRCA1 interaction shown\",\n      \"pmids\": [\"38159170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Lysosomal CTSB activity is required for efficient phagolysosomal fusion and acidification in microglia; myeloid-specific CTSB knockdown in zebrafish led to dysmorphic microglia containing undigested dead cells and accumulation of apoptotic cells during brain development, phenocopied in Ctsb-deficient mice.\",\n      \"method\": \"Myeloid-specific CTSB knockdown in zebrafish, Ctsb global KO mice, live imaging of phagolysosomal fusion and acidification, apoptosis markers, behavioral assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two independent model organisms (zebrafish and mouse), live imaging of lysosomal function, defined cellular process (efferocytosis), single lab preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nervous system-specific double knockout of CtsB and CtsL in mice leads to selective loss of specific Purkinje cell subpopulations (phospholipase C β4-positive, Zebrin II-negative), ubiquitin-positive aggregate accumulation in Purkinje cell perikarya and axons reflecting impaired autophagy-lysosomal degradation, and neuronal loss in thalamic nuclei.\",\n      \"method\": \"Conditional double-knockout mice (Nestin-Cre; CTSBflox/flox; CTSLflox/flox), electron microscopy, immunohistochemistry, behavioral testing\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean conditional KO with defined cellular phenotype, electron microscopy confirmation, but CtsB and CtsL are ablated together making CtsB-specific contributions ambiguous\",\n      \"pmids\": [\"40320169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Beauvericin (BEA) directly interacts with CTSB and acts as an uncompetitive inhibitor of its enzymatic activity; NMR analyses confirmed direct BEA-CTSB interaction, and enzyme kinetics established uncompetitive inhibition mechanism.\",\n      \"method\": \"NMR spectroscopy (direct interaction), enzyme kinetics (uncompetitive inhibition), molecular docking (binding site), CTSB activity assay in BMDCs and THP-1-derived DCs\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzyme kinetics with defined inhibition mechanism and NMR interaction validation, single lab preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Elevated lysosomal CTSB and cytoplasmic CTSB leakage in mouse models of neurological lysosomal storage diseases (MPS IIIC and sialidosis) triggers amyloidogenesis in cortical neurons; CTSB-deficient MPS IIIC mice or animals treated with irreversible CTSB inhibitor E64 showed drastic reduction of Thioflavin-S/APP-positive amyloid deposits and restoration of autophagy.\",\n      \"method\": \"Ctsb knockout in MPS IIIC mouse model, chronic E64 (CTSB inhibitor) treatment, Thioflavin-S/APP staining, P62/LC3 puncta, behavioral assays, cytoplasmic CTSB localization\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal approaches (genetic KO and pharmacological inhibition) in two LSD models, defined amyloidogenic mechanism, single lab preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Extralysosomal CTSB cleaves the C-terminal region of TAF1 (a core TFIID component) in oligodendrocytes during multiple sclerosis progression, impairing RNAPII promoter-proximal pausing and reducing expression of oligodendroglial myelination genes.\",\n      \"method\": \"Mass spectrometry/proteomics of MS brains, endoproteolysis assay for TAF1 cleavage by CTSB, Taf1 C-terminal deletion mouse model, brain transcriptomics, CTSB inhibitor experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — substrate (TAF1) identified and cleavage validated, in vivo model recapitulates transcriptomic consequences, single lab preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AAV-mediated overexpression of CTSB in skeletal muscle of APP/PS1 Alzheimer's disease mice improves motor coordination, memory function, and adult hippocampal neurogenesis, and shifts hippocampal, muscle, and plasma proteomic profiles toward wild-type; wildtype mice receiving Ctsb muscle overexpression developed memory deficits.\",\n      \"method\": \"AAV-vector muscle overexpression in APP/PS1 mice, behavioral testing (memory, motor), hippocampal neurogenesis assay, multi-tissue proteomics\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo functional rescue established but molecular mechanism of muscle-brain CTSB signaling not directly resolved, single lab preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CTSB cleaves sialin (a lysosomal nitrate transporter) to generate a proteolytic fragment called Sialin2 that localizes to mitochondria and scaffolds LKB1-AMPK complexes to activate AMPK-dependent mitochondrial biogenesis.\",\n      \"method\": \"Cryo-EM structure of Sialin2, microscale thermophoresis (nitrate binding), CTSB cleavage assay, subcellular fractionation, Co-IP for LKB1-AMPK scaffold\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — cryo-EM and in vitro cleavage assay described, but CTSB-specific cleavage mechanism is peripheral to the main paper focus; single lab preprint, mechanistic link to CTSB not fully validated\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CTSB promotes NLRP3-mediated pyroptosis in vascular endothelial cells (HUVECs) through NF-κB activation after being released from lysosomes upon lysosomal damage caused by Na+/Ca2+ overload; lentiviral CTSB overexpression increased and CTSB silencing decreased NLRP3-mediated pyroptosis.\",\n      \"method\": \"Lentiviral CTSB overexpression and silencing in HUVECs, western blot for NF-κB/NLRP3/GSDMD pathway, LDH/IL-1β release assay, ion overload measurement\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with pathway placement (NF-κB → NLRP3), multiple methods, single lab\",\n      \"pmids\": [\"40058708\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSB is a lysosomal cysteine protease that, beyond bulk protein degradation, performs specific proteolytic functions including cleavage of MCOLN1/TRPML1 to suppress TFEB-dependent lysosomal biogenesis, degradation of substrates such as RIP1, FPN, fibronectin, and TAF1 in extra-lysosomal compartments, and activation of NLRP3 inflammasome signaling upon lysosomal membrane permeabilization; its activity is regulated by endogenous inhibitors (CST6), post-translational modifications (K33-linked ubiquitination via ZRANB1; O-GlcNAcylation via OGT), transcriptional control (by HDAC3 and ETS1), and its gene expression is upregulated by an enhancer duplication causing keratolytic winter erythema, placing CTSB at the intersection of autophagy, inflammation, cell death, and tissue homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CTSB is a lysosomal cysteine endopeptidase whose proteolytic activity governs lysosomal homeostasis, autophagy, inflammation, and cell death across diverse tissues [#0, #4]. Within the lysosome it supports degradative function and organelle dynamics: it cleaves the calcium channel MCOLN1/TRPML1 to keep TFEB transcriptionally suppressed and thereby restrain lysosomal and autophagosome biogenesis [#0], and its activity is required for efficient phagolysosomal fusion and acidification, enabling microglial clearance of apoptotic cells during brain development [#13]. Loss of CTSB-dependent autophagic-lysosomal degradation, shown in combined nervous-system CtsB/CtsL knockout mice, causes ubiquitin-positive aggregate accumulation and selective neuronal loss [#14]. Beyond bulk turnover, CTSB executes specific cleavages of defined substrates: it degrades RIP1 to dampen TNF\\u03b1-driven NF-\\u03baB signaling [#2], degrades fibronectin to attenuate Wnt/\\u03b2-catenin signaling during adipogenesis [#3], binds and downregulates ferroportin to disrupt iron homeostasis and promote ferroptosis [#5], degrades SPHK1 to control osteoclast maturation [#1], and cleaves the TFIID component TAF1 to reprogram oligodendroglial transcription [#17]. Upon lysosomal membrane permeabilization, CTSB leaks into the cytoplasm where it activates the mitochondrial apoptosis pathway [#4] and NF-\\u03baB\\u2013NLRP3 inflammasome/pyroptosis signaling [#20], and contributes to neuronal amyloidogenesis in lysosomal storage disease models [#16]. CTSB abundance and localization are tightly regulated transcriptionally by HDAC3 and ETS1 [#2, #7], post-transcriptionally by METTL3-mediated m6A methylation [#8], and post-translationally by ZRANB1-dependent K33-linked deubiquitination [#6] and OGT-mediated O-GlcNAcylation, which promotes lysosomal retention and limits cytoplasmic leakage [#9]. A duplicated upstream enhancer driving keratinocyte CTSB overexpression causes keratolytic winter erythema, and a gain-of-function missense variant increasing endopeptidase activity causes dominant palmoplantar keratoderma [#11, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established that CTSB can act on an extracellular matrix substrate to shape a signaling pathway, linking its protease activity to fibronectin turnover and Wnt/\\u03b2-catenin attenuation during adipocyte differentiation.\",\n      \"evidence\": \"CTSB overexpression/inhibition in primary porcine preadipocytes with lipid assays and \\u03b2-catenin western blot, plus LiCl rescue\",\n      \"pmids\": [\"24878992\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Fibronectin degradation inferred rather than shown by direct in vitro cleavage\", \"single lab, single cell system\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined a homeostatic lysosomal substrate for CTSB by showing it cleaves MCOLN1/TRPML1 to suppress TFEB, revealing CTSB as a negative regulator of lysosomal and autophagosome biogenesis rather than only a bulk-degradation enzyme.\",\n      \"evidence\": \"Genetic knockout/inhibition with lysosome/autophagosome counts, TFEB activity, and MCOLN1 cleavage readouts\",\n      \"pmids\": [\"27786577\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab and cellular model\", \"site of MCOLN1 cleavage not mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected CTSB dosage to human disease by identifying an upstream enhancer duplication that drives keratinocyte-specific CTSB overexpression as the cause of keratolytic winter erythema.\",\n      \"evidence\": \"Targeted/whole-genome sequencing, enhancer reporter assays, qPCR/IHC, and segregation in two ethnic cohorts\",\n      \"pmids\": [\"28457472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream keratinocyte substrates of excess CTSB not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed that a gain-of-function CTSB missense variant directly elevates endopeptidase activity and causes dominant palmoplantar keratoderma, complementing the dosage mechanism with an activity mechanism.\",\n      \"evidence\": \"Whole-exome sequencing, cathepsin B enzymatic assay, and structural modelling of a disease variant\",\n      \"pmids\": [\"32683719\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single case/single lab\", \"tissue-level pathogenic substrate not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified SPHK1 as a CTSB substrate in osteoclasts and showed CST6 entry suppresses CTSB, placing CTSB within a tumor-bone signaling axis controlling osteoclast maturation.\",\n      \"evidence\": \"In vitro osteoclastogenesis, CTSB activity assay, SPHK1/p38 western blots, and an in vivo metastasis model\",\n      \"pmids\": [\"34815788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CTSB-SPHK1 cleavage not biochemically mapped\", \"single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked CTSB transcriptional control to inflammatory tone by showing HDAC3 represses CTSB and that excess CTSB degrades RIP1 to limit TNF\\u03b1/NF-\\u03baB signaling in macrophages.\",\n      \"evidence\": \"HDAC3-knockout macrophages, RIP1 degradation western blots, RNAseq, and CTSB-inhibitor rescue\",\n      \"pmids\": [\"35658939\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"RIP1 cleavage site not defined\", \"single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated the extra-lysosomal, lethal arm of CTSB by showing LMP-driven cytoplasmic CTSB release activates the mitochondrial apoptosis pathway in sepsis-associated kidney injury.\",\n      \"evidence\": \"LPS-treated HK-2 cells with LMP and mitochondrial-potential assays, apoptosis markers, and CA-074 inhibitor rescue\",\n      \"pmids\": [\"36713420\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct cytoplasmic substrate triggering apoptosis not identified\", \"single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Reported a nuclear function for CTSB in retinoblastoma cells affecting BRCA1 expression and STAT3/STING1 signaling, raising the possibility of CTSB action outside lysosome and cytoplasm.\",\n      \"evidence\": \"CTSB overexpression with nuclear translocation, comet assay, flow cytometry, and pathway western blots\",\n      \"pmids\": [\"38159170\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct CTSB-BRCA1 interaction shown; effects are correlative\", \"mechanism of nuclear import unknown\", \"single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Expanded the post-translational and transcriptional control of CTSB, identifying ZRANB1-dependent K33-linked deubiquitination, OGT-mediated O-GlcNAcylation controlling lysosomal retention/leakage, METTL3 m6A methylation, and ETS1-driven transcription.\",\n      \"evidence\": \"Ubiquitin/O-GlcNAc Co-IP and modification mapping, MeRIP and luciferase assays, ETS1 siRNA with RNA-seq across multiple cell systems\",\n      \"pmids\": [\"41035046\", \"41391522\", \"41466292\", \"40387924\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ETS1-CTSB promoter binding not directly confirmed\", \"each regulator characterized in a distinct disease context, generality unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established CTSB as a driver of ferroptosis and inflammatory cell death by direct ferroportin binding/downregulation and by NF-\\u03baB\\u2013NLRP3 pyroptosis activation following lysosomal damage.\",\n      \"evidence\": \"CTSB-FPN Co-IP/binding with knockdown and ferroptosis markers in vivo, plus lentiviral CTSB gain/loss with NF-\\u03baB/NLRP3/GSDMD readouts in HUVECs\",\n      \"pmids\": [\"39960586\", \"40058708\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FPN is cleaved or only bound is unresolved\", \"single lab per study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Tied CTSB to neurodegenerative and developmental brain phenotypes through autophagy-lysosomal degradation, microglial efferocytosis, and amyloidogenesis, while a TAF1-cleavage finding revealed a transcription-reprogramming role in oligodendrocytes.\",\n      \"evidence\": \"Conditional CtsB/CtsL double-KO mice with EM, zebrafish/mouse CTSB knockdown with live imaging (preprint), CTSB-KO/E64 in LSD models (preprint), and TAF1 cleavage assays with a Taf1-deletion mouse (preprint)\",\n      \"pmids\": [\"40320169\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CtsB-specific contribution ambiguous when ablated with CtsL\", \"several findings are single-lab preprints\", \"TAF1 cleavage site and access mechanism for nuclear/cytoplasmic CTSB unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CTSB escapes the lysosome and accesses extra-lysosomal and nuclear substrates (RIP1, TAF1, FPN, BRCA1) in a regulated rather than purely damage-induced manner remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying model for CTSB compartmental trafficking to non-lysosomal substrates\", \"direct cleavage sites for most substrates unmapped\", \"muscle-to-brain CTSB signaling mechanism unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 5, 17]},\n      {\"term_id\": \"GO:0008233\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 9, 13]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 20]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0, 14]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 5, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 20]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MCOLN1\", \"RIPK1\", \"SLC40A1\", \"SPHK1\", \"TAF1\", \"CST6\", \"ZRANB1\", \"OGT\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}