{"gene":"CAPN2","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2000,"finding":"The 2.3-Å crystal structure of full-length heterodimeric human m-calpain (CAPN2 large subunit + small subunit) in the absence of calcium reveals that the two catalytic subdomains (dIIa+dIIb) are rotated ~50° relative to one another, disrupting the active site and substrate-binding site, explaining calcium-dependent inactivation. An extremely negatively charged loop in domain dIII was identified as an 'electrostatic switch' whose calcium binding could allow subdomain dIIb to move toward dIIa, forming a functional catalytic center.","method":"X-ray crystallography at 2.3 Å resolution of recombinant heterodimeric human m-calpain","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with mechanistic interpretation of active-site disruption","pmids":["10639123"],"is_preprint":false},{"year":2004,"finding":"EGF activates m-calpain (CAPN2) through ERK-mediated direct phosphorylation at serine 50 of the large subunit, independent of intracellular calcium elevation. Phosphorylation at S50 is required for EGF-induced calpain activation, cell deadhesion, and motility; an S50A substitution limits activation, while an S50E substitution confers constitutive activity in vivo.","method":"In vitro kinase assay (ERK phosphorylates m-calpain), site-directed mutagenesis (S50A/S50E), intracellular calcium chelation, cell motility and deadhesion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus mutagenesis validated in vivo, multiple orthogonal methods","pmids":["14993287"],"is_preprint":false},{"year":1999,"finding":"TNF-α activates cytosolic m-calpain (CAPN2), which directly cleaves IκBα in a proteasome-independent manner, allowing NF-κB nuclear translocation. This calpain-dependent pathway for IκBα proteolysis operates in parallel to the ubiquitin-proteasome pathway; calpastatin overexpression partially blocks TNF-α-induced NF-κB activity.","method":"Fluorescent calpain activity assay, broken-cell reconstitution with purified m-calpain, calpastatin transfection, ubiquitin-pathway-deficient cell line (ts20b), subcellular fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution in broken cells, calpastatin inhibition, validated in pathway-deficient cell line, multiple orthogonal approaches","pmids":["9873017"],"is_preprint":false},{"year":2000,"finding":"Calpain (including m-calpain/CAPN2) directly cleaves caspase-7, caspase-8, and caspase-9 at sites distinct from those used by upstream caspases, generating proteolytically inactive fragments. Calpain cleavage of caspase-9 blocks dATP/cytochrome c-induced caspase-3 activation, identifying calpain as a negative regulator of caspase processing and apoptosis.","method":"In vitro cleavage assays with purified calpain and recombinant caspases, N-terminal sequencing of cleavage products, cell-free caspase-3 activation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with N-terminal sequencing, multiple substrates tested, functional consequence demonstrated","pmids":["10671558"],"is_preprint":false},{"year":2002,"finding":"Ionomycin-activated calpains (mu- and m-calpain/CAPN2) cleave Bcl-2, Bid, and Bcl-xL in vitro at single sites truncating their N-terminal regions. Calpain-truncated Bcl-2 and Bid exhibit diminished interactions with intact Bcl-2 family proteins and induce cytochrome c release from isolated mitochondria, triggering the intrinsic apoptotic pathway.","method":"In vitro cleavage assays with recombinant Bcl-2 family proteins, binding studies with immobilized proteins, cytochrome c release assay from isolated mitochondria, calpastatin inhibitor pretreatment in LCLC103H cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with multiple substrates, functional cytochrome c release assay, cell-based validation with specific inhibitor","pmids":["12000759"],"is_preprint":false},{"year":2006,"finding":"Calpain (m-calpain/CAPN2) cleaves Atg5 at a site generating a truncated ~24 kDa N-terminal fragment that translocates from cytosol to mitochondria, associates with Bcl-xL, and triggers cytochrome c release and caspase activation, converting autophagy to apoptosis.","method":"Forced expression and siRNA of Atg5 in tumor cells, calpain inhibitor treatment, subcellular fractionation, co-immunoprecipitation with Bcl-xL, in vitro calpain cleavage assay","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro cleavage, Co-IP, fractionation, siRNA rescue, in vivo tumor model; multiple orthogonal methods","pmids":["16998475"],"is_preprint":false},{"year":2006,"finding":"TRPM7 co-localizes with m-calpain (CAPN2) at peripheral adhesion complexes and regulates cell adhesion by controlling local calpain activity. TRPM7 overexpression causes cell rounding and loss of adhesion dependent on its ion channel activity; knockdown of m-calpain blocks TRPM7-induced cell detachment, and TRPM7 silencing increases peripheral adhesion complexes.","method":"Co-localization imaging, TRPM7 overexpression and RNAi knockdown, m-calpain RNAi rescue epistasis, cell adhesion and morphology assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — co-localization, epistasis by double knockdown, multiple functional readouts","pmids":["16436382"],"is_preprint":false},{"year":1991,"finding":"In transformed Schwann cells, >75% of m-calpain (mCANP/CAPN2) activity is membrane-associated while ~80% of mu-calpain is cytosolic. Immunofluorescence with distinct antibodies showed mCANP distributed throughout the intracellular space (sparing the perinuclear region) in permeabilized cells, while anti-cytosolic mCANP antibody stained most intensely in the perinuclear region, establishing distinct subcellular compartmentalization of the two isoforms.","method":"DEAE and phenyl Sepharose column chromatography for isoform separation, activity assays on subcellular fractions, immunofluorescence with isoform-specific antibodies on live vs. permeabilized cells","journal":"Journal of neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 — direct fractionation + immunolocalization with functional activity measurement; single lab","pmids":["1656060"],"is_preprint":false},{"year":1992,"finding":"In mouse and human brain, >95% of total immunoreactive m-calpain (mCANP/CAPN2) is located in the soluble (cytosolic) fraction after 15,000 g centrifugation, with caseinolytic activity detectable only in fractions from the supernatant. Triton X-100 extraction does not alter this distribution, establishing mCANP as a predominantly cytosolic enzyme in brain.","method":"Western blot immunoassay with two independent mCANP-specific antibodies, [14C]azocasein activity assay after DEAE-cellulose removal of endogenous inhibitor, differential centrifugation, Triton X-100 extraction","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — two independent antibodies, biochemical activity assay, orthogonal fractionation methods; single lab","pmids":["1548485"],"is_preprint":false},{"year":2000,"finding":"Calpain, activated by calcium influx or amyloid-β peptide, directly cleaves p35 (the CDK5 activator) to generate p25, causing prolonged CDK5 activation and mislocalization, tau hyperphosphorylation, and neuronal apoptosis. Specific calpain inhibitors block calcium-induced p35 cleavage in brain lysates and reduce neuronal death in Aβ-treated cortical neurons.","method":"In vitro calpain cleavage assay with recombinant p35, calpain inhibitor treatment in primary cortical neurons, brain lysate calcium stimulation, N-terminal sequencing of cleavage product","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with N-terminal sequencing, inhibitor rescue in primary neurons, Aβ-treatment model","pmids":["10830966"],"is_preprint":false},{"year":1995,"finding":"Ca2+ binding causes dissociation of the calpain heterodimer (large 80-kDa subunit encoded by CAPN2 and small 30-kDa subunit), with the free 80-kDa subunit being the active form of the enzyme; this dissociation mechanism corresponds to calpain activation.","method":"Biochemical dissociation studies and activity assays","journal":"Biological chemistry Hoppe-Seyler","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical characterization; foundational mechanistic review of experimental data from the field","pmids":["8561910"],"is_preprint":false},{"year":2003,"finding":"The capn2 promoter contains five consensus E-box binding sites for myogenic regulatory factors and one MEF-2 binding site. MyoD (and, with lesser efficiency, myogenin) transactivates capn2 expression specifically through these elements, particularly the MEF-2/E4-box region. Antisense oligonucleotides against MyoD specifically suppress capn2 upregulation during myogenesis, establishing MyoD as the pivotal regulator of capn2 transcription during myoblast fusion.","method":"Promoter deletion analysis, transient transfection with reporter constructs, overexpression of myogenic factors, antisense oligonucleotide knockdown of individual MRFs","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assays plus antisense KD, multiple MRFs tested; single lab","pmids":["12559913"],"is_preprint":false},{"year":2022,"finding":"Cisplatin activates CAPN1/CAPN2 calpain activity in esophageal cancer cells, which in turn activates BAK/BAX, triggering a caspase-9→caspase-3→GSDME signaling cascade that executes pyroptosis. Calpain inhibition or CAPN1/CAPN2 knockout suppresses cisplatin-induced pyroptosis and LDH release.","method":"Western blotting, LDH release assay, calpain activity assay, cell viability assay, CAPN1/CAPN2 knockout by gene editing, pharmacological calpain inhibition","journal":"Chemico-biological interactions","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO plus pharmacological inhibition, multiple functional readouts; single lab","pmids":["35525317"],"is_preprint":false},{"year":2012,"finding":"Proteomic profiling of hepatocellular carcinoma cell lines with different metastatic potential identified a CAPN2-centered proteolytic subnetwork including SPTBN1, ATP5B, and VIM that is more active in the highly metastatic cell line, with persistent proteolytic fragments of these substrates detected preferentially in the high-metastasis line.","method":"PROTOMAP platform (gel separation + mass spectrometry peptide mapping), bioinformatics network analysis comparing two HCC cell lines","journal":"Proteomics","confidence":"Low","confidence_rationale":"Tier 3 — proteomic substrate profiling without direct in vitro cleavage validation; single study","pmids":["22623320"],"is_preprint":false},{"year":2019,"finding":"CAPN2 knockdown in HBV-induced hepatic fibrosis cells suppresses expression of fibrosis markers α-SMA, COL3A1, COL1A1, and MAPK1, placing CAPN2 upstream of MAPK1 signaling in HBV-driven hepatic fibrosis.","method":"siRNA knockdown of CAPN2, western blot for fibrosis markers and MAPK1, RT-qPCR, immunohistochemistry in patient tissues","journal":"Journal of cellular biochemistry","confidence":"Low","confidence_rationale":"Tier 3 — single-method KD with limited mechanistic pathway resolution; single lab","pmids":["31680308"],"is_preprint":false},{"year":2017,"finding":"Silencing CAPN2 in castration-resistant prostate cancer cells induces G1 cell cycle arrest, reduces migration and invasion by decreasing MMP-2 and MMP-9 activation, and suppresses phosphorylation of AKT and mTOR, placing CAPN2 upstream of the AKT/mTOR signaling axis in CRPC.","method":"siRNA knockdown of CAPN2, cell cycle analysis, transwell migration/invasion assay, western blot for pAKT, pmTOR, MMP-2, MMP-9","journal":"BioMed research international","confidence":"Low","confidence_rationale":"Tier 3 — single-method KD with pathway readouts; no direct biochemical mechanistic link established","pmids":["28280729"],"is_preprint":false},{"year":2025,"finding":"ITLN1 binds directly to CAPN2 (via Co-IP/MS), enhancing CAPN2 protein stability by antagonizing the E3 ubiquitin ligase TRIM8, which directly ubiquitinates CAPN2 to promote its proteasomal degradation. The ITLN1-TRIM8-CAPN2 axis drives ZBP1-dependent PANoptosis in intestinal epithelial cells in Crohn's disease.","method":"Co-immunoprecipitation combined with mass spectrometry, western blot, RNA-seq, rescue experiments with shRNA and overexpression, IL-10 KO mouse model in vivo","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP/MS identifying TRIM8 as E3 ligase for CAPN2, rescue experiments, in vivo validation; single lab","pmids":["40520022"],"is_preprint":false},{"year":2024,"finding":"CAPN2 promotes apalutamide resistance in prostate cancer by inhibiting FOXO1 degradation and promoting its nuclear translocation, which then transcriptionally upregulates ATG5 to activate protective autophagy. ATF3 transcriptionally activates CAPN2 to drive this axis.","method":"RNA sequencing, western blotting, immunofluorescence, transmission electron microscopy, dual-fluorescence autophagy assay, nucleoplasmic protein isolation, shRNA knockdown","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods linking CAPN2 to FOXO1 nuclear translocation and ATG5 transcription; single lab","pmids":["38844946"],"is_preprint":false},{"year":2023,"finding":"CAPN2 loss-of-function in Xenopus laevis causes hypoplastic ventricle phenotypes, establishing that CAPN2 is essential for cardiac ventricle morphogenesis. Human CAPN2 variants (p.707C>T and p.1112C>T) found in multiple individuals with isolated hypoplastic left heart syndrome behave as hypomorphic alleles in this vertebrate model.","method":"Xenopus laevis morpholino-based loss-of-function, cardiac morphology phenotyping, exome sequencing of human HLHS cohort, functional hypomorph validation in vivo","journal":"HGG advances","confidence":"Medium","confidence_rationale":"Tier 2 — vertebrate in vivo loss-of-function with defined cardiac phenotype, human variant functional validation; single study","pmids":["37663545"],"is_preprint":false}],"current_model":"CAPN2 (m-calpain large subunit) is a calcium-dependent cysteine protease that, in the absence of calcium, adopts an inactive conformation with its catalytic subdomains misaligned by ~50°; calcium binding to a negatively charged 'electrostatic switch' loop in domain dIII allows active-site formation, and ERK-mediated phosphorylation at Ser50 provides an additional calcium-independent activation mechanism downstream of growth factor signaling. Active CAPN2 cleaves diverse substrates—including IκBα (activating NF-κB), p35 (generating p25/CDK5 to drive neurodegeneration), Bcl-2 family members (triggering intrinsic apoptosis), Atg5 (switching autophagy to apoptosis), and caspases-7/8/9 (inactivating them to suppress apoptosis)—positioning it as a context-dependent regulator of cell adhesion, migration, proteolysis, and cell death that is itself regulated transcriptionally by MyoD during myogenesis and post-translationally by TRIM8-mediated ubiquitination."},"narrative":{"teleology":[{"year":1991,"claim":"Determining where calpain isoforms reside in the cell was necessary before mechanistic studies; fractionation and immunofluorescence established that m-calpain is predominantly membrane-associated in Schwann cells yet cytosolic in brain, revealing tissue-dependent compartmentalization.","evidence":"Subcellular fractionation with activity assays and isoform-specific immunofluorescence in transformed Schwann cells and mouse/human brain","pmids":["1656060","1548485"],"confidence":"Medium","gaps":["Mechanism of membrane recruitment unresolved","No live-cell imaging to confirm dynamics","Tissue-specific regulatory factors not identified"]},{"year":1995,"claim":"How calcium activates the heterodimer was unclear; biochemical studies showed that Ca²⁺ induces dissociation of the 80-kDa and 30-kDa subunits, with the free large subunit representing the active enzyme.","evidence":"Biochemical dissociation and activity assays on purified calpain heterodimer","pmids":["8561910"],"confidence":"Medium","gaps":["Structural basis of dissociation not resolved at atomic level","In vivo dissociation dynamics not confirmed","Single-lab biochemical characterization"]},{"year":1999,"claim":"Whether calpain could directly participate in NF-κB signaling was unknown; reconstitution showed that TNFα-activated m-calpain cleaves IκBα independently of the proteasome, enabling NF-κB nuclear translocation.","evidence":"Broken-cell reconstitution with purified m-calpain, calpastatin overexpression, ubiquitin-pathway-deficient cell line","pmids":["9873017"],"confidence":"High","gaps":["Cleavage site on IκBα not mapped","Relative contribution of calpain vs. proteasome pathway in vivo not quantified"]},{"year":2000,"claim":"The structural basis of calpain autoinhibition was resolved: the 2.3-Å crystal structure of calcium-free m-calpain revealed a ~50° rotation between catalytic subdomains dIIa and dIIb that disrupts the active site, and identified the dIII electrostatic switch loop whose calcium binding would permit realignment.","evidence":"X-ray crystallography at 2.3 Å of recombinant full-length heterodimeric human m-calpain","pmids":["10639123"],"confidence":"High","gaps":["No calcium-bound structure to confirm predicted subdomain movement","Role of each individual calcium-binding site not dissected"]},{"year":2000,"claim":"Two key substrate classes were identified simultaneously: calpain cleaves caspases-7/8/9 at non-canonical sites to inactivate them (suppressing apoptosis), and cleaves p35 to generate the neurotoxic p25/CDK5 complex driving tau hyperphosphorylation and neurodegeneration.","evidence":"In vitro cleavage with N-terminal sequencing for caspases; recombinant p35 cleavage, calpain inhibitor rescue in Aβ-treated primary cortical neurons","pmids":["10671558","10830966"],"confidence":"High","gaps":["In vivo stoichiometry of caspase inactivation vs. activation pathways not determined","Isoform specificity (CAPN1 vs. CAPN2) for p35 cleavage not resolved"]},{"year":2002,"claim":"The role of calpain in the intrinsic apoptotic pathway was established when m-calpain was shown to cleave Bcl-2, Bid, and Bcl-xL, generating truncated forms that induce cytochrome c release from mitochondria.","evidence":"In vitro cleavage of recombinant Bcl-2 family proteins, binding studies, cytochrome c release from isolated mitochondria, calpastatin inhibition in cells","pmids":["12000759"],"confidence":"High","gaps":["Relative importance of each Bcl-2 family substrate in different apoptotic contexts unclear","Whether calpain-truncated Bid functions identically to caspase-8-truncated tBid not tested"]},{"year":2003,"claim":"How CAPN2 transcription is controlled during differentiation was unknown; promoter analysis revealed MyoD as the pivotal transactivator of CAPN2 through E-box and MEF-2 elements, linking calpain upregulation to the myogenic program.","evidence":"Promoter deletion/reporter assays, overexpression of myogenic factors, antisense oligonucleotide knockdown of MyoD","pmids":["12559913"],"confidence":"Medium","gaps":["Chromatin accessibility at the CAPN2 locus during myogenesis not examined","Whether other tissues use analogous transcriptional control is unknown","Single-lab study"]},{"year":2004,"claim":"A calcium-independent activation mechanism was discovered: ERK directly phosphorylates CAPN2 at Ser50 downstream of EGF, and this phosphorylation is necessary and sufficient for calpain activation, cell deadhesion, and motility.","evidence":"In vitro kinase assay, S50A/S50E mutagenesis, intracellular calcium chelation, cell motility assays","pmids":["14993287"],"confidence":"High","gaps":["Structural mechanism by which Ser50 phosphorylation bypasses calcium requirement not resolved","Whether other kinases phosphorylate this site in different contexts not tested"]},{"year":2006,"claim":"Two studies expanded the functional reach of CAPN2: TRPM7 ion channel activity was shown to regulate cell adhesion through local m-calpain activation at peripheral adhesion complexes, and calpain cleavage of Atg5 was identified as a molecular switch converting autophagy to apoptosis.","evidence":"TRPM7/m-calpain co-localization, epistasis by double knockdown; Atg5 in vitro cleavage, Co-IP with Bcl-xL, siRNA rescue, subcellular fractionation","pmids":["16436382","16998475"],"confidence":"High","gaps":["Identity of TRPM7-derived ions activating calpain (Ca²⁺ vs. others) not fully dissected","Whether Atg5 cleavage is CAPN1- or CAPN2-specific not determined"]},{"year":2022,"claim":"Beyond apoptosis, CAPN2 was linked to pyroptosis: cisplatin activates CAPN1/CAPN2 to trigger BAK/BAX activation and a caspase-9→caspase-3→GSDME cascade executing pyroptotic cell death in esophageal cancer cells.","evidence":"CAPN1/CAPN2 gene knockout, pharmacological calpain inhibition, LDH release and calpain activity assays","pmids":["35525317"],"confidence":"Medium","gaps":["Individual contributions of CAPN1 vs. CAPN2 not separated","Direct cleavage of BAK/BAX by calpain not demonstrated biochemically","Single cancer cell line study"]},{"year":2023,"claim":"A developmental role for CAPN2 was established when loss-of-function in Xenopus caused hypoplastic ventricle phenotypes, and human CAPN2 hypomorphic variants were identified in individuals with hypoplastic left heart syndrome.","evidence":"Morpholino knockdown in Xenopus laevis, cardiac phenotyping, exome sequencing of human HLHS cohort, functional variant validation in vivo","pmids":["37663545"],"confidence":"Medium","gaps":["Cardiac substrate(s) of CAPN2 responsible for ventricle morphogenesis unknown","Mouse knockout cardiac phenotype not reported","Small human cohort, not yet independently replicated"]},{"year":2025,"claim":"Post-translational regulation of CAPN2 stability was uncovered: the E3 ubiquitin ligase TRIM8 directly ubiquitinates CAPN2 for proteasomal degradation, and ITLN1 antagonizes this process to stabilize CAPN2 and drive ZBP1-dependent PANoptosis in Crohn's disease intestinal epithelium.","evidence":"Reciprocal Co-IP/MS, TRIM8 ubiquitination assays, shRNA/overexpression rescue, IL-10 KO mouse model","pmids":["40520022"],"confidence":"Medium","gaps":["Ubiquitination site(s) on CAPN2 not mapped","Whether TRIM8 regulation of CAPN2 operates outside intestinal epithelium is unknown","Single-lab study"]},{"year":null,"claim":"A calcium-bound crystal structure of full-length m-calpain that confirms the predicted subdomain realignment has not been reported, and the isoform-specific (CAPN1 vs. CAPN2) substrate selectivity and in vivo redundancy remain poorly defined.","evidence":"","pmids":[],"confidence":"High","gaps":["No calcium-bound full-length m-calpain structure","Isoform-specific substrate repertoire not systematically delineated","In vivo mouse knockout phenotype for CAPN2 incompletely characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,3,4,5,9]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,3,4,5,9]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7,8]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6,7]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,6]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[5,17]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[11,18]}],"complexes":["m-calpain heterodimer (CAPN2/CAPNS1)"],"partners":["CAPNS1","TRPM7","TRIM8","ITLN1","CAST"],"other_free_text":[]},"mechanistic_narrative":"CAPN2 encodes the catalytic large subunit of m-calpain, a calcium-dependent cysteine protease that serves as a context-dependent regulator of cell adhesion, migration, apoptosis, and inflammatory signaling. In the calcium-free state, the catalytic subdomains dIIa and dIIb are misaligned by ~50°, rendering the active site non-functional; calcium binding to a negatively charged electrostatic switch loop in domain dIII realigns the subdomains for catalysis, and ERK-mediated phosphorylation at Ser50 provides a calcium-independent activation route downstream of EGF signaling [PMID:10639123, PMID:14993287]. Active CAPN2 cleaves IκBα to activate NF-κB, p35 to generate the neurotoxic p25/CDK5 complex, Bcl-2 family members and Atg5 to trigger mitochondrial apoptosis, and caspases-7/8/9 at non-canonical sites to suppress apoptosis, positioning it as a pivotal switch between cell survival and death programs [PMID:9873017, PMID:10830966, PMID:12000759, PMID:16998475, PMID:10671558]. CAPN2 protein stability is regulated by TRIM8-mediated ubiquitination and proteasomal degradation, and its transcription during myogenesis is controlled by MyoD through E-box and MEF-2 elements in the CAPN2 promoter [PMID:40520022, PMID:12559913]."},"prefetch_data":{"uniprot":{"accession":"P17655","full_name":"Calpain-2 catalytic subunit","aliases":["Calcium-activated neutral proteinase 2","CANP 2","Calpain M-type","Calpain large polypeptide L2","Calpain-2 large subunit","Millimolar-calpain","M-calpain"],"length_aa":700,"mass_kda":80.0,"function":"Calcium-regulated non-lysosomal thiol-protease which catalyzes limited proteolysis of substrates involved in cytoskeletal remodeling and signal transduction. Proteolytically cleaves MYOC at 'Arg-226' (PubMed:17650508). Proteolytically cleaves CPEB3 following neuronal stimulation which abolishes CPEB3 translational repressor activity, leading to translation of CPEB3 target mRNAs (By similarity)","subcellular_location":"Cytoplasm; Cell membrane","url":"https://www.uniprot.org/uniprotkb/P17655/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CAPN2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CAPN2","total_profiled":1310},"omim":[{"mim_id":"618777","title":"CALPAIN 8; CAPN8","url":"https://www.omim.org/entry/618777"},{"mim_id":"616874","title":"TRANSMEMBRANE BAX INHIBITOR MOTIF-CONTAINING PROTEIN 4; TMBIM4","url":"https://www.omim.org/entry/616874"},{"mim_id":"616767","title":"CALPAIN, SMALL SUBUNIT 2; CAPNS2","url":"https://www.omim.org/entry/616767"},{"mim_id":"608839","title":"CALPAIN 12; CAPN12","url":"https://www.omim.org/entry/608839"},{"mim_id":"606401","title":"CALPAIN 9; CAPN9","url":"https://www.omim.org/entry/606401"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Connecting piece","reliability":"Supported"},{"location":"Mid piece","reliability":"Supported"},{"location":"Principal piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CAPN2"},"hgnc":{"alias_symbol":["mCANP","CANPml","CANPL2"],"prev_symbol":[]},"alphafold":{"accession":"P17655","domains":[{"cath_id":"-","chopping":"25-204","consensus_level":"high","plddt":94.423,"start":25,"end":204},{"cath_id":"3.90.70.10","chopping":"212-310_319-343","consensus_level":"high","plddt":90.8219,"start":212,"end":343},{"cath_id":"2.60.120.380","chopping":"357-393_407-418_429-436_460-513","consensus_level":"high","plddt":90.5665,"start":357,"end":513},{"cath_id":"1.10.238.10","chopping":"528-700","consensus_level":"high","plddt":87.9303,"start":528,"end":700}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P17655","model_url":"https://alphafold.ebi.ac.uk/files/AF-P17655-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P17655-F1-predicted_aligned_error_v6.png","plddt_mean":89.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CAPN2","jax_strain_url":"https://www.jax.org/strain/search?query=CAPN2"},"sequence":{"accession":"P17655","fasta_url":"https://rest.uniprot.org/uniprotkb/P17655.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P17655/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P17655"}},"corpus_meta":[{"pmid":"15621511","id":"PMC_15621511","title":"Identification and molecular characterization of the rainbow trout calpains (Capn1 and Capn2): their expression in muscle wasting during starvation.","date":"2005","source":"Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15621511","citation_count":47,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"35525317","id":"PMC_35525317","title":"Cisplatin-induced pyroptosis is mediated via the CAPN1/CAPN2-BAK/BAX-caspase-9-caspase-3-GSDME axis in esophageal cancer.","date":"2022","source":"Chemico-biological interactions","url":"https://pubmed.ncbi.nlm.nih.gov/35525317","citation_count":44,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"33731671","id":"PMC_33731671","title":"hnRNPK-regulated LINC00263 promotes malignant phenotypes through miR-147a/CAPN2.","date":"2021","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/33731671","citation_count":30,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"1656060","id":"PMC_1656060","title":"Calcium-activated neutral proteinase (CANP; calpain) activity in Schwann cells: immunofluorescence localization and compartmentation of mu- and 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calpain inhibition or knockout suppressed this cisplatin-induced pyroptosis.\",\n      \"method\": \"Western blotting, LDH release assay, calpain activity assay, cell viability assay, calpain knockout\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in single study establishing pathway axis\",\n      \"pmids\": [\"35525317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The capn2 gene promoter contains five E-box consensus binding sites for myogenic regulatory factors and one MEF-2 binding site; MyoD (and to a lesser extent myogenin) directly transactivates capn2 expression during myogenesis, with antisense oligonucleotide experiments confirming MyoD's specific and non-redundant role.\",\n      \"method\": \"Reporter gene transfection, overexpression of myogenic factors, antisense oligonucleotide knockdown\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (reporter assay + antisense knockdown) in single study\",\n      \"pmids\": [\"12559913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In transformed Schwann cells, mCANP (CAPN2) activity is predominantly membrane-associated (>75%), while muCANP (CAPN1) is predominantly cytosolic (~80%); immunohistochemistry of permeabilized cells showed mCANP distributed throughout intracellular space with perinuclear sparing, while cytosolic mCANP concentrated perinuclearly.\",\n      \"method\": \"Subcellular fractionation, DEAE and phenyl Sepharose chromatography, immunofluorescence of live and permeabilized cells\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — fractionation combined with immunolocalization in single study\",\n      \"pmids\": [\"1656060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"In mouse and human brain, mCANP (CAPN2) content and caseinolytic activity are localized predominantly in the cytosolic (soluble) fraction after 15,000g centrifugation, with >95% immunoreactive mCANP in the soluble fraction; Triton X-100 treatment did not alter this distribution.\",\n      \"method\": \"Western blot immunoassay with two different antibodies, [14C]azocasein activity assay after DEAE-cellulose fractionation\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal antibody validation combined with activity assay in single study\",\n      \"pmids\": [\"1548485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Proteomic profiling of hepatocellular carcinoma cell lines with different metastatic potential identified a CAPN2-centered proteolytic network in which CAPN2 cleaves substrates including SPTBN1, ATP5B, and VIM; this network is more active in the highly metastatic cell line.\",\n      \"method\": \"PROTOMAP platform (gel-based proteomics with peptide mapping), bioinformatics network analysis\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mass spectrometry-based substrate identification without direct enzymatic validation\",\n      \"pmids\": [\"22623320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Silencing CAPN2 in castration-resistant prostate cancer cells inhibits proliferation (G1 cell cycle arrest), reduces migration and invasion, decreases MMP-2 and MMP-9 activation, and suppresses phosphorylation of AKT and mTOR, placing CAPN2 upstream of the AKT/mTOR signaling pathway.\",\n      \"method\": \"siRNA knockdown, cell cycle analysis, transwell migration/invasion assay, MMP activity assay, western blot for p-AKT and p-mTOR\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal phenotypic assays with pathway readout in single study\",\n      \"pmids\": [\"28280729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CAPN2 overexpression promotes renal cell carcinoma migration, invasion, and proliferation by activating AKT/mTOR signaling, enhancing epithelial-mesenchymal transition, and increasing MMP9 levels; sh-CAPN2 knockdown reversed these effects.\",\n      \"method\": \"shRNA knockdown, CAPN2 overexpression, transwell assay, CCK-8 proliferation assay, western blot for p-AKT, p-mTOR, EMT markers, MMP9\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional gain/loss-of-function with multiple phenotypic readouts\",\n      \"pmids\": [\"29228653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITLN1 binds directly to CAPN2 and enhances its protein stability by antagonizing the E3 ubiquitin ligase TRIM8, which directly interacts with CAPN2 and mediates its ubiquitination and degradation; ITLN1-mediated stabilization of CAPN2 drives ZBP1-dependent PANoptosis in intestinal epithelial cells.\",\n      \"method\": \"Co-immunoprecipitation combined with mass spectrometry, rescue experiments, in vivo IL-10 KO mouse model, RNA-seq\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP/MS with orthogonal rescue experiments identifying PTM writer (TRIM8) and stabilizer (ITLN1)\",\n      \"pmids\": [\"40520022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CAPN2 promotes apalutamide resistance in prostate cancer cells by inhibiting FOXO1 degradation and facilitating FOXO1 nuclear translocation, where FOXO1 transcriptionally upregulates ATG5 to activate protective autophagy; ATF3 transcriptionally regulates CAPN2 to amplify this pathway.\",\n      \"method\": \"RNA sequencing, western blotting, immunofluorescence, nucleoplasmic protein isolation, dual-fluorescence autophagic flux assay, transmission electron microscopy\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing CAPN2-FOXO1-ATG5 pathway in single study\",\n      \"pmids\": [\"38844946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss-of-function of CAPN2 in Xenopus laevis causes hypoplastic cardiac ventricle morphogenesis phenotypes, establishing CAPN2 as essential for cardiac ventricle development; human CAPN2 variants (707C>T and 1112C>T) found in hypoplastic left heart syndrome patients behave as hypomorphic alleles in vivo.\",\n      \"method\": \"Xenopus laevis loss-of-function experiments, exome sequencing of human iHLHS cohort, gene-based association testing\",\n      \"journal\": \"HGG advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — vertebrate animal model loss-of-function with defined morphogenetic phenotype, supported by human genetic evidence\",\n      \"pmids\": [\"37663545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"miR-147a directly binds the 3'UTR of CAPN2 mRNA to suppress CAPN2 protein expression (validated by Ago2-IP and luciferase reporter assay); LINC00263 acts as a ceRNA sponge for miR-147a, thereby de-repressing CAPN2 to promote cancer cell invasiveness and proliferation; hnRNPK regulates this axis upstream.\",\n      \"method\": \"Ago2 immunoprecipitation, luciferase reporter assay, antisense oligonucleotide pulldown, small RNA sequencing, siRNA knockdown, overexpression\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3'UTR binding validated by Ago2-IP and reporter assay with functional rescue\",\n      \"pmids\": [\"33731671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CAPN2 promotes β-catenin nuclear translocation, activating the Wnt/β-catenin pathway to inhibit mitochondrial autophagy in HCC cells; miR-124-3p suppresses CAPN2 expression by directly targeting it, and amentoflavone upregulates miR-124-3p to inhibit CAPN2 and thus restore mitophagy.\",\n      \"method\": \"Dual-luciferase reporter assay confirming miR-124-3p/CAPN2 interaction, western blot, immunofluorescence for LC3, CAPN2 overexpression/inhibition rescue experiments\",\n      \"journal\": \"Toxicology research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, reporter assay plus western blot without reconstitution of CAPN2-β-catenin interaction\",\n      \"pmids\": [\"39050595\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAPN2 (m-calpain large subunit) is a calcium-activated cysteine protease that is predominantly membrane-associated in non-neuronal cells and cytosolic in brain; its transcription is directly activated by MyoD during myogenesis; it promotes cell migration, invasion, and proliferation via AKT/mTOR signaling and facilitates EMT and MMP activation; it mediates cisplatin-induced pyroptosis through a BAK/BAX-caspase-9-caspase-3-GSDME axis; it stabilizes FOXO1 to activate protective autophagy; its protein stability is regulated by TRIM8-mediated ubiquitination (opposed by ITLN1 binding); and it is required for cardiac ventricle morphogenesis in vivo.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"The 2.3-Å crystal structure of full-length heterodimeric human m-calpain (CAPN2 large subunit + small subunit) in the absence of calcium reveals that the two catalytic subdomains (dIIa+dIIb) are rotated ~50° relative to one another, disrupting the active site and substrate-binding site, explaining calcium-dependent inactivation. An extremely negatively charged loop in domain dIII was identified as an 'electrostatic switch' whose calcium binding could allow subdomain dIIb to move toward dIIa, forming a functional catalytic center.\",\n      \"method\": \"X-ray crystallography at 2.3 Å resolution of recombinant heterodimeric human m-calpain\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with mechanistic interpretation of active-site disruption\",\n      \"pmids\": [\"10639123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"EGF activates m-calpain (CAPN2) through ERK-mediated direct phosphorylation at serine 50 of the large subunit, independent of intracellular calcium elevation. Phosphorylation at S50 is required for EGF-induced calpain activation, cell deadhesion, and motility; an S50A substitution limits activation, while an S50E substitution confers constitutive activity in vivo.\",\n      \"method\": \"In vitro kinase assay (ERK phosphorylates m-calpain), site-directed mutagenesis (S50A/S50E), intracellular calcium chelation, cell motility and deadhesion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus mutagenesis validated in vivo, multiple orthogonal methods\",\n      \"pmids\": [\"14993287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"TNF-α activates cytosolic m-calpain (CAPN2), which directly cleaves IκBα in a proteasome-independent manner, allowing NF-κB nuclear translocation. This calpain-dependent pathway for IκBα proteolysis operates in parallel to the ubiquitin-proteasome pathway; calpastatin overexpression partially blocks TNF-α-induced NF-κB activity.\",\n      \"method\": \"Fluorescent calpain activity assay, broken-cell reconstitution with purified m-calpain, calpastatin transfection, ubiquitin-pathway-deficient cell line (ts20b), subcellular fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution in broken cells, calpastatin inhibition, validated in pathway-deficient cell line, multiple orthogonal approaches\",\n      \"pmids\": [\"9873017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Calpain (including m-calpain/CAPN2) directly cleaves caspase-7, caspase-8, and caspase-9 at sites distinct from those used by upstream caspases, generating proteolytically inactive fragments. Calpain cleavage of caspase-9 blocks dATP/cytochrome c-induced caspase-3 activation, identifying calpain as a negative regulator of caspase processing and apoptosis.\",\n      \"method\": \"In vitro cleavage assays with purified calpain and recombinant caspases, N-terminal sequencing of cleavage products, cell-free caspase-3 activation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with N-terminal sequencing, multiple substrates tested, functional consequence demonstrated\",\n      \"pmids\": [\"10671558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Ionomycin-activated calpains (mu- and m-calpain/CAPN2) cleave Bcl-2, Bid, and Bcl-xL in vitro at single sites truncating their N-terminal regions. Calpain-truncated Bcl-2 and Bid exhibit diminished interactions with intact Bcl-2 family proteins and induce cytochrome c release from isolated mitochondria, triggering the intrinsic apoptotic pathway.\",\n      \"method\": \"In vitro cleavage assays with recombinant Bcl-2 family proteins, binding studies with immobilized proteins, cytochrome c release assay from isolated mitochondria, calpastatin inhibitor pretreatment in LCLC103H cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with multiple substrates, functional cytochrome c release assay, cell-based validation with specific inhibitor\",\n      \"pmids\": [\"12000759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Calpain (m-calpain/CAPN2) cleaves Atg5 at a site generating a truncated ~24 kDa N-terminal fragment that translocates from cytosol to mitochondria, associates with Bcl-xL, and triggers cytochrome c release and caspase activation, converting autophagy to apoptosis.\",\n      \"method\": \"Forced expression and siRNA of Atg5 in tumor cells, calpain inhibitor treatment, subcellular fractionation, co-immunoprecipitation with Bcl-xL, in vitro calpain cleavage assay\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro cleavage, Co-IP, fractionation, siRNA rescue, in vivo tumor model; multiple orthogonal methods\",\n      \"pmids\": [\"16998475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TRPM7 co-localizes with m-calpain (CAPN2) at peripheral adhesion complexes and regulates cell adhesion by controlling local calpain activity. TRPM7 overexpression causes cell rounding and loss of adhesion dependent on its ion channel activity; knockdown of m-calpain blocks TRPM7-induced cell detachment, and TRPM7 silencing increases peripheral adhesion complexes.\",\n      \"method\": \"Co-localization imaging, TRPM7 overexpression and RNAi knockdown, m-calpain RNAi rescue epistasis, cell adhesion and morphology assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-localization, epistasis by double knockdown, multiple functional readouts\",\n      \"pmids\": [\"16436382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In transformed Schwann cells, >75% of m-calpain (mCANP/CAPN2) activity is membrane-associated while ~80% of mu-calpain is cytosolic. Immunofluorescence with distinct antibodies showed mCANP distributed throughout the intracellular space (sparing the perinuclear region) in permeabilized cells, while anti-cytosolic mCANP antibody stained most intensely in the perinuclear region, establishing distinct subcellular compartmentalization of the two isoforms.\",\n      \"method\": \"DEAE and phenyl Sepharose column chromatography for isoform separation, activity assays on subcellular fractions, immunofluorescence with isoform-specific antibodies on live vs. permeabilized cells\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct fractionation + immunolocalization with functional activity measurement; single lab\",\n      \"pmids\": [\"1656060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"In mouse and human brain, >95% of total immunoreactive m-calpain (mCANP/CAPN2) is located in the soluble (cytosolic) fraction after 15,000 g centrifugation, with caseinolytic activity detectable only in fractions from the supernatant. Triton X-100 extraction does not alter this distribution, establishing mCANP as a predominantly cytosolic enzyme in brain.\",\n      \"method\": \"Western blot immunoassay with two independent mCANP-specific antibodies, [14C]azocasein activity assay after DEAE-cellulose removal of endogenous inhibitor, differential centrifugation, Triton X-100 extraction\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two independent antibodies, biochemical activity assay, orthogonal fractionation methods; single lab\",\n      \"pmids\": [\"1548485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Calpain, activated by calcium influx or amyloid-β peptide, directly cleaves p35 (the CDK5 activator) to generate p25, causing prolonged CDK5 activation and mislocalization, tau hyperphosphorylation, and neuronal apoptosis. Specific calpain inhibitors block calcium-induced p35 cleavage in brain lysates and reduce neuronal death in Aβ-treated cortical neurons.\",\n      \"method\": \"In vitro calpain cleavage assay with recombinant p35, calpain inhibitor treatment in primary cortical neurons, brain lysate calcium stimulation, N-terminal sequencing of cleavage product\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with N-terminal sequencing, inhibitor rescue in primary neurons, Aβ-treatment model\",\n      \"pmids\": [\"10830966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Ca2+ binding causes dissociation of the calpain heterodimer (large 80-kDa subunit encoded by CAPN2 and small 30-kDa subunit), with the free 80-kDa subunit being the active form of the enzyme; this dissociation mechanism corresponds to calpain activation.\",\n      \"method\": \"Biochemical dissociation studies and activity assays\",\n      \"journal\": \"Biological chemistry Hoppe-Seyler\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical characterization; foundational mechanistic review of experimental data from the field\",\n      \"pmids\": [\"8561910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The capn2 promoter contains five consensus E-box binding sites for myogenic regulatory factors and one MEF-2 binding site. MyoD (and, with lesser efficiency, myogenin) transactivates capn2 expression specifically through these elements, particularly the MEF-2/E4-box region. Antisense oligonucleotides against MyoD specifically suppress capn2 upregulation during myogenesis, establishing MyoD as the pivotal regulator of capn2 transcription during myoblast fusion.\",\n      \"method\": \"Promoter deletion analysis, transient transfection with reporter constructs, overexpression of myogenic factors, antisense oligonucleotide knockdown of individual MRFs\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assays plus antisense KD, multiple MRFs tested; single lab\",\n      \"pmids\": [\"12559913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cisplatin activates CAPN1/CAPN2 calpain activity in esophageal cancer cells, which in turn activates BAK/BAX, triggering a caspase-9→caspase-3→GSDME signaling cascade that executes pyroptosis. Calpain inhibition or CAPN1/CAPN2 knockout suppresses cisplatin-induced pyroptosis and LDH release.\",\n      \"method\": \"Western blotting, LDH release assay, calpain activity assay, cell viability assay, CAPN1/CAPN2 knockout by gene editing, pharmacological calpain inhibition\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus pharmacological inhibition, multiple functional readouts; single lab\",\n      \"pmids\": [\"35525317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Proteomic profiling of hepatocellular carcinoma cell lines with different metastatic potential identified a CAPN2-centered proteolytic subnetwork including SPTBN1, ATP5B, and VIM that is more active in the highly metastatic cell line, with persistent proteolytic fragments of these substrates detected preferentially in the high-metastasis line.\",\n      \"method\": \"PROTOMAP platform (gel separation + mass spectrometry peptide mapping), bioinformatics network analysis comparing two HCC cell lines\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — proteomic substrate profiling without direct in vitro cleavage validation; single study\",\n      \"pmids\": [\"22623320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CAPN2 knockdown in HBV-induced hepatic fibrosis cells suppresses expression of fibrosis markers α-SMA, COL3A1, COL1A1, and MAPK1, placing CAPN2 upstream of MAPK1 signaling in HBV-driven hepatic fibrosis.\",\n      \"method\": \"siRNA knockdown of CAPN2, western blot for fibrosis markers and MAPK1, RT-qPCR, immunohistochemistry in patient tissues\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single-method KD with limited mechanistic pathway resolution; single lab\",\n      \"pmids\": [\"31680308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Silencing CAPN2 in castration-resistant prostate cancer cells induces G1 cell cycle arrest, reduces migration and invasion by decreasing MMP-2 and MMP-9 activation, and suppresses phosphorylation of AKT and mTOR, placing CAPN2 upstream of the AKT/mTOR signaling axis in CRPC.\",\n      \"method\": \"siRNA knockdown of CAPN2, cell cycle analysis, transwell migration/invasion assay, western blot for pAKT, pmTOR, MMP-2, MMP-9\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single-method KD with pathway readouts; no direct biochemical mechanistic link established\",\n      \"pmids\": [\"28280729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITLN1 binds directly to CAPN2 (via Co-IP/MS), enhancing CAPN2 protein stability by antagonizing the E3 ubiquitin ligase TRIM8, which directly ubiquitinates CAPN2 to promote its proteasomal degradation. The ITLN1-TRIM8-CAPN2 axis drives ZBP1-dependent PANoptosis in intestinal epithelial cells in Crohn's disease.\",\n      \"method\": \"Co-immunoprecipitation combined with mass spectrometry, western blot, RNA-seq, rescue experiments with shRNA and overexpression, IL-10 KO mouse model in vivo\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP/MS identifying TRIM8 as E3 ligase for CAPN2, rescue experiments, in vivo validation; single lab\",\n      \"pmids\": [\"40520022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CAPN2 promotes apalutamide resistance in prostate cancer by inhibiting FOXO1 degradation and promoting its nuclear translocation, which then transcriptionally upregulates ATG5 to activate protective autophagy. ATF3 transcriptionally activates CAPN2 to drive this axis.\",\n      \"method\": \"RNA sequencing, western blotting, immunofluorescence, transmission electron microscopy, dual-fluorescence autophagy assay, nucleoplasmic protein isolation, shRNA knockdown\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking CAPN2 to FOXO1 nuclear translocation and ATG5 transcription; single lab\",\n      \"pmids\": [\"38844946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CAPN2 loss-of-function in Xenopus laevis causes hypoplastic ventricle phenotypes, establishing that CAPN2 is essential for cardiac ventricle morphogenesis. Human CAPN2 variants (p.707C>T and p.1112C>T) found in multiple individuals with isolated hypoplastic left heart syndrome behave as hypomorphic alleles in this vertebrate model.\",\n      \"method\": \"Xenopus laevis morpholino-based loss-of-function, cardiac morphology phenotyping, exome sequencing of human HLHS cohort, functional hypomorph validation in vivo\",\n      \"journal\": \"HGG advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — vertebrate in vivo loss-of-function with defined cardiac phenotype, human variant functional validation; single study\",\n      \"pmids\": [\"37663545\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CAPN2 (m-calpain large subunit) is a calcium-dependent cysteine protease that, in the absence of calcium, adopts an inactive conformation with its catalytic subdomains misaligned by ~50°; calcium binding to a negatively charged 'electrostatic switch' loop in domain dIII allows active-site formation, and ERK-mediated phosphorylation at Ser50 provides an additional calcium-independent activation mechanism downstream of growth factor signaling. Active CAPN2 cleaves diverse substrates—including IκBα (activating NF-κB), p35 (generating p25/CDK5 to drive neurodegeneration), Bcl-2 family members (triggering intrinsic apoptosis), Atg5 (switching autophagy to apoptosis), and caspases-7/8/9 (inactivating them to suppress apoptosis)—positioning it as a context-dependent regulator of cell adhesion, migration, proteolysis, and cell death that is itself regulated transcriptionally by MyoD during myogenesis and post-translationally by TRIM8-mediated ubiquitination.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CAPN2 encodes the large catalytic subunit of m-calpain, a calcium-dependent cysteine protease that promotes cell migration, invasion, and proliferation through activation of AKT/mTOR signaling, induction of epithelial-mesenchymal transition, and enhancement of MMP-2/MMP-9 activity [PMID:28280729, PMID:29228653]. CAPN2 transcription is directly activated by MyoD during myogenesis through E-box elements in its promoter [PMID:12559913], and its protein stability is regulated by TRIM8-mediated ubiquitination, which is antagonized by ITLN1 binding [PMID:40520022]. CAPN2 stabilizes FOXO1 to promote protective autophagy via ATG5 transcriptional upregulation [PMID:38844946], and mediates cisplatin-induced pyroptosis through a BAK/BAX–caspase-9–caspase-3–GSDME axis [PMID:35525317]. Loss-of-function of CAPN2 causes hypoplastic cardiac ventricle morphogenesis in Xenopus, and hypomorphic human CAPN2 variants have been identified in hypoplastic left heart syndrome patients [PMID:37663545].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Determining the subcellular distribution of CAPN2 revealed that, unlike CAPN1, m-calpain is predominantly membrane-associated in non-neuronal cells, establishing a cell-type-specific localization framework for understanding differential calpain function.\",\n      \"evidence\": \"Subcellular fractionation and immunofluorescence in transformed Schwann cells\",\n      \"pmids\": [\"1656060\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of membrane association undefined\", \"No identification of membrane-targeting determinants\", \"Distribution not confirmed across diverse non-neuronal cell types\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"In contrast to non-neuronal cells, brain CAPN2 was shown to be >95% cytosolic, demonstrating that CAPN2 localization is tissue-dependent and not an intrinsic membrane-anchored protein.\",\n      \"evidence\": \"Western blot with two antibodies and caseinolytic activity assay in mouse and human brain fractions\",\n      \"pmids\": [\"1548485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis for tissue-specific localization unknown\", \"Whether localization shift correlates with functional specificity untested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of MyoD as a direct transcriptional activator of capn2 through E-box elements established how CAPN2 expression is induced during myogenesis, linking it to the muscle differentiation program.\",\n      \"evidence\": \"Reporter gene assays with capn2 promoter constructs, MyoD overexpression, and antisense oligonucleotide knockdown in myogenic cells\",\n      \"pmids\": [\"12559913\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ChIP confirmation of MyoD occupancy at endogenous capn2 promoter not performed\", \"Functional role of CAPN2 in differentiated muscle not addressed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Proteomic profiling identified a CAPN2-centered proteolytic network active in highly metastatic hepatocellular carcinoma cells, implicating substrates such as SPTBN1, ATP5B, and VIM and providing the first systems-level view of CAPN2 substrates in cancer.\",\n      \"evidence\": \"PROTOMAP gel-based proteomics with peptide mapping in HCC cell lines of differing metastatic potential\",\n      \"pmids\": [\"22623320\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Substrate cleavage not validated by direct in vitro enzyme assays\", \"Causal contribution of individual substrate cleavages to metastasis untested\", \"Single proteomic study without independent replication\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Bidirectional gain- and loss-of-function experiments in prostate and renal cancer cells established that CAPN2 acts upstream of AKT/mTOR signaling to drive proliferation, migration, invasion, EMT, and MMP activation, defining a core pro-tumorigenic signaling axis.\",\n      \"evidence\": \"siRNA/shRNA knockdown and overexpression with transwell assays, proliferation assays, and western blot for p-AKT, p-mTOR, EMT markers, MMP-2/9 in prostate and renal cancer cells\",\n      \"pmids\": [\"28280729\", \"29228653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical mechanism linking CAPN2 protease activity to AKT phosphorylation not identified\", \"Whether catalytic activity or scaffolding drives signaling is unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Post-transcriptional regulation of CAPN2 was mapped: miR-147a directly targets the CAPN2 3′UTR, and LINC00263 sponges miR-147a to de-repress CAPN2, revealing a ceRNA network controlling CAPN2 abundance in cancer.\",\n      \"evidence\": \"Ago2 immunoprecipitation, luciferase reporter assay, antisense oligonucleotide pulldown, and functional rescue in cancer cell lines\",\n      \"pmids\": [\"33731671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of LINC00263/miR-147a/CAPN2 axis not demonstrated\", \"Whether this regulatory axis operates in normal tissues unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Cisplatin-induced calpain activation (CAPN1/CAPN2) was shown to trigger BAK/BAX-dependent mitochondrial signaling leading to caspase-9/caspase-3 activation and GSDME cleavage, establishing CAPN2 as a mediator of drug-induced pyroptosis in esophageal cancer.\",\n      \"evidence\": \"Calpain activity assays, knockout, western blot, and LDH release in esophageal cancer cells treated with cisplatin\",\n      \"pmids\": [\"35525317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of CAPN1 versus CAPN2 not delineated\", \"Direct substrate of calpain in the BAK/BAX activation step not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Xenopus loss-of-function demonstrated that CAPN2 is required for cardiac ventricle morphogenesis, and identification of hypomorphic CAPN2 alleles in human hypoplastic left heart syndrome patients established a developmental and disease role.\",\n      \"evidence\": \"Xenopus laevis morpholino/CRISPR loss-of-function, exome sequencing of human iHLHS cohort, gene-based association testing\",\n      \"pmids\": [\"37663545\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proteolytic substrates mediating cardiac morphogenesis unknown\", \"Mouse knockout cardiac phenotype not reported\", \"Human variants not functionally tested in mammalian cardiomyocytes\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"CAPN2 was found to stabilize FOXO1 and promote its nuclear translocation, where FOXO1 transcriptionally upregulates ATG5 to activate protective autophagy, explaining a mechanism of apalutamide resistance in prostate cancer.\",\n      \"evidence\": \"RNA sequencing, nucleoplasmic fractionation, western blot, dual-fluorescence autophagic flux assay, and TEM in prostate cancer cells\",\n      \"pmids\": [\"38844946\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CAPN2 protease activity stabilizes rather than degrades FOXO1 is paradoxical and unexplained\", \"Whether CAPN2 cleaves a FOXO1 degradation signal or acts non-catalytically is unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The E3 ligase TRIM8 was identified as the direct ubiquitin writer targeting CAPN2 for degradation, and ITLN1 was shown to physically bind CAPN2 and antagonize TRIM8, providing the first defined post-translational stability mechanism for CAPN2.\",\n      \"evidence\": \"Co-immunoprecipitation/mass spectrometry, rescue experiments, and in vivo IL-10 KO mouse model with RNA-seq in intestinal epithelial cells\",\n      \"pmids\": [\"40520022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination sites on CAPN2 not mapped\", \"Whether TRIM8-mediated regulation is tissue-specific is unknown\", \"Structural basis of ITLN1-CAPN2 interaction undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct proteolytic substrates through which CAPN2 activates AKT/mTOR signaling and promotes cardiac morphogenesis remain unidentified, and the molecular basis for tissue-specific localization is unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of CAPN2-substrate or CAPN2-ITLN1 complexes\", \"In vivo mammalian knockout phenotyping incomplete\", \"Whether catalytic versus non-catalytic functions drive FOXO1 stabilization and AKT activation is unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CAPNS1\",\n      \"TRIM8\",\n      \"ITLN1\",\n      \"FOXO1\",\n      \"GSDME\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CAPN2 encodes the catalytic large subunit of m-calpain, a calcium-dependent cysteine protease that serves as a context-dependent regulator of cell adhesion, migration, apoptosis, and inflammatory signaling. In the calcium-free state, the catalytic subdomains dIIa and dIIb are misaligned by ~50°, rendering the active site non-functional; calcium binding to a negatively charged electrostatic switch loop in domain dIII realigns the subdomains for catalysis, and ERK-mediated phosphorylation at Ser50 provides a calcium-independent activation route downstream of EGF signaling [PMID:10639123, PMID:14993287]. Active CAPN2 cleaves IκBα to activate NF-κB, p35 to generate the neurotoxic p25/CDK5 complex, Bcl-2 family members and Atg5 to trigger mitochondrial apoptosis, and caspases-7/8/9 at non-canonical sites to suppress apoptosis, positioning it as a pivotal switch between cell survival and death programs [PMID:9873017, PMID:10830966, PMID:12000759, PMID:16998475, PMID:10671558]. CAPN2 protein stability is regulated by TRIM8-mediated ubiquitination and proteasomal degradation, and its transcription during myogenesis is controlled by MyoD through E-box and MEF-2 elements in the CAPN2 promoter [PMID:40520022, PMID:12559913].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Determining where calpain isoforms reside in the cell was necessary before mechanistic studies; fractionation and immunofluorescence established that m-calpain is predominantly membrane-associated in Schwann cells yet cytosolic in brain, revealing tissue-dependent compartmentalization.\",\n      \"evidence\": \"Subcellular fractionation with activity assays and isoform-specific immunofluorescence in transformed Schwann cells and mouse/human brain\",\n      \"pmids\": [\"1656060\", \"1548485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of membrane recruitment unresolved\", \"No live-cell imaging to confirm dynamics\", \"Tissue-specific regulatory factors not identified\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"How calcium activates the heterodimer was unclear; biochemical studies showed that Ca²⁺ induces dissociation of the 80-kDa and 30-kDa subunits, with the free large subunit representing the active enzyme.\",\n      \"evidence\": \"Biochemical dissociation and activity assays on purified calpain heterodimer\",\n      \"pmids\": [\"8561910\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of dissociation not resolved at atomic level\", \"In vivo dissociation dynamics not confirmed\", \"Single-lab biochemical characterization\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Whether calpain could directly participate in NF-κB signaling was unknown; reconstitution showed that TNFα-activated m-calpain cleaves IκBα independently of the proteasome, enabling NF-κB nuclear translocation.\",\n      \"evidence\": \"Broken-cell reconstitution with purified m-calpain, calpastatin overexpression, ubiquitin-pathway-deficient cell line\",\n      \"pmids\": [\"9873017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cleavage site on IκBα not mapped\", \"Relative contribution of calpain vs. proteasome pathway in vivo not quantified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The structural basis of calpain autoinhibition was resolved: the 2.3-Å crystal structure of calcium-free m-calpain revealed a ~50° rotation between catalytic subdomains dIIa and dIIb that disrupts the active site, and identified the dIII electrostatic switch loop whose calcium binding would permit realignment.\",\n      \"evidence\": \"X-ray crystallography at 2.3 Å of recombinant full-length heterodimeric human m-calpain\",\n      \"pmids\": [\"10639123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No calcium-bound structure to confirm predicted subdomain movement\", \"Role of each individual calcium-binding site not dissected\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Two key substrate classes were identified simultaneously: calpain cleaves caspases-7/8/9 at non-canonical sites to inactivate them (suppressing apoptosis), and cleaves p35 to generate the neurotoxic p25/CDK5 complex driving tau hyperphosphorylation and neurodegeneration.\",\n      \"evidence\": \"In vitro cleavage with N-terminal sequencing for caspases; recombinant p35 cleavage, calpain inhibitor rescue in Aβ-treated primary cortical neurons\",\n      \"pmids\": [\"10671558\", \"10830966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo stoichiometry of caspase inactivation vs. activation pathways not determined\", \"Isoform specificity (CAPN1 vs. CAPN2) for p35 cleavage not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The role of calpain in the intrinsic apoptotic pathway was established when m-calpain was shown to cleave Bcl-2, Bid, and Bcl-xL, generating truncated forms that induce cytochrome c release from mitochondria.\",\n      \"evidence\": \"In vitro cleavage of recombinant Bcl-2 family proteins, binding studies, cytochrome c release from isolated mitochondria, calpastatin inhibition in cells\",\n      \"pmids\": [\"12000759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance of each Bcl-2 family substrate in different apoptotic contexts unclear\", \"Whether calpain-truncated Bid functions identically to caspase-8-truncated tBid not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"How CAPN2 transcription is controlled during differentiation was unknown; promoter analysis revealed MyoD as the pivotal transactivator of CAPN2 through E-box and MEF-2 elements, linking calpain upregulation to the myogenic program.\",\n      \"evidence\": \"Promoter deletion/reporter assays, overexpression of myogenic factors, antisense oligonucleotide knockdown of MyoD\",\n      \"pmids\": [\"12559913\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chromatin accessibility at the CAPN2 locus during myogenesis not examined\", \"Whether other tissues use analogous transcriptional control is unknown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A calcium-independent activation mechanism was discovered: ERK directly phosphorylates CAPN2 at Ser50 downstream of EGF, and this phosphorylation is necessary and sufficient for calpain activation, cell deadhesion, and motility.\",\n      \"evidence\": \"In vitro kinase assay, S50A/S50E mutagenesis, intracellular calcium chelation, cell motility assays\",\n      \"pmids\": [\"14993287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which Ser50 phosphorylation bypasses calcium requirement not resolved\", \"Whether other kinases phosphorylate this site in different contexts not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Two studies expanded the functional reach of CAPN2: TRPM7 ion channel activity was shown to regulate cell adhesion through local m-calpain activation at peripheral adhesion complexes, and calpain cleavage of Atg5 was identified as a molecular switch converting autophagy to apoptosis.\",\n      \"evidence\": \"TRPM7/m-calpain co-localization, epistasis by double knockdown; Atg5 in vitro cleavage, Co-IP with Bcl-xL, siRNA rescue, subcellular fractionation\",\n      \"pmids\": [\"16436382\", \"16998475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of TRPM7-derived ions activating calpain (Ca²⁺ vs. others) not fully dissected\", \"Whether Atg5 cleavage is CAPN1- or CAPN2-specific not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Beyond apoptosis, CAPN2 was linked to pyroptosis: cisplatin activates CAPN1/CAPN2 to trigger BAK/BAX activation and a caspase-9→caspase-3→GSDME cascade executing pyroptotic cell death in esophageal cancer cells.\",\n      \"evidence\": \"CAPN1/CAPN2 gene knockout, pharmacological calpain inhibition, LDH release and calpain activity assays\",\n      \"pmids\": [\"35525317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Individual contributions of CAPN1 vs. CAPN2 not separated\", \"Direct cleavage of BAK/BAX by calpain not demonstrated biochemically\", \"Single cancer cell line study\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A developmental role for CAPN2 was established when loss-of-function in Xenopus caused hypoplastic ventricle phenotypes, and human CAPN2 hypomorphic variants were identified in individuals with hypoplastic left heart syndrome.\",\n      \"evidence\": \"Morpholino knockdown in Xenopus laevis, cardiac phenotyping, exome sequencing of human HLHS cohort, functional variant validation in vivo\",\n      \"pmids\": [\"37663545\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cardiac substrate(s) of CAPN2 responsible for ventricle morphogenesis unknown\", \"Mouse knockout cardiac phenotype not reported\", \"Small human cohort, not yet independently replicated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Post-translational regulation of CAPN2 stability was uncovered: the E3 ubiquitin ligase TRIM8 directly ubiquitinates CAPN2 for proteasomal degradation, and ITLN1 antagonizes this process to stabilize CAPN2 and drive ZBP1-dependent PANoptosis in Crohn's disease intestinal epithelium.\",\n      \"evidence\": \"Reciprocal Co-IP/MS, TRIM8 ubiquitination assays, shRNA/overexpression rescue, IL-10 KO mouse model\",\n      \"pmids\": [\"40520022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination site(s) on CAPN2 not mapped\", \"Whether TRIM8 regulation of CAPN2 operates outside intestinal epithelium is unknown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A calcium-bound crystal structure of full-length m-calpain that confirms the predicted subdomain realignment has not been reported, and the isoform-specific (CAPN1 vs. CAPN2) substrate selectivity and in vivo redundancy remain poorly defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No calcium-bound full-length m-calpain structure\", \"Isoform-specific substrate repertoire not systematically delineated\", \"In vivo mouse knockout phenotype for CAPN2 incompletely characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 3, 4, 5, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005357801\", \"supporting_discovery_ids\": [3, 4, 5, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [5, 17]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [11, 18]}\n    ],\n    \"complexes\": [\n      \"m-calpain heterodimer (CAPN2/CAPNS1)\"\n    ],\n    \"partners\": [\n      \"CAPNS1\",\n      \"TRPM7\",\n      \"TRIM8\",\n      \"ITLN1\",\n      \"CAST\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway term_ids. Let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"CAPN2 encodes the catalytic large subunit of m-calpain, a calcium-dependent cysteine protease that serves as a context-dependent regulator of cell adhesion, migration, apoptosis, and inflammatory signaling. In the calcium-free state, the catalytic subdomains dIIa and dIIb are misaligned by ~50°, rendering the active site non-functional; calcium binding to a negatively charged electrostatic switch loop in domain dIII realigns the subdomains for catalysis, and ERK-mediated phosphorylation at Ser50 provides a calcium-independent activation route downstream of EGF signaling [PMID:10639123, PMID:14993287]. Active CAPN2 cleaves IκBα to activate NF-κB, p35 to generate the neurotoxic p25/CDK5 complex, Bcl-2 family members and Atg5 to trigger mitochondrial apoptosis, and caspases-7/8/9 at non-canonical sites to suppress apoptosis, positioning it as a pivotal switch between cell survival and death programs [PMID:9873017, PMID:10830966, PMID:12000759, PMID:16998475, PMID:10671558]. CAPN2 protein stability is regulated by TRIM8-mediated ubiquitination and proteasomal degradation, and its transcription during myogenesis is controlled by MyoD through E-box and MEF-2 elements in the CAPN2 promoter [PMID:40520022, PMID:12559913].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Determining where calpain isoforms reside in the cell was necessary before mechanistic studies; fractionation and immunofluorescence established that m-calpain is predominantly membrane-associated in Schwann cells yet cytosolic in brain, revealing tissue-dependent compartmentalization.\",\n      \"evidence\": \"Subcellular fractionation with activity assays and isoform-specific immunofluorescence in transformed Schwann cells and mouse/human brain\",\n      \"pmids\": [\"1656060\", \"1548485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of membrane recruitment unresolved\", \"No live-cell imaging to confirm dynamics\", \"Tissue-specific regulatory factors not identified\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"How calcium activates the heterodimer was unclear; biochemical studies showed that Ca²⁺ induces dissociation of the 80-kDa and 30-kDa subunits, with the free large subunit representing the active enzyme.\",\n      \"evidence\": \"Biochemical dissociation and activity assays on purified calpain heterodimer\",\n      \"pmids\": [\"8561910\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of dissociation not resolved at atomic level\", \"In vivo dissociation dynamics not confirmed\", \"Single-lab biochemical characterization\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Whether calpain could directly participate in NF-κB signaling was unknown; reconstitution showed that TNFα-activated m-calpain cleaves IκBα independently of the proteasome, enabling NF-κB nuclear translocation.\",\n      \"evidence\": \"Broken-cell reconstitution with purified m-calpain, calpastatin overexpression, ubiquitin-pathway-deficient cell line\",\n      \"pmids\": [\"9873017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cleavage site on IκBα not mapped\", \"Relative contribution of calpain vs. proteasome pathway in vivo not quantified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The structural basis of calpain autoinhibition was resolved: the 2.3-Å crystal structure of calcium-free m-calpain revealed a ~50° rotation between catalytic subdomains dIIa and dIIb that disrupts the active site, and identified the dIII electrostatic switch loop whose calcium binding would permit realignment.\",\n      \"evidence\": \"X-ray crystallography at 2.3 Å of recombinant full-length heterodimeric human m-calpain\",\n      \"pmids\": [\"10639123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No calcium-bound structure to confirm predicted subdomain movement\", \"Role of each individual calcium-binding site not dissected\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Two key substrate classes were identified simultaneously: calpain cleaves caspases-7/8/9 at non-canonical sites to inactivate them (suppressing apoptosis), and cleaves p35 to generate the neurotoxic p25/CDK5 complex driving tau hyperphosphorylation and neurodegeneration.\",\n      \"evidence\": \"In vitro cleavage with N-terminal sequencing for caspases; recombinant p35 cleavage, calpain inhibitor rescue in Aβ-treated primary cortical neurons\",\n      \"pmids\": [\"10671558\", \"10830966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo stoichiometry of caspase inactivation vs. activation pathways not determined\", \"Isoform specificity (CAPN1 vs. CAPN2) for p35 cleavage not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The role of calpain in the intrinsic apoptotic pathway was established when m-calpain was shown to cleave Bcl-2, Bid, and Bcl-xL, generating truncated forms that induce cytochrome c release from mitochondria.\",\n      \"evidence\": \"In vitro cleavage of recombinant Bcl-2 family proteins, binding studies, cytochrome c release from isolated mitochondria, calpastatin inhibition in cells\",\n      \"pmids\": [\"12000759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance of each Bcl-2 family substrate in different apoptotic contexts unclear\", \"Whether calpain-truncated Bid functions identically to caspase-8-truncated tBid not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"How CAPN2 transcription is controlled during differentiation was unknown; promoter analysis revealed MyoD as the pivotal transactivator of CAPN2 through E-box and MEF-2 elements, linking calpain upregulation to the myogenic program.\",\n      \"evidence\": \"Promoter deletion/reporter assays, overexpression of myogenic factors, antisense oligonucleotide knockdown of MyoD\",\n      \"pmids\": [\"12559913\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chromatin accessibility at the CAPN2 locus during myogenesis not examined\", \"Whether other tissues use analogous transcriptional control is unknown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A calcium-independent activation mechanism was discovered: ERK directly phosphorylates CAPN2 at Ser50 downstream of EGF, and this phosphorylation is necessary and sufficient for calpain activation, cell deadhesion, and motility.\",\n      \"evidence\": \"In vitro kinase assay, S50A/S50E mutagenesis, intracellular calcium chelation, cell motility assays\",\n      \"pmids\": [\"14993287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which Ser50 phosphorylation bypasses calcium requirement not resolved\", \"Whether other kinases phosphorylate this site in different contexts not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Two studies expanded the functional reach of CAPN2: TRPM7 ion channel activity was shown to regulate cell adhesion through local m-calpain activation at peripheral adhesion complexes, and calpain cleavage of Atg5 was identified as a molecular switch converting autophagy to apoptosis.\",\n      \"evidence\": \"TRPM7/m-calpain co-localization, epistasis by double knockdown; Atg5 in vitro cleavage, Co-IP with Bcl-xL, siRNA rescue, subcellular fractionation\",\n      \"pmids\": [\"16436382\", \"16998475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of TRPM7-derived ions activating calpain (Ca²⁺ vs. others) not fully dissected\", \"Whether Atg5 cleavage is CAPN1- or CAPN2-specific not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Beyond apoptosis, CAPN2 was linked to pyroptosis: cisplatin activates CAPN1/CAPN2 to trigger BAK/BAX activation and a caspase-9→caspase-3→GSDME cascade executing pyroptotic cell death in esophageal cancer cells.\",\n      \"evidence\": \"CAPN1/CAPN2 gene knockout, pharmacological calpain inhibition, LDH release and calpain activity assays\",\n      \"pmids\": [\"35525317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Individual contributions of CAPN1 vs. CAPN2 not separated\", \"Direct cleavage of BAK/BAX by calpain not demonstrated biochemically\", \"Single cancer cell line study\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A developmental role for CAPN2 was established when loss-of-function in Xenopus caused hypoplastic ventricle phenotypes, and human CAPN2 hypomorphic variants were identified in individuals with hypoplastic left heart syndrome.\",\n      \"evidence\": \"Morpholino knockdown in Xenopus laevis, cardiac phenotyping, exome sequencing of human HLHS cohort, functional variant validation in vivo\",\n      \"pmids\": [\"37663545\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cardiac substrate(s) of CAPN2 responsible for ventricle morphogenesis unknown\", \"Mouse knockout cardiac phenotype not reported\", \"Small human cohort, not yet independently replicated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Post-translational regulation of CAPN2 stability was uncovered: the E3 ubiquitin ligase TRIM8 directly ubiquitinates CAPN2 for proteasomal degradation, and ITLN1 antagonizes this process to stabilize CAPN2 and drive ZBP1-dependent PANoptosis in Crohn's disease intestinal epithelium.\",\n      \"evidence\": \"Reciprocal Co-IP/MS, TRIM8 ubiquitination assays, shRNA/overexpression rescue, IL-10 KO mouse model\",\n      \"pmids\": [\"40520022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination site(s) on CAPN2 not mapped\", \"Whether TRIM8 regulation of CAPN2 operates outside intestinal epithelium is unknown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A calcium-bound crystal structure of full-length m-calpain that confirms the predicted subdomain realignment has not been reported, and the isoform-specific (CAPN1 vs. CAPN2) substrate selectivity and in vivo redundancy remain poorly defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No calcium-bound full-length m-calpain structure\", \"Isoform-specific substrate repertoire not systematically delineated\", \"In vivo mouse knockout phenotype for CAPN2 incompletely characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 3, 4, 5, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 4, 5, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [5, 17]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [11, 18]}\n    ],\n    \"complexes\": [\n      \"m-calpain heterodimer (CAPN2/CAPNS1)\"\n    ],\n    \"partners\": [\n      \"CAPNS1\",\n      \"TRPM7\",\n      \"TRIM8\",\n      \"ITLN1\",\n      \"CAST\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}