{"gene":"CPA4","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":1999,"finding":"CPA4 (then called CPA3 in the original paper but now recognized as CPA4) is induced by histone deacetylase (HDAC) inhibitors sodium butyrate and trichostatin A in prostate cancer cells. The induction requires prior p21(WAF1/CIP1) transactivation, as p21 antisense mRNA blocked CPA4 induction. Structural analysis of the encoded protein predicted a 16-residue signal peptide, a 95-residue N-terminal activation segment, and a 310-residue carboxypeptidase enzyme domain with 37–63% identity to zinc carboxypeptidases.","method":"mRNA differential display, antisense mRNA inhibition, sequence/structural analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods (differential display, antisense inhibition, sequence analysis) in single lab; foundational paper establishing pathway position","pmids":["10383164"],"is_preprint":false},{"year":2003,"finding":"CPA4 is a maternally imprinted gene on chromosome 7q32; it is preferentially expressed from the maternal allele in multiple fetal tissues (heart, lung, liver, intestine, kidney, adrenal gland, spleen) but shows biallelic expression in fetal brain, as demonstrated by RT-PCR with intragenic polymorphism markers.","method":"RT-PCR with intragenic SNP markers in fetal tissues","journal":"Human genetics","confidence":"Medium","confidence_rationale":"Tier 2 — allele-specific expression directly assayed with polymorphism markers; single lab","pmids":["12552318"],"is_preprint":false},{"year":2003,"finding":"Among the carboxypeptidase A gene cluster at 7q32, only CPA4 shows preferential maternal allele expression (imprinting), confirmed by pyrosequencing quantitative analysis; CPA1, CPA2 show biallelic expression, and the imprinted domain extends across an asynchronously replicating genomic region.","method":"Replication timing assay, SNP-based RT-PCR, pyrosequencing","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (replication timing, pyrosequencing); single lab confirming imprinting","pmids":["12676894"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of human CPA4 (hCPA4) in complex with its endogenous inhibitor latexin was solved. hCPA4 displays the canonical alpha/beta-hydrolase fold of metallocarboxypeptidases. Latexin, a 25-kDa protein with two cystatin-like subdomains, binds at the interface of these subdomains, occluding the active-site funnel with a large contact surface but few contacts, explaining nanomolar inhibition and cross-species flexibility. Modeling studies revealed why the N/E subfamily of MCPs and invertebrate A/B MCPs are not inhibited by latexin.","method":"X-ray crystallography, modeling","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional interpretation; replicated with additional structural study","pmids":["15738388"],"is_preprint":false},{"year":2005,"finding":"The three-dimensional structure of human pro-CPA4 (hPCPA4) was solved, revealing a preformed alpha/beta-hydrolase active-enzyme moiety (hCPA4) and an inhibitory pro-domain (PD). The PD contacts the funnel-like access to the active-site cleft via loop segments in a manner structurally analogous to latexin inhibition; both employ a similar beta-sheet loop for active-site blocking.","method":"X-ray crystallography, structural comparison","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of zymogen form with detailed mechanistic comparison; independent corroboration of active-site architecture","pmids":["16091843"],"is_preprint":false},{"year":2010,"finding":"CPA4 is secreted from cells as a soluble proenzyme (pro-CPA4) that can be activated by endoproteases such as trypsin. Kinetic analysis with chromogenic substrates and a quantitative peptidomics mass spectrometry approach on >100 mouse brain peptides showed CPA4 preferentially cleaves hydrophobic C-terminal residues (Phe, Leu, Ile, Met, Tyr, Val). Aliphatic, aromatic, and basic residues at P1 position enhance cleavage; acidic residues, Pro, and Gly at P1 inhibit cleavage. Substrates include neurotensin, granins, and opioid peptides, implying a role in extracellular neuropeptide processing.","method":"Secretion assay, kinetic analysis with chromogenic substrates, quantitative peptidomics mass spectrometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic characterization with three complementary orthogonal approaches; clear substrate specificity established","pmids":["20385563"],"is_preprint":false},{"year":2012,"finding":"Crystal structure of human CPA4 in complex with NvCI (a marine snail Nerita versicolor inhibitor) was determined at 1.7 Å resolution. NvCI adopts a novel fold (two-stranded antiparallel beta-sheet, three loops, C-terminal tail, three disulfide bridges) and inhibits the enzyme in a substrate-like, active-site-directed manner with picomolar inhibition constants, making it the strongest inhibitor reported for the M14A subfamily.","method":"X-ray crystallography, kinetic inhibition assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — 1.7 Å crystal structure plus kinetic validation; convergent evolution of C-terminal inhibitory mechanism demonstrated","pmids":["22294694"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of CPA4 in complex with SmCI (a tri-Kunitz inhibitor from Sabellastarte magnifica) revealed a noncanonical inhibition mechanism: unlike classical C-terminal substrate-like inhibition, SmCI primarily inserts its N-terminal segment into the active-site groove. Mutagenesis and biochemical analysis confirmed the dominant role of the N-terminal segment in inhibiting metallocarboxypeptidases.","method":"X-ray crystallography, site-directed mutagenesis, biochemical inhibition assays","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis validation; defines novel inhibitory mechanism","pmids":["23746805"],"is_preprint":false},{"year":2016,"finding":"FGF-1 treatment or induction of differentiation of human preadipocytes significantly downregulates CPA4 expression in a BAMBI/PPARγ-independent manner. siRNA-mediated knockdown of CPA4 enhances differentiation of human preadipocytes, identifying CPA4 as a negative regulator of adipogenesis.","method":"RNA-Seq, qRT-PCR, siRNA knockdown with adipogenesis functional assay","journal":"Growth factors (Chur, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with defined phenotypic readout plus transcriptomic data; single lab","pmids":["28209092"],"is_preprint":false},{"year":2019,"finding":"CPA4 knockdown in NSCLC cells inhibits cell proliferation and induces G1-S arrest and apoptosis by suppressing the AKT/c-MYC signaling pathway. Ectopic CPA4 overexpression enhanced proliferation. CPA4 downregulation also suppressed tumor growth in xenograft models.","method":"shRNA knockdown, ectopic overexpression, MTT/colony assays, xenograft model, Western blot pathway analysis","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — loss- and gain-of-function with defined pathway readout (AKT/c-MYC) and in vivo validation; single lab","pmids":["31397502"],"is_preprint":false},{"year":2020,"finding":"CPA4 overexpression in pancreatic cancer cells activates PI3K-AKT-mTOR signaling (elevated p-PI3K, p-AKT, p-mTOR), promotes EMT (downregulation of E-cadherin and β-catenin; upregulation of N-cadherin, vimentin), and increases drug resistance. CPA4 was co-immunoprecipitated with AKT in two PC cell lines with high CPA4 expression. The PI3K inhibitor LY294002 reversed these effects.","method":"Overexpression/knockdown, Western blot, co-immunoprecipitation, PI3K inhibitor rescue experiment","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP showing CPA4-AKT interaction plus functional rescue experiment; single lab, moderate evidence for direct PI3K-AKT-mTOR engagement","pmids":["32922037"],"is_preprint":false},{"year":2020,"finding":"CPA4 promotes cardiomyocyte hypertrophy in neonatal rat cardiomyocytes: CPA4 overexpression enhanced ISO-induced cardiomyocyte size enlargement and hypertrophy marker gene expression (β-Mhc, Anp, Bnp), while shRNA knockdown reduced them. The mechanism involves activation of PI3K-AKT-mTOR signaling by CPA4.","method":"Adenoviral overexpression, shRNA knockdown, cardiomyocyte hypertrophy assay, Western blot (PI3K-AKT-mTOR), in vivo mouse ISO model","journal":"Bioscience reports","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function in primary cells with defined pathway; single lab","pmids":["32347291"],"is_preprint":false},{"year":2024,"finding":"In anaplastic thyroid cancer, M2 macrophage-secreted CPA4 (identified by LC-MS/MS proteomics of conditioned medium) increases CPA4 expression in cancer cells. CPA4 knockdown suppressed proliferation, colony formation, migration, and invasion of ATC cells with decreased phosphorylation of STAT3, ERK, and AKT/mTOR and reduced EMT markers. Increased CPA4 in cancer cells fed back to polarize macrophages toward M2 phenotype, forming a positive feedback loop. Xenograft tumors did not develop after CPA4 knockdown.","method":"LC-MS/MS proteomics, conditioned medium coculture, siRNA/shRNA knockdown, xenograft model, Western blot","journal":"Thyroid : official journal of the American Thyroid Association","confidence":"Medium","confidence_rationale":"Tier 2 — proteomics identification plus loss-of-function with in vivo validation and pathway analysis; single lab","pmids":["38666696"],"is_preprint":false}],"current_model":"CPA4 is a secreted zinc metallocarboxypeptidase (M14A subfamily) that is activated from a proenzyme form by endoproteases, preferentially cleaves hydrophobic C-terminal residues from peptides including neuropeptides, is subject to endogenous inhibition by latexin via a large-interface active-site occlusion mechanism (structurally defined by X-ray crystallography), is transcriptionally induced downstream of HDAC inhibition via a p21-dependent pathway, is maternally imprinted at chromosome 7q32, acts as a negative regulator of adipogenesis, and promotes cancer cell proliferation, EMT, and hypertrophic cardiomyocyte growth primarily through activation of the PI3K-AKT-mTOR signaling axis, with evidence that it physically associates with AKT."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of CPA4 as an HDAC-inhibitor-responsive gene downstream of p21 established its transcriptional regulation and predicted it to be a secreted zinc carboxypeptidase, opening the question of its enzymatic specificity and biological function.","evidence":"Differential display, antisense mRNA inhibition, and sequence analysis in prostate cancer cells","pmids":["10383164"],"confidence":"Medium","gaps":["Enzymatic activity not directly demonstrated","Substrate specificity unknown","Mechanism linking p21 to CPA4 transcription undefined"]},{"year":2003,"claim":"Demonstration that CPA4 is maternally imprinted at 7q32—uniquely among the CPA gene cluster—suggested a distinct developmental role and dosage sensitivity for this metallocarboxypeptidase.","evidence":"Allele-specific RT-PCR with SNP markers, pyrosequencing, and replication-timing assays across fetal tissues","pmids":["12552318","12676894"],"confidence":"Medium","gaps":["Functional consequence of monoallelic expression unknown","Mechanism of imprinting (ICR, methylation) not defined","Biallelic expression in fetal brain unexplained"]},{"year":2005,"claim":"Crystal structures of both the mature CPA4–latexin complex and the pro-CPA4 zymogen revealed that active-site occlusion by the pro-domain and by latexin proceeds through structurally analogous β-sheet loop mechanisms, defining the molecular basis of CPA4 activation and endogenous inhibition.","evidence":"X-ray crystallography of hCPA4–latexin and pro-CPA4, with molecular modeling","pmids":["15738388","16091843"],"confidence":"High","gaps":["In vivo protease(s) responsible for pro-domain removal not identified","Physiological contexts where latexin regulates CPA4 unclear"]},{"year":2010,"claim":"Biochemical and peptidomic characterization established CPA4 as a secreted, trypsin-activatable carboxypeptidase with strong preference for hydrophobic C-terminal residues, identifying neuropeptides (neurotensin, granins, opioid peptides) as substrates and implicating CPA4 in extracellular peptide processing.","evidence":"Secretion assay, chromogenic substrate kinetics, and quantitative peptidomics on >100 mouse brain peptides","pmids":["20385563"],"confidence":"High","gaps":["In vivo neuropeptide processing by CPA4 not confirmed","Tissue-specific activation mechanism unknown","Relative contribution versus other MCPs in brain undetermined"]},{"year":2012,"claim":"Structural characterization of exogenous inhibitors NvCI and SmCI bound to CPA4 revealed two distinct inhibitory strategies—C-terminal substrate-like insertion and N-terminal groove occupation—broadening the understanding of metallocarboxypeptidase inhibition mechanisms.","evidence":"X-ray crystallography at 1.7 Å (NvCI) and mutagenesis-validated structure (SmCI)","pmids":["22294694","23746805"],"confidence":"High","gaps":["Therapeutic utility of these inhibitors against CPA4 untested in vivo","Endogenous N-terminal-type inhibitors of CPA4 not identified in mammals"]},{"year":2016,"claim":"CPA4 was identified as a negative regulator of adipogenesis, showing that its biological roles extend beyond peptide processing to differentiation control in mesenchymal lineages.","evidence":"siRNA knockdown enhancing human preadipocyte differentiation, supported by RNA-Seq and qRT-PCR","pmids":["28209092"],"confidence":"Medium","gaps":["Substrate or signaling target mediating anti-adipogenic effect not identified","Single knockdown approach without rescue","Relevance to in vivo adipose biology unconfirmed"]},{"year":2019,"claim":"Loss- and gain-of-function studies in NSCLC cells demonstrated that CPA4 promotes proliferation and suppresses apoptosis via the AKT/c-MYC axis, establishing a pro-oncogenic signaling role validated by xenograft experiments.","evidence":"shRNA knockdown, ectopic overexpression, in vivo xenograft, Western blot pathway analysis","pmids":["31397502"],"confidence":"Medium","gaps":["Whether enzymatic activity is required for AKT activation unknown","Direct versus indirect mechanism of AKT engagement not resolved"]},{"year":2020,"claim":"CPA4 was shown to physically associate with AKT by co-immunoprecipitation and to activate the full PI3K–AKT–mTOR cascade, driving EMT and drug resistance in pancreatic cancer, while separately promoting cardiomyocyte hypertrophy through the same pathway.","evidence":"Co-IP in pancreatic cancer cells, PI3K inhibitor rescue, overexpression/knockdown in neonatal cardiomyocytes with in vivo mouse ISO model","pmids":["32922037","32347291"],"confidence":"Medium","gaps":["CPA4–AKT interaction demonstrated by single co-IP without reciprocal pulldown or domain mapping","Whether CPA4 enzymatic activity is required for PI3K–AKT activation untested","Structural basis of CPA4–AKT association unknown"]},{"year":2024,"claim":"Proteomics identified CPA4 as an M2 macrophage-secreted factor that promotes anaplastic thyroid cancer proliferation and EMT while feeding back to sustain M2 polarization, establishing CPA4 as a mediator of tumor–stroma crosstalk via STAT3, ERK, and AKT/mTOR.","evidence":"LC-MS/MS of conditioned medium, coculture, siRNA/shRNA knockdown, xenograft model","pmids":["38666696"],"confidence":"Medium","gaps":["Receptor or mechanism of CPA4 uptake by cancer cells undefined","Whether CPA4 enzymatic activity or a non-catalytic surface mediates macrophage polarization unknown","Feedback loop not confirmed beyond single cell line system"]},{"year":null,"claim":"It remains unknown whether CPA4's pro-oncogenic and hypertrophic signaling functions depend on its carboxypeptidase catalytic activity or on a non-enzymatic scaffolding/binding role, and no in vivo physiological substrate for CPA4 has been confirmed.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Catalytic-dead mutant studies needed to dissect enzymatic vs. non-catalytic roles","In vivo substrates not validated","Knockout or conditional KO mouse phenotype not reported"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5,6,7]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[3,4,5]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[5,12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,10,11,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,4,5]}],"complexes":[],"partners":["AKT1","LXN"],"other_free_text":[]},"mechanistic_narrative":"CPA4 is a secreted zinc metallocarboxypeptidase of the M14A subfamily that is processed from a proenzyme form by endoproteases and preferentially removes hydrophobic C-terminal residues from peptide substrates including neuropeptides such as neurotensin and opioid peptides [PMID:20385563]. Structurally, the mature enzyme adopts a canonical α/β-hydrolase fold whose active-site funnel is occluded by the pro-domain in the zymogen and by the endogenous inhibitor latexin upon binding, both employing analogous β-sheet loop contacts [PMID:15738388, PMID:16091843]. CPA4 is a maternally imprinted gene at chromosome 7q32 whose transcription is induced downstream of histone deacetylase inhibition through a p21(WAF1/CIP1)-dependent pathway [PMID:10383164, PMID:12552318]. In cancer cells, CPA4 promotes proliferation, epithelial–mesenchymal transition, and drug resistance primarily through activation of the PI3K–AKT–mTOR signaling axis, with which it physically associates, and in the tumor microenvironment it participates in a positive feedback loop with M2-polarized macrophages [PMID:32922037, PMID:38666696]."},"prefetch_data":{"uniprot":{"accession":"Q9UI42","full_name":"Carboxypeptidase A4","aliases":["Carboxypeptidase A3"],"length_aa":421,"mass_kda":47.4,"function":"Metalloprotease that cleaves hydrophobic C-terminal residues with a preference for -Phe, -Leu, -Ile, -Met, -Tyr and -Val (PubMed:20385563). May function in peptide hormone and/or neuropeptide catabolism (PubMed:20385563)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q9UI42/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CPA4","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/CPA4","total_profiled":1310},"omim":[{"mim_id":"609561","title":"CARBOXYPEPTIDASE A5; CPA5","url":"https://www.omim.org/entry/609561"},{"mim_id":"609305","title":"LATEXIN; LXN","url":"https://www.omim.org/entry/609305"},{"mim_id":"607635","title":"CARBOXYPEPTIDASE A4; CPA4","url":"https://www.omim.org/entry/607635"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"},{"location":"Centriolar satellite","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"esophagus","ntpm":21.0},{"tissue":"skin 1","ntpm":53.9}],"url":"https://www.proteinatlas.org/search/CPA4"},"hgnc":{"alias_symbol":["CPA3"],"prev_symbol":[]},"alphafold":{"accession":"Q9UI42","domains":[{"cath_id":"3.30.70.340","chopping":"24-92","consensus_level":"high","plddt":90.3643,"start":24,"end":92},{"cath_id":"3.40.630.10","chopping":"121-418","consensus_level":"high","plddt":97.4494,"start":121,"end":418}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UI42","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UI42-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UI42-F1-predicted_aligned_error_v6.png","plddt_mean":93.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CPA4","jax_strain_url":"https://www.jax.org/strain/search?query=CPA4"},"sequence":{"accession":"Q9UI42","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UI42.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UI42/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UI42"}},"corpus_meta":[{"pmid":"32746878","id":"PMC_32746878","title":"Circular 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\"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in single lab establishing pathway position (p21 required upstream of CPA4 induction); no reconstitution or structural validation of enzymatic activity\",\n      \"pmids\": [\"10383164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CPA4 is a maternally imprinted gene at chromosome 7q32; RT-PCR with intragenic polymorphisms demonstrated preferential expression from the maternal allele in multiple fetal tissues (heart, lung, liver, intestine, kidney, adrenal gland, spleen) but not in fetal brain.\",\n      \"method\": \"RT-PCR with intragenic SNP markers to determine allele-specific expression\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct allele-specific RT-PCR across multiple tissues; single lab, single method\",\n      \"pmids\": [\"12552318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of human CPA4 in complex with the tri-Kunitz inhibitor SmCI revealed a noncanonical inhibition mechanism in which the inhibitor's N-terminal segment (rather than its C-terminus) penetrates the active site groove of hCPA4; mutagenesis and biochemical assays confirmed the N-terminal segment as the primary determinant of carboxypeptidase inhibition.\",\n      \"method\": \"X-ray crystallography (crystal structure of hCPA4–SmCI complex), site-directed mutagenesis, biochemical inhibition assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis and biochemical validation in a single study\",\n      \"pmids\": [\"23746805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CPA4 acts as a negative regulator of adipogenesis; siRNA-mediated knockdown of CPA4 in human preadipocytes enhanced their differentiation into mature adipocytes, and FGF-1-induced adipogenesis was accompanied by downregulation of CPA4 in a BAMBI/PPARγ-independent manner.\",\n      \"method\": \"siRNA knockdown, qRT-PCR, RNA-Seq, adipocyte differentiation assays\",\n      \"journal\": \"Growth factors\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular phenotype and pathway placement; single lab\",\n      \"pmids\": [\"28209092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CPA4 promotes non-small cell lung cancer cell proliferation via the AKT/c-MYC pathway; CPA4 knockdown suppressed proliferation, induced G1-S arrest, and promoted apoptosis in NSCLC cells and in xenograft models, while ectopic CPA4 overexpression enhanced proliferation.\",\n      \"method\": \"shRNA knockdown, ectopic overexpression, MTT assay, colony formation, Cellomics ArrayScan, xenograft tumor models, Western blot for AKT/c-MYC\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss- and gain-of-function with in vitro and in vivo validation; pathway assignment via protein-level readout; single lab\",\n      \"pmids\": [\"31397502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CPA4 overexpression promotes epithelial-to-mesenchymal transition (EMT) in pancreatic cancer cells by activating the PI3K-AKT-mTOR signaling pathway, as evidenced by upregulation of p-PI3K, p-AKT, p-mTOR, N-cadherin, and vimentin and downregulation of E-cadherin; the PI3K inhibitor LY294002 reversed CPA4-driven EMT and drug resistance. CPA4 was co-immunoprecipitated with AKT in pancreatic cancer cells.\",\n      \"method\": \"Overexpression and siRNA knockdown, Western blot, co-immunoprecipitation with AKT, PI3K inhibitor rescue (LY294002), cell invasion/migration assays, apoptosis assay\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus gain/loss-of-function with pathway inhibitor rescue; single lab\",\n      \"pmids\": [\"32922037\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CPA4 is a secreted zinc metallocarboxypeptidase whose catalytic active site can be inhibited via a noncanonical N-terminal mechanism (established by crystal structure and mutagenesis); its expression is regulated downstream of histone deacetylation and p21 transactivation, it is maternally imprinted at 7q32, it negatively regulates adipogenesis, and in cancer contexts it promotes proliferation and EMT by activating the AKT/c-MYC and PI3K-AKT-mTOR signaling pathways and physically associating with AKT.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"CPA4 (then called CPA3 in the original paper but now recognized as CPA4) is induced by histone deacetylase (HDAC) inhibitors sodium butyrate and trichostatin A in prostate cancer cells. The induction requires prior p21(WAF1/CIP1) transactivation, as p21 antisense mRNA blocked CPA4 induction. Structural analysis of the encoded protein predicted a 16-residue signal peptide, a 95-residue N-terminal activation segment, and a 310-residue carboxypeptidase enzyme domain with 37–63% identity to zinc carboxypeptidases.\",\n      \"method\": \"mRNA differential display, antisense mRNA inhibition, sequence/structural analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods (differential display, antisense inhibition, sequence analysis) in single lab; foundational paper establishing pathway position\",\n      \"pmids\": [\"10383164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CPA4 is a maternally imprinted gene on chromosome 7q32; it is preferentially expressed from the maternal allele in multiple fetal tissues (heart, lung, liver, intestine, kidney, adrenal gland, spleen) but shows biallelic expression in fetal brain, as demonstrated by RT-PCR with intragenic polymorphism markers.\",\n      \"method\": \"RT-PCR with intragenic SNP markers in fetal tissues\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — allele-specific expression directly assayed with polymorphism markers; single lab\",\n      \"pmids\": [\"12552318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Among the carboxypeptidase A gene cluster at 7q32, only CPA4 shows preferential maternal allele expression (imprinting), confirmed by pyrosequencing quantitative analysis; CPA1, CPA2 show biallelic expression, and the imprinted domain extends across an asynchronously replicating genomic region.\",\n      \"method\": \"Replication timing assay, SNP-based RT-PCR, pyrosequencing\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (replication timing, pyrosequencing); single lab confirming imprinting\",\n      \"pmids\": [\"12676894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of human CPA4 (hCPA4) in complex with its endogenous inhibitor latexin was solved. hCPA4 displays the canonical alpha/beta-hydrolase fold of metallocarboxypeptidases. Latexin, a 25-kDa protein with two cystatin-like subdomains, binds at the interface of these subdomains, occluding the active-site funnel with a large contact surface but few contacts, explaining nanomolar inhibition and cross-species flexibility. Modeling studies revealed why the N/E subfamily of MCPs and invertebrate A/B MCPs are not inhibited by latexin.\",\n      \"method\": \"X-ray crystallography, modeling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional interpretation; replicated with additional structural study\",\n      \"pmids\": [\"15738388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The three-dimensional structure of human pro-CPA4 (hPCPA4) was solved, revealing a preformed alpha/beta-hydrolase active-enzyme moiety (hCPA4) and an inhibitory pro-domain (PD). The PD contacts the funnel-like access to the active-site cleft via loop segments in a manner structurally analogous to latexin inhibition; both employ a similar beta-sheet loop for active-site blocking.\",\n      \"method\": \"X-ray crystallography, structural comparison\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of zymogen form with detailed mechanistic comparison; independent corroboration of active-site architecture\",\n      \"pmids\": [\"16091843\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CPA4 is secreted from cells as a soluble proenzyme (pro-CPA4) that can be activated by endoproteases such as trypsin. Kinetic analysis with chromogenic substrates and a quantitative peptidomics mass spectrometry approach on >100 mouse brain peptides showed CPA4 preferentially cleaves hydrophobic C-terminal residues (Phe, Leu, Ile, Met, Tyr, Val). Aliphatic, aromatic, and basic residues at P1 position enhance cleavage; acidic residues, Pro, and Gly at P1 inhibit cleavage. Substrates include neurotensin, granins, and opioid peptides, implying a role in extracellular neuropeptide processing.\",\n      \"method\": \"Secretion assay, kinetic analysis with chromogenic substrates, quantitative peptidomics mass spectrometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic characterization with three complementary orthogonal approaches; clear substrate specificity established\",\n      \"pmids\": [\"20385563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of human CPA4 in complex with NvCI (a marine snail Nerita versicolor inhibitor) was determined at 1.7 Å resolution. NvCI adopts a novel fold (two-stranded antiparallel beta-sheet, three loops, C-terminal tail, three disulfide bridges) and inhibits the enzyme in a substrate-like, active-site-directed manner with picomolar inhibition constants, making it the strongest inhibitor reported for the M14A subfamily.\",\n      \"method\": \"X-ray crystallography, kinetic inhibition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — 1.7 Å crystal structure plus kinetic validation; convergent evolution of C-terminal inhibitory mechanism demonstrated\",\n      \"pmids\": [\"22294694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of CPA4 in complex with SmCI (a tri-Kunitz inhibitor from Sabellastarte magnifica) revealed a noncanonical inhibition mechanism: unlike classical C-terminal substrate-like inhibition, SmCI primarily inserts its N-terminal segment into the active-site groove. Mutagenesis and biochemical analysis confirmed the dominant role of the N-terminal segment in inhibiting metallocarboxypeptidases.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, biochemical inhibition assays\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis validation; defines novel inhibitory mechanism\",\n      \"pmids\": [\"23746805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FGF-1 treatment or induction of differentiation of human preadipocytes significantly downregulates CPA4 expression in a BAMBI/PPARγ-independent manner. siRNA-mediated knockdown of CPA4 enhances differentiation of human preadipocytes, identifying CPA4 as a negative regulator of adipogenesis.\",\n      \"method\": \"RNA-Seq, qRT-PCR, siRNA knockdown with adipogenesis functional assay\",\n      \"journal\": \"Growth factors (Chur, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with defined phenotypic readout plus transcriptomic data; single lab\",\n      \"pmids\": [\"28209092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CPA4 knockdown in NSCLC cells inhibits cell proliferation and induces G1-S arrest and apoptosis by suppressing the AKT/c-MYC signaling pathway. Ectopic CPA4 overexpression enhanced proliferation. CPA4 downregulation also suppressed tumor growth in xenograft models.\",\n      \"method\": \"shRNA knockdown, ectopic overexpression, MTT/colony assays, xenograft model, Western blot pathway analysis\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss- and gain-of-function with defined pathway readout (AKT/c-MYC) and in vivo validation; single lab\",\n      \"pmids\": [\"31397502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CPA4 overexpression in pancreatic cancer cells activates PI3K-AKT-mTOR signaling (elevated p-PI3K, p-AKT, p-mTOR), promotes EMT (downregulation of E-cadherin and β-catenin; upregulation of N-cadherin, vimentin), and increases drug resistance. CPA4 was co-immunoprecipitated with AKT in two PC cell lines with high CPA4 expression. The PI3K inhibitor LY294002 reversed these effects.\",\n      \"method\": \"Overexpression/knockdown, Western blot, co-immunoprecipitation, PI3K inhibitor rescue experiment\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP showing CPA4-AKT interaction plus functional rescue experiment; single lab, moderate evidence for direct PI3K-AKT-mTOR engagement\",\n      \"pmids\": [\"32922037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CPA4 promotes cardiomyocyte hypertrophy in neonatal rat cardiomyocytes: CPA4 overexpression enhanced ISO-induced cardiomyocyte size enlargement and hypertrophy marker gene expression (β-Mhc, Anp, Bnp), while shRNA knockdown reduced them. The mechanism involves activation of PI3K-AKT-mTOR signaling by CPA4.\",\n      \"method\": \"Adenoviral overexpression, shRNA knockdown, cardiomyocyte hypertrophy assay, Western blot (PI3K-AKT-mTOR), in vivo mouse ISO model\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function in primary cells with defined pathway; single lab\",\n      \"pmids\": [\"32347291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In anaplastic thyroid cancer, M2 macrophage-secreted CPA4 (identified by LC-MS/MS proteomics of conditioned medium) increases CPA4 expression in cancer cells. CPA4 knockdown suppressed proliferation, colony formation, migration, and invasion of ATC cells with decreased phosphorylation of STAT3, ERK, and AKT/mTOR and reduced EMT markers. Increased CPA4 in cancer cells fed back to polarize macrophages toward M2 phenotype, forming a positive feedback loop. Xenograft tumors did not develop after CPA4 knockdown.\",\n      \"method\": \"LC-MS/MS proteomics, conditioned medium coculture, siRNA/shRNA knockdown, xenograft model, Western blot\",\n      \"journal\": \"Thyroid : official journal of the American Thyroid Association\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics identification plus loss-of-function with in vivo validation and pathway analysis; single lab\",\n      \"pmids\": [\"38666696\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CPA4 is a secreted zinc metallocarboxypeptidase (M14A subfamily) that is activated from a proenzyme form by endoproteases, preferentially cleaves hydrophobic C-terminal residues from peptides including neuropeptides, is subject to endogenous inhibition by latexin via a large-interface active-site occlusion mechanism (structurally defined by X-ray crystallography), is transcriptionally induced downstream of HDAC inhibition via a p21-dependent pathway, is maternally imprinted at chromosome 7q32, acts as a negative regulator of adipogenesis, and promotes cancer cell proliferation, EMT, and hypertrophic cardiomyocyte growth primarily through activation of the PI3K-AKT-mTOR signaling axis, with evidence that it physically associates with AKT.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CPA4 is a secreted zinc metallocarboxypeptidase comprising a signal peptide, an N-terminal activation segment, and a catalytic carboxypeptidase domain; its crystal structure reveals a noncanonical active-site inhibition mechanism in which an inhibitor's N-terminal segment, rather than its C-terminus, occupies the substrate-binding groove [PMID:23746805]. CPA4 is maternally imprinted at chromosome 7q32 with preferential maternal-allele expression in most fetal tissues [PMID:12552318], and its transcription is induced downstream of histone deacetylase inhibition in a p21(WAF1/CIP1)-dependent manner [PMID:10383164]. CPA4 negatively regulates adipogenesis in human preadipocytes [PMID:28209092] and, in cancer cells, promotes proliferation and epithelial-to-mesenchymal transition through activation of the AKT/c-MYC and PI3K-AKT-mTOR signaling pathways, physically associating with AKT [PMID:31397502, PMID:32922037].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The initial discovery established CPA4 as a p21-dependent, HDAC-inhibitor–inducible metallocarboxypeptidase gene, placing it downstream of chromatin-remodeling signals in prostate cancer cells and defining its domain architecture.\",\n      \"evidence\": \"mRNA differential display, antisense p21 blockade, and sequence analysis in LNCaP prostate cancer cells\",\n      \"pmids\": [\"10383164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Enzymatic activity and substrate specificity were predicted but not biochemically demonstrated\",\n        \"Mechanism linking p21 transactivation to CPA4 promoter induction was not identified\",\n        \"Relevance beyond prostate cancer cells was unknown\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that CPA4 is maternally imprinted at 7q32 established epigenetic regulation as a primary control mechanism and implied developmental significance.\",\n      \"evidence\": \"Allele-specific RT-PCR with intragenic SNPs across multiple human fetal tissues\",\n      \"pmids\": [\"12552318\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Imprinting control region and mechanism were not mapped\",\n        \"Brain-specific biallelic expression was unexplained\",\n        \"Functional consequence of monoallelic expression was not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The crystal structure of CPA4 in complex with an inhibitor revealed a noncanonical N-terminal inhibition mechanism, providing the first high-resolution model of the enzyme's active site and confirming its zinc metallocarboxypeptidase fold.\",\n      \"evidence\": \"X-ray crystallography of hCPA4–SmCI complex, site-directed mutagenesis, and biochemical inhibition assays\",\n      \"pmids\": [\"23746805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Endogenous substrates of CPA4 remain unidentified\",\n        \"Whether this inhibition mode reflects physiological regulation is unknown\",\n        \"No structure of CPA4 with a peptide substrate has been solved\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Knockdown studies in preadipocytes revealed a cell-autonomous role for CPA4 as a negative regulator of adipogenesis, expanding its functional repertoire beyond cancer.\",\n      \"evidence\": \"siRNA knockdown in human preadipocytes with RNA-Seq and adipocyte differentiation assays\",\n      \"pmids\": [\"28209092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The substrate or signaling mechanism through which CPA4 suppresses adipocyte differentiation was not identified\",\n        \"In vivo relevance for adipose tissue biology was not tested\",\n        \"Whether CPA4's catalytic activity is required for this effect is unknown\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Loss- and gain-of-function experiments in NSCLC cells and xenografts showed CPA4 promotes proliferation via AKT/c-MYC signaling, establishing its oncogenic activity in lung cancer.\",\n      \"evidence\": \"shRNA knockdown, ectopic overexpression, colony formation, xenograft models, and Western blot in NSCLC lines\",\n      \"pmids\": [\"31397502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether CPA4 directly activates AKT or acts through an intermediate was not determined\",\n        \"Catalytic dependence of the pro-proliferative effect was not tested\",\n        \"No reciprocal co-IP or direct binding assay was performed\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Co-immunoprecipitation of CPA4 with AKT and PI3K-inhibitor rescue in pancreatic cancer cells established a physical CPA4–AKT association and linked CPA4-driven EMT to the PI3K-AKT-mTOR axis.\",\n      \"evidence\": \"Co-IP, overexpression/siRNA, LY294002 rescue, invasion/migration assays in pancreatic cancer cells\",\n      \"pmids\": [\"32922037\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Co-IP was performed in one direction without reciprocal validation or domain-mapping\",\n        \"Whether CPA4 enzymatic activity is required for AKT activation is untested\",\n        \"Direct versus indirect nature of the CPA4–AKT interaction remains unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous substrate(s) of CPA4's carboxypeptidase activity, whether catalytic activity is required for its signaling and adipogenesis functions, and the molecular basis of its CPA4–AKT interaction remain unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No endogenous substrate has been identified\",\n        \"Catalytic-dead mutant studies have not been performed in any functional context\",\n        \"The imprinting control region and developmental role of monoallelic expression are undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AKT\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I notice I made a small error in the pathway entries — let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"CPA4 is a secreted zinc metallocarboxypeptidase comprising a signal peptide, an N-terminal activation segment, and a catalytic carboxypeptidase domain; its crystal structure reveals a noncanonical active-site inhibition mechanism in which an inhibitor's N-terminal segment, rather than its C-terminus, occupies the substrate-binding groove [PMID:23746805]. CPA4 is maternally imprinted at chromosome 7q32 with preferential maternal-allele expression in most fetal tissues [PMID:12552318], and its transcription is induced downstream of histone deacetylase inhibition in a p21(WAF1/CIP1)-dependent manner [PMID:10383164]. CPA4 negatively regulates adipogenesis in human preadipocytes [PMID:28209092] and, in cancer cells, promotes proliferation and epithelial-to-mesenchymal transition through activation of the AKT/c-MYC and PI3K-AKT-mTOR signaling pathways, physically associating with AKT [PMID:31397502, PMID:32922037].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The initial discovery established CPA4 as a p21-dependent, HDAC-inhibitor–inducible metallocarboxypeptidase gene, placing it downstream of chromatin-remodeling signals in prostate cancer cells and defining its domain architecture.\",\n      \"evidence\": \"mRNA differential display, antisense p21 blockade, and sequence analysis in LNCaP prostate cancer cells\",\n      \"pmids\": [\"10383164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Enzymatic activity and substrate specificity were predicted but not biochemically demonstrated\",\n        \"Mechanism linking p21 transactivation to CPA4 promoter induction was not identified\",\n        \"Relevance beyond prostate cancer cells was unknown\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that CPA4 is maternally imprinted at 7q32 established epigenetic regulation as a primary control mechanism and implied developmental significance.\",\n      \"evidence\": \"Allele-specific RT-PCR with intragenic SNPs across multiple human fetal tissues\",\n      \"pmids\": [\"12552318\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Imprinting control region and mechanism were not mapped\",\n        \"Brain-specific biallelic expression was unexplained\",\n        \"Functional consequence of monoallelic expression was not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The crystal structure of CPA4 in complex with an inhibitor revealed a noncanonical N-terminal inhibition mechanism, providing the first high-resolution model of the enzyme's active site and confirming its zinc metallocarboxypeptidase fold.\",\n      \"evidence\": \"X-ray crystallography of hCPA4–SmCI complex, site-directed mutagenesis, and biochemical inhibition assays\",\n      \"pmids\": [\"23746805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Endogenous substrates of CPA4 remain unidentified\",\n        \"Whether this inhibition mode reflects physiological regulation is unknown\",\n        \"No structure of CPA4 with a peptide substrate has been solved\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Knockdown studies in preadipocytes revealed a cell-autonomous role for CPA4 as a negative regulator of adipogenesis, expanding its functional repertoire beyond cancer.\",\n      \"evidence\": \"siRNA knockdown in human preadipocytes with RNA-Seq and adipocyte differentiation assays\",\n      \"pmids\": [\"28209092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The substrate or signaling mechanism through which CPA4 suppresses adipocyte differentiation was not identified\",\n        \"In vivo relevance for adipose tissue biology was not tested\",\n        \"Whether CPA4's catalytic activity is required for this effect is unknown\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Loss- and gain-of-function experiments in NSCLC cells and xenografts showed CPA4 promotes proliferation via AKT/c-MYC signaling, establishing its oncogenic activity in lung cancer.\",\n      \"evidence\": \"shRNA knockdown, ectopic overexpression, colony formation, xenograft models, and Western blot in NSCLC lines\",\n      \"pmids\": [\"31397502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether CPA4 directly activates AKT or acts through an intermediate was not determined\",\n        \"Catalytic dependence of the pro-proliferative effect was not tested\",\n        \"No reciprocal co-IP or direct binding assay was performed\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Co-immunoprecipitation of CPA4 with AKT and PI3K-inhibitor rescue in pancreatic cancer cells established a physical CPA4–AKT association and linked CPA4-driven EMT to the PI3K-AKT-mTOR axis.\",\n      \"evidence\": \"Co-IP, overexpression/siRNA, LY294002 rescue, invasion/migration assays in pancreatic cancer cells\",\n      \"pmids\": [\"32922037\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Co-IP was performed in one direction without reciprocal validation or domain-mapping\",\n        \"Whether CPA4 enzymatic activity is required for AKT activation is untested\",\n        \"Direct versus indirect nature of the CPA4–AKT interaction remains unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous substrate(s) of CPA4's carboxypeptidase activity, whether catalytic activity is required for its signaling and adipogenesis functions, and the molecular basis of its CPA4–AKT interaction remain unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No endogenous substrate has been identified\",\n        \"Catalytic-dead mutant studies have not been performed in any functional context\",\n        \"The imprinting control region and developmental role of monoallelic expression are undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AKT\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CPA4 is a secreted zinc metallocarboxypeptidase of the M14A subfamily that is processed from a proenzyme form by endoproteases and preferentially removes hydrophobic C-terminal residues from peptide substrates including neuropeptides such as neurotensin and opioid peptides [PMID:20385563]. Structurally, the mature enzyme adopts a canonical α/β-hydrolase fold whose active-site funnel is occluded by the pro-domain in the zymogen and by the endogenous inhibitor latexin upon binding, both employing analogous β-sheet loop contacts [PMID:15738388, PMID:16091843]. CPA4 is a maternally imprinted gene at chromosome 7q32 whose transcription is induced downstream of histone deacetylase inhibition through a p21(WAF1/CIP1)-dependent pathway [PMID:10383164, PMID:12552318]. In cancer cells, CPA4 promotes proliferation, epithelial–mesenchymal transition, and drug resistance primarily through activation of the PI3K–AKT–mTOR signaling axis, with which it physically associates, and in the tumor microenvironment it participates in a positive feedback loop with M2-polarized macrophages [PMID:32922037, PMID:38666696].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of CPA4 as an HDAC-inhibitor-responsive gene downstream of p21 established its transcriptional regulation and predicted it to be a secreted zinc carboxypeptidase, opening the question of its enzymatic specificity and biological function.\",\n      \"evidence\": \"Differential display, antisense mRNA inhibition, and sequence analysis in prostate cancer cells\",\n      \"pmids\": [\"10383164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymatic activity not directly demonstrated\", \"Substrate specificity unknown\", \"Mechanism linking p21 to CPA4 transcription undefined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that CPA4 is maternally imprinted at 7q32—uniquely among the CPA gene cluster—suggested a distinct developmental role and dosage sensitivity for this metallocarboxypeptidase.\",\n      \"evidence\": \"Allele-specific RT-PCR with SNP markers, pyrosequencing, and replication-timing assays across fetal tissues\",\n      \"pmids\": [\"12552318\", \"12676894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of monoallelic expression unknown\", \"Mechanism of imprinting (ICR, methylation) not defined\", \"Biallelic expression in fetal brain unexplained\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Crystal structures of both the mature CPA4–latexin complex and the pro-CPA4 zymogen revealed that active-site occlusion by the pro-domain and by latexin proceeds through structurally analogous β-sheet loop mechanisms, defining the molecular basis of CPA4 activation and endogenous inhibition.\",\n      \"evidence\": \"X-ray crystallography of hCPA4–latexin and pro-CPA4, with molecular modeling\",\n      \"pmids\": [\"15738388\", \"16091843\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo protease(s) responsible for pro-domain removal not identified\", \"Physiological contexts where latexin regulates CPA4 unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical and peptidomic characterization established CPA4 as a secreted, trypsin-activatable carboxypeptidase with strong preference for hydrophobic C-terminal residues, identifying neuropeptides (neurotensin, granins, opioid peptides) as substrates and implicating CPA4 in extracellular peptide processing.\",\n      \"evidence\": \"Secretion assay, chromogenic substrate kinetics, and quantitative peptidomics on >100 mouse brain peptides\",\n      \"pmids\": [\"20385563\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo neuropeptide processing by CPA4 not confirmed\", \"Tissue-specific activation mechanism unknown\", \"Relative contribution versus other MCPs in brain undetermined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Structural characterization of exogenous inhibitors NvCI and SmCI bound to CPA4 revealed two distinct inhibitory strategies—C-terminal substrate-like insertion and N-terminal groove occupation—broadening the understanding of metallocarboxypeptidase inhibition mechanisms.\",\n      \"evidence\": \"X-ray crystallography at 1.7 Å (NvCI) and mutagenesis-validated structure (SmCI)\",\n      \"pmids\": [\"22294694\", \"23746805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic utility of these inhibitors against CPA4 untested in vivo\", \"Endogenous N-terminal-type inhibitors of CPA4 not identified in mammals\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"CPA4 was identified as a negative regulator of adipogenesis, showing that its biological roles extend beyond peptide processing to differentiation control in mesenchymal lineages.\",\n      \"evidence\": \"siRNA knockdown enhancing human preadipocyte differentiation, supported by RNA-Seq and qRT-PCR\",\n      \"pmids\": [\"28209092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate or signaling target mediating anti-adipogenic effect not identified\", \"Single knockdown approach without rescue\", \"Relevance to in vivo adipose biology unconfirmed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Loss- and gain-of-function studies in NSCLC cells demonstrated that CPA4 promotes proliferation and suppresses apoptosis via the AKT/c-MYC axis, establishing a pro-oncogenic signaling role validated by xenograft experiments.\",\n      \"evidence\": \"shRNA knockdown, ectopic overexpression, in vivo xenograft, Western blot pathway analysis\",\n      \"pmids\": [\"31397502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether enzymatic activity is required for AKT activation unknown\", \"Direct versus indirect mechanism of AKT engagement not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"CPA4 was shown to physically associate with AKT by co-immunoprecipitation and to activate the full PI3K–AKT–mTOR cascade, driving EMT and drug resistance in pancreatic cancer, while separately promoting cardiomyocyte hypertrophy through the same pathway.\",\n      \"evidence\": \"Co-IP in pancreatic cancer cells, PI3K inhibitor rescue, overexpression/knockdown in neonatal cardiomyocytes with in vivo mouse ISO model\",\n      \"pmids\": [\"32922037\", \"32347291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CPA4–AKT interaction demonstrated by single co-IP without reciprocal pulldown or domain mapping\", \"Whether CPA4 enzymatic activity is required for PI3K–AKT activation untested\", \"Structural basis of CPA4–AKT association unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proteomics identified CPA4 as an M2 macrophage-secreted factor that promotes anaplastic thyroid cancer proliferation and EMT while feeding back to sustain M2 polarization, establishing CPA4 as a mediator of tumor–stroma crosstalk via STAT3, ERK, and AKT/mTOR.\",\n      \"evidence\": \"LC-MS/MS of conditioned medium, coculture, siRNA/shRNA knockdown, xenograft model\",\n      \"pmids\": [\"38666696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor or mechanism of CPA4 uptake by cancer cells undefined\", \"Whether CPA4 enzymatic activity or a non-catalytic surface mediates macrophage polarization unknown\", \"Feedback loop not confirmed beyond single cell line system\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown whether CPA4's pro-oncogenic and hypertrophic signaling functions depend on its carboxypeptidase catalytic activity or on a non-enzymatic scaffolding/binding role, and no in vivo physiological substrate for CPA4 has been confirmed.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic-dead mutant studies needed to dissect enzymatic vs. non-catalytic roles\", \"In vivo substrates not validated\", \"Knockout or conditional KO mouse phenotype not reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [9, 10, 11, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 10, 11, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AKT1\",\n      \"LXN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway entries - I accidentally included a GO: prefixed entry. Let me also re-examine validity.\n\n```json\n{\n  \"mechanistic_narrative\": \"CPA4 is a secreted zinc metallocarboxypeptidase of the M14A subfamily that is processed from a proenzyme form by endoproteases and preferentially removes hydrophobic C-terminal residues from peptide substrates including neuropeptides such as neurotensin and opioid peptides [PMID:20385563]. Structurally, the mature enzyme adopts a canonical α/β-hydrolase fold whose active-site funnel is occluded by the pro-domain in the zymogen and by the endogenous inhibitor latexin upon binding, both employing analogous β-sheet loop contacts [PMID:15738388, PMID:16091843]. CPA4 is a maternally imprinted gene at chromosome 7q32 whose transcription is induced downstream of histone deacetylase inhibition through a p21(WAF1/CIP1)-dependent pathway [PMID:10383164, PMID:12552318]. In cancer cells, CPA4 promotes proliferation, epithelial–mesenchymal transition, and drug resistance primarily through activation of the PI3K–AKT–mTOR signaling axis, with which it physically associates, and in the tumor microenvironment it participates in a positive feedback loop with M2-polarized macrophages [PMID:32922037, PMID:38666696].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of CPA4 as an HDAC-inhibitor-responsive gene downstream of p21 established its transcriptional regulation and predicted it to be a secreted zinc carboxypeptidase, opening the question of its enzymatic specificity and biological function.\",\n      \"evidence\": \"Differential display, antisense mRNA inhibition, and sequence analysis in prostate cancer cells\",\n      \"pmids\": [\"10383164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymatic activity not directly demonstrated\", \"Substrate specificity unknown\", \"Mechanism linking p21 to CPA4 transcription undefined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that CPA4 is maternally imprinted at 7q32—uniquely among the CPA gene cluster—suggested a distinct developmental role and dosage sensitivity for this metallocarboxypeptidase.\",\n      \"evidence\": \"Allele-specific RT-PCR with SNP markers, pyrosequencing, and replication-timing assays across fetal tissues\",\n      \"pmids\": [\"12552318\", \"12676894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of monoallelic expression unknown\", \"Mechanism of imprinting (ICR, methylation) not defined\", \"Biallelic expression in fetal brain unexplained\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Crystal structures of both the mature CPA4–latexin complex and the pro-CPA4 zymogen revealed that active-site occlusion by the pro-domain and by latexin proceeds through structurally analogous β-sheet loop mechanisms, defining the molecular basis of CPA4 activation and endogenous inhibition.\",\n      \"evidence\": \"X-ray crystallography of hCPA4–latexin and pro-CPA4, with molecular modeling\",\n      \"pmids\": [\"15738388\", \"16091843\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo protease(s) responsible for pro-domain removal not identified\", \"Physiological contexts where latexin regulates CPA4 unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical and peptidomic characterization established CPA4 as a secreted, trypsin-activatable carboxypeptidase with strong preference for hydrophobic C-terminal residues, identifying neuropeptides (neurotensin, granins, opioid peptides) as substrates and implicating CPA4 in extracellular peptide processing.\",\n      \"evidence\": \"Secretion assay, chromogenic substrate kinetics, and quantitative peptidomics on >100 mouse brain peptides\",\n      \"pmids\": [\"20385563\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo neuropeptide processing by CPA4 not confirmed\", \"Tissue-specific activation mechanism unknown\", \"Relative contribution versus other MCPs in brain undetermined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Structural characterization of exogenous inhibitors NvCI and SmCI bound to CPA4 revealed two distinct inhibitory strategies—C-terminal substrate-like insertion and N-terminal groove occupation—broadening the understanding of metallocarboxypeptidase inhibition mechanisms.\",\n      \"evidence\": \"X-ray crystallography at 1.7 Å (NvCI) and mutagenesis-validated structure (SmCI)\",\n      \"pmids\": [\"22294694\", \"23746805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic utility of these inhibitors against CPA4 untested in vivo\", \"Endogenous N-terminal-type inhibitors of CPA4 not identified in mammals\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"CPA4 was identified as a negative regulator of adipogenesis, showing that its biological roles extend beyond peptide processing to differentiation control in mesenchymal lineages.\",\n      \"evidence\": \"siRNA knockdown enhancing human preadipocyte differentiation, supported by RNA-Seq and qRT-PCR\",\n      \"pmids\": [\"28209092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate or signaling target mediating anti-adipogenic effect not identified\", \"Single knockdown approach without rescue\", \"Relevance to in vivo adipose biology unconfirmed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Loss- and gain-of-function studies in NSCLC cells demonstrated that CPA4 promotes proliferation and suppresses apoptosis via the AKT/c-MYC axis, establishing a pro-oncogenic signaling role validated by xenograft experiments.\",\n      \"evidence\": \"shRNA knockdown, ectopic overexpression, in vivo xenograft, Western blot pathway analysis\",\n      \"pmids\": [\"31397502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether enzymatic activity is required for AKT activation unknown\", \"Direct versus indirect mechanism of AKT engagement not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"CPA4 was shown to physically associate with AKT by co-immunoprecipitation and to activate the full PI3K–AKT–mTOR cascade, driving EMT and drug resistance in pancreatic cancer, while separately promoting cardiomyocyte hypertrophy through the same pathway.\",\n      \"evidence\": \"Co-IP in pancreatic cancer cells, PI3K inhibitor rescue, overexpression/knockdown in neonatal cardiomyocytes with in vivo mouse ISO model\",\n      \"pmids\": [\"32922037\", \"32347291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CPA4–AKT interaction demonstrated by single co-IP without reciprocal pulldown or domain mapping\", \"Whether CPA4 enzymatic activity is required for PI3K–AKT activation untested\", \"Structural basis of CPA4–AKT association unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proteomics identified CPA4 as an M2 macrophage-secreted factor that promotes anaplastic thyroid cancer proliferation and EMT while feeding back to sustain M2 polarization, establishing CPA4 as a mediator of tumor–stroma crosstalk via STAT3, ERK, and AKT/mTOR.\",\n      \"evidence\": \"LC-MS/MS of conditioned medium, coculture, siRNA/shRNA knockdown, xenograft model\",\n      \"pmids\": [\"38666696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor or mechanism of CPA4 uptake by cancer cells undefined\", \"Whether CPA4 enzymatic activity or a non-catalytic surface mediates macrophage polarization unknown\", \"Feedback loop not confirmed beyond single cell line system\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown whether CPA4's pro-oncogenic and hypertrophic signaling functions depend on its carboxypeptidase catalytic activity or on a non-enzymatic scaffolding/binding role, and no in vivo physiological substrate for CPA4 has been confirmed.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic-dead mutant studies needed to dissect enzymatic vs. non-catalytic roles\", \"In vivo substrates not validated\", \"Knockout or conditional KO mouse phenotype not reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 10, 11, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AKT1\",\n      \"LXN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}