{"gene":"XPNPEP2","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2000,"finding":"XPNPEP2 encodes a membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) localized to chromosome Xq25, which hydrolyzes N-terminal Xaa-Pro bonds in oligopeptides including bradykinin; the gene is partially expressed even from a translocated X chromosome, suggesting partial escape from X inactivation.","method":"Chromosomal mapping with somatic cell hybrids, mRNA expression analysis in translocation-carrier fibroblasts, sequence homology to pita bread-fold metallopeptidase family","journal":"Cytogenetics and cell genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct chromosomal localization and expression data from translocation carriers, single study","pmids":["10894934"],"is_preprint":false},{"year":2000,"finding":"XPNPEP2 (membrane aminopeptidase P) and XPNPEP1 (soluble aminopeptidase P) share conserved blocks corresponding to the proton shuttle and five divalent metal ligand binding sites characteristic of the pita bread-fold family (prototype: E. coli methionine aminopeptidase), indicating a common catalytic mechanism for Xaa-Pro hydrolysis.","method":"Sequence alignment and structural homology analysis across the pita bread-fold protein family","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 3 — sequence-based functional inference with strong structural context, single study","pmids":["10871044"],"is_preprint":false},{"year":2005,"finding":"A C-2399A single-nucleotide polymorphism (SNP) upstream of XPNPEP2 is associated with reduced plasma aminopeptidase P (APP) activity and increased incidence of ACE inhibitor-induced angioedema, placing XPNPEP2-encoded membrane APP as a key enzyme in bradykinin degradation during ACE inhibition.","method":"Variance-component QTL linkage analysis (genome-wide microsatellite scan), mutation screening, measured genotype analysis, case-control association study","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — linkage mapping plus functional APP activity assay plus case-control study, replicated in subsequent studies","pmids":["16175507"],"is_preprint":false},{"year":2006,"finding":"Plasma APP (encoded by XPNPEP2) activity is significantly reduced in patients experiencing hypersensitivity reactions during hemodialysis with AN69 membrane under ACE inhibitor treatment, and the C-2399A SNP at the XPNPEP2 locus predicts APP activity; recombinant APP is nonspecifically inhibited by some ACE inhibitors in vitro.","method":"Plasma APP activity assay, variance component analysis of hemodialysis patients and relatives, genotyping, recombinant APP inhibition assay","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 — enzymatic activity in patients and recombinant protein, single lab","pmids":["17003818"],"is_preprint":false},{"year":2007,"finding":"XPNPEP2 (membrane aminopeptidase P) is among at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) potentially capable of cleaving neuropeptide Y (NPY) at N-terminal positions in plasma and brain, as demonstrated by selective inhibitor-based activity assays and MALDI-TOF mass spectrometry.","method":"Selective enzyme inhibitors, activity assays in brain extracts and human plasma, MALDI-TOF mass spectrometry","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical methods in parallel, single study","pmids":["17223229"],"is_preprint":false},{"year":2010,"finding":"The XPNPEP2 C-2399A genotype associates with serum APP activity in both sexes, but APP activity is lower in men than in women independent of genotype; the A allele is specifically associated with increased risk of ACE inhibitor-induced angioedema in men (and particularly black men), revealing sex- and race-dependent effects of XPNPEP2 on bradykinin catabolism.","method":"Genotyping, serum APP activity measurement, multivariate case-control analysis (169 cases, 397 controls)","journal":"Pharmacogenetics and genomics","confidence":"High","confidence_rationale":"Tier 2 — large case-control with biochemical activity measurements, replicates prior linkage finding with sex stratification","pmids":["20625347"],"is_preprint":false},{"year":2011,"finding":"The XPNPEP2 promoter contains a minimal promoter region (-338 to -147 bp) and an enhancer region (-2,502 to -2,238 bp); the C-2399A SNP lies within the enhancer and differentially binds hepatic nuclear factor 4 (HNF4), which modulates transcriptional activation; the ATG haplotype (c.-2399A, c.-1612T, c.-393A) reduces promoter/reporter activity and plasma APP activity, and is significantly associated with ACE inhibitor-induced angioedema.","method":"Nested deletion luciferase reporter assays, HNF4 overexpression, haplotype association with plasma APP activity and angioedema case-control study","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1-2 — functional promoter dissection with reporter assays, transcription factor overexpression, and clinical association, multiple orthogonal methods in one study","pmids":["21898657"],"is_preprint":false},{"year":2015,"finding":"In rat ovarian development, Xpnpep2 expression is increased during CrVI-induced germ cell nest breakdown and decreased during postnatal follicle development; Xpnpep2 colocalizes with collagen types 3 and 4 and inversely regulates expression of Col1, Col3, and Col4 at multiple developmental stages, linking Xpnpep2 enzymatic activity to extracellular matrix remodeling in the ovary.","method":"Gestational CrVI exposure model, immunofluorescence colocalization, developmental stage-specific protein/mRNA expression analysis in rat ovaries","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple developmental time points, colocalization data, but mechanistic link to collagen regulation is correlative, single lab","pmids":["25568306"],"is_preprint":false},{"year":2017,"finding":"XPNPEP2 overexpression in cervical cancer cells (SiHa and HeLa) promotes cell invasion and migration without affecting proliferation or apoptosis, and induces epithelial-mesenchymal transition (EMT); XPNPEP2 also promotes tumor metastasis in xenograft mouse models.","method":"Overexpression in cancer cell lines, invasion/migration assays, EMT marker analysis, xenograft mouse metastasis model","journal":"Tumour biology","confidence":"Medium","confidence_rationale":"Tier 2 — loss/gain of function with defined phenotypic readout in vitro and in vivo, single lab","pmids":["28670957"],"is_preprint":false},{"year":2018,"finding":"Mutagenesis studies of bacterial small aminopeptidases-P (structural orthologs of human XPNPEP1/XPNPEP2) illuminate the importance of the DXRY sequence motif for aminopeptidase-P activity, and crystal structures confirm that absence of a dipeptide-selectivity loop distinguishes aminopeptidases-P from prolidases, suggesting common evolutionary origin with human XPNPEP2.","method":"Crystal structure determination of bacterial orthologs, site-directed mutagenesis, enzymatic substrate specificity assays","journal":"Proteins","confidence":"Medium","confidence_rationale":"Tier 1 — crystal structures plus mutagenesis plus enzymatic assays, but on bacterial orthologs not human XPNPEP2 directly","pmids":["30536999"],"is_preprint":false},{"year":2022,"finding":"XPNPEP2 is identified as the cell-surface receptor for the tumor-homing peptide TMTP1, which selectively targets highly metastatic tumor cells; serum XPNPEP2 exists in a secreted form detectable by Western blot, and elevated serum XPNPEP2 associates with lymph node metastasis in prostate cancer.","method":"Western blot (secreted form in serum), tissue array, IHC, ELISA in patient cohorts, receptor identification for TMTP1 peptide","journal":"Scientific reports","confidence":"Low","confidence_rationale":"Tier 3 — receptor identification noted but not mechanistically validated with binding assays; secreted form shown by Western blot only","pmids":["31296901"],"is_preprint":false},{"year":2026,"finding":"XPNPEP2 is essential for endothelial cell (EC) angiogenesis: XPNPEP2 deletion impairs EC proliferation, migration, and tubulogenesis in vitro, causes pathological changes in pulmonary artery wall, renal tissue, and retinal vasculature, and slows wound healing and tumor growth in mice. XPNPEP2 physically interacts with SLC25A6 (mitochondrial ADP/ATP carrier); XPNPEP2 deficiency reduces SLC25A6 via SIAH1-mediated ubiquitin-proteasomal degradation, leading to dysfunctional mitochondria (insufficient ATP, excess mROS, disrupted respiratory chain). Overexpression of XPNPEP2 rescues impaired angiogenesis and restores SLC25A6.","method":"XPNPEP2 KO mouse model, shRNA knockdown in ECs, co-immunoprecipitation (XPNPEP2–SLC25A6 interaction), SIAH1 ubiquitin degradation assay, mitochondrial function assays (ATP, mROS, respiration), tubulogenesis/migration assays, in vivo wound healing and tumor growth models","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 — KO mouse plus in vitro KD plus Co-IP plus mechanistic rescue experiments, multiple orthogonal methods in one study","pmids":["41573684"],"is_preprint":false}],"current_model":"XPNPEP2 encodes a GPI-anchored membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) that degrades bradykinin and related proline-containing peptides; its promoter is regulated by HNF4 via an upstream enhancer, and loss-of-function variants reduce plasma APP activity and predispose to bradykinin-mediated angioedema; in endothelial cells, XPNPEP2 is also required for angiogenesis by physically interacting with the mitochondrial carrier SLC25A6 and protecting it from SIAH1-mediated proteasomal degradation, thereby maintaining mitochondrial function."},"narrative":{"teleology":[{"year":2000,"claim":"Identifying XPNPEP2 as the gene encoding membrane-bound aminopeptidase P at Xq25 established the molecular basis for a previously characterized enzymatic activity that cleaves Xaa-Pro bonds in bradykinin.","evidence":"Chromosomal mapping with somatic cell hybrids, expression analysis in X-translocation carrier fibroblasts, and sequence homology to the pita bread-fold metallopeptidase family","pmids":["10894934","10871044"],"confidence":"Medium","gaps":["No direct structural data for human XPNPEP2 protein","Mechanism of partial X-inactivation escape not resolved","Physiological substrates beyond bradykinin not systematically catalogued"]},{"year":2005,"claim":"Linking the C-2399A upstream polymorphism to reduced plasma APP activity and ACE inhibitor-induced angioedema established XPNPEP2 as a pharmacogenomic determinant of bradykinin-mediated adverse drug reactions.","evidence":"Genome-wide microsatellite QTL linkage analysis, mutation screening, measured genotype analysis, and case-control association in angioedema patients","pmids":["16175507"],"confidence":"High","gaps":["Causal mechanism by which the SNP reduces expression not yet defined","Contribution of other bradykinin-degrading enzymes to angioedema risk not quantified"]},{"year":2010,"claim":"Demonstrating sex- and race-dependent effects of the XPNPEP2 C-2399A genotype on APP activity and angioedema risk revealed that genetic regulation of bradykinin catabolism is modified by non-genetic factors.","evidence":"Serum APP activity measurement and multivariate case-control analysis (169 cases, 397 controls) with sex and race stratification","pmids":["20625347"],"confidence":"High","gaps":["Biological basis for lower APP activity in men versus women unknown","Interaction between XPNPEP2 genotype and hormonal regulation not tested"]},{"year":2011,"claim":"Functional dissection of the XPNPEP2 promoter showed that HNF4 binds the C-2399A enhancer region and that the risk haplotype reduces transcriptional activity, providing a molecular mechanism for genotype-dependent variation in APP expression.","evidence":"Nested deletion luciferase reporter assays, HNF4 overexpression, and haplotype association with plasma APP activity and angioedema","pmids":["21898657"],"confidence":"High","gaps":["Chromatin context and tissue-specific enhancer activity not examined in endogenous locus","Whether other transcription factors co-regulate this enhancer is unknown"]},{"year":2017,"claim":"Showing that XPNPEP2 overexpression promotes invasion, migration, and EMT in cervical cancer cells extended XPNPEP2 function beyond peptide catabolism to a role in tumor metastasis.","evidence":"Overexpression in SiHa and HeLa cells, invasion/migration assays, EMT marker analysis, and xenograft mouse metastasis model","pmids":["28670957"],"confidence":"Medium","gaps":["Whether the pro-metastatic effect requires aminopeptidase catalytic activity or a non-enzymatic mechanism is unresolved","Downstream signaling pathways linking XPNPEP2 to EMT not identified"]},{"year":2026,"claim":"Demonstrating that XPNPEP2 is essential for endothelial angiogenesis through physical interaction with SLC25A6 and protection from SIAH1-mediated degradation revealed a non-catalytic, mitochondria-protective function distinct from its aminopeptidase activity.","evidence":"XPNPEP2 KO mouse, shRNA knockdown in ECs, co-immunoprecipitation of XPNPEP2–SLC25A6, SIAH1 ubiquitin degradation assay, mitochondrial function assays, and in vivo wound healing/tumor growth models","pmids":["41573684"],"confidence":"High","gaps":["Whether the aminopeptidase catalytic domain is required for SLC25A6 binding is unknown","How a GPI-anchored surface protein accesses mitochondrial SLC25A6 is mechanistically unclear","Independent replication of the XPNPEP2–SLC25A6 interaction in other labs is pending"]},{"year":null,"claim":"How XPNPEP2 integrates its dual roles as a bradykinin-degrading aminopeptidase and a non-enzymatic regulator of mitochondrial function in endothelial cells remains unresolved, as does whether its pro-metastatic activity is catalytic or structural.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural data for human XPNPEP2 protein to map interaction surfaces","Mechanism by which a GPI-anchored surface protein contacts intracellular SLC25A6 not defined","Relative contributions of enzymatic versus scaffolding functions to in vivo phenotypes untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,2,4,9]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,10,11]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,4,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,5,8]}],"complexes":[],"partners":["SLC25A6","SIAH1","HNF4A"],"other_free_text":[]},"mechanistic_narrative":"XPNPEP2 encodes a GPI-anchored, membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) that cleaves N-terminal Xaa-Pro bonds in peptide substrates including bradykinin and neuropeptide Y, functioning as a key enzyme in bradykinin catabolism [PMID:10894934, PMID:17223229]. The gene's promoter is regulated by an upstream enhancer containing the C-2399A polymorphism that differentially binds HNF4; the low-activity A allele reduces plasma aminopeptidase P activity and predisposes to ACE inhibitor-induced angioedema, with sex- and race-dependent penetrance [PMID:16175507, PMID:21898657, PMID:20625347]. Beyond peptidase activity, XPNPEP2 is essential for endothelial angiogenesis: it physically interacts with the mitochondrial carrier SLC25A6 and protects it from SIAH1-mediated proteasomal degradation, thereby maintaining mitochondrial ATP production and respiratory chain integrity; XPNPEP2 deletion in mice causes vascular pathology, impaired wound healing, and reduced tumor growth [PMID:41573684]."},"prefetch_data":{"uniprot":{"accession":"O43895","full_name":"Xaa-Pro aminopeptidase 2","aliases":["Aminoacylproline aminopeptidase","Membrane-bound aminopeptidase P","Membrane-bound APP","Membrane-bound AmP","mAmP","X-Pro aminopeptidase 2"],"length_aa":674,"mass_kda":75.6,"function":"Membrane-bound metalloprotease which catalyzes the removal of a penultimate prolyl residue from the N-termini of peptides, such as Arg-Pro-Pro. May play a role in the metabolism of the vasodilator bradykinin","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O43895/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/XPNPEP2","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/XPNPEP2","total_profiled":1310},"omim":[{"mim_id":"613553","title":"X-PROLYL AMINOPEPTIDASE 3; XPNPEP3","url":"https://www.omim.org/entry/613553"},{"mim_id":"610618","title":"ANGIOEDEMA, HEREDITARY, 3; HAE3","url":"https://www.omim.org/entry/610618"},{"mim_id":"602443","title":"X-PROLYL AMINOPEPTIDASE 1; XPNPEP1","url":"https://www.omim.org/entry/602443"},{"mim_id":"300909","title":"ANGIOEDEMA INDUCED BY ACE INHIBITORS, SUSCEPTIBILITY TO; AEACEI","url":"https://www.omim.org/entry/300909"},{"mim_id":"300145","title":"X-PROLYL AMINOPEPTIDASE 2; XPNPEP2","url":"https://www.omim.org/entry/300145"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":156.9},{"tissue":"kidney","ntpm":145.6}],"url":"https://www.proteinatlas.org/search/XPNPEP2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O43895","domains":[{"cath_id":"3.40.350.10","chopping":"51-196","consensus_level":"high","plddt":96.3274,"start":51,"end":196},{"cath_id":"3.40.350.10","chopping":"206-356","consensus_level":"medium","plddt":97.0611,"start":206,"end":356},{"cath_id":"3.90.230.10","chopping":"360-645","consensus_level":"medium","plddt":96.9926,"start":360,"end":645}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43895","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43895-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43895-F1-predicted_aligned_error_v6.png","plddt_mean":91.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XPNPEP2","jax_strain_url":"https://www.jax.org/strain/search?query=XPNPEP2"},"sequence":{"accession":"O43895","fasta_url":"https://rest.uniprot.org/uniprotkb/O43895.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43895/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43895"}},"corpus_meta":[{"pmid":"16175507","id":"PMC_16175507","title":"A variant in XPNPEP2 is associated with angioedema induced by angiotensin I-converting enzyme inhibitors.","date":"2005","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16175507","citation_count":101,"is_preprint":false},{"pmid":"25401373","id":"PMC_25401373","title":"Diagnosis and treatment of bradykinin-mediated angioedema: outcomes from an angioedema expert consensus meeting.","date":"2014","source":"International archives of allergy and immunology","url":"https://pubmed.ncbi.nlm.nih.gov/25401373","citation_count":81,"is_preprint":false},{"pmid":"17223229","id":"PMC_17223229","title":"Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4.","date":"2007","source":"Peptides","url":"https://pubmed.ncbi.nlm.nih.gov/17223229","citation_count":75,"is_preprint":false},{"pmid":"20625347","id":"PMC_20625347","title":"Sex-dependent and race-dependent association of XPNPEP2 C-2399A polymorphism with angiotensin-converting enzyme inhibitor-associated angioedema.","date":"2010","source":"Pharmacogenetics and genomics","url":"https://pubmed.ncbi.nlm.nih.gov/20625347","citation_count":68,"is_preprint":false},{"pmid":"10894934","id":"PMC_10894934","title":"Physical mapping of nine Xq translocation breakpoints and identification of XPNPEP2 as a premature ovarian failure candidate gene.","date":"2000","source":"Cytogenetics and cell genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10894934","citation_count":62,"is_preprint":false},{"pmid":"31040866","id":"PMC_31040866","title":"Identification of DNA-Methylated CpG Islands Associated With Gene Silencing in the Adult Body Tissues of the Ogye Chicken Using RNA-Seq and Reduced Representation Bisulfite Sequencing.","date":"2019","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31040866","citation_count":53,"is_preprint":false},{"pmid":"19178938","id":"PMC_19178938","title":"Genetic analysis of Factor XII and bradykinin 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MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/41514740","citation_count":0,"is_preprint":false},{"pmid":"41752838","id":"PMC_41752838","title":"Alteplase and Angioedema: Can Clinical Exome Sequencing Redefine the Paradigm?","date":"2026","source":"Life (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/41752838","citation_count":0,"is_preprint":false},{"pmid":"40236552","id":"PMC_40236552","title":"Development of a Cyclic TMTP1-Based PET Probe for Visualization of Hepatocellular Carcinoma.","date":"2025","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/40236552","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20850,"output_tokens":3144,"usd":0.054855},"stage2":{"model":"claude-opus-4-6","input_tokens":6493,"output_tokens":2060,"usd":0.125947},"total_usd":0.180802,"stage1_batch_id":"msgbatch_01BparvgRZ9S2LMidvaoo86K","stage2_batch_id":"msgbatch_01NkBfv9SVZWthhS7j6mU6G3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"XPNPEP2 encodes a membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) localized to chromosome Xq25, which hydrolyzes N-terminal Xaa-Pro bonds in oligopeptides including bradykinin; the gene is partially expressed even from a translocated X chromosome, suggesting partial escape from X inactivation.\",\n      \"method\": \"Chromosomal mapping with somatic cell hybrids, mRNA expression analysis in translocation-carrier fibroblasts, sequence homology to pita bread-fold metallopeptidase family\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct chromosomal localization and expression data from translocation carriers, single study\",\n      \"pmids\": [\"10894934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"XPNPEP2 (membrane aminopeptidase P) and XPNPEP1 (soluble aminopeptidase P) share conserved blocks corresponding to the proton shuttle and five divalent metal ligand binding sites characteristic of the pita bread-fold family (prototype: E. coli methionine aminopeptidase), indicating a common catalytic mechanism for Xaa-Pro hydrolysis.\",\n      \"method\": \"Sequence alignment and structural homology analysis across the pita bread-fold protein family\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — sequence-based functional inference with strong structural context, single study\",\n      \"pmids\": [\"10871044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A C-2399A single-nucleotide polymorphism (SNP) upstream of XPNPEP2 is associated with reduced plasma aminopeptidase P (APP) activity and increased incidence of ACE inhibitor-induced angioedema, placing XPNPEP2-encoded membrane APP as a key enzyme in bradykinin degradation during ACE inhibition.\",\n      \"method\": \"Variance-component QTL linkage analysis (genome-wide microsatellite scan), mutation screening, measured genotype analysis, case-control association study\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — linkage mapping plus functional APP activity assay plus case-control study, replicated in subsequent studies\",\n      \"pmids\": [\"16175507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Plasma APP (encoded by XPNPEP2) activity is significantly reduced in patients experiencing hypersensitivity reactions during hemodialysis with AN69 membrane under ACE inhibitor treatment, and the C-2399A SNP at the XPNPEP2 locus predicts APP activity; recombinant APP is nonspecifically inhibited by some ACE inhibitors in vitro.\",\n      \"method\": \"Plasma APP activity assay, variance component analysis of hemodialysis patients and relatives, genotyping, recombinant APP inhibition assay\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — enzymatic activity in patients and recombinant protein, single lab\",\n      \"pmids\": [\"17003818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XPNPEP2 (membrane aminopeptidase P) is among at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) potentially capable of cleaving neuropeptide Y (NPY) at N-terminal positions in plasma and brain, as demonstrated by selective inhibitor-based activity assays and MALDI-TOF mass spectrometry.\",\n      \"method\": \"Selective enzyme inhibitors, activity assays in brain extracts and human plasma, MALDI-TOF mass spectrometry\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical methods in parallel, single study\",\n      \"pmids\": [\"17223229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The XPNPEP2 C-2399A genotype associates with serum APP activity in both sexes, but APP activity is lower in men than in women independent of genotype; the A allele is specifically associated with increased risk of ACE inhibitor-induced angioedema in men (and particularly black men), revealing sex- and race-dependent effects of XPNPEP2 on bradykinin catabolism.\",\n      \"method\": \"Genotyping, serum APP activity measurement, multivariate case-control analysis (169 cases, 397 controls)\",\n      \"journal\": \"Pharmacogenetics and genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large case-control with biochemical activity measurements, replicates prior linkage finding with sex stratification\",\n      \"pmids\": [\"20625347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The XPNPEP2 promoter contains a minimal promoter region (-338 to -147 bp) and an enhancer region (-2,502 to -2,238 bp); the C-2399A SNP lies within the enhancer and differentially binds hepatic nuclear factor 4 (HNF4), which modulates transcriptional activation; the ATG haplotype (c.-2399A, c.-1612T, c.-393A) reduces promoter/reporter activity and plasma APP activity, and is significantly associated with ACE inhibitor-induced angioedema.\",\n      \"method\": \"Nested deletion luciferase reporter assays, HNF4 overexpression, haplotype association with plasma APP activity and angioedema case-control study\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional promoter dissection with reporter assays, transcription factor overexpression, and clinical association, multiple orthogonal methods in one study\",\n      \"pmids\": [\"21898657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In rat ovarian development, Xpnpep2 expression is increased during CrVI-induced germ cell nest breakdown and decreased during postnatal follicle development; Xpnpep2 colocalizes with collagen types 3 and 4 and inversely regulates expression of Col1, Col3, and Col4 at multiple developmental stages, linking Xpnpep2 enzymatic activity to extracellular matrix remodeling in the ovary.\",\n      \"method\": \"Gestational CrVI exposure model, immunofluorescence colocalization, developmental stage-specific protein/mRNA expression analysis in rat ovaries\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple developmental time points, colocalization data, but mechanistic link to collagen regulation is correlative, single lab\",\n      \"pmids\": [\"25568306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"XPNPEP2 overexpression in cervical cancer cells (SiHa and HeLa) promotes cell invasion and migration without affecting proliferation or apoptosis, and induces epithelial-mesenchymal transition (EMT); XPNPEP2 also promotes tumor metastasis in xenograft mouse models.\",\n      \"method\": \"Overexpression in cancer cell lines, invasion/migration assays, EMT marker analysis, xenograft mouse metastasis model\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss/gain of function with defined phenotypic readout in vitro and in vivo, single lab\",\n      \"pmids\": [\"28670957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mutagenesis studies of bacterial small aminopeptidases-P (structural orthologs of human XPNPEP1/XPNPEP2) illuminate the importance of the DXRY sequence motif for aminopeptidase-P activity, and crystal structures confirm that absence of a dipeptide-selectivity loop distinguishes aminopeptidases-P from prolidases, suggesting common evolutionary origin with human XPNPEP2.\",\n      \"method\": \"Crystal structure determination of bacterial orthologs, site-directed mutagenesis, enzymatic substrate specificity assays\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures plus mutagenesis plus enzymatic assays, but on bacterial orthologs not human XPNPEP2 directly\",\n      \"pmids\": [\"30536999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XPNPEP2 is identified as the cell-surface receptor for the tumor-homing peptide TMTP1, which selectively targets highly metastatic tumor cells; serum XPNPEP2 exists in a secreted form detectable by Western blot, and elevated serum XPNPEP2 associates with lymph node metastasis in prostate cancer.\",\n      \"method\": \"Western blot (secreted form in serum), tissue array, IHC, ELISA in patient cohorts, receptor identification for TMTP1 peptide\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — receptor identification noted but not mechanistically validated with binding assays; secreted form shown by Western blot only\",\n      \"pmids\": [\"31296901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"XPNPEP2 is essential for endothelial cell (EC) angiogenesis: XPNPEP2 deletion impairs EC proliferation, migration, and tubulogenesis in vitro, causes pathological changes in pulmonary artery wall, renal tissue, and retinal vasculature, and slows wound healing and tumor growth in mice. XPNPEP2 physically interacts with SLC25A6 (mitochondrial ADP/ATP carrier); XPNPEP2 deficiency reduces SLC25A6 via SIAH1-mediated ubiquitin-proteasomal degradation, leading to dysfunctional mitochondria (insufficient ATP, excess mROS, disrupted respiratory chain). Overexpression of XPNPEP2 rescues impaired angiogenesis and restores SLC25A6.\",\n      \"method\": \"XPNPEP2 KO mouse model, shRNA knockdown in ECs, co-immunoprecipitation (XPNPEP2–SLC25A6 interaction), SIAH1 ubiquitin degradation assay, mitochondrial function assays (ATP, mROS, respiration), tubulogenesis/migration assays, in vivo wound healing and tumor growth models\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO mouse plus in vitro KD plus Co-IP plus mechanistic rescue experiments, multiple orthogonal methods in one study\",\n      \"pmids\": [\"41573684\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XPNPEP2 encodes a GPI-anchored membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) that degrades bradykinin and related proline-containing peptides; its promoter is regulated by HNF4 via an upstream enhancer, and loss-of-function variants reduce plasma APP activity and predispose to bradykinin-mediated angioedema; in endothelial cells, XPNPEP2 is also required for angiogenesis by physically interacting with the mitochondrial carrier SLC25A6 and protecting it from SIAH1-mediated proteasomal degradation, thereby maintaining mitochondrial function.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"XPNPEP2 encodes a GPI-anchored, membrane-bound Xaa-Pro aminopeptidase (aminopeptidase P) that cleaves N-terminal Xaa-Pro bonds in peptide substrates including bradykinin and neuropeptide Y, functioning as a key enzyme in bradykinin catabolism [PMID:10894934, PMID:17223229]. The gene's promoter is regulated by an upstream enhancer containing the C-2399A polymorphism that differentially binds HNF4; the low-activity A allele reduces plasma aminopeptidase P activity and predisposes to ACE inhibitor-induced angioedema, with sex- and race-dependent penetrance [PMID:16175507, PMID:21898657, PMID:20625347]. Beyond peptidase activity, XPNPEP2 is essential for endothelial angiogenesis: it physically interacts with the mitochondrial carrier SLC25A6 and protects it from SIAH1-mediated proteasomal degradation, thereby maintaining mitochondrial ATP production and respiratory chain integrity; XPNPEP2 deletion in mice causes vascular pathology, impaired wound healing, and reduced tumor growth [PMID:41573684].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying XPNPEP2 as the gene encoding membrane-bound aminopeptidase P at Xq25 established the molecular basis for a previously characterized enzymatic activity that cleaves Xaa-Pro bonds in bradykinin.\",\n      \"evidence\": \"Chromosomal mapping with somatic cell hybrids, expression analysis in X-translocation carrier fibroblasts, and sequence homology to the pita bread-fold metallopeptidase family\",\n      \"pmids\": [\"10894934\", \"10871044\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No direct structural data for human XPNPEP2 protein\",\n        \"Mechanism of partial X-inactivation escape not resolved\",\n        \"Physiological substrates beyond bradykinin not systematically catalogued\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Linking the C-2399A upstream polymorphism to reduced plasma APP activity and ACE inhibitor-induced angioedema established XPNPEP2 as a pharmacogenomic determinant of bradykinin-mediated adverse drug reactions.\",\n      \"evidence\": \"Genome-wide microsatellite QTL linkage analysis, mutation screening, measured genotype analysis, and case-control association in angioedema patients\",\n      \"pmids\": [\"16175507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Causal mechanism by which the SNP reduces expression not yet defined\",\n        \"Contribution of other bradykinin-degrading enzymes to angioedema risk not quantified\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating sex- and race-dependent effects of the XPNPEP2 C-2399A genotype on APP activity and angioedema risk revealed that genetic regulation of bradykinin catabolism is modified by non-genetic factors.\",\n      \"evidence\": \"Serum APP activity measurement and multivariate case-control analysis (169 cases, 397 controls) with sex and race stratification\",\n      \"pmids\": [\"20625347\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Biological basis for lower APP activity in men versus women unknown\",\n        \"Interaction between XPNPEP2 genotype and hormonal regulation not tested\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Functional dissection of the XPNPEP2 promoter showed that HNF4 binds the C-2399A enhancer region and that the risk haplotype reduces transcriptional activity, providing a molecular mechanism for genotype-dependent variation in APP expression.\",\n      \"evidence\": \"Nested deletion luciferase reporter assays, HNF4 overexpression, and haplotype association with plasma APP activity and angioedema\",\n      \"pmids\": [\"21898657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Chromatin context and tissue-specific enhancer activity not examined in endogenous locus\",\n        \"Whether other transcription factors co-regulate this enhancer is unknown\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing that XPNPEP2 overexpression promotes invasion, migration, and EMT in cervical cancer cells extended XPNPEP2 function beyond peptide catabolism to a role in tumor metastasis.\",\n      \"evidence\": \"Overexpression in SiHa and HeLa cells, invasion/migration assays, EMT marker analysis, and xenograft mouse metastasis model\",\n      \"pmids\": [\"28670957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the pro-metastatic effect requires aminopeptidase catalytic activity or a non-enzymatic mechanism is unresolved\",\n        \"Downstream signaling pathways linking XPNPEP2 to EMT not identified\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Demonstrating that XPNPEP2 is essential for endothelial angiogenesis through physical interaction with SLC25A6 and protection from SIAH1-mediated degradation revealed a non-catalytic, mitochondria-protective function distinct from its aminopeptidase activity.\",\n      \"evidence\": \"XPNPEP2 KO mouse, shRNA knockdown in ECs, co-immunoprecipitation of XPNPEP2–SLC25A6, SIAH1 ubiquitin degradation assay, mitochondrial function assays, and in vivo wound healing/tumor growth models\",\n      \"pmids\": [\"41573684\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the aminopeptidase catalytic domain is required for SLC25A6 binding is unknown\",\n        \"How a GPI-anchored surface protein accesses mitochondrial SLC25A6 is mechanistically unclear\",\n        \"Independent replication of the XPNPEP2–SLC25A6 interaction in other labs is pending\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XPNPEP2 integrates its dual roles as a bradykinin-degrading aminopeptidase and a non-enzymatic regulator of mitochondrial function in endothelial cells remains unresolved, as does whether its pro-metastatic activity is catalytic or structural.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural data for human XPNPEP2 protein to map interaction surfaces\",\n        \"Mechanism by which a GPI-anchored surface protein contacts intracellular SLC25A6 not defined\",\n        \"Relative contributions of enzymatic versus scaffolding functions to in vivo phenotypes untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 2, 4, 9]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 10, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 4, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 5, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SLC25A6\",\n      \"SIAH1\",\n      \"HNF4A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}