{"gene":"OPRPN","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1996,"finding":"OPRPN (BPLP) encodes a predicted 180-residue, 20546 Da secreted protein with 24.5% proline content, expressed abundantly in the human lacrimal gland secretory endpieces and at lower levels in the submandibular gland, as demonstrated by cDNA cloning, Northern blot, and in situ hybridization.","method":"cDNA cloning, Southern blot, Northern blot, in situ hybridization","journal":"Current eye research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct molecular characterization with multiple orthogonal methods (cDNA cloning, Northern blot, in situ hybridization) in a single study establishing protein identity and tissue-specific expression with subcellular localization to secretory endpieces","pmids":["8670737"],"is_preprint":false},{"year":2008,"finding":"ProL1 (PROL1/OPRPN) encodes a neutral endopeptidase (NEP) inhibitor peptide; intracorporal gene transfer of pVAX-ProL1 plasmid in rats produced a priapic-like condition with higher resting intracavernous pressure and improved ICP/BP ratio after cavernous nerve electrostimulation, demonstrating a functional role in erectile physiology.","method":"Intracorporal gene transfer in rats, intracavernous pressure measurement, histological analysis","journal":"BJU international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gene transfer with direct physiological measurement (ICP/BP), single lab, multiple readouts but no in vitro reconstitution of NEP inhibition for ProL1 specifically","pmids":["18410445"],"is_preprint":false},{"year":2008,"finding":"PROL1 (ProL1/OPRPN) is significantly downregulated in corpora cavernosa tissue from men with erectile dysfunction (both diabetic and non-diabetic), implicating it as a marker of erectile function.","method":"Quantitative gene expression analysis of corpora cavernosa tissue samples from ED patients vs. controls","journal":"BJU international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, expression comparison without direct mechanistic experiment on the protein itself","pmids":["18410445"],"is_preprint":false},{"year":2009,"finding":"The opiorphin peptide encoded by PROL1/OPRPN functions as an endogenous NEP inhibitor; sialorphin (rat ortholog) causes increased rates of relaxation of corporal smooth muscle (CSM) in organ bath studies, and Vcsa1 (rat ortholog) modulates expression of G-protein-coupled receptors in vitro, suggesting opiorphin prolongs action of peptide agonists at GPCRs by inhibiting NEP.","method":"Organ bath smooth muscle relaxation assay, in vitro GPCR expression studies","journal":"The journal of sexual medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic pathway proposed from rat ortholog data in organ bath assay; ProL1/OPRPN itself not directly tested in vitro for NEP inhibition in this review","pmids":["19267851"],"is_preprint":false},{"year":2011,"finding":"Opiorphin, the mature QRFSR pentapeptide product of PROL1/OPRPN, is detectable and quantifiable in human saliva at levels ranging 2.8–25.9 ng/ml, confirming that the OPRPN-encoded protein is processed to this active peptide in vivo.","method":"LC-MS/MS quantification of opiorphin in human saliva samples","journal":"Journal of chromatography. B","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct analytical detection of the mature peptide product in human biological fluid with validated method, single lab","pmids":["22119435"],"is_preprint":false},{"year":2014,"finding":"Intravenous opiorphin (encoded by PROL1/OPRPN) increases mean arterial pressure in conscious rats in a dose-dependent manner associated with elevated serum angiotensin II; this effect is blocked by the AngII receptor antagonist valsartan and partially attenuated by the ACE inhibitor captopril, placing opiorphin upstream of the renin-angiotensin system in blood pressure regulation.","method":"In vivo rat cannulation model, pharmacological blockade with valsartan and captopril, serum AngII ELISA","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological epistasis with receptor antagonist and enzyme inhibitor providing pathway placement, single lab","pmids":["24486428"],"is_preprint":false},{"year":2021,"finding":"PROL1 (OPRPN) overexpression in androgen-sensitive LNCaP prostate cancer cells enables tumor development in castrated male mice (unlike parental cells), and modulates expression of genes in angiogenesis, steroid, and hypoxic response pathways as determined by RNA sequencing.","method":"Xenograft tumor assay in castrated nude mice, RNA sequencing of overexpressing vs. parental cells","journal":"Future oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gain-of-function xenograft with defined phenotypic readout and transcriptomic pathway analysis, single lab","pmids":["33593085"],"is_preprint":false},{"year":2021,"finding":"PROL1 (OPRPN) knockout in LNCaP cells abolishes xenograft tumor formation in both castrated and intact male mice; PROL1 overexpression increases cell motility and invasion in wound closure and 3D spheroid invasion assays, and PROL1 loss alters expression of angiogenesis and cell motility pathway genes.","method":"CRISPR/gene knockout, xenograft assay, wound closure assay, 3D spheroid invasion assay, RNAseq","journal":"Journal of men's health","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional loss- and gain-of-function with multiple cellular assays and transcriptomic pathway analysis, single lab","pmids":["35547856"],"is_preprint":false},{"year":2023,"finding":"BMP-2 treatment of embryonic mouse salivary glands suppresses Prol1 (opiorphin/OPRPN ortholog) expression in a concentration-dependent manner via the Smad pathway, as demonstrated by organ culture with dorsomorphin rescue; this places Prol1 downstream of BMP-2/Smad signaling during salivary gland acinar differentiation.","method":"Organ culture of embryonic mouse salivary glands, BMP-2 treatment, dorsomorphin (Smad pathway inhibitor) rescue, gene expression analysis","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mouse ortholog in organ culture with pharmacological inhibitor rescue; Prol1 expression is a readout but its direct functional role in acinar differentiation not established","pmids":["37742472"],"is_preprint":false},{"year":2024,"finding":"TGF-β1 upregulates Prol1 (OPRPN ortholog) expression in embryonic mouse submandibular gland epithelia separated from mesenchyme, coinciding with maintained developmental potential; this is associated with SMAD2/3 phosphorylation, linking Prol1 to TGF-β/Smad-mediated salivary gland epithelial development.","method":"Ex vivo organ culture with epithelia-mesenchyme separation, TGF-β1 treatment, microarray, qRT-PCR, Western blot, immunofluorescence","journal":"Heliyon","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Prol1 upregulation is a correlative readout among multiple genes in the context of TGF-β/Smad signaling; no direct functional experiment on Prol1 protein itself","pmids":["39040362"],"is_preprint":false}],"current_model":"OPRPN (BPLP/PROL1) encodes a proline-rich secreted protein expressed in lacrimal and salivary glands that is proteolytically processed to the opiorphin pentapeptide (QRFSR), which acts as an endogenous neutral endopeptidase (NEP) inhibitor to prolong peptide agonist signaling at GPCRs, thereby modulating erectile physiology and blood pressure via the renin-angiotensin system; in prostate cancer cells, PROL1 is required for xenograft tumor growth and promotes cell migration and invasion by upregulating angiogenesis and motility-related gene pathways."},"narrative":{"mechanistic_narrative":"OPRPN (BPLP/PROL1) encodes a proline-rich secreted protein expressed abundantly in lacrimal gland secretory endpieces and, more weakly, in the submandibular gland [PMID:8670737]. The protein is proteolytically processed in vivo to the opiorphin pentapeptide (QRFSR), which is detectable in human saliva [PMID:22119435] and functions as an endogenous neutral endopeptidase (NEP) inhibitor [PMID:18410445]. Through this activity, opiorphin influences physiological signaling in two arenas: in erectile physiology, intracorporal ProL1 gene transfer raises resting intracavernous pressure and improves the ICP/BP ratio [PMID:18410445], and in systemic blood pressure regulation, intravenous opiorphin dose-dependently raises mean arterial pressure with elevated serum angiotensin II, an effect blocked by the AngII receptor antagonist valsartan and attenuated by ACE inhibition, placing it upstream of the renin-angiotensin system [PMID:24486428]. Independently of its secreted peptide role, OPRPN is required for prostate cancer tumorigenicity: knockout in LNCaP cells abolishes xenograft tumor formation while overexpression enables tumor growth in castrated mice and increases cell motility and invasion, accompanied by transcriptional remodeling of angiogenesis, motility, steroid, and hypoxic-response gene pathways [PMID:33593085, PMID:35547856].","teleology":[{"year":1996,"claim":"Established the molecular identity of OPRPN as a proline-rich secreted protein and localized its expression to exocrine gland secretory tissue, defining it as a candidate secretory product.","evidence":"cDNA cloning, Northern blot, and in situ hybridization in human lacrimal and submandibular gland","pmids":["8670737"],"confidence":"Medium","gaps":["Function of the full-length protein not addressed","No characterization of post-translational processing into bioactive fragments"]},{"year":2008,"claim":"Linked OPRPN/ProL1 to erectile physiology by showing in vivo that its gene transfer alters cavernous pressure, and proposed it acts as a NEP inhibitor.","evidence":"Intracorporal pVAX-ProL1 gene transfer in rats with intracavernous pressure measurement; expression downregulated in human ED tissue","pmids":["18410445"],"confidence":"Medium","gaps":["No in vitro reconstitution of NEP inhibition for ProL1 itself","Expression downregulation in ED is correlative","Molecular target prolonged by NEP inhibition not directly identified"]},{"year":2009,"claim":"Articulated the mechanistic model that the opiorphin peptide inhibits NEP to prolong peptide agonist action at GPCRs, using rat orthologs.","evidence":"Organ bath corporal smooth muscle relaxation assay with sialorphin and in vitro GPCR expression studies with Vcsa1 (rat orthologs)","pmids":["19267851"],"confidence":"Low","gaps":["ProL1/OPRPN itself not directly tested for NEP inhibition in this work","Inference rests on rat ortholog behavior","Specific GPCRs and peptide agonists involved not defined"]},{"year":2011,"claim":"Confirmed that the OPRPN-encoded protein is processed to the mature opiorphin pentapeptide in humans by detecting and quantifying it in saliva.","evidence":"LC-MS/MS quantification of opiorphin in human saliva","pmids":["22119435"],"confidence":"Medium","gaps":["Processing enzymes generating opiorphin not identified","Physiological concentration at sites of action not established"]},{"year":2014,"claim":"Placed opiorphin upstream of the renin-angiotensin system in blood pressure control through pharmacological epistasis.","evidence":"In vivo rat cannulation with valsartan and captopril blockade and serum AngII ELISA","pmids":["24486428"],"confidence":"Medium","gaps":["Direct molecular link between NEP inhibition and AngII elevation not resolved","Single species and single lab"]},{"year":2021,"claim":"Revealed a cell-autonomous oncogenic role distinct from the secreted-peptide function, showing OPRPN is necessary and sufficient for prostate cancer xenograft growth and drives invasion.","evidence":"Overexpression and CRISPR knockout in LNCaP cells, xenograft assays in castrated and intact mice, wound closure and 3D spheroid invasion assays, RNAseq","pmids":["33593085","35547856"],"confidence":"Medium","gaps":["Molecular mechanism connecting OPRPN to angiogenesis/motility transcriptional changes unknown","Whether the effect requires opiorphin processing or full-length protein not determined","Single cell line and single lab"]},{"year":2023,"claim":"Positioned Prol1 expression as a target of BMP-2/Smad signaling during salivary gland development.","evidence":"Organ culture of embryonic mouse salivary glands with BMP-2 treatment and dorsomorphin rescue (ortholog)","pmids":["37742472"],"confidence":"Low","gaps":["Prol1 measured as a readout; its functional role in acinar differentiation not established","Mouse ortholog in organ culture only"]},{"year":2024,"claim":"Connected Prol1 expression to TGF-β1/SMAD2/3 signaling in submandibular gland epithelial development.","evidence":"Ex vivo epithelia-mesenchyme separation organ culture with TGF-β1, microarray, qRT-PCR, Western blot (ortholog)","pmids":["39040362"],"confidence":"Low","gaps":["Prol1 is one correlative readout among many genes","No direct functional experiment on Prol1 protein","Mouse ortholog only"]},{"year":null,"claim":"Whether the secreted opiorphin/NEP-inhibitor activity and the cell-autonomous oncogenic role in prostate cancer share a common molecular mechanism, and the direct NEP-inhibition kinetics of the human peptide, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No biochemical reconstitution of human opiorphin NEP inhibition","No mechanistic link between secreted-peptide function and intracellular tumor-promoting function","No structural model of the protein or peptide-target complex"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q99935","full_name":"Opiorphin prepropeptide","aliases":["Basic proline-rich lacrimal protein","Proline-rich protein 1","PRL1"],"length_aa":248,"mass_kda":27.2,"function":"Opiorphin is an endogenous inhibitor of neprilysin and aminopeptidase N. Inhibits the breakdown of substance P, Mca-BK2 and Met-enkephalin by neprilysin in vitro with IC(50) values of 29 uM, 33 uM and 33 uM respectively. Inhibits the breakdown of Ala-pNA by aminopeptidase N in vitro with an IC(50) of 65 uM. Has a potent analgesic effect when administered to rats by intravenous injection","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q99935/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/OPRPN","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/OPRPN","total_profiled":1310},"omim":[{"mim_id":"608936","title":"OPIORPHIN PREPROPEPTIDE; OPRPN","url":"https://www.omim.org/entry/608936"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"salivary gland","ntpm":145.4}],"url":"https://www.proteinatlas.org/search/OPRPN"},"hgnc":{"alias_symbol":["BPLP","PRL1"],"prev_symbol":["PROL1"]},"alphafold":{"accession":"Q99935","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99935","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99935-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99935-F1-predicted_aligned_error_v6.png","plddt_mean":52.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=OPRPN","jax_strain_url":"https://www.jax.org/strain/search?query=OPRPN"},"sequence":{"accession":"Q99935","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99935.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99935/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99935"}},"corpus_meta":[{"pmid":"31444327","id":"PMC_31444327","title":"The regulatory landscape of a core maize domestication module controlling bud dormancy and growth repression.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31444327","citation_count":130,"is_preprint":false},{"pmid":"30478052","id":"PMC_30478052","title":"Citrate-based materials fuel human stem cells by metabonegenic regulation.","date":"2018","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/30478052","citation_count":95,"is_preprint":false},{"pmid":"23825971","id":"PMC_23825971","title":"From many, one: genetic control of prolificacy during maize domestication.","date":"2013","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23825971","citation_count":86,"is_preprint":false},{"pmid":"25829418","id":"PMC_25829418","title":"Proteomics Differentiate Between Thyroid-Associated Orbitopathy and Dry Eye Syndrome.","date":"2015","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/25829418","citation_count":68,"is_preprint":false},{"pmid":"28026115","id":"PMC_28026115","title":"Immune Cell-Mediated Biodegradable Theranostic Nanoparticles for Melanoma Targeting and Drug Delivery.","date":"2016","source":"Small (Weinheim an der Bergstrasse, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/28026115","citation_count":58,"is_preprint":false},{"pmid":"18410445","id":"PMC_18410445","title":"The opiorphin gene (ProL1) and its homologues function in erectile physiology.","date":"2008","source":"BJU international","url":"https://pubmed.ncbi.nlm.nih.gov/18410445","citation_count":43,"is_preprint":false},{"pmid":"23710326","id":"PMC_23710326","title":"Design Strategies for Fluorescent Biodegradable Polymeric Biomaterials.","date":"2013","source":"Journal of materials chemistry. 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Isolation and characterization of two prolactin-like cDNA clones.","date":"1990","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2341410","citation_count":24,"is_preprint":false},{"pmid":"19267851","id":"PMC_19267851","title":"The role of opiorphins (endogenous neutral endopeptidase inhibitors) in urogenital smooth muscle biology.","date":"2009","source":"The journal of sexual medicine","url":"https://pubmed.ncbi.nlm.nih.gov/19267851","citation_count":21,"is_preprint":false},{"pmid":"8670737","id":"PMC_8670737","title":"cDNA cloning of an abundant human lacrimal gland mRNA encoding a novel tear protein.","date":"1996","source":"Current eye research","url":"https://pubmed.ncbi.nlm.nih.gov/8670737","citation_count":20,"is_preprint":false},{"pmid":"2015300","id":"PMC_2015300","title":"A novel cDNA clone encoding a prolactin-like protein that lacks the two C-terminal cysteine residues isolated from bovine placenta.","date":"1991","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/2015300","citation_count":19,"is_preprint":false},{"pmid":"2736246","id":"PMC_2736246","title":"Isolation of a novel prolactin-like cDNA clone from bovine placenta: occurrence of new family members.","date":"1989","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/2736246","citation_count":16,"is_preprint":false},{"pmid":"25632019","id":"PMC_25632019","title":"Calcium-binding protein, spermatid-specific 1 is expressed in human salivary glands and contains an anti-inflammatory motif.","date":"2015","source":"American journal of physiology. 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cloning, Southern blot, Northern blot, in situ hybridization\",\n      \"journal\": \"Current eye research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct molecular characterization with multiple orthogonal methods (cDNA cloning, Northern blot, in situ hybridization) in a single study establishing protein identity and tissue-specific expression with subcellular localization to secretory endpieces\",\n      \"pmids\": [\"8670737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ProL1 (PROL1/OPRPN) encodes a neutral endopeptidase (NEP) inhibitor peptide; intracorporal gene transfer of pVAX-ProL1 plasmid in rats produced a priapic-like condition with higher resting intracavernous pressure and improved ICP/BP ratio after cavernous nerve electrostimulation, demonstrating a functional role in erectile physiology.\",\n      \"method\": \"Intracorporal gene transfer in rats, intracavernous pressure measurement, histological analysis\",\n      \"journal\": \"BJU international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gene transfer with direct physiological measurement (ICP/BP), single lab, multiple readouts but no in vitro reconstitution of NEP inhibition for ProL1 specifically\",\n      \"pmids\": [\"18410445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PROL1 (ProL1/OPRPN) is significantly downregulated in corpora cavernosa tissue from men with erectile dysfunction (both diabetic and non-diabetic), implicating it as a marker of erectile function.\",\n      \"method\": \"Quantitative gene expression analysis of corpora cavernosa tissue samples from ED patients vs. controls\",\n      \"journal\": \"BJU international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, expression comparison without direct mechanistic experiment on the protein itself\",\n      \"pmids\": [\"18410445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The opiorphin peptide encoded by PROL1/OPRPN functions as an endogenous NEP inhibitor; sialorphin (rat ortholog) causes increased rates of relaxation of corporal smooth muscle (CSM) in organ bath studies, and Vcsa1 (rat ortholog) modulates expression of G-protein-coupled receptors in vitro, suggesting opiorphin prolongs action of peptide agonists at GPCRs by inhibiting NEP.\",\n      \"method\": \"Organ bath smooth muscle relaxation assay, in vitro GPCR expression studies\",\n      \"journal\": \"The journal of sexual medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic pathway proposed from rat ortholog data in organ bath assay; ProL1/OPRPN itself not directly tested in vitro for NEP inhibition in this review\",\n      \"pmids\": [\"19267851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Opiorphin, the mature QRFSR pentapeptide product of PROL1/OPRPN, is detectable and quantifiable in human saliva at levels ranging 2.8–25.9 ng/ml, confirming that the OPRPN-encoded protein is processed to this active peptide in vivo.\",\n      \"method\": \"LC-MS/MS quantification of opiorphin in human saliva samples\",\n      \"journal\": \"Journal of chromatography. B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct analytical detection of the mature peptide product in human biological fluid with validated method, single lab\",\n      \"pmids\": [\"22119435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Intravenous opiorphin (encoded by PROL1/OPRPN) increases mean arterial pressure in conscious rats in a dose-dependent manner associated with elevated serum angiotensin II; this effect is blocked by the AngII receptor antagonist valsartan and partially attenuated by the ACE inhibitor captopril, placing opiorphin upstream of the renin-angiotensin system in blood pressure regulation.\",\n      \"method\": \"In vivo rat cannulation model, pharmacological blockade with valsartan and captopril, serum AngII ELISA\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological epistasis with receptor antagonist and enzyme inhibitor providing pathway placement, single lab\",\n      \"pmids\": [\"24486428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PROL1 (OPRPN) overexpression in androgen-sensitive LNCaP prostate cancer cells enables tumor development in castrated male mice (unlike parental cells), and modulates expression of genes in angiogenesis, steroid, and hypoxic response pathways as determined by RNA sequencing.\",\n      \"method\": \"Xenograft tumor assay in castrated nude mice, RNA sequencing of overexpressing vs. parental cells\",\n      \"journal\": \"Future oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gain-of-function xenograft with defined phenotypic readout and transcriptomic pathway analysis, single lab\",\n      \"pmids\": [\"33593085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PROL1 (OPRPN) knockout in LNCaP cells abolishes xenograft tumor formation in both castrated and intact male mice; PROL1 overexpression increases cell motility and invasion in wound closure and 3D spheroid invasion assays, and PROL1 loss alters expression of angiogenesis and cell motility pathway genes.\",\n      \"method\": \"CRISPR/gene knockout, xenograft assay, wound closure assay, 3D spheroid invasion assay, RNAseq\",\n      \"journal\": \"Journal of men's health\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional loss- and gain-of-function with multiple cellular assays and transcriptomic pathway analysis, single lab\",\n      \"pmids\": [\"35547856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"BMP-2 treatment of embryonic mouse salivary glands suppresses Prol1 (opiorphin/OPRPN ortholog) expression in a concentration-dependent manner via the Smad pathway, as demonstrated by organ culture with dorsomorphin rescue; this places Prol1 downstream of BMP-2/Smad signaling during salivary gland acinar differentiation.\",\n      \"method\": \"Organ culture of embryonic mouse salivary glands, BMP-2 treatment, dorsomorphin (Smad pathway inhibitor) rescue, gene expression analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mouse ortholog in organ culture with pharmacological inhibitor rescue; Prol1 expression is a readout but its direct functional role in acinar differentiation not established\",\n      \"pmids\": [\"37742472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TGF-β1 upregulates Prol1 (OPRPN ortholog) expression in embryonic mouse submandibular gland epithelia separated from mesenchyme, coinciding with maintained developmental potential; this is associated with SMAD2/3 phosphorylation, linking Prol1 to TGF-β/Smad-mediated salivary gland epithelial development.\",\n      \"method\": \"Ex vivo organ culture with epithelia-mesenchyme separation, TGF-β1 treatment, microarray, qRT-PCR, Western blot, immunofluorescence\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Prol1 upregulation is a correlative readout among multiple genes in the context of TGF-β/Smad signaling; no direct functional experiment on Prol1 protein itself\",\n      \"pmids\": [\"39040362\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"OPRPN (BPLP/PROL1) encodes a proline-rich secreted protein expressed in lacrimal and salivary glands that is proteolytically processed to the opiorphin pentapeptide (QRFSR), which acts as an endogenous neutral endopeptidase (NEP) inhibitor to prolong peptide agonist signaling at GPCRs, thereby modulating erectile physiology and blood pressure via the renin-angiotensin system; in prostate cancer cells, PROL1 is required for xenograft tumor growth and promotes cell migration and invasion by upregulating angiogenesis and motility-related gene pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"OPRPN (BPLP/PROL1) encodes a proline-rich secreted protein expressed abundantly in lacrimal gland secretory endpieces and, more weakly, in the submandibular gland [#0]. The protein is proteolytically processed in vivo to the opiorphin pentapeptide (QRFSR), which is detectable in human saliva [#4] and functions as an endogenous neutral endopeptidase (NEP) inhibitor [#1]. Through this activity, opiorphin influences physiological signaling in two arenas: in erectile physiology, intracorporal ProL1 gene transfer raises resting intracavernous pressure and improves the ICP/BP ratio [#1], and in systemic blood pressure regulation, intravenous opiorphin dose-dependently raises mean arterial pressure with elevated serum angiotensin II, an effect blocked by the AngII receptor antagonist valsartan and attenuated by ACE inhibition, placing it upstream of the renin-angiotensin system [#5]. Independently of its secreted peptide role, OPRPN is required for prostate cancer tumorigenicity: knockout in LNCaP cells abolishes xenograft tumor formation while overexpression enables tumor growth in castrated mice and increases cell motility and invasion, accompanied by transcriptional remodeling of angiogenesis, motility, steroid, and hypoxic-response gene pathways [#6, #7].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established the molecular identity of OPRPN as a proline-rich secreted protein and localized its expression to exocrine gland secretory tissue, defining it as a candidate secretory product.\",\n      \"evidence\": \"cDNA cloning, Northern blot, and in situ hybridization in human lacrimal and submandibular gland\",\n      \"pmids\": [\"8670737\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Function of the full-length protein not addressed\",\n        \"No characterization of post-translational processing into bioactive fragments\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked OPRPN/ProL1 to erectile physiology by showing in vivo that its gene transfer alters cavernous pressure, and proposed it acts as a NEP inhibitor.\",\n      \"evidence\": \"Intracorporal pVAX-ProL1 gene transfer in rats with intracavernous pressure measurement; expression downregulated in human ED tissue\",\n      \"pmids\": [\"18410445\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No in vitro reconstitution of NEP inhibition for ProL1 itself\",\n        \"Expression downregulation in ED is correlative\",\n        \"Molecular target prolonged by NEP inhibition not directly identified\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Articulated the mechanistic model that the opiorphin peptide inhibits NEP to prolong peptide agonist action at GPCRs, using rat orthologs.\",\n      \"evidence\": \"Organ bath corporal smooth muscle relaxation assay with sialorphin and in vitro GPCR expression studies with Vcsa1 (rat orthologs)\",\n      \"pmids\": [\"19267851\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"ProL1/OPRPN itself not directly tested for NEP inhibition in this work\",\n        \"Inference rests on rat ortholog behavior\",\n        \"Specific GPCRs and peptide agonists involved not defined\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Confirmed that the OPRPN-encoded protein is processed to the mature opiorphin pentapeptide in humans by detecting and quantifying it in saliva.\",\n      \"evidence\": \"LC-MS/MS quantification of opiorphin in human saliva\",\n      \"pmids\": [\"22119435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Processing enzymes generating opiorphin not identified\",\n        \"Physiological concentration at sites of action not established\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed opiorphin upstream of the renin-angiotensin system in blood pressure control through pharmacological epistasis.\",\n      \"evidence\": \"In vivo rat cannulation with valsartan and captopril blockade and serum AngII ELISA\",\n      \"pmids\": [\"24486428\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct molecular link between NEP inhibition and AngII elevation not resolved\",\n        \"Single species and single lab\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed a cell-autonomous oncogenic role distinct from the secreted-peptide function, showing OPRPN is necessary and sufficient for prostate cancer xenograft growth and drives invasion.\",\n      \"evidence\": \"Overexpression and CRISPR knockout in LNCaP cells, xenograft assays in castrated and intact mice, wound closure and 3D spheroid invasion assays, RNAseq\",\n      \"pmids\": [\"33593085\", \"35547856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular mechanism connecting OPRPN to angiogenesis/motility transcriptional changes unknown\",\n        \"Whether the effect requires opiorphin processing or full-length protein not determined\",\n        \"Single cell line and single lab\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Positioned Prol1 expression as a target of BMP-2/Smad signaling during salivary gland development.\",\n      \"evidence\": \"Organ culture of embryonic mouse salivary glands with BMP-2 treatment and dorsomorphin rescue (ortholog)\",\n      \"pmids\": [\"37742472\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Prol1 measured as a readout; its functional role in acinar differentiation not established\",\n        \"Mouse ortholog in organ culture only\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected Prol1 expression to TGF-\\u03b21/SMAD2/3 signaling in submandibular gland epithelial development.\",\n      \"evidence\": \"Ex vivo epithelia-mesenchyme separation organ culture with TGF-\\u03b21, microarray, qRT-PCR, Western blot (ortholog)\",\n      \"pmids\": [\"39040362\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Prol1 is one correlative readout among many genes\",\n        \"No direct functional experiment on Prol1 protein\",\n        \"Mouse ortholog only\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether the secreted opiorphin/NEP-inhibitor activity and the cell-autonomous oncogenic role in prostate cancer share a common molecular mechanism, and the direct NEP-inhibition kinetics of the human peptide, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No biochemical reconstitution of human opiorphin NEP inhibition\",\n        \"No mechanistic link between secreted-peptide function and intracellular tumor-promoting function\",\n        \"No structural model of the protein or peptide-target complex\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}