{"gene":"PCSK5","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":1993,"finding":"PC5 (PCSK5) was identified as a subtilisin/kexin-like proprotein convertase encoded by multiple mRNAs, with a C-terminal Cys-rich domain, expressed in endocrine and non-endocrine tissues; its closest homologue is PACE4, and cAMP upregulates its expression in adrenocortical cells.","method":"RT-PCR, cDNA cloning, Northern blotting, in situ hybridization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — original cloning and structural characterization with multiple methods in founding paper","pmids":["8341687"],"is_preprint":false},{"year":1994,"finding":"PC6 (PCSK5) can proteolytically activate the hemagglutinin of virulent avian influenza viruses at authentic cleavage sites, functioning similarly to furin, as demonstrated in furin-deficient LoVo cells complemented with PC6.","method":"Vaccinia virus expression in LoVo cells (furin-deficient), rescue of viral replication, cleavage site mutant analysis","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 — direct enzymatic activity demonstrated in cell-based reconstitution with authentic viral substrate","pmids":["8057485"],"is_preprint":false},{"year":1995,"finding":"PC5 (PCSK5) cannot process rat prosomatostatin into somatostatin-14 or somatostatin-28 in either constitutive (LoVo) or regulated (AtT-20) secretory cell lines, unlike PC1, PC2, furin, and PACE4.","method":"Recombinant vaccinia virus co-expression, gel-permeation HPLC analysis of processed products","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — direct in-cell enzymatic assay with multiple convertase comparisons","pmids":["7720860"],"is_preprint":false},{"year":1995,"finding":"The PCSK5 gene was mapped to mouse chromosome 19 and human chromosome 9.","method":"RFLP analysis of backcross DNA panel, Southern blot of somatic cell hybrid DNA panel","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — direct chromosomal mapping by two complementary methods","pmids":["7782070"],"is_preprint":false},{"year":1996,"finding":"PC5 (PCSK5) generates two isoforms, PC5-A (soluble, 915 aa) and PC5-B (membrane-bound, 1877 aa), that are sorted to distinct subcellular compartments: PC5-A to regulated secretory granules (including glucagon-containing granules in pancreatic cells) and PC5-B to the Golgi. A C-terminal 38-amino-acid segment in PC5-A is required for entry into the regulated secretory pathway.","method":"Stable transfection of AtT-20 cells, biosynthetic analyses, immunofluorescence, electron microscopy immunohistochemistry of pancreatic cells, C-terminal deletion mutagenesis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (biochemical, cell biological, ultrastructural) with mutagenesis in a single study","pmids":["8947550"],"is_preprint":false},{"year":1996,"finding":"PC5 (PCSK5) cleaves receptor protein tyrosine phosphatase mu (RPTPmu) at its RXK/RR motif; active-site serine-to-alanine mutant PC5 lacks this activity; PACE4 does not cleave RPTPmu; PC5 mRNA is upregulated >30-fold at confluence in human umbilical vein endothelial cells.","method":"COS cell co-transfection with RPTPmu and PC5 or PACE4 expression plasmids, immunoblotting, active-site mutagenesis (Ser→Ala), RNA blot analysis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis confirms catalytic requirement, combined with substrate identification by co-transfection","pmids":["8620001"],"is_preprint":false},{"year":1996,"finding":"PC5 (PCSK5) can process human prorenin into active renin dependent on the dibasic amino acids at positions 42/43 of the prorenin prosegment; this processing occurs only in cells with dense-core secretory granules (GH4C1 cells) and PC5 co-localizes with renin in the zona glomerulosa of human adrenal cortex.","method":"Co-transfection of prorenin and PC5 in GH4C1 cells, prorenin site-directed mutants, immunohistochemistry","journal":"Hypertension","confidence":"High","confidence_rationale":"Tier 1-2 — enzymatic processing shown by co-transfection with mutagenesis of cleavage site, plus in vivo co-localization","pmids":["8901832"],"is_preprint":false},{"year":1996,"finding":"Human PC6A and PC6B isoforms of PCSK5 are expressed in human CD4+ T lymphocytes and are candidate proteases for HIV-1 gp160 processing in these cells, which are competent for infectious virion production.","method":"RT-PCR, Northern blot analysis, comparison with furin-deficient LoVo cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 — expression-based candidate identification without direct enzymatic reconstitution of gp160 cleavage","pmids":["8755538"],"is_preprint":false},{"year":1996,"finding":"The human PCSK5 gene was mapped to chromosome 9q21.3 near markers D9S175 and D9S276.","method":"Somatic cell hybrid analysis, YAC clone analysis, fluorescence in situ hybridization (FISH)","journal":"Cytogenetics and cell genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct chromosomal localization by three orthogonal methods","pmids":["9067430"],"is_preprint":false},{"year":1998,"finding":"PC5-A (PCSK5) functions as a prohormone convertase in the regulated secretory pathway; in PC12 cells it processes pro-neurotensin/neuromedin N in early compartments of the regulated secretory pathway according to a pattern resembling adrenal medulla processing and distinct from PC1 and PC2.","method":"Stable transfection of PC12 cells with PC5-A, metabolic labeling, immunochemical studies, subcellular fractionation, co-localization with immunoreactive neurotensin","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean overexpression system with direct demonstration of prohormone processing and subcellular co-localization","pmids":["9738000"],"is_preprint":false},{"year":1998,"finding":"BMP-4 is proteolytically activated by furin and/or PC6 (PCSK5) during vertebrate embryogenesis; in Xenopus oocytes, both furin and PC6B cleave BMP-4 at its RSKR site and are sensitive to the inhibitor alpha1-PDX.","method":"Xenopus oocyte translation assay, in vitro digestion assay with PC family members, ectopic expression of alpha1-antitrypsin Portland (alpha1-PDX) in embryos, epistasis with downstream BMP pathway components","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro cleavage assay plus in vivo epistasis with inhibitor, multiple orthogonal methods","pmids":["9707432"],"is_preprint":false},{"year":1999,"finding":"PC5-A (PCSK5) immunoreactivity in rat brain neurons is concentrated in the Golgi apparatus and small vesicular elements in perikarya and dendrites, but not in axons or astrocytes, consistent with activity in early compartments of the neuronal regulated secretory pathway.","method":"Immunohistochemistry with N-terminal specific antibody, co-localization with Golgi marker MG-160, absence of co-localization with synaptic marker Dynamin-1, absence in S-100alpha-positive glia","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — direct subcellular localization with multiple marker co-localization experiments","pmids":["10408612"],"is_preprint":false},{"year":2003,"finding":"Furin, PC5 (PCSK5), and PC7 activate VEGF-C by cleaving its precursor (proVEGF-C) at the dibasic motif HSIIRR↓SL; this processing is essential for VEGF-C-induced angiogenesis, lymphangiogenesis and tumor growth in vivo.","method":"Co-transfection in LoVo (furin-deficient) cells, in vitro digestion of synthetic fluorogenic peptide, inhibition with prosegment inhibitors, CHO cell xenograft model in nude mice with cleavage-site mutants","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro enzymatic assay combined with cell-based reconstitution and in vivo functional validation","pmids":["12782675"],"is_preprint":false},{"year":2003,"finding":"PC5A (PCSK5) co-localizes with alphav integrin in vascular smooth muscle cells (VSMCs) during vascular remodeling in vivo; endoproteolytic cleavage of alphav integrin by PC5 occurs in the trans-Golgi network, as shown by brefeldin A inhibition; furin mRNA is not upregulated during neointima formation, whereas PC5A mRNA is, indicating PC5 is the major convertase for alphav integrin activation in this context.","method":"Comparative immunocytochemistry, Northern blot, in situ hybridization, Golgi disruption with brefeldin A, balloon injury model in rodents","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple in vivo and cell biology methods supporting TGN cleavage, but no direct reconstitution of PC5 cleaving alphav","pmids":["12649739"],"is_preprint":false},{"year":2004,"finding":"PC5 (PCSK5) is required for alphav integrin endoproteolytic activation in vascular smooth muscle cells; PC5-specific antisense oligonucleotides and the pharmacological PC inhibitor dec-CMK block alphav cleavage, inhibit VSMC adhesion to vitronectin, inhibit migration on vitronectin, and reduce focal adhesion kinase (Y397) autophosphorylation and Akt activation without affecting ERK1/2 phosphorylation.","method":"Antisense oligonucleotides against PC5, pharmacological inhibitor (dec-CMK), immunoblotting, VSMC adhesion and migration assays, FAK/Akt/ERK phosphorylation analysis, immunohistochemistry of human endarterectomy lesions","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — specific loss-of-function (antisense + pharmacological) with defined cellular and signaling phenotypes, human tissue validation","pmids":["14970114"],"is_preprint":false},{"year":2004,"finding":"PC6 (PCSK5) is specifically induced in uterine stromal cells at the embryo attachment site during early pregnancy in mice; morpholino antisense oligonucleotide-mediated knockdown of PC6 in the mouse uterus completely blocks embryo implantation; PC6 is also dramatically upregulated during uterine decidualization in primates.","method":"In vivo morpholino antisense knockdown in mice, immunohistochemistry during early pregnancy (mouse, rhesus monkey, human), timed pregnancy studies","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 — in vivo loss-of-function with complete implantation failure phenotype, replicated in multiple species","pmids":["15601911"],"is_preprint":false},{"year":2006,"finding":"PCSK9 is inactivated by furin and/or PC5/6A through cleavage at the motif RFHR↓218; gain-of-function PCSK9 mutations (R218S, F216L, D374Y) associated with hypercholesterolemia result in loss of furin/PC5/6A processing; this cleavage may reduce PCSK9 lifetime and its ability to degrade LDL receptor.","method":"Cell transfection experiments, site-directed mutagenesis of PCSK9, immunoblotting for cleavage products, analysis of circulating human plasma","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct demonstration of substrate cleavage with multiple natural mutants tested, human plasma validation","pmids":["16912035"],"is_preprint":false},{"year":2006,"finding":"Poly-arginine peptides (up to nona-L-Arg) are potent nanomolar inhibitors of PC5/6A (Ki ~150 nM for nona-L-Arg), with nona-D-Arg being even more potent (Ki ~19 nM); positional scanning libraries reveal strong preference for basic residues in all positions of the PC5/6A active site.","method":"Positional scanning-synthetic peptide combinatorial library (PS-SPCL) screening, enzymatic inhibition assays (Ki determination)","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assay with systematic substrate/inhibitor characterization","pmids":["17012622"],"is_preprint":false},{"year":2007,"finding":"A predicted alpha-helix in the C-terminus of PC5/6A (PCSK5) is critical for targeting to dense-core secretory granules in AtT-20 cells, functioning by the same mechanism as the granule-targeting helices of PC1/3 and PC2; hydrophobic amino acid clustering in the helix correlates with granule-sorting efficiency.","method":"C-terminal domain fusion proteins targeting heterologous constitutively secreted protein, subcellular distribution analysis in AtT-20 cells, mutagenesis of predicted alpha-helix","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1-2 — structure-function mutagenesis with functional targeting assay in endocrine cells","pmids":["17645548"],"is_preprint":false},{"year":2008,"finding":"GDF11 is cleaved and activated by PCSK5A but not by PCSK5A-C470R; selectivity resides in a P1' Asn in the RSRR↓N cleavage motif; PCSK5 is essential for embryonic anteroposterior patterning, nephrogenesis, skeletal, and anorectal development, at least partly through GDF11 activation and consequent regulation of Hox gene paralogs (Hoxa, Hoxc, Hoxd) and Mnx1.","method":"ENU-induced mouse mutation (C470R), compound Pcsk5 mutants, epiblast-specific conditional deletion, in vitro and ex vivo cleavage assays, in situ hybridization, P1' mutagenesis, Gdf11-deficient embryo comparison","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution of substrate cleavage with mutagenesis, multiple genetic models, in vivo epistasis with Gdf11 knockout","pmids":["18519639"],"is_preprint":false},{"year":2008,"finding":"PC5/6 (PCSK5) is required for embryo implantation and is essential for anteroposterior patterning (extra vertebrae, tail agenesis, kidney agenesis) in a GDF11-dependent manner; Gdf11 P1' Asn confers selectivity for PC5/6 over other convertases; epiblast-specific deletion confirms the embryonic requirement.","method":"Conditional epiblast-specific Pcsk5 knockout (CD1/129/Sv/C57BL/6 background), in vitro and ex vivo cleavage assays, in situ hybridization for Pcsk5 and Gdf11, P1' Asn mutagenesis of cleavage motif","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — conditional genetic model with substrate specificity confirmed biochemically, replicated independently from PMID 18519639","pmids":["18378898"],"is_preprint":false},{"year":2008,"finding":"Furin, PACE4, PC5, and PC7 all cleave preprohepcidin at the RRRRR↓59DT motif to generate active hepcidin; site-directed mutagenesis of the cleavage site abrogates processing; hepcidin with RRRRR→SSSSS mutation is inactive as an inducer of ferroportin degradation.","method":"Cell transfection in Huh-7 and LoVo cells, inhibitor studies with alpha1-PDX and ppFurin, site-directed mutagenesis, in vitro peptide digestion, developmental expression analysis","journal":"Gut","confidence":"High","confidence_rationale":"Tier 1-2 — direct reconstitution in furin-deficient cells with multiple convertases, mutagenesis of cleavage site, functional readout","pmids":["18664504"],"is_preprint":false},{"year":2009,"finding":"PC5/6 (PCSK5) is protective against intestinal tumorigenesis; enterocyte-specific Pcsk5 knockout in the ApcMin/+ mouse model results in significantly higher tumor numbers in the duodenum and premature mortality; human intestinal tumors systematically downregulate PC5/6 expression.","method":"Enterocyte-specific conditional Pcsk5 knockout, ApcMin/+ double mutant mouse model, tumor enumeration, human tumor expression analysis","journal":"Molecular cancer","confidence":"High","confidence_rationale":"Tier 2 — clean conditional KO with defined in vivo phenotype, human tissue correlation","pmids":["19737405"],"is_preprint":false},{"year":2010,"finding":"Zebrafish PCSK5.1 and PCSK5.2 are co-orthologs of mammalian PCSK5; PC5.1-deficient embryos display abnormal neuromast deposition in the lateral line system and loss of normal touch response, demonstrating a role in sensory organ development.","method":"cDNA cloning of zebrafish PCSK5.1 and PCSK5.2, morpholino-mediated knockdown of PC5.1, synteny analysis, in situ hybridization","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function in zebrafish with specific sensory phenotype; ortholog confirmed by synteny","pmids":["20882679"],"is_preprint":false},{"year":2011,"finding":"PCSK5 (PC5/6) expression is selectively elevated during the transition from two-layer secondary to pre-antral follicle in the mouse ovary; activin A selectively enhances PCSK5 expression; inhibition of proconvertase activity blocks inhibin alpha- and beta-subunit maturation; overexpression of PC5/6 in furin-deficient cells increases inhibin alpha- and beta(B)-subunit maturation, identifying inhibin subunits as substrates of PCSK5.","method":"Real-time quantitative RT-PCR, inhibitor dec-RVKR-CMK in granulosa cells, overexpression of PC5/6 in furin-deficient cells, immunoblotting for inhibin subunit maturation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — substrate identification by gain-of-function in furin-deficient cells plus loss-of-function with inhibitor, two orthogonal approaches","pmids":["21408162"],"is_preprint":false},{"year":2015,"finding":"PC6 (PCSK5) cleaves the N-terminus of alpha-dystroglycan (alpha-DG-N) at a PC6-cleavage site near alpha-DG-N; this removal is required for embryo attachment to endometrial epithelial cells; PC6 knockdown reduces alpha-DG-N removal from the cell surface and blastocyst adhesion; mutating the PC6-cleavage site prevents alpha-DG-N removal and causes retention of full-length alpha-DG with loss of cell adhesiveness; alpha-DG-N is removed from endometrial tissue in vivo coinciding with receptivity.","method":"In vitro cleavage assay of PC6-cleavage site peptide, PC6 siRNA knockdown, site-directed mutagenesis of cleavage site, blastocyst adhesion assay, in vivo endometrial tissue analysis, flow cytometry for cell surface alpha-DG","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1-2 — direct enzymatic cleavage demonstrated, loss-of-function with knockdown and cleavage site mutagenesis, in vivo validation","pmids":["26077903"],"is_preprint":false},{"year":2017,"finding":"Osteopontin (OPN) is a novel substrate for PC5/6 (PCSK5) in bone; PC5/6A directly cleaves OPN at noncanonical and canonical consensus sequences, reducing full-length OPN (~70 kDa) to N-terminal (~50 kDa) and C-terminal (~18/16 kDa) fragments; PC5/6-knockout mice show altered OPN processing in bone and reduced mineralization; Pcsk5 and Opn are co-expressed in bone cells.","method":"In silico cleavage site analysis, ex vivo co-transfection of OPN and PC5/6, cell-free enzyme-substrate assay, mass spectrometry of cleavage products, micro-CT of KO embryos, in situ hybridization, immunoblotting of bone extracts from KO vs. WT mice","journal":"Bone","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay, mass spectrometry of cleavage sites, in vivo KO validation with multiple orthogonal methods","pmids":["29126984"],"is_preprint":false},{"year":2017,"finding":"Pcsk5 is required specifically in the cranio-cardiac mesoderm for cardiogenesis; conditional deletion in all epiblastic lineages recapitulates all developmental malformations except tracheo-esophageal defects; deletion specifically in cardiogenic or pharyngeal mesodermal progenitors (forming later from cranio-cardiac mesoderm) or in neural crest does not affect heart development.","method":"MRI of mouse embryo heart development, multiple tissue-specific conditional Cre-mediated Pcsk5 deletions (epiblast, cranio-cardiac mesoderm, cardiogenic progenitors, pharyngeal mesoderm, neural crest)","journal":"BMC developmental biology","confidence":"High","confidence_rationale":"Tier 2 — systematic conditional deletion mapping with multiple Cre lines and imaging phenotype","pmids":["28446132"],"is_preprint":false},{"year":2024,"finding":"PCSK5 activates precursor TGF-beta (pro-TGF-beta) by binding and cleaving at the pro-TGF-beta cleavage site, thereby activating the TGF-beta/SMAD2/3 pathway and promoting extracellular matrix expression in adventitial fibroblasts; this contributes to vascular fibrosis in Takayasu arteritis. Leflunomide inhibits PCSK5 and pro-TGF-beta binding, reducing TGF-beta activation.","method":"Co-immunoprecipitation of PCSK5 and pro-TGF-beta, overexpression of PCSK5 in adventitial fibroblasts, immunoblotting for mature TGF-beta and SMAD2/3 phosphorylation, ECM protein expression, leflunomide treatment in cells and patients","journal":"Journal of autoimmunity","confidence":"Medium","confidence_rationale":"Tier 2-3 — substrate binding demonstrated by Co-IP, gain-of-function with downstream signaling, but direct in vitro cleavage assay not shown","pmids":["38972101"],"is_preprint":false},{"year":2022,"finding":"The most efficiently cleaved PC5/6A fluorogenic substrate is acetyl-Arg-Arg-Tle-Lys-Arg-AMC (highest kcat/KM), establishing the active-site substrate preference of PC5/6A among a panel of novel synthetic substrates.","method":"In vitro enzymatic assay of novel fluorogenic peptide substrates with purified PC5/6A, kinetic characterization (kcat, KM, kcat/KM)","journal":"Analytical biochemistry","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic characterization with systematic substrate panel","pmids":["35964735"],"is_preprint":false},{"year":2001,"finding":"PC5 (PCSK5) processes pro-CCK into glycine-extended CCK 12 and CCK 22 in neuronal cell lines (GT1-7, SK-N-MC, SK-N-SH) that express PC5 but not PC1 or PC2, demonstrating a role for PC5 in CCK processing distinct from PC1/PC2.","method":"RT-PCR and Western blot for convertase expression, stable CCK overexpression, radioimmunoassay for pro-CCK cleavage products, gel filtration chromatography, carboxypeptidase B treatment","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based substrate processing with endogenous PC5 in PC1/PC2-null context; no direct reconstitution","pmids":["11457520"],"is_preprint":false},{"year":2005,"finding":"siRNA-mediated knockdown of PC5 (PCSK5) in STC-1 intestinal cells reduces CCK secretion (particularly CCK 22 in media) and causes a compensatory ~3-fold increase in PC2 mRNA and protein, providing direct evidence that PC5 is involved in CCK processing.","method":"Stable transfection with siRNA hairpin constructs targeting PC5, quantitative PCR, Western blot, CCK radioimmunoassay","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — direct loss-of-function (siRNA) with specific substrate (CCK 22) and compensatory response readout","pmids":["16266771"],"is_preprint":false}],"current_model":"PCSK5 (PC5/6) is a subtilisin/kexin-like serine endoprotease expressed as two main isoforms (soluble PC5/6A targeted to regulated secretory granules via a C-terminal alpha-helix sorting signal, and membrane-bound PC5/6B localized to the Golgi) that cleaves precursor proteins at basic amino acid motifs (K/R-Xn-K/R↓) to activate a wide range of substrates including GDF11 (with selectivity conferred by a P1' Asn in RSRR↓N), BMP-4, VEGF-C, PCSK9, pro-TGF-beta, alphav integrin, prorenin, hepcidin, osteopontin, alpha-dystroglycan N-terminus, inhibin subunits, CCK, and viral hemagglutinins, thereby playing essential in vivo roles in embryonic anteroposterior patterning, nephrogenesis, cardiogenesis, uterine receptivity/embryo implantation, bone mineralization, vascular remodeling, and intestinal tumor suppression."},"narrative":{"teleology":[{"year":1993,"claim":"Identification of PCSK5 as a new member of the proprotein convertase family established that subtilisin/kexin-like processing enzymes extend beyond furin and PC1/2, with expression in both endocrine and non-endocrine tissues.","evidence":"cDNA cloning, Northern blotting, and in situ hybridization from mouse tissues","pmids":["8341687"],"confidence":"High","gaps":["Endogenous substrates unknown","Enzymatic specificity versus furin/PACE4 not defined","No loss-of-function data"]},{"year":1994,"claim":"Demonstration that PC5/6 can proteolytically activate avian influenza hemagglutinin in furin-deficient cells established it as a functionally active basic-amino-acid-directed endoprotease with overlapping but distinct substrate capacity relative to furin.","evidence":"Vaccinia virus expression system in furin-deficient LoVo cells with rescue of viral replication","pmids":["8057485"],"confidence":"High","gaps":["Substrate selectivity rules not established","No known physiological substrates in mammals yet","Prosomatostatin shown not to be a substrate, highlighting unexplained specificity (PMID:7720860)"]},{"year":1996,"claim":"Discovery that PCSK5 generates two isoforms (soluble PC5-A and membrane-bound PC5-B) sorted to distinct compartments—secretory granules versus Golgi—resolved how one gene could serve both regulated and constitutive secretory pathways, with a C-terminal 38-residue segment directing granule entry.","evidence":"Stable transfection of AtT-20 cells, electron microscopy immunohistochemistry, C-terminal deletion mutagenesis","pmids":["8947550"],"confidence":"High","gaps":["Structural basis of the sorting signal not resolved at atomic level","Relative contributions of PC5-A vs PC5-B to specific substrate processing unknown"]},{"year":1996,"claim":"Identification of the first endogenous mammalian substrates—RPTPmu and prorenin—showed that PC5/6 operates on diverse precursor classes beyond neuropeptides, with active-site mutagenesis confirming catalytic dependence.","evidence":"COS cell co-transfection with active-site Ser→Ala mutant (RPTPmu), co-transfection in GH4C1 cells with prorenin cleavage-site mutants","pmids":["8620001","8901832"],"confidence":"High","gaps":["In vivo relevance of RPTPmu and prorenin cleavage by PC5 not tested genetically","Redundancy with furin for these substrates not resolved"]},{"year":1998,"claim":"PC5-A was shown to process pro-neurotensin/neuromedin N in early compartments of the regulated secretory pathway and BMP-4 in Xenopus oocytes, establishing roles in both neuroendocrine and developmental morphogen processing.","evidence":"Stable transfection in PC12 cells with metabolic labeling; Xenopus oocyte cleavage assays with alpha1-PDX inhibition and epistasis","pmids":["9738000","9707432"],"confidence":"High","gaps":["BMP-4 cleavage redundancy with furin not resolved genetically","P1' determinants of selectivity not yet identified"]},{"year":2001,"claim":"Evidence that PC5 processes pro-CCK in neuronal cell lines lacking PC1/PC2 extended the substrate repertoire to gut-brain peptide hormones, later confirmed by siRNA knockdown reducing CCK22 secretion.","evidence":"RT-PCR/Western blot for convertase expression in GT1-7 cells; siRNA knockdown of PC5 in STC-1 cells with CCK radioimmunoassay","pmids":["11457520","16266771"],"confidence":"Medium","gaps":["No direct in vitro reconstitution of PC5 cleaving pro-CCK","Compensatory PC2 upregulation upon PC5 knockdown complicates interpretation","In vivo genetic validation not performed"]},{"year":2003,"claim":"Identification of VEGF-C and alphav integrin as PC5 substrates connected the enzyme to angiogenesis/lymphangiogenesis and vascular smooth muscle cell biology, with VEGF-C cleavage validated in vivo via tumor xenografts and alphav processing linked to FAK/Akt signaling.","evidence":"LoVo cell reconstitution and CHO xenograft model for VEGF-C; antisense oligonucleotides and dec-CMK inhibitor in VSMCs, adhesion/migration assays, human endarterectomy tissue","pmids":["12782675","12649739","14970114"],"confidence":"High","gaps":["Relative contributions of furin, PC5, and PC7 to VEGF-C processing in specific tissues unresolved","Direct in vitro cleavage of alphav by purified PC5 not shown"]},{"year":2004,"claim":"In vivo knockdown of PC6 in the mouse uterus completely blocked embryo implantation, establishing the first essential non-redundant physiological role for PCSK5 in reproduction.","evidence":"Morpholino antisense knockdown in mouse uterus, immunohistochemistry in mouse/rhesus/human endometrium","pmids":["15601911"],"confidence":"High","gaps":["Identity of the critical substrate(s) mediating implantation not established","Genetic knockout confirmation not yet performed"]},{"year":2006,"claim":"Discovery that PC5/6A cleaves PCSK9 at RFHR↓218—with gain-of-function hypercholesterolemia mutations abolishing this cleavage—established a link between PCSK5 activity and cholesterol metabolism regulation.","evidence":"Cell transfection with PCSK9 mutants, immunoblotting, human plasma analysis","pmids":["16912035"],"confidence":"High","gaps":["In vivo significance of PC5/6A-mediated PCSK9 inactivation versus furin not genetically resolved","Relative contribution to circulating PCSK9 levels unknown"]},{"year":2008,"claim":"ENU mutagenesis and conditional knockout in mice revealed that PCSK5 is essential for embryonic anteroposterior patterning, kidney development, and skeletal organization primarily through activation of GDF11 at a P1' Asn-containing cleavage motif, resolving the key in vivo substrate and the molecular basis of selectivity over other convertases.","evidence":"ENU-induced C470R mutation, epiblast-specific conditional deletion, in vitro cleavage assays with P1' mutagenesis, comparison with Gdf11-knockout phenotype","pmids":["18519639","18378898"],"confidence":"High","gaps":["Whether all patterning phenotypes are GDF11-dependent or involve additional substrates","Crystal structure of PC5/6 explaining P1' Asn preference not available"]},{"year":2008,"claim":"Demonstration that PC5 cleaves preprohepcidin at the polybasic site for hepcidin maturation connected PCSK5 to systemic iron homeostasis, though with redundancy among multiple convertases.","evidence":"Cell transfection in Huh-7 and LoVo cells, site-directed mutagenesis of cleavage site, in vitro peptide digestion","pmids":["18664504"],"confidence":"High","gaps":["Relative in vivo importance of PC5 versus furin/PACE4/PC7 for hepcidin maturation unresolved","No genetic iron phenotype reported for Pcsk5 knockouts"]},{"year":2009,"claim":"Enterocyte-specific Pcsk5 knockout in ApcMin/+ mice demonstrated a tumor-suppressive function, with increased duodenal tumors and premature mortality, paralleled by systematic PCSK5 downregulation in human intestinal tumors.","evidence":"Conditional Pcsk5 knockout crossed to ApcMin/+ model, tumor enumeration, human tumor expression analysis","pmids":["19737405"],"confidence":"High","gaps":["Identity of the substrate(s) mediating tumor suppression unknown","Mechanism of PCSK5 downregulation in human tumors not defined"]},{"year":2015,"claim":"Identification of alpha-dystroglycan N-terminus as a PC6 substrate required for embryo attachment to endometrial epithelium provided a molecular mechanism for the implantation role discovered a decade earlier.","evidence":"In vitro cleavage of PC6-site peptide, PC6 siRNA knockdown, cleavage-site mutagenesis, blastocyst adhesion assay, in vivo endometrial tissue analysis","pmids":["26077903"],"confidence":"High","gaps":["Whether alpha-DG-N is the sole critical substrate for implantation or acts alongside others","Genetic rescue of implantation defect by alpha-DG-N removal not shown"]},{"year":2017,"claim":"Systematic conditional deletion across multiple Cre lines established that PCSK5 is required specifically in cranio-cardiac mesoderm for cardiogenesis, refining the tissue-of-action beyond what epiblast-wide deletion could show.","evidence":"Multiple tissue-specific Cre-mediated Pcsk5 deletions with MRI phenotyping of embryonic hearts","pmids":["28446132"],"confidence":"High","gaps":["The specific substrate(s) processed by PC5/6 in cranio-cardiac mesoderm for heart development remain unknown","Whether the cardiogenesis role is GDF11-dependent or involves distinct substrates not resolved"]},{"year":2017,"claim":"Identification of osteopontin as a direct PC5/6A substrate in bone, with KO mice showing altered OPN processing and reduced mineralization, established a role for PCSK5 in skeletal mineralization.","evidence":"Cell-free enzyme-substrate assay, mass spectrometry of cleavage products, micro-CT of KO embryos, in situ hybridization","pmids":["29126984"],"confidence":"High","gaps":["Whether OPN processing is the primary mechanism for mineralization defects or secondary to broader developmental abnormalities","Cleavage at noncanonical sites not fully characterized kinetically"]},{"year":2024,"claim":"Co-immunoprecipitation of PCSK5 with pro-TGF-beta and demonstration of enhanced SMAD2/3 signaling upon PCSK5 overexpression in adventitial fibroblasts linked the enzyme to vascular fibrosis in Takayasu arteritis, extending substrate repertoire to TGF-beta superfamily ligands beyond GDF11/BMP-4.","evidence":"Co-IP of PCSK5 and pro-TGF-beta, overexpression in fibroblasts, SMAD2/3 phosphorylation, leflunomide inhibition","pmids":["38972101"],"confidence":"Medium","gaps":["Direct in vitro cleavage assay of pro-TGF-beta by purified PC5/6 not shown","Specificity versus furin for pro-TGF-beta not tested","Leflunomide mechanism of inhibition not biochemically defined"]},{"year":null,"claim":"No crystal or cryo-EM structure of PC5/6 exists, and the structural basis for its P1' Asn selectivity, isoform-specific substrate channeling, and the identities of critical substrates in cardiogenesis and intestinal tumor suppression remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No atomic-resolution structure of PC5/6","Substrate identity for cardiogenesis unknown","Mechanism of tumor suppression in intestine uncharacterized at substrate level","Relative in vivo redundancy with furin and PACE4 for most substrates not genetically dissected"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,5,6,10,12,16,19,21,24,25,26,29]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[4,11,13]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[4,9,18]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,5,6,10,12,16,19,21,24,25,26,29]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[10,19,20,27]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,12,14,28]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,21]}],"complexes":[],"partners":["GDF11","BMP4","PCSK9","VEGFC","ITGAV","OPN","DAG1","TGFB1"],"other_free_text":[]},"mechanistic_narrative":"PCSK5 (PC5/6) is a subtilisin/kexin-family serine endoprotease that cleaves precursor proteins at basic amino acid motifs to activate a broad range of substrates in developmental, endocrine, vascular, and immune contexts. It exists as two isoforms—soluble PC5/6A, which is targeted to regulated secretory granules via a C-terminal alpha-helix sorting signal, and membrane-bound PC5/6B, which localizes to the Golgi—and processes substrates including GDF11 (with selectivity conferred by a P1' Asn), BMP-4, VEGF-C, PCSK9, pro-TGF-beta, alphav integrin, prorenin, hepcidin, osteopontin, alpha-dystroglycan N-terminus, inhibin subunits, CCK, and viral hemagglutinins [PMID:8341687, PMID:8947550, PMID:18519639, PMID:9707432, PMID:12782675, PMID:16912035, PMID:29126984, PMID:26077903]. Conditional genetic studies in mouse demonstrate that PCSK5 is essential for embryonic anteroposterior patterning and nephrogenesis largely through GDF11 activation and Hox gene regulation, for cardiogenesis via action in cranio-cardiac mesoderm, for uterine receptivity and embryo implantation, for bone mineralization through osteopontin processing, and for intestinal tumor suppression in the ApcMin/+ model [PMID:18378898, PMID:27, PMID:19737405, PMID:15601911, PMID:29126984]. In the vasculature, PCSK5 activates alphav integrin in smooth muscle cells to promote adhesion, migration, and FAK/Akt signaling, and cleaves pro-TGF-beta in adventitial fibroblasts to drive TGF-beta/SMAD2/3-dependent extracellular matrix production [PMID:14970114, PMID:38972101]."},"prefetch_data":{"uniprot":{"accession":"Q92824","full_name":"Proprotein convertase subtilisin/kexin type 5","aliases":["Proprotein convertase 5","PC5","Proprotein convertase 6","PC6","hPC6","Subtilisin/kexin-like protease PC5"],"length_aa":1860,"mass_kda":206.9,"function":"Serine endoprotease that processes various proproteins by cleavage at paired basic amino acids, recognizing the RXXX[KR]R consensus motif. Likely functions in the constitutive and regulated secretory pathways. Plays an essential role in pregnancy establishment by proteolytic activation of a number of important factors such as BMP2, CALD1 and alpha-integrins","subcellular_location":"Endomembrane system","url":"https://www.uniprot.org/uniprotkb/Q92824/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PCSK5","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PCSK5","total_profiled":1310},"omim":[{"mim_id":"607786","title":"PROPROTEIN CONVERTASE, SUBTILISIN/KEXIN-TYPE, 9; PCSK9","url":"https://www.omim.org/entry/607786"},{"mim_id":"603936","title":"GROWTH/DIFFERENTIATION FACTOR 11; GDF11","url":"https://www.omim.org/entry/603936"},{"mim_id":"600488","title":"PROPROTEIN CONVERTASE, SUBTILISIN/KEXIN-TYPE, 5; PCSK5","url":"https://www.omim.org/entry/600488"},{"mim_id":"600487","title":"PROPROTEIN CONVERTASE, SUBTILISIN/KEXIN-TYPE, 4; PCSK4","url":"https://www.omim.org/entry/600487"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"intestine","ntpm":24.4}],"url":"https://www.proteinatlas.org/search/PCSK5"},"hgnc":{"alias_symbol":["PC5","PC6","SPC6"],"prev_symbol":[]},"alphafold":{"accession":"Q92824","domains":[{"cath_id":"3.30.70.850","chopping":"36-108","consensus_level":"high","plddt":83.9464,"start":36,"end":108},{"cath_id":"3.40.50.200","chopping":"127-462","consensus_level":"high","plddt":91.3618,"start":127,"end":462},{"cath_id":"2.60.120.260","chopping":"464-603","consensus_level":"medium","plddt":90.7877,"start":464,"end":603},{"cath_id":"2.10.220.10","chopping":"1310-1356","consensus_level":"medium","plddt":82.4472,"start":1310,"end":1356},{"cath_id":"2.10.220.10","chopping":"1652-1730","consensus_level":"high","plddt":76.4458,"start":1652,"end":1730}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92824","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92824-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92824-F1-predicted_aligned_error_v6.png","plddt_mean":76.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCSK5","jax_strain_url":"https://www.jax.org/strain/search?query=PCSK5"},"sequence":{"accession":"Q92824","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92824.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92824/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92824"}},"corpus_meta":[{"pmid":"10026183","id":"PMC_10026183","title":"Mitochondrial 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TGF-β and SMAD3 signaling pathway activation.","date":"2024","source":"Journal of autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/38972101","citation_count":3,"is_preprint":false},{"pmid":"38110043","id":"PMC_38110043","title":"Genome-wide analysis in PC6 electroacupuncture to ameliorate carfilzomib-induced cardiotoxicity in mice.","date":"2023","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/38110043","citation_count":3,"is_preprint":false},{"pmid":"37570909","id":"PMC_37570909","title":"Development and Application of a Cleaved Amplified Polymorphic Sequence Marker (Phyto) Linked to the Pc5.1 Locus Conferring Resistance to Phytophthora capsici in Pepper (Capsicum annuum L.).","date":"2023","source":"Plants (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/37570909","citation_count":3,"is_preprint":false},{"pmid":"8664347","id":"PMC_8664347","title":"Human lactase-phlorizin hydrolase is not processed by furin, PC1/PC3, PC2, PACE4 and PC5/PC6A of the family of subtilisin-like proprotein processing proteases.","date":"1996","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/8664347","citation_count":3,"is_preprint":false},{"pmid":"12508314","id":"PMC_12508314","title":"Molecular characterization of the cDNA and localization of the mRNA encoding the prohormone convertase PC5-A in the European green frog.","date":"2003","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/12508314","citation_count":3,"is_preprint":false},{"pmid":"38553549","id":"PMC_38553549","title":"PCSK5 downregulation promotes the inhibitory effect of andrographolide on glioblastoma through regulating STAT3.","date":"2024","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38553549","citation_count":3,"is_preprint":false},{"pmid":"38764114","id":"PMC_38764114","title":"Effect of electroacupuncture at \"Neiguan\" (PC6) on pain and brain orexin 1 receptor in mice with 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mitochondrial autophagy during the ischemia and reperfusion phases in rats with myocardial ischemia-reperfusion injury].","date":"2025","source":"Zhongguo zhen jiu = Chinese acupuncture & moxibustion","url":"https://pubmed.ncbi.nlm.nih.gov/40369922","citation_count":1,"is_preprint":false},{"pmid":"9465315","id":"PMC_9465315","title":"[Neuronal differentiation of human small cell lung cancer cell line PC-6 by Solcoseryl].","date":"1997","source":"[Hokkaido igaku zasshi] The Hokkaido journal of medical science","url":"https://pubmed.ncbi.nlm.nih.gov/9465315","citation_count":1,"is_preprint":false},{"pmid":"25951641","id":"PMC_25951641","title":"[Effect of electro-acupuncture at Neiguan (PC6) and Lieque (LU7) on the expression of protein kinases in cardiomyocytes of myocardial ischemia rats].","date":"2015","source":"Zhongguo Zhong xi yi jie he za zhi Zhongguo Zhongxiyi jiehe zazhi = Chinese journal of integrated traditional and Western medicine","url":"https://pubmed.ncbi.nlm.nih.gov/25951641","citation_count":1,"is_preprint":false},{"pmid":"41566731","id":"PMC_41566731","title":"[Effect of electroacupuncture of \"Neiguan\" (PC6) and \"Shenmen\" (HT7) on cardiac function and neovascularization in rats with chronic heart failure based on Notch signaling pathway].","date":"2026","source":"Zhen ci yan jiu = Acupuncture research","url":"https://pubmed.ncbi.nlm.nih.gov/41566731","citation_count":1,"is_preprint":false},{"pmid":"40724834","id":"PMC_40724834","title":"Genetic Association of PCSK5 and MUC2 Gene Polymorphisms with Recurrent Pregnancy Loss (RPL).","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40724834","citation_count":0,"is_preprint":false},{"pmid":"33788447","id":"PMC_33788447","title":"[Effect of manual acupuncture of \"Shuigou\" (GV26)\"Neiguan\" (PC6) on neurological function and expression of apoptosis-related factors in brain tissues 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cloning, Northern blotting, in situ hybridization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning and structural characterization with multiple methods in founding paper\",\n      \"pmids\": [\"8341687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"PC6 (PCSK5) can proteolytically activate the hemagglutinin of virulent avian influenza viruses at authentic cleavage sites, functioning similarly to furin, as demonstrated in furin-deficient LoVo cells complemented with PC6.\",\n      \"method\": \"Vaccinia virus expression in LoVo cells (furin-deficient), rescue of viral replication, cleavage site mutant analysis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct enzymatic activity demonstrated in cell-based reconstitution with authentic viral substrate\",\n      \"pmids\": [\"8057485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"PC5 (PCSK5) cannot process rat prosomatostatin into somatostatin-14 or somatostatin-28 in either constitutive (LoVo) or regulated (AtT-20) secretory cell lines, unlike PC1, PC2, furin, and PACE4.\",\n      \"method\": \"Recombinant vaccinia virus co-expression, gel-permeation HPLC analysis of processed products\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in-cell enzymatic assay with multiple convertase comparisons\",\n      \"pmids\": [\"7720860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The PCSK5 gene was mapped to mouse chromosome 19 and human chromosome 9.\",\n      \"method\": \"RFLP analysis of backcross DNA panel, Southern blot of somatic cell hybrid DNA panel\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct chromosomal mapping by two complementary methods\",\n      \"pmids\": [\"7782070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PC5 (PCSK5) generates two isoforms, PC5-A (soluble, 915 aa) and PC5-B (membrane-bound, 1877 aa), that are sorted to distinct subcellular compartments: PC5-A to regulated secretory granules (including glucagon-containing granules in pancreatic cells) and PC5-B to the Golgi. A C-terminal 38-amino-acid segment in PC5-A is required for entry into the regulated secretory pathway.\",\n      \"method\": \"Stable transfection of AtT-20 cells, biosynthetic analyses, immunofluorescence, electron microscopy immunohistochemistry of pancreatic cells, C-terminal deletion mutagenesis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (biochemical, cell biological, ultrastructural) with mutagenesis in a single study\",\n      \"pmids\": [\"8947550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PC5 (PCSK5) cleaves receptor protein tyrosine phosphatase mu (RPTPmu) at its RXK/RR motif; active-site serine-to-alanine mutant PC5 lacks this activity; PACE4 does not cleave RPTPmu; PC5 mRNA is upregulated >30-fold at confluence in human umbilical vein endothelial cells.\",\n      \"method\": \"COS cell co-transfection with RPTPmu and PC5 or PACE4 expression plasmids, immunoblotting, active-site mutagenesis (Ser→Ala), RNA blot analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis confirms catalytic requirement, combined with substrate identification by co-transfection\",\n      \"pmids\": [\"8620001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PC5 (PCSK5) can process human prorenin into active renin dependent on the dibasic amino acids at positions 42/43 of the prorenin prosegment; this processing occurs only in cells with dense-core secretory granules (GH4C1 cells) and PC5 co-localizes with renin in the zona glomerulosa of human adrenal cortex.\",\n      \"method\": \"Co-transfection of prorenin and PC5 in GH4C1 cells, prorenin site-directed mutants, immunohistochemistry\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — enzymatic processing shown by co-transfection with mutagenesis of cleavage site, plus in vivo co-localization\",\n      \"pmids\": [\"8901832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human PC6A and PC6B isoforms of PCSK5 are expressed in human CD4+ T lymphocytes and are candidate proteases for HIV-1 gp160 processing in these cells, which are competent for infectious virion production.\",\n      \"method\": \"RT-PCR, Northern blot analysis, comparison with furin-deficient LoVo cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — expression-based candidate identification without direct enzymatic reconstitution of gp160 cleavage\",\n      \"pmids\": [\"8755538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The human PCSK5 gene was mapped to chromosome 9q21.3 near markers D9S175 and D9S276.\",\n      \"method\": \"Somatic cell hybrid analysis, YAC clone analysis, fluorescence in situ hybridization (FISH)\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct chromosomal localization by three orthogonal methods\",\n      \"pmids\": [\"9067430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PC5-A (PCSK5) functions as a prohormone convertase in the regulated secretory pathway; in PC12 cells it processes pro-neurotensin/neuromedin N in early compartments of the regulated secretory pathway according to a pattern resembling adrenal medulla processing and distinct from PC1 and PC2.\",\n      \"method\": \"Stable transfection of PC12 cells with PC5-A, metabolic labeling, immunochemical studies, subcellular fractionation, co-localization with immunoreactive neurotensin\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean overexpression system with direct demonstration of prohormone processing and subcellular co-localization\",\n      \"pmids\": [\"9738000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"BMP-4 is proteolytically activated by furin and/or PC6 (PCSK5) during vertebrate embryogenesis; in Xenopus oocytes, both furin and PC6B cleave BMP-4 at its RSKR site and are sensitive to the inhibitor alpha1-PDX.\",\n      \"method\": \"Xenopus oocyte translation assay, in vitro digestion assay with PC family members, ectopic expression of alpha1-antitrypsin Portland (alpha1-PDX) in embryos, epistasis with downstream BMP pathway components\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro cleavage assay plus in vivo epistasis with inhibitor, multiple orthogonal methods\",\n      \"pmids\": [\"9707432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PC5-A (PCSK5) immunoreactivity in rat brain neurons is concentrated in the Golgi apparatus and small vesicular elements in perikarya and dendrites, but not in axons or astrocytes, consistent with activity in early compartments of the neuronal regulated secretory pathway.\",\n      \"method\": \"Immunohistochemistry with N-terminal specific antibody, co-localization with Golgi marker MG-160, absence of co-localization with synaptic marker Dynamin-1, absence in S-100alpha-positive glia\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization with multiple marker co-localization experiments\",\n      \"pmids\": [\"10408612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Furin, PC5 (PCSK5), and PC7 activate VEGF-C by cleaving its precursor (proVEGF-C) at the dibasic motif HSIIRR↓SL; this processing is essential for VEGF-C-induced angiogenesis, lymphangiogenesis and tumor growth in vivo.\",\n      \"method\": \"Co-transfection in LoVo (furin-deficient) cells, in vitro digestion of synthetic fluorogenic peptide, inhibition with prosegment inhibitors, CHO cell xenograft model in nude mice with cleavage-site mutants\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro enzymatic assay combined with cell-based reconstitution and in vivo functional validation\",\n      \"pmids\": [\"12782675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PC5A (PCSK5) co-localizes with alphav integrin in vascular smooth muscle cells (VSMCs) during vascular remodeling in vivo; endoproteolytic cleavage of alphav integrin by PC5 occurs in the trans-Golgi network, as shown by brefeldin A inhibition; furin mRNA is not upregulated during neointima formation, whereas PC5A mRNA is, indicating PC5 is the major convertase for alphav integrin activation in this context.\",\n      \"method\": \"Comparative immunocytochemistry, Northern blot, in situ hybridization, Golgi disruption with brefeldin A, balloon injury model in rodents\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple in vivo and cell biology methods supporting TGN cleavage, but no direct reconstitution of PC5 cleaving alphav\",\n      \"pmids\": [\"12649739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PC5 (PCSK5) is required for alphav integrin endoproteolytic activation in vascular smooth muscle cells; PC5-specific antisense oligonucleotides and the pharmacological PC inhibitor dec-CMK block alphav cleavage, inhibit VSMC adhesion to vitronectin, inhibit migration on vitronectin, and reduce focal adhesion kinase (Y397) autophosphorylation and Akt activation without affecting ERK1/2 phosphorylation.\",\n      \"method\": \"Antisense oligonucleotides against PC5, pharmacological inhibitor (dec-CMK), immunoblotting, VSMC adhesion and migration assays, FAK/Akt/ERK phosphorylation analysis, immunohistochemistry of human endarterectomy lesions\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific loss-of-function (antisense + pharmacological) with defined cellular and signaling phenotypes, human tissue validation\",\n      \"pmids\": [\"14970114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PC6 (PCSK5) is specifically induced in uterine stromal cells at the embryo attachment site during early pregnancy in mice; morpholino antisense oligonucleotide-mediated knockdown of PC6 in the mouse uterus completely blocks embryo implantation; PC6 is also dramatically upregulated during uterine decidualization in primates.\",\n      \"method\": \"In vivo morpholino antisense knockdown in mice, immunohistochemistry during early pregnancy (mouse, rhesus monkey, human), timed pregnancy studies\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function with complete implantation failure phenotype, replicated in multiple species\",\n      \"pmids\": [\"15601911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PCSK9 is inactivated by furin and/or PC5/6A through cleavage at the motif RFHR↓218; gain-of-function PCSK9 mutations (R218S, F216L, D374Y) associated with hypercholesterolemia result in loss of furin/PC5/6A processing; this cleavage may reduce PCSK9 lifetime and its ability to degrade LDL receptor.\",\n      \"method\": \"Cell transfection experiments, site-directed mutagenesis of PCSK9, immunoblotting for cleavage products, analysis of circulating human plasma\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct demonstration of substrate cleavage with multiple natural mutants tested, human plasma validation\",\n      \"pmids\": [\"16912035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Poly-arginine peptides (up to nona-L-Arg) are potent nanomolar inhibitors of PC5/6A (Ki ~150 nM for nona-L-Arg), with nona-D-Arg being even more potent (Ki ~19 nM); positional scanning libraries reveal strong preference for basic residues in all positions of the PC5/6A active site.\",\n      \"method\": \"Positional scanning-synthetic peptide combinatorial library (PS-SPCL) screening, enzymatic inhibition assays (Ki determination)\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay with systematic substrate/inhibitor characterization\",\n      \"pmids\": [\"17012622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A predicted alpha-helix in the C-terminus of PC5/6A (PCSK5) is critical for targeting to dense-core secretory granules in AtT-20 cells, functioning by the same mechanism as the granule-targeting helices of PC1/3 and PC2; hydrophobic amino acid clustering in the helix correlates with granule-sorting efficiency.\",\n      \"method\": \"C-terminal domain fusion proteins targeting heterologous constitutively secreted protein, subcellular distribution analysis in AtT-20 cells, mutagenesis of predicted alpha-helix\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structure-function mutagenesis with functional targeting assay in endocrine cells\",\n      \"pmids\": [\"17645548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GDF11 is cleaved and activated by PCSK5A but not by PCSK5A-C470R; selectivity resides in a P1' Asn in the RSRR↓N cleavage motif; PCSK5 is essential for embryonic anteroposterior patterning, nephrogenesis, skeletal, and anorectal development, at least partly through GDF11 activation and consequent regulation of Hox gene paralogs (Hoxa, Hoxc, Hoxd) and Mnx1.\",\n      \"method\": \"ENU-induced mouse mutation (C470R), compound Pcsk5 mutants, epiblast-specific conditional deletion, in vitro and ex vivo cleavage assays, in situ hybridization, P1' mutagenesis, Gdf11-deficient embryo comparison\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution of substrate cleavage with mutagenesis, multiple genetic models, in vivo epistasis with Gdf11 knockout\",\n      \"pmids\": [\"18519639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PC5/6 (PCSK5) is required for embryo implantation and is essential for anteroposterior patterning (extra vertebrae, tail agenesis, kidney agenesis) in a GDF11-dependent manner; Gdf11 P1' Asn confers selectivity for PC5/6 over other convertases; epiblast-specific deletion confirms the embryonic requirement.\",\n      \"method\": \"Conditional epiblast-specific Pcsk5 knockout (CD1/129/Sv/C57BL/6 background), in vitro and ex vivo cleavage assays, in situ hybridization for Pcsk5 and Gdf11, P1' Asn mutagenesis of cleavage motif\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — conditional genetic model with substrate specificity confirmed biochemically, replicated independently from PMID 18519639\",\n      \"pmids\": [\"18378898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Furin, PACE4, PC5, and PC7 all cleave preprohepcidin at the RRRRR↓59DT motif to generate active hepcidin; site-directed mutagenesis of the cleavage site abrogates processing; hepcidin with RRRRR→SSSSS mutation is inactive as an inducer of ferroportin degradation.\",\n      \"method\": \"Cell transfection in Huh-7 and LoVo cells, inhibitor studies with alpha1-PDX and ppFurin, site-directed mutagenesis, in vitro peptide digestion, developmental expression analysis\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct reconstitution in furin-deficient cells with multiple convertases, mutagenesis of cleavage site, functional readout\",\n      \"pmids\": [\"18664504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PC5/6 (PCSK5) is protective against intestinal tumorigenesis; enterocyte-specific Pcsk5 knockout in the ApcMin/+ mouse model results in significantly higher tumor numbers in the duodenum and premature mortality; human intestinal tumors systematically downregulate PC5/6 expression.\",\n      \"method\": \"Enterocyte-specific conditional Pcsk5 knockout, ApcMin/+ double mutant mouse model, tumor enumeration, human tumor expression analysis\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean conditional KO with defined in vivo phenotype, human tissue correlation\",\n      \"pmids\": [\"19737405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Zebrafish PCSK5.1 and PCSK5.2 are co-orthologs of mammalian PCSK5; PC5.1-deficient embryos display abnormal neuromast deposition in the lateral line system and loss of normal touch response, demonstrating a role in sensory organ development.\",\n      \"method\": \"cDNA cloning of zebrafish PCSK5.1 and PCSK5.2, morpholino-mediated knockdown of PC5.1, synteny analysis, in situ hybridization\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function in zebrafish with specific sensory phenotype; ortholog confirmed by synteny\",\n      \"pmids\": [\"20882679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PCSK5 (PC5/6) expression is selectively elevated during the transition from two-layer secondary to pre-antral follicle in the mouse ovary; activin A selectively enhances PCSK5 expression; inhibition of proconvertase activity blocks inhibin alpha- and beta-subunit maturation; overexpression of PC5/6 in furin-deficient cells increases inhibin alpha- and beta(B)-subunit maturation, identifying inhibin subunits as substrates of PCSK5.\",\n      \"method\": \"Real-time quantitative RT-PCR, inhibitor dec-RVKR-CMK in granulosa cells, overexpression of PC5/6 in furin-deficient cells, immunoblotting for inhibin subunit maturation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — substrate identification by gain-of-function in furin-deficient cells plus loss-of-function with inhibitor, two orthogonal approaches\",\n      \"pmids\": [\"21408162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PC6 (PCSK5) cleaves the N-terminus of alpha-dystroglycan (alpha-DG-N) at a PC6-cleavage site near alpha-DG-N; this removal is required for embryo attachment to endometrial epithelial cells; PC6 knockdown reduces alpha-DG-N removal from the cell surface and blastocyst adhesion; mutating the PC6-cleavage site prevents alpha-DG-N removal and causes retention of full-length alpha-DG with loss of cell adhesiveness; alpha-DG-N is removed from endometrial tissue in vivo coinciding with receptivity.\",\n      \"method\": \"In vitro cleavage assay of PC6-cleavage site peptide, PC6 siRNA knockdown, site-directed mutagenesis of cleavage site, blastocyst adhesion assay, in vivo endometrial tissue analysis, flow cytometry for cell surface alpha-DG\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct enzymatic cleavage demonstrated, loss-of-function with knockdown and cleavage site mutagenesis, in vivo validation\",\n      \"pmids\": [\"26077903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Osteopontin (OPN) is a novel substrate for PC5/6 (PCSK5) in bone; PC5/6A directly cleaves OPN at noncanonical and canonical consensus sequences, reducing full-length OPN (~70 kDa) to N-terminal (~50 kDa) and C-terminal (~18/16 kDa) fragments; PC5/6-knockout mice show altered OPN processing in bone and reduced mineralization; Pcsk5 and Opn are co-expressed in bone cells.\",\n      \"method\": \"In silico cleavage site analysis, ex vivo co-transfection of OPN and PC5/6, cell-free enzyme-substrate assay, mass spectrometry of cleavage products, micro-CT of KO embryos, in situ hybridization, immunoblotting of bone extracts from KO vs. WT mice\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay, mass spectrometry of cleavage sites, in vivo KO validation with multiple orthogonal methods\",\n      \"pmids\": [\"29126984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Pcsk5 is required specifically in the cranio-cardiac mesoderm for cardiogenesis; conditional deletion in all epiblastic lineages recapitulates all developmental malformations except tracheo-esophageal defects; deletion specifically in cardiogenic or pharyngeal mesodermal progenitors (forming later from cranio-cardiac mesoderm) or in neural crest does not affect heart development.\",\n      \"method\": \"MRI of mouse embryo heart development, multiple tissue-specific conditional Cre-mediated Pcsk5 deletions (epiblast, cranio-cardiac mesoderm, cardiogenic progenitors, pharyngeal mesoderm, neural crest)\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic conditional deletion mapping with multiple Cre lines and imaging phenotype\",\n      \"pmids\": [\"28446132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCSK5 activates precursor TGF-beta (pro-TGF-beta) by binding and cleaving at the pro-TGF-beta cleavage site, thereby activating the TGF-beta/SMAD2/3 pathway and promoting extracellular matrix expression in adventitial fibroblasts; this contributes to vascular fibrosis in Takayasu arteritis. Leflunomide inhibits PCSK5 and pro-TGF-beta binding, reducing TGF-beta activation.\",\n      \"method\": \"Co-immunoprecipitation of PCSK5 and pro-TGF-beta, overexpression of PCSK5 in adventitial fibroblasts, immunoblotting for mature TGF-beta and SMAD2/3 phosphorylation, ECM protein expression, leflunomide treatment in cells and patients\",\n      \"journal\": \"Journal of autoimmunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — substrate binding demonstrated by Co-IP, gain-of-function with downstream signaling, but direct in vitro cleavage assay not shown\",\n      \"pmids\": [\"38972101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The most efficiently cleaved PC5/6A fluorogenic substrate is acetyl-Arg-Arg-Tle-Lys-Arg-AMC (highest kcat/KM), establishing the active-site substrate preference of PC5/6A among a panel of novel synthetic substrates.\",\n      \"method\": \"In vitro enzymatic assay of novel fluorogenic peptide substrates with purified PC5/6A, kinetic characterization (kcat, KM, kcat/KM)\",\n      \"journal\": \"Analytical biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic characterization with systematic substrate panel\",\n      \"pmids\": [\"35964735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PC5 (PCSK5) processes pro-CCK into glycine-extended CCK 12 and CCK 22 in neuronal cell lines (GT1-7, SK-N-MC, SK-N-SH) that express PC5 but not PC1 or PC2, demonstrating a role for PC5 in CCK processing distinct from PC1/PC2.\",\n      \"method\": \"RT-PCR and Western blot for convertase expression, stable CCK overexpression, radioimmunoassay for pro-CCK cleavage products, gel filtration chromatography, carboxypeptidase B treatment\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based substrate processing with endogenous PC5 in PC1/PC2-null context; no direct reconstitution\",\n      \"pmids\": [\"11457520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"siRNA-mediated knockdown of PC5 (PCSK5) in STC-1 intestinal cells reduces CCK secretion (particularly CCK 22 in media) and causes a compensatory ~3-fold increase in PC2 mRNA and protein, providing direct evidence that PC5 is involved in CCK processing.\",\n      \"method\": \"Stable transfection with siRNA hairpin constructs targeting PC5, quantitative PCR, Western blot, CCK radioimmunoassay\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct loss-of-function (siRNA) with specific substrate (CCK 22) and compensatory response readout\",\n      \"pmids\": [\"16266771\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCSK5 (PC5/6) is a subtilisin/kexin-like serine endoprotease expressed as two main isoforms (soluble PC5/6A targeted to regulated secretory granules via a C-terminal alpha-helix sorting signal, and membrane-bound PC5/6B localized to the Golgi) that cleaves precursor proteins at basic amino acid motifs (K/R-Xn-K/R↓) to activate a wide range of substrates including GDF11 (with selectivity conferred by a P1' Asn in RSRR↓N), BMP-4, VEGF-C, PCSK9, pro-TGF-beta, alphav integrin, prorenin, hepcidin, osteopontin, alpha-dystroglycan N-terminus, inhibin subunits, CCK, and viral hemagglutinins, thereby playing essential in vivo roles in embryonic anteroposterior patterning, nephrogenesis, cardiogenesis, uterine receptivity/embryo implantation, bone mineralization, vascular remodeling, and intestinal tumor suppression.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PCSK5 (PC5/6) is a subtilisin/kexin-family serine endoprotease that cleaves precursor proteins at basic amino acid motifs to activate a broad range of substrates in developmental, endocrine, vascular, and immune contexts. It exists as two isoforms—soluble PC5/6A, which is targeted to regulated secretory granules via a C-terminal alpha-helix sorting signal, and membrane-bound PC5/6B, which localizes to the Golgi—and processes substrates including GDF11 (with selectivity conferred by a P1' Asn), BMP-4, VEGF-C, PCSK9, pro-TGF-beta, alphav integrin, prorenin, hepcidin, osteopontin, alpha-dystroglycan N-terminus, inhibin subunits, CCK, and viral hemagglutinins [PMID:8341687, PMID:8947550, PMID:18519639, PMID:9707432, PMID:12782675, PMID:16912035, PMID:29126984, PMID:26077903]. Conditional genetic studies in mouse demonstrate that PCSK5 is essential for embryonic anteroposterior patterning and nephrogenesis largely through GDF11 activation and Hox gene regulation, for cardiogenesis via action in cranio-cardiac mesoderm, for uterine receptivity and embryo implantation, for bone mineralization through osteopontin processing, and for intestinal tumor suppression in the ApcMin/+ model [PMID:18378898, PMID:27, PMID:19737405, PMID:15601911, PMID:29126984]. In the vasculature, PCSK5 activates alphav integrin in smooth muscle cells to promote adhesion, migration, and FAK/Akt signaling, and cleaves pro-TGF-beta in adventitial fibroblasts to drive TGF-beta/SMAD2/3-dependent extracellular matrix production [PMID:14970114, PMID:38972101].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of PCSK5 as a new member of the proprotein convertase family established that subtilisin/kexin-like processing enzymes extend beyond furin and PC1/2, with expression in both endocrine and non-endocrine tissues.\",\n      \"evidence\": \"cDNA cloning, Northern blotting, and in situ hybridization from mouse tissues\",\n      \"pmids\": [\"8341687\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous substrates unknown\", \"Enzymatic specificity versus furin/PACE4 not defined\", \"No loss-of-function data\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstration that PC5/6 can proteolytically activate avian influenza hemagglutinin in furin-deficient cells established it as a functionally active basic-amino-acid-directed endoprotease with overlapping but distinct substrate capacity relative to furin.\",\n      \"evidence\": \"Vaccinia virus expression system in furin-deficient LoVo cells with rescue of viral replication\",\n      \"pmids\": [\"8057485\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate selectivity rules not established\", \"No known physiological substrates in mammals yet\", \"Prosomatostatin shown not to be a substrate, highlighting unexplained specificity (PMID:7720860)\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Discovery that PCSK5 generates two isoforms (soluble PC5-A and membrane-bound PC5-B) sorted to distinct compartments—secretory granules versus Golgi—resolved how one gene could serve both regulated and constitutive secretory pathways, with a C-terminal 38-residue segment directing granule entry.\",\n      \"evidence\": \"Stable transfection of AtT-20 cells, electron microscopy immunohistochemistry, C-terminal deletion mutagenesis\",\n      \"pmids\": [\"8947550\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the sorting signal not resolved at atomic level\", \"Relative contributions of PC5-A vs PC5-B to specific substrate processing unknown\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of the first endogenous mammalian substrates—RPTPmu and prorenin—showed that PC5/6 operates on diverse precursor classes beyond neuropeptides, with active-site mutagenesis confirming catalytic dependence.\",\n      \"evidence\": \"COS cell co-transfection with active-site Ser→Ala mutant (RPTPmu), co-transfection in GH4C1 cells with prorenin cleavage-site mutants\",\n      \"pmids\": [\"8620001\", \"8901832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of RPTPmu and prorenin cleavage by PC5 not tested genetically\", \"Redundancy with furin for these substrates not resolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"PC5-A was shown to process pro-neurotensin/neuromedin N in early compartments of the regulated secretory pathway and BMP-4 in Xenopus oocytes, establishing roles in both neuroendocrine and developmental morphogen processing.\",\n      \"evidence\": \"Stable transfection in PC12 cells with metabolic labeling; Xenopus oocyte cleavage assays with alpha1-PDX inhibition and epistasis\",\n      \"pmids\": [\"9738000\", \"9707432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"BMP-4 cleavage redundancy with furin not resolved genetically\", \"P1' determinants of selectivity not yet identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Evidence that PC5 processes pro-CCK in neuronal cell lines lacking PC1/PC2 extended the substrate repertoire to gut-brain peptide hormones, later confirmed by siRNA knockdown reducing CCK22 secretion.\",\n      \"evidence\": \"RT-PCR/Western blot for convertase expression in GT1-7 cells; siRNA knockdown of PC5 in STC-1 cells with CCK radioimmunoassay\",\n      \"pmids\": [\"11457520\", \"16266771\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct in vitro reconstitution of PC5 cleaving pro-CCK\", \"Compensatory PC2 upregulation upon PC5 knockdown complicates interpretation\", \"In vivo genetic validation not performed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of VEGF-C and alphav integrin as PC5 substrates connected the enzyme to angiogenesis/lymphangiogenesis and vascular smooth muscle cell biology, with VEGF-C cleavage validated in vivo via tumor xenografts and alphav processing linked to FAK/Akt signaling.\",\n      \"evidence\": \"LoVo cell reconstitution and CHO xenograft model for VEGF-C; antisense oligonucleotides and dec-CMK inhibitor in VSMCs, adhesion/migration assays, human endarterectomy tissue\",\n      \"pmids\": [\"12782675\", \"12649739\", \"14970114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of furin, PC5, and PC7 to VEGF-C processing in specific tissues unresolved\", \"Direct in vitro cleavage of alphav by purified PC5 not shown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"In vivo knockdown of PC6 in the mouse uterus completely blocked embryo implantation, establishing the first essential non-redundant physiological role for PCSK5 in reproduction.\",\n      \"evidence\": \"Morpholino antisense knockdown in mouse uterus, immunohistochemistry in mouse/rhesus/human endometrium\",\n      \"pmids\": [\"15601911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the critical substrate(s) mediating implantation not established\", \"Genetic knockout confirmation not yet performed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that PC5/6A cleaves PCSK9 at RFHR↓218—with gain-of-function hypercholesterolemia mutations abolishing this cleavage—established a link between PCSK5 activity and cholesterol metabolism regulation.\",\n      \"evidence\": \"Cell transfection with PCSK9 mutants, immunoblotting, human plasma analysis\",\n      \"pmids\": [\"16912035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of PC5/6A-mediated PCSK9 inactivation versus furin not genetically resolved\", \"Relative contribution to circulating PCSK9 levels unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"ENU mutagenesis and conditional knockout in mice revealed that PCSK5 is essential for embryonic anteroposterior patterning, kidney development, and skeletal organization primarily through activation of GDF11 at a P1' Asn-containing cleavage motif, resolving the key in vivo substrate and the molecular basis of selectivity over other convertases.\",\n      \"evidence\": \"ENU-induced C470R mutation, epiblast-specific conditional deletion, in vitro cleavage assays with P1' mutagenesis, comparison with Gdf11-knockout phenotype\",\n      \"pmids\": [\"18519639\", \"18378898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether all patterning phenotypes are GDF11-dependent or involve additional substrates\", \"Crystal structure of PC5/6 explaining P1' Asn preference not available\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstration that PC5 cleaves preprohepcidin at the polybasic site for hepcidin maturation connected PCSK5 to systemic iron homeostasis, though with redundancy among multiple convertases.\",\n      \"evidence\": \"Cell transfection in Huh-7 and LoVo cells, site-directed mutagenesis of cleavage site, in vitro peptide digestion\",\n      \"pmids\": [\"18664504\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo importance of PC5 versus furin/PACE4/PC7 for hepcidin maturation unresolved\", \"No genetic iron phenotype reported for Pcsk5 knockouts\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Enterocyte-specific Pcsk5 knockout in ApcMin/+ mice demonstrated a tumor-suppressive function, with increased duodenal tumors and premature mortality, paralleled by systematic PCSK5 downregulation in human intestinal tumors.\",\n      \"evidence\": \"Conditional Pcsk5 knockout crossed to ApcMin/+ model, tumor enumeration, human tumor expression analysis\",\n      \"pmids\": [\"19737405\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the substrate(s) mediating tumor suppression unknown\", \"Mechanism of PCSK5 downregulation in human tumors not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of alpha-dystroglycan N-terminus as a PC6 substrate required for embryo attachment to endometrial epithelium provided a molecular mechanism for the implantation role discovered a decade earlier.\",\n      \"evidence\": \"In vitro cleavage of PC6-site peptide, PC6 siRNA knockdown, cleavage-site mutagenesis, blastocyst adhesion assay, in vivo endometrial tissue analysis\",\n      \"pmids\": [\"26077903\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether alpha-DG-N is the sole critical substrate for implantation or acts alongside others\", \"Genetic rescue of implantation defect by alpha-DG-N removal not shown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Systematic conditional deletion across multiple Cre lines established that PCSK5 is required specifically in cranio-cardiac mesoderm for cardiogenesis, refining the tissue-of-action beyond what epiblast-wide deletion could show.\",\n      \"evidence\": \"Multiple tissue-specific Cre-mediated Pcsk5 deletions with MRI phenotyping of embryonic hearts\",\n      \"pmids\": [\"28446132\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific substrate(s) processed by PC5/6 in cranio-cardiac mesoderm for heart development remain unknown\", \"Whether the cardiogenesis role is GDF11-dependent or involves distinct substrates not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of osteopontin as a direct PC5/6A substrate in bone, with KO mice showing altered OPN processing and reduced mineralization, established a role for PCSK5 in skeletal mineralization.\",\n      \"evidence\": \"Cell-free enzyme-substrate assay, mass spectrometry of cleavage products, micro-CT of KO embryos, in situ hybridization\",\n      \"pmids\": [\"29126984\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether OPN processing is the primary mechanism for mineralization defects or secondary to broader developmental abnormalities\", \"Cleavage at noncanonical sites not fully characterized kinetically\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Co-immunoprecipitation of PCSK5 with pro-TGF-beta and demonstration of enhanced SMAD2/3 signaling upon PCSK5 overexpression in adventitial fibroblasts linked the enzyme to vascular fibrosis in Takayasu arteritis, extending substrate repertoire to TGF-beta superfamily ligands beyond GDF11/BMP-4.\",\n      \"evidence\": \"Co-IP of PCSK5 and pro-TGF-beta, overexpression in fibroblasts, SMAD2/3 phosphorylation, leflunomide inhibition\",\n      \"pmids\": [\"38972101\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct in vitro cleavage assay of pro-TGF-beta by purified PC5/6 not shown\", \"Specificity versus furin for pro-TGF-beta not tested\", \"Leflunomide mechanism of inhibition not biochemically defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No crystal or cryo-EM structure of PC5/6 exists, and the structural basis for its P1' Asn selectivity, isoform-specific substrate channeling, and the identities of critical substrates in cardiogenesis and intestinal tumor suppression remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution structure of PC5/6\", \"Substrate identity for cardiogenesis unknown\", \"Mechanism of tumor suppression in intestine uncharacterized at substrate level\", \"Relative in vivo redundancy with furin and PACE4 for most substrates not genetically dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 5, 6, 10, 12, 16, 19, 21, 24, 25, 26, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [4, 11, 13]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [4, 9, 18]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 5, 6, 10, 12, 16, 19, 21, 24, 25, 26, 29]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [10, 19, 20, 27]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 12, 14, 28]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GDF11\",\n      \"BMP4\",\n      \"PCSK9\",\n      \"VEGFC\",\n      \"ITGAV\",\n      \"OPN\",\n      \"DAG1\",\n      \"TGFB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}