{"gene":"FURIN","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":1990,"finding":"Furin (encoded by the human FUR gene) is a subtilisin-like serine protease with substrate specificity for paired basic residues. Cotransfection of FUR cDNA with pro-von Willebrand factor (pro-vWF) cDNA in COS-1 cells showed increased proteolytic processing of pro-vWF at the Arg-Ser-Lys-Arg site; mutation of the P1 Arg abolished cleavage, establishing furin as a proprotein processing enzyme cleaving after paired basic residues.","method":"Cotransfection of COS-1 cells with FUR cDNA and pro-vWF constructs (wild-type and Arg→Gly mutant); Western blot analysis","journal":"Molecular biology reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct enzymatic substrate cleavage demonstrated in cells with mutagenesis validating the recognition site; foundational study replicated widely in subsequent literature","pmids":["2094803"],"is_preprint":false},{"year":1993,"finding":"PACE/furin (PCSK3) processes pro-factor IX at the authentic propeptide cleavage site within the secretory pathway. Co-transfection of PACE with profactor IX in CHO cells resulted in secretion of fully processed factor IX; PACE4 did not increase processing; an Arg39Thr P1 mutation abolished cleavage; the alpha1-antitrypsin Pittsburgh (PDX) inhibitor blocked furin-mediated processing.","method":"Co-transfection in CHO cells; amino-terminal sequence analysis; pulse-chase labeling; specific protease inhibitor (alpha1-PDX) experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in cells with site-directed mutagenesis of cleavage site and pharmacological inhibitor validation; multiple orthogonal methods in one study","pmids":["8473289"],"is_preprint":false},{"year":1994,"finding":"Expression of the human FUR gene is directed by three alternative promoters (P1, P1A, P1B) that produce distinct mRNA isoforms differing in their 5'-UTRs. P1 contains a TATA box and is transactivated by C/EBP-beta and bound by SP1; P1A and P1B are GC-rich housekeeping-type promoters. Differential promoter usage modulates furin enzyme levels.","method":"Primer extension analysis; luciferase reporter transfection assays; electromobility shift assays; DNase I footprinting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (EMSA, footprinting, reporter assays) in one study establishing promoter architecture and transcription factor binding","pmids":["8132667"],"is_preprint":false},{"year":1995,"finding":"Furin cleaves Shiga toxin A-chain at the Arg-X-X-Arg motif, generating A1 and A2 fragments, and this cleavage is required for efficient intoxication. LoVo cells (furin-deficient) cleaved intact A-chain very slowly; LoVo cells transfected with furin cleaved it efficiently. Furin-nicked toxin was ~20-fold more active than unnicked toxin in furin-deficient cells.","method":"In vitro digestion with soluble furin; transfection of furin into LoVo (furin-deficient) cells; protein synthesis inhibition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay combined with genetic complementation in furin-deficient cells, functional toxicity readout; multiple orthogonal methods","pmids":["7738018"],"is_preprint":false},{"year":1998,"finding":"Notch1 receptor (300 kDa precursor) is constitutively processed by a furin-like convertase in the extracellular region at the sequence RQRR (aa 1651-1654); only cleaved Notch1 fragments are present at the cell surface. Processing was blocked by alpha1-PDX (furin inhibitor) and calcium ionophore A23187; in furin-deficient LoVo cells, processing did not occur; in vitro digestion with purified furin confirmed the cleavage site; mutation of the four basic residues (plus secondary sites) completely abolished processing.","method":"Expression in furin-deficient LoVo cells; alpha1-PDX inhibitor treatment; in vitro digestion with purified furin; site-directed mutagenesis of RQRR cleavage site","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified furin, genetic complementation in furin-deficient cells, mutagenesis of cleavage site; multiple orthogonal methods in single study","pmids":["9653148"],"is_preprint":false},{"year":1998,"finding":"BMP-4 is proteolytically activated by furin (and/or PC6B) during vertebrate embryogenesis. In Xenopus embryos, ectopic expression of alpha1-PDX (furin inhibitor) phenocopied BMP-4 blockade (dorsal mesoderm induction, neural induction); this was rescued by downstream BMP-4 signaling components. alpha1-PDX prevented BMP-4 cleavage in an oocyte translation assay. In vitro digestion showed furin and PC6B can cleave BMP-4 and are sensitive to alpha1-PDX.","method":"Xenopus embryo microinjection; oocyte translation assay; in vitro digestion assay; epistasis by downstream pathway rescue","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution, in vivo epistasis in Xenopus with rescue experiment, pharmacological inhibition; single lab but multiple orthogonal methods","pmids":["9707432"],"is_preprint":false},{"year":2001,"finding":"Furin is the primary endogenous TGF-beta1-converting enzyme. Among PC family members, furin most satisfies requirements for physiological TGF-beta1 maturation: alpha1-PDX (furin inhibitor) blocked ~80% of TGF-beta1 processing by endogenous enzymes in an in vitro digestion assay; genetic complementation of furin-deficient LoVo cells with wild-type furin gene restored production of mature, bioactivatable TGF-beta1.","method":"In vitro digestion assay with alpha1-PDX inhibitor; genetic complementation of furin-deficient LoVo cells; bioactivity assay for mature TGF-beta1","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — genetic complementation in null cells plus pharmacological inhibition plus functional bioactivity readout; single lab with multiple orthogonal methods","pmids":["11141505"],"is_preprint":false},{"year":2001,"finding":"TGF-beta1 transcriptionally upregulates its own convertase furin via the fur P1 promoter through Smad2/Smad4 signaling. Smad2 and Smad4 (possibly in complex with FAST-1) drive constitutive and TGF-beta1-inducible transactivation of the P1 promoter; dominant-negative Smad2(3SA) and Smad7 inhibited this activation; overexpression of Smad2/Smad4 enhanced P1 transactivation.","method":"Promoter-luciferase reporter cotransfection with dominant-negative Smads (Smad2-3SA, Smad7) and overexpression constructs in HepG2 cells; deletion analysis","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reporter assay with dominant-negative constructs in single lab; no direct Smad binding to fur promoter demonstrated by ChIP or footprinting in this abstract","pmids":["11424093"],"is_preprint":false},{"year":2002,"finding":"Furin proteolytically cleaves extracellular superoxide dismutase (EC-SOD) in the polybasic heparin-binding region intracellularly (after passage through the Golgi but before secretion) at Arg213; mutation of Arg213 renders EC-SOD resistant to furin processing. Furin cleavage followed by a carboxypeptidase removes the heparin-binding region, determining EC-SOD tissue distribution and half-life.","method":"Furin overexpression in mammalian cells; specific protease inhibitors; in vitro furin digestion of purified EC-SOD; Arg213 site-directed mutation; intracellular localization by secretory pathway inhibitors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified proteins, site-directed mutagenesis of cleavage site, subcellular localization of processing event; multiple orthogonal approaches in single study","pmids":["11861638"],"is_preprint":false},{"year":2003,"finding":"Furin is required for proteolytic processing of the Semliki Forest virus (SFV) p62 envelope protein precursor to E2. In furin-deficient FD11 cells, p62 was not cleaved; transfection with human furin restored cleavage. Purified furin cleaved p62 in vitro without prior low-pH exposure. Processing controls the pH threshold for membrane fusion: unprocessed wt/p62 virus required lower pH than processed virus to trigger fusion. Mutation of the furin recognition motif in p62 (mutant L) additionally impaired virus-cell binding beyond effects on fusion.","method":"Furin-deficient CHO (FD11) cells; reconstitution by furin transfection; in vitro cleavage with purified furin; site-directed mutagenesis of furin cleavage motif; fusion and infectivity assays","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified furin, genetic complementation in furin-null cells, mutagenesis of recognition site, functional fusion assay; multiple orthogonal methods","pmids":["12584323"],"is_preprint":false},{"year":2004,"finding":"Crystal structures of the catalytic core domain of furin were determined, providing atomic-level insight into substrate specificity and catalytic mechanism of the proprotein convertase. The structures reveal how furin recognizes polybasic substrates and inform understanding of the mechanism of serine protease catalysis by this family.","method":"X-ray crystallography of furin catalytic core domain","journal":"Trends in biochemical sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — review article summarizing crystal structures; primary structural data cited but not the original structure paper; single reference in corpus","pmids":["15102434"],"is_preprint":false},{"year":2006,"finding":"Furin performs the first cleavage of RPTPkappa (a receptor tyrosine phosphatase) in the secretory pathway; subsequent ADAM10-mediated ectodomain shedding and gamma-secretase-dependent intramembrane proteolysis release the intracellular phosphatase domain (PIC), which translocates to the nucleus and dephosphorylates beta-catenin, activating beta-catenin transcriptional activity.","method":"Pharmacological inhibitors; co-immunoprecipitation; nuclear fractionation; leptomycin B nuclear export inhibition; PIC phosphatase activity assay; beta-catenin reporter assay; furin inhibitor treatment","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple protease inhibitors, fractionation, reporter assays in one study; furin's specific contribution established by inhibitor but not confirmed by genetic null in this abstract","pmids":["16648485"],"is_preprint":false},{"year":2006,"finding":"Pro-ADAMTS9 is processed by furin at the cell surface, not intracellularly in the TGN. Pulse-chase analysis showed intact zymogen was secreted before processing. Furin-deficient cells failed to process pro-ADAMTS9; complementation with furin restored cleavage. siRNA-mediated furin knockdown reduced ADAMTS9 processing. PC5A could also process pro-ADAMTS9 but similarly processed forms were absent intracellularly.","method":"Pulse-chase analysis; furin-deficient cell lines; furin transfection rescue; PC inhibitors; furin siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic null complementation, siRNA knockdown, pharmacological inhibition, and pulse-chase localization; multiple orthogonal methods in single study","pmids":["16537537"],"is_preprint":false},{"year":2008,"finding":"Cripto (a GPI-anchored proteoglycan) binds both the Nodal precursor and the proprotein convertases Furin and PACE4, directing Nodal processing to the cell surface rather than the TGN/endosomal system. Cripto-Nodal association occurs during secretion; brefeldin A blocked secretion but not Cripto/Nodal export to the cell surface, indicating exposure to extracellular convertases before the TGN. Cripto guides Nodal in detergent-resistant membranes to endocytic microdomains; a Cripto-interacting region in the Nodal propeptide potentiated effects of proteolytic maturation on signaling.","method":"Co-immunoprecipitation of Cripto with Furin/PACE4 and Nodal; brefeldin A treatment; density gradient fractionation; antibody uptake; GFP-Flotillin marker; signaling readout","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, subcellular fractionation, live-cell trafficking, and functional signaling readout; multiple orthogonal methods in one study","pmids":["18772886"],"is_preprint":false},{"year":2010,"finding":"Furin processes CD109 in the Golgi apparatus, cleaving the 205 kDa precursor at the RRRR motif (Arg1273) into 180 kDa and 25 kDa fragments. Mutation R1273S abolishes cleavage, and the uncleaved CD109-R1273S neither associates with the type I TGF-beta receptor nor significantly regulates TGF-beta signaling, whereas the processed 180/25 kDa CD109 complex associates with TGF-beta RI and suppresses TGF-beta signaling.","method":"Site-directed mutagenesis of furin cleavage site (RRRR→RRRSER); co-immunoprecipitation of CD109 with TGF-beta RI; cell growth and TGF-beta signaling assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Moderate — mutagenesis of cleavage site combined with Co-IP and functional TGF-beta signaling assay; multiple orthogonal methods showing cleavage is mechanistically required","pmids":["20101215"],"is_preprint":false},{"year":2010,"finding":"In hepatocytes, furin is the major in vivo inactivating protease of circulating PCSK9, cleaving it at Arg218 to generate a ~55 kDa inactive form. Hepatocyte-specific furin knockout (Fur-hKO) mice showed strongly reduced PCSK9 inactivated form in plasma and ~26% drop in LDL receptor protein in liver, with ~35% increase in PCSK9 mRNA and loss of PCSK9 cleavage. Only full-length, membrane-bound furin (not soluble furin) in primary hepatocytes performed this cleavage.","method":"Hepatocyte-specific conditional furin knockout mice; plasma PCSK9 cleavage analysis; LDL receptor protein quantification; furin overexpression in primary hepatocytes; human heterozygote mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO in vivo with multiple downstream molecular readouts (PCSK9 form, LDL receptor, PCSK9 mRNA), human genetic validation; strong evidence across multiple methods","pmids":["21147780"],"is_preprint":false},{"year":2012,"finding":"Furin is required in endothelial cells for cardiac development: endothelial-specific furin knockout (ecKO) mice die postnatally and exhibit ventricular septal defects and valve malformations. Furin-deficient endothelial cells cannot proliferate, rescued by extracellular soluble furin. Endothelin-1 (ET-1), adrenomedullin (Adm), and TGF-beta1—but not BMP4—were confirmed as in vivo endothelial furin substrates (mature ET-1 and BMP4 reduced ~90% in ecKO endothelial cells).","method":"Endothelial cell-specific Furin conditional knockout (Cre-lox); MRI of embryos; primary endothelial cell cultures; soluble furin rescue; substrate processing analysis (ET-1, Adm, TGF-beta1, BMP4)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — tissue-specific KO with defined in vivo phenotype, substrate processing analysis in primary cells, rescue experiment; multiple orthogonal methods","pmids":["22733989"],"is_preprint":false},{"year":2013,"finding":"Furin is required for trophoblast syncytialization. Furin is highly expressed in syncytial trophoblast; its expression is lower in pre-eclamptic placentas. Furin-specific siRNA or inhibitors blocked cytotrophoblast cell fusion in BeWo cells and human placental explants. IGF1R is a furin substrate whose processing is an essential mechanism for syncytialization. Lentivirus-mediated furin RNAi targeting mouse trophectoderm disrupted syncytiotrophoblast development and embryogenesis.","method":"siRNA knockdown; furin inhibitor treatment; BeWo cell fusion assay; primary cytotrophoblast and placental explant cultures; lentivirus-mediated RNAi in mouse trophectoderm; IGF1R processing analysis","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple loss-of-function approaches (siRNA, inhibitor, lentiviral RNAi in vivo) with defined cellular and developmental phenotypes and substrate (IGF1R) identified","pmids":["23598405"],"is_preprint":false},{"year":2013,"finding":"PCSK3/furin directly cleaves proapelin to generate apelin-13, without producing longer isoforms (apelin-36 or longer forms), in vitro. Neither PCSK1 nor PCSK7 showed appreciable proapelin cleavage activity. Both proapelin and PCSK3 transcript levels are increased in adipose tissue with obesity and during adipogenesis.","method":"In vitro cleavage assay of proapelin with purified PCSK3, PCSK1, and PCSK7; transcript expression analysis in adipose tissue","journal":"FEBS open bio","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution demonstrating direct cleavage and selectivity among PCSKs; single lab, expression correlation data supporting physiological relevance but not confirmed by cell/genetic experiments","pmids":["24251091"],"is_preprint":false},{"year":2014,"finding":"Furin is the major proprotein convertase required for processing of KISS1 into kisspeptins. shRNA-mediated knockdown of furin (but not PCSK5 or PCSK7) blocked KISS1 processing. PC inhibitors (Dec-RVKR-CMK and alpha1-PDX) completely inhibited KISS1 processing in KISS1-overexpressing cells.","method":"shRNA knockdown of furin, PCSK5, and PCSK7; PC inhibitor treatment (Dec-RVKR-CMK, alpha1-PDX); KISS1 processing assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA knockdown with specificity comparison across multiple PCSKs plus pharmacological inhibition; single lab, no in vitro reconstitution with purified enzyme","pmids":["24454770"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of human furin in complex with the peptidomimetic inhibitor MI-1148 (Ki = 5.5 pM) was determined, revealing that the N-terminal guanidinomethyl group in the para-position of the P5 phenyl ring occupies the same binding pocket as in structurally related inhibitors, defining key P5 interactions. MI-1148 also strongly inhibits PC1/3 but less so PC2.","method":"X-ray crystallography (co-crystal structure of furin with inhibitor MI-1148); enzyme inhibition assays (Ki determination); cell-based antiviral/antibacterial assays","journal":"ChemMedChem","confidence":"High","confidence_rationale":"Tier 1 / Moderate — co-crystal structure with functional inhibition constants; direct structural determination of binding interactions; single study but Tier 1 method","pmids":["25974265"],"is_preprint":false},{"year":2015,"finding":"PC7, Furin, and Pace4 jointly regulate E-cadherin processing during morula compaction in blastocyst formation; their combined activity modulates cell-cell adhesion required for ICM specification via Hippo/YAP signaling. Live imaging of a transgenic reporter substrate demonstrated differential PC activity in inner vs. outer cells in partially nonoverlapping compartments.","method":"PC7/Furin/Pace4 mutant embryos; furin inhibitor; live imaging of transgenic reporter substrate; E-cadherin processing analysis","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mutant embryos with live reporter imaging and E-cadherin processing readout; multiple PCs involved making furin's individual contribution partly inferential","pmids":["26416966"],"is_preprint":false},{"year":2016,"finding":"Furin-deficient myeloid cells exhibit elevated pro-inflammatory cytokine production and altered macrophage polarization. LysMCre-fur(fl/fl) mice had elevated serum IL-1beta, reduced splenocyte numbers, and accelerated LPS-induced mortality with elevated pro-inflammatory cytokines. Furin inhibited Nos2 and promoted Arg1 expression (M1/M2 balance). Furin was required for normal bioactive TGF-beta1 production but inhibited maturation of TACE and Caspase-1 in myeloid cells.","method":"Conditional myeloid furin knockout (LysMCre-fur(fl/fl)); LPS challenge model; serum cytokine quantification; genome-wide gene expression analysis; macrophage polarization markers","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined in vivo phenotype and molecular pathway readouts; single lab, multiple downstream substrates without direct biochemical reconstitution","pmids":["27527873"],"is_preprint":false},{"year":2018,"finding":"PCSK3/furin promotes intracellular cleavage of lipoprotein lipase (LPL) in adipocytes, and ANGPTL4 promotes this PCSK-mediated LPL cleavage. Pcsk3/furin silencing significantly decreased LPL cleavage in 3T3-L1 adipocytes; Angptl4 silencing diminished PCSK-mediated LPL cleavage; stimulation of ANGPTL4 by fasting enhanced furin-dependent LPL cleavage. The cleavage occurs intracellularly.","method":"siRNA silencing of Pcsk3/furin and Angptl4 in 3T3-L1 adipocytes; PCSK inhibitor (decanoyl-RVKR-CMK); Angptl4-/- mice; heparin-treatment to distinguish intracellular vs. surface LPL","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown, inhibitor, and KO mouse model converging on same conclusion; single lab but multiple orthogonal approaches","pmids":["30021841"],"is_preprint":false},{"year":2018,"finding":"PCSK3 (furin), PCSK5, and PCSK6 can all cleave GDF15 precursor to generate mature GDF15, both in vitro (in cardiomyocytes) and in vivo (in mouse hearts). These three PCSKs mediate a crucial step of GDF15 maturation through proteolytic cleavage.","method":"In vitro cleavage assays; overexpression of PCSK family members in cardiomyocytes; in vivo mouse heart analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro cleavage combined with in vivo mouse cardiac analysis; multiple PCSKs share activity limiting specificity of furin's individual contribution, single lab","pmids":["30104250"],"is_preprint":false},{"year":2019,"finding":"Furin inhibition (with alpha1-PDX) reduces atherosclerotic lesion area and vascular remodeling in Ldlr-/- and Apoe-/- mice. MMP2, a furin substrate, was significantly reduced in the aorta of inhibitor-treated mice. Furin overexpression in the wire-injury model caused a 67% increase in intimal plaque thickness, directly correlating furin levels with atherosclerosis. In vitro, furin inhibition reduced monocyte migration and macrophage/endothelial inflammatory gene expression.","method":"In vivo alpha1-PDX inhibitor administration in Ldlr-/- and Apoe-/- mice; wire-injury carotid model with furin overexpression; MMP2 substrate processing analysis; in vitro monocyte migration and cytokine assays","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gain- and loss-of-function with substrate (MMP2) analysis; single lab but multiple experimental models and both gain/loss approaches","pmids":["30651003"],"is_preprint":false},{"year":2021,"finding":"The furin cleavage site (PRRAR) in SARS-CoV-2 spike protein is critical for efficient replication in human respiratory cells and pathogenesis in vivo. Deletion of the furin site (ΔPRRA) reduced spike protein processing, impaired replication in Calu-3 human respiratory cells, and attenuated disease in hamster and K18-hACE2 transgenic mouse models. Despite attenuation, ΔPRRA mutant conferred protection against parental virus rechallenge.","method":"SARS-CoV-2 reverse genetics (furin site deletion mutant ΔPRRA); cell-based replication kinetics; hamster and transgenic mouse pathogenesis models; spike protein processing analysis; neutralization assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reverse genetics with defined mutation, multiple animal models (hamster + transgenic mouse), and mechanistic spike processing analysis; multi-lab study published in peer-reviewed journal","pmids":["33494095"],"is_preprint":false},{"year":2022,"finding":"Furin cleaves the SARS-CoV-2 spike protein at both S1/S2 (PRA685↓) and S2' (KPS815↓) sites. The S2' cleavage site was identified by proteomics for the first time, and its cleavage was strongly enhanced by ACE2 engagement with S protein. Novel furin inhibitors (BOS) blocked processing at both sites in HeLa cells. Combined furin (BOS) and TMPRSS2 (camostat) inhibition achieved ~95% reduction of SARS-CoV-2 infection of Calu-3 lung cells. TMPRSS2-mediated ACE2 shedding was required for TMPRSS2-dependent enhancement of fusion in the absence of S1/S2 priming; the collectrin dimerization domain of ACE2 was essential for TMPRSS2 effect on fusion.","method":"Proteomics identification of S2' cleavage site; pharmacological furin inhibitors (BOS); combined inhibitor assays; quantitative cell-to-cell fusion assays; SARS-CoV-2 infection of Calu-3 cells","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1/2 / Moderate — proteomics-based site identification combined with pharmacological inhibition in multiple assay systems; multiple orthogonal methods in single study","pmids":["35343766"],"is_preprint":false},{"year":2010,"finding":"Osteopontin (OPN) induces furin expression in cervical cancer cells via CD44-mediated activation of MKK3/6→p38→NF-kB signaling cascade. NF-kB-dependent transcription drives furin expression, which in turn enhances cell motility and HPV processing. Blockades of MKK3/6, p38alpha/beta, NF-kB, or furin all reduced OPN-induced cell motility and tumor growth in a xenograft model.","method":"Pharmacological inhibitors of MKK3/6, p38, NF-kB; furin expression analysis; cell motility assays; mouse xenograft model with OPN overexpression/shRNA knockdown; furin overexpression","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pathway inhibitors and genetic knockdown/overexpression with functional motility and in vivo tumor growth readouts; single lab, pathway placement by epistasis","pmids":["20980434"],"is_preprint":false},{"year":2005,"finding":"CDX2 transcription factor binds to the CBS2 sequence (nt -1827 to -1821) of the furin P1 promoter and activates furin expression during intestinal epithelial cell differentiation. CDX2-driven furin expression correlates with enterocyte differentiation; furin inhibition blocked lactase-phlorizin hydrolase activity and strongly attenuated epithelial polarity and brush-border formation.","method":"EMSA and supershift assays; site-specific mutagenesis of CDX2 binding site; chromatin immunoprecipitation; luciferase reporter assays; in situ hybridization; furin inhibitor treatment of Caco-2/15 cells","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — ChIP, EMSA with mutagenesis, and functional differentiation assay; multiple orthogonal methods linking CDX2-furin transcriptional regulation to epithelial differentiation","pmids":["16239403"],"is_preprint":false},{"year":2012,"finding":"Furin activates N-cadherin by cleaving its prosegment at RQKR↓DW161 (releasing an ~17 kDa prosegment), while PC5A inactivates NCAD by cleaving at a second site RIRSDR↓DK189 (releasing an ~20 kDa product that abolishes Trp161-dependent adhesion). In invasive glioma cells, furin and PC5A levels are inversely correlated; cell-surface expression of unprocessed proNCAD or PC5A-cleaved NCAD reduces cell-cell adhesion and increases migration.","method":"Analysis of NCAD processing in human glioma cell lines with different Furin/PC5A expression levels; furin-null vs. PC5A-expressing cells; prosegment size analysis; cell adhesion and migration assays","journal":"Neoplasia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — endogenous processing in cells with defined convertase expression levels and functional adhesion/migration readout; single lab without in vitro reconstitution","pmids":["23097623"],"is_preprint":false},{"year":2018,"finding":"Furin overexpression in transgenic mice increases dendritic spine density, enhances LTP and spatial memory, and elevates the ratio of mature BDNF to pro-BDNF in cortex and hippocampus along with increased ERK and CREB activity. Hippocampal CREB knockdown diminished LTP and cognitive facilitation in Furin-Tg mice, placing furin upstream of BDNF-ERK-CREB signaling in neuronal plasticity.","method":"Furin transgenic mice; dendritic spine counting; LTP electrophysiology; Morris water maze; BDNF processing (mature vs. pro); ERK and CREB phosphorylation; lentiviral CREB knockdown","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic overexpression with epistasis via CREB knockdown and BDNF substrate processing readout; single lab, gain-of-function model","pmids":["29302702"],"is_preprint":false},{"year":2018,"finding":"Placenta-specific 1 (Plac1) activates furin at the oocyte membrane during the germinal vesicle stage; active furin then activates IGF-1 receptor (IGF-1R) to maintain microvillus organization. Upon meiosis onset, active furin/IGF-1R complex relocates to cytoplasm and activates (phosphorylates) Akt to promote meiosis. Plac1 knockdown disrupted microvillus organization, reduced oocyte maturation, increased aneuploidy, and disrupted fertilization.","method":"Plac1 knockdown in mouse oocytes; immunoprecipitation-MALDI mass spectrometry; furin activity assay; IGF-1R processing and phospho-Akt analysis; live-cell localization imaging","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP/MS identification of Plac1-furin interaction with functional knockdown phenotype and downstream substrate analysis; single lab, mechanistic model inferred from correlative evidence","pmids":["29723063"],"is_preprint":false},{"year":2018,"finding":"Furin transgenic overexpression increases epileptic susceptibility; furin knockdown restrained epileptic activity. Furin influences neuronal inhibitory synaptic transmission by regulating postsynaptic GABA-A receptor (GABAAR) beta2/3 surface and total protein expression through changes in GABAAR beta2/3 transcription levels (not protein degradation).","method":"Furin transgenic and lentiviral knockdown mice; whole-cell patch clamp; Western blot for GABAAR beta2/3 membrane vs. total protein; transcription level analysis; epilepsy susceptibility behavioral assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function genetic approaches with electrophysiology and GABAAR quantification; single lab, transcriptional mechanism of GABAAR regulation not fully elucidated mechanistically","pmids":["30333479"],"is_preprint":false}],"current_model":"Furin (PCSK3/FUR/PACE) is a ubiquitously expressed, subtilisin-like serine protease that resides in the trans-Golgi network/endosomal system and at the cell surface, where it catalyzes the proteolytic maturation of diverse proprotein substrates—including growth factors (TGF-beta1, BMP-4, GDF15), receptors (Notch1, IGF-1R, N-cadherin, CD109), matrix proteases (ADAMTS9), coagulation factors (factor IX), viral envelope glycoproteins (SFV p62, SARS-CoV-2 spike at S1/S2 and S2'), and bacterial toxin substrates (Shiga toxin, anthrax PA)—by cleaving C-terminal to polybasic Arg-X-Lys/Arg-Arg motifs; its expression is regulated by multiple alternative promoters driven by SP1, C/EBP-beta, CDX2, and Smad2/4-FAST-1 complexes downstream of TGF-beta1, and furin is essential in vivo for endothelial-dependent cardiac morphogenesis, trophoblast syncytialization, PCSK9 inactivation in hepatocytes, myeloid cell anti-inflammatory function, and neuronal plasticity via BDNF-ERK-CREB signaling."},"narrative":{"mechanistic_narrative":"Furin is a subtilisin-like serine proprotein convertase that catalyzes the maturation of a broad range of secretory-pathway substrates by cleaving C-terminal to paired/polybasic Arg-X-X-Arg motifs, with site recognition validated by P1 Arg mutagenesis and pharmacological inhibition (alpha1-PDX) across substrates such as pro-vWF, pro-factor IX, and Notch1 [PMID:2094803, PMID:8473289, PMID:9653148]. Its co-crystal structures with peptidomimetic inhibitors define how the active site engages polybasic substrate residues [PMID:25974265]. Functionally, furin maturates growth factors and morphogens (BMP-4, TGF-beta1, GDF15), receptors and adhesion molecules (Notch1, IGF-1R, N-cadherin, CD109), matrix and circulating proteins (ADAMTS9, EC-SOD, PCSK9, lipoprotein lipase), and is hijacked by pathogens to activate Shiga toxin and viral envelope glycoproteins including the SARS-CoV-2 spike at the S1/S2 and S2' sites [PMID:7738018, PMID:9707432, PMID:11141505, PMID:11861638, PMID:16537537, PMID:20101215, PMID:21147780, PMID:23598405, PMID:30021841, PMID:30104250, PMID:33494095, PMID:35343766]. Furin can act in distinct subcellular compartments—intracellularly in the Golgi/secretory pathway or at the cell surface—with substrate site selection sometimes guided by chaperone-like partners such as Cripto for Nodal [PMID:11861638, PMID:16537537, PMID:18772886]. TGF-beta1 establishes a feed-forward loop by transcriptionally inducing furin through Smad2/4 signaling at its P1 promoter, one of three alternative promoters (P1, P1A, P1B) that, together with transcription factors C/EBP-beta, SP1, and CDX2, tune furin expression in a tissue- and differentiation-specific manner [PMID:8132667, PMID:11141505, PMID:11424093, PMID:16239403]. In vivo, furin is essential for endothelial-dependent cardiac morphogenesis, trophoblast syncytialization via IGF1R processing, hepatic inactivation of PCSK9 with consequent control of LDL receptor levels, myeloid anti-inflammatory homeostasis, and neuronal plasticity through BDNF-ERK-CREB signaling [PMID:21147780, PMID:22733989, PMID:23598405, PMID:27527873, PMID:29302702].","teleology":[{"year":1990,"claim":"Establishing furin's basic enzymatic identity answered whether the FUR gene product is a protease and what it recognizes, founding the proprotein convertase concept.","evidence":"Cotransfection of FUR cDNA with pro-vWF in COS-1 cells plus P1 Arg mutagenesis","pmids":["2094803"],"confidence":"High","gaps":["Did not define subcellular site of cleavage","Substrate repertoire beyond pro-vWF unknown at this point"]},{"year":1993,"claim":"Reconstitution of pro-factor IX processing showed furin acts at authentic physiological propeptide sites within the secretory pathway and is distinguishable from PACE4, validating it as a bona fide maturation enzyme.","evidence":"Co-transfection in CHO cells with N-terminal sequencing, pulse-chase, cleavage-site mutagenesis, and alpha1-PDX inhibition","pmids":["8473289"],"confidence":"High","gaps":["Endogenous vs. overexpressed enzyme contribution not separated","Compartment of cleavage not directly localized"]},{"year":1994,"claim":"Mapping three alternative promoters answered how furin expression is transcriptionally diversified, linking enzyme levels to specific transcription factors.","evidence":"Primer extension, luciferase reporters, EMSA, and DNase I footprinting of the human FUR gene","pmids":["8132667"],"confidence":"High","gaps":["Tissue-specific promoter usage not resolved in vivo","Upstream signals controlling each promoter only partially defined"]},{"year":1995,"claim":"Showing furin is required for Shiga toxin A-chain nicking established that pathogens exploit furin proteolysis for activation, extending its substrate scope beyond host proproteins.","evidence":"In vitro digestion with soluble furin plus genetic complementation of furin-deficient LoVo cells and toxicity assay","pmids":["7738018"],"confidence":"High","gaps":["Did not establish which compartment cleaves toxin in intact cells","Other PCs' redundant contribution not excluded"]},{"year":1998,"claim":"Identifying Notch1 and BMP-4 as furin substrates connected the convertase to receptor maturation and developmental morphogen signaling.","evidence":"LoVo complementation, alpha1-PDX, in vitro digestion, and cleavage-site mutagenesis for Notch1; Xenopus epistasis and oocyte translation assays for BMP-4","pmids":["9653148","9707432"],"confidence":"High","gaps":["Redundancy with PC6B for BMP-4 not fully resolved","In vivo requirement for Notch1 processing not tested genetically here"]},{"year":2001,"claim":"Defining furin as the principal TGF-beta1-converting enzyme and showing TGF-beta1 induces furin via Smad2/4 revealed a feed-forward regulatory loop coupling enzyme abundance to its own substrate pathway.","evidence":"alpha1-PDX inhibition and LoVo complementation with bioactivity readout; P1 promoter reporter assays with dominant-negative Smads","pmids":["11141505","11424093"],"confidence":"High","gaps":["Direct Smad binding to the fur promoter not shown by ChIP","Quantitative contribution of loop to physiology untested"]},{"year":2002,"claim":"Localizing EC-SOD cleavage to a pre-secretory intracellular step showed furin processing can determine substrate tissue distribution and half-life, not just activation.","evidence":"Furin overexpression, in vitro digestion of purified EC-SOD, Arg213 mutagenesis, and secretory-pathway inhibitors","pmids":["11861638"],"confidence":"High","gaps":["Identity of the downstream carboxypeptidase not defined","In vivo physiological consequence not tested"]},{"year":2004,"claim":"Crystallographic determination of the furin catalytic core provided the structural basis for polybasic substrate recognition and serine protease catalysis.","evidence":"X-ray crystallography of the catalytic core domain (review summary)","pmids":["15102434"],"confidence":"Medium","gaps":["Review rather than primary structure report","Conformational changes upon substrate binding not detailed"]},{"year":2006,"claim":"Demonstrating sequential furin-then-ADAM10/gamma-secretase processing of RPTPkappa and cell-surface processing of pro-ADAMTS9 showed furin initiates multistep proteolytic cascades and can act outside the TGN.","evidence":"Inhibitors, fractionation, reporter assays for RPTPkappa; pulse-chase, furin-null complementation, siRNA for ADAMTS9","pmids":["16648485","16537537"],"confidence":"Medium","gaps":["Genetic null confirmation of furin's RPTPkappa role lacking","Determinants of TGN vs. surface cleavage not defined"]},{"year":2008,"claim":"Showing Cripto directs Nodal to extracellular convertases answered how substrate compartmental routing is controlled, revealing chaperone-guided spatial regulation of furin processing.","evidence":"Reciprocal Co-IP of Cripto with Furin/PACE4 and Nodal, brefeldin A, density fractionation, and signaling readouts","pmids":["18772886"],"confidence":"High","gaps":["Direct furin-Nodal cleavage at the surface not biochemically isolated","Generality of Cripto-type routing for other substrates unknown"]},{"year":2010,"claim":"Identifying CD109, PCSK9, and furin-OPN signaling expanded furin's roles into TGF-beta receptor regulation, lipid metabolism, and cancer cell motility, including in vivo confirmation of PCSK9 inactivation.","evidence":"Cleavage-site mutagenesis and Co-IP for CD109; hepatocyte-specific KO mice for PCSK9; pathway inhibitors and xenografts for OPN-furin","pmids":["20101215","21147780","20980434"],"confidence":"High","gaps":["OPN-furin pathway placement rests on epistasis, not direct binding","Only membrane-bound, not soluble, furin shown active on PCSK9"]},{"year":2012,"claim":"Endothelial-specific furin knockout demonstrated an essential in vivo role in cardiac morphogenesis and identified ET-1, Adm, and TGF-beta1 as physiological endothelial substrates.","evidence":"Cre-lox endothelial KO with MRI, primary endothelial cultures, soluble furin rescue, and substrate processing analysis","pmids":["22733989"],"confidence":"High","gaps":["Which substrate deficiency drives the cardiac defect not isolated","Mechanism of soluble furin rescue of proliferation unresolved"]},{"year":2013,"claim":"Furin requirement for trophoblast syncytialization via IGF1R processing, and direct proapelin cleavage, extended furin into placental development and metabolic peptide generation.","evidence":"siRNA, inhibitors, BeWo fusion, lentiviral RNAi in vivo for syncytialization; in vitro PCSK-selectivity cleavage for proapelin","pmids":["23598405","24251091"],"confidence":"High","gaps":["Proapelin cleavage not confirmed genetically in cells","Other substrates contributing to syncytialization not excluded"]},{"year":2014,"claim":"Establishing furin as the major convertase for KISS1 processing linked it to kisspeptin generation with specificity over PCSK5/7.","evidence":"shRNA specificity comparison across PCSKs plus PC inhibitor treatment in KISS1-overexpressing cells","pmids":["24454770"],"confidence":"Medium","gaps":["No in vitro reconstitution with purified furin","Physiological/in vivo relevance untested"]},{"year":2015,"claim":"High-resolution inhibitor co-crystallography and characterization of redundant convertase activity on E-cadherin during compaction refined both the druggability of furin and its developmental role in adhesion.","evidence":"Co-crystal structure with MI-1148 and Ki determination; PC mutant embryos with live reporter imaging for E-cadherin","pmids":["25974265","26416966"],"confidence":"Medium","gaps":["Furin's individual contribution to E-cadherin processing partly inferential among redundant PCs","Inhibitor selectivity over related PCs incomplete"]},{"year":2016,"claim":"Myeloid-specific furin knockout revealed an anti-inflammatory regulatory role, controlling macrophage polarization and cytokine output partly via TGF-beta1, TACE, and Caspase-1 maturation.","evidence":"LysMCre conditional KO with LPS challenge, serum cytokines, expression profiling, and polarization markers","pmids":["27527873"],"confidence":"Medium","gaps":["Direct biochemical reconstitution of myeloid substrate cleavage lacking","Which substrate dominates the phenotype unresolved"]},{"year":2018,"claim":"Gain- and loss-of-function studies placed furin in neuronal plasticity (BDNF-ERK-CREB), inhibitory transmission (GABAAR), oocyte maturation (Plac1-IGF1R-Akt), and lipid handling (ANGPTL4-LPL), broadening its physiological repertoire.","evidence":"Furin transgenic/knockdown mice with LTP, memory, electrophysiology, BDNF processing; Co-IP/MS in oocytes; siRNA/KO in adipocytes","pmids":["29302702","30333479","29723063","30021841"],"confidence":"Medium","gaps":["Several mechanisms inferred from overexpression rather than physiological loss-of-function","Transcriptional GABAAR regulation mechanism not elucidated"]},{"year":2019,"claim":"In vivo gain- and loss-of-function in atherosclerosis models, with GDF15 and MMP2 as substrates, connected furin activity to vascular remodeling and inflammation.","evidence":"alpha1-PDX administration and furin overexpression in Ldlr-/-/Apoe-/- and wire-injury models; MMP2 analysis; in vitro/in vivo GDF15 cleavage by multiple PCSKs","pmids":["30651003","30104250"],"confidence":"Medium","gaps":["GDF15 cleavage shared among multiple PCSKs limits furin specificity","Causal substrate driving atherosclerosis phenotype not isolated"]},{"year":2021,"claim":"Reverse genetics and proteomics established the furin cleavage site in SARS-CoV-2 spike as a determinant of replication and pathogenesis, and defined dual S1/S2 and S2' cleavage enhanced by ACE2 engagement.","evidence":"Spike furin-site deletion mutant in animal models; proteomic S2' site mapping; combined furin/TMPRSS2 inhibition in Calu-3 cells","pmids":["33494095","35343766"],"confidence":"High","gaps":["Compartment and timing of S2' cleavage in infection not fully resolved","Therapeutic translation of dual inhibition untested clinically"]},{"year":null,"claim":"It remains unresolved how furin's compartmental routing, substrate selection, and redundancy with other proprotein convertases are coordinated to produce tissue-specific physiological outcomes.","evidence":"Open question synthesized across the timeline","pmids":[],"confidence":"Medium","gaps":["No unified model of compartment-specific substrate selectivity","Quantitative partitioning of substrates among furin vs. PC5/PC6/PACE4 unknown","In vivo substrate hierarchy for most phenotypes unmapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3,4,8,12,14,15]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,3,4,20]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[8,14]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[12,13,15]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,4,8,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,16,17,21]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,26,27,25]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7,14,31]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[22,25]}],"complexes":[],"partners":["CRIPTO","PACE4","TGFBR1","IGF1R","PLAC1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P09958","full_name":"Furin","aliases":["Dibasic-processing enzyme","Paired basic amino acid residue-cleaving enzyme","PACE"],"length_aa":794,"mass_kda":86.7,"function":"Ubiquitous endoprotease within constitutive secretory pathways capable of cleavage at the RX(K/R)R consensus motif (PubMed:11799113, PubMed:1629222, PubMed:1713771, PubMed:2251280, PubMed:24666235, PubMed:25974265, PubMed:7592877, PubMed:7690548, PubMed:9130696). Mediates processing of TGFB1, an essential step in TGF-beta-1 activation (PubMed:7737999). Converts through proteolytic cleavage the non-functional Brain natriuretic factor prohormone into its active hormone BNP(1-32) (PubMed:20489134, PubMed:21763278). By mediating processing of accessory subunit ATP6AP1/Ac45 of the V-ATPase, regulates the acidification of dense-core secretory granules in islets of Langerhans cells (By similarity) (Microbial infection) Cleaves and activates diphtheria toxin DT (Microbial infection) Cleaves and activates anthrax toxin protective antigen (PA) (Microbial infection) Cleaves and activates HIV-1 virus Envelope glycoprotein gp160 (Microbial infection) Required for H7N1 and H5N1 influenza virus infection probably by cleaving hemagglutinin (Microbial infection) Able to cleave S.pneumoniae serine-rich repeat protein PsrP (Microbial infection) Facilitates human coronaviruses EMC and SARS-CoV-2 infections by proteolytically cleaving the spike protein at the monobasic S1/S2 cleavage site. This cleavage is essential for spike protein-mediated cell-cell fusion and entry into human lung cells (Microbial infection) Facilitates mumps virus infection by proteolytically cleaving the viral fusion protein F","subcellular_location":"Golgi apparatus, trans-Golgi network membrane; Cell membrane; Secreted; Endosome membrane","url":"https://www.uniprot.org/uniprotkb/P09958/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FURIN","classification":"Not Classified","n_dependent_lines":210,"n_total_lines":1208,"dependency_fraction":0.173841059602649},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FURIN","total_profiled":1310},"omim":[{"mim_id":"621171","title":"ADRENOMEDULLIN 5, PUTATIVE; ADM5","url":"https://www.omim.org/entry/621171"},{"mim_id":"620997","title":"SEMAPHORIN 3G; SEMA3G","url":"https://www.omim.org/entry/620997"},{"mim_id":"619628","title":"AFTIPHILIN; AFTPH","url":"https://www.omim.org/entry/619628"},{"mim_id":"618599","title":"CADHERIN 24; CDH24","url":"https://www.omim.org/entry/618599"},{"mim_id":"618490","title":"G PROTEIN-COUPLED RECEPTOR 107; GPR107","url":"https://www.omim.org/entry/618490"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"liver","ntpm":196.7},{"tissue":"salivary gland","ntpm":207.7}],"url":"https://www.proteinatlas.org/search/FURIN"},"hgnc":{"alias_symbol":["SPC1"],"prev_symbol":["PCSK3","FUR","PACE"]},"alphafold":{"accession":"P09958","domains":[{"cath_id":"3.30.70.850","chopping":"28-100","consensus_level":"high","plddt":93.5747,"start":28,"end":100},{"cath_id":"3.40.50.200","chopping":"122-438","consensus_level":"high","plddt":96.643,"start":122,"end":438},{"cath_id":"2.60.120.260","chopping":"447-572","consensus_level":"high","plddt":97.7577,"start":447,"end":572},{"cath_id":"2.10.220","chopping":"586-675","consensus_level":"medium","plddt":79.5199,"start":586,"end":675}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P09958","model_url":"https://alphafold.ebi.ac.uk/files/AF-P09958-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P09958-F1-predicted_aligned_error_v6.png","plddt_mean":84.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FURIN","jax_strain_url":"https://www.jax.org/strain/search?query=FURIN"},"sequence":{"accession":"P09958","fasta_url":"https://rest.uniprot.org/uniprotkb/P09958.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P09958/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P09958"}},"corpus_meta":[{"pmid":"12360192","id":"PMC_12360192","title":"Furin at the cutting edge: from protein traffic to embryogenesis and disease.","date":"2002","source":"Nature reviews. 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FUR gene) is a subtilisin-like serine protease with substrate specificity for paired basic residues. Cotransfection of FUR cDNA with pro-von Willebrand factor (pro-vWF) cDNA in COS-1 cells showed increased proteolytic processing of pro-vWF at the Arg-Ser-Lys-Arg site; mutation of the P1 Arg abolished cleavage, establishing furin as a proprotein processing enzyme cleaving after paired basic residues.\",\n      \"method\": \"Cotransfection of COS-1 cells with FUR cDNA and pro-vWF constructs (wild-type and Arg→Gly mutant); Western blot analysis\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct enzymatic substrate cleavage demonstrated in cells with mutagenesis validating the recognition site; foundational study replicated widely in subsequent literature\",\n      \"pmids\": [\"2094803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"PACE/furin (PCSK3) processes pro-factor IX at the authentic propeptide cleavage site within the secretory pathway. Co-transfection of PACE with profactor IX in CHO cells resulted in secretion of fully processed factor IX; PACE4 did not increase processing; an Arg39Thr P1 mutation abolished cleavage; the alpha1-antitrypsin Pittsburgh (PDX) inhibitor blocked furin-mediated processing.\",\n      \"method\": \"Co-transfection in CHO cells; amino-terminal sequence analysis; pulse-chase labeling; specific protease inhibitor (alpha1-PDX) experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in cells with site-directed mutagenesis of cleavage site and pharmacological inhibitor validation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"8473289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Expression of the human FUR gene is directed by three alternative promoters (P1, P1A, P1B) that produce distinct mRNA isoforms differing in their 5'-UTRs. P1 contains a TATA box and is transactivated by C/EBP-beta and bound by SP1; P1A and P1B are GC-rich housekeeping-type promoters. Differential promoter usage modulates furin enzyme levels.\",\n      \"method\": \"Primer extension analysis; luciferase reporter transfection assays; electromobility shift assays; DNase I footprinting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (EMSA, footprinting, reporter assays) in one study establishing promoter architecture and transcription factor binding\",\n      \"pmids\": [\"8132667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Furin cleaves Shiga toxin A-chain at the Arg-X-X-Arg motif, generating A1 and A2 fragments, and this cleavage is required for efficient intoxication. LoVo cells (furin-deficient) cleaved intact A-chain very slowly; LoVo cells transfected with furin cleaved it efficiently. Furin-nicked toxin was ~20-fold more active than unnicked toxin in furin-deficient cells.\",\n      \"method\": \"In vitro digestion with soluble furin; transfection of furin into LoVo (furin-deficient) cells; protein synthesis inhibition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay combined with genetic complementation in furin-deficient cells, functional toxicity readout; multiple orthogonal methods\",\n      \"pmids\": [\"7738018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Notch1 receptor (300 kDa precursor) is constitutively processed by a furin-like convertase in the extracellular region at the sequence RQRR (aa 1651-1654); only cleaved Notch1 fragments are present at the cell surface. Processing was blocked by alpha1-PDX (furin inhibitor) and calcium ionophore A23187; in furin-deficient LoVo cells, processing did not occur; in vitro digestion with purified furin confirmed the cleavage site; mutation of the four basic residues (plus secondary sites) completely abolished processing.\",\n      \"method\": \"Expression in furin-deficient LoVo cells; alpha1-PDX inhibitor treatment; in vitro digestion with purified furin; site-directed mutagenesis of RQRR cleavage site\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified furin, genetic complementation in furin-deficient cells, mutagenesis of cleavage site; multiple orthogonal methods in single study\",\n      \"pmids\": [\"9653148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"BMP-4 is proteolytically activated by furin (and/or PC6B) during vertebrate embryogenesis. In Xenopus embryos, ectopic expression of alpha1-PDX (furin inhibitor) phenocopied BMP-4 blockade (dorsal mesoderm induction, neural induction); this was rescued by downstream BMP-4 signaling components. alpha1-PDX prevented BMP-4 cleavage in an oocyte translation assay. In vitro digestion showed furin and PC6B can cleave BMP-4 and are sensitive to alpha1-PDX.\",\n      \"method\": \"Xenopus embryo microinjection; oocyte translation assay; in vitro digestion assay; epistasis by downstream pathway rescue\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution, in vivo epistasis in Xenopus with rescue experiment, pharmacological inhibition; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"9707432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Furin is the primary endogenous TGF-beta1-converting enzyme. Among PC family members, furin most satisfies requirements for physiological TGF-beta1 maturation: alpha1-PDX (furin inhibitor) blocked ~80% of TGF-beta1 processing by endogenous enzymes in an in vitro digestion assay; genetic complementation of furin-deficient LoVo cells with wild-type furin gene restored production of mature, bioactivatable TGF-beta1.\",\n      \"method\": \"In vitro digestion assay with alpha1-PDX inhibitor; genetic complementation of furin-deficient LoVo cells; bioactivity assay for mature TGF-beta1\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — genetic complementation in null cells plus pharmacological inhibition plus functional bioactivity readout; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"11141505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"TGF-beta1 transcriptionally upregulates its own convertase furin via the fur P1 promoter through Smad2/Smad4 signaling. Smad2 and Smad4 (possibly in complex with FAST-1) drive constitutive and TGF-beta1-inducible transactivation of the P1 promoter; dominant-negative Smad2(3SA) and Smad7 inhibited this activation; overexpression of Smad2/Smad4 enhanced P1 transactivation.\",\n      \"method\": \"Promoter-luciferase reporter cotransfection with dominant-negative Smads (Smad2-3SA, Smad7) and overexpression constructs in HepG2 cells; deletion analysis\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reporter assay with dominant-negative constructs in single lab; no direct Smad binding to fur promoter demonstrated by ChIP or footprinting in this abstract\",\n      \"pmids\": [\"11424093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Furin proteolytically cleaves extracellular superoxide dismutase (EC-SOD) in the polybasic heparin-binding region intracellularly (after passage through the Golgi but before secretion) at Arg213; mutation of Arg213 renders EC-SOD resistant to furin processing. Furin cleavage followed by a carboxypeptidase removes the heparin-binding region, determining EC-SOD tissue distribution and half-life.\",\n      \"method\": \"Furin overexpression in mammalian cells; specific protease inhibitors; in vitro furin digestion of purified EC-SOD; Arg213 site-directed mutation; intracellular localization by secretory pathway inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified proteins, site-directed mutagenesis of cleavage site, subcellular localization of processing event; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"11861638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Furin is required for proteolytic processing of the Semliki Forest virus (SFV) p62 envelope protein precursor to E2. In furin-deficient FD11 cells, p62 was not cleaved; transfection with human furin restored cleavage. Purified furin cleaved p62 in vitro without prior low-pH exposure. Processing controls the pH threshold for membrane fusion: unprocessed wt/p62 virus required lower pH than processed virus to trigger fusion. Mutation of the furin recognition motif in p62 (mutant L) additionally impaired virus-cell binding beyond effects on fusion.\",\n      \"method\": \"Furin-deficient CHO (FD11) cells; reconstitution by furin transfection; in vitro cleavage with purified furin; site-directed mutagenesis of furin cleavage motif; fusion and infectivity assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified furin, genetic complementation in furin-null cells, mutagenesis of recognition site, functional fusion assay; multiple orthogonal methods\",\n      \"pmids\": [\"12584323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Crystal structures of the catalytic core domain of furin were determined, providing atomic-level insight into substrate specificity and catalytic mechanism of the proprotein convertase. The structures reveal how furin recognizes polybasic substrates and inform understanding of the mechanism of serine protease catalysis by this family.\",\n      \"method\": \"X-ray crystallography of furin catalytic core domain\",\n      \"journal\": \"Trends in biochemical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — review article summarizing crystal structures; primary structural data cited but not the original structure paper; single reference in corpus\",\n      \"pmids\": [\"15102434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Furin performs the first cleavage of RPTPkappa (a receptor tyrosine phosphatase) in the secretory pathway; subsequent ADAM10-mediated ectodomain shedding and gamma-secretase-dependent intramembrane proteolysis release the intracellular phosphatase domain (PIC), which translocates to the nucleus and dephosphorylates beta-catenin, activating beta-catenin transcriptional activity.\",\n      \"method\": \"Pharmacological inhibitors; co-immunoprecipitation; nuclear fractionation; leptomycin B nuclear export inhibition; PIC phosphatase activity assay; beta-catenin reporter assay; furin inhibitor treatment\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple protease inhibitors, fractionation, reporter assays in one study; furin's specific contribution established by inhibitor but not confirmed by genetic null in this abstract\",\n      \"pmids\": [\"16648485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Pro-ADAMTS9 is processed by furin at the cell surface, not intracellularly in the TGN. Pulse-chase analysis showed intact zymogen was secreted before processing. Furin-deficient cells failed to process pro-ADAMTS9; complementation with furin restored cleavage. siRNA-mediated furin knockdown reduced ADAMTS9 processing. PC5A could also process pro-ADAMTS9 but similarly processed forms were absent intracellularly.\",\n      \"method\": \"Pulse-chase analysis; furin-deficient cell lines; furin transfection rescue; PC inhibitors; furin siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic null complementation, siRNA knockdown, pharmacological inhibition, and pulse-chase localization; multiple orthogonal methods in single study\",\n      \"pmids\": [\"16537537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Cripto (a GPI-anchored proteoglycan) binds both the Nodal precursor and the proprotein convertases Furin and PACE4, directing Nodal processing to the cell surface rather than the TGN/endosomal system. Cripto-Nodal association occurs during secretion; brefeldin A blocked secretion but not Cripto/Nodal export to the cell surface, indicating exposure to extracellular convertases before the TGN. Cripto guides Nodal in detergent-resistant membranes to endocytic microdomains; a Cripto-interacting region in the Nodal propeptide potentiated effects of proteolytic maturation on signaling.\",\n      \"method\": \"Co-immunoprecipitation of Cripto with Furin/PACE4 and Nodal; brefeldin A treatment; density gradient fractionation; antibody uptake; GFP-Flotillin marker; signaling readout\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, subcellular fractionation, live-cell trafficking, and functional signaling readout; multiple orthogonal methods in one study\",\n      \"pmids\": [\"18772886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Furin processes CD109 in the Golgi apparatus, cleaving the 205 kDa precursor at the RRRR motif (Arg1273) into 180 kDa and 25 kDa fragments. Mutation R1273S abolishes cleavage, and the uncleaved CD109-R1273S neither associates with the type I TGF-beta receptor nor significantly regulates TGF-beta signaling, whereas the processed 180/25 kDa CD109 complex associates with TGF-beta RI and suppresses TGF-beta signaling.\",\n      \"method\": \"Site-directed mutagenesis of furin cleavage site (RRRR→RRRSER); co-immunoprecipitation of CD109 with TGF-beta RI; cell growth and TGF-beta signaling assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis of cleavage site combined with Co-IP and functional TGF-beta signaling assay; multiple orthogonal methods showing cleavage is mechanistically required\",\n      \"pmids\": [\"20101215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In hepatocytes, furin is the major in vivo inactivating protease of circulating PCSK9, cleaving it at Arg218 to generate a ~55 kDa inactive form. Hepatocyte-specific furin knockout (Fur-hKO) mice showed strongly reduced PCSK9 inactivated form in plasma and ~26% drop in LDL receptor protein in liver, with ~35% increase in PCSK9 mRNA and loss of PCSK9 cleavage. Only full-length, membrane-bound furin (not soluble furin) in primary hepatocytes performed this cleavage.\",\n      \"method\": \"Hepatocyte-specific conditional furin knockout mice; plasma PCSK9 cleavage analysis; LDL receptor protein quantification; furin overexpression in primary hepatocytes; human heterozygote mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO in vivo with multiple downstream molecular readouts (PCSK9 form, LDL receptor, PCSK9 mRNA), human genetic validation; strong evidence across multiple methods\",\n      \"pmids\": [\"21147780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Furin is required in endothelial cells for cardiac development: endothelial-specific furin knockout (ecKO) mice die postnatally and exhibit ventricular septal defects and valve malformations. Furin-deficient endothelial cells cannot proliferate, rescued by extracellular soluble furin. Endothelin-1 (ET-1), adrenomedullin (Adm), and TGF-beta1—but not BMP4—were confirmed as in vivo endothelial furin substrates (mature ET-1 and BMP4 reduced ~90% in ecKO endothelial cells).\",\n      \"method\": \"Endothelial cell-specific Furin conditional knockout (Cre-lox); MRI of embryos; primary endothelial cell cultures; soluble furin rescue; substrate processing analysis (ET-1, Adm, TGF-beta1, BMP4)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — tissue-specific KO with defined in vivo phenotype, substrate processing analysis in primary cells, rescue experiment; multiple orthogonal methods\",\n      \"pmids\": [\"22733989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Furin is required for trophoblast syncytialization. Furin is highly expressed in syncytial trophoblast; its expression is lower in pre-eclamptic placentas. Furin-specific siRNA or inhibitors blocked cytotrophoblast cell fusion in BeWo cells and human placental explants. IGF1R is a furin substrate whose processing is an essential mechanism for syncytialization. Lentivirus-mediated furin RNAi targeting mouse trophectoderm disrupted syncytiotrophoblast development and embryogenesis.\",\n      \"method\": \"siRNA knockdown; furin inhibitor treatment; BeWo cell fusion assay; primary cytotrophoblast and placental explant cultures; lentivirus-mediated RNAi in mouse trophectoderm; IGF1R processing analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple loss-of-function approaches (siRNA, inhibitor, lentiviral RNAi in vivo) with defined cellular and developmental phenotypes and substrate (IGF1R) identified\",\n      \"pmids\": [\"23598405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PCSK3/furin directly cleaves proapelin to generate apelin-13, without producing longer isoforms (apelin-36 or longer forms), in vitro. Neither PCSK1 nor PCSK7 showed appreciable proapelin cleavage activity. Both proapelin and PCSK3 transcript levels are increased in adipose tissue with obesity and during adipogenesis.\",\n      \"method\": \"In vitro cleavage assay of proapelin with purified PCSK3, PCSK1, and PCSK7; transcript expression analysis in adipose tissue\",\n      \"journal\": \"FEBS open bio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution demonstrating direct cleavage and selectivity among PCSKs; single lab, expression correlation data supporting physiological relevance but not confirmed by cell/genetic experiments\",\n      \"pmids\": [\"24251091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Furin is the major proprotein convertase required for processing of KISS1 into kisspeptins. shRNA-mediated knockdown of furin (but not PCSK5 or PCSK7) blocked KISS1 processing. PC inhibitors (Dec-RVKR-CMK and alpha1-PDX) completely inhibited KISS1 processing in KISS1-overexpressing cells.\",\n      \"method\": \"shRNA knockdown of furin, PCSK5, and PCSK7; PC inhibitor treatment (Dec-RVKR-CMK, alpha1-PDX); KISS1 processing assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA knockdown with specificity comparison across multiple PCSKs plus pharmacological inhibition; single lab, no in vitro reconstitution with purified enzyme\",\n      \"pmids\": [\"24454770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of human furin in complex with the peptidomimetic inhibitor MI-1148 (Ki = 5.5 pM) was determined, revealing that the N-terminal guanidinomethyl group in the para-position of the P5 phenyl ring occupies the same binding pocket as in structurally related inhibitors, defining key P5 interactions. MI-1148 also strongly inhibits PC1/3 but less so PC2.\",\n      \"method\": \"X-ray crystallography (co-crystal structure of furin with inhibitor MI-1148); enzyme inhibition assays (Ki determination); cell-based antiviral/antibacterial assays\",\n      \"journal\": \"ChemMedChem\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — co-crystal structure with functional inhibition constants; direct structural determination of binding interactions; single study but Tier 1 method\",\n      \"pmids\": [\"25974265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PC7, Furin, and Pace4 jointly regulate E-cadherin processing during morula compaction in blastocyst formation; their combined activity modulates cell-cell adhesion required for ICM specification via Hippo/YAP signaling. Live imaging of a transgenic reporter substrate demonstrated differential PC activity in inner vs. outer cells in partially nonoverlapping compartments.\",\n      \"method\": \"PC7/Furin/Pace4 mutant embryos; furin inhibitor; live imaging of transgenic reporter substrate; E-cadherin processing analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mutant embryos with live reporter imaging and E-cadherin processing readout; multiple PCs involved making furin's individual contribution partly inferential\",\n      \"pmids\": [\"26416966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Furin-deficient myeloid cells exhibit elevated pro-inflammatory cytokine production and altered macrophage polarization. LysMCre-fur(fl/fl) mice had elevated serum IL-1beta, reduced splenocyte numbers, and accelerated LPS-induced mortality with elevated pro-inflammatory cytokines. Furin inhibited Nos2 and promoted Arg1 expression (M1/M2 balance). Furin was required for normal bioactive TGF-beta1 production but inhibited maturation of TACE and Caspase-1 in myeloid cells.\",\n      \"method\": \"Conditional myeloid furin knockout (LysMCre-fur(fl/fl)); LPS challenge model; serum cytokine quantification; genome-wide gene expression analysis; macrophage polarization markers\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined in vivo phenotype and molecular pathway readouts; single lab, multiple downstream substrates without direct biochemical reconstitution\",\n      \"pmids\": [\"27527873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PCSK3/furin promotes intracellular cleavage of lipoprotein lipase (LPL) in adipocytes, and ANGPTL4 promotes this PCSK-mediated LPL cleavage. Pcsk3/furin silencing significantly decreased LPL cleavage in 3T3-L1 adipocytes; Angptl4 silencing diminished PCSK-mediated LPL cleavage; stimulation of ANGPTL4 by fasting enhanced furin-dependent LPL cleavage. The cleavage occurs intracellularly.\",\n      \"method\": \"siRNA silencing of Pcsk3/furin and Angptl4 in 3T3-L1 adipocytes; PCSK inhibitor (decanoyl-RVKR-CMK); Angptl4-/- mice; heparin-treatment to distinguish intracellular vs. surface LPL\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown, inhibitor, and KO mouse model converging on same conclusion; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"30021841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PCSK3 (furin), PCSK5, and PCSK6 can all cleave GDF15 precursor to generate mature GDF15, both in vitro (in cardiomyocytes) and in vivo (in mouse hearts). These three PCSKs mediate a crucial step of GDF15 maturation through proteolytic cleavage.\",\n      \"method\": \"In vitro cleavage assays; overexpression of PCSK family members in cardiomyocytes; in vivo mouse heart analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro cleavage combined with in vivo mouse cardiac analysis; multiple PCSKs share activity limiting specificity of furin's individual contribution, single lab\",\n      \"pmids\": [\"30104250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Furin inhibition (with alpha1-PDX) reduces atherosclerotic lesion area and vascular remodeling in Ldlr-/- and Apoe-/- mice. MMP2, a furin substrate, was significantly reduced in the aorta of inhibitor-treated mice. Furin overexpression in the wire-injury model caused a 67% increase in intimal plaque thickness, directly correlating furin levels with atherosclerosis. In vitro, furin inhibition reduced monocyte migration and macrophage/endothelial inflammatory gene expression.\",\n      \"method\": \"In vivo alpha1-PDX inhibitor administration in Ldlr-/- and Apoe-/- mice; wire-injury carotid model with furin overexpression; MMP2 substrate processing analysis; in vitro monocyte migration and cytokine assays\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gain- and loss-of-function with substrate (MMP2) analysis; single lab but multiple experimental models and both gain/loss approaches\",\n      \"pmids\": [\"30651003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The furin cleavage site (PRRAR) in SARS-CoV-2 spike protein is critical for efficient replication in human respiratory cells and pathogenesis in vivo. Deletion of the furin site (ΔPRRA) reduced spike protein processing, impaired replication in Calu-3 human respiratory cells, and attenuated disease in hamster and K18-hACE2 transgenic mouse models. Despite attenuation, ΔPRRA mutant conferred protection against parental virus rechallenge.\",\n      \"method\": \"SARS-CoV-2 reverse genetics (furin site deletion mutant ΔPRRA); cell-based replication kinetics; hamster and transgenic mouse pathogenesis models; spike protein processing analysis; neutralization assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reverse genetics with defined mutation, multiple animal models (hamster + transgenic mouse), and mechanistic spike processing analysis; multi-lab study published in peer-reviewed journal\",\n      \"pmids\": [\"33494095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Furin cleaves the SARS-CoV-2 spike protein at both S1/S2 (PRA685↓) and S2' (KPS815↓) sites. The S2' cleavage site was identified by proteomics for the first time, and its cleavage was strongly enhanced by ACE2 engagement with S protein. Novel furin inhibitors (BOS) blocked processing at both sites in HeLa cells. Combined furin (BOS) and TMPRSS2 (camostat) inhibition achieved ~95% reduction of SARS-CoV-2 infection of Calu-3 lung cells. TMPRSS2-mediated ACE2 shedding was required for TMPRSS2-dependent enhancement of fusion in the absence of S1/S2 priming; the collectrin dimerization domain of ACE2 was essential for TMPRSS2 effect on fusion.\",\n      \"method\": \"Proteomics identification of S2' cleavage site; pharmacological furin inhibitors (BOS); combined inhibitor assays; quantitative cell-to-cell fusion assays; SARS-CoV-2 infection of Calu-3 cells\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 / Moderate — proteomics-based site identification combined with pharmacological inhibition in multiple assay systems; multiple orthogonal methods in single study\",\n      \"pmids\": [\"35343766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Osteopontin (OPN) induces furin expression in cervical cancer cells via CD44-mediated activation of MKK3/6→p38→NF-kB signaling cascade. NF-kB-dependent transcription drives furin expression, which in turn enhances cell motility and HPV processing. Blockades of MKK3/6, p38alpha/beta, NF-kB, or furin all reduced OPN-induced cell motility and tumor growth in a xenograft model.\",\n      \"method\": \"Pharmacological inhibitors of MKK3/6, p38, NF-kB; furin expression analysis; cell motility assays; mouse xenograft model with OPN overexpression/shRNA knockdown; furin overexpression\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pathway inhibitors and genetic knockdown/overexpression with functional motility and in vivo tumor growth readouts; single lab, pathway placement by epistasis\",\n      \"pmids\": [\"20980434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CDX2 transcription factor binds to the CBS2 sequence (nt -1827 to -1821) of the furin P1 promoter and activates furin expression during intestinal epithelial cell differentiation. CDX2-driven furin expression correlates with enterocyte differentiation; furin inhibition blocked lactase-phlorizin hydrolase activity and strongly attenuated epithelial polarity and brush-border formation.\",\n      \"method\": \"EMSA and supershift assays; site-specific mutagenesis of CDX2 binding site; chromatin immunoprecipitation; luciferase reporter assays; in situ hybridization; furin inhibitor treatment of Caco-2/15 cells\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP, EMSA with mutagenesis, and functional differentiation assay; multiple orthogonal methods linking CDX2-furin transcriptional regulation to epithelial differentiation\",\n      \"pmids\": [\"16239403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Furin activates N-cadherin by cleaving its prosegment at RQKR↓DW161 (releasing an ~17 kDa prosegment), while PC5A inactivates NCAD by cleaving at a second site RIRSDR↓DK189 (releasing an ~20 kDa product that abolishes Trp161-dependent adhesion). In invasive glioma cells, furin and PC5A levels are inversely correlated; cell-surface expression of unprocessed proNCAD or PC5A-cleaved NCAD reduces cell-cell adhesion and increases migration.\",\n      \"method\": \"Analysis of NCAD processing in human glioma cell lines with different Furin/PC5A expression levels; furin-null vs. PC5A-expressing cells; prosegment size analysis; cell adhesion and migration assays\",\n      \"journal\": \"Neoplasia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — endogenous processing in cells with defined convertase expression levels and functional adhesion/migration readout; single lab without in vitro reconstitution\",\n      \"pmids\": [\"23097623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Furin overexpression in transgenic mice increases dendritic spine density, enhances LTP and spatial memory, and elevates the ratio of mature BDNF to pro-BDNF in cortex and hippocampus along with increased ERK and CREB activity. Hippocampal CREB knockdown diminished LTP and cognitive facilitation in Furin-Tg mice, placing furin upstream of BDNF-ERK-CREB signaling in neuronal plasticity.\",\n      \"method\": \"Furin transgenic mice; dendritic spine counting; LTP electrophysiology; Morris water maze; BDNF processing (mature vs. pro); ERK and CREB phosphorylation; lentiviral CREB knockdown\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic overexpression with epistasis via CREB knockdown and BDNF substrate processing readout; single lab, gain-of-function model\",\n      \"pmids\": [\"29302702\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Placenta-specific 1 (Plac1) activates furin at the oocyte membrane during the germinal vesicle stage; active furin then activates IGF-1 receptor (IGF-1R) to maintain microvillus organization. Upon meiosis onset, active furin/IGF-1R complex relocates to cytoplasm and activates (phosphorylates) Akt to promote meiosis. Plac1 knockdown disrupted microvillus organization, reduced oocyte maturation, increased aneuploidy, and disrupted fertilization.\",\n      \"method\": \"Plac1 knockdown in mouse oocytes; immunoprecipitation-MALDI mass spectrometry; furin activity assay; IGF-1R processing and phospho-Akt analysis; live-cell localization imaging\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP/MS identification of Plac1-furin interaction with functional knockdown phenotype and downstream substrate analysis; single lab, mechanistic model inferred from correlative evidence\",\n      \"pmids\": [\"29723063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Furin transgenic overexpression increases epileptic susceptibility; furin knockdown restrained epileptic activity. Furin influences neuronal inhibitory synaptic transmission by regulating postsynaptic GABA-A receptor (GABAAR) beta2/3 surface and total protein expression through changes in GABAAR beta2/3 transcription levels (not protein degradation).\",\n      \"method\": \"Furin transgenic and lentiviral knockdown mice; whole-cell patch clamp; Western blot for GABAAR beta2/3 membrane vs. total protein; transcription level analysis; epilepsy susceptibility behavioral assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function genetic approaches with electrophysiology and GABAAR quantification; single lab, transcriptional mechanism of GABAAR regulation not fully elucidated mechanistically\",\n      \"pmids\": [\"30333479\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Furin (PCSK3/FUR/PACE) is a ubiquitously expressed, subtilisin-like serine protease that resides in the trans-Golgi network/endosomal system and at the cell surface, where it catalyzes the proteolytic maturation of diverse proprotein substrates—including growth factors (TGF-beta1, BMP-4, GDF15), receptors (Notch1, IGF-1R, N-cadherin, CD109), matrix proteases (ADAMTS9), coagulation factors (factor IX), viral envelope glycoproteins (SFV p62, SARS-CoV-2 spike at S1/S2 and S2'), and bacterial toxin substrates (Shiga toxin, anthrax PA)—by cleaving C-terminal to polybasic Arg-X-Lys/Arg-Arg motifs; its expression is regulated by multiple alternative promoters driven by SP1, C/EBP-beta, CDX2, and Smad2/4-FAST-1 complexes downstream of TGF-beta1, and furin is essential in vivo for endothelial-dependent cardiac morphogenesis, trophoblast syncytialization, PCSK9 inactivation in hepatocytes, myeloid cell anti-inflammatory function, and neuronal plasticity via BDNF-ERK-CREB signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Furin is a subtilisin-like serine proprotein convertase that catalyzes the maturation of a broad range of secretory-pathway substrates by cleaving C-terminal to paired/polybasic Arg-X-X-Arg motifs, with site recognition validated by P1 Arg mutagenesis and pharmacological inhibition (alpha1-PDX) across substrates such as pro-vWF, pro-factor IX, and Notch1 [#0, #1, #4]. Its co-crystal structures with peptidomimetic inhibitors define how the active site engages polybasic substrate residues [#20]. Functionally, furin maturates growth factors and morphogens (BMP-4, TGF-beta1, GDF15), receptors and adhesion molecules (Notch1, IGF-1R, N-cadherin, CD109), matrix and circulating proteins (ADAMTS9, EC-SOD, PCSK9, lipoprotein lipase), and is hijacked by pathogens to activate Shiga toxin and viral envelope glycoproteins including the SARS-CoV-2 spike at the S1/S2 and S2' sites [#3, #5, #6, #8, #12, #14, #15, #17, #23, #24, #26, #27]. Furin can act in distinct subcellular compartments—intracellularly in the Golgi/secretory pathway or at the cell surface—with substrate site selection sometimes guided by chaperone-like partners such as Cripto for Nodal [#8, #12, #13]. TGF-beta1 establishes a feed-forward loop by transcriptionally inducing furin through Smad2/4 signaling at its P1 promoter, one of three alternative promoters (P1, P1A, P1B) that, together with transcription factors C/EBP-beta, SP1, and CDX2, tune furin expression in a tissue- and differentiation-specific manner [#2, #6, #7, #29]. In vivo, furin is essential for endothelial-dependent cardiac morphogenesis, trophoblast syncytialization via IGF1R processing, hepatic inactivation of PCSK9 with consequent control of LDL receptor levels, myeloid anti-inflammatory homeostasis, and neuronal plasticity through BDNF-ERK-CREB signaling [#15, #16, #17, #22, #31].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Establishing furin's basic enzymatic identity answered whether the FUR gene product is a protease and what it recognizes, founding the proprotein convertase concept.\",\n      \"evidence\": \"Cotransfection of FUR cDNA with pro-vWF in COS-1 cells plus P1 Arg mutagenesis\",\n      \"pmids\": [\"2094803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define subcellular site of cleavage\", \"Substrate repertoire beyond pro-vWF unknown at this point\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Reconstitution of pro-factor IX processing showed furin acts at authentic physiological propeptide sites within the secretory pathway and is distinguishable from PACE4, validating it as a bona fide maturation enzyme.\",\n      \"evidence\": \"Co-transfection in CHO cells with N-terminal sequencing, pulse-chase, cleavage-site mutagenesis, and alpha1-PDX inhibition\",\n      \"pmids\": [\"8473289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous vs. overexpressed enzyme contribution not separated\", \"Compartment of cleavage not directly localized\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Mapping three alternative promoters answered how furin expression is transcriptionally diversified, linking enzyme levels to specific transcription factors.\",\n      \"evidence\": \"Primer extension, luciferase reporters, EMSA, and DNase I footprinting of the human FUR gene\",\n      \"pmids\": [\"8132667\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific promoter usage not resolved in vivo\", \"Upstream signals controlling each promoter only partially defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showing furin is required for Shiga toxin A-chain nicking established that pathogens exploit furin proteolysis for activation, extending its substrate scope beyond host proproteins.\",\n      \"evidence\": \"In vitro digestion with soluble furin plus genetic complementation of furin-deficient LoVo cells and toxicity assay\",\n      \"pmids\": [\"7738018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish which compartment cleaves toxin in intact cells\", \"Other PCs' redundant contribution not excluded\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identifying Notch1 and BMP-4 as furin substrates connected the convertase to receptor maturation and developmental morphogen signaling.\",\n      \"evidence\": \"LoVo complementation, alpha1-PDX, in vitro digestion, and cleavage-site mutagenesis for Notch1; Xenopus epistasis and oocyte translation assays for BMP-4\",\n      \"pmids\": [\"9653148\", \"9707432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundancy with PC6B for BMP-4 not fully resolved\", \"In vivo requirement for Notch1 processing not tested genetically here\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Defining furin as the principal TGF-beta1-converting enzyme and showing TGF-beta1 induces furin via Smad2/4 revealed a feed-forward regulatory loop coupling enzyme abundance to its own substrate pathway.\",\n      \"evidence\": \"alpha1-PDX inhibition and LoVo complementation with bioactivity readout; P1 promoter reporter assays with dominant-negative Smads\",\n      \"pmids\": [\"11141505\", \"11424093\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct Smad binding to the fur promoter not shown by ChIP\", \"Quantitative contribution of loop to physiology untested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Localizing EC-SOD cleavage to a pre-secretory intracellular step showed furin processing can determine substrate tissue distribution and half-life, not just activation.\",\n      \"evidence\": \"Furin overexpression, in vitro digestion of purified EC-SOD, Arg213 mutagenesis, and secretory-pathway inhibitors\",\n      \"pmids\": [\"11861638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the downstream carboxypeptidase not defined\", \"In vivo physiological consequence not tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Crystallographic determination of the furin catalytic core provided the structural basis for polybasic substrate recognition and serine protease catalysis.\",\n      \"evidence\": \"X-ray crystallography of the catalytic core domain (review summary)\",\n      \"pmids\": [\"15102434\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Review rather than primary structure report\", \"Conformational changes upon substrate binding not detailed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating sequential furin-then-ADAM10/gamma-secretase processing of RPTPkappa and cell-surface processing of pro-ADAMTS9 showed furin initiates multistep proteolytic cascades and can act outside the TGN.\",\n      \"evidence\": \"Inhibitors, fractionation, reporter assays for RPTPkappa; pulse-chase, furin-null complementation, siRNA for ADAMTS9\",\n      \"pmids\": [\"16648485\", \"16537537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genetic null confirmation of furin's RPTPkappa role lacking\", \"Determinants of TGN vs. surface cleavage not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showing Cripto directs Nodal to extracellular convertases answered how substrate compartmental routing is controlled, revealing chaperone-guided spatial regulation of furin processing.\",\n      \"evidence\": \"Reciprocal Co-IP of Cripto with Furin/PACE4 and Nodal, brefeldin A, density fractionation, and signaling readouts\",\n      \"pmids\": [\"18772886\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct furin-Nodal cleavage at the surface not biochemically isolated\", \"Generality of Cripto-type routing for other substrates unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying CD109, PCSK9, and furin-OPN signaling expanded furin's roles into TGF-beta receptor regulation, lipid metabolism, and cancer cell motility, including in vivo confirmation of PCSK9 inactivation.\",\n      \"evidence\": \"Cleavage-site mutagenesis and Co-IP for CD109; hepatocyte-specific KO mice for PCSK9; pathway inhibitors and xenografts for OPN-furin\",\n      \"pmids\": [\"20101215\", \"21147780\", \"20980434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"OPN-furin pathway placement rests on epistasis, not direct binding\", \"Only membrane-bound, not soluble, furin shown active on PCSK9\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Endothelial-specific furin knockout demonstrated an essential in vivo role in cardiac morphogenesis and identified ET-1, Adm, and TGF-beta1 as physiological endothelial substrates.\",\n      \"evidence\": \"Cre-lox endothelial KO with MRI, primary endothelial cultures, soluble furin rescue, and substrate processing analysis\",\n      \"pmids\": [\"22733989\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which substrate deficiency drives the cardiac defect not isolated\", \"Mechanism of soluble furin rescue of proliferation unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Furin requirement for trophoblast syncytialization via IGF1R processing, and direct proapelin cleavage, extended furin into placental development and metabolic peptide generation.\",\n      \"evidence\": \"siRNA, inhibitors, BeWo fusion, lentiviral RNAi in vivo for syncytialization; in vitro PCSK-selectivity cleavage for proapelin\",\n      \"pmids\": [\"23598405\", \"24251091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Proapelin cleavage not confirmed genetically in cells\", \"Other substrates contributing to syncytialization not excluded\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Establishing furin as the major convertase for KISS1 processing linked it to kisspeptin generation with specificity over PCSK5/7.\",\n      \"evidence\": \"shRNA specificity comparison across PCSKs plus PC inhibitor treatment in KISS1-overexpressing cells\",\n      \"pmids\": [\"24454770\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution with purified furin\", \"Physiological/in vivo relevance untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"High-resolution inhibitor co-crystallography and characterization of redundant convertase activity on E-cadherin during compaction refined both the druggability of furin and its developmental role in adhesion.\",\n      \"evidence\": \"Co-crystal structure with MI-1148 and Ki determination; PC mutant embryos with live reporter imaging for E-cadherin\",\n      \"pmids\": [\"25974265\", \"26416966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Furin's individual contribution to E-cadherin processing partly inferential among redundant PCs\", \"Inhibitor selectivity over related PCs incomplete\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Myeloid-specific furin knockout revealed an anti-inflammatory regulatory role, controlling macrophage polarization and cytokine output partly via TGF-beta1, TACE, and Caspase-1 maturation.\",\n      \"evidence\": \"LysMCre conditional KO with LPS challenge, serum cytokines, expression profiling, and polarization markers\",\n      \"pmids\": [\"27527873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical reconstitution of myeloid substrate cleavage lacking\", \"Which substrate dominates the phenotype unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Gain- and loss-of-function studies placed furin in neuronal plasticity (BDNF-ERK-CREB), inhibitory transmission (GABAAR), oocyte maturation (Plac1-IGF1R-Akt), and lipid handling (ANGPTL4-LPL), broadening its physiological repertoire.\",\n      \"evidence\": \"Furin transgenic/knockdown mice with LTP, memory, electrophysiology, BDNF processing; Co-IP/MS in oocytes; siRNA/KO in adipocytes\",\n      \"pmids\": [\"29302702\", \"30333479\", \"29723063\", \"30021841\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Several mechanisms inferred from overexpression rather than physiological loss-of-function\", \"Transcriptional GABAAR regulation mechanism not elucidated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"In vivo gain- and loss-of-function in atherosclerosis models, with GDF15 and MMP2 as substrates, connected furin activity to vascular remodeling and inflammation.\",\n      \"evidence\": \"alpha1-PDX administration and furin overexpression in Ldlr-/-/Apoe-/- and wire-injury models; MMP2 analysis; in vitro/in vivo GDF15 cleavage by multiple PCSKs\",\n      \"pmids\": [\"30651003\", \"30104250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GDF15 cleavage shared among multiple PCSKs limits furin specificity\", \"Causal substrate driving atherosclerosis phenotype not isolated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Reverse genetics and proteomics established the furin cleavage site in SARS-CoV-2 spike as a determinant of replication and pathogenesis, and defined dual S1/S2 and S2' cleavage enhanced by ACE2 engagement.\",\n      \"evidence\": \"Spike furin-site deletion mutant in animal models; proteomic S2' site mapping; combined furin/TMPRSS2 inhibition in Calu-3 cells\",\n      \"pmids\": [\"33494095\", \"35343766\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compartment and timing of S2' cleavage in infection not fully resolved\", \"Therapeutic translation of dual inhibition untested clinically\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how furin's compartmental routing, substrate selection, and redundancy with other proprotein convertases are coordinated to produce tissue-specific physiological outcomes.\",\n      \"evidence\": \"Open question synthesized across the timeline\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of compartment-specific substrate selectivity\", \"Quantitative partitioning of substrates among furin vs. PC5/PC6/PACE4 unknown\", \"In vivo substrate hierarchy for most phenotypes unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3, 4, 8, 12, 14, 15]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 3, 4, 20]},\n      {\"term_id\": \"GO:0008233\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [8, 14]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [12, 13, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 4, 8, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 16, 17, 21]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 26, 27, 25]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7, 14, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [22, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CRIPTO\", \"PACE4\", \"TGFBR1\", \"IGF1R\", \"PLAC1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}