{"gene":"F9","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2022,"finding":"Codon optimization (recoding) of F9 alters cotranslational folding kinetics, changes protein conformation, leads to suboptimal posttranslational modifications (e.g., gamma-carboxylation), and results in distinct MHC class II peptide presentation, indicating that synonymous codon substitutions in F9 can affect FIX structure, function, and immunogenicity.","method":"Ribosome profiling (translation kinetics), MHC-associated peptide proteomics assay, posttranslational modification analysis, structural conformation assessment of recoded vs. wild-type FIX constructs expressed in cells","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ribosome profiling, MHC peptide proteomics, PTM analysis) in a single study; not independently replicated","pmids":["35413099"],"is_preprint":false},{"year":2022,"finding":"Downregulation of F9 using sgRNA or shRNA in MCF7 breast cancer cells prevents the cell cycle arrest and senescent-like phenotype induced by CDK4/6 inhibitor palbociclib; conversely, treatment with recombinant FIX protein is sufficient to induce cell cycle arrest and a senescence-like state, identifying FIX as a regulator of CDK4/6 inhibitor-induced senescence.","method":"Genome-wide CRISPR/Cas9 loss-of-function screen; shRNA knockdown; recombinant FIX protein treatment; cell cycle and senescence phenotype assays in MCF7 and T47D cells with palbociclib and abemaciclib","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional CRISPR screen with orthogonal shRNA validation and recombinant protein rescue, single lab, confirmed in two cell lines and with two CDK4/6 inhibitors","pmids":["35184131"],"is_preprint":false},{"year":2022,"finding":"Missense mutations at FIX activation sites R191 and R226 impair FIX activation, leading to circulating dysfunctional FIX with variable antigen levels. The R191/R226 substitutions prolong the pharmacokinetic beta elimination half-life of infused FIX, acting as independent predictors of half-life extension, likely because endogenous dysfunctional FIX competes with infused FIX for binding (e.g., to collagen IV) over time.","method":"Recombinant expression of FIX variants; FIX activity and antigen assays in plasma; pharmacokinetic analysis in hemophilia B patients (GePKHIS study); regression analysis","journal":"Journal of thrombosis and haemostasis : JTH","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant expression plus clinical PK data in 30 patients with regression analysis; single study, moderate evidence","pmids":["34626083"],"is_preprint":false},{"year":2019,"finding":"FIX binds to collagen IV (Col4) in the subendothelial basement membrane, reducing plasma recovery of infused FIX. Dysfunctional endogenous FIX (e.g., FIXR333Q) that retains Col4-binding ability competes with infused wild-type FIX for Col4 binding, thereby impairing hemostatic efficacy of prophylactic therapy in CRM+ hemophilia B mice.","method":"Mouse hemophilia B model (CRM- and CRM+ mice expressing FIXR333Q); saphenous vein bleeding assay; infusion of wild-type FIX, FIXFC (Alprolix), and FIXAlb (Idelvion); binding competition analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo mouse model with multiple FIX variants, mechanistic competition for Col4 binding demonstrated, functional hemostatic readout; rigorous controls with multiple FIX products","pmids":["30992271"],"is_preprint":false},{"year":2015,"finding":"The FIX-Padua variant (R338L, arginine 338 to leucine) exhibits 8–12-fold increased specific clotting activity relative to wild-type FIX while having similar immunogenicity and thrombogenicity; AAV8-mediated liver delivery of FIX-Padua at reduced vector doses achieves sustained therapeutic FIX levels and can eradicate pre-existing FIX inhibitors without triggering new inhibitor formation.","method":"AAV8 gene delivery in hemophilia B dogs (naive and inhibitor-positive) and mice; FIX activity and antigen measurement; Bethesda assay for inhibitors; clotting time assays; immunogenicity and thrombogenicity challenge studies","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — large animal (dog) model with functional hemostatic assays and immunological readouts, replicated across multiple animals and confirmed in mice with orthogonal methods","pmids":["25568350"],"is_preprint":false},{"year":2018,"finding":"The FIX-Padua mutation (R338L in exon 8) causes a ~10-fold increase in FIX clotting activity with only a slight increase in FIX antigen (a type 2 gain-of-function defect), establishing that the Arg338 residue is critical for normal FIX catalytic regulation and that its substitution to leucine produces a hyperfunctional, prothrombotic FIX variant.","method":"Clinical and molecular characterization; FIX activity and antigen measurement; structural/functional inference from mutation analysis in patients with venous thrombosis","journal":"Clinical and applied thrombosis/hemostasis","confidence":"Low","confidence_rationale":"Tier 3 / Weak — clinical observational data and mutational characterization without direct in vitro biochemical reconstitution in this paper; findings corroborated by other studies","pmids":["30428703"],"is_preprint":false},{"year":2022,"finding":"Diverse F9 mutations cause FIX deficiency through distinct molecular mechanisms: large deletions/frameshifts produce truncated nonfunctional FIX; intronic mutations and some silent mutations cause aberrant splicing; promoter mutations cause hemophilia B Leyden; missense mutations impair FIX translation, protein folding, stability, posttranslational modifications (including vitamin K-dependent gamma-carboxylation), activation cleavage at R191/R226, or assembly of the functional Xase complex (with FVIIIa, FX, phospholipid, and Ca2+).","method":"Systematic review and synthesis of published mutation analyses; structural and functional characterization data from the literature","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — comprehensive synthesis of replicated findings across many studies; mechanistic conclusions are well-supported by the broader literature even though this paper itself is a review/synthesis","pmids":["35269902"],"is_preprint":false},{"year":2014,"finding":"Recombinant FIX-Fc fusion protein (rFIXFc) exploits physiological binding of the Fc domain to the neonatal Fc receptor (FcRn) to extend FIX half-life 3–4-fold compared to standard recombinant FIX, demonstrating that FcRn-mediated recycling is sufficient to prolong FIX circulatory persistence.","method":"Phase I/IIa and Phase III clinical pharmacokinetic studies; half-life measurement of rFIXFc vs. standard recombinant FIX in hemophilia B patients","journal":"Drug design, development and therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clinical PK data from Phase I–III studies demonstrating mechanism (FcRn binding); single mechanistic pathway but confirmed in multiple clinical trials","pmids":["24729686"],"is_preprint":false},{"year":2008,"finding":"The silent F9 mutation G17736A/Val107Val causes mild hemophilia B (FIX activity 15–20%) in five Swedish families; RT-PCR and cDNA sequencing excluded exon skipping or intron retention as mechanisms, suggesting the silent mutation may affect a splicing enhancer site or reduce translation rate and thereby alter cotranslational FIX protein folding in vivo.","method":"RT-PCR of lymphocyte mRNA; cDNA sequencing from codon 68 to 180; FIX activity and antigen measurement in patients","journal":"Haemophilia","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single family study with limited mechanistic resolution; proposed mechanisms (splicing enhancer disruption or codon-translation rate effect) not directly confirmed experimentally","pmids":["18459950"],"is_preprint":false},{"year":2012,"finding":"F9 genotype strongly predicts FIX inhibitor risk in hemophilia B: nonsense mutations and entire F9 gene deletions carry significantly higher inhibitor risk (OR 11.0 and 32.7, prevalence 14.3% and 44.5% respectively) compared to missense mutations (OR 0.05, prevalence 0.39%), establishing that the magnitude of FIX protein disruption (absence of FIX antigen) is the primary determinant of inhibitor formation.","method":"Case-control analysis in 52 unrelated Argentine hemophilia B patients; mutation analysis by conformation-sensitive gel electrophoresis, DNA sequencing, and multiplex ligation-dependent probe amplification; inhibitor detection by Bethesda assay","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic mutation-genotype/inhibitor analysis in a defined cohort with statistical case-control methodology; single-center, moderate evidence","pmids":["23093250"],"is_preprint":false},{"year":2014,"finding":"Large F9 gene deletions (11.1–884 kb) cause severe hemophilia B; breakpoint characterization revealed that non-homologous end joining (NHEJ) and microhomology-mediated break-induced replication (MMBIR) are the primary mechanisms generating these deletions, with non-allelic homologous recombination (NAHR) responsible for one deletion occurring between tandem LINE/L1 elements.","method":"AccuCopy technique for deletion identification; genome walking and primer walking for precise breakpoint characterization; microhomology and repetitive element analysis at breakpoint junctions in seven patients","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct molecular characterization of deletion breakpoints in seven patients with mechanistic inference from junction sequences; single study","pmids":["24816826"],"is_preprint":false},{"year":2014,"finding":"Oral delivery of chitosan nanoparticle-formulated FIX expression vectors to hemophilia B mice resulted in FIX expression exclusively in the small intestine, reaching transient FIX activity >14% of normal with partial phenotypic correction; bioengineered FIX variants with higher specific activity and improved tissue release enhanced this effect.","method":"Site-directed mutagenesis of FIX variants; chitosan nanoparticle formulation; oral delivery to FIX-knockout hemophilia B mice; RT-PCR and fluorescence staining of intestinal tissue; FIX activity assay","journal":"Journal of thrombosis and haemostasis : JTH","confidence":"Low","confidence_rationale":"Tier 3 / Weak — proof-of-concept in vivo study with transient expression; single lab, limited mechanistic depth about FIX protein function itself","pmids":["24679056"],"is_preprint":false}],"current_model":"Coagulation Factor IX (FIX) is a vitamin K-dependent serine protease that circulates in plasma and binds collagen IV in the subendothelial basement membrane; upon activation by cleavage at R191 and R226, FIXa assembles with FVIIIa, FX, phospholipid, and Ca2+ into the intrinsic Xase complex to activate FX; gain-of-function mutations (e.g., R338L/FIX-Padua) markedly increase catalytic activity while loss-of-function mutations cause hemophilia B through diverse mechanisms including impaired gamma-carboxylation, misfolding, aberrant splicing, or failure to form the Xase complex; FIX half-life can be extended by FcRn-mediated recycling via Fc-fusion, and dysfunctional circulating FIX competes with infused therapeutic FIX for collagen IV binding, impairing hemostatic efficacy; additionally, FIX has been identified as a regulator of CDK4/6 inhibitor-induced cellular senescence in cancer cells."},"narrative":{"mechanistic_narrative":"Coagulation Factor IX (FIX) is a vitamin K-dependent zymogen whose activation by cleavage at R191 and R226 enables assembly of the functional Xase complex with FVIIIa, FX, phospholipid, and Ca2+; disruption of any step in its biosynthesis or activation causes hemophilia B [PMID:35269902]. FIX biosynthesis is sensitive to translation kinetics: synonymous codon usage in F9 shapes cotranslational folding, posttranslational gamma-carboxylation, and ultimately conformation and immunogenicity [PMID:35413099]. The catalytic activity of FIX is tightly governed by Arg338, whose substitution to leucine (FIX-Padua, R338L) produces an 8–12-fold hyperfunctional, prothrombotic variant with preserved immunogenicity, a property exploited for low-dose AAV8 gene therapy [PMID:25568350, PMID:30428703]. In circulation FIX binds collagen IV in the subendothelial basement membrane; this interaction lowers plasma recovery, and dysfunctional endogenous FIX that retains collagen IV binding competes with infused therapeutic FIX, impairing hemostatic efficacy [PMID:30992271]. FIX persistence can be extended by Fc-fusion that engages FcRn-mediated recycling [PMID:24729686], while activation-site mutations at R191/R226 yield circulating dysfunctional FIX that prolongs infused FIX half-life through the same competition mechanism [PMID:34626083]. The molecular severity of F9 lesions also determines therapeutic risk: null genotypes (nonsense mutations and large deletions arising via NHEJ, MMBIR, and NAHR) abolish FIX antigen and carry markedly elevated inhibitor risk compared with missense alleles [PMID:23093250, PMID:24816826]. Beyond coagulation, FIX has been identified as a required regulator of CDK4/6 inhibitor-induced cellular senescence in breast cancer cells [PMID:35184131].","teleology":[{"year":2008,"claim":"Established that even a synonymous F9 mutation can cause clinical FIX deficiency, raising the question of whether codon-level effects on translation or splicing alter FIX biosynthesis.","evidence":"RT-PCR and cDNA sequencing of patient lymphocyte mRNA in five Swedish hemophilia B families with a silent Val107Val mutation","pmids":["18459950"],"confidence":"Low","gaps":["Proposed splicing-enhancer disruption or translation-rate effect not directly demonstrated","No in vitro reconstitution of the folding defect","Single-family observational cohort"]},{"year":2012,"claim":"Defined the genetic determinant of inhibitor formation, showing that absence of FIX antigen rather than amino-acid change drives immune risk.","evidence":"Case-control mutation-genotype analysis with Bethesda inhibitor assay in 52 Argentine hemophilia B patients","pmids":["23093250"],"confidence":"Medium","gaps":["Single-center cohort","Does not explain inhibitor mechanism at the molecular/immunological level","Limited number of null-genotype patients"]},{"year":2014,"claim":"Identified the mutational mechanisms generating large F9 deletions that produce severe, antigen-null hemophilia B.","evidence":"AccuCopy detection plus genome/primer walking breakpoint characterization in seven patients","pmids":["24816826"],"confidence":"Medium","gaps":["Seven-patient sample","Mechanism inferred from junction sequences","No functional consequence assays beyond deletion mapping"]},{"year":2014,"claim":"Demonstrated that FcRn-mediated recycling is sufficient to prolong FIX circulatory persistence, addressing the short half-life limitation of FIX therapy.","evidence":"Phase I–III clinical pharmacokinetic comparison of rFIXFc vs standard recombinant FIX in hemophilia B patients","pmids":["24729686"],"confidence":"Medium","gaps":["Mechanism shown via half-life, not direct FcRn binding kinetics in this study","Single fusion strategy"]},{"year":2014,"claim":"Showed that bioengineered higher-activity FIX variants could be delivered enterally, exploring routes to in vivo FIX production.","evidence":"Chitosan nanoparticle oral delivery of FIX vectors to FIX-knockout hemophilia B mice with intestinal expression and activity assays","pmids":["24679056"],"confidence":"Low","gaps":["Transient expression only","Proof-of-concept in single lab","Limited insight into FIX protein function itself"]},{"year":2015,"claim":"Translated the hyperfunctional FIX-Padua variant into a gene-therapy advantage, showing low-dose AAV8 delivery achieves sustained therapeutic levels without new inhibitors.","evidence":"AAV8 liver gene delivery in naive and inhibitor-positive hemophilia B dogs and mice with clotting, Bethesda, immunogenicity and thrombogenicity assays","pmids":["25568350"],"confidence":"High","gaps":["Long-term durability beyond study window not addressed","Thrombogenicity in larger populations not assessed","Mechanism of increased catalytic activity not biochemically dissected here"]},{"year":2018,"claim":"Established Arg338 as critical to normal FIX catalytic regulation by linking its R338L substitution to a type-2 gain-of-function, prothrombotic phenotype in patients.","evidence":"Clinical and molecular characterization with FIX activity/antigen measurement in venous thrombosis patients","pmids":["30428703"],"confidence":"Low","gaps":["No direct in vitro biochemical reconstitution in this study","Observational clinical data","Structural basis of hyperactivity not resolved"]},{"year":2019,"claim":"Defined collagen IV binding as a determinant of FIX plasma recovery and revealed that dysfunctional endogenous FIX impairs therapy by competing for this binding site.","evidence":"Hemophilia B mouse models (CRM- and CRM+ FIXR333Q) with saphenous vein bleeding assay and binding competition using multiple FIX products","pmids":["30992271"],"confidence":"High","gaps":["Competition shown in mouse model only","Structural details of the FIX–Col4 interface not defined","Generalizability across patient mutation spectrum not established"]},{"year":2021,"claim":"Showed that activation-site mutations producing circulating dysfunctional FIX paradoxically extend infused FIX half-life, consistent with the collagen IV competition model.","evidence":"Recombinant FIX variant expression plus clinical pharmacokinetic regression analysis in 30 hemophilia B patients (GePKHIS)","pmids":["34626083"],"confidence":"Medium","gaps":["Modest patient number","Competition mechanism inferred rather than directly measured in patients","Single study"]},{"year":2022,"claim":"Connected synonymous codon usage mechanistically to FIX folding, gamma-carboxylation, and immunogenicity, explaining how recoding alters protein quality and antigen presentation.","evidence":"Ribosome profiling, MHC-associated peptide proteomics, and PTM/conformation analysis of recoded vs wild-type FIX expressed in cells","pmids":["35413099"],"confidence":"Medium","gaps":["Not independently replicated","In vivo immunogenic consequences not tested","Single study with multiple methods in one system"]},{"year":2022,"claim":"Revealed a non-coagulation role for FIX as a required regulator of CDK4/6 inhibitor-induced senescence in cancer cells.","evidence":"Genome-wide CRISPR screen with shRNA validation and recombinant FIX rescue, in MCF7 and T47D cells with palbociclib and abemaciclib","pmids":["35184131"],"confidence":"Medium","gaps":["Mechanism downstream of FIX in senescence not defined","Single lab","Receptor/effector for FIX in cancer cells unidentified"]},{"year":null,"claim":"The molecular pathway by which FIX regulates CDK4/6 inhibitor-induced senescence, and how this relates to its coagulation function, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No receptor or signaling effector identified for FIX in senescence","Relationship between protease activity and senescence role unknown","Not validated in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,5,6]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[4,6]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,2]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[3,4,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,9,10]}],"complexes":["intrinsic Xase complex"],"partners":["F8","F10"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P00740","full_name":"Coagulation factor IX","aliases":["Christmas factor","Plasma thromboplastin component","PTC"],"length_aa":461,"mass_kda":51.8,"function":"Factor IX is a vitamin K-dependent plasma protein that participates in the intrinsic pathway of blood coagulation by converting factor X to its active form in the presence of Ca(2+) ions, phospholipids, and factor VIIIa (PubMed:8295821, PubMed:2592373, PubMed:20121197, PubMed:20121198, PubMed:1730085, PubMed:19846852, PubMed:39880037)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P00740/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/F9","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/F9","total_profiled":1310},"omim":[{"mim_id":"621143","title":"HOLOPROSENCEPHALY 10; HPE10","url":"https://www.omim.org/entry/621143"},{"mim_id":"620152","title":"HYPOMAGNESEMIA 7, RENAL, WITH OR WITHOUT DILATED CARDIOMYOPATHY; HOMG7","url":"https://www.omim.org/entry/620152"},{"mim_id":"620025","title":"DIAPHRAGMATIC HERNIA 4, WITH CARDIOVASCULAR DEFECTS; DIH4","url":"https://www.omim.org/entry/620025"},{"mim_id":"619525","title":"CONGENITAL DISORDER OF GLYCOSYLATION, TYPE IIw; CDG2W","url":"https://www.omim.org/entry/619525"},{"mim_id":"619114","title":"SET AND MYND DOMAIN-CONTAINING PROTEIN 5; SMYD5","url":"https://www.omim.org/entry/619114"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"liver","ntpm":659.1}],"url":"https://www.proteinatlas.org/search/F9"},"hgnc":{"alias_symbol":["FIX"],"prev_symbol":[]},"alphafold":{"accession":"P00740","domains":[{"cath_id":"-","chopping":"60-94","consensus_level":"medium","plddt":83.1823,"start":60,"end":94},{"cath_id":"2.10.25.10","chopping":"133-173","consensus_level":"high","plddt":89.7498,"start":133,"end":173},{"cath_id":"2.40.10.10","chopping":"177-183_228-461","consensus_level":"medium","plddt":89.3991,"start":177,"end":461}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P00740","model_url":"https://alphafold.ebi.ac.uk/files/AF-P00740-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P00740-F1-predicted_aligned_error_v6.png","plddt_mean":80.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=F9","jax_strain_url":"https://www.jax.org/strain/search?query=F9"},"sequence":{"accession":"P00740","fasta_url":"https://rest.uniprot.org/uniprotkb/P00740.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P00740/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P00740"}},"corpus_meta":[{"pmid":"20051983","id":"PMC_20051983","title":"DNA 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Hemophilia","url":"https://pubmed.ncbi.nlm.nih.gov/18459950","citation_count":24,"is_preprint":false},{"pmid":"35883121","id":"PMC_35883121","title":"Bone marrow mesenchymal stromal cells for diabetes therapy: touch, fuse, and fix?","date":"2022","source":"Stem cell research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/35883121","citation_count":23,"is_preprint":false},{"pmid":"35184131","id":"PMC_35184131","title":"Genome wide CRISPR/Cas9 screen identifies the coagulation factor IX (F9) as a regulator of senescence.","date":"2022","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/35184131","citation_count":23,"is_preprint":false},{"pmid":"20661723","id":"PMC_20661723","title":"The phosphoinositide-3-kinase/Akt pathway mediates the transient increase in Nanog expression during differentiation of F9 cells.","date":"2010","source":"Archives of pharmacal 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Insights from Brenthis butterflies.","date":"2023","source":"Molecular ecology","url":"https://pubmed.ncbi.nlm.nih.gov/37807966","citation_count":22,"is_preprint":false},{"pmid":"1601186","id":"PMC_1601186","title":"Expression and localization of villin, fimbrin, and myosin I in differentiating mouse F9 teratocarcinoma cells.","date":"1992","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/1601186","citation_count":22,"is_preprint":false},{"pmid":"34469692","id":"PMC_34469692","title":"Lin_F9: A Linear Empirical Scoring Function for Protein-Ligand Docking.","date":"2021","source":"Journal of chemical information and modeling","url":"https://pubmed.ncbi.nlm.nih.gov/34469692","citation_count":21,"is_preprint":false},{"pmid":"16236135","id":"PMC_16236135","title":"Apical membrane and junctional complex formation during simple epithelial cell differentiation of F9 cells.","date":"2005","source":"Genes to cells : devoted to molecular & cellular 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overexpression interferes with early events in F9 cell differentiation.","date":"1989","source":"Oncogene research","url":"https://pubmed.ncbi.nlm.nih.gov/2671866","citation_count":19,"is_preprint":false},{"pmid":"34626083","id":"PMC_34626083","title":"F9 missense mutations impairing factor IX activation are associated with pleiotropic plasma phenotypes.","date":"2021","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/34626083","citation_count":18,"is_preprint":false},{"pmid":"7848838","id":"PMC_7848838","title":"Follistatin expression in ES and F9 cells and in preimplantation mouse embryos.","date":"1994","source":"The International journal of developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/7848838","citation_count":18,"is_preprint":false},{"pmid":"16329137","id":"PMC_16329137","title":"Migration of F9 parietal endoderm cells is regulated by the ERK pathway.","date":"2006","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16329137","citation_count":18,"is_preprint":false},{"pmid":"32033956","id":"PMC_32033956","title":"Pseudomonas orientalis F9 Pyoverdine, Safracin, and Phenazine Mutants Remain Effective Antagonists against Erwinia amylovora in Apple Flowers.","date":"2020","source":"Applied and environmental microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/32033956","citation_count":18,"is_preprint":false},{"pmid":"12915914","id":"PMC_12915914","title":"Hepatic regeneration: If it ain't broke, don't fix it.","date":"2003","source":"Canadian journal of gastroenterology = Journal canadien de gastroenterologie","url":"https://pubmed.ncbi.nlm.nih.gov/12915914","citation_count":17,"is_preprint":false},{"pmid":"2516796","id":"PMC_2516796","title":"Plasminogen activator expression in F9 teratocarcinoma embryoid bodies and their endoderm derivatives.","date":"1989","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/2516796","citation_count":17,"is_preprint":false},{"pmid":"8360175","id":"PMC_8360175","title":"Specific uptake of retinol-binding protein by variant F9 cell lines.","date":"1993","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8360175","citation_count":17,"is_preprint":false},{"pmid":"2485243","id":"PMC_2485243","title":"Cell proliferation and expression of cytokeratin filaments in F9 embryonal carcinoma cells.","date":"1989","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/2485243","citation_count":17,"is_preprint":false},{"pmid":"26988465","id":"PMC_26988465","title":"Correlation between FIX genotype and pharmacokinetics of Nonacog alpha according to a multicentre Italian study.","date":"2016","source":"Haemophilia : the official journal of the World Federation of Hemophilia","url":"https://pubmed.ncbi.nlm.nih.gov/26988465","citation_count":16,"is_preprint":false},{"pmid":"16773043","id":"PMC_16773043","title":"Roles of the Nanog protein in murine F9 embryonal carcinoma cells and their endoderm-differentiated counterparts.","date":"2006","source":"Cell research","url":"https://pubmed.ncbi.nlm.nih.gov/16773043","citation_count":15,"is_preprint":false},{"pmid":"1406664","id":"PMC_1406664","title":"A DNA element that regulates expression of an endogenous retrovirus during F9 cell differentiation is E1A dependent.","date":"1992","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/1406664","citation_count":15,"is_preprint":false},{"pmid":"16860319","id":"PMC_16860319","title":"Galpha13 activation rescues moesin-depletion induced apoptosis in F9 teratocarcinoma cells.","date":"2006","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/16860319","citation_count":15,"is_preprint":false},{"pmid":"24816826","id":"PMC_24816826","title":"Characterisation of large F9 deletions in seven unrelated patients with severe haemophilia B.","date":"2014","source":"Thrombosis and haemostasis","url":"https://pubmed.ncbi.nlm.nih.gov/24816826","citation_count":15,"is_preprint":false},{"pmid":"36291091","id":"PMC_36291091","title":"To Fix or Not to Fix: Maintenance of Chromosome Ends Versus Repair of DNA Double-Strand Breaks.","date":"2022","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/36291091","citation_count":14,"is_preprint":false},{"pmid":"24679056","id":"PMC_24679056","title":"Oral gene therapy for hemophilia B using chitosan-formulated FIX mutants.","date":"2014","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/24679056","citation_count":14,"is_preprint":false},{"pmid":"2180751","id":"PMC_2180751","title":"Altered uvomorulin expression in a noncompacting mutant cell line of F9 embryonal carcinoma cells.","date":"1990","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/2180751","citation_count":14,"is_preprint":false},{"pmid":"35413099","id":"PMC_35413099","title":"Structural, functional, and immunogenicity implications of F9 gene recoding.","date":"2022","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/35413099","citation_count":13,"is_preprint":false},{"pmid":"20226026","id":"PMC_20226026","title":"Regulation of TFIIIB during F9 cell differentiation.","date":"2010","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/20226026","citation_count":13,"is_preprint":false},{"pmid":"25153150","id":"PMC_25153150","title":"Identification and characterization of germ cell genes expressed in the F9 testicular teratoma stem cell line.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25153150","citation_count":13,"is_preprint":false},{"pmid":"17993262","id":"PMC_17993262","title":"Moesin signalling induces F9 teratocarcinoma cells to differentiate into primitive extraembryonic endoderm.","date":"2007","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/17993262","citation_count":13,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48345,"output_tokens":3702,"usd":0.100282,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11161,"output_tokens":3556,"usd":0.072353,"stage2_stop_reason":"end_turn"},"total_usd":0.172635,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"Looking through the abstracts, I need to identify papers about the human/mammalian coagulation Factor IX (F9/FIX) gene, not the many papers about the F9 mouse embryonal carcinoma cell line or other unrelated uses of \"F9.\"\n\nRelevant papers about coagulation Factor IX (F9/FIX): PMIDs 25568350, 22103590, 35269902, 23093250, 34626083, 30428703, 28439985 (no - MASS-FIX is a mass spec method, not about the gene), 24729686, 30992271, 26988465, 24816826, 18459950, 35413099, 35184131, 24679056.\n\nLet me now extract mechanistic discoveries from these papers.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2022,\n      \"finding\": \"Codon optimization (recoding) of F9 alters cotranslational folding kinetics, changes protein conformation, leads to suboptimal posttranslational modifications (e.g., gamma-carboxylation), and results in distinct MHC class II peptide presentation, indicating that synonymous codon substitutions in F9 can affect FIX structure, function, and immunogenicity.\",\n      \"method\": \"Ribosome profiling (translation kinetics), MHC-associated peptide proteomics assay, posttranslational modification analysis, structural conformation assessment of recoded vs. wild-type FIX constructs expressed in cells\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ribosome profiling, MHC peptide proteomics, PTM analysis) in a single study; not independently replicated\",\n      \"pmids\": [\"35413099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Downregulation of F9 using sgRNA or shRNA in MCF7 breast cancer cells prevents the cell cycle arrest and senescent-like phenotype induced by CDK4/6 inhibitor palbociclib; conversely, treatment with recombinant FIX protein is sufficient to induce cell cycle arrest and a senescence-like state, identifying FIX as a regulator of CDK4/6 inhibitor-induced senescence.\",\n      \"method\": \"Genome-wide CRISPR/Cas9 loss-of-function screen; shRNA knockdown; recombinant FIX protein treatment; cell cycle and senescence phenotype assays in MCF7 and T47D cells with palbociclib and abemaciclib\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional CRISPR screen with orthogonal shRNA validation and recombinant protein rescue, single lab, confirmed in two cell lines and with two CDK4/6 inhibitors\",\n      \"pmids\": [\"35184131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Missense mutations at FIX activation sites R191 and R226 impair FIX activation, leading to circulating dysfunctional FIX with variable antigen levels. The R191/R226 substitutions prolong the pharmacokinetic beta elimination half-life of infused FIX, acting as independent predictors of half-life extension, likely because endogenous dysfunctional FIX competes with infused FIX for binding (e.g., to collagen IV) over time.\",\n      \"method\": \"Recombinant expression of FIX variants; FIX activity and antigen assays in plasma; pharmacokinetic analysis in hemophilia B patients (GePKHIS study); regression analysis\",\n      \"journal\": \"Journal of thrombosis and haemostasis : JTH\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant expression plus clinical PK data in 30 patients with regression analysis; single study, moderate evidence\",\n      \"pmids\": [\"34626083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FIX binds to collagen IV (Col4) in the subendothelial basement membrane, reducing plasma recovery of infused FIX. Dysfunctional endogenous FIX (e.g., FIXR333Q) that retains Col4-binding ability competes with infused wild-type FIX for Col4 binding, thereby impairing hemostatic efficacy of prophylactic therapy in CRM+ hemophilia B mice.\",\n      \"method\": \"Mouse hemophilia B model (CRM- and CRM+ mice expressing FIXR333Q); saphenous vein bleeding assay; infusion of wild-type FIX, FIXFC (Alprolix), and FIXAlb (Idelvion); binding competition analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo mouse model with multiple FIX variants, mechanistic competition for Col4 binding demonstrated, functional hemostatic readout; rigorous controls with multiple FIX products\",\n      \"pmids\": [\"30992271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The FIX-Padua variant (R338L, arginine 338 to leucine) exhibits 8–12-fold increased specific clotting activity relative to wild-type FIX while having similar immunogenicity and thrombogenicity; AAV8-mediated liver delivery of FIX-Padua at reduced vector doses achieves sustained therapeutic FIX levels and can eradicate pre-existing FIX inhibitors without triggering new inhibitor formation.\",\n      \"method\": \"AAV8 gene delivery in hemophilia B dogs (naive and inhibitor-positive) and mice; FIX activity and antigen measurement; Bethesda assay for inhibitors; clotting time assays; immunogenicity and thrombogenicity challenge studies\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — large animal (dog) model with functional hemostatic assays and immunological readouts, replicated across multiple animals and confirmed in mice with orthogonal methods\",\n      \"pmids\": [\"25568350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The FIX-Padua mutation (R338L in exon 8) causes a ~10-fold increase in FIX clotting activity with only a slight increase in FIX antigen (a type 2 gain-of-function defect), establishing that the Arg338 residue is critical for normal FIX catalytic regulation and that its substitution to leucine produces a hyperfunctional, prothrombotic FIX variant.\",\n      \"method\": \"Clinical and molecular characterization; FIX activity and antigen measurement; structural/functional inference from mutation analysis in patients with venous thrombosis\",\n      \"journal\": \"Clinical and applied thrombosis/hemostasis\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — clinical observational data and mutational characterization without direct in vitro biochemical reconstitution in this paper; findings corroborated by other studies\",\n      \"pmids\": [\"30428703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Diverse F9 mutations cause FIX deficiency through distinct molecular mechanisms: large deletions/frameshifts produce truncated nonfunctional FIX; intronic mutations and some silent mutations cause aberrant splicing; promoter mutations cause hemophilia B Leyden; missense mutations impair FIX translation, protein folding, stability, posttranslational modifications (including vitamin K-dependent gamma-carboxylation), activation cleavage at R191/R226, or assembly of the functional Xase complex (with FVIIIa, FX, phospholipid, and Ca2+).\",\n      \"method\": \"Systematic review and synthesis of published mutation analyses; structural and functional characterization data from the literature\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — comprehensive synthesis of replicated findings across many studies; mechanistic conclusions are well-supported by the broader literature even though this paper itself is a review/synthesis\",\n      \"pmids\": [\"35269902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Recombinant FIX-Fc fusion protein (rFIXFc) exploits physiological binding of the Fc domain to the neonatal Fc receptor (FcRn) to extend FIX half-life 3–4-fold compared to standard recombinant FIX, demonstrating that FcRn-mediated recycling is sufficient to prolong FIX circulatory persistence.\",\n      \"method\": \"Phase I/IIa and Phase III clinical pharmacokinetic studies; half-life measurement of rFIXFc vs. standard recombinant FIX in hemophilia B patients\",\n      \"journal\": \"Drug design, development and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clinical PK data from Phase I–III studies demonstrating mechanism (FcRn binding); single mechanistic pathway but confirmed in multiple clinical trials\",\n      \"pmids\": [\"24729686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The silent F9 mutation G17736A/Val107Val causes mild hemophilia B (FIX activity 15–20%) in five Swedish families; RT-PCR and cDNA sequencing excluded exon skipping or intron retention as mechanisms, suggesting the silent mutation may affect a splicing enhancer site or reduce translation rate and thereby alter cotranslational FIX protein folding in vivo.\",\n      \"method\": \"RT-PCR of lymphocyte mRNA; cDNA sequencing from codon 68 to 180; FIX activity and antigen measurement in patients\",\n      \"journal\": \"Haemophilia\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single family study with limited mechanistic resolution; proposed mechanisms (splicing enhancer disruption or codon-translation rate effect) not directly confirmed experimentally\",\n      \"pmids\": [\"18459950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"F9 genotype strongly predicts FIX inhibitor risk in hemophilia B: nonsense mutations and entire F9 gene deletions carry significantly higher inhibitor risk (OR 11.0 and 32.7, prevalence 14.3% and 44.5% respectively) compared to missense mutations (OR 0.05, prevalence 0.39%), establishing that the magnitude of FIX protein disruption (absence of FIX antigen) is the primary determinant of inhibitor formation.\",\n      \"method\": \"Case-control analysis in 52 unrelated Argentine hemophilia B patients; mutation analysis by conformation-sensitive gel electrophoresis, DNA sequencing, and multiplex ligation-dependent probe amplification; inhibitor detection by Bethesda assay\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic mutation-genotype/inhibitor analysis in a defined cohort with statistical case-control methodology; single-center, moderate evidence\",\n      \"pmids\": [\"23093250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Large F9 gene deletions (11.1–884 kb) cause severe hemophilia B; breakpoint characterization revealed that non-homologous end joining (NHEJ) and microhomology-mediated break-induced replication (MMBIR) are the primary mechanisms generating these deletions, with non-allelic homologous recombination (NAHR) responsible for one deletion occurring between tandem LINE/L1 elements.\",\n      \"method\": \"AccuCopy technique for deletion identification; genome walking and primer walking for precise breakpoint characterization; microhomology and repetitive element analysis at breakpoint junctions in seven patients\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct molecular characterization of deletion breakpoints in seven patients with mechanistic inference from junction sequences; single study\",\n      \"pmids\": [\"24816826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Oral delivery of chitosan nanoparticle-formulated FIX expression vectors to hemophilia B mice resulted in FIX expression exclusively in the small intestine, reaching transient FIX activity >14% of normal with partial phenotypic correction; bioengineered FIX variants with higher specific activity and improved tissue release enhanced this effect.\",\n      \"method\": \"Site-directed mutagenesis of FIX variants; chitosan nanoparticle formulation; oral delivery to FIX-knockout hemophilia B mice; RT-PCR and fluorescence staining of intestinal tissue; FIX activity assay\",\n      \"journal\": \"Journal of thrombosis and haemostasis : JTH\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — proof-of-concept in vivo study with transient expression; single lab, limited mechanistic depth about FIX protein function itself\",\n      \"pmids\": [\"24679056\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Coagulation Factor IX (FIX) is a vitamin K-dependent serine protease that circulates in plasma and binds collagen IV in the subendothelial basement membrane; upon activation by cleavage at R191 and R226, FIXa assembles with FVIIIa, FX, phospholipid, and Ca2+ into the intrinsic Xase complex to activate FX; gain-of-function mutations (e.g., R338L/FIX-Padua) markedly increase catalytic activity while loss-of-function mutations cause hemophilia B through diverse mechanisms including impaired gamma-carboxylation, misfolding, aberrant splicing, or failure to form the Xase complex; FIX half-life can be extended by FcRn-mediated recycling via Fc-fusion, and dysfunctional circulating FIX competes with infused therapeutic FIX for collagen IV binding, impairing hemostatic efficacy; additionally, FIX has been identified as a regulator of CDK4/6 inhibitor-induced cellular senescence in cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Coagulation Factor IX (FIX) is a vitamin K-dependent zymogen whose activation by cleavage at R191 and R226 enables assembly of the functional Xase complex with FVIIIa, FX, phospholipid, and Ca2+; disruption of any step in its biosynthesis or activation causes hemophilia B [#6]. FIX biosynthesis is sensitive to translation kinetics: synonymous codon usage in F9 shapes cotranslational folding, posttranslational gamma-carboxylation, and ultimately conformation and immunogenicity [#0]. The catalytic activity of FIX is tightly governed by Arg338, whose substitution to leucine (FIX-Padua, R338L) produces an 8–12-fold hyperfunctional, prothrombotic variant with preserved immunogenicity, a property exploited for low-dose AAV8 gene therapy [#4, #5]. In circulation FIX binds collagen IV in the subendothelial basement membrane; this interaction lowers plasma recovery, and dysfunctional endogenous FIX that retains collagen IV binding competes with infused therapeutic FIX, impairing hemostatic efficacy [#3]. FIX persistence can be extended by Fc-fusion that engages FcRn-mediated recycling [#7], while activation-site mutations at R191/R226 yield circulating dysfunctional FIX that prolongs infused FIX half-life through the same competition mechanism [#2]. The molecular severity of F9 lesions also determines therapeutic risk: null genotypes (nonsense mutations and large deletions arising via NHEJ, MMBIR, and NAHR) abolish FIX antigen and carry markedly elevated inhibitor risk compared with missense alleles [#9, #10]. Beyond coagulation, FIX has been identified as a required regulator of CDK4/6 inhibitor-induced cellular senescence in breast cancer cells [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that even a synonymous F9 mutation can cause clinical FIX deficiency, raising the question of whether codon-level effects on translation or splicing alter FIX biosynthesis.\",\n      \"evidence\": \"RT-PCR and cDNA sequencing of patient lymphocyte mRNA in five Swedish hemophilia B families with a silent Val107Val mutation\",\n      \"pmids\": [\"18459950\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Proposed splicing-enhancer disruption or translation-rate effect not directly demonstrated\", \"No in vitro reconstitution of the folding defect\", \"Single-family observational cohort\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the genetic determinant of inhibitor formation, showing that absence of FIX antigen rather than amino-acid change drives immune risk.\",\n      \"evidence\": \"Case-control mutation-genotype analysis with Bethesda inhibitor assay in 52 Argentine hemophilia B patients\",\n      \"pmids\": [\"23093250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-center cohort\", \"Does not explain inhibitor mechanism at the molecular/immunological level\", \"Limited number of null-genotype patients\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified the mutational mechanisms generating large F9 deletions that produce severe, antigen-null hemophilia B.\",\n      \"evidence\": \"AccuCopy detection plus genome/primer walking breakpoint characterization in seven patients\",\n      \"pmids\": [\"24816826\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Seven-patient sample\", \"Mechanism inferred from junction sequences\", \"No functional consequence assays beyond deletion mapping\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated that FcRn-mediated recycling is sufficient to prolong FIX circulatory persistence, addressing the short half-life limitation of FIX therapy.\",\n      \"evidence\": \"Phase I–III clinical pharmacokinetic comparison of rFIXFc vs standard recombinant FIX in hemophilia B patients\",\n      \"pmids\": [\"24729686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism shown via half-life, not direct FcRn binding kinetics in this study\", \"Single fusion strategy\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed that bioengineered higher-activity FIX variants could be delivered enterally, exploring routes to in vivo FIX production.\",\n      \"evidence\": \"Chitosan nanoparticle oral delivery of FIX vectors to FIX-knockout hemophilia B mice with intestinal expression and activity assays\",\n      \"pmids\": [\"24679056\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Transient expression only\", \"Proof-of-concept in single lab\", \"Limited insight into FIX protein function itself\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Translated the hyperfunctional FIX-Padua variant into a gene-therapy advantage, showing low-dose AAV8 delivery achieves sustained therapeutic levels without new inhibitors.\",\n      \"evidence\": \"AAV8 liver gene delivery in naive and inhibitor-positive hemophilia B dogs and mice with clotting, Bethesda, immunogenicity and thrombogenicity assays\",\n      \"pmids\": [\"25568350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term durability beyond study window not addressed\", \"Thrombogenicity in larger populations not assessed\", \"Mechanism of increased catalytic activity not biochemically dissected here\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established Arg338 as critical to normal FIX catalytic regulation by linking its R338L substitution to a type-2 gain-of-function, prothrombotic phenotype in patients.\",\n      \"evidence\": \"Clinical and molecular characterization with FIX activity/antigen measurement in venous thrombosis patients\",\n      \"pmids\": [\"30428703\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct in vitro biochemical reconstitution in this study\", \"Observational clinical data\", \"Structural basis of hyperactivity not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined collagen IV binding as a determinant of FIX plasma recovery and revealed that dysfunctional endogenous FIX impairs therapy by competing for this binding site.\",\n      \"evidence\": \"Hemophilia B mouse models (CRM- and CRM+ FIXR333Q) with saphenous vein bleeding assay and binding competition using multiple FIX products\",\n      \"pmids\": [\"30992271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Competition shown in mouse model only\", \"Structural details of the FIX–Col4 interface not defined\", \"Generalizability across patient mutation spectrum not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed that activation-site mutations producing circulating dysfunctional FIX paradoxically extend infused FIX half-life, consistent with the collagen IV competition model.\",\n      \"evidence\": \"Recombinant FIX variant expression plus clinical pharmacokinetic regression analysis in 30 hemophilia B patients (GePKHIS)\",\n      \"pmids\": [\"34626083\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Modest patient number\", \"Competition mechanism inferred rather than directly measured in patients\", \"Single study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected synonymous codon usage mechanistically to FIX folding, gamma-carboxylation, and immunogenicity, explaining how recoding alters protein quality and antigen presentation.\",\n      \"evidence\": \"Ribosome profiling, MHC-associated peptide proteomics, and PTM/conformation analysis of recoded vs wild-type FIX expressed in cells\",\n      \"pmids\": [\"35413099\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not independently replicated\", \"In vivo immunogenic consequences not tested\", \"Single study with multiple methods in one system\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed a non-coagulation role for FIX as a required regulator of CDK4/6 inhibitor-induced senescence in cancer cells.\",\n      \"evidence\": \"Genome-wide CRISPR screen with shRNA validation and recombinant FIX rescue, in MCF7 and T47D cells with palbociclib and abemaciclib\",\n      \"pmids\": [\"35184131\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism downstream of FIX in senescence not defined\", \"Single lab\", \"Receptor/effector for FIX in cancer cells unidentified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular pathway by which FIX regulates CDK4/6 inhibitor-induced senescence, and how this relates to its coagulation function, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No receptor or signaling effector identified for FIX in senescence\", \"Relationship between protease activity and senescence role unknown\", \"Not validated in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 6]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 2]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [3, 4, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 9, 10]}\n    ],\n    \"complexes\": [\"intrinsic Xase complex\"],\n    \"partners\": [\"F8\", \"F10\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}