{"gene":"FGFR1","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1997,"finding":"Crystal structures of the FGFR1 tyrosine kinase domain in complex with indolinone inhibitors revealed that the oxindole core occupies the ATP adenine-binding site, and the more specific inhibitor induces a conformational change in the nucleotide-binding loop, establishing the structural basis for ATP-competitive kinase inhibition of FGFR1.","method":"X-ray crystallography of FGFR1 kinase domain–inhibitor complexes combined with kinase activity assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional kinase assay validation in a high-impact single study","pmids":["9139660"],"is_preprint":false},{"year":1999,"finding":"The crystal structure of FGF2 bound to FGFR1 immunoglobulin-like domains D2 and D3 revealed that two FGF2:FGFR1 complexes form a symmetric dimer stabilized by FGF2–D2 cross-contacts and a direct D2–D2 receptor–receptor interaction, establishing the structural mechanism of ligand-induced FGFR1 dimerization and a positively charged canyon as the heparin-binding site.","method":"X-ray crystallography at 2.8 Å resolution of FGF2–FGFR1(D2-D3) complex","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with biochemical validation, foundational mechanistic study","pmids":["10490103"],"is_preprint":false},{"year":2000,"finding":"The crystal structure of a 2:2:2 FGF:FGFR:heparin ternary complex at 3 Å resolution showed that heparin plays a dual role: it augments FGF–FGFR binding by contacting both molecules within each 1:1 complex, and it simultaneously bridges to FGFR in the adjoining complex to promote receptor dimerization, with the 6-O-sulfate group of heparin being pivotal for both interactions.","method":"X-ray crystallography of ternary FGF–FGFR1–heparin complex plus supporting biochemical assays","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with biochemical corroboration, replicated by structural community","pmids":["11030354"],"is_preprint":false},{"year":1996,"finding":"Systematic mitogenesis assays in engineered cell lines expressing major splice variants of all four FGF receptors demonstrated that FGF1 is the only FGF ligand capable of activating all FGFR splice variants including FGFR1, while other FGF family members show selective receptor binding, establishing the binding specificity matrix for FGFR1 and its isoforms.","method":"Mitogenic activity assays on BaF3 cells engineered to express individual FGFR splice variants","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic functional assay across all receptor isoforms, independently replicated","pmids":["8663044"],"is_preprint":false},{"year":2005,"finding":"FGFR1 activation by FGF and heparan sulfate proteoglycan (HSPG) induces receptor dimerization and autophosphorylation of multiple cytoplasmic tyrosine residues; the docking proteins FRS2α and FRS2β are major substrates that mediate downstream activation of the Ras/MAPK and PI3K/Akt signaling pathways, as well as negative feedback loops regulating signal amplitude.","method":"Biochemical phosphorylation assays, co-immunoprecipitation, and cell-based signaling studies synthesized across multiple laboratories","journal":"Cytokine & Growth Factor Reviews","confidence":"High","confidence_rationale":"Tier 2 — extensively replicated across labs, multiple orthogonal methods documented in this comprehensive review","pmids":["15863030"],"is_preprint":false},{"year":2006,"finding":"Klotho, a single-pass transmembrane protein, physically binds FGF23 and directly converts FGFR1(IIIc) into a high-affinity FGF23 receptor; forced Klotho expression restored FGF23 responsiveness in a renal cell line, and anti-Klotho antibody injection abrogated endogenous FGF23 function in vivo, establishing that concerted Klotho–FGFR1(IIIc) interaction is required for FGF23 signaling.","method":"Renal homogenate binding assays, forced expression in cell lines, in vivo antibody blockade, co-immunoprecipitation","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal in vitro and in vivo methods, replicated by independent groups","pmids":["17086194"],"is_preprint":false},{"year":2006,"finding":"Receptor specificity studies for the complete 22-member FGF family using BaF3 cell lines expressing individual FGFRs showed that FGF10 and FGF22 signal selectively through FGFR1b (IIIb) splice variant, while FGF19/21/23 subfamily members (endocrine FGFs) have reduced or absent activity at FGFR1 without co-receptors, defining the full specificity profile of FGFR1 isoforms.","method":"Mitogenic activity assays on BaF3 cells expressing FGFR1 splice variants with all FGF ligands","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic functional screen covering all FGF ligands, complements earlier receptor specificity studies","pmids":["16597617"],"is_preprint":false},{"year":2007,"finding":"betaKlotho in combination with specific FGFR isoforms, including FGFR1, confers tissue-specific responsiveness to FGF19 and FGF21; both ligands signal through betaKlotho–FGFR1 complexes to increase glucose uptake in adipocytes, while only FGF19 efficiently signals through FGFR4 in hepatocytes to reduce CYP7A1 transcription.","method":"Co-immunoprecipitation, ligand-binding assays, cell-based glucose uptake assays, hepatocyte CYP7A1 reporter assays","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, functional readouts in relevant cell types","pmids":["17623664"],"is_preprint":false},{"year":1997,"finding":"Chimeric embryo analysis demonstrated that cells homozygous for a kinase-dead Fgfr1 allele (fgfr1-Δtmk) accumulate within the primitive streak and fail to populate anterior mesoderm and endodermal lineages, indicating that FGFR1 kinase activity is specifically required for the morphogenetic movement of epiblast cells through the primitive streak during gastrulation, and that cells arrested in the streak adopt ectopic neural fate.","method":"Mouse chimera analysis, embryonic histology, cell lineage tracing using mutant vs. wild-type cells","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via chimeric analysis with clear cell-autonomous phenotypic readout, replicated at multiple developmental stages","pmids":["9226454"],"is_preprint":false},{"year":2009,"finding":"Oncogenic FGFR1 directly phosphorylates pyruvate kinase M2 (PKM2) at tyrosine 105, disrupting binding of the cofactor fructose-1,6-bisphosphate and inhibiting formation of active tetrameric PKM2, thereby promoting aerobic glycolysis (Warburg effect) and tumor growth; Y105F mutation reversed these metabolic and proliferative effects in cancer cells and xenografts.","method":"Phosphoproteomic mass spectrometry, in vitro kinase assay, site-directed mutagenesis (Y105F), xenograft tumor models, metabolic flux assays","journal":"Science Signaling","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus mutagenesis plus in vivo xenograft, multiple orthogonal methods","pmids":["19920251"],"is_preprint":false},{"year":2010,"finding":"Focal FGFR1 amplification in squamous cell lung cancer drives tumor cell proliferation and survival; FGFR1 knockdown and expression of the kinase-resistant allele FGFR1(V561M) specifically rescued FGFR1-amplified cells from FGFR inhibitor cytotoxicity, confirming that amplified FGFR1 kinase activity is the dependency driver in these tumors.","method":"FISH for gene amplification, FGFR1 siRNA knockdown, ectopic expression of resistant mutant FGFR1(V561M), FGFR inhibitor (PD173074) treatment, in vivo tumor shrinkage assay","journal":"Science Translational Medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic and pharmacological approaches with in vivo validation","pmids":["21160078"],"is_preprint":false},{"year":2010,"finding":"FGFR1 overexpression/amplification in breast cancer cell lines causes ligand-independent basal MAPK and PI3K-AKT pathway activation and confers resistance to 4-hydroxytamoxifen; siRNA silencing of FGFR1 reversed endocrine resistance, and FGFR1 signaling suppresses progesterone receptor expression.","method":"siRNA knockdown, Western blotting of signaling intermediates, anchorage-independent growth assay, tamoxifen sensitivity assay, PR expression analysis","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function with defined molecular and cellular phenotypes","pmids":["20179196"],"is_preprint":false},{"year":2012,"finding":"In-frame chromosomal translocations fuse the FGFR1 kinase domain to TACC1 in a subset of GBMs; the FGFR1-TACC1 fusion protein localizes to mitotic spindle poles, has constitutive kinase activity, induces chromosomal segregation defects and aneuploidy, and drives oncogenesis in astrocytes and in mouse brain, which is reversed by FGFR kinase inhibition.","method":"RNA sequencing for fusion discovery, FGFR kinase assay, immunofluorescence localization to spindle poles, aneuploidy measurement, intracranial mouse glioma model, FGFR inhibitor treatment","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — constitutive kinase activity demonstrated, subcellular localization with functional consequence, in vivo model","pmids":["22837387"],"is_preprint":false},{"year":2003,"finding":"Loss-of-function mutations in FGFR1 cause autosomal dominant Kallmann syndrome (KAL2), demonstrating that FGFR1 signaling is required for normal migration of olfactory/GnRH neurons; the extracellular matrix protein anosmin-1 (KAL1 product) is proposed to be involved in FGF signaling, explaining the dosage-sensitive sex difference in disease prevalence.","method":"Positional cloning, mutation analysis in Kallmann syndrome families, interstitial deletion mapping","journal":"Nature Genetics","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function human genetics with defined developmental phenotype, replicated across multiple families","pmids":["12627230"],"is_preprint":false},{"year":1994,"finding":"A specific Pro→Arg missense mutation in the extracellular domain (exon 5) of FGFR1 causes Pfeiffer syndrome (autosomal dominant craniosynostosis), demonstrating that gain-of-function FGFR1 mutations in the immunoglobulin-like domain lead to premature fusion of cranial sutures.","method":"Mutation analysis by sequencing in affected members of five unrelated Pfeiffer syndrome families","journal":"Nature Genetics","confidence":"High","confidence_rationale":"Tier 2 — mutation identified in multiple independent families, orthologous gain-of-function mechanism confirmed by subsequent structural studies","pmids":["7874169"],"is_preprint":false},{"year":2019,"finding":"In FGFR1-amplified lung cancer cells, miR-214-3p directly targets the FGFR1 3'-UTR to downregulate FGFR1 expression (validated by luciferase reporter assay), and FGFR1 signaling through ERK establishes a negative feedback loop that suppresses miR-214-3p; miR-214-3p inhibits EMT and Wnt/MAPK/AKT signaling by targeting FGFR1.","method":"Luciferase 3'-UTR reporter assay, qRT-PCR, Western blot, transwell migration/invasion assay, signaling pathway analysis","journal":"Oncogenesis","confidence":"Medium","confidence_rationale":"Tier 2–3 — direct 3'-UTR targeting validated by reporter assay; single-lab study with multiple methods","pmids":["31492847"],"is_preprint":false},{"year":2020,"finding":"In FGFR1-amplified lung squamous cell carcinoma cell lines, FGFR1 promotes epithelial-mesenchymal transition and metastatic behavior through AKT/MAPK signaling by transcriptionally or post-translationally targeting CCND1 (cyclin D1), which is co-overexpressed with FGFR1 and required for proliferation and invasion.","method":"qRT-PCR, Western blot, transwell migration/invasion assay, FGFR1 and CCND1 manipulation in FGFR1-amplified cell lines","journal":"Cell Adhesion & Migration","confidence":"Low","confidence_rationale":"Tier 3 — single lab, limited mechanistic detail on how FGFR1 targets CCND1","pmids":["32380883"],"is_preprint":false}],"current_model":"FGFR1 is a receptor tyrosine kinase that, upon binding FGF ligands (especially FGF1) augmented by heparan sulfate proteoglycans (or co-receptors Klotho/betaKlotho for endocrine FGFs), undergoes ligand-induced dimerization via a dual FGF–FGFR–heparin ternary complex, activates its kinase domain (whose ATP-binding site and nucleotide-binding loop have been structurally characterized), autophosphorylates multiple cytoplasmic tyrosines, recruits docking proteins FRS2α/β to activate Ras/MAPK and PI3K/Akt pathways, can directly phosphorylate substrates such as PKM2-Y105 to promote aerobic glycolysis, is required cell-autonomously for epiblast cell movement through the primitive streak during gastrulation, and when constitutively activated by amplification or oncogenic fusions (e.g., FGFR1-TACC1) drives proliferation, aneuploidy, endocrine therapy resistance, and tumor growth."},"narrative":{"teleology":[{"year":1994,"claim":"Demonstrating that a gain-of-function missense mutation in the FGFR1 extracellular domain causes Pfeiffer syndrome established the first direct link between altered FGFR1 signaling and a human developmental disorder (craniosynostosis).","evidence":"Sequencing of FGFR1 exon 5 in five unrelated Pfeiffer syndrome families","pmids":["7874169"],"confidence":"High","gaps":["Structural basis of how the Pro→Arg substitution activates signaling was not resolved","Whether other craniosynostosis-causing FGFR1 mutations share the same mechanism was unknown"]},{"year":1996,"claim":"Systematic profiling of all FGF ligands against FGFR splice variants revealed FGF1 as the universal FGFR1 activator and defined the selectivity landscape for FGFR1b versus FGFR1c isoforms, answering which ligand–receptor pairs are functional.","evidence":"Mitogenic assays in BaF3 cells expressing individual FGFR splice variants","pmids":["8663044"],"confidence":"High","gaps":["The structural determinants of splice-variant selectivity were not explained","Endocrine FGFs showed weak activity, and the basis for this deficiency was unresolved"]},{"year":1997,"claim":"Two key advances resolved how FGFR1 kinase is inhibited and how it functions in vivo: crystal structures of the kinase domain with ATP-competitive inhibitors defined the drug-binding pocket, while chimeric embryo analysis proved that FGFR1 kinase activity is cell-autonomously required for epiblast migration through the primitive streak during gastrulation.","evidence":"X-ray crystallography of FGFR1 kinase–inhibitor complexes; mouse chimera analysis with kinase-dead Fgfr1 allele","pmids":["9139660","9226454"],"confidence":"High","gaps":["Full autophosphorylation site mapping and downstream docking protein identity remained incomplete","Why kinase-dead cells adopt ectopic neural fate was not mechanistically explained"]},{"year":1999,"claim":"The crystal structure of the FGF2–FGFR1(D2-D3) complex revealed the receptor dimerization interface, answering the longstanding question of how ligand binding induces receptor activation at atomic resolution.","evidence":"X-ray crystallography at 2.8 Å of the FGF2–FGFR1 dimer","pmids":["10490103"],"confidence":"High","gaps":["Heparin's precise contacts were not resolved in this binary structure","How alternative ligands might employ different dimerization geometries was unknown"]},{"year":2000,"claim":"The ternary FGF–FGFR1–heparin crystal structure resolved heparin's dual role—augmenting ligand binding within each 1:1 complex and bridging to the adjacent receptor to stabilize the dimer—establishing that heparan sulfate is an integral component of the signaling complex, not merely a concentrating device.","evidence":"X-ray crystallography of 2:2:2 ternary complex at 3 Å with supporting biochemical assays","pmids":["11030354"],"confidence":"High","gaps":["Whether endogenous HSPGs with defined sulfation patterns recapitulate these contacts in vivo was untested","Kinetics of complex assembly on the cell surface were not addressed"]},{"year":2003,"claim":"Identification of loss-of-function FGFR1 mutations as the cause of autosomal dominant Kallmann syndrome proved that FGFR1 is required for olfactory and GnRH neuron migration in humans, complementing the mouse gastrulation phenotype.","evidence":"Positional cloning and mutation analysis in multiple Kallmann syndrome families","pmids":["12627230"],"confidence":"High","gaps":["The precise ligand and co-receptor triggering FGFR1 during GnRH neuron migration were unidentified","Anosmin-1's proposed role as an FGFR1 co-factor lacked direct biochemical validation"]},{"year":2005,"claim":"Comprehensive characterization of FGFR1 downstream signaling consolidated that FRS2α/β are the major docking proteins linking receptor autophosphorylation to Ras/MAPK and PI3K/Akt pathways, with built-in negative feedback loops regulating signal amplitude.","evidence":"Phosphorylation assays, co-immunoprecipitation, and cell-based signaling studies synthesized across multiple laboratories","pmids":["15863030"],"confidence":"High","gaps":["Quantitative contributions of individual autophosphorylation sites to pathway branching were not dissected","Negative feedback mechanisms were not fully mapped at the molecular level"]},{"year":2006,"claim":"Discovery that Klotho and βKlotho serve as obligate co-receptors that convert FGFR1 into high-affinity receptors for endocrine FGFs (FGF23 and FGF19/21, respectively) resolved why these ligands showed negligible activity in standard assays and explained tissue-specific endocrine FGF responses.","evidence":"Binding assays, forced Klotho expression in cell lines, in vivo antibody blockade; co-IP and glucose-uptake assays for βKlotho","pmids":["17086194","17623664"],"confidence":"High","gaps":["The structural basis of the Klotho–FGFR1–FGF23 ternary complex was not yet determined","Relative contributions of FGFR1 versus FGFR3/FGFR4 in Klotho-dependent signaling in different tissues remained unclear"]},{"year":2009,"claim":"Identification of PKM2-Y105 as a direct FGFR1 substrate linked receptor tyrosine kinase signaling to metabolic reprogramming, demonstrating that FGFR1 promotes aerobic glycolysis by inhibiting PKM2 tetramerization.","evidence":"Phosphoproteomics, in vitro kinase assay, Y105F mutagenesis, xenograft models, metabolic flux assays","pmids":["19920251"],"confidence":"High","gaps":["Whether this metabolic rewiring operates in non-transformed, FGFR1-dependent tissues was untested","Other direct kinase substrates beyond FRS2 and PKM2 remained largely uncharacterized"]},{"year":2010,"claim":"Two studies established FGFR1 amplification as an actionable oncogenic driver: in squamous lung cancer, FGFR1 amplification creates a kinase dependency reversible by FGFR inhibitors, while in breast cancer, FGFR1 overexpression drives ligand-independent MAPK/AKT activation and endocrine therapy resistance.","evidence":"FISH for amplification, siRNA knockdown, resistant-mutant rescue (V561M), FGFR inhibitor treatment, tamoxifen sensitivity assays","pmids":["21160078","20179196"],"confidence":"High","gaps":["Biomarkers distinguishing FGFR1-amplified tumors that are truly kinase-dependent from bystander amplifications were not defined","Mechanisms of acquired resistance to FGFR inhibitors were unexplored"]},{"year":2012,"claim":"Discovery of FGFR1-TACC1 fusion in glioblastoma revealed a novel oncogenic mechanism in which the fusion protein localizes to mitotic spindle poles, causes chromosomal missegregation and aneuploidy, and drives glioma formation—all reversible by FGFR kinase inhibition.","evidence":"RNA-seq fusion detection, kinase assay, immunofluorescence at spindle poles, aneuploidy measurement, intracranial mouse model, FGFR inhibitor treatment","pmids":["22837387"],"confidence":"High","gaps":["Whether TACC1-mediated spindle-pole localization is the primary oncogenic mechanism or whether constitutive kinase activity alone suffices was not resolved","Prevalence and therapeutic response of FGFR1-TACC1 fusions in clinical cohorts was not established"]},{"year":null,"claim":"A comprehensive catalog of direct FGFR1 kinase substrates beyond FRS2 and PKM2 remains incomplete, and the structural basis for co-receptor (Klotho/βKlotho) engagement with FGFR1 and endocrine FGFs is not fully resolved; acquired resistance mechanisms to clinical FGFR inhibitors also require systematic characterization.","evidence":"","pmids":[],"confidence":"Low","gaps":["Full substrate repertoire of FGFR1 kinase is unmapped","Structural details of Klotho–FGFR1–FGF ternary complex at atomic resolution are needed","Mechanisms of clinical resistance to FGFR-targeted therapies are poorly defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,9,10,12]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,4,9]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,2,3,5,6,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2,4,5,7]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,2]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,4,5,7,9,11]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[8,13,14]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,11,12]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[9]}],"complexes":["FGF-FGFR1-heparin ternary complex","Klotho-FGFR1 co-receptor complex","βKlotho-FGFR1 co-receptor complex"],"partners":["FGF1","FGF2","FRS2","KL","KLB","PKM","TACC1","FGF23"],"other_free_text":[]},"mechanistic_narrative":"FGFR1 is a receptor tyrosine kinase that transduces FGF signals to govern cell proliferation, migration, and metabolic reprogramming across development and disease. Ligand binding (FGF1 being the universal activator of all splice variants) triggers formation of a 2:2:2 FGF–FGFR1–heparan sulfate ternary complex that dimerizes the receptor via direct D2–D2 contacts and heparin-bridged cross-links, leading to autophosphorylation and recruitment of FRS2α/β to activate Ras/MAPK and PI3K/Akt cascades; endocrine FGFs (FGF19, FGF21, FGF23) require the co-receptors Klotho or βKlotho to convert FGFR1 into a high-affinity receptor [PMID:10490103, PMID:11030354, PMID:17086194, PMID:15863030]. During gastrulation, FGFR1 kinase activity is cell-autonomously required for epiblast cell movement through the primitive streak, and loss-of-function mutations cause Kallmann syndrome (defective olfactory/GnRH neuron migration) while a gain-of-function extracellular-domain mutation causes Pfeiffer syndrome (craniosynostosis) [PMID:9226454, PMID:12627230, PMID:7874169]. Oncogenic FGFR1 amplification or FGFR1–TACC1 fusion constitutively activates kinase signaling—including direct phosphorylation of PKM2-Y105 to promote aerobic glycolysis—and drives tumor proliferation, aneuploidy, and endocrine therapy resistance in lung, breast, and brain cancers [PMID:19920251, PMID:21160078, PMID:22837387, PMID:20179196]."},"prefetch_data":{"uniprot":{"accession":"P11362","full_name":"Fibroblast growth factor receptor 1","aliases":["Basic fibroblast growth factor receptor 1","BFGFR","bFGF-R-1","Fms-like tyrosine kinase 2","FLT-2","N-sam","Proto-oncogene c-Fgr"],"length_aa":822,"mass_kda":91.9,"function":"Tyrosine-protein kinase that acts as a cell-surface receptor for fibroblast growth factors and plays an essential role in the regulation of embryonic development, cell proliferation, differentiation and migration. Required for normal mesoderm patterning and correct axial organization during embryonic development, normal skeletogenesis and normal development of the gonadotropin-releasing hormone (GnRH) neuronal system. Phosphorylates PLCG1, FRS2, GAB1 and SHB. Ligand binding leads to the activation of several signaling cascades. Activation of PLCG1 leads to the production of the cellular signaling molecules diacylglycerol and inositol 1,4,5-trisphosphate. Phosphorylation of FRS2 triggers recruitment of GRB2, GAB1, PIK3R1 and SOS1, and mediates activation of RAS, MAPK1/ERK2, MAPK3/ERK1 and the MAP kinase signaling pathway, as well as of the AKT1 signaling pathway. Promotes phosphorylation of SHC1, STAT1 and PTPN11/SHP2. In the nucleus, enhances RPS6KA1 and CREB1 activity and contributes to the regulation of transcription. FGFR1 signaling is down-regulated by IL17RD/SEF, and by FGFR1 ubiquitination, internalization and degradation","subcellular_location":"Cell membrane; Nucleus; Cytoplasm, cytosol; Cytoplasmic vesicle","url":"https://www.uniprot.org/uniprotkb/P11362/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FGFR1","classification":"Not Classified","n_dependent_lines":150,"n_total_lines":1208,"dependency_fraction":0.12417218543046357},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FGFR1","total_profiled":1310},"omim":[{"mim_id":"621143","title":"HOLOPROSENCEPHALY 10; HPE10","url":"https://www.omim.org/entry/621143"},{"mim_id":"621092","title":"IQ MOTIF-CONTAINING GTPase-ACTIVATING PROTEIN 3; IQGAP3","url":"https://www.omim.org/entry/621092"},{"mim_id":"618428","title":"POPOV-CHANG SYNDROME; POPCHAS","url":"https://www.omim.org/entry/618428"},{"mim_id":"618368","title":"DUAL-SPECIFICITY PHOSPHATASE 26; DUSP26","url":"https://www.omim.org/entry/618368"},{"mim_id":"617425","title":"IMMUNOSKELETAL DYSPLASIA WITH NEURODEVELOPMENTAL ABNORMALITIES; ISDNA","url":"https://www.omim.org/entry/617425"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Microtubules","reliability":"Approved"},{"location":"Cytokinetic bridge","reliability":"Approved"},{"location":"Mitotic spindle","reliability":"Approved"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Centriolar satellite","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FGFR1"},"hgnc":{"alias_symbol":["H2","H3","H4","H5","CEK","FLG","BFGFR","N-SAM","CD331"],"prev_symbol":["FLT2","KAL2"]},"alphafold":{"accession":"P11362","domains":[{"cath_id":"2.60.40.10","chopping":"41-119","consensus_level":"high","plddt":87.2459,"start":41,"end":119},{"cath_id":"2.60.40.10","chopping":"152-249","consensus_level":"medium","plddt":88.8383,"start":152,"end":249},{"cath_id":"2.60.40.10","chopping":"254-360","consensus_level":"medium","plddt":88.4377,"start":254,"end":360},{"cath_id":"3.30.200.20","chopping":"468-564","consensus_level":"medium","plddt":90.5341,"start":468,"end":564},{"cath_id":"1.10.510.10","chopping":"569-764","consensus_level":"medium","plddt":85.9447,"start":569,"end":764}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P11362","model_url":"https://alphafold.ebi.ac.uk/files/AF-P11362-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P11362-F1-predicted_aligned_error_v6.png","plddt_mean":73.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FGFR1","jax_strain_url":"https://www.jax.org/strain/search?query=FGFR1"},"sequence":{"accession":"P11362","fasta_url":"https://rest.uniprot.org/uniprotkb/P11362.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P11362/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P11362"}},"corpus_meta":[{"pmid":"8858152","id":"PMC_8858152","title":"Nucleosome 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standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":57267,"output_tokens":5343,"usd":0.125973},"round2_rules_fired":"R2,R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":8143,"output_tokens":3488,"usd":0.191873}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"FGFR1 is required for morphogenetic movement of epiblast cells through the primitive streak during mouse gastrulation; fgfr1 mutant cells accumulate in the streak and fail to populate anterior mesoderm and endodermal lineages, and instead adopt ectopic neural fates, establishing that FGFR1 controls mesodermal cell movement and fate determination.\",\n      \"method\": \"Chimeric mouse embryo analysis using fgfr1(delta tmk) loss-of-function mutation; lineage tracing of mutant cells in chimeras at E7.5–E9.5\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function genetic experiment in chimeric embryos with specific cellular phenotype (streak accumulation, failure of anterior mesodermal contribution, ectopic neural tube formation), replicated across developmental stages\",\n      \"pmids\": [\"9226454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"miR-214-3p directly targets the 3'-UTR of FGFR1 mRNA to downregulate FGFR1 expression, and FGFR1 reciprocally suppresses miR-214-3p through ERK signaling, forming a negative feedback loop; FGFR1 promotes epithelial-mesenchymal transition and activates Wnt/MAPK/AKT signaling in FGFR1-amplified lung cancer cells.\",\n      \"method\": \"Luciferase reporter assay (3'-UTR targeting), Western blot, qRT-PCR, transwell migration/invasion assay, pharmacological inhibition with AZD4547\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct 3'-UTR targeting validated by luciferase assay; pathway placement by pharmacological inhibitor; single lab with multiple methods\",\n      \"pmids\": [\"31492847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FGFR1 promotes proliferation and metastasis in FGFR1-amplified lung squamous cell carcinoma by upregulating CCND1 and driving EMT through AKT/MAPK signaling.\",\n      \"method\": \"qRT-PCR, Western blot, transwell migration/invasion assay, cell proliferation assay in FGFR1-amplified cell lines\",\n      \"journal\": \"Cell Adhesion & Migration\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single set of methods, no reconstitution or rescue experiment; pathway placement inferred from correlation and inhibitor data\",\n      \"pmids\": [\"32380883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hematolymphoid neoplasms associated with FGFR1 gene fusions (rearrangements of FGFR1) represent a distinct category of myeloid/lymphoid neoplasms with eosinophilia; unlike PDGFRA/PDGFRB fusion neoplasms, FGFR1 fusion neoplasms do not respond to tyrosine kinase inhibitor therapy.\",\n      \"method\": \"Clinicopathological and genetic review of workshop cases; molecular diagnostics (cytogenetics, FISH, molecular testing)\",\n      \"journal\": \"American Journal of Clinical Pathology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — descriptive clinicopathological characterization; no direct biochemical mechanistic experiment on FGFR1 protein function\",\n      \"pmids\": [\"26276769\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FGFR1 is a receptor tyrosine kinase that signals through downstream MAPK/AKT/Wnt pathways to control cell proliferation, epithelial-mesenchymal transition, and—most mechanistically established—morphogenetic movement of epiblast cells through the primitive streak during vertebrate gastrulation, with its loss causing mesodermal patterning defects and ectopic neural fate adoption; FGFR1 activity is post-transcriptionally regulated by miR-214-3p targeting its 3'-UTR, and FGFR1 reciprocally suppresses miR-214-3p via ERK signaling.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper, then extract discoveries only from KEEP papers.\n\n**Classification:**\n- Papers [1]-[30] in the main corpus (100 papers): Almost entirely about histone H3/H4 biology, histamine H3/H4 receptors, B7-H3/H4 immune molecules, or other unrelated genes. Only papers directly about FGFR1 protein are KEEP.\n- Paper [6] PMID:9226454 — FGFR1 chimeric analysis in mouse embryos → KEEP\n- Paper [31] PMID:9286594 — FGFR1 expression in developing head → KEEP (but descriptive/expression, no mechanism)\n- Paper [69] PMID:31492847 — miR-214-3p/FGFR1 regulatory mechanism → KEEP\n- Paper [74] PMID:26276769 — FGFR1 rearrangements in hematologic neoplasms → KEEP (but mostly descriptive)\n- Paper [83] PMID:32380883 — FGFR1 regulates CCND1/EMT via AKT/MAPK → KEEP\n- Paper [84] PMID:38066305 — DMG with FGFR1 co-alterations → KEEP (but mostly characterization)\n\nAll others are EXCLUDE (alias collision — histone H3/H4, histamine receptors H3/H4, B7-H3/H4, Na,K-ATPase H3-H4, prion H2/H3, etc.)\n\n**Additional gene2pubmed papers:**\n- PMID:15863030 — FGF/FGFR signaling, FGFR1 mechanisms → KEEP\n- PMID:17086194 — Klotho converts FGFR1 into FGF23 receptor → KEEP\n- PMID:8663044 — FGFR receptor specificity → KEEP\n- PMID:8417497 — FGFR structural/functional diversity → KEEP\n- PMID:11030354 — Crystal structure FGF-FGFR-heparin → KEEP\n- PMID:9139660 — Crystal structures FGFR1 kinase domain → KEEP\n- PMID:16597617 — Complete FGF family receptor specificity → KEEP\n- PMID:17623664 — betaKlotho + FGFR1 for FGF19/21 → KEEP\n- PMID:21160078 — FGFR1 amplification in squamous lung cancer → KEEP\n- PMID:22837387 — FGFR1-TACC1 fusion in GBM → KEEP\n- PMID:20179196 — FGFR1 amplification in breast cancer → KEEP\n- PMID:12627230 — Loss-of-function FGFR1 mutations in Kallmann syndrome → KEEP\n- PMID:7874169 — FGFR1 mutation in Pfeiffer syndrome → KEEP\n- PMID:10490103 — Crystal structure FGF2:FGFR1 → KEEP\n- PMID:19920251 — FGFR1 phosphorylates PKM2 → KEEP\n- PMID:26186194, PMID:28514442, PMID:33961781 — interactome networks (FGFR1 included but no specific mechanism) → borderline; include only if specific FGFR1 mechanism noted\n- PMID:22939624 — HSP90/CDC37 clients including kinases → KEEP if FGFR1 specifically mentioned\n- Others (cDNA sequencing, GO propagation, oligo-capping) → EXCLUDE (no FGFR1 mechanism)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"Crystal structures of the FGFR1 tyrosine kinase domain in complex with indolinone inhibitors revealed that the oxindole core occupies the ATP adenine-binding site, and the more specific inhibitor induces a conformational change in the nucleotide-binding loop, establishing the structural basis for ATP-competitive kinase inhibition of FGFR1.\",\n      \"method\": \"X-ray crystallography of FGFR1 kinase domain–inhibitor complexes combined with kinase activity assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional kinase assay validation in a high-impact single study\",\n      \"pmids\": [\"9139660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The crystal structure of FGF2 bound to FGFR1 immunoglobulin-like domains D2 and D3 revealed that two FGF2:FGFR1 complexes form a symmetric dimer stabilized by FGF2–D2 cross-contacts and a direct D2–D2 receptor–receptor interaction, establishing the structural mechanism of ligand-induced FGFR1 dimerization and a positively charged canyon as the heparin-binding site.\",\n      \"method\": \"X-ray crystallography at 2.8 Å resolution of FGF2–FGFR1(D2-D3) complex\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with biochemical validation, foundational mechanistic study\",\n      \"pmids\": [\"10490103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The crystal structure of a 2:2:2 FGF:FGFR:heparin ternary complex at 3 Å resolution showed that heparin plays a dual role: it augments FGF–FGFR binding by contacting both molecules within each 1:1 complex, and it simultaneously bridges to FGFR in the adjoining complex to promote receptor dimerization, with the 6-O-sulfate group of heparin being pivotal for both interactions.\",\n      \"method\": \"X-ray crystallography of ternary FGF–FGFR1–heparin complex plus supporting biochemical assays\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with biochemical corroboration, replicated by structural community\",\n      \"pmids\": [\"11030354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Systematic mitogenesis assays in engineered cell lines expressing major splice variants of all four FGF receptors demonstrated that FGF1 is the only FGF ligand capable of activating all FGFR splice variants including FGFR1, while other FGF family members show selective receptor binding, establishing the binding specificity matrix for FGFR1 and its isoforms.\",\n      \"method\": \"Mitogenic activity assays on BaF3 cells engineered to express individual FGFR splice variants\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic functional assay across all receptor isoforms, independently replicated\",\n      \"pmids\": [\"8663044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"FGFR1 activation by FGF and heparan sulfate proteoglycan (HSPG) induces receptor dimerization and autophosphorylation of multiple cytoplasmic tyrosine residues; the docking proteins FRS2α and FRS2β are major substrates that mediate downstream activation of the Ras/MAPK and PI3K/Akt signaling pathways, as well as negative feedback loops regulating signal amplitude.\",\n      \"method\": \"Biochemical phosphorylation assays, co-immunoprecipitation, and cell-based signaling studies synthesized across multiple laboratories\",\n      \"journal\": \"Cytokine & Growth Factor Reviews\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — extensively replicated across labs, multiple orthogonal methods documented in this comprehensive review\",\n      \"pmids\": [\"15863030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Klotho, a single-pass transmembrane protein, physically binds FGF23 and directly converts FGFR1(IIIc) into a high-affinity FGF23 receptor; forced Klotho expression restored FGF23 responsiveness in a renal cell line, and anti-Klotho antibody injection abrogated endogenous FGF23 function in vivo, establishing that concerted Klotho–FGFR1(IIIc) interaction is required for FGF23 signaling.\",\n      \"method\": \"Renal homogenate binding assays, forced expression in cell lines, in vivo antibody blockade, co-immunoprecipitation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal in vitro and in vivo methods, replicated by independent groups\",\n      \"pmids\": [\"17086194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Receptor specificity studies for the complete 22-member FGF family using BaF3 cell lines expressing individual FGFRs showed that FGF10 and FGF22 signal selectively through FGFR1b (IIIb) splice variant, while FGF19/21/23 subfamily members (endocrine FGFs) have reduced or absent activity at FGFR1 without co-receptors, defining the full specificity profile of FGFR1 isoforms.\",\n      \"method\": \"Mitogenic activity assays on BaF3 cells expressing FGFR1 splice variants with all FGF ligands\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic functional screen covering all FGF ligands, complements earlier receptor specificity studies\",\n      \"pmids\": [\"16597617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"betaKlotho in combination with specific FGFR isoforms, including FGFR1, confers tissue-specific responsiveness to FGF19 and FGF21; both ligands signal through betaKlotho–FGFR1 complexes to increase glucose uptake in adipocytes, while only FGF19 efficiently signals through FGFR4 in hepatocytes to reduce CYP7A1 transcription.\",\n      \"method\": \"Co-immunoprecipitation, ligand-binding assays, cell-based glucose uptake assays, hepatocyte CYP7A1 reporter assays\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, functional readouts in relevant cell types\",\n      \"pmids\": [\"17623664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Chimeric embryo analysis demonstrated that cells homozygous for a kinase-dead Fgfr1 allele (fgfr1-Δtmk) accumulate within the primitive streak and fail to populate anterior mesoderm and endodermal lineages, indicating that FGFR1 kinase activity is specifically required for the morphogenetic movement of epiblast cells through the primitive streak during gastrulation, and that cells arrested in the streak adopt ectopic neural fate.\",\n      \"method\": \"Mouse chimera analysis, embryonic histology, cell lineage tracing using mutant vs. wild-type cells\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via chimeric analysis with clear cell-autonomous phenotypic readout, replicated at multiple developmental stages\",\n      \"pmids\": [\"9226454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Oncogenic FGFR1 directly phosphorylates pyruvate kinase M2 (PKM2) at tyrosine 105, disrupting binding of the cofactor fructose-1,6-bisphosphate and inhibiting formation of active tetrameric PKM2, thereby promoting aerobic glycolysis (Warburg effect) and tumor growth; Y105F mutation reversed these metabolic and proliferative effects in cancer cells and xenografts.\",\n      \"method\": \"Phosphoproteomic mass spectrometry, in vitro kinase assay, site-directed mutagenesis (Y105F), xenograft tumor models, metabolic flux assays\",\n      \"journal\": \"Science Signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus mutagenesis plus in vivo xenograft, multiple orthogonal methods\",\n      \"pmids\": [\"19920251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Focal FGFR1 amplification in squamous cell lung cancer drives tumor cell proliferation and survival; FGFR1 knockdown and expression of the kinase-resistant allele FGFR1(V561M) specifically rescued FGFR1-amplified cells from FGFR inhibitor cytotoxicity, confirming that amplified FGFR1 kinase activity is the dependency driver in these tumors.\",\n      \"method\": \"FISH for gene amplification, FGFR1 siRNA knockdown, ectopic expression of resistant mutant FGFR1(V561M), FGFR inhibitor (PD173074) treatment, in vivo tumor shrinkage assay\",\n      \"journal\": \"Science Translational Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological approaches with in vivo validation\",\n      \"pmids\": [\"21160078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"FGFR1 overexpression/amplification in breast cancer cell lines causes ligand-independent basal MAPK and PI3K-AKT pathway activation and confers resistance to 4-hydroxytamoxifen; siRNA silencing of FGFR1 reversed endocrine resistance, and FGFR1 signaling suppresses progesterone receptor expression.\",\n      \"method\": \"siRNA knockdown, Western blotting of signaling intermediates, anchorage-independent growth assay, tamoxifen sensitivity assay, PR expression analysis\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function with defined molecular and cellular phenotypes\",\n      \"pmids\": [\"20179196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In-frame chromosomal translocations fuse the FGFR1 kinase domain to TACC1 in a subset of GBMs; the FGFR1-TACC1 fusion protein localizes to mitotic spindle poles, has constitutive kinase activity, induces chromosomal segregation defects and aneuploidy, and drives oncogenesis in astrocytes and in mouse brain, which is reversed by FGFR kinase inhibition.\",\n      \"method\": \"RNA sequencing for fusion discovery, FGFR kinase assay, immunofluorescence localization to spindle poles, aneuploidy measurement, intracranial mouse glioma model, FGFR inhibitor treatment\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — constitutive kinase activity demonstrated, subcellular localization with functional consequence, in vivo model\",\n      \"pmids\": [\"22837387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Loss-of-function mutations in FGFR1 cause autosomal dominant Kallmann syndrome (KAL2), demonstrating that FGFR1 signaling is required for normal migration of olfactory/GnRH neurons; the extracellular matrix protein anosmin-1 (KAL1 product) is proposed to be involved in FGF signaling, explaining the dosage-sensitive sex difference in disease prevalence.\",\n      \"method\": \"Positional cloning, mutation analysis in Kallmann syndrome families, interstitial deletion mapping\",\n      \"journal\": \"Nature Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function human genetics with defined developmental phenotype, replicated across multiple families\",\n      \"pmids\": [\"12627230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"A specific Pro→Arg missense mutation in the extracellular domain (exon 5) of FGFR1 causes Pfeiffer syndrome (autosomal dominant craniosynostosis), demonstrating that gain-of-function FGFR1 mutations in the immunoglobulin-like domain lead to premature fusion of cranial sutures.\",\n      \"method\": \"Mutation analysis by sequencing in affected members of five unrelated Pfeiffer syndrome families\",\n      \"journal\": \"Nature Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutation identified in multiple independent families, orthologous gain-of-function mechanism confirmed by subsequent structural studies\",\n      \"pmids\": [\"7874169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In FGFR1-amplified lung cancer cells, miR-214-3p directly targets the FGFR1 3'-UTR to downregulate FGFR1 expression (validated by luciferase reporter assay), and FGFR1 signaling through ERK establishes a negative feedback loop that suppresses miR-214-3p; miR-214-3p inhibits EMT and Wnt/MAPK/AKT signaling by targeting FGFR1.\",\n      \"method\": \"Luciferase 3'-UTR reporter assay, qRT-PCR, Western blot, transwell migration/invasion assay, signaling pathway analysis\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct 3'-UTR targeting validated by reporter assay; single-lab study with multiple methods\",\n      \"pmids\": [\"31492847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In FGFR1-amplified lung squamous cell carcinoma cell lines, FGFR1 promotes epithelial-mesenchymal transition and metastatic behavior through AKT/MAPK signaling by transcriptionally or post-translationally targeting CCND1 (cyclin D1), which is co-overexpressed with FGFR1 and required for proliferation and invasion.\",\n      \"method\": \"qRT-PCR, Western blot, transwell migration/invasion assay, FGFR1 and CCND1 manipulation in FGFR1-amplified cell lines\",\n      \"journal\": \"Cell Adhesion & Migration\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic detail on how FGFR1 targets CCND1\",\n      \"pmids\": [\"32380883\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FGFR1 is a receptor tyrosine kinase that, upon binding FGF ligands (especially FGF1) augmented by heparan sulfate proteoglycans (or co-receptors Klotho/betaKlotho for endocrine FGFs), undergoes ligand-induced dimerization via a dual FGF–FGFR–heparin ternary complex, activates its kinase domain (whose ATP-binding site and nucleotide-binding loop have been structurally characterized), autophosphorylates multiple cytoplasmic tyrosines, recruits docking proteins FRS2α/β to activate Ras/MAPK and PI3K/Akt pathways, can directly phosphorylate substrates such as PKM2-Y105 to promote aerobic glycolysis, is required cell-autonomously for epiblast cell movement through the primitive streak during gastrulation, and when constitutively activated by amplification or oncogenic fusions (e.g., FGFR1-TACC1) drives proliferation, aneuploidy, endocrine therapy resistance, and tumor growth.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FGFR1 is a receptor tyrosine kinase that controls cell movement, fate determination, and proliferation through activation of MAPK, AKT, and Wnt signaling cascades. During mouse gastrulation, FGFR1 is required for morphogenetic movement of epiblast cells through the primitive streak; in its absence, cells accumulate in the streak, fail to populate mesodermal and endodermal lineages, and instead adopt ectopic neural fates [PMID:9226454]. FGFR1 promotes epithelial-mesenchymal transition and drives proliferation through upregulation of targets including CCND1, and its expression is post-transcriptionally repressed by miR-214-3p targeting the FGFR1 3′-UTR, while FGFR1 reciprocally suppresses miR-214-3p via ERK signaling [PMID:31492847]. Chromosomal rearrangements producing FGFR1 fusion genes cause a distinct category of myeloid/lymphoid neoplasms with eosinophilia [PMID:26276769].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing that FGFR1 has a cell-autonomous role in gastrulation — specifically controlling the ability of epiblast cells to move through the primitive streak and adopt mesodermal/endodermal rather than neural fates — answered a fundamental question about how FGF signaling directs germ-layer formation.\",\n      \"evidence\": \"Chimeric mouse embryo analysis with fgfr1(Δtmk) loss-of-function mutation and lineage tracing at E7.5–E9.5\",\n      \"pmids\": [\"9226454\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Downstream signaling pathways mediating the streak migration and fate-switching phenotype were not identified\",\n        \"Whether FGFR1 controls cell movement versus cell survival in the streak was not fully resolved\",\n        \"Ligand specificity in vivo during gastrulation not determined\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Characterization of FGFR1 gene fusions as drivers of a distinct class of myeloid/lymphoid neoplasms with eosinophilia established that constitutive FGFR1 kinase activation is oncogenic and, unlike PDGFRA/PDGFRB fusions, is refractory to available TKI therapy.\",\n      \"evidence\": \"Clinicopathological and cytogenetic/FISH review of workshop cases\",\n      \"pmids\": [\"26276769\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct biochemical experiment on the fusion kinase mechanism was performed\",\n        \"Basis for TKI resistance of FGFR1 fusions not determined\",\n        \"Downstream signaling pathways activated by FGFR1 fusions not characterized\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of a miR-214-3p/FGFR1/ERK negative feedback loop and demonstration that FGFR1 activates Wnt/MAPK/AKT to drive EMT resolved how FGFR1 expression is post-transcriptionally tuned and linked FGFR1 to specific downstream pathways in cancer cells.\",\n      \"evidence\": \"Luciferase 3′-UTR reporter assay, Western blot, qRT-PCR, pharmacological inhibition (AZD4547), transwell assays in FGFR1-amplified lung cancer cells\",\n      \"pmids\": [\"31492847\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Feedback loop not validated in vivo or in non-lung-cancer contexts\",\n        \"Whether miR-214-3p regulation of FGFR1 operates during normal development is unknown\",\n        \"Direct versus indirect activation of Wnt pathway by FGFR1 not resolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis for FGFR1 kinase activation, the full repertoire of direct substrates, and the mechanistic connection between FGFR1 signaling and cell motility during gastrulation remain incompletely defined at the biochemical level.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No direct substrate identification experiments reported in the timeline\",\n        \"No structural or reconstitution studies of FGFR1 activation in the timeline\",\n        \"Role of specific FGF ligands in FGFR1-dependent gastrulation not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"FGFR1 is a receptor tyrosine kinase that transduces FGF signals to govern cell proliferation, migration, and metabolic reprogramming across development and disease. Ligand binding (FGF1 being the universal activator of all splice variants) triggers formation of a 2:2:2 FGF–FGFR1–heparan sulfate ternary complex that dimerizes the receptor via direct D2–D2 contacts and heparin-bridged cross-links, leading to autophosphorylation and recruitment of FRS2α/β to activate Ras/MAPK and PI3K/Akt cascades; endocrine FGFs (FGF19, FGF21, FGF23) require the co-receptors Klotho or βKlotho to convert FGFR1 into a high-affinity receptor [PMID:10490103, PMID:11030354, PMID:17086194, PMID:15863030]. During gastrulation, FGFR1 kinase activity is cell-autonomously required for epiblast cell movement through the primitive streak, and loss-of-function mutations cause Kallmann syndrome (defective olfactory/GnRH neuron migration) while a gain-of-function extracellular-domain mutation causes Pfeiffer syndrome (craniosynostosis) [PMID:9226454, PMID:12627230, PMID:7874169]. Oncogenic FGFR1 amplification or FGFR1–TACC1 fusion constitutively activates kinase signaling—including direct phosphorylation of PKM2-Y105 to promote aerobic glycolysis—and drives tumor proliferation, aneuploidy, and endocrine therapy resistance in lung, breast, and brain cancers [PMID:19920251, PMID:21160078, PMID:22837387, PMID:20179196].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that a gain-of-function missense mutation in the FGFR1 extracellular domain causes Pfeiffer syndrome established the first direct link between altered FGFR1 signaling and a human developmental disorder (craniosynostosis).\",\n      \"evidence\": \"Sequencing of FGFR1 exon 5 in five unrelated Pfeiffer syndrome families\",\n      \"pmids\": [\"7874169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of how the Pro→Arg substitution activates signaling was not resolved\", \"Whether other craniosynostosis-causing FGFR1 mutations share the same mechanism was unknown\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Systematic profiling of all FGF ligands against FGFR splice variants revealed FGF1 as the universal FGFR1 activator and defined the selectivity landscape for FGFR1b versus FGFR1c isoforms, answering which ligand–receptor pairs are functional.\",\n      \"evidence\": \"Mitogenic assays in BaF3 cells expressing individual FGFR splice variants\",\n      \"pmids\": [\"8663044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The structural determinants of splice-variant selectivity were not explained\", \"Endocrine FGFs showed weak activity, and the basis for this deficiency was unresolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Two key advances resolved how FGFR1 kinase is inhibited and how it functions in vivo: crystal structures of the kinase domain with ATP-competitive inhibitors defined the drug-binding pocket, while chimeric embryo analysis proved that FGFR1 kinase activity is cell-autonomously required for epiblast migration through the primitive streak during gastrulation.\",\n      \"evidence\": \"X-ray crystallography of FGFR1 kinase–inhibitor complexes; mouse chimera analysis with kinase-dead Fgfr1 allele\",\n      \"pmids\": [\"9139660\", \"9226454\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full autophosphorylation site mapping and downstream docking protein identity remained incomplete\", \"Why kinase-dead cells adopt ectopic neural fate was not mechanistically explained\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"The crystal structure of the FGF2–FGFR1(D2-D3) complex revealed the receptor dimerization interface, answering the longstanding question of how ligand binding induces receptor activation at atomic resolution.\",\n      \"evidence\": \"X-ray crystallography at 2.8 Å of the FGF2–FGFR1 dimer\",\n      \"pmids\": [\"10490103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Heparin's precise contacts were not resolved in this binary structure\", \"How alternative ligands might employ different dimerization geometries was unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The ternary FGF–FGFR1–heparin crystal structure resolved heparin's dual role—augmenting ligand binding within each 1:1 complex and bridging to the adjacent receptor to stabilize the dimer—establishing that heparan sulfate is an integral component of the signaling complex, not merely a concentrating device.\",\n      \"evidence\": \"X-ray crystallography of 2:2:2 ternary complex at 3 Å with supporting biochemical assays\",\n      \"pmids\": [\"11030354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous HSPGs with defined sulfation patterns recapitulate these contacts in vivo was untested\", \"Kinetics of complex assembly on the cell surface were not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of loss-of-function FGFR1 mutations as the cause of autosomal dominant Kallmann syndrome proved that FGFR1 is required for olfactory and GnRH neuron migration in humans, complementing the mouse gastrulation phenotype.\",\n      \"evidence\": \"Positional cloning and mutation analysis in multiple Kallmann syndrome families\",\n      \"pmids\": [\"12627230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The precise ligand and co-receptor triggering FGFR1 during GnRH neuron migration were unidentified\", \"Anosmin-1's proposed role as an FGFR1 co-factor lacked direct biochemical validation\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Comprehensive characterization of FGFR1 downstream signaling consolidated that FRS2α/β are the major docking proteins linking receptor autophosphorylation to Ras/MAPK and PI3K/Akt pathways, with built-in negative feedback loops regulating signal amplitude.\",\n      \"evidence\": \"Phosphorylation assays, co-immunoprecipitation, and cell-based signaling studies synthesized across multiple laboratories\",\n      \"pmids\": [\"15863030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contributions of individual autophosphorylation sites to pathway branching were not dissected\", \"Negative feedback mechanisms were not fully mapped at the molecular level\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that Klotho and βKlotho serve as obligate co-receptors that convert FGFR1 into high-affinity receptors for endocrine FGFs (FGF23 and FGF19/21, respectively) resolved why these ligands showed negligible activity in standard assays and explained tissue-specific endocrine FGF responses.\",\n      \"evidence\": \"Binding assays, forced Klotho expression in cell lines, in vivo antibody blockade; co-IP and glucose-uptake assays for βKlotho\",\n      \"pmids\": [\"17086194\", \"17623664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The structural basis of the Klotho–FGFR1–FGF23 ternary complex was not yet determined\", \"Relative contributions of FGFR1 versus FGFR3/FGFR4 in Klotho-dependent signaling in different tissues remained unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of PKM2-Y105 as a direct FGFR1 substrate linked receptor tyrosine kinase signaling to metabolic reprogramming, demonstrating that FGFR1 promotes aerobic glycolysis by inhibiting PKM2 tetramerization.\",\n      \"evidence\": \"Phosphoproteomics, in vitro kinase assay, Y105F mutagenesis, xenograft models, metabolic flux assays\",\n      \"pmids\": [\"19920251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this metabolic rewiring operates in non-transformed, FGFR1-dependent tissues was untested\", \"Other direct kinase substrates beyond FRS2 and PKM2 remained largely uncharacterized\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Two studies established FGFR1 amplification as an actionable oncogenic driver: in squamous lung cancer, FGFR1 amplification creates a kinase dependency reversible by FGFR inhibitors, while in breast cancer, FGFR1 overexpression drives ligand-independent MAPK/AKT activation and endocrine therapy resistance.\",\n      \"evidence\": \"FISH for amplification, siRNA knockdown, resistant-mutant rescue (V561M), FGFR inhibitor treatment, tamoxifen sensitivity assays\",\n      \"pmids\": [\"21160078\", \"20179196\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biomarkers distinguishing FGFR1-amplified tumors that are truly kinase-dependent from bystander amplifications were not defined\", \"Mechanisms of acquired resistance to FGFR inhibitors were unexplored\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery of FGFR1-TACC1 fusion in glioblastoma revealed a novel oncogenic mechanism in which the fusion protein localizes to mitotic spindle poles, causes chromosomal missegregation and aneuploidy, and drives glioma formation—all reversible by FGFR kinase inhibition.\",\n      \"evidence\": \"RNA-seq fusion detection, kinase assay, immunofluorescence at spindle poles, aneuploidy measurement, intracranial mouse model, FGFR inhibitor treatment\",\n      \"pmids\": [\"22837387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TACC1-mediated spindle-pole localization is the primary oncogenic mechanism or whether constitutive kinase activity alone suffices was not resolved\", \"Prevalence and therapeutic response of FGFR1-TACC1 fusions in clinical cohorts was not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive catalog of direct FGFR1 kinase substrates beyond FRS2 and PKM2 remains incomplete, and the structural basis for co-receptor (Klotho/βKlotho) engagement with FGFR1 and endocrine FGFs is not fully resolved; acquired resistance mechanisms to clinical FGFR inhibitors also require systematic characterization.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full substrate repertoire of FGFR1 kinase is unmapped\", \"Structural details of Klotho–FGFR1–FGF ternary complex at atomic resolution are needed\", \"Mechanisms of clinical resistance to FGFR-targeted therapies are poorly defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 9, 10, 12]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 4, 9]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 2, 3, 5, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 4, 5, 7]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 4, 5, 7, 9, 11]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 13, 14]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 11, 12]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\n      \"FGF-FGFR1-heparin ternary complex\",\n      \"Klotho-FGFR1 co-receptor complex\",\n      \"βKlotho-FGFR1 co-receptor complex\"\n    ],\n    \"partners\": [\n      \"FGF1\",\n      \"FGF2\",\n      \"FRS2\",\n      \"KL\",\n      \"KLB\",\n      \"PKM\",\n      \"TACC1\",\n      \"FGF23\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}