{"gene":"FSTL3","run_date":"2026-04-28T17:46:04","timeline":{"discoveries":[{"year":1998,"finding":"FSTL3 (FLRG) was identified as a secreted glycoprotein of the follistatin-module-protein family, cloned from a t(11;19)(q13;p13) translocation in B-cell chronic lymphocytic leukemia, establishing it as an evolutionarily conserved, secreted glycoprotein.","method":"cDNA cloning, molecular characterization of chromosomal translocation","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — original cloning with molecular characterization, foundational paper with 104 citations","pmids":["9671416"],"is_preprint":false},{"year":2001,"finding":"FSTL3 (FLRG) binds activin A directly, as demonstrated by immunoprecipitation and Far-Western blot analysis, establishing its role as an activin-binding antagonist.","method":"Immunoprecipitation, Far-Western blot","journal":"Experimental hematology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biochemical methods, replicated across multiple papers","pmids":["11274757"],"is_preprint":false},{"year":2001,"finding":"FSTL3 (FSRP) binds activin with similar affinity and selectivity as follistatin but does not bind heparin; it inhibits activin-mediated gene transcription in heterologous assays but is much less active than follistatin in the rat pituitary bioassay.","method":"Binding assays, transcriptional reporter assay, rat pituitary bioassay, transgenic mouse overexpression","journal":"Molecular and cellular endocrinology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including in vitro binding, reporter assay, and in vivo transgenic model","pmids":["11451569"],"is_preprint":false},{"year":2001,"finding":"FSTL3 (FLRG) gene transcription is activated by TGF-β via Smad proteins; a Smad-binding element in the FLRG promoter mediates TGF-β-inducible expression, and dominant-negative Smad3/Smad4 abolish this activation.","method":"Promoter deletion/point-mutation analysis, luciferase reporter assay, EMSA, dominant-negative Smad constructs, transfection in HepG2 cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted promoter analysis with mutagenesis and EMSA, replicated by subsequent papers","pmids":["11571638"],"is_preprint":false},{"year":2002,"finding":"Activin A induces FSTL3 (FLRG) and follistatin expression at both mRNA and protein levels via Smad proteins, and FSTL3 protein in turn inhibits activin A signaling and blocks activin A-induced growth inhibition of HepG2 cells, constituting a negative feedback loop.","method":"Transcriptional reporter assay, RT-PCR, protein expression analysis, growth inhibition assay, Smad pathway analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing feedback mechanism, replicated across labs","pmids":["11948405"],"is_preprint":false},{"year":2003,"finding":"FSTL3 binds activin B at approximately 10-fold lower potency than activin A, and is approximately 3-fold more effective at neutralizing activin A than activin B, demonstrating differential binding and neutralization specificity.","method":"Binding assays, 293 cell reporter assays for biological activity neutralization","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1-2 — quantitative binding and functional neutralization assays with both ligands","pmids":["12697670"],"is_preprint":false},{"year":2004,"finding":"FSTL3 lacks a heparin-binding sequence (HBS) and cannot associate with cell surfaces; mutational analysis showed that inserting the full FS domain 1 (including HBS) into FSTL3 confers heparin binding but abolishes activin binding, implying an evolutionary safeguard against surface binding by FSTL3.","method":"Mutational analysis, cell surface binding assays, heparin affinity binding, competitive activin binding assays, pituitary cell FSH secretion bioassay","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with multiple functional readouts","pmids":["15471966"],"is_preprint":false},{"year":2005,"finding":"FSTL3 (FLRG) physically interacts with fibronectin via type I motifs of fibronectin and follistatin domains of FSTL3 (identified by yeast two-hybrid screen and confirmed biochemically); this interaction promotes hematopoietic cell adhesion to fibronectin.","method":"Yeast two-hybrid screen, biochemical interaction assays, cell adhesion assays with hematopoietic cell line and primary cells","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2-3 — yeast two-hybrid plus cell adhesion functional assay, single lab","pmids":["16336961"],"is_preprint":false},{"year":2005,"finding":"FSTL3 (FLRG) directly interacts with ADAM12 via its cysteine-rich domain (identified by yeast two-hybrid); FSTL3 protein inhibits osteoclast differentiation from murine primary spleen cells and RAW264.7 macrophages stimulated with RANK-L and M-CSF.","method":"Yeast two-hybrid, direct interaction confirmation, osteoclast differentiation assay with primary murine cells and macrophage cell line","journal":"Biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2-3 — yeast two-hybrid with functional osteoclast assay, single lab","pmids":["15574124"],"is_preprint":false},{"year":2007,"finding":"Homozygous FSTL3 knockout mice develop increased pancreatic islet number and size, beta cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, attributable to increased activin and myostatin bioactivity in specific tissues in the absence of FSTL3 antagonism.","method":"FSTL3 knockout mouse model, histomorphometry, metabolic phenotyping, glucose tolerance testing, insulin sensitivity testing","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean knockout with multiple defined phenotypic readouts, highly cited foundational study","pmids":["17229845"],"is_preprint":false},{"year":2007,"finding":"TNF-α activates FSTL3 (FLRG) expression at the transcriptional level through NF-κB binding elements (5'-GGGAGAG/TTCC-3') located in four conserved 107-108 bp DNA repeats in the promoter; TGF-β via Smad proteins potentiates TNF-α-induced FSTL3 expression.","method":"Promoter deletion analysis, luciferase reporter assay, biochemical binding assays, phylogenetic analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 — promoter mutagenesis and reporter assay with defined elements, single lab","pmids":["17395406"],"is_preprint":false},{"year":2007,"finding":"Silencing FSTL3 (FLRG) in breast cancer cell lines induces growth inhibition via restoration of endogenous activin signaling (increased pSmad2, upregulation of activin target genes); growth inhibition is reversible by exogenous FSTL3 or soluble type II activin receptor.","method":"siRNA knockdown, transcriptional reporter assay, phospho-Smad2 measurement, RT-PCR for target genes, rescue experiments","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with specific rescue experiments defining mechanism","pmids":["17671190"],"is_preprint":false},{"year":2007,"finding":"Nuclear FSTL3 (FLRG) interacts with AF10 transcription factor (identified by yeast two-hybrid, confirmed by Far-Western blot and co-immunoprecipitation in COS-7 cells); the N-terminal PHD domain of AF10 mediates this interaction, and FSTL3 enhances AF10 homo-oligomerization and AF10-mediated transcriptional activation.","method":"Yeast two-hybrid, Far-Western blot, co-immunoprecipitation, transient transfection transactivation assay","journal":"Biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple interaction methods plus functional transcription assay, single lab","pmids":["17868029"],"is_preprint":false},{"year":2008,"finding":"The crystal structure of the FSTL3·activin A complex at 2.5 Å resolution shows that two FSTL3 molecules encircle one activin A dimer, blocking all receptor-binding sites; the N-terminal domain of FSTL3 forms a more intimate contact with activin A than the corresponding FS domain, and replacing the FSTL3 N-terminal domain with the FS N-terminal domain considerably lowers activin A affinity.","method":"X-ray crystallography (2.5 Å), domain-swap mutagenesis, binding affinity measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis validation; defines molecular mechanism of antagonism","pmids":["18768470"],"is_preprint":false},{"year":2013,"finding":"FSTL3 knockout mice develop markedly enlarged testes with increased Sertoli cell numbers and delayed age-related testicular regression; FSTL3 deletion leads to increased AKT signaling and SIRT1 expression in the testis, revealing cross-talk between TGF-β ligand signaling and AKT pathway in testicular homeostasis.","method":"FSTL3 knockout mouse model, histomorphometry, phosphoproteomics, Western blot for AKT/SIRT1","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined cellular and molecular phenotype, single lab","pmids":["23407452"],"is_preprint":false},{"year":2016,"finding":"In FSTL3 knockout mice, α-to-β cell transdifferentiation is increased, as shown by α-cell lineage tracing (Gluc-Cre/YFP); activin treatment of isolated islets significantly increases YFP+/Ins+ cells, demonstrating that increased activin signaling (due to absence of FSTL3 antagonism) drives α-to-β cell transdifferentiation.","method":"Genetic lineage tracing (Gluc-Cre/YFP), flow cytometry, FSTL3 KO mice, ex vivo islet activin treatment","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — definitive lineage tracing with KO model and ex vivo validation, multiple orthogonal readouts","pmids":["26727106"],"is_preprint":false},{"year":2019,"finding":"FSTL3 promotes lipid accumulation in macrophages by upregulating scavenger receptors CD36 and LOX-1 in a dose-dependent manner, and induces inflammatory cytokine secretion (IL-1β, MCP-1, TNF-α, MMP-9); FSTL3 expression is induced by oxidized LDL in macrophages.","method":"Cell-based assays, dose-response experiments, cytokine measurement, knockdown experiments","journal":"Journal of cardiovascular pharmacology","confidence":"Medium","confidence_rationale":"Tier 3 — cell-based functional assays with dose-response, single lab, no in vivo mechanistic validation","pmids":["31815869"],"is_preprint":false},{"year":2021,"finding":"FSTL3-neutralizing antibody FP-101 prevents FSTL3 from complexing with activin or related ligands; FP-101 treatment enhances insulin secretion and glucose responsiveness in dysfunctional mouse and human islets under diabetic conditions.","method":"Antibody development, in vitro neutralization assay, islet glucose-stimulated insulin secretion assay","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — functional antibody with defined mechanism and human islet validation, single lab","pmids":["33539535"],"is_preprint":false},{"year":2024,"finding":"FSTL3 binds to transcription factor c-Myc (at amino acids 354-406) to suppress its ubiquitination and increase its stability, thereby upregulating PDL1 and IDO1 expression; hypoxic tumor microenvironment induces FSTL3 expression via HIF1α in colorectal cancer cells.","method":"Co-immunoprecipitation, domain mapping, ubiquitination assay, Western blot, flow cytometry, immunocompetent tumor models","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP with domain mapping and functional in vivo validation, single lab","pmids":["38302412"],"is_preprint":false},{"year":2024,"finding":"Prenatal dexamethasone exposure increases KDM1B expression in fetal testicular Sertoli cells, decreasing H3K9me2 at the FSTL3 promoter and thereby increasing FSTL3 expression, which inhibits TGF-β signaling and CX43/E-cadherin expression, impairing blood-testis barrier function.","method":"Animal model (prenatal dexamethasone), ChIP for H3K9me2 at FSTL3 promoter, Western blot, TM4 Sertoli cell validation, human sample correlation","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 — epigenetic mechanism with ChIP evidence, in vivo and in vitro validation, single lab","pmids":["38472317"],"is_preprint":false},{"year":2025,"finding":"FSTL3 loss in OSCC induces cuproptosis susceptibility by suppressing SLC25A10, triggering mitochondrial succinate accumulation, which promotes succinylation and upregulation of DLAT, a key cuproptosis executor; FSTL3 also recruits erythroid progenitor cells (EPCs) via CCR5 upregulation to establish an immunosuppressive niche.","method":"CRISPR-Cas9 screening, metabolic profiling, succinylation assay, EPC recruitment assays, in vivo tumor models","journal":"Journal of dental research","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR screen with mechanistic follow-up, single lab, multiple readouts","pmids":["41996175"],"is_preprint":false},{"year":2025,"finding":"FSTL3 expressed by cancer-associated fibroblasts binds to transferrin receptor (TfR1) on cancer cells, activating the TfR1/AKT/mTOR pathway and elevating VE-Cadherin to support vasculogenic mimicry and metastatic progression in colon cancer.","method":"Binding assays, pathway activation analysis, in vitro and in vivo tumor models, FSTL3-targeting antibody inhibition studies, single-cell RNA sequencing","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 — binding and functional pathway assays in vitro and in vivo, single lab, novel receptor identification","pmids":["41053124"],"is_preprint":false}],"current_model":"FSTL3 is a secreted glycoprotein antagonist that binds and neutralizes TGF-β family ligands (primarily activin A/B, myostatin, GDF11) by encircling the ligand dimer with two FSTL3 molecules to block all receptor-binding sites (as shown by crystal structure); unlike follistatin, FSTL3 lacks a heparin-binding sequence and therefore cannot associate with cell surfaces, making it a freely circulating antagonist; its transcription is induced by TGF-β/activin A via Smad3/4, TNF-α via NF-κB, and HIF1α under hypoxia, forming negative feedback loops; physiologically, FSTL3 limits pancreatic β-cell mass and α-to-β transdifferentiation (by restraining activin signaling), regulates visceral fat and insulin sensitivity (via myostatin), controls testis size and aging, and modulates hematopoietic cell adhesion through fibronectin interaction; intranuclearly, FSTL3 enhances AF10-mediated transcription; in cancer contexts, FSTL3 can also stabilize c-Myc by suppressing ubiquitination, bind TfR1 to activate AKT/mTOR signaling, and suppress cuproptosis via SLC25A10/succinate/DLAT axis."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of FSTL3 as a new member of the follistatin-module family established a candidate TGF-β superfamily modulator, addressing whether additional secreted antagonists existed beyond follistatin.","evidence":"cDNA cloning from t(11;19) translocation in B-CLL","pmids":["9671416"],"confidence":"High","gaps":["No ligand-binding activity demonstrated at this stage","Disease relevance of translocation unclear"]},{"year":2001,"claim":"Demonstration that FSTL3 directly binds activin A with similar affinity to follistatin but lacks heparin binding established its identity as a soluble-only activin antagonist, resolving its functional relationship to follistatin.","evidence":"Immunoprecipitation, Far-Western blot, binding assays, reporter assays, and rat pituitary bioassay","pmids":["11274757","11451569"],"confidence":"High","gaps":["Structural basis for activin binding unknown","In vivo significance undemonstrated"]},{"year":2001,"claim":"Identification of Smad3/4-dependent transcriptional induction of FSTL3 by TGF-β and activin A revealed a negative feedback loop in which the ligand induces its own antagonist.","evidence":"Promoter deletion/mutation analysis, luciferase reporters, dominant-negative Smads in HepG2 cells","pmids":["11571638","11948405"],"confidence":"High","gaps":["Whether feedback operates in vivo in specific tissues not shown","Other transcriptional inputs not yet explored"]},{"year":2003,"claim":"Quantification of differential binding showed FSTL3 neutralizes activin A ~3-fold more potently than activin B, defining its ligand selectivity hierarchy.","evidence":"Quantitative binding and functional neutralization assays in 293 cells","pmids":["12697670"],"confidence":"High","gaps":["Binding to myostatin and GDF11 not yet measured","Mechanism of selectivity difference unresolved"]},{"year":2004,"claim":"Systematic mutagenesis demonstrated that the absence of a heparin-binding sequence in FSTL3 prevents cell-surface association, and that inserting one abolishes activin binding — establishing a structural trade-off that confines FSTL3 to the extracellular milieu.","evidence":"Domain-swap mutagenesis, heparin affinity, cell-surface binding, and pituitary FSH bioassay","pmids":["15471966"],"confidence":"High","gaps":["No crystal structure yet to explain the trade-off at atomic level"]},{"year":2005,"claim":"Discovery of FSTL3 interactions with fibronectin (promoting hematopoietic adhesion) and ADAM12 (inhibiting osteoclastogenesis) expanded its functional repertoire beyond ligand sequestration to extracellular matrix and cell differentiation contexts.","evidence":"Yeast two-hybrid screens, biochemical confirmation, hematopoietic adhesion and osteoclast differentiation assays","pmids":["16336961","15574124"],"confidence":"Medium","gaps":["Yeast two-hybrid interactions not confirmed by endogenous co-IP","In vivo relevance of fibronectin and ADAM12 interactions not tested","Whether these interactions depend on or compete with activin binding unknown"]},{"year":2007,"claim":"FSTL3 knockout mice revealed that endogenous FSTL3 restrains activin/myostatin bioactivity in specific tissues: its absence causes pancreatic β-cell hyperplasia, reduced visceral fat, improved insulin sensitivity, and enlarged testes, defining FSTL3 as a physiological regulator of metabolic and gonadal homeostasis.","evidence":"Constitutive FSTL3 KO mice with metabolic phenotyping, histomorphometry, glucose tolerance, and insulin sensitivity testing","pmids":["17229845","23407452"],"confidence":"High","gaps":["Tissue-specific contributions of FSTL3 not dissected (global KO)","Which ligand (activin vs. myostatin vs. GDF11) mediates each phenotype not resolved"]},{"year":2007,"claim":"TNF-α was shown to activate FSTL3 transcription via NF-κB elements, and nuclear FSTL3 was found to enhance AF10-mediated transcription, revealing both a new upstream inducer and an unexpected intranuclear function.","evidence":"Promoter mutagenesis/reporter assays for NF-κB; yeast two-hybrid, co-IP, and transactivation assays for AF10 interaction","pmids":["17395406","17868029"],"confidence":"Medium","gaps":["Nuclear localization mechanism and signal undefined","Transcriptional targets of AF10 enhanced by FSTL3 unknown","AF10 interaction not confirmed in endogenous setting"]},{"year":2008,"claim":"The 2.5 Å crystal structure of the FSTL3·activin A complex revealed the atomic mechanism of antagonism: two FSTL3 molecules wrap around the activin dimer, blocking all type I and type II receptor-binding epitopes, and showed the N-terminal domain makes uniquely intimate contacts.","evidence":"X-ray crystallography with domain-swap mutagenesis and affinity measurements","pmids":["18768470"],"confidence":"High","gaps":["No structure with myostatin or GDF11","Dynamics of complex assembly in solution unknown"]},{"year":2016,"claim":"Genetic lineage tracing in FSTL3 KO mice proved that increased activin signaling drives α-to-β cell transdifferentiation, establishing FSTL3 as a gatekeeper of islet cell identity.","evidence":"Gluc-Cre/YFP lineage tracing in FSTL3 KO, flow cytometry, ex vivo activin treatment of islets","pmids":["26727106"],"confidence":"High","gaps":["Whether therapeutic FSTL3 neutralization can replicate this in diabetic models not shown at this time point"]},{"year":2021,"claim":"An FSTL3-neutralizing antibody (FP-101) enhanced insulin secretion in dysfunctional mouse and human islets, providing proof-of-concept that targeting FSTL3 can restore β-cell function under diabetic conditions.","evidence":"Antibody neutralization assay, glucose-stimulated insulin secretion in isolated islets","pmids":["33539535"],"confidence":"Medium","gaps":["No in vivo efficacy data in diabetic animal models","Long-term safety and specificity not assessed"]},{"year":2024,"claim":"FSTL3 was found to stabilize c-Myc by directly binding and suppressing its ubiquitination under hypoxic HIF1α-driven induction, linking FSTL3 to immune evasion (PDL1/IDO1 upregulation) in colorectal cancer — a ligand-sequestration-independent oncogenic mechanism.","evidence":"Co-IP, domain mapping (aa 354–406), ubiquitination assay, immunocompetent tumor models","pmids":["38302412"],"confidence":"Medium","gaps":["Whether c-Myc stabilization occurs in non-hypoxic or non-cancer contexts unknown","Ubiquitin ligase displaced by FSTL3 not identified","Single-lab finding not yet replicated"]},{"year":2025,"claim":"Two studies expanded FSTL3's cancer biology: one identified TfR1 as a cell-surface receptor through which fibroblast-derived FSTL3 activates AKT/mTOR signaling and vasculogenic mimicry; the other showed FSTL3 loss triggers cuproptosis via SLC25A10/succinate/DLAT — both mechanisms independent of classical activin antagonism.","evidence":"Binding assays, scRNA-seq, in vivo tumor models (colon cancer); CRISPR screen, metabolic profiling, succinylation assay (OSCC)","pmids":["41053124","41996175"],"confidence":"Medium","gaps":["TfR1 interaction not confirmed by structural or biophysical methods","Cuproptosis link requires independent replication","Relationship between FSTL3's activin-binding and TfR1-binding surfaces uncharacterized"]},{"year":null,"claim":"Major open questions include tissue-specific versus circulating contributions of FSTL3 (no conditional KO studies), structures of FSTL3 complexes with myostatin/GDF11, the mechanism and physiological relevance of nuclear FSTL3, and whether the newly identified cancer-related functions (c-Myc stabilization, TfR1 binding, cuproptosis modulation) operate through activin-dependent or fully independent pathways.","evidence":"","pmids":[],"confidence":"Low","gaps":["No tissue-specific knockout models reported","No structural data for FSTL3–myostatin or FSTL3–GDF11 complexes","Nuclear localization signal and trafficking mechanism undefined","Activin-dependent vs. independent functions in tumors not delineated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,2,5,6,13]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[12]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[2,5,11,17]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,6,13]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[12]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,4,5,9,11,13,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9,14,15]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[9,16]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[18,20]}],"complexes":[],"partners":["INHBA","INHBB","FN1","ADAM12","MLLT10","MYC","TFRC"],"other_free_text":[]},"mechanistic_narrative":"FSTL3 is a secreted glycoprotein antagonist of TGF-β superfamily ligands that functions as a freely circulating inhibitor of activin A/B and myostatin signaling, forming negative feedback loops that regulate pancreatic β-cell mass, glucose homeostasis, gonadal development, and adiposity. Two FSTL3 molecules encircle one activin A dimer to block all receptor-binding sites, and unlike follistatin, FSTL3 lacks a heparin-binding sequence and therefore cannot associate with cell surfaces, restricting its activity to the extracellular space [PMID:18768470, PMID:15471966]. FSTL3 transcription is induced by activin/TGF-β via Smad3/4 and by TNF-α via NF-κB, establishing it as an inducible feedback antagonist; accordingly, FSTL3 knockout mice exhibit β-cell hyperplasia with enhanced α-to-β transdifferentiation, reduced visceral fat, improved insulin sensitivity, and enlarged testes [PMID:11571638, PMID:17395406, PMID:17229845, PMID:26727106, PMID:23407452]. In cancer contexts, FSTL3 stabilizes c-Myc by suppressing its ubiquitination under hypoxia-induced HIF1α-driven expression and can activate TfR1/AKT/mTOR signaling on tumor cells when secreted by cancer-associated fibroblasts [PMID:38302412, PMID:41053124]."},"prefetch_data":{"uniprot":{"accession":"O95633","full_name":"Follistatin-related protein 3","aliases":["Follistatin-like protein 3","Follistatin-related gene protein"],"length_aa":263,"mass_kda":27.7,"function":"Isoform 1 or the secreted form is a binding and antagonizing protein for members of the TGF-beta family, such as activin, BMP2 and MSTN. Inhibits activin A-, activin B-, BMP2- and MSDT-induced cellular signaling; more effective on activin A than on activin B. Involved in bone formation; inhibits osteoclast differentiation. Involved in hematopoiesis; involved in differentiation of hemopoietic progenitor cells, increases hematopoietic cell adhesion to fibronectin and seems to contribute to the adhesion of hematopoietic precursor cells to the bone marrow stroma. Isoform 2 or the nuclear form is probably involved in transcriptional regulation via interaction with MLLT10","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O95633/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FSTL3","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/FSTL3","total_profiled":1310},"omim":[{"mim_id":"605343","title":"FOLLISTATIN-LIKE 3; FSTL3","url":"https://www.omim.org/entry/605343"},{"mim_id":"168461","title":"CYCLIN D1; CCND1","url":"https://www.omim.org/entry/168461"},{"mim_id":"136470","title":"FOLLISTATIN; FST","url":"https://www.omim.org/entry/136470"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FSTL3"},"hgnc":{"alias_symbol":["FLRG","FSRP"],"prev_symbol":[]},"alphafold":{"accession":"O95633","domains":[{"cath_id":"3.90.290.10","chopping":"35-93","consensus_level":"high","plddt":89.2995,"start":35,"end":93},{"cath_id":"3.30.60.30","chopping":"180-239","consensus_level":"medium","plddt":97.3548,"start":180,"end":239}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95633","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95633-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95633-F1-predicted_aligned_error_v6.png","plddt_mean":85.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FSTL3","jax_strain_url":"https://www.jax.org/strain/search?query=FSTL3"},"sequence":{"accession":"O95633","fasta_url":"https://rest.uniprot.org/uniprotkb/O95633.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95633/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95633"}},"corpus_meta":[{"pmid":"17229845","id":"PMC_17229845","title":"FSTL3 deletion reveals roles for TGF-beta family ligands in glucose and fat homeostasis in adults.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17229845","citation_count":134,"is_preprint":false},{"pmid":"9671416","id":"PMC_9671416","title":"FLRG (follistatin-related gene), a new target of chromosomal rearrangement in malignant blood disorders.","date":"1998","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/9671416","citation_count":104,"is_preprint":false},{"pmid":"11948405","id":"PMC_11948405","title":"Transcription activation of FLRG and follistatin by activin A, through Smad proteins, participates in a negative feedback loop to modulate activin A function.","date":"2002","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/11948405","citation_count":79,"is_preprint":false},{"pmid":"12697670","id":"PMC_12697670","title":"Differential binding and neutralization of activins A and B by follistatin and follistatin like-3 (FSTL-3/FSRP/FLRG).","date":"2003","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/12697670","citation_count":62,"is_preprint":false},{"pmid":"17671190","id":"PMC_17671190","title":"Silencing of FLRG, an antagonist of activin, inhibits human breast tumor cell growth.","date":"2007","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/17671190","citation_count":61,"is_preprint":false},{"pmid":"18768470","id":"PMC_18768470","title":"The structure of FSTL3.activin A complex. Differential binding of N-terminal domains influences follistatin-type antagonist specificity.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18768470","citation_count":60,"is_preprint":false},{"pmid":"11451569","id":"PMC_11451569","title":"Follistatin-related protein (FSRP): a new member of the follistatin gene family.","date":"2001","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/11451569","citation_count":56,"is_preprint":false},{"pmid":"11274757","id":"PMC_11274757","title":"Expression of FLRG, a novel activin A ligand, is regulated by TGF-beta and during hematopoiesis [corrected].","date":"2001","source":"Experimental hematology","url":"https://pubmed.ncbi.nlm.nih.gov/11274757","citation_count":41,"is_preprint":false},{"pmid":"15471966","id":"PMC_15471966","title":"Heparin and activin-binding determinants in follistatin and FSTL3.","date":"2004","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/15471966","citation_count":40,"is_preprint":false},{"pmid":"19740438","id":"PMC_19740438","title":"Differential expression of follistatin and FLRG in human breast proliferative disorders.","date":"2009","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/19740438","citation_count":39,"is_preprint":false},{"pmid":"11571638","id":"PMC_11571638","title":"FLRG, an activin-binding protein, is a new target of TGFbeta transcription activation through Smad proteins.","date":"2001","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/11571638","citation_count":37,"is_preprint":false},{"pmid":"32280246","id":"PMC_32280246","title":"Up-Regulation of FSTL3, Regulated by lncRNA DSCAM-AS1/miR-122-5p Axis, Promotes Proliferation and Migration of Non-Small Cell Lung Cancer Cells.","date":"2020","source":"OncoTargets and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/32280246","citation_count":35,"is_preprint":false},{"pmid":"15451575","id":"PMC_15451575","title":"FLRG, member of the follistatin family, a new player in hematopoiesis.","date":"2004","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/15451575","citation_count":33,"is_preprint":false},{"pmid":"23407452","id":"PMC_23407452","title":"Follistatin-like 3 (FSTL3) mediated silencing of transforming growth factor β (TGFβ) signaling is essential for testicular aging and regulating testis size.","date":"2013","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/23407452","citation_count":32,"is_preprint":false},{"pmid":"17395406","id":"PMC_17395406","title":"Identification of NF-kappaB responsive elements in follistatin related gene (FLRG) promoter.","date":"2007","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/17395406","citation_count":24,"is_preprint":false},{"pmid":"28339962","id":"PMC_28339962","title":"FSTL3 is increased in renal dysfunction.","date":"2017","source":"Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association","url":"https://pubmed.ncbi.nlm.nih.gov/28339962","citation_count":24,"is_preprint":false},{"pmid":"16336961","id":"PMC_16336961","title":"A novel role for fibronectin type I domain in the regulation of human hematopoietic cell adhesiveness through binding to follistatin domains of FLRG and follistatin.","date":"2005","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/16336961","citation_count":22,"is_preprint":false},{"pmid":"15574124","id":"PMC_15574124","title":"FLRG, a new ADAM12-associated protein, modulates osteoclast differentiation.","date":"2005","source":"Biology of the 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endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/12039070","citation_count":7,"is_preprint":false},{"pmid":"34555811","id":"PMC_34555811","title":"Inhibition of FSTL3 abates the proliferation and metastasis of renal cell carcinoma via the GSK-3β/β-catenin signaling pathway.","date":"2021","source":"Aging","url":"https://pubmed.ncbi.nlm.nih.gov/34555811","citation_count":7,"is_preprint":false},{"pmid":"16737827","id":"PMC_16737827","title":"Purification of recombinant activin A using the second follistatin domain of follistatin-related gene (FLRG).","date":"2006","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/16737827","citation_count":6,"is_preprint":false},{"pmid":"40140870","id":"PMC_40140870","title":"Multiomic traits reveal that critical irinotecan-related core regulator FSTL3 promotes CRC progression and affects ferroptosis.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/40140870","citation_count":4,"is_preprint":false},{"pmid":"33539535","id":"PMC_33539535","title":"FSTL3-Neutralizing Antibodies Enhance Glucose-Responsive Insulin Secretion in Dysfunctional Male Mouse and Human Islets.","date":"2021","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/33539535","citation_count":4,"is_preprint":false},{"pmid":"29482497","id":"PMC_29482497","title":"Uteroglobin and FLRG concentrations in aqueous humor are associated with age in primary open angle glaucoma patients.","date":"2018","source":"BMC ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/29482497","citation_count":4,"is_preprint":false},{"pmid":"33314336","id":"PMC_33314336","title":"Expression and functional analysis of the Follistatin-like 3 (FSTL3) gene in the sheep ovary during the oestrous cycle.","date":"2020","source":"Reproduction in domestic animals = Zuchthygiene","url":"https://pubmed.ncbi.nlm.nih.gov/33314336","citation_count":3,"is_preprint":false},{"pmid":"40154584","id":"PMC_40154584","title":"FSTL3 promotes colorectal cancer by activating the HIF1 pathway.","date":"2025","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/40154584","citation_count":2,"is_preprint":false},{"pmid":"38472317","id":"PMC_38472317","title":"Prenatal dexamethasone exposure impairs rat blood-testis barrier function and sperm quality in adult offspring via GR/KDM1B/FSTL3/TGFβ signaling.","date":"2024","source":"Acta pharmacologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/38472317","citation_count":2,"is_preprint":false},{"pmid":"14692692","id":"PMC_14692692","title":"Purification, cDNA cloning, and secretory properties of FLRG protein from PC12 cells and the distribution of FLRG mRNA and protein in rat tissues.","date":"2003","source":"Archives of histology and cytology","url":"https://pubmed.ncbi.nlm.nih.gov/14692692","citation_count":2,"is_preprint":false},{"pmid":"38044354","id":"PMC_38044354","title":"Stroma-associated FSTL3 is a factor of calcium channel-derived tumor fibrosis.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38044354","citation_count":1,"is_preprint":false},{"pmid":"41053124","id":"PMC_41053124","title":"Cancer-associated fibroblasts expressing FSTL3 promote vasculogenic mimicry formation and drive colon cancer malignancy.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41053124","citation_count":0,"is_preprint":false},{"pmid":"41996175","id":"PMC_41996175","title":"FSTL3-Driven Cuproptosis Resistance and EPCs Promote OSCC Metastasis.","date":"2026","source":"Journal of dental research","url":"https://pubmed.ncbi.nlm.nih.gov/41996175","citation_count":0,"is_preprint":false},{"pmid":"30756375","id":"PMC_30756375","title":"Gene structure, recombinant expression and function characterization of Siniperca chuatsi Fsrp-3.","date":"2019","source":"Journal of fish biology","url":"https://pubmed.ncbi.nlm.nih.gov/30756375","citation_count":0,"is_preprint":false},{"pmid":"41871850","id":"PMC_41871850","title":"Cinnamaldehyde Regulates the EMT Process and Drug Resistance of Gastric Cancer Through FSTL3-Mediated Cytoskeletal Remodeling.","date":"2026","source":"Phytotherapy research : PTR","url":"https://pubmed.ncbi.nlm.nih.gov/41871850","citation_count":0,"is_preprint":false},{"pmid":"41522747","id":"PMC_41522747","title":"ZNF454-FSTL3 axis inhibits colorectal cancer progression by inhibiting HIF-1α-mediated glycolysis in hypoxia.","date":"2025","source":"Journal of gastrointestinal oncology","url":"https://pubmed.ncbi.nlm.nih.gov/41522747","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.03.06.25323530","title":"Plasma Levels of Activin A and Follistatin-Like-3 as Biomarkers for Pulmonary Hypertension in Advanced Heart Failure","date":"2025-03-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.06.25323530","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.13.24317296","title":"Higher burden of cerebral small vessel disease is associated with risk of incident stroke in community dwelling individuals","date":"2024-11-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.13.24317296","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.09.03.611067","title":"Placental Network Differences Among Obstetric Syndromes Identified With An Integrated Multiomics Approach","date":"2024-09-07","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.03.611067","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":27662,"output_tokens":4997,"usd":0.07897},"stage2":{"model":"claude-opus-4-6","input_tokens":8638,"output_tokens":3377,"usd":0.191422},"total_usd":0.270392,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"FSTL3 (FLRG) was identified as a secreted glycoprotein of the follistatin-module-protein family, cloned from a t(11;19)(q13;p13) translocation in B-cell chronic lymphocytic leukemia, establishing it as an evolutionarily conserved, secreted glycoprotein.\",\n      \"method\": \"cDNA cloning, molecular characterization of chromosomal translocation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — original cloning with molecular characterization, foundational paper with 104 citations\",\n      \"pmids\": [\"9671416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"FSTL3 (FLRG) binds activin A directly, as demonstrated by immunoprecipitation and Far-Western blot analysis, establishing its role as an activin-binding antagonist.\",\n      \"method\": \"Immunoprecipitation, Far-Western blot\",\n      \"journal\": \"Experimental hematology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical methods, replicated across multiple papers\",\n      \"pmids\": [\"11274757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"FSTL3 (FSRP) binds activin with similar affinity and selectivity as follistatin but does not bind heparin; it inhibits activin-mediated gene transcription in heterologous assays but is much less active than follistatin in the rat pituitary bioassay.\",\n      \"method\": \"Binding assays, transcriptional reporter assay, rat pituitary bioassay, transgenic mouse overexpression\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including in vitro binding, reporter assay, and in vivo transgenic model\",\n      \"pmids\": [\"11451569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"FSTL3 (FLRG) gene transcription is activated by TGF-β via Smad proteins; a Smad-binding element in the FLRG promoter mediates TGF-β-inducible expression, and dominant-negative Smad3/Smad4 abolish this activation.\",\n      \"method\": \"Promoter deletion/point-mutation analysis, luciferase reporter assay, EMSA, dominant-negative Smad constructs, transfection in HepG2 cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted promoter analysis with mutagenesis and EMSA, replicated by subsequent papers\",\n      \"pmids\": [\"11571638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Activin A induces FSTL3 (FLRG) and follistatin expression at both mRNA and protein levels via Smad proteins, and FSTL3 protein in turn inhibits activin A signaling and blocks activin A-induced growth inhibition of HepG2 cells, constituting a negative feedback loop.\",\n      \"method\": \"Transcriptional reporter assay, RT-PCR, protein expression analysis, growth inhibition assay, Smad pathway analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing feedback mechanism, replicated across labs\",\n      \"pmids\": [\"11948405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"FSTL3 binds activin B at approximately 10-fold lower potency than activin A, and is approximately 3-fold more effective at neutralizing activin A than activin B, demonstrating differential binding and neutralization specificity.\",\n      \"method\": \"Binding assays, 293 cell reporter assays for biological activity neutralization\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — quantitative binding and functional neutralization assays with both ligands\",\n      \"pmids\": [\"12697670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"FSTL3 lacks a heparin-binding sequence (HBS) and cannot associate with cell surfaces; mutational analysis showed that inserting the full FS domain 1 (including HBS) into FSTL3 confers heparin binding but abolishes activin binding, implying an evolutionary safeguard against surface binding by FSTL3.\",\n      \"method\": \"Mutational analysis, cell surface binding assays, heparin affinity binding, competitive activin binding assays, pituitary cell FSH secretion bioassay\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"15471966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"FSTL3 (FLRG) physically interacts with fibronectin via type I motifs of fibronectin and follistatin domains of FSTL3 (identified by yeast two-hybrid screen and confirmed biochemically); this interaction promotes hematopoietic cell adhesion to fibronectin.\",\n      \"method\": \"Yeast two-hybrid screen, biochemical interaction assays, cell adhesion assays with hematopoietic cell line and primary cells\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — yeast two-hybrid plus cell adhesion functional assay, single lab\",\n      \"pmids\": [\"16336961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"FSTL3 (FLRG) directly interacts with ADAM12 via its cysteine-rich domain (identified by yeast two-hybrid); FSTL3 protein inhibits osteoclast differentiation from murine primary spleen cells and RAW264.7 macrophages stimulated with RANK-L and M-CSF.\",\n      \"method\": \"Yeast two-hybrid, direct interaction confirmation, osteoclast differentiation assay with primary murine cells and macrophage cell line\",\n      \"journal\": \"Biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — yeast two-hybrid with functional osteoclast assay, single lab\",\n      \"pmids\": [\"15574124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Homozygous FSTL3 knockout mice develop increased pancreatic islet number and size, beta cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, attributable to increased activin and myostatin bioactivity in specific tissues in the absence of FSTL3 antagonism.\",\n      \"method\": \"FSTL3 knockout mouse model, histomorphometry, metabolic phenotyping, glucose tolerance testing, insulin sensitivity testing\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout with multiple defined phenotypic readouts, highly cited foundational study\",\n      \"pmids\": [\"17229845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TNF-α activates FSTL3 (FLRG) expression at the transcriptional level through NF-κB binding elements (5'-GGGAGAG/TTCC-3') located in four conserved 107-108 bp DNA repeats in the promoter; TGF-β via Smad proteins potentiates TNF-α-induced FSTL3 expression.\",\n      \"method\": \"Promoter deletion analysis, luciferase reporter assay, biochemical binding assays, phylogenetic analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter mutagenesis and reporter assay with defined elements, single lab\",\n      \"pmids\": [\"17395406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Silencing FSTL3 (FLRG) in breast cancer cell lines induces growth inhibition via restoration of endogenous activin signaling (increased pSmad2, upregulation of activin target genes); growth inhibition is reversible by exogenous FSTL3 or soluble type II activin receptor.\",\n      \"method\": \"siRNA knockdown, transcriptional reporter assay, phospho-Smad2 measurement, RT-PCR for target genes, rescue experiments\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with specific rescue experiments defining mechanism\",\n      \"pmids\": [\"17671190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Nuclear FSTL3 (FLRG) interacts with AF10 transcription factor (identified by yeast two-hybrid, confirmed by Far-Western blot and co-immunoprecipitation in COS-7 cells); the N-terminal PHD domain of AF10 mediates this interaction, and FSTL3 enhances AF10 homo-oligomerization and AF10-mediated transcriptional activation.\",\n      \"method\": \"Yeast two-hybrid, Far-Western blot, co-immunoprecipitation, transient transfection transactivation assay\",\n      \"journal\": \"Biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple interaction methods plus functional transcription assay, single lab\",\n      \"pmids\": [\"17868029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The crystal structure of the FSTL3·activin A complex at 2.5 Å resolution shows that two FSTL3 molecules encircle one activin A dimer, blocking all receptor-binding sites; the N-terminal domain of FSTL3 forms a more intimate contact with activin A than the corresponding FS domain, and replacing the FSTL3 N-terminal domain with the FS N-terminal domain considerably lowers activin A affinity.\",\n      \"method\": \"X-ray crystallography (2.5 Å), domain-swap mutagenesis, binding affinity measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis validation; defines molecular mechanism of antagonism\",\n      \"pmids\": [\"18768470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FSTL3 knockout mice develop markedly enlarged testes with increased Sertoli cell numbers and delayed age-related testicular regression; FSTL3 deletion leads to increased AKT signaling and SIRT1 expression in the testis, revealing cross-talk between TGF-β ligand signaling and AKT pathway in testicular homeostasis.\",\n      \"method\": \"FSTL3 knockout mouse model, histomorphometry, phosphoproteomics, Western blot for AKT/SIRT1\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular and molecular phenotype, single lab\",\n      \"pmids\": [\"23407452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In FSTL3 knockout mice, α-to-β cell transdifferentiation is increased, as shown by α-cell lineage tracing (Gluc-Cre/YFP); activin treatment of isolated islets significantly increases YFP+/Ins+ cells, demonstrating that increased activin signaling (due to absence of FSTL3 antagonism) drives α-to-β cell transdifferentiation.\",\n      \"method\": \"Genetic lineage tracing (Gluc-Cre/YFP), flow cytometry, FSTL3 KO mice, ex vivo islet activin treatment\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — definitive lineage tracing with KO model and ex vivo validation, multiple orthogonal readouts\",\n      \"pmids\": [\"26727106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FSTL3 promotes lipid accumulation in macrophages by upregulating scavenger receptors CD36 and LOX-1 in a dose-dependent manner, and induces inflammatory cytokine secretion (IL-1β, MCP-1, TNF-α, MMP-9); FSTL3 expression is induced by oxidized LDL in macrophages.\",\n      \"method\": \"Cell-based assays, dose-response experiments, cytokine measurement, knockdown experiments\",\n      \"journal\": \"Journal of cardiovascular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cell-based functional assays with dose-response, single lab, no in vivo mechanistic validation\",\n      \"pmids\": [\"31815869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FSTL3-neutralizing antibody FP-101 prevents FSTL3 from complexing with activin or related ligands; FP-101 treatment enhances insulin secretion and glucose responsiveness in dysfunctional mouse and human islets under diabetic conditions.\",\n      \"method\": \"Antibody development, in vitro neutralization assay, islet glucose-stimulated insulin secretion assay\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional antibody with defined mechanism and human islet validation, single lab\",\n      \"pmids\": [\"33539535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FSTL3 binds to transcription factor c-Myc (at amino acids 354-406) to suppress its ubiquitination and increase its stability, thereby upregulating PDL1 and IDO1 expression; hypoxic tumor microenvironment induces FSTL3 expression via HIF1α in colorectal cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, ubiquitination assay, Western blot, flow cytometry, immunocompetent tumor models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP with domain mapping and functional in vivo validation, single lab\",\n      \"pmids\": [\"38302412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Prenatal dexamethasone exposure increases KDM1B expression in fetal testicular Sertoli cells, decreasing H3K9me2 at the FSTL3 promoter and thereby increasing FSTL3 expression, which inhibits TGF-β signaling and CX43/E-cadherin expression, impairing blood-testis barrier function.\",\n      \"method\": \"Animal model (prenatal dexamethasone), ChIP for H3K9me2 at FSTL3 promoter, Western blot, TM4 Sertoli cell validation, human sample correlation\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epigenetic mechanism with ChIP evidence, in vivo and in vitro validation, single lab\",\n      \"pmids\": [\"38472317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FSTL3 loss in OSCC induces cuproptosis susceptibility by suppressing SLC25A10, triggering mitochondrial succinate accumulation, which promotes succinylation and upregulation of DLAT, a key cuproptosis executor; FSTL3 also recruits erythroid progenitor cells (EPCs) via CCR5 upregulation to establish an immunosuppressive niche.\",\n      \"method\": \"CRISPR-Cas9 screening, metabolic profiling, succinylation assay, EPC recruitment assays, in vivo tumor models\",\n      \"journal\": \"Journal of dental research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR screen with mechanistic follow-up, single lab, multiple readouts\",\n      \"pmids\": [\"41996175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FSTL3 expressed by cancer-associated fibroblasts binds to transferrin receptor (TfR1) on cancer cells, activating the TfR1/AKT/mTOR pathway and elevating VE-Cadherin to support vasculogenic mimicry and metastatic progression in colon cancer.\",\n      \"method\": \"Binding assays, pathway activation analysis, in vitro and in vivo tumor models, FSTL3-targeting antibody inhibition studies, single-cell RNA sequencing\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — binding and functional pathway assays in vitro and in vivo, single lab, novel receptor identification\",\n      \"pmids\": [\"41053124\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FSTL3 is a secreted glycoprotein antagonist that binds and neutralizes TGF-β family ligands (primarily activin A/B, myostatin, GDF11) by encircling the ligand dimer with two FSTL3 molecules to block all receptor-binding sites (as shown by crystal structure); unlike follistatin, FSTL3 lacks a heparin-binding sequence and therefore cannot associate with cell surfaces, making it a freely circulating antagonist; its transcription is induced by TGF-β/activin A via Smad3/4, TNF-α via NF-κB, and HIF1α under hypoxia, forming negative feedback loops; physiologically, FSTL3 limits pancreatic β-cell mass and α-to-β transdifferentiation (by restraining activin signaling), regulates visceral fat and insulin sensitivity (via myostatin), controls testis size and aging, and modulates hematopoietic cell adhesion through fibronectin interaction; intranuclearly, FSTL3 enhances AF10-mediated transcription; in cancer contexts, FSTL3 can also stabilize c-Myc by suppressing ubiquitination, bind TfR1 to activate AKT/mTOR signaling, and suppress cuproptosis via SLC25A10/succinate/DLAT axis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FSTL3 is a secreted glycoprotein antagonist of TGF-β superfamily ligands that functions as a freely circulating inhibitor of activin A/B and myostatin signaling, forming negative feedback loops that regulate pancreatic β-cell mass, glucose homeostasis, gonadal development, and adiposity. Two FSTL3 molecules encircle one activin A dimer to block all receptor-binding sites, and unlike follistatin, FSTL3 lacks a heparin-binding sequence and therefore cannot associate with cell surfaces, restricting its activity to the extracellular space [PMID:18768470, PMID:15471966]. FSTL3 transcription is induced by activin/TGF-β via Smad3/4 and by TNF-α via NF-κB, establishing it as an inducible feedback antagonist; accordingly, FSTL3 knockout mice exhibit β-cell hyperplasia with enhanced α-to-β transdifferentiation, reduced visceral fat, improved insulin sensitivity, and enlarged testes [PMID:11571638, PMID:17395406, PMID:17229845, PMID:26727106, PMID:23407452]. In cancer contexts, FSTL3 stabilizes c-Myc by suppressing its ubiquitination under hypoxia-induced HIF1α-driven expression and can activate TfR1/AKT/mTOR signaling on tumor cells when secreted by cancer-associated fibroblasts [PMID:38302412, PMID:41053124].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of FSTL3 as a new member of the follistatin-module family established a candidate TGF-β superfamily modulator, addressing whether additional secreted antagonists existed beyond follistatin.\",\n      \"evidence\": \"cDNA cloning from t(11;19) translocation in B-CLL\",\n      \"pmids\": [\"9671416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No ligand-binding activity demonstrated at this stage\", \"Disease relevance of translocation unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that FSTL3 directly binds activin A with similar affinity to follistatin but lacks heparin binding established its identity as a soluble-only activin antagonist, resolving its functional relationship to follistatin.\",\n      \"evidence\": \"Immunoprecipitation, Far-Western blot, binding assays, reporter assays, and rat pituitary bioassay\",\n      \"pmids\": [\"11274757\", \"11451569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for activin binding unknown\", \"In vivo significance undemonstrated\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of Smad3/4-dependent transcriptional induction of FSTL3 by TGF-β and activin A revealed a negative feedback loop in which the ligand induces its own antagonist.\",\n      \"evidence\": \"Promoter deletion/mutation analysis, luciferase reporters, dominant-negative Smads in HepG2 cells\",\n      \"pmids\": [\"11571638\", \"11948405\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether feedback operates in vivo in specific tissues not shown\", \"Other transcriptional inputs not yet explored\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Quantification of differential binding showed FSTL3 neutralizes activin A ~3-fold more potently than activin B, defining its ligand selectivity hierarchy.\",\n      \"evidence\": \"Quantitative binding and functional neutralization assays in 293 cells\",\n      \"pmids\": [\"12697670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding to myostatin and GDF11 not yet measured\", \"Mechanism of selectivity difference unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Systematic mutagenesis demonstrated that the absence of a heparin-binding sequence in FSTL3 prevents cell-surface association, and that inserting one abolishes activin binding — establishing a structural trade-off that confines FSTL3 to the extracellular milieu.\",\n      \"evidence\": \"Domain-swap mutagenesis, heparin affinity, cell-surface binding, and pituitary FSH bioassay\",\n      \"pmids\": [\"15471966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure yet to explain the trade-off at atomic level\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery of FSTL3 interactions with fibronectin (promoting hematopoietic adhesion) and ADAM12 (inhibiting osteoclastogenesis) expanded its functional repertoire beyond ligand sequestration to extracellular matrix and cell differentiation contexts.\",\n      \"evidence\": \"Yeast two-hybrid screens, biochemical confirmation, hematopoietic adhesion and osteoclast differentiation assays\",\n      \"pmids\": [\"16336961\", \"15574124\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Yeast two-hybrid interactions not confirmed by endogenous co-IP\", \"In vivo relevance of fibronectin and ADAM12 interactions not tested\", \"Whether these interactions depend on or compete with activin binding unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"FSTL3 knockout mice revealed that endogenous FSTL3 restrains activin/myostatin bioactivity in specific tissues: its absence causes pancreatic β-cell hyperplasia, reduced visceral fat, improved insulin sensitivity, and enlarged testes, defining FSTL3 as a physiological regulator of metabolic and gonadal homeostasis.\",\n      \"evidence\": \"Constitutive FSTL3 KO mice with metabolic phenotyping, histomorphometry, glucose tolerance, and insulin sensitivity testing\",\n      \"pmids\": [\"17229845\", \"23407452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific contributions of FSTL3 not dissected (global KO)\", \"Which ligand (activin vs. myostatin vs. GDF11) mediates each phenotype not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"TNF-α was shown to activate FSTL3 transcription via NF-κB elements, and nuclear FSTL3 was found to enhance AF10-mediated transcription, revealing both a new upstream inducer and an unexpected intranuclear function.\",\n      \"evidence\": \"Promoter mutagenesis/reporter assays for NF-κB; yeast two-hybrid, co-IP, and transactivation assays for AF10 interaction\",\n      \"pmids\": [\"17395406\", \"17868029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear localization mechanism and signal undefined\", \"Transcriptional targets of AF10 enhanced by FSTL3 unknown\", \"AF10 interaction not confirmed in endogenous setting\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The 2.5 Å crystal structure of the FSTL3·activin A complex revealed the atomic mechanism of antagonism: two FSTL3 molecules wrap around the activin dimer, blocking all type I and type II receptor-binding epitopes, and showed the N-terminal domain makes uniquely intimate contacts.\",\n      \"evidence\": \"X-ray crystallography with domain-swap mutagenesis and affinity measurements\",\n      \"pmids\": [\"18768470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure with myostatin or GDF11\", \"Dynamics of complex assembly in solution unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic lineage tracing in FSTL3 KO mice proved that increased activin signaling drives α-to-β cell transdifferentiation, establishing FSTL3 as a gatekeeper of islet cell identity.\",\n      \"evidence\": \"Gluc-Cre/YFP lineage tracing in FSTL3 KO, flow cytometry, ex vivo activin treatment of islets\",\n      \"pmids\": [\"26727106\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether therapeutic FSTL3 neutralization can replicate this in diabetic models not shown at this time point\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"An FSTL3-neutralizing antibody (FP-101) enhanced insulin secretion in dysfunctional mouse and human islets, providing proof-of-concept that targeting FSTL3 can restore β-cell function under diabetic conditions.\",\n      \"evidence\": \"Antibody neutralization assay, glucose-stimulated insulin secretion in isolated islets\",\n      \"pmids\": [\"33539535\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vivo efficacy data in diabetic animal models\", \"Long-term safety and specificity not assessed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"FSTL3 was found to stabilize c-Myc by directly binding and suppressing its ubiquitination under hypoxic HIF1α-driven induction, linking FSTL3 to immune evasion (PDL1/IDO1 upregulation) in colorectal cancer — a ligand-sequestration-independent oncogenic mechanism.\",\n      \"evidence\": \"Co-IP, domain mapping (aa 354–406), ubiquitination assay, immunocompetent tumor models\",\n      \"pmids\": [\"38302412\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether c-Myc stabilization occurs in non-hypoxic or non-cancer contexts unknown\", \"Ubiquitin ligase displaced by FSTL3 not identified\", \"Single-lab finding not yet replicated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Two studies expanded FSTL3's cancer biology: one identified TfR1 as a cell-surface receptor through which fibroblast-derived FSTL3 activates AKT/mTOR signaling and vasculogenic mimicry; the other showed FSTL3 loss triggers cuproptosis via SLC25A10/succinate/DLAT — both mechanisms independent of classical activin antagonism.\",\n      \"evidence\": \"Binding assays, scRNA-seq, in vivo tumor models (colon cancer); CRISPR screen, metabolic profiling, succinylation assay (OSCC)\",\n      \"pmids\": [\"41053124\", \"41996175\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TfR1 interaction not confirmed by structural or biophysical methods\", \"Cuproptosis link requires independent replication\", \"Relationship between FSTL3's activin-binding and TfR1-binding surfaces uncharacterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include tissue-specific versus circulating contributions of FSTL3 (no conditional KO studies), structures of FSTL3 complexes with myostatin/GDF11, the mechanism and physiological relevance of nuclear FSTL3, and whether the newly identified cancer-related functions (c-Myc stabilization, TfR1 binding, cuproptosis modulation) operate through activin-dependent or fully independent pathways.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No tissue-specific knockout models reported\", \"No structural data for FSTL3–myostatin or FSTL3–GDF11 complexes\", \"Nuclear localization signal and trafficking mechanism undefined\", \"Activin-dependent vs. independent functions in tumors not delineated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 2, 5, 6, 13]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [2, 5, 11, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 2, 6, 13]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 4, 5, 9, 11, 13, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9, 14, 15]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [9, 16]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [18, 20]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"INHBA\",\n      \"INHBB\",\n      \"FN1\",\n      \"ADAM12\",\n      \"MLLT10\",\n      \"MYC\",\n      \"TFRC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}