{"gene":"FDX1","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2010,"finding":"Human FDX1 (adrenodoxin) is specifically required for cytochrome P450-dependent steroid hormone biosynthesis (e.g., cholesterol to pregnenolone, aldosterone, cortisol) in mitochondria, whereas the related FDX2 is essential for Fe/S cluster and heme A biosynthesis. RNAi depletion of FDX1 did not impair Fe/S protein biogenesis, while FDX2 depletion caused severe Fe/S protein defects and iron accumulation. FDX2 could not efficiently substitute for FDX1 in steroid conversion assays, demonstrating distinct substrate specificity.","method":"RNAi depletion in human cells, steroid conversion assays, Fe/S protein activity measurements, iron uptake assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean KD with multiple orthogonal functional readouts, replicated across pathways","pmids":["20547883"],"is_preprint":false},{"year":2022,"finding":"FDX1 (but not FDX2) is specifically required for lipoyl cofactor biosynthesis in addition to steroidogenesis and heme a synthesis. FDX1 provides electrons to lipoyl synthase (LIAS) to initiate the radical chain reaction. Swapping small conserved sequence motifs between FDX1 and FDX2 changed their respective target specificities, identifying these motifs as determinants of functional specificity.","method":"RNAi/CRISPR loss-of-function, in vitro electron transfer assays, chimeric ferredoxin domain-swap experiments, lipoylation assays","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including domain-swap mutagenesis, in vitro reconstitution, and cellular KO phenotypes","pmids":["36280795"],"is_preprint":false},{"year":2023,"finding":"FDX1 directly binds lipoyl synthase (LIAS) and promotes LIAS functional interaction with the lipoyl carrier protein GCSH, thereby regulating cellular protein lipoylation. This function is independent of indirect regulation via Fe/S cluster biosynthesis. Loss of FDX1 results in loss of lipoylation of four TCA cycle enzymes, loss of cellular respiration, and conditional lethality under low glucose.","method":"Co-immunoprecipitation/direct binding assay, metabolite profiling, transcriptional profiling, siRNA knockdown, CRISPR KO","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding demonstrated, multiple orthogonal metabolic and transcriptional readouts, replicated in peer-reviewed and preprint","pmids":["37453661","36778498"],"is_preprint":false},{"year":2023,"finding":"FDX1 acts as a mitochondrial matrix reductase that catalyzes reduction of elesclomol-Cu(II) to Cu(I), releasing copper into the mitochondrial matrix where it metalates cytochrome c oxidase. FDX1 KO cells fail to rescue cytochrome c oxidase abundance/activity when treated with elesclomol in copper-deficient conditions, while copper delivery to non-mitochondrial cuproproteins is partially FDX1-independent.","method":"CRISPR KO, biochemical copper measurements, cytochrome c oxidase activity/abundance assays, genetic rescue experiments","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean CRISPR KO with multiple biochemical functional readouts, mechanistic distinction between FDX1-dependent and -independent pathways","pmids":["36848556"],"is_preprint":false},{"year":1998,"finding":"Crystal structure of truncated bovine adrenodoxin (Adx/FDX1 ortholog) Adx(4-108) at 1.85 Å resolution reveals a compact (α+β) fold with a large core domain and smaller interaction domain containing residues required for binding adrenodoxin reductase and cytochrome P450. The [2Fe-2S] cluster is located at the edge; charged residues form an asymmetric electric potential implicated in electrostatic steering of redox partner interactions. A domain motion linked to redox state change is suggested.","method":"X-ray crystallography (MAD phasing), electrostatic surface analysis","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional domain identification, foundational structural paper","pmids":["9551550"],"is_preprint":false},{"year":2023,"finding":"FDX1 is required for lipoylation under normoxia; under hypoxia (1% O2), FDX1 KO cells survive despite persistent loss of lipoylation, indicating that hypoxia rescues the lethality caused by lipoylation deficiency rather than restoring lipoylation via an alternative route.","method":"CRISPR KO, lipoylation western blot, hypoxic cell culture growth assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with multiple cellular and biochemical readouts distinguishing lipoylation from growth phenotype","pmids":["37481209"],"is_preprint":false},{"year":2017,"finding":"Both human FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/Acp) via residues near the Fe-S cluster, and both can donate electrons to support Fe-S cluster assembly on ISCU in vitro, though FDX2 binds the complex more tightly and supports faster cluster assembly than FDX1.","method":"NMR spectroscopy (interaction mapping), isothermal titration calorimetry, in vitro Fe-S cluster assembly assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted in vitro with multiple biophysical methods (NMR, ITC, functional assembly assay)","pmids":["28001042"],"is_preprint":false},{"year":2023,"finding":"FDX1 is essential for biogenesis of mitochondrial cytochrome c oxidase (CcO) in mammalian cells. FDX1 KO rat cardiomyocytes show reduced CcO abundance and assembly, decreased copper and heme a/a3 levels. Overexpression of COX15 (heme a synthase) partially rescues COX1 abundance, placing FDX1 upstream of COX15 in heme a biosynthesis and CcO assembly.","method":"CRISPR-Cas9 KO, mitochondrial respiration assays, BN-PAGE CcO assembly analysis, copper measurement, heme a measurement, genetic rescue (COX15 overexpression)","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 — clean CRISPR KO with multiple orthogonal assays and epistatic rescue experiment placing FDX1 upstream of COX15","pmids":["37858707"],"is_preprint":false},{"year":2025,"finding":"Deep mutational scanning identified two conserved solvent-exposed acidic residues on FDX1 alpha helix 3 (D136 and D139) as essential for both cuproptosis induction and lipoylation in cells, despite retaining enzymatic activity in vitro, indicating helix 3 is a critical protein-protein interaction interface. Additionally, dihydrolipoamide dehydrogenase (DLD) was identified as an alternative FDX1 reductase both in vitro and in cells.","method":"Deep mutational scanning, charge-reversal mutagenesis, cell-based cuproptosis and lipoylation assays, in vitro enzymatic assays, structural analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis combined with in vitro and cellular functional assays, plus new interactor identification","pmids":["41423452"],"is_preprint":false},{"year":2025,"finding":"EPR spectroscopy demonstrated direct electron transfer from reduced FDX1 to the elesclomol-Cu(II) complex both in vitro and in vivo. FDX1 has higher binding affinity for elesclomol-Cu(II) than its homolog FDX2, explaining the functional specificity. Elesclomol-Cu(II) is a more efficient electron acceptor from FDX1 than free Cu(II).","method":"Electron paramagnetic resonance (EPR) spectroscopy, molecular docking, low-temperature EPR measurements in vitro and in vivo","journal":"Chemistry (Weinheim an der Bergstrasse, Germany)","confidence":"High","confidence_rationale":"Tier 1 — direct spectroscopic evidence of electron transfer mechanism with biophysical binding characterization","pmids":["40484707"],"is_preprint":false},{"year":2025,"finding":"AKT1 phosphorylates FDX1, and this phosphorylation inhibits FDX1-induced cuproptosis and aerobic respiration while promoting glycolysis in triple-negative breast cancer cells. Copper activates AKT signaling which then suppresses FDX1 function.","method":"Phosphorylation assays, AKT1 inhibitor treatment, in vitro and in vivo functional assays, glycolysis and respiration measurements","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2-3 — identifies a PTM and pathway but detailed biochemical reconstitution of direct phosphorylation not fully described","pmids":["39976173"],"is_preprint":false},{"year":2020,"finding":"Allosteric coupling exists between substrate binding and adrenodoxin (FDX1/Adx) recognition in CYP24A1. Chemical cross-linking/MS and NMR revealed that Adx binding induces a conformational change in CYP24A1 F and G helices required for substrate binding. A semiconserved nonpolar interface contact may influence CYP24A1 regioselectivity.","method":"Chemical cross-linking coupled to mass spectrometry, NMR spectroscopy, CYP24A1 functional assays","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal biophysical methods revealing allosteric mechanism, single lab","pmids":["32259445"],"is_preprint":false},{"year":2017,"finding":"Transcription factors SF1 and cJUN cooperate to activate the Fdx1 promoter in Leydig cells. SF1 is recruited to regulatory elements between -124 and -306 bp of the Fdx1 promoter. RNAi demonstrated SF1 is required for Fdx1 transcriptional regulation, while cJUN cooperates with SF1 but is not individually essential.","method":"Promoter-reporter assays, chromatin immunoprecipitation, RNA interference, transfection in MA-10 and TM3 Leydig cells","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2-3 — ChIP and functional reporter assays with RNAi validation, single lab","pmids":["28274746"],"is_preprint":false},{"year":2005,"finding":"Overexpression of adrenodoxin (FDX1/Adx) in human cells induces ROS production in mitochondria, disrupts mitochondrial transmembrane potential, causes cytochrome c release, and activates caspases leading to apoptosis in a p53-independent manner.","method":"Transient overexpression, ROS measurement, mitochondrial membrane potential assay (ΔΨ), cytochrome c release assay, caspase activation assay, cell viability assays across 11 cell lines","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal mechanistic readouts of mitochondrial apoptosis pathway, single lab","pmids":["15927889"],"is_preprint":false},{"year":2023,"finding":"FDX1 interacts with G6PD and reduces its protein stability, leading to decreased NADPH and GSH levels, which enhances copper-induced cell death (cuproptosis) in endometriosis cells.","method":"Co-immunoprecipitation, protein stability assays, NADPH/GSH measurement, cell death assays, mouse model","journal":"Apoptosis : an international journal on programmed cell death","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP finding with partial functional follow-up, single lab","pmids":["37119432"],"is_preprint":false},{"year":2025,"finding":"p53 enhances FDX1-mediated cuproptosis in hepatocellular carcinoma via ferredoxin reductase (FDXR); p53 activation increases FDXR expression, which promotes FDX1 upregulation, leading to DLAT oligomerization and cuproptosis. FDXR knockdown reverses p53-mediated sensitization, placing FDXR between p53 and FDX1 in the cuproptosis pathway.","method":"p53 overexpression/knockdown, siRNA-mediated FDXR knockdown, DLAT oligomerization assays (western blot, immunofluorescence), cell viability assays, xenograft mouse model","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — epistatic pathway placement with multiple molecular readouts in vitro and in vivo","pmids":["40630211"],"is_preprint":false},{"year":2025,"finding":"PUMA directly binds FDX1 at its R155 site and promotes DLAT/DLST oligomerization and reduction of LIAS expression, activating cuproptosis. PUMA binding also increases FDX1 ubiquitination at K182, leading to FDX1 degradation.","method":"Co-immunoprecipitation, immunofluorescence, dual-luciferase assays, RNA immunoprecipitation, ubiquitination assays, xenograft mouse model","journal":"Cellular oncology (Dordrecht, Netherlands)","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP with site identification and functional readouts, single lab","pmids":["41212484"],"is_preprint":false},{"year":2025,"finding":"FDX1 overexpression triggers mitochondrial permeability transition pore opening, leading to cytosolic release of mitochondrial DNA and double-stranded RNA. These DAMPs activate cGAS and RIG-I/MDA5 sensors, triggering TBK1 phosphorylation and type I interferon response that reshapes the tumor microenvironment in ccRCC, linking FDX1 to innate immune activation independent of cuproptosis.","method":"FDX1 overexpression, mtDNA/mt-dsRNA cytosolic release assays, cGAS/RIG-I pathway activation assays (TBK1 phosphorylation), orthotopic syngeneic mouse models, flow cytometry","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 — multiple molecular readouts with in vivo validation, single lab, novel mechanistic axis","pmids":["41199656"],"is_preprint":false},{"year":2025,"finding":"FDX1 coordinates autophagic activity in ovarian cancer by modulating the AMPK and mTOR signaling pathways and preserving mitochondrial integrity/DLAT-DLST sulfation to maintain autophagic flux; FDX1 is predominantly localized to cytoplasm and mitochondria.","method":"FDX1 knockdown/overexpression, AMPK/mTOR pathway analysis, autophagic flux assays, mitochondrial integrity assays, in vivo xenograft","journal":"NPJ precision oncology","confidence":"Low","confidence_rationale":"Tier 3 — pathway placement based on KD/OE with signaling readouts, single lab, limited mechanistic detail","pmids":["40629130"],"is_preprint":false},{"year":2025,"finding":"METTL3-mediated m6A modification of FDX1 mRNA reduces FDX1 protein expression via the m6A reader FMR1, which inhibits FDX1 translation, thereby conferring resistance to cuproptosis in hepatocellular carcinoma.","method":"m6A-MeRIP, METTL3/FMR1 knockdown, FDX1 protein expression assays, cuproptosis sensitivity assays, xenograft models","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 — m6A mapping with functional reader identification and cellular/in vivo validation","pmids":["41501140"],"is_preprint":false},{"year":2023,"finding":"METTL16 lactylation at K229 (inhibited by SIRT2) promotes m6A modification on FDX1 mRNA, increasing FDX1 expression and thereby promoting cuproptosis in gastric cancer cells.","method":"m6A modification assays (MeRIP), METTL16 lactylation site mapping, SIRT2 inhibition, cuproptosis assays in vitro and in vivo","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — PTM (lactylation) writing/erasing with downstream m6A-FDX1 functional linkage, multiple methods","pmids":["37863889"],"is_preprint":false},{"year":2025,"finding":"FDX1 promotes elesclomol-induced PANoptosis in DLBCL by increasing IRF3 phosphorylation, which activates IFN-β-dependent signaling. FDX1 overexpression sensitizes DLBCL cells to elesclomol-Cu cell death both in vitro and in patient-derived xenografts.","method":"FDX1 overexpression/knockdown, IRF3 phosphorylation assays, IFN-β signaling assays, PDX models, patient cohort correlation analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway placement with in vivo PDX validation, single lab","pmids":["40240522"],"is_preprint":false},{"year":2025,"finding":"FDX1 directly binds FMR1 protein and upregulates its expression in ccRCC, which subsequently restrains Bcl-2 and N-cadherin while enhancing Cleaved Caspase-3 and E-cadherin expression; FMR1 knockdown reverses the anti-tumor effect of FDX1 overexpression.","method":"Co-IP assays, TMT proteomic sequencing, RNA-sequencing, orthotopic mouse models, FMR1 knockdown rescue assays","journal":"Cell death discovery","confidence":"Low","confidence_rationale":"Tier 3 — Co-IP with proteomic discovery and genetic rescue, single lab, limited biochemical mechanistic detail on FDX1-FMR1 interaction","pmids":["40118855"],"is_preprint":false},{"year":2025,"finding":"FDX1 regulates HIF-1α protein levels under severe hypoxia in glioblastoma cells, and FDX1 knockdown reduces hypoxia-induced phosphorylation/activation of ATM, DNA-PKcs, Akt, and EGFR, thereby sensitizing cells to radiation. HIF-1α does not reciprocally regulate FDX1, placing FDX1 upstream of HIF-1α in this pathway.","method":"siRNA knockdown, phosphorylation western blotting, radiation sensitivity assays, HIF-1α protein measurement under hypoxia","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 — KD with signaling readouts, single lab, epistatic inference from lack of reciprocal regulation","pmids":["40244269"],"is_preprint":false},{"year":2025,"finding":"The lncRNA PVT1 directly binds to the FDX1 promoter at the -104/-41 bp region, increases H3K27ac deposition, and recruits transcription factor SF1 to activate FDX1 transcription, thereby promoting cuproptosis in colorectal cancer.","method":"ChIRP (chromatin isolation by RNA purification), ChIP, luciferase reporter assays, molecular docking, xenograft model","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 — direct RNA-DNA binding demonstrated by ChIRP/ChIP with functional reporter validation","pmids":["40505346"],"is_preprint":false},{"year":2025,"finding":"NFKB1 directly binds the FDX1 promoter to transcriptionally upregulate FDX1 in glioblastoma cells, as validated by dual-luciferase assay. NFKB1 knockdown reduces FDX1 expression, and FDX1 overexpression partially rescues the anti-tumor effect of NFKB1 knockdown, placing NFKB1 upstream of FDX1.","method":"Dual-luciferase promoter assay, NFKB1 knockdown, FDX1 overexpression rescue, in vivo intracranial xenograft","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct promoter binding validated by reporter assay with genetic epistasis in vitro and in vivo","pmids":["40716652"],"is_preprint":false},{"year":2023,"finding":"miR-21-5p directly binds the 3'-UTR of FDX1 mRNA to mediate its degradation in clear cell renal cell carcinoma, as validated by luciferase reporter assay. miR-21-5p inhibition suppresses ccRCC cell growth and invasion in a manner compensated by FDX1 knockdown.","method":"3'-UTR luciferase reporter assay, miR-21-5p mimic/inhibitor, FDX1 knockdown rescue, cell growth/invasion assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct 3'-UTR binding validated with reporter assay and genetic rescue, single lab","pmids":["36611966"],"is_preprint":false}],"current_model":"FDX1 is a mitochondrial [2Fe-2S] ferredoxin that functions as an electron shuttle with distinct substrate specificity from its paralog FDX2: it reduces mitochondrial cytochrome P450 enzymes for steroid hormone biosynthesis, donates electrons to lipoyl synthase (LIAS) by direct binding to drive mitochondrial protein lipoylation (essential for TCA cycle function), supports heme a synthesis upstream of COX15 for cytochrome c oxidase biogenesis, and catalyzes the reduction of ionophore-bound Cu(II) to Cu(I) to release copper in mitochondria; its function is regulated post-translationally by AKT1-mediated phosphorylation and transcriptionally by SF1/cJUN and NFKB1, and its critical protein-protein interaction surface maps to acidic residues D136/D139 on alpha helix 3."},"narrative":{"teleology":[{"year":1998,"claim":"Determination of the crystal structure of the bovine FDX1 ortholog established the architectural basis for redox partner recognition, revealing a [2Fe-2S] cluster at the domain interface and an asymmetric charged surface that mediates electrostatic steering toward reductase and P450 partners.","evidence":"X-ray crystallography at 1.85 Å resolution with MAD phasing of truncated bovine adrenodoxin","pmids":["9551550"],"confidence":"High","gaps":["Structure was of a truncated construct; full-length human FDX1 structure not determined","Redox-state-dependent domain motion inferred but not captured in two states"]},{"year":2005,"claim":"Overexpression studies first linked FDX1 to mitochondrial ROS production and intrinsic apoptosis, demonstrating that excess FDX1 electron transfer disrupts mitochondrial membrane potential and triggers cytochrome c release independent of p53.","evidence":"Transient overexpression in 11 human cell lines with ROS, ΔΨm, cytochrome c release, and caspase activation measurements","pmids":["15927889"],"confidence":"Medium","gaps":["Overexpression artifact not ruled out—endogenous role in apoptosis unconfirmed","No loss-of-function counterpart performed"]},{"year":2010,"claim":"Functional separation of the two human ferredoxins resolved a long-standing question: FDX1 is specifically required for mitochondrial P450-dependent steroidogenesis, whereas FDX2 supports Fe-S cluster and heme A biogenesis, and the two cannot efficiently substitute for each other.","evidence":"RNAi depletion in human cells with steroid conversion assays and Fe-S protein activity measurements","pmids":["20547883"],"confidence":"High","gaps":["The molecular determinants of substrate specificity between FDX1 and FDX2 were not identified at this stage","Whether FDX1 had additional non-steroidogenic roles was unknown"]},{"year":2017,"claim":"NMR and calorimetry showed that FDX1 can bind the Fe-S assembly machinery (NFS1/ISD11/Acp) and support cluster assembly in vitro, but with lower affinity and rate than FDX2, explaining why FDX1 loss does not impair Fe-S biogenesis in cells.","evidence":"NMR interaction mapping, isothermal titration calorimetry, and reconstituted in vitro Fe-S assembly assays","pmids":["28001042"],"confidence":"High","gaps":["Whether FDX1 ever contributes meaningfully to Fe-S assembly under physiological conditions remains unclear"]},{"year":2017,"claim":"Transcriptional regulation of FDX1 in steroidogenic cells was mapped, showing SF1 and cJUN cooperatively activate the Fdx1 promoter in Leydig cells, with SF1 being the essential factor.","evidence":"Promoter-reporter assays, ChIP, and RNAi in MA-10 and TM3 Leydig cells","pmids":["28274746"],"confidence":"Medium","gaps":["Regulation in non-steroidogenic tissues not addressed","Whether SF1-dependent regulation is conserved in humans not shown"]},{"year":2020,"claim":"Cross-linking MS and NMR revealed that FDX1 binding to CYP24A1 allosterically remodels the P450 active site, establishing that FDX1 is not merely an electron donor but an allosteric regulator of P450 substrate binding and regioselectivity.","evidence":"Chemical cross-linking/MS and NMR of FDX1-CYP24A1 complex with functional assays","pmids":["32259445"],"confidence":"Medium","gaps":["Generalizability to other mitochondrial P450s not tested","Structural detail of the allosteric conformational change limited"]},{"year":2022,"claim":"A major expansion of FDX1 function was established: FDX1 specifically provides electrons to lipoyl synthase (LIAS) for lipoyl cofactor biosynthesis, and domain-swap chimeras between FDX1 and FDX2 identified short sequence motifs that determine target specificity.","evidence":"CRISPR KO, in vitro electron transfer assays, chimeric ferredoxin domain-swap mutagenesis, lipoylation assays","pmids":["36280795"],"confidence":"High","gaps":["Structural basis of FDX1-LIAS recognition not resolved at atomic level","Whether additional mitochondrial targets exist beyond steroidogenic P450s and LIAS was open"]},{"year":2023,"claim":"Multiple studies converged to show FDX1 directly binds LIAS and promotes its interaction with GCSH, that FDX1 loss abolishes lipoylation of four TCA cycle enzymes causing conditional lethality under normoxia, that FDX1 reduces ionophore-bound Cu(II) to deliver copper for cytochrome c oxidase metalation, and that FDX1 acts upstream of COX15 in heme a biosynthesis for CcO assembly.","evidence":"Co-IP/direct binding, CRISPR KO in human and rat cells, metabolite profiling, copper/heme measurements, COX15 genetic rescue, hypoxic rescue experiments","pmids":["37453661","36848556","37858707","37481209"],"confidence":"High","gaps":["Whether FDX1 directly reduces COX15 or acts via an intermediary is not determined","The relative contribution of each pathway (lipoylation, heme a, copper delivery) to the lethal phenotype is not fully dissected"]},{"year":2023,"claim":"Epitranscriptomic regulation of FDX1 was identified: METTL16-mediated m6A modification of FDX1 mRNA, controlled by METTL16 lactylation (inhibited by SIRT2), increases FDX1 expression and cuproptosis sensitivity in gastric cancer.","evidence":"MeRIP, METTL16 lactylation site mapping, SIRT2 inhibition, cuproptosis assays in vitro/in vivo","pmids":["37863889"],"confidence":"Medium","gaps":["Opposing result reported (METTL3/FMR1 decreases FDX1 in HCC); tissue- and m6A writer-specific effects not reconciled","Whether m6A regulation operates on FDX1 under normal physiology is unknown"]},{"year":2025,"claim":"Deep mutational scanning identified D136 and D139 on FDX1 alpha helix 3 as a critical protein–protein interaction interface essential for lipoylation and cuproptosis in cells, and discovered DLD as an alternative FDX1 reductase, expanding the FDX1 electron-supply network beyond FDXR.","evidence":"Systematic charge-reversal mutagenesis, cell-based lipoylation and cuproptosis assays, in vitro enzymatic assays","pmids":["41423452"],"confidence":"High","gaps":["No co-crystal structure of FDX1 with LIAS or other partners via helix 3","Physiological relevance of DLD as FDX1 reductase versus FDXR not quantified in vivo"]},{"year":2025,"claim":"EPR spectroscopy provided direct spectroscopic evidence that FDX1 transfers electrons to elesclomol-Cu(II) both in vitro and in vivo, with higher affinity for this substrate than FDX2, establishing the biophysical basis for FDX1-specific copper reduction.","evidence":"EPR spectroscopy, molecular docking, low-temperature EPR in vitro and in cells","pmids":["40484707"],"confidence":"High","gaps":["Whether FDX1 reduces physiological (non-elesclomol) copper complexes in mitochondria is not addressed","In vivo EPR was at low temperature, not under truly physiological conditions"]},{"year":2025,"claim":"Post-translational regulation of FDX1 was identified: AKT1 phosphorylates FDX1, inhibiting its function in cuproptosis and aerobic respiration while promoting glycolysis, with copper itself activating AKT signaling in a feedback loop.","evidence":"Phosphorylation assays, AKT1 inhibitor treatment, respiration and glycolysis measurements in triple-negative breast cancer cells","pmids":["39976173"],"confidence":"Medium","gaps":["Phosphorylation site on FDX1 not mapped","Direct in vitro kinase assay not fully described","Whether this regulatory axis operates in non-cancer cells unknown"]},{"year":2025,"claim":"FDX1 overexpression was shown to trigger mitochondrial permeability transition pore opening, cytosolic release of mtDNA and mt-dsRNA, and activation of cGAS/STING and RIG-I/MDA5 innate immune pathways, linking FDX1 to type I interferon signaling independent of cuproptosis.","evidence":"FDX1 overexpression with mtDNA/dsRNA release assays, TBK1 phosphorylation, syngeneic orthotopic mouse models","pmids":["41199656"],"confidence":"Medium","gaps":["Overexpression-driven; whether endogenous FDX1 levels activate this axis is unknown","Mechanism of mPTP opening by FDX1 not elucidated"]},{"year":null,"claim":"Key unresolved questions include: the atomic-resolution structural basis of FDX1 partner selectivity via helix 3, whether FDX1 reduces physiological (non-ionophore) copper carriers, the relative in vivo contributions of FDXR versus DLD as FDX1 reductases, and whether FDX1's reported roles in innate immune activation and autophagy regulation reflect primary electron-transfer functions or indirect metabolic consequences.","evidence":"","pmids":[],"confidence":"Low","gaps":["No co-crystal structure of FDX1 with any physiological partner","No identified physiological mitochondrial copper complex reduced by FDX1","Relative pathway contributions to lethality not quantitatively dissected"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,3,9]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0,1,3]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2,3,4,7]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,7]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,8,13]}],"complexes":[],"partners":["LIAS","COX15","NFS1","DLD","CYP24A1","GCSH","FDXR"],"other_free_text":[]},"mechanistic_narrative":"FDX1 is a mitochondrial [2Fe-2S] ferredoxin that serves as a specialized electron shuttle for multiple essential mitochondrial biosynthetic pathways, functionally distinct from its paralog FDX2. FDX1 donates electrons to mitochondrial cytochrome P450 enzymes for steroid hormone biosynthesis, to lipoyl synthase (LIAS) via direct binding to drive protein lipoylation required for TCA cycle function, and to COX15 for heme a synthesis during cytochrome c oxidase biogenesis; it also catalyzes reduction of ionophore-bound Cu(II) to Cu(I) for mitochondrial copper delivery [PMID:20547883, PMID:36280795, PMID:37453661, PMID:36848556, PMID:37858707]. Deep mutational scanning identified acidic residues D136/D139 on alpha helix 3 as a critical protein–protein interaction surface essential for lipoylation and cuproptosis in cells, while dihydrolipoamide dehydrogenase (DLD) functions as an alternative FDX1 reductase [PMID:41423452]. FDX1 expression is regulated transcriptionally by SF1/cJUN and NFKB1 and post-translationally by AKT1-mediated phosphorylation that inhibits its pro-oxidative and respiratory functions [PMID:28274746, PMID:40716652, PMID:39976173]."},"prefetch_data":{"uniprot":{"accession":"P10109","full_name":"Adrenodoxin, mitochondrial","aliases":["Adrenal ferredoxin","Ferredoxin-1","Hepatoredoxin"],"length_aa":184,"mass_kda":19.4,"function":"Essential for the synthesis of various steroid hormones (PubMed:20547883, PubMed:21636783). Participates in the reduction of mitochondrial cytochrome P450 for steroidogenesis (PubMed:20547883, PubMed:21636783). Transfers electrons from adrenodoxin reductase to CYP11A1, a cytochrome P450 that catalyzes cholesterol side-chain cleavage (PubMed:20547883, PubMed:21636783). 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(Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/41199656","citation_count":2,"is_preprint":false},{"pmid":"40843273","id":"PMC_40843273","title":"Tanshinone IIA promotes METTL3/METTL14-mediated FDX1 m6A modification to induce cuproptosis in bladder cancer.","date":"2025","source":"Toxicology research","url":"https://pubmed.ncbi.nlm.nih.gov/40843273","citation_count":2,"is_preprint":false},{"pmid":"41212484","id":"PMC_41212484","title":"Unraveling the miR-144-3p/PUMA pathway: a novel regulator of FDX1-mediated cuproptosis in colorectal cancer.","date":"2025","source":"Cellular oncology (Dordrecht, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/41212484","citation_count":2,"is_preprint":false},{"pmid":"39356718","id":"PMC_39356718","title":"C1-FDX is required for the assembly of mitochondrial complex I and subcomplexes of complex V in Arabidopsis.","date":"2024","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39356718","citation_count":2,"is_preprint":false},{"pmid":"40998065","id":"PMC_40998065","title":"Targeting FDX1 with Icaritin attenuates neuronal cuproptosis by reconciling mitochondrial fission-fusion dynamics and bioenergetic homeostasis.","date":"2025","source":"Free radical biology & medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40998065","citation_count":2,"is_preprint":false},{"pmid":"40354319","id":"PMC_40354319","title":"Modulation of Cuproptosis Pathway Genes (DLAT, FDX1) and Antioxidant Enzyme Activities in Obese Mice in Response to Quercetin and Calorie Restriction.","date":"2025","source":"DNA and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/40354319","citation_count":2,"is_preprint":false},{"pmid":"41355968","id":"PMC_41355968","title":"Precision targeting of FDX1-mediated cuproptosis by a ROS-responsive hydrogel for myocardial ischemia-reperfusion injury treatment.","date":"2026","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/41355968","citation_count":1,"is_preprint":false},{"pmid":"40629130","id":"PMC_40629130","title":"Modulating ovarian cancer progression through FDX1-driven autophagy.","date":"2025","source":"NPJ precision oncology","url":"https://pubmed.ncbi.nlm.nih.gov/40629130","citation_count":1,"is_preprint":false},{"pmid":"41423452","id":"PMC_41423452","title":"Deep Mutational Scanning of FDX1 Identifies Key Structural Determinants of Lipoylation and Cuproptosis.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41423452","citation_count":1,"is_preprint":false},{"pmid":"40449270","id":"PMC_40449270","title":"Mycobacterium tuberculosis stimulates cuproptosis by regulating Lnc-Gm5532 to target FDX1 for bacteria intracellular survival.","date":"2025","source":"International immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40449270","citation_count":1,"is_preprint":false},{"pmid":"40977283","id":"PMC_40977283","title":"Marine Natural Product Chagosendine C Induces Cuproptosis in Colorectal Cancer Cells by Targeting FDX1.","date":"2025","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/40977283","citation_count":1,"is_preprint":false},{"pmid":"41501140","id":"PMC_41501140","title":"METTL3-mediated m6A modification of FDX1 confers resistance to cuproptosis and promotes hepatocellular carcinoma progression.","date":"2026","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/41501140","citation_count":1,"is_preprint":false},{"pmid":"41100003","id":"PMC_41100003","title":"Integrated Multi-omics and Experimental Validation Reveal FDX1/LIAS-Mediated Cuproptosis as a Potential Driver of Diabetic Kidney Disease.","date":"2025","source":"Biological trace element 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research","url":"https://pubmed.ncbi.nlm.nih.gov/40691025","citation_count":1,"is_preprint":false},{"pmid":"40987411","id":"PMC_40987411","title":"Targeting cuproptosis by FDX1 in acetaminophen-induced liver injury.","date":"2025","source":"Chemico-biological interactions","url":"https://pubmed.ncbi.nlm.nih.gov/40987411","citation_count":0,"is_preprint":false},{"pmid":"39670641","id":"PMC_39670641","title":"Knocking Down LncRNA-GAS5 Restores the Inhibition of Cuprotosis Protein FDX-1 by Acinetobacter baumannii.","date":"2024","source":"Polish journal of microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/39670641","citation_count":0,"is_preprint":false},{"pmid":"41407052","id":"PMC_41407052","title":"Mitochondrial uncoupling sensitizes gastric cancer cells to elesclomol-induced cuproptosis via FDX1/DLAT upregulation.","date":"2025","source":"Free radical biology & 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in mitochondria, whereas the related FDX2 is essential for Fe/S cluster and heme A biosynthesis. RNAi depletion of FDX1 did not impair Fe/S protein biogenesis, while FDX2 depletion caused severe Fe/S protein defects and iron accumulation. FDX2 could not efficiently substitute for FDX1 in steroid conversion assays, demonstrating distinct substrate specificity.\",\n      \"method\": \"RNAi depletion in human cells, steroid conversion assays, Fe/S protein activity measurements, iron uptake assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with multiple orthogonal functional readouts, replicated across pathways\",\n      \"pmids\": [\"20547883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FDX1 (but not FDX2) is specifically required for lipoyl cofactor biosynthesis in addition to steroidogenesis and heme a synthesis. FDX1 provides electrons to lipoyl synthase (LIAS) to initiate the radical chain reaction. Swapping small conserved sequence motifs between FDX1 and FDX2 changed their respective target specificities, identifying these motifs as determinants of functional specificity.\",\n      \"method\": \"RNAi/CRISPR loss-of-function, in vitro electron transfer assays, chimeric ferredoxin domain-swap experiments, lipoylation assays\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including domain-swap mutagenesis, in vitro reconstitution, and cellular KO phenotypes\",\n      \"pmids\": [\"36280795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FDX1 directly binds lipoyl synthase (LIAS) and promotes LIAS functional interaction with the lipoyl carrier protein GCSH, thereby regulating cellular protein lipoylation. This function is independent of indirect regulation via Fe/S cluster biosynthesis. Loss of FDX1 results in loss of lipoylation of four TCA cycle enzymes, loss of cellular respiration, and conditional lethality under low glucose.\",\n      \"method\": \"Co-immunoprecipitation/direct binding assay, metabolite profiling, transcriptional profiling, siRNA knockdown, CRISPR KO\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding demonstrated, multiple orthogonal metabolic and transcriptional readouts, replicated in peer-reviewed and preprint\",\n      \"pmids\": [\"37453661\", \"36778498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FDX1 acts as a mitochondrial matrix reductase that catalyzes reduction of elesclomol-Cu(II) to Cu(I), releasing copper into the mitochondrial matrix where it metalates cytochrome c oxidase. FDX1 KO cells fail to rescue cytochrome c oxidase abundance/activity when treated with elesclomol in copper-deficient conditions, while copper delivery to non-mitochondrial cuproproteins is partially FDX1-independent.\",\n      \"method\": \"CRISPR KO, biochemical copper measurements, cytochrome c oxidase activity/abundance assays, genetic rescue experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean CRISPR KO with multiple biochemical functional readouts, mechanistic distinction between FDX1-dependent and -independent pathways\",\n      \"pmids\": [\"36848556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Crystal structure of truncated bovine adrenodoxin (Adx/FDX1 ortholog) Adx(4-108) at 1.85 Å resolution reveals a compact (α+β) fold with a large core domain and smaller interaction domain containing residues required for binding adrenodoxin reductase and cytochrome P450. The [2Fe-2S] cluster is located at the edge; charged residues form an asymmetric electric potential implicated in electrostatic steering of redox partner interactions. A domain motion linked to redox state change is suggested.\",\n      \"method\": \"X-ray crystallography (MAD phasing), electrostatic surface analysis\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional domain identification, foundational structural paper\",\n      \"pmids\": [\"9551550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FDX1 is required for lipoylation under normoxia; under hypoxia (1% O2), FDX1 KO cells survive despite persistent loss of lipoylation, indicating that hypoxia rescues the lethality caused by lipoylation deficiency rather than restoring lipoylation via an alternative route.\",\n      \"method\": \"CRISPR KO, lipoylation western blot, hypoxic cell culture growth assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with multiple cellular and biochemical readouts distinguishing lipoylation from growth phenotype\",\n      \"pmids\": [\"37481209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Both human FDX1 and FDX2 bind the cysteine desulfurase complex (NFS1/ISD11/Acp) via residues near the Fe-S cluster, and both can donate electrons to support Fe-S cluster assembly on ISCU in vitro, though FDX2 binds the complex more tightly and supports faster cluster assembly than FDX1.\",\n      \"method\": \"NMR spectroscopy (interaction mapping), isothermal titration calorimetry, in vitro Fe-S cluster assembly assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted in vitro with multiple biophysical methods (NMR, ITC, functional assembly assay)\",\n      \"pmids\": [\"28001042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FDX1 is essential for biogenesis of mitochondrial cytochrome c oxidase (CcO) in mammalian cells. FDX1 KO rat cardiomyocytes show reduced CcO abundance and assembly, decreased copper and heme a/a3 levels. Overexpression of COX15 (heme a synthase) partially rescues COX1 abundance, placing FDX1 upstream of COX15 in heme a biosynthesis and CcO assembly.\",\n      \"method\": \"CRISPR-Cas9 KO, mitochondrial respiration assays, BN-PAGE CcO assembly analysis, copper measurement, heme a measurement, genetic rescue (COX15 overexpression)\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean CRISPR KO with multiple orthogonal assays and epistatic rescue experiment placing FDX1 upstream of COX15\",\n      \"pmids\": [\"37858707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Deep mutational scanning identified two conserved solvent-exposed acidic residues on FDX1 alpha helix 3 (D136 and D139) as essential for both cuproptosis induction and lipoylation in cells, despite retaining enzymatic activity in vitro, indicating helix 3 is a critical protein-protein interaction interface. Additionally, dihydrolipoamide dehydrogenase (DLD) was identified as an alternative FDX1 reductase both in vitro and in cells.\",\n      \"method\": \"Deep mutational scanning, charge-reversal mutagenesis, cell-based cuproptosis and lipoylation assays, in vitro enzymatic assays, structural analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis combined with in vitro and cellular functional assays, plus new interactor identification\",\n      \"pmids\": [\"41423452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"EPR spectroscopy demonstrated direct electron transfer from reduced FDX1 to the elesclomol-Cu(II) complex both in vitro and in vivo. FDX1 has higher binding affinity for elesclomol-Cu(II) than its homolog FDX2, explaining the functional specificity. Elesclomol-Cu(II) is a more efficient electron acceptor from FDX1 than free Cu(II).\",\n      \"method\": \"Electron paramagnetic resonance (EPR) spectroscopy, molecular docking, low-temperature EPR measurements in vitro and in vivo\",\n      \"journal\": \"Chemistry (Weinheim an der Bergstrasse, Germany)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct spectroscopic evidence of electron transfer mechanism with biophysical binding characterization\",\n      \"pmids\": [\"40484707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AKT1 phosphorylates FDX1, and this phosphorylation inhibits FDX1-induced cuproptosis and aerobic respiration while promoting glycolysis in triple-negative breast cancer cells. Copper activates AKT signaling which then suppresses FDX1 function.\",\n      \"method\": \"Phosphorylation assays, AKT1 inhibitor treatment, in vitro and in vivo functional assays, glycolysis and respiration measurements\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — identifies a PTM and pathway but detailed biochemical reconstitution of direct phosphorylation not fully described\",\n      \"pmids\": [\"39976173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Allosteric coupling exists between substrate binding and adrenodoxin (FDX1/Adx) recognition in CYP24A1. Chemical cross-linking/MS and NMR revealed that Adx binding induces a conformational change in CYP24A1 F and G helices required for substrate binding. A semiconserved nonpolar interface contact may influence CYP24A1 regioselectivity.\",\n      \"method\": \"Chemical cross-linking coupled to mass spectrometry, NMR spectroscopy, CYP24A1 functional assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biophysical methods revealing allosteric mechanism, single lab\",\n      \"pmids\": [\"32259445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Transcription factors SF1 and cJUN cooperate to activate the Fdx1 promoter in Leydig cells. SF1 is recruited to regulatory elements between -124 and -306 bp of the Fdx1 promoter. RNAi demonstrated SF1 is required for Fdx1 transcriptional regulation, while cJUN cooperates with SF1 but is not individually essential.\",\n      \"method\": \"Promoter-reporter assays, chromatin immunoprecipitation, RNA interference, transfection in MA-10 and TM3 Leydig cells\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ChIP and functional reporter assays with RNAi validation, single lab\",\n      \"pmids\": [\"28274746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Overexpression of adrenodoxin (FDX1/Adx) in human cells induces ROS production in mitochondria, disrupts mitochondrial transmembrane potential, causes cytochrome c release, and activates caspases leading to apoptosis in a p53-independent manner.\",\n      \"method\": \"Transient overexpression, ROS measurement, mitochondrial membrane potential assay (ΔΨ), cytochrome c release assay, caspase activation assay, cell viability assays across 11 cell lines\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal mechanistic readouts of mitochondrial apoptosis pathway, single lab\",\n      \"pmids\": [\"15927889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FDX1 interacts with G6PD and reduces its protein stability, leading to decreased NADPH and GSH levels, which enhances copper-induced cell death (cuproptosis) in endometriosis cells.\",\n      \"method\": \"Co-immunoprecipitation, protein stability assays, NADPH/GSH measurement, cell death assays, mouse model\",\n      \"journal\": \"Apoptosis : an international journal on programmed cell death\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP finding with partial functional follow-up, single lab\",\n      \"pmids\": [\"37119432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"p53 enhances FDX1-mediated cuproptosis in hepatocellular carcinoma via ferredoxin reductase (FDXR); p53 activation increases FDXR expression, which promotes FDX1 upregulation, leading to DLAT oligomerization and cuproptosis. FDXR knockdown reverses p53-mediated sensitization, placing FDXR between p53 and FDX1 in the cuproptosis pathway.\",\n      \"method\": \"p53 overexpression/knockdown, siRNA-mediated FDXR knockdown, DLAT oligomerization assays (western blot, immunofluorescence), cell viability assays, xenograft mouse model\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistatic pathway placement with multiple molecular readouts in vitro and in vivo\",\n      \"pmids\": [\"40630211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PUMA directly binds FDX1 at its R155 site and promotes DLAT/DLST oligomerization and reduction of LIAS expression, activating cuproptosis. PUMA binding also increases FDX1 ubiquitination at K182, leading to FDX1 degradation.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, dual-luciferase assays, RNA immunoprecipitation, ubiquitination assays, xenograft mouse model\",\n      \"journal\": \"Cellular oncology (Dordrecht, Netherlands)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP with site identification and functional readouts, single lab\",\n      \"pmids\": [\"41212484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX1 overexpression triggers mitochondrial permeability transition pore opening, leading to cytosolic release of mitochondrial DNA and double-stranded RNA. These DAMPs activate cGAS and RIG-I/MDA5 sensors, triggering TBK1 phosphorylation and type I interferon response that reshapes the tumor microenvironment in ccRCC, linking FDX1 to innate immune activation independent of cuproptosis.\",\n      \"method\": \"FDX1 overexpression, mtDNA/mt-dsRNA cytosolic release assays, cGAS/RIG-I pathway activation assays (TBK1 phosphorylation), orthotopic syngeneic mouse models, flow cytometry\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple molecular readouts with in vivo validation, single lab, novel mechanistic axis\",\n      \"pmids\": [\"41199656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX1 coordinates autophagic activity in ovarian cancer by modulating the AMPK and mTOR signaling pathways and preserving mitochondrial integrity/DLAT-DLST sulfation to maintain autophagic flux; FDX1 is predominantly localized to cytoplasm and mitochondria.\",\n      \"method\": \"FDX1 knockdown/overexpression, AMPK/mTOR pathway analysis, autophagic flux assays, mitochondrial integrity assays, in vivo xenograft\",\n      \"journal\": \"NPJ precision oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — pathway placement based on KD/OE with signaling readouts, single lab, limited mechanistic detail\",\n      \"pmids\": [\"40629130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL3-mediated m6A modification of FDX1 mRNA reduces FDX1 protein expression via the m6A reader FMR1, which inhibits FDX1 translation, thereby conferring resistance to cuproptosis in hepatocellular carcinoma.\",\n      \"method\": \"m6A-MeRIP, METTL3/FMR1 knockdown, FDX1 protein expression assays, cuproptosis sensitivity assays, xenograft models\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — m6A mapping with functional reader identification and cellular/in vivo validation\",\n      \"pmids\": [\"41501140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL16 lactylation at K229 (inhibited by SIRT2) promotes m6A modification on FDX1 mRNA, increasing FDX1 expression and thereby promoting cuproptosis in gastric cancer cells.\",\n      \"method\": \"m6A modification assays (MeRIP), METTL16 lactylation site mapping, SIRT2 inhibition, cuproptosis assays in vitro and in vivo\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — PTM (lactylation) writing/erasing with downstream m6A-FDX1 functional linkage, multiple methods\",\n      \"pmids\": [\"37863889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX1 promotes elesclomol-induced PANoptosis in DLBCL by increasing IRF3 phosphorylation, which activates IFN-β-dependent signaling. FDX1 overexpression sensitizes DLBCL cells to elesclomol-Cu cell death both in vitro and in patient-derived xenografts.\",\n      \"method\": \"FDX1 overexpression/knockdown, IRF3 phosphorylation assays, IFN-β signaling assays, PDX models, patient cohort correlation analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway placement with in vivo PDX validation, single lab\",\n      \"pmids\": [\"40240522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX1 directly binds FMR1 protein and upregulates its expression in ccRCC, which subsequently restrains Bcl-2 and N-cadherin while enhancing Cleaved Caspase-3 and E-cadherin expression; FMR1 knockdown reverses the anti-tumor effect of FDX1 overexpression.\",\n      \"method\": \"Co-IP assays, TMT proteomic sequencing, RNA-sequencing, orthotopic mouse models, FMR1 knockdown rescue assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with proteomic discovery and genetic rescue, single lab, limited biochemical mechanistic detail on FDX1-FMR1 interaction\",\n      \"pmids\": [\"40118855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FDX1 regulates HIF-1α protein levels under severe hypoxia in glioblastoma cells, and FDX1 knockdown reduces hypoxia-induced phosphorylation/activation of ATM, DNA-PKcs, Akt, and EGFR, thereby sensitizing cells to radiation. HIF-1α does not reciprocally regulate FDX1, placing FDX1 upstream of HIF-1α in this pathway.\",\n      \"method\": \"siRNA knockdown, phosphorylation western blotting, radiation sensitivity assays, HIF-1α protein measurement under hypoxia\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD with signaling readouts, single lab, epistatic inference from lack of reciprocal regulation\",\n      \"pmids\": [\"40244269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The lncRNA PVT1 directly binds to the FDX1 promoter at the -104/-41 bp region, increases H3K27ac deposition, and recruits transcription factor SF1 to activate FDX1 transcription, thereby promoting cuproptosis in colorectal cancer.\",\n      \"method\": \"ChIRP (chromatin isolation by RNA purification), ChIP, luciferase reporter assays, molecular docking, xenograft model\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct RNA-DNA binding demonstrated by ChIRP/ChIP with functional reporter validation\",\n      \"pmids\": [\"40505346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NFKB1 directly binds the FDX1 promoter to transcriptionally upregulate FDX1 in glioblastoma cells, as validated by dual-luciferase assay. NFKB1 knockdown reduces FDX1 expression, and FDX1 overexpression partially rescues the anti-tumor effect of NFKB1 knockdown, placing NFKB1 upstream of FDX1.\",\n      \"method\": \"Dual-luciferase promoter assay, NFKB1 knockdown, FDX1 overexpression rescue, in vivo intracranial xenograft\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct promoter binding validated by reporter assay with genetic epistasis in vitro and in vivo\",\n      \"pmids\": [\"40716652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"miR-21-5p directly binds the 3'-UTR of FDX1 mRNA to mediate its degradation in clear cell renal cell carcinoma, as validated by luciferase reporter assay. miR-21-5p inhibition suppresses ccRCC cell growth and invasion in a manner compensated by FDX1 knockdown.\",\n      \"method\": \"3'-UTR luciferase reporter assay, miR-21-5p mimic/inhibitor, FDX1 knockdown rescue, cell growth/invasion assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct 3'-UTR binding validated with reporter assay and genetic rescue, single lab\",\n      \"pmids\": [\"36611966\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FDX1 is a mitochondrial [2Fe-2S] ferredoxin that functions as an electron shuttle with distinct substrate specificity from its paralog FDX2: it reduces mitochondrial cytochrome P450 enzymes for steroid hormone biosynthesis, donates electrons to lipoyl synthase (LIAS) by direct binding to drive mitochondrial protein lipoylation (essential for TCA cycle function), supports heme a synthesis upstream of COX15 for cytochrome c oxidase biogenesis, and catalyzes the reduction of ionophore-bound Cu(II) to Cu(I) to release copper in mitochondria; its function is regulated post-translationally by AKT1-mediated phosphorylation and transcriptionally by SF1/cJUN and NFKB1, and its critical protein-protein interaction surface maps to acidic residues D136/D139 on alpha helix 3.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FDX1 is a mitochondrial [2Fe-2S] ferredoxin that serves as a specialized electron shuttle for multiple essential mitochondrial biosynthetic pathways, functionally distinct from its paralog FDX2. FDX1 donates electrons to mitochondrial cytochrome P450 enzymes for steroid hormone biosynthesis, to lipoyl synthase (LIAS) via direct binding to drive protein lipoylation required for TCA cycle function, and to COX15 for heme a synthesis during cytochrome c oxidase biogenesis; it also catalyzes reduction of ionophore-bound Cu(II) to Cu(I) for mitochondrial copper delivery [PMID:20547883, PMID:36280795, PMID:37453661, PMID:36848556, PMID:37858707]. Deep mutational scanning identified acidic residues D136/D139 on alpha helix 3 as a critical protein–protein interaction surface essential for lipoylation and cuproptosis in cells, while dihydrolipoamide dehydrogenase (DLD) functions as an alternative FDX1 reductase [PMID:41423452]. FDX1 expression is regulated transcriptionally by SF1/cJUN and NFKB1 and post-translationally by AKT1-mediated phosphorylation that inhibits its pro-oxidative and respiratory functions [PMID:28274746, PMID:40716652, PMID:39976173].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Determination of the crystal structure of the bovine FDX1 ortholog established the architectural basis for redox partner recognition, revealing a [2Fe-2S] cluster at the domain interface and an asymmetric charged surface that mediates electrostatic steering toward reductase and P450 partners.\",\n      \"evidence\": \"X-ray crystallography at 1.85 Å resolution with MAD phasing of truncated bovine adrenodoxin\",\n      \"pmids\": [\"9551550\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure was of a truncated construct; full-length human FDX1 structure not determined\", \"Redox-state-dependent domain motion inferred but not captured in two states\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Overexpression studies first linked FDX1 to mitochondrial ROS production and intrinsic apoptosis, demonstrating that excess FDX1 electron transfer disrupts mitochondrial membrane potential and triggers cytochrome c release independent of p53.\",\n      \"evidence\": \"Transient overexpression in 11 human cell lines with ROS, ΔΨm, cytochrome c release, and caspase activation measurements\",\n      \"pmids\": [\"15927889\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression artifact not ruled out—endogenous role in apoptosis unconfirmed\", \"No loss-of-function counterpart performed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Functional separation of the two human ferredoxins resolved a long-standing question: FDX1 is specifically required for mitochondrial P450-dependent steroidogenesis, whereas FDX2 supports Fe-S cluster and heme A biogenesis, and the two cannot efficiently substitute for each other.\",\n      \"evidence\": \"RNAi depletion in human cells with steroid conversion assays and Fe-S protein activity measurements\",\n      \"pmids\": [\"20547883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular determinants of substrate specificity between FDX1 and FDX2 were not identified at this stage\", \"Whether FDX1 had additional non-steroidogenic roles was unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"NMR and calorimetry showed that FDX1 can bind the Fe-S assembly machinery (NFS1/ISD11/Acp) and support cluster assembly in vitro, but with lower affinity and rate than FDX2, explaining why FDX1 loss does not impair Fe-S biogenesis in cells.\",\n      \"evidence\": \"NMR interaction mapping, isothermal titration calorimetry, and reconstituted in vitro Fe-S assembly assays\",\n      \"pmids\": [\"28001042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FDX1 ever contributes meaningfully to Fe-S assembly under physiological conditions remains unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Transcriptional regulation of FDX1 in steroidogenic cells was mapped, showing SF1 and cJUN cooperatively activate the Fdx1 promoter in Leydig cells, with SF1 being the essential factor.\",\n      \"evidence\": \"Promoter-reporter assays, ChIP, and RNAi in MA-10 and TM3 Leydig cells\",\n      \"pmids\": [\"28274746\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Regulation in non-steroidogenic tissues not addressed\", \"Whether SF1-dependent regulation is conserved in humans not shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Cross-linking MS and NMR revealed that FDX1 binding to CYP24A1 allosterically remodels the P450 active site, establishing that FDX1 is not merely an electron donor but an allosteric regulator of P450 substrate binding and regioselectivity.\",\n      \"evidence\": \"Chemical cross-linking/MS and NMR of FDX1-CYP24A1 complex with functional assays\",\n      \"pmids\": [\"32259445\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generalizability to other mitochondrial P450s not tested\", \"Structural detail of the allosteric conformational change limited\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A major expansion of FDX1 function was established: FDX1 specifically provides electrons to lipoyl synthase (LIAS) for lipoyl cofactor biosynthesis, and domain-swap chimeras between FDX1 and FDX2 identified short sequence motifs that determine target specificity.\",\n      \"evidence\": \"CRISPR KO, in vitro electron transfer assays, chimeric ferredoxin domain-swap mutagenesis, lipoylation assays\",\n      \"pmids\": [\"36280795\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FDX1-LIAS recognition not resolved at atomic level\", \"Whether additional mitochondrial targets exist beyond steroidogenic P450s and LIAS was open\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Multiple studies converged to show FDX1 directly binds LIAS and promotes its interaction with GCSH, that FDX1 loss abolishes lipoylation of four TCA cycle enzymes causing conditional lethality under normoxia, that FDX1 reduces ionophore-bound Cu(II) to deliver copper for cytochrome c oxidase metalation, and that FDX1 acts upstream of COX15 in heme a biosynthesis for CcO assembly.\",\n      \"evidence\": \"Co-IP/direct binding, CRISPR KO in human and rat cells, metabolite profiling, copper/heme measurements, COX15 genetic rescue, hypoxic rescue experiments\",\n      \"pmids\": [\"37453661\", \"36848556\", \"37858707\", \"37481209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FDX1 directly reduces COX15 or acts via an intermediary is not determined\", \"The relative contribution of each pathway (lipoylation, heme a, copper delivery) to the lethal phenotype is not fully dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Epitranscriptomic regulation of FDX1 was identified: METTL16-mediated m6A modification of FDX1 mRNA, controlled by METTL16 lactylation (inhibited by SIRT2), increases FDX1 expression and cuproptosis sensitivity in gastric cancer.\",\n      \"evidence\": \"MeRIP, METTL16 lactylation site mapping, SIRT2 inhibition, cuproptosis assays in vitro/in vivo\",\n      \"pmids\": [\"37863889\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Opposing result reported (METTL3/FMR1 decreases FDX1 in HCC); tissue- and m6A writer-specific effects not reconciled\", \"Whether m6A regulation operates on FDX1 under normal physiology is unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Deep mutational scanning identified D136 and D139 on FDX1 alpha helix 3 as a critical protein–protein interaction interface essential for lipoylation and cuproptosis in cells, and discovered DLD as an alternative FDX1 reductase, expanding the FDX1 electron-supply network beyond FDXR.\",\n      \"evidence\": \"Systematic charge-reversal mutagenesis, cell-based lipoylation and cuproptosis assays, in vitro enzymatic assays\",\n      \"pmids\": [\"41423452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of FDX1 with LIAS or other partners via helix 3\", \"Physiological relevance of DLD as FDX1 reductase versus FDXR not quantified in vivo\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"EPR spectroscopy provided direct spectroscopic evidence that FDX1 transfers electrons to elesclomol-Cu(II) both in vitro and in vivo, with higher affinity for this substrate than FDX2, establishing the biophysical basis for FDX1-specific copper reduction.\",\n      \"evidence\": \"EPR spectroscopy, molecular docking, low-temperature EPR in vitro and in cells\",\n      \"pmids\": [\"40484707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FDX1 reduces physiological (non-elesclomol) copper complexes in mitochondria is not addressed\", \"In vivo EPR was at low temperature, not under truly physiological conditions\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Post-translational regulation of FDX1 was identified: AKT1 phosphorylates FDX1, inhibiting its function in cuproptosis and aerobic respiration while promoting glycolysis, with copper itself activating AKT signaling in a feedback loop.\",\n      \"evidence\": \"Phosphorylation assays, AKT1 inhibitor treatment, respiration and glycolysis measurements in triple-negative breast cancer cells\",\n      \"pmids\": [\"39976173\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphorylation site on FDX1 not mapped\", \"Direct in vitro kinase assay not fully described\", \"Whether this regulatory axis operates in non-cancer cells unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"FDX1 overexpression was shown to trigger mitochondrial permeability transition pore opening, cytosolic release of mtDNA and mt-dsRNA, and activation of cGAS/STING and RIG-I/MDA5 innate immune pathways, linking FDX1 to type I interferon signaling independent of cuproptosis.\",\n      \"evidence\": \"FDX1 overexpression with mtDNA/dsRNA release assays, TBK1 phosphorylation, syngeneic orthotopic mouse models\",\n      \"pmids\": [\"41199656\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression-driven; whether endogenous FDX1 levels activate this axis is unknown\", \"Mechanism of mPTP opening by FDX1 not elucidated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the atomic-resolution structural basis of FDX1 partner selectivity via helix 3, whether FDX1 reduces physiological (non-ionophore) copper carriers, the relative in vivo contributions of FDXR versus DLD as FDX1 reductases, and whether FDX1's reported roles in innate immune activation and autophagy regulation reflect primary electron-transfer functions or indirect metabolic consequences.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No co-crystal structure of FDX1 with any physiological partner\", \"No identified physiological mitochondrial copper complex reduced by FDX1\", \"Relative pathway contributions to lethality not quantitatively dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 3, 9]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 7]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 8, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"LIAS\",\n      \"COX15\",\n      \"NFS1\",\n      \"DLD\",\n      \"CYP24A1\",\n      \"GCSH\",\n      \"FDXR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}