{"gene":"SOD2","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1992,"finding":"Crystal structure of human mitochondrial manganese superoxide dismutase (SOD2) determined at 2.2 Å resolution, revealing a homotetrameric enzyme where each subunit has an N-terminal helical hairpin and C-terminal α/β domain contributing ligands to the catalytic Mn site; two identical 4-helix bundles formed from N-terminal helical hairpins create novel tetrameric interfaces that stabilize the active sites.","method":"X-ray crystallography","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with full structural characterization","pmids":["1394426"],"is_preprint":false},{"year":1995,"finding":"Homozygous knockout of Sod2 in mice causes neonatal lethality with dilated cardiomyopathy, hepatic lipid accumulation, and metabolic acidosis; cytochemical analysis revealed severe reduction of succinate dehydrogenase (complex II) and aconitase activities in the heart, establishing that SOD2 is required to protect mitochondrial enzymes from superoxide-mediated inactivation.","method":"Homologous recombination knockout mouse, cytochemical enzyme activity assays","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 1–2 — foundational knockout study with multiple orthogonal phenotypic and biochemical readouts, widely replicated","pmids":["7493016"],"is_preprint":false},{"year":1995,"finding":"TNF receptor 1 (TNF-R1), but not TNF-R2, mediates TNF/lymphotoxin-induced induction of MnSOD expression; overexpression of MnSOD (but not CuZn-SOD or EC-SOD) enhances cellular resistance to radiation, and mitochondrial matrix targeting is required—CuZn-SOD or EC-SOD fused to the MnSOD mitochondrial signal sequence confer protection, whereas MnSOD lacking its signal sequence does not.","method":"Receptor-specific knockout/overexpression, antisense RNA suppression, mitochondrial targeting signal swap constructs, radiation survival assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic constructs with functional rescue experiments establishing receptor specificity and mitochondrial localization requirement","pmids":["7599209"],"is_preprint":false},{"year":1995,"finding":"HIV-1 Tat protein (C-terminal region) suppresses MnSOD mRNA, protein, and activity in T cells and HeLa cells, reducing glutathione levels and shifting the cellular redox state toward oxidation, thereby potentiating TNF-induced NF-κB activation and cytotoxicity.","method":"Stable transfection with tat gene, Tat truncation mutants, enzyme activity assays, glutathione measurements","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cell systems with truncation mutant dissection of Tat domains, single lab","pmids":["7859743"],"is_preprint":false},{"year":1996,"finding":"A diallelic polymorphism (Ala-9Val) in the mitochondrial targeting sequence (MTS) of human MnSOD gene was identified; computational analysis predicts the Ala-9 allele forms a typical amphiphilic helix required for mitochondrial transport, while the Val-9 allele disrupts this helix, suggesting a functional polymorphism affecting mitochondrial import efficiency.","method":"Population sequencing, secondary structure prediction of MTS amphiphilic helix","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — structural prediction validated by population genetics; functional impact on import is computational, not directly measured in vitro","pmids":["8806673"],"is_preprint":false},{"year":1998,"finding":"Peroxynitrite completely inhibits MnSOD enzymatic activity in vitro via nitration of Tyr34 (active-site residue) and Tyr45/Tyr193, and oxidative formation of dityrosine cross-links producing higher-molecular-mass species; hydrogen peroxide or nitric oxide alone had no effect, identifying peroxynitrite as the specific inactivating oxidant.","method":"In vitro enzyme inactivation assay, electrospray mass spectrometry, real-time spectral analysis, tetranitromethane and HOCl controls","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro assay with mass spectrometry identification of modified residues and multiple oxidant comparisons","pmids":["9484232"],"is_preprint":false},{"year":1998,"finding":"SOD2 knockout mice treated with the SOD mimetic MnTBAP (which does not cross the blood-brain barrier) are rescued from cardiomyopathy and hepatic pathology but develop spongiform degeneration of cortex and brainstem nuclei with gliosis, demonstrating that SOD2 loss causes progressive neurodegeneration driven by mitochondrial ROS specifically within the CNS.","method":"Sod2-/- mice, pharmacological SOD mimetic rescue (MnTBAP), neuropathological analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic model with pharmacological rescue dissecting tissue-specific requirements; replicated finding","pmids":["9462746"],"is_preprint":false},{"year":2000,"finding":"A cis-acting element in the 3' UTR of MnSOD mRNA (MnSOD-RE) functions as a translational enhancer in vivo: insertion of MnSOD-RE downstream of a CAT reporter increased CAT activity ~400% without altering CAT mRNA levels, demonstrating post-transcriptional regulation of MnSOD at the translational level.","method":"Transient transfection of CAT-reporter constructs with/without MnSOD 3'UTR element, RNA and activity measurements","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay with matched controls in cell culture, single lab","pmids":["10872821"],"is_preprint":false},{"year":2002,"finding":"FOXO3a directly transcriptionally activates MnSOD (SOD2) in quiescent cells: FOXO3a increases MnSOD mRNA and protein, reduces ROS, and protects quiescent cells from glucose-deprivation-induced apoptosis; this mechanism operates in the absence of PKB/Akt activity and was confirmed in mammalian cells, extending the C. elegans DAF-16/MnSOD longevity model.","method":"Overexpression and dominant-negative FOXO3a constructs, mRNA/protein quantification, ROS measurement, apoptosis assay, PKB inhibition","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple complementary genetic approaches with mechanistic validation across systems; highly cited foundational paper","pmids":["12239572"],"is_preprint":false},{"year":2008,"finding":"Epigenetic silencing of SOD2 in human breast cancer cells is mediated by decreased dimethyl H3K4 and acetylated H3K9 histone marks at SOD2 regulatory elements, creating repressive chromatin that reduces SP-1, AP-1, and NF-κB binding; treatment with HDAC inhibitors trichostatin A or sodium butyrate reactivates SOD2 expression.","method":"Chromatin immunoprecipitation (ChIP) for histone marks and transcription factors, HDAC inhibitor treatment, gene expression assays","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP with multiple marks and transcription factors; single lab but orthogonal methods","pmids":["18845242"],"is_preprint":false},{"year":2010,"finding":"Nuclear SIRT1 induces MnSOD expression in cardiomyocytes; in failing hearts SIRT1 translocates to the nucleus where it upregulates MnSOD, increasing resistance to oxidative stress. Resveratrol enhances nuclear SIRT1 and MnSOD induction; MnSOD siRNA abrogates the protective effects of nuclear SIRT1, demonstrating MnSOD is a required downstream effector.","method":"Subcellular fractionation, siRNA knockdown, overexpression constructs, in vivo hamster heart failure model with resveratrol treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — genetic loss-of-function (siRNA) and pharmacological gain-of-function with in vivo validation; single lab","pmids":["20089851"],"is_preprint":false},{"year":2011,"finding":"SIRT3 directly binds, deacetylates, and activates SOD2 at Lys68; acetylation of SOD2 at K68 decreases its enzymatic activity. Elevated ROS stimulates SIRT3 transcription, leading to SOD2 deacetylation and activation. SIRT3 co-expression synergistically increases SOD2-mediated ROS reduction, while SIRT3 depletion cancels it.","method":"Co-immunoprecipitation, in vitro deacetylation assay, acetylation-mimic and deacetylation-mimic mutants, enzyme activity assay, ROS measurement, SIRT3 overexpression/depletion","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of deacetylation, site-specific mutagenesis, enzyme activity assay, and cell-based validation; highly cited","pmids":["21566644"],"is_preprint":false},{"year":2011,"finding":"SOD2 protein stability is regulated by the deubiquitinating enzyme USP36: endogenous USP36 interacts with SOD2 (co-immunoprecipitation, yeast two-hybrid), SOD2 undergoes K48-linked polyubiquitination and proteasomal degradation, and USP36 reduces SOD2 ubiquitination and extends its half-life.","method":"2-DE/MALDI-TOF/MS proteomics, co-immunoprecipitation, yeast two-hybrid, ubiquitination assay, cycloheximide chase","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal IP and yeast two-hybrid plus functional ubiquitination assay; single lab","pmids":["21268071"],"is_preprint":false},{"year":2013,"finding":"SOD2 is exclusively localized to mitochondria and is absent from peroxisomes in mammalian cells and tissues; established by double-immunofluorescence on frozen/paraffin sections, post-embedding immunoelectron microscopy on LR White and ultrathin cryo-sections, and Western blot of biochemically purified peroxisomal fractions from mouse liver.","method":"Multiple immunofluorescence modalities, immunoelectron microscopy with multiple gold techniques, subcellular fractionation/Western blot","journal":"Histochemistry and cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal morphological and biochemical methods across multiple tissues definitively resolving conflicting prior reports","pmids":["23744526"],"is_preprint":false},{"year":2013,"finding":"Cyclin D1/CDK4 translocates to mitochondria in response to low-dose ionizing radiation (LDIR) and directly phosphorylates MnSOD at serine-106 (S106), enhancing its enzymatic activity and mitochondrial respiration. A mitochondria-targeted dominant-negative CDK4 or MnSOD-S106A mutant abolishes LDIR-induced mitochondrial enhancement and adaptive radioprotection.","method":"Mitochondrial fractionation, in vitro kinase assay with site-directed mutagenesis (S106A), mitochondria-targeted dominant-negative CDK4, enzymatic activity assay, in vivo mouse LDIR model","journal":"Free radical biology & medicine","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis plus in vivo validation; identifies specific phosphorylation site","pmids":["25578653"],"is_preprint":false},{"year":2015,"finding":"SOD2 upregulation in cancer cells establishes a steady-state mitochondrial H2O2 flux that activates AMPK and drives metabolic reprogramming to aerobic glycolysis (Warburg effect); restricting MnSOD expression or inhibiting AMPK suppresses the metabolic switch, establishing a MnSOD→H2O2→AMPK→glycolysis axis.","method":"siRNA knockdown, AMPK inhibition, metabolic flux assays, cell viability assay, in vitro transformation assays, clinical specimen analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic interventions (SOD2 KD + AMPK inhibition) with metabolic readouts; independently corroborated by clinical data","pmids":["25651975"],"is_preprint":false},{"year":2015,"finding":"CRISPR/Cas9-generated SOD2-null human cells (HEK293T) are completely devoid of MnSOD protein and activity, exhibiting impaired clonogenic survival, disrupted mitochondrial ultrastructure, preferential glycolysis over oxidative phosphorylation, and significantly impaired activities of mitochondrial complex I and II (containing Fe/S centers susceptible to superoxide), rescuable by pharmacological SOD mimetic GC4419 or hypoxia.","method":"CRISPR/Cas9 biallelic gene disruption, enzyme activity assays (complex I, II, MnSOD), Seahorse metabolic profiling, electron microscopy, pharmacological rescue","journal":"Free radical biology & medicine","confidence":"High","confidence_rationale":"Tier 1–2 — complete genetic null with multiple orthogonal biochemical and metabolic readouts and pharmacological rescue","pmids":["26208779"],"is_preprint":false},{"year":2017,"finding":"Sirt3 impairment in hypertension leads to SOD2 hyperacetylation and reduced SOD2 activity; angiotensin II induces Sirt3 S-glutathionylation, which inactivates Sirt3 and causes SOD2 acetylation. Mitochondria-targeted H2O2 scavenging prevents Sirt3 S-glutathionylation and SOD2 acetylation. SOD2 acetylation inversely correlates with SOD2 activity and directly correlates with hypertension severity in both mouse models and human essential hypertension.","method":"Sirt3-/- and SOD2+/- mouse models, angiotensin II infusion, S-glutathionylation assay, acetylation/activity measurements, mCAT transgenic mice, human patient samples","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic mouse models plus human data with mechanistic pathway dissection; strong preponderance of evidence","pmids":["28684630"],"is_preprint":false},{"year":2017,"finding":"During osteoblast differentiation, SIRT3 increases SOD2 activity through deacetylation specifically at K68; SIRT3 and SOD2 knockdown both suppress osteoblast differentiation, and SOD2 overexpression rescues differentiation in SIRT3-deficient osteoblasts, placing SIRT3→SOD2(K68 deacetylation) as required for eliminating mitochondrial superoxide during osteoblast differentiation and bone formation.","method":"siRNA knockdown, overexpression, SIRT3-/- mouse model, mitochondrial superoxide measurement, deacetylation at K68, osteoblast differentiation assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 — genetic in vivo and in vitro models with site-specific mechanistic detail and rescue experiments","pmids":["28914882"],"is_preprint":false},{"year":2019,"finding":"Acetylation of SOD2 at lysine 68 (K68Ac) converts the enzyme from a homotetrameric superoxide dismutase to a monomeric peroxidase; the K68Q acetylation-mimic mutant behaves as a tumor promoter (not suppressor) in transformation and xenograft assays, cells expressing K68Q or physically K68-acetylated SOD2 exhibit resistance to tamoxifen, and cells selected for tamoxifen resistance show increased K68-Ac and monomeric MnSOD.","method":"In vitro transformation and xenograft assays, biochemical stoichiometry analysis, acetylation-mimic (K68Q) and physical K68-Ac protein, peroxidase activity assay, size-exclusion chromatography (monomer vs. tetramer), tamoxifen resistance selection","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — enzymatic activity reconstitution with acetylation mimics, structural (oligomeric state) characterization, and functional cancer biology validation","pmids":["31160585"],"is_preprint":false},{"year":2019,"finding":"Acetylation of SOD2 at K68 promotes a functional switch: K68Ac stabilizes HIF2α via increased mitochondrial ROS, which in turn drives transcription of stemness genes (Oct4, Sox2, Nanog) in breast cancer cells, linking mitochondrial SOD2 acetylation state to cancer stem cell reprogramming.","method":"K68 acetylation-mimic expression, HIF2α protein stabilization assay, stemness gene expression, ROS measurement, siRNA knockdown of HIF2α","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — acetylation mimic with defined downstream pathway via HIF2α; single lab","pmids":["31591207"],"is_preprint":false},{"year":2019,"finding":"A homozygous missense variant in SOD2 (c.542G>T, p.Gly181Val) causes lethal neonatal dilated cardiomyopathy in a human patient; patient fibroblasts show significantly elevated superoxide levels and reduced SOD2 catalytic activity; lentiviral complementation with wild-type SOD2 completely restores mitochondrial SOD2 activity.","method":"Exome sequencing, hydroethidine oxidation assay (superoxide measurement), enzyme activity assay in patient fibroblasts and muscle, lentiviral complementation with wild-type SOD2","journal":"Journal of medical genetics","confidence":"High","confidence_rationale":"Tier 1–2 — patient cells with biochemical loss of function confirmed by complementation rescue; direct causal link between SOD2 variant and disease established","pmids":["31494578"],"is_preprint":false},{"year":2019,"finding":"SOD2 mRNA translation is rapidly induced within 30 min of matrix detachment via the RNA-binding protein HuR/ELAVL1: anchorage-independence triggers cytosolic HuR accumulation, HuR binds SOD2 mRNA 3'UTR, and HuR siRNA knockdown abolishes the increase in SOD2 mRNA association with heavy polyribosomes and nascent SOD2 protein synthesis. p38 MAPK activation is required upstream of HuR-SOD2 mRNA interaction.","method":"Polyribosome profiling, RNA immunoprecipitation, HuR siRNA knockdown, p38 inhibition, nascent protein synthesis assay","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 — polyribosome profiling plus RIP and siRNA with kinase dependency established; single lab","pmids":["35594792"],"is_preprint":false},{"year":2021,"finding":"Propionylation of Sod2 at lysine 132 (K132) suppresses Sod2 enzymatic activity in zebrafish intestine; global lysine propionylation analysis identified K132 as the modified site, and biochemical assays confirmed K132 propionylation reduces activity. Sirt3 can remove the propionyl group (de-propionylation), restoring Sod2 activity.","method":"Global lysine propionylation proteomics, site-specific biochemical activity assay, Sirt3 de-propionylation assay, zebrafish intestinal model","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 1–2 — site-specific mass spectrometry identification of K132 propionylation with enzymatic activity validation and eraser identification; single organism model","pmids":["34142031"],"is_preprint":false},{"year":2021,"finding":"MnSOD K68 acetylation (K68Ac) causes monomeric SOD2 to incorporate iron (instead of manganese) at the active site, maximally inducing peroxidase activity; molecular dynamics of MnSOD-K68Ac and K68Q show significant change in charge distribution along α1 and α2 helices adjacent to the Mn2+ binding site, destabilizing the tetramer and explaining monomer enrichment and altered metal incorporation.","method":"Amber codon suppression to generate physically K68-Ac protein, peroxidase activity assay, metal analysis, molecular dynamics simulation, acetylation-mimic (K68Q) expression","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 1 — physical acetylation with enzymatic assay and molecular dynamics; single lab with computational support","pmids":["33867840"],"is_preprint":false},{"year":2006,"finding":"C/EBPβ is required for TNF-induced MnSOD expression and protection against TNF-induced apoptosis: C/EBPβ-deficient fibroblasts fail to induce MnSOD upon TNF stimulation and undergo apoptosis; ectopic C/EBPβ rescues MnSOD induction; MnSOD expression alone in C/EBPβ-deficient cells bypasses the requirement for C/EBPβ in survival. Mechanistically, C/EBPβ is required for NF-κB p65 binding to the intronic TNF-response element of MnSOD and for histone acetylation at that element.","method":"C/EBPβ-deficient fibroblasts, ectopic expression rescue, ChIP for NF-κB p65 and histone acetylation at MnSOD intronic element, MnSOD stable transfection","journal":"Apoptosis","confidence":"Medium","confidence_rationale":"Tier 2 — genetic loss-of-function with rescue and ChIP mechanistic dissection; single lab","pmids":["16850160"],"is_preprint":false}],"current_model":"SOD2 (MnSOD) is a homotetrameric manganese-containing enzyme exclusively localized to the mitochondrial matrix where it catalyzes dismutation of superoxide to H2O2; its enzymatic activity is regulated post-translationally by SIRT3-mediated deacetylation at K68 (activating), CDK4-mediated phosphorylation at S106 (activating), USP36-mediated deubiquitination (stabilizing), and peroxynitrite-mediated nitration of the active-site Tyr34 (inactivating); acetylation at K68 additionally switches SOD2 from a tetrameric superoxide dismutase to a monomeric peroxidase that incorporates iron and promotes cancer stem cell reprogramming via mtROS–HIF2α signaling, while transcriptional activation occurs through FOXO3a, NF-κB (requiring C/EBPβ co-factor), and nuclear SIRT1, and translational upregulation is mediated by HuR binding to a 3'UTR element in response to anchorage-independence."},"narrative":{"teleology":[{"year":1992,"claim":"Determination of the 2.2 Å crystal structure established that SOD2 operates as a homotetramer with a novel 4-helix-bundle interface that positions four independent Mn active sites, providing the first atomic framework for understanding catalysis and regulation.","evidence":"X-ray crystallography of human mitochondrial MnSOD","pmids":["1394426"],"confidence":"High","gaps":["Mechanism of superoxide entry into the active site channel not resolved at this resolution","No structure with substrate or product analogs"]},{"year":1995,"claim":"Mouse knockout studies answered whether SOD2 is essential: Sod2−/− mice die neonatally with dilated cardiomyopathy and loss of mitochondrial Fe–S cluster enzyme activities, establishing SOD2 as the non-redundant mitochondrial superoxide scavenger required for oxidative phosphorylation and organismal survival.","evidence":"Homozygous Sod2 knockout mice with cytochemical enzyme activity assays; complementary studies showed TNF-R1-mediated MnSOD induction and requirement for mitochondrial targeting","pmids":["7493016","7599209"],"confidence":"High","gaps":["Relative contributions of individual respiratory complex damage versus aconitase loss to lethality were not separated","Tissue-specific conditional knockouts not yet available at this stage"]},{"year":1998,"claim":"Two advances resolved tissue-specific vulnerability and a key inactivation mechanism: pharmacological SOD mimetic rescue of Sod2−/− cardiac/hepatic pathology unmasked an obligate role for SOD2 in preventing CNS spongiform neurodegeneration, and biochemical reconstitution showed peroxynitrite (not NO or H₂O₂ alone) inactivates SOD2 via Tyr34 nitration.","evidence":"MnTBAP rescue of Sod2−/− mice with neuropathology analysis; in vitro peroxynitrite inactivation with electrospray mass spectrometry mapping of Tyr34, Tyr45, Tyr193 modifications","pmids":["9462746","9484232"],"confidence":"High","gaps":["In vivo relevance of Tyr34 nitration in disease settings not yet demonstrated","Peroxynitrite-mediated dityrosine cross-linking stoichiometry and reversibility unclear"]},{"year":2002,"claim":"Identification of FOXO3a as a direct transcriptional activator of SOD2 linked insulin/Akt signaling to mitochondrial antioxidant defense, explaining how quiescent or nutrient-deprived cells upregulate SOD2 and connecting SOD2 to the conserved DAF-16/FOXO longevity pathway.","evidence":"Overexpression and dominant-negative FOXO3a constructs with mRNA, protein, ROS, and apoptosis readouts in mammalian cells","pmids":["12239572"],"confidence":"High","gaps":["Whether FOXO3a binds the SOD2 promoter directly or through intermediaries was not resolved by ChIP in this study","Relative contribution of FOXO3a versus NF-κB to SOD2 transcription in different cell types not quantified"]},{"year":2006,"claim":"Discovery that C/EBPβ is an obligate cofactor for NF-κB-dependent SOD2 induction resolved how TNF drives SOD2 transcription: C/EBPβ is required for NF-κB p65 binding and histone acetylation at the intronic TNF-response element, and SOD2 expression alone bypasses the survival requirement for C/EBPβ.","evidence":"C/EBPβ-deficient fibroblasts with ectopic rescue, ChIP for NF-κB p65 and histone acetylation at SOD2 intronic element","pmids":["16850160"],"confidence":"Medium","gaps":["Whether C/EBPβ physically interacts with p65 at the SOD2 locus or acts through chromatin remodeling was not distinguished","Role of C/EBPβ in non-TNF stimuli for SOD2 transcription not tested"]},{"year":2011,"claim":"Two regulatory mechanisms were defined: SIRT3 directly deacetylates SOD2 at K68 to activate its dismutase function, and USP36 deubiquitinates K48-linked polyubiquitin chains on SOD2 to prevent proteasomal degradation, establishing that SOD2 activity and abundance are under distinct post-translational control.","evidence":"In vitro deacetylation reconstitution with K68 mutagenesis and enzyme activity assays (SIRT3); co-IP, yeast two-hybrid, ubiquitination/cycloheximide chase (USP36)","pmids":["21566644","21268071"],"confidence":"High","gaps":["Identity of the E3 ubiquitin ligase targeting SOD2 for K48-linked ubiquitination was not determined","Relative contribution of K68 acetylation versus other acetylation sites to total SOD2 activity regulation not quantified"]},{"year":2013,"claim":"CDK4 was identified as a mitochondrial kinase that phosphorylates SOD2 at S106 to enhance activity in response to low-dose ionizing radiation, while rigorous immunolocalization definitively confirmed SOD2 is exclusively mitochondrial matrix-resident with no peroxisomal pool.","evidence":"In vitro kinase assay with S106A mutagenesis and mitochondria-targeted dominant-negative CDK4 in vivo; multi-modal immunoelectron microscopy and subcellular fractionation across tissues","pmids":["25578653","23744526"],"confidence":"High","gaps":["Whether CDK4-mediated S106 phosphorylation operates outside of radiation contexts is unknown","Phosphatase that reverses S106 phosphorylation not identified"]},{"year":2015,"claim":"Overexpressed SOD2 was shown to generate a sustained mitochondrial H₂O₂ flux that activates AMPK and drives aerobic glycolysis, revealing a paradoxical pro-tumorigenic role for the canonical tumor suppressor when expression is elevated in cancer cells.","evidence":"SOD2 siRNA, AMPK inhibition, Seahorse metabolic profiling, transformation assays, clinical specimen correlation","pmids":["25651975"],"confidence":"High","gaps":["Threshold of SOD2 expression at which the switch from tumor suppression to promotion occurs is not defined","Whether catalase co-expression fully reverses the metabolic reprogramming was not tested"]},{"year":2017,"claim":"The SIRT3–SOD2 K68 deacetylation axis was shown to operate in disease-relevant settings: angiotensin II-induced S-glutathionylation of SIRT3 causes SOD2 hyperacetylation in hypertension, and SIRT3-dependent SOD2 activation is required for osteoblast differentiation and bone formation.","evidence":"Sirt3−/−, SOD2+/− mice, angiotensin II infusion with human patient samples; SIRT3 knockdown/overexpression with SOD2 rescue in osteoblast differentiation","pmids":["28684630","28914882"],"confidence":"High","gaps":["Whether other SIRT3 substrates contribute to hypertensive pathology independently of SOD2 not fully excluded","Site-specific acetylation status of SOD2 in hypertensive human patients not mapped"]},{"year":2019,"claim":"K68 acetylation was found to fundamentally switch SOD2's quaternary structure and catalytic identity: acetylated K68 destabilizes the tetramer, favoring iron-incorporating monomers with peroxidase activity that stabilize HIF2α and drive cancer stemness gene expression, and a human homozygous SOD2 missense variant (G181V) was identified as a cause of lethal neonatal dilated cardiomyopathy, confirming the mouse phenotype in humans.","evidence":"Physical K68-Ac protein via amber codon suppression, size-exclusion chromatography, metal analysis, xenograft/transformation assays, HIF2α stabilization/siRNA; exome sequencing of patient with lentiviral complementation rescue in fibroblasts","pmids":["31160585","31591207","31494578"],"confidence":"High","gaps":["In vivo fraction of endogenous SOD2 that is monomeric/iron-bound in tumors not quantified","Whether peroxidase activity of monomeric SOD2 has physiological substrates beyond H₂O₂ is unknown"]},{"year":2021,"claim":"Molecular dynamics and physical K68-Ac reconstitution explained how acetylation destabilizes the α1/α2 helix interface to promote monomer formation and iron incorporation, and a novel acyl modification—K132 propionylation—was identified as an additional SIRT3-reversible mechanism that suppresses SOD2 activity.","evidence":"Amber codon suppression with metal and peroxidase assays plus molecular dynamics; global propionylation proteomics in zebrafish intestine with SIRT3 de-propionylation","pmids":["33867840","34142031"],"confidence":"Medium","gaps":["K132 propionylation has only been characterized in zebrafish; relevance in mammalian systems is untested","Full structural model of monomeric Fe-SOD2 at atomic resolution is lacking"]},{"year":null,"claim":"Key unresolved questions include the identity of the E3 ubiquitin ligase targeting SOD2, the structural basis of the tetramer-to-monomer transition at atomic resolution, the in vivo stoichiometry of K68 acetylation in normal versus tumor tissues, and whether the peroxidase activity of monomeric SOD2 has specific endogenous substrates or signaling targets beyond bulk H₂O₂.","evidence":"","pmids":[],"confidence":"Low","gaps":["E3 ligase for SOD2 ubiquitination unknown","No high-resolution structure of monomeric Fe-SOD2-K68Ac","Quantitative in vivo acetylation stoichiometry at K68 in human tissues not mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016209","term_label":"antioxidant activity","supporting_discovery_ids":[0,1,5,11,14,16,19]},{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,5,16,19,24]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,13,14,16]}],"pathway":[{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[1,5,6,15,16,17]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[15,16]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,25]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[19,20,21]}],"complexes":[],"partners":["SIRT3","CDK4","USP36","FOXO3A","ELAVL1","CEBPB","RELA"],"other_free_text":[]},"mechanistic_narrative":"SOD2 (MnSOD) is the principal mitochondrial matrix antioxidant enzyme, catalyzing dismutation of superoxide radical to hydrogen peroxide as a manganese-dependent homotetramer, thereby protecting Fe–S cluster-containing respiratory chain complexes (I, II) and aconitase from oxidative inactivation [PMID:1394426, PMID:7493016, PMID:26208779]. Its activity is positively regulated by SIRT3-mediated deacetylation at K68 and CDK4-mediated phosphorylation at S106, while peroxynitrite-mediated nitration of the active-site Tyr34 is inactivating [PMID:21566644, PMID:25578653, PMID:9484232]; acetylation at K68 switches SOD2 from a tetrameric dismutase to a monomeric iron-incorporating peroxidase that promotes cancer stemness via mtROS–HIF2α signaling [PMID:31160585, PMID:31591207]. Homozygous loss-of-function SOD2 variants cause lethal neonatal dilated cardiomyopathy in mice and humans, and transcriptional control is mediated by FOXO3a, NF-κB (requiring C/EBPβ cofactor), and nuclear SIRT1, with translational upregulation via HuR binding the SOD2 3′UTR upon matrix detachment [PMID:7493016, PMID:31494578, PMID:12239572, PMID:16850160, PMID:20089851, PMID:35594792]."},"prefetch_data":{"uniprot":{"accession":"P04179","full_name":"Superoxide dismutase [Mn], mitochondrial","aliases":[],"length_aa":222,"mass_kda":24.8,"function":"Destroys superoxide anion radicals which are normally produced within the cells and which are toxic to biological systems","subcellular_location":"Mitochondrion matrix","url":"https://www.uniprot.org/uniprotkb/P04179/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SOD2","classification":"Common 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gene structure analysis\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — foundational biochemical characterization replicated across multiple labs, consistent with the entire corpus\",\n      \"pmids\": [\"12126755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SOD2 is exclusively localized to mitochondria and is not present in peroxisomes, as demonstrated by double-immunofluorescence, immunoelectron microscopy, and biochemical subcellular fractionation of mouse liver.\",\n      \"method\": \"Double-immunofluorescence on frozen and paraffin sections, post-embedding immunoelectron microscopy, immunogold labeling of ultrathin cryosections, Western blot of purified subcellular fractions\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (immunofluorescence, immunoelectron microscopy, biochemical fractionation) in a single rigorous study\",\n      \"pmids\": [\"23744526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MnSOD enzymatic activity is regulated by reversible acetylation of specific, evolutionarily conserved lysine residues; SIRT3 deacetylates MnSOD in mitochondria, increasing its superoxide-scavenging activity in response to changes in nutrient or redox status.\",\n      \"method\": \"In vitro enzymatic activity assay, acetylation/deacetylation assays, SIRT3 overexpression and knockdown\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated across multiple studies with orthogonal methods; foundational finding confirmed by many independent labs\",\n      \"pmids\": [\"21386137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIRT3 deacetylates SOD2 at K68, enhancing its enzymatic activity; loss of SIRT3 leads to SOD2 hyperacetylation and reduced activity, increasing mitochondrial superoxide and promoting vascular oxidative stress and hypertension.\",\n      \"method\": \"SIRT3 knockout mice, SOD2+/- mice, SOD2 acetylation assay, mitochondrial O2•- measurement, endothelial function assays, analysis of human hypertensive subjects\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models (KO mice, haploinsufficient mice), in vitro and in vivo validation, confirmed in human subjects\",\n      \"pmids\": [\"28684630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CDK4, upon relocalization to mitochondria in response to low-dose ionizing radiation, directly phosphorylates MnSOD at serine-106 (S106), enhancing its enzymatic activity and mitochondrial respiration; expression of a dominant-negative CDK4 or MnSOD-S106 mutant reverses this effect.\",\n      \"method\": \"Mitochondria-targeted dominant negative CDK4 expression, MnSOD-S106 mutagenesis, in vitro kinase assay, MnSOD enzymatic activity assay, mitochondrial respiration measurement\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct phosphorylation demonstrated by mutagenesis and in vitro kinase assay, confirmed in vivo in mouse skin\",\n      \"pmids\": [\"25578653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Acetylation of MnSOD at lysine 68 (K68-Ac) converts the homotetramer into a monomer that functions as a peroxidase rather than a superoxide dismutase; K68-Ac is associated with tumor promotion, stem cell reprogramming via HIF2α, and resistance to tamoxifen in breast cancer.\",\n      \"method\": \"In vitro transformation assay, xenograft growth assay, acetylation mimic mutant (MnSOD-K68Q), biochemical stoichiometry analysis, peroxidase activity assay, physical K68-Ac protein characterization\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution and mutagenesis demonstrating functional switch from dismutase to peroxidase, confirmed by physical acetylation and mimic mutant\",\n      \"pmids\": [\"31160585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SOD2 K68 acetylation (K68-Ac) promotes stemness reprogramming in breast cancer by increasing mitochondrial ROS (mtROS), which stabilize HIF2α, a transcription factor upstream of stemness genes (Oct4, Sox2, Nanog).\",\n      \"method\": \"SOD2-K68Ac mimic expression, mtROS measurement, HIF2α stabilization assay, stemness gene expression analysis in breast cancer cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway established with multiple orthogonal methods in breast cancer cells\",\n      \"pmids\": [\"31591207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MnSOD K68 acetylation leads to cisplatin and doxorubicin resistance; the K68Q mimic monomer incorporates iron and maximally induces peroxidase activity; molecular dynamics shows that K68-Ac alters charge distribution near the Mn2+ binding site, destabilizing the tetramer.\",\n      \"method\": \"Acetylation mimic mutant expression, in vitro selection for drug resistance, molecular dynamics simulation, iron incorporation assay, peroxidase activity assay\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, mutagenesis, molecular dynamics, and functional assays in one study\",\n      \"pmids\": [\"33867840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"USP36, a deubiquitinating enzyme, interacts with SOD2 (identified by 2-DE, MALDI-TOF/MS, and co-immunoprecipitation), reduces its polyubiquitination, and stabilizes SOD2 protein by extending its half-life, preventing its degradation through the ubiquitin-proteasomal pathway.\",\n      \"method\": \"2-DE and MALDI-TOF/MS, co-immunoprecipitation, yeast two-hybrid, ubiquitination assay, protein half-life assay\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (MS, co-IP, yeast two-hybrid) establishing USP36 as a deubiquitinase for SOD2\",\n      \"pmids\": [\"21268071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SOD2 (MnSOD) upregulation in cancer cells generates a steady flow of mitochondrial H2O2 that activates AMPK and drives a metabolic shift to glycolysis (Warburg effect); restricting MnSOD expression or inhibiting AMPK suppresses the metabolic switch.\",\n      \"method\": \"MnSOD knockdown/overexpression, AMPK inhibition, mitochondrial H2O2 measurement, metabolic flux analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis and loss-of-function with defined metabolic phenotype, replicated in multiple cancer cell lines and clinical data\",\n      \"pmids\": [\"25651975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SOD2 null human cells (created by CRISPR/Cas9 biallelic disruption) exhibit impaired mitochondrial bioenergetics, perturbations in mitochondrial ultrastructure, preferential glycolysis over oxidative phosphorylation, and significantly impaired activities of mitochondrial complex I and II (due to disruption of Fe/S centers).\",\n      \"method\": \"CRISPR/Cas9 biallelic gene disruption, clonogenic assay, mitochondrial ultrastructure analysis (EM), bioenergetic profiling, complex I/II activity assays\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — clean genetic KO with multiple orthogonal functional phenotype readouts\",\n      \"pmids\": [\"26208779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIRT3 deacetylates SOD2 at K68 during osteoblast differentiation, enhancing SOD2 activity to eliminate excess mitochondrial superoxide; both SOD2 and SIRT3 knockdown suppressed osteoblast differentiation, and SIRT3-deficient mice exhibit osteopenia with osteoblast dysfunction.\",\n      \"method\": \"SOD2 and SIRT3 knockdown (siRNA), SIRT3 knockout mice, overexpression rescue, mitochondrial superoxide measurement, osteoblast differentiation assay\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro knockdown, in vivo KO mouse model, and rescue experiments with multiple readouts\",\n      \"pmids\": [\"28914882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIRT3 deacetylation of SOD2 is required for SIRT3-mediated protection against cadmium-induced mitochondrial superoxide-dependent autophagy; a catalytic mutant of SIRT3 (H248Y) lacking deacetylase activity cannot suppress Cd-induced autophagy.\",\n      \"method\": \"SIRT3 overexpression, catalytic mutant SIRT3(H248Y), co-immunoprecipitation, SOD2 acetylation assay, mitochondrial O2•- measurement, autophagy assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — active-site mutagenesis combined with biochemical and cellular assays\",\n      \"pmids\": [\"26120888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SOD2 gene silencing in human breast cancer cells is mediated by epigenetic changes including decreased dimethyl H3K4 and acetylated H3K9 at key regulatory elements, creating a repressive chromatin structure that impairs SP-1, AP-1, and NFκB binding; HDAC inhibitors reactivate SOD2 expression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), transcription factor ChIP, HDAC inhibitor treatment (trichostatin A, sodium butyrate)\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal ChIP experiments with HDAC inhibitor rescue establishing epigenetic mechanism\",\n      \"pmids\": [\"18845242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"TNF-R1 (but not TNF-R2) mediates TNF/LT-induced MnSOD expression; overexpression of MnSOD specifically in mitochondria (via its matrix signal sequence) but not cytoplasmic SOD1 or EC-SOD3 confers protection against radiation; MnSOD lacking the mitochondrial matrix signal does not provide protection.\",\n      \"method\": \"Receptor-specific TNF signaling dissection, MnSOD overexpression with/without mitochondrial targeting signal, antisense MnSOD knockdown, radiation survival assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — receptor assignment by domain-deletion/swap and functional rescue experiments\",\n      \"pmids\": [\"7599209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"C/EBPβ is required for TNF-induced MnSOD gene expression; C/EBPβ deficiency prevents TNF-induced MnSOD induction and sensitizes cells to apoptosis; mechanistically, C/EBPβ is required for NF-κB p65 binding to the intronic TNF response element of SOD2 and for histone acetylation at this element.\",\n      \"method\": \"C/EBPβ-deficient fibroblasts, ectopic C/EBPβ expression, MnSOD stable transfection (complementation), ChIP for NF-κB p65 and histone acetylation\",\n      \"journal\": \"Apoptosis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic complementation, ChIP, and specific rescue establishing chromatin mechanism\",\n      \"pmids\": [\"16850160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"miR-146a binds to a site in the SOD2 mRNA 3'UTR (confirmed by luciferase reporter assay) and downregulates SOD2 protein expression; antisense-miR-146a reverses the H2O2-induced decrease in SOD2 levels and rescues cell viability.\",\n      \"method\": \"Sequence analysis, luciferase reporter assay, miR-146a overexpression, antisense inhibition, Western blot\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase reporter validates binding, single lab study\",\n      \"pmids\": [\"23935993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A cis-element in the 3' UTR of MnSOD mRNA (MnSOD-response element, MnSOD-RE) functions as a translational enhancer in vivo, increasing CAT protein from a heterologous reporter by ~400% without changing mRNA levels when transfected into NIH/3T3 cells.\",\n      \"method\": \"Transfection of posttranscriptional reporter constructs, CAT activity assay, mRNA quantification\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional validation of a cis-regulatory element, single lab\",\n      \"pmids\": [\"10872821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Estradiol (E2) upregulates SOD2 in endothelial cells by tethering estrogen receptor (ER) to Sp1, increasing Sp1 binding to GC-box elements on the SOD2 promoter; ERα mediates E2-induced activation while ERβ maintains basal expression; SOD2 knockdown worsens ROS generation despite E2 presence.\",\n      \"method\": \"Promoter binding assay (Sp1/ER tethering), ER subtype-specific knockdown, SOD2 lentiviral knockdown/overexpression, ROS measurement, vascular function assay in mice\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mechanistic promoter analysis with in vivo gene therapy validation, single lab\",\n      \"pmids\": [\"25462070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HuR/ELAVL1 RNA-binding protein binds SOD2 mRNA in anchorage-independent conditions (triggered by p38 MAPK activation), increasing SOD2 mRNA translation as shown by polyribosome profiling; HuR siRNA knockdown prevents the increase in SOD2 association with heavy polyribosomes and nascent SOD2 protein synthesis.\",\n      \"method\": \"Polyribosome profiling, HuR siRNA knockdown, co-immunoprecipitation of HuR-SOD2 mRNA, p38 inhibition, nascent protein synthesis assay\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — polyribosome profiling combined with RNA-binding protein IP and specific KD with defined molecular phenotype\",\n      \"pmids\": [\"35594792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Propionylation of Sod2 at lysine 132 (K132) suppresses Sod2 activity; Sirt3 regulates Sod2 activity via de-propionylation; excess propionate causes K132-propionylated Sod2 and oxidative stress in zebrafish intestine.\",\n      \"method\": \"Global lysine propionylation proteomics, site-specific biochemical assay of K132-propionylated Sod2, Sirt3 modulation, Sod2 activity assay in zebrafish intestinal samples\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — site-specific modification identified by proteomics and validated by functional assay in vivo (zebrafish ortholog)\",\n      \"pmids\": [\"34142031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous missense variant in SOD2 (p.Gly181Val) causes lethal neonatal dilated cardiomyopathy; patient fibroblasts show increased superoxide levels and reduced SOD2 catalytic activity; lentiviral complementation with wild-type SOD2 completely restores mitochondrial SOD2 activity.\",\n      \"method\": \"Exome sequencing, hydroethidine oxidation assay for O2•-, SOD2 enzymatic activity assay in patient fibroblasts and muscle, lentiviral complementation\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — patient variant with biochemical validation and complementation rescue establishing causality\",\n      \"pmids\": [\"31494578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ACT001 directly binds IKKβ and inhibits its phosphorylation, thereby inhibiting NF-κB activation; this decreases NF-κB-targeted MnSOD expression, elevates ROS, and causes G2/M arrest and apoptosis in glioblastoma cells; IKKβ overexpression reverses MnSOD and NOX1 changes.\",\n      \"method\": \"Drug-target binding assay, IKKβ phosphorylation assay, NF-κB reporter, MnSOD expression rescue by IKKβ overexpression, iTRAQ proteomics, ROS measurement, cell cycle analysis\",\n      \"journal\": \"Journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding and epistatic rescue experiments, single lab\",\n      \"pmids\": [\"31901951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TNF signaling through intact TNF receptors is required for SOD2 activity elevation and adaptive radioprotection; transfection of SOD2 siRNA completely abolishes elevated SOD2 activity and eliminates the adaptive response; amifostine thiol (WR1065) activates NF-κB directly to elevate SOD2 independently of TNF receptor signaling.\",\n      \"method\": \"TNF receptor knockout cells and mice, SOD2 siRNA transfection, NF-κB activation assay, clonogenic survival assay, micronucleus assay in vivo\",\n      \"journal\": \"Radiation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO and siRNA knockdown with defined functional readouts, in vivo confirmation\",\n      \"pmids\": [\"23237540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SOD2 overexpression in dorsal root ganglion neurons decreases superoxide and blocks caspase-3 activation; SOD2 haploinsufficiency (SOD2+/-) in dissociated DRG cultures increases O2•-, activates caspase-3, and reduces neurite outgrowth under basal conditions exacerbated by hyperglycemia.\",\n      \"method\": \"SOD2 overexpression, SOD2+/- mouse neurons, caspase-3 activation assay, superoxide measurement, neurite outgrowth assay\",\n      \"journal\": \"Experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function in primary neurons with defined molecular readouts\",\n      \"pmids\": [\"17927981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MnSOD upregulation in senescent keratinocytes drives H2O2 overproduction that activates autophagic cell death; overexpression of MnSOD or exogenous H2O2 recapitulates this death, which is abolished by catalase or 3-methyladenine (autophagosome inhibitor) and anti-Atg5 siRNA.\",\n      \"method\": \"MnSOD overexpression, catalase treatment, 3-methyladenine, Atg5 siRNA, Lysotracker staining, LC3 vesiculation, transmission electron microscopy\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal inhibitors and genetic knockdown with defined phenotype, single lab\",\n      \"pmids\": [\"20856861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Caffeine binds directly to SIRT3 (Kd ~6.86×10⁻⁷ M), enhancing SIRT3 enzymatic activity and its affinity for substrates, leading to reduced SOD2 acetylation and increased SOD2 activity; a SIRT3 inhibitor (3-TYP) reverses caffeine-mediated SOD2 activation.\",\n      \"method\": \"In vitro binding assay (affinity measurement), SIRT3 enzymatic activity assay, SOD2 acetylation assay, SIRT3 inhibitor rescue in vitro and in vivo\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding affinity measured and functional rescue with specific inhibitor\",\n      \"pmids\": [\"33015038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Overexpression of SOD2 (mitochondrial) but not cytoplasmic SOD1 in Caveolin-1-deficient fibroblasts suppresses tumor growth promotion in xenograft assays, identifying a specific role for mitochondrial oxidative stress mediated by SOD2 in the cancer-associated fibroblast phenotype.\",\n      \"method\": \"Caveolin-1 shRNA knockdown, SOD2 overexpression vs. SOD1 overexpression, xenograft tumor growth assay\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — isoform-specific rescue experiment (SOD2 vs SOD1) with in vivo xenograft readout, single lab\",\n      \"pmids\": [\"21150282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PARK7 translocates into the nucleus of renal tubular cells following TGFβ1 treatment or UUO, where it induces SOD2 expression to reduce mitochondrial ROS and protect against renal fibrosis; PARK7 knockdown exacerbates fibrotic changes and ROS production.\",\n      \"method\": \"PARK7 nuclear translocation assay, PARK7 KD and overexpression, SOD2 expression analysis, ROS measurement, UUO mouse model\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — nuclear translocation with functional consequence, KD and OE with defined phenotype, in vivo confirmation\",\n      \"pmids\": [\"34093596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"REGγ (11S proteasome activator) interacts with and promotes degradation of PP2Acα, leading to increased phosphorylation and nuclear export of FoxO3a and subsequent decline of SOD2, ROS accumulation, and cardiac hypertrophy; introducing exogenous PP2Acα or SOD2 rescues REGγ-mediated ROS accumulation.\",\n      \"method\": \"Co-immunoprecipitation (REGγ-PP2Acα interaction), REGγ KO mouse (TAC model), PP2Acα/SOD2 overexpression rescue, protein phosphorylation and localization assays, SOD mimetic treatment in vivo\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — protein-protein interaction, KO model, and epistatic rescue establishing pathway order, single lab\",\n      \"pmids\": [\"32424140\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SOD2 (MnSOD) is a manganese-containing homotetrameric enzyme exclusively localized to the mitochondrial matrix, where it dismutates superoxide to H2O2; its enzymatic activity is regulated at multiple levels including transcription (via NF-κB, Sp1, C/EBPβ, and epigenetic modifications), post-transcriptional control (miR-146a, HuR-mediated translation), protein stability (USP36 deubiquitination), and reversible post-translational modifications (SIRT3-mediated deacetylation at K68 and K122 that activates dismutase activity, CDK4-mediated phosphorylation at S106 that boosts activity, and acetylation at K68 that converts the tetramer to a monomeric peroxidase with oncogenic properties including HIF2α-driven stemness and drug resistance).\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"Crystal structure of human mitochondrial manganese superoxide dismutase (SOD2) determined at 2.2 Å resolution, revealing a homotetrameric enzyme where each subunit has an N-terminal helical hairpin and C-terminal α/β domain contributing ligands to the catalytic Mn site; two identical 4-helix bundles formed from N-terminal helical hairpins create novel tetrameric interfaces that stabilize the active sites.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with full structural characterization\",\n      \"pmids\": [\"1394426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Homozygous knockout of Sod2 in mice causes neonatal lethality with dilated cardiomyopathy, hepatic lipid accumulation, and metabolic acidosis; cytochemical analysis revealed severe reduction of succinate dehydrogenase (complex II) and aconitase activities in the heart, establishing that SOD2 is required to protect mitochondrial enzymes from superoxide-mediated inactivation.\",\n      \"method\": \"Homologous recombination knockout mouse, cytochemical enzyme activity assays\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — foundational knockout study with multiple orthogonal phenotypic and biochemical readouts, widely replicated\",\n      \"pmids\": [\"7493016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"TNF receptor 1 (TNF-R1), but not TNF-R2, mediates TNF/lymphotoxin-induced induction of MnSOD expression; overexpression of MnSOD (but not CuZn-SOD or EC-SOD) enhances cellular resistance to radiation, and mitochondrial matrix targeting is required—CuZn-SOD or EC-SOD fused to the MnSOD mitochondrial signal sequence confer protection, whereas MnSOD lacking its signal sequence does not.\",\n      \"method\": \"Receptor-specific knockout/overexpression, antisense RNA suppression, mitochondrial targeting signal swap constructs, radiation survival assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic constructs with functional rescue experiments establishing receptor specificity and mitochondrial localization requirement\",\n      \"pmids\": [\"7599209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"HIV-1 Tat protein (C-terminal region) suppresses MnSOD mRNA, protein, and activity in T cells and HeLa cells, reducing glutathione levels and shifting the cellular redox state toward oxidation, thereby potentiating TNF-induced NF-κB activation and cytotoxicity.\",\n      \"method\": \"Stable transfection with tat gene, Tat truncation mutants, enzyme activity assays, glutathione measurements\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple cell systems with truncation mutant dissection of Tat domains, single lab\",\n      \"pmids\": [\"7859743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"A diallelic polymorphism (Ala-9Val) in the mitochondrial targeting sequence (MTS) of human MnSOD gene was identified; computational analysis predicts the Ala-9 allele forms a typical amphiphilic helix required for mitochondrial transport, while the Val-9 allele disrupts this helix, suggesting a functional polymorphism affecting mitochondrial import efficiency.\",\n      \"method\": \"Population sequencing, secondary structure prediction of MTS amphiphilic helix\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — structural prediction validated by population genetics; functional impact on import is computational, not directly measured in vitro\",\n      \"pmids\": [\"8806673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Peroxynitrite completely inhibits MnSOD enzymatic activity in vitro via nitration of Tyr34 (active-site residue) and Tyr45/Tyr193, and oxidative formation of dityrosine cross-links producing higher-molecular-mass species; hydrogen peroxide or nitric oxide alone had no effect, identifying peroxynitrite as the specific inactivating oxidant.\",\n      \"method\": \"In vitro enzyme inactivation assay, electrospray mass spectrometry, real-time spectral analysis, tetranitromethane and HOCl controls\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro assay with mass spectrometry identification of modified residues and multiple oxidant comparisons\",\n      \"pmids\": [\"9484232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SOD2 knockout mice treated with the SOD mimetic MnTBAP (which does not cross the blood-brain barrier) are rescued from cardiomyopathy and hepatic pathology but develop spongiform degeneration of cortex and brainstem nuclei with gliosis, demonstrating that SOD2 loss causes progressive neurodegeneration driven by mitochondrial ROS specifically within the CNS.\",\n      \"method\": \"Sod2-/- mice, pharmacological SOD mimetic rescue (MnTBAP), neuropathological analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic model with pharmacological rescue dissecting tissue-specific requirements; replicated finding\",\n      \"pmids\": [\"9462746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A cis-acting element in the 3' UTR of MnSOD mRNA (MnSOD-RE) functions as a translational enhancer in vivo: insertion of MnSOD-RE downstream of a CAT reporter increased CAT activity ~400% without altering CAT mRNA levels, demonstrating post-transcriptional regulation of MnSOD at the translational level.\",\n      \"method\": \"Transient transfection of CAT-reporter constructs with/without MnSOD 3'UTR element, RNA and activity measurements\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay with matched controls in cell culture, single lab\",\n      \"pmids\": [\"10872821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"FOXO3a directly transcriptionally activates MnSOD (SOD2) in quiescent cells: FOXO3a increases MnSOD mRNA and protein, reduces ROS, and protects quiescent cells from glucose-deprivation-induced apoptosis; this mechanism operates in the absence of PKB/Akt activity and was confirmed in mammalian cells, extending the C. elegans DAF-16/MnSOD longevity model.\",\n      \"method\": \"Overexpression and dominant-negative FOXO3a constructs, mRNA/protein quantification, ROS measurement, apoptosis assay, PKB inhibition\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary genetic approaches with mechanistic validation across systems; highly cited foundational paper\",\n      \"pmids\": [\"12239572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Epigenetic silencing of SOD2 in human breast cancer cells is mediated by decreased dimethyl H3K4 and acetylated H3K9 histone marks at SOD2 regulatory elements, creating repressive chromatin that reduces SP-1, AP-1, and NF-κB binding; treatment with HDAC inhibitors trichostatin A or sodium butyrate reactivates SOD2 expression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for histone marks and transcription factors, HDAC inhibitor treatment, gene expression assays\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with multiple marks and transcription factors; single lab but orthogonal methods\",\n      \"pmids\": [\"18845242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Nuclear SIRT1 induces MnSOD expression in cardiomyocytes; in failing hearts SIRT1 translocates to the nucleus where it upregulates MnSOD, increasing resistance to oxidative stress. Resveratrol enhances nuclear SIRT1 and MnSOD induction; MnSOD siRNA abrogates the protective effects of nuclear SIRT1, demonstrating MnSOD is a required downstream effector.\",\n      \"method\": \"Subcellular fractionation, siRNA knockdown, overexpression constructs, in vivo hamster heart failure model with resveratrol treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function (siRNA) and pharmacological gain-of-function with in vivo validation; single lab\",\n      \"pmids\": [\"20089851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIRT3 directly binds, deacetylates, and activates SOD2 at Lys68; acetylation of SOD2 at K68 decreases its enzymatic activity. Elevated ROS stimulates SIRT3 transcription, leading to SOD2 deacetylation and activation. SIRT3 co-expression synergistically increases SOD2-mediated ROS reduction, while SIRT3 depletion cancels it.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylation assay, acetylation-mimic and deacetylation-mimic mutants, enzyme activity assay, ROS measurement, SIRT3 overexpression/depletion\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of deacetylation, site-specific mutagenesis, enzyme activity assay, and cell-based validation; highly cited\",\n      \"pmids\": [\"21566644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SOD2 protein stability is regulated by the deubiquitinating enzyme USP36: endogenous USP36 interacts with SOD2 (co-immunoprecipitation, yeast two-hybrid), SOD2 undergoes K48-linked polyubiquitination and proteasomal degradation, and USP36 reduces SOD2 ubiquitination and extends its half-life.\",\n      \"method\": \"2-DE/MALDI-TOF/MS proteomics, co-immunoprecipitation, yeast two-hybrid, ubiquitination assay, cycloheximide chase\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal IP and yeast two-hybrid plus functional ubiquitination assay; single lab\",\n      \"pmids\": [\"21268071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SOD2 is exclusively localized to mitochondria and is absent from peroxisomes in mammalian cells and tissues; established by double-immunofluorescence on frozen/paraffin sections, post-embedding immunoelectron microscopy on LR White and ultrathin cryo-sections, and Western blot of biochemically purified peroxisomal fractions from mouse liver.\",\n      \"method\": \"Multiple immunofluorescence modalities, immunoelectron microscopy with multiple gold techniques, subcellular fractionation/Western blot\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal morphological and biochemical methods across multiple tissues definitively resolving conflicting prior reports\",\n      \"pmids\": [\"23744526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Cyclin D1/CDK4 translocates to mitochondria in response to low-dose ionizing radiation (LDIR) and directly phosphorylates MnSOD at serine-106 (S106), enhancing its enzymatic activity and mitochondrial respiration. A mitochondria-targeted dominant-negative CDK4 or MnSOD-S106A mutant abolishes LDIR-induced mitochondrial enhancement and adaptive radioprotection.\",\n      \"method\": \"Mitochondrial fractionation, in vitro kinase assay with site-directed mutagenesis (S106A), mitochondria-targeted dominant-negative CDK4, enzymatic activity assay, in vivo mouse LDIR model\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis plus in vivo validation; identifies specific phosphorylation site\",\n      \"pmids\": [\"25578653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SOD2 upregulation in cancer cells establishes a steady-state mitochondrial H2O2 flux that activates AMPK and drives metabolic reprogramming to aerobic glycolysis (Warburg effect); restricting MnSOD expression or inhibiting AMPK suppresses the metabolic switch, establishing a MnSOD→H2O2→AMPK→glycolysis axis.\",\n      \"method\": \"siRNA knockdown, AMPK inhibition, metabolic flux assays, cell viability assay, in vitro transformation assays, clinical specimen analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic interventions (SOD2 KD + AMPK inhibition) with metabolic readouts; independently corroborated by clinical data\",\n      \"pmids\": [\"25651975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CRISPR/Cas9-generated SOD2-null human cells (HEK293T) are completely devoid of MnSOD protein and activity, exhibiting impaired clonogenic survival, disrupted mitochondrial ultrastructure, preferential glycolysis over oxidative phosphorylation, and significantly impaired activities of mitochondrial complex I and II (containing Fe/S centers susceptible to superoxide), rescuable by pharmacological SOD mimetic GC4419 or hypoxia.\",\n      \"method\": \"CRISPR/Cas9 biallelic gene disruption, enzyme activity assays (complex I, II, MnSOD), Seahorse metabolic profiling, electron microscopy, pharmacological rescue\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — complete genetic null with multiple orthogonal biochemical and metabolic readouts and pharmacological rescue\",\n      \"pmids\": [\"26208779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Sirt3 impairment in hypertension leads to SOD2 hyperacetylation and reduced SOD2 activity; angiotensin II induces Sirt3 S-glutathionylation, which inactivates Sirt3 and causes SOD2 acetylation. Mitochondria-targeted H2O2 scavenging prevents Sirt3 S-glutathionylation and SOD2 acetylation. SOD2 acetylation inversely correlates with SOD2 activity and directly correlates with hypertension severity in both mouse models and human essential hypertension.\",\n      \"method\": \"Sirt3-/- and SOD2+/- mouse models, angiotensin II infusion, S-glutathionylation assay, acetylation/activity measurements, mCAT transgenic mice, human patient samples\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic mouse models plus human data with mechanistic pathway dissection; strong preponderance of evidence\",\n      \"pmids\": [\"28684630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"During osteoblast differentiation, SIRT3 increases SOD2 activity through deacetylation specifically at K68; SIRT3 and SOD2 knockdown both suppress osteoblast differentiation, and SOD2 overexpression rescues differentiation in SIRT3-deficient osteoblasts, placing SIRT3→SOD2(K68 deacetylation) as required for eliminating mitochondrial superoxide during osteoblast differentiation and bone formation.\",\n      \"method\": \"siRNA knockdown, overexpression, SIRT3-/- mouse model, mitochondrial superoxide measurement, deacetylation at K68, osteoblast differentiation assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic in vivo and in vitro models with site-specific mechanistic detail and rescue experiments\",\n      \"pmids\": [\"28914882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Acetylation of SOD2 at lysine 68 (K68Ac) converts the enzyme from a homotetrameric superoxide dismutase to a monomeric peroxidase; the K68Q acetylation-mimic mutant behaves as a tumor promoter (not suppressor) in transformation and xenograft assays, cells expressing K68Q or physically K68-acetylated SOD2 exhibit resistance to tamoxifen, and cells selected for tamoxifen resistance show increased K68-Ac and monomeric MnSOD.\",\n      \"method\": \"In vitro transformation and xenograft assays, biochemical stoichiometry analysis, acetylation-mimic (K68Q) and physical K68-Ac protein, peroxidase activity assay, size-exclusion chromatography (monomer vs. tetramer), tamoxifen resistance selection\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — enzymatic activity reconstitution with acetylation mimics, structural (oligomeric state) characterization, and functional cancer biology validation\",\n      \"pmids\": [\"31160585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Acetylation of SOD2 at K68 promotes a functional switch: K68Ac stabilizes HIF2α via increased mitochondrial ROS, which in turn drives transcription of stemness genes (Oct4, Sox2, Nanog) in breast cancer cells, linking mitochondrial SOD2 acetylation state to cancer stem cell reprogramming.\",\n      \"method\": \"K68 acetylation-mimic expression, HIF2α protein stabilization assay, stemness gene expression, ROS measurement, siRNA knockdown of HIF2α\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — acetylation mimic with defined downstream pathway via HIF2α; single lab\",\n      \"pmids\": [\"31591207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous missense variant in SOD2 (c.542G>T, p.Gly181Val) causes lethal neonatal dilated cardiomyopathy in a human patient; patient fibroblasts show significantly elevated superoxide levels and reduced SOD2 catalytic activity; lentiviral complementation with wild-type SOD2 completely restores mitochondrial SOD2 activity.\",\n      \"method\": \"Exome sequencing, hydroethidine oxidation assay (superoxide measurement), enzyme activity assay in patient fibroblasts and muscle, lentiviral complementation with wild-type SOD2\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — patient cells with biochemical loss of function confirmed by complementation rescue; direct causal link between SOD2 variant and disease established\",\n      \"pmids\": [\"31494578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SOD2 mRNA translation is rapidly induced within 30 min of matrix detachment via the RNA-binding protein HuR/ELAVL1: anchorage-independence triggers cytosolic HuR accumulation, HuR binds SOD2 mRNA 3'UTR, and HuR siRNA knockdown abolishes the increase in SOD2 mRNA association with heavy polyribosomes and nascent SOD2 protein synthesis. p38 MAPK activation is required upstream of HuR-SOD2 mRNA interaction.\",\n      \"method\": \"Polyribosome profiling, RNA immunoprecipitation, HuR siRNA knockdown, p38 inhibition, nascent protein synthesis assay\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — polyribosome profiling plus RIP and siRNA with kinase dependency established; single lab\",\n      \"pmids\": [\"35594792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Propionylation of Sod2 at lysine 132 (K132) suppresses Sod2 enzymatic activity in zebrafish intestine; global lysine propionylation analysis identified K132 as the modified site, and biochemical assays confirmed K132 propionylation reduces activity. Sirt3 can remove the propionyl group (de-propionylation), restoring Sod2 activity.\",\n      \"method\": \"Global lysine propionylation proteomics, site-specific biochemical activity assay, Sirt3 de-propionylation assay, zebrafish intestinal model\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — site-specific mass spectrometry identification of K132 propionylation with enzymatic activity validation and eraser identification; single organism model\",\n      \"pmids\": [\"34142031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MnSOD K68 acetylation (K68Ac) causes monomeric SOD2 to incorporate iron (instead of manganese) at the active site, maximally inducing peroxidase activity; molecular dynamics of MnSOD-K68Ac and K68Q show significant change in charge distribution along α1 and α2 helices adjacent to the Mn2+ binding site, destabilizing the tetramer and explaining monomer enrichment and altered metal incorporation.\",\n      \"method\": \"Amber codon suppression to generate physically K68-Ac protein, peroxidase activity assay, metal analysis, molecular dynamics simulation, acetylation-mimic (K68Q) expression\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — physical acetylation with enzymatic assay and molecular dynamics; single lab with computational support\",\n      \"pmids\": [\"33867840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"C/EBPβ is required for TNF-induced MnSOD expression and protection against TNF-induced apoptosis: C/EBPβ-deficient fibroblasts fail to induce MnSOD upon TNF stimulation and undergo apoptosis; ectopic C/EBPβ rescues MnSOD induction; MnSOD expression alone in C/EBPβ-deficient cells bypasses the requirement for C/EBPβ in survival. Mechanistically, C/EBPβ is required for NF-κB p65 binding to the intronic TNF-response element of MnSOD and for histone acetylation at that element.\",\n      \"method\": \"C/EBPβ-deficient fibroblasts, ectopic expression rescue, ChIP for NF-κB p65 and histone acetylation at MnSOD intronic element, MnSOD stable transfection\",\n      \"journal\": \"Apoptosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with rescue and ChIP mechanistic dissection; single lab\",\n      \"pmids\": [\"16850160\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SOD2 (MnSOD) is a homotetrameric manganese-containing enzyme exclusively localized to the mitochondrial matrix where it catalyzes dismutation of superoxide to H2O2; its enzymatic activity is regulated post-translationally by SIRT3-mediated deacetylation at K68 (activating), CDK4-mediated phosphorylation at S106 (activating), USP36-mediated deubiquitination (stabilizing), and peroxynitrite-mediated nitration of the active-site Tyr34 (inactivating); acetylation at K68 additionally switches SOD2 from a tetrameric superoxide dismutase to a monomeric peroxidase that incorporates iron and promotes cancer stem cell reprogramming via mtROS–HIF2α signaling, while transcriptional activation occurs through FOXO3a, NF-κB (requiring C/EBPβ co-factor), and nuclear SIRT1, and translational upregulation is mediated by HuR binding to a 3'UTR element in response to anchorage-independence.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SOD2 (MnSOD) is a manganese-dependent superoxide dismutase that functions as the primary mitochondrial defense against superoxide radicals, converting superoxide to hydrogen peroxide and molecular oxygen within the mitochondrial matrix, where it is essential for maintaining electron transport chain integrity and oxidative phosphorylation [PMID:12126755, PMID:26208779]. Its enzymatic activity is tightly controlled by reversible post-translational modifications: SIRT3-mediated deacetylation at K68 activates dismutase function [PMID:21386137, PMID:28684630], CDK4-mediated phosphorylation at S106 enhances activity [PMID:25578653], and acetylation at K68 converts the homotetramer into a monomeric peroxidase with oncogenic gain-of-function properties including HIF2α-dependent stemness reprogramming and chemotherapy resistance [PMID:31160585, PMID:31494207]. Transcriptional regulation of SOD2 occurs through NF-κB, C/EBPβ, and Sp1 acting on promoter and intronic elements, with epigenetic silencing via repressive histone marks in certain cancers [PMID:16850160, PMID:18845242]. A homozygous missense variant (p.Gly181Val) causes lethal neonatal dilated cardiomyopathy with loss of catalytic activity, rescued by wild-type SOD2 complementation [PMID:31494578].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing that TNF-R1/NF-κB signaling induces SOD2 expression and that its radioprotective function requires mitochondrial matrix targeting resolved how cytokine signaling specifically upregulates mitochondrial antioxidant defense.\",\n      \"evidence\": \"Receptor-specific TNF signaling dissection, MnSOD overexpression with and without mitochondrial targeting signal, radiation survival assay\",\n      \"pmids\": [\"7599209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signaling intermediates between TNF-R1 and NF-κB activation of SOD2 not fully mapped\", \"Whether other cytokine receptors similarly induce SOD2 not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Discovery of a translational enhancer element in the SOD2 3′UTR revealed that SOD2 output is controlled post-transcriptionally, not only at the transcriptional level.\",\n      \"evidence\": \"Heterologous reporter transfection with SOD2 3′UTR cis-element in NIH/3T3 cells\",\n      \"pmids\": [\"10872821\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trans-acting factor binding this element was not identified in this study\", \"Physiological stimuli that regulate this element in vivo remain unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Comprehensive biochemical characterization established SOD2 as a manganese-containing homotetramer synthesized with a mitochondrial leader peptide that catalyzes superoxide dismutation in the matrix.\",\n      \"evidence\": \"Biochemical purification, gene structure analysis, enzymatic characterization\",\n      \"pmids\": [\"12126755\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for metal selectivity not determined at atomic resolution in this study\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that C/EBPβ is required for NF-κB p65 recruitment and histone acetylation at the SOD2 intronic enhancer clarified the chromatin-level mechanism of TNF-induced SOD2 transcription.\",\n      \"evidence\": \"C/EBPβ-deficient fibroblasts, ectopic rescue, ChIP for NF-κB p65 and histone acetylation\",\n      \"pmids\": [\"16850160\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether C/EBPβ acts as a pioneer factor or co-activator at this locus not resolved\", \"Chromatin remodeling complexes involved not identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of repressive histone marks (decreased H3K4me2, H3K9ac) at the SOD2 locus in breast cancer cells, reversible by HDAC inhibitors, established epigenetic silencing as a mechanism for SOD2 downregulation in tumors.\",\n      \"evidence\": \"ChIP for histone modifications and transcription factors, HDAC inhibitor (TSA, sodium butyrate) rescue\",\n      \"pmids\": [\"18845242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific HDACs responsible not identified\", \"Whether DNA methylation cooperates with histone modifications at SOD2 not fully addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery that SIRT3 deacetylates conserved lysine residues on SOD2 to activate its dismutase function linked mitochondrial sirtuin signaling to antioxidant defense and nutrient sensing.\",\n      \"evidence\": \"In vitro deacetylation assays, SIRT3 overexpression and knockdown, enzymatic activity measurement\",\n      \"pmids\": [\"21386137\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of individual acetylation sites not resolved in initial study\", \"Whether other mitochondrial deacetylases also regulate SOD2 not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of USP36 as a deubiquitinase that stabilizes SOD2 protein by removing polyubiquitin chains revealed ubiquitin-proteasome-mediated turnover as a layer of SOD2 regulation.\",\n      \"evidence\": \"2-DE/MALDI-TOF MS identification, co-IP, yeast two-hybrid, ubiquitination and half-life assays\",\n      \"pmids\": [\"21268071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The E3 ubiquitin ligase that ubiquitinates SOD2 was not identified\", \"Physiological stimuli controlling USP36–SOD2 interaction unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Rigorous subcellular localization by immunoelectron microscopy and fractionation confirmed SOD2 is exclusively mitochondrial, excluding earlier suggestions of peroxisomal localization.\",\n      \"evidence\": \"Double-immunofluorescence, immunoelectron microscopy, immunogold labeling, Western blot of purified subcellular fractions in mouse liver\",\n      \"pmids\": [\"23744526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether submitochondrial distribution changes under stress not examined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstration that CDK4 translocates to mitochondria and directly phosphorylates SOD2 at S106 to enhance activity identified a cell-cycle kinase as a post-translational activator of mitochondrial antioxidant defense.\",\n      \"evidence\": \"Mitochondria-targeted dominant-negative CDK4, S106 mutagenesis, in vitro kinase assay, activity and respiration measurements\",\n      \"pmids\": [\"25578653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S106 phosphorylation affects tetramer stability not examined\", \"Phosphatase that reverses this modification not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SIRT3 deacetylation at K68 was shown to be physiologically important in vivo: loss of SIRT3 causes SOD2 hyperacetylation leading to vascular oxidative stress and hypertension in mice and humans, and impaired osteoblast differentiation with osteopenia.\",\n      \"evidence\": \"SIRT3 KO mice, SOD2+/- mice, human hypertensive subjects, osteoblast differentiation assays, SIRT3 KO bone phenotyping\",\n      \"pmids\": [\"28684630\", \"28914882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K68 acetylation status varies across tissues and aging not systematically mapped\", \"Contribution of other SIRT3 substrates to these phenotypes not fully dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SOD2 knockout by CRISPR/Cas9 demonstrated that complete loss of mitochondrial superoxide dismutase disrupts Fe-S cluster-dependent complexes I and II, collapses oxidative phosphorylation, and forces glycolytic metabolism.\",\n      \"evidence\": \"Biallelic CRISPR/Cas9 disruption, electron microscopy, bioenergetic profiling, complex I/II activity assays\",\n      \"pmids\": [\"26208779\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Fe-S cluster damage is direct or secondary to superoxide accumulation not resolved\", \"Long-term adaptive responses in SOD2-null cells not characterized\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SOD2 overexpression in cancer cells was shown to generate sustained H2O2 flux that activates AMPK and drives the Warburg metabolic shift, revealing a pro-tumorigenic signaling function for the dismutation product.\",\n      \"evidence\": \"MnSOD knockdown/overexpression, AMPK inhibition, metabolic flux analysis in multiple cancer cell lines\",\n      \"pmids\": [\"25651975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How cancer cells tolerate elevated H2O2 without apoptosis not fully explained\", \"Whether this mechanism operates in vivo tumors not directly shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The critical mechanistic insight that K68 acetylation converts SOD2 from a tetrameric dismutase to a monomeric peroxidase — with oncogenic gain-of-function including HIF2α stabilization, stemness gene induction, and chemoresistance — redefined SOD2 as a bifunctional enzyme whose quaternary structure dictates catalytic identity.\",\n      \"evidence\": \"K68Q acetylation-mimic mutant, peroxidase activity assay, xenograft assays, HIF2α stabilization, stemness marker analysis, cisplatin/doxorubicin resistance selection, molecular dynamics simulation\",\n      \"pmids\": [\"31160585\", \"31591207\", \"33867840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fraction of endogenous SOD2 that is K68-acetylated in tumors in vivo not quantified\", \"Whether monomeric peroxidase form incorporates iron in vivo not directly shown\", \"Structural basis for tetramer-to-monomer transition at atomic resolution lacking\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"A homozygous SOD2 missense variant (p.Gly181Val) was identified as the cause of lethal neonatal dilated cardiomyopathy, with lentiviral complementation fully restoring activity, establishing SOD2 as a Mendelian disease gene.\",\n      \"evidence\": \"Exome sequencing, SOD2 activity assay in patient fibroblasts, lentiviral wild-type SOD2 complementation\",\n      \"pmids\": [\"31494578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether heterozygous carriers have subclinical cardiac phenotypes not assessed\", \"Additional pathogenic variants in SOD2 not yet reported\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of HuR/ELAVL1 as a trans-acting factor that binds SOD2 mRNA and enhances its translation under anchorage-independent conditions via p38 MAPK connected post-transcriptional SOD2 regulation to anoikis resistance.\",\n      \"evidence\": \"Polyribosome profiling, HuR-SOD2 mRNA co-IP, HuR siRNA knockdown, p38 inhibition, nascent protein synthesis assay\",\n      \"pmids\": [\"35594792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific HuR binding site on SOD2 mRNA not mapped\", \"Relationship between HuR-mediated translation and the previously identified 3′UTR enhancer element not clarified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the E3 ligase targeting SOD2 for ubiquitin-dependent degradation, the structural mechanism of the K68-acetylation-driven tetramer-to-monomer switch at atomic resolution, and the quantitative fraction of monomeric peroxidase-form SOD2 in human tumors in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ubiquitin ligase for SOD2 unknown\", \"Atomic-resolution structure of K68-Ac monomeric form not determined\", \"In vivo stoichiometry of acetylated vs. deacetylated SOD2 in normal and disease tissues not systematically measured\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016209\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5, 10, 21]},\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 10, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 2, 3, 9, 10, 25]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 6, 7, 9, 21]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [14, 15, 24]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 4, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SIRT3\",\n      \"USP36\",\n      \"CDK4\",\n      \"ELAVL1\",\n      \"NFKB1\",\n      \"SP1\",\n      \"CEBPB\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SOD2 (MnSOD) is the principal mitochondrial matrix antioxidant enzyme, catalyzing dismutation of superoxide radical to hydrogen peroxide as a manganese-dependent homotetramer, thereby protecting Fe–S cluster-containing respiratory chain complexes (I, II) and aconitase from oxidative inactivation [PMID:1394426, PMID:7493016, PMID:26208779]. Its activity is positively regulated by SIRT3-mediated deacetylation at K68 and CDK4-mediated phosphorylation at S106, while peroxynitrite-mediated nitration of the active-site Tyr34 is inactivating [PMID:21566644, PMID:25578653, PMID:9484232]; acetylation at K68 switches SOD2 from a tetrameric dismutase to a monomeric iron-incorporating peroxidase that promotes cancer stemness via mtROS–HIF2α signaling [PMID:31160585, PMID:31591207]. Homozygous loss-of-function SOD2 variants cause lethal neonatal dilated cardiomyopathy in mice and humans, and transcriptional control is mediated by FOXO3a, NF-κB (requiring C/EBPβ cofactor), and nuclear SIRT1, with translational upregulation via HuR binding the SOD2 3′UTR upon matrix detachment [PMID:7493016, PMID:31494578, PMID:12239572, PMID:16850160, PMID:20089851, PMID:35594792].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Determination of the 2.2 Å crystal structure established that SOD2 operates as a homotetramer with a novel 4-helix-bundle interface that positions four independent Mn active sites, providing the first atomic framework for understanding catalysis and regulation.\",\n      \"evidence\": \"X-ray crystallography of human mitochondrial MnSOD\",\n      \"pmids\": [\"1394426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of superoxide entry into the active site channel not resolved at this resolution\", \"No structure with substrate or product analogs\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mouse knockout studies answered whether SOD2 is essential: Sod2−/− mice die neonatally with dilated cardiomyopathy and loss of mitochondrial Fe–S cluster enzyme activities, establishing SOD2 as the non-redundant mitochondrial superoxide scavenger required for oxidative phosphorylation and organismal survival.\",\n      \"evidence\": \"Homozygous Sod2 knockout mice with cytochemical enzyme activity assays; complementary studies showed TNF-R1-mediated MnSOD induction and requirement for mitochondrial targeting\",\n      \"pmids\": [\"7493016\", \"7599209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of individual respiratory complex damage versus aconitase loss to lethality were not separated\", \"Tissue-specific conditional knockouts not yet available at this stage\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Two advances resolved tissue-specific vulnerability and a key inactivation mechanism: pharmacological SOD mimetic rescue of Sod2−/− cardiac/hepatic pathology unmasked an obligate role for SOD2 in preventing CNS spongiform neurodegeneration, and biochemical reconstitution showed peroxynitrite (not NO or H₂O₂ alone) inactivates SOD2 via Tyr34 nitration.\",\n      \"evidence\": \"MnTBAP rescue of Sod2−/− mice with neuropathology analysis; in vitro peroxynitrite inactivation with electrospray mass spectrometry mapping of Tyr34, Tyr45, Tyr193 modifications\",\n      \"pmids\": [\"9462746\", \"9484232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of Tyr34 nitration in disease settings not yet demonstrated\", \"Peroxynitrite-mediated dityrosine cross-linking stoichiometry and reversibility unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of FOXO3a as a direct transcriptional activator of SOD2 linked insulin/Akt signaling to mitochondrial antioxidant defense, explaining how quiescent or nutrient-deprived cells upregulate SOD2 and connecting SOD2 to the conserved DAF-16/FOXO longevity pathway.\",\n      \"evidence\": \"Overexpression and dominant-negative FOXO3a constructs with mRNA, protein, ROS, and apoptosis readouts in mammalian cells\",\n      \"pmids\": [\"12239572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FOXO3a binds the SOD2 promoter directly or through intermediaries was not resolved by ChIP in this study\", \"Relative contribution of FOXO3a versus NF-κB to SOD2 transcription in different cell types not quantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that C/EBPβ is an obligate cofactor for NF-κB-dependent SOD2 induction resolved how TNF drives SOD2 transcription: C/EBPβ is required for NF-κB p65 binding and histone acetylation at the intronic TNF-response element, and SOD2 expression alone bypasses the survival requirement for C/EBPβ.\",\n      \"evidence\": \"C/EBPβ-deficient fibroblasts with ectopic rescue, ChIP for NF-κB p65 and histone acetylation at SOD2 intronic element\",\n      \"pmids\": [\"16850160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether C/EBPβ physically interacts with p65 at the SOD2 locus or acts through chromatin remodeling was not distinguished\", \"Role of C/EBPβ in non-TNF stimuli for SOD2 transcription not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Two regulatory mechanisms were defined: SIRT3 directly deacetylates SOD2 at K68 to activate its dismutase function, and USP36 deubiquitinates K48-linked polyubiquitin chains on SOD2 to prevent proteasomal degradation, establishing that SOD2 activity and abundance are under distinct post-translational control.\",\n      \"evidence\": \"In vitro deacetylation reconstitution with K68 mutagenesis and enzyme activity assays (SIRT3); co-IP, yeast two-hybrid, ubiquitination/cycloheximide chase (USP36)\",\n      \"pmids\": [\"21566644\", \"21268071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the E3 ubiquitin ligase targeting SOD2 for K48-linked ubiquitination was not determined\", \"Relative contribution of K68 acetylation versus other acetylation sites to total SOD2 activity regulation not quantified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"CDK4 was identified as a mitochondrial kinase that phosphorylates SOD2 at S106 to enhance activity in response to low-dose ionizing radiation, while rigorous immunolocalization definitively confirmed SOD2 is exclusively mitochondrial matrix-resident with no peroxisomal pool.\",\n      \"evidence\": \"In vitro kinase assay with S106A mutagenesis and mitochondria-targeted dominant-negative CDK4 in vivo; multi-modal immunoelectron microscopy and subcellular fractionation across tissues\",\n      \"pmids\": [\"25578653\", \"23744526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CDK4-mediated S106 phosphorylation operates outside of radiation contexts is unknown\", \"Phosphatase that reverses S106 phosphorylation not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Overexpressed SOD2 was shown to generate a sustained mitochondrial H₂O₂ flux that activates AMPK and drives aerobic glycolysis, revealing a paradoxical pro-tumorigenic role for the canonical tumor suppressor when expression is elevated in cancer cells.\",\n      \"evidence\": \"SOD2 siRNA, AMPK inhibition, Seahorse metabolic profiling, transformation assays, clinical specimen correlation\",\n      \"pmids\": [\"25651975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Threshold of SOD2 expression at which the switch from tumor suppression to promotion occurs is not defined\", \"Whether catalase co-expression fully reverses the metabolic reprogramming was not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The SIRT3–SOD2 K68 deacetylation axis was shown to operate in disease-relevant settings: angiotensin II-induced S-glutathionylation of SIRT3 causes SOD2 hyperacetylation in hypertension, and SIRT3-dependent SOD2 activation is required for osteoblast differentiation and bone formation.\",\n      \"evidence\": \"Sirt3−/−, SOD2+/− mice, angiotensin II infusion with human patient samples; SIRT3 knockdown/overexpression with SOD2 rescue in osteoblast differentiation\",\n      \"pmids\": [\"28684630\", \"28914882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other SIRT3 substrates contribute to hypertensive pathology independently of SOD2 not fully excluded\", \"Site-specific acetylation status of SOD2 in hypertensive human patients not mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"K68 acetylation was found to fundamentally switch SOD2's quaternary structure and catalytic identity: acetylated K68 destabilizes the tetramer, favoring iron-incorporating monomers with peroxidase activity that stabilize HIF2α and drive cancer stemness gene expression, and a human homozygous SOD2 missense variant (G181V) was identified as a cause of lethal neonatal dilated cardiomyopathy, confirming the mouse phenotype in humans.\",\n      \"evidence\": \"Physical K68-Ac protein via amber codon suppression, size-exclusion chromatography, metal analysis, xenograft/transformation assays, HIF2α stabilization/siRNA; exome sequencing of patient with lentiviral complementation rescue in fibroblasts\",\n      \"pmids\": [\"31160585\", \"31591207\", \"31494578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo fraction of endogenous SOD2 that is monomeric/iron-bound in tumors not quantified\", \"Whether peroxidase activity of monomeric SOD2 has physiological substrates beyond H₂O₂ is unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Molecular dynamics and physical K68-Ac reconstitution explained how acetylation destabilizes the α1/α2 helix interface to promote monomer formation and iron incorporation, and a novel acyl modification—K132 propionylation—was identified as an additional SIRT3-reversible mechanism that suppresses SOD2 activity.\",\n      \"evidence\": \"Amber codon suppression with metal and peroxidase assays plus molecular dynamics; global propionylation proteomics in zebrafish intestine with SIRT3 de-propionylation\",\n      \"pmids\": [\"33867840\", \"34142031\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"K132 propionylation has only been characterized in zebrafish; relevance in mammalian systems is untested\", \"Full structural model of monomeric Fe-SOD2 at atomic resolution is lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the E3 ubiquitin ligase targeting SOD2, the structural basis of the tetramer-to-monomer transition at atomic resolution, the in vivo stoichiometry of K68 acetylation in normal versus tumor tissues, and whether the peroxidase activity of monomeric SOD2 has specific endogenous substrates or signaling targets beyond bulk H₂O₂.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"E3 ligase for SOD2 ubiquitination unknown\", \"No high-resolution structure of monomeric Fe-SOD2-K68Ac\", \"Quantitative in vivo acetylation stoichiometry at K68 in human tissues not mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016209\", \"supporting_discovery_ids\": [0, 1, 5, 11, 14, 16, 19]},\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 5, 16, 19, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 13, 14, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [1, 5, 6, 15, 16, 17]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 25]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [19, 20, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SIRT3\", \"CDK4\", \"USP36\", \"FOXO3A\", \"ELAVL1\", \"CEBPB\", \"RELA\"],\n    \"other_free_text\": []\n  }\n}\n```"}