{"gene":"E2F1","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":2000,"finding":"P/CAF acetylates E2F1 in vitro at lysine residues adjacent to the DNA-binding domain; acetylation increases E2F1 DNA-binding ability, transcriptional activation potential, and protein half-life. The RB-associated histone deacetylase can deacetylate E2F1, reversing these effects.","method":"In vitro acetylation assay, site-directed mutagenesis, intracellular acetylation detection, functional transcription assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, multiple orthogonal functional readouts, single lab","pmids":["10675335"],"is_preprint":false},{"year":2006,"finding":"SirT1 physically binds E2F1 and inhibits its transcriptional and apoptotic activities. E2F1 transcriptionally induces SirT1 expression, forming a negative feedback loop. Knockdown of SirT1 increases E2F1-dependent apoptosis and sensitivity to etoposide.","method":"Co-immunoprecipitation, siRNA knockdown, transcriptional reporter assays, apoptosis assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, siRNA loss-of-function with defined apoptotic phenotype, multiple orthogonal methods in single lab","pmids":["16892051"],"is_preprint":false},{"year":2010,"finding":"Set9 methyltransferase methylates E2F1 at lysine-185, which prevents E2F1 accumulation during DNA damage and suppresses proapoptotic target gene p73 activation. LSD1 demethylase removes this mark, stabilizing E2F1 and enabling apoptotic function. Methylation at K185 inhibits acetylation and phosphorylation at distant sites while stimulating ubiquitination and proteasomal degradation.","method":"In vitro methylation assay, site-directed mutagenesis, siRNA knockdown, co-immunoprecipitation, apoptosis assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, epistasis between PTMs, multiple orthogonal readouts in single lab","pmids":["20603083"],"is_preprint":false},{"year":2012,"finding":"PRMT5 directly methylates E2F1 on arginine residues, promoting E2F1 protein stability reduction and decreased DNA-binding activity. Depleting PRMT5 causes increased E2F1 protein levels and apoptosis. DNA damage conditions reduce arginine methylation of E2F1, allowing its stabilization.","method":"In vitro methylation assay, PRMT5 depletion (siRNA), protein stability assays, DNA-binding assays, apoptosis assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay, loss-of-function with multiple functional readouts, single lab with orthogonal methods","pmids":["22327218"],"is_preprint":false},{"year":2005,"finding":"MDM2 stabilizes E2F1 protein by inhibiting its ubiquitination; MDM2 displaces SCF(SKP2), the E2F1 E3 ubiquitin ligase, through direct binding to E2F1, thereby prolonging E2F1 half-life independent of p53 and pRB.","method":"Co-immunoprecipitation, ubiquitination assays, half-life measurement, deletion mutant analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical ubiquitination assay, displacement of E3 ligase demonstrated, multiple orthogonal methods","pmids":["16170383"],"is_preprint":false},{"year":2015,"finding":"POH1 deubiquitylase binds to and deubiquitylates E2F1, stabilizing E2F1 protein. Conditional Poh1 knockout reduces E2F1 expression in primary mouse liver cells.","method":"Co-immunoprecipitation, deubiquitylation assay, conditional knockout mouse, western blot","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical deubiquitylation assay plus in vivo genetic knockout validation","pmids":["26510456"],"is_preprint":false},{"year":2010,"finding":"APC/C(Cdc20) ubiquitin ligase targets E2F1 for degradation specifically in prometaphase. Ectopic Cdc20 reduces E2F1 protein; Cdc20 knockdown causes E2F1 accumulation in prometaphase. Co-expression of DP1 with E2F1 blocks APC/C-induced E2F1 degradation.","method":"Co-expression experiments, siRNA knockdown, cell synchronization, western blot, protein stability assays","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based degradation assays with siRNA and overexpression, multiple conditions tested, single lab","pmids":["20948288"],"is_preprint":false},{"year":2018,"finding":"L3MBTL3 methyl-binding protein binds methylated E2F1 and recruits CRL4DCAF5 ubiquitin ligase to degrade E2F1 in a methylation-dependent manner, analogous to its regulation of DNMT1.","method":"Biochemical binding assays, ubiquitination/degradation assays, genetic deletion models","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical demonstration of methylation-dependent binding and ubiquitination, supported by genetic models","pmids":["29691401"],"is_preprint":false},{"year":2016,"finding":"PAD4 citrullinates E2F1 in inflammatory cells, which promotes E2F1 chromatin association at cytokine gene promoters. Citrullination augments binding of BRD4 to an acetylated domain of E2F1, and PAD4/BRD4/E2F1 coexist on cytokine gene promoters to drive inflammatory gene expression. Combined PAD4 and BRD4 inhibition disrupts this complex and suppresses cytokine expression.","method":"In vitro citrullination assay, ChIP, co-immunoprecipitation, pharmacological inhibition, murine arthritis model","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay plus ChIP and co-IP demonstrating complex, validated in vivo with pharmacological inhibition","pmids":["26989780"],"is_preprint":false},{"year":2020,"finding":"SUMOylation of E2F1 at lysine-266 (SUMO2 conjugation) inhibits E2F1 transcriptional activity upon oxidative stress, promoting cell cycle arrest for cell survival. SENP3 desumoylase interacts with E2F1; oxidative stress inhibits E2F1-SENP3 interaction, leading to accumulation of sumoylated E2F1.","method":"In vivo SUMOylation assays, site-directed mutagenesis (K266), co-immunoprecipitation, SENP3 knockdown, cell viability assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-specific mutagenesis combined with functional cell survival assays and co-IP identifying the eraser enzyme","pmids":["32541040"],"is_preprint":false},{"year":2020,"finding":"SUMOylation enhances E2F1 binding to the EZH2 promoter, increasing EZH2 transcription. Knockdown of SAE2 (SUMO-activating enzyme) or pharmacological inhibition of SUMOylation reduces E2F1 binding to the EZH2 promoter and decreases EZH2 mRNA and protein levels.","method":"SAE2 siRNA knockdown, pharmacological SUMOylation inhibition, ChIP, qRT-PCR, western blot","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating promoter binding change, loss-of-function with two independent methods (siRNA + drug), single lab","pmids":["32816857"],"is_preprint":false},{"year":2004,"finding":"E2F1 induces p53 phosphorylation and apoptosis through the ATM/NBS1 signaling pathway. In ATM-deficient primary human fibroblasts, E2F1-induced p53 phosphorylation and apoptosis are impaired. E2F1 also induces ATM- and NBS1-dependent phosphorylation of Chk2 at Thr68. ATM autophosphorylation at Ser1981 is absent, suggesting E2F1 activates ATM through a mechanism distinct from DNA double-strand breaks.","method":"Primary fibroblast studies with ATM-deficient and NBS1-mutant cells, phosphorylation assays (p53, Chk2, γH2AX), apoptosis assays","journal":"Molecular cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetically defined cell lines (ATM-/-, NBS1 mutant), multiple phosphorylation targets measured, clearly establishes pathway position","pmids":["15140942"],"is_preprint":false},{"year":2014,"finding":"E2F1 is phosphorylated at serine 31 (mouse Ser29) by ATM or ATR in response to DNA damage, which promotes E2F1 protein stabilization and recruitment to sites of DNA damage. This phosphorylation is required for DNA repair and suppression of UV-induced carcinogenesis; S29A knock-in mice show reduced DNA repair and increased skin tumor susceptibility.","method":"Knock-in mouse model (S29A mutation), UV radiation experiments, DNA repair assays, ChIP at damage sites, tumor incidence measurement","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1 / Strong — knock-in mouse model with site-specific mutation, multiple orthogonal endpoints (repair, localization, tumorigenesis) validated in vivo","pmids":["24741006"],"is_preprint":false},{"year":2012,"finding":"p38 MAPK-MK2 axis regulates E2F1 expression in response to epirubicin; MK2 directly phosphorylates E2F1 at Ser-364 in vitro, contributing to E2F1 induction by epirubicin. E2F1 in turn promotes FOXM1 expression.","method":"In vitro phosphorylation assay, pharmacological inhibitors, siRNA knockdown, knockout MEFs, transfection assays","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation assay identifies specific site, supported by multiple genetic/pharmacological loss-of-function approaches, single lab","pmids":["22802261"],"is_preprint":false},{"year":1994,"finding":"E2F1 and DP1 heterodimerize through their hydrophobic heptad repeat domains (E2F1 residues 206–283 interacting with DP1 residues 196–245). The adenovirus E4 protein interacts with the DP1 subunit (not E2F1 directly) to stabilize the E2F1-DP1 complex on the E2 promoter.","method":"Yeast two-hybrid assay, co-expression/co-immunoprecipitation in SAOS-2 cells, deletion mutagenesis","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — yeast two-hybrid with deletion mapping plus cell-based co-IP validation, domain-level resolution of interaction","pmids":["8207796"],"is_preprint":false},{"year":2002,"finding":"ARF induces proteolysis of free E2F1 and relocalizes it to the nucleolus, inhibiting E2F1-activated transcription. However, the E2F1/DP1 heterodimer is refractory to ARF-induced relocalization or degradation; coexpression of DP1 prevents ARF from targeting E2F1.","method":"Co-immunoprecipitation, fluorescence microscopy (relocalization), protein stability/degradation assays, transcription reporter assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (localization, degradation, transcription), single lab; clear positive and negative findings about the free vs. complexed forms","pmids":["12446760"],"is_preprint":false},{"year":2008,"finding":"E2F1 is a potent inhibitor of beta-catenin/TCF-dependent transcription in a GSK3/APC-independent manner. CDK8, a colorectal oncoprotein, phosphorylates/represses E2F1 activity, protecting beta-catenin transcription from E2F1-mediated inhibition. E2F1-induced apoptosis is partly mediated through suppression of beta-catenin activity.","method":"Genetic epistasis (Drosophila and mammalian cells), reporter assays, CDK8 overexpression/knockdown, E2F1 overexpression, apoptosis assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis in multiple systems (Drosophila and mammalian), reporter assays, CDK8 functional connection demonstrated, replicated across labs/models","pmids":["18794899"],"is_preprint":false},{"year":2008,"finding":"The aryl hydrocarbon receptor (AHR) physically interacts with E2F1 independently of RB (demonstrated by co-IP from RB-negative cell extracts). AHR and E2F1 co-occupy the Apaf1 promoter at an E2F1 binding site. AHR activation represses E2F1-dependent transcription of Apaf1 and TAp73, attenuating E2F1-induced apoptosis.","method":"Co-immunoprecipitation (RB-negative cells), ChIP, siRNA knockdown, apoptosis assays, reporter assays","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP in RB-null cells, ChIP co-occupancy, functional siRNA validation, single lab","pmids":["18524851"],"is_preprint":false},{"year":2009,"finding":"E2F1 transcriptionally induces EZH2 expression; EZH2 in turn antagonizes E2F1-dependent Bim induction via histone methylation, suppressing E2F1's proapoptotic activity. RNAi depletion of EZH2 enhances E2F1-dependent Bim expression and promotes apoptosis.","method":"RNAi, reporter assays, western blot, apoptosis assays","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function RNAi with defined apoptotic phenotype, establishes feedback pathway, single lab","pmids":["19893569"],"is_preprint":false},{"year":2009,"finding":"The CDK4-pRB-E2F1 pathway directly regulates Kir6.2 expression in pancreatic beta cells. E2F1 binds the Kir6.2 promoter (ChIP from tissues), and E2F1 genetic inactivation leads to decreased Kir6.2 expression, impaired insulin secretion, and glucose intolerance. CDK4 is activated by glucose through the insulin pathway to activate E2F1.","method":"ChIP from pancreatic tissue, E2f1 knockout mice, Kir6.2 rescue experiments, glucose tolerance tests, insulin secretion assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP from tissues, genetic knockout with specific metabolic phenotype, rescue experiment restores function","pmids":["19597485"],"is_preprint":false},{"year":2015,"finding":"E2F1 directly binds to the promoters of lipogenic genes including Fasn in hepatocytes (ChIP-Seq confirmed); E2F1 deficiency reduces glycolysis and de novo fatty acid synthesis. E2F1 expression increases in response to feeding and insulin through CDK4/pRB pathway activation. E2f1 deletion abrogates hepatic steatosis in NAFLD mouse models.","method":"ChIP-Seq, E2f1 knockout mice, primary hepatocyte experiments, murine NAFLD models, reporter assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP-Seq with direct promoter binding, genetic knockout with specific metabolic phenotype, multiple NAFLD models","pmids":["26619117"],"is_preprint":false},{"year":2017,"finding":"E2F1 binds to and transactivates the PCSK9 promoter (ChIP-Seq), increasing PCSK9 expression and thus promoting LDLR degradation to inhibit cholesterol clearance. E2f1 deletion leads to decreased Pcsk9 expression and increased LDLR expression and LDL uptake.","method":"ChIP-Seq, PCSK9 promoter reporter assays, E2f1 knockout mice, LDL uptake assays","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP-Seq plus reporter assays confirming direct transcriptional regulation, genetic knockout with defined metabolic phenotype","pmids":["28515357"],"is_preprint":false},{"year":2018,"finding":"E2F1 directly binds the Sirt6 promoter and suppresses Sirt6 transcription, thereby enhancing glycolysis (increased glucose uptake and lactate production). A DNA-binding-deficient E2F1 mutant cannot enhance glycolysis. HDAC1 deacetylates E2F1 and diminishes its suppression of Sirt6; acetylated E2F1 binds the Sirt6 promoter more strongly.","method":"ChIP, Sirt6 promoter reporter assays, E2F1 overexpression with DNA-binding mutant, siRNA knockdown, glucose uptake/lactate assays, HDAC inhibitor treatment","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assays with mutagenesis, functional metabolic readouts, single lab","pmids":["25816777"],"is_preprint":false},{"year":2018,"finding":"E2F1 associates with DP1 to bind the KPNA2 promoter and induce KPNA2 expression. KPNA2, as a nuclear import factor, mediates nuclear localization of E2F1. E2F7 competes with DP1 to block E2F1-induced KPNA2 activation; mutation of E2F7 dimerization residues or E2F1 DNA-binding domain abolishes this competition.","method":"ChIP, promoter reporter assays, mutagenesis, co-immunoprecipitation, nuclear fractionation, siRNA knockdown","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assays with domain mutagenesis, functional localization consequence, single lab","pmids":["30254209"],"is_preprint":false},{"year":2013,"finding":"p53 physically interacts with E2F1 upon DNA damage to form a p53-E2F1-DNA complex on the PLK1 promoter, repressing E2F1-dependent PLK1 transcription. Mutation of E2F1 binding sites in the PLK1 promoter abolishes p53-mediated suppression.","method":"Co-immunoprecipitation, EMSA, ChIP, re-ChIP, promoter deletion/substitution mutagenesis, reporter assays","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EMSA, ChIP/re-ChIP demonstrating ternary complex, promoter mutagenesis, single lab","pmids":["24076372"],"is_preprint":false},{"year":2018,"finding":"Nuclear PTEN (phosphorylation-deficient PTEN-4A mutant) physically interacts with E2F1 and associates with chromatin at E2F1 DNA-binding site-containing promoters, suppressing E2F1-mediated transcription. The C2 domain of PTEN is required for this suppression. Cancer-associated C2 domain mutations lose the ability to suppress E2F1-mediated transcription.","method":"Co-immunoprecipitation, ChIP, promoter reporter assays, deletion/point mutagenesis, nuclear fractionation","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and ChIP with domain mutagenesis demonstrating physical interaction and chromatin co-occupancy, single lab","pmids":["29108454"],"is_preprint":false},{"year":2009,"finding":"RRP1B is an E2F1-specific transcriptional target that forms a complex with E2F1 on selective proapoptotic target gene promoters (including apoptotic gene promoters). RRP1B is required for E2F1-induced apoptosis in response to DNA-damaging agents.","method":"Promoter analysis, ChIP, co-immunoprecipitation, RRP1B knockdown, apoptosis assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and co-IP demonstrating complex formation at specific promoters, loss-of-function with defined apoptotic phenotype, single lab","pmids":["20040599"],"is_preprint":false},{"year":2014,"finding":"RORα binds to the heptad repeat and marked box region of E2F1, suppresses E2F1-regulated transcription, and inhibits E2F1 acetylation and DNA-binding activity by recruiting HDAC1 to the complex. HDAC1 knockdown or HDAC inhibition partially rescues E2F1 activity repressed by RORα.","method":"Co-immunoprecipitation, domain mapping, reporter assays, HDAC1 knockdown, HDAC inhibitor treatment, mammary cell proliferation assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with domain mapping, functional rescue experiments with HDAC inhibition, single lab","pmids":["24891616"],"is_preprint":false},{"year":2010,"finding":"E2F1 activates the p27Kip1 promoter in vivo and induces p27 mRNA and protein expression. E2F1 binds the p27 promoter by ChIP. siRNA depletion of endogenous E2F1 reduces basal p27 levels, and siRNA inhibition of p27 enhances E2F1 transcriptional activity and accelerates cell cycle progression, constituting a negative feedback loop.","method":"ChIP, siRNA knockdown, reporter assays, western blot, cell cycle analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating direct promoter binding, dual siRNA epistasis establishing feedback loop, single lab","pmids":["15713665"],"is_preprint":false},{"year":2005,"finding":"E2F1 directly regulates DNMT1 expression via conserved E2F binding sites in the DNMT1 promoter. In Rb-/- cells, Dnmt1 transcripts show aberrant cell cycle regulation, leading to aberrant methylation of the Peg3 tumor suppressor locus.","method":"Promoter analysis, cell cycle expression profiling in Rb-/- cells, methylation analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined binding sites, genetic loss-of-function (Rb-/-) with specific methylation outcome, single lab","pmids":["15867357"],"is_preprint":false},{"year":2010,"finding":"E2F1 activity antagonizes RB-induced autophagy; RB binding to E2F1 is required for autophagy induction, and downregulation of E2F1 results in high levels of autophagy. Thus, RB induces autophagy by repressing E2F1 activity.","method":"RB overexpression, E2F1 knockdown (siRNA), autophagy assays, genetic epistasis with p16INK4a and p27/kip1","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA loss-of-function with defined autophagy phenotype, epistasis with upstream regulators, single lab","pmids":["20807803"],"is_preprint":false},{"year":2011,"finding":"E2F1 induces cell growth and mTORC1 activity in a manner dependent on E2F1's DNA-binding and transcriptional activity. E2F1 induces translocation of mTORC1 to late endosome vesicles in a leucine-dependent mechanism. TSC2 overexpression does not block E2F1-induced mTORC1 activation, indicating the pathway bypasses TSC2/Rheb.","method":"E2F1 overexpression with DNA-binding mutant controls, immunolocalization studies, mTORC1 activity assays (S6K phosphorylation), TSC2 epistasis experiments","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional mutagenesis (DNA-binding mutant), organelle localization, epistasis with TSC2, single lab","pmids":["21283628"],"is_preprint":false},{"year":2005,"finding":"E2F1 promotes apoptosis through the ATM signaling pathway using a mechanism distinct from classical DNA double-strand break induction, as ATM autophosphorylation at Ser1981 is absent but Chk2 Thr68 phosphorylation is ATM-dependent.","method":"ATM-deficient and NBS1-mutant primary fibroblasts, phosphorylation assays","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetically defined cell lines establishing pathway requirement, single lab (overlapping with PMID 15140942)","pmids":["15190206"],"is_preprint":false},{"year":2022,"finding":"In Drosophila, small upstream open reading frames (uORFs) in the 5' UTR of E2f1 mRNA limit E2F1 translation. TOR signaling can bypass uORF-mediated translational repression to promote E2F1 protein synthesis. EGFR signaling also enhances E2F1 translation but through a mechanism less dependent on 5'UTR uORFs. Both pathways regulate cell proliferation via E2F1 protein levels.","method":"Transgenic Drosophila with E2f1 5'UTR mutants, genetic epistasis with TOR/EGFR pathway mutants, cell proliferation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic mutant rescue in Drosophila with defined cis-regulatory elements, genetic epistasis, ortholog of mammalian E2F1","pmids":["35074910"],"is_preprint":false},{"year":2017,"finding":"PI3Kδ activation in response to mRNA translation stress (triggered by EBV EBNA1 gly-ala repeat) induces E2F1 mRNA translation. PI3Kδ inhibition with Idelalisib suppresses E2F1 and c-Myc levels and causes cell death in EBNA1-induced B cell lymphomas.","method":"PI3Kδ pharmacological inhibition, E2F1 translation assays, B cell lymphoma cell death assays","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific PI3Kδ inhibitor with defined translational output, in vivo lymphoma model validation, single lab","pmids":["29235459"],"is_preprint":false},{"year":2006,"finding":"EGFR co-immunoprecipitates with E2F1 in an EGF-dependent manner. Nuclear EGFR and E2F1 co-occupy the B-Myb promoter in vivo (ChIP). Co-expression of EGFR and E2F1 synergistically activates B-Myb promoter, dependent on both E2F and EGFR binding sites.","method":"Co-immunoprecipitation, ChIP, promoter reporter assays with site mutagenesis, co-expression in EGFR-null CHO cells","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus ChIP for complex at promoter, functional mutagenesis, single lab","pmids":["16299810"],"is_preprint":false},{"year":2005,"finding":"c-Myc activates transcription of a miRNA cluster (miR-17-5p, miR-20a among others) on human chromosome 13. miR-17-5p and miR-20a negatively regulate E2F1 protein translation, while c-Myc also activates E2F1 transcription—establishing a mechanism where c-Myc simultaneously drives and limits E2F1 expression.","method":"Chromatin immunoprecipitation (c-Myc at miRNA locus), miRNA overexpression with E2F1 reporter assays, northern blot","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP confirming direct transcriptional activation, functional miRNA reporter assays confirming translational repression, replicated by independent labs","pmids":["15944709"],"is_preprint":false},{"year":2014,"finding":"E2F1 directly activates transcription of the miR-224/miR-452 cluster through transactivation of the GABRE gene promoter. miR-224/miR-452 targets the metastasis suppressor TXNIP, which provides feedback inhibition of E2F1. This E2F1-miR-224/452-TXNIP axis drives EMT and invasion in melanoma.","method":"ChIP, reporter assays, miRNA overexpression/depletion, in vivo lung metastasis assay, TXNIP 3'UTR targeting validation","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for direct promoter binding, functional in vivo metastasis validation, single lab","pmids":["25341426"],"is_preprint":false},{"year":2012,"finding":"E2F1 directly binds the p27 promoter and p53 tumor suppressor interacts with E2F1, and in response to DNA damage, p53-E2F1 complex forms on specific gene promoters to modulate transcriptional outcomes.","method":"Co-immunoprecipitation, ChIP","journal":"The Journal of biological chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-IP data referenced in multiple papers but original evidence from a single method, overlapping with PMID 24076372 for p53-E2F1 complex","pmids":["15713665"],"is_preprint":false},{"year":2018,"finding":"E2F1 directly transcriptionally activates AUF1 in HCC (binding to AUF1 promoter), and E2F1 promotes hepatic gluconeogenesis through transcriptional regulation of gluconeogenic genes including Pck1; CDK4-RB1-E2F1 canonical pathway is directly involved.","method":"ChIP, E2F1 overexpression/knockout, primary hepatocyte gluconeogenesis assays, diabetic mouse models","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus genetic models with defined metabolic phenotype, multiple mouse models, single lab","pmids":["29526568"],"is_preprint":false}],"current_model":"E2F1 is a transcription factor that is released from RB repression upon CDK-mediated RB phosphorylation at the G1/S boundary, whereupon free E2F1 drives expression of S-phase and lipogenic/metabolic genes; its activity and stability are tightly controlled by a network of post-translational modifications—including acetylation (by P/CAF, reversed by RB-associated HDAC), phosphorylation (by ATM/ATR at Ser31 and MK2 at Ser364), lysine methylation (by Set9, reversed by LSD1), arginine methylation (by PRMT5), SUMOylation (SUMO2 at K266, reversed by SENP3), citrullination (by PAD4), and ubiquitination (by SCF-SKP2/APC/C-Cdc20, stabilized by MDM2 and deubiquitylated by POH1 and Cezanne)—that collectively determine its protein stability, DNA-binding capacity, subcellular localization, and transcriptional target selection to dictate opposing outcomes of cell cycle progression, DNA repair, apoptosis, and metabolic regulation (lipogenesis, gluconeogenesis, cholesterol homeostasis)."},"narrative":{"mechanistic_narrative":"E2F1 is a sequence-specific transcription factor that operates downstream of the CDK4-RB axis to drive proliferative, apoptotic, and metabolic gene programs, with its activity dictated by both heterodimerization and an extensive post-translational modification code [PMID:8207796, PMID:26619117]. DNA binding requires heterodimerization with DP1 through reciprocal hydrophobic heptad-repeat domains, and the E2F1-DP1 complex resists the degradation and nucleolar relocalization that ARF imposes on free E2F1 monomers [PMID:8207796, PMID:12446760]. A dense PTM network sets E2F1 abundance and target selection: P/CAF acetylation near the DNA-binding domain raises DNA-binding affinity, transactivation, and stability and is reversed by RB-associated/HDAC1 deacetylation, while Set9 methylation at K185 and PRMT5 arginine methylation destabilize E2F1 and curb its proapoptotic output, with LSD1 demethylation and DNA-damage signals reversing this restraint [PMID:10675335, PMID:20603083, PMID:22327218, PMID:25816777]. Protein turnover is controlled by competing ubiquitin machinery—SCF(SKP2) and APC/C(Cdc20) promote degradation, MDM2 stabilizes E2F1 by displacing SCF(SKP2), and the deubiquitylases POH1 and methyl-dependent CRL4(DCAF5) recruitment via L3MBTL3 further tune levels [PMID:16170383, PMID:26510456, PMID:20948288, PMID:29691401]. Genotoxic stress stabilizes and activates E2F1 through ATM/ATR phosphorylation at Ser31, which is required for recruitment to damage sites, DNA repair, and tumor suppression, and through an ATM/NBS1 axis that phosphorylates p53 and Chk2 to drive apoptosis [PMID:15140942, PMID:24741006]. Beyond proliferation, E2F1 is a central metabolic regulator that binds promoters of lipogenic (Fasn), gluconeogenic (Pck1), cholesterol-handling (Pcsk9), and glycolytic genes and controls insulin secretion via Kir6.2, such that E2f1 loss protects against hepatic steatosis [PMID:19597485, PMID:26619117, PMID:28515357, PMID:29526568]. Its proapoptotic versus prosurvival outcomes are shaped by interacting partners and feedback loops including SirT1, EZH2, p53, AHR, and SUMOylation/SENP3 [PMID:16892051, PMID:32541040, PMID:18524851, PMID:19893569, PMID:24076372].","teleology":[{"year":1994,"claim":"Established the structural basis of E2F1 function by defining how it acquires DNA-binding competence through obligate heterodimerization with DP1.","evidence":"Yeast two-hybrid and co-IP with deletion mapping in SAOS-2 cells","pmids":["8207796"],"confidence":"High","gaps":["Does not address regulation of the dimer in normal cell-cycle context","No structural model of the complex on DNA"]},{"year":2000,"claim":"Showed that acetylation is a direct activating switch on E2F1, linking enzyme-mediated modification to DNA binding, transactivation, and stability.","evidence":"In vitro P/CAF acetylation, site-directed mutagenesis, transcription assays","pmids":["10675335"],"confidence":"High","gaps":["In vitro assays do not establish physiological stoichiometry","Did not resolve which lysines dominate in vivo"]},{"year":2004,"claim":"Positioned E2F1 upstream of the ATM/NBS1-p53 apoptotic axis, showing E2F1 activates this pathway by a route distinct from canonical double-strand breaks.","evidence":"ATM-deficient and NBS1-mutant primary fibroblasts with phosphorylation and apoptosis readouts","pmids":["15140942","15190206"],"confidence":"High","gaps":["Mechanism by which E2F1 activates ATM without Ser1981 autophosphorylation unresolved","Does not identify direct E2F1-ATM contact"]},{"year":2005,"claim":"Defined opposing ubiquitin-pathway control of E2F1 stability, showing MDM2 stabilizes E2F1 by displacing its SCF(SKP2) ligase independent of p53 and pRB.","evidence":"Co-IP, ubiquitination and half-life assays with deletion mutants","pmids":["16170383"],"confidence":"High","gaps":["Did not map the degron displaced by MDM2","In vivo relevance not tested genetically"]},{"year":2005,"claim":"Connected E2F1 to a c-Myc feedforward/feedback circuit in which Myc both activates E2F1 transcription and represses E2F1 translation via a miRNA cluster.","evidence":"ChIP at the miRNA locus and miRNA reporter assays for E2F1 repression","pmids":["15944709"],"confidence":"High","gaps":["Quantitative balance of activation vs repression in vivo unclear"]},{"year":2009,"claim":"Demonstrated that E2F1 is a direct transcriptional regulator of metabolic genes controlling insulin secretion, extending its role beyond proliferation.","evidence":"ChIP from pancreatic tissue, E2f1 knockout mice, Kir6.2 rescue, glucose tolerance tests","pmids":["19597485"],"confidence":"High","gaps":["Does not address coordination with cell-cycle target program"]},{"year":2010,"claim":"Showed that lysine methylation by Set9 acts as a degradation-promoting brake on DNA-damage-induced E2F1 stabilization and apoptosis, reversed by LSD1.","evidence":"In vitro methylation, mutagenesis, siRNA, co-IP, apoptosis assays","pmids":["20603083"],"confidence":"High","gaps":["Crosstalk hierarchy among PTMs only partially mapped","Reader of K185 methylation not identified here"]},{"year":2010,"claim":"Identified cell-cycle-phase-specific destruction of E2F1 by APC/C(Cdc20) in prometaphase, blocked by DP1 co-expression.","evidence":"Cell synchronization, Cdc20 overexpression/knockdown, stability assays","pmids":["20948288"],"confidence":"Medium","gaps":["Degron recognized by APC/C not mapped","Single lab, no reciprocal in vivo validation"]},{"year":2012,"claim":"Showed arginine methylation by PRMT5 destabilizes E2F1 and limits its DNA binding, with DNA damage relieving this mark to enable proapoptotic function.","evidence":"In vitro methylation, PRMT5 siRNA, stability and DNA-binding assays","pmids":["22327218"],"confidence":"High","gaps":["Specific arginine residues and crosstalk with K185 methylation not fully resolved"]},{"year":2014,"claim":"Established that ATM/ATR phosphorylation at Ser31 is required in vivo for E2F1-dependent DNA repair and tumor suppression.","evidence":"S29A knock-in mice, UV experiments, ChIP at damage sites, tumor incidence","pmids":["24741006"],"confidence":"High","gaps":["Mechanism of recruitment to damage sites not molecularly defined"]},{"year":2015,"claim":"Defined E2F1 as a master driver of hepatic lipogenesis and glycolysis acting downstream of feeding/insulin via CDK4-pRB.","evidence":"ChIP-Seq, E2f1 knockout mice, NAFLD models, primary hepatocytes","pmids":["26619117"],"confidence":"High","gaps":["Does not separate transcriptional from cell-cycle effects on metabolism"]},{"year":2015,"claim":"Identified POH1 as a deubiquitylase that stabilizes E2F1, adding a counterweight to E2F1 ubiquitination in vivo.","evidence":"Co-IP, deubiquitylation assay, conditional Poh1 knockout liver","pmids":["26510456"],"confidence":"High","gaps":["Which E2F1 ubiquitin marks POH1 removes not specified"]},{"year":2016,"claim":"Revealed citrullination by PAD4 as a modification that redirects E2F1 to cytokine promoters and recruits BRD4 to drive inflammatory transcription.","evidence":"In vitro citrullination, ChIP, co-IP, pharmacological inhibition, arthritis model","pmids":["26989780"],"confidence":"High","gaps":["Citrullinated residues not mapped","Generalizability beyond inflammatory cells unclear"]},{"year":2017,"claim":"Extended E2F1's metabolic reach to cholesterol homeostasis by showing it transactivates PCSK9 to promote LDLR degradation.","evidence":"ChIP-Seq, PCSK9 reporter assays, E2f1 knockout mice, LDL uptake assays","pmids":["28515357"],"confidence":"High","gaps":["Interaction with lipogenic program coordination not addressed"]},{"year":2018,"claim":"Showed methylation-dependent recruitment of CRL4(DCAF5) via the reader L3MBTL3 couples E2F1 methylation to its degradation.","evidence":"Biochemical methyl-binding and ubiquitination assays, genetic deletion models","pmids":["29691401"],"confidence":"Medium","gaps":["Which methyl mark is read not pinned down","In vivo significance limited"]},{"year":2018,"claim":"Linked E2F1 to gluconeogenic control, showing it transcriptionally activates Pck1 and AUF1 through the CDK4-RB1-E2F1 pathway.","evidence":"ChIP, E2F1 overexpression/knockout, hepatocyte gluconeogenesis assays, diabetic mice","pmids":["29526568"],"confidence":"Medium","gaps":["Single lab; coordination with lipogenic program not resolved"]},{"year":2020,"claim":"Identified SUMO2 conjugation at K266 as a stress-responsive brake that inhibits E2F1 transactivation to favor survival, reversed by SENP3.","evidence":"In vivo SUMOylation, K266 mutagenesis, co-IP, SENP3 knockdown, viability assays","pmids":["32541040"],"confidence":"High","gaps":["How oxidative stress disrupts the E2F1-SENP3 interaction mechanistically unclear"]},{"year":null,"claim":"How the dozens of competing PTMs, partner proteins, and feedback loops are integrated in real time to select between proliferative, apoptotic, and metabolic E2F1 target programs remains unresolved.","evidence":"No single study reconstitutes the combinatorial PTM/partner code governing E2F1 target selection","pmids":[],"confidence":"Low","gaps":["No integrated model linking PTM combinations to specific gene-program outputs","Stoichiometry and temporal order of modifications in vivo unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,14,19,20,21,22,39]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,3,22,23,24]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[23,25,35]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6,19,28,30]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,19,20,21,39]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[11,12]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[1,11,18,26]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[19,20,21,22,39]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[33,34,36]}],"complexes":["E2F1-DP1 heterodimer"],"partners":["TFDP1","RB1","MDM2","SIRT1","AHR","PTEN","TP53","BRD4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q01094","full_name":"Transcription factor E2F1","aliases":["PBR3","Retinoblastoma-associated protein 1","RBAP-1","Retinoblastoma-binding protein 3","RBBP-3","pRB-binding protein E2F-1"],"length_aa":437,"mass_kda":46.9,"function":"Transcription activator that binds DNA cooperatively with DP proteins through the E2 recognition site, 5'-TTTC[CG]CGC-3' found in the promoter region of a number of genes whose products are involved in cell cycle regulation or in DNA replication (PubMed:10675335, PubMed:12717439, PubMed:17050006, PubMed:17704056, PubMed:18625225, PubMed:28992046). The DRTF1/E2F complex functions in the control of cell-cycle progression from G1 to S phase (PubMed:10675335, PubMed:12717439, PubMed:17704056). E2F1 binds preferentially RB1 in a cell-cycle dependent manner (PubMed:10675335, PubMed:12717439, PubMed:17704056). It can mediate both cell proliferation and TP53/p53-dependent apoptosis (PubMed:8170954). Blocks adipocyte differentiation by binding to specific promoters repressing CEBPA binding to its target gene promoters (PubMed:20176812). Directly activates transcription of PEG10 (PubMed:17050006, PubMed:18625225, PubMed:28992046). Positively regulates transcription of RRP1B (PubMed:20040599)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q01094/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/E2F1","classification":"Not Classified","n_dependent_lines":230,"n_total_lines":1208,"dependency_fraction":0.19039735099337748},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/E2F1","total_profiled":1310},"omim":[{"mim_id":"621290","title":"E2F1-REGULATED INHIBITOR OF CELL DEATH, NONCODING; ERICD","url":"https://www.omim.org/entry/621290"},{"mim_id":"621239","title":"INTEGRATOR COMPLEX SUBUNIT 15; INTS15","url":"https://www.omim.org/entry/621239"},{"mim_id":"621189","title":"LONG INTERGENIC NONCODING RNA 2525; LINC02525","url":"https://www.omim.org/entry/621189"},{"mim_id":"620544","title":"PPP1R13B DIVERGENT TRANSCRIPT, NONCODING; PPP1R13BDT","url":"https://www.omim.org/entry/620544"},{"mim_id":"620335","title":"CELL DIVISION CYCLE 20B; CDC20B","url":"https://www.omim.org/entry/620335"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Centrosome","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":32.4}],"url":"https://www.proteinatlas.org/search/E2F1"},"hgnc":{"alias_symbol":["RBP3"],"prev_symbol":["RBBP3"]},"alphafold":{"accession":"Q01094","domains":[{"cath_id":"1.10.10.10","chopping":"127-193","consensus_level":"medium","plddt":87.5518,"start":127,"end":193},{"cath_id":"-","chopping":"254-299","consensus_level":"medium","plddt":89.672,"start":254,"end":299}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q01094","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q01094-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q01094-F1-predicted_aligned_error_v6.png","plddt_mean":62.03},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=E2F1","jax_strain_url":"https://www.jax.org/strain/search?query=E2F1"},"sequence":{"accession":"Q01094","fasta_url":"https://rest.uniprot.org/uniprotkb/Q01094.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q01094/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q01094"}},"corpus_meta":[{"pmid":"15944709","id":"PMC_15944709","title":"c-Myc-regulated 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The RB-associated histone deacetylase can deacetylate E2F1, reversing these effects.\",\n      \"method\": \"In vitro acetylation assay, site-directed mutagenesis, intracellular acetylation detection, functional transcription assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, multiple orthogonal functional readouts, single lab\",\n      \"pmids\": [\"10675335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SirT1 physically binds E2F1 and inhibits its transcriptional and apoptotic activities. E2F1 transcriptionally induces SirT1 expression, forming a negative feedback loop. Knockdown of SirT1 increases E2F1-dependent apoptosis and sensitivity to etoposide.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, transcriptional reporter assays, apoptosis assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, siRNA loss-of-function with defined apoptotic phenotype, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"16892051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Set9 methyltransferase methylates E2F1 at lysine-185, which prevents E2F1 accumulation during DNA damage and suppresses proapoptotic target gene p73 activation. LSD1 demethylase removes this mark, stabilizing E2F1 and enabling apoptotic function. Methylation at K185 inhibits acetylation and phosphorylation at distant sites while stimulating ubiquitination and proteasomal degradation.\",\n      \"method\": \"In vitro methylation assay, site-directed mutagenesis, siRNA knockdown, co-immunoprecipitation, apoptosis assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, epistasis between PTMs, multiple orthogonal readouts in single lab\",\n      \"pmids\": [\"20603083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PRMT5 directly methylates E2F1 on arginine residues, promoting E2F1 protein stability reduction and decreased DNA-binding activity. Depleting PRMT5 causes increased E2F1 protein levels and apoptosis. DNA damage conditions reduce arginine methylation of E2F1, allowing its stabilization.\",\n      \"method\": \"In vitro methylation assay, PRMT5 depletion (siRNA), protein stability assays, DNA-binding assays, apoptosis assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay, loss-of-function with multiple functional readouts, single lab with orthogonal methods\",\n      \"pmids\": [\"22327218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MDM2 stabilizes E2F1 protein by inhibiting its ubiquitination; MDM2 displaces SCF(SKP2), the E2F1 E3 ubiquitin ligase, through direct binding to E2F1, thereby prolonging E2F1 half-life independent of p53 and pRB.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, half-life measurement, deletion mutant analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical ubiquitination assay, displacement of E3 ligase demonstrated, multiple orthogonal methods\",\n      \"pmids\": [\"16170383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"POH1 deubiquitylase binds to and deubiquitylates E2F1, stabilizing E2F1 protein. Conditional Poh1 knockout reduces E2F1 expression in primary mouse liver cells.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitylation assay, conditional knockout mouse, western blot\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical deubiquitylation assay plus in vivo genetic knockout validation\",\n      \"pmids\": [\"26510456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"APC/C(Cdc20) ubiquitin ligase targets E2F1 for degradation specifically in prometaphase. Ectopic Cdc20 reduces E2F1 protein; Cdc20 knockdown causes E2F1 accumulation in prometaphase. Co-expression of DP1 with E2F1 blocks APC/C-induced E2F1 degradation.\",\n      \"method\": \"Co-expression experiments, siRNA knockdown, cell synchronization, western blot, protein stability assays\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based degradation assays with siRNA and overexpression, multiple conditions tested, single lab\",\n      \"pmids\": [\"20948288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"L3MBTL3 methyl-binding protein binds methylated E2F1 and recruits CRL4DCAF5 ubiquitin ligase to degrade E2F1 in a methylation-dependent manner, analogous to its regulation of DNMT1.\",\n      \"method\": \"Biochemical binding assays, ubiquitination/degradation assays, genetic deletion models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical demonstration of methylation-dependent binding and ubiquitination, supported by genetic models\",\n      \"pmids\": [\"29691401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PAD4 citrullinates E2F1 in inflammatory cells, which promotes E2F1 chromatin association at cytokine gene promoters. Citrullination augments binding of BRD4 to an acetylated domain of E2F1, and PAD4/BRD4/E2F1 coexist on cytokine gene promoters to drive inflammatory gene expression. Combined PAD4 and BRD4 inhibition disrupts this complex and suppresses cytokine expression.\",\n      \"method\": \"In vitro citrullination assay, ChIP, co-immunoprecipitation, pharmacological inhibition, murine arthritis model\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay plus ChIP and co-IP demonstrating complex, validated in vivo with pharmacological inhibition\",\n      \"pmids\": [\"26989780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SUMOylation of E2F1 at lysine-266 (SUMO2 conjugation) inhibits E2F1 transcriptional activity upon oxidative stress, promoting cell cycle arrest for cell survival. SENP3 desumoylase interacts with E2F1; oxidative stress inhibits E2F1-SENP3 interaction, leading to accumulation of sumoylated E2F1.\",\n      \"method\": \"In vivo SUMOylation assays, site-directed mutagenesis (K266), co-immunoprecipitation, SENP3 knockdown, cell viability assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-specific mutagenesis combined with functional cell survival assays and co-IP identifying the eraser enzyme\",\n      \"pmids\": [\"32541040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SUMOylation enhances E2F1 binding to the EZH2 promoter, increasing EZH2 transcription. Knockdown of SAE2 (SUMO-activating enzyme) or pharmacological inhibition of SUMOylation reduces E2F1 binding to the EZH2 promoter and decreases EZH2 mRNA and protein levels.\",\n      \"method\": \"SAE2 siRNA knockdown, pharmacological SUMOylation inhibition, ChIP, qRT-PCR, western blot\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating promoter binding change, loss-of-function with two independent methods (siRNA + drug), single lab\",\n      \"pmids\": [\"32816857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"E2F1 induces p53 phosphorylation and apoptosis through the ATM/NBS1 signaling pathway. In ATM-deficient primary human fibroblasts, E2F1-induced p53 phosphorylation and apoptosis are impaired. E2F1 also induces ATM- and NBS1-dependent phosphorylation of Chk2 at Thr68. ATM autophosphorylation at Ser1981 is absent, suggesting E2F1 activates ATM through a mechanism distinct from DNA double-strand breaks.\",\n      \"method\": \"Primary fibroblast studies with ATM-deficient and NBS1-mutant cells, phosphorylation assays (p53, Chk2, γH2AX), apoptosis assays\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetically defined cell lines (ATM-/-, NBS1 mutant), multiple phosphorylation targets measured, clearly establishes pathway position\",\n      \"pmids\": [\"15140942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"E2F1 is phosphorylated at serine 31 (mouse Ser29) by ATM or ATR in response to DNA damage, which promotes E2F1 protein stabilization and recruitment to sites of DNA damage. This phosphorylation is required for DNA repair and suppression of UV-induced carcinogenesis; S29A knock-in mice show reduced DNA repair and increased skin tumor susceptibility.\",\n      \"method\": \"Knock-in mouse model (S29A mutation), UV radiation experiments, DNA repair assays, ChIP at damage sites, tumor incidence measurement\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — knock-in mouse model with site-specific mutation, multiple orthogonal endpoints (repair, localization, tumorigenesis) validated in vivo\",\n      \"pmids\": [\"24741006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"p38 MAPK-MK2 axis regulates E2F1 expression in response to epirubicin; MK2 directly phosphorylates E2F1 at Ser-364 in vitro, contributing to E2F1 induction by epirubicin. E2F1 in turn promotes FOXM1 expression.\",\n      \"method\": \"In vitro phosphorylation assay, pharmacological inhibitors, siRNA knockdown, knockout MEFs, transfection assays\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation assay identifies specific site, supported by multiple genetic/pharmacological loss-of-function approaches, single lab\",\n      \"pmids\": [\"22802261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"E2F1 and DP1 heterodimerize through their hydrophobic heptad repeat domains (E2F1 residues 206–283 interacting with DP1 residues 196–245). The adenovirus E4 protein interacts with the DP1 subunit (not E2F1 directly) to stabilize the E2F1-DP1 complex on the E2 promoter.\",\n      \"method\": \"Yeast two-hybrid assay, co-expression/co-immunoprecipitation in SAOS-2 cells, deletion mutagenesis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — yeast two-hybrid with deletion mapping plus cell-based co-IP validation, domain-level resolution of interaction\",\n      \"pmids\": [\"8207796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ARF induces proteolysis of free E2F1 and relocalizes it to the nucleolus, inhibiting E2F1-activated transcription. However, the E2F1/DP1 heterodimer is refractory to ARF-induced relocalization or degradation; coexpression of DP1 prevents ARF from targeting E2F1.\",\n      \"method\": \"Co-immunoprecipitation, fluorescence microscopy (relocalization), protein stability/degradation assays, transcription reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (localization, degradation, transcription), single lab; clear positive and negative findings about the free vs. complexed forms\",\n      \"pmids\": [\"12446760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"E2F1 is a potent inhibitor of beta-catenin/TCF-dependent transcription in a GSK3/APC-independent manner. CDK8, a colorectal oncoprotein, phosphorylates/represses E2F1 activity, protecting beta-catenin transcription from E2F1-mediated inhibition. E2F1-induced apoptosis is partly mediated through suppression of beta-catenin activity.\",\n      \"method\": \"Genetic epistasis (Drosophila and mammalian cells), reporter assays, CDK8 overexpression/knockdown, E2F1 overexpression, apoptosis assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis in multiple systems (Drosophila and mammalian), reporter assays, CDK8 functional connection demonstrated, replicated across labs/models\",\n      \"pmids\": [\"18794899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The aryl hydrocarbon receptor (AHR) physically interacts with E2F1 independently of RB (demonstrated by co-IP from RB-negative cell extracts). AHR and E2F1 co-occupy the Apaf1 promoter at an E2F1 binding site. AHR activation represses E2F1-dependent transcription of Apaf1 and TAp73, attenuating E2F1-induced apoptosis.\",\n      \"method\": \"Co-immunoprecipitation (RB-negative cells), ChIP, siRNA knockdown, apoptosis assays, reporter assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP in RB-null cells, ChIP co-occupancy, functional siRNA validation, single lab\",\n      \"pmids\": [\"18524851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"E2F1 transcriptionally induces EZH2 expression; EZH2 in turn antagonizes E2F1-dependent Bim induction via histone methylation, suppressing E2F1's proapoptotic activity. RNAi depletion of EZH2 enhances E2F1-dependent Bim expression and promotes apoptosis.\",\n      \"method\": \"RNAi, reporter assays, western blot, apoptosis assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function RNAi with defined apoptotic phenotype, establishes feedback pathway, single lab\",\n      \"pmids\": [\"19893569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The CDK4-pRB-E2F1 pathway directly regulates Kir6.2 expression in pancreatic beta cells. E2F1 binds the Kir6.2 promoter (ChIP from tissues), and E2F1 genetic inactivation leads to decreased Kir6.2 expression, impaired insulin secretion, and glucose intolerance. CDK4 is activated by glucose through the insulin pathway to activate E2F1.\",\n      \"method\": \"ChIP from pancreatic tissue, E2f1 knockout mice, Kir6.2 rescue experiments, glucose tolerance tests, insulin secretion assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP from tissues, genetic knockout with specific metabolic phenotype, rescue experiment restores function\",\n      \"pmids\": [\"19597485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"E2F1 directly binds to the promoters of lipogenic genes including Fasn in hepatocytes (ChIP-Seq confirmed); E2F1 deficiency reduces glycolysis and de novo fatty acid synthesis. E2F1 expression increases in response to feeding and insulin through CDK4/pRB pathway activation. E2f1 deletion abrogates hepatic steatosis in NAFLD mouse models.\",\n      \"method\": \"ChIP-Seq, E2f1 knockout mice, primary hepatocyte experiments, murine NAFLD models, reporter assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP-Seq with direct promoter binding, genetic knockout with specific metabolic phenotype, multiple NAFLD models\",\n      \"pmids\": [\"26619117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"E2F1 binds to and transactivates the PCSK9 promoter (ChIP-Seq), increasing PCSK9 expression and thus promoting LDLR degradation to inhibit cholesterol clearance. E2f1 deletion leads to decreased Pcsk9 expression and increased LDLR expression and LDL uptake.\",\n      \"method\": \"ChIP-Seq, PCSK9 promoter reporter assays, E2f1 knockout mice, LDL uptake assays\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP-Seq plus reporter assays confirming direct transcriptional regulation, genetic knockout with defined metabolic phenotype\",\n      \"pmids\": [\"28515357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"E2F1 directly binds the Sirt6 promoter and suppresses Sirt6 transcription, thereby enhancing glycolysis (increased glucose uptake and lactate production). A DNA-binding-deficient E2F1 mutant cannot enhance glycolysis. HDAC1 deacetylates E2F1 and diminishes its suppression of Sirt6; acetylated E2F1 binds the Sirt6 promoter more strongly.\",\n      \"method\": \"ChIP, Sirt6 promoter reporter assays, E2F1 overexpression with DNA-binding mutant, siRNA knockdown, glucose uptake/lactate assays, HDAC inhibitor treatment\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assays with mutagenesis, functional metabolic readouts, single lab\",\n      \"pmids\": [\"25816777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"E2F1 associates with DP1 to bind the KPNA2 promoter and induce KPNA2 expression. KPNA2, as a nuclear import factor, mediates nuclear localization of E2F1. E2F7 competes with DP1 to block E2F1-induced KPNA2 activation; mutation of E2F7 dimerization residues or E2F1 DNA-binding domain abolishes this competition.\",\n      \"method\": \"ChIP, promoter reporter assays, mutagenesis, co-immunoprecipitation, nuclear fractionation, siRNA knockdown\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assays with domain mutagenesis, functional localization consequence, single lab\",\n      \"pmids\": [\"30254209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"p53 physically interacts with E2F1 upon DNA damage to form a p53-E2F1-DNA complex on the PLK1 promoter, repressing E2F1-dependent PLK1 transcription. Mutation of E2F1 binding sites in the PLK1 promoter abolishes p53-mediated suppression.\",\n      \"method\": \"Co-immunoprecipitation, EMSA, ChIP, re-ChIP, promoter deletion/substitution mutagenesis, reporter assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EMSA, ChIP/re-ChIP demonstrating ternary complex, promoter mutagenesis, single lab\",\n      \"pmids\": [\"24076372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Nuclear PTEN (phosphorylation-deficient PTEN-4A mutant) physically interacts with E2F1 and associates with chromatin at E2F1 DNA-binding site-containing promoters, suppressing E2F1-mediated transcription. The C2 domain of PTEN is required for this suppression. Cancer-associated C2 domain mutations lose the ability to suppress E2F1-mediated transcription.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, promoter reporter assays, deletion/point mutagenesis, nuclear fractionation\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and ChIP with domain mutagenesis demonstrating physical interaction and chromatin co-occupancy, single lab\",\n      \"pmids\": [\"29108454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RRP1B is an E2F1-specific transcriptional target that forms a complex with E2F1 on selective proapoptotic target gene promoters (including apoptotic gene promoters). RRP1B is required for E2F1-induced apoptosis in response to DNA-damaging agents.\",\n      \"method\": \"Promoter analysis, ChIP, co-immunoprecipitation, RRP1B knockdown, apoptosis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and co-IP demonstrating complex formation at specific promoters, loss-of-function with defined apoptotic phenotype, single lab\",\n      \"pmids\": [\"20040599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RORα binds to the heptad repeat and marked box region of E2F1, suppresses E2F1-regulated transcription, and inhibits E2F1 acetylation and DNA-binding activity by recruiting HDAC1 to the complex. HDAC1 knockdown or HDAC inhibition partially rescues E2F1 activity repressed by RORα.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, reporter assays, HDAC1 knockdown, HDAC inhibitor treatment, mammary cell proliferation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with domain mapping, functional rescue experiments with HDAC inhibition, single lab\",\n      \"pmids\": [\"24891616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"E2F1 activates the p27Kip1 promoter in vivo and induces p27 mRNA and protein expression. E2F1 binds the p27 promoter by ChIP. siRNA depletion of endogenous E2F1 reduces basal p27 levels, and siRNA inhibition of p27 enhances E2F1 transcriptional activity and accelerates cell cycle progression, constituting a negative feedback loop.\",\n      \"method\": \"ChIP, siRNA knockdown, reporter assays, western blot, cell cycle analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating direct promoter binding, dual siRNA epistasis establishing feedback loop, single lab\",\n      \"pmids\": [\"15713665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"E2F1 directly regulates DNMT1 expression via conserved E2F binding sites in the DNMT1 promoter. In Rb-/- cells, Dnmt1 transcripts show aberrant cell cycle regulation, leading to aberrant methylation of the Peg3 tumor suppressor locus.\",\n      \"method\": \"Promoter analysis, cell cycle expression profiling in Rb-/- cells, methylation analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined binding sites, genetic loss-of-function (Rb-/-) with specific methylation outcome, single lab\",\n      \"pmids\": [\"15867357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"E2F1 activity antagonizes RB-induced autophagy; RB binding to E2F1 is required for autophagy induction, and downregulation of E2F1 results in high levels of autophagy. Thus, RB induces autophagy by repressing E2F1 activity.\",\n      \"method\": \"RB overexpression, E2F1 knockdown (siRNA), autophagy assays, genetic epistasis with p16INK4a and p27/kip1\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA loss-of-function with defined autophagy phenotype, epistasis with upstream regulators, single lab\",\n      \"pmids\": [\"20807803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"E2F1 induces cell growth and mTORC1 activity in a manner dependent on E2F1's DNA-binding and transcriptional activity. E2F1 induces translocation of mTORC1 to late endosome vesicles in a leucine-dependent mechanism. TSC2 overexpression does not block E2F1-induced mTORC1 activation, indicating the pathway bypasses TSC2/Rheb.\",\n      \"method\": \"E2F1 overexpression with DNA-binding mutant controls, immunolocalization studies, mTORC1 activity assays (S6K phosphorylation), TSC2 epistasis experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional mutagenesis (DNA-binding mutant), organelle localization, epistasis with TSC2, single lab\",\n      \"pmids\": [\"21283628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"E2F1 promotes apoptosis through the ATM signaling pathway using a mechanism distinct from classical DNA double-strand break induction, as ATM autophosphorylation at Ser1981 is absent but Chk2 Thr68 phosphorylation is ATM-dependent.\",\n      \"method\": \"ATM-deficient and NBS1-mutant primary fibroblasts, phosphorylation assays\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetically defined cell lines establishing pathway requirement, single lab (overlapping with PMID 15140942)\",\n      \"pmids\": [\"15190206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Drosophila, small upstream open reading frames (uORFs) in the 5' UTR of E2f1 mRNA limit E2F1 translation. TOR signaling can bypass uORF-mediated translational repression to promote E2F1 protein synthesis. EGFR signaling also enhances E2F1 translation but through a mechanism less dependent on 5'UTR uORFs. Both pathways regulate cell proliferation via E2F1 protein levels.\",\n      \"method\": \"Transgenic Drosophila with E2f1 5'UTR mutants, genetic epistasis with TOR/EGFR pathway mutants, cell proliferation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic mutant rescue in Drosophila with defined cis-regulatory elements, genetic epistasis, ortholog of mammalian E2F1\",\n      \"pmids\": [\"35074910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PI3Kδ activation in response to mRNA translation stress (triggered by EBV EBNA1 gly-ala repeat) induces E2F1 mRNA translation. PI3Kδ inhibition with Idelalisib suppresses E2F1 and c-Myc levels and causes cell death in EBNA1-induced B cell lymphomas.\",\n      \"method\": \"PI3Kδ pharmacological inhibition, E2F1 translation assays, B cell lymphoma cell death assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific PI3Kδ inhibitor with defined translational output, in vivo lymphoma model validation, single lab\",\n      \"pmids\": [\"29235459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EGFR co-immunoprecipitates with E2F1 in an EGF-dependent manner. Nuclear EGFR and E2F1 co-occupy the B-Myb promoter in vivo (ChIP). Co-expression of EGFR and E2F1 synergistically activates B-Myb promoter, dependent on both E2F and EGFR binding sites.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, promoter reporter assays with site mutagenesis, co-expression in EGFR-null CHO cells\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus ChIP for complex at promoter, functional mutagenesis, single lab\",\n      \"pmids\": [\"16299810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"c-Myc activates transcription of a miRNA cluster (miR-17-5p, miR-20a among others) on human chromosome 13. miR-17-5p and miR-20a negatively regulate E2F1 protein translation, while c-Myc also activates E2F1 transcription—establishing a mechanism where c-Myc simultaneously drives and limits E2F1 expression.\",\n      \"method\": \"Chromatin immunoprecipitation (c-Myc at miRNA locus), miRNA overexpression with E2F1 reporter assays, northern blot\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP confirming direct transcriptional activation, functional miRNA reporter assays confirming translational repression, replicated by independent labs\",\n      \"pmids\": [\"15944709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"E2F1 directly activates transcription of the miR-224/miR-452 cluster through transactivation of the GABRE gene promoter. miR-224/miR-452 targets the metastasis suppressor TXNIP, which provides feedback inhibition of E2F1. This E2F1-miR-224/452-TXNIP axis drives EMT and invasion in melanoma.\",\n      \"method\": \"ChIP, reporter assays, miRNA overexpression/depletion, in vivo lung metastasis assay, TXNIP 3'UTR targeting validation\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for direct promoter binding, functional in vivo metastasis validation, single lab\",\n      \"pmids\": [\"25341426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"E2F1 directly binds the p27 promoter and p53 tumor suppressor interacts with E2F1, and in response to DNA damage, p53-E2F1 complex forms on specific gene promoters to modulate transcriptional outcomes.\",\n      \"method\": \"Co-immunoprecipitation, ChIP\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-IP data referenced in multiple papers but original evidence from a single method, overlapping with PMID 24076372 for p53-E2F1 complex\",\n      \"pmids\": [\"15713665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"E2F1 directly transcriptionally activates AUF1 in HCC (binding to AUF1 promoter), and E2F1 promotes hepatic gluconeogenesis through transcriptional regulation of gluconeogenic genes including Pck1; CDK4-RB1-E2F1 canonical pathway is directly involved.\",\n      \"method\": \"ChIP, E2F1 overexpression/knockout, primary hepatocyte gluconeogenesis assays, diabetic mouse models\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus genetic models with defined metabolic phenotype, multiple mouse models, single lab\",\n      \"pmids\": [\"29526568\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"E2F1 is a transcription factor that is released from RB repression upon CDK-mediated RB phosphorylation at the G1/S boundary, whereupon free E2F1 drives expression of S-phase and lipogenic/metabolic genes; its activity and stability are tightly controlled by a network of post-translational modifications—including acetylation (by P/CAF, reversed by RB-associated HDAC), phosphorylation (by ATM/ATR at Ser31 and MK2 at Ser364), lysine methylation (by Set9, reversed by LSD1), arginine methylation (by PRMT5), SUMOylation (SUMO2 at K266, reversed by SENP3), citrullination (by PAD4), and ubiquitination (by SCF-SKP2/APC/C-Cdc20, stabilized by MDM2 and deubiquitylated by POH1 and Cezanne)—that collectively determine its protein stability, DNA-binding capacity, subcellular localization, and transcriptional target selection to dictate opposing outcomes of cell cycle progression, DNA repair, apoptosis, and metabolic regulation (lipogenesis, gluconeogenesis, cholesterol homeostasis).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"E2F1 is a sequence-specific transcription factor that operates downstream of the CDK4-RB axis to drive proliferative, apoptotic, and metabolic gene programs, with its activity dictated by both heterodimerization and an extensive post-translational modification code [#14, #20]. DNA binding requires heterodimerization with DP1 through reciprocal hydrophobic heptad-repeat domains, and the E2F1-DP1 complex resists the degradation and nucleolar relocalization that ARF imposes on free E2F1 monomers [#14, #15]. A dense PTM network sets E2F1 abundance and target selection: P/CAF acetylation near the DNA-binding domain raises DNA-binding affinity, transactivation, and stability and is reversed by RB-associated/HDAC1 deacetylation, while Set9 methylation at K185 and PRMT5 arginine methylation destabilize E2F1 and curb its proapoptotic output, with LSD1 demethylation and DNA-damage signals reversing this restraint [#0, #2, #3, #22]. Protein turnover is controlled by competing ubiquitin machinery—SCF(SKP2) and APC/C(Cdc20) promote degradation, MDM2 stabilizes E2F1 by displacing SCF(SKP2), and the deubiquitylases POH1 and methyl-dependent CRL4(DCAF5) recruitment via L3MBTL3 further tune levels [#4, #5, #6, #7]. Genotoxic stress stabilizes and activates E2F1 through ATM/ATR phosphorylation at Ser31, which is required for recruitment to damage sites, DNA repair, and tumor suppression, and through an ATM/NBS1 axis that phosphorylates p53 and Chk2 to drive apoptosis [#11, #12]. Beyond proliferation, E2F1 is a central metabolic regulator that binds promoters of lipogenic (Fasn), gluconeogenic (Pck1), cholesterol-handling (Pcsk9), and glycolytic genes and controls insulin secretion via Kir6.2, such that E2f1 loss protects against hepatic steatosis [#19, #20, #21, #39]. Its proapoptotic versus prosurvival outcomes are shaped by interacting partners and feedback loops including SirT1, EZH2, p53, AHR, and SUMOylation/SENP3 [#1, #9, #17, #18, #24].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established the structural basis of E2F1 function by defining how it acquires DNA-binding competence through obligate heterodimerization with DP1.\",\n      \"evidence\": \"Yeast two-hybrid and co-IP with deletion mapping in SAOS-2 cells\",\n      \"pmids\": [\"8207796\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address regulation of the dimer in normal cell-cycle context\", \"No structural model of the complex on DNA\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed that acetylation is a direct activating switch on E2F1, linking enzyme-mediated modification to DNA binding, transactivation, and stability.\",\n      \"evidence\": \"In vitro P/CAF acetylation, site-directed mutagenesis, transcription assays\",\n      \"pmids\": [\"10675335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro assays do not establish physiological stoichiometry\", \"Did not resolve which lysines dominate in vivo\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Positioned E2F1 upstream of the ATM/NBS1-p53 apoptotic axis, showing E2F1 activates this pathway by a route distinct from canonical double-strand breaks.\",\n      \"evidence\": \"ATM-deficient and NBS1-mutant primary fibroblasts with phosphorylation and apoptosis readouts\",\n      \"pmids\": [\"15140942\", \"15190206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which E2F1 activates ATM without Ser1981 autophosphorylation unresolved\", \"Does not identify direct E2F1-ATM contact\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined opposing ubiquitin-pathway control of E2F1 stability, showing MDM2 stabilizes E2F1 by displacing its SCF(SKP2) ligase independent of p53 and pRB.\",\n      \"evidence\": \"Co-IP, ubiquitination and half-life assays with deletion mutants\",\n      \"pmids\": [\"16170383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map the degron displaced by MDM2\", \"In vivo relevance not tested genetically\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Connected E2F1 to a c-Myc feedforward/feedback circuit in which Myc both activates E2F1 transcription and represses E2F1 translation via a miRNA cluster.\",\n      \"evidence\": \"ChIP at the miRNA locus and miRNA reporter assays for E2F1 repression\",\n      \"pmids\": [\"15944709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative balance of activation vs repression in vivo unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that E2F1 is a direct transcriptional regulator of metabolic genes controlling insulin secretion, extending its role beyond proliferation.\",\n      \"evidence\": \"ChIP from pancreatic tissue, E2f1 knockout mice, Kir6.2 rescue, glucose tolerance tests\",\n      \"pmids\": [\"19597485\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address coordination with cell-cycle target program\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed that lysine methylation by Set9 acts as a degradation-promoting brake on DNA-damage-induced E2F1 stabilization and apoptosis, reversed by LSD1.\",\n      \"evidence\": \"In vitro methylation, mutagenesis, siRNA, co-IP, apoptosis assays\",\n      \"pmids\": [\"20603083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crosstalk hierarchy among PTMs only partially mapped\", \"Reader of K185 methylation not identified here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified cell-cycle-phase-specific destruction of E2F1 by APC/C(Cdc20) in prometaphase, blocked by DP1 co-expression.\",\n      \"evidence\": \"Cell synchronization, Cdc20 overexpression/knockdown, stability assays\",\n      \"pmids\": [\"20948288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Degron recognized by APC/C not mapped\", \"Single lab, no reciprocal in vivo validation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed arginine methylation by PRMT5 destabilizes E2F1 and limits its DNA binding, with DNA damage relieving this mark to enable proapoptotic function.\",\n      \"evidence\": \"In vitro methylation, PRMT5 siRNA, stability and DNA-binding assays\",\n      \"pmids\": [\"22327218\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific arginine residues and crosstalk with K185 methylation not fully resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established that ATM/ATR phosphorylation at Ser31 is required in vivo for E2F1-dependent DNA repair and tumor suppression.\",\n      \"evidence\": \"S29A knock-in mice, UV experiments, ChIP at damage sites, tumor incidence\",\n      \"pmids\": [\"24741006\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of recruitment to damage sites not molecularly defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined E2F1 as a master driver of hepatic lipogenesis and glycolysis acting downstream of feeding/insulin via CDK4-pRB.\",\n      \"evidence\": \"ChIP-Seq, E2f1 knockout mice, NAFLD models, primary hepatocytes\",\n      \"pmids\": [\"26619117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not separate transcriptional from cell-cycle effects on metabolism\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified POH1 as a deubiquitylase that stabilizes E2F1, adding a counterweight to E2F1 ubiquitination in vivo.\",\n      \"evidence\": \"Co-IP, deubiquitylation assay, conditional Poh1 knockout liver\",\n      \"pmids\": [\"26510456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which E2F1 ubiquitin marks POH1 removes not specified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Revealed citrullination by PAD4 as a modification that redirects E2F1 to cytokine promoters and recruits BRD4 to drive inflammatory transcription.\",\n      \"evidence\": \"In vitro citrullination, ChIP, co-IP, pharmacological inhibition, arthritis model\",\n      \"pmids\": [\"26989780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Citrullinated residues not mapped\", \"Generalizability beyond inflammatory cells unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended E2F1's metabolic reach to cholesterol homeostasis by showing it transactivates PCSK9 to promote LDLR degradation.\",\n      \"evidence\": \"ChIP-Seq, PCSK9 reporter assays, E2f1 knockout mice, LDL uptake assays\",\n      \"pmids\": [\"28515357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interaction with lipogenic program coordination not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed methylation-dependent recruitment of CRL4(DCAF5) via the reader L3MBTL3 couples E2F1 methylation to its degradation.\",\n      \"evidence\": \"Biochemical methyl-binding and ubiquitination assays, genetic deletion models\",\n      \"pmids\": [\"29691401\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which methyl mark is read not pinned down\", \"In vivo significance limited\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked E2F1 to gluconeogenic control, showing it transcriptionally activates Pck1 and AUF1 through the CDK4-RB1-E2F1 pathway.\",\n      \"evidence\": \"ChIP, E2F1 overexpression/knockout, hepatocyte gluconeogenesis assays, diabetic mice\",\n      \"pmids\": [\"29526568\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; coordination with lipogenic program not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified SUMO2 conjugation at K266 as a stress-responsive brake that inhibits E2F1 transactivation to favor survival, reversed by SENP3.\",\n      \"evidence\": \"In vivo SUMOylation, K266 mutagenesis, co-IP, SENP3 knockdown, viability assays\",\n      \"pmids\": [\"32541040\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How oxidative stress disrupts the E2F1-SENP3 interaction mechanistically unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the dozens of competing PTMs, partner proteins, and feedback loops are integrated in real time to select between proliferative, apoptotic, and metabolic E2F1 target programs remains unresolved.\",\n      \"evidence\": \"No single study reconstitutes the combinatorial PTM/partner code governing E2F1 target selection\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No integrated model linking PTM combinations to specific gene-program outputs\", \"Stoichiometry and temporal order of modifications in vivo unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 14, 19, 20, 21, 22, 39]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 3, 22, 23, 24]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": []}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [23, 25, 35]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6, 19, 28, 30]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 19, 20, 21, 39]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [11, 12]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [1, 11, 18, 26]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [19, 20, 21, 22, 39]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [33, 34, 36]}\n    ],\n    \"complexes\": [\"E2F1-DP1 heterodimer\"],\n    \"partners\": [\"TFDP1\", \"RB1\", \"MDM2\", \"SIRT1\", \"AHR\", \"PTEN\", \"TP53\", \"BRD4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}