{"gene":"RRM2","run_date":"2026-04-28T20:42:06","timeline":{"discoveries":[{"year":2015,"finding":"A single conserved tryptophan residue (W688 equivalent in mammalian RRM1) mediates the physical interaction between the catalytic subunit RRM1 and the regulatory subunit RRM2; mutation of this residue abolishes RRM1–RRM2 binding and is lethal in homozygous mice, establishing that RRM1–RRM2 complex formation is essential for mammalian ribonucleotide reductase (RNR) activity and development.","method":"Mutagenesis in mouse model (knock-in Rrm1-WG/WG), proteomic/interaction analysis, genetic epistasis in mice","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo genetic model with defined molecular interaction, multiple orthogonal methods (proteomics, genetics, cell biology)","pmids":["26077802"],"is_preprint":false},{"year":2015,"finding":"Increased Rrm2 gene dosage in mice produces supraphysiological RNR activity, reduces chromosomal breakage at common fragile sites, and significantly extends the lifespan of ATR-mutant mice, demonstrating that RRM2-driven dNTP supply is a conserved mammalian mechanism that protects against replication stress-induced genomic instability.","method":"Transgenic mouse genetics (Rrm2 overexpression), RNR activity assay, cytogenetic fragile-site analysis, survival analysis of ATR-mutant mice","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo genetic rescue with biochemical activity measurement, replicated across multiple mouse genotypes","pmids":["25838540"],"is_preprint":false},{"year":2016,"finding":"BRCA1 acts as a transcriptional co-activator of RRM2 in glioblastoma; BRCA1 depletion reduces RRM2 expression, increases replication stress and DNA damage, and impairs tumor growth, placing RRM2 downstream of BRCA1 in a protective replication-stress response pathway.","method":"siRNA/shRNA knockdown of BRCA1, Western blot, DNA fiber assay, γH2AX immunofluorescence, xenograft tumor models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in vitro and in vivo, mechanistic pathway placement","pmids":["27845331"],"is_preprint":false},{"year":2006,"finding":"RRM2 overexpression in pancreatic adenocarcinoma cells activates NF-κB transcription factor activity and upregulates MMP-9 expression in an NF-κB-dependent manner, thereby enhancing cellular invasiveness; RNAi-mediated silencing of RRM2 reverses these effects.","method":"RRM2 overexpression and RNAi knockdown, NF-κB reporter assay, invasion assay, MMP-9 Western blot","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — clean gain- and loss-of-function with defined pathway readout, single lab","pmids":["17222798"],"is_preprint":false},{"year":2009,"finding":"RRM2 overexpression in human cancer cells decreases thrombospondin-1 (TSP-1) expression and increases VEGF production at the mRNA and protein level, promoting tumor angiogenesis; siRNA-mediated RRM2 knockdown reverses both effects and reduces endothelial chemotaxis and vascularization in xenografts.","method":"RRM2 overexpression and siRNA knockdown, RT-PCR, ELISA, endothelial chemotaxis assay, in vivo xenograft vascularization","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal gain/loss of function with multiple in vitro and in vivo readouts, single lab","pmids":["19250552"],"is_preprint":false},{"year":2013,"finding":"RRM2 depletion in head and neck and lung cancer cells induces apoptosis through the intrinsic (mitochondrial) pathway by reducing Bcl-2 protein stability; RRM2 and Bcl-2 co-localize intracellularly and show significant co-expression in patient tissues, indicating RRM2 directly regulates Bcl-2 protein degradation.","method":"siRNA knockdown, Western blot, confocal microscopy, tissue fractionation, gene overexpression/knockdown, immunohistochemistry, quantum dot immunofluorescence in patient specimens","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods linking RRM2 to Bcl-2 stability with in vivo validation, single lab","pmids":["23719266"],"is_preprint":false},{"year":2020,"finding":"RRM2 inhibits ferroptosis in liver cancer cells by sustaining glutathione (GSH) synthesis via interaction with glutathione synthetase (GSS); phosphorylation of RRM2 at Threonine 33 (T33) normally blocks the RRM2–GSS interaction, preventing their co-degradation by the proteasome; under ferroptotic stress, dephosphorylation of T33 promotes RRM2–GSS binding, leading to simultaneous proteasomal degradation of both proteins.","method":"Co-immunoprecipitation, proximity ligation assay (PLA), immunofluorescence, phosphorylation mutagenesis, proteasome inhibition, cell viability and ferroptosis assays","journal":"Cancer cell international","confidence":"High","confidence_rationale":"Tier 1–2 — site-specific phosphorylation mutagenesis combined with co-IP, PLA, and functional ferroptosis assays in a single study","pmids":["33372599"],"is_preprint":false},{"year":2021,"finding":"RRM2 stabilizes ANXA1 protein and activates the AKT signaling pathway in renal cell carcinoma cells, promoting sunitinib resistance; this function is independent of RRM2's ribonucleotide reductase enzymatic activity.","method":"RRM2 knockdown/overexpression, co-IP, Western blot, cell viability assays, xenograft mouse model, patient tissue analysis","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP establishes interaction, enzymatic-independence tested, validated in vivo, single lab","pmids":["34319001"],"is_preprint":false},{"year":2022,"finding":"USP7 deubiquitinase directly interacts with and deubiquitinates RRM2 during S phase of the cell cycle, stabilizing RRM2 protein; USP7 knockdown reduces RRM2 levels, causes DNA replication stress, and induces cellular senescence in melanoma cells; ectopic RRM2 expression rescues the senescent phenotype caused by USP7 depletion.","method":"shRNA knockdown, co-IP, proteomics/transcriptomics, ectopic RRM2 expression rescue, in vivo PDX drop-out screens","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — direct interaction shown by co-IP, functional rescue with ectopic RRM2, in vivo validation, mechanistic pathway defined","pmids":["36130505"],"is_preprint":false},{"year":2023,"finding":"USP12 deubiquitinase directly interacts with and deubiquitinates RRM2, stabilizing its protein level in non-small cell lung cancer cells; USP12 knockdown reduces RRM2 protein, induces DNA replication stress, and retards tumor growth in vivo.","method":"Co-IP, Western blot, ubiquitination assay, USP12 knockdown, xenograft tumor model","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — direct interaction and deubiquitination shown, in vivo validation, single lab","pmids":["37341611"],"is_preprint":false},{"year":2021,"finding":"MYBL2 transcription factor directly binds the RRM2 gene promoter and activates its transcription during S phase in colorectal cancer cells, forming a complex with TAF15 and MuvB components; this transcriptional activation is essential for RRM2-dependent DNA synthesis and cell cycle progression.","method":"Chromatin immunoprecipitation (ChIP), promoter reporter assay, MYBL2 knockdown/overexpression, rescue experiments, xenograft model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP confirms direct promoter binding, functional rescue experiments, in vivo validation, single lab","pmids":["34234118"],"is_preprint":false},{"year":2023,"finding":"E2F8 transcription factor directly binds the RRM2 promoter and activates its transcription in lung adenocarcinoma, driving RRM2-dependent DNA synthesis and cell cycle progression; combined E2F8 knockdown with WEE1 inhibitor MK-1775 synergistically suppresses RRM2 levels and tumor growth.","method":"Luciferase reporter assay, ChIP-qPCR, DNA pulldown-Western blot, overexpression/knockdown experiments, xenograft model","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — direct promoter binding confirmed by multiple methods, functional rescue, in vivo validation, single lab","pmids":["37863324"],"is_preprint":false},{"year":2016,"finding":"HPV31 maintains elevated RRM2 levels in differentiating keratinocytes through viral E7 expression and activation of the ATR-Chk1-E2F1 signaling axis; RRM2 depletion blocks productive HPV31 replication, demonstrating that RRM2 provides dNTPs essential for viral DNA synthesis in differentiating cells.","method":"RRM2 siRNA knockdown, dNTP pool measurement, Western blot, quantitative viral DNA replication assay","journal":"Virology","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with specific viral replication readout, pathway placement via E7/ATR-Chk1-E2F1 axis, single lab","pmids":["27764728"],"is_preprint":false},{"year":2018,"finding":"The synthetic compound DHS (trans-4,4'-dihydroxystilbene) targets RRM2 and induces cyclin F-mediated proteasomal degradation of RRM2, reducing RNR activity and dNTP synthesis, thereby inhibiting DNA replication, causing S-phase arrest and apoptosis in cancer cells.","method":"Molecular docking, Western blot, RNR activity assay, dNTP quantification, cell cycle flow cytometry, xenograft models","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical RNR activity assay plus dNTP measurement and molecular docking identifies RRM2 as target; cyclin F-mediated degradation mechanism defined; validated in vivo","pmids":["30518875"],"is_preprint":false},{"year":2020,"finding":"The translational repressor 4E-BP1 specifically regulates RRM2 protein levels in a cap-dependent translation-dependent manner; mTORC1/2 inhibition (but not mTORC1 alone) activates 4E-BP1, inhibits protein synthesis, and selectively reduces RRM2 protein; CRISPR/Cas9 knockout of 4E-BP1 rescues RRM2 levels under mTORC1/2 inhibition.","method":"CRISPR/Cas9 4E-BP1 knockout, mTOR inhibitor treatment, mutant 4E-BP1 inducible expression, Western blot, xenograft model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — genetic rescue experiment (CRISPR KO) plus pharmacological and inducible expression approaches, in vivo validation","pmids":["33191406"],"is_preprint":false},{"year":2022,"finding":"RRM2 expression is regulated at the protein level by the ubiquitin-proteasome system during the cell cycle; WEE1 kinase is involved in a degradation pathway of RRM2, and inhibition of WEE1 (by MK-1775) reduces RRM2 protein, with this effect synergizing with transcriptional suppression of RRM2 by MYBL2 knockdown.","method":"WEE1 inhibitor treatment, Western blot, combination knockdown experiments, xenograft model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic approaches, in vivo validation, mechanistic pathway established","pmids":["34234118"],"is_preprint":false},{"year":2024,"finding":"IGF2BP3 stabilizes RRM2 mRNA in an m6A-dependent manner (reading m6A modifications on RRM2 mRNA) in hepatocellular carcinoma, sustaining RRM2 protein expression and GSH synthesis to suppress ferroptosis; ChIP and dual-luciferase assays confirmed FOXM1 transcriptionally activates IGF2BP3; overexpression of RRM2 rescues ferroptosis and malignant phenotypes induced by IGF2BP3 knockdown.","method":"m6A RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP), ChIP assay, dual-luciferase reporter, co-IP, ferroptosis assays, rescue experiments, xenograft model","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (MeRIP, RIP, ChIP, luciferase, rescue) establishing m6A-dependent mRNA stabilization mechanism, in vivo validation","pmids":["39630361"],"is_preprint":false},{"year":2023,"finding":"FOXM1 transcription factor directly binds to the RRM2 promoter and regulates its transcriptional activity in small cell lung cancer; miR-1 targets CXCR4, which prevents FOXM1 from binding the RRM2 promoter, thus downregulating RRM2 and suppressing SCLC growth and metastasis.","method":"Chromatin immunoprecipitation (ChIP), dual-luciferase assay, miR-1 gain/loss of function, intracardiac mouse metastasis model, transcriptomic analysis","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP confirms direct FOXM1-RRM2 promoter binding, in vivo metastasis model, single lab","pmids":["36597126"],"is_preprint":false},{"year":2011,"finding":"Oncogenic KRAS signaling upregulates RRM2 expression in colorectal cancer cells; re-expression of KRAS in KRAS-disrupted HKe3 cells restores RRM2 protein; RRM2 knockdown impairs KRAS-driven cell proliferation under serum-starved conditions and anchorage-independent growth.","method":"KRAS re-expression in isogenic cell lines, lentiviral shRNA knockdown of RRM2, Western blot, cell proliferation and colony formation assays","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 2 — isogenic KRAS cell line pair with RRM2 rescue, clean loss-of-function with defined phenotype, single lab","pmids":["21873171"],"is_preprint":false},{"year":2013,"finding":"Elevated AKT signaling in breast cancer cells transcriptionally upregulates RRM2 expression, and RRM2 mediates AKT-induced tamoxifen resistance by increasing DNA repair capacity and protecting from tamoxifen-induced apoptosis; RNAi knockdown of RRM2 reverses tamoxifen-resistant growth and activates proapoptotic pathways.","method":"Gene expression profiling, RNAi knockdown, small-molecule RRM2 inhibitor (didox), cell proliferation and apoptosis assays, in vivo xenograft model","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — gene expression profiling plus functional RNAi rescue, in vivo validation, single lab","pmids":["24362250"],"is_preprint":false},{"year":2021,"finding":"RRM2 silencing in lung adenocarcinoma cells induces cGAS/STING pathway activation and its downstream targets in a STING-dependent manner, increases CD8+ T cell infiltration in tumors, and synergizes with radiation to further activate cGAS/STING signaling and promote apoptosis.","method":"shRNA RRM2 knockdown, Western blot, flow cytometry (CD8+ T cells), immunohistochemistry, xenograft mouse model, combination with irradiation","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 — STING-dependence established by genetic epistasis, in vivo immune cell infiltration, single lab","pmids":["33858512"],"is_preprint":false},{"year":2022,"finding":"RRM2 interacts with CDK1 in chicken myoblasts (ortholog study); forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition in neuroblastoma, and RRM2 co-overexpression with MYCN accelerates tumor formation and activates ATR-CHK1 signaling in a zebrafish model; combined RRM2-CHK1 inhibition is synergistic in high-risk neuroblastoma.","method":"Co-immunoprecipitation, zebrafish tumor model (MYCN + RRM2 co-overexpression), CHK1 inhibitor treatment, patient-derived xenograft experiments","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — zebrafish genetic model plus PDX in vivo validation, CHK1 inhibitor epistasis, single lab","pmids":["35857500"],"is_preprint":false},{"year":2024,"finding":"p53 deficiency leads to downregulation of SIRT7, which is the decrotonylase for RRM2; loss of SIRT7 results in increased lysine crotonylation of RRM2 at K283 (RRM2-K283Cr), which upregulates RRM2 protein and promotes cisplatin resistance by inhibiting apoptosis in colon cancer cells.","method":"SILAC-based quantitative crotonylome, p53 knockout cells, SIRT7 knockdown/overexpression, site-specific mutagenesis (K283), apoptosis assays","journal":"Frontiers in molecular biosciences","confidence":"Medium","confidence_rationale":"Tier 1–2 — proteome-wide crotonylation mapping plus site-specific mutagenesis and genetic erasure (SIRT7) identifies decrotonylation mechanism, single lab","pmids":["38894712"],"is_preprint":false},{"year":2016,"finding":"In gastric cancer cells, RRM2 activates AKT, IKBα, and NF-κB signaling in a time-dependent manner; AKT and NF-κB inhibitors (GSK690693 and BAY117082) block RRM2-induced increases in MMP-2 and MMP-9 expression and cellular invasion, demonstrating that RRM2 promotes invasiveness via an AKT/NF-κB axis.","method":"RRM2 stimulation, pharmacological AKT and NF-κB inhibitors, Western blot, invasion and migration assays","journal":"Die Pharmazie","confidence":"Low","confidence_rationale":"Tier 3 — pharmacological inhibitor epistasis only, no direct binding assay, single lab","pmids":["27348973"],"is_preprint":false},{"year":2019,"finding":"RRM2 silencing in multiple myeloma cells inhibits RNR enzymatic activity, induces apoptosis through increased Bax and cleaved caspase-3/PARP, and activates the DNA-damage response (γH2AX); RRM2 knockdown inhibits the Wnt/β-catenin pathway by increasing GSK-3β phosphorylation.","method":"siRNA knockdown, RNR activity assay, Western blot, Annexin V apoptosis assay, flow cytometry","journal":"Molecular medicine reports","confidence":"Low","confidence_rationale":"Tier 3 — single lab, Western blot-based pathway inference without direct mechanistic link between RRM2 and Wnt components","pmids":["31322175"],"is_preprint":false},{"year":2024,"finding":"lncOCMRL1 suppresses RRM2 ubiquitination in oral squamous cell carcinoma cells, stabilizing RRM2 protein and thereby inducing epithelial-mesenchymal transition (EMT) to promote proliferation, invasion, and migration.","method":"RNA pull-down, RIP, mass spectrometry, Western blot, ubiquitination assay, invasion/migration assays, in vivo xenograft model","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — RNA pull-down and mass spectrometry identify lncRNA-protein interaction; ubiquitination assay directly shows suppression of RRM2 ubiquitination; in vivo validation","pmids":["39343925"],"is_preprint":false},{"year":2020,"finding":"The lncRNA lincNMR binds to YBX1 (identified by in vivo RNA Antisense Purification mass spectrometry) and regulates RRM2, TYMS, and TK1 expression; lincNMR depletion reduces dNTP pools and causes proliferation defects rescued by exogenous dNTPs, placing lincNMR upstream of YBX1 which then controls RRM2 expression and nucleotide metabolism.","method":"Triple-label SILAC proteomics, in vivo RNA Antisense Purification mass spectrometry (RAP-MS), siRNA knockdown, dNTP quantification, dNTP rescue experiments, ChIP (YBX1 promoter binding)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 — RAP-MS identifies direct lncRNA-YBX1 interaction; dNTP rescue experiment provides functional validation; multiple orthogonal methods, replicated across cancer cell lines","pmids":["32587247"],"is_preprint":false},{"year":2022,"finding":"RRM2 promotes osteogenic differentiation of mouse embryo fibroblasts via the canonical Wnt/β-catenin signaling pathway; RRM2 overexpression increases β-catenin protein, p-GSK-3β/GSK-3β ratio, and downstream Wnt target gene expression, while RRM2 knockdown has opposite effects.","method":"Adenoviral RRM2 overexpression, siRNA knockdown, Western blot, RT-qPCR, ALP activity assay, Alizarin Red S staining","journal":"Experimental and therapeutic medicine","confidence":"Low","confidence_rationale":"Tier 3 — no direct binding between RRM2 and Wnt components shown; pathway inference from Western blot, single lab","pmids":["36160885"],"is_preprint":false}],"current_model":"RRM2 (ribonucleotide reductase regulatory subunit M2) forms the active RNR holoenzyme by physically binding the catalytic subunit RRM1 via a conserved residue essential for mammalian viability; as the rate-limiting subunit it catalyzes ribonucleoside diphosphate reduction to maintain dNTP pools for DNA replication and repair. Beyond its enzymatic role, RRM2 is regulated at multiple post-translational levels — stabilized by the deubiquitinases USP7 and USP12, degraded via cyclin F- and WEE1-dependent ubiquitination, and subject to crotonylation at K283 (decrotonylated by SIRT7). Its expression is transcriptionally driven by E2F family members (E2F1, E2F2, E2F8), MYBL2, FOXM1, and BRCA1, and post-transcriptionally controlled by YBX1 (via lincNMR) and IGF2BP3-mediated m6A-dependent mRNA stabilization. RRM2 protein also exerts enzymatic-activity-independent functions — it stabilizes ANXA1 to activate AKT signaling, regulates Bcl-2 protein stability to suppress apoptosis, interacts with GSS to sustain glutathione synthesis and block ferroptosis, and activates NF-κB/MMP-9 to drive invasion — collectively linking RRM2 to cancer cell survival, drug resistance, angiogenesis, and immune evasion."},"narrative":{"teleology":[{"year":2006,"claim":"Whether RRM2 influences cellular phenotypes beyond dNTP supply was unknown; overexpression in pancreatic cancer cells activated NF-κB and upregulated MMP-9, establishing a non-canonical role for RRM2 in promoting invasion.","evidence":"RRM2 overexpression and RNAi in pancreatic cancer cells with NF-κB reporter and invasion assays","pmids":["17222798"],"confidence":"Medium","gaps":["No direct physical interaction between RRM2 and NF-κB pathway components demonstrated","Enzymatic-activity independence not tested"]},{"year":2009,"claim":"The relationship between RRM2 and tumor angiogenesis was undefined; gain- and loss-of-function experiments showed RRM2 suppresses TSP-1 and induces VEGF, promoting angiogenesis in vivo.","evidence":"RRM2 overexpression/siRNA, ELISA, endothelial chemotaxis, xenograft vascularization","pmids":["19250552"],"confidence":"Medium","gaps":["Mechanism linking RRM2 to TSP-1 repression not identified","Whether this requires RNR catalytic activity is unknown"]},{"year":2013,"claim":"Whether RRM2 directly regulates apoptotic machinery was unknown; RRM2 depletion destabilized Bcl-2 protein and triggered intrinsic apoptosis, and the two proteins co-localize, linking RRM2 to anti-apoptotic signaling beyond dNTP supply.","evidence":"siRNA knockdown, confocal co-localization, tissue immunohistochemistry in head/neck and lung cancer","pmids":["23719266"],"confidence":"Medium","gaps":["Direct binding between RRM2 and Bcl-2 not shown by co-IP or structural methods","Whether stabilization requires RRM2 enzymatic activity untested"]},{"year":2015,"claim":"The structural basis for RRM1–RRM2 holoenzyme assembly was unresolved; identification of a single conserved tryptophan mediating the interaction, with lethality upon its mutation in mice, established this contact as essential for RNR function and development.","evidence":"Rrm1-WG/WG knock-in mice, proteomic interaction analysis, genetic epistasis","pmids":["26077802"],"confidence":"High","gaps":["Full atomic-resolution structure of the mammalian RRM1–RRM2 interface not reported","Whether compensatory interactions exist in specific tissues unknown"]},{"year":2015,"claim":"Whether increasing RRM2/dNTP levels could rescue replication stress in vivo was untested; Rrm2 transgenic mice showed reduced fragile-site breakage and extended lifespan of ATR-mutant animals, proving RRM2-driven dNTP supply is a conserved genome-protection mechanism.","evidence":"Transgenic Rrm2-overexpressing mice, RNR activity assay, fragile-site cytogenetics, ATR-mutant survival analysis","pmids":["25838540"],"confidence":"High","gaps":["Tissue-specific thresholds of dNTP sufficiency not defined","Whether dNTP-independent functions of RRM2 also contribute to rescue unclear"]},{"year":2016,"claim":"Upstream transcriptional regulators of RRM2 in replication-stress contexts were incompletely mapped; BRCA1 was shown to co-activate RRM2 transcription, with BRCA1 loss reducing RRM2 and increasing replication stress in glioblastoma.","evidence":"BRCA1 knockdown, DNA fiber assay, γH2AX staining, xenograft models","pmids":["27845331"],"confidence":"High","gaps":["Whether BRCA1 binds the RRM2 promoter directly or acts through intermediates not fully resolved","Generalizability beyond glioblastoma untested"]},{"year":2016,"claim":"How viruses co-opt host dNTP synthesis in differentiated cells was unclear; HPV31 E7 was shown to maintain RRM2 via ATR-Chk1-E2F1, and RRM2 depletion abolished productive viral replication, establishing RRM2 as essential for viral DNA synthesis.","evidence":"RRM2 siRNA in differentiating keratinocytes, dNTP measurement, viral DNA replication assay","pmids":["27764728"],"confidence":"Medium","gaps":["Whether other HPV types use the same mechanism untested","Direct E2F1 binding to RRM2 promoter not shown in this study"]},{"year":2018,"claim":"The E3 ligase pathway controlling RRM2 turnover was not fully defined; cyclin F was identified as mediating proteasomal degradation of RRM2 upon drug treatment, linking cell-cycle-dependent ubiquitination to RNR activity control.","evidence":"Molecular docking, RNR activity assay, dNTP quantification, cyclin F epistasis, xenograft","pmids":["30518875"],"confidence":"Medium","gaps":["Direct cyclin F–RRM2 binding site not mapped","Whether cyclin F targets RRM2 constitutively or only under drug stress unclear"]},{"year":2020,"claim":"Post-transcriptional control of RRM2 protein was incompletely understood; 4E-BP1 was shown to selectively repress RRM2 cap-dependent translation downstream of mTORC1/2 signaling, adding a translational layer to RRM2 regulation.","evidence":"CRISPR/Cas9 4E-BP1 knockout, mTOR inhibitor treatment, inducible 4E-BP1 expression, xenograft","pmids":["33191406"],"confidence":"Medium","gaps":["Specific 5'UTR features of RRM2 mRNA conferring 4E-BP1 sensitivity not identified","Whether this mechanism operates in non-cancer cells untested"]},{"year":2020,"claim":"Whether RRM2 regulates ferroptosis was unknown; RRM2 was found to interact with GSS in a phosphorylation-dependent manner (T33), sustaining GSH synthesis and suppressing ferroptosis; dephosphorylation promotes co-degradation of both proteins.","evidence":"Co-IP, proximity ligation assay, T33 phospho-mutagenesis, proteasome inhibition, ferroptosis assays in liver cancer cells","pmids":["33372599"],"confidence":"High","gaps":["Kinase responsible for T33 phosphorylation not identified","Whether this mechanism is independent of RNR catalytic activity not tested"]},{"year":2020,"claim":"How lncRNAs regulate nucleotide metabolism was unclear; lincNMR was shown to bind YBX1, which controls RRM2 expression; lincNMR depletion reduced dNTP pools rescuable by exogenous dNTPs, placing a lncRNA–RBP axis upstream of RRM2.","evidence":"RAP-MS, triple-label SILAC, siRNA, dNTP rescue across multiple cancer cell lines","pmids":["32587247"],"confidence":"High","gaps":["Whether YBX1 acts transcriptionally or post-transcriptionally on RRM2 mRNA not fully resolved","Stoichiometry of lincNMR–YBX1 complex unknown"]},{"year":2021,"claim":"Whether RRM2 has functions independent of its RNR enzymatic activity was formally untested; RRM2 was shown to stabilize ANXA1 and activate AKT signaling to drive sunitinib resistance in renal cell carcinoma, independently of catalytic activity.","evidence":"Co-IP, enzymatic-activity-independent mutant, xenograft, patient tissue analysis","pmids":["34319001"],"confidence":"Medium","gaps":["Structural basis of the RRM2–ANXA1 interaction unknown","Whether enzymatic-independent functions extend to other cancer types untested"]},{"year":2021,"claim":"How RRM2 loss affects anti-tumor immunity was unknown; RRM2 silencing activated the cGAS/STING pathway in a STING-dependent manner, increased CD8+ T cell infiltration, and synergized with radiation.","evidence":"shRNA knockdown, flow cytometry, IHC, xenograft with irradiation in lung adenocarcinoma","pmids":["33858512"],"confidence":"Medium","gaps":["Whether cytosolic DNA from replication stress or another signal triggers cGAS not resolved","Immunocompetent syngeneic model not used"]},{"year":2021,"claim":"Direct transcriptional activators of RRM2 during S phase were incompletely catalogued; MYBL2 was shown to directly bind the RRM2 promoter in complex with TAF15 and MuvB, activating transcription essential for DNA synthesis.","evidence":"ChIP, promoter reporter, knockdown/overexpression rescue, xenograft in colorectal cancer cells","pmids":["34234118"],"confidence":"Medium","gaps":["Whether MYBL2–MuvB complex is the dominant S-phase driver versus E2F factors is unclear","Interplay among multiple transcription factors at the RRM2 promoter not mapped simultaneously"]},{"year":2022,"claim":"How RRM2 protein is stabilized during S phase was undefined; USP7 was identified as a deubiquitinase that directly binds and deubiquitinates RRM2 in S phase, with USP7 loss causing replication stress and senescence rescued by ectopic RRM2.","evidence":"Co-IP, proteomics, shRNA, ectopic RRM2 rescue, PDX dropout screen in melanoma","pmids":["36130505"],"confidence":"High","gaps":["Whether USP7 and USP12 act redundantly or in distinct contexts unknown","Ubiquitin chain type specificity not determined"]},{"year":2022,"claim":"WEE1 kinase was implicated in RRM2 protein turnover; WEE1 inhibition reduced RRM2 protein and synergized with MYBL2 knockdown, defining convergent transcriptional and post-translational control axes.","evidence":"WEE1 inhibitor MK-1775, combination with MYBL2 knockdown, xenograft","pmids":["34234118"],"confidence":"Medium","gaps":["Whether WEE1 acts directly on RRM2 or via CDK-mediated phosphorylation-dependent ubiquitination unresolved","Direct WEE1–RRM2 interaction not demonstrated"]},{"year":2023,"claim":"Whether additional deubiquitinases regulate RRM2 was unknown; USP12 was identified as a second DUB that directly deubiquitinates RRM2, with USP12 loss reducing RRM2 and causing replication stress in NSCLC.","evidence":"Co-IP, ubiquitination assay, USP12 knockdown, xenograft","pmids":["37341611"],"confidence":"Medium","gaps":["Relationship and potential redundancy between USP7 and USP12 on RRM2 not tested","Whether USP12 regulation is cell-cycle-phase specific unknown"]},{"year":2023,"claim":"E2F8 was identified as a direct transcriptional activator of RRM2 in lung adenocarcinoma; combined E2F8 knockdown with WEE1 inhibition synergistically depleted RRM2, showing convergent therapeutic vulnerability.","evidence":"ChIP-qPCR, DNA pulldown, luciferase reporter, knockdown/overexpression, xenograft","pmids":["37863324"],"confidence":"Medium","gaps":["Relative contributions of E2F1, E2F8, and MYBL2 to RRM2 transcription across tissues not compared","Whether E2F8 cooperates with or competes with E2F1 at the RRM2 promoter unknown"]},{"year":2023,"claim":"FOXM1 was shown to directly bind the RRM2 promoter in SCLC, adding another transcription factor to the regulatory network; miR-1/CXCR4 axis suppresses FOXM1–RRM2 signaling and metastasis.","evidence":"ChIP, dual-luciferase, miR-1 gain/loss of function, intracardiac metastasis model","pmids":["36597126"],"confidence":"Medium","gaps":["How CXCR4 signaling enables FOXM1 promoter binding mechanistically is unclear","Whether FOXM1 and MYBL2 bind the same or distinct RRM2 promoter regions unknown"]},{"year":2024,"claim":"A novel post-translational modification — lysine crotonylation at K283 — was identified on RRM2; SIRT7 decrotonylates this site, and p53 loss reduces SIRT7, leading to RRM2 hyper-crotonylation and cisplatin resistance.","evidence":"SILAC crotonylome, p53 KO cells, SIRT7 knockdown/overexpression, K283 mutagenesis, apoptosis assays in colon cancer","pmids":["38894712"],"confidence":"Medium","gaps":["Writer enzyme (crotonyltransferase) for K283 not identified","How crotonylation stabilizes RRM2 protein mechanistically is unresolved"]},{"year":2024,"claim":"Post-transcriptional stabilization of RRM2 mRNA by m6A was established; IGF2BP3 reads m6A marks on RRM2 mRNA to sustain its expression, linking epitranscriptomic regulation to GSH synthesis and ferroptosis suppression.","evidence":"MeRIP, RIP, ChIP, dual-luciferase, rescue experiments, xenograft in hepatocellular carcinoma","pmids":["39630361"],"confidence":"Medium","gaps":["Specific m6A sites on RRM2 mRNA not mapped at single-nucleotide resolution","Whether m6A regulation of RRM2 operates in normal tissue homeostasis unknown"]},{"year":null,"claim":"A unified quantitative model integrating the multiple transcriptional (E2F1, E2F8, MYBL2, FOXM1, BRCA1), translational (4E-BP1), and post-translational (USP7, USP12, cyclin F, WEE1, SIRT7/K283Cr) regulatory inputs that converge on RRM2 protein levels across cell cycle phases and stress conditions has not been constructed.","evidence":"","pmids":[],"confidence":"Low","gaps":["No integrated systems-level model of RRM2 regulation across cell cycle and stress contexts","Structural basis of RRM2 enzymatic-activity-independent protein–protein interactions (ANXA1, GSS, Bcl-2) unresolved","T33 kinase identity and upstream signaling controlling RRM2–GSS interaction unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,13]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,6,7]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5,6]}],"pathway":[{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[0,1,8,9]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,6,13,26]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[8,10,11,15]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,6,20]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,7,19,23]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[20]}],"complexes":["Ribonucleotide reductase (RNR) holoenzyme (RRM1–RRM2)"],"partners":["RRM1","USP7","USP12","GSS","ANXA1","YBX1","CDK1","SIRT7"],"other_free_text":[]},"mechanistic_narrative":"RRM2 encodes the regulatory subunit of ribonucleotide reductase (RNR), whose physical association with the catalytic subunit RRM1 via a conserved tryptophan residue is essential for holoenzyme activity, dNTP synthesis, and mammalian viability [PMID:26077802]. As the rate-limiting component of RNR, RRM2-driven dNTP supply protects against replication stress–induced genomic instability at common fragile sites and is transcriptionally activated by E2F1/E2F8, MYBL2, FOXM1, and BRCA1, while its protein turnover is governed by cyclin F– and WEE1-dependent ubiquitination countered by USP7 and USP12 deubiquitination and by SIRT7-mediated decrotonylation at K283 [PMID:25838540, PMID:36130505, PMID:37341611, PMID:34234118, PMID:36597126, PMID:38894712]. Beyond its enzymatic role in nucleotide metabolism, RRM2 exerts catalytic-activity-independent functions including stabilization of ANXA1 to activate AKT signaling, regulation of Bcl-2 protein stability to suppress apoptosis, and interaction with glutathione synthetase (GSS) to sustain glutathione synthesis and inhibit ferroptosis [PMID:34319001, PMID:23719266, PMID:33372599]. RRM2 silencing activates cGAS/STING innate immune signaling and increases tumor CD8+ T cell infiltration, linking its depletion to anti-tumor immunity [PMID:33858512]."},"prefetch_data":{"uniprot":{"accession":"P31350","full_name":"Ribonucleoside-diphosphate reductase subunit M2","aliases":["Ribonucleotide reductase small chain","Ribonucleotide reductase small subunit"],"length_aa":389,"mass_kda":44.9,"function":"Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. Inhibits Wnt signaling","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P31350/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RRM2","classification":"Common Essential","n_dependent_lines":1206,"n_total_lines":1208,"dependency_fraction":0.9983443708609272},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RRM2","total_profiled":1310},"omim":[{"mim_id":"621055","title":"POLYADENYLATE-BINDING PROTEIN, CYTOPLASMIC, 1-LIKE; PABPC1L","url":"https://www.omim.org/entry/621055"},{"mim_id":"621023","title":"RNA-BINDING MOTIF PROTEIN 23; RBM23","url":"https://www.omim.org/entry/621023"},{"mim_id":"620109","title":"DDB1- AND CUL4-ASSOCIATED FACTOR 15; DCAF15","url":"https://www.omim.org/entry/620109"},{"mim_id":"619141","title":"FRONTOTEMPORAL DEMENTIA AND/OR AMYOTROPHIC LATERAL SCLEROSIS 5; FTDALS5","url":"https://www.omim.org/entry/619141"},{"mim_id":"612681","title":"CUGBP- AND ELAV-LIKE FAMILY, MEMBER 6; CELF6","url":"https://www.omim.org/entry/612681"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":41.5},{"tissue":"lymphoid tissue","ntpm":54.1}],"url":"https://www.proteinatlas.org/search/RRM2"},"hgnc":{"alias_symbol":["FLJ25102"],"prev_symbol":["C2orf48"]},"alphafold":{"accession":"P31350","domains":[{"cath_id":"1.10.620.20","chopping":"124-356","consensus_level":"medium","plddt":91.981,"start":124,"end":356}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P31350","model_url":"https://alphafold.ebi.ac.uk/files/AF-P31350-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P31350-F1-predicted_aligned_error_v6.png","plddt_mean":79.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RRM2","jax_strain_url":"https://www.jax.org/strain/search?query=RRM2"},"sequence":{"accession":"P31350","fasta_url":"https://rest.uniprot.org/uniprotkb/P31350.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P31350/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P31350"}},"corpus_meta":[{"pmid":"34319001","id":"PMC_34319001","title":"RRM2 Regulates Sensitivity to Sunitinib and PD-1 Blockade in Renal Cancer by Stabilizing ANXA1 and Activating the AKT Pathway.","date":"2021","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/34319001","citation_count":132,"is_preprint":false},{"pmid":"33372599","id":"PMC_33372599","title":"RRM2 protects against ferroptosis and is a tumor biomarker for liver cancer.","date":"2020","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/33372599","citation_count":124,"is_preprint":false},{"pmid":"17404105","id":"PMC_17404105","title":"Potent siRNA inhibitors of ribonucleotide reductase subunit RRM2 reduce cell proliferation in vitro and in vivo.","date":"2007","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/17404105","citation_count":124,"is_preprint":false},{"pmid":"27845331","id":"PMC_27845331","title":"BRCA1-regulated RRM2 expression protects glioblastoma cells from endogenous replication stress and promotes tumorigenicity.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27845331","citation_count":104,"is_preprint":false},{"pmid":"33227712","id":"PMC_33227712","title":"Inhibiting RRM2 to enhance the anticancer activity of chemotherapy.","date":"2020","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/33227712","citation_count":102,"is_preprint":false},{"pmid":"23719266","id":"PMC_23719266","title":"RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy.","date":"2013","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/23719266","citation_count":101,"is_preprint":false},{"pmid":"32587247","id":"PMC_32587247","title":"The lncRNA lincNMR regulates nucleotide metabolism via a YBX1 - 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RRM2 Partially Folded States and Their Significance to ALS Pathogenesis.","date":"2018","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/30309612","citation_count":24,"is_preprint":false},{"pmid":"35248107","id":"PMC_35248107","title":"LncRNA HOTAIR facilitates proliferation and represses apoptosis of retinoblastoma cells through the miR-20b-5p/RRM2/PI3K/AKT axis.","date":"2022","source":"Orphanet journal of rare diseases","url":"https://pubmed.ncbi.nlm.nih.gov/35248107","citation_count":22,"is_preprint":false},{"pmid":"30027502","id":"PMC_30027502","title":"Nano-Diamino-Tetrac (NDAT) Enhances Resveratrol-Induced Antiproliferation by Action on the RRM2 Pathway in Colorectal Cancers.","date":"2018","source":"Hormones & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/30027502","citation_count":22,"is_preprint":false},{"pmid":"30106091","id":"PMC_30106091","title":"An enhanced RRM2 siRNA delivery to rheumatoid arthritis fibroblast-like synoviocytes through a 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mouse model (knock-in Rrm1-WG/WG), proteomic/interaction analysis, genetic epistasis in mice\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo genetic model with defined molecular interaction, multiple orthogonal methods (proteomics, genetics, cell biology)\",\n      \"pmids\": [\"26077802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Increased Rrm2 gene dosage in mice produces supraphysiological RNR activity, reduces chromosomal breakage at common fragile sites, and significantly extends the lifespan of ATR-mutant mice, demonstrating that RRM2-driven dNTP supply is a conserved mammalian mechanism that protects against replication stress-induced genomic instability.\",\n      \"method\": \"Transgenic mouse genetics (Rrm2 overexpression), RNR activity assay, cytogenetic fragile-site analysis, survival analysis of ATR-mutant mice\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo genetic rescue with biochemical activity measurement, replicated across multiple mouse genotypes\",\n      \"pmids\": [\"25838540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"BRCA1 acts as a transcriptional co-activator of RRM2 in glioblastoma; BRCA1 depletion reduces RRM2 expression, increases replication stress and DNA damage, and impairs tumor growth, placing RRM2 downstream of BRCA1 in a protective replication-stress response pathway.\",\n      \"method\": \"siRNA/shRNA knockdown of BRCA1, Western blot, DNA fiber assay, γH2AX immunofluorescence, xenograft tumor models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in vitro and in vivo, mechanistic pathway placement\",\n      \"pmids\": [\"27845331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"RRM2 overexpression in pancreatic adenocarcinoma cells activates NF-κB transcription factor activity and upregulates MMP-9 expression in an NF-κB-dependent manner, thereby enhancing cellular invasiveness; RNAi-mediated silencing of RRM2 reverses these effects.\",\n      \"method\": \"RRM2 overexpression and RNAi knockdown, NF-κB reporter assay, invasion assay, MMP-9 Western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean gain- and loss-of-function with defined pathway readout, single lab\",\n      \"pmids\": [\"17222798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RRM2 overexpression in human cancer cells decreases thrombospondin-1 (TSP-1) expression and increases VEGF production at the mRNA and protein level, promoting tumor angiogenesis; siRNA-mediated RRM2 knockdown reverses both effects and reduces endothelial chemotaxis and vascularization in xenografts.\",\n      \"method\": \"RRM2 overexpression and siRNA knockdown, RT-PCR, ELISA, endothelial chemotaxis assay, in vivo xenograft vascularization\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss of function with multiple in vitro and in vivo readouts, single lab\",\n      \"pmids\": [\"19250552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RRM2 depletion in head and neck and lung cancer cells induces apoptosis through the intrinsic (mitochondrial) pathway by reducing Bcl-2 protein stability; RRM2 and Bcl-2 co-localize intracellularly and show significant co-expression in patient tissues, indicating RRM2 directly regulates Bcl-2 protein degradation.\",\n      \"method\": \"siRNA knockdown, Western blot, confocal microscopy, tissue fractionation, gene overexpression/knockdown, immunohistochemistry, quantum dot immunofluorescence in patient specimens\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking RRM2 to Bcl-2 stability with in vivo validation, single lab\",\n      \"pmids\": [\"23719266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RRM2 inhibits ferroptosis in liver cancer cells by sustaining glutathione (GSH) synthesis via interaction with glutathione synthetase (GSS); phosphorylation of RRM2 at Threonine 33 (T33) normally blocks the RRM2–GSS interaction, preventing their co-degradation by the proteasome; under ferroptotic stress, dephosphorylation of T33 promotes RRM2–GSS binding, leading to simultaneous proteasomal degradation of both proteins.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation assay (PLA), immunofluorescence, phosphorylation mutagenesis, proteasome inhibition, cell viability and ferroptosis assays\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — site-specific phosphorylation mutagenesis combined with co-IP, PLA, and functional ferroptosis assays in a single study\",\n      \"pmids\": [\"33372599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RRM2 stabilizes ANXA1 protein and activates the AKT signaling pathway in renal cell carcinoma cells, promoting sunitinib resistance; this function is independent of RRM2's ribonucleotide reductase enzymatic activity.\",\n      \"method\": \"RRM2 knockdown/overexpression, co-IP, Western blot, cell viability assays, xenograft mouse model, patient tissue analysis\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP establishes interaction, enzymatic-independence tested, validated in vivo, single lab\",\n      \"pmids\": [\"34319001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP7 deubiquitinase directly interacts with and deubiquitinates RRM2 during S phase of the cell cycle, stabilizing RRM2 protein; USP7 knockdown reduces RRM2 levels, causes DNA replication stress, and induces cellular senescence in melanoma cells; ectopic RRM2 expression rescues the senescent phenotype caused by USP7 depletion.\",\n      \"method\": \"shRNA knockdown, co-IP, proteomics/transcriptomics, ectopic RRM2 expression rescue, in vivo PDX drop-out screens\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction shown by co-IP, functional rescue with ectopic RRM2, in vivo validation, mechanistic pathway defined\",\n      \"pmids\": [\"36130505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP12 deubiquitinase directly interacts with and deubiquitinates RRM2, stabilizing its protein level in non-small cell lung cancer cells; USP12 knockdown reduces RRM2 protein, induces DNA replication stress, and retards tumor growth in vivo.\",\n      \"method\": \"Co-IP, Western blot, ubiquitination assay, USP12 knockdown, xenograft tumor model\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction and deubiquitination shown, in vivo validation, single lab\",\n      \"pmids\": [\"37341611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MYBL2 transcription factor directly binds the RRM2 gene promoter and activates its transcription during S phase in colorectal cancer cells, forming a complex with TAF15 and MuvB components; this transcriptional activation is essential for RRM2-dependent DNA synthesis and cell cycle progression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), promoter reporter assay, MYBL2 knockdown/overexpression, rescue experiments, xenograft model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP confirms direct promoter binding, functional rescue experiments, in vivo validation, single lab\",\n      \"pmids\": [\"34234118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"E2F8 transcription factor directly binds the RRM2 promoter and activates its transcription in lung adenocarcinoma, driving RRM2-dependent DNA synthesis and cell cycle progression; combined E2F8 knockdown with WEE1 inhibitor MK-1775 synergistically suppresses RRM2 levels and tumor growth.\",\n      \"method\": \"Luciferase reporter assay, ChIP-qPCR, DNA pulldown-Western blot, overexpression/knockdown experiments, xenograft model\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct promoter binding confirmed by multiple methods, functional rescue, in vivo validation, single lab\",\n      \"pmids\": [\"37863324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HPV31 maintains elevated RRM2 levels in differentiating keratinocytes through viral E7 expression and activation of the ATR-Chk1-E2F1 signaling axis; RRM2 depletion blocks productive HPV31 replication, demonstrating that RRM2 provides dNTPs essential for viral DNA synthesis in differentiating cells.\",\n      \"method\": \"RRM2 siRNA knockdown, dNTP pool measurement, Western blot, quantitative viral DNA replication assay\",\n      \"journal\": \"Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific viral replication readout, pathway placement via E7/ATR-Chk1-E2F1 axis, single lab\",\n      \"pmids\": [\"27764728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The synthetic compound DHS (trans-4,4'-dihydroxystilbene) targets RRM2 and induces cyclin F-mediated proteasomal degradation of RRM2, reducing RNR activity and dNTP synthesis, thereby inhibiting DNA replication, causing S-phase arrest and apoptosis in cancer cells.\",\n      \"method\": \"Molecular docking, Western blot, RNR activity assay, dNTP quantification, cell cycle flow cytometry, xenograft models\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical RNR activity assay plus dNTP measurement and molecular docking identifies RRM2 as target; cyclin F-mediated degradation mechanism defined; validated in vivo\",\n      \"pmids\": [\"30518875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The translational repressor 4E-BP1 specifically regulates RRM2 protein levels in a cap-dependent translation-dependent manner; mTORC1/2 inhibition (but not mTORC1 alone) activates 4E-BP1, inhibits protein synthesis, and selectively reduces RRM2 protein; CRISPR/Cas9 knockout of 4E-BP1 rescues RRM2 levels under mTORC1/2 inhibition.\",\n      \"method\": \"CRISPR/Cas9 4E-BP1 knockout, mTOR inhibitor treatment, mutant 4E-BP1 inducible expression, Western blot, xenograft model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic rescue experiment (CRISPR KO) plus pharmacological and inducible expression approaches, in vivo validation\",\n      \"pmids\": [\"33191406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RRM2 expression is regulated at the protein level by the ubiquitin-proteasome system during the cell cycle; WEE1 kinase is involved in a degradation pathway of RRM2, and inhibition of WEE1 (by MK-1775) reduces RRM2 protein, with this effect synergizing with transcriptional suppression of RRM2 by MYBL2 knockdown.\",\n      \"method\": \"WEE1 inhibitor treatment, Western blot, combination knockdown experiments, xenograft model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic approaches, in vivo validation, mechanistic pathway established\",\n      \"pmids\": [\"34234118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IGF2BP3 stabilizes RRM2 mRNA in an m6A-dependent manner (reading m6A modifications on RRM2 mRNA) in hepatocellular carcinoma, sustaining RRM2 protein expression and GSH synthesis to suppress ferroptosis; ChIP and dual-luciferase assays confirmed FOXM1 transcriptionally activates IGF2BP3; overexpression of RRM2 rescues ferroptosis and malignant phenotypes induced by IGF2BP3 knockdown.\",\n      \"method\": \"m6A RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP), ChIP assay, dual-luciferase reporter, co-IP, ferroptosis assays, rescue experiments, xenograft model\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (MeRIP, RIP, ChIP, luciferase, rescue) establishing m6A-dependent mRNA stabilization mechanism, in vivo validation\",\n      \"pmids\": [\"39630361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FOXM1 transcription factor directly binds to the RRM2 promoter and regulates its transcriptional activity in small cell lung cancer; miR-1 targets CXCR4, which prevents FOXM1 from binding the RRM2 promoter, thus downregulating RRM2 and suppressing SCLC growth and metastasis.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), dual-luciferase assay, miR-1 gain/loss of function, intracardiac mouse metastasis model, transcriptomic analysis\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP confirms direct FOXM1-RRM2 promoter binding, in vivo metastasis model, single lab\",\n      \"pmids\": [\"36597126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Oncogenic KRAS signaling upregulates RRM2 expression in colorectal cancer cells; re-expression of KRAS in KRAS-disrupted HKe3 cells restores RRM2 protein; RRM2 knockdown impairs KRAS-driven cell proliferation under serum-starved conditions and anchorage-independent growth.\",\n      \"method\": \"KRAS re-expression in isogenic cell lines, lentiviral shRNA knockdown of RRM2, Western blot, cell proliferation and colony formation assays\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — isogenic KRAS cell line pair with RRM2 rescue, clean loss-of-function with defined phenotype, single lab\",\n      \"pmids\": [\"21873171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Elevated AKT signaling in breast cancer cells transcriptionally upregulates RRM2 expression, and RRM2 mediates AKT-induced tamoxifen resistance by increasing DNA repair capacity and protecting from tamoxifen-induced apoptosis; RNAi knockdown of RRM2 reverses tamoxifen-resistant growth and activates proapoptotic pathways.\",\n      \"method\": \"Gene expression profiling, RNAi knockdown, small-molecule RRM2 inhibitor (didox), cell proliferation and apoptosis assays, in vivo xenograft model\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gene expression profiling plus functional RNAi rescue, in vivo validation, single lab\",\n      \"pmids\": [\"24362250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RRM2 silencing in lung adenocarcinoma cells induces cGAS/STING pathway activation and its downstream targets in a STING-dependent manner, increases CD8+ T cell infiltration in tumors, and synergizes with radiation to further activate cGAS/STING signaling and promote apoptosis.\",\n      \"method\": \"shRNA RRM2 knockdown, Western blot, flow cytometry (CD8+ T cells), immunohistochemistry, xenograft mouse model, combination with irradiation\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — STING-dependence established by genetic epistasis, in vivo immune cell infiltration, single lab\",\n      \"pmids\": [\"33858512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RRM2 interacts with CDK1 in chicken myoblasts (ortholog study); forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition in neuroblastoma, and RRM2 co-overexpression with MYCN accelerates tumor formation and activates ATR-CHK1 signaling in a zebrafish model; combined RRM2-CHK1 inhibition is synergistic in high-risk neuroblastoma.\",\n      \"method\": \"Co-immunoprecipitation, zebrafish tumor model (MYCN + RRM2 co-overexpression), CHK1 inhibitor treatment, patient-derived xenograft experiments\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — zebrafish genetic model plus PDX in vivo validation, CHK1 inhibitor epistasis, single lab\",\n      \"pmids\": [\"35857500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"p53 deficiency leads to downregulation of SIRT7, which is the decrotonylase for RRM2; loss of SIRT7 results in increased lysine crotonylation of RRM2 at K283 (RRM2-K283Cr), which upregulates RRM2 protein and promotes cisplatin resistance by inhibiting apoptosis in colon cancer cells.\",\n      \"method\": \"SILAC-based quantitative crotonylome, p53 knockout cells, SIRT7 knockdown/overexpression, site-specific mutagenesis (K283), apoptosis assays\",\n      \"journal\": \"Frontiers in molecular biosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — proteome-wide crotonylation mapping plus site-specific mutagenesis and genetic erasure (SIRT7) identifies decrotonylation mechanism, single lab\",\n      \"pmids\": [\"38894712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In gastric cancer cells, RRM2 activates AKT, IKBα, and NF-κB signaling in a time-dependent manner; AKT and NF-κB inhibitors (GSK690693 and BAY117082) block RRM2-induced increases in MMP-2 and MMP-9 expression and cellular invasion, demonstrating that RRM2 promotes invasiveness via an AKT/NF-κB axis.\",\n      \"method\": \"RRM2 stimulation, pharmacological AKT and NF-κB inhibitors, Western blot, invasion and migration assays\",\n      \"journal\": \"Die Pharmazie\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological inhibitor epistasis only, no direct binding assay, single lab\",\n      \"pmids\": [\"27348973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RRM2 silencing in multiple myeloma cells inhibits RNR enzymatic activity, induces apoptosis through increased Bax and cleaved caspase-3/PARP, and activates the DNA-damage response (γH2AX); RRM2 knockdown inhibits the Wnt/β-catenin pathway by increasing GSK-3β phosphorylation.\",\n      \"method\": \"siRNA knockdown, RNR activity assay, Western blot, Annexin V apoptosis assay, flow cytometry\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, Western blot-based pathway inference without direct mechanistic link between RRM2 and Wnt components\",\n      \"pmids\": [\"31322175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"lncOCMRL1 suppresses RRM2 ubiquitination in oral squamous cell carcinoma cells, stabilizing RRM2 protein and thereby inducing epithelial-mesenchymal transition (EMT) to promote proliferation, invasion, and migration.\",\n      \"method\": \"RNA pull-down, RIP, mass spectrometry, Western blot, ubiquitination assay, invasion/migration assays, in vivo xenograft model\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA pull-down and mass spectrometry identify lncRNA-protein interaction; ubiquitination assay directly shows suppression of RRM2 ubiquitination; in vivo validation\",\n      \"pmids\": [\"39343925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The lncRNA lincNMR binds to YBX1 (identified by in vivo RNA Antisense Purification mass spectrometry) and regulates RRM2, TYMS, and TK1 expression; lincNMR depletion reduces dNTP pools and causes proliferation defects rescued by exogenous dNTPs, placing lincNMR upstream of YBX1 which then controls RRM2 expression and nucleotide metabolism.\",\n      \"method\": \"Triple-label SILAC proteomics, in vivo RNA Antisense Purification mass spectrometry (RAP-MS), siRNA knockdown, dNTP quantification, dNTP rescue experiments, ChIP (YBX1 promoter binding)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — RAP-MS identifies direct lncRNA-YBX1 interaction; dNTP rescue experiment provides functional validation; multiple orthogonal methods, replicated across cancer cell lines\",\n      \"pmids\": [\"32587247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RRM2 promotes osteogenic differentiation of mouse embryo fibroblasts via the canonical Wnt/β-catenin signaling pathway; RRM2 overexpression increases β-catenin protein, p-GSK-3β/GSK-3β ratio, and downstream Wnt target gene expression, while RRM2 knockdown has opposite effects.\",\n      \"method\": \"Adenoviral RRM2 overexpression, siRNA knockdown, Western blot, RT-qPCR, ALP activity assay, Alizarin Red S staining\",\n      \"journal\": \"Experimental and therapeutic medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — no direct binding between RRM2 and Wnt components shown; pathway inference from Western blot, single lab\",\n      \"pmids\": [\"36160885\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RRM2 (ribonucleotide reductase regulatory subunit M2) forms the active RNR holoenzyme by physically binding the catalytic subunit RRM1 via a conserved residue essential for mammalian viability; as the rate-limiting subunit it catalyzes ribonucleoside diphosphate reduction to maintain dNTP pools for DNA replication and repair. Beyond its enzymatic role, RRM2 is regulated at multiple post-translational levels — stabilized by the deubiquitinases USP7 and USP12, degraded via cyclin F- and WEE1-dependent ubiquitination, and subject to crotonylation at K283 (decrotonylated by SIRT7). Its expression is transcriptionally driven by E2F family members (E2F1, E2F2, E2F8), MYBL2, FOXM1, and BRCA1, and post-transcriptionally controlled by YBX1 (via lincNMR) and IGF2BP3-mediated m6A-dependent mRNA stabilization. RRM2 protein also exerts enzymatic-activity-independent functions — it stabilizes ANXA1 to activate AKT signaling, regulates Bcl-2 protein stability to suppress apoptosis, interacts with GSS to sustain glutathione synthesis and block ferroptosis, and activates NF-κB/MMP-9 to drive invasion — collectively linking RRM2 to cancer cell survival, drug resistance, angiogenesis, and immune evasion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RRM2 encodes the regulatory subunit of ribonucleotide reductase (RNR), whose physical association with the catalytic subunit RRM1 via a conserved tryptophan residue is essential for holoenzyme activity, dNTP synthesis, and mammalian viability [PMID:26077802]. As the rate-limiting component of RNR, RRM2-driven dNTP supply protects against replication stress–induced genomic instability at common fragile sites and is transcriptionally activated by E2F1/E2F8, MYBL2, FOXM1, and BRCA1, while its protein turnover is governed by cyclin F– and WEE1-dependent ubiquitination countered by USP7 and USP12 deubiquitination and by SIRT7-mediated decrotonylation at K283 [PMID:25838540, PMID:36130505, PMID:37341611, PMID:34234118, PMID:36597126, PMID:38894712]. Beyond its enzymatic role in nucleotide metabolism, RRM2 exerts catalytic-activity-independent functions including stabilization of ANXA1 to activate AKT signaling, regulation of Bcl-2 protein stability to suppress apoptosis, and interaction with glutathione synthetase (GSS) to sustain glutathione synthesis and inhibit ferroptosis [PMID:34319001, PMID:23719266, PMID:33372599]. RRM2 silencing activates cGAS/STING innate immune signaling and increases tumor CD8+ T cell infiltration, linking its depletion to anti-tumor immunity [PMID:33858512].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Whether RRM2 influences cellular phenotypes beyond dNTP supply was unknown; overexpression in pancreatic cancer cells activated NF-κB and upregulated MMP-9, establishing a non-canonical role for RRM2 in promoting invasion.\",\n      \"evidence\": \"RRM2 overexpression and RNAi in pancreatic cancer cells with NF-κB reporter and invasion assays\",\n      \"pmids\": [\"17222798\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct physical interaction between RRM2 and NF-κB pathway components demonstrated\", \"Enzymatic-activity independence not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The relationship between RRM2 and tumor angiogenesis was undefined; gain- and loss-of-function experiments showed RRM2 suppresses TSP-1 and induces VEGF, promoting angiogenesis in vivo.\",\n      \"evidence\": \"RRM2 overexpression/siRNA, ELISA, endothelial chemotaxis, xenograft vascularization\",\n      \"pmids\": [\"19250552\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking RRM2 to TSP-1 repression not identified\", \"Whether this requires RNR catalytic activity is unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Whether RRM2 directly regulates apoptotic machinery was unknown; RRM2 depletion destabilized Bcl-2 protein and triggered intrinsic apoptosis, and the two proteins co-localize, linking RRM2 to anti-apoptotic signaling beyond dNTP supply.\",\n      \"evidence\": \"siRNA knockdown, confocal co-localization, tissue immunohistochemistry in head/neck and lung cancer\",\n      \"pmids\": [\"23719266\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding between RRM2 and Bcl-2 not shown by co-IP or structural methods\", \"Whether stabilization requires RRM2 enzymatic activity untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The structural basis for RRM1–RRM2 holoenzyme assembly was unresolved; identification of a single conserved tryptophan mediating the interaction, with lethality upon its mutation in mice, established this contact as essential for RNR function and development.\",\n      \"evidence\": \"Rrm1-WG/WG knock-in mice, proteomic interaction analysis, genetic epistasis\",\n      \"pmids\": [\"26077802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full atomic-resolution structure of the mammalian RRM1–RRM2 interface not reported\", \"Whether compensatory interactions exist in specific tissues unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Whether increasing RRM2/dNTP levels could rescue replication stress in vivo was untested; Rrm2 transgenic mice showed reduced fragile-site breakage and extended lifespan of ATR-mutant animals, proving RRM2-driven dNTP supply is a conserved genome-protection mechanism.\",\n      \"evidence\": \"Transgenic Rrm2-overexpressing mice, RNR activity assay, fragile-site cytogenetics, ATR-mutant survival analysis\",\n      \"pmids\": [\"25838540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific thresholds of dNTP sufficiency not defined\", \"Whether dNTP-independent functions of RRM2 also contribute to rescue unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Upstream transcriptional regulators of RRM2 in replication-stress contexts were incompletely mapped; BRCA1 was shown to co-activate RRM2 transcription, with BRCA1 loss reducing RRM2 and increasing replication stress in glioblastoma.\",\n      \"evidence\": \"BRCA1 knockdown, DNA fiber assay, γH2AX staining, xenograft models\",\n      \"pmids\": [\"27845331\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether BRCA1 binds the RRM2 promoter directly or acts through intermediates not fully resolved\", \"Generalizability beyond glioblastoma untested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"How viruses co-opt host dNTP synthesis in differentiated cells was unclear; HPV31 E7 was shown to maintain RRM2 via ATR-Chk1-E2F1, and RRM2 depletion abolished productive viral replication, establishing RRM2 as essential for viral DNA synthesis.\",\n      \"evidence\": \"RRM2 siRNA in differentiating keratinocytes, dNTP measurement, viral DNA replication assay\",\n      \"pmids\": [\"27764728\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether other HPV types use the same mechanism untested\", \"Direct E2F1 binding to RRM2 promoter not shown in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The E3 ligase pathway controlling RRM2 turnover was not fully defined; cyclin F was identified as mediating proteasomal degradation of RRM2 upon drug treatment, linking cell-cycle-dependent ubiquitination to RNR activity control.\",\n      \"evidence\": \"Molecular docking, RNR activity assay, dNTP quantification, cyclin F epistasis, xenograft\",\n      \"pmids\": [\"30518875\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct cyclin F–RRM2 binding site not mapped\", \"Whether cyclin F targets RRM2 constitutively or only under drug stress unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Post-transcriptional control of RRM2 protein was incompletely understood; 4E-BP1 was shown to selectively repress RRM2 cap-dependent translation downstream of mTORC1/2 signaling, adding a translational layer to RRM2 regulation.\",\n      \"evidence\": \"CRISPR/Cas9 4E-BP1 knockout, mTOR inhibitor treatment, inducible 4E-BP1 expression, xenograft\",\n      \"pmids\": [\"33191406\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific 5'UTR features of RRM2 mRNA conferring 4E-BP1 sensitivity not identified\", \"Whether this mechanism operates in non-cancer cells untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether RRM2 regulates ferroptosis was unknown; RRM2 was found to interact with GSS in a phosphorylation-dependent manner (T33), sustaining GSH synthesis and suppressing ferroptosis; dephosphorylation promotes co-degradation of both proteins.\",\n      \"evidence\": \"Co-IP, proximity ligation assay, T33 phospho-mutagenesis, proteasome inhibition, ferroptosis assays in liver cancer cells\",\n      \"pmids\": [\"33372599\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for T33 phosphorylation not identified\", \"Whether this mechanism is independent of RNR catalytic activity not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"How lncRNAs regulate nucleotide metabolism was unclear; lincNMR was shown to bind YBX1, which controls RRM2 expression; lincNMR depletion reduced dNTP pools rescuable by exogenous dNTPs, placing a lncRNA–RBP axis upstream of RRM2.\",\n      \"evidence\": \"RAP-MS, triple-label SILAC, siRNA, dNTP rescue across multiple cancer cell lines\",\n      \"pmids\": [\"32587247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether YBX1 acts transcriptionally or post-transcriptionally on RRM2 mRNA not fully resolved\", \"Stoichiometry of lincNMR–YBX1 complex unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Whether RRM2 has functions independent of its RNR enzymatic activity was formally untested; RRM2 was shown to stabilize ANXA1 and activate AKT signaling to drive sunitinib resistance in renal cell carcinoma, independently of catalytic activity.\",\n      \"evidence\": \"Co-IP, enzymatic-activity-independent mutant, xenograft, patient tissue analysis\",\n      \"pmids\": [\"34319001\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of the RRM2–ANXA1 interaction unknown\", \"Whether enzymatic-independent functions extend to other cancer types untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"How RRM2 loss affects anti-tumor immunity was unknown; RRM2 silencing activated the cGAS/STING pathway in a STING-dependent manner, increased CD8+ T cell infiltration, and synergized with radiation.\",\n      \"evidence\": \"shRNA knockdown, flow cytometry, IHC, xenograft with irradiation in lung adenocarcinoma\",\n      \"pmids\": [\"33858512\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether cytosolic DNA from replication stress or another signal triggers cGAS not resolved\", \"Immunocompetent syngeneic model not used\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Direct transcriptional activators of RRM2 during S phase were incompletely catalogued; MYBL2 was shown to directly bind the RRM2 promoter in complex with TAF15 and MuvB, activating transcription essential for DNA synthesis.\",\n      \"evidence\": \"ChIP, promoter reporter, knockdown/overexpression rescue, xenograft in colorectal cancer cells\",\n      \"pmids\": [\"34234118\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MYBL2–MuvB complex is the dominant S-phase driver versus E2F factors is unclear\", \"Interplay among multiple transcription factors at the RRM2 promoter not mapped simultaneously\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"How RRM2 protein is stabilized during S phase was undefined; USP7 was identified as a deubiquitinase that directly binds and deubiquitinates RRM2 in S phase, with USP7 loss causing replication stress and senescence rescued by ectopic RRM2.\",\n      \"evidence\": \"Co-IP, proteomics, shRNA, ectopic RRM2 rescue, PDX dropout screen in melanoma\",\n      \"pmids\": [\"36130505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP7 and USP12 act redundantly or in distinct contexts unknown\", \"Ubiquitin chain type specificity not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"WEE1 kinase was implicated in RRM2 protein turnover; WEE1 inhibition reduced RRM2 protein and synergized with MYBL2 knockdown, defining convergent transcriptional and post-translational control axes.\",\n      \"evidence\": \"WEE1 inhibitor MK-1775, combination with MYBL2 knockdown, xenograft\",\n      \"pmids\": [\"34234118\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether WEE1 acts directly on RRM2 or via CDK-mediated phosphorylation-dependent ubiquitination unresolved\", \"Direct WEE1–RRM2 interaction not demonstrated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether additional deubiquitinases regulate RRM2 was unknown; USP12 was identified as a second DUB that directly deubiquitinates RRM2, with USP12 loss reducing RRM2 and causing replication stress in NSCLC.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, USP12 knockdown, xenograft\",\n      \"pmids\": [\"37341611\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship and potential redundancy between USP7 and USP12 on RRM2 not tested\", \"Whether USP12 regulation is cell-cycle-phase specific unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"E2F8 was identified as a direct transcriptional activator of RRM2 in lung adenocarcinoma; combined E2F8 knockdown with WEE1 inhibition synergistically depleted RRM2, showing convergent therapeutic vulnerability.\",\n      \"evidence\": \"ChIP-qPCR, DNA pulldown, luciferase reporter, knockdown/overexpression, xenograft\",\n      \"pmids\": [\"37863324\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of E2F1, E2F8, and MYBL2 to RRM2 transcription across tissues not compared\", \"Whether E2F8 cooperates with or competes with E2F1 at the RRM2 promoter unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"FOXM1 was shown to directly bind the RRM2 promoter in SCLC, adding another transcription factor to the regulatory network; miR-1/CXCR4 axis suppresses FOXM1–RRM2 signaling and metastasis.\",\n      \"evidence\": \"ChIP, dual-luciferase, miR-1 gain/loss of function, intracardiac metastasis model\",\n      \"pmids\": [\"36597126\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How CXCR4 signaling enables FOXM1 promoter binding mechanistically is unclear\", \"Whether FOXM1 and MYBL2 bind the same or distinct RRM2 promoter regions unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A novel post-translational modification — lysine crotonylation at K283 — was identified on RRM2; SIRT7 decrotonylates this site, and p53 loss reduces SIRT7, leading to RRM2 hyper-crotonylation and cisplatin resistance.\",\n      \"evidence\": \"SILAC crotonylome, p53 KO cells, SIRT7 knockdown/overexpression, K283 mutagenesis, apoptosis assays in colon cancer\",\n      \"pmids\": [\"38894712\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Writer enzyme (crotonyltransferase) for K283 not identified\", \"How crotonylation stabilizes RRM2 protein mechanistically is unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Post-transcriptional stabilization of RRM2 mRNA by m6A was established; IGF2BP3 reads m6A marks on RRM2 mRNA to sustain its expression, linking epitranscriptomic regulation to GSH synthesis and ferroptosis suppression.\",\n      \"evidence\": \"MeRIP, RIP, ChIP, dual-luciferase, rescue experiments, xenograft in hepatocellular carcinoma\",\n      \"pmids\": [\"39630361\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific m6A sites on RRM2 mRNA not mapped at single-nucleotide resolution\", \"Whether m6A regulation of RRM2 operates in normal tissue homeostasis unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A unified quantitative model integrating the multiple transcriptional (E2F1, E2F8, MYBL2, FOXM1, BRCA1), translational (4E-BP1), and post-translational (USP7, USP12, cyclin F, WEE1, SIRT7/K283Cr) regulatory inputs that converge on RRM2 protein levels across cell cycle phases and stress conditions has not been constructed.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No integrated systems-level model of RRM2 regulation across cell cycle and stress contexts\",\n        \"Structural basis of RRM2 enzymatic-activity-independent protein–protein interactions (ANXA1, GSS, Bcl-2) unresolved\",\n        \"T33 kinase identity and upstream signaling controlling RRM2–GSS interaction unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [0, 1, 8, 9]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 6, 13, 26]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [8, 10, 11, 15]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 6, 20]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 7, 19, 23]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [20]}\n    ],\n    \"complexes\": [\n      \"Ribonucleotide reductase (RNR) holoenzyme (RRM1–RRM2)\"\n    ],\n    \"partners\": [\n      \"RRM1\",\n      \"USP7\",\n      \"USP12\",\n      \"GSS\",\n      \"ANXA1\",\n      \"YBX1\",\n      \"CDK1\",\n      \"SIRT7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}