{"gene":"NOP2","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1994,"finding":"Yeast Nop2p (ortholog of human NOP2/p120) is an essential nucleolar protein required for cell viability; it localizes primarily to the nucleolus as determined by indirect immunofluorescence and nuclear fractionation, and its overexpression alters nucleolar morphology (detachment from nuclear envelope, fragmentation) without affecting ribosome subunit synthesis levels.","method":"Indirect immunofluorescence, subcellular fractionation, electron microscopy, GAL10-driven overexpression, SDS-PAGE","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (immunofluorescence, fractionation, EM) in a foundational paper with genetic characterization of an essential gene","pmids":["7806561"],"is_preprint":false},{"year":2001,"finding":"Temperature-sensitive nop2 alleles in S. cerevisiae cause defective processing of 27S pre-rRNA to mature 25S rRNA and dramatic reductions in 60S ribosome subunits under non-permissive conditions, without significantly affecting 40S subunits or 18S rRNA, establishing Nop2p as a trans-acting factor required for large ribosomal subunit biogenesis and rRNA processing.","method":"Molecular genetics (temperature-sensitive alleles), ribosome subunit analysis, pre-rRNA processing assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — six independent conditional alleles with consistent phenotypes, multiple orthogonal methods (subunit analysis, rRNA processing), rigorous genetic characterization","pmids":["11452018"],"is_preprint":false},{"year":2014,"finding":"LncRNA-hPVT1 binds to NOP2 protein (identified by RNA pulldown and mass spectrometry) and enhances stability of NOP2 protein, with NOP2 being required for PVT1-mediated promotion of HCC cell proliferation, cell cycling, and stem cell-like properties.","method":"RNA pulldown, mass spectrometry, gain-of-function and loss-of-function experiments","journal":"Hepatology (Baltimore, Md.)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — RNA pulldown + MS identification of binding, functional rescue experiment confirming NOP2 dependence, single lab","pmids":["25043274"],"is_preprint":false},{"year":2015,"finding":"RNAi-mediated knockdown of Nop2 in mouse preimplantation embryos causes developmental arrest at morula stage with reduced blastomere numbers, increased apoptosis, impaired cell-lineage specification, and global reduction of all RNA species including rRNA, snRNA, snoRNA, and mRNA, demonstrating that NOP2 is required for RNA processing and/or stability during preimplantation development.","method":"RNAi knockdown in mouse embryos, RNA quantification, apoptosis assays, lineage marker analysis","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular and molecular phenotypes, multiple readouts, single lab","pmids":["26632338"],"is_preprint":false},{"year":2016,"finding":"NOL1 (NOP2) was identified as a TERC-binding protein associated with catalytically active telomerase; NOL1 binds to the TCF-binding element of the cyclin D1 promoter and activates its transcription; telomerase is recruited to the cyclin D1 promoter in a TERC-dependent manner through interaction with NOL1, further enhancing cyclin D1 transcription; depletion of NOL1 suppresses cyclin D1 promoter activity and induces growth arrest and altered cell cycle distributions.","method":"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), promoter reporter assays, siRNA knockdown","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction assays, ChIP, functional promoter assays, single lab with multiple orthogonal methods","pmids":["26906424"],"is_preprint":false},{"year":2019,"finding":"NOP2 depletion in mouse preimplantation embryos disrupts nucleolar maturation (increased nucleolus precursor body ratio, decreased nucleolus size ratio by TEM) and reduces rRNA abundance (by qPCR and FISH), impairs first lineage specification (reduced TEAD4, NANOG, KLF4), with conserved function confirmed in bovine embryos.","method":"RNAi knockdown, transmission electron microscopy, RNA-seq, FISH, qPCR, immunofluorescence","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (TEM, FISH, RNA-seq, qPCR) in a single lab, conservation confirmed in a second mammalian species","pmids":["31908012"],"is_preprint":false},{"year":2020,"finding":"NOP2 suppresses HIV-1 transcription and promotes viral latency by: (1) associating with HIV-1 5' LTR chromatin, (2) competing with HIV-1 Tat protein for binding to TAR RNA, and (3) contributing to m5C methylation of TAR RNA; the RNA methyltransferase catalytic domain (MTD) of NOP2 mediates its competition with Tat and binding with TAR.","method":"Loss- and gain-of-function analyses, chromatin immunoprecipitation, RNA immunoprecipitation, RNA methylation assays, domain mutagenesis, HIV-1 latency reactivation assays","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal mechanistic assays (ChIP, RIP, methylation, domain mutagenesis, functional latency assays), single lab with comprehensive mechanistic dissection","pmids":["32176734"],"is_preprint":false},{"year":2022,"finding":"Human NOP2/NSUN1 catalyzes deposition of m5C at position 4447 on 28S rRNA (identified by miCLIP-seq); NOP2/NSUN1 also binds the 5'ETS region of pre-rRNA and regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs (U3 and U8), facilitating their recruitment to pre-90S ribosomal particles and stable assembly into snoRNP complexes; both WT and catalytically inactive NOP2/NSUN1 rescue rRNA processing defects and snoRNP assembly in knockdown background, demonstrating m5C catalytic activity is dispensable for ribosome biogenesis.","method":"miCLIP-seq, siRNA knockdown, complementation with WT and catalytic mutant, snoRNP assembly assays, pre-rRNA processing analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — miCLIP-seq for substrate identification, mutagenesis separating catalytic from non-catalytic functions, complementation rescue experiments, multiple orthogonal approaches in one study","pmids":["36161484"],"is_preprint":false},{"year":2023,"finding":"NOP2 catalyzes m5C modification of c-Myc mRNA in an EIF3A-dependent manner; m5C methylation of c-Myc mRNA induces its degradation dependent on EIF3A, thereby reducing c-Myc expression and reprogramming glucose metabolism; MAZ transcription factor directly controls NOP2 expression in HCC.","method":"m5C methylation assays, RNA immunoprecipitation, RNA stability assays, EIF3A co-functional experiments, ChIP for MAZ binding, loss-of-function assays","journal":"Research (Washington, D.C.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mechanistic assays (RIP, methylation, stability, epistasis with EIF3A), single lab","pmids":["37398932"],"is_preprint":false},{"year":2023,"finding":"NOP2 methylates XPD mRNA at m5C sites, enhancing XPD mRNA stability; NOP2 overexpression elevated XPD expression and inhibited HCC cell proliferation, migration, and invasion in vitro.","method":"m5C methylation assays, RNA stability assays, in vitro functional assays","journal":"Neoplasma","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited mechanistic detail in abstract, single method for m5C-stability link","pmids":["37498063"],"is_preprint":false},{"year":2023,"finding":"NAT10-mediated ac4C modification of Nop2 mRNA stabilizes it and enhances translation; NAT10 knockdown decreases ac4C on Nop2 mRNA and reduces NOP2 RNA and protein abundance; NOP2 depletion inhibits translation of transcription factor TEAD4, leading to defective Cdx2 expression and failure of trophectoderm fate specification; exogenous Nop2 mRNA partially rescues abnormal development.","method":"acRIP-PCR, single-cell sequencing, RNA-seq, embryonic phenotype monitoring, mRNA rescue experiments","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — acRIP-PCR biochemical validation plus genetic rescue, multiple molecular and phenotypic readouts, single lab","pmids":["37768430"],"is_preprint":false},{"year":2024,"finding":"NOP2 deposits m5C on EZH2 mRNA, stabilizing it in an ALYREF (m5C reader)-dependent manner; NOP2/ALYREF/EZH2 axis promotes EMT in lung cancer cells; EZH2 counteracts NOP2 effects on H3K27me3 occupancy at the E-cadherin promoter, repressing E-cadherin expression.","method":"RNA-seq, methylated RNA immunoprecipitation (MeRIP), RNA stability assays, ChIP, in vitro and in vivo functional assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MeRIP for m5C substrate identification, ChIP for downstream epigenetic mechanism, RNA stability assays, single lab with multiple orthogonal approaches","pmids":["39013911"],"is_preprint":false},{"year":2024,"finding":"NOP2 stimulates m5C modification of APOL1 mRNA; m5C reader YBX1 recognizes and binds the m5C site in the 3'-UTR of APOL1 mRNA, stabilizing it; NOP2/APOL1 axis activates PI3K-Akt signaling to promote ccRCC progression.","method":"m5C bisulfite sequencing, RNA-seq, RIP/MeRIP RT-qPCR, luciferase reporter assay, RNA stability assay, loss/gain-of-function assays","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bisulfite sequencing for m5C identification, MeRIP and RIP for reader recruitment, RNA stability assays, multiple orthogonal methods, single lab","pmids":["39309431"],"is_preprint":false},{"year":2025,"finding":"NSUN1 (NOP2) isoform 3 selectively interacts with TDP-43 independently of RNA in human cells; aberrant Nsun1 activity drives TDP-43-induced m5C-RNA hypermethylation in a Drosophila model; Nsun1 downregulation alleviates TDP-43-induced neurodegeneration, lifespan deficits, and cytoplasmic accumulation of TDP-43; NSUN1 is nucleolar and interacts with TDP-43 in both nucleolar and nucleoplasmic compartments.","method":"TDP-43 interactome mapping (co-IP/MS), Drosophila genetic epistasis, m5C-RNA quantification, isoform-specific interaction assays, postmortem human brain analysis","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — interactome mapping, genetic epistasis in Drosophila, isoform-specific protein interaction (RNA-independent), supported by human postmortem data; single lab","pmids":["41188020"],"is_preprint":false},{"year":2025,"finding":"NOP2 catalyzes m5C modification of COL1A1 mRNA, stabilizing it; tranilast treatment reduces NOP2 expression and directly interacts with NOP2 (by RIP), decreasing m5C on COL1A1 mRNA, reducing COL1A1 expression, and suppressing hypertrophic scar fibroblast proliferation, migration, and invasion.","method":"MeRIP, RIP, dual luciferase reporter assay, dot blot, cell functional assays","journal":"Tissue & cell","confidence":"Low","confidence_rationale":"Tier 3 / Weak — MeRIP and RIP assays supporting mechanism, single lab, limited independent validation","pmids":["41260007"],"is_preprint":false},{"year":2026,"finding":"NOP2 knockout in zebrafish (CRISPR/Cas9) causes embryonic lethality within 3-5 dpf with microcephaly and cerebral edema; nop2 deficiency impairs differentiation of neural progenitors, activates p53-dependent apoptosis in neural cells, and compromises pre-ribosomal particle processing; genetic epistasis shows tp53 mutation partially rescues neurogenic defects and cerebral edema but not microcephaly, establishing ribosome biogenesis defects as the primary molecular lesion upstream of p53 apoptosis.","method":"CRISPR/Cas9 knockout, Ribo-seq, ribosome processing assays, p53 epistasis experiments, histology/immunostaining","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with Ribo-seq and genetic epistasis (tp53 rescue), multiple orthogonal phenotypic and molecular readouts, single lab","pmids":["41631357"],"is_preprint":false},{"year":2026,"finding":"NOP2 promotes glycolysis in larynx cancer by depositing m5C on TPI1 mRNA, stabilizing it; NOP2 silencing reduces m5C modification on TPI1 mRNA and decreases TPI1 mRNA stability; overexpression of TPI1 rescues impaired glycolysis caused by NOP2 knockdown.","method":"MeRIP, RIP, dual-luciferase reporter assay, RNA stability assay, functional metabolic assays, xenograft models","journal":"Molecular carcinogenesis","confidence":"Low","confidence_rationale":"Tier 3 / Weak — MeRIP and rescue experiments supporting mechanism, single lab, recent publication with no independent replication","pmids":["41498196"],"is_preprint":false},{"year":2026,"finding":"NOP2 deposits m5C on LMNB2 mRNA, enhancing its stability and elevating LMNB2 protein levels; LMNB2 overexpression rescues the suppressed malignant phenotypes induced by NOP2 knockdown in colorectal cancer cells, establishing LMNB2 as a critical downstream effector of NOP2.","method":"MeRIP-seq, RIP-seq, transcriptomic sequencing, RNA stability assays, rescue overexpression experiments, in vitro and in vivo functional assays","journal":"Cancer medicine","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — multi-omics approach (MeRIP-seq, RIP-seq, RNA-seq) plus rescue experiments, single lab, recent publication","pmids":["40366008"],"is_preprint":false},{"year":2026,"finding":"NOP2-mediated m5C deposition on SCD mRNA facilitates recruitment of m5C reader YBX1, stabilizing SCD mRNA and boosting SCD expression; the NOP2/YBX1/SCD axis orchestrates lipid metabolism reprogramming (altering saturated, monounsaturated, and polyunsaturated fatty acid distribution) to suppress lipid peroxidation and protect bladder cancer cells from ferroptosis.","method":"MeRIP, RIP, RNA stability assays, lipid profiling, in vitro and xenograft functional assays","journal":"International journal of biological sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — MeRIP and RIP supporting m5C-reader-target axis, single lab, very recent publication","pmids":["42088435"],"is_preprint":false},{"year":2026,"finding":"NOP2 stabilizes NFKB1 mRNA through m5C modification; NOP2 knockdown inhibits NFKB1 transcription by decreasing m5C modification on NFKB1 mRNA; NFKB1 overexpression restores inflammation and apoptosis inhibited by NOP2 knockdown in LPS-induced bronchial epithelial cells, establishing a NOP2/m5C/NFKB1 axis in COPD.","method":"MeRIP, RNA stability assays, rescue overexpression, in vivo rat COPD model, cytokine measurement","journal":"Journal of biochemical and molecular toxicology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — MeRIP and rescue experiments, single lab, very recent publication","pmids":["41766206"],"is_preprint":false},{"year":2026,"finding":"In MYC-driven liver cancer cells, NOP2 (rRNA m5C-methyltransferase) expression is regulated by both MYC overexpression and methionine abundance; NOP2 knockdown reduces methylation of multiple 28S rRNA residues and selectively inhibits MYC-driven (but not RAS-driven) liver cancer cell proliferation and in vivo tumor growth.","method":"Heavy isotope methionine tracing, NOP2 knockdown, rRNA methylation analysis, in vivo tumor growth assays, methionine depletion experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isotope tracing for metabolic link, rRNA methylation analysis, selective epistasis with MYC vs RAS context, preprint not yet peer-reviewed","pmids":["41659612"],"is_preprint":true}],"current_model":"NOP2/NSUN1 is an S-adenosylmethionine-dependent RNA methyltransferase that deposits m5C at position 4447 on 28S rRNA and also methylates diverse mRNA targets (c-Myc, EZH2, APOL1, TPI1, LMNB2, SCD, NFKB1, COL1A1, TAR RNA); beyond its catalytic role, NOP2 regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNPs (U3, U8), is required for nucleolar maturation and large ribosomal subunit biogenesis (established from yeast to mammals), competes with HIV-1 Tat for TAR RNA binding to suppress viral transcription, interacts with TDP-43 isoform 3 to drive m5C hypermethylation linked to ALS/FTD neurodegeneration, binds the cyclin D1 promoter to activate its transcription in concert with telomerase/TERC, and its mRNA stability is itself regulated by NAT10-mediated ac4C modification."},"narrative":{"mechanistic_narrative":"NOP2 (NSUN1/p120) is an essential nucleolar S-adenosylmethionine-dependent RNA methyltransferase that couples ribosome biogenesis to RNA m5C modification and serves as a trans-acting factor in large ribosomal subunit production [PMID:7806561, PMID:11452018, PMID:36161484]. In yeast, Nop2p is an essential nucleolar protein whose loss blocks processing of 27S pre-rRNA to mature 25S rRNA and depletes 60S subunits specifically, defining its role in large-subunit biogenesis [PMID:7806561, PMID:11452018]. The human enzyme deposits m5C at position 4447 of 28S rRNA, but its function in pre-rRNA processing is largely non-catalytic: NOP2/NSUN1 binds the 5'ETS of pre-rRNA and forms complexes with box C/D snoRNAs U3 and U8, facilitating their recruitment to pre-90S particles and stable snoRNP assembly, with catalytically inactive enzyme fully rescuing processing defects [PMID:36161484]. This ribosome-biogenesis function is the primary physiological lesion in vivo: NOP2 is required for nucleolar maturation, lineage specification, and embryonic development across mouse and bovine embryos, and its zebrafish knockout causes microcephaly and cerebral edema with impaired pre-ribosomal processing driving p53-dependent apoptosis upstream of the neurogenic phenotype [PMID:26632338, PMID:31908012, PMID:41631357]. Beyond rRNA, NOP2 acts as an m5C 'writer' on numerous mRNAs—including c-Myc, EZH2, APOL1, TPI1, LMNB2, SCD, and NFKB1—where methylation modulates transcript stability through m5C readers ALYREF and YBX1, reprogramming metabolism, EMT, and proliferation in multiple cancers [PMID:36161484, PMID:37398932, PMID:39013911, PMID:39309431]. NOP2 also has nuclear regulatory roles: it binds the cyclin D1 promoter and, together with TERC-associated telomerase, activates its transcription [PMID:26906424], and it represses HIV-1 transcription by associating with the 5' LTR and competing with Tat for TAR RNA binding through its methyltransferase domain [PMID:32176734]. NOP2 isoform 3 interacts with TDP-43 independently of RNA and drives m5C-RNA hypermethylation linked to TDP-43 neurodegeneration [PMID:41188020], and its own mRNA is stabilized by NAT10-mediated ac4C modification [PMID:37768430].","teleology":[{"year":1994,"claim":"Established NOP2 as an essential nucleolar protein, anchoring its biology to the nucleolus before any molecular activity was known.","evidence":"Immunofluorescence, subcellular fractionation, EM, and overexpression of yeast Nop2p","pmids":["7806561"],"confidence":"High","gaps":["No catalytic activity or substrate defined","Mechanism of nucleolar morphology change unexplained"]},{"year":2001,"claim":"Defined the first concrete mechanistic role—a trans-acting factor needed for 27S-to-25S pre-rRNA processing and 60S subunit production—distinguishing large- from small-subunit biogenesis.","evidence":"Temperature-sensitive nop2 alleles with ribosome subunit and pre-rRNA processing analysis in S. cerevisiae","pmids":["11452018"],"confidence":"High","gaps":["Whether processing requires catalytic methylation unresolved","No direct RNA or protein partners identified"]},{"year":2016,"claim":"Extended NOP2 beyond the nucleolus to transcriptional control, showing it activates the cyclin D1 promoter in concert with TERC-associated telomerase.","evidence":"Co-IP, ChIP, promoter reporter assays, siRNA in human cells","pmids":["26906424"],"confidence":"Medium","gaps":["Mechanism of promoter binding specificity unclear","Single lab"]},{"year":2015,"claim":"Demonstrated NOP2 is required for mammalian preimplantation development with global RNA reduction, linking the molecular role to organismal phenotype.","evidence":"RNAi knockdown in mouse embryos with RNA quantification and lineage analysis","pmids":["26632338"],"confidence":"Medium","gaps":["Cannot separate rRNA from mRNA contribution","Catalytic requirement not tested"]},{"year":2020,"claim":"Revealed a host-defense function: NOP2 suppresses HIV-1 transcription by occupying the LTR and competing with Tat for TAR RNA via its methyltransferase domain.","evidence":"ChIP, RIP, RNA methylation, domain mutagenesis, and latency reactivation assays","pmids":["32176734"],"confidence":"High","gaps":["Relative contribution of TAR m5C versus Tat competition not quantified","Single lab"]},{"year":2022,"claim":"Identified the human rRNA substrate (m5C4447 on 28S) and, critically, separated catalytic from non-catalytic functions—showing snoRNP-mediated pre-rRNA processing is methylation-independent.","evidence":"miCLIP-seq, complementation with WT and catalytic mutant, snoRNP assembly assays","pmids":["36161484"],"confidence":"High","gaps":["Functional consequence of m5C4447 itself undefined","Structural basis of U3/U8 recruitment unknown"]},{"year":2023,"claim":"Opened the mRNA m5C-writer paradigm, showing NOP2 methylates c-Myc mRNA in an EIF3A-dependent manner to control its degradation and metabolic reprogramming.","evidence":"m5C/RIP/RNA stability assays and EIF3A epistasis in HCC cells","pmids":["37398932"],"confidence":"Medium","gaps":["Mechanism coupling m5C to EIF3A-dependent decay unclear","Single lab"]},{"year":2024,"claim":"Generalized NOP2 mRNA methylation to reader-dependent stabilization, identifying ALYREF and YBX1 as readers for EZH2 and APOL1 transcripts driving EMT and PI3K-Akt signaling.","evidence":"MeRIP/bisulfite sequencing, RIP, RNA stability, ChIP in lung and renal cancer cells","pmids":["39013911","39309431"],"confidence":"Medium","gaps":["Target selectivity determinants unknown","Each axis from a single lab"]},{"year":2025,"claim":"Linked NOP2 to neurodegeneration, showing isoform-3 interacts with TDP-43 RNA-independently and drives pathogenic m5C hypermethylation.","evidence":"Co-IP/MS interactome, Drosophila genetic epistasis, postmortem human brain analysis","pmids":["41188020"],"confidence":"Medium","gaps":["Human disease causation not established","Isoform-specific interaction surface undefined"]},{"year":2026,"claim":"Established ribosome biogenesis as the primary in vivo lesion, with p53-dependent apoptosis as a downstream consequence of NOP2 loss in a vertebrate.","evidence":"CRISPR/Cas9 zebrafish knockout, Ribo-seq, tp53 genetic epistasis","pmids":["41631357"],"confidence":"Medium","gaps":["Microcephaly persists despite p53 rescue—additional pathway implicated","Catalytic versus non-catalytic contribution not dissected"]},{"year":2026,"claim":"Broadened the mRNA m5C-stabilization mechanism across diverse disease contexts (TPI1, LMNB2, SCD, NFKB1) implicating glycolysis, ferroptosis resistance, and inflammation.","evidence":"MeRIP, RIP, RNA stability and rescue assays across multiple cancer and disease models","pmids":["41498196","40366008","42088435","41766206"],"confidence":"Low","gaps":["Each axis is single-lab without independent replication","Direct methylation site mapping limited in several studies"]},{"year":2026,"claim":"Connected NOP2 rRNA methylation to oncogenic metabolic demand, showing MYC and methionine availability tune NOP2 and selectively support MYC-driven tumor growth.","evidence":"Heavy-isotope methionine tracing, rRNA methylation analysis, MYC vs RAS epistasis (preprint)","pmids":["41659612"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Causal link between specific 28S sites and proliferation not established"]},{"year":null,"claim":"How NOP2 selects its diverse mRNA substrates and how its catalytic m5C activity is functionally apportioned between rRNA, mRNA, and viral RNA targets remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of substrate recognition","No unifying determinant of mRNA target selection","Catalytic vs non-catalytic contributions undissected across most contexts"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[6,7,8,11,12]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,6,7]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[7,8]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[0,7,13]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,7]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,5,15]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[4,6]}],"complexes":["box C/D snoRNP (U3/U8)","pre-90S ribosomal particle"],"partners":["TDP-43","EIF3A","ALYREF","YBX1","TERC","PVT1","NAT10"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P46087","full_name":"28S rRNA (cytosine(4447)-C(5))-methyltransferase","aliases":["Nucleolar protein 1","Nucleolar protein 2 homolog","Proliferating-cell nucleolar antigen p120","Proliferation-associated nucleolar protein p120"],"length_aa":812,"mass_kda":89.3,"function":"S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C(5) position of cytosine 4447 in 28S rRNA (PubMed:26196125). Required for efficient rRNA processing and 60S ribosomal subunit biogenesis (PubMed:24120868, PubMed:36161484). Regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs and facilitates the recruitment of U3 and U8 snoRNAs to pre-90S ribosomal particles and their stable assembly into snoRNP complexes (PubMed:36161484). May play a role in the regulation of the cell cycle and the increased nucleolar activity that is associated with the cell proliferation (PubMed:24120868)","subcellular_location":"Nucleus, nucleolus; Nucleus","url":"https://www.uniprot.org/uniprotkb/P46087/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NOP2","classification":"Common Essential","n_dependent_lines":1201,"n_total_lines":1208,"dependency_fraction":0.9942052980132451},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000111641","cell_line_id":"CID000953","localizations":[{"compartment":"nucleolus_gc","grade":3}],"interactors":[{"gene":"NIP7","stoichiometry":4.0},{"gene":"TRAP1","stoichiometry":4.0},{"gene":"LMNB1","stoichiometry":0.2},{"gene":"RBM8A","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2},{"gene":"SRP68","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000953","total_profiled":1310},"omim":[{"mim_id":"620779","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, AUTOSOMAL RECESSIVE 82; MRT82","url":"https://www.omim.org/entry/620779"},{"mim_id":"620204","title":"RNA, U12 SMALL NUCLEAR; RNU12","url":"https://www.omim.org/entry/620204"},{"mim_id":"619012","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 48; COXPD48","url":"https://www.omim.org/entry/619012"},{"mim_id":"618630","title":"tRNA METHYLTRANSFERASE SUBUNIT 11-2; TRMT112","url":"https://www.omim.org/entry/618630"},{"mim_id":"617491","title":"NOP2/SUN RNA METHYLTRANSFERASE FAMILY, MEMBER 3; NSUN3","url":"https://www.omim.org/entry/617491"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NOP2"},"hgnc":{"alias_symbol":["NOP120","NSUN1","p120"],"prev_symbol":["NOL1"]},"alphafold":{"accession":"P46087","domains":[{"cath_id":"-","chopping":"225-306","consensus_level":"medium","plddt":83.922,"start":225,"end":306},{"cath_id":"3.30.70.1170","chopping":"310-369","consensus_level":"medium","plddt":92.054,"start":310,"end":369},{"cath_id":"3.40.50.150","chopping":"373-587","consensus_level":"high","plddt":92.3819,"start":373,"end":587}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P46087","model_url":"https://alphafold.ebi.ac.uk/files/AF-P46087-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P46087-F1-predicted_aligned_error_v6.png","plddt_mean":62.22},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NOP2","jax_strain_url":"https://www.jax.org/strain/search?query=NOP2"},"sequence":{"accession":"P46087","fasta_url":"https://rest.uniprot.org/uniprotkb/P46087.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P46087/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P46087"}},"corpus_meta":[{"pmid":"25043274","id":"PMC_25043274","title":"Oncofetal long noncoding RNA PVT1 promotes proliferation and stem cell-like property of hepatocellular carcinoma cells by stabilizing NOP2.","date":"2014","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/25043274","citation_count":385,"is_preprint":false},{"pmid":"37398932","id":"PMC_37398932","title":"NOP2-mediated m5C Modification of c-Myc in an EIF3A-Dependent Manner to Reprogram Glucose Metabolism and Promote Hepatocellular Carcinoma Progression.","date":"2023","source":"Research (Washington, D.C.)","url":"https://pubmed.ncbi.nlm.nih.gov/37398932","citation_count":95,"is_preprint":false},{"pmid":"36161484","id":"PMC_36161484","title":"Human NOP2/NSUN1 regulates ribosome biogenesis through non-catalytic complex formation with box C/D snoRNPs.","date":"2022","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/36161484","citation_count":82,"is_preprint":false},{"pmid":"23816522","id":"PMC_23816522","title":"Expression of NOL1/NOP2/sun domain 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of human NOP2/p120) is an essential nucleolar protein required for cell viability; it localizes primarily to the nucleolus as determined by indirect immunofluorescence and nuclear fractionation, and its overexpression alters nucleolar morphology (detachment from nuclear envelope, fragmentation) without affecting ribosome subunit synthesis levels.\",\n      \"method\": \"Indirect immunofluorescence, subcellular fractionation, electron microscopy, GAL10-driven overexpression, SDS-PAGE\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (immunofluorescence, fractionation, EM) in a foundational paper with genetic characterization of an essential gene\",\n      \"pmids\": [\"7806561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Temperature-sensitive nop2 alleles in S. cerevisiae cause defective processing of 27S pre-rRNA to mature 25S rRNA and dramatic reductions in 60S ribosome subunits under non-permissive conditions, without significantly affecting 40S subunits or 18S rRNA, establishing Nop2p as a trans-acting factor required for large ribosomal subunit biogenesis and rRNA processing.\",\n      \"method\": \"Molecular genetics (temperature-sensitive alleles), ribosome subunit analysis, pre-rRNA processing assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — six independent conditional alleles with consistent phenotypes, multiple orthogonal methods (subunit analysis, rRNA processing), rigorous genetic characterization\",\n      \"pmids\": [\"11452018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"LncRNA-hPVT1 binds to NOP2 protein (identified by RNA pulldown and mass spectrometry) and enhances stability of NOP2 protein, with NOP2 being required for PVT1-mediated promotion of HCC cell proliferation, cell cycling, and stem cell-like properties.\",\n      \"method\": \"RNA pulldown, mass spectrometry, gain-of-function and loss-of-function experiments\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — RNA pulldown + MS identification of binding, functional rescue experiment confirming NOP2 dependence, single lab\",\n      \"pmids\": [\"25043274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RNAi-mediated knockdown of Nop2 in mouse preimplantation embryos causes developmental arrest at morula stage with reduced blastomere numbers, increased apoptosis, impaired cell-lineage specification, and global reduction of all RNA species including rRNA, snRNA, snoRNA, and mRNA, demonstrating that NOP2 is required for RNA processing and/or stability during preimplantation development.\",\n      \"method\": \"RNAi knockdown in mouse embryos, RNA quantification, apoptosis assays, lineage marker analysis\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular and molecular phenotypes, multiple readouts, single lab\",\n      \"pmids\": [\"26632338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NOL1 (NOP2) was identified as a TERC-binding protein associated with catalytically active telomerase; NOL1 binds to the TCF-binding element of the cyclin D1 promoter and activates its transcription; telomerase is recruited to the cyclin D1 promoter in a TERC-dependent manner through interaction with NOL1, further enhancing cyclin D1 transcription; depletion of NOL1 suppresses cyclin D1 promoter activity and induces growth arrest and altered cell cycle distributions.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), promoter reporter assays, siRNA knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction assays, ChIP, functional promoter assays, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26906424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"NOP2 depletion in mouse preimplantation embryos disrupts nucleolar maturation (increased nucleolus precursor body ratio, decreased nucleolus size ratio by TEM) and reduces rRNA abundance (by qPCR and FISH), impairs first lineage specification (reduced TEAD4, NANOG, KLF4), with conserved function confirmed in bovine embryos.\",\n      \"method\": \"RNAi knockdown, transmission electron microscopy, RNA-seq, FISH, qPCR, immunofluorescence\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (TEM, FISH, RNA-seq, qPCR) in a single lab, conservation confirmed in a second mammalian species\",\n      \"pmids\": [\"31908012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NOP2 suppresses HIV-1 transcription and promotes viral latency by: (1) associating with HIV-1 5' LTR chromatin, (2) competing with HIV-1 Tat protein for binding to TAR RNA, and (3) contributing to m5C methylation of TAR RNA; the RNA methyltransferase catalytic domain (MTD) of NOP2 mediates its competition with Tat and binding with TAR.\",\n      \"method\": \"Loss- and gain-of-function analyses, chromatin immunoprecipitation, RNA immunoprecipitation, RNA methylation assays, domain mutagenesis, HIV-1 latency reactivation assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal mechanistic assays (ChIP, RIP, methylation, domain mutagenesis, functional latency assays), single lab with comprehensive mechanistic dissection\",\n      \"pmids\": [\"32176734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Human NOP2/NSUN1 catalyzes deposition of m5C at position 4447 on 28S rRNA (identified by miCLIP-seq); NOP2/NSUN1 also binds the 5'ETS region of pre-rRNA and regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs (U3 and U8), facilitating their recruitment to pre-90S ribosomal particles and stable assembly into snoRNP complexes; both WT and catalytically inactive NOP2/NSUN1 rescue rRNA processing defects and snoRNP assembly in knockdown background, demonstrating m5C catalytic activity is dispensable for ribosome biogenesis.\",\n      \"method\": \"miCLIP-seq, siRNA knockdown, complementation with WT and catalytic mutant, snoRNP assembly assays, pre-rRNA processing analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — miCLIP-seq for substrate identification, mutagenesis separating catalytic from non-catalytic functions, complementation rescue experiments, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"36161484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NOP2 catalyzes m5C modification of c-Myc mRNA in an EIF3A-dependent manner; m5C methylation of c-Myc mRNA induces its degradation dependent on EIF3A, thereby reducing c-Myc expression and reprogramming glucose metabolism; MAZ transcription factor directly controls NOP2 expression in HCC.\",\n      \"method\": \"m5C methylation assays, RNA immunoprecipitation, RNA stability assays, EIF3A co-functional experiments, ChIP for MAZ binding, loss-of-function assays\",\n      \"journal\": \"Research (Washington, D.C.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mechanistic assays (RIP, methylation, stability, epistasis with EIF3A), single lab\",\n      \"pmids\": [\"37398932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NOP2 methylates XPD mRNA at m5C sites, enhancing XPD mRNA stability; NOP2 overexpression elevated XPD expression and inhibited HCC cell proliferation, migration, and invasion in vitro.\",\n      \"method\": \"m5C methylation assays, RNA stability assays, in vitro functional assays\",\n      \"journal\": \"Neoplasma\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited mechanistic detail in abstract, single method for m5C-stability link\",\n      \"pmids\": [\"37498063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NAT10-mediated ac4C modification of Nop2 mRNA stabilizes it and enhances translation; NAT10 knockdown decreases ac4C on Nop2 mRNA and reduces NOP2 RNA and protein abundance; NOP2 depletion inhibits translation of transcription factor TEAD4, leading to defective Cdx2 expression and failure of trophectoderm fate specification; exogenous Nop2 mRNA partially rescues abnormal development.\",\n      \"method\": \"acRIP-PCR, single-cell sequencing, RNA-seq, embryonic phenotype monitoring, mRNA rescue experiments\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — acRIP-PCR biochemical validation plus genetic rescue, multiple molecular and phenotypic readouts, single lab\",\n      \"pmids\": [\"37768430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NOP2 deposits m5C on EZH2 mRNA, stabilizing it in an ALYREF (m5C reader)-dependent manner; NOP2/ALYREF/EZH2 axis promotes EMT in lung cancer cells; EZH2 counteracts NOP2 effects on H3K27me3 occupancy at the E-cadherin promoter, repressing E-cadherin expression.\",\n      \"method\": \"RNA-seq, methylated RNA immunoprecipitation (MeRIP), RNA stability assays, ChIP, in vitro and in vivo functional assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MeRIP for m5C substrate identification, ChIP for downstream epigenetic mechanism, RNA stability assays, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"39013911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NOP2 stimulates m5C modification of APOL1 mRNA; m5C reader YBX1 recognizes and binds the m5C site in the 3'-UTR of APOL1 mRNA, stabilizing it; NOP2/APOL1 axis activates PI3K-Akt signaling to promote ccRCC progression.\",\n      \"method\": \"m5C bisulfite sequencing, RNA-seq, RIP/MeRIP RT-qPCR, luciferase reporter assay, RNA stability assay, loss/gain-of-function assays\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bisulfite sequencing for m5C identification, MeRIP and RIP for reader recruitment, RNA stability assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"39309431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NSUN1 (NOP2) isoform 3 selectively interacts with TDP-43 independently of RNA in human cells; aberrant Nsun1 activity drives TDP-43-induced m5C-RNA hypermethylation in a Drosophila model; Nsun1 downregulation alleviates TDP-43-induced neurodegeneration, lifespan deficits, and cytoplasmic accumulation of TDP-43; NSUN1 is nucleolar and interacts with TDP-43 in both nucleolar and nucleoplasmic compartments.\",\n      \"method\": \"TDP-43 interactome mapping (co-IP/MS), Drosophila genetic epistasis, m5C-RNA quantification, isoform-specific interaction assays, postmortem human brain analysis\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — interactome mapping, genetic epistasis in Drosophila, isoform-specific protein interaction (RNA-independent), supported by human postmortem data; single lab\",\n      \"pmids\": [\"41188020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NOP2 catalyzes m5C modification of COL1A1 mRNA, stabilizing it; tranilast treatment reduces NOP2 expression and directly interacts with NOP2 (by RIP), decreasing m5C on COL1A1 mRNA, reducing COL1A1 expression, and suppressing hypertrophic scar fibroblast proliferation, migration, and invasion.\",\n      \"method\": \"MeRIP, RIP, dual luciferase reporter assay, dot blot, cell functional assays\",\n      \"journal\": \"Tissue & cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — MeRIP and RIP assays supporting mechanism, single lab, limited independent validation\",\n      \"pmids\": [\"41260007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP2 knockout in zebrafish (CRISPR/Cas9) causes embryonic lethality within 3-5 dpf with microcephaly and cerebral edema; nop2 deficiency impairs differentiation of neural progenitors, activates p53-dependent apoptosis in neural cells, and compromises pre-ribosomal particle processing; genetic epistasis shows tp53 mutation partially rescues neurogenic defects and cerebral edema but not microcephaly, establishing ribosome biogenesis defects as the primary molecular lesion upstream of p53 apoptosis.\",\n      \"method\": \"CRISPR/Cas9 knockout, Ribo-seq, ribosome processing assays, p53 epistasis experiments, histology/immunostaining\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with Ribo-seq and genetic epistasis (tp53 rescue), multiple orthogonal phenotypic and molecular readouts, single lab\",\n      \"pmids\": [\"41631357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP2 promotes glycolysis in larynx cancer by depositing m5C on TPI1 mRNA, stabilizing it; NOP2 silencing reduces m5C modification on TPI1 mRNA and decreases TPI1 mRNA stability; overexpression of TPI1 rescues impaired glycolysis caused by NOP2 knockdown.\",\n      \"method\": \"MeRIP, RIP, dual-luciferase reporter assay, RNA stability assay, functional metabolic assays, xenograft models\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — MeRIP and rescue experiments supporting mechanism, single lab, recent publication with no independent replication\",\n      \"pmids\": [\"41498196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP2 deposits m5C on LMNB2 mRNA, enhancing its stability and elevating LMNB2 protein levels; LMNB2 overexpression rescues the suppressed malignant phenotypes induced by NOP2 knockdown in colorectal cancer cells, establishing LMNB2 as a critical downstream effector of NOP2.\",\n      \"method\": \"MeRIP-seq, RIP-seq, transcriptomic sequencing, RNA stability assays, rescue overexpression experiments, in vitro and in vivo functional assays\",\n      \"journal\": \"Cancer medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multi-omics approach (MeRIP-seq, RIP-seq, RNA-seq) plus rescue experiments, single lab, recent publication\",\n      \"pmids\": [\"40366008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP2-mediated m5C deposition on SCD mRNA facilitates recruitment of m5C reader YBX1, stabilizing SCD mRNA and boosting SCD expression; the NOP2/YBX1/SCD axis orchestrates lipid metabolism reprogramming (altering saturated, monounsaturated, and polyunsaturated fatty acid distribution) to suppress lipid peroxidation and protect bladder cancer cells from ferroptosis.\",\n      \"method\": \"MeRIP, RIP, RNA stability assays, lipid profiling, in vitro and xenograft functional assays\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — MeRIP and RIP supporting m5C-reader-target axis, single lab, very recent publication\",\n      \"pmids\": [\"42088435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP2 stabilizes NFKB1 mRNA through m5C modification; NOP2 knockdown inhibits NFKB1 transcription by decreasing m5C modification on NFKB1 mRNA; NFKB1 overexpression restores inflammation and apoptosis inhibited by NOP2 knockdown in LPS-induced bronchial epithelial cells, establishing a NOP2/m5C/NFKB1 axis in COPD.\",\n      \"method\": \"MeRIP, RNA stability assays, rescue overexpression, in vivo rat COPD model, cytokine measurement\",\n      \"journal\": \"Journal of biochemical and molecular toxicology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — MeRIP and rescue experiments, single lab, very recent publication\",\n      \"pmids\": [\"41766206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In MYC-driven liver cancer cells, NOP2 (rRNA m5C-methyltransferase) expression is regulated by both MYC overexpression and methionine abundance; NOP2 knockdown reduces methylation of multiple 28S rRNA residues and selectively inhibits MYC-driven (but not RAS-driven) liver cancer cell proliferation and in vivo tumor growth.\",\n      \"method\": \"Heavy isotope methionine tracing, NOP2 knockdown, rRNA methylation analysis, in vivo tumor growth assays, methionine depletion experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isotope tracing for metabolic link, rRNA methylation analysis, selective epistasis with MYC vs RAS context, preprint not yet peer-reviewed\",\n      \"pmids\": [\"41659612\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NOP2/NSUN1 is an S-adenosylmethionine-dependent RNA methyltransferase that deposits m5C at position 4447 on 28S rRNA and also methylates diverse mRNA targets (c-Myc, EZH2, APOL1, TPI1, LMNB2, SCD, NFKB1, COL1A1, TAR RNA); beyond its catalytic role, NOP2 regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNPs (U3, U8), is required for nucleolar maturation and large ribosomal subunit biogenesis (established from yeast to mammals), competes with HIV-1 Tat for TAR RNA binding to suppress viral transcription, interacts with TDP-43 isoform 3 to drive m5C hypermethylation linked to ALS/FTD neurodegeneration, binds the cyclin D1 promoter to activate its transcription in concert with telomerase/TERC, and its mRNA stability is itself regulated by NAT10-mediated ac4C modification.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NOP2 (NSUN1/p120) is an essential nucleolar S-adenosylmethionine-dependent RNA methyltransferase that couples ribosome biogenesis to RNA m5C modification and serves as a trans-acting factor in large ribosomal subunit production [#0, #1, #7]. In yeast, Nop2p is an essential nucleolar protein whose loss blocks processing of 27S pre-rRNA to mature 25S rRNA and depletes 60S subunits specifically, defining its role in large-subunit biogenesis [#0, #1]. The human enzyme deposits m5C at position 4447 of 28S rRNA, but its function in pre-rRNA processing is largely non-catalytic: NOP2/NSUN1 binds the 5'ETS of pre-rRNA and forms complexes with box C/D snoRNAs U3 and U8, facilitating their recruitment to pre-90S particles and stable snoRNP assembly, with catalytically inactive enzyme fully rescuing processing defects [#7]. This ribosome-biogenesis function is the primary physiological lesion in vivo: NOP2 is required for nucleolar maturation, lineage specification, and embryonic development across mouse and bovine embryos, and its zebrafish knockout causes microcephaly and cerebral edema with impaired pre-ribosomal processing driving p53-dependent apoptosis upstream of the neurogenic phenotype [#3, #5, #15]. Beyond rRNA, NOP2 acts as an m5C 'writer' on numerous mRNAs—including c-Myc, EZH2, APOL1, TPI1, LMNB2, SCD, and NFKB1—where methylation modulates transcript stability through m5C readers ALYREF and YBX1, reprogramming metabolism, EMT, and proliferation in multiple cancers [#7, #8, #11, #12]. NOP2 also has nuclear regulatory roles: it binds the cyclin D1 promoter and, together with TERC-associated telomerase, activates its transcription [#4], and it represses HIV-1 transcription by associating with the 5' LTR and competing with Tat for TAR RNA binding through its methyltransferase domain [#6]. NOP2 isoform 3 interacts with TDP-43 independently of RNA and drives m5C-RNA hypermethylation linked to TDP-43 neurodegeneration [#13], and its own mRNA is stabilized by NAT10-mediated ac4C modification [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established NOP2 as an essential nucleolar protein, anchoring its biology to the nucleolus before any molecular activity was known.\",\n      \"evidence\": \"Immunofluorescence, subcellular fractionation, EM, and overexpression of yeast Nop2p\",\n      \"pmids\": [\"7806561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No catalytic activity or substrate defined\", \"Mechanism of nucleolar morphology change unexplained\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Defined the first concrete mechanistic role—a trans-acting factor needed for 27S-to-25S pre-rRNA processing and 60S subunit production—distinguishing large- from small-subunit biogenesis.\",\n      \"evidence\": \"Temperature-sensitive nop2 alleles with ribosome subunit and pre-rRNA processing analysis in S. cerevisiae\",\n      \"pmids\": [\"11452018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether processing requires catalytic methylation unresolved\", \"No direct RNA or protein partners identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended NOP2 beyond the nucleolus to transcriptional control, showing it activates the cyclin D1 promoter in concert with TERC-associated telomerase.\",\n      \"evidence\": \"Co-IP, ChIP, promoter reporter assays, siRNA in human cells\",\n      \"pmids\": [\"26906424\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of promoter binding specificity unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated NOP2 is required for mammalian preimplantation development with global RNA reduction, linking the molecular role to organismal phenotype.\",\n      \"evidence\": \"RNAi knockdown in mouse embryos with RNA quantification and lineage analysis\",\n      \"pmids\": [\"26632338\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cannot separate rRNA from mRNA contribution\", \"Catalytic requirement not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed a host-defense function: NOP2 suppresses HIV-1 transcription by occupying the LTR and competing with Tat for TAR RNA via its methyltransferase domain.\",\n      \"evidence\": \"ChIP, RIP, RNA methylation, domain mutagenesis, and latency reactivation assays\",\n      \"pmids\": [\"32176734\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of TAR m5C versus Tat competition not quantified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the human rRNA substrate (m5C4447 on 28S) and, critically, separated catalytic from non-catalytic functions—showing snoRNP-mediated pre-rRNA processing is methylation-independent.\",\n      \"evidence\": \"miCLIP-seq, complementation with WT and catalytic mutant, snoRNP assembly assays\",\n      \"pmids\": [\"36161484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of m5C4447 itself undefined\", \"Structural basis of U3/U8 recruitment unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Opened the mRNA m5C-writer paradigm, showing NOP2 methylates c-Myc mRNA in an EIF3A-dependent manner to control its degradation and metabolic reprogramming.\",\n      \"evidence\": \"m5C/RIP/RNA stability assays and EIF3A epistasis in HCC cells\",\n      \"pmids\": [\"37398932\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism coupling m5C to EIF3A-dependent decay unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Generalized NOP2 mRNA methylation to reader-dependent stabilization, identifying ALYREF and YBX1 as readers for EZH2 and APOL1 transcripts driving EMT and PI3K-Akt signaling.\",\n      \"evidence\": \"MeRIP/bisulfite sequencing, RIP, RNA stability, ChIP in lung and renal cancer cells\",\n      \"pmids\": [\"39013911\", \"39309431\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target selectivity determinants unknown\", \"Each axis from a single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked NOP2 to neurodegeneration, showing isoform-3 interacts with TDP-43 RNA-independently and drives pathogenic m5C hypermethylation.\",\n      \"evidence\": \"Co-IP/MS interactome, Drosophila genetic epistasis, postmortem human brain analysis\",\n      \"pmids\": [\"41188020\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human disease causation not established\", \"Isoform-specific interaction surface undefined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established ribosome biogenesis as the primary in vivo lesion, with p53-dependent apoptosis as a downstream consequence of NOP2 loss in a vertebrate.\",\n      \"evidence\": \"CRISPR/Cas9 zebrafish knockout, Ribo-seq, tp53 genetic epistasis\",\n      \"pmids\": [\"41631357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Microcephaly persists despite p53 rescue—additional pathway implicated\", \"Catalytic versus non-catalytic contribution not dissected\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Broadened the mRNA m5C-stabilization mechanism across diverse disease contexts (TPI1, LMNB2, SCD, NFKB1) implicating glycolysis, ferroptosis resistance, and inflammation.\",\n      \"evidence\": \"MeRIP, RIP, RNA stability and rescue assays across multiple cancer and disease models\",\n      \"pmids\": [\"41498196\", \"40366008\", \"42088435\", \"41766206\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Each axis is single-lab without independent replication\", \"Direct methylation site mapping limited in several studies\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Connected NOP2 rRNA methylation to oncogenic metabolic demand, showing MYC and methionine availability tune NOP2 and selectively support MYC-driven tumor growth.\",\n      \"evidence\": \"Heavy-isotope methionine tracing, rRNA methylation analysis, MYC vs RAS epistasis (preprint)\",\n      \"pmids\": [\"41659612\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Causal link between specific 28S sites and proliferation not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How NOP2 selects its diverse mRNA substrates and how its catalytic m5C activity is functionally apportioned between rRNA, mRNA, and viral RNA targets remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of substrate recognition\", \"No unifying determinant of mRNA target selection\", \"Catalytic vs non-catalytic contributions undissected across most contexts\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [6, 7, 8, 11, 12]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 6, 7]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [0, 7, 13]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 7]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 5, 15]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"complexes\": [\"box C/D snoRNP (U3/U8)\", \"pre-90S ribosomal particle\"],\n    \"partners\": [\"TDP-43\", \"EIF3A\", \"ALYREF\", \"YBX1\", \"TERC\", \"PVT1\", \"NAT10\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}