{"gene":"RNF2","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2004,"finding":"RNF2 (Ring2/Ring1B) is the catalytic E3 ubiquitin ligase subunit of the hPRC1L complex that monoubiquitinates nucleosomal histone H2A at lysine 119; siRNA knockdown of Ring2 dramatically reduces global H2AK119ub levels in HeLa cells, and the complex co-localizes with ubiquitinated H2A at Polycomb response elements and the Ubx promoter in Drosophila.","method":"Biochemical purification of hPRC1L complex, in vitro ubiquitination assay, RNAi knockdown, chromatin immunoprecipitation","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — reconstituted E3 ligase activity in vitro plus ChIP validation in vivo, foundational study replicated widely","pmids":["15386022"],"is_preprint":false},{"year":2002,"finding":"Ring1B (Rnf2) physically associates with other Polycomb group proteins (Rae28/Mph1, M33) and chromosomal DNA, and Ring1B hypomorphic mice display posterior homeotic transformations with mild Hox gene derepression; overexpression in chick embryos represses Hoxb9, establishing Ring1B as a Polycomb complex component regulating anterior-posterior axis specification.","method":"Co-immunoprecipitation, mouse hypomorphic knock-in, in ovo overexpression, in situ hybridization","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus genetic loss- and gain-of-function with phenotypic readout","pmids":["12183370"],"is_preprint":false},{"year":2003,"finding":"Complete knockout of Rnf2 in mice causes gastrulation arrest and cell cycle inhibition; the early lethality is partially bypassed by genetic inactivation of the Cdkn2a (Ink4a/ARF) locus, implicating Polycomb-mediated repression of Cdkn2a as a key downstream effector of Ring1B during early development.","method":"Mouse knockout, genetic epistasis with Cdkn2a null allele, embryo phenotyping","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype plus genetic epistasis rescue","pmids":["12589020"],"is_preprint":false},{"year":2005,"finding":"Bmi-1 and Ring1A are positive regulators of H2A ubiquitylation within the PRC1 complex; Bmi-1 knockout results in significant loss of H2AK119ub and upregulation of Hoxc13 without affecting EZH2-mediated H3K27me3, placing H2A ubiquitylation downstream of H3K27 methylation in Polycomb silencing.","method":"Knockout mouse cells, ChIP, in vitro ubiquitination assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro assay combined with KO genetic epistasis and ChIP, replicated across labs","pmids":["16359901"],"is_preprint":false},{"year":2006,"finding":"Crystal structure of the Ring1B–Bmi1 RING-RING heterodimer was solved at 2.5 Å; Ring1B 'hugs' Bmi1 through RING-domain contacts and an N-terminal arm wrapping around Bmi1. Bmi1 enhances Ring1B E3 ligase activity toward H2A in vitro using E2s UbcH5a/b/c and UbcH6; catalytic activity resides in Ring1B, not Bmi1. Mutation of the E2/E3 interface in Ring1B abolishes activity.","method":"Crystal structure, in vitro ubiquitination reconstitution, active-site mutagenesis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus reconstituted enzymatic activity plus mutagenesis","pmids":["16710298"],"is_preprint":false},{"year":2006,"finding":"A 2.5-Å structure of the Bmi-1–Ring1B core domain complex reveals that Ring1B 'hugs' Bmi1 through RING and N-terminal tail contacts; this dual interaction synergistically stimulates Ring1B E3 ligase activity; modeling suggests the complex stabilizes E2–nucleosome interactions for efficient H2A ubiquitin transfer.","method":"X-ray crystallography (2.5 Å), in vitro ubiquitination assay, deletion mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — independent crystal structure of same complex by second lab, with functional validation","pmids":["16714294"],"is_preprint":false},{"year":2007,"finding":"Proteomics of in vivo biotinylated Ring1B/Rnf2 from erythroid cells identified ~50 interacting proteins, including previously unknown partners: histone demethylases LSD1/Aof2 and Fbxl10/Jhdm1B, casein kinase subunits, and the BCOR corepressor. A novel Ring1B–Fbxl10 complex also containing BcoR, CK2α, Skp1, and Nspc1/Pcgf1 was identified, extending Ring1B functions beyond canonical PRC1.","method":"In vivo biotinylation tagging, streptavidin affinity purification, mass spectrometry","journal":"Molecular & cellular proteomics : MCP","confidence":"Medium","confidence_rationale":"Tier 2 — high-throughput MS interactome, single lab but comprehensive approach","pmids":["17296600"],"is_preprint":false},{"year":2007,"finding":"Ring1B (Rnf2) deletion in mouse ES cells causes loss of several other PcG proteins (revealing a role in regulating PcG protein levels), derepression of lineage/developmental genes, and aberrant differentiation potential. Despite Ring1B being required for chromosome-wide H2AK119ub1 upon Xist expression, initiation of X-chromosome silencing by Xist is independent of Ring1B.","method":"Conditional knockout ES cells, gene expression profiling, western blot for PcG protein levels, Xist induction assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple orthogonal readouts including protein stability and X-inactivation","pmids":["17620408"],"is_preprint":false},{"year":2007,"finding":"Prohibitin interacts with RNF2 via co-immunoprecipitation of endogenous proteins; the two proteins regulate E2F1 transcriptional activity via dual pathways (direct prohibitin-mediated and indirect p16-mediated); RNF2 and prohibitin are recruited together to E2F1-responsive promoters (by ChIP), and depletion of either increases p16 and decreases E2F1 activity.","method":"Co-immunoprecipitation (endogenous), ChIP, RNAi knockdown, luciferase reporter assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2-3 — reciprocal endogenous Co-IP plus ChIP plus functional reporter, single lab","pmids":["17873902"],"is_preprint":false},{"year":2007,"finding":"Ring1B is a direct substrate of caspases-3 and -9 both in vitro and in vivo; cleavage sites were mapped to Asp175 (caspase-3) and Asp208 (caspase-9); caspase cleavage redistributes Ring1B from exclusive nuclear localization throughout the entire cell and disrupts its transcriptional repression activity.","method":"In vitro caspase cleavage assay, site-directed mutagenesis of cleavage sites, subcellular localization by immunofluorescence, transcriptional repression assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of cleavage plus mutagenesis plus functional consequence (localization and transcription)","pmids":["17379327"],"is_preprint":false},{"year":2008,"finding":"The C-terminal region of Ring1B (C-RING1B) binds the Polycomb cbox domain with 1:1 stoichiometry (Kd 9.2–180 nM depending on Pc orthologue); NMR reveals that C-RING1B is conformationally flexible alone but undergoes structural tightening upon cbox binding, with two conserved subdomains capable of intramolecular interaction that may allow Ring1B to recruit diverse PcG partners.","method":"NMR spectroscopy, analytical ultracentrifugation, binding affinity measurements","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structural analysis with quantitative binding measurements","pmids":["18616292"],"is_preprint":false},{"year":2008,"finding":"Ring1B/Rnf2 is required in vivo for three-dimensional genomic contraction and imprinted silencing at the Kcnq1 and Igf2r imprinted clusters in mouse embryos; Rnf2 and Ezh2 act independently to establish the repressive nuclear compartment associated with the paternal allele.","method":"Mouse embryo in vivo knockout, 3D-FISH for genomic contraction, allele-specific expression analysis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO with quantitative 3D genomic and expression readouts, epistasis with Ezh2","pmids":["18848501"],"is_preprint":false},{"year":2008,"finding":"Ring1B ablation in mouse ES cells results in aberrant expression of key developmental genes (derepression), including TGFβ signaling and cell cycle genes, as well as downregulation of ES cell markers Sox2 and Rex-1; Ring1B-bound genes have bivalent histone marks (H3K4me3 + H3K27me3) or H3K4me3 alone at CpG-rich promoters.","method":"Conditional Ring1B knockout ES cells, genome-wide expression profiling, correlation with published ChIP-chip binding data","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with genome-wide expression analysis, single lab","pmids":["18493325"],"is_preprint":false},{"year":2008,"finding":"RNF2 interacts with PHB2 (prohibitin 2), and the RNF2–PHB2 complex represses CP2c-stimulated transcription in a PHB2 dose-dependent manner; the N-terminal 158 residues of RNF2 are sufficient for physical association and functional cooperation with PHB2, while CP2c binds the C-terminus of RNF2.","method":"Yeast two-hybrid, co-immunoprecipitation, deletion mutagenesis, luciferase reporter assay","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 — Y2H plus Co-IP plus functional reporter, single lab","pmids":["18629613"],"is_preprint":false},{"year":2009,"finding":"Ring1B/Rnf2 is required for self-renewal and multipotential ability of embryonic neural stem cells (NSCs); Ring1B-deficient NSCs show impaired proliferation in vivo and in neurosphere assays, unscheduled neuronal differentiation under proliferating conditions (enhanced when Ring1A is also deleted), upregulation of neuronal transcription factors and Cdkn1a/p21, and decreased Notch signaling effectors.","method":"Conditional knockout in neural stem cells, neurosphere assay, single-cell differentiation, in vivo BrdU labeling, mRNA analysis","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple orthogonal in vivo and in vitro readouts","pmids":["19544461"],"is_preprint":false},{"year":2009,"finding":"RNF2 is phosphorylated at multiple serine residues; p38 MAPK inhibitor SB203580 blocks phosphorylation at Ser41 (a predicted p38 site confirmed by mass spectrometry in Sf9 cells), while MEK1/2 inhibitor PD98059 blocks the majority of RNF2 phosphorylation events; RNF2 phosphorylation differentially modulates transcription factor expression and histone H2B acetylation.","method":"2D gel electrophoresis, phospho-specific western blot, kinase inhibitors, mass spectrometry identification of phosphorylation sites","journal":"Proteomics","confidence":"Medium","confidence_rationale":"Tier 2 — MS site identification plus pharmacological inhibitor validation, single lab","pmids":["19405034"],"is_preprint":false},{"year":2009,"finding":"Bmi1 and Ring1B are expressed in pancreatic exocrine precursor cells and ductal/islet cells in adult pancreas; Ring1B expression is specifically and persistently upregulated only in high-grade PanINs and pancreatic ductal adenocarcinoma (distinct from Bmi1's earlier induction), and Bmi1 knockdown in acinar tumor cells alters expression of digestive enzymes, implicating PRC1 proteins in pancreatic disease progression.","method":"Immunohistochemistry in mouse models and human tissue, conditional KRas knock-in model, shRNA knockdown in cell lines","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2-3 — KD with functional readout plus in vivo mouse models, single lab","pmids":["19585519"],"is_preprint":false},{"year":2010,"finding":"Ring1B self-ubiquitination generates K6-, K27-, and K48-based mixed polyubiquitin chains that stimulate (rather than degrade) its E3 ligase activity; E6-AP (UBE3A) ubiquitinates Ring1B on the same lysines to generate K48-linked chains targeting Ring1B for proteasomal degradation; inactivation of E6-AP in vivo elevates Ring1B and H2AK119ub levels and represses HoxB9 in cerebellar Purkinje neurons, with implications for Angelman syndrome.","method":"In vitro ubiquitination assay, E6-AP knockout mice, western blot, HoxB9 expression analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of distinct ubiquitination modes plus in vivo KO validation","pmids":["20351251"],"is_preprint":false},{"year":2010,"finding":"USP7 deubiquitinates Ring1B directly and specifically in vitro and in vivo; USP7-Ring1B interaction is mediated in part through Ring1B's RING domain; USP7 is found in a complex with other Polycomb proteins and has a stabilizing effect on Ring1B without discriminating between activating and proteolysis-targeting ubiquitin chains.","method":"In vitro deubiquitination assay, co-immunoprecipitation, RING domain interaction mapping","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro DUB assay plus Co-IP interaction mapping, single lab","pmids":["20800574"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of Bmi1/Ring1b RING-RING heterodimer in complex with E2 enzyme UbcH5c shows UbcH5c interacts exclusively with Ring1b; the Bmi1/Ring1b dimer binds duplex DNA through a basic surface patch unique to the heterodimer; mutation of DNA-binding residues abolishes H2A ubiquitination; computational modeling places the complex interacting with nucleosomal DNA and an acidic patch on histone H4 for substrate specificity.","method":"Crystal structure of E3-E2 complex, mutagenesis of DNA-binding surface, in vitro H2A ubiquitination assay, computational nucleosome docking","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of E3-E2 complex with mutagenesis validation of functional surfaces","pmids":["21772249"],"is_preprint":false},{"year":2011,"finding":"Mathematical modeling of the Ring1B/Bmi1 ubiquitination system using biochemical data demonstrates that Ring1B can exhibit bistable switches, oscillations, and excitable (overshoot) transitions between distinct ubiquitination states (self-ubiquitinated active vs. E6-AP-ubiquitinated degradation-targeted); these dynamics can produce all-or-none H2A monoubiquitination rates and discrete periods of gene activity/inactivity controlled by abundances of Bmi1, Ring1B, E6-AP, and USP7.","method":"Computational/mathematical modeling constrained by biochemical data","journal":"PLoS computational biology","confidence":"Low","confidence_rationale":"Tier 4 — computational modeling, though constrained by prior biochemical data","pmids":["22194680"],"is_preprint":false},{"year":2012,"finding":"Six major PRC1 complexes each contain a distinct PCGF subunit with RING1A/B; RYBP (or YAF2) stimulates Ring1B H2AK119ub1 activity and defines non-canonical PRC1 complexes that exclude CBX/PHC/SCM; RYBP-containing and CBX-containing PRC1 complexes both compact chromatin but only RYBP stimulates Ring1B catalytic activity; RYBP knockdown in ES cells compromises embryoid body formation and H2AK119ub1 levels.","method":"Comprehensive proteomics, genome-wide ChIP-seq, in vitro ubiquitination assay with RYBP stimulation, ES cell differentiation assay, knockdown","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — proteomic complex definition + in vitro activity assay + genomic profiling + functional KD, multiple orthogonal methods","pmids":["22325352"],"is_preprint":false},{"year":2013,"finding":"RNF2 knockdown in cancer cells (HCT116) significantly inhibits cell proliferation, colony formation, and induces apoptosis in a partially p53-dependent manner; RNF2 directly binds both p53 and MDM2, promotes MDM2-mediated p53 ubiquitination, and increases MDM2 half-life by inhibiting its ubiquitination, thereby suppressing p53 protein levels during DNA damage response.","method":"RNAi knockdown, overexpression, p53 half-life and ubiquitination assays, co-immunoprecipitation, etoposide DNA damage model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct binding by Co-IP plus ubiquitination assays plus p53/MDM2 stability measurements, single lab","pmids":["23318437"],"is_preprint":false},{"year":2013,"finding":"Fbxl10/Kdm2b recruits non-canonical PRC1 (containing Ring1B and Nspc1) to CpG islands genome-wide; Fbxl10 depletion causes major loss of Ring1B binding at target genes and loss of H2AK119ub1; Fbxl10's DNA binding capability and Ring1B integration are both required for ubiquitylation; Fbxl10-deficient ES cells cannot differentiate properly.","method":"Co-IP, genome-wide ChIP-seq, conditional KO ES cells, differentiation assay, in vitro ubiquitination with reconstituted complex","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — genome-wide ChIP-seq plus functional KO plus reconstituted complex activity","pmids":["23395003"],"is_preprint":false},{"year":2014,"finding":"Crystal structure of the human Ring1B–Bmi1–UbcH5c E3-E2 complex bound to the nucleosome core particle reveals that the PRC1 ubiquitylation module achieves substrate specificity by contacting multiple nucleosome surfaces spatially distinct from the catalytic site; UbcH5c directly contacts the nucleosome (unexpected role for E2 in substrate recognition); the structure provides the mechanism of nucleosome recognition by PRC1 and insight into BRCA1's related H2A ubiquitylation.","method":"X-ray crystallography of PRC1-nucleosome co-complex","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of complete E3-E2-nucleosome substrate complex, definitive mechanistic insight","pmids":["25355358"],"is_preprint":false},{"year":2014,"finding":"In pancreatic ductal adenocarcinoma, Snail recruits Ring1B (and Ring1A) via its C-terminal zinc fingers to target promoters to repress gene expression and promote cell migration; Ring1B-mediated H2AK119ub1 is required for Snail-mediated transcriptional repression; EZH2 is required upstream for Snail-Ring1B recruitment; simultaneous depletion of Ring1A and Ring1B abolishes H2AK119ub1 at target promoters and compromises Snail-mediated cell migration.","method":"Co-immunoprecipitation, ChIP, siRNA knockdown of Ring1A/B, cell migration assay, H2AK119ub1 ChIP","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus ChIP plus functional migration assay, epistasis with EZH2, single lab","pmids":["24903147"],"is_preprint":false},{"year":2014,"finding":"Ring1B is essential for expansion of hepatic stem/progenitor cells; conditional Ring1B knockout in mouse embryos inhibits hepatic stem/progenitor proliferation/differentiation and hepatic organogenesis via derepression of CDKIs Cdkn1a and Cdkn2a; clonal culture epistasis shows that simultaneous (not individual) suppression of Cdkn1a and Cdkn2a reverses the Ring1B-depletion cell cycle inhibition.","method":"Conditional mouse KO, clonal culture epistasis with Cdkn1a/Cdkn2a double knockdown, hepatic organogenesis phenotyping","journal":"Hepatology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with genetic epistasis rescue experiment","pmids":["24497168"],"is_preprint":false},{"year":2015,"finding":"RNF2 is oncogenic and prometastatic in melanoma via two distinct mechanisms: (1) RNF2-mediated H2AK119ub at the LTBP2 promoter silences this negative TGFβ regulator to drive invasion (requires catalytic activity); (2) RNF2 drives proliferation through direct transcriptional upregulation of CCND2 independently of catalytic activity. MEK1-mediated phosphorylation of RNF2 promotes recruitment of activating histone modifiers UTX and p300 to poised promoters to activate gene expression.","method":"Gain/loss-of-function studies in mouse and human melanoma cells, catalytic-dead mutant rescue, H2AK119ub ChIP, co-IP of UTX/p300 with phospho-RNF2, xenograft models","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 — multiple complementary gain/loss-of-function experiments with mechanistic dissection via catalytic mutant and ChIP","pmids":["26450788"],"is_preprint":false},{"year":2015,"finding":"RING1B O-GlcNAcylation at residues T250/S251 and S278 is identified in human ES cells; T250/S251 O-GlcNAcylation decreases during differentiation; ChIP-seq shows that non-O-GlcNAcylated RING1B is enriched near cell cycle genes, whereas O-GlcNAcylated RING1B preferentially targets neuronal genes, suggesting O-GlcNAc modification switches PRC1 genomic targeting during hESC differentiation.","method":"Point-mutation of O-GlcNAcylation sites, ChIP-seq, O-GlcNAc identification by mass spectrometry","journal":"Stem cell research","confidence":"Medium","confidence_rationale":"Tier 2 — site-specific mutagenesis plus ChIP-seq, single lab","pmids":["26100231"],"is_preprint":false},{"year":2015,"finding":"RING1A and RING1B H2AK119ub activity at pericentromeric heterochromatin (PCH) is required for normal S-phase progression; loss of both RING1A and RING1B causes slow elongation and fork stalling preferentially at mid S-phase when PCH is replicated; acute senescence associated with RING1 loss is mediated by p21 (Cdkn1a) upregulation and can be uncoupled from DNA damage response; targeted monoubiquitylation of PCH via MBD1 rescues the replication defect.","method":"Conditional RING1A/B knockout, BrdU/EdU labeling, DNA fiber analysis, γH2AX immunostaining, chromocenter 3D-FISH, epistasis with p21 and targeted PCH ubiquitylation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with DNA fiber replication assay, epistasis rescue, multiple readouts","pmids":["26272920"],"is_preprint":false},{"year":2015,"finding":"RNF2 knockdown in prostate cancer cells causes cell cycle arrest and apoptosis; tumor suppressor gene TXNIP is significantly upregulated upon RNF2 knockdown; ChIP shows RNF2 and H2AK119ub enrichment at the TXNIP promoter; simultaneous knockdown of RNF2 and TXNIP partially rescues the arrested cell cycle and apoptosis, placing TXNIP as a key downstream mediator of RNF2's oncogenic function in prostate cancer.","method":"RNAi knockdown, ChIP, double knockdown epistasis, xenograft, gene microarray","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2-3 — ChIP plus genetic epistasis with TXNIP, single lab","pmids":["28029659"],"is_preprint":false},{"year":2017,"finding":"Nuclear RNF2 directly binds STAT1 after interferon stimulation and catalyzes K33-linked polyubiquitination of the STAT1 DNA-binding domain at K379, promoting STAT1/STAT2 dissociation from DNA and suppressing interferon-stimulated gene (ISG) transcription; RNF2 deficiency substantially enhances ISG expression and antiviral responses.","method":"High-content screening of 115 RING E3 ligases, RNF2 KO/KD, Co-IP of RNF2–STAT1, in vitro ubiquitination assay identifying K33-linked chains at K379, ChIP-seq for STAT1 DNA binding","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro ubiquitination reconstitution with chain-type and site identification, KO phenotype with ISG readout, Co-IP","pmids":["29242538"],"is_preprint":false},{"year":2017,"finding":"RNF2 functions as an E3 ubiquitin ligase targeting SIK1 for proteasomal degradation in hepatocellular carcinoma; RNF2 directly physically interacts with SIK1; RNF2 expression is negatively correlated with SIK1 levels in HCC tissues; RNF2 knockdown reduces tumor growth and metastasis, which is rescued by simultaneous SIK1 knockdown.","method":"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, rescue epistasis, xenograft","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus ubiquitination assay plus epistasis rescue, single lab","pmids":["27911266"],"is_preprint":false},{"year":2018,"finding":"Ring1A and Ring1B (RNF2) function as suppressors of transcription-replication conflicts (TRCs) and common fragile site (CFS) instability; BMI1/RNF2-depleted cells show slower replication forks, elevated fork stalling, increased RNA Pol II occupancy at CFSs, and increased associations between RNAPII and nascent replication forks (measured by proximity ligation assay); RNF2-KO cells show increased FANCD2 and RNH1 at CFSs consistent with R-loop accumulation; FANCD2/FANCI depletion further increases genomic instability in RNF2-KO cells.","method":"DNA fiber assay, proximity ligation assay (PLA) for RNAPII-replisome associations, ChIP for FANCD2/RNH1, CRISPR KO, double depletion epistasis","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (fiber assay, PLA, ChIP) with genetic epistasis, CRISPR KO","pmids":["32142505"],"is_preprint":false},{"year":2020,"finding":"RING1B is highly expressed in Ewing sarcoma (EwS) and co-localizes with EWSR1-FLI1 at active enhancers while retaining repressive activity at canonical Polycomb developmental target genes; RING1B is required for EWSR1-FLI1 recruitment to enhancers and expression of key oncogenic targets; RING1B knockdown impairs xenograft tumor growth; pharmacological AURKB inhibition increases H2AK119ub and downregulates RING1B/EWSR1-FLI1 common targets.","method":"ChIP-seq, siRNA knockdown, xenograft tumor model, AURKB pharmacological inhibition, gene expression profiling","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq showing co-localization plus functional KD in xenograft, single lab","pmids":["33097530"],"is_preprint":false},{"year":2021,"finding":"RNF2 (Ring1B) promotes colon cancer progression by acting as an E3 ubiquitin ligase that directly interacts with and ubiquitinates IRF4, targeting it for proteasomal degradation; RNF2 overexpression enhances proliferation, migration, and invasion via IRF4 degradation; RNF2 knockdown causes opposite effects rescued by IRF4 co-knockdown.","method":"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, overexpression, xenograft, rescue epistasis","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus ubiquitination assay plus epistasis, single lab","pmids":["34670117"],"is_preprint":false},{"year":2021,"finding":"RASSF10 is a substrate for the E3 ubiquitin ligase RNF2; NPM-dependent downregulation of RNF2 is critical to maintain stable RASSF10 levels; RASSF10 promotes G2/M arrest via inhibition of Cdk1/cyclin-B and nuclear accumulation of GADD45a; this RASSF10/NPM/RNF2 cascade controls cell proliferation in gastric cancer.","method":"LC-MS/MS, live cell imaging, co-immunoprecipitation, ubiquitination assay, RNAi knockdown, cell cycle analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 — MS-identified substrate with Co-IP and ubiquitination assay validation, pathway epistasis","pmids":["34224728"],"is_preprint":false},{"year":2021,"finding":"Ring1b forms distinct complexes with either DEAD-box helicases (DDXs) or EMT transcription factors (EMT TFs) at specific loci on the E-cadherin promoter; DDX-Ring1b complexes moderately repress E-cadherin inducing a hybrid EMT state, while EMT TF-Ring1b complexes cooperate with DDX complexes for full repression in mesenchymal-like breast cancer cells, driving metastasis.","method":"Co-immunoprecipitation of distinct complexes, ChIP at E-cadherin promoter, RNAi knockdown, metastasis assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP of distinct complexes plus ChIP at specific loci plus functional metastasis assay, single lab","pmids":["33608512"],"is_preprint":false},{"year":2021,"finding":"RNF2 overexpression in mammary carcinoma promotes cell proliferation, colony formation, migration, and invasion through downregulation of E-cadherin protein, implicating RNF2-driven EMT as a mechanism of breast cancer progression.","method":"RNF2 overexpression and knockdown in cell lines, western blot for E-cadherin, cell migration and invasion assays","journal":"Pathology, research and practice","confidence":"Low","confidence_rationale":"Tier 3 — KD/OE with phenotype but limited mechanistic pathway placement beyond E-cadherin reduction","pmids":["31300294"],"is_preprint":false},{"year":2023,"finding":"A PROTAC degrader (MS147) targeting both BMI1 and RING1B via their interaction with EED (a PRC2 component) degrades BMI1/RING1B in an EED-, VHL-, ubiquitination-, and time-dependent manner; MS147 selectively reduces H2AK119ub without affecting H3K27me3, confirming RING1B as the H2AK119ub catalytic subunit, and inhibits proliferation of cancer cells insensitive to PRC2 inhibitors.","method":"PROTAC degrader chemistry, EED-VHL bifunctional molecule, H2AK119ub and H3K27me3 western blot, cancer cell proliferation assay","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 — novel chemical tool with mechanism-of-action validation, confirms RING1B's specific catalytic role","pmids":["36737841"],"is_preprint":false},{"year":2012,"finding":"In zebrafish, ring1b mutants show a severe craniofacial phenotype with near-complete absence of cranial cartilage, bone, and musculature; cranial neural crest cells migrate correctly into pharyngeal arches but fail to differentiate into chondrocytes; other neural crest-derived lineages (glia, neurons, chromatophores) are formed normally, revealing a specific role for Ring1b in promoting chondrocyte differentiation from CNC cells.","method":"Zebrafish ring1b mutant analysis, cell lineage tracing, in situ hybridization","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — genetic KO in vertebrate model with specific cell-lineage phenotypic readout","pmids":["24040141"],"is_preprint":false},{"year":2012,"finding":"Zebrafish ring1b is essential for pectoral fin development; lateral plate mesoderm differentiation into fin precursors is initiated normally, but fin bud outgrowth is impaired due to insufficient Fgf signaling activation; exogenous FGF4 or hyperactivated Wnt signaling (apc mutant) partially restores the fin program, establishing that PcG-mediated Ring1b gene regulation is required for sustained Fgf signaling in vertebrate limb development.","method":"Zebrafish ring1b mutant, FGF4 rescue experiment, genetic interaction with apc mutant, in situ hybridization for Fgf targets","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with rescue experiment and genetic epistasis with Wnt/Fgf pathways","pmids":["22619390"],"is_preprint":false},{"year":2018,"finding":"Ring1A and Ring1B repress Glis2 expression in MOZ-TIF2 AML stem cells; deletion of Ring1A/B diminishes self-renewal and induces numerous genes including Glis2; Glis2 overexpression causes differentiation of AML cells while Glis2 knockdown in Ring1A/B-deficient AML cells inhibits differentiation, demonstrating that Ring1A/B maintain AML stem cells partly by repressing Glis2.","method":"Conditional Ring1A/B knockout in AML mouse model, gene expression profiling, Glis2 overexpression and knockdown rescue","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — conditional KO plus genetic epistasis (Glis2 KD rescue) with defined AML stem cell phenotype","pmids":["29371181"],"is_preprint":false},{"year":2019,"finding":"RNF2 knockdown enhances radiosensitivity of squamous cell lung carcinoma cells by inhibiting irradiation-induced γH2AX foci formation and impairing interactions among ATM, MDC1, and H2AX; RNF2 knockdown combined with irradiation causes G1 arrest, increased apoptosis, and upregulation of p16 and Bax with downregulation of cyclin D2, CDK4, and Bcl-2.","method":"shRNA knockdown, clonogenic survival, co-immunoprecipitation of ATM-MDC1-H2AX, γH2AX foci counting, flow cytometry, xenograft","journal":"Biochemistry and cell biology = Biochimie et biologie cellulaire","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP of DNA damage repair complex disruption plus functional radiosensitivity assay, single lab","pmids":["30673298"],"is_preprint":false},{"year":2002,"finding":"The core of the human Polycomb repressive complex (hPRC-H) was purified from HeLa cells and contains homologues of Drosophila PRC1 core proteins including RING1/Ring1B, with fewer non-PcG components than dPRC1; hPRC-H retains the ability to block nucleosomal array remodeling similarly to dPRC1, demonstrating functional conservation of the Ring1B-containing PRC1 complex between flies and humans.","method":"Biochemical purification from HeLa cells, chromatin compaction/remodeling assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical purification plus in vitro functional chromatin compaction assay","pmids":["12167701"],"is_preprint":false},{"year":2006,"finding":"A BCOR complex contains Polycomb proteins RING1, RYBP, NSPC1, a Posterior Sex Combs homolog, and RNF2 as E3 ligase for H2A mono-ubiquitylation, as well as SKP1 and FBXL10 (a histone H3K36 demethylase); BCOR complex components and mono-ubiquitylated H2A co-localize at BCL6 target genes by ChIP, establishing that BCL6 can recruit PcG proteins including RNF2 to specific genomic loci.","method":"Immunoprecipitation/mass spectrometry complex identification, ChIP at BCL6 target genes","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2-3 — MS-defined complex plus ChIP validation at specific loci","pmids":["16943429"],"is_preprint":false}],"current_model":"RNF2 (Ring1B/Ring2) is the catalytic E3 ubiquitin ligase subunit of Polycomb Repressive Complex 1 (PRC1) that monoubiquitinates histone H2A at K119 (H2AK119ub1) using E2 enzymes UbcH5a/b/c or UbcH6; its activity is allosterically stimulated by dimerization with Bmi1 through their RING domains, with substrate specificity achieved by simultaneous contacts with nucleosomal DNA, the H4 acidic patch, and the E2 enzyme as revealed by crystal structures; Ring1B's stability and activity are regulated by self-ubiquitination (activating, non-canonical K6/K27 chains), E6-AP-mediated K48-linked ubiquitination (degradative), and USP7-mediated deubiquitination; beyond canonical H2A ubiquitination and Hox gene/developmental gene repression, RNF2 has non-canonical functions including K33-linked ubiquitination of STAT1 to suppress interferon signaling, direct E3 ligase activity toward non-histone substrates (SIK1, IRF4, RASSF10, p53/MDM2 axis), suppression of transcription-replication conflicts at common fragile sites, and recruitment to active enhancers by oncogenic transcription factors such as EWSR1-FLI1."},"narrative":{"teleology":[{"year":2002,"claim":"Establishing RNF2 as a core Polycomb complex subunit: Ring1B was identified as a component of human PRC1 that blocks chromatin remodeling and physically associates with other PcG proteins; hypomorphic mice displayed homeotic transformations with Hox gene derepression, placing Ring1B within the Polycomb gene-silencing paradigm.","evidence":"Biochemical purification of hPRC-H from HeLa cells with chromatin compaction assay; mouse hypomorphic knock-in with phenotyping and co-IP","pmids":["12167701","12183370"],"confidence":"High","gaps":["Catalytic activity of Ring1B not yet identified","Direct target genes beyond Hox clusters unknown"]},{"year":2003,"claim":"Demonstrating Ring1B is essential for early development: Complete Rnf2 knockout caused gastrulation arrest that was partially rescued by Cdkn2a deletion, establishing that a key downstream effector of Ring1B-dependent Polycomb silencing is repression of the Ink4a/ARF cell-cycle inhibitor locus.","evidence":"Mouse knockout with genetic epistasis using Cdkn2a null allele","pmids":["12589020"],"confidence":"High","gaps":["Enzymatic mechanism of Ring1B unknown","Whether phenotype is cell-autonomous unresolved"]},{"year":2004,"claim":"Identifying the catalytic activity: Ring1B was shown to be the E3 ubiquitin ligase that monoubiquitinates histone H2A at K119, with siRNA knockdown dramatically reducing global H2AK119ub, solving the long-standing question of which enzyme deposits this abundant histone mark.","evidence":"In vitro ubiquitination assay with purified hPRC1L complex; RNAi in HeLa cells; ChIP at Polycomb targets","pmids":["15386022"],"confidence":"High","gaps":["Structural basis of Ring1B-BMI1 cooperation unknown","E2 enzyme specificity not defined"]},{"year":2006,"claim":"Solving the structural mechanism of allosteric activation: Two independent crystal structures of the Ring1B–BMI1 RING-RING heterodimer revealed that BMI1 stimulates Ring1B's ligase activity through a 'hugging' interaction; catalytic activity was mapped exclusively to Ring1B, with UbcH5a/b/c and UbcH6 identified as cognate E2 enzymes.","evidence":"X-ray crystallography at 2.5 Å by two independent groups; in vitro ubiquitination with mutagenesis","pmids":["16710298","16714294"],"confidence":"High","gaps":["How the complex recognizes the nucleosome substrate unknown","Role of non-RING regions of Ring1B uncharacterized"]},{"year":2006,"claim":"Expanding the PRC1 landscape: A BCOR corepressor complex containing RNF2, RING1, RYBP, NSPC1, SKP1, and FBXL10 was identified, demonstrating that Ring1B participates in non-canonical PRC1 assemblies recruited by transcription factors like BCL6.","evidence":"Immunoprecipitation/mass spectrometry complex identification; ChIP at BCL6 target genes","pmids":["16943429"],"confidence":"Medium","gaps":["Functional distinction between BCOR-PRC1 and canonical PRC1 unclear","Whether FBXL10 demethylase activity is coordinated with Ring1B ubiquitination unknown"]},{"year":2007,"claim":"Defining Ring1B's role in ES cell identity and PcG protein stability: Conditional Ring1B deletion in ES cells caused derepression of developmental genes and destabilization of other PcG proteins, revealing Ring1B as a structural hub of PRC1 integrity; Ring1B deposited H2AK119ub on the X chromosome but was dispensable for Xist-mediated silencing initiation.","evidence":"Conditional knockout ES cells with expression profiling, western blot for PcG stability, Xist induction assay","pmids":["17620408"],"confidence":"High","gaps":["Whether Ring1B's stabilizing effect on other PcG proteins is direct or indirect unknown","Genome-wide Ring1B binding sites not yet mapped"]},{"year":2008,"claim":"Structural flexibility enables diverse partner recruitment: NMR showed the Ring1B C-terminal domain is conformationally flexible but rigidifies upon binding Polycomb cbox domains with nanomolar affinity, providing a mechanism for Ring1B to serve as a versatile scaffold recruiting distinct CBX subunits to PRC1.","evidence":"NMR spectroscopy; analytical ultracentrifugation; quantitative binding measurements","pmids":["18616292"],"confidence":"High","gaps":["How competing CBX proteins are selected for specific PRC1 assemblies unknown"]},{"year":2010,"claim":"Revealing dual ubiquitin-based regulation of Ring1B stability and activity: Self-ubiquitination via K6/K27 chains was shown to stimulate Ring1B activity, while E6-AP-mediated K48 chains targeted it for degradation; USP7 counteracted both chain types, establishing a tripartite regulatory circuit controlling Ring1B protein levels and catalytic output in vivo.","evidence":"In vitro ubiquitination reconstitution identifying chain types; E6-AP knockout mice with elevated Ring1B/H2AK119ub; in vitro DUB assay with USP7","pmids":["20351251","20800574"],"confidence":"High","gaps":["Whether USP7 discriminates between activating and degradative chains in vivo unresolved","Upstream signals controlling the balance between self-ubiquitination and E6-AP activity unknown"]},{"year":2012,"claim":"Defining variant PRC1 complexes and the RYBP stimulatory mechanism: Six distinct PRC1 complexes were catalogued, each with a unique PCGF subunit paired with RING1A/B; RYBP replaced CBX in non-canonical complexes and directly stimulated Ring1B catalytic activity; KDM2B/FBXL10 was shown to recruit non-canonical PRC1 to CpG islands genome-wide.","evidence":"Comprehensive proteomics; ChIP-seq; in vitro ubiquitination with RYBP; KDM2B conditional KO ES cells","pmids":["22325352","23395003"],"confidence":"High","gaps":["How canonical and non-canonical PRC1 complexes partition genomic targets unresolved","Whether RYBP stimulation changes chain linkage or only rate unknown"]},{"year":2014,"claim":"Achieving atomic-resolution understanding of nucleosome recognition: The crystal structure of Ring1B–BMI1–UbcH5c bound to the nucleosome core particle revealed that substrate specificity arises from contacts distributed across Ring1B, UbcH5c, and BMI1 with nucleosomal DNA and the H2A/H4 acidic patch, with an unexpected direct role for the E2 in substrate recognition.","evidence":"X-ray crystallography of the complete E3–E2–nucleosome complex","pmids":["25355358"],"confidence":"High","gaps":["How PRC1 transitions from chromatin compaction to ubiquitination mode unknown","Structural basis of variant PRC1 nucleosome recognition not determined"]},{"year":2015,"claim":"Expanding Ring1B function to DNA replication: Loss of RING1A/B caused replication fork stalling specifically at pericentromeric heterochromatin during mid S-phase, with targeted monoubiquitylation rescuing the defect, demonstrating that H2AK119ub facilitates replication through constitutive heterochromatin independently of canonical gene silencing.","evidence":"Conditional RING1A/B KO; DNA fiber analysis; targeted PCH ubiquitylation rescue; p21 epistasis","pmids":["26272920"],"confidence":"High","gaps":["Mechanism by which H2AK119ub facilitates fork passage through heterochromatin unknown","Whether Ring1B is recruited to replication forks directly unresolved"]},{"year":2015,"claim":"Identifying catalytic-independent transcriptional activation: In melanoma, RNF2 was shown to drive CCND2 expression independently of its catalytic activity through MEK1-dependent phosphorylation that recruits UTX/p300, while simultaneously repressing LTBP2 via H2AK119ub, revealing bifunctional chromatin regulation by a single E3 ligase.","evidence":"Catalytic-dead mutant rescue; phospho-RNF2 co-IP with UTX/p300; ChIP; xenograft","pmids":["26450788"],"confidence":"High","gaps":["Phosphorylation sites mediating UTX/p300 recruitment not mapped","Whether catalytic-independent activation is a general or context-specific mechanism unknown"]},{"year":2017,"claim":"Discovering non-canonical K33-linked ubiquitination of a non-histone substrate: RNF2 was found to catalyze K33-linked polyubiquitination of STAT1 at K379 after interferon stimulation, promoting STAT1/STAT2 dissociation from DNA and suppressing innate antiviral responses, establishing a direct role for RNF2 in innate immune regulation through a non-degradative, non-histone ubiquitin linkage.","evidence":"Screen of 115 RING E3 ligases; RNF2 KO; in vitro ubiquitination with K33 linkage identification; ChIP-seq for STAT1","pmids":["29242538"],"confidence":"High","gaps":["Whether K33-linked ubiquitination requires a specific E2 partner distinct from canonical H2A ubiquitination unknown","Physiological significance in viral infection models in vivo not fully established"]},{"year":2018,"claim":"Suppressing transcription-replication conflicts at fragile sites: BMI1/RNF2 depletion increased RNA Pol II–replisome collisions and R-loop markers at common fragile sites, with genetic epistasis showing cooperation with FANCD2/FANCI, positioning PRC1 as a guardian of genome stability at replication-transcription interfaces.","evidence":"DNA fiber assay; proximity ligation assay for RNAPII–replisome; ChIP for FANCD2/RNH1; CRISPR KO; double depletion epistasis","pmids":["32142505"],"confidence":"High","gaps":["Whether Ring1B's E3 activity or chromatin compaction function mediates TRC suppression unknown","Direct ubiquitination targets at fragile sites not identified"]},{"year":2020,"claim":"Co-option at active enhancers by an oncogenic transcription factor: In Ewing sarcoma, RING1B co-localized with EWSR1-FLI1 at active enhancers rather than repressed Polycomb targets, and was required for EWSR1-FLI1 enhancer recruitment and oncogenic gene expression, revealing context-dependent repurposing of PRC1 machinery for transcriptional activation.","evidence":"ChIP-seq co-localization; siRNA KD with xenograft; AURKB pharmacological perturbation","pmids":["33097530"],"confidence":"Medium","gaps":["Mechanism by which RING1B facilitates EWSR1-FLI1 enhancer binding unknown","Whether H2AK119ub is deposited or absent at these active enhancers not resolved"]},{"year":2021,"claim":"Broadening the non-histone substrate repertoire: RNF2 was shown to ubiquitinate and degrade IRF4 in colon cancer, SIK1 in hepatocellular carcinoma, and RASSF10 in gastric cancer, establishing a pattern of RNF2 functioning as a conventional degradative E3 ligase for non-histone substrates in oncogenic contexts.","evidence":"Co-IP and ubiquitination assays for each substrate; epistasis rescue experiments; xenograft models","pmids":["34670117","27911266","34224728"],"confidence":"Medium","gaps":["Whether non-histone ubiquitination occurs within or outside PRC1 complexes unknown","Chain linkage types for these substrates not determined","Independent replication across labs lacking for individual substrates"]},{"year":null,"claim":"Key unresolved questions include: how variant PRC1 complexes partition between canonical repressive and non-canonical activating functions genome-wide; the structural basis by which different PCGF subunits alter Ring1B substrate specificity; whether Ring1B's roles at replication forks and fragile sites require catalytic activity or chromatin compaction; and how post-translational modifications (phosphorylation, O-GlcNAcylation) coordinate Ring1B's diverse functions in different cellular contexts.","evidence":"","pmids":[],"confidence":"High","gaps":["No genome-wide comparison of Ring1B substrates across variant PRC1 complexes","Structural models of variant PRC1–nucleosome complexes lacking","In vivo separation of catalytic vs. structural Ring1B functions at fragile sites not achieved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,5,17,19,21,24,31,32,35,36]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,4,17,31]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[0,24]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[19]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[8,27]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,9,31]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[1,11,24,29]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[7,11,29]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,3,4,21,24,29]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,7,12,27,31]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,14,26,40,41]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,17,31,32,35,36]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[2,26,29]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[33,43]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[27,34,42]}],"complexes":["PRC1 (canonical, CBX-containing)","PRC1 (non-canonical, RYBP-containing)","BCOR complex","KDM2B/FBXL10-PRC1 complex"],"partners":["BMI1","RYBP","RING1","KDM2B","USP7","UBE3A","BCOR","PCGF1"],"other_free_text":[]},"mechanistic_narrative":"RNF2 (Ring1B/RING2) is the catalytic E3 ubiquitin ligase subunit of Polycomb Repressive Complex 1 (PRC1) and is essential for monoubiquitination of histone H2A at lysine 119, a modification central to Polycomb-mediated transcriptional silencing of developmental genes including Hox clusters and cell-cycle inhibitors such as Cdkn2a and Cdkn1a [PMID:15386022, PMID:12589020, PMID:19544461]. Crystal structures show that RNF2 forms a RING-RING heterodimer with BMI1 (or other PCGF subunits), which allosterically stimulates its ligase activity; the E3–E2–nucleosome co-crystal reveals that substrate specificity arises from simultaneous contacts of Ring1B, UbcH5c, and BMI1 with nucleosomal DNA and the histone acidic patch [PMID:16710298, PMID:25355358]. RNF2 stability is regulated by competing ubiquitin signals—activating self-ubiquitination via K6/K27 chains versus E6-AP-mediated K48-linked degradative ubiquitination, balanced by USP7 deubiquitination—and its genomic targeting is modulated by O-GlcNAcylation, MEK-dependent phosphorylation, and association with variant PRC1 complexes recruited by adaptors such as RYBP and KDM2B/FBXL10 [PMID:20351251, PMID:20800574, PMID:22325352, PMID:23395003, PMID:26100231]. Beyond canonical H2AK119ub-dependent gene silencing, RNF2 catalyzes K33-linked ubiquitination of STAT1 to suppress interferon signaling, ubiquitinates non-histone substrates including SIK1, IRF4, and RASSF10 for proteasomal degradation, suppresses transcription-replication conflicts at common fragile sites, and cooperates with oncogenic transcription factors at active enhancers [PMID:29242538, PMID:27911266, PMID:34670117, PMID:32142505, PMID:33097530]."},"prefetch_data":{"uniprot":{"accession":"Q99496","full_name":"E3 ubiquitin-protein ligase RING2","aliases":["Huntingtin-interacting protein 2-interacting protein 3","HIP2-interacting protein 3","Protein DinG","RING finger protein 1B","RING1b","RING finger protein 2","RING finger protein BAP-1","RING-type E3 ubiquitin transferase RING2"],"length_aa":336,"mass_kda":37.7,"function":"E3 ubiquitin-protein ligase that mediates monoubiquitination of 'Lys-119' of histone H2A (H2AK119Ub), thereby playing a central role in histone code and gene regulation (PubMed:15386022, PubMed:16359901, PubMed:21772249, PubMed:25355358, PubMed:25519132, PubMed:26151332, PubMed:33864376). H2AK119Ub gives a specific tag for epigenetic transcriptional repression and participates in X chromosome inactivation of female mammals. May be involved in the initiation of both imprinted and random X inactivation (By similarity). Essential component of a Polycomb group (PcG) multiprotein PRC1-like complex, a complex class required to maintain the transcriptionally repressive state of many genes, including Hox genes, throughout development (PubMed:16359901, PubMed:26151332). PcG PRC1 complex acts via chromatin remodeling and modification of histones, rendering chromatin heritably changed in its expressibility (PubMed:26151332). E3 ubiquitin-protein ligase activity is enhanced by BMI1/PCGF4 (PubMed:21772249). Acts as the main E3 ubiquitin ligase on histone H2A of the PRC1 complex, while RING1 may rather act as a modulator of RNF2/RING2 activity (Probable). Association with the chromosomal DNA is cell-cycle dependent. In resting B- and T-lymphocytes, interaction with AURKB leads to block its activity, thereby maintaining transcription in resting lymphocytes (By similarity). Also acts as a negative regulator of autophagy by mediating ubiquitination of AMBRA1, leading to its subsequent degradation (By similarity)","subcellular_location":"Nucleus; Cytoplasm; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q99496/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RNF2","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RING1","stoichiometry":10.0},{"gene":"CSNK2B","stoichiometry":4.0},{"gene":"DYNC1I2","stoichiometry":4.0},{"gene":"H2AFZ","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"HMGA1","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2},{"gene":"PDCD6IP","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RNF2","total_profiled":1310},"omim":[{"mim_id":"619460","title":"LUO-SCHOCH-YAMAMOTO SYNDROME; LUSYAM","url":"https://www.omim.org/entry/619460"},{"mim_id":"618844","title":"L3MBTL HISTONE METHYL-LYSINE-BINDING PROTEIN 3; L3MBTL3","url":"https://www.omim.org/entry/618844"},{"mim_id":"617543","title":"POLYCOMB GROUP RING FINGER PROTEIN 3; PCGF3","url":"https://www.omim.org/entry/617543"},{"mim_id":"617438","title":"CHROMOBOX 6; CBX6","url":"https://www.omim.org/entry/617438"},{"mim_id":"617407","title":"POLYCOMB GROUP RING FINGER PROTEIN 5; PCGF5","url":"https://www.omim.org/entry/617407"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RNF2"},"hgnc":{"alias_symbol":["BAP-1","BAP1","DING","HIPI3","RING1B","RING2"],"prev_symbol":[]},"alphafold":{"accession":"Q99496","domains":[{"cath_id":"3.10.20.90","chopping":"224-330","consensus_level":"high","plddt":84.9423,"start":224,"end":330}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99496","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99496-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99496-F1-predicted_aligned_error_v6.png","plddt_mean":77.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RNF2","jax_strain_url":"https://www.jax.org/strain/search?query=RNF2"},"sequence":{"accession":"Q99496","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99496.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99496/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99496"}},"corpus_meta":[{"pmid":"30202049","id":"PMC_30202049","title":"BAP1 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replicated by Li et al. 2006 JBC\",\n      \"pmids\": [\"16710298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"2.5 Å crystal structure of Bmi1–Ring1B core domain complex showed Ring1B forms extensive RING domain contacts with Bmi1, and the N-terminal tail of Ring1B wraps around Bmi1; both interaction regions synergistically stimulate E3 ligase activity toward histone H2A; the complex stabilizes the E2 enzyme–nucleosomal substrate interaction for efficient ubiquitin transfer.\",\n      \"method\": \"X-ray crystallography (2.5 Å), domain mapping, in vitro ubiquitination assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — independent crystal structure and biochemical reconstitution corroborating EMBO J findings\",\n      \"pmids\": [\"16714294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Proteomics screen (biotinylation-tag pulldown + mass spectrometry) of RNF2 interactors in erythroid cells identified a novel Ring1B–Fbxl10 complex that also includes Bcl6 corepressor (BcoR), CK2alpha, Skp1, and Nspc1/Pcgf1, as well as histone demethylases LSD1/Aof2 and Fbxl10/Jhdm1B, extending known RNF2 protein complexes beyond PRC1 and E2F6.com-1.\",\n      \"method\": \"In vivo biotinylation tag pulldown, mass spectrometry interactome\",\n      \"journal\": \"Molecular & cellular proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS interactome with single-step purification; single lab, multiple complex members identified\",\n      \"pmids\": [\"17296600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ring1B (RNF2) is essential for maintaining levels of multiple PcG proteins in mouse ES cells (deletion causes loss of other PcG proteins) and is the primary E3 ligase responsible for chromosome-wide H2AK119ub1 upon Xist expression; however, Ring1B is not required for the initiation of Xist-mediated silencing, revealing a dissociation between H2A ubiquitination and X-inactivation initiation.\",\n      \"method\": \"Conditional knockout mouse ES cells, ChIP, gene expression analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple orthogonal readouts, defines pathway position\",\n      \"pmids\": [\"17620408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Prohibitin (PHB) interacts directly with RNF2 via co-immunoprecipitation; the two proteins co-regulate E2F1 transcriptional activity via dual pathways: direct prohibitin-mediated repression and indirect p16-CDK4-Rb pathway; ChIP showed RNF2 is recruited to E2F1-responsive promoters together with prohibitin.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, luciferase reporter assay, siRNA knockdown\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — reciprocal co-IP with functional ChIP validation; single lab\",\n      \"pmids\": [\"17873902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ring1B (RNF2) is a direct substrate of caspase-3 and caspase-9; cleavage sites were mapped to Asp175 (caspase-3) and Asp208 (caspase-9); caspase cleavage causes redistribution of Ring1B from exclusive nuclear localization to throughout the cell and disrupts its transcriptional repression activity.\",\n      \"method\": \"In vitro caspase cleavage assay, site-directed mutagenesis, subcellular localization by imaging, transcriptional repression assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro cleavage with mutagenesis mapping cleavage sites plus in vivo localization consequence\",\n      \"pmids\": [\"17379327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In vivo, Polycomb proteins Ezh2 and Rnf2 are independently required for genomic contraction of imprinted clusters (Kcnq1 and Igf2r) and for paternal-specific imprinted silencing in early mouse embryos; Rnf2 contributes to formation of repressive nuclear compartments marked by PcG proteins and repressive histone modifications.\",\n      \"method\": \"Genetic knockout in mouse embryos, 3D-FISH, immunofluorescence, RNA FISH\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function with multiple orthogonal readouts; defined role in genomic imprinting\",\n      \"pmids\": [\"18848501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NMR analysis of the C-terminal region of RING1B (C-RING1B) shows conformational disorder when alone but undergoes conformational tightening upon binding the Polycomb (Pc) cbox domain; the interaction is 1:1 with Kd 9.2–180 nM; the full C-RING1B region is required for cbox binding, with intramolecular interactions within C-RING1B that are stabilized by cbox.\",\n      \"method\": \"NMR, analytical ultracentrifugation, surface plasmon resonance/binding kinetics\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural characterization with binding quantification\",\n      \"pmids\": [\"18616292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RNF2 interacts with PHB2; PHB2 and CP2c bind to the N- and C-terminals of RNF2 respectively; RNF2 represses CP2c-stimulated transcription in a PHB2 dose-dependent manner, with the RNF2(1–158) region sufficient for physical and functional cooperation with PHB2.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, luciferase reporter assay, deletion mutant mapping\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid plus co-IP and reporter assay; single lab\",\n      \"pmids\": [\"18629613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RNF2 is phosphorylated at multiple serine residues; p38 MAPK phosphorylates RNF2 at Ser41, and ERK1/2 (MEK1/2) mediates the majority of RNF2 phosphorylation events; RNF2 expressed in Sf9 cells undergoes co-translational Met1 excision coupled to N-acetylation of Ser2 and phosphorylation of Ser41; differential phosphorylation modulates expression of transcription factors and histone 2B acetylation.\",\n      \"method\": \"2D electrophoresis, western blot with phospho-specific antibodies, kinase inhibitors (SB203580, PD98059), mass spectrometry\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — mass spectrometry identification plus pharmacological inhibitor validation; single lab\",\n      \"pmids\": [\"19405034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Self-ubiquitination of Ring1B generates noncanonical K6/K27/K48-based mixed polyubiquitin chains that stimulate (not degrade) its E3 ligase activity; E6-AP ubiquitinates the same Ring1B lysines with canonical chains to target Ring1B for proteasomal degradation; inactivation of E6-AP increases Ring1B and H2AK119ub levels with consequent repression of HoxB9.\",\n      \"method\": \"In vitro ubiquitination assay, E6-AP knockout cells, western blot, gene expression analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro reconstitution, KO cells, and pathway epistasis; single lab with multiple methods\",\n      \"pmids\": [\"20351251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"USP7 deubiquitinates Ring1B both in vitro and in vivo; the interaction is mediated in part through the Ring1B RING domain; USP7 is found in a complex with other PcG proteins; USP7 does not discriminate between the activating and proteolysis-targeting ubiquitin chains on Ring1B and has an overall stabilizing effect.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination assay, western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro DUB assay plus in vivo co-IP; single lab\",\n      \"pmids\": [\"20800574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The Bmi1/Ring1b RING-RING heterodimer binds directly to duplex DNA through a basic surface patch unique to the Bmi1/Ring1b dimer (not present on individual subunits); mutation of residues on this surface abolishes H2A ubiquitination activity; computational modeling with the crystal structure of Bmi1/Ring1b–UbcH5c suggests Ring1b contacts both nucleosomal DNA and an acidic patch on histone H4 for H2A monoubiquitination.\",\n      \"method\": \"Crystal structure of Bmi1/Ring1b–UbcH5c complex, mutagenesis, in vitro H2A ubiquitination assay, computational modeling\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and functional validation\",\n      \"pmids\": [\"21772249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RNF2 knockdown significantly inhibits cell proliferation and induces apoptosis in cancer cells in a partially p53-dependent manner; RNF2 directly binds both p53 and MDM2, promotes MDM2-mediated p53 ubiquitination and degradation, and increases MDM2 half-life by inhibiting its ubiquitination; overexpression of RNF2 decreases p53 protein levels and p53 ubiquitination.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, in vitro ubiquitination assay, pulse-chase half-life assay, isogenic p53+/+ vs p53-/- cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding shown by co-IP, functional ubiquitination assay, and genetic epistasis with p53 KO cells\",\n      \"pmids\": [\"23318437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ring1B interacts directly with the transcriptional repressor Snail via the carboxyl zinc fingers of Snail; Ring1B and Ring1A are recruited to Snail target promoters, deposit H2AK119ub1, and mediate transcriptional repression and cell migration in pancreatic cancer; EZH2 is required for Snail-Ring1A/B recruitment to target promoters and forms distinct complexes with Snail from the Ring1B-containing complex.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, siRNA double knockdown (Ring1A/B), cell migration assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, ChIP, and functional epistasis with dual knockdown\",\n      \"pmids\": [\"24903147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RNF2-mediated monoubiquitination of H2AK119 at the LTBP2 promoter silences LTBP2 (a negative regulator of TGFβ signaling), driving RNF2-dependent invasive/metastatic behavior in melanoma; separately, RNF2-driven proliferation (via CCND2 upregulation) does not require its E3 catalytic activity but instead depends on MEK1-mediated phosphorylation of RNF2, which recruits activating histone modifiers UTX and p300 to poised promoters.\",\n      \"method\": \"Gain/loss-of-function in mouse and human systems, ChIP, catalytic-dead mutant, MEK1 phosphorylation assay, co-immunoprecipitation\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — multiple orthogonal methods including catalytic mutant, phosphorylation studies, and ChIP; mechanistic dissection of two distinct pathways\",\n      \"pmids\": [\"26450788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RING1B O-GlcNAcylation at residues T250/S251 and S278 regulates its chromatin target-gene selection in human embryonic stem cells; non-O-GlcNAcylated RING1B is enriched near cell cycle genes whereas O-GlcNAcylated RING1B is preferentially enriched near neuronal genes; T250/S251 O-GlcNAcylation decreases during differentiation, suggesting O-GlcNAc regulates PRC1 retargeting during differentiation.\",\n      \"method\": \"Point mutation, ChIP-sequencing, mass spectrometry identification of O-GlcNAc sites\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — PTM mapped by mass spectrometry and mutagenesis, ChIP-seq for functional consequence; single lab\",\n      \"pmids\": [\"26100231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RING1B and RING1A are required for H2AK119ub at pericentromeric regions; loss of RING1 proteins causes slow replication fork elongation and stalling specifically during mid S-phase (when pericentromeric heterochromatin replicates), accumulation of DNA double-strand breaks at chromocenters, and acute p21-dependent senescence; targeted monoubiquitination of pericentromeric heterochromatin via MBD1 fusion rescued altered replication.\",\n      \"method\": \"Conditional knockout, EdU incorporation, DNA fiber assay, immunofluorescence, rescue by targeted H2Aub\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean conditional KO with multiple replication readouts and functional rescue\",\n      \"pmids\": [\"26272920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nuclear RNF2 directly binds STAT1 after interferon stimulation and catalyzes K33-linked polyubiquitination of the STAT1 DNA-binding domain at K379, promoting dissociation of the STAT1/STAT2 complex from DNA and suppressing interferon-stimulated gene transcription; RNF2 deficiency substantially enhances ISG expression and antiviral responses.\",\n      \"method\": \"High-content E3 ligase screen, co-immunoprecipitation, ubiquitin linkage-specific antibodies, ChIP, RNF2 knockout cells\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding and K33-specific ubiquitination demonstrated with linkage-specific tools plus KO phenotype\",\n      \"pmids\": [\"29242538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RNF2 functions as an E3 ligase that directly interacts with SIK1 and targets it for ubiquitination and proteasomal degradation in hepatocellular carcinoma cells; RNF2 expression is negatively correlated with SIK1 levels in HCC tissues.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, siRNA knockdown, xenograft model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — direct interaction co-IP plus ubiquitination assay; single lab\",\n      \"pmids\": [\"27911266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"BMI1 and RNF2 suppress transcription-replication conflicts (TRCs) at common fragile sites (CFSs); depletion of BMI1 or RNF2 causes slower replication forks, elevated fork stalling, increased RNA Pol II occupancy at CFSs, and increased associations between RNAPII and nascent replication forks (as shown by proximity ligation assays), indicating increased TRC incidences; FANCD2 and RNH1 accumulate at CFSs in RNF2 KO cells consistent with increased R-loop-associated replication stress.\",\n      \"method\": \"CRISPR-KO, DNA fiber assay, ChIP, proximity ligation assay, FANCD2/FANCI genetic epistasis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR KO with multiple orthogonal methods and genetic epistasis; defines non-canonical role of RNF2\",\n      \"pmids\": [\"32142505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RING1B colocalizes with the EWSR1-FLI1 oncogenic fusion at active enhancers in Ewing sarcoma while retaining canonical repressive activity at Polycomb-regulated developmental genes; RING1B is necessary for EWSR1-FLI1 recruitment to target enhancers and expression of key oncogenic targets; RING1B knockdown impairs xenograft tumor growth and EWSR1-FLI1-regulated gene expression.\",\n      \"method\": \"ChIP-seq, knockdown/re-expression, xenograft tumor model, AURKB pharmacological inhibition\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq demonstrating colocalization, functional knockdown with tumor growth assay; defined non-canonical activating role\",\n      \"pmids\": [\"33097530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RNF2 functions as an E3 ligase that ubiquitinates IRF4 to promote its proteasomal degradation in colon cancer cells; RNF2 co-immunoprecipitates with IRF4 and promotes IRF4 ubiquitination; overexpression of RNF2 increases proliferation, migration, and invasion by suppressing IRF4.\",\n      \"method\": \"Co-immunoprecipitation, in vitro/in vivo ubiquitination assay, xenograft model\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP and ubiquitination assay; single lab\",\n      \"pmids\": [\"34670117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RASSF10 is a substrate for RNF2-mediated ubiquitination and degradation; NPM-dependent downregulation of RNF2 expression maintains stable RASSF10 levels required for mitotic arrest; RNF2 was identified as a negative regulator of RASSF10 through LC-MS/MS and biochemical approaches.\",\n      \"method\": \"LC-MS/MS, co-immunoprecipitation, in vitro ubiquitination assay, live cell imaging, siRNA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — MS substrate identification plus ubiquitination assay; single lab\",\n      \"pmids\": [\"34224728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ring1b forms distinct complexes with DEAD-box helicases (DDXs) or EMT transcription factors at the E-cadherin promoter in breast cancer cells; DDX-Ring1b complexes moderately inhibit E-cadherin (early hybrid EMT), while EMT TF-Ring1b complexes cooperate to further repress E-cadherin in mesenchymal-like cells via PRC1-dependent H2A ubiquitination.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, knockdown/overexpression, cell migration assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP and ChIP; single lab with functional consequence readout\",\n      \"pmids\": [\"33608512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MS147, a bifunctional degrader (PROTAC) using an EED binder linked to VHL ligand, degrades both BMI1 and RING1B via an EED-, VHL-, ubiquitination-, and time-dependent mechanism, reducing H2AK119ub; demonstrates that RING1B can be selectively depleted via its interacting partner EED within the PRC1 complex.\",\n      \"method\": \"PROTAC degrader, western blot, ubiquitination assay, cancer cell proliferation assay\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic validation of degradation pathway using multiple dependency conditions; single lab\",\n      \"pmids\": [\"36737841\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RNF2 (Ring1B) is the catalytic E3 ubiquitin ligase subunit of Polycomb Repressive Complex 1 (PRC1) that monoubiquitinates histone H2A at K119 (H2AK119ub1) through its RING domain in heterodimer with BMI1—which enhances but does not carry catalytic activity—using E2 enzymes including UbcH5a/b/c; RNF2 self-ubiquitination with noncanonical chains activates its ligase activity while E6-AP-mediated canonical ubiquitination targets it for degradation, a balance regulated by USP7 deubiquitination; RNF2 is phosphorylated by p38 MAPK and ERK and O-GlcNAcylated at T250/S251, modifications that alter chromatin targeting and downstream gene activation; beyond canonical transcriptional repression of developmental genes, RNF2 suppresses transcription-replication conflicts at common fragile sites, can act as a non-canonical transcriptional activator (e.g., via MEK1 phosphorylation-driven UTX/p300 recruitment), mediates K33-linked ubiquitination of STAT1-K379 to suppress interferon signaling, and acts as an E3 ligase for non-histone substrates including MDM2/p53, SIK1, IRF4, and RASSF10; caspase-3/9 cleavage at Asp175/Asp208 redistributes RNF2 from nucleus to cytoplasm and disrupts its repressive function during apoptosis.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from KEEP papers.\n\n**Classification notes:**\n- Papers about BAP1 (BRCA1-associated protein 1) = EXCLUDE (different gene, not RNF2/Ring1B)\n- Papers about Arabidopsis RING1A/RING1B = EXCLUDE (plant symbol collision)\n- Papers about RNF2/Ring1B/Ring2 (canonical mammalian/vertebrate PRC1 E3 ligase) = KEEP\n- Generic interactome/phosphoproteomics papers with no specific RNF2 mechanism = EXCLUDE\n- Paper [49] DING protein = EXCLUDE (alias collision - \"DING\" is an alias but describes unrelated protein)\n- Paper [50] Arabidopsis RING1A/RING1B = EXCLUDE (plant collision)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"RNF2 (Ring2/Ring1B) is the catalytic E3 ubiquitin ligase subunit of the hPRC1L complex that monoubiquitinates nucleosomal histone H2A at lysine 119; siRNA knockdown of Ring2 dramatically reduces global H2AK119ub levels in HeLa cells, and the complex co-localizes with ubiquitinated H2A at Polycomb response elements and the Ubx promoter in Drosophila.\",\n      \"method\": \"Biochemical purification of hPRC1L complex, in vitro ubiquitination assay, RNAi knockdown, chromatin immunoprecipitation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted E3 ligase activity in vitro plus ChIP validation in vivo, foundational study replicated widely\",\n      \"pmids\": [\"15386022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Ring1B (Rnf2) physically associates with other Polycomb group proteins (Rae28/Mph1, M33) and chromosomal DNA, and Ring1B hypomorphic mice display posterior homeotic transformations with mild Hox gene derepression; overexpression in chick embryos represses Hoxb9, establishing Ring1B as a Polycomb complex component regulating anterior-posterior axis specification.\",\n      \"method\": \"Co-immunoprecipitation, mouse hypomorphic knock-in, in ovo overexpression, in situ hybridization\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus genetic loss- and gain-of-function with phenotypic readout\",\n      \"pmids\": [\"12183370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Complete knockout of Rnf2 in mice causes gastrulation arrest and cell cycle inhibition; the early lethality is partially bypassed by genetic inactivation of the Cdkn2a (Ink4a/ARF) locus, implicating Polycomb-mediated repression of Cdkn2a as a key downstream effector of Ring1B during early development.\",\n      \"method\": \"Mouse knockout, genetic epistasis with Cdkn2a null allele, embryo phenotyping\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype plus genetic epistasis rescue\",\n      \"pmids\": [\"12589020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Bmi-1 and Ring1A are positive regulators of H2A ubiquitylation within the PRC1 complex; Bmi-1 knockout results in significant loss of H2AK119ub and upregulation of Hoxc13 without affecting EZH2-mediated H3K27me3, placing H2A ubiquitylation downstream of H3K27 methylation in Polycomb silencing.\",\n      \"method\": \"Knockout mouse cells, ChIP, in vitro ubiquitination assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro assay combined with KO genetic epistasis and ChIP, replicated across labs\",\n      \"pmids\": [\"16359901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structure of the Ring1B–Bmi1 RING-RING heterodimer was solved at 2.5 Å; Ring1B 'hugs' Bmi1 through RING-domain contacts and an N-terminal arm wrapping around Bmi1. Bmi1 enhances Ring1B E3 ligase activity toward H2A in vitro using E2s UbcH5a/b/c and UbcH6; catalytic activity resides in Ring1B, not Bmi1. Mutation of the E2/E3 interface in Ring1B abolishes activity.\",\n      \"method\": \"Crystal structure, in vitro ubiquitination reconstitution, active-site mutagenesis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus reconstituted enzymatic activity plus mutagenesis\",\n      \"pmids\": [\"16710298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A 2.5-Å structure of the Bmi-1–Ring1B core domain complex reveals that Ring1B 'hugs' Bmi1 through RING and N-terminal tail contacts; this dual interaction synergistically stimulates Ring1B E3 ligase activity; modeling suggests the complex stabilizes E2–nucleosome interactions for efficient H2A ubiquitin transfer.\",\n      \"method\": \"X-ray crystallography (2.5 Å), in vitro ubiquitination assay, deletion mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — independent crystal structure of same complex by second lab, with functional validation\",\n      \"pmids\": [\"16714294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Proteomics of in vivo biotinylated Ring1B/Rnf2 from erythroid cells identified ~50 interacting proteins, including previously unknown partners: histone demethylases LSD1/Aof2 and Fbxl10/Jhdm1B, casein kinase subunits, and the BCOR corepressor. A novel Ring1B–Fbxl10 complex also containing BcoR, CK2α, Skp1, and Nspc1/Pcgf1 was identified, extending Ring1B functions beyond canonical PRC1.\",\n      \"method\": \"In vivo biotinylation tagging, streptavidin affinity purification, mass spectrometry\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — high-throughput MS interactome, single lab but comprehensive approach\",\n      \"pmids\": [\"17296600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ring1B (Rnf2) deletion in mouse ES cells causes loss of several other PcG proteins (revealing a role in regulating PcG protein levels), derepression of lineage/developmental genes, and aberrant differentiation potential. Despite Ring1B being required for chromosome-wide H2AK119ub1 upon Xist expression, initiation of X-chromosome silencing by Xist is independent of Ring1B.\",\n      \"method\": \"Conditional knockout ES cells, gene expression profiling, western blot for PcG protein levels, Xist induction assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple orthogonal readouts including protein stability and X-inactivation\",\n      \"pmids\": [\"17620408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Prohibitin interacts with RNF2 via co-immunoprecipitation of endogenous proteins; the two proteins regulate E2F1 transcriptional activity via dual pathways (direct prohibitin-mediated and indirect p16-mediated); RNF2 and prohibitin are recruited together to E2F1-responsive promoters (by ChIP), and depletion of either increases p16 and decreases E2F1 activity.\",\n      \"method\": \"Co-immunoprecipitation (endogenous), ChIP, RNAi knockdown, luciferase reporter assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — reciprocal endogenous Co-IP plus ChIP plus functional reporter, single lab\",\n      \"pmids\": [\"17873902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ring1B is a direct substrate of caspases-3 and -9 both in vitro and in vivo; cleavage sites were mapped to Asp175 (caspase-3) and Asp208 (caspase-9); caspase cleavage redistributes Ring1B from exclusive nuclear localization throughout the entire cell and disrupts its transcriptional repression activity.\",\n      \"method\": \"In vitro caspase cleavage assay, site-directed mutagenesis of cleavage sites, subcellular localization by immunofluorescence, transcriptional repression assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of cleavage plus mutagenesis plus functional consequence (localization and transcription)\",\n      \"pmids\": [\"17379327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The C-terminal region of Ring1B (C-RING1B) binds the Polycomb cbox domain with 1:1 stoichiometry (Kd 9.2–180 nM depending on Pc orthologue); NMR reveals that C-RING1B is conformationally flexible alone but undergoes structural tightening upon cbox binding, with two conserved subdomains capable of intramolecular interaction that may allow Ring1B to recruit diverse PcG partners.\",\n      \"method\": \"NMR spectroscopy, analytical ultracentrifugation, binding affinity measurements\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural analysis with quantitative binding measurements\",\n      \"pmids\": [\"18616292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ring1B/Rnf2 is required in vivo for three-dimensional genomic contraction and imprinted silencing at the Kcnq1 and Igf2r imprinted clusters in mouse embryos; Rnf2 and Ezh2 act independently to establish the repressive nuclear compartment associated with the paternal allele.\",\n      \"method\": \"Mouse embryo in vivo knockout, 3D-FISH for genomic contraction, allele-specific expression analysis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with quantitative 3D genomic and expression readouts, epistasis with Ezh2\",\n      \"pmids\": [\"18848501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ring1B ablation in mouse ES cells results in aberrant expression of key developmental genes (derepression), including TGFβ signaling and cell cycle genes, as well as downregulation of ES cell markers Sox2 and Rex-1; Ring1B-bound genes have bivalent histone marks (H3K4me3 + H3K27me3) or H3K4me3 alone at CpG-rich promoters.\",\n      \"method\": \"Conditional Ring1B knockout ES cells, genome-wide expression profiling, correlation with published ChIP-chip binding data\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with genome-wide expression analysis, single lab\",\n      \"pmids\": [\"18493325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RNF2 interacts with PHB2 (prohibitin 2), and the RNF2–PHB2 complex represses CP2c-stimulated transcription in a PHB2 dose-dependent manner; the N-terminal 158 residues of RNF2 are sufficient for physical association and functional cooperation with PHB2, while CP2c binds the C-terminus of RNF2.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, deletion mutagenesis, luciferase reporter assay\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Y2H plus Co-IP plus functional reporter, single lab\",\n      \"pmids\": [\"18629613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ring1B/Rnf2 is required for self-renewal and multipotential ability of embryonic neural stem cells (NSCs); Ring1B-deficient NSCs show impaired proliferation in vivo and in neurosphere assays, unscheduled neuronal differentiation under proliferating conditions (enhanced when Ring1A is also deleted), upregulation of neuronal transcription factors and Cdkn1a/p21, and decreased Notch signaling effectors.\",\n      \"method\": \"Conditional knockout in neural stem cells, neurosphere assay, single-cell differentiation, in vivo BrdU labeling, mRNA analysis\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple orthogonal in vivo and in vitro readouts\",\n      \"pmids\": [\"19544461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RNF2 is phosphorylated at multiple serine residues; p38 MAPK inhibitor SB203580 blocks phosphorylation at Ser41 (a predicted p38 site confirmed by mass spectrometry in Sf9 cells), while MEK1/2 inhibitor PD98059 blocks the majority of RNF2 phosphorylation events; RNF2 phosphorylation differentially modulates transcription factor expression and histone H2B acetylation.\",\n      \"method\": \"2D gel electrophoresis, phospho-specific western blot, kinase inhibitors, mass spectrometry identification of phosphorylation sites\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS site identification plus pharmacological inhibitor validation, single lab\",\n      \"pmids\": [\"19405034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Bmi1 and Ring1B are expressed in pancreatic exocrine precursor cells and ductal/islet cells in adult pancreas; Ring1B expression is specifically and persistently upregulated only in high-grade PanINs and pancreatic ductal adenocarcinoma (distinct from Bmi1's earlier induction), and Bmi1 knockdown in acinar tumor cells alters expression of digestive enzymes, implicating PRC1 proteins in pancreatic disease progression.\",\n      \"method\": \"Immunohistochemistry in mouse models and human tissue, conditional KRas knock-in model, shRNA knockdown in cell lines\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KD with functional readout plus in vivo mouse models, single lab\",\n      \"pmids\": [\"19585519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Ring1B self-ubiquitination generates K6-, K27-, and K48-based mixed polyubiquitin chains that stimulate (rather than degrade) its E3 ligase activity; E6-AP (UBE3A) ubiquitinates Ring1B on the same lysines to generate K48-linked chains targeting Ring1B for proteasomal degradation; inactivation of E6-AP in vivo elevates Ring1B and H2AK119ub levels and represses HoxB9 in cerebellar Purkinje neurons, with implications for Angelman syndrome.\",\n      \"method\": \"In vitro ubiquitination assay, E6-AP knockout mice, western blot, HoxB9 expression analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of distinct ubiquitination modes plus in vivo KO validation\",\n      \"pmids\": [\"20351251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"USP7 deubiquitinates Ring1B directly and specifically in vitro and in vivo; USP7-Ring1B interaction is mediated in part through Ring1B's RING domain; USP7 is found in a complex with other Polycomb proteins and has a stabilizing effect on Ring1B without discriminating between activating and proteolysis-targeting ubiquitin chains.\",\n      \"method\": \"In vitro deubiquitination assay, co-immunoprecipitation, RING domain interaction mapping\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro DUB assay plus Co-IP interaction mapping, single lab\",\n      \"pmids\": [\"20800574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of Bmi1/Ring1b RING-RING heterodimer in complex with E2 enzyme UbcH5c shows UbcH5c interacts exclusively with Ring1b; the Bmi1/Ring1b dimer binds duplex DNA through a basic surface patch unique to the heterodimer; mutation of DNA-binding residues abolishes H2A ubiquitination; computational modeling places the complex interacting with nucleosomal DNA and an acidic patch on histone H4 for substrate specificity.\",\n      \"method\": \"Crystal structure of E3-E2 complex, mutagenesis of DNA-binding surface, in vitro H2A ubiquitination assay, computational nucleosome docking\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of E3-E2 complex with mutagenesis validation of functional surfaces\",\n      \"pmids\": [\"21772249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mathematical modeling of the Ring1B/Bmi1 ubiquitination system using biochemical data demonstrates that Ring1B can exhibit bistable switches, oscillations, and excitable (overshoot) transitions between distinct ubiquitination states (self-ubiquitinated active vs. E6-AP-ubiquitinated degradation-targeted); these dynamics can produce all-or-none H2A monoubiquitination rates and discrete periods of gene activity/inactivity controlled by abundances of Bmi1, Ring1B, E6-AP, and USP7.\",\n      \"method\": \"Computational/mathematical modeling constrained by biochemical data\",\n      \"journal\": \"PLoS computational biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational modeling, though constrained by prior biochemical data\",\n      \"pmids\": [\"22194680\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Six major PRC1 complexes each contain a distinct PCGF subunit with RING1A/B; RYBP (or YAF2) stimulates Ring1B H2AK119ub1 activity and defines non-canonical PRC1 complexes that exclude CBX/PHC/SCM; RYBP-containing and CBX-containing PRC1 complexes both compact chromatin but only RYBP stimulates Ring1B catalytic activity; RYBP knockdown in ES cells compromises embryoid body formation and H2AK119ub1 levels.\",\n      \"method\": \"Comprehensive proteomics, genome-wide ChIP-seq, in vitro ubiquitination assay with RYBP stimulation, ES cell differentiation assay, knockdown\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — proteomic complex definition + in vitro activity assay + genomic profiling + functional KD, multiple orthogonal methods\",\n      \"pmids\": [\"22325352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RNF2 knockdown in cancer cells (HCT116) significantly inhibits cell proliferation, colony formation, and induces apoptosis in a partially p53-dependent manner; RNF2 directly binds both p53 and MDM2, promotes MDM2-mediated p53 ubiquitination, and increases MDM2 half-life by inhibiting its ubiquitination, thereby suppressing p53 protein levels during DNA damage response.\",\n      \"method\": \"RNAi knockdown, overexpression, p53 half-life and ubiquitination assays, co-immunoprecipitation, etoposide DNA damage model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct binding by Co-IP plus ubiquitination assays plus p53/MDM2 stability measurements, single lab\",\n      \"pmids\": [\"23318437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Fbxl10/Kdm2b recruits non-canonical PRC1 (containing Ring1B and Nspc1) to CpG islands genome-wide; Fbxl10 depletion causes major loss of Ring1B binding at target genes and loss of H2AK119ub1; Fbxl10's DNA binding capability and Ring1B integration are both required for ubiquitylation; Fbxl10-deficient ES cells cannot differentiate properly.\",\n      \"method\": \"Co-IP, genome-wide ChIP-seq, conditional KO ES cells, differentiation assay, in vitro ubiquitination with reconstituted complex\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genome-wide ChIP-seq plus functional KO plus reconstituted complex activity\",\n      \"pmids\": [\"23395003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structure of the human Ring1B–Bmi1–UbcH5c E3-E2 complex bound to the nucleosome core particle reveals that the PRC1 ubiquitylation module achieves substrate specificity by contacting multiple nucleosome surfaces spatially distinct from the catalytic site; UbcH5c directly contacts the nucleosome (unexpected role for E2 in substrate recognition); the structure provides the mechanism of nucleosome recognition by PRC1 and insight into BRCA1's related H2A ubiquitylation.\",\n      \"method\": \"X-ray crystallography of PRC1-nucleosome co-complex\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of complete E3-E2-nucleosome substrate complex, definitive mechanistic insight\",\n      \"pmids\": [\"25355358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In pancreatic ductal adenocarcinoma, Snail recruits Ring1B (and Ring1A) via its C-terminal zinc fingers to target promoters to repress gene expression and promote cell migration; Ring1B-mediated H2AK119ub1 is required for Snail-mediated transcriptional repression; EZH2 is required upstream for Snail-Ring1B recruitment; simultaneous depletion of Ring1A and Ring1B abolishes H2AK119ub1 at target promoters and compromises Snail-mediated cell migration.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, siRNA knockdown of Ring1A/B, cell migration assay, H2AK119ub1 ChIP\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus ChIP plus functional migration assay, epistasis with EZH2, single lab\",\n      \"pmids\": [\"24903147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ring1B is essential for expansion of hepatic stem/progenitor cells; conditional Ring1B knockout in mouse embryos inhibits hepatic stem/progenitor proliferation/differentiation and hepatic organogenesis via derepression of CDKIs Cdkn1a and Cdkn2a; clonal culture epistasis shows that simultaneous (not individual) suppression of Cdkn1a and Cdkn2a reverses the Ring1B-depletion cell cycle inhibition.\",\n      \"method\": \"Conditional mouse KO, clonal culture epistasis with Cdkn1a/Cdkn2a double knockdown, hepatic organogenesis phenotyping\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with genetic epistasis rescue experiment\",\n      \"pmids\": [\"24497168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RNF2 is oncogenic and prometastatic in melanoma via two distinct mechanisms: (1) RNF2-mediated H2AK119ub at the LTBP2 promoter silences this negative TGFβ regulator to drive invasion (requires catalytic activity); (2) RNF2 drives proliferation through direct transcriptional upregulation of CCND2 independently of catalytic activity. MEK1-mediated phosphorylation of RNF2 promotes recruitment of activating histone modifiers UTX and p300 to poised promoters to activate gene expression.\",\n      \"method\": \"Gain/loss-of-function studies in mouse and human melanoma cells, catalytic-dead mutant rescue, H2AK119ub ChIP, co-IP of UTX/p300 with phospho-RNF2, xenograft models\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary gain/loss-of-function experiments with mechanistic dissection via catalytic mutant and ChIP\",\n      \"pmids\": [\"26450788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RING1B O-GlcNAcylation at residues T250/S251 and S278 is identified in human ES cells; T250/S251 O-GlcNAcylation decreases during differentiation; ChIP-seq shows that non-O-GlcNAcylated RING1B is enriched near cell cycle genes, whereas O-GlcNAcylated RING1B preferentially targets neuronal genes, suggesting O-GlcNAc modification switches PRC1 genomic targeting during hESC differentiation.\",\n      \"method\": \"Point-mutation of O-GlcNAcylation sites, ChIP-seq, O-GlcNAc identification by mass spectrometry\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — site-specific mutagenesis plus ChIP-seq, single lab\",\n      \"pmids\": [\"26100231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RING1A and RING1B H2AK119ub activity at pericentromeric heterochromatin (PCH) is required for normal S-phase progression; loss of both RING1A and RING1B causes slow elongation and fork stalling preferentially at mid S-phase when PCH is replicated; acute senescence associated with RING1 loss is mediated by p21 (Cdkn1a) upregulation and can be uncoupled from DNA damage response; targeted monoubiquitylation of PCH via MBD1 rescues the replication defect.\",\n      \"method\": \"Conditional RING1A/B knockout, BrdU/EdU labeling, DNA fiber analysis, γH2AX immunostaining, chromocenter 3D-FISH, epistasis with p21 and targeted PCH ubiquitylation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with DNA fiber replication assay, epistasis rescue, multiple readouts\",\n      \"pmids\": [\"26272920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RNF2 knockdown in prostate cancer cells causes cell cycle arrest and apoptosis; tumor suppressor gene TXNIP is significantly upregulated upon RNF2 knockdown; ChIP shows RNF2 and H2AK119ub enrichment at the TXNIP promoter; simultaneous knockdown of RNF2 and TXNIP partially rescues the arrested cell cycle and apoptosis, placing TXNIP as a key downstream mediator of RNF2's oncogenic function in prostate cancer.\",\n      \"method\": \"RNAi knockdown, ChIP, double knockdown epistasis, xenograft, gene microarray\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ChIP plus genetic epistasis with TXNIP, single lab\",\n      \"pmids\": [\"28029659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nuclear RNF2 directly binds STAT1 after interferon stimulation and catalyzes K33-linked polyubiquitination of the STAT1 DNA-binding domain at K379, promoting STAT1/STAT2 dissociation from DNA and suppressing interferon-stimulated gene (ISG) transcription; RNF2 deficiency substantially enhances ISG expression and antiviral responses.\",\n      \"method\": \"High-content screening of 115 RING E3 ligases, RNF2 KO/KD, Co-IP of RNF2–STAT1, in vitro ubiquitination assay identifying K33-linked chains at K379, ChIP-seq for STAT1 DNA binding\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro ubiquitination reconstitution with chain-type and site identification, KO phenotype with ISG readout, Co-IP\",\n      \"pmids\": [\"29242538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RNF2 functions as an E3 ubiquitin ligase targeting SIK1 for proteasomal degradation in hepatocellular carcinoma; RNF2 directly physically interacts with SIK1; RNF2 expression is negatively correlated with SIK1 levels in HCC tissues; RNF2 knockdown reduces tumor growth and metastasis, which is rescued by simultaneous SIK1 knockdown.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, rescue epistasis, xenograft\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus ubiquitination assay plus epistasis rescue, single lab\",\n      \"pmids\": [\"27911266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ring1A and Ring1B (RNF2) function as suppressors of transcription-replication conflicts (TRCs) and common fragile site (CFS) instability; BMI1/RNF2-depleted cells show slower replication forks, elevated fork stalling, increased RNA Pol II occupancy at CFSs, and increased associations between RNAPII and nascent replication forks (measured by proximity ligation assay); RNF2-KO cells show increased FANCD2 and RNH1 at CFSs consistent with R-loop accumulation; FANCD2/FANCI depletion further increases genomic instability in RNF2-KO cells.\",\n      \"method\": \"DNA fiber assay, proximity ligation assay (PLA) for RNAPII-replisome associations, ChIP for FANCD2/RNH1, CRISPR KO, double depletion epistasis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (fiber assay, PLA, ChIP) with genetic epistasis, CRISPR KO\",\n      \"pmids\": [\"32142505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RING1B is highly expressed in Ewing sarcoma (EwS) and co-localizes with EWSR1-FLI1 at active enhancers while retaining repressive activity at canonical Polycomb developmental target genes; RING1B is required for EWSR1-FLI1 recruitment to enhancers and expression of key oncogenic targets; RING1B knockdown impairs xenograft tumor growth; pharmacological AURKB inhibition increases H2AK119ub and downregulates RING1B/EWSR1-FLI1 common targets.\",\n      \"method\": \"ChIP-seq, siRNA knockdown, xenograft tumor model, AURKB pharmacological inhibition, gene expression profiling\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq showing co-localization plus functional KD in xenograft, single lab\",\n      \"pmids\": [\"33097530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RNF2 (Ring1B) promotes colon cancer progression by acting as an E3 ubiquitin ligase that directly interacts with and ubiquitinates IRF4, targeting it for proteasomal degradation; RNF2 overexpression enhances proliferation, migration, and invasion via IRF4 degradation; RNF2 knockdown causes opposite effects rescued by IRF4 co-knockdown.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, overexpression, xenograft, rescue epistasis\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus ubiquitination assay plus epistasis, single lab\",\n      \"pmids\": [\"34670117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RASSF10 is a substrate for the E3 ubiquitin ligase RNF2; NPM-dependent downregulation of RNF2 is critical to maintain stable RASSF10 levels; RASSF10 promotes G2/M arrest via inhibition of Cdk1/cyclin-B and nuclear accumulation of GADD45a; this RASSF10/NPM/RNF2 cascade controls cell proliferation in gastric cancer.\",\n      \"method\": \"LC-MS/MS, live cell imaging, co-immunoprecipitation, ubiquitination assay, RNAi knockdown, cell cycle analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — MS-identified substrate with Co-IP and ubiquitination assay validation, pathway epistasis\",\n      \"pmids\": [\"34224728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ring1b forms distinct complexes with either DEAD-box helicases (DDXs) or EMT transcription factors (EMT TFs) at specific loci on the E-cadherin promoter; DDX-Ring1b complexes moderately repress E-cadherin inducing a hybrid EMT state, while EMT TF-Ring1b complexes cooperate with DDX complexes for full repression in mesenchymal-like breast cancer cells, driving metastasis.\",\n      \"method\": \"Co-immunoprecipitation of distinct complexes, ChIP at E-cadherin promoter, RNAi knockdown, metastasis assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP of distinct complexes plus ChIP at specific loci plus functional metastasis assay, single lab\",\n      \"pmids\": [\"33608512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RNF2 overexpression in mammary carcinoma promotes cell proliferation, colony formation, migration, and invasion through downregulation of E-cadherin protein, implicating RNF2-driven EMT as a mechanism of breast cancer progression.\",\n      \"method\": \"RNF2 overexpression and knockdown in cell lines, western blot for E-cadherin, cell migration and invasion assays\",\n      \"journal\": \"Pathology, research and practice\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD/OE with phenotype but limited mechanistic pathway placement beyond E-cadherin reduction\",\n      \"pmids\": [\"31300294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A PROTAC degrader (MS147) targeting both BMI1 and RING1B via their interaction with EED (a PRC2 component) degrades BMI1/RING1B in an EED-, VHL-, ubiquitination-, and time-dependent manner; MS147 selectively reduces H2AK119ub without affecting H3K27me3, confirming RING1B as the H2AK119ub catalytic subunit, and inhibits proliferation of cancer cells insensitive to PRC2 inhibitors.\",\n      \"method\": \"PROTAC degrader chemistry, EED-VHL bifunctional molecule, H2AK119ub and H3K27me3 western blot, cancer cell proliferation assay\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel chemical tool with mechanism-of-action validation, confirms RING1B's specific catalytic role\",\n      \"pmids\": [\"36737841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In zebrafish, ring1b mutants show a severe craniofacial phenotype with near-complete absence of cranial cartilage, bone, and musculature; cranial neural crest cells migrate correctly into pharyngeal arches but fail to differentiate into chondrocytes; other neural crest-derived lineages (glia, neurons, chromatophores) are formed normally, revealing a specific role for Ring1b in promoting chondrocyte differentiation from CNC cells.\",\n      \"method\": \"Zebrafish ring1b mutant analysis, cell lineage tracing, in situ hybridization\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO in vertebrate model with specific cell-lineage phenotypic readout\",\n      \"pmids\": [\"24040141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Zebrafish ring1b is essential for pectoral fin development; lateral plate mesoderm differentiation into fin precursors is initiated normally, but fin bud outgrowth is impaired due to insufficient Fgf signaling activation; exogenous FGF4 or hyperactivated Wnt signaling (apc mutant) partially restores the fin program, establishing that PcG-mediated Ring1b gene regulation is required for sustained Fgf signaling in vertebrate limb development.\",\n      \"method\": \"Zebrafish ring1b mutant, FGF4 rescue experiment, genetic interaction with apc mutant, in situ hybridization for Fgf targets\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with rescue experiment and genetic epistasis with Wnt/Fgf pathways\",\n      \"pmids\": [\"22619390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ring1A and Ring1B repress Glis2 expression in MOZ-TIF2 AML stem cells; deletion of Ring1A/B diminishes self-renewal and induces numerous genes including Glis2; Glis2 overexpression causes differentiation of AML cells while Glis2 knockdown in Ring1A/B-deficient AML cells inhibits differentiation, demonstrating that Ring1A/B maintain AML stem cells partly by repressing Glis2.\",\n      \"method\": \"Conditional Ring1A/B knockout in AML mouse model, gene expression profiling, Glis2 overexpression and knockdown rescue\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO plus genetic epistasis (Glis2 KD rescue) with defined AML stem cell phenotype\",\n      \"pmids\": [\"29371181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RNF2 knockdown enhances radiosensitivity of squamous cell lung carcinoma cells by inhibiting irradiation-induced γH2AX foci formation and impairing interactions among ATM, MDC1, and H2AX; RNF2 knockdown combined with irradiation causes G1 arrest, increased apoptosis, and upregulation of p16 and Bax with downregulation of cyclin D2, CDK4, and Bcl-2.\",\n      \"method\": \"shRNA knockdown, clonogenic survival, co-immunoprecipitation of ATM-MDC1-H2AX, γH2AX foci counting, flow cytometry, xenograft\",\n      \"journal\": \"Biochemistry and cell biology = Biochimie et biologie cellulaire\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP of DNA damage repair complex disruption plus functional radiosensitivity assay, single lab\",\n      \"pmids\": [\"30673298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The core of the human Polycomb repressive complex (hPRC-H) was purified from HeLa cells and contains homologues of Drosophila PRC1 core proteins including RING1/Ring1B, with fewer non-PcG components than dPRC1; hPRC-H retains the ability to block nucleosomal array remodeling similarly to dPRC1, demonstrating functional conservation of the Ring1B-containing PRC1 complex between flies and humans.\",\n      \"method\": \"Biochemical purification from HeLa cells, chromatin compaction/remodeling assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical purification plus in vitro functional chromatin compaction assay\",\n      \"pmids\": [\"12167701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A BCOR complex contains Polycomb proteins RING1, RYBP, NSPC1, a Posterior Sex Combs homolog, and RNF2 as E3 ligase for H2A mono-ubiquitylation, as well as SKP1 and FBXL10 (a histone H3K36 demethylase); BCOR complex components and mono-ubiquitylated H2A co-localize at BCL6 target genes by ChIP, establishing that BCL6 can recruit PcG proteins including RNF2 to specific genomic loci.\",\n      \"method\": \"Immunoprecipitation/mass spectrometry complex identification, ChIP at BCL6 target genes\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — MS-defined complex plus ChIP validation at specific loci\",\n      \"pmids\": [\"16943429\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RNF2 (Ring1B/Ring2) is the catalytic E3 ubiquitin ligase subunit of Polycomb Repressive Complex 1 (PRC1) that monoubiquitinates histone H2A at K119 (H2AK119ub1) using E2 enzymes UbcH5a/b/c or UbcH6; its activity is allosterically stimulated by dimerization with Bmi1 through their RING domains, with substrate specificity achieved by simultaneous contacts with nucleosomal DNA, the H4 acidic patch, and the E2 enzyme as revealed by crystal structures; Ring1B's stability and activity are regulated by self-ubiquitination (activating, non-canonical K6/K27 chains), E6-AP-mediated K48-linked ubiquitination (degradative), and USP7-mediated deubiquitination; beyond canonical H2A ubiquitination and Hox gene/developmental gene repression, RNF2 has non-canonical functions including K33-linked ubiquitination of STAT1 to suppress interferon signaling, direct E3 ligase activity toward non-histone substrates (SIK1, IRF4, RASSF10, p53/MDM2 axis), suppression of transcription-replication conflicts at common fragile sites, and recruitment to active enhancers by oncogenic transcription factors such as EWSR1-FLI1.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RNF2 (Ring1B) is the catalytic RING-domain E3 ubiquitin ligase of Polycomb Repressive Complex 1 (PRC1) that monoubiquitinates histone H2A at K119 to enforce transcriptional silencing of developmental genes, imprinted loci, and pericentromeric heterochromatin, while also functioning as a non-canonical transcriptional activator and an E3 ligase for non-histone substrates. Structural studies show that RNF2 heterodimerizes with BMI1 through extensive RING–RING contacts and an N-terminal wrapping arm; BMI1 stimulates but does not itself carry catalytic activity, and the heterodimer contacts nucleosomal DNA via a basic surface patch essential for H2A ubiquitination [PMID:16710298, PMID:21772249]. Beyond canonical H2AK119ub-mediated repression, RNF2 suppresses transcription–replication conflicts at common fragile sites [PMID:32142505], catalyzes K33-linked ubiquitination of STAT1 to limit interferon signaling [PMID:29242538], and targets non-histone substrates including MDM2/p53, SIK1, IRF4, and RASSF10 for proteasomal degradation [PMID:23318437, PMID:27911266, PMID:34670117, PMID:34224728]. RNF2 activity is tuned by self-ubiquitination with noncanonical K6/K27/K48 chains that stimulate its ligase function, counterbalanced by E6-AP-mediated canonical ubiquitination for degradation and USP7-mediated deubiquitination, as well as by phosphorylation (p38/ERK/MEK1) and O-GlcNAcylation that redirect chromatin targeting [PMID:20351251, PMID:19405034, PMID:26450788, PMID:26100231].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Determining which subunit of PRC1 carries catalytic E3 ligase activity was essential; two independent crystal structures of the Ring1B–Bmi1 RING heterodimer established that Ring1B is the catalytic subunit for H2A ubiquitination while Bmi1 serves as an allosteric activator.\",\n      \"evidence\": \"X-ray crystallography (2.5 Å) with in vitro E3 ligase assays and active-site mutagenesis in two independent studies\",\n      \"pmids\": [\"16710298\", \"16714294\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nucleosome-level structural basis of substrate recognition not yet resolved\", \"Relative contributions of E2 enzymes (UbcH5 family vs UbcH6) in vivo unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"RNF2 was shown to exist in multiple distinct complexes beyond canonical PRC1, to be essential for genome-wide H2AK119ub including on the inactive X chromosome, and to be subject to caspase cleavage that disrupts its nuclear localization during apoptosis—expanding its functional scope well beyond a single repressive complex.\",\n      \"evidence\": \"Biotinylation-tag interactomics (mass spectrometry), conditional KO ES cells with ChIP and RNA analysis, and in vitro caspase cleavage with mutagenesis\",\n      \"pmids\": [\"17296600\", \"17620408\", \"17379327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of Ring1B–Fbxl10 complex not established at this point\", \"Physiological relevance of caspase cleavage to PcG target gene derepression in vivo unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"RNF2's roles were extended to genomic imprinting (maintaining repressive chromatin at imprinted clusters) and its C-terminal region was structurally characterized as an intrinsically disordered domain that undergoes conformational tightening upon binding the Polycomb chromobox domain, explaining how PRC1 subunits are assembled.\",\n      \"evidence\": \"Genetic KO in mouse embryos with 3D-FISH/RNA-FISH; NMR and SPR binding analysis of C-RING1B–Pc cbox interaction\",\n      \"pmids\": [\"18848501\", \"18616292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Ring1B-Pc interaction is required for all PRC1 targeting or only at specific loci unknown\", \"Molecular mechanism of imprinted locus compaction by RNF2 unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The discovery that RNF2 self-ubiquitination with noncanonical K6/K27/K48 chains activates its ligase activity, while E6-AP-mediated canonical ubiquitination targets it for degradation, revealed a chain-type–dependent regulatory switch; USP7 was identified as a stabilizing deubiquitinase that does not distinguish between these chain types.\",\n      \"evidence\": \"In vitro reconstituted ubiquitination, E6-AP knockout cells, co-IP and in vitro DUB assays\",\n      \"pmids\": [\"20351251\", \"20800574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How chain-type specificity is determined in vivo remains unclear\", \"Whether USP7's inability to discriminate chain types has regulatory consequences at specific loci unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The crystal structure of the Bmi1/Ring1b–UbcH5c ternary complex revealed that the heterodimer contacts nucleosomal DNA via a basic surface patch unique to the dimer interface, and that mutation of this surface abolishes H2A ubiquitination, defining the structural basis for nucleosome recognition.\",\n      \"evidence\": \"Crystal structure with mutagenesis and in vitro H2A ubiquitination assay\",\n      \"pmids\": [\"21772249\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full cryo-EM structure of Ring1B–Bmi1 on an intact nucleosome not yet available at this time\", \"Contribution of the H2A acidic patch interaction to substrate specificity not fully tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"RNF2 was shown to function as an E3 ligase for non-histone substrates, directly binding MDM2 and p53 to stabilize MDM2 and promote p53 degradation, establishing a direct oncogenic mechanism independent of H2A ubiquitination.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitination, pulse-chase, isogenic p53+/+ vs p53−/− cell comparison\",\n      \"pmids\": [\"23318437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RNF2's E3 activity toward MDM2/p53 requires BMI1 or occurs as a monomer unclear\", \"Relative contribution of histone vs non-histone substrates to RNF2's pro-proliferative effect not delineated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Three studies collectively revealed that RNF2 operates through mechanistically distinct pathways: catalytic H2AK119ub-dependent silencing (e.g., LTBP2 for invasion), catalytic-activity-independent gene activation via MEK1-mediated phosphorylation recruiting UTX/p300, O-GlcNAcylation-directed chromatin retargeting, and H2AK119ub-dependent maintenance of pericentromeric replication integrity.\",\n      \"evidence\": \"Catalytic-dead mutant, MEK1 phosphorylation assay, ChIP-seq, O-GlcNAc mass spectrometry and mutagenesis, conditional KO with DNA fiber assays and targeted rescue\",\n      \"pmids\": [\"26450788\", \"26100231\", \"26272920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the MEK1 phosphorylation site(s) on RNF2 not mapped\", \"How O-GlcNAcylation mechanistically redirects RNF2 to neuronal vs cell-cycle gene targets unknown\", \"Whether pericentromeric replication defects are direct consequences of lost H2Aub or secondary effects unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"RNF2 was established as an E3 ligase for non-histone substrates STAT1 and SIK1: K33-linked ubiquitination of STAT1-K379 suppresses interferon signaling by dissociating STAT1/STAT2 from DNA, while ubiquitination of SIK1 promotes its proteasomal degradation in hepatocellular carcinoma.\",\n      \"evidence\": \"Ubiquitin linkage-specific antibodies and ChIP in RNF2 KO cells for STAT1; co-IP and ubiquitination assay for SIK1\",\n      \"pmids\": [\"29242538\", \"27911266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K33-linked ubiquitination of STAT1 depends on BMI1 not tested\", \"Structural basis for RNF2 recognition of non-histone substrates unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"RNF2 was found to suppress transcription-replication conflicts at common fragile sites and to colocalize with the EWSR1-FLI1 oncofusion at active enhancers in Ewing sarcoma, broadening its role beyond canonical repression to include replication-stress prevention and oncogene-dependent gene activation.\",\n      \"evidence\": \"CRISPR-KO with DNA fiber assays, proximity ligation assays, and ChIP-seq in Ewing sarcoma with knockdown/xenograft models\",\n      \"pmids\": [\"32142505\", \"33097530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether H2AK119ub deposition is required for TRC suppression or another RNF2 activity mediates this unclear\", \"Mechanism by which RING1B is recruited to EWSR1-FLI1 enhancers unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Additional non-histone substrates IRF4 and RASSF10 were identified as RNF2 ubiquitination targets for proteasomal degradation, and RNF2 was shown to participate in context-dependent complexes with DEAD-box helicases or EMT transcription factors to regulate E-cadherin in epithelial–mesenchymal transition.\",\n      \"evidence\": \"Co-IP and ubiquitination assays for IRF4 and RASSF10; ChIP and co-IP at the E-cadherin promoter\",\n      \"pmids\": [\"34670117\", \"34224728\", \"33608512\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for RNF2 recognition of diverse non-histone substrates remains unresolved\", \"Whether DDX–Ring1b complexes represent stable assemblies or transient interactions unclear\", \"Each non-histone substrate identified by a single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include how RNF2 discriminates among its diverse histone and non-histone substrates, the structural basis for nucleosome engagement by full-length PRC1, the precise phosphorylation sites mediating the catalytic-activity-independent activating function, and how post-translational modifications (O-GlcNAc, phosphorylation, ubiquitin chain type) are integrated to direct RNF2 to specific genomic loci in different cell states.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length PRC1–nucleosome structure available\", \"No systematic substrate-specificity analysis across cell types\", \"Integration of multiple PTMs on RNF2 function not studied in a unified system\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 10, 12, 13, 18, 19, 22, 23]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 1, 10, 12, 18]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3, 15, 21]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 1, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 5, 6, 18]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [6, 17]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 1, 3, 6, 12, 16, 17]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3, 14, 15, 18, 21]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 6, 16]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [17, 20]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [10, 11, 13, 19, 22, 23]}\n    ],\n    \"complexes\": [\n      \"PRC1\",\n      \"Ring1B-Fbxl10/BcoR complex\",\n      \"E2F6.com-1\"\n    ],\n    \"partners\": [\n      \"BMI1\",\n      \"USP7\",\n      \"SNAI1\",\n      \"STAT1\",\n      \"MDM2\",\n      \"PHB\",\n      \"PHB2\",\n      \"PCGF1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"RNF2 (Ring1B/RING2) is the catalytic E3 ubiquitin ligase subunit of Polycomb Repressive Complex 1 (PRC1) and is essential for monoubiquitination of histone H2A at lysine 119, a modification central to Polycomb-mediated transcriptional silencing of developmental genes including Hox clusters and cell-cycle inhibitors such as Cdkn2a and Cdkn1a [PMID:15386022, PMID:12589020, PMID:19544461]. Crystal structures show that RNF2 forms a RING-RING heterodimer with BMI1 (or other PCGF subunits), which allosterically stimulates its ligase activity; the E3–E2–nucleosome co-crystal reveals that substrate specificity arises from simultaneous contacts of Ring1B, UbcH5c, and BMI1 with nucleosomal DNA and the histone acidic patch [PMID:16710298, PMID:25355358]. RNF2 stability is regulated by competing ubiquitin signals—activating self-ubiquitination via K6/K27 chains versus E6-AP-mediated K48-linked degradative ubiquitination, balanced by USP7 deubiquitination—and its genomic targeting is modulated by O-GlcNAcylation, MEK-dependent phosphorylation, and association with variant PRC1 complexes recruited by adaptors such as RYBP and KDM2B/FBXL10 [PMID:20351251, PMID:20800574, PMID:22325352, PMID:23395003, PMID:26100231]. Beyond canonical H2AK119ub-dependent gene silencing, RNF2 catalyzes K33-linked ubiquitination of STAT1 to suppress interferon signaling, ubiquitinates non-histone substrates including SIK1, IRF4, and RASSF10 for proteasomal degradation, suppresses transcription-replication conflicts at common fragile sites, and cooperates with oncogenic transcription factors at active enhancers [PMID:29242538, PMID:27911266, PMID:34670117, PMID:32142505, PMID:33097530].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing RNF2 as a core Polycomb complex subunit: Ring1B was identified as a component of human PRC1 that blocks chromatin remodeling and physically associates with other PcG proteins; hypomorphic mice displayed homeotic transformations with Hox gene derepression, placing Ring1B within the Polycomb gene-silencing paradigm.\",\n      \"evidence\": \"Biochemical purification of hPRC-H from HeLa cells with chromatin compaction assay; mouse hypomorphic knock-in with phenotyping and co-IP\",\n      \"pmids\": [\"12167701\", \"12183370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic activity of Ring1B not yet identified\", \"Direct target genes beyond Hox clusters unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating Ring1B is essential for early development: Complete Rnf2 knockout caused gastrulation arrest that was partially rescued by Cdkn2a deletion, establishing that a key downstream effector of Ring1B-dependent Polycomb silencing is repression of the Ink4a/ARF cell-cycle inhibitor locus.\",\n      \"evidence\": \"Mouse knockout with genetic epistasis using Cdkn2a null allele\",\n      \"pmids\": [\"12589020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Enzymatic mechanism of Ring1B unknown\", \"Whether phenotype is cell-autonomous unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identifying the catalytic activity: Ring1B was shown to be the E3 ubiquitin ligase that monoubiquitinates histone H2A at K119, with siRNA knockdown dramatically reducing global H2AK119ub, solving the long-standing question of which enzyme deposits this abundant histone mark.\",\n      \"evidence\": \"In vitro ubiquitination assay with purified hPRC1L complex; RNAi in HeLa cells; ChIP at Polycomb targets\",\n      \"pmids\": [\"15386022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Ring1B-BMI1 cooperation unknown\", \"E2 enzyme specificity not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Solving the structural mechanism of allosteric activation: Two independent crystal structures of the Ring1B–BMI1 RING-RING heterodimer revealed that BMI1 stimulates Ring1B's ligase activity through a 'hugging' interaction; catalytic activity was mapped exclusively to Ring1B, with UbcH5a/b/c and UbcH6 identified as cognate E2 enzymes.\",\n      \"evidence\": \"X-ray crystallography at 2.5 Å by two independent groups; in vitro ubiquitination with mutagenesis\",\n      \"pmids\": [\"16710298\", \"16714294\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the complex recognizes the nucleosome substrate unknown\", \"Role of non-RING regions of Ring1B uncharacterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Expanding the PRC1 landscape: A BCOR corepressor complex containing RNF2, RING1, RYBP, NSPC1, SKP1, and FBXL10 was identified, demonstrating that Ring1B participates in non-canonical PRC1 assemblies recruited by transcription factors like BCL6.\",\n      \"evidence\": \"Immunoprecipitation/mass spectrometry complex identification; ChIP at BCL6 target genes\",\n      \"pmids\": [\"16943429\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional distinction between BCOR-PRC1 and canonical PRC1 unclear\", \"Whether FBXL10 demethylase activity is coordinated with Ring1B ubiquitination unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defining Ring1B's role in ES cell identity and PcG protein stability: Conditional Ring1B deletion in ES cells caused derepression of developmental genes and destabilization of other PcG proteins, revealing Ring1B as a structural hub of PRC1 integrity; Ring1B deposited H2AK119ub on the X chromosome but was dispensable for Xist-mediated silencing initiation.\",\n      \"evidence\": \"Conditional knockout ES cells with expression profiling, western blot for PcG stability, Xist induction assay\",\n      \"pmids\": [\"17620408\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Ring1B's stabilizing effect on other PcG proteins is direct or indirect unknown\", \"Genome-wide Ring1B binding sites not yet mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Structural flexibility enables diverse partner recruitment: NMR showed the Ring1B C-terminal domain is conformationally flexible but rigidifies upon binding Polycomb cbox domains with nanomolar affinity, providing a mechanism for Ring1B to serve as a versatile scaffold recruiting distinct CBX subunits to PRC1.\",\n      \"evidence\": \"NMR spectroscopy; analytical ultracentrifugation; quantitative binding measurements\",\n      \"pmids\": [\"18616292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How competing CBX proteins are selected for specific PRC1 assemblies unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealing dual ubiquitin-based regulation of Ring1B stability and activity: Self-ubiquitination via K6/K27 chains was shown to stimulate Ring1B activity, while E6-AP-mediated K48 chains targeted it for degradation; USP7 counteracted both chain types, establishing a tripartite regulatory circuit controlling Ring1B protein levels and catalytic output in vivo.\",\n      \"evidence\": \"In vitro ubiquitination reconstitution identifying chain types; E6-AP knockout mice with elevated Ring1B/H2AK119ub; in vitro DUB assay with USP7\",\n      \"pmids\": [\"20351251\", \"20800574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP7 discriminates between activating and degradative chains in vivo unresolved\", \"Upstream signals controlling the balance between self-ubiquitination and E6-AP activity unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defining variant PRC1 complexes and the RYBP stimulatory mechanism: Six distinct PRC1 complexes were catalogued, each with a unique PCGF subunit paired with RING1A/B; RYBP replaced CBX in non-canonical complexes and directly stimulated Ring1B catalytic activity; KDM2B/FBXL10 was shown to recruit non-canonical PRC1 to CpG islands genome-wide.\",\n      \"evidence\": \"Comprehensive proteomics; ChIP-seq; in vitro ubiquitination with RYBP; KDM2B conditional KO ES cells\",\n      \"pmids\": [\"22325352\", \"23395003\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How canonical and non-canonical PRC1 complexes partition genomic targets unresolved\", \"Whether RYBP stimulation changes chain linkage or only rate unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Achieving atomic-resolution understanding of nucleosome recognition: The crystal structure of Ring1B–BMI1–UbcH5c bound to the nucleosome core particle revealed that substrate specificity arises from contacts distributed across Ring1B, UbcH5c, and BMI1 with nucleosomal DNA and the H2A/H4 acidic patch, with an unexpected direct role for the E2 in substrate recognition.\",\n      \"evidence\": \"X-ray crystallography of the complete E3–E2–nucleosome complex\",\n      \"pmids\": [\"25355358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PRC1 transitions from chromatin compaction to ubiquitination mode unknown\", \"Structural basis of variant PRC1 nucleosome recognition not determined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Expanding Ring1B function to DNA replication: Loss of RING1A/B caused replication fork stalling specifically at pericentromeric heterochromatin during mid S-phase, with targeted monoubiquitylation rescuing the defect, demonstrating that H2AK119ub facilitates replication through constitutive heterochromatin independently of canonical gene silencing.\",\n      \"evidence\": \"Conditional RING1A/B KO; DNA fiber analysis; targeted PCH ubiquitylation rescue; p21 epistasis\",\n      \"pmids\": [\"26272920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which H2AK119ub facilitates fork passage through heterochromatin unknown\", \"Whether Ring1B is recruited to replication forks directly unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying catalytic-independent transcriptional activation: In melanoma, RNF2 was shown to drive CCND2 expression independently of its catalytic activity through MEK1-dependent phosphorylation that recruits UTX/p300, while simultaneously repressing LTBP2 via H2AK119ub, revealing bifunctional chromatin regulation by a single E3 ligase.\",\n      \"evidence\": \"Catalytic-dead mutant rescue; phospho-RNF2 co-IP with UTX/p300; ChIP; xenograft\",\n      \"pmids\": [\"26450788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation sites mediating UTX/p300 recruitment not mapped\", \"Whether catalytic-independent activation is a general or context-specific mechanism unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovering non-canonical K33-linked ubiquitination of a non-histone substrate: RNF2 was found to catalyze K33-linked polyubiquitination of STAT1 at K379 after interferon stimulation, promoting STAT1/STAT2 dissociation from DNA and suppressing innate antiviral responses, establishing a direct role for RNF2 in innate immune regulation through a non-degradative, non-histone ubiquitin linkage.\",\n      \"evidence\": \"Screen of 115 RING E3 ligases; RNF2 KO; in vitro ubiquitination with K33 linkage identification; ChIP-seq for STAT1\",\n      \"pmids\": [\"29242538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K33-linked ubiquitination requires a specific E2 partner distinct from canonical H2A ubiquitination unknown\", \"Physiological significance in viral infection models in vivo not fully established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Suppressing transcription-replication conflicts at fragile sites: BMI1/RNF2 depletion increased RNA Pol II–replisome collisions and R-loop markers at common fragile sites, with genetic epistasis showing cooperation with FANCD2/FANCI, positioning PRC1 as a guardian of genome stability at replication-transcription interfaces.\",\n      \"evidence\": \"DNA fiber assay; proximity ligation assay for RNAPII–replisome; ChIP for FANCD2/RNH1; CRISPR KO; double depletion epistasis\",\n      \"pmids\": [\"32142505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Ring1B's E3 activity or chromatin compaction function mediates TRC suppression unknown\", \"Direct ubiquitination targets at fragile sites not identified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Co-option at active enhancers by an oncogenic transcription factor: In Ewing sarcoma, RING1B co-localized with EWSR1-FLI1 at active enhancers rather than repressed Polycomb targets, and was required for EWSR1-FLI1 enhancer recruitment and oncogenic gene expression, revealing context-dependent repurposing of PRC1 machinery for transcriptional activation.\",\n      \"evidence\": \"ChIP-seq co-localization; siRNA KD with xenograft; AURKB pharmacological perturbation\",\n      \"pmids\": [\"33097530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which RING1B facilitates EWSR1-FLI1 enhancer binding unknown\", \"Whether H2AK119ub is deposited or absent at these active enhancers not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Broadening the non-histone substrate repertoire: RNF2 was shown to ubiquitinate and degrade IRF4 in colon cancer, SIK1 in hepatocellular carcinoma, and RASSF10 in gastric cancer, establishing a pattern of RNF2 functioning as a conventional degradative E3 ligase for non-histone substrates in oncogenic contexts.\",\n      \"evidence\": \"Co-IP and ubiquitination assays for each substrate; epistasis rescue experiments; xenograft models\",\n      \"pmids\": [\"34670117\", \"27911266\", \"34224728\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether non-histone ubiquitination occurs within or outside PRC1 complexes unknown\", \"Chain linkage types for these substrates not determined\", \"Independent replication across labs lacking for individual substrates\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how variant PRC1 complexes partition between canonical repressive and non-canonical activating functions genome-wide; the structural basis by which different PCGF subunits alter Ring1B substrate specificity; whether Ring1B's roles at replication forks and fragile sites require catalytic activity or chromatin compaction; and how post-translational modifications (phosphorylation, O-GlcNAcylation) coordinate Ring1B's diverse functions in different cellular contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No genome-wide comparison of Ring1B substrates across variant PRC1 complexes\", \"Structural models of variant PRC1–nucleosome complexes lacking\", \"In vivo separation of catalytic vs. structural Ring1B functions at fragile sites not achieved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 5, 17, 19, 21, 24, 31, 32, 35, 36]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 4, 17, 31]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 24]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 9, 31]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1, 11, 24, 29]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [7, 11, 29]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 3, 4, 21, 24, 29]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 7, 12, 27, 31]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 14, 26, 40, 41]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 17, 31, 32, 35, 36]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 26, 29]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [33, 43]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [27, 34, 42]}\n    ],\n    \"complexes\": [\n      \"PRC1 (canonical, CBX-containing)\",\n      \"PRC1 (non-canonical, RYBP-containing)\",\n      \"BCOR complex\",\n      \"KDM2B/FBXL10-PRC1 complex\"\n    ],\n    \"partners\": [\n      \"BMI1\",\n      \"RYBP\",\n      \"RING1\",\n      \"KDM2B\",\n      \"USP7\",\n      \"UBE3A\",\n      \"BCOR\",\n      \"PCGF1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}