{"gene":"RNF40","run_date":"2026-06-10T06:43:37","timeline":{"discoveries":[{"year":2002,"finding":"RNF40 (STARING) was identified as a novel RING finger E3 ubiquitin-protein ligase that binds syntaxin 1, recruits the E2 enzyme UbcH8, and facilitates ubiquitination and proteasome-dependent degradation of syntaxin 1.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, direct binding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding assays, E3 ligase activity demonstrated in cells, E2 recruitment shown; single lab but multiple orthogonal methods","pmids":["12121982"],"is_preprint":false},{"year":2000,"finding":"RNF40 (RBP95) directly binds the retinoblastoma protein (pRb) via an LXCXE motif; this interaction requires the LXCXE motif of RBP95 and the pocket domain of pRb. RBP95 also homodimerizes through a leucine zipper and localizes to the nucleus.","method":"In vitro binding assay, in vivo co-immunoprecipitation, point mutagenesis of LXCXE motif, GFP fusion nuclear localization imaging","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — reciprocal in vitro and in vivo binding with mutagenesis; single lab, single study","pmids":["10944455"],"is_preprint":false},{"year":2011,"finding":"RNF40 forms a heterodimeric E3 ubiquitin ligase complex with RNF20 that monoubiquitinates histone H2B at lysine 120 (H2B-K120ub1), facilitating histone H3K4 and H3K79 methylation and transcriptional regulation.","method":"Knockdown/depletion experiments, chromatin immunoprecipitation, Western blot for histone marks","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — activity demonstrated by multiple independent labs using complementary methods (knockdown, ChIP, histone mark analysis)","pmids":["22021426","22354749"],"is_preprint":false},{"year":2011,"finding":"The tumor suppressor CDC73 interacts with RNF20 and RNF40 at discrete residues and is required for maintenance of H2B-K120 monoubiquitination; loss of nuclear CDC73 significantly reduces H2Bub1 levels without affecting H3K4me3.","method":"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, Western blot for histone marks, analysis of CDC73 mutant parathyroid tumors","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid, co-IP, and functional knockdown with histone mark readout in a single rigorous study","pmids":["22021426"],"is_preprint":false},{"year":2011,"finding":"RNF40 depletion results in sustained H2AX phosphorylation, decreased H3K56 acetylation, and impaired recruitment of the FACT complex (specifically SUPT16H) to chromatin following DNA double-strand breaks (DSBs), leading to defects in DNA end resection and timely DNA repair.","method":"siRNA knockdown, immunofluorescence for γH2AX and H3K56ac, chromatin fractionation, flow cytometry for checkpoint activation","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple phenotypic readouts with mechanistic pathway placement (FACT recruitment), single lab","pmids":["22031019"],"is_preprint":false},{"year":2012,"finding":"Deficiency in Rnf20/Rnf40 (Bre1a/b) leads to replication-associated double-strand breaks arising from aberrant RNA-DNA structures (R-loops), chromosomal instability, and breakage-fusion-bridge cycles, establishing a role for the RNF20/RNF40 complex in genome stability maintenance.","method":"Bre1-deficient cell line generation, cytogenetic analysis, R-loop detection assay, DNA content analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with multiple mechanistic readouts (R-loops, DSBs, chromosomal rearrangements), single lab","pmids":["22354749"],"is_preprint":false},{"year":2014,"finding":"Arsenite directly binds to the RING finger domains of RNF20 and RNF40 via cysteine residues, inhibiting H2B ubiquitination in cells, impairing BRCA1 and RAD51 recruitment to DSB sites, and compromising DSB repair.","method":"In vitro binding assay, cellular H2B ubiquitination assay, immunofluorescence for BRCA1/RAD51 recruitment, comet assay for DSB repair","journal":"Journal of the American Chemical Society","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro direct binding plus cellular functional consequences; single lab, multiple orthogonal methods","pmids":["25170678"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of the RNF20 RING domain reveals it is a homodimer that specifically interacts with the Ube2B~Ub conjugate; the RING domains of RNF20 and RNF40 form a stable heterodimer with E3 ligase activity. Mutagenesis identified key contacts at the E3–E2 and E3–ubiquitin interfaces required for ubiquitin transfer.","method":"X-ray crystallography, mutagenesis, in vitro ubiquitin transfer assay","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with mutagenesis and in vitro functional assay; single lab but multiple orthogonal methods","pmids":["27569044"],"is_preprint":false},{"year":2019,"finding":"RNF20 and RNF40 are required for DSB repair via both homologous recombination and class switch recombination (NHEJ) in mouse B cells; DSBs trigger a global increase in H2Bub1 regulated jointly by ATM and ATR kinases, and H2AX phosphorylation is dispensable for H2Bub1 induction.","method":"Genetic knockout in B cells, class switch recombination assay, HR assay, Western blot for histone marks, inhibitor studies (ATM/ATR)","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with functional repair assays and epistasis with ATM/ATR; single lab","pmids":["30692271"],"is_preprint":false},{"year":2019,"finding":"Loss of RNF40 in colorectal cancer cells decreases nuclear localization of NF-κB following TNF-α treatment and reduces expression of NF-κB-associated cytokines; colon-specific Rnf40 deletion in mice reduces colitis burden.","method":"siRNA knockdown, NF-κB nuclear localization by immunofluorescence, cytokine mRNA measurement, in vivo conditional knockout mouse model of colitis","journal":"Journal of Crohn's & colitis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro mechanism (NF-κB localization) confirmed in vivo with conditional knockout; single lab","pmids":["30321325"],"is_preprint":false},{"year":2019,"finding":"RNF40 depletion in colorectal cancer cells induces apoptosis via elevated caspase 3/7 activity, associated with reduced anti-apoptotic and increased pro-apoptotic BCL2 family member expression; H2Bub1 directly occupies the transcribed regions of anti-apoptotic genes.","method":"siRNA knockdown, flow cytometry (Annexin V, propidium iodide), caspase 3/7 activity assay, mRNA-seq, ChIP for H2Bub1, caspase inhibitor rescue (Z-VAD-FMK)","journal":"Clinical epigenetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP, apoptosis assays, rescue experiment), single lab","pmids":["31266541"],"is_preprint":false},{"year":2020,"finding":"RNF40-driven H2B monoubiquitination is essential for transcriptional activation of RHO/ROCK/LIMK pathway components and proper actin-cytoskeleton dynamics in HER2+ breast cancer, acting through trans-histone crosstalk with H3K4 trimethylation.","method":"Tissue-specific Rnf40 knockout mouse model (mammary), cell culture RNF40 depletion, ChIP for histone marks, transcriptome analysis, actin cytoskeleton imaging","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo conditional KO plus mechanistic in vitro analysis with ChIP; single lab","pmids":["33070155"],"is_preprint":false},{"year":2020,"finding":"RNF40 is required for early reprogramming to iPSCs; loss of RNF40-mediated H2Bub1 impairs early gene activation, controls EZH2 expression, and promotes resolution of H3K4me3/H3K27me3 bivalency on pluripotency genes.","method":"siRNA knockdown during reprogramming, iPSC colony counting, mRNA-seq, ChIP for H3K4me3, H3K27me3, H2Bub1","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined cellular phenotype and ChIP mechanistic follow-up; single lab","pmids":["32341358"],"is_preprint":false},{"year":2020,"finding":"RNF40 has a stage-dependent function in osteoblasts: it is required for early lineage specification but dispensable in mature osteoblasts. RNF40 loss decreases osteoclast number/function by reducing RANKL (Tnfsf11) expression, which is a direct H2Bub1 target gene in osteoblasts.","method":"Osteoblast-specific conditional Rnf40 knockout mouse, micro-CT bone analysis, osteoclast function assays, ChIP for H2Bub1 on Tnfsf11 locus","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo conditional KO with mechanistic ChIP evidence; single lab","pmids":["32901120"],"is_preprint":false},{"year":2021,"finding":"RNF20 and RNF40 regulate Vitamin D Receptor (VDR) gene expression and VDR target genes in intestinal epithelial cells via H3K4me3 occupancy at the Vdr locus; intestinal-specific deletion of Rnf20 or Rnf40 causes spontaneous colorectal inflammation in mice.","method":"Conditional intestinal Rnf20/Rnf40 knockout mice, mRNA-seq, ChIP-seq for H3K4me3 and H2Bub1, IBD patient biopsy ChIP-seq","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo conditional KO with genome-wide ChIP-seq and patient validation; multiple orthogonal methods across model and human tissue","pmids":["34088983"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structures of the RNF20/RNF40-hRAD6A ubiquitin transfer complex on nucleosomal H2B were captured using chemical trapping; RNF40 directly binds nucleosomal DNA, revealing a conserved E3/E2/nucleosome interaction pattern. An unconventional non-hydrophobic E3 RING–E2 interface positions the E2 directly above the target lysine residue.","method":"Chemical trapping of transient ubiquitin transfer intermediate, cryo-electron microscopy structure determination, mutagenesis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure plus chemical trapping and mutagenesis; multiple orthogonal methods in a single rigorous study","pmids":["37633270"],"is_preprint":false},{"year":2023,"finding":"RNF40/H2Bub1 axis promotes cancer stem cell properties and drug tolerance in TNBC by supporting the glycolytic program and pro-tumorigenic YAP1 signaling.","method":"RNF40 depletion (siRNA/shRNA), transcriptome analysis, ChIP for H2Bub1, cancer stem cell functional assays, metabolic flux analysis","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — loss-of-function with mechanistic pathway placement (glycolysis, YAP1); single lab, single study","pmids":["37770435"],"is_preprint":false},{"year":2024,"finding":"RNF40 directly ubiquitinates LIMA1 protein via an interaction requiring the 1–166 aa fragment of LIMA1, promoting its proteasome-dependent degradation in the cytoplasm and thereby suppressing LIMA1-mediated lipid accumulation.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, domain deletion mapping, lipid content measurement, Western blot","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — co-IP with domain mapping, ubiquitination assay, functional lipid readout; single lab, single study","pmids":["38909032"],"is_preprint":false},{"year":2025,"finding":"RNF40 catalyzes K6- and K11-linked polyubiquitination of KDM6A, targeting it for autophagic degradation via TAX1BP1, thereby restricting coronavirus receptor expression and infection.","method":"Genetic knockdown/overexpression of RNF40, ubiquitin linkage-specific analysis, autophagic degradation assay, viral infection assay in primary human airway cells","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mechanistic ubiquitination characterization with linkage specificity and functional viral readout; single lab, single study","pmids":["41691482"],"is_preprint":false},{"year":2025,"finding":"RNF40 facilitates K48-linked polyubiquitination and proteasomal degradation of Parkin in cerebrovascular endothelial cells, thereby inhibiting mitophagy; Rnf40 knockdown in spontaneously hypertensive rats restores mitophagy and tight junction proteins, improving cerebrovascular barrier function.","method":"AAV-mediated Rnf40 knockdown in SHR rat model, ubiquitination assay (K48 linkage), mitophagy assay, tight junction protein Western blot, cerebral blood flow measurement","journal":"CNS neuroscience & therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo knockdown with mechanistic ubiquitination linkage data; single lab, single study","pmids":["39777866"],"is_preprint":false},{"year":2026,"finding":"Crystal structure of the RNF20/RNF40-WAC complex (modeled by AlphaFold with experimental validation) reveals extensive interfaces with WAC; these interactions are required for efficient RNF20/RNF40-catalyzed H2Bub1 in vitro and in vivo, with electrostatic interactions at the interface encoding binding specificity distinct from the yeast Bre1-Lge1 complex.","method":"Crystal structure (Bre1-Lge1), AlphaFold model (RNF20/RNF40-WAC), in vitro ubiquitination assay, in vivo functional assays, mutagenesis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural data combined with in vitro and in vivo mutagenesis and functional assays; single study but multiple orthogonal methods","pmids":["41533567"],"is_preprint":false},{"year":2026,"finding":"H2B S112 GlcNAcylation allosterically stimulates RNF20/RNF40-RAD6A-mediated H2B K120 monoubiquitination; cryo-EM of a chemically trapped complex shows GlcNAc interacts with the E2 enzyme RAD6A (not the E3 RNF40/RNF20), enhancing nucleophilicity of H2B K120 for ubiquitin transfer. The C2 N-acetyl group and β-configuration of C1 on the GlcNAc moiety are essential.","method":"Chemical synthesis of GlcNAc-modified nucleosomes, cryo-EM structure of trapped complex, mutagenesis, kinetic ubiquitination assay, structure-activity relationship analysis","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with chemical trapping, mutagenesis, and quantitative kinetics; single study with multiple rigorous orthogonal methods","pmids":["41495224"],"is_preprint":false},{"year":2025,"finding":"RNF20/RNF40 and H2Bub1 are dispensable for transcription restart after DNA damage; RNF20/RNF40, SET1/COMPASS, and DOT1L are not required for RNAPII elongation restoration following transcription-blocking lesions.","method":"Genetic depletion of RNF20/RNF40, SET1/COMPASS, DOT1L; transcription restart assay after DNA damage; ChIP for H2Bub1 and H3K4me3","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic loss-of-function with functional transcription restart assay; preprint, single lab, negative mechanistic finding","pmids":[],"is_preprint":true},{"year":2024,"finding":"RNF40 physically interacts with RTF1 and is required for H2B monoubiquitination-dependent Th17 cell differentiation; loss of RNF40 impairs Th17 differentiation while leaving regulatory T cells unaffected.","method":"Genetic knockdown/KO of RNF40 in T cells, Th17 differentiation assay, H2Bub1 ChIP, co-immunoprecipitation of RNF40-RTF1","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP, functional differentiation assay; preprint only","pmids":[],"is_preprint":true}],"current_model":"RNF40 is a RING-type E3 ubiquitin ligase that functions as an obligate heterodimer with RNF20; together they monoubiquitinate histone H2B at lysine 120 (H2Bub1) using the E2 enzyme RAD6A/UbcH8—a reaction whose structural mechanism is now defined by cryo-EM showing RNF40 binds nucleosomal DNA and positions the E2 above the target lysine—and this mark promotes downstream H3K4 and H3K79 methylation, transcriptional elongation, DNA double-strand break repair via HR and NHEJ, genome stability, NF-κB signaling, VDR-dependent intestinal homeostasis, and cell lineage decisions; independently, RNF40 targets non-histone substrates including syntaxin 1, LIMA1, Parkin, and KDM6A for ubiquitin-mediated degradation."},"narrative":{"mechanistic_narrative":"RNF40 is a RING-type E3 ubiquitin ligase that, as an obligate heterodimer with RNF20, monoubiquitinates histone H2B at lysine 120 (H2Bub1) to control chromatin state, transcription, genome stability, and cell-fate decisions [PMID:22021426, PMID:22354749, PMID:27569044]. Cryo-EM of a chemically trapped ubiquitin-transfer intermediate shows RNF40 directly engages nucleosomal DNA and, through an unconventional non-hydrophobic RING–E2 interface, positions the E2 enzyme RAD6A directly above H2B K120 [PMID:37633270]; this catalysis is allosterically stimulated by H2B S112 GlcNAcylation acting on the E2 to enhance K120 nucleophilicity [PMID:41495224], requires CDC73 for mark maintenance [PMID:22021426], and depends on extensive interfaces with the cofactor WAC [PMID:41533567]. H2Bub1 in turn promotes trans-histone H3K4 and H3K79 methylation and gene activation [PMID:22021426, PMID:22354749, PMID:33070155], and the complex maintains genome integrity by limiting R-loop-associated replication breaks and supporting double-strand break repair through both homologous recombination and class-switch/NHEJ pathways under ATM/ATR control [PMID:22354749, PMID:30692271]. Through these chromatin functions RNF40 governs diverse programs: VDR-dependent intestinal epithelial homeostasis whose loss drives spontaneous colorectal inflammation [PMID:34088983], NF-κB-driven cytokine expression in colitis [PMID:30321325], anti-apoptotic gene expression in colorectal cancer [PMID:31266541], iPSC reprogramming via resolution of H3K4me3/H3K27me3 bivalency [PMID:32341358], osteoblast lineage specification and RANKL expression [PMID:32901120], and pro-tumorigenic cytoskeletal and metabolic signaling in breast cancer [PMID:33070155, PMID:37770435]. Independently of histone modification, RNF40 ubiquitinates non-histone substrates for degradation—syntaxin 1 [PMID:12121982], LIMA1 to suppress lipid accumulation [PMID:38909032], Parkin via K48 linkages to inhibit mitophagy [PMID:39777866], and KDM6A via K6/K11 linkages for autophagic turnover that restricts coronavirus receptor expression [PMID:41691482].","teleology":[{"year":2000,"claim":"First defined RNF40 as a nuclear protein with a discrete protein-interaction architecture, establishing it as a candidate regulatory factor before its enzymatic identity was known.","evidence":"In vitro and in vivo binding with LXCXE mutagenesis showing pRb interaction, leucine-zipper homodimerization, and nuclear localization","pmids":["10944455"],"confidence":"Medium","gaps":["Functional consequence of the pRb interaction unresolved","Relationship of homodimerization to later RNF20 heterodimer not addressed"]},{"year":2002,"claim":"Established RNF40 as a bona fide RING E3 ubiquitin ligase that recruits an E2 and degrades a specific substrate, defining its core catalytic activity.","evidence":"Co-IP, ubiquitination assay, and proteasome-inhibitor experiments showing syntaxin 1 binding, UbcH8 recruitment, and degradation","pmids":["12121982"],"confidence":"High","gaps":["Did not connect activity to histone substrates","Physiological context of syntaxin 1 turnover not defined"]},{"year":2011,"claim":"Identified the central function of RNF40 as a heterodimeric H2B K120 monoubiquitin ligase coupled to downstream histone methylation, and showed CDC73 is required to maintain the mark.","evidence":"Knockdown, ChIP, yeast two-hybrid, and histone-mark Westerns in cells and parathyroid tumor analysis","pmids":["22021426","22354749"],"confidence":"High","gaps":["Genome-wide target spectrum not yet mapped","Mechanism coupling H2Bub1 to H3K4/H3K79 methylation not structurally defined"]},{"year":2011,"claim":"Placed RNF40 in the DNA double-strand break response, linking H2Bub1 to chromatin remodeling and end resection.","evidence":"siRNA knockdown with γH2AX/H3K56ac imaging, chromatin fractionation, and FACT (SUPT16H) recruitment analysis","pmids":["22031019"],"confidence":"Medium","gaps":["Direct ubiquitination targets at break sites not identified","Relative contribution to resection versus checkpoint signaling unclear"]},{"year":2012,"claim":"Extended the genome-stability role by showing the complex prevents R-loop-driven replication breaks and chromosomal instability.","evidence":"Bre1-deficient cells with cytogenetics, R-loop detection, and DNA content analysis","pmids":["22354749"],"confidence":"Medium","gaps":["Molecular basis of R-loop suppression not defined","Whether effect is direct or transcription-mediated unresolved"]},{"year":2014,"claim":"Demonstrated the RING cysteines are a functional vulnerability, with arsenite directly inhibiting H2Bub1 and DSB repair.","evidence":"In vitro binding, cellular H2B ubiquitination assay, BRCA1/RAD51 immunofluorescence, and comet assay","pmids":["25170678"],"confidence":"Medium","gaps":["In vivo relevance of arsenite inhibition not established","Selectivity over other RING E3s not addressed"]},{"year":2016,"claim":"Provided the first structural basis for catalysis, defining the RING heterodimer and its contacts with the E2~ubiquitin conjugate.","evidence":"X-ray crystallography of the RING domain with mutagenesis and in vitro ubiquitin-transfer assays","pmids":["27569044"],"confidence":"High","gaps":["Did not include the nucleosome substrate","Mechanism of lysine selection unresolved"]},{"year":2019,"claim":"Resolved the DSB repair pathway dependency and the upstream kinase control of damage-induced H2Bub1.","evidence":"B-cell knockouts with class-switch and HR assays plus ATM/ATR inhibitor epistasis","pmids":["30692271"],"confidence":"Medium","gaps":["How ATM/ATR signal to the complex mechanistically unknown","Direct phosphorylation targets not identified"]},{"year":2019,"claim":"Connected RNF40 to inflammatory and apoptotic transcriptional programs in the intestine and colorectal cancer.","evidence":"siRNA knockdown, NF-κB localization imaging, cytokine and mRNA-seq, H2Bub1 ChIP, apoptosis assays, and conditional colitis mouse models","pmids":["30321325","31266541"],"confidence":"Medium","gaps":["Direct versus indirect control of NF-κB nuclear import unclear","Cell-type specificity of pro-survival gene dependence not delineated"]},{"year":2020,"claim":"Established context-specific developmental and oncogenic roles for RNF40-dependent H2Bub1 across reprogramming, osteoblasts, and breast cancer.","evidence":"Conditional knockout mice and depletion with transcriptomics, ChIP for histone marks, and lineage/phenotype assays","pmids":["32341358","32901120","33070155"],"confidence":"Medium","gaps":["Determinants of stage-dependent dispensability unknown","Mechanism selecting specific target loci per cell type unresolved"]},{"year":2021,"claim":"Defined a physiological intestinal homeostasis circuit in which RNF40/RNF20 control VDR expression, validated in human IBD tissue.","evidence":"Intestinal conditional knockout mice with ChIP-seq for H3K4me3/H2Bub1, mRNA-seq, and IBD patient biopsy ChIP-seq","pmids":["34088983"],"confidence":"High","gaps":["Causal hierarchy between H3K4me3 and VDR transcription not fully resolved","Therapeutic implications untested"]},{"year":2023,"claim":"Delivered the mechanistic structure of catalysis on the nucleosome, showing RNF40 reads nucleosomal DNA and positions the E2 over the target lysine, and linked the activity to TNBC stemness and metabolism.","evidence":"Cryo-EM of chemically trapped transfer complex with mutagenesis, plus depletion with metabolic flux and stem-cell assays","pmids":["37633270","37770435"],"confidence":"High","gaps":["How nucleosome engagement is regulated in vivo unclear","Druggability of the interface not tested"]},{"year":2024,"claim":"Expanded the non-histone substrate repertoire, showing RNF40 degrades LIMA1 to suppress lipid accumulation.","evidence":"Co-IP, domain-mapping ubiquitination assay, proteasome inhibition, and lipid content measurement","pmids":["38909032"],"confidence":"Medium","gaps":["Physiological setting of LIMA1 regulation limited to single study","Relationship to nuclear H2Bub1 function unaddressed"]},{"year":2025,"claim":"Defined linkage-specific non-histone ubiquitination of Parkin and KDM6A, coupling RNF40 to mitophagy control and antiviral receptor regulation.","evidence":"In vivo knockdown (SHR rats, airway cells), K48/K6/K11 linkage analysis, mitophagy and autophagic degradation assays, and viral infection readouts","pmids":["39777866","41691482"],"confidence":"Medium","gaps":["Determinants of linkage-type selection unknown","Each substrate documented by a single study"]},{"year":2026,"claim":"Resolved cofactor and allosteric control of catalysis, identifying WAC as a binding partner required for efficient H2Bub1 and H2B S112 GlcNAcylation as an E2-directed stimulator.","evidence":"Crystal/AlphaFold structures with mutagenesis and in vitro/in vivo ubiquitination assays; cryo-EM of GlcNAc-modified nucleosome with kinetics and SAR","pmids":["41533567","41495224"],"confidence":"High","gaps":["In vivo regulation of H2B GlcNAcylation upstream of RNF40 unmapped","Interplay of WAC with CDC73 and RTF1 at chromatin not integrated"]},{"year":null,"claim":"It remains unresolved which contexts require H2Bub1 versus non-histone substrate ubiquitination, and how upstream signals route RNF40 between these activities and select specific genomic or protein targets.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of substrate selection between histone and non-histone targets","Transcription-restart studies (preprint) report H2Bub1 dispensable for RNAPII restart, contrasting elongation roles","Th17/RTF1 link rests on a single preprint Co-IP"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,2,7,17,18,19]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,15,17,18,19]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[15]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,2]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[2,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[17]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[2,15]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,11,12,14]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[4,5,8]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,17,19]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[18,19]}],"complexes":["RNF20/RNF40 H2B ubiquitin ligase heterodimer"],"partners":["RNF20","RAD6A","UBCH8","CDC73","WAC","RTF1","RB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75150","full_name":"E3 ubiquitin-protein ligase BRE1B","aliases":["95 kDa retinoblastoma-associated protein","RBP95","RING finger protein 40","RING-type E3 ubiquitin transferase BRE1B"],"length_aa":1001,"mass_kda":113.7,"function":"Component of the RNF20/40 E3 ubiquitin-protein ligase complex that mediates monoubiquitination of 'Lys-120' of histone H2B (H2BK120ub1). H2BK120ub1 gives a specific tag for epigenetic transcriptional activation and is also prerequisite for histone H3 'Lys-4' and 'Lys-79' methylation (H3K4me and H3K79me, respectively). It thereby plays a central role in histone code and gene regulation. The RNF20/40 complex forms a H2B ubiquitin ligase complex in cooperation with the E2 enzyme UBE2A or UBE2B; reports about the cooperation with UBE2E1/UBCH are contradictory. Required for transcriptional activation of Hox genes (Microbial infection) Promotes the human herpesvirus 8 (KSHV) lytic cycle by inducing the expression of lytic viral genes including the latency switch gene RTA/ORF50","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O75150/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RNF40","classification":"Common Essential","n_dependent_lines":668,"n_total_lines":1208,"dependency_fraction":0.5529801324503312},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000103549","cell_line_id":"CID001763","localizations":[{"compartment":"nucleoplasm","grade":3},{"compartment":"nuclear_punctae","grade":2}],"interactors":[{"gene":"WAC","stoichiometry":10.0},{"gene":"RNF20","stoichiometry":10.0},{"gene":"METTL3","stoichiometry":4.0},{"gene":"C9ORF16","stoichiometry":0.2},{"gene":"NOMO1","stoichiometry":0.2},{"gene":"PRPF19","stoichiometry":0.2},{"gene":"RBM12","stoichiometry":0.2},{"gene":"SNRNP200","stoichiometry":0.2},{"gene":"PLRG1","stoichiometry":0.2},{"gene":"HNRNPR","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001763","total_profiled":1310},"omim":[{"mim_id":"617233","title":"WD REPEAT-CONTAINING PROTEIN 70; WDR70","url":"https://www.omim.org/entry/617233"},{"mim_id":"614802","title":"MSL COMPLEX SUBUNIT 2; MSL2","url":"https://www.omim.org/entry/614802"},{"mim_id":"614801","title":"MSL COMPLEX SUBUNIT 1; MSL1","url":"https://www.omim.org/entry/614801"},{"mim_id":"610506","title":"PAF1 HOMOLOG, PAF1/RNA POLYMERASE II COMPLEX COMPONENT; PAF1","url":"https://www.omim.org/entry/610506"},{"mim_id":"607700","title":"RING FINGER PROTEIN 40; RNF40","url":"https://www.omim.org/entry/607700"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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direct binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding assays, E3 ligase activity demonstrated in cells, E2 recruitment shown; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"12121982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"RNF40 (RBP95) directly binds the retinoblastoma protein (pRb) via an LXCXE motif; this interaction requires the LXCXE motif of RBP95 and the pocket domain of pRb. RBP95 also homodimerizes through a leucine zipper and localizes to the nucleus.\",\n      \"method\": \"In vitro binding assay, in vivo co-immunoprecipitation, point mutagenesis of LXCXE motif, GFP fusion nuclear localization imaging\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — reciprocal in vitro and in vivo binding with mutagenesis; single lab, single study\",\n      \"pmids\": [\"10944455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"RNF40 forms a heterodimeric E3 ubiquitin ligase complex with RNF20 that monoubiquitinates histone H2B at lysine 120 (H2B-K120ub1), facilitating histone H3K4 and H3K79 methylation and transcriptional regulation.\",\n      \"method\": \"Knockdown/depletion experiments, chromatin immunoprecipitation, Western blot for histone marks\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — activity demonstrated by multiple independent labs using complementary methods (knockdown, ChIP, histone mark analysis)\",\n      \"pmids\": [\"22021426\", \"22354749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The tumor suppressor CDC73 interacts with RNF20 and RNF40 at discrete residues and is required for maintenance of H2B-K120 monoubiquitination; loss of nuclear CDC73 significantly reduces H2Bub1 levels without affecting H3K4me3.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, Western blot for histone marks, analysis of CDC73 mutant parathyroid tumors\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid, co-IP, and functional knockdown with histone mark readout in a single rigorous study\",\n      \"pmids\": [\"22021426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"RNF40 depletion results in sustained H2AX phosphorylation, decreased H3K56 acetylation, and impaired recruitment of the FACT complex (specifically SUPT16H) to chromatin following DNA double-strand breaks (DSBs), leading to defects in DNA end resection and timely DNA repair.\",\n      \"method\": \"siRNA knockdown, immunofluorescence for γH2AX and H3K56ac, chromatin fractionation, flow cytometry for checkpoint activation\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple phenotypic readouts with mechanistic pathway placement (FACT recruitment), single lab\",\n      \"pmids\": [\"22031019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Deficiency in Rnf20/Rnf40 (Bre1a/b) leads to replication-associated double-strand breaks arising from aberrant RNA-DNA structures (R-loops), chromosomal instability, and breakage-fusion-bridge cycles, establishing a role for the RNF20/RNF40 complex in genome stability maintenance.\",\n      \"method\": \"Bre1-deficient cell line generation, cytogenetic analysis, R-loop detection assay, DNA content analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with multiple mechanistic readouts (R-loops, DSBs, chromosomal rearrangements), single lab\",\n      \"pmids\": [\"22354749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Arsenite directly binds to the RING finger domains of RNF20 and RNF40 via cysteine residues, inhibiting H2B ubiquitination in cells, impairing BRCA1 and RAD51 recruitment to DSB sites, and compromising DSB repair.\",\n      \"method\": \"In vitro binding assay, cellular H2B ubiquitination assay, immunofluorescence for BRCA1/RAD51 recruitment, comet assay for DSB repair\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro direct binding plus cellular functional consequences; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"25170678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of the RNF20 RING domain reveals it is a homodimer that specifically interacts with the Ube2B~Ub conjugate; the RING domains of RNF20 and RNF40 form a stable heterodimer with E3 ligase activity. Mutagenesis identified key contacts at the E3–E2 and E3–ubiquitin interfaces required for ubiquitin transfer.\",\n      \"method\": \"X-ray crystallography, mutagenesis, in vitro ubiquitin transfer assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with mutagenesis and in vitro functional assay; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"27569044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RNF20 and RNF40 are required for DSB repair via both homologous recombination and class switch recombination (NHEJ) in mouse B cells; DSBs trigger a global increase in H2Bub1 regulated jointly by ATM and ATR kinases, and H2AX phosphorylation is dispensable for H2Bub1 induction.\",\n      \"method\": \"Genetic knockout in B cells, class switch recombination assay, HR assay, Western blot for histone marks, inhibitor studies (ATM/ATR)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with functional repair assays and epistasis with ATM/ATR; single lab\",\n      \"pmids\": [\"30692271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of RNF40 in colorectal cancer cells decreases nuclear localization of NF-κB following TNF-α treatment and reduces expression of NF-κB-associated cytokines; colon-specific Rnf40 deletion in mice reduces colitis burden.\",\n      \"method\": \"siRNA knockdown, NF-κB nuclear localization by immunofluorescence, cytokine mRNA measurement, in vivo conditional knockout mouse model of colitis\",\n      \"journal\": \"Journal of Crohn's & colitis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro mechanism (NF-κB localization) confirmed in vivo with conditional knockout; single lab\",\n      \"pmids\": [\"30321325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RNF40 depletion in colorectal cancer cells induces apoptosis via elevated caspase 3/7 activity, associated with reduced anti-apoptotic and increased pro-apoptotic BCL2 family member expression; H2Bub1 directly occupies the transcribed regions of anti-apoptotic genes.\",\n      \"method\": \"siRNA knockdown, flow cytometry (Annexin V, propidium iodide), caspase 3/7 activity assay, mRNA-seq, ChIP for H2Bub1, caspase inhibitor rescue (Z-VAD-FMK)\",\n      \"journal\": \"Clinical epigenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP, apoptosis assays, rescue experiment), single lab\",\n      \"pmids\": [\"31266541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RNF40-driven H2B monoubiquitination is essential for transcriptional activation of RHO/ROCK/LIMK pathway components and proper actin-cytoskeleton dynamics in HER2+ breast cancer, acting through trans-histone crosstalk with H3K4 trimethylation.\",\n      \"method\": \"Tissue-specific Rnf40 knockout mouse model (mammary), cell culture RNF40 depletion, ChIP for histone marks, transcriptome analysis, actin cytoskeleton imaging\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional KO plus mechanistic in vitro analysis with ChIP; single lab\",\n      \"pmids\": [\"33070155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RNF40 is required for early reprogramming to iPSCs; loss of RNF40-mediated H2Bub1 impairs early gene activation, controls EZH2 expression, and promotes resolution of H3K4me3/H3K27me3 bivalency on pluripotency genes.\",\n      \"method\": \"siRNA knockdown during reprogramming, iPSC colony counting, mRNA-seq, ChIP for H3K4me3, H3K27me3, H2Bub1\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined cellular phenotype and ChIP mechanistic follow-up; single lab\",\n      \"pmids\": [\"32341358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RNF40 has a stage-dependent function in osteoblasts: it is required for early lineage specification but dispensable in mature osteoblasts. RNF40 loss decreases osteoclast number/function by reducing RANKL (Tnfsf11) expression, which is a direct H2Bub1 target gene in osteoblasts.\",\n      \"method\": \"Osteoblast-specific conditional Rnf40 knockout mouse, micro-CT bone analysis, osteoclast function assays, ChIP for H2Bub1 on Tnfsf11 locus\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional KO with mechanistic ChIP evidence; single lab\",\n      \"pmids\": [\"32901120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RNF20 and RNF40 regulate Vitamin D Receptor (VDR) gene expression and VDR target genes in intestinal epithelial cells via H3K4me3 occupancy at the Vdr locus; intestinal-specific deletion of Rnf20 or Rnf40 causes spontaneous colorectal inflammation in mice.\",\n      \"method\": \"Conditional intestinal Rnf20/Rnf40 knockout mice, mRNA-seq, ChIP-seq for H3K4me3 and H2Bub1, IBD patient biopsy ChIP-seq\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo conditional KO with genome-wide ChIP-seq and patient validation; multiple orthogonal methods across model and human tissue\",\n      \"pmids\": [\"34088983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of the RNF20/RNF40-hRAD6A ubiquitin transfer complex on nucleosomal H2B were captured using chemical trapping; RNF40 directly binds nucleosomal DNA, revealing a conserved E3/E2/nucleosome interaction pattern. An unconventional non-hydrophobic E3 RING–E2 interface positions the E2 directly above the target lysine residue.\",\n      \"method\": \"Chemical trapping of transient ubiquitin transfer intermediate, cryo-electron microscopy structure determination, mutagenesis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure plus chemical trapping and mutagenesis; multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"37633270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RNF40/H2Bub1 axis promotes cancer stem cell properties and drug tolerance in TNBC by supporting the glycolytic program and pro-tumorigenic YAP1 signaling.\",\n      \"method\": \"RNF40 depletion (siRNA/shRNA), transcriptome analysis, ChIP for H2Bub1, cancer stem cell functional assays, metabolic flux analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — loss-of-function with mechanistic pathway placement (glycolysis, YAP1); single lab, single study\",\n      \"pmids\": [\"37770435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RNF40 directly ubiquitinates LIMA1 protein via an interaction requiring the 1–166 aa fragment of LIMA1, promoting its proteasome-dependent degradation in the cytoplasm and thereby suppressing LIMA1-mediated lipid accumulation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, domain deletion mapping, lipid content measurement, Western blot\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — co-IP with domain mapping, ubiquitination assay, functional lipid readout; single lab, single study\",\n      \"pmids\": [\"38909032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RNF40 catalyzes K6- and K11-linked polyubiquitination of KDM6A, targeting it for autophagic degradation via TAX1BP1, thereby restricting coronavirus receptor expression and infection.\",\n      \"method\": \"Genetic knockdown/overexpression of RNF40, ubiquitin linkage-specific analysis, autophagic degradation assay, viral infection assay in primary human airway cells\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mechanistic ubiquitination characterization with linkage specificity and functional viral readout; single lab, single study\",\n      \"pmids\": [\"41691482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RNF40 facilitates K48-linked polyubiquitination and proteasomal degradation of Parkin in cerebrovascular endothelial cells, thereby inhibiting mitophagy; Rnf40 knockdown in spontaneously hypertensive rats restores mitophagy and tight junction proteins, improving cerebrovascular barrier function.\",\n      \"method\": \"AAV-mediated Rnf40 knockdown in SHR rat model, ubiquitination assay (K48 linkage), mitophagy assay, tight junction protein Western blot, cerebral blood flow measurement\",\n      \"journal\": \"CNS neuroscience & therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo knockdown with mechanistic ubiquitination linkage data; single lab, single study\",\n      \"pmids\": [\"39777866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Crystal structure of the RNF20/RNF40-WAC complex (modeled by AlphaFold with experimental validation) reveals extensive interfaces with WAC; these interactions are required for efficient RNF20/RNF40-catalyzed H2Bub1 in vitro and in vivo, with electrostatic interactions at the interface encoding binding specificity distinct from the yeast Bre1-Lge1 complex.\",\n      \"method\": \"Crystal structure (Bre1-Lge1), AlphaFold model (RNF20/RNF40-WAC), in vitro ubiquitination assay, in vivo functional assays, mutagenesis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural data combined with in vitro and in vivo mutagenesis and functional assays; single study but multiple orthogonal methods\",\n      \"pmids\": [\"41533567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"H2B S112 GlcNAcylation allosterically stimulates RNF20/RNF40-RAD6A-mediated H2B K120 monoubiquitination; cryo-EM of a chemically trapped complex shows GlcNAc interacts with the E2 enzyme RAD6A (not the E3 RNF40/RNF20), enhancing nucleophilicity of H2B K120 for ubiquitin transfer. The C2 N-acetyl group and β-configuration of C1 on the GlcNAc moiety are essential.\",\n      \"method\": \"Chemical synthesis of GlcNAc-modified nucleosomes, cryo-EM structure of trapped complex, mutagenesis, kinetic ubiquitination assay, structure-activity relationship analysis\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with chemical trapping, mutagenesis, and quantitative kinetics; single study with multiple rigorous orthogonal methods\",\n      \"pmids\": [\"41495224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RNF20/RNF40 and H2Bub1 are dispensable for transcription restart after DNA damage; RNF20/RNF40, SET1/COMPASS, and DOT1L are not required for RNAPII elongation restoration following transcription-blocking lesions.\",\n      \"method\": \"Genetic depletion of RNF20/RNF40, SET1/COMPASS, DOT1L; transcription restart assay after DNA damage; ChIP for H2Bub1 and H3K4me3\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic loss-of-function with functional transcription restart assay; preprint, single lab, negative mechanistic finding\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RNF40 physically interacts with RTF1 and is required for H2B monoubiquitination-dependent Th17 cell differentiation; loss of RNF40 impairs Th17 differentiation while leaving regulatory T cells unaffected.\",\n      \"method\": \"Genetic knockdown/KO of RNF40 in T cells, Th17 differentiation assay, H2Bub1 ChIP, co-immunoprecipitation of RNF40-RTF1\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP, functional differentiation assay; preprint only\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"RNF40 is a RING-type E3 ubiquitin ligase that functions as an obligate heterodimer with RNF20; together they monoubiquitinate histone H2B at lysine 120 (H2Bub1) using the E2 enzyme RAD6A/UbcH8—a reaction whose structural mechanism is now defined by cryo-EM showing RNF40 binds nucleosomal DNA and positions the E2 above the target lysine—and this mark promotes downstream H3K4 and H3K79 methylation, transcriptional elongation, DNA double-strand break repair via HR and NHEJ, genome stability, NF-κB signaling, VDR-dependent intestinal homeostasis, and cell lineage decisions; independently, RNF40 targets non-histone substrates including syntaxin 1, LIMA1, Parkin, and KDM6A for ubiquitin-mediated degradation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RNF40 is a RING-type E3 ubiquitin ligase that, as an obligate heterodimer with RNF20, monoubiquitinates histone H2B at lysine 120 (H2Bub1) to control chromatin state, transcription, genome stability, and cell-fate decisions [#2, #7]. Cryo-EM of a chemically trapped ubiquitin-transfer intermediate shows RNF40 directly engages nucleosomal DNA and, through an unconventional non-hydrophobic RING–E2 interface, positions the E2 enzyme RAD6A directly above H2B K120 [#15]; this catalysis is allosterically stimulated by H2B S112 GlcNAcylation acting on the E2 to enhance K120 nucleophilicity [#21], requires CDC73 for mark maintenance [#3], and depends on extensive interfaces with the cofactor WAC [#20]. H2Bub1 in turn promotes trans-histone H3K4 and H3K79 methylation and gene activation [#2, #11], and the complex maintains genome integrity by limiting R-loop-associated replication breaks and supporting double-strand break repair through both homologous recombination and class-switch/NHEJ pathways under ATM/ATR control [#5, #8]. Through these chromatin functions RNF40 governs diverse programs: VDR-dependent intestinal epithelial homeostasis whose loss drives spontaneous colorectal inflammation [#14], NF-\\u03baB-driven cytokine expression in colitis [#9], anti-apoptotic gene expression in colorectal cancer [#10], iPSC reprogramming via resolution of H3K4me3/H3K27me3 bivalency [#12], osteoblast lineage specification and RANKL expression [#13], and pro-tumorigenic cytoskeletal and metabolic signaling in breast cancer [#11, #16]. Independently of histone modification, RNF40 ubiquitinates non-histone substrates for degradation\\u2014syntaxin 1 [#0], LIMA1 to suppress lipid accumulation [#17], Parkin via K48 linkages to inhibit mitophagy [#19], and KDM6A via K6/K11 linkages for autophagic turnover that restricts coronavirus receptor expression [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"First defined RNF40 as a nuclear protein with a discrete protein-interaction architecture, establishing it as a candidate regulatory factor before its enzymatic identity was known.\",\n      \"evidence\": \"In vitro and in vivo binding with LXCXE mutagenesis showing pRb interaction, leucine-zipper homodimerization, and nuclear localization\",\n      \"pmids\": [\"10944455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the pRb interaction unresolved\", \"Relationship of homodimerization to later RNF20 heterodimer not addressed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Established RNF40 as a bona fide RING E3 ubiquitin ligase that recruits an E2 and degrades a specific substrate, defining its core catalytic activity.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, and proteasome-inhibitor experiments showing syntaxin 1 binding, UbcH8 recruitment, and degradation\",\n      \"pmids\": [\"12121982\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not connect activity to histone substrates\", \"Physiological context of syntaxin 1 turnover not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the central function of RNF40 as a heterodimeric H2B K120 monoubiquitin ligase coupled to downstream histone methylation, and showed CDC73 is required to maintain the mark.\",\n      \"evidence\": \"Knockdown, ChIP, yeast two-hybrid, and histone-mark Westerns in cells and parathyroid tumor analysis\",\n      \"pmids\": [\"22021426\", \"22354749\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genome-wide target spectrum not yet mapped\", \"Mechanism coupling H2Bub1 to H3K4/H3K79 methylation not structurally defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placed RNF40 in the DNA double-strand break response, linking H2Bub1 to chromatin remodeling and end resection.\",\n      \"evidence\": \"siRNA knockdown with \\u03b3H2AX/H3K56ac imaging, chromatin fractionation, and FACT (SUPT16H) recruitment analysis\",\n      \"pmids\": [\"22031019\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination targets at break sites not identified\", \"Relative contribution to resection versus checkpoint signaling unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended the genome-stability role by showing the complex prevents R-loop-driven replication breaks and chromosomal instability.\",\n      \"evidence\": \"Bre1-deficient cells with cytogenetics, R-loop detection, and DNA content analysis\",\n      \"pmids\": [\"22354749\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of R-loop suppression not defined\", \"Whether effect is direct or transcription-mediated unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated the RING cysteines are a functional vulnerability, with arsenite directly inhibiting H2Bub1 and DSB repair.\",\n      \"evidence\": \"In vitro binding, cellular H2B ubiquitination assay, BRCA1/RAD51 immunofluorescence, and comet assay\",\n      \"pmids\": [\"25170678\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of arsenite inhibition not established\", \"Selectivity over other RING E3s not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided the first structural basis for catalysis, defining the RING heterodimer and its contacts with the E2~ubiquitin conjugate.\",\n      \"evidence\": \"X-ray crystallography of the RING domain with mutagenesis and in vitro ubiquitin-transfer assays\",\n      \"pmids\": [\"27569044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not include the nucleosome substrate\", \"Mechanism of lysine selection unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolved the DSB repair pathway dependency and the upstream kinase control of damage-induced H2Bub1.\",\n      \"evidence\": \"B-cell knockouts with class-switch and HR assays plus ATM/ATR inhibitor epistasis\",\n      \"pmids\": [\"30692271\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How ATM/ATR signal to the complex mechanistically unknown\", \"Direct phosphorylation targets not identified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected RNF40 to inflammatory and apoptotic transcriptional programs in the intestine and colorectal cancer.\",\n      \"evidence\": \"siRNA knockdown, NF-\\u03baB localization imaging, cytokine and mRNA-seq, H2Bub1 ChIP, apoptosis assays, and conditional colitis mouse models\",\n      \"pmids\": [\"30321325\", \"31266541\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect control of NF-\\u03baB nuclear import unclear\", \"Cell-type specificity of pro-survival gene dependence not delineated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established context-specific developmental and oncogenic roles for RNF40-dependent H2Bub1 across reprogramming, osteoblasts, and breast cancer.\",\n      \"evidence\": \"Conditional knockout mice and depletion with transcriptomics, ChIP for histone marks, and lineage/phenotype assays\",\n      \"pmids\": [\"32341358\", \"32901120\", \"33070155\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Determinants of stage-dependent dispensability unknown\", \"Mechanism selecting specific target loci per cell type unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined a physiological intestinal homeostasis circuit in which RNF40/RNF20 control VDR expression, validated in human IBD tissue.\",\n      \"evidence\": \"Intestinal conditional knockout mice with ChIP-seq for H3K4me3/H2Bub1, mRNA-seq, and IBD patient biopsy ChIP-seq\",\n      \"pmids\": [\"34088983\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal hierarchy between H3K4me3 and VDR transcription not fully resolved\", \"Therapeutic implications untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Delivered the mechanistic structure of catalysis on the nucleosome, showing RNF40 reads nucleosomal DNA and positions the E2 over the target lysine, and linked the activity to TNBC stemness and metabolism.\",\n      \"evidence\": \"Cryo-EM of chemically trapped transfer complex with mutagenesis, plus depletion with metabolic flux and stem-cell assays\",\n      \"pmids\": [\"37633270\", \"37770435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How nucleosome engagement is regulated in vivo unclear\", \"Druggability of the interface not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Expanded the non-histone substrate repertoire, showing RNF40 degrades LIMA1 to suppress lipid accumulation.\",\n      \"evidence\": \"Co-IP, domain-mapping ubiquitination assay, proteasome inhibition, and lipid content measurement\",\n      \"pmids\": [\"38909032\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological setting of LIMA1 regulation limited to single study\", \"Relationship to nuclear H2Bub1 function unaddressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined linkage-specific non-histone ubiquitination of Parkin and KDM6A, coupling RNF40 to mitophagy control and antiviral receptor regulation.\",\n      \"evidence\": \"In vivo knockdown (SHR rats, airway cells), K48/K6/K11 linkage analysis, mitophagy and autophagic degradation assays, and viral infection readouts\",\n      \"pmids\": [\"39777866\", \"41691482\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Determinants of linkage-type selection unknown\", \"Each substrate documented by a single study\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Resolved cofactor and allosteric control of catalysis, identifying WAC as a binding partner required for efficient H2Bub1 and H2B S112 GlcNAcylation as an E2-directed stimulator.\",\n      \"evidence\": \"Crystal/AlphaFold structures with mutagenesis and in vitro/in vivo ubiquitination assays; cryo-EM of GlcNAc-modified nucleosome with kinetics and SAR\",\n      \"pmids\": [\"41533567\", \"41495224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo regulation of H2B GlcNAcylation upstream of RNF40 unmapped\", \"Interplay of WAC with CDC73 and RTF1 at chromatin not integrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved which contexts require H2Bub1 versus non-histone substrate ubiquitination, and how upstream signals route RNF40 between these activities and select specific genomic or protein targets.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of substrate selection between histone and non-histone targets\", \"Transcription-restart studies (preprint) report H2Bub1 dispensable for RNAPII restart, contrasting elongation roles\", \"Th17/RTF1 link rests on a single preprint Co-IP\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 2, 7, 17, 18, 19]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 15, 17, 18, 19]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [2, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [2, 15]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 11, 12, 14]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [4, 5, 8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 17, 19]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [18, 19]}\n    ],\n    \"complexes\": [\n      \"RNF20/RNF40 H2B ubiquitin ligase heterodimer\"\n    ],\n    \"partners\": [\n      \"RNF20\",\n      \"RAD6A\",\n      \"UbcH8\",\n      \"CDC73\",\n      \"WAC\",\n      \"RTF1\",\n      \"RB1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}