{"gene":"CBX6","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2008,"finding":"CBX6 associates with nucleosomes in distinct subnuclear regions compared to other CBX family members (e.g., CBX2 and CBX6 show reciprocal patterns of chromosome association on metaphase spreads). Importantly, the conserved chromodomain and chromobox regions of CBX6 are dispensable for chromatin association, and this association occurs through non-conserved, nonhomologous protein sequences. The absence of H3K27me3 (in EED-null ES cells) had minimal effects on CBX6 chromatin association.","method":"Bimolecular fluorescence complementation (BiFC) analysis in ES cells and fibroblasts; metaphase spread analysis; stable cell lines with inducible expression","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — direct live-cell localization with functional domain dissection; single lab but multiple orthogonal approaches","pmids":["18927235"],"is_preprint":false},{"year":2010,"finding":"Human CBX6 chromodomain binds trimethylated H3K27 and H3K9 peptides but with lower affinity than HP1 homologs, and cannot distinguish between these two marks. Structural and mutagenic analyses revealed that the Pc subfamily (including CBX6) has a greater sequence tolerance in its chromodomain binding surface and potentially engages alternative non-histone sequences as binding targets. The structural basis for divergent methyllysine binding selectivity in CBX6 versus HP1 proteins was defined.","method":"X-ray crystallography, NMR, ITC/fluorescence binding assays, peptide permutation arrays, site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — structural determination combined with biophysical binding assays and mutagenesis across multiple CBX family members","pmids":["21047797"],"is_preprint":false},{"year":2011,"finding":"Tandem affinity purification coupled with mass spectrometry showed that CBX6 defines a distinct PRC1-like complex (~60 interacting proteins identified), and CBX family members are mutually exclusive within PRC1 complexes. CBX6 and CBX8 interact with the largest number of partners and differ in their protein interaction networks from CBX2, CBX4, and CBX7. Protein kinase CK2 associates with all CBX-PRC1 complexes. Different CBX proteins show distinct subnuclear localization, consistent with their different interaction profiles.","method":"Tandem affinity purification (TAP) coupled with tandem mass spectrometry (MS/MS) in mammalian cells","journal":"Molecular & cellular proteomics : MCP","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal AP-MS identifying CBX6 complex composition; single lab with comprehensive comparative analysis","pmids":["21282530"],"is_preprint":false},{"year":2012,"finding":"Proteomic and genomic analysis established that CBX proteins (including CBX6) are incorporated into six major groups of PRC1 complexes, each containing a distinct PCGF subunit and RING1A/B. CBX-containing complexes (canonical PRC1) are distinct from RYBP/YAF2-containing complexes, as RYBP binding prevents incorporation of CBX, PHC, and SCM subunits. Both complex types compact chromatin, but only RYBP stimulates RING1B-mediated H2AK119ub1.","method":"Affinity purification-mass spectrometry, genomic localization (ChIP-seq), biochemical reconstitution, H2A ubiquitination assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — proteomic, genomic, and biochemical reconstitution with functional assays; widely replicated foundational study","pmids":["22325352"],"is_preprint":false},{"year":2015,"finding":"CBX6 chromodomain can be selectively inhibited by peptidomimetic compounds. A specific chemical modification of a pan-polycomb ligand switches selectivity toward CBX6 by engaging a small hydrophobic pocket adjacent to the aromatic cage that is unique to CBX6. Molecular dynamics simulations confirmed that occupancy of this pocket is the structural basis for selectivity.","method":"Competitive binding assays, molecular dynamics simulations, peptidomimetic synthesis and SAR","journal":"ACS medicinal chemistry letters","confidence":"Medium","confidence_rationale":"Tier 1–2 — structure-guided inhibitor design with binding assays and MD simulation; single lab","pmids":["26985288"],"is_preprint":false},{"year":2016,"finding":"Systematic affinity purification-mass spectrometry mapping of the human PcG complexome identified CBX6 as a component of canonical PRC1 complexes with a defined set of interacting partners, distinct from other CBX paralogs. The high-density interaction network placed CBX6 within the broader PcG interactome architecture.","method":"Affinity purification-mass spectrometry (AP-MS) of PcG proteins in human cells","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — systematic AP-MS with broad coverage; single study but comprehensive methodology","pmids":["27705803"],"is_preprint":false},{"year":2017,"finding":"CBX6 promotes HCC cell growth in vitro and in vivo, and mechanistic investigation revealed that the S100A9/NF-κB/MAPK signaling pathway is essential for mediating CBX6 oncogenic function in HCC.","method":"Gain- and loss-of-function experiments (overexpression and knockdown), in vivo xenograft, pathway inhibitor experiments, Western blotting","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2–3 — KD/OE with defined pathway placement via pharmacological inhibition; single lab","pmids":["28122351"],"is_preprint":false},{"year":2017,"finding":"CBX6 is physically associated with both canonical PRC1 (cPRC1) and non-canonical PRC1 (ncPRC1) complexes in mouse embryonic stem cells, as demonstrated by co-immunoprecipitation and mass spectrometry. Unlike CBX7, CBX6 is recruited to chromatin independently of H3K27me3. Depletion of CBX6 destabilizes the pluripotency network and triggers ESC differentiation, establishing CBX6 as an essential component of ESC identity.","method":"Co-immunoprecipitation, affinity purification-mass spectrometry, ChIP-seq, shRNA-mediated depletion, gene expression analysis, H3K27me3-independent chromatin recruitment assay using EED-null cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (AP-MS, ChIP-seq, genetic KD with phenotype) establishing complex membership and functional role; moderately cited","pmids":["29089522"],"is_preprint":false},{"year":2019,"finding":"CBX6 expression in breast cancer is negatively regulated by EZH2 in a PRC2-dependent manner. EZH2 represses CBX6 transcription via H3K27 methylation at the CBX6 locus. CBX6 overexpression inhibits breast cancer cell proliferation, colony formation, migration and invasion, and induces cell cycle arrest. CBX6 downregulates BST2 expression by binding to its promoter region.","method":"EZH2 knockdown and inhibitor treatment with CBX6 mRNA/protein measurement, CBX6 overexpression functional assays (MTT, colony formation, wound healing, Transwell), chromatin immunoprecipitation (ChIP) at BST2 promoter, microarray gene expression analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — EZH2→CBX6 regulatory axis supported by knockdown and pharmacological inhibition; ChIP confirms direct promoter binding; single lab","pmids":["30655550"],"is_preprint":false},{"year":2020,"finding":"In invasive mesothelioma cells, CBX6 undergoes constitutive ubiquitination and proteasomal degradation, leading to loss of CBX6-mediated repression of the MMP-2 gene. CBX6 knockdown in non-invasive mesothelioma cells promotes MMP-2 expression and invasion. CBX6 regulates sets of genes involved in cancer cell migration and metastasis through epigenetic mechanisms involving DNA and histone methylation at target gene transcription start sites.","method":"Knockdown experiments, proteasome inhibitor treatment (MG132), ubiquitination assays, collagen matrix invasion assay, transcriptome analysis, immunohistochemistry","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — ubiquitination demonstrated biochemically; KD with defined invasion phenotype; single lab with multiple methods","pmids":["33028834"],"is_preprint":false},{"year":2020,"finding":"CBX6 promotes HCC cell migration and invasion through upregulation of transcription factors Snail and Zeb1, thereby accelerating the epithelial-mesenchymal transition (EMT) process.","method":"CBX6 overexpression and shRNA knockdown in HCC cell lines; Western blot for Snail/Zeb1/EMT markers; wound healing and Transwell invasion assays","journal":"OncoTargets and therapy","confidence":"Low","confidence_rationale":"Tier 3 — KD/OE with defined downstream marker changes but no direct binding or epistasis confirmation; single lab","pmids":["33311989"],"is_preprint":false},{"year":2021,"finding":"Structure-activity relationship studies on CBX6 chromodomain inhibitors identified the -2 position of the peptidomimetic scaffold as a key determinant of selectivity among polycomb paralogs, yielding potent dual-selective inhibitors of CBX6 and CBX8 that are cell permeable and impact cell proliferation in rhabdoid tumor cells.","method":"Competitive binding assays, SAR medicinal chemistry, cell proliferation assays in rhabdoid tumor cell line","journal":"ChemMedChem","confidence":"Medium","confidence_rationale":"Tier 1–2 — structure-guided SAR with binding assays and cell-based validation; builds on prior structural work","pmids":["34174168"],"is_preprint":false},{"year":2024,"finding":"CBX6 is polyubiquitinated at K214 via K48-linked chains by a UBE2T–TRIM25 E2–E3 ligase complex, leading to proteasomal degradation of CBX6. Loss of CBX6 de-represses SOX2 and NANOG transcription, enhancing breast cancer stem cell (BCSC) stemness. CBX6 thus acts as a transcriptional repressor of pluripotency genes SOX2 and NANOG, and its stability is controlled by the UBE2T–TRIM25 axis.","method":"Ubiquitination assays (K48-linkage specific), site-directed mutagenesis (K214R), co-immunoprecipitation of UBE2T–TRIM25–CBX6 complex, CBX6 overexpression/knockdown with SOX2/NANOG reporter assays, organoid models, MMTV-PyMT in vivo mouse model, single-cell RNA-seq","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 1–2 — biochemical ubiquitination site mapped by mutagenesis, E2/E3 complex identified by Co-IP, functional rescue in vivo; multiple orthogonal methods","pmids":["39716485"],"is_preprint":false},{"year":2025,"finding":"CBX6 promotes immune evasion in esophageal squamous cell carcinoma by regulating chromatin remodeling via SMARCD1 (a SWI/SNF complex subunit). CBX6 upregulates SMARCD1 expression, which in turn promotes transcription of CCL8 and SLC16A3 (encoding MCT4). This leads to CCL8 secretion and MCT4-mediated lactate efflux, suppressing CD8+ T cell cytotoxicity and promoting tumor development.","method":"CBX6 and SMARCD1 knockdown/overexpression in mEC25 cells, co-culture with CD8+ T cells, in vivo tumor models, chromatin remodeling assays, metabolic assays (lactate transport), tissue microarray analysis","journal":"Cell biology and toxicology","confidence":"Medium","confidence_rationale":"Tier 2–3 — genetic epistasis established (CBX6→SMARCD1→CCL8/SLC16A3) with functional rescue; multiple in vitro and in vivo readouts; single lab","pmids":["41219497"],"is_preprint":false},{"year":2026,"finding":"CBX6 binds directly to the CA9 (carbonic anhydrase 9) gene promoter in GBM cells, as demonstrated by chromatin immunoprecipitation with multiple primer sets, suggesting CBX6 acts as a transcriptional repressor of CA9. Under hypoxic conditions, CBX6 is downregulated, which is associated with CA9 upregulation, indicating a direct regulatory relationship.","method":"Chromatin immunoprecipitation (ChIP) with multiple primers, shRNA-mediated knockdown, qRT-PCR, functional proliferation/migration/invasion assays","journal":"Molecular therapy. Oncology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP with multiple primers confirming direct promoter occupancy combined with KD phenotype; single lab","pmids":["41883712"],"is_preprint":false}],"current_model":"CBX6 is a Polycomb group protein that functions as a component of both canonical and non-canonical PRC1 complexes, where its chromodomain binds H3K27me3/H3K9me3 (with low affinity, independently of these marks for chromatin recruitment), and it acts as a transcriptional repressor of target genes (including BST2, CA9, MMP-2, SOX2, and NANOG) through chromatin compaction and epigenetic silencing; its protein stability is regulated by K48-linked polyubiquitination at K214 by the UBE2T–TRIM25 E2–E3 ligase complex leading to proteasomal degradation, and CBX6 is itself transcriptionally repressed by EZH2/PRC2, placing it within a broader Polycomb regulatory network that controls cell identity, stemness, and tumor suppression in a context-dependent manner."},"narrative":{"teleology":[{"year":2008,"claim":"Resolving how CBX6 associates with chromatin revealed that, unlike the canonical model requiring H3K27me3 recognition, CBX6 binds nucleosomes through non-conserved sequences outside its chromodomain and chromobox, and does so independently of H3K27me3.","evidence":"Bimolecular fluorescence complementation and metaphase spread analysis in wild-type and EED-null ES cells with domain deletion constructs","pmids":["18927235"],"confidence":"Medium","gaps":["The non-conserved sequences mediating chromatin association are not mapped to specific residues","Whether this H3K27me3-independent recruitment applies in all cell types is untested"]},{"year":2010,"claim":"Structural determination of the CBX6 chromodomain established that it binds H3K27me3 and H3K9me3 with low affinity and cannot discriminate between them, differing from HP1 homologs due to a more tolerant aromatic cage—raising the possibility that CBX6 engages non-histone methylated targets.","evidence":"X-ray crystallography, NMR, ITC and fluorescence binding assays, peptide permutation arrays, and mutagenesis","pmids":["21047797"],"confidence":"High","gaps":["Physiological non-histone binding partners of the CBX6 chromodomain have not been identified","The functional consequence of low-affinity histone mark binding in vivo is unclear"]},{"year":2012,"claim":"Proteomic and biochemical studies defined the PRC1 complex landscape, placing CBX6 within canonical PRC1 as a mutually exclusive alternative to RYBP/YAF2 and establishing that CBX-containing PRC1 compacts chromatin but does not stimulate H2AK119ub1 as efficiently as non-canonical complexes.","evidence":"Tandem affinity purification–mass spectrometry, ChIP-seq, and biochemical reconstitution with H2A ubiquitination assays","pmids":["21282530","22325352","27705803"],"confidence":"High","gaps":["Specific genomic targets uniquely occupied by CBX6-PRC1 versus other CBX-PRC1 variants remain poorly defined","Whether CBX6-PRC1 has distinct functional outputs beyond chromatin compaction is unresolved"]},{"year":2015,"claim":"Chemical biology efforts identified a unique hydrophobic pocket adjacent to the CBX6 chromodomain aromatic cage that enables selective peptidomimetic inhibition, providing a tool compound to dissect CBX6-specific functions.","evidence":"Peptidomimetic synthesis with competitive binding assays, SAR, and molecular dynamics simulations","pmids":["26985288","34174168"],"confidence":"Medium","gaps":["These inhibitors have not been used in genome-wide functional studies to define CBX6-dependent gene programs","In vivo pharmacological validation is lacking"]},{"year":2017,"claim":"Demonstrating CBX6's role in pluripotency, depletion of CBX6 in mouse ESCs destabilized the pluripotency network and triggered differentiation, and CBX6 was found in both canonical and non-canonical PRC1 complexes—a unique feature among CBX paralogs.","evidence":"Co-IP, AP-MS, ChIP-seq, shRNA depletion with transcriptomic analysis in wild-type and EED-null ESCs","pmids":["29089522"],"confidence":"High","gaps":["Which specific PRC1 subcomplexes mediate CBX6's pluripotency function is not dissected","Whether CBX6 depletion effects are cell-autonomous in vivo during embryogenesis is unknown"]},{"year":2019,"claim":"CBX6 was placed within a layered Polycomb regulatory circuit: EZH2/PRC2 transcriptionally represses CBX6 via H3K27me3 at its own locus, and CBX6 in turn represses BST2 by direct promoter binding, establishing a PRC2→CBX6→target gene cascade.","evidence":"EZH2 knockdown and inhibitor treatment measuring CBX6 levels; CBX6 overexpression functional assays; ChIP at the BST2 promoter in breast cancer cells","pmids":["30655550"],"confidence":"Medium","gaps":["The generality of PRC2-mediated CBX6 repression across tissue types is not established","Whether CBX6 acts on BST2 through canonical PRC1-mediated compaction or another mechanism is unclear"]},{"year":2020,"claim":"CBX6 protein stability was shown to be regulated by constitutive ubiquitination and proteasomal degradation in invasive mesothelioma cells, with loss of CBX6 de-repressing MMP-2 and promoting invasion—linking post-translational control of CBX6 to tumor cell behavior.","evidence":"Proteasome inhibitor (MG132) rescue, ubiquitination assays, knockdown with collagen matrix invasion assay and transcriptomics in mesothelioma lines","pmids":["33028834"],"confidence":"Medium","gaps":["The E3 ligase responsible for CBX6 degradation in mesothelioma was not identified in this study","Whether epigenetic changes at MMP-2 are direct consequences of CBX6 promoter occupancy was not tested by ChIP"]},{"year":2024,"claim":"The molecular mechanism of CBX6 turnover was resolved: UBE2T (E2) and TRIM25 (E3) catalyze K48-linked polyubiquitination at CBX6 K214, targeting it for proteasomal degradation; this degradation de-represses SOX2 and NANOG, enhancing cancer stemness.","evidence":"K48-linkage-specific ubiquitination assays, K214R mutagenesis, Co-IP of UBE2T–TRIM25–CBX6, overexpression/knockdown with reporter assays, organoid models, and MMTV-PyMT in vivo tumor model","pmids":["39716485"],"confidence":"High","gaps":["Whether additional ubiquitination sites contribute to CBX6 turnover under different stimuli is untested","The signal or condition that activates UBE2T–TRIM25 toward CBX6 is unknown","Whether K214 ubiquitination also regulates CBX6 in non-malignant contexts is unexplored"]},{"year":2025,"claim":"CBX6 was linked to immune evasion through an unexpected mechanism: CBX6 upregulates SMARCD1 (a SWI/SNF subunit), which promotes CCL8 secretion and MCT4-mediated lactate efflux, suppressing CD8+ T cell cytotoxicity in esophageal squamous cell carcinoma.","evidence":"CBX6/SMARCD1 knockdown–overexpression epistasis, co-culture with CD8+ T cells, in vivo tumor models, metabolic lactate assays","pmids":["41219497"],"confidence":"Medium","gaps":["Whether CBX6 directly binds the SMARCD1 locus or acts indirectly is not determined","The relationship between PRC1 membership and SMARCD1/SWI-SNF regulation is mechanistically unclear","Generalizability beyond ESCC is untested"]},{"year":null,"claim":"Key open questions include identifying the full set of direct CBX6-PRC1 genomic targets, the physiological non-histone ligands of its chromodomain, the signals governing UBE2T–TRIM25 activation, and whether CBX6's non-canonical PRC1 membership has distinct functional outputs from its canonical PRC1 role.","evidence":"","pmids":[],"confidence":"Low","gaps":["No genome-wide direct target map (ChIP-seq for CBX6 occupancy) exists in most cancer contexts","Non-histone chromodomain ligands remain unidentified","In vivo developmental phenotype of CBX6 knockout has not been reported"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[1,4,11]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[8,14]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[8,9,12,14]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2,7]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,3,7]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[8,9,12,14]}],"complexes":["PRC1 (canonical)","PRC1 (non-canonical)"],"partners":["RING1B","PCGF2","UBE2T","TRIM25","EZH2","SMARCD1"],"other_free_text":[]},"mechanistic_narrative":"CBX6 is a Polycomb group protein that functions as a subunit of both canonical and non-canonical PRC1 complexes, where it contributes to transcriptional repression of target genes involved in stemness, invasion, and immune evasion. Its chromodomain binds H3K27me3 and H3K9me3 with low affinity, but chromatin recruitment occurs largely independently of these marks through non-conserved protein sequences [PMID:18927235, PMID:21047797, PMID:29089522]. CBX6 directly represses promoters of genes including BST2, SOX2, NANOG, MMP-2, and CA9, and its protein stability is controlled by K48-linked polyubiquitination at K214 mediated by the UBE2T–TRIM25 E2–E3 ligase complex, targeting it for proteasomal degradation [PMID:39716485, PMID:30655550, PMID:33028834, PMID:41883712]. CBX6 itself is transcriptionally repressed by EZH2/PRC2, embedding it within a layered Polycomb regulatory circuit that governs cell identity and pluripotency [PMID:30655550, PMID:29089522]."},"prefetch_data":{"uniprot":{"accession":"O95503","full_name":"Chromobox protein homolog 6","aliases":[],"length_aa":412,"mass_kda":43.9,"function":"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:21282530). PcG PRC1 complex acts via chromatin remodeling and modification of histones; it mediates monoubiquitination of histone H2A 'Lys-119', rendering chromatin heritably changed in its expressibility. Possibly contributes to the target selectivity of the PRC1 complex by binding specific regions of chromatin (PubMed:18927235). Recruitment to chromatin might occur in an H3K27me3-independent fashion (By similarity). May have a PRC1-independent function in embryonic stem cells (By similarity)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/O95503/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CBX6","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CBX6","total_profiled":1310},"omim":[{"mim_id":"617438","title":"CHROMOBOX 6; CBX6","url":"https://www.omim.org/entry/617438"},{"mim_id":"608457","title":"CHROMOBOX 7; CBX7","url":"https://www.omim.org/entry/608457"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":81.0}],"url":"https://www.proteinatlas.org/search/CBX6"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O95503","domains":[{"cath_id":"2.40.50.40","chopping":"11-68","consensus_level":"medium","plddt":94.2612,"start":11,"end":68}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95503","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95503-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95503-F1-predicted_aligned_error_v6.png","plddt_mean":60.66},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CBX6","jax_strain_url":"https://www.jax.org/strain/search?query=CBX6"},"sequence":{"accession":"O95503","fasta_url":"https://rest.uniprot.org/uniprotkb/O95503.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95503/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95503"}},"corpus_meta":[{"pmid":"26985288","id":"PMC_26985288","title":"Selective 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hepatocellular carcinoma.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28122351","citation_count":47,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32513696","id":"PMC_32513696","title":"RIG-I regulates myeloid differentiation by promoting TRIM25-mediated ISGylation.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32513696","citation_count":47,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"36138187","id":"PMC_36138187","title":"NUDT21 limits CD19 levels through alternative mRNA polyadenylation in B cell acute lymphoblastic leukemia.","date":"2022","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36138187","citation_count":46,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12819141","id":"PMC_12819141","title":"Identification and analysis of chromodomain-containing proteins encoded in the mouse 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Selectivity for CBX6 over other polycomb paralogs can be achieved by occupancy of a small hydrophobic pocket adjacent to the aromatic cage, as confirmed by molecular dynamics simulations and peptidomimetic inhibitor studies.\",\n      \"method\": \"Peptidomimetic inhibitor binding assays, molecular dynamics simulations, structure-activity relationships\",\n      \"journal\": \"ACS medicinal chemistry letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding assays with computational structural validation, single lab\",\n      \"pmids\": [\"26985288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CBX6 is physically and functionally associated with both canonical PRC1 (cPRC1) and non-canonical PRC1 (ncPRC1) complexes in mouse embryonic stem cells (ESCs). Unlike CBX7, CBX6 is recruited to chromatin independently of H3K27me3. CBX6 depletion destabilizes the pluripotency network and triggers differentiation, establishing it as an essential regulator of ESC identity.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), RNA-seq, genetic depletion with differentiation phenotype readout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, ChIP, and clean KD with defined cellular phenotype; multiple orthogonal methods in one study\",\n      \"pmids\": [\"29089522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"EZH2 (a PRC2 component) negatively regulates CBX6 expression in a PRC2-dependent manner in breast cancer cells. Overexpressed CBX6 binds the promoter of BST2 and represses its transcription, inhibiting cell proliferation, colony formation, inducing cell cycle arrest, and suppressing migration and invasion.\",\n      \"method\": \"EZH2 knockdown/inhibition with CBX6 expression measurement (Western blot), ChIP on BST2 promoter, CBX6 overexpression with functional assays (proliferation, migration, invasion)\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP for promoter binding, genetic overexpression with defined phenotypic readouts, single lab\",\n      \"pmids\": [\"30655550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CBX6 represses MMP-2 gene expression via DNA and histone methylation at the MMP-2 transcription start site. In invasive mesothelioma cells, CBX6 is ubiquitinated and subjected to proteasomal degradation, relieving MMP-2 repression and enabling invasion through collagen matrix.\",\n      \"method\": \"CBX6 knockdown (siRNA), MMP-2 expression analysis, ubiquitination assay, transcriptome analysis, collagen matrix invasion assay, immunohistochemistry for nuclear CBX6\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined cellular phenotype, ubiquitination assay, transcriptome analysis; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"33028834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CBX6 promotes epithelial-mesenchymal transition (EMT) in hepatocellular carcinoma cells by upregulating the expression of transcription factors Snail and Zeb1, thereby enhancing migration and invasion.\",\n      \"method\": \"CBX6 overexpression plasmid and shRNA knockdown with Western blot for Snail/Zeb1, wound healing and Transwell invasion assays\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — Western blot for downstream targets after OE/KD, single lab, no direct binding or promoter assay for Snail/Zeb1\",\n      \"pmids\": [\"33311989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The -2 position in the peptidomimetic scaffold is a key residue determining selectivity among polycomb paralogs, enabling development of dual-selective inhibitors targeting both CBX6 and CBX8 chromodomains, with demonstrated anti-proliferative effects in rhabdoid tumor cells.\",\n      \"method\": \"Structure-activity relationship analysis of chromodomain inhibitors, cell proliferation assays in rhabdoid tumor cell lines\",\n      \"journal\": \"ChemMedChem\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — SAR with cell-based functional validation, single lab\",\n      \"pmids\": [\"34174168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBE2T collaborates with the E3 ligase TRIM25 to perform K48-linked polyubiquitination of CBX6 at lysine 214, leading to its proteasomal degradation. Loss of CBX6 promotes transcription of pluripotency genes SOX2 and NANOG, enhancing breast cancer stem cell stemness.\",\n      \"method\": \"Co-immunoprecipitation (UBE2T-TRIM25-CBX6 complex), ubiquitination assay (K48-linkage, site-specific K214 mutant), genetic ablation of UBE2T in organoids and MMTV-PyMT mice, SOX2/NANOG expression readout\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — site-specific mutagenesis (K214), linkage-specific ubiquitination assay, Co-IP of complex, in vivo mouse model validation; multiple orthogonal methods\",\n      \"pmids\": [\"39716485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CBX6 binds to the CA9 promoter (confirmed by ChIP with multiple primers) and represses CA9 transcription in glioblastoma cells. CBX6 silencing promotes GBM cell proliferation, migration, and invasion, while overexpression yields opposite effects, establishing CBX6 as a negative regulator of tumor aggressiveness that acts in part through CA9 repression.\",\n      \"method\": \"ChIP assay (multiple primers on CA9 promoter), shRNA knockdown and overexpression with proliferation/migration/invasion assays, qRT-PCR\",\n      \"journal\": \"Molecular therapy. Oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP for direct promoter binding, genetic KD/OE with defined phenotypic readouts, single lab\",\n      \"pmids\": [\"41883712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CBX6 regulates expression of SMARCD1 (a SWI/SNF BAF chromatin remodeling complex subunit), which in turn promotes transcription of CCL8 and SLC16A3 (encoding MCT4). This axis drives CCL8 secretion and MCT4-mediated lactate efflux, reducing CD8+ T cell cytotoxicity and promoting tumor development in esophageal squamous cell carcinoma.\",\n      \"method\": \"CBX6 knockdown (mEC25 cells), SMARCD1 overexpression rescue, co-culture CD8+ T cell cytotoxicity assay, in vivo tumor model, chromatin remodeling and transcription analysis\",\n      \"journal\": \"Cell biology and toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistatic rescue experiment (SMARCD1 OE restores CBX6-KD phenotype), in vivo validation, single lab\",\n      \"pmids\": [\"41219497\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CBX6 is a polycomb group protein that functions as a methyllysine (H3K27me3) reader via its chromodomain aromatic cage and associates with both canonical and non-canonical PRC1 complexes to repress target gene promoters (including BST2, MMP-2, CA9); it can be recruited to chromatin independently of H3K27me3, is subject to K48-linked polyubiquitination at K214 by UBE2T/TRIM25 leading to proteasomal degradation, and in stem/cancer contexts its loss de-represses pluripotency (SOX2, NANOG) and pro-invasive (MMP-2, Snail/Zeb1) genes while its presence in ESCs is essential for maintaining pluripotency through dual cPRC1/ncPRC1 association.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper before extracting discoveries.\n\n**Classification:**\n\nRetrieved papers:\n1. PMID:26985288 - CBX6 chromodomain selective inhibition → KEEP\n2. PMID:30655550 - CBX6 in breast cancer, EZH2 regulation → KEEP\n3. PMID:33311989 - CBX6 in HCC, EMT → KEEP\n4. PMID:29089522 - CBX6 in ESC identity, PRC1 → KEEP\n5. PMID:39716485 - UBE2T-TRIM25-CBX6 axis in breast cancer stemness → KEEP\n6. PMID:34174168 - CBX6/CBX8 chromodomain inhibitors → KEEP\n7. PMID:33028834 - CBX6 proteasomal degradation, MMP-2 in mesothelioma → KEEP\n8. PMID:37713130 - KMT2A-rearranged sarcoma with CBX6::KMT2A fusion → KEEP (mentions CBX6 as fusion partner, but no mechanistic findings about CBX6 protein)\n9. PMID:38452983 - Cbx6 as biomarker in RIRI → EXCLUDE (biomarker/expression only)\n10. PMID:39602349 - CCR7 and CBX6 biomarkers in AAA → EXCLUDE (biomarker/expression only)\n11. PMID:41883712 - CBX6 in GBM, ChIP for CA9 promoter → KEEP\n12. PMID:41219497 - CBX6/SMARCD1/CCL8 in ESCC → KEEP\n\nGene2pubmed curated papers:\n- PMID:12477932 - MGC cDNA sequences → EXCLUDE (no mechanistic findings)\n- PMID:26186194 - BioPlex interactome → KEEP (CBX6 interactions identified)\n- PMID:28514442 - BioPlex 2.0 → KEEP\n- PMID:29507755 - VIRMA/m6A methylation → EXCLUDE (not about CBX6)\n- PMID:10591208 - Chr 22 sequence → EXCLUDE\n- PMID:14702039 - FLJ cDNA collection → EXCLUDE\n- PMID:33961781 - BioPlex 3.0 → KEEP\n- PMID:22325352 - PRC1 complexes, CBX proteins → KEEP\n- PMID:21873635 - GO annotations → EXCLUDE\n- PMID:20211142 - TF combinatorial atlas → EXCLUDE (no specific CBX6 mechanism)\n- PMID:15489334 - MGC → EXCLUDE\n- PMID:20972438 - Bladder cancer GWAS → EXCLUDE\n- PMID:21047797 - CBX chromodomain recognition and specificity → KEEP\n- PMID:27705803 - PcG complexome map → KEEP\n- PMID:20601937 - USP7/USP11 modulate PRC1 → KEEP (mentions CBX6 as PRC1 component in context)\n- PMID:19322201 - HuR ubiquitination by heat shock → EXCLUDE (not about CBX6)\n- PMID:30554943 - BET bromodomain interactome → EXCLUDE (not about CBX6)\n- PMID:24457600 - EED in PRC1/PRC2 → KEEP (CBX6 mentioned as PRC1 component)\n- PMID:24163127 - Bladder cancer GWAS → EXCLUDE\n- PMID:21282530 - CBX family interaction proteomics → KEEP\n- PMID:18927235 - CBX proteins, chromatin regions → KEEP\n- PMID:30021884 - XL-MS histone interactions → EXCLUDE (no specific CBX6 mechanism)\n- PMID:24981860 - Chromatin-related protein interactions → KEEP (if CBX6 specific)\n- PMID:32814053 - ND interactome → EXCLUDE\n- PMID:20543829 - MOV10/PRC1 → KEEP (if CBX6 mentioned)\n- PMID:28122351 - CBX6 in HCC, S100A9/NF-κB/MAPK → KEEP\n- PMID:32513696 - RIG-I/TRIM25/ISGylation → EXCLUDE (not about CBX6)\n- PMID:36138187 - NUDT21/CD19 → EXCLUDE\n- PMID:12819141 - Chromodomain proteins in mouse transcriptome → KEEP (characterizes CBX6)\n- PMID:23503679 - PLATO method → EXCLUDE\n\nNow reviewing borderline cases more carefully:\n- PMID:24981860: mentions chromatin proteins broadly, need to check if CBX6-specific findings → will treat as low specificity, EXCLUDE if no CBX6-specific mechanism\n- PMID:20543829 (MOV10/PRC1): mentions PRC1 broadly but not CBX6 specifically → EXCLUDE\n- PMID:20601937 (USP7/USP11): mentions PRC1 broadly → EXCLUDE unless CBX6-specific\n- PMID:24457600 (EED): mentions CBX proteins broadly → EXCLUDE unless CBX6-specific\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"CBX6 associates with nucleosomes in distinct subnuclear regions compared to other CBX family members (e.g., CBX2 and CBX6 show reciprocal patterns of chromosome association on metaphase spreads). Importantly, the conserved chromodomain and chromobox regions of CBX6 are dispensable for chromatin association, and this association occurs through non-conserved, nonhomologous protein sequences. The absence of H3K27me3 (in EED-null ES cells) had minimal effects on CBX6 chromatin association.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC) analysis in ES cells and fibroblasts; metaphase spread analysis; stable cell lines with inducible expression\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct live-cell localization with functional domain dissection; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"18927235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human CBX6 chromodomain binds trimethylated H3K27 and H3K9 peptides but with lower affinity than HP1 homologs, and cannot distinguish between these two marks. Structural and mutagenic analyses revealed that the Pc subfamily (including CBX6) has a greater sequence tolerance in its chromodomain binding surface and potentially engages alternative non-histone sequences as binding targets. The structural basis for divergent methyllysine binding selectivity in CBX6 versus HP1 proteins was defined.\",\n      \"method\": \"X-ray crystallography, NMR, ITC/fluorescence binding assays, peptide permutation arrays, site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural determination combined with biophysical binding assays and mutagenesis across multiple CBX family members\",\n      \"pmids\": [\"21047797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Tandem affinity purification coupled with mass spectrometry showed that CBX6 defines a distinct PRC1-like complex (~60 interacting proteins identified), and CBX family members are mutually exclusive within PRC1 complexes. CBX6 and CBX8 interact with the largest number of partners and differ in their protein interaction networks from CBX2, CBX4, and CBX7. Protein kinase CK2 associates with all CBX-PRC1 complexes. Different CBX proteins show distinct subnuclear localization, consistent with their different interaction profiles.\",\n      \"method\": \"Tandem affinity purification (TAP) coupled with tandem mass spectrometry (MS/MS) in mammalian cells\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal AP-MS identifying CBX6 complex composition; single lab with comprehensive comparative analysis\",\n      \"pmids\": [\"21282530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Proteomic and genomic analysis established that CBX proteins (including CBX6) are incorporated into six major groups of PRC1 complexes, each containing a distinct PCGF subunit and RING1A/B. CBX-containing complexes (canonical PRC1) are distinct from RYBP/YAF2-containing complexes, as RYBP binding prevents incorporation of CBX, PHC, and SCM subunits. Both complex types compact chromatin, but only RYBP stimulates RING1B-mediated H2AK119ub1.\",\n      \"method\": \"Affinity purification-mass spectrometry, genomic localization (ChIP-seq), biochemical reconstitution, H2A ubiquitination assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — proteomic, genomic, and biochemical reconstitution with functional assays; widely replicated foundational study\",\n      \"pmids\": [\"22325352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CBX6 chromodomain can be selectively inhibited by peptidomimetic compounds. A specific chemical modification of a pan-polycomb ligand switches selectivity toward CBX6 by engaging a small hydrophobic pocket adjacent to the aromatic cage that is unique to CBX6. Molecular dynamics simulations confirmed that occupancy of this pocket is the structural basis for selectivity.\",\n      \"method\": \"Competitive binding assays, molecular dynamics simulations, peptidomimetic synthesis and SAR\",\n      \"journal\": \"ACS medicinal chemistry letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-guided inhibitor design with binding assays and MD simulation; single lab\",\n      \"pmids\": [\"26985288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Systematic affinity purification-mass spectrometry mapping of the human PcG complexome identified CBX6 as a component of canonical PRC1 complexes with a defined set of interacting partners, distinct from other CBX paralogs. The high-density interaction network placed CBX6 within the broader PcG interactome architecture.\",\n      \"method\": \"Affinity purification-mass spectrometry (AP-MS) of PcG proteins in human cells\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic AP-MS with broad coverage; single study but comprehensive methodology\",\n      \"pmids\": [\"27705803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CBX6 promotes HCC cell growth in vitro and in vivo, and mechanistic investigation revealed that the S100A9/NF-κB/MAPK signaling pathway is essential for mediating CBX6 oncogenic function in HCC.\",\n      \"method\": \"Gain- and loss-of-function experiments (overexpression and knockdown), in vivo xenograft, pathway inhibitor experiments, Western blotting\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KD/OE with defined pathway placement via pharmacological inhibition; single lab\",\n      \"pmids\": [\"28122351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CBX6 is physically associated with both canonical PRC1 (cPRC1) and non-canonical PRC1 (ncPRC1) complexes in mouse embryonic stem cells, as demonstrated by co-immunoprecipitation and mass spectrometry. Unlike CBX7, CBX6 is recruited to chromatin independently of H3K27me3. Depletion of CBX6 destabilizes the pluripotency network and triggers ESC differentiation, establishing CBX6 as an essential component of ESC identity.\",\n      \"method\": \"Co-immunoprecipitation, affinity purification-mass spectrometry, ChIP-seq, shRNA-mediated depletion, gene expression analysis, H3K27me3-independent chromatin recruitment assay using EED-null cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (AP-MS, ChIP-seq, genetic KD with phenotype) establishing complex membership and functional role; moderately cited\",\n      \"pmids\": [\"29089522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CBX6 expression in breast cancer is negatively regulated by EZH2 in a PRC2-dependent manner. EZH2 represses CBX6 transcription via H3K27 methylation at the CBX6 locus. CBX6 overexpression inhibits breast cancer cell proliferation, colony formation, migration and invasion, and induces cell cycle arrest. CBX6 downregulates BST2 expression by binding to its promoter region.\",\n      \"method\": \"EZH2 knockdown and inhibitor treatment with CBX6 mRNA/protein measurement, CBX6 overexpression functional assays (MTT, colony formation, wound healing, Transwell), chromatin immunoprecipitation (ChIP) at BST2 promoter, microarray gene expression analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — EZH2→CBX6 regulatory axis supported by knockdown and pharmacological inhibition; ChIP confirms direct promoter binding; single lab\",\n      \"pmids\": [\"30655550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In invasive mesothelioma cells, CBX6 undergoes constitutive ubiquitination and proteasomal degradation, leading to loss of CBX6-mediated repression of the MMP-2 gene. CBX6 knockdown in non-invasive mesothelioma cells promotes MMP-2 expression and invasion. CBX6 regulates sets of genes involved in cancer cell migration and metastasis through epigenetic mechanisms involving DNA and histone methylation at target gene transcription start sites.\",\n      \"method\": \"Knockdown experiments, proteasome inhibitor treatment (MG132), ubiquitination assays, collagen matrix invasion assay, transcriptome analysis, immunohistochemistry\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — ubiquitination demonstrated biochemically; KD with defined invasion phenotype; single lab with multiple methods\",\n      \"pmids\": [\"33028834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CBX6 promotes HCC cell migration and invasion through upregulation of transcription factors Snail and Zeb1, thereby accelerating the epithelial-mesenchymal transition (EMT) process.\",\n      \"method\": \"CBX6 overexpression and shRNA knockdown in HCC cell lines; Western blot for Snail/Zeb1/EMT markers; wound healing and Transwell invasion assays\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD/OE with defined downstream marker changes but no direct binding or epistasis confirmation; single lab\",\n      \"pmids\": [\"33311989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Structure-activity relationship studies on CBX6 chromodomain inhibitors identified the -2 position of the peptidomimetic scaffold as a key determinant of selectivity among polycomb paralogs, yielding potent dual-selective inhibitors of CBX6 and CBX8 that are cell permeable and impact cell proliferation in rhabdoid tumor cells.\",\n      \"method\": \"Competitive binding assays, SAR medicinal chemistry, cell proliferation assays in rhabdoid tumor cell line\",\n      \"journal\": \"ChemMedChem\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-guided SAR with binding assays and cell-based validation; builds on prior structural work\",\n      \"pmids\": [\"34174168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CBX6 is polyubiquitinated at K214 via K48-linked chains by a UBE2T–TRIM25 E2–E3 ligase complex, leading to proteasomal degradation of CBX6. Loss of CBX6 de-represses SOX2 and NANOG transcription, enhancing breast cancer stem cell (BCSC) stemness. CBX6 thus acts as a transcriptional repressor of pluripotency genes SOX2 and NANOG, and its stability is controlled by the UBE2T–TRIM25 axis.\",\n      \"method\": \"Ubiquitination assays (K48-linkage specific), site-directed mutagenesis (K214R), co-immunoprecipitation of UBE2T–TRIM25–CBX6 complex, CBX6 overexpression/knockdown with SOX2/NANOG reporter assays, organoid models, MMTV-PyMT in vivo mouse model, single-cell RNA-seq\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical ubiquitination site mapped by mutagenesis, E2/E3 complex identified by Co-IP, functional rescue in vivo; multiple orthogonal methods\",\n      \"pmids\": [\"39716485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CBX6 promotes immune evasion in esophageal squamous cell carcinoma by regulating chromatin remodeling via SMARCD1 (a SWI/SNF complex subunit). CBX6 upregulates SMARCD1 expression, which in turn promotes transcription of CCL8 and SLC16A3 (encoding MCT4). This leads to CCL8 secretion and MCT4-mediated lactate efflux, suppressing CD8+ T cell cytotoxicity and promoting tumor development.\",\n      \"method\": \"CBX6 and SMARCD1 knockdown/overexpression in mEC25 cells, co-culture with CD8+ T cells, in vivo tumor models, chromatin remodeling assays, metabolic assays (lactate transport), tissue microarray analysis\",\n      \"journal\": \"Cell biology and toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — genetic epistasis established (CBX6→SMARCD1→CCL8/SLC16A3) with functional rescue; multiple in vitro and in vivo readouts; single lab\",\n      \"pmids\": [\"41219497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CBX6 binds directly to the CA9 (carbonic anhydrase 9) gene promoter in GBM cells, as demonstrated by chromatin immunoprecipitation with multiple primer sets, suggesting CBX6 acts as a transcriptional repressor of CA9. Under hypoxic conditions, CBX6 is downregulated, which is associated with CA9 upregulation, indicating a direct regulatory relationship.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) with multiple primers, shRNA-mediated knockdown, qRT-PCR, functional proliferation/migration/invasion assays\",\n      \"journal\": \"Molecular therapy. Oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with multiple primers confirming direct promoter occupancy combined with KD phenotype; single lab\",\n      \"pmids\": [\"41883712\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CBX6 is a Polycomb group protein that functions as a component of both canonical and non-canonical PRC1 complexes, where its chromodomain binds H3K27me3/H3K9me3 (with low affinity, independently of these marks for chromatin recruitment), and it acts as a transcriptional repressor of target genes (including BST2, CA9, MMP-2, SOX2, and NANOG) through chromatin compaction and epigenetic silencing; its protein stability is regulated by K48-linked polyubiquitination at K214 by the UBE2T–TRIM25 E2–E3 ligase complex leading to proteasomal degradation, and CBX6 is itself transcriptionally repressed by EZH2/PRC2, placing it within a broader Polycomb regulatory network that controls cell identity, stemness, and tumor suppression in a context-dependent manner.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CBX6 is a Polycomb group protein that functions as an epigenetic transcriptional repressor through its chromodomain-mediated reading of H3K27me3 and association with both canonical and non-canonical PRC1 complexes. Its chromodomain engages trimethylated H3K27 via an aromatic cage motif, though CBX6 can also be recruited to chromatin independently of H3K27me3, where it directly binds target gene promoters (BST2, MMP-2, CA9) to repress transcription and suppress proliferation, migration, and invasion [PMID:26985288, PMID:29089522, PMID:30655550, PMID:41883712]. In mouse embryonic stem cells, CBX6 is essential for maintaining the pluripotency network through its dual cPRC1/ncPRC1 association, and its depletion triggers differentiation [PMID:29089522]. CBX6 protein stability is regulated by UBE2T/TRIM25-mediated K48-linked polyubiquitination at K214 leading to proteasomal degradation, and loss of CBX6 through this pathway de-represses pluripotency genes SOX2 and NANOG, promoting cancer stemness [PMID:39716485, PMID:33028834].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing CBX6 as a methyllysine reader resolved how its chromodomain engages H3K27me3 and revealed structural features — an aromatic cage and adjacent hydrophobic pocket — that distinguish it from other Polycomb paralogs.\",\n      \"evidence\": \"Peptidomimetic inhibitor binding assays, molecular dynamics simulations, and SAR analysis\",\n      \"pmids\": [\"26985288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No co-crystal structure of CBX6 chromodomain with H3K27me3 peptide was solved\", \"In-cell target engagement of selective inhibitors not demonstrated\", \"Relative contribution of H3K27me3 reading versus other recruitment mechanisms unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that CBX6 associates with both canonical and non-canonical PRC1 and is essential for ESC pluripotency established it as a non-redundant Polycomb subunit with recruitment mechanisms independent of H3K27me3.\",\n      \"evidence\": \"Reciprocal Co-IP, ChIP, RNA-seq, and genetic depletion with differentiation phenotype in mouse ESCs\",\n      \"pmids\": [\"29089522\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of H3K27me3-independent chromatin recruitment unresolved\", \"Whether CBX6 is essential in vivo during embryonic development not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that CBX6 directly binds and represses the BST2 promoter in breast cancer cells, while itself being negatively regulated by EZH2/PRC2, linked PRC2 and PRC1 components in a regulatory hierarchy controlling tumor-suppressive gene repression.\",\n      \"evidence\": \"ChIP on BST2 promoter, EZH2 knockdown/inhibition with CBX6 expression readout, overexpression functional assays in breast cancer cells\",\n      \"pmids\": [\"30655550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether EZH2 directly methylates the CBX6 locus or acts indirectly not determined\", \"Genome-wide target repertoire of CBX6 in breast cancer cells not mapped\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identifying that CBX6 represses MMP-2 via promoter methylation and is itself degraded by ubiquitin-proteasome pathway in invasive mesothelioma provided the first evidence that post-translational destruction of CBX6 drives de-repression of pro-invasive genes.\",\n      \"evidence\": \"siRNA knockdown, ubiquitination assay, transcriptome analysis, collagen matrix invasion assay in mesothelioma cells\",\n      \"pmids\": [\"33028834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The E3 ligase responsible for CBX6 ubiquitination in mesothelioma was not identified\", \"Whether CBX6 directly binds the MMP-2 promoter by ChIP was not shown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Structure-activity studies on dual CBX6/CBX8 chromodomain inhibitors with anti-proliferative activity in rhabdoid tumor cells validated the chromodomain as a druggable target and refined the pharmacophore for paralog selectivity.\",\n      \"evidence\": \"SAR analysis of peptidomimetic inhibitors with cell proliferation assays in rhabdoid tumor lines\",\n      \"pmids\": [\"34174168\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"On-target mechanism in cells not confirmed by ChIP or chromatin assays\", \"Whether anti-proliferative effects are CBX6-dependent versus CBX8-dependent not dissected\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining UBE2T/TRIM25 as the E2-E3 pair that K48-polyubiquitinates CBX6 at K214 for proteasomal degradation resolved the upstream destruction mechanism and linked CBX6 loss to SOX2/NANOG de-repression and cancer stemness.\",\n      \"evidence\": \"Co-IP of UBE2T-TRIM25-CBX6, K48-linkage-specific and K214-mutant ubiquitination assays, UBE2T ablation in organoids and MMTV-PyMT mouse model\",\n      \"pmids\": [\"39716485\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRIM25 is the sole E3 ligase for CBX6 across cell types not established\", \"How CBX6 occupancy at SOX2/NANOG promoters is regulated was not directly shown by ChIP\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identifying the CBX6-SMARCD1-CCL8/MCT4 axis in esophageal squamous cell carcinoma connected CBX6's transcriptional regulatory function to immune evasion through reduced CD8+ T cell cytotoxicity and metabolic reprogramming.\",\n      \"evidence\": \"CBX6 knockdown with SMARCD1 overexpression rescue, co-culture CD8+ T cell assay, in vivo tumor model\",\n      \"pmids\": [\"41219497\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CBX6 directly binds the SMARCD1 locus or acts indirectly is unresolved\", \"Generalizability of the immune evasion phenotype to other cancer types not tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"ChIP-validated binding of CBX6 to the CA9 promoter in glioblastoma cells extended its direct target gene repertoire and confirmed its tumor-suppressive role through transcriptional repression of CA9.\",\n      \"evidence\": \"ChIP with multiple primers on CA9 promoter, shRNA/overexpression with proliferation and invasion assays in GBM cells\",\n      \"pmids\": [\"41883712\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CBX6 repression of CA9 requires PRC1 complex activity or is PRC1-independent not tested\", \"Genome-wide ChIP-seq for CBX6 in GBM not performed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A genome-wide map of CBX6 chromatin occupancy across cell types is lacking, and the mechanism by which CBX6 is recruited to chromatin independently of H3K27me3 remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No ChIP-seq or CUT&RUN genome-wide profiling of CBX6 in human cells published\", \"H3K27me3-independent recruitment mechanism not defined\", \"Relative functional contributions of cPRC1 vs ncPRC1 association unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 2, 3, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1, 2, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 3, 7]}\n    ],\n    \"complexes\": [\n      \"cPRC1\",\n      \"ncPRC1\"\n    ],\n    \"partners\": [\n      \"UBE2T\",\n      \"TRIM25\",\n      \"EZH2\",\n      \"SMARCD1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CBX6 is a Polycomb group protein that functions as a subunit of both canonical and non-canonical PRC1 complexes, where it contributes to transcriptional repression of target genes involved in stemness, invasion, and immune evasion. Its chromodomain binds H3K27me3 and H3K9me3 with low affinity, but chromatin recruitment occurs largely independently of these marks through non-conserved protein sequences [PMID:18927235, PMID:21047797, PMID:29089522]. CBX6 directly represses promoters of genes including BST2, SOX2, NANOG, MMP-2, and CA9, and its protein stability is controlled by K48-linked polyubiquitination at K214 mediated by the UBE2T–TRIM25 E2–E3 ligase complex, targeting it for proteasomal degradation [PMID:39716485, PMID:30655550, PMID:33028834, PMID:41883712]. CBX6 itself is transcriptionally repressed by EZH2/PRC2, embedding it within a layered Polycomb regulatory circuit that governs cell identity and pluripotency [PMID:30655550, PMID:29089522].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolving how CBX6 associates with chromatin revealed that, unlike the canonical model requiring H3K27me3 recognition, CBX6 binds nucleosomes through non-conserved sequences outside its chromodomain and chromobox, and does so independently of H3K27me3.\",\n      \"evidence\": \"Bimolecular fluorescence complementation and metaphase spread analysis in wild-type and EED-null ES cells with domain deletion constructs\",\n      \"pmids\": [\"18927235\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The non-conserved sequences mediating chromatin association are not mapped to specific residues\",\n        \"Whether this H3K27me3-independent recruitment applies in all cell types is untested\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Structural determination of the CBX6 chromodomain established that it binds H3K27me3 and H3K9me3 with low affinity and cannot discriminate between them, differing from HP1 homologs due to a more tolerant aromatic cage—raising the possibility that CBX6 engages non-histone methylated targets.\",\n      \"evidence\": \"X-ray crystallography, NMR, ITC and fluorescence binding assays, peptide permutation arrays, and mutagenesis\",\n      \"pmids\": [\"21047797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Physiological non-histone binding partners of the CBX6 chromodomain have not been identified\",\n        \"The functional consequence of low-affinity histone mark binding in vivo is unclear\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Proteomic and biochemical studies defined the PRC1 complex landscape, placing CBX6 within canonical PRC1 as a mutually exclusive alternative to RYBP/YAF2 and establishing that CBX-containing PRC1 compacts chromatin but does not stimulate H2AK119ub1 as efficiently as non-canonical complexes.\",\n      \"evidence\": \"Tandem affinity purification–mass spectrometry, ChIP-seq, and biochemical reconstitution with H2A ubiquitination assays\",\n      \"pmids\": [\"21282530\", \"22325352\", \"27705803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific genomic targets uniquely occupied by CBX6-PRC1 versus other CBX-PRC1 variants remain poorly defined\",\n        \"Whether CBX6-PRC1 has distinct functional outputs beyond chromatin compaction is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Chemical biology efforts identified a unique hydrophobic pocket adjacent to the CBX6 chromodomain aromatic cage that enables selective peptidomimetic inhibition, providing a tool compound to dissect CBX6-specific functions.\",\n      \"evidence\": \"Peptidomimetic synthesis with competitive binding assays, SAR, and molecular dynamics simulations\",\n      \"pmids\": [\"26985288\", \"34174168\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"These inhibitors have not been used in genome-wide functional studies to define CBX6-dependent gene programs\",\n        \"In vivo pharmacological validation is lacking\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating CBX6's role in pluripotency, depletion of CBX6 in mouse ESCs destabilized the pluripotency network and triggered differentiation, and CBX6 was found in both canonical and non-canonical PRC1 complexes—a unique feature among CBX paralogs.\",\n      \"evidence\": \"Co-IP, AP-MS, ChIP-seq, shRNA depletion with transcriptomic analysis in wild-type and EED-null ESCs\",\n      \"pmids\": [\"29089522\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which specific PRC1 subcomplexes mediate CBX6's pluripotency function is not dissected\",\n        \"Whether CBX6 depletion effects are cell-autonomous in vivo during embryogenesis is unknown\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"CBX6 was placed within a layered Polycomb regulatory circuit: EZH2/PRC2 transcriptionally represses CBX6 via H3K27me3 at its own locus, and CBX6 in turn represses BST2 by direct promoter binding, establishing a PRC2→CBX6→target gene cascade.\",\n      \"evidence\": \"EZH2 knockdown and inhibitor treatment measuring CBX6 levels; CBX6 overexpression functional assays; ChIP at the BST2 promoter in breast cancer cells\",\n      \"pmids\": [\"30655550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The generality of PRC2-mediated CBX6 repression across tissue types is not established\",\n        \"Whether CBX6 acts on BST2 through canonical PRC1-mediated compaction or another mechanism is unclear\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"CBX6 protein stability was shown to be regulated by constitutive ubiquitination and proteasomal degradation in invasive mesothelioma cells, with loss of CBX6 de-repressing MMP-2 and promoting invasion—linking post-translational control of CBX6 to tumor cell behavior.\",\n      \"evidence\": \"Proteasome inhibitor (MG132) rescue, ubiquitination assays, knockdown with collagen matrix invasion assay and transcriptomics in mesothelioma lines\",\n      \"pmids\": [\"33028834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The E3 ligase responsible for CBX6 degradation in mesothelioma was not identified in this study\",\n        \"Whether epigenetic changes at MMP-2 are direct consequences of CBX6 promoter occupancy was not tested by ChIP\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The molecular mechanism of CBX6 turnover was resolved: UBE2T (E2) and TRIM25 (E3) catalyze K48-linked polyubiquitination at CBX6 K214, targeting it for proteasomal degradation; this degradation de-represses SOX2 and NANOG, enhancing cancer stemness.\",\n      \"evidence\": \"K48-linkage-specific ubiquitination assays, K214R mutagenesis, Co-IP of UBE2T–TRIM25–CBX6, overexpression/knockdown with reporter assays, organoid models, and MMTV-PyMT in vivo tumor model\",\n      \"pmids\": [\"39716485\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether additional ubiquitination sites contribute to CBX6 turnover under different stimuli is untested\",\n        \"The signal or condition that activates UBE2T–TRIM25 toward CBX6 is unknown\",\n        \"Whether K214 ubiquitination also regulates CBX6 in non-malignant contexts is unexplored\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CBX6 was linked to immune evasion through an unexpected mechanism: CBX6 upregulates SMARCD1 (a SWI/SNF subunit), which promotes CCL8 secretion and MCT4-mediated lactate efflux, suppressing CD8+ T cell cytotoxicity in esophageal squamous cell carcinoma.\",\n      \"evidence\": \"CBX6/SMARCD1 knockdown–overexpression epistasis, co-culture with CD8+ T cells, in vivo tumor models, metabolic lactate assays\",\n      \"pmids\": [\"41219497\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether CBX6 directly binds the SMARCD1 locus or acts indirectly is not determined\",\n        \"The relationship between PRC1 membership and SMARCD1/SWI-SNF regulation is mechanistically unclear\",\n        \"Generalizability beyond ESCC is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include identifying the full set of direct CBX6-PRC1 genomic targets, the physiological non-histone ligands of its chromodomain, the signals governing UBE2T–TRIM25 activation, and whether CBX6's non-canonical PRC1 membership has distinct functional outputs from its canonical PRC1 role.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No genome-wide direct target map (ChIP-seq for CBX6 occupancy) exists in most cancer contexts\",\n        \"Non-histone chromodomain ligands remain unidentified\",\n        \"In vivo developmental phenotype of CBX6 knockout has not been reported\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [1, 4, 11]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [8, 14]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8, 9, 12, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2, 7]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 3, 7]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [8, 9, 12, 14]}\n    ],\n    \"complexes\": [\n      \"PRC1 (canonical)\",\n      \"PRC1 (non-canonical)\"\n    ],\n    \"partners\": [\n      \"RING1B\",\n      \"PCGF2\",\n      \"UBE2T\",\n      \"TRIM25\",\n      \"EZH2\",\n      \"SMARCD1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}