{"gene":"SAFB","run_date":"2026-06-10T07:46:29","timeline":{"discoveries":[{"year":1996,"finding":"SAF-B (SAFB1) was purified from HeLa cells as a novel nuclear protein that specifically binds scaffold/matrix attachment region (S/MAR) DNA. The cDNA encodes an 849-amino acid protein with two putative bipartite nuclear localization signals and aberrant SDS-PAGE migration due to high charged residue content. SAF-B was found as an abundant chromatin component but not a nuclear matrix component.","method":"Protein purification to near-homogeneity, immunoscreening cDNA library, antibody generation, subcellular fractionation","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical purification, cDNA cloning, and fractionation in a foundational single study with multiple orthogonal methods","pmids":["8600450"],"is_preprint":false},{"year":1997,"finding":"HET (SAFB1) binds to the hsp27 promoter region containing an imperfect ERE and TATA box. A GST-fusion of partial HET clone demonstrated direct binding to the hsp27 promoter fragment in gel-retardation assays. HET localizes to the nuclear matrix in breast cancer cell lines, and overexpression caused a dose-dependent decrease of hsp27 promoter activity in transient transfection reporter assays.","method":"Gel-shift (EMSA), GST-pulldown, nuclear matrix fractionation, transient transfection with luciferase reporter","journal":"Journal of cellular biochemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (EMSA, GST-fusion binding, fractionation, reporter assay) in a single study","pmids":["9328833"],"is_preprint":false},{"year":1998,"finding":"SAF-B interacts with RNA polymerase II and a subset of SR proteins (serine/arginine-rich RNA processing factors). SAF-B localizes to the nucleus in a speckled pattern co-incident with SR protein SC35. Overexpression of SAF-B induced an increase of the 10S E1A splice product and repressed activity of an S/MAR-flanked CAT reporter gene, indicating SAF-B couples S/MAR chromatin organization with transcription and pre-mRNA splicing.","method":"Co-immunoprecipitation, immunofluorescence colocalization, E1A splicing reporter assay, CAT reporter assay with S/MAR elements","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP with RNA Pol II and SR proteins, colocalization, and functional splicing/reporter assays in one study","pmids":["9671816"],"is_preprint":false},{"year":2000,"finding":"HET/SAF-B is an estrogen receptor (ER)-interacting protein. In vitro binding assays showed HET binds to the ER DNA-binding domain and hinge region. Co-immunoprecipitation revealed HET/SAF-B and ER associate in cell lines with or without estradiol, but binding is increased by tamoxifen. HET/SAF-B enhances tamoxifen antagonism of estrogen-induced ER transactivation and, at high concentrations, represses both estrogen- and tamoxifen-induced ER activity in a manner dependent on ER-DBD interaction.","method":"In vitro binding assay, co-immunoprecipitation, transactivation reporter assay","journal":"Molecular endocrinology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vitro binding plus reciprocal co-IP plus functional reporter assay with domain-mapping, multiple orthogonal methods in one study","pmids":["10707955"],"is_preprint":false},{"year":2000,"finding":"SAF-B interacts specifically with p45 and p42 isoforms of AUF1/hnRNP D (but not p40/p37) via yeast two-hybrid and co-localizes with these isoforms as nuclear speckles. The p45/p42-specific C-terminal sequence mediates nuclear retention and interaction with SAF-B. The p45/p42–SAF-B complex acts as a negative regulator of gene expression.","method":"Yeast two-hybrid screening, nuclear colocalization (immunofluorescence), heterokaryon shuttling assay, gene expression reporter assay","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid plus colocalization; interaction confirmed in two ways but no reciprocal Co-IP from mammalian cells reported","pmids":["10933876"],"is_preprint":false},{"year":2000,"finding":"Overexpression of HET/SAF-B caused growth arrest, formation of multinucleated cells, and was inversely correlated with cell proliferation in breast cancer cell lines, demonstrating a direct role for SAFB1 in cell division and growth control.","method":"Transient transfection with GFP-fusion, cell proliferation assays, Western blot in breast tumor samples","journal":"Clinical cancer research : an official journal of the American Association for Cancer Research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — GFP-fusion overexpression phenotype and multiple approaches (modulation methods) from single lab","pmids":["10999774"],"is_preprint":false},{"year":2005,"finding":"SAFB1 interacts directly with the nuclear receptor corepressor N-CoR. This interaction is mediated in vitro and in vivo through the C-terminal region of SAFB1 (aa 600–915) and N-terminal region of N-CoR (aa 1–373). SAFB1 and N-CoR are co-recruited to the pS2 promoter in the absence of estrogen and are co-released upon estrogen addition. SAFB1-mediated repression of ER activity is significantly reduced by N-CoR siRNA knockdown, indicating the interaction is necessary for SAFB1's repressive activity.","method":"Co-immunoprecipitation, co-fractionation, colocalization, in vitro binding with defined domains, siRNA knockdown, chromatin immunoprecipitation (ChIP), reporter assay","journal":"Molecular endocrinology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (reciprocal Co-IP, in vitro binding with domain mapping, ChIP, siRNA functional rescue) from single lab with strong mechanistic detail","pmids":["16195251"],"is_preprint":false},{"year":2007,"finding":"During apoptosis, SAFB1 undergoes dynamic relocalization: it moves to the nucleolus within 15 min of apoptosis induction (before cytochrome c release), then forms a peri-nucleolar ring-like structure (after cytochrome c release, before PARP cleavage). The peri-nucleolar ring depends on RNA integrity and is mediated by the S/K and R/E coiled-coil domains (not the SAP DNA-binding or RRM RNA-binding domains). SAFB1 is subsequently cleaved by caspase-3, with the determinant for cleavage located in the DNA-binding domain.","method":"Live-cell fluorescence imaging, deletion mutant analysis, RNase treatment, caspase-3 cleavage assay, time-course fractionation","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with domain deletion mutants and biochemical caspase cleavage assay, single lab","pmids":["17643427"],"is_preprint":false},{"year":2008,"finding":"SAFB1 directly binds the E-box element of the human xanthine oxidoreductase (hXOR) promoter. SAFB1, Ku86, and BRG1 associate with each other in pulldown, co-immunoprecipitation, and ChIP assays. SAFB1 silencing increases hXOR expression. Oncostatin M (OSM) induces phosphorylation of SAFB1 and promotes hXOR mRNA expression in a manner inhibited by silencing DNA-PK catalytic subunit or SAFB1.","method":"GST-pulldown, co-immunoprecipitation, chromatin immunoprecipitation, siRNA knockdown, promoter reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (pulldown, Co-IP, ChIP, KD) from single lab","pmids":["18772145"],"is_preprint":false},{"year":2009,"finding":"SAFB1 and SAFB2 occupy promoters of endogenous target genes including immune regulators and apoptotic genes (BBC3, NEDD9, OPG) in MCF-7 cells. ChIP-on-chip identified 541 SAFB1/SAFB2-binding sites. Most target genes are induced upon SAFB1/SAFB2 depletion. 12% of estrogen-regulated genes depend on SAFB1, primarily estrogen-repressed apoptotic genes, confirming SAFB1's primary role as a corepressor.","method":"Chromatin immunoprecipitation-on-chip (ChIP-on-chip), gene expression microarray, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-scale ChIP-on-chip combined with expression arrays and siRNA, single lab","pmids":["19901029"],"is_preprint":false},{"year":2013,"finding":"SAFB1 (chromatin scaffold protein) is a component of the DNA damage response. SAFB1 undergoes highly dynamic exchange at damaged chromatin in a PARP1- and poly(ADP-ribose)-dependent manner (measured by FRAP). SAFB1 cooperates with histone acetylation to allow efficient γH2AX spreading and genotoxic stress signaling. Loss of SAFB1 impairs cell-cycle checkpoint activation and increases susceptibility to replicative stress.","method":"FRAP (live-cell imaging at damaged chromatin), siRNA knockdown, γH2AX spreading assay, cell-cycle checkpoint assay, PARP inhibitor treatment","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — FRAP directly measures dynamic exchange at damage sites, combined with PAR-dependency assay, γH2AX spreading, and checkpoint functional readouts; multiple orthogonal approaches","pmids":["24055346"],"is_preprint":false},{"year":2013,"finding":"Safb1 functions as a positive regulator of myogenic differentiation. Safb1 co-immunoprecipitated with MyoD and co-localized on myogenic gene promoters. Knockdown of Safb1 caused persistence of the repressive H3K27me3 mark and Polycomb methyltransferase Ezh2 at myogenic promoters, and blocked recruitment of myogenin and SWI/SNF ATPase Brg1. Overexpression of Safb1 caused premature expression of muscle structural proteins and enlarged myotubes.","method":"Co-immunoprecipitation with MyoD, ChIP for histone marks and chromatin regulators, siRNA knockdown, overexpression in C2C12 myoblasts","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ChIP with multiple marks, and gain/loss-of-function with defined cellular phenotype, multiple orthogonal methods in single study","pmids":["23609547"],"is_preprint":false},{"year":2015,"finding":"SAFB is SUMOylated by SUMO-1 at ribosomal protein gene promoters. SUMOylated SAFB stimulates both RNA polymerase II binding to promoters and pre-mRNA splicing. Depletion of SAFB decreased RNA Pol II binding to promoters and impaired nuclear mRNA processing without affecting mRNA stability.","method":"ChIP for SUMO-1 and RNA Pol II, SAFB depletion (siRNA), splicing assays, promoter binding assays","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and siRNA knockdown with functional readouts from single lab; SUMOylation of SAFB inferred from ChIP co-occupancy rather than direct SUMO modification mapping","pmids":["25800734"],"is_preprint":false},{"year":2015,"finding":"iCLIP mapping demonstrated that SAFB1 binds RNA genome-wide with enrichment in exons, ncRNAs, 3' and 5' UTRs, recognizing a purine-rich GAAGA (core AGA/GAA/AAG) motif. SAFB1 regulates alternative splicing of NCAM1 via these motifs (mutating the AGA/GAA/AAG sites abolished SAFB1-dependent splicing changes). SAFB1 knockdown altered dendritic spine density in hippocampal neurons.","method":"iCLIP (individual-nucleotide resolution CLIP), RT-PCR, NCAM1 minigene splicing assay with motif mutagenesis, exon array, neuronal knockdown and spine density imaging","journal":"BMC biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — iCLIP provides nucleotide-resolution RNA binding map, corroborated by minigene mutagenesis establishing motif requirement, and neuronal functional phenotype; multiple orthogonal methods in single study","pmids":["26694817"],"is_preprint":false},{"year":2016,"finding":"FUS interacts with nuclear matrix-associated protein SAFB1 in a DNA-dependent manner, as shown by yeast two-hybrid screening and co-immunoprecipitation. The N-terminal SAP (DNA-binding) domain of SAFB1 is required for its localization to the chromatin-bound fraction and for splicing regulation. Depletion of SAFB1 reduced FUS localization to the chromatin-bound fraction and splicing activity, suggesting SAFB1 tethers FUS to chromatin. FUS and SAFB1 also interact with androgen receptor (AR) to regulate ligand-dependent transcription. ALS-linked FUS mutants sequestered endogenous SAFB1 into cytoplasmic aggregates.","method":"Yeast two-hybrid, co-immunoprecipitation, chromatin fractionation, siRNA knockdown, splicing assay, AR transactivation assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by Co-IP, chromatin fractionation with domain-mapping, and functional splicing/transcription readouts; single lab","pmids":["27731383"],"is_preprint":false},{"year":2017,"finding":"SAFB directly binds the TAK1 promoter (shown by ChIP) and represses TAK1 transcription, thereby suppressing downstream NF-κB signaling. Ectopic SAFB expression inhibited NF-κB activity and aggressive CRC phenotypes in vitro and in vivo; overexpression of TAK1 rescued these effects, establishing the SAFB–TAK1–NF-κB axis.","method":"Chromatin immunoprecipitation (ChIP), luciferase reporter assay, Western blot, RT-PCR, siRNA/overexpression in vitro and in vivo (xenograft)","journal":"Clinical cancer research : an official journal of the American Association for Cancer Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP establishes direct promoter binding, epistasis with TAK1 overexpression rescue, in vitro and in vivo functional data; single lab","pmids":["28912140"],"is_preprint":false},{"year":2019,"finding":"SAFB interacts with major satellite repeat RNAs via its R/G-rich region, and these RNAs promote phase separation driven by SAFB. Depletion of SAFB leads to decondensation of pericentromeric heterochromatin, increased interchromosomal interactions adjacent to pericentromeric regions, and decreased genomic compartmentalization, demonstrating SAFB stabilizes heterochromatin architecture through an RNA-dependent phase separation mechanism.","method":"RNA immunoprecipitation, phase separation assay, Hi-C (3D genome organization), SAFB depletion (siRNA/knockout), domain mapping of R/G-rich region","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — Hi-C genome organization, RNA-IP, phase separation assay, and domain-specific loss-of-function provide multiple orthogonal lines of evidence in one study","pmids":["31677973"],"is_preprint":false}],"current_model":"SAFB1 (HET/SAF-B) is a multifunctional nuclear scaffold protein that directly binds S/MAR DNA and RNA (via a purine-rich GAAGA motif), couples chromatin organization to transcription and pre-mRNA splicing by interacting with RNA Pol II, SR proteins, FUS, and MyoD, functions as an estrogen receptor corepressor through direct ER binding (enhanced by tamoxifen) and cooperative interaction with N-CoR, represses target gene transcription by binding promoter elements (including the hsp27 and hXOR promoters and the TAK1 promoter to suppress NF-κB), undergoes SUMO-1 modification to stimulate Pol II recruitment and splicing at ribosomal protein genes, is dynamically recruited to damaged chromatin in a PARP1/PAR-dependent manner to facilitate γH2AX spreading and checkpoint activation, stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation via its R/G-rich region, and is cleaved by caspase-3 during apoptosis after a characteristic nucleolar-to-peri-nucleolar redistribution mediated by its coiled-coil domains."},"narrative":{"mechanistic_narrative":"SAFB (SAFB1; also called HET/SAF-B) is a multifunctional nuclear scaffold protein that directly binds scaffold/matrix attachment region (S/MAR) DNA and integrates higher-order chromatin organization with transcription and RNA processing [PMID:8600450, PMID:9671816]. Through its SAP DNA-binding domain it tethers itself to chromatin and physically associates with RNA polymerase II and SR splicing factors, localizing to SC35 nuclear speckles and coupling S/MAR chromatin to pre-mRNA splicing [PMID:9671816, PMID:27731383]; SUMO-1 modification at ribosomal protein gene promoters enhances Pol II recruitment and splicing [PMID:25800734]. iCLIP maps SAFB1 to a purine-rich GAAGA motif genome-wide and shows it controls alternative splicing of targets such as NCAM1, with consequences for neuronal dendritic spine density [PMID:26694817]. SAFB acts predominantly as a transcriptional corepressor: it binds the estrogen receptor DNA-binding domain (an interaction strengthened by tamoxifen) and cooperates with the corepressor N-CoR, which is required for its repressive activity, to silence estrogen-repressed apoptotic genes [PMID:10707955, PMID:16195251, PMID:19901029]. It also directly represses defined promoters including hsp27, the hXOR E-box (in complex with Ku86 and BRG1), and the TAK1 promoter, the latter suppressing downstream NF-κB signaling and tumor-aggressive phenotypes [PMID:9328833, PMID:18772145, PMID:28912140]. Conversely, SAFB1 promotes myogenic differentiation by associating with MyoD and enabling loss of repressive H3K27me3/Ezh2 and recruitment of myogenin and Brg1 at muscle gene promoters [PMID:23609547]. SAFB1 is recruited to damaged chromatin in a PARP1/poly(ADP-ribose)-dependent manner to facilitate γH2AX spreading and checkpoint activation [PMID:24055346], and it stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation mediated by its R/G-rich region binding satellite repeat RNAs [PMID:31677973]. During apoptosis SAFB1 relocalizes from nucleolus to a peri-nucleolar ring via its coiled-coil domains and is cleaved by caspase-3 [PMID:17643427].","teleology":[{"year":1996,"claim":"Established the molecular identity of SAFB as a chromatin protein that specifically recognizes S/MAR DNA, defining its foundational role in nuclear architecture.","evidence":"Protein purification, cDNA cloning, and subcellular fractionation from HeLa cells","pmids":["8600450"],"confidence":"High","gaps":["No functional consequence of S/MAR binding established","Domain responsible for DNA binding not yet mapped"]},{"year":1997,"claim":"Showed SAFB directly binds a specific promoter (hsp27) and represses its activity, introducing SAFB as a sequence-targeted transcriptional repressor.","evidence":"EMSA, GST-pulldown, nuclear matrix fractionation, and luciferase reporter assays in breast cancer cells","pmids":["9328833"],"confidence":"High","gaps":["Mechanism of repression not defined","No corepressor partner identified"]},{"year":1998,"claim":"Connected SAFB's chromatin role to RNA processing by demonstrating physical and functional coupling with RNA Pol II and SR proteins.","evidence":"Co-IP, SC35 colocalization, and E1A/S-MAR splicing and CAT reporter assays","pmids":["9671816"],"confidence":"High","gaps":["Direct RNA target sequences not identified","Domain mediating SR-protein/Pol II contact unmapped"]},{"year":2000,"claim":"Defined SAFB as an estrogen receptor corepressor by mapping its binding to the ER DNA-binding/hinge region and showing tamoxifen-enhanced antagonism.","evidence":"In vitro binding, co-IP, and ER transactivation reporter assays with domain mapping","pmids":["10707955"],"confidence":"High","gaps":["Corepressor machinery recruited by SAFB not yet identified","Endogenous ER target genes not defined"]},{"year":2000,"claim":"Expanded SAFB's RNA-processing interactome and linked it to negative gene regulation through isoform-specific binding to AUF1/hnRNP D.","evidence":"Yeast two-hybrid, nuclear colocalization, heterokaryon shuttling, and reporter assays","pmids":["10933876"],"confidence":"Medium","gaps":["No reciprocal Co-IP from mammalian cells","Target transcripts of the complex not identified"]},{"year":2000,"claim":"Linked SAFB to growth control by showing overexpression drives growth arrest and multinucleation in breast cancer cells.","evidence":"GFP-fusion overexpression, proliferation assays, and tumor sample Western blots","pmids":["10999774"],"confidence":"Medium","gaps":["Molecular basis of growth arrest unresolved","Single-lab overexpression phenotype"]},{"year":2005,"claim":"Identified N-CoR as the corepressor required for SAFB-mediated ER repression, providing a mechanistic basis for its repressive activity at endogenous promoters.","evidence":"Reciprocal Co-IP, in vitro domain-mapped binding, ChIP at pS2, and siRNA functional rescue","pmids":["16195251"],"confidence":"High","gaps":["Whether additional corepressors act at other targets unknown","Dynamics of co-release upon estrogen not structurally resolved"]},{"year":2008,"claim":"Demonstrated context-specific repression and signal-responsive regulation of SAFB via the hXOR promoter and an OSM/DNA-PK phosphorylation input.","evidence":"GST-pulldown, Co-IP, ChIP, siRNA, and promoter reporter assays","pmids":["18772145"],"confidence":"Medium","gaps":["Phosphorylation sites on SAFB not mapped","Functional role of Ku86/BRG1 association not dissected"]},{"year":2009,"claim":"Defined the genome-wide promoter occupancy and corepressor logic of SAFB1/SAFB2, confirming a predominant role in repressing estrogen-regulated apoptotic genes.","evidence":"ChIP-on-chip, expression microarray, and siRNA knockdown in MCF-7 cells","pmids":["19901029"],"confidence":"Medium","gaps":["Direct vs indirect target distinction limited","Functional redundancy of SAFB1 vs SAFB2 not resolved"]},{"year":2013,"claim":"Placed SAFB1 in the DNA damage response as a PARP1/PAR-recruited factor enabling γH2AX spreading and checkpoint activation.","evidence":"FRAP at damage sites, PARP inhibition, γH2AX spreading, and checkpoint assays with siRNA","pmids":["24055346"],"confidence":"High","gaps":["Direct PAR-binding domain not defined","Mechanism coupling SAFB to γH2AX spreading unresolved"]},{"year":2013,"claim":"Revealed a positive transcriptional role for SAFB1 in myogenic differentiation by relieving Polycomb repression and enabling myogenin/Brg1 recruitment.","evidence":"Co-IP with MyoD, ChIP for histone marks and chromatin regulators, and gain/loss-of-function in C2C12 cells","pmids":["23609547"],"confidence":"High","gaps":["How SAFB1 directs Ezh2/H3K27me3 removal mechanistically unknown","Generality beyond muscle lineage untested"]},{"year":2015,"claim":"Showed SUMO-1 modification at ribosomal protein gene promoters as a switch that stimulates Pol II recruitment and pre-mRNA splicing by SAFB.","evidence":"ChIP for SUMO-1 and Pol II, siRNA depletion, and splicing assays","pmids":["25800734"],"confidence":"Medium","gaps":["SUMOylation inferred from ChIP co-occupancy rather than direct site mapping","SUMO E3 ligase not identified"]},{"year":2015,"claim":"Provided a nucleotide-resolution RNA-binding map defining the GAAGA motif and demonstrating direct control of alternative splicing with a neuronal phenotype.","evidence":"iCLIP, NCAM1 minigene mutagenesis, exon array, and hippocampal neuron knockdown","pmids":["26694817"],"confidence":"High","gaps":["Structural basis of motif recognition unknown","Breadth of physiologically relevant splicing targets incomplete"]},{"year":2016,"claim":"Established SAFB1 as a chromatin tether for FUS via its SAP domain and linked it to AR-regulated transcription and ALS-relevant cytoplasmic sequestration.","evidence":"Yeast two-hybrid, Co-IP, chromatin fractionation with domain mapping, and splicing/AR transactivation assays","pmids":["27731383"],"confidence":"Medium","gaps":["DNA-dependence of FUS interaction not fully resolved","Disease relevance of sequestration in patient tissue untested"]},{"year":2017,"claim":"Defined the SAFB–TAK1–NF-κB axis whereby SAFB directly represses TAK1 to suppress NF-κB signaling and colorectal cancer aggressiveness.","evidence":"ChIP, reporter assays, and TAK1 rescue epistasis in vitro and in xenografts","pmids":["28912140"],"confidence":"Medium","gaps":["Whether N-CoR or other corepressors mediate TAK1 repression untested","Single-lab in vivo model"]},{"year":2019,"claim":"Demonstrated that SAFB stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation, defining a structural genome-organizing function.","evidence":"RNA-IP of satellite RNAs, phase separation assays, Hi-C, and R/G-rich domain loss-of-function","pmids":["31677973"],"confidence":"High","gaps":["Quantitative phase-separation parameters in vivo not defined","How this links to its transcriptional/splicing roles unclear"]},{"year":null,"claim":"It remains unresolved how SAFB's distinct activities — S/MAR scaffolding, RNA-guided phase separation, sequence-specific transcriptional repression, splicing regulation, and DNA-damage signaling — are coordinated and switched within a single protein.","evidence":"","pmids":[],"confidence":"Low","gaps":["No integrated model linking phase separation, chromatin scaffolding, and transcriptional output","Post-translational switches (SUMO, phosphorylation, caspase cleavage) not unified","Functional division of labor between SAFB1 and SAFB2 not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,1,8,15]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[13,16]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,6,9,11,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,14]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[7]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[0,16]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,6,9,15]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2,13,14]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[10]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[11,16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,15]}],"complexes":[],"partners":["ESR1","NCOR1","FUS","MYOD","AUF1/HNRNP D","RNA POL II","BRG1","KU86"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q15424","full_name":"Scaffold attachment factor B1","aliases":["HSP27 estrogen response element-TATA box-binding protein","HSP27 ERE-TATA-binding protein"],"length_aa":915,"mass_kda":102.6,"function":"Binds to scaffold/matrix attachment region (S/MAR) DNA and forms a molecular assembly point to allow the formation of a 'transcriptosomal' complex (consisting of SR proteins and RNA polymerase II) coupling transcription and RNA processing (PubMed:9671816). Functions as an estrogen receptor corepressor and can also bind to the HSP27 promoter and decrease its transcription (PubMed:12660241). Thereby acts as a negative regulator of cell proliferation (PubMed:12660241). When associated with RBMX, binds to and stimulates transcription from the SREBF1 promoter (By similarity)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q15424/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SAFB","classification":"Not Classified","n_dependent_lines":152,"n_total_lines":1208,"dependency_fraction":0.12582781456953643},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RBM14","stoichiometry":4.0},{"gene":"SNRPC","stoichiometry":4.0},{"gene":"ATG101","stoichiometry":0.2},{"gene":"ATG13","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2},{"gene":"DDX21","stoichiometry":0.2},{"gene":"RBMX","stoichiometry":0.2},{"gene":"RNF40","stoichiometry":0.2},{"gene":"SNRPA","stoichiometry":0.2},{"gene":"SNRPB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SAFB","total_profiled":1310},"omim":[{"mim_id":"620992","title":"SAFB-LIKE TRANSCRIPTION MODULATOR; 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chromatin from a repressed to an activated state.","date":"2013","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/23609547","citation_count":27,"is_preprint":false},{"pmid":"24448643","id":"PMC_24448643","title":"Natural variation of heterokaryon incompatibility gene het-c in Podospora anserina reveals diversifying selection.","date":"2014","source":"Molecular biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/24448643","citation_count":27,"is_preprint":false},{"pmid":"18802666","id":"PMC_18802666","title":"Flexible heteroarotinoid (Flex-Het) SHetA2 inhibits angiogenesis in vitro and in vivo.","date":"2008","source":"Investigational new drugs","url":"https://pubmed.ncbi.nlm.nih.gov/18802666","citation_count":27,"is_preprint":false},{"pmid":"28777818","id":"PMC_28777818","title":"Gluc-HET, a complementary chick embryo model for the characterization of antidiabetic compounds.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28777818","citation_count":27,"is_preprint":false},{"pmid":"26694817","id":"PMC_26694817","title":"iCLIP identifies novel roles for SAFB1 in regulating RNA processing and neuronal function.","date":"2015","source":"BMC biology","url":"https://pubmed.ncbi.nlm.nih.gov/26694817","citation_count":26,"is_preprint":false},{"pmid":"18772145","id":"PMC_18772145","title":"Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18772145","citation_count":26,"is_preprint":false},{"pmid":"9435787","id":"PMC_9435787","title":"Reactivity in vegetative incompatibility of the HET-E protein of the fungus Podospora anserina is dependent on GTP-binding activity and a WD40 repeated domain.","date":"1997","source":"Molecular & general genetics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/9435787","citation_count":26,"is_preprint":false},{"pmid":"16093664","id":"PMC_16093664","title":"Heterochromatic distribution of HeT-A- and TART-like sequences in several Drosophila species.","date":"2005","source":"Cytogenetic and genome research","url":"https://pubmed.ncbi.nlm.nih.gov/16093664","citation_count":25,"is_preprint":false},{"pmid":"28074361","id":"PMC_28074361","title":"Partially-deuterated samples of HET-s(218-289) fibrils: assignment and deuterium isotope effect.","date":"2017","source":"Journal of biomolecular NMR","url":"https://pubmed.ncbi.nlm.nih.gov/28074361","citation_count":24,"is_preprint":false},{"pmid":"22677387","id":"PMC_22677387","title":"Degradation of fungal prion HET-s(218-289) induces formation of a generic amyloid fold.","date":"2012","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/22677387","citation_count":24,"is_preprint":false},{"pmid":"7517558","id":"PMC_7517558","title":"Drosophila telomere transposon HeT-A produces a transcript with tightly bound protein.","date":"1994","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/7517558","citation_count":24,"is_preprint":false},{"pmid":"8889517","id":"PMC_8889517","title":"Escape from het-6 incompatibility in Neurospora crassa partial diploids involves preferential deletion within the ectopic segment.","date":"1996","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8889517","citation_count":24,"is_preprint":false},{"pmid":"22817742","id":"PMC_22817742","title":"SAFB1- and SAFB2-mediated transcriptional repression: relevance to cancer.","date":"2012","source":"Biochemical Society transactions","url":"https://pubmed.ncbi.nlm.nih.gov/22817742","citation_count":23,"is_preprint":false},{"pmid":"24380733","id":"PMC_24380733","title":"Distribution and evolution of het gene homologs in the basidiomycota.","date":"2013","source":"Fungal genetics and biology : FG & B","url":"https://pubmed.ncbi.nlm.nih.gov/24380733","citation_count":23,"is_preprint":false},{"pmid":"20164530","id":"PMC_20164530","title":"Structural determination and tryptophan fluorescence of heterokaryon incompatibility C2 protein (HET-C2), a fungal glycolipid transfer protein (GLTP), provide novel insights into glycolipid specificity and membrane interaction by the GLTP fold.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20164530","citation_count":23,"is_preprint":false},{"pmid":"8391971","id":"PMC_8391971","title":"The genomic organization of HeT-A retroposons in Drosophila melanogaster.","date":"1993","source":"Chromosoma","url":"https://pubmed.ncbi.nlm.nih.gov/8391971","citation_count":23,"is_preprint":false},{"pmid":"11035941","id":"PMC_11035941","title":"Molecular and functional analyses of incompatibility genes at het-6 in a population of Neurospora crassa.","date":"2000","source":"Fungal genetics and biology : FG & B","url":"https://pubmed.ncbi.nlm.nih.gov/11035941","citation_count":23,"is_preprint":false},{"pmid":"11815245","id":"PMC_11815245","title":"Some new methodological aspects of the hen's egg test for micronucleus induction (HET-MN).","date":"2002","source":"Mutation research","url":"https://pubmed.ncbi.nlm.nih.gov/11815245","citation_count":23,"is_preprint":false},{"pmid":"26219477","id":"PMC_26219477","title":"Theme and variations: evolutionary diversification of the HET-s functional amyloid motif.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26219477","citation_count":22,"is_preprint":false},{"pmid":"25259627","id":"PMC_25259627","title":"Structural basis for inhibition of mycobacterial and human adenosine kinase by 7-substituted 7-(Het)aryl-7-deazaadenine ribonucleosides.","date":"2014","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25259627","citation_count":22,"is_preprint":false},{"pmid":"15069641","id":"PMC_15069641","title":"Expression of the telomeric retrotransposon HeT-A in Drosophila melanogaster is correlated with cell proliferation.","date":"2004","source":"Development genes and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/15069641","citation_count":22,"is_preprint":false},{"pmid":"28784759","id":"PMC_28784759","title":"Chaperonin GroEL accelerates protofibril formation and decorates fibrils of the Het-s prion protein.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/28784759","citation_count":21,"is_preprint":false},{"pmid":"26354382","id":"PMC_26354382","title":"Ochratoxin A induces DNA damage and G2 phase arrest in human esophageal epithelium Het-1A cells in vitro.","date":"2015","source":"The Journal of toxicological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/26354382","citation_count":21,"is_preprint":false},{"pmid":"33123313","id":"PMC_33123313","title":"Synergistic Carcinogenesis of HPV18 and MNNG in Het-1A Cells through p62-KEAP1-NRF2 and PI3K/AKT/mTOR Pathway.","date":"2020","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/33123313","citation_count":20,"is_preprint":false},{"pmid":"17643427","id":"PMC_17643427","title":"SAFB re-distribution marks steps of the apoptotic process.","date":"2007","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/17643427","citation_count":19,"is_preprint":false},{"pmid":"27939293","id":"PMC_27939293","title":"Telomeric Retrotransposon HeT-A Contains a Bidirectional Promoter that Initiates Divergent Transcription of piRNA Precursors in Drosophila Germline.","date":"2016","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/27939293","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":46416,"output_tokens":5461,"usd":0.110581,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13342,"output_tokens":4946,"usd":0.09518,"stage2_stop_reason":"end_turn"},"total_usd":0.205761,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"Looking through the abstracts, I need to identify papers about the canonical human/mammalian SAFB (also known as HET or SAFB1) protein, and extract mechanistic findings.\n\nPapers 1-6, 9, 11, 14-15, 17, 20, 22-23, 25-26, 29-30, 32-36, 38-39, 41, 43, 46, 48, 51, 54, 60-61, 69, 72, 84, 96 — these are about fungal HET-s prion or Drosophila HeT-A retrotransposons, not the human SAFB protein. SKIP.\n\nPapers 10, 34, 36, 49, 52, 55, 70-71, 76, 81, 86, 88, 89, 91 — fungal het genes (Neurospora, Podospora). SKIP.\n\nPapers 18, 47 — mouse \"het\" mutation (head tilt/otoconia). SKIP.\n\nPapers 4, 22, 29, 39, 62, 64, 82, 85, 90, 95, 100 — Drosophila HeT-A telomeric elements. SKIP.\n\nPapers 8, 21, 37, 42, 68, 73, 77, 78, 92, 94 — unrelated chemistry/biology. SKIP.\n\nPapers 24, 40, 56, 65, 97, 98 — HET-1A esophageal cell line studies (not SAFB protein). SKIP.\n\nPapers 63 — CLAN/NACHT protein. SKIP.\n\nPapers about SAFB (human): 7, 12, 13, 16, 19, 27, 28, 31, 44, 45, 53, 57, 58, 59, 66, 67, 74, 75, 79, 80, 87, 99. INCLUDE.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"SAF-B (SAFB1) was purified from HeLa cells as a novel nuclear protein that specifically binds scaffold/matrix attachment region (S/MAR) DNA. The cDNA encodes an 849-amino acid protein with two putative bipartite nuclear localization signals and aberrant SDS-PAGE migration due to high charged residue content. SAF-B was found as an abundant chromatin component but not a nuclear matrix component.\",\n      \"method\": \"Protein purification to near-homogeneity, immunoscreening cDNA library, antibody generation, subcellular fractionation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical purification, cDNA cloning, and fractionation in a foundational single study with multiple orthogonal methods\",\n      \"pmids\": [\"8600450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"HET (SAFB1) binds to the hsp27 promoter region containing an imperfect ERE and TATA box. A GST-fusion of partial HET clone demonstrated direct binding to the hsp27 promoter fragment in gel-retardation assays. HET localizes to the nuclear matrix in breast cancer cell lines, and overexpression caused a dose-dependent decrease of hsp27 promoter activity in transient transfection reporter assays.\",\n      \"method\": \"Gel-shift (EMSA), GST-pulldown, nuclear matrix fractionation, transient transfection with luciferase reporter\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (EMSA, GST-fusion binding, fractionation, reporter assay) in a single study\",\n      \"pmids\": [\"9328833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SAF-B interacts with RNA polymerase II and a subset of SR proteins (serine/arginine-rich RNA processing factors). SAF-B localizes to the nucleus in a speckled pattern co-incident with SR protein SC35. Overexpression of SAF-B induced an increase of the 10S E1A splice product and repressed activity of an S/MAR-flanked CAT reporter gene, indicating SAF-B couples S/MAR chromatin organization with transcription and pre-mRNA splicing.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence colocalization, E1A splicing reporter assay, CAT reporter assay with S/MAR elements\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP with RNA Pol II and SR proteins, colocalization, and functional splicing/reporter assays in one study\",\n      \"pmids\": [\"9671816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"HET/SAF-B is an estrogen receptor (ER)-interacting protein. In vitro binding assays showed HET binds to the ER DNA-binding domain and hinge region. Co-immunoprecipitation revealed HET/SAF-B and ER associate in cell lines with or without estradiol, but binding is increased by tamoxifen. HET/SAF-B enhances tamoxifen antagonism of estrogen-induced ER transactivation and, at high concentrations, represses both estrogen- and tamoxifen-induced ER activity in a manner dependent on ER-DBD interaction.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation, transactivation reporter assay\",\n      \"journal\": \"Molecular endocrinology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding plus reciprocal co-IP plus functional reporter assay with domain-mapping, multiple orthogonal methods in one study\",\n      \"pmids\": [\"10707955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SAF-B interacts specifically with p45 and p42 isoforms of AUF1/hnRNP D (but not p40/p37) via yeast two-hybrid and co-localizes with these isoforms as nuclear speckles. The p45/p42-specific C-terminal sequence mediates nuclear retention and interaction with SAF-B. The p45/p42–SAF-B complex acts as a negative regulator of gene expression.\",\n      \"method\": \"Yeast two-hybrid screening, nuclear colocalization (immunofluorescence), heterokaryon shuttling assay, gene expression reporter assay\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid plus colocalization; interaction confirmed in two ways but no reciprocal Co-IP from mammalian cells reported\",\n      \"pmids\": [\"10933876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Overexpression of HET/SAF-B caused growth arrest, formation of multinucleated cells, and was inversely correlated with cell proliferation in breast cancer cell lines, demonstrating a direct role for SAFB1 in cell division and growth control.\",\n      \"method\": \"Transient transfection with GFP-fusion, cell proliferation assays, Western blot in breast tumor samples\",\n      \"journal\": \"Clinical cancer research : an official journal of the American Association for Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — GFP-fusion overexpression phenotype and multiple approaches (modulation methods) from single lab\",\n      \"pmids\": [\"10999774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SAFB1 interacts directly with the nuclear receptor corepressor N-CoR. This interaction is mediated in vitro and in vivo through the C-terminal region of SAFB1 (aa 600–915) and N-terminal region of N-CoR (aa 1–373). SAFB1 and N-CoR are co-recruited to the pS2 promoter in the absence of estrogen and are co-released upon estrogen addition. SAFB1-mediated repression of ER activity is significantly reduced by N-CoR siRNA knockdown, indicating the interaction is necessary for SAFB1's repressive activity.\",\n      \"method\": \"Co-immunoprecipitation, co-fractionation, colocalization, in vitro binding with defined domains, siRNA knockdown, chromatin immunoprecipitation (ChIP), reporter assay\",\n      \"journal\": \"Molecular endocrinology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (reciprocal Co-IP, in vitro binding with domain mapping, ChIP, siRNA functional rescue) from single lab with strong mechanistic detail\",\n      \"pmids\": [\"16195251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"During apoptosis, SAFB1 undergoes dynamic relocalization: it moves to the nucleolus within 15 min of apoptosis induction (before cytochrome c release), then forms a peri-nucleolar ring-like structure (after cytochrome c release, before PARP cleavage). The peri-nucleolar ring depends on RNA integrity and is mediated by the S/K and R/E coiled-coil domains (not the SAP DNA-binding or RRM RNA-binding domains). SAFB1 is subsequently cleaved by caspase-3, with the determinant for cleavage located in the DNA-binding domain.\",\n      \"method\": \"Live-cell fluorescence imaging, deletion mutant analysis, RNase treatment, caspase-3 cleavage assay, time-course fractionation\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with domain deletion mutants and biochemical caspase cleavage assay, single lab\",\n      \"pmids\": [\"17643427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SAFB1 directly binds the E-box element of the human xanthine oxidoreductase (hXOR) promoter. SAFB1, Ku86, and BRG1 associate with each other in pulldown, co-immunoprecipitation, and ChIP assays. SAFB1 silencing increases hXOR expression. Oncostatin M (OSM) induces phosphorylation of SAFB1 and promotes hXOR mRNA expression in a manner inhibited by silencing DNA-PK catalytic subunit or SAFB1.\",\n      \"method\": \"GST-pulldown, co-immunoprecipitation, chromatin immunoprecipitation, siRNA knockdown, promoter reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (pulldown, Co-IP, ChIP, KD) from single lab\",\n      \"pmids\": [\"18772145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SAFB1 and SAFB2 occupy promoters of endogenous target genes including immune regulators and apoptotic genes (BBC3, NEDD9, OPG) in MCF-7 cells. ChIP-on-chip identified 541 SAFB1/SAFB2-binding sites. Most target genes are induced upon SAFB1/SAFB2 depletion. 12% of estrogen-regulated genes depend on SAFB1, primarily estrogen-repressed apoptotic genes, confirming SAFB1's primary role as a corepressor.\",\n      \"method\": \"Chromatin immunoprecipitation-on-chip (ChIP-on-chip), gene expression microarray, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-scale ChIP-on-chip combined with expression arrays and siRNA, single lab\",\n      \"pmids\": [\"19901029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SAFB1 (chromatin scaffold protein) is a component of the DNA damage response. SAFB1 undergoes highly dynamic exchange at damaged chromatin in a PARP1- and poly(ADP-ribose)-dependent manner (measured by FRAP). SAFB1 cooperates with histone acetylation to allow efficient γH2AX spreading and genotoxic stress signaling. Loss of SAFB1 impairs cell-cycle checkpoint activation and increases susceptibility to replicative stress.\",\n      \"method\": \"FRAP (live-cell imaging at damaged chromatin), siRNA knockdown, γH2AX spreading assay, cell-cycle checkpoint assay, PARP inhibitor treatment\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — FRAP directly measures dynamic exchange at damage sites, combined with PAR-dependency assay, γH2AX spreading, and checkpoint functional readouts; multiple orthogonal approaches\",\n      \"pmids\": [\"24055346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Safb1 functions as a positive regulator of myogenic differentiation. Safb1 co-immunoprecipitated with MyoD and co-localized on myogenic gene promoters. Knockdown of Safb1 caused persistence of the repressive H3K27me3 mark and Polycomb methyltransferase Ezh2 at myogenic promoters, and blocked recruitment of myogenin and SWI/SNF ATPase Brg1. Overexpression of Safb1 caused premature expression of muscle structural proteins and enlarged myotubes.\",\n      \"method\": \"Co-immunoprecipitation with MyoD, ChIP for histone marks and chromatin regulators, siRNA knockdown, overexpression in C2C12 myoblasts\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ChIP with multiple marks, and gain/loss-of-function with defined cellular phenotype, multiple orthogonal methods in single study\",\n      \"pmids\": [\"23609547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SAFB is SUMOylated by SUMO-1 at ribosomal protein gene promoters. SUMOylated SAFB stimulates both RNA polymerase II binding to promoters and pre-mRNA splicing. Depletion of SAFB decreased RNA Pol II binding to promoters and impaired nuclear mRNA processing without affecting mRNA stability.\",\n      \"method\": \"ChIP for SUMO-1 and RNA Pol II, SAFB depletion (siRNA), splicing assays, promoter binding assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and siRNA knockdown with functional readouts from single lab; SUMOylation of SAFB inferred from ChIP co-occupancy rather than direct SUMO modification mapping\",\n      \"pmids\": [\"25800734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"iCLIP mapping demonstrated that SAFB1 binds RNA genome-wide with enrichment in exons, ncRNAs, 3' and 5' UTRs, recognizing a purine-rich GAAGA (core AGA/GAA/AAG) motif. SAFB1 regulates alternative splicing of NCAM1 via these motifs (mutating the AGA/GAA/AAG sites abolished SAFB1-dependent splicing changes). SAFB1 knockdown altered dendritic spine density in hippocampal neurons.\",\n      \"method\": \"iCLIP (individual-nucleotide resolution CLIP), RT-PCR, NCAM1 minigene splicing assay with motif mutagenesis, exon array, neuronal knockdown and spine density imaging\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — iCLIP provides nucleotide-resolution RNA binding map, corroborated by minigene mutagenesis establishing motif requirement, and neuronal functional phenotype; multiple orthogonal methods in single study\",\n      \"pmids\": [\"26694817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FUS interacts with nuclear matrix-associated protein SAFB1 in a DNA-dependent manner, as shown by yeast two-hybrid screening and co-immunoprecipitation. The N-terminal SAP (DNA-binding) domain of SAFB1 is required for its localization to the chromatin-bound fraction and for splicing regulation. Depletion of SAFB1 reduced FUS localization to the chromatin-bound fraction and splicing activity, suggesting SAFB1 tethers FUS to chromatin. FUS and SAFB1 also interact with androgen receptor (AR) to regulate ligand-dependent transcription. ALS-linked FUS mutants sequestered endogenous SAFB1 into cytoplasmic aggregates.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, chromatin fractionation, siRNA knockdown, splicing assay, AR transactivation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by Co-IP, chromatin fractionation with domain-mapping, and functional splicing/transcription readouts; single lab\",\n      \"pmids\": [\"27731383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SAFB directly binds the TAK1 promoter (shown by ChIP) and represses TAK1 transcription, thereby suppressing downstream NF-κB signaling. Ectopic SAFB expression inhibited NF-κB activity and aggressive CRC phenotypes in vitro and in vivo; overexpression of TAK1 rescued these effects, establishing the SAFB–TAK1–NF-κB axis.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), luciferase reporter assay, Western blot, RT-PCR, siRNA/overexpression in vitro and in vivo (xenograft)\",\n      \"journal\": \"Clinical cancer research : an official journal of the American Association for Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP establishes direct promoter binding, epistasis with TAK1 overexpression rescue, in vitro and in vivo functional data; single lab\",\n      \"pmids\": [\"28912140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SAFB interacts with major satellite repeat RNAs via its R/G-rich region, and these RNAs promote phase separation driven by SAFB. Depletion of SAFB leads to decondensation of pericentromeric heterochromatin, increased interchromosomal interactions adjacent to pericentromeric regions, and decreased genomic compartmentalization, demonstrating SAFB stabilizes heterochromatin architecture through an RNA-dependent phase separation mechanism.\",\n      \"method\": \"RNA immunoprecipitation, phase separation assay, Hi-C (3D genome organization), SAFB depletion (siRNA/knockout), domain mapping of R/G-rich region\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Hi-C genome organization, RNA-IP, phase separation assay, and domain-specific loss-of-function provide multiple orthogonal lines of evidence in one study\",\n      \"pmids\": [\"31677973\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SAFB1 (HET/SAF-B) is a multifunctional nuclear scaffold protein that directly binds S/MAR DNA and RNA (via a purine-rich GAAGA motif), couples chromatin organization to transcription and pre-mRNA splicing by interacting with RNA Pol II, SR proteins, FUS, and MyoD, functions as an estrogen receptor corepressor through direct ER binding (enhanced by tamoxifen) and cooperative interaction with N-CoR, represses target gene transcription by binding promoter elements (including the hsp27 and hXOR promoters and the TAK1 promoter to suppress NF-κB), undergoes SUMO-1 modification to stimulate Pol II recruitment and splicing at ribosomal protein genes, is dynamically recruited to damaged chromatin in a PARP1/PAR-dependent manner to facilitate γH2AX spreading and checkpoint activation, stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation via its R/G-rich region, and is cleaved by caspase-3 during apoptosis after a characteristic nucleolar-to-peri-nucleolar redistribution mediated by its coiled-coil domains.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SAFB (SAFB1; also called HET/SAF-B) is a multifunctional nuclear scaffold protein that directly binds scaffold/matrix attachment region (S/MAR) DNA and integrates higher-order chromatin organization with transcription and RNA processing [#0, #2]. Through its SAP DNA-binding domain it tethers itself to chromatin and physically associates with RNA polymerase II and SR splicing factors, localizing to SC35 nuclear speckles and coupling S/MAR chromatin to pre-mRNA splicing [#2, #14]; SUMO-1 modification at ribosomal protein gene promoters enhances Pol II recruitment and splicing [#12]. iCLIP maps SAFB1 to a purine-rich GAAGA motif genome-wide and shows it controls alternative splicing of targets such as NCAM1, with consequences for neuronal dendritic spine density [#13]. SAFB acts predominantly as a transcriptional corepressor: it binds the estrogen receptor DNA-binding domain (an interaction strengthened by tamoxifen) and cooperates with the corepressor N-CoR, which is required for its repressive activity, to silence estrogen-repressed apoptotic genes [#3, #6, #9]. It also directly represses defined promoters including hsp27, the hXOR E-box (in complex with Ku86 and BRG1), and the TAK1 promoter, the latter suppressing downstream NF-\\u03baB signaling and tumor-aggressive phenotypes [#1, #8, #15]. Conversely, SAFB1 promotes myogenic differentiation by associating with MyoD and enabling loss of repressive H3K27me3/Ezh2 and recruitment of myogenin and Brg1 at muscle gene promoters [#11]. SAFB1 is recruited to damaged chromatin in a PARP1/poly(ADP-ribose)-dependent manner to facilitate \\u03b3H2AX spreading and checkpoint activation [#10], and it stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation mediated by its R/G-rich region binding satellite repeat RNAs [#16]. During apoptosis SAFB1 relocalizes from nucleolus to a peri-nucleolar ring via its coiled-coil domains and is cleaved by caspase-3 [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established the molecular identity of SAFB as a chromatin protein that specifically recognizes S/MAR DNA, defining its foundational role in nuclear architecture.\",\n      \"evidence\": \"Protein purification, cDNA cloning, and subcellular fractionation from HeLa cells\",\n      \"pmids\": [\"8600450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No functional consequence of S/MAR binding established\", \"Domain responsible for DNA binding not yet mapped\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed SAFB directly binds a specific promoter (hsp27) and represses its activity, introducing SAFB as a sequence-targeted transcriptional repressor.\",\n      \"evidence\": \"EMSA, GST-pulldown, nuclear matrix fractionation, and luciferase reporter assays in breast cancer cells\",\n      \"pmids\": [\"9328833\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of repression not defined\", \"No corepressor partner identified\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Connected SAFB's chromatin role to RNA processing by demonstrating physical and functional coupling with RNA Pol II and SR proteins.\",\n      \"evidence\": \"Co-IP, SC35 colocalization, and E1A/S-MAR splicing and CAT reporter assays\",\n      \"pmids\": [\"9671816\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct RNA target sequences not identified\", \"Domain mediating SR-protein/Pol II contact unmapped\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined SAFB as an estrogen receptor corepressor by mapping its binding to the ER DNA-binding/hinge region and showing tamoxifen-enhanced antagonism.\",\n      \"evidence\": \"In vitro binding, co-IP, and ER transactivation reporter assays with domain mapping\",\n      \"pmids\": [\"10707955\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Corepressor machinery recruited by SAFB not yet identified\", \"Endogenous ER target genes not defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Expanded SAFB's RNA-processing interactome and linked it to negative gene regulation through isoform-specific binding to AUF1/hnRNP D.\",\n      \"evidence\": \"Yeast two-hybrid, nuclear colocalization, heterokaryon shuttling, and reporter assays\",\n      \"pmids\": [\"10933876\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reciprocal Co-IP from mammalian cells\", \"Target transcripts of the complex not identified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Linked SAFB to growth control by showing overexpression drives growth arrest and multinucleation in breast cancer cells.\",\n      \"evidence\": \"GFP-fusion overexpression, proliferation assays, and tumor sample Western blots\",\n      \"pmids\": [\"10999774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of growth arrest unresolved\", \"Single-lab overexpression phenotype\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified N-CoR as the corepressor required for SAFB-mediated ER repression, providing a mechanistic basis for its repressive activity at endogenous promoters.\",\n      \"evidence\": \"Reciprocal Co-IP, in vitro domain-mapped binding, ChIP at pS2, and siRNA functional rescue\",\n      \"pmids\": [\"16195251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional corepressors act at other targets unknown\", \"Dynamics of co-release upon estrogen not structurally resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated context-specific repression and signal-responsive regulation of SAFB via the hXOR promoter and an OSM/DNA-PK phosphorylation input.\",\n      \"evidence\": \"GST-pulldown, Co-IP, ChIP, siRNA, and promoter reporter assays\",\n      \"pmids\": [\"18772145\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphorylation sites on SAFB not mapped\", \"Functional role of Ku86/BRG1 association not dissected\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the genome-wide promoter occupancy and corepressor logic of SAFB1/SAFB2, confirming a predominant role in repressing estrogen-regulated apoptotic genes.\",\n      \"evidence\": \"ChIP-on-chip, expression microarray, and siRNA knockdown in MCF-7 cells\",\n      \"pmids\": [\"19901029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect target distinction limited\", \"Functional redundancy of SAFB1 vs SAFB2 not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed SAFB1 in the DNA damage response as a PARP1/PAR-recruited factor enabling \\u03b3H2AX spreading and checkpoint activation.\",\n      \"evidence\": \"FRAP at damage sites, PARP inhibition, \\u03b3H2AX spreading, and checkpoint assays with siRNA\",\n      \"pmids\": [\"24055346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PAR-binding domain not defined\", \"Mechanism coupling SAFB to \\u03b3H2AX spreading unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a positive transcriptional role for SAFB1 in myogenic differentiation by relieving Polycomb repression and enabling myogenin/Brg1 recruitment.\",\n      \"evidence\": \"Co-IP with MyoD, ChIP for histone marks and chromatin regulators, and gain/loss-of-function in C2C12 cells\",\n      \"pmids\": [\"23609547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SAFB1 directs Ezh2/H3K27me3 removal mechanistically unknown\", \"Generality beyond muscle lineage untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed SUMO-1 modification at ribosomal protein gene promoters as a switch that stimulates Pol II recruitment and pre-mRNA splicing by SAFB.\",\n      \"evidence\": \"ChIP for SUMO-1 and Pol II, siRNA depletion, and splicing assays\",\n      \"pmids\": [\"25800734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SUMOylation inferred from ChIP co-occupancy rather than direct site mapping\", \"SUMO E3 ligase not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Provided a nucleotide-resolution RNA-binding map defining the GAAGA motif and demonstrating direct control of alternative splicing with a neuronal phenotype.\",\n      \"evidence\": \"iCLIP, NCAM1 minigene mutagenesis, exon array, and hippocampal neuron knockdown\",\n      \"pmids\": [\"26694817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of motif recognition unknown\", \"Breadth of physiologically relevant splicing targets incomplete\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established SAFB1 as a chromatin tether for FUS via its SAP domain and linked it to AR-regulated transcription and ALS-relevant cytoplasmic sequestration.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, chromatin fractionation with domain mapping, and splicing/AR transactivation assays\",\n      \"pmids\": [\"27731383\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"DNA-dependence of FUS interaction not fully resolved\", \"Disease relevance of sequestration in patient tissue untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the SAFB\\u2013TAK1\\u2013NF-\\u03baB axis whereby SAFB directly represses TAK1 to suppress NF-\\u03baB signaling and colorectal cancer aggressiveness.\",\n      \"evidence\": \"ChIP, reporter assays, and TAK1 rescue epistasis in vitro and in xenografts\",\n      \"pmids\": [\"28912140\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether N-CoR or other corepressors mediate TAK1 repression untested\", \"Single-lab in vivo model\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated that SAFB stabilizes pericentromeric heterochromatin architecture through RNA-dependent phase separation, defining a structural genome-organizing function.\",\n      \"evidence\": \"RNA-IP of satellite RNAs, phase separation assays, Hi-C, and R/G-rich domain loss-of-function\",\n      \"pmids\": [\"31677973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative phase-separation parameters in vivo not defined\", \"How this links to its transcriptional/splicing roles unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how SAFB's distinct activities \\u2014 S/MAR scaffolding, RNA-guided phase separation, sequence-specific transcriptional repression, splicing regulation, and DNA-damage signaling \\u2014 are coordinated and switched within a single protein.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No integrated model linking phase separation, chromatin scaffolding, and transcriptional output\", \"Post-translational switches (SUMO, phosphorylation, caspase cleavage) not unified\", \"Functional division of labor between SAFB1 and SAFB2 not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1, 8, 15]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [13, 16]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 6, 9, 11, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [0, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 6, 9, 15]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 13, 14]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [11, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ESR1\", \"NCOR1\", \"FUS\", \"MyoD\", \"AUF1/hnRNP D\", \"RNA Pol II\", \"BRG1\", \"Ku86\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}