{"gene":"SAFB2","run_date":"2026-06-10T07:46:29","timeline":{"discoveries":[{"year":2003,"finding":"SAFB2 functions as an estrogen receptor (ERα) corepressor; its overexpression inhibits cell proliferation. SAFB1 and SAFB2 interact directly through a C-terminal domain, resulting in additive transcriptional repression activity. Unlike SAFB1, SAFB2 is found in both cytoplasm and nucleus.","method":"Overexpression/reporter assays for corepressor activity; direct protein interaction demonstrated; subcellular localization by fractionation/imaging","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple functional assays (corepressor, proliferation, interaction), single lab, direct interaction and localization experimentally established","pmids":["12660241"],"is_preprint":false},{"year":2003,"finding":"SAFB2 interacts with vinexin, a protein involved in linking signaling to the cytoskeleton, consistent with its cytoplasmic localization.","method":"Co-immunoprecipitation / interaction assay","journal":"The Journal of biological chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single interaction experiment mentioned in abstract without detailed follow-up","pmids":["12660241"],"is_preprint":false},{"year":2007,"finding":"Endogenous SAFB2 exists in large nuclear complexes (up to 670 kDa), distinct from SAFB1 which is predominantly monomeric or in smaller complexes. Stable core complexes containing SAFB1, SAFB2, Sam68, and hnRNPG exist independently of intact nucleic acids. SAFB2 acts as a negative regulator of a tra2-beta variable exon (alternative splicing). No stable interaction was detected between SAFB proteins and SR or SR-related splicing regulators.","method":"Size-exclusion chromatography, novel monospecific antisera, splicing reporter assays, nucleic-acid-independence experiments","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple orthogonal methods (gel filtration, immunodetection, splicing assays), single lab","pmids":["17200140"],"is_preprint":false},{"year":2012,"finding":"SAFB1 and SAFB2 colocalize with ERα in the nucleus of living cells after estradiol treatment; co-IP confirmed ERα interaction with both SAFB1 and SAFB2 in the presence of E2. FRAP analysis showed that SAFB1 and SAFB2 each decrease ERα intranuclear mobility, and coexpression causes a synergistic reduction in ERα dynamics, leading to cooperative inhibition of ERα-mediated transcription and cell proliferation.","method":"Chimeric fluorescent protein live-cell imaging, Co-immunoprecipitation, Fluorescence Recovery After Photobleaching (FRAP), proliferation assays","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus FRAP with functional readout, single lab, multiple orthogonal methods","pmids":["22566185"],"is_preprint":false},{"year":2015,"finding":"SAFB2-knockout mice are viable and fertile (in contrast to SAFB1-knockout mice), but show significantly increased testis weight associated with an increased number of Sertoli cells. Loss of SAFB2 alters androgen receptor function and expression, implicating SAFB2 in Sertoli cell differentiation and activity.","method":"SAFB2-null mouse generation, histological and cell-count analysis, paralog-specific antibodies for expression analysis","journal":"Disease models & mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean knockout mouse with specific phenotypic readout and mechanistic link to androgen receptor, single lab","pmids":["26092125"],"is_preprint":false},{"year":2020,"finding":"SAFB2 is an accessory protein of the Microprocessor complex required for processing of suboptimal stem-loop structures in clustered primary miRNA transcripts (e.g., pri-miR-15a requires neighboring pri-miR-16-1 and SAFB2 for efficient cleavage). SAFB2 enables binding and processing of suboptimal Microprocessor substrates in cis within clustered pri-miRNA transcripts.","method":"CRISPR/Cas9 screen, biochemical co-factor assays, miRNA processing assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — unbiased CRISPR screen plus mechanistic follow-up in multiple clustered miRNA contexts, rigorous genetic and biochemical validation","pmids":["32502422"],"is_preprint":false},{"year":2023,"finding":"SAFB2 interacts with NFAT5 mRNA (by RIP assay) and destabilizes NFAT5 mRNA, leading to suppression of the Wnt/β-catenin signaling pathway in breast cancer cells. Overexpression of SAFB2 inhibits proliferation, migration, and invasion while promoting apoptosis, effects that are partially rescued by NFAT5 overexpression.","method":"RNA immunoprecipitation (RIP), mRNA stability assay (actinomycin D), western blotting, CCK8/colony formation/EdU proliferation assays, wound healing, transwell assays","journal":"Molecular biotechnology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — RIP plus mRNA stability assay plus functional rescue, single lab with multiple complementary methods","pmids":["36652182"],"is_preprint":false},{"year":2025,"finding":"Epistatic analysis places SAFB2 downstream of ERH in the cluster assistance pathway: ERH may mediate Microprocessor transfer between hairpins, while SAFB2 (especially SAFB2) mediates recognition and stable binding of a suboptimal miRNA hairpin after Microprocessor transfer. SAFB2 associates with the N-terminus of DROSHA. Both SAFB1/2 and ERH are required for Microprocessor feedback regulation via processing of pri-miR-1306.","method":"Mutant cell lines, epistasis genetic tests, biochemical interaction assays, genome-wide miRNA profiling","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis plus biochemical tests, preprint not yet peer-reviewed, single lab","pmids":["bio_10.1101_2025.09.09.675111"],"is_preprint":true},{"year":2025,"finding":"ERH-mediated cluster assistance is independent of its direct association with SAFB2 (as shown by disrupting the ERH-SAFB2 interaction, which did not abolish cluster assistance). Loss of SAFB1/2 and ERH produce overlapping but not identical defects in primary miRNA biogenesis. Both SAFB2 and ERH are required for efficient Microprocessor feedback regulation via pri-miR-1306 processing.","method":"SAFB1/2 deletion and ERH deletion cell lines, miRNA transcriptome profiling, protein interaction disruption experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic knockouts with transcriptome-level phenotyping and mechanistic interaction dissection, preprint not peer-reviewed","pmids":["bio_10.1101_2025.09.23.678008"],"is_preprint":true}],"current_model":"SAFB2 is a multifunctional nuclear (and partially cytoplasmic) scaffold attachment factor that acts as an ERα corepressor by directly interacting with ERα and restricting its intranuclear mobility, forms large nuclear complexes with SAFB1, Sam68, and hnRNPG to negatively regulate alternative splicing, destabilizes NFAT5 mRNA to suppress Wnt/β-catenin signaling, and functions as an accessory factor of the Microprocessor complex—specifically enabling stable binding and cleavage of suboptimal stem-loop hairpins in clustered primary miRNA transcripts after Microprocessor transfer, a step that is epistatic to ERH action in the cluster assistance pathway."},"narrative":{"mechanistic_narrative":"SAFB2 is a multifunctional scaffold attachment factor that acts at the intersection of transcriptional control, RNA processing, and signaling, distributing between the nucleus and cytoplasm [PMID:12660241]. As a transcriptional corepressor it interacts directly with estrogen receptor α (ERα) upon estradiol stimulation and, together with its paralog SAFB1, restricts ERα intranuclear mobility, cooperatively inhibiting ERα-driven transcription and cell proliferation [PMID:12660241, PMID:22566185]. SAFB2 assembles into large nuclear complexes containing SAFB1, Sam68, and hnRNPG that persist independently of nucleic acids and negatively regulate alternative splicing of a tra2-beta variable exon [PMID:17200140]. In small-RNA biogenesis, SAFB2 functions as an accessory factor of the Microprocessor complex, associating with the N-terminus of DROSHA and enabling stable binding and cleavage of suboptimal stem-loop hairpins within clustered primary miRNA transcripts, acting downstream of ERH in the cluster-assistance pathway and contributing to Microprocessor feedback regulation [PMID:32502422, PMID:bio_10.1101_2025.09.09.675111]. SAFB2 also binds and destabilizes NFAT5 mRNA, thereby suppressing Wnt/β-catenin signaling and restraining proliferation, migration, and invasion in breast cancer cells [PMID:36652182]. Consistent with a tissue-specific physiological role, SAFB2-null mice are viable and fertile but display increased testis weight and Sertoli cell number linked to altered androgen receptor function [PMID:26092125].","teleology":[{"year":2003,"claim":"Established SAFB2 as an ERα corepressor and defined its relationship to SAFB1, answering whether the paralog is functionally redundant or distinct.","evidence":"Overexpression/reporter corepressor assays, direct interaction mapping, and subcellular fractionation/imaging","pmids":["12660241"],"confidence":"Medium","gaps":["Did not define the structural basis of ERα repression","Cytoplasmic function of SAFB2 left unexplained","Vinexin interaction noted but not followed up"]},{"year":2007,"claim":"Showed SAFB2 resides in large, stable nuclear core complexes with SAFB1, Sam68, and hnRNPG and regulates alternative splicing, framing it as a scaffold within an RNA-processing assembly rather than a free monomer.","evidence":"Size-exclusion chromatography, monospecific antisera, splicing reporter and nucleic-acid-independence assays","pmids":["17200140"],"confidence":"Medium","gaps":["Stoichiometry and architecture of the 670 kDa complex unresolved","Range of regulated splicing targets not defined","No SR-protein interaction detected, leaving the mechanism of splicing repression open"]},{"year":2012,"claim":"Defined the mechanism of ERα repression by showing SAFB1/SAFB2 reduce ERα intranuclear mobility, explaining how corepression and antiproliferation are achieved.","evidence":"Live-cell fluorescent imaging, reciprocal Co-IP, FRAP, and proliferation assays","pmids":["22566185"],"confidence":"Medium","gaps":["Does not identify the chromatin or genomic loci where ERα is immobilized","Synergy mechanism between paralogs not biochemically defined"]},{"year":2015,"claim":"Provided in vivo physiological role via a knockout, distinguishing SAFB2 from the lethal/infertile SAFB1 phenotype and linking it to androgen receptor function.","evidence":"SAFB2-null mouse with histology, cell counts, and paralog-specific expression analysis","pmids":["26092125"],"confidence":"Medium","gaps":["Molecular basis of altered androgen receptor function not established","Connection between Sertoli cell phenotype and SAFB2's RNA/transcription roles unclear"]},{"year":2020,"claim":"Identified SAFB2 as a Microprocessor accessory factor required for processing suboptimal hairpins in clustered pri-miRNAs, revealing a previously unknown role in miRNA biogenesis.","evidence":"Unbiased CRISPR/Cas9 screen plus biochemical co-factor and miRNA processing assays in clustered contexts (e.g., pri-miR-15a/16-1)","pmids":["32502422"],"confidence":"High","gaps":["Direct contact between SAFB2 and Microprocessor not yet mapped at this stage","Determinants of substrate suboptimality recognition undefined"]},{"year":2025,"claim":"Placed SAFB2 mechanistically within the cluster-assistance pathway, showing it acts downstream of ERH and binds the DROSHA N-terminus to stabilize suboptimal hairpins after Microprocessor transfer.","evidence":"Epistasis genetic tests, biochemical interaction assays, and genome-wide miRNA profiling in mutant cell lines (preprint)","pmids":["bio_10.1101_2025.09.09.675111","bio_10.1101_2025.09.23.678008"],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","ERH-SAFB2 interaction is dispensable for cluster assistance, leaving the functional role of that contact unclear","Structural detail of SAFB2-DROSHA recognition lacking"]},{"year":null,"claim":"How SAFB2's distinct activities — ERα corepression, splicing regulation, mRNA destabilization, and Microprocessor assistance — are integrated, regulated, and partitioned between compartments remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model connecting transcriptional, splicing, and miRNA-processing roles","Regulation of SAFB2 nuclear/cytoplasmic partitioning unknown","Substrate-recognition code for suboptimal pri-miRNA hairpins undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,5,6]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2,5]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6]}],"complexes":["Microprocessor complex","SAFB1-SAFB2-Sam68-hnRNPG nuclear complex"],"partners":["SAFB1","ESR1","DROSHA","ERH","KHDRBS1","RBMX"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q14151","full_name":"Scaffold attachment factor B2","aliases":[],"length_aa":953,"mass_kda":107.5,"function":"Binds to scaffold/matrix attachment region (S/MAR) DNA. Can function as an estrogen receptor corepressor and can also inhibit cell proliferation","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q14151/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SAFB2","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"TOP1","stoichiometry":4.0},{"gene":"ATG101","stoichiometry":0.2},{"gene":"ATG13","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2},{"gene":"DDX21","stoichiometry":0.2},{"gene":"EMC9","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"HMGA1","stoichiometry":0.2},{"gene":"IPO7","stoichiometry":0.2},{"gene":"LSS","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SAFB2","total_profiled":1310},"omim":[{"mim_id":"620992","title":"SAFB-LIKE TRANSCRIPTION MODULATOR; SLTM","url":"https://www.omim.org/entry/620992"},{"mim_id":"615241","title":"TERMINAL DIFFERENTIATION-INDUCED NONCODING RNA; TINCR","url":"https://www.omim.org/entry/615241"},{"mim_id":"608066","title":"SCAFFOLD ATTACHMENT FACTOR B2; SAFB2","url":"https://www.omim.org/entry/608066"},{"mim_id":"602895","title":"SCAFFOLD ATTACHMENT FACTOR B; SAFB","url":"https://www.omim.org/entry/602895"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SAFB2"},"hgnc":{"alias_symbol":["KIAA0138"],"prev_symbol":[]},"alphafold":{"accession":"Q14151","domains":[{"cath_id":"1.10.720","chopping":"29-76","consensus_level":"medium","plddt":87.7423,"start":29,"end":76},{"cath_id":"3.30.70.330","chopping":"405-487","consensus_level":"medium","plddt":89.2422,"start":405,"end":487},{"cath_id":"1.20.5","chopping":"617-698","consensus_level":"medium","plddt":90.7376,"start":617,"end":698}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14151","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14151-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14151-F1-predicted_aligned_error_v6.png","plddt_mean":54.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SAFB2","jax_strain_url":"https://www.jax.org/strain/search?query=SAFB2"},"sequence":{"accession":"Q14151","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14151.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14151/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14151"}},"corpus_meta":[{"pmid":"12660241","id":"PMC_12660241","title":"SAFB2, a new scaffold attachment factor homolog and estrogen receptor corepressor.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12660241","citation_count":81,"is_preprint":false},{"pmid":"32502422","id":"PMC_32502422","title":"SAFB2 Enables the Processing of Suboptimal Stem-Loop Structures in Clustered Primary miRNA Transcripts.","date":"2020","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/32502422","citation_count":51,"is_preprint":false},{"pmid":"14587024","id":"PMC_14587024","title":"Scaffold attachment factors SAFB1 and SAFB2: Innocent bystanders or critical players in breast tumorigenesis?","date":"2003","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14587024","citation_count":48,"is_preprint":false},{"pmid":"17200140","id":"PMC_17200140","title":"Alternative RNA splicing complexes containing the scaffold attachment factor SAFB2.","date":"2007","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/17200140","citation_count":41,"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":"22566185","id":"PMC_22566185","title":"Scaffold attachment factor B (SAFB)1 and SAFB2 cooperatively inhibit the intranuclear mobility and function of ERα.","date":"2012","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22566185","citation_count":17,"is_preprint":false},{"pmid":"19077293","id":"PMC_19077293","title":"No germline mutations in supposed tumour suppressor genes SAFB1 and SAFB2 in familial breast cancer with linkage to 19p.","date":"2008","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19077293","citation_count":12,"is_preprint":false},{"pmid":"26092125","id":"PMC_26092125","title":"Scaffold attachment factor B2 (SAFB2)-null mice reveal non-redundant functions of SAFB2 compared with its paralog, SAFB1.","date":"2015","source":"Disease models & mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/26092125","citation_count":7,"is_preprint":false},{"pmid":"36652182","id":"PMC_36652182","title":"SAFB2 Inhibits the Progression of Breast Cancer by Suppressing the Wnt/β-Catenin Signaling Pathway via NFAT5.","date":"2023","source":"Molecular biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/36652182","citation_count":4,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.23.678008","title":"Dual function of ERH in primary miRNA biogenesis","date":"2025-09-23","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.23.678008","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.09.09.675111","title":"Separable roles for Microprocessor and its cofactors ERH and SAFB1/2 during microRNA cluster assistance","date":"2025-09-10","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.09.675111","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.08.26.672363","title":"Chromatin signalling pathways and FANCE amplification affect ATR inhibitor sensitivity in metastatic breast cancer","date":"2025-08-31","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.26.672363","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7783,"output_tokens":2312,"usd":0.029014,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9537,"output_tokens":2702,"usd":0.057618,"stage2_stop_reason":"end_turn"},"total_usd":0.086632,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"SAFB2 functions as an estrogen receptor (ERα) corepressor; its overexpression inhibits cell proliferation. SAFB1 and SAFB2 interact directly through a C-terminal domain, resulting in additive transcriptional repression activity. Unlike SAFB1, SAFB2 is found in both cytoplasm and nucleus.\",\n      \"method\": \"Overexpression/reporter assays for corepressor activity; direct protein interaction demonstrated; subcellular localization by fractionation/imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple functional assays (corepressor, proliferation, interaction), single lab, direct interaction and localization experimentally established\",\n      \"pmids\": [\"12660241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SAFB2 interacts with vinexin, a protein involved in linking signaling to the cytoskeleton, consistent with its cytoplasmic localization.\",\n      \"method\": \"Co-immunoprecipitation / interaction assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single interaction experiment mentioned in abstract without detailed follow-up\",\n      \"pmids\": [\"12660241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Endogenous SAFB2 exists in large nuclear complexes (up to 670 kDa), distinct from SAFB1 which is predominantly monomeric or in smaller complexes. Stable core complexes containing SAFB1, SAFB2, Sam68, and hnRNPG exist independently of intact nucleic acids. SAFB2 acts as a negative regulator of a tra2-beta variable exon (alternative splicing). No stable interaction was detected between SAFB proteins and SR or SR-related splicing regulators.\",\n      \"method\": \"Size-exclusion chromatography, novel monospecific antisera, splicing reporter assays, nucleic-acid-independence experiments\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple orthogonal methods (gel filtration, immunodetection, splicing assays), single lab\",\n      \"pmids\": [\"17200140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SAFB1 and SAFB2 colocalize with ERα in the nucleus of living cells after estradiol treatment; co-IP confirmed ERα interaction with both SAFB1 and SAFB2 in the presence of E2. FRAP analysis showed that SAFB1 and SAFB2 each decrease ERα intranuclear mobility, and coexpression causes a synergistic reduction in ERα dynamics, leading to cooperative inhibition of ERα-mediated transcription and cell proliferation.\",\n      \"method\": \"Chimeric fluorescent protein live-cell imaging, Co-immunoprecipitation, Fluorescence Recovery After Photobleaching (FRAP), proliferation assays\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus FRAP with functional readout, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22566185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SAFB2-knockout mice are viable and fertile (in contrast to SAFB1-knockout mice), but show significantly increased testis weight associated with an increased number of Sertoli cells. Loss of SAFB2 alters androgen receptor function and expression, implicating SAFB2 in Sertoli cell differentiation and activity.\",\n      \"method\": \"SAFB2-null mouse generation, histological and cell-count analysis, paralog-specific antibodies for expression analysis\",\n      \"journal\": \"Disease models & mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean knockout mouse with specific phenotypic readout and mechanistic link to androgen receptor, single lab\",\n      \"pmids\": [\"26092125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SAFB2 is an accessory protein of the Microprocessor complex required for processing of suboptimal stem-loop structures in clustered primary miRNA transcripts (e.g., pri-miR-15a requires neighboring pri-miR-16-1 and SAFB2 for efficient cleavage). SAFB2 enables binding and processing of suboptimal Microprocessor substrates in cis within clustered pri-miRNA transcripts.\",\n      \"method\": \"CRISPR/Cas9 screen, biochemical co-factor assays, miRNA processing assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — unbiased CRISPR screen plus mechanistic follow-up in multiple clustered miRNA contexts, rigorous genetic and biochemical validation\",\n      \"pmids\": [\"32502422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SAFB2 interacts with NFAT5 mRNA (by RIP assay) and destabilizes NFAT5 mRNA, leading to suppression of the Wnt/β-catenin signaling pathway in breast cancer cells. Overexpression of SAFB2 inhibits proliferation, migration, and invasion while promoting apoptosis, effects that are partially rescued by NFAT5 overexpression.\",\n      \"method\": \"RNA immunoprecipitation (RIP), mRNA stability assay (actinomycin D), western blotting, CCK8/colony formation/EdU proliferation assays, wound healing, transwell assays\",\n      \"journal\": \"Molecular biotechnology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — RIP plus mRNA stability assay plus functional rescue, single lab with multiple complementary methods\",\n      \"pmids\": [\"36652182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Epistatic analysis places SAFB2 downstream of ERH in the cluster assistance pathway: ERH may mediate Microprocessor transfer between hairpins, while SAFB2 (especially SAFB2) mediates recognition and stable binding of a suboptimal miRNA hairpin after Microprocessor transfer. SAFB2 associates with the N-terminus of DROSHA. Both SAFB1/2 and ERH are required for Microprocessor feedback regulation via processing of pri-miR-1306.\",\n      \"method\": \"Mutant cell lines, epistasis genetic tests, biochemical interaction assays, genome-wide miRNA profiling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis plus biochemical tests, preprint not yet peer-reviewed, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.09.09.675111\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ERH-mediated cluster assistance is independent of its direct association with SAFB2 (as shown by disrupting the ERH-SAFB2 interaction, which did not abolish cluster assistance). Loss of SAFB1/2 and ERH produce overlapping but not identical defects in primary miRNA biogenesis. Both SAFB2 and ERH are required for efficient Microprocessor feedback regulation via pri-miR-1306 processing.\",\n      \"method\": \"SAFB1/2 deletion and ERH deletion cell lines, miRNA transcriptome profiling, protein interaction disruption experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic knockouts with transcriptome-level phenotyping and mechanistic interaction dissection, preprint not peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.09.23.678008\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SAFB2 is a multifunctional nuclear (and partially cytoplasmic) scaffold attachment factor that acts as an ERα corepressor by directly interacting with ERα and restricting its intranuclear mobility, forms large nuclear complexes with SAFB1, Sam68, and hnRNPG to negatively regulate alternative splicing, destabilizes NFAT5 mRNA to suppress Wnt/β-catenin signaling, and functions as an accessory factor of the Microprocessor complex—specifically enabling stable binding and cleavage of suboptimal stem-loop hairpins in clustered primary miRNA transcripts after Microprocessor transfer, a step that is epistatic to ERH action in the cluster assistance pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SAFB2 is a multifunctional scaffold attachment factor that acts at the intersection of transcriptional control, RNA processing, and signaling, distributing between the nucleus and cytoplasm [#0]. As a transcriptional corepressor it interacts directly with estrogen receptor α (ERα) upon estradiol stimulation and, together with its paralog SAFB1, restricts ERα intranuclear mobility, cooperatively inhibiting ERα-driven transcription and cell proliferation [#0, #3]. SAFB2 assembles into large nuclear complexes containing SAFB1, Sam68, and hnRNPG that persist independently of nucleic acids and negatively regulate alternative splicing of a tra2-beta variable exon [#2]. In small-RNA biogenesis, SAFB2 functions as an accessory factor of the Microprocessor complex, associating with the N-terminus of DROSHA and enabling stable binding and cleavage of suboptimal stem-loop hairpins within clustered primary miRNA transcripts, acting downstream of ERH in the cluster-assistance pathway and contributing to Microprocessor feedback regulation [#5, #7]. SAFB2 also binds and destabilizes NFAT5 mRNA, thereby suppressing Wnt/β-catenin signaling and restraining proliferation, migration, and invasion in breast cancer cells [#6]. Consistent with a tissue-specific physiological role, SAFB2-null mice are viable and fertile but display increased testis weight and Sertoli cell number linked to altered androgen receptor function [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established SAFB2 as an ERα corepressor and defined its relationship to SAFB1, answering whether the paralog is functionally redundant or distinct.\",\n      \"evidence\": \"Overexpression/reporter corepressor assays, direct interaction mapping, and subcellular fractionation/imaging\",\n      \"pmids\": [\"12660241\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not define the structural basis of ERα repression\", \"Cytoplasmic function of SAFB2 left unexplained\", \"Vinexin interaction noted but not followed up\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed SAFB2 resides in large, stable nuclear core complexes with SAFB1, Sam68, and hnRNPG and regulates alternative splicing, framing it as a scaffold within an RNA-processing assembly rather than a free monomer.\",\n      \"evidence\": \"Size-exclusion chromatography, monospecific antisera, splicing reporter and nucleic-acid-independence assays\",\n      \"pmids\": [\"17200140\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and architecture of the 670 kDa complex unresolved\", \"Range of regulated splicing targets not defined\", \"No SR-protein interaction detected, leaving the mechanism of splicing repression open\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the mechanism of ERα repression by showing SAFB1/SAFB2 reduce ERα intranuclear mobility, explaining how corepression and antiproliferation are achieved.\",\n      \"evidence\": \"Live-cell fluorescent imaging, reciprocal Co-IP, FRAP, and proliferation assays\",\n      \"pmids\": [\"22566185\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not identify the chromatin or genomic loci where ERα is immobilized\", \"Synergy mechanism between paralogs not biochemically defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Provided in vivo physiological role via a knockout, distinguishing SAFB2 from the lethal/infertile SAFB1 phenotype and linking it to androgen receptor function.\",\n      \"evidence\": \"SAFB2-null mouse with histology, cell counts, and paralog-specific expression analysis\",\n      \"pmids\": [\"26092125\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of altered androgen receptor function not established\", \"Connection between Sertoli cell phenotype and SAFB2's RNA/transcription roles unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified SAFB2 as a Microprocessor accessory factor required for processing suboptimal hairpins in clustered pri-miRNAs, revealing a previously unknown role in miRNA biogenesis.\",\n      \"evidence\": \"Unbiased CRISPR/Cas9 screen plus biochemical co-factor and miRNA processing assays in clustered contexts (e.g., pri-miR-15a/16-1)\",\n      \"pmids\": [\"32502422\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct contact between SAFB2 and Microprocessor not yet mapped at this stage\", \"Determinants of substrate suboptimality recognition undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed SAFB2 mechanistically within the cluster-assistance pathway, showing it acts downstream of ERH and binds the DROSHA N-terminus to stabilize suboptimal hairpins after Microprocessor transfer.\",\n      \"evidence\": \"Epistasis genetic tests, biochemical interaction assays, and genome-wide miRNA profiling in mutant cell lines (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.09.09.675111\", \"bio_10.1101_2025.09.23.678008\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not yet peer-reviewed\", \"ERH-SAFB2 interaction is dispensable for cluster assistance, leaving the functional role of that contact unclear\", \"Structural detail of SAFB2-DROSHA recognition lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SAFB2's distinct activities — ERα corepression, splicing regulation, mRNA destabilization, and Microprocessor assistance — are integrated, regulated, and partitioned between compartments remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model connecting transcriptional, splicing, and miRNA-processing roles\", \"Regulation of SAFB2 nuclear/cytoplasmic partitioning unknown\", \"Substrate-recognition code for suboptimal pri-miRNA hairpins undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 5, 6]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\"Microprocessor complex\", \"SAFB1-SAFB2-Sam68-hnRNPG nuclear complex\"],\n    \"partners\": [\"SAFB1\", \"ESR1\", \"DROSHA\", \"ERH\", \"KHDRBS1\", \"RBMX\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}