{"gene":"SSBP2","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":2019,"finding":"Crystal structure of the human LDB1/SSBP2 complex at 2.8-Å resolution revealed that the LDB1 dimerization domain contains an NTF2-like subdomain and a helix 4-helix 5 subdomain forming the dimerization interface, with two LCCDs flanking the core DDs and each LCCD forming extensive interactions with an SSBP2 dimer. The conserved linker between LDB1 DD and LCCD covers a potential ligand-binding pocket of the LDB1 NTF2-like subdomain.","method":"X-ray crystallography (2.8-Å resolution) with biochemical validation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with biochemical validation; multiple orthogonal methods in a single rigorous study","pmids":["31892537"],"is_preprint":false},{"year":2019,"finding":"Crystal structure of the LUFS domain of human SSBP2 at 1.52-Å resolution showed that it forms a homo-tetramer, with an alpha-helix C-terminal to the LisH motif mediating tetramerization (dimerization of dimers).","method":"X-ray crystallography (1.52-Å resolution)","journal":"Protein science : a publication of the Protein Society","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure with structural analysis of tetramerization interface","pmids":["30676665"],"is_preprint":false},{"year":2010,"finding":"SSBP2 binds and stabilizes the transcriptional cofactor LDB1 by protecting it from proteasomal degradation. Loss of Ssbp2 causes increased LDB1 turnover in the thymus, and stage-specific upregulation of Ssbp2 regulates LDB1 turnover during T-cell differentiation. The LDB1-containing complex target pTalpha is reduced in Ssbp2−/− immature thymocytes.","method":"Gene targeting (Ssbp2−/− mice), Western blot for LDB1 protein levels, transcript analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with defined molecular phenotype (LDB1 turnover), replicated across tissues and developmental stages","pmids":["20348955"],"is_preprint":false},{"year":2005,"finding":"Inducible expression of SSBP2 in the AML cell line U937 causes loss of clonogenicity, G1 arrest, partial differentiation, and downregulation of C-MYC expression, establishing SSBP2 as a regulator of hematopoietic growth and differentiation.","method":"Inducible expression system in U937 cells, clonogenicity assay, flow cytometry (cell cycle), Western blot (C-MYC)","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean gain-of-function with multiple cellular readouts in a single lab","pmids":["15782145"],"is_preprint":false},{"year":2014,"finding":"SSBP2 is required for hematopoietic stem and progenitor cell (HSPC) function in vivo: Ssbp2−/− mice show hypoplastic hematopoietic tissues, reduced lymphoid-primed multipotent progenitors, delayed recovery from 5-fluorouracil treatment, and diminished multilineage reconstitution. Ssbp2−/− HSPCs show dramatic reduction of Notch1 transcripts and increased E2a and Cdkn1a expression, consistent with SSBP2 regulating LDB1-dependent gene programs.","method":"Ssbp2−/− mouse knockout, bone marrow transplantation, 5-fluorouracil treatment, RT-PCR for Notch1/E2a/Cdkn1a","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout with multiple orthogonal functional assays and defined molecular targets","pmids":["25238756"],"is_preprint":false},{"year":2009,"finding":"SSBP2 is specifically phosphorylated by the ZNF198-FGFR1 fusion kinase (but not by wild-type FGFR1) in HEK293 cells, as confirmed by anti-phosphotyrosine immunoprecipitation/MS and protein-specific immunoprecipitation/Western blot.","method":"Anti-phosphotyrosine immunoprecipitation, mass spectrometry, protein-specific immunoprecipitation, Western blot","journal":"Proteomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal immunoprecipitation and MS confirmation; single lab with two orthogonal methods","pmids":["19658100"],"is_preprint":false},{"year":2023,"finding":"In Xenopus laevis, Ssbp2 interacts with the Ldb1-Lhx1 complex (identified by tandem-affinity purification from kidney-induced animal caps), and Ssbp2 knockdown prevents normal morphogenesis and differentiation of the glomus and convoluted renal tubules of the pronephros.","method":"Tandem-affinity purification, morpholino knockdown in Xenopus, histological/morphological analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — affinity purification identifies complex membership, loss-of-function gives defined morphological phenotype; single lab","pmids":["37794075"],"is_preprint":false},{"year":2010,"finding":"In HEK293 cells (which constitutively express adenoviral E1B55K), SSBP2 is aberrantly recruited to PML nuclear bodies in response to stress stimuli (nuclear export inhibition, etoposide, hydroxyurea, gamma irradiation), suggesting E1B55K subverts normal SSBP2 localization and function.","method":"Immunofluorescence localization of SSBP2 under stress conditions in HEK293 cells vs. normal cells","journal":"Journal of molecular signaling","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single-lab localization study without functional rescue or mechanistic dissection","pmids":["20540776"],"is_preprint":false},{"year":2021,"finding":"Ssbp2 is highly expressed in podocytes and interacts with LDB1 and LMX1B; Ssbp2 null mice spontaneously develop glomerulosclerosis, tubular casts, interstitial fibrosis, and inflammation, suggesting a role in the LDB1-LMX1B transcriptional network in kidney.","method":"GWAS in mice, single-cell transcriptomics, Ssbp2 null mouse phenotyping","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo null mouse phenotype with single-cell transcriptomic expression data and pathway annotation; single lab","pmids":["34893534"],"is_preprint":false},{"year":2025,"finding":"SSBP2, SSBP3, and SSBP4 colocalize with LDB1 genome-wide (ChIP-seq). LDB1—not single-stranded DNA—is the predominant genome-wide chromatin tether of SSBP3. SSBP3 depletion in SSBP2/4 knockout erythroid cells globally weakens LDB1-dependent chromatin loops and lowers nascent transcription without displacing LDB1 from chromatin. SSBP3 stabilizes LDB1 homodimers in solution, providing a mechanism by which SSBPs enable LDB1-mediated enhancer-promoter looping.","method":"ChIP-seq, CRISPR knockout, acute auxin-inducible degron depletion, chromatin tethering, biochemical dimerization assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in a single preprint; not yet peer-reviewed","pmids":["bio_10.1101_2025.06.05.658047"],"is_preprint":true},{"year":2025,"finding":"MYB transcriptionally represses SSBP2 expression in gastric cancer cells, and SSBP2 in turn negatively regulates ISL1 expression, forming an MYB/SSBP2/ISL1 regulatory axis that controls glycolysis, proliferation, invasion, and migration.","method":"EMSA, yeast one-hybrid, dual-luciferase assay, ChIP-PCR, Co-IP, pull-down, immunofluorescence, CCK-8, Transwell, xenograft","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (EMSA, ChIP, Co-IP, luciferase) in a single lab confirming transcriptional repression and downstream pathway","pmids":["41024119"],"is_preprint":false}],"current_model":"SSBP2 is a transcriptional cofactor that, through its conserved LUFS domain (which forms a homo-tetramer), binds and stabilizes the architectural protein LDB1 by protecting it from proteasomal degradation; structural studies reveal that SSBP2 dimers interact extensively with LDB1's conserved LCCD, enabling LDB1 homodimerization and LDB1-mediated enhancer-promoter chromatin looping, thereby regulating tissue-specific gene expression programs (including Notch1, pTalpha, and ISL1) in hematopoiesis, T-cell differentiation, and kidney organogenesis, and acting as a tumor suppressor whose loss promotes leukemia and lymphoma."},"narrative":{"mechanistic_narrative":"SSBP2 is a transcriptional cofactor that controls tissue-specific gene expression programs by binding and stabilizing the architectural protein LDB1 and enabling LDB1-dependent enhancer-promoter chromatin looping [PMID:20348955, PMID:bio_10.1101_2025.06.05.658047]. Its conserved LUFS domain forms a homo-tetramer through an alpha-helix C-terminal to the LisH motif [PMID:30676665], and SSBP2 dimers engage the LDB1 LCCD subdomains that flank the LDB1 dimerization core, an interaction resolved at atomic resolution [PMID:31892537]. Functionally, SSBP2 protects LDB1 from proteasomal degradation, and its loss accelerates LDB1 turnover, reducing output of LDB1-containing complexes including pTalpha during T-cell differentiation [PMID:20348955]. Through this LDB1 axis, SSBP2 sustains hematopoietic stem and progenitor cell function and regulates downstream programs such as Notch1, E2a, and Cdkn1a [PMID:25238756], and its inducible expression in AML cells arrests growth, drives partial differentiation, and downregulates C-MYC [PMID:15782145], consistent with a tumor-suppressive role in hematopoiesis. SSBP2 participates in LDB1-LIM-homeodomain transcriptional networks during organogenesis, interacting with Ldb1-Lhx1 in Xenopus pronephros development [PMID:37794075] and with LDB1-LMX1B in podocytes, where Ssbp2 loss causes glomerulosclerosis and renal fibrosis [PMID:34893534]. In gastric cancer, SSBP2 lies within an MYB/SSBP2/ISL1 axis in which MYB represses SSBP2 and SSBP2 in turn represses ISL1 to limit glycolysis, proliferation, and invasion [PMID:41024119].","teleology":[{"year":2005,"claim":"Established that SSBP2 is not merely a passive cofactor but an active regulator of hematopoietic growth and differentiation, providing the first functional readout of its tumor-suppressive potential.","evidence":"Inducible SSBP2 expression in U937 AML cells with clonogenicity, cell-cycle, and C-MYC assays","pmids":["15782145"],"confidence":"Medium","gaps":["Mechanism linking SSBP2 to C-MYC downregulation not defined","Single cell line, gain-of-function only","No direct chromatin or LDB1 link demonstrated here"]},{"year":2009,"claim":"Showed that SSBP2 is a substrate of an oncogenic fusion kinase, connecting it to aberrant signaling in myeloproliferative disease.","evidence":"Anti-phosphotyrosine IP/MS and reciprocal IP/Western in HEK293 cells expressing ZNF198-FGFR1","pmids":["19658100"],"confidence":"Medium","gaps":["Functional consequence of SSBP2 phosphorylation unknown","Phosphosite not mapped","Overexpression system in non-hematopoietic cells"]},{"year":2010,"claim":"Defined the core biochemical function of SSBP2 — stabilizing LDB1 against proteasomal degradation — and tied it to a developmental program through pTalpha regulation in thymocytes.","evidence":"Ssbp2-/- mice, LDB1 Western blots across tissues and T-cell differentiation stages, transcript analysis","pmids":["20348955"],"confidence":"High","gaps":["Does not resolve which E3 ligase degrades LDB1","Structural basis of stabilization not addressed","Direct chromatin targets not mapped"]},{"year":2010,"claim":"Suggested that viral oncoproteins can subvert SSBP2 by relocalizing it to PML nuclear bodies under stress, hinting at a stress-responsive regulatory layer.","evidence":"Immunofluorescence of SSBP2 under stress stimuli in E1B55K-expressing HEK293 cells","pmids":["20540776"],"confidence":"Low","gaps":["Single-lab localization study without functional rescue","No mechanistic dissection of relocalization","Physiological relevance outside adenovirus-transformed cells unclear"]},{"year":2014,"claim":"Demonstrated an in vivo requirement for SSBP2 in HSPC function and identified LDB1-dependent gene targets (Notch1, E2a, Cdkn1a) underlying the phenotype.","evidence":"Ssbp2-/- mice, bone marrow transplantation, 5-FU challenge, RT-PCR of target genes","pmids":["25238756"],"confidence":"High","gaps":["Direct vs. indirect regulation of Notch1 not separated","Genome-wide binding not mapped","Cell-autonomy of individual target effects unresolved"]},{"year":2019,"claim":"Provided the structural basis for the SSBP2-LDB1 interaction and for SSBP2 self-assembly, explaining how SSBP2 dimers engage LDB1 and how LUFS-mediated tetramerization is achieved.","evidence":"Crystal structures of the LDB1/SSBP2 complex (2.8 Å) and the SSBP2 LUFS domain (1.52 Å) with biochemical validation","pmids":["31892537","30676665"],"confidence":"High","gaps":["Functional impact of the LDB1 NTF2-like ligand-binding pocket unknown","Stoichiometry on chromatin in vivo not established","Does not link structure to looping activity directly"]},{"year":2021,"claim":"Extended the LDB1-SSBP2 network to kidney, showing SSBP2 acts within an LDB1-LMX1B transcriptional complex required to prevent glomerular disease.","evidence":"Mouse GWAS, single-cell transcriptomics, Ssbp2 null mouse phenotyping","pmids":["34893534"],"confidence":"Medium","gaps":["Direct LMX1B target genes in podocytes not defined","Whether stabilization mechanism applies to LMX1B-LDB1 unknown","Single lab"]},{"year":2023,"claim":"Confirmed SSBP2 membership in an LDB1-LIM-homeodomain (Ldb1-Lhx1) complex in a second developmental context and showed a loss-of-function morphogenesis defect.","evidence":"Tandem-affinity purification and morpholino knockdown in Xenopus pronephros","pmids":["37794075"],"confidence":"Medium","gaps":["Direct transcriptional targets in pronephros not identified","LDB1-stabilization mechanism not tested here","Single organism/lab"]},{"year":2025,"claim":"Identified SSBP2 as a node in an MYB/SSBP2/ISL1 axis controlling cancer metabolism and aggressiveness, placing it in a gastric cancer regulatory circuit.","evidence":"EMSA, yeast one-hybrid, luciferase, ChIP-PCR, Co-IP, pull-down, functional and xenograft assays","pmids":["41024119"],"confidence":"Medium","gaps":["Whether ISL1 repression by SSBP2 is LDB1-dependent unclear","Direct vs. indirect ISL1 regulation not fully separated","Single lab"]},{"year":2025,"claim":"Provided the genome-wide and biochemical mechanism by which SSBP family proteins enable LDB1-mediated looping — tethering via LDB1 rather than ssDNA and stabilizing LDB1 homodimers to maintain chromatin loops and transcription.","evidence":"ChIP-seq, CRISPR knockout, auxin-inducible degron depletion, chromatin tethering and dimerization assays in erythroid cells (preprint)","pmids":["bio_10.1101_2025.06.05.658047"],"confidence":"Medium","gaps":["Not yet peer-reviewed","Functional redundancy/specificity between SSBP2/3/4 not fully resolved","SSBP2-specific contribution distinct from SSBP3 not isolated"]},{"year":null,"claim":"How SSBP2 isoform/paralog specificity and post-translational signals (e.g., phosphorylation) select among distinct LDB1-LIM-homeodomain programs across tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No tissue-specific target map distinguishing SSBP2 from SSBP3/4","Functional role of SSBP2 phosphorylation undefined","Identity of the LDB1-degrading machinery SSBP2 protects against unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[2,3,4,10]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,9]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[7,8,9]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,4,9,10]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,6,8]}],"complexes":["LDB1-SSBP2 complex","LDB1-Lhx1 complex","LDB1-LMX1B complex"],"partners":["LDB1","LHX1","LMX1B","ISL1","MYB"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P81877","full_name":"Single-stranded DNA-binding protein 2","aliases":["Sequence-specific single-stranded-DNA-binding protein 2"],"length_aa":361,"mass_kda":37.8,"function":"","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P81877/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SSBP2","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SSBP2","total_profiled":1310},"omim":[{"mim_id":"613273","title":"INST3- AND NABP-INTERACTING PROTEIN; INIP","url":"https://www.omim.org/entry/613273"},{"mim_id":"611347","title":"INTEGRATOR COMPLEX SUBUNIT 3; INTS3","url":"https://www.omim.org/entry/611347"},{"mim_id":"607391","title":"SINGLE-STRANDED DNA-BINDING PROTEIN 4; SSBP4","url":"https://www.omim.org/entry/607391"},{"mim_id":"607390","title":"SINGLE-STRANDED DNA-BINDING PROTEIN 3; SSBP3","url":"https://www.omim.org/entry/607390"},{"mim_id":"607389","title":"SINGLE-STRANDED DNA-BINDING PROTEIN 2; SSBP2","url":"https://www.omim.org/entry/607389"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SSBP2"},"hgnc":{"alias_symbol":["HSPC116"],"prev_symbol":[]},"alphafold":{"accession":"P81877","domains":[{"cath_id":"-","chopping":"15-57","consensus_level":"medium","plddt":92.5056,"start":15,"end":57},{"cath_id":"-","chopping":"60-97","consensus_level":"medium","plddt":84.4729,"start":60,"end":97}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P81877","model_url":"https://alphafold.ebi.ac.uk/files/AF-P81877-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P81877-F1-predicted_aligned_error_v6.png","plddt_mean":54.47},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SSBP2","jax_strain_url":"https://www.jax.org/strain/search?query=SSBP2"},"sequence":{"accession":"P81877","fasta_url":"https://rest.uniprot.org/uniprotkb/P81877.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P81877/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P81877"}},"corpus_meta":[{"pmid":"18618714","id":"PMC_18618714","title":"Novel SSBP2-JAK2 fusion gene resulting from a t(5;9)(q14.1;p24.1) in pre-B acute lymphocytic leukemia.","date":"2008","source":"Genes, chromosomes & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/18618714","citation_count":57,"is_preprint":false},{"pmid":"15782145","id":"PMC_15782145","title":"SSBP2, a candidate tumor suppressor gene, induces growth arrest and differentiation of myeloid leukemia cells.","date":"2005","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/15782145","citation_count":48,"is_preprint":false},{"pmid":"20348955","id":"PMC_20348955","title":"SSBP2 is an in vivo tumor suppressor and regulator of LDB1 stability.","date":"2010","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/20348955","citation_count":32,"is_preprint":false},{"pmid":"22472174","id":"PMC_22472174","title":"SSBP2 variants are associated with survival in glioblastoma patients.","date":"2012","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/22472174","citation_count":23,"is_preprint":false},{"pmid":"31892537","id":"PMC_31892537","title":"Crystal structure of human LDB1 in complex with SSBP2.","date":"2019","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/31892537","citation_count":22,"is_preprint":false},{"pmid":"25238756","id":"PMC_25238756","title":"Requirement for ssbp2 in hematopoietic stem cell maintenance and stress response.","date":"2014","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/25238756","citation_count":16,"is_preprint":false},{"pmid":"19658100","id":"PMC_19658100","title":"Phosphorylation of the SSBP2 and ABL proteins by the ZNF198-FGFR1 fusion kinase seen in atypical myeloproliferative disorders as revealed by phosphopeptide-specific MS.","date":"2009","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/19658100","citation_count":16,"is_preprint":false},{"pmid":"30676665","id":"PMC_30676665","title":"Crystal structure of the LUFS domain of human single-stranded DNA binding Protein 2 (SSBP2).","date":"2019","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/30676665","citation_count":10,"is_preprint":false},{"pmid":"37794075","id":"PMC_37794075","title":"Xenopus Ssbp2 is required for embryonic pronephros morphogenesis and terminal differentiation.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/37794075","citation_count":5,"is_preprint":false},{"pmid":"34893534","id":"PMC_34893534","title":"GWAS in Mice Maps Susceptibility to HIV-Associated Nephropathy to the Ssbp2 Locus.","date":"2021","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/34893534","citation_count":4,"is_preprint":false},{"pmid":"20540776","id":"PMC_20540776","title":"Adenoviral oncoprotein E1B55K mediates colocalization of SSBP2 and PML in response to stress.","date":"2010","source":"Journal of molecular signaling","url":"https://pubmed.ncbi.nlm.nih.gov/20540776","citation_count":4,"is_preprint":false},{"pmid":"31882468","id":"PMC_31882468","title":"Low Expression of Single-stranded DNA Binding Protein 2 (SSBP2) Predicts Unfavourable Postoperative Outcomes in Patients With Clear Cell Renal Cell Carcinoma.","date":"2020","source":"In vivo (Athens, Greece)","url":"https://pubmed.ncbi.nlm.nih.gov/31882468","citation_count":3,"is_preprint":false},{"pmid":"38107066","id":"PMC_38107066","title":"Treatment for a primary multidrug-resistant B-cell acute lymphoblastic leukemia patient carrying a SSBP2-CSF1R fusion gene: a case report.","date":"2023","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/38107066","citation_count":2,"is_preprint":false},{"pmid":"41024119","id":"PMC_41024119","title":"Transcription factor MYB regulates glycolysis to promote the transfer and malignant progression of gastric cancer through the SSBP2/ISL1 axis.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/41024119","citation_count":1,"is_preprint":false},{"pmid":"37090653","id":"PMC_37090653","title":"Xenopus Ssbp2 is required for embryonic pronephros morphogenesis and terminal differentiation.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37090653","citation_count":0,"is_preprint":false},{"pmid":"42171857","id":"PMC_42171857","title":"Myeloid/lymphoid neoplasm with FLT3 gene fusion: report of a case with a novel t(5;13)(q13;q12) SSBP2::FLT3 fusion.","date":"2026","source":"Journal of hematopathology","url":"https://pubmed.ncbi.nlm.nih.gov/42171857","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.05.658047","title":"Single-stranded DNA binding proteins are essential components of the architectural LDB1 protein complex","date":"2025-06-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.05.658047","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10439,"output_tokens":2836,"usd":0.036929,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10108,"output_tokens":3726,"usd":0.071845,"stage2_stop_reason":"end_turn"},"total_usd":0.108774,"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\": 2019,\n      \"finding\": \"Crystal structure of the human LDB1/SSBP2 complex at 2.8-Å resolution revealed that the LDB1 dimerization domain contains an NTF2-like subdomain and a helix 4-helix 5 subdomain forming the dimerization interface, with two LCCDs flanking the core DDs and each LCCD forming extensive interactions with an SSBP2 dimer. The conserved linker between LDB1 DD and LCCD covers a potential ligand-binding pocket of the LDB1 NTF2-like subdomain.\",\n      \"method\": \"X-ray crystallography (2.8-Å resolution) with biochemical validation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with biochemical validation; multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"31892537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structure of the LUFS domain of human SSBP2 at 1.52-Å resolution showed that it forms a homo-tetramer, with an alpha-helix C-terminal to the LisH motif mediating tetramerization (dimerization of dimers).\",\n      \"method\": \"X-ray crystallography (1.52-Å resolution)\",\n      \"journal\": \"Protein science : a publication of the Protein Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure with structural analysis of tetramerization interface\",\n      \"pmids\": [\"30676665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SSBP2 binds and stabilizes the transcriptional cofactor LDB1 by protecting it from proteasomal degradation. Loss of Ssbp2 causes increased LDB1 turnover in the thymus, and stage-specific upregulation of Ssbp2 regulates LDB1 turnover during T-cell differentiation. The LDB1-containing complex target pTalpha is reduced in Ssbp2−/− immature thymocytes.\",\n      \"method\": \"Gene targeting (Ssbp2−/− mice), Western blot for LDB1 protein levels, transcript analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with defined molecular phenotype (LDB1 turnover), replicated across tissues and developmental stages\",\n      \"pmids\": [\"20348955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Inducible expression of SSBP2 in the AML cell line U937 causes loss of clonogenicity, G1 arrest, partial differentiation, and downregulation of C-MYC expression, establishing SSBP2 as a regulator of hematopoietic growth and differentiation.\",\n      \"method\": \"Inducible expression system in U937 cells, clonogenicity assay, flow cytometry (cell cycle), Western blot (C-MYC)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean gain-of-function with multiple cellular readouts in a single lab\",\n      \"pmids\": [\"15782145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SSBP2 is required for hematopoietic stem and progenitor cell (HSPC) function in vivo: Ssbp2−/− mice show hypoplastic hematopoietic tissues, reduced lymphoid-primed multipotent progenitors, delayed recovery from 5-fluorouracil treatment, and diminished multilineage reconstitution. Ssbp2−/− HSPCs show dramatic reduction of Notch1 transcripts and increased E2a and Cdkn1a expression, consistent with SSBP2 regulating LDB1-dependent gene programs.\",\n      \"method\": \"Ssbp2−/− mouse knockout, bone marrow transplantation, 5-fluorouracil treatment, RT-PCR for Notch1/E2a/Cdkn1a\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout with multiple orthogonal functional assays and defined molecular targets\",\n      \"pmids\": [\"25238756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SSBP2 is specifically phosphorylated by the ZNF198-FGFR1 fusion kinase (but not by wild-type FGFR1) in HEK293 cells, as confirmed by anti-phosphotyrosine immunoprecipitation/MS and protein-specific immunoprecipitation/Western blot.\",\n      \"method\": \"Anti-phosphotyrosine immunoprecipitation, mass spectrometry, protein-specific immunoprecipitation, Western blot\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal immunoprecipitation and MS confirmation; single lab with two orthogonal methods\",\n      \"pmids\": [\"19658100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In Xenopus laevis, Ssbp2 interacts with the Ldb1-Lhx1 complex (identified by tandem-affinity purification from kidney-induced animal caps), and Ssbp2 knockdown prevents normal morphogenesis and differentiation of the glomus and convoluted renal tubules of the pronephros.\",\n      \"method\": \"Tandem-affinity purification, morpholino knockdown in Xenopus, histological/morphological analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — affinity purification identifies complex membership, loss-of-function gives defined morphological phenotype; single lab\",\n      \"pmids\": [\"37794075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In HEK293 cells (which constitutively express adenoviral E1B55K), SSBP2 is aberrantly recruited to PML nuclear bodies in response to stress stimuli (nuclear export inhibition, etoposide, hydroxyurea, gamma irradiation), suggesting E1B55K subverts normal SSBP2 localization and function.\",\n      \"method\": \"Immunofluorescence localization of SSBP2 under stress conditions in HEK293 cells vs. normal cells\",\n      \"journal\": \"Journal of molecular signaling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single-lab localization study without functional rescue or mechanistic dissection\",\n      \"pmids\": [\"20540776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ssbp2 is highly expressed in podocytes and interacts with LDB1 and LMX1B; Ssbp2 null mice spontaneously develop glomerulosclerosis, tubular casts, interstitial fibrosis, and inflammation, suggesting a role in the LDB1-LMX1B transcriptional network in kidney.\",\n      \"method\": \"GWAS in mice, single-cell transcriptomics, Ssbp2 null mouse phenotyping\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo null mouse phenotype with single-cell transcriptomic expression data and pathway annotation; single lab\",\n      \"pmids\": [\"34893534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SSBP2, SSBP3, and SSBP4 colocalize with LDB1 genome-wide (ChIP-seq). LDB1—not single-stranded DNA—is the predominant genome-wide chromatin tether of SSBP3. SSBP3 depletion in SSBP2/4 knockout erythroid cells globally weakens LDB1-dependent chromatin loops and lowers nascent transcription without displacing LDB1 from chromatin. SSBP3 stabilizes LDB1 homodimers in solution, providing a mechanism by which SSBPs enable LDB1-mediated enhancer-promoter looping.\",\n      \"method\": \"ChIP-seq, CRISPR knockout, acute auxin-inducible degron depletion, chromatin tethering, biochemical dimerization assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in a single preprint; not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.05.658047\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MYB transcriptionally represses SSBP2 expression in gastric cancer cells, and SSBP2 in turn negatively regulates ISL1 expression, forming an MYB/SSBP2/ISL1 regulatory axis that controls glycolysis, proliferation, invasion, and migration.\",\n      \"method\": \"EMSA, yeast one-hybrid, dual-luciferase assay, ChIP-PCR, Co-IP, pull-down, immunofluorescence, CCK-8, Transwell, xenograft\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (EMSA, ChIP, Co-IP, luciferase) in a single lab confirming transcriptional repression and downstream pathway\",\n      \"pmids\": [\"41024119\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SSBP2 is a transcriptional cofactor that, through its conserved LUFS domain (which forms a homo-tetramer), binds and stabilizes the architectural protein LDB1 by protecting it from proteasomal degradation; structural studies reveal that SSBP2 dimers interact extensively with LDB1's conserved LCCD, enabling LDB1 homodimerization and LDB1-mediated enhancer-promoter chromatin looping, thereby regulating tissue-specific gene expression programs (including Notch1, pTalpha, and ISL1) in hematopoiesis, T-cell differentiation, and kidney organogenesis, and acting as a tumor suppressor whose loss promotes leukemia and lymphoma.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SSBP2 is a transcriptional cofactor that controls tissue-specific gene expression programs by binding and stabilizing the architectural protein LDB1 and enabling LDB1-dependent enhancer-promoter chromatin looping [#2, #9]. Its conserved LUFS domain forms a homo-tetramer through an alpha-helix C-terminal to the LisH motif [#1], and SSBP2 dimers engage the LDB1 LCCD subdomains that flank the LDB1 dimerization core, an interaction resolved at atomic resolution [#0]. Functionally, SSBP2 protects LDB1 from proteasomal degradation, and its loss accelerates LDB1 turnover, reducing output of LDB1-containing complexes including pTalpha during T-cell differentiation [#2]. Through this LDB1 axis, SSBP2 sustains hematopoietic stem and progenitor cell function and regulates downstream programs such as Notch1, E2a, and Cdkn1a [#4], and its inducible expression in AML cells arrests growth, drives partial differentiation, and downregulates C-MYC [#3], consistent with a tumor-suppressive role in hematopoiesis. SSBP2 participates in LDB1-LIM-homeodomain transcriptional networks during organogenesis, interacting with Ldb1-Lhx1 in Xenopus pronephros development [#6] and with LDB1-LMX1B in podocytes, where Ssbp2 loss causes glomerulosclerosis and renal fibrosis [#8]. In gastric cancer, SSBP2 lies within an MYB/SSBP2/ISL1 axis in which MYB represses SSBP2 and SSBP2 in turn represses ISL1 to limit glycolysis, proliferation, and invasion [#10].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that SSBP2 is not merely a passive cofactor but an active regulator of hematopoietic growth and differentiation, providing the first functional readout of its tumor-suppressive potential.\",\n      \"evidence\": \"Inducible SSBP2 expression in U937 AML cells with clonogenicity, cell-cycle, and C-MYC assays\",\n      \"pmids\": [\"15782145\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking SSBP2 to C-MYC downregulation not defined\", \"Single cell line, gain-of-function only\", \"No direct chromatin or LDB1 link demonstrated here\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed that SSBP2 is a substrate of an oncogenic fusion kinase, connecting it to aberrant signaling in myeloproliferative disease.\",\n      \"evidence\": \"Anti-phosphotyrosine IP/MS and reciprocal IP/Western in HEK293 cells expressing ZNF198-FGFR1\",\n      \"pmids\": [\"19658100\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of SSBP2 phosphorylation unknown\", \"Phosphosite not mapped\", \"Overexpression system in non-hematopoietic cells\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the core biochemical function of SSBP2 — stabilizing LDB1 against proteasomal degradation — and tied it to a developmental program through pTalpha regulation in thymocytes.\",\n      \"evidence\": \"Ssbp2-/- mice, LDB1 Western blots across tissues and T-cell differentiation stages, transcript analysis\",\n      \"pmids\": [\"20348955\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve which E3 ligase degrades LDB1\", \"Structural basis of stabilization not addressed\", \"Direct chromatin targets not mapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Suggested that viral oncoproteins can subvert SSBP2 by relocalizing it to PML nuclear bodies under stress, hinting at a stress-responsive regulatory layer.\",\n      \"evidence\": \"Immunofluorescence of SSBP2 under stress stimuli in E1B55K-expressing HEK293 cells\",\n      \"pmids\": [\"20540776\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single-lab localization study without functional rescue\", \"No mechanistic dissection of relocalization\", \"Physiological relevance outside adenovirus-transformed cells unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated an in vivo requirement for SSBP2 in HSPC function and identified LDB1-dependent gene targets (Notch1, E2a, Cdkn1a) underlying the phenotype.\",\n      \"evidence\": \"Ssbp2-/- mice, bone marrow transplantation, 5-FU challenge, RT-PCR of target genes\",\n      \"pmids\": [\"25238756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs. indirect regulation of Notch1 not separated\", \"Genome-wide binding not mapped\", \"Cell-autonomy of individual target effects unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the structural basis for the SSBP2-LDB1 interaction and for SSBP2 self-assembly, explaining how SSBP2 dimers engage LDB1 and how LUFS-mediated tetramerization is achieved.\",\n      \"evidence\": \"Crystal structures of the LDB1/SSBP2 complex (2.8 Å) and the SSBP2 LUFS domain (1.52 Å) with biochemical validation\",\n      \"pmids\": [\"31892537\", \"30676665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional impact of the LDB1 NTF2-like ligand-binding pocket unknown\", \"Stoichiometry on chromatin in vivo not established\", \"Does not link structure to looping activity directly\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended the LDB1-SSBP2 network to kidney, showing SSBP2 acts within an LDB1-LMX1B transcriptional complex required to prevent glomerular disease.\",\n      \"evidence\": \"Mouse GWAS, single-cell transcriptomics, Ssbp2 null mouse phenotyping\",\n      \"pmids\": [\"34893534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct LMX1B target genes in podocytes not defined\", \"Whether stabilization mechanism applies to LMX1B-LDB1 unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Confirmed SSBP2 membership in an LDB1-LIM-homeodomain (Ldb1-Lhx1) complex in a second developmental context and showed a loss-of-function morphogenesis defect.\",\n      \"evidence\": \"Tandem-affinity purification and morpholino knockdown in Xenopus pronephros\",\n      \"pmids\": [\"37794075\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional targets in pronephros not identified\", \"LDB1-stabilization mechanism not tested here\", \"Single organism/lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified SSBP2 as a node in an MYB/SSBP2/ISL1 axis controlling cancer metabolism and aggressiveness, placing it in a gastric cancer regulatory circuit.\",\n      \"evidence\": \"EMSA, yeast one-hybrid, luciferase, ChIP-PCR, Co-IP, pull-down, functional and xenograft assays\",\n      \"pmids\": [\"41024119\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ISL1 repression by SSBP2 is LDB1-dependent unclear\", \"Direct vs. indirect ISL1 regulation not fully separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided the genome-wide and biochemical mechanism by which SSBP family proteins enable LDB1-mediated looping — tethering via LDB1 rather than ssDNA and stabilizing LDB1 homodimers to maintain chromatin loops and transcription.\",\n      \"evidence\": \"ChIP-seq, CRISPR knockout, auxin-inducible degron depletion, chromatin tethering and dimerization assays in erythroid cells (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.06.05.658047\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not yet peer-reviewed\", \"Functional redundancy/specificity between SSBP2/3/4 not fully resolved\", \"SSBP2-specific contribution distinct from SSBP3 not isolated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SSBP2 isoform/paralog specificity and post-translational signals (e.g., phosphorylation) select among distinct LDB1-LIM-homeodomain programs across tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No tissue-specific target map distinguishing SSBP2 from SSBP3/4\", \"Functional role of SSBP2 phosphorylation undefined\", \"Identity of the LDB1-degrading machinery SSBP2 protects against unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [2, 3, 4, 10]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [7, 8, 9]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 4, 9, 10]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 6, 8]}\n    ],\n    \"complexes\": [\n      \"LDB1-SSBP2 complex\",\n      \"LDB1-Lhx1 complex\",\n      \"LDB1-LMX1B complex\"\n    ],\n    \"partners\": [\n      \"LDB1\",\n      \"LHX1\",\n      \"LMX1B\",\n      \"ISL1\",\n      \"MYB\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}