Affinage

SSBP2

Single-stranded DNA-binding protein 2 · UniProt P81877

Length
361 aa
Mass
37.8 kDa
Annotated
2026-06-10
16 papers in source corpus 11 papers cited in narrative 11 extracted findings
Cross-family judge faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2005 Medium

    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

    PMID:15782145

    Open questions at the time
    • Mechanism linking SSBP2 to C-MYC downregulation not defined
    • Single cell line, gain-of-function only
    • No direct chromatin or LDB1 link demonstrated here
  2. 2009 Medium

    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

    PMID:19658100

    Open questions at the time
    • Functional consequence of SSBP2 phosphorylation unknown
    • Phosphosite not mapped
    • Overexpression system in non-hematopoietic cells
  3. 2010 High

    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

    PMID:20348955

    Open questions at the time
    • Does not resolve which E3 ligase degrades LDB1
    • Structural basis of stabilization not addressed
    • Direct chromatin targets not mapped
  4. 2010 Low

    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

    PMID:20540776

    Open questions at the time
    • Single-lab localization study without functional rescue
    • No mechanistic dissection of relocalization
    • Physiological relevance outside adenovirus-transformed cells unclear
  5. 2014 High

    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

    PMID:25238756

    Open questions at the time
    • Direct vs. indirect regulation of Notch1 not separated
    • Genome-wide binding not mapped
    • Cell-autonomy of individual target effects unresolved
  6. 2019 High

    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

    PMID:30676665 PMID:31892537

    Open questions at the time
    • 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
  7. 2021 Medium

    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

    PMID:34893534

    Open questions at the time
    • Direct LMX1B target genes in podocytes not defined
    • Whether stabilization mechanism applies to LMX1B-LDB1 unknown
    • Single lab
  8. 2023 Medium

    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

    PMID:37794075

    Open questions at the time
    • Direct transcriptional targets in pronephros not identified
    • LDB1-stabilization mechanism not tested here
    • Single organism/lab
  9. 2025 Medium

    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

    PMID:41024119

    Open questions at the time
    • Whether ISL1 repression by SSBP2 is LDB1-dependent unclear
    • Direct vs. indirect ISL1 regulation not fully separated
    • Single lab
  10. 2025 Medium

    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)

    PMID:bio_10.1101_2025.06.05.658047

    Open questions at the time
    • Not yet peer-reviewed
    • Functional redundancy/specificity between SSBP2/3/4 not fully resolved
    • SSBP2-specific contribution distinct from SSBP3 not isolated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How SSBP2 isoform/paralog specificity and post-translational signals (e.g., phosphorylation) select among distinct LDB1-LIM-homeodomain programs across tissues remains unresolved.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140110 transcription regulator activity 4 GO:0060090 molecular adaptor activity 3 GO:0098772 molecular function regulator activity 2
Localization
GO:0005634 nucleus 3 GO:0005694 chromosome 1
Pathway
R-HSA-74160 Gene expression (Transcription) 4 R-HSA-1266738 Developmental Biology 3 R-HSA-4839726 Chromatin organization 1
Partners
ISL1LDB1LHX1LMX1BMYB
Complex memberships
LDB1-LMX1B complexLDB1-Lhx1 complexLDB1-SSBP2 complex

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2019 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. X-ray crystallography (2.8-Å resolution) with biochemical validation Proceedings of the National Academy of Sciences of the United States of America High 31892537
2019 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). X-ray crystallography (1.52-Å resolution) Protein science : a publication of the Protein Society High 30676665
2010 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. Gene targeting (Ssbp2−/− mice), Western blot for LDB1 protein levels, transcript analysis Oncogene High 20348955
2005 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. Inducible expression system in U937 cells, clonogenicity assay, flow cytometry (cell cycle), Western blot (C-MYC) Oncogene Medium 15782145
2014 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. Ssbp2−/− mouse knockout, bone marrow transplantation, 5-fluorouracil treatment, RT-PCR for Notch1/E2a/Cdkn1a Journal of immunology (Baltimore, Md. : 1950) High 25238756
2009 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. Anti-phosphotyrosine immunoprecipitation, mass spectrometry, protein-specific immunoprecipitation, Western blot Proteomics Medium 19658100
2023 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. Tandem-affinity purification, morpholino knockdown in Xenopus, histological/morphological analysis Scientific reports Medium 37794075
2010 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. Immunofluorescence localization of SSBP2 under stress conditions in HEK293 cells vs. normal cells Journal of molecular signaling Low 20540776
2021 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. GWAS in mice, single-cell transcriptomics, Ssbp2 null mouse phenotyping Journal of the American Society of Nephrology : JASN Medium 34893534
2025 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. ChIP-seq, CRISPR knockout, acute auxin-inducible degron depletion, chromatin tethering, biochemical dimerization assay bioRxivpreprint Medium bio_10.1101_2025.06.05.658047
2025 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. EMSA, yeast one-hybrid, dual-luciferase assay, ChIP-PCR, Co-IP, pull-down, immunofluorescence, CCK-8, Transwell, xenograft Cancer cell international Medium 41024119

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2008 Novel SSBP2-JAK2 fusion gene resulting from a t(5;9)(q14.1;p24.1) in pre-B acute lymphocytic leukemia. Genes, chromosomes & cancer 57 18618714
2005 SSBP2, a candidate tumor suppressor gene, induces growth arrest and differentiation of myeloid leukemia cells. Oncogene 48 15782145
2010 SSBP2 is an in vivo tumor suppressor and regulator of LDB1 stability. Oncogene 32 20348955
2012 SSBP2 variants are associated with survival in glioblastoma patients. Clinical cancer research : an official journal of the American Association for Cancer Research 23 22472174
2019 Crystal structure of human LDB1 in complex with SSBP2. Proceedings of the National Academy of Sciences of the United States of America 22 31892537
2014 Requirement for ssbp2 in hematopoietic stem cell maintenance and stress response. Journal of immunology (Baltimore, Md. : 1950) 16 25238756
2009 Phosphorylation of the SSBP2 and ABL proteins by the ZNF198-FGFR1 fusion kinase seen in atypical myeloproliferative disorders as revealed by phosphopeptide-specific MS. Proteomics 16 19658100
2019 Crystal structure of the LUFS domain of human single-stranded DNA binding Protein 2 (SSBP2). Protein science : a publication of the Protein Society 10 30676665
2023 Xenopus Ssbp2 is required for embryonic pronephros morphogenesis and terminal differentiation. Scientific reports 5 37794075
2021 GWAS in Mice Maps Susceptibility to HIV-Associated Nephropathy to the Ssbp2 Locus. Journal of the American Society of Nephrology : JASN 4 34893534
2010 Adenoviral oncoprotein E1B55K mediates colocalization of SSBP2 and PML in response to stress. Journal of molecular signaling 4 20540776
2020 Low Expression of Single-stranded DNA Binding Protein 2 (SSBP2) Predicts Unfavourable Postoperative Outcomes in Patients With Clear Cell Renal Cell Carcinoma. In vivo (Athens, Greece) 3 31882468
2023 Treatment for a primary multidrug-resistant B-cell acute lymphoblastic leukemia patient carrying a SSBP2-CSF1R fusion gene: a case report. Frontiers in oncology 2 38107066
2025 Transcription factor MYB regulates glycolysis to promote the transfer and malignant progression of gastric cancer through the SSBP2/ISL1 axis. Cancer cell international 1 41024119
2026 Myeloid/lymphoid neoplasm with FLT3 gene fusion: report of a case with a novel t(5;13)(q13;q12) SSBP2::FLT3 fusion. Journal of hematopathology 0 42171857
2023 Xenopus Ssbp2 is required for embryonic pronephros morphogenesis and terminal differentiation. bioRxiv : the preprint server for biology 0 37090653

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