LDOC1

LDOC1 is a nuclear leucine-zipper protein that functions as a tumor suppressor by restraining NF-κB, JAK2/STAT3, PI3K/Akt, and Wnt/β-catenin signaling pathways and by regulating chromatin organization through control of histone H2B monoubiquitination. LDOC1 directly inhibits NF-κB transcriptional activity by suppressing p65/p50 expression and nuclear translocation, thereby reducing downstream cytokine production including IL-6 (PMID:12712434, PMID:28510691, PMID:26637328); it also forms a ternary complex with phospho-JAK2 and the E3 ubiquitin ligase LNX1 to promote ubiquitin-dependent proteasomal degradation of pJAK2, blocking STAT3 activation (PMID:30634502). LDOC1 interacts with histone H2B, H2Bub1, PSMA1, and THAP12 to limit global H2Bub1 levels and regulate chromatin accessibility at metastasis-related gene loci, and its loss enhances TGF-β-induced epithelial–mesenchymal plasticity (PMID:41484780). In the placenta, LDOC1 knockout causes aberrant trophoblast giant cell differentiation and progesterone overproduction leading to delayed parturition (PMID:25468940).

1. 1999 Medium

   The initial characterization of LDOC1 established it as a nuclear protein with a leucine-zipper-like motif and SH3-binding domain, providing the structural basis for subsequent interaction studies.

   Evidence EGFP fusion imaging and Northern blot in human cell lines

   PMID:10403563

   Open questions at the time

   • No interaction partners or functional consequence identified
   • Localization confirmed only by overexpressed fusion protein
2. 2003 High

   LDOC1 was shown to suppress NF-κB transcriptional activity and sensitize cancer cells to TNF-α/PMA-induced apoptosis, establishing NF-κB inhibition as its core tumor-suppressive mechanism.

   Evidence NF-κB luciferase reporter, stable transfection, and viability assays in BxPC-3 pancreatic cancer cells

   PMID:12712434

   Open questions at the time

   • Molecular mechanism of NF-κB inhibition not defined
   • No loss-of-function validation
3. 2005 High

   Two studies revealed that LDOC1 interacts with MZF-1 to potentiate apoptosis through mitochondrial and caspase pathways, and that WAVE3 sequesters LDOC1 from the nucleus to the cytoplasm to antagonize its pro-apoptotic function, establishing regulation of LDOC1 by subcellular relocalization.

   Evidence Co-immunoprecipitation, pulldown with domain mapping, fluorescence microscopy, annexin V/JC-1 flow cytometry

   PMID:15670815 PMID:16272576

   Open questions at the time

   • Physiological relevance of WAVE3-LDOC1 axis in tumors not demonstrated
   • p53 stabilization mechanism not molecularly defined
4. 2013 Medium

   Restoration of LDOC1 (with BEX1) in oral squamous cell carcinoma cells confirmed NF-κB suppression through reduced p50/p65 protein and demonstrated growth inhibition in vivo, extending the NF-κB axis to a second cancer type.

   Evidence Ectopic expression, Western blot for p50/p65, in vitro and xenograft growth assays

   PMID:23362108

   Open questions at the time

   • Individual contribution of LDOC1 versus BEX1 not fully separated
   • Mechanism of p50/p65 protein reduction unclear
5. 2014 High

   Knockout of Ldoc1 (Sirh7) in mice revealed its non-oncological role in trophoblast giant cell differentiation and placental endocrine control, demonstrating that LDOC1 restrains progesterone and PL1 production to ensure timely parturition.

   Evidence Ldoc1 knockout mouse, placental histology, P4 and PL1 hormone measurement

   PMID:25468940

   Open questions at the time

   • Molecular targets of LDOC1 in trophoblasts not identified
   • Whether NF-κB or JAK2/STAT3 pathways are involved in placental phenotype is unknown
6. 2015 Medium

   Cigarette smoke condensate was shown to silence LDOC1 via DNMT1/DNMT3A-mediated promoter hypermethylation, and LDOC1 loss promoted proliferation/clonogenicity, linking an environmental carcinogen to epigenetic LDOC1 inactivation.

   Evidence CSC treatment, methylation-specific PCR, DNMT nuclear accumulation, knockdown proliferation assays in oral keratinocytes

   PMID:26317789

   Open questions at the time

   • Direct DNMT recruitment to LDOC1 promoter not shown by ChIP
   • Whether CSC-induced methylation is reversible in vivo is untested
7. 2016 Medium

   Identification of GNL3L as a direct LDOC1 interactor established a mechanism by which LDOC1 destabilizes GNL3L and reverses GNL3L-driven NF-κB/p65 activation and proliferation.

   Evidence Co-immunoprecipitation, ectopic expression/knockdown, NF-κB reporter, proliferation assay

   PMID:27764577

   Open questions at the time

   • Mechanism of GNL3L destabilization (proteasomal? transcriptional?) not defined
   • In vivo relevance not tested
8. 2017 Medium

   Stable LDOC1 knockdown in ependymoma cells increased RELA transcription and IL-6 secretion, and demethylation restored LDOC1 expression, demonstrating that epigenetic LDOC1 silencing drives NF-κB-dependent cytokine production in brain tumors.

   Evidence Stable shRNA knockdown, ELISA for IL-6, 5-AZA-DC demethylation in ependymoma cell lines

   PMID:28510691

   Open questions at the time

   • Whether LDOC1 directly regulates RELA transcription or acts indirectly is unknown
   • Single cell line system
9. 2019 High

   LDOC1 was shown to bridge pJAK2 to the E3 ligase LNX1, promoting ubiquitin-dependent pJAK2 degradation and STAT3 inactivation, revealing an adaptor function in targeted protein turnover and a second major signaling axis suppressed by LDOC1.

   Evidence Co-immunoprecipitation, ubiquitination assay, confocal microscopy, in vivo xenograft with LDOC1 knockdown

   PMID:30634502

   Open questions at the time

   • Structural basis of ternary complex formation unknown
   • Whether LDOC1 similarly directs degradation of other substrates is unexplored
10. 2019 Medium

    Exosomal miR-4532 from AML cells was identified as a negative regulator of LDOC1 in hematopoietic stem cells, linking LDOC1 suppression to JAK2/STAT3-mediated disruption of normal hematopoiesis in the leukemic niche.

    Evidence Luciferase reporter for miR-4532–LDOC1 3′UTR, exosome co-culture, CFU assay, Western blot for pJAK2/pSTAT3

    PMID:31842997

    Open questions at the time

    • In vivo validation of exosomal miR-4532 niche effect not performed
    • Whether LDOC1 is the sole relevant target of miR-4532 is unclear
11. 2019 Medium

    LDOC1 was found to suppress Wnt/β-catenin signaling, reducing β-catenin nuclear localization and Wnt5a levels, broadening LDOC1's tumor-suppressive reach to a third major oncogenic pathway.

    Evidence Lentiviral overexpression, Western blot and immunofluorescence for β-catenin, Transwell assays, xenograft imaging in osteosarcoma and colorectal cancer cells

    PMID:28240050 PMID:31002361

    Open questions at the time

    • Direct molecular mechanism linking LDOC1 to Wnt pathway components not identified
    • Relationship between Wnt suppression and NF-κB suppression unclear
12. 2020 Medium

    LDOC1 deficiency was shown to enhance PI3K/Akt activation and inhibitory GSK-3β phosphorylation, leading to increased IL-1β production, establishing a PI3K/Akt/GSK-3β axis as another pathway restrained by LDOC1.

    Evidence Loss/gain-of-function, PI3K/Akt inhibitors, constitutively active GSK-3β(S9A) mutant, IL-1β ELISA upon Candida stimulation

    PMID:33120999

    Open questions at the time

    • Direct target of LDOC1 in PI3K/Akt pathway not identified
    • Relevance to cancer versus innate immunity not delineated
13. 2024 Medium

    The lncRNA LINC01270 was identified as a ceRNA sponging miR-326 to protect LDOC1 mRNA, establishing a second miRNA-based regulatory axis controlling LDOC1-dependent NF-κB suppression.

    Evidence siRNA knockdown, luciferase reporter, miRNA interactome analysis

    PMID:39682774

    Open questions at the time

    • In vivo ceRNA axis validation lacking
    • Relative importance of miR-326 versus miR-4532 in LDOC1 regulation unknown
14. 2025 High

    LDOC1 was revealed to regulate chromatin organization by interacting with H2B, H2Bub1, PSMA1, and THAP12 to control H2Bub1 levels, chromatin accessibility, and expression of metastasis-related genes, representing a fundamental epigenetic mechanism distinct from its signaling pathway functions.

    Evidence Co-immunoprecipitation, proximity ligation assay, ChIP-seq, ATAC-seq, MNase digestion, transcriptomics, migration/adhesion assays

    PMID:41484780

    Open questions at the time

    • Whether H2Bub1 regulation underlies LDOC1's effects on NF-κB, JAK2/STAT3, and Wnt pathways is untested
    • Structural basis of LDOC1-H2Bub1 interaction unknown
15. 2025 Medium

    H3K27me3-mediated silencing at the LDOC1 locus was shown to be required for PFA ependymoma growth, and LDOC1 restoration suppressed NF-κB/IL-6 and tumor growth in vivo, confirming LDOC1 as a bona fide tumor suppressor in this brain tumor.

    Evidence ChIP for H3K27me3, lentiviral LDOC1 restoration, in vivo tumor competition assay, IL-6 ELISA

    PMID:39901723

    Open questions at the time

    • Whether H3K27me3 silencing is driven by EZH2 or other methyltransferases at LDOC1 not tested
    • Therapeutic strategies to restore LDOC1 in PFA not explored

• It remains unknown whether LDOC1's epigenetic function (H2Bub1 regulation) mechanistically underlies its suppression of NF-κB, JAK2/STAT3, PI3K/Akt, and Wnt/β-catenin signaling, or whether these represent independent parallel functions; no structural model of LDOC1 or its complexes exists.
• No structure of LDOC1 or any of its complexes determined
• Hierarchy among multiple suppressed pathways unresolved
• Physiological relevance of LDOC1 in non-cancer adult tissues beyond placenta unknown