LDOC1 connects histone H2B monoubiquitination to tumor cell plasticity in non-small cell lung cancer.

BACKGROUND: Non-small cell lung cancer (NSCLC) remains a leading cause of cancer-related mortality, partly because epigenetic dysregulation drives tumor progression and metastasis. We previously showed that leucine zipper downregulated in cancer 1 (LDOC1) modulates the metastatic potential of NSCLC cells. The structural features of LDOC1 suggest that it can interact with nuclear histones, and although it lacks a canonical nuclear localization signal, it predominantly localizes to the nucleus in NSCLC cells; its loss causes broad transcriptomic changes, supporting a role for LDOC1 as an epigenetic regulator acting through histone modifications. METHODS: The levels of histone proteins were assessed in NSCLC cell lines with either LDOC1 knockdown or ectopic expression. Transcriptomic profiling, ChIP-seq, ATAC-seq, MNase digestion assays, flow cytometry, coimmunoprecipitation, proximity ligation assays, immunofluorescence staining, immunohistochemistry, and functional assays were conducted. Clinical relevance was analyzed with archived NSCLC samples and using datasets from the UCSC Xena database. RESULTS: LDOC1 interacts with histone H2B and H2Bub1 as well as with PSMA1 to promote their proteasomal degradation, thereby limiting global H2Bub1 levels. Despite increasing global H2Bub1 abundance, LDOC1 knockdown caused a pronounced loss of chromatin-bound H2Bub1 and enhanced chromatin compaction, effects that were partially mediated by the LDOC1-THAP12 interaction. THAP12 overexpression increased LDOC1 recovery in nuclear histone fractions. Integrated transcriptomic and epigenomic analyses revealed that the LDOC1-H2Bub1 axis regulates key metastasis-related genes involved in cytoskeletal remodeling, cell adhesion, and epithelial-mesenchymal (E-M) transition. Functionally, LDOC1 loss enhanced TGF-β-induced E-M plasticity, promoted a hybrid E/M phenotype, reduced adhesion, and altered migration dynamics. In clinical samples, H2Bub1 was significantly upregulated in spread through air spaces (STAS) and inversely correlated with LDOC1 expression. High H2Bub1 expression predicted shorter progression-free survival in EGFRᵂᵀ NSCLC patients receiving chemotherapy, and TCGA data linked LDOC1 downregulation to KRAS-mutant lung adenocarcinoma. CONCLUSIONS: LDOC1-mediated chromatin remodeling, through regulation of H2Bub1 recruitment and turnover, represents a key mechanism promoting NSCLC progression. The LDOC1-H2Bub1 axis, potentially involving THAP12, shapes chromatin accessibility and metastatic transcriptional programs, providing mechanistic and clinical insights into tumor aggressiveness and therapeutic response.