CBX3 Downregulates HLTF to Activate PI3K/AKT Signaling Promoting Cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive cancer with poor response to chemotherapy or radiation, necessitating novel therapeutic approaches. Epigenetic regulation, which is reversible, plays a significant role in cancer progression. CBX3 (HP1γ), a key heterochromatin protein, regulates gene expression by interacting with histone H3 lysine 9 trimethyl (H3K9me3) markers. While CBX3 is linked to tumor progression in various cancers, its role in CCA remains unclear. This study reveals that CBX3 and H3K9me3 enrich the HLTF promoter, a gene involved in chromatin remodeling and DNA repair. HLTF is often inactivated by hypermethylation in other cancers, suggesting tumor-suppressive properties. Depleting CBX3 in CCA cells elevates HLTF expression, reducing proliferation, while HLTF silencing reverses this effect. Furthermore, HLTF overexpression inhibits PI3K-AKT signaling activated by CBX3. These findings suggest CBX3 promotes CCA progression by suppressing HLTF expression.