BRD9 Enhances Activation of Pregnane X Receptor Pathway and the Resistance of Hepatocellular Carcinoma Cells to Molecular Targeted Agents
Tongya Yu, Nianrong Zhang, Jun zhang, Junli Pang, Xinshan Deng, Huiwei Sun, Yantao Chai, Xiaojuan Li, Yue Wang, Fan FengIntroduction/Objective:
Bromodomain-containing protein 9 (BRD9) is a newly identified oncogenic regulatory factor in multiple human malignancies, yet its precise roles in hepatocellular carcinoma (HCC) remain largely unknown. This study aimed to investigate the function and mechanism of BRD9 in HCC, particularly its involvement in molecular targeted drug resistance.
Methods:
BRD9 expression was either overexpressed or knocked down in HCC cells. PXR transcription factor activity was assessed using luciferase reporter assays, quantitative polymerase chain reaction (qPCR), and chromatin immunoprecipitation (ChIP). HCC cells were treated with serial concentrations of molecularly targeted drugs. Antitumor activity was evaluated by MTT assays, colony formation assays, flow cytometry for apoptosis analysis, and subcutaneous tumor models. Drug metabolic rates were quantified using high-performance liquid chromatography (HPLC).
Results:
Overexpression of BRD9 significantly enhanced the transcriptional activity of PXR and promoted the expression of PXR-dependent multidrug resistance-related genes, including CYP3A4 and ABCB1. Mechanistically, BRD9 overexpression facilitated the recruitment of PXR to the promoter and enhancer regions of CYP3A4, thereby accelerating the metabolic clearance of sorafenib in HCC cells. Functionally, enforced expression of BRD9 rendered HCC cells more resistant to molecularly targeted agents, whereas knockdown of BRD9 sensitized them to these drugs. Furthermore, combination therapy experiments demonstrated that the BRD9 smallmolecule inhibitor I-BRD9 exerted synergistic antitumor activity with sorafenib against HCC cells.
Discussion:
These findings reveal that BRD9 mediates molecular targeted drug resistance in HCC through enhancing the transcription factor activation of PXR. This mechanism provides a potential therapeutic target for overcoming drug resistance in HCC, and the synergistic effect of IBRD9 with sorafenib suggests a promising combination strategy.
Conclusion:
BRD9 promotes resistance to molecular targeted drugs in HCC via PXR-dependent transcriptional activation. Targeting BRD9 may represent a novel approach to sensitize HCC cells to existing therapies.