High Expression of G9a Induces Cisplatin Resistance in Hepatocellular Carcinoma

Chemotherapeutic drug resistance is the main obstacle that affects the efficacy of current therapies of hepatocellular carcinoma (HCC), which needs to be addressed urgently. High expression of histone methyltransferase G9a was reported to play a pivotal role in the progression of HCC. Regulatory mechanism of aberrant activation of G9a in HCC and the association with subsequent cisplatin (DDP) resistance still remains ambiguous. This study strived to investigate mechanism of G9a overexpression and its impact on cisplatin resistance in HCC cells.

In this experimental study, we investigated effects of different concentrations of cisplatin in combination with BIX-01294 or PR-619 on viability and apoptosis of HuH7 and SNU387 cells via CCK-8 kit and flow cytometric analysis, respectively. Colony formation capacity was applied to evaluate effect of cisplatin with or without BIX-01294 on cell proliferation, and western blotting was used to verify expression level of the related proteins. Global mRNA expression profile analysis was adopted to identify differentially expressed genes associated with overexpression of G9a.

We observed that overexpression of G9a admittedly promoted cisplatin resistance in HCC cells. Global mRNA expression profile analysis after G9a inhibition showed that DNA repair and cell cycle progression were downregulated. Moreover, we identified that deubiquitination enzymes (DUBs) stabilized high expression of G9a in HCC through deubiquitination. Additionally, cisplatin could significantly inhibit proliferation of DUBs-deficient HCC cells, while promoting their apoptosis.

Collectively, our data indicated that DUBs stabilize G9a through deubiquitination, thereby participating in the cisplatin resistance of HCC cells. The elucidation of this mechanism contributes to propose a potential alternative intervention strategy for the treatment of HCC patients harboring high G9a levels.