Depletion of Bmi-1 enhances 5-fluorouracil-induced apoptosis and autophagy in hepatocellular carcinoma cells.

5-fluorouracil (5-FU) is one of the standard chemoradiotherapy regimens for hepatocellular carcinoma (HCC) treatment. B-cell-specific Moloney murine leukemia virus insertion site 1 (Bmi-1) has been demonstrated to regulate proliferation. Additionally, Bmi-1 overexpression has been identified in HCC cell lines and correlates with the advanced invasive stage of tumor progression and poor prognosis. In this study, we examined the effects of 5-FU treatment on cell growth in HCC cells with or without Bmi-1 depletion. The IC(50) values of 5-FU were significantly decreased to a greater extent in cells with Bmi-1 knockdown. Depletion of Bmi-1 increased sensitivity of the cells to 5-FU and increased apoptosis. Knockdown of endogenous Bmi-1 led to a substantial reduction in the levels of phospho-AKT and Bcl-2 with a concomitant increase in the levels of Bax. Additionally, 5-FU induced the conversion/turnover of microtubule-associated protein 1 light chain 3 (LC3). Knockdown of endogenous Bmi-1 led to an increase in the levels of Beclin-1 and the accumulation of LC3-II. Together, these findings reveal that Bmi-1 depletion enhanced the chemosensitivity of HCC cells by inducing apoptosis and autophagy, which is associated with the PI3K/AKT and Bcl-2/Beclin-1 pathways.