Silencing Bmi1 expression suppresses cancer stemness and enhances chemosensitivity in endometrial cancer cells

Abstract

Background: Bmi1, a polycomb group gene, is essential for self-renewal of stem cells and is frequently upregulated in various cancer cells. We aimed to investigate the effect of Bmi1 silencing on cancer stemness and chemosensitivity in endometrial cancer using targeted siRNA approach in HEC1A and Ishikawa cells.

Methods: Cell viability after treatment with Bmi1 siRNA was assessed using the MTT assay, and cell apoptosis was visualized using the TdT-mediated dUTP nick-end labeling (TUNEL) method. Western blotting, migration assays and invasion assays were performed to detect changes in the stem-like properties of cancer cells. To evaluate the anticancer effect of Bmi1 silencing, HEC1A and Ishikawa cells were treated with 100 nM Bmi1 siRNA and/or 40 μM cisplatin.

Results: In the MTT assay, compared to control, viability of HEC1A and Ishikawa cells significantly decreased after Bmi1 siRNA treatment in a dose-dependent manner. Bmi1 silencing using siRNA increased the expression of cleaved caspase-3 and cleaved poly adenosine diphosphate-ribose polymerase polymerase (PARP) as observed in the western blot analysis. Apoptosis significantly increased in the HEC1A and Ishikawa cells treated with 100 nM Bmi1 siRNA for 48 h than in the control cells in TUNEL assay. SOX2 and Oct4 expression decreased in the HEC1A and Ishikawa cells treated with Bmi1 siRNA, while E-cadherin expression increased. Further, migratory and invasive properties were significantly inhibited by Bmi1 siRNA treatment in both cell lines. Notably, viability of HEC1A and Ishikawa cells decreased more when they were concurrently treated with Bmi1 siRNA and cisplatin compared to when they were treated with Bmi1 siRNA or cisplatin alone.

Conclusion: Bmi1 silencing suppresses cancer stemness in HEC1A and Ishikawa cells. Concurrent treatment with Bmi1 siRNA and cisplatin resulted in additive anticancer effect with a cell line-specific pattern, which was higher than that shown by cisplatin treatment alone.

Keywords: Bmi1; Chemoresistance; Cisplatin; Endometrial cancer cells; Epithelial–mesenchymal transition.