Abstract
Abstract We have shown previously that benzyl isothiocyanate (BITC), a nontoxic small-molecule constituent of edible cruciferous vegetables (eg, garden cress) inhibits breast cancer stem cells (bCSC) in vitro and in vivo but the underlying mechanisms are not fully understood. Bmi-1 is a member of the polycomb group family of proteins that function in the epigenetic silencing of genes governing self-renewal, differentiation, and proliferation. The present study was undertaken to investigate the role of Bmi-1 in BITC-mediated inhibition of bCSC. BITC treatment downregulated protein level of Bmi-1 in cultured human breast cancer cells (MCF-7, SUM159 and MDA-MB-231), and in MDA-MB-231 xenografts in vivo. Ectopic expression of Bmi-1 alone was sufficient to drive stemness in MCF-7 cells. In addition, Bmi-1 overexpression in MCF-7 cells conferred marked protection against BITC-mediated inhibition of bCSC as evidenced by mammosphere frequency and aldehyde dehydrogenase 1 (ALDH1) activity. Consistent with these observations, silencing of Bmi-1 in SUM159 cells remarkably reduced the portion of bCSC. Apoptosis induced by BITC was also partially attenuated by overexpression of Bmi-1 in MCF-7 cells but its silencing had no effect on BITC-induced apoptosis in SUM159 cells. Previous studies have shown that miRNA128 inhibits cell proliferation and self-renewal by direct regulation of Bmi-1. BITC treatment modestly but statistically significantly increased the expression of miRNA128 in both MCF-7 and SUM159 cells. Inhibition of miRNA128 increased the mammosphere formation in MCF-7 and SUM159 cells and partially attenuated BITC-mediated inhibition of mammosphere formation. These observations led us to conclude that Bmi-1 is a novel target of BITC-mediated inhibition of bCSC. This study was supported by the grant RO1 CA129347 awarded by the National Cancer Institute. Citation Format: Su-Hyeong Kim, Shivendra V. Singh. The role of Bmi-1 in benzyl isothiocyanate-mediated suppression of breast cancer stem cell self-renewal. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 224. doi:10.1158/1538-7445.AM2014-224
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