The role of polycomb group protein Bmi-1 and Notch4 in breast cancer stem cell inhibition by benzyl isothiocyanate

Abstract

We showed previously that garden cress constituent benzyl isothiocyanate (BITC) inhibits self-renewal of breast cancer stem cells (bCSC) in vitro and in vivo. The present study offers novel insights into the mechanism by which BITC inhibits bCSC. Flow cytometry and mammosphere assay was performed to quantify bCSC fraction. Protein expression was determined by western blotting. Apoptosis was assessed by flow cytometry using Annexin V-propidium iodide method. Cell migration was determined by Boyden chamber assay. BITC treatment resulted in a marked decrease in protein level of polycomb group protein B-lymphoma Moloney murine leukemia virus insertion region-1 (Bmi-1) in cultured human breast cancer cells (MCF-7, SUM159, MDAMB-231 and MDA-MB-361) and MDA-MB-231 xenografts in vivo. Overexpression (MCF-7) or knockdown (SUM159 and MDA-MB-231) of Bmi-1 protein had no meaningful impact on the BITC’s ability to inhibit cell viability and cell migration and/or induce apoptosis. On the other hand, inhibition of bCSC markers (aldehyde dehydrogenase 1 activity and mammosphere frequency) resulting from BITC exposure was significantly altered by Bmi-1 overexpression and knockdown. BITC was previously shown to cause activation of Notch1, Notch2 and Notch4 in association with induction of γ-secretase complex component Nicastrin, which are also implicated in maintenance of cancer stemness. BITC-mediated inhibition of bCSC was augmented by knockdown of Notch4 and Nicastrin, but not by RNA interference of Notch1 or Notch2. The present study highlights important roles for Bmi-1 and Notch4 in BITC-mediated suppression of bCSC.

miR-203 inhibits proliferation and self-renewal of leukemia stem cells by targeting survivin and Bmi-1

“…4B,C ). These data are consistent with previous reports that characterized Bmi-1 as a cancer stem cell regulator 26 27 . To explore whether Bmi-1 is a direct miR-203 target, we transfected LSCs with miR-203 or miR-NC, then used immuno-fluorescence to detect Bmi-1.…”

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