RNAi-mediated silencing of the Bmi-1 gene causes growth inhibition and enhances doxorubicin-induced apoptosis in MCF-7 cells

Xiang-Mei Wu,Hong-Juan Cui,You-Quan Bu,Fa-Ping Yi,Yan-Yan Shi,Joyeeta Sengupta,Tao Liu,Chen-Fu Yuan,Xing Liu,Fang-Zhou Song

doi:10.1590/s1415-47572009005000092

Xiang-Mei Wu, Hong-Juan Cui + Show 8 more

Open Access

https://doi.org/10.1590/s1415-47572009005000092

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Abstract

The oncogene Bmi-1 is a member of the Polycomb group gene family. Its expression is found to be greatly increased in a number of malignant tumors including breast cancer. This could suggest Bmi-1 as a potent therapeutic target. In this study, RNAi was introduced to down-regulate the expression of Bmi-1 in a highly malignant breast adenocarcinoma cell line, MCF-7. A thorough study of the biological behavior and chemosensitivity changes of the MCF-7 cells was carried out in context to the therapeutic potential of Bmi-1. The results obtained indicated that siRNA targeting of Bmi-1 could lead to an efficient and specific inhibition of endogenous Bmi-1 activity. The mRNA and protein expression of Bmi-1 were determined by RT-PCR and Western blot, respectively. Furthermore, silencing of Bmi-1 resulted in a drastic inhibition of the growth of MCF-7 cells as well as G1 /S phase transition. The number of target cells was found to increase in phase G 0 /G 1 and decrease in the S phase, but no increase in the basal level of apoptosis was noticed. On the other hand, a reduction in the expression of cyclin D1 and an increase in the expression of p21 were also noticed. Silencing of Bmi-1 made the MCF-7 cells more sensitive to the chemotherapeutic agent doxorubicin and induced a significantly higher percentage of apoptotic cells. Here, we report on a study regarding the RNAi-mediated silencing of the Bmi-1 gene in breast cancer.

Highlights

Breast cancer is one of the most common malignancies affecting women worldwide
In the first phase of our study, we determined the silencing of the Bmi-1 gene activity in the targeted MCF-7 cells
MCF-7 cells were transiently transfected with pSuper-retro/Bmi-1 si and pSuper-retro/Green Fluorescent Protein (GFP) si

Summary

Introduction

Breast cancer is one of the most common malignancies affecting women worldwide. Despite the recent development of various therapeutic strategies, the prognosis for this cancer still remains poor. More efforts are needed to understand its molecular pathway in order to develop an effective therapy to achieve cure. Bmi-1 (B-cell-specific moloney murine leukemia virus insertion site 1) was originally identified as an oncogenic partner of c-Myc in murine lymphomagenesis (Haupt et al, 1993; Van Lohuizen et al, 1991). It is a component of the Polycomb repressive complex 1, which represses gene expression through chromatin modifications (ValkLingbeek et al, 2004). Other studies demonstrated that Bmi-1 regulates the differentiation and clonogenic self-renewal of I-type neuroblastoma cells (Cui et al, 2006)

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