MicroRNA 34c Gene Down-regulation via DNA Methylation Promotes Self-renewal and Epithelial-Mesenchymal Transition in Breast Tumor-initiating Cells

Fengyan Yu,Yu Jiao,Yinghua Zhu,Ying Wang,Jingde Zhu,Xiuying Cui,Yujie Liu,Yinghua He,Eun-Young Park,Hongyu Zhang,Xiaobin Lv,Kelong Ma,Fengxi Su,Jong Hoon Park,Erwei Song

doi:10.1074/jbc.m111.280768

Abstract

Tumor-initiating cells (T-ICs), a subpopulation of cancer cells with stem cell-like properties, are related to tumor relapse and metastasis. Our previous studies identified a distinct profile of microRNA (miRNA) expression in breast T-ICs (BT-ICs), and the dysregulated miRNAs contribute to the self-renewal and tumorigenesis of these cells. However, the underlying mechanisms for miRNA dysregulation in BT-ICs remain obscure. In the present study, we demonstrated that the expression and function of miR-34c were reduced in the BT-ICs of MCF-7 and SK-3rd cells, a breast cancer cell line enriched for BT-ICs. Ectopic expression of miR-34c reduced the self-renewal of BT-ICs, inhibited epithelial-mesenchymal transition, and suppressed migration of the tumor cells via silencing target gene Notch4. Furthermore, we identified a single hypermethylated CpG site in the promoter region of miR-34c gene that contributed to transcriptional repression of miR-34c in BT-ICs by reducing DNA binding activities of Sp1. Therefore, miR-34c reduction in BT-ICs induced by a single hypermethylated CpG site in the promoter region promotes self-renewal and epithelial-mesenchymal transition of BT-ICs.

Highlights

The mechanisms for miRNA dysregulation in breast Tumor-initiating cells (T-ICs) (BT-ICs) remain obscure
We used an miRNA microarray analysis to compare the miRNA expression levels between the BT-ICs and the differentiated breast cancer cells in our previous study, and we observed that miR34c expression was reduced in the BT-ICs [5]
Our results revealed that primary miR-34b/c (Fig. 1A) and mature miR-34c (Fig. 1B) levels were down-regulated in the BT-ICs compared with the differentiated breast cancer cells. miR-34b expression was reduced in the BT-ICs (Fig. 1C)

Summary

Introduction

The mechanisms for miRNA dysregulation in BT-ICs remain obscure. Results: Single hypermethylated CpG site in the promoter region of miR-34c gene repressed miR-34c expression by reducing DNA binding activities of Sp1 and promoted self-renewal and EMT of BT-ICs. We demonstrated that the expression and function of miR-34c were reduced in the BT-ICs of MCF-7 and SK-3rd cells, a breast cancer cell line enriched for BT-ICs. Ectopic expression of miR-34c reduced the self-renewal of BTICs, inhibited epithelial-mesenchymal transition, and suppressed migration of the tumor cells via silencing target gene Notch. We identified a single hypermethylated CpG site in the promoter region of miR-34c gene that contributed to transcriptional repression of miR-34c in BT-ICs by reducing DNA binding activities of Sp1. MiR-34c reduction in BT-ICs induced by a single hypermethylated CpG site in the promoter region promotes self-renewal and epithelial-mesenchymal transition of BT-ICs

Objectives

Results

Conclusion