DACT2 silencing by promoter CpG methylation disrupts its regulation of epithelial-to-mesenchymal transition and cytoskeleton reorganization in breast cancer cells.

Tingxiu Xiang,Qian Tao,Weiyan Peng,Lili Li,Yichao Fan,Michael Oberst,Chunhong Li,Junhao Mu,Kathleen Kelly,Yixiao Feng,Ying Ying,Guosheng Ren

doi:10.18632/oncotarget.12341

Abstract

Wnt signaling plays an important role in breast carcinogenesis. DAPPER2 (DACT2) functions as an inhibitor of canonical Wnt signaling and plays distinct roles in different cell contexts, with its role in breast tumorigenesis unclear. We investigated DACT2 expression in breast cancer cell lines and primary tumors, as well as its functions and molecular mechanisms. Results showed that DACT2 expression was silenced in 9/9 of cell lines. Promoter CpG methylation of DACT2 was detected in 89% (8/9) of cell lines, as well as in 73% (107/147) of primary tumors, but only in 20% (1/5) of surgical margin tissues and in none of normal breast tissues. Demethylation of BT549 and T47D cell lines with 5-aza-2'-deoxycytidine restored DACT2 expression along with promoter demethylation, suggesting that its downregulation in breast cancer is dependent on promoter methylation. Furthermore, ectopic expression of DACT2 induced breast cell apoptosis in vitro, and further inhibited breast tumor cell proliferation, migration and EMT, through antagonizing Wnt/β-catenin and Akt/GSK-3 signaling. Thus, these results demonstrate that DACT2 functions as a tumor suppressor for breast cancer but was frequently disrupted epigenetically in this cancer.

Highlights

Breast cancer is a highly heterogeneous cancer associated with alterations in multiple signal pathways
We performed RT-PCR analysis to examine DACT2 expression in nine breast cancer cell lines
The results indicated that promoter methylation is a major mechanism of DACT2 silencing in breast cancer cells

Summary

Introduction

Breast cancer is a highly heterogeneous cancer associated with alterations in multiple signal pathways. Wnt signaling plays a key role during breast carcinogenesis and progression [1–2]. Binding of Wnt to frizzled (Fz) and low density lipoprotein receptor related protein (LRP)-5/6 results in the activation of dishevelled (Dvl), which promotes β-catenin stabilization and nuclear translocation to act as a transcriptional coactivator of lymphoid enhancing factor-1 and T-cell factor-1 (LEF/ TCF) transcription factors to activate the transcription of multiple target genes [4]. The Wnt/Ca2+-PCP pathway appears to involve a Wnt ligand and Fz, but does not involve LRP-5/6 co-receptors and β-catenin. Activation of this pathway leads to the association of Dvl with Rac, Rho and Rho-associated kinase (ROCK), resulting in the restructuring of cytoskeleton

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Conclusion