DACT1, an antagonist to Wnt/β-catenin signaling, suppresses tumor cell growth and is frequently silenced in breast cancer.

Xuedong Yin,Xinrong Luo,Jianbo Huang,Lili Li,Kathleen Kelly,Xingsheng Shu,Weiyan Peng,Tingxiu Xiang,Qian Tao,Xianwei Su,Ying Yuan,Michael Oberst,Guosheng Ren

doi:10.1186/bcr3399

Abstract

IntroductionAberrant activation of Wnt/β-catenin signaling plays an important role in the pathogenesis of breast cancer. DACT1 (Dapper/Frodo) has been identified as involved in antagonizing Wnt/β-catenin signaling through interacting with Dishevelled (Dvl), a central mediator of Wnt signaling, whereas its role in breast tumorigenesis remains unclear.MethodsWe examined DACT1 expression in breast cancer cell lines and primary tumors with semiquantitative or quantitative RT-PCR and immunochemistry, and further evaluated the promoter methylation of DACT1 with methylation-specific PCR (MSP). We also explored the tumor-suppressive functions of DACT1 in vivo and in vitro, and its related mechanism in breast cancer.ResultsWe identified DACT1 as a methylated target in our breast cancer epigenome study. Here, we further investigated DACT1 expression in multiple breast cell lines and primary tumors, and further studied its function and molecular mechanisms. We found that DACT1 expression was silenced in eight (88.9%) of nine breast cancer cell lines, and its protein levels were obviously reduced in breast tumors compared with paired surgical-margin tissues. Promoter CpG methylation of DACT1 was detected in five (55.6%) of nine breast cancer cell lines and 40 (29.9%) of 134 primary tumors, but not in surgical-margin tissues and normal breast tissues. Demethylation treatment of breast cancer cell lines restored DACT1 expression along with promoter demethylation, suggesting that an epigenetic mechanism mediates DACT1 silencing in breast cancer. Functional assays showed that ectopic expression of DACT1 could inhibit breast tumor cell proliferation in vivo and in vitro through inducing apoptosis, and further suppress tumor cell migration through antagonizing the Wnt/β-catenin signaling pathway.ConclusionsOur study demonstrates that DACT1 could function as a tumor suppressor but was frequently downregulated in breast cancer.

Highlights

Aberrant activation of Wnt/b-catenin signaling plays an important role in the pathogenesis of breast cancer
DACT1 is frequently reduced in breast cancer We first examined DACT1 expression in a panel of human normal adult tissues and fetal tissues, as well as breast cancer cell lines, by using semiquantitative RTPCR
Results showed that DACT1 was widely expressed in human normal tissues and fetal tissues, including normal breast tissues (Figure 1A, C), but was frequently silenced or downregulated in breast cancer cell lines studied (Figure 1C)

Summary

Introduction

Aberrant activation of Wnt/b-catenin signaling plays an important role in the pathogenesis of breast cancer. DACT1 (Dapper/Frodo) has been identified as involved in antagonizing Wnt/b-catenin signaling through interacting with Dishevelled (Dvl), a central mediator of Wnt signaling, whereas its role in breast tumorigenesis remains unclear. Wnt/b-catenin signaling plays an important role in multiple tumorigenesis, including breast cancer [6]. Epigenetic silencing of negative regulators of WNT signaling is crucial for the aberrant activation of WNT/b-catenin signaling in tumor pathogenesis [5,7]. DACT1, a homologue of Dapper, located at chromosomal region 14q23.1, was first identified as a Dishevelled (Dvl)-associated antagonist of Wnt/b-catenin and JNK signaling pathways [8,9], DACT1 is expressed during embryonic development in the adult brains of mice [10,11], but studies on its role in tumorigenesis are scanty. Its expression and biologic functions in breast cancer pathogenesis are unknown

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Conclusion