Dickkopf-related protein 2 induces G0/G1 arrest and apoptosis through suppressing Wnt/β-catenin signaling and is frequently methylated in breast cancer.

Junhao Mu,Shuman Li,Yan Zhang,Tingxiu Xiang,Zhenfang Du,Guosheng Ren,Qian Tao,Zhu Qiu,Li Lu,Tianli Hui,Lili Li,Lin Ye,Jiangxia Fan,Qianqian Li,Bianfei Shao,Qian Xiao

doi:10.18632/oncotarget.17055

Abstract

Dickkopf-related protein 2 (DKK2) is one of the antagonists of Wnt/β-catenin signaling, with its downregulation reported in multiple cancers. However, how DKK2 contributes to breast tumorigenesis remains unclear. We examined its expression and promoter methylation in 10 breast tumor cell lines, 98 primary tumors, and 21 normal breast tissues. Compared with normal tissues, DKK2 was frequently silenced in breast cell lines (7/8). DKK2 promoter methylation was detected in 77.8% of cell lines and 86.7% of breast tumors; while rarely detected in normal breast tissues (19%), indicating common DKK2 methylation in breast cancer. Ectopic expression of DKK2 changed breast tumor cell morphology, inhibited cell proliferation and colony formation by inducing G0/G1 cell cycle arrest and apoptosis, and suppressed tumor cell migration by reversing epithelial-mesenchymal transition (EMT) and downregulating stem cell markers. Moreover, restored expression of DKK2 in MCF7 cells disrupted the microtube formation of human umbilical vein endothelial cells on Matrigel®. In vivo, the growth of MDA-MB-231 cells in nude mice was markedly decreased after stable expression of DKK2. DKK2 suppressed canonical Wnt/β-catenin signaling by inhibiting β-catenin activity with decreased active β-catenin protein. Thus, our findings demonstrate that DKK2 functions as a tumor suppressor through inhibiting cell proliferation and inducing apoptosis via regulating Wnt signaling during breast tumorigenesis.

Highlights

Wnt/β-catenin pathway is critical to multiple tumorigenesis [1]
Our findings demonstrate that Dickkopf-related protein 2 (DKK2) functions as a tumor suppressor through inhibiting cell proliferation and inducing apoptosis via regulating Wnt signaling during breast tumorigenesis
We showed that DKK2 mRNA level was significantly lower in breast cancer tissues than that in paired surgical-margins by qRT-PCR (*p < 0.05) (Figure 2C)

Summary

Introduction

Wnt/β-catenin pathway is critical to multiple tumorigenesis [1]. Both genetic and epigenetic changes cause abnormal activation of Wnt pathway components that are involved in multiple cell functions, contributing to tumor initiation and development.Wnt signaling is comprised of canonical Wnt/βcatenin and non-canonical Wnt signaling that are independent of β-catenin [2]. Wnt/β-catenin pathway is critical to multiple tumorigenesis [1]. Both genetic and epigenetic changes cause abnormal activation of Wnt pathway components that are involved in multiple cell functions, contributing to tumor initiation and development. A majority of breast cancer studies reveals that Wnt antagonists can be regulated by epigenetic changes. DNA www.impactjournals.com/oncotarget methylation is frequently detected in this pathway in multiple cancers, especially Wnt antagonists are frequently down-regulated by promoter CpG methylation, suggesting that aberrant epigenetic changes towards Wnt signaling, rather than gene deletion or mutation, are involved in breast tumorigenesis [2, 6,7,8,9,10]

Methods

Results

Discussion

Conclusion