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

Abstract

// Junhao Mu 1, * , Tianli Hui 1, * , Bianfei Shao 1 , Lili Li 2 , Zhenfang Du 2 , Li Lu 2 , Lin Ye 1 , Shuman Li 1 , Qianqian Li 3 , Qian Xiao 1 , Zhu Qiu 1 , Yan Zhang 1 , Jiangxia Fan 1 , Guosheng Ren 1 , Qian Tao 1, 2 and Tingxiu Xiang 1 1 Chongqing Key Laboratory of Molecular Oncology and Epigenetics, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China 2 Cancer Epigenetics Laboratory, Department of Clinical Oncology, State Key Laboratory of Oncology in South China, Sir YK Pao Center for Cancer and Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong and CUHK Shenzhen Research Institute, Hong Kong 3 Chinese Medicine Hospital of Linyi City, Shandong, China * These authors have contributed equally to this work Correspondence to: Qian Tao, email: [e-mail] Tingxiu Xiang, email: [e-mail] Keywords: DKK2, tumor suppressor, methylation, cancer, Wnt signaling Received: December 07, 2016      Accepted: March 20, 2017      Published: April 12, 2017 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.