Protocadherin 17 functions as a tumor suppressor suppressing Wnt/β-catenin signaling and cell metastasis and is frequently methylated in breast cancer
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Xuedong Yin1,*, Tingxiu Xiang1,*, Junhao Mu1, Haitao Mao2, Lili Li2, Xin Huang2, Chunhong Li3, Yixiao Feng1, Xinrong Luo1, Yuxian Wei1, Weiyan Peng1, Guosheng Ren1, Qian Tao1,2
1Chongqing Key Laboratory of Molecular Oncology and Epigenetics, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China
2Cancer 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
3Oncology Department, Suining Sichuan Center Hospital, Sichuan, China
*These authors contributed equally to this work
Guosheng Ren, email: [email protected]
Qian Tao, email: [email protected]
Keywords: tumor suppressor, PCDH17, methylation, cancer, β-catenin
Received: November 27, 2015 Accepted: May 28, 2016 Published: June 16, 2016
Protocadherins play important roles in the regulation of cell adhesion and signaling transduction. Aberrant expression of protocadherins has been shown to be associated with multiple tumorigenesis. We previously identified PCDH17, encoding protocadherin 17, as a frequently methylated and downregulated tumor suppressor gene (TSG) in gastric and colorectal cancers. Here, we examined the abnormalities and functions of PCDH17 in breast cancer pathogenesis. We used PCR and immunohistochemistry to check its expression pattern in breast tumor cell lines and primary tumors. Methylation-specific PCR (MSP) was applied to examine its promoter methylation status in breast tumor cell lines and primary tumors. The biological functions of PCDH17 in breast tumor cells were assessed using in vitro and in vivo assays. We found that PCDH17 was frequently downregulated or silenced in 78% (7/9) of breast tumor cell lines, as well as 89% (32/36) of primary tumors. Downregulation of PCDH17 in breast cancer was mainly due to the methylation of its promoter. Ectopic expression of PCDH17 in breast tumor cells inhibited cell proliferation and mobility through arresting cell cycle and inducing apoptosis. In breast tumor cells, PCDH17 significantly suppressed the active β-catenin level and its downstream target gene expression. Thus, we found that PCDH17 functions as a tumor suppressor inhibiting Wnt/β-catenin signaling and metastasis in breast cancer but is frequently methylated in primary tumors which could be a potential biomarker.
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