Silencing NKD2 by promoter region hypermethylation promotes gastric cancer invasion and metastasis by up-regulating SOX18 in human gastric cancer

// Yan Jia 1, 2, * , Baoping Cao 1, 3, * , Yunsheng Yang 1 , Enqiang Linghu 1 , Qimin Zhan 4 , Youyong Lu 5 , Yingyan Yu 6 , James G. Herman 7 , Mingzhou Guo 1 1 Department of Gastroenterology & Hepatology, Chinese PLA General Hospital, Beijing 100853, China 2 Department of Breast Oncology, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, and Key Laboratory of Cancer Prevention and Therapy, Tianjin 300060, China 3 Medical College of NanKai University, Tianjin 300071, China 4 State Key Laboratory of Molecular Oncology, Cancer Institute and Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100021, China 5 Laboratory of Molecular Oncology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital/Institute, Beijing 100142, China 6 Shanghai Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200240, China 7 The Hillman Cancer Center, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA * These authors have contributed equally to this work Correspondence to: Mingzhou Guo, e-mail: mzguo@hotmail.com James G. Herman, e-mail: Hermanj3@upmc.edu Keywords: NKD1, NKD2, SOX18, DNA methylation, gastric cancer Received: April 23, 2015 Accepted: September 02, 2015 Published: September 14, 2015 ABSTRACT Naked cuticle homolog2 ( NKD2 ) is located in chromosome 5p15.3, which is frequently loss of heterozygosity in human colorectal and gastric cancers. In order to understand the mechanism of NKD2 in gastric cancer development, 6 gastric cancer cell lines and 196 cases of human primary gastric cancer samples were involved. Methylation specific PCR (MSP), gene expression array, flow cytometry, transwell assay and xenograft mice model were employed in this study. The expression of NKD1 and NKD2 was silenced by promoter region hypermethylation. NKD1 and NKD2 were methylated in 11.7% (23/196) and 53.1% (104/196) in human primary gastric cancer samples. NKD2 methylation is associated with cell differentiation, TNM stage and distant metastasis significantly (all P < 0.05), and the overall survival time is longer in NKD2 unmethylated group compared to NKD2 methylated group ( P < 0.05). Restoration of NKD2 expression suppressed cell proliferation, colony formation, cell invasion and migration, induced G2/M phase arrest, and sensitized cancer cells to docetaxel. NKD2 inhibits SOX18 and MMP-2,7,9 expression and suppresses BGC823 cell xenograft growth. In conclusion, NKD2 methylation may serve as a poor prognostic and chemo-sensitive marker in human gastric cancer. NKD2 impedes gastric cancer metastasis by inhibiting SOX18.