title: REC8 functions as a tumor suppressor and is epigenetically downregulated in gastric cancer, especially in EBV-positive subtype.
abstract: REC8 meiotic recombination protein (REC8) was found to be preferentially methylated in gastric cancer (GC) using promoter methylation array. We aimed to elucidate the epigenetic alteration and biological function of REC8 in GC. REC8 was downregulated in 100% (3/3) of Epstein-Barr virus (EBV)-positive and 80% (8/10) of EBV-negative GC cell lines by promoter methylation, but the expression could be restored through demethylation treatment. Protein expression of REC8 was significantly lower in human primary gastric tumors than in adjacent non-tumor tissues. A negative correlation between methylation and mRNA expression of REC8 was observed in 223 gastric samples of The Cancer Genome Atlas study (r=-0.7018, P<0.001). The methylation level (%) of the REC8 promoter was significantly higher in EBV-positive gastric tumors than in EBV-negative gastric tumors, as shown by bisulfite genomic sequencing (77.6 (69.3-80.5) vs 51.4 (39.5-62.3), median (interquartile range); P<0.001); methylation levels in both subtypes of tumors were significantly higher than in normal stomach tissues (14.8 (4.2-24.0)) (both P<0.001). Multivariate analysis revealed that REC8 methylation was an independent factor for poor survival in GC patients (hazard ratio=1.68, P<0.05). REC8 expression significantly suppressed cell viability, clonogenicity and cell cycle progression; it induced apoptosis and inhibited migration of AGS-EBV (EBV-positive) and BGC823 (EBV-negative) GC cells, and it suppressed tumorigenicity in nude mice. In contrast, knockdown of REC8 in gastric epithelial immortalized GES-1 cells significantly increased cell viability, clonogenicity and migration ability. The tumor-suppressive effect of REC8 is mediated at least in part by the downregulation of genes involved in cell growth (G6PD, SLC2A1, NOL3, MCM2, SNAI1 and SNAI2), and the upregulation of apoptosis/migration inhibitors (GADD45G and LDHA) and tumor suppressors (PinX1, IGFBP3 and ETS2). In conclusion, REC8 is a novel tumor suppressor that is commonly downregulated by promoter methylation in GC, especially in the EBV-associated subtype. Promoter methylation of REC8 is an independent risk factor for the shortened survival of GC patients.
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: J
authors.initials: J
authors.lastname: Yu
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Q
authors.initials: Q
authors.lastname: Liang
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: K
authors.initials: K
authors.lastname: Wang
authors.affiliation: Department of Gastrointestinal Oncology, Peking University Cancer Hospital and Institute, Beijing, China.
authors.forename: J
authors.initials: J
authors.lastname: Gao
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Department of Surgery, State Key Laboratory of Digestive Disease, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: P W Y
authors.initials: PW
authors.lastname: Chiu
authors.affiliation: Department of Surgery, State Key Laboratory of Digestive Disease, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: E K W
authors.initials: EK
authors.lastname: Ng
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, CUHK Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: J J Y
authors.initials: JJ
authors.lastname: Sung
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D002465:Cell Movement; D019175:DNA Methylation; D015536:Down-Regulation; D044127:Epigenesis, Genetic; D020031:Epstein-Barr Virus Infections / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D009368:Neoplasm Transplantation; D011379:Prognosis; D013274:Stomach Neoplasms / Q000235:genetics* / Q000821:virology*; D016019:Survival Analysis
chemical_list: D018797:Cell Cycle Proteins; C507675:REC8 protein, human