miR-218, consisting of miR-218-1 at 4p15.31 and miR-218-2 at 5q35.1, was significantly decreased in esophageal squamous cell carcinoma (ESCC) in our previous study. The aim of this study was to determine whether aberrant methylation is associated with miR-218 repression. Bisulfite sequencing analysis (BSP), methylation specific PCR (MSP), and 5-aza-2'-deoxycytidine treatment assay were applied to determine the methyaltion status of miR-218 in cells and clinical samples. In vitro assays were performed to explore the role of miR-218. Results showed that miR-218-1 was significantly CpG hypermethylated in tumor tissues (81%, 34/42) compared with paired non-tumor tissues (33%, 14/42) (p < 0.05). However, no statistical difference was found in miR-218-2. Accordingly, expression of miR-218 was negatively correlated with miR-218-1 methylation status (p < 0.05). After demethylation treatment by 5-aza-2'-deoxycytidine, there was a 2.53- and 2.40-fold increase of miR-218 expression in EC109 and EC9706, respectively. miR-218 suppressed cell proliferation and arrested cells at G1 phase by targeting 3' untranslated region (3'UTR) of roundabout guidance receptor 1 (ROBO1). A negative correlation was found between miR-218 and ROBO1 mRNA expression in clinical samples. In conclusion, our results support that aberrant CpG hypermethylation at least partly accounts for miR-218 silencing in ESCC, which impairs its tumor-suppressive function.
Keywords: CpG methylation; ROBO1; esophageal cancer; miR-218.