Background: MicroRNAs are associated with tumor genesis and progression in various carcinomas. MicroRNA-148a (miR-148a) was reported to have low expression in gastrointestinal cancers, and might be regulated by promoter region DNA methylation.
Methods: Bisulfite-modified sequencing was used to determine the promoter region DNA methylation status of human gastrointestinal cancer cell lines. Expression levels of miR-148a in cell lines treated with 5-aza-2'-deoxycytidine were determined by quantitative real-time polymerase chain reaction. Total DNA was extracted from the tissues of 64 patients with gastric cancer and 51 patients with colorectal cancer. Methylation status was determined by methylation-specific polymerase chain reaction. All statistical analyses were performed with SPSS 17.0 software.
Results: The promoter regions of genes in human gastrointestinal cancer cell lines were all hypermethylated, except for HT-29, and the expression of miR-148a tended to be higher than in controls after treatment with 5-aza-2'-deoxycytidine. The methylation-specific polymerase chain reaction results showed that 56.25% of gastric cancer tissues and 19.61% of colorectal cancer tissues were hypermethylated. A strong correlation was found between the expression of miR-148a and the methylation status of promoter regions (P<0.001, chi-square test and Pearson's correlation). Furthermore, promoter region CpG site hypermethylation of miR-148a was correlated with increased tumor size (P=0.01) in gastric cancer after analyzing the correlation between methylation status and clinicopathologic characteristics.
Conclusion: The promoter region CpG sites were hypermethylated in gastrointestinal cancers. Promoter region hypermethylation status was associated with the expression of miR-148a and tumor invasiveness in gastric cancer, and may prove to be a new biomarker and method for treating gastric cancer.
Keywords: CpG site; clinicopathologic characteristics; methylation; microRNAs.