Hypermethylation of the microRNA miR-124, miR-125b, miR-127, and miR-129 in ovarian carcinoma is involved in suppression of their expression and associated with both the development and progression of ovarian cancer

Rationale: We have previously identified a group of microRNA genes (MIR-107, MIR-1258, MIR-130b, MIR-34b/c, MIR-9-1, MIR-9-3 et al.), whose methylation was involved into the development and progression of ovarian cancer. Aim: To expand the range of microRNA genes hypermethylated in ovarian cancer and to study the role of this modification in the pathogenesis and progression of ovarian cancer. Materials and methods: The study was performed on a series of 76 ovarian cancer and 13 peritoneal metastases samples. The method of bisulfite DNA conversion followed by methylation-specific polymerase chain reaction (PCR) was used to assess the methylation status of the microRNA genes; the expression of these genes was measured by quantitative real-time PCR. Results: Compared to histologically unchanged ovarian tissue, there was a significant increase in methylation frequencies in the tumor samples for 6 microRNA genes studied: MIR-124-1, MIR-124-2, MIR-124-3, MIR-125B-1, MIR-127, and MIR-129-2 (p ≤ 10-3). The expression level of 4 microRNAs (miR-124-3p, miR-125b-5p, miR-127-5p, miR-129-5p) encoded by these genes was suppressed, with a significant correlation between changes in their expression levels and the gene methylation (rs = 0.63–0.94, p ≤ 10-4). In addition, there were statistically significant associations between methylation of 5 genes (MIR-124-2, MIR-124-3, MIR-125B-1, MIR-127, and MIR-129-2) and the parameters of cancer progression, such as its clinical stage, metastatic spread, tumor size and invasion, and to a lesser extent with a decrease in the differentiation grade. The association of 5 microRNA genes with metastatic spread was confirmed by the analysis of peritoneal macro-metastases from 13 patients. Conclusion: We have demonstrated the functional significance of aberrant methylation in a group of microRNA genes for suppression of their expression in ovarian carcinomas. There is an association of microRNA gene hypermethylation with the progression of ovarian cancer, including metastatic spread to the peritoneum.