Methylation-associated silencing of miR-638 promotes endometrial carcinoma progression by targeting MEF2C

Promoter methylation-associated silencing of cancer-associated microRNAs (miRNAs) is a common epigenetic mechanism during tumorigenesis in various types of human cancer. However, this has not been comprehensively examined in endometrial carcinoma (EC). In the present study, an miRNA microarray consisting of 1,347 common human miRNAs was used to select potential tumor suppressive miRNAs that were hyper-methylated in EC. This led to the identification of miR-638, miR-210 and miR-3665. The methylation status of miR-638 was examined by bisulfite sequencing polymerase chain reaction and miR-638 expression was measured by TaqMan miRNA assays. EC cell lines transfected with vectors overexpressing miR-638, its target gene myocyte enhancer factor 2C (MEF2C) or both, were constructed. Dual-luciferase reporter assays, a xenograft mouse model and rescue experiments were designed to study miR-638 and its target gene MEF2C. The results indicated that the promoter region of miR-638 was highly methylated and the expression of miR-638 was significantly downregulated in cancerous tissues from 42 patients with EC who underwent surgical resection. Additionally, a low expression of miR-638 was significantly associated with advanced Federation of Gynecology and Obstetrics stage and was demonstrated to indicate shorter disease-free survival. Functional studies indicated that the overexpression of miR-638 in EC cell lines inhibited in vitro tumor progression and in vivo tumorigenicity. MEF2C was verified as a direct target of miR-638 and was demonstrated to mediate the tumor-suppressive function of miR-638 in EC.