circRNA circ_POLA2 increases microRNA-31 methylation to promote endometrial cancer cell proliferation

Circular RNA (circRNA) circ_POLA2 is an oncogene in lung and cervical cancers. However, the role of circ_POLA2 in other types of cancer is unknown. The present study investigated the role of circ_POLA2 in endometrial cancer (EC). The mRNA expression levels of circ_POLA2 and microRNA (miR)-31 in EC and paired adjacent normal tissues were analyzed using reverse transcription-quantitative (RT-qPCR). Overexpression of circ_POLA2 was achieved in the EC cell lines, and its effects on miR-31 mRNA expression level and methylation were evaluated using RT-qPCR and methylation-specific PCR (MSP), respectively. Cell proliferation was assessed using a Cell Counting Kit-8 assay. The results indicated that circ_POLA2 was highly expressed in EC tissue and inversely correlated with miR-31 mRNA expression level. MSP analysis showed that circ_POLA2 overexpression increased miR-31 methylation and RT-qPCR analysis showed that circ_POLA2 overexpression decreased miR-31 mRNA expression level. Furthermore, circ_POLA2 overexpression also increased EC cell proliferation, while miR-31 overexpression decreased cell proliferation. Finally, circ_POLA2 overexpression reduced the effects of miR-31 overexpression. In conclusion, circ_POLA2 may increase miR-31 methylation of miR-31 in EC cells to promote cancer cell proliferation.