MiR-212/132 is epigenetically downregulated by SOX4/EZH2-H3K27me3 feedback loop in ovarian cancer cells

Both miR-212 and miR-132 are usually downregulated in ovarian cancer and act as tumor suppressors. However, the mechanism of their downregulation in ovarian cancer is not clear. In this study, we investigated the regulative effects of miR-212 and miR-132 on SOX4 expression in ovarian cancer cells and also studied whether there is a feedback regulation between miR-212/miR-132 and SOX4 via an epigenetic mechanism. The results showed that both EZH2 and SOX4 overexpressions significantly repressed miR-212 and miR-132 expressions in SKOV3 and OV2008 cells. Immunoprecipitation assay showed that there are interactions among SOX4, EZH2, and H3K27me3, and ChIP assay confirmed significant enrichment of EZH2 and H3K27me3 in the promoter region of miR-212/132. Both pri-miR-212 and pri-miR-132 expressions decreased after enforced EZH2 or SOX4 expression. Western blot and dual-luciferase assay confirmed that miR-212 and miR-132 can target the same sites in the 3'UTR of SOX4 mRNA and suppress its expression in ovarian cancer cells. MiR-132 or miR-212 overexpression or knockdown of endogenous SOX4 reduced epithelial-mesenchymal transition (EMT)-like properties. Therefore, we infer that the SOX4/EZH2 complex can silence miR-212 and miR-132 expressions via binding to the promoter region and promoting H3K27me3, while miR-212 and miR-132 can directly bind to the 3'UTR of SOX4 and suppress its expression. This forms a MiR-132/212-SOX4/EZH2-H3K27me3 feedback loop in ovarian cancer cells. Functionally, SOX4 is a downstream effector of miR-212/132 modulating EMT of ovarian cancer cells.