MiR-129-5p is downregulated in breast cancer cells partly due to promoter H3K27m3 modification and regulates epithelial-mesenchymal transition and multi-drug resistance.

OBJECTIVE

In this study, we firstly studied whether H3K27me3 modification is a mechanism of miR-129-5p downregulation in breast cancer and further investigated the functional role of miR-129-5p in epithelial-to-mesenchymal transition (EMT) and in multi-drug resistance (MDR) of the cancer cells.

MATERIALS AND METHODS

Immunoprecipitation (IP) and Chromatin Immunoprecipitation (ChIP) assay were performed to detect the association among SOX4, EZH2 and H3K27me3 and their enrichment in the promoter region of miR-129-2. Western blot and immunofluorescent staining were performed to detect the expression of epithelial and mesenchymal markers. MTT assay was applied to test drug sensitivity.

RESULTS

Enforced EZH2 and SOX4 expression resulted in suppressed miR-129-5p level in MCF-7 cells. There was an interaction among SOX4, EZH2 and H3K27me3 modification and they were significantly enriched in the region upstream of transcription start of miR-129-2. MCF-7 cells transfected with miR-129-5p mimics had significantly suppressed SOX4 expression. MCF-7 cells with miR-129-5p overexpression had significantly restored E-cadherin expression and suppressed N-cadherin and Vimentin expression. The drug sensitivity assay showed that miR-129-5p substantially reduced IC50 of ADM, VCR and PTX in MCF-7/ADM cells CONCLUSIONS: There is a reciprocal regulation between miR-129-5p and SOX4 via the SOX4/EZH2 complex mediated H3K27me3 modification in breast cancer cells. MiR-129-5p is an important miRNA modulating EMT and MDR in breast cancer cells.