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

Q.-X. Luan, B.-G. Zhang, X.-J. Li, M.-Y. Guo

Department of Laboratory Medicine, Qingdao Municipal Hospital, Qingdao, Shandong, China. meiyanguo1@outlook.com

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• Oncology

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.

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