Repression Of Mir-125b-1 By Epigenetic Mechanisms In Breast Cancer Cell Lines

miR-125b-1 downregulates targets as ERBB2, BAK1 and ETS1. These targets are involved in cell proliferation, apoptosis and cell migration, respectively. Previous studies on tumor cells reveal that downregulation of miR-125b-1 is associated with poor prognosis in breast cancer patients. DNA methylation of the miR-125b-1 promoter can repress its expression, in addition, this promoter is embedded in an intermediate CpG island thus, DNA methylation and histone modifications could also affect its transcription. Repression by DNA methylation has been well characterized, but there is no information about the role of histone modifications in the regulation of miR-125b-1 promoter. We evaluated the enrichment of two histone modifications involved in gene repression, H3K9me3 and H3K27me3, on the miR-125b-1 promoter of two breast cancer cell lines, a luminal A, MCF 7, and a triple negative, MDA-MB-231, compared with a non-transformed breast cell line, MCF 10A. We found that breast cancer cell lines are enriched with H3K27me3 and H3K9me3 in MCF 7 and MDA-MB-231, respectively. Then, we focused on reactivating miR-125b-1 in MCF 7 using an EZH2 inhibitor. After the treatment with the EZH2 inhibitor, we evaluated the transcriptional levels of the pri-miR-125b-1 and the mature miR-125b by qRT-PCR. Our results suggest that transcripts, pri-miRNA and mature miRNA, increase their expression levels after the treatment in the MCF7 cell line, but not in the MDA-MB-231 and MCF 10A cell lines. Subsequently, we evaluated the BAK1 expression and protein levels to investigate whether the miR-125b-1 reactivation could affect some targets. We observed a 60% and 70% decrease in the expression and protein levels of after treatment with the EZH2 inhibitor. To determine if the H3K9me3 is involved on miR-125b-1 silencing in MDA-MB-231, we over-expressed KDM4B/JMJD2B to reactivate this miRNA. Then, we evaluated the transcript. A three-fold increase was observed compared. We conclude that the miR-125b-1 can be repressed by different epigenetic mechanisms depending on the breast cancer subtype; the miR-125b-1 reactivation by removing the repression histone modification marks affect the expression of BAK1, a pro-apoptotic target. Citation Format: Fernanda Cisneros-Soberanis, Marco Alonso Andonegui, Clementina Castro, Luis Alonso Herrera. Repression of miR-125b-1 by epigenetic mechanisms in breast cancer cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-171.