Abstract 5041: Characterization of the miR-125b1 promoter in breast cancer cell lines

Abstract

Abstract In cancer cells, transcriptional gene silencing has been associated with genetic and epigenetic defects. The disruption of DNA methylation patterns and covalent histone marks has been associated with cancer development. Until recently, microRNA (miRNA) gene silencing was not well understood. In particular, miR-125b1 has been suggested to be a miRNA with tumor suppressor activity, and it has been shown to be deregulated in various human cancers. In this study, we characterized the promoter of the miR-125b1 and the modifications associated with gene silencing. We studied in silico the miR-125b1 locus to delimit the promoter region and then, we characterized the promoter activity by the luciferase assay, cloning a fragment in the 5′ extreme close to the transcriptional start site of the miR-125b1 gene. We found that this sequence has promoter activity and it is unidirectional. Subsequently, we analyzed the DNA methylation status in the CpG island promoter and found that it was methylated in breast cancer cell lines compared with a non-transformed breast cell line. To determine the effect of DNA methylation in the CpG island of miR-125b1 on the expression of this gene, we performed a qRT-PCR assay. We observed a significant reduction on the expression of miR-125b1 in cancer cells lines in comparison with a non-transformed cell line, suggesting that DNA methylation at the CpG island might reduce the expression of miR-125b1. Our data suggest that the fragment in the 5′ extreme close to the transcriptional start site of the miR-125b1 gene is a functional and unidirectional promoter. Also, the CpG island in this region is methylated in breast cancer cell lines and this methylation is associated with the silencing of the miR-125b1 gene. This work was supported by the Consejo Nacional de Ciencia y Tecnología (CONACyT: 83959) and the Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica of the Universidad Nacional Autónoma de México (PAPIIT, IN213311). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5041. doi:1538-7445.AM2012-5041