Abstract 1896: miR-500a is involved in breast cancer-related gene expression pathways and associated with patients survival
Authors: Aushev Vasily N. , Degli Esposti Davide , Lee Eunjee , Vargas Hector , Herceg Zdenko , Zhu Jun , Chen Jia 
Published: July 2016

Abstract
MicroRNAs act as negative regulators of target genes by reducing their mRNA level. Despite numerous algorithms of target prediction, many microRNAs targets are still not known with enough confidence, making unclear their actual role in biological processes. In this study, we used an integrative approach combining bioinformatics and in vitro experiments to identify hsa-miR-500a as a key player in breast cancer survival.
The Cancer Genome Atlas (TCGA, dataset release of 2012) data were analyzed using recently developed bioinformatics algorithm (Lee et al., 2015) that considers not only expression levels of microRNAs, but also its “activity”, determined by the relative changes of expression of potential target genes. High “activity” of miR-500a (hsa-miR-500a-5p, MIMAT0004773) was significantly correlated with poor survival of patients with ER-positive breast cancer. Noteworthy, in both TCGA and GEO (Gene Expression Omnibus) datasets, this form was typically expressed at very low levels (∼26th percentile in ranking among detectable microRNAs) while another strand, miR-500a* (hsa-miR-500a-3p, MIMAT0002871) was hundred times more abundant (∼81th percentile ranking), but did not correlate with the survival.
We carried out functional validation of miR-500a in a set of breast cancer cell lines including estrogen receptor (ER)-positive MCF-7, ER-negative MDA-MB-231 and their derivatives. In order to define actual targets (direct and indirect), MCF-7 cells were transfected with miR-500a mimics or inhibitors (miRCURY LNA, Exiqon), followed by analysis of gene expression with Illumina Human HT-12 microarray. Genes that displayed the strongest suppression upon transfection with miR-500a mimics are involved in hormone signaling: members of aldo-keto reductase family known for steroid hormones processing and thioredoxin reductase that can regulate transcriptional activity of estrogen receptors. We found that expression of miR-500a is increased in highly tumorigenic derivative of MDA-MB-231 cell line comparing to its low tumorigenic parental cell line. D3H2LN cell line (a MDA-MB-231-derived line by introducing luciferase construct) displayed higher proliferation rates and enhanced spheroids formation capacities comparing to the parental cell line; RNA-seq (by Illumina HiSeq) also revealed that this cell line has higher level of miR-500a expression and lower level of some genes detected as potential miR-500a targets.
Our results indicate potential role of miR-500a in regulation of signaling pathways involved in breast cancer progression. Experimental data lend further support in its functional role in breast cancer survival, which may help develop future intervention strategies.
Citation Format: Vasily N. Aushev, Davide Degli Esposti, Eunjee Lee, Hector Vargas, Zdenko Herceg, Jun Zhu, Jia Chen. miR-500a is involved in breast cancer-related gene expression pathways and associated with patients survival. [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 1896.