Selenium-gene interactions involving microRNAs

Abstract

Selenium (Se) is an essential nutrient for health. In mammals Se is incorporated into ~25 selenoproteins in the form of the amino-acid selenocysteine encoded by the UGA codon through a complex interacting with selenocysteine insertion sequence (SECIS) in the 3’Unstralated Region. The selenoproteins have functions in antioxidant defence and redox control, thyroid hormone metabolism and mitochondrial metabolism. Previous scientific work has found that Se also affects a group of downstream targets. The aim of my work is to investigate whether expression of selenoproteins or the downstream targets affected by Se is regulated through epigenetic mechanisms involving microRNAs, a small non-coding RNA species that regulates a gene or groups of genes by binding to the mRNA 3’UTR. Gut epithelial Caco-2 cells were grown in either Se deficient or Se-supplemented medium for 72h. RNA extracted and miRNA expression analysed using a custom-designed human genome V2 Agilent 8x15K array. In addition, global mRNA transcriptome expression was analysed using an Illumina HumanRef-8 v3 microarray. Se supply increased the expression of thirteen miRNAs and 53 mRNAs the observed differences were confirmed by real time PCR. miR-185 was selected as a further target of investigation because of its high sensitivity to Se. Bioinformatic analysis of the Se susceptible miRNAs and Se sensitive genes was carried out using miRWalk, MicroCosmo, microRNA.org, miRBase and microRNA.org algorithms and Ingenuity Pathway Analysis. This identified miR-185 recognition elements in the Se-sensitive mRNAs for Glutathione peroxidise 2 (GPX2), Glutathione peroxidise 3 (GPX3), and Selenophosphate Synthetase 2 (SEPHS2). Expression of GPX2 and SEPHS2 was altered by miR-188 with a specific anti-miR and affected differently according to miRNA exposure. The data suggests that these mRNAs are targets of miR-185. In conclusion, the experiment indicates that miRNA expression as regulation of target genes is regulated by Se supply in Caco-2 cells.