The Micro-Ribonucleic Acid (miRNA) miR-206 Targets the Human Estrogen Receptor- (ER) and Represses ER Messenger RNA and Protein Expression in Breast Cancer Cell Lines

Micro-RNAs are small noncoding RNAs, which di-minish the stability and/or translation ofmRNAs. This study examined whether miR-206, previously shown to be elevated in estrogen receptor (ER)-negative breast cancer, regulates the expression of ER. Two putative miR-206 sites, (hER1 and hER2), were found in silico within the 3-untranslated region of human ERmRNA. Transfection of MCF-7 cells with pre-miR-206 or 2-O-methyl antagomiR-206 specifi-cally decreased or increased, respectively, ER mRNA levels. Overexpression of pre-miR-206 re-duced ER and -actin protein levels, with no effect on ER, E-cadherin, or glyceraldehyde-3-phosphate dehydrogenase. Reporter constructs containing the hER1 or hER2 binding sites inserted into the 3