Adams, B.D., Furneaux, H. and White, B.
Notes: This study investigated the mechanism of silencing of the estrogen receptor α mRNA in the human breast cancer cell line, MCF-7. The authors initially used software for miRNA target prediction to analyze the 3´ UTR of the human ERα gene for potential miR-206 target sites. Two potential targets, designated hERα1 and hERα2, were identified. ERα levels were repressed in a dose-dependent manner in MCF-7 cells transfected with a synthetic pre-miR-206 duplex, and transfection of an miR-206 expression construct into MCF-7 cells also resulted in specific inhibition of ERα expression, as measured by real-time PCR and Northern blot assays. A luciferase reporter assay was then used to determine whether miR-206 interacted directly with the hERα1 and hERα2 sites in the ERα 3´UTR. Luciferase reporter constructs containing either the hERα1 or hERα2 cloned 3´ of the firefly luciferase gene showed miR-206-medisted repression of luciferase expression in HeLa cells. Mutation of the hERα1 or hERα2 sites to disrupt hybridization with the 5´ region of miR-206 restored luciferase activity, as did co-transfection with an miRNA antagonist of miR-206. Transformation of the luciferase constructs into the breast cancer cell lines, MCF-7 and MDA-MB-231, both of which expressed high levels of miR-206 as measured by real-time PCR, resulted in repression of luciferase activity. Treatment with estrogen was then shown to reduce miR-206 levels in MCF-7 cells. Luciferase assays were used to confirm this result, and levels of luciferase activity from the reporter constructs were increased upon exposure to estrogen, indicating that ERα agonists were able to decrease miR-206 levels in MCF- cells. (3603)