The effect of miRNA overexpression on gene expression profile of MCF-7 cells

To identify microRNAs impacting estrogen receptor ERα expression in breast cancer, we have screened ER-positive breast cancer cells with a library of pre-miRs, and systematically monitored the ERα expression by protein lysate microarrays. There was a significant enrichment of the in silico predicted ERα targeting microRNAs among the hits. The most potent pre-miRs miR-18a/b, miR-193b, miR-206, and miR-302c, were confirmed to directly target ERα and to repress estrogen-responsive genes. The effect of miRNA overexpression on gene expression profile of MCF-7 cells was studied. Furthermore, miR-18a and miR-18b showed increased expression in ERα-negative as compared to ERα-positive clinical tumors. In summary, we present systematic and direct functional and correlative clinical evidence on microRNAs inhibiting ERα signaling in breast cancer. MCF-7 cells (300 000 per well on 6-well plates) were transfected with an siRNA for ERα or with Ambion pre-miR™ constructs for miR-18a, miR-193b, miR-206, miR-302c, or pre-miR negative control #1 (scrambled pre-miR) at 20 nM, and incubated for 24h.