Expression levels of miR-15a, miR-15b, miR-16 and miR-128 in breast cancer cell lines. Levels of the indicated microRNAs were determined by real time PCR in the following cell lines: MCF-10A, untransformed human mammary epithelial cells; MCF-7, mammary carcinomas with expression of the estrogen receptor (ER+); MDA-MB-231, BT549, MDA-MB-436, and DU4475, triple-negative mammary carcinomas. Data are normalized by signals for RNU6-2 as controls, and presented as relative expression levels to that in MCF-10A cells as 1.0. The bars indicate S.E.M. from 3–5 experiments, and the asterisk indicates statistically higher (p < 0.05) levels of each miRNA in the particular cell line than in MCF-10A cells.