The MCF7 and MCF 10A cell lines were obtained from American Type Culture Collection (ATCC) and cultured at 37 °C, 5% CO2 in a humidified atmosphere. MCF7 were cultured in Dulbecco's Modified Eagle's Medium (DMEM) High Glucose with 10% fetal bovine serum (both from HyClone) and 10 µg/mL insulin (Thermo Fisher Scientific). MCF 10A were cultured in DMEM: F12 (HyClone) with 5% horse serum (Sigma-Aldrich), 10 µg/mL insulin, 20 ng/mL EGF (Thermo Fisher Scientific), 100 ng/mL cholera toxin and 500 ng/mL hydrocortisone (both from Sigma-Aldrich). Cells were harvested in TRI Reagent (Sigma-Aldrich) for extraction of total RNA according to the manufacturer's instructions. Depletion of small RNAs was performed with the RNeasy Mini kit (QIAGEN) using the