Identification of differently expressed miRNAs between Tamoxifen sensitive cells and Tamoxifen resistant cells

Tamoxifen is the most widely administered adjuvant first-line hormone therapy for Estrogen receptor α (ERα) positive breast cancer patients. However, one from three patients will develop resistance, while the underlying molecular mechanisms are currently unclear. Recent studies reported that abnormal expression of miRNAs played a role in cancer progress. To study the potential function of miRNAs in tamoxifen resistance, Affymetrix GeneChip® miRNA 3.0 microarray was employed to identify differentially expressed miRNAs between tamoxifen sensitive MCF7 parent (MCF7-Pa) cells and induced resistant (MCF7-Re) cells. The human breast cancer MCF7 cell line was obtained from the American Type Culture Collection (Manassas, VA, USA). MCF7 parent (MCF7-Pa) cells were cultured in DMEM supplemented with 10% fetal bovine serum (FBS) and 40U/ml insulin. MCF7-derived tamoxifen resistant sublines (MCF7-Re) were developed by culturing in 1640 medium without phenol red (Life Technologies, USA) supplemented with 5% charcoal-stripped FBS (cFBS) (HyClone, USA) and 1 uM 4-hydroxytamoxifen (Sigma-Aldrich, MO, USA) for 1 year. After cultured in RPMI 1640 medium without phenol red supplemented with 5% cFBS and without tamoxifen for 7 days, MCF7-Pa and MCF7-Re cells total RNA was harvested using TRIzol® reagent (Life Technologies, USA) according to the manufacturer’s instructions. RNA extraction and miRNA profile detection was provided by CapitalBio Corporation (Beijing, China) as generated as the manufacturer's recommendations (Affymetrix).