5AZA-induced Gene Expression in Human Breast Cancer Cell Lines and Benign Primary Mammary Epithelial Cell Cultures

The goal of this experiment was to identify genes that were expressed at higher levels in benign human mammary epithelial cells than in breast cancer cell lines and that were induced by 5AZA treatment in breast cancer cell lines. Six breast cancer cell lines were selected for demethylation studies based on known tumor suppressor gene expression regulation by promoter region hypermethylation: HCC1569 (CCND2), HCC1954 (SCGB3A1, APC, RASSF1A), MCF-7 (RAR-beta2), MDA-MB-231 (ESR1), UACC3199 (BRCA1), and BT-549 (hypermethylator phenotype). Other than MCF10A we specifically avoided immortalized benign human mammary epithelial cell lines for this experiment as these cells frequently show tumor suppressor gene methylation (e.g. p16) and gene expression profiles that are intermediate between normal breast epithelial cells and breast cancer. Instead, we opted to test six first-passage benign human mammary epithelial cell cultures (HME) generated in serum-free media from small fragments of normal breast tissue obtained from young women undergoing fibroadenoma excision. The 5AZA dose (0.5 microM) was selected based on evaluation of growth curves and induction of BNC1, SERPINB, and TKTL1 gene expression measured by RT-PCR in benign and malignant cells. The breast cancer cell lines, HME cultures, and MC10A cells were treated with 0.5 microM 5AZA (Sigma-Aldrich, St. Louis, MO) in DMSO or DMSO alone for six days after which the cells were harvested, and RNA prepared using the Illumina TotalPrep kit (AMIL1791, Life Technologies, Grand Island, NY). Whole genome expression was assessed using the Illumina HumanWG-6-v3 chip Gene expression was evaluated in 6 breast cancer cell lines, 6 primary breast epithelial cell cultures, and MCF10A cells after 6 days in DMSO or DMSO plus 0.5 microM 5AZA.