Transcriptional Profiling of Responses to Estrogen and Progesterone in Mammary Gland. Mus musculus

Epidemiological studies have shown that a full-term pregnancy at early age can decrease the breast cancer risk up to one-half. Pregnancy has been shown to prevent carcinogen-induced mammary tumors in rodents as well. The protective effect of pregnancy can be mimicked by administration of estrogen and progesterone to nulliparous rodents in amounts that are similar to those during pregnancy and alters responsiveness of p53 to DNA damage. Ovariectomized mice were treated with estrogen (E), progesterone (P), both estrogen and progesterone (E + P), or vehicle (V) alone and global expression profiles was analyzed to identify the mechanisms by which estrogen and progesterone combine to sensitize p53 function. Keywords: comparative hormone treatment Overall design: Twenty ovariectomized animals were used for examine transcriptional effects of hormones by microarray. The hormones were administered by daily i.p. injection for 4 days.Treatment groups included: 4 animals receiving 2ug 17-beta-estrogen (E), 4 animals receiving 1mg progesterone (P), 5 animals receiving both estrogen and progesterone (E+P) and 4 animals receiving 100ul sesame oil (V). Epithelial-free fat pads from 3 animals receiving E+P were also analyzed to distinguish responses to E+P in the stroma (E+P CFP). Lymph nodes were removed from mammary glands at the time of collection.