Expression data from MCF-7 cells stimulated by Estrogen or IGF-I

Although estrogen receptor (ER) and insulin-like growth factor (IGF) signaling are important for normal mammary development and breast cancer, cross-talk between these pathways, particularly at the level of gene transcription, remains poorly understood. We performed microarray analysis on MCF-7 breast cancer cells treated with estradiol (E2) or IGF-I for 3hr or 24hr. IGF-I regulated mRNA of 5-10-fold more genes than estradiol, and many genes were co-regulated by both ligands. Importantly, expression of these co-regulated genes correlated with poor prognosis of human breast cancer. Closer examination revealed enrichment of repressed transcripts. Interestingly, a number of potential tumor suppressors were down-regulated by IGF-I and estradiol. In fact, BLNK, one of the top repressed genes, is a potential growth suppressor in breast cancer cells. Analysis of three down-regulated genes showed that E2-mediated repression occurred independently of IGF-IR, and IGF-I-mediated repression occurred independently of ER. However, repression by IGF-I or estradiol required common downstream kinases. In conclusion, E2 and IGF-I co-regulate a set of genes that affect breast cancer outcome. There is enrichment of repressed transcripts, and the down-regulation is independent at the receptor level. This may be important clinically, as tumors with active ER and IGF-IR signaling may require co-targeting of both pathways. KEYWORDS: multiple group comparison Microarray analysis on MCF-7 breast cancer cells treated with estradiol (E2) or IGF-I for 3hr or 24hr.