Mapping of the estrogen receptor: GATA-3 interactome in MCF-7 human mammary carcinoma cells

C63

Estrogens regulate the growth, differentiation and death of diverse target tissues, both within and outside of the reproductive system. Uncoupling of regulatory mechanisms can result in the initiation and progression of estrogen target tissue malignancies such as mammary, uterine and ovarian cancer. Most of the physiological actions of estrogens are mediated by the estrogen receptors (ER) α and β, which are ligand-activated transcription factors regulating a wide spectrum of estrogen-sensitive genes. ER signaling is carried out in conjunction with co-activators/repressors and other transcription factors. We have previously used a chromatin immunoprecipitation (ChIP)-paired end ditag (PET) cloning and sequencing strategy to comprehensively map the ERα binding sites in MCF-7 human mammary carcinoma cells following estrogen administration. We have now used a bioinformatics approach to identify which of the known transcription factor matrices are highly enriched in ER binding regions and found that one of them binds the zinc-finger transcription factor, GATA-3. GATA-3 expression is highly correlated with ERα status in breast tumors, and it has recently been reported that GATA-3 is essential for maintaining ERα expression in MCF-7 cells. By conducting ChIP-reChIP experiments, we have shown that GATA-3 and ERα binds to the same DNA fragments in MCF-7 cells, and by utilizing custom-made NimbleGen ChIP-on-chip arrays containing the universe of MCF-7 ER binding sites (>40,000 validated ChIP-PET, ChIP-chip and predicted EREs), we have identified GATA-3 and ERα cooccupancy at a large number of sites. We have also observed a good correlation between in silico predicted and in vivo validated GATA-3 binding sites. GATA-3 is co-localized with ER at both proximal and distal binding sites, and we are currently carrying out long-range interaction of GATA-3 binding sites in a genome-wide manner to map the 3-dimensional network of GATA-3.