Estrogen receptor α regulates expression of the breast cancer 1 associated ring domain 1 (BARD1) gene through intronic DNA sequence

We have used a chromatin immunoprecipitation (ChIP)-based cloning strategy to isolate and identify genes associated with estrogen receptor α (ERα) in MCF-7 human breast cancer cells. One of the gene regions isolated was a 288 bp fragment from the ninth intron of the breast cancer 1 associated ring domain (BARD1) gene. We demonstrated that ERα associated with this region of the endogenous BARD 1 gene in MCF-7 cells, that ERα bound to three of five ERE half sites located in the 288 bp BARD1 region, and that this 288 bp BARD1 region conferred estrogen responsiveness to a heterologous promoter. Importantly, treatment of MCF-7 cells with estrogen increased BARD1 mRNA and protein levels. These findings demonstrate that ChIP cloning strategies can be utilized to successfully isolate regulatory regions that are far removed from the transcription start site and assist in identifying cis elements involved in conferring estrogen responsiveness.