Genomic Structure of the Promoters of the Human Estrogen Receptor-α Gene Demonstrate Changes in Chromatin Structure Induced by AP2γ

Abstract

Expression of human estrogen receptor-α (ERα) involves the activity from several promoters that give rise to alternate untranslated 5′ exons. However, the genomic locations of the alternate 5′ exons have not been reported previously. We have developed a contig map of the human ERα gene that includes all of the known alternate 5′ exons. By using S1 nuclease and 5′-rapid amplification of cDNA ends, the cap sites for the alternate ERα transcripts E and H were identified. DNase I-hypersensitive sites specific to ERα-positive cells were associated with each of the cap sites. A DNase I-hypersensitive site, HS1, was localized to binding sites for AP2 in the untranslated region of exon 1 and was invariably present in the chromatin structure of ERα-positive cells. Overexpression of AP2γ in human mammary epithelial cells generated the HS1-hypersensitive site. The ERα promoter was induced by AP2γ in mammary epithelial cells, and trans-activation was dependent upon the region of the promoter containing the HS1 site. These results demonstrate that AP2γ trans-activates the ERα gene in hormone-responsive tumors by inducing changes in the chromatin structure of the ERα promoter. These data are further evidence for a critical role for AP2 in the oncogenesis of hormone-responsive breast cancers.