Interaction of TFAP2C with the Estrogen Receptor-alpha Promoter Is Controlled by Chromatin Structure

Purpose: Transcriptional regulation of estrogen receptor-alpha (ER alpha) involves both epigenetic mechanisms and trans-active factors, such as TFAP2C, which induces ER alpha transcription through an AP-2 regulatory region in the ER alpha promoter. Attempts to induce endogenous ER alpha expression in ER alpha-negative breast carcinomas by forced overexpression of TFAP2C have not been successful. We hypothesize that epigenetic chromatin structure alters the activity of TFAP2C at the ER alpha promoter. Experimental Design: DNA methylation, histone acetylation, and chromatin accessibility were examined at the ER alpha promoter in a panel of breast carcinoma cell lines. TFAP2C and polymerase II binding were analyzed by chromatin immunoprecipitation. Epigenetic chromatin structure was altered using drug treatment with 5-aza-2'-deoxycytidine (AZA) and trichostatin A (TSA). Results: The ER alpha promoter in the ER alpha-negative lines MDA-MB-231, MCF10A, and MCF75C show CpG island methylation, histone 3 lysine 9 deacetylation, and decreased chromatin accessibility compared with ER alpha-positive cell lines MCF7 and T47-D. Treatment with AZA/TSA increased chromatin accessibility at the ER alpha promoter and allowed TFAP2C to induce ER alpha expression in ER alpha-negative cells. Chromatin immunoprecipitation analysis showed that binding of TFAP2C to the ER alpha promoter is blocked in ER alpha- negative cells but that treatment with AZA/TSA enabled TFAP2C and polymerase 11 binding. Conclusion: We conclude that the activity of TFAP2C at specific target genes depends upon epigenetic chromatin structure. Furthermore, the combination of increasing chromatin accessibility and inducing TFAP2C provides a more robust activation of the ER alpha gene in ER alpha-negative breast cancer cells.