Interaction of TFAP2C with the estrogen receptor-α promoter is controlled by chromatin structure

Abstract

Purpose: Transcriptional regulation of estrogen receptor-α (ERα) involves both epigenetic mechanisms and trans-active factors, such as TFAP2C, which induces ERα transcription through an AP-2 regulatory region in the ERα promoter. Attempts to induce endogenous ERα expression in ERα-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 ERα promoter. Experimental Design: DNA methylation, histone acetylation, and chromatin accessibility were examined at the ERα 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 ERα promoter in the ERα-negative lines MDA-MB-231, MCF10A, and MCF75C show CpG island methylation, histone 3 lysine 9 deacetylation, and decreased chromatin accessibility compared with ERα-positive cell lines MCF7 and T47-D. Treatment with AZA/TSA increased chromatin accessibility at the ERα promoter and allowed TFAP2C to induce ERα expression in ERα-negative cells. Chromatin immunoprecipitation analysis showed that binding of TFAP2C to the ERα promoter is blocked in ERα- negative cells but that treatment with AZA/TSA enabled TFAP2C and polymerase II 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 ERα gene in ERα-negative breast cancer cells. © 2009 American Association for Cancer Research.