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

Transcriptional regulation of estrogen receptor-alpha (ERalpha) involves both epigenetic mechanisms and trans-active factors, such as TFAP2C, which induces ERalpha transcription through an AP-2 regulatory region in the ERalpha promoter. Attempts to induce endogenous ERalpha expression in ERalpha-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 ERalpha promoter.

DNA methylation, histone acetylation, and chromatin accessibility were examined at the ERalpha 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).

The ERalpha promoter in the ERalpha-negative lines MDA-MB-231, MCF10A, and MCF7-5C show CpG island methylation, histone 3 lysine 9 deacetylation, and decreased chromatin accessibility compared with ERalpha-positive cell lines MCF7 and T47-D. Treatment with AZA/TSA increased chromatin accessibility at the ERalpha promoter and allowed TFAP2C to induce ERalpha expression in ERalpha-negative cells. Chromatin immunoprecipitation analysis showed that binding of TFAP2C to the ERalpha promoter is blocked in ERalpha-negative cells but that treatment with AZA/TSA enabled TFAP2C and polymerase II binding.

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 ERalpha gene in ERalpha-negative breast cancer cells.