Transcriptional induction by the estrogen receptor ERα involves the ordered and cyclical recruitment of cofactors and the formation of a transcriptionally permissive chromatin structure generated by posttranslational histone modifications and nucleosome remodelling. Activation of the ERα target gene pS2 has additionally been shown to involve the cyclical methylation and demethylation of promoter CpGs and inhibition of this process prevents the demethylation and subsequent transcriptional activation of pS2. This work focuses on identifying the mechanisms underlying the rapid methylation/demethylation changes during the transcriptional cycling of ERα target genes in breast cancer cell lines in order to establish the relationship between epigenetic modifications, ERα recruitment and the initiation of transcription at target genes.
The proteins mediating DNA methylation have been discovered, however the identification of DNA demethylases in humans has remained elusive. The recent discovery that methyl groups can be oxidised to hydroxymethyl groups by the TET family of proteins presents a mechanism whereby the transcriptionally repressive methyl mark can effectively be removed from promoters. Our experiments have shown that TET2 is recruited to the pS2 promoter simultaneously with ERα, suggesting that TET-mediated oxidation plays a role in transcriptional activation.