Abstract
ER1 is often down-regulated in breast cancer compared to normal breast but mechanisms surrounding this are unclear. We examined whether loss of heterozygosity (LOH) or methylation at ER promoters (0N, 0K) and/or untranslated exon 0N were involved in ER down-regulation in breast cancer tissues and cell lines and if treatment with the de-methylating agent 5-aza-deoxycytidine and/or the histone deacetylase inhibitor Trichostatin A could influence expression in vitro. We found no evidence of correlation between LOH at 14q22-24 (genomic locus containing ER/ESR2), and ER1 expression in primary breast cancers. A negative correlation between ER1 mRNA expression and methylation status was observed for promoter 0N in BT-20, MDA-MB-453 and T47D cells. Promoter 0K was consistently unmethylated. In primary breast tumours, methylation of the untranslated exon 0N, downstream of promoter 0N, but not of promoter 0N itself, correlated with down-regulation of ER. In MDA-MB-453 cells, treatment with 5-aza-deoxycytidine was sufficient to induce ER1 expression from the 0N promoter while in BT-20 both agents were required. Examination of various sites on ESR2 highlighted epigenetic but not genetic regulation of ER1. In particular methylation adjacent to promoter 0N was a key regulatory event for ER1 silencing. A combination of de-methylating agents and histone deacetylase inhibitors fully restored ER1 expression which may offer a novel therapeutic angle for breast cancer management.