p53 Binds to Estrogen Receptor 1 Promoter in Human Breast Cancer Cells

p53 is a tumor suppressor protein that regulates estrogen receptor 1 (ESR1) expression. To investigate the mechanism of ESR1 gene regulation by p53, chromatin immunoprecipitation was applied to assess the binding of p53, DNMT1, HDAC1 and MeCP2 to both silenced ESR1 promoter in MDA-MB-468 cells and active ESR1 promoter in MCF-7 breast cancer cells. The results of chromatin immunoprecipitation experiments showed that p53 protein binds to both unmethylated CpG island of the ESR1 promoter in the ER-positive MCF-7 and the hypermethylated ESR1 promoter in the ER-negative MDA-MB-468 cells. However, repression complex including DNMT1, HDAC1 and MeCP2 is only associated with silenced ESR1 in ER-negative MDA-MB-468 human breast cancer cells. In addition, ectopically expressed wild type p53 failed to reactivate the ESR1 gene in these cells. These results suggest that specific p53 mutations may contribute to loss of estrogen receptor alpha expression in breast tumors and also support the hypothesis that mutant p53 is likely to impact DNA methylation.