Involvement of DNA methylation in the control of the expression of an estrogen-induced breast-cancer-associated protein (pS2) in human breast cancers.

pS2 gene has been used to investigate the relationship between alterations of DNA methylation patterns in human tumors and gene expression. The expression of pS2, which is transcriptionally controlled by estrogens in breast cancer cell lines, is restricted to estrogen-receptor-rich human breast tumors. We found that the CCGG site within the promoter/enhancer sequence of pS2 was hypomethylated in estrogen-receptor-rich breast tumors expressing this gene. The amount of DNA molecules unmethylated at this site was related to the amount of pS2 mRNA detected in the samples. The demethylation of this region, which contains the estrogen responsive element, was confirmed by genomic sequencing. Transient expression of functional human estrogen receptors stimulated the expression of the endogenous pS2 in HeLa cells, but failed, in BT-20 cells, to stimulate expression of this gene. Since the promoter/enhancer region of pS2 is unmethylated in HeLa cells and methylated in BT-20 cells, these data also support the hypothesis that DNA methylation might be involved in the control of pS2 expression.