Aberrant methylation of promoter CpG islands is known to be responsible for the alteration and silencing of genes in cancer. The data presented here describes that the CpG methylations of ERα and ERβ are found in breast cancer tissues, and methylation exerts a considerable effect on gene silencing, investigated by bisulfite genomic sequencing and reverse transcriptase polymerase chain reaction. Consequently, hypermethylation of the ERα and ERβ genes was found in 66.0% and 50.0% of 50 breast cancers, respectively. Eleven of 50 samples (22.0%) did not show any methylation of either ERα or ERβ, whereas 19 samples (38.0%) showed methylation of both ERα and ERβ. The tumors that showed aberrant methylation of ERα and ERβ did not express mRNA, compared with unmethylated cases (p<0.01). The methylated case was negatively correlated with the expression of the ERα protein (p<0.01). In addition, ERβ methylation demonstrated significant associations with the lower level of Ki67 (9.36±2.43 versus 19.68±3.42, p=0.02). Although the number of samples was relatively small, our results suggest that DNA methylation in ERα and ERβ are present in breast cancer tissue, and that the methylation causes a significant effect on transcriptional silencing. Furthermore, the CpG methylation of the ERβ gene seems to play a role in cell proliferation of breast cancer tissue.

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