CpG methylation as a basis for breast tumor-specific loss of NES1/kallikrein 10 expression

The normal epithelial cell-specific-1 (NES1)/kallikrein 10 gene is expresse d in normal mammary epithelial cells, but its expression is dramatically de creased in breast cancer cell lines. Now, we have cloned and characterized the active promoter region of NES1. Using a luciferase reporter system, we demonstrate that most tumor cell lines are able to support full or partial transcription from the NES1 promoter, suggesting a role for promoter-indepe ndent cis-acting mechanisms of loss of NES1 expression. We show that hyperm ethylation of the NES1 gene represents one such mechanism. Using methylatio n-specific PCR and sequence analysis of sodium bisulfite-treated genomic DN A, we demonstrate a strong correlation between exon 3 hypermethylation and loss of NES1 mRNA expression in a panel of breast cancer cell lines and in primary tumors. Treatment of NES1-nonexpressing cells with a demethylating agent led to reexpression of NES1, suggesting an important role of hypermet hylation in the loss of NES1 expression. We suggest that hypermethylation i s responsible for tumor-specific loss of NES1 gene expression. Our results also suggest that hypermethylation of the NES1 gene may serve as a potentia l marker for breast cancer.