PCDH17 gene promoter demethylation and cell cycle arrest by genistein in gastric cancer.

Protocadherin 17 (PCDH17) is a member of the cadherin superfamily, but little is known about its functions. We focused on it as a candidate tumor suppressor gene (TSG) and hypothesized that PCDH17 may be susceptible to promoter methylation and gene silencing. Genistein has been reported to upregulate mRNA expression in many TSGs. We further tried to determine whether genistein could increase transcriptional PCDH17 by promoter demethylation. Gastric cancer cell line AGS and normal gastric cell line Ges-1 were treated with genistein and 5-aza-2'-deoxycytidine (5Aza-C). Fluorescence-activated cell sorting was performed to analyze cell cycle and apoptosis, and cell proliferation was examined by cell viability assay. PCDH17 mRNA expression in pairs of gastric cancer and normal tissue samples and cell lines were determined by quantitative real-time polymerase chain reaction. Bisulfite-modified polymerase chain reaction, cloning and sequencing were used to examine promoter methylation. We found genistein has an anti-proliferative effect on cancer cell growth through induction of cell cycle arrest. PCDH17 mRNA expression was down-regulated in cancer tissues, and PCDH17 promoter in cancer tissues was hyper-methylated in comparison with normal ones. Genistein and 5Aza-C induced PCDH17 mRNA expression in AGS, but not in Ges-1. Furthermore, genistein and 5Aza-C treatment significantly decreased promoter methylation in putative methylation target regions in AGS, reactivating PCDH17 expression. These results suggest that silencing of PCDH17 expression through promoter hypermethylation leads to loss of its tumor-suppressive activity. Genistein showed similar effects to that of 5Aza-C. Our results indicate that genistein is a novel, advantageous therapeutic agent for treating gastric cancer.