Promoter hypermethylation of multiple genes in hydatidiform mole choriocarcinoma

Abstract

Promoter hypermethylation has been known to be an important pathway for gene inactivation and contributes to the carcinogenesis of many human tumors. Little is currently known about the methylation status of tumor suppressor genes in hydatidiform mole and choriocarcinoma. Methylation status of the promoter regions of six genes, p16, HIC-1, TIMP3, GSTP1, death-associated protein kinase (DAPK), and E-cadherin, was investigated in 54 cases of hydatidiform mole, five cases of choriocarcinoma, and 10 cases of normal first trimester placenta by methylation-specific polymerase chain reaction (MSP). Immunohistochemical expression of p16, TIMP3, and E-cadherin and quantitative real-time RT-PCR of p16 was also performed. Of the six genes examined, the promoter region of four genes (E-cadherin, HIC-1, p16, TIMP3) in choriocarcinoma and three genes (E-cadherin, HIC-1, p16) in hydatidiform mole exhibited aberrant methylation at various frequencies whereas none was methylated in normal placenta. TIMP3 was methylated in choriocarcinoma but not in hydatidiform mole. In hydatidiform moles and choriocarcinomas, there was a significant correlation between methylation and reduced expression of p16, E-cadherin and TIMP3 (P < 0.001). Fifteen of the 54 patients with hydatidiform mole developed gestational trophoblastic neoplasia requiring chemotherapy. Promoter hypermethylation of p16, but not E-cadherin and HIC-1, was significantly correlated to the development of gestational trophoblastic neoplasia (P = 0.001, 0.084, and 0.551, respectively). Expression of p16 in patients subsequently developing gestational trophoblastic neoplasia was also significantly lower than in regressed cases (P = 0.026), as confirmed by quantitative real-time RT-PCR. Our findings indicated that multiple genes were hypermethylated in hydatidiform mole and choriocarcinoma. Repression of TIMP3 by promoter hypermethylation may be related to the development of choriocarcinoma. Methylation and expression status of p16 may serve as a potential marker predicting gestational trophoblastic neoplasia.