Aberrant methylation of breast and ovarian cancer susceptibility gene 1 in chemosensitive human ovarian cancer cells does not involve the phosphatidylinositol 3'-kinase-Akt pathway

Methylation is an important silencing mechanism of breast and ovarian cancer susceptibility gene 1 (BRCA1) expression in sporadic ovarian cancer. However, the role of BRCA1 methylation in chemotherapy in sporadic ovarian cancer and the related pathways have not been understood completely. This study has determined the roles of BRCA1 hypermethylation in chemotherapy of sporadic ovarian cancer and its related signaling pathways. We used bisulfite sequencing, real-time polymerase chain reaction, and western blotting to check the methylation state and expression levels of BRCA1 of the following cell lines: platinum-sensitive human ovarian cancer cell line COC1, platinum-resistant cell line COC1/DDP, SKOV-3, and 5-Aza-dC treated COC1. The cisplatin sensitivity of ovarian cancer cells was examined by MTS (methyl-thiazol tetrazolium) assay. Tumorigenicity in vivo and DDP-based chemosensitivity were compared among the above cells. Phosphatidylinositol 3'-kinase (PI3K)-Akt pathway activation in ovarian cancer cells was studied by western blotting. The frequency of BRCA1 methylation in the COC1 cell line was higher than in COC1/DDP and SKOV-3 cell lines, whereas the mRNA and protein expression of BRCA1 were lower than in the COC1/DDP and SKOV-3 cell lines. DNA demethylation decreased the chemosensitivity of COC1 cells and partially increased the expression levels of BRCA1. The activation of the PI3K-Akt pathway was low in ovarian cancer cells. Our results indicate that hypermethylation of BRCA1 might play an important role in the chemosensitivity of ovarian cancer, and that the PI3K-Akt pathway is not involved in this response. (Cancer Sci 2010).