Study of the CpG methylation status of ER alpha gene in estrogen receptor alpha-negative breast cancer cell lines and the role of hydralazine demethylation

Abstract

To detect the 5'CpG island methylation of estrogen receptor (ER) alpha gene promotor region in ER alpha-negative human breast cancer cell lines (MDA-MB-231 and MDA-MB-435) and breast cancer tissues; and to investigate the possibility of hydralazine in restoring the expression of ER alpha gene through demethylation. The CpG island methylation status of ER alpha gene promotor region-A, B and C in ER alpha-negative human breast cancer cell lines (MDA-MB-231 and MDA-MB-435) and 20 cases of breast cancer tissues were analyzed using methylation-specific polymerase chain reaction (MSP). The mRNA expression profile of ER alpha isoforms (ERalpha-A, ERalpha-B and ERalpha-C) and coding region in ER alpha gene were analyzed by using RT-PCR, after hydralazine treatment. In the two cell lines studied, CpG island was methylated in ERalpha-A and ERalpha-B but not ERalpha-C. Among them, methylation of CpG island in ERalpha-A was obtained in 13 breast tumor cases; methylation of ERalpha-B seen in 10 tumor cases; methylation of both ERalpha-A and ERalpha-B seen in 9 cases; and methylation of ERalpha-C was obtained in only 1 case. The positivity rates were 65%, 50%, 45% and 5% respectively. The ER alpha gene non-expression in breast cancer is probably associated with CpG island methylation in ER alpha gene promotor region A and B, and the level of methylation is enhanced as advance of tumors in clinical stage. Hydralazine, served as a demethylating agent enables to restore the expression of ER alpha gene.