Ferguson A T, Lapidus R G, Baylin S B, Davidson N E
Johns Hopkins Oncology Center, Baltimore, Maryland 21231, USA.
Cancer Res. 1995 Jun 1;55(11):2279-83.
Approximately one third of breast cancers grow independently of estrogen, lack detectable estrogen receptor (ER) protein, and rarely respond to hormonal treatment. Previous studies correlated the lack of ER gene expression in ER-negative breast tumor cells with hypermethylation of a CpG island in the 5' region of the ER gene. In order to determine whether demethylation of the ER gene in the ER-negative human breast cancer cell line MDA-MB-231 could affect ER transcription, cells were treated with two inhibitors of DNA methylation, 5-azacytidine or 5-aza-2'-deoxycytidine. DNA from cells treated with either drug became partially demethylated at several methylation-sensitive restriction enzyme sites, including HhaI, NotI, and SacII, within the ER CpG island. This demethylation correlated with reexpression of the ER gene as detected by reverse transcriptase-PCR and production of ER protein as detected by Western blot analysis. ER produced in drug-treated cells was functionally active as demonstrated by its ability to activate transcription of estrogen-responsive genes. These results suggest that DNA methylation of the ER CpG island may play a role in suppression of ER gene expression in ER-negative breast cancer cells.
大约三分之一的乳腺癌独立于雌激素生长，缺乏可检测到的雌激素受体（ER）蛋白，并且很少对激素治疗产生反应。先前的研究将ER阴性乳腺肿瘤细胞中ER基因表达的缺失与ER基因5'区域中一个CpG岛的高甲基化相关联。为了确定ER阴性人乳腺癌细胞系MDA-MB-231中ER基因的去甲基化是否会影响ER转录，用两种DNA甲基化抑制剂5-氮杂胞苷或5-氮杂-2'-脱氧胞苷处理细胞。用这两种药物处理的细胞的DNA在ER CpG岛内的几个甲基化敏感限制性酶切位点（包括HhaI、NotI和SacII）处发生了部分去甲基化。这种去甲基化与通过逆转录酶-PCR检测到的ER基因的重新表达以及通过蛋白质印迹分析检测到的ER蛋白的产生相关。药物处理细胞中产生的ER具有功能活性，这通过其激活雌激素反应性基因转录的能力得以证明。这些结果表明，ER CpG岛的DNA甲基化可能在ER阴性乳腺癌细胞中ER基因表达的抑制中起作用。
