DNA methylation-related vitamin D receptor insensitivity in breast cancer
DNA methylation-related vitamin D receptor insensitivity in breast cancer
复制标题
DOI：
10.4161/cbt.10.1.11994
复制
发表时间：
2010-07-01
影响因子：
3.6
通讯作者：
Umbricht, Christopher B.
中科院分区：
文献类型：
--
作者：
Marik, Radharani;Fackler, MaryJo;Umbricht, Christopher B.
骨化三醇（1 α，25（OH）（2）-维生素D3）与维生素D受体（VDR）结合并调节正常乳腺的分化，因此可用于乳腺癌的治疗或预防。然而，许多乳腺癌细胞对骨化三醇具有耐药性。在本研究中，我们研究了抗性机制和VDR启动子超甲基化的表观遗传沉默的作用。VDR启动子区的亚硫酸氢盐测序显示在上游和转录起始位点附近约700个碱基对（bp）处的甲基化CpG岛。VDR CpG岛被5 '脱氧氮杂胞苷处理去甲基化，并且这伴随着乳腺癌细胞系中VDR mRNA水平的平行增加。定量甲基化特异性PCR分析证实了这些CpG岛在原发性肿瘤中的高甲基化，以及其在正常乳腺组织中的缺失。在乳腺癌中检测到的VDR转录本主要是5-截短的，而正常乳腺组织表达全长转录本。与这一观察结果相一致，与正常乳腺样本相比，乳腺癌中含有VDR反应元件（VDRE）的基因（如细胞色素p450羟化酶、p21或C/EBP）表达不足。用5 '脱氧氮杂胞苷（AZA）处理恢复了VDR活性较长转录物的表达，同时增加了含VDRE基因的表达。因此，启动子甲基化介导的VDR功能变体表达的沉默可能有助于降低VDR途径下游效应子的表达，并导致乳腺癌中骨化三醇不敏感。这些数据表明，VDR甲基化的药理学逆转可以重新建立乳腺癌细胞对使用骨化三醇的分化治疗的易感性。
Calcitriol (1 alpha, 25(OH)(2)-Vitamin D3) binds to the vitamin D receptor (VDR) and regulates differentiation of the normal mammary gland, and may therefore be useful in breast cancer treatment or prevention. Many breast cancer cells are, however, resistant to Calcitriol. In this study, we investigated the resistance mechanism and the role of epigenetic silencing of VDR by promoter hypermethylation. Bisulfite sequencing of the VDR promoter region revealed methylated CpG islands at -700 base pairs (bp) upstream and near the transcription start site. VDR CpG islands were demethylated by 5'deoxy-azacytidine treatment, and this was accompanied by a parallel increase in VDR mRNA levels in breast cancer cell lines. Quantitative methylation-specific PCR analyses confirmed hypermethylation of these CpG islands in primary tumors, and its absence in normal breast tissue. VDR transcripts detected in breast cancers were predominantly 5-truncated, while normal breast tissue expressed full-length transcripts. Consistent with this observation, genes containing the VDR-responsive element (VDRE), such as cytochrome p450 hydroxylases, p21 or C/EBP were underexpressed in breast cancers compared to normal breast samples. Expression of the active longer transcripts of VDR was restored with 5'deoxy-Azacytidine (AZA) treatment, with a concurrent increase in expression of VDRE-containing genes. Thus, promoter methylation-mediated silencing of expression of the functional variants of VDR may contribute to reduced expression of downstream effectors of the VDR pathway and subsequent Calcitriol insensitivity in breast cancer. These data suggest that pharmacological reversal of VDR methylation may re-establish breast cancer cell susceptibility to differentiation therapy using Calcitriol.