Altered chromatin structure associated with methylation-induced gene silencing in cancer cells: correlation of accessibility, methylation, MeCP2 binding and acetylation
Altered chromatin structure associated with methylation-induced gene silencing in cancer cells: correlation of accessibility, methylation, MeCP2 binding and acetylation
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DOI：
10.1093/nar/29.22.4598
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发表时间：
2001-11-15
影响因子：
14.9
通讯作者：
Jones, PA
中科院分区：
文献类型：
--
作者：
Nguyen, CT;Gonzales, FA;Jones, PA
在人类癌症中，通过启动子CpG岛的高甲基化来沉默肿瘤抑制基因是有充分证据的，并且可能是由甲基CpG结合蛋白(如MeCP2)介导的，这些蛋白在体内与染色质修饰物和转录抑制物相关。然而，甲基化和染色质结构在基因表达调控中的确切动态还不是很清楚。在这项研究中，我们利用甲基化敏感消化、完整核MSPL可及性和染色质免疫沉淀(ChlP)分析了p14(ARF)/p16(1NK4A)基因座上三个CpG岛的甲基化状态和染色质结构。我们证明了在人类癌细胞系中存在与肿瘤抑制基因沉默相关的染色质结构的改变，包括CpG岛甲基化、染色质缩合、组蛋白去乙酰化和MeCP2结合。数据表明，MeCP2可以与启动子和外显子上的甲基化CpG岛结合；当MeCP2结合在外显子上时，不会干扰转录，这表明该蛋白在转录抑制之外具有更广泛的作用。在没有甲基化的情况下，研究表明，位于启动子和外显子的CpG岛在相关组蛋白H3的乙酰化水平上显示出显著的差异，这表明染色质的重塑可以通过甲基化独立的过程实现，这可能解释了为什么非启动子CpG岛比启动子岛更容易从头甲基化。
Silencing of tumor-suppressor genes by hypermethylation of promoter CpG islands is well documented in human cancer and may be mediated by methyl-CpG-binding proteins, like MeCP2, that are associated in vivo with chromatin modifiers and transcriptional repressors. However, the exact dynamic between methylation and chromatin structure in the regulation of gene expression is not well understood. In this study, we have analyzed the methylation status and chromatin structure of three CpG islands in the p14(ARF)/p16(1NK4A) locus in a series of normal and cancer cell lines using methylation-sensitive digestion, Mspl accessibility in intact nuclei and chromatin immunoprecipitation (ChlP) assays. We demonstrate the existence of an altered chromatin structure associated with the silencing of tumor-suppressor genes in human cancer cell lines involving CpG island methylation, chromatin condensation, histone deacetylation and MeCP2 binding. The data showed that MeCP2 could bind to methylated CpG islands in both promoters and exons; MeCP2 does not interfere with transcription when bound at an exon, suggesting a more generalized role for the protein beyond transcriptional repression. In the absence of methylation, it is demonstrated that CpG islands located in promoters versus exons display marked differences in the levels of acetylation of associated histone H3, suggesting that chromatin remodeling can be achieved by methylation-independent processes and perhaps explaining why non-promoter CpG islands are more susceptible to de novo methylation than promoter islands.