Synergy of demethylation and histone deacetylase inhibition in the re-expression of genes silenced in cancer
Synergy of demethylation and histone deacetylase inhibition in the re-expression of genes silenced in cancer
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DOI：
10.1038/5047
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发表时间：
1999-01-01
期刊：
影响因子：
30.8
通讯作者：
Baylin, SB
中科院分区：
文献类型：
--
作者：
Cameron, EE;Bachman, KE;Baylin, SB
密集甲基化的DNA与转录抑制染色质相关，其特征是存在低乙酰化组蛋白（1,2）。最近，这两种表观遗传过程被动态地联系起来。甲基cpg结合蛋白MeCP2似乎位于具有组蛋白去乙酰化酶活性的复合物中（3,4）。体外实验中，MeCP2可以介导甲基化启动子模板上转录抑制染色质的形成，而这一过程可以通过组蛋白去乙酰化酶特异性抑制剂曲古霉素A （trichostatin A， TSA）逆转（3-5）。然而，对于甲基化和组蛋白去乙酰化酶活性在稳定抑制密集甲基化内源性启动子转录中的相对作用知之甚少，例如印迹基因的沉默等位基因(6)、女性失活X染色体上的基因(7)和癌细胞中失活的肿瘤抑制基因（8,9）。我们在这里表明，在肿瘤细胞中，高甲基化基因MLH1， TIMP3 (TIMP3), CDKN2B （INK4B, p15）和CDKN2A （INK4, p16）不能被TSA单独激活，我们已经证明TSA单独可以上调非甲基化基因的表达。然而，在低剂量5-aza-2'脱氧胞苷（5Aza-dC）存在下，经过最小的去甲基化和轻微的基因再激活，TSA治疗导致每个基因的强烈重新表达。TSA不促进基因的去甲基化，并且没有任何治疗改变与高甲基化启动子相关的染色质结构。因此，尽管DNA甲基化和组蛋白去乙酰化似乎是癌症基因沉默的协同层，但密集的CpG岛甲基化对这些位点沉默状态的稳定维持起主导作用。
Densely methylated DNA associates with transcriptionally repressive chromatin characterized by the presence of underacetylated histones(1,2). Recently, these two epigenetic processes have been dynamically linked. The methyl-CpG-binding protein MeCP2 appears to reside in a complex with histone deacetylase activity(3,4). MeCP2 can mediate formation of transcriptionally repressive chromatin on methylated promoter templates in vitro, and this process can be reversed by trichostatin A (TSA), a specific inhibitor of histone deacetylase(3-5). Little is known, however, about the relative roles of methylation and histone deacetylase activity in the stable inhibition of transcription on densely methylated endogenous promoters, such as those for silenced alleles of imprinted genes(6), genes on the female inactive X chromosome(7) and tumour-suppressor genes inactivated in cancer cells(8,9). We show here that the hypermethylated genes MLH1, TIMP3 (TIMP3), CDKN2B (INK4B, p15) and CDKN2A (INK4, p16) cannot be transcriptionally reactivated with TSA alone in tumour cells in which we have shown that TSA alone can upregulate the expression of non-methylated genes. Following minimal demethylation and slight gene reactivation in the presence of low dose 5-aza-2'deoxycytidine (5Aza-dC), however, TSA treatment results in robust re-expression of each gene. TSA does not contribute to demethylation of the genes, and none of the treatments alter the chromatin structure associated with the hypermethylated promoters. Thus, although DNA methylation and histone deacetylation appear to act as synergistic layers for the silencing of genes in cancer, dense CpG island methylation is dominant for the stable maintenance of a silent state at these loci.