DNA methylation reactivates GAD1 expression in cancer by preventing CTCF-mediated polycomb repressive complex 2 recruitment
DNA methylation reactivates GAD1 expression in cancer by preventing CTCF-mediated polycomb repressive complex 2 recruitment
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DOI：
10.1038/onc.2015.423
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发表时间：
2016-07-28
期刊：
影响因子：
8
通讯作者：
Sun，S.
中科院分区：
文献类型：
--
作者：
Yan，H.;Tang，G.;Sun，S.
γ-氨基丁酸（GABA）和谷氨酸脱羧酶1（GAD 1）（合成GABA的酶）的水平在肿瘤组织中显著增加。然而，这一增长背后的机制仍然难以捉摸。而不是沉默基因转录，我们表明，GAD 1启动子在结肠癌和肝癌细胞中是高甲基化的，导致高水平的GAD 1的生产。GAD 1是H3 K27 me 3沉默的靶基因。负责GAD 1再激活的关键位点被定位到GAD 1第三内含子内的DNA甲基化敏感性CTCF结合位点（CTCF-BS 3）。染色体构型捕获（3C）分析表明，在正常细胞中通过CTCF自身二聚化形成染色体内环（CTCF结合未甲基化的CTCF-BS 3和CTCF-BS 2）。CTCF二聚体然后与Zeste 12同源物的抑制子（SUZ 12）相互作用，SUZ 12是Polycomb抑制复合物2（PRC 2）的结构域，促进H3 K27的甲基化和GAD 1表达的沉默。在癌细胞中，这种沉默被DNA甲基化抑制。这些发现强烈表明GAD 1通过DNA甲基化重新激活，这为DNA甲基化和CTCF在癌细胞中主动协调致癌基因表达提供了模型。
Levels of γ-aminobutyric acid (GABA) and glutamic acid decarboxylase 1 (GAD1), the enzyme that synthesizes GABA, are significantly increased in neoplastic tissues. However, the mechanism underlying this increase remains elusive. Instead of silencing gene transcription, we showed that the GAD1 promoter was hypermethylated in both colon and liver cancer cells, leading to the production of high levels of GAD1. GAD1 is a target gene that is silenced by H3K27me3. The key locus responsible for GAD1 reactivation was mapped to a DNA methylation-sensitive CTCF-binding site (CTCF-BS3) within the third intron of GAD1. Chromosome configuration capture (3C) analysis indicated that an intrachromosomal loop was formed by CTCF self-dimerisation in normal cells (CTCF binds to both unmethylated CTCF-BS3 and CTCF-BS2). The CTCF dimer then interacted with suppressor of zeste 12 homologue (SUZ12), which is a domain of Polycomb repressive complex 2 (PRC2), promoting the methylation of H3K27 and the silencing of GAD1 expression. This silencing was shown to be inhibited by DNA methylation in cancer cells. These findings strongly suggest that GAD1 is reactivated by DNA methylation, which provided a model for DNA methylation and the active orchestration of oncogenic gene expression by CTCF in cancer cells.