Department of Biochemistry and Molecular Biology, Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
J Cell Biol. 2011 May 2;193(3):475-87. doi: 10.1083/jcb.201101021.
Monoallelic expression of IGF2 is regulated by CCCTC binding factor (CTCF) binding to the imprinting control region (ICR) on the maternal allele, with subsequent formation of an intrachromosomal loop to the promoter region. The N-terminal domain of CTCF interacts with SUZ12, part of the polycomb repressive complex-2 (PRC2), to silence the maternal allele. We synthesized decoy CTCF proteins, fusing the CTCF deoxyribonucleic acid-binding zinc finger domain to CpG methyltransferase Sss1 or to enhanced green fluorescent protein. In normal human fibroblasts and breast cancer MCF7 cell lines, the CTCF decoy proteins bound to the unmethylated ICR and to the IGF2 promoter region but did not interact with SUZ12. EZH2, another part of PRC2, was unable to methylate histone H3-K27 in the IGF2 promoter region, resulting in reactivation of the imprinted allele. The intrachromosomal loop between the maternal ICR and the IGF2 promoters was not observed when IGF2 imprinting was lost. CTCF epigenetically governs allelic gene expression of IGF2 by orchestrating chromatin loop structures involving PRC2.
IGF2 的单等位基因表达受 CCCTC 结合因子（CTCF）与母等位基因上的印迹控制区（ICR）结合的调节，随后形成到启动子区域的染色体内环。CTCF 的 N 端结构域与 SUZ12 相互作用，后者是多梳抑制复合物-2（PRC2）的一部分，从而沉默母等位基因。我们合成了诱饵 CTCF 蛋白，将 CTCF 脱氧核糖核酸结合锌指结构域与 CpG 甲基转移酶 Sss1 或增强型绿色荧光蛋白融合。在正常的人类成纤维细胞和乳腺癌 MCF7 细胞系中，CTCF 诱饵蛋白与未甲基化的 ICR 和 IGF2 启动子区域结合，但不与 SUZ12 相互作用。PRC2 的另一个组成部分 EZH2 无法在 IGF2 启动子区域上甲基化组蛋白 H3-K27，导致印迹等位基因的重新激活。当 IGF2 印迹丢失时，未观察到母性 ICR 和 IGF2 启动子之间的染色体内环。CTCF 通过协调涉及 PRC2 的染色质环结构来表观遗传地控制 IGF2 的等位基因表达。
