CTCF-dependent enhancer-blocking by alternative chromatin loop formation
CTCF-dependent enhancer-blocking by alternative chromatin loop formation
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DOI：
10.1073/pnas.0808506106
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发表时间：
2008-12-23
影响因子：
11.1
通讯作者：
Dean, Ann
中科院分区：
文献类型：
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作者：
Hou, Chunhui;Zhao, Hui;Dean, Ann
绝缘子阻断增强子的机制尚不清楚。我们探索了人类β-珠蛋白HS 5的活性，HS 5是CTCF依赖性鸡HS 4绝缘子的直系同源物。在β-珠蛋白基因座控制区（LCR）和转基因下游基因之间放置的HS 5的额外拷贝实现了增强子阻断剂的经典预测。异位HS 5不干扰LCR，但通过干扰RNA pol II、激活因子和共激活因子募集以及下游β-珠蛋白基因的表观遗传修饰来阻断基因激活。在这些作用的基础上，异位HS 5破坏β-珠蛋白和LCR之间的染色质环形成，而是与内源性HS 5形成新的环，其在拓扑学上分离LCR。增强子阻断和绝缘子环形成都依赖于异位HS 5中的完整CTCF位点，并且对siRNA敲低CTCF蛋白敏感。因此，CTCF位点的内在成环活性可以使LCR功能无效。
The mechanism underlying enhancer-blocking by insulators is unclear. We explored the activity of human beta-globin HS5, the orthologue of the CTCF-dependent chicken HS4 insulator. An extra copy of HS5 placed between the beta-globin locus control region (LCR) and downstream genes on a transgene fulfills the classic predictions for an enhancer-blocker. Ectopic HS5 does not perturb the LCR but blocks gene activation by interfering with RNA pol II, activator and coactivator recruitment, and epigenetic modification at the downstream beta-globin gene. Underlying these effects, ectopic HS5 disrupts chromatin loop formation between beta-globin and the LCR, and instead forms a new loop with endogenous HS5 that topologically isolates the LCR. Both enhancer-blocking and insulator-loop formation depend on an intact CTCF site in ectopic HS5 and are sensitive to knock-down of the CTCF protein by siRNA. Thus, intrinsic looping activity of CTCF sites can nullify LCR function.