The Wistar Institute, Philadelphia, PA, USA.
EMBO J. 2012 Nov 5;31(21):4165-78. doi: 10.1038/emboj.2012.266. Epub 2012 Sep 25.
The contribution of human subtelomeric DNA and chromatin organization to telomere integrity and chromosome end protection is not yet understood in molecular detail. Here, we show by ChIP-Seq that most human subtelomeres contain a CTCF- and cohesin-binding site within ∼1-2 kb of the TTAGGG repeat tract and adjacent to a CpG-islands implicated in TERRA transcription control. ChIP-Seq also revealed that RNA polymerase II (RNAPII) was enriched at sites adjacent to the CTCF sites and extending towards the telomere repeat tracts. Mutation of CTCF-binding sites in plasmid-borne promoters reduced transcriptional activity in an orientation-dependent manner. Depletion of CTCF by shRNA led to a decrease in TERRA transcription, and a loss of cohesin and RNAPII binding to the subtelomeres. Depletion of either CTCF or cohesin subunit Rad21 caused telomere-induced DNA damage foci (TIF) formation, and destabilized TRF1 and TRF2 binding to the TTAGGG proximal subtelomere DNA. These findings indicate that CTCF and cohesin are integral components of most human subtelomeres, and important for the regulation of TERRA transcription and telomere end protection.
人类端粒下 DNA 和染色质组织对端粒完整性和染色体末端保护的贡献在分子细节上尚不清楚。在这里，我们通过 ChIP-Seq 显示，大多数人类端粒下区域在 TTAGGG 重复序列的约 1-2 kb 内含有一个 CTCF 和黏合蛋白结合位点，并且与涉及 TERRA 转录控制的 CpG 岛相邻。ChIP-Seq 还表明，RNA 聚合酶 II（RNAPII）在与 CTCF 位点相邻的位点处富集，并向端粒重复序列延伸。质粒载体启动子中 CTCF 结合位点的突变以依赖于取向的方式降低转录活性。通过 shRNA 耗尽 CTCF 导致 TERRA 转录减少，以及黏合蛋白和 RNAPII 与端粒下区域的结合减少。耗尽 CTCF 或黏合蛋白亚基 Rad21 会导致端粒诱导的 DNA 损伤焦点（TIF）形成，并使 TRF1 和 TRF2 与 TTAGGG 近端端粒下 DNA 的结合不稳定。这些发现表明 CTCF 和黏合蛋白是大多数人类端粒下区域的组成部分，对于 TERRA 转录和端粒末端保护的调节很重要。
