爪蟾端粒结合蛋白 2 在端粒末端保护和复制中的重要作用。

Essential roles of Xenopus TRF2 in telomere end protection and replication.

机构信息

Laboratory of Cell Cycle Regulation, Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.

出版信息

Genes Cells. 2011 Jun;16(6):728-39. doi: 10.1111/j.1365-2443.2011.01520.x. Epub 2011 May 10.

Abstract

TRF1 and TRF2 are double-stranded (ds) telomere DNA-binding proteins and the core members of shelterin, a complex that provides the structural and functional basis of telomere functions. We have reported that unlike mammalian TRF1 that constitutively binds to chromatin, Xenopus TRF1 (xTRF1) associates with mitotic chromatin but dissociates from interphase chromatin reconstituted in Xenopus egg extracts. This finding raised the possibility that xTRF1 and Xenopus TRF2 (xTRF2) contribute to telomere functions in a manner different from mammalian TRF1 and TRF2. Here, we focused on the role of xTRF2. We prepared chromatin reconstituted in egg extracts immunodepleted for xTRF2. Compared to mock-depleted nuclei, DNA damage response at telomeres was activated, and bulk DNAs were poorly replicated in xTRF2-depleted nuclei. The replication defect was rescued by inactivating ATR through the addition of anti-ATR neutralizing antibody, suggesting that ATR plays a role in the defect. Interestingly, the bulk DNA replication defect, but not the DNA damage response at telomeres, was rescued by supplementing the xTRF2-depleted extracts with recombinant xTRF2 (rTRF2). We propose that xTRF2 is required for both efficient replication of bulk DNA and protection from the activation of the DNA damage checkpoints pathway, and that those two functions are mechanistically separable.

摘要

端粒结合因子 1(TRF1)和端粒结合因子 2(TRF2)是双链(ds)端粒 DNA 结合蛋白,也是庇护体(shelterin)的核心成员,庇护体为端粒功能提供结构和功能基础。我们曾报道,不同于组成型结合染色质的哺乳动物 TRF1,非洲爪蟾 TRF1(xTRF1)与有丝分裂染色质结合,但与非洲爪蟾卵提取物中重组的间期染色质分离。这一发现提示 xTRF1 和非洲爪蟾 TRF2(xTRF2)可能以不同于哺乳动物 TRF1 和 TRF2 的方式参与端粒功能。在此,我们关注 xTRF2 的作用。我们制备了用抗 xTRF2 抗体免疫耗竭卵提取物中 xTRF2 后的染色质。与未耗竭的核相比,xTRF2 耗竭核中端粒处的 DNA 损伤反应被激活,大量 DNA 复制不良。ATR 通过添加抗 ATR 中和抗体失活后,复制缺陷得到挽救,表明 ATR 在该缺陷中起作用。有趣的是,大量 DNA 复制缺陷,但不是端粒处的 DNA 损伤反应,通过用重组 xTRF2(rTRF2)补充 xTRF2 耗竭提取物而得到挽救。我们提出,xTRF2 对于大量 DNA 的有效复制和防止 DNA 损伤检查点途径的激活都是必需的,并且这两个功能在机制上是可分离的。

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