Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA.
Cell Cycle. 2012 Jun 15;11(12):2337-47. doi: 10.4161/cc.20810.
A variety of telomere protection programs are utilized to preserve telomere structure. However, the complex nature of telomere maintenance remains elusive. The Timeless protein associates with the replication fork and is thought to support efficient progression of the replication fork through natural impediments, including replication fork block sites. However, the mechanism by which Timeless regulates such genomic regions is not understood. Here, we report the role of Timeless in telomere length maintenance. We demonstrate that Timeless depletion leads to telomere shortening in human cells. This length maintenance is independent of telomerase, and Timeless depletion causes increased levels of DNA damage, leading to telomere aberrations. We also show that Timeless is associated with Shelterin components TRF1 and TRF2. Timeless depletion slows telomere replication in vitro, and Timeless-depleted cells fail to maintain TRF1-mediated accumulation of replisome components at telomeric regions. Furthermore, telomere replication undergoes a dramatic delay in Timeless-depleted cells. These results suggest that Timeless functions together with TRF1 to prevent fork collapse at telomere repeat DNA and ensure stable maintenance of telomere length and integrity.
多种端粒保护程序被用于保护端粒结构。然而，端粒维持的复杂性质仍然难以捉摸。Timeless 蛋白与复制叉结合，被认为可以支持复制叉通过自然障碍的有效进展，包括复制叉阻滞位点。然而，Timeless 调节这些基因组区域的机制尚不清楚。在这里，我们报告了 Timeless 在端粒长度维持中的作用。我们证明，Timeless 的耗竭导致人类细胞中端粒缩短。这种长度维持不依赖于端粒酶，并且 Timeless 的耗竭导致 DNA 损伤水平增加，导致端粒异常。我们还表明，Timeless 与 Shelterin 成分 TRF1 和 TRF2 相关联。Timeless 的耗竭在体外减缓端粒复制，并且 Timeless 耗竭的细胞不能维持 TRF1 介导的在端粒区域的复制酶成分的积累。此外，端粒复制在 Timeless 耗竭的细胞中经历显著延迟。这些结果表明，Timeless 与 TRF1 一起作用，以防止端粒重复 DNA 上的叉崩溃，并确保端粒长度和完整性的稳定维持。
