CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China.
CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China.
J Genet Genomics. 2018 Sep 20;45(9):467-476. doi: 10.1016/j.jgg.2018.09.001. Epub 2018 Sep 19.
It has been well documented that Tel1 positively regulates telomere-end resection by promoting Mre11-Rad50-Xrs2 (MRX) activity, while Rif2 negatively regulates telomere-end resection by inhibiting MRX activity. At uncapped telomeres, whether Tel1 or Rif2 plays any role remains largely unknown. In this work, we examined the roles of Tel1 and Rif2 at uncapped telomeres in yku70Δ and/or cdc13-1 mutant cells cultured at non-permissive temperature. We found that deletion of TEL1 exacerbates the temperature sensitivity of both yku70Δ and cdc13-1 cells. Further epistasis analysis indicated that MRX and Tel1 function in the same pathway in telomere protection. Consistently, TEL1 deletion increases accumulation of Exo1-dependent telomeric single-stranded DNA (ssDNA) at uncapped telomeres, which stimulates checkpoint-dependent cell cycle arrest. Moreover, TEL1 deletion in yku70Δ cells facilitates Rad51-dependent Y' recombination. In contrast, RIF2 deletion in yku70Δ cells decreases the accumulation of telomeric ssDNA after 8 h of incubation at the non-permissive temperature of 37 °C and suppresses the temperature sensitivity of yku70Δ cells, likely due to the increase of Mre11 association at telomeres. Collectively, our findings indicate that Tel1 and Rif2 regulate telomere protection at uncapped telomeres via their roles in balancing MRX activity in telomere resection.
已有大量文献证明，Tel1 通过促进 Mre11-Rad50-Xrs2（MRX）活性正向调控端粒末端切除，而 Rif2 通过抑制 MRX 活性负向调控端粒末端切除。在无帽端粒处，Tel1 或 Rif2 是否发挥作用尚不清楚。在这项工作中，我们在非许可温度下培养的 yku70Δ 和/或 cdc13-1 突变细胞中，研究了 Tel1 和 Rif2 在无帽端粒处的作用。我们发现，TEL1 的缺失加剧了 yku70Δ 和 cdc13-1 细胞的温度敏感性。进一步的遗传分析表明，MRX 和 Tel1 在端粒保护中发挥相同的作用。一致地，TEL1 的缺失增加了无帽端粒处依赖 Exo1 的端粒单链 DNA（ssDNA）的积累，从而刺激了检查点依赖性的细胞周期停滞。此外，TEL1 在 yku70Δ 细胞中的缺失促进了 Rad51 依赖性的 Y'重组。相比之下， Rif2 在 yku70Δ 细胞中的缺失减少了在非许可温度 37°C 孵育 8 小时后端粒 ssDNA 的积累，并抑制了 yku70Δ 细胞的温度敏感性，这可能是由于 Mre11 在端粒处的结合增加所致。总之，我们的发现表明，Tel1 和 Rif2 通过调节端粒切除中 MRX 活性的平衡来调节无帽端粒处的端粒保护。
