Graduate Institute of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei 100, Taiwan.
Department of Anatomy, Physiology and Biochemistry, The Swedish University of Agricultural Sciences, Biomedical Center, S-751 23 Uppsala, Sweden.
J Biol Chem. 2010 Aug 27;285(35):27327-27335. doi: 10.1074/jbc.M110.137042. Epub 2010 Jun 16.
Cellular supply of dNTPs is essential in the DNA replication and repair processes. Here we investigated the regulation of thymidine kinase 1 (TK1) in response to DNA damage and found that genotoxic insults in tumor cells cause up-regulation and nuclear localization of TK1. During recovery from DNA damage, TK1 accumulates in p53-null cells due to a lack of mitotic proteolysis as these cells are arrested in the G(2) phase by checkpoint activation. We show that in p53-proficient cells, p21 expression in response to DNA damage prohibits G(1)/S progression, resulting in a smaller G(2) fraction and less TK1 accumulation. Thus, the p53 status of tumor cells affects the level of TK1 after DNA damage through differential cell cycle control. Furthermore, it was shown that in HCT-116 p53(-/-) cells, TK1 is dispensable for cell proliferation but crucial for dTTP supply during recovery from DNA damage, leading to better survival. Depletion of TK1 decreases the efficiency of DNA repair during recovery from DNA damage and generates more cell death. Altogether, our data suggest that more dTTP synthesis via TK1 take place after genotoxic insults in tumor cells, improving DNA repair during G(2) arrest.
细胞内 dNTP 的供应对于 DNA 复制和修复过程至关重要。在这里，我们研究了胸苷激酶 1（TK1）在应对 DNA 损伤时的调节作用，发现肿瘤细胞中的遗传毒性刺激会导致 TK1 的上调和核定位。在 DNA 损伤恢复期间，由于缺乏有丝分裂蛋白水解，p53 缺失的细胞中 TK1 积累，因为这些细胞由于 checkpoint 激活而停滞在 G2 期。我们表明，在 p53 功能正常的细胞中，DNA 损伤引起的 p21 表达阻止了 G1/S 期进展，导致较小的 G2 分数和较少的 TK1 积累。因此，肿瘤细胞的 p53 状态通过差异细胞周期控制影响 DNA 损伤后 TK1 的水平。此外，研究表明，在 HCT-116 p53(-/-)细胞中，TK1 对于 DNA 损伤恢复期间的细胞增殖不是必需的，但对于 dTTP 的供应至关重要，从而提高了生存能力。TK1 的耗竭降低了 DNA 修复的效率，并导致更多的细胞死亡。总之，我们的数据表明，在肿瘤细胞受到遗传毒性刺激后，通过 TK1 进行更多的 dTTP 合成，改善了 G2 期阻滞期间的 DNA 修复。
