Alao John P, Sjölander Johanna J, Baar Juliane, Özbaki-Yagan Nejla, Kakoschky Bianca, Sunnerhagen Per
Department of Chemistry and Molecular Biology, Lundberg Laboratory, University of Gothenburg, Box 462, SE-405 30, Göteborg, Sweden.
Mol Microbiol. 2014 May;92(4):777-96. doi: 10.1111/mmi.12592. Epub 2014 Apr 14.
Cdc25 is required for Cdc2 dephosphorylation and is thus essential for cell cycle progression. Checkpoint activation requires dual inhibition of Cdc25 and Cdc2 in a Rad3-dependent manner. Caffeine is believed to override activation of the replication and DNA damage checkpoints by inhibiting Rad3-related proteins in both Schizosaccharomyces pombe and mammalian cells. In this study, we have investigated the impact of caffeine on Cdc25 stability, cell cycle progression and checkpoint override. Caffeine induced Cdc25 accumulation in S. pombe independently of Rad3. Caffeine delayed cell cycle progression under normal conditions but advanced mitosis in cells treated with replication inhibitors and DNA-damaging agents. In the absence of Cdc25, caffeine inhibited cell cycle progression even in the presence of hydroxyurea or phleomycin. Caffeine induces Cdc25 accumulation in S. pombe by suppressing its degradation independently of Rad3. The induction of Cdc25 accumulation was not associated with accelerated progression through mitosis, but rather with delayed progression through cytokinesis. Caffeine-induced Cdc25 accumulation appears to underlie its ability to override cell cycle checkpoints. The impact of Cdc25 accumulation on cell cycle progression is attenuated by Srk1 and Mad2. Together our findings suggest that caffeine overrides checkpoint enforcement by inducing the inappropriate nuclear localization of Cdc25.
Cdc25是Cdc2去磷酸化所必需的，因此对细胞周期进程至关重要。检查点激活需要以Rad3依赖的方式对Cdc25和Cdc2进行双重抑制。在粟酒裂殖酵母和哺乳动物细胞中，咖啡因被认为通过抑制Rad3相关蛋白来克服复制和DNA损伤检查点的激活。在本研究中，我们研究了咖啡因对Cdc25稳定性、细胞周期进程和检查点克服的影响。咖啡因在粟酒裂殖酵母中诱导Cdc25积累，且不依赖于Rad3。咖啡因在正常条件下延迟细胞周期进程，但在经复制抑制剂和DNA损伤剂处理的细胞中促进有丝分裂。在没有Cdc25的情况下，即使存在羟基脲或博来霉素，咖啡因也会抑制细胞周期进程。咖啡因通过独立于Rad3抑制其降解来诱导粟酒裂殖酵母中Cdc25的积累。Cdc25积累的诱导与有丝分裂进程的加速无关，而是与胞质分裂进程的延迟有关。咖啡因诱导的Cdc25积累似乎是其克服细胞周期检查点能力的基础。Srk1和Mad2减弱了Cdc25积累对细胞周期进程的影响。我们的研究结果共同表明，咖啡因通过诱导Cdc25不适当的核定位来克服检查点执行。
