Department of Zoology and Physiology, University of Wyoming Laramie, WY, USA.
Front Oncol. 2012 Aug 9;2:93. doi: 10.3389/fonc.2012.00093. eCollection 2012.
Cell division in yeast is a highly regulated and well studied event. Various checkpoints are placed throughout the cell cycle to ensure faithful segregation of sister chromatids. Unexpected events, such as DNA damage or oxidative stress, cause the activation of checkpoint(s) and cell cycle arrest. Malfunction of the checkpoints may induce cell death. We previously showed that under oxidative stress, the budding yeast cohesin Mcd1, a homolog of human Rad21, was cleaved by the caspase-like protease Esp1. The cleaved Mcd1 C-terminal fragment was then translocated to mitochondria, causing apoptotic cell death. In the present study, we demonstrated that Bir1 plays an important role in spindle assembly checkpoint and cell death. Similar to H(2)O(2) treatment, deletion of BIR1 using a BIR1-degron strain caused degradation of the securin Pds1, which binds and inactivates Esp1 until metaphase-anaphase transition in a normal cell cycle. BIR1 deletion caused an increase level of ROS and mis-location of Bub1, a major protein for spindle assembly checkpoint. In wild type, Bub1 was located at the kinetochores, but was primarily in the cytoplasm in bir1 deletion strain. When BIR1 was deleted, addition of nocodazole was unable to retain the Bub1 localization on kinetochores, further suggesting that Bir1 is required to activate and maintain the spindle assembly checkpoint. Our study suggests that the BIR1 function in cell cycle regulation works in concert with its anti-apoptosis function.
酵母细胞的分裂是一个高度调控和研究充分的过程。在细胞周期的各个阶段都设置了各种检查点，以确保姐妹染色单体的忠实分离。意外事件，如 DNA 损伤或氧化应激，会导致检查点的激活和细胞周期停滞。检查点的故障可能会导致细胞死亡。我们之前曾表明，在氧化应激下，芽殖酵母黏合蛋白 Mcd1（人类 Rad21 的同源物）被半胱天冬酶样蛋白酶 Esp1 切割。然后，被切割的 Mcd1 C 端片段被转移到线粒体，导致凋亡性细胞死亡。在本研究中，我们证明了 Bir1 在纺锤体组装检查点和细胞死亡中起着重要作用。与 H2O2 处理相似，使用 BIR1-degron 菌株删除 BIR1 会导致 securin Pds1 的降解，该蛋白在正常细胞周期中与 Esp1 结合并使其失活，直到有丝分裂-后期过渡。BIR1 缺失导致 ROS 水平升高和 Bub1 定位错误，Bub1 是纺锤体组装检查点的主要蛋白。在野生型中，Bub1 位于动粒上，但在 bir1 缺失菌株中主要位于细胞质中。当 BIR1 缺失时，添加 nocodazole 无法将 Bub1 定位保留在动粒上，进一步表明 Bir1 是激活和维持纺锤体组装检查点所必需的。我们的研究表明，BIR1 在细胞周期调控中的功能与其抗凋亡功能协同作用。
