Protein phosphatase 2A regulates MPF activity and sister chromatid cohesion in budding yeast
Protein phosphatase 2A regulates MPF activity and sister chromatid cohesion in budding yeast
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DOI：
10.1016/s0960-9822(02)70784-7
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发表时间：
1996-12-01
期刊：
影响因子：
9.2
通讯作者：
Murray, AW
中科院分区：
文献类型：
--
作者：
Minshull, J;Straight, A;Murray, AW
背景：有丝分裂受成熟促进因子（maturity promoting factor，MPF）的调控，MPF是Cdc 2/28-cyclin B复合物的活性形式。细胞周期蛋白B丰度水平的增加和Cdc 2/28的抑制性磷酸盐的损失驱动细胞进入有丝分裂，而细胞周期蛋白B破坏使MPF失活并驱动细胞退出有丝分裂。具有缺陷纺锤体的细胞在有丝分裂中被纺锤体组装检查点阻止，其防止有丝分裂周期蛋白的破坏和MPF的失活。我们已经调查了纺锤体组装检查点，细胞周期蛋白破坏，Cdc 2/28的抑制性磷酸化，退出有丝分裂。结果：以前的特点是芽殖酵母疯突变体缺乏纺锤体组装检查点之间的关系。纺锤体解聚不能阻止它们在有丝分裂中的发生，因为它们不能稳定细胞周期蛋白B。相比之下，一个新分离的突变体在芽殖酵母CDC 55基因，编码蛋白磷酸酶2A（PP 2A）调节亚基，显示出不同的检查点缺陷。在纺锤体缺陷的情况下，这些细胞分离它们的姐妹染色单体并离开有丝分裂而不诱导细胞周期蛋白B破坏。尽管B型细胞周期蛋白的持久性，cdc 55突变细胞的MPF。两个实验表明，这种失活是由于Cdc 28上的抑制性磷酸化：磷酸酪氨酸在Cdc 55 Delta细胞中积累在Cdc 28上，其纺锤体已经解聚，而Cdc 28上缺乏抑制性磷酸化位点的cdc 28突变体允许纺锤体缺陷阻止cdc 55突变体在有丝分裂中具有活跃的MPF和未分离的姐妹染色单体。我们的结论是蛋白磷酸酶活性的扰动允许MPF被抑制磷酸化而不是细胞周期蛋白破坏失活。在这些条件下，姐妹染色单体分离似乎是。调节MPF活性，而不是蛋白质降解。我们讨论了PP 2A和Cdc 28磷酸化在细胞周期控制中的作用，以及新的有丝分裂退出途径在适应纺锤体组装检查点的长期激活中发挥作用的可能性。
Background: Mitosis is regulated by MPF (maturation promoting factor), the active form of Cdc2/28-cyclin B complexes. Increasing levels of cyclin B abundance and the loss of inhibitory phosphates from Cdc2/28 drives cells into mitosis, whereas cyclin B destruction inactivates MPF and drives cells out of mitosis. Cells with defective spindles are arrested in mitosis by the spindle-assembly checkpoint, which prevents the destruction of mitotic cyclins and the inactivation of MPF. We have investigated the relationship between the spindle-assembly checkpoint, cyclin destruction, inhibitory phosphorylation of Cdc2/28, and exit from mitosis.Results: The previously characterized budding yeast mad mutants lack the spindle-assembly checkpoint. Spindle depolymerization does not arrest them in mitosis because they cannot stabilize cyclin B. In contrast, a newly isolated mutant in the budding yeast CDC55 gene, which encodes a protein phosphatase 2A (PP2A) regulatory subunit, shows a different checkpoint defect. In the presence of a defective spindle, these cells separate their sister chromatids and leave mitosis without inducing cyclin B destruction. Despite the persistence of B-type cyclins, cdc55 mutant cells inactivate MPF. Two experiments show that this inactivation is due to inhibitory phosphorylation on Cdc28: phosphotyrosine accumulates on Cdc28 in cdc55 Delta cells whose spindles have been depolymerized, and a cdc28 mutant that lacks inhibitory phosphorylation sites on Cdc28 allows spindle defects to arrest cdc55 mutants in mitosis with active MPF and unseparated sister chromatids.Conclusions: We conclude that perturbations of protein phosphatase activity allow MPF to be inactivated by inhibitory phosphorylation instead of by cyclin destruction. Under these conditions, sister chromatid separation appears to be. regulated by MPF activity rather than by protein degradation. We discuss the role of PP2A and Cdc28 phosphorylation in cell-cycle control, and the possibility that the novel mitotic exit pathway plays a role in adaptation to prolonged activation of the spindle-assembly checkpoint.