Tinker-Kulberg R L, Morgan D O
Department of Physiology, University of California, San Francisco, California 94143-0444, USA.
Genes Dev. 1999 Aug 1;13(15):1936-49. doi: 10.1101/gad.13.15.1936.
The separation of sister chromatids in anaphase is followed by spindle disassembly and cytokinesis. These events are governed by the anaphase-promoting complex (APC), which triggers the ubiquitin-dependent proteolysis of key regulatory proteins: anaphase requires the destruction of the anaphase inhibitor Pds1, whereas mitotic exit requires the destruction of mitotic cyclins and the inactivation of Cdk1. We find that Pds1 is not only an inhibitor of anaphase, but also blocks cyclin destruction and mitotic exit by a mechanism independent of its effects on sister chromatid separation. Pds1 is also required for the mitotic arrest and inhibition of cyclin destruction that occurs after DNA damage. Even in anaphase cells, where Pds1 levels are normally low, DNA damage stabilizes Pds1 and prevents cyclin destruction and mitotic exit. Pds1 blocks cyclin destruction by inhibiting its binding partner Esp1. Mutations in ESP1 delay cyclin destruction; overexpression of ESP1 causes premature cyclin destruction in cells arrested in metaphase by spindle defects and in cells arrested in metaphase and anaphase by DNA damage. The effects of Esp1 are dependent on Cdc20 (an activating subunit of the APC) and on several additional proteins (Cdc5, Cdc14, Cdc15, Tem1) that form a regulatory network governing mitotic exit. We speculate that the inhibition of cyclin destruction by Pds1 may contribute to the ordering of late mitotic events by ensuring that mitotic exit is delayed until after anaphase is initiated. In addition, the stabilization of Pds1 after DNA damage provides a mechanism to delay both anaphase and mitotic exit while DNA repair occurs.
后期姐妹染色单体分离之后紧接着纺锤体解体和胞质分裂。这些事件受后期促进复合物（APC）调控，该复合物触发关键调控蛋白的泛素依赖性蛋白水解：后期需要破坏后期抑制因子Pds1，而有丝分裂退出需要破坏有丝分裂周期蛋白并使Cdk1失活。我们发现，Pds1不仅是后期的抑制因子，还通过一种独立于其对姐妹染色单体分离影响的机制来阻断周期蛋白的破坏和有丝分裂退出。DNA损伤后发生的有丝分裂停滞和周期蛋白破坏的抑制也需要Pds1。即使在后期细胞中，Pds1水平通常较低，但DNA损伤会使Pds1稳定，并阻止周期蛋白破坏和有丝分裂退出。Pds1通过抑制其结合伴侣Esp1来阻断周期蛋白的破坏。ESP1中的突变会延迟周期蛋白的破坏；ESP1的过表达会导致因纺锤体缺陷而停滞在中期的细胞以及因DNA损伤而停滞在中期和后期的细胞中周期蛋白过早破坏。Esp1的作用依赖于Cdc20（APC的一个激活亚基）以及几种其他蛋白质（Cdc5、Cdc14、Cdc15、Tem1），这些蛋白质形成一个调控有丝分裂退出的网络。我们推测，Pds1对周期蛋白破坏的抑制可能通过确保有丝分裂退出延迟到后期开始之后，从而有助于后期有丝分裂事件的有序进行。此外，DNA损伤后Pds1的稳定提供了一种机制，在DNA修复发生时延迟后期和有丝分裂退出。
