Sivakumar Sushama, Gorbsky Gary J
Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA.
Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
Biol Open. 2017 Nov 15;6(11):1672-1679. doi: 10.1242/bio.026930.
Kinetochores move chromosomes on dynamic spindle microtubules and regulate signaling of the spindle checkpoint. The spindle- and kinetochore-associated (Ska) complex, a hexamer composed of two copies of Ska1, Ska2 and Ska3, has been implicated in both roles. Phosphorylation of kinetochore components by the well-studied mitotic kinases Cdk1, Aurora B, Plk1, Mps1, and Bub1 regulate chromosome movement and checkpoint signaling. Roles for the opposing phosphatases are more poorly defined. Recently, we showed that the C terminus of Ska1 recruits protein phosphatase 1 (PP1) to kinetochores. Here we show that PP1 and protein phosphatase 2A (PP2A) both promote accumulation of Ska at kinetochores. Depletion of PP1 or PP2A by siRNA reduces Ska binding at kinetochores, impairs alignment of chromosomes to the spindle midplane, and causes metaphase delay or arrest, phenotypes that are also seen after depletion of Ska. Artificial tethering of PP1 to the outer kinetochore protein Nuf2 promotes Ska recruitment to kinetochores, and it reduces but does not fully rescue chromosome alignment and metaphase arrest defects seen after Ska depletion. We propose that Ska has multiple functions in promoting mitotic progression and that kinetochore-associated phosphatases function in a positive feedback cycle to reinforce Ska complex accumulation at kinetochores.
动粒在动态的纺锤体微管上移动染色体，并调节纺锤体检查点的信号传导。纺锤体和动粒相关（Ska）复合体是一种由两个拷贝的Ska1、Ska2和Ska3组成的六聚体，已被证明在这两种作用中都发挥作用。经过充分研究的有丝分裂激酶Cdk1、Aurora B、Plk1、Mps1和Bub1对动粒成分的磷酸化作用调节染色体移动和检查点信号传导。而相对应的磷酸酶的作用则了解得较少。最近，我们发现Ska1的C末端将蛋白磷酸酶1（PP1）募集到动粒。在此我们表明，PP1和蛋白磷酸酶2A（PP2A）都促进Ska在动粒处的积累。通过小干扰RNA（siRNA）耗尽PP1或PP2A会减少Ska在动粒处的结合，损害染色体与纺锤体中平面的对齐，并导致中期延迟或停滞，这些表型在耗尽Ska后也会出现。将PP1人工拴系到外动粒蛋白Nuf2上会促进Ska募集到动粒，并且会减少但不能完全挽救在耗尽Ska后出现的染色体对齐和中期停滞缺陷。我们提出，Ska在促进有丝分裂进程中具有多种功能，并且动粒相关磷酸酶在一个正反馈循环中发挥作用，以加强Ska复合体在动粒处的积累。
