Biocenter, Division of Molecular Pathophysiology, Innsbruck Medical University, A-6020 Innsbruck, Austria.
J Cell Biol. 2012 Sep 3;198(5):847-63. doi: 10.1083/jcb.201110060.
Chromokinesins are microtubule plus end-directed motor proteins that bind to chromosome arms. In Xenopus egg cell-free extracts, Xkid and Xklp1 are essential for bipolar spindle formation but the functions of the human homologues, hKID (KIF22) and KIF4A, are poorly understood. By using RNAi-mediated protein knockdown in human cells, we find that only co-depletion delayed progression through mitosis in a Mad2-dependent manner. Depletion of hKID caused abnormal chromosome arm orientation, delayed chromosome congression, and sensitized cells to nocodazole. Knockdown of KIF4A increased the number and length of microtubules, altered kinetochore oscillations, and decreased kinetochore microtubule flux. These changes were associated with failures in establishing a tight metaphase plate and an increase in anaphase lagging chromosomes. Co-depletion of both chromokinesins aggravated chromosome attachment failures, which led to mitotic arrest. Thus, hKID and KIF4A contribute independently to the rapid and correct attachment of chromosomes by controlling the positioning of chromosome arms and the dynamics of microtubules, respectively.
染色质运动蛋白是微管正极定向的马达蛋白，能与染色体臂结合。在非洲爪蟾卵无细胞提取物中，Xkid 和 Xklp1 对形成两极纺锤体是必需的，但人类同源物 hKID（KIF22）和 KIF4A 的功能知之甚少。通过在人细胞中使用 RNAi 介导的蛋白敲低，我们发现只有共同耗竭以 Mad2 依赖的方式延迟有丝分裂的进展。hKID 的耗竭导致染色体臂取向异常、染色体向心延迟，并使细胞对诺考达唑敏感。KIF4A 的敲低增加了微管的数量和长度，改变了着丝粒的振荡，并减少了着丝粒微管的通量。这些变化与中期板的紧密建立失败以及后期滞后染色体的增加有关。两种染色质运动蛋白的共同耗竭加剧了染色体附着失败，导致有丝分裂停滞。因此，hKID 和 KIF4A 分别通过控制染色体臂的定位和微管的动力学，对染色体的快速和正确附着做出贡献。
