Kanada Masamitsu, Nagasaki Akira, Uyeda Taro Q P
Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan.
Exp Cell Res. 2009 Oct 1;315(16):2705-14. doi: 10.1016/j.yexcr.2009.06.027. Epub 2009 Jul 1.
The dynamics of astral and midzone microtubules (MTs) must be separately regulated during cell division, but the mechanism of selective stabilization of midzone MTs is poorly understood. Here we show that, in HT1080 cells, activation of Rho is required to stabilize midzone MTs, and to maintain the midzone structures after anaphase onset or during cytokinesis. Ect2-depleted cells undergoing conventional cytokinesis (cytokinesis A) or contractile ring-independent cytokinesis (cytokinesis B) formed abnormally thin bundles of midzone MTs. C3-loaded mitotic cells with inactivated Rho showed similar but more severe disorganization of midzone MTs. In addition, the bundles of astral MTs were abnormally abundant along the cell periphery in both Ect2-depleted and C3-loaded mitotic cells. Mitotic kinesin-like protein 1 (MKLP1), a component of the spindle midzone required for bundling of MTs, was localized only in the narrower equatorial regions in Ect2-depleted cells, and disappeared from the midzone accompanying the progression of the mitotic phase in C3-loaded cells. Stabilization of MTs by taxol was sufficient to maintain the midzone structures in C3-loaded mitotic cells. These results, when combined with a preceding analysis on another, microtubule-associated Rho GEF (C.J. Bakal, D. Finan, J. LaRose, C.D. Wells, G. Gish, S. Kulkarni, P. DeSepulveda, A. Wilde, R. Rottapel, The Rho GTP exchange factor Lfc promotes spindle assembly in early mitosis, Proc. Natl. Acad. Sci. U. S. A. 102 (2005) 9529-9534), suggest that mammalian cells have two potential steps that require active Rho for the stabilization of midzone MTs during mitosis and cytokinesis.
星体微管和中间区微管(MTs)的动力学在细胞分裂过程中必须分别进行调节,但中间区微管选择性稳定的机制仍知之甚少。在此我们表明,在HT1080细胞中,Rho的激活是稳定中间区微管以及在后期开始后或胞质分裂期间维持中间区结构所必需的。经历传统胞质分裂(胞质分裂A)或独立于收缩环的胞质分裂(胞质分裂B)的Ect2缺失细胞形成了异常细的中间区微管束。Rho失活的C3负载有丝分裂细胞显示出类似但更严重的中间区微管紊乱。此外,在Ect2缺失和C3负载的有丝分裂细胞中,星体微管束沿细胞周边异常丰富。有丝分裂驱动蛋白样蛋白1(MKLP1)是微管束形成所需的纺锤体中间区的一个组成部分,仅定位在Ect2缺失细胞中较窄的赤道区域,并在C3负载细胞中随着有丝分裂期的进展从中间区消失。紫杉醇对微管的稳定作用足以维持C3负载有丝分裂细胞中的中间区结构。这些结果与之前对另一种微管相关Rho鸟苷酸交换因子的分析相结合(C.J. Bakal、D. Finan、J. LaRose、C.D. Wells、G. Gish、S. Kulkarni、P. DeSepulveda、A. Wilde、R. Rottapel,《Rho GTP交换因子Lfc促进有丝分裂早期纺锤体组装》,《美国国家科学院院刊》102 (2005) 9529 - 9534)表明,哺乳动物细胞有两个潜在步骤,在有丝分裂和胞质分裂期间需要活性Rho来稳定中间区微管。