Suzuki Hideaki, Akiyama Nobutake, Tsuji Megumi, Ohashi Toya, Saito Saburo, Eto Yoshikatsu
Department of Gene Therapy, Institute of DNA Medicine, Department of Pediatrics, Institute of DNA Medicine, The Jikei University School of Medicine, Nishi-shinbashi, Minato-ku, Tokyo, Japan.
Cell Cycle. 2006 May;5(10):1094-101. doi: 10.4161/cc.5.10.2747. Epub 2006 May 15.
The conserved protein Shugoshin (Sgo) plays a role in the maintenance of centromeric cohesion in mitosis and meiosis. Human Shugoshin (hSgo) was first identified as an overexpressed protein in breast cancers. Here we demonstrate that hSgo mediates kinetochore-driven formation of kinetochore -microtubules (MTs) during bipolar spindle assembly. The regulated overexpression of full-length hSgo, or of truncated proteins containing both the conserved N-terminal coiled-coil domain and C-terminal basic domain, resulted in hSgo localization at centromere at early mitosis and was associated with aberrant nucleation and formation of bundles of kinetochore-MTs. The mid-portion of hSgo, between the N- and C-terminal domains, includes both a functional domain for centromeric cohesion and a regulatory domain for spindle assembly. The cells overexpressing natural alternative splicing isoforms, which are almost completely defective for the mid-portion of the hSgo protein, showed premature centromere separation (PCS) and aberrant MT connections. These isoforms are mildly overexpressed in HEK293 cells. On the other hand, cells expressing a truncated protein, defective in the lysine-rich region of the mid-portion, arrested at mitosis due to persistent abnormal MT connections and not because of PCS. Aberrant MT connections were predominantly observed in spindle regions where chromosomes were clustered. Interestingly, we also found that hSgo is rapidly exchanged at kinetochores at early mitosis. Based on these results, we conclude that hSgo may be diffusible and have a role in proper kinetochores MTs attachment.
保守蛋白守护蛋白（Sgo）在有丝分裂和减数分裂中着丝粒黏连的维持过程中发挥作用。人类守护蛋白（hSgo）最初被鉴定为乳腺癌中一种过表达的蛋白。在此我们证明，hSgo在双极纺锤体组装过程中介导着丝粒驱动的动粒微管（MTs）形成。全长hSgo或包含保守的N端卷曲螺旋结构域和C端碱性结构域的截短蛋白的调控性过表达，导致hSgo在有丝分裂早期定位于着丝粒，并与动粒MTs的异常成核和成束形成相关。hSgo在N端和C端结构域之间的中部，既包含着丝粒黏连的功能结构域，也包含纺锤体组装的调控结构域。过表达天然可变剪接异构体的细胞，其hSgo蛋白中部几乎完全缺失功能，表现出着丝粒过早分离（PCS）和异常的MT连接。这些异构体在HEK293细胞中轻度过表达。另一方面，表达一种在中部富含赖氨酸区域有缺陷的截短蛋白的细胞，由于持续的异常MT连接而非PCS，在有丝分裂时停滞。异常的MT连接主要在染色体聚集的纺锤体区域观察到。有趣的是，我们还发现hSgo在有丝分裂早期在动粒处快速交换。基于这些结果，我们得出结论，hSgo可能是可扩散的，并在动粒MTs的正确附着中发挥作用。
