Department for Molecular Biomedical Research, VIB, Ghent, Belgium.
PLoS One. 2010 Feb 15;5(2):e9203. doi: 10.1371/journal.pone.0009203.
Kaiso is a BTB/POZ zinc finger protein known as a transcriptional repressor. It was originally identified through its in vitro association with the Armadillo protein p120ctn. Subcellular localization of Kaiso in cell lines and in normal and cancerous human tissues revealed that its expression is not restricted to the nucleus. In the present study we monitored Kaiso's subcellular localization during the cell cycle and found the following: (1) during interphase, Kaiso is located not only in the nucleus, but also on microtubular structures, including the centrosome; (2) at metaphase, it is present at the centrosomes and on the spindle microtubules; (3) during telophase, it accumulates at the midbody. We found that Kaiso is a genuine PCM component that belongs to a pericentrin molecular complex. We analyzed the functions of different domains of Kaiso by visualizing the subcellular distribution of GFP-tagged Kaiso fragments throughout the cell cycle. Our results indicate that two domains are responsible for targeting Kaiso to the centrosomes and microtubules. The first domain, designated SA1 for spindle-associated domain 1, is located in the center of the Kaiso protein and localizes at the spindle microtubules and centrosomes; the second domain, SA2, is an evolutionarily conserved domain situated just before the zinc finger domain and might be responsible for localizing Kaiso towards the centrosomal region. Constructs containing both SA domains and Kaiso's aminoterminal BTB/POZ domain triggered the formation of abnormal centrosomes. We also observed that overexpression of longer or full-length Kaiso constructs led to mitotic cell arrest and frequent cell death. Knockdown of Kaiso accelerated cell proliferation. Our data reveal a new target for Kaiso at the centrosomes and spindle microtubules during mitosis. They also strongly imply that Kaiso's function as a transcriptional regulator might be linked to the control of the cell cycle and to cell proliferation in cancer.
Kaiso 是一种 BTB/POZ 锌指蛋白，作为转录抑制剂而被人们所熟知。它最初是通过与 Armadillo 蛋白 p120ctn 的体外结合而被鉴定出来的。在细胞系以及正常和癌变的人类组织中 Kaiso 的亚细胞定位表明，它的表达并不局限于细胞核。在本研究中，我们在细胞周期过程中监测 Kaiso 的亚细胞定位，结果发现：（1）在间期中，Kaiso 不仅位于细胞核中，还位于微管结构上，包括中心体；（2）在中期，它存在于中心体和纺锤体微管上；（3）在末期，它在中间体上聚集。我们发现 Kaiso 是 PCM 的真正组成部分，属于中心粒蛋白复合物。我们通过在整个细胞周期中可视化 GFP 标记的 Kaiso 片段的亚细胞分布，分析 Kaiso 的不同结构域的功能。我们的结果表明，有两个结构域负责将 Kaiso 靶向到中心体和微管上。第一个结构域，命名为纺锤体相关结构域 1（SA1），位于 Kaiso 蛋白的中心，定位于纺锤体微管和中心体上；第二个结构域，SA2，是一个进化上保守的结构域，位于锌指结构域之前，可能负责将 Kaiso 定位到中心体区域。包含 SA 结构域和 Kaiso 的氨基末端 BTB/POZ 结构域的构建体触发了异常中心体的形成。我们还观察到，过表达较长或全长 Kaiso 构建体导致有丝分裂细胞停滞和频繁的细胞死亡。Kaiso 的敲低加速了细胞增殖。我们的数据揭示了 Kaiso 在有丝分裂过程中在中心体和纺锤体微管上的新靶点。它们还强烈暗示，Kaiso 作为转录调节剂的功能可能与细胞周期的控制和癌症中的细胞增殖有关。
