Functional relationship among PLK2, PLK4 and ROCK2 to induce centrosome amplification

The presence of more than 2 centrosomes (centrosome amplification) leads to defective mitosis and chromosome segregation errors, is frequently found in a variety of cancer types, and believed to be the major cause of chromosome instability. One mechanism for generation of amplified centrosomes is over-duplication of centrosomes in a single cell cycle, which is expected to occur when cells are temporarily arrested. There are a growing number of kinases that are critical for induction and promotion of centrosome amplification in the cell cycle-arrested cells, including Rho-associated kinase (ROCK2), Polo-like kinase 2 (PLK2) and PLK4. Here, we tested whether these kinases induce centrosome amplification in a linear pathway or parallel pathways. We first confirmed that ROCK2, PLK2 and PLK4 are all essential for centrosomes to re-duplicate in the cells arrested by exposure to DNA synthesis inhibitor. Using the centrosome amplification rescue assay, we found that PLK2 indirectly activates ROCK2 via phosphorylating nucleophosmin (NPM), and PLK4 functions downstream of ROCK2 to drive centrosome amplification in the arrested cells.

当细胞内中心体（centrosome）数量超过2个时，即发生中心体扩增（centrosome amplification），该现象会引发有丝分裂异常与染色体分离错误，常见于多种癌症类型中，且被认为是染色体不稳定（chromosome instability）的主要诱因。中心体扩增的产生机制之一，是单个细胞周期内中心体发生过度复制，而该情况通常出现在细胞被暂时性阻滞的状态下。目前已有越来越多的激酶被证实，在细胞周期阻滞的细胞中可诱导并促进中心体扩增，其中包括Rho相关激酶（Rho-associated kinase, ROCK2）、Polo样激酶2（Polo-like kinase 2, PLK2）以及PLK4。本研究旨在探究上述激酶诱导中心体扩增的通路模式，即其作用是通过线性通路还是平行通路实现。本研究首先证实，在经DNA合成抑制剂处理后发生阻滞的细胞中，ROCK2、PLK2与PLK4均为中心体再次复制所必需的调控因子。通过中心体扩增挽救实验，我们发现PLK2可通过磷酸化核仁磷酸蛋白（nucleophosmin, NPM）间接激活ROCK2，而PLK4则作用于ROCK2的下游，以驱动阻滞状态下细胞的中心体扩增。