FLJ25439, a novel cytokinesis-associated protein, induces tetraploidization and maintains chromosomal stability via enhancing expression of endoplasmic reticulum stress chaperones

Investigation of the mechanisms leading to aneuploidy and polyploidy is critical to cancer research. Previous studies have provided strong evidence of the importance of tetraploidization as an early step in tumorigenesis. In cancer cells, tetraploid cells may contribute to abnormal mitotic progression, which may be associated with cytokinesis failure. Tetraploidy leads to genomic instability due to centrosome and chromosome over-replication. Until now, the mechanism by which cells maintain tetraploid status has been unknown. Here, we identified a novel D box-containing protein, FLJ25439, which displays a dynamic expression profile during mitosis/cytokinesis with the midbody as the most prominent associated structure. To understand the function of FLJ25439, we established stable cell lines overexpressing FLJ25439. FLJ25439-overexpression cells grew slower and displayed a tetraploid DNA content in comparison with diploid parental cells. They also showed aberrant mitosis and dysregulated expression of p53, pRb and p21, suggesting a defect in cell cycle progression. To explore the molecular mechanisms responsible for FLJ25439-induced tetraploidization, we conducted a comparative analysis of the global protein expression patterns of wild type and overexpressors using proteomics and bioinformatics approaches. Protein category profiling indicated that FLJ25439 is involved in pathways related to anti-apoptosis, protein folding, the cell cycle, and cytoskeleton regulation. Specifically, genotoxic-stress- and ER stress-related chaperone proteins greatly contributed to the FLJ25439 overexpression phenotypes. The results of this study pave the way to our further understanding of the role of this novel cytokinesis-related protein in protecting cells from environmental stress and tetraploid formation.

探寻非整倍体（aneuploidy）与多倍体（polyploidy）的形成机制，对癌症研究至关重要。既往研究已提供充分证据，证实四倍体化（tetraploidization）是肿瘤发生的早期关键环节。在癌细胞中，四倍体细胞可引发异常有丝分裂进程，该现象往往与胞质分裂（cytokinesis）失败相关。由于中心体与染色体过度复制，四倍体状态会诱发基因组不稳定性。迄今为止，细胞维持四倍体状态的具体机制仍未明确。本研究中，我们鉴定出一种新型含D框结构域的蛋白FLJ25439，该蛋白在有丝分裂/胞质分裂过程中呈现动态表达模式，其中与中间体（midbody）的关联最为显著。为解析FLJ25439的功能，我们构建了稳定过表达FLJ25439的细胞系。与二倍体亲本细胞相比，过表达FLJ25439的细胞生长速率更慢，且DNA含量呈现四倍体特征；同时这些细胞还表现出有丝分裂异常，以及p53、pRb与p21的表达失调，提示细胞周期进程存在缺陷。为探究FLJ25439诱导四倍体化的分子机制，我们采用蛋白质组学与生物信息学方法，对野生型细胞与过表达细胞的全蛋白表达谱开展了比较分析。蛋白类别分析结果显示，FLJ25439参与了抗凋亡、蛋白质折叠、细胞周期以及细胞骨架调控等相关通路。具体而言，与基因毒性应激及内质网（ER）应激相关的分子伴侣蛋白，在FLJ25439过表达的表型中发挥了关键调控作用。本研究结果为进一步阐明该新型胞质分裂相关蛋白在抵御环境应激及抑制四倍体形成中的功能奠定了重要研究基础。