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.

探究非整倍体（aneuploidy）与多倍体（polyploidy）的形成机制，是癌症研究领域的关键课题。既往研究已充分证实，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，该现象常与胞质分裂（cytokinesis）失败相关。由于中心体与染色体过度复制，四倍体状态会导致基因组不稳定性。截至目前，细胞维持四倍体状态的具体机制仍未明确。本研究鉴定出一种新型含D盒（D box）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谱，其中与中体（midbody）的结合最为显著。为解析FLJ25439的生物学功能，本研究构建了稳定过表达FLJ25439的细胞系。与二倍体亲本细胞相比，过表达FLJ25439的细胞生长速度更慢，且DNA含量呈现四倍体特征；同时，这些细胞表现出异常有丝分裂，且p53、pRb及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，本研究采用蛋白质组学（proteomics）与生物信息学（bioinformatics）方法，对野生型细胞与过表达细胞的全蛋白质组表达谱进行了比较分析。蛋白类别谱分析结果显示，FLJ25439参与抗凋亡、蛋白质折叠、细胞周期及细胞骨架调控等相关通路。具体而言，基因毒性应激与内质网（ER）应激相关的分子伴侣蛋白，在FLJ25439过表达的细胞表型中发挥了关键作用。本研究结果为进一步阐明这一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作用奠定了重要基础。