Huang Guanqun, Meng Lingjun, Tsai Robert Y L
Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX 77030, USA; Department of general surgery, The Fifth Affiliated Hospital of Guangzhou Medical University, Guangzhou 510700, China.
Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX 77030, USA.
Cell Death Discov. 2015;1:15060-. doi: 10.1038/cddiscovery.2015.60. Epub 2015 Nov 23.
Nucleostemin (NS) protects the genome from replication-induced DNA damage and plays an indispensable role in maintaining the continuous proliferation of both p53-wildtype and mutant cells. Yet, some outcomes of NS-deficient cells appear to be shaped by their p53 status, which stimulates conflicting claims on the role of p53 in executing the NS function. This disparity was conveniently attributed to the usual suspect of cell-type variations. To provide a definitive resolution, we investigated the interplay between NS and p53 in two pairs of isogenic cells, . genetically modified mouse embryonic fibroblast (MEF) cells and HCT116 human colon cancer cells. In MEF cells, p53 deletion further compromises rather than rescues the proliferative potential of NS-depleted cells without changing their G2/M arrest fate before prophase entry. The detrimental effect of p53 loss in NS-depleted MEF cells correlates with a dramatic increase of polyploid giant cells (PGCs) (up to 24%), which indicates aberrant mitosis. To determine how p53 shapes the response of cells to NS depletion at the molecular level, we showed that p53 turns on the expression of reprimo and MDM2 in NS-deficient MEF cells. In the absence of p53, NS-deficient MEF cells exhibit increased levels of phosphorylated cdc2 (Y15) protein and cyclin B1. In cancer (HCT116) cells, NS loss leads to G2/M arrest under both p53wt and p53ko conditions and increases phosphorylated cdc2 more in p53ko than in p53wt cells, as it does in MEF cells. Unlike its effect in MEF cells, NS depletion decreases tumor growth and increases the expression of reprimo and cyclin B1 in a p53-independent manner in HCT116 cells. Our data indicate that the p53 status of NS-deficient cells orchestrates how they respond to G2/M arrest in a normal vs. cancer cell distinct fashion.
核干细胞因子（NS）可保护基因组免受复制诱导的DNA损伤，并在维持p53野生型和突变型细胞的持续增殖中发挥不可或缺的作用。然而，NS缺陷细胞的一些结果似乎受其p53状态的影响，这引发了关于p53在执行NS功能中作用的相互矛盾的观点。这种差异通常归因于常见的细胞类型变异。为了提供明确的解决方案，我们在两对同基因细胞中研究了NS和p53之间的相互作用，即基因改造的小鼠胚胎成纤维细胞（MEF）和HCT116人结肠癌细胞。在MEF细胞中，p53缺失进一步损害而非挽救NS缺失细胞的增殖潜力，且在前期进入之前不改变其G2/M期阻滞命运。p53缺失对NS缺失的MEF细胞的有害影响与多倍体巨细胞（PGC）的显著增加（高达24%）相关，这表明有丝分裂异常。为了确定p53如何在分子水平上塑造细胞对NS缺失的反应，我们发现p53开启了NS缺陷MEF细胞中repromo和MDM2的表达。在没有p53的情况下，NS缺陷的MEF细胞中磷酸化cdc2（Y15）蛋白和细胞周期蛋白B1的水平升高。在癌症（HCT116）细胞中，NS缺失在p53wt和p53ko条件下均导致G2/M期阻滞，并且在p53ko细胞中比在p53wt细胞中更多地增加磷酸化cdc2，就像在MEF细胞中一样。与在MEF细胞中的作用不同，NS缺失以p53独立的方式降低HCT116细胞中的肿瘤生长并增加repromo和细胞周期蛋白B1的表达。我们的数据表明，NS缺陷细胞的p53状态以正常细胞与癌细胞不同的方式协调它们对G2/M期阻滞的反应。
