Institute of Biochemistry and Molecular Biology, Ulm University, Ulm, Germany.
Institute of Biochemistry and Molecular Biology, Ulm University, Ulm, Germany.
Biochim Biophys Acta Mol Cell Res. 2019 May;1866(5):882-895. doi: 10.1016/j.bbamcr.2019.01.010. Epub 2019 Feb 1.
The nucleolus is a subnuclear compartment, which governs ribosome biogenesis. Moreover, it functions as hub in the stress response by orchestrating a variety of processes, such as regulation of cell cycle progression, senescence and apoptosis. Emerging evidence links the nucleolus also to the control of genomic stability and the development of human malignancies. Peter Pan (PPAN) is an essential ribosome biogenesis factor localized to nucleoli and mitochondria. We earlier showed that PPAN depletion triggers p53-independent nucleolar stress and apoptosis. In this study we investigated the precise localization of nucleolar PPAN during cell cycle and its function in cell cycle regulation. We show that PPAN knockdown impairs cell proliferation and induces G0/G1 as well as later G2/M cell cycle arrest in cancer cells. Although PPAN knockdown stabilizes the tumor suppressor p53 and induces CDKN1A/p21, the proliferation defects occur largely in a p53/p21-independent manner. We noticed a reduced number of knockdown cells entering cytokinesis and an elevation of binucleation. PPAN knockdown is also associated with increased H2A.X phosphorylation (γH2A.X) in cancer cells. We evaluated a potential signaling axis through the DNA damage response kinases ATM and ATR and alternatively apoptosis as a potent driver of γH2A.X. Interestingly, PPAN knockdown does not involve activation of ATM/ATR. Instead, γH2A.X is generated as a consequence of apoptosis induction in cancer cells. Strikingly, PPAN depletion in human fibroblasts did neither provoke apoptosis nor H2A.X phosphorylation, but recapitulated p53 stabilization. In summary, our data underline the notion that the PPAN-mediated, p53-independent nucleolar stress response has multiple facets.
核仁是一个亚核区，它负责核糖体的生物发生。此外，它还作为应激反应的中心，通过协调多种过程发挥作用，如细胞周期进程的调节、衰老和凋亡。新出现的证据将核仁与基因组稳定性的控制和人类恶性肿瘤的发展联系起来。彼得潘（PPAN）是一种必需的核糖体生物发生因子，定位于核仁区和线粒体。我们之前的研究表明，PPAN 的耗竭会引发 p53 非依赖性核仁应激和细胞凋亡。在本研究中，我们研究了细胞周期中核仁区 PPAN 的精确定位及其在细胞周期调控中的功能。我们发现，PPAN 敲低会损害细胞增殖，并诱导癌细胞发生 G0/G1 期以及后期 G2/M 期细胞周期阻滞。尽管 PPAN 敲低会稳定肿瘤抑制因子 p53 并诱导 CDKN1A/p21，但增殖缺陷主要以 p53/p21 非依赖性方式发生。我们注意到，敲低细胞进入胞质分裂的数量减少，双核化增加。PPAN 敲低还与癌细胞中 H2A.X 磷酸化（γH2A.X）的增加有关。我们评估了一个潜在的信号轴，该信号轴通过 DNA 损伤反应激酶 ATM 和 ATR，以及替代的细胞凋亡，作为 γH2A.X 的一个有效驱动因素。有趣的是，PPAN 敲低不涉及 ATM/ATR 的激活。相反，γH2A.X 的产生是癌细胞中细胞凋亡诱导的结果。引人注目的是，人成纤维细胞中 PPAN 的耗竭既不会引发细胞凋亡，也不会引发 H2A.X 磷酸化，但会重新激活 p53。总之，我们的数据强调了这样一种观点，即 PPAN 介导的、p53 非依赖性核仁应激反应具有多个方面。
