Vakifahmetoglu H, Olsson M, Orrenius S, Zhivotovsky B
Division of Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
Oncogene. 2006 Sep 14;25(41):5683-92. doi: 10.1038/sj.onc.1209569. Epub 2006 May 1.
Recent findings have established caspase-2 as an important apical regulator in apoptotic pathways leading from DNA damage to release of mitochondrial cytochrome c and subsequent activation of effector caspases. Yet, the molecular map connecting the embarking stimuli of genotoxic stress with caspase-2 activation remains to be elucidated. Here, we address the question of potential caspase-2 regulators by examining 5-fluorouracil (5-FU)-induced apoptosis in wild-type and p53-deficient human colon carcinoma cells. Apoptosis was observed only in p53(+/+) cells and was preceded by caspase-2 activation. Hence, although no direct interaction between p53 and caspase-2 was observed in the cell system used, our data clearly demonstrate that a functional connection between these two proteins is essential for initiation of the 5-FU-induced apoptotic process. Proposed mediators of caspase-2 activation include PIDDosome complex proteins PIDD and RAIDD. Surprisingly, the presence of a complex encompassing at least RAIDD, PIDD and caspase-2 was verified in both p53(+/+) and p53(-/-) cells, also in the absence of 5-FU treatment. Thus, our results confirm the participation of PIDD and RAIDD in PIDDosome complex formation but question their role as sole mediators of caspase-2 activation. This assumption was further supported by siRNA transfections targeting PIDD or RAIDD. In conclusion, our findings support the hypothesis of p53 as an upstream regulator of caspase activity and provide data concerning caspase-2 processing mechanisms. As suppression of caspase-2 expression in 5-FU-treated cells also affects the level of the p53 protein, possibilities of a reciprocal interaction between these proteins are discussed.
最近的研究结果已证实，半胱天冬酶 - 2是凋亡途径中的一个重要顶端调节因子，该凋亡途径从DNA损伤开始，导致线粒体细胞色素c释放，随后激活效应半胱天冬酶。然而，将基因毒性应激的起始刺激与半胱天冬酶 - 2激活联系起来的分子图谱仍有待阐明。在此，我们通过检测5-氟尿嘧啶（5-FU）诱导的野生型和p53缺陷型人结肠癌细胞凋亡，来探讨潜在的半胱天冬酶 - 2调节因子问题。仅在p53(+/+)细胞中观察到凋亡，且凋亡之前有半胱天冬酶 - 2的激活。因此，尽管在所使用的细胞系统中未观察到p53与半胱天冬酶 - 2之间的直接相互作用，但我们的数据清楚地表明，这两种蛋白质之间的功能联系对于启动5-FU诱导的凋亡过程至关重要。推测的半胱天冬酶 - 2激活介质包括PIDDosome复合物蛋白PIDD和RAIDD。令人惊讶的是，在p53(+/+)和p53(-/-)细胞中，即使在没有5-FU处理的情况下，也证实存在至少包含RAIDD、PIDD和半胱天冬酶 - 2的复合物。因此，我们的结果证实了PIDD和RAIDD参与PIDDosome复合物的形成，但对它们作为半胱天冬酶 - 2激活的唯一介质的作用提出了质疑。靶向PIDD或RAIDD的siRNA转染进一步支持了这一假设。总之，我们的研究结果支持p53作为半胱天冬酶活性上游调节因子的假说，并提供了有关半胱天冬酶 - 2加工机制的数据。由于在5-FU处理的细胞中抑制半胱天冬酶 - 2的表达也会影响p53蛋白的水平，因此讨论了这些蛋白质之间相互作用的可能性。
