Lukovic Dunja, Komoriya Akira, Packard Beverly Z, Ucker David S
Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago, IL 60612, USA.
Exp Cell Res. 2003 Oct 1;289(2):384-95. doi: 10.1016/s0014-4827(03)00289-1.
Molecular studies of the physiological cell death process have focused attention on the role of effector caspases as critical common elements of the lethal mechanism. Diverse death signals act afferently via distinct signaling pathways to activate these resident proenzyme molecules post-translationally. Whether this molecular convergence represents the mechanistic point of irreversible commitment to cell death has not been established. That a number of caspase substrates are proteins that serve important roles in cellular homeostasis has led to the view that the acquisition of this activity must be the determinative step in cell death. Observations that caspases serve in a regulatory role to catalyze the appearance of new activities involved in orderly cellular dissolution challenge this model of death as a simple process of proteolytic destruction. We found previously that caspase-dependent nuclear cyclin dependent kinase 2 (Cdk2) activity appears to be necessary for cell death. Employing direct cytofluorimetric analyses of intracellular caspase activity and colony forming assays, we now show that transient blockade of caspase-dependent Cdk2 activity confers long-lived sparing from death on cells otherwise triggered to die and fully replete with caspase activity. These data demonstrate that caspases, while necessary for apoptosis, are not sufficient to exert lethality. Caspase activation per se does not represent an irreversible point of commitment to physiological cell death.
对生理性细胞死亡过程的分子研究已将注意力集中在效应半胱天冬酶作为致死机制关键共同要素的作用上。多种死亡信号通过不同的信号通路传入，以在翻译后激活这些驻留的酶原分子。这种分子汇聚是否代表对细胞死亡不可逆转的决定性机制尚未确定。许多半胱天冬酶底物是在细胞内稳态中起重要作用的蛋白质，这导致人们认为获得这种活性必定是细胞死亡的决定性步骤。有观察表明，半胱天冬酶起到调节作用，催化参与有序细胞溶解的新活性的出现，这对将死亡视为蛋白水解破坏的简单过程的模型提出了挑战。我们之前发现，半胱天冬酶依赖性核细胞周期蛋白依赖性激酶2（Cdk2）活性似乎是细胞死亡所必需的。利用对细胞内半胱天冬酶活性的直接细胞荧光分析和集落形成试验，我们现在表明，对半胱天冬酶依赖性Cdk2活性的短暂阻断可使原本被触发死亡且半胱天冬酶活性完全充足的细胞长期免于死亡。这些数据表明，半胱天冬酶虽然是细胞凋亡所必需的，但不足以发挥致死作用。半胱天冬酶激活本身并不代表对生理性细胞死亡不可逆转的决定性点。
