Liu G-Y, Hung Y-C, Hsu P-C, Liao Y-F, Chang W-H, Tsay G J, Hung H-C
Institute of Immunology, Chung Shan Medical University Hospital, Taichung, Taiwan, Republic of China.
Apoptosis. 2005 May;10(3):569-81. doi: 10.1007/s10495-005-1891-2.
Ornithine decarboxylase (ODC) plays an essential role in various biological functions, including cell proliferation, differentiation and cell death. However, how it prevents the cell apoptotic mechanism is still unclear. Previous studies have demonstrated that decreasing the activity of ODC by difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, causes the accumulation of intracellular reactive oxygen species (ROS) and cell arrest, thus inducing cell death. These findings might indicate how ODC exerts anti-oxidative and anti-apoptotic effects. In our study, tumor necrosis factor alpha (TNF-alpha) induced apoptosis in HL-60 and Jurkat T cells. The kinetic studies revealed that the TNF-alpha -induced apoptotic process included intracellular ROS generation (as early as 1 h after treatment), the activation of caspase 8 (3 h), the cleavage of Bid (3 h) and the disruption of mitochondrial membrane potential (Delta psi(m)) (6 h). Furthermore, ROS scavengers, such as glutathione (GSH) and catalase, maintained Delta psi(m) and prevented apoptosis upon treatment. Putrescine and overexpression of ODC had similar effects as ROS scavengers in decreasing intracellular ROS and preventing the disruption of Delta psi(m) and apoptosis. Inhibition of ODC by DFMO in HL-60 cells only could increase ROS generation, but did not disrupt Delta psi(m) or induce apoptosis. However, DFMO enhanced the accumulation of ROS, disruption of Delta psi(m) and apoptosis when cells were treated with TNF-alpha . ODC overexpression avoided the decline of Bcl-2, prevented cytochrome c release from mitochondria and inhibited the activation of caspase 8, 9 and 3. Overexpression of Bcl-2 maintained Delta psi(m) and prevented apoptosis, but could not reduce ROS until four hours after TNF-alpha treatment. According to these data, we suggest that TNF-alpha induces apoptosis mainly by a ROS-dependent, mitochondria-mediated pathway. Furthermore, ODC prevents TNF-alpha -induced apoptosis by decreasing intracellular ROS to avoid Bcl-2 decline, maintain Delta psi(m), prevent cytochrome c release and deactivate the caspase cascade pathway.
鸟氨酸脱羧酶（ODC）在多种生物学功能中发挥着重要作用，包括细胞增殖、分化和细胞死亡。然而，它如何阻止细胞凋亡机制仍不清楚。先前的研究表明，通过使用ODC的不可逆抑制剂二氟甲基鸟氨酸（DFMO）降低ODC的活性，会导致细胞内活性氧（ROS）积累和细胞停滞，从而诱导细胞死亡。这些发现可能表明ODC如何发挥抗氧化和抗凋亡作用。在我们的研究中，肿瘤坏死因子α（TNF-α）诱导HL-60和Jurkat T细胞凋亡。动力学研究表明，TNF-α诱导的凋亡过程包括细胞内ROS生成（早在处理后1小时）、半胱天冬酶8激活（3小时）、Bid裂解（3小时）和线粒体膜电位（Δψm）破坏（6小时）。此外，ROS清除剂，如谷胱甘肽（GSH）和过氧化氢酶，在处理后维持Δψm并防止凋亡。腐胺和ODC的过表达在降低细胞内ROS、防止Δψm破坏和凋亡方面与ROS清除剂有相似的作用。仅在HL-60细胞中用DFMO抑制ODC可增加ROS生成，但不会破坏Δψm或诱导凋亡。然而，当细胞用TNF-α处理时，DFMO会增强ROS积累、Δψm破坏和凋亡。ODC过表达避免了Bcl-2的下降，防止细胞色素c从线粒体释放，并抑制半胱天冬酶8、9和3的激活。Bcl-2过表达维持Δψm并防止凋亡，但直到TNF-α处理后4小时才能降低ROS。根据这些数据，我们认为TNF-α主要通过ROS依赖性、线粒体介导的途径诱导凋亡。此外，ODC通过降低细胞内ROS来防止TNF-α诱导的凋亡，以避免Bcl-2下降，维持Δψm，防止细胞色素c释放并使半胱天冬酶级联途径失活。
