Chao Tung Hui, Chang Meng-Ya, Su Shu-Jem, Su Shu-Hui
Institute of Medical Sciences, College of Medicine, Tzu-Chi University, Hualien 97004, Taiwan.
Institute of Medical Sciences, College of Medicine, Tzu-Chi University, Hualien 97004, Taiwan; Department of Medical Research, Buddhist Tzu-Chi General Hospital, Hualien, Taiwan.
Free Radic Biol Med. 2014 Sep;74:175-87. doi: 10.1016/j.freeradbiomed.2014.05.023. Epub 2014 Jun 6.
Proteasomes are highly expressed in rapidly growing neoplastic cells and essential for controlling the cell cycle process and mitochondrial homeostasis. Pharmacological inhibition of the proteasome shows a significant anticancer effect on hematopoietic malignancies that is usually associated with the generation of reactive oxygen species. In this study, we comprehensively investigated the role of endogenous oxidants in various cellular events of K562 leukemic cells in response to treatment with MG132, a proteasome inhibitor. MG132 at 1.4 µM potently triggered G2/M arrest, mitochondrial depolarization, and apoptosis. By such treatment, the protein level of inducible nitric oxide synthase (iNOS) was doubled and cellular oxidants, including nitric oxide, superoxide, and their derivatives, were increasingly produced. In MG132-treated cells, the increase in iNOS-derived oxidants was responsible for mitochondrial depolarization and caspase-dependent apoptosis, but was insignificant in G2/M arrest. The amount of iNOS was negatively correlated with that of manganese superoxide dismutase (MnSOD). Whereas iNOS activity was inhibited by aminoguanidine, cellular MnSOD levels as well as mitochondrial membrane potentials were upregulated, and consequentially G2/M arrest and apoptosis were thoroughly reversed. It is suggested that cells rich in functional mitochondria possess improved proteasome activity, which antagonizes the cytotoxic and cytostatic effects of MG132. In contrast to iNOS, endothelial NOS-driven cGMP-dependent signaling promoted mitochondrial function and survival of MG132-stressed cells. In conclusion, the functional interplay of proteasomes and mitochondria is crucial for leukemic cell growth, wherein iNOS plays a key role.
蛋白酶体在快速生长的肿瘤细胞中高度表达，对控制细胞周期进程和线粒体稳态至关重要。蛋白酶体的药理学抑制对造血系统恶性肿瘤显示出显著的抗癌作用，这通常与活性氧的产生有关。在本研究中，我们全面研究了内源性氧化剂在K562白血病细胞响应蛋白酶体抑制剂MG132处理的各种细胞事件中的作用。1.4 μM的MG132有效地引发了G2/M期阻滞、线粒体去极化和细胞凋亡。通过这种处理，诱导型一氧化氮合酶（iNOS）的蛋白水平翻倍，包括一氧化氮、超氧化物及其衍生物在内的细胞氧化剂产生增加。在MG132处理的细胞中，iNOS衍生的氧化剂增加导致线粒体去极化和半胱天冬酶依赖性细胞凋亡，但在G2/M期阻滞中不明显。iNOS的量与锰超氧化物歧化酶（MnSOD）的量呈负相关。虽然氨基胍抑制了iNOS的活性，但细胞MnSOD水平以及线粒体膜电位上调，结果G2/M期阻滞和细胞凋亡被完全逆转。提示富含功能性线粒体的细胞具有更高的蛋白酶体活性，这拮抗了MG132的细胞毒性和细胞生长抑制作用。与iNOS相反，内皮型NOS驱动的cGMP依赖性信号促进了MG132应激细胞的线粒体功能和存活。总之，蛋白酶体和线粒体的功能相互作用对白血病细胞生长至关重要，其中iNOS起关键作用。
