Li Quan, Sato Eisuke F, Kira Yukimi, Nishikawa Manabu, Utsumi Kozo, Inoue Masayasu
Department of Biochemistry and Molecular Pathology, Osaka City University Medical School, 1-4-3 Asahimachi, Abeno, Osaka 545-8585, Japan.
Free Radic Biol Med. 2006 Jan 1;40(1):173-81. doi: 10.1016/j.freeradbiomed.2005.09.037. Epub 2005 Oct 21.
A small amount of reactive oxygen species (ROS) is generated through aerobic respiration even under physiological conditions. Because ROS are known to have various deteriorating actions, the way cells could evade the effects of ROS in and around mitochondria would determine the fate of cells. We previously reported that Cu,Zn-superoxide dismutase (SOD1), a cytosolic enzyme, is also localized in mitochondria in various types of cells. Therefore, we undertook this study to elucidate the physiological significance of SOD1 localization in and around mitochondria. We analyzed the effects of various reagents that could modulate mitochondrial respiration, ROS metabolism, and subcellular localization of SOD1 and cytochrome c. Using rat liver mitochondria, we have shown that Ca2+, Fe2+, or long-chain fatty acids increased the mitochondrial generation of ROS and that the resulting ROS oxidized the critical thiol groups in adenine nucleotide translocase (ANT). The oxidation of ANT induced mitochondrial swelling followed by the release of SOD1 and cytochrome c. Although inhibitors of electron transport, such as rotenone, antimycin A, and KCN, also increased ROS generation, they failed to (i) oxidize the critical thiol groups in ANT, (ii) induce swelling, and (iii) release SOD1 and cytochrome c. These results suggest that the oxidation of ANT thiols and the opening of the membrane permeability transition pores induce the release of both SOD1 and cytochrome c. We demonstrated that the loss of SOD1 increases the susceptibility of mitochondria to oxidative stresses and that the simultaneous release of SOD1 enhances the vicious cycle of apoptotic reactions triggered by the released cytochrome c. Therefore, SOD1 must have important roles in protecting mitochondria from ROS-induced injury. Our data also suggest that SOD1 release parallels cytochrome c release under all conditions. We propose that intramembranously localized SOD1 is a third reagent (along with AIF) that will regulate apoptosis.
即使在生理条件下，通过有氧呼吸也会产生少量活性氧（ROS）。由于已知ROS具有多种破坏作用，细胞逃避线粒体内部及周围ROS影响的方式将决定细胞的命运。我们之前报道过，作为一种胞质酶的铜锌超氧化物歧化酶（SOD1）也定位于多种类型细胞的线粒体中。因此，我们开展了这项研究以阐明SOD1定位于线粒体内部及周围的生理意义。我们分析了各种能够调节线粒体呼吸、ROS代谢以及SOD1和细胞色素c亚细胞定位的试剂的作用。利用大鼠肝脏线粒体，我们发现Ca2+、Fe2+或长链脂肪酸会增加线粒体ROS的生成，并且由此产生的ROS会氧化腺嘌呤核苷酸转位酶（ANT）中的关键巯基。ANT的氧化会导致线粒体肿胀，随后SOD1和细胞色素c释放。尽管电子传递抑制剂，如鱼藤酮、抗霉素A和KCN，也会增加ROS的生成，但它们未能（i）氧化ANT中的关键巯基，（ii）诱导肿胀，以及（iii）释放SOD1和细胞色素c。这些结果表明，ANT巯基的氧化和膜通透性转换孔的开放会诱导SOD1和细胞色素c的释放。我们证明SOD1的缺失会增加线粒体对氧化应激的敏感性，并且SOD1的同时释放会增强由释放的细胞色素c引发的凋亡反应的恶性循环。因此，SOD1在保护线粒体免受ROS诱导的损伤方面必定具有重要作用。我们的数据还表明，在所有条件下SOD1的释放都与细胞色素c的释放平行。我们提出膜内定位的SOD1是第三种（与凋亡诱导因子一起）调节细胞凋亡的试剂。
