Brustovetsky Tatiana, Antonsson Bruno, Jemmerson Ronald, Dubinsky Janet M, Brustovetsky Nickolay
Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
J Neurochem. 2005 Aug;94(4):980-94. doi: 10.1111/j.1471-4159.2005.03248.x.
Cleaved or truncated BID (tBID) is known to oligomerize both BAK and BAX. Previously, BAK and BAX lacing the C-terminal fragment (BAXDeltaC) were shown to induce modest cytochrome c (Cyt c) release from rat brain mitochondria when activated by tBID. We now show that tBID plus monomeric full-length BAX induce extensive release of Cyt c, Smac/DIABLO, and Omi/HtrA2 (but not endonuclease G and the apoptosis inducing factor) comparable to the release induced by alamethicin. This occurs independently of the permeability transition without overt changes in mitochondrial morphology. The mechanism of the release may involve formation of reactive oxygen species (ROS) and activation of calcium-independent phospholipase A(2) (iPLA(2)). Indeed, increased ROS production and activated iPLA(2) were observed prior to massive Cyt c release. Furthermore, the extent of inhibition of Cyt c release correlated with the degree of suppression of iPLA(2) by the inhibitors propranolol, dibucaine, 4-bromophenacyl bromide, and bromenol lactone. Consistent with a requirement for iPLA(2) in Cyt c release from brain mitochondria, synthetic liposomes composed of lipids mimicking the outer mitochondrial membrane (OMM) but lacing iPLA(2) failed to release 10 kDa fluorescent dextran (FD-10) in response to tBID plus BAX. We propose that tBID plus BAX activate ROS generation, which subsequently augments iPLA(2) activity leading to changes in the OMM that allow translocation of certain mitochondrial proteins from the intermembrane space.
已知裂解或截短的BID（tBID）可使BAK和BAX形成寡聚体。此前研究表明，缺乏C末端片段的BAK和BAX（BAXDeltaC）在被tBID激活时，会从大鼠脑线粒体中诱导适度的细胞色素c（Cyt c）释放。我们现在发现，tBID加上单体全长BAX可诱导Cyt c、Smac/DIABLO和Omi/HtrA2的大量释放（但不包括核酸内切酶G和凋亡诱导因子），其释放量与短杆菌肽诱导的释放量相当。这一过程独立于通透性转换，且线粒体形态无明显变化。释放机制可能涉及活性氧（ROS）的形成以及钙非依赖性磷脂酶A2（iPLA(2)）的激活。事实上，在大量Cyt c释放之前就观察到ROS生成增加和iPLA(2)被激活。此外，Cyt c释放的抑制程度与普萘洛尔、丁卡因、4-溴苯甲酰溴和溴酚内酯等抑制剂对iPLA(2)的抑制程度相关。与iPLA(2)参与脑线粒体Cyt c释放的需求一致，由模拟线粒体外膜（OMM）但缺乏iPLA(2)的脂质组成的合成脂质体在tBID加BAX作用下未能释放10 kDa荧光葡聚糖（FD-10）。我们提出，tBID加BAX激活ROS生成，随后增强iPLA(2)活性，导致OMM发生变化，从而允许某些线粒体蛋白从膜间隙转运。
