Alimonti J B, Shi L, Baijal P K, Greenberg A H
Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba R3E 0V9, Canada.
J Biol Chem. 2001 Mar 9;276(10):6974-82. doi: 10.1074/jbc.M008444200. Epub 2000 Dec 12.
Many cell death pathways converge at the mitochondria to induce release of apoptogenic proteins and permeability transition, resulting in the activation of effector caspases responsible for the biochemical and morphological alterations of apoptosis. The death receptor pathway has been described as a triphasic process initiated by the activation of apical caspases, a mitochondrial phase, and then the final phase of effector caspase activation. Granzyme B (GrB) activates apical and effector caspases as well as promotes cytochrome c (cyt c) release and loss of mitochondrial membrane potential. We investigated how GrB affects mitochondria utilizing an in vitro cell-free system and determined that cyt c release and permeability transition are initiated by distinct mechanisms. The cleavage of cytosolic BID by GrB results in truncated BID, initiating mitochondrial cyt c release. BID is the sole cytosolic protein responsible for this phenomenon in vitro, yet caspases were found to participate in cyt c release in some cells. On the other hand, GrB acts directly on mitochondria in the absence of cytosolic S100 proteins to open the permeability transition pore and to disrupt the proton electrochemical gradient. We suggest that GrB acts by two distinct mechanisms on mitochondria that ultimately lead to mitochondrial dysfunction and cellular demise.
许多细胞死亡途径在线粒体处汇聚，诱导凋亡蛋白释放和通透性转变，从而导致负责凋亡生化和形态改变的效应半胱天冬酶激活。死亡受体途径被描述为一个三相过程，始于顶端半胱天冬酶激活，接着是线粒体阶段，最后是效应半胱天冬酶激活的终末阶段。颗粒酶B（GrB）可激活顶端和效应半胱天冬酶，还能促进细胞色素c（cyt c）释放以及线粒体膜电位丧失。我们利用体外无细胞系统研究了GrB如何影响线粒体，并确定cyt c释放和通透性转变是由不同机制启动的。GrB对胞质BID的切割导致截短的BID，从而启动线粒体cyt c释放。BID是体外负责这一现象的唯一胞质蛋白，但发现半胱天冬酶在某些细胞的cyt c释放中发挥作用。另一方面，在没有胞质S100蛋白的情况下，GrB直接作用于线粒体，打开通透性转变孔并破坏质子电化学梯度。我们认为，GrB通过两种不同机制作用于线粒体，最终导致线粒体功能障碍和细胞死亡。
