Kominsky Douglas J, Bickel Ryan J, Tyler Kenneth L
Department of Neurology, University of Colorado Health Science Center, Denver, Colorado 80262, USA.
J Virol. 2002 Nov;76(22):11414-24. doi: 10.1128/jvi.76.22.11414-11424.2002.
Many viruses belonging to diverse viral families with differing structure and replication strategies induce apoptosis both in cultured cells in vitro and in tissues in vivo. Despite this fact, little is known about the specific cellular apoptotic pathways induced during viral infection. We have previously shown that reovirus-induced apoptosis of HEK cells is initiated by death receptor activation but requires augmentation by mitochondrial apoptotic pathways for its maximal expression. We now show that reovirus infection of HEK cells is associated with selective cytosolic release of the mitochondrial proapoptotic factors cytochrome c and Smac/DIABLO, but not the release of apoptosis-inducing factor. Release of these factors is not associated with loss of mitochondrial transmembrane potential and is blocked by overexpression of Bcl-2. Stable expression of caspase-9b, a dominant-negative form of caspase-9, blocks reovirus-induced caspase-9 activation but fails to significantly reduce activation of the key effector caspase, caspase-3. Smac/DIABLO enhances apoptosis through its action on cellular inhibitor of apoptosis proteins (IAPs). Reovirus infection is associated with selective down-regulation of cellular IAPs, including c-IAP1, XIAP, and survivin, effects that are blocked by Bcl-2 expression, establishing the dependence of IAP down-regulation on mitochondrial events. Taken together, these results are consistent with a model in which Smac/DIABLO-mediated inhibition of IAPs, rather than cytochrome c-mediated activation of caspase-9, is the key event responsible for mitochondrial augmentation of reovirus-induced apoptosis. These studies provide the first evidence for the association of Smac/DIABLO with virus-induced apoptosis.
许多属于不同病毒家族、具有不同结构和复制策略的病毒，在体外培养细胞和体内组织中均可诱导细胞凋亡。尽管如此，对于病毒感染过程中诱导的特定细胞凋亡途径却知之甚少。我们先前已表明，呼肠孤病毒诱导的HEK细胞凋亡由死亡受体激活引发，但需要线粒体凋亡途径的增强作用才能实现最大程度的表达。我们现在发现，HEK细胞感染呼肠孤病毒与线粒体促凋亡因子细胞色素c和Smac/DIABLO的选择性胞质释放有关，但与凋亡诱导因子的释放无关。这些因子的释放与线粒体跨膜电位的丧失无关，并被Bcl-2的过表达所阻断。caspase-9的显性负性形式caspase-9b的稳定表达可阻断呼肠孤病毒诱导的caspase-9激活，但未能显著降低关键效应半胱天冬酶caspase-3的激活。Smac/DIABLO通过作用于细胞凋亡抑制蛋白（IAP）来增强细胞凋亡。呼肠孤病毒感染与细胞IAP的选择性下调有关，包括c-IAP1、XIAP和生存素，这些效应被Bcl-2表达所阻断，从而确立了IAP下调对线粒体事件的依赖性。综上所述，这些结果与一个模型一致，即Smac/DIABLO介导的IAP抑制而非细胞色素c介导的caspase-9激活是呼肠孤病毒诱导的凋亡中线粒体增强的关键事件。这些研究为Smac/DIABLO与病毒诱导的凋亡之间的关联提供了首个证据。
