Cross J R, Postigo A, Blight K, Downward J
Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.
Cell Death Differ. 2008 Jun;15(6):997-1008. doi: 10.1038/cdd.2008.14. Epub 2008 Feb 15.
Mitochondrial dysfunction mediated by Bax and Bak is a critical step in mammalian cell apoptosis. However, the molecular mechanism of Bax activation remains unknown and has been difficult to investigate due to its rapid and stochastic nature. It is currently unclear whether mitochondria play a passive role in the initiation of apoptosis, remaining unaffected by cell stresses until Bax and Bak are active, or whether they actively participate in Bax/Bak activation. Here, two viral proteins, E1B19K and BHRF1, are examined for their ability to block Bax activation at different steps and thereby reveal the timing of mitochondrial changes during apoptosis. We demonstrate that BHRF1 strongly inhibits Bax activation but not upstream apoptotic signaling events, while E1B19K permits initial stages of Bax activation but prevents the subsequent oligomerization of Bax that is required for mitochondrial dysfunction. In this defined system we show that changes in mitochondrial ultrastructure, characteristic of cells undergoing apoptosis, precede Bax activation and are not blocked by E1B19K and BHRF1. We suggest that the ability of mitochondria to respond to apoptotic stress prior to Bax activation indicates that these organelles may play a direct role in activating Bax.
由Bax和Bak介导的线粒体功能障碍是哺乳动物细胞凋亡的关键步骤。然而，Bax激活的分子机制仍然未知，并且由于其快速和随机的性质而难以研究。目前尚不清楚线粒体在细胞凋亡起始过程中是发挥被动作用，在Bax和Bak激活之前不受细胞应激影响，还是积极参与Bax/Bak激活。在这里，研究了两种病毒蛋白E1B19K和BHRF1在不同步骤阻断Bax激活的能力，从而揭示细胞凋亡过程中线粒体变化的时间。我们证明BHRF1强烈抑制Bax激活，但不抑制上游凋亡信号事件，而E1B19K允许Bax激活的初始阶段，但阻止随后Bax的寡聚化，而这是线粒体功能障碍所必需的。在这个明确的系统中，我们表明，经历凋亡的细胞所特有的线粒体超微结构变化先于Bax激活，并且不受E1B19K和BHRF1的阻断。我们认为，线粒体在Bax激活之前对凋亡应激作出反应的能力表明，这些细胞器可能在激活Bax中发挥直接作用。
