Altered cytochrome c display precedes apoptotic cell death in Drosophila.

Drosophila affords a genetically well-defined system to study apoptosis in vivo. It offers a powerful extension to in vitro models that have implicated a requirement for cytochrome c in caspase activation and apoptosis. We found that an overt alteration in cytochrome c anticipates programmed cell death (PCD) in Drosophila tissues, occurring at a time that considerably precedes other known indicators of apoptosis. The altered configuration is manifested by display of an otherwise hidden epitope and occurs without release of the protein into the cytosol. Conditional expression of the Drosophila death activators, reaper or grim, provoked apoptogenic cytochrome c display and, surprisingly, caspase activity was necessary and sufficient to induce this alteration. In cell-free studies, cytosolic caspase activation was triggered by mitochondria from apoptotic cells but identical preparations from healthy cells were inactive. Our observations provide compelling validation of an early role for altered cytochrome c in PCD and suggest propagation of apoptotic physiology through reciprocal, feed-forward amplification involving cytochrome c and caspases.

果蝇提供了一个遗传学上定义明确的系统来在体内研究细胞凋亡。它是对体外模型的有力扩展，体外模型表明细胞色素c在半胱天冬酶激活和细胞凋亡中是必需的。我们发现细胞色素c的明显改变预示着果蝇组织中的程序性细胞死亡（PCD），这种改变发生的时间远远早于其他已知的细胞凋亡指标。这种改变的构象表现为原本隐藏的表位的显现，并且在蛋白质不释放到细胞质的情况下发生。果蝇死亡激活因子（收割者或冷酷）的条件性表达引发了致凋亡的细胞色素c的显现，令人惊讶的是，半胱天冬酶活性对于诱导这种改变是必要且充分的。在无细胞研究中，来自凋亡细胞的线粒体触发了细胞质中的半胱天冬酶激活，而来自健康细胞的相同制剂则没有活性。我们的观察结果有力地证实了改变的细胞色素c在PCD中的早期作用，并表明通过涉及细胞色素c和半胱天冬酶的相互、前馈放大来传播凋亡生理过程。