Conformational change-dependent formation of active BAX complexes in mammalian cells

促凋亡的BCL-2蛋白BAX在超过细胞凋亡应激阈值后，可透过线粒体外膜（OMM）并启动caspase级联反应。活性BAX形成具有大细胞质组分的多mda复合物，难以与膜渗透功能相协调。我们最近的研究结果表明，活性BAX要么在离散的膜积分复合物中积累，要么在大的膜相关结构中积累。这种BAX复合物的二元性对应于两种独立的促凋亡功能：(I)膜相关BAX复合物直接结合并激活caspase-9， （II）而较小的，离散的BAX复合物从线粒体释放细胞色素c，启动凋亡细胞对caspase的激活。我们的研究结果表明，在缺乏大BAX复合物的细胞中，尽管细胞色素c释放，但膜通透性会导致caspase活性显著降低，而大BAX复合物单独诱导caspase活性并降低膜通透性。BAX复合物和凋亡小体共同确保完全的caspase激活，从而防止由部分caspase激活引起的基因组不稳定。该项目将阐明在哺乳动物细胞中，这两种活性BAX复合物的形成在多大程度上是保守的。此外，我们将研究在不同的哺乳动物细胞中这两种复合物的形成是否存在差异。我们将分析构象变化诱导不同功能复合物选择性形成的共同原理，以及不同复合物形成对细胞应激反应的影响。不同哺乳动物细胞凋亡调节的差异可能是不同哺乳动物肿瘤形成和应激抵抗的显著差异的基础。该项目将阐明BAX调控在哺乳动物中的保守程度，以及实现细胞凋亡差异调控的过程。

The pro-apoptotic BCL-2 protein BAX permeabilizes the outer mitochondrial membrane (OMM) and initiates the caspase cascade after surpassing the cellular threshold of apoptotic stress. Active BAX forms multi-MDa complexes with large cytosolic fractions that are difficult to reconcile with a function in membrane permeabilization. Our recent results show that active BAX accumulates either in discrete membrane-integral complexes or in large membrane-associated structures. This duality of BAX complexes corresponds to two independent pro-apoptotic functions: (I) membrane-associated BAX complexes directly bind and activate caspase-9, (II) whereas smaller, discrete BAX complexes release cytochrome c from mitochondria, initiating activation of caspases by the apoptosome. Our results show that membrane permeabilization in cells lacking large BAX complexes results in significantly lower caspase activity despite cytochrome c release, whereas large BAX complexes alone induce caspase activity with reduced membrane permeabilization. BAX complexes and apoptosomes together ensure complete caspase activation and therefore prevent genomic instability resulting from partial caspase activation. This project will clarify the extent to which the formation of the two active BAX complex species is conserved in mammalian cells. Furthermore, we will investigate whether differences exist in the formation of both complexes in different mammalian cells. We will analyze the common principle of conformational change-induced selective formation of functionally different complexes and the effect of different complex formation on the cell stress response. Differential apoptosis regulation in different mammals could underlie the significant differences in tumor formation and stress resistance in different mammalian species. This project will clarify the extent to which BAX regulation is conserved in mammals and the processes that enable differential apoptosis regulation.