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

促凋亡BCL-2蛋白BAX使线粒体外膜（OMM）透化，并在超过凋亡应激的细胞阈值后启动半胱天冬酶级联反应。活性BAX与大的胞质组分形成多MDa复合物，其难以与膜透化功能相协调。我们最近的研究结果表明，活跃的BAX积累在离散的膜积分复合物或在大型膜相关结构。BAX复合物的这种二元性对应于两种独立的促凋亡功能：（I）膜相关的BAX复合物直接结合并激活半胱天冬酶-9，（II）而较小的离散BAX复合物从线粒体释放细胞色素c，通过线粒体启动半胱天冬酶的激活。我们的研究结果表明，尽管细胞色素c释放，但缺乏大BAX复合物的细胞中的膜透化导致caspase活性显着降低，而大BAX复合物单独诱导caspase活性降低膜透化。BAX复合物和核糖体一起确保完全的半胱天冬酶活化，因此防止由部分半胱天冬酶活化引起的基因组不稳定性。该项目将阐明两种活性BAX复合物的形成在哺乳动物细胞中保守的程度。此外，我们将调查是否存在差异，在不同的哺乳动物细胞中的两种复合物的形成。我们将分析构象变化诱导的功能不同的复合物的选择性形成的共同原则和不同的复合物形成对细胞应激反应的影响。不同哺乳动物的细胞凋亡调节差异可能是不同哺乳动物物种在肿瘤形成和应激抗性方面存在显著差异的基础。该项目将阐明BAX调节在哺乳动物中的保守程度以及能够进行差异凋亡调节的过程。

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.