Caspase-activated mitochondrial depolarization

描述（由申请人提供）：虽然凋亡可以由多种信号启动，但相关的形态学变化是不变的。这是基于多种凋亡信号激活由线粒体释放凋亡因子启动的共同死亡途径的能力。这些因子中至少有两个与半胱天冬酶的激活有关。虽然大多数死亡信号需要从线粒体释放因子来激活下游的半胱天冬酶，但在许多情况下，来自死亡受体的信号可以绕过线粒体。我们已经确定Bcl-2/XL可以阻断细胞色素c的释放，尽管它不能阻断死亡受体诱导的细胞凋亡。相反，线粒体膜电位（δ Sigma m）的损失程度与细胞色素c释放的细胞相同。维持δ σ m需要抑制下游半胱天冬酶。综上所示，Bcl-2/XL具有控制凋亡因子释放的功能，而caspases介导δ Sigma m的丢失。这表明caspases除了靶向细胞骨架和基因组外，还靶向线粒体失活。根据本文提供的初步数据，我们假设启动半胱天冬酶靶向线粒体以解除电子传递的偶联。这导致了活性氧的产生。为了防止活性氧的过量产生，可能会损害邻近细胞或吞噬细胞效应半胱天冬酶使线粒体去极化。该建议的目的是进一步表征caspase依赖性线粒体去极化，并分离导致δ Sigma m损失的因素。这些结果也对确定细胞凋亡的“不归点”有影响。我们还将研究抑制caspase依赖性去极化对细胞从死亡刺激中恢复的能力以及恢复细胞的表型的影响。这提示了细胞凋亡在肿瘤发生和耐药癌症中的作用。

DESCRIPTION (provided by applicant): While apoptosis can be initiated by a wide variety of signals, the associated morphologic changes are invariant. This is based on the ability of diverse apoptotic signals to activate a common death pathway that is initiated by the release of apoptogenic factors from the mitochondria. At least two of these factors are involved in the activation of caspases. While most death signals require the release of factors from the mitochondria to activate the downstream caspases, signaling from death receptors can, in many cases, bypass the mitochondria. We have determined that Bcl-2/XL block cytochrome c release despite being unable to block death receptor-induced apoptosis. In contrast, loss of mitochondrial membrane potential (delta Sigma m) occurred to the same degree as in cells that cytochrome c release was observed. Maintenance of delta Sigma m required the inhibition of downstream caspases. Taken together these data suggest that Bcl-2/XL functions to control the release of apoptogenic factors while caspases mediate loss of Delta Sigma m. This suggests that in addition to targeting the cytoskeleton and genome, caspases target the mitochondria for inactivation. Based on the preliminary data presented within, we hypothesize that initiator caspases target the mitochondria to uncouple electron transport. This results in the production of reactive oxygen species. To prevent excessive production of reactive oxygen species that could be damaging to neighboring cells or the phagocyte effector caspases depolarize the mitochondria. The aims of this proposal are designed to further characterize caspase-dependent mitochondrial depolarization as well as to isolate the factor(s) responsible for loss of delta Sigma m. These results also have implications in the determination of the "point of no return" in apoptosis. We will also examine the effects of inhibiting caspase-dependent depolarization on the ability of cells to recover from a death stimulus as well as the phenotype of cells that recover. This has implications on the role of apoptosis in tumorigenesis and drug resistant cancer.