Caspase-activated mitochondrial depolarization

描述(由申请人提供)：虽然细胞凋亡可以由多种信号启动，但相关的形态变化是不变的。这是基于不同的凋亡信号激活共同的死亡途径的能力，该途径是由线粒体释放的促凋亡因子启动的。这些因素中至少有两个参与了caspase的激活。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氨酸酶，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，尽管不能阻断死亡受体诱导的细胞凋亡，但Bcl2/XL却能阻断细胞色素c的释放。相反，线粒体膜电位(Delta Sigma M)的丧失程度与细胞内细胞色素c释放的程度相同。β-Sigma m的维持需要抑制下游的caspase。综上所述，这些数据表明，bc l-2/xl的功能是控制凋亡因子的释放，而caspase介导的是Delta Sigma m的丢失。这表明，除了靶向细胞骨架和基因组外，caspase还靶向线粒体以使其失活。基于文中给出的初步数据，我们假设启动子caspase以线粒体为靶标来解偶联电子传递。这导致了活性氧物种的产生。为了防止过度产生可能损害邻近细胞或吞噬细胞效应器的活性氧物种，半胱氨酸天冬氨酸酶使线粒体去极化。该方案的目的是进一步研究caspase依赖的线粒体去极化，并分离导致β-Sigma m丢失的因子(S)。这些结果对确定细胞凋亡的“不归路点”也有一定的意义。我们还将研究抑制caspase依赖的去极化对细胞从死亡刺激中恢复的能力以及恢复的细胞表型的影响。这对细胞凋亡在肿瘤发生和耐药癌症中的作用有一定的意义。

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.