Reversal of apoptosis:an in vivo mechanism for cytoprotection and mutagenesis

描述（由申请人提供）：细胞凋亡在多细胞生物的发育和体内平衡中起着至关重要的作用，通过雕刻组织，删除不需要的结构，消除异常，受伤或危险的细胞。此外，靶向凋亡通路是治疗顽固性疾病（如癌症）的重要策略，而限制细胞凋亡可能有利于治疗缺血性损伤和退行性疾病。虽然凋亡调节因子的功能丧失或获得可以人为地使细胞存活超过正常检查点，但细胞凋亡通常被认为是一个本质上不可逆的过程。然而，我们最近发现了人类和小鼠细胞晚期凋亡的自然可逆性。垂死的细胞可以逆转细胞凋亡并存活下来，尽管它们通过了之前被认为是不归路的检查点，包括caspase-3激活和DNA损伤。简单地洗去凋亡诱导剂就足以使大多数垂死细胞存活，大多数凋亡标志消失，表明凋亡逆转是一种内源性细胞机制。值得注意的是，虽然大多数细胞完全恢复，但一小部分逆转凋亡的细胞保留了遗传改变，并以比对照细胞更高的频率发生致癌转化。我们认为细胞凋亡的逆转可能是一种生理机制，具有多种有益功能。原则上，在执行阶段阻止细胞凋亡可以促进细胞的存活，如神经元和心肌细胞，这些细胞是难以替代的。另外，这种恢复

DESCRIPTION (provided by applicant): Apoptosis plays essential roles in development and homeostasis in multicellular organisms by sculpting tissues, deleting unwanted structures, and eliminating abnormal, injured or dangerous cells. In addition, targeting apoptotic pathways is an important strategy for treatment of intractable diseases such as cancer, whereas limiting apoptosis may be beneficial for treating ischemic injury and degenerative disorders. Although loss- or gain-of-function of apoptotic regulators can artificially allow cells to survive beyond normal checkpoints, apoptosis is generally assumed to be an intrinsically irreversible process. However, we recently discovered a natural reversibility of late-stage apoptosis in human and mouse cells. Dying cells can reverse apoptosis and survive, despite having passed through checkpoints previously believed to be the point of no return, including caspase-3 activation and DNA damage. Simply washing away apoptotic inducers is sufficient to allow the majority of dying cells to survive and most hallmarks of apoptosis to vanish, indicating that reversal of apoptosis is an endogenous cellular mechanism. Notably, while most cells recover completely, a small fraction of cells that reverse apoptosis retain genetic alterations and undergo oncogenic transformation at a higher frequency than control cells. We propose that reversal of apoptosis may be a physiological mechanism that can serve several beneficial functions. Arrest of apoptosis at the execution stage could in principle promote survival of cells, such as neurons and heart muscle cells, which are difficult to replace. Alternatively or in addition, this recovery process, which we have named anastasis (Greek for rising to life), could promote genetic and phenotypic diversity in response to environmental or physiological stresses that initiate apoptosis. A negative side effect of this otherwise beneficial process is oncogenic transformation. We have developed and tested a biosensor to detect cells that have undergone anastasis in vivo in Drosophila melanogaster. In specific aim 1 we will test the hypothesis that anastasis functions to salvage cells that are difficult to replace, thus limiting permanent tissue damage following transient insults. We also propose to develop a similar biosensor for use in mammalian cells. In specific aim 2 we propose to initiate studies of the molecular mechanisms controlling anastasis. The proposed work has the potential to lead to a new understanding of and treatments for degenerative diseases and cancer.