Control of caspase activation in apoptosis

描述(申请人提供)：抑制细胞凋亡是癌症的特征之一，它与细胞增殖增加一起导致肿瘤的发生。随着细胞的恶性转化，葡萄糖代谢发生改变，但这些代谢变化在肿瘤发生中的重要性尚不完全清楚。此外，新陈代谢变化如何可能与抑制对肿瘤发生至关重要的细胞凋亡有关尚不清楚。在这项建议中，我们使用生物化学功能强大的非洲爪哇卵/卵母细胞模型系统来检验细胞的营养状态可以调节细胞的生存或死亡倾向的假设。在前期的工作中，我们已经确定了一条由卵母细胞/卵细胞的代谢状态控制的信号通路，并证明了通过戊糖磷酸途径产生NADPH对这些细胞的生存至关重要。这种调控的靶标是一种凋亡蛋白caspase2。具体地说，在丰富的NADPH或足够的葡萄糖-6-磷酸存在下抑制细胞死亡，以驱动戊糖磷酸途径的运行，这是由于钙钙调素依赖的激酶II(CaMKII)抑制caspase2的磷酸化。相反，在细胞死亡(营养耗尽后)之前激活caspase 2之前，caspase 2在CaMKII磷酸化位点去磷酸化。与这些观察结果一致的是，能够逃避CaMKII磷酸化的caspase 2突变变体可以推翻NADPH介导的细胞凋亡抑制。初步数据表明，半胱氨酸天冬氨酸酶的代谢调节也有助于其他类型细胞的凋亡控制。因此，我们假设，在一生中(对于卵母细胞)细胞营养的逐渐耗尽或致癌过程中磷酸戊糖途径的异常操作，可能导致无法驱动抑制caspase 2所需的NADPH产生，从而导致细胞死亡。这项提议的目标是了解营养利用途径如何控制细胞凋亡的蛋白水解酶caspase2。

DESCRIPTION (provided by applicant): Inhibition of apoptosis is one of the hallmarks of cancer, which, together with increased cellular proliferation, leads to tumorigenesis. Following malignant transformation of cells, glucose metabolism is altered, but the importance of these metabolic changes in tumorigenesis is not entirely clear. Moreover, how metabolic changes may be linked to the inhibition of apoptosis important for tumorigenesis is not known. In this proposal, we use the biochemically powerful Xenopus egg/oocyte model system to examine the hypothesis that a cell's nutrient status can regulate the propensity of a cell to live or die. In preliminary work, we have identified a signaling pathway controlled by the metabolic state of the oocyte/egg and have demonstrated that generation of NADPH by the pentose phosphate pathway is critical for survival of these cells. The target of this regulation is an apoptotic protease, caspase 2. Specifically, inhibition of cell death in the presence of abundant NADPH, or sufficient glucose- 6-phosphate to drive operation of the pentose phosphate pathway, resulted from the inhibitory phosphorylation of caspase 2 by Calcium calmodulin-dependent kinase II (CaMKII). Conversely, activation of caspase 2 prior to cell death (following nutrient depletion) was preceded by dephosphorylation of caspase 2 at the CaMKII phosphorylation site. Consistent with these observations, a mutant variant of caspase 2 able to escape phosphorylation by CaMKII could override NADPH-mediated inhibition of apoptosis. Preliminary data indicate that metabolic regulation of caspases contribute to apoptotic control in other cell types as well. Thus, we hypothesize that the gradual exhaustion of cellular nutrients over the course of a lifetime (in the case of the oocyte) or aberrant operation of the pentose phosphate pathway during carcinogenesis, may result in an inability to drive the NADPH production required to suppress caspase 2, thereby contributing to cell death. The goal of this proposal is to understand how nutrient utilization pathways control the apoptotic protease, caspase 2.