Control of caspase activation in apoptosis

描述（由申请人提供）：细胞凋亡的抑制是癌症的标志之一，其与增加的细胞增殖一起导致肿瘤发生。细胞恶性转化后，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，代谢变化如何与对肿瘤发生重要的细胞凋亡抑制有关尚不清楚。在这个提议中，我们使用生物化学强大的爪蟾卵/卵母细胞模型系统来研究细胞的营养状态可以调节细胞生存或死亡的倾向的假设。在初步工作中，我们已经确定了一个信号通路控制的卵母细胞/卵子的代谢状态，并证明了NADPH的戊糖磷酸途径的产生是这些细胞的生存至关重要。这种调节的目标是凋亡蛋白酶，半胱天冬酶2。具体而言，在存在丰富的NADPH或足够的葡萄糖-6-磷酸以驱动戊糖磷酸途径的操作的情况下，细胞死亡的抑制是由钙钙调蛋白依赖性激酶II（CaMKII）抑制半胱天冬酶2的磷酸化引起的。相反，在细胞死亡之前（在营养物耗尽之后）半胱天冬酶2的激活之前，在CaMKII磷酸化位点的半胱天冬酶2的去磷酸化。与这些观察结果一致，能够逃避CaMKII磷酸化的caspase 2的突变变体可以覆盖NADPH介导的细胞凋亡抑制。初步数据表明，半胱天冬酶的代谢调节也有助于其他细胞类型的凋亡控制。因此，我们假设，细胞营养物质在一生中（在卵母细胞的情况下）或在致癌过程中戊糖磷酸途径的异常操作的逐渐耗尽，可能导致无法驱动抑制半胱天冬酶2所需的NADPH产生，从而导致细胞死亡。这项计划的目的是了解营养利用途径如何控制凋亡蛋白酶caspase 2。

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.