Control of caspase activation in apoptosis

描述（由申请人提供）：抑制细胞凋亡是癌症的标志之一，它与细胞增殖增加一起导致肿瘤发生。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，代谢变化如何与肿瘤发生中重要的细胞凋亡抑制联系起来尚不清楚。在这个提议中，我们使用生物化学功能强大的爪蟾卵/卵母细胞模型系统来检验细胞的营养状况可以调节细胞生存或死亡倾向的假设。在前期工作中，我们已经确定了一个由卵母细胞/卵的代谢状态控制的信号通路，并证明了戊糖磷酸途径产生NADPH对这些细胞的存活至关重要。这种调控的目标是凋亡蛋白酶caspase 2。具体来说，由于钙调素依赖性激酶II （CaMKII）对caspase 2的抑制磷酸化，在存在丰富的NADPH或足够的葡萄糖- 6-磷酸来驱动戊糖磷酸途径的操作时，抑制细胞死亡。相反，在细胞死亡之前（营养耗尽后），caspase 2的激活是在CaMKII磷酸化位点caspase 2去磷酸化之前进行的。与这些观察结果一致，caspase 2的突变变体能够逃脱CaMKII的磷酸化，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，我们假设在一生中细胞营养物质的逐渐耗尽（在卵母细胞的情况下）或在癌变过程中戊糖磷酸途径的异常操作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。这项建议的目的是了解营养利用途径如何控制凋亡蛋白酶，半胱天冬酶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.