Role of the pentose phosphate pathway in tumorigenesis

 描述(申请人提供)：本申请旨在确定P53家族蛋白对磷酸戊糖途径(PPP)的调节，以及该代谢途径在肿瘤发生中的作用。癌细胞的新陈代谢与正常细胞有很大的不同。这种代谢重新编程满足了癌细胞对快速产生大分子和有效解毒活性氧物种(ROS)的需求。大分子生物合成和ROS解毒都需要NADPH(烟酰胺腺嘌呤二核苷酸磷酸，还原型)，即细胞内还原的等价物。NADPH用于还原生物合成过程，也是各种抗氧化剂系统的终极还原剂。NADPH的一个主要来源是PPP，这是一种葡萄糖代谢途径，也为细胞提供从头合成核苷酸的核糖。 我们的初步结果表明，PPP受P53及其结构同源物TAp73的调节。P53是一种卓越的肿瘤抑制基因，也是人类肿瘤中最常见的突变基因。然而，P53如何阻止肿瘤的形成还不是很清楚，仍然是肿瘤生物学的一个中心问题。与P53不同的是，TAp73在人类肿瘤中很少发生突变，而是经常过度表达。目前尚不清楚TAp73是否为肿瘤细胞提供了优势，如果是，其潜在机制可能是什么。我们发现P53直接与PPP的限速酶葡萄糖-6-磷酸脱氢酶(G6PD)结合并使其失活。通过这种抑制作用，P53调节葡萄糖代谢、NADPH的产生和生物合成。我们还表明，TAp73支持肿瘤细胞的增殖。在机制上，TAp73增强G6PD基因的表达，增加PPP通量，引导葡萄糖合成NADPH和核糖，用于大分子合成和ROS的解毒。总之，这些发现揭示了P53和TAp73在新陈代谢和增殖中的作用。他们还表明，PPP可能是调节细胞增殖的焦点，也是癌症治疗的有价值的靶点。 我们计划进一步研究P53和TAp73对G6PD的调节，以及G6PD和PPP在肿瘤发生中的作用。我们的中心假设是，P53和TAp73对G6PD的调节对于控制生物合成和抗氧化反应是重要的，而由于P53失活和TAp73上调导致的PPP过度活跃有助于肿瘤的发生。我们提出了三个特定的目标：1)阐明P53和TAp73调节G6PD的机制；2)确定G6PD在致癌转化中的活性；3)确定G6PD在肿瘤进展中的作用。这些研究将极大地提高我们对P53家族蛋白功能和肿瘤细胞代谢重编程的理解。它们还可能为靶向P53和TAp73调节的代谢酶作为癌症新疗法提供理论依据。

 DESCRIPTION (provided by applicant): This application seeks to define the regulation of the pentose phosphate pathway (PPP) by p53 family proteins, and the role of this metabolic pathway in tumorigenesis. Cancer cells are markedly different from normal cells in their metabolism. This metabolic reprogramming meets the demand of cancer cells for rapid production of macromolecules and effective detoxification of reactive oxygen species (ROS). Both macromolecule biosynthesis and ROS detoxification require NADPH (nicotinamide adenine dinucleotide phosphate, reduced), the intracellular reducing equivalent. NADPH is used in reductive biosynthetic processes and is also the ultimate reducing agent for various anti-oxidant systems. A major source of NADPH is the PPP, a glucose metabolic pathway that also provides cells with ribose for de novo nucleotide synthesis. Our preliminary results revealed that the PPP is regulated by both p53 and its structural homologue, TAp73. p53 is a preeminent tumor suppressor, and it is the most frequently mutated gene in human tumors. Nevertheless, how p53 prevents tumor formation is not well understood, and remains a central issue in tumor biology. In contrast to p53, TAp73 is rarely mutated in human tumors, and instead is often over-expressed. It is unclear whether TAp73 affords an advantage to tumor cells and if so, what the underlying mechanism may be. We have found that p53 directly binds to and inactivates glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP. Through this inhibition, p53 regulates glucose metabolism, NADPH production, and biosynthesis. We have also shown that TAp73 supports tumor cell proliferation. Mechanistically, TAp73 enhances the expression of the G6PD gene, increases PPP flux, and directs glucose to the production of NADPH and ribose, for the synthesis of macromolecules and detoxification of ROS. Together, these findings shed important light on the roles of p53 and TAp73 in metabolism and proliferation. They also suggest that the PPP may be a focal point of regulation for cell proliferation and a valuable target for cancer therapy. We plan to further investigate the regulation of G6PD by p53 and TAp73, and role of the G6PD and the PPP in tumorigenesis. Our central hypothesis is that the regulation of G6PD by p53 and TAp73 is important for controlling biosynthesis and anti-oxidant response, and a hyperactive PPP due to p53 inactivation and TAp73 up-regulation contributes to tumorigenesis. We propose three specific aims: 1) Elucidate the mechanisms by which p53 and TAp73 regulate G6PD, 2) Define the activity of G6PD in oncogenic transformation, and 3) Determine the role of G6PD in the progression of cancer. The proposed studies will significantly improve our understanding of the functions of the p53 family proteins and the metabolic reprogramming in tumor cells. They will also likely provide a rationale for targeting p53- and TAp73-regulated metabolic enzymes as a new therapy for cancer.