Exploring the Role of Nitrogen Metabolism in Cancer

项目总结/摘要 致癌驱动基因突变和肿瘤抑制基因丢失如何促进肿瘤发生， 与癌症相关的细胞代谢改变。大部分的努力都集中在与 大多数癌细胞摄取葡萄糖只是为了释放大部分的葡萄糖碳作为乳酸盐， 称为有氧糖酵解或“瓦尔堡效应”。这种看似浪费的新陈代谢让癌症感到困惑 生物学家几十年来然而，有氧糖酵解已被证明是一种可持续的方式，以支持 糖酵解中间体的连续生产，所述糖酵解中间体用于蛋白质，脂质， 和核酸。十多年前，汤普森实验室开始分析肿瘤对 谷氨酰胺，细胞外液中第二常见的营养素。而葡萄糖是由 当癌细胞主要在胞质溶胶中时，我们发现谷氨酰胺主要在线粒体中代谢。 与葡萄糖类似，我们发现大部分以谷氨酰胺形式吸收的碳以乳酸形式分泌， 这个过程现在被称为氨解。从那时起，对多巴胺分解的研究集中在以下方面的作用： 谷氨酰胺作为回补底物，在碳从TCA中取出时维持线粒体功能 以柠檬酸盐的形式循环以促进脂肪酸生物合成，并以天冬氨酸盐的形式循环以支持核苷酸生物合成。 体内肿瘤细胞对谷氨酰胺的亲合力和谷氨酰胺催化剂维持氧化还原的能力 通过TCA循环回补的磷酸化已经在体内得到证实。但是，作用 氨解在支持肿瘤氮代谢中的作用还不太清楚。虽然抑制剂 谷氨酰胺代谢已经在癌症治疗中进行了探索，但它们在临床上的成功部分受到限制， 因为我们对肿瘤氮代谢的了解还不够。了解氮的作用 支持癌细胞存活和生长的代谢已成为Thompson的中心焦点。 实验室我们目前正在探索谷氨酰胺依赖的线粒体谷氨酸 积累为细胞提供了还原氮的细胞内储备， 线粒体支持从头多胺产生、氨基酸生物合成和谷胱甘肽产生。 我们还在研究线粒体谷氨酸的不同命运如何受到生长因子的调节， 以及癌基因和肿瘤抑制因子。而正常的线粒体谷氨酸是由 细胞外谷氨酰胺摄取，我们还计划测试是否乳酸和氨的组合， 在营养不良的条件下，肿瘤微环境（TME）中积累的蛋白质可以用来恢复 线粒体谷氨酸和胞质谷氨酰胺的水平，支持适应性翻译和细胞存活。 这些结果将有助于阐明癌细胞对氮的亲和力是如何根据营养物质的可用性得到满足的， 特定致癌突变和肿瘤抑制基因丢失的存在。获得的见解将有助于 为癌症的诊断和治疗提供新的方法。

PROJECT SUMMARY/ABSTRACT There has been a renewed interest in how oncogenic driver mutations and tumor suppressor losses contribute to cancer-associated alterations in cellular metabolism. Much of the effort has been focused on the avidity with which most cancer cells take up glucose only to release most of the glucose carbon as lactate, a process known as aerobic glycolysis or the “Warburg Effect”. This seemingly wasteful metabolism has puzzled cancer biologists for decades. Nevertheless, aerobic glycolysis has been shown to be a sustainable way to support the continuous production of glycolytic intermediates that are utilized in de novo synthesis of proteins, lipids, and nucleic acids. Over a decade ago, the Thompson laboratory embarked on analyzing tumor utilization of glutamine, the second most common nutrient present in extracellular fluid. While glucose is metabolized by cancer cells primarily in the cytosol, we found that glutamine was metabolized primarily in the mitochondria. Similar to glucose, we found that the majority of the carbon taken up as glutamine was secreted as lactate, a process now known as glutaminolysis. Since that time, the study of glutaminolysis has focused on the role of glutamine as an anaplerotic substrate to maintain mitochondrial function as carbon is taken out of the TCA cycle in the form of citrate to fuel fatty acid biosynthesis and as aspartate to support nucleotide biosynthesis. Tumor cell avidity for glutamine in vivo and the ability of glutamine catabolism to maintain oxidative phosphorylation through TCA cycle anaplerosis has been confirmed in vivo. However, the role of glutaminolysis in supporting tumor nitrogen metabolism is less well understood. Although inhibitors of glutamine metabolism have been explored in cancer therapy, their success in the clinic has been limited in part because of our incomplete knowledge of tumor nitrogen metabolism. Understanding the role of nitrogen metabolism in supporting cancer cell survival and growth has become the central focus of the Thompson laboratory. We are currently exploring the hypothesis that glutamine-dependent mitochondrial glutamate accumulation provides the cell with an intracellular reserve of reduced nitrogen that can be directed toward mitochondrial support of de novo polyamine production, amino acid biosynthesis, and glutathione generation. We are also studying how the differential fates of mitochondrial glutamate are regulated by growth factors, as well as by oncogenes and tumor suppressors. While the normal pool of mitochondrial glutamate is fed by extracellular glutamine uptake, we also plan to test whether the combination of lactate and ammonia that accumulates in the tumor microenvironment (TME) under nutrient-poor conditions can be utilized to restore mitochondrial glutamate and cytosolic glutamine to levels that support adaptive translation and cell survival. These results will help clarify how cancer cell avidity for nitrogen is satisfied based on nutrient availability and the presence of specific oncogenic mutations and tumor suppressor losses. The insights gained will help to shape new approaches for the diagnosis and treatment of cancer.