Glutamine synthetase in cancer cell metabolism and oncogenesis

总结 代谢失调长期以来被认为是肿瘤疾病的一个关键标志。的一个主要 肿瘤细胞中的代谢变化是通过谷氨酰胺分解增加谷氨酰胺（Gln）的使用：Gln通过 谷氨酸脱氢酶（GLUD）将谷氨酸脱氢酶（GLS）转化为谷氨酸（谷氨酸，Glu） 转化为α-酮戊二酸（aKG）进入三羧酸（TCA）循环进行回补（补充代谢产物） 能量生产或生物合成的中间体）。众所周知，致癌性c-Myc（下文称为c-Myc）是一种致癌基因。 称为Myc）通过直接反式激活Gln转运蛋白SLC 1A 5的表达来增强Gln的利用 和SLC 7A 5/SLC 3A 2，以及通过GLS 1的转录抑制来增加GLS 1的表达， 阻遏物微RNA（miR）-23 a/B。药理学靶向GLS 1正被积极追求作为一种抗- 癌症的治疗方法，虽然到目前为止收效甚微。另一方面，最近的几项研究，包括 来自我们实验室的研究指出了谷氨酰胺合成的重要性，至少在某些细胞/组织类型中是如此。Gln是 由谷氨酸和氨缩合，在谷氨酰胺合成酶（GS，也 称为谷氨酸氨连接酶，GLUL）。利用稳定同位素代谢物示踪，我们最近 据报道，这种合成的Gln不是通过氨解用于为TCA循环提供燃料;相反，它用于 几个TCA独立的合成代谢过程，包括核苷酸的生物合成和必需的转运， 个氨基酸重要的是，GS表达的升高促进了Gln限制下的细胞存活;抑制GS表达促进了Gln限制下的细胞存活。 GS导致Gln限制后细胞增殖减少和细胞死亡增加，并减缓异种移植瘤 增长此外，我们最近报道Myc可以诱导GS在许多癌细胞中表达， 线我们还发现，在几种小鼠模型中，Myc激活与GS表达呈正相关 和人类患者样品中。这些发现使我们提出以下假设：致癌Myc， 至少在某些细胞/组织类型中，上调GS表达以促进Gln产生， 合成代谢使用（远离TCA循环），从而促进肿瘤发生。我们提出两个具体的 目的是研究这一假设：1）研究代谢和细胞生物学后果，以及调节 在Myc激活的情况下增加的GS表达;和2）确定GS在Myc-1中的体内作用。 驱动代谢重编程和肿瘤发生。如果完成，这项研究将提供一个新的维度 了解癌细胞中Myc失调的功能，以及治疗癌症的潜在新靶点。 Myc驱动的肿瘤

SUMMARY Dysregulated metabolism has long been recognized as a key hallmark of neoplastic disease. One of the major metabolic changes in tumor cells is increased glutamine (Gln) usage via glutaminolysis: Gln is deaminated by glutaminase (GLS) to glutamate (glutamic acid, Glu), which is converted by glutamate dehydrogenase (GLUD) to α-ketoglutarate (aKG) to enter the tricarboxylic acid (TCA) cycle for anaplerosis (replenishment of metabolic intermediates for energy production or biosynthesis). It is well recognized that oncogenic c-Myc (hereafter referred to as Myc) enhances Gln usage by directly transactivating the expression of Gln transporters SLC1A5 and SLC7A5/SLC3A2, and by increasing GLS1 expression via transcriptional suppression of the GLS1 repressor micro RNAs (miR)-23a/b. Pharmacologically targeting GLS1 is being actively pursued as an anti- cancer approach, although thus far with little success. On the other hand, several recent studies, including those from our laboratory, point to the importance of Gln synthesis, at least in certain cell/tissue types. Gln is synthesized de novo by condensation of Glu and ammonia, catalyzed by the enzyme Gln synthetase (GS, also known as glutamate ammonia ligase, GLUL). Using stable isotope-based metabolite tracing, we recently reported that this synthesized Gln is not used via glutaminolysis to fuel the TCA cycle; rather it is used for several TCA-independent anabolic processes including biosynthesis of nucleotides and transport of essential amino acids. Importantly, elevated expression of GS promoted cell survival under Gln limitation; inhibition of GS led to decreased cell proliferation and increased cell death upon Gln limitation, and slowed xenograft tumor growth. Moreover, we recently reported that Myc can induce the expression of GS in a number of cancer cell lines. We also found a positive correlation between Myc activation and GS expression several mouse models and in human patient samples. These findings lead us to propose the following hypothesis: oncogenic Myc, at least in certain cell/tissue types, upregulates GS expression to promote Gln production and its anabolic usage (away from the TCA cycle), thereby facilitating oncogenesis. We propose two Specific Aims to study this hypothesis: 1) Study the metabolic and cell biological consequences, and the regulation of increased GS expression in the context of Myc activation; and 2) Determine the in vivo role of GS in Myc- driven metabolic reprogramming and oncogenesis. If accomplished, this study will provide a novel dimension to understanding the functions of dysregulated Myc in cancer cells and a potential new target for treatment of Myc-driven tumors.