Mechanisms of metabolic reprogramming by PIK3CA oncogenic mutations

 描述(申请人提供)：新陈代谢重新编程是癌症的标志之一。“Warburg效应”和谷氨酰胺依赖是发生在癌细胞中的两个众所周知的代谢重编程事件。人们很早就知道，大多数癌细胞依赖谷氨酰胺生长。然而，癌细胞依赖谷氨酰胺的机制还不是很清楚。PIK3CA编码磷脂酰肌醇3-激酶的p110α催化亚基，在多种人类肿瘤中经常发生突变，其中包括20%到30%的结直肠癌。我们的初步研究表明，携带致癌基因PIK3CA突变的结直肠癌细胞对谷氨酰胺的依赖性更强，这表明突变的PIK3CA可能是重新编程癌细胞中谷氨酰胺代谢的驱动力。此外，我们的基因表达分析表明，在含有α3CA突变的结直肠癌细胞中，GPT2的表达水平上调。GPT2是一种催化谷氨酸转化为PIK3CA的酶。GPT2基因敲除使PIK3CA突变细胞生长对谷氨酰胺的依赖性降低，而GPT2过表达使PIK3CA野生型(WT)细胞对谷氨酰胺缺乏更加敏感。值得注意的是，我们发现氨基氧乙酸酯(AOA)，一种抑制GPT2酶活性的小化合物，可以抑制携带致癌基因PIK3CA突变的结直肠癌移植瘤的生长，但不抑制WT PIK3CA。这些结果使我们假设致癌的PIK3CA/p110GPT2轴突变-α轴重新编程结直肠癌的代谢，从而使癌细胞依赖谷氨酰胺。我们认为，靶向谷氨酰胺代谢将是治疗携带PIK3CA突变的结直肠癌患者的有效方法。为了验证我们的假设并阐明突变型p110α重编程癌症代谢的分子机制，我们提出了以下目标：(1)描述突变型p110α上调GPT2表达的信号通路；(2)确定p110α-GPT2轴如何重编程结直肠癌中的谷氨酰胺代谢；以及(3)在临床前模型中确定靶向谷氨酰胺代谢是否是治疗携带PIK3CA突变的结直肠癌的有效方法。我们提出的研究调查了一个创新的概念，即致癌的PIK3CA突变重新编程结直肠癌的代谢，并使癌症依赖谷氨酰胺。此外，我们的研究可能提供一种新的精确治疗方法，针对携带PIK3CA突变的结直肠癌患者的谷氨酰胺代谢。鉴于PIK3CA在各种人类癌症中经常发生突变，我们预计我们拟议的研究将对结直肠癌以外的概念和治疗产生更广泛的影响。

 DESCRIPTION (provided by applicant): Metabolic reprogramming is one of the hallmarks of cancer. The "Warburg effect" and glutamine dependency are two well-known metabolic reprogramming events that occur in cancer cells. It has long been known that most cancer cells are dependent on glutamine to grow. However, the mechanisms by which cancer cells become dependent on glutamine are not well understood. PIK3CA, which encodes the p110α catalytic subunit of phosphatidylinositol 3-kinase, is frequently mutated in a variety of human cancers including 20 to 30% of colorectal cancers. Our preliminary studies demonstrate that colorectal cancer cells harboring oncogenic PIK3CA mutations are more dependent on glutamine, suggesting that mutant PIK3CA may be a driving force that reprograms glutamine metabolism in cancer cells. Moreover, our gene expression analyses show that expression levels of GPT2, an enzyme that catalyzes conversion of glutamate to α-keto-glutarate, are up- regulated in colorectal cancer cells harboring PIK3CA mutations. Knockdown of GPT2 makes PIK3CA mutant cell growth less dependent on glutamine, whereas overexpression of GPT2 renders PIK3CA wild-type (WT) cell more sensitive to glutamine deprivation. Remarkably, we found that aminooxyacetate (AOA), a small compound which inhibits GPT2 enzymatic activity, suppresses xenograft tumor growth of colorectal cancers harboring oncogenic PIK3CA mutations, but not WT PIK3CA. These results lead us to hypothesize that the oncogenic PIK3CA/p110α mutant-GPT2 axis reprograms colorectal cancer metabolism and thus renders cancer cells dependent on glutamine. We propose that targeting glutamine metabolism will be an effective treatment for colorectal cancer patients harboring PIK3CA mutations. To test our hypotheses and to elucidate the molecular mechanisms by which mutant p110α reprograms cancer metabolism, we propose the following aims: (1) delineate the signaling pathway by which mutant p110α up-regulates GPT2 expression; (2) determine how the p110α-GPT2 axis reprograms glutamine metabolism in colorectal cancer; and (3) determine in preclinical models if targeting glutamine metabolism is an effective treatment for colorectal cancers harboring PIK3CA mutations. Our proposed studies investigate an innovative concept that oncogenic PIK3CA mutations reprogram colorectal cancer metabolism and render cancers dependent on glutamine. Moreover, our studies may provide a novel precision therapy that targets glutamine metabolism in colorectal cancer patients harboring PIK3CA mutations. Given that PIK3CA is frequently mutated in a variety of human cancers, we expect that our proposed studies will have broader conceptual and therapeutic impacts that extend beyond colorectal cancer.