Ilic Nina, Birsoy Kıvanç, Aguirre Andrew J, Kory Nora, Pacold Michael E, Singh Shambhavi, Moody Susan E, DeAngelo Joseph D, Spardy Nicole A, Freinkman Elizaveta, Weir Barbara A, Tsherniak Aviad, Cowley Glenn S, Root David E, Asara John M, Vazquez Francisca, Widlund Hans R, Sabatini David M, Hahn William C
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02215.
Broad Institute of MIT and Harvard University, Cambridge, MA 02142.
Proc Natl Acad Sci U S A. 2017 Apr 25;114(17):E3434-E3443. doi: 10.1073/pnas.1617922114. Epub 2017 Apr 10.
Oncogenic mutations are found in a significant fraction of human cancers, but therapeutic inhibition of PI3K has only shown limited success in clinical trials. To understand how mutant PIK3CA contributes to cancer cell proliferation, we used genome scale loss-of-function screening in a large number of genomically annotated cancer cell lines. As expected, we found that mutant cancer cells require but also require the expression of the TCA cycle enzyme 2-oxoglutarate dehydrogenase (OGDH). To understand the relationship between oncogenic PIK3CA and OGDH function, we interrogated metabolic requirements and found an increased reliance on glucose metabolism to sustain mutant cell proliferation. Functional metabolic studies revealed that OGDH suppression increased levels of the metabolite 2-oxoglutarate (2OG). We found that this increase in 2OG levels, either by OGDH suppression or exogenous 2OG treatment, resulted in aspartate depletion that was specifically manifested as auxotrophy within mutant cells. Reduced levels of aspartate deregulated the malate-aspartate shuttle, which is important for cytoplasmic NAD regeneration that sustains rapid glucose breakdown through glycolysis. Consequently, because mutant cells exhibit a profound reliance on glucose metabolism, malate-aspartate shuttle deregulation leads to a specific proliferative block due to the inability to maintain NAD/NADH homeostasis. Together these observations define a precise metabolic vulnerability imposed by a recurrently mutated oncogene.
致癌突变在相当一部分人类癌症中被发现，但PI3K的治疗性抑制在临床试验中仅取得了有限的成功。为了了解突变型PIK3CA如何促进癌细胞增殖，我们在大量经过基因组注释的癌细胞系中进行了全基因组功能丧失筛选。正如预期的那样，我们发现突变癌细胞不仅需要三羧酸循环酶2-氧代戊二酸脱氢酶（OGDH）的表达，而且还需要其表达。为了了解致癌性PIK3CA与OGDH功能之间的关系，我们研究了代谢需求，发现突变细胞增殖对葡萄糖代谢的依赖性增加。功能性代谢研究表明，OGDH抑制会增加代谢物2-氧代戊二酸（2OG）的水平。我们发现，无论是通过OGDH抑制还是外源性2OG处理，2OG水平的这种增加都会导致天冬氨酸耗竭，这在突变细胞中具体表现为营养缺陷。天冬氨酸水平的降低会使苹果酸-天冬氨酸穿梭失调，这对于细胞质NAD再生很重要，而细胞质NAD再生通过糖酵解维持快速的葡萄糖分解。因此，由于突变细胞对葡萄糖代谢表现出严重的依赖性，苹果酸-天冬氨酸穿梭失调会导致特定的增殖阻滞，因为无法维持NAD/NADH稳态。这些观察结果共同定义了一种由反复突变的致癌基因所导致的精确代谢脆弱性。
