Cofactor Balance by Nicotinamide Nucleotide Transhydrogenase (NNT) Coordinates Reductive Carboxylation and Glucose Catabolism in the Tricarboxylic Acid (TCA) Cycle
Cofactor Balance by Nicotinamide Nucleotide Transhydrogenase (NNT) Coordinates Reductive Carboxylation and Glucose Catabolism in the Tricarboxylic Acid (TCA) Cycle
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DOI：
10.1074/jbc.m112.396796
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发表时间：
2013-05-03
影响因子：
4.8
通讯作者：
Stephanopoulos, Gregory
中科院分区：
文献类型：
--
作者：
Gameiro, Paulo A.;Laviolette, Laura A.;Stephanopoulos, Gregory
癌症和增殖细胞表现出对谷氨酰胺衍生碳的需求增加，以支持合成代谢过程。此外，最近发现异柠檬酸脱氢酶1（IDH 1）和2（IDH 2）对α-酮戊二酸的还原羧化作用是谷氨酰胺合成柠檬酸盐的主要来源。NAD（P）H/NAD（P）（+）辅因子在三羧酸（TCA）循环中协调葡萄糖和谷氨酰胺利用中的作用尚未得到很好的理解，还原羧化反应的NADPH来源仍未探索。烟酰胺核苷酸转氢酶（NNT）是一种线粒体酶，其将还原当量从NADH转移到NADPH。在这里，我们表明，敲低NNT抑制谷氨酰胺的TCA循环的贡献，并激活SkMel 5黑色素瘤细胞中的葡萄糖催化剂。葡萄糖氧化的增加部分通过丙酮酸羧化酶发生，并使NNT敲除细胞对葡萄糖剥夺更敏感。重要的是，敲低NNT抑制SkMel 5和786-O肾癌细胞中的还原羧化。NNT的过表达足以刺激谷氨酰胺氧化和还原羧化，而它抑制TCA循环中的葡萄糖催化剂。NAD（P）H/NAD（P）+比值的受损支持了这些观察结果。我们的研究结果强调了NNT通过氧化还原平衡调节中心碳代谢的作用，呼吁其他机制协调底物偏好以维持功能性TCA循环。
Cancer and proliferating cells exhibit an increased demand for glutamine-derived carbons to support anabolic processes. In addition, reductive carboxylation of alpha-ketoglutarate by isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) was recently shown to be a major source of citrate synthesis from glutamine. The role of NAD(P)H/NAD(P)(+) cofactors in coordinating glucose and glutamine utilization in the tricarboxylic acid (TCA) cycle is not well understood, with the source(s) of NADPH for the reductive carboxylation reaction remaining unexplored. Nicotinamide nucleotide transhydrogenase (NNT) is a mitochondrial enzyme that transfers reducing equivalents from NADH to NADPH. Here, we show that knockdown of NNT inhibits the contribution of glutamine to the TCA cycle and activates glucose catabolism in SkMel5 melanoma cells. The increase in glucose oxidation partially occurred through pyruvate carboxylase and rendered NNT knockdown cells more sensitive to glucose deprivation. Importantly, knocking down NNT inhibits reductive carboxylation in SkMel5 and 786-O renal carcinoma cells. Overexpression of NNT is sufficient to stimulate glutamine oxidation and reductive carboxylation, whereas it inhibits glucose catabolism in the TCA cycle. These observations are supported by an impairment of the NAD(P) H/NAD(P)+ ratios. Our findings underscore the role of NNT in regulating central carbon metabolism via redox balance, calling for other mechanisms that coordinate substrate preference to maintain a functional TCA cycle.