Metabolite control of transcription

总结：越来越清楚的是，基因组中编码的许多蛋白质的转录是由小的代谢物控制的，这些代谢物的浓度取决于环境条件。因此，消耗富含碳水化合物的饮食导致编码形成前体乙酰辅酶A所需的糖酵解的主要酶以及产生脂肪合成所需的NADPH的己糖单磷酸途径的酶的基因的转录。这种转录因子被称为ChREBP，对饮食中的碳水化合物有反应。结合SREBP（由Brown和Goldstein描述的固醇响应性结合蛋白）的作用以及对胰岛素的响应，这两种转录因子在肥胖症、II型糖尿病和血管疾病中具有重要意义。ChREBP的这种优雅的协调控制由简单的己糖单磷酸途径代谢物木酮糖5-P发挥（Veech RL，PNAC 2003;100：5578-80）。 吡啶核苷酸的氧化还原状态的变化是代谢状态变化的标志，并且已知通过酒精摄入而深刻改变。现在已知许多转录因子受吡啶核苷酸的氧化还原状态控制。其中包括：NPAS 2，所谓的负责昼夜节律的时钟基因（Rutter J等人，Science 2003;293：510-4）; CtBP，在发育和转化中起作用的转录辅阻遏物，（Fjeld C等人，PNAS 2003;100：9202-7）; Oct-1，调节核组蛋白表达的转录因子，H2 B，（McKnight S，Cell 2003;114：150-2）。 Sir 2基因沉默子被认为在酵母热量限制的生命延长特性中起核心作用，C. elegans线虫，and in mammals哺乳动物as well. 在最近的工作中，与其他小组如NIH合作完成，我们已经表明成肌细胞中SIR 2的活性受游离胞质NAD+/NADH的变化控制（Fulco M等，Mol Cell 2003;12：51-62）。 目前认为，这种酶的活性是由烟酰胺的抑制作用控制的，Ki超过150微摩尔。我们正在继续研究不同饮食条件下Sirt 1含量的变化。目前尚不清楚控制如何与NAD+/NADH比率的变化相关。不言而喻，NAD+/NADH的变化是酒精摄入和酮症的特征，因此预计会改变上述转录因子的活性。 减少胰岛素/IGF信号传导允许生物体通过调节滞育状态在不适宜的条件下存活，由此生物体储存脂质，降低生育力，增加抗应激性，并具有增加的寿命。雷帕霉素靶点（TOR）对生长因子、氨基酸、氧张力和能量状态的变化做出反应;然而，目前尚不清楚TOR如何促进生理稳态和疾病状况。在这里，我们表明，降低果蝇TOR的功能会导致脂质储存和葡萄糖水平降低。重要的是，这种dTOR活性的降低阻断了与胰岛素应答转录因子dFOXO活性增加相关的胰岛素抵抗和代谢综合征表型。dTOR功能的降低还可以防止心脏功能的年龄依赖性下降，并延长寿命。因此，dTOR活性的调节可能是调节代谢和衰老的古老的“系统生物学”手段，具有重要的进化、生理和临床意义。 对本研究所方案的意义 肥胖和减少肥胖的方法是NIH路线图的主要目标。了解膳食碳水化合物在肥胖发生中的作用对于理解和纠正这个问题具有重要意义。我们在这一领域的出版物已被广泛接受，现在是新的莱宁格生物化学教科书中脂肪生成代谢控制的标准参考。此外，Sir 2活性的控制被认为是热量限制延长寿命特性的关键步骤。因此，由乙醇摄入引起的NAD+/NADH比率变化的能力对NIAAA以及白藜芦醇（红葡萄酒的类黄酮成分）的能力具有重要意义，白藜芦醇刺激Sir 2活性。

Summary: It is becoming increasingly clear that transcription of many of the proteins encoded in the genome is controlled by small metabolites whose concentrations vary depending upon environmental conditions. Thus consuming a diet rich in carbohydrate leads to the transcription of the genes encoding the major enzymes of glycolysis required to form the precursor acetyl CoA as well as the enzymes of the hexose monophosphate pathway producing the NADPH required for fat synthesis. The transcription factor is called ChREBP and responds to dietary carbohydrate. Combined with the effects of SREBP, the sterol responsive binding protein described by Brown and Goldstein, and responsive to insulin, these two transcription factors are of major importance in obesity, type II diabetes and vascular diseases. This elegant coordinated control of ChREBP is exerted by the simple hexose monophosphate pathway metabolite, xylulose 5-P (Veech RL, PNAC 2003;100:5578-80). Changes in the redox state of the pyridine nucleotides are the hallmark of changes in metabolic status and is known to be profoundly altered by alcohol ingestion. A number of transcription factors are now known to be controlled by the redox state of the pyridine nucleotides. These include: NPAS2, the so-called clock gene responsible for circadian rhythm (Rutter J et al, Science 2003;293:510-4) CtBP, the transcriptional co-repressor playing a role in development and transformation, (Fjeld C et al, PNAS 2003;100:9202-7) Oct-1, the transcription factor regulating expression of nuclear histones, H2B, (McKnight S, Cell 2003;114:150-2). Sir2, the gene silencer thought to play a central role in the life extending properties of caloric restriction in yeast, C. elegans, and in mammals as well. In recent work, done in colaboration with other groups as NIH, we have shown that the activity of SIR2 in myoblasts is controlled by changes in the free cytosolic NAD+/NADH (Fulco M et al, Mol Cell 2003;12:51-62). Currently it is thought that the activity of this enzyme is controlled by inhibition by nicotinamide with a Ki of over 150 micromolar. We are continuing the examination of changes induced in the amount of Sirt1 present in different dietary conditions. It is not now clear how control is related to change in the NAD+/NADH ratio. It goes without saying that changes in NAD+/NADH are characteristic of both alcohol ingestion and ketosis and would therefore be expected to alter the activity of the above listed transcription factors. Reducing insulin/IGF signaling allows for organismal survival during periods of inhospitable conditions by regulating the diapause state, whereby the organism stockpiles lipids, reduces fertility, increases stress resistance, and has an increased lifespan. The Target of Rapamycin (TOR) responds to changes in growth factors, amino acids, oxygen tension, and energy status; however, it is unclear how TOR contributes to physiological homeostasis and disease conditions. Here, we show that reducing the function of Drosophila TOR results in decreased lipid stores and glucose levels. Importantly, this reduction of dTOR activity blocks the insulin resistance and metabolic syndrome phenotypes associated with increased activity of the insulin responsive transcription factor, dFOXO. Reduction in dTOR function also protects against age-dependent decline in heart function and increases longevity. Thus, the regulation of dTOR activity may be an ancient "systems biological" means of regulating metabolism and senescence, that has important evolutionary, physiological, and clinical implications. SIGNIFICANCE TO THE PROGRAMS OF THIS INSTITUTE Obesity and methods to reduce it, is a major target of the NIH roadmap. Work in understanding the role of dietary carbohydrate in the genesis of obesity is of importance in understanding and correcting this problem. Our publication in this area has been well received and is now the standard reference on the metabolic control of lipogenesis in the new Lehningers textbook of biochemistry. In addition, the control of Sir2 activity is considered to be a key step in the life extending properties of caloric restriction. The ability of a changing NAD+/NADH ratio, which results from ethanol ingestion, is therefore of major significance to the NIAAA as well as the ability of resveratrol, a flavinoid component of red wine, which stimulates Sir2 activity.