Nutritional and Hormonal Regulation of Hepatic Genes

哺乳动物调节其遗传信息的表达以响应营养和代谢信号；然而，目前对这些过程中涉及的分子机制知之甚少。这项建议的长期目标是了解代谢调节的一个系统：在肝细胞中发生的对产脂酶基因的转录诱导，以响应葡萄糖代谢的增加。超过15种参与甘油三酯形成过程的酶和蛋白质被诱导，以响应肝细胞中葡萄糖的升高。我们以前已经在这些基因的5‘-侧翼区定义了一个特定的保守调控序列，这是这种调控所必需的和充分的，并将该序列命名为碳水化合物反应元件(CHORE)。最近，我们通过凝胶迁移率改变分析从肝脏中检测到一种核蛋白(S)，它与家务活形成复合体。这种复合体在各种功能活跃的琐事中被检测到，但在失去支持葡萄糖反应能力的突变体中检测不到。我们推测该蛋白(S)是肝细胞中一种新的葡萄糖信号通路的终末靶点，我们将其命名为糖类反应因子。为了揭示这一新的途径，我们将首先分析新的ChoRF复合体的分子性质，该复合体与造脂酶基因的葡萄糖调节序列结合。初步证据表明，碱性/螺旋-环-螺旋/PAS转录因子家族的成员参与了转录调控。我们将纯化和克隆候选因子，并评估它们在ChoRF复合体的形成和葡萄糖对成脂基因表达的调节中的作用。我们还将评估ChoRF和SREBP在介导肝细胞中葡萄糖和胰岛素的作用中的各自作用。SREBP是参与脂肪生成控制的第二个转录因子。这两个信号共同协调动物对碳水化合物饮食的反应。最后，我们将探讨肝细胞糖代谢改变时调节ChoRF的分子机制。这些研究应该能让我们破译肝细胞可以“感觉”葡萄糖代谢增加并通过改变其转录程序做出反应的信号过程。

Mammals regulate the expression of their genetic information in response to nutritional and metabolic signals; however, little is currently known regarding the molecular mechanisms involved in these processes. The long range goal of this proposal is to understand one system of metabolic regulation: the transcriptional induction of lipogenic enzyme genes that occurs in the hepatocyte in response to increased glucose metabolism. Over fifteen enzymes and proteins involved in the process of triglyceride formation are induced in response to elevated glucose in the hepatocyte. We have previously defined a specific conserved regulatory sequence in the 5'- flanking region of several of these genes that is necessary and sufficient for this regulation and designated this sequence the carbohydrate response element (ChoRE). Recently, we have detected by electrophoretic mobility shift assay a nuclear protein(s) from liver that forms a complex with the ChoRE. This complex is detected with a variety of functionally active ChoREs, but not with mutants that have lost the ability to support the glucose response. We postulate that this protein(s), which we will designate as ChoRF for carbohydrate responsive factor, is the end-target of a novel glucose-signaling pathway in the hepatocyte. To unravel this novel pathway, we will first analyze the molecular nature of the novel ChoRF complex that binds to glucose regulatory sequences of the lipogenic enzyme genes. Preliminary evidence suggests that members of the basic/helix- loop-helix/PAS family of transcription factors are involved in regulation. We will purify and clone candidate factors and evaluate their role in the formation of the ChoRF complex and glucose regulation of lipogenic gene expression. We will also evaluate the respective roles of ChoRF and SREBP, a second transcription factor involved in lipogenic control, in mediating the actions of glucose and insulin in the hepatocyte. These two signals work together to coordinate the response of the animal to carbohydrate diet. Finally, we will explore the molecular mechanism responsible for ChoRF regulation in response to altered glucose metabolism in the hepatocyte. These studies should permit us to decipher the signaling process by which hepatocytes can 'sense' increased glucose metabolism and respond by changing its transcriptional program.