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，目前知之甚少，关于这些过程中涉及的分子机制。 这个提议的长期目标是了解一个代谢调节系统：在肝细胞中发生的脂肪生成酶基因的转录诱导，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响应于肝细胞中升高的葡萄糖而被诱导。 我们先前已经在这些基因中的几个的5 '-侧翼区域中定义了一个特定的保守调节序列，该序列对于这种调节是必要的和足够的，并将该序列命名为碳水化合物反应元件（ChoRE）。 最近，我们通过电泳迁移率变动分析检测到来自肝脏的与ChoRE形成复合物的核蛋白。 该复合物被检测到具有多种功能活性的ChoRE，但不具有已经失去支持葡萄糖反应的能力的突变体。 我们假设这种蛋白质（我们将其命名为碳水化合物响应因子的ChoRF）是肝细胞中新型葡萄糖信号传导途径的终末靶标。 为了解开这一新的途径，我们将首先分析新的ChoRF复合物的分子性质，该复合物与脂肪生成酶基因的葡萄糖调节序列结合。初步证据表明，转录因子的基本/螺旋-环-螺旋/PAS家族的成员参与调节。 我们将纯化和克隆候选因子，并评估它们在ChoRF复合物形成和葡萄糖调节脂肪生成基因表达中的作用。 我们还将评估ChoRF和SREBP（参与脂肪生成控制的第二种转录因子）在介导葡萄糖和胰岛素在肝细胞中的作用方面的各自作用。 这两种信号共同作用，协调动物对碳水化合物饮食的反应。 最后，我们将探讨负责ChoRF调节的分子机制，以响应肝细胞中葡萄糖代谢的改变。 这些研究应该使我们能够破译信号传导过程，肝细胞可以“感知”葡萄糖代谢增加，并通过改变其转录程序作出反应。

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.