Carbohydrate Regulation of Hepatic Gene Expression

碳水化合物对肝基因表达的调节

• 批准号: 6837591
• 负责人: KOSAKU UYEDA
• 金额: $ 26.65万
• 依托单位: UT SOUTHWESTERN MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6837591
• 关键词: DNA binding protein; biological signal transduction; carbohydrate metabolism; enzyme activity; gene deletion mutation; gene expression; gene targeting; genetic transcription; genetically modified animals; glucose; glucose metabolism; laboratory mouse; laboratory rat; lipid biosynthesis; liver; mass spectrometry; molecular cloning; phosphoprotein phosphatase; phosphorylation; protein transport; steroid biosynthesis; transcription factor

DESCRIPTION (provided by applicant): Evolutional pressure has favored the ability to efficiently store nutrients as fat during abundant food supply as a safeguard against occasional famine. Due to the abundance of the food supply and dramatic changes in modern lifestyle, these genes may now contribute to major epidemic of obesity, especially in the US where over a half of population is overweight. This is predicted to be a major public health problem in the near future. The liver is the principal organ responsible for the conversion of excess dietary carbohydrate into triglycerides. Ingestion of high carbohydrate diet induces transcription of more than 15 genes involved in the metabolic conversion of glucose to storage fat. Until recently, it was thought that insulin and glucagons regulate the transcription of these genes. However, it has been shown that nutrients themselves play an important role in the regulation of transcription independent of insulin. The mechanism by which excess carbohydrate generates a signal to induce the transcription of lipogenesis enzyme gene is not known. We have identified and characterized a new transcription factor termed "Carbohydrate response element binding protein, ChREBP" which responds to high glucose and induce the liver pyruvate kinase (LPK) gene and lipogenic genes. Our goal is to understand how excess glucose, independent of insulin, activates the transcription. We have shown that glucose and cAMP are adversary in the lipognesis, cAMP and AMP inhibit ChREBP by phosphorylation at the specific sites which are mediated by protein kinase A and AMPprotein kinase. Glucose reverses the inhibition and activates ChREBP to favor triglycerides synthesis. We propose that glucose activates the transcription of these genes by dephosphorylation catalyzed by a specific protein phosphatase that is activated by a glucose-signaling compound. Our specific objectives for the current application are: (1) identify the specific protein phosphatases (PPase) in cytosol and in nucleus that are responsible for the nuclear import and the DNA binding activity of ChREBP. (2) Detect and identify a glucose signaling compound which activates the PPases and the transcription. (3) Investigate the mechanism of import and export of ChREBP. The important question is whether the import and export of ChREBP are regulated only by phosphorylation and dephosphorylation. Determine the genes altered by the ChREBP gene knockout and characterize the resulting physiological and biochemical changes in these mice in order to understand the roles of ChREBP in vivo. Produce other crosses with ChREBP-/- such as ob/ob mice by breeding our knockout mice with the ob/ob animals for potential elimination of obesity. Other possibility is to produce a combination of ChREBP-/- and SREBP-/- that inhibit the major portion of lipogenesis in liver.

描述（由申请人提供）：进化的压力有利于在食物供应充足时有效地将营养素储存为脂肪的能力，以防止偶尔的饥荒。由于食物供应的丰富和现代生活方式的巨大变化，这些基因现在可能导致肥胖症的主要流行，特别是在美国，超过一半的人口超重。预计在不久的将来，这将是一个重大的公共卫生问题。肝脏是负责将过量的膳食碳水化合物转化为甘油三酯的主要器官。摄入高碳水化合物饮食诱导超过15个基因的转录，这些基因参与葡萄糖向储存脂肪的代谢转化。直到最近，人们才认为胰岛素和胰高血糖素调节这些基因的转录。然而，它已被证明，营养物质本身发挥重要作用，在转录的调节独立于胰岛素。过量碳水化合物产生信号以诱导脂肪生成酶基因转录的机制尚不清楚。 我们已经确定并表征了一种新的转录因子，称为“碳水化合物反应元件结合蛋白，ChREBP”，其响应于高糖并诱导肝脏丙酮酸激酶（LPK）基因和脂肪生成基因。我们的目标是了解多余的葡萄糖如何独立于胰岛素激活转录。我们发现葡萄糖和cAMP在脂肪生成中是敌对的，cAMP和AMP通过蛋白激酶A和AMP蛋白激酶介导的特异性位点磷酸化抑制ChREBP。葡萄糖逆转了这种抑制作用并激活ChREBP以促进甘油三酯合成。我们认为，葡萄糖激活这些基因的转录通过去磷酸化催化的一种特定的蛋白磷酸酶，被激活的葡萄糖信号化合物。 我们当前应用程序的具体目标是： (1)鉴定细胞质和细胞核中负责ChREBP的核输入和DNA结合活性的特异性蛋白磷酸酶（PPase）。 (2)检测并鉴定激活PPases和转录的葡萄糖信号化合物。 (3)探讨ChREBP的输入输出机制。重要的问题是ChREBP的输入和输出是否仅受磷酸化和去磷酸化的调节。 确定ChREBP基因敲除改变的基因，并表征这些小鼠中产生的生理和生化变化，以了解ChREBP在体内的作用。通过将我们的基因敲除小鼠与ob/ob动物交配，产生其他与ChREBP-/-杂交的小鼠，如ob/ob小鼠，以潜在消除肥胖。其他可能性是产生ChREBP-/-和SREBP-/-的组合，其抑制肝脏中脂肪生成的主要部分。