Mechanisms of Regulation of GLUT4 Expression

描述(申请人提供)：GLUT4是哺乳动物组织中负责胰岛素介导的葡萄糖摄取的主要葡萄糖转运蛋白。它是在肌肉和脂肪组织中表达的主要促进性葡萄糖转运蛋白亚型。在正常和糖尿病小鼠模型中，GLUT4表达仅增加2到3倍，就能显著增加葡萄糖的摄取，纠正后者的糖尿病表型。因此，GLUT4水平的调节是治疗胰岛素抵抗状态(包括糖尿病)的一个有吸引力的分子靶点。增强GLUT4表达的一种直接方法是提高基因的转录速率。在胰岛素缺乏和运动等生理状态下，GLUT4基因的表达受到转录调控，如果开发出一种合适的系统来快速筛选这些化合物，就有可能开发一种药物干预来增强GLUT4基因的转录。为了达到这些目标，我们必须首先了解GLUT4基因转录调控的分子基础。利用转基因小鼠，我们已经证明了调控人GLUT4启动子的顺式元件位于转录起始点5‘端的895bp内。该区域包含两个主要的监管结构域，称为结构域I和MEF2结构域。在转基因小鼠中，这些元件协同作用，支持报告基因在GLUT4表达组织中的受调控表达。MEF2结构域与心肌细胞增强因子2(MEF2)家族的异构体结合，而结构域I结合本实验室最近克隆的一种新的转录激活因子--GLUT4增强因子(GLUT4 Enhenger Factor)。我们认为GLUT4基因的组织特异性以及激素和代谢调节都是通过这两个调节域进行的。这项建议的主要目的是了解GLUT4基因转录的组织特异性、激素和代谢调节的调节机制。为了实现这些目标，人们提出了以下目标：1)确定全球环境基金的功能结构域；2)在培养细胞中研究全球环境基金和MEF2蛋白之间的相互作用；以及3)在胰岛素缺乏或胰岛素抵抗的转基因小鼠模型中，确定全球环境基金和MEF2调节GIut4基因调控的机制。

DESCRIPTION (provided by applicant): GLUT4 is the primary glucose transport protein responsible for insulin-mediated glucose uptake in mammalian tissues. It is the predominant facilitative glucose transporter isoform expressed in muscle and in adipose tissue. As little as a 2- to 3-fold increase in GLUT4 expression has been shown to markedly enhance glucose uptake in both normal and diabetic mouse models, correcting the diabetic phenotype in the latter. Modulation of GLUT4 levels is therefore an attractive molecular target for therapeutic intervention insulin-resistant states, including diabetes mellitus. A straightforward approach to enhance GLUT4 expression is to increase the transcription rate of the gene. Glut4 gene expression is transcriptionally regulated in physiologic states such insulin-deficiency and exercise, and it is likely that a pharmacological intervention can be developed to enhance glut4 gene transcription provided that a suitable system for rapid screening of these compounds is developed. To reach these goals, we must first understand the molecular basis for transcriptional regulation of the glut4 gene. Using transgenic mice, we have shown that cis-elements regulating the human glut4 promoter are located within 895 bp located immediately 5' of the transcription initiation site. This region contains two major regulatory domains, referred to as Domain I and the MEF2 domain. In transgenic mice, these elements function cooperatively to support regulated expression of a reporter gene in GLUT4-expressing tissues. The MEF2 domain binds isoforms of the Myocyte Enhancer Factor 2 (MEF2) family of transcription factors, while Domain I binds GEF (Glut4 Enhancer Factor), a novel activator of transcription recently cloned in our laboratory. We propose that both the tissue-specific and the hormonal and metabolic regulation of the GLUT4 gene are carried out through these 2 regulatory domains. The primary goal of this proposal to understand the mechanisms of regulation of tissue-specific, hormonal and metabolic regulation of glut4 gene transcription. To achieve these goals, the following aims are proposed: 1) to define the functional domains of GEF; 2) examine the interaction between GEF and MEF2 proteins in cultured cells; and 3) to determine the mechanisms by which GEF and MEF2 regulate GIut4 gene regulation in transgenic mouse models of insulin deficiency or insulin resistance.