Mechanisms of Regulation of GLUT4 Expression

描述（由申请方提供）：GLUT 4是负责哺乳动物组织中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，GLUT 4表达的2- 3倍增加已显示出显著增强葡萄糖摄取，纠正后者的糖尿病表型。因此，GLUT 4水平的调节是治疗干预胰岛素抵抗状态（包括糖尿病）的有吸引力的分子靶标。增强GLUT 4表达的直接方法是增加基因的转录速率。Glut 4基因表达在生理状态如胰岛素缺乏和运动中受到转录调节，并且很可能可以开发药理学干预以增强Glut 4基因转录，前提是开发用于快速筛选这些化合物的合适系统。为了达到这些目标，我们必须首先了解转录调控的基因的分子基础。使用转基因小鼠，我们已经表明，顺式元件调节人类p144启动子位于895 bp内位于转录起始位点的5'端。该区域包含两个主要的调节结构域，称为结构域I和MEF 2结构域。在转基因小鼠中，这些元件协同作用以支持报告基因在GLUT 4表达组织中的调节表达。MEF 2结构域结合肌细胞增强因子2（MEF 2）家族转录因子的亚型，而结构域I结合GEF（Glut 4增强因子），这是我们实验室最近克隆的一种新型转录激活因子。我们认为GLUT 4基因的组织特异性和激素代谢调控都是通过这两个调控域进行的。本提案的主要目标是了解组织特异性、激素和代谢调节的调节机制，以调节BMP 4基因的转录。为了实现这些目标，提出了以下目标：1）确定GEF的功能结构域; 2）检测培养细胞中GEF和MEF 2蛋白之间的相互作用; 3）确定GEF和MEF 2在胰岛素缺乏或胰岛素抵抗的转基因小鼠模型中调节GIut 4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.