The GLUT4 glucose transporter is the major isoform expressed in muscle and adipose tissue, the two tissue types primarily responsible for the maintenance of whole body glucose homeostasis. The GLUT4 isoform plays a key role in this process by facilitating the uptake of glucose in these tissues in response to insulin stimulation. Regulation of GLUT4 glucose transporter functions occurs at multiple levels, several of which are associated with insulin resistance and diabetes. For example, multiple studies have documented that GLUT4 expression is decreased in states of insulin-deficient diabetes and fasting. Further patient studies have suggested a correlation in adipose tissue expression of GLUT4 with NIDDM. More recently, both the tissue-specific pattern as well as the hormonal/metabolic regulation of GLUT4 expression have been shown to occur at the transcriptional level. Based upon the central role of the GLUT4 gene in the pathophysiology associated with diabetes, we have proposed a series of studies to address the tissue-specific and hormonal/metabolic regulation of this gene. The basic molecular events involved in GLUT4 gene regulation are clearly important issues which are necessary for our understanding of adipose and muscle-specific gene regulation as well as for the control of glucose homeostasis, metabolism and energy production. We therefore plan to continue our studies delineating the molecular mechanisms responsible for the hormonal/metabolic and tissue-specific regulation of the insulin- responsive GLUT4 gene. This will be accomplished by detailed analysis of GLUT4 promoter function and identification of cis-DNA regulatory elements using several complementary approaches. These studies will then allow for the characterization and isolation of tissue-specific DNA binding factors responsible for the hormonal/metabolic (insulin-deficient diabetes and fasting/refeeding states) and tissue-specific (white adipose, brown adipose, cardiac and skeletal muscle) regulation of this gene.
