Hormonal/metabolic regulation of the human GLUT4/muscle-fat facilitative glucose transporter gene in transgenic mice.

To examine the hormonal/metabolic as well as tissue-specific expression of the GLUT4/muscle-fat facilitative glucose transporter gene, we have generated several transgenic mouse lines expressing a human GLUT4 mini-gene which extends 5.3 kilobases (kb) upstream of transcription start and terminates within exon 10. This construct (hGLUT4-11.5) was expressed in a tissue-specific pattern identical to the endogenous mouse GLUT4 gene. The transcription initiation sites of the transgenic construct were similar to the GLUT4 gene expressed in human tissues. To investigate the hormonal/metabolic-dependent regulation of GLUT4, the transgenic animals were made insulin-deficient by streptozotocin (STZ) treatment. In these animals, STZ-induced diabetes resulted in a parallel decrease in endogenous mouse GLUT4 mRNA and the transgenic human GLUT4 mRNA in white adipose tissue, brown adipose tissue, and cardiac muscle. Similarly, insulin treatment of the STZ-diabetic animals restored both the endogenous mouse and transgenic human GLUT4 mRNA levels. To further define cis-regulatory regions responsible for this hormonal/metabolic regulation, the same analysis was performed on transgenic animals which carry 2.4 kb of the human GLUT4 5'-flanking region fused to a CAT reporter gene (hGLUT4[2.4]-CAT). This reporter construct responded similarly to the human GLUT4 mini-gene demonstrating that the element(s) controlling hormonal/metabolic regulation and tissue specificity all reside exclusively within 2.4 kb of the transcriptional initiation site.