Localization of Exercise- and Denervation-Responsive Elements in the Mouse GLUT4 Gene

Abstract

Exercise training increases the expression of GLUT4 in skeletal muscle. Previous studies demonstrated that the exercise-responsive element(s) of the murine GLUT4 gene are located between bases −1001 and −442 relative to the transcription start site. To further characterize the regulatory elements in the GLUT4 gene, the regulation of GLUT4 minigenes containing −701, −551, −442, or −423 bp of the 5′-flanking region was studied in transgenic mice. All minigenes studied showed significant expression in skeletal muscle and heart, including the −423 GLUT4 minigene that lacked the myocyte enhancer factor 2 (MEF2)-binding domain (-CTAAAAATAG-) located between bases −437 and −428. The −701- and −551-bp constructs were expressed in brown adipose tissues while the −442 and −423 constructs were not. In skeletal muscle, either swimming or treadmill running up-regulated GLUT4 minigene mRNA levels in −701 and −551 transgenic mice, but not in the −442 and −423 transgenic mice. Denervation of the gastrocnemius muscle by sectioning of the sciatic nerve down-regulated minigene and endogenous GLUT4 mRNAs in all −701, −551, −442, and −423 transgenic mice. These data indicate that exercise-responsive element(s) and brown adipocyte specific element(s) are located within 109 bp between bases −551 and −442 of the GLUT4 gene, but that the cis-element for denervation-induced down-regulation of the GLUT4 gene is located downstream of base −423. Finally, the MEF2 binding site between bases −437 and −428 is not necessary for expression of GLUT4 in skeletal muscles and heart; the cis-element mediating this effect is also located downstream of base −423.