Ikemoto S, Thompson K S, Itakura H, Lane M D, Ezaki O
Division of Clinical Nutrition, National Institute of Health and Nutrition, Tokyo, Japan.
Proc Natl Acad Sci U S A. 1995 Jan 31;92(3):865-9. doi: 10.1073/pnas.92.3.865.
The effects of a GLUT4 mini-transgene (containing 7 kb of 5' flanking and 1 kb of 3' flanking sequence and all exons and introns of the GLUT4 gene as well as a small foreign DNA tag) and of exercise training on expression of GLUT4 and glycemic control in mice were investigated. Transgenic mice harboring the minigene expressed < or = 2-fold the normal level of GLUT4 mRNA and protein in skeletal (gastrocnemius) muscle and adipose tissue. This modest tissue-specific increase in GLUT4 expression led to an unexpectedly rapid blood glucose clearance rate following oral glucose administration. In nontransgenic animals exercise caused a 1.5-fold increase in expression of GLUT4 mRNA and protein as well as a significant improvement of glycemic control. In transgenic animals harboring the minigene exercise increased expression of GLUT4 mRNA and protein derived from the minigene and endogenous gene and led to a further improvement of glycemic control. These findings indicate that the cis-regulatory element(s) controlling exercise-induced expression of the GLUT4 gene is located within the nucleotide sequence encompassed by the GLUT4 minigene. The fact that glycemic control is markedly improved by a relatively low level of expression of GLUT4 caused by the transfected minigene and is further enhanced by exercise in transgenic animals demonstrates that GLUT4 plays a pivotal role in glucose homeostasis in vivo. Of the effectors--i.e., cAMP, insulin, and arachidonic acid--known to down-regulate expression of GLUT4 by 3T3-L1 adipocytes in culture, only the decline in circulating arachidonate level in vivo correlated with up-regulation of GLUT4 caused by exercise.
研究了GLUT4微型转基因（包含7 kb的5'侧翼和1 kb的3'侧翼序列以及GLUT4基因的所有外显子和内含子以及一个小的外源DNA标签）和运动训练对小鼠GLUT4表达和血糖控制的影响。携带该微型基因的转基因小鼠在骨骼肌（腓肠肌）和脂肪组织中表达的GLUT4 mRNA和蛋白质水平比正常水平高不到2倍。GLUT4表达的这种适度的组织特异性增加导致口服葡萄糖后血糖清除率意外地快速提高。在非转基因动物中，运动使GLUT4 mRNA和蛋白质的表达增加了1.5倍，同时血糖控制也有显著改善。在携带微型基因的转基因动物中，运动增加了源自微型基因和内源基因的GLUT4 mRNA和蛋白质的表达，并进一步改善了血糖控制。这些发现表明，控制GLUT4基因运动诱导表达的顺式调节元件位于GLUT4微型基因所包含的核苷酸序列内。转染的微型基因导致的相对较低水平的GLUT4表达能显著改善血糖控制，并且在转基因动物中运动可进一步增强这种改善，这一事实表明GLUT4在体内葡萄糖稳态中起关键作用。在已知能下调培养的3T3-L1脂肪细胞中GLUT4表达的效应物（即cAMP、胰岛素和花生四烯酸）中，只有体内循环花生四烯酸水平的下降与运动引起的GLUT4上调相关。
