Stabilization of glucose transporter mRNA by insulin/IGF-1 and glucose deprivation

Chronic exposure of L6 myocytes to insulin/IGF-1 or glucose deprivation results in an increase in the level of brain-type glucose transporter (GLUT1) mRNA. We have investigated the effects of insulin and glucose deprivation on GLUT1 mRNA stability. The half-life of GLUT1 mRNA in control cells was 2-2.5 h. Insulin increased GLUT1 mRNA levels by 5- to 10-fold, and GLUT1 mRNA half-life and transcription by 2-fold. Glucose deprivation increased GLUT1 mRNA level by 2- to 4-fold and half-life by 2-fold. The effects of insulin and glucose deprivation on GLUT1 mRNA stability were additive. Cycloheximide partially blocked the induction of GLUT1 mRNA by insulin but not by glucose deprivation. GLUT1 mRNA was decreased to basal levels within 12h following insulin withdrawal or glucose refeeding. Cycloheximide did not block this de-induction, suggesting that insulin and glucose deprivation do not increase GLUT1 mRNA expression by inhibiting the synthesis of ribonucleases. These findings indicate that insulin/IGF-1 increases both GLUT1 mRNA stability and transcription by both protein synthesis-dependent and independent mechanisms, whereas glucose deprivation enhances GLUT1 mRNA stability by mechanisms independent of de novo protein synthesis.