Differential regulation of the GLUT-1 and GLUT-4 glucose transport systems by glucose and insulin in L6 muscle cells in culture.

The regulation by glucose and insulin of the muscle-specific facilitative glucose transport system GLUT-4 was investigated in L6 muscle cells in culture. Hexose transport activity, mRNA expression, and the subcellular localization of the GLUT-4 protein were analyzed. As observed previously (Walker, P. S., Ramlal, T., Sarabia, V., Koivisto, U.-M., Bilan, P. J., Pessin, J. E., and Klip, A. (1990) J. Biol. Chem. 265, 1516-1523), 24 h of glucose starvation and 24 h of insulin treatment each increase glucose transport activity severalfold. Here we report a differential regulation of the GLUT-4 and GLUT-1 transport systems under these conditions. (a) The level of GLUT-4 mRNA was not affected by glucose starvation and was diminished by prolonged (24 h) administration of insulin; in contrast, the level of GLUT-1 mRNA was elevated under both conditions. (b) Glucose starvation and prolonged insulin administration increased the amount of both GLUT-4 and GLUT-1 proteins in the plasma membrane. (c) In intracellular membranes, glucose starvation elevated, and prolonged insulin administration reduced, the GLUT-4 protein content. In contrast, the GLUT-1 protein content in these membranes decreased with glucose starvation and increased with insulin treatment. Glucose transport was rapidly curbed upon refeeding glucose to glucose-starved cells, with half-maximal reversal after 30 min and maximal reversal after 4 h. This was followed by a marked decrease in the levels of GLUT-1 mRNA without major changes in GLUT-4 mRNA. Neither 2-deoxy-D-glucose nor 3-O-methyl-D-glucose could substitute for D-glucose in these effects. It is proposed that glucose and insulin differentially regulate the two glucose transport systems in L6 muscle cells and that the rapid down-regulation of hexose transport activity by glucose is regulated by post-translational mechanisms.