Hyperosmotic shock induces both activation and translocation of glucose transporters in mammalian cells

Abstract

The effect of osmotic stress on sugar transport was investigated in Clone 9 epithelial cells, which express the glucose uniporter GLUT1, and in 3T3-L1 adipocytes, which express both GLUT1 and GLUT4. An acute hyperosmotic shock increased the uptake of sugars in both cell types. In Clone 9 cells, this was followed by a regulatory volume increase (RVI) response. Stimulation of transport was rapid and reversible, with half-lives (t 1/2) for stimulation of 2-deoxy-D-glucose uptake of 5.6 +/- 0.9 (n=6) and 22.7 +/- 1.5 (n=4) min for Clone 9 cells and adipocytes respectively. The effect was dose dependent, reaching a maximum at 1.1 osM of 2.9 +/- 0.1-fold (n=3) for Clone 9 cells and 8.2 +/- 0.8-fold (n=3) for adipocytes. In the latter, this stimulation correlated with translocation of the glucose transporter isoform GLUT4 to the cell surface and was not significantly different from that elicited by 160 nM insulin (7.6 +/- 1.2-fold, n=3). The effect of osmotic shock was not, however, influenced by inhibitors of either phosphoinositide 3-kinase (PI 3-kinase) (wortmannin, 250 nM) or of p38 mitogen-activated protein kinase (p38 MAP kinase) (SB203580, 20 microM), which reportedly prevent GLUT4 translocation and/or activation by insulin respectively. These inhibitors also had no effect on the stimulation of transport by osmotic shock in Clone 9 cells. However, in contrast to adipocytes, the effect of osmotic shock on glucose transport in Clone 9 cells reflected primarily a change in the intrinsic activity of cell surface transporters and there was only a minor change in their subcellular distribution as assessed by cell immunostaining or no change as assessed by surface biotinylation. These results indicate that the response of cells to osmotic shock can involve changes both in transporter activity and location. The signal transduction pathways involved include neither PI 3-kinase nor the classical, osmotically-activated component, p38 MAP kinase.

δ‐Opioid receptors stimulate GLUT1‐mediated glucose uptake through Src‐ and IGF‐1 receptor‐dependent activation of PI3‐kinase signalling in CHO cells

“…Alternatively, d-opioid receptors might have stimulated glucose transport by increasing the catalytic activity of GLUT1 already present in the plasma membranes. This type of regulation has been proposed for other stimuli, such as inhibition of oxidative phosphorylation and osmotic stress, which have also been found to increase glucose transport without affecting membrane GLUT1 levels (Shetty et al, 1993;Koseoglu and Ismail Beigi, 1999;Barros et al, 2001). However, the precise mechanisms affecting GLUT1 intrinsic catalytic activity have not yet been elucidated and remain to be defined also for the regulation by d-opioid receptors.…”

Acute Modulation of Sugar Transport in Brain Capillary Endothelial Cell Cultures during Activation of the Metabolic Stress Pathway

“…GLUT1 recruitment to the plasma membrane occurs in response to acute metabolic stress in rat liver epithelial cells in vitro (25) and in response to growth factor stimulation in bovine retinal endothelial cells (26). We therefore set out to examine whether cultured brain microvessel endothelial cells respond to acute metabolic stress with increased sugar transport capacity and, if so, to test the hypothesis that increased V max for sugar uptake results from recruitment of intracellular GLUT1 to the plasma membrane.…”

Activators of AMP-activated protein kinase enhance GLUT4 translocation and its glucose transport activity in 3T3-L1 adipocytes

“…After entering into cells, AICAR is phosphorylated, and the reaction product 5-aminoimidazole-4-carboxamide ribonucleotide mimics the action of AMP to activate AMPK (6, 19). In the case of skeletal myocytes, activation of AMPK through physiological stimulation such as muscle contraction or by the pharmacological activator AICAR leads to a significant increase of glucose uptake mediated by the translocation of GLUT4 (10,20).It has been reported that GLUT4 translocation is accelerated by stimulation other than by insulin, such as hyperosmolar shock and bradykinin (2,4,15), but the precise mechanism has not yet been elucidated. In addition, although AMPK activation by AICAR in adipocytes has also been observed to increase glucose uptake under basal conditions (27), it seems to be still unclear whether or not its increase is mediated by GLUT4 translocation.…”

“…It has been reported that GLUT4 translocation is accelerated by stimulation other than by insulin, such as hyperosmolar shock and bradykinin (2,4,15), but the precise mechanism has not yet been elucidated. In addition, although AMPK activation by AICAR in adipocytes has also been observed to increase glucose uptake under basal conditions (27), it seems to be still unclear whether or not its increase is mediated by GLUT4 translocation.…”