Abstract
Most mammalian cells rely on an external supply of glucose for survival, proliferation, and function. Glucose enters cells through specific transporter molecules at the plasma membrane by a facilitative process that does not expend energy. Regulation of glucose transport into cells is thought to occur largely through transporter expression at the cell surface, but the extent to which the intrinsic properties of glucose transporters are regulated is at present controversial. Using a bone marrow-derived cell line that responds to the hemopoietic growth factor, interleukin-3 (IL-3), we investigated IL-3 regulation of glucose transport. IL-3 significantly increased 2-deoxyglucose (2-DOG) uptake within 1 h (26 +/- 8.0%, n = 11) with a maximum 73% increase after 6 h. Withdrawal of IL-3 resulted in decreased uptake within 1 h and this continued to decline to 43% of initial uptake by 16 h. To determine whether these changes in 2-DOG uptake were associated with corresponding changes in glucose transporter expression, subtype-specific antisera against Glut-1 and Glut-3 were used. Little change in membrane expression of these transporters was observed prior to 16 h. Fractionation of cell membranes on Nycodenz gradients showed that the majority of each transporter subtype was associated with the plasma membrane (63-93%) and that transporter distribution did not change markedly in response to addition or withdrawal of IL-3. These results demonstrate that IL-3 regulates glucose uptake by modulating the intrinsic transporting ability of glucose transporters. Decreased transporter affinity for 2-DOG and 3-O-methylglucose was observed following IL-3 withdrawal. Similar affinity changes were observed with 2-DOG following exposure of IL-3-stimulated cells to the protein kinase inhibitors, genistein and staurosporine. In contrast, the tyrosine phosphatase inhibitor, vanadate, acted like IL-3 to increase transporter affinity for glucose. Together these results demonstrate that IL-3 acts to maintain the intrinsic transport properties of glucose transporters without markedly affecting their expression or translocation.
Highlights
The energy requirements of most mammalian cells are met through a continuous supply of glucose which circulates in the blood or is supplied in culture medium
Changes in transporter expression may contribute to this effect. These results provide strong independent evidence that IL-3 acts through its receptor to modulate the intrinsic transport function of glucose transporters on hemopoietic cells, and raise the possibility that cell survival, growth, proliferation, and function may be regulated by growth factors and cytokines at the level of glucose transport in addition to other levels of metabolic and cell cycle control
In this study we show that treatment of serum-starved 32D cells with IL-3 promotes 2-DOG uptake by a mechanism that cannot be fully explained in terms of increased glucose transporter expression or translocation of stored transporters to the plasma membrane
Summary
Through a continuous supply of glucose which circulates in the blood or is supplied in culture medium. IL-3 was shown to maintain the affinity of transporters for glucose without altering Vmax, whereas IL-3 withdrawal resulted in an increase in Km and these changes were associated with protein phosphorylation [24] In these studies, both Ba/F3 and 32D cells are presumed to express predominantly Glut-1 as the major transporter subtype as has been shown for other cultured hemopoietic cells. Both Ba/F3 and 32D cells are presumed to express predominantly Glut-1 as the major transporter subtype as has been shown for other cultured hemopoietic cells These studies suggest that growth factors may act to regulate glucose transport in hemopoietic cells by modulating the activation state of glucose transporters. These results provide strong independent evidence that IL-3 acts through its receptor to modulate the intrinsic transport function of glucose transporters on hemopoietic cells, and raise the possibility that cell survival, growth, proliferation, and function may be regulated by growth factors and cytokines at the level of glucose transport in addition to other levels of metabolic and cell cycle control
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