THE HEMATOPOIETIC GROWTH-FACTOR, INTERLEUKIN-3, PROMOTES GLUCOSE-TRANSPORT BY INCREASING THE SPECIFIC ACTIVITY AND MAINTAINING THE AFFINITYFOR GLUCOSE OF PLASMA-MEMBRANE GLUCOSE TRANSPORTERS

Most mammalian cells rely on an external supply of glucose for surviva l, proliferation, and function, Glucose enters cells through specific transporter molecules at tile plasma membrane by a facilitative proces s that does not expend energy, Regulation of glucose transport into ce lls is thought to occur largely through transporter expression at the cell surface, but the extent to which the intrinsic properties of gluc ose transporters are regulated is at present controversial, Using a bo ne marrow-derived cell line that responds to the hemopoietic growth fa ctor, 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 rand thi s continued to decline to 43% of initial uptake by 16 h, To determine whether these changes in 2-DOG uptake were associated with correspondi ng changes in glucose transporter expression, subtype-specific antiser a against. Glut-1 and Glut-3 were used, Little change in membrane expr ession of these transporters was observed prior to 16 h, Fractionation of cell membranes on Nycodenz gradients showed that the majority of e ach transporter subtype was associated with the plasma membrane (63-93 %) and that transporter distribution did not change markedly in respon se to addition or withdrawal of IL-3, These results demonstrate that I L-3 regulates glucose uptake by modulating the: intrinsic transporting ability of glucose transporters, Decreased transporter affinity for 2 -DOG and 3-8-methylglucose was observed following IL-3 withdrawal, Sim ilar affinity changes were observed with 2-DOG following exposure of I L-3-stimulated cells to the protein kinase inhibitors, genistein and s taurosporine, In contrast, the tyrosine phosphatase inhibitor, vanadat e, acted hire IL-3 to increase transporter affinity for glucose, Toget her these results demonstrate that IL-3 acts to maintain the intrinsic transport properties of glucose transporters without markedly affecti ng their expression or translocation.