EFFECTS OF 2-DEOXY-D-GLUCOSE ON THE FUNCTIONAL-STATE OF THE RAT MYOBLAST GLUT-1 TRANSPORTER

Based on the rationale that internalized 2-deoxy-D-glucose (dGlc) is t oxic to cells, glucose transport (GLUT) defective myoblast mutants hav e been isolated by their ability to grow in glucose-free medium contai ning dGlc. Recent studies revealed that the GLUT 1 transport process w as activated when GLUT 3(-) GLUT 4(-) mutants were grown in glucose-fr ee medium [1]. It was therefore puzzling why these GLUT3(-)GLUT4(-) my oblasts could survive in the presence of dGlc during the mutant select ion process. The present study revealed that GLUT 1 transport affinity in dGlc-grown cells was at least four folds lower than that in contro l cells. This loss of GLUT 1 transport activity was apparent only afte r exposure to the toxic sugar analogues for more than 10 hrs. This dal e-mediated effect was not due to competitive inhibition by the residua l dGlc carried over from growth medium, changes in glycolytic enzymes, nor accumulation of the negatively charged dGlc-6-PO4. In fact, GLUT 1 transcript level was elevated in dGlc-treated cells. Both immunoprec ipitation and immunoblotting studies indicated that the size of the GL UT 1 transporter in dGlc-grown myoblasts was reduced from 52 kDa to th at of the unglycosylated form (38 kDa). These findings suggest that gr owth in the presence of dGlc inhibits glycosylation of the GLUT 1 tran sporter, thus reducing its transport affinity. This inability of the G LUT 1 transporter to take up dGlc may therefore explain why GLUT 3(-)G LUT 4(-) mutants are able to grow in the presence of the toxic dGlc du ring the mutant selection procedure.