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 toxic to cells, glucose transport (GLUT) defective myoblast mutants have been isolated by their ability to grow in glucose‐free medium containing dGlc. Recent studies revealed that the GLUT 1 transport process was activated when GLUT 3‐ GLUT 4‐ mutants were grown in glucose‐free medium [1]. It was therefore puzzling why these GLUT3‐ GLUT4‐ myoblasts could survive in the presence of dGlc during the mutant selection process. The present study revealed that GLUT 1 transport affinity in dGlc‐grown cells was at least four folds lower than that in control cells. This loss of GLUT 1 transport activity was apparent only after exposure to the toxic sugar analogues for more than 10 hrs. This dGlc‐mediated effect was not due to competitive inhibition by the residual 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 immunoprecipitation and immunoblotting studies indicated that the size of the GLUT 1 transporter in dGlc‐grown myoblasts was reduced from 52 kDa to that of the unglycosylated form (38 kDa). These findings suggest that growth in the presence of dGlc inhibits glycosylation of the GLUT 1 transporter, thus reducing its transport affinity. This inability of the GLUT 1 transporter to take up dGlc may therefore explain why GLUT 3‐ GLUT 4‐ mutants are able to grow in the presence of the toxic dGlc during the mutant selection procedure.