Direct inhibition of the hexose transporter GLUT1 by tyrosine kinase inhibitors

The facilitative hexose transporter GLUT1 is a multifunctional protein that transports hexoses and dehydroascorbic acid, the oxidized form of vitamin C, and interacts with several molecules structurally unrelated to the trans ported substrates. Here we analyzed in detail the interaction of GLUT1 with a group of tyrosine kinase inhibitors that include natural products of the family of flavones and isoflavones and synthetic compounds such as the tyr phostins. These compounds inhibited, in a dose-dependent manner, the transp ort of hexoses and dehydroascorbic acid in human myeloid HL-60 cells, in tr ansfected Chinese hamster ovary cells overexpressing GLUT1, and in normal h uman erythrocytes, and blocked the glucose-displaceable binding of cytochal asin B to GLUT1 in erythrocyte ghosts. Kinetic analysis of transport data i ndicated that only tyrosine kinase inhibitors with specificity for ATP bind ing sites inhibited the transport activity of GLUT1 in a competitive manner . In contrast, those inhibitors that are competitive with tyrosine but not with ATP failed to inhibit hexose uptake or did so in a noncompetitive mann er. These results, together with recent evidence demonstrating that GLUT1 i s a nucleotide binding protein, support the concept that the inhibitory eff ect on transport is related to the direct interaction of the inhibitors wit h GLUT1. We conclude that predicted nucleotide-binding motifs present in GL UT1 are important for the interaction of the tyrosine kinase inhibitors wit h the transporter and may participate directly in the binding transport of substrates by GLUT1.