Expression of Facilitative Glucose Transporter Isoforms in Human Brain Tumors

The expression of facilitative glucose transporter (GLUT) isoforms in human astrocytic tumors was examined. Reverse transcriptase-polymerase chain reaction of a surgically biopsied glioblastoma was carried out using the degenerative oligonucleotide primers corresponding to the sequences of the human facilitative glucose transporter family, and polymerase chain reaction products were hybridized with human GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5 cDNA probes. The results showed that a biopsied glioblastoma expressed GLUT1, GLUT3, and GLUT4 glucose transporter genes. Northern blot analysis of total RNA (10 micrograms) from a biopsied glioblastoma showed the transcripts of only GLUT1 and GLUT3, suggesting that the expression of insulin-responsive glucose transporter GLUT4 mRNA is relatively low. Immunoblot analysis of biopsied glioblastoma tissues by polyclonal antibodies against the C-terminal synthetic peptides of GLUT1, GLUT3, and GLUT4 showed a single band of each polypeptide. However, elevated expression of GLUT1 and GLUT3 glucose transporters was not observed in the glioblastoma. Astrocytic tumor tissues (n = 14) were also examined immunohistochemically. Reactive products for GLUT1 were observed in the luminal surface of capillaries in all cases, whereas tumor cells were positive for GLUT1 in only two of 14 cases. GLUT3 was positive in astrocytic tumor cells in all cases. Three of 14 cases expressed the GLUT4 protein, which was localized in the cytoplasm of tumor cells. These results suggest that the facilitative glucose transport may be altered in astrocytic tumor cells and thus display a significant change in glucose metabolism.