GENE-EXPRESSION OF GLUT3 AND GLUT1 GLUCOSE TRANSPORTERS IN HUMAN BRAIN-TUMORS

GLUT3 glucose transporter gene expression is confined to neurons, whil e GLUT1 gene expression is limited to endothelial cells in normal brai n. Thus far, neither of the GLUT genes has been shown to be consistent ly expressed in glial cells in adult brain in vivo under normal condit ions. However, GLUT gene expression may be aberrant in human brain gli al tumors. The present investigation shows that the GLUT1 and GLUT3 tr anscripts are differentially expressed in a series of 20 human brain t umors. The GLUT1/actin mRNA ratio increased in parallel to the astrocy toma grade, compared to a control human brain cortex, although no chan ge in this ratio was seen in 5 meningiomas. Immunoreactive GLUT1 prote in was not detectable in human brain tumors, including high-grade glio mas. Both 4.2 or 2.7 kb GLUT3/actin mRNA ratios showed a linear correl ation with the glioma grade (P < 0.025), and the GLUT3-immunoreactive protein was also expressed in high grade gliomas. These studies provid e evidence for induction of GLUT1 and GLUT3 gene expression in maligna nt glial cells, and the mRNA levels correlate with the biologic aggres siveness of the tumor. The detection of immunoreactive GLUT3, but not GLUT1, in the high grade gliomas suggest the GLUT3 isoform may be the predominant glucose transporter in highly malignant glial cells of hum an brain.