ABNORMAL FACILITATIVE GLUCOSE TRANSPORTER GENE-EXPRESSION IN HUMAN ISLET-CELL TUMORS

Our previous studies have shown that increased expression of GLUT1/ery throcyte and GLUT3/brain type glucose transporter genes in human tumor s is associated with cellular transformation. We have now determined t he levels of messenger RNAs (mRNAs) encoding these two glucose transpo rter isoforms as well as that of GLUT2/liver isoform in insulin-, gluc agon-, and gastrin-secreting islet cell tumors. Northern blot analysis and reverse transcriptase-polymerase chain reaction revealed the pres ence of GLUT1 and GLUT3 mRNA in all human islet cell tumors and normal islets examined. In contrast, GLUT2 mRNA, which is present at high le vels in normal islets, was not detected in insulinomas or other types of islet cell tumors. These results imply that GLUT1 and GLUT3 are pri marily responsible for glucose uptake by these tumors.