CHARACTERIZATION OF THE AVIAN GLUT1 GLUCOSE-TRANSPORTER - DIFFERENTIAL REGULATION OF GLUT1 AND GLUT3 IN CHICKEN-EMBRYO FIBROBLASTS

Vertebrate cells that are transformed by oncogenes such as v-src or ar e stimulated by mitogens have increased rates of glucose uptake. In ro dent cells, the mechanisms whereby glucose transport is up-regulated a re well understood. Stimulation of glucose transport involves an eleva tion in mRNA encoding the GLUT1 glucose transporter that is controlled at the levels of both transcription and mRNA stability. Cloning and s equencing of chicken GLUT1 cDNA showed that it shares 95% amino acid s equence similarity to mammalian GLUT1s. Nevertheless, unlike mammalian GLUT1 mRNA, it was not induced by v-src, serum addition, or treatment with the tumor promoter 12-O-tetradecanoylphorbol 13-acetate in chick en embryo fibroblasts. Rather, the induction of glucose transport in c hicken embryo fibroblasts by v-src, serum, and 12-O-tetradecanoylphorb ol 13-acetate was associated with induction of GLUT3 mRNA level and GL UT3 transcription. Rat fibroblasts were also found to express both GLU T1 and GLUT3 isoforms, but v-src induced GLUT1 and not GLUT3. This sug gests that animal cells require both a basal and an upregulatable gluc ose transporter and that these functions have been subsumed by differe nt GLUT isoforms in avian and mammalian cells.