Characterization of glucose transporter in cultured human retinal pigment epithelial cells: gene expression and effect of growth factors.

PURPOSE To investigate gene and protein expression of glucose transporter isoforms in cultured human retinal pigment epithelial cells. To investigate growth factor-dependent stimulation of glucose transport and the effect of growth factors on the gene and protein expression in retinal pigment epithelial cells. METHODS Glucose transport activity was analyzed by [3H]2-deoxyglucose uptake studies. Gene and protein expression of glucose transporter isoforms were analyzed by polymerase chain reaction, Northern blot analysis, and Western blot analysis. RESULTS Polymerase chain reaction, nucleotide sequencing, and Southern blot analyses revealed that the retinal pigment epithelial cells express GLUT-1, -3, and -5 genes. Northern and Western blot analysis detected only GLUT-1 transcripts and protein. A 24-hour exposure to fetal bovine serum (15%), basic fibroblast growth factor (50 ng/ml), platelet-derived growth factor (10 ng/ml), epidermal growth factor (50 ng/ml), and insulin-like growth factor-1 (50 ng/ml) significantly stimulated [3H]2-deoxyglucose uptake in cultured human retinal pigment epithelial cells. Western blot analysis showed that serum and platelet-derived growth factor induced an increase of GLUT-1 protein in the membrane preparation in the cells. Serum, fibroblast growth factor, platelet-derived growth factor, and insulin-like growth factor-1 did not increase GLUT-1 gene expression to an appreciable level, as shown by Northern blot analysis. CONCLUSION Cultured human retinal pigment epithelial cells dominantly express GLUT-1 gene and protein with minor expression of GLUT-3 and -5 genes. Fetal bovine serum, fibroblast growth factor, platelet-derived growth factor, epidermal growth factor, and insulin-like growth factor-1 significantly, although modestly, increase glucose transport activity of the cells.