Enhancive effects of D-glucose and its analogs on expression of d-glucose-unrelated transgenes in mammalian cells.

We studied the effects of d-glucose on transgene expression in mammalian cells by a reporter gene assay using CV-1 cells and a CMV promoter-controlled EGFP gene. Treatment of CV-1 cells with 5% d-glucose unchanged the number of fluorescent cells in fluorescence microscopic observation but significantly intensified fluorescence in the fluorometric assay. Furthermore, EGFP itself and mRNA became more abundant in Western blot and quantitative RT–PCR analyses of 5% d-glucose-treated cells, respectively. These results indicate that elevated d-glucose can activate transgene expression via transcriptional stimulation, at least in part. The same concentrations of l-glucose led to only negligible increases in transgene expression, indicating that d-glucose's effect is different from its osmotic effect. The d-glucose-induced augmentation of fluorescence was observed not only in the experiment using the CMV promoter-controlled EGFP gene but also in experiments using the SV40 and RSV promoter-controlled ones, suggesting that elevated d-glucose can enhance transgene expression regulated by various promoters commonly used in transgene expression. The assessment of d-glucose analogs for their enhancive effects on transgene expression revealed that 1,6-anhydro-d-glucose and β-methyl-d-glucoside had stronger effects than d-glucose. From this result, we can expect to find more effective carbohydrates to enhance transgene expression. The α- and β-M-d-glucosides, which are slightly different from each other in three-dimensional structure, exerted largely distinct stimulative effects on transgene expression, suggesting that fundamental rules determine the enhancive effects of saccharides and that the modification of the saccharide by applying such rules will enable us to develop more powerful substances for transgene expression.