Regulation of Glucose-Transporter Gene Expression by Insulin in Cultured Human Fibroblasts

To clarify the effect of insulin on glucose-transporter (GT) biosynthesis, we determined GT mRNA levels in human cultured skin fibroblasts, using HepG2 GT cDNA as a probe. Insulin specifically increased the GT mRNA level in a time- and dose-dependent manner. Time-course study demonstrated that the mRNA level peaked within 3 h of insulin (1 × 10⁻⁷ M) addition. After remaining elevated for several hours, mRNA decreased and returned to the basal level after 24 h. In the cell strains from seven normal subjects, the mean (±SE) GT mRNA level determined after 3 h of treatment with 1 × 10⁻⁷ M insulin was 164.3 ± 8.5% of the level found in untreated control cells. The insulin dose-response curve of GT mRNA levels showed that the maximum stimulation was elicited at 1 × 10⁻⁷ M, and the half-maximum stimulation occurred at ∼5 × 10⁻¹⁰ M. Degradation rates of GT mRNA determined in the presence of actinomycin D were not different between insulin-treated and untreated cells. These results suggest that insulin increases GT gene expression in cultured human fibroblasts.