Regulation of sugar transport in cultured diploid human skin fibroblasts

Publisher Website
Google Scholar
Abstract
The regulation of hexose transport under glucose‐starvation conditions was studied in cultured human skin fibroblasts. Glucose starvation enhanced the transport of 2‐DG and 3‐O‐methyl‐D‐glucose (3‐OMG) but not of L‐glucose. Glucose‐starvation enhanced transport was inhibited by cytochalasin B (10 μM). The starvation‐induced change in 2‐DG transport was due to an increase in the Vmax of both the high and low affinity transport sites (2.8‐ and 2.4‐fold, respectively) with no effect on their Kms. The presence of 5.55 mM galactose, fructose, or L‐glucose in the medium resulted in transport increases similar to those seen in glucose‐starved cells, while the presence of 5.55 mM glucose, mannose, or 3‐OMG repressed 2‐DG transport. Glucose‐starvation enhancement of 2‐DG transport was blocked by cycloheximide (20 μg/ml) but not by actinomycin D (0.03 μg/ml) or α‐amanitin (3.5 μM). Readdition of glucose (5.55 mM) for six hours to glucose‐starved cells led to a rapid decrease in hexose transport that could be blocked by cycloheximide but not actinomycin D. Although readdition of 3‐OMG to glucose‐starved cells had little effect on reversing the transport increases, glucose plus 3‐OMG were more effective than glucose alone. Serum containing cultures (10% v/v) of glucose‐fed or glucose‐starved cells exhibited rapid decreases in 2‐DG transport when exposed to glucose‐containing serum‐free medium. These decreases were prevented by employing glucose‐free, serum‐free medium. The data indicate that hexose transport regulation in cultured human fibrob asts involves protein synthesis of hexose carriers balanced by interactions of glucose with a regulatory protein(s) and glucose metabolism as they affect the regulation and/or turnover of the carrier molecules.