Cell-Specific Carbohydrate Metabolism Regulates S14 Gene Transcription

Carbohydrate administration rapidly regulates hepatic mRNA-S14 content. Both sucrose and fructose but not glucose increase the transcription of hepatic mRNA-S14 in vivo. In primary hepatocyte cultures, mRNA-S14 transcription responds to either fructose or glucose. To test the hypothesis that the difference in hexose response is due to differences in cellular metabolism, we studied the regulation of this gene with a transient transfection assay system in Chinese hamster ovary (CHO) cells, hamster pancreatic β-cells (HIT), and primary hepatocytes. In HIT cells, glucose stimulation of the expression vector pS14CAT(5 kilobases [kb]) containing 4.9 kb of 5′-flanking DNA was threefold greater than fructose. Glucose also gave a fourfold greater response at 27.5 mM than at 2.2 mM. In CHO cells, pS14CAT(5 kb) showed a twofold greater response to fructose than to glucose. The differential response to the hexoses in the two cell lines is a result of cell-specific metabolism. Without glucose in the media, both CHO and HIT cells used pyruvate for energy. However, glucose addition to CHO cells enhances glycolysis and hexose shunt pathway activity while inhibiting pyruvate oxidation and S14 gene transcription. In contrast, addition of glucose to HIT cells leads to enhanced tricarboxylic acid cycle activity to oxidize pyruvate and an associated stimulation of S14 transcription. We confirmed these conclusions in primary hepatocyte cultures. Addition of 27.5 mM glucose led to a twofold increase in endogenous mRNA-S14 accumulation, a twofold increase in transfected pS14LUC (5 kb) activity, and a parallel twofold increase in pyruvate oxidation. Thus, the different transcriptional responses of the S14 gene to fructose and glucose are attributable to cell-specific metabolism. Our data show that the metabolic regulation of mRNA-S14 gene transcription correlates with the rate of cellular pyruvate oxidation.