Transcriptional regulation of the glucose-6-phosphatase gene by cAMP/vasoactive intestinal peptide in the intestine. Role of HNF4alpha, CREM, HNF1alpha, and C/EBPalpha.

Gluconeogenesis is induced in both the liver and intestine by increased cAMP levels. However, hepatic and intestinal glucose production can have opposite effects on glucose homeostasis. Glucose release into the portal vein by the intestine increases glucose uptake and reduces food intake. In contrast, glucose production by the liver contributes to hyperglycemia in type II diabetes. Glucose-6-phosphatase (Glc6Pase) is the key enzyme of gluconeogenesis in both the liver and intestine. Here we specify the cAMP/protein kinase A regulation of the Glc6Pase gene in the intestine compared with the liver. Similarly to the liver, the molecular mechanism of cAMP/protein kinase A regulation involves cAMP-response element-binding protein, HNF4alpha, CAAT/enhancer-binding protein, and HNF1. In contrast to the situation in the liver, we find that different isoforms of CAAT/enhancer-binding protein and HNF1 contribute to the specific regulation of the Glc6Pase gene in the intestine. Moreover, we show that cAMP-response element binding modulator specifically contributes to the regulation of the Glc6Pase gene in the intestine but not in the liver. These results allow us to identify intestine-specific regulators of the Glc6Pase gene and to improve the understanding of the differences in the regulation of gluconeogenesis in the intestine compared with the liver.