Regulation of hepatic 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase gene expression by glucagon

The control of hepatic 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase gene expression by glucagon was studied. Intraperitoneal administration of glucagon rapidly decreased the fructose 2,6-bisphosphate content by phosphorylation of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase and diminution of its Vmax. Immunologic studies using a specific liver antibody showed that the amount of enzyme rapidly decreased. Northern blot analysis showed that the isozyme expressed is the adult liver form. The 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase mRNA content decreased, whereas that of phosphoenolpyruvate carboxykinase increased, and that of albumin did not change. Run-on transcription assays with isolated nuclei showed inhibition in the relative transcription rate of the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase gene and a stimulation of phosphoenolpyruvate carboxykinase gene. The regulation of mRNA stability of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase by glucagon was also studied. The half-life of mRNA decreased in the presence of glucagon, suggesting that proteins modulated by a glucagon-dependent process are regulating its stability. The time course of mRNA levels correlated with the transcription inhibition of gene and destabilization of mRNA, indicating that glucagon modulates 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase gene expression at both transcriptional and posttranscriptional levels.