remnant which culminate in the coordinated waves of DNA The activity and messenger RNA (mRNA) levels of glusynthesis and mitosis. 4,5 Therefore, cell proliferation and the cokinase, and the concentration and mRNA levels of its maintenance of glucose homeostasis must take place in a regulatory protein, were analyzed during liver regenersynchronous manner.
ation. The activity of glucokinase and the concentration
Hormonal regulation of hepatic glycolysis and gluconeoof its regulatory protein decreased to 30% and 50%, regenesis is brought about by allosteric modulators, by enzyme spectively, after liver resection, remaining low after 1 modification by phosphorylation or dephosphorylation, and week. No significant variations in the level of these prothrough the control of gene expression of several key regulateins were found in sham-operated animals. The regulatory enzymes. These enzymes control hepatic glucose productory protein/glucokinase molar ratio increased during tion and utilization through the regulation of three major the replicative phase, to a maximum at 48 hours. The substrate cycles: between glucose and glucose-6-phosphate, mRNA levels of glucokinase and of its regulatory protein fructose-6-phosphate and fructose-1,6-bisphosphate, and decreased rapidly after partial hepatectomy to miniphosphoenolpyruvate and pyruvate. 6,7 The fructose 6-phosmum values at 6 hours (15%) and at 12 hours (4%), respecphate/fructose-1,6-bisphosphate substrate cycle is also regutively, returning to normal values at 24 hours and 168 lated by a subcycle in which the amount of the regulatory hours, respectively. Sham-operated animals showed a molecule fructose-2,6-bisphosphate is controlled by the bisimilar decrease in mRNA levels during the prereplicafunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bistive phase of liver regeneration, suggesting that the iniphosphatase. [6][7][8][9][10] Coordinate changes in amount, activity, and tial effects observed in the gene expression of these progene expression of these regulatory enzymes have been reteins were due to surgical stress. During the replicative ported during liver regeneration. 11-14 phase, a specific inhibition of the regulatory protein's
The liver contains a regulatory protein that inhibits glucogene expression was observed in the regenerating liver.
kinase competitively with respect to glucose. 15 The effect of A decrease in the content of regulatory protein and the this protein is greatly reinforced by fructose-6-phosphate and glucokinase activity, and an increase in the molar ratio antagonized by fructose 1-phosphate. The glucokinase reguof these two proteins correlate with the observed delatory protein has been purified from rat liver and a complecrease in glycolytic flux, providing further evidence that mentary DNA (cDNA) encoding this protein has been cloned the phosphorylation of glucose is a control point in the and characterized. 16,17 The glucokinase regulatory protein is glycolytic/gluconeogenic flux during liver regeneration.
expressed, similarly to glucokinase, in the liver but not in (HEPATOLOGY 1997;25:324-328.)
the brain, skeletal muscle, heart, spleen, or kidney. 18,19 Starvation and diabetes cause a marked decrease in the expres-In the liver that remains after partial hepatectomy, sion of glucokinase, the activity of which fell to about 10%marked changes in the composition and energy metabolism 20% of the control level after 7 days. However, the level of take place before the onset of mitotic activity. Hepatic metabregulatory protein only decreased to about 50%. 19 olism is shifted from the utilization of carbohydrates to the
The aim of the present study was to determine whether increased utilization of lipids, and the glycolytic/gluconeogenmessenger RNA (mRNA) and protein levels of the glucokiesis ratio decreases, maintaining glucose homeostasis. [1][2][3] It nase regulatory protein were modulated during rat liver rehas been reported that there is a twofold increase in the generation and, if so, to analyze the contribution of the glucogluconeogenic flux from lactate, and a decrease to less than kinase regulatory protein to the control of glucokinase 20% in the glycolytic flux from glucose in hepatocyte suspenactivity during this proliferative process. sions that are derived from regenerating liver. 1 In addition, partial hepatectomy produces metabolic changes in the liver
Methods
Chemicals. [a-32 P]Deoxycytidine triphosphate (3,000 Ci/mmol) and N-Hybond membranes were from Amersham Iberica S.A.