Hormonal regulation of L-type pyruvate kinase in rat liver cells in culture

Administration of ATP-MgCl2 following hemorrhage and resuscitation increases hepatic phosphoenolpyruvate carboxykinase and decreases pyruvate kinase activities

Since administration of ATP-MgCl2 following trauma and hemorrhagic shock improves tissue perfusion as well as cell and organ function, the aim of this study was to determine whether this agent has any salutary effects on the hepatic rate-controlling enzymes specific for gluconeogenesis, such as phosphoenolpyruvate carboxykinase (PEPCK), and for glycolysis, such as pyruvate kinase (PK), under such conditions. To study this, rats underwent a 5-cm midline laparotomy (i.e., trauma-induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of maximum bleed out volume was returned in the form of Ringer's lactate (RL). The animals were then resuscitated with 3 times the volume of shed blood with RL over 45 min, followed by 2 times RL with ATP-MgCl2 (50 micromol/kg body wt.) or an equivalent volume of normal saline over 95 min. Hepatic PEPCK, PK and glucokinase activities were determined 4 h after the completion of resuscitation. The mRNA levels of PEPCK and PK in the isolated hepatocytes were determined by Northern blot analysis. The results indicate that glucokinase activity was not significantly altered after hemorrhage, irrespective of ATP-MgCl2 treatment. Although the mRNA levels of PEPCK were similar in all groups, PEPCK activity decreased significantly after hemorrhage. ATP-MgCl2 treatment, however, restored PEPCK activity. Hemorrhage resulted in an increase in PK activity and its mRNA. ATP-MgCl2 treatment significantly decreased PK activity and the mRNA. Thus, up-regulation of the gluconeogenic enzyme, PEPCK, and down-regulation of the glycolytic enzyme, PK, by ATP-MgCl2 may be responsible, in part, for the beneficial effects of this agent following trauma-hemorrhage and resuscitation.

Gene expression in hepatocyte-like lines established by targeted carcinogenesis in transgenic mice

New hepatocyte-like cell lines (mhAT) were derived from the liver of a transgenic mouse expressing SV40 early genes under the direction of the liver-specific antithrombin III gene promoter (ATIII-TSV40). Their differentiated phenotypes were improved and stabilized by the use of liver-specific growth media (arginine-free, glucose-free, or low-fructose/glucose-free medium). The best differentiated lines display a very high level of albumin, transferrin, and L-type pyruvate kinase (L-PK) gene expression that is comparable to that observed in the mouse liver. Abundance of the aldolase B and phosphoenolpyruvate carboxykinase (PEPCK) transcripts varied from 5 to 35% of the in vivo concentrations while abundance of the alpha-fetoprotein and phenylalanine hydroxylase transcripts remained very low. Hormonal (cAMP and insulin) and nutritional (glucose) gene controls of PEPCK and L-PK were, at least partially, conserved. mhAT cells are readily transfectable by the calcium phosphate coprecipitation technique and exhibit a liver-specific pattern of expression of exogenous genes. Thus, mhAT cells seem suitable for the analysis of the regulatory regions involved in the tissue-specific transcription of genes. This work demonstrates, therefore, the great efficiency of targeted carcinogenesis in transgenic mice to create new differentiated cell lines. The availability of various lines of liver-specific cells with different phenotypes will constitute useful tools to establish correlations between expression of trans-acting factors and control of the phenotype.

Enzyme activity patterns of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucose-6-phosphate-dehydrogenase and malic enzyme in human liver

The distribution patterns of the enzyme activities of phosphoenolpyruvate carboxykinase, pyruvate kinase, glucose-6-phosphate-dehydrogenase and malic enzyme were determined in the liver acini of men and women by microquantitative means. The activity of PEPCK was higher in men compared to the activity in women. In both sexes no heterotopic distribution pattern was observed. PK activity of men was higher, but in both sexes no heterotopic distribution was detectable. G6PDH and ME showed relatively low activity. The distribution of G6PDH and ME activity was to some extent different in men and women. Yet their heterotopic patterns were not particularly distinct.

Endotoxin increases the liver fructose 2,6-bisphosphate concentration in fasted rats

Following endotoxin administration to fasted rats, the liver fructose 2,6-bisphosphate level is significantly increased within 1 hr, is elevated 2.3-fold by 3 hrs, and remains elevated 2 to 3-fold for at least 24 hrs. This increase in the potent allosteric activator of phosphofructokinase occurs when there is no change in the liver Glc 6-P, glycogen or cAMP concentrations, or in the activities of phosphoenolpyruvate carboxykinase or pyruvate kinase. The increase in fructose 2,6-bisphosphate concentration accounts for the increased phosphofructokinase activity previously observed in hepatocytes isolated 18 hours following endotoxin administration to rats (1). By stimulating the phosphofructokinase/Fru 1,6-bisphosphate cycle in the direction of glycolysis, fructose 2,6-bisphosphate is likely the factor responsible for decreased gluconeogenesis in endotoxemia.

Independent regulation of pyruvate kinase expression by cyclic AMP and prostaglandin F2 alpha in mouse mastocytoma cells

P-815 mouse mastocytoma cells express the K isozyme of pyruvate kinase and the specific activity of this enzyme is increased in response to N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate, 8-bromoadenosine 3':5'-cyclic monophosphate, cholera toxin, and epinephrine, all of which also elevate the intracellular concentration of adenosine 3':5'-cyclic monophosphate. Prostaglandin F2 alpha also increases the cellular activity of this enzyme, but does not increase the adenosine 3':5'-cyclic monophosphate levels. Under all these conditions, the increase in enzymatic activity is accompanied by an equivalent increase in the pyruvate kinase protein level. However, neither the rate of enzyme synthesis nor the level of pyruvate kinase mRNA is elevated by N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate. On the other hand, it does increase the enzyme's half-life. In contrast, prostaglandin F2 alpha increases the rate of synthesis and the level of pyruvate kinase K mRNA, but has no influence on the rate of degradation. Therefore, these cells have two mechanisms which increase pyruvate kinase K levels. One operates via an increase in cAMP level and results in a decrease in the rate of degradation, whereas the other minimizes an upsurge in cAMP levels but still increases pyruvate kinase K activity by increasing its rate of synthesis.