Regulation of rat liver phosphoenolpyruvate carboxykinase (GTP) messenger ribonucleic acid activity by N6,O2'-dibutyryladenosine 3',5'-phosphate

Abstract

N6,O2''-Dibutyryl cAMP (Bt2cAMP) induces the synthesis of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (GTP) in rat liver by increasing the activity of mRNA coding for this enzyme (mRNAPEPCK) more than 20-fold (from < 0.01% to > 0.20% of total mRNA activity), as determined by using in vitro translation systems which measure only active mRNAPEPCK. The increase in mRNAPEPCK activity could result from increased synthesis, increased processing or decreased inactivation rates. Actinomycin D and cordycepin inhibit mRNAPEPCK induction by 89 and 70%, respectively, a result that indicates a requirement for ongoing RNA synthesis but that does not distinguish which of these steps is regulated by cAMP. A kinetic approach, not involving RNA synthesis inhibitors, was used to determine the half-life of mRNAPEPCK both during a period of deinduction following glucose feeding and during a subsequent induction by Bt2cAMP. An estimated half-life of 20 .+-. 5 min during both of these periods indicates that Bt2cAMP has no effect on the rate of inactivation of mRNAPEPCK. Bt2cAMP probably effects the increase in activity of mRNAPEPCK by promoting its synthesis or processing.