Cyclic AMP Stabilizes the MRNA for Phosphoenolpyruvate Carboxykinase (GTP) Against Degradation

It is now well established that cAMP induces the transcription rate of the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) and that this induction is dependent on a nucleotide domain located within the promoter-regulatory region of the gene (Short, J. M., Wynshaw-Boris, A., Short, H. P., and Hanson, R. W. (1986) J. Biol. Chem. 261, 9721-9726). We report here that cAMP also stabilizes phosphoenolpyruvate carboxykinase mRNA against degradation. Using two independent experimental approaches, we show that the half-life of the mRNA for phosphoenolpyruvate carboxykinase is extended when FTO-2B rat hepatoma cells are exposed to dibutyryl cyclic AMP (Bt2cAMP). In the first experiment, the rate of decay of phosphoenolpyruvate carboxykinase mRNA was determined in cells incubated in the presence of insulin, which has been shown to block the transcription rate of the gene for the enzyme. Under these conditions, the half-life of phosphoenolpyruvate carboxykinase mRNA was 30 min. However, in cells incubated in the presence of Bt2cAMP, the mRNA decayed with a half-life of 150 min. In the other experiment, mRNA stability was measured under steady state conditions, utilizing a "pulse-chase" approach. The apparent half-life of phosphoenolpyruvate carboxykinase mRNA increased from 40 min to over 250 min in Bt2cAMP-treated cells. No significant change in the stability of total cellular RNA was noted. Other experiments have shown that the transcription rate of the gene for phosphoenolpyruvate carboxykinase peaks within the first 20 min after exposing the cells to Bt2cAMP and then levels off, while the abundance of the mRNA reaches a maximum at about 90 min and remains at this level thereafter. Thus, the long term effect of cAMP on the expression of the gene coding for phosphoenolpyruvate carboxykinase occurs at least in part, through an alteration in the degradation rate of the mRNA for this enzyme.