Insulin and cyclic AMP act at different levels on transcription of the L-type pyruvate kinase gene

We previously demonstrated that, in hepatocytes in primary culture, the role of insulin on induction of L-type pyruvate kinase (L-PK) gene expression was mainly to induce glucokinase synthesis, needed for glucose phosphorylation to glucose 6-phosphate. However, we show here that when hepatocytes have been isolated from rats starved for 72 h, glucose and constitutive glucokinase expression was not sufficient to fully stimulate the L-PR promoter, low insulin concentrations being still required. In addition, activation remains sensitive to cAMP inhibition, but cannot he reproduced in the absence of insulin by a competitive cAMP antagonist. We propose that both insulin and cAMP act on expression of the L-PK gene at, at least, two levels: positive and negative regulation of glucokinase gene expression, and more downstream levels.