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

An immortalized rat liver cell line (RLC) expresses two isozymes of pyruvate kinase, the adult liver or L-type isozyme and an M-type isozyme presumed to be the M2-type. In RLC cells incubated in serum-free medium, the addition of 0.1 microM insulin maintained the initial level of L-type pyruvate kinase when it was high and induced the L-type isozyme when it was low. The addition of 1.0 mM dibutyryl cAMP and 0.5 mM theophylline decreased the L-type isozyme, even in the presence of insulin. The amount of M2-type isozyme was relatively constant under the conditions used. Regulation of the amount of L-type pyruvate kinase by both insulin and cAMP occurred primarily through changes in the rate of L-pyruvate kinase protein synthesis and translatable mRNA levels. These results are consistent with the in vivo observations that both insulin and glucagon regulate the rate of L-pyruvate kinase gene transcription and that cAMP is the dominant regulator of L-pyruvate kinase gene expression.