Glucose-dependent and -independent effect of insulin on gene expression

Insulin action on gene expression can be glucose-dependent or -independent. Accumulation of aldolase B mRNA and of an unidentified 5.4-kilobase mRNA as well as accumulation of L-type pyruvate kinase mRNAs (Decaux, J.F., Antoine, B., and Kahn, A. (1989) J. Biol. Chem. 264, 11584-11590) in cultured hepatocytes isolated from fasted rats require the presence of both glucose and insulin, these agents not being effective individually. In contrast, maintaining the amount of albumin and transferrin mRNAs in these hepatocytes requires the presence of insulin alone, glucose having no effect by itself. Transcription of the albumin gene, investigated by run-on assay, is active in the presence of insulin alone, with or without glucose, whereas transcription of the aldolase B gene is stimulated by glucose and insulin together, but not by insulin or glucose alone. In addition, the stability of the albumin and aldolase B mRNAs in cultured hepatocytes is lowered in the absence of glucose and insulin together as compared to the stability in the presence of one or both agents. These results confirm that transduction of the insulin signal occurs via distinct pathways; one of these pathways could involve a secondary insulin-dependent modification of metabolite concentration, whereas other pathways could be more directly related to the activity(ies) of the occupied insulin receptor.