Induction of cytoskeletal gene expression by insulin

Insulin has rapid pleiotropic effects on cellular metabolism. In certain cell types, insulin can cause morphological changes by inducing rearrangements of cytoskeletal components, but the regulation of cytoskeletal gene expression by insulin has not been previously described. In the present work insulin was found to rapidly, but transiently, increase transcription of the cytoskeletal beta-actin and alpha-tubulin genes in rat H4IIE hepatoma cells. Insulin-induced transcription of beta-actin mRNA was evident within 5 min and was maximal by 10-15 min at 1000% above control levels. beta-Actin transcription was induced at insulin concentrations as low as 5 x 10(-12) M insulin and was maximal at 5 x 10(-9) M. Transcription of the alpha-tubulin gene was also rapidly stimulated by physiological concentrations of insulin, but only to 300-400% above basal levels. For both the beta-actin and alpha-tubulin genes, the induction of transcription was transient, with a return to basal levels by 60-120 min. Transcription of neither the skeletal or cardiac alpha-actin gene nor the beta-tubulin gene was altered by insulin administration. Messenger RNA levels for the beta-actin and alpha-tubulin genes increased, but to a lesser extent than transcription, since these mRNAs were abundant and stable before the transient induction of transcription. Inhibitors of protein synthesis, in the presence or absence of insulin, also acutely stimulated transcription of these genes.