Regulation of beta-actin gene transcription by insulin and phorbol esters

Insulin and the phorbol ester, phorbol 12-myristate 13-acetate, induce beta-actin gene transcription in H4 cells. This occurred rapidly, with a maximum 15-fold stimulation following 15 min of insulin (5 x 10(-9) M) or phorbol ester (1 microgram/ml) exposure. The increase in beta-actin transcription was transitory, returning to baseline within 120 min. Pretreatment of cells with phorbol ester for 24 h, reducing functional protein kinase C activity, abolished the ability of phorbol esters to increase beta-actin transcription. When insulin was added to phorbol ester-pretreated cells the insulin-induced increase in beta-actin transcription was reduced by 40-60%. These findings support our hypothesis that a common regulatory signal is utilized by both insulin and phorbol esters for the complete induction of specific genes.