Rapid events in growth hormone action. Induction of c-fos and c-jun transcription in 3T3-F442A preadipocytes

To investigate early events in GH action, we examined whether GH altered the expression of c-fos and c-jun mRNA in 3T3-F442A cells. The rapid induction of these early response protooncogenes is one of the initial events in stimulation of cell proliferation and differentiation by a variety of growth factors. In 3T3-F442A preadipocytes, which differentiate in response to GH, treatment with GH for 15-30 min transiently increased the expression of c-fos and c-jun mRNA at GH concentrations in the physiological range (10-500 ng/ml). Both genes were superinduced by GH in the presence of cycloheximide. Nuclear run-on experiments indicated that the effect of GH on c-fos and c-jun occurred at the level of gene transcription, indicating that in the 3T3-F442A preadipocytes, GH acts similarly to other growth factors which induce c-fos and c-jun. Chronic preincubation with the phorbol ester phorbol 12-myristate 13-acetate interfered with the induction of c-fos by GH, suggesting that diacylglycerol and protein kinase C are involved in this effect of GH. Insulin-like growth factor-I and insulin were less effective than equimolar concentrations of GH in inducing c-fos expression. Taken together, these findings are consistent with coordinated expression of c-fos and c-jun playing an early role in responses to GH in 3T3-F442A cells.