Mitogenic effect of prostaglandin E1 in Swiss 3T3 cells: Role of cyclic AMP

Abstract

Addition of prostaglandin E₁ (PGE₁) to quiescent cultures of Swiss 3T3 cells rapidly elevates the intracellular levels of cAMP and increases the activity of adenylate cyclase in particulate fractions of these cells. In the presence of insulin, PGE₁ stimulates the reinitiation of DNA synthesis. Both effects (increase in cellular cAMP and stimulation of DNA synthesis) are markedly potentiated by 1‐methyl‐3‐isobutyl xanthine (IBMX) or by 4‐(3‐butoxy‐4 methoxy benzyl)‐2‐imidazolidine (Ro 20–1724), both of which are potent inhibitors of cyclic nucleotide phosphodiesterase activity. In the presence of 50 μM IBMX, PGE₁ caused a dose‐dependent increase in cAMP levels and in [³H]thymidine incorporation into acid‐insoluble material at concentrations (5–50 ng/ml) that are orders of magnitude lower than those used in previous studies (50 μg/ml) to demonstrate growth‐inhibitory effects. Thus, the inhibitory effects produced by adding high concentrations of PGE₁ on the initiation of DNA synthesis in Swiss 3T3 cells are not mediated by cAMP and should be regarded as nonspecific. In contrast, the mitogenic activity of PGE₁ parallels its ability to increase the intracellular levels of cAMP. The findings support the propostion that a sustained increase in the level of this cyclic nucleotide acts as a mitogenic signal for confluent and quiescent Swiss 3T3 cells.