Bombesin stimulation of c-fos expression and mitogenesis in Swiss 3T3 cells: the role of prostaglandin E2-mediated cyclic AMP accumulation.

Bombesin is a potent mitogen for Swiss 3T3 cells and can stimulate DNA synthesis in the absence of any other growth factor. This effect is mediated by multiple synergistic signaling pathways, including an accumulation of intracellular cyclic AMP (cAMP) and an increase in c-fos mRNA expression. The cyclooxygenase inhibitor indomethacin abolished prostaglandin E2 release and substantially depressed cAMP levels induced by bombesin (EC50 congruent to 10 nM). In contrast, indomethacin at 1 microM did not affect 80K phosphorylation or Ca2+ mobilization by bombesin, indicating that cAMP synthesis can occur through a phospholipase C-independent pathway. Indomethacin caused a 30 to 35% decrease in c-fos induction and DNA synthesis in cells treated with bombesin (EC50 congruent to 40 nM). Significantly, the inhibitory effect of indomethacin was reversed in the presence of forskolin, a direct activator of adenylate cyclase. We conclude that cAMP plays a regulatory role in c-fos induction and mitogenesis in Swiss 3T3 cells treated with bombesin.