Recent studies have suggested that
prostaglandin E(2) (
PGE(2)) subtype receptors (EP) are involved in cellular proliferation and
tumor development. We studied the role of EP(1) and EP(4)
PGE(2) subtype receptor antagonists
AH-6809 and AH-23848B, respectively, in serum-induced 3T6 fibroblast proliferation. This was significantly reduced in a dose-dependent manner (IC(50) approximately 100 and approximately 30 microM, respectively) to an almost complete inhibition, without any cytotoxic effect. However, the effect of each antagonist on 3T6 cell cycle progression clearly differed. Whereas the EP(1) antagonist increased the G(0)/G(1) population, the EP(4) antagonist brought about an accumulation of cells in early S phase. These effects were associated with a decrease in
cyclin D and E levels in AH-6809-treated 3T6 cells and lower
cyclin A levels in AH-23848B-treated fibroblasts with respect to control cells. The G(0)/G(1) accumulation caused by
AH-6809 seems to be intracellular Ca(2+) concentration ([Ca(2+)](i)) dependent, because a 6-h 1 microM
thapsigargin treatment allowed G(0)/G(1)-arrested cells to enter S phase. Similarly, treatment with 20 microM
forskolin for 6 h allowed S-phase and G(2)/M progression of AH-23848B-treated cells. This study shows that the inhibitory effect of the EP(1) and EP(4) antagonists on serum-induced 3T6 fibroblast growth is due to their effect at various levels of the cell cycle machinery, suggesting that
PGE(2) interaction with its different subtype receptors regulates progression through the cell cycle by modulating cAMP and [Ca(2+)](i).