Effect of retinoic acid on prostaglandin F(2α)-induced phospholipase D activity in osteoblast-like cells

We previously reported that prostaglandin F(2α) (PGF(2α)) activates phosphatidylcholine-hydrolyzing phospholipase D independently from the activation of protein kinase C (PKC) in osteoblast-like MC3T3-E1 cells, and reported that pertussis toxin-sensitive GTP-binding protein (G-protein) is involved in the PGF(2α)-induced phospholipase D activation. In this study, we examined the effect of retinoic acid (RA) on the phospholipase D activity stimulated by PGF(2α) in these cells. The pretreatment of RA markedly inhibited the formation of choline induced by PGF(2α) (10 μM) in a dose-dependent manner in the range between 1 nM and 0.1 μM. This inhibitory effect of RA was dependent on the time of pretreatment up to 8 h. However, RA had little effect on the choline formation induced by NaF, a G-protein activator, or 12-O-tetradecanoylphorbol-13-acetate, an activator of PKC. These results strongly suggest that RA suppresses the phospholipase D activated by PGF(2α) in osteoblast-like cells and that the effect of RA is exerted at the point between PGF(2α) receptor and G-protein.