Effect of retinoic acid on prostaglandin F2 alpha-induced prostaglandin E2 synthesis in osteoblast-like cells

Carbonyl Reductase 3 (CBR3) Mediates 9-cis-Retinoic Acid-Induced Cytostatis and is a Potential Prognostic Marker for Oral Malignancy

The molecular mechanisms of growth suppression by retinoic acid (RA) were examined. Our results suggest that the cytostatic effects of RA could be mediated by the activation of endogenous CBR3 gene in oral squamous cell carcinomas (OSCCs), and the expression is a potential marker for oral malignancy.

Mechanisms involved in prostaglandin-induced increase in bone resorption in neonatal mouse calvaria

Prostaglandins (PG) E1, E2 and F2alpha induce bone resorption in isolated neonatal parietal bone cultures, and an associated increase in interleukin-6 (IL-6) production. Indomethacin had little effect on the response to PGE2, or the relatively non-selective EP receptor agonists 11-deoxy PGE1 and misoprostol, but blocked the effects of PGF2alpha and the F receptor agonist fluprostenol, indicating an indirect action via release of other prostaglandins. It is more likely that there is positive autoregulation of prostaglandins production in this preparation mediated via stimulation of F receptors. The effects of selective EP receptor agonists sulprostone (EP1,3) and 17-phenyl trinor PGE2(EP1), indicated the involvement of EP2 and/or EP4 receptors, which signal via cAMP. The relatively weak increase in IL-6 production by misoprostol (with respect to resorption) suggests that these responses are controlled by different combination of EP2 and EP4 receptors. The PKA activator, forskolin, induced small increases in bone resorption at lower concentrations (50-500 ng/ml) but a reversal of this effect, and inhibition of resorption induced by other stimuli (PTH, PGE2), at higher concentrations (0.5-5 microg/ml). IL-6 production was markedly increased only at the higher concentrations. The inhibitory effect of forskolin may be a calcitonin-mimetic effect. PMA induced both resorption and IL-6 production which were both blocked by indomethacin, indicating a role for PKC in the control of prostaglandin production.

Effect of retinoic acid on prostaglandin F2 alpha-induced phospholipase D activity in osteoblast-like cells

We previously reported that prostaglandin F2 alpha (PGF2 alpha) 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 PGF2 alpha-induced phospholipase D activation. In this study, we examined the effect of retinoic acid (RA) on the phospholipase D activity stimulated by PGF2 alpha in these cells. The pretreatment of RA markedly inhibited the formation of choline induced by PGF2 alpha (10 microM) in a dose-dependent manner in the range between 1 nM and 0.1 microM. 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 PGF2 alpha in osteoblast-like cells and that the effect of RA is exerted at the point between PGF2 alpha receptor and G-protein.