PROTEIN-KINASE-C ACTIVATION AMPLIFIES PROSTAGLANDIN-F2-ALPHA-INDUCED PROSTAGLANDIN-E2 SYNTHESIS IN OSTEOBLAST-LIKE CELLS

In cloned osteoblast-like cells, MC3T3-E1, prostaglandin F2-alpha (PGF2-alpha) stimulated arachidonic acid (AA) release in a dose-dependent manner in the range between 1 nM and 10-mu-M. 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C (PKC) activator, which by itself had little effect on AA release, markedly amplified the release of AA stimulated by PGF2-alpha in a dose-dependent manner. 4 alpha-phorbol 12,13-didecanoate, a phorbol ester which is inactive for PKC, showed little effect on the PGF2-alpha-induced AA release. 1-oleoyl-2-acetylglycerol (OAG), a specific activator for PKC, mimicked TPA by enhancement of the AA release induced by PGF2-alpha. H-7, a PKC inhibitor, markedly suppressed the effect of OAG on PGF2-alpha-induced AA release. Quinacrine, a phospholipase A2 inhibitor, showed partial inhibitory effect on PGF2-alpha-induced AA release, while it suppressed the amplification by OAG of PGF2-alpha-induced AA release almost to the control level. Furthermore, TPA enhanced the AA release induced by melittin, known as a phospholipase A2 activator. On the other hand, TPA inhibited the formation of inositol trisphosphate stimulated by PGF2-alpha. Under the same condition, PGF2-alpha indeed stimulated prostaglandin E2 (PGE2) synthesis and TPA markedly amplified the PGF2-alpha-induced PGE2 synthesis as well as AA release. These results indicate that the activation of PKC amplifies PGF2-alpha-induced both AA release and PGE2 synthesis through the potentiation of phospholipase A2 activity in osteoblast-like cells.