Protein kinase C activation amplifies prostaglandin F2α‐induced prostaglandin E2 synthesis in osteoblast‐like cells

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Abstract
In cloned osteoblast-like cells, MC3T3-E1, prostaglandin F2α (PGF2α) stimulated arachidonic acid (AA) release in a dose-dependent manner in the range between 1 nM and 10 μM. 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 PGF2α in a dose-dependent manner, 4 α-phorbol 12, 13-didecanoate, a phorbol ester which is inactive for PKC, showed little effect on the PGF2α-induced AA release. 1-oleoyl-2-acetylglycerol (OAG), a specific activator for PKC, mimicked TPA by enhancement of the AA release induced by PGF2α. H-7, a PKC inhibitor, markedly suppressed the effect of OAG on PGF2α-induced AA release. Quinacrine, a phospholipase A2 inhibitor, showed partial inhibitory effect on PGF2α-induced AA release, while it suppressed the amplification by OAG of PGF2α-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 triphosphate stimulated by PGF2α. Under the same condition, PGF2α indeed stimulated prostaglandin E2 (PGE2) synthesis and TPA markedly amplified the PGF2α-induced PGE2 synthesis as well as AA release. These results indicate that the activation of PKC amplifies PGF2α-induced both AA release and PGE2 synthesis through the potentiation of phospholipase A2 activity in osteoblast-like cells.

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