Involvement of prostaglandin endoperoxide H synthase-2 in osteoclast-like cell formation induced by interleukin-1β

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Abstract
Interleukin-1β (IL-1β) stimulates osteoclast-like cell formation via prostaglandin E2 (PGE2) production. However, the regulatory mechanism for the production of PGE2 in bone cells is still unclear. Recently, it has been shown that two prostaglandin endoperoxide H synthase (PGHS) isozymes exist, termed PGSH-1 and PGHS-2. We report here that IL-1β induces PGE2 production in bone marrow culture induced by a PGHS-2-dependent mechanism. IL-1β stimulated the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNC) and the production of PGE2 in mouse bone marrow cultures. The dose response curves for the indomethacin inhibition of TRAP-positive MNC formation and PGE2 production were nearly identical. Cycloheximide (CHX) suppressed IL-1β-induced PGE2 production, suggesting that the production of PGE2 induced by IL-1β required de novo protein synthesis. Northern blot analysis determined that IL-1β induced PGHS-2 expression by 30 minutes and mRNA levels were maximal by 1–2 h. Cycloheximide potentiated the accumulation of PGHS-2 mRNA linearly up to 8 h. Dexamethasone, an inhibitor of the induction of PGHS-2, inhibited IL-1β-induced PGHS-2 mRNA expression and also suppressed IL-1β-stimulated formation of TRAP-positive MNC. Furthermore NS-398, as a selective PGHS-2 inhibitor, completely inhibited IL-1β-induced TRAP-positive MNC formation. Moreover, IL-1β-induced PGHS-2 mRNA expression and formation of TRAP-positive MNC were inhibited by calphostin C, a selective inhibitor of protein kinase C (PKC). These results indicate that IL-lβ-induced formation of osteoclast-like cells requires PKC activation, induction of PGHS-2, and subsequent prostaglandin synthesis by this enzyme.