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Involvement of p42/p44 mitogen‐activated protein kinase in prostaglandin f2α‐stimulated induction of heat shock protein 27 in osteoblasts

We previously reported that prostaglandin F2α (PGF2α) activates both phosphoinositide‐hydrolyzing phospholipase C and phosphatidylcholine‐hydrolyzing phospholipase D in osteoblast‐like MC3T3‐E1 cells and then induces the activation of protein kinase C (PKC). In this study, we investigated the effect of PGF2α on the induction of heat shock protein 27 (HSP27), a low‐molecular‐weight heat shock protein, in these cells. PGF2α significantly induced the accumulation of HSP27 dose‐dependently within the range of 10 nM to 10 μM. PGF2α stimulated the increase in the levels of mRNA for HSP27. A total of 10 nM 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), an activator of PKC, induced the accumulation of HSP27. The stimulative effect of PGF2α was reduced in the PKC down‐regulated cells. Calphostin C, a specific inhibitor of PKC, suppressed the PGF2α‐induced HSP27 accumulation as well as that induced by TPA. HSP27 induction by PGF2α was reduced by U‐73122, a phospholipase C inhibitor, or propranolol, a phosphatidic acid phosphohydrolase inhibitor. PGF2α and TPA stimulated p42/p44 mitogen‐activated protein (MAP) kinase. PD98059, an inhibitor of the upstream kinase that activates p42/p44 MAP kinase, suppressed the induction of HSP27 stimulated by PGF2α or TPA. PD98059 and calphostin C reduced the levels of mRNA for HSP27 increased by PGF2α. These results indicate that PGF2α stimulates the induction of HSP27 via p42/p44 MAP kinase activation, which depends on upstream PKC activation in osteoblasts. J. Cell. Biochem. 75:610–619, 1999. © 1999 Wiley‐Liss, Inc.