Involvement of p42/p44 MAP kinase in endothelin-1-induced interleukin-6 synthesis in osteoblast-like cells

We previously reported that endothelin-1 induces synthesis of interleukin-6 (IL-6) via activation of protein kinase C in osteoblast-like MC3T3-E1 cells. In the present study, we further investigated whether p42/p44 mitogen-activated protein (MAP) kinase is involved in endothelin-1-induced IL-6 synthesis in these cells. Endothelin-1 stimulated p42/p44 MAP kinase activation in a dose-dependent manner in the range between 0.1 nmol/L and 0.1 micromol/L. PD98059, a specific inhibitor of the upstream kinase that activates p42/p44 MAP kinase, suppressed endothelin-1-induced IL-6 synthesis as well as endothelin-1-activated p42/p44 MAP kinase. Both p42/p44 MAP kinase activation and IL-6 synthesis induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C-activating phorbol ester, were reduced by PD98059. Calphostin C, a highly specific inhibitor of protein kinase C, suppressed endothelin-1-stimulated p42/p44 MAP kinase activation as well as endothelin-1-induced IL-6 synthesis. These results strongly suggest that protein kinase C-dependent p42/p44 MAP kinase activation is involved in endothelin-1-induced IL-6 synthesis in osteoblast-like cells.