Basic fibroblast growth factor induces interleukin-6 synthesis in osteoblasts: Autoregulation by protein kinase C

We previously reported that basic fibroblast growth factor (bFGF) stimulates both phospholipases C and D via independent pathways in osteoblastlike MC3T3-E1 cells. In this study, we investigated the effect of bFGF on interleukin-6 (IL-6) synthesis in these cells. bFGF stimulated the IL-6 synthesis dose-dependently in the range between 1 and 30 ng/ml. The depletion of extracellular Ca²⁺ by EGTA suppressed the bFGF-induced IL-6 synthesis. TMB-8, an inhibitor of intracellular Ca²⁺ mobilization, also inhibited the IL-6 synthesis by bFGF. bFGF stimulated the Ca²⁺ influx from extracellular space. Genistein, a tyrosine kinase inhibitor, suppressed the bFGF-induced Ca²⁺ influx. Staurosporine, an inhibitor for protein kinases, enhanced the bFGF-induced IL-6 synthesis. Calphostin C, a highly potent and specific inhibitor for protein kinase C (PKC), also enhanced the IL-6 synthesis by bFGF. The bFGF-induced IL-6 synthesis was amplified in PKC down-regulated cells. U-73122, a phospholipase C inhibitor, enhanced the bFGF induced IL-6 synthesis. Propranolol, a phosphatidic acid phosphohydrolase inhibitor, also enhanced the IL-6 synthesis by bFGF. These results strongly suggest that bFGF stimulates IL-6 synthesis, which depends on intracellular Ca²⁺ mobilization in osteoblastlike cells, and that the IL-6 synthesis by bFGF is autoregulated due to PKC activation.