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Basic fibroblast growth factor (bFGF) is a potent mitogen for bone. In this study, we utilized the clonal rat osteoblastic cell line, Py1a, to examine signal transduction by bFGF and to determine the role of mitogen activated protein kinases (MAPK) and induction of c-fos mRNA in the mitogenic response to bFGF. Stimulation of [3H]thymidine incorporation (TDR) into DNA by bFGF was determined in the presence of phorbol myristate acetate of (PMA) to down-regulate the protein kinase C (PKC) pathway, genistein, an inhibitor of tyrosine kinase and H-7, a PKC inhibitor, bFGF 10(-8) M and PMA 10(-7) M increased TDR by 242 and 245%, respectively. Treatment with bFGF or PMA for 5 or 30 minutes increased tyrosine phosphorylation of multiple proteins, and immunoblotting with MAPK-specific antibody revealed that two of these bands were the 42 and 44 kD isoforms of MAPK. PMA and bFGF induced c-fos mRNA expression at 30 minutes. Genistein at 10 micrograms/ml blocked the mitogenic effect of bFGF and partially inhibited the mitogenic effect of PMA. Genistein at 100 micrograms/ml also blocked both bFGF- and PMA-induced increases in c-fos mRNA. A 24 h pretreatment with PMA at 10(-7) M inhibited the mitogenic response, tyrosine phosphorylation of MAPK, and induction of c-fos mRNA subsequent to the addition of PMA, but not bFGF. H-7 at 50 microM blocked bFGF-induced mitogenesis and c-fos induction, but did not inhibit bFGF-induced tyrosine phosphorylation of MAPK. In this study, we show that the signaling pathway of bFGF and PMA are similar in that they both induce tyrosine phosphorylation of MAP kinases and activate c-fos. However, the signaling pathways ultimately diverge in that once the PKC pathway is down-regulated by PMA pretreatment or blocked by the PKC inhibitor H-7, tyrosine phosphorylation of MAP kinase, c-fos induction, and the mitogenic effect of PMA is blocked. In contrast, down-regulation of the PKC pathway inhibits c-fos and the mitogenic response to bFGF, but not bFGF's effects on tyrosine phosphorylation of MAP kinase.

We determined whether basic fibroblast growth factor (bFGF) regulated the expression of IL-6 and NFIL-6 in osteoblasts. In mouse osteoblastic MC3T3-E1 cells, bFGF (10(-8) M) increased NFIL-6 mRNA 2-fold at 30 minutes and 3-fold at 2 h. IL-6 mRNA was increased by bFGF 10(-8) M after 1 h. IL-6 protein was detectable in control cultures but was significantly increased by bFGF (10(-8) M) at 4 h. Immunofluorescence analysis of MC3T3-E1 cells showed primarily cytoplasmic and perinuclear NFIL-6 staining in control cultures while bFGF-treated cells showed increased NFIL-6 staining at 2 and 4 h. Western blotting revealed that bFGF increased NFIL-6 protein at 2 h. In calvarial mouse osteoblasts, bFGF 10(-8) M induced IL-6 mRNA as early as 1 h and significantly increased IL-6 protein levels as early as 2 h. In conclusion, bFGF stimulates IL-6 and NFIL-6 mRNA in osteoblasts. The increase in NFIL-6 mRNA was associated with increased NFIL-6 protein. The increase in IL-6 mRNA was also associated with increased IL-6 protein. We propose that activations of NFIL-6 and IL-6 may be important mediators of the effects of bFGF on bone cells.