ALUMINOFLUORIDE-STIMULATED AND EPIDERMAL GROWTH FACTOR-STIMULATED DNA-SYNTHESIS IN MOB 3-4-F2 CELLS

In attempt to study the mechanism of F--induced, osteoblast-mediated bone formation, we tried to show the characteristics of Al-F complex-induced mitogenesis in osteoblastic cells. The MOB 3-4-F2 cell line, an osteoblast-like cell line derived from neonatal mouse calvaria, responded to F- (1-2 mM) combined with Al3+ and epidermal growth factor (EGF, 0.01-100 ng/ml) with increased DNA synthesis. Of the several types of Al-F complexes, AlF4- is thought to act as a mitogenic factor. On the other hand, NaF at high concentrations (> 2 mM) markedly decreased cell viability. The AlF4--stimulated DNA synthesis at least with a delay of 48 hr, while EGF stimulated DNA synthesis within a few hours (4-6 hr). Both 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) and staurosporine, inhibitors of protein kinase C (PKC), further enhanced DNA synthesis in AlF4--treated cells, whereas 12-O-tetradecanoyl-13-acetate (TPA), an activator of PKC, decreased the DNA synthesis. In EGF-treated cells, staurosporine and TPA, but not H-7, decreased DNA synthesis. In addition, indomethacin, an inhibitor of cyclooxygenase, partly inhibited the EGF-induced mitogenesis, which, however, was restored by addition of PGE2. AlF4-, as well as EGF, stimulated the release of arachidonic acid and its metabolites. Indomethacin failed to inhibit the AlF4--induced mitogenesis. Thus, the mitogenic response of MOB 3-4-F2 cells to F- in the presence of Al3+ had the following characteristics: (1) it was effective over a narrow range, (2) it had a slow onset, (3) included a PKC-sensitive mechanism and (4) a PG(E2)-independent mechanism. In contrast, a wide range of EGF concentrations rapidly stimulated DNA synthesis by a PKC-sensitive, PG(E2)-dependent mechanism in these cells.