Aluminofluoride‐ and Epidermal Growth Factor‐Stimulated DNA Synthesis in MOB 3‐4‐F2 Cells

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Abstract
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 calyaria, responded to F−(1‐2 mM) combined with Al3+and epidermal growth factor (EGF, 0.01–10. ng/ml) with increased DNA synthesis. Of the several types of Al‐F complexs, A1F4−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.

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