Human skeletal growth factor stimulates collagen synthesis and inhibits proliferation in a clonal osteoblast cell line (MC3T3‐E1)

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Abstract
Human skeletal growth factor (hSGF), an 11‐kD polypeptide purified from human bone, has been proposed to be a local regulator of bone formation. To investigate the underlying cellular mechanisms in an in vitro model system, we examined the effects of hSGF on proliferation and collagen synthesis in cells of the clonal osteoblast cell line MC3T3‐E1. This line was isolated from newborn mouse calvarial cells and retains many characteristics of mature osteoblasts (Sudo, H., et al., (1984) J. Cell Biol. 96:191). A 14‐hr treatment with hSGF increased noncollagenous protein synthesis to 215% of unstimulated controls and increased collagen synthesis to 630% of controls as determined by [3H]proline incorporation and high‐pressure liquid chromatographic separation of [3H]proline and [3H]hydroxyproline in acid hydrolysates of trichloroacetic acid‐insoluble protein. HSGF did not increase cell number over a 48‐hr period and caused a reversible inhibition of DNA synthesis. Half‐maximal hSGF concentration for stimulation of [3H]proline incorporation and inhibition of [3H]thymidine incorporation was 100 ng/ml. HSGF also inhibited DNA synthesis in cells stimulated by serum. In contrast, hSGF stimulated both collagen synthesis and DNA synthesis in primary cultures of chick embryo bone cells, which may be developmentally less mature than MC3T3‐E1 cells. The results suggest that hSGF directly stimulated mature osteoblast matrix synthetic activity and that hSGF has differential effects on proliferation of osteoblast progenitor cells and mature osteoblasts.