Skeletal growth factor is produced by human osteoblast-like cells in culture.

Human bone cells isolated from femoral heads were cultured in BGJb medium containing bovine serum albumin (100 micrograms/ml), insulin (1 microgram/ml) and epidermal growth factor (10 ng/ml), and the conditioned medium collected. The medium was concentrated, chromatographed using HPLC gel filtration (TSK 2000 SW), and assayed for mitogenic activity using [3H]thymidine incorporation into embryonic chick calvarial cells. The conditioned medium contained mitogenic activity which eluted with a different elution time than insulin or epidermal growth factor. Characterization of this activity suggests that it was due to human skeletal growth factor (SGF), a mitogen which had been previously isolated from human bone matrix. Common properties include: stimulation of DNA synthesis in cultured embryonic chick calvarial cells, competition with human SGF for binding to anti-SGF antibodies, elution from HPLC gel filtration as a large factor (Mr 100,000) under native conditions but as a small factor (Mr 10,000) under dissociative conditions (4 M guanidine HCl), elution time on HPLC reverse-phase chromatography (small SGF), inactivation by dithiothreitol, stability to heat, acidic or alkaline conditions and inactivation by trypsin and chymotrypsin. These observations provide evidence that human bone cells produce SGF. Conditioned medium from human skin cell cultures also contained mitogenic activity. However, the activity was less than that from bone cells and did not cross-react with the rat anti-SGF antibodies.