Effect of protein and steroidal osteotropic agents on differentiation and epidermal growth factor‐mediated growth of the CFK1 osseous cell line

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Abstract
The effects of factors known to influence bone metabolism were examined using the osseous cell line CFK1. Parathyroid hormone (PTH) and dexamethasone (DEX) appeared to enhance the formation of cell foci of CFK1 cells in culture whereas retinoic acid (RA) caused a marked alteration in individual cell morphology. Bone morphogenetic protein (BMP-2) and PTH increased alkaline phosphatase activity, however, this index of differentiation was suppressed by epidermal growth factor (EGF), DEX, and RA. BMP-2 and EGF each stimulated DNA synthesis in a dose-dependent manner and enhanced cell numbers, but, no synergistic response of EGF and BMP-2 was observed. PTH and DEX failed to significantly alter cell number of EGF-stimulated DNA synthesis or cell proliferation. Although RA treatment of CFK1 cells resulted in a reduction in cell number compared to control, pretreatment with RA enhanced EGF-stimulated DNA synthesis and proliferative effects. At least part of this effect was by increasing the EGF receptor binding capacity of the cells. Furthermore, using cell cycle analysis, addition of EGF stimulated the progression of RA-treated cells into the DNA synthesis (S) phase with a reduced lag time. EGF and BMP-2, therefore, appear to exert a role in the expansion dynamics of the CFK1 population although BMP-2 may also enhance differentiation. PTH and DEX may act primarily to modulate the differentiated function of the CFK1 cells. RA inhibited cell proliferation and may mediate differentiation towards a less established cell population with upregulation of EGF receptors. The CFK1 cell model may, therefore, provide insight into microenvironmental control of growth and differentiation of precursor osseous cells.