Effects of genistein, tyrphostin, and pertussis toxin on EGF-induced mitogenesis in primary culture and clonal osteoblastic cells

Epidermal growth factor (EGF) has been found to stimulate proliferation in a variety of cell types. The EGF receptor is known to have tyrosine kinase activity [1], however, the role of this signal mechanism has not been established in bone cells. The aim of this study was to determine whether tyrosine kinase activity and G inhibitory (G_i) proteins are involved in EGF-stimulated proliferation in the osteoblastic cell line G292 and in primary culture osteoblasts isolated from neonatal rat calvaria. Cell proliferation was measured by ³H-thymidine incorporation using liquid scintillation spectrometry. EGF stimulates a dose-dependent increase in proliferation of G292 and primary culture cells above control. Genistein was able to inhibit the effects of EGF in the G292 cells. In the primary culture cells, genistein with EGF appeared to enhance proliferation compared with EGF alone or genistein alone. Tyrphostin 25, on the other hand, inhibited the EGF response in both of these cell types. Inactivation of G_i proteins with pertussis toxin was able to inhibit EGF-induced mitogenesis in the neonatal rat osteoblasts but did not appear to specifically inhibit this response in the G292 cells. These results suggest that although both of these osteoblastic cell types increase proliferation in response to EGF, their signal pathways are different.