Effect of fibroblast growth factor-1 on the expression of early growth response-1 in human periodontal ligament cells

Background and Objectives: Early growth response‐1 is a nuclear transcription factor implicated in regulating cell proliferation. Fibroblast growth factor‐1 is the prototypic fibroblast growth factor involved in the proliferation and differentiation of various cell types. Expression of early growth response‐1 induced by fibroblast growth factor‐1 thus may be very important for cell growth, during both development and wound healing in oral tissue. However, little is known about the expression and kinetics of early growth response‐1 in fibroblast growth factor‐1‐stimulated oral cells. The aim of this study was to investigate the effects of fibroblast growth factor‐1 on the expression of early growth response‐1 in human periodontal ligament cells. Material and Methods: Periodontal ligament cells were cultured in medium containing 1, 10 or 100 ng/mL of fibroblast growth factor‐1 for 45 min or with 10 ng/mL of fibroblast growth factor‐1 for 15, 30, 45, 60 or 120 min. The proliferation of periodontal ligament cells was evaluated by measuring 5‐bromo‐2′‐deoxyuridine incorporation. The expression of early growth response‐1 mRNA and protein, and the localization of early growth response‐1 protein, were examined by western blotting, northern blotting and immunocytostaining. Results: 5‐Bromo‐2′‐deoxyuridine incorporation correlated directly with increases in fibroblast growth factor‐1 concentration, and 5‐bromo‐2′‐deoxyuridine incorporation peaked 45 min after starting treatment. Early growth response‐1 protein was expressed in response to a concentration of fibroblast growth factor‐1 as low as 1 ng. Peak expression of early growth response‐1 mRNA was observed at 15 min and that of early growth response‐1 protein at 60 min. The 140‐kDa early growth response‐1 protein was not detected in the nuclear fraction, and the peak expression of the 80‐kDa early growth response‐1 protein occurred at 60 min. Early growth response‐1 localized in or around the nucleus at 30 min. Conclusion: These results show that a concentration of fibroblast growth factor‐1 as low as 1 ng induces the expression of early growth response‐1 protein, and that the 80‐kDa early growth response‐1 protein functions in the nucleus of periodontal ligament cells treated with fibroblast growth factor‐1.