EPIDERMAL GROWTH-FACTOR INDUCES EGR-1 MESSENGER-RNA AND PROTEIN IN MOUSE OSTEOBLASTIC CELLS

The nuclear signaling events activated when epidermal growth factor (E GF) interacts with osteoblasts to produce effects on growth and differ entiation are not clearly understood, and may include induction of imm ediate early genes such as Egr-1, a zinc finger transcription factor. In the present study, Northern analyses were performed to define the e ffects of EGF on the expression of Egr-1 mRNA in MC3T3-E1 mouse osteob lastic cells. Following treatment of quiescent, subconfluent MC3T3-E1 cells with 0.1-100 ng/ml EGF for various periods, maximal induction of Egr-1 mRNA occurred when cells were treated for 30-60 minutes with 1- 10 ng/ml EGF. Inhibition of protein kinase C activity by pretreatment with 1 mu M chelerythrine chloride or by prolonged stimulation with 50 ng/ml tetradecanoyl phorbol acetate (TPA) partially diminished the in duction of Egr-1 by EGF. Using an immunohistochemical approach, 10 ng/ ml EGF was observed to induce Egr-1 protein within 30-60 minutes and t his induction was localized to the nucleus. These observations indicat e that EGF induces Egr-1 mRNA and protein via protein kinase C and oth er signaling pathways, and that Egr-1 may be part of the regulatory ne twork mediating the actions of EGF on growth and differentiation of os teoblasts.