Regulation of the Epidermal Growth Factor Receptor in Fetal Rat Lung Fibroblasts during Late Gestation*

Lung epithelial cell differentiation is predominantly regulated by mesenchymal-epithelial cell communication. We have previously shown that epidermal growth factor (EGF) positively influences this process, and that EGF receptor (EGF-R) binding in fetal rat lung fibroblasts peaks on d18-19 of gestation, just before the onset of augmented surfactant synthesis. This regulation of EGF-R in late gestation fetal lung fibroblasts may control the timing of mesenchymal-epithelial cell communication leading to surfactant synthesis. Hormones and growth factors exert positive and negative influences on lung development, but whether they regulate the EGF-R is unknown. We hypothesized that positive [EGF, cortisol, retinoic acid (RA)] and negative [transforming growth-factor-beta1 (TGF-beta1), dihydrotestosterone (DHT)] regulators of lung cell development regulate the EGF-R in the fetal lung. We studied EGF-R binding and protein abundance in sex-specific fetal rat lung fibroblasts cultured at d17, d19, and d21. EGF-R binding was significantly elevated after RA (both sexes d17 and d19, females d21) and after DHT (females d19) treatment. EGF and cortisol had minimal or inhibitory effects on EGF-R binding. Western blot analysis showed that the observed changes in EGF-R binding were associated with similar changes in EGF-R protein. We conclude that factors that affect lung maturation continue to regulate EGF-R in a developmental, sex-specific manner during late gestation.