DIFFERENTIAL INFLUENCE OF EGF, TGFβ1, DHT, AND CORTISOL ON EGF-RECEPTOR(EGF-R) BINDING ACTIVITY IN LATE GESTATION FETAL RAT LUNG FIBROBLASTS.† 335

Lung cell differentiation is predominantly regulated by Fibroblast-Type II cell communication. We have shown that EGF is important in controlling the timing of this process and that EGF-R binding activity peaks on day 18-19 of gestation in fetal rat lung fibroblasts and declines thereafter, in agreement with regulation of this cell-cell communication. Hormones and growth factors exert positive and negative influences on lung cell differentiation, but whether they regulate EGF-R binding is unknown. We hypothesize that positive[EGF, Cortisol] and negative [TGFβ1, dihydrotestosterone (DHT)] regulators of lung cell differentiation affect EGF-R binding activity. We studied this in differentiated fetal lung fibroblasts at the time in late gestation when EGF-R activity is declining. Sex-specific fetal rat lung fibroblasts of day 21 (term=22) were cultured in DMEM + 10% fetal calf serum as control or with either: 1) EGF (10ng/ml); 2) Cortisol (10^-8M); 3) TGFβ1 (2ng/ml); 4) DHT (10^-8M). At confluence specific EGF binding was measured as the difference between total binding (measured using 0.4 ng/ml¹²⁵ I-EGF) and nonspecific binding (measured in the presence of a 500-fold excess of unlabelled EGF). Specific EGF-binding was elevated in fibroblasts grown in TGFβ1 (245±212 cpm/nmol DNA) and in DHT(280±81) as compared to controls (153±91) or to cells grown in EGF (192±55) or in Cortisol (153±55) [Mean±SD; N=4-9/condition]. This difference was present in both sexes, for example in female fibroblasts: TGFβ1 (270±87), DHT (265±91) vs. Control (127±18), EGF (165±10) and Cortisol (135±46). These data are consistent with postive factors advancing terminal differentiation (i.e. further decreasing EGF-R binding) while negative factors mimic an earlier stage of differentiation (i.e. increasing EGF-R binding). We conclude that factors that promote or inhibit the initiation of developmental differentiation regulate EGF-R activity even after cell-cell communication is established. This indicates that such factors continue to regulate the progression of lung cellular developmental differentiation. (HL 37930 and the Deutsche Forschungsgemeinschaft)