Epidermal Growth Factor (EGF)-Like Transforming Growth Factor (TGF) Activity and EGF Receptors in Ovine Fetal Tissues: Possible Role for TGF in Ovine Fetal Development

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Abstract
To determine whether epidermal growth factor (EGF) or EGF-like transforming growth factors (TGFs) are present in ovine fetal tissues, we have tested acid-ethanol extracts of ovine fetal kidney for the ability to induce anchorage-independent growth of normal rat kidney fibroblasts in soft agar and to compete with 125I-mouse EGF for binding to receptors in sheep liver. The fetal kidney extract (20-1000 μg protein/ml) stimulated a dose-dependent increase in the number of soft agar colonies of normal rat kidney cells. Approximately 70% of these colonies measured > 3100 μM2. The fetal kidney extract was dissolved in 1 M acetic acid and chromatographed on Bio-Gel P 10. Two peaks of TGF-like activity, with approximate MW 14.5K (peak 1) and 9K (peak 2), eluted from the column. Half-maximal effects of pooled peaks 1 and 2 on colony formation were achieved using 100 and 20 μg protein/ml, respectively. Peaks 1 and 2 also competed with 125I-mouse EGF for binding to EGF receptors in ovine fetal liver but had no activity in a homologous mouse EGF radioimmunoassay sensitive to 15 pg mouse EGF. Neither TGF activity nor EGF receptor binding activity was detected in Bio-Gel fractions co-eluting with 125I-mouse EGF. Specific 125I-EGF binding sites in fetal liver were detected as early as midgestation, and the number of EGF binding sites increased markedly in late gestation, exceeding the number of EGF binding sites in the livers of pregnant ewes. These findings demonstrate the presence of TGF-like activity in ovine fetal kidney and high affinity EGF receptors in ovine fetal liver. The absence of EGF receptor activity in Bio-Gel fractions coeluting with 125I-mouse EGF suggests that TGF may predominate in the ovine fetus and may play an EGF-like role in ovine fetal development.