Secretion of epidermal growth factor-like mitogens by cultured cells from bovine anterior pituitary glands

We have partially characterized growth factor activity secreted by early cultures of cells derived from bovine calf pituitary glands. Serum-free, chemically defined culture medium conditioned by pituitary cells stimulated DNA synthesis in rat kidney fibroblasts (NRK cells) equivalent to unconditioned medium containing 3 X 10(-10) M epidermal growth factor (EGF). The conditioned medium contained activity which competed with 125I-EGF for binding to EGF-receptors which was also equivalent to competition by 3 X 10(-10) M EGF in a radioreceptor assay. Secondary pituitary cultures produced about 10-fold more competing activity than did primary cultures and the production rate of the EGF-competing activity by the secondary cultures remained stable for over 4 weeks. Bio-Gel P-60 chromatography in 1 M acetic acid of an extract of conditioned medium resolved three peaks of EGF-competing activity. These peaks chromatographed with apparent mol wts of 17,000, 9,000, and 6,000. These peaks of activity were not as a result of EGF-binding proteins in the culture medium. The 6,000 mol wt peak contained activity which competed equally well with EGF for EGF receptor and antimouse EGF antibody binding. The 17,000 and 9,000 mol wt activities competed more effectively for binding to receptors than antibodies. The mitogenic activity in the three peaks correlated with the receptor-competing activity. However, the 17,000 and 9,000 mol wt peaks but not the 6,000 mol wt peak contained transforming growth factor activity capable of stimulating NRK cells to assume anchorage independent growth. These results suggest that a subpopulation of cells in pituitary glands secrete EGF and EGF-like transforming growth factors.