Secretion of Epidermal Growth Factor-Like Mitogens by Cultured Cells from Bovine Anterior Pituitary Glands*

Abstract

Growth factor activity secreted by early cultures of cells derived from bovine calf pituitary glands was partially characterized. 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 .times. 10-10 M epidermal growth factor (EGF). The conditioned medium contained activity which competed with 125I-EGF for binding EGF-receptors which was also equivalent to competition by 3 .times. 10-10 M EGF in a radioreceptor assay. Secondary pituitary cultures produced .apprx. 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 > 4 wk. Bio-Gel P-60 chromatography in 1 M acetic acid of an extract of conditioned medium resolved 3 peaks of EGF-competing activity. These peaks chromatographed with apparent MW of 17,000, 9000 and 6000. These peaks of activity were not as a result of EGF binding proteins in the culture medium. The 6000 MW peak contained activity which competed equally well with EGF for EGF receptor and antimouse EGF antibody binding. The 17,000 and 9000 MW activities competed more effectively for binding to receptors than antibodies. The mitogenic activity in the 3 peaks correlated with the receptor-competing activity. The 17,000 and 9000 MW peaks, but not the 6000 MW peak contained transforming growth factor activity capable of stimulating NRK cells to assume anchorage independent growth. A subpopulation of cells in pituitary glands secrete EGF and EGF-like transforming growth factors.