Mouse prepro-epidermal growth factor synthesis by the kidney and other tissues

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Abstract
Epidermal growth factor (EGF), a protein comprising 53 amino acids, is derived from a precursor of 1,217 amino acids that includes at least seven EGF-like sequences1,2. EGF has diverse biological activities (see refs 3–6): it is a potent mitogen for many tissue culture cells, inhibits gastric acid secretion from the intestinal mucosa and promotes healing of the corneal epithelium. EGF given to fetal animals accelerates several developmental processes including palate formation, incisor eruption, eyelid opening and lung maturation. However, the physiological roles of EGF in vivo are unknown. The presence of high-affinity receptors in many fetal7 and adult tissues4 suggests that EGF is involved in normal cellular functions. Immunocytochemical studies have revealed the presence of EGF in mouse8 and human Submaxillary glands9,10, rat brain11 and human intestine9,10. The low levels of EGF in extracts from many tissues12,13 may reflect sequestration rather than synthesis of the polypeptide. We show here that several mouse tissues contain preproEGF mRNA and that it is synthesized mainly in the distal tubules of the kidney. PreproEGF does not seem to be processed to EGF or other peptides in this tissue.