Although epidermal growth factor (EGF) stimulates the growth of various cells in vitro, the biological role of this polypeptide is not known. Evidence that EGF may function as an autocrine or paracrine factor is suggested from previous studies demonstrating submaxillary gland preproEGF mRNA in other organs. We have shown that primary cultures of mouse uterine epithelial cells possess specific binding sites (Kd approximately 1.8 nM) for 125I-EGF and approximately 50 x 10-3 receptors/cell. EGF stimulated proliferation of the uterine cells in vitro, whereas other known growth factors did not. Immunolocalization of EGF in pronase-treated sections of the mouse uterus revealed staining at the luminal aspect of epithelial cells. Localization required protease treatment and the material reactive with anti-EGF antiserum was apparently not estrogen-dependent since this pattern of staining was readily observed in uteri from animals ovariectomized for over two weeks. Protease-treatment of sections was also required for localization of EGF in epithelial cells of the mouse kidney and mammary gland (mid-pregnant). We have found that kidney EGF occurs predominantly as the apparent precursor form (140 kDa) bound to cell membranes. Thus, it is likely that the observed pattern of EGF localization in uterus represents a membrane-bound form of the precursor. Hybridization with a 32-P-labelled cDNA probe for submaxillary gland preproEGF mRNA occurred with samples of uterine mRNA, although at much lower levels than that of kidney and submaxillary gland. The level of preproEGF mRNA increased in immature mouse uteri following treatment with estrogen. Northern blot analysis of uterine A+ mRNA from estrogen-treated mice revealed a single band of 4.9 kilobases, equivalent to that of submaxillary gland preproEGF mRNA. Studies are in progress to further understand the synthesis sorting and processing of the EGF precursor in different organs and the potential for various hormones to regulate these events.
