EGF receptor regulation in normal mouse mammary gland

Estrogen (E), progesterone (P), and epidermal growth factor (EGF) are known to regulate growth and development of the normal mammary gland, and it is possible that EGF may interact with E and/or P. Estrogen (ER), progesterone (PR), and EGF receptors (EGF‐R) have been detected in both mammary epithelial and stromal cells, and the relative roles of the various cells types in hormone‐dependent growth regulation are not known. The present studies were undertaken to determine if E and/or P influence EGF action by exerting a regulatory effect on EGF‐R levels and which cell types are affected. The comparative effects of ovariectomy and hormone treatments on EGF‐R levels were examined in immature, pubertal 5‐week‐old and sexually mature 10‐week‐old female mice. EGF‐R were characterized as a single class of high affinity sites and EGF‐R concentration was 2‐fold higher in glands of 5‐week‐old mice. Ovariectomy had no significant effect on EGF‐R concentration in either age group, and treatment with E and/or P had no effect on EGF‐R levels in either epithelial or stromal cells in 5‐week‐old mice. In contrast, E+P treatment caused a 2‐fold increase in receptor concentration in 10‐week‐old mice in the mammary epithelium. Thus it appears that the developmental state of the gland may determine the nature and extent of the interaction of EGF, E, and P. © 1992 Wiley‐Liss, Inc.