DEBRA M. MORIARITY AND C. RICHARD SAVAGE, JR.
Received January 7, 1980
Adult rat liver parenchymal cells in primary culture exhibit specific saturable binding of 125I-labeled murine epidermal growth factor (EGF). The Scatchard plot of the binding data obtained at 36°C was curvilinear yielding two apparent dissociation constants of 1.5 x 10-10 M and 1.2 X 10-9 M with 27,000 and 57,000 sites per cell, respectively. The binding data obtained at 2 degrees C yielded a linear Scatchard plot with an apparent dissociation constant of 4.4 X 10-9 M and 78,000 sites per cell. Exposure of the hepatocytes to EGF at 36°C resulted in a loss of EGF binding capacity due to down regulation of receptors. The cells recovered the capacity to bind EGF upon incubation in medium which did not contain EGF; this recovery was inhibited by cycloheximide. The cultures appeared to internalize and degrade bound EGF at 36°C but not at 2°C. The degradation of EGF was inhibited by chloroquine, an inhibitor of lysosomal enzymes. These data indicate that liver specifically binds and further processes EGF, and therefore, may be a physiological target tissue for this growth factor.