Epidermal growth factor. Relationship between receptor regulation and mitogenesis in 3T3 cells.

Abstract

Exposure of confluent nondividing 3T3 cells to 10 nm mouse epidermal growth factor (EGF) at 37/sup 0/, followed by incubation for 4.5 h at 37/sup 0/, leads to a 70 to 85% reduction in the binding capacity for /sup 125/I-EGF. Scatchard analysis of the binding data indicate that the reduction of /sup 125/I-EGF binding is due to a decrease in the number of available EGF-receptors per cell, without any change in the affinity of the receptors for EGF. This modulation of the EGF-receptor by the growth factor, termed ''down regulation,'' is dependent on temperature, EGF concentration, time, and the physiological state of the cell. Receptor loss occurs at physiological EGF concentrations (0.1 to 10 nm) which span the concentration range which is mitogenic for 3T3 cells. Maximal stimulation of either (/sup 3/H)thymidine uptake or cell division occurs at 1 nm EGF, a concentration at which only 20% of the EGF-receptor sites are occupied and down regulation is only 55% complete. Low EGF concentrations (< or = to 1 nm) result in down regulation of unoccupied EGF-receptors. Down regulation of the EGF-receptor also occurs in SV 40-transformed 3T3 cells. Growing 3T3 cells exposed to EGF also loose available EGF-receptors. In contrastmore » to confluent cells, dividing 3T3 cells rapidly replace EGF-receptors on the surface of the cell, in the presence of EGF.« less