Functional receptors for epidermal growth factor in an epithelial-cell line derived from the rat small intestine

Epidermal growth factor (EGF) regulates the proliferation of cells of a rat intestinal epithelial-cell line (RIE-1) in culture. Confluent RIE-1 cells were stimulated to proliferate by EGF with a half-maximal effect at 1-2 ng/ml. In contrast, the growth of sparse RIE-1 cells was inhibited by the growth factor. Binding studies at 4°C with ¹²⁵I-EGF identified two classes of binding sites for EGF on RIE-1 cells, one of high affinity (K(D) = 1.8 x 10^-10 M; 1.8 x 10⁴ receptors/cell) and one of lower affinity (K(D) = 5.2 x 10^-9 M; 6.3 x 10⁴ receptors/cell). After binding to the cells at 37° C, ¹²⁵I-EGF was rapidly internalized and subsequently degraded. Degradation products were released into the medium after a lag of 15-30 min. The degradation of ¹²⁵I-EGF did not occur at 4°C and was inhibited at 37°C by chloroquine, methylamine or NH₄Cl, but not by colchicine. Exposure of RIE-1 cells to EGF caused a time- and dose-dependent loss of EGF receptors from the cell surface. The recovery of receptors after the removal of EGF was retarded in the absence of serum and prevented by the presence of cycloheximide or actinomycin D. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis separation of the ¹²⁵I-EGF-receptor complex from RIE-1 cells after covalently cross-linkin with disuccinimidyl suberate indicated a receptor of M(r) ≠ 160 000. The demonstration of functional EGF receptors in this cell line provides further evidence that EGF may regulate intestinal-epithelial-cell physiology.