Specific receptors for epidermal growth factor in rat intestinal microvillus membranes

Epidermal growth factor (EGF) is present in high concentrations in milk, salivary, and pancreaticobiliary secretions. EGF, delivered to the intestinal lumen by these fluids, appears to influence intestinal proliferation. Because EGF exerts its mitogenic effect through binding to specific membrane-bound receptors, binding studies of ¹²⁵I-labeled EGF to purified microvillus membrane (MVM) preparations from fetal, newborn, and adult rat small intestine were performed. Using the membrane filter technique, binding of ¹²⁵I-EGF to adult MVM was specific, saturable, and reversible. Adult and fetal MVM binding was rapid and reached a plateau after 30 min at both 20 and 37°C. No binding was detected at 4°C. Specific binding increased linearly from 0 to 75 μg MVM protein. Scatchard analysis revealed a single class of receptors in fetal and adult MVM with an association constant of 1.0 ± 0.35 x 10⁹ and 2.3 ± 1.6 x 10⁹ M^-1, respectively. Binding capacity was 435.0 ± 89 and 97.7 ± 41.3 fmol ¹²⁵I-EGF bound/mg MVM protein for fetal and adult MVM, respectively. Newborn MVM binding was negligible. After binding, cross-linking utilizing disuccinimidyl suberate, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography revealed a 170-kDa receptor. These data demonstrate specific receptors for EGF on MVM of rat small intestine and, thus, suggest a mechanism for the intraluminal regulation of enterocyte proliferation by EGF.