Recycling of epidermal growth factor-receptor complexes in A431 cells

The fate of epidermal growth factor (EGF) after internalization by human carcinoma A431 cells has been studied. Cells were allowed to internalize 125I-EGF for 10 min at 37 degrees C and treated with acid/salt solution to remove non-internalized ligand. Further incubation of these '125I-EGF-loaded' cells at 37 degrees C results in rapid recycling of internalized 125I-EGF-receptor complexes back to the cell surface. Recycling was assessed by measuring the increase in plasma membrane pool of 125I-EGF-receptor complexes as they became sensitive to acid/salt treatment, cross-linking with the membrane impermeant reagent bis(sulfosuccinimidyl)suberate and competitive substitution by unlabeled EGF. Moreover, redistribution of 125I-EGF-receptor complexes from endosomes to the plasma membrane was demonstrated using a subcellular fractionation technique. More than 50% of the total internalized EGF was found to be capable of recycling. The rate of recycling was significantly higher than that of EGF degradation in lysosomes. It was shown that EGF/receptor recycling is an energy-requiring and temperature-dependent process. Fluorescence microscopy studies demonstrate that endosomes located in a region adjacent to the Golgi complex are involved in the the recycling of EGF-receptor complexes in A431 cells. The data obtained suggest that dissociation of EGF from internalized receptor is not necessary for EGF receptor recycling.