Lysosomal targeting of epidermal growth factor receptors via a kinase- dependent pathway is mediated by the receptor carboxyl-terminal residues 1022-1123

Abstract

Binding of epidermal growth factor (EGF) to its receptor induces rapid internalization and degradation of both ligand and receptor via the lysosomal pathway. To study the mechanism of intracellular sorting of EGF-EGF receptor complexes to lysosomes, NIH 3T3 cells transfected with wild-type and mutant EGF receptors were employed. The kinetics of 125I-EGF trafficking was analyzed using low concentrations of the ligand to avoid saturation of the specific sorting system. The relative size of the pool of internalized 125I-EGF-receptor complexes that were capable of recycling decreased as receptors traversed the endosomal system. The rate of 125I-EGF sequestration from the recycling pathway correlated with the rate of 125I- EGF transition from early to late endosomes as measured by Percoll gradient fractionation. Deletion of the last 63 amino acids of the EGF receptor cytoplasmic tail did not inhibit the process of sequestration and targeting to the late endosomes and lysosomes. Truncation of the 123 residues, however, resulted in impaired lysosomal targeting and increased recycling of EGF. Receptor mutant in which 165 residues were deleted displayed maximal ability to recycle and a minimal extent of sorting to the late endosomes. The data suggest that two regions of the EGF receptor molecule, residues 1022-1063 and to a lesser extent residues 1063-1123, contribute in the regulation of routing of EGF receptors to the degradation pathway. The kinase-negative receptor mutant recycled EGF more intensively compared with the wild-type receptor, and the transport of this mutant to late endosomes was inhibited. These results support the view that the receptor kinase activity is important for ligand-induced sorting of EGF receptors to the pathway of lysosomal degradation.