A leucine-based determinant in the epidermal growth factor receptor juxtamembrane domain is required for the efficient transport of ligand-receptor complexes to lysosomes

Ligand binding causes the epidermal growth factor (EGF) receptor to undergo accelerated internalization with eventual degradation in lysosomes. The go al of this study was to investigate the molecular basis of endocytic sortin g, focussing on post-internalization events. We have identified a sequence located between amino acid residues 675 and 697, encompassing a dileucine m otif at residues 679 and 680, that enhances endosome-to-lysosome transport when conformational restraints in the EGF receptor carboxyl terminus are re moved by truncation. The same dileucine motif is also necessary for efficie nt lysosomal transport of ligand-occupied full-length EGF receptors, A L679 A,L680A substitution diminished the degradation of occupied full-length EGF receptors without affecting internalization but had a significant effect o n recycling. Rapid recycling of mutant receptors resulted in reduced intrac ellular retention of occupied EGF receptors and delayed down-regulation of cell surface receptors, We propose that the L679A,L680A substitution acts p rimarily to impair transport of ligand-receptor complexes through an early endosomal compartment, diverting occupied receptors to a recycling compartm ent at the expense of incorporation into lysosome transport vesicles. We al so found that mutant receptors with truncations at the distal half of tyros ine kinase domain (residues 809-957) were not efficiently delivered to the cell surface but were destroyed in an endoplasmic reticulum-associated degr adative pathway.