A tyrosine‐based sorting signal in the β2 integrin cytoplasmic domain mediates its recycling to the plasma membrane and is required for ligand‐supported migration

Integrins play pivotal roles in supporting shear‐ and mechanical‐stress‐resistant cell adhesion and migration. These functions require the integrity of the short β subunit cytoplasmic domains, which contain multiple, highly conserved tyrosine‐based endocytic signals, typically found in receptors undergoing regulated, clathrin‐dependent endocytosis. We hypothesized that these sequences may control surface integrin dynamics in statically adherent and/or locomoting cells via regulated internalization and polarized recycling of the receptors. By using site‐directed mutagenesis and ectopic expression of the αL/β2 integrin in Chinese hamster ovary cells, we found that Y735 in the membrane‐proximal YRRF sequence is selectively required for recycling of spontaneously internalized receptors to the cell surface and to growth factor‐induced membrane ruffles. Disruption of this motif by non‐conservative substitutions has no effect on the receptor's adhesive function, but diverts internalized integrins from a recycling compartment into a degradative pathway. Conversely, the non‐conservative F754A substitution in the membrane‐proximal NPLF sequence abrogates ligand‐dependent adhesion and spreading without affecting receptor recycling. Both of these mutants display a severe impairment in ligand‐supported migration, suggesting the existence in integrin cytoplasmic domains of independent signals regulating apparently unrelated functions that are required to sustain cell migration over specific ligands.