Surface expression of Fcγ receptor III (CD16) on chemoattractant-stimulated neutrophils is determined by both surface shedding and translocation from intracellular storage compartments

Abstract

Stimulation of neutrophils (PMN) with chemoattractants markedly increases surface expression of several membrane proteins, including the complement receptors, CRI and CR3, by translocation from intracellular storage compartments to the cell surface. When we stimulated freshly-isolated PMN with FMLP, we observed little net change in surface Fcγ receptor (R) III expression. However, if elastase was first used to cleave most (85-90%) of the Fcγ R III from the PMN surface, subsequent treatment with FMLP induced a rapid renewal of surface Fcγ R III, achieving levels of ∼ 70% of that originally present on the cell surface after 15 min, suggesting translocation of intracellular receptors. This was confirmed by demonstrating concomitant depletion of > 80% of the intracellular Fcγ R III. Studies of density gradient fractions of N2-cavitated PMN indicated at least two distinct intracellular membrane fractions that contain Fcγ R III. Shedding of Fcγ R III induced by FMLP was about half-maximal by 15 min and nearly complete by 60 min. Stoichiometric assessment of FMLP-induced changes in PMN surface and intracellular Fcγ R III showed a marked depletion in intracellular Fcγ R III, little net change in surface Fcγ R III, and a large overall loss of total cell Fcγ R III that could be attributed to shedding. We conclude that stimulation by chemoattractants causes a rapid translocation of intracellular Fcγ R III to the PMN surface that is roughly balanced by the concomitant FMLP-induced shedding of this receptor.