INTERNALIZATION OF N-FORMYL PEPTIDE CHEMOTACTIC RECEPTOR-LIGAND COMPLEX BY HUMAN NEUTROPHILS - THE ROLE OF THE RECEPTORS 2-KDA EXTERNAL DOMAIN AND CARBOHYDRATES

We treated human neutrophils with papain to remove the external 2-kDa domain and along with it the two oligosaccharide side chains of the N- formyl peptide chemotactic receptor and investigated what effect their absence has on the ligand-receptor complex internalization. After pre labeling of the cells with I-125-hexapeptide for 5 min at 22 degrees C , about 95% of the bound radioactivity was located on the cell surface . During the first 5-min incubation at 37 degrees C both the control a nd papain-treated cells internalized 73% of the receptor-ligand comple xes suggesting that internalization is very rapid in human neutrophils and that removal of the external domain and the carbohydrates of the receptor does not affect the rate. However, the truncated receptor-lig and complexes were degraded at a faster rate because the radioactivity released into the medium was significantly higher and correspondingly the acid-resistant radioactivity significantly lower in the papain-tr eated neutrophils than in control cells already at 5 min and all subse quent time points. The radioactivity accumulated in the medium of the control and papain-treated neutrophils represented inactivated I-125-h exapeptide as less than 5% of it at 5, 30 and 120 min were capable of rebinding. No receptor recycling was detected in either cells. These r esults indicate that removal of the 2-kDa external domain and the carb ohydrates of the N-formyl chemotactic receptors has little effect on t he internalization rate of the receptor-ligand complexes but accelerat es markedly their intracellular degradation.