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Cleavage of the transferrin receptor by human granulocytes: Preferential proteolysis of the exosome‐bound TFR
Author(s) -
Johnstone Rose M.
Publication year - 1996
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199608)168:2<333::aid-jcp12>3.0.co;2-4
Subject(s) - transferrin receptor , proteolysis , reticulocyte , cleavage (geology) , receptor , biology , microvesicles , exosome , protease , erythropoiesis , granulocyte , cytoplasm , microbiology and biotechnology , biochemistry , chemistry , enzyme , immunology , rna , medicine , anemia , paleontology , microrna , fracture (geology) , gene
In contrast with other mammalian granulocytes, human granulocytes rapidly cleave the transferrin receptor (TFR) from sheep exosomes. Proteolysis of TFR from exosomes is more rapid and more extensive than that from the sheep reticulocyte cell surface itself, although little difference in cleavage is seen when immunoprecipitates or when immobilized, solubilized receptors from the two sources are compared. Circulating exosomes but not the plasma membrane fraction from seven species of immature red cells or erythropoietic cells show the presence of a peptide of ∼18 kD recognized by an antibody to the cytoplasmic domain of the TFR. This 18 kD peptide is virtually absent from the corresponding cellular plasma membranes including human reticulocyte membranes. Taken together, the data are consistent with the conclusion that the exosomes released to the circulation from maturing red cells are the principal source of the soluble, circulating, truncated TFR. The granulocyte protease appears to be present on the cell surface and not released into the medium after short (30 min) periods of incubation at 37°C. The protease is inhibited by PMSF but only at high (1 mM) concentrations. Using sheep exosome bound‐TFR as substrate, human granulocytes exceed other granulocytes in their capacity to cleave TFR, suggesting that this may be a key factor for the prominent amount of circulating, soluble receptor found in human sera during periods of elevated reticulocyte levels. Human exosomes, unlike those from other species, contain little native size TFR. Truncated receptor containing the cytoplasmic domain being predominant in human exosomes. © 1996 Wiley‐Liss, Inc.