Exosome formation during maturation of mammalian and avian reticulocytes: Evidence that exosome release is a major route for externalization of obsolete membrane proteins

Abstract

We have assessed whether exosome formation is a significant route for loss of plasma membrane functions during sheep reticulocyte maturation in vitro. Although the recovery of transferrin binding activity in exosomes is at best approximately 25-30% of the lost activity, recoveries of over 50% of the lost receptor can be obtained if 125I-labelled transferrin receptor is measured using an that receptor instability may contribute to the less than quantitative recovery of the transferrin receptor. Significantly higher (75-80%) levels of the nucleoside transporter can be recovered in exosomes during red cell maturation using 3H-nitrobenzylthioinosine binding to measure the nucleoside transporter. These data suggest that exosome formation is a major route for removal of plasma membrane proteins during reticulocyte maturation and plasma membrane remodelling. We have also shown that both in vivo and in vitro, embryonic chicken reticulocytes form exosomes which contain the transferrin receptor. Thus, exosome formation is not restricted to mammalian red cells, but also occurs in red cells, which retain organelles, such as nuclei and mitochondria, into the mature red cell stage.

Human Erythrocyte Membranes Contain a Cytochrome b561 That May Be Involved in Extracellular Ascorbate Recycling

“…Because DCytb shows Asc-dependent FeCN reductase activity when expressed in yeast (27), it is possible that it includes part of the erythroblast iron reduction/uptake system. However, all components of the hemoglobin-synthesizing system, as well as the transferrin receptor and the ability to take up iron, are lost during the maturation of reticulocytes (52)(53)(54)(55)(56). Furthermore, DMT-1 (divalent metal transporter 1), which works in concert with DCytb for iron uptake (57), was not detected in the membrane fractions of mature human erythrocytes by ion trap mass spectrometry (45).…”

Identification of Individual Exosome-Like Vesicles by Surface Enhanced Raman Spectroscopy

“…By inward budding of late endosomes, multivesicular bodies are formed which then fuse with the limiting membrane of the cell concomitantly releasing the exosomes. [3] This mechanism allows the cell to discard waste material [4,5] and is associated with intercellular communication. [6,7] Exosomes are of interest for diagnostic and prognostic applications as they contain molecules derived directly from the parent cell.…”

Autophagy and multivesicular bodies: two closely related partners

“…However, in specialized cell types such as reticulocytes, precursors of the mature red blood cell, TfR is accumulated in the internal vesicles of MVBs and released into the extracellular medium by fusion of MVBs with the limiting plasma membrane (i.e. exosomes) [2][3][4][5][6][7] ( Figure 1). Each cargo protein, destined for either recycling or exocytosis (TfR) or degradation (EGFR), transits through the sorting (early) endosome, where they are selected and targeted to each specific pathway.…”