Loss of the transferrin receptor during the maturation of sheep reticulocytes in vitro. An immunological approach

Abstract

Sheep reticulocyte-specific antiserum absorbed with mature sheep red cells has been used to isolate and identify reticulocyte-specific plasma-membrane proteins and to monitor their loss during incubation in vitro. Specific precipitation of labelled plasma-membrane proteins is obtained when detergent-solubilized extracts of 125I-labelled reticulocyte plasma membranes are incubated with this antiserum and Staphyloccus aureus, but not when mature-cell plasma membranes are treated similarly. During maturation of reticulocytes in vitro (up to 4 days at 37 degrees C), there is a marked decrease in the immunoprecipitable material. The anti-reticulocyte-specific antibodies have been identified as anti-(transferrin receptor) antibodies. By using these antibodies as a probe, the transferrin receptor has been shown to have a subunit molecular weight of 93 000. The data are consistent with reported molecular weights of this receptor and with the proposal that the receptor may exist as a dimer, since [125I]iodotyrosyl-peptide maps of the 93 000- and 186 000-mol.wt. components isolated are shown to be identical. Evidence is presented for the transmembrane nature of the receptor and for the presence of different binding sites for transferrin and these antibodies on the receptor.

Association of phorbol ester-induced hyperphosphorylation and reversible regulation of transferrin membrane receptors in HL60 cells.

“…It is a 180-kilodalton phosphorylated glycoprotein in its nonreduced homodimeric form (4)(5)(6). It is present in large amounts on the surface of rapidly proliferating cells of both malignant and normal origin (4), and it drastically diminishes when cells are induced to terminally differentiate (7)(8)(9).…”

Energy depletion retards the loss of membrane transport during reticulocyte maturation.

“…During maturation and aging of the mammalian erythrocyte, the activities of many enzymes (1-6), membrane transport systems (7)(8)(9)(10), and other membrane components (11)(12)(13)(14)(15) are dramatically decreased. These changes have been shown indirectly by comparing, activities in young and old populations of erythrocytes and, more directly, by following the activity in newly formed cells as they mature and increase in density during in vivo maturation (see, for example, ref.…”

Extracellular Vesicles (EVs); Basic Science, Clinical Relevance and Applications

“…Thirty years ago, two papers had been published within a week of each other-reported that, in reticulocytes, transferrin receptors associated with small vesicles are literally jettisoned from maturing blood reticulocytes into the extracellular space [14,15]. The name "exosome" for these extracellular vesicles was coined a few years later by Rose Johnstone, although the term was initially introduced for vesicles ranging from 40 to 1,000 nm that are released by a variety of cultured cells [19], later, this nomenclature was adopted for 40-100-nm vesicles released during reticulocyte differentiation as a consequence of multivesicular endosome (MVE) fusion with the plasma membrane [20,21].…”

“…Regardless the mechanisms; interaction between EVs and recipient cell membrane may include: (i) ligand/receptor binding, (ii) fusion, (iii) internalization of their content or, combination of these [26]. Extracellular vesicles may directly activate the recipient cell by acting as signaling complexes [77,78]. It worthwhile to mention that during cell exocytosis, proteins embedded in the vesicle membrane fuse and become part of the plasma membrane and the side of the protein that was facing the inside of the vesicle now faces the outside of the cell.…”