Hsp-70 is closely associated with the transferrin receptor in exosomes from maturing reticulocytes.
The presence of the heat shock protein (hsp-70) has been detected in exocytosed vesicles (which are named exosomes) from mammalian and avian immature red cells (i.e. reticulocytes) as well as from a differentiating avian erythroleukaemic cell line. The close, but non-covalent, association of hsp-70 with the transferrin receptor (TFR) in exosomes is demonstrated by: (1) the ability to cross-link hsp-70 to TFR; (2) the co-immunoprecipitation of hsp-70 and TFR with an antibody against TFR, and the co-immunoprecipitation of TFR and hsp-70 with antibody against hsp-70; and (3) the retention of TFR by hsp-70 bound to ATP-agarose and the simultaneous elution of both proteins by excess ATP. Semi-quantitative analysis of the relative efficiency of cross-linking of these proteins in exosomes versus plasma membranes shows that TFR in exosomes is preferentially bound to hsp-70. From an analysis of the relative amounts of hsp-70 and TFR regenerated from the cross-linked complex, the ratio of TFR monomer bound to hsp-70 is approximately 1.5 to 1. Given the presence of hsp-70 in exosomes from several species and its close association with TFR (the major protein lost during reticulocyte maturation) it is proposed that hsp-70 plays a role in exosome formation and/or release in immature red cells.
Mathew
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Department of Biochemistry, McGill University, Montréal, Quebec, Canada.
Bell
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Johnstone
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D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism; D002412:Cations / Q000494:pharmacology; D002846:Chromatography, Affinity; D003432:Cross-Linking Reagents / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000737:chemistry; D005089:Exocytosis / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D015151:Immunoblotting; D017830:Octoxynol / Q000494:pharmacology; D011233:Precipitin Tests; D011990:Receptors, Transferrin / Q000276:immunology / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism*; D012685:Sepharose; D012756:Sheep; D013388:Succinimides / Q000378:metabolism
D000911:Antibodies, Monoclonal; D002412:Cations; D003432:Cross-Linking Reagents; D018840:HSP70 Heat-Shock Proteins; D011990:Receptors, Transferrin; D013388:Succinimides; D017830:Octoxynol; D012685:Sepharose; C011240:dithiobis(succinimidylpropionate)