Loss of specific chaperones involved in membrane glycoprotein biosynthesis during the maturation of human erythroid progenitor cells.
The production of erythrocytes requires the massive synthesis of red cell-specific proteins including hemoglobin, cytoskeletal proteins, as well as membrane glycoproteins glycophorin A (GPA) and anion exchanger 1 (AE1). We found that during the terminal differentiation of human CD34(+) erythroid progenitor cells in culture, key components of the endoplasmic reticulum (ER) protein translocation (Sec61alpha), glycosylation (OST48), and protein folding machinery, chaperones BiP, calreticulin (CRT), and Hsp90 were maintained to allow efficient red cell glycoprotein biosynthesis. Unexpected was the loss of calnexin (CNX), an ER glycoprotein chaperone, and ERp57, a protein-disulfide isomerase, as well as a major decrease of the cytosolic chaperones, Hsc70 and Hsp70, components normally involved in membrane glycoprotein folding and quality control. AE1 can traffic to the cell surface in mouse embryonic fibroblasts completely deficient in CNX or CRT, whereas disruption of the CNX/CRT-glycoprotein interactions in human K562 cells using castanospermine did not affect the cell-surface levels of endogenous GPA or expressed AE1. These results demonstrate that CNX and ERp57 are not required for major glycoprotein biosynthesis during red cell development, in contrast to their role in glycoprotein folding and quality control in other cells.
Patterson
Sian T
ST
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Li
Jing
J
Kang
Jeong-Ah
JA
Wickrema
Amittha
A
Williams
David B
DB
Reithmeier
Reinhart A F
RA
D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism; D018952:Antigens, CD34 / Q000378:metabolism; D037281:Calnexin / Q000235:genetics / Q000378:metabolism; D037282:Calreticulin / Q000378:metabolism; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015672:Erythroid Precursor Cells / Q000166:cytology* / Q000378:metabolism*; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D020014:K562 Cells; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D001457:Anion Exchange Protein 1, Erythrocyte; D018952:Antigens, CD34; D037282:Calreticulin; D050883:HSC70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D012333:RNA, Messenger; D037281:Calnexin