Characterization of three erythropoietin (Epo)-binding proteins in various
human Epo-responsive cell lines and in cells transfected with human
Epo-receptor cDNA [see comments]
T Takahashi, S Chiba, N Hirano, Y Yazaki and H Hirai
Third Department of Internal Medicine, Faculty of Medicine, University of
Tokyo, Japan.
Molecular cloning of a cDNA for a mouse erythropoietin (Epo) receptor
(EpoR) has facilitated the understanding of the structure of this receptor.
However, there is, as yet, no explanation for the discrepancy between the
protein recognized by specific antibodies against mouse EpoR and the
unexpectedly larger species that can be cross-linked to labeled Epo. It is
unclear whether the product of an unidentified gene is included in the EpoR
complex. In the present study, we directly compared the cross-linking
patterns for human EpoR that were endogenously expressed in three types of
Epo-responsive cell, and that was artificially expressed in
nonhematopoietic cells after transfection with cDNA for human EpoR. We
observed that 85-kD and 105-kD proteins formed ligand-receptor complexes in
all the human Epo-responsive cells and, furthermore, that the formation of
a complex derived from the 70- kD protein was dependent on the level of
expression of the cloned EpoR mRNA in these cells. By contrast, a prominent
cross-linked band derived from the 70-kD protein and a weaker band derived
from the 80- to 85-kD protein, but no band derived from the 105-kD protein,
could be shown in the case of nonhematopoietic cells transfected with the
human EpoR cDNA. These observations suggest that the cloned cDNA for human
EpoR alone does not allow generation of the complete EpoR in
nonhematopoietic cells and that the 105-kD Epo-binding protein may
represent the product of an as yet unidentified gene that is expressed in
hematopoietic cells.
Volume 85,
Issue 1,
pp. 106-114,
01/01/1995
Copyright © 1995 by The American Society of Hematology
