Expression and modulation of specific, high affinity binding sites for
erythropoietin on the human erythroleukemic cell line K562
JK Fraser, FK Lin and MV Berridge
Malaghan Institute of Medical Research, Wellington School of Medicine,
Wellington Hospital, New Zealand.
Erythroid differentiation is mediated by several interacting factors which
include the glycoprotein hormone erythropoietin (Epo), interleukin-3 (IL-3)
in the mouse, and erythroid-potentiating activity (EPA) in humans. Each of
these factors binds to specific cell surface receptors on responsive target
cells, but the way in which these factors interact to modulate
erythropoiesis is unknown. In the present study, we used the human
erythroleukemic cell line K562 to examine expression and regulation of the
receptor for Epo using 125I-labeled, bioactive recombinant human Epo. K562
cells expressed low numbers of a single class of high-affinity Epo
receptors corresponding to 4 to 6 receptors per K562 cell (KD = 270 to 290
pmol/L). Treatment of K562 cell cultures with medium conditioned by the
EPA-secreting cell line U937 (U937CM) increased receptor expression 2.6 to
3.5-fold to 13 to 17 receptors/cell (KD = 260 to 300 pmol/L). That all of
the Epo receptor- potentiating activity in U937CM was accounted for by EPA
was shown by a similar increase in Epo receptor expression on K562 cells
with recombinant EPA. The effect of U937CM on Epo receptors was reversed by
culturing cells in inducer-free medium for 3 days. Medium conditioned by
the 5637 cell line had no effect on Epo receptors on K562 cells. In
methylcellulose culture, U937CM and Epo acted synergistically to increase
erythroid differentiation of K562. Similarly, U937CM stimulated human cord
blood CFU-E growth under conditions in which Epo was limiting or in excess.
Increases in Epo receptor expression on K562 cells and on CFU-E in response
to EPA may mediate the effects of Epo on these cells.
Volume 71,
Issue 1,
pp. 104-109,
01/01/1988
Copyright © 1988 by The American Society of Hematology
