Induction of erythropoietin receptors during aclacinomycin-mediated erythroid differentiation of K562 leukemia cells.

Human K562 leukemia cells have been induced to differentiate along the erythroid lineage by aclacinomycin (ACM), an anthracyclic antitumor drug. During differentiation over 3 days in culture, the expression and the nature of erythropoietin (EPO) receptors have been analyzed using 125I-labeled bioactive recombinant human EPO. Aclacinomycin at 20 nM, the concentration inducing optimum differentiation, progressively increased EPO-specific binding. On day 3, EPO binding was nine-fold higher than that of the controls (1031 +/- 101 cpm/5 x 10(6) cells versus 112 +/- 15 cpm); with various concentrations of ACM, the increase in EPO binding appeared to parallel the recruitment of hemoglobin-producing cells. However, at 95% of growth inhibition, EPO binding remained constant while the percentage of differentiated cells decreased. Specific binding was reversible, saturable, and proportional to cell number; bound EPO was displaced by unlabeled EPO. Scatchard analysis of the equilibrium binding data suggested the existence of a single class of EPO receptors with an apparent Kd of 867 +/- 458 pM, corresponding to 400 +/- 142 receptors per cell. Affinity cross-linking of 125I-EPO using disuccinimidyl suberate followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions demonstrated that EPO was preferentially cross-linked to a protein of approximately 116 kD. Taken together, these results demonstrate that, in addition to cytostatic properties, antitumor drugs such as ACM can modulate the expression of differentiation factor receptors on the surface of leukemic cells.