Expression of the erythropoietin receptor on a human myeloma cell line

We demonstrated the expression of the erythropoietin (EPO) receptor by a human myeloma cell line (MM-S1) which was established in our laboratory. EPO dose-dependently stimulated the proliferation of MM-S1 cells. Binding of radioiodinated EPO (125I-Epo) to MM-S1 cells was competitively inhibited by unlabeled EPO, but not by other recombinant cytokines. Specific binding of 125I-Epo to MM-S1 cells was saturable, and the Scatchard analysis revealed 330 EPO binding sites per cell with a Kd of 0.56 nmol/L. Bound EPO was internalized by MM-S1 cells during incubation at 37 degrees C. This is the first report describing the expression of the EPO receptor by human cells other than those of the erythroid lineage.