Murine erythroleukaemia cells (Friend cells) possess high‐affinity binding sites for erythropoietin

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Abstract
Murine erythroleukaemia cells represent erythroid precursors blocked near the CFU-E or proerythroblast stage. In contrast to their non-leukaemic equivalents, neither their proliferation nor their differentiation seems to be affected by erythropoietin. However, we show in this paper that both uncommitted and committed, benzidine-positive, cells bind iodinated erythropoietin. The binding is of high affinity (Kd = 490 +/- 160 pM) and reversible with a half-life of the complex of 77 +/- 19 min. The number of binding sites is low (300-600 per cell). In contrast the haematopoietic non-erythroid cell lines HL 60 and L 1210 and the myeloid-erythroid human cell line K 562 do not exhibit specific binding. If these binding sites represent true hormone receptors, their presence on a permanent cell line should facilitate erythropoietin receptor purification.