KU 812: A pluripotent human cell line with spontaneous erythroid terminal maturation

Abstract

A human leukemic cell line KU 812 was recently established and described as a basophilic cell line. In the present study we show that KU 812 and two of its clones are at least bipotent: in addition to a minor component of basophils, the majority of KU 812 cells belongs to the erythroid cell lineage with a significant percentage (about 15%) of mature hemoglobinized erythroblasts. This terminal differentiation is associated with the synchronized synthesis of the main erythroid proteins, including glycophorins, spectrin β chain, band 3, and hemoglobin. The predominant hemoglobins are adult, fetal, and Bart's hemoglobin. Adult hemoglobin represented up to 75% of all hemoglobins in the KU 812 F clone in passages containing a high number of mature erythroblasts. Transcripts of all human globin chains were present with ten times less embryonic chain messenger RNA (mRNA) than α-, β- or γ-chain mRNA. Hemin slightly increased the total hemoglobin production of the cell line, especially γ-globin chain synthesis, but did not modify the percentage of hemoglobinized cells. Phorbol myristate acetate (PMA) had a complex effect, inducing a proportion of KU 812 cells to adhere to the plastic culture flask. The adherent cell fraction expressed a very low level of specific erythroid proteins, but their ultrastructure was consistent with immature erythroid cells. In contrast, approximately 40% of the nonadherent cells were mature erythroid cells. Cell-sorting experiments showed that this paradoxic effect of PMA is mostly due to cell selection, the more mature cells being unable to adhere. In addition, KU 812 F was found to be sensitive to erythropoietin, which slightly increased its plating efficiency range (from 0% to 50%) in semisolid medium and enhanced hemoglobin accumulation twofold. In binding experiments using 125I erythropoietin, a single class of high-affinity Epo receptors (Kd: 250 pM) was detected by binding with a density of 205 receptors per cell. The KU 812 cell line is therefore a unique model for studying cell commitment toward different hematopoietic lineages and erythroid differentiation.