ERYTHROPOIETIN-DEPENDENT INDUCTION OF HEMOGLOBIN-SYNTHESIS IN A CYTOKINE-DEPENDENT CELL-LINE M-TAT

M-TAT is a cytokine-dependent cell line with the potential to differen tiate along the erythroid and megakaryocytic lineages. We cultured M-T AT cells long term (>1 year) in the continuous presence of erythropoie tin (EPO), granulocyte-macrophage colony-stimulating factor (GM-CSF), or stem cell factor (SCF). These long term cultures are referred to as M-TAT/EPO, M-TAT/GM-CSF, and M-TAT/SCF cells, respectively. Hemoglobi n concentration and gamma-globin and erythroid delta-aminolevulinate s ynthase mRNA levels were significantly higher in M-TAT/EPO cells than in M-TAT/GM-CSF cells. When the supplemented cytokine was switched fro m GM-CSF to EPO, hemoglobin synthesis in M-TAT/GM-CSF cells increased rapidly (within 5 h), and the level of GATA-1 mRNA increased. In contr ast, the addition of GM-CSF to the M-TAT/EPO cell culture decreased th e amount of hemoglobin, even in the presence of EPO, indicating that t he EPO signal for erythroid differentiation is suppressed by GM-CSF. T hus, erythroid development of M-TAT cells is promoted by EPO and suppr essed by GM-CSF. These results support the hypothesis that EPO activel y influences the programming of gene expression required for erythroid progenitor cell differentiation.