Abstract
HML/SE is a cytokine-dependent cell line established from childhood acute megakaryoblastic leukemia. Granulocyte-macrophage colony-stimulating factor or stem cell factor (SCF) alone could stimulate proliferation of HML/SE cells, however interleukin-3, interleukin-6, granulocyte colony-stimulating factor and thrombopoietin could not. Although erythropoietin (EPO) alone stimulated neither proliferation nor differentiation of HML/SE cells, it did stimulate proliferation of HML/SE cells and production of hemoglobin in the presence of SCF. SCF activated the human EPO receptor promoter and induced EPO receptor gene expression. Given these results, we speculate that HML/SE cells acquired responsiveness to EPO via the EPO receptor induced by SCF. Mutation analysis of putative transcription factor binding sites in the human EPO receptor promoter suggested that Sp1, rather than the GATA-1 binding site, contributed to the induction of the hEPOR gene. Although it is well documented that hematopoietic stem cells and primitive progenitors require both an early-acting cytokine and a lineage-specific cytokine to differentiate to a certain lineage, related mechanisms are not well understood. HML/SE may serve as an excellent model system to analyze functions of early-acting cytokine SCF and lineage-specific cytokine EPO related to proliferation and differentiation of hematopoietic stem cells.
Highlights
Proliferation and differentiation of hematopoietic stem/progenitor cells are modulated by cytokines such as interleukin-3 (IL-3),1 granulocyte-macrophage colony-stimulating factor (GM-CSF), stem cell factor (SCF), interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), erythropoietin (EPO) [1, 2], and thrombopoietin (TPO) [3]
Cytokines and Antibodies—Recombinant human (h) EPO, hGM-CSF, hIL-3, and hTPO were provided by Kirin Brewery (Tokyo, Japan), recombinant hSCF and hG-CSF were from Amgen Inc. (Thousand Oaks, CA), and recombinant hIL-6 was from Tosoh Co. (Kanagawa, Japan)
Reduced levels of CFU-E in these mice [21] means that generation of CFU-E from pluri-potent stem cell is largely dependent on SCF
Summary
Several studies indicated that hematopoietic stem cells required both groups of these cytokines to differentiate and maturate to the certain lineages in vitro. Early-acting cytokines can effectively interact with late-acting cytokines in the production of more mature cells [4] In both humans and mice, hematopoietic progenitors lose their responsiveness to IL-3 as they differentiate [4, 5]. The down-regulation of early-acting cytokine receptors and up-regulation of lineage-specific late-acting cytokine receptors may possibly occur as hematopoietic stem/progenitor cells differentiate. Hematopoietic cytokines can be classified into lineage-nonspecific early-acting cytokines and lineage-specific late-acting cytokines by biological activities and target cells [1] Cytokines such as SCF, IL-3, and GM-CSF belong to the former group and EPO, G-CSF, and TPO
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