Granulocyte-macrophage colony-stimulating factor and erythropoietin act competitively to induce two different programs of differentiation in the human pluripotent cell line UT-7

Abstract

The UT-7 cell line was established from a patient with a megakaryoblastic leukemia (Komatsu et al, Cancer Res 51: 341, 1991). Its proliferation is strictly dependent on the presence of hematopoietic growth factors including erythropoietin (Epo), granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-3 (IL-3). We investigated the differentiation capacities of this cell line under the action of several growth factors, using immunomarkers, flow cytometry, and ultrastructural techniques. In the presence of GM-CSF and IL-3, eosinophil and basophil promyelocytes were detected, as well as a few cells with erythroid and megakaryocytic (MK) differentiation features. In contrast, Epo induced a marked erythroid differentiation with an increase of glycophorin A expression, accompanied by a few hemoglobinized cells. Differentiation induced by the growth factors took 24 to 48 hours to begin, and increased with cell passages to a plateau at 2 weeks of culture. However, this was not only due to a cell selection because the differential effects of Epo and GM-CSF were observed from a single cell clone and the phenotype could be reversed by opposite growth factors, even after a long period of culture. We subsequently investigated the phenotype of UT-7 in the presence of combinations of Epo, IL-3, and GM-CSF, and showed that GM-CSF and IL-3 act predominantly over Epo. This effect was mediated by a rapid downmodulation of Epo receptors by GM-CSF at messenger RNA and binding sites levels, without a change in receptor affinities. On the other hand, Epo had no effect on number and affinity of GM-CSF receptors. This study shows that UT-7 is a growth factor-dependent pluripotent cell line in which commitment may be directed by a hierarchical action of growth factors through an early and rapid transmodulation of growth factor receptors.

Thrombopoietin activates a STAT5-like factor in hematopoietic cells.

“…Our data suggested that the three cytokines TPO, GM-CSF and EPO, activate similar JAK/STATs pathway in the same cell, since all activate JAK2 and not JAK1 (this report; Ihle et al, 1994) and all three activate STAT5 and not STAT1-4 (this report;Lamer et al, 1993;Yamamoto et al, 1994). Since these three cytokines induce cell proliferation of the UT7 cells but trigger different differentiation programs (Hermine et al, 1992; and unpublished data), our results would be consistent with a role of JAK2/STAT5 in cell proliferation rather than in cell differentiation. This hypothesis is further strengthened by our findings that PRL and IL-3-which mainly allow the hematopoietic BAF-3 cells to proliferate-also activate STAT5 in BAF-3 cells, and by the possible activation of STAT5 by a number of other cytokines (see above).…”

Erythropoietin induces the association of phosphatidylinositol 3′‐kinase with a tyrosine‐phosphorylated protein complex containing the erythropoietin receptor

“…The levels of PtdIns 3-kinase stimulation produced by the various growth factors could be explained, at least in part, by the relative number of growth-factor membrane receptors. UT7 cells exhibit only 200 high-affinity GM-CSF receptors, 7000 erythropoietin receptors [41] and more than 60000 SCF receptors (Mayeux, P., unpublished results). The number of IL-3 and IL-6 receptors has not been determined.…”

Prolactin, growth hormone, erythropoietin and granulocyte-macrophage colony stimulating factor induce MGF-Stat5 DNA binding activity.

“…EPO and GM-CSF, for example, both induce the same factor in the multipotential hematopoietic cell line UT7. Both cytokines induce the proliferation of UT7 cells, but the cytokines have distinct effects on the differentiation of UT7 cells (Komatsu et al, 1991;Hermine et al, 1992). It is reasonable to suggest that MGF-StatS activation might be important for the common effect, proliferation, via the regulation of an overlapping subset of target genes induced by EPO and GM-CSF.…”