Stimulation of Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) Production and Its Role as an Autocrine Inducer of CD 14 Upregulation in Human Myeloid Leukemia Cells

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Abstract
Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that takes part in the growth and differentiation of normal and leukemic hematopoietic cells. Because of its potential significance in the etiopathogenesis of myeloid leukemia, we have studied the extracellular stimuli leading to GM-CSF secretion from a human myeloid leukemia cell line, K-562, and have demonstrated an important role for the cytokine in the differentiation process of this cell line. TNF-α, IL-1β, phorbol ester (PMA), and calcium ionophore A23187 were found to stimulate GM-CSF production from K-562 cells. PMA caused the cells to differentiate into megakaryocytic lineage, whereas treatment with A23187 resulted in increased expression of monocyte/macrophage marker CD 14. Neutralization of the GM-CSF activity in the culture medium, as well as blocking of its receptors, resulted in suppression of the increase in CD14 expression and partially restored the proliferative capacity in cells exposed to A23187. Autocrine GM-CSF secretion did not appear to play an important role in PMA-induced megakaryocytic differentiation. These results suggest that autocrine GM-CSF secretion may be associated with differentiation of myeloid leukemic cells without any significant growth stimulatory activity.

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