We have previously shown that nitric oxide (NO) is involved in the hydroxyurea-induced increase of gamma-globin gene expression in cultured human erythroid progenitor cells and that hydroxyurea increases NO production in endothelial cells via endothelial NO synthase (NOS). Here we report that co-culture of human bone marrow endothelial cells with erythroid progenitor cells induced gamma-globin mRNA expression (1.8 fold), and was further elevated (2.4 fold) in the presence of hydroxyurea (40 μM). Based on these results, NOS-dependent stimulation of NO levels by bradykinin and lipopolysaccharide has been observed in endothelial (up to 0.3 μM of NO) and macrophage cells (up to 6 μM of NO), respectively. Bradykinin slightly increased gamma-globin mRNA levels in erythroid progenitor cells, but failed to increase gamma-globin mRNA levels in endothelial/erythroid cell co-cultures indicating that stimulation of endothelial cell production of NO alone is not sufficient to induce gamma-globin expression. In contrast, lipopolysaccharide and interferon-gamma mutually increased gamma-globin gene expression (2 fold) in macrophage/erythroid cell co-cultures. In addition, hydroxyurea (5–100 μM) induced NOS-dependent production of NO in human (up to 0.7 μM) and mouse macrophages (up to 1.2 μM). Co-culture studies of macrophages with erythroid progenitor cells also resulted in induction of gamma-globin mRNA expression (up to 3 fold) in the presence of hydroxyurea (20–100 μM). These results demonstrate a mechanism by which hydroxyurea may induce globin genes and affect changes in the phenotype of hematopoietic cells via the common paracrine effect of bone marrow stromal cells.

Author notes

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