Abstract

Histamine and recombinant granulocyte colony-stimulating factor (rG-CSF) stimulated the differentiation of murine myeloblasts and promyelocytes to mature neutrophils. In connection with this, myeloperoxidase activity of these progenitor cells was decreased by either histamine or rG-CSF treatment. After pretreatment with histamine at 1 microM, both differentiation and the decrease in myeloperoxidase activity of myeloblasts and promyelocytes induced by rG-CSF were significantly augmented. Binding assays using 125I-labeled rG-CSF showed that the number of rG-CSF binding sites on the surface of neutrophil progenitor cells increased after histamine treatment. The histamine-induced increase in rG-CSF binding appeared to be definitely through H2 receptors. Furthermore, the increase in rG-CSF binding sites due to histamine treatment seemed to take place in association with the externalization of G-CSF receptors, because 1) the binding increase was observed in the presence of cycloheximide, 2) no concomitant increase in [3H]leucine uptake was elicited, and 3) colchicine and cytochalasin D effectively prevented the increase in rG-CSF binding due to histamine. In neutrophil progenitors, cAMP contents increased very rapidly and significantly after either histamine or rG-CSF treatment. Moreover, dibutyryl-cAMP increased rG-CSF binding to neutrophil progenitor cells in a dose-dependent fashion. However, when progenitor cells were pretreated with protein kinase A inhibitors, the histamine-induced increase in rG-CSF binding was remarkably decreased. This result seems to indicate that the stimulatory effects of histamine on rG-CSF binding to progenitor cells are intimately related to the cAMP-protein kinase A system in neutrophil progenitors. Moreover, c-myc mRNA expression in neutrophil progenitors was markedly reduced by either histamine or rG-CSF treatment. It was concluded that rG-CSF-induced differentiation of murine neutrophil progenitors was augmented by histamine pretreatment mainly due to an increase in rG-CSF receptors on these cells and this increase might be related to the externalization of rG-CSF receptors.