The human neutrophil lactoferrin (Lf), a cationic iron-binding glycoprotein, has an inhibitor role on granulocyte macrophage colony- stimulating factor (GM-CSF) production via interleukin-1 (IL-1). The nuclear localization of Lf suggests that it may be involved in the transcriptional regulation of GM-CSF gene expression. To explore this possibility, the effect of Lf on GM-CSF gene expression was investigated in various cell lines and in primary cultures of fibroblasts. Down-regulation of GM-CSF mRNA level was observed in Lf-transfected embryonic fibroblasts induced to produce GM-CSF by IL-1β. In 5637 cell-line and in embryonic fibroblasts, co-transfection experiments, in which an Lf expression vector was used together with a vector carrying a reporter gene linked to the GM-CSF promoter, revealed that Lf reduces the activity of the GM-CSF promoter. This effect is marked in IL- 1β-stimulated cells. These findings suggest that Lf plays a negative role in GM-CSF expression at the transcriptional level, perhaps through the mediation of IL-1β.
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