Lactoferrin as a Possible Transcriptional Regulator

Lactoferrin (Lf) from human neutrophils has an inhibitory effect on granulocyte-macrophage colony-stimulating factor (GM-CSF) production via Interleukin-1 (IL-1). The nuclear localization of Lf and its ability to bind DNA suggest that it may be involved in the transcriptional regulation of GM-CSF. To explore this possibility, we used two different cell lines: 5637 with constitutive production of GM-CSF and IL-1s, and human embryonal fibroblasts with a low basal GM-CSF production inducible by IL-1s. In 5637 cell line, possessing a specific Lf receptor and being able to internalize Lf and translocate it into the nucleus, the levels of GM-CSF and IL-1s mRNA were not modified by incubation of cells in an Lf-containing medium or by transfection with an expression vector containing Lf cDNA, although the level of secreted GM-CSF was slightly reduced. In embryonal fibroblasts, induced by IL-1s treatment, downregulation of GM-CSF mRNA was demon-strated after transfection with the Lf expression vector. In both cell types, cotransfection with the Lf expression vector and a plasmid containing 2.0 kb of GM-CSF promoter sequence fused to the CAT reporter gene caused a net reduction of promoter activity. These results suggest that Lf plays a negative role in GM-CSF transcription, probably mediated by IL-1s.