Induction of interferon regulatory factor 1 expression in human dermal endothelial cells by interferon-γ and tumor necrosis factor-α is transcriptionally regulated and requires iron

Interferon regulatory factor-1 is a transcription factor that is linked to the expression of genes important in the initiation of the inflammatory response and the control of cell cycle. In this study, we determined that the generation of interferon regulatory factor-1 expression in human dermal microvascular endothelial cells was transcriptionally mediated by tumor necrosis factor-alpha or interferon-gamma via iron-dependent pathways. The induction of interferon regulatory factor-1 protein and the upregulation of interferon regulatory factor-1 mRNA levels was inhibited when cells were pretreated with the iron chelators 2-2-dipyridyl or deferoxamine. This inhibition of interferon regulatory factor-1 expression was associated with loss of interferon regulatory factor-1 binding to the interferon-stimulated response element as assessed by electrophoretic mobility shift assay. Addition of exogenous iron with the iron chelator resulted in reconstitution of cytokine responsiveness, thus demonstrating iron as the target for the chelator effect. Both tumor necrosis factor-alpha and interferon-gamma-induced interferon regulatory factor-1 gene transcription, as assessed by the measurement of unspliced, nascent, heterogeneous nuclear RNA, and treatment with iron chelators blocked tumor necrosis factor-alpha or interferon-gamma mediated interferon regulatory factor-1 gene transcription. Iron was not essential, however, for the association of interferon regulatory factor-1 mRNA with polyribosomes, suggesting iron was not essential for interferon regulatory factor-1 protein translation. Through such inhibitory regulation on pro-inflammatory transcription factors, iron chelators may serve as anti-inflammatory agents.