Iron chelators and hypoxia mimetics inhibit IFNgamma-mediated Jak-STAT signaling.

Treatment of cultured cells with iron chelators causes profound changes in gene expression and inhibition of cytokine signaling pathways, suggesting an important role for iron in inflammation. We have previously shown the treatment of cells with chelators which preferentially bind iron inhibits IFNgamma-mediated induction of IFN regulatory factor 1 in endothelial cells. To define the mechanisms mediating inhibition of IFNgamma-induced genes, we examined IFNgamma-induced signaling pathways in EC after treatment with chelators. Treatment resulted in inhibition of IFNgamma-induced STAT1 nuclear translocation. This was associated with inhibition of IFNgamma-induced STAT1 phosphorylation and loss of expression of the R1 subunit of the IFNgamma receptor (IFNgammaR) complex, without changes in expression of IFNgammaR complex subunits. Downregulation of IFNgammaR1 was not mediated through alterations in IFNgammaR1 gene transcription, but was induced by inhibition of IFNgammaR1 mRNA translation superimposed on a constitutively high receptor turnover through endosomal degradation. Furthermore, inhibition of IFNgamma signaling and downregulation of IFNgammaR1 was also mediated by nonmetal-binding hypoxia mimetics and reduced oxygen tensions. These data suggest that the target for chelator effects may be through iron requirements for oxygen-requiring dioxygenase enzymes.

Furunculosis due to Mycobacterium mageritense associated with footbaths at a nail salon.

We report two cases of lower-extremity furunculosis caused by Mycobacterium mageritense. Both patients were patrons of the same nail salon, where they received footbaths prior to pedicures. M. mageritense bacteria isolated from two whirlpool footbaths were determined to be closely related to the patient isolates by pulsed-field gel electrophoresis.

Iron chelators inhibit VCAM-1 expression in human dermal microvascular endothelial cells.

Vascular cell adhesion molecule (VCAM)-1 expression may be coupled to redox-sensitive regulatory pathways, and iron may play a role in generation of reactive oxygen species that participate in these signaling pathways. To investigate the role of iron in TNF alpha-induced VCAM-1 gene expression, human dermal microvascular endothelial cells (HDMEC) were stimulated with TNF alpha in the presence of iron chelators and examined for expression of VCAM-1. The iron chelators dipyridyl (DP) and desferoxamine (DFO) inhibited VCAM-1 protein and mRNA induction in a concentration- and time-dependent manner. The induction of VCAM-1 was not inhibited by nonmetal binding reactive oxygen species (ROS) scavengers, implying a direct effect of iron in the expression of these adhesion molecules. The effect of iron was mediated at the level of gene transcription since pretreatment with DP abrogated the TNF alpha-mediated up-regulation of VCAM-1 heterogeneous nuclear RNA. Pretreatment of HDMEC with DP prior to TNFalpha treatment had no effect on p65 nuclear localization, DNA binding, or serine phosphorylation. DP pretreatment inhibited TNF alpha- and IFN gamma-mediated interferon regulatory factor 1 (IRF-1) protein expression, although restoration of IRF-1 expression failed to reconstitute VCAM-1 expression. DP treatment also blocked VCAM-1 induction in human umbilical vein endothelium and blocked induction of a host of NF-kB activated genes in HDMEC including ICAM-1, IL-8, and tissue factor. I kappa B alpha, an NF-kappa B inducible and constitutively accessible gene not requiring chromatin remodeling for transcription, was not affected by DP treatment. These data suggest that iron plays a critical role in TNF alpha mediated VCAM-1 induction in HDMEC, and the target for iron effects may be IRF-1, NF-kappa B, and potentially chromatin remodeling.

Induction of interferon regulatory factor 1 expression in human dermal endothelial cells by interferon-gamma and tumor necrosis factor-alpha 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 up-regulation 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.