Signaling role of intracellular iron in NF-kappa B activation

Xiong, S.G., She, H.Y., Takeuchi, H., Han, B., Engelhardt, J.F., Barton, C.H., Zandi, E., Giulivi, C. and Tsukamoto, H. (2003) Signaling role of intracellular iron in NF-kappa B activation. The Journal of Biological Chemistry, 278 (20), 17646-17654. (doi:10.1074/jbc.M210905200).

Abstract

Iron chelators inhibit endotoxin-induced NF-B activation in hepatic macrophages (HMs), suggesting a role for the intracellular chelatable pool of iron in NF-B activation. The present study tested this hypothesis. Analysis of Fe59-loaded HMs stimulated with lipopolysaccharide (LPS), revealed a previously unreported, transient rise in intracellular low molecular weight (LMW)·Fe59 complex ([LMW·Fe]i) at 2 min returning to the basal level within 15 min. The [LMW·Fe]i response preceded IB kinase (IKK) (15 min) and NF-B (30 min) activation. Iron chelators (1,2-dimethyl-3-hydroxypyridin-4-one and N,N'-bis-2-hydroxybenzylethylenediamine-N,N'-diacetic acid) abrogated the [LMW·Fe]i response and IKK and NF-B activation. The [LMW·Fe]i response was also observed in tumor necrosis factor (TNF)-stimulated HMs and RAW264.7 cells treated with LPS and interferon- but not in primary rat hepatocytes or myofibroblastic cells exposed to LPS or TNF. Both [LMW·Fe]i response and IKK activation in LPS-stimulated HMs were inhibited by diphenylene iodonium (nonspecific inhibitor for flavin-containing oxidases), L-N6-(1-iminoethyl)lysine (selective iNOS inhibitor), and adenoviral-mediated expression of a dominant negative mutant of Rac1 or Cu,Zn-superoxide dismutase, suggesting the role of ·NO and O in mediating the iron signaling. In fact, this inhibition was recapitulated by a cell-permeable scavenger of ONOO, 5,10,15,20-tetrakis (4-sulfonatophenyl)porphyrinato iron (III) chloride. Conversely, ONOO alone induced both [LMW·Fe]i response and IKK activation. Finally, direct addition of ferrous iron to cultured HMs activated IKK and NF-B. These results support a novel signaling role for [LMW·Fe]i in IKK activation, which appears to be induced by ONOO and selectively operative in macrophages.

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