Signaling role of intracellular iron in NF-kappaB activation.
Iron chelators inhibit endotoxin-induced NF-kappaB activation in hepatic macrophages (HMs), suggesting a role for the intracellular chelatable pool of iron in NF-kappaB activation. The present study tested this hypothesis. Analysis of Fe(59)-loaded HMs stimulated with lipopolysaccharide (LPS), revealed a previously unreported, transient rise in intracellular low molecular weight (LMW).Fe(59) complex ([LMW.Fe](i)) at </=2 min returning to the basal level within 15 min. The [LMW.Fe](i) response preceded IkappaB kinase (IKK) (>/=15 min) and NF-kappaB (>/=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-kappaB activation. The [LMW.Fe](i) response was also observed in tumor necrosis factor alpha (TNFalpha)-stimulated HMs and RAW264.7 cells treated with LPS and interferon-gamma but not in primary rat hepatocytes or myofibroblastic cells exposed to LPS or TNFalpha. Both [LMW.Fe](i) response and IKK activation in LPS-stimulated HMs were inhibited by diphenylene iodonium (nonspecific inhibitor for flavin-containing oxidases), l-N(6)-(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(2)() 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-kappaB. 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.
Xiong
Shigang
S
Department of Pathology and Molecular Microbiology and Immunology, Keck School of Medicine of the University of Southern California, Los Angeles, California 90033, USA.
She
Hongyun
H
Takeuchi
Heigo
H
Han
Bora
B
Engelhardt
John F
JF
Barton
C H
CH
Zandi
Ebrahim
E
Giulivi
Cecilia
C
Tsukamoto
Hidekazu
H
D000818:Animals; D027682:Cation Transport Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D051550:I-kappa B Kinase; D015151:Immunoblotting; D007455:Iodine / Q000494:pharmacology; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008297:Male; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D000099173:Natural Resistance-associated Macrophage Protein 1
D027682:Cation Transport Proteins; D002614:Chelating Agents; D051550:I-kappa B Kinase; D007455:Iodine; D007501:Iron; D008070:Lipopolysaccharides; D016328:NF-kappa B; D009861:Onium Compounds; D017346:Protein Serine-Threonine Kinases; D014409:Tumor Necrosis Factor-alpha; D000099173:Natural Resistance-associated Macrophage Protein 1; C007517:diphenyleneiodonium; C496564:Chuk protein, mouse; C496562:Ikbkb protein, mouse; C496566:Ikbke protein, mouse