Effects of interferon-gamma and lipopolysaccharide on macrophage iron metabolism are mediated by nitric oxide-induced degradation of iron regulatory protein 2.
Iron regulatory proteins (IRP-1 and IRP-2) control the synthesis of transferrin receptors (TfR) and ferritin by binding to iron-responsive elements, which are located in the 3'-untranslated region and the 5'-untranslated region of their respective mRNAs. Cellular iron levels affect binding of IRPs to iron-responsive elements and consequently expression of TfR and ferritin. Moreover, NO(*), a redox species of nitric oxide that interacts primarily with iron, can activate IRP-1 RNA binding activity resulting in an increase in TfR mRNA levels. Recently we found that treatment of RAW 264.7 cells (a murine macrophage cell line) with NO(+) (nitrosonium ion, which causes S-nitrosylation of thiol groups) resulted in a rapid decrease in RNA binding of IRP-2 followed by IRP-2 degradation, and these changes were associated with a decrease in TfR mRNA levels (Kim, S., and Ponka, P. (1999) J. Biol. Chem. 274, 33035-33042). In this study, we demonstrated that stimulation of RAW 264.7 cells with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) increased IRP-1 binding activity, whereas RNA binding of IRP-2 decreased and was followed by a degradation of this protein. Moreover, the decrease of IRP-2 binding/protein levels was associated with a decrease in TfR mRNA levels in LPS/IFN-gamma-treated cells, and these changes were prevented by inhibitors of inducible nitric oxide synthase. Furthermore, LPS/IFN-gamma-stimulated RAW 264.7 cells showed increased rates of ferritin synthesis. These results suggest that NO(+)-mediated degradation of IRP-2 plays a major role in iron metabolism during inflammation.
Kim
S
S
Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital and Departments of Physiology and Medicine, McGill University, 3755 Cote Ste-Catherine Road, Montreal, Quebec H3T 1E2, Canada.
Ponka
P
P
D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005290:Ferric Compounds / Q000494:pharmacology; D005293:Ferritins / Q000096:biosynthesis; D007371:Interferon-gamma / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism*; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D011485:Protein Binding / Q000187:drug effects; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005290:Ferric Compounds; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D008070:Lipopolysaccharides; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011990:Receptors, Transferrin; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; D005293:Ferritins; D007501:Iron; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2; C013531:ferric ammonium citrate