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The role of nitric oixde [i.e. oxide] in macrophage iron metabolism /

Authors
Publisher
McGill University
Publication Date
Keywords
  • Biology
  • Cell.
Disciplines
  • Biology

Abstract

In this study, I investigated various aspects of iron metabolism in inflammatory macrophages treated with NO donors or cytokines, since in activated macrophages NO is one of the major effector molecules produced by the enzyme called NO synthase. I stimulated RAW 264.7 cells (a murine macrophage cell line) with interferon-gamma (IFN-gamma) and lipopolysaccharide (LIPS), a treatment that induces NO synthase and NO production in these cells. I showed that LIPS and IFN-gamma increased IRP1 binding, but decreased RNA-binding of IRP2, followed by its degradation. Moreover, the decrease of IRP2 binding/protein levels was associated with a decrease in TfR mRNA levels and an increase in ferritin synthesis in LPS/IFN-gamma treated cells, and these changes could be prevented by inhibitors of inducible NO synthase. I also showed that IRP2 is a target for nitrosonium ion (NO+) which causes S-nitrosylation of this protein, leading to its degradation via the ubiquitin-proteasome pathway. NO+-mediated IRP2 degradation was associated with a dramatic decrease in TfR mRNA levels and an increase in ferritin synthesis associated with an increase in iron incorporation into ferritin. These changes occurred without any change in the IRE binding activity of IRP1, strongly suggesting that IRP2 alone can play a key role in controlling iron metabolism. Importantly, the unique 73 amino acid region of IRP2 contains 5 cysteines, and I showed that mutation of one of these cysteine (Cys178) blocked the degradation of IRP2 in NO+-treated cells. Taken together, these observations suggest that S-nitrosylation represents a signal for IRP2 ubiquitination and consequent proteasomal degradation, and that this may be an important mechanism in controlling iron homeostasis in macrophages. (Abstract shortened by UMI.)

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