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Iron‐responsive degradation of iron‐regulatory protein 1 does not require the Fe–S cluster
Author(s) -
Clarke Stephen L,
Vasanthakumar Aparna,
Anderson Sheila A,
Pondarré Corinne,
Koh Cheryl M,
Deck Kathryn M,
Pitula Joseph S,
Epstein Charles J,
Fleming Mark D,
Eisenstein Richard S
Publication year - 2006
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7600954
Subject(s) - aconitase , cytosol , biology , phosphorylation , microbiology and biotechnology , mutant , rna , protein degradation , serine , biochemistry , enzyme , gene , mitochondrion
The generally accepted role of iron‐regulatory protein 1 (IRP1) in orchestrating the fate of iron‐regulated mRNAs depends on the interconversion of its cytosolic aconitase and RNA‐binding forms through assembly/disassembly of its Fe–S cluster, without altering protein abundance. Here, we show that IRP1 protein abundance can be iron‐regulated. Modulation of IRP1 abundance by iron did not require assembly of the Fe–S cluster, since a mutant with all cluster‐ligating cysteines mutated to serine underwent iron‐induced protein degradation. Phosphorylation of IRP1 at S138 favored the RNA‐binding form and promoted iron‐dependent degradation. However, phosphorylation at S138 was not required for degradation. Further, degradation of an S138 phosphomimetic mutant was not blocked by mutation of cluster‐ligating cysteines. These findings were confirmed in mouse models with genetic defects in cytosolic Fe–S cluster assembly/disassembly. IRP1 RNA‐binding activity was primarily regulated by IRP1 degradation in these animals. Our results reveal a mechanism for regulating IRP1 action relevant to the control of iron homeostasis during cell proliferation, inflammation, and in response to diseases altering cytosolic Fe–S cluster assembly or disassembly.