Iron-responsive degradation of iron-regulatory protein 1 does not require the Fe-S cluster.
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.
Clarke
Stephen L
SL
Department of Nutritional Sciences, University of Wisconsin, Madison, WI 53706, USA.
Vasanthakumar
Aparna
A
Anderson
Sheila A
SA
Pondarré
Corinne
C
Koh
Cheryl M
CM
Deck
Kathryn M
KM
Pitula
Joseph S
JS
Epstein
Charles J
CJ
Fleming
Mark D
MD
Eisenstein
Richard S
RS
D000818:Animals; D002460:Cell Line; D006427:Hemin / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000502:physiology*; D035941:Iron Regulatory Protein 1 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism
D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012694:Serine; D006427:Hemin; D007501:Iron; D035941:Iron Regulatory Protein 1