title: Iron-responsive degradation of iron-regulatory protein 1 does not require the Fe-S cluster.
abstract: 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.
authors.affiliation: Department of Nutritional Sciences, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Clarke
authors.forename: Aparna
authors.initials: A
authors.lastname: Vasanthakumar
authors.forename: Sheila A
authors.initials: SA
authors.lastname: Anderson
authors.forename: Corinne
authors.initials: C
authors.lastname: Pondarré
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Koh
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Deck
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Pitula
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Epstein
authors.forename: Mark D
authors.initials: MD
authors.lastname: Fleming
authors.forename: Richard S
authors.initials: RS
authors.lastname: Eisenstein
mesh_terms: 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
chemical_list: D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012694:Serine; D006427:Hemin; D007501:Iron; D035941:Iron Regulatory Protein 1