title: Overexpression of mitochondrial ferritin causes cytosolic iron depletion and changes cellular iron homeostasis.
abstract: Cytosolic ferritin sequesters and stores iron and, consequently, protects cells against iron-mediated free radical damage. However, the function of the newly discovered mitochondrial ferritin (MtFt) is unknown. To examine the role of MtFt in cellular iron metabolism, we established a cell line that stably overexpresses mouse MtFt under the control of a tetracycline-responsive promoter. The overexpression of MtFt caused a dose-dependent iron deficiency in the cytosol that was revealed by increased RNA-binding activity of iron regulatory proteins (IRPs) along with an increase in transferrin receptor levels and decrease in cytosolic ferritin. Consequently, the induction of MtFt resulted in a dramatic increase in cellular iron uptake from transferrin, most of which was incorporated into MtFt. The induction of MtFt caused a shift of iron from cytosolic ferritin to MtFt. In addition, iron inserted into MtFt was less available for chelation than that in cytosolic ferritin and the expression of MtFt was associated with decreased mitochondrial and cytosolic aconitase activities, the latter being consistent with the increase in IRP-binding activity. In conclusion, our results indicate that overexpression of MtFt causes a dramatic change in intracellular iron homeostasis and that shunting iron to MtFt likely limits its availability for active iron proteins.
authors.affiliation: Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital and Department of Physiology, McGill University, 3755 Cote Ste-Catherine Rd, Montreal, QC H3T 1E2, Canada.
authors.forename: Guangjun
authors.initials: G
authors.lastname: Nie
authors.forename: Alex D
authors.initials: AD
authors.lastname: Sheftel
authors.forename: Sangwon F
authors.initials: SF
authors.lastname: Kim
authors.forename: Prem
authors.initials: P
authors.lastname: Ponka
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003600:Cytosol / Q000737:chemistry*; D005293:Ferritins / Q000235:genetics / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D007501:Iron / Q000378:metabolism*; D000090463:Iron Deficiencies; D035925:Iron-Regulatory Proteins / Q000378:metabolism; D051379:Mice; D024101:Mitochondrial Proteins / Q000235:genetics / Q000502:physiology; D014162:Transfection
chemical_list: D035925:Iron-Regulatory Proteins; D024101:Mitochondrial Proteins; D005293:Ferritins; D007501:Iron; D000154:Aconitate Hydratase