title: Cadmium-induced aggregation of iron regulatory protein-1.
abstract: Iron regulatory protein-1 (IRP-1) is central to regulation of iron homeostasis, and has been shown to be sensitive to Cd(2+) in vitro. Although Cd(2+) induces disulfide-bond formation in many proteins, the critical cysteine residues for iron binding in IRP-1 were shown not to be involved in Cd-induced IRP-1 aggregation in vitro. Here we show that Cd(2+) causes polymerization and aggregation of IRP-1 in vitro and in vivo, and decreases in a dose-dependent manner both its RNA-binding and aconitase enzymatic activities, as well as its cytosolic expression. We have used two-dimensional electrophoresis to demonstrate thiol-dependent self-association of purified recombinant IRP-1 treated with Cd(2+), as well as self-association in Cd(2+)-exposed mesangial cells. Circular dichroism spectra confirm significant conformational changes in the purified protein upon Cd(2+) exposure. Following Cd(2+) treatment, there is increased translocation of inactive IRP-1 to the actin cytoskeletal fraction, and this translocation is diminished by both antioxidant (BHA) treatment and inhibition of CaMK-II. These changes differ from those elicited by manipulation of iron levels. Cadmium-induced translocation of proteins to cellular compartments, and particularly to the cytoskeleton, is becoming a recognized event in Cd(2+) toxicity. Polymer-dependent translocation of IRP-1 in Cd(2+)-exposed cells may underlie effects of Cd(2+) on iron homeostasis.
authors.affiliation: University of Toronto, Laboratory Medicine and Pathobiology, 1 King's College Circle, Toronto, ON M5S 1A8, Canada.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: University of Toronto, Laboratory Medicine and Pathobiology, 1 King's College Circle, Toronto, ON M5S 1A8, Canada.
authors.forename: Weiqun
authors.initials: W
authors.lastname: Xiao
authors.affiliation: University of Toronto, Laboratory Medicine and Pathobiology, 1 King's College Circle, Toronto, ON M5S 1A8, Canada. Electronic address: doug.templeton@utoronto.ca.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Templeton
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001665:Binding Sites; D019256:Cadmium Chloride / Q000633:toxicity*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D002942:Circular Dichroism; D003599:Cytoskeleton / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D035941:Iron Regulatory Protein 1 / Q000378:metabolism*; D050527:Mesangial Cells / Q000187:drug effects* / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D058105:Polymerization; D011487:Protein Conformation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D012313:RNA / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
chemical_list: D000975:Antioxidants; D047428:Protein Kinase Inhibitors; D011994:Recombinant Proteins; D012313:RNA; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D035941:Iron Regulatory Protein 1; D019256:Cadmium Chloride
keywords: Cadmium ion; Calcium/calmodulin-dependent protein kinase-II; Cytoskeleton; Iron regulatory protein-1; Mesangial cell