title: RNA silencing of the mitochondrial ABCB7 transporter in HeLa cells causes an iron-deficient phenotype with mitochondrial iron overload.
abstract: X-linked sideroblastic anemia with ataxia (XLSA/A) is caused by defects of the transporter ABCB7 and is characterized by mitochondrial iron deposition and excess of protoporphyrin in erythroid cells. We describe ABCB7 silencing in HeLa cells by performing sequential transfections with siRNAs. The phenotype of the ABCB7-deficient cells was characterized by a strong reduction in proliferation rate that was not rescued by iron supplementation, by evident signs of iron deficiency, and by a large approximately 6-fold increase of iron accumulation in the mitochondria that was poorly available to mitochondrial ferritin. The cells showed an increase of protoporphyrin IX, a higher sensitivity to H(2)O(2) toxicity, and a reduced activity of mitochondrial superoxide dismutase 2 (SOD2), while the activity of mitochondrial enzymes, such as citrate synthase or succinate dehydrogenase, and ATP content were not decreased. In contrast, aconitase activity, particularly that of the cytosolic, IRP1 form, was reduced. The results support the hypothesis that ABCB7 is involved in the transfer of iron from mitochondria to cytosol, and in the maturation of cytosolic Fe/S enzymes. In addition, the results indicate that anemia in XLSA/A is caused by the accumulation of iron in a form that is not readily usable for heme synthesis.
authors.affiliation: Dipartimento Materno Infantile e Tecnologie Biomediche, University of Brescia, Spedali Civili, Viale Europa 11, 25123 Brescia, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Cavadini
authors.forename: Giorgio
authors.initials: G
authors.lastname: Biasiotto
authors.forename: Maura
authors.initials: M
authors.lastname: Poli
authors.forename: Sonia
authors.initials: S
authors.lastname: Levi
authors.forename: Rosanna
authors.initials: R
authors.lastname: Verardi
authors.forename: Isabella
authors.initials: I
authors.lastname: Zanella
authors.forename: Manuela
authors.initials: M
authors.lastname: Derosas
authors.forename: Rosaria
authors.initials: R
authors.lastname: Ingrassia
authors.forename: Marcella
authors.initials: M
authors.lastname: Corrado
authors.forename: Paolo
authors.initials: P
authors.lastname: Arosio
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000235:genetics*; D018798:Anemia, Iron-Deficiency / Q000235:genetics* / Q000378:metabolism; D000756:Anemia, Sideroblastic / Q000235:genetics* / Q000378:metabolism; D001259:Ataxia / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D040181:Genetic Diseases, X-Linked / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006418:Heme / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D007501:Iron / Q000378:metabolism; D019190:Iron Overload / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology
chemical_list: C113037:ABCB7 protein, human; D018528:ATP-Binding Cassette Transporters; D024101:Mitochondrial Proteins; D034741:RNA, Small Interfering; D006418:Heme; D007501:Iron