RNA silencing of the mitochondrial ABCB7 transporter in HeLa cells causes an iron-deficient phenotype with mitochondrial iron overload.
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.
Cavadini
Patrizia
P
Dipartimento Materno Infantile e Tecnologie Biomediche, University of Brescia, Spedali Civili, Viale Europa 11, 25123 Brescia, Italy.
Biasiotto
Giorgio
G
Poli
Maura
M
Levi
Sonia
S
Verardi
Rosanna
R
Zanella
Isabella
I
Derosas
Manuela
M
Ingrassia
Rosaria
R
Corrado
Marcella
M
Arosio
Paolo
P
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
C113037:ABCB7 protein, human; D018528:ATP-Binding Cassette Transporters; D024101:Mitochondrial Proteins; D034741:RNA, Small Interfering; D006418:Heme; D007501:Iron