Superoxide-dependent iron uptake: a new role for anion exchange protein 2.
Lung cells import iron across the plasma membrane as ferrous (Fe2+) ion by incompletely understood mechanisms. We tested the hypothesis that human bronchial epithelial (HBE) cells import non-transferrin-bound iron (NTBI) using superoxide-dependent ferri-reductase activity involving anion exchange protein 2 (AE2) and extracellular bicarbonate (HCO3-). HBE cells that constitutively express AE2 mRNA by reverse transcriptase-polymerase chain reaction and AE2 protein by Western analysis avidly transported NTBI after exposure to either Fe2+ or Fe3+, but reduction of Fe3+ to Fe2+ was first required. The ability of HBE cells to reduce Fe3+ and transport Fe2+ was inhibited by active extracellular superoxide dismutase (SOD). Similarly, HBE cells that overexpress Cu,Zn SOD after adenoviral infection with AdSOD1 showed diminished iron uptake. The role of AE2 in iron uptake was indicated by three lines of evidence: (i) lack of both iron reduction and iron transport in bicarbonate-free buffer at controlled pH, (ii) failure of HBE cells treated with stilbene AE inhibitors to reduce Fe3+ or transport iron, and (iii) inhibition of iron uptake in HBE cells by inhibition of AE2 protein expression with antisense oligonucleotides. We thus disclose a novel ferri-reductase mechanism of NTBI uptake by human lung cells that employs superoxide exchange for HCO3- by AE2 protein in the plasma membrane.
Ghio
Andrew J
AJ
P.O. Box 3315, Duke University Medical Center, Durham, NC 27710, USA.
Nozik-Grayck
Eva
E
Turi
Jennifer
J
Jaspers
Ilona
I
Mercatante
Danielle R
DR
Kole
Ryszard
R
Piantadosi
Claude A
CA
D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D027321:Anion Transport Proteins; D017920:Antiporters; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D006801:Humans; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism; D064606:SLC4A Proteins; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1; D013481:Superoxides / Q000378:metabolism*
D027321:Anion Transport Proteins; D017920:Antiporters; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D064606:SLC4A Proteins; C000606290:SOD1 protein, human; D013481:Superoxides; D007501:Iron; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1