Published ahead of print on June 5, 2003, doi:10.1165/rcmb.2003-0070OC
© 2003 American Thoracic Society DOI: 10.1165/rcmb.2003-0070OC Superoxide-Dependent Iron UptakeA New Role for Anion Exchange Protein 2Departments of Medicine and Pediatrics, Duke University Medical Center, Durham; National Health and Environmental Effects Research Laboratory, Office of Research and Development, Environmental Protection Agency, Research Triangle Park; Center for Environmental Medicine and Lung Biology, University of North Carolina, Chapel Hill; and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina Address correspondence to: Claude A. Piantadosi, P.O. Box 3315, Duke University Medical Center, Durham, NC 27710. E-mail: piant001{at}mc.duke.edu 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.
Abbreviations: anion exchange, AE • bronchial epithelial growth medium, BEGM • bathophenanthroline disulfonate, BPS • 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, DIDS • ferric ammonium citrate, FAC • human bronchial epithelial cells, HBE cells • Hanks' balanced salt solution, HBSS • non–transferrin-bound iron, NTBI • phosphate-buffered saline, PBS • sodium dodecyl sulfate, SDS • 4-acetamido-4'-isothiocyanatostilbene-2,2'disulfonic acid, SITS • superoxide dismutase, SOD This article has been cited by other articles:
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