Solute carrier 11a1 (Slc11a1; formerly Nramp1) regulates metabolism and release of iron acquired by phagocytic, but not transferrin-receptor-mediated, iron uptake.
Solute carrier 11a1 (Slc11a1; formerly Nramp1; where Nramp stands for natural-resistance-associated macrophage protein) is a proton/bivalent cation antiporter that localizes to late endosomes/lysosomes and controls resistance to pathogens. In the present study the role of Slc11a1 in iron turnover is examined in macrophages transfected with Slc11a1(Gly169) (wild-type) or Slc11a1(Asp169) (mutant=functional null) alleles. Following direct acquisition of transferrin (Tf)-bound iron via the Tf receptor, iron uptake and release was equivalent in wild-type and mutant macrophages and was not influenced by interferon-gamma/lipopolysaccharide activation. Following phagocytosis of [(59)Fe]Tf-anti-Tf immune complexes, iron uptake was equivalent and up-regulated similarly with activation, but intracellular distribution was markedly different. In wild-type macrophages most iron was in the soluble (60%) rather than insoluble (12%) fraction, with 28% ferritin (Ft)-bound. With activation, the soluble component increased to 82% at the expense of Ft-bound iron (<5%). In mutant macrophages, 40-50% of iron was in insoluble form, 50-60% was soluble and <5% was Ft-bound. Western-blot analysis confirmed failure of mutant macrophages to degrade complexes 24 h after phagocytic uptake. Confocal microscopy showed that complexes were within lysosome-associated membrane protein 1-positive vesicles in wild-type and mutant macrophages at 30 min and 24 h, implying failure in the degradative process in mature phagosomes in mutant macrophages. NO-mediated iron release was 2.4-fold higher in activated wild-type macrophages compared with mutant macrophages. Overall, our data suggest that iron acquired by phagocytosis and degradation is retained within the phagosomal compartment in wild-type macrophages, and that NO triggers iron release by direct secretion of phagosomal contents rather than via the cytoplasm.
Mulero
Victoriano
V
Department of Immunology and Bacteriology, Western Infirmary, University of Glasgow, Glasgow G11 6NT, Scotland, UK.
Searle
Susan
S
Blackwell
Jenefer M
JM
Brock
Jeremy H
JH
D000483:Alleles; D000818:Animals; D017209:Apoptosis; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000502:physiology*; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D009154:Mutation; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D010587:Phagocytosis; D013997:Time Factors; D014162:Transfection; D014168:Transferrin / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D000099173:Natural Resistance-associated Macrophage Protein 1
D027682:Cation Transport Proteins; D002412:Cations; D007501:Iron; D009569:Nitric Oxide; D009573:Nitrites; D014168:Transferrin; D000099173:Natural Resistance-associated Macrophage Protein 1