Disease relevance of Slc11a2

• Hepatic and/or duodenal response patterns of iron metabolism genes, such as Trfr, cybrd1, and Slc11a2, explained the transition from early postnatal iron deficiency to iron overload by 12 weeks of age [1].
• Microcytic anemia (mk) mice and Belgrade (b) rats have severe iron deficiency anemia due to defects in intestinal iron transport and erythroid iron utilization [2].
• Based on these observations and on reports that show that the closely related Nramp2 gene is a metal ion transporter, we evaluated the effect of iron on the growth of Mycobacterium avium within macrophages as well as on the stability of Nramp1 mRNA [3].

High impact information on Slc11a2

• Endosomal acidification leads to iron release, and iron is transported out of the endosome through the activity of divalent metal transporter 1 (DMT1, formerly Nramp2), a transmembrane iron transporter that functions only at low pH [4].
• Homozygous mk/mk mice have microcytic, hypochromic anaemia due to severe defects in intestinal iron absorption and erythroid iron utilization [5].
• We report the identification of a strong candidate gene for mk, and suggest that the phenotype is a consequence of a missense mutation in Nramp2 (ref. 5), a previously identified gene of unknown function [5].
• The mk allele carries a missense mutation that causes substitution of valine by alanine at amino acid 173 of the p45 NF-E2 protein [6].
• These findings suggest that Nramp2 plays a key role in the metabolism of transferrin-bound iron by transporting free Fe2+ across the endosomal membrane and into the cytoplasm [7].

Biological context of Slc11a2

• However, inactivation of murine Hfe ameliorates the phenotype of animals lacking Slc11a2 [8].
• Slc11a2 is required for intestinal iron absorption and erythropoiesis but dispensable in placenta and liver [8].
• Previous reports concerning gene expression levels of the duodenal iron transporters DMT1 and IREG1 in HH patients and animal models are controversial, however, and in many cases only mRNA expression levels were investigated [9].
• Both Fugu paralogs are more Slc11a2-like based on sequence homology and phylogenetic studies [10].
• Interestingly, in Trf(hpx) homozygotes, DMT1 expression was strongly induced in the villus brush border when compared to control animals [11].

Anatomical context of Slc11a2

• Coexpression of DMT1 and TfR in reticulocytes was also detected by double immunofluorescence and confocal microscopy [12].
• Iron transport and expression of the 2 isoforms of DMT1 was studied in erythroid cells that consume large quantities of iron for biosynthesis of hemoglobin [12].
• Hfe(-/-) mice do not necessarily display features of iron deficiency in the duodenum, indicated by an increase in mRNA and protein levels of DMT1 and Ireg1 [9].
• These results indicate that Dmt1 can be modulated by the enterocyte iron level, whereas Hephaestin and Ireg1 expression respond to systemic rather than local signals of iron status [13].
• In this study, RAW264.7 macrophages and 2 independently derived murine Sertoli cells lines, TM4 and 15P-1, were used to further study the subcellular localization of Nramp2/DMT1 in phagocytic cells, including possible recruitment to the phagosomal membrane [14].

Associations of Slc11a2 with chemical compounds

• Using the fluorescent, metal-sensitive dye calcein, and a combination of membrane-permeant and -impermeant iron chelators, Nramp2 transport was measured and quantitated with respect to kinetic parameters and at steady state [15].
• Iron uptake by Nramp2 at the plasma membrane was into the nonferritin-bound, calcein-accessible so-called "labile iron pool." Ion selectivity experiments show that Nramp2 isoform II can also transport Co(2+) and Cd(2+) but not Mg(2+) into the calcein-accessible pool [15].
• Interferon-gamma and lipopolysaccharide regulate the expression of Nramp2 and increase the uptake of iron from low relative molecular mass complexes by macrophages [16].
• The effect of intracellular iron concentration and nitrogen monoxide on Nramp2 expression and non-transferrin-bound iron uptake [17].
• However, there was no change in Nramp2 mRNA expression in LMTK- cells after a 20-h incubation with either the Fe chelator, desferrioxamine (DFO), the Fe donor, ferric ammonium citrate (FAC), or the NO generator, S-nitroso-N-acetylpenicillamine (SNAP) [17].

Physical interactions of Slc11a2

• As Nramp2 can transport Fe from non-Tf-bound Fe, the effect of preincubation with DFO and FAC was also examined on Fe uptake from [59Fe]nitrilotriacetate and [59Fe]citrate [17].

Regulatory relationships of Slc11a2

• Nramp2 is a widely expressed metal-ion transporter that is involved in dietary iron absorption in the duodenum and iron uptake from transferrin in peripheral tissues [18].
• Induction of Nramp2 in activated mouse macrophages is dissociated from regulation of the Nramp1, classical inflammatory genes, and genes involved in iron metabolism [18].

Other interactions of Slc11a2

• Divalent metal transporter 1 (DMT1) is the major transferrin-independent iron uptake system at the apical pole of intestinal cells, but it may also transport iron across the membrane of acidified endosomes in peripheral tissues [12].
• Slc11a2 is also required for normal hemoglobin production during the development of erythroid precursors [8].
• In contrast to the previously described macrophage-specific Nramp gene, Nramp2 mRNAs were found to be expressed at low levels in all tissues tested [19].
• We examined the expression of the ferric reductase Dcytb, DMT1 and some other genes involved in Fe metabolism in tissues of mice dosed with PHZ [20].
• Nramp2/DMT1 was also found associated with erythrocyte-containing phagosomes in RAW macrophages and with the periphery of sperm-containing phagosomes in Sertoli cells [14].

Analytical, diagnostic and therapeutic context of Slc11a2

• Immunofluorescence with permeabilized and intact cells established that Nramp2 isoform II is expressed at the plasma membrane and demonstrated the predicted extracytoplasmic location of the TM7-TM8 loop [15].
• METHODS: Immunoblotting and immunohistochemistry with specific affinity purified anti-DMT1 polyclonal antibodies were used to study expression and localization of DMT1 in mouse kidney [21].
• Analysis of the distribution of Nramp2 mRNA transcripts in normal mouse tissues by Northern blotting revealed that the Nramp2 gene produces several mRNAs, including prominent 3.3- and 2.3-kb species generated by the use of alternative polyadenylation signals [19].
• A striking reduction of DMT1 protein in peripheral blood mononuclear cells was demonstrated by Western blot analysis [22].
• The Nramp2-IRE and/or -nonIRE transcripts were up-regulated in all mouse strains analyzed after treatment with interferon-gamma and lipopolysaccharide. cDNA microarray analysis revealed that Nramp2 regulation is controlled discordantly from other iron-regulated genes and classical macrophage-activation genes in different mouse strains [18].

References