Expression of NRAMP1 molecule in human peripheral blood leukocytes

DMT1 and iron transport

Many past and recent advances in the field of iron metabolism have relied upon the discovery of divalent metal transporter 1, DMT1 in 1997. DMT1 is the major iron transporter and contributes non-heme iron uptake in most types of cell. Each DMT1 isoform exhibits different expression patterns in cell-type specificity and distinct subcellular distribution, which enables cells to uptake both transferrin-bound and non-transferrin-bound irons efficiently. DMT1 expression is regulated by iron through the translational and degradation pathways to ensure iron homeostasis. It is considered that mammalian iron transporters including DMT1 cannot transport ferric iron but ferrous iron. Being reduced to ferrous state is likely to damage cells and tissues through the production of reactive oxygen species. Recently, iron chaperones have been identified, which can provide an answer to how ferrous iron is transported safely in cytosol. We summarize DMT1 expression depending on the types of cell or tissue and the function and mechanism of one of the iron chaperones, PCBP2.

Association of SLC11A1 (NRAMP1) polymorphisms with pulmonary Mycobacterium avium complex infection

Although genetic variants in SLC11A1 (NRAMP1) have been associated with mycobacterial diseases, these findings have not been extensively validated in pulmonary Mycobacterium avium complex (MAC) infection. This study investigated the genomic structure of SLC11A1 and its association with MAC infection. Nineteen polymorphic loci were genotyped in European descendents and the Japanese population. Linkage disequilibrium (LD) structures and frequencies of major haplotypes differed between these 2 populations. Tag single nucleotide polymorphisms (SNPs) were chosen from the data set, and 6 polymorphic sites were genotyped in 122 pulmonary MAC cases and 211 controls from Japan. We observed that the T allele of rs2279014 in the 3' untranslated region was associated with protection from MAC disease when comparing allele frequencies with an odds ratio of 0.582 (95% confidence interval 0.379-0.894, p = 0.013). The frequencies of haplotypes constructed with the above 6 variants did not differ between cases and controls. Allele-specific expression imbalance of SLC11A1 mRNA was evaluated in peripheral blood cells from heterozygous individuals, but no difference was observed among haplotypes. Although the significance was modest, rs2279014 is in strong LD with nearby SNPs and further studies are required for conclusive validation.

Macrophage and Leishmania: An Unacceptable Coexistence

Research over the past year has revealed several significant and interesting advances in the biology of macrophage, key cells responsible in body's host defense against invading pathogens and in immune responses. Perturbation of macrophage surface with different bacterial pathogens leads to activate general signal transduction pathways of macrophages, including activation of NADPH oxidase, nitric oxide synthase, and so on. However, in this review, the results of macrophage interactions only with Leishmania parasites, which harbors the host macrophages, are discussed. It appears that interference in transduction of regulatory signals during leishmanial invasion lead to an inadequate leishmanicidal response. In this connection, information concerning regulation of MHC molecules and other current events related to macrophage function after invasion by the parasites are also discussed.

Human natural resistance-associated macrophage protein 2: gene cloning and protein identification

The Lsh/Ity/Bcg locus in the mouse genome regulates macrophage activation for antimicrobial activity against intracellular pathogens, and mouse Nramp1 (natural resistance-associated macrophage protein) gene was isolated as its candidate. The human NRAMP1 gene was subsequently isolated and its gene product was identified in macrophage/monocyte cells. Recently, a second Nramp gene, Nramp2, was found in mouse and human genomes. In the present study, we report the cloning and characterization of the human NRAMP2 gene, which is approximately 42 kb in length, containing 16 exons. The transcription start site was determined by 5'-RACE method, and the promoter was located between -246 bp to 145 bp in a region relative to the transcription start site, able to drive the luciferase reporter gene in HeLa cells. We also raised a polyclonal antibody against the glutathione S-transferase fusion protein containing the NH2-terminal 86 amino acids of human NRAMP2. The protein product of the human NRAMP2 gene is apparently present in human cultured cell lines as a 64 kDa protein recognized by this antibody, which is consistent with the molecular mass deduced from the human NRAMP2 cDNA.

Human natural resistance-associated macrophage protein is a new type of microtubule-associated protein

Natural resistance-associated macrophage protein 1 (NRAMP1) is a putative membrane protein that dominates natural resistance to infection. An NRAMP1-glutathione S-transferase fusion protein was used to test the ability of the NRAMP1 NH2-terminal domain to bind to taxol-stabilized microtubules. Co-sedimentation analysis showed that the fusion protein binds to microtubules. Although the NH2-terminal domain of the NRAMP1 molecule has structural homology with the Pro-rich region of microtubule-associated protein 4 (MAP4), the presence of the MAP4 microtubule-binding domain fragment had little effect on the binding of the fusion protein to microtubules.

Complete nucleotide sequence of human NRAMP2 cDNA

The mouse Lsh/Ity/Bcg locus regulates macrophage activation for antimicrobial activity against intracellular pathogens, and the Nramp1 gene was isolated as its candidate. In the present study, a full length cDNA for human NRAMP2 has been isolated and characterized. Nucleotide sequence analysis reveals that the cDNA, 4142 bp in length, coded for a protein of 561 amino acid residues with a molecular weight mass of 61,456. Predicted amino acid sequence analysis of the NRAMP2 molecule indicates that NRAMP1 and NRAMP2 sequences share 64% identical residues overall, whereas only 21% at the NH2-terminal cytoplasmic domain, where the NRAMP1 molecule was associated with microtubules, was found to be identical. This suggests that the NH2-terminal region of the NRAMP2 molecule may have a particular function, different from that of the NRAMP1 molecule.