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Nramp1 locus encodes a 65 kDa interferon-gamma-inducible protein in murine macrophages
P G Atkinson1, J M Blackwell, C H Barton
1University of Southampton, Biochemistry and Molecular Biology Division, School of Biological Sciences, Bassett Crescent East, Southampton SO16 7PX, U.K.
Abstract:
The murine Nramp1 (natural-resistance-associated macrophage protein) locus, formerly known as Ity/Lsh/Bcg, was isolated previously on the basis of chromosomal location, and as conferring natural resistance to infection against intracellular macrophage pathogens. The gene encodes a transporter molecule of unknown function. We have prepared polyclonal antisera against the C-terminal 35 amino acids of murine Nramp1. This serum is reactive towards a 65 kDa protein, expressed in murine macrophage cells from resistant or susceptible mice stimulated with interferon-gamma and lipopolysaccharide, but not in non-macrophage cells. Evidence indicates that Nramp1 is localized in a subcellular membrane rather than at the cell surface. This evidence includes: the identification of conserved endocytic targeting motifs following inspection of human and murine Nramp sequences; the enrichment of Nramp1, following magnetic selection of phagolysosomal vesicles from activated macrophages that were allowed to phagocytose magnetic, IgG-coated beads; confocal microscopy. These studies place Nramp1 on a membrane in close proximity to obligate intracellular pathogens. A link between Nramp1 and divalent-cation transport is suggested by sequence similarity with yeast SMF1. Evidence showing modulation of Nramp1 protein levels by iron chelation provides a direct link with Nramp1 function and divalent-cation metabolism.
Insights
Researchers identified the Nramp1 (natural-resistance-associated macrophage protein 1) transporter in macrophages. This protein is crucial for natural resistance against intracellular pathogens and is involved in divalent-cation metabolism.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- The Nramp1 locus confers natural resistance to intracellular macrophage pathogens.
- Nramp1 encodes a transporter protein with a previously unknown function.
- Understanding Nramp1's role is key to combating infections in macrophages.
Purpose of the Study:
- To characterize the Nramp1 protein and determine its cellular localization and function.
- To investigate the role of Nramp1 in macrophage resistance to pathogens.
Main Methods:
- Generation of polyclonal antisera against murine Nramp1.
- Western blot analysis of Nramp1 expression in stimulated macrophages.
- Confocal microscopy and magnetic selection of phagolysosomal vesicles.
- Analysis of Nramp1 sequence for targeting motifs.
- Iron chelation assays to assess Nramp1 function.
Main Results:
- A 65 kDa Nramp1 protein is expressed in activated murine macrophages.
- Nramp1 is localized to a subcellular membrane, likely within phagolysosomal vesicles.
- Sequence analysis revealed conserved endocytic targeting motifs.
- Nramp1 levels are modulated by iron chelation, suggesting a role in divalent-cation metabolism.
Conclusions:
- Nramp1 is a macrophage-specific protein localized to membranes near intracellular pathogens.
- Nramp1 plays a role in divalent-cation metabolism and natural resistance to infection.
- Further research into Nramp1 function could lead to new therapeutic strategies.