Function and Mechanism of Action of Dictyostelium Nramp1 (Slc11a1) in Bacterial Infection

Abstract

Dictyostelium amoebae are professional phagocytes, which ingest bacteria as the principal source of food. We have cloned the Dictyostelium homologue of human natural resistance-associated membrane protein 1 (Nramp1) [solute carrier family 11 member 1 (Slc11a1)], an endo-lysosomal membrane protein that confers on macrophages resistance to infection by a variety of intracellular bacteria and protozoa. The Dictyostelium Nramp1 gene encodes a protein of 53 kDa with 11 putative transmembrane domains. The Nramp1 gene is transcribed during the growth-phase and downregulated to barely detectable levels upon starvation. To gain insights into their intracellular localization, we fused Nramp1 or the vatB subunit of the V-H þ ATPase with green fluorescent protein and expressed in cells. Green fluorescent protein-vatB was inserted in membranes of all acidic compartments and the contractile vacuole network and decorated macropinosomes and phagosomes. Green fluorescent protein-Nramp1 decorated macropinosomes and phagosomes, in addition to intracellular vesicular compartments positive for endosomal SNARE protein Vti1 or vacuolin, a marker of the exocytic pathway. Nramp1 disruption generated mutants that were more permissive hosts than wild-type cells for intracellular growth of Legionella pneumophila and Micobacterium avium. Nramp1 overexpression protected cells from L. pneumophila infection. Evidence is provided that Nramp1 transports metal cations out of the phagolysosome in an ATP-dependent process and that L. pneumophila and M. avium use different mechanisms to neutralize Nramp1 activity.

Phosphoinositides differentially regulate bacterial uptake and Nramp1-induced resistance toLegionellainfection inDictyostelium

“…In Dictyostelium nramp1-null mutants display increased susceptibility to infection by Legionella and Mycobacterium. Conversely, overexpressing the Nramp1 protein protects Dictyostelium cells against Legionella (Peracino et al, 2006). Here, we show that the latter effect is reversed by inhibiting PI3K.…”

“…We finally show that pharmacological PI3K inactivation also interferes with Nramp1-induced resistance to infection. Nramp1 (also named Slc11a1) is a divalent metal transporter with preference for iron and manganese, which is found on the membrane of phagosomes and endolysosomes (Cellier et al, 2007;Courville et al, 2006;Nevo and Nelson, 2006;Peracino et al, 2006). Nramp1-deficient mice are more sensitive to infection by invasive bacteria, and NRAMP1 polymorphisms in humans have been linked to mycobacterial diseases, such as leprosy and tuberculosis (Courville et al, 2006;Nevo and Nelson, 2006).…”

NAIP and Ipaf Control Legionella pneumophila Replication in Human Cells

“…On the other hand, full innate intracellular resistance to L. pneumophila (and certainly other intracellular bacteria) depends on many additional mechanisms such as types I and II IFN-as well as TNF-␣-mediated effects, and perhaps also on Nramp1, antimicrobial peptides, or immunity-related GTPases (13,15,(45)(46)(47)(48)(49)(50). It might thus be conceivable that in case of L. pneumophila infection, one of these last mentioned resistance mechanisms is less functional in human cells compared with mice resulting in an overall stronger replication of Legionella in human cells compared with, for example, C57BL/6 macrophages despite functional hNAIP and hIpaf.…”

Characterization of chicken natural resistance-associated macrophage protein encoding genes (Nramp1 and Nramp2) and association with salmonellosis resistance

“…There are two Nramp genes that are associated with diseases in vertebrates. Nramp1 (also called SLC11A1) restricts microbial access to essential micronutrients such as Fe 2+ , Mn 2+ , Co 2+ , and Zn 2+ within professional phagosomes (Boyer et al, 2002;Jabado et al, 2000Jabado et al, , 2003Peracino et al, 2006;Cellier et al, 2007). It defends against various intracellular pathogens including Salmonella typhimurim, Leishmania donovani and Mycobacterium bovis (Vidal et al, 1993;Blackwell et al, 1999Blackwell et al, , 2000Blackwell et al, , 2003.…”