Oxidant regulation of the bivalent cation transporter Nramp1

Nramp1 (murine natural resistance-associated macrophage protein 1 gene)/Slc11a1 (solute carrier family 11 member a1 gene) encodes a bivalent-metal/iron transporter that is expressed within late endosomes/lysosomes of macrophages. A functionally null Nramp1 allele that exhibits impaired bivalent cation transport enables excessive growth of intracellular pathogens. Iron is important for many cellular activities, including defence against pathogens; however, redox-active/free iron can participate in Fenton chemistry that generates reactive oxygen species. Using Raw264.7 cells, non-functional for Nramp1, and stable Nramp1 transfectants, we have examined the effects of impaired bivalent cation transport on macrophage function using glutathione depletion as OS (oxidant stress). Our results demonstrate that OS itself is a signal for increasing Nramp1 transcription and that Nramp1 expression protects against OS. We suggest that OS-mediated protection by Nramp1 function may arise from direct removal of redox-active bivalent cations from a cytosolic pool. We show that OS transcriptional responses are probably mediated by the Sp1 transcription factor.