CELL-SPECIFIC AND INDUCIBLE NRAMP1 GENE-EXPRESSION IN MOUSE MACROPHAGES IN-VITRO AND IN-VIVO

Mutations in the Nramp1 gene abolish natural resistance to infections with many unrelated intracellular parasites in vivo. Global cDNA ampli fication was used to analyze Nramp1 mRNA expression in bone marrow-der ived cell colonies corresponding to either undifferentiated progenitor s or to mature lymphoid, erythroid, and myeloid lineages, Nramp1 mRNA was detected in mature myeloid colonies expressing molecular markers f or either the monocyte/macrophage or granulocytic lineages. Having est ablished constitutive expression of Nramp1 in phagocytic cells, the pa rameters of inducible Nramp1 expression by cytokines and lipopolysacch aride (LPS) were studied in the mouse macrophage cell line RAW 264.7. LPS caused up-regulation of Nramp1 expression in a time- and dose-depe ndent fashion. This induction required de novo protein synthesis and w as abrogated by treatment with cycloheximide. Treatment with interfero n-gamma (IFN-gamma) also caused a modest but reproducible twofold indu ction of Nramp1 mRNA expression. In addition, maximum Nramp1 mRNA indu ction in RAW 264.7 cells was observed after pretreatment with IFN-gamm a followed by LPS exposure. In vivo, Nramp1 mRNA expression could be u p-regulated in macrophage populations by intraperitoneal injection of either LPS or thioglycollate. Together these results indicate that Nra mp1 is expressed in professional phagocytes of the myeloid lineage and can be further up-regulated during macrophage activation in response to infectious, inflammatory, or cytokine stimuli. Finally, the pattern s of constitutive and inducible expression of Nramp1 have been compare d to those of the inducible nitric oxide synthase (iNOS) gene in the s ame cells.