Cloning of porcine NRAMP1 and its induction by lipopolysaccharide, tumor necrosis factor alpha, and interleukin-1beta: role of CD14 and mitogen-activated protein kinases.

The gene for natural resistance-associated macrophage protein 1 (NRAMP1) plays a dominant role in controlling the resistance of inbred mice to infection with intracellular bacteria, such as Mycobacteria, Salmonella, and Leishmania. NRAMP1 is a membrane protein with a consensus transport motif present in one of the intracellular loops. Although its functions remain unclear, recent clues suggest that NRAMP1 protein plays a potential role in ion transport, which presumably accounts for the ability of this single protein to regulate the intraphagosomal replication of several species of antigenically unrelated intracellular pathogens. Expression of NRAMP1 in mice can be induced by lipopolysaccharide (LPS) or bacterial infection; however, little is known about the mechanisms of induction. Here, we report the cloning of the full-length cDNA for porcine NRAMP1, which had over 85% identity in amino acid sequence to its congeners from humans, mice, cattle, and sheep. As for its mammalian congeners, expression of porcine NRAMP1 mRNA was cell and tissue specific and was highest in macrophages. Investigation of the molecular mechanisms by which NRAMP1 is induced showed that LPS-induced expression in macrophages, neutrophils, and peripheral blood mononuclear cells was time and dose dependent and was mediated primarily through CD14. Induction of NRAMP1 required de novo protein synthesis, and mitogen-activated protein kinases (MAPK) were essential. Blockage of either p38 or p42/44 MAPK pathways suppressed the expression of NRAMP1 to basal levels. These findings suggest that bacterial infection and proinflammatory mediators induce NRAMP1 expression via activation of MAPK pathways.