c-Myc Represses and Miz-1 Activates the Murine Natural Resistance-associated Protein 1 Promoter

Abstract Iron is essential for growth, and impaired iron homoeostasis through a non-conserved mutation within murineNramp1, also termed Slc11a1, contributes to susceptibility to infection. Nramp1 depletes the macrophage cytosol of iron, with effects on iron-regulated gene expression and iron-dependent processes. Wu and colleagues (Wu, K.-J., Polack, A., and Dalla-Favera, R. (1999) Science 283, 676–679) showed converse control of iron regulatory protein expression (IRP2) and H-ferritin by c-Myc, suggesting a role for c-Myc in enhancing cytoplasmic iron levels for growth. We investigated if c-Myc also regulates Nramp1 expression. We show an inverse correlation with cell growth, and in co-transfection experiments c-Myc represses the Nramp1 promoter. Within theNramp1 promoter we identified six non-canonical E boxes, which are not important for c-Myc repression. By deletion analysis the repressor site maps to one or more initiator elements flanking the transcriptional initiation site. Co-transfections with the c-Myc interacting zinc finger protein (Miz-1) show that Miz-1 can overcome c-Myc repression of Nramp1, and, from a deletion construct lacking E box sites, Miz-1 activates the Nramp1promoter. These studies reinforce the link between c-Myc and iron regulation and provide further evidence that c-Myc negatively regulates genes that decrease the iron content of the cytosol. The results provide further support for a divalent cation antiporter function forNramp1.