SummaryThe Escherichia coli mntH (formerly yfeP) gene encodes a putative membrane protein (MntH) highly similar to members of the eukaryotic Nramp family of divalent metal ion transporters. To determine the function of E. coli MntH, a null mutant was created and MntH was overexpressed both in wild-type E. coli and in the metal-dependent mutant hflB1(Ts). At the restrictive temperature 428C, the mntH null mutation reduces the suppression of hflB1(Ts) thermosensitivity by exogenous divalent metals. Conversely, overexpression of MntH restores growth at 428C, increases suppression of the ts phenotype by Fe(II) and Ni(II) and renders hflB1(Ts) cells hypersensitive to Mn(II). Transport studies in intact cells show that MntH selectively facilitates uptake of 54 Mn(II) and 55 Fe(II) in a temperature-, time-and proton-dependent manner. Competition studies in uptake assays and growth inhibition experiments in hflB1(Ts) mutants together indicate that MntH is a divalent metal cation transporter of broad substrate specificity. The functional characteristics of MntH suggest that it corresponds to the previously described manganese transporter of E. coli. This study indicates that proton-dependent divalent metal ion uptake has been preserved in the Nramp family from bacteria to humans.

The natural resistance-associated macrophage protein 1 (Nramp1) is a proton-dependent transporter of divalent metals. We studied NRAMP1 expression during HL-60 differentiation induced by VD and VD agonists. NRAMP1 and CD14 gene expression differed in kinetics of induction, mRNA levels and stability, and response to VD combined with PMA, whereas a combination of VD and IFN-γ induced similar up-regulation. NRAMP1 protein expression paralleled the accumulation of mRNA and was localized in the phagosomal membrane after phagocytosis. A promoter construct extending 647 bp upstream of NRAMP1 ATG showed myeloid-specific transcription in transient trasfection assays, which was up-regulated by VD in HL-60. In HL-60 clones stably transfected with this construct, transcription was apparently induced through indirect VD genomic effects, and there was accordance between the levels of reporter transcription and endogenous NRAMP1 mRNA in response to VD but not to IFN-γ. Thus, VD genomic effects stimulate NRAMP1 transcription and protein expression in maturing phagocytes.