Differential localization of divalent metal transporter 1 with and withoutiron response element in rat PC12 and sympathetic neuronal cells

Two isoforms of divalent metal transporter 1 (DMT1) (Nramp2 and DCT1) are e ncoded by two mRNA species, one of which contains an iron response element (IRE) motif in the 3'-noncoding region. The subcellular distribution of the two isoforms of DMT1 is distinct, and the -IRE species accumulates in the nucleus of neuronal or neuronal-like cells. Reverse transcription-PCR and W estern blot analysis of PC12 cells reveals that these cells express both fo rms of DMT1. Immunofluorescence and immunoblotting studies, using immunospe cific antibodies to the -IRE form of DMT1, demonstrate that this form of th e transporter, in PC12 cells, is predominantly localized in the nucleus, ce ll membrane, and neurites with only weak staining of the cell body. Studies using antibodies to the +IRE form indicate that this species of DMT1 is di stributed within vesicles in the cell body and neurite projections, with mi nimal nuclear staining. Similar staining patterns are observed for the two forms of DMT1 in cultures of sympathetic ganglion neurons isolated from per inatal rat pups. To determine whether nuclear localization of the -IRE form of DMT1 is constrained to neuronal or neuronal-like cells, immunocytochemi cal studies were performed with human embryonic kidney 293T (HEK293T), HEP2 G hepatoma and medulloblastoma, and rat Schwann cells. The -IRE-specific an tibodies stained nuclei from medulloblastoma, whereas little nuclear staini ng was observed with HEK293T, hepatoma, or Schwann cells. The unexpected fi nding that the -IRE species of DMT1 selectively accumulates in the nucleus of neuronal and neuronal-like cells leads us to postulate that the two prot eins may have different functions in vivo.