Functional Expression of the Human hZIP2 Zinc Transporter

Abstract

Zinc is an essential nutrient for humans, yet we know little about how this metal ion is taken up by mammalian cells. In this report, we describe the characterization of hZip2, a human zinc transporter identified by its similarity to zinc transporters recently characterized in fungi and plants. hZip2 is a member of the ZIP family of eukaryotic metal ion transporters that includes two other human genes, hZIP1 and hZIP3, and genes in mice and rats. To test whether hZip2 is a zinc transporter, we examined 65 Zn uptake activity in transfected K562 erythroleukemia cells expressing hZip2 from the CMV promoter. hZip2-expressing cells accumulated more zinc than control cells because of an increased initial zinc uptake rate. This activity was time-, temperature-, and concentration-dependent and saturable with an apparent K m of 3 M. hZip2 zinc uptake activity was inhibited by several other transition metals, suggesting that this protein may transport other substrates as well. hZip2 activity was not energy-dependent, nor did it require K ؉ or Na ؉ gradients. Zinc uptake by hZip2 was stimulated by HCO 3 Ϫ treatment, suggesting a Zn 2؉ -HCO 3 Ϫ cotransport mechanism. Finally, hZip2 was exclusively localized in the plasma membrane. These results indicate that hZip2 is a zinc transporter, and its identification provides one of the first molecular tools to study zinc uptake in mammalian cells.

Zinc transport mediated by barley ZIP proteins are induced by low pH

“…1). The study by Gaither and Edie (2000) 14 was therefore not confirmed in the present study as we observed a completely reverse effect in response to decreasing the pH on the apoplastic side of plant ZIP transport proteins, in terms of the Zn 2+ transport capacity. However, it should be noted that it has previously been observed that Zn 2+ uptake mediated by IRT1 from Arabidopsis only was measurable at low pH (pH 4.2).…”

“…Only a few studies have investigated the activity of ZIP proteins in vivo, mostly in terms of identification of amino acid residues important for transport activity. 14,16 An urgent need for investigating the precise mechanism in which the transport of metal ions occur via ZIP proteins are therefore required. Expression in heterologous systems such as Xenopus Oocytes could elucidate more aspects on the potential role of proton activity and membrane potentials.…”

Identification of mouse SLC39A8 as the transporter responsible for cadmium-induced toxicity in the testis

“…Therefore, ZIP8 is not a Cd transporter per se but likely has evolved to transport one or more essential metals. Other members of the SLC39 family have been shown to transport divalent Zn, Fe, and Mn (39,(41)(42)(43)(44)(45)(46). During the course of uptake studies, we found that the transport of 0.25 M CdCl 2 was 50% inhibited by divalent Zn and Mn at concentrations of 13 M and 2.9 M, respectively (data not shown).…”

“…In mammalian-cultured cells, many studies of Cd transport and inhibition of divalent cation transport by Cd have shown Cd uptake and toxicity (11,42,43,(60)(61), but there were no studies correlating Cd uptake with toxicity in any organ or specific cell type of any intact vertebrate.…”

Zn2+-stimulated Endocytosis of the mZIP4 Zinc Transporter Regulates Its Location at the Plasma Membrane

“…The hallmark features of ZIP proteins include eight transmembrane domains, the fourth of which contains fully conserved histidyl and glycyl residues in a putative amphipathic ␣-helix. In humans, 14 ZIP proteins have been identified by data base sequence comparisons (5), and at least two of these proteins, hZIP1 and hZIP2, function as zinc importers when expressed in K562 cells (6,7). Recently, another ZIP family member, hZIP4 (SLC39A4), was shown to be mutated in the inherited disorder of zinc deficiency, acrodermatitis enteropathica (AE) 1 (8,9).…”