Overexpression of the zinc transporter Zip14 increases non‐transferrin‐bound iron uptake in cells

Abstract

Zip14 is a member of the SLC39A zinc transporter family, which is involved in zinc uptake by cells. Furthermore, up-regulation of Zip14 by IL-6 likely contributes to the hepatic zinc accumulation and hypozincemia of inflammation. At least one member of the SLC39A family, IRT1 from Arabidopsis thaliana, is a metal transporter that can transport other trace elements, such as iron and manganese, in addition to zinc. The objective of this study was to analyze the capability of Zip14 to mediate non-transferrin-bound iron uptake by transiently transfecting HEK293H cells with mouse Zip14 cDNA. This transfection increased 65Zn uptake by many fold compared to a transfection with vector alone. Addition of ferric citrate inhibited Zip14-mediated 65Zn uptake in the transfected cells, suggesting that iron competes with zinc for this transporter. After transfection, 59Fe uptake was also assayed by incubating the cells at pH 7.0 with 59Fe-labeled ferric citrate. Thereafter, cells were treated with the proteolytic enzyme Pronase to remove plasma membrane-bound iron. Zip14-overexpressing cells internalized more 59Fe over time (P < 0.05) than did cells transfected with empty vector. After 60 min of incubation, this difference was close to four fold. The addition of a 10-fold molar excess of the ferrous chelator bathophenanthroline inhibited 90% of Zip14-mediated iron uptake. Collectively, these results indicate that Zip14 can mediate the uptake of non-transferrin-bound ferrous iron by cells at physiologic pH. Since Zip14 is very highly expressed in the liver compared to other tissues, this member of the SLC39A transporter family could be involved in hepatic iron accumulation during iron overload conditions such as hemochromatosis. Supported by NIH grants DK065064 and DK31127.