Differential regulation of zinc transporter 1, 2, and 4 mRNA expression by dietary zinc in rats

Zinc metabolism is well regulated over a wide range of dietary intakes to help maintain cellular zinc-dependent functions. Expression of transporter molecules, which influence zinc influx and efflux across the plasma and intracellular membranes, contributes to this regulation. We have examined in rats the comparative response of zinc transporters 1, 2, and 4 (ZnT-1, ZnT-2 and ZnT-4) to dietary zinc. ZnT-1 and ZnT-4 are expressed ubiquitously, whereas ZnT-2 is limited to small intestine, kidney, placenta and, in some cases, the liver. When zinc intake was low (<1 mg Zn/kg), ZnT-2 mRNA was extremely low in small intestine and kidney compared with an adequate intake (30 mg Zn/kg). ZnT-1 and ZnT-2 mRNAs were markedly greater in both tissues when a supplemental zinc intake (180 mg Zn/kg) was provided. ZnT-4 was refractory to changes in zinc intake. When zinc was provided as a single oral dose (70 mg/kg body), ZnT-1 and ZnT-2 mRNA levels were increased many fold in small intestine, liver and kidney, whereas ZnT-4 gene expression was not changed. The expression of ZnT-1 and ZnT-2 is comparable to zinc-induced changes in metallothionein mRNA levels, suggesting a similar mode of regulation for these genes. The relative differential in regulation by zinc is ZnT-2 > ZnT-1 > ZnT-4. These data provide evidence that, in an animal model, zinc transporter expression is responsive to zinc under physiologically relevant conditions.