The role of ZIP8 down-regulation in cadmium-resistant metallothionein-null cells

The mechanisms of cellular cadmium uptake in mammalian cells remain obscure. To solve this problem, we established cadmium-resistant cells (A7 and B5) from metallothionein-null mouse cells, and found that cadmium accumulation was markedly suppressed in these cells. DNA microarray and real-time PCR analyses revealed that expressions of ZIP (Zrt-, Irt-related protein) 8 and ZIP14 were down-regulated in A7 and B5 cells. In particular, both mRNA and protein levels of ZIP8 were markedly suppressed in A7 and B5 cells. Introduction of short hairpin RNA (shRNA) of ZIP8 into parental cells reduced the accumulation of cadmium to about 35% of that of mock-transfected cells, whereas the introduction of shRNA of divalent metal transporter 1 hardly changed cadmium accumulation. Thus, the cadmium resistance in A7 and B5 cells may be conferred primarily by the down-regulation of ZIP8. In mouse tissues, high expression of ZIP8 was noted in the liver, kidney, lung and testis. These data suggest that ZIP8 plays an important role in cellular uptake of cadmium.