Effects of intracellular zinc depletion on metallothionein and ZIP2 transporter expression and apoptosis

Zinc is critical for the functional and structural integrity of cells. We have used the monocytic cell line THP-1 as a model in which to study both the responsiveness of metallothionein and ZIP2 transporter expression to zinc depletion induced by the intracellular zinc chelator TPEN [N,N,N',N'-tetrakis(2-pyridylmethyl) ethylenediamine] and the extent of concomitant apoptosis. Metallothionein expression increased proportionately with the addition of zinc to the medium and decreased with TPEN treatment. When treated with TPEN, both THP-1 cells and human peripheral blood mononuclear cells exhibited marked decreases in cellular zinc concentrations and increases in ZIP2 mRNA expression. These results suggest that cells attempt to homeostatically adjust to zinc depletion. When THP-1 cells were treated with >5 microM TPEN, cell viability decreased, and cells entered the early stages of apoptosis. These data show that metallothionein and ZIP2 expression are inversely related during zinc depletion and that apoptosis is concurrent with these changes.