Table 1. Effect of MT and ZnT1 expression on zinc toxicity.
| Cell line* | Zinc,* μM | Zinc bound to MT,† fmol per cell | Zinc toxicity‡ (ED50), μM |
|---|---|---|---|
| ZnS (3286) | 30 | None | 23 |
| ZnS-Aza c1 | 75 | 0.33 | 86 |
| ZnS-Aza c2 | 75 | 0.30 | 80 |
| ZnS-Aza c3 | 75 | 0.27 | 108 |
| ZnS-3121 c2 | 75 | 0.52 | 98 |
| ZnS-3121 c3 | 75 | 0.92 | 134 |
| ZnR (3038) | 125 | None | 161 |
| ZnR-Aza c4 | 125 | 0.27 | 215 |
| ZnR-Aza c5 | 125 | 0.13 | 190 |
| ZnR-Aza c6 | 125 | 0.16 | 192 |
| ZnR-3121 c7 | 125 | 0.08 | 158 |
| ZnR-3121 c10 | 125 | 0.71 | 204 |
| ZnR-3121 c11 | 125 | 0.27 | 160 |
| ZnR-3121 c12 | 125 | 0.29 | 172 |
*
Cell clones with Mt gene expression were isolated after treatment with azacytidine (Aza) or transfection with the cosmid (3121). Cells were grown in the presence of the indicated concentration of zinc for 16-18 h to measure MT.
†
MT protein was assayed with a cadmium-binding assay and expressed as MT-bound zinc. For comparison, when grown in 4 μM Zn, ZnS and ZnR cells have ≈0.30 and 0.25 fmol Zn per cell, respectively. Both cells have ≈0.6 fmol Zn per cell when grown in the 75 or 125 μM Zn, respectively. Thus, most of these clones that express MT increase total zinc content by 50-100%.
‡
Zinc toxicity was measured as shown in Fig. 2.