Involvement of differential metallothionein expression in free radical sensitivity of RTG-2 and CHSE-214 cells

The role of metallothionein (MT) in free radical regulation and scavenging was investigated using two fish cell lines, the rainbow trout gonadal (RTG-2) cell line and the chinook salmon embryonic (CHSE-214) cell line. Exposure of RTG-2 cells to H2O2 resulted in upregulation of both MT mRNA and MT protein and was also demonstrated by immunocytochemistry, confirming that MT was regulated by free radicals. We then compared the H2O2 resistance in RTG-2 and CHSE-214 cells following metal treatment with Zn or Cd to induce MT. Comparison of survival of control cells and metal-exposed cells showed that metal treatment, which induced MT, significantly raised the H2O2 tolerance in a dose-dependent manner in RTG-2 cells, while no increased H2O2 resistance was observed in CHSE-214 cells. Transient over-expression of MT in CHSE-214: 59 cells also resulted in a dose-dependent increase in resistance to H2O2 exposure. The raised resistance against H2O2 in metal treated RTG-2 cells as well as transfected CHSE-214: 59 cells strongly demonstrate that MT is involved in the protection against H2O2 and suggest a physiologically important function for MT when cells or whole organisms are exposed to oxidative stress.