Enhanced sensitivity to oxidative stress in cultured embryonic cells from transgenic mice deficient in metallothionein I and II genes.

Embryonic cells from transgenic mice with targeted disruption of metallothionein I and II genes expressed no detectable metallothionein either constitutively or after treatment with cadmium, in contrast to cultured cells that were wild type or heterozygous for the loss of the metallothionein genes. Metallothionein null cells were most sensitive to the cytotoxic effects of cadmium, the membrane permeant oxidant tert-butylhydroperoxide, and the redox cycling toxin paraquat. No marked differences were seen among the wild type, heterozygous, or metallothionein null cells in glutathione levels or in the activity of CuZn-superoxide dismutase, glutathione peroxidase, or catalase. Nevertheless, metallothionein null cells were more sensitive to tert-butylhydroperoxide-induced oxidation as ascertained by confocal microscopic imaging of dichlorofluoroscein fluorescence. These results indicate basal metallothionein levels can function to regulate intracellular redox status in mammalian cells.