Influence of metallothionein-1 localization on its function

Metallothioneins (MTs) have a major role to play in metal metabolism, and m ay also protect DNA against oxidative damage. MT protein has been found loc alized in the nucleus during S-phase. The mRNA encoding the MT-1 isoform ha s a perinuclear localization, and is associated with the cytoskeleton; this targeting, due to signals within the 3'-untranslated region (3'-UTR), faci litates nuclear localization of MT-I during S-phase [Levadoux, Mahon, Beatt ie, Wallace and Hesketh (1999) J. Biol. Chem. 274, 34961-34966]. Using cell s transfected with MT gene constructs differing in their 3'-UTRs, the role of MT protein in the nucleus has been studied. Chinese hamster ovary cells were transfected with either the full MT gene (MTMT cells) or with the MT 5 '-UTR and coding region linked to the 3'-UTR of glutathione peroxidase (MTG SH cells). Cell survival following exposure to oxidative stress and chemica l agents was higher in cells expressing the native MT gene than in cells wh ere MT localization was disrupted, or in untransfected cells. Also, MTMT ce lls showed less DNA damage than MTGSH cells in response to either hydrogen peroxide or mutagen. After exposure to UV light or mutagen, MTMT cells show ed less apoptosis than MTCSH cells, as assessed by DNA fragmentation and fl ow cytometry. The data indicate that the perinuclear localization of MT mRN A is important for the function of MT in a protective role against DNA dama ge and apoptosis induced by external stress.