Overexpression of metallothionein-II sensitizes rodent cells to apoptosis induced by DNA cross-linking agent through inhibition of NF-kappa B activation.

DNA cross-linking agents such as mitomycin C (MMC) and cisplatin are used as chemotherapeutic agents in cancer treatment. However, the molecular mechanism underlying their antitumor activity is not entirely clear. Critical steps in cytotoxicity toward cross-linking agents can involve DNA repair efficiency, inhibition of replication, cell-cycle checkpoints, regulation, and induction of apoptosis. The complexity of the mechanisms of the mammalian cell defense against cross-linking agents is reflected by the existence of many complementation groups identified in rodent cells that are specifically sensitive to MMC. We recently showed that increased induction of apoptosis contributes to the MMC sensitivity of the group represented by the V-H4 hamster mutant cell line. In this study, through the analyses of a substractive library, we discovered that sensitive V-H4 cells display a 40-fold increase of steady-state expression of metallothionein II (MT-II) mRNA compared with resistant parental V79 cells. Down-regulation of MT-II by antisense oligonucleotides partially restores MMC resistance in V-H4 cells, indicating that MT-II overexpression is directly involved in MMC hypersensitivity of these cells. MTs have been reported to regulate the activation of NF-kappaB, one of the key proteins that modulates the apoptotic response. Here we found that NF-kappaB activation by MMC is impaired in V-H4 cells and is partially restored following down-regulation of MT-II by antisense oligonucleotides. All these data suggest that the overexpression of MT-II in V-H4 cells impairs NF-kappaB activation by MMC, resulting in decreased cell survival and enhanced induction of apoptosis.