Activation of nuclear factor kappaB: potential role in metallothionein-mediated mitogenic response.

The antiapoptotic response and enhanced cellular proliferation observed in neoplastic cells on overexpression of metallothionein (MT) have been well documented. We have investigated the mechanisms associated with this phenomenon by using MT inducers that increased MT transcripts and stimulated growth in MCF-7 cells. A MT antisense phosphorothioate oligonucleotide inhibited growth induction by >50%, suggesting a potential role of MT in mediating the mitogenic effects of these agents. Mobility shift assays using oligonucleotides encompassing the consensus nuclear factor kappaB (NFkappaB) binding site and anti-MT antibody revealed activation and a specific interaction of NFkappaB with MT. Cotransfection experiments using expression and reporter constructs demonstrated that MT caused transactivation of NFkappaB. Gel shift assays using purified proteins showed a specific interaction between MT and the p50 subunit of NFkappaB. These data indicate that MT may be involved in the interaction of NFkappaB with the DNA-binding domain and further suggest a potential role for NFkappaB in mediating the antiapoptotic effects of MT.