Cisplatin mimics ARF tumor suppressor regulation of RelA (p65) nuclear factor-κB transactivation

The ReIA (p65) nuclear factor-kappa B (NF-kappa B) subunit can contribute towards tumor cell survival through inducing the expression of a variety of antiapoptotic genes. However, the NF-kappa B response can show great diversity and is not always antiapoptotic. Here, we find that cisplatin, a DNA cross-linking agent and commonly used anticancer compound, does not affect ReIA nuclear translocation but modulates its transcriptional activity. Similar to other genotoxic agents, such as daunorubicin and UV light, cisplatin treatment in the U-2 OS osteosarcoma cell line represses ReIA activity and inhibits expression of the NF-kappa B antiapoptotic target gene Bcl-x(L). The mechanism through which cisplatin achieves these effects is different to daunorubicin and UV light but shows great similarity to the ReIA regulatory pathway induced by the ARF tumor suppressor: cisplatin regulation of ReIA requires ATR/Chk1 activity, represses Bcl-x(L) but not XIAP expression, and results in phosphorylation of ReIA at TWO. In contrast to these results, another chemotherapeutic drug etoposide activates NF-kappa B and induces expression of these target genes. Thus, within a single tumor cell line, there is great heterogeneity in the NT-kappa B response to different, commonly used chemotherapeutic drugs. These observations suggest that it might be possible to minimize the ability of ReIA to inhibit cancer therapy by diagnostically predicting the type of chemotherapeutic drug most compatible with NF-kappa B functionality in a tumor cell type. Moreover, our data indicate that at least with respect to RelA, cisplatin functions as an ARF mimic. Other drugs capable of mimicking this aspect of ARF function might therefore have therapeutic potential.