DNA Damage and Cellular Stress Responses Inhibition of the Nedd8 System Sensitizes Cells to DNA Interstrand Cross-linking Agents

The Fanconi anemia pathway is required for repair of DNA interstrand cross-links (ICL). Fanconi anemia pathway–deficient cells are hypersensitive to DNA ICL–inducing drugs such as cisplatin. Conversely, hyperactiva-tion of the Fanconi anemia pathway is a mechanism that may underlie cellular resistance to DNA ICL agents. Modulating FANCD2 monoubiquitination, a key step in the Fanconi anemia pathway, may be an effective therapeutic approach to conferring cellular sensitivity to ICL agents. Here, we show that inhibition of the Nedd8 conjugation system increases cellular sensitivity to DNA ICL–inducing agents. Mechanistically, the Nedd8 inhibition, either by siRNA-mediated knockdown of Nedd8-conjugating enzymes or treatment with a Nedd8-activating enzyme inhibitor MLN4924, suppressed DNA damage–induced FANCD2 monoubiquitination and CHK1 phosphorylation. Our data indicate that inhibition of the Fanconi anemia pathway is largely responsible for the heightened cellular sensitivity to DNA ICLs upon Nedd8 inhibition. These results suggest that a combination of Nedd8 inhibition with ICL-inducing agents may be an effective strategy for sensitizing a subset of drug-resistant cancer cells. Mol Cancer Res; 1–9. 2012 AACR