Cisplatin Binds to MDM2 RING Finger Domain and Inhibits the Ubiquitination Activity

Cisplatin is an anticancer drug widely used in clinics; it induces the apoptosis of cancer cells by targeting DNA. One significant feature of the cisplatin induced apoptosis is the elevation of p53 level in tumor cells. However, it is not clear how cisplatin can elevate the p53 level in tumor cells. The p53 level in cells is controlled by its negative regulator protein MDM2, and the over-expression of MDM2 leads to cisplatin resistance. In this work, we found that cisplatin is highly reactive to the RING finger domain of MDM2. Cisplatin can directly bind to cysteine residues at the zinc-coordination site of MDM2-RF, leading to the release of zinc ions from the protein. ESI-MS spectra showed that each MDM2-RF protein tends to bind two platinum atoms, implying each zinc-binding domain can bind one platinum moiety. The zinc-ejection from MDM2-RF results in the structure perturbation of the protein, therefore disrupts the function of the protein. Gel electrophoresis and Western blot analyses reveal that the platination of MDM2-RF inhibits its ubiquitination activity. As MDM2-mediated ubiquitination is the key step of p53 degradation, this result suggests that the MDM2-RF platination could contribute to the cisplatin induced cell apoptosis via p53 elevation.