Mdm2/Mdmx and Mdm2/c‐Abl Interactions are Accompanied by Reductions in Mdm2/p53 interaction in Zinc‐Depleted Human Hepatoblastoma Cells

Abstract

Mdmx has been shown to interact with Mdm2, interfere with Mdm2 degradation, and inhibit Mdm2‐mediated p53 degradation. The influence of zinc deficiency on the interaction of Mdm2/p53, Mdm2/Mdmx, and cAbl/Mdm2 was examined in human hepatoblastoma (HepG2) cells. Cells were cultured in zinc‐deficient (ZD0.2 and ZD0.4 with 0.2 and 0.4 uM zinc, respectively) or zinc normal (ZN with 4 uM zinc) medium. Mdm2/p53, Mdmx/Mdm2, and c‐Abl/mdm2 interactions were detected by Immunoprecipitation assays. Interestingly, Mdm2/p53 interaction was significantly decreased in ZD0.2 and ZD0.4 cells as compared with ZN cells. In addition, Mdm2/p53 interaction was significantly lower in ZD0.2 cells as compared with ZD0.4 cells. Importantly, the amount of Mdmx bound to Mdm2 was increased in ZD0.2 and ZD0.4 cells as compared with ZN cells. c‐Abl/Mdm2 interaction was higher in ZD0.2 and ZD0.4 cell than in ZN cells. Moreover, p‐Tyr of Mdm2, which is known to impair the interaction of Mdm2 with p53, was found to be higher in ZD cells as compared with ZN cells. Zinc depletion in ZD0.2 and ZD0.4 cells increased the phosphorylation of p53 at serine 15 and 392 but not at serine 20. In conclusion, we believe that this increase in phosphorylation of p53 at serine 15 is the most direct way that zinc deficiency stabilizes p53 and enhances the accumulation of nuclear p53 and Mdm2 in zinc deficient HepG2 cells. Moreover, Mdm2 interacts with Mdmx or c‐Abl and may also contribute to the accumulation of nuclear p53 and Mdm2 in zinc deficient cells.