MDM2 and glioblastoma: Apart from loss or mutation of the p53 gene, further mechanisms that result in p53 inactivation in GBM include impairment of p53 protein stability and suppression of p53 gene expression through amplification of p53 inhibitor genes, such as MDM2 and MDM4 [47,48], genetic deletion and methylation of the p53 inducer ARF [49], genomic loss of ATM, CHEK2 [50], mutation of Parkin [51], overexpression of NFIA, and miR-141-3o [52,53], Bcl2 [54,55], and MIF [56].