MDM2 and glioblastoma: mRNA levels of the cyclin-dependent kinase (CDK) inhibitor p21 (WAF1/CIP1; CDKN1a) [41] were not significantly changed in the three cell lines, while mRNA levels of MDM2, which induces ubiquitin-dependent degradation of [42,43] were decreased in the si-hVDAC1-treated GBM tumours, but not in A549 or MDA-MB-231–derived xenografts (Figure 6G).