EEF1A2 inactivates p53 by way of PI3K/AKT/mTOR-dependent stabilization of MDM4 in hepatocellular carcinoma


  • Potential conflict of interest: Nothing to report.

  • Supported by the Deutsche Forschungsgemeinschaft DFG SFB/TRR77 (subprojects B4 to L.Z., B5 to R.P, B.R., P.S., T.L., Z2 to J.L.B.), Graduiertenkolleg 1172 to J.W. and M.Z., Ev168/2-1 to M.E, and Do622/2-1 to F.D.; National Institutes of Health grants R21CA131625 and R01CA136606 to X.C.; P30DK026743 for UCSF Liver Center; Siemens/DAAD Post Graduate Programme to V.K.; LOEWE initiative Oncogenic Signaling Frankfurt to M.Z. (funded by the Hessian Ministry of Higher Education, Research and the Arts; funding reference number III L 4-518/55.004 (2009)) and institutional funds of the Georg-Speyer-Haus by the German Federal Ministry of Health (BMG) and the Ministry of Higher Education, Research and the Arts of the state of Hessen (HMWK) to M.Z.


Mouse Double Minute homolog 4 (MDM4) gene up-regulation often occurs in human hepatocellular carcinoma (HCC), but the molecular mechanisms responsible for its induction remain poorly understood. Here we investigated the role of the phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog/mammalian target of rapamycin (PI3K/AKT/mTOR) axis in the regulation of MDM4 levels in HCC. The activity of MDM4 and the PI3K/AKT/mTOR pathway was modulated in human HCC cell lines by way of silencing and overexpression experiments. Expression of main pathway components was analyzed in an AKT mouse model and human HCCs. MDM4 inhibition resulted in growth restraint of HCC cell lines both in vitro and in vivo. Inhibition of the PI3K-AKT and/or mTOR pathways lowered MDM4 protein levels in HCC cells and reactivated p53-dependent transcription. Deubiquitination by ubiquitin-specific protease 2a and AKT-mediated phosphorylation protected MDM4 from proteasomal degradation and increased its protein stability. The eukaryotic elongation factor 1A2 (EEF1A2) was identified as an upstream inducer of PI3K supporting MDM4 stabilization. Also, we detected MDM4 protein up-regulation in an AKT mouse model and a strong correlation between the expression of EEF1A2, activated/phosphorylated AKT, and MDM4 in human HCC (each rho > 0.8, P < 0.001). Noticeably, a strong activation of this cascade was associated with shorter patient survival. Conclusion: The EEF1A2/PI3K/AKT/mTOR axis promotes the protumorigenic stabilization of the MDM4 protooncogene in human HCC by way of a posttranscriptional mechanism. The activation level of the EEF1A2/PI3K/AKT/mTOR/MDM4 axis significantly influences the survival probability of HCC patients in vivo and may thus represent a promising molecular target. (Hepatology 2014;59:1886–1899)