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

Abstract

Mouse Double Minute homolog 4 (MDM4) gene upregulation 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 via 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. De-ubiquitination by ubiquitin-specific protease 2a and AKT-mediated phosphorylation protected MDM4 from proteasomal degradation and increased AKT protein stability. The eukaryotic elongation factor 1A2 (EEF1A2) was identified as an upstream inducer of PI3K supporting MDM4 stabilization. Also, we detected MDM4 protein upregulation in an AKT mouse model and a strong correlation between the expression of EEF1A2, activated/phosphorylated AKT, and MDM4 in human HCC (each rho>.8, P<.001). Noticeably, a strong activation of this cascade was associated with shorter patients' survival. Conclusions The EEF1A2/PI3K/AKT/mTOR axis promotes the protumorigenic stabilization of the MDM4 protooncogene in human HCC via a post-transcriptional 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.

Protumorigenic role of Timeless in hepatocellular carcinoma

“…3a), eeF1a2, v-akt murine thymoma viral oncogene homolog (AKT), and β-actin (Fig. 3B) were downregulated following TIM knockdown suggesting that tIm may activate the protumorigenic eeF1a2/aKt/mDm4 axis (21). In line, transcriptional activation of some p53 target genes was seen following tIm knockdown in p53-wild-type cells indicating reactivation of p53 function in these cells (Fig.…”

“…We have previously identified eeF1a2 as a candidate oncogene in human hepatocarcinogenesis (20). EEF1A2 acts as an upstream inducer of the PI3K/aKt/mtoR axis leading to functional inactivation of p53 by posttranslational stabilization of the mouse double minute homolog 4 (MDM4) in human HCCs (21).…”

“…however, eeF1a2 exerts an anti-apoptotic function, which may explain its role in tumorigenesis (19). We have previously identified eeF1a2 as a candidate oncogene in human hepatocarcinogenesis and demonstrated that EEF1A2 overexpression was strongly associated with the survival probability of HCC patients (20,21).…”

LncRNA NEAT1 Promotes Deterioration of Hepatocellular Carcinoma Based on In Vitro Experiments, Data Mining, and RT-qPCR Analysis

“…MADM4, a P53 binding protein homolog, is a critical negative modulator of tumor suppressor P53 [45]. Pellegrino et al [46] showed that MDM4 . acted as an oncogene in HCC by interacting with the PI3K-AKT/mTOR pathways.…”

DNA-PKcs deficiency sensitizes the human hepatoma HepG2 cells to cisplatin and 5-fluorouracil through suppression of the PI3K/Akt/NF-κB pathway

“…The PI3K/Akt pathway is frequently activated in various malignancies, which consequently activates the prosurvival pathways and enhances the chemoresistance through NFjB activation and p53 inhibition [12,13]. Arenobufagin induces apoptosis and autophagy in the HCC cells through inhibition of PI3K/Akt pathway [14].…”