UBE2M Drives Hepatocellular Cancer Progression as a p53 Negative Regulator by Binding to MDM2 and Ribosomal Protein L11.

Ju-Ha Kim,Jieon Park,Hyo-Jung Lee,Chi-Hoon Ahn,Deok-Yong Sim,Bum-Sang Shim,Sung-Hoon Kim,Eunji Im,Ji Hoon Jung,Bonglee Kim,Woon-Yi Park

doi:10.3390/cancers13194901

Abstract

Simple SummaryHerein, the oncogenic role of UBE2M as an E2 NEDD8-conjugating enzyme was explored in hepatocellular carcinoma (HCC) cells, since neddylation plays a critical role in tumorigenesis. To address this issue, human tissue array and TCGA analysis were conducted in HCCs to find overexpression of UBE2M in HCCs. In addition, a differential profile was confirmed in UBE2M-depleted HepG2 cells. Furthermore, UBE2M depletion activated p53 expression and stability, while the ectopic expression of UBE2M disturbed p53 activation and enhanced degradation of exogenous p53 mediated by MDM2 in HepG2 cells via binding to MDM2 and ribosomal protein L11 by immunoprecipitation and immunofluorescence. These findings provide evidence that UBE2M is critically involved in liver cancer progression as a p53 negative regulator by binding to MDM2 and ribosomal protein L11.Though UBE2M, an E2 NEDD8-conjugating enzyme, is overexpressed in HepG2, Hep3B, Huh7 and PLC/PRF5 HCCs with poor prognosis by human tissue array and TCGA analysis, its underlying oncogenic mechanism remains unclear. Herein, UBE2M depletion suppressed viability and proliferation and induced cell cycle arrest and apoptosis via cleavages of PARP and caspase 3 and upregulation of p53, Bax and PUMA in HepG2, Huh7 and Hep3B cells. Furthermore, UBE2M depletion activated p53 expression and stability, while the ectopic expression of UBE2M disturbed p53 activation and enhanced degradation of exogenous p53 mediated by MDM2 in HepG2 cells. Interestingly, UBE2M binds to MDM2 or ribosomal protein L11, but not p53 in HepG2 cells, despite crosstalk between p53 and UBE2M. Consistently, the colocalization between UBE2M and MDM2 was observed by immunofluorescence. Notably, L11 was required in p53 activation by UBE2M depletion. Furthermore, UBE2M depletion retarded the growth of HepG2 cells in athymic nude mice along with elevated p53. Overall, these findings suggest that UBE2M promotes cancer progression as a p53 negative regulator by binding to MDM2 and ribosomal protein L11 in HCCs.

Highlights

Hepatocellular carcinoma (HCC) is known as the sixth most common cancer and the third leading cause of cancer-associated mortality in the world [1]
These findings suggest that UBE2M promotes cancer progression as a p53 negative regulator by binding to MDM2 and ribosomal protein L11 in HCCs
UBE2M was overexpressed in human hepatocellular carcinoma (HCC), such as HepG2, Hep3B, Huh7 cells and PLC/PRF5 cells, but not in normal hepatocytes by Western blotting (Figure 1A) and tissues array (Figure 1D)

Summary

Introduction

Hepatocellular carcinoma (HCC) is known as the sixth most common cancer and the third leading cause of cancer-associated mortality in the world [1]. HCC has been associated with neddylation [2] and various signaling pathways [3] and is genetically and phenotypically regarded as a heterogeneous cancer [4]. Neddylation is considered as one of important signaling pathways in tumorigenesis, since post-translational modification critically modulates protein activation by ubiquitin-proteasome system (UPS) [5,6,7]. UBE2M is known as one of the neddylation ligase complexes, such as cullin-RING ligases (CRLs), RBX1 and ROC1, for poly-ubiquitin conjugation [14] and targets degradation of UBE2F [15,16,17] and p27 (Kip1) [18]. UBE2M acts as a stress-inducible dual gene for neddylation and ubiquitylation [19] and promotes proliferation and migration in HCCs via activation of β catenin and cyclin D1 [20], along with overexpression in several cancers, including HCCs [21], H1299 lung cancer [22] and osteosarcoma [23]

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