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

Though UBE2M, an E2 NEDD8 conjugating enzyme, is dysregulated in human osteosarcoma, lung cancer and hepatocellular carcinoma (HCC), the underlying oncogenic mechanism and clinical significance of UBE2M still remain unclear in HCCs so far. Thus, in the current study,UBE2M was overexpressed in HCCs with poor prognosis by human tissue array and TCGA analysis. 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 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.