The regulatory mechanism of deubiquitin ligase USP9X in nasopharyngeal carcinoma cell proliferation through FOXM1-mediated glycolysis / 肿瘤

ABSTRACT

Objective:To explore whether the deubiquitinating enzyme deubiquitin ligase 9X(USP9X)affects the proliferation of nasopharyngeal carcinoma(NPC)cells via regulating forkhead box Ml(FOXM1)mediated glycolysis. Methods:Western blotting and real-time fluorescence quantitative PCR,respectively,were used to detect the protein and mRNA expression levels of USP9X in NPC tissue and normal nasal mucosa tissue.NPC cells(CNE2 and HNE2)were infected with lentivirus carrying specific shRNA targeting USP9X gene(shUSP9X)or full-length USP9X gene(Flag-USP9X)for USP9X overexpression.CCK-8 assay was used to evaluate the effect of USP9X silencing or overexpression on the proliferation of NPC cells.Cellular energy metabolism assay and extracellular acidification rate(ECAR)assay were performed to investigate the impact of USP9X alteration on the glycolysis of NPC cells.The interaction between USP9X and FOXM1 was analyzed using ubibrowser_v3/database,co-immunoprecipitation,and ZDOCK software,and the changes in FOXM1 protein ubiquitination levels upon USP9X silencing was examined.Real-time fluorescence quantitative PCR and Western blotting,respectively,were used to detect the effect of USP9X alteration on the expression of FOXM1 mRNA and protein in NPC cells.Finally,FOXM1 expression was restored in USP9X silencing CNE2 cells by expression of recombinant plasmid Flag-FOXM1 carrying full-length FOXM1 gene through lentiviral infection.CCK-8 assay was used to evaluate the effect of FOXM1 upregulation on the proliferation of CNE2 cells.Cellular energy metabolism assay and ECAR assay were used to investigate the effect of FOXM1 upregulation on the glycolysis of CNE2 cells. Results:Compared with normal nasal mucosa tissue,the expression levels of USP9X mRNA and protein were significantly increased in NPC tissues(P＜0.05).After USP9X downregulation,the proliferation and glycolysis of CNE2 cells was significantly inhibited as indicated by the results of CCK-8 assay,cellular energy metabolism assay and ECAR assay(P＜0.05).In contrast,the proliferation and glycolysis of HNE2 cells was significantly enhanced after USP9X upregulation(P＜0.05).The interaction between USP9X and FOXM1 was confirmed by ubibrowser_v3/database,co-immunoprecipitation,and ZDOCK software analysis.Silencing USP9X could significantly increase FOXM1 ubiquitination in CNE2 cells.Overexpressing FOXM1 in low-USP9X CNE2 cells restored the proliferation and glycolysis activity of NPC cells(P＜0.05). Conclusion:USP9X can enhance NPC cell glycolysis by inhibiting FOXM1 ubiquitination and subsequent degradation,thereby promoting NCP cell proliferation.USP9X may be a potential novel therapeutic target for the treatment of NPC.