METTL3-Mediated m6A Methylation of USP21 Contributes to Hepatocellular Carcinoma Progression by Stabilizing H2BFS Through Deubiquitination.

Deubiquitinases play essential roles in hepatocellular carcinoma (HCC) progression, however, the role of ubiquitin-specific peptidase 21 (USP21) in HCC development remains unclear. The present work aims to analyze the effect of USP21 on tumor property of HCC cells and the underlying mechanism. mRNA expression levels of USP21 and H2BFS were analyzed by quantitative real-time polymerase chain reaction. Protein expression of USP21, E-cadherin, N-cadherin, Vimentin, H2BFS and methyltransferase 3 (METTL3) was assessed by western blotting assay or immunohistochemistry assay. Clonogenicity assay was used to analyze cell proliferation. Flow cytometry assay was performed to quantify apoptotic rate of cells. Wound-healing assay and transwell assay were conducted to analyze cell migration and invasion, respectively. Xenograft mouse model assay was performed to determine the effect of USP21 knockdown on tumor formation. m6A RNA immunoprecipitation assay (MeRIP) was used to analyze the effect of METTL3 silencing on methylated level of USP21. USP21 expression was upregulated in HCC tissues and cells when compared with control groups. USP21 silencing inhibited proliferation, migration and invasion and induced apoptosis of HCC cells, accompanied by the increased E-cadherin protein expression and decreased N-cadherin and Vimentin protein expression. Moreover, USP21 knockdown delayed tumor formation in vivo. USP21 stabilized H2BFS by deubiquitination, and H2BFS overexpression attenuated USP21 silencing-induced effects in HCC cells. Further, METTL3-mediated m6A methylation of USP21. METTL3-mediated m6A methylation of USP21 promoted HCC progression by stabilizing H2BFS through deubiquitination.