BCA, bicinchoninic acid; CHX, cycloheximide; CSN5, COP9 signalosome 5; Cancer biology; DUB, deubiquitinating enzymes; EBNA1, Epstein­Barr nuclear antigen 1; Epigenetics; FDA, U.S. Food and Drug Administration; FOXO4, forkhead box O4; GC, gastric cancer; GEPIA, Gene-Expression Profiling Interactive Analysis; Gastric cancer; H2O2, hydrogen peroxidase; HAUSP, herpes virus-associated ubiquitin-specific protease; HDN, well differentiated matched adjacent normal tissues; HDT, well differentiated tumor tissues; ICP0, infected cell protein 0; IL-2, interleukin 2; Immunosuppression; Immunotherapy; MDM2, murine double minute-2; PBMC, peripheral blood mononuclear cells; PBS, phosphate buffer saline; PD-1, programmed cell death protein 1; PD-L1; PD-L1, programmed death ligand-1; PDN, poor differentiated matched adjacent normal tissues; PDT, poor differentiated tumor tissues; PTMs, post-translational modifications; RIPA, radioimmunoprecipitation; TCGA, the Cancer Genome Atlas; TCR, T cell receptor; TILs, tumor-infiltrating T cells; USP18, ubiquitin specific peptidase 18; USP22, ubiquitin specific peptidase 22; USP38, ubiquitin specific peptidase 38; USP7; USP7, ubiquitin-specific processing protease 7; USP9X, ubiquitin specific peptidase 9 X-linked; Ubiquitination; WB, Western blotting; irAEs, immune-related adverse effects; qRT-PCR, quantitative real time polymerase chain reaction