ISG15 and urinary bladder carcinoma: Emerging evidence have reported that USP18 predominantly plays a role in removing interferon‐stimulated gene 15 (ISG15), regarded as a ubiquitin‐like protein (Ubl), from substrate proteins.[25, 26] We first explored whether the protein stability of PD‐L1 was regulated by lncRNA BCCE4 using a cycloheximide (CHX) chase assay and observed that endogenous PD‐L1 was unstable and degraded rapidly in bladder cancer cells transfected with si‐BCCE4 (Figure S29A, Supporting Information).