Combining Transarterial Chemoembolisation With Reduced Deubiquitinase Activity Reduces Hepatocellular Carcinoma Progression.

To investigate the interplay between ubiquitin-specific protease 21 (USP21) and programmed death-ligand 1 (PD-L1) in the context of Transarterial chemoembolisation (TACE) treatment for hepatocellular carcinoma (HCC) and explore a novel combinatorial strategy to enhance therapeutic efficacy. USP21 was silenced in HCC cells and in two distinct mouse models: a diethylnitrosamine (DEN)-induced orthotopic HCC model and a HepG2 subcutaneous xenograft model. The effects of USP21 knockdown, TACE and their combination on tumour growth, proliferation, invasion and apoptosis were evaluated. The regulation of PD-L1 by USP21 was studied through co-immunoprecipitation and deubiquitination assays. Rescue experiments were performed by overexpressing PD-L1. Silencing USP21 attenuated HCC cell proliferation and invasion. Combining TACE with USP21 knockdown significantly enhanced antitumour effects compared to monotherapies. USP21 interacted with and deubiquitinated PD-L1, stabilising its expression. Cycloheximide chase assays with densitometric quantification demonstrated that USP21 significantly prolonged the half-life of PD-L1 protein. Overexpression of PD-L1 reversed the inhibitory effects of USP21 silencing and the enhanced therapeutic efficacy of the TACE/USP21 knockdown combination. USP21 stabilises PD-L1 through deubiquitination, promoting HCC progression and immune evasion. Silencing USP21 enhances the therapeutic efficacy of TACE by modulating PD-L1 expression, suggesting a promising combinatorial strategy for HCC treatment.