SIRT2-mediated deacetylation activates USP22 catalytic function for PD-L1 protein stabilization and tumor immune escape.

Immune checkpoint blockade (ICB), including PD-1/PD-L1 inhibitors, has transformed cancer therapy but benefits only a subset of patients. Understanding how PD-L1 is regulated and identifying strategies to overcome resistance remain critical. Here, we identify SIRT2 as a key positive regulator of PD-L1 across multiple human cancers. Unexpectedly, SIRT2 did not act at the transcriptional level but stabilized PD-L1 protein by preventing ubiquitin-mediated degradation. Mechanistically, SIRT2 maintained the protein stability of USP22, a PD-L1 deubiquitinase. Loss of SIRT2 reduced USP22 levels, whereas ectopic USP22 fully rescued PD-L1 expression and reversed the enhanced antitumor immunity induced by SIRT2 inhibition. We further show that SIRT2 directly deacetylates USP22 at K382 and K505 within its catalytic domain, promoting USP22 deubiquitinase activity and protecting both itself and its substrates from degradation. Our findings reveal a molecular mechanism by which an acetylation-deacetylation switch dynamically regulates deubiquitinase catalytic activity. Therapeutically, SIRT2 inhibition synergized with PD-1/PD-L1 blockade and USP22 inhibition to enhance antitumor immunity. Consistently, protein, but not mRNA, levels of SIRT2, USP22, and PD-L1 positively correlated in human bladder cancer and melanoma. Together, these findings define a SIRT2/USP22/PD-L1 axis driving tumor immune evasion and highlight SIRT2 as a promising target to improve ICB efficacy.