SIRT2-mediated deacetylation activates USP22 catalytic function for PD-L1 protein stabilization and tumor immune escape
Na Li, Qiong Gao, Huijun Jia, Guoqing Xue, Yuanzhang Zhou, Shengnan Wang, Suxian Ma, Bingjin Hu, Zhuoyue Zhao, Chen Su, Yinghong Liu, Wenxuan Xi, Zhonghao Li, Donna D. Zhang, Peng Chu, Zhaolin Sun, Deyu Fang
Na Li, Qiong Gao, Huijun Jia, Guoqing Xue, Yuanzhang Zhou, Shengnan Wang, Suxian Ma, Bingjin Hu, Zhuoyue Zhao, Chen Su, Yinghong Liu, Wenxuan Xi, Zhonghao Li, Donna D. Zhang, Peng Chu, Zhaolin Sun, Deyu Fang
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Research Article Immunology Oncology

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

Abstract

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.

Authors

Na Li, Qiong Gao, Huijun Jia, Guoqing Xue, Yuanzhang Zhou, Shengnan Wang, Suxian Ma, Bingjin Hu, Zhuoyue Zhao, Chen Su, Yinghong Liu, Wenxuan Xi, Zhonghao Li, Donna D. Zhang, Peng Chu, Zhaolin Sun, Deyu Fang

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Figure 2

SIRT2 inhibits PD-L1 ubiquitination by regulating USP22.

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SIRT2 inhibits PD-L1 ubiquitination by regulating USP22. (A) Western blo...
(A) Western blot analysis of deubiquitinases in SIRT2-KO T24 cells, including USP9X, USP5, USP7, USP8, USP20, USP22, and CSN5. (B) Quantification of PD-L1 expression. (C) Western blot analysis of USP22 protein levels in SIRT2-KO MB49 cells. (D–F) SIRT2-KO T24 cells were transfected with or without Myc-USP22, and PD-L1 expression was assessed by Western blotting and flow cytometry 36 hours after transfection. (G) RT-qPCR analysis of USP22 mRNA levels in WT and SIRT2-KO T24 cells. (H) Analysis of the interaction between Myc-USP22 and Flag-SIRT2 in HEK293T cells. (I) Co-IP analysis of endogenous interaction between SIRT2 and USP22 in T24 cells. (J and K) Structural modeling of SIRT2-USP22 interaction. (J) Simulated interaction diagram. (K) Dot plot representing predicted interacting amino acid residues. Blue box: N-terminal region of USP22; orange box, C-terminal region of USP22. (L) Analysis of endogenous USP22 acetylation in WT and SIRT2-KO T24 cells. (M) USP22 acetylation was detected by immunoprecipitating with anti-Myc antibodies followed by blotting with anti–pan-acetylation antibodies. (N) In vitro analysis of SIRT2 deacetylation of acetyl-USP22. Data are shown as mean ± SD. Statistical significance was determined using unpaired 2-tailed Student’s t test for B and G and 1-way ANOVA for F. **P < 0.01; ***P < 0.001.