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
View: Text | PDF
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

×

Figure 1

SIRT2 positively regulates PD-L1 expression in multiple cancer cell types.

Options: View larger image (or click on image) Download as PowerPoint
SIRT2 positively regulates PD-L1 expression in multiple cancer cell type...
(A and B) T24 bladder cancer cells were transiently transfected with siRNAs targeting each of the 7 sirtuins. PD-L1 protein expression was assessed by Western blotting. Representative immunoblots are shown in A, and quantitative analysis from 3 independent experiments is presented in B. (C–E) CRISPR-mediated KO of SIRT2 in T24 cells was confirmed by Western blot (C, top panel). The effect on PD-L1 expression was examined by Western blot (C, middle panel) and flow cytometry (D, representative plots; E, quantified data from 3 independent experiments). (F–H) The impact of SIRT2 KO on PD-L1 expression was similarly assessed in MB49 murine bladder cancer cells. (I and J) T24 cells were treated with TM or SirReal2 at each indicated concentration for 8 hours, and PD-L1 expression levels were determined by Western blotting. (K–N) RT-qPCR analysis of SIRT2 (K and M) and PD-L1 (L and N) mRNA levels in T24 and MB49 cells following CRISPR-mediated SIRT2 deletion. WCL, whole-cell lysate. (O) Ubiquitination assay of PD-L1 in WT and SIRT2-KO T24 cells. (P) Western blot analysis of PD-L1 protein levels in SIRT2 KO T24 cells, with or without treatment with the proteasome inhibitor MG132. (Q) Interaction between Myc-tagged PD-L1 and Flag-tagged SIRT2. HEK293T cells were cotransfected with Myc-PD-L1 and Flag-SIRT2, followed by co-IP using an anti-Flag antibody to assess protein interaction. (R) Co-IP analysis of endogenous SIRT2 and PD-L1 interaction in T24 cells. Data are shown as mean ± SD. Statistical significance was determined using 1-way ANOVA for B and unpaired 2-tailed Student’s t test for E, H, and K–N. *P < 0.05; ***P < 0.001.