由于PD-L1的表达水平影响PD-1/PD-L1抗体的治疗效果，因此，明确肿瘤细胞中调节PD-L1表达的分子机制有助于设计新的免疫治疗策略。我们前期研究发现，TRAF3促进PD-L1 K63连接的多聚泛素化修饰，从而稳定PD-L1。通过筛选去泛素化酶抑制剂发现，USP8抑制剂DUBs-IN-2显著上调PD-L1。USP8与PD-L1发生相互作用，去除PD-L1 K63多聚泛素化修饰并降低PD-L1表达。在此基础上，本项目进一步研究TRAF3和USP8介导的K63多聚泛素化修饰调控PD-L1的分子机制。在肿瘤临床样品中检测TRAF3、USP8的表达与PD-L1相关性。并且，利用小鼠肿瘤模型研究USP8抑制剂DUBs-IN-2与PD-L1抗体联用对肿瘤的治疗效果。该研究将揭示TRAF3-USP8调节PD-L1的分子机制以及对免疫治疗效果的影响，为临床上肿瘤治疗提供新的思路和方法。

Previous reports have demonstrated that the expression level of PD-L1 in tumor cells affects the therapeutic efficacy of PD-1/PD-L1 blockade. Therefore, exploring the molecular mechanism of PD-L1 regulation in tumor cells will be useful to design new immunotherapeutic strategies. Our primary results showed that TRAF3 promotes K63-linked poly-ubiquitination of PD-L1, thereby stabilizing PD-L1. Through screening inhibitors of deubiquitinating enzymes, we found that the USP8 inhibitor DUBs-IN-2 dramatically upregulates PD-L1. Furthermore, we found that USP8 specifically interacts with PD-L1 and removes K63-linked poly-ubiquitination of PD-L1, thereby decreaing PD-L1. This study will further explore the molecular mechanism of TRAF3 and USP8-mediated K63-linkded poly-ubiquitination for PD-L1 regulation. We will also detect the correlation of TRAF3 and USP8 expression with PD-L1 in tumor clinical specimens. Lastly, we will investigate whether DUBs-IN-2 could syngergize with PD-1/PD-L1 blockade to improve the therapeutic efficacy in syngeinic mouse model. This study will reveal the molecular mechansim of TRAF3-USP8 in regulating PD-L1 stability and the efficacy of cancer immunotherapy, which will provide new insights for cancer thrapy in clinics.