阐明肿瘤免疫逃逸的机制是理解肺癌发生与演进、探索免疫治疗新策略的核心基础。我们前期发现泛素特异性蛋白酶2(USP2)通过蛋白质降解途径调控肺癌细胞保护性“外衣”—CD47的稳定表达，在激活“Do not eat me”信号中发挥重要作用，但机制不清；进一步证据表明USP2和CD47是RagA的结合蛋白且三者共存于细胞内体，USP2是RagA的去泛素化酶。本项目提出“USP2介导RagA去泛素化抑制CD47内吞和降解，稳定CD47表达并锚定于细胞膜，从而逃逸免疫杀伤”的假说，拟采用Co-IP、GST pull-down、基因定点突变等技术明确USP2在CD47内吞-溶酶体降解中的作用及USP2泛素化修饰影响RagA GTP/GDP的结合能力，揭示RagA去泛素化在USP2调控CD47稳定表达中的机制及临床学意义；结果可望为深入认识肺癌免疫逃逸的源动力机制及探索肺癌诊疗新策略提供新思路和靶点。

To clarify the mechanism of tumor immune escape is the core to understand the initiation and progression of lung cancer, and investigate the novel strategy for immunotherapy. Our preliminary studies showed that ubiquitin specific protease 2 (USP2) played a crucial role in the activation of “Do not eat me” signaling by regulating the stable expression of lung cancer-protective "coat" CD47, which is dependent on protein degradation pathway. However, the detailed mechanism remains unclear. Further evidence suggested that both USP2 and CD47 were binding proteins for RagA and these three proteins coexisted in tumor cell endosome, and USP2 is a deubiquitination enzyme of RagA. The project proposed the hypothesis that USP2 mediates RagA deubiquitination to inhibit CD47 endocytosis and degradation, CD47 is stably expressed and anchored to the cell membrane, and subsequently lead to evade immune killing. Multiple molecular techniques including IP, GST pull-down and deletion mutation will be applied to decipher the role of USP2 in CD47 endocytosis and lysosomal degradation, the influence of USP2 ubiquitination modification on the ability of RagA binding to GTP/GDP, and elucidate the mechanism involved in RagA deubiquitination of USP2 regulating stable expression of CD47 and its clinical significance. The results are expected to provide new ideas and targets for further understanding the original mechanism of lung cancer immune escape and exploring new strategies for lung cancer diagnosis and treatment.