去泛素化酶USP7调控SAMHD1稳定性对结肠癌奥沙利铂化疗敏感性的影响及机制研究

奥沙利铂是结肠癌化疗一线药物，但其疗效存在较大个体差异，因此提高其化疗敏感性意义重大。SAMHD1是一种dNTP水解酶，最新研究提示其可不依赖水解酶活性参与DNA损伤修复。我们发现：1.奥沙利铂诱导SAMHD1蛋白泛素化减弱而表达量增加，与DNA损伤修复因子CtIP结合增强；2.敲减SAMHD1可增加奥沙利铂诱导的细胞凋亡和DNA损伤，减少结肠癌细胞存活率；3.去泛素化酶USP7与SAMHD1结合，去泛素化修饰SAMHD1并稳定其表达；4.靶向抑制USP7可减弱奥沙利铂诱导的SAMHD1增加，提高结肠癌细胞对奥沙利铂的敏感性。由此建立工作假说：USP7去泛素化修饰SAMHD1蛋白并稳定其表达，SAMHD1与CtIP结合，修复奥沙利铂诱导的DNA损伤，影响结肠癌奥沙利铂化疗敏感性。本项目拟阐明USP7-SAMHD1-CtIP通路影响结肠癌奥沙利铂化疗疗效的分子机制，为结肠癌治疗提供有效靶点。

Oxaliplatin is a first-line chemotherapy drug for colon cancer, but its efficacy varies greatly among individuals. Therefore, it is of great significance to improve the sensitivity to oxaliplatin chemotherapy. SAMHD1 is a hydrolase of dNTP, which is involved in DNA damage repair independently of the activity of hydrolase according to recent studies. We found that: 1. Oxaliplatin induced decreased ubiquitination and increased expression of SAMHD1 protein, and enhanced the binding between SAMHD1 and DNA damage repair factor CtIP; 2. SAMHD1 knockdown increased oxaliplatin-induced apoptosis and DNA damage as well as decreased survival rate in colon cancer cells; 3. USP7 binds to SAMHD1, and mediates deubiquitination of SAMHD1 protein and stabilizes its expression; 4. Targeted inhibition of USP7 can reduce the oxaliplatin-induced increase of SAMHD1 protein and improve the sensitivity of colon cancer cells to oxaliplatin. Therefore, a working hypothesis was established: USP7 mediated deubiquitination of SAMHD1 protein and stabilized its expression, and SAMHD1 combined with CtIP to repair oxaliplatin-induced DNA damage, thus affecting the sensitivity of colon cancer to oxaliplatin chemotherapy. This project aims to clarify the molecular mechanism of USP7-SAMHD1-CtIP pathway affecting the efficacy of oxaliplatin chemotherapy in colon cancer, and to provide an effective target for the treatment of colon cancer.