SIRT5通过影响胞浆游离DNA水平促进大肠癌细胞免疫逃逸的机制研究

Tumor escaping from immune surveillance system is critical for colorectal cancer progression. Ectopic accumulation of cytosolic DNA induces the activation of the STING pathway, which mediates the IFN-β dependent cancer immunoevasive. Currently, we found that knockdown of lysine deacylase SIRT5 significantly elevated the cytosolic DNA accumulation in colorectal cancer cells, along with an increase in transcription of IFN-β and downstream chemokines. We therefore assume that SIRT5 may be emerging as a potential regulator of tumor immunity during the development of colorectal cancer. Based on our former results, in this study we aim to (1) clarify the role of SIRT5 in regulation of IFN-β-dependent antitumor immunity in colorectal cancer. (2) explore the effect and the molecular mechanisms of SIRT5 in suppressing cytosolic DNA accumulation in colorectal cancer cells. (3) confirm that SIRT5 regulates tumoral immune escape via inhibiting cytosolic DNA-induced STING-TBK1-IRF3 pathway-mediated IFN-β production. Our research may provide theoretical basis for potential immunotherapeutic target, and has important guiding significance for overcoming the weak responses to current immunotherapies in colorectal cancer.

肿瘤免疫逃逸是大肠癌进展的重要因素。胞浆DNA异常积聚可以诱导STING通路激活，引起IFN-β相关的肿瘤免疫清除。近来我们发现，静默去酰化酶SIRT5显着增加大肠癌细胞胞浆游离DNA水平，以及IFN-β及下游趋化因子转录。据此，我们推测SIRT5可能参与大肠癌发生发展过程中的肿瘤免疫调控。本研究拟在前期工作的基础上，通过组织标本、细胞学实验等明确：1、大肠癌中SIRT5参与调节IFN-β相关肿瘤免疫的作用。2、SIRT5抑制肿瘤胞浆DNA产生及其分子机制。3、SIRT5是否通过影响STING-TBK1-IRF3通路识别胞浆游离DNA，从而抑制IFN-β相关的肿瘤免疫清除，参与大肠癌免疫逃逸。本课题的实施将为大肠癌免疫治疗提供新的理论依据，对克服目前大肠癌免疫治疗效果不佳的问题，具有重要指导意义。

在我们既往研究中，报道了去乙酰化酶家族成员sirtuin5（SIRT5）在结直肠癌中高表达。在本课题，我们进一步证明抑制SIRT5调控肿瘤免疫通路，同时引起核苷酸合成所必需的核糖-5-磷酸减少，进一步造成持续且不可修复的肿瘤细胞DNA损伤，最终导致细胞周期阻滞和肿瘤细胞凋亡增强。这些敲低SIRT5所导致的结果可通过核苷回补而逆转。在机制探讨方面，本课题发现SIRT5通过去甲基化依赖的方式激活转酮醇酶(TKT)，而TKT是非氧化磷酸戊糖途径中的关键酶。此外，体内及体外肿瘤模型中，本课题验证了TKT是SIRT5诱导的肿瘤恶性表型所必需的。综上所述，在结直肠癌中抑制SIRT5表达通过翻译后修饰调控DNA损伤修复从而抑制肿瘤生长，这些结果表明SIRT5可以作为结直肠癌治疗的一个潜在靶点。