CSN5介导的免疫逃逸在结肠炎相关结直肠癌发生发展中的作用及其机制研究

Nonresolving inflammation in the intestine predisposes individuals to colitis-associated carcinoma (CAC), which leads to high morbidity and mortality. Immune escape of tumor cells is closely related to the development of CAC. Up to now, the upper regulatory pathway of immune escape of colorectal cancer cells is still poorly understood. Our preliminary studies have shown that the number of macrophages and the secretion of TNF-α in colorectal cancer tissue were significantly higher than that in adjacent normal tissue in the CAC model, and the protein levels of CSN5 (COP9 signalosome subunit 5) and PD-L1 (programmed cell death-ligand 1) were significantly increased. However, the infiltration of CD8+ T lymphocyte was significantly reduced. Our results indicated that TNF-α may promote the immune escape of colorectal cancer cells through activating the p65/CSN5/PD-L1 axis. Various molecular biology methods will be adopted to investigate the mechanism of CSN5 in regulating the immune escape of colorectal cancer cells, which leads to the progression of CAC, in cancer cell-T cell co-culture system and in CSN5 gut-specific knock-out mice. The aim of this study is to investigate the exact role of p65/CSN5/PD-L1 axis in the development of CAC and verify the chemopreventive activity of CSN5 inhibitor. Our study not only provides a new perspective for the pathogenesis of colorectal cancer, but also has important guiding significance for the development of chemopreventive drugs.

结肠炎诱发的结肠癌亚型称为结肠炎相关结直肠癌（CAC）。CAC的发生发展与肿瘤细胞的免疫逃逸密切相关，但其具体机制不详。本课题前期研究证明：小鼠CAC模型肿瘤组织中巨噬细胞数及TNF-α分泌量明显增多，CSN5（COP9 signalosome subunit 5）和PD-L1的蛋白水平显著升高，而CD8+T淋巴细胞浸润明显减少；TNF-α可上调HCT116结肠癌细胞中CSN5和PD-L1的蛋白水平，并抑制T淋巴细胞的免疫效应。为此，我们提出假说：TNF-α可通过激活p65/CSN5/PD-L1信号通路轴促进结肠癌细胞的免疫逃逸。为验证这一假说，本课题拟利用共培养体系和CSN5肠道特异性基因敲除小鼠，多方面阐明CSN5介导结肠癌细胞免疫逃逸的确切机制，明确CSN5抑制剂基于免疫增敏效应的化学预防作用，试图为CAC发病机制的研究提供新的视点，同时为结肠癌化学预防药物的研发提供新策略。

结肠癌的发生发展与肿瘤细胞的免疫逃逸密切相关。结肠癌组织中浸润的巨噬细胞是肿瘤微环境的重要组成部分，在肿瘤的发生和发展中起重要作用。然而，巨噬细胞源性的细胞因子促进结直肠癌(CRC)细胞免疫逃逸的确切分子机制目前尚不清楚。本课题体内外结果证明：在AOM诱导的结肠癌模型中，脂多糖(LPS)或高胆固醇饮食(HCD)诱导的巨噬细胞可显著促进结直肠癌的发生发展；LPS和poly (I:C)可显著增加CT26细胞同种异体移植瘤的体积；巨噬细胞分泌的CCL5可抑制T淋巴细胞对HT29细胞的杀伤作用，并通过稳定PD-L1促进结肠癌细胞的免疫逃逸。随后，通过对其分子机制进行探究，本课题发现CCL5可促进核因子kappa-B p65/STAT3复合物的结合并提高COP9信号小体5 (CSN5)的转录活性，而CSN5可通过抑制PD-L1的泛素化提高PD-L1的稳定性。人源CRC样本中，CCL5与p-p65、p-STAT3、CSN5以及PD-L1的表达水平密切相关。最后，本课题采用AOM-LPS诱导的结肠癌模型及同种异体移植瘤模型评价了CSN5抑制剂C-15的化学预防作用。综上，本课题利用结肠癌细胞-T淋巴细胞共培养体系和小鼠结肠癌模型，多方面阐明了CSN5介导结肠癌细胞免疫逃逸的确切机制，明确了CSN5抑制剂基于免疫增敏效应的化学预防作用，试图为CRC发病机制的研究提供新的视点，同时为结肠癌化学预防药物的研发提供新策略。