具核梭杆菌通过激活NF-κB/MAPK信号通路致PD-L1表达上调影响大肠癌免疫逃避的分子机制

In our previous study, we have demonstrated the underlying molecular mechanism that the fusobacterium nucleatum (F.nucleatum) could stimulate NF-κB/MAPK signaling pathway through activation of TLR4 cascade in the progression of colorectal cancer. It has been reported that these signaling pathways are associated with an increased the secretion of IL-6. Meanwhile, we have also found that Fn was abnormally enrichment in colorectal cancer (MSI-High) patients, and a large number of CD68+/PD-L1+ macrophages were infiltrated in the colorectal cancer tissues. On the basis of the present preliminary results, we are try to to clarify whether fusobacterium nucleatum (Fn) could combine with tumor associated macrophages (TAMs) by activating TLR4 receptor, and further simulating the secretion of IL-6 in colorectal cancer through in vitro and in vivo experiments. Meanwhile, we are try to explore the potential molecular mechanisms that IL-6 in the tumor microenvironment could regulate the expression of TAMs or other mesenchymal cells, and further induced the upregulation of PD-L1, so as to construct the signalling shaft (Fn-TLR4-NF-κB/MAPK-IL-6-PD-L1) in the colorectal cancer. In addition, using the Metronidazole, probiotics, and the inhibitors of key molecular targets (PD-1/PD-L1 and CSF-1R) to prevent and target therapy for colorectal cancer in animal models, and then assess tumor size, tumor numbers and survival for these animals, further to reveal its effect of the target therapy and improve F. nucleatum-induced resistance of immunosensor inhibitor in colorectal cancer.

申请人前期研究中阐明具核梭杆菌(F.nucleatum)与大肠癌细胞表面TLR-4受体结合激活NF-κB/MAPK信号通路致大肠癌的发生发展，并且已有文献报道这些信号通路均与IL-6的分泌增加有关，同时课题组发现MSI-H患者肠癌组织中Fn异常富集且存在大量CD68+/PD-L1+的巨噬细胞浸润。因此本课题建立在已有研究的基础上，拟利用离体细胞和动物模型实验明确Fn是否通过TLR-4受体结合肿瘤相关巨噬细胞(TAMs)等间质细胞，并激活下游NF-κB/MAPK信号途径，从而促进IL-6分泌；同时拟探索肿瘤微环境中IL-6进一步调控免疫细胞致PD-L1表达上调的分子机制，从而构建大肠癌中Fn—TLR-4—NFκB/MAPK—IL-6—PD-L1的调控体系；并利用甲硝唑、益生菌和PD-1/PD-L1抑制剂在大肠癌动物模型中进行干预及靶向治疗，阐明拮抗Fn可改善Fn诱导的免疫检查点抑制剂耐药。

结直肠癌(CRC)仍然是全球癌症相关死亡的主要原因之一，包括免疫检查点抑制剂(ICB)在内的免疫治疗对大多数pMMR的结直肠癌患者没有显著的治疗效果。越来越多的证据表明，具核梭杆菌(Fn)感染与CRC的发生和发展有关。在本研究中，研究人员发现Fn感染的CRC样本中肿瘤相关巨噬细胞富集。研究人员的发现进一步表明，Fn感染可以通过上调肿瘤相关巨噬细胞中PD-L1的表达，通过IL-6信号级联抑制宿主的抗肿瘤免疫。ICB治疗在临床队列研究中发现可以显著提高fn阳性CRC的生存期。有趣的是，临床数据分析表明，Fn感染与ICB在CRC以外不同类型癌症中的疗效增强也有关。因此，研究人员的研究结果揭示了肠道微生物组和肿瘤免疫微环境之间的重要相互作用，对CRC和其他癌症的免疫治疗具有一定的临床意义。