IKKα调控肠道炎症及肠炎相关性大肠癌的机理研究

NF-κB is a master regulator of inflammatory responses in responses to a variety of stimuli in different types of tissues and cells. The pivotal role of NF-κB in regulating colon inflammation and colitis-associated colon cancer has been extensively studied and validated in different models. Conditional knockout mouse model has validated the key function of classical NF-κB signaling in maintaining intestine immune homeostasis. By contrast, the role of noncanonical NF-κB signaling in colon inflammation and colitis-associated cancer is largely unknown. The classical NF-κB signaling is controlled by the IκB Kinase (IKK) complex composed of IKKα, IKKβ, and NEMO. While classical NF-κB activation rely more on IKKβ than IKKα for proper activation, noncanonical NF-κB signaling depend on IKKα homodimer for downstream signaling transduction and physiological functions such as secondary lymphoid organ development, bone metabolism, and T cell differentiation. In our previous studies, we have identified a tumor suppressor function of IKKα in epithelial tissues through both NF-κB dependent and independent manners. Although IKKα gene mutations have been reported in human skin lesions and cancer genome sequencing, the function of IKKα in intestinal epithelial cells and colon inflammation is still not well understood. Based on our previous studies, we hypothesize that IKKα regulate intestine inflammation and colitis-associated cancer through noncanonical NF-κB signaling. To test this hypothesis, we propose to set up chemical-induced colitis and colon cancer mouse model with in vivo knockdown of IKKα expression, and to study the function of IKKα in controlling classical and noncanonical NF-κB signaling in intestine epithelial cells and immune cells, maintaining local immune microenvironment homeostasis, and protecting mice from inflammation and colitis-associated cancer. We will further investigate IKKα expression pattern in human colon cancer tissues and the correlation between IKKα expression and disease progression, thereby determining the clinical relevance of our study. The proposed study will define the physiological function of IKKα in colon inflammation and cancer, and may provide new sights for prevention and therapeutics for inflammation-associated colitis and colon cancer.

作为控制炎症反应的关键转录因子，NF-κB在肠道炎症和大肠癌的发病机理中发挥重要作用。小鼠肠道中条件性剔除经典的NF-κB通路会破坏天然免疫的平衡，从而导致肠道炎症。然而非经典NF-κB通路在肠道炎症和炎性相关大肠癌中的功能尚未明确。IKKα作为一个IKK激酶亚基既可激活经典NF-κB通路，亦可独立激活非经典NF-κB通路，来参与调控T细胞分化，外周淋巴发育等。我们前期研究已表明在表皮细胞中IKKα可通过不依赖NF-κB的下游信号来抑制肿瘤发生。多种肿瘤中均有IKKα基因突变的报道，但IKKα在肠道表皮细胞和肠道免疫中的功能尚不明晰。我们拟利用肠道表皮细胞和小鼠的肠炎及大肠癌模型，来研究IKKα在肠道表皮细胞中对经典、非经典NF-κB通路和下游炎症因子表达的调控，以及对天然细胞的招募和肠道免疫微环境形成的影响，进而确认IKKα激酶在肠道炎症及炎症相关性肠癌发病机制中的作用。

IKKα激酶在肠道表皮细胞和肠道免疫中的功能尚不明晰。我们前期研究表明在皮肤表皮细胞中IKKα可通过不依赖NF-κB的下游信号来抑制肿瘤发生。在本项目中，我们利用肠癌和小鼠巨噬细胞模型，以及纳米递送技术来研究IKKα在肠癌表皮细胞和巨噬细胞中对下游免疫反应的调控，从机制和转化角度研究了IKKα激酶介导的下游信号通路对免疫反应以及抗肿瘤效应的调控。在本项目我们取得以下进展： .1. IKKalpha对肠癌上皮细胞和巨噬细胞中的非经典NF-kB通路和氧化还原代谢的调控：我们发现在体外培养的小鼠巨噬细胞和肠癌细胞中，敲低或敲除IKKalpha以后，p100->p52水平和免疫抑制分子IDO-1的表达并没有显著变化；因此，在上皮细胞中这些通路可能并不占主要地位；在我们与美国NCI研究小组的合作研究中，我们发现IKKalpha能够调控肺上皮细胞中过氧化物基团（ROS）的产生，从而抑制K-Ras突变诱导的肺癌发生 （PNAS，2018）；..2.利用纳米材料调节IKKalpha介导的天然免疫通路：我们在实验开始阶段尝试利用纳米材料包裹递送siRNA敲低IKKα；同时我们发现纳米材料递送免疫佐剂的效果也很好。为此我们开发了一种新的纳米材料，用来包裹天然免疫激动剂制作肿瘤疫苗，使用该纳米多聚物材料负载天然免疫受体激动剂CpG可以增强疫苗的抗肿瘤效果(Immunotherapy 2018)；..3. IKKalpha调节巨噬细胞吞噬凋亡细胞以后的免疫耐受反应：在敲除IKKalpha的巨噬细胞和树突状细胞中，我们意外的发现，IKKalpha的缺失显著抑制巨噬细胞吞噬凋亡细胞以后的免疫抑制性细胞因子如TGF-beta, IL-10的表达上调。机制研究表明，IKKalpha通过AhR受体调节这些免疫抑制性细胞因子的表达。我们目前正在巨噬细胞特异敲除的小鼠上验证这些发现。..在执行的四年间，该项目进展比较顺利，基本完成预期的各项目标。在本项目支持下，本课题组共发表学术论文6篇，申请国际专利1项，联合培养1名博士研究生。本课题的发现丰富了现有的对于IKKalpha调节固有免疫系统的机制理解，开发了基于纳米载体和天然免疫激动剂为组分的纳米疫苗，为发展新的针对自身免疫类疾病及癌症的治疗提供了潜在的新靶点和治疗手段。.