DDX家族分子DDX39在结肠癌炎症和肿瘤发生中的作用和机制研究

Molecular regulatory mechanisms of inflammation and carcinogenesis are important scientific research field in inflammatory bowel disease (IBD)-related colorectal cancer. Bowel macrophages play important roles in IBD, and the regulatory mechanisms of its activation have attracted much attention. DDX family members are important regulators in innate immune response and inflammation. For example, RIG-I (DDX58)-deficient mice can develop spontaneous colitis. However, the roles of DDX family members in the regulation of inflammation still need systemic investigation, especially for IBD-related colorectal cancer carcinogenesis. Hence, we examined the expression of DDX family members in bowel macrophages of AOM/DSS-induced colon cancer, and found that DDX39 expression in bowel macrophages was significantly inhibited. Based on this data, we constructed the conditional knockout mouse of DDX39, and generated macrophage-specific and intestinal epithelium-specific knockout mouse of DDX39. We found that AOM/DSS-induced colon cancer was significantly increased by macrophage-specific DDX39 deficiency, but not intestinal epithelium-specific DDX39 deficiency. Hence, DDX39 expression in macrophages may be important for the IBD-related colon cancer carcinogenesis. Based on these findings, we intend to investigate the roles of DDX39 in the regulation of macrophage activation, inflammation, and IBD-related colon cancer carcinogenesis, so as to suggest new regulatory mechanisms of inflammation and cancer in the colon.

炎症和肿瘤发生的分子调控机制是结肠癌尤其是炎性肠病相关结肠癌中的重大科学问题，肠道巨噬细胞的活化在炎性肠病中发挥关键作用，其活化的调控机制目前受广泛关注。DDX家族分子在天然免疫和炎症中发挥重要调控作用，如DDX58缺陷小鼠能够自发肠道炎症。然而，目前仍缺乏DDX家族分子在炎症调控中的系统研究，在结肠癌炎症和肿瘤发生中仍无报道。据此，我们在AOM/DSS小鼠结肠癌炎症和肿瘤发生模型中，系统检测了DDX家族分子的表达，发现DDX39在癌组织肠道巨噬细胞中表达显著降低。我们进而构建了DDX39条件敲除小鼠，发现DDX39全身敲除和巨噬细胞敲除的小鼠结肠癌诱导发生显著增加，而肠上皮敲除小鼠无显著变化，提示DDX39极有可能通过调控肠道巨噬细胞介导的炎症反应，进而调控结肠癌发生。据此，本研究拟探求DDX39在巨噬细胞活化及其介导的炎症和肿瘤发生中的调控机制，从炎性肠病调控角度提出结肠癌发生新机制。

巨噬细胞在结直肠癌的发生发展中发挥着重要的作用。本课题组前期研究结果提示DDX家族分子成员DDX39在小鼠结肠癌模型中巨噬细胞表达异常下调，我们进而构建了DDX39条件敲除小鼠，发现DDX39全身敲除和巨噬细胞敲除的小鼠结肠癌诱导发生显著增加，而肠上皮敲除小鼠无显著变化，提示DDX39极有可能通过调控肠道巨噬细胞介导的炎症反应，进而调控结肠癌发生。基于上述假设，我们分别从DDX39在结直肠癌中临床病理相关性和DDX39在巨噬细胞模型中的作用两个角度开展研究，并且探求巨噬细胞中DDX39的潜在调控机制。.主要的研究结论如下：.一、DDX39在结直肠癌中的临床相关性.1、结直肠癌上皮组织及间质组织中DDX39的表达量较正常、癌旁、腺瘤中的表达明显降低。.2、结直肠癌上皮及间质中DDX39蛋白的表达水平分别与肿瘤部位、分化程度、TNM分期、血清CEA、血清CA199相关。.3、结直肠癌上皮及间质中DDX39低表达组较高表达组的总生存率和无病生存率低、预后差。.二、DDX39对巨噬细胞功能状态影响.1、结直肠癌组织中DDX39表达于巨噬细胞，但不表达于M2型巨噬细胞。.2、体外巨噬细胞模型中M2型巨噬细胞中DDX39的表达低于M1型巨噬细胞。.3、干扰巨噬细胞模型中的DDX39表达，巨噬细胞向M2型巨噬细胞分化，且对肠癌细胞的增殖有促进作用。.三、巨噬细胞中DDX39的表达调控机制.1、巨噬细胞与肠癌细胞共培养模型中，DDX39在巨噬细胞中的表达水平降低，且巨噬细胞向M2型巨噬细胞方向分化。.2、肠癌细胞来源的外泌体能够被巨噬细胞吞噬。.3、肠癌细胞来源的外泌体能够降低巨噬细胞中DDX39的表达，且促进巨噬细胞向M2方向分化。.在我们的结论中，DDX39在结直肠癌组织中巨噬细胞的表达有很强的临床相关性，且体外巨噬细胞模型证明DDX39在促肿瘤巨噬细胞中的表达水平显著低于抑肿瘤巨噬细胞，并且DDX39能够影响巨噬细胞的功能状态。此外巨噬细胞中DDX39的表达受到肠癌来源外泌体的影响，并且可能是肠癌来源外泌体对巨噬细胞功能的调控靶点。因此，DDX39对巨噬细胞功能的调控机制及其在外泌体调控通路中的作用有进一步深入研究的价值。