NDRG2在结肠癌分化过程中对Skp2的转录调控机制和功能的研究

The differentiation status of colon cancer is highly correlated with the cell proliferation and metastasis capacity, which has a serious impact on the survival and prognosis of clinical patients. Thus, it is urgent to find effective differentiation-regulatory molecules for early diagnosis and targeting therapy in colon cancer. NDRG2 is a tumor-suppressor gene and firstly reported in our group. Previous study shows that NDRG2 is lower-expressed in colon cancer tissues and cells, and positively correlated with the tumor differentiation status. We recently observed that NDRG2 can induce colon cancer cell differentiation, probably through the transcriptional repression of Skp2, which is a substrate recognition factor in E3 ligase SCF complex, suggesting a tumor suppressor role of NDRG2 in colon cancer. In the current project, we are planning to start with the analysis of the correlation of NDRG2 and Skp2 expressions with the tumor differentiation status, stage and prognosis in the clinical samples. Second, we are going to uncover the specific mechanism of NDRG2 transcriptional regulating Skp2 with its functional domain. Finally, we will explore the impact of this regulation on tumor differentiation, which contribute to the biological behavior alterations of colon cancer in both proliferation and metastasis. This project is critical for the significance of both the early diagnosis and treatment of colon cancer and extending the value of NDRG2 in clinical application.

结肠癌的分化程度与其增殖、转移能力密切相关，严重影响着临床患者的生存和预后。寻找有效的分化调节分子对于结肠癌的早期诊断和靶向治疗均具有重要的意义。NDRG2是课题组首先报道的肿瘤抑制基因，前期研究结果显示，NDRG2在结肠癌组织和细胞中均呈低表达，并且与结肠癌的分化程度呈正相关。我们近期发现，NDRG2可促进结肠癌细胞分化，并可能是通过转录抑制E3泛素连接酶Skp2的表达发挥作用，提示了NDRG2发挥肿瘤抑制功能的作用方式和相关机制。本项目拟从临床样本入手分析NDRG2、Skp2等分子和结肠癌分化、分期和预后的相关性；从分子水平阐明NDRG2对Skp2调控的具体机制并初步定义其功能结构域，从细胞和动物水平探讨NDRG2调控Skp2对结肠癌分化的影响，并进一步导致肿瘤增殖和转移等生物学行为的改变。本研究对于结肠癌的早期诊断和治疗、扩展NDRG2的临床应用价值均具有重要的指导意义。

结肠癌的分化程度与其增殖、转移和患者预后密切相关。寻找有效的分化调节分子对于结肠癌的早期诊断和靶向治疗均具有重要的意义。本项目在研究中探讨了肿瘤抑制基因NDRG2在调控结肠癌分化中的重要意义，并对其相关机制进行了详细解读。我们在早期研究中发现了NDRG2在结肠癌组织和细胞中均呈低表达，并且与结肠癌的分化程度呈正相关。通过本项目的研究，我们证实了NDRG2对结肠癌细胞的分化调节依赖于泛素连接酶Skp2的活性，并取得了以下的重要发现：1.在结肠癌病人和NDRG2敲除小鼠的结肠组织中，NDRG2表达与Skp2呈显著负相关，并且与细胞的分期分级呈负相关；2. NDRG2在结肠癌细胞中转录抑制Skp2的表达，并进一步增强Skp2泛素化的靶蛋白p21和p27的表达；3. 利用shRNA干涉p21和p27表达后，NDRG2诱导细胞分化的能力显著下降，细胞增殖能力增强，说明p21和p27在介导NDRG2调控细胞分化的过程中是必需因素；4. 机制研究显示，NDRG2通过诱导AKT和GSK-3β去磷酸化的方式，抑制了β-catenin的核转位能力，并进一步阻碍了β-catenin/TCF复合体在Skp2基因启动子上的定位，抑制了Skp2的转录过程；5. 通过构建一系列的NDRG2截短突变体，我们证明了NDRG2的N端结构域是调控Skp2和细胞分化的关键区域；6. 此外，我们利用大量的结肠癌临床样本进行生存预后分析，得到NDRG2low /Skp2high的基因表达特征与患者的预后具有显著的负相关，并认为这一表达特征可用于结肠癌临床诊断及患者预后评估。