Akt/FoxO3a转录调控SIRT6的分子机制及其在结直肠癌中的功能研究

Oncogenic Akt family is one of the most important regulatory factors for tumor cell malignant phenotype. In our previous study, we found that inhibition Akt activity obviously activated the transcriptional factor FoxO3a, leading colon cancer cell apoptosis. However, the role of FoxO3a and its downstream during cancer cell apoptosis is unclear. Using gene expression profile chip combined with biological information analysis techniques, we identified sirt6 as a new direct downstream gene of FoxO3a in colon cancer cell. Furthermore, knocking down SIRT6 inhibited cell apoptosis and desensitized colon cell to antitumor drug. SIRT6 acetylates downstream factor to regulate its transcription regulation. On this basis, this project will focus on (1) further investigating the regulatory mechanism of SIRT6 by Akt/FoxO3a; (2) exploring how SIRT6 regulates downstream signal transcription to promote colon cancer cell apoptosis; (3) further confirming the essential role of Akt/FoxO3 on SIRT6 transcription in colon cancer by using xenograft mouse model; (4) analyzing the correlation of development, metastasis and prognosis of colon cancer with expression of SIRT6 and FoxO3a transcriptional activity using clinical specimen from colon cancer patients. This study is of great significance for clarifying the transcriptional mechanism of SIRT6 by FoxO3a and revealing the role of SIRT6 in tumorigenesis.

Akt家族是肿瘤恶性表型的重要调节子。我们前期研究发现，靶向抑制Akt活性显著激活转录因子FoxO3a并诱导结直肠癌细胞凋亡，但此过程中FoxO3a功能及下游机制不清楚。以结直肠癌细胞为模型，利用全基因表达谱芯片结合生物信息技术，我们初步鉴定出一个新的FoxO3a直接下游靶基因sirt6。并发现，干扰SIRT6表达降低癌细胞凋亡及药物抗肿瘤效果。SIRT6通过去乙酰化调控下游转录。以此为基础，本项目（1）进一步研究Akt/FoxO3a转录调控SIRT6的分子机制；（2）探讨SIRT6调控下游信号转录及诱导细胞凋亡的机制；（3）以异种移植裸鼠模型验证Akt/FoxO3a对SIRT6转录在结直肠癌中的功能；（4）利用结直肠癌病人标本分析FoxO3a转录活性、SIRT6表达与结直肠癌发生发展及预后相关性。这对阐明FoxO3a对SIRT6的转录调控机制，及SIRT6在肿瘤细胞中的功能具有重要意义。

SIRT6的表达与肿瘤的发生发展密切相关,且在多种肿瘤中起着关键的调节作用。本项目在课题组前期工作的基础上，以结直肠癌为模型，提出并验证Akt对SIRT6调控机制及其在细胞凋亡中的功能。结合分子影像活细胞成像技术与细胞生物学基础研究，建立小分子 PI3K/Akt抑制剂→Akt活性降低→FoxO3a去磷酸化激活→SIRT6转录上调→去乙酰化抑制Survivin转录→细胞凋亡的新联系。主要利用各种结直肠癌细胞系，异种移植小鼠模型，结直肠癌病人临床标本，在体内外多层面进行验证。从原创性的角度研究了FoxO3a对SIRT6的转录调控，并阐明其详细的作用机制。首次提出SIRT6通过下调促存活蛋白survivin诱导结直肠癌细胞凋亡。此外，我们还发现SIRT6在自噬及免疫中的新功能。这将为寻找基于靶向Akt/SIRT6的药物提供潜在的实验依据。