转录因子FOXF2在胃癌中的功能研究及其作为胃癌分子诊断标志物的应用价值

Gastric cancer (GC) is the fifth most common overall cause of cancer death worldwide. In addition of clear defined genes and pathways important in the initiation and progression of GC, genome wide DNA methylation analyses has led to the identification of new GC subgroups and novel tumor suppressor genes. However, the functional consequence and clinical application of the tumor suppressor genes silenced by aberrant promoter CpG islands hypermethylation has not yet been fully explored. ..We recently identified that forkhead box F2 (FOXF2), encoding a 46 kDa protein with strong expression in gastrointestinal tract, was identified to be preferentially methylated in GC by genome-wide promoter CpG island screening. TCGA clinical data supports a negative association between FOXF2 promoter methylation and mRNA expression. Our preliminary data indicated that FOXF2 were significantly decreased in GC and gastric cancer cell lines compared with adjacent normal tissue through promoter CpG island methylation. Restoration of FOXF2 suppressed cancer cell viability, arrested G1 phase cell cycle, and induced apoptosis in vitro. Furthermore, we found that overexpression of FOXF2 into GC cells negatively regulated WNT signaling pathway using luciferase reporter assay and WNT pathway PCR array. We therefore hypothesize that FOXF2 may exert tumor suppressive property through direct regulated key player of WNT pathway and correlate with poor GC clinical outcomes. ..In a series of studies using cellular and animal models, we aim to identity FOXF2 function by overexpression / knockdown experiments. We will also investigate core mechanism of FOXF2 in suppressive of GC growth, and identify the bona fide targets of FOXF2 by chromatin immunoprecipitation (ChIP). Finally we will evaluate FOXF2 expression level in patients with gastric cancer and its clinical implication by mean of immunohistochemistry and promoter DNA methylation detection. ..The expected findings of these studies will provide new molecular insight into the mechanism of FOXF2 tumor suppressive effect on GC, which may provide a novel target for therapeutic intervention. Furthermore, our study may clarify the clinical potential of FOXF2 as a prognostic biomarker for GC.

胃癌是我国常见的肿瘤。异常的DNA甲基化是胃癌发生发展的一个重要标志。我们利用DNA甲基化芯片及基因表达芯片发现转录因子FOXF2在胃癌中由于高度甲基化而表现出转录抑制。FOXF2在胃癌发生发展过程中的分子机制、及其在临床胃癌标本中的表达水平、应用价值尚不清楚。我们的前期研究显示FOXF2在胃癌细胞中可以抑制WNT信号通路，具备抑癌基因的特性。本课题拟在已有实验基础上进行如下研究：1）在胃癌细胞中过表达或沉默FOXF2，观察对肿瘤恶性表型及对裸鼠皮下成瘤性的影响，从而揭示其功能； 2）寻找FOXF2的直接下游WNT通路靶基因，利用染色质免疫共沉淀和FOXF2突变体等方法证实FOXF2和可能靶基因的关系，从而揭示FOXF2调节WNT信号通路的分子机制；3）探讨FOXF2在胃癌中的的表达，分析胃癌临床标本中FOXF2启动子甲基化，及其表达水平与胃癌临床参数的相关性。

胃癌是我国常见的肿瘤。异常的DNA甲基化是胃癌发生发展的一个重要标志。我们利用DNA甲基化芯片及基因表达芯片发现转录因子FOXF2在胃癌中因启动子高甲基化而出现转录抑制。在胃癌细胞中过表达FOXF2可显著抑制细胞增殖和克隆集落形成能力、诱导G1-S期细胞周期阻滞、引发凋亡。过表达FOXF2可显著减缓免疫缺陷裸鼠(BALB/c)皮下瘤的生长。敲低FOXF2可引发相反的生物学效果。在分子机制的研究方面，我们发现FOXF2引起β-catenin蛋白泛素化降解，该过程不依赖于GSK-3β蛋白。FOXF2作为转录因子通过上调E3连接酶IRF2BPL的转录表达，从而引发β-catenin蛋白降解。FOXF2启动子高甲基化是胃患者总体生存率的独立风险因子。