转录因子EHF在胃癌发生及发展中的作用

Gastric cancer is one of the most common cancer in the world and the mortality of gastric cancer is the second leading cause for cancer-related death.It is often not detected until it is at an advanced stage, consequently, the 5-year survival rate is very poor (10%-20%). Epidemiological evidences indicate that environmental factors play a key role in human carcinogenesis. Among the environmental factors, diet and H. pylori infection are the most common suspects in gastric tumorigenesis. In addition to environmental factors, like other human cancers, initiation and progression of gastric cancer involves multiple genetic and epigenetic alterations. These molecular events lead to gain-of-function in oncogenes and loss-of-function in tumor suppressor genes, ultimately contributing to gastric carcinogenesis. ETS factors represent one of the largest families of transcriptional regulators and play an important role in angiogenesis,organogenesis and embryogenesis. The previous studies have demonstrated that several ETS genes are aberrantly expressed in human cancers and contribute to human carcinogenesis. However, the molecular mechanisms remain poorly understood, particularly in gastric cancer. Strikingly, our preliminary data showed that transcription factor EHF, a mumber of ETS family, was overexpressed in primary gastric tumors as compared with normal gastric tissues. Moreover, this gene was frequently amplified in gastric cancer. More importantly, EHF amplification was significantly associated with poor survival of gastric cancer patients. Knock-down of EHF in gastric cancer cells remarkably inhibited cell proliferation, colony formation, and induced cell cycle arrest and apoptosis, suggesting that EHF may be a novel oncogene in gastric cancer. The aim of this project was to further clarify the biological role and molecular mechanisms of transcription factor EHF in the initiation and progression of gastric cancer, and identify its downstream target genes using ChIP-Seq and gene expression microarray approaches.

胃癌是常见的恶性肿瘤之一，其死亡率居癌症相关死亡的第二位。由于早期胃癌不易发现，其五年生存率仅为10%-20%。其发生除与饮食、H. pylori感染等有关外，也涉及诸多的遗传与表观遗传学改变，这些事件最终导致癌基因的过度激活和抑癌基因的表达下调甚至失活。ETS基因编码一类重要的转录因子，在血管生成、胚胎形成及组织器官的发育中发挥重要的调节作用。研究显示一些ETS基因参与了恶性肿瘤的发生及发展，但具体的分子机制仍不明确。我们的前期结果发现ETS家族成员EHF在胃癌组织中高表达并发生高频率的基因扩增，且该基因的异常扩增与胃癌患者的不良预后显著相关。此外，沉默胃癌细胞中的EHF基因能显著抑制肿瘤细胞增殖、克隆形成，并诱导细胞发生周期阻滞及凋亡，提示EHF可能是一个新的胃癌促进因子。本项目在此基础上，进一步明确转录因子EHF的生物学功能，并鉴定其基因调控网络，阐明其参与胃癌发生及发展的分子机制。

胃癌是常见的恶性肿瘤之一，其死亡率居癌症相关死亡的第二位。由于早期胃癌不易发现，其五年生存率仅为10%-20%。其发生除与饮食、H. pylori感染等有关外，也涉及诸多的遗传与表观遗传学改变，这些事件最终导致癌基因的过度激活和抑癌基因的表达下调甚至失活。ETS基因编码一类重要的转录因子，在血管生成、胚胎形成及组织器官的发育中发挥重要的调节作用。研究显示一些ETS基因参与了恶性肿瘤的发生及发展，但具体的分子机制仍不明确。我们的前期结果发现ETS家族成员EHF在胃癌组织中高表达并发生高频率的基因扩增，且该基因的异常扩增与胃癌患者的不良预后显著相关。此外，沉默胃癌细胞中的EHF基因能显著抑制肿瘤细胞增殖、克隆形成及裸鼠成瘤能力，并诱导细胞发生周期阻滞及凋亡，提示EHF可能是一个新的胃癌促进因子。本项目在此基础上，进一步明确转录因子EHF的生物学功能，并鉴定其基因调控网络，阐明其参与胃癌发生及发展的分子机制。结果显示，转录辅激活因子AIB1与 EHF在胃癌组织的表达具有显著相关性，敲减AIB1后EHF表达显著下调，提示AIB1可能作为EHF的辅激活因子参与其表达调控。EHF表达下调后上皮标志物E-cadherin 表达上调，间质标志物Vimentin表达下调，从而参与调控胃癌细胞的EMT进程；敲减胃癌细胞系EHF后MMP-2、MMP-7、MMP-9、MMP-14的表达显著下调。另外，Western Blot结果也显示EHF表达下调后可抑制 PI3K/Akt 及MAPK 信号通路的活性。EHF与HER家族基因在胃癌组织中的表达呈正相关，于胃癌细胞系敲减EHF后HER2、HER3及HER4的表达显著下调；本项目利用双荧光素酶报告基因、ChIP及EMSA结果证明EHF可通过直接转录激活HER2以及间接激活HER3和HER4参与胃癌的发生与发展。