LncRNA GAS5通过结合转录因子E2F4抑制PRC2复合体促进膀胱癌细胞凋亡的机制的研究

LncRNA GAS5 is generally regarded as a tumor suppressor to induce cancer cells apoptosis. However, the underlying mechanism is not clear. Our previous study revealed that GAS5 was down-regulated in bladder cancer tissues, and its level was negatively correlated to clinical stage. GAS5 binded to transcription factor E2F4 to inhibited EZH2 transcription and thereby inducing apoptosis of bladder cancer cells . By online prediction and our analysis, we speculated that GAS5 directly targeted to E2F4 DBD to inhibit the regulation of E2F4 on transcription of the target genes. The pre-experiments showed that GAS5 was also expressed in human blood, and GAS5 inhibited SUZ12 and EED expression and SUZ12 transcriptional activity in bladder cancer cells. Meanwhile, we found there existed E2F4 binding sites in the domains of SUZ12 and EED promoters, which demonstrated that SUZ12 and EED are also target genes of E2F4. As well as EZH2, SUZ12 and EED constitute to PRC2 complex, which plays an key role in apoptosis. Hence, we surmised that GAS5 inhibited PRC2 by targeted to E2F4 to induce bladder cancer cells apoptosis. In this study, we would like to illustrate the relationship between serous GAS5 level and clinical character of bladder cancer，investigate the binding sites between GAS5 and E2F4, and analyze the regulation of GAS5 on PRC2. The completion of this study will illustrate the underlying mechanism that GAS5 induces apoptosis of bladder cancer cells, and help to find a new biomarker for bladder cancer diagnosis and a promising target for bladder cancer therapy.

GAS5促肿瘤细胞凋亡的机制不明确。申请者前期研究发现，膀胱癌组织GAS5水平与临床分期呈负性相关，GAS5通过结合转录因子E2F4抑制EZH2的转录，诱导膀胱癌细胞凋亡。通过软件预测与分析，我们推测GAS5通过直接结合E2F4的DBD抑制E2F4对靶基因的调控。本项目的预实验发现，人血清中有GAS5表达，GAS5抑制SUZ12、EED蛋白的表达与SUZ12的转录活性，SUZ12、EED启动子区均含有E2F4结合位点，这表明SUZ12与EED均为E2F4的靶基因。SUZ12、EED、EZH2是PRC2的主要组成部分，PRC2在肿瘤细胞凋亡中发挥关键性作用，与膀胱癌发生发展密切相关。本课题拟就血清中GAS5的表达与膀胱癌临床病理的关系、GAS5与E2F4的结合位点、GAS5对PRC2的调控展开研究。本项目的完成将阐明GAS5促膀胱癌细胞凋亡的机制，并为膀胱癌提供新的诊断指标与治疗靶点。

背景：LncRNA GAS5主要影响肿瘤细胞凋亡与增殖，在多种肿瘤中表现出了较强的抑癌作用，但GAS5促膀胱癌细胞凋亡的机制尚不明确。.主要研究内容：1）GAS5的表达水平与膀胱癌临床病理的关系；2）GAS5对EZH2、SUZ12、EED转录的调控作用；3）GAS5与E2F4蛋白的结合机制。.重要结果：1）GAS5表达水平在膀胱癌组织中显著下调，且肌层浸润性膀胱癌中低表达率明显高于非肌层浸润性膀胱癌；2）GAS5通过结合转录因子E2F4抑制EZH2、SUZ12、EED转录，进而抑制PRC2复合体的形成；3）GAS5可与E2F4的DBD区域直接结合。.科学意义：阐明GAS5通过结合转录因子E2F4抑制PRC2复合体形成促进膀胱癌细胞凋亡的机制，为GAS5作为膀胱癌的治疗靶点提供有力的理论支持。这对其他肿瘤也具有参考价值。