GCN5乙酰化转录因子ATF3调控胃癌细胞表达抑癌基因p16的机制研究

Gastric cancer is one of the most common malignancies clinically, of which the morbidity and mortality are ranked number one in the digestive tract malignant tumors in our country. Although many studies have detected the functional defect of tumor suppressor gene 16 in gastric cancer tissues, several studies of others and us in recent years found that p16 was upregulated in most gastric cancer tissues, and mainly distributed in the cytoplasm, and was correlated with the tumor clinicopathological features. In addition, the transcription factor ATF3 and transcription cofactor GCN5 which has acetyltransferase activity were also upregulated in gastric cancer cells. Considering that the molecular basis and clinical significance of p16 up-expression, subcellular localization and function were poorly understood, and the relationship among p16, ATF3 and GCN5 also remains unclear, our study, firstly, prepares to explore the influence of subcellular localization of p16 on tumor clinicopathological features and patients’ survival time. Thereafter, starting from the role of transcription factors and their posttranscriptional modification, we will research the roles of ATF3 and the effects of ATF3 acetylation mediated by GCN5 on its own transcriptional activity, as well as the regulation function and molecular mechanism by which acetylated ATF3 regulates p16 expression. The purpose of this study is to provide useful theoretical and experimental basis for future clinical pathological diagnosis and prognosis assessment.

胃癌是临床上常见的恶性肿瘤之一，其发病率和死亡率居我国消化道恶性肿瘤首位。尽管许多研究发现，胃癌组织中能检出抑癌基因p16功能的缺失，但近年来他人和我们研究均发现，p16在多数胃癌组织中高表达，且主要分布于胞浆，并与肿瘤的临床病理学特征相关。此外，胃癌细胞中转录因子ATF3和具有乙酰基转移酶活性的转录辅因子GCN5也呈高表达。鉴于p16在肿瘤中高表达、亚细胞定位和行使功能的分子基础和临床意义知之甚少，且p16、ATF3和GCN5三者之间关系尚不明了，故本研究拟先探讨p16的亚细胞定位对肿瘤临床病理学特征和患者生存期的影响，然后再从转录因子的作用及其翻译后修饰着手，研究ATF3的作用以及其被GCN5乙酰化修饰后对本身转录活性的影响和对p16基因表达的调控作用与分子机制，其目的在于为今后临床病理诊断和预后评估提供有用的理论和实验依据。

胃癌是临床上常见的恶性肿瘤之一，其发病率和死亡率居我国消化道恶性肿瘤首位。一些研究指出胃癌组织中抑癌基因p16功能存在缺失，但近年来发现p16在多数胃癌组织中高表达，且主要分布于胞浆。此外，胃癌细胞中转录因子ATF3和具有乙酰基转移酶活性的转录辅因子GCN5也呈高表达。为了探究p16在肿瘤中高表达、亚细胞定位和行使功能的分子基础和临床意义以及p16、ATF3和GCN5三者之间关系，本研究先观察了p16表达及亚细胞定位对胃癌临床病理学特征和患者生存期的影响，再从转录因子的作用及其翻译后修饰着手，研究GCN5和ATF3乙酰化状态对p16基因表达的调控作用与分子机制，并观察了p16、ATF3和GCN5对胃癌细胞生物学行为的影响。对胃癌组织标本的研究发现p16在正常胃粘膜中低表达，多数肿瘤组织中有不同程度p16的表达，且多定位于胞浆而非胞核。p16胞浆和胞核阳性更多地分布于Lauren肠型和混合型以及HER-2蛋白过表达的病例，p16胞核阳性肿瘤浸润深度更浅，更不易出现淋巴结的转移。而p16出现阳性表达比起完全阴性的患者不容易出现远处转移。生存分析显示p16胞浆和胞核的高表达预后更好。此外，转录因子ATF3和GCN5在胃癌中也有高表达。体外实验表明p16、ATF3和GCN5在胃癌细胞株中有不同程度的表达，且p16定位于胞浆内。ATF3转录调节p16的表达，且p16启动子上ATF3的结合位点被首次鉴定。乙酰化修饰可以促进ATF3对p16的转录活性，发挥抑制肿瘤细胞增殖和迁移、促进凋亡的作用，而GCN5通过未知的途径负向调节ATF3和p16的表达，发挥促进肿瘤增殖和迁移、抑制凋亡的效应。该课题揭示了虽然核蛋白p16在胃癌组织中出现分布异常，但其高表达（尤其是胞核高表达）仍然是预后良好的指征。ATF3经乙酰化修饰调节自身的转录活性从而正向调控p16的转录表达，发挥抗肿瘤作用。GCN5负向调节ATF3和p16发挥促肿瘤效应。上述研究结果为今后临床预后评估及药物研发提供有用的理论和实验依据。