HCMV病毒源性抑癌基因UL138在胃癌中下调的机制研究及干预效应

Gastric cancer (GC) represents one of the most common cancers in our country. However, the etiology and pathogenesis has not been clearly elucidated. Recently, accumulating evidences suggest that human cytomegalovirus (HCMV) may act as an important cancer-promoting virus and specifically involved in the development of some human malignancies. We previously also confirmed that gastric cancer was associated with HCMV infection and found for the first time that HCMV UL138 gene could act as a virus-origin tumor inhibitor in GC. The expression of UL138 was down-regulated both in GC tissues and GC cells. Overexpression of UL138 in human GC cells inhibited cell viability and induced apoptosis by interacting with heat shock protein 70 (HSP70). At the same time, our previous experiments further indicated that the downregulation of UL138 expression in GC cells was due mainly to the regulation of UL138 protein translation initiation mediated by internal ribosome entry site (IRES)-like sequence by specific proteins in GC cells. Based on our previous studies, in this project, we will further clarify the key molecules and their molecular mechanism which specifically inhibits UL138 protein translation initiation in GC cells by using RNA pull-down technology, bicistronic luciferase reporter system and RNA immunoprecipitation technology (RIP), Western blot and immunohistochemistry, et al. The effect of these potential molecules in UL138 expression and subsequent tumor inhibitor will be further evaluated in GC cells and animal GC tumor model. From the perspective of the pathogen and host interactions, our study will clarify the mechanisms of the specific down-regulation of HCMV-derived tumor suppressor gene UL138 in GC, which will provide a new target and strategy for the specific prevention and treatment of GC based on UL138 specific anti-tumor effect.

胃癌是我国高发的恶性肿瘤，病因和致病机制尚未阐明。研究提示人群普遍感染的人巨细胞病毒（HCMV）是一种促癌病毒，参与多种肿瘤的发生发展。我们前期也证实HCMV感染与胃癌相关，但发现UL138基因是一个病毒源性抑癌基因。它在胃癌组织与细胞均选择性低表达，上调其表达可通过与热休克蛋白70结合而特异诱导肿瘤细胞凋亡，进一步发现胃癌细胞蛋白对IRES样序列介导的蛋白起始翻译调控从而抑制UL138表达。本项目将在前期基础上，采用RNA pull-down、双顺反子荧光素酶报告系统、RNA免疫共沉淀（RIP）等技术，进一步明确胃癌细胞中特异抑制UL138蛋白起始翻译的关键分子及其调控机制，并在细胞水平及动物移植瘤模型上评价关键候选分子的干预对UL138表达及诱导的抗肿瘤效应。本研究从病原体与宿主互作角度进一步阐明UL138表达的调控机制，为基于UL138抗肿瘤效应的胃癌特异防治提供全新的策略和靶点。

从病原与宿主互作角度，利用肿瘤细胞自身携带的病毒，寻找可特异抑制肿瘤细胞增殖转移相关的病毒基因，进而采用有效方式启动或增强其抑制效应，将是防控肿瘤防控全新思路和靶点。我们前期研究发现，人巨细胞病毒（HCMV）是胃癌组织中常见感染的病毒，约40%~60%胃癌肿瘤组织存在HCMV感染，进而发现，HCMV UL138基因是一个病毒源性抑癌基因，具有抑制肿瘤生长并促进胃癌细胞凋亡的作用。本项目阐述了胃癌细胞中pUL138表达的调控机制。我们发现，含UL138的1.4kb转录本不但是HCMV感染胃癌细胞优势转录本，也是表达pUL138蛋白的主要转录本，与预期胃癌细胞内的蛋白对UL138转录本mRNA 5’-UTR中 IRES样序列介导的蛋白起始翻译调控是抑制pUL138表达的关键机制不同，同属于ULb’区UL133-138簇的pUL135通过对UL138转录本的3’UTR区域调控是胃癌细胞抑制pUL138蛋白表达主要机制。另外，我们还发现， pUL135基因是一个新的HCMV病毒源性抑癌基因，体内外实验均证明pUL135具有明显抑制胃癌细胞侵袭和转移的能力。进一步研究发现，pUL135可通过与细胞骨架调控蛋白的相互作用，阻断Actin细胞骨架的重构，从而抑制胃癌细胞的侵袭和迁移。这些结果提示，利用UL/b’区UL133-138基因簇的UL135与UL138基因对胃癌细胞抑制转移或促进肿瘤细胞凋亡的效应，是HCMV阳性胃癌患者潜在的内源性控制肿瘤的理想靶标，也是全新的抗胃癌治疗基因和靶点。