DNA Polymerase Beta and Gastric Cancer

描述(申请人提供)：胃癌是一个全球性的健康问题，肿瘤发病率和死亡率都很高。环境和遗传因素都是促进基因组不稳定和可能的胃癌发生的重要因素。基因组完整性的维持依赖于许多机制，这些机制特别允许DNA复制的保真度和受损DNA的修复。这些过程需要大量的蛋白质，包括DNA聚合酶β(POLβ)。POLβ通过其在碱基切除修复(BER)中的作用，是保护DNA氧化损伤的关键酶。到目前为止，大约30%的肿瘤表达Polβ变异蛋白，有几个肿瘤过度表达Polβ蛋白。如果POLβ基因发生缺陷，将会造成DNA损伤，导致基因组不稳定。基因组不稳定发生在两种不同的途径中，一种是在核苷酸水平上导致突变率增加，另一种是染色体不稳定导致染色体数量异常或重排。对来自不同癌细胞的PolB基因进行直接测序发现了许多突变，包括L22P胃癌相关的Pol beta变体(DRP裂解酶缺陷)。已有文献证明Polβ的DRP裂解酶活性可保护细胞免受烷化剂的细胞毒性。数据显示，L22P缺乏DRP裂解酶，DNA结合亲和力较低，这与该突变与人类癌症有关的可能性是一致的。为了进一步了解L22P在BER中的生物学后果，特别是L22P表达对DNA修复保真度和染色体稳定性的影响，我们将评估表达L22P变异体Pol？后的基因组不稳定性。这项研究的目的是确定L22P胃癌相关的POLβ变异是否诱导基因组不稳定并促进肿瘤的发生。具体地说，我们将通过突变和染色体异常研究来回答L22P如何诱导基因组不稳定。为了实现我们的目标，我们将构建L22P条件敲入转基因小鼠，并研究幽门螺杆菌感染后的自发肿瘤形成和宿主遗传易感性。该项目将有助于获得机械数据，以促进我们对宿主遗传因素和环境刺激的基本了解，从而加速胃癌的发生或发展。

DESCRIPTION (provided by applicant): Gastric cancer is a global health problem with a high rate of tumor incidence and mortality. Environmental and genetic factors are both important to promote genomic instability and possibly gastric carcinogenesis. The maintenance of genome integrity is dependent on numerous mechanisms, which notably allow fidelity of DNA replication and repair of damaged DNA. Those processes require a large number of proteins including DNA polymerase beta (Pol beta). Pol beta is a key enzyme for the protection of oxidative DNA lesions via its role in base excision repair (BER). Approximately 30% of tumors studied to date express Pol beta variant proteins, and several tumors over express Pol beta. If Pol beta becomes defective, DNA damage will be left resulting in genomic instability. Genomic instability occurs in two different pathways, one resulting in an increased mutation rate at the nucleotide level and the other corresponding to chromosomal instability leading to abnormal chromosome numbers or rearrangement. Direct sequencing of the PolB gene from different cancer cells identified a number of mutations including L22P gastric cancer associated variant of Pol beta (dRP lyase deficient). It is well documented that dRP lyase activity of Pol beta protect cells from cytotoxicity of alkylating agents. Data showing that L22P lacks dRP lyase and has less DNA-binding affinity are consistent with the possibility that this variant is linked to human cancer. In order to further our understanding of the biological consequences of L22P in BER and, in particular, the effect of L22P expression on DNA repair fidelity as well as chromosomal stability, we will assess genomic instability after expressing L22P variant of Pol ?. The goal of this study is to determine whether the L22P gastric cancer-associated Pol beta variant induces genomic instability and promotes tumorigenesis. Specifically, we will focus to answer how L22P induces genomic instability using mutagenesis and chromosomal aberration studies. To achieve our objective, we will construct L22P conditional knock-in transgenic mice and characterize spontaneous tumorigenesis as well as host genetic predisposition after Helicobacter infection. This project will help to get mechanistic data that could promote our basic understanding of the host genetic factors and environmental stimuli to accelerate initiation or progression of gastric cancer.