DNA Polymerase Beta and Gastric Cancer

描述（由申请人提供）：胃癌是一个全球性的健康问题，肿瘤发病率和死亡率很高。环境和遗传因素对促进基因组不稳定性和可能的胃癌发生都很重要。基因组完整性的维持依赖于许多机制，特别是允许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（Pol β）。Pol β是通过其在碱基切除修复（BER）中的作用来保护氧化DNA损伤的关键酶。迄今为止研究的约30%的肿瘤表达Pol β变体蛋白，并且几种肿瘤过度表达Pol β。如果Pol beta有缺陷，DNA损伤将导致基因组不稳定。基因组不稳定性发生在两种不同的途径中，一种导致核苷酸水平突变率增加，另一种对应于染色体不稳定，导致染色体数量异常或重排。来自不同癌细胞的PolB基因的直接测序鉴定了许多突变，包括L22P胃癌相关的Pol β变体（dRP裂解酶缺陷）。据充分记载，Pol β的dRP裂解酶活性保护细胞免受烷化剂的细胞毒性。显示L22P缺乏dRP裂解酶并且具有较低的DNA结合亲和力的数据与该变体与人类癌症相关的可能性一致。为了进一步了解L22 P在BER中的生物学后果，特别是L22 P表达对DNA修复保真度以及染色体稳定性的影响，我们将评估表达Pol？的L22 P变体后的基因组不稳定性。本研究的目的是确定L22P胃癌相关Pol β变体是否诱导基因组不稳定性并促进肿瘤发生。具体而言，我们将集中回答如何L22 P诱导基因组不稳定性使用诱变和染色体畸变的研究。为了实现我们的目标，我们将构建L22P条件性基因敲入转基因小鼠，并表征自发性肿瘤发生以及螺杆菌感染后的宿主遗传易感性。本项目将有助于获得机制数据，可以促进我们对宿主遗传因素和环境刺激加速胃癌发生或发展的基本认识。

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.