Background: DNA polymerase β is one of the key enzymes for DNA repair and it was reported that about 30 percent of different types of cancers carried mutations in its coding gene Polb. However, it is still controversial whether it is true or false because of the small sample size in these studies. In current study, we performed genetic screening of promoter and coding regions of Polb gene in 69 Chinese lung cancer patients using Sanger sequencing method, so as to elucidate real mutation frequency of Polb mutations in Chinese Han population.
Methods: Salting out extraction method was used to get the genome DNAs from tumor and normal matched tissues of 69 lung cancer patients. The promoter and 14 coding regions of Polb gene were then amplified using these DNAs as the template. After purification, amplicons were sequenced and aligned to the wild type Polb gene in NCBI database, in order to find out the mutated sites of Polb gene in Chinese lung cancer patients.
Results: In this study, we totally found only 5 mutated sites in Polb gene. In detail, 3 mutations (-196G>T, -188_-187insCGCCC, -168C>A) were located in the promoter region; 2 mutations (587C>G, 612A>T) were found in coding regions. Specially, mutations of -188_-187insCGCCC and 587C>G (resulting to the amino acid substitution of Thr to Ser at position 196) had never been reported by other groups before. However, all these 5 mutated sites could be detected in both tumor and matched normal tissues, which inferred that they are not lung tumor specific mutations.
Conclusions: No lung tumor specific mutations of Polb gene could be found in Chinese lung cancer patients and Polb gene mutation might not be a molecular marker for Chinese lung cancer patients.
【中文题目：肺癌组织中DNA聚合酶β基因突变的研究】 【中文摘要：背景与目的 DNA聚合酶β是参与DNA损伤修复的关键酶之一，国外有学者认为其编码基因Polb在30%的肿瘤中存在遗传突变，但受到所用标本量的限制，这一结论是否准确尚无定论。本研究基于基因测序技术，通过对69例肺癌患者组织标本的基因筛查，旨在明确DNA聚合酶β的基因突变在中国汉族人群肺癌患者中的发生频率。方法 利用盐析法提取69例肺癌患者的癌及癌旁组织基因组DNA，并用于扩增Polb基因全部14个外显子区及启动子区。通过与NCBI数据库中野生型基因序列进行比对，系统分析肺癌组织中的Polb基因突变及其频率。结果 相对于野生型，本研究共发现5种突变类型，其中3种（-196G>T, -188_-187insCGCCC, -168C>A）位于启动子区，2种（587C>G, 612A>T）位于外显子区，突变类型-188_-187insCGCCC和587C>G尚未见文献报道，后者可引起第196位氨基酸由苏氨酸突变为丝氨酸。另一方面，癌和癌旁组中均可检测到所有5种突变类型，提示这些突变并非肺癌组织所特有。结论 肺癌组织中未发现特异性表达的Polb基因突变位点，Polb基因突变可能不是中国汉族肺癌患者的肿瘤标志物。 】 【中文关键词：DNA聚合酶β；肺肿瘤；PCR扩增；突变分析】.
Keywords: DNA polymerase β; Lung neoplasms; Mutation analysis; PCR amplification.