Asp312Asn Polymorphisms Research Articles

Association of the DNA repair gene XPD Asp312Asn polymorphism with p53 gene mutations in tobacco-related non-small cell lung cancer

Lung cancer, a disease related mostly to tobacco smoke exposure and a leading cause of cancer-related death in industrialized countries, is frequently associated with mutations in the p53 tumor suppressor gene. Genetic differences resulting in inter-individual variation in DNA repair capacity may in part account for susceptibility of a cell to genotoxic agents leading to somatic mutations, including p53 mutations, and eventual transformation of a normal cell into a malignant phenotype. The objective of this study is to investigate the relationship between the polymorphisms of two DNA repair genes, the nucleotide excision repair xeroderma pigmentosum group D (XPD) gene (codons 312 and 751) and the base excision repair X-ray repair cross-complementing group 1 (XRCC1) gene (codon 399), and p53 mutations among lung cancer patients. Lung tumors from 204 smokers with non-small cell lung cancer (NSCLC) were analyzed for mutations in exons 5-8 of the p53 gene and genotypes of XPD and XRCC1. p53 mutations were found in 20% (40/204) of the patients. Patients with the XPD codon 312 Asn allele were less likely to have p53 mutations (13.8%) than XPD 312 Asp/Asp (27.3%) [odds ratio (OR) 0.43, 95% confidence interval (CI) 0.20-0.89, P = 0.023]. No association was found between p53 mutations and either XPD Lys751Gln or XRCC1 Arg399Gln. However, the p53 mutation frequency increased with the increased number of the combined genotypes among XPD 312WT (Asp/Asp), XPD 751VT (Lys/Gln or Gln/Gln) or XRCC1 399VT (Arg/Gln or Gln/Gln) (P = 0.01, trend test). These results suggest that individuals who smoke and have the XPD codon 312 Asp/Asp genotype may be at a greater risk of p53 mutations, especially if combined with other polymorphisms that may result in deficient DNA repair.

Sequence variations in the DNA repair gene XPD and risk of lung cancer in a Chinese population.

Variation in DNA repair capacity, which is believed to be largely determined by genetic traits, is linked to risk of certain cancers. The Asp312Asn and Lys751Gln polymorphisms in the xeroderma pigmentosum complementary group D (XPD) gene may alter DNA repair capacity. We thus examined the hypothesis that these 2 XPD polymorphisms are associated with risk of lung cancer via a large hospital-based, case-control study among Chinese. The study subjects consisted of 1,006 patients with primary lung cancer and 1,020 age- and sex-matched population controls. XPD genotypes were determined using PCR-RFLP techniques, and the associations between genotypes and risk of lung cancer were estimated by odds ratios (ORs) and their 95% confidence intervals (CIs) calculated by unconditional logistic regression. Subjects homozygous for the 312Asn/Asn genotype had an increased risk of lung cancer (adjusted OR = 10.33, 95% CI = 1.29-82.50) compared with subjects homozygous for the 312Asp/Asp genotype. The 751Gln/Gln genotype was also associated with increased risk for the cancer compared with the 751Lys/Lys genotype (adjusted OR = 2.71, 95% CI = 1.01-7.24). Stratification analysis revealed that the increased risk was mainly confined to lung squamous cell carcinoma, with the ORs being 20.50 (95% CI = 2.25-179.05) for the 312Asn/Asn genotype and 4.24 (95% CI = 1.34-13.38) for the 751Gln/Gln genotype, respectively. Haplotype analysis with the 2 polymorphisms suggested these polymorphisms might be in linkage disequilibrium with a different causative locus or act together with other functional variants in or close to the XPD locus.

Simultaneous detection of the exon 10 polymorphism and a novel intronic single base insertion polymorphism in the XPD gene using single strand conformation polymorphism.

We developed a new method based on the single strand conformation polymorphism (SSCP) technique for the detection of a G23591A (Asp312Asn) polymorphism in exon 10 of the XPD gene. In the process we also identified a novel polymorphism 23623C-ins (IVS10+17C-ins) in intron 10 of the same gene. With this newly developed SSCP-based method of genotyping we could detect both polymorphisms in the same assay and thus consequently determine the haplotype. In order to determine the population frequency of the novel polymorphism and the haplotype frequency, 302 healthy individuals were genotyped. The allelic frequency of the 23623C-ins intronic polymorphism was 0.16, whereas the frequency of the variant allele for the G23591A polymorphism was 0.39. Forty-three individuals (14%) were heterozygous for both polymorphisms but none carried polymorphic variants for both G23591A and 23623C-ins on the same allele. The effect of the novel intronic insertion polymorphism, which is located 16 nt downstream of the 3'-end of exon 10 of the XPD gene and involves a mononucleotide C repeat sequence, on expression remains to be determined.

Influence of common XPD and XRCC1 variant alleles on p53 mutations in lung tumors.

The DNA repair proteins XPD and XRCC1 are involved in the nucleotide and base excision repair of DNA lesions induced by many tobacco and environmental carcinogens. Common variant alleles at the XPD (312Asn, 751Gln) and XRCC1 (399Gln) loci have been identified and associated with increased risk for lung cancer. We therefore investigated a possible effect of these variant alleles on the frequency and spectrum of p53 mutations in the tumors of 97 Swedish lung cancer patients (56 never-smokers and 41 age-, gender-, and hospital-matched ever-smokers). The p53 gene was mutated in 4 never-smokers (7%) and 11 ever-smokers (27%). Smoking-related transversion-type mutations predominated over transitions among smokers (8:3), but not among never-smokers (1:3). None of the variant alleles altered the overall frequency of p53 mutation. Transversions, however, were marginally increased among patients with at least one XPD variant allele compared with patients who were wild-type homozygotes (73% vs. 25% for the Asp312Asn polymorphism, P = 0.095; 78% vs. 33% for Lys751Gln, P = 0.085). Five of six women or six of seven smokers who carried at least one XPD 751Gln allele had p53 transversion. The XRCC1 variant allele did not show any effect on the p53 mutation. We conclude that the XPD variant alleles may be associated with an increased frequency of smoking-related p53 mutations in lung tumors, presumably due to reduced DNA repair proficiency.

Polymorphisms of the DNA repair gene XPD and risk of lung cancer in a Chinese population

Previous studies suggested that suboptimal DNA repair capacity is associated with cancer risk and that the Asp312Asn and Lys751Gln polymorphisms in the xeroderma pigmentosum complementary group D ( XPD) gene may influence DNA repair capacity. We therefore tested the hypothesis that these two XPD polymorphisms are associated with susceptibility to lung cancer in a hospital-based, case–control study in a Chinese population. Genotypes were determined by polymerase chain reaction-based restriction fragment length polymorphism methods in 383 healthy controls and 351 patients with lung cancer. We found that those who carried at least one 312Asn variant allele had an increased risk of squamous cell carcinoma (SCC) of the lung compared with those with the 312Asp/Asp genotype (adjusted odds ratio (OR), 1.80; 95% confidence interval (CI), 1.10–2.96). Compared with those having the 751Lys/Lys genotype, subjects carrying at least one variant 751 Gln allele were at a borderline increased risk of SCC of the lung (adjusted OR, 1.52; 95% CI, 0.94–2.46). Furthermore, stratified analysis suggested a multiplicative interaction between tobacco smoking and the Asp312Asn polymorphism on risk of SCC of the lung. The adjusted ORs of SCC of the lung for the variant XPD 312Asn genotype alone, for smoking ⩾29 pack-years alone, and for both the factors combined were 1.04 (95% CI, 0.37–2.94), 4.74 (95% CI, 2.88–9.49), and 14.32 (95% CI, 5.80–35.2), respectively. Similar results were evident for the Lys751Gln polymorphism that was in the linkage disequilibrium with the variant 312Asn allele. These data suggest that the two polymorphisms in the XPD gene may influence risk of smoking-related SCC of the lung.

Polymorphisms of DNA repair genes XRCC1 and XPD and their associations with risk of esophageal squamous cell carcinoma in a Chinese population.

Esophageal squamous cell carcinoma (ESCC), which is prevalent in China, is believed to be induced by environmental carcinogens. Accumulating evidence has shown that individual variation in DNA repair capacity resulting from genetic polymorphism influences risk of environmental carcinogenesis. We therefore investigated the associations between genetic polymorphisms in the DNA repair genes XRCC1 (Arg194Trp and Arg399Gln) and XPD (Asp312Asn and Lys751Gln) and risk of ESCC in an at-risk Chinese population. Genotypes were determined by a PCR-based approach in 433 patients with ESCC and 524 frequency-matched normal controls. We found that individuals with Trp/Trp genotype at XRCC1 Arg194Trp site had a 2-fold increased risk of this disease compared to Arg/Arg genotype (adjusted OR = 1.98; 95% CI 1.26-3.12). Furthermore, when compared to Arg/Arg and Arg/Trp genotype combined, homozygote for Trp/Trp genotype significantly increased the risk of developing ESCC, with the adjusted OR being 2.07 (95% CI 1.34-3.20). However, the XRCC1 Arg399Gln polymorphism was not significantly associated with risk of ESCC, with the adjusted OR being 0.87 (95% CI 0.55-1.37). Neither Asp312Asn nor Lys751Gln polymorphisms in the XPD gene influenced risk of ESCC in our study. These findings suggest that DNA repair gene XRCC1 but not XPD might play a role in esophageal carcinogenesis and might represent a genetic determinant in the development of the cancer.