TP53 and DNA-repair gene polymorphisms genotyping as a low-cost lung adenocarcinoma screening tool.

AIM: TP53 and DNA repair polymorphisms have been proposed as cancer risk factors. This study evaluated the usability of TP53 Arg72Pro single-nucleotide polymorphism, X RCC1 Arg399Gln and RAD51 G135C as a low-cost lung adenocarcinoma screening tool. PATIENTS AND METHODS: This case-control study included 78 atients with lung adenocarcinoma and 79 healthy matched controls. TP53, XRCC1 and RAD51 genotyping was done by PCR followed by restriction length polymorphism. Descriptive analyses included genotype and allelic frequencies and deviations of the frequencies from those expected under Hardy-Weinberg equilibrium were assessed using the χ2 test. The OR and 95% CIs were calculated as an estimate of relative risk, with significance set at p value <0.05. RESULTS: The TP53 codon 72 Pro allele and the XRCC1 codon 399 Arg allele in a homozygous state were associated with lung adenocarcinoma (p=0.037; OR (95% CI) 2.42 (1.10 to 5.31)), that is, p=0.037; OR (95% CI) 2.16 (1.08 to 4.33), respectively. Also, carriers of the TP53 codon 72 Pro allele and the XRCC1 codon 399 ArgArg genotype older than 50 showed an even higher risk of developing lung adenocarcinoma (p=0.03 in both cases). CONCLUSIONS: The TP53 codon 72 Arg allele and XRCC1 codon 399 Gln allele are likely to have a protective effect against lung adenocarcinoma, especially in individuals older than 50 years of age. XRCC1 and TP53 genotyping might be a useful low-cost tool for evaluating individual lung cancer risk, leading to earlier detection and management of this disease.

Gene Expression Biodosimetry: Quantitative Assessment of Radiation Dose with Total Body Exposure of Rats.

BACKGROUND: Accurate dose assessment and correct identification of irradiated from non-irradiated people are goals of biological dosimetry in radiation accidents. OBJECTIVES: Changes in the FDXR and the RAD51 gene expression (GE) levels were here analyzed in response to total body exposure (TBE) to a 6 MV x-ray beam in rats. We determined the accuracy for absolute quantification of GE to predict the dose at 24 hours. MATERIALS AND METHODS: For this in vivo experimental study, using simple randomized sampling, peripheral blood samples were collected from a total of 20 Wistar rats at 24 hours following exposure of total body to 6 MV X-ray beam energy with doses (0.2, 0.5, 2 and 4 Gy) for TBE in Linac Varian 2100C/D (Varian, USA) in Golestan Hospital, in Ahvaz, Iran. Also, 9 rats was irradiated with a 6MV X-ray beam at doses of 1, 2, 3 Gy in 6MV energy as a validation group. A sham group was also included. After RNA extraction and DNA synthesis, GE changes were measured by the QRT-PCR technique and an absolute quantification strategy by taqman methodology in peripheral blood from rats. ROC analysis was used to distinguish irradiated from non-irradiated samples (qualitative dose assessment) at a dose of 2 Gy. RESULTS: The best fits for mean of responses were polynomial equations with a R2 of 0.98 and 0.90 (for FDXR and RAD51 dose response curves, respectively). Dose response of the FDXR gene produced a better mean dose estimation of irradiated "validation" samples compared to the RAD51 gene at doses of 1, 2 and 3 Gy. FDXR gene expression separated the irradiated rats from controls with a sensitivity, specificity and accuracy of 87.5%, 83.5% and 81.3%, respectively, 24 hours after dose of 2 Gy. These values were significantly (p<0.05) higher than the 75%, 75% and 75%, respectively, obtained using gene expression of RAD51 analysis at a dose of 2 Gy. CONCLUSIONS: Collectively, these data suggest that absolute quantification by gel purified quantitative RT-PCR can be used to measure the mRNA copies for GE biodosimetry studies at comparable accuracy to similar methods. In the case of TBE with 6MV energy, FDXR gene expression analysis is more precise than that with RAD51 for quantitative and qualitative dose assessment.

Homologous recombination restarts blocked replication forks at the expense of genome rearrangements by template exchange.

Template switching induced by stalled replication forks has recently been proposed to underlie complex genomic rearrangements. However, the resulting models are not supported by robust physical evidence. Here, we analyzed replication and recombination intermediates in a well-defined fission yeast system that blocks replication forks. We show that, in response to fork arrest, chromosomal rearrangements result from Rad52-dependent nascent strand template exchange occurring during fork restart. This template exchange occurs by both Rad51-dependent and -independent mechanisms. We demonstrate that Rqh1, the BLM homolog, limits Rad51-dependent template exchange without affecting fork restart. In contrast, we report that the Srs2 helicase promotes both fork restart and template exchange. Our data demonstrate that template exchange occurs during recombination-dependent fork restart at the expense of genome rearrangements.