High RAD51 Gene Expression is Associated with Aggressive Biology and with Poor Survival in Breast Cancer

Purpose: Although DNA repair mechanism is a key to prevent carcinogenesis, its activation in established cancer cells may support their proliferation and aggravate cancer progression. RAD51 cooperates with BRCA2 and is essential in the homologous recombination of DNA repair. To this end, we hypothesized that RAD51 gene expression is associated with cancer cell proliferation and poor prognosis of breast cancer (BC) patients.Methods: A total of 8515 primary BC patients with transcriptome and clinical data from 17 independent cohorts were analyzed. Median was used to divide each cohort into high and low RAD51 expression groups.Results: High RAD51 expression enriched DNA repair gene set and was correlated with DNA repair-related genes. Nottingham histological grade, Ki67 expression and cell proliferation-related gene sets (E2F Targets, G2M Checkpoint and Myc Targets) were all significantly associated with the high RAD51 BC. RAD51 expression was positively correlated with Homologous Recombination Deficiency, as well as both mutation burden and neoantigen that accompanied with higher infiltration of immune cells. Primary BC with lymph node metastases were associated with high expression of RAD51 in 2 cohorts. There was no strong correlation between RAD51 expression and drug sensitivity in cell lines, and RAD51 expression was lower after the neoadjuvant chemotherapy compared to before the treatment. High RAD51 BC was associated with poor prognosis consistently in 3 independent cohorts.Conclusion: RAD51 gene expression is associated with aggressive cancer biology, cancer cell proliferation, and poor survival in breast cancer.

RAD51 Gene Family Structure and Function

Accurate DNA repair and replication are critical for genomic stability and cancer prevention. RAD51 and its gene family are key regulators of DNA fidelity through diverse roles in double-strand break repair, replication stress, and meiosis. RAD51 is an ATPase that forms a nucleoprotein filament on single-stranded DNA. RAD51 has the function of finding and invading homologous DNA sequences to enable accurate and timely DNA repair. Its paralogs, which arose from ancient gene duplications of RAD51, have evolved to regulate and promote RAD51 function. Underscoring its importance, misregulation of RAD51, and its paralogs, is associated with diseases such as cancer and Fanconi anemia. In this review, we focus on the mammalian RAD51 structure and function and highlight the use of model systems to enable mechanistic understanding of RAD51 cellular roles. We also discuss how misregulation of the RAD51 gene family members contributes to disease and consider new approaches to pharmacologically inhibit RAD51.

Modification of PARP4, XRCC3, and RAD51 Gene Polymorphisms on the Relation between Bisphenol A Exposure and Liver Abnormality

Repair genes may play critical roles in the relationships between environmental exposure and health outcomes. However, no evidence is available about the effect of repair gene polymorphisms on the relationship between bisphenol A (BPA) exposure and liver abnormality. Therefore, we evaluated the effect of nine genotyped polymorphisms in three repair genes, poly(ADP-ribose) polymerase family member 4 (PARP4), X-ray repair cross complementing 3 (XRCC3), and RAD51 recombinase (RAD51), on the relationship between BPA exposure and liver abnormality using repeated measures data for an elderly population. A significant association between BPA levels and liver abnormality was found only in elders with the PARP4 G-C-G haplotype, XRCC3 G-A-G haplotype, or RAD51 T-A-A haplotype (odds ratio (OR) = 2.16 and p = 0.0014 for PARP4; OR = 1.57 and p = 0.0249 for XRCC3; OR = 1.43 and p = 0.0422 for RAD51). Particularly, PARP4 and XRCC3 showed significant interactions with BPA exposure in relation to liver abnormality (p < 0.05 for both genes). These results indicate that PARP4, XRCC3, and RAD51 gene polymorphisms have modification effects on the relationship between BPA exposure and liver abnormality.

Genetic Polymorphisms in the RAD51 Gene with a Risk of Head and Neck Cancer and Esophageal Cancer: A Meta-Analysis

Background. The role of RAD51 gene polymorphisms with the development of head and neck cancer (HNC) and esophageal cancer (EC) remains controversial. This meta-analysis was conducted to evaluate the correlation between the RAD51 polymorphisms and these two cancers quantitatively. Methods. Databases of PubMed, Web of Science, and Embase were used to search relevant papers prior to August 17, 2019. STATA 11.0 was performed to observe the correlation. Results. Ten relevant papers were enrolled in our analysis. Overall, a significant correlation was observed between the rs1801320 polymorphism and the increased risk of these two cancers (OR=1.32, 95%CI=1.03‐1.71 for C vs. G; OR=1.50, 95%CI=1.03‐2.19 for CG vs. GG; and OR=1.44, 95%CI=1.05‐1.99 for CC+CG vs. GG). In subgroup analyses, an increased risk was found for EC (OR=2.07, 95%CI=1.01‐4.25 for C vs. G; OR=2.08, 95%CI=1.17‐3.71 for CC vs. GG; and OR=1.78, 95%CI=1.00‐3.15 for CC vs. CG+GG), but not for HNC. Moreover, our analysis revealed that no statistical evidence of correlation was discovered between the polymorphism of rs1801321 and the increased risk of HNC. However, stratified analysis based on ethnicity suggested that rs1801321 polymorphism was related to the decreased risk of HNC among Caucasians (OR=0.82, 95%CI=0.72‐0.95 for T vs. G). Conclusions. rs1801320 polymorphism was strongly associated with the risk of these two associated cancers, especially with esophageal cancer. Moreover, our results revealed that rs1801321 polymorphism was correlated to the decreased risk of HNC among Caucasians.

P11.48 Dose-dependent effects of radiation exposure on the cell culture of glioblastoma G01, obtained from the patient with a long-term survival

Background: The predictors of a favorable prognosis regarding radiation exposure in patients with glioblastoma have not been studied enough, therefore, the search for factors determining a tumor response to the combined chemoradiation treatment is an actual task at present. DNA repair protein RAD51 homolog 1 (RAD51) is a crucial protein for homologous recombination and its inhibition has been shown to sensitize glioma stem cells to irradiation. Materials and Methods: G01 primary glioblastoma cell culture was obtained from tumor tissues from patient with long term survival (42 month).An irradiation with the energy of 6 MeV was carried out in 1 fraction 20,40,60,80,100,125,150,200,250 Gy with Linac. mRNA expression of the RAD51 gene, XRCC6, XRCC5 genes, relative amount of RAD51 protein and Ku70, Ku80 proteins, proliferative activity of cell culture was evaluated by RT-PCR, Western blotting, MTT-test, respectively.Results: When G01 cells were irradiated with doses from 5 to 180 Gy there was a uniform linear decrease in the population of proliferating cells compared to the control, but at a dose of 200 Gy a rise to 24% was observed. The mRNA expression of the RAD51 gene increased 2 times after irradiation at a dose of 20 Gy compared with control and then increased, reaching a peak at the level of 100,250 Gy. Minimal expression was observed after irradiation at a dose of 20 and also decreased at 200 Gy. The mRNA expression of the XRCC5 gene increased 2-fold after irradiation at a dose of 20 Gy compared with control and then decreased, remaining at the same level. Minimal expression was observed after irradiation at a dose of 200Gy. The relative amount of Ku80 protein reached a peak at a dose of 100 Gy, followed by a decrease. Maximum expression level of mRNA of the XRCC6 gene was observed after irradiation at a dose of 250Gy. The relative amount of Ku70 protein also decreased at 200 Gy and reached a peak at a dose of 250 Gy. Conclusions: After irradiation transplantable G01 cell culture from patient with long term survival a linear decrease in proliferative activity depending on the dose was observed with an decrease in mRNA expression of Rad51 gene and the relative amount of RAD51,Ku70 in dose level of 200Gy that could potentially indicate sensitivity point to radiation exposure in these cell culture. Further studies using cell cultures from patients may help in understanding the mechanisms of radioresistance and radiosensitivity in glioblastoma.The research was supported financially by RFBR (Project No. 18-29-01061).