Oxidative stress, oxidative DNA damage and resulting mutations play a role in colorectal carcinogenesis. Impaired equilibrium between DNA damage formation, antioxidant status, and DNA repair capacity is responsible for the accumulation of genetic mutations and genomic instability. The lesion-specific DNA glycosylases, e.g., hOGG1 and MUTYH, initiate the repair of oxidative DNA damage. Hereditary syndromes (MUTYH-associated polyposis, NTHL1-associated tumor syndrome) with germline mutations causing a loss-of-function in base excision repair glycosylases, serve as straight forward evidence on the role of oxidative DNA damage and its repair. Altered or inhibited function of above glycosylases result in an accumulation of oxidative DNA damage and contribute to the adenoma-adenocarcinoma transition. Oxidative DNA damage, unless repaired, often gives rise G:C > T:A mutations in tumor suppressor genes and proto-oncogenes with subsequent occurrence of chromosomal copy-neutral loss of heterozygosity. For instance, G>T transversions in position c.34 of a KRAS gene serves as a pre-screening tool for MUTYH-associated polyposis diagnosis. Since sporadic colorectal cancer represents more complex and heterogenous disease, the situation is more complicated. In the present study we focused on the roles of base excision repair glycosylases (hOGG1, MUTYH) in colorectal cancer patients by investigating tumor and adjacent mucosa tissues. Although we found downregulation of both glycosylases and significantly lower expression of hOGG1 in tumor tissues, accompanied with G>T mutations in KRAS gene, oxidative DNA damage and its repair cannot solely explain the onset of sporadic colorectal cancer. In this respect, other factors (especially microenvironment) per se or in combination with oxidative DNA damage warrant further attention. Base excision repair characteristics determined in colorectal cancer tissues and their association with disease prognosis have been discussed as well.

• Keywords
• BER glycosylases, DNA repair, Oxidative DNA damage, colorectal cancer,
• MeSH
• DNA Glycosylases * genetics   metabolism   MeSH
• Adenomatous Polyposis Coli MeSH
• Colorectal Neoplasms * pathology   MeSH
• Humans MeSH
• Tumor Microenvironment MeSH
• DNA Repair genetics   MeSH
• Oxidative Stress genetics   MeSH
• Proto-Oncogene Proteins p21(ras) genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA Glycosylases * MeSH
• mutY adenine glycosylase MeSH Browser
• oxoguanine glycosylase 1, human MeSH Browser
• Proto-Oncogene Proteins p21(ras) MeSH

This optimized protocol (including links to instruction videos) describes a comet-based in vitro DNA repair assay that is relatively simple, versatile, and inexpensive, enabling the detection of base and nucleotide excision repair activity. Protein extracts from samples are incubated with agarose-embedded substrate nucleoids ('naked' supercoiled DNA) containing specifically induced DNA lesions (e.g., resulting from oxidation, UVC radiation or benzo[a]pyrene-diol epoxide treatment). DNA incisions produced during the incubation reaction are quantified as strand breaks after electrophoresis, reflecting the extract's incision activity. The method has been applied in cell culture model systems, human biomonitoring and clinical investigations, and animal studies, using isolated blood cells and various solid tissues. Once extracts and substrates are prepared, the assay can be completed within 2 d.

• MeSH
• Cell Line MeSH
• Comet Assay methods   MeSH
• Humans MeSH
• DNA Repair * MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

There is ample evidence for the essential involvement of DNA repair and DNA damage response in the onset of solid malignancies, including ovarian cancer. Indeed, highpenetrance germline mutations in DNA repair genes are important players in familial cancers: BRCA1, BRCA2 mutations or mismatch repair, and polymerase deficiency in colorectal, breast, and ovarian cancers. Recently, some molecular hallmarks (e.g., TP53, KRAS, BRAF, RAD51C/D or PTEN mutations) of ovarian carcinomas were identified. The manuscript overviews the role of DNA repair machinery in ovarian cancer, its risk, prognosis, and therapy outcome. We have attempted to expose molecular hallmarks of ovarian cancer with a focus on DNA repair system and scrutinized genetic, epigenetic, functional, and protein alterations in individual DNA repair pathways (homologous recombination, non-homologous end-joining, DNA mismatch repair, base- and nucleotide-excision repair, and direct repair). We suggest that lack of knowledge particularly in non-homologous end joining repair pathway and the interplay between DNA repair pathways needs to be confronted. The most important genes of the DNA repair system are emphasized and their targeting in ovarian cancer will deserve further attention. The function of those genes, as well as the functional status of the entire DNA repair pathways, should be investigated in detail in the near future.

• Keywords
• DNA repair, carcinogenesis, ovarian cancer, prognosis, therapy response,
• Publication type
• Journal Article MeSH
• Review MeSH

Oxidative stress with subsequent premutagenic oxidative DNA damage has been implicated in colorectal carcinogenesis. The repair of oxidative DNA damage is initiated by lesion-specific DNA glycosylases (hOGG1, NTH1, MUTYH). The direct evidence of the role of oxidative DNA damage and its repair is proven by hereditary syndromes (MUTYH-associated polyposis, NTHL1-associated tumor syndrome), where germline mutations cause loss-of-function in glycosylases of base excision repair, thus enabling the accumulation of oxidative DNA damage and leading to the adenoma-colorectal cancer transition. Unrepaired oxidative DNA damage often results in G:C>T:A mutations in tumor suppressor genes and proto-oncogenes and widespread occurrence of chromosomal copy-neutral loss of heterozygosity. However, the situation is more complicated in complex and heterogeneous disease, such as sporadic colorectal cancer. Here we summarized our current knowledge of the role of oxidative DNA damage and its repair on the onset, prognosis and treatment of sporadic colorectal cancer. Molecular and histological tumor heterogeneity was considered. Our study has also suggested an additional important source of oxidative DNA damage due to intestinal dysbiosis. The roles of base excision repair glycosylases (hOGG1, MUTYH) in tumor and adjacent mucosa tissues of colorectal cancer patients, particularly in the interplay with other factors (especially microenvironment), deserve further attention. Base excision repair characteristics determined in colorectal cancer tissues reflect, rather, a disease prognosis. Finally, we discuss the role of DNA repair in the treatment of colon cancer, since acquired or inherited defects in DNA repair pathways can be effectively used in therapy.

• Keywords
• DNA repair, base excision repair (BER)glycosylases, colorectal cancer, oxidative DNA damage,
• MeSH
• Cellular Microenvironment MeSH
• Molecular Targeted Therapy MeSH
• DNA Glycosylases metabolism   MeSH
• Colorectal Neoplasms etiology   metabolism   pathology   therapy   MeSH
• Humans MeSH
• Disease Susceptibility * MeSH
• Cell Transformation, Neoplastic genetics   metabolism   MeSH
• DNA Repair MeSH
• Oxidative Stress * MeSH
• DNA Damage * MeSH
• Intestinal Mucosa metabolism   microbiology   pathology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• DNA Glycosylases MeSH

Interindividual differences in DNA repair systems may play a role in modulating the individual risk of developing colorectal cancer. To better ascertain the role of DNA repair gene polymorphisms on colon and rectal cancer risk individually, we evaluated 15,419 single nucleotide polymorphisms (SNPs) within 185 DNA repair genes using GWAS data from the Colon Cancer Family Registry (CCFR) and the Genetics and Epidemiology of Colorectal Cancer Consortium (GECCO), which included 8,178 colon cancer, 2,936 rectum cancer cases and 14,659 controls. Rs1800734 (in MLH1 gene) was associated with colon cancer risk (p-value = 3.5 × 10-6 ) and rs2189517 (in RAD51B) with rectal cancer risk (p-value = 5.7 × 10-6 ). The results had statistical significance close to the Bonferroni corrected p-value of 5.8 × 10-6 . Ninety-four SNPs were significantly associated with colorectal cancer risk after Binomial Sequential Goodness of Fit (BSGoF) procedure and confirmed the relevance of DNA mismatch repair (MMR) and homologous recombination pathways for colon and rectum cancer, respectively. Defects in MMR genes are known to be crucial for familial form of colorectal cancer but our findings suggest that specific genetic variations in MLH1 are important also in the individual predisposition to sporadic colon cancer. Other SNPs associated with the risk of colon cancer (e.g., rs16906252 in MGMT) were found to affect mRNA expression levels in colon transverse and therefore working as possible cis-eQTL suggesting possible mechanisms of carcinogenesis.

• Keywords
• DNA repair, cancer susceptibility, colon cancer, genome-wide association studies, rectal cancer, single nucleotide polymorphisms,
• MeSH
• Biological Variation, Population genetics   MeSH
• DNA Modification Methylases genetics   MeSH
• DNA-Binding Proteins genetics   MeSH
• Adult MeSH
• DNA Repair Enzymes genetics   MeSH
• Genetic Predisposition to Disease * MeSH
• Risk Assessment MeSH
• Polymorphism, Single Nucleotide MeSH
• Carcinogenesis genetics   MeSH
• Colon pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• MutL Protein Homolog 1 genetics   MeSH
• Tumor Suppressor Proteins genetics   MeSH
• Rectal Neoplasms genetics   pathology   MeSH
• Colonic Neoplasms genetics   pathology   MeSH
• DNA Repair genetics   MeSH
• Registries statistics & numerical data   MeSH
• Rectum pathology   MeSH
• Aged MeSH
• Case-Control Studies MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• DNA Modification Methylases MeSH
• DNA-Binding Proteins MeSH
• DNA Repair Enzymes MeSH
• MGMT protein, human MeSH Browser
• MLH1 protein, human MeSH Browser
• MutL Protein Homolog 1 MeSH
• Tumor Suppressor Proteins MeSH
• RAD51B protein, human MeSH Browser

DNA repair processes are involved in both the onset and treatment efficacy of colorectal cancer (CRC). A change of a single nucleotide causing an amino acid substitution in the corresponding protein may alter the efficiency of DNA repair, thus modifying the CRC susceptibility and clinical outcome. We performed a candidate gene approach in order to analyze the association of non-synonymous single nucleotide polymorphisms (nsSNPs) in the genes covering the main DNA repair pathways with CRC risk and clinical outcome modifications. Our candidate polymorphisms were selected according to the foremost genomic and functional prediction databases. Sixteen nsSNPs in 12 DNA repair genes were evaluated in cohorts from the Czech Republic and Austria. Apart from the tumor-node-metastasis (TNM) stage, which occurred as the main prognostic factor in all of the performed analyses, we observed several significant associations of different nsSNPs with survival and clinical outcomes in both cohorts. However, only some of the genes (REV3L, POLQ, and NEIL3) were prominently defined as prediction factors in the classification and regression tree analysis; therefore, the study suggests their association for patient survival. In summary, we provide observational and bioinformatics evidence that even subtle alterations in specific proteins of the DNA repair pathways may contribute to CRC susceptibility and clinical outcome.

• Keywords
• DNA repair genes, colorectal cancer susceptibility, functional single nucleotide polymorphism, survival analysis,
• MeSH
• Survival Analysis MeSH
• DNA-Binding Proteins genetics   MeSH
• DNA-Directed DNA Polymerase genetics   MeSH
• DNA Polymerase theta MeSH
• Adult MeSH
• Genetic Predisposition to Disease MeSH
• Polymorphism, Single Nucleotide MeSH
• Cohort Studies MeSH
• Colorectal Neoplasms genetics   mortality   pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Neoplasm Metastasis MeSH
• N-Glycosyl Hydrolases genetics   MeSH
• Odds Ratio MeSH
• DNA Repair genetics   MeSH
• Disease-Free Survival MeSH
• Aged MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Czech Republic MeSH
• Austria MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• DNA-Directed DNA Polymerase MeSH
• N-Glycosyl Hydrolases MeSH
• NEIL3 protein, human MeSH Browser
• REV3L protein, human MeSH Browser

Genetic variations in 3' untranslated regions of target genes may affect microRNA binding, resulting in differential protein expression. microRNAs regulate DNA repair, and single-nucleotide polymorphisms in miRNA binding sites (miRSNPs) may account for interindividual differences in the DNA repair capacity. Our hypothesis is that miRSNPs in relevant DNA repair genes may ultimately affect cancer susceptibility and impact prognosis.In the present study, we analysed the association of polymorphisms in predicted microRNA target sites of double-strand breaks (DSBs) repair genes with colorectal cancer (CRC) risk and clinical outcome. Twenty-one miRSNPs in non-homologous end-joining and homologous recombination pathways were assessed in 1111 cases and 1469 controls. The variant CC genotype of rs2155209 in MRE11A was strongly associated with decreased cancer risk when compared with the other genotypes (OR 0.54, 95% CI 0.38-0.76, p = 0.0004). A reduced expression of the reporter gene was observed for the C allele of this polymorphism by in vitro assay, suggesting a more efficient interaction with potentially binding miRNAs. In colon cancer patients, the rs2155209 CC genotype was associated with shorter survival while the TT genotype of RAD52 rs11226 with longer survival when both compared with their respective more frequent genotypes (HR 1.63, 95% CI 1.06-2.51, p = 0.03 HR 0.60, 95% CI 0.41-0.89, p = 0.01, respectively).miRSNPs in DSB repair genes involved in the maintenance of genomic stability may have a role on CRC susceptibility and clinical outcome.

• Keywords
• 3′UTR polymorphisms, MRE11A, colorectal cancer risk and clinical outcomes, double-strand break repair (DSBR) genes, miRNA binding sites,
• MeSH
• 3' Untranslated Regions genetics   MeSH
• Rad52 DNA Repair and Recombination Protein genetics   MeSH
• Adult MeSH
• Genetic Predisposition to Disease MeSH
• Genotype MeSH
• MRE11 Homologue Protein genetics   MeSH
• Polymorphism, Single Nucleotide * MeSH
• Colorectal Neoplasms genetics   pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• MicroRNAs genetics   MeSH
• Survival Rate MeSH
• Young Adult MeSH
• Biomarkers, Tumor genetics   MeSH
• Follow-Up Studies MeSH
• DNA Repair genetics   MeSH
• Prognosis MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Case-Control Studies MeSH
• Binding Sites MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 3' Untranslated Regions MeSH
• Rad52 DNA Repair and Recombination Protein MeSH
• MRE11 Homologue Protein MeSH
• MicroRNAs MeSH
• MRE11 protein, human MeSH Browser
• Biomarkers, Tumor MeSH
• RAD52 protein, human MeSH Browser