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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies using rodent cells indicate that a deficiency in XRCC1 results in reduced single-strand break repair, increased sensitivity to DNA-damaging agents, and elevated levels of sister chromatid exchange (SCE). Epidemiological studies have suggested an association of certain human XRCC1 polymorphisms with genetic instability and cancer susceptibility. However, investigations on the molecular functions of XRCC1 in human cells are limited. To determine the contributions of this nonenzymatic scaffold protein, we suppressed XRCC1 levels in several human cell lines using small interfering RNA (siRNA) technology. We report that XRCC1 down-regulation in HeLa cells leads to a concomitant decrease in the DNA ligase 3 protein level and an impaired nick ligation capacity. In addition, depletion of XRCC1 resulted in a significantly increased sensitivity to the alkylating agent methyl methanesulfonate and the thymidine base analog 5-hydroxymethyl-2'-deoxyuridine, a slightly increased sensitivity to ethyl methanesulfonate and 1,3-bis(2-chloroethyl)-1-nitrosourea, and no change in the response to camptothecin. We also discovered that a 70-80% reduction in XRCC1 protein leads to an elevated level of SCE in both HeLa cells and normal human fibroblasts, but does not affect chromosome aberrations in the diploid fibroblasts. Last, XRCC1 siRNA transfection led to an approximately 40% decrease in the survival of BRCA2-deficient cells, supporting a model whereby the accumulation of unrepaired SSBs leads to the accumulation of cytotoxic DNA double strand breaks following replication fork collapse in cells defective in homologous recombination.
Environ Mol Mutagen 2007 Jul
PMID:XRCC1 down-regulation in human cells leads to DNA-damaging agent hypersensitivity, elevated sister chromatid exchange, and reduced survival of BRCA2 mutant cells. 1760 93

Autosomal dominant cancer predisposition genes for common cancers such as breast cancer and colorectal cancer have been well recognized for over a decade. Monoallelic mutations in these genes are associated with high risks of adult-onset cancer. In recent years, it has become apparent that biallelic mutations in some of these genes, such as BRCA2, MSH2 and MLH1, result in distinctive phenotypes, including childhood cancer predisposition. Conversely, it has also become evident that some genes which cause autosomal recessive cancer predisposition syndromes such as Fanconi anaemia and ataxia-telangiectasia are associated with modestly increased risks of adult cancers in monoallelic mutation carriers. These observations raise interesting implications with respect to the identification and phenotypic characterization of cancer predisposition genes.
Hum Mol Genet 2007 Apr 15
PMID:Cancer genes associated with phenotypes in monoallelic and biallelic mutation carriers: new lessons from old players. 1761 48

BACH1 (also known as FANCJ and BRIP1) is a DNA helicase that directly interacts with the C-terminal BRCT repeat of the breast cancer susceptibility protein BRCA1. Previous biochemical and functional analyses have suggested a role for the BACH1 homolog in Caenorhabditis elegans during DNA replication. Here, we report the association of BACH1 with a distinct BRCA1/BRCA2-containing complex during the S phase of the cell cycle. Depletion of BACH1 or BRCA1 using small interfering RNAs results in delayed entry into the S phase of the cell cycle. Such timely progression through S phase requires the helicase activity of BACH1. Importantly, cells expressing a dominant negative mutation in BACH1 that results in a defective helicase displayed increased activation of DNA damage checkpoints and genomic instability. BACH1 helicase is silenced during the G(1) phase of the cell cycle and is activated through a dephosphorylation event as cells enter S phase. These results point to a critical role for BACH1 helicase activity not only in the timely progression through the S phase but also in maintaining genomic stability.
Mol Cell Biol 2007 Oct
PMID:Activation of BRCA1/BRCA2-associated helicase BACH1 is required for timely progression through S phase. 1766 83

To assess whether DNA repair gene variants influence the clinical behaviour of lung cancer we examined the impact of a comprehensive panel of 109 non-synonymous single-nucleotide polymorphisms (nsSNPs) in 50 DNA repair genes on overall survival (OS) in 700 lung cancer patients. Fifteen nsSNPs were associated with OS, significantly greater than that expected (P = 0.04). SNPs associated with prognosis mapped primarily to two repair pathways--nucleotide excision repair (NER): ERCC5 D1104H (P = 0.004); ERCC6 G399D (P = 0.023), ERCC6 Q1413R (P = 0.025), POLE (P = 0.014) and base excision repair: APEX1 D148E (P = 0.028); EXO1 E670G (P = 0.007); POLB P242R (P = 0.018). An increasing number of variant alleles in EXO1 was associated with a poorer prognosis [hazard ratio (HR) = 1.24; P = 0.0009]. A role for variation in NER and BRCA2/FA pathway genes as determinants of OS was provided by an analysis restricted to the 456 patients treated with platinum-based agents. Our data indicate that the pathway-based approach has the potential to generate prognostic markers of clinical outcome.
Hum Mol Genet 2007 Oct 01
PMID:Genetic variation in the DNA repair genes is predictive of outcome in lung cancer. 1785 54

The contribution of BRCA1 and BRCA2 to familial and non-familial forms of breast cancer has been difficult to accurately estimate because of the myriad of potential genetic and epigenetic mechanisms that can ultimately influence their expression and involvement in cellular activities. As one of these potential mechanisms, we investigated whether allelic imbalance (AI) of BRCA1 or BRCA2 expression was associated with an increased risk of developing breast cancer. By developing a quantitative approach utilizing allele-specific real-time PCR, we first evaluated AI caused by nonsense-mediated mRNA decay in patients with frameshift mutations in BRCA1 and BRCA2. We next measured AI for BRCA1 and BRCA2 in lymphocytes from three groups: familial breast cancer patients, non-familial breast cancer patients and age-matched cancer-free females. The AI ratios of BRCA1, but not BRCA2, in the lymphocytes from familial breast cancer patients were found to be significantly increased as compared to cancer-free women (BRCA1: 0.424 versus 0.211, P = 0.00001; BRCA2: 0.206 versus 0.172, P = 0.38). Similarly, the AI ratios were greater for BRCA1 and BRCA2 in the lymphocytes of non-familial breast cancer cases versus controls (BRCA1: 0.353, P = 0.002; BRCA2: 0.267, P = 0.03). Furthermore, the distribution of under-expressed alleles between cancer-free controls and familial cases was significantly different for both BRCA1 and BRCA2 gene expression (P < 0.02 and P < 0.02, respectively). In conclusion, we have found that AI affecting BRCA1 and to a lesser extent BRCA2 may contribute to both familial and non-familial forms of breast cancer.
Hum Mol Genet 2008 May 01
PMID:Allelic imbalance in BRCA1 and BRCA2 gene expression is associated with an increased breast cancer risk. 1820 50

A single Rad52-related protein is evident by blast analysis of the Ustilago maydis genome database. Mutants created by disruption of the structural gene exhibited few discernible defects in resistance to UV, ionizing radiation, chemical alkylating or cross-linking agents. No deficiency was noted in spontaneous mutator activity, allelic recombination or meiosis. GFP-Rad51 foci were formed in rad52 cells following DNA damage, but were initially less intense than normal suggesting a possible role for Rad52 in formation of the Rad51 nucleoprotein filament. A search for interacting genes that confer a synthetic fitness phenotype with rad52 after DNA damage by UV irradiation identified the genes for Mph1, Ercc1 and the Rad51 paralogue Rec2. Testing known mutants in recombinational repair revealed an additional interaction with the BRCA2 orthologue Brh2. Suppression of the rec2 mutant's UV sensitivity by overexpressing Brh2 was found to be dependent on Rad52. The results suggest that Rad52 serves in an overlapping, compensatory role with both Rec2 and Brh2 to promote and maintain formation of the Rad51 nucleoprotein filament.
Mol Microbiol 2008 Mar
PMID:Compensatory role for Rad52 during recombinational repair in Ustilago maydis. 1820 29

Fanconi anemia (FA) predisposes to hematopoietic failure, birth defects, leukemia, and squamous cell carcinoma of the head and neck (HNSCC) and cervix. The FA/BRCA pathway includes 8 members of a core complex and 5 downstream gene products closely linked with BRCA1 or BRCA2. Precancerous lesions are believed to trigger the DNA damage response (DDR), and we focused on the DDR in FA and its putative role as a checkpoint barrier to cancer. In primary fibroblasts with mutations in the core complex FANCA protein, we discovered that basal expression and phosphorylation of ATM (ataxia telangiectasia mutated) and p53 induced by irradiation (IR) or mitomycin C (MMC) were upregulated. This heightened response appeared to be due to increased basal levels of ATM in cultured FANCA-mutant cells, highlighting the new observation that ATM can be regulated at the transcriptional level in addition to its well-established activation by autophosphorylation. Functional analysis of this response using gamma-H2AX foci as markers of DNA double-stranded breaks (DSBs) demonstrated abnormal persistence of only MMC- and not IR-induced foci. Thus, we describe a processing defect that leads to general DDR upregulation but specific persistence of DNA crosslinker-induced damage response foci. Underscoring the significance of these findings, we found resistance to DNA crosslinker-induced cell cycle arrest and apoptosis in a TP53-mutant, patient-derived HNSCC cell line, whereas a lymphoblastoid cell line derived from this same individual was not mutated at TP53 and retained DNA crosslinker sensitivity. Our results suggest that cancer in FA may arise from selection for cells that escape from a chronically activated DDR checkpoint.
Mol Med
PMID:Upregulated ATM gene expression and activated DNA crosslink-induced damage response checkpoint in Fanconi anemia: implications for carcinogenesis. 1822 51

In mammals, small multigene families generate spliceosomal U snRNAs that are nearly as abundant as rRNA. Using the tandemly repeated human U2 genes as a model, we show by footprinting with DNase I and permanganate that nearly all sequences between the enhancer-like distal sequence element and the initiation site are protected during interphase whereas the upstream half of the U2 snRNA coding region is exposed. We also show by chromatin immunoprecipitation that the SNAPc complex, which binds the TATA-like proximal sequence element, is removed at metaphase but remains bound under conditions that induce locus-specific metaphase fragility of the U2 genes, such as loss of CSB, BRCA1, or BRCA2 function, treatment with actinomycin D, or overexpression of the tetrameric p53 C terminus. We propose that the U2 snRNA promoter establishes a persistently open state to facilitate rapid reinitiation and perhaps also to bypass TFIIH-dependent promoter melting; this open state would then be disassembled to allow metaphase chromatin condensation.
Mol Cell Biol 2008 Jun
PMID:Human U2 snRNA genes exhibit a persistently open transcriptional state and promoter disassembly at metaphase. 1837 97

Antigenic variation in Trypanosoma brucei has selected for the evolution of a massive archive of silent Variant Surface Glycoprotein (VSG) genes, which are activated by recombination into specialized expression sites. Such VSG switching can occur at rates substantially higher than background mutation and is dependent on homologous recombination, a core DNA repair reaction. A key regulator of homologous recombination is BRCA2, a protein that binds RAD51, the enzyme responsible for DNA strand exchange. Here, we show that T. brucei BRCA2 has undergone a recent, striking expansion in the number of BRC repeats, a sequence element that mediates interaction with RAD51. T. brucei BRCA2 mutants are shown to be significantly impaired in antigenic variation and display genome instability. By generating BRCA2 variants with reduced BRC repeat numbers, we show that the BRC expansion is crucial in determining the efficiency of T. brucei homologous recombination and RAD51 localization. Remarkably, however, this appears not to be a major determinant of the activation of at least some VSG genes.
Mol Microbiol 2008 Jun
PMID:Trypanosoma brucei BRCA2 acts in antigenic variation and has undergone a recent expansion in BRC repeat number that is important during homologous recombination. 1843 Jan 40

Increasingly, the molecular genetics laboratory has to assess the biological significance of changes (variants) in a DNA sequence. Using the large genes BRCA1 and BRCA2 as examples, some approaches used to determine the biological significance of DNA variants are described. These include the characterization of the variant through a review of the literature and the various databases to assess if it has previously been described. Potential difficulties with the various databases that are available are described. Other considerations include the co-inheritance of the variant with other DNA changes, and its evolutionary conservation. Determining the possible effect of the variant on protein function is described in terms of the Grantham assessment as well as identifying functional domains. Studies looking at the distribution of the variant in both the population and the family can also help in assessing its significance. Loss of the variant in a tumor sample would imply that it is not deleterious. Ultimately, it is not any single parameter that helps determine the DNA variants biological significance. Usually this requires multiple lines of evidence.
Methods Mol Med 2008
PMID:Evaluating DNA sequence variants of unknown biological significance. 1845 91


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