Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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The RAD51 gene is a homologue of Escherichia coli recA which plays a central role in homologous recombination and DNA repair. This paper describes the identification of the RAD51 gene from the trypanosomatid parasite Leishmania major. The LmRAD51 gene codes for a 377 amino acid polypeptide with a predicted molecular mass of 41259 Da that is highly homologous to the Rad51 family of proteins. Recombinant L. major Rad51 protein (LmRad51) was over-expressed in a bacterial expression system, purified to homogeneity and shown to bind DNA and exhibit DNA-stimulated ATPase activity, consistent with previously reported biochemical characteristics of Rad51 protein. Although LmRad51 expression is below the level of detection in exponentially growing cultures of Leishmania, high levels of LmRad51 mRNA and protein expression can be detected following exposure to the DNA-damaging agent phleomycin. LmRAD51 is one of the first examples of a DNA damage-inducible gene to be characterised in Leishmania, and will be invaluable in studying the contribution of homologous recombination to Leishmania virulence.
Mol Biochem Parasitol 2001 Jul
PMID:Identification and characterisation of a RAD51 gene from Leishmania major. 1142 Jan 7

We previously cloned recA-homolog genes from a basidiomycete, Coprinus cinereus, and obtained the recombinant proteins (Nara et al., Mol. Gen. Genet. 262, 781-789, 1999, see Ref. 1; Nara and Sakaguchi, Biochem. Biophys. Res. Commun. 275, 97-102, 2000, see Ref. 2). The primary purpose of the present study was to characterize the biochemical properties of the recombinant LIM15/DMC1 (CoLIM15) and RAD51 (CoRAD51) proteins. We purified the recombinant proteins, and their molecular masses were 37 and 35 kDa, respectively. Both enzymes showed DNA-dependent ATPase activity and ATP-dependent strand exchange reaction in vitro. CoRad51 was a five- to sixfold stronger DNA-dependent ATPase and showed greater dependency on single-stranded DNA than CoLim15. In meiosis, both enzymes were highly accumulated in the meiotic tissue at leptotene and zygotene stages at which the homologous chromosomes pair, but disappeared just before the pachytene stage at which they recombine. From these and the previously reported results, we discuss here the relationships between the enzymes and meiosis.
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PMID:Strand exchange reaction in vitro and DNA-dependent ATPase activity of recombinant LIM15/DMC1 and RAD51 proteins from Coprinus cinereus. 1143 77

Werner's syndrome (WS) is a rare autosomal recessive disorder that arises as a consequence of mutations in a gene coding for a protein that is a member of RecQ family of DNA helicases, WRN. The cellular function of WRN is still unclear, but on the basis of the cellular phenotypes of WS and of RecQ yeast mutants, its possible role in controlling recombination and/or in maintenance of genomic integrity during S-phase has been envisaged. With the use of two drugs, camptothecin and hydroxyurea, which produce replication-associated DNA damage and/or inhibit replication fork progression, we find that WS cells have a slower rate of repair associated with DNA damage induced in the S-phase and a reduced induction of RAD51 foci. As a consequence, WS cells undergo apoptotic cell death more than normal cells, even if they arrest and resume DNA synthesis at an apparently normal rate. Furthermore, we report that WS cells show a higher background level of DNA strand breaks and an elevated spontaneous induction of RAD51 foci. Our findings support the hypothesis that WRN could be involved in the correct resolution of recombinational intermediates that arise from replication arrest due to either DNA damage or replication fork collapse.
Mol Biol Cell 2001 Aug
PMID:Werner's syndrome protein is required for correct recovery after replication arrest and DNA damage induced in S-phase of cell cycle. 1151 25

RAD51 is one of six mitotic human homologs of the E. coli RecA protein (RAD51-Paralogs) that play a central role in homologous recombination and repair of DNA double-strand breaks (DSBs). Here we demonstrate that RAD51 is important for resistance to cisplatin and mitomycin C in cells expressing the BCR/ABL oncogenic tyrosine kinase. BCR/ABL significantly enhances the expression of RAD51 and several RAD51-Paralogs. RAD51 overexpression is mediated by a STAT5-dependent transcription as well as by inhibition of caspase-3-dependent cleavage. Phosphorylation of the RAD51 Tyr-315 residue by BCR/ABL appears essential for enhanced DSB repair and drug resistance. Induction of the mammalian RecA homologs establishes a unique mechanism for DNA damage resistance in mammalian cells transformed by an oncogenic tyrosine kinase.
Mol Cell 2001 Oct
PMID:BCR/ABL regulates mammalian RecA homologs, resulting in drug resistance. 1168 15

We performed genetic association studies in a population-based breast cancer case-control study analysing polymorphisms in genes involved in homologous recombination (NBS1, RAD52, RAD51, XRCC2 and XRCC3) and non-homologous end-joining (KU70/80 and LIG4). These DNA double-strand break repair genes are candidates for breast cancer susceptibility. Genotype results were available for up to 2205 cases and 1826 controls. In the homologous recombination (HR) pathway, genotype frequencies differed between cases and controls for two polymorphisms in XRCC3; T241M (P=0.015) and IVS5 A>G at nt 17893 (P=0.008). Homozygous carriers of M241 were associated with an increased risk [odds ratio (OR) MM versus TT=1.3 (95% confidence interval (CI) 1.1-1.6)], while the rare allele of IVS5A>G was associated with a dominant protective effect [OR AG versus AA=0.8 (0.7-0.9)]. The association of a rare variant in XRCC2 (R188H) was marginally significant [P=0.07; OR HH versus RR=2.6 (1.0-6.7)]. In the non-homologous end-joining (NHEJ) pathway, a polymorphism in LIG4 (T>C at nt 1977) was associated with a decrease in breast cancer risk [P=0.09; OR CC versus TT=0.7 (0.4-1.0)]. No significant association was found for 12 other polymorphisms in the other genes studied. For XRCC3, we found evidence for four common haplotypes and four rarer ones that appear to have arisen by recombination. Two haplotypes, AGC and GGC, were associated with non-significant reductions in breast cancer risk, and the rare GAT haplotype was associated with a significantly increased risk. These data provide some evidence that variants in XRCC2 and LIG4 alter breast cancer risk, together with stronger evidence that variants of XRCC3 are associated with risk. If these results can be confirmed, understanding the functional basis should improve our understanding of the role of DNA repair in breast carcinogenesis.
Hum Mol Genet 2002 Jun 01
PMID:Variants in DNA double-strand break repair genes and breast cancer susceptibility. 1202 82

An acquired genetic instability, resulting from the loss of some types of DNA repair, is an early event in the development of a subset of human cancers. The involvement of BRCA1 and BRCA2 in the homologous recombination repair (HRR) of double-strand breaks in DNA implicates this pathway in the suppression of breast cancer. A family of proteins related to human RAD51, including XRCC2, are essential components of this repair pathway. Using site-directed mutagenesis of XRCC2, we show that non-conservative substitution or deletion of amino acid 188 of XRCC2 can significantly affect cellular sensitivity to DNA damage, and that a polymorphic variant at this site (R188H ), present on 6% of chromosomes in the population, has a weak effect on damage sensitivity. We tested the hypothesis that the R188H polymorphism could be a low-penetrance susceptibility factor for breast cancer, by genotyping 521 women with breast cancer and a total of 895 control women. Carriage of the rare allele of XRCC2 R188H was associated with breast cancer overall [odds ratio 1.3; 95% confidence interval (CI)=(1.0, 1.8)] and when younger-onset cases with a positive family history were compared with older controls with no family history [odds ratio 1.9; 95% CI=(1.0, 3.8)]. These results support the hypothesis that subtle variation in DNA repair capacity may influence cancer susceptibility in the population.
Hum Mol Genet 2002 Jun 01
PMID:A potential role for the XRCC2 R188H polymorphic site in DNA-damage repair and breast cancer. 1202 85

Fusion tyrosine kinases (FTKs) such as BCR/ABL, TEL/ABL, TEL/JAK2, TEL/PDGF beta R, TEL/TRKC(L), and NPM/ALK arise from reciprocal chromosomal translocations and cause acute and chronic leukemias and non-Hodgkin's lymphoma. FTK-transformed cells displayed drug resistance against the cytostatic drugs cisplatin and mitomycin C. These cells were not protected from drug-mediated DNA damage, implicating activation of the mechanisms preventing DNA damage-induced apoptosis. Various FTKs, except TEL/TRKC(L), can activate STAT5, which may be required to induce drug resistance. We show that STAT5 is essential for FTK-dependent upregulation of RAD51, which plays a central role in homology-dependent recombinational repair (HRR) of DNA double-strand breaks (DSBs). Elevated levels of Rad51 contributed to the induction of drug resistance and facilitation of the HRR in FTK-transformed cells. In addition, expression of antiapoptotic protein Bcl-xL was enhanced in cells transformed by the FTKs able to activate STAT5. Moreover, cells transformed by all examined FTKs displayed G(2)/M delay upon drug treatment. Individually, elevated levels of Rad51, Bcl-xL, or G(2)/M delay were responsible for induction of a modest drug resistance. Interestingly, combination of these three factors in nontransformed cells induced drug resistance of a magnitude similar to that observed in cells expressing FTKs activating STAT5. Thus, we postulate that RAD51-dependent facilitation of DSB repair, antiapoptotic activity of Bcl-xL, and delay in progression through the G(2)/M phase work in concert to induce drug resistance in FTK-positive leukemias and lymphomas.
Mol Cell Biol 2002 Jun
PMID:Fusion tyrosine kinases induce drug resistance by stimulation of homology-dependent recombination repair, prolongation of G(2)/M phase, and protection from apoptosis. 1202 32

Loss of mismatch repair (MMR) leads to a complex mutator phenotype that appears to drive the development of a subset of colon cancers. Here we show that MMR-deficient tumour cell lines are highly sensitive to the toxic effects of thymidine relative to MMR-proficient lines. This sensitivity was not a direct consequence of MMR deficiency or alterations of DNA precursor metabolism. Instead, MMR-defective tumour cell lines are also defective in homologous recombination repair (HRR) induced by DNA double-strand breaks. Furthermore, a frameshift mutation of the human RAD51 paralog XRCC2 found in the MMR-deficient uterine tumour cell line SKUT-1 can confer thymidine sensitivity when introduced into a MMR-proficient line. Like other cells with defective XRCC2, SKUT-1 is sensitive to mitomycin C, and MMR-proficient cells expressing the mutant XRCC2 allele become more sensitive to this agent. These data suggest that the thymidine sensitivity of MMR-deficient tumour cell lines may be a consequence of defects in the HRR pathway. The increased thymidine sensitivity and the loss of an important pathway for the repair of DNA double-strand breaks create new opportunities for therapies directed specifically against this subset of tumours.
Hum Mol Genet 2002 Sep 01
PMID:Defects in homologous recombination repair in mismatch-repair-deficient tumour cell lines. 1218 71

XRCC3 is a RAD51 paralog that functions in the repair of DNA double-strand breaks (DSBs) by homologous recombination (HR). XRCC3 mutation causes severe chromosome instability. We find that XRCC3 mutant cells display radically altered HR product spectra, with increased gene conversion tract lengths, increased frequencies of discontinuous tracts, and frequent local rearrangements associated with HR. These results indicate that XRCC3 function is not limited to HR initiation, but extends to later stages in formation and resolution of HR intermediates, possibly by stabilizing heteroduplex DNA. The results further demonstrate that HR defects can promote genomic instability not only through failure to initiate HR (leading to nonhomologous repair) but also through aberrant processing of HR intermediates. Both mechanisms may contribute to carcinogenesis in HR-deficient cells.
Mol Cell 2002 Aug
PMID:XRCC3 controls the fidelity of homologous recombination: roles for XRCC3 in late stages of recombination. 1219 83

Repair of double-strand breaks by gene conversions between homologous sequences located on different Saccharomyces cerevisiae chromosomes or plasmids requires RAD51. When repair occurs between inverted repeats of the same plasmid, both RAD51-dependent and RAD51-independent repairs are found. Completion of RAD51-independent plasmid repair events requires RAD52, RAD50, RAD59, TID1 (RDH54), and SRS2 and appears to involve break-induced replication coupled to single-strand annealing. Surprisingly, RAD51-independent recombination requires much less homology (30 bp) for strand invasion than does RAD51-dependent repair (approximately 100 bp); in fact, the presence of Rad51p impairs recombination with short homology. The differences between the RAD51- and RAD50/RAD59-dependent pathways account for the distinct ways that two different recombination processes maintain yeast telomeres in the absence of telomerase.
Mol Cell Biol 2002 Sep
PMID:Characterization of RAD51-independent break-induced replication that acts preferentially with short homologous sequences. 1219 38


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