Results 1 - 10 of 7050
Results 1 - 10 of 7050. Search took: 0.031 seconds
|Sort by: date | relevance|
[en] Excision repair cross-complementing group 2 (ERCC2) plays important roles in the repair of DNA damage and adducts. Single nucleotide polymorphisms (SNPs) of ERCC2 gene are suspected to influence the risks of oral cancer. We performed a meta-analysis to systematically summarize the possible association of ERCC2 rs1799793 and rs13181 polymorphisms with oral cancer risks. We retrieved the relevant articles from PubMed and Embase databases. Studies were selected using specific criteria. ORs and 95% CIs were calculated to assess the association. All analyses were performed using the Stata software. Six studies were included in this meta-analysis. There were no significant associations between ERCC2 rs1799793 and rs13181 polymorphism with overall oral cancer risk. In the stratified analysis by ethnicity, no significant associations were found. In the stratified analysis by tumor type, the risk of oral leukoplakia was significant associated with rs13181 polymorphism (AC vs. AA: OR = 1.28, 95% CI = 1.01-1.62, P = 0.546 for heterogeneity, I2 = 0.0%; CC vs. AA: OR = 1.94, 95% CI = 0.99-3.79, P = 0.057 for heterogeneity, I2 = 60.1%; dominant model AC + CC vs. AA: OR = 1.35, 95% CI = 1.08–1.69, P = 0.303 for heterogeneity, I2 = 17.6%; allele C vs. A: OR = 1.38, 95% CI = 1.04–1.82. P = 0.043 for heterogeneity, I2 = 56.4%). Rs13181 in ERCC2 gene might be associated with oral leukoplakia risk
[en] Our laboratory focuses on the base excision repair (BER) mechanism that is responsible for the removal of damaged bases in DNA. Oxidative DNA damage is generated spontaneously by the endogenous metabolism of the cells or induced exogenously by chemical or physical agents. Our aim is to understand how BER complexes are assembled in the context of the cell nucleus in response to genotoxic stress. We previously found that after treatments generating oxidized bases into cellular DNA BER complexes are assembled on the chromatin. In the case of the 8-oxoguanine (8-oxoG) mutagenic lesion, assembly of the BER complex depends on the recruitment to the chromatin of OGG1, the DNA glycosylase that recognizes and excises the lesion. Surprisingly, characterization of OGG1 mutants that are not able to recognize 8-oxoG showed that the recruitment of this initiator protein does not require the recognition of the damaged base. This suggests that there are other mechanisms that allow recruitment of the enzyme to chromatin and thus initiation of the repair of the 8-oxoG by the BER. We performed a high-throughput siRNA screen in human cells to identify proteins required for the recruitment of OGG1 to chromatin. Among the candidates issued from the screen, two groups of proteins were selected for further study: members of the mediator and cohesin complexes. In this project, we explored the role of these proteins in OGG1 relocalization after an oxidative stress. Our studies confirmed the requirement of essential proteins for OGG1 recruitment: cohesins subunits (SMC1, SMC3 and RAD21), mediator subunits including the central protein MED14, and CDK subunits (MED12, MED13, Cyclin C and CDK8). Requirement of all these proteins is independent of the cell cycle. Furthermore we show that recruitment of OGG1 is essential for its 8-oxoG repair function. Microscopy studies revealed recruitment and colocalization of two mediator subunits (MED12 and CDK8) with OGG1 on euchromatin domains after an oxidative stress. Finally, the association between OGG1 and its partners, specifically after an oxidative stress, was validated by FLIM-FRET microscopy and co-immunoprecipitation. To conclude, these results show for the first time a link between repair of oxidized bases and mediator and cohesin complexes, both of them being already involved in other DNA repair pathways. The identification of molecular mechanisms and new factors involved in the repair of oxidized bases may ultimately provide new elements for the management of diseases such as cancer and neurodegenerative diseases. (author)
[fr]Les composants cellulaires sont constamment exposes a un stress oxydatif, lie a l'environnement et au metabolisme cellulaire. Les especes reactives de l'oxygene produites par ce stress induisent de nombreuses lesions dans l'ADN, telles que l'oxydation des bases, la formation de sites abasiques ou la cassure de brins d'ADN. Ces dommages sont corriges par un panel de systemes de reparation, qui jouent un role critique dans la survie cellulaire et dans la prevention de pathologies telles que les maladies neurodegeneratives ou le cancer. La modification de bases est le type de dommage le plus abondant, genere spontanement ou par des agents exogenes. Notre laboratoire s'interesse ainsi au systeme de reparation par excision de base (BER), qui elimine les bases nucleotidiques alterees. Des etudes anterieures ont montre la formation 'd'usines de reparation du BER' suite a des traitements induisant l'oxydation des bases dont la forme la plus courante est la 8-oxoguanine (8-oxoG). Dans le cas de cette lesion mutagene, l'assemblage du complexe BER depend du recrutement d'OGG1 a la chromatine, l'enzyme qui reconnait et excise la 8-oxoG. Cependant, ce recrutement ne necessite pas la reconnaissance de la 8-oxoG, indiquant que d'autres signaux interviennent pour initier la reparation de la 8-oxoG par OGG1. Un crible a haut debit a ete realise dans des cellules humaines pour rechercher des proteines impliquees dans le recrutement d'OGG1. Deux complexes ont ete identifies, les cohesines et le mediateur de la transcription. Dans ce projet de recherche, nous avons explore le role de ces proteines dans la relocalisation d'OGG1 suite a un stress oxydatif. Nos etudes ont tout d'abord permis d'identifier des proteines essentielles au recrutement d'OGG1: les proteines formant l'anneau de cohesines (SMC1, SMC3 et RAD21), plusieurs sous-unites du mediateur dont MED14, ainsi que le module CDK (MED12, MED13, Cycline C et CDK8). De plus, ces proteines sont necessaires pour le recrutement d'OGG1 tout au long du cycle cellulaire. Nos resultats montrent que la relocalisation d'OGG1 sur la chromatine est liee a sa fonction de reparation de la 8-oxoG. Nous avons d'autre part montre que deux sous-unites du mediateur (MED12 et CDK8) sont relocalisees dans l'euchromatine, comme OGG1, de facon dependante du corps du mediateur et des cohesines. Enfin, l'association d'OGG1 avec ses partenaires a ete validee par microscopie FLIM-FRET et co-immunoprecipitation dans des conditions de stress oxydatif. En conclusion, ces resultats montrent pour la premiere fois un lien entre la reparation des bases oxydees et les complexes du mediateur et des cohesines, tous deux connus pour leur participation a d'autres voies de reparation de l'ADN. L'identification des mecanismes moleculaires et de nouveaux facteurs impliques dans la reparation des bases oxydees pourrait fournir a terme des elements essentiels pour la prise en charge de maladies telles que le cancer ou les maladies neurodegeneratives.
[en] In 2002, Al-Tassan and co-workers described for the first time a recessive form of inherited polyposis associated with germline mutations of MUTYH, a gene encoding a base excision repair (BER) protein that counteracts the DNA damage induced by the oxidative stress. MUTYH-associated polyposis (MAP) is now a well-defined cancer susceptibility syndrome, showing peculiar molecular features that characterize disease progression. However, some aspects of MAP, including diagnostic criteria, genotype-phenotype correlations, pathogenicity of variants, as well as relationships between BER and other DNA repair pathways, are still poorly understood. A deeper knowledge of the MUTYH expression pattern is likely to refine our understanding of the protein role and, finally, to improve guidances for identifying and handling MAP patients.
[en] Ionising radiation produces clustered DNA damages (two or more lesions within one or two helical turns of the DNA) which could challenge the repair mechanism(s) of the cell. Using purified base excision repair (BER) enzymes and synthetic oligonucleotides a number of recent studies have established the excision of a lesion within clustered damage sites is compromised. Evidence will be presented that the efficiency of repair of lesions within a clustered DNA damage site is reduced, relative to that of the isolated lesions, since the lifetime of both lesions is extended by up to four fold. Simple clustered damage sites, comprised of single-strand breaks, abasic sites and base damages, one or five bases 3' or 5' to each other, were synthesised in oligonucleotides and repair carried out in mammalian cell nuclear extracts. The rate of repair of the single-strand break/abasic site within these clustered damage sites is reduced, mainly due to inhibition of the DNA ligase. The mechanism of repair of the single-strand break/abasic site shows some asymmetry. Repair appears to be by the short-patch BER pathway when the lesions are 5' to each other. In contrast, when the lesions are 3' to each other repair appears to proceed along the long-patch BER pathway. The lesions within the cluster are processed sequentially, the single-strand break/abasic site being repaired before excision of 8-oxoG, limiting the formation of double-strand breaks to <2%. Stalled processing of clustered DNA damage extends the lifetime of the lesions to an extent that could have biological consequences, e.g. if the lesions are still present during transcription and/or at replication mutations could arise
[en] Radiation can damage cellular components, including DNA. Organisms have developed a panoply of means of dealing with DNA damage. Some repair paths have rather narrow substrate specificity (e.g. photolyases), which act on specific pyrimidine photoproducts in a specific type (e.g., DNA) and conformation (double-stranded B conformation) of nucleic acid. Others, for example, nucleotide excision repair, deal with larger classes of damages, in this case bulky adducts in DNA. A detailed discussion of DNA repair mechanisms is beyond the scope of this article, but one can be found in the excellent book of Friedberg et al. for further detail. However, some DNA damages and paths for repair of those damages important for photobiology will be outlined below as a basis for the specific examples of genetic and molecular analysis that will be presented below
[en] Defined cellular mechanisms have evolved that recognize and repair DNA to protect the integrity of its structure and sequence when encountering assaults from endogenous and exogenous sources. There are five major DNA repair pathways: mismatch repair, nucleotide excision repair, direct repair, base excision repair and DNA double strand break repair (including non-homologous end joining and homologous recombination repair). Aberrant activation of the Hedgehog (Hh) signaling pathway is a feature of many cancer types. The Hh pathway has been documented to be indispensable for epithelial-mesenchymal transition, invasion and metastasis, cancer stemness, and chemoresistance. The functional transcription activators of the Hh pathway include the GLI proteins. Inhibition of the activity of GLI can interfere with almost all DNA repair types in human cancer, indicating that Hh/GLI functions may play an important role in enabling tumor cells to survive lethal types of DNA damage induced by chemotherapy and radiotherapy. Thus, Hh signaling presents an important therapeutic target to overcome DNA repair-enabled multi-drug resistance and consequently increase chemotherapeutic response in the treatment of cancer
[en] Single-strand break repair (SSBR) and base excision repair (BER) of modified bases and abasic sites share several players. Among them is XRCC1, an essential scaffold protein with no enzymatic activity, required for the coordination of both pathways. XRCC1 is recruited to SSBR by PARP-1, responsible for the initial recognition of the break. The recruitment of XRCC1 to BER is still poorly understood. Here we show by using both local and global induction of oxidative DNA base damage that XRCC1 participation in BER complexes can be distinguished from that in SSBR by several criteria. We show first that XRCC1 recruitment to BER is independent of PARP. Second, unlike SSBR complexes that are assembled within minutes after global damage induction, XRCC1 is detected later in BER patches, with kinetics consistent with the repair of oxidized bases. Third, while XRCC1-containing foci associated with SSBR are formed both in eu- and heterochromatin domains, BER complexes are assembled in patches that are essentially excluded from heterochromatin and where the oxidized bases are detected. (authors)
[en] The hypoxia-activated prodrug TH-302 is reduced at its nitroimidazole group and selectively under hypoxic conditions releases the DNA cross-linker bromo-isophosphoramide mustard (Br-IPM). Here, we have explored the effect of Chk1 inhibition on TH-302-mediated pharmacological activities. We employed in vitro cell viability, DNA damage, cellular signaling assays and the in vivo HT29 human tumor xenograft model to study the effect of Chk1inhibition on TH-302 antitumor activities. TH-302 cytotoxicity is greatly enhanced by Chk1 inhibition in p53-deficient but not in p53-proficient human cancer cell lines. Chk1 inhibitors reduced TH-302-induced cell cycle arrest via blocking TH-302-induced decrease of phosphorylation of histone H3 and increasing Cdc2-Y15 phosphorylation. Employing the single-cell gel electrophoresis (comet) assay, we observed a potentiation of the TH-302 dependent tail moment. TH-302 induced γH2AX and apoptosis were also increased upon the addition of Chk1 inhibitor. Potentiation of TH-302 cytotoxicity by Chk1 inhibitor was only observed in cell lines proficient in, but not deficient in homology-directed DNA repair. We also show that combination treatment led to lowering of Rad51 expression levels as compared to either agent alone. In vivo data demonstrate that Chk1 inhibitor enhances TH-302 anti-tumor activity in p53 mutant HT-29 human tumor xenografts, supporting the hypothesis that these in vitro results can translate to enhanced in vivo efficacy of the combination. TH-302-mediated in vitro and in vivo anti-tumor activities were greatly enhanced by the addition of Chk1 inhibitors. The preclinical data presented in this study support a new approach for the treatment of p53-deficient hypoxic cancers by combining Chk1 inhibitors with the hypoxia-activated prodrug TH-302