TtcA a new tRNA-thioltransferase with an Fe-S cluster

International audienceTtcA catalyzes the post-transcriptional thiolation of cytosine 32 in some tRNAs. The enzyme from Es-cherichia coli was homologously overexpressed in E. coli. The purified enzyme is a dimer containing an iron–sulfur cluster and displays activity in in vitro assays. The type and properties of the cluster were investigated using a combination of UV-visible absorption , EPR and M ¨ ossbauer spectroscopy, as well as by site-directed mutagenesis. These studies demonstrated that the TtcA enzyme contains a redox-active and oxygen-sensitive [4Fe-4S] cluster, chelated by only three cysteine residues and absolutely essential for activity. TtcA is unique tRNA-thiolating enzyme using an iron–sulfur cluster for catalyzing a non-redox reaction

Intracerebral delivery of Carboplatin in combination with either 6 MV Photons or monoenergetic synchrotron X-rays are equally efficacious for treatment of the F98 rat glioma.

International audienceABSTRACT: BACKGROUND: The purpose of the present study was to compare side-by-side the therapeutic efficacy of a 6-day infusion of carboplatin, followed by X-irradiation with either 6 MV photons or synchrotron X-rays, tuned above the K-edge of Pt, for treatment of F98 glioma bearing rats. METHODS: Carboplatin was administered intracerebrally (i.c.) to F98 glioma bearing rats over 6 days using AlzetTM osmotic pumps starting 7 days after tumor implantation. Radiotherapy was delivered in a single 15 Gy fraction on day 14 using a conventional 6 MV linear accelerator (LINAC) or 78.8 keV synchrotron X-rays. RESULTS: Untreated control animals had a median survival time (MeST) of 33 days. Animals that received either carboplatin alone or irradiation alone with either 78.8 keV or 6 MV had a MeSTs 38 and 33 days, respectively. Animals that received carboplatin in combination with X-irradiation had a MeST of > 180 days with a 55% cure rate, irrespective of whether they were irradiated with either 78.8 KeV synchrotron X-rays or 6MV photons. CONCLUSIONS: These studies have conclusively demonstrated the equivalency of i.c. delivery of carboplatin in combination with X-irradiation with either 6 MV photons or synchrotron X-rays

Undetectable levels of N6-methyl adenine in mouse DNA: Cloning and analysis of PRED28, a gene coding for a putative mammalian DNA adenine methyltransferase.

International audienceThree methylated bases, 5-methylcytosine, N4-methylcytosine and N6-methyladenine (m6A), can be found in DNA. However, to date, only 5-methylcytosine has been detected in mammalian genomes. To reinvestigate the presence of m6A in mammalian DNA, we used a highly sensitive method capable of detecting one N6-methyldeoxyadenosine per million nucleosides. Our results suggest that the total mouse genome contains, if any, less than 10(3) m6A. Experiments were next performed on PRED28, a putative mammalian N6-DNA methyltransferase. The murine PRED28 encodes two alternatively spliced RNA. However, although recombinant PRED28 proteins are found in the nucleus, no evidence for an adenine-methyltransferase activity was detected

First Steps Towards an Understanding of a Mode ofCarcinogenic Action for Vanadium Pentoxide

Inhalation of vanadium pentoxide clearly increases the incidence of alveolar/bronchiolar neoplasms in male and female B6C3F1 mice at all concentrations tested (1, 2 or 4 mg/m3), whereas responses in F344/N rats was, at most, ambiguous. While vanadium pentoxide is mutagenic in vitro and possibly in vivo in mice, this does not explain the species or site specificity of the neoplastic response. A nose-only inhalation study was conducted in female B6C3F1 mice (0, 0.25, 1 and 4 mg/m3, 6 h/day for 16 days) to explore histopathological, biochemical (α-tocopherol, glutathione and F2-isoprostane) and genetic (comet assays and 9 specific DNA-oxo-adducts) changes in the lungs. No treatment related histopathology was observed at 0.25 mg/m3. At 1 and 4 mg/m3, exposure-dependent increases were observed in lung weight, alveolar histiocytosis, sub-acute alveolitis and/or granulocytic infiltration and a generally time-dependent increased cell proliferation rate of histiocytes. Glutathione was slightly increased, whereas there were no consistent changes in α-tocopherol or 8-isoprostane F2α. There was no evidence for DNA strand breakage in lung or BAL cells, but there was an increase in 8-oxodGuo DNA lesions that could have been due to vanadium pentoxide induction of the lesions or inhibition of repair of spontaneous lesions. Thus, earlier reports of histopathological changes in the lungs after inhalation of vanadium pentoxide were confirmed, but no evidence has yet emerged for a genotoxic mode of action. Evidence is weak for oxidative stress playing any role in lung carcinogenesis at the lowest effective concentrations of vanadium pentoxide

Photosensibilisation des acides nucleiques

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 82975 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Radiation-induced formation of tandem lesions: mechanistic aspect

International audienceDuring the last three decades considerable efforts have been made to determine the nature and quantify the amount of lesions produced in double stranded (ds)DNA exposed to oxidative stress. Nowadays, an almost complete decomposition pathway of the four DNA bases mediated by hydroxyl radicals and one electron-oxidation, the two damaging species of such a stress, is available. About 70 different DNA lesions have been identified and some of them have been quantified in cells exposed to ionizing radiations. Regarding the chemical aspects of formation of these lesions, most of the reactions identified at the nucleoside level were also found to occur in double stranded (ds)DNA. However, differences exist and some modifications were found to be generated specifically in dsDNA. This highlights the fact that the 3D structure of DNA somehow plays an important role in the decomposition of the initially generated radicals. Attention will be focused during the presentation on the formation of complex DNA lesions that could be significantly generated through a single oxidation event. Such damages are different to so-called locally multiple damage sites that are produced specifically by radiations as a consequence of multiple ionization processes. These include tandem DNA lesions generated through peroxidation reactions and also intra-and inter-strand crosslinks. These examples indicate that the described mechanisms of decomposition of the DNA bases could be different in dsDNA compared to that observed for free nucleosides. Moreover, this also indicates that in a cellular environment, biomolecules surrounding DNA could also play a role in the mechanisms of decomposition of initially produced DNA radicals. To further delineate the mechanisms of radiation-mediated decomposition of DNA bases in dsDNA both experimental and theoretical approaches are required

Radiation-induced formation of complex DNA lesions

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L’effet d’une contamination de cellules avec des nanoparticules: Le déséquilibre du pool de nucléotides comme biomarqueur de stress

National audienceLes nucléotides sont des molécules constitutives des acides nucléiques comme l’ADN et l’ARN - leur liaison déterminant la succession des bases impliquées, par exemple, dans la formation de la double hélice de l’ADN. Dans les cellules, les nucléotides participent à la régulation de l’expression génétique et bien évidemment à la synthèse des acides nucléiques. Le maintien de la balance du « pool » de nucléotides est très finement régulé tout au long du cycle cellulaire. Par conséquence, toute dérégulation de cette balance peut avoir des conséquences très délétères pour la cellule. Récemment, nous avons montré en utilisant une approche protéomique que des enzymes impliquées dans le métabolisme des nucléotides étaient dérégulées suite à une contamination avec des nanoparticules. Il paraît donc opportun de vérifier ces résultats préliminaires. Le projet consiste donc à développer une méthode analytique permettant le dosage quantitatif des nucléotides intracellulaires, et à appliquer cette méthode pour étudier l’effet d’une contamination, in vitro, de cellules A549 avec des nanoparticules d’argent

Radiochimie et lésions de l’ADN

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