The Alkylating Agent Methyl Methanesulfonate Triggers Lipid Alterations at the Inner Nuclear Membrane That Are Independent from Its DNA-Damaging Ability.

In order to tackle the study of DNA repair pathways, the physical and chemical agents creating DNA damage, the genotoxins, are frequently employed. Despite their utility, their effects are rarely restricted to DNA, and therefore simultaneously harm other cell biomolecules. Methyl methanesulfonate (MMS) is an alkylating agent that acts on DNA by preferentially methylating guanine and adenine bases. It is broadly used both in basic genome stability research and as a model for mechanistic studies to understand how alkylating agents work, such as those used in chemotherapy. Nevertheless, MMS exerts additional actions, such as oxidation and acetylation of proteins. In this work, we introduce the important notion that MMS also triggers a lipid stress that stems from and affects the inner nuclear membrane. The inner nuclear membrane plays an essential role in virtually all genome stability maintenance pathways. Thus, we want to raise awareness that the relative contribution of lipid and genotoxic stresses when using MMS may be difficult to dissect and will matter in the conclusions drawn from those studies.

ATR/Chk1/Smurf1 pathway determines cell fate after DNA damage by controlling RhoB abundance.

ATM- and RAD3-related (ATR)/Chk1 and ataxia-telangiectasia mutated (ATM)/Chk2 signalling pathways play critical roles in the DNA damage response. Here we report that the E3 ubiquitin ligase Smurf1 determines cell apoptosis rates downstream of DNA damage-induced ATR/Chk1 signalling by promoting degradation of RhoB, a small GTPase recognized as tumour suppressor by promoting death of transformed cells. We show that Smurf1 targets RhoB for degradation to control its abundance in the basal state. DNA damage caused by ultraviolet light or the alkylating agent methyl methanesulphonate strongly activates Chk1, leading to phosphorylation of Smurf1 that enhances its self-degradation, hence resulting in a RhoB accumulation to promote apoptosis. Suppressing RhoB levels by overexpressing Smurf1 or blocking Chk1-dependent Smurf1 self-degradation significantly inhibits apoptosis. Hence, our study unravels a novel ATR/Chk1/Smurf1/RhoB pathway that determines cell fate after DNA damage, and raises the possibility that aberrant upregulation of Smurf1 promotes tumorigenesis by excessively targeting RhoB for degradation.

Investigations on potential co-mutagenic effects of formaldehyde.

The genotoxicity and mutagenicity of formaldehyde (FA) has been well-characterized during the last years. Besides its known direct DNA-damaging and mutagenic activity in sufficiently exposed cells, FA at low concentrations might also enhance the mutagenic and carcinogenic effects of other environmental mutagens by interfering with the repair of DNA lesions induced by these mutagens. To further assess potential co-mutagenic effects of FA, we exposed A549 human lung cells to FA in combination with various mutagens and measured the induction and removal of DNA damage by the comet assay and the production of chromosomal mutations by the cytokinesis-block micronucleus assay (CBMN assay). The mutagens tested were ionizing radiation (IR), (±)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), N-nitroso-N-methylurea (methyl nitrosourea; MNU) and methyl methanesulfonate (MMS). FA (10-75µM) did not enhance the genotoxic and mutagenic activity of these mutagens under the test conditions applied. FA alone and in combination with MNU or MMS did not affect the expression (mRNA level) of the gene of the O(6)-methylguanine-DNA methyltransferase (MGMT) in A549 cells. The results of these experiments do not support the assumption that low FA concentrations might interfere with the repair of DNA damage induced by other mutagens.

Recruitment of HRDC domain of WRN and BLM to the sites of DNA damage induced by mitomycin C and methyl methanesulfonate.

The HRDC (helicase and RNase D C-terminal) domain at the C-terminal of WRNp (Werner protein) (1150-1229 amino acids) and BLMp (Bloom protein) (1212-1292 amino acids) recognize laser microirradiation-induced DNA dsbs (double-strand breaks). However, their role in the recognition of DNA damage other than dsbs has not been reported. In this work, we show that HRDC domain of both the proteins can be recruited to the DNA damage induced by MMS (methyl methanesulfonate) and MMC (methyl mitomycin C). GFP (green fluorescent protein)-tagged HRDC domain produces distinct foci-like respective wild-types after DNA damage induced by the said agents and co-localize with γ-H2AX. However, in time course experiment, we observed that the foci of HRDC domain exist after 24 h of removal of the damaging agents, while the foci of full-length protein disappear completely. This indicates that the repair events are not completed by the presence of protein corresponding to only the HRDC domain. Consequently, cells overexpressing the HRDC domain fail to survive after DNA damage, as determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. Moreover, 24 h after removal of damaging agents, the extent of DNA damage is greater in cells overexpressing HRDC domain compared with corresponding wild-types, as observed by comet assay. Thus, our observations suggest that HRDC domain of both WRN and BLM can also recognize different types of DNA damages, but for the successful repair they fail to respond to subsequent repair events.

Enhancement of methyl methanesulfonate-induced base excision repair in the presence of selenomethionine on p53-dependent pathway.

Selenomethionine (SeMet) has been identified as a chemopreventive antioxidant to activate p53-mediated nucleotide excision repair. In this study, we examined whether p53-mediated base excision repair (BER) might be induced by SeMet. When methyl methanesulfonate, a BER-inducing agent, was treated in the cells, DNA damage was rapidly decreased in the presence of SeMet. In addition, our data showed that the removal of apurinic/apyrimidinic sites was significantly enhanced in the presence of SeMet. Furthermore, we observed that the expression of gadd45a, known to involve BER as one of the p53 downstream genes, was increased by SeMet in p53 wild-type RKO cells. Those results supported the proposal that BER activity might be dependent on wild-type p53 under the modulation of gadd45a expression in response to SeMet. We suggested that p53-dependent BER activity as a distinct mechanism of SeMet might play an important role to prevent cancer caused by various oxidative stresses.

Antigenotoxic effect of allicin against SCEs induced by methyl methanesulphonate in cultured mammalian cells.

Allicin, one of the sulphur compounds of garlic (Allium sativum), possesses antioxidant and thiol disulphide exchange activity and is also shown to cause a variety of activities potentially useful for human health. In this investigation, the effect of 1,5,10 and 20 microM of allicin was determined for inhibiting the rate of SCE induced by 60 microM of MMS. Cultured human lymphocytes from two female donors were used for the experiment. The levels of SCEs were lowered by allicin suggesting its antigenotoxic activity in mammalian cells in vitro.

Inhibitory effect of chamomile essential oil on the sister chromatid exchanges induced by daunorubicin and methyl methanesulfonate in mouse bone marrow.

Different preparations of chamomile (Matricaria chamomilla) are used to treat various diseases, including inflammation and cancer; however, no studies on the plant's antigenotoxic capacity have been made. The aim of the present work was to determine the inhibitory effect of the chamomile essential oil (CO), on the sister chromatid exchanges (SCEs) produced by daunorubicin and methyl methanesulfonate (MMS) in mouse bone marrow cells. CO was analyzed and was found to contain 13 compounds, mainly bisabolol and its oxides, chamazulene, farnesene, germacrene and other sesquiterpenes. Initially, a toxic and a genotoxic analysis of CO were made; both showed negative results. To determine whether CO can inhibit the mutagenic effects induced by daunorubicin, one group of mice was administered corn oil, another group was treated with the mutagen (10 mg/kg), a third group was treated with 500 mg/kg of CO; three other groups were treated first with CO (5, 50 and 500 mg/kg) and then with 10 mg/kg of daunorubicin. In the case of MMS, the experimental groups consisted of the following: the negative control group which was administered corn oil, a group treated with 25 mg/kg of MMS, a group treated with 1000 mg/kg of CO, and three groups treated first with CO (250, 500 and 1000 mg/kg) and then with MMS (25 mg/kg). The results indicated a dose-dependent inhibitory effect on the SCEs formed by both mutagens. In the case of daunorubicin, a statistically significant result was observed in the three tested doses: from the lowest to the highest dose, the inhibitory values corresponded to 25.7, 63.1 and 75.5%. No alterations were found with respect to the cellular proliferation kinetics, but a reduction in the mitotic index was detected. As regards MMS, the inhibitory values were 24.8, 45.8 and 60.6%; no alterations were found in either the cellular proliferation kinetics or in the mitotic indices. Our results suggest that CO may be an effective antimutagen that could be considered for further study.

Cell division transforms mutagenic lesions into deletion-recombinagenic lesions in yeast cells.

Cell proliferation has been recognized as an important factor in human and experimental carcinogenesis. Point mutations as well as larger chromosomal rearrangements are involved in the initiation of cancer. In this paper we compared the relative potencies of radiation and chemical carcinogens for inducing point mutations vs. deletions in cell cycle arrested with dividing cells of Saccharomyces cerevisiae. Point mutation substrates and deletion (DEL) recombination substrates were constructed with the genes CDC28 and TUB2 that are required for cell cycle progression through G1 and G2, respectively. The carcinogens ionizing radiation, UV, MMS, EMS and 4-NQO induced point mutations in G1 and in G2 arrested as well as in dividing cells. UV, MMS, EMS and 4-NQO caused very weak if any increases in DEL recombination in G1 or G2 arrested cells, but large increases in dividing cells. When cells treated with carcinogen either in G1 or G2 were allowed to progress through the cell cycle, a time-dependent increase in DEL recombination was seen. Ionizing radiation and the site-specific endonuclease I-SceI, which both directly create double-strand breaks, induced DEL recombination in G1 as well as in G2 arrested cells. In conclusion, UV-, MMS-, EMS- and 4-NQO-induced DNA damage was converted during DNA replication to a lesion capable of inducing DEL recombination which is probably a DNA strand break. Thus, cell proliferation is not necessary to turn DNA alkylation or UV damage into a mutagenic lesion but to convert the damage into a lesion that induces DNA deletions. These results are discussed with respect to mechanisms of carcinogenesis.

Molecular cloning and genetic characterization of the Saccharomyces cerevisiae NGS1/MRE11 gene.

The Saccharomyces cerevisiae ngs1-1 mutant was previously identified by its enhanced sensitivity to simple DNA-alkylating agents such as methyl methanesulfonate but not to UV. Molecular cloning and sequencing of NGS1 as a putative DNA-alkylation repair gene revealed that it isidentical to MRE11, a gene that is involved in DNA recombinational repair. In order to investigate functional domains of the Mre11 protein, nucleotide-sequence alterations of a number of mre11 mutant alleles, including ngs1-1, mre11-1 (ts), mre11-2, mre11-3 and mre11-58, were determined. Most of these mutations map to the N-terminus ofMre11, emphasizing the importance of this highly conserved domain. The ngs1-1 and mre11-3 mutants carry nonsense mutations resulting in truncated proteins. Missense mutations were found in mre11-1 (ts), mre11-2 and mre11-58, of which mre11-2 and mre11-58 mapped to the conserved phosphoesterase domains, indicating the involvement of these motifs in the formation and/or processing of DNA double-strand breaks. Finally, mitotic-recombination assays show that the mre11 delta mutation enhances inter-chromosomal recombination but decreases the intra-chromosomal deletion frequency. In addition, MRE11 appears to play different roles during spontaneous and alkylation-induced homologous mitotic recombination.

Enhancement by peroxisome proliferators of the susceptibility to DNA damage in the liver of male F344 rats.

Effects of [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (Wy-14643) or di(2-ethylhexyl) phthalate (DEHP) as peroxisome proliferators on the susceptibility of liver DNA to damage by N-nitrosodimethylamine (DMN) or methyl methane sulfonate (MMS) were investigated. Male F344 rats were administered Wy-14643 or DEHP, orally, for 1 or 10 weeks. At 1 week, the susceptibility to hepatic DNA damage by DMN or MMS was significantly increased in the Wy-14643- or DEHP-treated rats. The enhancement of the susceptibility persisted for up to 10 weeks in both peroxisome proliferator-treated groups. These findings suggest that the high susceptibility to DNA damage caused by peroxisome proliferators would amplify the DNA damage action such as spontaneous damage, leading to an increase in the risk of initiation in the hepatocarcinogenesis.

A negative phase II trial methylene dimethane sulphonate in advanced ovarian cancer (Cancer Research Campaign Phase I/II Trials Committee).

Methylene dimethane sulphonate (MDMS), the first member of the homologous series of dimethane sulphonic acid esters, was administered to 19 patients with advanced epithelial ovarian cancer. All patients had received prior chemotherapy and in addition 3 had received prior radiotherapy. MDMS was given as an i.v. bolus injection at a dose of 125mg m-2 and repeated in a q35 day schedule. Ten patients received only one course, six two courses, two three courses and one four courses. The major toxicity was thrombocytopenia which was cumulative. Serious neutropenia did not occur and no infective episodes requiring i.v. antibiotics were seen. Seven patients experience hair loss and four nausea and vomiting. Sixteen patients were evaluable for response but no objective remissions were seen although three patients had stable disease lasting at least 8 weeks. MDMS is therefore not recommended for further trial in epithelial ovarian carcinoma.

Phase I clinical trial of methylene dimethane sulfonate.

Methylene dimethane sulfonate is the first member of the homologous series of straight-chain diol sulfonates. It was selected for phase I testing because of high activity in the rat Yoshida sarcoma system and a possible novel site of alkylation due to its small molecular size. Methylene dimethane sulfonate was administered as a rapid iv bolus infusion to 39 patients at doses ranging from 14 to 225 mg/m2. Nausea and vomiting were not severe but total alopecia occurred in the majority of patients at doses greater than 100 mg/m2. The dose-limiting toxic effect was thrombocytopenia, which was cumulative with lower, more prolonged nadirs following successive courses. The median time to platelet count nadir was 21 days, with recovery by 35 days. A minor response was seen in one patient with an adenocarcinoma of the lung. The recommended dose for phase II studies is 125 mg/m2 for patients who have received prior chemotherapy and 150 mg/m2 for those who have not, in an every 35-day schedule.

Detection of the cytogenetic effect of inhaled aerosols by the micronucleus test.

The induction of micronuclei in mice exposed to aerosols of the following 6 genotoxic chemicals by inhalation was examined: cyclophosphamide (CP), methyl methanesulfonate (MMS), mitomycin C (MMC), dimethylnitrosamine (DMN), ethylcarbamate and colchicine. Exposure of mice to CP aerosols at a theoretical concentration of 2426 mg/m3 for 29, 81 and 139 min induced 0.6, 1.0 and 2.3% micronucleated polychromatic erythrocytes (MNPCEs) in bone marrow 24 h after the termination of exposure. The other chemicals except for DMN showed a similar exposure-response relationship following in vivo exposures to their aerosols. The results obtained in this study suggest that the cytogenetic effect of inhaled aerosols can be detected by the micronucleus test, and the method described in the present report is useful as a rapid in vivo test for atmospheric aerosols.

Methyl methane sulfonate induced enhancement of Friend viral leukemogenesis.

Exposure to the chemical carcinogen, methyl methane sulfonate, enhanced leukemogenesis in mice given threshold doses of Friend leukemia virus, as shown by peripheral white blood cell counts, splenomegaly and survival.