[RPN4 the yeast transcription factor promotes the complex defence against methyi, methanesulfonate]

Methyl methanesulfonate (MMS) is an alkylating agent commonly used in models of genotoxic stress. It methylates bases in DNA but also leads to oxidative stress. The transcription factor Rpn4 protects yeast cells from toxic effect of MMS. Although Rpn4 is a major regulator of ubiquitin-proteasome system (UPS), a number of data points to its participation in the stress response regardless of the UPS. We have demonstrated that under the methyl methanesulfonate stress Rpn4 promotes the regulation of several genes involved in DNA repair, antioxidant response and glucose metabolism. We suggest a mechanism of complex action of Rpn4 in the stress response.

Linking genotoxic responses with cytotoxic and behavioural or physiological consequences: differential sensitivity of echinoderms (Asterias rubens) and marine molluscs (Mytilus edulis)

Integrated laboratory studies addressed multiple biomarker responses in the sea star (Asterias rubens) and the blue mussel (Mytilus edulis) exposed to a range of concentrations of direct and indirect acting genotoxins: methyl methane sulfonate (MMS) and cyclophosphamide (CP; an environmentally relevant anti-cancer pharmaceutical), respectively, in order to determine if the expressed genotoxicity has knock-on effects at the higher levels of biological organisation. The experimental design aimed to concurrently evaluate biomarkers of behavioural and physiological conditions (i.e. 'righting time' and 'clearance rate' for sea stars and mussels, respectively) in addition to cytotoxicity (neutral red retention assay), induction of micronuclei (Mn) and DNA strand breaks (as determined by the Comet assay). The protocol also included the determination of the maximum tolerated concentration (MTC), prior to genotoxic evaluation. The 3d MTC, as determined by the survival of the organisms, showed sea stars to be more sensitive than mussels to MMS (18 and 32 mg L(-1), respectively) and CP (56 and 180 mg L(-1), respectively). For both species and chemicals, cytotoxicity was not found to be significantly different compared to controls. Apart from the MMS exposure to sea stars (which showed 100% mortality at higher concentrations after 5d exposure), clear dose-response relationships were observed for both genotoxicity endpoints in each species. Following exposure to CP, good correlations were also found between the behavioural and physiological responses and genetic damage in each species (sea stars-MN vs. RT: R=0.73; Comet vs. RT: R=0.91; mussels-MN vs. CR: R=0.69; Comet vs. CR: R=0.72). This integrated approach, applying non-invasive assays to simultaneously determine the responses at different levels of biological organisation, indicates the potential value of behavioural and physiological measures in determining the toxicity of chemicals to marine organisms and highlights also the relevance of including adult echinoderms in environmental studies.

Strong intra-species variability in the metabolic conversion of six procarcinogens to somatic cell recombinagens in Drosophila

Genetic heterogeneity in response to genotoxic carcinogens requiring metabolic conversion has been studied in Drosophila, using seven different genotypes in combination with the w/w+ eye mosaic assay for mitotic recombination. The set of tester strains examined consisted of four wild-type laboratory strains (Berlin-K, BK; Oregon-K, OK; Leiden-S, LS; and 91-C), and three DDT-resistant strains (91-R; Hikone-R, HR; and Haag-79, HG). Drosophila larvae heterozygous for the wild-type report gene w+ were exposed to benz[a]anthracene (BA), benzo[a]pyrene (BP), 9,10-dimethyl-anthracene (DA), monocrotaline (MC), N-nitrosodimethylamine (DMN) or vinyl bromide (VBr). The primary conclusion regarding this study is the up to 60-fold variation between different genotypes in mosaic spot frequencies induced by those procarcinogens and the non-existence of just one genotype to function as a 'super-strain' in the activation of different classes of procarcinogens. By contrast, the seven Drosophila strains show a similar response to the direct-acting agent methyl methanesulphonate. Among the six procarcinogens selected for this study, DMN and MC are readily detectable in all the distinct genotypes. Less satisfactory in terms of test performance are the either negative or weak test responses with BA in all four-wild type strains (LS, BK, OK and 91-C), and the weakly positive results for vinyl bromide in LS, BK and OK. The best overall test response was provided by strains HG and HR. It is concluded that the combined application of strains HG and HR safely and reliably should detect somatic cell recombinagens in the Drosophila w/w+ system.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimethanesulphonate esters in receptor mapping studies. 1. Benzene 1,2-, 1,3- and 1,4-diol, dimethanol and diethanol dimethanesulphonates and anti-tumour activity

The anti-tumour activities of nine aromatic dimethanesulphonate esters were examined. Their biological effects have been related to both their chemical reactivity and to the computer-modelled vectorial positions of the centres of alkylation of the compounds. One compound (19) has shown activity between sensitive and resistant Yoshida tumours in vivo and also shows the highest activity between these two cell lines in vitro. In its minimal energy form, this compound would require to interact with converging nucleophilic centres about 6 A apart, and it is tentatively suggested that this may be an appropriate dimension for a receptor which is required to be alkylated in order to show anti-tumour activity.

Simple method for precise determination of chemical lethality in the L-arabinose resistance test of Salmonella typhimurium

A simple method is described for the determination of the lethal effects of chemicals assayed with the L-arabinose resistance test of Salmonella typhimurium. The method uses a mixed culture of 2 isogenic bacterial strains which are distinguished on the basis of their different nutritional requirements: sensitivity or resistance to L-arabinose, auxotrophy or prototrophy to histidine and leucine. BA13 (the mutation indicator strain) is the strain for routine screening of mutagens and allows the selection of forward mutation from L-arabinose sensitivity to L-arabinose resistance. BAL13 (the survival indicator strain) is a derivative of BA13. Both bacterial strains are found to be equally sensitive to the lethal effects of mutagens. The method described permits the measurement of cell survival at the same high cell concentration as used in the measurement of the mutant yield and in the same type of minimal medium with L-arabinose and glycerol, except for the histidine supplement in the mutant plates or the leucine in the survival plates.