[Connectivity between soxS gene expression and adaptive resistance to the SoxRS-regulon inducers in E. coli cells]. / Vzaimosviaz' ékspressii gana soxS s razvitiem adaptivnoi rezistentnosti k induktoram SoxRS-regulona v kletkakh E. coli.

Development of the adaptive response (AR) to the SoxRS-inducers-menadione (O2(-.)-donor), dinitrosyl-iron complex (NO donor) and their simultaneous action was studied in E. coli. Two AR parameters were used: an increasing in viability and decreasing in the soxS gene (SoxRS-regulon) expression in adapted cells. It was shown that namely peroxynitrite (ONOO-), being formed inside the cells from O2-. and NO, was the most cytotoxic agent among the drugs tested. On the one side, an increase in resistance to menadione treatment was selectively demonstrated in adapted E. coli delta oxyR mutant cells, defective in OxyR-regulon activity. On the other side, a decrease in soxS gene expression was marked in the experiments with menadione, as well So, an AR to O2-. superoxide anion was selectively regulated by the SoxRS DNA-repair pathway. OxyR-regulon that is selectively activated by the most redox-cycling agents and controls AR to these agents doesn't provide development of the AR to O2-..

[Heat shock inhibits the induced expression of the SOS genes and SoxRS regulons in Escherichia coli]. / Teplovoi shok reguliruet indutsirovannuiu ékspressiiu genov SOS- i SoxRS-regulonov v Escherichia coli.

Oxidative stress formed in Escherichia coli cells is known to bring about a complex induction of alternative DNA repair processes, including SOS, SoxRS, and heat-shock response (HSR). The modification by heat shock of the expression of sfiA and soxS genes induced by oxidative agents H2O2, menadione and 4-nitroquinoline-1-oxide (4NQO) was studied for the first time. Quantitative parameters of gene expression were examined in E. coli strains with fused genes (promoters) sfiA::lacZ and soxS::lacZ. The expression of these genes induced by cell treatment with H2O2, but not menadione or 4NQO, was shown to decrease selectively after exposure to heat shock. Since genetic activity of menadione and 4NQO depends mainly on the formation of superoxide anion O2-, it is assumed that the effect of selective inhibition by heat-shock of sfiA and soxS gene expression in experiments with H2O2 is connected with activity of DnaK heat shock protein, which, unlike other heat-shock proteins, cannot be induced by superoxide anion O2-.

[The new antitumor drug cycloplatam: cytotoxicity and DNA interstrand cross-linking]. / Novyi protivoopukholevyi preparat tsikoplatam: tsitotoksichnost' i mezhnitevye sshivki DNK.

Cytotoxicity genetic mechanisms such as induction of SOS-repair, excision repair and interstrand coupling induced by cycloplatam or ammine (cyclopentyl amine)-S(-) malatoplatinum (II), a new antitumor drug, were for the first time studied in comparison to those of the known drug cis-diammine dichloroplatinum (II) (DDP) in a model system of Escherichia coli. In the cells of E. coli the cycloplatam cytotoxicity was much lower than that of DDP. Both the drugs induced SOS-repair in E. coli PQ37. In a concentration of 25 microM DDP was 20 times as active as cycloplatam. In concentrations of 40 to 100 microM the difference leveled. Both the drugs induced interstrand coupling in specimens of pure DNA from calf thymus and E. coli. When the cells of the wild type E. coli AB1157 were incubated in the presence of the drugs only DDP induced the DNA interstrand coupling. No correlation between the DNA interstrand coupling induced by cycloplatam or DDP and cytotoxicity of the drugs was observed.

[Expression and functions of adaptive response genes in Escherichia coli treated with mono- and bifunctional alkylating agents. Interference with SOS response]. / Ekspressiia i funktsii genov adaptivnogo otveta v Escherichia coli pri deistvii mono- i bifunktsional'nykh akliliruiushchikh agentov. Interferentsiia s SOS-otvetom.

The expression of genes belonging to the Ada regulon of Escherichia coli under the action of mono- and bifunctional alkylating agents--high-efficiency antitumor HMM, ACNU, and BCNU preparations--was studied. The functional specificity of the alkA, alkB, and aidB1 genes concerning both the structure and volume of DNA alkylation and the specificity of cell preadaptation was revealed. Additional experimental evidence for the role of the aidB1 gene as a unique "hazard gene", a component of the E. coli ada operon, was obtained. A phenomenon of positive interference between alternative SOS and Ada responses was observed for the first time upon gene expression.

[The genetic activity of superlow doses of antitumor antibiotics and 2-nitrofluorene: the ecological aspects of the problem]. / Geneticheskaia aktivnost' supermalykh doz protivoopukholevykh antibiotikov i 2-nitrofluorena: ékologicheskie aspekty problemy.

The genetic (mutagenic) activity of ultralow doses (below 1 x 10(-12)M of the antitumor antibiotics, anthracyclines and bleomycin, as well as the typical pollutant and component of the urban atmosphere 2-nitrofluorene, was studied on the model of Salmonella typhimurium LT2 TA98 his D3052. It was shown for the first time that carminomycin and 2-nitrofluorene at 1 x 10(-17) and 1 x 10(-22) M induced a two- to threefold increase in the number of revertants-prototrophs over the spontaneous background. The areas of increase (1 x 10(-15) M) and decrease (1 x 10(-19) and 1 x 10(-21) M) in the number of mutants, as compared with the spontaneous background, were found in the curve of dose dependence of the number of mutants in the presence of bleomycin. The results obtained were discussed in terms of their ecological importance.

[Genotoxic and mutagenic activity of antineoplastic anthracyclines and their aglycones: study in two test-systems]. / Genotoksicheskaia i mutagennaia aktivnost' protivoopukholevykh antratsiklinov i ikh aglikonov: izuchenie v test-sistemakh.

Mutagenic (Ames tests) and genotoxic (SOS chromotest) activities of highly-efficient natural anthracycline monosaccharides possessing antitumor activity-daunorubicin (also known as daunomycin or rubomycin), doxorubicin (adriamycin), and carminomycin-were studied. At the same time, the hypothesis was tested that intercalation of the antibiotic moiety into the helix of cell DNA, which was mediated by the saccharide amino group, played a crucial role in genotoxicity of these anthracyclines. The hydrolysis products of these antibiotics (the corresponding aglycones) and aclacynomycin A (an anthracycline trisaccharide), as well as aclavinone (its derivative aglycone), were studied. All these compounds lacked the saccharide amino group necessary for intercalation. It was found that all anthracycline monosaccharides studied had a strong mutagenic effect on strain TA98 and a moderate effect on strain TA100 of Salmonella typhimurium. Aclacynomycin A was found to have no mutagenic effect on any strain. Lack of the glycoside amino group did not necessarily result in loss of mutagenic activity in the derivative aglycones of anthracycline monosaccharides: they exhibited moderate mutagenic activity in strain TA98 and low but significant activity in strain TA100. The S9 microsomal fraction did not alter the mutagenic activity of either anthracycline monosaccharides or their aglycones; however, it dramatically increased the mutagenic activity of aclavinone: correspondence between positive responses in Ames tests and the SOS chromotest was found. Apparently, the mutagenic activity of the substances studied in bacterial cells was mediated by inducing the SOS-repair process. If the compound contained the amino glycoside moiety, functional and structural precursors of the SOS response were formed via intercalation of the reagents into the DNA duplex; if the substance did not contain this moiety, the precursors were formed via ionic interaction.

[Correlation of cytotoxic activity of mutant forms of tumor necrosis factor alpha with changes in the level of free sphingosine in murine liver]. / Korreliatsiia tsitotoksicheskoi aktivnosti mutantnykh form faktora nekroza opukholei-alpha s izmeneniem urovnia svobodnogo sfingozina v pecheni myshei.

Sphingosine, the product of enzymatic degradation of sphingomyelin, displays a high cytotoxic activity and is accumulated in animal organs under the action of the tumour necrosis factor (TNF alpha). To elucidate the role of sphingosine in the realization of TNF cytotoxicity, TNF mutants were obtained which differed in their cytotoxic action on L929 cells. The wild strain of TNF and the mutant having a deletion in position 67-71 displayed the highest toxicity and sharply stimulated sphingosine accumulation in mouse hepatocytes. A moderate increase in the sphingosine content was induced by mutants with point and double mutations in positions E127Q, I155L and V150I displaying a much lower toxicity in comparison with the wild strain. The toxic, mutagenic and antimutagenic activities of sphingosine were investigated. Despite the high degree of cytotoxicity, sphingosine did not display any mutagenic activity but had a pronounced antimutagenic effect on E. coli cells. The role of phospholipid enzymatic degradation products in activation of sphingomyelin cycle enzymes stimulating of sphingosine accumulation in animal cells under the action of TNF alpha is discussed.

[Oxidative and SOS-response in Escherichia coli and their interference]. / Oksidativnyi i SOS-otvety v Escherichia coli i ikh interferentsiia.

Interference between the oxidative and SOS responses in Escherichia coli was studied. The oxidative response involves both reactive oxygen scavenging system and DNA repair systems which are distinct from either the SOS or adaptive response to alkylating agents. The oxyR gene is a positive regulatory gene for the oxidative response and controls at least 9 proteins which are induced by treatment with H2O2. This gene is not a portion of the SOS regulon that involves at least 17 different genes in E. coli and controls the SOS response--another inducible and nonspecific repair activity. The SOS response was measured in E. coli PQ37 by means of a sfiA: :lacZ operon fusion according to "SOS Chromotest" in a completely automated system "Bioscreen C" (Labsystems, Finland). Our data have shown that: 1) H2O2 was a potent inducer of sfiA gene--one of the SOS genes; 2) there was strong negative effect of the oxidative response on the subsequent induction of the SOS response. In common with our previous findings it should be concluded that there is an interference between the SOS response--on the one hand, and the adaptive and oxidative responses--on the other. The nonspecific heat shock response is proposed to be a main key in these interferences.

[Interference of inducible repair processes in Escherichia coli]. / Interferentsiia indutsibel'nykh reparatsionnykh protsessov v Escherichia coli.

Radiation and the majority of chemical mutagens produce lesions in the DNA of cells which provoke the induction--as a reverse response--of some inducible repair processes. One of them is the adaptive response--highly specific in the repair of damages, induced by alkylating agents. This repair pathway decreases the toxic and mutagenic effects of many alkylating agents and can be induced in Escherichia coli cells exposed to sublethal concentrations of the same agents. By contrast, the SOS repair pathway in E. coli is non-specific and transient phenomenon which leads, among other things, to bacterial mutagenesis. It is controlled by the regulatory RecA protein which in its activated form promotes the cleavage of LexA repressor, allowing for the increased transcription of about 17 repressed genes--SOS regulon. The latter is not associated with the adaptive response. Nevertheless, there are experimental data indicating that the adaptive response is able to reduce some functions of the SOS repair activity--W-reactivation, W-mutagenesis and lambda phage induction. A relatively new bacterial short-term assay for genotoxicity, the SOS chromotest with E. coli PQ37 as an indicator organism, makes it possible to measure SOS induction indirectly, on the basis of a simple colorimetric assay. In the present study, the SOS chromotest in a completely automated system "Bioscreen C" was used to study interference between the adaptive and SOS responses in E. coli. Our data indicate that there is an inhibitory effect of the adaptive response on the SOS induction, as well as the negative interference between two successive SOS responses, at a transcriptional level of the SOS induction.