Mutation Research Letters最新文献

Treatment of HeLa cells with cadmium chloride and zinc chloride increases the survival rate of nitrous acid-treated adenovirus 2 (ade2). This increase is maximal if the time interval between cell treatment and virus infection is delayed by 36 h. The induction process requires protein synthesis only during the 3-h period immediately following treatment; cycloheximide does not prevent the expression of enhanced reactivation if added to the cells after this time.

We have previously established an immunoblastic B lymphoma cell line, designated HOB1. This cell line is hypersensitive to a wide spectrum of chemotherapeutic agents. Two co-regulated polypeptides around 64 kDa (termed p64) were induced 10–30-fold in response to adriamycin and some other drugs at the IC₅₀ (the concentration inhibiting cell growth by 50%). These inducible proteins are localized as monomeric forms in the cytosolic fraction, with isoelectric points of pH = 6.2 (major protein) and pH = 7.0 (minor protein). An adriamycin-resistant cell line was established from HOB1 cells. The p64 inducibility was dramatically reduced in resistant HOB1 cells or unrelated cell lines which show phenotypic resistant to adriamycin toxicity. The loss of p64 inducibility in resistance cells is not due to a failure of cells to take up adriamycin since drug accumulation kinetics remained the same as in the parental cells.

Three kinds of diphenyl ether herbicides, 4-nitrophenyl 2,4,6-trichlorophenyl ether (CNP, chlornitrofen), 2,4-dichlorophenyl 3-methoxy-4-nitrophenyl ether (chlomethoxynil) and 2,4-dichlorophenyl 3-methoxycarbonyl-4-nitrophenyl ether (bifenox), were tested for mutagenicity in Salmonella typhimurium YG1026 and YG1021, which have high nitroreductase activity, and also in S. typhimurium TA100 and TA98. CNP and chlomethoxynil showed mutagenicity in S. typhimurium YG1026, without S9 mix, inducing 50 and 304 revertants per μg. These mutagenicities were suppressed by the addition of S9 mix. CNP and chlomethoxynil were also mutagenic to YG1021 with and without S9 mix, and their mutagenicities were lower than those to YG1026. On the other hand, bifenox was mutagenic to YG1026 only with S9 mix, inducing 3.0 revertants per μg. These three herbicides showed no mutagenicity in S. typhimurium TA100 and TA98 either with or without S9 mix.

Cells in human peripheral blood were treated in vitro with increasing concentrations of melatonin (0.5 or 1.0 or 2.0 mM) for 20 min at 37 ± 1°C and then exposed to 150 cGy γ-radiation from a ¹³⁷Cs source. The lymphocytes which were pre-treated with melatonin exhibited a significant and concentration-dependent decrease in the frequency of radiation-induced chromosome damage as compared with the irradiated cells which did not receive the pre-treatment. The extent of the reduction in radiation-induced chromosome damage observed with 2.0 mM melatonin was similar to that found in lymphocytes pre-treated with 1.0 M dimethyl sulfoxide, a known free radical scavenger. Melatonin at 2.0 mM (a 500 X lower concentration) was as effective in decreasing the radiation-induced chromosome damage as dimethyl sulfoxide at 1.0 M. These observations may have implications for human protection against damage due to endogenously produced free radicals and also due to exposure to free radical producing physical and chemical mutagens and carcinogens.

The potential of benzene to produce DNA adducts in B6C3F1 mice was investigated by the nuclease P1-enhanced ³²P-postlabeling assay. The mice were daily treated i.p. with 500 mg/kg benzene in olive oil for 4 days, and the liver, mammary gland, and bone marrow were collected 24 h after the last treatment. Thin-layer chromatograms obtained with treated-tissue DNA specimens were qualitatively identical to those from corresponding olive oil-treated (control) tissue DNA. Quantitative evaluations revealed that there was no treatment-related increase in radioactivity on the chromatograms at or near the locations where the major in vitro adducts of phenol, hydroquinone and benzoquinone migrated. Benzene treatment, however, resulted in a decrease in the levels of certain endogenous adducts, the biological significance of which is unknown. Our results indicate that benzene treatment does not produce detectable levels of aromatic DNA adducts in mouse tissues.

Transgenic mouse models are being used with increasing frequency for mutational and toxicological studies. One such system, MutaMouse, contains a stably integrated lambda-gt10LacZ shuttle vector in the mouse genome. We describe the use of dual color fluorescence in situ hybridization (FISH) with Mus musculus whole chromosome paints and lambda DNA to map the integration site of the lambda transgene to band C on mouse chromosome 3.

The heterocyclic amines (HA) 2-aminodipyridol[1,2-a:3′2-d]imidazole (Glu-P-2), 2-amino-3,4-dimethylimidazo- [4,5-f]quinoline (MeIQ) and 2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were mutagenic in V79 cells (Chinese hamster lung fibrobalsts) using 6-thioguanine resistance as the marker of mutagenicity. Pancreas duct epithelial cells (DEC) from untreated hamsters, homogenates of pancreas ducts from untreated hamsters and those fed a high fat diet and human DEC were used to activate the heterocyclic amines. When hamster cells and tissues were used the optimum mutation frequencies ( mutants/10⁶ survivors) measured were: Glu-P-2, 10±1; MeIQ, 28±2 (DEC), 12±2 (control, duct homogenate, and 21±2 (high fat diet fed, duct homogenate); PhIP, 61±5. When human DEC were used the optimum mutation frequencies were: MeIQ, 32±4; PhIP, 35±3.3,8-Dimethylimidazo[4,5-f]quinoxaline, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]dole and 3-amino-1-methyl-5H-pyridol[4,3-b]indole were not mutagenic in this assay

DNA topoisomerases modify supercoiled DNA through concerted breaking and rejoining of the DNA strands and consequently play a key role in DNA biosynthesis and processing. It has been suggested that topoisomerases may facilitate access to damaged sites of excision repair enzymes due to their property to relax supercoiled DNA. We show here that treatment with nalidixic acid and novobiocin, which affects topoisomerase II activity among other targets, impairs the incision of 8-methoxypsoralen photoinduced DNA interstrand cross-links in normal human fibroblasts. Since cells derived from Fanconi anemia (FA) demonstrate hypersensitivity to DNA cross-linking agents associated with a reduced repair efficiency of cross-links, we compared the effects of different topoisomerase I and II inhibitors on FA and normal lymphoblasts. No differences were found in growth inhibition or induction of chromosome aberrations between FA and normal cells. The specificity of inhibitors is questionable and even if topoisomerases are indeed inhibited alternative pathways may be involved. However, our observations provisionally suggested that topoisomerases activities are normal in FA cells.

The hypoxanthine guanine phosphoribosyltranferase (HPRT) gene is mutated by a variety of genotoxic in adult rat liver (ARL) epithelial cell lines. By polymerase chain reaction (PRC) amplification and DNA sequencing of rat ARL cell HPRT gene sequences with mouse-and rat-specific oligonucleotides, a large portion of the rat HPRT transcriptional promoter region was sequenced. This region exhibits approximately 60% homology with the corresponding mouse sequence, contains a similar G/C-rich region at its 3′ end, and contains a similar series of 6-nucleotide (nt) GGGCGG repeats. To determine if this region is a target for mutation by different genotoxins, HPRT-deficient ARL, mutants induced by 2-acetylaminofluorence (AAF), $\text{N-}\text{methyl}\text{-N′-}\text{nitro}\text{-N-}\text{nitrosoguanidine}$ (MNNG), or 7,12-dimethyl-benz[ita]anthracene (DMBA) were isolated and studied. A 1003-nt fragment of predominantly HPRT regulatory sequences was amplified by PCR using purified genomic DNA from 17 independent mutants and sequenced directly. None of the 17 mutants examined exhibited any alterations in the transcriptional regulatory region or the 5′ untranslated region of HPRT exon 1 after direct sequencing analysis of PCR product. In addition, none of the 2-AAF-induced mutants exhibited differences in in vitro transcription rates as determined by nuclear run-on analysis. These data suggest that regulatory sequences of the HPRT gene are not a primary target for mutation by the genotoxins studied.