Diethylsulphate and methylnitrosourea affect different targets in Chinese hamster fibroblasts: possible mechanisms of aneuploidy induction by these agents

Diethyl sulfate-induced cell cycle arrest and apoptosis in human bronchial epithelial 16HBE cells

In this study, we investigated the effects of diethyl sulfate (DES) on cell proliferation, cell cycle progression and apoptosis in human bronchial epithelial 16HBE cells. Cells were treated with various doses of DES (0, 0.5, 1.0, 2.0, 4.0 or 8.0mM) for 12, 24 or 36h. Cell proliferation and apoptosis were determined by MTT assay and flow cytometer, respectively. The results showed that DES inhibited cell proliferation in a dose- and time-dependent manner, and induced significant apoptosis in 16HBE cells. Apoptosis related proteins measurement results revealed that DES-induced apoptosis was concurrent with the increasing of Bax and cleavage fragment caspase-3 and the decreasing of Bcl-2 and full length procaspase-3. When cells were incubated with 2.0mM of DES for several time intervals, S and G2/M phase accumulation was observed. Further analysis indicated that both DES-induced G1/S transition acceleration and S arrest resulted in S phase accumulation, and that DES-induced G2/M arrest resulted in G2/M phase accumulation. Western blotting results demonstrated that after DES treatment p-chk1 (Ser345) and p-chk2 (Thr68) levels decreased in G1 cells, and increased in S and G2/M cells. In addition, the increasing of chk1 and chk2 were also induced by DES treatment. With the increase in the dose of DES, p53 levels first increased (0.5-4.0mM) and then decreased (8.0mM). Down-regulation of p53 by RNA interference increased 4.0mM of DES-induced apoptosis but did not affect 2.0mM DES-induced cell cycle arrest. In conclusion, DES inhibits 16HBE cells proliferation in a dose- and time-dependent behavior. Within the sublethal dose, DES induces S and G2/M arrest through activating DNA damage checkpoints. Within the lethal dose, DES induces apoptosis through evoking apoptosis programs. p53 might play an important role in the transition between evoking cell cycle arrest/pro-survival and apoptosis programs upon DES exposure.

Can mutagenicity information be useful in an Integrated Testing Strategy (ITS) for skin sensitization?

Our previous work has investigated the utility of mutagenicity data in the development and application of Integrated Testing Strategies (ITS) for skin sensitization by focusing on the chemical mechanisms at play and substantiating these with experimental data where available. The hybrid expert system TIMES (Tissue Metabolism Simulator) was applied in the identification of the chemical mechanisms since it encodes a comprehensive set of established structure-activity relationships for both skin sensitization and mutagenicity. Based on the evaluation, the experimental determination of mutagenicity was thought to be potentially helpful in the evaluation of skin sensitization potential. This study has evaluated the dataset reported by Wolfreys and Basketter (Cutan. Ocul. Toxicol. 23 (2004), pp. 197-205). Upon an update of the experimental data, the original reported concordance of 68% was found to increase to 88%. There were several compounds that were 'outliers' in the two experimental evaluations which are discussed from a mechanistic basis. The discrepancies were found to be mainly associated with the differences between skin and liver metabolism. Mutagenicity information can play a significant role in evaluating sensitization potential as part of an ITS though careful attention needs to be made to ensure that any information is interpreted in the appropriate context.

Extracellular-regulated kinase-mitogen-activated protein kinase cascade: unsolved issues

This review point out several aspects regarding the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase (Erk) network, which are still pending issues in the understanding how this pathway integrate information to drive cell fates. Focusing on the role of Erk during cell cycle, it has to be underlined that Erk downstream effectors, which are required for mitosis progression and contribute to aneuploidy during tumorigenesis, remain to be determined. In addition to the identity of the terminal enzymes or effectors of Erk, it has to be stressed that the dynamic nature of the Erk signal is itself a key factor in cell phenotype decisions. Development of biophotonics strategies for monitoring the Erk network at the spatiotemporal level in living cells, as well as computational and hypothesis-driven approaches, are called to unravel the principles by which signaling networks create biochemical and biological specificities. Finally, Erk dynamics might also be impacted by other post-translational modification than phosphorylation, such as O-GlcNAcylation.

Aneugenic potential of the nitrogen mustard analogues melphalan, chlorambucil and p-N,N-bis(2-chloroethyl)aminophenylacetic acid in cell cultures in vitro

Melphalan (MEL), chlorambucil (CAB) and p-N,N-bis(2-chloroethyl)aminophenylacetic acid (PHE) are nitrogen mustard analogues, which are clinically used as chemotherapeutic agents. They also exert carcinogenic activity. The aim of this study was to investigate the aneugenic potential of the above drugs and the possible mechanism responsible for this activity. The Cytokinesis Block Micronucleus (CBMN) assay in combination with fluorescence in situ hybridization (FISH) was used in human lymphocyte cultures to evaluate micronucleus (MN) frequency. Pancentromeric probe (alpha-satellite) was applied to identify chromosomes in micronuclei and an X-chromosome specific centromeric probe was used to asses micronucleation and non-disjunction of this chromosome in binucleated cells. The effect of the above compounds on the organization of mitotic apparatus, as a possible target of chemicals with aneugenic potential, was investigated in C(2)C(12) mouse cell line by double immunofluorescence of alpha- and gamma-tubulin. We found that the studied drugs increased MN frequency in a linear dose-dependent manner primarily by chromosome breakage and in a lesser extent by an aneugenic mechanism. Non-disjunction and micronucleation of X-chromosome were also induced. Abnormal metaphase cells were linearly increased with concentration and characterized by abnormal centrosome number. Interphase cells with micronuclei and abnormal centrosome number were also observed. Since nitrogen mustards are highly reactive agents, with low selectivity and form covalent bonds with different nucleophilic sites in proteins and nucleic acids, it is reasonable to consider that one possible pathway for nitrogen mustard analogues to exert their aneugenic activity is through reaction with nucleophilic moieties of proteins or genes that are involved in the duplication and/or separation of centrosomes, resulting in abnormal centrosome number. Based on our results the carcinogenicity of nitrogen mustard analogues studied may be attributed not only to their activity to trigger gene mutation and chromosome breakage, but also to their aneugenic potential. Further studies are warranted to clarify the above two hypotheses.