The influence of DNA methylation on topoisomerase II activity and its possible link with genomic instability in different cell lines of the syrian hamster.
An altered DNA methylation pattern is one of the possible consequences of mammalian neoplasia and also occurs in cultured cells after treatment with certain toxic or carcinogenic substances. Another consequence which can often be seen in the same cells is genomic instability. Analysis of micronucleus frequencies and chromosome numbers in primary and tumour Syrian hamster cell lines revealed genomic instability in the tumour cell lines. We hypothesized that changes in DNA methylation result in altered DNA conformation and that certain proteins like topoisomerase II may then be impaired in their interaction with the DNA. The altered topoisomerase II activity may cause incorrect chromatin distribution during mitosis resulting in micronucleus formation. We compared methylation patterns and topoisomerase II cleavage patterns of DNA from primary and tumour cell lines. Using Southern blot analysis with a PCR-amplified Syrian hamster specific probe after MspI/HpaII cleavage, altered methylation in the DNA from the tumour cells could be demonstrated. Topoisomerase II cleavage experiments showed decreased activity in the tumour cell lines. This further confirmed the influence of DNA methylation changes on topoisomerase II activity.
Kirchner
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S
Institute of Pharmacology and Toxicology, University of Würzburg, Versbacher Str. 9, 97078 Würzburg, Germany.
Schiffmann
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Stopper
H
H