The high rate of endoreduplication in the repair deficient CHO mutant EM9 parallels a reduced level of methylated deoxycytidine in DNA

The role of the DNA hypermethylating agent Budesonide in the decatenating activity of DNA topoisomerase II

Catenations between sister chromatids result from DNA replication and must be resolved to ensure proper chromatid segregation in mitosis. Functionally active Topoisomerase II (Topo II), through its mechanism of concerted breaking and rejoining of double stranded DNA, is required to carry out this fundamental process. In previous studies we have shown that modifications in DNA sequence by halogenated pyrimidines and by the demethylating agent 5-azacytidine leads to malfunction of Topo II that results in an increased yield of endorreduplicated cells as a result of segregation failure. In the present work we have evaluated the possible influence of the methylating agent Budesonide to modify the frequency of endoreduplicated cells in AA8 Chinese hamster cell population. Our results seem to indicate that when Budesonide was administered for two consecutive cell cycles did induce an increase in the yield of endoreduplicated cells, as previously observed for the hypomethylating agent 5-azaC. We have also examined the possible relationship between extensive hypermethylation induced by Budesonide in DNA and stabilization of cleavable complexes by m-AMSA. Taken as a whole, our results show that the degree of methylation in DNA correlates with the effectiveness of m-AMSA to stabilize the Topo II-DNA complexes and to induce DNA cleavage. These findings evidence for the first time the functional importance of DNA hyper- and hypomethylation changes as epigenetic factors able to modulate Topo II activity for proper chromosome segregation.