DNA Methyltransferase1 post-transcriptional silencing induces aneuploidy and cell cycle arrest in human cells.

The regulation of chromatin structure is a dynamic and complex process that is modulated by epigenetic mechanisms. Malfunctioning of these processes can cause gene expression alteration and could compromise important events such as chromosome condensation and segregation. Imbalance in cytosine methylation and deregulation of DNA-methyltransferases (DNMTs), and of DNMT1 in particular, is frequent in human cancers. To investigate DNMT1 implication in the generation of aneuploidy we evaluated the effects of its depletion by RNA-interference both in primary human cells (IMR90) and in near diploid human tumor (HCT116) cells. Posttranscriptional silencing of DNMT1 induced aneuploidy, cell proliferation delay and cell cycle arrest in HCT116 cells and in IMR90 cells respectively. The cell cycle arrest was transient because cells re-entered the cycle after that the effects of siRNAs targeting DNMT1 ended. Cells missing DNMT1 showed increased levels of the p53 tumor suppressor gene that could be responsible for the observed cell cycle arrest. In fact when DNMT1 and p53 were simultaneously silenced cells did not arrest. Finally DNMT1 depletion was associated to global DNA demethylation in tumor cells and to partially decondensed pericentromeric chromatin in IMR90 cells. Our results suggest that DNMT1 loss induces cell aneuploidy, probably by affecting the correct chromosome segregation altering pericentromeric structure by demethylation, and it activates a cell cycle arrest pathway p53 mediated in IMR90 cells