Bypass of cell cycle arrest induced by transient DNMT1 post-transcriptional silencing triggers aneuploidy in human cells

Background: Aneuploidy has been acknowledged as a major source of genomic instability in cancer, and it is often considered the result of chromosome segregation errors including those caused by defects in genes controlling the mitotic spindle assembly, centrosome duplication and cell-cycle checkpoints. Aneuploidy and chromosomal instability has been also correlated with epigenetic alteration, however the molecular basis of this correlation is poorly understood. Results: To address the functional connection existing between epigenetic changes and aneuploidy, we used RNA-interference to silence the DNMT1 gene, encoding for a highly conserved member of the DNA methyltransferases. DNMT1 depletion slowed down proliferation of near-diploid human tumor cells (HCT116) and triggered G1 arrest in primary human fibroblasts (IMR90), by inducing p53 stabilization and, in turn, p21(waf1) transactivation. Remarkably, p53 increase was not caused by DNA damage and was not observed after p14-ARF post-transcriptional silencing. Interestingly, DNMT1 silenced cells with p53 or p14-ARF depleted did not arrest in G1 but, instead, underwent DNA hypomethylation and became aneuploid. Conclusion: Our results suggest that DNMT1 depletion triggers a p14ARF/p53 dependent cell cycle arrest to counteract the aneuploidy induced by changes in DNA methylation.