Aneuploidy is a major source of genomic instabilityin cancer, resulting from chromosome segregationerrors caused by defects in genes controllingcorrect mitotic spindle assembly, centrosomeduplication and cell cycle checkpoints.Interestingly in aneuploid cells some of thesegenes, although not mutated, were underexpressedsuggesting the involvement of epigeneticalterations. DNA methylation and histonemodifications are the main epigenetic modificationsoccurring in cells. DNA methyl-transferase 1(Dnmt1) is known to restore DNA methylationpatterns during cell divisions. We investigated theeffects of DNMT1 silencing by RNA-interferenceon the generation of aneuploidy in primary humanfibroblasts (IMR90) and stable near-diploid humantumor cells (HCT116). Dnmt1 depletion inducedaneuploidy in addition to cell proliferation delay inHCT116 cells and transient G1 arrest in IMR90cells. IMR90-siDNTM1 cells showed increasedlevels of the TP53 tumor suppressor. Moreover,cells where DNMT1 and TP53 weresimultaneously silenced entered the cell cycle,suggesting TP53 as likely responsible for theobserved G1 arrest. DNMT1 downregulation wasalso associated to global DNA demethylation inHCT116 cells and to partially decondensedpericentromeric chromatin in IMR90 cells. Ourresults suggest that Dnmt1 depletion triggers a cellcycle arrest pathway mediated by TP53 in IMR90cells, whose dysfunction induces aneuploidy likelyaffecting the correct chromosome segregation byaltering pericentromeric structure.
|Number of pages||38|
|Publication status||Published - 2010|