Impact of G2 checkpoint defect on centromeric instability.

Centromeric instability is characterized by dynamic formation of centromeric breaks, deletions, isochromosomes and translocations, which are commonly observed in cancer. So far, however, the mechanisms of centromeric instability in cancer cells are still poorly understood. In this study, we tested the hypothesis that G(2) checkpoint defect promotes centromeric instability. Our observations from multiple approaches consistently support this hypothesis. We found that overexpression of cyclin B1, one of the pivotal genes driving G(2) to M phase transition, impaired G(2) checkpoint and promoted the formation of centromeric aberrations in telomerase-immortalized cell lines. Conversely, centromeric instability in cancer cells was ameliorated through reinforcement of G(2) checkpoint by cyclin B1 knockdown. Remarkably, treatment with KU55933 for only 2.5 h, which abrogated G(2) checkpoint, was sufficient to produce centromeric aberrations. Moreover, centromeric aberrations constituted the major form of structural abnormalities in G(2) checkpoint-defective ataxia telangiectasia cells. Statistical analysis showed that the frequencies of centromeric aberrations in G(2) checkpoint-defective cells were always significantly overrepresented compared with random assumption. As there are multiple pathways leading to G(2) checkpoint defect, our finding offers a broad explanation for the common occurrence of centromeric aberrations in cancer cells.