Centrosome amplification plays a key role in the origin of chromosomal instability through the establishment of multipolar mitoses and unequal chromosome segregation. However, the molecular mechanisms responsible of the development of centrosome amplification are not well understood. In this study, we used breast cancer cell lines with different phenotypes to investigate the relationship between genotoxic stress, activation of the G1/S checkpoint and centrosome amplification. Centrosome amplification was not seen in the MCF-7 cell line with wild-type p53 following genotoxic stress. These cells showed activation of the G1/S checkpoint indicated by upregulation of p21/waf1, retinoblastoma hyperphosphorylation and downregulation of cyclin A. In contrast, MCF-7 cells with abrogated p53 function and the MDA-MB 231 cell line amplified their centrosome upon introduction of DNA damage. In these cells centrosome amplification was linked to inactivation of the G1/S checkpoint. Furthermore, addition of roscovitine, a potent cdk inhibitor, to genotoxic agents inhibited centrosome amplification by rescuing the G1/S checkpoint in the MDA-MB 231 cell line. Interestingly, to test if centrosome amplification was strictly dependent on the loss of p53 function, we utilized an MCF-7 cell line expressing a constitutively active raf-1 protein but still retained a wild-type p53 phenotype. Following genotoxic stress these cells developed a partially amplified centrosome phenotype indicating that loss of p53 plays a major role in the development of centrosome amplification. Taken together our results demonstrate that anticancer drugs targeting the DNA replication process induce centrosome amplification only in subtypes of breast cancer cells lacking the G1/S checkpoint. In addition, these studies provide a therapeutic rationale to inhibit centrosome amplification and chromosomal instability by using cdk inhibitors in association with conventional chemotherapeutic agents.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]