Background

We have previously identified 25 kinases that regulate sensitivity to the microtubule-stabilising drug, paclitaxel. Silencing these kinases by small-interfering RNA (siRNA), results in resistance to paclitaxel-induced cytotoxicity and dramatic alterations in DNA ploidy, multinucleation and centrosome amplification independent of drug treatment. These data suggest that the molecular pathways that maintain chromosome stability and mitotic fidelity are required for paclitaxel sensitivity.

Method

To further address this, we have investigated the function of the 25 kinases in mitosis, using a combination of fixed and live-cell microscopy. In order to assess the in vivo relevance of these kinases we examined whether lower expression held prognostic power across several breast cancer datasets.

Results

We found that several of these genes regulate mitotic progression and the formation of a bipolar mitotic spindle, and upon depletion, lead to increased rates of chromosome missegregation during anaphase. This supports the hypothesis that mechanisms of chromosomal instability that are common in cancer cells, predispose to paclitaxel resistance. Low expression of MAST3, CAMK1 and SKAP1 correlates with poor prognosis in breast cancer in vivo (P<0.05). Interestingly, MAST3 and CAMK1 have strikingly similar mitotic phenotypes after silencing; cells arrest in early mitosis and show an increased frequency of anaphase errors that may contribute to chromosomal instability.

Conclusion

In summary, we have identified novel regulators of mitotic transition that may be important for maintaining chromosomal stability. These kinases influence taxane sensitivity in vitro and hold prognostic power in breast cancer patients in vivo.