The prevailing model suggests that cell fate after mitotic arrest depends on two independent and competing networks that control cyclin B1 degradation and the generation of death signals. However, recent evidence for Cdk1/cyclin B1-mediated phosphorylation and inactivation of anti-apoptotic Bcl-2 proteins suggests the existence of significant crosstalk and interdependence between these pathways. Further, the nature of the mitotic death signals has remained elusive. In this study, the hypothesis was tested that fate after mitotic arrest is dictated by the robustness of Cdk1/cyclin B1 signaling to Bcl-2 proteins, and to identify signals which may represent a mitotic death signature. It was shown that when treated with Taxol, slippage-resistant HT29 colon carcinoma cells display robust Cdk1 activity and extensive Mcl-1/Bcl-xL phosphorylation and die in mitosis, whereas slippage-prone DLD-1 colon carcinoma cells display weak Cdk1 activity and partial and transient Mcl-1/Bcl-xL phosphorylation and die in subsequent interphase or survive. Furthermore, modulation of this signaling axis, either by inhibition of Cdk1 in slippage-resistant HT29 or by enforcing mitotic arrest in slippage-prone DLD-1 cells, evokes a switch in fate, indicating that the strength of Cdk1 signaling to Bcl-2 proteins is a key determinant of outcome. It is proposed that loss of anti-apoptotic Bcl-2 protein function is the major driver of mitotic death and that phosphorylation and degradation of Mcl-1 and phosphorylation of Bcl-xL (and Bcl-2 when present) represent key elements of a mitotic death signature. Further, these findings were confirmed in ovarian, prostate and cervical cancer cell lines. Overall, the results of this dissertation provide novel insight into the pathways that regulate mitotic death, suggest that the robustness of these signaling events may be useful as a marker to define susceptibility to anti-mitotic drugs, and encourage a revision in the current model describing fate after mitotic arrest.
|Advisor:||Chambers, Timothy C.|
|Commitee:||Cannon, Martin J., Price, Peter M., Suva, Larry J., Tackett, Alan J.|
|School:||University of Arkansas for Medical Sciences|
|Department:||Interdisciplinary Biomedical Sciences|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 74/09(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Cellular biology, Biochemistry|
|Keywords:||Anti-apoptosis, Bcl-2 proteins, Mitotic arrest, Mitotic death, Spindle assembly checkpoint|
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