| Summary: | Mitosis is a highly coordinated event which ensures the equal segregation of the
cytoplasmic and genetic material into two daughter cells. A key regulatory process in
ensuring the temporal fidelity of mitosis involves reversible protein phosphorylation
mediated by protein kinases and phosphatases.
The major known protein kinase required for triggering mitosis is the cyclindependent
kinase, Cdc2. Recent evidence suggests that Cdc2-independent protein kinase
signaling pathways are also involved in mitosis. The murine mammary tumour cell line,
FT210, has a temperature-sensitive mutation in the cdc2 gene that causes cell cycle arrest in
late G2 at the non-permissive temperature. This arrest can be overcome, and mitotic events
induced, by protein phosphatase inhibitors. This experimental system allows distinction
between Cdc2-independent and -dependent pathways at mitosis. This allows for
identification and investigation of the roles of protein kinases in Cdc2-independent mitotic
pathways.
I have used an in-gel protein kinase renaturation assay to identify two kinases that
are activated independently of Cdc2 at mitosis: a novel 45 kDa mitotic protein kinase and a
cell cycle-regulated novel 60 kDa histone-specific mitotic kinase.
The 45 kDa protein kinase, p45, was active only at mitosis. p45 kinase activity was
detected in all cell lines tested suggesting an essential role in cell division. The p45 kinase
was determined to be unrelated to the known 46 kDa kinases, JNK1 and MAPKAP
kinase-2.
The histone kinase was also active only at mitosis. The identification of this
histone-specific mitotic kinase confirms the existence of Cdc2-independent pathways for
chromosome condensation at mitosis.
I also investigated the regulation of the mitotic kinase, polo-like kinase-1 (Plk1), in
Cdc2 mutant cells. Plk1 was inactive at the non-permissive temperature and therefore
requires Cdc2-dependent signaling pathways for activity. Plk1 is involved in regulating
chromosome segregation during mitosis. These results further strengthen the role of Cdc2
in the regulation of mitotic microtubule dynamics. === Medicine, Faculty of === Biochemistry and Molecular Biology, Department of === Graduate
|
|---|
