Doctor of Philosophy
Dr. David Litchfield
Protein kinase CK2 is a serine/threonine kinase with a multitude of substrates and roles in many cellular processes, including mitosis. CK2 is constitutively active, yet we hypothesize that CK2 is indeed regulated in mitosis through subtle means, enabling CK2 to perform its functions unique to cell division. Our aims were to examine the roles of mitotic phosphorylation, subcellular localization, and interplay with mitotic kinases in the regulation of CK2 activity.
We first examined the role of four highly conserved mitotic phosphorylation sites located in the unique C-terminus of CK2α. Phosphospecific antibodies generated against the sites show that CK2α phosphorylation is temporally regulated and occurs during prophase and metaphase during normal mitotic progression. Proper phosphorylation of CK2α is required for proper mitotic progression, as stable cell lines expressing phosphorylation site mutants of CK2α display severe mitotic defects.
We next examined the impact of these phosphorylation events on the subcellular localization of CK2. We show that CK2α, but not CK2α’, localizes to the mitotic spindle. Localization of CK2α to the mitotic spindle is phosphodependent, and requires the peptidyl-prolyl isomerase Pin1. These results are a rare example of functional divergence between the two catalytic isoforms of CK2, and suggest that the role of CK2α phosphorylation during mitosis is to promote localization of CK2 to the mitotic spindle. Finally, we examined the possibility that CK2 activity during mitosis is regulated through hierarchal phosphorylation events, wherein CK2 would phosphorylate proteins only after priming phosphorylation events catalyzed by other mitotic kinases, particularly Cdk1. As this phenomenon has never been systematically investigated, we have investigated the consensus requirements for CK2 primed phosphorylation, and in particular Cdk/CK2 hierarchical phosphorylation. A genome-wide search for potential mitotic substrates matching the consensus sequence suggests that Cdk1/CK2 hierarchical phosphorylation may indeed contribute to mitotic signaling, particularly on the mitotic spindle.
Taken together, our results confirm the importance of CK2 in mitotic cell division, and highlight several examples of subtle regulation of CK2, through phosphorylation, subcellular localization, and interplay with other protein kinases. This helps explain how CK2, a constitutively active kinase, can participate in tightly regulated cellular processes like mitosis.
St. Denis, Nicole A., "Mitotic Regulation of Protein Kinase CK2" (2010). Electronic Thesis and Dissertation Repository. 25.