Expression and regulation of protein kinase CK2 during the cell cycle
There are indications from genetic, biochemical and cell biological studies that protein kinase CK2 (formerly casein kinase II) has a variety of functions at different stages in the cell cycle. To further characterize CK2 and its potential roles during cell cycle progression, one of the objectives of this study was to systematically examine the expression of all three subunits of CK2 at different stages in the cell cycle. To achieve this objective, we examined levels of CK2α, CK2α′ and CK2β on immunoblots as well as CK2 activity in samples prepared from: (i) elutriated populations of MANCA (Burkitt lymphoma) cells, (ii) serum-stimulated GL30-92/R (primary human fibroblasts) cells and (iii) drug-arrested chicken bursal lymphoma BK3 A cells. On immunoblots, we observed a significant and co-ordinate increase in the expression of CK2α and CK2α′ following serum stimulation of quiescent human fibroblasts. By comparison, no major fluctuations in CK2 activity were detected during any other stages during the cell cycle. Furthermore, we did not observe any dramatic differences between the relative levels of CK2α to CK2α′ during different stages in the cell cycle. However, we observed a significant increase in the amount of CK2β relative to CK2α in cells arrested with nocodazole. We also examined the activity of CK2 in extracts or in immunoprecipitates prepared from drug-arrested cells. Of particular interest is the observation that the activity of CK2 is not changed in nocodazole-arrested cells. Since CK2 is maximally phosphorylated in these cells, this result suggests that the phosphorylation of CK2 by p34cdc2 does not affect the catalytic activity of CK2. However, the activity of CK2 was increased by incubation with p34cdc2 in vitro. Since this activation was independent of ATP we speculate that p34cdc2 may have an associated factor that stimulates CK2 activity. Collectively, the observations that relative levels of CK2β increase in mitotic cells, that CK2α and CK2β are phosphorylated in mitotic cells and that p34cdc2 affects CK2 activity in vitro suggest that CK2 does have regulatory functions associated with cell division. (Mol Cell Biochem 191: 213–222, 1999)
Key wordsprotein kinase CK2 (CK2) cell cycle p34cdc2 mitosis CK2 activation cell synchrony
Unable to display preview. Download preview PDF.
- 3.Tuazon PT, Traugh JA: Casein Kinase I and II — Multipotential serine protein kinases: Structure, function, and regulation. In: P. Greenard, and G.A. Robinson (eds). Advances in Second Messenger and Phosphoprotein Research, Raven Press, Ltd., New York, 1991,pp 123–164Google Scholar
- 19.Litchfield DW, Bosc DG, Slominski E: The protein kinase from mitotic human cells that phosphorylate Ser209 on the casein kinase II β subunit is p34cdc2. Biochim Biophys Acta 13873: 1–10, 1995Google Scholar
- 42.McCann R, Glover CVC: Evidence for the physiological interaction of yeast Cdc37 and casein kinase II. Mol Biol Cell (Supp) 6: 133a, 1995Google Scholar